Recent advances in the adaptations of adipose tissue to physical activity: Morphology and adipose tissue cellularity

White adipose tissue (WAT) is located beneath the skin as subcutaneous adipose tissue (SAT), around internal organs as visceral adipose tissue (VAT), pericardial and epicardial adipose tissue, and inside muscles in human beings. Recent studies indicate that developmental and patterning genes are differentially expressed in SAT and VAT, and some of these genes exhibit changes in expression that closely correlate with the extent of obesity and pattern of fat distribution. Furthermore, the development of adipocytes from mesenchymal stem/progenitor cells is thought to be mediated by developmental signaling molecules including nodal, Wnt/wingless (Wg), bone morphogenetic proteins (BMPs), fibroblast growth factors (FGF), and others. Of these, BMPs and the FGF family have been suggested to play a role in maintaining energy homeostasis. However, it remains unclear whether these developmental and patterning genes are associated with morphological changes in WAT in response to exercise training (TR). On the other hand, when TR reduces the number of adipocytes in WAT, it increases preadipocyte factor 1 mRNA expression but down-regulates peroxisome proliferator-activated receptor-γ mRNA expression in stromal-vascular fraction cells, including adipose tissue-derived stromal cells, via the up-regulation of hypoxia-inducible factor-1α, which may also up-regulate the mRNA expression of vascular endothelial growth factor-A and its receptor. The purpose of this review is to summarize the research to date on the morphology of WAT and adipose tissue cellularity in exercise adaptation.