Role of RhoB in the Regulation of Pulmonary Endothelial and Smooth Muscle Cell Responses to Hypoxia

Abstract

Rationale RhoA and Rho kinase contribute to pulmonary vasoconstriction and vascular remodeling in pulmonary hypertension. RhoB, a protein homologous to RhoA and activated by hypoxia, regulates neoplastic growth and vasoconstriction but its role in the regulation of pulmonary vascular function is not known. Objective To determine the role of RhoB in pulmonary endothelial and smooth muscle cell responses to hypoxia and in pulmonary vascular remodeling in chronic hypoxia-induced pulmonary hypertension. Methods and Results Hypoxia increased expression and activity of RhoB in human pulmonary artery endothelial and smooth muscle cells, coincidental with activation of RhoA. Hypoxia or adenoviral overexpression of constitutively activated RhoB increased actomyosin contractility, induced endothelial permeability, and promoted cell growth; dominant negative RhoB or manumycin, a farnesyltransferase inhibitor that targets the vascular function of RhoB, inhibited the effects of hypoxia. Coordinated activation of RhoA and RhoB maximized the hypoxia-induced stress fiber formation caused by RhoB/mammalian homolog of Drosophila diaphanous-induced actin polymerization and RhoA/Rho kinase-induced phosphorylation of myosin light chain on Ser19. Notably, RhoB was specifically required for hypoxia-induced factor-1α stabilization and for hypoxia-and platelet-derived growth factor-induced cell proliferation and migration. RhoB deficiency in mice markedly attenuated development of chronic hypoxia-induced pulmonary hypertension, despite compensatory expression of RhoA in the lung. Conclusions RhoB mediates adaptational changes to acute hypoxia in the vasculature, but its continual activation by chronic hypoxia can accentuate vascular remodeling to promote development of pulmonary hypertension. RhoB is a potential target for novel approaches (eg, farnesyltransferase inhibitors) aimed at regulating pulmonary vascular tone and structure. (Circ Res. 2012;110:1423–1434.)

Tipifarnib prevents development of hypoxia-induced pulmonary hypertension

“…Mice were treated twice daily by oral gavage with either vehicle (2% carboxymethylcellulose in PBS) or tipifarnib (100 mg/kg/body weight).Treatments started one day prior hypoxia exposure. Development of PH was verified as described previously 4 . At 2 weeks, the animals were weighed and anesthetized (Hypnorm 0.25 mL/kg; Midazolam 25 mg/kg IP), and right ventricular systolic pressure (RVSP) was measured in a closed chest via direct cardiac puncture in the spontaneously breathing, anesthetized animal.…”

Lung Circulation

“…ROCK activation is necessary for PASMC migration and proliferation (212,366,465), and while acute administration of ROCK inhibitors markedly reduces right ventricular systolic pressure in most preclinical models (448,449,647), prolonged inhibition of ROCK reduces vascular remodeling in CH mice (160,286). At least part of the mechanism by which ROCK modulates PASMC function occurs via cytoskeletal rearrangement in PASMCs and ECs, with RhoB contributing to hypoxia-induced migration and proliferation in both cell types (702). ROCK also converges with other mechanisms involved in remodeling, as ROCK activation is a consequence of several growth factors (546), opens Ca 2+ channels (382,665), and stimulates the activity of NHE1 (642).…”

Why drugs fail in clinical trials in pulmonary arterial hypertension, and strategies to succeed in the future

“…RhoA and RhoC are exclusively geranyl-geranylated. RhoB, recently shown to have a fundamental role in hypoxia-induced pulmonary hypertension (Wojciak-Stothard et al, 2012), is both farnesylated and geranylgeranylated (Ridley, 2006). Allosteric modeling suggests that the doses of simvastatin used in animal studies translate into 22 to 220mg/day in humans.…”