Paracrine role for endothelial IGF-1 receptor in white adipocyte beiging
There are at least two distinct types of thermogenic adipocyte in mammals: a pre-existing form established during development, termed classical brown adipocytes and an inducible form, beige adipocytes1-3. Various environmental cues can stimulate a process frequently referred to as beiging of white adipose tissue (WAT), leading to enhanced thermogenesis and obesity resistance 4, 5. Whilst beiging of WAT as a therapeutic goal for obesity and obesity-related complications has attracted much attention6-9; therapeutics stimulating beiging without deleterious side-effects remain elusive10. The endothelium lines all blood vessels and is therefore in close proximity to all cells. Many studies support the possibility that the endothelium acts as a paracrine organ11-14. We explored the potential role of endothelial insulin-like growth factor-1 receptor (IGF-1R) as a paracrine modulator of WAT phenotype. Here we show that a reduction in endothelial IGF-1R expression in the presence of nutrient excess leads to white adipocyte beiging, increases whole-body energy expenditure and enhances insulin sensitivity via a non-cell autonomous paracrine mechanism. We demonstrate that this is mediated by endothelial release of malonic acid, which we show, using prodrug analogues, has potentially therapeutically-relevant properties in the treatment of metabolic disease.