Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by a sustained elevation in the pulmonary artery pressure and subsequent right
heart failure. The activation of Rho/
Rho-kinase activity and the beneficial effect of
Rho-kinase inhibition have been demonstrated in several experimental models of
pulmonary hypertension. However, it remains unclear whether
Rho-kinase inhibitors can also be used against
pulmonary hypertension associated with mutations in the type II
bone morphogenetic protein receptor (BMPRII) gene. Transgenic mice expressing a dominant-negative BMPRII gene (with an
arginine to termination mutation at
amino acid 899) in smooth muscle by a
tetracycline-gene switch system (SM22-tet-BMPR2(R899X) mice) were examined. They developed an elevated right ventricular systolic pressure (RVSP), right ventricular (RV)
hypertrophy, muscularization of small pulmonary arteries, and an associated disturbed blood flow in their lungs. The Rho/
Rho-kinase activity and Smad activity were determined by a Western blot analysis by detecting
GTP-RhoA and the phosphorylation of
myosin phosphatase target subunit 1, Smad1, and Smad2. In the lungs of SM22-tet-BMPR2(R899X) mice, the Rho/
Rho-kinase activity was elevated significantly, whereas the Smad activity was almost unchanged.
Fasudil, a
Rho-kinase inhibitor, significantly decreased RVSP, alleviated RV
hypertrophy and muscularization of small pulmonary arteries, and improved blood flow in SM22-tet-BMPR2(R899X) mice, although it did not alter Smad signaling. Our study demonstrates that Rho/
Rho-kinase signaling is activated via a Smad-independent pathway in an animal model of
pulmonary hypertension with a BMPRII mutation in the cytoplasmic tail domain.
Rho-kinase inhibition is therefore a possible therapeutic approach for the treatment of PAH associated with genetic mutation.