Microglia: A pharmacological target for the treatment of age-related cognitive decline and Alzheimer's disease

Drug screening targeting TREM2-TYROBP transmembrane binding

TREM2 encodes a microglial membrane receptor involved in the disease-associated microglia (DAM) phenotype whose activation requires the transmembrane interaction with TYROBP. Mutations in TREM2 represent a high-impact risk factor for Alzheimer's disease (AD) which turned TREM2 into a significant drug target. We present a bacterial two-hybrid (B2H) system designed for high-throughput screening of modulators for the TREM2-TYROBP transmembrane interaction. In a pilot study, 315 FDA-approved drugs were analyzed to identify potential binding modifiers. Our pipeline includes multiple filtering steps to ensure candidate specificity. The screening suggested two potential candidates that were finally assayed in the human microglial cell line HMC3. Upon stimulation with anti-TREM2 mAb, pSYK/SYK ratios were calculated in the presence of the candidates. As a result, we found that varenicline, a smoking cessation medication, can be considered as a transmembrane agonist of the TREM2-TYROBP interaction.

Predicting the Beneficial Effects of Cognitive Stimulation and Transcranial Direct Current Stimulation in Amnestic Mild Cognitive Impairment with Clinical, Inflammation, and Human Microglia Exposed to Serum as Potential Markers: A Double-Blind Placebo-Controlled Randomized Clinical Trial

In amnestic mild cognitive impairment (aMCI), neuroinflammation evolves during disease progression, affecting microglial function and potentially accelerating the pathological process. Currently, no effective treatment exists, leading to explorations of various symptomatic approaches, though few target the underlying physiological mechanisms. Modulating inflammatory processes may be critical in slowing disease progression. Cognitive stimulation (CS) and transcranial direct current stimulation (tDCS) applied to the left dorsolateral prefrontal cortex (l-DLPFC) show promise, but the results are heterogeneous. Thus, a randomized, double-blind, placebo-controlled clinical trial is currently underway. The first-stage results were examined after three weeks of intervention in two groups: active tDCS combined with CS and sham tDCS combined with CS. Twenty-two participants underwent two assessments: T0 (baseline) and T1 (after 15 sessions of tDCS, active or sham, and 9 sessions of CS). The results demonstrated that CS improved cognition, increased brain-derived neurotrophic factor (BDNF) levels, and reduced peripheral proinflammatory cytokine levels (interleukin IL-6 and chemokine CX3CL1) in serum. This decrease in IL-6 may promote microglial proliferation and survival as a modulatory effect response, while the increase in BDNF might suggest a regulatory mechanism in microglia-neuron interaction responses. However, tDCS did not enhance the cognitive or modulatory effects of CS, suggesting that longer interventions might be required to achieve substantial benefits.

Design, synthesis, and pharmacological characterization of sulfonylurea-based NLRP3 inhibitors: Towards an effective therapeutic strategy for Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder that severely diminishes the quality of life for millions. The NLRP3 inflammasome, a critical mediator of inflammation, has emerged as a promising therapeutic target for AD. In this study, we report the development and optimization of a novel series of sulfonylurea-based NLRP3 inhibitors, with a focus on compound MC1 for the treatment of AD. Utilizing the co-crystal structure of MCC950 in complex with NLRP3 as a guide, we employed a hybrid approach of computer-aided drug design and traditional medicinal chemistry to perform two iterative optimization cycles. This strategy led to the synthesis and evaluation of 40 sulfonylurea derivatives, culminating in the identification of MC1 as the lead candidate. MC1 exhibited enhanced NLRP3 inhibitory activity and demonstrated high binding affinity to NLRP3, effectively blocking NLRP3 activation induced by diverse stimuli such as ATP and Nigericin, without perturbing upstream processes like reactive oxygen species (ROS) generation. In vivo experiments in AD mouse models revealed that MC1 significantly ameliorated cognitive deficits, surpassing the performance of MCC950. Importantly, MC1 showed no signs of hepatotoxicity or adverse effects on the central nervous system. These findings suggest that MC1 holds strong potential as a lead compound for further development in AD therapy, providing a new scaffold for NLRP3 inhibition with improved safety and efficacy profiles.

The mechanisms, hallmarks, and therapies for brain aging and age-related dementia

Age-related cognitive decline and dementia are significant manifestations of brain aging. As the elderly population grows rapidly, the health and socio-economic impacts of cognitive dysfunction have become increasingly significant. Although clinical treatment of dementia has faced considerable challenges over the past few decades, with limited breakthroughs in slowing its progression, there has been substantial progress in understanding the molecular mechanisms and hallmarks of age-related dementia (ARD). This progress brings new hope for the intervention and treatment of this disease. In this review, we categorize the latest findings in ARD biomarkers into four stages based on disease progression: Healthy brain, pre-clinical, mild cognitive impairment, and dementia. We then systematically summarize the most promising therapeutic approaches to prevent or slow ARD at four levels: Genome and epigenome, organelle, cell, and organ and organism. We emphasize the importance of early prevention and detection, along with the implementation of combined treatments as multimodal intervention strategies, to address brain aging and ARD in the future.

Sulfatide deficiency-induced astrogliosis and myelin lipid dyshomeostasis are independent of Trem2-mediated microglial activation

Disrupted lipid homeostasis and neuroinflammation often co-exist in neurodegenerative disorders including Alzheimer's disease (AD). However, the intrinsic connection and causal relationship between these deficits remain elusive. Our previous studies show that the loss of sulfatide (ST), a class of myelin-enriched lipids, causes AD-like neuroinflammatory responses, cognitive impairment, bladder enlargement, as well as lipid dyshomeostasis. To better understand the relationship between neuroinflammation and lipid disruption induced by ST deficiency, we established a ST-deficient mouse model with constitutive Trem2 knockout and studied the impact of Trem2 in regulating ST deficiency-induced microglia-mediated neuroinflammation, astrocyte activation and lipid disruption. Our study demonstrates that Trem2 regulates ST deficiency-induced microglia-mediated neuroinflammatory pathways and astrogliosis at the transcriptomic level, but not astrocyte activation at the protein level, suggesting that Trem2 is indispensable for ST deficiency-induced microglia-mediated neuroinflammation but not astrogliosis. Meanwhile, ST loss-induced lipidome disruption and free water retention were consistently observed in the absence of Trem2 . Collectively, these results emphasize the essential role of Trem2 in mediating lipid loss-associated microglia-mediated neuroinflammation, but not both astrogliosis and myelin lipid disruption. Moreover, we demonstrated that attenuating neuroinflammation has a limited impact on brain ST loss-induced lipidome alteration or AD-like peripheral disorders. Our findings suggest that preserving lipidome and astrocyte balance may be crucial in decelerating the progression of AD.

Effects of obesogenic diet and 17β-estradiol in female mice with APOE 3/3, 3/4, and 4/4 genotypes

The main genetic risk factor for Alzheimer's disease (AD) is the apolipoprotein E ε4 allele (APOE4). AD risk associated with APOE4 disproportionately affects women. Furthermore, human and rodent studies indicate that the cognitive deficits associated with APOE4 are greater in females. One modifiable AD risk factor is obesity during middle age. Given that approximately two-thirds of US adults are overweight, it is important to understand how obesity affects AD risk, how it interacts with APOE4, and the extent to which its detrimental effects can be mitigated with therapeutics. One intervention study for women is estrogen-based hormone therapy, which can exert numerous health benefits when administered in early middle age. No experimental studies have examined the interactions among APOE4, obesity, and hormone therapy in aging females. To begin to explore these issues, we considered how obesity outcomes are affected by treatment with estradiol at the onset of middle age in female mice with human APOE3 and APOE4. Furthermore, to explore how gene dosage affects outcomes, we compared mice homozygous for APOE3 (3/3) and homozygous (4/4) or hemizygous (3/4) for APOE4. Mice were examined over a 4-month period that spans the transition into reproductive senescence, a normal age-related change that models many aspects of human perimenopause. Beginning at 5 months of age, mice were maintained on a control diet (10% fat) or high-fat diet (HFD; 60% fat). After 8 weeks, by which time obesity was present in all HFD groups, mice were implanted with an estradiol or vehicle capsule that was maintained for the final 8 weeks. Animals were assessed on a range of metabolic and neural measures. Overall, APOE4 was associated with poorer metabolic function and cognitive performance. However, an obesogenic diet induced relatively greater impairments in metabolic function and cognitive performance in APOE3/3 mice. Estradiol treatment improved metabolic and cognitive outcomes across all HFD groups, with APOE4/4 generally exhibiting the greatest benefit. APOE3/4 mice were intermediate to the homozygous genotypes on many measures but also exhibited unique profiles. Together, these findings highlight the importance of the APOE genotype as a modulator of the risks associated with obesity and the beneficial outcomes of estradiol.

Primary microglia cell cultures in translational research: Strengths and limitations

Microglia are the resident macrophages in the central nervous system, accounting for 10-15% of the cell mass in the brain. Next to their physiological role in development, monitoring neuronal function and the maintenance of homeostasis, microglia are crucial in the brain's immune defense. Brain injury and chronic neurological disorders are associated with neuroinflammation, in which microglia activation is a central element. Microglia acquire a wide spectrum of activation states in the diseased or injured brain, some of which are neurotoxic. The investigation of microglia (patho)physiology and therapeutic interventions targeting neuroinflammation is a substantial challenge. In addition to in vivo approaches, the application of in vitro model systems has gained significant ground and is essential to complement in vivo work. Primary microglia cultures have proved to be a useful tool. Microglia cultures have offered the opportunity to explore the mechanistic, molecular elements of microglia activation, the microglia secretome, and the efficacy of therapeutic treatments against neuroinflammation. As all model systems, primary microglia cultures have distinct strengths and limitations to be weighed when experiments are designed and when data are interpreted. Here, we set out to provide a succinct overview of the advantages and pitfalls of the use of microglia cultures, which instructs the refinement and further development of this technique to remain useful in the toolbox of microglia researchers. Since there is no conclusive therapy to combat neurotoxicity linked to neuroinflammation in acute brain injury or neurodegenerative disorders, these research tools remain essential to explore therapeutic opportunities.

Use of adeno-associated viruses for transgenic modulation of microglia structure and function: A review of technical considerations and challenges

Microglia play a central role in the etiology of many neuropathologies. Transgenic tools are a powerful experiment approach to gain reliable and specific control over microglia function. Adeno-associated virus (AAVs) vectors are already an indispensable tool in neuroscience research. Despite ubiquitous use of AAVs and substantial interest in the role of microglia in the study of central nervous system (CNS) function and disease, transduction of microglia using AAVs is seldom reported. This review explores the challenges and advancements made in using AAVs for expressing transgenes in microglia. First, we will examine the functional anatomy of the AAV capsid, which will serve as a basis for subsequent discussions of studies exploring the relationship between capsid mutations and microglia transduction efficacy. After outlining the functional anatomy of AAVs, we will consider the experimental evidence demonstrating AAV-mediated transduction of microglia and microglia-like cell lines followed by an examination of the most promising experimental approaches identified in the literature. Finally, technical limitations will be considered in future applications of AAV experimental approaches.

The proteomic landscape of microglia in health and disease

Microglia are the resident immune cells of the central nervous system (CNS) and as such play crucial roles in regulating brain homeostasis. Their presence in neurodegenerative diseases is known, with neurodegeneration-associated risk genes heavily expressed in microglia, highlighting their importance in contributing to disease pathogenesis. Transcriptomics studies have uncovered the heterogeneous landscape of microglia in health and disease, identifying important disease-associated signatures such as DAM, and insight into both the regional and temporal diversity of microglia phenotypes. Quantitative mass spectrometry methods are ever increasing in the field of neurodegeneration, utilised as ways to identify disease biomarkers and to gain deeper understanding of disease pathology. Proteins are the main mechanistic indicators of cellular function, yet discordance between transcript and proteomic findings has highlighted the need for in-depth proteomic phenotypic and functional analysis to fully understand disease kinetics at the cellular and molecular level. This review details the current progress of using proteomics to define microglia biology, the relationship between gene and protein expression in microglia, and the future of proteomics and emerging methods aiming to resolve heterogeneous cell landscapes.

Case report: Rapidly progressive neurocognitive disorder with a fatal outcome in a patient with PU.1 mutated agammaglobulinemia

Introduction

PU.1-mutated agammaglobulinemia (PU.MA) represents a recently described autosomal-dominant form of agammaglobulinemia caused by mutation of the SPI1 gene. This gene codes for PU.1 pioneer transcription factor important for the maturation of monocytes, B lymphocytes, and conventional dendritic cells. Only six cases with PU.MA, presenting with chronic sinopulmonary and systemic enteroviral infections, have been previously described. Accumulating literature evidence suggests a possible relationship between SPI1 mutation, microglial phagocytic dysfunction, and the development of Alzheimer's disease (AD).

Case description

We present a Caucasian female patient born from a non-consanguineous marriage, who was diagnosed with agammaglobulinemia at the age of 15 years when the immunoglobulin replacement therapy was started. During the following seventeen years, she was treated for recurrent respiratory and intestinal infections. At the age of 33 years, the diagnosis of celiac-like disease was established. Five years later progressive cognitive deterioration, unstable gait, speech disturbances, and behavioral changes developed. Comprehensive microbiological investigations were negative, excluding possible infective etiology. Brain MRI, 18FDG-PET-CT, and neuropsychological testing were suggestive for a diagnosis of a frontal variant of AD. Clinical exome sequencing revealed the presence of a novel frameshift heterozygous variant c.441dup in exon 4 of the SPI1 gene. Despite intensive therapy, the patient passed away a few months after the onset of the first neurological symptoms.

Conclusion

We describe the first case of PU.MA patient presenting with a rapidly progressive neurocognitive deterioration. The possible role of microglial dysfunction in patients with SPI1 mutation could explain their susceptibility to neurodegenerative diseases thus highlighting the importance of genetic testing in patients with inborn errors of immunity. Since PU.MA represents a newly described form of agammaglobulinemia, our case expands the spectrum of manifestations associated with SPI1 mutation.

Microglia in Neurodegenerative Diseases

Neurodegenerative diseases are manifested by a progressive death of neural cells, resulting in the deterioration of central nervous system (CNS) functions, ultimately leading to specific behavioural and cognitive symptoms associated with affected brain regions. Several neurodegenerative disorders are caused by genetic variants or mutations, although the majority of cases are sporadic and linked to various environmental risk factors, with yet an unknown aetiology. Neuroglial changes are fundamental and often lead to the pathophysiology of neurodegenerative diseases. In particular, microglial cells, which are essential for maintaining CNS health, become compromised in their physiological functions with the exposure to environmental risk factors, genetic variants or mutations, as well as disease pathology. In this chapter, we cover the contribution of neuroglia, especially microglia, to several neurodegenerative diseases, including Nasu-Hakola disease, Parkinson's disease, amyotrophic lateral sclerosis, Alzheimer's disease, Huntington's disease, infectious disease-associated neurodegeneration, and metal-precipitated neurodegeneration. Future research perspectives for the field pertaining to the therapeutic targeting of microglia across these disease conditions are also discussed.

Neuroprotective Mechanisms of Salidroside in Alzheimer's Disease: A Systematic Review and Meta-analysis of Preclinical Studies

Alzheimer's disease (AD) is a neurodegenerative disease of the central nervous system that occurs in old age and pre-aging, characterized by progressive cognitive dysfunction and behavioral impairment. Salidroside (Sal) is a phenylpropanoid mainly isolated from Rhodiola species with various pharmacological effects. However, the exact anti-AD mechanism of Sal has not been clearly elucidated. This meta-analysis aims to investigate the possible mechanisms by which Sal exerts its anti-AD effects by evaluating behavioral indicators and biochemical characteristics. A total of 20 studies were included, and the results showed that the Sal treatment significantly improved behavior abnormalities in AD animal models. With regard to neurobiochemical indicators, Sal treatment could effectively increase the antioxidant enzyme superoxide dismutase, decrease the oxidative stress indicator malondialdehyde, and decrease the inflammatory indicators interleukin 1β, interleukin 6, and tumor necrosis factor α. Sal treatment was effective in reducing neuropathological indicators, such as amyloid-β levels and the number of apoptotic cells. When the relevant literature on the treatment of rodent AD models is combined with Sal, the therapeutic potential of Sal through multiple mechanisms was confirmed. However, further confirmation by higher quality studies, larger sample sizes, and more comprehensive outcome evaluations in clinical trials is needed in the future.

Microglia Depletion Attenuates the Pro-Resolving Activity of the Formyl Peptide Receptor 2 Agonist AMS21 Related to Inhibition of Inflammasome NLRP3 Signalling Pathway: A Study of Organotypic Hippocampal Cultures

Microglial cells have been demonstrated to be significant resident immune cells that maintain homeostasis under physiological conditions. However, prolonged or excessive microglial activation leads to disturbances in the resolution of inflammation (RoI). Formyl peptide receptor 2 (FPR2) is a crucial player in the RoI, interacting with various ligands to induce distinct conformational changes and, consequently, diverse biological effects. Due to the poor pharmacokinetic properties of endogenous FPR2 ligands, the aim of our study was to evaluate the pro-resolving effects of a new ureidopropanamide agonist, compound AMS21, in hippocampal organotypic cultures (OHCs) stimulated with lipopolysaccharide (LPS). Moreover, to assess whether AMS21 exerts its action via FPR2 specifically located on microglial cells, we conducted a set of experiments in OHCs depleted of microglial cells using clodronate. We demonstrated that the protective and anti-inflammatory activity of AMS21 manifested as decreased levels of lactate dehydrogenase (LDH), nitric oxide (NO), and proinflammatory cytokines IL-1β and IL-6 release evoked by LPS in OHCs. Moreover, in LPS-stimulated OHCs, AMS21 treatment downregulated NLRP3 inflammasome-related factors (CASP1, NLRP3, PYCARD) and this effect was mediated through FPR2 because it was blocked by the FPR2 antagonist WRW4 pre-treatment. Importantly this beneficial effect of AMS21 was only observed in the presence of microglial FPR2, and absent in OHCs depleted with microglial cells using clodronate. Our results strongly suggest that the compound AMS21 exerts, at nanomolar doses, protective and anti-inflammatory properties and an FPR2 receptor located specifically on microglial cells mediates the anti-inflammatory response of AMS21. Therefore, microglial FPR2 represents a promising target for the enhancement of RoI.

Neuroprotective Effects of Leptin on the APP/PS1 Alzheimer's Disease Mouse Model: Role of Microglial and Neuroinflammation

Background

Microglia are closely linked to Alzheimer's disease (AD) many years ago; however, the pathological mechanisms of AD remain unclear. The purpose of this study was to determine whether leptin affected microglia in the hippocampus of young and aged male APP/PS1 mice.

Objective

In a transgenic model of AD, we investigated the association between intraperitoneal injection of leptin and microglia.

Methods

We intraperitoneal injection of leptin (1mg/kg) every day for one week and analyzed inflammatory markers in microglia in the hippocampus of adult (6 months) and aged (12 months) APP/PS1 mice.

Results

In all leptin treatment group, the brain Aβ levels were decrease. We found increased levels of IL-1β, IL-6 and microglial activation in the hippocampus of adult mice. Using aged mice as an experimental model for chronic neuroinflammation and leptin resistance, the number of Iba-1+ microglia and the levels of IL-1β/IL-6 in the hippocampus were greatly increased as compared to the adult. But between the leptin treatment and un-treatment, there were no difference.

Conclusion

Leptin signaling would regulate the activation of microglia and the release of inflammatory factors, but it is not the only underlying mechanism in the neuroprotective effects of AD pathogenesis.

The prevalence and risk factors for cognitive impairment in obesity and NAFLD

BACKGROUND

Severe obesity may be accompanied by cognitive dysfunction and NAFLD, but the associations remain unclear. We describe the prevalence and features of cognitive dysfunction and examine the associations between cognitive dysfunction and the presence and severity of NAFLD, and the associations between cognitive dysfunction and signs of other obesity-related comorbidities and neuronal damage.

METHODS

A cross-sectional study of patients with a body mass index of 35 kg/m2 underwent evaluation for bariatric surgery. They were screened for adiposity-related comorbidity and underwent a liver biopsy and basic cognitive testing with the Continuous Reaction Time test, the Portosystemic Encephalopathy Syndrome test, and the Stroop Test. A representative subgroup also underwent the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). The primary study outcome was "cognitive impairment," defined as ≥2 abnormal basic cognitive tests and/or an abnormal RBANS. The Triggering Receptor Expressed on Myeloid Cells 2 (TREM2) served as a biomarker for neuronal damage.

RESULTS

We included 180 patients; 72% were women, age 46 ± 12 years, 78% had NAFLD, and 30% with NASH without cirrhosis. 8% were cognitively impaired by the basic tests and 41% by RBANS results. Most impaired were executive and short-time memory functions. There were no associations between cognitive impairment and BMI, NAFLD presence or severity, or metabolic comorbidities. Male sex (OR: 3.67, 95% CI, 1.32-10.27) and using 2 or more psychoactive medications (5.24, 95% CI, 1.34-20.4) were associated with impairment. TREM2 was not associated with cognitive impairment.

CONCLUSIONS

Nearly half of this severely obese study cohort exhibited measurable multidomain cognitive impairment. This was not dependent on NAFLD or another adiposity comorbidity.