ObjectiveEndoplasmic reticulum (ER) stress and mitochondrial function affected intramuscular fat accumulation. However, there is no clear evident on the effect of the regulation of ER stress and mitochondrial function by Angiotensin-converting enzyme 2 (ACE2) on the prevention of intramuscular fat metabolism. We investigated the effects of ACE2 on ER stress and mitochondrial function in skeletal muscle lipid metabolism.MethodsThe triglyceride (TG) content in skeletal muscle of ACE2 knockout mice and Ad-ACE2-treated db/db mice were detected by assay kits. Meanwhile, the expression of lipogenic genes (ACCα, SREBP-1c, LXRα, CPT-1α, PGC-1α and PPARα), ER stress and mitochondrial function related genes (GRP78, eIF2α, ATF4, BCL-2, and SDH6) were analyzed by RT-PCR. Lipid metabolism, ER stress and mitochondrial function related genes were analyzed by RT-PCR in ACE2-overexpression C2C12 cell. Moreover, the IKKβ/NFκB/IRS-1 pathway was determined using lysate sample from skeletal muscle of ACE2 knockout mice.ResultsACE2 deficiency in vivo is associated with increased lipid accumulation in skeletal muscle. The ACE2 knockout mice displayed an elevated level of ER stress and mitochondrial dysfunctions in skeletal muscle. In contrast, activation of ACE2 can ameliorate ER stress and mitochondrial function, which slightly accompanied by reduced TG content and down-regulated the expression of skeletal muscle lipogenic proteins in the db/db mice. Additionally, ACE2 improved skeletal muscle lipid metabolism and ER stress genes in the C2C12 cells. Mechanistically, endogenous ACE2 improved lipid metabolism through the IKKβ/NFκB/IRS-1 pathway in skeletal muscle.ConclusionsACE2 was first reported to play a notable role on intramuscular fat regulation by improving endoplasmic reticulum and mitochondrial function. This study may provide a strategy for treating insulin resistance in skeletal muscle.

Background: Previous works indicated that the stress on the endoplasmic reticulum (ER) affected nonalcoholic fatty liver disease (NAFLD). However, there is no clear evident on the effect of the regulation of ER stress by angiotensin-converting enzyme 2 (ACE2) on the prevention of NAFLD.Methods: HepG2 cells were treated with thapsigargin (Tg) or palmitic acid (PA).We analysed ACE2 expression using Western-blotting analyses. ER stress-related proteins were detected in ACE2 knockout mice and Ad-ACE2-treated db/db mice by immunofluorescence or Western-blotting analyses. In ACE2-overexpression HepG2 cells, the triglyceride (TG), total cholesterol (TC), and glycogen content were detected by assay kits. Meanwhile, the expression of hepatic lipogenic proteins (ACCα, SREBP-1c, FAS, and LXRα), enzymes for gluconeogenesis (PEPCK, G6Pase, and IRS2), and IKKβ/NFκB/IRS1/Akt pathway were analysed by Western-blotting analyses.Results: ACE2 was significantly increased in Tg/PA-induced cultured hepatocytes.Additionally, ACE2 knockout mice displayed elevated levels of ER stress, while Ad-ACE2-treated db/db mice showed reduced ER stress in liver. Furthermore, activation of ACE2 can ameliorate ER stress, accompanied by decreased TG content, increased intracellular glycogen, and downregulated expression of hepatic lipogenic proteins and enzymes for gluconeogenesis in Tg/PA-induced hepatocytes. As a consequence of anti-ER stress, the activation of ACE2 led to improved glucose and lipid metabolism through the IKKβ/NFκB/IRS1/Akt pathway.Conclusions: This is the first time documented that ACE2 had a notable alleviating role in ER stress-induced hepatic steatosis and glucose metabolism via the IKKβ/NFκB/IRS1/Akt-mediated pathway. This study may further provide insight into a novel underlying mechanism and a strategy for treating NAFLD. KEYWORDS ACE2, endoplasmic reticulum, glucose metabolism, hepatic steatosis Xi Cao and Li-Ni Song contribute equally to this article.

Identification of key regulators of energy homeostasis holds important therapeutic promise for metabolic disorders, such as obesity and diabetes. ACE2 cleaves angiotensin II (Ang II) to generate Ang-(1-7) which acts mainly through the Mas1 receptor. Here, we identify ACE2 pathway as a critical regulator in the maintenance of thermogenesis and energy expenditure. We found that ACE2 is highly expressed in brown adipose tissue (BAT) and that cold stimulation increases ACE2 and Ang-(1-7) levels in BAT and serum. Ace2 knockout mice (Ace2-/y) and Mas1 knockout mice (Mas1-/-) displayed impaired thermogenesis. Mice transplanted with brown adipose tissue from Mas1-/- display metabolic abnormalities consistent with those seen in the Ace2 and Mas1 knockout mice. In contrast, impaired thermogenesis of Leprdb/db obese diabetic mice and high-fat diet-induced obese mice were ameliorated by overexpression of Ace2 or continuous infusion of Ang-(1-7). Activation of ACE2 pathway was associated with improvement of metabolic parameters, including blood glucose, lipids and energy expenditure in multiple animal models. Consistently, ACE2 pathway remarkably enhanced the browning of white adipose tissue. Mechanistically, we showed that ACE2 pathway activated Akt/FoxO1 and PKA pathway, leading to induction of UCP1 and activation of mitochondrial function. Our data propose that adaptive thermogenesis requires regulation of ACE2 pathway and highlight novel potential therapeutic targets for the treatment of metabolic disorders.