Role of adipose mRNA modifications in metabolic disease

摘要 过量的白色脂肪组织（WAT）是肥胖的标志，也是肥胖相关性肥胖的致病因素。 疾病脂肪因子的脂肪分泌在肥胖症中也失调，进一步损害了WAT与 其他组织。基因转录和蛋白质翻译后水平的研究已成为热点 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 将遗传控制与负责细胞活动和功能的蛋白质的翻译联系起来。像 除了蛋白质修饰之外，RNA在其生命周期中也被广泛且可逆地修饰。N6-甲基腺苷 (m6A)是主要的RNA修饰，并由Mettl 3/Mettl 14甲基转移酶复合物催化 (m6A作者）。YTHD家族蛋白（m6 A阅读器）与m6 A-甲基化RNA结合并调节前mRNA 剪接、核输出、衰变和/或靶转录物的翻译。Mettl 3、Mettl 14或Mettl 15的全局缺失 Ythdc 1导致小鼠胚胎/新生儿死亡，证明了m6 A系统在 发展和生存。然而，基于m6 A的表观转录组学重编程尚未被探索。 WAT，我们对肥胖中RNA修饰和代谢的理解存在差距。在 初步研究，我们产生并表征了脂肪细胞特异性Mettl 14（Mettl 14 Δfat）和Ythdc 1 （Ythdc 1 Δfat）敲除小鼠。值得注意的是，Mettl 14 Δfat和Ythdc 1 Δfat小鼠对饮食诱导的肥胖具有抗性。 肥胖、2型糖尿病和肝脏脂肪变性。基因表达分析表明，Mettl 14和Ythdc 1 靶向脂解机制、β肾上腺素能信号传导（刺激脂解）、胰岛素信号传导（抑制 脂解）和脂肪因子分泌。因此，在Mettl 14 Δ肥胖小鼠中，WAT脂解显著升高 和Ythdc 1 Δ肥胖小鼠，特别是在β肾上腺素能刺激条件下，有助于WAT降低。 在Mettl 14 Δfat和Ythdc 1 Δfat小鼠中，脂肪脂联素表达升高，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Mettl 14诱导m6 A 在控制脂解机制的mRNA中选择性甲基化，β肾上腺素能信号传导，胰岛素信号传导， 和脂肪因子表达。Ythdc 1直接结合并调节代谢（前体mRNA剪接，核 这些m6 A修饰的mRNA的输出，衰变），从而指导脂解，WAT生长和脂肪因子- 介导的脂肪与其他组织的串扰。我们将在三个目标中检验这个假设。目标1：确定 Mettl 14是否通过RNA m6 A甲基化抑制脂解并增加WAT扩增。目标二是 确定Ythdc 1是否通过调节其代谢抑制脂解并促进WAT扩张。 结合RNA。目的3是描绘Mettl 14/Ythdc 1轴是否协调脂肪串扰与其他 组织通过脂肪因子。这些结果有望建立一个新的基于脂肪Mettl 14/m6 A/Ythdc 1的 肥胖和代谢性疾病中的表观转录组重编程范例。

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.