Bone Marrow Adipose Tissue in Relation to Bone and Energy Metabolism in Obesity and Type 2 Diabetes Mellitus

Bone marrow contains not only blood-forming cells but also adipose tissue and mesenchymal stromal cells that can develop into bone-forming cells or fat cells. Bone marrow adipose tissue (BMAT) is increasingly recognized as an active component of the bone marrow environment that may influence bone remodeling, skeletal strength, and whole-body metabolism. In people with obesity, fracture risk may be increased even when bone mineral density is normal or elevated. This suggests that changes in bone quality, bone marrow fat, and the function of bone marrow mesenchymal stromal cells (BM-MSCs) may contribute to obesity-related bone fragility. The present application describes only the interventional study, which is part of a broader research project entitled "Bone Marrow Adipose Tissue in Relation to Bone and Energy Metabolism in Obesity and Type 2 Diabetes Mellitus." The broader project also includes a cross-sectional study evaluating BMAT and BM-MSC characteristics in participants with different metabolic and skeletal conditions. However, the cross-sectional component is not included in this application and is therefore not described further here. The interventional study will investigate whether weight loss induced by caloric restriction modifies the bone marrow environment in obese non-diabetic premenopausal women. Lean healthy premenopausal women will serve as a comparison group. Participants in the intervention group will follow a formula-based very-low-calorie diet using Cambridge Weight Plan formula products, providing approximately 2.5-3.35 MJ (600-800 kcal) per day for 8 weeks. This will be followed by a 4-month low-calorie diet phase and subsequently by a weight-maintenance phase. Participants will receive nutritional counselling, and dietary adherence, body weight, physical activity, and clinical status will be monitored during scheduled study visits. The study will evaluate whether the dietary intervention changes the amount and lipid composition of vertebral BMAT and whether these changes are associated with changes in bone and metabolic parameters. Vertebral BMAT will be assessed in the lumbar spine using magnetic resonance imaging and proton magnetic resonance spectroscopy. These methods allow non-invasive measurement of bone marrow fat content and assessment of its saturated and unsaturated lipid fractions. Bone mineral density and body composition will be assessed using dual-energy X-ray absorptiometry, with particular attention to the total hip and femoral neck. Abdominal adipose tissue distribution will be evaluated using magnetic resonance imaging. Blood samples will be used to assess glucose and lipid metabolism, bone turnover, inflammatory markers, hormones, and adipokines. Bone marrow aspirates and subcutaneous adipose tissue samples will be collected at baseline and after 6 months to study BM-MSCs and adipose tissue-derived mesenchymal stromal cells. Laboratory analyses will examine their cellular composition, ability to differentiate into bone-forming and fat cells, metabolic activity, oxidative stress, cellular senescence, gene-expression profiles, and other molecular characteristics. Single-cell RNA sequencing will be used to characterize specific BM-MSC subpopulations and identify transcriptional profiles associated with metabolic activity and cellular senescence. Bone marrow plasma and other biological samples will also undergo metabolomic, lipidomic, and proteomic profiling to identify molecules associated with the bone marrow microenvironment, metabolic status, bone health, and the response to caloric restriction. By integrating imaging, clinical, biochemical, cellular, and molecular data, the interventional study aims to determine whether diet-induced weight loss can improve the bone marrow environment and modify factors associated with obesity-related bone fragility. The findings may support the identification of new imaging, cellular, and molecular biomarkers of bone health and provide a scientific basis for future strategies to prevent or treat metabolic bone complications associated with obesity.