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 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 Cavβ2 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 Cavα1.2 and the Akt-dependent phosphorylation status of Cavβ2 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 Cavβ2 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 Cavα1.2 retrograde trafficking and protein degradation through prevention of dynamin-mediated LTCC endocytosis; ii) promotion of Cavα1.2 anterograde trafficking by blocking Kir/Gem-dependent sequestration of Cavβ2, thus facilitating the chaperoning of Cavα1.2; and iii) promotion of Cavα1.2 transcription by prevention of Kir/Gem-mediated shuttling of Cavβ2 to the nucleus, where it limits the transcription of Cavα1.2 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 Cavβ2 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 Cavβ2 MP as a novel therapeutic tool for the improvement of cardiac conditions correlated with alterations in LTCC levels and function.
- drug therapy
- calcium modulator
- protein trafficking
- L-type calcium channels
- diabetic cardiomyopathy
- Received January 19, 2016.
- Revision received May 9, 2016.
- Accepted June 27, 2016.