In adult skin in vivo, the stimulation of pericytes by TGF-β and platelet-derived growth factor beta (PDGF-β) promotes angiogenesis and the differentiation of pericytes to fibroblasts, suggesting that collagen-producing mesenchymal cells in SSc may be originally from pericytes [64]. The gene discussed is TGFB1; the disease is systemic sclerosis.