BACKGROUND: Pathological cardiac remodeling and afterload-induced increases in energy demand together contribute to heart failure (HF). Lysosome-assisted processes, such as autophagy, coupled with alterations in mitochondrial oxidative capacity, play important roles in cardiac remodeling and HF. Furthermore, the lysosome is a hub for multiple signaling pathways governing hypertrophic growth. The TFEB (transcription factor EB) has emerged as a key regulator of lysosomal genes and mitochondrial function in multiple tissues, especially in response to external stress. METHODS: Leveraging a cardiomyocyte-specific TFEB knockout mouse (CTKO), pressure overload was induced by transverse aortic constriction (TAC) to elucidate the role of TFEB under hypertrophic stress conditions. Echocardiography was employed to assess cardiac function, and hearts were subsequently harvested for transcriptomic, proteomic, and metabolomic analyses. To glean further insight into the molecular mechanisms involved, we studied neonatal rat ventricular myocytes exposed to phenylephrine, an in vitro model of cardiomyocyte hypertrophy. RESULTS: We report that TFEB is rapidly activated and translocates to the nucleus in cardiomyocytes exposed to hypertrophic stress conditions, triggering a lysosomal gene program independent of autophagy gene changes. At baseline, contractile function measured by echocardiography appeared normal in these mice compared with their Cre-negative littermates. However, in pressure-overload stress induced by TAC, CTKO mice manifested an amplified hypertrophic response, leading rapidly to HF. Unlike WT hearts, CTKO hearts failed to increase lysosomal capacity after TAC. They manifested an increase in the steady-state levels of autophagosome-associated proteins, such as LC3II and p62, as well as accumulation of ubiquitinated proteins, suggesting a defect in protein turnover. Interestingly, CTKO mice harbored altered mitochondrial structure, reduced oxidative capacity, and reduced abundance of peroxisome PGC-1α-b (proliferator-activated receptor-1 alpha-b). Furthermore, CTKO hearts manifested reduced expression of key enzymes within metabolic pathways essential for normal myocardial metabolism, including fatty acid metabolism, carbon metabolism, and branched-chain amino acid metabolism. Surprisingly, AMPK (AMP-activated protein kinase) signaling, while normal at baseline, was significantly decreased in CTKO hearts after TAC. This reliance on TFEB for growth trigger-induced AMPK signaling was also observed in vitro in cells exposed to phenylephrine, as were the antihypertrophic effects of TFEB activation, supporting a direct role of TFEB in this process. Finally, we report that exogenous activation of AMPK in the absence of TFEB can completely rescue the exacerbated hypertrophic response both in vitro and in vivo, independent of lysosomal function. Notably, blunting of the hypertrophic response did not impact the decreased contractile function observed in TAC-treated CTKO mice, highlighting the importance of TFEB in regulating mitochondrial function in response to stress. CONCLUSIONS: Our findings demonstrate that TFEB antagonizes pathological hypertrophic cardiac remodeling through upregulation of lysosomal capacity, maintaining mitochondrial energetic function, and promoting AMPK signaling.
Daou et al. (Tue,) studied this question.