Differential expression of microRNAs during allograft rejection.

MicrorRNA are small noncoding RNA molecules that regulate the posttranscriptional expression of target genes. In addition to being involved in many biologic processes, microRNAs are important regulators in innate and adaptive immune responses. Distinct sets of expressed microRNAs are found in different cell types and tissues and aberrant expression of microRNAs is associated with many disease states. MicroRNA expression was examined in a model of heterotopic heart transplantation by microarray analyses and a unique profile was detected in rejecting allogeneic transplants (BALB/c → C57BL/6) as compared to syngeneic transplants (C57BL/6 → C57BL/6). The microRNA miR-182 was significantly increased in rejecting cardiac allografts and in mononuclear cells that infiltrate the grafts. Forkhead box (FOX) proteins are a family of important transcription factors and FOXO1 is a target of miR-182. As miR-182 increases after transplant, there is a concomitant posttranscriptional decrease in FOXO1 expression in heart allografts that is localized to both the cardiomyocytes and CD3(+) T cells. The microRNA miR-182 is significantly increased in both peripheral blood mononuclear cells and plasma during graft rejection suggesting potential as a biomarker of graft status. Our results identify microRNAs that may regulate alloimmune responses and graft outcomes.