The SRCAP Chromatin Remodeling Complex Promotes Oxidative Metabolism During Prenatal Heart Development

In mammals,the heart is the first organ to develop in order to establish a functional circulatory system that is vital for organismal growth.Currently,it is increasingly realized that mitochondrial function and energy metabolism play critical roles in the maturation of cardiomyocytes and heart development.However,compared with postnatal cardiomyocytes,understanding of the mitochondria and metabolism of prenatal cardiomyocytes is largely lacking.Research shows that embryonic cardiomyocytes undergo a metabolic transition from exclusive anaerobic glycolysis to predominantly oxidative metabolism,which is necessary for heart development.But current knowledge of this transition is still shallow,and the specific time period during which the transition appears is uncertain.In order to improve the understanding of this transition,we first performed RNA-seq,western blot,and electron microscopy analysis of ventricular cells at different embryonic heart development stages.According to the results,we found that cardiomyocytes were in a low-energy state,mitochondria were immature,and the respiratory chain was not well established at E10.5.However,by E14.5,cardiomyocytes were full of energy,mitochondrial structures had matured,and respiratory chain members were significantly highly expressed.During this period,genes involved in aerobic metabolism rose significantly.Based on these,we pointed out a critical metabolic transition window: E10.5-E14.5.The activity of VHL-HIF signaling pathway,which regulates anaerobic metabolism,gradually decreases during E10.5-E14.5,and HIF1? is almost not detected in the middle and late stages of embryonic development,while the level of aerobic metabolism gradually increases.Accordingly,we speculated that there must exist novel regulators and mechanisms to advance oxidative metabolism in the embryonic cardiomyocytes.ATP-dependent chromatin remodeling complexes regulate gene expression by moving,ejecting,or restructuring the composition of nucleosomes and participate in the regulation of many biological processes,including metabolic pathways.The SRCAP complex is one of the ATP-dependent chromatin remodeling complexes and controls the replacement of H2 A with the histone variant H2 A.Z in the promoter region to regulate gene expression.In our further studies,we found with surprise that the protein levels of Znhit1,YL-1,and H2 A.Z,the core subunits of the SRCAP complex,were significantly increased between E11.5-E12.5,which coincided with the time window of metabolic transition.Therefore,we suggested that the SRCAP complex might be involved in regulating this switch.So we utilized Tnnt2-Cre and Mef2c-AHF-Cre to knock out Znhit1 in cardiomyocytes and anterior heart field progenitors,respectively,to disrupt the SRCAP complex and then investigated the role of this complex.It was found that disruption of the SRCAP complex severely reduced the expression of genes involved in oxidative metabolism,caused mitochondrial abnormalities,decreased levels of respiratory chain proteins,and greatly curtailed ATP production.We further demonstrated through CUT&Tag experiments that the SRCAP complex could directly bind to the promoters of key genes related to fatty acid ?-oxidation,TCA cycle,Co Q10 biosynthesis,and respiratory chain protein stability,thereby activating gene expression and ultimately promoting aerobic metabolism of cardiomyocytes.Rather than being involved in regulating cardiac progenitors specialization and cardiomyocytes differentiation,this complex promotes aerobic metabolism to enhance the energy production efficiency of cardiomyocytes after E10.5,thereby meeting the demands of normal cardiac development and contraction.The VHL-HIF pathway promotes anaerobic metabolism,and the activity of this pathway gradually decreases between E10.5-E14.5,while the activity of the SRCAP complex gradually increases to enhances aerobic metabolism.The coordination of these two regulatory mechanisms guarantees the completion of the metabolic switch during embryonic heart development.We have for the first time established a panoramic temporal picture of the myocardial transcriptome,mitochondrial morphogenesis,respiratory complex,and metabolic feature spanning from the early period of heart development to the end of embryogenesis and point out that E10.5-E14.5 is the key time window for metabolic transition.And we also identified that the SRCAP complex is involved in the regulation of this transition by promoting oxidative metabolism.Our study fills the gap in the regulation of oxidative metabolism during embryonic heart development and deepens the understanding of the role of mitochondria and energy metabolism in heart development.This study also sheds light on understanding the transcriptional regulation of Co Q10 biosynthesis.Coenzyme Q10(Co Q10)is crucial for electron transport chain activity and ATP production.Its biosynthesis requires at least 13 genes and mutations of these genes in humans cause many common diseases,including encephalopathy and cardiomyopathy.So far,little is known about the transcriptional regulation of Co Q10 biosynthesis.In our study,disruption of the SRCAP complex abolished the expression of the 12 genes out of these 13 genes.Thus,the SRCAP complex may be the first identified regulator of Co Q10 biosynthesis.