Allograft rejection is a common complication post heart transplant (HTx) and can be confirmed by endomyocardial biopsy (EBx) only. There is however an increasing need to identify non-invasive biomarkers of cardiac allograft rejection. In this regard, microRNAs (miRNAs) are potential targets of choice as their role in disease pathophysiology is becoming increasingly evident. MiRNAs are highly conserved, small noncoding RNA molecules that negatively regulate gene expression. We hypothesized, that changes in miRNA profile in HTx recipient with rejection are distinct and identifiable. Accordingly, in this preliminary feasibility study, we compared the expression of miRNA in formalin-fixed, paraffin-embedded (FFPE) EBx samples from post HTx patients with different degrees of rejection. A total of 12 samples were obtained in three groups of patients showing none=0 (n=3), mild=1 (n=3) and severe=2 (n=6) stages of cellular rejection per ISHLT guidelines. The investigator analyzing the samples was blind to any information regarding clinical status of the patient or results of the EBx. The method allowed the extraction of optimum amounts of total RNA and high quality miRNA from FFPE samples, irrespective of timing of tissue sampling. The miRNA were subjected to RNA sequence analysis and miRNA clusters were matched on MIRbase human genome database (hg19). Out of total 6000 miRNA listed in MIRbase, 171 differentially expressed miRNA were identified. Among these, the Let family miRNA (i.e. let-7e*, let-7f-2*0) were distinctly deregulated during rejection. This finding is of particular interest because, while let-7 members are known to participate in cardiovascular differentiation of embryonic stem cells, cardiovascular diseases are associated with the aberrant expression of let-7 members. This is the first report of successful isolation of (i) miRNA from FFPE – Ebx's and (ii) identification of let-mRNA from FFPE tissue in HTx. Our findings suggest that this method may be employed to identify specific miRNA in different stages of rejection. Further investigation to understand the function of miRNA target genes will help promote the understanding of molecular mechanisms for HTx rejection and potentially identify novel biomarkers for diagnosis and early treatment of allograft rejection.

CITATION INFORMATION: Nog R., Gupta C., Fallon J., Panza J., Haque N. Isolation and Profiling of miRNAs from Formalin Fixed Paraffin Embedded Endomyocardial Tissues from Human Heart Transplant Recipients Am J Transplant. 2017;17 (suppl 3).

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