Identification of Diabetic Nephropathy Biomarkers Through Transcriptomics
Condition: Type 2 Diabetes; Type 2 Diabetes With Renal Manifestations
MeSH terms: Diabetic Nephropathies; Diabetes Mellitus; Diabetes Mellitus, Type 2
Study type: Observational

Summary: 
      According to the different epidemiological studies in Mexico the prevalence of diabetic
      nephropathy is 9.1%-40% in diabetic patients, however the complication is subdiagnosed when
      we see the numbers of uncontrolled diabetics (75%) and patients that are under continuous
      screening to prevent complications development (only 12.6% had an annual albuminuria
      measurement). In addition, Mexican have an increased susceptibility to developing diabetic
      nephropathy. These data highlight the need to identify new biomarkers that could help us to
      identify those patients at high risk for developing diabetic nephropathy, in order to take
      preventing measures to delay the progress of the disease to CKD and improve the quality of
      the patients. Thus, the comparison of transcriptomic profile between diabetic patients with
      and without diabetic nephropathy is the first step to characterize this complication. In
      addition, we will be able to identify diabetic nephropathy biomarkers for development of new
      diagnostic tools and even to find therapeutic targets in Mexican from Hospital Juárez de
      México.
    

Detailed description: 
      Type 2 diabetes (T2D) is defined as a group of metabolic diseases characterized by chronic
      hyperglycemia, resulting from defects in insulin secretion, insulin action or both. According
      to the National Health Survey 2012, in Mexico, approximately 1 out of 10 persons is affected
      with T2D, though is important to mention that these data only reflect subjects previously
      diagnosed with the disease, but we expect a two fold increase in this number when including
      newly diagnosed T2D patients. In addition, the prevalence of T2D in younger age groups has
      increased (25% of diabetes cases in Mexico occurs in young adults <43 years of age), which
      implies >20 years living with the disease. In consequence, T2D is found among the leading
      causes of death, which represents a health burden for the country.

      It has been estimated that more than 40% of people with diabetes will develop chronic kidney
      disease (CKD), accounting for about 40% of all patients beginning renal replacement therapy.
      In the Instituto Mexicano del Seguro Social, nephropathy is among the five leading causes of
      medical care in general hospitals in the area and in high-specialty hospitals. A study in
      Tuxtla Gutiérrez, Chiapas, informed a 35% incidence of nephropathy was observed in diabetic
      patients. Cueto-Manzano et al., reported a 40% incidence of early nephropathy and 29% of
      established nephropathy in 756 diabetic patients from Jalisco. Other study in Mexico that
      included 3,609 diabetic patients in Guanajuato, reported a 23.8% of diabetic nephropathy. A
      recent study conducted in the State of Mexico, which included 44 458 subjects diagnosed with
      T2D, registered the presence of diabetic nephropathy in 9.1% .

      Diabetic kidney disease is uncommon if diabetes is less than one decade duration. The highest
      incidence rates of 3% per year are on average seen 10 to 20 years after diabetes onset, after
      which the rate of nephropathy tapers off. It is important to say that a diabetic patient for
      20 to 25 years without clinical signs of diabetic nephropathy has low chance to develop such
      complication. The progression of T2D to diabetic nephropathy has become a health problem, not
      only for the costs to health sector, but to the worsening of life quality of the patient and
      the outcomes.

      The main risk factors of progression to diabetic nephropathy includes: hyperglycemia,
      response to drugs, and long duration of diabetes, high blood pressure, obesity and
      dyslipidemia. Most of these factors are modifiable by drugs or changes in life style.
      Therefore, the management of the modifiable risk factors is a key for preventing and delaying
      the decline in renal function. Early diagnosis of diabetic nephropathy is another essential
      component in the management of diabetes and its complications such as nephropathy. The
      American Diabetes Association (ADA) recommends the routine screening to diabetic subjects
      with progressive diabetic nephropathy and CKD. The most widely accepted guidelines of
      National Kidney Foundation were implicating in measuring glomerular filtration rate (GFR) and
      stages of CKD using serum creatinine in patients. However, due to creatinine undergo tubular
      secretion in addition to glomerular filtration and its extrarenal elimination via the
      gastrointestinal tract, particularly in advanced renal failure, the GFR could be
      overestimated. In case of GFR, the techniques are overwhelming due to invasive methods and
      some markers are difficult to handle. Another marker used in the clinic is microalbuminuria,
      in most patients, the first sign of diabetic nephropathy is the moderate increase of urinary
      albumin excretion, i.e. 30-300 mg/g creatinine in a urine sample (also termed
      microalbuminuria). Patients who develop macroalbuminuria (>30-300 mg/g creatinine) are at
      high risk for developing diabetic nephropathy. Nonetheless, approximately up to 40% of
      patients with moderate albuminuria returns to normoalbuminuria. Moreover, up to 50% of
      patients with type 1 diabetes or T2D experience a decline in eGFR, despite the presence of
      only moderate albuminuria or even normoalbuminuria. Consequently, the actual markers
      available in the clinic are inaccurate, so it is necessary the identification of new markers
      that can recognize those patients at high risk for developing diabetic nephropathy to delay
      the progress of the complications taking the adequate measures.

      The transcriptomics

      The development of new technologies in the genomic era had allow the accelerated advance in
      system biology and the generation of knowledge in kidney development, homeostasis, and
      disease. In this context, transcriptome signatures associated with specific disease states
      can provide great information about pathogenic mechanisms and bring to light priority gene
      expression biomarker candidates . In addition, comparison of transcriptomes allows the
      identification of genes that are differentially expressed in distinct populations.

      In general, the RNA-Seq technology is very useful for differential expression analysis, in
      which is commonly adopted five steps. First, the RNA samples are fragmented into small
      complementary DNA sequences (cDNA) and then sequenced from a high throughput platform.
      Second, the small generated sequences are mapped to a transcriptome. Third, the expression
      levels for each gene or isoform are estimated. Fourth, the mapped data are normalized and,
      e.g. using statistical and machine learning methods, the differentially expressed genes
      (DEGs) are identified. Finally, the relevance of the produced data is finally evaluated from
      a biological context.

      A recent study by O´Conell et al. identified a set of 13 genes that was predictive for the
      development of renal fibrosis at 1 year of renal transplant, through microarray expression
      analysis of renal allograft recipients' biopsies. Thus, the authors suggest that the set of
      13 genes could be used to identify kidney transplant recipients at risk of allograft loss
      before the development of irreversible damage. A study by Ju et al., revealed that epidermal
      growth factor (EGF) a tubule-specific protein critical for cell differentiation and
      regeneration, predicted eGFR, throughout transcriptome analysis on microdissected
      tubulointerstitial components of human renal biopsies of patients with CKD. In addition, the
      amount of EGF protein in urine (uEGF) showed significant correlation with intrarenal EGF
      mRNA, interstitial fibrosis/tubular atrophy, eGFR and rate of eGFR loss, suggesting that uEGF
      could be a good predictor of CKD progression. Other study demonstrated that serum miRNA
      profile is affected by hemodialysis contributing to subfertility and increased risk for
      cancer development. Therefore, transcriptomics could provide better diagnostic tools,
      prognostic biomarkers, and signaling pathways amenable to therapeutic targeting.
    

Observational model: Case-Control
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        Mexican patients with Type 2 Diabetes with or without Diabetic Nephropathy
      
Biospecimen description: 
      RNA from urine and total blood
    
Keywords: Type 2 Diabetes; transcriptomics; microalbuminuria; biomarkers