In aged mice, the cardiomyocyte-specific deletion of Tfeb induces heart failure with reduced ejection fraction, a condition that becomes more severe under starvation

Background:

The nutrient-sensitive transcription factor EB (TFEB) plays a pivotal role in maintaining energy balance in cardiomyocytes by regulating fatty acid oxidation (FAO), glucose oxidation (GO), and oxidative phosphorylation (OXPHOS). In conditions of normal nutrition, TFEB is phosphorylated by mTORC1, which results in its retention in an inactive state within the cytoplasm. Conversely, in the absence of nutrients, mTORC1 is inactivated, thereby enabling TFEB to enter the nucleus and stimulate the transcription of specific target genes. Our previous studies demonstrated that the deletion of TFEB specifically in cardiomyocytes resulted in a mild reduction in cardiac function and increased cardiac remodeling in young mice (11 weeks old). However, the impact of the lack of TFEB in cardiomyocytes on the heart's vulnerability to nutrient deprivation in older mice (40 weeks old) remains to be investigated.

Methods:

Cardiomyocyte-specific aged male Tfeb knockout mice (cKO, Tfeb^{loxP/loxP; αMHC-CRE}) were generated and wild-type littermates (WT, Tfeb^loxP/loxP) were used as controls. Both groups were subjected to 48h of starvation, while additional WT and cardiomyocyte-specific aged male Tfeb cKO mice with unrestricted food access served as controls. The mice were then assessed using echocardiography, morphological analysis, and histological examination. Furthermore, Western blotting, proteomics, and metabolomics were employed to quantify alterations in biomarkers associated with cardiac stress and remodeling, metabolic shifts, and OXPHOS.

Results:

The cardiac function of aged cKO mice was significantly impaired compared to WT and younger cKO mice, with an EF of ca. 50%. Furthermore, aged cKO mice showed increased cardiac fibrosis compared to WT mice. In addition, a further decline in cardiac function (EF ≤ 40%) and increased cardiac remodeling were observed in cKO mice compared to WT controls after starvation. In addition, cKO mice showed a more pronounced reduction in body weight in the liver and brown adipose tissue during starvation. The expression of genes associated with FAO, GO and OXPHOS was found to be decreased in the hearts of starved cKO mice compared to starved WT mice. Proteomics from all experimental groups was consistent with the gene expression findings, indicating a reduction in proteins associated with OXPHOS, FAO and the TCA cycle. Starvation was also demonstrated by metabolomic evaluation, which showed that in WT and cKO mice, the known biomarkers of skeletal muscle toxicity and the breakdown products of the contractile actin/myosin proteins 1- and 3-methylhistidine were identified with higher abundance in starved mice compared to fed mice. Under starvation conditions, cKO mice showed an accumulation of several sphingolipids, amino acids and, in contrast, lower concentrations of acylcarnitines compared to WT mice. The lower levels of acylcarnitines in cKO mice are consistent with reduced FAO.

Conclusions:

Deletion of TFEB results in impaired cardiac performance in aged mice. Furthermore, in circumstances of starvation, the absence of TFEB has been demonstrated to exacerbate cardiac remodeling, alter the metabolome and significantly impair cardiac function in these mice. These findings indicate that TFEB plays a pivotal role in maintaining cardiac structure and function during starvation. However, further research is necessary to elucidate the molecular mechanisms underlying this phenotype.