EHD3-Dependent Endosome Pathway Regulates Cardiac Membrane Excitability and Physiology
Rationale: Cardiac function is dependent on the coordinate activities of membrane ion channels, transporters, pumps, and hormone receptors to dynamically tune the membrane electrochemical gradient in response to acute and chronic stress. While our knowledge of membrane proteins has rapidly advanced over the past decade, our understanding of the subcellular pathways governing the trafficking and localization of integral membrane proteins is limited, and essentially unstudied in vivo. In heart, to our knowledge, there are no in vivo mechanistic studies that directly link endosome-based machinery with cardiac physiology.
Objective: Define the in vivo roles of endosome-based cellular machinery for cardiac membrane protein trafficking, myocyte excitability, and cardiac physiology.
Methods and Results: We identify the endosome-based EHD3 pathway as essential for cardiac physiology. EHD3-/- hearts display structural and functional defects including bradycardia and rate variability, conduction block, and blunted response to adrenergic stimulation. Mechanistically, EHD3 is critical for membrane protein trafficking, as EHD3-/- myocytes display reduced expression/localization of Na/Ca exchanger and Cav1.2 with a parallel reduction in INCX and ICa,L. Functionally, EHD3-/- myocytes show increased sarcoplasmic reticulum [Ca], increased spark frequency, and reduced expression/localization of ankyrin-B, a binding partner for EHD3 and Na/Ca exchanger. Finally, we show that in vivo EHD3-/- defects are due to cardiac-specific roles of EHD3 as mice with cardiac-selective EHD3 deficiency demonstrate both structural and electrical phenotypes.
Conclusions: These data provide new insight into the critical role of endosome-based pathways in membrane protein targeting and cardiac physiology. EHD3 is a critical component of protein trafficking in heart and is essential for the proper membrane targeting of select cellular proteins that maintain excitability.
- Received April 7, 2014.
- Revision received April 20, 2014.
- Accepted April 23, 2014.