Functional study and epigenetic targets analyses of SIRT1 in intramuscular preadipocytes via ChIP-seq and mRNA-seq

The SIRT1 epigenetic regulator is involved in hepatic lipid homoeostasis. However, the role of SIRT1 in regulating intramuscular fat deposition as well as the pathways and potential epigenetic targets involved remain unknown. Herein, we investigate SIRT1 function, its genome-wide epigenetic target profile, and transcriptomic changes under SIRT1 overexpression during yak intramuscular preadipocytes differentiation. To this end, we analysed the relationship between SIRT1 and intramuscular fat content as well as lipid metabolism-related genes in longissimus dorsi tissue. We found that SIRT1 expression negatively correlates with intramuscular fat content as well as with the expression of genes related to lipid synthesis, while positively correlating with that of fatty acid oxidation-involved genes. SIRT1 overexpression in intramuscular preadipocytes significantly reduced adipose differentiation marker expression, intracellular triacylglycerol content, and lipid deposition. Chromatin immunoprecipitation coupled with high-throughput sequencing of H3K4ac (a known direct target of SIRT1) and high-throughput mRNA sequencing results revealed that SIRT1 may regulate intramuscular fat deposition via three potential new transcription factors (NRF1, NKX3.1, and EGR1) and four genes (MAPK1, RXRA, AGPAT1, and HADH) implicated in protein processing within the endoplasmic reticulum pathway and the MAPK signalling pathway in yaks. Our study provides novel insights into the role of SIRT1 in regulating yak intramuscular fat deposition and may help clarify the mechanistic determinants of yak meat characteristics.

沉默信息调节因子1（SIRT1）作为表观遗传调控因子，参与肝脏脂质稳态的维持。然而，SIRT1在肌内脂肪沉积调控中的作用，以及其所涉及的信号通路与潜在表观遗传靶点，目前仍不明确。本研究针对牦牛肌内前体脂肪细胞分化过程中SIRT1过表达的情况，探究SIRT1的功能、全基因组表观遗传靶点谱以及转录组变化。为此，我们分析了背最长肌组织中SIRT1表达与肌内脂肪含量、脂质代谢相关基因之间的关联。研究发现，SIRT1的表达水平与肌内脂肪含量及脂质合成相关基因的表达呈负相关，而与参与脂肪酸氧化的基因表达呈正相关。在肌内前体脂肪细胞中过表达SIRT1，可显著降低脂肪分化标志物的表达水平、细胞内甘油三酯含量以及脂质沉积量。通过对SIRT1已知直接靶点组蛋白H3赖氨酸4乙酰化（H3K4ac）进行染色质免疫共沉淀-高通量测序（ChIP-seq），结合高通量mRNA测序结果，我们发现，在牦牛体内，SIRT1可能通过3种潜在新型转录因子（NRF1、NKX3.1及EGR1）以及4种参与内质网通路蛋白加工与丝裂原活化蛋白激酶（MAPK）信号通路的基因（MAPK1、RXRA、AGPAT1及HADH），调控肌内脂肪沉积。本研究为阐明SIRT1调控牦牛肌内脂肪沉积的作用机制提供了全新视角，也有助于明确牦牛肉品质特性的分子调控基础。