Intracellular O-linked glycosylation directly regulates cardiomyocyte L-type Ca2+ channel activity and excitation-contraction coupling

Basic Res Cardiol. 2020 Sep 10;115(6):59. doi: 10.1007/s00395-020-00820-0.

Abstract

Cardiomyocyte L-type Ca2+ channels (Cavs) are targets of signaling pathways that modulate channel activity in response to physiologic stimuli. Cav regulation is typically transient and beneficial but chronic stimulation can become pathologic; therefore, gaining a more complete understanding of Cav regulation is of critical importance. Intracellular O-linked glycosylation (O-GlcNAcylation), which is the result of two enzymes that dynamically add and remove single N-acetylglucosamines to and from intracellular serine/threonine residues (OGT and OGA respectively), has proven to be an increasingly important post-translational modification that contributes to the regulation of many physiologic processes. However, there is currently no known role for O-GlcNAcylation in the direct regulation of Cav activity nor is its contribution to cardiac electrical signaling and EC coupling well understood. Here we aimed to delineate the role of O-GlcNAcylation in regulating cardiomyocyte L-type Cav activity and its subsequent effect on EC coupling by utilizing a mouse strain possessing an inducible cardiomyocyte-specific OGT-null-transgene. Ablation of the OGT-gene in adult cardiomyocytes (OGTKO) reduced OGT expression and O-GlcNAcylation by > 90%. Voltage clamp recordings indicated an ~ 40% reduction in OGTKO Cav current (ICa), but with increased efficacy of adrenergic stimulation, and Cav steady-state gating and window current were significantly depolarized. Consistently, OGTKO cardiomyocyte intracellular Ca2+ release and contractility were diminished and demonstrated greater beat-to-beat variability. Additionally, we show that the Cav α1 and β2 subunits are O-GlcNAcylated while α2δ1 is not. Echocardiographic analyses indicated that the reductions in OGTKO cardiomyocyte Ca2+ handling and contractility were conserved at the whole-heart level as evidenced by significantly reduced left-ventricular contractility in the absence of hypertrophy. The data indicate, for the first time, that O-GlcNAc signaling is a critical and direct regulator of cardiomyocyte ICa achieved through altered Cav expression, gating, and response to adrenergic stimulation; these mechanisms have significant implications for understanding how EC coupling is regulated in health and disease.

Keywords: Cardiomyocyte; EC coupling; Ion channel gating; Isoproterenol; O-GlcNAc; Voltage-gated Ca2+ channel.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenergic beta-Agonists / pharmacology
  • Animals
  • Calcium Channels, L-Type / metabolism*
  • Excitation Contraction Coupling* / drug effects
  • Glycosylation
  • Ion Channel Gating
  • Isoproterenol / pharmacology
  • Male
  • Membrane Potentials
  • Mice, Knockout
  • Myocytes, Cardiac / drug effects
  • Myocytes, Cardiac / enzymology*
  • N-Acetylglucosaminyltransferases / genetics
  • N-Acetylglucosaminyltransferases / metabolism*
  • Ventricular Function, Left* / drug effects

Substances

  • Adrenergic beta-Agonists
  • Cacnb2 protein, mouse
  • Calcium Channels, L-Type
  • N-Acetylglucosaminyltransferases
  • Ogt protein, mouse
  • Isoproterenol