Abstract:
α 2 -macroglobulin-related agents for treating or preventing a fibrotic disorder associated with fibrillogenesis are disclosed along with methods for using the agents, as well as methods for producing agents suited for use in the disclosed methods for treating or preventing a fibrotic disorder.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/839,019, filed Aug. 21, 2006, incorporated herein by reference as if set forth in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with United States government support awarded by the following agencies: NIH GM063471, GM071679 and AR047746. The United States government has certain rights in this invention. 
    
    
     BACKGROUND 
     α 2 -macroglobulin (α 2 M) is a member of an α-macroglobulin family of proteins found in plasma and egg whites of a broad range of animal species. α 2 M is present in human plasma at relatively high levels (i.e., 2-4 mg/ml) and is produced by several cell types, such as hepatocytes, lung fibroblasts, macrophages, astrocytes and tumor cells. Borth W, “Alpha 2-macroglobulin. A multifunctional binding and targeting protein with possible roles in immunity and autoimmunity,” Ann. N.Y. Acad. Sci. 737:267-272 (1994), incorporated herein by reference as if set forth in its entirety. 
     α 2 M was initially thought to function in plasma and tissue as a humoral defense barrier that binds host or foreign peptides and particles via exposed 39 amino acid “bait regions” present on each of four identical 185 kDa subunits. Each bait region contains sites at which various proteinases, or other nucleophiles, can cleave the subunits, thereby activating α 2 M by changing the subunit conformation, and exposing a highly reactive internal thioester. Borth W, “Alpha 2-macroglobulin, a multifunctional binding protein with targeting characteristics,” FASEB J. 6:3345-3353 (1992); and Sottrup-Jensen L, “Alpha-macroglobulins: structure, shape, and mechanism of proteinase complex formation,” J. Biol. Chem. 264:11539-11542 (1989). The thioester covalently binds and entraps the proteinase or nucleophile, inhibiting further activity by steric hindrance. For example, α 2 M inhibits metalloproteinases belonging to a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) family, see Tortorella M, et al., “Alpha 2-macroglobulin is a novel substrate for ADAMTS-4 and ADAMTS-5 and represents an endogenous inhibitor of these enzymes,” J. Biol. Chem. 279:17554-17561 (2004), but was previously reported that it does not inhibit proteinases with astacin-like protease domains, see Baker A, et al., “Metalloproteinase inhibitors: biological actions and therapeutic opportunities,” J. Cell Sci. 115:3719-3727 (2002). 
     Activated α 2 M is also a targeting carrier for cytokines or growth factors (e.g., TGF-β, PDGF; IL-1β, basic FGF and NGF) involved in modulating biological responses of various cell types. The cytokine or growth factor dissociates either on the cell surface of a cell expressing the low-density lipoprotein receptor-related protein (LPR) or in an endocytic compartment within the cell expressing the LPR. Activated α 2 M binds to LRP, which results in rapid clearance of α 2 M-proteinase complexes from the plasma or extracellular space for subsequent catabolism. In addition, α 2 M functions as a protective factor against many pathogens by binding to certain peptides (e.g. toxins or cell surface proteins) of some parasites, bacteria and viruses. 
     Bone morphogenetic protein-1 (BMP-1) is a prototype of a subgroup of structurally similar, secreted metalloproteinases having an astacin-like protease domain, CUB protein-protein interaction domains and EGF motifs. Bond J &amp; Benyon R, “The astacin family of metalloendopeptidases,” Protein Sci. 4:1247-1261 (1995). In mammals, members of this subgroup proteolytically cleave precursors into mature, extracellular matrix-(ECM) forming proteins. Members of this subgroup also activate some members of the TGF-β superfamily in a broad range of species by cleaving extracellular protein antagonists. Thus, mammalian BMP-1-like proteinases (i.e., BMP-1, mammalian Tolloid (mTLD) and mammalian Tolloid-like 1 and 2 (mTLL-1 and mTLL-2, respectively)) are likely to be involved in forming ECM and in signaling by certain TGF-β-like molecules in morphogenetic events and homeostasis. 
     BMP-1 and Tolloid-like proteinases have a distinct protein domain, structure that includes (starting at the N-terminus) a signal peptide (for secretion), a prodomain (that must be cleaved to activate the proteinase), a conserved protease domain found in the astacin M12A family of metzincin metalloproteases, and then a number of CUB and EGF-like protein-protein interaction domains. See Ge G &amp; Greenspan D, “Developmental roles of the BMP1/TLD metalloproteinases,” Birth Defects Res. (Part C) 78:47-68 (2006); and Hopkins D, et al., “The bone morphogenetic protein 1/Tolloid-like metalloproteinases,” Matrix Biol. (Epub ahead of print, May 18, 2007), each of which is incorporated herein by reference as if set forth in its entirety. These proteinases play diverse roles in morphogenetic events, via biosynthetic cleavage of precursors into mature functional proteins involved in formation of the ECM, and via activation of certain members of the TGFβ superfamily of growth factors. Greenspan D, “Biosynthetic processing of collagen molecules,” Top. Curr. Chem. 247:149-183 (2005). 
     In particular, BMP-1-like proteinases (1) process type I-III procollagen C-propeptides to yield the major fibrous components of ECM; (2) cleave a zymogen to produce active lysyl oxidase enzyme that catalyzes covalent cross-linking in collagen fibers; and (3) process procollagen N-propeptides, and in some cases C-propeptides, of the minor fibrillar collagen types V and XI. Ge G, et al., “Bone morphogenetic protein-1/tolloid-related metalloproteinases process osteoglycin and enhance its ability to regulate collagen fibrillogenesis,” J. Biol. Chem. 279:41626-41633 (2004). The latter are incorporated into growing fibrils of collagen types I and II, respectively, and appear to control the geometries of the resulting heterotypic fibrils. 
     Because BMP-1-like proteinases provide most, if not all procollagen C-proteinase (pCP) activity in vivo, and because C-propeptide removal is essential for collagen fibrillogenesis, the BMP-1-like proteinases are attractive targets for therapeutic interventions where inhibition of collagen fibrillogenesis is desirable. Although the formation of collagen fibrils is essential to morphogenesis and to healing of wounds and bone fractures in the adult, excessive formation of fibrous collagenous ECM causes much morbidity in the general population. These conditions include keloids (excessive skin scarring), surgical adhesions, and deep-seated fibroses of organs including lungs, liver and kidneys. The deep-seated fibroses are particularly ominous, as the replacement of parenchymal tissue by scar tissue composed essentially of fibrous, collagenous ECM destroys organ function. 
     Accordingly, there is a need for new methods and compositions for treating fibrotic disorders, particularly those that inhibit the activities of BMP-1-like proteinases. 
     BRIEF SUMMARY 
     In a first aspect, the present invention is summarized as a method of inhibiting a BMP-1-like proteinase in a human or non-human animal experiencing or susceptible to a fibrotic disorder caused by the BMP-1-like proteinase that includes administering to the animal an amount of an inhibitor of a BMP-1-like proteinase effective to reduce BMP-1-like proteinase activity in the animal, where the reduction is characterized by a reduction in severity or occurrence of the fibrotic disorder. 
     In some embodiments of the first aspect, the administered inhibitor is natural or modified α 2 M, and in related embodiments the α 2 M is modified-relative to natural α 2 M in that in place of a native bait region, a bait region of probiglycan, a small leucine-rich proteoglycan precursor, is present. 
     In a second aspect, the present invention is summarized as a method for engineering an inhibitor of a BMP-1-like proteinase from a naturally-occurring α 2 M protein having a bait region that includes substituting the bait region with a bait region from a protein other than α 2 M protein that is cleaved by BMP-1 to produce an engineered α 2 M protein. In a related embodiment, the other protein can be a probiglycan, and can be a probiglycan from a human. The source of the naturally occurring α 2 M protein is not critical, as long as the engineered protein contains a bait region that can be cleaved by a BMP-1-like proteinase. 
     These and other features, aspects and advantages of the present invention will become better understood from the description that follows. In the description, reference is made to the accompanying drawings, which form a part hereof and in which there is shown by way of illustration, not limitation, embodiments of the invention. The description of preferred embodiments is not intended to limit the invention but rather to cover all modifications, equivalents and alternatives. Reference should therefore be made to the claims recited herein for interpreting the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments described herein will be better understood and features, aspects and advantages other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such detailed description makes reference to the following drawings, wherein: 
         FIG. 1  shows α 2 M as a candidate substrate for cleavage by BMP-1-like proteinases. The bait region from human α 2 M (residues 667-705) is aligned with the cleavage sites of a number of protein substrates of BMP-1-like proteinases, including growth differentiation factor 11 (GDF-11), myostatin, procollagens I-III and the pro-α2(V) and pro-α1 (VII) procollagen chains, a γ2 chain of laminin 5, probiglycan and an N-terminal cleavage site of chordin immediately beneath the α 2 M sequence is the probiglycan sequence that substitutes for the native bait region in a mutant α 2 M (b-α 2 M). Vertical arrows mark the sites of potential ADAMTS-2 cleavage sites in α 2 M and b-α 2 M. Aspartate residues conserved at the P1′ positions of the various scissile bonds are in boldface, as are aromatic side chains, previously noted NH 2 -terminal to scissile bonds in many previously identified substrates of BMP-1-like proteinases. Phe 684 , Tyr 685  and Asp 688  of the α 2 M sequence are similarly presented in boldface; 
         FIG. 2  shows that BMP-1 cleaves and forms a complex with α 2 M. ( FIG. 2A ) Electrophoretic patterns on an SDS-PAGE gel are compared for human α 2 M incubated in the absence (α 2 M) or presence (α 2 M+BMP-1) of BMP-1. BMP-1 alone (BMP-1) was electrophoresed in the final lane, to act as a marker for the corresponding band in the α 2 M+BMP-1 lane. The gel was stained with Coomassie Brilliant Blue R-250. The arrows denote the cleavage products of α 2 M. Numbers to the left of the gel correspond to the positions and approximate sizes, in kDa, of molecular mass markers. ( FIGS. 2B and 2C ) Western blots, using anti-Flag antibodies for the detection of tagged BMP-1, of α 2 M incubated alone (α 2 M) or with BMP-1 (α 2 M+BMP-1). BMP-1 starting material [BMP-1(s)] or BMP-1 incubated in the absence of α 2 M [BMP-1(0)], were co-electrophoresed as controls. SDS-PAGE of samples was carried out under reducing ( FIG. 2B ) or non-reducing ( FIG. 2C ) conditions. Numbers to the left of the blots correspond to the positions and approximate sizes, in kDa, of molecular mass markers. Western blots probed with anti-α 2 M antibodies show α 2 M to co-localize to the same high molecular weight forms as BMP-1 under both reducing ( FIG. 2D ) and non-reducing ( FIG. 2E ) conditions; 
         FIG. 3  shows the time- and dose-dependent inhibition of BMP-1 procollagen C-proteinase activity by native and recombinant forms of α 2 M. ( FIG. 3A ) 30 nM BMP-1 was incubated with 30 nM α 2 M for 0, 10, 30, 60, 90, 120, 240, and 360 min (plasma α 2 M and recombinant wild type α 2 M) or for 0, 2, 5, 10, 30, 120, 240, and 360 min (b-α 2 M) at 37° C. Cleavage reaction samples were analyzed by SDS-PAGE on 7.5% acrylamide gels, followed by Western blotting with anti-α 2 M antibodies, quantification with NIH Image software, and plotting of relative percentage cleavage of α 2 M vs time in minutes. ( FIG. 3B ) 9.4 nM BMP- was preincubated with 0, 4.7, 9.4, 18.7, 37.5, 56.2, 75.0, or 93.7 nM α 2 M for 2 hours at 37° C., followed by incubation with 400 ng  3 H-radiolabeled type I procollagen. Cleavage reaction samples were analyzed by SDS-PAGE on 5% gels, followed by scanning of autofluorograms, quantification of bands, using NIH Image software, and plotting of relative percent cleavage of procollagen vs nM concentration of α 2 M. Non-linear regression was performed using SigmaPlot; 
         FIG. 4  shows that α 2 M inhibits probiglycan cleavage by BMP-1. Western blot analysis, using anti-human biglycan antibody LF-51 (available from National Institutes of Health) raised against amino acids 27-40 of SEQ ID NO:2 (GVLDPDSVTPTYSA)—the mature region of biglycan—was employed to monitor the processing of probiglycan to biglycan by incubation for 5, 10 or 30 minutes with BMP-1 (proBGN+BMP-1) or with BMP-1 preincubated with α 2 M (proBGN+α 2 M). The upper and lower arrows denote probiglycan and mature biglycan, respectively. Numbers to the left of the blot correspond to the positions and approximate sizes, in kDa, of molecular mass markers; 
         FIG. 5  shows that methylamine-treated α 2 M is neither cleaved nor complexed by BMP-1 and does not inhibit cleavage of probiglycan by BMP-1. ( FIG. 5A ) Electrophoretic patterns on an SDS-PAGE gel are compared for human α 2 M preincubated either alone (α 2 M) or with methylamine (M-α 2 M) and then incubation of BMP-1 with either the untreated (α 2 M+BMP-1) or methylamine-treated (M-α 2 M+BMP-1) α 2 M samples. The gel was stained with Coomassie Brilliant Blue R-250. The arrow denotes BMP-1. Numbers to the left of the blot and gel correspond to the positions and approximate sizes, in kDa, of molecular mass markers. ( FIG. 5B ) A western blot, using anti-Flag antibodies to detect tagged BMP-1, of BMP-1 alone (BMP-1) or BMP-1 incubated with untreated α 2 M [BMP-1+α 2 M(s)] or with α 2 M preincubated in the absence [BMP-1+α 2 M(o)] or presence [BMP-1+M-α 2 M] of methylamine. ( FIG. 5C ) Western blot analysis using LF-51 antibody was employed to monitor the processing of probiglycan to biglycan by incubation alone (−), with BMP-1 (BMP-1), or with BMP-1 preincubated with α 2 M [BMP-1+α 2 M(s)] or with BMP-1 preincubated with α 2 M that had itself been preincubated either in the presence (BMP-1+M-α 2 M) or absence [BMP-1+α 2 M(0)] of methylamine. Numbers to the left of the blot correspond to the positions and approximate sizes, in kDa, of molecular mass markers; 
         FIG. 6  shows that substituting the probiglycan bait region sequences in place of the native α 2 M bait region enhances α 2 M inhibition of BMP-1˜25-fold. ( FIG. 6A ) A Western blot probed with anti-α 2 M is shown of plasma α 2 M, or recombinant wild type α 2 M (rα 2 M) or mutant (b-α 2 M) α 2 M incubated in the presence (+) or absence (−) of BMP-1. ( FIGS. 6B and 6C ) 9.4 nM BMP-1 was preincubated with 0, 4.7, 9.4, 18.7, 37.5, 56.2, 75.0, or 93.7 nM wild type α 2 M ( FIG. 6B ) or 0, 0.47, 0.94, 1.87, 3.75, 5.62, 9.4, or 18.7 nM b-α 2 M ( FIG. 6C ) for 2 hours at 37° C., followed by incubation with 400 ng  3 H-radiolabeled type I procollagen. Cleavage reaction samples were analyzed by SDS-PAGE on 5% gels, followed by scanning of autofluorograms, quantification of bands, using NIH Image software, and plotting of relative percent cleavage of substrate vs nM concentration of α 2 M. Non-linear regression was performed using SigmaPlot. ( FIG. 6D ) A Western blot is shown of recombinant wild type (rα 2 M) or mutant (b-α 2 M) α 2 M cross-linked with glutaraldehyde. ( FIG. 6E ) An autofluorogram shows the SDS-PAGE electrophoretic patterns of  35 S-radiolabeled BMP-1 incubated alone, or in the presence of plasma α 2 M (α 2 M) or recombinant wild type α 2 M (rα 2 M) or mutant (b-α 2 M) α 2 M. Numbers to the left of the autofluorogram correspond to the positions and approximate sizes, in kDa, of molecular mass markers; 
         FIG. 7  shows that α 2 M can inhibit procollagen processing by cells. ( FIG. 7A ) Western blots of media and cell layer samples of MC-3T3 cells incubated in the presence of 20 nM α 2 M or b-α 2 M, or an equivalent volume of buffer (−). Blots were probed with anti-α1(I) C-telopeptide antibodies. ( FIG. 7B ) The media sample blot was scanned and quantified using NIH Image software to provide the graft shown in which the percentage of total signal each for the wild-type α 2 M lane and for the b-α 2 M lane is given for uncleaved pro-α1(I) chains (pro), pCα1(I) (pC) and pNα1(I) (pN) processing intermediates, and completely processed mature α1(I) chains [col1 (I)]; and 
         FIG. 8  shows the relative conservation of amino acid residues flanking BMP-1 cleavage sites. ( FIG. 8A ) Sequence logo of the thirty-six positions around the cleavage site. The sequence logo was produced by the WebLogo application of Crooks et al. for sequences flanking the BMP-1 cleavage sites of twenty-six published and unpublished substrates. Crooks et al., “WebLogo: a sequence logo generator,” Genome Res. 14:1188-1190 (2004). Height of each letter is proportional to the corresponding amino acid and the overall height of each stack is proportional to the sequence conservation at that position. Sequence conservation, measured in bits, has a maximum theoretical value of 4.32. The cleavage site resides between positions eighteen and nineteen. ( FIG. 8B ) Logged nominal p-values of the goodness of fit tests across the positions around the cleavage site. For each position, a chi-square goodness-of-fit test is employed for testing the null hypothesis that all amino acids have equal probability of occurrence at that site. Plotted are nominal p-values of the tests in the log 10 scale. Horizontal dashed gray lines correspond to p-value cut-offs of 0.05 and 0.05/36, respectively. The second cut-off is the Bonferroni adjusted multiple testing cut-off for controlling the overall Type-I error rate at the nominal level of 0.05. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Disclosed herein is a site for cleavage of α 2 M by some astacin-like proteinases, particularly BMP-1. See also, Zhang Y, et al., “Inhibition of bone morphogenetic protein 1 by native and altered forms of alpha2-macroglobulin,” J. Biol. Chem. 281:39096-39104 (2006), incorporated herein by reference as if set forth in its entirety. Cleavage at this site by BMP-1 results in formation of covalent complexes with cleaved α 2 M and potent inhibition of BMP-1 proteolytic activities. Also, a modified α 2 M, containing the probiglycan BMP-1 cleavage site in place of the native bait region, has enhanced ability to inhibit BMP-1 and to inhibit procollagen I processing by cells. 
     One inhibits a BMP-1-like proteinase such as BMP-1, mTLD, mTLL-1 or mTLL-2 in a human or non-human animal by administering an amount of an inhibitor of a BMP-1-like proteinase effective to reduce BMP-1-like proteinase activity in the animal. BMP-1-like proteinase activity is inhibited relative to pre-administration activity by at least 60%, alternatively by at least 75%, alternatively by at least 80%, alternatively by at least 85% and alternatively by at least 90%. The route of delivery varies depending upon the type of disorder being treated. That is, the inhibitor is administered topically for disorders such as keloids or for preventing excess scarring after cornea surgery or after other surgeries as well. Other routes of delivery include inhalation for pulmonary fibrosis. Furthermore, systemic delivery is contemplated for a surgical adhesion or for deep-seated fibroses of an organ. Preferred inhibitor delivery routes are topical and intravenous. The skilled artisan will appreciate the desirability of non-invasive administration of the agent. For topical delivery, creams, lotions or ointments comprising the inhibitor are a preferred delivery vehicle. For intravenous administration, the agent is provided in a pharmaceutically acceptable carrier, such as saline. 
     The inhibitor is natural or modified α 2 M. As described further below, the modified α 2 M is modified relative to natural α 2 M in that in place of the native bait region, a bait region of probiglycan, a small leucine-rich proteoglycan precursor, is present. The number of doses a human or non-human animal receives, the time allowed between doses and the length of time the human or non-human animal receives a natural or modified α 2 M can depend on the severity of the fibrotic disorder. Dosage level and the time between doses can be modified in accord with clinical assessment of the human or non-human animal. 
     It is contemplated that the methods described herein can be used with any fibrotic disorder, especially those disorders involving deposition of collagen I. Examples of fibrotic disorders include, but are not limited to, a keloid or other abnormal wound healing, a surgical adhesion or deep-seated fibroses of an organ. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the embodiments, the preferred methods and materials are now described. 
     As used herein, an “effective amount” refers to that concentration of α 2 M or of a modified α 2 M that is effective in attenuating fibrillogenesis and, hence, a fibrotic disorder. 
     As used herein, a “BMP-1-like proteinase” refers to a proteinase including, without limitation, BMP-1, mTLD, mTLL-1 and mTLL-2 that possesses an astacin-like protease domain, CUB protein-protein interaction domains and EGF motifs. 
     The invention embraced by the claims recited below will be more fully understood upon consideration of the following non-limiting Examples. 
     EXAMPLES 
     Example 1 
     Inhibition of BMP-1 by α 2 M 
     Methods: 
     Cleavage of α 2 M by BMP-1: 200 nM Flag-tagged recombinant BMP-1, prepared and purified as previously described, was incubated overnight at 37° C. with 200 nM human α 2 M (Sigma-Aldrich; St. Louis, Mo.) in 50 mM Tris-HCl, pH 7.5, 100 mM NaCl and 10 mM CaCl 2 . Scott I, et al., “Mammalian BMP-1/Tolloid-related metalloproteinases, including novel family member-mammalian Tolloid-like 2, have differential enzymatic activities and distributions of expression relevant to patterning and skeletogenesis,” Dev. Biol. 213:283-300 (1999). Subsequently, reaction proteins were analyzed by SDS-PAGE under reducing conditions on a 7.5% gel and staining with Coomassie Brilliant Blue R-250. For Western blot analysis, 320 nM BMP-1 was incubated with 200 nM α 2 M at 37° C. overnight, and the samples were loaded on a 7.5% gels and separated by SDS-PAGE, under both nonreducing and reducing conditions. Separated proteins were transferred to polyvinylidene difluoride membranes and probed with a 1:5,000 dilution of anti-FLAG antibody (Sigma-Aldrich). Subsequently, membranes were incubated with a 1:25,000 dilution of goat anti-mouse IgG HRP conjugate as the secondary antibody. 
     For a dose-dependence study, α 2 M was pre-incubated with BMP-1 for 2 hours at 37° C. The study of time-dependent inhibition of BMP-1 by α 2 M indicates that complex formation between α 2 M and BMP-1 is complete (reaches equilibrium) after 2 hours pre-incubation, under the conditions used. Thus, the rate of procollagen processing is proportional to the amount of active BMP-1 remaining uncomplexed to α 2 M. 
     Time-Dependent Inhibition of BMP-1 Cleavage of Probiglcyan by α 2 M: 15 ng BMP-1 (9.4 nM) was preincubated with or without 5 times the amount of α 2 M (47.0 nM) in 50 mM Tris-HCl, pH 7.5, 100 mM NaCl and 10 mM CaCl 2  for 2 hours at 37° C. Subsequently, 450 ng probiglycan, prepared as previously described in Scott et al., was added to a final volume of 20 μl and incubated overnight. Scott I, et al., “Bone morphogenetic protein-1 processes probiglycan,” J. Biol. Chem. 275:30504-30511 (2000). Cleavage reactions were quenched by adding 4 μl chondroitinase ABC (a mixture of 10 μl 0.01 U/μl protease-free chondroitinase ABC (Seikaguku Corp.; Tokyo, Japan), 40 μl 6× chondroitinase buffer (100 mM Tris-HCl, pH 8.0, 240 mM NaAc, 0.25 mM EDTA) and 10 μl 500 mM EDTA), followed by incubation at 37° C. for 4 hours. Samples were subjected to SDS-PAGE on a 10% gel and Western blot analysis was performed, using anti-probiglycan antibody LF51 at a 1:5,000 dilution, and a 1:25,000 dilution of goat-anti-rabbit IgG horse radish peroxidase (HRP) conjugate, as the secondary antibody. 
     Inactivation of α 2 M by Methylamine: 1 mg/ml α 2 M was incubated with 50 mM Tris-HCl, pH 7.1 in the presence or absence of 20 mM methylamine 20 hours, followed by dialysis against 50 mM Tris-HCl, pH 7.5, 100 mM NaCl. Both methylamine-treated and control α 2 M samples were tested for ability to be cleaved by BMP-1 and for ability to inhibit BMP-1 cleavage of probiglycan. 
     Production of recombinant α 2 M: Human α 2 M (NM — 000014; SEQ ID NO:14 and SEQ ID NO:15) sequences were PCR-amplified from human placenta cDNA in three fragments. The following primers were used: fragment 1 (amino acids 24-416 of SEQ ID NO:15), 5′-GCTAGCAGACTACAAAGACGATGACGACAAGTCAGTCTCTGGAAAACCGCAGTAT-3′ (SEQ ID NO:16; forward) and 5′-CAGTAAGAGAGGTACCCATAAC-3′ (SEQ ID NO:17; reverse); fragment 2 (amino acids 416-1052 of SEQ ID NO:15), 5′-GTTATGGGTACCTCTCGTTACTG-3′ (SEQ ID NO:18; forward) and 5′-ATGTAGGCTCGAGCTTGGGC-3′ (SEQ ID NO:19; reverse); fragment 3 (amino acids 1052-1474 of SEQ ID NO:15), 5′-GCCCAAGCTCGAGCCTACAT-3′ (SEQ ID NO:20; forward) and 5-GCGGCCGCTCAAGCATTTrCCAAGATCTTTGCTG-3′ (SEQ ID NO: 21; reverse). 
     PCR products were assembled into the full-length α 2 M sequence into pBlueScript II KS+ (Stratagene), and cloned downstream of (and adjoined via an NheI site to) BM40/SPARC signal peptide sequences, between the HindIII and NotI of the tetracycline-inducible expression vector pcDNA4/TO (Invitrogen Corp.; Carlsbad, Calif.). The resulting construct expresses full-length α 2 M, except that the native signal peptide is replaced by the BM40 signal peptide, for optimization of secretion. In addition, upon cleavage of the signal peptide, a FLAG epitope remains at the NH 2 -terminus of α 2 M sequences. 
     To generate mutant α 2 M, an MfeI site was introduced into the 5′-end of α 2 M bait region sequences, without changing the encoded protein, via two-step PCR. Primers used were: primer 1: 5′-GATATGTACAGCTTCCTAGAGGA-3′ (SEQ ID NO:22); primer 2: 5′-GTTGCAATTGTGGACACATTTTGGGTTTACGA-3′ (SEQ ID NO:23); primer 3: 5′-TCCACAATTGCAACAGTATGAAATGCATGGACCT-3′ (SEQ ID NO:24); and primer 4: 5′-CTTTCGTACGGTCTCCGTGTGA-3′ (SEQ ID NO:25). PCR amplicons of primer 1 and 2, 3 and 4 were then used as templates for PCR amplification using primers 1 and 4. The resulting amplicon was cloned between BsrG I and BsiW I sites in the α 2 M sequence. 
     Biglycan sequences were PCR amplified with primers 5′-GAGAGAATTCTGGGACTTCACCCTGGACGA-3′ (SEQ ID NO:26; forward) and 5′-GAAAGGTACCATGGCGCTGTAGGTGGGTGT-3′ (SEQ ID NO:27; reverse). The amplicon was then digested with EcoRI and KpnI, and cloned between MfeI and BsiWI sites in the modified α 2 M sequences. In the resulting mutant α 2 M (b-α 2 M) the sequences flanking the human probiglycan BMP-1 cleavage site substitute for the bait region (see  FIG. 1 ). 
     293 T-REx cells (Invitrogen Corp.) were maintained in Dulbecco&#39;s Modified Eagle&#39;s medium (DMEM), with 5 μg/ml blasticidin and 10% fetal bovine serum (FBS). Cells at 80% confluence were transfected with 1 μg expression plasmid/35 mm culture dish using Lipofectamine (Invitrogen Corp.). After 48 hours, cells were selected in the same type of medium supplemented with 200 μg/ml Zeocin. Production of secreted α 2 M, upon induction with 1 μg/ml tetracycline, was detected via Western blot. 
     Confluent cells were washed twice with phosphate buffered saline (PBS) and incubated in serum-free DMEM 15 minutes at 37° C. Cells were then washed once with PBS, followed by addition of serum-free DMEM containing 1 μg/ml tetracycline, to induce protein expression, and 40 μg/ml soybean trypsin inhibitor. Conditioned medium was harvested every 24 hours, and protease inhibitors were added to final concentrations of 5 mM EDTA, 1 mM phenylmethylsulfonyl fluoride, 1 mM N-ethylmaleimide, and 1 mM p-aminobenzoic acid. Conditioned medium was centrifuged to remove debris and supernatants were stored at −70° C. FLAG-tagged α 2 M and b-α 2 M were affinity-purified from conditioned medium using an anti-FLAG M2 column (Sigma-Aldrich), following manufacturer&#39;s instructions. 
     Cross-linking: 6.9 nM recombinant α 2 M or b-α 2 M were incubated 5 minutes with 80 mM glutaraldehyde (Sigma) in PBS at room temperature. Cross-linking was terminated by adding glycine to a final concentration of 0.2 M. Samples were separated by SDS-PAGE on 4-15% acrylamide gradient gels and were subjected to immunoblotting. 
     Determination of K i  Values and second-order Rate Constants for BMP-1-α 2 M Interactions: Confluent 293 T-Rex cells producing recombinant BMP-1 were washed twice with PBS, and incubated 15 minutes in scrum-free, Cys/Met-free DMEM at 37° C. Cells were then washed once with PBS, followed by addition of serum-free DMEM containing 1 μg/ml tetracycline, to induce protein expression, 40 μg/ml soybean trypsin inhibitor and 60 μCi/ml Pro-Mix  35 S cell labeling mix (Amersham). Conditioned medium was harvested every 24 hours, and protease inhibitors were added to final concentrations of 1 mM phenylmethylsulfonyl fluoride, 1 mM N-ethylmaleimide, and 1 mM p-aminobenzoic acid. Metabolically  35 S-radiolabeled BMP-1 was affinity-purified from conditioned medium using an anti-FLAG M2 column (Sigma), following manufacturer&#39;s instructions. 
     40 nM  35 S-labeled BMP-1 was incubated with 20, 40, 80, 160, and 240 nM plasma α 2 M, or recombinant wild type α 2 M or with 5, 10, 20, 40, and 80 nM b-α 2 M at 37° C. in 50 mM Tris-HCl, pH 7.5, 100 mM NaCl and 10 mM CaCl 2 . Reactions were stopped at 10, 30, 60, 90 and 120 minutes (plasma α 2 M and recombinant wild type α 2 M), or at 2, 5, 10, 20 and 30 minutes (b-α 2 M) by adding. SDS-PAGE sample buffer and boiling 5 minutes at 95° C. Protein samples were separated on 7.5% acrylamide SDS-PAGE gels, which were then treated with EN 3 HANCE (DuPont) and exposed to film. Percentages of BMP-1 incorporated into high molecular weight complexes were determined by densitometry and kinetic parameters were determined essentially via the method of Enghild J, et al, “Interaction of human rheumatoid synovial collagenase (matrix metalloproteinase 1) and stromelysin (matrix metalloproteinase 3) with human alpha 2-macroglobulin and chicken ovostatin. Binding kinetics and identification of matrix metalloproteinase cleavage sites,” J. Biol. Chem. 264:8779-8785 (1989). 
     Inhibition of Collagen Processing by Cells: 2×10 5  MC-3T3-E1 cells were plated in a 24 well plate, allowed to attach overnight, and then treated with 50 μg/ml ascorbate in DMEM 10% FBS for 24 hours. Cells were washed twice with PBS, and incubated in serum-free DMEM 15 minutes at 37° C. Cells were then washed once with PBS, followed by addition of serum-free DMEM containing 50 μg/ml ascorbate, 40 μg/ml soybean trypsin inhibitor, and 20 nM α 2 M or b-α 2 M, or an equivalent volume of buffer (50 mM Tris-HCl, pH 7.5, 150 mM NaCl). Conditioned medium was harvested after 24 hours as described above. Cell layers were washed twice with ice-cold PBS, and scraped into hot SDS-sample buffer. Medium and cell layer samples were subjected to SDS-PAGE on acrylamide gels, transferred to nitrocellulose membranes and probed with anti-collagen α1(I) C-telopeptide polyclonal antibody LF67 (a generous gift from Larry Fisher), as described. 
     Amino Acid Specificity Analysis of Identified Cleavage Sites of BMP-1-like Proteinases: We investigated the amino acid sequence specificity of the cleavage sites of twenty-six substrates of BMP-1-like proteinases by considering a thirty-six amino acid region around these sites. The sequence logo of the sequences is given in  FIG. 8A , in which the cleavage site is between positions 18 and 19. It is easily observed that positions around the cleavage site exhibit bias towards certain amino acids. We further tested, for each of the thirty-six positions, the null hypothesis that the amino acid composition of the site follows a random amino acid distribution, which assigns an equal occurrence probability to each amino acid. The nominal p-values from the chi-square goodness-of-fit test of each position are plotted in  FIG. 8B  on the log 10 scale. P-value cut-offs of 0.05 and 0.05/36 are marked as gray dashed horizontal lines on this plot. The second cut-off is the Bonferroni adjusted multiple testing cut-off that provides the control of the overall Type-I error rate at level 0.05. We observe that positions 13, 16, 17, 18, 19, 20 and 21 exhibit strong evidence against the null hypothesis of equal amino acid frequency. Furthermore, although positions 7 and 23 do not pass the Bonferroni adjusted p-value cut-off, they have quite small p-values (0.0016 and 0.002, respectively). 
     Results: 
     BMP-1 Cleaves α 2 M: Perusal of the amino acid sequence of the α 2 M bait region found a site comprising residues Ser 687 , Asp 688  and surrounding residues that resembled the majority of known BMP-1 cleavage sites ( FIG. 1 ). The resemblance resided primarily in the placement of Phe 684  and Tyr 686  3 and 4 residues, respectively, NH 2 -terminal to Asp 688 , since residues with aromatic side chains are frequently found in positions P2-P5, and an Asp is almost always found in the P1′ position of previously identified substrates of BMP-1-like proteinases ( FIG. 1 ). Moreover, the majority of previously characterized cleavage sites of BMP-1-like proteinases have residues with small side chains in the P1 positions ( FIG. 1 ), such that the placement of α 2 M Ser 687  in relationship to Asp 688 , Phe 684  and Tyr 686  is also reminiscent of a BMP-1 cleavage site. 
     As can be seen ( FIG. 2A ), α 2 M incubated alone at 37° C. overnight was stable. In contrast, 185-kDa α 2 M incubated at 37° C. overnight in the presence of BMP-1 was cleaved to produce two bands of ˜100- and ˜85-kDa. NH 2 -terminal amino acid sequencing of the 85-kDa band yielded the sequence SVSGKPQYMV (SEQ ID NO:28), which corresponds to the NH 2 -terminus of secreted α 2 M. NH 2 -terminal amino acid sequencing of the 100-kDa band yielded the sequence DVMGRGHXR (SEQ ID NO:29, wherein X represents an unidentified residue), thus demonstrating that BMP-1 cleaves α 2 M at the predicted site between Ser 687  and Asp 688  within the bait region. 
     Cleaved α 2 M Forms a Complex with BMP-1: As can be seen ( FIG. 2B ), in the presence of α 2 M, BMP-1, which is normally detected on SDS-PAGE gels as a ˜90-kDa monomer can be detected as a ˜270-kDa form on a reduced gel. This result is consistent with the interpretation that a single cleaved 100-kDa C-terminal portion of α 2 M forms a ˜190-kDa covalent complex with a single molecule of BMP-1. Under non-reducing conditions ( FIG. 2C ), BMP-1 can be detected as even higher molecular weight forms. The 85-kDa NH 2 -terminal and the 100-kDa COOH-terminal fragments of cleaved α 2 M can remain covalently bound, via disulfide linkage, and this form can be linked to other 85-kDa and 185-kDa forms via disulfide bonds. Thus, the high molecular weight forms observed under non-reducing conditions likely represent BMP-1 covalently bound, via thioester, to 185-, 270- and 375-kDa disulfide bonded oligomers, although the exact identity of each band on the non-reducing-gel remains somewhat speculative. The above interpretations are consistent with Western blots probed with anti-α 2 M antibodies, which show α 2 M to co-localize to the same high molecular weight forms as BMP-1 under both reducing ( FIG. 2D ) and non-reducing ( FIG. 2E ) conditions. The observation here of covalent binding of BMP-1 to the 100-kDa α 2 M cleavage product is consistent with the mechanism whereby α 2 M has been found to covalently bind other proteinases that it inhibits. 
     α 2 M Inhibits the pCP Activity of BMP-1: Since the first identified, and best characterized activity of BMP-1 is as a pCP, Kessler E, et al., “Bone morphogenetic protein-1: the type I procollagen C-proteinase,” Science 271:360-362 (1996), we next sought to determine whether this activity is inhibited in the presence of α 2 M. Control experiments demonstrated that BMP-1 achieves maximum cleavage of plasma α 2 M by 2 hours ( FIG. 3A ). Thus, to gauge the effect of α 2 M-BMP-1 interaction on BMP-1 pCP activity, a constant amount of BMP-1 (9.4 nM) was preincubated 2 hours with increasing concentrations of α 2 M (0, 4.7, 9.4, 18.7, 37.5, 56.2, 75.0, or 93.7 nM), prior to incubation with  3 H-radiolabeled type I procollagen. Reaction mixtures were subjected to SDS-PAGE and cleavage of procollagen was measured by densitometric analysis of autofluorograms. As can be seen ( FIG. 3B ), prior incubation with α 2 M led to potent inhibition of BMP-1 pCP activity, with a calculated IC 50  of 4.8 nM. 
     α 2 M Inhibits the Cleavage of Probiglycan by BMP-1: As can be seen ( FIG. 4 ), whereas BMP-1 was able to completely convert probiglycan to biglycan after 30 minutes under assay conditions, preincubation with a five-fold molar excess of α 2 M for 2 hours prior to incubation with probiglycan resulted in inhibition of a majority of probiglycan processing. Thus, α 2 M appears to be a general inhibitor of BMP-1 activity against various substrates. 
     Mechanism of α 2 M Inhibition of BMP-1: As can be seen, BMP-1 was unable to cleave methylamine-treated α 2 M ( FIG. 5A ). In addition, α 2 M pretreated with methylamine did not form complexes with BMP-1 ( FIG. 5B ). Furthermore, α 2 M pretreated with methylamine was unable to inhibit the processing of probiglycan to biglycan by BMP-1 ( FIG. 5C ). Inability of BMP-1 to cleave methylamine-treated α 2 M was probably the consequence of the conformational change induced in α 2 M by interaction of methylamine with the α 2 M thioester. Subsequent to this conformational change, the bait region is presumably not available to proteinases for cleavage. Together, these results bolster the conclusion that inhibition and complexing of BMP-1 by α 2 M involves formation of a thioester bond between BMP-1 and α 2 M, and a consequent α 2 M conformational change. 
     Example 2 
     Efficiency of b-α 2 M 
     Methods and Results: 
     b-α 2 M has enhanced ability to inhibit BMP-1: We previously noted wide differences in the efficiency (e.g., percent cleavage and rate of cleavage) with which different substrates art cleaved by BMP-1 (unpublished data). One of the substrates processed most efficiently by BMP-1 is probiglycan. We therefore sought to determine whether we could enhance the ability of α 2 M to inhibit BMP-1 by replacing the native bait region with sequences surrounding the probiglycan scissile bond (see  FIG. 1 ). 
     As can be seen ( FIG. 6A ), b-α 2 M is cleaved by BMP-1 more readily than recombinant wild-type α 2 M (rα 2 M). When the pCP inhibitory activities of varying concentrations of rα 2 M and b-α 2 M were measured ( FIGS. 6B and 6C ), they led to IC 50  values of 133 nM and 1.88 nM, respectively. The IC 50  value of 133 nm for rα 2 M suggests considerably less effectiveness in BMP-1 inhibition than the 4.82 value obtained for serum α 2 M ( FIG. 3B , Table I); whereas the b-α 2 M IC 50  value of 1.88 is consistent with increased inhibitory effectiveness. Although cross-linking experiments demonstrated both recombinant wild type α 2 M and b-α 2 M to form tetramers ( FIG. 6D ), some small difference in folding and/or post-translational modification appears to render the recombinant wild type protein somewhat less effective at BMP-1 inhibition than the corresponding protein from plasma. Importantly however, b-α 2 M is shown to have markedly improved efficiency in inhibiting BMP-1 compared to wild type α 2 M prepared under identical conditions, or compared to plasma α 2 M. The improved efficiency of interaction of b-α 2 M with BMP-1, compared to wild type α 2 M, is further illustrated by comparing the rapidity with which b-α 2 M is cleaved by BMP-1 compared to cleavage of wild type recombinant or plasma α 2 M ( FIG. 3A ). 
     To obtain a quantitative comparison of the rates of interaction of BMP-1 with the various wild type and mutant forms of α 2 M, we employed the methodology of Enghild et al., supra, which involves quantification of covalent proteinase-α 2 M complex formation, subsequent to incubation of radiolabeled proteinase with α 2 M.  FIG. 6E  shows that subsequent to 2 hour co-incubation of 40 nM  35 S-radiolabeled BMP-1 with 40 nM α 2 M, considerably more BMP-1 is incorporated into complexes with b-α 2 M (42% of sample), than with wild type recombinant (12% of sample) or plasma (28% of sample) α 2 M. Time course experiments conducted with a fixed amount of  35 S-radiolabeled BMP-1 (40 nM) incubated with increasing amounts of each form of α 2 M, as in Enghild et al., supra, provided K i  values of 25.2, 39.5, and 36.4 nM for b-α 2 M, and wild type recombinant and plasma α 2 M, respectively. Second order rate constants obtained from the same data showed b-α 2 M to be 23.69-fold more effective in interacting with BMP-1 than was recombinant α 2 M prepared under identical conditions and 15.69-fold more effective than wild type α 2 M from plasma (Table I). 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 Relative BMP-1 inhibitory effectiveness 
               
               
                 of plasma and recombinant α 2 M forms 
               
             
          
           
               
                   
                 K i   
                 k 2   
                 2 nd -order rate constant 
                 Relative 
               
               
                   
                 (nM) 
                 (s −1 ) 
                 (M −1 s −1 ) 
                 effectiveness 
               
               
                   
                   
               
             
          
           
               
                 Plasma α 2 M 
                 25.2 
                 0.20 
                 8.10 × 10 6   
                 1.51 
               
               
                 Recombinant α 2 M 
                 39.5 
                 0.21 
                 5.36 × 10 6   
                 1 
               
               
                 Recombinant b-α 2 M 
                 36.4 
                 4.60 
                 1.07 × 10 8   
                 23.69 
               
               
                   
               
             
          
         
       
     
     α 2 M Inhibition of Procollagen Processing by Cells: As α 2 M is capable of inhibiting the pCP activity of BMP-1, we determined whether it might be able to inhibit the processing of procollagen by cells. Towards this end, MC-3T3-E1 murine osteoblastic cells were incubated either alone or in the presence of rα 2 M or b-α 2 M. The levels of processing of procollagen and insertion into the cell layer were compared. As can be seen ( FIG. 7 ), MC-3T3 processing of procollagen was inhibited by both recombinant wild type (r) α 2 M and mutant (b)-α 2 M. However, in the case of media from rα 2 M-treated cells, most detectable collagenous material was the in the form of processing intermediate pNα1(I) (in which the N-, but not the C-propeptide is retained), or mature α1(I) chains; whereas, in media from b-α 2 M-treated cells, most detectable collagenous material was in the form of unprocessed pro-α1(I) chains ( FIGS. 7A and 7B ). These results show efficient inhibition of cellular BMP-1-like proteins by b-α 2 M, and less efficient inhibition by wild-type α 2 M. 
     The appearances of pNα1(I) chains in the wild type α 2 M-treated sample and of procollagen in the b-α 2 M-treated sample indicate that both forms of α 2 M are able to inhibit N-propeptide cleavage in cell culture by the proteinase ADAMTS-2. This is consistent with a previous report that α 2 M is capable of inhibiting ADAMTS-2 in vitro. Colige A, et al., “Domains and maturation processes that regulate the activity of ADAMTS-2, a metalloproteinase cleaving the aminopropeptide of fibrillar procollagens types I-III and V,” J. Biol. Chem. 280:34397-34408 (2005). b-α 2 M may retain the ability to inhibit ADAMTS-2, as a potential ADAMTS-2 cleavage site at the N-terminus of the native bait region is retained in the b-α 2 M sequence ( FIG. 1 ). 
     Collagen was not detected in the media of untreated cells ( FIG. 7A ), presumably because of efficient processing and insertion of mature collagen into the cell layer. Untreated cell layers contained only fully processed mature α1(I) chains, whereas cell layers of cultures treated with either wild type α 2 M or b-α 2 M contained both mature α1(I) chains and pNα1(I) forms ( FIG. 7A ). pCα1(I) forms (in which the C-, but not the N-propeptide is retained) were detected only in the media of b-α 2 M-treated cultures ( FIG. 7A ), and were not found in the cell layers of any of the cultures, presumably because pCα1(I) chains are not inserted into ECM under normal circumstances. Treatment of MC-3T3-E1 cells with plasma α 2 M (data not shown), yielded effects on procollagen processing similar to those obtained from treatment of cells with recombinant wild type α 2 M. 
     Example 3 
     Prophetic 
     Treatment of Fibrotic Disorders 
     A subject experiencing or at risk for a fibrotic disorder, such as lung fibrosis, kidney fibrosis or keloids is administered a an inhalant, injection or topical lotion (e.g., cream or ointment), respectively, comprising α 2 M or a modified α 2 M in an amount effective to reduce occurrence or severity of the fibrotic disorder. For example, a subject predisposed to keloids applies a topical cream, lotion or ointment comprising α 2 M or a modified α 2 M at least once a day. After treatment, fibrosis is prevented or reduced. 
     The invention can be tested by ascertaining anti-fibrotic effects in a model system in which pulmonary fibrosis is induced in mice via intratracheal (IT) instillation of bleomycin (2 U/kg). At 3 and 5 days following instillation with bleomycin, mice can be given IT installations of 40 nM wild type or altered α 2 M (30 μl/mouse), or PBS, as a negative control. Two weeks after initial bleomycin instillation, lung tissue can be isolated and subjected to histological (via hematoxylin and eosin staining and light microscopy) and ultrastructural (electron microscopic) analyses to test for septal thickening and reduction of alveolar space, typical of pulmonary fibrosis. Similarly, Masson trichrome-staining of paraffin sections and a Sircol assay, can be performed to determine the extent of deposition of collagenous matrix in lung (a strong indicator of fibrosis). These and additional tests of fibrotic outcome can be performed essentially as described previously. See, e.g., Giri S, et al., “Antifibrotic effect of Decorin in a bleomycin hamster model of lung fibrosis,” Biochem. Pharmacol. 54:1205-1216 (1997); and Avivi-Green C, et al., “Discoidin domain receptor 1-deficient mice are resistant to bleomycin-induced lung fibrosis,” Am. J. Respir. Crit. Care Med. 174:420-427 (2006), each of which is incorporated herein by reference as if set forth in its entirety. 
     The invention has been described in connection with what are presently considered to be the most practical and preferred embodiments. However, the present invention has been presented by way of illustration and is not intended to be limited to the disclosed embodiments. Accordingly, those skilled in the art will realize that the invention is intended to encompass all modifications and alternative arrangements within the spirit and scope of the invention as set forth in the appended claims.