Abstract Body: Background:
Metabolic remodeling is a hallmark of heart failure. Serine is a non-essential amino acid that contributes to purine synthesis, redox, protein synthesis, and 1-carbon metabolism. It is transported into cells from the circulation or formed by de novo synthesis (SdS) from glycolytic intermediates. We have found that human failing myocardium has reduced serine and lower expression of genes involved in SdS. Yet, the contribution of SdS pathway to cardiac remodeling remains poorly defined.
Methods and Results:
Human failing myocardium exhibits a significant reduction in PHGDH (the rate-limiting SdS enzyme) expression. SiRNA-mediated silencing of PHGDH in cardiomyocytes reduced intracellular serine and induced dose-dependent cytotoxicity. This is associated with reduced purines (ATP, ADP, and GTP), oxidative stress, and activation of AMP-kinase. Co-incubation with reducing agent DTT and ribose rescued the cytotoxicity. PHGDH inhibition also lowered the abundance of multiple amino acids associated with reduced de novo protein synthesis. Stimulation of cardiomyocytes with endothelin-1 (ET-1) increased native PHGDH expression, while siRNA-mediated suppression of PHGDH attenuated ET-1–induced hypertrophic growth and expression of hypertrophic stress markers (Nppa, Nppb, Myh7, and Acta1), and shifted cellular metabolism toward glycolysis with reduced oxidative respiration. Stable isotope tracing identified distinct metabolic fates of serine derived from SdS versus exogenous serine. To assess in vivo relevance, cardiomyocyte-specific PHGDH-KO heterozygous mice (PHGDH^-/+; αMHC-Cre) were subjected to transverse aortic constriction (TAC). Whereas there was no basal phenotype, PHGDH +/- mice developed significantly reduced ejection fractions, increased ventricular dilation and greater fibrosis after 4-wks of transaortic constriction (TAC). Metabolomic profiling revealed TAC resulted in increase in amino acids, one-carbon metabolites, and nucleotides, and a decline in TCA-cycle intermediates in wild type heart, were all significantly blunted in PHGDH^-/+ hearts.
Conclusion:
Our findings identify cardiomyocyte serine de novo synthesis (SdS) as an important regulator of cellular redox balance, one-carbon/purine metabolism, amino acid availability, and growth pathways required for adaptation to pressure overload. Impaired PHGDH-mediated SdS may therefore limit metabolic and structural adaptation during cardiac stress and contribute to heart failure progression.