title: Syndecan-4 is a key determinant of collagen cross-linking and passive myocardial stiffness in the pressure-overloaded heart.
abstract: OBJECTIVE
  Diastolic dysfunction is central to the development of heart failure. To date, there is no effective treatment and only limited understanding of its molecular basis. Recently, we showed that the transmembrane proteoglycan syndecan-4 increases in the left ventricle after pressure overload in mice and man, and that syndecan-4 via calcineurin/nuclear factor of activated T-cells (NFAT) promotes myofibroblast differentiation and collagen production upon mechanical stress. The aim of this study was to investigate whether syndecan-4 affects collagen cross-linking and myocardial stiffening in the pressure-overloaded heart.
  
  
  RESULTS
  Aortic banding (AB) caused concentric hypertrophy and increased passive tension of left ventricular muscle strips, responses that were blunted in syndecan-4(-/-) mice. Disruption of titin anchoring by salt extraction of actin and myosin filaments revealed that the effect of syndecan-4 on passive tension was due to extracellular matrix remodelling. Expression and activity of the cross-linking enzyme lysyl oxidase (LOX) increased with mechanical stress and was lower in left ventricles and cardiac fibroblasts from syndecan-4(-/-) mice, which exhibited less collagen cross-linking after AB. Expression of osteopontin (OPN), a matricellular protein able to induce LOX in cardiac fibroblasts, was up-regulated in hearts after AB, in mechanically stressed fibroblasts and in fibroblasts overexpressing syndecan-4, calcineurin, or NFAT, but down-regulated in fibroblasts lacking syndecan-4 or after NFAT inhibition. Interestingly, the extracellular domain of syndecan-4 facilitated LOX-mediated collagen cross-linking.
  
  
  CONCLUSIONS
  Syndecan-4 exerts a dual role in collagen cross-linking, one involving its cytosolic domain and NFAT signalling leading to collagen, OPN, and LOX induction in cardiac fibroblasts; the other involving the extracellular domain promoting LOX-dependent cross-linking.
authors.affiliation: Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway k.l.m.herum@medisin.uio.no.
authors.forename: Kate M
authors.initials: KM
authors.lastname: Herum
authors.affiliation: Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway Department of Genetics, Harvard Medical School, Boston, MA, USA.
authors.forename: Ida G
authors.initials: IG
authors.lastname: Lunde
authors.affiliation: Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway Department of Cardiothoracic Surgery, Oslo University Hospital Ullevål, Oslo, Norway.
authors.forename: Biljana
authors.initials: B
authors.lastname: Skrbic
authors.affiliation: Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway.
authors.forename: William E
authors.initials: WE
authors.lastname: Louch
authors.affiliation: Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway.
authors.forename: Almira
authors.initials: A
authors.lastname: Hasic
authors.affiliation: Clinical and Biomedical Engineering, Oslo University Hospital Ullevål, Oslo, Norway.
authors.forename: Sigurd
authors.initials: S
authors.lastname: Boye
authors.affiliation: Department of Cardiovascular Physiology, Ruhr University Bochum, Bochum, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Unger
authors.affiliation: Department of Pathology, Oslo University Hospital Rikshospitalet, Oslo, Norway.
authors.forename: Sverre-Henning
authors.initials: SH
authors.lastname: Brorson
authors.affiliation: Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway.
authors.forename: Ivar
authors.initials: I
authors.lastname: Sjaastad
authors.affiliation: Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway Department of Cardiothoracic Surgery, Oslo University Hospital Ullevål, Oslo, Norway.
authors.forename: Theis
authors.initials: T
authors.lastname: Tønnessen
authors.affiliation: Department of Cardiovascular Physiology, Ruhr University Bochum, Bochum, Germany.
authors.forename: Wolfgang A
authors.initials: WA
authors.lastname: Linke
authors.affiliation: Department of Clinical Sciences, Lund University, Malmö, Sweden.
authors.forename: Maria F
authors.initials: MF
authors.lastname: Gomez
authors.affiliation: Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway.
authors.forename: Geir
authors.initials: G
authors.lastname: Christensen
mesh_terms: D000818:Animals; D003094:Collagen / Q000378:metabolism*; D005109:Extracellular Matrix / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism*; D006321:Heart / Q000503:physiopathology; D006333:Heart Failure / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009206:Myocardium / Q000378:metabolism*; D008249:Protein-Lysine 6-Oxidase / Q000378:metabolism; D013312:Stress, Physiological; D053671:Syndecan-4 / Q000235:genetics / Q000378:metabolism*
chemical_list: C508306:Sdc4 protein, mouse; D053671:Syndecan-4; D003094:Collagen; D008249:Protein-Lysine 6-Oxidase
keywords: Collagen cross-linking; Lysyl oxidase; Myocardial stiffness; Myofibroblast; Syndecan-4