Hypoxic upregulation of arginase II in human lung endothelial cells

Abstract

Activated arginase has been implicated in many diseases including cancer, immune cell dysfunction, infections, and vascular disease. Enhanced arginase activity has been reported in lungs of patients with pulmonary artery hypertension. We used hypoxia as a model for pulmonary hypertension and studied the effect of exposure to hypoxia on arginase activity in human lung microvascular endothelial cells (HMVEC). Hypoxia induces upregulation of arginase activity as well as mRNA and protein levels of arginase II (Arg II), the only arginase isoform we were able to identify in HMVEC. In endothelial cells, arginase shares and competes for the substrate l-arginine with nitric oxide (NO) synthase (NOS). Through regulation of substrate availability for NOS, arginase is able to modulate NO production. To evaluate the role of Arg II in regulation of NO production under hypoxia, we compared NO output (RFL-6 reporter assay) in cells with normal and silenced Arg II. Exposure to hypoxia led to an increase in NO levels produced by HMVEC. Inhibition of Arg II by specific small interfering RNA or by the pharmacological inhibitor BEC additionally enhanced the levels of NO. Another possible role for activated arginase is involvement in regulation of cell proliferation. However, we showed that hypoxia decreased cell proliferation and upregulated Arg II did not have an effect on cell proliferation. Since hypoxia-inducible factors (HIF) are a family of transcriptional factors activated by hypoxia, we tested the possibility of involvement of HIF-1 and HIF-2 in regulation of Arg II under hypoxia. The silencing of HIF-2 but not HIF-1 prevented the activation of Arg II by hypoxia.

Upregulation of arginase-II contributes to decreased age-related myocardial contractile reserve

“…This present study conWrms those Wndings and extends this observation to show and upregulation in aging cardiac tissue, more speciWcally cardiac myocytes. This is consistent with the upregulation and increased expression of Arg-II in old endothelial cells (Krotova et al 2010) and endothelial cells exposed to and atherogenic stimulus (Ryoo et al 2008(Ryoo et al , 2011Santhanam et al 2008) and may contribute to NOS uncoupling or the production of peroxinitrate. This in turn will lead to a change in the nitroso-redox milieu of the cell (Berkowitz 2007;Kim et al 2009a).…”

Hypoxic Proliferation of Osteosarcoma Cells Depends on Arginase II

“…This finding is consistent with recent work in human lung endothelial cells, where arginase inhibition using small molecule inhibitors completely prevented hypoxiainduced cellular proliferation [7]. Recently, Krotova et al [27] found that silencing HIF-2 in lung endothelial cells prevented hypoxia-induced arginase II expression. Similarly, Takeda et al [28] found that in thioglycollate-elicited mouse peritoneal macrophages arginase II was induced by Th2 mediated HIF-2 activation.…”

Arginase Inhibition Prevents Inflammation and Remodeling in a Guinea Pig Model of Chronic Obstructive Pulmonary Disease

“…Increased metabolism of L-arginine by enhanced arginase II activity in the endothelium has been shown to contribute to the reduced L-arginine and NO levels (Morris et al, 2003;Xu et al, 2004). In addition, hypoxia, which is a major contributor in COPDrelated pulmonary hypertension, upregulates arginase in human lung microvascular endothelial cells (Krotova et al, 2010). Our data suggest that COPD-associated pulmonary hypertension can effectively be targeted by inhalation of arginase inhibitors.…”