Shifting equilibriums in Alzheimer's disease: the complex roles of microglia in neuroinflammation, neuronal survival and neurogenesis

Abnormal Functional Attributes of Central Executive Network in Patients with Mild Cognitive Impairment Associated with End-Stage Renal Disease

RATIONALE AND OBJECTIVES

To assess changes in the central executive network (CEN) of patients with mild cognitive impairment (MCI) associated with end-stage renal disease (ESRD).

METHODS

A total of 121 patients with ESRD and 66 healthy controls (HCs) were enrolled. Patients were divided into an MCI group (n = 67) and a cognitively unimpaired group (n = 54). All participants underwent resting-state functional magnetic resonance imaging and were evaluated using the Montreal Cognitive Assessment (MoCA). The functional attributes of the CEN were calculated using three methods of functional connectivity (FC) analysis. Relationships among imaging features, cognitive scale scores, and clinical data were assessed, and a model was constructed to diagnose MCI in patients with ESRD.

RESULTS

The comparison of the three groups showed that there were significant differences in the FC values of five connection pairs within the CEN, and the CEN demonstrated significant differences in connectivity to ten brain regions. In patients with MCI associated with ESRD, the information transmission efficiency of the CEN was reduced, which demonstrates the characteristics of a random network to some extent. Significant correlations were observed among imaging parameters, cognitive scale scores, and clinical data. The diagnostic model constructed based on these results demonstrated excellent discrimination and calibration.

CONCLUSION

Alterations in the function of the CEN provide relevant bases for revealing the neuropathological mechanism of MCI in patients with ESRD. The diagnostic model developed in this study may help to establish more reliable imaging markers for detecting early cognitive impairment in this patient population.

Proximity Labeling Proteomics Reveals Kv1.3 Potassium Channel Immune Interactors in Microglia

Microglia are resident immune cells of the brain and regulate its inflammatory state. In neurodegenerative diseases, microglia transition from a homeostatic state to a state referred to as disease-associated microglia (DAM). DAM express higher levels of proinflammatory signaling molecules, like STAT1 and TLR2, and show transitions in mitochondrial activity toward a more glycolytic response. Inhibition of Kv1.3 decreases the proinflammatory signature of DAM, though how Kv1.3 influences the response is unknown. Our goal was to identify the potential proteins interacting with Kv1.3 during transition to DAM. We utilized TurboID, a biotin ligase, fused to Kv1.3 to evaluate potential interacting proteins with Kv1.3 via mass spectrometry in BV-2 microglia following TLR4-mediated activation. Electrophysiology, Western blotting, and flow cytometry were used to evaluate Kv1.3 channel presence and TurboID biotinylation activity. We hypothesized that Kv1.3 contains domain-specific interactors that vary during a TLR4-induced inflammatory response, some of which are dependent on the PDZ-binding domain on the C terminus. We determined that the N terminus of Kv1.3 is responsible for trafficking Kv1.3 to the cell surface and mitochondria (e.g., NUDC, TIMM50). Whereas, the C terminus interacts with immune signaling proteins in a lipopolysaccharide-induced inflammatory response (e.g., STAT1, TLR2, and C3). There are 70 proteins that rely on the C-terminal PDZ-binding domain to interact with Kv1.3 (e.g., ND3, Snx3, and Sun1). Furthermore, we used Kv1.3 blockade to verify functional coupling between Kv1.3 and interferon-mediated STAT1 activation. Overall, we highlight that the Kv1.3 potassium channel functions beyond conducting the outward flux of potassium ions in an inflammatory context and that Kv1.3 modulates the activity of key immune signaling proteins, such as STAT1 and C3.

Alzheimer's Disease and COVID-19 Pathogenic Overlap: Implications for Drug Repurposing

As COVID-19 continues, a safe, cost-effective treatment strategy demands continued inquiry. Chronic neuroinflammatory disorders may appear to be of little relevance in this regard; often indolent and progressive disorders characterized by neuroinflammation (such as Alzheimer's disease (AD)) are fundamentally dissimilar in etiology and symptomology to COVID-19's rapid infectivity and pathology. However, the two disorders share extensive pathognomonic features, including at membrane, cytoplasmic, and extracellular levels, culminating in analogous immunogenic destruction of their respective organ parenchyma. We hypothesize that these mechanistic similarities may extent to therapeutic targets, namely that it is conceivable an agent against AD's immunopathy may have efficacy against COVID-19 and vice versa. It is notable that while extensively investigated, no agent has yet demonstrated significant therapeutic efficacy against AD's cognitive and memory declines. Yet this very failure has driven the development of numerous agents with strong mechanistic potential and clinical characteristics. Having already approved for clinical trials, these agents may be an expedient starting point in the urgent search for an effective COVID-19 therapy. Herein, we review the overlapping Alzheimer's/ COVID-19 targets and theorize several initial platforms.

SIRT2 as a potential new therapeutic target for Alzheimer's disease

Alzheimer's disease is the most common cause of dementia globally with an increasing incidence over the years, bringing a heavy burden to individuals and society due to the lack of an effective treatment. In this context, sirtuin 2, the sirtuin with the highest expression in the brain, has emerged as a potential therapeutic target for neurodegenerative diseases. This review summarizes and discusses the complex roles of sirtuin 2 in different molecular mechanisms involved in Alzheimer's disease such as amyloid and tau pathology, microtubule stability, neuroinflammation, myelin formation, autophagy, and oxidative stress. The role of sirtuin 2 in all these processes highlights its potential implication in the etiology and development of Alzheimer's disease. However, its presence in different cell types and its enormous variety of substrates leads to apparently contradictory conclusions when it comes to understanding its specific functions. Further studies in sirtuin 2 research with selective sirtuin 2 modulators targeting specific sirtuin 2 substrates are necessary to clarify its specific functions under different conditions and to validate it as a novel pharmacological target. This will contribute to the development of new treatment strategies, not only for Alzheimer's disease but also for other neurodegenerative diseases.

Targeting Progranulin as an Immuno-Neurology Therapeutic Approach

Immuno-neurology is an emerging therapeutic strategy for dementia and neurodegeneration designed to address immune surveillance failure in the brain. Microglia, as central nervous system (CNS)-resident myeloid cells, routinely perform surveillance of the brain and support neuronal function. Loss-of-function (LOF) mutations causing decreased levels of progranulin (PGRN), an immune regulatory protein, lead to dysfunctional microglia and are associated with multiple neurodegenerative diseases, including frontotemporal dementia caused by the progranulin gene (GRN) mutation (FTD-GRN), Alzheimer's disease (AD), Parkinson's disease (PD), limbic-predominant age-related transactivation response deoxyribonucleic acid binding protein 43 (TDP-43) encephalopathy (LATE), and amyotrophic lateral sclerosis (ALS). Immuno-neurology targets immune checkpoint-like proteins, offering the potential to convert aging and dysfunctional microglia into disease-fighting cells that counteract multiple disease pathologies, clear misfolded proteins and debris, promote myelin and synapse repair, optimize neuronal function, support astrocytes and oligodendrocytes, and maintain brain vasculature. Several clinical trials are underway to elevate PGRN levels as one strategy to modulate the function of microglia and counteract neurodegenerative changes associated with various disease states. If successful, these and other immuno-neurology drugs have the potential to revolutionize the treatment of neurodegenerative disorders by harnessing the brain's immune system and shifting it from an inflammatory/pathological state to an enhanced physiological/homeostatic state.

SIRT2 Inhibition Rescues Neurodegenerative Pathology but Increases Systemic Inflammation in a Transgenic Mouse Model of Alzheimer's Disease

Sirtuin 2 (SIRT2) has been proposed to have a central role on aging, inflammation, cancer and neurodegenerative diseases; however, its specific function remains controversial. Recent studies propose SIRT2 pharmacological inhibition as a therapeutic strategy for several neurodegenerative diseases including Alzheimer's disease (AD). Surprisingly, none of these published studies regarding the potential interest of SIRT2 inhibition has assessed the peripheral adverse side consequences of this treatment. In this study, we demonstrate that the specific SIRT2 inhibitor, the compound 33i, does not exhibit genotoxic or mutagenic properties. Moreover, pharmacological treatment with 33i, improved cognitive dysfunction and long-term potentiation, reducing amyloid pathology and neuroinflammation in the APP/PS1 AD mouse model. However, this treatment increased peripheral levels of the inflammatory cytokines IL-1β, TNF, IL-6 and MCP-1. Accordingly, peripheral SIRT2 inhibition with the blood brain barrier impermeable compound AGK-2, worsened the cognitive capacities and increased systemic inflammation. The analysis of human samples revealed that SIRT2 is increased in the brain but not in the serum of AD patients. These results suggest that, although SIRT2 pharmacological inhibition may have beneficial consequences in neurodegenerative diseases, its pharmacological inhibition at the periphery would not be recommended and the systemic adverse side effects should be considered. This information is essential to maximize the therapeutic potential of SIRT2 inhibition not only for AD but also for other neurodegenerative diseases.

Association of Selenium Levels with Neurodegenerative Disease: A Systemic Review and Meta-Analysis

BACKGROUND

Neurodegenerative diseases (NDs) have posed significant challenges to public health, and it is crucial to understand their mechanisms in order to develop effective therapeutic strategies. Recent studies have highlighted the potential role of selenium in ND pathogenesis, as it plays a vital role in maintaining cellular homeostasis and preventing oxidative damage. However, a comprehensive analysis of the association between selenium and NDs is still lacking.

METHOD

Five public databases, namely PubMed, Web of Science, EMBASE, Cochrane and Clinical Trials, were searched in our research. Random model effects were chosen, and Higgins inconsistency analyses (I2), Cochrane's Q test and Tau2 were calculated to evaluate the heterogeneity.

RESULT

The association of selenium in ND patients with Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS) and Huntington's disease (HD) was studied. A statistically significant relationship was only found for AD patients (SMD = -0.41, 95% CI (-0.64, -0.17), p < 0.001), especially for erythrocytes. However, no significant relationship was observed in the analysis of the other four diseases.

CONCLUSION

Generally, this meta-analysis indicated that AD patients are strongly associated with lower selenium concentrations compared with healthy people, which may provide a clinical reference in the future. However, more studies are urgently needed for further study and treatment of neurodegenerative diseases.

The Adult Neurogenesis Theory of Alzheimer's Disease

Alzheimer's disease starts in neural stem cells (NSCs) in the niches of adult neurogenesis. All primary factors responsible for pathological tau hyperphosphorylation are inherent to adult neurogenesis and migration. However, when amyloid pathology is present, it strongly amplifies tau pathogenesis. Indeed, the progressive accumulation of extracellular amyloid-β deposits in the brain triggers a state of chronic inflammation by microglia. Microglial activation has a significant pro-neurogenic effect that fosters the process of adult neurogenesis and supports neuronal migration. Unfortunately, this "reactive" pro-neurogenic activity ultimately perturbs homeostatic equilibrium in the niches of adult neurogenesis by amplifying tau pathogenesis in AD. This scenario involves NSCs in the subgranular zone of the hippocampal dentate gyrus in late-onset AD (LOAD) and NSCs in the ventricular-subventricular zone along the lateral ventricles in early-onset AD (EOAD), including familial AD (FAD). Neuroblasts carrying the initial seed of tau pathology travel throughout the brain via neuronal migration driven by complex signals and convey the disease from the niches of adult neurogenesis to near (LOAD) or distant (EOAD) brain regions. In these locations, or in close proximity, a focus of degeneration begins to develop. Then, tau pathology spreads from the initial foci to large neuronal networks along neural connections through neuron-to-neuron transmission.

Breaking the circulus vitiosus of neuroinflammation: Resveratrol attenuates the human glial cell response to cytokines

Neuroinflammation is both cause and effect of many neurodegenerative disorders. Activation of astrocytes and microglia leads to the release of cytokines and reactive oxygen species followed by blood-brain barrier leakage and neurotoxicity. Transient neuroinflammation is considered to be largely protective, however, chronic neuroinflammation contributes to the pathology of Alzheimer's disease, multiple sclerosis, traumatic brain injury, and many more. In this study, we focus on the aspect of cytokine-induced neuroinflammation in human microglia and astrocytes. Here we show by mRNA and protein analysis that cytokines, released not only by microglia but also by astrocytes, lead to a circuit of proinflammatory activation. Moreover, we present how the natural compound resveratrol can stop the circuit of proinflammatory activation and facilitate return to resting conditions. These results will contribute to distinguishing between the causes and the effects of neuroinflammation, a better understanding of underlying mechanisms, and potential treatment options.

Alzheimer’s Disease from the Amyloidogenic Theory to the Puzzling Crossroads between Vascular, Metabolic and Energetic Maladaptive Plasticity

Alzheimer’s disease (AD) is a progressive and degenerative disease producing the most common type of dementia worldwide. The main pathogenetic hypothesis in recent decades has been the well-known amyloidogenic hypothesis based on the involvement of two proteins in AD pathogenesis: amyloid β (Aβ) and tau. Amyloid deposition reported in all AD patients is nowadays considered an independent risk factor for cognitive decline. Vascular damage and blood–brain barrier (BBB) failure in AD is considered a pivotal mechanism for brain injury, with increased deposition of both immunoglobulins and fibrin. Furthermore, BBB dysfunction could be an early sign of cognitive decline and the early stages of clinical AD. Vascular damage generates hypoperfusion and relative hypoxia in areas with high energy demand. Long-term hypoxia and the accumulation within the brain parenchyma of neurotoxic molecules could be seeds of a self-sustaining pathological progression. Cellular dysfunction comprises all the elements of the neurovascular unit (NVU) and neuronal loss, which could be the result of energy failure and mitochondrial impairment. Brain glucose metabolism is compromised, showing a specific region distribution. This energy deficit worsens throughout aging. Mild cognitive impairment has been reported to be associated with a glucose deficit in the entorhinal cortex and in the parietal lobes. The current aim is to understand the complex interactions between amyloid β (Aβ) and tau and elements of the BBB and NVU in the brain. This new approach aimed at the study of metabolic mechanisms and energy insufficiency due to mitochondrial impairment would allow us to define therapies aimed at predicting and slowing down the progression of AD.

The Putative Role of Neuroinflammation in the Interaction between Traumatic Brain Injuries, Sleep, Pain and Other Neuropsychiatric Outcomes: A State-of-the-Art Review

Sleep disturbances are widely prevalent following a traumatic brain injury (TBI) and have the potential to contribute to numerous post-traumatic physiological, psychological, and cognitive difficulties developing chronically, including chronic pain. An important pathophysiological mechanism involved in the recovery of TBI is neuroinflammation, which leads to many downstream consequences. While neuroinflammation is a process that can be both beneficial and detrimental to individuals' recovery after sustaining a TBI, recent evidence suggests that neuroinflammation may worsen outcomes in traumatically injured patients, as well as exacerbate the deleterious consequences of sleep disturbances. Additionally, a bidirectional relationship between neuroinflammation and sleep has been described, where neuroinflammation plays a role in sleep regulation and, in turn, poor sleep promotes neuroinflammation. Given the complexity of this interplay, this review aims to clarify the role of neuroinflammation in the relationship between sleep and TBI, with an emphasis on long-term outcomes such as pain, mood disorders, cognitive dysfunctions, and elevated risk of Alzheimer's disease and dementia. In addition, some management strategies and novel treatment targeting sleep and neuroinflammation will be discussed in order to establish an effective approach to mitigate long-term outcomes after TBI.

Novel neuroprotective pyromeconic acid derivatives with concurrent anti-Aβ deposition, anti-inflammatory, and anti-oxidation properties for treatment of Alzheimer's disease

We synthesized a series of novel pyromeconic acid-styrene hybrid compounds and measured their activities in inhibiting Aβ_1-42 self-aggregation and promoting disaggregation, and their anti-inflammatory and antioxidant properties. The most potent compound, compound 30, had IC₅₀ values of 11.15 μM and 6.87 μM for inhibition of fibril aggregation and promotion of fibril disaggregation, respectively. Because of its redox metal chelating property, 30 also inhibited Cu²⁺-induced Aβ_1-42 fibril aggregation and promoted fibril disaggregation with IC₅₀ of 3.69 μM and 3.35 μM, respectively. Molecular docking demonstrated that 30 interacted with key amino acids of Aβ_1-42, and the reliability of the complex was confirmed by molecular dynamics. In addition, 30 displayed excellent antioxidative activity (oxygen radical absorbance capacity = 2.65 Trolox equivalents) and moderate anti-inflammatory activity and neuroprotection in cell culture assays. Compound 30 was safe in acute toxicity test in mice, and it exhibited favorable pharmacokinetic properties, particularly, accumulation in the hippocampus (maximum ratio of hippocampus to plasma = 7.12). Compound 30 alleviated cognitive deficits in scopolamine-induced amnesia mice; this property may have been attributed to reducing neuroinflammation by inhibiting ionized calcium binding adapter molecule 1 and glial fibrillary acidic protein expression and reducing oxidative stress by activating the Nrf2/HO-1 signaling pathway. In view of its many properties, we envision that 30 is a promising lead for the treatment of Alzheimer's disease.

Mechanisms of abnormal adult hippocampal neurogenesis in Alzheimer's disease

Alzheimer's disease (AD) is a degenerative disease of the central nervous system, the most common type of dementia in old age, which causes progressive loss of cognitive functions such as thoughts, memory, reasoning, behavioral abilities and social skills, affecting the daily life of patients. The dentate gyrus of the hippocampus is a key area for learning and memory functions, and an important site of adult hippocampal neurogenesis (AHN) in normal mammals. AHN mainly consists of the proliferation, differentiation, survival and maturation of newborn neurons and occurs throughout adulthood, but the level of AHN decreases with age. In AD, the AHN will be affected to different degrees at different times, and its exact molecular mechanisms are increasingly elucidated. In this review, we summarize the changes of AHN in AD and its alteration mechanism, which will help lay the foundation for further research on the pathogenesis and diagnostic and therapeutic approaches of AD.

The Defensive Interactions of Prominent Infectious Protozoan Parasites: The Host's Complement System

The complement system exerts crucial functions both in innate immune responses and adaptive humoral immunity. This pivotal system plays a major role dealing with pathogen invasions including protozoan parasites. Different pathogens including parasites have developed sophisticated strategies to defend themselves against complement killing. Some of these strategies include the employment, mimicking or inhibition of host's complement regulatory proteins, leading to complement evasion. Therefore, parasites are proven to use the manipulation of the complement system to assist them during infection and persistence. Herein, we attempt to study the interaction´s mechanisms of some prominent infectious protozoan parasites including Plasmodium, Toxoplasma, Trypanosoma, and Leishmania dealing with the complement system. Moreover, several crucial proteins that are expressed, recruited or hijacked by parasites and are involved in the modulation of the host´s complement system are selected and their role for efficient complement killing or lysis evasion is discussed. In addition, parasite's complement regulatory proteins appear as plausible therapeutic and vaccine targets in protozoan parasitic infections. Accordingly, we also suggest some perspectives and insights useful in guiding future investigations.

Promoted CD4+ T cell-derived IFN-γ/IL-10 by photobiomodulation therapy modulates neurogenesis to ameliorate cognitive deficits in APP/PS1 and 3xTg-AD mice

Background

The immune system has been implicated in synaptic plasticity, inflammation, and the progression of Alzheimer's disease (AD). However, there were few studies on improving the niche microenvironment of neural stem cells (NSCs) in the brain of AD to promote adult hippocampal neurogenesis (AHN) by regulating the function of non-parenchymal immune cells.

Methods

The lymph nodes of amyloid precursor protein/presenilin 1 (APP/PS1) and 3xTg (APP/PS1/tau) mouse models of AD were treated with photobiomodulation therapy (PBMT) for 10 J/cm² per day for 1 month (10 min for each day), T lymphocytes isolated from these two AD models were treated with PBMT for 2 J/cm² (5 min for each time). The NSCs isolated from hippocampus of these two AD models at E14, and the cells were co-cultivated with PBMT-treated T lymphocyte conditioned medium for NSCs differentiation.

Results

Our results showed that PBMT treatment could promote AHN and reverse cognitive deficits in AD mouse model. The expression of interferon-γ (IFN-γ) and interleukin-10 (IL-10) was upregulated in the brain of these two AD models after PBMT treated, which was induced by the activation of Janus kinase 2 (JAK2)-mediated signal transducer and activator of transcription 4 (STAT4)/STAT5 signaling pathway in CD4⁺ T cells. In addition, elevated CD4⁺ T cell levels and upregulated transforming growth factor-β1 (TGFβ1)/insulin-like growth factors-1 (IGF-1)/brain-derived neurotrophic factor (BDNF) protein expression levels were also detected in the brain. More importantly, co-cultivated the PBMT-treated T lymphocyte conditioned medium with NSCs derived from these two AD models was shown to promote NSCs differentiation, which was reflected in the upregulation of both neuronal class-III β-tubulin (Tuj1) and postsynaptic density protein 95 (PSD95), but the effects of PBMT was blocked by reactive oxygen species (ROS) scavenger or JAK2 inhibitor.

Conclusion

Our research suggests that PBMT exerts a beneficial neurogenesis modulatory effect through activating the JAK2/STAT4/STAT5 signaling pathway to promote the expression of IFN-γ/IL-10 in non-parenchymal CD4⁺ T cells, induction of improvement of brain microenvironmental conditions and alleviation of cognitive deficits in APP/PS1 and 3xTg-AD mouse models.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02617-5.

Different phenotypes of microglia in animal models of Alzheimer disease

Microglia are immune-competent cells that are critically involved in maintaining normal brain function. A prominent characteristic of Alzheimer disease (AD) is microglial proliferation and activation concentrated around amyloid plaques in the brain. Recent research has revealed numerous microglial phenotypes related to aging and AD, apart from the traditional M1 and M2 types. Redox signalling modulates the acquisition of the classical or alternative microglia activation phenotypes. The numerous microglial functions can be achieved through these multiple phenotypes, which are associated with distinct molecular signatures.

Examination of Longitudinal Alterations in Alzheimer’s Disease-Related Neurogenesis in an APP/PS1 Transgenic Mouse Model, and the Effects of P33, a Putative Neuroprotective Agent Thereon

Neurogenesis plays a crucial role in cognitive processes. During aging and in Alzheimer’s disease (AD), altered neurogenesis and neuroinflammation are evident both in C57BL/6J, APP_Swe/PS1_dE9 (Tg) mice and humans. AD pathology may slow down upon drug treatment, for example, in a previous study of our group P33, a putative neuroprotective agent was found to exert advantageous effects on the elevated levels of APP, Aβ, and neuroinflammation. In the present study, we aimed to examine longitudinal alterations in neurogenesis, neuroinflammation and AD pathology in a transgenic (Tg) mouse model, and assessed the putative beneficial effects of long-term P33 treatment on AD-specific neurological alterations. Hippocampal cell proliferation and differentiation were significantly reduced between 8 and 12 months of age. Regarding neuroinflammation, significantly elevated astrogliosis and microglial activation were observed in 6- to 7-month-old Tg animals. The amounts of the molecules involved in the amyloidogenic pathway were altered from 4 months of age in Tg animals. P33-treatment led to significantly increased neurogenesis in 9-month-old animals. Our data support the hypothesis that altered neurogenesis may be a consequence of AD pathology. Based on our findings in the transgenic animal model, early pharmacological treatment before the manifestation of AD symptoms might ameliorate neurological decline.

Altered abundances of human immunoglobulin M and immunoglobulin G subclasses in Alzheimer's disease frontal cortex

The immune system has been described to play a role in the development of Alzheimer’s disease (AD), but the distribution of immunoglobulins and their subclasses in brain tissue has not been explored. In this study, examination of pathologically diagnosed frontal cortex gray matter revealed significantly higher levels of IgM and IgG in late-stage AD (Braak and Braak stages V and VI) compared to age-matched controls. While levels of IgG2 and IgG4 constant region fragments were higher in late-stage AD, concentration of native–state IgG4 with free Fc regions was increased in AD III and VI. RNA analysis did not support parenchymal B-cell production of IgG4 in AD III and V, indicating possible peripheral or meningeal B-cell involvement. Changes in the profile of IgM, IgG and IgG subclasses in AD frontal cortex may provide insight into understanding disease pathogenesis and progression.

Uncommon Noninvasive Biomarkers for the Evaluation and Monitoring of the Etiopathogenesis of Alzheimer's Disease

Background:

Alzheimer´s disease (AD) is the most widespread dementia in the world, followed by vascular dementia. Since AD is a heterogeneous disease that shows several varied phenotypes, it is not easy to make an accurate diagnosis, so it arises when the symptoms are clear and the disease is already very advanced. Therefore, it is important to find out biomarkers for AD early diagnosis that facilitate treatment or slow down the disease. Classic biomarkers are obtained from cerebrospinal fluid and plasma, along with brain imaging by positron emission tomography. Attempts have been made to discover uncommon biomarkers from other body fluids, which are addressed in this update.

Objective:

This update aims to describe recent biomarkers from minimally invasive body fluids for the patients, such as saliva, urine, eye fluid or tears.

Methods:

Biomarkers were determined in patients versus controls by single tandem mass spectrometry, and immunoassays. Metabolites were identified by nuclear magnetic resonance, and microRNAs with genome-wide high-throughput real-time polymerase chain reaction-based platforms.

Results:

Biomarkers from urine, saliva, and eye fluid were described, including peptides/proteins, metabolites, and some microRNAs. The association with AD neuroinflammation and neurodegeneration was analyzed, highlighting the contribution of matrix metalloproteinases, the immune system and microglia, as well as the vascular system.

Conclusion:

Unusual biomarkers have been developed, which distinguish each stage and progression of the disease, and are suitable for the early AD diagnosis. An outstanding relationship of biomarkers with neuroinflammation and neurodegeneration was assessed, clearing up concerns of the etiopathogenesis of AD.

Hydrogen-rich water ameliorates neuropathological impairments in a mouse model of Alzheimer's disease through reducing neuroinflammation and modulating intestinal microbiota

Hydrogen exhibits the potential to treat Alzheimer's disease. Stereotactic injection has been previously used as an invasive method of administering active hydrogen, but this method has limitations in clinical practice. In this study, triple transgenic (3×Tg) Alzheimer's disease mice were treated with hydrogen-rich water for 7 months. The results showed that hydrogen-rich water prevented synaptic loss and neuronal death, inhibited senile plaques, and reduced hyperphosphorylated tau and neurofibrillary tangles in 3×Tg Alzheimer's disease mice. In addition, hydrogen-rich water improved brain energy metabolism disorders and intestinal flora imbalances and reduced inflammatory reactions. These findings suggest that hydrogen-rich water is an effective hydrogen donor that can treat Alzheimer's disease. This study was approved by the Animal Ethics and Welfare Committee of Shenzhen University, China (approval No. AEWC-20140615-002) on June 15, 2014.

Detection and Functional Evaluation of the P2X7 Receptor in hiPSC Derived Neurons and Microglia-Like Cells

A large body of evidence suggests the involvement of the ATP-gated purinergic receptor P2X7 (P2X7R) in neurodegenerative diseases, including Alzheimer's disease. While it is well-described to be present and functional on microglia cells contributing to inflammatory responses, some reports suggest a neuronal expression of the receptor as well. Here, we present experimental results showing P2X7 receptors to be expressed on human hiPSC-derived microglia-like cells, hiPSC-derived neuronal progenitors and hiPSC-derived matured neuronal cells. By applying cell surface protein detection assays, we show that P2X7R is not localized on the cell membrane, despite being detected in neuronal cells and thus may not be available for directly mediating neurotoxicity. On hiPSC-derived microglia-like cells, a clear membranous expression was detected. Additionally, we have not observed differences in P2X7R functions between control and familial Alzheimer's disease patient-derived neuronal cells. Functional assays employing a P2X7R antagonist JNJ 47965567 confirm these findings by showing P2X7R-dependent modulation of microglia-like cells viability upon treatment with P2X7R agonists ATP and BzATP, while the same effect was absent from neuronal cells. Since the majority of P2X7R research was done on rodent models, our work on human hiPSC-derived cells presents a valuable contribution to the field, extending the work on animal models to the human cellular system and toward clinical translation.

Probable Reasons for Neuron Copper Deficiency in the Brain of Patients with Alzheimer’s Disease: The Complex Role of Amyloid

Alzheimer’s disease is a progressive neurodegenerative disorder that eventually leads the affected patients to die. The appearance of senile plaques in the brains of Alzheimer’s patients is known as a main symptom of this disease. The plaques consist of different components, and according to numerous reports, their main components include beta-amyloid peptide and transition metals such as copper. In this disease, metal dyshomeostasis leads the number of copper ions to simultaneously increase in the plaques and decrease in neurons. Copper ions are essential for proper brain functioning, and one of the possible mechanisms of neuronal death in Alzheimer’s disease is the copper depletion of neurons. However, the reason for the copper depletion is as yet unknown. Based on the available evidence, we suggest two possible reasons: the first is copper released from neurons (along with beta-amyloid peptides), which is deposited outside the neurons, and the second is the uptake of copper ions by activated microglia.

Intracellular and extracelluar cyclic GMP in the brain and the hippocampus

Cyclic Guanosine-Monophosphate (cGMP) is implicated as second messenger in a plethora of pathways and its effects are executed mainly by cGMP-dependent protein kinases (PKG). It is involved in both peripheral (cardiovascular regulation, intestinal secretion, phototransduction, etc.) and brain (hippocampal synaptic plasticity, neuroinflammation, cognitive function, etc.) processes. Stimulation of hippocampal cGMP signaling have been proved to be beneficial in animal models of aging, Alzheimer's disease or hepatic encephalopathy, restoring different cognitive functions such as passive avoidance, object recognition or spatial memory. However, even when some inhibitors of cGMP-degrading enzymes (PDEs) are already used against peripheral pathologies, their utility as neurological treatments is still under clinical investigation. Additionally, it has been demonstrated a list of cGMP roles as not second but first messenger. The role of extracellular cGMP has been specially studied in hippocampal function and cognitive impairment in animal models and it has emerged as an important modulator of neuroinflammation-mediated cognitive alterations and hippocampal synaptic plasticity malfunction. Specifically, it has been demonstrated that extracellular cGMP decreases hippocampal IL-1β levels restoring membrane expression of glutamate receptors in the hippocampus and cognitive function in hyperammonemic rats. The mechanisms implicated are still unclear and might involve complex interactions between hippocampal neurons, astrocytes and microglia. Membrane targets for extracellular cGMP are still poorly understood and must be addressed in future studies.

Differences in Immune-Related Genes Underlie Temporal and Regional Pathological Progression in 3xTg-AD Mice

The prevalence of Alzheimer’s disease (AD), the most common cause of age-associated dementia, is estimated to increase over the next decades. Evidence suggests neuro-immune signaling deregulation and risk genes beyond the amyloid-β (Aβ) deposition in AD pathology. We examined the temporal profile of inflammatory mediators and microglia deactivation/activation in the brain cortex and hippocampus of 3xTg-AD mice at 3- and 9-month-old. We found upregulated APP processing, decreased expression of CD11b, CX3CR1, MFG-E8, TNF-α, IL-1β, MHC-II and C/EBP-α and increased miR-146a in both brain regions in 3-month-old 3xTG-AD mice, suggestive of a restrictive regulation. Enhanced TNF-α, IL-1β, IL-6, iNOS, SOCS1 and Arginase 1 were only present in the hippocampus of 9-month-old animals, though elevation of HMGB1 and reduction of miR-146a and miR-124 were common features in the hippocampus and cortex regions. miR-155 increased early in the cortex and later in both regions, supporting its potential as a biomarker. Candidate downregulated target genes by cortical miR-155 included Foxo3, Runx2 and CEBPβ at 3 months and Foxo3, Runx2 and Socs1 at 9 months, which are implicated in cell survival, but also in Aβ pathology and microglia/astrocyte dysfunction. Data provide new insights across AD state trajectory, with divergent microglia phenotypes and inflammatory-associated features, and identify critical targets for drug discovery and combinatorial therapies.

Lycium barbarum extract promotes M2 polarization and reduces oligomeric amyloid-β-induced inflammatory reactions in microglial cells

Lycium barbarum (LB) is a traditional Chinese medicine that has been demonstrated to exhibit a wide variety of biological functions, such as antioxidation, neuroprotection, and immune modulation. One of the main mechanisms of Alzheimer's disease is that microglia activated by amyloid beta (Aβ) transform from the resting state to an M1 state and release pro-inflammatory cytokines to the surrounding environment. In the present study, immortalized microglial cells were pretreated with L. barbarum extract for 1 hour and then treated with oligomeric Aβ for 23 hours. The results showed that LB extract significantly increased the survival of oligomeric Aβ-induced microglial cells, downregulated the expression of M1 pro-inflammatory markers (inducible nitric oxide synthase, tumor necrosis factor α, interleukin-6, and interleukin-1β), and upregulated the expression of M2 anti-inflammatory markers (arginase-1, chitinase-like protein 3, and interleukin-4). LB extract also inhibited the oligomeric Aβ-induced secretion of tumor necrosis factor α, interleukin-6, and interleukin-1β in microglial cells. The results of in vitro cytological experiments suggest that, in microglial cells, LB extract can inhibit oligomeric Aβ-induced M1 polarization and concomitant inflammatory reactions, and promote M2 polarization.

Neuronal ROS-induced glial lipid droplet formation is altered by loss of Alzheimer's disease-associated genes

A growing list of Alzheimer's disease (AD) genetic risk factors is being identified, but the contribution of each variant to disease mechanism remains largely unknown. We have previously shown that elevated levels of reactive oxygen species (ROS) induces lipid synthesis in neurons leading to the sequestration of peroxidated lipids in glial lipid droplets (LD), delaying neurotoxicity. This neuron-to-glia lipid transport is APOD/E-dependent. To identify proteins that modulate these neuroprotective effects, we tested the role of AD risk genes in ROS-induced LD formation and demonstrate that several genes impact neuroprotective LD formation, including homologs of human ABCA1, ABCA7, VLDLR, VPS26, VPS35, AP2A, PICALM, and CD2AP Our data also show that ROS enhances Aβ42 phenotypes in flies and mice. Finally, a peptide agonist of ABCA1 restores glial LD formation in a humanized APOE4 fly model, highlighting a potentially therapeutic avenue to prevent ROS-induced neurotoxicity. This study places many AD genetic risk factors in a ROS-induced neuron-to-glia lipid transfer pathway with a critical role in protecting against neurotoxicity.

MUTYH Actively Contributes to Microglial Activation and Impaired Neurogenesis in the Pathogenesis of Alzheimer's Disease

Oxidative stress is a major risk factor for Alzheimer's disease (AD), which is characterized by brain atrophy, amyloid plaques, neurofibrillary tangles, and loss of neurons. 8-Oxoguanine, a major oxidatively generated nucleobase highly accumulated in the AD brain, is known to cause neurodegeneration. In mammalian cells, several enzymes play essential roles in minimizing the 8-oxoguanine accumulation in DNA. MUTYH with adenine DNA glycosylase activity excises adenine inserted opposite 8-oxoguanine in DNA. MUTYH is reported to actively contribute to the neurodegenerative process in Parkinson and Huntington diseases and some mouse models of neurodegenerative diseases by accelerating neuronal dysfunction and microgliosis under oxidative conditions; however, whether or not MUTYH is involved in AD pathogenesis remains unclear. In the present study, we examined the contribution of MUTYH to the AD pathogenesis. Using postmortem human brains, we showed that various types of MUTYH transcripts and proteins are expressed in most hippocampal neurons and glia in both non-AD and AD brains. We further introduced MUTYH deficiency into App ^{NL-G-F/NL-G-F} knock-in AD model mice, which produce humanized toxic amyloid-β without the overexpression of APP protein, and investigated the effects of MUTYH deficiency on the behavior, pathology, gene expression, and neurogenesis. MUTYH deficiency improved memory impairment in App ^{NL-G-F/NL-G-F} mice, accompanied by reduced microgliosis. Gene expression profiling strongly suggested that MUTYH is involved in the microglial response pathways under AD pathology and contributes to the phagocytic activity of disease-associated microglia. We also found that MUTYH deficiency ameliorates impaired neurogenesis in the hippocampus, thus improving memory impairment. In conclusion, we propose that MUTYH, which is expressed in the hippocampus of AD patients as well as non-AD subjects, actively contributes to memory impairment by inducing microgliosis with poor neurogenesis in the preclinical AD phase and that MUTYH is a novel therapeutic target for AD, as its deficiency is highly beneficial for ameliorating AD pathogenesis.

Investigating the Effect of Inosine on Brain Purinergic Receptors and Neurotrophic and Neuroinflammatory Parameters in an Experimental Model of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative pathology characterized by progressive impairment of memory, associated with neurochemical alterations and limited therapy. The aim of this study was to evaluate the effects of inosine on memory, neuroinflammatory cytokines, neurotrophic factors, expression of purinergic receptors, and morphological changes in the hippocampus and cerebral cortex of the rats with AD induced by streptozotocin (STZ). Male rats were divided into four groups: I, control; II, STZ; III, STZ plus inosine (50 mg/kg); and IV, STZ plus inosine (100 mg/kg). The animals received intracerebroventricular injections of STZ or buffer. Three days after the surgical procedure, animals were treated with inosine (50 mg/kg or 100 mg/kg) for 25 days. Inosine was able to prevent memory deficits and decreased the immunoreactivity of the brain A2A adenosine receptor induced by STZ. Inosine also increased the levels of brain anti-inflammatory cytokines (IL-4 and IL-10) and the expression of brain-derived neurotrophic factor and its receptor. Changes induced by STZ in the molecular layer of the hippocampus were attenuated by treatment with inosine. Inosine also protected against the reduction of immunoreactivity for synaptophysin induced by STZ in CA3 hippocampus region. However, inosine did not prevent the increase in GFAP in animals exposed to STZ. In conclusion, our findings suggest that inosine has therapeutic potential for AD through the modulation of different brain mechanisms involved in neuroprotection.

Effect of pyrroloquinoline quinone on lipopolysaccharide-induced autophagy in HAPI microglia cells

Background

Pyrroloquinoline quinone (PQQ) is involved in various physiological and biochemical processes, including antioxidant, cell proliferation, and mitochondrial formation. It plays a vital role in protecting neurons. However, the effect of PQQ on microglia, an inflammatory cell of the central nervous system (CNS), is still unclear. This study aimed to investigate the biological role and neuroprotective mechanism of PQQ in HAPI microglial cells exposed to lipopolysaccharide (LPS).

Methods

Western blot (WB) was used to detect apoptosis and autophagy-related molecules Bax, Bcl2, active-caspase-3, caspase-3, LC3, lysosomal associated membrane protein 2 (LAMP2), AKT, tumor necrosis factor receptor (TNFR) 1, and TNFR2 expression. The phosphatidylinositol 3-kinase (PI3K)/Akt inhibitor LY294002 was used to block the Akt pathway. WB detected the effects of PI3K on autophagy and TNFR1 and TNFR2 expression. The localization of active-caspase-3, caspase-3, LC3, LAMP2, TNFR1, and TNFR2 in cells was observed by immunofluorescence staining. The effect of PQQ on the cell cycle was examined by flow cytometry. We used 5-Ethynyl-2’-deoxyuridine (EdU) assay to detect cell proliferation. The migration ability of cells under different conditions was detected by scratch test and Transwell assay.

Results

Our results showed that there were different effects on the apoptosis-related molecules Bcl2/Bax and active-caspase-3/caspase in HAPI microglial cells treated with PQQ at different times. PQQ had no significant effect on the LC3b/a ratio in the early stage, which was upregulated in the later stage. The expression of LAMP2 was significantly increased in both early and late stages after PQQ treatment. At the same time, we found that PQQ can reverse the translocation of LAMP2 from the cytoplasm to the nucleus in LPS-induced HAPI microglia. After PQQ treatment, TNFR1 was significantly decreased, but TNFR2 increased in LPS-induced HAPI microglia. It may be that PQQ works through the PI3K/Akt signaling pathway to up-regulate LC3, LAMP2, and TNFR1 and down-regulate TNFR2 in LPS-induced HAPI microglia. However, PQQ has little effect on LPS-induced proliferation, cell cycle, and migration of HAPI microglia.

Conclusions

In LPS-induced HAPI microglia, PQQ reduces the apoptosis level and increases that of autophagy. In addition, PQQ changes the distribution of LAMP2 in the cytoplasm and nucleus, which is regulated through the PI3K/Akt signaling pathway.

IKK2/NF-κB Activation in Astrocytes Reduces amyloid β Deposition: A Process Associated with Specific Microglia Polarization

Alzheimer's disease (AD) is a common neurodegenerative disease that is accompanied by pronounced neuroinflammatory responses mainly characterized by marked microgliosis and astrogliosis. However, it remains open as to how different aspects of astrocytic and microglial activation affect disease progression. Previously, we found that microglia expansion in the spinal cord, initiated by IKK2/NF-κB activation in astrocytes, exhibits stage-dependent beneficial effects on the progression of amyotrophic lateral sclerosis. Here, we investigated the impact of NF-κB-initiated neuroinflammation on AD pathogenesis using the APP23 mouse model of AD in combination with conditional activation of IKK2/NF-κB signaling in astrocytes. We show that NF-κB activation in astrocytes triggers a distinct neuroinflammatory response characterized by striking astrogliosis as well as prominent microglial reactivity. Immunohistochemistry and Congo red staining revealed an overall reduction in the size and number of amyloid plaques in the cerebral cortex and hippocampus. Interestingly, isolated primary astrocytes and microglia cells exhibit specific marker gene profiles which, in the case of microglia, point to an enhanced plaque clearance capacity. In contrast, direct IKK2/NF-κB activation in microglia results in a pro-inflammatory polarization program. Our findings suggest that IKK2/NF-κB signaling in astrocytes may activate paracrine mechanisms acting on microglia function but also on APP processing in neurons.

Western diet as a trigger of Alzheimer's disease: From metabolic syndrome and systemic inflammation to neuroinflammation and neurodegeneration

An excess of saturated fatty acids and simple sugars in the diet is a known environmental risk factor of Alzheimer's disease (AD) but the holistic view of the interacting processes through which such diet may contribute to AD pathogenesis is missing. We addressed this need through extensive analysis of published studies investigating the effects of western diet (WD) on AD development in humans and laboratory animals. We reviewed WD-induced systemic alterations comprising metabolic changes, induction of obesity and adipose tissue inflammation, gut microbiota dysbiosis and acceleration of systemic low-grade inflammation. Next we provide an overview of the evidence demonstrating that WD-associated systemic alterations drive impairment of the blood-brain barrier (BBB) and development of neuroinflammation paralleled by accumulation of toxic amyloid. Later these changes are followed by dysfunction of synaptic transmission, neurodegeneration and finally memory and cognitive impairment. We conclude that WD can trigger AD by acceleration of inflammaging, and that BBB impairment induced by metabolic and systemic inflammation play the central role in this process. Moreover, the concurrence of neuroinflammation and Aβ dyshomeostasis, which by reciprocal interactions drive the vicious cycle of neurodegeneration, contradicts Aβ as the primary trigger of AD. Given that in 2019 the World Health Organization recommended focusing on modifiable risk factors in AD prevention, this overview of the sequential, complex pathomechanisms initiated by WD, which can lead from peripheral disturbances to neurodegeneration, can support future prevention strategies.

Inhibition of microglia overactivation restores neuronal survival in a mouse model of CDKL5 deficiency disorder

Background

CDKL5 deficiency disorder (CDD), a severe neurodevelopmental disorder characterized by early onset epilepsy, intellectual disability, and autistic features, is caused by mutations in the CDKL5 gene. Evidence in animal models of CDD showed that absence of CDKL5 negatively affects neuronal survival, as well as neuronal maturation and dendritic outgrowth; however, knowledge of the substrates underlying these alterations is still limited. Neuroinflammatory processes are known to contribute to neuronal dysfunction and death. Recent evidence shows a subclinical chronic inflammatory status in plasma from CDD patients. However, to date, it is unknown whether a similar inflammatory status is present in the brain of CDD patients and, if so, whether this plays a causative or exacerbating role in the pathophysiology of CDD.

Methods

We evaluated microglia activation using AIF-1 immunofluorescence, proinflammatory cytokine expression, and signaling in the brain of a mouse model of CDD, the Cdkl5 KO mouse, which is characterized by an impaired survival of hippocampal neurons that worsens with age. Hippocampal neuron survival was determined by DCX, NeuN, and cleaved caspase-3 immunostaining in Cdkl5 KO mice treated with luteolin (10 mg/kg), a natural anti-inflammatory flavonoid. Since hippocampal neurons of Cdkl5 KO mice exhibit increased susceptibility to excitotoxic stress, we evaluated neuronal survival in Cdkl5 KO mice injected with NMDA (60 mg/kg) after a 7-day treatment with luteolin.

Results

We found increased microglial activation in the brain of the Cdkl5 KO mouse. We found alterations in microglial cell morphology and number, increased levels of AIF-1 and proinflammatory cytokines, and activation of STAT3 signaling. Remarkably, treatment with luteolin recovers microglia alterations as well as neuronal survival and maturation in Cdkl5 KO mice, and prevents the increase in NMDA-induced cell death in the hippocampus.

Conclusions

Our results suggest that neuroinflammatory processes contribute to the pathogenesis of CDD and imply the potential usefulness of luteolin as a treatment option in CDD patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02204-0.

Reassessment of Pioglitazone for Alzheimer's Disease

Alzheimer's disease is a quintessential 'unmet medical need', accounting for ∼65% of progressive cognitive impairment among the elderly, and 700,000 deaths in the United States in 2020. In 2019, the cost of caring for Alzheimer's sufferers was $244B, not including the emotional and physical toll on caregivers. In spite of this dismal reality, no treatments are available that reduce the risk of developing AD or that offer prolonged mitiagation of its most devestating symptoms. This review summarizes key aspects of the biology and genetics of Alzheimer's disease, and we describe how pioglitazone improves many of the patholophysiological determinants of AD. We also summarize the results of pre-clinical experiments, longitudinal observational studies, and clinical trials. The results of animal testing suggest that pioglitazone can be corrective as well as protective, and that its efficacy is enhanced in a time- and dose-dependent manner, but the dose-effect relations are not monotonic or sigmoid. Longitudinal cohort studies suggests that it delays the onset of dementia in individuals with pre-existing type 2 diabetes mellitus, which small scale, unblinded pilot studies seem to confirm. However, the results of placebo-controlled, blinded clinical trials have not borne this out, and we discuss possible explanations for these discrepancies.

Microglia in Neurodegenerative Events-An Initiator or a Significant Other?

A change in microglia structure, signaling, or function is commonly associated with neurodegeneration. This is evident in the patient population, animal models, and targeted in vitro assays. While there is a clear association, it is not evident that microglia serve as an initiator of neurodegeneration. Rather, the dynamics imply a close interaction between the various cell types and structures in the brain that orchestrate the injury and repair responses. Communication between microglia and neurons contributes to the physiological phenotype of microglia maintaining cells in a surveillance state and allows the cells to respond to events occurring in their environment. Interactions between microglia and astrocytes is not as well characterized, nor are interactions with other members of the neurovascular unit; however, given the influence of systemic factors on neuroinflammation and disease progression, such interactions likely represent significant contributes to any neurodegenerative process. In addition, they offer multiple target sites/processes by which environmental exposures could contribute to neurodegenerative disease. Thus, microglia at least play a role as a significant other with an equal partnership; however, claiming a role as an initiator of neurodegeneration remains somewhat controversial.

Nicotine and its metabolite cotinine target MD2 and inhibit TLR4 signaling

Nicotine is the principal alkaloid of tobacco often manufactured into cigarettes and belongs to a highly addictive class of drugs. Nicotine attenuates the neuroinflammation induced by microglial activation. However, the molecular target(s) underlying anti-inflammatory action of nicotine has not been fully understood. Considering the psychoactive substances morphine, cocaine, and methamphetamine act as xenobiotic-associated molecular patterns and can be specifically sensed by the innate immune receptor Toll-like receptor 4 (TLR4), here we sought to delineate whether nicotine and/or its metabolite cotinine may be recognized by the innate immune system via myeloid differentiation protein 2 (MD2), an accessory protein of TLR4 that is responsible for ligand recognition. MD2-intrinsic fluorescence titrations, surface plasmon resonance, and competitive displacement binding assays with curcumin (MD2 probe) demonstrated that both nicotine and cotinine targeted the lipopolysaccharide (LPS; TLR4 agonist) binding pocket of MD2 with similar affinities. The cellular thermal shift assay indicated that nicotine binding increased, while cotinine binding decreased, MD2 stability. These biophysical binding results were further supported by in silico simulations. In keeping with targeting MD2, both nicotine and cotinine inhibited LPS-induced production of nitric oxide and tumor necrosis factor alpha (TNF-α) and blocked microglial activation. Neither a pan nicotinic acetylcholine receptor (nAChR) inhibitor nor RNAi for nAChRs abolished the suppressive effect of nicotine- and cotinine-induced neuroinflammation. These data indicate that TLR4 inhibition by nicotine and cotinine at the concentrations tested in BV-2 cells is independent of classic neuronal nAChRs and validate that MD2 is a direct target of nicotine and cotinine in the inhibition of innate immunity.

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Nicotine and cotinine bind to MD2 in microglia cell

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Nicotine and cotinine inhibit the expression of pro-inflammatory factors

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The activity of nicotine and cotinine in microglia is independent of nAChRs

Chronic unpredictable stress negatively regulates hippocampal neurogenesis and promote anxious depression-like behavior via upregulating apoptosis and inflammatory signals in adult rats

Psychological and physical stress play a pivotal role in etiology of anxiety and depression. Chronic psychological and physical stress modify various physiological phenomena, as a consequence of which oxidative stress, decreased neurotransmitter level, elevated corticosterone level and altered NSC homeostasis is observed. However, the precise mechanism by which chronic stress induce anxious depression and modify internal milieu is still unknown. Herein, we show that exposure to CUS increase oxidative stress, microgliosis, astrogliosis while it reduces hippocampal NSC proliferation, neuronal differentiation and maturation in adult rats. CUS exposure in rats reduce dopamine and serotonin level in cortex and hippocampus, which result in increased anxiety and depression-like phenotypes. We also found elevated level of NF-κB and TNF-α while decreased anti-inflammatory cytokine IL-10 level, that led to increased expression of Bax and cleaved Caspase-3 whereas down regulation of antiapoptotic protein Bcl2. Additionally, CUS altered adult hippocampal neurogenesis, increased gliosis and neuronal apoptosis in cerebral cortex and hippocampus which might be associated with reduced AKT and increased ERK signaling, as seen in the rat brain tissue. Taken together, these results indicate that CUS induce oxidative stress and neuroinflammation which directly affects NSC dynamics, monoamines levels and behavioral functions in adult rats.

Mechanisms of the Procognitive Effects of Xanthotoxin and Umbelliferone on LPS-Induced Amnesia in Mice

Neuroinflammation plays an essential role in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease. Although coumarins have been shown to improve cognitive function in animal models and exert anti-inflammatory effects in cell cultures, the exact mechanism of their neuroprotective effects has not yet been fully elucidated. The present study aimed to investigate the neuroprotective effects of xanthotoxin (furanocoumarin) and umbelliferone (simple coumarin) in lipopolysaccharide-induced cognitive dysfunction in mice. For evaluation memory and learning processes, a passive avoidance test was used. Furthermore, acetylcholinesterase level and impact on the tumor necrosis factor α, interleukin 10 levels in the whole brain, and cyclooxygenase-II in hippocampus was established. Subchronic administration of both coumarins (15 mg/kg) enhanced the learning and memory function, but only the xanthotoxin improved cognitive processes impaired by lipopolysaccharide (0.8 mg/kg) administration. Behavioral results stay in line with acetylcholinesterase level in the brain. A statistically significant decrease in the level of tumor necrosis factor α and cyclooxygenase-II in lipopolysaccharide-treated rodents after coumarins' administration was observed. Together, our findings demonstrate that both coumarins improved cognitive functions, but only xanthotoxin significantly enhanced the learning and memory function and reduced the level of acetylcholinesterase in lipopolysaccharide-treated mice. This effect may suggest that only furanocoumarin-xanthotoxin attenuates neuroinflammation and enhances cholinergic neurotransmission, thus it can be a potential remedy with procognitive potential effective in treatment of neuroinflammatory disease.

Toxoplasma Infection Induces Sustained Up-Regulation of Complement Factor B and C5a Receptor in the Mouse Brain via Microglial Activation: Implication for the Alternative Complement Pathway Activation and Anaphylatoxin Signaling in Cerebral Toxoplasmosis

Toxoplasma gondii is a neurotropic protozoan parasite, which is linked to neurological manifestations in immunocompromised individuals as well as severe neurodevelopmental sequelae in congenital toxoplasmosis. While the complement system is the first line of host defense that plays a significant role in the prevention of parasite dissemination, Toxoplasma artfully evades complement-mediated clearance via recruiting complement regulatory proteins to their surface. On the other hand, the details of Toxoplasma and the complement system interaction in the brain parenchyma remain elusive. In this study, infection-induced changes in the mRNA levels of complement components were analyzed by quantitative PCR using a murine Toxoplasma infection model in vivo and primary glial cells in vitro. In addition to the core components C3 and C1q, anaphylatoxin C3a and C5a receptors (C3aR and C5aR1), as well as alternative complement pathway components properdin (CFP) and factor B (CFB), were significantly upregulated 2 weeks after inoculation. Two months post-infection, CFB, C3, C3aR, and C5aR1 expression remained higher than in controls, while CFP upregulation was transient. Furthermore, Toxoplasma infection induced significant increase in CFP, CFB, C3, and C5aR1 in mixed glial culture, which was abrogated when microglial activation was inhibited by pre-treatment with minocycline. This study sheds new light on the roles for the complement system in the brain parenchyma during Toxoplasma infection, which may lead to the development of novel therapeutic approaches to Toxoplasma infection-induced neurological disorders.

Inflammation/bioenergetics-associated neurodegenerative pathologies and concomitant diseases: a role of mitochondria targeted catalase and xanthophylls

Various inflammatory stimuli are able to modify or even "re-program" the mitochondrial metabolism that results in generation of reactive oxygen species. In noncommunicable chronic diseases such as atherosclerosis and other cardiovascular pathologies, type 2 diabetes and metabolic syndrome, these modifications become systemic and are characterized by chronic inflammation and, in particular, "neuroinflammation" in the central nervous system. The processes associated with chronic inflammation are frequently grouped into "vicious circles" which are able to stimulate each other constantly amplifying the pathological events. These circles are evidently observed in Alzheimer's disease, atherosclerosis, type 2 diabetes, metabolic syndrome and, possibly, other associated pathologies. Furthermore, chronic inflammation in peripheral tissues is frequently concomitant to Alzheimer's disease. This is supposedly associated with some common genetic polymorphisms, for example, Apolipoprotein-E ε4 allele carriers with Alzheimer's disease can also develop atherosclerosis. Notably, in the transgenic mice expressing the recombinant mitochondria targeted catalase, that removes hydrogen peroxide from mitochondria, demonstrates the significant pathology amelioration and health improvements. In addition, the beneficial effects of some natural products from the xanthophyll family, astaxanthin and fucoxanthin, which are able to target the reactive oxygen species at cellular or mitochondrial membranes, have been demonstrated in both animal and human studies. We propose that the normalization of mitochondrial functions could play a key role in the treatment of neurodegenerative disorders and other noncommunicable diseases associated with chronic inflammation in ageing. Furthermore, some prospective drugs based on mitochondria targeted catalase or xanthophylls could be used as an effective treatment of these pathologies, especially at early stages of their development.

Amyloid beta is an early responder cytokine and immunopeptide of the innate immune system

A molecular level conceptualization of the pathogenesis of Alzheimer's disease (AD) remains elusive with many competing hypotheses, particularly via proteopathic and immunopathic mechanisms. However, these need not be competitive. If amyloid beta (Aβ) is regarded as an "early responder cytokine," then proteopathic considerations become encompassed within an overarching hybrid proteopathic-immunopathic mechanism. As argued in this commentary, Aβ is in fact a molecular constituent of the innate immune system. Aβ is an antimicrobial peptide (AMP) functioning not only as a killer peptide, but also as a modulatory immunopeptide. Aβ satisfies the definition of a cytokine, exhibiting interdependency with other cytokines. Aβ also satisfies the functional definition of a chemokine, existing within the AMP-chemokine spectrum. Aβ, like conventional cytokines, both binds to and is released by microglial cells. Finally, Aβ interacts with the complement and Toll-like receptor systems analogously to established cytokines. Aβ may thus be regarded as an effector molecule of innate immunity.

Role of Microglia in Modulating Adult Neurogenesis in Health and Neurodegeneration

Microglia are the resident immune cells of the brain, constituting the powerhouse of brain innate immunity. They originate from hematopoietic precursors that infiltrate the developing brain during different stages of embryogenesis, acquiring a phenotype characterized by the presence of dense ramifications. Microglial cells play key roles in maintaining brain homeostasis and regulating brain immune responses. They continuously scan and sense the brain environment to detect any occurring changes. Upon detection of a signal related to physiological or pathological processes, the cells are activated and transform to an amoeboid-like phenotype, mounting adequate responses that range from phagocytosis to secretion of inflammatory and trophic factors. The overwhelming evidence suggests that microglia are crucially implicated in influencing neuronal proliferation and differentiation, as well as synaptic connections, and thereby cognitive and behavioral functions. Here, we review the role of microglia in adult neurogenesis under physiological conditions, and how this role is affected in neurodegenerative diseases.

MG53 Protects hUC-MSCs against Inflammatory Damage and Synergistically Enhances Their Efficacy in Neuroinflammation Injured Brain through Inhibiting NLRP3/Caspase-1/IL-1β Axis

The inflammatory microenvironment in a lesion is not conducive to the survival of stem cells. Improving the inflammatory microenvironment may be an alternative strategy to enhance the efficacy of stem cells. We evaluated the therapeutic effect and molecular mechanism of mitsugumin53 (MG53) on lipopolysaccharide (LPS)-induced damage in human umbilical cord mesenchymal stem cells (hUC-MSCs) and in C57/BL6 mice. MG53 significantly promoted the proliferation and migration of hUC-MSCs, protected hUC-MSCs against LPS-induced apoptosis and mitochondrial dysfunction, and reversed LPS-induced inflammatory cytokine release. Furthermore, MG53 combined with hUC-MSCs transplantation improved LPS-induced memory impairment and activated neurogenesis by promoting the migration of hUC-MSCs and enhancing βIII-tubulin and doublecortin (DCX) expression. MG53 protein combined with hUC-MSCs improved the M1/M2 phenotype polarization of microglia accompanied by lower inducible nitric oxide synthase (iNOS) expression and higher arginase 1 (ARG1) expression. MG53 significantly suppressed the expression of tumor necrosis factor α (TNF-α), Toll-like receptor 4 (TLR4), nucleotide oligomerization domain-like receptor protein 3 (NLRP3), cleaved-caspase-1, and interleukin (IL)-1β to alleviate LPS-induced neuroinflammation on hUC-MSCs and C57/BL6 mice. In conclusion, our results indicated that MG53 could protect hUC-MSCs against LPS-induced inflammatory damage and facilitate their efficacy in LPS-treated C57/BL6 mice partly by inhibiting the NLRP3/caspase-1/IL-1β axis.

Cerebrolysin in the therapy of mild cognitive impairment and dementia due to Alzheimer's disease: 30 years of clinical use

Alzheimer's disease (AD) is the most common neurocognitive disorder and a global health problem. The prevalence of AD is growing dramatically, especially in low- and middle-income countries, and will reach 131.5 million cases worldwide by 2050. Therefore, developing a disease-modifying therapy capable of delaying or even preventing the onset and progression of AD has become a world priority, and is an unmet need. The pathogenesis of AD, considered as the result of an imbalance between resilience and risk factors, begins many years before the typical clinical picture develops and involves multiple pathophysiological mechanisms. Since the pathophysiology of AD is multifactorial, it is not surprising that all attempts done to modify the disease course with drugs directed towards a single therapeutic target have been unsuccessful. Thus, combined modality therapy, using multiple drugs with a single mechanism of action or multi-target drugs, appears as the most promising strategy for both effective AD therapy and prevention. Cerebrolysin, acting as a multitarget peptidergic drug with a neurotrophic mode of action, exerts long-lasting therapeutic effects on AD that could reflect its potential utility for disease modification. Clinical trials demonstrated that Cerebrolysin is safe and efficacious in the treatment of AD, and may enhance and prolong the efficacy of cholinergic drugs, particularly in moderate to advanced AD patients. In this review, we summarize advances of therapeutic relevance in the pathogenesis and the biomarkers of AD, paying special attention to neurotrophic factors, and present results of preclinical and clinical investigations with Cerebrolysin in AD.

Chlorzoxazone exhibits neuroprotection against Alzheimer's disease by attenuating neuroinflammation and neurodegeneration in vitro and in vivo

Alzheimer's disease (AD), a complex and an age-related brain disease, is induced by the accumulation of amyloid beta (Aβ) and neuroinflammation. Chlorzoxazone (CZ) is a classical FDA-approved drug, and shows anti-inflammatory effects. However, up until now, its regulatory role in AD has not been investigated. Therefore, in this study we attempted to explore if CZ could be an effective therapeutic strategy for AD treatment. At first, the in vitro study was performed to mimic AD using Aβ. We found that Aβ caused p65 nuclear translocation in both primary microglial cells and astrocytes, which were, however, restrained by CZ treatments. Meanwhile, CZ incubation markedly decreased the expression of pro-inflammatory cytokines including tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β). Aβ deposition was also markedly reduced in glial cells treated with CZ. Importantly, we found that glial activation and its-related pro-inflammation induced by Aβ led to obvious neurodegeneration and neuroinflammation, which were effectively attenuated by CZ pre-treatment in the isolated primary cortical neurons. Then, the in vivo study was performed using APP/PS1 mice with AD. Behavior tests showed that CZ administration effectively improved cognitive deficits in AD mice. Neuron death in hippocampus of AD mice was also inhibited by CZ. Aβ accumulation in brain was markedly decreased in CZ-treated AD mice. We finally found that hippocampal glial activation in AD mice was obviously blocked by CZ supplementation, along with remarkable decreases in TNF-α, IL-1β and p65 nuclear translocation. Together, these findings above demonstrated that CZ could inhibit glial activation and inflammatory response, contributing to the suppression of neurodegeneration and neuroinflammation. Therefore, CZ may be an effective therapeutic strategy for AD treatment.

Restoring regulatory T-cell dysfunction in Alzheimer's disease through ex vivo expansion

Inflammation is a significant component of Alzheimer’s disease pathology. While neuroprotective microglia are important for containment/clearance of Amyloid plaques and maintaining neuronal survival, Alzheimer inflammatory microglia may play a detrimental role by eliciting tau pathogenesis and accelerating neurotoxicity. Regulatory T cells have been shown to suppress microglia-mediated inflammation. However, the role of regulatory T cells in ameliorating the proinflammatory immune response in Alzheimer’s disease requires further investigation. Forty-six patients with Alzheimer disease, 42 with mild cognitive impairment and 41 healthy controls were studied. The phenotypes of peripheral regulatory T cells were assessed with multicolour flow cytometry. Regulatory T cells were co-cultured with responder T cells and proliferation was determined by ³H-thymidine incorporation. In separate experiments, regulatory T cells were added to induced pluripotent stem cell-derived pro-inflammatory macrophages and changes in interleukin-6/tumour necrosis-alpha transcripts and protein levels were measured. Freshly isolated regulatory T cells were expanded ex vivo in the presence of CD3/CD28 expander beads, interleukin-2 and rapamycin to promote their suppressive function. We found that the suppressive function of regulatory T cells on responder T-cell proliferation was compromised at the Alzheimer disease stage, compared with mild cognitive impairment and healthy controls. CD25 mean fluorescence intensity in regulatory T-cell population was also reduced in Alzheimer dementia patients. Regulatory T cells did not suppress pro-inflammatory macrophages at baseline. Following ex vivo expansion, regulatory T-cell suppression of responder T-cell proliferation and pro-inflammatory macrophage activation increased in both patients and controls. Expanded regulatory T cells exerted their immunoregulatory function on pro-inflammatory macrophages through a contact-mediated mechanism. In conclusion, regulatory T-cell immunophenotype and function are compromised in Alzheimer’s disease. Following ex vivo expansion, the immunomodulatory function of regulatory T cells is enhanced even at advanced stages of Alzheimer’s disease. Restoration of regulatory T-cell function could be explored as a means to modulate the inflammatory status of Alzheimer’s disease.

Arginase Inhibition Supports Survival and Differentiation of Neuronal Precursors in Adult Alzheimer's Disease Mice

Adult neurogenesis is a complex physiological process, which plays a central role in maintaining cognitive functions, and consists of progenitor cell proliferation, newborn cell migration, and cell maturation. Adult neurogenesis is susceptible to alterations under various physiological and pathological conditions. A substantial decay of neurogenesis has been documented in Alzheimer’s disease (AD) patients and animal AD models; however, several treatment strategies can halt any further decline and even induce neurogenesis. Our previous results indicated a potential effect of arginase inhibition, with norvaline, on various aspects of neurogenesis in triple-transgenic mice. To better evaluate this effect, we chronically administered an arginase inhibitor, norvaline, to triple-transgenic and wild-type mice, and applied an advanced immunohistochemistry approach with several biomarkers and bright-field microscopy. Remarkably, we evidenced a significant reduction in the density of neuronal progenitors, which demonstrate a different phenotype in the hippocampi of triple-transgenic mice as compared to wild-type animals. However, norvaline showed no significant effect upon the progenitor cell number and constitution. We demonstrated that norvaline treatment leads to an escalation of the polysialylated neuronal cell adhesion molecule immunopositivity, which suggests an improvement in the newborn neuron survival rate. Additionally, we identified a significant increase in the hippocampal microtubule-associated protein 2 stain intensity. We also explore the molecular mechanisms underlying the effects of norvaline on adult mice neurogenesis and provide insights into their machinery.