Human bone marrow adipose tissue is a metabolically active and insulin sensitive distinct fat depot.

CONTEXT: Bone marrow (BM) in adult long bones is rich in adipose tissue, but the functions of BM adipocytes are largely unknown. We set out to elucidate the metabolic and molecular characteristics of BM adipose tissue (BMAT) in humans. OBJECTIVE: Our aim was to determine if BMAT is an insulin sensitive tissue, and whether the insulin sensitivity is altered in obesity or type 2 diabetes (T2DM). DESIGN: This was a cross-sectional and longitudinal study. SETTING: The study was conducted in a clinical research center. PATIENTS OR OTHER PARTICIPANTS: BMAT glucose uptake was assessed in 23 morbidly obese subjects (9 with T2DM) and 9 healthy controls with normal body weight. In addition, glucose uptake was assessed in another 11 controls during cold exposure. BMAT samples for molecular analyses were collected from non-DM patients undergoing knee arthroplasty. INTERVENTION(S): Obese subjects were assessed before and 6 months after bariatric surgery and controls at one time point. MAIN OUTCOME MEASURE: We used positron emission tomography imaging with 2-[18F]fluoro-2-deoxy-D-glucose tracer to characterize glucose uptake in femoral and vertebral BMAT. BMAT molecular profile was assessed using quantitative RT-PCR. RESULTS: Insulin enhances glucose uptake in human BMAT. Femoral BMAT insulin sensitivity was impaired in obese patients with T2DM compared to controls but it improved after bariatric surgery. Furthermore, gene expression analysis revealed that BMAT was distinct from brown and white adipose tissue. CONCLUSIONS: BMAT is a metabolically active, insulin sensitive and molecularly distinct fat depot that may play a role in whole body energy metabolism.