The level of prosaposin is decreased in the skin of patients with psoriasis vulgaris

Ceramides are the most abundant lipids constituting the intercellular matri x of the skin stratum corneum and their critical role in skin homeostasis h as been extensively documented. Their concentration in the skin highly depe nds on the rate of availability of the enzymes involved in ceramide generat ion. The aim of this study was to investigate whether the concentration of prosaposin was altered in the skin of patients with psoriasis vulgaris. Pro saposin, the precursor of saposins (sphingolipid activator proteins), was m easured in lesional and nonlesional skin of psoriatic patients and in norma l skin from surgical patients, both at the mRNA and at the protein level. D ensitometric analysis of reverse transcriptase-polymerase chain reaction ba nds separated by gel-electrophoresis showed a progressive decrease of prosa posin mRNA expression in nonlesional and lesional psoriatic skin, being sub stantially decreased in lesional psoriatic skin compared with normal contro l skin. Immunohistochemical analysis showed a significant decrease of prosa posin level in the stratum corneum of psoriatic lesional skin (both in acti ve-type and in chronic-type plaque) compared with nonlesional and with norm al skin (p < 0.01), and in psoriatic nonlesional skin compared with normal control (p < 0.05). Immunolocalization of sphingomyelinase in lesional and nonlesional psoriatic skin showed a decrease in the level of this enzyme in the stratum corneum of psoriatic lesional, compared with nonlesional skin. These results support the concept that disturbance of epidermal barrier fu nction caused by derangement in ceramide generation can be crucial for the development of psoriatic skin diseases.