M6A Regulates Liver Metabolic Disorders and Hepatogenous Diabetes

Yuhuan Li,Qingyang Zhang,Guanshen Cui,Fang Zhao,Xin Tian,Bao-Fa Sun,Ying Yang,Wei Li

doi:10.1016/j.gpb.2020.06.003

Abstract

N6-methyladenosine (m6A) is one of the most abundant modifications on mRNAs and plays important roles in various biological processes. The formation of m6A is catalyzed by a methyltransferase complex (MTC) containing a key factor methyltransferase-like 3 (Mettl3). However, the functions of Mettl3 and m6A modification in hepatic lipid and glucose metabolism remain unclear. Here, we showed that both Mettl3 expression and m6A level increased in the livers of mice with high fat diet (HFD)-induced metabolic disorders. Overexpression of Mettl3 aggravated HFD-induced liver metabolic disorders and insulin resistance. In contrast, hepatocyte-specific knockout of Mettl3 significantly alleviated HFD-induced metabolic disorders by slowing weight gain, reducing lipid accumulation, and improving insulin sensitivity. Mechanistically, Mettl3 depletion-mediated m6A loss caused extended RNA half-lives of metabolism-related genes, which consequently protected mice against HFD-induced metabolic syndrome. Our findings reveal a critical role of Mettl3-mediated m6A in HFD-induced metabolic disorders and hepatogenous diabetes.

Highlights

methyltransferase-like 3 4 (Mettl3) expression and m6A level increased in High Fat Diet (HFD) mice To explore the potential role of m6A in regulation of lipid and glucose metabolism in HFD-induced obese mice, we first measured the relative mRNA levels of m6A
Compared with conditional overexpression mice (cOE)-Mut mice, total cholesterol (TC) in serum of cOE mice increased, while there was no significant change in total triglyceride (TG) (Figure 2E, F). there was no significant change in serum insulin level (Figure 2G), further analysis showed that cOE mice presented significant worse glucose tolerance (Figure 2H, I) and insulin sensitivity (Figure 2J, K) than cOE-Mut mice in HFD condition, evaluated by the glucose tolerance test (GTT) and the insulin tolerance test (ITT), respectively. These results indicated that Mettl3 overexpression can aggravate liver metabolic disorders and hepatogenous diabetes, suggesting that high levels of Mettl3 may be a risk factor for HFD-induced metabolic syndrome
Given that m6A is mainly reported to play a negative role in mRNA stability regulation, we focused on the m6A-containing up-regulated genes in conditional knockout (cKO)-HFD mice liver, performed gene ontology analysis, and found that these genes were enriched in insulin response and lipid metabolic related processes (Figure 4E). qRT-PCR further validated the expression of these candidate genes which were down-regulated in Ctrl-HFD mouse liver while up-regulated in cKO-HFD mouse liver, such as Lpin1, Pck1, G6pc, Lpin2, peroxisome proliferator activator receptor α (Pparα), and Hc (Figure 4F), and most of these genes were more stable in cKO mouse liver due to Mettl3 depletion induced m6A loss, indicated by mRNA stability assay (Figure 4G-L)

Summary

Introduction

N6-methyladenosine (m6A), the most prevalent mRNA modification in eukaryotes [1], 3 is catalyzed by a methyltransferase complex including methyltransferase-like 3 4 (Mettl3), methyltransferase-like 14 (Mettl14), Wilms’ tumor 1-associating protein 5 (Wtap), among which Mettl3 functions as the catalytic subunit [2, 3]. m6A 6 methylation can be reversed by at least two eraser enzymes, fat-mass and 7 obesity-associated protein (Fto) and α-ketoglutarate-dependent dioxygenase alkB 8 homolog 5 (Alkbh5) [4, 5], and is mainly recognized by YTH domain-containing 9 family ‘reader’ proteins [6,7,8,9,10]. We inactivated Mettl3 in the mouse liver using the Alb-Cre mediated Mettl3 conditional knockout (cKO) model and confirmed Mettl3 ablation protects mice against HFD-induced liver metabolic disorders and insulin resistance, mechanism analysis suggested that Mettl3 deletion alters expression pattern of liver lipid and glucose metabolism genes, extends mRNA stability of an important regulator of liver metabolism--Lpin1.

Results

Conclusion