Molecular Mechanisms Of ACE2 On Islet Function Through Gut-Islet Axis Mediated By Tryptophan

Objective:Angiotensin-converting enzyme 2(ACE2)plays a vital role in regulating intestinal tryptophan(Trp)transport and maintaining amino acid homeostasis.It has emerged that a strong relationship exists between the Trp and glucolipid metabolism and energy balance,although the exact mechanism by which Trp imbalance affects islet function under metabolic stress remains elusive.This study investigates the possible role of ACE2 and Trp in regulating glucolipid metabolism and islet function under metabolic stress.Methods:The changes of intestinal ACE2 and B~0AT1 and their regulated Trp metabolic were evaluated in a high-fat diet-induced metabolic stress model in ACE2 knockout and AAV-mediated ACE2 overexpression mice.The regulation effect and protective mechanism of Trp on glucolipid metabolism and islet function were observed by the gavage of exogenous Trp.Immunofluorescence and WB were used to detect the localization and expression of intestinal ACE2 and B~0AT1.Serum Trp levels were detected by enzyme-linked immunosorbent assay.The glucose metabolism of mice was evaluated by intraperitoneal injection glucose tolerance test and intraperitoneal injection insulin tolerance test.Immunofluorescence,WB,and q PCR were used to detect the changes in key transcription factors regulating islet function.In addition,the changes of GLP-1 signal in the gut and islet were detected by immunofluorescence technique.Bax and Bcl-2immunohistochemical staining were performed on pancreatic sections to evaluate the apoptosis level of islet cells.The metabolic stress model of pancreaticβcell line Min6 induced by palmitic acid was established in vitro.The effects of Trp on oxidative stress and mitochondrial function were detected by immunofluorescence,WB,electron microscopy,flow cytometry and,q PCR.Results:The B~0AT1 transporter was co-localized with ACE2 in brush-border epithelial cells on the villi of the small intestine.The expression of intestinal ACE2 and B~0AT1 and serum Trp levels were significantly down-regulated under metabolic stress,and this effect was further accelerated by the ACE2 deficiency.Nevertheless,intestinal ACE2overexpression via AAV-mediated significantly increased intestinal B~0AT1 expression and serum level of Trp in HFD-fed mice.In addition,ACE2 knockout significantly weakened the protective effect of exogenous Trp intervention on glucolipid metabolism and islet function,while AAV-induced ACE2 overexpression enhanced the protective effect of Trp on islet function.Notably,Trp potentiated glucagon-like peptide-1(GLP-1)production and its release from intestinal and pancreatic alpha cells through a mechanism involving up-regulation of prohormonal convertase 1/3(PC1/3)and down-regulation of DPP4 expression.Meanwhile,Trp-treated Min6 cells exhibited to ameliorate mitochondrial oxidative stress and safely guard Min6 cells against excess reactive oxygen species(ROS)exposure,thereby reducing apoptosis and enhancing cell activity.Conclusion:This study emphasizes that intestinal ACE2 plays an important role in connecting the intestinal environment with the function of islet cells by regulating Trp transport under metabolic stress and may constitute a novel"gut-islet axis"signaling molecular pathway.Upregulation of intestinal ACE2 improves the sensitivity and function of islet cells through the Trp-mediated gut-islet axis network,prevents the occurrence and progression of diabetes,and provides evidence for the effectiveness of regulating amino acid homeostasis in the treatment of obesity and diabetes.