Membrane-anchored Serine Protease Matriptase Is a Trigger of Pulmonary Fibrogenesis.

RATIONALE: Idiopathic pulmonary fibrosis (IPF) is a devastating disease that remains refractory to current therapies. OBJECTIVES: To characterize the expression and activity of the membrane-anchored serine protease matriptase in IPF in humans and unravel its potential role in human and experimental pulmonary fibrogenesis. METHODS: Matriptase expression was assessed in tissue specimens from patients with IPF versus control subjects using quantitative reverse transcriptase-polymerase chain reaction, immunohistochemistry, and Western blotting, while matriptase activity was monitored by fluorogenic substrate cleavage. Matriptase-induced fibroproliferative responses and the receptor involved were characterized in human primary pulmonary fibroblasts by Western blot, viability, and migration assays. In the murine model of bleomycin-induced pulmonary fibrosis, the consequences of matriptase depletion, either by using the pharmacological inhibitor camostat mesilate (CM), or by genetic down-regulation using matriptase hypomorphic mice, were characterized by quantification of secreted collagen and immunostainings. MEASUREMENTS AND MAIN RESULTS: Matriptase expression and activity were up-regulated in IPF and bleomycin-induced pulmonary fibrosis. In cultured human pulmonary fibroblasts, matriptase expression was significantly induced by transforming growth factor-ß. Furthermore, matriptase elicited signaling via protease-activated receptor-2 (PAR-2), and promoted fibroblast activation, proliferation, and migration. In the experimental bleomycin model, matriptase depletion, by the pharmacological inhibitor CM or by genetic down-regulation, diminished lung injury, collagen production, and transforming growth factor-ß expression and signaling. CONCLUSIONS: These results implicate increased matriptase expression and activity in the pathogenesis of pulmonary fibrosis in human IPF and in an experimental mouse model. Overall, targeting matriptase, or treatment by CM, which is already in clinical use for other diseases, may represent potential therapies for IPF.

Dysregulated renin-angiotensin-aldosterone system contributes to pulmonary arterial hypertension.

RATIONALE: Patients with idiopathic pulmonary arterial hypertension (iPAH) often have a low cardiac output. To compensate, neurohormonal systems such as the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system are up-regulated, but this may have long-term negative effects on the progression of iPAH. OBJECTIVES: Assess systemic and pulmonary RAAS activity in patients with iPAH and determine the efficacy of chronic RAAS inhibition in experimental PAH. METHODS: We collected 79 blood samples from 58 patients with iPAH in the VU University Medical Center Amsterdam (between 2004 and 2010) to determine systemic RAAS activity. MEASUREMENTS AND MAIN RESULTS: We observed increased levels of renin, angiotensin (Ang)I, and AngII, which were associated with disease progression (P < 0.05) and mortality (P < 0.05). To determine pulmonary RAAS activity, lung specimens were obtained from patients with iPAH (during lung transplantation, n = 13) and control subjects (during lobectomy or pneumonectomy for cancer, n = 14). Local RAAS activity in pulmonary arteries of patients with iPAH was increased, demonstrated by elevated angiotensin-converting enzyme activity in pulmonary endothelial cells and increased AngII type 1 (AT(1)) receptor expression and signaling. In addition, local RAAS up-regulation was associated with increased pulmonary artery smooth muscle cell proliferation via enhanced AT(1) receptor signaling in patients with iPAH compared with control subjects. Finally, to determine the therapeutic potential of RAAS activity, we assessed the chronic effects of an AT(1) receptor antagonist (losartan) in the monocrotaline PAH rat model (60 mg/kg). Losartan delayed disease progression, decreased right ventricular afterload and pulmonary vascular remodeling, and restored right ventricular-arterial coupling in rats with PAH. CONCLUSIONS: Systemic and pulmonary RAAS activities are increased in patients with iPAH and are associated with increased pulmonary vascular remodeling. Chronic inhibition of RAAS by losartan is beneficial in experimental PAH.

A critical role for p130Cas in the progression of pulmonary hypertension in humans and rodents.

RATIONALE: Pulmonary arterial hypertension (PAH) is a progressive and fatal disease characterized by pulmonary arterial muscularization due to excessive pulmonary vascular cell proliferation and migration, a phenotype dependent upon growth factors and activation of receptor tyrosine kinases (RTKs). p130(Cas) is an adaptor protein involved in several cellular signaling pathways that control cell migration, proliferation, and survival. OBJECTIVES: We hypothesized that in experimental and human PAH p130(Cas) signaling is overactivated, thereby facilitating the intracellular transmission of signal induced by fibroblast growth factor (FGF)2, epidermal growth factor (EGF), and platelet-derived growth factor (PDGF). MEASUREMENTS AND MAIN RESULTS: In patients with PAH, levels of p130(Cas) protein and/or activity are higher in the serum, in the walls of distal pulmonary arteries, in cultured smooth muscle cells (PA-SMCs), and in pulmonary endothelial cells (P-ECs) than in control subjects. These abnormalities in the p130(Cas) signaling were also found in the chronically hypoxic mice and monocrotaline-injected rats as models of human PAH. We obtained evidence for the convergence and amplification of the growth-stimulating effect of the EGF-, FGF2-, and PDGF-signaling pathways via the p130(Cas) signaling pathway. We found that daily treatment with the EGF-R inhibitor gefitinib, the FGF-R inhibitor dovitinib, and the PDGF-R inhibitor imatinib started 2 weeks after a subcutaneous monocrotaline injection substantially attenuated the abnormal increase in p130(Cas) and ERK1/2 activation and regressed established pulmonary hypertension. CONCLUSIONS: Our findings demonstrate that p130(Cas) signaling plays a critical role in experimental and idiopathic PAH by modulating pulmonary vascular cell migration and proliferation and by acting as an amplifier of RTK downstream signals.