p38α‐MAPK‐deficient myeloid cells ameliorate symptoms and pathology of APP ‐transgenic Alzheimer's disease mice

Puerarin mitigates cognitive decline and white matter injury via CD36-Mediated microglial phagocytosis in chronic cerebral hypoperfusion

BACKGROUND

Chronic cerebral hypoperfusion (CCH) contributes significantly to white matter injury (WMI) and cognitive impairment, often leading to vascular dementia (VaD). Inefficient clearance of myelin debris by microglia impedes white matter repair, making microglia-mediated myelin clearance a promising therapeutic strategy for WMI. Puerarin (Pu), an isoflavonoid monomer from Pueraria lobata, is known for its neuroprotective, anti-inflammatory, and immunoregulatory properties. However, its effects and underlying mechanisms in counteracting CCH-induced damage remain unclear. In this study, we aimed to investigate the therapeutic effects and underlying mechanisms of puerarin in a CCH mouse model.

METHODS

Right unilateral common carotid artery occlusion (rUCCAO) was used to model CCH in C57BL/6J mice. Puerarin (400 mg/kg/day) was administered intraperitoneally for 10 consecutive days starting immediately post-surgery. Cognitive function was assessed by the Morris Water Maze (MWM) test. WMI, remyelination, neuroinflammation, and microglial phagocytosis were evaluated by western blotting, immunofluorescence staining, RT-PCR, or flow cytometry both in vivo and in vitro.

RESULTS

Puerarin treatment significantly improved cognitive performance and mitigated WMI in rUCCAO mice. These effects were associated with enhanced microglial phagocytosis and remyelination, reduced neuroinflammation, and increased CD36 expression. Additionally, puerarin also increased the levels of IL-10 and phosphorylated STAT3 (p-STAT3) in brain tissues. Notably, IL-10 neutralization reversed these benefits effects by reducing microglial myelin debris uptake, downregulating STAT3 phosphorylation and CD36 expression.

CONCLUSIONS

Our findings demonstrate that puerarin has significant therapeutic potential in treating CCH-related cognitive impairments and WMI by modulating CD36-mediated microglial myelin clearance through the IL-10/STAT3 pathway. However, our study was reliant on preclinical animal models, further studies are needed to explore applicability in human subjects.

Egln3 expression in microglia enhances the neuroinflammatory responses in Alzheimer's disease

Alzheimer's disease (AD), characterized by cognitive and behavioral abnormalities, is the most prevalent neurodegenerative disease worldwide. Neuroinflammation, which is induced by microglial activation, resulting in the expression of a multitude of inflammatory factors, is one of the principal characteristics of AD. Herein, we found that Egln3 is differentially expressed in microglia in the brains of AD mice. Egln3 is a member of the Egln family of proline hydroxylases, which regulates a variety of biological processes, including transcription, the cell cycle, and apoptosis, through hydroxylation, ubiquitylation, and participation in glycolysis. To further observe the effects of Egln3 on cognitive function, we utilized APP/PS1 mice as a pathological model of AD to conduct behavioral experiments and assess the expression levels of Aβ and inflammatory factors. The specific mechanisms by which Egln3 affects microglial activation were analyzed using in vitro experiments and transcriptome sequencing. The results of these analyses demonstrated that Egln3 is highly expressed in microglia in AD. Inhibition of Egln3 expression in the brains of APP/PS1 mice improves neuroinflammatory responses and cognitive function, indicating that a high expression of Egln3 promotes AD progression. Furthermore, our findings indicate that Egln3 could activate the MAPK pathway, which in turn contributes to the aggravation of neuroinflammation. Inhibition of the MAPK pathway results in attenuation of the pro-inflammatory state of microglia. Consequently, Egln3 may exacerbate neuroinflammation and promote AD progression via the MAPK pathway in microglia, making it a promising target for AD-related therapies.

Dual inhibition of butyrylcholinesterase and p38α mitogen-activated protein kinase: A new approach for the treatment of Alzheimer's disease

The simultaneous targeting of neuroinflammation and cholinergic hypofunction, the key pathological changes in Alzheimer's disease (AD), is not addressed by drugs currently in clinical trials, highlighting a critical therapeutic gap. We propose that dual-acting small molecules that inhibit butyrylcholinesterase (BChE) and mitogen-activated protein kinase p38α (p38α MAPK) represent a novel strategy to combat AD. This hypothesis is supported by cellular and animal studies as well as in silico modelling showing that it is possible to act simultaneously on both enzymes. Amyloid beta (Aβ) plaques trigger a pro-inflammatory microglial response that overactivates p38α MAPK, leading to increased Aβ synthesis, tau hyperphosphorylation, and altered synaptic plasticity. Overactivated microglia exacerbate neuroinflammation and cholinergic degeneration, ultimately leading to cognitive impairment. Structural similarities between the binding sites of BChE and p38α MAPK provide a promising basis for the development of dual inhibitors that could alleviate AD symptoms and address the underlying pathology.

Mechanistic and therapeutic role of NLRP3 inflammasome in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder, has emerged as the most common form of dementia in the elderly. Several pathological hallmarks have been identified, including neuroinflammation. A comprehensive insight into the underlying mechanisms that can fuel the development of novel therapeutic approaches is necessary because of the alarmingly rapid increase in the frequency of incidence. Recently, NLRP3 inflammasome was identified as a critical mediator of neuroinflammation. Activation of nucleotide-binding domain (NOD)-like receptor protein 3 (NLRP3) inflammasome by amyloid, neurofibrillary tangles, impaired autophagy and endoplasmic reticulum stress, triggers the release of pro-inflammatory cytokines such as IL-1β and IL-18. Subsequently, these cytokines can promote neurodegeneration and cognitive impairment. It is well established that genetic or pharmacological ablation of NLRP3 alleviates AD-related pathological features in in vitro and in vivo models. Therefore, several synthetic and natural compounds have been identified that exhibit the potential to inhibit NLRP3 inflammasome and alleviate AD-associated pathology. The current review article will highlight the various mechanisms by which activation of NLRP3 inflammation occurs during Alzheimer's disease, and how it influences neuroinflammation, neurodegeneration and cognitive impairment. Moreover, we will summarise the different small molecules that possess the potential to inhibit NLRP3 and can pave the path for developing novel therapeutic interventions for AD.

GSNOR negatively regulates the NLRP3 inflammasome via S-nitrosation of MAPK14

Hyperactivation of the NLRP3 inflammasome has been implicated in the pathogenesis of numerous diseases. However, the precise molecular mechanisms that modulate the transcriptional regulation of NLRP3 remain largely unknown. In this study, we demonstrated that S-nitrosoglutathione reductase (GSNOR) deficiency in macrophages leads to significant increases in the Nlrp3 and Il-1β expression levels and interleukin-1β (IL-1β) secretion in response to NLRP3 inflammasome stimulation. Furthermore, in vivo experiments utilizing Gsnor-/- mice revealed increased disease severity in both lipopolysaccharide (LPS)-induced septic shock and dextran sodium sulfate (DSS)-induced colitis models. Additionally, we showed that both LPS-induced septic shock and DSS-induced colitis were ameliorated in Gsnor-/- Nlrp3-/- double-knockout (DKO) mice. Mechanistically, GSNOR deficiency increases the S-nitrosation of mitogen-activated protein kinase 14 (MAPK14) at the Cys211 residue and augments MAPK14 kinase activity, thereby promoting Nlrp3 and Il-1β transcription and stimulating NLRP3 inflammasome activity. Our findings suggested that GSNOR is a regulator of the NLRP3 inflammasome and that reducing the level of S-nitrosylated MAPK14 may constitute an effective strategy for alleviating diseases associated with NLRP3-mediated inflammation.

Downregulation of miR-181c-5p in Alzheimer's disease weakens the response of microglia to Aβ phagocytosis

Alzheimer's disease (AD) is an age-associated neurodegenerative disease. Recently, studies have demonstrated the potential involvement of microRNA-181c-5p (miR-181c-5p) in AD. However, the mechanism through which miR-181c-5p is responsible for the onset and progression of this disease remains unclear, and our study aimed to explore this problem. Differential expression analysis of the AD dataset was performed to identify dysregulated genes. Based on hypergeometric analysis, AD differential the upstream regulation genes miR-181c-5p was found. We constructed a model where SH-SY5Y and BV2 cells were exposed to Aβ1-42 to simulate AD. Levels of tumor necrosis factor-alpha, interleukin-6, and IL-1β were determined using enzyme-linked immunosorbent assay or reverse transcription quantitative polymerase chain reaction. Phosphorylation levels of p-P38 and P38 were detected by Western blot. The level of apoptosis in BV2 cells under Aβ1-42 stress was exacerbated by miR-181c-5p mimic. Downregulated miR-181c-5p impaired the phagocytosis and degradation of Aβ by BV2 cells. The release of proinflammatory cytokines in BV2 cells with Aβ1-42 stress was alleviated by miR-181c-5p upregulation. Additionally, miR-181c-5p downregulation alleviated the phosphorylation of P38 in Aβ1-42-induced SH-SY5Y cells. In conclusion, miR-181c-5p improves the phagocytosis of Aβ by microglial cells in AD patients, thereby reducing neuroinflammation.

Inflammation and Brain Structure in Alzheimer's Disease and Other Neurodegenerative Disorders: a Mendelian Randomization Study

Previous in vitro and post-mortem studies have reported the role of inflammation in neurodegenerative disorders. However, the association between inflammation and brain structure in vivo and the transcriptome-driven functional basis with relevance to neurodegenerative disorders remains elusive. The aim of the present study is to identify the association among inflammation, brain structure, and neurodegenerative disorders at genetic and transcriptomic levels. Genetic variants associated with inflammatory cytokines were selected from the latest and largest genome-wide association studies of European ancestry. Neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and dementia with Lewy bodies (DLB) and brain structure imaging measures were selected as the outcomes. Two-sample Mendelian randomization analyses were conducted to identify the causal associations. Single-nucleus transcriptome data of the occipitotemporal cortex was further analyzed to identify the differential expressed genes in AD, which were tested for biological processes and protein interaction network. MR analysis indicated that genetically predicted TREM2 and sTREM2 were significantly associated with AD (TREM2: z-score = -9.088, p-value = 1.02 × 10-19; sTREM2: z-score = -7.495, p-value = 6.61 × 10-14). The present study found no evidence to support the causal associations between other inflammatory cytokines and the risks of AD, PD, ALS, or DLB. Genetically predicted TREM2 was significantly associated with the cortical thickness of inferior temporal (z-score = -4.238, p-value = 2.26 × 10-5) and pole temporal (z-score = -4.549, p-value = 5.40 × 10-6). In the occipitotemporal cortex samples, microglia were the main source of TREM2 gene and showed increasing expression of genes associated with inflammation and immunity. The present study has leveraged genetic and transcriptomic data to identify the association among TREM2, temporal lobe, and AD and the underlying cellular and molecular basis, thus providing a new perspective on the role of TREM2 in AD and insights into the complex associations among inflammation, brain structure, and neurodegenerative disorders, particularly AD.

Xinshubao tablet rescues cognitive dysfunction in a mouse model of vascular dementia: Involvement of neurogenesis and neuroinflammation

Vascular dementia (VaD) represents a severe cognitive dysfunction syndrome closed linked to cardiovascular function. In the present study, we assessed the potential of Xinshubao tablet (XSB), a traditional Chinese prescription widely used for cardiovascular diseases, to mitigate neuropathological damage in a mouse model of VaD and elucidated the underlying mechanisms. Our findings revealed that oral administration of XSB rescued the cardiac dysfunction resulting from bilateral common carotid artery stenosis (BCAS), improved the cerebral blood flow (CBF) and cognitive function, reduced white matter injury, inhibited excessive microglial and astrocytic activation, stimulated hippocampal neurogenesis, and reduced neural apoptosis in the brains of BCAS mice. Mechanistically, RNA-seq analysis indicated that XSB treatment was significantly associated with neuroinflammation, vasculature development, and synaptic transmission, which were further confirmed by q-PCR assays. Western blot results revealed that XSB treatment hindered the nuclear translocation of nuclear factor-κB (NF-κB), thereby suppressing the NF-κB signaling pathway. These results collectively demonstrated that XSB could ameliorate cognitive dysfunction caused by BCAS through regulating CBF, reducing white matter lesions, suppressing glial activation, promoting neurogenesis, and mitigating neuroinflammation. Notably, the NF-κB signaling pathway emerged as a pivotal player in this mechanism.

Modulation of Alzheimer's disease brain pathology in mice by gut bacterial depletion: the role of IL-17a

Gut bacteria regulate brain pathology of Alzheimer's disease (AD) patients and animal models; however, the underlying mechanism remains unclear. In this study, 3-month-old APP-transgenic female mice with and without knock-out of Il-17a gene were treated with antibiotics-supplemented or normal drinking water for 2 months. The antibiotic treatment eradicated almost all intestinal bacteria, which led to a reduction in Il-17a-expressing CD4-positive T lymphocytes in the spleen and gut, and to a decrease in bacterial DNA in brain tissue. Depletion of gut bacteria inhibited inflammatory activation in both brain tissue and microglia, lowered cerebral Aβ levels, and promoted transcription of Arc gene in the brain of APP-transgenic mice, all of which effects were abolished by deficiency of Il-17a. As possible mechanisms regulating Aβ pathology, depletion of gut bacteria inhibited β-secretase activity and increased the expression of Abcb1 and Lrp1 in the brain or at the blood-brain barrier, which were also reversed by the absence of Il-17a. Interestingly, a crossbreeding experiment between APP-transgenic mice and Il-17a knockout mice further showed that deficiency of Il-17a had already increased Abcb1 and Lrp1 expression at the blood-brain barrier. Thus, depletion of gut bacteria attenuates inflammatory activation and amyloid pathology in APP-transgenic mice via Il-17a-involved signaling pathways. Our study contributes to a better understanding of the gut-brain axis in AD pathophysiology and highlights the therapeutic potential of Il-17a inhibition or specific depletion of gut bacteria that stimulate the development of Il-17a-expressing T cells.

Study on the Pharmacological Mechanism of Icariin for the Treatment of Alzheimer's Disease Based on Network Pharmacology and Molecular Docking Techniques

The purpose of this study is to explore the pharmacological mechanism of icariin (ICA) in the treatment of Alzheimer's disease (AD) based on network pharmacology and network molecular docking technology. In order to investigate the regulatory effect of ICA on the expression level of AD pathological phosphorylation regulatory proteins, this study further explored the possible molecular mechanism of ICA regulating AD autophagy through network pharmacology. Macromolecular docking network was verified by Autodock Vina 1.1.2 software. The main active ingredients of ICA, the physicochemical properties, and pharmacokinetic information of ICA were predicted using online databases and relevant information. The results showed that the targets of MAPK3, AKT1, HSP90AA1, ESR1, and HSP90AA1 were more critical in the treatment of AD. Autophagy, apoptosis, senescence factors, phosphatidylinositide 3-kinase/protein kinase B (P13K/AKT) signaling pathway, MAKP, mTOR, and other pathways were significantly associated with AD. Docking of ICA with HIF-1, BNIP3, PINK1, and Parkin pathway molecules showed that the key targets of the signaling pathway were more stably bound to ICA, which may provide a better pathway for ICA to regulate autophagy by providing a better pathway. ICA can improve AD, and its mechanism may be related to the P13K/AKT, MAKP, and mTOR signaling pathways, thereby regulating autophagy-related proteins.

Oxytocin alleviates cognitive and memory impairments by decreasing hippocampal microglial activation and synaptic defects via OXTR/ERK/STAT3 pathway in a mouse model of sepsis-associated encephalopathy

BACKGROUND

Sepsis-associated encephalopathy (SAE) is a diffuse brain dysfunction, characterized by cognitive and memory impairments closely linked to hippocampal dysfunction. Though it is well-known that SAE is a diffuse brain dysfunction with microglial activation, the pathological mechanisms of SAE are not well established and effective clinical interventions are lacking. Oxytocin (OXT) is reported to have anti-inflammatory and neuroprotective roles. However, the effects of OXT on SAE and the underlying mechanisms are not clear.

METHODS

SAE was induced in adult C57BL/6J male mice by cecal ligation and perforation (CLP) surgery. Exogenous OXT was intranasally applied after surgery. Clinical score, survivor rate, cognitive and memory behaviors, and hippocampal neuronal and non-neuronal functions were evaluated. Cultured microglia challenged with lipopolysaccharide (LPS) were used to investigate the effects of OXT on microglial functions, including inflammatory cytokines release and phagocytosis. The possible intracellular signal pathways involved in the OXT-induced neuroprotection were explored with RNA sequencing.

RESULTS

Hippocampal OXT level decreases, while the expression of OXT receptor (OXTR) increases around 24 h after CLP surgery. Intranasal OXT application at a proper dose increases mouse survival rate, alleviates cognitive and memory dysfunction, and restores hippocampal synaptic function and neuronal activity via OXTR in the SAE model. Intraperitoneal or local administration of the OXTR antagonist L-368,899 in hippocampal CA1 region inhibited the protective effects of OXT. Moreover, during the early stages of sepsis, hippocampal microglia are activated, while OXT application reduces microglial phagocytosis and the release of inflammatory cytokines, thereby exerting a neuroprotective effect. OXT may improve the SAE outcomes via the OXTR-ERK-STAT3 signaling pathway.

CONCLUSION

Our study uncovers the dysfunction of the OXT signal in SAE and shows that intranasal OXT application at a proper dose can alleviate SAE outcomes by reducing microglial overactivation, suggests that OXT may be a promising therapeutic approach in managing SAE patients.

TAK1 Improves Cognitive Function via Suppressing RIPK1-Driven Neuronal Apoptosis and Necroptosis in Rats with Chronic Hypertension

Chronic hypertension is a major risk factor for cognitive impairment, which can promote neuroinflammation and neuronal loss in the central nervous system. Transforming growth factor β-activated kinase 1 (TAK1) is a key molecular component in determining cell fate and can be activated by inflammatory cytokines. This study aimed to investigate the role of TAK1 in mediating neuronal survival in the cerebral cortex and hippocampus under chronic hypertensive conditions. To that end, we used stroke-prone renovascular hypertension rats (RHRSP) as chronic hypertension models. Adeno-associated virus (AAV) designed to overexpress or knock down TAK1 expression were injected into the lateral ventricles of rats and the subsequent effects on cognitive function and neuronal survival under chronic hypertensive conditions were assessed. We found that, TAK1 knockdown in RHRSP markedly increased neuronal apoptosis and necroptosis and induced cognitive impairment, which could be reversed by Nec-1s, an inhibitor of receptor interacting protein kinase 1 (RIPK1). In contrast, overexpression of TAK1 in RHRSP significantly suppressed neuronal apoptosis and necroptosis and improved cognitive function. Further knockdown of TAK1 in sham-operated rats received similar phenotype with RHRSP. The results have been verified in vitro. In this study, we provide in vivo and in vitro evidence that TAK1 improves cognitive function by suppressing RIPK1-driven neuronal apoptosis and necroptosis in rats with chronic hypertension.