RIPK1 activation mediates neuroinflammation and disease progression in multiple sclerosis

Structure-based discovery of a 4,5-Dihydropyrazole-cored PET ligand for imaging of receptor-interacting serine/threonine-protein kinase 1 (RIPK1) in the brain

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) regulates programmed cell death and inflammation, contributing to a wide range of human pathologies, including inflammatory disorders, neurodegenerative conditions, and cancer. Despite this, no RIPK1 positron emission tomography (PET) ligand with significant in vivo specificity has been reported to date. In this work, we designed and synthesized a new family of dihydropyrazole-cored ligands suitable for 18F-labeling at the late stage. Among these, WL8 showed a strong binding affinity to RIPK1 (EC50 = 19.9 nM, Kd = 25 nM) and was successfully labeled with 18F in the 6-position of pyridine ring, yielding a high radiochemistry yield of 27.9 % (decay-corrected) and a high molar activity of 18.8-31.2 GBq/μmol. In in vitro autoradiography, [18F]WL8 showed some specific binding in the brain sections of rats and lipopolysaccharide (LPS) model mice. Preliminary PET studies in rat brains revealed that [18F]WL8 could efficiently penetrate the blood-brain barrier and was rapidly washed out. As anticipated, [18F]WL8 exhibited a high initial uptake (brain2min = 4.80 % ID/g) in mouse brains, followed by a rapid washout (brain60min = 0.14 % ID/g), although no clear specific binding to RIPK1 was observed. Moderate in vivo stability was noted for [18F]WL8 in mouse brains with 35.2 % of the parent fraction remaining after 30 min post-administration. Altogether, our work broadens the landscape and offers a new chemotype for RIPK1 PET ligand development.

Mechanisms of ozone-induced neurotoxicity in the development and progression of dementia: a brief review

Dementia encompasses a spectrum of neurodegenerative disorders significantly impacting global health, with environmental factors increasingly recognized as crucial in their etiology. Among these, ozone, has been identified as a potential exacerbator of neurodegenerative processes, particularly in Alzheimer's disease (AD). Ozone exposure induces the production of reactive oxygen species (ROS), which penetrate the BBB, leading to oxidative damage in neuronal cells. This oxidative stress is closely linked with mitochondrial dysfunction and lipid peroxidation, processes that are foundational to the pathology observed in dementia, such as neuronal death and protein aggregation. Furthermore, ozone triggers chronic neuroinflammation, exacerbating these neurodegenerative processes and perpetuating a cycle of CNS damage. Recent studies highlight the role of peripheral biomarkers like High Mobility Group Box 1 (HMGB1) and Triggering Receptor Expressed on Myeloid cells 2 (TREM2) in mediating ozone's effects. Disruption of these and other identified proteins by ozone exposure impairs microglial function and response to amyloid plaques, suggesting a novel pathway through which ozone may influence AD pathology via immune dysregulation. This review discusses the concept of a bidirectional lung-brain axis, illustrating that systemic responses to air pollutants like ozone may reflect and contribute to neurodegenerative processes in the CNS. By delineating these mechanisms, we emphasize the critical need for integrating environmental health management into strategies for the prevention and treatment of dementia.

Neurodegeneration and demyelination in multiple sclerosis

Progressive multiple sclerosis (PMS) is an immune-initiated neurodegenerative condition that lacks effective therapies. Although peripheral immune infiltration is a hallmark of relapsing-remitting MS (RRMS), PMS is associated with chronic, tissue-restricted inflammation and disease-associated reactive glial states. The effector functions of disease-associated microglia, astrocytes, and oligodendrocyte lineage cells are beginning to be defined, and recent studies have made significant progress in uncovering their pathologic implications. In this review, we discuss the immune-glia interactions that underlie demyelination, failed remyelination, and neurodegeneration with a focus on PMS. We highlight the common and divergent immune mechanisms by which glial cells acquire disease-associated phenotypes. Finally, we discuss recent advances that have revealed promising novel therapeutic targets for the treatment of PMS and other neurodegenerative diseases.

Preclinical Evaluation of Dihydropyrazole-Cored Positron Emission Tomography (PET) Ligands for Imaging of Receptor-Interacting Serine/Threonine Protein Kinase 1 (RIPK1) in the Brain

Receptor-interacting serine/threonine protein kinase 1 (RIPK1) has emerged as an important regulator of pathologic cell death and inflammation and is implicated in the pathologies of various central nervous system diseases. In this study, we reported the development of three potent dihydropyrazole-cored RIPK1 positron emission tomography (PET) ligands [18F]WL1-3. Among these, [18F]WL1 showed specific binding to RIPK1 in mouse brain sections in vitro through autoradiography and exhibited favorable brain kinetics in mice, characterized by a high initial uptake (brain2 min = 4.89% ID/g) and rapid washout (brain60 min = 0.21% ID/g). PET studies in rat brains revealed that [18F]WL1 could readily penetrate the brain with specific binding confirmed by inhibition effects of unlabeled WL1 and GSK'547. Notably, [18F]WL1 showed significant potential in imaging the alterations of RIPK1 in a rat brain of tumor necrosis factor α-induced systemic inflammatory response syndrome model. These findings may pave the way for the future design of potent RIPK1 PET ligands.

RIPK1 inhibition mitigates neuroinflammation and rescues depressive-like behaviors in a mouse model of LPS-induced depression

BACKGROUND

Depression is often linked to inflammation in the brain. Researchers have been exploring ways to reduce this inflammation to improve depression symptoms. One potential target is a protein called RIPK1, which is known to contribute to brain inflammation. However, it's unclear how RIPK1 influences depression. Our study aims to determine whether RIPK1 inhibition could alleviate neuroinflammation-associated depression and elucidate its underlying mechanisms.

METHODS

To investigate our research objectives, we established a neuroinflammation mouse model by administering LPS. Behavioral and biochemical assessments were conducted on these mice. The findings were subsequently validated through in vitro experiments.

RESULTS

Using LPS-induced depression models, we investigated RIPK1's role, observing depressive-like behaviors accompanied by elevated cytokines, IBA-1, GFAP levels, and increased inflammatory signaling molecules and NO/H2O2. Remarkably, Necrostatin (Nec-1 S), a RIPK1 inhibitor, mitigated these changes. We further found altered expression and phosphorylation of eIF4E, PI3K/AKT/mTOR, and synaptic proteins in hippocampal tissues, BV2, and N2a cells post-LPS treatment, which Nec-1 S also ameliorated. Importantly, eIF4E inhibition reversed some of the beneficial effects of Nec-1 S, suggesting a complex interaction between RIPK1 and eIF4E in LPS-induced neuroinflammation. Moreover, citronellol, a RIPK1 agonist, significantly altered eIF4E phosphorylation, indicating RIPK1's potential upstream regulatory role in eIF4E and its contribution to neuroinflammation-associated depression.

CONCLUSION

These findings propose RIPK1 as a pivotal mediator in regulating neuroinflammation and neural plasticity, highlighting its significance as a potential therapeutic target for depression.

The iron maiden: Oligodendroglial metabolic dysfunction in multiple sclerosis and mitochondrial signaling

Multiple sclerosis (MS) is an autoimmune disease, governed by oligodendrocyte (OL) dystrophy and central nervous system (CNS) demyelination manifesting variable neurological impairments. Mitochondrial mechanisms may drive myelin biogenesis maintaining the axo-glial unit according to dynamic requisite demands imposed by the axons they ensheath. The promotion of OL maturation and myelination by actively transporting thyroid hormone (TH) into the CNS and thereby facilitating key transcriptional and metabolic pathways that regulate myelin biogenesis is fundamental to sustain the profound energy demands at each axo-glial interface. Deficits in regulatory functions exerted through TH for these physiological roles to be orchestrated by mature OLs, can occur in genetic and acquired myelin disorders, whereby mitochondrial efficiency and eventual dysfunction can lead to profound oligodendrocytopathy, demyelination and neurodegenerative sequelae. TH-dependent transcriptional and metabolic pathways can be dysregulated during acute and chronic MS lesion activity depriving OLs from critical acetyl-CoA biochemical mechanisms governing myelin lipid biosynthesis and at the same time altering the generation of iron metabolism that may drive ferroptotic mechanisms, leading to advancing neurodegeneration.

Ripks and Neuroinflammation

Neuroinflammation is an immune response in the central nervous system and poses a significant threat to human health. Studies have shown that the receptor serine/threonine protein kinase family (RIPK) family, a popular research target in inflammation, has been shown to play an essential role in neuroinflammation. It is significant to note that the previous reviews have only examined the link between RIPK1 and neuroinflammation. However, it has yet to systematically analyze the relationship between the RIPK family and neuroinflammation. Activation of RIPK1 promotes neuroinflammation. RIPK1 and RIPK3 are responsible for the control of cell death, including apoptosis, necrosis, and inflammation. RIPK1 and RIPK3 regulate inflammatory responses through the release of damage in necroptosis. RIPK1 and RIPK3 regulate inflammatory responses by releasing damage-associated molecular patterns (DAMPs) during necrosis. In addition, activated RIPK1 nuclear translocation and its interaction with the BAF complex leads to upregulation of chromatin modification and inflammatory gene expression, thereby triggering inflammation. Although RIPK2 is not directly involved in regulating cell death, it is considered an essential target for treating neurological inflammation. When the peptidoglycan receptor detects peptidoglycan IE-DAP or MDP in bacteria, it prompts NOD1 and NOD2 to recruit RIPK2 and activate the XIAP E3 ligase. This leads to the K63 ubiquitination of RIPK2. This is followed by LUBAC-mediated linear ubiquitination, which activates NF-KB and MAPK pathways to produce cytokines and chemokines. In conclusion, there are seven known members of the RIPK family, but RIPK4, RIPK5, RIPK6, and RIPK7 have not been linked to neuroinflammation. This article seeks to explore the potential of RIPK1, RIPK2, and RIPK3 kinases as therapeutic interventions for neuroinflammation, which is associated with Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), ischemic stroke, Parkinson's disease (PD), multiple sclerosis (MS), and traumatic brain injury (TBI).

Necroptosis and autoimmunity

Autoimmunity is a normal physiological state that requires immunological homeostasis and surveillance, whereas necroptosis is a type of inflammatory cell death. When necroptosis occurs, various immune system cells must perform their appropriate duties to preserve immunological homeostasis, whether the consequence is expanding or limiting the inflammatory response and the pathological condition is cleared or progresses to the autoimmune disease stage. This article discusses necroptosis based on RIP homotypic interaction motif (RHIM) interaction under various physiological and pathological situations, with the RIPK1-RIPK3-MLKL necrosome serving as the regulatory core. In addition, the cell biology of necroptosis involved in autoimmunity and its application in autoimmune diseases were also reviewed.

Non-canonical autophosphorylation of RIPK1 drives timely pyroptosis to control Yersinia infection

Caspase-8-dependent pyroptosis has been shown to mediate host protection from Yersinia infection. For this mode of cell death, the kinase activity of receptor-interacting protein kinase 1 (RIPK1) is required, but the autophosphorylation sites required to drive caspase-8 activation have not been determined. Here, we show that non-canonical autophosphorylation of RIPK1 at threonine 169 (T169) is necessary for caspase-8-mediated pyroptosis. Mice with alanine in the T169 position are highly susceptible to Yersinia dissemination. Mechanistically, the delayed formation of a complex containing RIPK1, ZBP1, Fas-associated protein with death domain (FADD), and caspase-8 abrogates caspase-8 maturation in T169A mice and leads to the eventual activation of RIPK3-dependent necroptosis in vivo; however, this is insufficient to protect the host, suggesting that timely pyroptosis during early response is specifically required to control infection. These results position RIPK1 T169 phosphorylation as a driver of pyroptotic cell death critical for host defense.

Low intensity repetitive transcranial magnetic stimulation enhances remyelination by newborn and surviving oligodendrocytes in the cuprizone model of toxic demyelination

In people with multiple sclerosis (MS), newborn and surviving oligodendrocytes (OLs) can contribute to remyelination, however, current therapies are unable to enhance or sustain endogenous repair. Low intensity repetitive transcranial magnetic stimulation (LI-rTMS), delivered as an intermittent theta burst stimulation (iTBS), increases the survival and maturation of newborn OLs in the healthy adult mouse cortex, but it is unclear whether LI-rTMS can promote remyelination. To examine this possibility, we fluorescently labelled oligodendrocyte progenitor cells (OPCs; Pdgfrα-CreER transgenic mice) or mature OLs (Plp-CreER transgenic mice) in the adult mouse brain and traced the fate of each cell population over time. Daily sessions of iTBS (600 pulses; 120 mT), delivered during cuprizone (CPZ) feeding, did not alter new or pre-existing OL survival but increased the number of myelin internodes elaborated by new OLs in the primary motor cortex (M1). This resulted in each new M1 OL producing ~ 471 µm more myelin. When LI-rTMS was delivered after CPZ withdrawal (during remyelination), it significantly increased the length of the internodes elaborated by new M1 and callosal OLs, increased the number of surviving OLs that supported internodes in the corpus callosum (CC), and increased the proportion of axons that were myelinated. The ability of LI-rTMS to modify cortical neuronal activity and the behaviour of new and surviving OLs, suggests that it may be a suitable adjunct intervention to enhance remyelination in people with MS.

Characterization of pathological stages in a mouse model of progressive multiple sclerosis

The purpose of this study was to analyze and elucidate the mechanisms of non-obese diabetes-experimental autoimmune encephalomyelitis (NOD-EAE), an animal model of progressive multiple sclerosis (MS), and to compare the pathological features with those observed in human progressive MS. Pathological analysis, flow cytometry analysis, immunohistochemical staining, and transcriptome analysis were performed at each pathological stage of the NOD-EAE mice to characterize each pathological stage in the lesion. The NOD-EAE mice showed a biphasic pattern of disease progression once in remission. The longitudinal profile of demyelination and inflammatory cell infiltration in the spinal cord was consistent with the pathological score. In the chronic phase of the disease, fibrosis and lymph follicle formation, characteristic of progressive human MS, were observed. Here we describe the pathological profile and transcriptome analysis of the NOD-EAE mice and verify that this model has similar features to those of human progressive MS. Our findings suggest that this model recapitulates lymph follicle formation, a disease hallmark of progressive MS, and fibrosis, a feature complicating the pathogenesis of MS in the chronic phase. This model may be useful for evaluating the efficacy of therapeutic agents and for mechanistic analysis.

Perioperative stroke deteriorates white matter integrity by enhancing cytotoxic CD8+ T-cell activation

AIM

To explore the regulatory mechanisms of microglia-mediated cytotoxic CD8+ T-cell infiltration in the white matter injury of perioperative stroke (PIS).

METHODS

Adult male C57BL/6 mice were subjected to ileocolic bowel resection (ICR) 24 h prior to permanent distant middle cerebral artery occlusion (dMCAO) to establish model PIS. White matter injury, functional outcomes, peripheral immune cell infiltration, and microglia phenotype were assessed up to 28 days after dMCAO using behavioral phenotyping, immunofluorescence staining, transmission electron microscopy, western blot, and FACS analysis.

RESULTS

We found surgery aggravated white matter injury and deteriorated sensorimotor deficits up to 28 days following PIS. The PIS mice exhibited significantly increased activation of peripheral and central CD8+ T cells, while significantly reduced numbers of mature oligodendrocytes compared to IS mice. Neutralizing CD8+ T cells partly reversed the aggravated demyelination following PIS. Pharmacological blockage or genetic deletion of receptor-interacting protein kinase 1 (RIPK1) activity could alleviate CD8+ T-cell infiltration and demyelination in PIS mice.

CONCLUSION

Surgery exacerbates demyelination and worsens neurological function by promoting infiltration of CD8+ T cells and microglia necroptosis, suggesting that modulating interactions of CD8+ T cells and microglia could be a novel therapeutic target of long-term neurological deficits of PIS.

Neuroinflammation-on-a-chip for multiple sclerosis research: a narrative review

Introduction

Multiple sclerosis (MS) is a chronic inflammatory condition that impacts the central nervous system. It is distinguished by processes like demyelination, gliosis, neuro-axonal harm, and inflammation. The prevailing theory suggests that MS originates from an immune response directed against the body's own antigens within the central nervous system.

Aim

The main aim of this research paper "Neuroinflammation-on-a-Chip" for studying multiple sclerosis is to enhance our comprehension of MS development, demonstrate the application of cutting-edge technology, and potentially provide valuable insights for therapeutic approaches.

Methods

The available literature for this Narrative Review was searched on various bibliographic databases, PubMed, NCBI, and many other medical references using an individually verified, prespecified approach. Studies regarding the significance of MS and its neuroinflammatory pathogenesis in addition to the development and optimization of neuroinflammatory-on-a-chip and the advancement in innovations in this field have been reviewed in this research for a better understanding of "Neuroinflammation-on-a-chip for multiple sclerosis". The level of evidence of the included studies was considered as per the Centre for Evidence-Based Medicine recommendations.

Results

Several studies have indicated that the brain-chip model closely mimics cortical brain tissue compared to commonly used conventional cell culture methods like the Transwell culture system. Additionally, these studies have clearly demonstrated that further research using brain chips has the potential to enhance our understanding of the molecular mechanisms and roles of blood-brain barrier (BBB) transporters in both normal and disease conditions.

Conclusion

Understanding neuroinflammation processes remains essential to establish new MS treatments approaches. The utilization of brain chips promises to advance our understanding of the molecular processes involving BBB transporters, both in normal and diseased states. Further research needs to be addressed in order to enhance the performance and understanding of neuroinflammation on a chip, hence aiming to provide more effective treatments for all CNS diseases.

Upregulation of Neuroinflammation-Associated Genes in the Brain of SARS-CoV-2-Infected Mice

Neurological manifestations are a significant complication of coronavirus disease 2019 (COVID-19), but the underlying mechanisms are yet to be understood. Recently, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-induced neuroinvasion and encephalitis were observed in K18-hACE2 mice, leading to mortality. Our goal in this study was to gain insights into the molecular pathogenesis of neurological manifestations in this mouse model. To analyze differentially expressed genes (DEGs) in the brains of mice following SARS-CoV-2 infection, we performed NanoString gene expression analysis using three individual animal samples at 1, 3, and 6 days post-infection. We identified the DEGs by comparing them to animals that were not infected with the virus. We found that genes upregulated at day 6 post-infection were mainly associated with Toll-like receptor (TLR) signaling, RIG-I-like receptor (RLR) signaling, and cell death pathways. However, downregulated genes were associated with neurodegeneration and synaptic signaling pathways. In correlation with gene expression profiles, a multiplexed immunoassay showed the upregulation of multiple cytokines and chemokines involved in inflammation and cell death in SARS-CoV-2-infected brains. Furthermore, the pathway analysis of DEGs indicated a possible link between TLR2-mediated signaling pathways and neuroinflammation, as well as pyroptosis and necroptosis in the brain. In conclusion, our work demonstrates neuroinflammation-associated gene expression profiles, which can provide key insight into the severe disease observed in COVID-19 patients.

Mitigation of CXCL10 secretion by metabolic disorder drugs in microglial-mediated neuroinflammation

Metabolic disorders are associated with several neurodegenerative diseases. We previously identified C-X-C motif chemokine ligand 10 (CXCL10), also known as interferon gamma-induced protein 10 (IP-10), as a major contributor to the type I interferon response in microglial-mediated neuroinflammation. Therefore, we hypothesized FDA-approved metabolic disorder drugs that attenuate CXCL10 secretion may be repurposed as a treatment for neurodegenerative diseases. Screening, dose curves, and cytotoxicity assays in LPS-stimulated microglia yielded treprostinil (hypertension), pitavastatin (hyperlipidemia), and eplerenone (hypertension) as candidates that significantly reduced CXCL10 secretion (in addition to other pro-inflammatory mediators) without impacting cell viability. Altogether, these data suggest metabolic disorder drugs that attenuate CXCL10 as potential treatments for neurodegenerative disease through mitigating microglial-mediated neuroinflammation.

Astrocytic RIPK3 exerts protective anti-inflammatory activity during viral encephalitis via induction of serpin protease inhibitors

Flaviviruses pose a significant threat to public health due to their ability to infect the central nervous system (CNS) and cause severe neurologic disease. Astrocytes play a crucial role in the pathogenesis of flavivirus encephalitis through their maintenance of blood-brain barrier (BBB) integrity and their modulation of immune cell recruitment and activation within the CNS. We have previously shown that receptor interacting protein kinase-3 (RIPK3) is a central coordinator of neuroinflammation during CNS viral infection, a function that occurs independently of its canonical function in inducing necroptotic cell death. To date, however, roles for necroptosis-independent RIPK3 signaling in astrocytes are poorly understood. Here, we use mouse genetic tools to induce astrocyte-specific deletion, overexpression, and chemogenetic activation of RIPK3 to demonstrate an unexpected anti-inflammatory function for astrocytic RIPK3. RIPK3 activation in astrocytes was required for host survival in multiple models of flavivirus encephalitis, where it restricted neuropathogenesis by limiting immune cell recruitment to the CNS. Transcriptomic analysis revealed that, despite inducing a traditional pro-inflammatory transcriptional program, astrocytic RIPK3 paradoxically promoted neuroprotection through the upregulation of serpins, endogenous protease inhibitors with broad immunomodulatory activity. Notably, intracerebroventricular administration of SerpinA3N in infected mice preserved BBB integrity, reduced leukocyte infiltration, and improved survival outcomes in mice lacking astrocytic RIPK3. These findings highlight a previously unappreciated role for astrocytic RIPK3 in suppressing pathologic neuroinflammation and suggests new therapeutic targets for the treatment of flavivirus encephalitis.

Metformin attenuates lung ischemia-reperfusion injury and necroptosis through AMPK pathway in type 2 diabetic recipient rats

BACKGROUND

Diabetes mellitus (DM) can aggravate lung ischemia-reperfusion (I/R) injury and is a significant risk factor for recipient mortality after lung transplantation. Metformin protects against I/R injury in a variety of organs. However, the effect of metformin on diabetic lung I/R injury remains unclear. Therefore, this study aimed to observe the effect and mechanism of metformin on lung I/R injury following lung transplantation in type 2 diabetic rats.

METHODS

Sprague-Dawley rats were randomly divided into the following six groups: the control + sham group (CS group), the control + I/R group (CIR group), the DM + sham group (DS group), the DM + I/R group (DIR group), the DM + I/R + metformin group (DIRM group) and the DM + I/R + metformin + Compound C group (DIRMC group). Control and diabetic rats underwent the sham operation or left lung transplantation operation. Lung function, alveolar capillary permeability, inflammatory response, oxidative stress, necroptosis and the p-AMPK/AMPK ratio were determined after 24 h of reperfusion.

RESULTS

Compared with the CIR group, the DIR group exhibited decreased lung function, increased alveolar capillary permeability, inflammatory responses, oxidative stress and necroptosis, but decreased the p-AMPK/AMPK ratio. Metformin improved the function of lung grafts, decreased alveolar capillary permeability, inflammatory responses, oxidative stress and necroptosis, and increased the p-AMPK/AMPK ratio. In contrast, the protective effects of metformin were abrogated by Compound C.

CONCLUSIONS

Metformin attenuates lung I/R injury and necroptosis through AMPK pathway in type 2 diabetic lung transplant recipient rats.

Itaconate inhibits corticosterone-induced necroptosis and neuroinflammation via up-regulating menin in HT22 cells

Corticosterone (CORT) damages hippocampal neurons as well as induces neuroinflammation. The tricarboxylic acid cycle metabolite itaconate has an anti-inflammatory role. Necroptosis is a form of programmed cell death, also known as inflammatory cell death. Menin is a multifunctional scaffold protein, which deficiency aggravates neuroinflammation. In this study, we explored whether itaconate inhibits CORT-induced neuroinflammation as well as necroptosis and further investigated the mediatory role of Menin in this protective effect of itaconate by using an exposure of CORT to HT22 cells (a hippocampal neuronal cell line). The viability of HT22 cells was examined by the cell counting kit 8 (CCK-8). The morphology of HT22 cells was observed by transmission electron microscope (TEM). The expressions of necroptosis-related proteins (p-RIP1/RIP1, p-RIP3/RIP3, and p-MLKL/MLKL) were evaluated by western blotting. The contents of inflammatory factors were detected by an enzyme-linked immunosorbent assay (ELISA) kit. Our results showed that CORT increases the contents of pro-inflammatory factors (IL-1β, TNF-α) as well as decreases the contents of anti-inflammatory factors (IL-4, IL-10) in HT22 cells. We also found that CORT increases the expressions of necroptosis-related proteins (p-RIP1/RIP1, p-RIP3/RIP3, and p-MLKL/MLKL) and decreases the cell viability in HT22 cells, indicating that CORT induces necroptosis in HT22 cells. Itaconate improves CORT-induced neuroinflammation and necroptosis. Furthermore, itaconate upregulates the expression of Menin in CORT-exposed HT22 cells. Importantly, silencing Menin abolishes the antagonistic effect of itaconate on CORT-induced necroptosis and neuroinflammation. In brief, these results indicated that itaconate protects HT22 cells against CORT-induced neuroinflammation and necroptosis via upregulating Menin.

A guide to cell death pathways

Regulated cell death mediated by dedicated molecular machines, known as programmed cell death, plays important roles in health and disease. Apoptosis, necroptosis and pyroptosis are three such programmed cell death modalities. The caspase family of cysteine proteases serve as key regulators of programmed cell death. During apoptosis, a cascade of caspase activation mediates signal transduction and cellular destruction, whereas pyroptosis occurs when activated caspases cleave gasdermins, which can then form pores in the plasma membrane. Necroptosis, a form of caspase-independent programmed necrosis mediated by RIPK3 and MLKL, is inhibited by caspase-8-mediated cleavage of RIPK1. Disruption of cellular homeostatic mechanisms that are essential for cell survival, such as normal ionic and redox balance and lysosomal flux, can also induce cell death without invoking programmed cell death mechanisms. Excitotoxicity, ferroptosis and lysosomal cell death are examples of such cell death modes. In this Review, we provide an overview of the major cell death mechanisms, highlighting the latest insights into their complex regulation and execution, and their relevance to human diseases.

Edaravone Dexborneol mitigates pathology in animal and cell culture models of Alzheimer's disease by inhibiting neuroinflammation and neuronal necroptosis

BACKGROUND

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease with limited disease-modifying treatments. Drug repositioning strategy has now emerged as a promising approach for anti-AD drug discovery. Using 5×FAD mice and Aβ-treated neurons in culture, we tested the efficacy of Y-2, a compounded drug containing the antioxidant Edaravone (Eda), a pyrazolone and (+)-Borneol, an anti-inflammatory diterpenoid from cinnamon, approved for use in amyotrophic lateral sclerosis patients.

RESULTS

We examined effects of Y-2 versus Eda alone by i.p. administered in 8-week-old 5×FAD mice (females) for 4 months by comparing cognitive function, Aβ pathologies, neuronal necroptosis and neuroinflammation. Using primary neurons and astrocytes, as well as neuronal and astrocytic cell lines, we elucidated the molecular mechanisms of Y-2 by examining neuronal injury, astrocyte-mediated inflammation and necroptosis. Here, we find that Y-2 improves cognitive function in AD mice. Histopathological data show that Y-2, better than Eda alone, markedly ameliorates Aβ pathologies including Aβ burden, astrogliosis/microgliosis, and Tau phosphorylation. In addition, Y-2 reduces Aβ-induced neuronal injury including neurite damage, mitochondrial impairment, reactive oxygen species production and NAD+ depletion. Notably, Y-2 inhibits astrocyte-mediated neuroinflammation and attenuates TNF-α-triggered neuronal necroptosis in cell cultures and AD mice. RNA-seq further demonstrates that Y-2, compared to Eda, indeed upregulates anti-inflammation pathways in astrocytes.

CONCLUSIONS

Our findings infer that Y-2, better than Eda alone, mitigates AD pathology and may provide a potential drug candidate for AD treatment.

Oxidative stress involvement in the molecular pathogenesis and progression of multiple sclerosis: a literature review

Multiple sclerosis (MS) is an autoimmune debilitating disease of the central nervous system caused by a mosaic of interactions between genetic predisposition and environmental factors. The pathological hallmarks of MS are chronic inflammation, demyelination, and neurodegeneration. Oxidative stress, a state of imbalance between the production of reactive species and antioxidant defense mechanisms, is considered one of the key contributors in the pathophysiology of MS. This review is a comprehensive overview of the cellular and molecular mechanisms by which oxidant species contribute to the initiation and progression of MS including mitochondrial dysfunction, disruption of various signaling pathways, and autoimmune response activation. The detrimental effects of oxidative stress on neurons, oligodendrocytes, and astrocytes, as well as the role of oxidants in promoting and perpetuating inflammation, demyelination, and axonal damage, are discussed. Finally, this review also points out the therapeutic potential of various synthetic antioxidants that must be evaluated in clinical trials in patients with MS.

Inhibiting RIPK1-driven neuroinflammation and neuronal apoptosis mitigates brain injury following experimental subarachnoid hemorrhage

RIPK1, a receptor-interacting serine/threonine protein kinase, plays a crucial role in maintaining cellular and tissue homeostasis by integrating inflammatory responses and cell death signaling pathways including apoptosis and necroptosis, which have been implicated in diverse physiological and pathological processes. Suppression of RIPK1 activation is a promising strategy for restraining the pathological progression of many human diseases. Neuroinflammation and neuronal apoptosis are two pivotal factors in the pathogenesis of brain injury following subarachnoid hemorrhage (SAH). In this study, we established in vivo and in vitro models of SAH to investigate the activation of RIPK1 kinase in both microglia and neurons. We observed the correlation between RIPK1 kinase activity and microglia-mediated inflammation as well as neuronal apoptosis. We then investigated whether inhibition of RIPK1 could alleviate neuroinflammation and neuronal apoptosis following SAH, thereby reducing brain edema and ameliorating neurobehavioral deficits. Additionally, the underlying mechanisms were also explored. Our research findings revealed the activation of RIPK1 kinase in both microglia and neurons following SAH, as marked by the phosphorylation of RIPK1 at serine 166. The upregulation of p-RIPK1(S166) resulted in a significant augmentation of inflammatory cytokines and chemokines, including TNF-α, IL-6, IL-1α, CCL2, and CCL5, as well as neuronal apoptosis. The activation of RIPK1 in microglia and neurons following SAH could be effectively suppressed by administration of Nec-1 s, a specific inhibitor of RIPK1. Consequently, inhibition of RIPK1 resulted in a downregulation of inflammatory cytokines and chemokines and attenuation of neuronal apoptosis after SAH in vitro. Furthermore, the administration of Nec-1 s effectively mitigated neuroinflammation, neuronal apoptosis, brain edema, and neurobehavioral deficits in mice following SAH. Our findings suggest that inhibiting RIPK1 kinase represents a promising therapeutic strategy for mitigating brain injury after SAH by attenuating RIPK1-driven neuroinflammation and neuronal apoptosis.

Binding of RAGE and RIPK1 induces cognitive deficits in chronic hyperglycemia-derived neuroinflammation

AIMS

Chronic hyperglycemia-induced inflammation of the hippocampus is an important cause of cognitive deficits in diabetic patients. The receptor for advanced glycation end products (RAGE), which is widely expressed in the hippocampus, is a crucial factor in this inflammation and the associated cognitive deficits. We aimed to reveal the underlying mechanism by which RAGE regulates neuroinflammation in the pathogenesis of diabetes-induced cognitive impairment.

METHODS

We used db/db mice as a model for type 2 diabetes to investigate whether receptor-interacting serine/threonine protein kinase 1 (RIPK1), which is expressed in microglia in the hippocampal region, is a key protein partner for RAGE. GST pull-down assays and AutoDock Vina simulations were performed to identify the key structural domain in RAGE that binds to RIPK1. Western blotting, co-immunoprecipitation (Co-IP), and immunofluorescence (IF) were used to detect the levels of key proteins or interaction between RAGE and RIPK1. Cognitive deficits in the mice were assessed with the Morris water maze (MWM) and new object recognition (NOR) and fear-conditioning tests.

RESULTS

RAGE binds directly to RIPK1 via the amino acid sequence (AAs) 362-367, thereby upregulating phosphorylation of RIPK1, which results in activation of the NLRP3 inflammasome in microglia and ultimately leads to cognitive impairments in db/db mice. We mutated RAGE AAs 362-367 to reverse neuroinflammation in the hippocampus and improve cognitive function, suggesting that RAGE AAs 362-367 is a key structural domain that binds directly to RIPK1. These results also indicate that hyperglycemia-induced inflammation in the hippocampus is dependent on direct binding of RAGE and RIPK1.

CONCLUSION

Direct interaction of RAGE and RIPK1 via AAs 362-367 is an important mechanism for enhanced neuroinflammation in the hyperglycemic environment and is a key node in the development of cognitive deficits in diabetes.

RIPK1 inhibitors: A key to unlocking the potential of necroptosis in drug development

Within the field of medical science, there is a great deal of interest in investigating cell death pathways in the hopes of discovering new drugs. Over the past two decades, pharmacological research has focused on necroptosis, a cell death process that has just been discovered. Receptor-interacting protein kinase 1 (RIPK1), an essential regulator in the cell death receptor signalling pathway, has been shown to be involved in the regulation of important events, including necrosis, inflammation, and apoptosis. Therefore, researching necroptosis inhibitors offers novel ways to treat a variety of disorders that are not well-treated by the therapeutic medications now on the market. The research and medicinal potential of RIPK1 inhibitors, a promising class of drugs, are thoroughly examined in this study. The journey from the discovery of Necrostatin-1 (Nec-1) to the recent advancements in RIPK1 inhibitors is marked by significant progress, highlighting the integration of traditional medicinal chemistry approaches with modern technologies like high-throughput screening and DNA-encoded library technology. This review presents a thorough exploration of the development and therapeutic potential of RIPK1 inhibitors, a promising class of compounds. Simultaneously, this review highlights the complex roles of RIPK1 in various pathological conditions and discusses potential inhibitors discovered through diverse pathways, emphasizing their efficacy against multiple disease models, providing significant guidance for the expansion of knowledge about RIPK1 and its inhibitors to develop more selective, potent, and safe therapeutic agents.

Global trends in PANoptosis research: bibliometrics and knowledge graph analysis

PANoptosis has recently been discovered as a new type of cell death. PANoptosis mainly refers to the significant interaction among the three programmed cell death pathways of apoptosis, necroptosis, and pyroptosis. Despite this, only a few studies have examined the systematic literature in this area. By analyzing the bibliometric data for PANoptosis, we can visualize the current hotspots and predicted trends in research. This study analyzed bibliometric indicators using the Histcite Pro 2.0 tool, which searches the Web of Science for PANoptosis literature published between 2016 and 2022. A bibliometric analysis was performed using Histcite Pro 2.0, while research trends and hotspots were visualized using VOSviewer, CiteSpace and BioBERT. The output of related literature was low in the four years from the first presentation of PANoptosis in 2016 to 2020. The volume of relevant literature grew exponentially between 2020 and 2022. The United States and China play a leading role in this field. Although China started late, its research in this field is developing rapidly. As research progressed, more focus was placed on the relationship between PANoptosis and pyroptosis, as well as apoptosis and necrosis. Now is a rapid development stage of PANoptosis research. Most of the research focuses on the cellular level, and the focus is more on the treatment of tumor-related diseases. The current focus of this area is PANoptosis mechanisms in cancer and inflammation. It can be seen from the burst analysis of keywords that caspase1 and host defense have consistently been research hotspots in the field of PANoptosis, while the frequency of NLRC4, causes of autoinflammation, recognition, NLRP3, and Gasdermin D has gradually increased, all of which have become research hotspots in recent years. Finally, we used the BioBERT biomedical language model to mine the most documented genes and diseases in the PANoptosis field articles, pointing out the direction for subsequent research steps. According to a bibliometric analysis, researchers have shown an increased interest in PANoptosis over the past few years. Researchers initially focused on the molecular mechanism of PANoptosis and pyroptosis, apoptosis, and necroptosis. The role of PANoptosis in diseases and conditions such as inflammation and tumors is one of the current research hotspots in this area. The focus is more on treating inflammation-related diseases, which will become the key development direction of future research.

Safety, pharmacokinetics, and target engagement of a brain penetrant RIPK1 inhibitor, SAR443820 (DNL788), in healthy adult participants

SAR443820 (DNL788) is a selective, orally bioavailable, brain penetrant inhibitor of receptor-interacting serine/threonine protein kinase 1 (RIPK1). This phase I first-in-human healthy participant study (NCT05795907) was comprised of three parts: randomized, double-blind, placebo-controlled single ascending dose (SAD; part 1a); 14-day multiple ascending dose (MAD; part 2) parts that evaluated safety, tolerability, pharmacokinetics (PK), and pharmacodynamics of SAR443820; and a separate open-label, single-dose part 1b (PK-cerebrospinal fluid [CSF]) to assess SAR443820 levels in CSF. SAR443820 was well-tolerated in healthy participants, and no treatment discontinuation related to an adverse event (AE) occurred. Most common AEs were dizziness and headache. No clinically meaningful changes were noted in laboratory values, vital signs, or electrocardiogram parameters. SAR443820 had a favorable PK profile, with plasma half-lives (geometric mean) ranged between 5.7-8.0 h and 7.2-8.9 h after single and repeated doses, respectively. There were no major deviations from dose proportionality for maximum concentration and area under the curve across SAR443820 doses. Mean CSF-to-unbound plasma concentration ratio ranged from 0.8 to 1.3 over time (assessed up to 10 h postdose), indicating high brain penetrance. High levels of inhibition of activated RIPK1, as measured by decrease in pS166-RIPK1, were achieved in both SAD and MAD parts, with a maximum median inhibition from baseline close to 90% at predose (Ctrough ) after multiple dosing in MAD, reflecting a marked RIPK1 target engagement at the peripheral level. These results support further development of SAR443820 in phase II trials in amyotrophic lateral sclerosis (NCT05237284) and multiple sclerosis (NCT05630547).

Necrostatin-1s Suppresses RIPK1-driven Necroptosis and Inflammation in Periventricular Leukomalacia Neonatal Mice

Periventricular leukomalacia (PVL), a predominant form of brain injury in preterm survivors, is characterized by hypomyelination and microgliosis and is also the major cause of long-term neurobehavioral abnormalities in premature infants. Receptor-interacting protein kinase 1 (RIPK1) plays a pivotal role in mediating cell death and inflammatory signaling cascade. However, very little is known about the potential effect of RIPK1 in PVL and the underlying mechanism. Herein, we found that the expression level of RIPK1 was drastically increased in the brain of PVL neonatal mice models, and treatment of PVL neonatal mice with Necrostatin-1s (Nec-1s), an inhibitor of RIPK1, greatly ameliorated cerebral ischemic injury, exhibiting an increase of body weights, reduction of cerebral infarct size, neuronal loss, and occurrence of necrosis-like cells, and significantly improved the long-term abnormal neurobehaviors of PVL. In addition, Nec-1s significantly suppressed hypomyelination and promoted the differentiation of oligodendrocyte precursor cells (OPCs), as demonstrated by the increased expression levels of MBP and Olig2, the decreased expression level of GPR17, a significant increase in the number of CC-1-positive cells, and suppression of myelin ultrastructure impairment. Moreover, the mechanism of neuroprotective effects of Nec-1s against PVL is closely associated with its suppression of the RIPK1-mediated necrosis signaling molecules, RIPK1, PIPK3, and MLKL. More importantly, inhibition of RIPK1 could reduce microglial inflammatory injury by triggering the M1 to M2 microglial phenotype, appreciably decreasing the levels of M1 marker CD86 and increasing the levels of M2 markers Arg1 or CD206 in PVL mice. Taken together, inhibition of RIPK1 markedly ameliorates the brain injury and long-term neurobehavioral abnormalities of PVL mice through the reduction of neural cell necroptosis and reversing neuroinflammation.

Neuroinflammation, memory, and depression: new approaches to hippocampal neurogenesis

As one of most common and severe mental disorders, major depressive disorder (MDD) significantly increases the risks of premature death and other medical conditions for patients. Neuroinflammation is the abnormal immune response in the brain, and its correlation with MDD is receiving increasing attention. Neuroinflammation has been reported to be involved in MDD through distinct neurobiological mechanisms, among which the dysregulation of neurogenesis in the dentate gyrus (DG) of the hippocampus (HPC) is receiving increasing attention. The DG of the hippocampus is one of two niches for neurogenesis in the adult mammalian brain, and neurotrophic factors are fundamental regulators of this neurogenesis process. The reported cell types involved in mediating neuroinflammation include microglia, astrocytes, oligodendrocytes, meningeal leukocytes, and peripheral immune cells which selectively penetrate the blood-brain barrier and infiltrate into inflammatory regions. This review summarizes the functions of the hippocampus affected by neuroinflammation during MDD progression and the corresponding influences on the memory of MDD patients and model animals.

Noteworthy perspectives on microglia in neuropsychiatric disorders

Microglia are so versatile that they not only provide immune surveillance for central nervous system, but participate in neural circuitry development, brain blood vessels formation, blood-brain barrier architecture, and intriguingly, the regulation of emotions and behaviors. Microglia have a profound impact on neuronal survival, brain wiring and synaptic plasticity. As professional phagocytic cells in the brain, they remove dead cell debris and neurotoxic agents via an elaborate mechanism. The functional profile of microglia varies considerately depending on age, gender, disease context and other internal or external environmental factors. Numerous studies have demonstrated a pivotal involvement of microglia in neuropsychiatric disorders, including negative affection, social deficit, compulsive behavior, fear memory, pain and other symptoms associated with major depression disorder, anxiety disorder, autism spectrum disorder and schizophrenia. In this review, we summarized the latest discoveries regarding microglial ontogeny, cell subtypes or state spectrum, biological functions and mechanistic underpinnings of emotional and behavioral disorders. Furthermore, we highlight the potential of microglia-targeted therapies of neuropsychiatric disorders, and propose outstanding questions to be addressed in future research of human microglia.

Receptor-interacting protein kinase 1 (RIPK1) regulates cervical cancer cells via NF-κB-TNF-α pathway: An in vitro study

INTRODUCTION

Cervical cancer (CC) is associated with high morbidity and mortality rates in women. Members of the receptor-interacting protein kinase (RIPK) family are important regulators of inflammation and cell death. However, the characteristics, molecular functions, and expression mechanisms of RIPK1 in CC remain unclear.

MATERIAL AND METHODS

To determine whether RIPK1 can be used for targeted therapy of CC, we assessed the clinical importance, biological function, and potential impact of RIPK1 in CC in 50 patients with CC. We utilized immunohistochemical staining, transfection, western blotting, cell counting kit-8 assay, colony formation assay, and wound healing assays among others, to elucidate the role of RIPK1 in CC.

RESULTS

RIPK1 expression was higher in tumor tissues than in paracancerous tissues. Poor prognosis of CC was linked to RIPK1 upregulation. Furthermore, silencing RIPK1 significantly inhibited the proliferation, migration, and invasion of CC cells in vitro. We also established that RIPK1 increased cell migration, invasion, and multiplication by regulating nuclear factor kappa-B (NF-κB) and tumor necrosis factor (TNF).

DISCUSSION

RIPK1 activates NF-κB and regulates TNF release to enhance the proliferation and spread of CC cells while suppressing their apoptosis. Therefore, RIPK1 plays a key role in the formation and progression of CC and is a potential target for CC treatment.

Pathogenic mechanisms and potential therapeutic targets for Parkinson disease revealed by bioinformatic analysis of necroptosis and immune cell infiltration

Parkinson disease (PD) is an age-dependent neurodegenerative disease with very high prevalence by age 80 years. Necroptosis is a newly identified form of programmed cell death implicated in neurodegenerative diseases, but has not yet been conclusively associated with PD. This study examined the contributions of necroptosis to PD using bioinformatics analysis. Datasets GSE26927, GSE49036, and GSE54536 from the gene expression omnibus database were analyzed for differentially expressed genes (DEGs). These DEGs were then subjected to gene ontology and Kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analysis to identify associated functions and signaling mechanisms. Necroptosis-related differentially expressed genes (NRDEGs) were then identified by the overlap of DEGs and the necroptosis gene set hsa04217. The STRING database and Cytoscape software were then used to build and visualize a protein-protein interaction network and identify hubs and key functional modules among NRDEGs. In addition, immune cell type abundance was analyzed based on DEGs using ImmuCellAI. The identified DEGs, KEGG pathway enrichment terms, and protein-protein interaction network structures of NRDEGs were validated using an independent dataset (GSE54536). The necroptosis pathway was significantly enriched and activated in PD samples. Thirteen NRDEGs were identified in the GSE26927 and GSE49036 datasets, including receptor interacting serine/threonine kinase 1, CASP8 and FADD like apoptosis regulator, TNFRSF1A associated via death domain, and interleukin 1 beta, of which 6 were validated in the GSE54536 dataset. According to gene ontology and KEGG analyses, these NRDEGs are involved in necroptosis-related processes, apoptosis, B cell receptor signaling pathways, and NOD-like receptor signaling pathways. Analysis of DEGs also revealed significant increases in CD8 + T cell and Tex cell infiltration and significant decreases in B cell and T gamma delta cell infiltration within the PD brain. Necroptosis pathways are active in PD and associated with immune cell infiltration. The factors controlling necroptotic signaling and immune infiltration identified in this study may be valuable diagnostic markers and therapeutic targets for PD.

An autonomous activation of interleukin-17 receptor signaling sustains inflammation and promotes disease progression

Anti-interleukin-17 (IL-17) therapy has been used in various autoimmune diseases. However, the efficacy is unexpectedly limited in several IL-17-associated diseases, and the mechanism of limited efficacy remains unclear. Here, we show that a molecular complex containing the adaptor molecule Act1 and tyrosine phosphatase SHP2 mediated autonomous IL-17R signaling that accelerated and sustained inflammation. SHP2, aberrantly augmented in various autoimmune diseases, was induced by IL-17A itself in astrocytes and keratinocytes, sustaining chemokine production even upon anti-IL-17 therapies. Mechanistically, SHP2 directly interacted with and dephosphorylated Act1, which replaced Act1-TRAF5 complexes and induced IL-17-independent activation of IL-17R signaling. Genetic or pharmacologic inactivation of SHP2, or blocking Act1-SHP2 interaction, paralyzed both IL-17-induced and IL-17-independent signaling and attenuated primary or relapsing experimental autoimmune encephalomyelitis. Therefore, Act1-SHP2 complexes mediate an alternative pathway for autonomous activation of IL-17R signaling, targeting which could be a therapeutic option for IL-17-related diseases in addition to current antibody therapies.

Identification of mitochondrial related signature associated with immune microenvironment in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disease. Mitochondrial dysfunction and immune responses are important factors in the pathogenesis of AD, but their crosstalk in AD has not been studied. In this study, the independent role and interaction of mitochondria-related genes and immune cell infiltration in AD were investigated using bioinformatics methods.

METHODS

The datasets of AD were obtained from NCBI Gene Expression Omnibus (GEO), and the data of mitochondrial genes was from MitoCarta3.0 database. Subsequently, differential expression genes (DEGs) screening and GSEA functional enrichment analysis were performed. The intersection of DEGs and mitochondrial related genes was used to obtain MitoDEGs. The MitoDEGs most relevant to AD were determined by Least absolute shrinkage and selection operator and multiple support vector machine recursive feature elimination, as well as protein-protein interactions (PPI) network and random forest. The infiltration of 28 kinds of immune cells in AD was analyzed by ssGSEA, and the relationship between hub MitoDEGs and the proportion of immune infiltration was studied. The expression levels of hub MitoDEGs were verified in cell models and AD mice, and the role of OPA1 in mitochondrial damage and neuronal apoptosis was investigated.

RESULTS

The functions and pathways of DEGs were significantly enriched in AD, including immune response activation, IL1R pathway, mitochondrial metabolism, oxidative damage response and electron transport chain-oxphos system in mitochondria. Hub MitoDEGs closely related to AD were obtained based on PPI network, random forest and two machine learning algorithms. Five hub MitoDEGs associated with neurological disorders were identified by biological function examination. The hub MitoDEGs were found to be correlated with memory B cell, effector memory CD8 T cell, activated dendritic cell, natural killer T cell, type 17 T helper cell, Neutrophil, MDSC, plasmacytoid dendritic cell. These genes can also be used to predict the risk of AD and have good diagnostic efficacy. In addition, the mRNA expression levels of BDH1, TRAP1, OPA1, DLD in cell models and AD mice were consistent with the results of bioinformatics analysis, and expression levels of SPG7 showed a downward trend. Meanwhile, OPA1 overexpression alleviated mitochondrial damage and neuronal apoptosis induced by Aβ1-42.

CONCLUSIONS

Five potential hub MitoDEGs most associated with AD were identified. Their interaction with immune microenvironment may play a crucial role in the occurrence and prognosis of AD, which provides a new insight for studying the potential pathogenesis of AD and exploring new targets.

Distinct Th17 effector cytokines differentially promote microglial and blood-brain barrier inflammatory responses during post-infectious encephalitis

Group A Streptococcus (GAS) infections can cause neuropsychiatric sequelae in children due to post-infectious encephalitis. Multiple GAS infections induce migration of Th17 lymphocytes from the nose into the brain, which are critical for microglial activation, blood-brain barrier (BBB) and neural circuit impairment in a mouse disease model. How endothelial cells (ECs) and microglia respond to GAS infections, and which Th17-derived cytokines are essential for these responses are unknown. Using single-cell RNA sequencing and spatial transcriptomics, we found that ECs downregulate BBB genes and microglia upregulate interferon-response, chemokine and antigen-presentation genes after GAS infections. Several microglial-derived chemokines were elevated in patient sera. Administration of a neutralizing antibody against interleukin-17A (IL-17A), but not ablation of granulocyte-macrophage colony-stimulating factor (GM-CSF) in T cells, partially rescued BBB dysfunction and microglial expression of chemokine genes. Thus, IL-17A is critical for neuropsychiatric sequelae of GAS infections and may be targeted to treat these disorders.

RIPK1-Induced A1 Reactive Astrocytes in Brain in MPTP-Treated Murine Model of Parkinson's Disease

Neuroinflammation is one of the hallmarks of Parkinson's disease, including the massive activation of microglia and astrocytes and the release of inflammatory factors. Receptor-interacting protein kinase 1 (RIPK1) is reported to mediate cell death and inflammatory signaling, and is markedly elevated in the brain in PD mouse models. Here, we aim to explore the role of RIPK1 in regulating the neuroinflammation of PD. C57BL/6J mice were intraperitoneally injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 20 mg/kg four times/day), followed by necrostatin-1 treatment (Nec-1, RIPK1 inhibitor; 1.65 mg/kg once daily for seven days. Notably, the first Nec-1 was given 12 h before MPTP modeling). Behavioral tests indicated that inhibition of RIPK1 greatly relieved motor dysfunction and anxiety-like behaviors of PD mice. It also increased striatal TH expression, rescue the loss of dopaminergic neurons, and reduce activation of astrocytes in the striatum of PD mice. Furthermore, inhibition of RIPK1 expression reduced A1 astrocytes' relative gene expression (CFB, H2-T23) and inflammatory cytokine or chemokine production (CCL2, TNF-α, IL-1β) in the striatum of PD mice. Collectively, inhibition of RIPK1 expression can provide neuroprotection to PD mice, probably through inhibition of the astrocyte A1 phenotype, and thus RIPK1 might be an important target in PD treatment.

Unwinding the modalities of necrosome activation and necroptosis machinery in neurological diseases

Necroptosis, a regulated form of cell death, is involved in the genesis and development of various life-threatening diseases, including cancer, neurological disorders, cardiac myopathy, and diabetes. Necroptosis initiates with the formation and activation of a necrosome complex, which consists of RIPK1, RIPK2, RIPK3, and MLKL. Emerging studies has demonstrated the regulation of the necroptosis cell death pathway through the implication of numerous post-translational modifications, namely ubiquitination, acetylation, methylation, SUMOylation, hydroxylation, and others. In addition, the negative regulation of the necroptosis pathway has been shown to interfere with brain homeostasis through the regulation of axonal degeneration, mitochondrial dynamics, lysosomal defects, and inflammatory response. Necroptosis is controlled by the activity and expression of signaling molecules, namely VEGF/VEGFR, PI3K/Akt/GSK-3β, c-Jun N-terminal kinases (JNK), ERK/MAPK, and Wnt/β-catenin. Herein, we briefly discussed the implication and potential of necrosome activation in the pathogenesis and progression of neurological manifestations, such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, traumatic brain injury, and others. Further, we present a detailed picture of natural compounds, micro-RNAs, and chemical compounds as therapeutic agents for treating neurological manifestations.

Aberrantly activated TAK1 links neuroinflammation and neuronal loss in Alzheimer's disease mouse models

Neuroinflammation is causally associated with Alzheimer's disease (AD) pathology. Reactive glia cells secrete various neurotoxic factors that impair neuronal homeostasis eventually leading to neuronal loss. Although the glial activation mechanism in AD has been relatively well studied, how it perturbs intraneuronal signaling, which ultimately leads to neuronal cell death, remains poorly understood. Here, we report that compound stimulation with the neurotoxic factors TNF and glutamate aberrantly activates neuronal TAK1 (also known as MAP3K7), which promotes the pathogenesis of AD in mouse models. Glutamate-induced Ca2+ influx shifts TNF signaling to hyper-activate TAK1 enzymatic activity through Ca2+/calmodulin-dependent protein kinase II, which leads to necroptotic cellular damage. Genetic ablation and pharmacological inhibition of TAK1 ameliorated AD-associated neuronal loss and cognitive impairment in the AD model mice. Our findings provide a molecular mechanism linking cytokines, Ca2+ signaling and neuronal necroptosis in AD.

Comparing RNA-sequencing datasets from astrocytes, oligodendrocytes, and microglia in multiple sclerosis identifies novel dysregulated genes relevant to inflammation and myelination

Central nervous system (CNS) inflammation is a key factor in multiple sclerosis (MS). Invasion of peripheral immune cells into the CNS resulting from an unknown signal or combination of signals results in activation of resident immune cells and the hallmark feature of the disease: demyelinating lesions. These lesion sites are an amalgam of reactive peripheral and central immune cells, astrocytes, damaged and dying oligodendrocytes, and injured neurons and axons. Sustained inflammation affects cells directly located within the lesion site and further abnormalities are apparent diffusely throughout normal-appearing white matter and grey matter. It is only relatively recently, using animal models, new tissue sampling techniques, and next-generation sequencing, that molecular changes occurring in CNS resident cells have been broadly captured. Advances in cell isolation through Fluorescence Activated Cell Sorting (FACS) and laser-capture microdissection together with the emergence of single-cell sequencing have enabled researchers to investigate changes in gene expression in astrocytes, microglia, and oligodendrocytes derived from animal models of MS as well as from primary patient tissue. The contribution of some dysregulated pathways has been followed up in individual studies; however, corroborating results often go unreported between sequencing studies. To this end, we have consolidated results from numerous RNA-sequencing studies to identify and review novel patterns of differentially regulated genes and pathways occurring within CNS glial cells in MS. This article is categorized under: Neurological Diseases > Molecular and Cellular Physiology.

hnRNP A1 dysfunction in oligodendrocytes contributes to the pathogenesis of multiple sclerosis

Oligodendrocyte (OL) damage and death are prominent features of multiple sclerosis (MS) pathology, yet mechanisms contributing to OL loss are incompletely understood. Dysfunctional RNA binding proteins (RBPs), hallmarked by nucleocytoplasmic mislocalization and altered expression, have been shown to result in cell loss in neurologic diseases, including in MS. Since we previously observed that the RBP heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) was dysfunctional in neurons in MS, we hypothesized that it might also contribute to OL pathology in MS and relevant models. We discovered that hnRNP A1 dysfunction is characteristic of OLs in MS brains. These findings were recapitulated in the experimental autoimmune encephalomyelitis (EAE) mouse model of MS, where hnRNP A1 dysfunction was characteristic of OLs, including oligodendrocyte precursor cells and mature OLs in which hnRNP A1 dysfunction correlated with demyelination. We also found that hnRNP A1 dysfunction was induced by IFNγ, indicating that inflammation influences hnRNP A1 function. To fully understand the effects of hnRNP A1 dysfunction on OLs, we performed siRNA knockdown of hnRNP A1, followed by RNA sequencing. RNA sequencing detected over 4000 differentially expressed transcripts revealing alterations to RNA metabolism, cell morphology, and programmed cell death pathways. We confirmed that hnRNP A1 knockdown was detrimental to OLs and induced apoptosis and necroptosis. Together, these data demonstrate a critical role for hnRNP A1 in proper OL functioning and survival and suggest a potential mechanism of OL damage and death in MS that involves hnRNP A1 dysfunction.

The double-edged functions of necroptosis

Necroptosis refers to a regulated form of cell death induced by a variety of stimuli. Although it has been implicated in the pathogenesis of many diseases, there is evidence to support that necroptosis is not purely a detrimental process. We propose that necroptosis is a "double-edged sword" in terms of physiology and pathology. On the one hand, necroptosis can trigger an uncontrolled inflammatory cascade response, resulting in severe tissue injury, disease chronicity, and even tumor progression. On the other hand, necroptosis functions as a host defense mechanism, exerting antipathogenic and antitumor effects through its powerful pro-inflammatory properties. Moreover, necroptosis plays an important role during both development and regeneration. Misestimation of the multifaceted features of necroptosis may influence the development of therapeutic approaches targeting necroptosis. In this review, we summarize current knowledge of the pathways involved in necroptosis as well as five important steps that determine its occurrence. The dual role of necroptosis in a variety of physiological and pathological conditions is also highlighted. Future studies and the development of therapeutic strategies targeting necroptosis should fully consider the complicated properties of this type of regulated cell death.

Bioluminescent RIPoptosome Assay for FADD/RIPK1 Interaction Based on Split Luciferase Assay in a Human Neuroblastoma Cell Line SH-SY5Y

Different programed cell death (PCD) modalities involve protein-protein interactions in large complexes. Tumor necrosis factor α (TNFα) stimulated assembly of receptor-interacting protein kinase 1 (RIPK1)/Fas-associated death domain (FADD) interaction forms Ripoptosome complex that may cause either apoptosis or necroptosis. The present study addresses the interaction of RIPK1 and FADD in TNFα signaling by fusion of C-terminal (CLuc) and N-terminal (NLuc) luciferase fragments to RIPK1-CLuc (R1C) or FADD-NLuc (FN) in a caspase 8 negative neuroblastic SH-SY5Y cell line, respectively. In addition, based on our findings, an RIPK1 mutant (R1C K612R) had less interaction with FN, resulting in increasing cell viability. Moreover, presence of a caspase inhibitor (zVAD.fmk) increases luciferase activity compared to Smac mimetic BV6 (B), TNFα -induced (T) and non-induced cell. Furthermore, etoposide decreased luciferase activity, but dexamethasone was not effective in SH-SY5Y. This reporter assay might be used to evaluate basic aspects of this interaction as well as for screening of necroptosis and apoptosis targeting drugs with potential therapeutic application.

Role of the caspase-8/RIPK3 axis in Alzheimer's disease pathogenesis and Aβ-induced NLRP3 inflammasome activation

The molecular mediators of cell death and inflammation in Alzheimer's disease (AD) have yet to be fully elucidated. Caspase-8 is a critical regulator of several cell death and inflammatory pathways; however, its role in AD pathogenesis has not yet been examined in detail. In the absence of caspase-8, mice are embryonic lethal due to excessive receptor interacting protein kinase 3-dependent (RIPK3-dependent) necroptosis. Compound RIPK3 and caspase-8 mutants rescue embryonic lethality, which we leveraged to examine the roles of these pathways in an amyloid β-mediated (Aβ-mediated) mouse model of AD. We found that combined deletion of caspase-8 and RIPK3, but not RIPK3 alone, led to diminished Aβ deposition and microgliosis in the mouse model of AD carrying human presenilin 1 and amyloid precursor protein with 5 familial AD mutations (5xFAD). Despite its well-known role in cell death, caspase-8 did not appear to affect cell loss in the 5xFAD model. In contrast, we found that caspase-8 was a critical regulator of Aβ-driven inflammasome gene expression and IL-1β release. Interestingly, loss of RIPK3 had only a modest effect on disease progression, suggesting that inhibition of necroptosis or RIPK3-mediated cytokine pathways is not critical during midstages of Aβ amyloidosis. These findings suggest that therapeutics targeting caspase-8 may represent a novel strategy to limit Aβ amyloidosis and neuroinflammation in AD.

Role of DAMPs and cell death in autoimmune diseases: the example of multiple sclerosis

Multiple sclerosis is a chronic neuroinflammatory demyelinating disease of the central nervous system (CNS) of unknown etiology and still incompletely clarified pathogenesis. The disease is generally considered a disorder resulting from a complex interplay between environmental risk factors and predisposing causal genetic variants. To examine the etiopathogenesis of the disease, two complementary pre-clinical models are currently discussed: the "outside-in" model proposing a peripherally elicited inflammatory/autoimmune attack against degraded myelin as the cause of the disease, and the "inside-out" paradigm implying a primary cytodegenerative process of cells in the CNS that triggers secondary reactive inflammatory/autoimmune responses against myelin debris. In this review, the integrating pathogenetic role of damage-associated molecular patterns (DAMPs) in these two scenario models is examined by focusing on the origin and sources of these molecules, which are known to promote neuroinflammation and, via activation of pattern recognition receptor-bearing antigen-presenting cells, drive and shape autoimmune responses. In particular, environmental factors are discussed that are conceptually defined as agents which produce endogenous DAMPs via induction of regulated cell death (RCD) or act themselves as exogenous DAMPs. Indeed, in the field of autoimmune diseases, including multiple sclerosis, recent research has focused on environmental triggers that cause secondary events in terms of subroutines of RCD, which have been identified as prolific sources of DAMPs. Finally, a model of a DAMP-driven positive feed-forward loop of chronic inflammatory demyelinating processes is proposed, aimed at reconciling the competing "inside-out" and "outside-in" paradigms.

Fluid dynamics in aging-related dementias

Recent human and animal model experimental studies revealed novel pathways for fluid movement, immune cell trafficking and metabolic waste clearance in CNS. These studies raise the intriguing possibility that the newly discovered pathways, including the glymphatic system, lymphatic meningeal vessels and skull-brain communication channels, are impaired in aging and neurovascular and neurodegenerative diseases associated with dementia, including Alzheimer's disease (AD) and AD-related dementia. We provide an overview of the glymphatic and dural meningeal lymphatic systems, review current methods and approaches used to study glymphatic flow in humans and animals, and discuss current evidence and controversies related to its role in CNS flow homeostasis under physiological and pathophysiological conditions. Non-invasive imaging approaches are needed to fully understand the mechanisms and pathways driving fluid movement in CNS and their roles across lifespan including healthy aging and aging-related dementia.

Necroptosis in CNS diseases: Focus on astrocytes

In the last few years, necroptosis, a recently described type of cell death, has been reported to play an important role in the development of various brain pathologies. Necroptosis is a cell death mechanism that has morphological characteristics similar to necrosis but is mediated by fundamentally different molecular pathways. Necroptosis is initiated by signaling through the interaction of RIP1/RIP3/MLKL proteins (receptor-interacting protein kinase 1/receptor-interacting protein kinase 3/mixed lineage kinase domain-like protein). RIPK1 kinase is usually inactive under physiological conditions. It is activated by stimulation of death receptors (TNFR1, TNFR2, TLR3, and 4, Fas-ligand) by external signals. Phosphorylation of RIPK1 results in the formation of its complex with death receptors. Further, complexes with the second member of the RIP3 and MLKL cascade appear, and the necroptosome is formed. There is enough evidence that necroptosis plays an important role in the pathogenesis of brain ischemia and neurodegenerative diseases. In recent years, a point of view that both neurons and glial cells can play a key role in the development of the central nervous system (CNS) pathologies finds more and more confirmation. Astrocytes play complex roles during neurodegeneration and ischemic brain damage initiating both impair and protective processes. However, the cellular and molecular mechanisms that induce pathogenic activity of astrocytes remain veiled. In this review, we consider these processes in terms of the initiation of necroptosis. On the other hand, it is important to remember that like other types of programmed cell death, necroptosis plays an important role for the organism, as it induces a strong immune response and is involved in the control of cancerogenesis. In this review, we provide an overview of the complex role of necroptosis as an important pathogenetic component of neuronal and astrocyte death in neurodegenerative diseases, epileptogenesis, and ischemic brain damage.

Targeting Neuroinflammation to Alleviate Chronic Olfactory Dysfunction in Long COVID: A Role for Investigating Disease-Modifying Therapy (DMT)?

Chronic olfactory dysfunction after SARS-CoV-2 infection occurs in approximately 10% of patients with COVID-19-induced anosmia, and it is a growing public health concern. A regimen of olfactory training and anti-neuroinflammatory therapy with co-ultramicronized palmitoylethanolamide with luteolin (um-PEA-LUT) has shown promising results in clinical trials; however, approximately 15% of treated patients do not achieve full recovery of a normal olfactory threshold, and almost 5% have no recovery. Disease-modifying therapies (DMTs), which are used to treat autoimmune neuroinflammation in multiple sclerosis (MS), have not been studied for treating persistent inflammation in refractory post-COVID-19 smell disorder. This study evaluated COVID-19-related smell loss and MS-related smell loss, comparing the responses to different therapies. Forty patients with MS and 45 reporting post-COVID-19 olfactory disorders were included in the study. All patients underwent nasal endoscopy and were evaluated by using validated Sniffin' Sticks testing. The patients with long COVID were treated for three months with um-PEA-LUT plus olfactory training. The patients with MS were treated with DMTs. Olfactory functions before and after treatment were analyzed in both groups. At the experimental endpoint, 13 patients in the COVID-19 group treated with um-PEA-LUT had residual olfactory impairment versus 10 patients in the MS group treated with DMTs. The severity of the persistent olfactory loss was lower in the MS group, and the patients with MS treated with IFN-beta and glatiramer acetate had the preservation of olfactory function. These data provide a rationale for considering prospective trials investigating the efficacy of DMTs for post-COVID-19 olfactory disorders that are refractory to um-PEA-LUT with olfactory training. This study is the first to consider the role of DMT in treating refractory post-viral olfactory loss in patients with long COVID.

Targeting RIPK1 kinase for modulating inflammation in human diseases

Receptor-Interacting Serine/Threonine-Protein Kinase 1 (RIPK1) is a master regulator of TNFR1 signaling in controlling cell death and survival. While the scaffold of RIPK1 participates in the canonical NF-κB pathway, the activation of RIPK1 kinase promotes not only necroptosis and apoptosis, but also inflammation by mediating the transcriptional induction of inflammatory cytokines. The nuclear translocation of activated RIPK1 has been shown to interact BAF-complex to promote chromatin remodeling and transcription. This review will highlight the proinflammatory role of RIPK1 kinase with focus on human neurodegenerative diseases. We will discuss the possibility of targeting RIPK1 kinase for the treatment of inflammatory pathology in human diseases.

Necroptosis and Alzheimer's Disease: Pathogenic Mechanisms and Therapeutic Opportunities

Alzheimer's disease (AD) is considered to be the most common neurodegenerative disease, with clinical symptoms encompassing progressive memory loss and cognitive impairment. Necroptosis is a form of programmed necrosis that promotes cell death and neuroinflammation, which further mediates the pathogenesis of several neurodegenerative diseases, especially AD. Current evidence has strongly suggested that necroptosis is activated in AD brains, resulting in neuronal death and cognitive impairment. We searched the PubMed database, screening all articles published before September 28, 2022 related to necroptosis in the context of AD pathology. The keywords in the search included: "necroptosis", "Alzheimer's disease", "signaling pathways", "Aβ", Aβo", "Tau", "p-Tau", "neuronal death", "BBB damage", "neuroinflammation", "microglia", "mitochondrial dysfunction", "granulovacuolar degeneration", "synaptic loss", "axonal degeneration", "Nec-1", "Nec-1s", "GSK872", "NSA", "OGA", "RIPK1", "RIPK3", and "MLKL". Results show that necroptosis has been involved in multiple pathological processes of AD, including amyloid-β aggregation, Tau accumulation, neuronal death, and blood-brain barrier damage, etc. More importantly, existing research on AD necroptosis interventions, including drug intervention and potential gene targets, as well as its current clinical development status, was discussed. Finally, the issues pertaining to necroptosis in AD were presented. Accordingly, this review may provide further insight into clinical perspectives and challenges for the future treatment of AD by targeting the necroptosis pathway.

New Insights into Risk Genes and Their Candidates in Multiple Sclerosis

Oligodendrocytes are central nervous system glial cells that wrap neuronal axons with their differentiated myelin membranes as biological insulators. There has recently been an emerging concept that multiple sclerosis could be triggered and promoted by various risk genes that appear likely to contribute to the degeneration of oligodendrocytes. Despite the known involvement of vitamin D, immunity, and inflammatory cytokines in disease progression, the common causes and key genetic mechanisms remain unknown. Herein, we focus on recently identified risk factors and risk genes in the background of multiple sclerosis and discuss their relationships.

Chronic oligodendrocyte injury in central nervous system pathologies

Myelin, the membrane surrounding neuronal axons, is critical for central nervous system (CNS) function. Injury to myelin-forming oligodendrocytes (OL) in chronic neurological diseases (e.g. multiple sclerosis) ranges from sublethal to lethal, leading to OL dysfunction and myelin pathology, and consequent deleterious impacts on axonal health that drive clinical impairments. This is regulated by intrinsic factors such as heterogeneity and age, and extrinsic cellular and molecular interactions. Here, we discuss the responses of OLs to injury, and perspectives for therapeutic targeting. We put forward that targeting mature OL health in neurological disease is a promising therapeutic strategy to support CNS function.