Shikonin inhibits CEBPD downregulation in IL­17­treated HaCaT cells and in an imiquimod­induced psoriasis model.

Psoriasis is a chronic inflammatory skin disease characterized by well­defined scaly papules and plaques. Interleukin (IL)­17 is involved in its pathogenesis and promotes the proliferation of epidermal keratinocytes through signal transducer and activator of transcription 3 (STAT3) activation. Shikonin, a natural naphthoquinone isolated from Lithospermum erythrorhizon, possesses anti­inflammatory and immunosuppressive properties and can suppress IL­17­induced vascular endothelial growth factor expression by inhibiting the JAK/STAT3 pathway. In the present study, MTS, iCELLigence and RT­qPCR were used to determine the optimal concentration and duration of IL­17 or shikonin acting on HaCaT cells. The changes in the expression levels of genes associated with the IL­6/STAT3 pathway in differentially treated cells were analyzed via RT2Profiler™ PCR Array. Small interfering RNA was used to silence the expression levels of the target gene CCAAT/enhancer­binding protein δ (CEBPD). Western blotting and immunohistochemistry were used to evaluate the effect of shikonin on imiquimod­induced psoriasis in mice and the expression levels of CEBPD. Shikonin reversed IL­17­mediated downregulation of the tumor suppressor CEBPD in HaCaT cells. Moreover, low levels of CEBPD in the imiquimod­induced mouse model of psoriasis were restored by shikonin treatment, which ameliorated excessive keratinocyte proliferation. Taken together, these findings suggest that CEBPD plays a key role in the pathogenesis of psoriasis and can be targeted by shikonin as a potential therapeutic strategy.

Shikonin induces apoptosis and suppresses growth in keratinocytes via CEBP-δ upregulation.

Shikonin is an active compound of the oriental medicinal plant, Leptospermum erythrorhizon, which has been previously shown to inhibit psoriasis-like inflammation. However, the underlying mechanism is unclear. In the present study, the mechanisms of keratinocyte proliferation and apoptosis in psoriasis in response to shikonin were explored both in vitro and in vivo. Our results showed that shikonin significantly inhibits cell proliferation and induces apoptosis in both HaCaT and LV-STAT3 HaCaT cells by targeting CEBPD, while a decrease in cell survival, proliferation and viability were found through flow-cytometry and MTS assay. Furthermore, gavage with shikonin markedly alleviated psoriasis-like manifestations in IMQ-induced BALB/c mice clinically (PASI Score) and histopathologically. Immunohistochemistry revealed that shikonin potently suppresses the JAK/STAT3 signaling pathway in local skin lesions and increases CEBPD expression. These results imply that shikonin inhibits keratinocyte proliferation and induces apoptosis, which results in psoriasis treatment through the JAK/STAT3 dependent pathway. In addition, the activation of JAK/STAT3 downregulates CEBPD in HaCaT cells and IMQ-induced BALB/c mice. However, shikonin can reverse these effects, suggesting that CEBPD may be a potential therapeutic target for psoriasis.