N 6 -methyladenosine (m 6 A), the most abundant internal modification on mRNAs in eukaryotes, play roles in adipogenesis. However, the underlying mechanism remains largely unclear. Here, we show that m 6 A plays a critical role in regulating macroautophagy/autophagy and adipogenesis through targeting Atg5 and Atg7. Mechanistically, knockdown of FTO, a well-known m 6 A demethylase, decreased the expression of ATG5 and ATG7, leading to attenuation of autophagosome formation, thereby inhibiting autophagy and adipogenesis. We proved that FTO directly targeted Atg5 and Atg7 transcripts and mediated their expression in an m 6 A-dependent manner. Further study identified that Atg5 and Atg7 were the targets of YTHDF2 (YTH N6-methyladenosine RNA binding protein 2). Upon FTO silencing, Atg5 and Atg7 transcripts with higher m 6 A levels were captured by YTHDF2, which resulted in mRNA degradation and reduction of protein expression, thus alleviating autophagy and adipogenesis. Furthermore, we generated an adipose-selective fto knockout mouse and find that FTO deficiency decreased white fat mass and impairs ATG5-and ATG7-dependent autophagy in vivo. Together, these findings unveil the functional importance of the m 6 A methylation machinery in autophagy and adipogenesis regulation, which expands our understanding of such interplay that is essential for development of therapeutic strategies in the prevention and treatment of obesity.

Bone marrow stem cells (BMSCs) are multipotent stem cells that can regenerate mesenchymal tissues, such as adipose tissue, bone, and muscle. Recent studies have shown that N6‐methyladenosine (m6A) methylation, one of the most prevalent epigenetic modifications, is involved in the development process. However, whether it plays roles in BMSC differentiation is still elusive. Here, we found that the deletion of m6A “writer” protein methyltransferase‐like (METTL)3 in porcine BMSCs (pBMSCs) could promote adipogenesis and janus kinase (JAK)1 protein expression via an m6A‐dependent way. Knockdown of METTL3 decreased mRNA m6A levels of JAK1, leading to enhanced YTH m6A RNA binding protein 2 (YTHDF2)‐dependent JAK1 mRNA stability. We further demonstrated that JAK1 activated signal transducer and activator of transcription (STAT) 5 through regulation of its phosphorylation to bind to the promoter of CCAAT/enhancer binding protein (C/EBP) β, which could ultimately lead to a modulated adipogenic process. Collectively, our results reveal an orchestrated network linking the m6A methylation and JAK1/STAT5/C/EBPβ pathway in pBMSCs adipogenic differentiation. Our findings provide novel insights into the underlying molecular mechanisms of m6A modification in the regulation of BMSCs differentiating into adipocytes, which may pave a way to develop more effective therapeutic strategies in stem cell regenerative medicine and the treatment of obesity.—Yao, Y., Bi, Z., Wu, R., Zhao, Y., Liu, Y., Liu, Q., Wang, Y., Wang, X. METTL3 inhibits BMSC adipogenic differentiation by targeting the JAKl/STAT5/C/EBPβ pathway via an m6A‐YTHDF2–dependent manner. FASEB J. 33, 7529–7544 (2019). http://www.fasebj.org

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N (6)-methyladenosine (m(6)A) is the most abundant and reversible internal modification ubiquitously occurring in eukaryotic mRNA, albeit the significant biological roles of m(6)A methylation have remained largely unclear. The well-known DNA and histone methylations play crucial roles in epigenetic modification of biologic processes in eukaryotes. Analogously, the dynamic and reversible m(6)A RNA modification, which is installed by methyltransferase (METTL3, METTL14, and WTAP), reversed by demethylases (FTO, ALKBH5) and mediated by m(6)A-binding proteins (YTHDF1-3, YTHDC1), may also have a profound impact on gene expression regulation. Recent discoveries of the distributions, functions, and mechanisms of m(6)A modification suggest that this methylation functionally modulates the eukaryotic transcriptome to influence mRNA transcription, splicing, nuclear export, localization, translation, and stability. This reversible mRNA methylation shed light on a new dimension of post-transcriptional regulation of gene expression at the RNA level. m(6)A methylation also plays significant and broad roles in various physiological processes, such as development, fertility, carcinogenesis, stemness, early mortality, meiosis and circadian cycle, and links to obesity, cancer, and other human diseases. This review mainly describes the current knowledge of m(6)A and perspectives on future investigations.

Our findings provide mechanistic insights into how mA is involved in the EGCG regulation of adipogenesis and shed light on its anti-obesity effect.