OCLN and systemic sclerosis: In SSc, damage factors such as TGF-β, vascular endothelial growth factor, hypoxic stress response, and reactive oxygen species act on vascular endothelial cells, and may cause abnormalities in the function and structure of endothelial cells.These abnormalities lead to the downregulation of tight junctions (claudin, occludin and JAMs family proteins), adhesion junctions (VE-cadherin and catenin proteins), and gap junctions between cells, which in turn destroys the integrity of vessels and finally causes vascular leakage [20, 21].