Regulation of extracellular matrix gene expression and biosynthetic pathways in pulmonary fibroblasts by HSF1

Abstract

Idiopathic pulmonary fibrosis (IPF) is a chronic and rapidly progressing lung disease that is characterized by extensive tissue remodeling, impaired gas exchange, and a poor prognosis. The pathogenesis of IPF involves epithelial cell death, leukocyte infiltration and cytokine production, enhanced deposition of collagen and remodeling of the extracellular matrix (ECM). One key event in the progression of IPF is the activation of fibroblasts that is mediated by TGF‐beta, which leads to tissue remodeling. We have investigated a possible role for the transcription factor, heat shock factor 1 (HSF1) in the expression of pro‐fibrotic genes in TGF‐beta treated fibroblasts. siRNA was used to silence the expression of HSF1 in pulmonary fibroblast cell lines, MRC‐5 and IMR‐90. Cells were treated with TGF‐beta for 0, 8, and 24 h, after which RNA and protein samples were collected. RNA samples were analyzed by real‐time PCR to assess differences in the expression of several target genes with known roles in the production and remodeling of ECM, and results were verified by Western blot. Silencing HSF1 altered the expression of several ECM‐related genes in both cell lines, indicting role for HSF1 in the control of ECM biogenesis and remodeling by TGF‐beta stimulated fibroblasts, and a possible significance for HSF1 activity in the etiology of IPF. In addition to components of fibrillar collagen (COL1A1, COL1A2), the expression of several genes that function in the biogenesis of collagen fibers also were impaired by HSF1 silencing, including proteins with proline hydroxylase (P4HA2), lysyl hydroxylase (PLOD1), prolyl isomerase (FKBP4); and chaperone activities (SERPINE1, SERPINH1). In contrast to its effects on fibrillar collagen biogenesis, HSF1 silencing enhanced the expression of genes involved in elastic fibers production, including: elastin (ELN) microfibrillar‐associated protein 4 (MFAP4); and fibulin 5 (FBLN5). This observation is consistent with the finding by others that the ratio of collagen and elastin fibers is altered in IPF, further indicating a unique role for HSF1 in controlling the composition of the ECM in this disease.Support or Funding InformationFunding provided by the Leahi Fund of the Hawaii Community Foundation