Ion channels as convergence points in the pathology of pulmonary arterial hypertension.
Biochemical Society transactions 49:4 (2021) 1855-1865
Abstract:Pulmonary arterial hypertension (PAH) is a fatal disease of the cardiopulmonary system that lacks curative treatments. The main pathological event in PAH is elevated vascular resistance in the pulmonary circulation, caused by abnormal vasoconstriction and vascular remodelling. Ion channels are key determinants of vascular smooth muscle tone and homeostasis, and four PAH channelopathies (KCNK3, ABCC8, KCNA5, TRPC6) have been identified so far. However, the contribution of ion channels in other forms of PAH, which account for the majority of PAH patients, has been less well characterised. Here we reason that a variety of triggers of PAH (e.g. BMPR2 mutations, hypoxia, anorectic drugs) that impact channel function may contribute to the onset of the disease. We review the molecular mechanisms by which these 'extrinsic' factors converge on ion channels and provoke their dysregulation to promote the development of PAH. Ion channels of the pulmonary vasculature are therefore promising therapeutic targets because of the modulation they provide to both vasomotor tone and proliferation of arterial smooth muscle cells.
Water Nanoconfined in a Hydrophobic Pore: MD Simulations and Water Models
Abstract:Water molecules within biological ion channels are in a nano-confined environment and therefore exhibit novel behaviours which differ from that of bulk water. Here, we investigate the phenomenon of hydrophobic gating, the process by which a nanopore may spontaneously de-wet to form a ‘vapour lock’ if the pore is sufficiently hydrophobic and/or narrow. Notably, this occurs without steric occlusion of the pore. Using molecular dynamics simulations with both additive and polarisable (AMOEBA) force fields, we investigate this wetting/de-wetting behaviour in the TMEM175 ion channel. We examine how a range of rigid fixed-charge (i.e. additive) and polarisable water models affect wetting/de-wetting in both the wild-type structure and in mutants chosen to cover a range of nanopore radii and pore-lining hydrophobicities. Crucially, we find that the rigid fixed-charge water models lead to similar wetting/de-wetting behaviours, but that the polarisable water model resulted in an increased wettability of the hydrophobic gating region of the pore. This has significant implications for molecular simulations of nano-confined water, as it implies that polarisability may need to be included if we are to gain detailed mechanistic insights into wetting/de-wetting processes. These findings are of importance for the design of functionalised biomimetic nanopores (for e.g. sensing or desalination), as well as for furthering our understanding of the mechanistic processes underlying biological ion channel function.
Effects of Ionic Strength on Gating and Permeation of TREK-2 K2P channels
Abstract:In addition to the classical voltage-dependent behavior mediated by voltage-sensing-domains (VSD), a growing number of voltage-dependent gating behaviors are being described in ion channels that lack canonical VSDs. A common thread in their mechanism of action is the contribution of the permeating ion to this voltage sensing process. The polymodal K2P K + channel TREK2 responds to membrane voltage through a gating process that is mediated by the interaction of K + with its selectivity filter. Recently, we have found that this action can be modulated by small molecule agonists (e.g. BL1249) which appear to have an electrostatic influence on K + binding within the inner cavity and produce an increase in the single-channel conductance of TREK-2 channels. Here, we directly probed this K + -dependent gating process by recording both macroscopic and single-channel currents of TREK-2 in the presence of high concentrations of internal K + . Surprisingly we found that the channel is inhibited by high internal K + concentrations and that this is mediated by the concomitant increase in ionic-strength. However, we were still able to determine that the increase in single channel conductance in the presence of BL1249 was blunted in high ionic-strength, whilst its activatory effect (on channel open probability) persisted. These effects are consistent with an electrostatic mechanism of action of negatively charged activators such as BL1249 on permeation, but also suggest that their influence on channel gating is more complex.
KCNK18 biallelic variants associated with intellectual disability and neurodevelopmental disorders alter TRESK channel activity
International Journal of Molecular Sciences MDPI 22:11 (2021) 6064
Abstract:The TWIK-related spinal cord potassium channel (TRESK) is encoded by KCNK18, and variants in this gene have previously been associated with susceptibility to familial migraine with aura (MIM #613656). A single amino acid substitution in the same protein, p.Trp101Arg, has also been associated with intellectual disability (ID), opening the possibility that variants in this gene might be involved in different disorders. Here, we report the identification of KCNK18 biallelic missense variants (p.Tyr163Asp and p.Ser252Leu) in a family characterized by three siblings affected by mild-to-moderate ID, autism spectrum disorder (ASD) and other neurodevelopment-related features. Functional characterization of the variants alone or in combination showed impaired channel activity. Interestingly, Ser252 is an important regulatory site of TRESK, suggesting that alteration of this residue could lead to additive downstream effects. The functional relevance of these mutations and the observed co-segregation in all the affected members of the family expand the clinical variability associated with altered TRESK function and provide further insight into the relationship between altered function of this ion channel and human disease.
Kcnj16 (Kir5.1) gene ablation causes subfertility and increases the prevalence of morphologically abnormal spermatozoa
International Journal of Molecular Sciences MDPI 22:11 (2021) 5972