First recognized more than 30 years ago, glycine protects cells against rupture from diverse types of injury. This robust and widely observed effect has been speculated to target a late downstream process common to multiple modes of tissue injury. The molecular target of glycine that mediates cytoprotection, however, remains elusive. Here, we show that glycine works at the level of NINJ1, a newly identified executioner of plasma membrane rupture in pyroptosis, necrosis, and post-apoptosis lysis. NINJ1 is thought to cluster within the plasma membrane to cause cell rupture. We demonstrate that the execution of pyroptotic cell rupture is similar for human and mouse NINJ1, and that NINJ1 knockout functionally and morphologically phenocopies glycine cytoprotection in macrophages undergoing lytic cell death. Next, we show that glycine prevents NINJ1 clustering by either direct or indirect mechanisms. In pyroptosis, glycine preserves cellular integrity but does not affect upstream inflammasome activities or accompanying energetic cell death. By positioning NINJ1 clustering as a glycine target, our data resolve a long-standing mechanism for glycine-mediated cytoprotection. This new understanding will inform the development of cell preservation strategies to counter pathologic lytic cell death.
Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice, with a prevalence that increases alongside the ageing population worldwide. The management of AF involves restoration of sinus rhythm through antiarrhythmic drug therapy. Yet, these medications have only modest efficacy in achieving long-term success, have not shown to result in a mortality benefit, are frequently not tolerated and have associated adverse side effects. Therefore, catheter ablation has become a valuable treatment approach for AF and even a viable first-line strategy in select cases. Traditionally, the combination of radiofrequency energy and a three-dimensional electroanatomical mapping system has been used to guide catheter ablation for AF. However, single-procedural efficacy and long-term outcomes still remain suboptimal for many patients, particularly those with persistent or long-standing AF. Recent advances in ablation technology and strategy, therefore, provide new procedural approaches for catheter-based treatment with the aim of overcoming current challenges in procedural duration and overall success. The aim of this paper was to provide an updated review of the current practices and techniques relating to ablation for AF and to compare the use of these strategies for paroxysmal and persistent AF.
Chronic pain has been widely recognized as a major public health problem that impacts multiple aspects of patient quality of life. Unfortunately, chronic pain is often resistant to conventional analgesics, which are further limited by their various side effects. New therapeutic strategies and targets are needed to better serve the millions of people suffering from this devastating disease. To this end, recent clinical and preclinical studies have implicated the epidermal growth factor receptor signaling pathway in chronic pain states. EGFR is one of four members of the ErbB family of receptor tyrosine kinases that have key roles in development and the progression of many cancers. EGFR functions by activating many intracellular signaling pathways following binding of various ligands to the receptor. Several of these signaling pathways, such as phosphatidylinositol 3-kinase, are known mediators of pain. EGFR inhibitors are known for their use as cancer therapeutics but given recent evidence in pilot clinical and preclinical investigations, may have clinical use for treating chronic pain. Here, we review the clinical and preclinical evidence implicating EGFR in pathological pain states and provide an overview of EGFR signaling highlighting how EGFR and its ligands drive pain hypersensitivity and interact with important pain pathways such as the opioid system.
The epidermal growth factor receptor (EGFR) is a central regulator of cell physiology. EGFR is activated by ligand binding, triggering receptor dimerization, activation of kinase activity, and intracellular signaling. EGFR is transiently confined within various plasma membrane nanodomains, yet how this may contribute to regulation of EGFR ligand binding is poorly understood. To resolve how EGFR nanoscale compartmentalization gates ligand binding, we developed single-particle tracking methods to track the mobility of ligand-bound and total EGFR, in combination with modeling of EGFR ligand binding. In comparison to unliganded EGFR, ligand-bound EGFR is more confined and distinctly regulated by clathrin and tetraspanin nanodomains. Ligand binding to unliganded EGFR occurs preferentially in tetraspanin nanodomains, and disruption of tetraspanin nanodomains impairs EGFR ligand binding and alters the conformation of the receptor’s ectodomain. We thus reveal a mechanism by which EGFR confinement within tetraspanin nanodomains regulates receptor signaling at the level of ligand binding.
First recognized more than 30 years ago, glycine is known to protect cells against plasma membrane rupture from diverse types of tissue injury. This robust and widely observed effect has been speculated to target a late downstream process common to multiple modes of tissue injury. The molecular target and mechanism of glycine cytoprotection, however, remain entirely elusive. We hypothesized that glycine targets ninjurin-1 (NINJ1), a newly identified executioner of plasma membrane rupture in pyroptosis, necrosis, and apoptotic cell death. This common terminal effector is thought to cluster within the plasma membrane to cause cell rupture. Here, we first demonstrate that NINJ1 knockout functionally and morphologically phenocopies glycine cytoprotection in macrophages stimulated to undergo lytic cell death. Glycine treatment in NINJ1 knockout cells provides no additional protective effect. Next, we show that glycine treatment prevents NINJ1 clustering within the plasma membrane thereby preserving its integrity. By identifying NINJ1 as a glycine target, our data help resolve the long-standing mechanism of glycine cytoprotection. This new understanding will inform the development of cell and tissue preservation strategies for pathologic conditions associated with lytic cell death pathways.Graphical abstract
The membrane proteins Ninjurin1 (NINJ1) and Ninjurin2 (NINJ2) are upregulated by nerve injury to increase cell adhesion and promote axonal growth in neurons. NINJ1, but not NINJ2, has also been shown to play an essential role in pyroptosis by promoting plasma membrane rupture downstream of gasdermin D (GSDMD) pore formation, as well as in lytic cell death mediated by other pathways. Recombinant NINJ1 and NINJ2 purified in detergent show irregular rings of various diameters as well as curved filaments. While NINJ1 and NINJ2 both formed ring-like structures when mixed with liposomes, strikingly, only NINJ1, but not NINJ2, ruptures liposome membranes, leading to their dissolution. Because of the better feasibility, we determined the cryo-EM structure of NINJ1 ring segments from detergent by segmenting the irregular rings into shorter fragments. Each NINJ1 subunit contains a transmembrane (TM) helical hairpin (⍺3 and ⍺4) that likely mediates NINJ1 membrane localization, as well as the side-by-side interaction between adjacent subunits. There are two extracellular domain amphipathic helices (⍺1 and ⍺2), among which ⍺1 crosses over to the neighboring subunit at the outside facing surface of the ring, to link NINJ1 subunits together into chains. As such, the inner face of the rings is hydrophobic whereas the outer face of the rings is hydrophilic and should repel membranes. Live cell imaging of NINJ1-deficient THP-1 cells reconstituted with NINJ1-eGFP uncovers the pinching off of NINJ1 rings from the cell surface and the loss of NINJ1 to the culture supernatant in oligomerized forms upon inflammasome activation. Formation of rings is also confirmed by super-resolution imaging of endogenous NINJ1 using anti-NINJ1 antibody. These data suggest that membrane insertion of amphipathic helices and formation of rings with a hydrophilic outer surface underlie the mechanism for NINJ1 to pinch off membranes as if it were a nanodisc-forming amphipathic polymer, leading to membrane rupture and lysis during cell death.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.