PPARγ mediates innate immunity by regulating the 1α,25-dihydroxyvitamin D3 induced hBD-3 and cathelicidin in human keratinocytes.
BACKGROUND
Production of antimicrobial peptides (AMPs) is the primary mechanism by which skin innate immunity protects against infection. Hormonally active vitamin D3 (1α,25-dihydroxyvitamin D3; 1,25D₃) is a vital regulator of skin innate immunity, and has been shown to increase the expression and function of AMPs.


OBJECTIVE
PPARγ is a ligand-activated nuclear receptor and plays a role in keratinocyte differentiation and cutaneous homeostasis. In this study, we investigate whether 1,25D₃-activated PPARγ signaling regulates AMP expression in keratinocytes.


METHODS
Subconfluent keratinocytes were treated with 1,25D₃ for the indicated times. The mRNA and protein levels of AMPs were detected by RT-PCR and Western blot, and the DNA binding activation of PPARγ, VDRE and AP-1 was investigated by EMSA. To examine the role of PPARγ, the recombinant adenovirus carrying a dominant-negative form of PPARγ (dn-PPARγ) was constructed and transfected into keratinocytes.


RESULTS
We show here that 1,25D₃ significantly enhances hBD-3 and cathelicidin expression in keratinocytes. Expression of dn-PPARγ did not affect binding to the vitamin D-responsive element (VDRE), which is crucial for cathelicidin induction by VD3; however, it did decrease 1,25D₃ induction of both hBD-3 and cathelicidin. Inhibition of the p38, ERK, and JNK signaling pathways blocked hBD-3 expression, whereas only p38 inhibition suppressed cathelicidin induction. dn-PPARγ had no effect on ERK and JNK activity, but inhibited p38 phosphorylation and suppressed 1,25D₃-induced AP-1 activation via effects on Fra1 and c-Fos proteins.


CONCLUSIONS
In conclusion, PPARγ regulates the 1,25D₃-induced hBD-3 and cathelicidin expression in keratinocytes through the regulation of AP-1 and p38 activity.
Department of Dermatology, Ehime University School of Medicine, Japan. daixiuju@m.ehime-u.ac.jp
Xiuju
X
Dai
Koji
K
Sayama
Mikiko
M
Tohyama
Yuji
Y
Shirakata
Yasushi
Y
Hanakawa
Sho
S
Tokumaru
Lujun
L
Yang
Satoshi
S
Hirakawa
Koji
K
Hashimoto
D023181:Antimicrobial Cationic Peptides / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D001483:Base Sequence; D002117:Calcitriol / Q000494:pharmacology; D002478:Cells, Cultured; D017931:DNA Primers / Q000235:genetics; D006801:Humans; D007113:Immunity, Innate / Q000187:drug effects; D015603:Keratinocytes / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000276:immunology; D047495:PPAR gamma / Q000037:antagonists & inhibitors / Q000235:genetics / Q000276:immunology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology; D018808:Transcription Factor AP-1 / Q000378:metabolism; D023083:beta-Defensins / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D054804:Cathelicidins
D023181:Antimicrobial Cationic Peptides; C422950:DEFB103A protein, human; D017931:DNA Primers; D047495:PPAR gamma; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D023083:beta-Defensins; D048051:p38 Mitogen-Activated Protein Kinases; D002117:Calcitriol; D054804:Cathelicidins