Peri-arteriolar Myofibroblast Differentiation in the Pathobiology of IPAH

摘要

ABSTRACT Idiopathic and familial syndromes of pulmonary arterial hypertension (IPAH/FPAH) typically are associated with muscularization and obstruction of pulmonary arterial microperfusion circuits in the lung. We propose that the pathobiology of PAH represents a dysfunctional, peri-vascular wound healing response based on a functional deficit in the ability of the recently discovered Pur ¿ DNA-binding protein to repress TGF¿1 signaling in the lung. Excessive transcriptional activation of wound-healing genes due to unchecked collaborative interaction between serum response factor (SRF) and TGF¿1-regulated Smad proteins 2 and 3 results in accelerated peri-arteriolar myofibroblast (MFB) differentiation and adventitial fibrosis with loss of pulmonary arterial compliance and eventual right heart failure. Smads 2 and 3 normally dissociate gene-inhibitory SRF-Pur ¿ protein complexes to allow activation of the smooth muscle ¿-actin (SM¿A) and type I collagen ¿2-subunit promoters as a first step in the MFB differentiation process. We will test the hypothesis that the SRF-Pur¿ inhibitory complex is unstable in PAH-derived MFBs due to over-active PI3K/Akt feed-forward signaling kinases and/or impaired feed-back inhibition mediated by sub-optimal MEK1/Erk1,2/Egr-1 signaling. In Aim 1, we propose to characterize the sub-cellular compartmentalization of transcriptional activators and repressors implicated in peri-arteriolar myofibroblast differentiation and remodeling in IPAH/FPAH syndromes using an immunocytochemistry approach. For Aim 2, we will define the biochemical dysfunction that causes excess peri-arteriolar myofibroblast differentiation in IPAH/FPAH syndromes using epigenetic/metabolic approaches that target SRF-Pur ¿ physical interplay in pulmonary artery adventitial fibroblasts isolated from normal or disease-affected donors. We have developed solid-phase ELISA tools to quantitatively evaluate protein:protein and protein:DNA interactions that uniquely regulate the process of adventitial MFB differentiation. The assembly of a specialized transcriptional regulatory complex capable of triggering prototypical gene responses in MFBs represents a convergence point for complex vascular-disease signaling consisting of multiple compensatory and patient-specific layers of control. We expect that knowledge gained could further basic understanding of rate-limiting interactions that foster loss of arterial compliance typically associated with the most devastating IPAH/FPAH disease syndromes. Future detailed analysis of the protein biochemistry of activator-repressor dynamic interplay could reveal novel targets for therapeutic management of pulmonary arterial disease and right heart failure that may ultimately improve patient long-term survival.