COMP negatively influences keratinocyte proliferation via α5β1-integrin: Potential relevance of altered COMP expression in psoriasis

ABSTRACT In psoriasis, non-lesional skin shows alterations at the dermal–epidermal junction (DEJ) compared to healthy skin. Cartilage oligomeric matrix protein (COMP) is part of the papillary dermis of healthy skin, and its expression has not yet been studied in psoriatic skin. In this study, we found that COMP localization extended deeper into the dermis and formed a more continuous layer in psoriatic non-lesional skin compared to healthy skin, while in psoriatic lesions, COMP showed a partially discontinuous deposition at the DEJ. COMP and β1-integrin showed strong co-localization in non-lesional skin, where the laminin layer within the basement membrane (BM) is discontinuous. In in vitro models, the presence of exogenous COMP decreased the proliferation rate of keratinocytes and this proliferation-suppressing effect was diminished by blocking α5β1-integrin. Our results suggest that COMP can interact with α5β1-integrin of basal keratinocytes through the disrupted BM, and this interaction might stabilize the epidermis in the non-lesional state by contributing to the suppression of keratinocyte proliferation. The antiproliferative effect of COMP is likely to be relevant to other skin diseases in which chronic non-healing wounds are coupled with massive COMP accumulation.