Genetic Ablation of PDGF-Dependent Signaling Pathways Abolishes Vascular Remodeling and Experimental Pulmonary Hypertension

Objective: Despite modern therapies, pulmonary arterial hypertension (PAH) harbors a high mortality. Vascular remodeling is a hallmark of the disease. Recent clinical studies revealed that antiremodeling approaches with tyrosine-kinase inhibitors such as imatinib are effective, but its applicability is limited by significant side effects. Although imatinib has multiple targets, expression analyses support a role for platelet-derived growth factor (PDGF) in the pathobiology of the disease. However, its precise role and downstream signaling events have not been established.

Approach and results: Patients with PAH exhibit enhanced expression and phosphorylation of β PDGF receptor (βPDGFR) in remodeled pulmonary arterioles, particularly at the binding sites for phophatidyl-inositol-3-kinase and PLCγ at tyrosine residues 751 and 1021, respectively. These signaling molecules were identified as critical downstream mediators of βPDGFR-mediated proliferation and migration of pulmonary arterial smooth muscle cells. We, therefore, investigated mice expressing a mutated βPDGFR that is unable to recruit phophatidyl-inositol-3-kinase and PLCγ (βPDGFR(F3/F3)). PDGF-dependent Erk1/2 and Akt phosphorylation, cyclin D1 induction, and proliferation, migration, and protection against apoptosis were abolished in βPDGFR(F3/F3) pulmonary arterial smooth muscle cells. On exposure to chronic hypoxia, vascular remodeling of pulmonary arteries was blunted in βPDGFR(F3/F3) mice compared with wild-type littermates. These alterations led to protection from hypoxia-induced PAH and right ventricular hypertrophy.

Conclusions: By means of a genetic approach, our data provide definite evidence that the activated βPDGFR is a key contributor to pulmonary vascular remodeling and PAH. Selective disruption of PDGF-dependent phophatidyl-inositol-3-kinase and PLCγ activity is sufficient to abolish these pathogenic responses in vivo, identifying these signaling events as valuable targets for antiremodeling strategies in PAH.