Microglial-to-neuronal CCR5 signaling regulates autophagy in neurodegeneration

CCR5 antagonist maraviroc alleviates doxorubicin-induced neuroinflammation and neurobehavioral deficiency by regulating NF-κB/NLRP3 signaling in a breast cancer mouse model

The chemotherapeutic agent Doxorubicin (DOX) is known to cause chemotherapy-induced cognitive impairment (CICI). Maraviroc, a potent C-C chemokine receptor 5 (CCR5) antagonist, shows neuroprotective properties, while its role in CICI remains unclear. This study determined the therapeutic potential of maraviroc on CICI. Adult C57BL/6J mice with implanted breast cancer cells received four weekly intraperitoneal injections of saline (Control group), 5 mg/kg DOX (DOX group), 10 mg/kg maraviroc (MVC group), or 5 mg/kg DOX with 10 mg/kg maraviroc (DOX + MVC group). The Morris Water Maze (MWM) was used for neurobehavioural test. Western blot analysis and immunofluorescence were used to evaluate the expressions of inflammatory markers, apoptosis-related proteins, and synaptic-related proteins. The volume and weight of tumor were also evaluated after treatments. DOX treatment significantly increased chemokines (CCL3, CCL4) and inflammatory cytokines (IL-1β, TNF-α) in tumor-bearing mice hippocampus. While maraviroc administration reduced hippocampal proinflammatory factors compared to the DOX group. Furthermore, it also lowered apoptosis markers, restored synaptic proteins levels, and inhibited the NF-κB/NLRP3 pathway. Accordingly, maraviroc treatment significantly improved DOX-induced neurobehavioural impairments as evidenced by an increased number of platform crossings and percentage of target quadrant time in the MWM test. Additionally, when combined with DOX, maraviroc had additional inhibitory effects on tumor growth. These findings suggest that maraviroc can mitigate DOX-induced CICI by suppressing elevated proinflammatory chemokines and cytokines through the NF-κB/NLRP3 pathway, potentially offering an anti-tumor benefit. This research presents a promising therapeutic approach for DOX-induced CICI, enhancing the safety and efficacy of cancer treatments.

Neurotropic virus infection and neurodegenerative diseases: Potential roles of autophagy pathway

Neurodegenerative diseases (NDs) constitute a group of disorders characterized by the progressive deterioration of nervous system functionality. Currently, the precise etiological factors responsible for NDs remain incompletely elucidated, although it is probable that a combination of aging, genetic predisposition, and environmental stressors participate in this process. Accumulating evidence indicates that viral infections, especially neurotropic viruses, can contribute to the onset and progression of NDs. In this review, emerging evidence supporting the association between viral infection and NDs is summarized, and how the autophagy pathway mediated by viral infection can cause pathological aggregation of cellular proteins associated with various NDs is discussed. Furthermore, autophagy-related genes (ARGs) involved in Herpes simplex virus (HSV-1) infection and NDs are analyzed, and whether these genes could link HSV-1 infection to NDs is discussed. Elucidating the mechanisms underlying NDs is critical for developing targeted therapeutic approaches that prevent the onset and slow the progression of NDs.

Catecholamines and Parkinson's disease: tyrosine hydroxylase (TH) over tetrahydrobiopterin (BH4) and GTP cyclohydrolase I (GCH1) to cytokines, neuromelanin, and gene therapy: a historical overview

The author identified the genes and proteins of human enzymes involved in the biosynthesis of catecholamines (dopamine, norepinephrine, epinephrine) and tetrahydrobiopterin (BH4): tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), dopamine β-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT), and GTP cyclohydrolase I (GCH1). In Parkinson's disease (PD), the activities and levels of mRNA and protein of all catecholamine-synthesizing enzymes are decreased, especially in dopamine neurons in the substantia nigra. Hereditary GCH1 deficiency results in reductions in the levels of BH4 and the activities of TH, causing decreases in dopamine levels. Severe deficiencies in GCH1 or TH cause severe decreases in dopamine levels leading to severe neurological symptoms, whereas mild decreases in TH activity in mild GCH1 deficiency or in mild TH deficiency result in only modest reductions in dopamine levels and symptoms of DOPA-responsive dystonia (DRD, Segawa disease) or juvenile Parkinsonism. DRD is a treatable disease and small doses of L-DOPA can halt progression. The death of dopamine neurons in PD in the substantia nigra may be related to (i) inflammatory effect of extra neuronal neuromelanin, (ii) inflammatory cytokines which are produced by activated microglia, (iii) decreased levels of BDNF, and/or (iv) increased levels of apoptosis-related factors. This review also discusses progress in gene therapies for the treatment of PD, and of GCH1, TH and AADC deficiencies, by transfection of TH, AADC, and GCH1 via adeno-associated virus (AAV) vectors.

SARS-CoV-2 Spike Protein 1 Causes Aggregation of α-Synuclein via Microglia-Induced Inflammation and Production of Mitochondrial ROS: Potential Therapeutic Applications of Metformin

Abnormal aggregation of α-synuclein is the hallmark of neurodegenerative diseases, classified as α-synucleinopathies, primarily occurring sporadically. Their onset is associated with an interaction between genetic susceptibility and environmental factors such as neurotoxins, oxidative stress, inflammation, and viral infections. Recently, evidence has suggested an association between neurological complications in long COVID (sometimes referred to as 'post-acute sequelae of COVID-19') and α-synucleinopathies, but its underlying mechanisms are not completely understood. In this study, we first showed that SARS-CoV-2 Spike protein 1 (S1) induces α-synuclein aggregation associated with activation of microglial cells in the rodent model. In vitro, we demonstrated that S1 increases aggregation of α-synuclein in BE(2)M-17 dopaminergic neurons via BV-2 microglia-mediated inflammatory responses. We also identified that S1 directly affects aggregation of α-synuclein in dopaminergic neurons through increasing mitochondrial ROS, though only under conditions of sufficient α-Syn accumulation. In addition, we observed a synergistic effect between S1 and the neurotoxin MPP+ S1 treatment. Combined with a low dose of MPP+, it boosted α-synuclein aggregation and mitochondrial ROS production compared to S1 or the MPP+ treatment group. Furthermore, we evaluated the therapeutic effects of metformin. The treatment of metformin suppressed the S1-induced inflammatory response and α-synucleinopathy. Our findings demonstrate that S1 promotes α-synucleinopathy via both microglia-mediated inflammation and mitochondrial ROS, and they provide pathological insights, as well as a foundation for the clinical management of α-synucleinopathies and the onset of neurological symptoms after the COVID-19 outbreak.

Alzheimer's disease associated isoforms of human CD33 distinctively modulate microglial cell responses in 5XFAD mice

Microglia play diverse pathophysiological roles in Alzheimer's disease (AD), with genetic susceptibility factors skewing microglial cell function to influence AD risk. CD33 is an immunomodulatory receptor associated with AD susceptibility through a single nucleotide polymorphism that modulates mRNA splicing, skewing protein expression from a long protein isoform (CD33M) to a short isoform (CD33m). Understanding how human CD33 isoforms differentially impact microglial cell function in vivo has been challenging due to functional divergence of CD33 between mice and humans. We address this challenge by studying transgenic mice expressing either of the human CD33 isoforms crossed with the 5XFAD mouse model of amyloidosis and find that human CD33 isoforms have opposing effects on the response of microglia to amyloid-β (Aβ) deposition. Mice expressing CD33M have increased Aβ levels, more diffuse plaques, fewer disease-associated microglia, and more dystrophic neurites compared to 5XFAD control mice. Conversely, CD33m promotes plaque compaction and microglia-plaque contacts, and minimizes neuritic plaque pathology, highlighting an AD protective role for this isoform. Protective phenotypes driven by CD33m are detected at an earlier timepoint compared to the more aggressive pathology in CD33M mice that appears at a later timepoint, suggesting that CD33m has a more prominent impact on microglia cell function at earlier stages of disease progression. In addition to divergent roles in modulating phagocytosis, scRNAseq and proteomics analyses demonstrate that CD33m+ microglia upregulate nestin, an intermediate filament involved in cell migration, at plaque contact sites. Overall, our work provides new functional insights into how CD33, as a top genetic susceptibility factor for AD, modulates microglial cell function.

Correction of symptoms of Huntington disease by genistein through FOXO3-mediated autophagy stimulation

Huntington disease (HD) is a neurodegenerative disorder caused by a mutation in the HTT gene. The expansion of CAG triplets leads to the appearance of misfolded HTT (huntingtin) forming aggregates and leading to impairment of neuronal functions. Here we demonstrate that stimulation of macroautophagy/autophagy by genistein (4',5,7-trihydroxyisoflavone or 5,7-dihydroxy-3-(4-hydroxyphenyl)-4 H-1-benzopyran-4-one) caused a reduction of levels of mutated HTT in brains of HD mice and correction of their behavior as assessed in a battery of cognitive, anxiety and motor tests, even if the compound was administered after symptoms had developed in the animals. Biochemical and immunological parameters were also improved in HD mice. Studies on molecular mechanisms of genistein-mediated stimulation of autophagy in HD cells indicated the involvement of the FOXO3-related pathway. In conclusion, treatment with genistein stimulates the autophagy process in the brains of HD mice, leading to correction of symptoms of HD, suggesting that it might be considered as a potential drug for this disease. Combined with a very recently published report indicating that impaired autophagy may be a major cause of neurodegenerative changes, these results may indicate the way to the development of effective therapeutic approaches for different neurodegenerative diseases by testing compounds (or possibly combinations of compounds) capable of stimulating autophagy and/or unblocking this process.Abbreviations: CNS: central nervous system; EPM: elevated plus-maze; GOT1/ASPAT: glutamic-oxaloacetic transaminase 1, soluble; GPT/ALAT/ALT: glutamic pyruvic transaminase, soluble; HD: Huntington disease; HTT: huntingtin; IL: interleukin; mHTT: mutant huntingtin; NOR: novel object recognition; MWM: Morris water maze; OF: open field; ROS: reactive oxygen species; TNF: tumor necrosis factor.

Duloxetine protected indomethacin-induced gastric mucosal injury by increasing serotonin-dependent RANTES expression and activating PI3K-AKT-VEGF pathway

Antidepressant duloxetine has been shown protective effect on indomethacin-induced gastric ulcer, which was escorted by inflammation in the gastric mucosa. Cytokines are the principal mediators of inflammation. Thus, by screening the differential expression of cytokines in the gastric mucosa using cytokine array at 3 h after indomethacin exposure, when the gastric ulcer began to format, we found that indomethacin increased cytokines which promoted inflammation responses, whereas duloxetine decreased pro-inflammatory cytokines increased by indomethacin and increased RANTES expression. RANTES was consistently increased by pretreated with both 5 mg/kg and 20 mg/kg duloxetine at 3 h and 6 h after indomethacin exposure in male rats. Selective blockade of RANTES-CCR5 axis by a functional antagonist Met-RANTES or a CCR5 antagonist maraviroc suppressed the protection of duloxetine. Considering the pharmacologic action of duloxetine on reuptake of monoamine neurotransmitters, we examined the serotonin (5-HT), norepinephrine and dopamine contents in the blood and discovered 20 mg/kg duloxetine increased 5-HT levels in platelet-poor plasma, while treatment with 5-HT promoted expression of RANTES in the gastric mucosa and alleviated the indomethacin-induced gastric injury. Furthermore, duloxetine activated PI3K-AKT-VEGF signaling pathway, which was regulated by RANTES-CCR5, and selective inhibitor of VEGF receptor axitinib blocked the prophylactic effect of duloxetine. Furthermore, duloxetine also protected gastric mucosa from indomethacin in female rats, and RANTES was increased by duloxetine after 6 h after indomethacin exposure too. Together, our results identified the role of cytokines, particularly RANTES, and the underlying mechanisms in gastroprotective effect of duloxetine against indomethacin, which advanced our understanding in inflammatory modulation by monoamine-based antidepressants.

Microglial cytokines poison neuronal autophagy via CCR5, a druggable target

In the prodromal phase of neurodegenerative diseases, microglia switch to an activated state resulting in increased secretion of pro-inflammatory factors. We reported that C - C chemokine ligand 3 (CCL3), C - C chemokine ligand 4 (CCL4) and C - C chemokine ligand 5 (CCL5) contained in the secretome of activated microglia inhibit neuronal autophagy via a non-cell autonomous mechanism. These chemokines bind and activate neuronal C - C chemokine receptor type 5 (CCR5), which, in turn, promotes phosphoinositide 3-kinase (PI3K) - protein kinase B (PKB, or AKT) - mammalian target of rapamycin complex 1 (mTORC1) pathway activation, which inhibits autophagy, thus causing the accumulation of aggregate-prone proteins in the cytoplasm of neurons. The levels of CCR5 and its chemokine ligands are increased in the brains of pre-manifesting Huntington disease (HD) and tauopathy mouse models. CCR5 accumulation might be due to a self-amplifying mechanism, since CCR5 is a substrate of autophagy and CCL5-CCR5-mediated autophagy inhibition impairs CCR5 degradation. Furthermore, pharmacological, or genetic inhibition of CCR5 rescues mTORC1-autophagy dysfunction and improves neurodegeneration in HD and tauopathy mouse models, suggesting that CCR5 hyperactivation is a pathogenic signal driving the progression of these diseases.

CCR5 and inflammatory storm

Chemokines and their corresponding receptors play crucial roles in orchestrating inflammatory and immune responses, particularly in the context of pathological conditions disrupting the internal environment. Among these receptors, CCR5 has garnered considerable attention due to its significant involvement in the inflammatory cascade, serving as a pivotal mediator of neuroinflammation and other inflammatory pathways associated with various diseases. However, a notable gap persists in comprehending the intricate mechanisms governing the interplay between CCR5 and its ligands across diverse and intricate inflammatory pathologies. Further exploration is warranted, especially concerning the inflammatory cascade instigated by immune cell infiltration and the precise binding sites within signaling pathways. This study aims to illuminate the regulatory axes modulating signaling pathways in inflammatory cells by providing a comprehensive overview of the pathogenic processes associated with CCR5 and its ligands across various disorders. The primary focus lies on investigating the pathomechanisms associated with CCR5 in disorders related to neuroinflammation, alongside the potential impact of aging on these processes and therapeutic interventions. The discourse culminates in addressing current challenges and envisaging potential future applications, advocating for innovative research endeavors to advance our comprehension of this realm.

Unveiling the role of astrocytes in postoperative cognitive dysfunction

Alzheimer's disease (AD) is the most common neurodegenerative disorder, characterized by progressive cognitive decline and the accumulation of amyloid-beta plaques, tau tangles, and neuroinflammation in the brain. Postoperative cognitive dysfunction (POCD) is a prevalent and debilitating condition characterized by cognitive decline following neuroinflammation and oxidative stress induced by procedures. POCD and AD are two conditions that share similarities in the underlying mechanisms and pathophysiology. Compared to normal aging individuals, individuals with POCD are at a higher risk for developing AD. Emerging evidence suggests that astrocytes, the most abundant glial cells in the central nervous system, play a critical role in the pathogenesis of these conditions. Comprehensive functions of astrocyte in AD has been extensively explored, but very little is known about POCD may experience late-onset AD pathogenesis. Herein, in this context, we mainly explore the multifaceted roles of astrocytes in the context of POCD, highlighting their involvement in neuroinflammation, neurotransmitter regulation, synaptic plasticity and neurotrophic support, and discuss how POCD may augment the onset of AD. Additionally, we discuss potential therapeutic strategies targeting astrocytes to mitigate or prevent POCD, which hold promise for improving the quality of life for patients undergoing surgeries and against AD in the future.

Pharmacological advances in anti-retroviral therapy for human immunodeficiency virus-1 infection: A comprehensive review

The discovery of anti-retroviral (ARV) drugs over the past 36 years has introduced various classes, including nucleoside/nucleotide reverse transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors, protease inhibitor, fusion, and integrase strand transfer inhibitors inhibitors. The introduction of combined highly active anti-retroviral therapies in 1996 was later proven to combat further ARV drug resistance along with enhancing human immunodeficiency virus (HIV) suppression. As though the development of ARV therapies was continuously expanding, the variation of action caused by ARV drugs, along with its current updates, was not comprehensively discussed, particularly for HIV-1 infection. Thus, a range of HIV-1 ARV medications is covered in this review, including new developments in ARV therapy based on the drug's mechanism of action, the challenges related to HIV-1, and the need for combination therapy. Optimistically, this article will consolidate the overall updates of HIV-1 ARV treatments and conclude the significance of HIV-1-related pharmacotherapy research to combat the global threat of HIV infection.

Microbiota-gut-brain axis and its therapeutic applications in neurodegenerative diseases

The human gastrointestinal tract is populated with a diverse microbial community. The vast genetic and metabolic potential of the gut microbiome underpins its ubiquity in nearly every aspect of human biology, including health maintenance, development, aging, and disease. The advent of new sequencing technologies and culture-independent methods has allowed researchers to move beyond correlative studies toward mechanistic explorations to shed light on microbiome-host interactions. Evidence has unveiled the bidirectional communication between the gut microbiome and the central nervous system, referred to as the "microbiota-gut-brain axis". The microbiota-gut-brain axis represents an important regulator of glial functions, making it an actionable target to ameliorate the development and progression of neurodegenerative diseases. In this review, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases. As the gut microbiome provides essential cues to microglia, astrocytes, and oligodendrocytes, we examine the communications between gut microbiota and these glial cells during healthy states and neurodegenerative diseases. Subsequently, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases using a metabolite-centric approach, while also examining the role of gut microbiota-related neurotransmitters and gut hormones. Next, we examine the potential of targeting the intestinal barrier, blood-brain barrier, meninges, and peripheral immune system to counteract glial dysfunction in neurodegeneration. Finally, we conclude by assessing the pre-clinical and clinical evidence of probiotics, prebiotics, and fecal microbiota transplantation in neurodegenerative diseases. A thorough comprehension of the microbiota-gut-brain axis will foster the development of effective therapeutic interventions for the management of neurodegenerative diseases.

cGAS-STING signalling regulates microglial chemotaxis in genome instability

Defective DNA damage signalling and repair is a hallmark of age-related and genetic neurodegenerative disease. One mechanism implicated in disease progression is DNA damage-driven neuroinflammation, which is largely mediated by tissue-resident immune cells, microglia. Here, we utilise human microglia-like cell models of persistent DNA damage and ATM kinase deficiency to investigate how genome instability shapes microglial function. We demonstrate that upon DNA damage the cytosolic DNA sensing cGAS-STING axis drives chronic inflammation and a robust chemokine response, exemplified by production of CCL5 and CXCL10. Transcriptomic analyses revealed that cell migratory pathways were highly enriched upon IFN-β treatment of human iPSC-derived microglia, indicating that the chemokine response to DNA damage mirrors type I interferon signalling. Furthermore, we find that STING deletion leads to a defect in microglial chemotaxis under basal conditions and upon ATM kinase loss. Overall, this work provides mechanistic insights into cGAS-STING-dependent neuroinflammatory mechanisms and consequences of genome instability in the central nervous system.

The type-I interferon response potentiates seeded tau aggregation and exacerbates tau pathology

INTRODUCTION

Signatures of a type-I interferon (IFN-I) response are observed in the post mortem brain in Alzheimer's disease (AD) and other tauopathies. However, the effect of the IFN-I response on pathological tau accumulation remains unclear.

METHODS

We examined the effects of IFN-I signaling in primary neural culture models of seeded tau aggregation and P301S-tau transgenic mouse models in the context of genetic deletion of the IFN-I receptor (IFNAR).

RESULTS

Polyinosinic:polycytidylic acid (PolyI:C), a synthetic analog of viral nucleic acids, evoked a potent cytokine response that enhanced seeded aggregation of tau in an IFN-I-dependent manner. IFN-I-induced vulnerability could be pharmacologically prevented and was intrinsic to neurons. Aged P301S-tau mice lacking Ifnar1 had significantly reduced tau pathology compared to mice with intact IFN signaling.

DISCUSSION

We identify a critical role for IFN-I in potentiating tau aggregation. IFN-I is therefore identified as a potential therapeutic target in AD and other tauopathies.

HIGHLIGHTS

Type-I IFN (IFN-I) promotes seeded tau aggregation in neural cultures. IFNAR inhibition prevents IFN-I driven sensitivity to tau aggregation. IFN-I driven vulnerability is intrinsic to neurons. Tau pathology is significantly reduced in aged P301S-tau mice lacking IFNAR.

Top 100 most-cited articles on tau protein: a bibliometric analysis and evidence mapping

Background

Tau, a microtubule-associated protein extensively distributed within the central nervous system (CNS), exhibits close associations with various neurodegenerative disorders. Here, we aimed to conduct a qualitative and quantitative bibliometric study of the top 100 most-cited publications on tau protein and reveal the current research hotspots and future perspectives.

Methods

The relevant literature was retrieved from the Web of Science Core Collection. CiteSpace (v6.2.R4) and VOSviewer (1.6.19) were adopted for bibliometric analysis with statistical and visual analysis.

Results

Citations per article ranged from 615 to 3,123, with a median number of 765.5 times. "Neuroscience" emerged as the most extensively researched subject in this field. The USA has emerged as the leading country, with a publication record (n = 65), total citations (n = 66,543), strong centrality (0.29), and extensive international collaborations. Harvard University (n = 11) and the University of California, San Francisco (n = 11) were the top two institutions in terms of publications. Neuron dominated with 13 articles in the 37 high-quality journals. M. Goedert from the MRC Laboratory of Molecular Biology was the most productive (n = 9) and top co-cited (n = 179) author. The most frequently studied keywords were Alzheimer's disease (n = 38). Future research is anticipated to intensify its focus on the pathogenesis of various tau-related diseases, emphasizing the phosphorylation and structural alterations of tau protein, particularly in Alzheimer's disease.

Conclusion

The pathogenesis of various tau-related diseases, including the phosphorylation and structural alterations of the tau protein, will be the primary focus of future research, with particular emphasis on Alzheimer's disease as a central area of investigation.

Platinum Nanozymes Counteract Photoreceptor Degeneration and Retina Inflammation in a Light-Damage Model of Age-Related Macular Degeneration

Degeneration of photoreceptors in age-related macular degeneration (AMD) is associated with oxidative stress due to the intense aerobic metabolism of rods and cones that if not properly counterbalanced by endogenous antioxidant mechanisms can precipitate photoreceptor degeneration. In spite of being a priority eye disease for its high incidence in the elderly, no effective treatments for AMD exist. While systemic administration of antioxidants has been unsuccessful in slowing down degeneration, locally administered rare-earth nanoparticles were shown to be effective in preventing retinal photo-oxidative damage. However, because of inherent problems of dispersion in biological media, limited antioxidant power, and short lifetimes, these NPs are still confined to the preclinical stage. Here we propose platinum nanoparticles (PtNPs), potent antioxidant nanozymes, as a therapeutic tool for AMD. PtNPs exhibit high catalytic activity at minimal concentrations and protect primary neurons against oxidative insults and the ensuing apoptosis. We tested the efficacy of intravitreally injected PtNPs in preventing or mitigating light damage produced in dark-reared albino Sprague-Dawley rats by in vivo electroretinography (ERG) and ex vivo retina morphology and electrophysiology. We found that both preventive and postlesional treatments with PtNPs increased the amplitude of ERG responses to light stimuli. Ex vivo recordings demonstrated the selective preservation of ON retinal ganglion cell responses to light stimulation in lesioned retinas treated with PtNPs. PtNPs administered after light damage significantly preserved the number of photoreceptors and inhibited the inflammatory response to degeneration, while the preventive treatment had a milder effect. The data indicate that PtNPs can effectively break the vicious cycle linking oxidative stress, degeneration, and inflammation by exerting antioxidant and anti-inflammatory actions. The increased photoreceptor survival and visual performances in degenerated retinas, together with their high biocompatibility, make PtNPs a potential strategy to cure AMD.

The role of glial autophagy in Alzheimer's disease

Although Alzheimer's disease is the most pervasive neurodegenerative disorder, the mechanism underlying its development is still not precisely understood. Available data indicate that pathophysiology of this disease may involve impaired autophagy in glial cells. The dysfunction is manifested as reduced ability of astrocytes and microglia to clear abnormal protein aggregates. Consequently, excessive accumulation of amyloid beta plaques and neurofibrillary tangles activates microglia and astrocytes leading to decreased number of mature myelinated oligodendrocytes and death of neurons. These pathologic effects of autophagy dysfunction can be rescued by pharmacological activation of autophagy. Therefore, a deeper understanding of the molecular mechanisms involved in autophagy dysfunction in glial cells in Alzheimer's disease may lead to the development of new therapeutic strategies. However, such strategies need to take into consideration differences in regulation of autophagy in different types of neuroglia.

The association of microbial infection and adaptive immune cell activation in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia. Early symptoms include the loss of memory and mild cognitive ability; however, as the disease progresses, these symptoms can present with increased severity manifesting as mood and behaviour changes, disorientation, and a loss of motor/body control. AD is one of the leading causes of death in the UK, and with an ever-increasing ageing society, patient numbers are predicted to rise posing a significant global health emergency. AD is a complex neurophysiological disorder where pathology is characterized by the deposition and aggregation of misfolded amyloid-beta (Aβ)-protein that in-turn promotes excessive tau-protein production which together drives neuronal cell dysfunction, neuroinflammation, and neurodegeneration. It is widely accepted that AD is driven by a combination of both genetic and immunological processes with recent data suggesting that adaptive immune cell activity within the parenchyma occurs throughout disease. The mechanisms behind these observations remain unclear but suggest that manipulating the adaptive immune response during AD may be an effective therapeutic strategy. Using immunotherapy for AD treatment is not a new concept as the only two approved treatments for AD use antibody-based approaches to target Aβ. However, these have been shown to only temporarily ease symptoms or slow progression highlighting the urgent need for newer treatments. This review discusses the role of the adaptive immune system during AD, how microbial infections may be contributing to inflammatory immune activity and suggests how adaptive immune processes can pose as therapeutic targets for this devastating disease.

Heterogeneous complement and microglia activation mediates stress-induced synapse loss

Spatially heterogeneous synapse loss is a characteristic of many psychiatric and neurological disorders, but the underlying mechanisms are unclear. Here, we show that spatially-restricted complement activation mediates stress-induced heterogeneous microglia activation and synapse loss localized to the upper layers of the mouse medial prefrontal cortex (mPFC). Single cell RNA sequencing also reveals a stress-associated microglia state marked by high expression of the apolipoprotein E gene (ApoE high ) localized to the upper layers of the mPFC. Mice lacking complement component C3 are protected from stress-induced layer-specific synapse loss, and the ApoE high microglia population is markedly reduced in the mPFC of these mice. Furthermore, C3 knockout mice are also resilient to stress-induced anhedonia and working memory behavioral deficits. Our findings suggest that region-specific complement and microglia activation can contribute to the disease-specific spatially restricted patterns of synapse loss and clinical symptoms found in many brain diseases.

Lysosomal acidification dysfunction in microglia: an emerging pathogenic mechanism of neuroinflammation and neurodegeneration

Microglia are the resident innate immune cells in the brain with a major role in orchestrating immune responses. They also provide a frontline of host defense in the central nervous system (CNS) through their active phagocytic capability. Being a professional phagocyte, microglia participate in phagocytic and autophagic clearance of cellular waste and debris as well as toxic protein aggregates, which relies on optimal lysosomal acidification and function. Defective microglial lysosomal acidification leads to impaired phagocytic and autophagic functions which result in the perpetuation of neuroinflammation and progression of neurodegeneration. Reacidification of impaired lysosomes in microglia has been shown to reverse neurodegenerative pathology in Alzheimer's disease. In this review, we summarize key factors and mechanisms contributing to lysosomal acidification impairment and the associated phagocytic and autophagic dysfunction in microglia, and how these defects contribute to neuroinflammation and neurodegeneration. We further discuss techniques to monitor lysosomal pH and therapeutic agents that can reacidify impaired lysosomes in microglia under disease conditions. Finally, we propose future directions to investigate the role of microglial lysosomal acidification in lysosome-mitochondria crosstalk and in neuron-glia interaction for more comprehensive understanding of its broader CNS physiological and pathological implications.