GPR97 depletion aggravates imiquimod-induced psoriasis pathogenesis via amplifying IL-23/IL-17 axis signal pathway

Skin psoriasis is defined as receiving external stimulation to activate skin dendritic cells (DCs) which can release interleukin 23 (IL-23) to interlink the innate and adaptive immunity as well as induce T helper 17 (Th17) cell differentiation leading to elevated production of interleukin 17 (IL-17) for keratinocytes over production. This autoimmune loop in psoriasis pathogenesis is influenced by G protein-coupled receptor (GPCR) signalling transduction, and in particular, function of adhesion molecule GPR97 in psoriasis endures to be utterly addressed. In this research, our team allocated GPR97 depletion (GPR97^-/-), GPR97 conditional depletion on dendritic cell (DC-cKO), and keratin 14-conditional knockout (K14-cKO) mice models to explore the function of GPR97 which influences keratinocytes and skin immunity. It was found that significantly aggravated psoriasis-like lesion in GPR97^-/- mice. In addition, hyperproliferative keratinocytes as well as accumulation of DCs and Th17 cells were detected in imiquimod (IMQ)-induced GPR97^-/- mice, which was consistent with the results in DC-cKO and K14-cKO psoriasis model. Additional investigations indicated that beclomethasone dipropionate (BDP), an agonist of GPR97, attenuated the psoriasis-like skin disease and restricted HaCaT cells abnormal proliferation as well as Th17 cells differentiation. Particularly, we found that level of NF-κB p65 was increased in GPR97^-/- DCs and BDP could inhibit p65 activation in DCs. Role of GPR97 is indispensable and this adhesion receptor may affect immune cell enrichment and function in skin and alter keratinocytes proliferation as well as differentiation in psoriasis.