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METRNL is a recently identified secreted protein with emerging functions. This study is to find major cellular source of circulating METRNL and to determine METRNL novel function. Here, we show METRNL is abundant in human and mouse vascular endothelium and released by endothelial cells using endoplasmic reticulum-Golgi apparatus pathway. By creating endothelial cell-specific Metrnl knockout mice, combined with bone marrow transplantation to produce bone marrow-specific deletion of Metrnl, we demonstrate that most of circulating METRNL (approximately 75%) originates from the endothelial cells. Both endothelial and circulating METRNL decrease in atherosclerosis mice and patients. By generating endothelial cell-specific Metrnl knockout in apolipoprotein E-deficient mice, combined with bone marrow-specific deletion of Metrnl in apolipoprotein E-deficient mice, we further demonstrate that endothelial METRNL deficiency accelerates atherosclerosis. Mechanically, endothelial METRNL deficiency causes vascular endothelial dysfunction including vasodilation impairment via reducing eNOS phosphorylation at Ser1177 and inflammation activation via enhancing NFκB pathway, which promotes the susceptibility of atherosclerosis. Exogenous METRNL rescues METRNL deficiency induced endothelial dysfunction. These findings reveal that METRNL is a new endothelial substance not only determining the circulating METRNL level but also regulating endothelial function for vascular health and disease. METRNL is a therapeutic target against endothelial dysfunction and atherosclerosis.
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Objective To study the effect of nicotinamide mononucleotide (NMN) on the mortality of the lipopoly-saccharide (LPS)-induced endotoxic shock mouse model. Methods 10-week-old C57BL/6J male mice were randomly divided into groups, and were injected intraperitoneally (i.p.) with LPS (10 mg/kg) to induce endotoxic shock models. NMN was i.p. injected in three ways: (1) 0.5 h after modeling, doses of 10, 30, 100 and 300 mg/kg; (2) 0.5 h before modeling, doses of 30, 100, 300 and 600 mg/kg; or (3) 0.5 and 12 h after modeling, dose of 300 mg/kg each time. The death times of each group were recorded, and the survival curves were drawn. Results Compared with the solvent control group, NMN at different doses given 0.5 h after or before modeling didn’t improve the survival rate or delay the death time of endotoxic shock mice; But when given at 0.5 and 12 h 300 mg/kg after modeling, NMN accelerated the death of mice and increased the mortality of mice. NMN products by two manufacturers showed similar effects. Conclusion NMN has no therapeutic effect on LPS-induced endotoxic shock, and repeated administration of NMN after endotoxic shock will increase the mortality.
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Objective To study the effects of atherosclerotic high-fat diet on body weight, blood glucose, blood lipid levels and atherosclerotic plaque formation in mice, and to determine the effect of fasting time on the results of blood lipid testing. Methods 10-week-old male ApoE knockout (ApoE-/-) mice were given high-fat diet and normal diet. The atherosclerotic plaques were observed four months later. 10 week old C57BL/6J male mice were given regular diet for 4 weeks, regular diet for 2 weeks + high-fat diet for two or four weeks. Body weight、liver、glucose, and the serum lipid levels were examined. The influence of fasting for 12 h, 6 h or no fasting on blood lipid detection results before sacrificing were studied. Results The atherosclerotic plaque area of ApoE-/- mice given high-fat diet increased significantly (P<0.01). C57BL/6J mice given high-fat diet gained weight (P<0.01). The glucose, TC, LDL-c and HDL-c were also increased in C57BL/6J mice with liver fat accumulation while the level of TG was significantly decreased(P<0.01). Compared with the fasting 12 h group, serum triglyceride (TG) was significantly increased (P<0.01）in fasting 6 h and no fasting groups. Conclusion The atherosclerotic high-fat diet can accelerate the formation of atherosclerotic plaques in ApoE-/- mice, significantly increase blood sugar, TC and LDL-c levels, but significantly reduce TG values.. The fasting time can affect serum triglyceride (TG) level.
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Objective To establish and optimize a mouse myocardial infarction (MI) model, and to use twice limb lead ECGs immediately after coronary ligation and 4 h after surgery to evaluate the occurrence of myocardial infarction. Methods Twenty-nine male C57BL/6J mice were anesthetized with isoflurane. then a myocardial infarction model was established by ligating the left anterior descending (LAD) coronary artery through the third/fourth intercostal space of left anterior chest. Immediate and 4 h postoperative limb lead ECGs were performed. Twenty-four hours after surgery, the chest was opened and the occurrence of myocardial infarction was evaluated. The heart samples were taken for TTC staining to determine the infarct area and calculate the infarct area. Results During the mice underwent coronary artery ligation the intraoperative mortality was 6.8% (2/29), and the early postoperative (<4 h) mortality was 10.3% (3/29). The 24 h survival rate was 82.8% (24/29). 24 hours after TTC staining confirmed the occurrence of infarction, the myocardial infarction model was established. The success rate of the model was 79.3% (23/29), and the average infarct size (infarcted myocardial weight / whole ventricular weight) was (28 ± 6)%; The mice successfully established by the model showed obvious ST-T changes in the ECG at 4 hours after surgery, suggesting that a myocardial infarction has occurred. Conclusions The mouse myocardial infarction model was successfully established. The combined use of ECG immediately after surgery and 4 h after surgery could be used as a rapid and non-invasive evaluation method for mouse myocardial infarction.
