Functional alpha1- And beta2-adrenergic Receptors in Human Osteoblasts

J Cell Physiol. 2009 Jul;220(1):267-75. doi: 10.1002/jcp.21761.

Abstract

Central (hypothalamic) control of bone mass is proposed to be mediated through beta2-adrenergic receptors (beta2-ARs). While investigations in mouse bone cells suggest that epinephrine enhances both RANKL and OPG mRNA via both beta-ARs and alpha-ARs, whether alpha-ARs are expressed in human bone cells is controversial. The current study investigated the expression of alpha1-AR and beta2-AR mRNA and protein and the functional role of adrenergic stimulation in human osteoblasts (HOBs). Expression of alpha1B- and beta2-ARs was examined by RT-PCR, immunofluorescence microscopy and Western blot (for alpha1B-ARs). Proliferation in HOBs was assessed by (3)H-thymidine incorporation and expression of RANKL and OPG was determined by quantitative RT-PCR. RNA message for alpha1B- and beta2-ARs was expressed in HOBs and MG63 human osteosarcoma cells. alpha1B- and beta2-AR immunofluorescent localization in HOBs was shown for the first time by deconvolution microscopy. alpha1B-AR protein was identified in HOBs by Western blot. Both alpha1-agonists and propranolol (beta-blocker) increased HOB replication but fenoterol, a beta2-agonist, inhibited it. Fenoterol nearly doubled RANKL mRNA and this was inhibited by propranolol. The alpha1-agonist cirazoline increased OPG mRNA and this increase was abolished by siRNA knockdown of alpha1B-ARs in HOBs. These data indicate that both alpha1-ARs and beta2-ARs are present and functional in HOBs. In addition to beta2-ARs, alpha1-ARs in human bone cells may play a role in modulation of bone turnover by the sympathetic nervous system.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenergic alpha-Agonists / pharmacology
  • Adrenergic alpha-Antagonists / pharmacology
  • Adrenergic beta-Agonists / pharmacology
  • Adrenergic beta-Antagonists / pharmacology
  • Blotting, Western
  • Cell Proliferation
  • Cells, Cultured
  • Dose-Response Relationship, Drug
  • Gene Knockdown Techniques
  • Humans
  • Microscopy, Fluorescence
  • Osteoblasts / drug effects
  • Osteoblasts / metabolism*
  • Osteoprotegerin / metabolism
  • RANK Ligand / metabolism
  • RNA Interference
  • RNA, Messenger / metabolism
  • RNA, Small Interfering / metabolism
  • Receptors, Adrenergic, alpha-1 / drug effects
  • Receptors, Adrenergic, alpha-1 / genetics
  • Receptors, Adrenergic, alpha-1 / metabolism*
  • Receptors, Adrenergic, beta-2 / drug effects
  • Receptors, Adrenergic, beta-2 / genetics
  • Receptors, Adrenergic, beta-2 / metabolism*
  • Reverse Transcriptase Polymerase Chain Reaction

Substances

  • ADRA1B protein, human
  • Adra1b protein, mouse
  • Adrenergic alpha-Agonists
  • Adrenergic alpha-Antagonists
  • Adrenergic beta-Agonists
  • Adrenergic beta-Antagonists
  • Osteoprotegerin
  • RANK Ligand
  • RNA, Messenger
  • RNA, Small Interfering
  • Receptors, Adrenergic, alpha-1
  • Receptors, Adrenergic, beta-2
  • TNFRSF11B protein, human
  • TNFSF11 protein, human