Role of FKBP5 in adipose tissue function: Implications for obesity and insulin sensitivity

FK506-binding protein 51 (FKBP51, encoded by the FKBP5 gene) is a key regulator of glucocorticoid signaling and has been implicated in metabolism and insulin sensitivity, but its specific role in human adipose tissue remains unclear. This study investigated the role of FKBP51 in human adipose tissue and its impact on glucose metabolism and insulin signaling. FKBP5 was measured in paired subcutaneous (SAT) and omental (OAT) adipose tissue samples from 56 subjects with and without obesity, and in SAT from individuals with obesity during weight loss up to 104 weeks post-bariatric surgery. Furthermore, FKBP51 knockdown adipocytes were used to study its effects on insulin signaling and glucose uptake. FKBP5 gene expression, but not protein expression, was significantly lower in obese individuals in both SAT and OAT compared to lean and overweight subjects, and it inversely correlated with insulin resistance measured by homeostatic model assessment of insulin resistance (HOMA-IR). After bariatric surgery, FKBP5 expression in SAT increased to levels similar to those in non-obese controls. Knockdown of FKBP5 in human adipocytes reduced GLUT1 gene expression and insulin-stimulated AKT Ser473 phosphorylation, however, maximal insulin-stimulated glucose uptake rate remained unchanged. Our findings suggest that FKBP5 levels in adipose tissue are reduced in obesity, and this decrease impairs insulin signaling in adipocytes without altering maximal glucose capacity, indicating a limited effect on glucose uptake under the tested conditions.