Background: Aging-dependent decline of autophagy contributes to cardiac dysfunction and ischemic intolerance. Transcription factor EB (TFEB) is a master transcriptional regulator of the autophagy-lysosome pathway. The present study aimed to characterize the role of TFEB in the autophagic decrease with aging.
Methods and Results: We analyzed age-associated autophagic changes in male C57BL/6 young (4-6 mo) and aged (22-24 mo) mice. The results demonstrated that TFEB expressed predominantly as a SUMOylated form in cardiomyocyte nuclei and this SUMOylation of TFEB declined in aged heart associated with autophagy reduction. Interestingly, SUMOylation of TFEB was unaffected by rapamycin. Rapamycin induced translocation of TFEB into nucleus but lower level of nuclear TFEB in aged hearts than that seen in young hearts (P<0.05). SUMO1 downregulation by adeno-associated-virus-mediated small hairpin RNA (rAAV9-shSUMO1) significantly reduced nuclear TFEB levels (P<0.05), depressed cardiac autophagy and accelerated cardiomyocyte contractile dysfunction with worse hypoxia/reoxygenation (H/R) injury (all P<0.05). Therefore, impaired SUMOylation decreased nuclear TFEB during aging. By contrast, SUMO1 restitution significantly augmented nuclear SUMOylated TFEB with enhanced autophagy and ultimately reduced infarct size in aged heart. However, knockdown of cardiac TFEB blocked the protective effect of upregulation of SUMO1 in aged hearts, resulted in decline of autophagy and worse in vivo I/R injury.
Conclusions: The present study newly demonstrates that SUMOylation is a critical post-translational modification that regulates cardiac TFEB. Impaired SUMOylation of TFEB aggravates decline of autophagy in the senescent heart. Targeting SUMO1 may provide a novel therapeutic strategy for the treatment of aging-related loss of cardioprotection.