Early long-term administration of the CSF1R inhibitor PLX3397 ablates microglia and reduces accumulation of intraneuronal amyloid, neuritic plaque deposition and pre-fibrillar oligomers in 5XFAD mouse model of Alzheimer's disease

Spinal astrocyte-derived M-CSF mediates microglial reaction and drives visceral hypersensitivity following DSS-induced colitis

Visceral hypersensitivity is one of the most prevalent symptoms of inflammatory bowel disease (IBD), and it can be difficult to cure despite achieving endoscopic remission. Accumulating studies have described that macrophage colony-stimulating factor (M-CSF) modulates neuroinflammation in the central nervous system (CNS) and the development of chronic pain, while the underlying mechanism for whether and how M-CSF/CSF1R signaling pathway regulates visceral hypersensitivity following colitis remains unknown. In the present study, using the dextran sulfate sodium (DSS)-induced colitis model, we determined that microglial accumulation occurred in the spinal dorsal horn during remission phase. The reactive microglia released inflammatory factor, increased neuronal excitability in the dorsal horn, and produced chronic visceral pain behaviors in DSS-treated adult male mice. In addition, we also found significantly increased signaling mediated by astrocytic M-CSF and microglial CSF1R in dorsal horn in the mice with colitis. Exogenous M-CSF induced microglial activation, neuronal hyperactivity and behavioral hypersensitivity in the control group, inhibition of astrocyte/microglia by fluorocitrate/minocycline significantly suppressed microglial and neuronal activity, and relieved the visceral hypersensitivity in the model mice. Overall, our experimental study uncovers the critical involvement of spinal astrocyte-derived M-CSF and reactive microglia in the initiation and maintenance of visceral hypersensitivity following colitis, thereby identifying spinal M-CSF as a target for treating chronic visceral pain. This may provide more accurate theoretical guidance for clinical patients with IBD.

Dysregulated ac4C modification of mRNA in a mouse model of early-stage Alzheimer's disease

BACKGROUND

The identification and intervention of Alzheimer's Disease (AD) in its early-stage allows for the timely implementation of lifestyle modifications and therapeutic strategies. Although dysregulation of protein expression has been reported in the brain from AD patients and AD animal models, the underlying mechanisms remain poorly understood. N4-acetylcytidine (ac4C), the only known form of RNA acetylation in eukaryotes, has recently been shown to regulate mRNA stability and translation efficiency. However, the dysregulation of ac4C associated with abnormal protein expression levels in the brain of early-stage mouse models of AD remains to be elucidated.

METHODS

This study investigated ac4C modifications, mRNA and protein expression in the hippocampus of 3 and 6-month-old 5×FAD mice, a mouse model of AD, and wild-type (WT) littermates. The multi-omics analysis was performed: acetylated RNA immunoprecipitation followed by next-generation sequencing (acRIP-seq) to identify ac4C mRNAs, deep RNA sequencing (RNA-seq) to quantify mRNA abundance, and label-free quantitative proteomics to assess protein expression levels. In addition, we used acRIP-qPCR, regular qPCR and western blots to verify the ac4C, mRNA and protein levels of some key genes that were identified by the high-throughput assays.

RESULTS

Proteomic analysis revealed significant change of protein expression in the hippocampus of 3-months-old 5×FAD mice, compared with WT littermates. In contrast, RNA-seq analysis indicated that there were no substantial alterations in mRNA expression levels in the hippocampus of 3-months-old 5×FAD mice, compared to WT littermates. Strikingly, acRIP-seq revealed notable variations in ac4C modification on mRNAs, particularly those associated with synaptic structure and function, in the hippocampus of 3-months-old 5×FAD mice, compared with WT littermates. The ac4C modifications were found to be correlated with protein expression changes. Genes that are essential for synaptic function and cognition, including GRIN1, MAP2, and DNAJC6, exhibited reduced ac4C and protein levels in 3-months-old 5×FAD mice, without any corresponding changes in the mRNA levels, compared with WT littermates. Moreover, only a small part of dysregulated ac4C mRNAs identified in the 3-month-old 5×FAD mice were found in the 6-month-old 5×FAD mice.

CONCLUSIONS

Altogether these results identified abnormal ac4C modification of mRNAs that may contribute to the dysregulation of protein synthesis in the hippocampus from an early-stage mouse model of AD.

Circadian rhythms and the light-dark cycle interact to regulate amyloid plaque accumulation and tau phosphorylation in 5xFAD mice

Background

Circadian disruption has long been appreciated as a downstream consequence of Alzheimer's Disease in humans. However, an upstream role for behavioral circadian disruption in regulating AD pathology remains an open question.

Methods

To determine the role of the central circadian clock in the suprachiasmatic nucleus (SCN) in regulating amyloid pathology, we crossed the 5xFAD amyloid mouse model with mice harboring deletion of the critical clock gene Bmal1 in GABAergic neurons using VGAT-iCre, which is expressed in >95% of SCN cells. To examine the role the light-dark cycle in this process, we aged these mice in either regular 12:12 light-dark (LD) or constant darkness (DD) conditions. Transcriptional, behavioral, and physiological rhythms were examined in VGAT-iCre; 5xFAD; Bmal1 fl/fl (VGAT-BMAL1KO;5xFAD) mice under varying light conditions. Amyloid plaque deposition, peri-plaque tau phosphorylation, and other pathology was examined by immunohistochemistry, and transcriptomic changes were examined by high-throughput qPCR.

Results

VGAT-BMAL1KO;5xFAD mice showed loss of SCN BMAL1 expression and severe disruption of behavioral rhythms in both LD and DD, with loss of day-night rhythms in consolidated sleep and blunting of rhythmic clock gene expression in the brain. Surprisingly, VGAT-BMAL1KO;5xFAD mice kept under LD showed reduced total plaque accumulation and peri-plaque tau phosphorylation, compared to Cre-negative controls. These changes were gated by the light-dark cycle, as they were absent in VGAT-BMAL1KO;5xFAD mice kept in DD conditions. Total plaque accumulation was also reduced in control 5xFAD mice kept in DD as compared to LD, suggesting a general effect of light-dark cycle on amyloid aggregation. Expression of murine presenilin 1 (Psen1) -- which catalyzes the processing of sAPPβ into Aβ -- as well as APP cleavage to C-terminal fragments, were suppressed in VGAT-BMAL1KO;5xFAD under LD conditions.

Conclusions

These studies elucidated an interaction between the circadian clock in GABAergic neurons and the light-dark cycle in regulating amyloid pathology and suggest that decoupling the central clock form the light-dark cycle may reduce APP cleavage and plaque formation. These results call into question the proposed simple positive feedback loop between circadian rhythm disruption and Alzheimer's Disease pathology.

Pharmacological Inhibition of Microglial Proliferation Supports Blood-Brain Barrier Integrity in Experimental Autoimmune Encephalomyelitis

Blood-brain barrier dysfunction (BBB) is a primary characteristic of experimental autoimmune encephalomyelitis (EAE), an experimental model of multiple sclerosis (MS). We have previously shown that blocking microglial proliferation using GW2580, a selective inhibitor of CSF1R (Colony stimulating factor 1 receptor), reduced disease progression and severity and prevented the relapse phase. However, whether this was due to effects of GW2580 on the functional integrity of the BBB was not determined. Therefore, here, we examine BBB properties in rats during EAE under GW2580 treatment. Our data suggest that blocking early microglial proliferation through selective targeting of CSF1R signaling has a therapeutic effect in EAE by protecting BBB integrity and reducing peripheral immune cell infiltration. Taken together, our results identify a novel mechanism underlying the effects of GW2580, which could offer a novel therapy for MS.

Development of cerebral microhemorrhages in a mouse model of hypertension

Cerebral microhemorrhages (CMH) are the pathological substrate for MRI-demonstrable cerebral microbleeds, which are associated with cognitive impairment and stroke. Aging and hypertension are the main risk factors for CMH. In this study, we investigated the development of CMH in a mouse model of aging and hypertension. Hypertension was induced in aged (17-month-old) female and male C57BL/6J mice via angiotensin II (Ang II), a potent vasoconstrictor. We investigated the vascular origin of CMH using three-dimensional images of 1-mm thick brain sections. We examined Ang II-induced CMH formation with and without telmisartan, an Ang II type 1 receptor (AT1R) blocker. To evaluate the effect of microglia and perivascular macrophages on CMH formation, mice were treated with PLX3397, a selective colony-stimulating factor 1 receptor (CSF1R) inhibitor, to achieve microglial and macrophage depletion. Iba-1 and CD206 labeling were used to study the relative contributions of microglia and macrophages, respectively, on CMH formation. CMH quantification was performed with analysis of histological sections labeled with Prussian blue. Vessels surrounding CMH were primarily of capillary size range (< 10 μm in diameter). Ang II-infused mice exhibited elevated blood pressure (p < 0.0001) and CMH burden (p < 0.001). CMH burden was significantly correlated with mean arterial pressure in mice with and without Ang II (r = 0.52, p < 0.05). Ang II infusion significantly increased Iba-1 immunoreactivity (p < 0.0001), and CMH burden was significantly correlated with Iba-1 in mice with and without Ang II (r = 0.32, p < 0.05). Telmisartan prevented elevation of blood pressure due to Ang II infusion and blocked Ang II-induced CMH formation without affecting Iba-1 immunoreactivity. PLX3397 treatment reduced Iba-1 immunoreactivity in Ang II-infused mice (p < 0.001) and blocked Ang II-induced CMH (p < 0.0001). No significant association between CMH burden and CD206 reactivity was observed. Our findings demonstrate Ang II infusion increases CMH burden. CMH in this model appear to be capillary-derived and Ang II-induced CMH are largely mediated by blood pressure. In addition, microglial activation may represent an alternate pathway for CMH formation. These observations emphasize the continuing importance of blood pressure control and the role of microglia in hemorrhagic cerebral microvascular disease.

Gut microbiota-derived 3-indoleacetic acid confers a protection against sepsis-associated encephalopathy through microglial aryl hydrocarbon receptors

BACKGROUND

The gut microbiota significantly contributes to the pathogenesis of central nervous system disorders. Among the bioactive molecules produced by the gut microbiota, 3-indoleacetic acid (IAA) has been shown to attenuate oxidative stress and inflammatory responses. This experiment aimed to determine the impacts of IAA on sepsis-associated encephalopathy (SAE) and the underlying mechanisms.

METHODS

A total of 34 septic patients and 24 healthy controls were included in the analysis of the clinical correlation between fecal IAA and septic encephalopathy. Fecal microbiota transplantation was used to verify the role of the gut microbiota and its metabolites in SAE. Male C57BL/6 mice aged six to eight weeks, pre-treated with IAA via oral gavage, were subjected to the cecal ligation and puncture (CLP) procedures. This treatment was administered either in combination with an aryl hydrocarbon receptor (AhR) antagonist, CH223191, or a CSF1R inhibitor, PLX3397, to eliminate microglia. Both immunofluorescence staining and enzyme-linked immunosorbent assays were used to evaluate microglia activation and inflammatory cytokine secretion. Behavioral assessments were conducted to quantify neurological deficits.

RESULTS

A decreased fecal level of IAA was observed in the patients with sepsis-associated delirium (SAD), a manifestation of SAE. A reduced IAA level was significantly associated with worsen clinical outcomes. Fecal microbiota transplantation from the SAD patients induced an SAE-like phenotype in mice, but supplementing exogenous IAA improved the SAE-like phenotype, mediated by microglia. IAA effectively binded with the aryl hydrocarbon receptor (AhR). Furthermore, IAA increased the nuclear activity of AhR in the lipopolysaccharide (LPS)-treated microglial cells, leading to reduced secretion of inflammatory cytokines. The AhR inhibitor CH223191 counteracted the protective effect of IAA against SAE in mice.

CONCLUSIONS

Gut microbiota-derived IAA confers a protection against SAE by activating AhR in microglia, improving neuronal and cognitive impairments. Thus, IAA holds the promise as a potential therapeutic agent for managing SAE.

Icariin maintaining TMEM119-positive microglial population improves hippocampus-associated memory in senescent mice in relation to R-3-hydroxybutyric acid metabolism

ETHNOPHARMACOLOGICAL RELEVANCE

Epimedium Tourn. ex L. is a traditional Chinese medicine used for thousands of years in China to treat forgetfulness. Icariin is a principal component of the genus Epimedium.

AIM OF THE STUDY

The metabolic mechanism of icariin treating forgetfulness is explored.

MATERIALS AND METHODS

A D-galactose-induced senescent mouse model was employed. The cognitive performance of mice was assessed in the fear conditioning test. Hippocampal pathology was assessed in the immunohistochemistry assay. Plasma metabolome was analyzed using GC-MS method, and the differential metabolites were further identified by UPLC-MS/MS or GC-MS method. The liver function, including ALT and AST, was assessed by enzyme reaction. Icariin was administered intraperitoneally at 50 and 100 mg/kg. Mice were administered five consecutive days per week for 8 weeks.

RESULTS

Icariin treatment improved hippocampus-related fear memory but not amygdala-related memory, whereas Pexidartinib (PLX3397), a microglial scavenger, did not. Icariin treatment maintained the TMEM119-positive microglial population and decreased the accumulation of the senescent biomarker p16 in the dorsal hippocampus in senescent mouse brains, whereas PLX3397 did not. Notably, p16 in the CA2 subregion significantly decreased in icariin-treated mice than the other hippocampal subregions. The senescent mice exhibited the circulating metabolic characteristics of mild ketoacidosis, active tricarboxylic acid (TCA) cycle, lactic acidosis, hyperglycemia, active detoxification, active cis-oleic acid metabolism, and inhibitory GABA shut. R-3-Hydroxybutyric acid primarily produced in the liver was selectively and robustly decreased by icariin treatment, which was not observed with PLX3397 treatment. The TCA cycle was rescued in senescent mice by icariin treatment. Icariin also protected liver function (plasma ALT) in D-gal-induced senescent mice.

CONCLUSIONS

Icariin may protect mouse hippocampal cognition from D-gal-induced senescence by protecting microglial homeostasis, and facilitating the utilization of R-3-hydroxybutyric acid is one of the underpins.

Ellagic Acid: A Green Multi-Target Weapon That Reduces Oxidative Stress and Inflammation to Prevent and Improve the Condition of Alzheimer's Disease

Oxidative stress (OS), generated by the overrun of reactive species of oxygen and nitrogen (RONS), is the key cause of several human diseases. With inflammation, OS is responsible for the onset and development of clinical signs and the pathological hallmarks of Alzheimer's disease (AD). AD is a multifactorial chronic neurodegenerative syndrome indicated by a form of progressive dementia associated with aging. While one-target drugs only soften its symptoms while generating drug resistance, multi-target polyphenols from fruits and vegetables, such as ellagitannins (ETs), ellagic acid (EA), and urolithins (UROs), having potent antioxidant and radical scavenging effects capable of counteracting OS, could be new green options to treat human degenerative diseases, thus representing hopeful alternatives and/or adjuvants to one-target drugs to ameliorate AD. Unfortunately, in vivo ETs are not absorbed, while providing mainly ellagic acid (EA), which, due to its trivial water-solubility and first-pass effect, metabolizes in the intestine to yield UROs, or irreversible binding to cellular DNA and proteins, which have very low bioavailability, thus failing as a therapeutic in vivo. Currently, only UROs have confirmed the beneficial effect demonstrated in vitro by reaching tissues to the extent necessary for therapeutic outcomes. Unfortunately, upon the administration of food rich in ETs or ETs and EA, URO formation is affected by extreme interindividual variability that renders them unreliable as novel clinically usable drugs. Significant attention has therefore been paid specifically to multitarget EA, which is incessantly investigated as such or nanotechnologically manipulated to be a potential "lead compound" with protective action toward AD. An overview of the multi-factorial and multi-target aspects that characterize AD and polyphenol activity, respectively, as well as the traditional and/or innovative clinical treatments available to treat AD, constitutes the opening of this work. Upon focus on the pathophysiology of OS and on EA's chemical features and mechanisms leading to its antioxidant activity, an all-around updated analysis of the current EA-rich foods and EA involvement in the field of AD is provided. The possible clinical usage of EA to treat AD is discussed, reporting results of its applications in vitro, in vivo, and during clinical trials. A critical view of the need for more extensive use of the most rapid diagnostic methods to detect AD from its early symptoms is also included in this work.

A Study on Potential Sources of Perineuronal Net-Associated Sema3A in Cerebellar Nuclei Reveals Toxicity of Non-Invasive AAV-Mediated Cre Expression in the Central Nervous System

Semaphorin 3A (Sema3A) is an axon guidance molecule, which is also abundant in the adult central nervous system (CNS), particularly in perineuronal nets (PNNs). PNNs are extracellular matrix structures that restrict plasticity. The cellular sources of Sema3A in PNNs are unknown. Most Sema3A-bearing neurons do not express Sema3A mRNA, suggesting that Sema3A may be released from other neurons. Another potential source of Sema3A is the choroid plexus. To identify sources of PNN-associated Sema3A, we focused on the cerebellar nuclei, which contain Sema3A+ PNNs. Cerebellar nuclei neurons receive prominent input from Purkinje cells (PCs), which express high levels of Sema3A mRNA. By using a non-invasive viral vector approach, we overexpressed Cre in PCs, the choroid plexus, or throughout the CNS of Sema3Afl/fl mice. Knocking out Sema3A in PCs or the choroid plexus was not sufficient to decrease the amount of PNN-associated Sema3A. Alternatively, knocking out Sema3A throughout the CNS induced a decrease in PNN-associated Sema3A. However, motor deficits, microgliosis, and neurodegeneration were observed, which were due to Cre toxicity. Our study represents the first attempt to unravel cellular sources of PNN-associated Sema3A and shows that non-invasive viral-mediated Cre expression throughout the CNS could lead to toxicity, complicating the interpretation of Cre-mediated Sema3A knock-out.

Microglia depletion reduces neurodegeneration and remodels extracellular matrix in a mouse Parkinson's disease model triggered by α-synuclein overexpression

Chronic neuroinflammation with sustained microglial activation occurs in Parkinson's disease (PD), yet the mechanisms and exact contribution of these cells to the neurodegeneration remains poorly understood. In this study, we induced progressive dopaminergic neuron loss in mice via rAAV-hSYN injection to cause the neuronal expression of α-synuclein, which produced neuroinflammation and behavioral alterations. We administered PLX5622, a colony-stimulating factor 1 receptor inhibitor, for 3 weeks prior to rAAV-hSYN injection, maintaining it for 8 weeks to eliminate microglia. This chronic treatment paradigm prevented the development of motor deficits and concomitantly preserved dopaminergic neuron cell and weakened α-synuclein phosphorylation. Gene expression profiles related to extracellular matrix (ECM) remodeling were increased after microglia depletion in PD mice, which were further validated on protein level. We demonstrated that microglia exert adverse effects during α-synuclein-overexpression-induced neuronal lesion formation, and their depletion remodels ECM and aids recovery following insult.

Microglia depletion reduces human neuronal APOE4-related pathologies in a chimeric Alzheimer's disease model

Despite strong evidence supporting the important roles of both apolipoprotein E4 (APOE4) and microglia in Alzheimer's disease (AD) pathogenesis, the effects of microglia on neuronal APOE4-related AD pathogenesis remain elusive. To examine such effects, we utilized microglial depletion in a chimeric model with induced pluripotent stem cell (iPSC)-derived human neurons in mouse hippocampus. Specifically, we transplanted homozygous APOE4, isogenic APOE3, and APOE-knockout (APOE-KO) iPSC-derived human neurons into the hippocampus of human APOE3 or APOE4 knockin mice and then depleted microglia in half of the chimeric mice. We found that both neuronal APOE and microglial presence were important for the formation of Aβ and tau pathologies in an APOE isoform-dependent manner (APOE4 > APOE3). Single-cell RNA sequencing analysis identified two pro-inflammatory microglial subtypes with elevated MHC-II gene expression enriched in chimeric mice with human APOE4 neuron transplants. These findings highlight the concerted roles of neuronal APOE, especially APOE4, and microglia in AD pathogenesis.

Preferential clustering of microglia and astrocytes around neuritic plaques during progression of Alzheimer's disease neuropathological changes

Neuroinflammation plays an important role in the pathological cascade of Alzheimer's disease (AD) along with aggregation of extracellular amyloid-β (Aβ) plaques and intracellular aggregates of tau protein. In animal models of amyloidosis, local immune activation is centered around Aβ plaques, which are usually of uniform morphology, dependent on the transgenic model used. In postmortem human brains a diversity of Aβ plaque morphologies is seen including diffuse plaques (non-neuritic plaques, non-NP), dense-core plaques, cotton-wool plaques, and NP. In a recent study, we demonstrated that during the progression of Alzheimer's disease neuropathologic changes (ADNC), a transformation of non-NP into NP occurs which is tightly linked to the emergence of cortical, but not hippocampal neurofibrillary tangle (NFT) pathology. This highlights the central role of NP in AD pathogenesis as well as brain region-specific differences in NP formation. In order to correlate the transformation of plaque types with local immune activation, we quantified the clustering and phenotype of microglia and accumulation of astrocytes around non-NP and NP during the progression of ADNC. We hypothesize that glial clustering occurs in response to formation of neuritic dystrophy around NP. First, we show that Iba1-positive microglia preferentially cluster around NP. Utilizing microglia phenotypic markers, we furthermore demonstrate that CD68-positive phagocytic microglia show a strong preference to cluster around NP in both the hippocampus and frontal cortex. A similar preferential clustering is observed for CD11c and ferritin-positive microglia in the frontal cortex, while this preference is less pronounced in the hippocampus, highlighting differences between hippocampal and cortical Aβ plaques. Glial fibrillary acidic protein-positive astrocytes showed a clear preference for clustering around NP in both the frontal cortex and hippocampus. These data support the notion that NP are intimately associated with the neuroimmune response in AD and underscore the importance of the interplay of protein deposits and the immune system in the pathophysiology of AD.

Border-associated macrophages: From physiology to therapeutic targets in Alzheimer's disease

Border-associated macrophages (BAMs) constitute a highly heterogeneous group of central nervous system-resident macrophages at the brain boundaries. Despite their significance, BAMs have mainly been overlooked compared to microglia, resulting in a limited understanding of their functions. However, recent advancements in single-cell immunophenotyping and transcriptomic analyses of BAMs have revealed a previously unrecognized complexity in these cells, in addition to their critical roles under non-pathological conditions and diseases like Alzheimer's disease (AD), Parkinson's disease, glioma, and ischemic stroke. In this review, we discuss the origins, self-renewal capabilities, and extensive heterogeneity of BAMs, and clarify their important physiological functions such as immune monitoring, waste removal and vascular permeability regulation. We also summarize experimental evidence linking BAMs to the progression of AD. Finally, we review therapeutic strategies targeting brain innate immune cells mainly focusing on strategies aimed at modulating BAMs to treat AD and evaluate their potential in clinical applications.

Ketone body metabolism and the NLRP3 inflammasome in Alzheimer's disease

Alzheimer's disease (AD) is a degenerative brain disorder and the most common form of dementia. AD pathology is characterized by senile plaques and neurofibrillary tangles (NFTs) composed of amyloid-β (Aβ) and hyperphosphorylated tau, respectively. Neuroinflammation has been shown to drive Aβ and tau pathology, with evidence suggesting the nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome as a key pathway in AD pathogenesis. NLRP3 inflammasome activation in microglia, the primary immune effector cells of the brain, results in caspase-1 activation and secretion of IL-1β and IL-18. Recent studies have demonstrated a dramatic interplay between the metabolic state and effector functions of immune cells. Microglial metabolism in AD is of particular interest, as ketone bodies (acetone, acetoacetate (AcAc), and β-hydroxybutyrate (BHB)) serve as an alternative energy source when glucose utilization is compromised in the brain of patients with AD. Furthermore, reduced cerebral glucose metabolism concomitant with increased BHB levels has been demonstrated to inhibit NLRP3 inflammasome activation. Here, we review the role of the NLRP3 inflammasome and microglial ketone body metabolism in AD pathogenesis. We also highlight NLRP3 inflammasome inhibition by several ketone body therapies as a promising new treatment strategy for AD.

Berberine chloride loaded nano-PEGylated liposomes attenuates imidacloprid-induced neurotoxicity by inhibiting NLRP3/Caspase-1/GSDMD-mediated pyroptosis

Concerns have been expressed about imidacloprid (IMI), one of the most often used pesticides, and its potential neurotoxicity to non-target organisms. Chronic neuroinflammation is central to the pathology of several neurodegenerative disorders. Hence, exploring the molecular mechanism by which IMI would trigger neuroinflammation is particularly important. This study examined the neurotoxic effects of oral administration of IMI (45 mg/kg/day for 30 days) and the potential neuroprotective effect of berberine (Ber) chloride loaded nano-PEGylated liposomes (Ber-Lip) (10 mg/kg, intravenously every other day for 30 days) using laboratory rat. The histopathological changes, anti-oxidant and oxidative stress markers (GSH, SOD, and MDA), proinflammatory cytokines (IL1β and TNF-α), microglia phenotype markers (CD86 and iNOS for M1; CD163 for M2), the canonical pyroptotic pathway markers (NLRP3, caspase-1, GSDMD, and IL-18) and Alzheimer's disease markers (Neprilysin and beta amyloid [Aβ] deposits) were assessed. Oral administration of IMI resulted in apparent cerebellar histopathological alterations, oxidative stress, predominance of M1 microglia phenotype, significantly upregulated NLRP3, caspase-1, GSDMD, IL-18 and Aβ deposits and significantly decreased Neprilysin expression. Berberine reduced the IMI-induced aberrations in the measured parameters and improved the IMI-induced histopathological and ultrastructure alterations brought on by IMI. This study highlights the IMI neurotoxic effect and its potential contribution to the development of Alzheimer's disease and displayed the neuroprotective effect of Ber-Lip.

Partial microglial depletion and repopulation exert subtle but differential effects on amyloid pathology at different disease stages

Colony-stimulating factor-1-receptor (CSF1R) inhibitors have been widely used to rapidly deplete microglia from the brain, allowing the remaining microglia population to self-renew and repopulate. These new-born microglia are thought to be "rejuvenated" and have been shown to be beneficial in several disease contexts and in normal aging. Their role in Alzheimer's disease (AD) is thus of great interest as they represent a potential disease-modifying therapy. Here, we explored the differential effects of microglial depletion and repopulation during amyloid pathology progression using 5xFAD mice. We utilized the CSF1R inhibitor PLX3397 to induce microglial self-renewal and tracked microglia-plaque dynamics with in vivo imaging. We observed transient improvement in plaque burden on different timescales depending on the animal's age. While the improvement in plaque burden did not persist in any age group, renewing microglia during mid- to late-pathology might still be beneficial as we observed a potential improvement in microglial sensitivity to noradrenergic signaling. Altogether, our findings provide further insights into the therapeutic potential of microglial renewal in AD.

Microglial CD2AP deficiency exerts protection in an Alzheimer's disease model of amyloidosis

BACKGROUND

The CD2-associated protein (CD2AP) was initially identified in peripheral immune cells and regulates cytoskeleton and protein trafficking. Single nucleotide polymorphisms (SNPs) in the CD2AP gene have been associated with Alzheimer's disease (AD). However, the functional role of CD2AP, especially its role in microglia during AD onset, remains elusive.

METHODS

CD2AP protein levels in cultured primary cells and in 5xFAD mice was studied. Microglial CD2AP-deficient mice were crossed with 5xFAD mice and the offspring were subjected to neuropathological assessment, behavioral tests, electrophysiology, RNA-seq, Golgi staining, and biochemistry analysis. Primary microglia were also isolated for assessing their uptake and morphology changes.

RESULTS

We find that CD2AP is abundantly expressed in microglia and its levels are elevated in the brain of AD patients and the 5xFAD model mice at pathological stages. We demonstrate that CD2AP haploinsufficiency in microglia significantly attenuates cognitive and synaptic deficits, weakens the response of microglia to Aβ and the formation of disease-associated microglia (DAM), and alleviates synapse loss in 5xFAD mice. We show that CD2AP-deficient microglia exhibit compromised uptake ability. In addition, we find that CD2AP expression is positively correlated with the expression of the complement C1q that is important for synapse phagocytosis and the formation of DAM in response to Aβ deposition. Moreover, we reveal that CD2AP interacts with colony stimulating factor 1 receptor (CSF1R) and regulates CSF1R cell surface levels, which may further affect C1q expression.

CONCLUSIONS

Our results demonstrate that CD2AP regulates microgliosis and identify a protective function of microglial CD2AP deficiency against Aβ deposition, suggesting the importance of detailed investigation of AD-associated genes in different brain cells for thoroughly understanding their exact contribution to AD.

Neuroinflammation in Alzheimer disease

Increasing evidence points to a pivotal role of immune processes in the pathogenesis of Alzheimer disease, which is the most prevalent neurodegenerative and dementia-causing disease of our time. Multiple lines of information provided by experimental, epidemiological, neuropathological and genetic studies suggest a pathological role for innate and adaptive immune activation in this disease. Here, we review the cell types and pathological mechanisms involved in disease development as well as the influence of genetics and lifestyle factors. Given the decade-long preclinical stage of Alzheimer disease, these mechanisms and their interactions are driving forces behind the spread and progression of the disease. The identification of treatment opportunities will require a precise understanding of the cells and mechanisms involved as well as a clear definition of their temporal and topographical nature. We will also discuss new therapeutic strategies for targeting neuroinflammation, which are now entering the clinic and showing promise for patients.

Homeostatic microglia initially seed and activated microglia later reshape amyloid plaques in Alzheimer's Disease

The role of microglia in the amyloid cascade of Alzheimer's disease (AD) is debated due to conflicting findings. Using a genetic and a pharmacological approach we demonstrate that depletion of microglia before amyloid-β (Aβ) plaque deposition, leads to a reduction in plaque numbers and neuritic dystrophy, confirming their role in plaque initiation. Transplanting human microglia restores Aβ plaque formation. While microglia depletion reduces insoluble Aβ levels, soluble Aβ concentrations stay consistent, challenging the view that microglia clear Aβ. In later stages, microglial depletion decreases plaque compaction and increases neuritic dystrophy, suggesting a protective role. Human microglia with the TREM2R47H/R47H mutation exacerbate plaque pathology, emphasizing the importance of non-reactive microglia in the initiation of the amyloid cascade. Adaptive immune depletion (Rag2-/-) does not affect microglia's impact on plaque formation. These findings clarify conflicting reports, identifying microglia as key drivers of amyloid pathology, and raise questions about optimal therapeutic strategies for AD.

Amyloid-β-activated microglia can induce compound proteinopathies

Neuropathological features of Alzheimer's disease include amyloid plaques, neurofibrillary tangles and Lewy bodies, with the former preceding the latter two. However, it is not fully understood how these compound proteinopathies are interconnected. Here, we show that transplantation of amyloid-β oligomer-activated microglia into the striatum of naïve mice was sufficient to generate all the features of Alzheimer's disease, including widespread tauopathy and synucleinopathy, gliosis, neuroinflammation, synapse loss, neuronal death, and cognitive and motor deficits. These pathological features were eliminated by microglia depletion and anti-inflammatory drug administration. Our results suggest the crucial roles of microglia-driven inflammation in development of mixed pathology. This study provides not only mechanistic insights into amyloid-β oligomer-triggered proteinopathies but also a novel animal model recapitulating the salient features of Alzheimer's disease.

Mitigating neurodegenerative diseases: the protective influence of baicalin and baicalein through neuroinflammation regulation

Neurodegenerative diseases (NDDs) represent a category of serious illnesses characterized by the progressive deterioration of neuronal structure and function. The exploration of natural compounds as potential therapeutic agents has gained increasing attention in recent years owing to their wide range of pharmacological activities and minimal side effects. Baicalin (BAI) and baicalein (BE), polyphenolic flavonoids, derived from the root of Scutellaria baicalensis, evidently show potential in treating NDDs. This review provides an overview of the current understanding of the roles of BAI and BE in alleviating neuroinflammation, a pivotal pathological process implicated in various NDDs. Studies conducted prior to clinical trials have shown that BAI and BE exert protective effects on the nervous system in different animal models of NDDs. Furthermore, mechanistic studies indicate that BAI and BE exert anti-inflammatory effects by inhibiting pro-inflammatory cytokines, suppressing microglial activation, and regulating microglial phenotypes. These effects are mediated through the modulation of inflammatory signaling cascades, including Toll-like receptor 4 (TLR4), mitogen-activated protein kinase (MAPK), amp-activated protein kinase (AMPK), NOD-like receptor thermal protein domain-associated protein 3 (NLRP3) inflammasome, and nuclear factor erythroid 2-related factor 2 (Nrf2)/hemoglobin oxygenase-1 (HO-1). Overall, BAI and BE exhibit promising potential as natural compounds with anti-inflammatory properties and offer innovative therapeutic approaches for managing NDDs.

AD-Like Neuropsychiatric Dysfunction in a Mice Model Induced by a Combination of High-Fat Diet and Intraperitoneal Injection of Streptozotocin

Increasing data suggest a crucial relationship between glycolipid metabolic disorder and neuropsychiatric injury. The aim of this study is to investigate the behavioral performance changes and neuropathological injuries in mice challenged with high-fat diet (HFD) and streptozotocin (STZ). The glucose metabolism indicators and behavioral performance were detected. The mRNA expression of IL-1β, IL-6, TNF-α, ocln, zo-1, and clnds and protein expression of APP, p-Tau, p-IRS1, p-AKT, p-ERK, and TREM1/2 were measured. The fluorescence intensities of MAP-2, NeuN, APP, p-Tau, GFAP, and IBA-1 were observed. The results showed that combination of HFD and STZ/I.P. could induce glucose metabolic turmoil and Alzheimer's disease (AD)-like neuropsychiatric dysfunction in mice, as indicated by the increased concentrations of fasting blood glucose and impaired learning and memory ability. Moreover, the model mice presented increased levels of APP, p-Tau, p-IRS1, TREM2, IL-1β, IL-6, TNF-α, ocln, zo-1, and clnds; decreased levels of p-AKT, p-ERK, and TREM1; and neuron damage and the hyperactivation of astrocytes and microglia in the hippocampus as compared with control mice. Only male mice were used in this study. Although AD and type 2 diabetes mellitus (T2DM) are distinct pathologies, our results suggested that combination of HFD and STZ/I.P., a widely used T2DM modeling method, could successfully induce AD-like behavioral impairments and neuropathological injuries in mice; the mechanism might be involved with neuroinflammation and its associated dysfunction of IRS1/AKT/ERK signaling pathway. Our findings further support the potential overlap between T2DM and AD pathophysiology, providing insight into the mechanisms underlying the comorbidity of these diseases.

Progress in the mechanisms of pain associated with neurodegenerative diseases

Neurodegenerative diseases (NDDs) represent a class of neurological disorders characterized by the progressive degeneration or loss of neurons, impacting millions of individuals globally. In addition to the typical manifestations, pain is a prevalent symptom associated with NDDs, seriously impacting the quality of life for patients. The pathogenesis of pain associated with NDDs is intricate and multifaceted. Currently, the clinical management of NDDs-related pain symptoms predominantly relies on conventional pharmacological agents or physical therapy. However, these approaches often fail to produce satisfactory outcomes. This article summarizes the underlying mechanisms of major NDDs-associated pain: Neuroinflammation, Brain and spinal cord dysfunctions, Mitochondrial dysfunction, Risk gene and pathological protein, as well as Receptor, channel, and neurotransmitter. While numerous studies have investigated the downstream pathological processes associated with these mechanisms, there remains a significant gap in identifying the key initiating factors. Specifically, there is insufficient evidence for the upstream elements that activate microglia and astrocytes in neuroinflammation leading to pain in NDDs. Likewise, there is an absence of upstream factors elucidating how dysfunctions in the brain and spinal cord, as well as mitochondrial impairments, contribute to the development of pain. Furthermore, the specific mechanisms through which hallmark pathological proteins related to NDDs contribute to these pathological processes remain inadequately understood. The objective of this article is to synthesize the existing mechanisms underlying pain associated with NDDs, including Alzheimer's disease, Parkinson's disease, Huntington's disease, Schizophrenia, Amyotrophic lateral sclerosis, and Multiple sclerosis, while also identifying gaps and deficiencies in these mechanisms. This paper offers insights for future research trajectories. Given the intricate pathogenesis of NDDs-related pain, it emphasizes that a promising short-term strategy is combination therapy-intervening concurrently in multiple pathological processes-akin to the cocktail approach utilized in treating acquired immunodeficiency syndrome (AIDS). For long-term advancements, achieving breakthroughs in the treatment of the NDDs themselves will remain essential for alleviating accompanying pain symptoms.

Non-canonical pathways associated to Amyloid beta and tau protein dyshomeostasis in Alzheimer's disease: A narrative review

Alzheimer's Disease (AD) is the most common form of dementia among elderly people. This disease imposes a significant burden on the healthcare system, society, and economy due to the increasing global aging population. Current trials with drugs or bioactive compounds aimed at reducing cerebral Amyloid beta (Aβ) plaques and tau protein neurofibrillary tangles, which are the two main hallmarks of this devastating neurodegenerative disease, have not provided significant results in terms of their neuropathological outcomes nor met the expected clinical end-points. Ageing, genetic and environmental risk factors, along with different clinical symptoms suggest that AD is a complex and heterogeneous disorder with multiple interconnected pathological pathways rather than a single disease entity. In the present review, we highlight and discuss various non-canonical, Aβ-independent mechanisms, like gliosis, unhealthy dietary intake, lipid and sugar signaling, and cerebrovascular damage that contribute to the onset and development of AD. We emphasize that challenging the traditional "amyloid cascade hypothesis" may improve our understanding of this age-related complex syndrome and help fight the progressive cognitive decline in AD.

Insights into the advances in therapeutic drugs for neuroinflammation-related diseases

Studies have shown that neurodegenerative diseases such as AD and PD are related to neuroinflammation. Neuroinflammation is a common inflammatory condition that can lead to a variety of dysfunction in the body. At present, it is no medications specifically approved to prevent or cure neuroinflammation, so even though many drugs can temporarily control the neurological symptoms of neuroinflammation, but no one can reverse the progress of neuroinflammation, let al.one completely cure neuroinflammation. Therefore, it is urgent to develop new drug development for neuroinflammation treatment. In this review, we highlight the therapeutic advancement in the field of neurodegenerative disorders, by focusing on the impact of neuroinflammation treatment has on these conditions, and the effective drugs for the treatment of neuroinflammation and neurodegenerative diseases and their latest research progress are reviewed according to the related signaling pathway, as well as the prospect of their clinical application is also discussed. The purpose of this review is to enable specialists to better understand the mechanisms underlying neuroinflammation and anti-inflammatory drugs, promote the development of therapeutic drugs for neuroinflammation and neurodegenerative diseases, and further provide therapeutic references for clinical neurologists.

The Effect of Pexidartinib on Neuropathic Pain via Influences on Microglia and Neuroinflammation in Mice

BACKGROUND

Chronic pain is a debilitating medical condition that lacks effective treatments. Increasing evidence suggests that microglia and neuroinflammation underlie pain pathophysiology, which therefore supports a potential strategy for developing pain therapeutics. Here, our study is testing the hypothesis that the promise of pain amelioration can be achieved using the small-molecule pexidartinib (PLX-3397), a previously food and drug administration (FDA)-approved cancer medicine and a colony-stimulating factor-1 receptor (CSF-1R) inhibitor that display microglia-depleting properties.

METHOD

We used the previously reported chronic constriction injury (CCI) mouse model, in which PLX-3397 or vehicle was orally administrated to mice daily for 21 days, then applied to the CCI model, followed by PLX-3397 or vehicle administration for an additional 28 days. Additionally, we examined microglia-related neuroinflammation markers using positron emission tomography (PET) neuroimaging and immunofluorescence (IF).

RESULTS

We showed that PLX-3397 significantly ameliorated pain-related behavioral changes throughout the entire experimental period after CCI (vehicle versus PLX-3397 at day 14, effect size: 2.57, P = .002). Microglia changes were first analyzed by live-animal PET neuroimaging, revealing PLX-3397-associated reduction of microglia by probing receptor-interacting serine/threonine-protein kinase 1 (RIPK1), a protein primarily expressed in microglia, which were further corroborated by postmortem immunohistochemistry (IHC) analysis using antibodies for microglia, including ionized Ca2+ binding adaptor molecule 1 (Iba-1) (somatosensory cortex, hindlimb area; vehicle versus PLX-3397, effect size 3.6, P = .011) and RIPK1 (somatosensory cortex, hindlimb area; vehicle versus PLX-3397, effect size 2.9, P = .023. The expression of both markers decreased in the PLX-3397 group. Furthermore, we found that PLX-3397 led to significant reductions in various proteins, including inducible nitric oxide synthase (iNOS) (somatosensory cortex, hindlimb area; vehicle versus PLX-3397, effect size: 2.3, P = .048), involved in neuroinflammation through IHC.

CONCLUSIONS

Collectively, our study showed PLX-3397-related efficacy in ameliorating pain linked to the reduction of microglia and neuroinflammation in mice. Furthermore, our research provided new proof-of-concept data supporting the promise of testing PLX-3397 as an analgesic.

N-acetyltransferase 10 mediates cognitive dysfunction through the acetylation of GABABR1 mRNA in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a critical neurological complication of sepsis and represents a crucial factor contributing to high mortality and adverse prognosis in septic patients. This study explored the contribution of NAT10-mediated messenger RNA (mRNA) acetylation in cognitive dysfunction associated with SAE, utilizing a cecal ligation and puncture (CLP)-induced SAE mouse model. Our findings demonstrate that CLP significantly upregulates NAT10 expression and mRNA acetylation in the excitatory neurons of the hippocampal dentate gyrus (DG). Notably, neuronal-specific Nat10 knockdown improved cognitive function in septic mice, highlighting its critical role in SAE. Proteomic analysis, RNA immunoprecipitation, and real-time qPCR identified GABABR1 as a key downstream target of NAT10. Nat10 deletion reduced GABABR1 expression, and subsequently weakened inhibitory postsynaptic currents in hippocampal DG neurons. Further analysis revealed that microglia activation and the release of inflammatory mediators lead to the increased NAT10 expression in neurons. Microglia depletion with PLX3397 effectively reduced NAT10 and GABABR1 expression in neurons, and ameliorated cognitive dysfunction induced by SAE. In summary, our findings revealed that after CLP, NAT10 in hippocampal DG neurons promotes GABABR1 expression through mRNA acetylation, leading to cognitive dysfunction.

Microglial Drivers of Alzheimer's Disease Pathology: An Evolution of Diverse Participating States

Microglia, the resident immune-competent cells of the brain, become dysfunctional in Alzheimer's disease (AD), and their aberrant immune responses contribute to the accumulation of pathological proteins and neuronal injury. Genetic studies implicate microglia in the development of AD, prompting interest in developing immunomodulatory therapies to prevent or ameliorate disease. However, microglia take on diverse functional states in disease, playing both protective and detrimental roles in AD, which largely overlap and may shift over the disease course, complicating the identification of effective therapeutic targets. Extensive evidence gathered using transgenic mouse models supports an active role of microglia in pathology progression, though results vary and can be contradictory between different types of models and the degree of pathology at the time of study. Here, we review microglial immune signaling and responses that contribute to the accumulation and spread of pathological proteins or directly affect neuronal health. We additionally explore the use of induced pluripotent stem cell (iPSC)-derived models to study living human microglia and how they have contributed to our knowledge of AD and may begin to fill in the gaps left by mouse models. Ultimately, mouse and iPSC-derived models have their own limitations, and a comprehensive understanding of microglial dysfunction in AD will only be established by an integrated view across models and an appreciation for their complementary viewpoints and limitations.

Exploring advancements in early detection of Alzheimer's disease with molecular assays and animal models

Alzheimer's Disease (AD) is a challenging neurodegenerative condition, with overwhelming implications for affected individuals and healthcare systems worldwide. Animal models have played a crucial role in studying AD pathogenesis and testing therapeutic interventions. Remarkably, studies on the genetic factors affecting AD risk, such as APOE and TREM2, have provided valuable insights into disease mechanisms. Early diagnosis has emerged as a crucial factor in effective AD management, as demonstrated by clinical studies emphasizing the benefits of initiating treatment at early stages. Novel diagnostic technologies, including RNA sequencing of microglia, offer promising avenues for early detection and monitoring of AD progression. Therapeutic strategies remain to evolve, with a focus on targeting amyloid beta (Aβ) and tau pathology. Advances in animal models, such as APP-KI mice, and the advancement of anti-Aβ drugs signify progress towards more effective treatments. Therapeutically, the focus has shifted towards intricate approaches targeting multiple pathological pathways simultaneously. Strategies aimed at reducing Aβ plaque accumulation, inhibiting tau hyperphosphorylation, and modulating neuroinflammation are actively being explored, both in preclinical models and clinical trials. While challenges continue in developing validated animal models and translating preclinical findings to clinical success, the continuing efforts in understanding AD at molecular, cellular, and clinical levels offer hope for improved management and eventual prevention of this devastating disease.

Inflammatory aspects of Alzheimer's disease

Alzheimer´s disease (AD) stands out as the most common chronic neurodegenerative disorder. AD is characterized by progressive cognitive decline and memory loss, with neurodegeneration as its primary pathological feature. The role of neuroinflammation in the disease course has become a focus of intense research. While microglia, the brain's resident macrophages, have been pivotal to study central immune inflammation, recent evidence underscores the contributions of other cellular entities to the neuroinflammatory process. In this article, we review the inflammatory role of microglia and astrocytes, focusing on their interactions with AD's core pathologies, amyloid beta deposition, and tau tangle formation. Additionally, we also discuss how different modes of regulated cell death in AD may impact the chronic neuroinflammatory environment. This review aims to highlight the evolving landscape of neuroinflammatory research in AD and underscores the importance of considering multiple cellular contributors when developing new therapeutic strategies.

Therapeutic Targets in Innate Immunity to Tackle Alzheimer's Disease

There is an urgent need for effective disease-modifying therapeutic interventions for Alzheimer's disease (AD)-the most prevalent cause of dementia with a profound socioeconomic burden. Most clinical trials targeting the classical hallmarks of this disease-β-amyloid plaques and neurofibrillary tangles-failed, showed discrete clinical effects, or were accompanied by concerning side effects. There has been an ongoing search for novel therapeutic targets. Neuroinflammation, now widely recognized as a hallmark of all neurodegenerative diseases, has been proven to be a major contributor to AD pathology. Here, we summarize the role of neuroinflammation in the pathogenesis and progression of AD and discuss potential targets such as microglia, TREM2, the complement system, inflammasomes, and cytosolic DNA sensors. We also present an overview of ongoing studies targeting specific innate immune system components, highlighting the progress in this field of drug research while bringing attention to the delicate nature of innate immune modulations in AD.

Switch to phagocytic microglia by CSFR1 inhibition drives amyloid-beta clearance from glutamatergic terminals rescuing LTP in acute hippocampal slices

Microglia, traditionally regarded as innate immune cells in the brain, drive neuroinflammation and synaptic dysfunctions in the early phases of Alzheimer disease (AD), acting upstream to Aβ accumulation. Colony stimulating factor 1-receptor (CSF-1R) is predominantly expressed on microglia and its levels are significantly increased in neurodegenerative diseases, possibly contributing to the chronic inflammatory microglial response. On the other hand, CSF-1R inhibitors confer neuroprotection in preclinical models of neurodegenerative diseases. Here, we determined the effects of the CSF-1R inhibitor PLX3397 on the Aβ-mediated synaptic alterations in ex vivo hippocampal slices. Electrophysiological findings show that PLX3397 rescues LTP impairment and neurotransmission changes induced by Aβ. In addition, using confocal imaging experiments, we demonstrate that PLX3397 stimulates a microglial transition toward a phagocytic phenotype, which in turn promotes the clearance of Aβ from glutamatergic terminals. We believe that the selective pruning of Aβ-loaded synaptic terminals might contribute to the restoration of LTP and excitatory transmission alterations observed upon acute PLX3397 treatment. This result is in accordance with the mechanism proposed for CSF1R inhibitors, that is to eliminate responsive microglia and replace it with newly generated, homeostatic microglia, capable of promoting brain repair. Overall, our findings identify a connection between the rapid microglia adjustments and the early synaptic alterations observed in AD, possibly highlighting a novel disease-modifying target.

Strategies to dissect microglia-synaptic interactions during aging and in Alzheimer's disease

Age is the largest risk factor for developing Alzheimer's disease (AD), a neurodegenerative disorder that causes a progressive and severe dementia. The underlying cause of cognitive deficits seen in AD is thought to be the disconnection of neural circuits that control memory and executive functions. Insight into the mechanisms by which AD diverges from normal aging will require identifying precisely which cellular events are driven by aging and which are impacted by AD-related pathologies. Since microglia, the brain-resident macrophages, are known to have critical roles in the formation and maintenance of neural circuits through synaptic pruning, they are well-positioned to modulate synaptic connectivity in circuits sensitive to aging or AD. In this review, we provide an overview of the current state of the field and on emerging technologies being employed to elucidate microglia-synaptic interactions in aging and AD. We also discuss the importance of leveraging genetic diversity to study how these interactions are shaped across more realistic contexts. We propose that these approaches will be essential to define specific aging- and disease-relevant trajectories for more personalized therapeutics aimed at reducing the effects of age or AD pathologies on the brain. This article is part of the Special Issue on "Microglia".

Broken strands, broken minds: Exploring the nexus of DNA damage and neurodegeneration

Neurodegenerative disorders are primarily characterized by neuron loss progressively leading to cognitive decline and the manifestation of incurable and debilitating conditions, such as Alzheimer's, Parkinson's, and Huntington's diseases. Loss of genome maintenance causally contributes to age-related neurodegeneration, as exemplified by the premature appearance of neurodegenerative features in a growing family of human syndromes and mice harbouring inborn defects in DNA repair. Here, we discuss the relevance of persistent DNA damage, key DNA repair mechanisms and compromised genome integrity in age-related neurodegeneration highlighting the significance of investigating these connections to pave the way for the development of rationalized intervention strategies aimed at delaying the onset of neurodegenerative disorders and promoting healthy aging.

Aspergillusidone G Potentiates the Anti-Inflammatory Effects of Polaprezinc in LPS-Induced BV2 Microglia: A Bioinformatics and Experimental Study

Neuroinflammation is one of the main mechanisms involved in the progression of neurodegenerative diseases (NDs), and microglial activation is the main feature of neuroinflammation. Polaprezinc (Pol), a chelator of L-carnosine and zinc, is widely used as a clinical drug for gastric ulcers. However, its potential effects on NDs remain unexplored. In LPS-induced BV-2 microglia, we found that Pol reduced the generation of NO and ROS and revealed inhibited expression of iNOS, COX-2, and inflammatory factors such as IL-6, TNF-α, and 1L-1β by Pol using qRT-PCR and Western blotting. These effects were found to be associated with the suppression of the NF-κB signaling pathway. Moreover, we evaluated the potential synergistic effects of aspergillusidone G (Asp G) when combined with Pol. Remarkably, co-treatment with low doses of Asp G enhanced the NO inhibition by Pol from approximately 30% to 80% in LPS-induced BV2 microglia, indicating a synergistic anti-inflammatory effect. A bioinformatics analysis suggested that the synergistic mechanism of Asp G and Pol might be attributed to several targets, including NFκB1, NRF2, ABL1, TLR4, and PPARα. These findings highlight the anti-neuroinflammatory properties of Pol and its enhanced efficacy when combined with Asp G, proposing a novel therapeutic strategy for managing neuroinflammation in NDs.

Targeting Microglia in Alzheimer's Disease: Pathogenesis and Potential Therapeutic Strategies

Microglia, as resident macrophages in the central nervous system, play a multifunctional role in the pathogenesis of Alzheimer's disease (AD). Their clustering around amyloid-β (Aβ) deposits is a core pathological feature of AD. Recent advances in single-cell RNA sequencing (scRNA-seq) and single-nucleus RNA sequencing (snRNA-seq) have revealed dynamic changes in microglial phenotypes over time and across different brain regions during aging and AD progression. As AD advances, microglia primarily exhibit impaired phagocytosis of Aβ and tau, along with the release of pro-inflammatory cytokines that damage synapses and neurons. Targeting microglia has emerged as a potential therapeutic approach for AD. Treatment strategies involving microglia can be broadly categorized into two aspects: (1) enhancing microglial function: This involves augmenting their phagocytic ability against Aβ and cellular debris and (2) mitigating neuroinflammation: Strategies include inhibiting TNF-α signaling to reduce the neuroinflammatory response triggered by microglia. Clinical trials exploring microglia-related approaches for AD treatment have garnered attention. Additionally, natural products show promise in enhancing beneficial effects and suppressing inflammatory responses. Clarifying microglial dynamics, understanding their roles, and exploring novel therapeutic approaches will advance our fight against AD.

The emerging role of brain neuroinflammatory responses in Alzheimer's disease

As the most common cause of dementia, Alzheimer's disease (AD) is characterized by neurodegeneration and synaptic loss with an increasing prevalence in the elderly. Increased inflammatory responses triggers brain cells to produce pro-inflammatory cytokines and accelerates the Aβ accumulation, tau protein hyper-phosphorylation leading to neurodegeneration. Therefore, in this paper, we discuss the current understanding of how inflammation affects brain activity to induce AD pathology, the inflammatory biomarkers and possible therapies that combat inflammation for AD.

The neuroinflammatory role of microglia in Alzheimer's disease and their associated therapeutic targets

INTRODUCTION

Alzheimer's disease (AD), the main cause of dementia, is characterized by synaptic loss and neurodegeneration. Amyloid-β (Aβ) accumulation, hyperphosphorylation of tau protein, and neurofibrillary tangles (NFTs) in the brain are considered to be the initiating factors of AD. However, this hypothesis falls short of explaining many aspects of AD pathogenesis. Recently, there has been mounting evidence that neuroinflammation plays a key role in the pathophysiology of AD and causes neurodegeneration by over-activating microglia and releasing inflammatory mediators.

METHODS

PubMed, Web of Science, EMBASE, and MEDLINE were used for searching and summarizing all the recent publications related to inflammation and its association with Alzheimer's disease.

RESULTS

Our review shows how inflammatory dysregulation influences AD pathology as well as the roles of microglia in neuroinflammation, the possible microglia-associated therapeutic targets, top neuroinflammatory biomarkers, and anti-inflammatory drugs that combat inflammation.

CONCLUSION

In conclusion, microglial inflammatory reactions are important factors in AD pathogenesis and need to be discussed in more detail for promising therapeutic strategies.

Spinal motor neuron development and metabolism are transcriptionally regulated by Nuclear Factor IA

Neural circuits governing all motor behaviors in vertebrates rely on the proper development of motor neurons and their precise targeting of limb muscles. Transcription factors are essential for motor neuron development, regulating their specification, migration, and axonal targeting. While transcriptional regulation of the early stages of motor neuron specification is well-established, much less is known about the role of transcription factors in the later stages of maturation and terminal arborization. Defining the molecular mechanisms of these later stages is critical for elucidating how motor circuits are constructed. Here, we demonstrate that the transcription factor Nuclear Factor-IA (NFIA) is required for motor neuron positioning, axonal branching, and neuromuscular junction formation. Moreover, we find that NFIA is required for proper mitochondrial function and ATP production, providing a new and important link between transcription factors and metabolism during motor neuron development. Together, these findings underscore the critical role of NFIA in instructing the assembly of spinal circuits for movement.

Current understanding on TREM-2 molecular biology and physiopathological functions

Triggering receptor expressed on myeloid cells 2 (TREM-2), a glycosylated receptor belonging to the immunoglobin superfamily and especially expressed in the myeloid cell lineage, is frequently explained as a reminiscent receptor for both adaptive and innate immunity regulation. TREM-2 is also acknowledged to influence NK cell differentiation via the PI3K and PLCγ signaling pathways, as well as the partial activation or direct inhibition of T cells. Additionally, TREM-2 overexpression is substantially linked to cell-specific functions, such as enhanced phagocytosis, reduced toll-like receptor (TLR)-mediated inflammatory cytokine production, increased transcription of anti-inflammatory cytokines, and reshaped T cell function. Whereas TREM-2-deficient cells exhibit diminished phagocytic function and enhanced proinflammatory cytokines production, proceeding to inflammatory injuries and an immunosuppressive environment for disease progression. Despite the growing literature supporting TREM-2+ cells in various diseases, such as neurodegenerative disorders and cancer, substantial facets of TREM-2-mediated signaling remain inadequately understood relevant to pathophysiology conditions. In this direction, herein, we have summarized the current knowledge on TREM-2 biology and cell-specific TREM-2 expression, particularly in the modulation of pivotal TREM-2-dependent functions under physiopathological conditions. Furthermore, molecular regulation and generic biological relevance of TREM-2 are also discussed, which might provide an alternative approach for preventing or reducing TREM-2-associated deformities. At last, we discussed the TREM-2 function in supporting an immunosuppressive cancer environment and as a potential drug target for cancer immunotherapy. Hence, summarized knowledge of TREM-2 might provide a window to overcome challenges in clinically effective therapies for TREM-2-induced diseases in humans.

Microglia and amyloid plaque formation in Alzheimer's disease - Evidence, possible mechanisms, and future challenges

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive decline that severely affects patients and their families. Genetic and environmental risk factors, such as viral infections, synergize to accelerate the aging-associated neurodegeneration. Genetic risk factors for late-onset AD (LOAD), which accounts for most AD cases, are predominantly implicated in microglial and immune cell functions. As such, microglia play a major role in formation of amyloid beta (Aβ) plaques, the major pathological hallmark of AD. This review aims to provide an overview of the current knowledge regarding the role of microglia in Aβ plaque formation, as well as their impact on morphological and functional diversity of Aβ plaques. Based on this discussion, we seek to identify challenges and opportunities in this field with potential therapeutic implications.

Zinc utilization by microglia in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia defined by two key pathological characteristics in the brain, amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. Microglia, the primary innate immune cells of the central nervous system (CNS), provide neuroprotection through Aβ and tau clearance but may also be neurotoxic by promoting neuroinflammation to exacerbate Aβ and tau pathogenesis in AD. Recent studies have demonstrated the importance of microglial utilization of nutrients and trace metals in controlling their activation and effector functions. Trace metals, such as zinc, have essential roles in brain health and immunity, and zinc dyshomeostasis has been implicated in AD pathogenesis. As a result of these advances, the mechanisms by which zinc homeostasis influences microglial-mediated neuroinflammation in AD is a topic of continuing interest since new strategies to treat AD are needed. Here, we review the roles of zinc in AD, including zinc activation of microglia, the associated neuroinflammatory response, and the application of these findings in new therapeutic strategies.

Neuritic Plaques - Gateways to Understanding Alzheimer's Disease

Extracellular deposits of amyloid-β (Aβ) in the form of plaques are one of the main pathological hallmarks of Alzheimer's disease (AD). Over the years, many different Aβ plaque morphologies such as neuritic plaques, dense cored plaques, cotton wool plaques, coarse-grain plaques, and diffuse plaques have been described in AD postmortem brain tissues, but correlation of a given plaque type with AD progression or AD symptoms is not clear. Furthermore, the exact trigger causing the development of one Aβ plaque morphological subtype over the other is still unknown. Here, we review the current knowledge about neuritic plaques, a subset of Aβ plaques surrounded by swollen or dystrophic neurites, which represent the most detrimental and consequential Aβ plaque morphology. Neuritic plaques have been associated with local immune activation, neuronal network dysfunction, and cognitive decline. Given that neuritic plaques are at the interface of Aβ deposition, tau aggregation, and local immune activation, we argue that understanding the exact mechanism of neuritic plaque formation is crucial to develop targeted therapies for AD.

Dynamic neuroinflammatory profiles predict Alzheimer's disease pathology in microglia-containing cerebral organoids

Neuroinflammation and the underlying dysregulated immune responses of microglia actively contribute to the progression and, likely, the initiation of Alzheimer's disease (AD). Fine-tuned therapeutic modulation of immune dysfunction to ameliorate disease cannot be achieved without the characterization of diverse microglial states that initiate unique, and sometimes contradictory, immune responses that evolve over time in chronic inflammatory environments. Because of the functional differences between human and murine microglia, untangling distinct, disease-relevant reactive states and their corresponding effects on pathology or neuronal health may not be possible without the use of human cells. In order to profile shifting microglial states in early AD and identify microglia-specific drivers of disease, we differentiated human induced pluripotent stem cells (iPSCs) carrying a familial AD PSEN2 mutation or its isogenic control into cerebral organoids and quantified the changes in cytokine concentrations over time with Luminex XMAP technology. We used partial least squares (PLS) modeling to build cytokine signatures predictive of disease and age to identify key differential patterns of cytokine expression that inform the overall organoid immune milieu and quantified the corresponding changes in protein pathology. AD organoids exhibited an overall reduction in cytokine secretion after an initial amplified immune response. We demonstrate that reduced synapse density observed in the AD organoids is prevented with microglial depletion. Crucially, these differential effects of dysregulated immune signaling occurred without the accumulation of pathological proteins. In this study, we used microglia-containing AD organoids to quantitatively characterize an evolving immune milieu, made up of a diverse of collection of activation patterns and immune responses, to identify how a dynamic, overall neuroinflammatory state negatively impacts neuronal health and the cell-specific contribution of microglia.

Rbm8a regulates neurogenesis and reduces Alzheimer's disease-associated pathology in the dentate gyrus of 5×FAD mice

Alzheimer's disease is a prevalent and debilitating neurodegenerative condition that profoundly affects a patient's daily functioning with progressive cognitive decline, which can be partly attributed to impaired hippocampal neurogenesis. Neurogenesis in the hippocampal dentate gyrus is likely to persist throughout life but declines with aging, especially in Alzheimer's disease. Recent evidence indicated that RNA-binding protein 8A (Rbm8a) promotes the proliferation of neural progenitor cells, with lower expression levels observed in Alzheimer's disease patients compared with healthy people. This study investigated the hypothesis that Rbm8a overexpression may enhance neurogenesis by promoting the proliferation of neural progenitor cells to improve memory impairment in Alzheimer's disease. Therefore, Rbm8a overexpression was induced in the dentate gyrus of 5×FAD mice to validate this hypothesis. Elevated Rbm8a levels in the dentate gyrus triggered neurogenesis and abated pathological phenotypes (such as plaque formation, gliosis reaction, and dystrophic neurites), leading to ameliorated memory performance in 5×FAD mice. RNA sequencing data further substantiated these findings, showing the enrichment of differentially expressed genes involved in biological processes including neurogenesis, cell proliferation, and amyloid protein formation. In conclusion, overexpressing Rbm8a in the dentate gyrus of 5×FAD mouse brains improved cognitive function by ameliorating amyloid-beta-associated pathological phenotypes and enhancing neurogenesis.

Neuronal activation of nucleus accumbens by local methamphetamine administration induces cognitive impairment through microglial inflammation in mice

More than half of methamphetamine (METH) users present with cognitive impairment, making it difficult for them to reintegrate into society. However, the mechanisms of METH-induced cognitive impairment remain unclear. METH causes neuronal hyperactivation in the nucleus accumbens (NAc) by aberrantly releasing dopamine, which triggers dependence. In this study, to clarify the involvement of hyperactivation of NAc in METH-induced cognitive impairment, mice were locally microinjected with METH into NAc (mice with METH (NAc)) and investigated their cognitive phenotype. Mice with METH (NAc) exhibited cognitive dysfunction in behavioral analyses and decreased long-term potentiation in the hippocampus, with NAc activation confirmed by expression of FosB, a neuronal activity marker. In the hippocampus of mice with METH (NAc), activated microglia, but not astroglia, and upregulated microglia-related genes, Il1b and C1qa were observed. Finally, administration of minocycline, a tetracycline antibiotic with suppressive effect on microglial activation, to mice with METH (NAc) ameliorated cognitive impairment and synaptic dysfunction by suppressing the increased expression of Il1b and C1qa in the hippocampus. In conclusion, activation of NAc by injection of METH into NAc elicited cognitive impairment by facilitating immune activation in mice. This study suggests that immunological intervention could be a therapeutic strategy for addiction-related cognitive disturbances.

Colony Stimulating Factor-1 Receptor: An emerging target for neuroinflammation PET imaging and AD therapy

Although neuroinflammation is a significant pathogenic feature of many neurologic disorders, its precise function in-vivo is still not completely known. PET imaging enables the longitudinal examination, quantification, and tracking of different neuroinflammation biomarkers in living subjects. Particularly, PET imaging of Microglia, specialised dynamic immune cells crucial for maintaining brain homeostasis in central nervous system (CNS), is crucial for staging the neuroinflammation. Colony Stimulating Factor- 1 Receptor (CSF-1R) PET imaging is a novel method for the quantification of neuroinflammation. CSF-1R is mainly expressed on microglia, and neurodegenerative disorders greatly up-regulate its expression. The present review primarily focuses on the development, pros and cons of all the CSF-1R PET tracers reported for neuroinflammation imaging. Apart from neuroinflammation imaging, CSF-1R inhibitors are also reported for the therapy of neurodegenerative diseases such as Alzheimer's disease (AD). AD is a prevalent, advancing, and fatal neurodegenerative condition that have the characteristic feature of persistent neuroinflammation and primarily affects the elderly. The aetiology of AD is profoundly influenced by amyloid-beta (Aβ) plaques, intracellular neurofibrillary tangles, and microglial dysfunction. Increasing evidence suggests that CSF-1R inhibitors (CSF-1Ri) can be helpful in preclinical models of neurodegenerative diseases. This review article also summarises the most recent developments of CSF-1Ri-based therapy for AD.

Pyrrolopyrimidine based CSF1R inhibitors: Attempted departure from Flatland

The colony-stimulating factor 1 receptor (CSF1R) is an attractive target for inflammation disorders and cancers. Based on a series of pyrrolo[2,3-d]pyrimidine containing two carbo-aromatic rings, we have searched for new CSF1R inhibitors having a higher fraction of sp3-atoms. The phenyl unit in the 4-amino group could efficiently be replaced by tetrahydropyran (THP) retaining inhibitor potency. Exchanging the 6-aryl group with cyclohex-2-ene units also resulted in highly potent compounds, while fully saturated ring systems at C-6 led to a loss of activity. The structure-activity relationship study evaluating THP containing pyrrolo[2,3-d]pyrimidine derivates identified several highly active inhibitors by enzymatic studies. A comparison of 11 pairs of THP and aromatic compounds showed that inhibitors containing THP had clear benefits in terms of enzymatic potency, solubility, and cell toxicity. Guided by cellular experiments in Ba/F3 cells, five CSF1R inhibitors were further profiled in ADME assays, indicating the para-aniline derivative 16t as the most attractive compound for further development.

SARM1 Promotes Neurodegeneration and Memory Impairment in Mouse Models of Alzheimer's Disease

Neuroinflammation plays a crucial role in the pathogenesis and progression of Alzheimer's disease (AD). The Sterile Alpha and Toll Interleukin Receptor Motif-containing protein 1 (SARM1) has been shown to promote axonal degeneration and is involved in neuroinflammation. However, the role of SARM1 in AD remains unclear. In this study, we found that SARM1 was reduced in hippocampal neurons of AD model mice. Interestingly, conditional knockout (CKO) of SARM1 in the central nervous system (CNS, SARM1Nestin-CKO mice) delayed the cognitive decline in APP/PS1 AD model mice. Furthermore, SARM1 deletion reduced the Aβ deposition and inflammatory infiltration in the hippocampus and inhibited neurodegeneration in APP/PS1 AD model mice. Further investigation into the underlying mechanisms revealed that the signaling of tumor necrosis factor-α (TNF-α) was downregulated in the hippocampus tissues of APP/PS1;SARM1Nestin-CKO mice, thereby alleviating the cognitive decline, Aβ deposition and inflammatory infiltration. These findings identify unrecognized functions of SARM1 in promoting AD and reveal the SARM1-TNF-α pathway in AD model mice.

Hyperbaric oxygen alleviates selective domains of cognitive and motor deficits in female 5xFAD mice

Treatment of Alzheimer's disease (AD) has been limited to managing of symptoms or anti-amyloid therapy with limited results and uncertainty. Seeking out new therapies that can reverse the effects of this devastating disease is important. Hyperbaric oxygen (HBO) therapy could be such a candidate as it has been shown to improve brain function in certain neurological conditions. Furthermore, the role sex plays in the vulnerability/resilience to AD remains equivocal. An understanding of what makes one sex more vulnerable to AD could unveil new pathways for therapy development. In this study, we investigated the effects of HBO on cognitive, motor, and affective function in a mouse model of AD (5xFAD) and assessed protein oxidation in peripheral tissues as a safety indicator. The motor and cognitive abilities of 5xFAD mice were significantly impaired. HBO therapy improved cognitive flexibility and associative learning of 5xFAD females but not males, but HBO had no effect other aspects of cognition. HBO also reversed AD-related declines in balance but had no impact on gait and anxiety-like behavior. HBO did not affect body weights or oxidative stress in peripheral tissues. Our study provides further support for HBO therapy as a potential treatment for AD and emphasizes the importance of considering sex as a biological variable in therapeutic development. Further investigations into the underlying mechanisms of HBO's sex-specific responses are warranted, as well as optimizing treatment protocols for maximum benefits.