Abstract Body: Introduction: Rewiring of cardiac metabolism and impaired mitochondrial oxidative capacity play important roles in heart failure (HF). TFEB (transcription factor EB) has emerged as a key regulator of metabolism and mitochondrial function in multiple tissues. However, its role in cardiac metabolism remains unclear.

Methods: Experiments were performed using cardiomyocyte-specific TFEB knockout mice (CTKO) and control littermates subjected to TAC or sham surgeries for one week. Echocardiography was employed to assess ventricular contractile function, and hearts were harvested for further analyses.

Results: We report that TFEB is rapidly activated and translocates to the nucleus in cardiomyocytes exposed to hypertrophic stress. Whereas contractile function under basal conditions remained normal in CTKO mice compared with Cre-negative littermates, in the setting of pressure-overload stress induced by TAC, CTKO mice manifested an amplified hypertrophic response leading rapidly to HF. Interestingly, CTKO mice exhibited marked alterations in mitochondrial cristae ultrastructure as assessed by electron microscopy. Consistent with these structural abnormalities, functional assessment using high-resolution respirometry revealed significantly diminished maximal respiratory capacity and combined complex I and II-supported respiration in CTKO mice under sham and TAC conditions compared with FL/FL controls. Furthermore, using proteomic analysis we found that CTKO hearts manifested reduced expression of key enzymes within metabolic pathways essential for normal myocardial metabolism, including fatty acid, carbon, and branched-chain amino acid metabolism. Transcriptomic analysis demonstrated marked downregulation of respiratory electron transport chain-related genes, as well as peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a master regulator of mitochondrial biogenesis and energy metabolism, in CTKO hearts subjected to TAC. Isoform-specific qPCR revealed selective suppression of the PGC-1α-b isoform, whereas PGC-1α-a expression remained unchanged in CTKO hearts. Consistent with these in vivo findings, TFEB overexpression in NRVMs selectively upregulated PGC-1α-b, supporting a model in which TFEB drives PGC-1α transcription via the alternative promoter.

Conclusion: Overall, our findings identify TFEB as a key regulator of myocardial metabolic homeostasis and mitochondrial oxidative capacity under both basal and hypertrophic stress conditions.