Recent advances on the structure and the function relationships of the TRPV4 ion channel.

The members of the superfamily of Transient Receptor Potential (TRP) ion channels are physiologically important molecules that have been studied for many years and are still being intensively researched. Among the vanilloid TRP subfamily, the TRPV4 ion channel is an interesting protein due to its involvement in several essential physiological processes and in the development of various diseases. As in other proteins, changes in its function that lead to the development of pathological states, have been closely associated with modification of its regulation by different molecules, but also by the appearance of mutations which affect the structure and gating of the channel. In the last few years, some structures for the TRPV4 channel have been solved. Due to the importance of this protein in physiology, here we discuss the recent progress in determining the structure of the TRPV4 channel, which has been achieved in three species of animals (Xenopus tropicalis, Mus musculus, and Homo sapiens), highlighting conserved features as well as key differences among them and emphasizing the binding sites for some ligands that play crucial roles in its regulation.

Crucial role for Sodium Hydrogen Exchangers in SGLT2 inhibitor-induced arterial relaxations.

Introduction: Sodium dependent glucose transporter 2 (SGLT2 or SLC5A2) inhibitors effectively lower blood glucose and are also approved treatments for heart failure independent of raised glucose. One component of the cardioprotective effect is reduced cardiac afterload but the mechanisms underlying peripheral relaxation are ill defined and variable. We speculated that SGLT2 inhibitors promoted arterial relaxation via the release of the potent vasodilator calcitonin gene-related peptide (CGRP) from sensory nerves independent of glucose transport. Experimental approach: The functional effects of SGLT2 inhibitors (dapagliflozin, empagliflozin, ertugliflozin) and the sodium/hydrogen exchanger 1 (NHE1) blocker cariporide were determined on pre-contracted mesenteric and renal arteries from male Wistar rats using Wire-Myography. SGLT2, NHE1, CGRP and TRPV1 expression in both arteries was determined by Western blot and immunohistochemistry. Kv7.4/5/KCNE4 and TRPV1 currents were measured in the presence and absence of dapagliflozin and empagliflozin. Results: All SGLT2 inhibitors produced a concentration dependent relaxation (1µM-100µM) of mesenteric arteries that was considerably greater than in renal arteries. Cariporide relaxed mesenteric arteries but not renal arteries. Immunohistochemistry with TRPV1 and CGRP antibodies revealed a dense innervation of sensory nerves in mesenteric arteries that was absent in renal arteries. Consistent with a greater sensory nerve component, the TRPV1 agonist capsaicin produced significantly greater relaxations in mesenteric arteries compared to renal arteries. Relaxations to dapagliflozin, empagliflozin and cariporide were attenuated by incubation with the CGRP receptor antagonist BIBN-4096, the Kv7 blocker linopirdine and the TRPV1 antagonist AMG-517 as well as by depletion of neuronal CGRP. Neither dapagliflozin nor empagliflozin directly activated heterologously expressed TRPV1 channels or Kv7 channels. Strikingly, only NHE1 colocalised with TRPV1 in sensory nerves, and cariporide pre-application prevented the relaxant response to SGLT2 inhibitors. Conclusions: SGLT2 inhibitors relax mesenteric arteries by a novel mechanism involving the release of CGRP from sensory nerves following inhibition of the Na + /H + exchanger.

Modes of action of lysophospholipids as endogenous activators of the TRPV4 ion channel.

The Transient Receptor Potential Vanilloid 4 (TRPV4) channel has been shown to function in many physiological and pathophysiological processes. Despite abundant information on its importance in physiology, very few endogenous agonists for this channel have been described, and very few underlying mechanisms for its activation have been clarified. TRPV4 is expressed by several types of cells, such as vascular endothelial, and skin and lung epithelial cells, where it plays pivotal roles in their function. In the present study, we show that TRPV4 is activated by lysophosphatidic acid (LPA) in both endogenous and heterologous expression systems, pinpointing this molecule as one of the few known endogenous agonists for TRPV4. Importantly, LPA is a bioactive glycerophospholipid, relevant in several physiological conditions, including inflammation and vascular function, where TRPV4 has also been found to be essential. Here we also provide mechanistic details of the activation of TRPV4 by LPA and another glycerophospholipid, lysophosphatidylcholine (LPC), and show that LPA directly interacts with both the N- and C-terminal regions of TRPV4 to activate this channel. Moreover, we show that LPC activates TRPV4 by producing an open state with a different single-channel conductance to that observed with LPA. Our data suggest that the activation of TRPV4 can be finely tuned in response to different endogenous lipids, highlighting this phenomenon as a regulator of cell and organismal physiology. KEY POINTS: The Transient Receptor Potential Vaniloid (TRPV) 4 ion channel is a widely distributed protein with important roles in normal and disease physiology for which few endogenous ligands are known. TRPV4 is activated by a bioactive lipid, lysophosphatidic acid (LPA) 18:1, in a dose-dependent manner, in both a primary and a heterologous expression system. Activation of TRPV4 by LPA18:1 requires residues in the N- and C-termini of the ion channel. Single-channel recordings show that TRPV4 is activated with a decreased current amplitude (conductance) in the presence of lysophosphatidylcholine (LPC) 18:1, while LPA18:1 and GSK101 activate the channel with a larger single-channel amplitude. Distinct single-channel amplitudes produced by LPA18:1 and LPC18:1 could differentially modulate the responses of the cells expressing TRPV4 under different physiological conditions.

Unconventional interactions of the TRPV4 ion channel with beta-adrenergic receptor ligands.

The transient receptor potential vanilloid 4 (TRPV4) ion channel is present in different tissues including those of the airways. This channel is activated in response to stimuli such as changes in temperature, hypoosmotic conditions, mechanical stress, and chemicals from plants, lipids, and others. TRPV4's overactivity and/or dysfunction has been associated with several diseases, such as skeletal dysplasias, neuromuscular disorders, and lung pathologies such as asthma and cardiogenic lung edema and COVID-19-related respiratory malfunction. TRPV4 antagonists and blockers have been described; nonetheless, the mechanisms involved in achieving inhibition of the channel remain scarce, and the search for safe use of these molecules in humans continues. Here, we show that the widely used bronchodilator salbutamol and other ligands of ß-adrenergic receptors inhibit TRPV4's activation. We also demonstrate that inhibition of TRPV4 by salbutamol is achieved through interaction with two residues located in the outer region of the pore and that salbutamol leads to channel closing, consistent with an allosteric mechanism. Our study provides molecular insights into the mechanisms that regulate the activity of this physiopathologically important ion channel.

TRPV4: A Physio and Pathophysiologically Significant Ion Channel.

Transient Receptor Potential (TRP) channels are a family of ion channels whose members are distributed among all kinds of animals, from invertebrates to vertebrates. The importance of these molecules is exemplified by the variety of physiological roles they play. Perhaps, the most extensively studied member of this family is the TRPV1 ion channel; nonetheless, the activity of TRPV4 has been associated to several physio and pathophysiological processes, and its dysfunction can lead to severe consequences. Several lines of evidence derived from animal models and even clinical trials in humans highlight TRPV4 as a therapeutic target and as a protein that will receive even more attention in the near future, as will be reviewed here.

TRPV1: Structure, Endogenous Agonists, and Mechanisms.

The Transient Receptor Potential Vanilloid 1 (TRPV1) channel is a polymodal protein with functions widely linked to the generation of pain. Several agonists of exogenous and endogenous nature have been described for this ion channel. Nonetheless, detailed mechanisms and description of binding sites have been resolved only for a few endogenous agonists. This review focuses on summarizing discoveries made in this particular field of study and highlighting the fact that studying the molecular details of activation of the channel by different agonists can shed light on biophysical traits that had not been previously demonstrated.