title: Neutral sphingomyelinase 2 deficiency increases hyaluronan synthesis by up-regulation of Hyaluronan synthase 2 through decreased ceramide production and activation of Akt.
abstract: Fibroblasts from the fro/fro mouse, with a deletion in the Smpd3 gene coding for the active site of neutral sphingomyelinase 2 (NSMase2), secreted increased amounts of hyaluronan (HA). This was reversed by transfection with the Smpd3 gene, suggesting a connection between sphingolipid and glycosaminoglycan metabolism. The deficiency of NSMase2 resulted in storage of sphingomyelin (SM) and cholesterol with a 50% reduction in ceramides (Cer). RT-PCR and Western blot analysis showed that increased HA secretion resulted from increased hyaluronan synthase 2 (HAS2) activity localized to sphingolipid-enriched lipid rafts. Although cholesterol levels were also elevated in lipid rafts from mouse fibroblasts deficient in lysosomal acid SMase activity (deletion of the Smpd1(-/-) gene), there was no increase in HA secretion. We then showed that in fro/fro fibroblasts, the reduced ceramide was associated with decreased phosphorylation of protein phosphatase 2A (PP2A) and increased phosphorylation of its substrate Akt-p, together with PI3K, PDK1, mTOR (mammalian target of rapamycin), and p70S6K, although PTEN was unaffected. Exogenous ceramide, as well as inhibitors of Akt (Akt inhibitor VIII), PI 3-kinase (LY294002 and wortmannin), and mTOR (rapamycin) reduced secretion of HA, whereas the NSMase2 inhibitor GW4869 increased HA synthesis and secretion. We propose that NSMase2/Cer are the key mediators of the regulation of HA synthesis, via microdomains and the Akt/mTOR pathway.
authors.affiliation: Department of Pediatrics, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Jingdong
authors.initials: J
authors.lastname: Qin
authors.forename: Evgeny
authors.initials: E
authors.lastname: Berdyshev
authors.forename: Christophe
authors.initials: C
authors.lastname: Poirer
authors.forename: Nancy B
authors.initials: NB
authors.lastname: Schwartz
authors.forename: Glyn
authors.initials: G
authors.lastname: Dawson
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D002518:Ceramides / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism; D020869:Gene Expression Profiling; D015971:Gene Expression Regulation, Enzymologic; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006025:Glycosaminoglycans / Q000737:chemistry; D000076002:Hyaluronan Synthases; D006820:Hyaluronic Acid / Q000096:biosynthesis*; D021962:Membrane Microdomains / Q000737:chemistry; D051379:Mice; D010013:Osteogenesis Imperfecta / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction; D013107:Sphingolipids / Q000737:chemistry; D013108:Sphingomyelin Phosphodiesterase / Q000096:biosynthesis* / Q000172:deficiency*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D002518:Ceramides; D006025:Glycosaminoglycans; D013107:Sphingolipids; D006820:Hyaluronic Acid; D014453:Glucuronosyltransferase; C491099:Has2 protein, mouse; D000076002:Hyaluronan Synthases; C546842:MTOR protein, human; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; C491483:Smpd3 protein, mouse; D013108:Sphingomyelin Phosphodiesterase