Arginase II Promotes Macrophage Inflammatory Responses Through Mitochondrial Reactive Oxygen Species, Contributing to Insulin Resistance and Atherogenesis

Abstract

BackgroundMacrophage‐mediated chronic inflammation is mechanistically linked to insulin resistance and atherosclerosis. Although arginase I is considered antiinflammatory, the role of arginase II (Arg‐II) in macrophage function remains elusive. This study characterizes the role of Arg‐II in macrophage inflammatory responses and its impact on obesity‐linked type II diabetes mellitus and atherosclerosis.Methods and ResultsIn human monocytes, silencing Arg‐II decreases the monocytes’ adhesion to endothelial cells and their production of proinflammatory mediators stimulated by oxidized low‐density lipoprotein or lipopolysaccharides, as evaluated by real‐time quantitative reverse transcription‐polymerase chain reaction and enzyme‐linked immunosorbent assay. Macrophages differentiated from bone marrow cells of Arg‐II–deficient (Arg‐II−/−) mice express lower levels of lipopolysaccharide‐induced proinflammatory mediators than do macrophages of wild‐type mice. Importantly, reintroducing Arg‐II cDNA into Arg‐II−/− macrophages restores the inflammatory responses, with concomitant enhancement of mitochondrial reactive oxygen species. Scavenging of reactive oxygen species by N‐acetylcysteine prevents the Arg‐II–mediated inflammatory responses. Moreover, high‐fat diet–induced infiltration of macrophages in various organs and expression of proinflammatory cytokines in adipose tissue are blunted in Arg‐II−/− mice. Accordingly, Arg‐II−/− mice reveal lower fasting blood glucose and improved glucose tolerance and insulin sensitivity. Furthermore, apolipoprotein E (ApoE)–deficient mice with Arg‐II deficiency (ApoE−/−Arg‐II−/−) display reduced lesion size with characteristics of stable plaques, such as decreased macrophage inflammation and necrotic core. In vivo adoptive transfer experiments reveal that fewer donor ApoE−/−Arg‐II−/− than ApoE−/−Arg‐II+/+ monocytes infiltrate into the plaque of ApoE−/−Arg‐II+/+ mice. Conversely, recipient ApoE−/−Arg‐II−/− mice accumulate fewer donor monocytes than do recipient ApoE−/−Arg‐II+/+ animals.ConclusionsArg‐II promotes macrophage proinflammatory responses through mitochondrial reactive oxygen species, contributing to insulin resistance and atherogenesis. Targeting Arg‐II represents a potential therapeutic strategy in type II diabetes mellitus and atherosclerosis. (J Am Heart Assoc. 2012;1:e000992 doi: 10.1161/JAHA.112.000992.)

Polarization of Macrophages toward M2 Phenotype Is Favored by Reduction in iPLA2β (Group VIA Phospholipase A2)

“…Both pro (39)-and anti-inflammatory (40) consequences have been linked with Arg2 expression. A recent report used genetic approaches to demonstrate a proinflammatory role of Arg2 in the development of type 2 diabetes (T2D) and atherosclerosis (41). Our findings of higher Arg1 and blunted induction of Arg2 in the iPLA 2 ␤ Ϫ/Ϫ , relative to WT macrophages support the possibility that Arg2 is a proinflammatory marker under classical activation conditions, as might exist in an in vivo inflamma- iPLA 2 ␤ and Macrophage Polarization OCTOBER 28, 2016 • VOLUME 291 • NUMBER 44 tory milieu such as T1D.…”

p38 mitogen-activated protein kinase is involved in arginase-II-mediated eNOS-Uncoupling in Obesity

“…Compelling evidence implicates that Arg-II plays a dominant role in eNOSuncoupling in human and mouse blood vessels [10,11]. Our recent studies demonstrate that genetic ablation of Arg-II in mice reduces atherosclerosis on the ApoE -/-background, improves glucose homeostasis and insulin sensitivity in mice fed a high fat diet (HFD), which is at least partly attributable to dampening of macrophage inflammatory responses [12]. Moreover, genetic ablation of Arg-II slows down endothelial senescence and protects mice from age-associated endothelial inflammatory responses through inhibition of eNOS-uncoupling [10], implying a causative role of Arg-II in eNOS-uncoupling and endothelial dysfunction in aging.…”

“…Preparation of mouse aortic tissue and endothelium cell extract, SDS-PAGE, transfer of SDS gels to an Immobilon-P membrane (Millipore) were performed as previously described [12]. The resultant membrane was incubated overnight with the corresponding primary antibody (1:2500 for eNOS, 1:500 for phosphoSer1177-eNOS, 1:200 for arginase-II and 1:1000 for p38mapk and phospho-Thr180/Tyr182-p38mapk) at 4°C with gentle agitation after blocking with 5% skimmed milk.…”

Reactive Oxygen Species in Inflammation and Tissue Injury

“…Macrophages isolated from mice deficient in the autophagy proteins LC3B and ATG16L1 have enhanced NLRP3 inflammasome activation and produced higher IL-1b and IL-18 on LPS challenge (310,367). MtROS has also been implicated in increasing oxidative stress through cross-talk with nitric oxide synthases (NOSs) (293 the macrophage inflammatory response that contributes to insulin resistance and atherogenesis (293). Recent reports have highlighted an interesting concept of cross-talk between MtROS and NADPH oxidase, which can drive both feed-forward and feedback regulations of NADPH oxidases (73,96).…”

Arginase inhibition attenuates arteriogenesis and interferes with M2 macrophage accumulation

“…Ming et al have shown in human monocytes that arginase 2 silencing decreases monocyte adhesion on ECs; furthermore, that arginase 2 deficiency limits macrophage content in atherosclerotic plaques. 11,30 Although it is not clear why silencing arginase in monocytes results in their reduced adhesion to ECs, one explanation might be that more L-arginine is bioavailable for NOS2, representing the major form of NOS in monocytes, and that resulting increased activity of NOS2 and hence NO production interferes with leukocyte adhesion. A prerequisite for monocyte extravasation is their interaction with endothelial ICAM1.…”