Abstract
Growth-Associated Protein-43 (GAP-43) is a calmodulin-binding protein, originally found in neurons, that in skeletal muscle regulates the handling of intracellular Ca(2+) dynamics. According to its role in Ca(2+) regulation, myotubes from GAP-43 knockout (GAP-43(-/-)) mice display alterations in spontaneous Ca(2+) oscillations and increased Ca(2+) release. The emerging hypothesis is that GAP-43 regulates CaM interactions with RyR and DHPR Ca(2+) 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 Ca(2+) 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, Ca(2+) alterations, and high mitochondria ROS levels (O(2)(•-)) together with increased oxidized functional proteins. Treatment with a CaM inhibitor (W7) restored Ca(2+) and ROS alterations, possibly due to high mitochondrial Ca(2+) entry by a mitochondrial Ca(2+) uniporter. Indeed, Ru360 was able to abolish O(2)(•-) mitochondrial production. Our results suggest that GAP-43 has a key role in the regulation of Ca(2+) and ROS homeostasis, alterations to which could trigger heart disease.