Possible role of BMP-4 in the hyper-pigmentation of psoriatic plaques after anti-TNF-α treatment

Psoriasis over-expresses several inflammatory mediators, which impacts the activity of melanocytes. Tyrosinase (Tyr) and microphthalmia-associated transcription factor (MITF) are the primary regulators of melanogenesis. Furthermore, bone morphogenetic proteins (BMPs) modulate various pathobiologic processes including inflammation, melanogenesis and melanomagenesis. To determine the association between psoriasis and melanogenesis, psoriatic lesional skin was screened through gene expression, immunohistochemistry, immunogold staining and melanin content assays. The present study detected a decreased expression of Tyr, MITF and BMP-4 in psoriatic lesional skin compared with healthy skin. Tyr, BMP-4 and melanin content were also evaluated in the psoriatic lesional skin of patients receiving adalimumab therapy, before and after 16 weeks of treatment. TNF-α blockade modulated the Tyr, BMP-4 and melanin content of the patient skin lesions, which supported the hypothesis that hyper-pigmentation may occur in areas of psoriatic plaque after biological treatment. The present study confirmed the influence of the psoriatic pro-inflammatory network on melanogenesis, exerting an inhibitory effect mediated by TNF-α. Furthermore, the results regarding BMP-4 in the present study add another important element to the mechanism of psoriasis.