MicroRNA-145-5p restricts cardiac scar resolution during cardiac regeneration

Abstract Background Human hearts have a very limited capacity to renew cardiomyocytes following injury. The lost myocardium is permanently replaced with noncontractile fibrotic tissue, consequently leading to heart failure. In contrast, zebrafish retain cardiac regenerative capacity during their lifetime. After injury, zebrafish hearts undergo transient fibrotic scarring that subsequently resolves and is replaced with new cardiomyocytes over time. Thus, understanding the molecular mechanisms governing cardiac scar resolution in zebrafish could offer insights into enhancing the regenerative capacities of human hearts. Objective We aimed to decipher the molecular pathways associated with zebrafish cardiac scar resolution. Methods We investigated the mRNA and miRNA responses to injury at 14 days post-injury by high-throughput transcriptome profiling of RNAs isolated from healthy or cryoinjured hearts. The prediction of miRNA-mRNA interactions was performed to identify the most differentially expressed miRNAs and their target genes. These miRNAs and genes were validated in zebrafish regenerating hearts and in the left ventricles of ischemic cardiomyopathy or dilated cardiomyopathy patients. The potential role of identified miRNAs in cardiac scar resolution was investigated in human cardiac fibroblasts. Results Principal component analyses identify two distinct clusters in both the mRNAome and miRNAome corresponding to healthy and injured hearts, indicating significant changes in transcriptome profiles during zebrafish cardiac regeneration. Gene set enrichment analyses indicate that molecular pathways involved in extracellular matrix organization and inflammatory response are markedly activated whereas genes associated with mitochondrial organization and oxidative phosphorylation are downregulated in injured hearts. We observed the downregulation of miR-145-5p and the upregulation of procollagen V in the injured hearts. In contrast to zebrafish, in the left ventricles of ischemic cardiomyopathy patients, miR-145-5p is significantly upregulated and procollagen V α1 is downregulated. Theoretical prediction of miRNA-mRNA interactions indicates procollagen V α1 is negatively correlated with miR-145-5p. Overexpression of miR-145-5p in human cardiac fibroblasts downregulates collagen V α1 and alpha smooth muscle actin, upregulates procollagen I and matrix metalloproteinase 9, and inhibits cell proliferation and migration. In contrast, inhibition of miR-145-5p upregulates collagen V α1 and alpha smooth muscle actin, downregulates procollagen I and matrix metalloproteinase 9, and stimulates cell proliferation and migration. Conclusion Our study suggests that miR-145-5p may play a role in the suppression of myofibroblast transdifferentiation via collagen V α1, which restricts scar resolution and cardiac repair.