Auxiliary trafficking subunit GJA1-20k protects Connexin43 from degradation and limits ventricular arrhythmias.

Connexin 43 (Cx43) gap junctions provide intercellular coupling which ensures rapid action potential propagation and synchronized heart contraction. Altered Cx43 localization and reduced gap junction coupling occur in failing hearts, contributing to ventricular arrhythmias and sudden cardiac death. Recent reports have found that an internally translated Cx43 isoform, GJA1-20k, is an auxiliary subunit for the trafficking of Cx43 in heterologous expression systems. Here, we have created a mouse model by using CRISPR technology to mutate a single internal translation initiation site in Cx43 (M213L mutation), which generates full length Cx43 but not GJA1-20k. We find that GJA1M213L/M213L mice have severely abnormal electrocardiograms despite preserved contractile function, reduced total Cx43, reduced gap junctions, and die suddenly at two to four weeks of age. Heterozygous GJA1M213L/WT mice survive to adulthood with increased ventricular ectopy. Biochemical experiments indicate that cytoplasmic Cx43 has a half life that is 50% shorter than membrane associated Cx43. Without GJA1-20k, poorly trafficked Cx43 is degraded. The data support that GJA1-20k, an endogenous entity translated independently of Cx43, is critical for Cx43 gap junction trafficking, maintenance of Cx43 protein, and normal electrical function of the mammalian heart.