LAUSR

Simple Summary Metabolic syndrome refers to a cluster of various risk factors commonly associated with cardiovascular diseases and diabetes. Upregulation of angiotensin-converting enzyme 2 (ACE2), a key member of the renin–angiotensin system (RAS), is in general protective against cardiovascular diseases and diabetes. Peptide IRW was previously shown to upregulate ACE2 in spontaneously hypertensive rats, but not the skeletal muscle ACE2 in a high-fat-diet (HFD)-induced insulin-resistant mouse model. The study aims to investigate the regulatory role of peptide IRW on aortic ACE2 and its associated signaling pathways in HFD-induced insulin-resistant mice. Our results indicated that upregulation of aortic ACE2 by peptide IRW in HFD-induced insulin-resistant mice is responsible for the activation of the pathways associated with vasodilation of blood vessels, which might play a role in improving insulin resistance and glucose metabolism. Abstract This study aims to investigate the effect of tripeptide IRW on the local renin–angiotensin system (RAS), particularly angiotensin-converting enzyme 2 (ACE2), and their association with signaling pathways in the aorta of a high-fat-diet (HFD)-induced insulin-resistant mouse model. C57BL/6 mice were fed HFD (45% of the total calories) for six weeks, and then IRW was added to the diet (45 mg/kg body weight (BW)) for another eight weeks. ACE2 mRNA expression and protein level(s) were increased (p < 0.05), while angiotensin II receptor (AT1R) and angiotensin-converting enzyme (ACE) protein abundance was significantly reduced (p < 0.05) in the aorta of HFD mice treated by IRW. IRW supplementation also improved glucose transporter 4 (GLUT4) abundance (p < 0.05) alongside AMP-activated protein kinase (AMPK) (p < 0.05), Sirtuin 1 (SIRT1) (p < 0.05), and endothelial nitric oxide synthase (eNOS) (p < 0.05) expression. IRW downregulated the levels of endothelin 1 (ET-1) and p38 mitogen-activated protein kinases (p38 MAPK, p < 0.05). Furthermore, the levels of AMPK and eNOS in vascular smooth muscle cells (VSMCs) were significantly reduced in ACE2 knockdown cells treated with or without IRW (p < 0.01). In conclusion, this study provided new evidence of the regulatory role of IRW on the aortic ACE2 against metabolic syndrome (MetS) in an HFD-induced insulin-resistant model.