Ion Channel Dysregulation Following Intracerebral Hemorrhage

Injury to the brain after intracerebral hemorrhage (ICH) results from numerous complex cellular mechanisms. At present, effective therapy for ICH is limited and a better understanding of the mechanisms of brain injury is necessary to improve prognosis. There is increasing evidence that ion channel dysregulation occurs at multiple stages in primary and secondary brain injury following ICH. Ion channels such as TWIK-related K+ channel 1, sulfonylurea 1 transient receptor potential melastatin 4 and glutamate-gated channels affect ion homeostasis in ICH. They in turn participate in the formation of brain edema, disruption of the blood-brain barrier, and the generation of neurotoxicity. In this review, we summarize the interaction between ions and ion channels, the effects of ion channel dysregulation, and we discuss some therapeutics based on ion-channel modulation following ICH.

The P2X7 receptor in mood disorders: Emerging target in immunopsychiatry, from bench to bedside

Psychiatric disorders are among the most burdensome disorders worldwide. Though therapies have evolved over the last decades, treatment resistance still affects many patients. Recently, neuroimmune systems have been identified as important factors of mood disorder biology. The underlying dysregulation in neuroimmune cross-talk is driven by genetic risk factors and accumulating adverse environmental influences like chronic psychosocial stress. These result in a cluster of proinflammatory cytokines and quantitative and functional changes of immune cell populations (e.g., microglia, monocytes, T cells), varying by disease entity and state. Among the emerging immune targets, purinergic signalling revolving around the membranous and ATP specific P2X7 receptor (P2X7R) has gained wider attention and clinical studies making use of antagonistic drugs are on-going. Still, no clinically meaningful applications have been identified so far. A major problem is the often overly simplified approach taken to translate findings from bench to bedside. Therefore, the present review focuses on purinergic signalling via P2X7R in the context of recent advances in immunopsychiatric mood disorder research. Our aim is to provide an overview of the current P2X7R-related findings, from bench to bedside. First, we summarize the characteristics of purinergic signalling and P2X7R, followed by a depiction of genetic and clinical data connecting P2X7R to mood disorders. We close with our perspective on current developments and discuss changes necessary to translate the evident potential of P2X7R signalling modulation into meaningful clinical application. This article is part of the Special Issue on 'Purinergic Signaling: 50 years'.

Physiologic roles of P2 receptors in leukocytes

Since their discovery in the 1970s, purinergic receptors have been shown to play key roles in a wide variety of biologic systems and cell types. In the immune system, purinergic receptors participate in innate immunity and in the modulation of the adaptive immune response. In particular, P2 receptors, which respond to extracellular nucleotides, are widely expressed on leukocytes, causing the release of cytokines and chemokines and the formation of inflammatory mediators, and inducing phagocytosis, degranulation, and cell death. The activity of these receptors is regulated by ectonucleotidases-expressed in these same cell types-which regulate the availability of nucleotides in the extracellular environment. In this article, we review the characteristics of the main purinergic receptor subtypes present in the immune system, focusing on the P2 family. In addition, we describe the physiologic roles of the P2 receptors already identified in leukocytes and how they can positively or negatively modulate the development of infectious diseases, inflammation, and pain.

Using Symmetrical Organic Cation Solutions to Study P2X7 Ion Permeation

P2X7 receptors are ATP-gated ion channels permeable to metal cations, such as Na⁺, K⁺, and Ca²⁺. They also exhibit permeability to various large molecular weight species, reaching up to 900 Da, in a process known as macropore formation, which is a unique functional hallmark across the P2X family. While well-documented in a range of different cell types, the molecular mechanism underlying this phenomenon is poorly understood, and has been clouded through the use of electrophysiological methodology prone to artifacts as a result of significant changes in ionic concentrations in asymmetric conditions. In this chapter, we discuss the permeation properties of P2X7, the related methodological challenges and the use of symmetrical organic cation solutions as a useful technique for probing P2X7 permeation.

The P2X7 purinergic receptor: from physiology to neurological disorders

Purine nucleotides are well established as extracellular signaling molecules. P2X receptors are ATP-gated cation channels that mediate fast excitatory transmission in diverse regions of the brain and spinal cord. Several P2X receptor subtypes, including P2X(7), have the unusual property of changing their ion selectivity during prolonged exposure to ATP, which results in progressive dilation of the channel pore and the development of permeability to molecules as large as 900 Da. The P2X(7) receptor was originally described in cells of hematopoietic origin, including macrophages, microglia, and certain lymphocytes, and mediates the influx of Ca(2+) and Na(+) ions, as well as the release of proinflammatory cytokines. P2X(7) receptors may affect neuronal cell death through their ability to regulate the processing and release of interleukin-1beta, a key mediator in neurodegeneration, chronic inflammation, and chronic pain. Activation of P2X(7) receptors provides an inflammatory stimulus, and P2X(7) receptor-deficient mice have substantially attenuated inflammatory responses, including models of neuropathic and chronic inflammatory pain. Moreover, P2X(7) receptor activity, by regulating the release of proinflammatory cytokines, may be involved in the pathophysiology of depression. The P2X(7) receptor may thus represent a critical communication link between the nervous and immune systems, while providing a target for therapeutic exploitation. This review discusses the current biology and cellular signaling pathways of P2X(7) receptor function, as well as insights into the role for this receptor in neurological/psychiatric diseases, outstanding questions, and the therapeutic potential of P2X(7) receptor antagonism.