Marrow Adipose Tissue

Marrow adipose tissue
Illustration of MSC differentiation into adipocytes and osteoblasts
Anatomical terminology []

Marrow adipose tissue (MAT) increases in states of low bone density -osteoporosis,anorexia nervosa/ caloric restriction, skeletal unweighting, anti-diabetes therapies). The marrow adipocytes originate from mesenchymal stem cell (MSC) progenitors that also give rise to osteoblasts, among other cell types. Thus, it is thought that MAT results from preferential MSC differentiation into the adipocyte, rather than osteoblast, lineage in the setting of osteoporosis. Since MAT is increased in the setting of obesity and is suppressed by endurance exercise, or vibration , it is likely that MAT physiology- in the setting of mechanical input/exercise- approximates that of white adipose tissue (WAT).

MAT has qualities of both white and brown fat.Subcutaneous white fat contain excess energy, indicating a clear evolutionary advantage during times of scarcity. WAT is also the source of adipokines and inflammatory markers which have both positive (e.g., adiponectin) and negative effects on metabolic and cardiovascular endpoints. Visceral abdominal fat (VAT) is a distinct type of WAT that is "proportionally associated with negative metabolic and cardiovascular morbidity", regenerates cortisol, and recently has been tied to decreased bone formation Both types of WAT substantially differ from brown adipose tissue (BAT) as by a group of proteins that help BAT’s thermogenic role. MAT, by its "specific marrow location, and its adipocyte origin from at least LepR+ marrow MSC is separated from non-bone fat storage by larger expression of bone transcription factors", and likely indicates a different fat phenotype. Recently, MAT was noted to "produce a greater proportion of adiponectin - an adipokine associated with improved metabolism - than WAT", suggesting an endocrine function for this depot, akin, but different, from that of WAT.