Abstract 129: Smyd1 is an Essential Regulator of Adaptive Response to Glucose Starvation in Cardiomyocytes

Abstract

Smyd1, a muscle-specific histone methyltransferase, has been implicated in global metabolic remodeling in cardiac hypertrophy and failure. We previously showed that cardiac-specific ablation of Smyd1 in mice led to metabolic perturbations prior to overt cardiac dysfunction, suggesting that Smyd1 positively regulates cardiac metabolism. However, the role of Smyd1 in adaptive response to nutritional stress (NS) in cardiomyocytes is largely unknown. Here, we found that glucose deprivation-induced NS led to upregulation of Smyd1 in cultured rat neonatal ventricular myocytes (NRVMs) (FC=1.87, p<0.05), which was associated with the increased mRNA level of PGC-1α, a key regulator of mitochondrial energetics (FC=2.71, p<0.05). Strikingly, siRNA-mediated knockdown of Smyd1 (Smyd1-KD) in NRVM prior to glucose starvation led to extensive cell death not observed in control NRVMs (scrambled siRNA), suggesting that Smyd1 is required for cell survival in NS. To elucidate the mechanism how Smyd1 is involved in adaptive response to NS, we performed unbiased proteomic and metabolomic screening of Smyd1-KD NRVMs. Bioinformatic analysis of proteins and metabolites that were differentially expressed in Smyd1-KD NRVM revealed that oxidative phosphorylation was the most perturbed metabolic pathway in Smyd1-KD NRVMs, concomitant with a reduction in mitochondrial substrates (BCAAs; pyruvate; lactate, all p<0.05). Gene expression analyses using RT-PCR and RNA-seq in Smyd1-KD NRVMs further identified PGC-1α and Perm1 (the muscle-specific PGC-1α and ESRR induced regulator) as potential downstream targets of Smyd1 in regulation of cardiac energetics (FC=-1.92 and -1.66, respectively, both p<0.05). Consistent with downregulation of Perm1, the known Perm1-target genes (Tfb1m; Ctp1b; Glut4; Myl2) were all downregulated at the mRNA levels in Smyd1-KD NRVMs (p<0.05). Lastly, Smyd1-KD NRVMs exhibited accelerated loss of mitochondrial membrane potential during hypoxia, revealing an increased vulnerability to metabolic stress. Taken together, these results show that Smyd1 is an essential regulator of adaptive response and cell survival during metabolic insults, presumably through regulating PGC-1α/Perm1 gene expression.