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Cardioprotection specific for the G protein Gi2 in chronic adrenergic signaling through beta 2-adrenoceptors

Katharina Foerster1, Ferdi Groner, Jan Matthes

  • 1Department of Pharmacology, University of Cologne, Gleueler Strasse 24, 50931 Cologne, Germany.

Proceedings of the National Academy of Sciences of the United States of America
|November 13, 2003
PubMed

Insights

Inhibitory Gi proteins, specifically G alpha i2, are crucial for the protective effects of beta 2-adrenoceptor overexpression in the heart. Reduced G alpha i2 impairs survival and accelerates heart failure in transgenic mice.

Area of Science:

  • Cardiovascular Physiology
  • Molecular Cardiology
  • G Protein-Coupled Receptor Signaling

Background:

  • Beta-adrenoceptors (beta 1 and beta 2) regulate cardiac function via distinct signaling pathways.
  • Beta 2-adrenoceptors activate inhibitory Gi proteins, unlike beta 1-adrenoceptors.
  • Overexpression of beta 2-adrenoceptors in mice affects survival differently than beta 1-adrenoceptor overexpression.

Purpose of the Study:

  • To investigate the role of inhibitory Gi proteins in the chronic effects of human beta 2-adrenoceptor overexpression in transgenic mice.
  • To determine the impact of G alpha i2 subunit inactivation on the cardiac pathology and survival of beta 2-adrenoceptor overexpressing mice.

Main Methods:

  • Crossbreeding of beta 2-adrenoceptor transgenic mice with mice lacking the G alpha i2 gene.
  • Analysis of survival rates, cardiac hypertrophy, heart failure progression, and calcium channel activity in resulting mouse lines.
  • Pertussis toxin treatment in vitro to assess Gi protein involvement in channel activity.

Main Results:

  • Inactivation of G alpha i2 significantly reduced survival in beta 2-adrenoceptor transgenic mice, with homozygous knockouts dying shortly after birth.
  • Heterozygous G alpha i2 inactivation led to accelerated cardiac hypertrophy and earlier heart failure.
  • Calcium channel activity was suppressed in G alpha i2 deficient mice, but restored by pertussis toxin, suggesting a role for G alpha i3.

Conclusions:

  • G alpha i2 plays a critical protective role in the chronic signaling of overexpressed beta 2-adrenoceptors, promoting survival and delaying cardiac pathology.
  • Beta 2-adrenoceptor signaling diverges at the Gi level, with G alpha i2 mediating protective effects and another Gi isoform (likely G alpha i3) mediating calcium channel suppression.

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