Iron accumulation in microglia triggers a cascade of events that leads to altered metabolism and compromised function in APP/PS1 mice

Metabolic reprogramming of the inflammatory response in the nervous system: the crossover between inflammation and metabolism

Metabolism is a fundamental process by which biochemicals are broken down to produce energy (catabolism) or used to build macromolecules (anabolism). Metabolism has received renewed attention as a mechanism that generates molecules that modulate multiple cellular responses. This was first identified in cancer cells as the Warburg effect, but it is also present in immunocompetent cells. Studies have revealed a bidirectional influence of cellular metabolism and immune cell function, highlighting the significance of metabolic reprogramming in immune cell activation and effector functions. Metabolic processes such as glycolysis, oxidative phosphorylation, and fatty acid oxidation have been shown to undergo dynamic changes during immune cell response, facilitating the energetic and biosynthetic demands. This review aims to provide a better understanding of the metabolic reprogramming that occurs in different immune cells upon activation, with a special focus on central nervous system disorders. Understanding the metabolic changes of the immune response not only provides insights into the fundamental mechanisms that regulate immune cell function but also opens new approaches for therapeutic strategies aimed at manipulating the immune system.

Knockdown of microglial iron import gene, Slc11a2, worsens cognitive function and alters microglial transcriptional landscape in a sex-specific manner in the APP/PS1 model of Alzheimer's disease

BACKGROUND

Microglial cell iron load and inflammatory activation are significant hallmarks of late-stage Alzheimer's disease (AD). In vitro, microglia preferentially upregulate the iron importer, divalent metal transporter 1 (DMT1, gene name Slc11a2) in response to inflammatory stimuli, and excess iron can augment cellular inflammation, suggesting a feed-forward loop between iron import mechanisms and inflammatory signaling. However, it is not understood whether microglial iron import mechanisms directly contribute to inflammatory signaling and chronic disease in vivo. These studies determined the effects of microglial-specific knockdown of Slc11a2 on AD-related cognitive decline and microglial transcriptional phenotype.

METHODS

In vitro experiments and RT-qPCR were used to assess a role for DMT1 in amyloid-β-associated inflammation. To determine the effects of microglial Slc11a2 knockdown on AD-related phenotypes in vivo, triple-transgenic Cx3cr1Cre-ERT2;Slc11a2flfl;APP/PS1+or - mice were generated and administered corn oil or tamoxifen to induce knockdown at 5-6 months of age. Both sexes underwent behavioral analyses to assess cognition and memory (12-15 months of age). Hippocampal CD11b+ microglia were magnetically isolated from female mice (15-17 months) and bulk RNA-sequencing analysis was conducted.

RESULTS

DMT1 inhibition in vitro robustly decreased Aβ-induced inflammatory gene expression and cellular iron levels in conditions of excess iron. In vivo, Slc11a2KD APP/PS1 female, but not male, mice displayed a significant worsening of memory function in Morris water maze and a fear conditioning assay, along with significant hyperactivity compared to control WT and APP/PS1 mice. Hippocampal microglia from Slc11a2KD APP/PS1 females displayed significant increases in Enpp2, Ttr, and the iron-export gene, Slc40a1, compared to control APP/PS1 cells. Slc11a2KD cells from APP/PS1 females also exhibited decreased expression of markers associated with subsets of disease-associated microglia (DAMs), such as Apoe, Ctsb, Ly9, Csf1, and Hif1α.

CONCLUSIONS

This work suggests a sex-specific role for microglial iron import gene Slc11a2 in propagating behavioral and cognitive phenotypes in the APP/PS1 model of AD. These data also highlight an association between loss of a DAM-like phenotype in microglia and cognitive deficits in Slc11a2KD APP/PS1 female mice. Overall, this work illuminates an iron-related pathway in microglia that may serve a protective role during disease and offers insight into mechanisms behind disease-related sex differences.

Lactylation: A Novel Post-Translational Modification with Clinical Implications in CNS Diseases

Lactate, an important metabolic product, provides energy to neural cells during energy depletion or high demand and acts as a signaling molecule in the central nervous system. Recent studies revealed that lactate-mediated protein lactylation regulates gene transcription and influences cell fate, metabolic processes, inflammation, and immune responses. This review comprehensively examines the regulatory roles and mechanisms of lactylation in neurodevelopment, neuropsychiatric disorders, brain tumors, and cerebrovascular diseases. This analysis indicates that lactylation has multifaceted effects on central nervous system function and pathology, particularly in hypoxia-induced brain damage. Highlighting its potential as a novel therapeutic target, lactylation may play a significant role in treating neurological diseases. By summarizing current findings, this review aims to provide insights and guide future research and clinical strategies for central nervous system disorders.

Targeting ferroptosis in neuroimmune and neurodegenerative disorders for the development of novel therapeutics

Neuroimmune and neurodegenerative ailments impose a substantial societal burden. Neuroimmune disorders involve the intricate regulatory interactions between the immune system and the central nervous system. Prominent examples of neuroimmune disorders encompass multiple sclerosis and neuromyelitis optica. Neurodegenerative diseases result from neuronal degeneration or demyelination in the brain or spinal cord, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. The precise underlying pathogenesis of these conditions remains incompletely understood. Ferroptosis, a programmed form of cell death characterised by lipid peroxidation and iron overload, plays a pivotal role in neuroimmune and neurodegenerative diseases. In this review, we provide a detailed overview of ferroptosis, its mechanisms, pathways, and regulation during the progression of neuroimmune and neurodegenerative diseases. Furthermore, we summarise the impact of ferroptosis on neuroimmune-related cells (T cells, B cells, neutrophils, and macrophages) and neural cells (glial cells and neurons). Finally, we explore the potential therapeutic implications of ferroptosis inhibitors in diverse neuroimmune and neurodegenerative diseases.

Knockdown of microglial iron import gene, DMT1, worsens cognitive function and alters microglial transcriptional landscape in a sex-specific manner in the APP/PS1 model of Alzheimer's disease

Background

Microglial cell iron load and inflammatory activation are significant hallmarks of late-stage Alzheimer's disease (AD). In vitro, microglia preferentially upregulate the iron importer, divalent metal transporter 1 (DMT1, gene name Slc11a2) in response to inflammatory stimuli, and excess iron can augment cellular inflammation, suggesting a feed-forward loop between iron import mechanisms and inflammatory signaling. However, it is not understood whether microglial iron import mechanisms directly contribute to inflammatory signaling and chronic disease in vivo. These studies determined the effects of microglial-specific knockdown of Slc11a2 on AD-related cognitive decline and microglial transcriptional phenotype.

Methods

In vitro experiments and RT-qPCR were used to assess a role for DMT1 in amyloid-β-associated inflammation. To determine the effects of microglial Slc11a2 knockdown on AD-related phenotypes in vivo, triple-transgenic Cx3cr1 Cre - ERT2 ;Slc11a2 flfl;APP/PS1 + or - mice were generated and administered corn oil or tamoxifen to induce knockdown at 5-6 months of age. Both sexes underwent behavioral analyses to assess cognition and memory (12-15 months of age). Hippocampal CD11b + microglia were magnetically isolated from female mice (15-17 months) and bulk RNA-sequencing analysis was conducted.

Results

DMT1 inhibition in vitro robustly decreased Aβ-induced inflammatory gene expression and cellular iron levels in conditions of excess iron. In vivo, Slc11a2 KD APP/PS1 female, but not male, mice displayed a significant worsening of memory function in Morris water maze and a fear conditioning assay, along with significant hyperactivity compared to control WT and APP/PS1 mice. Hippocampal microglia from Slc11a2 KD APP/PS1 females displayed significant increases in Enpp2, Ttr, and the iron-export gene, Slc40a1, compared to control APP/PS1 cells. Slc11a2 KD cells from APP/PS1 females also exhibited decreased expression of markers associated with disease-associated microglia (DAMs), such as Apoe, Ctsb, Csf1, and Hif1α.

Conclusions

This work suggests a sex-specific role for microglial iron import gene Slc11a2 in propagating behavioral and cognitive phenotypes in the APP/PS1 model of AD. These data also highlight an association between loss of a DAM-like phenotype in microglia and cognitive deficits in Slc11a2 KD APP/PS1 female mice. Overall, this work illuminates an iron-related pathway in microglia that may serve a protective role during disease and offers insight into mechanisms behind disease-related sex differences.

Single-cell RNA sequencing reveals the evolution of the immune landscape during perihematomal edema progression after intracerebral hemorrhage

BACKGROUND

Perihematomal edema (PHE) after post-intracerebral hemorrhage (ICH) has complex pathophysiological mechanisms that are poorly understood. The complicated immune response in the post-ICH brain constitutes a crucial component of PHE pathophysiology. In this study, we aimed to characterize the transcriptional profiles of immune cell populations in human PHE tissue and explore the microscopic differences between different types of immune cells.

METHODS

9 patients with basal ganglia intracerebral hemorrhage (hematoma volume 50-100 ml) were enrolled in this study. A multi-stage profile was developed, comprising Group1 (n = 3, 0-6 h post-ICH, G1), Group2 (n = 3, 6-24 h post-ICH, G2), and Group3 (n = 3, 24-48 h post-ICH, G3). A minimal quantity of edematous tissue surrounding the hematoma was preserved during hematoma evacuation. Single cell RNA sequencing (scRNA-seq) was used to map immune cell populations within comprehensively resected PHE samples collected from patients at different stages after ICH.

RESULTS

We established, for the first time, a comprehensive landscape of diverse immune cell populations in human PHE tissue at a single-cell level. Our study identified 12 microglia subsets and 5 neutrophil subsets in human PHE tissue. What's more, we discovered that the secreted phosphoprotein-1 (SPP1) pathway served as the basis for self-communication between microglia subclusters during the progression of PHE. Additionally, we traced the trajectory branches of different neutrophil subtypes. Finally, we also demonstrated that microglia-produced osteopontin (OPN) could regulate the immune environment in PHE tissue by interacting with CD44-positive cells.

CONCLUSIONS

As a result of our research, we have gained valuable insight into the immune-microenvironment within PHE tissue, which could potentially be used to develop novel treatment modalities for ICH.

Glycometabolic Reprogramming of Microglia in Neurodegenerative Diseases: Insights from Neuroinflammation

Neurodegenerative diseases (ND) are conditions defined by progressive deterioration of the structure and function of the nervous system. Some major examples include Alzheimer's disease (AD), Parkinson's disease (PD), and Amyotrophic lateral sclerosis (ALS). These diseases lead to various dysfunctions, like impaired cognition, memory, and movement. Chronic neuroinflammation may underlie numerous neurodegenerative disorders. Microglia, an important immunocell in the brain, plays a vital role in defending against neuroinflammation. When exposed to different stimuli, microglia are activated and assume different phenotypes, participating in immune regulation of the nervous system and maintaining tissue homeostasis. The immunological activity of activated microglia is affected by glucose metabolic alterations. However, in the context of chronic neuroinflammation, specific alterations of microglial glucose metabolism and their mechanisms of action remain unclear. Thus, in this paper, we review the glycometabolic reprogramming of microglia in ND. The key molecular targets and main metabolic pathways are the focus of this research. Additionally, this study explores the mechanisms underlying microglial glucose metabolism reprogramming in ND and offers an analysis of the most recent therapeutic advancements. The ultimate aim is to provide insights into the development of potential treatments for ND.

Role of ferroptosis in neuroimmunity and neurodegeneration in multiple sclerosis revealed by multi-omics data

Previous studies have found that ferroptosis plays an important role in a variety of neurological diseases. However, the precise role of ferroptosis in the multiple sclerosis patients remains uncertain. We defined and validated a computational metric of ferroptosis levels. The ferroptosis scores were computed using the AUCell method, which reflects the enrichment scores of ferroptosis-related genes through gene ranking. The reliability of the ferroptosis score was assessed using various methods, involving cells induced to undergo ferroptosis by six different ferroptosis inducers. Through a comprehensive approach integrating snRNA-seq, spatial transcriptomics, and spatial proteomics data, we explored the role of ferroptosis in multiple sclerosis. Our findings revealed that among seven sampling regions of different white matter lesions, the edges of active lesions exhibited the highest ferroptosis score, which was associated with activation of the phagocyte system. Remyelination lesions exhibit the lowest ferroptosis score. In the cortex, ferroptosis score were elevated in neurons, relevant to a variety of neurodegenerative disease-related pathways. Spatial transcriptomics demonstrated a significant co-localization among ferroptosis score, neurodegeneration and microglia, which was verified by spatial proteomics. Furthermore, we established a diagnostic model of multiple sclerosis based on 24 ferroptosis-related genes in the peripheral blood. Ferroptosis might exhibits a dual role in the context of multiple sclerosis, relevant to both neuroimmunity and neurodegeneration, thereby presenting a promising and novel therapeutic target. Ferroptosis-related genes in the blood that could potentially serve as diagnostic and prognostic markers for multiple sclerosis.

The Irony of Iron: The Element with Diverse Influence on Neurodegenerative Diseases

Iron accumulation in the brain is a common feature of many neurodegenerative diseases. Its involvement spans across the main proteinopathies involving tau, amyloid-beta, alpha-synuclein, and TDP-43. Accumulating evidence supports the contribution of iron in disease pathologies, but the delineation of its pathogenic role is yet challenged by the complex involvement of iron in multiple neurotoxicity mechanisms and evidence supporting a reciprocal influence between accumulation of iron and protein pathology. Here, we review the major proteinopathy-specific observations supporting four distinct hypotheses: (1) iron deposition is a consequence of protein pathology; (2) iron promotes protein pathology; (3) iron protects from or hinders protein pathology; and (4) deposition of iron and protein pathology contribute parallelly to pathogenesis. Iron is an essential element for physiological brain function, requiring a fine balance of its levels. Understanding of disease-related iron accumulation at a more intricate and systemic level is critical for advancements in iron chelation therapies.

Senescence and aging differentially alter key metabolic pathways in murine brain microglia

Microglia, the resident immune cells of the central nervous system, are critically involved in maintaining brain homeostasis. With age, microglia display morphological and functional alterations that have been associated with cognitive decline and neurodegeneration. Although microglia seem to participate in an increasing number of biological processes which require a high energy demand, little is known about their metabolic regulation under physiological and pathophysiological conditions and during aging/senescence. Here, we determined mRNA expression levels of critical rate limiting enzymes in several key metabolic pathways including glycolysis, pentose phosphate pathway, fatty acid oxidation and synthesis in association with oxidative phosphorylation in microglia, both under aging and senescent conditions. We found strong evidence for different metabolic changes occuring in senescent vs. aged microglia cells. While senescent microglia display a hypermetabolic state as indicated by increased expression of key enzymes involved in glycolysis and pentose phosphate pathway, aging microglia are rather in a state of hypometabolism. Our findings indicate that studies involving aging and senescent microglia require a clear differentiation between these microglial states due to profound metabolic differences observed here. Understanding metabolic changes in senescent and aged microglia may lead to novel strategies to decrease over-activation of these cells due to aging, which is associated to the process of inflamm-aging and neurodegeneration.

Microglial-specific knockdown of iron import gene, Slc11a2, blunts LPS-induced neuroinflammatory responses in a sex-specific manner

Neuroinflammation and microglial iron load are significant hallmarks found in several neurodegenerative diseases. In in vitro systems, microglia preferentially upregulate the iron importer, divalent metal transporter 1 (DMT1, gene name Slc11a2) in response to inflammatory stimuli, and it has been shown that iron can augment cellular inflammation, suggesting a feed-forward loop between mechanisms involved in iron import and inflammatory signaling. However, it is not understood how microglial iron import mechanisms contribute to inflammation in vivo, or whether altering a microglial iron-related gene affects the inflammatory response. These studies aimed to determine the effect of knocking down microglial iron import gene Slc11a2 on the inflammatory response in vivo. We generated a novel model of tamoxifen-inducible, microglial-specific Slc11a2 knockdown using Cx3cr1Cre-ERT2 mice. Transgenic male and female mice were administered intraperitoneal saline or lipopolysaccharide (LPS) and assessed for sickness behavior post-injection. Plasma cytokines and microglial bulk RNA sequencing (RNASeq) analyses were performed at 4 h post-LPS, and microglia were collected for gene expression analysis after 24 h. A subset of mice was assessed in a behavioral test battery following LPS-induced sickness recovery. Control male, but not female, mice significantly upregulated microglial Slc11a2 at 4 and 24 h following LPS. In Slc11a2 knockdown mice, we observed an improvement in the acute behavioral sickness response post-LPS in male, but not female, animals. Microglia from male, but not female, knockdown animals exhibited a significant decrease in LPS-provoked pro-inflammatory cytokine expression after 24 h. RNASeq data from male knockdown microglia 4 h post-LPS revealed a robust downregulation in inflammatory genes including Il6, Tnfα, and Il1β, and an increase in anti-inflammatory and homeostatic markers (e.g., Tgfbr1, Cx3cr1, and Trem2). This corresponded with a profound decrease in plasma pro-inflammatory cytokines 4 h post-LPS. At 4 h, male knockdown microglia also upregulated expression of markers of iron export, iron recycling, and iron homeostasis and decreased iron storage and import genes, along with pro-oxidant markers such as Cybb, Nos2, and Hif1α. Overall, this work elucidates how manipulating a specific gene involved in iron import in microglia alters acute inflammatory signaling and overall cell activation state in male mice. These data highlight a sex-specific link between a microglial iron import gene and the pro-inflammatory response to LPS in vivo, providing further insight into the mechanisms driving neuroinflammatory disease.

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.

Metabolic Reprogramming in Gliocyte Post-cerebral Ischemia/ Reperfusion: From Pathophysiology to Therapeutic Potential

Ischemic stroke is a leading cause of disability and death worldwide. However, the clinical efficacy of recanalization therapy as a preferred option is significantly hindered by reperfusion injury. The transformation between different phenotypes of gliocytes is closely associated with cerebral ischemia/ reperfusion injury (CI/RI). Moreover, gliocyte polarization induces metabolic reprogramming, which refers to the shift in gliocyte phenotype and the overall transformation of the metabolic network to compensate for energy demand and building block requirements during CI/RI caused by hypoxia, energy deficiency, and oxidative stress. Within microglia, the pro-inflammatory phenotype exhibits upregulated glycolysis, pentose phosphate pathway, fatty acid synthesis, and glutamine synthesis, whereas the anti-inflammatory phenotype demonstrates enhanced mitochondrial oxidative phosphorylation and fatty acid oxidation. Reactive astrocytes display increased glycolysis but impaired glycogenolysis and reduced glutamate uptake after CI/RI. There is mounting evidence suggesting that manipulation of energy metabolism homeostasis can induce microglial cells and astrocytes to switch from neurotoxic to neuroprotective phenotypes. A comprehensive understanding of underlying mechanisms and manipulation strategies targeting metabolic pathways could potentially enable gliocytes to be reprogrammed toward beneficial functions while opening new therapeutic avenues for CI/RI treatment. This review provides an overview of current insights into metabolic reprogramming mechanisms in microglia and astrocytes within the pathophysiological context of CI/RI, along with potential pharmacological targets. Herein, we emphasize the potential of metabolic reprogramming of gliocytes as a therapeutic target for CI/RI and aim to offer a novel perspective in the treatment of CI/RI.

Improving Blood Monocyte Energy Metabolism Enhances Its Ability to Phagocytose Amyloid-β and Prevents Alzheimer's Disease-Type Pathology and Cognitive Deficits

Deficiencies in the clearance of peripheral amyloid β (Aβ) play a crucial role in the progression of Alzheimer's disease (AD). Previous studies have shown that the ability of blood monocytes to phagocytose Aβ is decreased in AD. However, the exact mechanism of Aβ clearance dysfunction in AD monocytes remains unclear. In the present study, we found that blood monocytes in AD mice exhibited decreases in energy metabolism, which was accompanied by cellular senescence, a senescence-associated secretory phenotype, and dysfunctional phagocytosis of Aβ. Improving energy metabolism rejuvenated monocytes and enhanced their ability to phagocytose Aβ in vivo and in vitro. Moreover, enhancing blood monocyte Aβ phagocytosis by improving energy metabolism alleviated brain Aβ deposition and neuroinflammation and eventually improved cognitive function in AD mice. This study reveals a new mechanism of impaired Aβ phagocytosis in monocytes and provides evidence that restoring their energy metabolism may be a novel therapeutic strategy for AD.

Cortical Iron Accumulation as an Imaging Marker for Neurodegeneration in Clinical Cognitive Impairment Spectrum: A Quantitative Susceptibility Mapping Study

OBJECTIVE

Cortical iron deposition has recently been shown to occur in Alzheimer's disease (AD). In this study, we aimed to evaluate how cortical gray matter iron, measured using quantitative susceptibility mapping (QSM), differs in the clinical cognitive impairment spectrum.

MATERIALS AND METHODS

This retrospective study evaluated 73 participants (mean age ± standard deviation, 66.7 ± 7.6 years; 52 females and 21 males) with normal cognition (NC), 158 patients with mild cognitive impairment (MCI), and 48 patients with AD dementia. The participants underwent brain magnetic resonance imaging using a three-dimensional multi-dynamic multi-echo sequence on a 3-T scanner. We employed a deep neural network (QSMnet+) and used automatic segmentation software based on FreeSurfer v6.0 to extract anatomical labels and volumes of interest in the cortex. We used analysis of covariance to investigate the differences in susceptibility among the clinical diagnostic groups in each brain region. Multivariable linear regression analysis was performed to study the association between susceptibility values and cognitive scores including the Mini-Mental State Examination (MMSE).

RESULTS

Among the three groups, the frontal (P < 0.001), temporal (P = 0.004), parietal (P = 0.001), occipital (P < 0.001), and cingulate cortices (P < 0.001) showed a higher mean susceptibility in patients with MCI and AD than in NC subjects. In the combined MCI and AD group, the mean susceptibility in the cingulate cortex (β = -216.21, P = 0.019) and insular cortex (β = -276.65, P = 0.001) were significant independent predictors of MMSE scores after correcting for age, sex, education, regional volume, and APOE4 carrier status.

CONCLUSION

Iron deposition in the cortex, as measured by QSMnet+, was higher in patients with AD and MCI than in NC participants. Iron deposition in the cingulate and insular cortices may be an early imaging marker of cognitive impairment related neurodegeneration.

Metabolic regulation of microglial phagocytosis: Implications for Alzheimer's disease therapeutics

Microglia, the resident immune cells of the brain, are increasingly implicated in the regulation of brain health and disease. Microglia perform multiple functions in the central nervous system, including surveillance, phagocytosis and release of a variety of soluble factors. Importantly, a majority of their functions are closely related to changes in their metabolism. This natural inter-dependency between core microglial properties and metabolism offers a unique opportunity to modulate microglial activities via nutritional or metabolic interventions. In this review, we examine the existing scientific literature to synthesize the hypothesis that microglial phagocytosis of amyloid beta (Aβ) aggregates in Alzheimer's disease (AD) can be selectively enhanced via metabolic interventions. We first review the basics of microglial metabolism and the effects of common metabolites, such as glucose, lipids, ketone bodies, glutamine, pyruvate and lactate, on microglial inflammatory and phagocytic properties. Next, we examine the evidence for dysregulation of microglial metabolism in AD. This is followed by a review of in vivo studies on metabolic manipulation of microglial functions to ascertain their therapeutic potential in AD. Finally, we discuss the effects of metabolic factors on microglial phagocytosis of healthy synapses, a pathological process that also contributes to the progression of AD. We conclude by enlisting the current challenges that need to be addressed before strategies to harness microglial phagocytosis to clear pathological protein deposits in AD and other neurodegenerative disorders can be widely adopted.

Fundamental Neurochemistry Review: Microglial immunometabolism in traumatic brain injury

Traumatic brain injury (TBI) is a devastating neurological disorder caused by a physical impact to the brain that promotes diffuse damage and chronic neurodegeneration. Key mechanisms believed to support secondary brain injury include mitochondrial dysfunction and chronic neuroinflammation. Microglia and brain-infiltrating macrophages are responsible for neuroinflammatory cytokine and reactive oxygen species (ROS) production after TBI. Their production is associated with loss of homeostatic microglial functions such as immunosurveillance, phagocytosis, and immune resolution. Beyond providing energy support, mitochondrial metabolic pathways reprogram the pro- and anti-inflammatory machinery in immune cells, providing a critical immunometabolic axis capable of regulating immunologic response to noxious stimuli. In the brain, the capacity to adapt to different environmental stimuli derives, in part, from microglia's ability to recognize and respond to changes in extracellular and intracellular metabolite levels. This capacity is met by an equally plastic metabolism, capable of altering immune function. Microglial pro-inflammatory activation is associated with decreased mitochondrial respiration, whereas anti-inflammatory microglial polarization is supported by increased oxidative metabolism. These metabolic adaptations contribute to neuroimmune responses, placing mitochondria as a central regulator of post-traumatic neuroinflammation. Although it is established that profound neurometabolic changes occur following TBI, key questions related to metabolic shifts in microglia remain unresolved. These include (a) the nature of microglial mitochondrial dysfunction after TBI, (b) the hierarchical positions of different metabolic pathways such as glycolysis, pentose phosphate pathway, glutaminolysis, and lipid oxidation during secondary injury and recovery, and (c) how immunometabolism alters microglial phenotypes, culminating in chronic non-resolving neuroinflammation. In this basic neurochemistry review article, we describe the contributions of immunometabolism to TBI, detail primary evidence of mitochondrial dysfunction and metabolic impairments in microglia and macrophages, discuss how major metabolic pathways contribute to post-traumatic neuroinflammation, and set out future directions toward advancing immunometabolic phenotyping in TBI.

Microglial Metabolic Reprogramming: Emerging Insights and Therapeutic Strategies in Neurodegenerative Diseases

Microglia, the resident immune cells of the central nervous system, play a critical role in maintaining brain homeostasis. However, in neurodegenerative conditions, microglial cells undergo metabolic reprogramming in response to pathological stimuli, including Aβ plaques, Tau tangles, and α-synuclein aggregates. This metabolic shift is characterized by a transition from oxidative phosphorylation (OXPHOS) to glycolysis, increased glucose uptake, enhanced production of lactate, lipids, and succinate, and upregulation of glycolytic enzymes. These metabolic adaptations result in altered microglial functions, such as amplified inflammatory responses and diminished phagocytic capacity, which exacerbate neurodegeneration. This review highlights recent advances in understanding the molecular mechanisms underlying microglial metabolic reprogramming in neurodegenerative diseases and discusses potential therapeutic strategies targeting microglial metabolism to mitigate neuroinflammation and promote brain health. Microglial Metabolic Reprogramming in Neurodegenerative Diseases This graphical abstract illustrates the metabolic shift in microglial cells in response to pathological stimuli and highlights potential therapeutic strategies targeting microglial metabolism for improved brain health.

The Role of Cellular Defense Systems of Ferroptosis in Parkinson's Disease and Alzheimer's Disease

Parkinson's disease (PD) and Alzheimer's disease (AD) are the most common rapidly developing neurodegenerative diseases that lead to serious health and socio-economic consequences. Ferroptosis is a non-apoptotic form of cell death; there is growing evidence to support the notion that ferroptosis is involved in a variety of pathophysiological contexts, and there is increasing interest in the role of ferroptosis in PD and AD. Simultaneously, cells may have evolved four defense systems to counteract the toxic effects of ferroptosis occasioned by lipid peroxidation. This review, which focuses on the analysis of ferroptosis in the PD and AD context, outlines four cellular defense systems against ferroptosis and how each of them is involved in PD and AD.

Metabolic reprogramming and polarization of microglia in Parkinson's disease: Role of inflammasome and iron

Parkinson's disease (PD) is a slowly progressive neurodegenerative disease characterized by α-synuclein aggregation and dopaminergic neuronal death. Recent evidence suggests that neuroinflammation is an early event in the pathogenesis of PD. Microglia are resident immune cells in the central nervous system that can be activated into either pro-inflammatory M1 or anti-inflammatory M2 phenotypes as found in peripheral macrophages. To exert their immune functions, microglia respond to various stimuli, resulting in the flexible regulation of their metabolic pathways. Inflammasomes activation in microglia induces metabolic shift from oxidative phosphorylation to glycolysis, and leads to the polarization of microglia to pro-inflammatory M1 phenotype, finally causing neuroinflammation and neurodegeneration. In addition, iron accumulation induces microglia take an inflammatory and glycolytic phenotype. M2 phenotype microglia is more sensitive to ferroptosis, inhibition of which can attenuate neuroinflammation. Therefore, this review highlights the interplay between microglial polarization and metabolic reprogramming of microglia. Moreover, it will interpret how inflammasomes and iron regulate microglial metabolism and phenotypic shifts, which provides a promising therapeutic target to modulate neuroinflammation and neurodegeneration in PD and other neurodegenerative diseases.

Cortical superficial siderosis is associated with reactive astrogliosis in cerebral amyloid angiopathy

BACKGROUND

Cortical superficial siderosis (cSS) has recently emerged as one of the most important predictors of symptomatic intracerebral hemorrhage and is a risk factor for post-stroke dementia in cerebral amyloid angiopathy (CAA). However, it remains unknown whether cSS is just a marker of severe CAA pathology or may itself contribute to intracerebral hemorrhage risk and cognitive decline. cSS is a chronic manifestation of convexal subarachnoid hemorrhage and is neuropathologically characterized by iron deposits in the superficial cortical layers. We hypothesized that these iron deposits lead to local neuroinflammation, a potentially contributory pathway towards secondary tissue injury.

METHODS

Accordingly, we assessed the distribution of inflammatory markers in relation to cortical iron deposits in post-mortem tissue from CAA cases. Serial sections from the frontal, parietal, temporal, and occipital lobes of nineteen autopsy cases with CAA were stained with Perls' Prussian blue (iron) and underwent immunohistochemistry against glial fibrillary acidic protein (GFAP, reactive astrocytes) and cluster of differentiation 68 (CD68, activated microglia/macrophages). Digitized sections were uploaded to the cloud-based Aiforia® platform, where deep-learning algorithms were utilized to detect tissue, iron deposits, and GFAP-positive and CD68-positive cells.

RESULTS

We observed a strong local relationship between cortical iron deposits and reactive astrocytes. Like cSS-related iron, reactive astrocytes were mainly found in the most superficial layers of the cortex. Although we observed iron within both astrocytes and activated microglia/macrophages on co-stains, there was no clear local relationship between the density of microglia/macrophages and the density of iron deposits.

CONCLUSION

Iron deposition resulting from cSS is associated with local reactive astrogliosis.

Contemporary Antiretroviral Therapy Dysregulates Iron Transport and Augments Mitochondrial Dysfunction in HIV-Infected Human Microglia and Neural-Lineage Cells

HIV-associated cognitive dysfunction during combination antiretroviral therapy (cART) involves mitochondrial dysfunction, but the impact of contemporary cART on chronic metabolic changes in the brain and in latent HIV infection is unclear. We interrogated mitochondrial function in a human microglia (hμglia) cell line harboring inducible HIV provirus and in SH-SY5Y cells after exposure to individual antiretroviral drugs or cART, using the MitoStress assay. cART-induced changes in protein expression, reactive oxygen species (ROS) production, mitochondrial DNA copy number, and cellular iron were also explored. Finally, we evaluated the ability of ROS scavengers or plasmid-mediated overexpression of the antioxidant iron-binding protein, Fth1, to reverse mitochondrial defects. Contemporary antiretroviral drugs, particularly bictegravir, depressed multiple facets of mitochondrial function by 20-30%, with the most pronounced effects in latently infected HIV+ hμglia and SH-SY5Y cells. Latently HIV-infected hμglia exhibited upregulated glycolysis. Increases in total and/or mitochondrial ROS, mitochondrial DNA copy number, and cellular iron accompanied mitochondrial defects in hμglia and SH-SY5Y cells. In SH-SY5Y cells, cART reduced mitochondrial iron-sulfur-cluster-containing supercomplex and subunit expression and increased Nox2 expression. Fth1 overexpression or pre-treatment with N-acetylcysteine prevented cART-induced mitochondrial dysfunction. Contemporary cART impairs mitochondrial bioenergetics in hμglia and SH-SY5Y cells, partly through cellular iron accumulation; some effects differ by HIV latency.

Role of microglial metabolic reprogramming in Parkinson's disease

Parkinson's disease (PD) is a common age-related neurodegenerative disorder characterized by damage to nigrostriatal dopaminergic neurons. Key pathogenic mechanisms underlying PD include alpha-synuclein misfolding and aggregation, impaired protein clearance, mitochondrial dysfunction, oxidative stress, and neuroinflammation. However, to date, no study has confirmed the specific pathogenesis of PD. Similarly, current PD treatment methods still have shortcomings. Although some emerging therapies have proved effective for PD, the specific mechanism still needs further clarification. Metabolic reprogramming, a term first proposed by Warburg, is applied to the metabolic energy characteristics of tumor cells. Microglia have similar metabolic characteristics. Pro-inflammatory M1 type and anti-inflammatory M2 type are the two types of activated microglia, which exhibit different metabolic patterns in glucose, lipid, amino acid, and iron metabolism. Additionally, mitochondrial dysfunction may be involved in microglial metabolic reprogramming by activating various signaling mechanisms. Functional changes in microglia resulting from metabolic reprogramming can cause changes in the brain microenvironment, thus playing an important role in neuroinflammation or tissue repair. The involvement of microglial metabolic reprogramming in PD pathogenesis has been confirmed. Neuroinflammation and dopaminergic neuronal death can effectively be reduced by inhibiting certain metabolic pathways in M1 microglia or reverting M1 cells to the M2 phenotype. This review summarizes the relationship between microglial metabolic reprogramming and PD and provides strategies for PD treatment.

CARD9 attenuates Aβ pathology and modifies microglial responses in an Alzheimer's disease mouse model

Recent advances have highlighted the importance of several innate immune receptors expressed by microglia in Alzheimer's disease (AD). In particular, mounting evidence from AD patients and experimental models indicates pivotal roles for TREM2, CD33, and CD22 in neurodegenerative disease progression. While there is growing interest in targeting these microglial receptors to treat AD, we still lack knowledge of the downstream signaling molecules used by these receptors to orchestrate immune responses in AD. Notably, TREM2, CD33, and CD22 have been described to influence signaling associated with the intracellular adaptor molecule CARD9 to mount downstream immune responses outside of the brain. However, the role of CARD9 in AD remains poorly understood. Here, we show that genetic ablation of CARD9 in the 5xFAD mouse model of AD results in exacerbated amyloid beta (Aβ) deposition, increased neuronal loss, worsened cognitive deficits, and alterations in microglial responses. We further show that pharmacological activation of CARD9 promotes improved clearance of Aβ deposits from the brains of 5xFAD mice. These results help to establish CARD9 as a key intracellular innate immune signaling molecule that regulates Aβ-mediated disease and microglial responses. Moreover, these findings suggest that targeting CARD9 might offer a strategy to improve Aβ clearance in AD.

Hemolytic iron regulation in traumatic brain injury and alcohol use

Hemorrhage is a major component of traumatic brain injury (TBI). Red blood cells, accumulated at the hemorrhagic site, undergo hemolysis upon energy depletion and release free iron into the central nervous system. This iron must be managed to prevent iron neurotoxicity and ferroptosis. As prior alcohol consumption is often associated with TBI, we examined iron regulation in a rat model of chronic alcohol feeding subjected to fluid percussion-induced TBI. We found that alcohol consumption prior to TBI altered the expression profiles of the lipocalin 2/heme oxygenase 1/ferritin iron management system. Notably, unlike TBI alone, TBI following chronic alcohol consumption sustained the expression of all three regulatory proteins for 1, 3, and 7 days post-injury. In addition, alcohol significantly affected TBI-induced expression of ferritin light chain at 3 days post-injury. We also found that alcohol exacerbated TBI-induced activation of microglia at 7 days post-injury. Finally, we propose that microglia may also play a role in iron management through red blood cell clearance.

Identification of biomarkers differentiating Alzheimer's disease from other neurodegenerative diseases by integrated bioinformatic analysis and machine-learning strategies

Background

Alzheimer's disease (AD) is the most common neurodegenerative disease, imposing huge mental and economic burdens on patients and society. The specific molecular pathway(s) and biomarker(s) that distinguish AD from other neurodegenerative diseases and reflect the disease progression are still not well studied.

Methods

Four frontal cortical datasets of AD were integrated to conduct differentially expressed genes (DEGs) and functional gene enrichment analyses. The transcriptional changes after the integrated frontal cortical datasets subtracting the cerebellar dataset of AD were further compared with frontal cortical datasets of frontotemporal dementia and Huntingdon's disease to identify AD-frontal-associated gene expression. Integrated bioinformatic analysis and machine-learning strategies were applied for screening and determining diagnostic biomarkers, which were further validated in another two frontal cortical datasets of AD by receiver operating characteristic (ROC) curves.

Results

Six hundred and twenty-six DEGs were identified as AD frontal associated, including 580 downregulated genes and 46 upregulated genes. The functional enrichment analysis revealed that immune response and oxidative stress were enriched in AD patients. Decorin (DCN) and regulator of G protein signaling 1 (RGS1) were screened as diagnostic biomarkers in distinguishing AD from frontotemporal dementia and Huntingdon's disease of AD. The diagnostic effects of DCN and RGS1 for AD were further validated in another two datasets of AD: the areas under the curve (AUCs) reached 0.8148 and 0.8262 in GSE33000, and 0.8595 and 0.8675 in GSE44770. There was a better value for AD diagnosis when combining performances of DCN and RGS1 with the AUCs of 0.863 and 0.869. Further, DCN mRNA level was correlated to CDR (Clinical Dementia Rating scale) score (r = 0.5066, p = 0.0058) and Braak staging (r = 0.3348, p = 0.0549).

Conclusion

DCN and RGS1 associated with the immune response may be useful biomarkers for diagnosing AD and distinguishing the disease from frontotemporal dementia and Huntingdon's disease. DCN mRNA level reflects the development of the disease.

The Role of Iron Metabolism, Lipid Metabolism, and Redox Homeostasis in Alzheimer's Disease: from the Perspective of Ferroptosis

In the development of Alzheimer's disease (AD), cell death is common. Novel cell death form-ferroptosis is discovered in recent years. Ferroptosis is an iron-regulated programmed cell death mechanism and has been identified in AD clinical samples. Typical characteristics of ferroptosis involve the specific changes in cell morphology, iron-dependent aggregation of reactive oxygen species (ROS) and lipid peroxides, loss of glutathione (GSH), inactivation of glutathione peroxidase 4 (GPX4), and a unique group of regulatory genes. Increasing evidence demonstrates that ferroptosis may be associated with neurological dysfunction in AD. However, the underlying mechanisms have not been fully elucidated. This article reviews the potential role of ferroptosis in AD, the involvement of ferroptosis in the pathological progression of AD through the mechanisms of iron metabolism, lipid metabolism, and redox homeostasis, as well as a range of potential therapies targeting ferroptosis for AD. Intervention strategies based on ferroptosis are promising for Alzheimer's disease treatment at present, but further researches are still needed.

Recent Development in the Understanding of Molecular and Cellular Mechanisms Underlying the Etiopathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that leads to dementia and patient death. AD is characterized by intracellular neurofibrillary tangles, extracellular amyloid beta (Aβ) plaque deposition, and neurodegeneration. Diverse alterations have been associated with AD progression, including genetic mutations, neuroinflammation, blood-brain barrier (BBB) impairment, mitochondrial dysfunction, oxidative stress, and metal ion imbalance.Additionally, recent studies have shown an association between altered heme metabolism and AD. Unfortunately, decades of research and drug development have not produced any effective treatments for AD. Therefore, understanding the cellular and molecular mechanisms underlying AD pathology and identifying potential therapeutic targets are crucial for AD drug development. This review discusses the most common alterations associated with AD and promising therapeutic targets for AD drug discovery. Furthermore, it highlights the role of heme in AD development and summarizes mathematical models of AD, including a stochastic mathematical model of AD and mathematical models of the effect of Aβ on AD. We also summarize the potential treatment strategies that these models can offer in clinical trials.

COVID-19-induced neurological symptoms: focus on the role of metal ions

Neurological symptoms are prevalent in both the acute and post-acute phases of coronavirus disease 2019 (COVID-19), and they are becoming a major concern for the prognosis of COVID-19 patients. Accumulation evidence has suggested that metal ion disorders occur in the central nervous system (CNS) of COVID-19 patients. Metal ions participate in the development, metabolism, redox and neurotransmitter transmission in the CNS and are tightly regulated by metal ion channels. COVID-19 infection causes neurological metal disorders and metal ion channels abnormal switching, subsequently resulting in neuroinflammation, oxidative stress, excitotoxicity, neuronal cell death, and eventually eliciting a series of COVID-19-induced neurological symptoms. Therefore, metal homeostasis-related signaling pathways are emerging as promising therapeutic targets for mitigating COVID-19-induced neurological symptoms. This review provides a summary for the latest advances in research related to the physiological and pathophysiological functions of metal ions and metal ion channels, as well as their role in COVID-19-induced neurological symptoms. In addition, currently available modulators of metal ions and their channels are also discussed. Collectively, the current work offers a few recommendations according to published reports and in-depth reflections to ameliorate COVID-19-induced neurological symptoms. Further studies need to focus on the crosstalk and interactions between different metal ions and their channels. Simultaneous pharmacological intervention of two or more metal signaling pathway disorders may provide clinical advantages in treating COVID-19-induced neurological symptoms.

An aging, pathology burden, and glial senescence build-up hypothesis for late onset Alzheimer's disease

Alzheimer's disease (AD) predominantly occurs as a late onset (LOAD) form involving neurodegeneration and cognitive decline with progressive memory loss. Risk factors that include aging promote accumulation of AD pathologies, such as amyloid-beta and tau aggregates, as well as inflammation and oxidative stress. Homeostatic glial states regulate and suppress pathology buildup; inflammatory states exacerbate pathology by releasing pro-inflammatory cytokines. Multiple stresses likely induce glial senescence, which could decrease supportive functions and reinforce inflammation. In this perspective, we hypothesize that aging first drives AD pathology burden, whereafter AD pathology putatively induces glial senescence in LOAD. We hypothesize that increasing glial senescence, particularly local senescent microglia accumulation, sustains and drives perpetuating buildup and spread of AD pathologies, glial aging, and further senescence. We predict that increasing glial senescence, particularly local senescent microglia accumulation, also transitions individuals from healthy cognition into mild cognitive impairment and LOAD diagnosis. These pathophysiological underpinnings may centrally contribute to LOAD onset, but require further mechanistic investigation.

Lactate and Lactylation in the Brain: Current Progress and Perspectives

As the final product of glycolysis, lactate features not only as an energy substrate, a metabolite, and a signaling molecule in a variety of diseases-such as cancer, inflammation, and sepsis-but also as a regulator of protein lactylation; this is a newly proposed epigenetic modification that is considered to be crucial for energy metabolism and signaling in brain tissues under both physiological and pathological conditions. In this review, evidence on lactylation from studies on lactate metabolism and disease has been summarized, revealing the function of lactate and its receptors in the regulation of brain function and summarizing the levels of lactylation expression in various brain diseases. Finally, the function of lactate and lactylation in the brain and the potential mechanisms of intervention in brain diseases are presented and discussed, providing optimal perspectives for future research on the role of lactylation in the brain.

CSF ferritin in the clinicopathological progression of Alzheimer's disease and associations with APOE and inflammation biomarkers

BACKGROUND

A putative role for iron in driving Alzheimer's disease (AD) progression is complicated by previously reported associations with neuroinflammation, apolipoprotein E and AD proteinopathy. To establish how iron interacts with clinicopathological features of AD and at what disease stage iron influences cognitive outcomes, we investigated the association of cerebrospinal fluid (CSF) biomarkers of iron (ferritin), inflammation (acute phase response proteins) and apolipoproteins with pathological biomarkers (CSF Aβ42/t-tau, p-tau181), clinical staging and longitudinal cognitive deterioration in subjects from the BioFINDER cohort, with replication of key results in the Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort.

METHODS

Ferritin, acute phase response proteins (n=9) and apolipoproteins (n=6) were measured in CSF samples from BioFINDER (n=1239; 4 years cognitive follow-up) participants stratified by cognitive status (cognitively unimpaired, mild cognitive impairment, AD) and for the presence of amyloid and tangle pathology using CSF Aβ42/t-tau (A+) and p-tau181 (T+). The ferritin and apolipoprotein E associations were replicated in the ADNI (n=264) cohort.

RESULTS

In both cohorts, ferritin and apoE were elevated in A-T+ and A+T+ subjects (16%-40%), but not clinical diagnosis. Other apolipoproteins and acute phase response proteins increased with clinical diagnosis, not pathology. CSF ferritin was positively associated with p-tau181, which was mediated by apolipoprotein E. An optimised threshold of ferritin predicted cognitive deterioration in mild cognitive impairment subjects in the BioFINDER cohort, especially those people classified as A-T- and A+T-.

CONCLUSIONS

CSF markers of iron and neuroinflammation have distinct associations with disease stages, while iron may be more intimately associated with apolipoprotein E and tau pathology.

Mitochondrial control of microglial phagocytosis by the translocator protein and hexokinase 2 in Alzheimer's disease

Microglial phagocytosis is an energetically demanding process that plays a critical role in the removal of toxic protein aggregates in Alzheimer's disease (AD). Recent evidence indicates that a switch in energy production from mitochondrial respiration to glycolysis disrupts this important protective microglial function and may provide therapeutic targets for AD. Here, we demonstrate that the translocator protein (TSPO) and a member of its mitochondrial complex, hexokinase-2 (HK), play critical roles in microglial respiratory-glycolytic metabolism and phagocytosis. Pharmacological and genetic loss-of-function experiments showed that TSPO is critical for microglial respiratory metabolism and energy supply for phagocytosis, and its expression is enriched in phagocytic microglia of AD mice. Meanwhile, HK controlled glycolytic metabolism and phagocytosis via mitochondrial binding or displacement. In cultured microglia, TSPO deletion impaired mitochondrial respiration and increased mitochondrial recruitment of HK, inducing a switch to glycolysis and reducing phagocytosis. To determine the functional significance of mitochondrial HK recruitment, we developed an optogenetic tool for reversible control of HK localization. Displacement of mitochondrial HK inhibited glycolysis and improved phagocytosis in TSPO-knockout microglia. Mitochondrial HK recruitment also coordinated the inflammatory switch to glycolysis that occurs in response to lipopolysaccharide in normal microglia. Interestingly, cytosolic HK increased phagocytosis independent of its metabolic activity, indicating an immune signaling function. Alzheimer's beta amyloid drastically stimulated mitochondrial HK recruitment in cultured microglia, which may contribute to microglial dysfunction in AD. Thus, targeting mitochondrial HK may offer an immunotherapeutic approach to promote phagocytic microglial function in AD.

Acute Stress, Induced by IFNγ + Aβ, and Chronic Stress, Induced by Age, Affect Microglia in a Sex-Specific Manner

Microglial phenotype changes in the aged brain, and also in neurodegenerative diseases, and it is generally accepted that these changes at least contribute to the inflammation that can have detrimental effects on brain health. Accumulating data have determined that there are multiple microglial activation states with consistent findings indicating that with stressors including age, a switch towards an inflammatory phenotype occurs. Among the changes that accompany this is a change in metabolism, whereby glycolysis is increased in microglia. Here, we asked whether sex impacted on the response of microglia to two stressors, interferon-γ + amyloid-β (IFNγ  + Aβ) and age. The data show that IFNγ  + Aβ triggered cells from female mice to adopt a glycolytic phenotype. Metabolism was also altered with age; microglia from aged male mice responded by increasing oxidative phosphorylation, and microglial motility was preserved, contrasting with microglia from female mice where motility was compromised. We conclude that sex is a significant variable in the responses of microglia to stressors.

PFKFB3 knockdown attenuates Amyloid β-Induced microglial activation and retinal pigment epithelium disorders in mice

Age-related macular degeneration (AMD) is characterized by progressive accumulation of drusen deposits and retinal pigment epithelium (RPE) disorders. As the main component of drusen, amyloid β (Aβ) plays a critical role in activating microglia and causing neuroinflammation in AMD pathogenesis. However, the role of activated microglia-mediated neuroinflammation in RPE senescence remains unclear. Recent evidence indicates that inflammatory microglia are glycolytic and driven by an increase in 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), an enzyme described as the master regulator of glycolysis. In this study, we mimicked the retinal inflammatory microenvironment of AMD by intravitreal injection of oligomeric Aβ_1-40 in mice, which resulted in activation of microglia and upregulation of PFKFB3. RNA sequencing was performed to evaluate PFKFB3-mediated microglial activation. The effect of microglial activation on RPE disorders was assessed using gene knockout experiments, immunofluorescence, CCK-8 assay, and β-galactosidase staining. Intravitreal Aβ_1-40 injection induced proinflammatory activation of microglia by upregulating PFKFB3 and resulted in RPE disorders, which was verified in heterozygous Pfkfb3-deficient mice (Pfkfb3^+/-) mice, Aβ_1-40-activated microglial cell line BV2, and co-culture of RPE cell line ARPE19. RNA sequencing revealed that PFKFB3 mainly affected innate immune processes during Aβ_1-40-induced retinal inflammation. PFKFB3 knockdown inhibited RPE disorders and rescued the retinal structure and function. Overall, the modulation of PFKFB3-mediated microglial glycolysis and activation is a promising strategy for AMD treatment.

The role of ApoE-mediated microglial lipid metabolism in brain aging and disease

Microglia are a unique population of immune cells resident in the brain that integrate complex signals and dynamically change phenotypes in response to the brain microenvironment. In recent years, single-cell sequencing analyses have revealed profound cellular heterogeneity and context-specific transcriptional plasticity of microglia during brain development, aging, and disease. Emerging evidence suggests that microglia adapt phenotypic plasticity by flexibly reprogramming cellular metabolism to fulfill distinct immune functions. The control of lipid metabolism is central to the appropriate function and homeostasis of the brain. Microglial lipid metabolism regulated by apolipoprotein E (ApoE), a crucial lipid transporter in the brain, has emerged as a critical player in regulating neuroinflammation. The ApoE gene allelic variant, ε4, is associated with a greater risk for neurodegenerative diseases. In this review, we explore novel discoveries in microglial lipid metabolism mediated by ApoE. We elaborate on the functional impact of perturbed microglial lipid metabolism on the underlying pathogenesis of brain aging and disease.

Microglia isolation from aging mice for cell culture: A beginner's guide

Microglia, the innate immune cell of the central nervous system, play significant roles in brain development, maintenance, homeostasis, and neuroinflammation. Although numerous methods have been developed to isolate microglia from embryonic or postnatal mouse brains, still major difficulties exist in isolating microglia from adult mice, often resulting in low yield and risk of cellular activation. Therefore, there is a need for a more efficient method to isolate pure and high-yield microglia from adult mice to study various neurodegenerative diseases. The aim of this study was to develop a fully functional protocol for the isolation of microglia by comparing different protocols. We investigated the efficacy of three protocols in terms of cell yield, purity, cellular activation, cellular aging, and migration properties and proposed the modified protocol (PROTOCOL 1), which provides an optimal yield of functional microglial cells with a minimum of material and equipment and allows young researchers with little experience to isolate microglia and helps them to delve deeper into the world of neuroscience.

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

As individuals age, microglia, the resident immune cells of the central nervous system (CNS), become less effective at preserving brain circuits. Increases in microglial inflammatory activity are thought to contribute to age-related declines in cognitive functions and to transitions toward mild cognitive impairment (MCI) and Alzheimer's disease (AD). As microglia possess receptors for communicating with the CNS environment, pharmacological therapies targeting these pathways hold potential for promoting homeostatic microglial functions within the aging CNS. Preclinical and early phase clinical trials investigating the therapeutic effects of pharmacological agents acting on microglia, including reactive oxygen species, TREM2, fractalkine signaling, the complement cascade, and the NLRP3 inflammasome, are currently underway; however, important questions remain unanswered. Current challenges include target selectivity, as many of the signaling pathways are expressed in other cell types. Furthermore, microglia are a heterogenous cell population with transcriptomic, proteomic, and microscopy studies revealing distinct microglial states, whose activities and abundance shift across the lifespan. For example, homeostatic microglia can transform into pathological states characterized by markers of oxidative stress. Selective pharmacological targeting aimed at limiting transitions to pathological states or promoting homeostatic or protective states, could help to avoid potentially harmful off-target effects on beneficial states or other cell types. In this mini-review we cover current microglial pathways of interest for the prevention and treatment of age-related cognitive decline and CNS disorders of aging focusing on MCI and AD. We also discuss the heterogeneity of microglia described in these conditions and how pharmacological agents could target specific microglial states.

Energy Crisis Links to Autophagy and Ferroptosis in Alzheimer's Disease: Current Evidence and Future Avenues

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases worldwide. The occult nature of the onset and the uncertainty of the etiology largely impede the development of therapeutic strategies for AD. Previous studies revealed that the disorder of energy metabolism in the brains of AD patients appears far earlier than the typical pathological features of AD, suggesting a tight association between energy crisis and the onset of AD. Energy crisis in the brain is known to be induced by the reductions in glucose uptake and utilization, which may be ascribed to the diminished expressions of cerebral glucose transporters (GLUTs), insulin resistance, mitochondrial dysfunctions, and lactate dysmetabolism. Notably, the energy sensors such as peroxisome proliferators-activated receptor (PPAR), transcription factor EB (TFEB), and AMP-activated protein kinase (AMPK) were shown to be the critical regulators of autophagy, which play important roles in regulating beta-amyloid (Aβ) metabolism, tau phosphorylation, neuroinflammation, iron dynamics, as well as ferroptosis. In this study, we summarized the current knowledge on the molecular mechanisms involved in the energy dysmetabolism of AD and discussed the interplays existing between energy crisis, autophagy, and ferroptosis. In addition, we highlighted the potential network in which autophagy may serve as a bridge between energy crisis and ferroptosis in the progression of AD. A deeper understanding of the relationship between energy dysmetabolism and AD may provide new insight into developing strategies for treating AD; meanwhile, the energy crisis in the progression of AD should gain more attention.

Ferroptosis: a potential therapeutic target for Alzheimer's disease

The most prevalent dementia-causing neurodegenerative condition is Alzheimer's disease (AD). The aberrant buildup of amyloid β and tau hyperphosphorylation are the two most well-known theories about the mechanisms underlying AD development. However, a significant number of pharmacological clinical studies conducted around the world based on the two aforementioned theories have not shown promising outcomes, and AD is still not effectively treated. Ferroptosis, a non-apoptotic programmed cell death defined by the buildup of deadly amounts of iron-dependent lipid peroxides, has received more attention in recent years. A wealth of data is emerging to support the role of iron in the pathophysiology of AD. Cell line and animal studies applying ferroptosis modulators to the treatment of AD have shown encouraging results. Based on these studies, we describe in this review the underlying mechanisms of ferroptosis; the role that ferroptosis plays in AD pathology; and summarise some of the research advances in the treatment of AD with ferroptosis modulators. We hope to contribute to the clinical management of AD.

The Role of Insulin Signaling in Hippocampal-Related Diseases: A Focus on Alzheimer's Disease

Alzheimer's disease (AD) is a global concern and has become a major public health event affecting human health. Insulin is a metabolic hormone secreted mainly by the peripheral tissue pancreas. In recent years, more and more evidence has proved that insulin regulates various functions of the brain. The hippocampus, one of the earliest brain regions affected by AD, is widely distributed with insulin receptors. Studies have shown that type 2 diabetes mellitus, characterized by insulin resistance, is closely related to AD, which has drawn extensive attention to the relationship between hippocampal insulin signaling and AD. Therefore, we provide an overview of intranasal insulin administration on memory and its underlying mechanism. We also highlight the molecular link between hippocampal insulin resistance and AD and provide a theoretical basis for finding new therapeutic targets for AD in clinical practice.

The association between cerebrospinal ferritin and soluble triggering receptor expressed on myeloid cells 2 along Alzheimer's continuum

Brain iron accumulation, which is indicated in the cerebrospinal fluid (CSF) ferritin, is associated with the development of Alzheimer's Disease (AD). Studies have indicated that iron deposition might participate in Alzheimer's pathology through the induction of microglial activation. A soluble triggering receptor expressed on myeloid cells 2 (sTrem2) in CSF is increasingly recognized as a reliable indicator for microglia activity in the brain and participates in the development of neuroinflammation. However, the association between CSF ferritin and sTrem2 under the AD continuum has not been well-established. We enrolled individuals from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. Participants were classified into healthy controls (HC, n = 46) and AD continuum (n = 105) in the combined strata of Amyloid/Tau/Neurodegeneration (ATN) mode and Clinical Dementia Rating (CDR) criteria. The associations between CSF ferritin (indicating iron burden) and sTrem2, as well as AD pathology, which is reflected by Aβ42, t-tau, and p-tau in CSF, were explored. CSF ferritin was significantly associated with sTrem2 among all participants (β = 0.517, P < 0.001, FDR < 0.001), HC (β = 0.749, P = 0.006, FDR = 0.010), and AD continuum (β = 0.488, P < 0.001, FDR < 0.001), respectively. However, ferritin predicted the accelerated sTrem2 level in those with high ferritin (β = 0.549, P = 0.036, FDR = 0.045). In conclusion, CSF ferritin serves as a potential biomarker of Trem2-indicated microglia function.

How location and cellular signaling combine to activate the NLRP3 inflammasome

NOD-, LRR-, and pyrin domain-containing 3 (NLRP3) is a cytosolic innate immune sensor of cellular stress signals, triggered by infection and sterile inflammation. Upon detection of an activating stimulus, NLRP3 transitions from an inactive homo-oligomeric multimer into an active multimeric inflammasome, which promotes the helical oligomeric assembly of the adaptor molecule ASC. ASC oligomers provide a platform for caspase-1 activation, leading to the proteolytic cleavage and activation of proinflammatory cytokines in the IL-1 family and gasdermin D, which can induce a lytic form of cell death. Recent studies investigating both the cellular requirement for NLRP3 activation and the structure of NLRP3 have revealed the complex regulation of NLRP3 and the multiple steps involved in its activation. This review presents a perspective on the biochemical and cellular processes controlling the assembly of the NLRP3 inflammasome with particular emphasis on structural regulation and the role of organelles. We also highlight the latest research on metabolic control of this inflammatory pathway and discuss promising clinical targets for intervention.

New Target for Prevention and Treatment of Neuroinflammation: Microglia Iron Accumulation and Ferroptosis

Microglia play an important role in maintaining central nervous system homeostasis and are the major immune cells in the brain. In response to internal or external inflammatory stimuli, microglia are activated and release numerous inflammatory factors, thus leading to neuroinflammation. Inflammation and microglia iron accumulation promote each other and jointly promote the progression of neuroinflammation. Inhibiting microglia iron accumulation prevents neuroinflammation. Ferroptosis is an iron-dependent phospholipid peroxidation-driven type of cell death regulation. Cell iron accumulation causes the peroxidation of cell membrane phospholipids and damages the cell membrane. Ultimately, this process leads to cell ferroptosis. Iron accumulation or phospholipid peroxidation in microglia releases a large number of inflammatory factors. Thus, inhibiting microglia ferroptosis may be a new target for the prevention and treatment of neuroinflammation.

Mitochondrial dysfunction in microglia: a novel perspective for pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease in the elderly globally. Emerging evidence has demonstrated microglia-driven neuroinflammation as a key contributor to the onset and progression of AD, however, the mechanisms that mediate neuroinflammation remain largely unknown. Recent studies have suggested mitochondrial dysfunction including mitochondrial DNA (mtDNA) damage, metabolic defects, and quality control (QC) disorders precedes microglial activation and subsequent neuroinflammation. Therefore, an in-depth understanding of the relationship between mitochondrial dysfunction and microglial activation in AD is important to unveil the pathogenesis of AD and develop effective approaches for early AD diagnosis and treatment. In this review, we summarized current progress in the roles of mtDNA, mitochondrial metabolism, mitochondrial QC changes in microglial activation in AD, and provide comprehensive thoughts for targeting microglial mitochondria as potential therapeutic strategies of AD.

Ultrastructural characterization of dark microglia during aging in a mouse model of Alzheimer's disease pathology and in human post-mortem brain samples

A diverse heterogeneity of microglial cells was previously described in Alzheimer's disease (AD) pathology, including dark microglia, a state characterized by ultrastructural markers of cellular stress. To provide novel insights into the roles of dark microglia during aging in the context of AD pathology, we performed a quantitative density and ultrastructural analysis of these cells using high-throughput scanning electron microscopy in the ventral hippocampus CA1 stratum lacunosum-moleculare of 20-month-old APP-PS1 vs C57BL/6J male mice. The density of dark microglia was significantly higher in APP-PS1 vs C57BL/6J mice, with these cells accounting for nearly half of all microglia observed near amyloid-beta (Aβ) plaques. This dark microglial state interacted more with dystrophic neurites compared to other APP-PS1 microglia and possessed glycogen granules, associated with a metabolic shift toward glycolysis, which provides the first ultrastructural evidence of their presence in microglia. Dark microglia were further observed in aging human post-mortem brain samples showing similar ultrastructural features as in mouse. Overall, our results provide a quantitative ultrastructural characterization of a microglial state associated with cellular stress (i.e., dark microglia) that is primarily restricted near Aβ plaques and dystrophic neurites. The presence of this microglial state in the aging human post-mortem brain is further revealed.

Serotonin 5-HT6 Receptor Ligands and Butyrylcholinesterase Inhibitors Displaying Antioxidant Activity-Design, Synthesis and Biological Evaluation of Multifunctional Agents against Alzheimer's Disease

Neurodegeneration leading to Alzheimer’s disease results from a complex interplay of a variety of processes including misfolding and aggregation of amyloid beta and tau proteins, neuroinflammation or oxidative stress. Therefore, to address more than one of these, drug discovery programmes focus on the development of multifunctional ligands, preferably with disease-modifying and symptoms-reducing potential. Following this idea, herein we present the design and synthesis of multifunctional ligands and biological evaluation of their 5-HT₆ receptor affinity (radioligand binding assay), cholinesterase inhibitory activity (spectroscopic Ellman’s assay), antioxidant activity (ABTS assay) and metal-chelating properties, as well as a preliminary ADMET properties evaluation. Based on the results we selected compound 14 as a well-balanced and potent 5-HT₆ receptor ligand (K_i = 22 nM) and human BuChE inhibitor (IC₅₀ = 16 nM) with antioxidant potential expressed as a reduction of ABTS radicals by 35% (150 μM). The study also revealed additional metal-chelating properties of compounds 15 and 18. The presented compounds modulating Alzheimer’s disease-related processes might be further developed as multifunctional ligands against the disease.

Aβ and Tau Regulate Microglia Metabolism via Exosomes in Alzheimer’s Disease

One of the most striking hallmarks shared by various neurodegenerative diseases, including Alzheimer’s disease (AD), is microglia-mediated neuroinflammation. The main pathological features of AD are extracellular amyloid-β (Aβ) plaques and intracellular tau-containing neurofibrillary tangles in the brain. Amyloid-β (Aβ) peptide and tau protein are the primary components of the plaques and tangles. The crosstalk between microglia and neurons helps maintain brain homeostasis, and the metabolic phenotype of microglia determines its polarizing phenotype. There are currently many research and development efforts to provide disease-modifying therapies for AD treatment. The main targets are Aβ and tau, but whether there is a causal relationship between neurodegenerative proteins, including Aβ oligomer and tau oligomer, and regulation of microglia metabolism in neuroinflammation is still controversial. Currently, the accumulation of Aβ and tau by exosomes or other means of propagation is proposed as a regulator in neurological disorders, leading to metabolic disorders of microglia that can play a key role in the regulation of immune cells. In this review, we propose that the accumulation of Aβ oligomer and tau oligomer can propagate to adjacent microglia through exosomes and change the neuroinflammatory microenvironment by microglia metabolic reprogramming. Clarifying the relationship between harmful proteins and microglia metabolism will help people to better understand the mechanism of crosstalk between neurons and microglia, and provide new ideas for the development of AD drugs.

Regulation of microglia phagocytosis and potential involvement of exercise

Microglia are considered the main phagocytic cells in the central nervous system, remodeling neural circuits by pruning synapses during development. Microglial phagocytosis is also a crucial process in maintaining adult brain homeostasis and clearing potential toxic factors, which are recognized to be associated with neurodegenerative and neuroinflammatory disorders. For example, microglia can engulf amyloid-β plaques, myelin debris, apoptotic cells, and extracellular harmful substances by expressing a variety of specific receptors on the cell surface or by reprogramming intracellular glucose and lipid metabolism processes. Furthermore, physical exercise has been implicated to be one of the non-pharmaceutical treatments for various nervous system diseases, which is closely related to neuroplasticity and microglia functions including proliferation, activation, and phagocytosis. This review focuses on the central regulatory mechanisms related to microglia phagocytosis and the potential role of exercise training in this process.