最先端研究セミナー

Abstract:

Epigenetic control of metabolism in cardiomyocytes remains poorly understood. Smyd1, a muscle-specific histone methyltransferase, is thought to be involved in chromatin remodeling and gene expression control¹. We recently showed that cardiac-specific ablation of Smyd1 in mice (Smyd1-KO mice) led to global downregulation of metabolism concurrent with the development of cellular hypertrophy and heart failure². In these findings, the potential involvement of Smyd1 in regulation of cardiac metabolism was confounded by possible metabolic effects of heart failure. We hypothesized that the effects of Smyd1 on metabolism are primary and independent of the structural disease. Using our previously established proteomics and metabolomics approach^{3, 4}, we performed metabolic profiling of Smyd1-KO mice before the onset of hypertrophy or hemodynamic dysfunction. Our multisystems analysis revealed that oxidative phosphorylation (OXPHOS) was the most perturbed metabolic process in these mice, manifested by downregulation in the components of electron transport chain and significant changes in the levels of TCA cycle intermediates, acylcarnitines, and branched-chain amino acids (BCAAs). In addition, targeted qPCR showed that PPARa, RXRa, and PGC-1a, the transcriptional regulators of cardiac energetics, were downregulated in Smyd-1KO mice (all p<0.05). To further ascertain the direct effect of Smyd1 on metabolism, we performed proteomic, metabolomic, and targeted gene expression analyses in neonatal rat ventricular myocytes (NRVMs) 24-48 hours after siRNA-mediated knockdown of Smyd1 (Smyd1-KD) or scrambled siRNA (control). Consistent with findings in Smyd1-KO mice, OXPHOS was dysregulated in Smyd1-KD NRVMs, concomitant with a reduction in mitochondrial substrates (BCAAs; pyruvate; lactate, all p<0.05). Remarkably, the acute knockdown of Smyd1 led to a ~50% reduction in mRNA level of PGC-1a (p<0.05), but no significant change in PPARa. Lastly, Smyd1-KD NRVMs exhibited accelerated loss of mitochondrial membrane potential during hypoxia, revealing an increased vulnerability to metabolic stress. These results show that Smyd1 regulates mitochondrial energetics in the cardiomyocyte, possibly through regulation of PGC-1a expression.

References:

[1] Gottlieb PD, Pierce SA, Sims RJ, Yamagishi H, Weihe EK, Harriss JV, Maika SD, Kuziel WA, King HL, Olson EN, Nakagawa O, Srivastava D: Bop encodes a muscle-restricted protein containing MYND and SET domains and is essential for cardiac differentiation and morphogenesis. Nature genetics 2002, 31:25-32.

[2] Franklin S, Kimball T, Rasmussen TL, Rosa Garrido M, Chen H, Tran T, Miller MR, Gray R, Jiang S, Ren S, Wang Y, Tucker HO, Vondriska TM: The chromatin binding protein Smyd1 restricts adult mammalian heart growth. American journal of physiology Heart and circulatory physiology 2016:ajpheart 00235 2016.

[3] Shibayama J, Yuzyuk TN, Cox J, Makaju A, Miller M, Lichter J, Li H, Leavy JD, Franklin S, Zaitsev AV: Metabolic remodeling in moderate synchronous versus dyssynchronous pacing-induced heart failure: integrated metabolomics and proteomics study. PloS one 2015, 10:e0118974.

[4] Shibayama J, Taylor TG, Venable PW, Rhodes NL, Gil RB, Warren M, Wende AR, Abel ED, Cox J, Spitzer KW, Zaitsev AV: Metabolic determinants of electrical failure in ex-vivo canine model of cardiac arrest: evidence for the protective role of inorganic pyrophosphate. PloS one 2013, 8:e57821.

担当分野：　分子遺伝学分野　尾池（内線：5142）

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