TRPV4 mutations and cytotoxic hypercalcemia in axonal Charcot-Marie-Tooth neuropathies

Department of Neurology and Division of Peripheral Nerve Diseases, Mayo Clinic Foundation, Rochester, MN 55905, USA.
Neurology (Impact Factor: 8.29). 02/2011; 76(10):887-94. DOI: 10.1212/WNL.0b013e31820f2de3
Source: PubMed


To improve understanding of TRPV4-associated axonal Charcot-Marie-Tooth (CMT) neuropathy phenotypes and their debated pathologic mechanism.
A total of 17 CMT2C phenotypic families with vocal cord and diaphragmatic involvement and 36 clinically undifferentiated CMT2 subjects underwent sequencing analysis of the coding region of TRPV4. Functional studies of mutant proteins were performed using transiently transfected cells for TRPV4 subcellular localization, basal and stimulated Ca(2+) channel analysis, and cell viability assay with or without channel blockade.
Two TRPV4 mutations R232C and R316H from 17 CMT2C families were identified in the ankyrin repeat domains. The R316H is a novel de novo mutation found in a patient with CMT2C phenotype. The family with R232C mutation had individuals with and without vocal cord and diaphragm involvement. Both mutant TRPV4 proteins had normal subcellular localization in HEK293 and HeLa cells. Cells transfected with R232C and R316H displayed increased intracellular Ca(2+) levels and reversible cell death by the TRPV channel antagonist, ruthenium red.
TRPV4 ankyrin domain alterations including a novel de novo mutation cause axonal CMT2. Individuals with the same mutation may have nondistinct CMT2 or have phenotypic CMT2C with vocal cord paresis. Reversible hypercalcemic gain-of-function of mutant TRPV4 instead of loss-of-function appears to be pathologically important. The reversibility of cell death by channel blockade provides an attractive area of investigation in consideration of treatable axonal degeneration.

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Available from: Teepu Siddique,
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    • "Pt, patient; M, male; F, female; UL, upper limb; LL, lower limb; DTR, deep tendon reflexes; VCP, vocal cord pralysis; Hgt, height in centiles; abn, abnormalities; þ, present; 0, absent; ND, child declined testing. the neurological phenotype are located in the N-terminal end of TRPV4 affecting just four residues of the ankyrin repeat domain (residues 232, 269, 315, and 316) [Auer-Grumbach et al., 2010; Chen et al., 2010; Deng et al., 2010; Landour e et al., 2010; Zimo n et al., 2010; Klein et al., 2011] (see Supporting Information eFig. 1—available online), while those underlying the skeletal dysplasia group span the gene including the ankyrin repeat domain but do not affect these 4 key residues [Dai et al., 2010]. "
    Neuromuscular Disorders 03/2011; 21. DOI:10.1016/S0960-8966(11)70059-1 · 2.64 Impact Factor
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    Neurology 02/2011; 76(10):856-7. DOI:10.1212/WNL.0b013e31820f2e9a · 8.29 Impact Factor
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    ABSTRACT: Mutations in TRPV4 have been linked to three distinct axonal neuropathies. However, the pathogenic mechanism underlying these disorders remains unclear. Both gain and loss of calcium channel activity of the mutant TRPV4 have been suggested. Here, we show that the three previously reported TRPV4 mutant channels have a physiological localization and display an increased calcium channel activity, leading to increased cytotoxicity in three different cell types. Patch clamp experiments showed that cells expressing mutant TRPV4 have much larger whole-cell currents than those expressing the wild-type TRPV4 channel. Single channel recordings showed that the mutant channels have higher open probability, due to a modification of gating, and no change in single-channel conductance. These data support the hypothesis that a "gain of function" mechanism, possibly leading to increased intracellular calcium influx, underlies the pathogenesis of the TRPV4-linked axonal neuropathies, and may have immediate implications for designing rational therapies.
    Journal of Biological Chemistry 03/2011; 286(19):17281-91. DOI:10.1074/jbc.M111.237685 · 4.57 Impact Factor
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