Glutamine: A novel player in maintaining skeletal strength and body fitness in obese mice

Background and aims: Glutamine plays a key role in cellular metabolism and tissue homeostasis. In obesity, circulating glutamine levels decline, accompanied by impaired bone homeostasis and increased fracture risk. While dietary glutamine supplementation shows metabolic benefits, its effects on bone and fat metabolism remain unclear. This study investigates whether glutamine supplementation mitigates obesity-induced alterations in bone and fat metabolism. Methods: C57BL/6J male mice were subjected to a 2-month dietary intervention with either high-fat diet (HFD) or HFD supplemented with glutamine (HFD + G) and low-fat diet (LFD) as a control group. Body weight, fat mass, glucose tolerance, white adipose tissue (WAT) morphology, and bone parameters were analyzed. Functional assays of adipose-derived mesenchymal stem cells (AT-MSCs) and bone marrow stromal cells (BMSCs) assessed metabolic phenotype and differentiation potential. Glutamine turnover was evaluated, and findings were extended to human BMSCs to assess sex-specific patterns of glutaminolysis. Results: Glutamine supplementation attenuated body weight gain, fat mass, and WAT weight, along with improved glucose tolerance compared to HFD-fed mice. In WAT, glutamine reduced adipocyte hypertrophy and inflammation, while in AT-MSCs it suppressed obesity-driven hyper-metabolic phenotype by shifting cells toward quiescence. In bone, glutamine improved bone quality, along with reduced bone marrow adiposity and decreased bone resorption. BMSCs from glutamine-treated mice showed decreased adipogenic and increased osteogenic potential, supported by enhanced glutamine turnover, which maintained the stemness of the cells and reduced the inflammation induced by obesity. In human BMSCs, glutamine metabolism displayed sex-specific differences, underscoring its physiological relevance.