title: Hyaluronan synthesis mediates the fibrotic response of keratocytes to transforming growth factor beta.
abstract: TGFβ induces fibrosis in healing corneal wounds, and in vitro corneal keratocytes up-regulate expression of several fibrosis-related genes in response to TGFβ. Hyaluronan (HA) accumulates in healing corneas, and HA synthesis is induced by TGFβ by up-regulation of HA synthase 2. This study tested the hypothesis that HA acts as an extracellular messenger, enhancing specific fibrotic responses of keratocytes to TGFβ. HA synthesis inhibitor 4-methylumbelliferone (4MU) blocked TGFβ induction of HA synthesis in a concentration-dependent manner. 4MU also inhibited TGFβ-induced up-regulation of α-smooth muscle actin, collagen type III, and extra domain A-fibronectin. Chemical analogs of 4MU also inhibited fibrogenic responses in proportion to their inhibition of HA synthesis. 4MU, however, showed no effect on TGFβ induction of luciferase by the 3TP-Lux reporter plasmid. Inhibition of HA using siRNA to HA synthase 2 reduced TGFβ up-regulation of smooth muscle actin, fibronectin, and cell division. Similarly, brief treatment of keratocytes with hyaluronidase reduced TGFβ responses. These results suggest that newly synthesized cell-associated HA acts as an extracellular enhancer of wound healing and fibrosis in keratocytes by augmenting a limited subset of the cellular responses to TGFβ.
authors.affiliation: Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Naxin
authors.initials: N
authors.lastname: Guo
authors.forename: Xuan
authors.initials: X
authors.lastname: Li
authors.forename: Mary M
authors.initials: MM
authors.lastname: Mann
authors.forename: Martha L
authors.initials: ML
authors.lastname: Funderburgh
authors.forename: Yiqin
authors.initials: Y
authors.lastname: Du
authors.forename: James L
authors.initials: JL
authors.lastname: Funderburgh
mesh_terms: D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D003315:Cornea / Q000166:cytology / Q000473:pathology; D005355:Fibrosis; D014453:Glucuronosyltransferase / Q000235:genetics / Q000378:metabolism; D006801:Humans; D000076002:Hyaluronan Synthases; D006820:Hyaluronic Acid / Q000096:biosynthesis*; D006821:Hyaluronoglucosaminidase / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D015603:Keratinocytes / Q000187:drug effects* / Q000473:pathology* / Q000502:physiology; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D007527:Isoenzymes; D010982:Platelet-Derived Growth Factor; D016212:Transforming Growth Factor beta; D006820:Hyaluronic Acid; D014453:Glucuronosyltransferase; D000076002:Hyaluronan Synthases; D006821:Hyaluronoglucosaminidase