Mechanisms of enhancing skeletal muscle EC coupling by ERC1

Skeletal muscle excitation-contraction (EC) coupling is a fundamental process in muscle physiology, in which an electrical signal, the action potential in the motor neuron, is converted into a mechanical response, muscle contraction. Protein complexes called voltage-gated calcium channels, consisting of the pore-forming CaV1.1 and additional CaV auxiliary subunits, mediate this signal transduction process by sensing the electrical signal and physically activating the opening of calcium release channels (ryanodine receptors; RyR1) in an intracellular compartment, the sarcoplasmic reticulum. Skeletal muscle EC coupling was recently reconstituted in heterologous cell systems, defining the set of skeletal muscle specific proteins (CaV1.1, CaVß1a, STAC3 and RyR1 ) necessary for this process. However, this does not exclude the involvement of ubiquitous proteins in this process. Recently, ERC1, a scaffold protein which has been implicated in the assembly of neuronal synapses and in cell motility, was shown to associate to calcium channel complexes and boost calcium influx in different synapses. A ubiquitous isoform of ERC1 is also strongly expressed in skeletal muscle, but its function is elusive. Our unpublished results demonstrate that ERC1 expression in skeletal muscle myotubes increases CaV1.1 currents, and, most importantly, voltage- induced calcium release. In this research project, we will take advantage of a newly generated genetic muscle cell model (ERC1 KO) and a range of available and new molecular constructs to analyze the effects of ERC1 overexpression or deletion on CaV1.1 function and on EC coupling in skeletal muscle myotubes. Additionally, we aim to identify the minimal ERC1 fragment necessary to augment CaV1.1 currents and EC coupling, and to explore potential therapeutic strategies based on this novel EC coupling modulator.