Abstract
Introduction: Asian Indians show “thin fat phenotype” characterized by higher visceral adipose tissue(VAT) and lower subcutaneous adipose tissue(SAT) mass and their higher cardio-metabolic risk has been attributed to this fat distribution. However, the underlying molecular pathology and role of these adipose depots in the pathogenesis of T2D in them remains unknown.Hypothesis: The comparison of transcription profiles of abdominal VAT and SAT and their correlation with diabetes related intermediate phenotypic traits could shed some light on their role in the pathophysiology of diabetes.MethodologySubjects: 19 diabetics (M: F ratio, 8:11) and 16 age and BMI matched controls (M: F ratio 5:11) undergoing abdominal surgery (non-malignant and non-infective conditions).Clinical Parameters: Anthropometry, Serum glucose, insulin, HOMA-R, HbA1c, lipid profile, FFA, adipocytokines. Abdominal VAT, SAT and liver fat were estimated by MRI.Adipose tissue biopsy: SAT and VAT samples were taken during surgery. Genome-wide gene expression profiling of these biopsies was performed using Affymetrix GeneChipPrimeView® arrays. The data was submitted to NCBI-GEO (Accession # GSE78721). Selected genes were validated by qPCR. Gene set enrichment analysis (GSEA) for functional and Weighted Gene Correlation Analysis (WGCNA) for statistical comparison was done.Results:Diabetics had higher waist circumference (p=0.05), HOMA-R (p=0.0002), Visceral fat content (p=0.02) and adipocyte size (p=0.02)GSEA: diabetics vs. controls: In VAT 16 gene sets were upregulated (FDR < 25%) enriching various immune system and inflammation-related pathways. In SAT too, various inflammatory genes were upregulated however they were statistically non-significant (FDR > 25%). Moreover, 12 out of 16 significantly enriched pathways in VAT were among the top 20 pathways in SAT. GSEA in diabetics: VAT vs SAT: None of the gene sets were found significant at FDR < 25% which substantiated our hypothesis that overall pathophysioloigcal alteration in both depots are similar. WGCNA for statistical comparison of VAT and SAT depots The correlation between measures of average gene expression and overall connectivity between both depots was significantly positive. Several modules of co-expressed genes in both VAT and SAT showed positive as well as negative correlation with various intermediate phenotypic traits of diabetes. In both depots they enriched several pathways otherwise known to be associated with pathological adipose tissue like inflammation, adipogenesis etc.
Conclusions
In Asian Indians, diabetes pathology inflicts similar molecular alternations in VAT and SAT, which are more intense in the former. The role of both adipose depots in the pathophysiology of diabetes is along similar lines and they enrich several molecular pathways which are otherwise known to be implicated in pathological adipose tissue.
Role of Subcutaneous Adipose Tissue in the Pathogenesis of Insulin Resistance