Matrix metalloproteinases as mediators of tissue injury in different forms of cutaneous lupus erythematosus

Background Matrix metalloproteinases (MMPs) contribute to tissue destruction, regeneration, inflammation and apoptosis and several of them are upregulated by ultraviolet (UV) radiation in skin. Although some MMPs associate with organ manifestations of systemic lupus erythematosus (SLE), their role in cutaneous lupus erythematosus (LE) is elusive. Objectives Our aim was to evaluate the expression of MMPs in SLE, subacute cutaneous LE (SCLE) and discoid LE (DLE) skin lesions and their relation to apoptosis and epidermal changes. Methods Lesional skin biopsies from 20 patients with SLE, 20 with DLE and 17 with SCLE, and from UVA/UVB‐photoprovoked skin of healthy volunteers were immunostained using antibodies to multiple MMPs and tissue inhibitors of metalloproteinases (TIMPs). The TUNEL (terminal deoxynucleotidyl transferase‐mediated deoxyuridine triphosphate nick end labelling) method was used for detection of apoptosis. Results MMP‐3, ‐10, ‐19 and ‐26 were abundantly expressed by keratinocytes in SLE, DLE and SCLE skin samples. MMP‐7 was detected in keratinocytes in regions of oedema and vacuolization especially in SLE and SCLE, while MMP‐14 was only occasionally observed in keratinocytes. Photoprovocation did not induce MMP‐10 or ‐26 expression in skin of healthy volunteers. Epithelial TIMP‐1 expression was low while occasional positive fibroblasts were seen in the dermis. TIMP‐3 was abundantly expressed in the epidermis, endothelial cells and macrophages. Conclusions Different subtypes of cutaneous LE are fairly similar in their MMP expression profile. MMP‐3 and ‐10 mediate both epidermal changes and dermal tissue remodelling but are not present in lymphocytes. Low expression of TIMP‐1 suggests that lupus skin is characterized by proteolytic events, and targeted action using selective MMP inhibitors may reduce lupus‐induced damage in inflamed tissues.