Homeobox genes encode transcription factors that control local patterns of cell growth, differentiation, apoptosis and adhesion during development. Although homeobox genes are also expressed during post-natal development, relatively little is known about their regulation end functions in pulmonary vascular homeostasis and disease. Recent work in our laboratory has established that the expression of two paired-related homeobox genes, Prx1 and Prx2, is suppressed in normal adult pulmonary arteries (PAs). In contrast, these genes are expressed in the adventitia, and thereafter in the media, of hypertensive PAs where they co-localize with the pro-proliferative glycoprotein tenascin-C (TN-C). Since remodeling of the extracellular matrix (ECM) by proteases is critical to the pathogenesis of pulmonary vascular disease, we investigated whether changes in vascular smooth muscle cell (SMC) adhesion to the ECM regulate Prx1 and Prx2: SMCs cultured on native type I collagen (an alpha2beta1 integrin ligand that suppresses ERK1/2 MAPK activity) showed low levels of Prx1 and Prx2 mRNA expression. In contrast, cells maintained on denatured type I collagen (an alphavbeta3 integrin ligand that activates ERK1/2) showed high levels of expression of both genes. At a functional level, expression of Prx1 significantly increased SMC growth and TN-C gene transcription. These findings support the general hypotheses that Prx genes are regulated by changes in cell adhesion to the ECM, and that Prx proteins play key roles in remodeling PM by controlling cell growth and the expression of morphoregulatory molecules, including TN-C. To test this hypothesis, we will: (1) Determine how type I collagen, beta3 integrins and ERK1/2 MAPKs regulate Prx genes and their encoded proteins in PA adventitial fibroblasts and medial SMCs; (2) Elucidate how Prx proteins control the transcription of TN-C, and identify other gene targets that interact with Prx proteins, and (3) Ascertain how Prx gene expression in the adventitial layer of intact cultured PAs influences the behavior of surrounding adventitial fibroblasts and adjacent medial SMCs within intact PAs. Collectively, these study will identify gene and protein networks that are responsible for enhanced Prx1 and Prx2 expression, and will demonstrate how Prx gene targets, including TN-C, are controlled within remodeling PAs.
