TRPV4 Antagonism Prevents Mechanically Induced Myotonia

Abstract

Objective Myotonia is caused by involuntary firing of skeletal muscle action potentials and causes debilitating stiffness. Current treatments are insufficiently efficacious and associated with side effects. Myotonia can be triggered by voluntary movement (electrically induced myotonia) or percussion (mechanically induced myotonia). Whether distinct molecular mechanisms underlie these triggers is unknown. Our goal was to identify ion channels involved in mechanically induced myotonia and to evaluate block of the channels involved as a novel approach to therapy. Methods We developed a novel system to enable study of mechanically induced myotonia using both genetic and pharmacologic mouse models of myotonia congenita. We extended ex vivo studies of excitability to in vivo studies of muscle stiffness. Results As previous work suggests activation of transient receptor potential vanilloid 4 (TRPV4) channels by mechanical stimuli in muscle, we examined the role of this cation channel. Mechanically induced myotonia was markedly suppressed in TRPV4‐null muscles and in muscles treated with TRPV4 small molecule antagonists. The suppression of mechanically induced myotonia occurred without altering intrinsic muscle excitability, such that myotonia triggered by firing of action potentials (electrically induced myotonia) was unaffected. When injected intraperitoneally, TRPV4 antagonists lessened the severity of myotonia in vivo by approximately 80%. Interpretation These data demonstrate that there are distinct molecular mechanisms triggering electrically induced and mechanically induced myotonia. Our data indicates that activation of TRPV4 during muscle contraction plays an important role in triggering myotonia in vivo. Elimination of mechanically induced myotonia by TRPV4 inhibition offers a new approach to treating myotonia. ANN NEUROL 2020;88:297–308.

Multiubiquitination of TRPV4 reduces channel activity independent of surface localization

“…A second TRPV4 KO mouse line ( Fig. S1 B ) was generated by the Jackson Laboratory and previously characterized by our laboratory ( 42 ).…”

“…To determine whether endogenous TRPV4 protein is ubiquitinated in cells and whole tissue, we assessed an immortalized rat sensory neuron cell line (50B11 cells), the Madin-Darby canine kidney (MDCK) epithelial cell line, and mouse choroid plexus tissue; all of which express robust levels of TRPV4 (32,38,39). To immunopurify endogenous TRPV4, we used an anti-TRPV4 antibody that detects TRPV4 protein in cultured primary choroid plexus epithelial cells (40), kidney, and choroid plexus derived from wild type (WT), but not Trpv4 null mice (40)(41)(42) (Supplementary Fig 1A-B). Using this antibody, we achieved robust TRPV4 immunoprecipitation with little background compare to whole cell lysate inputs (Supplementary Fig.…”

Ion Channel Gene Mutations Causing Skeletal Muscle Disorders: Pathomechanisms and Opportunities for Therapy

“…Besides peripheral neuropathies, a very recent study elegantly showed that skeletal muscle TRPV4 channels are involved in mechanically induced myotonia because the latter is inhibited by TRPV4 inhibitors or missing in muscles of TRPV4 −/− mice [ 157 ]. The authors proposed that mechanical stimulation of muscle fibers induces the opening of TRPV4 channels, leading to sarcolemma depolarization that is normally dampened by ClC-1 chloride currents.…”

“…The authors proposed that mechanical stimulation of muscle fibers induces the opening of TRPV4 channels, leading to sarcolemma depolarization that is normally dampened by ClC-1 chloride currents. In myotonic muscles, the defective ClC-1 chloride channel cannot counteract the TRPV4-induced depolarization that, in turn, triggers hyperexcitability [ 157 ].…”

The mechanism underlying transient weakness in myotonia congenita

“…Based on studies of sustained depolarizations (sometimes termed plateau potentials) in neurons, a family of ion channels that might contribute is the transient receptor potential (TRP) ion channel family (Yan et al, 2009;Phelan et al, 2012). Members of the TRP ion channel family are expressed in skeletal muscle (Brinkmeier, 2011;Gailly, 2012), and we recently found that activation of TRPV4 plays a role in triggering percussion myotonia (Dupont et al, 2020).…”