Arginase inhibitor attenuates pulmonary artery hypertension induced by hypoxia.

Hypoxia-induced pulmonary arterial hypertension (HPAH) is a refractory disease characterized by increased proliferation of pulmonary vascular smooth cells and progressive pulmonary vascular remodeling. The level of nitric oxide (NO), a potential therapeutic vasodilator, is low in PAH patients. L-arginine can be converted to either beneficial NO by nitric oxide synthases or to harmful urea by arginase. In the present study, we aimed to investigate whether an arginase inhibitor, S-(2-boronoethyl)-L-cysteine ameliorates HPAH in vivo and vitro. In a HPAH mouse model, we assessed right ventricle systolic pressure (RVSP) by an invasive method, and found that RSVP was elevated under hypoxia, but was attenuated upon arginase inhibition. Human pulmonary artery smooth muscle cells (HPASMCs) were cultured under hypoxic conditions, and their proliferative capacity was determined by cell counting and flow cytometry. The levels of cyclin D1, p27, p-Akt, and p-ERK were detected by RT-PCR or Western blot analysis. Compared to hypoxia group, arginase inhibitor inhibited HPASMCs proliferation and reduced the levels of cyclin D1, p-Akt, p-ERK, while increasing p27 level. Moreover, in mouse models, compared to control group, hypoxia increased cyclin D1 expression but reduced p27 expression, while arginase inhibitor reversed the effects of hypoxia. Taken together, these results suggest that arginase plays an important role in increased proliferation of HPASMCs induced by hypoxia and it is a potential therapeutic target for the treatment of pulmonary hypertensive disorders.

Regulatory T cells protect against hypoxia-induced pulmonary arterial hypertension in mice.

Pulmonary arterial hypertension (PAH) is a life­threatening disease characterized by the complex proliferation of the pulmonary vascular endothelium and progressive pulmonary vascular remodeling. CD4+CD25+ regulatory T cells (Tregs) have been the focus of numerous studies into PAH. The present study aimed to investigate the role and mechanisms of Tregs in hypoxia­induced PAH. A total of 60 male mice were divided at random into three groups: Normoxia group, hypoxia control group and Tregs group. Measurements were obtained of the right ventricle systolic pressure (RVSP) and the Fulton's index; in addition, the mRNA and protein expression of pro­inflammatory cytokines including monocyte chemotactic protein 1 (MCP­1), interleukin (IL)­1ß and IL­6, as well as the anti­inflammatory cytokine IL­10 in the lungs were determined by reverse transcription quantitative polymerase chain reaction and western blot analysis in vivo. Human pulmonary artery smooth muscle cells (HPASMCs) were cultured under hypoxic condition with or without Tregs for 48 h, and the proliferation rate and cell cycle of HPASMCs were determined. In addition, the protein levels of phosphorylated (p)­Akt and p­extracellular signal­regulated kinase (ERK) were measured in HPASMCs in vitro. The results showed that Treg treatment significantly reduced the increased the hypoxia­induced RVSP and Fulton's index, decreased pro­inflammatory cytokine expression as well as enhanced IL­10 levels in vivo. Furthermore, Treg treatment significantly reduced HPASMCs proliferation and the expression of cyclin D1, cyclin­dependent kinase (CDK)4, p­Akt and p­ERK, as well as increased p27 expression in vitro. In conclusion, the results of the present study indicated that Tregs protected against hypoxia­induced PAH in mice; the mechanisms of which may proceed via the suppression of the inflammatory response, as Tregs were found to enhance anti­inflammatory cytokine levels, inhibit HPASMCs proliferation and regulate the cell cycle. These results therefore indicated that Tregs may be a potential novel target for the treatment of PAH.