ABSTRACT
Pulmonary hypertension is associated with remodeling of the smooth muscle layer of pulmonary arteries, manifested by reduced smooth muscle cell (SMC) contractility and enhanced motility and growth. These responses are underlied by increased dynamics of the peripheral actin network. Thus, we hypothesized that pulmonary hypertension is associated with upregulation of two proteins that regulate the dynamics of peripheral actin filaments, i.e., profilin and cofilin. We also analyzed the expression of LIMK2, which regulates the actin remodeling capacity of cofilin by phosphorylation. Experimental inflammation was induced by incubation of cultured pulmonary artery SMCs (PASMCs) with inflammatory mediators in vitro, and by subcutaneous administration of monocrotaline to Sprague-Dawley rats in vivo. Expression of messenger RNA (mRNA) was assessed by quantitative RT-PCR, protein levels and phosphorylation were analyzed by immunoblotting. Immune and Masson trichrome stained lung cryosections were analyzed by microscopy. PDGF, IL-1beta, ET-1 and TNFalpha upregulated the profilin, cofilin-2 and LIMK2 mRNA in cultured pulmonary artery SMCs (PASMCs). Along with the development of rat pulmonary artery and right ventricular hypertrophy, monocrotaline treatment also induced the mRNA and protein contents of profilin, cofilin-2 and LIMK2 in PASMCs. The cofilin upregulation was paralleled by a relative decrease of the phospho-cofilin content. The upregulation of profilin, cofilin and LIMK2 in experimental inflammation suggests that by intensifying the remodeling of subcortical actin filaments these proteins may contribute to the enhanced invasiveness and growth of SMCs, and to the development of increased vascular resistance and pulmonary hypertension.
