Ligand-activated PPARδ upregulates α-smooth muscle actin expression in human dermal fibroblasts: A potential role for PPARδ in wound healing

J Dermatol Sci. 2015 Dec;80(3):186-95. doi: 10.1016/j.jdermsci.2015.10.005. Epub 2015 Oct 9.

Abstract

Background: The phenotypic changes that accompany differentiation of resident fibroblasts into myofibroblasts are important aspects of the wound healing process. Recent studies showed that peroxisome proliferator-activated receptor (PPAR) δ plays a critical role in wound healing.

Objective: To determine whether the nuclear receptor PPARδ can modulate the differentiation of human dermal fibroblasts (HDFs) into myofibroblasts.

Methods: These studies were undertaken in primary HDFs using Western blot analyses, small interfering (si)RNA-mediated gene silencing, reporter gene assays, chromatin immunoprecipitation (ChIP), migration assays, collagen gel contraction assays, and real-time PCR.

Results: Activation of PPARδ by GW501516, a specific ligand of PPARδ, specifically upregulated the myofibroblast marker α-smooth muscle actin (α-SMA) in a time- and concentration-dependent manner. This induction was significantly inhibited by the presence of siRNA against PPARδ, indicating that PPARδ is involved in myofibroblast transdifferentiation of HDFs. Ligand-activated PPARδ increased α-SMA promoter activity in a dual mode by directly binding a direct repeat-1 (DR1) site in the α-SMA promoter, and by inducing expression of transforming growth factor (TGF)-β, whose downstream effector Smad3 interacts with a Smad-binding element (SBE) in another region of the promoter. Mutations in these cis-elements totally abrogated transcriptional activation of the α-SMA gene by the PPARδ ligand; thus both sites represent novel types of PPARδ response elements. GW501516-activated PPARδ also increased the migration and contractile properties of HDFs, as demonstrated by Transwell and collagen lattice contraction assays, respectively. In addition, PPARδ-mediated upregulation of α-SMA was correlated with elevated expression of myofibroblast markers such as collagen I and fibronectin, with a concomitant reduction in expression of the epithelial marker E-cadherin.

Conclusion: PPARδ plays pivotal roles in wound healing by promoting fibroblast-to-myofibroblast differentiation via TGF-β/Smad3 signaling.

Keywords: Human dermal fibroblast; Myofibroblast; PPARδ; Smad3; α-SMA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / genetics
  • Actins / metabolism*
  • Cadherins / metabolism
  • Cell Differentiation*
  • Cell Movement
  • Cells, Cultured
  • Collagen Type I / metabolism
  • Fibroblasts
  • Fibronectins / metabolism
  • Humans
  • Ligands
  • PPAR delta / drug effects*
  • PPAR delta / genetics
  • PPAR delta / metabolism*
  • Promoter Regions, Genetic
  • RNA, Small Interfering / pharmacology
  • Response Elements
  • Signal Transduction
  • Skin / cytology
  • Smad3 Protein / metabolism
  • Thiazoles / pharmacology*
  • Transcriptional Activation
  • Transforming Growth Factor beta / genetics
  • Transforming Growth Factor beta / metabolism
  • Up-Regulation / drug effects
  • Wound Healing*

Substances

  • ACTA2 protein, human
  • Actins
  • Cadherins
  • Collagen Type I
  • Fibronectins
  • GW 501516
  • Ligands
  • PPAR delta
  • RNA, Small Interfering
  • Smad3 Protein
  • Thiazoles
  • Transforming Growth Factor beta