Spastin-mediated severing of glutamylated microtubules controls cardiomyocyte coupling.

Cardiac ischemia-reperfusion injury frequently induces malignant arrhythmias because of connexin 43 (Cx43) mislocalization and impaired cardiomyocyte coupling; yet, effective therapies targeting this mechanism remain scarce. Here we show that ischemic cardiomyopathy in humans and ischemia-reperfusion in mice promote the accumulation and stabilization of glutamylated microtubules, disrupting targeted Cx43 trafficking. This remodeling of the glutamylated microtubule network is mediated by the microtubule-severing enzyme spastin. Spastin overexpression in cardiomyocytes reduced microtubule density, whereas its deficiency caused accumulation of glutamylated, stabilized microtubules. Although cardiomyocyte-specific spastin knockout mice displayed normal cardiac structure and function at baseline, they were highly susceptible to stress-induced malignant arrhythmias. Mechanistically, spastin deficiency impaired microtubule plus end dynamics and Cx43 transport. Notably, genetic or pharmacological reduction of microtubule glutamylation before ischemia-reperfusion preserved Cx43 localization and mitigated oxidative stress-induced injury. Together, these findings identify microtubule glutamylation as a key regulator of cardiac electrical stability and a promising therapeutic target in ischemia-reperfusion injury.