Relaxin inhibits renal myofibroblast differentiation via RXFP1, the nitric oxide pathway, and Smad2

FASEB J. 2009 Apr;23(4):1219-29. doi: 10.1096/fj.08-120857. Epub 2008 Dec 10.


The hormone relaxin inhibits renal myofibroblast differentiation by interfering with TGF-beta1/Smad2 signaling. However, the pathways involved in the relaxin-TGF-beta1/Smad2 interaction remain unknown. This study investigated the signaling mechanisms by which human gene-2 (H2) relaxin regulates myofibroblast differentiation in vitro by examining its effects on mixed populations of fibroblasts and myofibroblasts propagated from injured rat kidneys. Cultures containing approximately 60-70% myofibroblasts were used to determine which relaxin receptors, G-proteins, and signaling pathways were involved in the H2 relaxin-mediated regulation of alpha-smooth muscle actin (alpha-SMA; a marker of myofibroblast differentiation). H2 relaxin only inhibited alpha-SMA immunostaining and collagen concentration in the presence of relaxin family peptide receptor 1 (RXFP1). H2 relaxin also induced a transient rise in cAMP in the presence of G(i/o) inhibition, and a sustained increase in extracellular signal-regulated kinase (ERK)-1/2 phosphorylation. Furthermore, inhibition of neuronal nitric oxide synthase (nNOS), NO, and cGMP significantly blocked the inhibitory effects of relaxin on alpha-SMA and Smad2 phosphorylation, while the NO inhibitor, L-nitroarginine methyl ester (hydrochloride) (L-NAME) significantly blocked the inhibitory actions of relaxin on collagen concentration in vivo. These findings suggest that relaxin signals through RXFP1, and a nNOS-NO-cGMP-dependent pathway to inhibit Smad2 phosphorylation and interfere with TGF-beta1-mediated renal myofibroblast differentiation and collagen production.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Differentiation / drug effects*
  • Cells, Cultured
  • Fibroblasts / cytology
  • Fibroblasts / drug effects*
  • Humans
  • Immunohistochemistry
  • Male
  • Mice
  • Nitric Oxide / metabolism*
  • RNA, Messenger / metabolism
  • Rats
  • Receptors, G-Protein-Coupled / genetics
  • Receptors, G-Protein-Coupled / metabolism*
  • Receptors, Peptide / genetics
  • Receptors, Peptide / metabolism*
  • Recombinant Proteins / metabolism
  • Recombinant Proteins / pharmacology
  • Relaxin / genetics
  • Relaxin / metabolism
  • Relaxin / pharmacology*
  • Signal Transduction / drug effects*
  • Smad2 Protein / genetics
  • Smad2 Protein / metabolism*


  • RNA, Messenger
  • Receptors, G-Protein-Coupled
  • Receptors, Peptide
  • Recombinant Proteins
  • Rxfp1 protein, rat
  • Smad2 Protein
  • Smad2 protein, rat
  • Nitric Oxide
  • Relaxin