Deep Subcutaneous Adipose Tissue: A Distinct Abdominal Adipose Depot

Objective: Abdominal visceral (VAT) and subcutaneous adipose tissue (SAT) display significam metabolic differences, with VAT showing a functional association to metabolic/cardiovascular disorders. A third abdominal adipose layer, derived by the division of SAT and identified as deep subcutaneous adipose tissue (dSAT), may play a significant and independent metabolic role. The aim of this study was to evaluate depot-specific differences in the expression of proteins key to adipocyte metabolism in a lean population to establish a potential physiologic role for dSAT. Research Methods and Procedures: Adipocytes and preadipocytes were isolated from whole biopsies taken from superficial SAT (sSAT), dSAT, and VAT samples obtained from 10 healthy normal weight patients (7 women and 3 men), with a mean age of 56.4 ± 4.04 years and a mean BMI of 23.1 ± 0.5 kg/m². Samples were evaluated for depot-specific differences in insulin sensitivity using adiponectin, glucose transport protein 4 (GLUT4), and resistin mRNA and protein expression, glucocorticoid metabolism by 11β-hydroxysteroid dehydrogenase type-1 (11β-HSD1) expression, and alterations in the adipokines leptin and tumor necrosis factor-α (TNF-α). Results: Although no regional differences in expression were observed for adiponectin or TNF-α, dSAT whole biopsies and adipocytes, while intermediary to both sSAT and VAT, reflected more of the VAT expression profile of 11β-HSD1, leptin, and resistin. Only in the case of the intracellular pool of GLUT4 proteins in whole biopsies was an independent pattern of expression observed for dSAT. In an evaluation of the homeostatic model, dSAT 11β-HSD1 protein (r = 0.9573, p = 0.0002) and TNF-α mRNA (r = 0.8210, p = 0.0236) correlated positively to the homeostatic model. Discussion: Overall, dSAT seems to be a distinct abdominal adipose depot supporting an independent metabolic function that may have a potential role in the development of obesity-associated complications.