Redaelli, S. | Search bioRxiv

bioRxiv2024

BMP signaling promotes heart regeneration via alleviation of replication stress

One hallmark of aging is a decline in tissue regeneration, which can be caused by DNA replication stress. Whether highly regenerative species like zebrafish are immune from such hindrances to replication is unknown. In contrast to most mammals, adult zebrafish achieve complete heart regeneration via cell cycle entry and proliferation of mature cardiomyocytes. We found that cycling cardiomyocytes experience replication stress, which is induced by the demands of regeneration, but does not occur during physiological heart growth. Since zebrafish cardiomyocyte regeneration is remarkably efficient, heart regeneration appears to depend on elevated capabilities to overcome replication stress. Indeed, pharmacological inhibition of ATM and ATR kinases revealed that DNA damage response signaling is essential for heart regeneration. Using inducible overexpression of ligands and inhibitors of the Bone Morphogenetic Protein (BMP)-Smad pathway, combined with analysis of genetic mutants, we found that BMP signaling alleviates cardiomyocyte replication stress. In the absence of BMP signaling, cardiomyocytes become arrested in the S-phase of the cell cycle, which prevents progression to mitosis and results in heart regeneration failure. Interestingly, BMP signaling can also rescue neonatal mouse cardiomyocytes and human fibroblasts from hydroxyurea-induced replication stress. DNA fiber spreading assays in human cancer cells and human hematopoietic stem and progenitor cells (HSPCs) indicate that BMP signaling acts directly on replication dynamics by accelerating DNA replication fork progression and by facilitating their re-start after replication stress-induced stalling. Our results identify the ability to overcome replication stress as key factor for the elevated heart regeneration capacity in zebrafish. Notably, the conserved capability of BMP signaling to promote stress-free DNA replication might unlock new avenues towards anti-aging and pro-regenerative applications in humans.

developmental biology↗

bioRxiv2023

BMP7 promotes cardiomyocyte regeneration

Zebrafish has a remarkable and lifelong ability for cardiac regeneration after severe damage, whereas mammals lose their innate capacity for heart regeneration during early postnatal development. This study aimed to investigate whether the decreased production of growth factors during postnatal mammalian development contributes to the exit of cardiomyocytes from the cell cycle and the reduction in cardiac regenerative ability. We identified growth factors with declining expression levels during early postnatal life in the mouse model and assessed the pro-proliferative ability of these factors on neonatal murine primary cardiomyocytes in vitro. Our findings confirmed the previously reported pro-proliferative effects of NRG1, IL1b, RANKL, IGF2 and IL6, while also identifying novel potential pro-regenerative growth factors. Among them, BMP7 exhibited the most pronounced efficacy. Bmp7 knockdown interfered with the proliferation of neonatal mouse cardiomyocytes in culture and adult bmp7 mutant zebrafish displayed reduced cardiomyocyte proliferation during heart regeneration, indicating that Bmp7 is crucial for cardiomyocyte proliferation in the regenerative stages of mouse and zebrafish hearts. Conversely, bmp7 overexpression was sufficient to boost cardiomyocyte cycling in regenerating zebrafish hearts, while BMP7 administration stimulated mouse cardiomyocyte cycling at postnatal-day-7, when cardiomyocytes ceased to proliferate, and enhanced cardiomyocyte regeneration in vivo in adult mice following myocardial infarction. Mechanistically, BMP7-induced proliferation was mediated by type I BMP receptors BMPR1A and ACVR1, and type II receptors ACVR2A and BMPR2. Downstream signalling involved SMAD5, ERK and AKT. In conclusion, the administration of BMP7 holds promise as a strategy to stimulate heart regeneration following cardiac injury.

molecular biology↗