Growth-Associated Protein-43 Loss Promotes Ca2+ and ROS Imbalance in Cardiomyocytes

Growth-Associated Protein-43 (GAP-43) is a calmodulin-binding protein, originally found in neurons, that in skeletal muscle regulates the handling of intracellular Ca²⁺ dynamics. According to its role in Ca²⁺ regulation, myotubes from GAP-43 knockout (GAP-43^-/-) mice display alterations in spontaneous Ca²⁺ oscillations and increased Ca²⁺ release. The emerging hypothesis is that GAP-43 regulates CaM interactions with RyR and DHPR Ca²⁺ channels. The loss of GAP-43 promotes cardiac hypertrophy in newborn GAP-43^-/- mice, extending the physiological role of GAP-43 in cardiac muscle. We investigated the role of GAP-43 in cardiomyocytes derived from the hearts of GAP-43^-/- mice, evaluating intracellular Ca²⁺ variations and the correlation with the levels of reactive oxygen species (ROS), considering their importance in cardiovascular physiology. In GAP-43^-/- cardiomyocytes, we found the increased expression of markers of cardiac hypertrophy, Ca²⁺ alterations, and high mitochondria ROS levels (O₂^•-) together with increased oxidized functional proteins. Treatment with a CaM inhibitor (W7) restored Ca²⁺ and ROS alterations, possibly due to high mitochondrial Ca²⁺ entry by a mitochondrial Ca²⁺ uniporter. Indeed, Ru360 was able to abolish O₂^•- mitochondrial production. Our results suggest that GAP-43 has a key role in the regulation of Ca²⁺ and ROS homeostasis, alterations to which could trigger heart disease.