Keratinocyte aquaporin‐3 expression induced by histone deacetylase inhibitors is mediated in part by peroxisome proliferator‐activated receptors (PPARs)

The water and glycerol channel, aquaporin‐3 (AQP3), plays an important role in the skin epidermis, with effects on hydration, permeability barrier repair and wound healing; therefore, information about the mechanisms regulating its expression is important for a complete understanding of skin function physiologically and in disease conditions. We previously demonstrated that histone deacetylase inhibitors (HDACi) induce the mRNA and protein expression of AQP3, in part through the p53 family, transcription factors for which acetylation is known to affect their regulatory activity. Another set of transcription factors previously shown to induce AQP3 expression and/or regulate skin function are the peroxisome proliferator‐activated receptors (PPARs). Since there are reports that PPARs are also acetylated, we examined the involvement of these nuclear hormone receptors in HDACi‐induced AQP3 expression. We first verified that a PPARγ agonist upregulated AQP3 mRNA and protein levels and that this increase was blocked by a PPARγ antagonist. We then showed that the PPARγ antagonist also inhibited AQP3 expression induced both by a broad‐spectrum HDACi and an HDAC3‐selective inhibitor. Interestingly, a PPARα antagonist also inhibited HDACi‐induced AQP3 expression. These antagonist effects were observed in both primary mouse and normal human keratinocytes. Furthermore, PPARγ overexpression enhanced HDACi‐stimulated AQP3 mRNA levels. Thus, our results suggest that PPARγ and/or PPARα may play a role in regulating AQP3 levels in the skin; based on the ability of PPAR agonists to promote epidermal differentiation and/or inhibit proliferation, topical PPAR agonists might be considered as a therapy for hyperproliferative skin disorders, such as psoriasis.