Background:
Atrial fibrillation (AF) is the most common cardiac arrhythmia, and increases a patient’s stroke risk five-fold. Reduced atrial contractility (stunning) is observed in AF and contributes to stroke risk; however, the mechanisms responsible for atrial stunning in AF are unknown. Recent data from our laboratory indicate that protein phosphatase 1 (PP1) dephosphorylation of myosin light chain 2a (MLC2a) may contribute to atrial stunning in AF.
Objective:
To determine how the PP1 regulatory subunit 12C (PPP1R12C) and catalytic (PPP1c) subunits modify atrial sarcomere phosphorylation in AF.
Methods:
We evaluated the protein expression, binding and phosphorylation among PPP1R12C, PPP1c, and MLC2a in transfected HL-1 cells, murine atrial tissue (Pitx2null
+/–
mice, with a genetic predisposition AF), and in HEK cells. An inhibitor of PPP1R12C phosphorylation, BDP5290, was used to enhance the PPP1R12C-PPP1C interaction.
Results:
In
Pitx2
null
+/–
mice, PPP1R12C was increased by 2-fold (
P
<0.01) and associated with a 40% reduction in S-19-MLC2a phosphorylation versus WT mice (
P
<0.058). BDP5290 increased PPP1R12C-PPP1C binding by >3-fold in HL-1 cells (
P
<0.01). BDP5290 reduced MLC2a phosphorylation by 40% through an enhanced interaction with PPP1R12C by >3-fold in HEK cells (
P
<0.01).
Conclusion:
In
Pitx2
null+/-
mice, increased expression of PPP1R12C is associated with PP1 holoenzyme targeting to sarcomeric MLC2a, and is associated with reduced S19-MLC2a phosphorylation. Additionally, BDP5290 enhances the PPP1R12C-PPP1C interaction and models PP1 activity in AF. Future studies will examine the effects of both AF and BDP5290 upon atrial contractility in vitro.
Impaired local regulation of ryanodine receptor type-2 by protein phosphatase 1 promotes atrial fibrillation
