The Notch pathway plays a key role in differentiation, proliferation, and influencing cell fate decision in multiple organisms and tissues including the epidermis and its appendages. The role of Notch-1 in psoriasis has not been widely evaluated; therefore, the current study aimed to evaluate its role in etiopathogenesis of this common skin disease. The current study used immunohistochemical technique to evaluate Notch-1 expression in 35 lesional biopsies of patients having chronic plaque psoriasis in comparison with normal skin biopsies, representing the control group. Notch-1 was expressed in the epidermis of both normal and psoriatic skins; however, the intensity was in favor of psoriatic lesion, and the nuclear form of Notch-1 was more frequently and diffusely seen in psoriasis. Exacerbation of psoriasis as assessed by the Psoriasis Area and Severity Index score was significantly associated with intense (P = .005) and nuclear form of Notch-1 expression (P = .0001). The nuclear form of Notch-1 was also correlated with female sex (P = .043). From this study, up-regulation and not down-regulation of Notch-1 may have a role in pathogenesis of psoriasis. The nuclear form is responsible for the exacerbation of symptoms, and it is the one that may disappear by the effect of psoralen and ultraviolet A radiation (PUVA) therapy.
