Research On The Mechanism Of The Inhibitory Function Of Endostatin On Dietary-induced Obesity

Endostatin is a well-known endogenous angiogenesis inhibitor. Although angiogenesis has been considered as a potential therapeutic target for obesity, the regulatory role of endostatin on adipogenesis and dietary-induced obesity has never been demonstrated.In the current study, we revealed that endostatin inhibited dietary-induced obesity and its related metabolic disorders including insulin resistance, glucose intolerance, and hepatic steatosis. Furthermore, our results demonstrated that endostatin reduced the vascular density in white adipose tissue(WAT) of high fat diet(HFD)-fed mice. Meanwhile, endostatin inhibited HFD-induced up-regulation of angiogenic factors including Vascular Endothelial Growth Factor(VEGF), Fibroblast Growth Factor(FGF)-2, and placental growth factor(PlGF) in WAT. Using the transwell migration assasy, wound healing migration assay, tube formation assasy in vitro and matrigel plug assasy in vivo, we found that endostatin inhibited the angiogenic anctivities of endothelial cell induced by secretory products of adipocytes. Thus, the anti-angiogenic function of endostatin also contributes to its obesity-inhibitory activity.Furthermore, we found that Endostatin also inhibited the expression of several master transcription factors of adipogenesis, including peroxisome proliferator-activated receptor gamma(PPARγ), CCAAT/enhancer binding protein α(C/EBPα) and C/EBPβ in WAT of HFD-fed mice. Interestingly, endostatin directly inhibited adipogenesis in vitro. Moreover,our results showed that nucleolin, the functional receptor of endostain, could highly express on the cell-surface of preadipocytes during adipogenesis. Therefore, endostatin could be internalized by preadipocytes. Using Co-IP and imunoflorosensce, we found that endostatin interacted and co-localized with Sam68 in the nuclei of preadipocytes. Moreover, endostatin bond to the NK domain of Sam68 which regulates the specificity of interactions between Sam68 and RNA elements. We further revealed that this interaction competitively impaired the binding of Sam68 to intron 5 of mTOR, causing an error in mTOR transcript, which consequently decreased the expression of mTOR. Next,using Western blot, we found endostatin decreased activities of mTORC1 pathway in vitro and in vivo. Taken together, because its interaction with Sam68, endostatin decreased the expression of mTOR, and impaired the activity of mTORC1, and then led to defects in adipogenesis.In conclusion, through the combined functions on adipogenesis and angiogenesis, endostatin prevents dietary-induced obesity and its related metabolic disorders. The new anti-obesity and anti-adipogenic functions of endostatin provide new insights into the biological relevance of this protein, which leads to potential clinical therapeutic application for obesity and its related metabolic syndromes.