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


CONCLUSIONS
PPARδ plays pivotal roles in wound healing by promoting fibroblast-to-myofibroblast differentiation via TGF-β/Smad3 signaling.
Department of Animal Biotechnology, Konkuk University, Seoul 143-701, Republic of Korea.
Sun Ah
SA
Ham
Department of Animal Biotechnology, Konkuk University, Seoul 143-701, Republic of Korea.
Jung Seok
JS
Hwang
Department of Animal Biotechnology, Konkuk University, Seoul 143-701, Republic of Korea.
Taesik
T
Yoo
Department of Animal Biotechnology, Konkuk University, Seoul 143-701, Republic of Korea.
Won Jin
WJ
Lee
Department of Nursing, Semyung University, Chungbuk 390-711, Republic of Korea.
Kyung Shin
KS
Paek
Department of Animal Biotechnology, Konkuk University, Seoul 143-701, Republic of Korea.
Jae-Wook
JW
Oh
Department of Animal Biotechnology, Konkuk University, Seoul 143-701, Republic of Korea.
Chan-Kyu
CK
Park
Department of Animal Biotechnology, Konkuk University, Seoul 143-701, Republic of Korea.
Jin-Hoi
JH
Kim
Department of Animal Biotechnology, Konkuk University, Seoul 143-701, Republic of Korea.
Jung Tae
JT
Do
Department of Biomedical Science, CHA University, Seongnam, Gyeonggi-Do 463-400, Republic of Korea.
Jae-Hwan
JH
Kim
Department of Animal Biotechnology, Konkuk University, Seoul 143-701, Republic of Korea. Electronic address: hgseo@konkuk.ac.kr.
Han Geuk
HG
Seo
D000199:Actins / Q000235:genetics / Q000378:metabolism*; D015820:Cadherins / Q000378:metabolism; D002454:Cell Differentiation; D002465:Cell Movement; D002478:Cells, Cultured; D024042:Collagen Type I / Q000378:metabolism; D005347:Fibroblasts; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D008024:Ligands; D047494:PPAR delta / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000494:pharmacology; D020218:Response Elements; D015398:Signal Transduction; D012867:Skin / Q000166:cytology; D051900:Smad3 Protein / Q000378:metabolism; D013844:Thiazoles / Q000494:pharmacology*; D015533:Transcriptional Activation; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects; D014945:Wound Healing
C541116:ACTA2 protein, human; D000199:Actins; D015820:Cadherins; D024042:Collagen Type I; D005353:Fibronectins; C425931:GW 501516; D008024:Ligands; D047494:PPAR delta; D034741:RNA, Small Interfering; D051900:Smad3 Protein; D013844:Thiazoles; D016212:Transforming Growth Factor beta
Human dermal fibroblast; Myofibroblast; PPARδ; Smad3; α-SMA