Novel mechanisms of glucocorticoid-induced insulin resistance in human adipose tissue

Abstract: The global prevalence of obesity and type 2 diabetes (T2D) is increasing. From a public health perspective, it is therefore of interest to identify common underlying mechanisms of these comorbidities. Glucocorticoids are steroid hormones that are important in stress regulation in mammals. Elevated glucocorticoid levels are associated with insulin resistance (IR) and T2D-like phenotypes. Here, glucocorticoids are used to model a state of IR in human adipose tissue to identify potential pharmacological targets.In Paper I the impact of T2D on lipid turnover was examined in a cohort of 20 T2D subjects and 20 healthy controls. Plasma levels of non-esterified fatty acids (NEFA) were shown to be elevated in T2D subjects during oral glucose tolerance test (OGTT) compared to healthy controls. In vitro lipolysis and assessments of mRNA and metabolites in subcutaneous adipose tissue (SAT) were performed. Results showed that elevated NEFA levels in T2D subjects could be attributed to impaired lipid storage.In Paper II we explored the role of cannabinoid receptor type 1 (CNR1) in glucocorticoid-induced IR. The CNR1 gene was upregulated after exposure to glucocorticoids in SAT. Moreover, CNR1 gene expression in SAT was associated with markers of IR and elevated in T2D subjects compared to healthy controls. Furthermore, using a CNR1-specific antagonist, we found that CNR1 may mediate lipolysis in SAT.In Paper III-IV, we examined the role of FK506 protein 5 (FKBP51) in glucocorticoid-induced IR. Its corresponding gene, FKBP5, was found to be upregulated in SAT and omental adipose tissue (OAT) following glucocorticoid-exposure. In addition, FKBP5 gene expression in SAT was associated with markers of IR and tended to be elevated in T2D subjects compared to healthy controls. Furthermore, co-incubating an FKBP51-specific inhibitor with glucocorticoids in SAT partly prevented glucocorticoid-impaired adipocyte glucose uptake.We identified CNR1 and FKBP51 as potential pharmacological targets in T2D and glucocorticoid-induced IR. Both were shown to be elevated in human adipose tissue after glucocorticoid-exposure. Their SAT gene expression levels were also associated with markers of IR and tended to be elevated in T2D. Both may be involved in perturbations of adipocyte metabolism, including glucose and lipid metabolism.