Abstract: 【Objective】 The aim of this study was to investigate the function and mechanism of miR-137-3p in the differentiation of preadipocytes 3T3-L1.【Method】 3T3-L1 cells at the 0,2,4,6 and 8 days of induced differentiation were collected and the expression of miR-137-3p was detected by Real-time quantitative PCR.miR-137-3p mimics,miR-137-3p inhibitor and negative control (NC) were transfected into 3T3-L1 cells and induced lipid differentiation.Oil red O staining was performed to observe the formation of lipid droplets.The relative expressions of lipogenic marker genes CAAT enhancer binding protein α (C/EBPα),C/EBPβ,peroxisome proliferator-activated receptor γ (PPARγ) and fatty acid binding protein 4 (FABP4) were detected by Real-time quantitative PCR.The protein expression of C/EBPβ,PPARγ and FABP4 were detected by Western blotting.The target genes of miR-137-3p were predicted using TargetScan online website,and the binding sites with miR-137-3p in the 3'-UTR region of candidate target genes were compared for sequence conservation between different species.miR-137-3p mimics,NC and 3'-UTR-WT and 3'-UTR-Mut vectors were co-transfected into HEK293T cells,respectively.Dual luciferase reporting assay was used to detect the targeting relationship between miR-137-3p and MYC-related factor X (MAX) gene.3T3-L1 cells were transfected with siMAX and siNC,and the relative expression of C/EBPα,C/EBPβ,PPARγ and FABP4 genes were detected by Real-time quantitative PCR,and the expression of C/EBPβ,PPARγ and FABP4 proteins were detected by Western blotting.【Result】 In the process of lipogenic differentiation of 3T3-L1 cells,compared with day 0,the relative expression of miR-137-3p on days 2,4,6 and 8 was extremely significantly decreased (P＜0.01).Compared with NC group,the number and size of lipid droplets in miR-137-3p mimics group were significantly decreased,the relative expression of C/EBPα,C/EBPβ,PPARγ and FABP genes in miR-137-3p mimics group were extremely significantly or significantly decreased (P＜0.01 or P＜0.05),the expression of C/EBPβ,PPARγ and FABP4 proteins were down-regulated.The results of oil red O staining,mRNA and protein expression of adipogenic differentiation marker genes in miR-137-3p inhibitor group were opposite.The results of target gene prediction indicated that the 3'-UTR region sequence of MAX had a predicted binding site with miR-137-3p,which was highly conserved among different species.Compared with NC group,the expression of MAX gene in mimics group was extremely significantly decreased (P＜0.01),while that of inhibitor group was significantly increased (P＜0.05).Compared with siNC group,knockdown of MAX gene significantly reduced the number and size of lipid droplets,the mRNA expression of C/EBPα,C/EBPβ,PPARγ and FABP4 genes were extremely significantly down-regulated (P＜0.01),and the protein expressions of C/EBPβ,PPARγ and FABP4 were decreased.【Conclusion】 The expression of endogenous miR-137-3p was decreased during the differentiation of 3T3-L1 preadipocytes,and miR-137-3p might inhibit the adipogenic differentiation of 3T3-L1 preadipocytes by down-regulating the expression of MAX gene.

Key words: miR-137-3p; 3T3-L1 preadipocytes; MAX gene; adipocyte differentiation