Mice lacking growth-associated protein 43 develop cardiac remodeling and hypertrophy

Growth-associated protein 43 (GAP43) is found in skeletal muscle, localized near the calcium release units. In interaction with calmodulin (CaM), it indirectly modulates the activity of dihydropyridine and ryanodine Ca²⁺ channels. GAP43-CaM interaction plays a key role in intracellular Ca²⁺ homeostasis and, consequently, in skeletal muscle activity. The control of intracellular Ca²⁺ signaling is also an important functional requisite in cardiac physiology. The aim of this study is to define the impact of GAP43 on cardiac tissue at macroscopic and cellular levels, using GAP43 knockout (GAP43^-/-) newborn C57/BL6 mice. Hearts from newborn GAP43^-/- mice were heavier than hearts from wild-type (WT) ones. In these GAP43^-/- hearts, histological section analyses revealed a thicker ventricular wall and interventricular septum with a reduced ventricular chamber area. In addition, increased collagen deposits between fibers and increased expression levels of myosin were observed in hearts from GAP43^-/- mice. Cardiac tropism and rhythm are controlled by multiple intrinsic and extrinsic factors, including cellular events such those linked to intracellular Ca²⁺ dynamics, in which GAP43 plays a role. Our data revealed that, in the absence of GAP43, there were cardiac morphological alterations and signs of hypertrophy, suggesting that GAP43 could play a role in the functional processes of the whole cardiac muscle. This paves the way for further studies investigating GAP43 involvement in signaling dynamics at the cellular level.