Little is known about the regulation of epimerase activity. Transforming growth factor (TGF)-β-stimulated fibroblasts have reduced levels of epimerase activity, a reduced expression of D4ST1 and an increased expression of C4ST1, resulting in CS/DS with a considerably lower amount of IdoA 26. This effect is further increased by combined treatment with TGF-β, epidermal growth factor and platelet-derived growth factor (PDGF) (9). In another study, PDGF promoted the migration of fibroblasts, comprising a mechanism that is proposed to involve the up-regulation of IdoA in the proteoglycan CD44 27.
