Hypothermic Treatment Alleviates Myocardial Hypertrophy in bmp10-/- Zebrafish

Background: Cardiac hypertrophy is a major pathological feature of various cardiovascular diseases. Owing to the simple cardiac structure, rapid development, and genetic tractability, zebrafish are an ideal model for studying cardiac pathology. Zebrafish lacking Bone morphogenetic protein 10 (bmp10-/-) develop myocardial hypertrophy under normothermic conditions (28 °C). However, the long-term effects of chronic cold exposure on cardiac function and survival in this model remain unclear. Therefore, this study utilized the bmp10-/- zebrafish model to systematically evaluate the therapeutic potential of chronic hypothermia in attenuating myocardial hypertrophy and to elucidate the underlying molecular mechanisms. Methods: This study was conducted in three sequential phases. Phase I: bmp10-/- (homozygous mutant, HO) zebrafish at 6 weeks post-fertilization (wpf) were maintained under normothermic (28 °C) or hypothermic (15 °C) conditions for 2 weeks to evaluate the effects of cold exposure on myocardial hypertrophy. Phase II: Building on the Phase I findings, bmp10-/- zebrafish were subjected to adaptive temperature-switching between normothermic and hypothermic conditions until 10 wpf to assess the temporal effects of cold exposure on cardiac remodeling. Phase III: Pharmacological validation experiments were performed to identify key regulatory genes mediating hypothermia-induced cardioprotection. Results: Long-term cold exposure significantly attenuated myocardial hypertrophy induced by bmp10 deficiency. Given that hypoxia-inducible factor-1 (HIF-1) is a canonical transcriptional regulator of cellular hypoxic responses and that the stability of HIF-1 is tightly controlled by prolyl hydroxylases such as Egl-9 family hypoxia-inducible factor 3 (EGLN3), the involvement of this pathway was further evaluated. These findings indicate that inhibition of EGLN3 activity stabilizes and activates HIF-1 signaling, thereby mediating cardioprotective effects under hypothermic conditions. Conclusions: This study elucidates the functional interplay between the EGLN3 and HIF-1 signaling pathways. Under chronic hypothermia, EGLN3 modulates HIF-1 stability, contributing to the downregulation of BCL2-interacting protein 3 (BNIP3) and facilitating cardiomyocyte injury repair.