title: Serelaxin-mediated signal transduction in human vascular cells: bell-shaped concentration-response curves reflect differential coupling to G proteins.
abstract: OBJECTIVE
  In a recently conducted phase III clinical trial, RELAX-AHF, serelaxin infusion over 48 h improved short- and long-term clinical outcomes in patients with acute heart failure. In this study we used human primary cells from the umbilical vasculature to better understand the signalling mechanisms activated by serelaxin.
  
  
  METHODS
  We examined the acute effects of serelaxin on signal transduction mechanisms in primary human umbilical vascular cells and its chronic actions on markers of cardiovascular function and disease.
  
  
  RESULTS
  The RXFP1 receptor, the cognate serelaxin receptor, was expressed at the cell surface in HUVECs and human umbilical vein smooth muscle cells (HUVSMCs), human umbilical artery smooth muscle cells (HUASMCs) and human cardiac fibroblasts (HCFs), but not human umbilical artery endothelial cells. In HUVECs and HUVSMCs, serelaxin increased cAMP, cGMP accumulation and pERK1/2, and the concentration-response curves (CRCs) were bell-shaped. Similar bell-shaped CRCs for cGMP and pERK1/2 were observed in HCFs, whereas in HUASMCs, serelaxin increased cAMP, cGMP and pERK1/2 with sigmoidal CRCs. Gαi/o and lipid raft disruption, but not Gαs inhibition, altered the serelaxin CRC for cAMP and cGMP accumulation in HUVSMC but not HUASMC. Longer term serelaxin exposure increased the expression of neuronal NOS, VEGF, ETβ receptors and MMPs (gelatinases) in RXFP1 receptor-expressing cells.
  
  
  CONCLUSIONS
  Serelaxin caused acute and chronic changes in human umbilical vascular cells that were cell background dependent. Bell-shaped CRCs that were observed only in venous cells and fibroblasts involved Gαi/o located within membrane lipid rafts.
authors.affiliation: Drug Discovery Biology, Monash Institute of Pharmacology, Monash University, Melbourne, Vic., Australia.
authors.forename: M
authors.initials: M
authors.lastname: Sarwar
authors.forename: C S
authors.initials: CS
authors.lastname: Samuel
authors.forename: R A
authors.initials: RA
authors.lastname: Bathgate
authors.forename: D R
authors.initials: DR
authors.lastname: Stewart
authors.forename: R J
authors.initials: RJ
authors.lastname: Summers
mesh_terms: D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D042783:Endothelial Cells / Q000187:drug effects* / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism; D044023:Receptor, Endothelin B / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D018000:Receptors, Peptide / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D012065:Relaxin / Q000494:pharmacology*; D015398:Signal Transduction; D014469:Umbilical Arteries / Q000166:cytology; D014471:Umbilical Veins / Q000166:cytology; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: C417543:RXFP1 protein, human; D044023:Receptor, Endothelin B; D043562:Receptors, G-Protein-Coupled; D018000:Receptors, Peptide; D011994:Recombinant Proteins; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; C577649:serelaxin protein, human; D012065:Relaxin; D052248:Nitric Oxide Synthase Type I; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; C522361:MMP2 protein, human; D020778:Matrix Metalloproteinase 2; C579270:MMP9 protein, human; D020780:Matrix Metalloproteinase 9; D019204:GTP-Binding Proteins