Biomarkers for skin involvement and fibrotic activity in scleroderma

Systemic sclerosis (scleroderma, SSc) is characterized as a severe and very heterogeneous disease with a bright variation of skin and organ manifestations in individual patients. The pathogenesis is still not fully elucidated; however, it is known that this disease starts with an initial vascular damage, which then leads to an inflammatory process and finally promotes the development of an accumulation of collagen and other extracellular matrix (ECM) components. As a result of the heterogeneous characteristics of this multisystem, autoimmune disease, it is always a challenge to identify high-risk patients and to monitor the fibrotic activity also in response to therapies. This can be achieved by several physical methods including the mRSS, the durometer and ultrasound determination of skin thickness. However, this also requires the use of laboratory biomarkers, which are easily detectable and that reflect the inflammatory and/or fibrotic activity. As skin correlates well with the extent of fibrosis also in other organs, we focused in this review on biomarkers which reflect skin involvement of scleroderma patients. These include growth factors, cytokines and proteases as well as their inhibitors. Moreover, several ECM proteins, especially the collagens have been determined in skin biopsies and in blood/serum samples. Determination of proteins has been supported by mRNA levels using PCR techniques and expression analysis of gene expression patterns. This review summarizes all non-invasive physical and laboratory examinations, which permit a better understanding of the fibrotic activity of the disease, can be effectively used to assess potential therapeutic response and help to find better treatment options.