Parallels between oncogene-driven cardiac hyperplasia and heart regeneration in zebrafish

Abstract

The human heart is poorly regenerative and cardiac tumors are extremely rare. Whether the adult zebrafish myocardium is responsive to oncogene overexpression and how this condition affects its intrinsic regenerative capacity remains unknown. Here, we have established a strategy of inducible and reversible expression of HRASG12V in zebrafish cardiomyocytes. This approach stimulated a hyperplastic cardiac enlargement within 16 days. The phenotype was suppressed by rapamycin-mediated inhibition of TOR signaling. As TOR signaling is also required for heart restoration after cryoinjury, we compared transcriptomes of hyperplastic and regenerating ventricles. Both conditions were associated with upregulation of cardiomyocyte dedifferentiation and proliferation factors, as well as with similar microenvironmental responses, such as deposition of nonfibrillar Collagen XII and recruitment of immune cells. Among the differentially expressed genes, many proteasome and cell-cycle regulators were upregulated only in oncogene-expressing hearts. Preconditioning of the heart with short-term oncogene expression accelerated cardiac regeneration after cryoinjury, revealing a beneficial synergism between both programs. Identification of the molecular bases underlying the interplay between detrimental hyperplasia and advantageous regeneration provides new insights into cardiac plasticity in adult zebrafish.

Skeletal muscle regeneration after extensive cryoinjury of caudal myomeres in adult zebrafish

“…In mice, TOR signaling is essential for the regulation of myogenic gene expression in muscle stem cells 86 – 90 , suggesting a conserved role of this pathway among vertebrates. In adult zebrafish, TOR is required for heart and retina regeneration 91 , 92 . Further studies will elucidate the molecular mechanisms underlying the rapamycin-mediated impairment of muscle regeneration.…”