Desmin intermediate filaments and tubulin detyrosination stabilize growing microtubules in the cardiomyocyte
In heart failure, an increased abundance of post-translationally detyrosinated microtubules stiffens the cardiomyocyte and impedes its contractile function. Detyrosination promotes interactions between microtubules, desmin intermediate filaments and the sarcomere to increase cytoskeletal stiffness, yet the mechanism by which this occurs is unknown. We hypothesized that detyrosination may regulate the growth and shrinkage of dynamic microtubules to facilitate interactions with desmin and the sarcomere. Through a combination of biochemical assays and direct observation of growing microtubule plus-ends in adult cardiomyocytes, we find that desmin is required to stabilize growing microtubules at the sarcomere Z-disk, where desmin also rescue shrinking microtubules from continued depolymerization. Further, reducing detyrosination (tyrosination) promotes frequent depolymerization and inefficient growth of microtubules. This is concomitant with tyrosination promoting the interaction of microtubules with the depolymerizing protein complex of end-binding protein 1 (EB1) and CAP-Gly domain containing linker protein 1 (CLIP1/CLIP170). The futile growth of tyrosinated microtubules reduces their opportunity for stabilizing interactions at the Z-disk, coincident with tyrosination globally reducing microtubule lifetimes and stability. These data provide a model for how intermediate filaments and tubulin detyrosination establish long-lived and physically reinforced microtubules in the cardiomyocyte, and inform on the mechanism of action for therapies that target microtubules for the treatment of cardiac disease.