Protective mitochondrial fission induced by stress-responsive protein GJA1-20k.

Daisuke Shimura,Junco S Warren,Shaohua Xiao,Joseph A Palatinus,Jared Rutter,Esther Nuebel,Robin M Shaw,Rachel Baum,Steven E Valdez,TingTing Hong

doi:10.7554/elife.69207

Abstract

The Connexin43 gap junction gene GJA1 has one coding exon, but its mRNA undergoes internal translation to generate N-terminal truncated isoforms of Connexin43 with the predominant isoform being only 20 kDa in size (GJA1-20k). Endogenous GJA1-20k protein is not membrane bound and has been found to increase in response to ischemic stress, localize to mitochondria, and mimic ischemic preconditioning protection in the heart. However, it is not known how GJA1-20k benefits mitochondria to provide this protection. Here, using human cells and mice, we identify that GJA1-20k polymerizes actin around mitochondria which induces focal constriction sites. Mitochondrial fission events occur within about 45 s of GJA1-20k recruitment of actin. Interestingly, GJA1-20k mediated fission is independent of canonical Dynamin-Related Protein 1 (DRP1). We find that GJA1-20k-induced smaller mitochondria have decreased reactive oxygen species (ROS) generation and, in hearts, provide potent protection against ischemia-reperfusion injury. The results indicate that stress responsive internally translated GJA1-20k stabilizes polymerized actin filaments to stimulate non-canonical mitochondrial fission which limits ischemic-reperfusion induced myocardial infarction.

Highlights

Ischemia-Reperfusion (I/R) injury is known to induce excessive reactive oxygen species (ROS) in mitochondria, which results in cellular dysfunction and organ damage
Mitochondrial size after GJA1 knock-down can be rescued by siRNA resistant
These data suggest that the short GJA1-20k isoform, but not full-length Cx43, reduces mitochondrial size

Summary

Introduction

Ischemia-Reperfusion (I/R) injury is known to induce excessive reactive oxygen species (ROS) in mitochondria, which results in cellular dysfunction and organ damage. The phenomenon of ischemic preconditioning, first described thirty-five years ago (Murry et al., 1986), is a potent yet ironic protection of organs from ischemia-induced damage achieved by preceding the full ischemic insult with shorter bouts of ischemia. Related to preconditioning is the perplexing dynamic regulation of mitochondria itself Mitochondria undergo both fission and fusion in an adaptive equilibrium which directly affects cellular activity and response to stress s(Friedman and Nunnari, 2014, Youle and van der Bliek, 2012). It is not clear if an overall shift to fission or fusion is sufficient to define mitochondrial fidelity, or whether a change in the fission-fusion equilibrium occurs secondary to multiple distinct pathways which could be either beneficial or harmful, depending on the pathway taken

Methods

Results

Conclusion