Epigenomic regulation of adipogenesis and adipose expansion

I. 我们研究了组蛋白H3 K4、H3 K9、H3 K27和H3 K36上的位点特异性甲基转移酶在脂肪形成和PPARgamma调节中的作用。我们以前报道过H3 K4 me 1/2甲基转移酶MLL 3/MLL 4和相关的PTIP控制PPARgamma和C/EBPa的诱导，并且是脂肪形成所必需的（Cho YW，Cell Metab 2009; Lee JE，eLife 2013; Jang Y，NAR 2019），H3 K9甲基转移酶G9 a抑制PPARgamma表达和脂肪生成（Wang L，EMBO J 2013），H3 K27甲基转移酶Ezh 2组成型抑制Wnt基因以促进脂肪形成（Wang L，PNAS 2010），并且在祖细胞中通过组蛋白H3.3突变体H3.3K36M消耗Nsd 2介导的H3 K36甲基化损害脂肪组织发育和功能（Zhuang L，Nat Comm 2018）。我们还表明，表观基因组阅读器Brd 4控制细胞身份基因诱导，并且对于体内脂肪形成至关重要（Lee JE，Nat Comm 2017）。总之，这些研究结果表明，表观基因组因子在脂肪形成的调控中起着关键作用（Lee JE，MCB 2019中综述）。 二. 使用条件性基因敲除小鼠和前脂肪细胞，我们惊讶地发现，尽管配体结合的糖皮质激素受体（GR）加速了培养物中的脂肪生成，但内源性GR在培养物和小鼠中对脂肪生成不利（Park Y，MCB 2017 a）。 我们还发现，转录因子（TF）KLF 4和Krox 20在培养物和小鼠中对脂肪形成有抑制作用（Park Y，MCB 2017 b）。 三. 我们分析了增强子表观基因组写入器（MLL 4，CBP），脂肪形成TF（EBF 2，C/EBPa，C/EBPb，PPARgamma），共激活因子MED 1，RNA聚合酶II以及表观基因组（H3 K4 me 1/2/3，H3 K9 me 2，H3 K27 me 3，H3 K36 me 3，H3 K27 ac），转录组的基因组结合，以及来源于小鼠BAT的永生化前脂肪细胞脂肪形成过程中的染色质开放。我们的数据为理解培养物中棕色脂肪形成的表观基因组调控提供了丰富的资源（Lai B，NAR 2017）。 四. C/EBPb和C/EBPd在培养物中脂肪形成开始后数小时内被诱导。它们直接促进主成脂TF PPARgamma和C/EBPa的表达，并且是体内脂肪形成所需的。我们报道了MLL 3/MLL 4/PTIP相关蛋白PAGR 1与磷酸化CREB和配体活化GR合作，在脂肪形成的早期直接控制C/EBPb和C/EBPd的诱导（Lee JE，MCB 2020）。 诉 在2021年，我们报道了BAF是SWI/SNF染色质重塑复合物，与MLL 4和活性增强子上的谱系决定性TF（LDTF）共定位。BAF是脂肪生成所需的，而富含启动子的SWI/SNF复合物PBAF是必需的（Park Y，Nat Comm 2021）。 六. MED 1通常用作一般转录辅激活因子复合物介体的替代物，用于鉴定活性增强子。MED 1是体外成纤维细胞向脂肪细胞表型转化所必需的，但其在体内脂肪发育和扩增中的作用尚未报道。在这里，我们表明，MED 1通常是不需要在培养过程中的脂肪形成的转录和MED 1是在小鼠脂肪组织的发展。相反，MED 1是出生后脂肪扩张和诱导脂肪酸和甘油三酯合成基因所必需的，在幼崽从高脂肪母乳饮食转换为碳水化合物为主的食物后。在脂肪形成过程中，MED 1是诱导LDTF、PPAR和C/EBP的必需因子，但在分化晚期是脂质积累所必需的。从机制上讲，MED 1通过促进脂肪生成TF ChREBP和SREBP 1a依赖性的中介体向活性增强子的募集来控制脂肪生成基因的诱导。总之，我们的研究结果确定了MED 1作为出生后脂肪扩张所需的脂肪生成辅激活剂的基因特异性调节作用（Jang Y，Genes Dev 2021）。

I. We have investigated the roles of site-specific methyltransferases on histone H3K4, H3K9, H3K27, and H3K36 in regulation of adipogenesis and PPARgamma. We reported previously that H3K4me1/2 methyltransferases MLL3/MLL4 and associated PTIP control the induction of PPARgamma and C/EBPa and are essential for adipogenesis (Cho YW, Cell Metab 2009; Lee JE, eLife 2013; Jang Y, NAR 2019), that H3K9 methyltransferase G9a represses PPARgamma expression and adipogenesis (Wang L, EMBO J 2013), that H3K27 methyltransferase Ezh2 constitutively represses Wnt genes to facilitate adipogenesis (Wang L, PNAS 2010), and that depletion of Nsd2-mediated H3K36 methylation by histone H3.3 mutant H3.3K36M in progenitor cells impairs adipose tissue development and function (Zhuang L, Nat Comm 2018). We also showed that the epigenomic reader Brd4 controls cell identity gene induction and is essential for adipogenesis in vivo (Lee JE, Nat Comm 2017). Together, these findings indicate that epigenomic factors play critical roles in the regulation of adipogenesis (reviewed in Lee JE, MCB 2019). II. Using conditional knockout mice and preadipocytes, we found surprisingly that although ligand-bound glucocorticoid receptor (GR) accelerates adipogenesis in culture, endogenous GR is dispensable for adipogenesis in culture and in mice (Park Y, MCB 2017a). We also found that Transcription factors (TFs) KLF4 and Krox20 are dispensable for adipogenesis in culture and in mice (Park Y, MCB 2017b). III. We profiled genomic binding of enhancer epigenomic writers (MLL4, CBP), adipogenic TFs (EBF2, C/EBPa, C/EBPb, PPARgamma), coactivator MED1, RNA Polymerase II, as well as epigenome (H3K4me1/2/3, H3K9me2, H3K27me3, H3K36me3, H3K27ac), transcriptome, and chromatin opening during adipogenesis of immortalized preadipocytes derived from mouse BAT. Our data provide a rich resource for understanding epigenomic regulation of brown adipogenesis in culture (Lai B, NAR 2017). IV. C/EBPb and C/EBPd are induced within hours after initiation of adipogenesis in culture. They directly promote expression of master adipogenic TFs PPARgamma and C/EBPa and are required for adipogenesis in vivo. We reported that MLL3/MLL4/PTIP-associated protein PAGR1 cooperates with phosphorylated CREB and ligand-activated GR to directly control the induction of C/EBPb and C/EBPd in the early phase of adipogenesis (Lee JE, MCB 2020). V. In 2021, we reported that BAF is the SWI/SNF chromatin remodeling complex that colocalizes with MLL4 and lineage-determining TFs (LDTFs) on active enhancers. BAF is required for adipogenesis while the promoter enriched SWI/SNF complex PBAF is dispensable (Park Y, Nat Comm 2021). VI. MED1 often serves as a surrogate of the general transcription coactivator complex Mediator for identifying active enhancers. MED1 is required for phenotypic conversion of fibroblasts to adipocytes in vitro, but its role in adipose development and expansion in vivo has not been reported. Here, we show that MED1 is not generally required for transcription during adipogenesis in culture and that MED1 is dispensable for adipose tissue development in mice. Instead, MED1 is required for postnatal adipose expansion and the induction of fatty acid and triglyceride synthesis genes after pups switch diet from high-fat maternal milk to carbohydrate-based chow. During adipogenesis, MED1 is dispensable for induction of LDTFs PPAR and C/EBP but is required for lipid accumulation in the late phase of differentiation. Mechanistically, MED1 controls the induction of lipogenesis genes by facilitating lipogenic TF ChREBP- and SREBP1a-dependent recruitment of Mediator to active enhancers. Together, our findings identify a gene-specific regulatory role of MED1 as a lipogenesis coactivator required for postnatal adipose expansion (Jang Y, Genes Dev 2021).