Abstract:
A method for promoting conversion of cells into cardiomyocytic tissue is carried out by contacting fibrotic tissue (e.g., scar tissue) with a microRNA oligonucleotide or combination of microRNA oligonucleotides. The methods lead to direct reprogramming of fibroblasts to cardiomyocytes or cardiomyoblasts.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/399,178, filed Jul. 8, 2010, which is incorporated herein by reference in its entirety. 
     
    
     STATEMENT AS TO FEDERALLY SPONSORED RESEARCH 
       [0002]    This invention was made with Government support under National Institutes of Health awards HL073219 and HL081744. The Government has certain rights in the invention. 
     
    
     INCORPORATION-BY-REFERENCE 
       [0003]    The contents of the text file named “35327-509001WO_ST25.txt,” which was created on Jul. 8, 2011 and is 381 KB in size, are hereby incorporated by reference in their entirety. 
       FIELD OF THE INVENTION 
       [0004]    This invention relates generally to the field of cardiology. 
       BACKGROUND OF THE INVENTION 
       [0005]    Heart disease is the number one killer of men and women worldwide. Generally, heart tissue has a limited capacity for regeneration or self-renewal. After a patient recovers from a myocardial infarction, the organ still bears a scar, and heart function is diminished. The ability to regenerate damaged organs such as the heart remains elusive. As such, there is a pressing need in the art to develop new strategies for the regeneration of damaged organs. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention provides a solution to the clinical problem of non-functional scar tissue in an organ such as the heart after injury or disease. Accordingly, a method for promoting conversion of cardiac fibrotic tissue into cardiomyocytic tissue is carried out by contacting fibrotic tissue (e.g., scar tissue) with a micro-ribonucleic acid (microRNA/miRNA) oligonucleotide, a combination of microRNA oligonucleotides, or a combination of microRNAs and small molecules. The methods lead to direct reprogramming of differentiated cells such as fibroblasts to cardiomyocytes or cardiomyocyte progenitors. 
         [0007]    The methods described herein are useful in directly reprogramming cardiac fibroblasts, other differentiated cell types such as adipocytes, or hematopoietic cells such as CD34 +  cord blood cells, to cardiomyocytes or cardiomyocyte progenitor cells. The reprogramming is carried out in vivo (e.g., in situ at the site of fibrotic or scar tissue) or ex vivo. In the latter case, the reprogrammed cells are administered to the subject after the cells have been cultured and reprogrammed by incubating them with oligonucleotides or lentiviral constructs and optionally other factors ex vivo. The subject is preferably a mammal in need of such treatment, e.g., a subject that has been diagnosed with scar tissue (e.g., cardiac fibrotic tissue) or a predisposition thereto. The mammal can be, e.g., any mammal, e.g., a human, a primate, a mouse, a rat, a dog, a cat, a horse, as well as livestock or animals grown for food consumption, e.g., cattle, sheep, pigs, chickens, and goats. In a preferred embodiment, the mammal is a human. 
         [0008]    The microRNA oligonucleotides lead to transient overexpression of the desired microRNA in the target cell or tissue. Thus, the oligonucleotide increases the level of an endogenous microRNA sequence. Similarly, administration of microRNA delivery constructs such as lentiviruses lead to expression of microRNAs (stem loop sequence or mature sequence) in the cells. Preferred mir oligonucleotides (or corresponding miR-expressing delivery constructs) are selected from the group consisting of mir1, mir133 (or mir133a), mir138, mir206, mir208, mir499, and mir126 as well as the following combinations: mir1; mir1, mir133a, mir208; mir1, mir133a, mir206; mir1, mir133a, mir208, mir499-5p, mir1, mir133a, mir206, mir499-5p; mir1, mir133; mir1, mir138; mir1, mir206; mir1, mir208; mir133, mir138; mir133, mir206; mir133, mir208; mir138, mir206; mir138, mir208; mir206, mir208; mir1, mir138, mir208; mir1, mir206, mir208; mir138, mir206, mir208; mir1, mir133, mir206; mir1, mir133, mir208; mir1, mir138, mir206; mir133, mir138, mir208; and mir133, mir138, mir206. Preferred oligonucleotide compositions include the combination of 1, 133a, and 206; the combination of 1, 133a, and 208; the combination of 1, 206, and 208; the combination of 1, 133a, 208, and 499-5p; the combination of 1, 133a, 206, and 499-5p; 1; 206; as well as the combination of mir1, mir138, and mir208. The compositions are introduced into a cell by any method known to preserve the viability of the cell, e.g., transfection or transduction. Transfection is the process of introducing nucleic acids into cells by non-viral methods, and transduction is the process whereby foreign DNA is introduced into another cell via a viral vector. 
         [0009]    Nucleotide sequences of these preferred oligonucleotide constructs or combinations of constructs (and their corresponding mature forms) are listed below. Exemplary oligomeric compounds (stem-loop precursors) range in size from 50-90 nucleotides in length (or any length within that range, with an average length of approximately 70 nucleotides), and exemplary mature oligonucleotide compounds are 17 to 25 subunits in length, e.g., oligomeric compounds are 17, 18, 19, 20, 21, 22, 23, 24 or 25 subunits in length. For example, a stem-loop precursor is approximately 70 nucleotides and the mature nucleotide product is approximately 22 nucleotides in length. The uncapitalized “mir-” refers to the pre-miRNA, while a capitalized “miR-” refers to the mature form. A pre-microRNA comprises a stem-loop secondary structure. 
         [0000]    
       
         
               
             
           
               
                 Mmu-miR-1 
               
               
                 STEM-LOOP 
               
               
                 (SEQ ID NO: 1) 
               
               
                 GCUUGGGACACAUACUUCUUUAUAUGCCCAUAUGAACCUGCUAAGCUAUG 
               
               
                   
               
               
                 GAAUGUAAAGAAGUAUGUAUUUCAGGC 
               
               
                   
               
               
                 MATURE 
               
               
                 (SEQ ID NO: 2) 
               
               
                 UGGAAUGUAAAGAAGUAUGUAU 
               
               
                   
               
               
                 Mmu-miR-133a 
               
               
                 STEM-LOOP 
               
               
                 (SEQ ID NO: 3) 
               
               
                 GCUAAAGCUGGUAAAAUGGAACCAAAUCGCCUCUUCAAUGGAUUUGGUCC 
               
               
                   
               
               
                 CCUUCAACCAGCUGUAGC 
               
               
                   
               
               
                 MATURE 
               
               
                 (SEQ ID NO: 4) 
               
               
                 UUUGGUCCCCUUCAACCAGCUG 
               
               
                   
               
               
                 Mmu-miR-206 
               
               
                 STEM-LOOP 
               
               
                 (SEQ ID NO: 5) 
               
               
                 CCAGGCCACAUGCUUCUUUAUAUCCUCAUAGAUAUCUCAGCACUAUGGAA 
               
               
                   
               
               
                 UGUAAGGAAGUGUGUGGUUUUGG 
               
               
                   
               
               
                 MATURE 
               
               
                 (SEQ ID NO: 6) 
               
               
                 UGGAAUGUAAGGAAGUGUGUGG 
               
               
                   
               
               
                 Mmu-miR-208a 
               
               
                 STEM-LOOP 
               
               
                 (SEQ ID NO: 7) 
               
               
                 UUCCUUUGACGGGUGAGCUUUUGGCCCGGGUUAUACCUGACACUCACGUA 
               
               
                   
               
               
                 UAAGACGAGCAAAAAGCUUGUUGGUCAGAGGAG 
               
               
                   
               
               
                 MATURE 
               
               
                 (SEQ ID NO: 8) 
               
               
                 AUAAGACGAGCAAAAAGCUUGU 
               
               
                   
               
               
                 Human miR-1-1 
               
               
                 STEM-LOOP 
               
               
                 (SEQ ID NO: 9) 
               
               
                 UGGGAAACAUACUUCUUUAUAUGCCCAUAUGGACCUGCUAAGCUAUGGAA 
               
               
                   
               
               
                 UGUAAAGAAGUAUGUAUCUCA 
               
               
                   
               
               
                 Human miR-1-2 
               
               
                 STEM-LOOP 
               
               
                 (SEQ ID NO: 10) 
               
               
                 ACCUACUCAGAGUACAUACUUCUUUAUGUACCCAUAUGAACAUACAAUGC 
               
               
                   
               
               
                 UAUGGAAUGUAAAGAAGUAUGUAUUUUUGGUAGGC 
               
               
                   
               
               
                 MATURE SEQUENCE FOR BOTH miR1 STEM-LOOPS: 
               
               
                 (SEQ ID NO: 11) 
               
               
                 UGGAAUGUAAAGAAGUAUGUAU 
               
               
                   
               
               
                 Human miR-133a 
               
               
                 Human miR-133a-1 
               
               
                 STEM-LOOP 
               
               
                 (SEQ ID NO: 12) 
               
               
                 ACAAUGCUUUGCUAGAGCUGGUAAAAUGGAACCAAAUCGCCUCUUCAAUG 
               
               
                   
               
               
                 GAUUUGGUCCCCUUCAACCAGCUGUAGCUAUGCAUUGA 
               
               
                   
               
               
                 Human miR-133a-2 
               
               
                 STEM-LOOP 
               
               
                 (SEQ ID NO: 13) 
               
               
                 GGGAGCCAAAUGCUUUGCUAGAGCUGGUAAAAUGGAACCAAAUCGACUGU 
               
               
                   
               
               
                 CCAAUGGAUUUGGUCCCCUUCAACCAGCUGUAGCUGUGCAUUGAUGGCGC 
               
               
                   
               
               
                 CG 
               
               
                   
               
               
                 MATURE SEQUENCE FOR BOTH miR133a STEM LOOPS 
               
               
                 (SEQ ID NO: 14) 
               
               
                 UUUGGUCCCCUUCAACCAGCUG 
               
               
                   
               
               
                 Human miR-206 
               
               
                 STEM-LOOP 
               
               
                 (SEQ ID NO: 15) 
               
               
                 UGCUUCCCGAGGCCACAUGCUUCUUUAUAUCCCCAUAUGGAUUACUUUGC 
               
               
                   
               
               
                 UAUGGAAUGUAAGGAAGUGUGUGGUUUCGGCAAGUG 
               
               
                   
               
               
                 MATURE SEQUENCE FOR miR-206 
               
               
                 (SEQ ID NO: 16) 
               
               
                 UGGAAUGUAAGGAAGUGUGUGG 
               
               
                   
               
               
                 Human miR-208a 
               
               
                 STEM-LOOP 
               
               
                 (SEQ ID NO: 17) 
               
               
                 UGACGGGCGAGCUUUUGGCCCGGGUUAUACCUGAUGCUCACGUAUAAGAC 
               
               
                   
               
               
                 GAGCAAAAAGCUUGUUGGUCA 
               
               
                   
               
               
                 MATURE SEQUENCE FOR miR-208 
               
               
                 (SEQ ID NO:18) 
               
               
                 AUAAGACGAGCAAAAAGCUUGU 
               
               
                   
               
               
                 Human miR-138-1 
               
               
                 STEM-LOOP 
               
               
                 (SEQ ID NO: 19) 
               
               
                 CCCUGGCAUGGUGUGGUGGGGCAGCUGGUGUUGUGAAUCAGGCCGUUGCC 
               
               
                   
               
               
                 AAUCAGAGAACGGCUACUUCACAACACCAGGGCCACACCACACUACAGG 
               
               
                   
               
               
                 Human miR-138-2 
               
               
                 STEM-LOOP 
               
               
                 (SEQ ID NO: 20) 
               
               
                 CGUUGCUGCAGCUGGUGUUGUGAAUCAGGCCGACGAGCAGCGCAUCCUCU 
               
               
                   
               
               
                 UACCCGGCUAUUUCACGACACCAGGGUUGCAUCA 
               
               
                   
               
               
                 MATURE SEQUENCE FOR BOTH miR-138-1 and miR-138-2 
               
               
                 (SEQ ID NO: 21) 
               
               
                 AGCUGGUGUUGUGAAUCAGGCCG 
               
               
                   
               
               
                 Human miR-499-5p 
               
               
                 STEM-LOOP (MMu-miR-499) 
               
               
                 (SEQ ID NO: 29) 
               
               
                 GGGUGGGCAGCUGUUAAGACUUGCAGUGAUGUUUAGCUCCUCUGCAUGUG 
               
               
                   
               
               
                 AACAUCACAGCAAGUCUGUGCUGCUGCCU 
               
               
                   
               
               
                 MATURE (Mmu-miR-499/Hsa-miR-499-5p; 
               
               
                 sequence is conserved) 
               
               
                   
               
               
                 (SEQ ID NO: 30) 
               
               
                 UUAAGACUUGCAGUGAUGUUU 
               
             
          
         
       
     
         [0010]    Optionally, the microRNA or combination of microRNAs is administered with another compound such as a small molecule or recombinant protein to increase reprogramming efficiencies. Such molecules suitable for increasing the efficiency of conversion to cardiac myocytes include bone morphogenetic protein 4 (BMP4), Janus protein tyrosine kinase (JAK)-1 inhibitor [e.g., 2-(1,1-Dimethylethyl)-9-fluoro-3,6-dihydro-7H-benz[h]-imidaz[4,5-f]isoquinolin-7-one, Pyridone 6, P6, DBI (420099 JAK Inhibitor I)], RG108, R(+)Bay K 8644, PS48, A83-01, and histone deacetylase inhibitors (HDIs) such as valproic acid. 
         [0011]    The methods lead to fibrotic tissue or other tissue types or cells being directly reprogrammed into cardiomyocytic tissue without a stem cell intermediary state. The treated tissue is characterized by an increased expression of a cardiomyocyte marker protein after having been contacted with the compositions (single oligonucleotides or combinations thereof) compared to the level of the cardiomyocyte marker protein before the contacting step. For example, the increase is 10%, 25%, 50%, 2-fold, 5-fold, 10-fold or more compared to the level of expression before treatment. Exemplary marker proteins include cardiac troponin, sarcomeric actinin, L-type calcium channel, brachyury, Flk1, Islet1, Mesp1, Gata4, Mef2c, Hand2, and TroponinT2. 
         [0012]    The fibrotic tissue to be treated is present in a heart diagnosed as comprising cardiac myocardial infarction or other forms of cardiac disease such as ischemic heart disease, hypertrophic cardiomyopathies, valvular heart disease, and/or congenital cardiomyopathies. For example, the tissue is contacted with microRNA oligonucleotide compositions or viral (e.g., lentiviral) constructs expressing microRNAs after fibrosis has developed as a result of myocardial infarction or other cardiac disease process, e.g., days (1, 2, 3, 4, 5, 6 days after), weeks (1, 2, 4, 6, 8), months (2, 4, 6, 8, 10, 12), or even a year or more after the primary tissue insult. The fibrotic tissue is contacted ex vivo or in situ. In the case in which the organ is treated in a subject, e.g., a human patient, the compositions are delivered locally or systemically, e.g., using intravenous administration or direct injection into cardiac tissue. Other delivery schemes include oral, nasal, intradermal, transdermal, subcutaneous, intramuscular, intraperitoneal, suppository, and sublingual administration. For example, the compositions are administered by direct injection into cardiac tissue. Other delivery modes are characterized by sustained release, controlled release, or delayed release. Administration of the compositions may be via any common route so long as the target tissue is available via that route. The compositions are administered as pharmaceutically acceptable compositions, e.g., formulated with a pharmaceutically acceptable carrier or excipient. In general, dosage is from 0.01 μg to 100 g per kg of body weight, from 0.1 μg to 10 g per kg of body weight, from 1.0 μg to 1 g per kg of body weight, from 10.0 μg to 100 mg per kg of body weight, from 100 μg to 10 mg per kg of body weight, or from 1 mg to 5 mg per kg of body weight, and may be given once or more daily, weekly, monthly or yearly. Examples of dosages based on small animal studies are in the range of 80 mg/kg for single or multiple dosages. However, it is expected with appropriate modification dosages 1-25 mg/kg for single to three repeated dosages will confer clinical benefit in human subjects. 
         [0013]    In contrast to other methods that may inhibit fibrosis, the compositions and methods described herein reverse fibrosis that has occurred. Fibrotic tissue or fibroblasts are directly reprogrammed using microRNAs into a cardiomyocyte lineage without going through a stem cell phenotype. 
         [0014]    An alternative method of restoring tissue specific function to fibrotic tissue in an organ is therefore carried out by providing patient-derived fibroblasts and transfecting the fibroblasts with a microRNA or combination of microRNAs described above. Preferably the fibroblasts are dermal fibroblasts obtained from the skin of the patient to be treated. Alternatively, the fibroblasts are cardiac fibroblasts or epidermal keratinocytes. In one example, the transfection occurs ex vivo. Cells directly reprogrammed in this manner are useful for cell replacement therapy, in which the reprogrammed cells are infused or injected into an anatomical site that requires repair or regeneration of tissue. The cells are also for direct screening assays or pharmacogenomics analysis, because large quantities of cells are reprogrammed using the methods and compositions described herein. Alternatively, the transfection occurs in situ. 
         [0015]    The invention therefore includes a purified population of primary fibroblasts comprising an exogenous microRNA oligonucleotide construct or combination of constructs listed above as well as a purified population of cardiomyocytes or cardiomyocyte progenitors that were produced using the primary fibroblasts comprising the reprogramming oligonucleotides. Each population is substantially free of stem cells, e.g., the population is at least 85%, 90%, 95%, 99%, or 100% transfected fibroblasts or at least 85%, 90%, 95%, 99%, or 100% reprogrammed myoblasts, cardiomyocytes, or cardiomyocyte progenitors. Cells are purified by virtue of selection based on cell surface markers as well as other cell selection techniques well known in the art. 
         [0016]    As was discussed above, the cells are useful for therapeutic applications such as direct administration to a subject or as a component of another therapeutic intervention or device. For example, the invention encompasses a stent or catheter comprising primary fibroblasts comprising the reprogramming transgene sequence or comprising reprogrammed functional cells (e.g., characterized as expressing an increased level of a desired mIR). 
         [0017]    The composition and methods of the invention include several advantages over previous methods of reprogramming cells. For example, unlike methods that employ reprogramming to a stem cell phenotype and subsequent differentiation of this cell population, the direct reprogramming methods of the invention do not involve an intermediate stage of a stem cell phenotype. The use of miRNAs for direct reprogramming rather than transcription factors can regulate in parallel multiple genes or pathways that are responsible for the reprogramming effects. In addition, additional advantages of the use of small oligonucleotides rather than gene provides include ease of the production and development for biologic therapy. 
         [0018]    The invention represents the first demonstration of direct reprogramming of fibroblasts to cardiomyocytes, i.e., it is the first evidence that miRs have the ability to modulate direct reprogramming. The compositions and methods described herein offer an approach to treating cardiac disease long after the initial symptoms have occurred by directly replacing fibrotic tissue with viable functional cardiomyocytes. In addition to clinical applications, the compositions and methods are useful for testing drugs and molecules for target discovery 
         [0019]    All polynucleotides (i.e., microRNAs) and polypeptides of the invention are purified and/or isolated. Specifically, as used herein, an “isolated” or “purified” nucleic acid molecule, polynucleotide, polypeptide, or protein, is substantially free of other cellular material, or culture medium when produced by recombinant techniques, or chemical precursors or other chemicals when chemically synthesized. Purified compounds are at least 60% by weight (dry weight) the compound of interest. Preferably, the preparation is at least 75%, more preferably at least 90%, and most preferably at least 99%, by weight the compound of interest. For example, a purified compound is one that is at least 90%, 91%, 92%, 93%, 94%, 95%, 98%, 99%, or 100% (w/w) of the desired compound by weight. Purity is measured by any appropriate standard method, for example, by column chromatography, thin layer chromatography, or high-performance liquid chromatography (HPLC) analysis. A purified or isolated polynucleotide (ribonucleic acid (RNA) or deoxyribonucleic acid (DNA)) is free of the genes or sequences that flank it in its naturally-occurring state. Purified also defines a degree of sterility that is safe for administration to a human subject, e.g., lacking infectious or toxic agents. 
         [0020]    Similarly, by “substantially pure” is meant a nucleotides (i.e., microRNAs) and polypeptides that have been separated from the components that naturally accompany it. Typically, the nucleotides and polypeptides are substantially pure when they are at least 60%, 70%, 80%, 90%, 95%, or even 99%, by weight, free from the proteins and naturally-occurring organic molecules with they are naturally associated. 
         [0021]    The terms “treating” and “treatment” as used herein refer to the administration of an agent or formulation to a clinically symptomatic individual afflicted with an adverse condition, disorder, or disease, so as to effect a reduction in severity and/or frequency of symptoms, eliminate the symptoms and/or their underlying cause, and/or facilitate improvement or remediation of damage. The terms “preventing” and “prevention” refer to the administration of an agent or composition to a clinically asymptomatic individual who is susceptible to a particular adverse condition, disorder, or disease, and thus relates to the prevention of the occurrence of symptoms and/or their underlying cause. 
         [0022]    By the terms “effective amount” and “therapeutically effective amount” of a formulation or formulation component is meant a sufficient amount of the formulation or component to provide the desired effect. For example, by “an effective amount” is meant an amount of a microRNA to directly reprogram cardiac fibroblasts to myoblasts in a subject. Ultimately, the attending physician or veterinarian decides the appropriate amount and dosage regimen. 
         [0023]    As described herein, small molecules include, but are not limited to, peptides, peptidomimetics (e.g., peptoids), amino acids, amino acid analogs, polynucleotides, polynucleotide analogs, nucleotides, nucleotide analogs, organic and inorganic compounds (including heterorganic and organomettallic compounds) having a molecular weight less than about 5,000 grams per mole, organic or inorganic compounds having a molecular weight less than about 2,000 grams per mole, organic or inorganic compounds having a molecular weight less than about 1,000 grams per mole, organic or inorganic compounds having a molecular weight less than about 500 grams per mole, and salts, esters, and other pharmaceutically acceptable forms of such compounds. A small molecule inhibitor is a compound that is less than 2000 daltons in mass. The molecular mass of the inhibitory compounds is preferably less than 1000 daltons, more preferably less than 600 daltons, e.g., the compound is less than 500 daltons, 400 daltons, 300 daltons, 200 daltons, or 100 daltons. 
         [0024]    The transitional term “comprising,” which is synonymous with “including,” “containing,” or “characterized by,” is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. By contrast, the transitional phrase “consisting of” excludes any element, step, or ingredient not specified in the claim. The transitional phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps “and those that do not materially affect the basic and novel characteristic(s)” of the claimed invention. 
         [0025]    Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All published foreign patents and patent applications cited herein are incorporated herein by reference. Genbank and NCBI submissions indicated by accession number cited herein are incorporated herein by reference. All other published references, documents, manuscripts and scientific literature cited herein are incorporated herein by reference. In the case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a diagram showing mIR involvement in cardiac myocyte function. 
           [0027]      FIG. 2  is a heat map and bar graphs showing the results of miRNA profiling studies. 
           [0028]      FIG. 3  is a diagram showing iPS differentiation to cardiac cells. 
           [0029]      FIG. 4  is a series of photomicrographs showing the results of an experiment wherein cardiac fibroblasts were isolated and cultured from transgenic mice expressing Myosin heavy chain-driven CFP. Myosin heavy chain expression is restricted to muscle cells and therefore is turned on once reprogramming has been accomplished. Representative images of cardiac fibroblasts transfected with miR1 and costained with an antibody recognizing CFP 7 days following the initial transfection are shown. Confocal images were obtained of anti-CFP staining (red channel) and endogenous CFP expression (blue channel). 
           [0030]      FIG. 5  is a heat map showing results of a two-way clustering analysis of candidate microRNA combinations and negative controls versus cardiac differentiation marker expression (obtained using QR-PCR). 
           [0031]      FIG. 6  is a photomicrograph showing immunostaining 6 days post-transfection with microRNA oligonucleotides. The figure shows a merged display of (A) cardiac fibroblasts transfected with mir138, mir208 and (B) mock-treated cardiac fibroblasts stained 6 days post-transfection for expression of cardiac troponin I (AlexaFluor, green) and DAPI (red). 
           [0032]      FIG. 7  is a series of photomicrographs showing immunostained cardiac fibroblasts after transfection with a combination of miR1, miR133, and miR206. The nucleus of cells was stained blue with 4′,6-diamidino-2-phenylindole (DAPI). Cells that have been fibroblasts at some point in their lifetime were stained red with Fsp1Cre. Cardiomyocytes were stained green with cardiac troponin, a marker not expressed in fibroblasts. 
           [0033]      FIG. 8  is a series of photomicrographs showing an immunostained neonatal heart that was injected with lentivirus expressing miR-1. The neonate was injected at age 3-4 days old. Two weeks later, the hearts was harvested, fixed, and stained. The neonates are from a transgenic line where the red (tomato) reporter is a marker of cells derived from the fibroblastic lineage. Cells expressing red/tomato are/were a fibroblast at some point during their lifetime. Cardiac myocyte-specific marker cardiac troponin is shown in green. The arrows point to co-localization of red and green, and demonstrate in vivo evidence of miR-induced reprogramming. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    MicroRNAs (miR) are small (about 22-nucleotide) RNAs that are derived from larger pre-mirs. MiRs act as repressors of target mRNAs by promoting their degradation, when their sequences are perfectly complementary, or inhibiting translation when their sequences contain mismatches. Micro (mi)RNAs are emerging as important regulators of cellular differentiation, their importance underscored by the fact that they are often dysregulated during carcinogenesis 
       Reprogramming 
       [0035]    Reprogramming is process by which cells change phenotype, state of differentiation, or function. For example, the cellular process governs the transformation of a somatic cell into a pluripotent stem cell. This process is exploited as a tool for creating patient-specific pluripotent cells that are useful in cell replacement therapies. In “direct reprogramming”, the differentiated state of a specialized somatic cell is reversed to another type (e.g., endocrine cells to exocrine cells or fibroblasts to neurons or, as described herein, cardiomyocytes). This process useful for creating patient-specific pluripotent cells for cell replacement therapies. Suitable starting populations for reprogramming include adipocytes, CD34 +  cord blood cells, and fibroblasts. 
         [0036]    Adipocytes are an exemplary population for reprogramming. Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat. Although the lineage of adipocytes is still unclear, preadipocytes are undifferentiated fibroblasts that can be stimulated to form adipocytes. CD34 +  cord blood cells are also an exemplary population for reprogramming. CD34+ cells are hematopoietic stem cells present in umbilical cord blood. 
         [0037]    Optionally, fibroblasts are the starting population for reprogramming. Fibroblasts are traditionally defined as cells of mesenchymal origin that produce interstitial collagen (in contrast to myocytes that form collagen type IV as part of their basement membrane, fibroblasts also produce types I, III and VI). In general, fibroblasts lack a basement membrane and tend have multiple processes or sheet-like extensions. They contain an oval nucleus (with 1 or 2 nucleoli), extensive rough endoplasmic reticulum, a prominent Golgi apparatus, and abundant cytoplasmic granular material. Specific markers are scarce; however, DDR2 is useful as a marker. This marker is expressed in fibroblasts and other cells but not other cardiac cells. The mesenchymal cells that form the cardiac fibroblast population are believed to be derived from two principal sources: (1) the pro-epicardial organ, and (2) the epithelial-mesenchymal transformation during the formation of cardiac valves. Differentiation to cardiac fibroblasts is regulated by programmed sequences of growth factors, including FGF and PDGF. Cardiac fibroblast differentiation and heart disease 
         [0000]    
       
                 
         
             
             
         
       
     
         [0038]    As described herein, factors, e.g., microRNA sequences, have been defined that lead to reversal of fibrosis. These microRNA compositions induce the process of direct reprogramming and lead to enhancement of cardiac tissue repair/regeneration procedures as well as better efficiency for cell therapy. 
       Fibroblast to Cardiovascular Cell Type 
       [0039]    the process of direct reprogramming is carried out as follows. Fibroblasts, e.g., cardiac fibroblasts, skin or other type of fibroblasts are isolated using known methods. Factors were screened to determine which ones reverse the fibroblast to cardiovascular cell lineage. A miRNA/siRNA approach was chosen. Protocols for transfection and viral over-expression are known in the art. Following reprogramming, the treated cells are assay to determine the level of expression of cardiac cell markers. 
         [0000]    Genes Involved with Cardiac Myocyte Specification 
         [0040]    Markers of multipotent cardiovascular progenitors/cardiac myocytes include early mesodermal markes such as Brachyury, early cardiovascular progenitor cell markers such Flk1, markers of early commited cardiomyocyte progenitors such as Nkx2-5, Islet1, Mesp1, Gata4, Mef2c, Hand2, and mature cardiomyocyte markers such Troponin T2, Actinin, and alpha Myosin heavy chain. As described in detail below, TBX5 also plays a role in heart development. Gene sequences are provided below. 
         [0000]    Direct Reprogramming of Cardiac Fibroblasts to Cardiac Myocyte Fate by Employment of miRNA Mimics or Antagonists 
         [0041]    Somatic cells have been reprogrammed to an embryonic-like state via viral transfection of four pluripotency factors (Takahashi et al., 2006, Cell 126, 663-676). Transcription factors have also been used to induce cellular reprogramming. A specific combination of three transcription factors (Zhou et al., 2008, Nature 455, 627-632) was employed to reprogram adult exocrine pancreatic cells in vivo to insulin-producing 13-cells representing the potential for switching gene expression in living organisms. Another study demonstrated that two cardiac transcription factors Gata4 and Tbx5 along with the chromatin-remodeling complex Baf60c, are capable of inducing programming and transdifferentiation of embryonic mouse mesoderm (Takeuchi et al., 2009, Nature 459, 708-711) to beating heart tissue. The central premise underlying the majority of these studies is the use of key transcription factors overexpression to redirect or control cell fate. The methods described herein preferably do not involve the use of transcription factors. 
         [0042]    Prior to the invention, the possibility that a switch in gene expression induced by the introduction of key microRNAs as an alternative to transcription factors for direct reprogramming has heretofore not been reported. MicroRNAs are 21-23 nucleotide-long RNA molecules that represent an integral component of the regulatory machinery driving gene expression at the post-transcriptional level. Individual microRNAs are capable of modulating the expression of hundreds of genes (Zhao et al., 2007, Trends Biochem Sci 32, 189-197) and are rapidly being regarded as powerful regulators of both developmental and pathological processes (Judson et al., 2009, Nature Biotechnology 27:459-461; Cordes et al., 2009, Nature 460:705-711). Since microRNAs are capable of regulating the expression of several more gene targets, they are potent at switching gene expression and inducing cellular reprogramming. 
         [0043]    Specific tissues and progenitor cell populations express distinct microRNA profiles, thereby suggesting a role for microRNAs in governing and/or directing cell fate decisions. Thus, studies were undertaken to elucidate the role for microRNAs as a therapeutic to activate key molecular programs inducing tissue regeneration. This approach is particularly suitable for treatment of cardiovascular conditions where there is a significant need to improve cardiac repair and remodeling in acquired heart disease. For example, one application of the cardiac specific miRNAs described herein is administration of a mirRNA mimic alone or combination of mimics for different miRNAs in the fibrotic heart and reversion of the fibrosis by direct reprogramming of the fibroblasts to a cardiac myocyte fate and thus a replacement of the scar tissue by new functional myocytes. 
       Reprogramming Efficiency-Enhancing Molecules 
       [0044]    Optionally, the microRNA or combination of microRNAs is administered with a small molecule or other agent (e.g., an recombinant protein) to increase reprogramming efficiencies. Small molecules suitable for increasing the efficiency of conversion to cardiac myocytes include valproic acid, bone morphogenetic protein 4 (BMP4), Janus protein tyrosine kinase (JAK) inhibitor 1, RG108, R(+)Bay K 8644, PS48, and A83-01. These agents are delivered (e.g., infused or injected) to the subject before, after, or together with miR oligonucleotides or microRNA-expressing viral constructs. In the case of ex vivo reprogramming, the agents are added to the cell culture media. 
         [0045]    Valproic acid (VPA; 2-propylpentanoic acid; C 8 H 16 O 2 ) is a chemical compound that has found clinical use as an anticonvulsant and mood-stabilizing drug, primarily in the treatment of epilepsy, bipolar disorder, and major depression. Valproic acid also blocks the voltage-gated sodium channels and T-type calcium channels. These mechanisms make valproic acid a broad spectrum anticonvulsant drug. Serum or plasma valproic acid concentrations are generally in a range of 20-100 mg/L during controlled therapy. 
         [0046]    Valproic acid (VPA; 2-propyl-pentanoic acid) has been used for mood stabilization and the treatment of epilepsy for several decades (Perucca E CNS Drugs 2002, 16:695-714). VPA is a histone deacetylase (HDAC) inhibitor and plays a role in modifying chromatin structure and gene expression (Hsieh J, et al., Proc Natl Acad Sci USA 2004, 101:16659-64; Jenuwein T, Allis CD: Science 2001, 293:1074-80). VPA has also been found to affect various signaling systems, including the extracellular signal-regulated kinase (ERK), protein kinase C (PKC), and the Wnt/β-catenin pathways (Blaheta R A et al., Curr Med Chem 2002, 9:1417-33; Gurvich N, Klein P S: Pharmacol Ther 2002, 96:45-66; Rosenberg G: Cell Mol Life Sci 2007, 64:2090-103). VPA alters the Wnt/β-catenin signaling by directly or indirectly (Gould T D et al., Neuropsychopharmacology 2004, 29:32-8; Gould T D, Manji H K: Neuroscientist 2002, 8:497-511) inhibiting the activity of glycogen synthase kinase 3β (GSK3β). VPA also regulates the differentiation and proliferation of various cells, including mesenchymal and hematopoietic stem cells, neuroblastoma cells, primary neurons, and neural progenitor cells (NPCs). 
         [0047]    Valproic acid, which has been utlilized as a drug for treating certain seizure disorders, is administered locally at the site of desired location, e.g., the site of fibrotic tissue or the site at which reprogramming is induced by miR delivery or systemically. A therapeutic range for the drug is currently established at 50-120 μg/mL and is taken as a tablet, slow release tablet, a liquid, or sprinkled on soft food. For example, valproic acid can be administered intravenously daily (3 g/24 hours) (Mink et al., 2011, Clin Neurol Neurosurg. Jun 22). 
         [0048]    Valproic acid is available from Stemgent, and used at a final concentration of about 0.01 mM to about 10 mM, e.g., about 0.1 mM to about 5 mM or about 1 mM to about 3 mM. Preferably, valproic acid is used at a final concentration of about 2 mM. Valproic acid is administered in about one dose to about 5 doses, e.g., about 1 dose, about 2 doses, about 3 doses, about 4 doses, or about 5 doses. Preferably, valproic acid is administered in 2 doses. Valproic acid is administered about 1 hour to about 96 hours prior to miR transfection and about 1 hour to about 96 hours after miR transfection, e.g., about 12 hours to about 72 hours or about 24 hours to about 60 hours prior to and after miR transfection. Preferably, valproic acid is administered in two doses: one dose at 48 hours prior to miR transfection and one dose at 48 hours post-transfection. 
         [0049]    Bone morphogenetic proteins (BMPs) are a group of growth factors also known as cytokines and as metabologens. Originally discovered by their ability to induce the formation of bone and cartilage, BMPs are now considered to constitute a group of pivotal morphogenetic signals, orchestrating tissue architecture throughout the body. Signal transduction through BMPRs results in mobilization of members of the SMAD family of proteins. The signaling pathways involving BMPs, BMPRs and Smads are important in the development of the heart, central nervous system, and cartilage, as well as post-natal bone development. BMP4 plays an important role in the onset of endochondral bone formation in humans. It is involved in muscle development, bone mineralization, and uteric bud development. BMP4 is also of crucial importance for cardiac development and differentiation. 
         [0050]    BMP-4 is available from Stemgent, and used at a final concentration of about 0.1 ηg/mL to about 100 ηg/mL, e.g., about 1 ηg/mL to about 50 ηg/mL or about 10 ηg/mL to about 30 ηg/mL. Preferably, BMP-4 is used at a final concentration of about 20 ηg/mL. BMP-4 is administered every day beginning about 1 day to about 14 days before or after transfection of miRs, e.g., BMP-4 is administered about 2 days to about 13 days or about 5 days to about 10 days before or after transfection of miRs. Preferably, BMP-4 is administered 7 days post-transfection of miRs. Subsequently, BMP-4 is administered once/day for about 1 day, about 2 days, about 3 days, about 4 days, about 5 days, about 6 days, about 7 days, about 8 days, about 9 days, or about 10 days. Preferably, BMP-4 is administered every day for cells in culture. 
         [0051]    JAK inhibitor 1(2-(1,1-Dimethylethyl)-9-fluoro-3,6-dihydro-7H-benz[h]-imidaz[4,5-f]isoquinolin-7-one, Pyridone 6, P6, DBI (420099 JAK Inhibitor I); C 18 H 16 FN 3 O) is a potent, reversible, cell-permeable, and ATP-competitive inhibitor of Janus protein tyrosine kinases (JAKs). This molecule displays potent inhibitory activity against JAK1 (IC50=15 nM for murine JAK1), JAK2 (IC50=1 nM), JAK3 (Ki=5 nM), and Tyk2 (IC50=1 nM), and also inhibits other kinases at much higher concentrations. JAK inhibitor 1 also inhibits IL-2- and IL-4-dependent proliferation of CTLL cells and blocks the phosphorylation of STATS. This molecule also induces the growth inhibition of multiple myeloma cells expressing activated JAKs and STAT3. 
         [0052]    The JAK inhibitor 1 is available from EMD Biosciences, and used at a final concentration of about 0.001 μM to about 10 μM, e.g., about 0.01 μM to about 5 μM or about 0.1 μM to about 1 μM. Preferably, the JAK inhibitor 1 is used at a final concentration of about 0.5 μM. The JAK inhibitor 1 is administered about 1 hour to about 96 hours before or after transfection of miRs, e.g., the JAK inhibitor 1 is administered once/day beginning about 12 hours to about 72 hours or about 24 hours to about 60 hours before or after transfection of miRs. Preferably, the JAK inhibitor 1 is administered 48 hours post-transfection of miRs. The JAK Inhibitor 1 is administered once/day for about 1 day, about 2 days, about 3 days, about 4 days, about 5 days, about 6 days, about 7 days, about 8 days, about 9 days, or about 10 days. Preferably, the JAK inhibitor 1 is administered every day for 5 days. 
         [0053]    Small molecule inhibitors of JAK-1 such as (INCB018424 (Ruxolitinib) and INCB028050; Incyte Corp.) have been shown to be effective in rheumatoid arthritis models when administered orally. For example INCB028050 is used at a dosage of 10 mg/kg in rodents. Both these inhibitors as well as JAK Inhibitor I (2-(1,1-Dimethylethyl)-9-fluoro-3,6-dihydro-7H-benz[h]-imidaz[4,5-f]isoquinolin-7-one, Pyridone 6, P6, DBI (catalog #420099 from EMD biosciences) have IC 50  values in the nanomolar range. In the case of #420099, the IC 50  values against JAK1 and JAK2 are reported to be 15 nM and 1 nM respectively. In the case of INCB018424, the reported IC 50  values for JAK1 and JAK2 are 3 and 5 nM respectively. INCB018424 and INCB028050 are currently being utilized in clinical trials (Fridman J. S. et al., (2010) Selective Inhibition of JAK1 and JAK2 Is Efficacious in Rodent Models of Arthritis: Preclinical Characterization of INCB028050. J. Immunol. 184 (9) 5298-5307). 
         [0054]    RG108 (2-(1,3-Dioxo-1,3-dihydro-2H-isoindol-2-yl)-3-(1H-indol-3-yl)propionic acid, N-Phthalyl-L-tryptophan; C 19 H 14 N 2 O 4 ) is a potent and specific DNA methyltransferase (DNMT) inhibitor. It causes demethylation and reactivation of tumor suppressor genes and can be used to enhance reprogramming. RG108 has been found to inhibit human tumor cell line proliferation and increases doubling time in culture. This molecule is soluble to 100 mM in DMSO and to 100 mM in ethanol. 
         [0055]    RG108 is available from Stemgent, and used at a final concentration of about 0.001 μM to about 10 μM, e.g., about 0.001 μM to about 5 μM or about 0.01 μM to about 0.1 μM. Preferably, RG108 is used at a final concentration of about 0.04 μM. RG108 is administered in about one dose to about 5 doses, e.g., about 1 dose, about 2 doses, about 3 doses, about 4 doses, or about 5 doses. Preferably, RG108 is administered in 2 doses. RG108 is administered about 1 hour to about 96 hours prior to miR transfection and about 1 hour to about 96 hours after miR transfection, e.g., about 12 hours to about 72 hours or about 24 hours to about 60 hours prior to and after miR transfection. Preferably, RG108 is administered in two doses: one dose at 48 hours prior to miR transfection and one dose at 48 hours post-transfection. 
         [0056]    R(+)Bay K 8644 (R-(+)-1,4-Dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-3-pyridinecarboxylic acid methyl ester; C 16 H is F 3 N 2 O 4 ) is a L-type Ca 2+ -channel blocker with negative inotropic and vasodilatatory effects in vivo. This enantiomer has opposite effects to the racemate (±)-Bay K 8644 and (S)-(−)-enantiomer. In combination with BIX-01294, this molecule helps generate induced pluripotent stem cells (iPSCs) from mouse embryonic fibroblasts (MEFs). This molecule is soluble to 100 mM in ethanol and to 100 mM in DMSO. 
         [0057]    R(+)Bay K 8644 is available from Stemgent, and used at a final concentration of about 0.01 μM to about 10 μM, e.g., about 0.1 μM to about 5 μM or about 1 μM to about 3 Preferably, R(+)Bay K 8644 is used at a final concentration of about 2 R(+)Bay K 8644 is administered in about one dose to about 5 doses, e.g., about 1 dose, about 2 doses, about 3 doses, about 4 doses, or about 5 doses. Preferably, R(+)Bay K 8644 is administered in 2 doses. R(+)Bay K 8644 is administered about 1 hour to about 96 hours prior to miR transfection and about 1 hour to about 96 hours after miR transfection, e.g., about 12 hours to about 72 hours or about 24 hours to about 60 hours prior to and after miR transfection. Preferably, R(+)Bay K 8644 is administered in two doses: one dose at 48 hours prior to miR transfection and one dose at 48 hours post-transfection. 
         [0058]    PS48 (5-(4-Chloro-phenyl)-3-phenyl-pent-2-enoic acid; C 17 H 15 ClO 2 ) is a PDK1 (phosphoinositide-dependent protein kinase 1) activator which binds to the HM/PIF binding pocket rather than the ATP-binding site. PS48 is one of only a few truly allosteric compounds targeting a regulatory binding site on a protein kinase catalytic domain that is not adjacent to or overlapping with the ATP-binding site. This molecule is soluble in DMSO 
         [0059]    PS48 is available from Stemgent, and used at a final concentration of about 0.01 μM to about 10 μM, e.g., about 0.1 μM to about 8 μM or about 4 μM to about 6 Preferably, PS48 is used at a final concentration of about 5 PS48 is administered in about one dose to about 5 doses, e.g., about 1 dose, about 2 doses, about 3 doses, about 4 doses, or about 5 doses. Preferably, PS48 is administered in 2 doses. PS48 is administered about 1 hour to about 96 hours prior to miR transfection and about 1 hour to about 96 hours after miR transfection, e.g., about 12 hours to about 72 hours or about 24 hours to about 60 hours prior to and after miR transfection. Preferably, PS48 is administered in two doses: one dose at 48 hours prior to miR transfection and one dose at 48 hours post-transfection. 
         [0060]    A83-01 (3-(6-Methyl-2-pyridinyl)-N-phenyl-4-(4-quinolinyl)-1H-pyrazole-1-carbothioamide; C 25 H 19 N 5 S) is a TGFβ kinase/activin receptor like kinase (ALK5) inhibitor. It blocks the phosphorylation of Smad2 and inhibits TGFIβ-induced epithelial-to-mesenchymal transition. A83-01 is more potent than small molecule SB431542, and inhibits differentiation of rat induced pluripotent stem cells (iPSCs) and increases clonal expansion efficiency. Small molecule A83-01 helps maintain homogeneity and long-term in vitro self-renewal of human iPSCs. This molecule is soluble in DMSO to 100 mM. 
         [0061]    A83-01 is available from Stemgent, and used at a final concentration of about 0.01 μM to about 10 μM, e.g., about 0.1 μM to about 5 μM or about 0.4 μM to about 0.6 μM. Preferably, A83-01 is used at a final concentration of about 0.5 μM. A83-01 is administered in about one dose to about 5 doses, e.g., about 1 dose, about 2 doses, about 3 doses, about 4 doses, or about 5 doses. Preferably, A83-01 is administered in 2 doses. A83-01 is administered about 1 hour to about 96 hours prior to miR transfection and about 1 hour to about 96 hours after miR transfection, e.g., about 12 hours to about 72 hours or about 24 hours to about 60 hours prior to and after miR transfection. Preferably, A83-01 is administered in two doses: one dose at 48 hours prior to miR transfection and one dose at 48 hours post-transfection. 
       Example 1 
     Reprogramming of Cardiac Fibroblasts 
       [0062]    Mouse cardiac fibroblasts were transfected with specific combinations of distinct microRNAs significant to cardiac and/or muscle tissue. Quantitative real-time PCR (QRT-PCR) and immunocytochemistry (ICC) were employed to assess a switch in gene expression as early as 3 days following transfection. These techniques make use of specific primers (QRT-PCR) and antibodies (ICC) to detect the expression/upregulation of cardiac differentiation markers. Such markers include MADS box transcription enhancer factor 2, polypeptide C (MEF2C), NK2 transcription factor related, locus 5 (NKX2.5), GATA binding protein 4 (GATA4), heart and neural crest derivatives expressed 2 (HAND2), ISL1 transcription factor, LIM homeodomain (ISL1), troponin I type 3 (cardiac) (TNNI3). Sequences provided below. 
         [0063]    The specific combinations of particular microRNAs required to induce cellular reprogramming were initially identified from two screens using all candidate microRNAs transfected individually as well as in all possible double and triple combinations with each other.  FIG. 5  shows a two-way clustering of cardiac differentiation marker upregulation (from QRT-PCR) against a series of different microRNA combinations and negative controls from one such screen. Analyses such as this one facilitated the elucidation of gene regulation patterns by candidate microRNAs either individually or when specifically combined with other microRNAs. Combinations selected were identified as those that mediated cardiac differentiation marker upregulation at both the RNA and protein levels 3 days and 6 days post-transfection ( FIG. 6 ). 
         [0064]    A total of 65 microRNAs and combinations were tested. Exemplary microRNA combinations capable of inducing cellular reprogramming are listed below. 
         [0000]    1. mir1
 
2. mir133
 
3. mir138
 
4. mir206
 
5. mir208
 
6. mir1, mir133
 
7. mir1, mir138
 
8. mir1, mir206
 
9. mir1, mir208
 
10. mir133, mir138
 
11. mir133, mir206
 
12. mir133, mir208
 
13. mir138, mir206
 
14. mir138, mir208
 
15. mir206, mir208
 
16. mir1, mir138, mir208
 
17. mir1, mir206, mir208
 
18. mir138, mir206, mir208
 
19. mir1, mir133, mir206
 
20. mir1, mir133, mir208
 
21. mir1, mir138, mir206
 
22. mir133, mir138, mir208
 
23. mir133, mir138, mir206
 
24. mir126
 
25. mir1, mir138, mir108
 
26. mir1, mir133a, mir208, mir499-5p
 
27. mir1, mir133a, mir206, mir499-5p
 
28. mir499-5p
 
       Example 2 
     Utilization of Specific microRNAs to Direct Reprogramming of Cardiac Fibroblasts to Cardiac Myocytes 
       [0065]    As described in detail below, because of their plasticity and presumed higher propensity for cell conversion, neonatal cardiac fibroblasts were reprogrammed into cardiac myocytes. Immunostaining methods were used to further investigate whether the microRNA-transfected cell populations express markers that are characteristic of cardiomyocytes. The organization of the expression of these proteins was also determined. 
         [0066]    The results presented in  FIG. 7  show examples of cardiac markers that are “turned on” in microRNA-transfected neonatal cardiac fibroblasts two weeks post-transfection. As shown in  FIG. 7 , cardiac fibroblasts were immunostained two weeks after transfection with a combination of miR1, miR133, and miR206. The nucleus of cells was stained blue with 4′,6-diamidino-2-phenylindole (DAPI). Cells that have been fibroblasts at some point in their lifetime were stained red with Fsp1Cre. Cardiomyocytes were stained green with cardiac troponin, a marker not expressed in fibroblasts. The results presented in  FIG. 7  show that the combination of miR1, miR133, and miR206 induces cardiac fibroblasts to express cardiac myocytes markers. Specifically, this combination of microRNAs induced the expression of cardiac troponin, sarcomeric actinin and the L-type Calcium channel. 
         [0067]    Genetic tools and cell sorting methods were utilized to determine the efficiencies of microRNA-induced cell conversion in both neonatal cardiac fibroblasts and tail tip fibroblasts. The efficiency of converting cardiac fibroblasts and tail tip fibroblasts to cardiac myocytes using the methods described herein is between 3-5% of the overall cell population. Specifically, cardiac fibroblasts were isolated from a transgenic model where the cyan fluorescent protein (CFP) reporter is driven by the myosin heavy chain alpha (alphaMHC) reporter, which is specifically “turned on” in cardiac myocytes. Thus, the starting cell population of cardiac fibroblasts is CFP negative. Seven days post-transfection with miRs (and small molecules) the CFP positive cell population was sorted, and this percentage was subtracted from the negative control. Therefore, this overall percentage is the efficiency of conversion to a cardiac myocyte-like phenotype, e.g., between 3-5% of the overall cell population. The efficiency of conversion to cardiac myocytes was increased to &gt;30-50% by the addition of efficiency-enhancing molecules such as JAK inhibitor 1 to the combination of miRs. 
         [0068]    Transfection rate efficiencies were measured 48 hours post-transfection, and range between 70-90% depending on the miR and combination. Specifically, to determine transfection rate efficiencies, a small fraction of cells that were transfected were removed, and RNA was isolated from them. Downregulation of known target genes of the miRs used in the study is then assessed using quantitative PCR. 
         [0069]    In some cases, microRNA or a combination of microRNAs is administered with a small molecule to increase reprogramming efficiencies. Small molecules suitable for increasing the efficiency of conversion to cardiac myocytes include valproic acid, bone morphogenetic protein 4 (BMP4), JAK inhibitor 1, RG108, R(+)Bay K 8644, PS48, and A83-01. 
         [0070]    The microRNA-transfected and subsequently reprogrammed cell populations have been isolated using genetic tools. Spontaneous contractile events have been observed in these cells maintained in culture. This functional property of the cells indicates that they have been reprogrammed into cardiac myocytes. 
         [0071]    In a separate set of experiments, the microRNAs or microRNA combinations described herein are delivered (in lentiviral form) into a transgenic mouse model to determine whether these microRNAs convert cardiac fibroblasts into cardiac myocytes in vivo. 
         [0072]    Exemplary sequences for use in compositions and methods of the invention include the following: Human HAND2 (NC — 000004.11; SEQ ID NO: 22), Human Isl-1 (NC — 000005.9; SEQ ID NO: 23), Human MEF2C(NC — 000005.9; SEQ ID NO: 24), Human MYH6 (AC — 000057.1; SEQ ID NO: 25), Human Nkx2.5 (NG — 013340.1; SEQ ID NO: 26), Human Tnni3 (NG — 007866.1; SEQ ID NO: 27), Human-Gata4 (SEQ ID NO: 28), Human TBX5 (AB051068.1; SEQ ID NO: 31). 
         [0073]    The sequences identified by the Genbank accession numbers provided below are incorporated herein by reference. 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Marker 
                 Genebank Number 
                 Genome Reference 
               
               
                   
               
             
             
               
                 Human HAND2 
                 GI:12545384 
                 NC_000004.11 
               
               
                 Human Isl-1 
                 GI:115387114 
                 NC_000005.9 
               
               
                 Human MEF2C 
                 Isoform 1: GI:19923215 
                 NC_000005.9 
               
               
                   
                 Isoform 2: GI:196114945 
               
               
                 Human MYH6 
                 GI:156104908 
                 AC_000057.1 
               
               
                 Human Nkx2.5 
                 Isoform 1: GI:4758090 
                 NG_013340.1 
               
               
                   
                 Isoform 2: GI:260898750 
               
               
                   
                 Isoform 3: GI:260898752 
               
               
                 Human Tnni3 
                 GI:151101270 
                 NG_007866.1 
               
               
                 Human - Gata4 
                 GI:33188461 
                 NG_008177.1 
               
               
                 Human TBX5 
                 GI:14041801 
                 AB051068.1 
               
               
                   
               
             
          
         
       
     
       Example 3 
     Reprogramming of Cardiac Fibroblasts into Cardiac Myocytes In Vivo 
       [0074]    The microRNAs or microRNA combinations described herein were delivered (in lentiviral form) into a transgenic mouse model to determine whether the microRNAs convert cardiac fibroblasts into cardiac myocytes in vivo. 
         [0075]    MicroRNA-expressing lentivirus constructs were purchased from Thermo Scientific (formerly Open Biosystems) in purified form. The following miRIDIAN shMIMIC microRNAs (followed by the catalog #) were used: 
         [0000]    1. Non-silencing control—HMR5872
 
2. miR-499-5p—VSH5841-101207453
 
3. miR-133a—VSH5841-101208056
 
4. miR1—VSH5841-101208392
 
5. miR208a—VSH5841-101207644
 
         [0076]    MicroRNA/miRNA oligonucleotides or a combination of microRNA oligonucleotides are optionally delivered utilizing a lentivirus. In addition to Thermo Scientific, microRNA delivery systems are available from other suppliers such as BioSettia (San Diego, Calif. USA). For example, human microRNA (hsa-miRNA) precursors and approximately 100 bp of upstream and downstream flanking genomic sequences are PCR amplified and cloned into a self-inactivated (SIN) lentiviral vector to generate a lenti-miRNA collection. The miRNA lentivirus is a ready-to-use lentiviral stock. For example, each individual miRNA in the human lentiviral collection was cloned from its native context, including the stem-loop precursor sequence and approximately 100 bp of upstream and downstream flanking sequences to ensure that the miRNA is properly expressed and processed, and that it would function similarly to its endogenous form. Lentiviral transduction is one of the most effective delivery systems to express miRNA, shRNA, and cDNA. Unlike the retroviral system, the lentiviral integration is cell cycle independent. The genetic materials encoded by the lentivirus are efficiently delivered into both dividing and non-dividing cells. The lenti-miRNA viral genome is integrated into the host chromosome, thereby stably expressing the miRNA in transduced cell lines. 
         [0077]    The miR-expressing lentivirus were injected intramyocardially or infused at a dose of 2×10 6  pfu per mouse.  FIG. 8  shows an exemplary image from a miR-1 injected heart. Heart tissue of a neonatal mouse was injected with lentivirus expressing miR-1. The neonate was injected at age 3-4 days old and two weeks later, the heart was harvested, fixed and stained. These neonates are from a transgenic line where the red (tomato) reporter is a marker of cells derived from the fibroblastic lineage. If a cell expresses red/tomato, it is/has been a fibroblast at some point during its developmental lineage. The green is from staining of the section with the cardiac myocyte-specific marker cardiac troponin.  FIG. 8  demonstrates in vivo evidence of miR-induced direct reprogramming as shown by co-localization of red and green (the arrows are pointing to co-localization of red and green in the boxed area of the image). 
       Other Embodiments 
       [0078]    While the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims. 
         [0079]    The patent and scientific literature referred to herein establishes the knowledge that is available to those with skill in the art. All United States patents and published or unpublished United States patent applications cited herein are incorporated by reference. All published foreign patents and patent applications cited herein are hereby incorporated by reference. Genbank and NCBI submissions indicated by accession number cited herein are hereby incorporated by reference. All other published references, documents, manuscripts and scientific literature cited herein are hereby incorporated by reference. 
         [0080]    While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.