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Wild-type and brachyolmia-causing mutant TRPV4 channels respond directly to stretch force.

ABSTRACT: Whether animal ion channels functioning as mechanosensors are directly activated by stretch force or indirectly by ligands produced by the stretch is a crucial question. TRPV4, a key molecular model, can be activated by hypotonicity, but the mechanism of activation is unclear. One model has this channel being activated by a downstream product of phospholipase A(2), relegating mechanosensitivity to the enzymes or their regulators. We expressed rat TRPV4 in Xenopus oocytes and repeatedly examined >200 excised patches bathed in a simple buffer. We found that TRPV4 can be activated by tens of mm Hg pipette suctions with open probability rising with suction even in the presence of relevant enzyme inhibitors. Mechanosensitivity of TRPV4 provides the simplest explanation of its various force-related physiological roles, one of which is in the sensing of weight load during bone development. Gain-of-function mutants cause heritable skeletal dysplasias in human. We therefore examined the brachyolmia-causing R616Q gain-of-function channel and found increased whole-cell current densities compared with wild-type channels. Single-channel analysis revealed that R616Q channels maintain mechanosensitivity but have greater constitutive activity and no change in unitary conductance or rectification.

SUBMITTER: Loukin S

PROVIDER: S-EPMC2930716 | biostudies-literature | 2010 Aug

REPOSITORIES: biostudies-literature

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Wild-type and brachyolmia-causing mutant TRPV4 channels respond directly to stretch force.

Loukin Stephen S Zhou Xinliang X Su Zhenwei Z Saimi Yoshiro Y Kung Ching C

The Journal of biological chemistry 20100706 35

Whether animal ion channels functioning as mechanosensors are directly activated by stretch force or indirectly by ligands produced by the stretch is a crucial question. TRPV4, a key molecular model, can be activated by hypotonicity, but the mechanism of activation is unclear. One model has this channel being activated by a downstream product of phospholipase A(2), relegating mechanosensitivity to the enzymes or their regulators. We expressed rat TRPV4 in Xenopus oocytes and repeatedly examined ...[more]

PMID: 20605796

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Project description:Background: Dysregulation of TRPV4-mediated signaling has been associated with inflammation and tissue fibrosis, both of which are key features in the pathophysiology of lymphatic system diseases; however, the expression and functional roles of lymphatic TRPV4 channels remain largely unexplored. Methods: We generated a single-cell RNA sequencing dataset from microdissected mouse collecting lymphatic vessels to characterize the expression of Trpv4. Using a novel Trpv4fx/fx mouse strain and the Cre-lines Prox1-CreERT2 and LysM-Cre we assessed the role of TRPV4 channels in lymphatic endothelial cells (LECs) and peri-lymphatic myeloid cells, respectively. Confocal microscopy and extensive functional experimentation on isolated and pressurized lymphatics, including measurements of intracellular calcium activity, were employed to validate our scRNAseq findings and to elucidate the underlying mechanisms. Clinical significance was assessed using biopsies from breast cancer-related lymphedema (BCRL) patients. Results: We characterized the single-cell transcriptome of collecting lymphatic vessels and surrounding tissues. Trpv4 was highly enriched in LECs and in a subset of Lyve1+ macrophages displaying a tissue-resident profile. In clinical samples, BCRL was associated with increased infiltration of macrophages co-expressing LYVE1 and TRPV4. Pharmacological activation of TRPV4 channels led to contractile dysregulation in isolated collecting lymphatics. The response was multi-phasic, including initial vasospasm and subsequent vasodilation and inhibition of contractions, which was associated with the activation of thromboxane A2 receptors (TXA2Rs) in lymphatic muscle cells (LMCs) by secreted prostanoids from TRPV4+ myeloid cells, and increased nitric oxide (and perhaps other vasodilatory prostanoids) from LECs. The TXA2R-mediated vasospasm resulted from increased mobilization of calcium from intracellular stores through IP3 receptors and store-operated calcium entry. Conclusions: Our results uncovered a novel mechanism of lymphatic contractile dysregulation mediated by the crosstalk between TRPV4-expressing myeloid cells, including LYVE1+ macrophages, and LMCs or LECs. These findings highlight potentially important roles of TRPV4 channels in lymphatic dysfunction associated with inflammation, including secondary lymphedema.

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Wild-type and brachyolmia-causing mutant TRPV4 channels respond directly to stretch force.

Publications

Wild-type and brachyolmia-causing mutant TRPV4 channels respond directly to stretch force.

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