Inhibition of profibrotic signaling in fibroblasts from patients with idiopathic pulmonary fibrosis by histone deacetylase-inhibitors or pirfenidone

Abstract

Introduction: Idiopathic pulmonary fibrosis (IPF) is a fatal disease characterized by distorted pulmonary structure and the excessive deposition of extracellular matrix (ECM) proteins, such as collagen. Myofibroblasts are the primary collagen-producing cells in IPF lungs, and their accumulation within pathologic lesions called fibroblast foci (FF) is a hallmark of IPF. To explore new drugs for IPF, we investigated the therapeutic potential of histone deacetylase inhibitors (HDACi), because we have discovered a significant overexpression of Class-I/-II/-III HDAC enzymes in IPF fibroblasts/myofibroblasts. Methods: Primary IPF fibroblasts were incubated for 30h with the HDACi panobinostat (LBH589, 85nmol) or valproic acid (VPA, 1.5mM), or with the IPF drug pirfenidone (2.7mM). Results: Treatment of primary IPF fibroblasts with the pan-HDACi panobinostat resulted in significantly reduced expression of genes associated with fibrogenesis (ACTA2, COL1A1, COL3A1, FN), cell survival (BIRC5 = survivin), proliferation (CCND1), as well as in suppression of HDAC7, and was paralleled by induction of severe ER stress (ATF6, CHOP) and apoptosis (p21, PUMA, cleaved caspase-3). Blockade of Class-I-HDACs by VPA was also associated with reduced expression of BIRC5, but profibrotic gene expression was not greatly altered. Finally, the direct comparison panobinostat – versus pirfenidone therapy showed also for pirfenidone treated IPF fibroblasts a significant downregulation of COL1A1, COL3A1, and FN, but not of CCND1. Furthermore, the profibrotic genes CNN1 and P4HTM were exclusively reduced by pirfenidone -, but not by panobinostat treatment. Importantly, pirfenidone treatment lead also to a significant downregulation of the cancer-associated gene BIRC5, but was not associated with induction of ER stress and pro-apoptotic signaling. Finally, pirfenidone did not greatly affect expression of HDAC proteins. Conclusions: We conclude that generation and apoptosis resistance of IPF fibroblasts/myofibroblasts are mediated due to enhanced activity of HDAC proteins, and that panobinostat can present a novel therapeutic option (in addition to pirfenidone) for progressive fibrotic lung diseases.