# P21‐Activated Kinase 2 as a Novel Target for Ventricular Tachyarrhythmias Associated with Cardiac Adrenergic Stress and Hypertrophy

## TL;DR

This study shows that P21-activated kinase 2 (Pak2) can protect against dangerous heart rhythms caused by stress and heart enlargement, suggesting it as a new treatment target.

## Contribution

Pak2 is identified as a novel regulator of ROS-induced CaMKII activation and calcium dynamics in stressed hearts.

## Key findings

- Pak2 deficiency increases triggered ventricular arrhythmias and disrupts calcium handling in stressed hearts.
- Pak2 overexpression and activation reduce arrhythmias and improve cardiac function in hypertrophic models.
- Pak2 regulates mitochondrial oxidative stress and ROS production, impacting Ca2+ homeostasis.

## Abstract

Ventricular arrhythmias associated with cardiac adrenergic stress and hypertrophy pose a significant clinical challenge. We explored ventricular anti‐arrhythmic effects of P21‐activated kinase 2 (Pak2), comparing in vivo and ex vivo cardiomyocyte‐specific Pak2 knockout (Pak2cko) or overexpression (Pak2ctg) murine models, under conditions of acute adrenergic stress, and hypertrophy following chronic transverse aortic constriction (TAC). Pak2 was downregulated 5 weeks following the latter TAC challenge. Cellular physiological, optical action potential and Ca2+ transient, measurements, demonstrated increased incidences of triggered ventricular arrhythmias, and prolonged action potential durations (APD) and altered Ca2+ transients with increases in their beat‐to beat variations, in Pak2cko hearts. Electron microscopic, proteomic, and molecular biological methods revealed a mitochondrial localization of stress‐related proteins on proteomic and phosphoproteomic analyses, particularly in TAC stressed Pak2cko mice. They further yielded accompanying evidence for mitochondrial oxidative stress, increased reactive oxygen species (ROS) biosynthesis, reduced mitochondrial complexes I‐V, diminished ATP synthesis and elevated NADPH oxidase 4 (NOX4) levels. Pak2 overexpression and the novel Pak2 activator JB2019A ameliorated these effects, enhanced cardiac function and decreased the frequencies of triggered ventricular arrhythmias. Pak2 activation thus protects against ventricular arrhythmia associated with cardiac stress and hypertrophy, through unique mechanisms offering potential novel therapeutic anti‐arrhythmic targets.

Ca2+/calmodulin‐dependent kinase II (CaMKII) activation is likely driven by oxidative stress, particularly excessive reactive oxygen species (ROS) production. This study identifies P21‐activated kinase 2 (Pak2) as a novel regulator of ROS‐induced CaMKII activation and abnormal Ca2⁺ dynamics in acute adrenergic and chronic pressure‐overload stressed hearts. Thus, Pak2's regulation of ROS production and Ca2⁺ homeostasis may represent a novel therapeutic target for alleviating cardiac ventricular arrhythmias associated with adrenergic stress and pathological hypertrophy.