PPARγ mediates innate immunity by regulating the 1α,25-dihydroxyvitamin D3 induced hBD-3 and cathelicidin in human keratinocytes.

Abstract

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.

DOI: 10.1016/j.jdermsci.2010.09.008

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@article{Dai2010PPARMI, title={PPARγ mediates innate immunity by regulating the 1α,25-dihydroxyvitamin D3 induced hBD-3 and cathelicidin in human keratinocytes.}, author={Xiuju Dai and Koji Sayama and Mikiko Tohyama and Yuji Shirakata and Yasushi Hanakawa and Sho Tokumaru and Lujun Yang and Satoshi Hirakawa and Koji Hashimoto}, journal={Journal of dermatological science}, year={2010}, volume={60 3}, pages={179-86} }