Involvement of midkine in autoimmune and autoinflammatory diseases.

Midkine (MK) is a heparin-binding growth factor that markedly expressed during embryogenesis but downregulated to inconsiderable levels in healthy adults. However, MK is upregulated during tissue repair and in many pathologic conditions, mostly malignancies and inflammatory diseases. MK promotes a number of functions in target cells such as migration, proliferation, survival, growth, reproduction and repair, angiogenesis, and gene expression. It acts as a pro-inflammatory cytokine and contributes to chronic inflammation via promoting chemotaxis and tissue infiltration of neutrophils and macrophages. Furthermore, MK upregulated the production of various inflammatory mediators (i.e. interleukin (IL) 6 and IL8). Recent studies have demonstrated strong evidence that MK is involved in the onset and progression of autoimmune rheumatic diseases, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and Sjögren's syndrome (SS) and other autoimmune conditions such as multiple sclerosis (MS). Additionally, it has been shown that MK is overexpressed in two major clinically defined forms of inflammatory bowel diseases (IBD), Crohn's disease (CD) and ulcerative colitis (UC), which are classified as autoinflammatory diseases. Taken together, MK is involved in the pathogenesis of autoimmune and autoinflammatory diseases and may serve as an indicator and biomarker in these conditions. Furthermore, MK inhibitors are expected to contribute in the management of these diseases.