COL18A1 and systemic sclerosis: Over the years, several circulating elements including proangiogenic molecules (e.g., VEGF, endoglin, and ET-1), antiangiogenic factors (e.g., VEGF165b, endostatin, and pentraxin-3), cell adhesion molecules, neurovascular guidance molecules, and sirtuins have been associated with SSc clinical features of impaired angiogenesis and proposed as vascular biomarkers [44,45].