Peptidomimetic Targeting of Cavβ2 Overcomes Dysregulation of the L-Type Calcium Channel Density and Recovers Cardiac Function

BACKGROUND: L-type calcium channels (LTCCs) play important roles in regulating cardiomyocyte physiology, which is governed by appropriate LTCC trafficking to and density at the cell surface. Factors influencing the expression, half-life, subcellular trafficking, and gating of LTCCs are therefore critically involved in conditions of cardiac physiology and disease. METHODS: Yeast 2-hybrid screenings, biochemical and molecular evaluations, protein interaction assays, fluorescence microscopy, structural molecular modeling, and functional studies were used to investigate the molecular mechanisms through which the LTCC Ca-v beta 2 chaperone regulates channel density at the plasma membrane. RESULTS: On the basis of our previous results, we found a direct linear correlation between the total amount of the LTCC pore-forming Ca-v alpha 1.2 and the Akt-dependent phosphorylation status of Ca-v beta 2 both in a mouse model of diabetic cardiac disease and in 6 diabetic and 7 nondiabetic cardiomyopathy patients with aortic stenosis undergoing aortic valve replacement. Mechanistically, we demonstrate that a conformational change in Ca-v beta 2 triggered by Akt phosphorylation increases LTCC density at the cardiac plasma membrane, and thus the inward calcium current, through a complex pathway involving reduction of Ca-v alpha 1.2 retrograde trafficking and protein degradation through the prevention of dynaminmediated LTCC endocytosis; promotion of Ca-v alpha 1.2 anterograde trafficking by blocking Kir/ Gem-dependent sequestration of Ca-v beta 2, thus facilitating the chaperoning of Ca-v alpha 1.2; and promotion of Ca-v alpha 1.2 transcription by the prevention of Kir/Gem-mediated shuttling of Ca-v beta 2 to the nucleus, where it limits the transcription of Ca-v alpha 1.2 through recruitment of the heterochromatin protein 1. epigenetic repressor to the Cacna1c promoter. On the basis of this mechanism, we developed a novel mimetic peptide that, through targeting of Ca-v beta 2, corrects LTCC lifecycle alterations, facilitating the proper function of cardiac cells. Delivery of mimetic peptide into a mouse model of diabetic cardiac disease associated with LTCC abnormalities restored impaired calcium balance and recovered cardiac function. CONCLUSIONS: We have uncovered novel mechanisms modulating LTCC trafficking and life cycle and provide proof of concept for the use of Ca-v beta 2 mimetic peptide as a novel therapeutic tool for the improvement of cardiac conditions correlated with alterations in LTCC levels and function.