Peptidomimetic Targeting of Ca v β2 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 an 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 two-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 β2 chaperone regulates channel density at the plasma membrane. Results —Based on our previous results, we found a direct linear correlation between the total amount of the LTCC pore-forming Ca v α1.2 and the Akt-dependent phosphorylation status of Ca v β2 both in a mouse model of diabetic cardiac disease and in 6 diabetic and 7 non-diabetic cardiomyopathy patients with aortic stenosis undergoing aortic valve replacement. Mechanistically, we demonstrate that a conformational change in Ca v β2 triggered by Akt phosphorylation increases LTCC density at the cardiac plasma membrane, and thus the inward calcium current, through a complex pathway involving: i) reduction of Ca v α1.2 retrograde trafficking and protein degradation through prevention of dynamin-mediated LTCC endocytosis; ii) promotion of Ca v α1.2 anterograde trafficking by blocking Kir/Gem-dependent sequestration of Ca v β2, thus facilitating the chaperoning of Ca v α1.2; and iii) promotion of Ca v α1.2 transcription by prevention of Kir/Gem-mediated shuttling of Ca v β2 to the nucleus, where it limits the transcription of Ca v α1.2 through recruitment of the HP1γ epigenetic repressor to the Cacna1c promoter. Based on this mechanism, we developed a novel mimetic peptide (MP) that through targeting of Ca v β2 corrects LTCC life cycle alterations, facilitating the proper function of cardiac cells. Delivery of MP into a mouse model of diabetic cardiac disease associated with LTCC abnormalities restored impaired calcium balance and recovered cardiac function. Conclusions —Here, we have uncovered novel mechanisms modulating LTCC trafficking and life cycle and provide proof-of-concept for the use of Ca v β2 MP as a novel therapeutic tool for the improvement of cardiac conditions correlated with alterations in LTCC levels and function.