Identification And Functional Verification Of Visceral Adipose Tissue-Specific Susceptibility Genes For Type 2 Diabetes

Background:Emerging evidence has revealed the presence of ectopic and visceral fat deposition in type 2 diabetes(T2D).Dysfunctional visceral adipose tissue(VAT)in obesity is associated with T2D but underlying mechanisms remain unclear.This study aimed to access the causal relationship between visceral obesity and T2D and subsequently to screen VAT-specific candidate genes for T2D pathogenesis.Methods:We examined the genetic correlation and causal relationship between VAT and T2D using LD Score regression(LDSC)and bi-directional Mendelian randomization(MR)followed by multivariable MR(MVMR)analysis.221 genetic variants were selected as instrumental variables(IVs)for the predicted VAT mass from UK Biobank(N=325,153).Two large-scale summary-level datasets of T2D(26,676 cases and 132,532 controls for discovery analysis,and 12,931cases and 57,196 controls for replication analysis)were included as outcomes.We further conducted a transcriptome-wide association study(TWAS)leveraging the prediction models and a large-scale T2D GWAS(74,124 cases and 824,006 controls)to identify T2D candidate genes in VAT and used summary-data-based MR(SMR)and colocalization to map causal genes.We performed enrichment and single-cell RNA-seq analyses to determine the cell-specific localization of TWAS-identified genes.We also conducted knockdown experiments in 3T3-L1 pre-adipocytes to evaluate the effect of Pabpc4 on glucose and lipid metabolism.Results:According to LDSC results,the predicted VAT was genetically correlated with T2D(r_g=0.575;95%CI 0.508-0.642;P=7.85E-66 for DIAGRAM,and r_g=0.331;95%CI 0.262-0.400;P=9.21E-21 for 70Kfor T2D).MR analyses showed a causal relationship between genetically increased VAT mass and T2D risk[IVW,the odds ratio(95%CI)per unit increased VAT:2.48(2.21-2.79);P=9.28E-54].These findings were further confirmed by MVMR and replication analyses.Ten VAT-specific candidate genes were associated with T2D risk after Bonferroni correction(P<4.04E-06),including five causal genes supported by SMR and colocalization:PABPC4(1p34.3),CCNE2(8q22.1),HAUS6(9p22.1),CWF19L1(10q24.31),and CCDC92(12q24.31).Combined with enrichment analyses,clarifying cell-type specificity with single-cell RNA-seq data indicated that most TWAS-identified candidate genes appear more likely to be associated with adipocytes in VAT.Knockdown experiments confirmed that Pabpc4showed a vital effect on the glucose and lipid metabolism in 3T3-L1adipocytes.Conclusions:Our MR analyses suggest that lifelong exposure to elevated VAT mass might increase the risk of T2D.TWAS-identified candidate genes show a casual effect on T2D risk and warrant investigation by further functional studies.The expression of Pabpc4plays a key role in glucose and lipid metabolism of 3T3-L1 adipocytes and may be a key factor in the pathogenesis of T2D.