Microglia priming by interleukin-6 signaling is enhanced in aged mice

Microglial pro-inflammatory mechanisms induced by monomeric C-reactive protein are counteracted by soluble epoxide hydrolase inhibitors

Monomeric C-reactive protein (mCRP) is a pro-inflammatory molecule generated by the dissociation of native CRP. Clinical and experimental studies suggest that mCRP deposition in the brain induces Alzheimer's disease (AD) pathology and cognitive loss. Pathological neuroinflammation is increasingly suggested as relevant in AD. Innovative therapies against neuroinflammation are desperately needed, and inhibitors of the enzyme soluble epoxide hydrolase (sEH) are a promising new generation of anti-inflammatory drugs. Mouse primary microglia and BV2 cell line cultures were exposed to mCRP to analyze its pro-inflammatory mechanisms. sEH inhibitors, both newly synthesized UB-SCG-55 and UB-SCG-65, and the reference agent TPPU, were tested for their anti-inflammatory action against mCRP. Phenotypic changes were analyzed through cell imaging techniques, as well as molecular analysis of inflammatory mediators and gene activation pathways. Results show that mCRP triggers a pro-inflammatory response through three main inflammatory pathways: iNOS, NLRP3, and COX-2, followed by increased cytokine generation. Polarization of microglia toward a M1-like phenotype was confirmed by morphological analysis. Also, mCRP can bind to and cross the cell membrane, providing further insight into its mechanisms of action. sEH inhibitors were effective against mCRP induction of a reactive microglial phenotype. The first-line compound UB-SCG-55 emerged as the most potent anti-inflammatory against mCRP injury. Therefore, the direct activation of microglia by mCRP provides evidence of its role in triggering and exacerbating neurodegenerative diseases with a neuroinflammatory component, such as AD. Furthermore, the protection given by inhibitors of sEH confirms its potential as innovative drugs against deleterious effects of neuroinflammation.

Inflammation and metabolic dysfunction underly anhedonia-like behavior in antidepressant resistant male rats

Inflammation and metabolic dysfunction impair dopamine neurotransmission, which is thought to serve as a critical mechanism underpinning motivational deficits such as anhedonia across a range of psychiatric and neurological disorders. This difficult-to-treat transdiagnostic symptom has important implications for treatment resistant depression (TRD), and may warrant more targeted therapeutic approaches that address the underlying pathophysiological mechanisms. Using the adrenocorticotrophic hormone (ACTH) model of antidepressant treatment resistance we characterized the relationship between antidepressant-like and anhedonia-like behavioral responses to bupropion, mesocortical tyrosine hydroxylase (TH) expression, chronic low-grade inflammation, and metabolic changes in male rats. We demonstrate that chronic ACTH elicited both an antidepressant resistant- and anhedonia-like phenotype in forced swim and effort-related choice behavioral tasks, respectively. This was associated with decreased TH expression in the brain, increased central and peripheral markers of inflammation, and peripheral metabolic disturbances, including impairment of immune cell insulin action. Multivariate analysis revealed that peripheral interleukin-6 (IL-6) levels, immune cell glucose uptake and disturbance of nucleotide metabolism were strongly associated with anhedonia-like behavior. Post-hoc analyses further confirmed strong correlations between TH expression, inflammation and behavioral performance. These data suggest that stress hormone-induced upregulation of inflammation concurrent with the impairment of insulin-mediated glucose uptake into immune cells is associated with disruption of nucleotide metabolism, and potential impaired central dopamine synthesis contributing to the behavioral expression of anhedonia. These results suggest that immunometabolic perturbations concomitant with impaired insulin action at the level of the immune cell result in a metabolically deficient state that directly impacts nucleotide precursors essential for dopamine synthesis and effortful behavior. These results highlight the potential for immune and metabolic markers for individualized treatment of refractory depression and anhedonia.

Pioneering pain management with botulinum toxin type A: From anti-inflammation to regenerative therapies

In the present paper, a comprehensive review was conducted to evaluate the performance of botulinum toxin type A (BTX-A) in managing various types of pain, including myofascial, muscular temporomandibular joint pain, orofacial pain, chronic migraines, and more. Firstly, the mechanism of action and anti-inflammatory effects of BTX-A was introduced. Following this, recent advancements in BTX-A applications were discussed, with an emphasis on emerging combination therapies, regenerative medicine, and personalized treatment strategies. Unlike previous reviews, this study explored a broader spectrum of pain conditions and highlighted BTX-A's versatility and potential as a long-term, minimally invasive pain management option. Additionally, the importance of tailoring BTX-A treatment was emphasized through the integration of biomarkers, genetic factors, and optimized dosing regimens to enhance efficacy and minimize side effects. Novel combinations with regenerative therapies, such as stem cells and tissue engineering, were identified as promising avenues for joint and nerve repair, providing both symptomatic relief and tissue regeneration. Furthermore, digital health tools and artificial intelligence were suggested as innovative approaches to monitor treatment responses and optimize dosing protocols in real-time, advancing personalized pain management. Overall, this review underscores BTX-A's potential in comprehensive and patient-centered pain management and offers recommendations to guide future studies in optimizing BTX-A therapy.

Age-associated microglial transcriptome leads to diminished immunogenicity and dysregulation of MCT4 and P2RY12/P2RY13 related functions

The aging process is marked by a time-dependent deterioration in cellular functions, particularly the immune and neural systems. Understanding the phenotype acquisition of microglia, the sentinel immune cells of the brain, is crucial for understanding the nature of age-related neurological diseases. However, the specific phenotype adopted by microglia during aging remains a subject of debate and is contingent on the chosen experimental model. To address these unresolved questions, we employed a novel and highly controlled approach utilizing long-term cultivated BV-2 microglia, exempted from additional external stimuli. Our findings revealed that aged microglial cells, in comparison to their younger counterparts, acquire a distinct gene expression profile, primarily characterized by alterations in microglial immune response. Indeed, pro-inflammatory stimulated aged and young BV-2 microglia exhibited similar transcriptomic profiles, yet the response intensity to the stimulus was markedly muted in the aged microglia. Functional neurotoxic assays confirmed diminished neuronal death in coculture with aged, activated microglia, underscoring a compromised immune response. Furthermore, a subsequent comparative analysis of aged BV-2 microglia with established transcriptomic microglial datasets from aged mice and humans identified 13 overlapping genes, laying the foundation for identifying core microglial aging signature. Particularly noteworthy were SLC16A3 and P2RY13, which consistently exhibited upregulation and downregulation, respectively, across all datasets. Additionally, four other genes-CAPG, LGALS3BP, NRIP1, and P2RY12-were found to share regulatory patterns in response to both aging and extrinsic activation. An in-depth investigation focused on SLC16A3, encoding the high-affinity lactate transporter MCT4, revealed disruptions in extracellular acidification rate and lactate concentration with age. Microglial purine sensing and motility capacities, regulated by P2RY12/P2RY13, displayed age-related alterations. Remarkably, protein analysis in human brain tissue validated the observed upregulation of MCT4 and downregulation of P2RY12 in aged microglia. In conclusion, our study unveils a distinct phenotype in aged microglia characterized by compromised immune responsiveness. Through the integration of in vitro cultured BV-2 microglia with primary microglia datasets, we identify critical molecular determinants of microglial cellular aging confirmed in human-aged brain tissue. This comprehensive approach offers potential insights for understanding and potentially reprogramming aged microglia, with implications for combating age-related neurological disorders.

From Physiology to Pathology of Astrocytes: Highlighting Their Potential as Therapeutic Targets for CNS Injury

In the mammalian central nervous system (CNS), astrocytes are the ubiquitous glial cells that have complex morphological and molecular characteristics. These fascinating cells play essential neurosupportive and homeostatic roles in the healthy CNS and undergo morphological, molecular, and functional changes to adopt so-called 'reactive' states in response to CNS injury or disease. In recent years, interest in astrocyte research has increased dramatically and some new biological features and roles of astrocytes in physiological and pathological conditions have been discovered thanks to technological advances. Here, we will review and discuss the well-established and emerging astroglial biology and functions, with emphasis on their potential as therapeutic targets for CNS injury, including traumatic and ischemic injury. This review article will highlight the importance of astrocytes in the neuropathological process and repair of CNS injury.

Histamine stimulates human microglia to alter cellular prion protein expression via the HRH2 histamine receptor

Although the cellular prion protein (PrPC) has been evolutionarily conserved, the role of this protein remains elusive. Recent evidence indicates that PrPC may be involved in neuroinflammation and the immune response in the brain, and its expression may be modified via various mechanisms. Histamine is a proinflammatory mediator and neurotransmitter that stimulates numerous cells via interactions with histamine receptors 1-4 (HRH1-4). Since microglia are the innate immune cells of the central nervous system, we hypothesized that histamine-induced stimulation regulates the expression of PrPC in human-derived microglia. The human microglial clone 3 (HMC3) cell line was treated with histamine, and intracellular calcium levels were measured via a calcium flux assay. Cytokine production was monitored by enzyme-linked immunosorbent assay (ELISA). Western blotting and quantitative reverse transcription-polymerase chain reaction were used to determine protein and gene expression of HRH1-4. Flow cytometry and western blotting were used to measure PrPC expression levels. Fluorescence microscopy was used to examine Iba-1 and PrPC localization. HMC3 cells stimulated by histamine exhibited increased intracellular calcium levels and increased release of IL-6 and IL-8, while also modifying PrPC localization. HMC3 stimulated with histamine for 6 and 24 hours exhibited increased surface PrPC expression. Specifically, we found that stimulation of the HRH2 receptor was responsible for changes in surface PrPC. Histamine-induced increases in surface PrPC were attenuated following inhibition of the HRH2 receptor via the HRH2 antagonist ranitidine. These changes were unique to HRH2 activation, as stimulation of HRH1, HRH3, or HRH4 did not alter surface PrPC. Prolonged stimulation of HMC3 decreased PrPC expression following 48 and 72 hours of histamine stimulation. HMC3 cells can be stimulated by histamine to undergo intracellular calcium influx. Surface expression levels of PrPC on HMC3 cells are altered by histamine exposure, primarily mediated by HRH2. While histamine exposure also increases release of IL-6 and IL-8 in these cells, this cytokine release is not fully dependent on PrPC levels, as IL-6 release is only partially reduced and IL-8 release is unchanged under the conditions of HRH2 blockade that prevent PrPC changes. Overall, this suggests that PrPC may play a role in modulating microglial responses.

Microglia ameliorate delirium-like phenotypes in a murine model of acute ventilator-induced lung injury

BACKGROUND

Delirium affects 50-85% of patients on mechanical ventilation and is associated with increased mortality, prolonged hospitalization, and a three-fold higher risk of dementia. Microglia, the resident immune cells of the brain, exhibit both neuroprotective and neurotoxic functions; however, their effects in mechanical ventilation-induced acute lung injury (VILI) are unknown. We hypothesize that in a model of short-term VILI, microglia play a neuroprotective role to ameliorate delirium-like phenotypes.

METHODS

Microglia depletion (n = 18) was accomplished using an orally administered colony stimulating factor 1 receptor inhibitor, while controls received a vehicle diet (n = 18). We then compared extent of neuronal injury in the frontal cortex and hippocampus using cleaved caspase-3 (CC3) and multiple delirium-like behaviors in microglia depleted and non-microglia depleted male mice (C57BL/6 J aged 4-9 months) following VILI. Delirium-like behaviors were evaluated using the Open Field, Elevated Plus Maze, and Y-maze assays. We subsequently evaluated whether repopulation of microglia (n = 14 repopulation, 14 vehicle) restored the phenotypes.

RESULTS

Frontal/hippocampal neuronal CC3 levels were significantly higher in microglia depleted VILI mice compared to vehicle-treated VILI controls (p < 0.01, p < 0.01, respectively). These structural changes were accompanied by worse delirium-like behaviors in microglia depleted VILI mice compared to vehicle controls. Specifically, microglia depleted VILI mice demonstrated: (1) significantly increased time in the periphery of the Open Field (p = 0.01), (2) significantly increased coefficient of variation (p = 0.02), (3) trend towards reduced time in the open arms of the Elevated Plus Maze (p = 0.09), and (4) significantly decreased spontaneous alternations on Y-maze (p < 0.01). There was a significant inverse correlation between frontal CC3 and percent spontaneous alternations (R2 = 0.51, p < 0.01). Microglia repopulation showed a near-complete return to vehicle levels of delirium like-behaviors.

CONCLUSIONS

This study demonstrates that microglia depletion exacerbates structural and functional delirium-like phenotypes after VILI, while subsequent repopulation of microglia restores these phenotypes. These findings suggest a neuroprotective role for microglia in ameliorating neuronal and functional delirium-like phenotypes and call for consideration of interventions that leverage endogenous microglia physiology to mitigate delirium.

Microglia signaling in health and disease - Implications in sex-specific brain development and plasticity

Microglia, the intrinsic neuroimmune cells residing in the central nervous system (CNS), exert a pivotal influence on brain development, homeostasis, and functionality, encompassing critical roles during both aging and pathological states. Recent advancements in comprehending brain plasticity and functions have spotlighted conspicuous variances between male and female brains, notably in neurogenesis, neuronal myelination, axon fasciculation, and synaptogenesis. Nevertheless, the precise impact of microglia on sex-specific brain cell plasticity, sculpting diverse neural network architectures and circuits, remains largely unexplored. This article seeks to unravel the present understanding of microglial involvement in brain development, plasticity, and function, with a specific emphasis on microglial signaling in brain sex polymorphism. Commencing with an overview of microglia in the CNS and their associated signaling cascades, we subsequently probe recent revelations regarding molecular signaling by microglia in sex-dependent brain developmental plasticity, functions, and diseases. Notably, C-X3-C motif chemokine receptor 1 (CX3CR1), triggering receptors expressed on myeloid cells 2 (TREM2), calcium (Ca2+), and apolipoprotein E (APOE) emerge as molecular candidates significantly contributing to sex-dependent brain development and plasticity. In conclusion, we address burgeoning inquiries surrounding microglia's pivotal role in the functional diversity of developing and aging brains, contemplating their potential implications for gender-tailored therapeutic strategies in neurodegenerative diseases.

Increased alpha-synuclein and neuroinflammation in the substantia nigra triggered by systemic inflammation are reversed by targeted inhibition of the receptor for advanced glycation end products (RAGE)

The receptor for advanced glycation end products (RAGE) is a protein of the immunoglobulin superfamily capable of regulating inflammation. Considering the role of this receptor in the initiation and establishment of neuroinflammation, and the limited understanding of the function of RAGE in the maintenance of this condition, this study describes the effects of RAGE inhibition in the brain, through an intranasal treatment with the antagonist FPS-ZM1, in an animal model of chronic neuroinflammation induced by acute intraperitoneal injection of lipopolysaccharide (LPS). Seventy days after LPS administration (2 mg/kg, i.p.), Wistar rats received, intranasally, 1.2 mg of FPS-ZM1 over 14 days. On days 88 and 89, the animals were submitted to the open-field test and were killed on day 90 after the intraperitoneal injection of LPS. Our results indicate that blockade of encephalic RAGE attenuates LPS-induced chronic neuroinflammation in different brain regions. Furthermore, we found that intranasal FPS-ZM1 administration reduced levels of gliosis markers, RAGE ligands, and α-synuclein in the substantia nigra pars compacta. Additionally, the treatment also reversed the increase in S100 calcium-binding protein B (RAGE ligand) in the cerebrospinal fluid and the cognitive-behavioral deficits promoted by LPS-less time spent in the central zone of the open-field arena (more time in the lateral zones), decreased total distance traveled, and increased number of freezing episodes. In summary, our study demonstrates the prominent role of RAGE in the maintenance of a chronic neuroinflammatory state triggered by a single episode of systemic inflammation and also points to possible future RAGE-based therapeutic approaches to treat conditions in which chronic neuroinflammation and increased α-synuclein levels could play a relevant role, such as in Parkinson's disease.

Exploratory assessment of the effect of systemic administration of soluble glycoprotein 130 on cognitive performance and chemokine levels in a mouse model of experimental traumatic brain injury

Uncontrolled neuroinflammation mediates traumatic brain injury (TBI) pathology and impairs recovery. Interleukin-6 (IL-6), a pleiotropic inflammatory regulator, is associated with poor clinical TBI outcomes. IL-6 operates via classical-signaling through membrane-bound IL-6 receptor (IL-6R) and trans-signaling through soluble IL-6 receptor (s)IL-6R. IL-6 trans-signaling specifically contributes to neuropathology, making it a potential precision therapeutic TBI target. Soluble glycoprotein 130 (sgp130) prevents IL-6 trans-signaling, sparing classical signaling, thus is a possible treatment. Mice received either controlled cortical impact (CCI) (6.0 ± 0.2 m/s; 2 mm; 50-60ms) or sham procedures. Vehicle (VEH) or sgp130-Fc was subcutaneously administered to sham (VEH or 1 µg) and CCI (VEH, 0.25 µg or 1 µg) mice on days 1, 4, 7, 10 and 13 post-surgery to assess effects on cognition [Morris Water Maze (MWM)] and ipsilateral hemisphere IL-6 related biomarkers (day 21 post-surgery). CCI + sgp130-Fc groups (0.25 µg and 1 µg) were combined for analysis given similar behavior/biomarker outcomes. CCI + VEH mice had longer latencies and path lengths to the platform and increased peripheral zone time versus Sham + VEH and Sham + sgp130-Fc mice, suggesting injury-induced impairments in learning and anxiety. CCI + sgp130-Fc mice had shorter platform latencies and path lengths and had decreased peripheral zone time, indicating a therapeutic benefit of sgp130-Fc after injury on learning and anxiety. Interestingly, Sham + sgp130-Fc mice had shorter platform latencies, path lengths and peripheral zone times than Sham + VEH mice, suggesting a beneficial effect of sgp130-Fc, independent of injury. CCI + VEH mice had increased brain IL-6 and decreased sgp130 levels versus Sham + VEH and Sham + sgp130-Fc mice. There was no treatment effect on IL-6, sIL6-R or sgp130 in Sham + VEH versus Sham + sgp130-Fc mice. There was also no treatment effect on IL-6 in CCI + VEH versus CCI + sgp130-Fc mice. However, CCI + sgp130-Fc mice had increased sIL-6R and sgp130 versus CCI + VEH mice, demonstrating sgp130-Fc treatment effects on brain biomarkers. Inflammatory chemokines (MIP-1β, IP-10, MIG) were increased in CCI + VEH mice versus Sham + VEH and Sham + sgp130-Fc mice. However, CCI + sgp130-Fc mice had decreased chemokine levels versus CCI + VEH mice. IL-6 positively correlated, while sgp130 negatively correlated, with chemokine levels. Overall, we found that systemic sgp130-Fc treatment after CCI improved learning, decreased anxiety and reduced CCI-induced brain chemokines. Future studies will explore sex-specific dosing and treatment mechanisms for sgp130-Fc therapy.

Microglia at the blood brain barrier in health and disease

The blood brain barrier (BBB) plays a crucial role in maintaining brain homeostasis by selectively preventing the entry of substances from the peripheral blood into the central nervous system (CNS). Comprised of endothelial cells, pericytes, and astrocytes, this highly regulated barrier encompasses the majority of the brain's vasculature. In addition to its protective function, the BBB also engages in significant crosstalk with perivascular macrophages (MΦ) and microglia, the resident MΦ of the brain. These interactions play a pivotal role in modulating the activation state of cells comprising the BBB, as well as MΦs and microglia, themselves. Alterations in systemic metabolic and inflammatory states can promote endothelial cell dysfunction, reducing the integrity of the BBB and potentially allowing peripheral blood factors to leak into the CNS compartment. This may mediate activation of perivascular MΦs, microglia, and astrocytes, and initiate further immune responses within the brain parenchyma, suggesting neuroinflammation can be triggered by signaling from the periphery, without primary injury or disease originating within the CNS. The intricate interplay between the periphery and the CNS through the BBB highlights the importance of understanding the role of microglia in mediating responses to systemic challenges. Despite recent advancements, our understanding of the interactions between microglia and the BBB is still in its early stages, leaving a significant gap in knowledge. However, emerging research is shedding light on the involvement of microglia at the BBB in various conditions, including systemic infections, diabetes, and ischemic stroke. This review aims to provide a comprehensive overview of the current research investigating the intricate relationship between microglia and the BBB in health and disease. By exploring these connections, we hope to advance our understanding of the role of brain immune responses to systemic challenges and their impact on CNS health and pathology. Uncovering these interactions may hold promise for the development of novel therapeutic strategies for neurological conditions that involve immune and vascular mechanisms.

Astrocytes in ischemic stroke: Crosstalk in central nervous system and therapeutic potential

In the central nervous system (CNS), a large group of glial cells called astrocytes play important roles in both physiological and disease conditions. Astrocytes participate in the formation of neurovascular units and interact closely with other cells of the CNS, such as microglia and neurons. Stroke is a global disease with high mortality and disability rate, most of which are ischemic stroke. Significant strides in understanding astrocytes have been made over the past few decades. Astrocytes respond strongly to ischemic stroke through a process known as activation or reactivity. Given the important role played by reactive astrocytes (RAs) in different spatial and temporal aspects of ischemic stroke, there is a growing interest in the potential therapeutic role of astrocytes. Currently, interventions targeting astrocytes, such as mediating astrocyte polarization, reducing edema, regulating glial scar formation, and reprogramming astrocytes, have been proven in modulating the progression of ischemic stroke. The aforementioned potential interventions on astrocytes and the crosstalk between astrocytes and other cells of the CNS will be summarized in this review.

Glaucoma: from pathogenic mechanisms to retinal glial cell response to damage

Glaucoma is a neurodegenerative disease of the retina characterized by the irreversible loss of retinal ganglion cells (RGCs) leading to visual loss. Degeneration of RGCs and loss of their axons, as well as damage and remodeling of the lamina cribrosa are the main events in the pathogenesis of glaucoma. Different molecular pathways are involved in RGC death, which are triggered and exacerbated as a consequence of a number of risk factors such as elevated intraocular pressure (IOP), age, ocular biomechanics, or low ocular perfusion pressure. Increased IOP is one of the most important risk factors associated with this pathology and the only one for which treatment is currently available, nevertheless, on many cases the progression of the disease continues, despite IOP control. Thus, the IOP elevation is not the only trigger of glaucomatous damage, showing the evidence that other factors can induce RGCs death in this pathology, would be involved in the advance of glaucomatous neurodegeneration. The underlying mechanisms driving the neurodegenerative process in glaucoma include ischemia/hypoxia, mitochondrial dysfunction, oxidative stress and neuroinflammation. In glaucoma, like as other neurodegenerative disorders, the immune system is involved and immunoregulation is conducted mainly by glial cells, microglia, astrocytes, and Müller cells. The increase in IOP produces the activation of glial cells in the retinal tissue. Chronic activation of glial cells in glaucoma may provoke a proinflammatory state at the retinal level inducing blood retinal barrier disruption and RGCs death. The modulation of the immune response in glaucoma as well as the activation of glial cells constitute an interesting new approach in the treatment of glaucoma.

A glance through the effects of CD4+ T cells, CD8+ T cells, and cytokines on Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia. Unfortunately, despite numerous studies, an effective treatment for AD has not yet been established. There is remarkable evidence indicating that the innate immune mechanism and adaptive immune response play significant roles in the pathogenesis of AD. Several studies have reported changes in CD8+ and CD4+ T cells in AD patients. This mini-review article discusses the potential contribution of CD4+ and CD8+ T cells reactivity to amyloid β (Aβ) protein in individuals with AD. Moreover, this mini-review examines the potential associations between T cells, heme oxygenase (HO), and impaired mitochondria in the context of AD. While current mathematical models of AD have not extensively addressed the inclusion of CD4+ and CD8+ T cells, there exist models that can be extended to consider AD as an autoimmune disease involving these T cell types. Additionally, the mini-review covers recent research that has investigated the utilization of machine learning models, considering the impact of CD4+ and CD8+ T cells.

Interleukin-6 in Traumatic Brain Injury: A Janus-Faced Player in Damage and Repair

Traumatic brain injury (TBI) is a common and often devastating illness, with wide-ranging public health implications. In addition to the primary injury, victims of TBI are at risk for secondary neurological injury by numerous mechanisms. Current treatments are limited and do not target the profound immune response associated with injury. This immune response reflects a convergence of peripheral and central nervous system-resident immune cells whose interaction is mediated in part by a disruption in the blood-brain barrier (BBB). The diverse family of cytokines helps to govern this communication and among these, Interleukin (IL)-6 is a notable player in the immune response to acute neurological injury. It is also a well-established pharmacological target in a variety of other disease contexts. In TBI, elevated IL-6 levels are associated with worse outcomes, but the role of IL-6 in response to injury is double-edged. IL-6 promotes neurogenesis and wound healing in animal models of TBI, but it may also contribute to disruptions in the BBB and the progression of cerebral edema. Here, we review IL-6 biology in the context of TBI, with an eye to clarifying its controversial role and understanding its potential as a target for modulating the immune response in this disease.

In silico evaluation of the role of lisdexamfetamine on attention-deficit/hyperactivity disorder common psychiatric comorbidities: mechanistic insights on binge eating disorder and depression

Attention-deficit/hyperactivity disorder (ADHD) is a psychiatric condition well recognized in the pediatric population that can persist into adulthood. The vast majority of patients with ADHD present psychiatric comorbidities that have been suggested to share, to some extent, the pathophysiological mechanism of ADHD. Lisdexamfetamine (LDX) is a stimulant prodrug approved for treating ADHD and, in the US, also for binge eating disorder (BED). Herein, we evaluated, through a systems biology-based in silico method, the efficacy of a virtual model of LDX (vLDX) as ADHD treatment to improve five common ADHD psychiatric comorbidities in adults and children, and we explored the molecular mechanisms behind LDX's predicted efficacy. After the molecular characterization of vLDX and the comorbidities (anxiety, BED, bipolar disorder, depression, and tics disorder), we created a protein-protein interaction human network to which we applied artificial neural networks (ANN) algorithms. We also generated virtual populations of adults and children-adolescents totaling 2,600 individuals and obtained the predicted protein activity from Therapeutic Performance Mapping System models. The latter showed that ADHD molecular description shared 53% of its protein effectors with at least one studied psychiatric comorbidity. According to the ANN analysis, proteins targeted by vLDX are predicted to have a high probability of being related to BED and depression. In BED, vLDX was modeled to act upon neurotransmission and neuroplasticity regulators, and, in depression, vLDX regulated the hypothalamic-pituitary-adrenal axis, neuroinflammation, oxidative stress, and glutamatergic excitotoxicity. In conclusion, our modeling results, despite their limitations and although requiring in vitro or in vivo validation, could supplement the design of preclinical and potentially clinical studies that investigate treatment for patients with ADHD with psychiatric comorbidities, especially from a molecular point of view.

Ceftriaxone ameliorates hippocampal synapse loss by inhibiting microglial/macrophages activation in glial glutamate transporter-1 dependent manner in the APP/PS1 mouse model of Alzheimer's disease

Synapse loss is a major contributor to cognitive dysfunction in Alzheimer's disease (AD). Impairments in the expression and/or glutamate uptake activity of glia glutamate transporter-1 (GLT-1) contribute to synapse loss in AD. Hence, targeting the restoration of GLT-1 activity may have potential for alleviating synapse loss in AD. Ceftriaxone (Cef) can upregulate the expression and glutamate uptake activity of GLT-1 in many disease models, including those for AD. The present study investigated the effects of Cef on synapse loss and the role of GLT-1 using APP/PS1 transgenic and GLT-1 knockdown APP/PS1 AD mice. Furthermore, the involvement of microglia in the process was investigated due to its important role in synapse loss in AD. We found that Cef treatment significantly ameliorated synapse loss and dendritic degeneration in APP/PS1 AD mice, evidenced by an increased dendritic spine density, decreased dendritic beading density, and upregulated levels of postsynaptic density protein 95 (PSD95) and synaptophysin. The effects of Cef were suppressed by GLT-1 knockdown in GLT-1^+/-/APP/PS1 AD mice. Simultaneously, Cef treatment inhibited ionized calcium binding adapter molecule 1 (Iba1) expression, decreased the proportion of CD11b⁺CD45^hi cells, declined interleukin-6 (IL-6) content, and reduced the co-expression of Iba1 with PSD95 or synaptophysin in APP/PS1 AD mice. In conclusion, Cef treatment ameliorated synapse loss and dendritic degeneration in APP/PS1 AD mice in a GLT-1-dependent manner, and the inhibitory effect of Cef on the activation of microglia/macrophages and their phagocytosis for synaptic elements contributed to the mechanism.

The Vicious Cycle of Melanoma-Microglia Crosstalk: Inter-Melanoma Variations in the Brain-Metastasis-Promoting IL-6/JAK/STAT3 Signaling Pathway

Previous studies from our lab demonstrated that the crosstalk between brain-metastasizing melanoma cells and microglia, the macrophage-like cells of the central nervous system, fuels progression to metastasis. In the present study, an in-depth investigation of melanoma-microglia interactions elucidated a pro-metastatic molecular mechanism that drives a vicious melanoma-brain-metastasis cycle. We employed RNA-Sequencing, HTG miRNA whole transcriptome assay, and reverse phase protein arrays (RPPA) to analyze the impact of melanoma-microglia interactions on sustainability and progression of four different human brain-metastasizing melanoma cell lines. Microglia cells exposed to melanoma-derived IL-6 exhibited upregulated levels of STAT3 phosphorylation and SOCS3 expression, which, in turn, promoted melanoma cell viability and metastatic potential. IL-6/STAT3 pathway inhibitors diminished the pro-metastatic functions of microglia and reduced melanoma progression. SOCS3 overexpression in microglia cells evoked microglial support in melanoma brain metastasis by increasing melanoma cell migration and proliferation. Different melanomas exhibited heterogeneity in their microglia-activating capacity as well as in their response to microglia-derived signals. In spite of this reality and based on the results of the present study, we concluded that the activation of the IL-6/STAT3/SOCS3 pathway in microglia is a major mechanism by which reciprocal melanoma-microglia signaling engineers the interacting microglia to reinforce the progression of melanoma brain metastasis. This mechanism may operate differently in different melanomas.

Chronic acetyl-L-carnitine treatment alleviates behavioral deficits and neuroinflammation through enhancing microbiota derived-SCFA in valproate model of autism

Autism spectrum disorder is characterized by a variety of cellular and molecular abnormalities which leads to autism-associated behaviors. Besides behavioral defects, these individuals also suffer from various associated disorders such as gastrointestinal deficit, altered gut microbiota composition and their metabolite. This study examined the effect of ALC on microbiota SCFA production and its effects on brain inflammation in VPA autism model. After prenatal exposure to valproate (600 mg/kg, i.p.) on embryonic day 12.5, followed by ALC treatment (100 mg/kg during postnatal days 23-51, p.o.), ASD-like behaviors, SCFAs amount in feces, intestine integrity (Occludin and ZO-1 tight junction proteins), systemic and brain inflammation (TNF-α and IL-1β) were assessed. Then, Golgi-Cox staining and Western blot for Iba1 protein were utilized to identify the changes in microglia profile in cerebral cortex. In the VPA model, we found that induction of autism was associated with demoted levels of SCFAs in feces and disintegration of intestine tissue which led to elevated level of TNF-α in the plasma. Further, we characterized an increased number of microglia in our histology evaluation and Iba1 protein in cerebral cortex. We also observed elevated level of TNF-α and IL-1β in the cerebral cortex of VPA rat. All these abnormalities were significantly alleviated by ALC treatment. Overall, our findings suggest that alleviation of behavioral abnormalities by ALC therapy in the VPA model of autism is associated with an improvement in the gut microbiota SCFAs, intestinal barrier and recovery of microglia and inflammation in the brain.

Role of Polymorphonuclear Myeloid-Derived Suppressor Cells and Neutrophils in Ischemic Stroke

Background Immune cells play a vital role in the pathology of ischemic stroke. Neutrophils and polymorphonuclear myeloid-derived suppressor cells share a similar phenotype and have attracted increasing attention in immune regulation research, yet their dynamics in ischemic stroke remain elusive. Methods and Results Mice were randomly divided into 2 groups and intraperitoneally treated with anti-Ly6G (lymphocyte antigen 6 complex locus G) monoclonal antibody or saline. Distal middle cerebral artery occlusion and transient middle cerebral artery occlusion were applied to induce experimental stroke, and mice mortality was recorded until 28 days after stroke. Green fluorescent nissl staining was used to measure infarct volume. Cylinder and foot fault tests were used to evaluate neurological deficits. Immunofluorescence staining was conducted to confirm Ly6G neutralization and detect activated neutrophils and CD11b⁺Ly6G⁺ cells. Fluorescence-activated cell sorting was performed to evaluate polymorphonuclear myeloid-derived suppressor cell accumulation in brains and spleens after stroke. Anti-Ly6G antibody successfully depleted Ly6G expression in mice cortex but did not alter cortical physiological vasculature. Prophylactic anti-Ly6G antibody treatment ameliorated ischemic stroke outcomes in the subacute phase. Moreover, using immunofluorescence staining, we found that anti-Ly6G antibody suppressed activated neutrophil infiltration into parenchyma and decreased neutrophil extracellular trap formation in penumbra after stroke. Additionally, prophylactic anti-Ly6G antibody treatment reduced polymorphonuclear myeloid-derived suppressor cell accumulation in the ischemic hemisphere. Conclusions Our study suggested a protective effect of prophylactic anti-Ly6G antibody administration against ischemic stroke by reducing activated neutrophil infiltration and neutrophil extracellular trap formation in parenchyma and suppressing polymorphonuclear myeloid-derived suppressor cell accumulation in the brain. This study may provide a novel therapeutic approach for ischemic stroke.

Age and sex drive differential behavioral and neuroimmune phenotypes during postoperative pain

Surgical procedures in the geriatric population are steadily increasing, driven by improved healthcare technologies and longer lifespans. However, effective postoperative pain treatments are lacking, and this diminishes quality of life and recovery. Here we present one of the first preclinical studies to pursue sex- and age-specific differences in postoperative neuroimmune phenotypes and pain. We found that aged males, but not females, had a delayed onset of mechanical hypersensitivity post-surgery and faster resolution than young counterparts. This sex-specific age effect was accompanied by decreased paw innervation and increased local inflammation. Additionally, we find evidence of an age-dependent decrease in hyperalgesic priming and perioperative changes in nociceptor populations and spinal microglia in the aged. These findings suggest that impaired neuronal function and maladaptive inflammatory mechanisms influence postoperative pain development in advanced age. Elucidation of these neuroimmune phenotypes across age and sex enables the development of novel therapies that can be tailored for improved pain relief.

Serum levels of IL-6 are associated with cognitive impairment in the salus in apulia population-based study

Growing evidence suggests that inflammation contributes to brain aging and neurodegeneration. This study investigates the relationship between global cognitive as well executive function and the inflammatory markers IL-6, CRP, and TNF-α in a population-based study of older adults. A population-based sample, of older people in Southern Italy, was enrolled. We measured serum levels of IL-6, CRP, and TNF-α. We also administered two neuropsychological tests: Mini-Mental State Examination and Frontal Assessment Battery. Rank-based regression models were performed to investigate the relationship between inflammatory markers and cognitive functions, including major demographic and clinical confounders for adjustment. The sample consisted of 1929 subjects aged between 65 and 95 years. Multivariate linear regression analysis revealed that higher serum levels of IL-6 were associated with lower MMSE and FAB scores even after adjustment for demographic data and cardiovascular risk factors. No significant associations were found between cognitive functioning and serum levels of CRP and TNF-α. Our results suggest that higher levels of IL-6 were associated with cognitive impairment in an older adult population of Southern Italy.

Clcf1/Crlf1a-mediated signaling is neuroprotective and required for Müller glia proliferation in the light-damaged zebrafish retina

Zebrafish possess the innate ability to fully regenerate any neurons lost following a retinal injury. This response is mediated by Müller glia that reprogram and divide asymmetrically to produce neuronal precursor cells that differentiate into the lost neurons. However, little is understood about the early signals that induce this response. Ciliary neurotrophic factor (CNTF) was previously shown to be both neuroprotective and pro-proliferative within the zebrafish retina, however CNTF is not expressed following injury. Here we demonstrate that alternative ligands of the Ciliary neurotrophic factor receptor (CNTFR), such as Cardiotrophin-like cytokine factor 1 (Clcf1) and Cytokine receptor-like factor 1a (Crlf1a), are expressed within Müller glia of the light-damaged retina. We found that CNTFR, Clcf1, and Crlf1a are required for Müller glia proliferation in the light-damaged retina. Furthermore, intravitreal injection of CLCF1/CRLF1 protected against rod photoreceptor cell death in the light-damaged retina and induced proliferation of rod precursor cells in the undamaged retina, but not Müller glia. While rod precursor cell proliferation was previously shown to be Insulin-like growth factor 1 receptor (IGF-1R)-dependent, co-injection of IGF-1 with CLCF1/CRLF1 failed to induce further proliferation of either Müller glia or rod precursor cells. Together, these findings demonstrate that CNTFR ligands have a neuroprotective effect and are required for induction of Müller glia proliferation in the light-damaged zebrafish retina.

Defining the role of Interleukin-6 for the development of perioperative neurocognitive disorders: Evidence from clinical and preclinical studies

For most, staying "mentally sharp" as they age is a very high priority that may be thwarted by the consequences of a postoperative complication unrelated to the disorder which necessitated the surgical intervention. Perioperative neurocognitive disorder (PND) is an overarching term for cognitive impairment in surgical patients, that includes conditions from delirium to dementia, affecting more than 7 million patients annually in the US, and which threatens both functional independence and life. Clinical trials and meta-analyses have identified the association between PNDs and increased perioperative levels of Interleukin-6 (IL-6), a pleiotropic cytokine that is both necessary and sufficient for postoperative memory decline in a preclinical model of PND. Recently, we reported that, in adult male wild-type mice subjected to tibial fracture under general anesthesia, IL-6 trans-signaling in hippocampal CA1 neurons mediates surgery-induced memory impairment. As there are no therapeutic options for preventing or reversing PNDs, patients and their caregivers, as well as the healthcare industry, endure staggering costs. Olamkicept, a highly selective IL-6 trans-signaling blocker has shown to be efficacious and safe in clinical trials involving patients with inflammatory bowel disease, another condition for which IL-6 trans-signaling is the mediating mechanism. Subject to a demonstration that olamkicept is effective in preventing cognitive impairment in vulnerable (aged and Alzheimer's Disease) preclinical PND models, clinical trials involving aged and/or cognitively impaired surgical patients should be undertaken to study olamkicept's utility for PNDs.

Pain and aging: A unique challenge in neuroinflammation and behavior

Chronic pain is one of the most common, costly, and potentially debilitating health issues facing older adults, with attributable costs exceeding $600 billion annually. The prevalence of pain in humans increases with advancing age. Yet, the contributions of sex differences, age-related chronic inflammation, and changes in neuroplasticity to the overall experience of pain are less clear, given that opposing processes in aging interact. This review article examines and summarizes pre-clinical research and clinical data on chronic pain among older adults to identify knowledge gaps and provide the base for future research and clinical practice. We provide evidence to suggest that neurodegenerative conditions engender a loss of neural plasticity involved in pain response, whereas low-grade inflammation in aging increases CNS sensitization but decreases PNS sensitivity. Insights from preclinical studies are needed to answer mechanistic questions. However, the selection of appropriate aging models presents a challenge that has resulted in conflicting data regarding pain processing and behavioral outcomes that are difficult to translate to humans.

Systemic maternal inflammation promotes ASD via IL-6 and IFN-γ

Autism spectrum disorder (ASD) is a neurological disorder that manifests during early development, impacting individuals through their ways of communicating, social behaviors, and their ability to perform day-to-day activities. There have been different proposed mechanisms on how ASD precipitates within a patient, one of which being the impact cytokines have on fetal development once a mother's immune system has been activated (referred to as maternal immune activation, MIA). The occurrence of ASD has long been associated with elevated levels of several cytokines, including interleukin-6 (IL-6) and interferon gamma (IFN-γ). These proinflammatory cytokines can achieve high systemic levels in response to immune activating pathogens from various extrinsic sources. Transfer of cytokines such as IL-6 across the placental barrier allows accumulation in the fetus, potentially inducing neuroinflammation and consequently altering neurodevelopmental processes. Individuals who have been later diagnosed with ASD have been observed to have elevated levels of IL-6 and other proinflammatory cytokines during gestation. Moreover, the outcome of MIA has been associated with neurological effects such as impaired social interaction and an increase in repetitive behavior in animal models, supporting a mechanistic link between gestational inflammation and development of ASD-like characteristics. The present review attempts to provide a concise overview of the available preclinical and clinical data that suggest cross-talk between IL-6 and IFN-γ through both extrinsic and intrinsic factors as a central mechanism of MIA that may promote the development of ASD.

Regulatory T-Cells Suppress Cytotoxic T Lymphocyte Responses against Microglia

Regulatory T-cells (Tregs) play pivotal roles during infection, cancer, and autoimmunity. In our previous study, we demonstrated a role for the PD-1:PD-L1 pathway in controlling cytolytic responses of CD8⁺ T lymphocytes against microglial cells presenting viral peptides. In this study, we investigated the role of Tregs in suppressing CD8⁺ T-cell-mediated cytotoxicity against primary microglial cells. Using in vitro cytotoxicity assays and flow cytometry, we demonstrated a role for Tregs in suppressing antigen-specific cytotoxic T-lymphocyte (CTL) responses against microglia loaded with a model peptide (SIINFEKL). We went on to show a significant decrease in the frequency of IFN-γ- and TNF-producing CD8⁺ T-cells when cultured with Tregs. Interestingly, a significant increase in the frequency of granzyme B- and Ki67-producing CTLs was observed. We also observed a significant decrease in the production of interleukin (IL)-6 by microglia. On further investigation, we found that Tregs significantly reduced MHC class 1 (MHC-1) expression on IFN-γ-treated microglial cells. Taken together, these studies demonstrate an immunosuppressive role for Tregs on CTL responses generated against primary microglia. Hence, modulation of Treg cell activity in combination with negative immune checkpoint blockade may stimulate anti-viral T-cell responses to more efficiently clear viral infection from microglial cell reservoirs.

Impact of aging on animal models of Parkinson's disease

Aging is the biggest risk factor for developing Parkinson's disease (PD), the second most common neurodegenerative disorder. Several animal models have been developed to explore the pathophysiology underlying neurodegeneration and the initiation and spread of alpha-synuclein-related PD pathology, and to investigate biomarkers and therapeutic strategies. However, bench-to-bedside translation of preclinical findings remains suboptimal and successful disease-modifying treatments remain to be discovered. Despite aging being the main risk factor for developing idiopathic PD, most studies employ young animals in their experimental set-up, hereby ignoring age-related cellular and molecular mechanisms at play. Consequently, studies in young animals may not be an accurate reflection of human PD, limiting translational outcomes. Recently, it has been shown that aged animals in PD research demonstrate a higher susceptibility to developing pathology and neurodegeneration, and present with a more disseminated and accelerated disease course, compared to young animals. Here we review recent advances in the investigation of the role of aging in preclinical PD research, including challenges related to aged animal models that are limiting widespread use. Overall, current findings indicate that the use of aged animals may be required to account for age-related interactions in PD pathophysiology. Thus, although the use of older animals has disadvantages, a model that better represents clinical disease within the elderly would be more beneficial in the long run, as it will increase translational value and minimize the risk of therapies failing during clinical studies. Furthermore, we provide recommendations to manage the challenges related to aged animal models.

CD11bhigh B Cells Increase after Stroke and Regulate Microglia

Recent studies have highlighted the deleterious contributions of B cells to post-stroke recovery and cognitive decline. Different B cell subsets have been proposed on the basis of expression levels of transcription factors (e.g., T-bet) as well as specific surface proteins. CD11b (α-chain of integrin) is expressed by several immune cell types and is involved in regulation of cell motility, phagocytosis, and other essential functions of host immunity. Although B cells express CD11b, the CD11b^high subset of B cells has not been well characterized, especially in immune dysregulation seen with aging and after stroke. Here, we investigate the role of CD11b^high B cells in immune responses after stroke in young and aged mice. We evaluated the ability of CD11b^high B cells to influence pro- and anti-inflammatory phenotypes of young and aged microglia (MG). We hypothesized that CD11b^high B cells accumulate in the brain and contribute to neuroinflammation in aging and after stroke. We found that CD11b^high B cells are a heterogeneous subpopulation of B cells predominantly present in naive aged mice. Their frequency increases in the brain after stroke in young and aged mice. Importantly, CD11b^high B cells regulate MG phenotype and increase MG phagocytosis in both ex vivo and in vivo settings, likely by production of regulatory cytokines (e.g., TNF-α). As both APCs and adaptive immune cells with long-term memory function, B cells are uniquely positioned to regulate acute and chronic phases of the post-stroke immune response, and their influence is subset specific.

Exacerbated immune response of the brain to peripheral immune challenge in post-septic mice

BACKGROUND

Mounting evidence indicates that sepsis can induce long-lasting brain dysfunction. Recently, it has been proposed that the brain may become more sensitive to systemic inflammation if microglial cells are already primed. Microglial priming has been demonstrated in aging, traumatic brain injury, and neurodegenerative diseases. There is evidence suggesting that systemic inflammation may also prime microglia. This study aimed to investigate the brain's response to a second immune challenge in sepsis survivors and the possible role of microglial priming.

METHODS

Adult BALB/c mice were intraperitoneally (ip) injected with 5 mg/kg lipopolysaccharide (LPS) for sepsis induction. One month later, mice received a second immune challenge (LPS, 0.33 mg/kg). A cohort of mice was sacrificed 2 h post-LPS injection to measure inflammatory mediators mRNA expression. The second cohort of mice was tested on a battery of behavioral tests and then sacrificed, and brain tissues were removed for biochemical analyses.

RESULTS

Results showed that in septic mice, secondary LPS challenge induced heightened neuroinflammation compared to the control mice, as evident by a significant increase of IL-1β, TNF-α, and iNOS mRNA expression. In the immunochallenged septic mice, the anti-inflammatory cytokine IL-10 expression was also significantly increased compared to the control mice. Sepsis induction significantly disrupted the recognition ability in the novel object recognition, but the second immune challenge had no significant effect. However, immunochallenged septic mice exhibited more anxiety-like behavior in the marble burying task and intensive depressive-like behavior in the forced swim test. Additionally, the second immune challenge reduced arginase-1 levels in septic but not control mice. On the other hand, CIITA levels were increased more significantly in the LPS injected control mice compared to septic mice. Neither sepsis nor the second immune challenge significantly affected inhibitory avoidance behavior and Aβ1-42 levels in brain tissue.

CONCLUSION

Our finding suggests that low-grade immune challenge can induce exacerbated behavioral change and exaggerated inflammatory response in the brain of post-septic mice.

Protective Signature of IFNγ-Stimulated Microglia Relies on miR-124-3p Regulation From the Secretome Released by Mutant APP Swedish Neuronal Cells

Microglia-associated inflammation and miRNA dysregulation are key players in Alzheimer’s disease (AD) pathophysiology. Previously, we showed miR-124 upregulation in APP Swedish SH-SY5Y (SWE) and PSEN1 iPSC-derived neurons and its propagation by the secretome (soluble and exosomal fractions). After modulation with miR-124 mimic/inhibitor, we identified common responsive mechanisms between such models. We also reported miR-124 colocalization with microglia in AD patient hippocampi. Herein, we determined how miR-124 modulation in SWE cells influences microglia polarized subtypes in the context of inflammation. We used a coculture system without cell-to-cell contact formed by miR-124 modulated SWE cells and human CHME3 microglia stimulated with interferon-gamma (IFNγ-MG), in which we assessed their adopted gene/miRNA profile and proteomic signature. The increase of miR-124 in SWE cells/secretome (soluble and exosomal) was mimicked in IFNγ-MG. Treatment of SWE cells with the miR-124 inhibitor led to RAGE overexpression and loss of neuronal viability, while the mimic caused RAGE/HMGB1 downregulation and prevented mitochondria membrane potential loss. When accessing the paracrine effects on microglia, SWE miR-124 inhibitor favored their IFNγ-induced inflammatory signature (upregulated RAGE/HMGB1/iNOS/IL-1β; downregulated IL-10/ARG-1), while the mimic reduced microglia activation (downregulated TNF-α/iNOS) and deactivated extracellular MMP-2/MMP-9 levels. Microglia proteomics identified 113 responsive proteins to SWE miR-124 levels, including a subgroup of 17 proteins involved in immune function/inflammation and/or miR-124 targets. A total of 72 proteins were downregulated (e.g., MAP2K6) and 21 upregulated (e.g., PAWR) by the mimic, while the inhibitor also upregulated 21 proteins and downregulated 17 (e.g., TGFB1, PAWR, and EFEMP1). Other targets were associated with neurodevelopmental mechanisms, synaptic function, and vesicular trafficking. To examine the source of miR-124 variations in microglia, we silenced the RNase III endonuclease Dicer1 to block miRNA canonical biogenesis. Despite this suppression, the coculture with SWE cells/exosomes still raised microglial miR-124 levels, evidencing miR-124 transfer from neurons to microglia. This study is pioneer in elucidating that neuronal miR-124 reshapes microglia plasticity and in revealing the relevance of neuronal survival in mechanisms underlying inflammation in AD-associated neurodegeneration. These novel insights pave the way for the application of miRNA-based neuropharmacological strategies in AD whenever miRNA dysregulated levels are identified during patient stratification.

Microbiota-microglia connections in age-related cognition decline

Aging is an inevitable process that all individuals experience, of which the extent differs among individuals. It has been recognized as the risk factor of neurodegenerative diseases by affecting gut microbiota compositions, microglia, and cognition abilities. Aging-induced changes in gut microbiota compositions have a critical role in orchestrating the morphology and functions of microglia through the gut-brain axis. Gut microbiota communicates with microglia by its secreted metabolites and neurotransmitters. This is highly associated with age-related cognitive declines. Here, we review the main composition of microbiota in the aged individuals, outline the changes of the brain in age-related cognitive decline from a neuroinflammation perspective, especially the changes of morphology and functions of microglia, discuss the crosstalk between microbiota and microglia in the aged brain and further highlight the role of microbiota-microglia connections in neurodegenerative diseases (Alzheimer's disease and Parkinson's disease).

Emerging Evidence for the Widespread Role of Glutamatergic Dysfunction in Neuropsychiatric Diseases

The monoamine model of depression has long formed the basis of drug development but fails to explain treatment resistance or associations with stress or inflammation. Recent animal research, clinical trials of ketamine (a glutamate receptor antagonist), neuroimaging research, and microbiome studies provide increasing evidence of glutamatergic dysfunction in depression and other disorders. Glutamatergic involvement across diverse neuropathologies including psychoses, neurodevelopmental, neurodegenerative conditions, and brain injury forms the rationale for this review. Glutamate is the brain's principal excitatory neurotransmitter (NT), a metabolic and synthesis substrate, and an immune mediator. These overlapping roles and multiple glutamate NT receptor types complicate research into glutamate neurotransmission. The glutamate microcircuit comprises excitatory glutamatergic neurons, astrocytes controlling synaptic space levels, through glutamate reuptake, and inhibitory GABA interneurons. Astroglia generate and respond to inflammatory mediators. Glutamatergic microcircuits also act at the brain/body interface via the microbiome, kynurenine pathway, and hypothalamus-pituitary-adrenal axis. Disruption of excitatory/inhibitory homeostasis causing neuro-excitotoxicity, with neuronal impairment, causes depression and cognition symptoms via limbic and prefrontal regions, respectively. Persistent dysfunction reduces neuronal plasticity and growth causing neuronal death and tissue atrophy in neurodegenerative diseases. A conceptual overview of brain glutamatergic activity and peripheral interfacing is presented, including the common mechanisms that diverse diseases share when glutamate homeostasis is disrupted.

Kampo formulas alleviate aging-related emotional disturbances and neuroinflammation in male senescence-accelerated mouse prone 8 mice

Aging-induced neuroinflammation, also known as neuroinflammaging, plays a pivotal role in emotional disturbances, including depression and anxiety, in older individuals, thereby leading to cognitive dysfunction. Although numerous studies have focused on therapeutic strategies for cognitive impairment in older individuals, little research has been performed on treating its preceding emotional disturbances. Here, we examined whether Kampo formulas (kososan [KS], nobiletin-rich kososan [NKS], and hachimijiogan [HJG]) can ameliorate aging-induced emotional disturbances and neuroinflammation in mice. The depression-like behaviors observed in SAMP8 mice, relative to normally aging SAMR1 mice, were significantly prevented by treatment with Kampo formulas for 13 weeks. Western blot analysis revealed that hippocampal neuroinflammation was significantly abrogated by Kampo formulas. KS and NKS also significantly attenuated the hippocampal neuroinflammatory priming induced by lipopolysaccharide (LPS, 0.33 mg/kg, i.p.) challenge in SAMP8 mice. Hippocampal IL-1β, IL-6, and MCP-1 levels were significantly decreased in NKS-treated SAMP8 mice. KS and NKS showed significantly reduced tau accumulation in the brains of SAMP8 mice. RNA-sequencing revealed that each Kampo formula led to unique dynamics of hippocampal gene expression and appeared to abrogate hippocampal inflammatory responses. HJG significantly blocked the LPS-induced increase in serum IL-6 and MCP-1. These results suggest that Kampo formulas would be useful for treating aging-induced depression, in part by regulating neuroinflammatory pathways. This finding may pave the way for the development of therapeutic strategies for aging-related emotional disturbances, which may contribute to the prevention of cognitive dysfunction in older individuals.

Neuroinflammation: Molecular Mechanisms And Therapeutic Perspectives

BACKGROUND

Neuroinflammation is a key component in the etiopathogenesis of neurological diseases and brain aging. This process involves the brain immune system that modulates synaptic functions and protects neurons from infection or damage. Hence, the knowledge of neuroinflammation related pathways and modulation by drugs or natural compounds is functional to developing therapeutic strategies aimed at preserving, maintaining and restoring brain health.

OBJECTIVE

This review article summarizes the basics of neuroinflammation and related signaling pathways, the success of the dietary intervention in clinical practice and the possible development of RNA-based strategies for treating neurological diseases.

METHODS

Pubmed search from 2012 to 2022 with the keywords neuroinflammation and molecular mechanisms in combination with diet, miRNA and non-coding RNA.

RESULTS

Glial cells-play a crucial role in neuroinflammation, but several pathways can be activated in response to different inflammatory stimuli, inducing cell death by apoptosis, pyroptosis or necroptosis. The dietary intervention has immunomodulatory effects and could limit the inflammatory process induced by microglia and astrocytes. Thus by inhibiting neuroinflammation and improving the symptoms of a variety of neurological diseases, diet exerts pleiotropic neuroprotective effects independently from the spectrum of pathophysiological mechanisms underlying the specific disorder. Furthermore, data from animal models revealed that altered expression of specific noncoding RNAs, in particular microRNAs, contributes to neuroinflammatory diseases; consequently, RNA-based strategies may be promising to alleviate the consequences of neuroinflammation.

CONCLUSION

Further studies are needed to identify the molecular pathways and the new pharmacological targets in neuroinflammation to lay the basis for more effective and selective therapies to be applied, in parallel to dietary intervention, in the treatment of neuroinflammation-based diseases.

Specific microglial phagocytic phenotype and decrease of lipid oxidation in white matter areas during aging: Implications of different microenvironments

Physiological aging is characterized by an imbalance of pro-inflammatory and anti-inflammatory mediators leading to neuroinflammation. Microglial cells, which are highly regulated by the local microenvironment, undergo specific changes depending upon the brain area during aging. The aim of this study was to evaluate the influence of age over microglial cells along different brain areas and microenvironments. For this purpose, transgenic mice with overproduction of either the anti-inflammatory IL-10 cytokine or the pro-inflammatory IL-6 cytokine were used. Our results show that, during aging, microglial cells located in white matter (WM) areas maintain their phagocytic capacity but present a specific phagocytic phenotype with receptors involved in myelin recognition, arguing for aging-derived myelin damage. Whereas IL-10 overproduction anticipates the age-related microglial phagocytic phenotype, maintaining it over time, IL-6 overproduction exacerbates this phenotype in aging. These modifications were linked with a higher efficiency of myelin engulfment by microglia in aged transgenic animals. Moreover, we show, in a novel way, lower lipid oxidation during aging in WM areas, regardless of the genotype. The novelty of the insights presented in this study open a window to deeply investigate myelin lipid oxidation and the role of microglial cells in its regulation during physiological aging.

The Impact of Obesity on Microglial Function: Immune, Metabolic and Endocrine Perspectives

Increased life expectancy in combination with modern life style and high prevalence of obesity are important risk factors for development of neurodegenerative diseases. Neuroinflammation is a feature of neurodegenerative diseases, and microglia, the innate immune cells of the brain, are central players in it. The present review discusses the effects of obesity, chronic peripheral inflammation and obesity-associated metabolic and endocrine perturbations, including insulin resistance, dyslipidemia and increased glucocorticoid levels, on microglial function.

The old guard: Age-related changes in microglia and their consequences

Among all major organs, the brain is one of the most susceptible to the inexorable effects of aging. Throughout the last decades, several studies in human cohorts and animal models have revealed a plethora of age-related changes in the brain, including reduced neurogenesis, oxidative damage, mitochondrial dysfunction and cell senescence. As the main immune effectors and first responders of the nervous tissue, microglia are at the center of these events. These cells experience irrevocable changes as a result from cumulative exposure to environmental triggers, such as stress, infection and metabolic dysregulation. The age-related immunosenescent phenotype acquired by microglia is characterized by profound modifications in their transcriptomic profile, secretome, morphology and phagocytic activity, which compromise both their housekeeping and defensive functions. As a result, aged microglia are no longer capable of establishing effective immune responses and sustaining normal synaptic activity, directly contributing to age-associated cognitive decline and neurodegeneration. This review discusses how lifestyle and environmental factors drive microglia dysfunction at the molecular and functional level, also highlighting possible interventions to reverse aging-associated damage to the nervous and immune systems.

Increased IL-6 receptor expression and signaling in ageing cartilage can be explained by loss of TGF-β-mediated IL-6 receptor suppression

OBJECTIVE

Osteoarthritis (OA) development is strongly associated with ageing, possibly due to age-related changes in transforming growth factor-β (TGF-β) signaling in cartilage. Recently, we showed that TGF-β suppresses interleukin (IL)-6 receptor (IL-6R) expression in chondrocytes. As IL-6 is involved in cartilage degeneration, we hypothesized that age-related loss of TGF-β signaling results in increased IL-6R expression and signaling in ageing cartilage.

DESIGN

Bovine articular cartilage was collected and immediately processed to study age-related changes in IL-6R expression using qPCR and IHC (age-range: 0.5-14 years). Moreover, cartilage from young and aged cows was stimulated with rhIL-6 and/or rhTGF-β1 to measure IL-6-induced p-STAT3 using Western blot. Expression of STAT3-responsive genes was analyzed using qPCR.

RESULTS

Expression of IL-6 receptor (bIL-6R) significantly increased in cartilage upon ageing (slope: 0.32, 95%CI: 0.20-0.45), while expression of glycoprotein 130 (bGP130) was unaffected. Cartilage stimulation with IL-6 showed increased induction of p-STAT3 upon ageing (slope: 0.14, 95%CI: 0.08-0.20). Furthermore, IL-6-mediated induction of STAT3-responsive genes like bSOCS3 and bMMP3 was increased in aged compared to young cartilage. Interestingly, the ability of TGF-β to suppress bIL6R expression in young cartilage was lost upon ageing (slope: 0.21, 95%CI: 0.13-0.30). Concurrently, an age-related loss in TGF-β-mediated suppression of IL-6-induced p-STAT3 and bSOCS3 expression was observed.

CONCLUSIONS

Ageing results in enhanced IL-6R expression and subsequent IL-6-induced p-STAT3 signaling in articular cartilage. This is likely caused by age-related loss of protective TGF-β signaling, resulting in loss of TGF-β-mediated IL-6R suppression. Because of the detrimental role of IL-6 in cartilage, this mechanism may be involved in age-related OA development.

Senescence Is Associated With Elevated Intracellular Resting [Ca2 +] in Mice Skeletal Muscle Fibers. An in vivo Study

Aging causes skeletal muscles to become atrophied, weak, and easily fatigued. Here, we have tested the hypothesis that normal aging in skeletal muscle cells is associated with Ca²⁺ intracellular dyshomeostasis and oxidative stress. Intracellular Ca²⁺ concentration ([Ca²⁺]_i), resting intracellular Na⁺ concentration ([Na⁺]_i) and reactive oxygen species (ROS) production were measured in vivo (superficial gastrocnemius fibers) using double-barreled ion-selective microelectrodes, and in vitro [isolated single flexor digitorum brevis fibers] using fluorescent ROS sensor CM-H2DCFDA in young (3 months of age), middle-aged (12 months of age), and aged (24 months of age) mice. We found an age-related increase in [Ca²⁺]_i from 121 ± 4 nM in young muscle cells which rose to 255 ± 36 nM in middle-aged and to 409 ± 25 nM in aged cells. [Na⁺]_i also showed an age-dependent elevation, increasing from 8 ± 0.5 mM in young muscle fibers, to 12 ± 1 mM in middle-aged and to 17 ± 1 mM in old muscle fibers. Using the fluorescent ROS sensor CM-H2DCFDA we found that these increases in intracellular cation concentrations were associated with significantly increased basal ROS production as demonstrated by age related increases in the rate of dichlorodihydrofluorescein fluorescence. To determine is this could be modified by reducing ROS and/or blocking sarcolemmal Ca²⁺ influx we administered flufenamic acid (FFA), a non-steroidal anti-inflammatory drug which is also a non-selective blocker of the transient receptor potential canonical channels (TRPCs), for 4 weeks to determine if this would have a beneficial effect. FFA treatment reduced both basal ROS production and muscle [Ca²⁺]_i and [Na⁺]_i in middle-aged and aged muscle fibers compared to fibers and muscles of untreated 12 and 24-months old mice. [Ca²⁺]_i was reduced to 134 ± 8 nM in middle-aged muscle and to 246 ± 40 nM in muscle from aged mice. Likewise [Na⁺]_i was reduced to 9 ± 0.7 mM in middle-aged muscles and to 13 ± 1 mM in muscle from aged mice. FFA treatment also reduced age associated increases in plasma interleukin 6 and tumor necrosis factor-alpha (TNF-α) concentrations which were elevated in 12 and 24-months old mice compared to young mice and decreased age-related muscle damage as indicated by a reduction in serum creatine kinase (CK) activity. Our data provides a direct demonstration that normal aging is associated with a significant elevation [Ca²⁺]_i, [Na⁺]_i, and intracellular ROS production in skeletal muscle fibers. Furthermore, the fact that FFA reduced the intracellular [Ca²⁺], [Na⁺], and ROS production as well as the elevated IL6, TNF-α, and CK levels, led us to suggest that its pharmacological effect may be related to its action both as a TRPC channel blocker and as an anti-inflammatory.

Chronic exposure to IL-6 induces a desensitized phenotype of the microglia

Background

When the homeostasis of the central nervous system (CNS) is altered, microglial cells become activated displaying a wide range of phenotypes that depend on the specific site, the nature of the activator, and particularly the microenvironment generated by the lesion. Cytokines are important signals involved in the modulation of the molecular microenvironment and hence play a pivotal role in orchestrating microglial activation. Among them, interleukin-6 (IL-6) is a pleiotropic cytokine described in a wide range of pathological conditions as a potent inducer and modulator of microglial activation, but with contradictory results regarding its detrimental or beneficial functions. The objective of the present study was to evaluate the effects of chronic IL-6 production on the immune response associated with CNS-axonal anterograde degeneration.

Methods

The perforant pathway transection (PPT) paradigm was used in transgenic mice with astrocyte-targeted IL6-production (GFAP-IL6Tg). At 2, 3, 7, 14, and 21 days post-lesion, the hippocampal areas were processed for immunohistochemistry, flow cytometry, and protein microarray.

Results

An increase in the microglia/macrophage density was observed in GFAP-IL6Tg animals in non-lesion conditions and at later time-points after PPT, associated with higher microglial proliferation and a major monocyte/macrophage cell infiltration. Besides, in homeostasis, GFAP-IL6Tg showed an environment usually linked with an innate immune response, with more perivascular CD11b⁺/CD45^high/MHCII⁺/CD86⁺ macrophages, higher T cell infiltration, and higher IL-10, IL-13, IL-17, and IL-6 production. After PPT, WT animals show a change in microglia phenotype expressing MHCII and co-stimulatory molecules, whereas transgenic mice lack this shift. This lack of response in the GFAP-IL6Tg was associated with lower axonal sprouting.

Conclusions

Chronic exposure to IL-6 induces a desensitized phenotype of the microglia.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-020-02063-1.

Potential caveats of putative microglia-specific markers for assessment of age-related cerebrovascular neuroinflammation

BACKGROUND

The ability to distinguish resident microglia from infiltrating myeloid cells by flow cytometry-based surface phenotyping is an important technique for examining age-related neuroinflammation. The most commonly used surface markers for the identification of microglia include CD45 (low-intermediate expression), CD11b, Tmem119, and P2RY12.

METHODS

In this study, we examined changes in expression levels of these putative microglia markers in in vivo animal models of stroke, cerebral amyloid angiopathy (CAA), and aging as well as in an ex vivo LPS-induced inflammation model.

RESULTS

We demonstrate that Tmem119 and P2RY12 expression is evident within both CD45^int and CD45^high myeloid populations in models of stroke, CAA, and aging. Interestingly, LPS stimulation of FACS-sorted adult microglia suggested that these brain-resident myeloid cells can upregulate CD45 and downregulate Tmem119 and P2RY12, making them indistinguishable from peripherally derived myeloid populations. Importantly, our findings show that these changes in the molecular signatures of microglia can occur without a contribution from the other brain-resident or peripherally sourced immune cells.

CONCLUSION

We recommend future studies approach microglia identification by flow cytometry with caution, particularly in the absence of the use of a combination of markers validated for the specific neuroinflammation model of interest. The subpopulation of resident microglia residing within the "infiltrating myeloid" population, albeit small, may be functionally important in maintaining immune vigilance in the brain thus should not be overlooked in neuroimmunological studies.

The role of cap-dependent translation in aged-related changes in neuroimmunity and affective behaviors

Translation regulation in the context of aged-associated inflammation and behavioral impairments is not well characterized. Aged individuals experience lower life quality due to behavioral impairments. In this study, we used young and aged transgenic mice that are unable to activate the cap-binding protein, eukaryotic translation initiation factor 4E (eIF4E) to examine the role of protein translation control in aging, memory, depression, and anxiety. To determine how products of cap-dependent translation play a permissive role in aged-associated inflammation, we assessed levels of pro-inflammatory cytokines in various brain regions involved in the above-mentioned behaviors. We found that functional eIF4E is not necessary for age-related deficits in spatial and short-term memory but is important for depressive and anxiety-like behavior and this is correlated with pro-inflammatory cytokines in discrete brain regions. Thus, we have begun to elucidate a role for eIF4E phosphorylation in the context of aged-related behavioral impairments and chronic low-grade inflammation that may help identify novel immune modulators for therapeutic targets and decrease the burden of self-care among the geriatric population.

Astrocyte Crosstalk in CNS Inflammation

Astrocytes control multiple processes in the nervous system in health and disease. It is now clear that specific astrocyte subsets or activation states are associated with specific genomic programs and functions. The advent of novel genomic technologies has enabled rapid progress in the characterization of astrocyte heterogeneity and its control by astrocyte interactions with other cells in the central nervous system (CNS). In this review, we provide an overview of the multifaceted roles of astrocytes in the context of CNS inflammation, highlighting recent discoveries on astrocyte subsets and their regulation. We explore mechanisms of crosstalk between astrocytes and other cells in the CNS in the context of neuroinflammation and neurodegeneration and discuss how these interactions shape pathological outcomes.

Maternal Immune Activation Sensitizes Male Offspring Rats to Lipopolysaccharide-Induced Microglial Deficits Involving the Dysfunction of CD200-CD200R and CX3CL1-CX3CR1 Systems

Early life challenges resulting from maternal immune activation (MIA) may exert persistent effects on the offspring, including the development of psychiatric disorders, such as schizophrenia. Recent evidence has suggested that the adverse effects of MIA may be mediated by neuron-microglia crosstalk, particularly CX3CL1-CX3CR1 and CD200-CD200R dyads. Therefore, the present study assessed the behavioural parameters resembling schizophrenia-like symptoms in the adult male offspring of Sprague-Dawley rats that were exposed to MIA and to an additional acute lipopolysaccharide (LPS) challenge in adulthood, according to the "two-hit" hypothesis of schizophrenia. Simultaneously, we aimed to clarify the role of the CX3CL1-CX3CR1 and CD200-CD200R axes and microglial reactivity in the brains of adult offspring subjected to MIA and the "second hit" wit LPS. In the present study, MIA generated a range of behavioural changes in the adult male offspring, including increased exploratory activity and anxiety-like behaviours. The most intriguing finding was observed in the prepulse inhibition (PPI) test, where the deficit in the sensorimotor gating was age-dependent and present only in part of the rats. We were able to distinguish the occurrence of two groups: responsive and non-responsive (without the deficit). Concurrently, based on the results of the biochemical studies, MIA disrupted mainly the CD200-CD200R system, while the changes of the CX3CL1-CX3CR1 axis were less evident in the frontal cortex of adult non-responsive offspring. MIA markedly affected the immune regulators of the CD200-CD200R pathway as we observed an increase in cortical IL-6 release in the responsive group and IL-4 in the non-responsive offspring. Importantly, the "second hit" generated disturbances at the behavioural and biochemical levels mostly in the non-responsive adult animals. Those offspring were characterized both by disturbed PPI and "priming" microglia. Altogether, the exposure to MIA altered the immunomodulatory mechanisms, including the CD200-CD200R axis, in the brain and sensitized animals to subsequent immunological challenges, leading to the manifestation of schizophrenia-like alterations.

eIF4E phosphorylation modulates pain and neuroinflammation in the aged

The aged population has a higher probability of developing chronic pain from acute insults because of age-associated low-grade inflammation. Several emerging studies have shown a crucial role of cap-dependent translation in the development of chronic pain in young adult animals; however, its role in the aged has never been reported. Acute and chronic inflammatory responses, including pain, are altered over age, and understanding how cap-dependent translation can represent an important and druggable pathway is imperative for understanding its therapeutic potential. Here we have tested how an inflammatory stimulus, complete Freund's adjuvant (CFA), affects spontaneous and evoked pain, as well as inflammation in young versus aged mice that lack functional cap-dependent translation machinery (eukaryotic translation initiation factor 4E (eIF4E)) compared with age-matched wild-type (WT) mice. Interestingly, we found that CFA-induced acute pain and inflammation are modulated by eIF4E phosphorylation in aged but not young animals. Aged transgenic animals showed attenuated paw temperature and inflammation, as well as a mitigation in the onset and quicker resolution in mechanical and thermal hypersensitivity. We found that levels of interleukin (IL)-1β and tumor necrosis factor (TNF)-α are elevated in dorsal root ganglia in aged WT and eIF4E transgenic groups, despite faster resolution of acute inflammation and pain in the aged eIF4E transgenic animals. We propose that these cytokines are important in mediating the observed behavioral responses in the young and represent an alternate pathway in the development of age-associated inflammation and behavioral consequences. These findings demonstrate that eIF4E phosphorylation can be a key target for treating inflammatory pain in the aged.

Epigenetic reduction of miR-214-3p upregulates astrocytic colony-stimulating factor-1 and contributes to neuropathic pain induced by nerve injury

Emerging evidence has indicated that colony-stimulating factor-1 (CSF1) modulates neuroinflammation in the central nervous system and the development of neuropathic pain, while the underlying mechanism remains unknown. Here, we identified the increased expression of CSF1 derived from activated astrocytes in the ipsilateral dorsal horn in rats with spinal nerve ligation (SNL). Suppression of CSF1 expression alleviated neuroinflammation, neuronal hyperexcitability, and glutamatergic receptor subunit upregulation in the dorsal horn and improved SNL-induced pain behavior. We also found reduced miR-214-3p expression in the ipsilateral dorsal horn following an SNL procedure; miR-214-3p directly bound to the 3'-UTR of CSF1 mRNA and negatively regulated CSF1 expression. Intrathecal delivery of miR-214-3p mimic reversed the enhanced expression of CSF1 and astrocyte overactivity and alleviated the IL-6 upregulation and pain behavior induced by SNL. Moreover, suppression of spinal miR-214-3p increased astrocyte reactivity, promoted CSF1 and IL-6 production, and induced pain hypersensitivity in naive animals. Furthermore, SNL induced the expression of DNA methyltransferase 3a (DNMT3a) that was associated with the hypermethylation of the miR-214-3p promoter, leading to reduced miR-214-3p expression in the model rodents. Treatment with the DNMT inhibitor zebularine significantly reduced cytosine methylation in the miR-214-3p promoter; this reduced methylation consequently increased the expression of miR-214-3p and decreased the content of CSF1 in the ipsilateral dorsal horn and, further, attenuated IL-6 production and pain behavior in rats with SNL. Together, our data indicate that the DNMT3a-mediated epigenetic suppression of miR-214-3p enhanced CSF1 production in astrocytes, which subsequently induced neuroinflammation and pain behavior in SNL model rats.