Microglia, neuroinflammation, and beta-amyloid protein in Alzheimer's disease

Krüppel-like factor 5 accelerates the pathogenesis of Alzheimer’s disease via BACE1-mediated APP processing

Background

The deposition of β-amyloid (Aβ) in the brain plays a major role in the pathogenesis of Alzheimer’s disease (AD). Aβ is generated via amyloid precursor protein (APP) cleavage through the amyloidogenic pathway. In this pathway, β-secretase (BACE1) is the first and rate-limiting enzyme. Its expression increases through an unknown mechanism in patients with AD. Thus, the key regulatory mechanism of BACE1 in the AD process should be revealed to understand the pathogenesis of AD and explore the key treatment targets of AD.

Methods

Here, APPswe/PS1dE9 (APP/PS1) mice were employed to observe the Krüppel-like factor 5 (KLF5) and BACE1 levels in the serum and brain tissues. HT22 cells were used to explore the relationship between KLF5 and BACE1.

Results

In this study, KLF5 was found to be a novel transcription factor that positively regulated BACE1 by binding to the BACE1 promoter. The KLF5 levels significantly increased not only in the CSF and serum of patients with AD but also in the brain tissue of APP/PS1 mice. They were closely related to cognitive capacity. KLF5 accelerated APP amyloidogenic metabolism and promoted Aβ synthesis through BACE1. Silencing BACE1 could block the KLF5-induced amyloidogenic process of APP. ML264 ameliorated the cognitive deficits and slowed down APP amyloidogenic cleavage in APP/PS1 mice.

Conclusion

The findings above suggest that upregulation of KLF5 might be a critical element in AD progression by accelerating BACE1-mediated APP amyloidogenic cleavage. The inhibition of KLF5 or the combined inhibitory effect of KLF5 and the BACE1 promoter might be a potential strategy to prevent AD pathogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-01050-3.

Neuroprotective Effect of Stearidonic Acid on Amyloid β-Induced Neurotoxicity in Rat Hippocampal Cells

Dietary intake of omega-3 fatty acids found in fish has been reported to reduce the risk of Alzheimer's Disease (AD). Stearidonic acid (SDA), a plant-based omega-3 fatty acid, has been targeted as a potential surrogate for fish-based fatty acids. However, its role in neuronal degeneration is unknown. This study was designed to evaluate effects of SDA on Amyloid-β(A-β)-induced neurotoxicity in rat hippocampal cells. Results showed that SDA effectively converted to eicosapentaenoic acid (EPA) in hippocampal cells. Aβ-induced apoptosis in H19-7 cells was protected by SDA pretreatment as evidenced by its regulation on the expression of relevant pro- and anti-apoptotic genes, as well as the inhibition on caspase activation. SDA also protected H19-7 cells from Aβ-induced oxidative stress by regulating the expression of relevant pro- and anti-oxidative genes, as well as the improvement in activity of catalase. As for Aβ/LPS-induced neuronal inflammation, SDA pretreatment reduced the release of IL-1β and TNFα. Further, we found that the anti-Aβ effect of SDA involves its inhibition on the expression of amyloid precursor protein and the regulation on MAPK signaling. These results demonstrated that SDAs have neuroprotective effect in Aβ-induced H19-7 hippocampal cells. This beneficial effect of SDA was attributed to its antiapoptotic, antioxidant, and anti-inflammatory properties.

Morphological and biomolecular targets in retina and vitreous from Reelin-deficient mice (Reeler): Potential implications for age-related macular degeneration in Alzheimer’s dementia

The neurosensory retina is an outgrowth of the Central Nervous System (CNS), and the eye is considered “a window to the brain.” Reelin glycoprotein is directly involved in neurodevelopment, in synaptic plasticity, learning and memory. Consequently, abnormal Reelin signaling has been associated with brain neurodegeneration but its contributing role in ocular degeneration is still poorly explored. To this aim, experimental procedures were assayed on vitreous or retinas obtained from Reeler mice (knockout for Reelin protein) at different postnatal days (p) p14, p21 and p28. At p28, a significant increase in the expression of Amyloid Precursor Protein (APP) and its amyloidogenic peptide (Aβ1-42 along with truncated tau fragment (i.e., NH2htau)- three pathological hallmarks of Alzheimer’s disease (AD)-were found in Reeler mice when compared to their age-matched wild-type controls. Likewise, several inflammatory mediators, such as Interleukins, or crucial biomarkers of oxidative stress were also found to be upregulated in Reeler mice by using different techniques such as ELLA assay, microchip array or real-time PCR. Taken together, these findings suggest that a dysfunctional Reelin signaling enables the expression of key pathological features which are classically associated with AD neurodegenerative processes. Thus, this work suggests that Reeler mouse might be a suitable animal model to study not only the pathophysiology of developmental processes but also several neurodegenerative diseases, such as AD and Age-related Macular Degeneration (AMD), characterized by accumulation of APP and/or Aβ1-42, NH2htau and inflammatory markers.

Targeting the liver in dementia and cognitive impairment: Dietary macronutrients and diabetic therapeutics

Many people living with dementia and cognitive impairment have dysfunctional mitochondrial and insulin-glucose metabolism resembling type 2 diabetes mellitus and old age. Evidence from human trials shows that nutritional interventions and anti-diabetic medicines that target nutrient-sensing pathways overcome these deficits in glucose and energy metabolism and can improve cognition and/or reduce symptoms of dementia. The liver is the main organ that mediates the systemic effects of diets and many diabetic medicines; therefore, it is an intermediate target for such dementia interventions. A challenge is the efficacy of these treatments in older age. Solutions include the targeted hepatic delivery of diabetic medicines using nanotechnologies and titration of macronutrients to optimize hepatic energy metabolism.

Cannabidiol for neurodegenerative disorders: A comprehensive review

Despite the significant advances in neurology, the cure for neurodegenerative conditions remains a formidable task to date. Among various factors arising from the complex etiology of neurodegenerative diseases, neuroinflammation and oxidative stress play a major role in pathogenesis. To this end, some phytocannabinoids isolated from Cannabis sativa (widely known as marijuana) have attracted significant attention as potential neurotherapeutics. The profound effect of ∆9-tetrahydrocannabinol (THC), the major psychoactive component of cannabis, has led to the discovery of the endocannabinoid system as a molecular target in the central nervous system (CNS). Cannabidiol (CBD), the major non-psychoactive component of cannabis, has recently emerged as a potential prototype for neuroprotective drug development due to its antioxidant and anti-inflammatory properties and its well-tolerated pharmacological behavior. This review briefly discusses the role of inflammation and oxidative stress in neurodegeneration and demonstrates the neuroprotective effect of cannabidiol, highlighting its general mechanism of action and disease-specific pathways in Parkinson's disease (PD) and Alzheimer's disease (AD). Furthermore, we have summarized the preclinical and clinical findings on the therapeutic promise of CBD in PD and AD, shed light on the importance of determining its therapeutic window, and provide insights into identifying promising new research directions.

Effect of tricyclic 1,2-thiazine derivatives in neuroinflammation induced by preincubation with lipopolysaccharide or coculturing with microglia-like cells

Background

Alzheimer’s disease (AD) is considered the most common cause of dementia among the elderly. One of the modifiable causes of AD is neuroinflammation. The current study aimed to investigate the influence of new tricyclic 1,2-thiazine derivatives on in vitro model of neuroinflammation and their ability to cross the blood–brain barrier (BBB).

Methods

The potential anti-inflammatory effect of new tricyclic 1,2-thiazine derivatives (TP1, TP4, TP5, TP6, TP7, TP8, TP9, TP10) was assessed in SH-SY5Y cells differentiated to the neuron-like phenotype incubated with bacterial lipopolysaccharide (5 or 50 μg/ml) or THP-1 microglial cell culture supernatant using MTT, DCF-DA, Griess, and fast halo (FHA) assays. Additionally, for cultures preincubated with 50 µg/ml lipopolysaccharide (LPS), a cyclooxygenase (COX) activity assay was performed. Finally, the potential ability of tested compounds to cross the BBB was evaluated by computational studies. Molecular docking was performed with the TLR4/MD-2 complex to assess the possibility of binding the tested compounds in the LPS binding pocket. Prediction of ADMET parameters (absorption, distribution, metabolism, excretion and toxicity) was also conducted.

Results

The unfavorable effect of LPS and co-culture with THP-1 cells on neuronal cell viability was counteracted with TP1 and TP4 in all tested concentrations. Tested compounds reduced the oxidative and nitrosative stress induced by both LPS and microglia activation and also reduced DNA damage. Furthermore, new derivatives inhibited total COX activity. Additionally, new compounds would cross the BBB with high probability and reach concentrations in the brain not lower than in the serum. The binding affinity at the TLR4/MD-2 complex binding site of TP4 and TP8 compounds is similar to that of the drug donepezil used in Alzheimer's disease. The ADMET analysis showed that the tested compounds should not be toxic and should show high intestinal absorption.

Conclusions

New tricyclic 1,2-thiazine derivatives exert a neuroregenerative effect in the neuroinflammation model, presumably via their inhibitory influence on COX activity and reduction of oxidative and nitrosative stress.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43440-022-00414-8.

Isorhamnetin Attenuated the Release of Interleukin-6 from β-Amyloid-Activated Microglia and Mitigated Interleukin-6-Mediated Neurotoxicity

Alzheimer's disease (AD), characterized by the abnormal accumulation of β-amyloid (Aβ), is the most prevalent type of dementia, and it is associated with progressive cognitive decline and memory loss. Aβ accumulation activates microglia, which secrete proinflammatory factors associated with Aβ clearance impairment and cause neurotoxicity, generating a vicious cycle among Aβ accumulation, activated microglia, and proinflammatory factors. Blocking this cycle can be a therapeutic strategy for AD. Using Aβ-activated HMC3 microglial cells, we observed that isorhamnetin, a main constituent of Oenanthe javanica, reduced the Aβ-triggered secretion of interleukin- (IL-) 6 and downregulated the expression levels of the microglial activation markers ionized calcium binding adaptor molecule 1 (IBA1) and CD11b and the inflammatory marker nuclear factor-κB (NF-κB). Treatment of the SH-SY5Y-derived neuronal cells with the Aβ-activated HMC3-conditioned medium (HMC3-conditioned medium) or IL-6 increased reactive oxygen species production, upregulated cleaved caspase 3 expression, and reduced neurite outgrowth, whereas treatment with isorhamnetin counteracted these neurodegenerative presentations. In the SH-SY5Y-derived neuronal cells, IL-6 upregulated the phosphorylation of tyrosine kinase 2 (TYK2) and signal transducer and activator of transcription 1 (STAT1), whereas isorhamnetin normalized this abnormal phosphorylation. Overexpression of TYK2 attenuated the neuroprotective effect of isorhamnetin on IL-6-induced neurotoxicity. Our findings demonstrate that isorhamnetin exerts its neuroprotective effect by mediating the neuroinflammatory IL-6/TYK2 signaling pathway, suggesting its potential for treating AD.

Interleukin 22 and its association with neurodegenerative disease activity

It is worth noting that neuroinflammation is well recognized as a symptom of neurodegenerative diseases (NDs). The regulation of neuroinflammation becomes an attractive focus for innovative ND treatment technologies. There is evidence that IL-22 is associated with the development and progression of a wide assortment of NDs. For example, IL-22 can activate glial cells, causing them to generate pro-inflammatory cytokines and encourage lymphocyte infiltration in the brain. IL-22 mRNA is highly expressed in Alzheimer’s disease (AD) patients, and a high expression of IL-22 has also been detected in the brains of patients with other NDs. We examine the role of IL-22 in the development and treatment of NDs in this review, and we believe that IL-22 has therapeutic potential in these diseases.

Therapeutic properties of multi-cannabinoid treatment strategies for Alzheimer’s disease

Alzheimer’s disease (AD) is a debilitating neurodegenerative disease characterized by declining cognition and behavioral impairment, and hallmarked by extracellular amyloid-β plaques, intracellular neurofibrillary tangles (NFT), oxidative stress, neuroinflammation, and neurodegeneration. There is currently no cure for AD and approved treatments do not halt or slow disease progression, highlighting the need for novel therapeutic strategies. Importantly, the endocannabinoid system (ECS) is affected in AD. Phytocannabinoids, including cannabidiol (CBD) and Δ⁹-tetrahydrocannabinol (THC), interact with the ECS, have anti-inflammatory, antioxidant, and neuroprotective properties, can ameliorate amyloid-β and NFT-related pathologies, and promote neurogenesis. Thus, in recent years, purified CBD and THC have been evaluated for their therapeutic potential. CBD reversed and prevented the development of cognitive deficits in AD rodent models, and low-dose THC improved cognition in aging mice. Importantly, CBD, THC, and other phytochemicals present in Cannabis sativa interact with each other in a synergistic fashion (the “entourage effect”) and have greater therapeutic potential when administered together, rather than individually. Thus, treatment of AD using a multi-cannabinoid strategy (such as whole plant cannabis extracts or particular CBD:THC combinations) may be more efficacious compared to cannabinoid isolate treatment strategies. Here, we review the current evidence for the validity of using multi-cannabinoid formulations for AD therapy. We discuss that such treatment strategies appear valid for AD therapy but further investigations, particularly clinical studies, are required to determine optimal dose and ratio of cannabinoids for superior effectiveness and limiting potential side effects. Furthermore, it is pertinent that future in vivo and clinical investigations consider sex effects.

Dual PET-fMRI reveals a link between neuroinflammation, amyloid binding and compensatory task-related brain activity in Alzheimer's disease

The interplay among neuropathological mechanisms underlying Alzheimer’s disease (AD), as neuroinflammation and amyloid-beta (Aβ), as well their impact on neuronal function remains elusive. A major gap in knowledge is the functional impact of neuroinflammation. The posterior cingulate cortex (PCC), as the most prominent site of amyloid pathology in AD, is a pivotal region to investigate the concomitant presence of pathophysiological mechanisms such as microglia activation, indexing neuroinflammation, and changes in task related activity. Here we used a dual PET approach to simultaneously study Aβ load and neuroinflammation (TSPO uptake marker), using ¹¹C-PiB and ¹¹C-PK11195 radiotracers, respectively and fMRI to study task related neural activation in an AD sample (n = 19) and matched controls (n = 19). Here we show significantly increased Aβ deposition, neuroinflammation and brain activity related to a visual object working memory task in this key region. Microglia activation was associated with increased brain activity specifically in patients, independently of amyloid binding, raising the possibility that abnormal brain activity might be restored in clinical trials aimed at reducing microglia activation.

Multimodal PET-fMRI imaging of Alzheimer’s disease patients and healthy controls suggests that microglia activation in the posterior cingulate cortex is associated with increased brain activity in Alzheimer’s disease, and independent of amyloid accumulation.

The Protective Effects of Acetazolamide Against Homocysteine-Induced Blood-Brain-Barrier Disruption by Regulating the Activation of the Wnt/β-Catenin Signaling Pathway

Acetazolamide (AZA) is a carbonic anhydrase inhibitor (CAI) with neuroprotective effects. Hyperhomocysteinemia is associated with blood-brain-barrier (BBB) disruption in brain disorders. A previous study indicated that AZA might have a new role in brain disorders. However, its function in hyperhomocysteinemia-related BBB disruption has not been reported. Here, we aim to clarify the role of AZA in homocysteine (Hcy)-mediated BBB dysfunction using both in vivo and in vitro assays. We found that AZA improved memory and cognitive function, and reduced brain edema in Hcy-stimulated hyperhomocysteinemia model rats. This protective effect of AZA on hyperhomocysteinemia rats was accompanied by improved BBB permeability and increased expression levels of the tight junction proteins, occludin, and claudin-5. The in vitro assay results show that AZA prevented Hcy-induced cell injury and attenuated the increased permeability in Hcy-treated bEnd.3 brain endothelial cells. The Hcy-induced decrease in occludin and claudin-5, and increase in MMP-2 and MMP-9 expression levels were attenuated by AZA in bEnd.3 cells. Moreover, the Hcy-induced downregulation of the Wnt/β-catenin signaling pathway in bEnd.3 cells was abolished by AZA. Inhibition of Wnt/β-catenin by ICG-001 reversed the protective effects of AZA in Hcy-treated bEnd.3 cells. We also prove that this process is mediated by WTAP. These findings suggest that acetazolamide mitigated the Hcy-induced compromised brain vascular endothelial integrity by regulating the activation of the Wnt/β-catenin signaling pathway.

PILRA polymorphism modifies the effect of APOE4 and GM17 on Alzheimer's disease risk

PILRA (rs1859788 A > G) has been suggested to be a protective variant for Alzheimer's disease (AD) and is an entry co-receptor for herpes simplex virus-1. We conducted a nested case-control study of 360 1:1-matched AD subjects. Interactions between the PILRA-A allele, APOE risk variants (ε3/ε4 or ε4/ε4) and GM17 for AD risk were modelled. The associations were cross-validated using two independent whole-genome sequencing datasets. We found negative interactions between PILRA-A and GM17 (OR 0.72, 95% CI 0.52-1.00) and between PILRA-A and APOE risk variants (OR 0.56, 95% CI 0.32-0.98) in the discovery dataset. In the replication cohort, a joint effect of PILRA and PILRA × GM 17/17 was observed for the risk of developing AD (p .02). Here, we report a negative effect modification by PILRA on APOE and GM17 high-risk variants for future AD risk in two independent datasets. This highlights the complex genetics of AD.

New insights into the role and mechanisms of ginsenoside Rg1 in the management of Alzheimer's disease

Alzheimer's disease (AD) is a common neurodegenerative disorder in the elderly characterized by memory loss and cognitive dysfunction. The pathogenesis of AD is complex. One-targeted anti-AD drugs usually fail to delay AD progression. Traditional Chinese medicine records have documented the use of the roots of Panax ginseng (ginseng roots) and its prescriptions to treat dementia. Ginsenoside Rg1, the main ginsenoside component of ginseng roots, exhibits a certain therapeutic effect in the abovementioned diseases, suggesting its potential in the management of AD. Therefore, we combed the pathogenesis of AD and currently used anti-AD drugs, and reviewed the availability, pharmacokinetics, and pharmaceutic studies of ginsenoside Rg1. This review summarizes the therapeutic effects and mechanisms of ginsenoside Rg1 and its deglycosylated derivatives in AD in vivo and in vitro. The main mechanisms include improvement in Aβ and Tau pathologies, regulation of synaptic function and intestinal microflora, and reduction of inflammation, oxidative stress, and apoptosis. The underlying mechanisms mainly involve the regulation of PKC, MAPK, PI3K/Akt, CDK5, GSK-3β, BDNF/TrkB, PKA/CREB, FGF2/Akt, p21WAF1/CIP1, NF-κB, NLRP1, TLR3, and TLR4 signaling pathways. As the effects and underlying mechanisms of ginsenoside Rg1 on AD have not been systematically reviewed, we have provided a comprehensive review and shed light on the future directions in the utilization of ginsenoside Rg1 and ginseng roots as well as the development of anti-AD drugs.

MiR-483-3p improves learning and memory abilities via XPO1 in Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD), a common form of dementia, has been reported to influence 27 million individuals globally. Several risk factors including oxidative stress, gut microbiota imbalance, and cognitive activity are reported to be closely associated with the initiation or progression of AD. Although miR-483-3p was identified to be downregulated in AD patient serum. However, the biological role and mechanism of miR-483-3p remained unknown in AD. Here, we explored the role of miR-483-3p in AD.

METHODS

Sprague-Dawley rats were injected with homocysteine (Hcy) to establish an AD animal model. The Morris water maze tests and contextual fear tests were conducted to assess the cognitive and memory abilities of rats. TUNEL staining was utilized to determine cell apoptosis. Luciferase reporter assay was used to evaluate the binding relation between miR-483-3p and exportin 1 (XPO1).

RESULTS

Homocysteine treatment (400 μg/kg) induced the learning, cognitive and memory defects of rats. miR-483-3p was downregulated in Hcy-treated rat hippocampus. Functionally, miR-483-3p alleviated cell apoptosis and impairments of learning and memory abilities in Hcy-treated rats. In addition, miR-483-3p inhibited cell apoptosis and protein level of AD-associated factors (APP, BACE1, and Aβ1-42) in PC12 cells. In mechanism, miR-483-3p was confirmed to target XPO1 in PC12 cells. XPO1 displayed high level in rat hippocampus and was negatively correlated with miR-483-3p levels. Finally, XPO1 overexpression rescued the suppressive effect of miR-483-3p on cell apoptosis and protein levels of AD-associated factors.

CONCLUSIONS

miR-483-3p alleviates neural cell apoptosis and impairments of learning and memory abilities by targeting XPO1 in AD.

Heterozygous expression of the Alzheimer's disease-protective PLCγ2 P522R variant enhances Aβ clearance while preserving synapses

BACKGROUND

A rare coding variant, P522R, in the phospholipase C gamma 2 (PLCG2) gene has been identified as protective against late-onset Alzheimer's disease (AD), but the mechanism is unknown. PLCG2 is exclusively expressed in microglia within the central nervous system, and altered microglial function has been implicated in the progression of AD.

METHODS

Healthy control hiPSCs were CRISPR edited to generate cells heterozygous and homozygous for the PLCG2P522R variant. Microglia derived from these hiPSC's were used to investigate the impact of PLCγ2P522R on disease relevant processes, specifically microglial capacity to take up amyloid beta (Aβ) and synapses. Targeted qPCR assessment was conducted to explore expression changes in core AD linked and microglial genes, and mitochondrial function was assessed using an Agilent Seahorse assay.

RESULTS

Heterozygous expression of the P522R variant resulted in increased microglial clearance of Aβ, while preserving synapses. This was associated with the upregulation of a number of genes, including the anti-inflammatory cytokine Il-10, and the synapse-linked CX3CR1, as well as alterations in mitochondrial function, and increased cellular motility. The protective capacity of PLCγ2P522R appeared crucially dependent on (gene) 'dose', as cells homozygous for the variant showed reduced synapse preservation, and a differential gene expression profile relative to heterozygous cells.

CONCLUSION

These findings suggest that PLCγ2P522R may result in increased surveillance by microglia, and prime them towards an anti-inflammatory state, with an increased capacity to respond to increasing energy demands, but highlights the delicate balance of this system, with increasing PLCγ2P522R 'dose' resulting in reduced beneficial impacts.

Role of Microglia in Herpesvirus-Related Neuroinflammation and Neurodegeneration

Neuroinflammation is defined as an inflammatory state within the central nervous system (CNS). Microglia conprise the resident tissue macrophages of the neuronal tissue. Upon viral infection of the CNS, microglia become activated and start to produce inflammatory mediators important for clearance of the virus, but an excessive neuroinflammation can harm nearby neuronal cells. Herpesviruses express several molecular mechanisms, which can modulate apoptosis of infected neurons, astrocytes and microglia but also divert immune response initiated by the infected cells. In this review we also describe the link between virus-related neuroinflammation, and development of neurodegenerative diseases.

Modulation of MAPK- and PI3/AKT-Dependent Autophagy Signaling by Stavudine (D4T) in PBMC of Alzheimer’s Disease Patients

Background: Aβ₄₂ deposition plays a pivotal role in AD pathogenesis by inducing the activation of microglial cells and neuroinflammation. This process is antagonized by microglia-mediated clearance of Aβ plaques. Activation of the NLRP3 inflammasome is involved in neuroinflammation and in the impairments of Aβ-plaque clearance. On the other hand, stavudine (D4T) downregulates the NLRP3 inflammasome and stimulates autophagy-mediated Aβ-clearing in a THP-1-derived macrophages. Methods: We explored the effect of D4T on Aβ autophagy in PBMC from AD patients that were primed with LPS and stimulated with Aβ oligomers in the absence/presence of D4T. We analyzed the NLRP3 activity by measuring NLRP3-ASC complex formation by AMNIS FlowSight and pro-inflammatory cytokine (IL-1β, IL-18 and Caspase-1) production by ELISA. The phosphorylation status of p38, ERK, AKT, p70, and the protein expression of CREB, LAMP2A, beclin-1, Caspase-3 and Bcl2 were analyzed by Western blot. Results: Data showed that D4T: (1) downregulates NLRP3 inflammasome activation and the production of down-stream pro-inflammatory cytokines in PBMC; (2) stimulates the phosphorylation of AKT, ERK and p70 as well as LAMP2A, beclin-1 and Bcl2 expression and reduces Caspase-3 expression, suggesting an effect of this compound on autophagy; (3) increases phospho-CREB, which is a downstream target of p-ERK and p-AKT, inducing anti-inflammatory cytokine production and resulting in a possible decrease of Aβ-mediated cytotoxicity; and (4) reduces the phosphorylation of p38, a protein involved in the production of pro-inflammatory cytokines and tau hyperphosphorylation. Conclusions: D4T reduces the activation of the NLRP3 inflammasome, and it might stimulate autophagy as well as the molecular mechanism that modulates Aβ cytotoxicity, and D4T might reduce inflammation in the cells of AD patients. It could be very interesting to check the possible beneficial effects of D4T in the clinical scenario.

Galectin-3 Involvement in Cognitive Processes for New Therapeutic Considerations

Cognitive impairment may be a consequence of the normal aging process, but it may also be the hallmark of various neurodegenerative and psychiatric diseases. Early identification of individuals at particular risk for cognitive decline is critical, as it is imperative to maintain a cognitive reserve in these neuropsychiatric entities. In recent years, galectin-3 (Gal-3), a member of the galectin family, has received considerable attention with respect to aspects of neuroinflammation and neurodegeneration. The mechanisms behind the putative relationship between Gal-3 and cognitive impairment are not yet clear. Intrigued by this versatile molecule and its unique modular architecture, the latest data on this relationship are presented here. This mini-review summarizes recent findings on the mechanisms by which Gal-3 affects cognitive functioning in both animal and human models. Particular emphasis is placed on the role of Gal-3 in modulating the inflammatory response as a fine-tuner of microglia morphology and phenotype. A review of recent literature on the utility of Gal-3 as a biomarker is provided, and approaches to strategically exploit Gal-3 activities with therapeutic intentions in neuropsychiatric diseases are outlined.

Physiology and pharmacology of amyloid precursor protein

Amyloid precursor protein (APP) is an evolutionarily conserved transmembrane protein and a well-characterized precursor protein of amyloid-beta (Aβ) peptides, which accumulate in the brains of individuals with Alzheimer's disease (AD)-related pathologies. Aβ has been extensively investigated since the amyloid hypothesis in AD was proposed. Besides Aβ, previous studies on APP and its proteolytic cleavage products have suggested their diverse pathological and physiological functions. However, their roles still have not been thoroughly understood. In this review, we extensively discuss the evolutionarily-conserved biology of APP, including its structure and processing pathway, as well as recent findings on the physiological roles of APP and its fragments in the central nervous system and peripheral nervous system. We have also elaborated upon the current status of APP-targeted therapeutic approaches for AD treatment by discussing inhibitors of several proteases participating in APP processing, including α-, β-, and γ-secretases. Finally, we have highlighted the future perspectives pertaining to further research and the potential clinical role of APP.

Animal Models for Neuroinflammation and Potential Treatment Methods

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating chronic disease of unknown etiology and without effective treatment options. The onset of ME/CFS is often associated with neuroinflammation following bacterial or viral infection. A positron emission tomography imaging study revealed that the degree of neuroinflammation was correlated with the severity of several symptoms in patients with ME/CFS. In animal studies, lipopolysaccharide- and polyinosinic-polycytidylic acid-induced models are thought to mimic the pathological features of ME/CFS and provoke neuroinflammation, characterized by increased levels of proinflammatory cytokines and activation of microglia. In this review, we described the anti-inflammatory effects of three compounds on neuroinflammatory responses utilizing animal models. The findings of the included studies suggest that anti-inflammatory substances may be used as effective therapies to ameliorate disease symptoms in patients with ME/CFS.

The Periodontal Pathogen Fusobacterium nucleatum Exacerbates Alzheimer's Pathogenesis via Specific Pathways

Alzheimer's Disease (AD) is the most common form of dementia in older adults and has a devastating impact on the patient's quality of life, which creates a significant socio-economic burden for the affected individuals and their families. In recent years, studies have identified a relationship between periodontitis and AD. Periodontitis is an infectious/inflammatory disease that destroys the supporting periodontal structure leading to tooth loss. Dysbiosis of the oral microbiome plays a significant role in the onset and development of periodontitis exhibiting a shift to overgrowth of pathobionts in the normal microflora with increasing local inflammation. Fusobacterium nucleatum is a common pathogen that significantly overgrows in periodontitis and has also been linked to various systemic diseases. Earlier studies have reported that antibodies to F. nucleatum can be detected in the serum of patients with AD or cognitive impairment, but a causal relationship and a plausible mechanism linking the two diseases have not been identified. In this study, we conducted both in vivo and in vitro experiments and found that F. nucleatum activates microglial cells causing morphological changes, accelerated proliferation and enhanced expression of TNF-α and IL-1β in microglial cells. In our in vivo experiments, we found that F. nucleatum-induced periodontitis resulted in the exacerbation of Alzheimer's symptoms in 5XFAD mice including increased cognitive impairment, beta-amyloid accumulation and Tau protein phosphorylation in the mouse cerebrum. This study may suggest a possible link between a periodontal pathogen and AD and F. nucleatum could be a risk factor in the pathogenesis of AD. We are currently further identifying the pathways through which F. nucleatum modulates molecular elements in enhancing AD symptoms and signs. Data are available via ProteomeXchange with identifier PXD033147.

Non-Coding RNAs as Novel Regulators of Neuroinflammation in Alzheimer's Disease

Alzheimer’s disease (AD) is one of the most common causes of dementia. Although significant breakthroughs have been made in understanding the progression and pathogenesis of AD, it remains a worldwide problem and a significant public health burden. Thus, more efficient diagnostic and therapeutic strategies are urgently required. The latest research studies have revealed that neuroinflammation is crucial in the pathogenesis of AD. Non-coding RNAs (ncRNAs), including long noncoding RNAs (lncRNAs), microRNAs (miRNAs), circular RNAs (circRNAs), PIWI-interacting RNAs (piRNAs), and transfer RNA-derived small RNAs (tsRNAs), have been strongly associated with AD-induced neuroinflammation. Furthermore, several ongoing pre-clinical studies are currently investigating ncRNA as disease biomarkers and therapeutic interventions to provide new perspectives for AD diagnosis and treatment. In this review, the role of different types of ncRNAs in neuroinflammation during AD are summarized in order to improve our understanding of AD etiology and aid in the translation of basic research into clinical practice.

Neuroprotective Potency of Neolignans in Magnolia officinalis Cortex Against Brain Disorders

In recent years, neurological diseases including Alzheimer’s disease, Parkinson’s disease and stroke are one of the main causes of death in the world. At the same time, the incidence of psychiatric disorders including depression and anxiety has been increasing. Accumulating elderly and stressed people suffer from these brain disorders, which is undoubtedly a huge burden on the modern aging society. Neolignans, the main active ingredients in Magnolia officinalis cortex, were reported to have neuroprotective effects. In addition, the key bioactive ingredients of neolignans, magnolol (1) and honokiol (2), were proved to prevent and treat neurological diseases and psychiatric disorders by protecting nerve cells and brain microvascular endothelial cells (BMECs). Furthermore, neolignans played a role in protecting nerve cells via regulation of neuronal function, suppression of neurotoxicity, etc. This review summarizes the neuroprotective effect, primary mechanisms of the leading neolignans and provides new prospects for the treatment of brain disorders in the future.

γ-Glutamylcysteine attenuates amyloid-β oligomers-induced neuroinflammation in microglia via blocking NF-κB signaling pathway

Alzheimer's disease (AD) is the most prevalent neurogenerative disease, characterized by progressive memory loss and cognitive deficits. Intracellular neurofibrillary tangles (NFTs) and amyloid-β (Aβ)-formed neuritic plaques are major pathological features of AD. Aβ evokes activation of microglia to release inflammatory mediators and ROS to induce neurotoxicity, leading to neurodegeneration. γ-Glutamylcysteine (γ-GC), an intermediate dipeptide of the GSH-synthesis pathway and possessing anti-inflammatory and anti-oxidative properties, represents a relatively unexplored option for AD treatment. In the present study, we investigated the anti-inflammatory effect of γ-GC on Aβ oligomer (AβO)-induced neuroinflammation and the associated molecular mechanism in microglia. The results showed that γ-GC reduced AβO-induced release of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and nitric oxide (NO), and the expression of inducible NO synthase (iNOS) and cyclooxygenase 2 (COX-2). γ-GC decreased ROS and MDA production and increased the GSH level, GSH/GSSG ratio, and SOD activity in AβO-treated microglia. Mechanistically, γ-GC inhibited activation of nuclear factor kappa B (NF-κB), and upregulated the nuclear receptor-related 1 (Nurr1) protein expression to suppress the transcriptional effect of NF-κB on the inflammatory genes. Besides, γ-GC suppressed the AβO-induced neuroinflammation in mice. These findings suggested that γ-GC might represent a potential therapeutic agent for anti-neuroinflammation.

Neuroprotective potential of curcuminoids in modulating Alzheimer's Disease via multiple signaling pathways

Alzheimer's disease (AD) is a progressive and frequent neurodegenerative disease of elderly people. In the 21st century, owing to the increasing prevalence of AD, there is a crucial need for finding better and effective pharmacotherapeutic approaches. This review article demonstrated the various sources and possible metabolic pathways of curcuminoids obtained from Curcuma longa herb, to prevent and treat AD but the information related to the metabolic fate of curcuminoids is deficient. Different in vitro and in vivo research studies demonstrating the mechanisms by which curcuminoids attenuated AD have been summarized. Administration of curcuminoids has been indicated to inhibit hyperphosphorylation of tau protein, deposition, and oligomerization of amyloid beta plaques in several AD models. Curcuminoids also chelate metals and form complexes, have antioxidant properties, mediates neuroinflammatory signaling pathways by modifying microglial cells activity, inhibit acetylcholinesterase activities and also modulates other associated signaling pathways including insulin signaling pathways and heme-oxygenase pathway. Briefly curcuminoids exhibit the capability to be more productive and efficacious compared to many recent treatments due to their antioxidant, delayed neuron degeneration and anti-inflammatory potential. Although their effectiveness as a curative agent is considered to be reduced due to their low bioavailability, If the issue of curcuminoids' low bioavailability is resolved then curcuminoid-based medications are hopefully on the horizon against AD.

Metabolic Reprogramming of Microglia Enhances Proinflammatory Cytokine Release through EphA2/p38 MAPK Pathway in Alzheimer’s Disease

Background: The activation of microglia and neuroinflammation has been implicated in the pathogenesis of Alzheimer’s disease (AD), but the exact roles of microglia and the underlying mechanisms remain unclear. Objective: To clarify how the metabolic reprogramming of microglia induce by amyloid-β (Aβ)1-42 to affect the release of proinflammatory cytokines in AD. Methods: MTS assay was used to detect the viability of BV2 cells treated with different concentrations of Aβ1-42 for different periods of time. The expression levels of proinflammatory cytokines were determined by qRT-PCR and western blot assay in BV2 cells and hippocampus of mice. RNA sequencing was applied to evaluate the gene expression profiles in response to HK2 knockdown in BV2 cells treated with Aβ1-42. Results: Low concentrations of Aβ1-42 increased the viability of BV2 cells and promoted the release of proinflammatory cytokines, and this process is accompanied by increased glycolysis. Inhibition of glycolysis significantly downregulated the release of proinflammatory cytokines in BV2 cells and hippocampus of mice treated with Aβ1-42. The results of RNA sequencing revealed the expression of chemokine ligand 2 (Cxcl2) and ephrin receptor tyrosine kinase A2 (EphA2) were significantly downregulated when knocked down HK2 in BV2 cells. Subsequently, the expression of proinflammatory cytokines was downregulated in BV2 cell after knocking down EphA2. Conclusion: This study demonstrated that EphA2/p38 MAPK pathway is involved the release of proinflammatory cytokines in microglia induced by Aβ1-42 in AD, which is accompanied by metabolic reprogramming from oxidative phosphorylation (OXPHOS) to glycolysis.

The circadian clock protein Rev-erbα provides neuroprotection and attenuates neuroinflammation against Parkinson's disease via the microglial NLRP3 inflammasome

BACKGROUND

Circadian disturbance is a common nonmotor complaint in Parkinson's disease (PD). The molecular basis underlying circadian rhythm in PD is poorly understood. Neuroinflammation has been identified as a key contributor to PD pathology. In this study, we explored the potential link between the core clock molecule Rev-erbα and the microglia-mediated NLR family pyrin domain-containing 3 (NLRP3) inflammasome in PD pathogenesis.

METHODS

We first examined the diurnal Rev-erbα rhythms and diurnal changes in microglia-mediated inflammatory cytokines expression in the SN of MPTP-induced PD mice. Further, we used BV2 cell to investigate the impacts of Rev-erbα on NLRP3 inflammasome and microglial polarization induced by 1-methyl-4-phenylpyridinium (MPP⁺) and αsyn pre-formed fibril. The role of Rev-erbα in regulating microglial activation via NF-κB and NLRP3 inflammasome pathway was then explored. Effects of SR9009 against NLRP3 inflammasome activation, microgliosis and nigrostriatal dopaminergic degeneration in the SN and striatum of MPTP-induced PD mice were studied in detail.

RESULTS

BV2 cell-based experiments revealed the role of Rev-erbα in regulating microglial activation and polarization through the NF-κB and NLRP3 inflammasome pathways. Circadian oscillation of the core clock gene Rev-erbα in the substantia nigra (SN) disappeared in MPTP-induced PD mice, as well as diurnal changes in microglial morphology. The expression of inflammatory cytokines in SN of the MPTP-induced mice were significantly elevated. Furthermore, dopaminergic neurons loss in the nigrostriatal system were partially reversed by SR9009, a selective Rev-erbα agonist. In addition, SR9009 effectively reduced the MPTP-induced glial activation, microglial polarization and NLRP3 inflammasome activation in the nigrostriatal system.

CONCLUSIONS

These observations suggest that the circadian clock protein Rev-erbα plays an essential role in attenuating neuroinflammation in PD pathology, and provides a potential therapeutic target for PD treatment.

Microbiota-microglia connections in age-related cognition decline

Aging is an inevitable process that all individuals experience, of which the extent differs among individuals. It has been recognized as the risk factor of neurodegenerative diseases by affecting gut microbiota compositions, microglia, and cognition abilities. Aging‐induced changes in gut microbiota compositions have a critical role in orchestrating the morphology and functions of microglia through the gut‐brain axis. Gut microbiota communicates with microglia by its secreted metabolites and neurotransmitters. This is highly associated with age‐related cognitive declines. Here, we review the main composition of microbiota in the aged individuals, outline the changes of the brain in age‐related cognitive decline from a neuroinflammation perspective, especially the changes of morphology and functions of microglia, discuss the crosstalk between microbiota and microglia in the aged brain and further highlight the role of microbiota‐microglia connections in neurodegenerative diseases (Alzheimer's disease and Parkinson's disease).

Potential neuroprotection by Dendrobium nobile Lindl alkaloid in Alzheimer's disease models

At present, treatments for Alzheimer's disease can temporarily relieve symptoms but cannot prevent the decline of cognitive ability and other neurodegenerative changes. Dendrobium nobile Lindl alkaloid is the main active component of Dendrobium nobile Lindl. Dendrobium nobile Lindl alkaloid has been shown to resist aging, prolong life span, and exhibit immunomodulatory effects in animals. This review summarizes the mechanisms behind the neuroprotective effects reported in Alzheimer's disease animal models. The neuroprotective effects of Dendrobium nobile Lindl alkaloid have not been studied in patients. The mechanisms by which Dendrobium nobile Lindl alkaloid has been reported to improve cognitive dysfunction in Alzheimer's disease animal models may be associated with extracellular amyloid plaque production, regulation of tau protein hyperphosphorylation, inhibition of neuroinflammation and neuronal apoptosis, activation of autophagy, and enhanced synaptic connections.

Alzheimer’s Disease Biomarkers Revisited From the Amyloid Cascade Hypothesis Standpoint

Alzheimer’s disease (AD) is the most common neurodegenerative disease worldwide. Amyloid beta (Aβ) is one of the proteins which aggregate in AD, and its key role in the disease pathogenesis is highlighted in the amyloid cascade hypothesis, which states that the deposition of Aβ in the brain parenchyma is a crucial initiating step in the future development of AD. The sensitivity of instruments used to measure proteins in blood and cerebrospinal fluid has significantly improved, such that Aβ can now successfully be measured in plasma. However, due to the peripheral production of Aβ, there is significant overlap between diagnostic groups. The presence of pathological Aβ within the AD brain has several effects on the cells and surrounding tissue. Therefore, there is a possibility that using markers of tissue responses to Aβ may reveal more information about Aβ pathology and pathogenesis than looking at plasma Aβ alone. In this manuscript, using the amyloid cascade hypothesis as a starting point, we will delve into how the effect of Aβ on the surrounding tissue can be monitored using biomarkers. In particular, we will consider whether glial fibrillary acidic protein, triggering receptor expressed on myeloid cells 2, phosphorylated tau, and neurofilament light chain could be used to phenotype and quantify the tissue response against Aβ pathology in AD.

Neuroepigenetic Mechanisms of Action of Ultrashort Peptides in Alzheimer's Disease

Epigenetic regulation of gene expression is necessary for maintaining higher-order cognitive functions (learning and memory). The current understanding of the role of epigenetics in the mechanism of Alzheimer’s disease (AD) is focused on DNA methylation, chromatin remodeling, histone modifications, and regulation of non-coding RNAs. The pathogenetic links of this disease are the misfolding and aggregation of tau protein and amyloid peptides, mitochondrial dysfunction, oxidative stress, impaired energy metabolism, destruction of the blood–brain barrier, and neuroinflammation, all of which lead to impaired synaptic plasticity and memory loss. Ultrashort peptides are promising neuroprotective compounds with a broad spectrum of activity and without reported side effects. The main aim of this review is to analyze the possible epigenetic mechanisms of the neuroprotective action of ultrashort peptides in AD. The review highlights the role of short peptides in the AD pathophysiology. We formulate the hypothesis that peptide regulation of gene expression can be mediated by the interaction of short peptides with histone proteins, cis- and transregulatory DNA elements and effector molecules (DNA/RNA-binding proteins and non-coding RNA). The development of therapeutic agents based on ultrashort peptides may offer a promising addition to the multifunctional treatment of AD.

Connecting the Dots Between Hypercholesterolemia and Alzheimer’s Disease: A Potential Mechanism Based on 27-Hydroxycholesterol

Alzheimer’s disease (AD), the most common cause of dementia, is a complex and multifactorial disease involving genetic and environmental factors, with hypercholesterolemia considered as one of the risk factors. Numerous epidemiological studies have reported a positive association between AD and serum cholesterol levels, and experimental studies also provide evidence that elevated cholesterol levels accelerate AD pathology. However, the underlying mechanism of hypercholesterolemia accelerating AD pathogenesis is not clear. Here, we review the metabolism of cholesterol in the brain and focus on the role of oxysterols, aiming to reveal the link between hypercholesterolemia and AD. 27-hydroxycholesterol (27-OHC) is the major peripheral oxysterol that flows into the brain, and it affects β-amyloid (Aβ) production and elimination as well as influencing other pathogenic mechanisms of AD. Although the potential link between hypercholesterolemia and AD is well established, cholesterol-lowering drugs show mixed results in improving cognitive function. Nevertheless, drugs that target cholesterol exocytosis and conversion show benefits in improving AD pathology. Herbs and natural compounds with cholesterol-lowering properties also have a potential role in ameliorating cognition. Collectively, hypercholesterolemia is a causative risk factor for AD, and 27-OHC is likely a potential mechanism for hypercholesterolemia to promote AD pathology. Drugs that regulate cholesterol metabolism are probably beneficial for AD, but more research is needed to unravel the mechanisms involved in 27-OHC, which may lead to new therapeutic strategies for AD.

Luteolin alleviates cognitive impairment in Alzheimer's disease mouse model via inhibiting endoplasmic reticulum stress-dependent neuroinflammation

Luteolin is a flavonoid in a variety of fruits, vegetables, and herbs, which has shown anti-inflammatory, antioxidant, and anti-cancer neuroprotective activities. In this study, we investigated the potential beneficial effects of luteolin on memory deficits and neuroinflammation in a triple-transgenic mouse model of Alzheimer's disease (AD) (3 × Tg-AD). The mice were treated with luteolin (20, 40 mg · kg^-1 · d^-1, ip) for 3 weeks. We showed that luteolin treatment dose-dependently improved spatial learning, ameliorated memory deficits in 3 × Tg-AD mice, accompanied by inhibiting astrocyte overactivation (GFAP) and neuroinflammation (TNF-α, IL-1β, IL-6, NO, COX-2, and iNOS protein), and decreasing the expression of endoplasmic reticulum (ER) stress markers GRP78 and IRE1α in brain tissues. In rat C6 glioma cells, treatment with luteolin (1, 10 µM) dose-dependently inhibited LPS-induced cell proliferation, excessive release of inflammatory cytokines, and increase of ER stress marker GRP78. In conclusion, luteolin is an effective agent in the treatment of learning and memory deficits in 3 × Tg-AD mice, which may be attributable to the inhibition of ER stress in astrocytes and subsequent neuroinflammation. These results provide the experimental basis for further research and development of luteolin as a therapeutic agent for AD.

TAPPing into the potential of inducible tau/APP transgenic mice

AIMS

Our understanding of the pathological interactions between amyloidosis and tauopathy in Alzheimer's disease is incomplete. We sought to determine if the relative timing of the amyloidosis and tauopathy is critical for amyloid-enhanced tauopathy.

METHODS

We crossed an inducible tauopathy model with two β-amyloid models utilising the doxycycline-repressible transgenic system to modulate timing and duration of human tau expression in the context of amyloidosis and then assessed tauopathy, amyloidosis and gliosis.

RESULTS

We combined inducible rTg4510 tau with APPswe/PS1dE9 [Line 85 (L85)] mice to examine the interactions between Aβ and tauopathy at different stages of amyloidosis. When we initially suppressed mutant human tau expression for 14-15 months and subsequently induced tau expression for 6 months, severe amyloidosis with robust tauopathy resulted in rTg4510/L85 but not rTg4510 mice. When we suppressed mutant tau for 7 months before inducing expression for a subsequent 6 months in another cohort of rTg4510/L85 and rTg4510 mice, only rTg4510/L85 mice displayed robust tauopathy. Lastly, we crossed rTg4510 mice to tet-regulated APPswe/ind [Line 107 (L107)] mice, using doxycycline to initially suppress both transgenes for 1 month before inducing expression for 5 months to model early amyloidosis. In contrast to rTg4510, rTg4510/L107 mice rapidly developed amyloidosis, accompanied by robust tauopathy.

CONCLUSIONS

These data suggest that tau misfolding is exacerbated by both newly forming Aβ deposits in younger brain and mature deposits in older brains. Refined use and repurposing of these models provide new tools to explore the intersection of ageing, amyloid and tauopathy and to test interventions to disrupt the amyloid cascade.

Hydrogen sulfide-induced post-translational modification as a potential drug target

Hydrogen sulfide (H₂S) is one of the three known gas signal transducers, and since its potential physiological role was reported, the literature on H₂S has been increasing. H₂S is involved in processes such as vasodilation, neurotransmission, angiogenesis, inflammation, and the prevention of ischemia-reperfusion injury, and its mechanism remains to be further studied. At present, the role of post-translational processing of proteins has been considered as a possible mechanism for the involvement of H₂S in a variety of physiological processes. Current studies have shown that H₂S is involved in S-sulfhydration, phosphorylation, and S-nitrosylation of proteins, etc. This paper focuses on the effects of protein modification involving H₂S on physiological and pathological processes, looking forward to providing guidance for subsequent research.

Aberrant Cerebral Iron Trafficking Co-morbid With Chronic Inflammation: Molecular Mechanisms and Pharmacologic Intervention

The redox properties that make iron an essential nutrient also make iron an efficient pro-oxidant. Given this nascent cytotoxicity, iron homeostasis relies on a combination of iron transporters, chaperones, and redox buffers to manage the non-physiologic aqueous chemistry of this first-row transition metal. Although a mechanistic understanding of the link between brain iron accumulation (BIA) and neurodegenerative diseases is lacking, BIA is co-morbid with the majority of cognitive and motor function disorders. The most prevalent neurodegenerative disorders, including Alzheimer's Disease (AD), Parkinson's Disease (PD), Multiple System Atrophy (MSA), and Multiple Sclerosis (MS), often present with increased deposition of iron into the brain. In addition, ataxias that are linked to mutations in mitochondrial-localized proteins (Friedreich's Ataxia, Spinocerebellar Ataxias) result in mitochondrial iron accumulation and degradation of proton-coupled ATP production leading to neuronal degeneration. A comorbidity common in the elderly is a chronic systemic inflammation mediated by primary cytokines released by macrophages, and acute phase proteins (APPs) released subsequently from the liver. Abluminal inflammation in the brain is found downstream as a result of activation of astrocytes and microglia. Reasonably, the iron that accumulates in the brain comes from the cerebral vasculature via the microvascular capillary endothelial cells whose tight junctions represent the blood-brain barrier. A premise amenable to experimental interrogation is that inflammatory stress alters both the trans- and para-cellular flux of iron at this barrier resulting in a net accumulation of abluminal iron over time. This review will summarize the evidence that lends support to this premise; indicate the mechanisms that merit delineation; and highlight possible therapeutic interventions based on this model.

Failure of Alzheimer’s Mice Brain Resident Neural Precursor Cells in Supporting Microglia-Mediated Amyloid β Clearance

The failure of brain microglia to clear excess amyloid β (Aβ) is considered a leading cause of the progression of Alzheimer’s disease pathology. Resident brain neural precursor cells (NPCs) possess immune-modulatory and neuro-protective properties, which are thought to maintain brain homeostasis. We have recently showed that resident mouse brain NPCs exhibit an acquired decline in their trophic properties in the Alzheimer’s disease brain environment. Therefore, we hypothesized that functional NPCs may support microglial phagocytic activity, and that NPCs derived from the adult AD mouse brain may fail to support the clearance of Aβ by microglia. We first identified in the AD brain, in vivo and ex vivo, a subpopulation of microglia that express high Aβ phagocytic activity. Time-lapse microscopy showed that co-culturing newborn NPCs with microglia induced a significant increase in the fraction of microglia with high Aβ phagocytic activity. Freshly isolated NPCs from adult wild type, but not AD, mouse brain, induced an increase in the fraction of microglia with high Aβ phagocytic activity. Finally, we showed that NPCs also possess the ability to promote Aβ degradation within the microglia with high Aβ phagocytic activity. Thus, resident brain NPCs support microglial function to clear Aβ, but NPCs derived from the AD environment fail to do so. We suggest that the failure of AD brain NPCs to support Aβ clearance from the brain by microglia may accelerate disease pathology.

Influence of the Microbiota-Gut-Brain Axis on Cognition in Alzheimer’s Disease

The gut microbiota is made up of trillions of microbial cells including bacteria, viruses, fungi, and other microbial bodies and is greatly involved in the maintenance of proper health of the host body. In particular, the gut microbiota has been shown to not only be involved in brain development but also in the modulation of behavior, neuropsychiatric disorders, and neurodegenerative diseases including Alzheimer’s disease. The precise mechanism by which the gut microbiota can affect the development of Alzheimer’s disease is unknown, but the gut microbiota is thought to communicate with the brain directly via the vagus nerve or indirectly through signaling molecules such as cytokines, neuroendocrine hormones, bacterial components, neuroactive molecules, or microbial metabolites such as short-chain fatty acids. In particular, interventions such as probiotic supplementation, fecal microbiota transfer, and supplementation with microbial metabolites have been used not only to study the effects that the gut microbiota has on behavior and cognitive function, but also as potential therapeutics for Alzheimer’s disease. A few of these interventions, such as probiotics, are promising candidates for the improvement of cognition in Alzheimer ’s disease and are the focus of this review.

Exosomes Mediate APP Dysregulation via APP-miR-185-5p Axis

APP misexpression plays a crucial role in triggering a complex pathological cascade, leading to Alzheimer’s disease (AD). But how the expression of APP is regulated in pathological conditions remains poorly understood. In this study, we found that the exosomes isolated from AD mouse brain promoted APP expression in neuronal N2a cells. Moreover, exosomes derived from N2a cells with ectopic expression of APP (APP-EXO) also induced APP dysregulation in normal N2a cells. Surprisingly, the effects of APP-EXO on APP expression in recipient cells were not mediated by the direct transferring of APP gene products. Instead, the effects of APP-EXO were highly likely mediated by the reduction of the expression levels of exosomal miR-185-5p. We found that the 3′UTR of APP transcripts binds to miR-185-5p, therefore inhibiting the sorting of miR-185-5p to exosomes. N2a cell-derived exosomes with less amount of miR-185-5p exert similar roles in APP expression to APP-EXO. Lastly, we demonstrated a significant decline of serum exosomal miR-185-5p in AD patients and AD mice, versus the corresponding controls. Together, our results demonstrate a novel mechanism in the exosome-dependent regulation of APP, implying exosomes and exosomal miRNAs as potential therapeutic targets and biomarkers for AD treatment and diagnosis, respectively.

Tangeretin Inhibits BACE1 Activity and Attenuates Cognitive Impairments in AD Model Mice

Tangeretin (TAN) exhibits many bioactivities, including neuroprotective effects. However, the efficacy of TAN in Alzheimer's disease (AD) has not been sufficiently investigated. In the present study, we integrated behavioral tests, pathology assessment, and biochemical analyses to elucidate the antidementia activity of TAN in APPswe/PSEN1dE9 transgenic (Tg) mice. At supplementation levels of 100 mg/kg body weight per day, TAN significantly attenuated the cognitive impairment of Tg mice in behavioral tests. These effects were associated with less synaptic impairments and fewer β-amyloid accumulations after TAN administration. Furthermore, our study revealed that TAN possessed powerful inhibitory activity against β-secretase both in vitro and in vivo, which played a crucial role in the process of Aβ generation. These findings indicate that TAN is a potential drug for preventing AD pathology. The key mechanism underlying the antidementia effect of TAN may include its inhibitory activity against β-secretase.

Anti-Inflammatory Anthranilate Analogue Enhances Autophagy through mTOR and Promotes ER-Turnover through TEX264 during Alzheimer-Associated Neuroinflammation

Autophagy degrades impaired organelles and toxic proteins to maintain cellular homeostasis. Dysregulated autophagy is a pathogenic participant in Alzheimer's disease (AD) progression. In early-stage AD, autophagy is beneficially initiated by mild endoplasmic reticulum (ER) stress to alleviate cellular damage and inflammation. However, chronic overproduction of toxic Aβ oligomers eventually causes Ca²⁺ dysregulation in the ER, subsequently elevating ER-stress and impairing autophagy. Our previous work showed that a novel anthranilate analogue (SI-W052) inhibited lipopolysaccharide (LPS)-induced tumor necrosis factor (TNF)-α and interleukin (IL)-6 on microglia. To investigate its mechanism of action, herein, we postulate that SI-W052 exhibits anti-inflammatory activity through ER-stress-mediated autophagy. We initially demonstrate that autophagy inhibits inflammation, but it becomes impaired during acute inflammation. SI-W052 significantly induces the conversion ratio of LC3 II/I and inhibits LPS-upregulated p-mTOR, thereby restoring impaired autophagy to modulate inflammation. Our signaling study further indicates that SI-W052 inhibits the upregulation of ER-stress marker genes, including Atf4 and sXbp1/tXbp1, explaining compound activity against IL-6. This evidence encouraged us to evaluate ER-stress-triggered ER-phagy using TEX264. ER-phagy mediates ER-turnover by the degradation of ER fragments to maintain homeostasis. TEX264 is an important ER-phagy receptor involved in ATF4-mediated ER-phagy under ER-stress. In our study, elevated TEX264 degradation is identified during inflammation; SI-W052 enhances TEX264 expression, producing a positive effect in ER-turnover. Our knockdown experiment further verifies the important role of TEX264 in SI-W052 activity against IL-6 and ER-stress. In conclusion, this study demonstrates that an anthranilate analogue is a novel neuroinflammation agent functioning through ER-stress-mediated autophagy and ER-phagy mechanisms.

A Comprehensive Review on the Role of the Gut Microbiome in Human Neurological Disorders

The human body is full of an extensive number of commensal microbes, consisting of bacteria, viruses, and fungi, collectively termed the human microbiome. The initial acquisition of microbiota occurs from both the external and maternal environments, and the vast majority of them colonize the gastrointestinal tract (GIT). These microbial communities play a central role in the maturation and development of the immune system, the central nervous system, and the GIT system and are also responsible for essential metabolic pathways. Various factors, including host genetic predisposition, environmental factors, lifestyle, diet, antibiotic or nonantibiotic drug use, etc., affect the composition of the gut microbiota. Recent publications have highlighted that an imbalance in the gut microflora, known as dysbiosis, is associated with the onset and progression of neurological disorders. Moreover, characterization of the microbiome-host cross talk pathways provides insight into novel therapeutic strategies. Novel preclinical and clinical research on interventions related to the gut microbiome for treating neurological conditions, including autism spectrum disorders, Parkinson's disease, schizophrenia, multiple sclerosis, Alzheimer's disease, epilepsy, and stroke, hold significant promise. This review aims to present a comprehensive overview of the potential involvement of the human gut microbiome in the pathogenesis of neurological disorders, with a particular emphasis on the potential of microbe-based therapies and/or diagnostic microbial biomarkers. This review also discusses the potential health benefits of the administration of probiotics, prebiotics, postbiotics, and synbiotics and fecal microbiota transplantation in neurological disorders.

Naproxen as a potential candidate for promoting rivastigmine anti-Alzheimer activity against aluminum chloride-prompted Alzheimer's-like disease in rats; neurogenesis and apoptosis modulation as a possible underlying mechanism

BACKGROUND AND AIM

Alzheimer's disease (AD) is one of the leading causes of dependence and disability among the elderly worldwide. The traditional anti-Alzheimer medication, rivastigmine, one of the cholinesterase inhibitors (ChEIs), fails to achieve a definitive cure. We tested the hypothesis that naproxen administration to the rivastigmine-treated aluminum chloride (AlCl3) Alzheimer's rat model could provide an additive neuroprotective effect compared to rivastigmine alone.

MATERIALS AND METHODS

The studied groups were control (Cont), AlCl₃ treated (Al), rivastigmine treated (RIVA), naproxen treated (Napro), and combined rivastigmine and naproxen treated (RIVA + Napro). Rats' memory, spatial learning, and cognitive behavior were assessed followed by evaluation of hippocampal acetylcholinesterase (AChE) activity. Hippocampal and cerebellar histopathology were thoroughly examined. Activated caspase-3 and the neuroepithelial stem cells marker; nestin expressions were immunohistochemically assayed.

RESULTS

AD rats displayed significantly impaired memory and cognitive function, augmented hippocampal AChE activity; massive neurodegeneration associated with enhanced astrogliosis, apoptosis, and impaired neurogenesis. Except for the enhancement of neurogenesis and suppression of apoptosis, the combination therapy had no additional neuroprotective benefit over rivastigmine-only therapy.

CONCLUSION

Naproxen's efficacy was established by its ability to function at the cellular level, improved neurogenesis, and decreased, apoptosis without having an additional mitigating impact on cognitive impairment in rivastigmine-treated AD rats.

Nano-Honokiol ameliorates the cognitive deficits in TgCRND8 mice of Alzheimer's disease via inhibiting neuropathology and modulating gut microbiota

Introduction

Honokiol (HO) exerts neuroprotective effects in several animal models of Alzheimer's disease (AD), but the poor dissolution hampers its bioavailability and therapeutic efficacy.

Objectives

A novel honokiol nanoscale drug delivery system (Nano-HO) with smaller size and excellent stability was developed in this study to improve the solubility and bioavailability of HO. The anti-AD effects of Nano-HO was determined.

Methods

Male TgCRND8 mice were daily orally administered Nano-HO or HO at the same dosage (20 mg/kg) for 17 consecutive weeks, followed by assessment of the spatial learning and memory functions using the Morris Water Maze test (MWMT).

Results

Our pharmacokinetic study indicated that the oral bioavailability was greatly improved by Nano-HO. In addition, Nano-HO significantly improved cognitive deficits and inhibited neuroinflammation via suppressing the levels of TNF-α, IL-6 and IL-1β in the brain, preventing the activation of microglia (IBA-1) and astrocyte (GFAP), and reducing β-amyloid (Aβ) deposition in the cortex and hippocampus of TgCRND8 mice. Moreover, Nano-HO was more effective than HO in modulating amyloid precursor protein (APP) processing via suppressing β-secretase, as well as enhancing Aβ-degrading enzymes like neprilysin (NEP). Furthermore, Nano-HO more markedly inhibited tau hyperphosphorylation via decreasing the ratio of p-Tau (Thr 205)/tau and regulating tau-related apoptosis proteins (caspase-3 and Bcl-2). In addition, Nano-HO more markedly attenuated the ratios of p-JNK/JNK and p-35/CDK5, while enhancing the ratio of p-GSK-3β (Ser9)/GSK-3β. Finally, Nano-HO prevented the gut microflora dysbiosis in TgCRND8 mice in a more potent manner than free HO.

Conclusion

Nano-HO was more potent than free HO in improving cognitive impairments in TgCRND8 mice via inhibiting Aβ deposition, tau hyperphosphorylation and neuroinflammation through suppressing the activation of JNK/CDK5/GSK-3β signaling pathway. Nano-HO also more potently modulated the gut microbiota community to protect its stability than free HO. These results suggest that Nano-HO has good potential for further development into therapeutic agent for AD treatment.

Suppression of Fli-1 protects against pericyte loss and cognitive deficits in Alzheimer's disease

Brain pericytes regulate cerebral blood flow, maintain the integrity of the blood-brain barrier (BBB) and facilitate the removal of amyloid β (Aβ) which is critical to healthy brain activity. Pericyte loss has been observed in brains from patients with Alzheimer's disease (AD) and animal models. Our previous data demonstrated that friend leukemia virus integration 1 (Fli-1), an ETS transcription factor, governs pericyte viability in murine sepsis; however, the role of Fli-1 and its impact on pericyte loss in AD remains unknown. Here, we demonstrated that Fli-1 expression was up-regulated in postmortem brains from a cohort of human AD donors and in 5xFAD mice, which corresponded with a decreased pericyte number, elevated inflammatory mediators, and increased Aβ accumulation as compared to cognitively normal individuals and WT mice. Antisense oligonucleotide Fli-1 Gapmer administrated via intrahippocampal injection decelerated pericyte loss, decreased inflammatory response, ameliorated cognitive deficits, improved BBB dysfunction, and reduced Aβ deposition in 5xFAD mice. Fli-1 Gapmer-mediated inhibition of Fli-1 protected against Aβ accumulation-induced human brain pericyte apoptosis in vitro. Overall, these studies indicate that Fli-1 contributes to pericyte loss, inflammatory response, Aβ deposition, vascular dysfunction and cognitive decline, and suggest that inhibition of Fli-1 may represent novel therapeutic strategies for AD.