Angiotensin-(1-7) attenuates lung fibrosis by way of Mas receptor in acute lung injury

Background

Pulmonary fibrosis occurs in approximately 60% of patients with acute respiratory distress syndrome and has been significantly correlated with a poor outcome. The overexpression of angiotensin (Ang) II can induce lung inflammation and fibrosis. This observation, coupled with the knowledge that Ang-(1-7) is considered to be an endogenous antagonist of Ang II, led us to hypothesize that Ang-(1-7) would prevent lung remodeling in patients with acute respiratory distress syndrome.

Materials and methods

The protocol involved five groups: (1) control, (2) lipopolysaccharide (LPS), (3) losartan as a positive control group, (4) Ang-(1-7), and (5) [D-Ala7]-Ang-(1-7) (A779), an antagonist of the Ang-(1-7) receptor. Acute lung injury was induced by an intratracheal injection of LPS 5 mg/kg in C57BL/6 mice. Losartan (10 mg/kg) was administered by gavage daily, starting from 1 d before LPS stimulation. Ang-(1-7) or A779 in saline (100 ng/kg/min) was infused subcutaneously 1 h before acute lung injury induction for 3 or 7 d. The lung tissues were harvested for analysis at day 3 or 7 after injection of LPS.

Results

LPS stimulation resulted in significantly increased inflammation, edema, and lung collagen production. With Ang-(1-7) treatment, the lung fibrosis score and hydroxyproline level were significantly reduced, and the expression of transforming growth factor-β and Smad2/3 were decreased on days 3 and 7. Losartan attenuated lung fibrosis similarly to Ang-(1-7) after LPS exposure. In the A779 group, a tendency was seen to aggravate collagen deposition and lung remodeling.

Conclusions

These findings indicate an antiremodeling role for Ang-(1-7) in acute lung injury, similar to the blocker of Ang II receptor, that might be at least partially mediated through an Ang-(1-7) receptor.     

Mas在肿瘤中的研究进展

肾素-血管紧张素系统是肿瘤微环境的重要组成部分,在肿瘤代谢,血管生成和侵袭中发挥重要作用。Mas是该系统ACE2-Ang-(l-7)-Mas轴的重要成分,是一种重要的致癌基因,在多种癌组织中均表达。主要针对Mas在肿瘤形成中所涉及的相关通路进行简要综述。     

肢体缺血再灌注后肺损伤小鼠肺组织AT1R和Mas受体蛋白表达变化

目的:通过观察小鼠肢体缺血再灌注(LIR)后不同时点肺组织血管紧张素Ⅱ1型受体(AT1R)和Mas受体蛋白表达与肺损伤的变化,探讨局部组织AT1R和Mas受体蛋白表达失衡在LIR急性肺损伤(ALI)中的作用。方法:42只8周龄雄性ICR小鼠随机分为7组,每组6只,其中1组作为对照组,其余6组为再灌注0.5 h、1h、2 h、4 h、6 h和12 h模型组。模型组小鼠用橡皮圈结扎双后肢根部,缺血2 h后剪断橡皮圈,分别于再灌注后不同时点眼球取血处死小鼠。取肺组织计算脏器系数和湿/干重比;肺泡灌洗液细胞计数和蛋白浓度检测;肺组织病理切片常规HE染色观察肺组织形态变化并进行病理损伤评分;Western blot检测肺组织AT1R和Mas受体蛋白的表达。结果:模型组小鼠肺脏器系数、湿/干重比、肺泡灌洗液细胞计数和蛋白浓度在LIR后显著升高。病理学结果显示,LIR后不同时点小鼠肺组织出现肺泡壁毛细血管扩张和充血、间质和肺泡水肿、血管壁和支气管壁炎症细胞浸润、肺泡间隔增厚、炎症细胞浸润及肺气肿等不同程度的损伤变化,且随着再灌注时间的延长,肺损伤评分逐渐升高。Western blot结果显示,AT1R蛋白在再灌注0.5 h时开始升高,1 h达到最高,之后随再灌注时间的延长,AT1R表达逐渐降低;Mas受体蛋白随再灌注时间延长逐渐升高。结论:LIR引起急性肺损伤,并随再灌注时间的延长损伤逐渐加重;AT1R和Mas受体蛋白表达的变化可能与小鼠LIR后急性肺损伤有关。     

黄芪通过ACE2/Mas途径改善代谢综合征大鼠早期肾功能损害

探讨黄芪影响代谢综合征(MS)大鼠肾脏血管紧张素转换酶2(ACE2)以及血管紧张素1-7(Ang 1-7)受体Mas蛋白的表达及其抗氧化作用。将80只雄性SD大鼠分为:正常对照组、MS组、黄芪组、缬沙坦组。MS大鼠予以高脂肪高盐饲料,饮用10%果糖水制备代谢综合征动物模型,黄芪组予以黄芪6.0 g·kg^-1·d^-1灌胃,缬沙坦组予以缬沙坦30.0 mg·kg^-1·d^-1灌胃,MS组以及对照组予以同体积生理盐水灌胃,干预4周后行一般指标、生化指标以及血压测定,放免法检测血及肾组织血管紧张素Ⅱ(AngⅡ)、丙二醛(MDA)、一氧化氮(NO)和超氧化物歧化酶(SOD)水平,免疫蛋白印迹法检测各组大鼠肾组织Mas受体,ACE,ACE2,AT1R的表达。结果显示,与对照组比较,MS组、黄芪组大鼠收缩压、舒张压、体质量、空腹血糖、空腹胰岛素水平、甘油三酯、血清游离脂肪酸以及血浆、肾组织AngⅡ水平明显升高(P<0.05);缬沙坦组大鼠收缩压、舒张压与MS组比较明显降低;MS组大鼠肾组织NO含量以及SOD活性下降,经黄芪干预后较MS明显增高;黄芪治疗后较MS组大鼠肾脏组织中MDA水平明显降低(P<0.01)。与对照组比较,MS组肾组织中ACE和AT1R的表达明显升高,而ACE2和Mas受体的表达降低(均P<0.05);与MS组比较,MS+黄芪组肾组织中Mas受体的表达升高较显著,而MS+缬沙坦组AT1R的表达降低更明显(均P<0.05)。结论:黄芪可以提高肾脏组织Mas的表达,降低ACE表达,改变肾脏局部的AngⅡ,MDA,NO和SOD水平,从而对早期受损伤的肾组织起保护作用。     

AngⅡ对肝星状细胞中ACE 2和Mas受体mRNA的影响

目的：体外培养肝星状细胞（HSC）,从分子生物学的角度探索其是否有ACE 2和Mas受体mRNA的表达,以及血管紧张素转换酶抑制剂（ACEI）贝那普利对二者的影响。方法大鼠肝星状细胞株（HSC-T 6）按实验计划分组处理（正常对照组、AngⅡ组、AngⅡ＋贝那普利组、贝那普利组）,提取总RNA,逆转录后应用RTFQ PCR的方法测量ACE 2及Mas受体 mRNA的基因水平。结果 ACE 2、Mas受体mRNA在各组中均有表达;与对照组相比,AngⅡ组中二者的表达均较高,差异有统计学意义（P〈0.05）;在AngⅡ＋贝那普利组,二者均较AngⅡ组升高,差异有统计学意义（P〈0.05）。结论 AngⅡ可使肝星状细胞激活,活化后的HSC的ACE 2、Mas受体mRNA的基因表达水平升高,从而发挥其抗肝纤维化的作用。     

Effects of angiotensin II and its metabolites in the rat coronary vascular bed: is angiotensin III the preferred ligand of the angiotensin AT2 receptor?

Aminopeptidases metabolize angiotensin II to angiotensin-(2-8) (=angiotensin III) and angiotensin-(3-8) (=angiotensin IV), and carboxypeptidases generate angiotensin-(1-7) from angiotensin I and II. Angiotensin-converting enzyme (ACE) inhibitors and/or angiotensin II type 1 (AT1) receptor blockers affect the concentrations of these metabolites, and they may thus contribute to the beneficial effects of these drugs, possibly through stimulation of non-classical angiotensin AT receptors. Here, we investigated the effects of angiotensin II, angiotensin III, angiotensin IV and angiotensin-(1-7) in the rat coronary vascular bed, with or without angiotensin AT1 - or angiotensin II type 2 (AT2) receptor blockade. Results were compared to those in rat iliac arteries and abdominal aortas. Angiotensin II, angiotensin III and angiotensin IV constricted coronary arteries via angiotensin AT1 receptor stimulation, angiotensin III and angiotensin IV being approximately 20- and approximately 8000-fold less potent than angiotensin II. The angiotensin AT2 receptor antagonist PD123319 greatly enhanced the constrictor effects of angiotensin III, starting at angiotensin III concentrations in the low nanomolar range. PD123319 enhanced the angiotensin II-induced constriction at submicromolar angiotensin II concentrations only. Angiotensin-(1-7) exerted no effects in the coronary circulation, although, at micromolar concentrations, it blocked angiotensin AT1 receptor-induced constriction. Angiotensin AT2 receptor-mediated relaxation did not occur in iliac arteries and abdominal aortas, and the constrictor effects of the angiotensin metabolites in these vessels were identical to those in the coronary vascular bed. In conclusion, angiotensin AT2 receptor activation in the rat coronary vascular bed results in vasodilation, and angiotensin III rather than angiotensin II is the preferred endogenous agonist of these receptors. Angiotensin II, angiotensin III, angiotensin IV and angiotensin-(1-7) do not exert effects through non-classical angiotensin AT receptors in the rat coronary vascular bed, iliac artery or aorta.     

Angiotensin-(1-7) attenuated long-term hypoxia-stimulated cardiomyocyte apoptosis by inhibiting HIF-1α nuclear translocation via Mas receptor regulation

Extreme hypoxia often leads to myocardial apoptosis and causes heart failure. Angiotensin-(1-7)Ang-(1-7) is well known for its cardio-protective effects. However, the effects of Ang-(1-7) on long-term hypoxia (LTH)-induced apoptosis remain unknown. In this study, we found that Ang-(1-7) reduced myocardial apoptosis caused by hypoxia through the Mas receptor. Activation of the Ang-(1-7)/Mas axis down-regulated the hypoxia pro-apoptotic signaling cascade by decreasing the protein levels of hypoxia-inducible factor 1α (HIF-1α) and insulin-like growth factor binding protein-3 (IGFBP3). Moreover, the Ang-(1-7)/Mas axis further inhibited HIF-1α nuclear translocation. On the other hand, Ang-(1-7) activated the IGF1R/PI3K/Akt signaling pathways, which mediate cell survival. However, the above effects were abolished by A779 treatment or silencing of Mas expression. Taken together, our findings indicate that the Ang-(1-7)/Mas axis protects cardiomyocytes from LTH-stimulated apoptosis. The protective effect of Ang-(1-7) is associated with the inhibition of HIF-1α nuclear translocation and the induction of IGF1R and Akt phosphorylation.