Role of adipose mRNA modifications in metabolic disease

摘要 过多的白色脂肪组织(WAT)是肥胖的标志，也是肥胖相关的致病因素 疾病。肥胖患者脂肪因子的脂肪分泌也受到失调，进一步损害了Wat串扰 其他纸巾。广泛的研究集中在基因转录和蛋白质翻译后 修改并大大提高了我们对Wat生长和功能的理解。重要的是，mRNA 将基因控制与负责细胞活动和功能的蛋白质的翻译联系起来。喜欢 除了蛋白质修饰，RNA在其生命周期中也被广泛和可逆地修饰。N6-甲基腺苷 (M6A)是主要的RNA修饰，由METTL3/Mettl14甲基转移酶复合体催化 (m6a作家)。YTHD家族蛋白(m6A阅读器)与m6A甲基化的RNA结合并调节前-mRNA 目标转录本的剪接、核输出、衰退和/或翻译。全局删除METTL3、Mettl14或 Ythdc1导致小鼠胚胎/新生儿死亡，表明M6A系统在 发展和生存。然而，基于m6A的表位转录重新编程还没有在 我们对肥胖中的RNA修饰和新陈代谢的理解存在差距。在 初步研究，我们克隆并鉴定了脂肪细胞特异性的Mettl14(Mettl14ΔFAT)和Ythdc1 (Ythdc1Δ脂肪)基因敲除小鼠。值得注意的是，Mettl14Δ肥胖和Ythdc1Δ肥胖小鼠都对饮食诱导产生了抵抗力 肥胖、2型糖尿病和肝脏脂肪变性。基因表达分析表明，Mettl14和Ythdc1 靶向脂解机制、β肾上腺素能信号(刺激脂解)、胰岛素信号(抑制 脂肪分解)和脂肪因子分泌。一致地，在Mettl14Δ肥胖小鼠中WAT脂解显著升高 和Ythdc1Δ肥胖小鼠，特别是在β肾上腺素刺激的条件下，有助于减少WAT。 脂联素在Mett14Δ肥胖和Ythdc1Δ肥胖小鼠中的表达增加，有助于改善 胰岛素抵抗、葡萄糖代谢和肝脏脂肪变性。我们假设Mettl14诱导M6A 控制脂肪分解机制的mRNAs选择性甲基化，β肾上腺素能信号，胰岛素信号， 和脂肪因子的表达。Ythdc1直接结合并调节新陈代谢(前mRNA剪接，核 这些m6A修饰的mRNA的输出、衰退)，从而引导脂肪分解、水分生长和脂肪因子- 介导脂肪与其他组织的串扰。我们将在三个目标中检验这一假设。目标1是确定 Mettl14是否通过RNA m6A甲基化抑制脂解和增加WAT扩张。目标2是 确定Ythdc1是否通过调节其代谢抑制脂解和促进WAT扩张 结合的RNA。目标3是描述Mettl14/Ythdc1轴是否协调脂肪与其他 脂肪因子产生的组织。这一结果有望建立一种新的以脂肪金属14/m6A/Ythdc1为基础的 肥胖和代谢性疾病中的表位转录重编程范例。

Abstract Excessive white adipose tissue (WAT) is a hallmark of obesity and a causal factor for obesity-associated disease. Adipose secretion of adipokines is also dysregulated in obesity, further impairing WAT crosstalk with other tissues. Extensive research has been focused on gene transcriptions and protein posttranslational modifications and substantially advanced our understanding of WAT growth and functions. Importantly, mRNA connects the genetic control to translation of proteins responsible for cellular activities and functions. Like protein modifications, RNA is also extensively and reversibly modified in its life cycle. N6-methyladenosine (m6A) is the predominant RNA modification and catalyzed by a Mettl3/Mettl14 methyltransferase complex (m6A writer). YTHD family proteins (m6A readers) bind to m6A-methylated RNAs and regulate pre-mRNA splicing, nuclear export, decay, and/or translation of target transcripts. Global deletion of Mettl3, Mettl14, or Ythdc1 results in embryonic/neonatal death in mice, demonstrating the essential role of the m6A system in development and survival. However, m6A-based epitranscriptomic reprogramming has not been explored in WAT, and there is a gap in our understanding of RNA modifications and metabolism in obesity. In the preliminary study, we generated and characterized adipocyte-specific Mettl14 (Mettl14Δfat) and Ythdc1 (Ythdc1Δfat) knockout mice. Remarkably, both Mettl14Δfat and Ythdc1Δfat mice were resistant to diet-induced obesity, type 2 diabetes, and liver steatosis. Gene expression analysis suggested that Mettl14 and Ythdc1 target the lipolysis machinery, β adrenergic signaling (stimulating lipolysis), insulin signaling (suppressing lipolysis), and adipokine secretion. Consistently, WAT lipolysis was substantially elevated in Mettl14Δfat mice and Ythdc1Δfat mice, particularly under β adrenergic-stimulated conditions, contributing to WAT reduction. Adipose adiponectin expression was elevated in Mettl14Δfat and Ythdc1Δfat mice, contributing to improved insulin resistance, glucose metabolism, and liver steatosis. We hypothesize that Mettl14 induces m6A methylation selectively in mRNAs governing the lipolysis machinery, β adrenergic signaling, insulin signaling, and adipokine expression. Ythdc1 directly binds to and regulates the metabolism (pre-mRNA splicing, nuclear export, decay) of these m6A-modificed mRNAs, thereby guiding lipolysis, WAT growth, and adipokine- mediated adipose crosstalk with other tissues. We will test this hypothesis in 3 Aims. Aim 1 is to determine whether Mettl14 inhibits lipolysis and increases WAT expansion through RNA m6A methylation. Aim 2 is to determine whether Ythdc1 suppresses lipolysis and promotes WAT expansion by regulating metabolism of its bound RNAs. Aim 3 is to delineate whether Mettl14/Ythdc1 axis coordinates adipose crosstalk with other tissues via adipokines. The outcomes are expected to establish a new adipose Mettl14/m6A/Ythdc1-based epitranscriptomic reprogramming paradigm in obesity and metabolic disease.