1Universitätsmedizin Greifswald Klinik und Poliklinik für Innere Medizin B Greifswald, Deutschland; 2Interfakultäres Institut für Genetik und Funktionelle Genomforschung Greifswald, Deutschland; 3Instituts für Immunologie Universitätsmedizin Greifswald Greifswald, Deutschland; 4Universitätsklinikum Schleswig-Holstein Innere Medizin III mit den Schwerpunkten Kardiologie, Angiologie und internistische Intensivmedizin Kiel, Deutschland
Background:
Left ventricular hypertrophy (LVH) and heart failure with reduced ejection fraction (HFrEF) is accompanied by metabolic remodeling that is caused by a switch from fatty acid (FAO) to glucose oxidation (GO). The nutrient-sensitive transcription factor EB (TFEB) is involved in these processes. TFEB promotes the expression of genes involved in FAO (e.g., PPARGC1A/PGC-1α, PPARA/PPARα), GO and oxidative phosphorylation (OXPHOS). If TFEB supports the maintenance of energy homeostasis in the heart and to prevent unwanted metabolic remodeling is uncertain.
Methods:
To examine the effect of TFEB on cardiomyocyte energy homeostasis, Tfeb was overexpressed in neonatal rat ventricular cardiac myocytes (NRVCM) using adeno-associated virus type 6 (AAV6) for 24 and 96 hours. AAV6-luciferase transduced NRVM were used as controls. Western blot analyses, mass spectrometry, quantitative real-time PCR and mitochondrial function test by Seahorse measurements were performed.
Results:
Overexpression of Tfeb increased the expression of its target genes PPARGC1A and PPARA, and reduced the abundance of β-MyHC that is associated with cardiac remodeling. Mass spectrometry analyses revealed an increase in mitochondria-associated proteins after 96 hours of Tfeb overexpression indicating an activation of OXPHOS Tfeb overexpression increased total ATP-production rates in NRVM (+60%, p<0.0001 vs controls). This effect was caused by a four-fold increase in glycolysis-dependent ATP-production (p<0.0001 vs controls) whereas OXPHOS-dependent ATP production remained unchanged in response to TFEB. Respiratory data analysis showed no alterations in basal respiration but a ~30% increase (p<0.05) in maximum respiration indicative for an augmented spared respiratory capacity in response to Tfeb overexpression.
Conclusions:
Tfeb overexpression increases glycolytic ATP production rates, as well as maximum respiration, resulting in an increased spare respiratory capacity in NRVCMs. This increased respiratory capacity, along with improved energy supply, may support cardiomyocyte stress response. Hence, Tfeb overexpression results in a better energy supply in cardiomyocytes.