Regulation of late cornified envelope genes relevant to psoriasis risk by plant-derived cyanidin.

The PSORS4 genetic risk factor for psoriasis is a deletion of two late cornified envelope (LCE) genes (LCE3C_LCE3Bdel) in a cluster of five LCE3 genes with a proposed role in skin repair. We previously showed that 1,25-dihydroxyvitamin D3 (1,25D) modestly upregulates transcripts from all five LCE3 genes as monitored by real time PCR in primary human keratinocytes. Herein we report that cyanidin, a plant-derived compound with anti-inflammatory/anti-oxidant properties, upregulates expression of all five LCE3 genes in cultures of differentiating primary human keratinocytes to a greater extent that does 1,25D. This action of cyanidin is dependent on the differentiation state of the keratinocytes, with a stronger effect after the cells have been incubated with 1.2mM calcium for 24h. Competition displacement assays using radiolabeled 1,25D revealed that cyanidin directly competes as a ligand for vitamin D receptor (VDR) binding with an estimated IC50 of 500µM. However, 20µM cyanidin is sufficient to upregulate LCE3 genes. The 25-fold discrepancy between the cyanidin concentration required for upregulating LCE3 genes in intact keratinocytes vs. that required for direct binding to VDR in vitro suggests that cyanidin may be: (a) metabolized to a more active VDR ligand in keratinocytes and/or (b) functioning via a non-VDR mediated mechanism. The fact that cyanidin is the most potent upregulator of global LCE3 gene expression reported to date suggests that this or related compounds may have potential in psoriasis therapy.

Control of late cornified envelope genes relevant to psoriasis risk: upregulation by 1,25-dihydroxyvitamin D3 and plant-derived delphinidin.

Psoriasis is a chronic inflammatory skin disease featuring abnormal keratinocyte proliferation and differentiation. A genetic risk factor for psoriasis (PSORS4) is a deletion of LCE3B and LCE3C genes encoding structural proteins in terminally differentiated keratinocytes. Because analogs of 1,25-dihydroxyvitamin D3 (1,25D) are used in psoriasis treatment, we hypothesized that 1,25D acts via the vitamin D receptor (VDR) to upregulate expression of LCE 3A/3D/3E genes, potentially mitigating the absence of LCE3B/LCE3C gene products. Results in a human keratinocyte line, HaCaT, suggested that 1,25D, low affinity VDR ligands docosahexaenoic acid and curcumin, along with a novel candidate ligand, delphinidin, induce LCE transcripts as monitored by qPCR. Further experiments in primary human keratinocytes preincubated with 1.2 mM calcium indicated that 1,25D and 10 µM delphinidin upregulate all five LCE3 genes (LCE3A-E). Competition binding assays employing radiolabeled 1,25D revealed that delphinidin binds VDR weakly (IC50 ≈ 1 mM). However, 20 µM delphinidin was capable of upregulating a luciferase reporter gene in a VDRE-dependent manner in a transfected keratinocyte cell line (KERTr). These results are consistent with a scenario in which delphinidin is metabolized to an active compound that then stimulates LCE3 transcription in a VDR/VDRE-dependent manner. We propose that upregulation of LCE genes may be part of the therapeutic effect of 1,25D to ameliorate psoriasis by providing sufficient LCE proteins, especially in individuals missing the LCE3B and 3C genes. Results with delphinidin further suggest that this compound or its metabolite(s) might offer an alternative to 1,25D in psoriasis therapy.