Annexin A4 Deficient Ventricular Myocytes Display Advanced Hypertrophy and Electrical Remodeling With Chronic β-Adrenoceptor Stimulation.

Annexin A4 (A4) is a negative modulator of adenylyl cyclase type 5 (AC5) with increased expression in failing human hearts. Here, we investigated whether A4 deficiency contributes to cardiac electrical and structural remodeling induced by chronic stimulation of β-adrenergic receptors (βAR). A4-deficient mice (gene trapped, GT) and wild-type (WT) were infused for 7 days with isoprenaline (ISO) or NaCl as control. Myocytes of ISO-treated GT (GTISO) displayed more hypertrophy, increased action potential duration, reduced K+-current Ito, preserved L-type Ca2+ current ICaL with a negative shift of voltage dependence of activation, in line with increased AC/cAMP/PKA signaling, and increased NCX1 versus WTISO. At the molecular level, mRNA levels for Kcnd3, Kcnip2, Cacna1c decreased at unchanged protein levels of Kv4.2, Kv4.3, KChIP2, α1C, independent of genotype, suggesting posttranslational modifications of the channels underlying Ito and ICaL. Chronic ISO-induced βAR desensitization and redox stress were confirmed by decreased cAMP production and lower mRNA levels of Adrb1, Adcy5/6, and Sod2, and reduced response to acute ISO, with no additional genotype-dependent effects on calcium handling or contractility. Nevertheless, GTISO cardiomyocytes retained a greater cAMP response to acute ISO, in line with AC5 disinhibition and preserved β2AR and Gαs/i, suggesting genotype-dependent differences in β-adrenergic signaling under stress. mRNA levels of Anxa4 were increased in hypertrophied WTISO vs. normal WTNaCl hearts, supporting a protective role for A4. Overall, the advanced remodeling in A4-deficient myocytes detected in response to chronic βAR stimulation proposes using A4 peptide as a therapeutic tool to prevent the progression of cardiac electrical remodeling.