HMGB1 gene silencing inhibits neuroinflammation via down-regulation of NF-κB signaling in primary hippocampal neurons induced by Aβ25–35

Innate neuroimmunity across aging and neurodegeneration: a perspective from amyloidogenic evolvability

In Alzheimer's Disease (AD), amyloidogenic proteins (APs), such as β-amyloid (Aβ) and tau, may act as alarmins/damage-associated molecular patterns (DAMPs) to stimulate neuroinflammation and cell death. Indeed, recent evidence suggests that brain-specific type 2 immune networks may be important in modulating amyloidogenicity and brain homeostasis. Central to this, components of innate neuroimmune signaling, particularly type 2 components, assume distinctly specialized roles in regulating immune homeostasis and brain function. Whereas balanced immune surveillance stems from normal type 2 brain immune function, appropriate microglial clearance of aggregated misfolded proteins and neurotrophic and synaptotrophic signaling, aberrant pro-inflammatory activity triggered by alarmins might disrupt this normal immune homeostasis with reduced microglial amyloid clearance, synaptic loss, and ultimately neurodegeneration. Furthermore, since increased inflammation may in turn cause neurodegeneration, it is predicted that AP aggregation and neuroinflammation could synergistically promote even more damage. The reasons for maintaining such adverse biological conditions which have not been weeded out during evolution remain unclear. Here, we discuss these issues from a viewpoint of amyloidogenic evolvability, namely, aEVO, a hypothetic view of an adaptation to environmental stress by AP aggregates. Speculatively, the interaction of AP aggregation and neuroinflammation for aEVO in reproduction, which is evolutionally beneficial, might become a co-activating relationship which promotes AD pathogenesis through antagonistic pleiotropy. If validated, simultaneously suppressing both AP aggregation and specific innate neuroinflammation could greatly increase therapeutic efficacy in AD. Overall, combining a better understanding of innate neuroimmunity in aging and disease with the aEVO hypothesis may help uncover novel mechanism of pathogenesis of AD, leading to improved diagnostics and treatments.

Chemokine CX3CL1 (Fractalkine) Signaling and Diabetic Encephalopathy

Diabetes mellitus (DM) is the most common metabolic disease in humans, and its prevalence is increasing worldwide in parallel with the obesity pandemic. A lack of insulin or insulin resistance, and consequently hyperglycemia, leads to many systemic disorders, among which diabetic encephalopathy (DE) is a long-term complication of the central nervous system (CNS), characterized by cognitive impairment and motor dysfunctions. The role of oxidative stress and neuroinflammation in the pathomechanism of DE has been proven. Fractalkine (CX3CL1) has unique properties as an adhesion molecule and chemoattractant, and by acting on its only receptor, CX3CR1, it regulates the activity of microglia in physiological states and neuroinflammation. Depending on the clinical context, CX3CL1-CX3CR1 signaling may have neuroprotective effects by inhibiting the inflammatory process in microglia or, conversely, maintaining/intensifying inflammation and neurotoxicity. This review discusses the evidence supporting that the CX3CL1-CX3CR1 pair is neuroprotective and other evidence that it is neurotoxic. Therefore, interrupting the vicious cycle within neuron-microglia interactions by promoting neuroprotective effects or inhibiting the neurotoxic effects of the CX3CL1-CX3CR1 signaling axis may be a therapeutic goal in DE by limiting the inflammatory response. However, the optimal approach to prevent DE is simply tight glycemic control, because the elimination of dysglycemic states in the CNS abolishes the fundamental mechanisms that induce this vicious cycle.

Impact of Helicobacter pylori and metabolic syndrome on mast cell activation-related pathophysiology and neurodegeneration

Both Helicobacter pylori (H. pylori) infection and metabolic syndrome (MetS) are highly prevalent worldwide. The emergence of relevant research suggesting a pathogenic linkage between H. pylori infection and MetS-related cardio-cerebrovascular diseases and neurodegenerative disorders, particularly through mechanisms involving brain pericyte deficiency, hyperhomocysteinemia, hyperfibrinogenemia, elevated lipoprotein-a, galectin-3 overexpression, atrial fibrillation, and gut dysbiosis, has raised stimulating questions regarding their pathophysiology and its translational implications for clinicians. An additional stimulating aspect refers to H. pylori and MetS-related activation of innate immune cells, mast cells (MC), which is an important, often early, event in systemic inflammatory pathologies and related brain disorders. Synoptically, MC degranulation may play a role in the pathogenesis of H. pylori and MetS-related obesity, adipokine effects, dyslipidemia, diabetes mellitus, insulin resistance, arterial hypertension, vascular dysfunction and arterial stiffness, an early indicator of atherosclerosis associated with cardio-cerebrovascular and neurodegenerative disorders. Meningeal MC can be activated by triggers including stress and toxins resulting in vascular changes and neurodegeneration. Likewise, H.pylori and MetS-related MC activation is linked with: (a) vasculitis and thromboembolic events that increase the risk of cardio-cerebrovascular and neurodegenerative disorders, and (b) gut dysbiosis-associated neurodegeneration, whereas modulation of gut microbiota and MC activation may promote neuroprotection. This narrative review investigates the intricate relationship between H. pylori infection, MetS, MC activation, and their collective impact on pathophysiological processes linked to neurodegeneration. Through a comprehensive search of current literature, we elucidate the mechanisms through which H. pylori and MetS contribute to MC activation, subsequently triggering cascades of inflammatory responses. This highlights the role of MC as key mediators in the pathogenesis of cardio-cerebrovascular and neurodegenerative disorders, emphasizing their involvement in neuroinflammation, vascular dysfunction and, ultimately, neuronal damage. Although further research is warranted, we provide a novel perspective on the pathophysiology and management of brain disorders by exploring potential therapeutic strategies targeting H. pylori eradication, MetS management, and modulation of MC to mitigate neurodegeneration risk while promoting neuroprotection.

HSK3486 Inhibits Colorectal Cancer Growth by Promoting Oxidative Stress and ATPase Inhibitory Factor 1 Activation

BACKGROUND

HSK3486 (ciprofol), a new candidate drug similar to propofol, exerts sedative and hypnotic effects through gamma-aminobutyric acid type A receptors; however, its potential role in colorectal cancer is currently unknown.

AIMS

This study aimed to evaluate the effects of HSK3486 on colorectal cancer cell proliferation.

METHODS

Imaging was performed to detect reactive oxygen species and mitochondrial membrane potential. Western blotting was used to determine the expression of target signals. The HSK3486 molecular mechanism was investigated through ATPase inhibitory factor 1 knockdown and xenograft model experiments to assess mitochondrial function in colorectal cancer cells.

RESULTS

Cell Counting Kit-8 and Annexin V/propidium iodide double staining assays showed that HSK3486 inhibited colorectal cancer cell proliferation in a concentration-dependent manner. In addition, HSK3486 treatment increased the expression of B-cell lymphoma-2-associated X, cleaved caspase 3, and cleaved poly (ADP-ribose) polymerase, whereas myeloid cell leukemia-1 and B-cell lymphoma 2 expression decreased. HSK3486 promoted mitochondrial dysfunction by inducing ATPase inhibitor factor 1 expression. Furthermore, HSK3486 promoted oxidative stress, as shown by the increase in reactive oxygen species and lactate dehydrogenase levels, along with a decrease in mitochondrial membrane potential and ATP levels. ATPase inhibitor factor 1 small interfering RNA pretreatment dramatically increased the mitochondrial membrane potential and tumor size in a xenograft model following exposure to HSK3486.

CONCLUSION

Collectively, our findings revealed that HSK3486 induces oxidative stress, resulting in colorectal cancer cell apoptosis, making it a potential candidate therapeutic strategy for colorectal cancer.

Triaging between post-translational modification of cell cycle regulators and their therapeutics in neurodegenerative diseases

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, present challenges in healthcare because of their complicated etiologies and absence of healing remedies. Lately, the emerging role of post-translational modifications (PTMs), in the context of cell cycle regulators, has garnered big interest as a potential avenue for therapeutic intervention. The review explores the problematic panorama of PTMs on cell cycle regulators and their implications in neurodegenerative diseases. We delve into the dynamic phosphorylation, acetylation, ubiquitination, SUMOylation, Glycation, and Neddylation that modulate the key cell cycle regulators, consisting of cyclins, cyclin-dependent kinases (CDKs), and their inhibitors. The dysregulation of these PTMs is related to aberrant cell cycle in neurons, which is one of the factors involved in neurodegenerative pathologies. Moreover, the effect of exogenous activation of CDKs and CDK inhibitors through PTMs on the signaling cascade was studied in postmitotic conditions of NDDs. Furthermore, the therapeutic implications of CDK inhibitors and associated alteration in PTMs were discussed. Lastly, we explored the putative mechanism of PTMs to restore normal neuronal function that might reverse NDDs.

Age-Dependent and Aβ-Induced Dynamic Changes in the Subcellular Localization of HMGB1 in Neurons and Microglia in the Brains of an Animal Model of Alzheimer's Disease

HMGB1 is a prototypical danger-associated molecular pattern (DAMP) molecule that co-localizes with amyloid beta (Aβ) in the brains of patients with Alzheimer's disease. HMGB1 levels are significantly higher in the cerebrospinal fluid of patients. However, the cellular and subcellular distribution of HMGB1 in relation to the pathology of Alzheimer's disease has not yet been studied in detail. Here, we investigated whether HMGB1 protein levels in brain tissue homogenates (frontal cortex and striatum) and sera from Tg-APP/PS1 mice, along with its cellular and subcellular localization in those regions, differed. Total HMGB1 levels were increased in the frontal cortices of aged wildtype (7.5 M) mice compared to young (3.5 M) mice, whereas total HMGB1 levels in the frontal cortices of Tg-APP/PS1 mice (7.5 M) were significantly lower than those in age-matched wildtype mice. In contrast, total serum HMGB1 levels were enhanced in aged wildtype (7.5 M) mice and Tg-APP/PS1 mice (7.5 M). Further analysis indicated that nuclear HMGB1 levels in the frontal cortices of Tg-APP/PS1 mice were significantly reduced compared to those in age-matched wildtype controls, and cytosolic HMGB1 levels were also significantly decreased. Triple-fluorescence immunohistochemical analysis indicated that HMGB1 appeared as a ring shape in the cytoplasm of most neurons and microglia in the frontal cortices of 9.5 M Tg-APP/PS1 mice, indicating that nuclear HMGB1 is reduced by aging and in Tg-APP/PS1 mice. Consistent with these observations, Aβ treatment of both primary cortical neuron and primary microglial cultures increased HMGB1 secretion in the media, in an Aβ-dose-dependent manner. Our results indicate that nuclear HMGB1 might be translocated from the nucleus to the cytoplasm in both neurons and microglia in the brains of Tg-APP/PS1 mice, and that it may subsequently be secreted extracellularly.

Long-Term Exposure of Cultured Astrocytes to High Glucose Impact on Their LPS-Induced Activation

Diabetes mellitus is associated with various complications, mainly caused by the chronic exposure of the cells to high glucose (HG) concentrations. The effects of long-term HG exposure in vitro accompanied by lipopolysaccharide (LPS) application on astrocytes are relatively unknown. We used cell medium with normal (NG, 5.5 mM) or high glucose (HG, 25 mM) for rat astrocyte cultures and measured the release of NO, IL-6, β-hexosaminidase and cell survival in response to LPS. We first demonstrated that HG long-term incubation of astrocytes increased the release of β-hexosaminidase without decreasing MTT-detected cell survival, suggesting that there is no cell membrane damage or astrocyte death but could be lysosome exocytosis. Different from what was observed for NG, all LPS concentrations tested at HG resulted in an increase in IL-6, and this was detected for both 6 h and 48 h treatments. Interestingly, β-hexosaminidase level increased after 48 h of LPS and only at HG. The NO release from astrocytes also increased with LPS application at HG but was less significant. These data endorsed the original hypothesis that long-term hyperglycemia increases proinflammatory activation of astrocytes, and β-hexosaminidase could be a specific marker of excessive activation of astrocytes associated with exocytosis.

Expression of high-mobility group box-1 in eutopic/ectopic endometrium and correlations with inflammation-related factors in adenomyosis

OBJECTIVE

To investigate the expression of HMGB1 and toll-like receptor 4 (TLR4) in adenomyosis eutopic/ectopic endometrium.

METHODS

Twenty patients with adenomyosis and 20 controls, all undergoing laparoscopy, were recruited from September 2015 to July 2016. Samples were collected from the endometrium without adenomyosis (CE), the eutopic endometrium with adenomyosis (EuE), and the ectopic endometrium with adenomyosis (EE). The mRNA and protein expression of HMGB1 and TLR4, and interleukin-6 (IL-6) and interleukin-8 (IL-8) RNA expression levels were measured.

RESULTS

The average age of the adenomyosis women was 43.4 ± 5.3 years; their BMI was 23.3 ± 2.3 kg/m2. The control group included women aged 38.8 ± 9.8 years, with BMI 22.2 ± 3.4 kg/m2. The mRNA expression levels of HMGB1, TLR4, IL-6, and IL-8 in the EE and EuE groups were higher than those in the CE group (p < .01), and those in the EE group were higher than those in the EuE group (p < .01). The protein expression levels of HMGB1 and TLR4 in the EE and EuE groups were higher than those in the CE group (p < .01); they were higher in the EE group than the ones in the EuE group (p < .01). HMGB1 mRNA was significantly positively correlated with TLR4 in EuE and EC patients (r = 0.538 and r = 0.916, p < .01), as well as with IL-6 (r = 0.470 and r = 0.976, p < .01) and IL-8 (r = 0.574 and r = 0.650, p < .01).

CONCLUSIONS

The overexpression of HMGB1 and TLR4 in EuE and EE is positively correlated with IL-6 and IL-8 expression. The HMGB1 signaling-mediated immune-inflammatory system might be involved in the development of adenomyosis.

ADAMTS-13 and HMGB1-induced oxidative stress in Taenia multiceps-infected animals

This study investigated the cytotoxic effects of oxidative stress (OS), high mobility group box 1 (HMGB1), ADAMTS (A disintegrin and metalloproteinase with thrombospondin motifs), and neuropathology associated with coenurus cerebralis (Taenia multiceps). ADAMTS-13, HMGB1, glutathione reductase (GR), copper/zinc superoxide dismutase (Cu/Zn SOD), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) expression levels were studied. The study found that ADAMTS-13 (P < 0.005), HMGB1 (P < 0.005), GR (P < 0.005), Cu/Zn SOD (P < 0.005), and 8-OHdG (P < 0.005) levels were significantly higher in T. multiceps (c. cerebralis)-infected animals compared to healthy control animals. This study's most important finding was that HMGB1 up-regulation in neurons, endothelial cells, and glial cells can directly cause brain parenchymal destruction and that HMGB1-mediated oxidative stress plays a crucial role in the neuropathogenesis of coenurosis. The results also showed that increased levels of ADAMTS-13 may play a pivotal role in regulating and protecting the blood-brain barrier integrity and neuroprotection. These findings also suggest that ADAMTS-13 and HMGB1 compete in the prevention or formation of microthrombi, which was regarded as a remarkable finding. ADAMTS-13 and HMGB1 are valuable biomarkers for disease risk assessment, estimating host neuropathy following T. multiceps (c. cerebralis) exposure, and providing a new therapeutic target. This is the first study to show that HMGB1 and ADAMTS-13 are expressed in reactive cells and are associated with neuroimmunopathology in coenurosis.

H3K27 acetylation-induced FSTL1 upregulation by P300/RUNX1 co-activation exacerbated autophagy-mediated neuronal damage and NF-κB-stimulated inflammation in Alzheimer's disease

Follistatin-like protein 1 (FSTL1) has been demonstrated to participate in the pathogenesis of several neurological diseases. The current study informed the role of H3K27 acetylation-induced FSTL1 upregulation in Alzheimer's disease (AD). Our investigation discovered the upregulated FSTL1 expression and enhanced autophagy activity in AD. FSTL1 knockdown successfully attenuated the injuries of Aβ1-42-challenged SH-SY5Y cells through the inhibition of autophagy activity. Besides, FSTL1 deficiency suppresses the inflammatory response and NF-κB signaling in AD. Moreover, it was found that p300 was recruited by transcriptional factor RUNX1 to stimulate the H3K27 acetylation in FSTL1 promoter region, which caused the upregulation of FSTL1 in AD. To summarize, p300 acted as a co-activator of RUNX1 to trigger the activation of FSTL1 in AD, resulting in the exacerbated injuries and inflammatory responses of Aβ1-42-induced SH-SY5Y cells.

Role of neuroinflammation in neurodegeneration development

Studies in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease and Amyotrophic lateral sclerosis, Huntington's disease, and so on, have suggested that inflammation is not only a result of neurodegeneration but also a crucial player in this process. Protein aggregates which are very common pathological phenomenon in neurodegeneration can induce neuroinflammation which further aggravates protein aggregation and neurodegeneration. Actually, inflammation even happens earlier than protein aggregation. Neuroinflammation induced by genetic variations in CNS cells or by peripheral immune cells may induce protein deposition in some susceptible population. Numerous signaling pathways and a range of CNS cells have been suggested to be involved in the pathogenesis of neurodegeneration, although they are still far from being completely understood. Due to the limited success of traditional treatment methods, blocking or enhancing inflammatory signaling pathways involved in neurodegeneration are considered to be promising strategies for the therapy of neurodegenerative diseases, and many of them have got exciting results in animal models or clinical trials. Some of them, although very few, have been approved by FDA for clinical usage. Here we comprehensively review the factors affecting neuroinflammation and the major inflammatory signaling pathways involved in the pathogenicity of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Amyotrophic lateral sclerosis. We also summarize the current strategies, both in animal models and in the clinic, for the treatment of neurodegenerative diseases.

Effects of Diabetes Mellitus-Related Dysglycemia on the Functions of Blood-Brain Barrier and the Risk of Dementia

Diabetes mellitus is one of the most common metabolic diseases worldwide, and its long-term complications include neuropathy, referring both to the peripheral and to the central nervous system. Detrimental effects of dysglycemia, especially hyperglycemia, on the structure and function of the blood-brain barrier (BBB), seem to be a significant backgrounds of diabetic neuropathy pertaining to the central nervous system (CNS). Effects of hyperglycemia, including excessive glucose influx to insulin-independent cells, may induce oxidative stress and secondary innate immunity dependent inflammatory response, which can damage cells within the CNS, thus promoting neurodegeneration and dementia. Advanced glycation end products (AGE) may exert similar, pro-inflammatory effects through activating receptors for advanced glycation end products (RAGE), as well as some pattern-recognition receptors (PRR). Moreover, long-term hyperglycemia can promote brain insulin resistance, which may in turn promote Aβ aggregate accumulation and tau hyperphosphorylation. This review is focused on a detailed analysis of the effects mentioned above towards the CNS, with special regard to mechanisms taking part in the pathogenesis of central long-term complications of diabetes mellitus initiated by the loss of BBB integrity.

Inhibition of glycolysis prevents behavioural changes in mice with MK801-induced SCZ model by alleviating lactate accumulation and lactylation

Schizophrenia (SCZ) is a debilitating neuropsychiatric disorder with a complex aetiology. Cognitive symptoms and hippocampal changes have been implicated in the pathophysiology of SCZ. Changes in metabolites level and up-regulated glycolysis have been reported in previous studies, which may be related to the hippocampal dysfunction in SCZ. However, the pathological mechanism of glycolysis involved in the pathogenesis of SCZ remains unclear. Therefore, the change of glycolysis level and the involvement in SCZ need to be further studied. In our study, MK801 was used to induce an SCZ mouse model and cell model in vivo and in vitro. Western blotting was performed to evaluate the levels of glycolysis, metabolites, and lactylation in hippocampal tissue of mice with SCZ or cell models. The level of high mobility group protein 1 (HMGB1) in the medium of MK801-treated primary hippocampal neurons was examined. Apoptosis was evaluated in HMGB1-treated hippocampal neurons by flow cytometry. The glycolysis inhibitor 2-DG prevented behavioural changes in the MK801-induced SCZ mouse model. The lactate accumulation and level of lactylation were alleviated in the hippocampal tissue of MK801-treated mice. Glycolysis was enhanced, and lactate accumulated in MK-801-treated primary hippocampal neurons. In addition, the level of HMGB1 increased in the medium and induced apoptosis in primary hippocampal neurons. Together, the data showed that glycolysis and lactylation increased in the MK801-induced SCZ model in vivo and in vitro, and this effect could be prevented by 2-DG (a glycolysis inhibitor). Glycolytic related HMGB1 upregulation may induce apoptosis in hippocampal neurons downstream.

The role of high mobility group box 1 in neuroinflammatory related diseases

High mobility group box 1 (HMGB1) is a ubiquitous and highly conserved non-histone DNA-binding protein with different biological functions according to its subcellular localization. It is widely believed that HMGB1, which is released into the extracellular space, plays a key role in the inflammatory response. In recent years, numerous studies have shown that the development of various neurological diseases such as epilepsy, Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), cerebrovascular disease and traumatic brain injury (TBI) are inextricably linked to inflammation. We will review the mechanisms of HMGB1 and its receptors in nervous system inflammation to provide a basis for further development of new HMGB1-based therapies.

Neutrophil Extracellular Traps in Cerebral Ischemia/Reperfusion Injury: Friend and Foe

Cerebral ischemic injury, one of the leading causes of morbidity and mortality worldwide, triggers various central nervous system (CNS) diseases, including acute ischemic stroke (AIS) and chronic ischemia-induced Alzheimer's disease (AD). Currently, targeted therapies are urgently needed to address neurological disorders caused by cerebral ischemia/reperfusion injury (CI/RI), and the emergence of neutrophil extracellular traps (NETs) may be able to relieve the pressure. Neutrophils are precursors to brain injury following ischemic stroke and exert complicated functions. NETs extracellularly release reticular complexes of neutrophils, i.e., double-stranded DNA (dsDNA), histones, and granulins. Paradoxically, NETs play a dual role, friend and foe, under different conditions, for example, physiological circumstances, infection, neurodegeneration, and ischemia/reperfusion. Increasing evidence indicates that NETs exert anti-inflammatory effects by degrading cytokines and chemokines through protease at a relatively stable and moderate level under physiological conditions, while excessive amounts of NETs release (NETosis) irritated by CI/RI exacerbate the inflammatory response and aggravate thrombosis, disrupt the blood-brain barrier (BBB), and initiates sequential neuron injury and tissue damage. This review provides a comprehensive overview of the machinery of NETs formation and the role of an abnormal cascade of NETs in CI/RI, as well as other ischemia-induced neurological diseases. Herein, we highlight the potential of NETs as a therapeutic target against ischemic stroke that may inspire translational research and innovative clinical approaches.

The Role of High Mobility Group Box 1 (HMGB1) in Neurodegeneration: A Systematic Review

BACKGROUND

High mobility group box 1 (HMGB1) protein is a damage-associated molecular pattern (DAMP) that plays an important role in the repair and regeneration of tissue injury. It also acts as a pro-inflammatory cytokine through the activation of toll-like receptor 4 (TLR4) and receptor for advanced glycation end products (RAGE), to elicit the neuroinflammatory response. HMGB1 may aggravate several cellular responses, which may lead to pathological inflammation and cellular death. Thus, there have been a considerable amount of research into the pathological role of HMGB1 in diseases. However, whether the mechanism of action of HMGB1 is similar in all neurodegenerative disease pathology remains to be determined.

OBJECTIVE

Therefore, this systematic review aimed to critically evaluate and elucidate the role of HMGB1 in the pathology of neurodegeneration based on the available literature.

METHODS

A comprehensive literature search was performed on four databases; EMBASE, PubMed, Scopus, and CINAHL Plus.

RESULTS

A total of 85 articles were selected for critical appraisal, after subjecting to the inclusion and exclusion criteria in this study. The selected articles revealed that HMGB1 levels were found elevated in most neurodegeneration except in Huntington's disease and Spinocerebellar ataxia, where the levels were found decreased. This review also showcased that HMGB1 may act on distinctive pathways to elicit its pathological response leading to the various neurodegeneration processes/ diseases.

CONCLUSION

While there have been promising findings in HMGB1 intervention research, further studies may still be required before any HMGB1 intervention may be recommended as a therapeutic target for neurodegenerative diseases.

Toll-Like Receptor 4: A Promising Therapeutic Target for Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that primarily manifests as memory deficits and cognitive impairment and has created health challenges for patients and society. In AD, amyloid β-protein (Aβ) induces Toll-like receptor 4 (TLR4) activation in microglia. Activation of TLR4 induces downstream signaling pathways and promotes the generation of proinflammatory cytokines, such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β), which also trigger the activation of astrocytes and influence amyloid-dependent neuronal death. Therefore, TLR4 may be an important molecular target for treating AD by regulating neuroinflammation. Moreover, TLR4 regulates apoptosis, autophagy, and gut microbiota and is closely related to AD. This article reviews the role of TLR4 in the pathogenesis of AD and a range of potential therapies targeting TLR4 for AD. Elucidating the regulatory mechanism of TLR4 in AD may provide valuable clues for developing new therapeutic strategies for AD.

Receptor for Advanced Glycation End Products (RAGE): A Pivotal Hub in Immune Diseases

As a critical molecule in the onset and sustainment of inflammatory response, the receptor for advanced glycation end products (RAGE) has a variety of ligands, such as advanced glycation end products (AGEs), S100/calcium granule protein, and high-mobility group protein 1 (HMGB1). Recently, an increasing number studies have shown that RAGE ligand binding can initiate the intracellular signal cascade, affect intracellular signal transduction, stimulate the release of cytokines, and play a vital role in the occurrence and development of immune-related diseases, such as systemic lupus erythematosus, rheumatoid arthritis, and Alzheimer’s disease. In addition, other RAGE signaling pathways can play crucial roles in life activities, such as inflammation, apoptosis, autophagy, and endoplasmic reticulum stress. Therefore, the strategy of targeted intervention in the RAGE signaling pathway may have significant therapeutic potential, attracting increasing attention. In this paper, through the systematic induction and analysis of RAGE-related signaling pathways and their regulatory mechanisms in immune-related diseases, we provide theoretical clues for the follow-up targeted intervention of RAGE-mediated diseases.

HMGB1 signaling pathway in diabetes-related dementia: Blood-brain barrier breakdown, brain insulin resistance, and Aβ accumulation

Diabetes contributes to the onset of various diseases, including cancer and cardiovascular and neurodegenerative diseases. Recent studies have highlighted the similarities and relationship between diabetes and dementia as an important issue for treating diabetes-related cognitive deficits. Diabetes-related dementia exhibits several features, including blood-brain barrier disruption, brain insulin resistance, and Aβ over-accumulation. High-mobility group box1 (HMGB1) is a protein known to regulate gene transcription and cellular mechanisms by binding to DNA or chromatin via receptor for advanced glycation end-products (RAGE) and toll-like receptor 4 (TLR4). Recent studies have demonstrated that the interplay between HMGB1, RAGE, and TLR4 can impact both neuropathology and diabetic alterations. Herein, we review the recent research regarding the roles of HMGB1-RAGE-TLR4 axis in diabetes-related dementia from several perspectives and emphasize the importance of the influence of HMGB1 in diabetes-related dementia.

Roles of neuronal toll-like receptors in neuropathic pain and central nervous system injuries and diseases

Toll-like receptors (TLRs) are innate immune receptors that are expressed in immune cells as well as glia and neurons of the central and peripheral nervous systems. They are best known for their role in the host defense in response to pathogens and for the induction of inflammation in infectious and non-infectious diseases. In the central nervous system (CNS), TLRs modulate glial and neuronal functions as well as innate immunity and neuroinflammation under physiological or pathophysiological conditions. The majority of the studies on TLRs in CNS pathologies investigated their overall contribution without focusing on a particular cell type, or they analyzed TLRs in glia and infiltrating immune cells in the context of neuroinflammation and cellular activation. The role of neuronal TLRs in CNS diseases and injuries has received little attention and remains underappreciated. The primary goal of this review is to summarize findings demonstrating the pivotal and unique roles of neuronal TLRs in neuropathic pain, Alzheimer's disease, Parkinson's disease and CNS injuries. We discuss how the current findings warrant future investigations to better define the specific contributions of neuronal TLRs to these pathologies. We underline the paucity of information regarding the role of neuronal TLRs in other neurodegenerative, demyelinating, and psychiatric diseases. We draw attention to the importance of broadening research on neuronal TLRs in view of emerging evidence demonstrating their distinctive functional properties.

Role of Lipocalin-2 in Amyloid-Beta Oligomer-Induced Mouse Model of Alzheimer's Disease

Lipocalin-2 (LCN2) is an inflammatory protein with diverse functions in the brain. Although many studies have investigated the mechanism of LCN2 in brain injuries, the effect of LCN2 on amyloid-toxicity-related memory deficits in a mouse model of Alzheimer’s disease (AD) has been less studied. We investigated the role of LCN2 in human AD patients using a mouse model of AD. We created an AD mouse model by injecting amyloid-beta oligomer (AβO) into the hippocampus. In this model, animals exhibited impaired learning and memory. We found LCN2 upregulation in the human brain frontal lobe, as well as a positive correlation between white matter ischemic changes and serum LCN2. We also found increased astrocytic LCN2, microglia activation, iron accumulation, and blood–brain barrier disruption in AβO-treated hippocampi. These findings suggest that LCN2 is involved in a variety of amyloid toxicity mechanisms, especially neuroinflammation and oxidative stress.

NLRP3 Inflammasome-Dependent Increases in High Mobility Group Box 1 Involved in the Cognitive Dysfunction Caused by Tau-Overexpression

Tau hyperphosphorylation is a characteristic alteration present in a range of neurological conditions, such as traumatic brain injury (TBI) and neurodegenerative diseases. Treatments targeting high-mobility group box protein 1 (HMGB1) induce neuroprotective effects in these neuropathologic conditions. However, little is known about the interactions between hyperphosphorylated tau and HMGB1 in neuroinflammation. We established a model of TBI with controlled cortical impacts (CCIs) and a tau hyperphosphorylation model by injecting the virus encoding human P301S tau in mice, and immunofluorescence, western blotting analysis, and behavioral tests were performed to clarify the interaction between phosphorylated tau (p-tau) and HMGB1 levels. We demonstrated that p-tau and HMGB1 were elevated in the spatial memory-related brain regions in mice with TBI and tau-overexpression. Animals with tau-overexpression also had significantly increased nucleotide-binding oligomerization domain-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome activation, which manifested as increases in apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), activating caspase-1 and interleukin 1 beta (IL-1β) levels. In addition, NLRP3^–/– mice and the HMGB1 inhibitor, glycyrrhizin, were used to explore therapeutic strategies for diseases with p-tau overexpression. Compared with wild-type (WT) mice with tau-overexpression, downregulation of p-tau and HMGB1 was observed in NLRP3^–/– mice, indicating that HMGB1 alterations were NLRP3-dependent. Moreover, treatment with glycyrrhizin at a late stage markedly reduced p-tau levels and improved performance in the Y- and T-mazes and the ability of tau-overexpressing mice to build nests, which revealed improvements in spatial memory and advanced hippocampal function. The findings identified that p-tau has a triggering role in the modulation of neuroinflammation and spatial memory in an NLRP3-dependent manner, and suggest that treatment with HMGB1 inhibitors may be a better therapeutic strategy for tauopathies.

Curcumin improves memory deficits by inhibiting HMGB1-RAGE/TLR4-NF-κB signalling pathway in APPswe/PS1dE9 transgenic mice hippocampus

Amyloid‐β (Aβ) deposition in the brain has been implicated in the development of Alzheimer's disease (AD), and neuroinflammation generates AD progression. Therapeutic effects of anti‐inflammatory approaches in AD are still under investigation. Curcumin, a potent anti‐inflammatory and antioxidant, has demonstrated therapeutic potential in AD models. However, curcumin's anti‐inflammatory molecular mechanisms and its associated cognitive impairment mechanisms in AD remain unclear. The high‐mobility group box‐1 protein (HMGB1) participates in the regulation of neuroinflammation. Herein, we attempted to evaluate the anti‐inflammatory effects of chronic oral administration of curcumin and HMGB1 expression in APP/PS1 transgenic mice AD model. We found that transgenic mice treated with a curcumin diet had shorter escape latencies and showed a significant increase in percent alternation, when compared with transgenic mice, in the Morris water maze and Y‐maze tests. Additionally, curcumin treatment could effectively decrease HMGB1 protein expression, advanced glycosylation end product‐specific receptor (RAGE), Toll‐like receptors‐4 (TLR4) and nuclear factor kappa B (NF‐κB) in transgenic mice hippocampus. However, amyloid plaques detected with thioflavin‐S staining in transgenic mice hippocampus were not affected by curcumin treatment. In contrast, curcumin significantly decreased GFAP‐positive cells, as assessed by immunofluorescence staining. Taken together, these data indicate that oral administration of curcumin may be a promising agent to attenuate memory deterioration in AD mice, probably inhibiting the HMGB1‐RAGE/TLR4‐NF‐κB inflammatory signalling pathway.

Relationship Between Amyloid-β Deposition and Blood-Brain Barrier Dysfunction in Alzheimer's Disease

Amyloid-β (Aβ) is the predominant pathologic protein in Alzheimer's disease (AD). The production and deposition of Aβ are important factors affecting AD progression and prognosis. The deposition of neurotoxic Aβ contributes to damage of the blood-brain barrier. However, the BBB is also crucial in maintaining the normal metabolism of Aβ, and dysfunction of the BBB aggravates Aβ deposition. This review characterizes Aβ deposition and BBB damage in AD, summarizes their interactions, and details their respective mechanisms.

Class IIa HDAC Downregulation Contributes to Surgery-Induced Cognitive Impairment Through HMGB1-Mediated Inflammatory Response in the Hippocampi of Aged Mice

Objective

Perioperative neurocognitive disorders (PND) are a common complication in the elderly. Histone deacetylases (HDACs) are a class of enzymes that control the acetylation status of intracellular proteins. Thus, we explored whether HDACs trigger the release of high mobility group box 1 (HMGB1) through altering the acetylation status in the hippocampi of aged mice.

Materials and Methods

The effect of the Class IIa HDAC in PND was explored using an in vivo form of splenectomy. Sixteen-month-old healthy male C57BL/6J mice were randomly divided into five groups: control, anesthesia plus sham surgery, anesthesia plus splenectomy, LMK235 treatment, and PBS treatment. The hippocampi were harvested on either first, third, or seventh postoperative day. Cognitive function was assessed via a Morris water maze (MWM) test. Quantitative RT-PCR, Western blots and ELISAs were carried out to assess the targeted gene expression at transcriptional and translational levels.

Results

Splenectomy led to a significant deficiency in spatial memory acquisition, marked decreases in mRNA and protein levels of HDAC4 and HDAC5 in the hippocampus, and increases in the levels of total HMGB1 and acetylated HMGB1. In a similar fashion to splenectomy, treatment with the HDAC4/5 inhibitor LMK235 produced impaired spatial memory and an increase in the expression of HMGB1 and its acetylated counterpart in the hippocampus.

Conclusion

These results suggest that surgery leads to PND through class IIa HDAC downregulation-triggered HMGB1 release in hippocampus of aged mice. HDACs may be a potential therapeutic target for postoperative cognitive dysfunction.

Meta-Analysis of Methamphetamine Modulation on Amyloid Precursor Protein through HMGB1 in Alzheimer's Disease

The deposition of amyloid-beta (Aβ) through the cleavage of amyloid-beta precursor protein (APP) is a biomarker of Alzheimer’s disease (AD). This study used QIAGEN Ingenuity Pathway Analysis (IPA) to conduct meta-analysis on the molecular mechanisms by which methamphetamine (METH) impacts AD through modulating the expression of APP. All the molecules affected by METH and APP were collected from the QIAGEN Knowledge Base (QKB); 78 overlapping molecules were identified. Upon simulation of METH exposure using the “Molecule Activity Predictor” feature, eight molecules were found to be affected by METH and exhibited activation relationships on APP expression at a confidence of p = 0.000453 (Z-score = 3.51, two-tailed). Core Analysis of these eight molecules identified High Mobility Group Box protein 1 (HMGB1) signaling pathway among the top 5 canonical pathways with most overlap with the 8-molecule dataset. Simulated METH exposure increased APP expression through HMGB1 at a confidence of p < 0.00001 (Z-score = 7.64, two-tailed). HMGB1 is a pathogenic hallmark in AD progression. It not only increases the production of inflammatory mediators, but also mediates the disruption of the blood-brain barrier. Our analyses suggest the involvement of HMGB1 signaling pathway in METH-induced modulation of APP as a potential casual factor of AD.

Alzheimer's Disease Pathogenesis: Role of Autophagy and Mitophagy Focusing in Microglia

Alzheimer's disease (AD) is a debilitating neurological disorder, and currently, there is no cure for it. Several pathologic alterations have been described in the brain of AD patients, but the ultimate causative mechanisms of AD are still elusive. The classic hallmarks of AD, including amyloid plaques (Aβ) and tau tangles (tau), are the most studied features of AD. Unfortunately, all the efforts targeting these pathologies have failed to show the desired efficacy in AD patients so far. Neuroinflammation and impaired autophagy are two other main known pathologies in AD. It has been reported that these pathologies exist in AD brain long before the emergence of any clinical manifestation of AD. Microglia are the main inflammatory cells in the brain and are considered by many researchers as the next hope for finding a viable therapeutic target in AD. Interestingly, it appears that the autophagy and mitophagy are also changed in these cells in AD. Inside the cells, autophagy and inflammation interact in a bidirectional manner. In the current review, we briefly discussed an overview on autophagy and mitophagy in AD and then provided a comprehensive discussion on the role of these pathways in microglia and their involvement in AD pathogenesis.

Silenced lncRNA H19 and up-regulated microRNA-129 accelerates viability and restrains apoptosis of PC12 cells induced by Aβ25-35 in a cellular model of Alzheimer's disease

Accumulating data manifest that long non-coding RNA (lncRNAs) are involved in all kinds of neurodegenerative disorders, consisting of the onset and progression of Alzheimer's disease (AD). The study was for the research of the mechanism of lncRNA H19 (H19) in viability and apoptosis of PC12 cells induced by Aβ_25-35 in a cellular model of AD with the regulation of microRNA (miR)-129 and high mobility group box-1 protein (HMGB1). An AD cellular model of PC12 cells was established using Aβ_25-35. The Aβ_25-35-induced PC12 cells were transfected with si-H19 or miR-129 mimic to figure their roles in cell viability,apoptosis, mitochondrial membrane potential dysfunction and oxidative stress in AD. Luciferase reporter assay and RNA-pull down assay were employed for verification of the binding relationship between H19 and miR-129 and the targeting relationship between miR-129 and HMGB1. An AD mouse model was induced and brain tissues were collected. H19, miR-129 and HMGB1 were detected in Aβ_25-35-treated cells and brain tissues of AD mice. Elevated H19, HMGB1 and decreased miR-129 were found in Aβ_25-35-treated PC12 cells as well as in brain tissues of AD mice. Silenced H19 or elevated miR-129 promoted viability, inhibited apoptosis, prevented mitochondrial membrane potential dysfunction and decreased oxidative stress in Aβ_25-35-treated PC12 cells. H19 could specifically bind to miR-129. MiR-129 specifically suppressed HMGB1 expression. This study suggests that silenced H19 and up-regulated miR-129 accelerates viability and represses apoptosis of PC12 cells stimulated by Aβ_25-35 in AD, which is beneficial for AD treatment.

TLR4 Targeting as a Promising Therapeutic Strategy for Alzheimer Disease Treatment

Alzheimer disease (AD) is a devastating neurodegenerative disorder characterized by extracellular accumulation of amyloid-beta and formation of intracellular neurofibrillary tangles. Microglia activation and neuroinflammation play important roles in the pathogenesis of AD; Toll-like receptor 4 (TLR4)-a key component of the innate immune system-in microglia is also thought to be involved based on the observed association between TLR gene polymorphisms and AD risk. TLR4 has been shown to exert both detrimental and beneficial effects on AD-related pathologies. In preclinical models, experimental manipulations targeting TLR4 were shown to improve learning and memory, which was related to inhibition of pro-inflammatory cytokine release and reduction of oxidative stress. In this review, we summarize the key evidence supporting TLR4 as a promising therapeutic target in AD treatment.

Role of Innate Immune Receptor TLR4 and its endogenous ligands in epileptogenesis

Understanding the interplay between the innate immune system, neuroinflammation, and epilepsy might offer a novel perspective in the quest of exploring new treatment strategies. Due to the complex pathology underlying epileptogenesis, no disease-modifying treatment is currently available that might prevent epilepsy after a plausible epileptogenic insult despite the advances in pre-clinical and clinical research. Neuroinflammation underlies the etiopathogenesis of epilepsy and convulsive disorders with Toll-like receptor (TLR) signal transduction being highly involved. Among TLR family members, TLR4 is an innate immune system receptor and lipopolysaccharide (LPS) sensor that has been reported to contribute to epileptogenesis by regulating neuronal excitability. Herein, we discuss available evidence on the role of TLR4 and its endogenous ligands, the high mobility group box 1 (HMGB1) protein, the heat shock proteins (HSPs) and the myeloid related protein 8 (MRP8), in epileptogenesis and post-traumatic epilepsy (PTE). Moreover, we provide an account of the promising findings of TLR4 modulation/inhibition in experimental animal models with therapeutic impact on seizures.

HMGB1-Mediated Neuroinflammatory Responses in Brain Injuries: Potential Mechanisms and Therapeutic Opportunities

Brain injuries are devastating conditions, representing a global cause of mortality and morbidity, with no effective treatment to date. Increased evidence supports the role of neuroinflammation in driving several forms of brain injuries. High mobility group box 1 (HMGB1) protein is a pro-inflammatory-like cytokine with an initiator role in neuroinflammation that has been implicated in Traumatic brain injury (TBI) as well as in early brain injury (EBI) after subarachnoid hemorrhage (SAH). Herein, we discuss the implication of HMGB1-induced neuroinflammatory responses in these brain injuries, mediated through binding to the receptor for advanced glycation end products (RAGE), toll-like receptor4 (TLR4) and other inflammatory mediators. Moreover, we provide evidence on the biomarker potential of HMGB1 and the significance of its nucleocytoplasmic translocation during brain injuries along with the promising neuroprotective effects observed upon HMGB1 inhibition/neutralization in TBI and EBI induced by SAH. Overall, this review addresses the current advances on neuroinflammation driven by HMGB1 in brain injuries indicating a future treatment opportunity that may overcome current therapeutic gaps.

Amyloid Proteins and Peripheral Neuropathy

Painful peripheral neuropathy affects millions of people worldwide. Peripheral neuropathy develops in patients with various diseases, including rare familial or acquired amyloid polyneuropathies, as well as some common diseases, including type 2 diabetes mellitus and several chronic inflammatory diseases. Intriguingly, these diseases share a histopathological feature-deposits of amyloid-forming proteins in tissues. Amyloid-forming proteins may cause tissue dysregulation and damage, including damage to nerves, and may be a common cause of neuropathy in these, and potentially other, diseases. Here, we will discuss how amyloid proteins contribute to peripheral neuropathy by reviewing the current understanding of pathogenic mechanisms in known inherited and acquired (usually rare) amyloid neuropathies. In addition, we will discuss the potential role of amyloid proteins in peripheral neuropathy in some common diseases, which are not (yet) considered as amyloid neuropathies. We conclude that there are many similarities in the molecular and cell biological defects caused by aggregation of the various amyloid proteins in these different diseases and propose a common pathogenic pathway for "peripheral amyloid neuropathies".

Impact of HMGB1, RAGE, and TLR4 in Alzheimer's Disease (AD): From Risk Factors to Therapeutic Targeting

Alzheimer’s disease (AD) is a devastating neurodegenerative disorder and a leading cause of dementia, with accumulation of amyloid-beta (Aβ) and neurofibrillary tangles (NFTs) as defining pathological features. AD presents a serious global health concern with no cure to date, reflecting the complexity of its pathogenesis. Recent evidence indicates that neuroinflammation serves as the link between amyloid deposition, Tau pathology, and neurodegeneration. The high mobility group box 1 (HMGB1) protein, an initiator and activator of neuroinflammatory responses, has been involved in the pathogenesis of neurodegenerative diseases, including AD. HMGB1 is a typical damage-associated molecular pattern (DAMP) protein that exerts its biological activity mainly through binding to the receptor for advanced glycation end products (RAGE) and toll-like receptor 4 (TLR4). RAGE and TLR4 are key components of the innate immune system that both bind to HMGB1. Targeting of HMGB1, RAGE, and TLR4 in experimental AD models has demonstrated beneficial effects in halting AD progression by suppressing neuroinflammation, reducing Aβ load and production, improving spatial learning, and inhibiting microglial stimulation. Herein, we discuss the contribution of HMGB1 and its receptor signaling in neuroinflammation and AD pathogenesis, providing evidence of its beneficial effects upon therapeutic targeting.

Repetitive high-frequency transcranial magnetic stimulation reverses depressive-like behaviors and protein expression at hippocampal synapses in chronic unpredictable stress-treated rats by enhancing endocannabinoid signaling

The anti-depressant effect of repetitive transcranial magnetic stimulation (rTMS), a clinically-useful treatment for depression, is associated with changes to the endocannabinoid system (ECS). However, it is currently unknown whether different frequencies of rTMS alter the ECS differently. To test this, rats exposed to chronic unpredictable stress (CUS) were treated with rTMS at two different frequencies (5 (high) or 1 Hz (low), 1.26 Tesla) for 7 consecutive days. Twenty-four hours after the final rTMS treatment, we evaluated depressive-like behaviors and the expression of several synaptic proteins and ECS-related proteins in the hippocampus. In addition, we knocked-down diacylglycerol lipase alpha (DAGLα) and cannabinoid type 1 receptor (CB1R), two important components of the ECS, and measured depressive-like behaviors and synaptic protein expression following rTMS. Furthermore, we measured the expression levels of several components of the ECS system in hippocampal-derived astrocytes and neurons exposed to repetitive magnetic stimulation (rMS) with different parameters (5 or 1 Hz, 0.84 or 1.26 Tesla). Interestingly, we found that only high-frequency rTMS ameliorated depressive-like behaviors and normalized the expression of hippocampal synaptic proteins in CUS-treated rats; this effect was eliminated by knockdown of DAGLα or CB1R. Moreover, we found that rMS at 5 Hz increased the expression of DAGLα and CB1R in hippocampal astrocytes and neurons. Collectively, our results suggest that high-frequency rTMS exerts its anti-depressant effect by up-regulating DAGLα and CB1R.

HMGB1/RAGE pro-inflammatory axis promotes vascular endothelial cell apoptosis in limb ischemia/reperfusion injury

OBJECTIVE

High-Mobility Group Box 1 (HMGB1) promotes vascular injuries induced by limb Ischemia and Reperfusion (IR), but the molecular mechanisms are not well understood. This study aimed to investigate the role of Receptor for Advanced-Glycation End products (RAGE) in HMGB1-regulated inflammatory response and vascular injury in limb IR using the rat IR and cellular Hypoxia and Reoxygenation (HR) models.

METHODS

We analyzed the vascular structure and elastic fiber deposition in rat femoral arteries by histological staining. We determined gene expression in vascular tissues and cells by quantitative RT-PCR, Western blotting and immunofluorescence; analyzed the protein levels in rat serum or cell supernatant by ELISA; and assessed protein interaction by co-immunoprecipitation. We used CCK-8 for analyzing cell viability, and assessed apoptosis by Hoechst staining and flow cytometry.

RESULTS

RAGE inhibition by FPS-ZM1 significantly repressed rat vascular injury that was induced by limb IR treatment. HMGB1 and RAGE expression, P38, ERK1/2, P65 and IKBa phosphorylation, as well as HIF-1a, NLRP3, Caspase-1, TNF-a and IL-6 expression and P65 in nucleus, increased in femoral arteries of a rat IR model and HUVEC undergoing HR treatment, whereas all the factors except HMGB1 and RAGE were inhibited by FPS-ZM1 treatment. In addition, we found that HMGB1 binds with RAGE in HUVEC undergoing HR treatment, which was suppressed by FPS-ZM1. Finally, the apoptosis of HUVEC also increased by HR treatment, but repressed under FPS-ZM1 treatment.

CONCLUSION

HMGB1 binds with RAGE to promote vascular inflammation and endothelial cell apoptosis, which mediates vascular injury during acute limb IR.