Microglia function during brain development: New insights from animal models

Santa-maria is a glial phagocytic receptor that acts with SIMU to recognize and engulf apoptotic neurons

The elimination of superfluous neurons via apoptosis and subsequent glial phagocytosis is crucial for the development of the central nervous system (CNS). In Drosophila, two glial phagocytic receptors, six-microns-under (SIMU) and Draper, mediate the phagocytosis of apoptotic neurons during embryogenesis. However, in simu;draper double-mutant embryos, some apoptotic neurons are still engulfed by the glia, suggesting the involvement of additional receptors. Here, we discover the Drosophila CD36 homolog Santa-maria, a transmembrane receptor, which is specifically expressed in embryonic phagocytic glia and plays a major role in the recognition and engulfment steps of phagocytosis. Our data demonstrate that santa-maria genetically interacts with simu and draper, while the protein product binds apoptotic cells and physically interacts with the SIMU protein. Moreover, we reveal that triple knockout of genes for all three glial phagocytic receptors (i.e., simu, draper, and santa-maria) causes partial lethality, thus illuminating their role in development, particularly in the developing nervous system.

Sigma-1 receptor modulation by fluvoxamine ameliorates valproic acid-induced autistic behavior in rats: Involvement of chronic ER stress modulation, enhanced autophagy and M1/M2 microglia polarization

Autism spectrum disorder (ASD) is a neurodevelopmental disorder. While, fluvoxamine (FVX) is an antidepressant and widely prescribed to ASD patients, clinical results are inconclusive and the mechanism of FVX in the management of ASD is unclear. This study determined the potential therapeutic impact of FVX, a sigma-1 receptor (S1R) agonist, against the valproic acid (VPA)-induced model of autism. On gestational day 12.5, Wistar pregnant rats were given a single intraperitoneal (i.p.) injection of either VPA (600 mg/kg) or normal saline (10 mL/kg, vehicle-control). Starting on postnatal day (PND) 21 to PND 50, FVX (30 mg/kg, P·O. daily) and NE-100, (S1R) antagonist, (1 mg/kg, i.p. daily) were given to male pups. Behavior tests and histopathological changes were identified at the end of the experiment. In addition, the cerebellum biomarkers of endoplasmic reticulum (ER) stress and autophagy were assessed. Microglial cell polarization to M1 and M2 phenotypes was also assessed. FVX effectively mitigated the histopathological alterations in the cerebellum caused by VPA. FVX enhanced sociability and stereotypic behaviors in addition to its noteworthy impact on autophagy enhancement, ER stress deterioration, and controlling microglial cell polarization. The current investigation confirmed that the S1R agonist, FVX, can lessen behavioral and neurochemical alterations in the VPA-induced rat model of autism.

Ontogenetic Neuroimmune Changes Following Prenatal Alcohol Exposure: Implications for Neurobehavioral Function

This chapter reviews the enduring effects of prenatal alcohol exposure (PAE) on neuroimmune function across the lifespan, including discussion of associated neurobehavioral alterations. Alcohol has potent teratogenic effects, with a large body of work linking PAE to perturbations in neuroimmune function. These PAE-related neuroimmune disturbances may have downstream effects on neurobehavioral function given the critical role of the neuroimmune system in central nervous system development. The neuroimmune system matures over time, playing distinct roles depending on the developmental processes occurring within that maturational stage. This chapter thus takes an ontogenetic approach to understanding how PAE induces unique neuroimmune changes across the lifespan, beginning with a review of changes in early life before moving into adolescence and ending in adulthood. The focus will be on work utilizing rodent models, which allow for more tightly controlled conditions than are possible in human research. The chapter concludes with a discussion of possible mechanisms underlying the developmental changes in neuroimmune function following PAE, with a specific focus on the role of the gut microbiota.

Morphological and Molecular Biological Changes in the Hippocampus and Prefrontal Cortex of the Brain of Newborn Male and Female Wistar Rats after LPS-Induced Activation of the Maternal Immune Response

Infectious and inflammatory processes during pregnancy in women provoke maternal immunity activation (MIA) and increase the risk of neuropsychiatric disorders in children. These disorders can lead to neurodegenerative diseases later in life. To study these effects, we evaluated the morphological and molecular biological changes in the hippocampus and prefrontal cortex of male and female Wistar rats on the 1st day of postnatal ontogenesis after LPS-induced MIA. The level of calprotectin in the blood serum of postpartum rats, the number and morphological properties of microglial cells in the hippocampus, and the expression of proinflammatory, stem, and adaptation markers in fragments of the prefrontal cortex in offspring of both sexes were determined. It was found that LPS-induced MIA had a negative effect on the developing offspring, with an increase in the level of expression of Nfκb and App in the prefrontal cortex of newborns being observed. Sex differences in morphological and molecular biological changes in the brains of newborn Wistar rats were also revealed: the number of microglial cells increased in male rats, while the number of ramified microglial cells decreased in female rats. In addition, only in females, the expression levels of the mRNA markers for stem cells, Sox2 and Sox9, decreased, while the expression level of Hif1α, which has a neuroprotective effect, increased only in males. These data may explain the differences in the incidence of neurodegenerative diseases among elderly patients of different sexes.

Microglia heterogeneity during neuroinflammation and neurodegeneration in the mouse retina

Microglia play important roles in maintaining homeostasis and immunoreactive defense in the central nervous system including retina. To accomplish such a wide range of functions, microglia are highly heterogeneous. Dark microglia (DM) were recently identified by electron microscopy (EM). However, the specific correlation between microglial morphological phenotypes, including DM, and physiological or pathological conditions remains poorly understood. We established acute and chronic neuroinflammatory models by Lipopolysaccharide (LPS) and light-induced photoreceptor neurodegeneration model to explore these questions in the mouse retina. Immunofluorescence and EM were used to detect microglia in these models. Our light microscopy (LM) results reveal that the withdrawal phenotype is predominant in acute neuroinflammation models, both in vitro and in vivo, while the dystrophic microglia are the major phenotype in chronic neuroinflammation and neurodegeneration models in vivo. Ultrastructurally, acute models exhibit high electron dense processes, but not somas, while chronic models show high electron dense somas and processes. Given the consistency between LM and EM, we propose that DM-like somas and processes likely indicate a dystrophic population. It's important to note, however, that DM may not represent a single specific microglia phenotype, but rather a dynamic transformation of gradually activated microglia. Finally, we provide evidence for the presence of DM in mouse retinas in the neuroinflammatory model and the neurodegenerative model. This research provides valuable insights into investigating microglia phenotypes through both LM and EM.

Role of Maternal Immune Factors in Neuroimmunology of Brain Development

Inflammation during pregnancy may occur due to various factors. This condition, in which maternal immune system activation occurs, can affect fetal brain development and be related to neurodevelopmental diseases. MIA interacts with the fetus's brain development through maternal antibodies, cytokines, chemokines, and microglial cells. Antibodies are associated with the development of the nervous system by two mechanisms: direct binding to brain inflammatory factors and binding to brain antigens. Cytokines and chemokines have an active presence in inflammatory processes. Additionally, glial cells, defenders of the nervous system, play an essential role in synaptic modulation and neurogenesis. Maternal infections during pregnancy are the most critical factors related to MIA; however, several studies show the relation between these infections and neurodevelopmental diseases. Infection with specific viruses, such as Zika, cytomegalovirus, influenza A, and SARS-CoV-2, has revealed effects on neurodevelopment and the onset of diseases such as schizophrenia and autism. We review the relationship between maternal infections during pregnancy and their impact on neurodevelopmental processes.

Microglia-mediated neuron death requires TNF and is exacerbated by mutant Huntingtin

Microglia, the resident immune cells of the brain, regulate the balance of inflammation in the central nervous system under healthy and pathogenic conditions. Huntington's disease (HD) is a chronic neurodegenerative disease characterized by activated microglia and elevated concentrations of pro-inflammatory cytokines within the brain. Chronic hyperactivation of microglia is associated with brain pathology and eventual neuron death. However, it is unclear which specific cytokines are required for neuron death and whether HD neurons may be hypersensitive to neuroinflammation. We assessed the profile of microglia-secreted proteins in response to LPS and IFNγ, and a conditioned media paradigm was used to examine the effects of these secreted proteins on cultured neuronal cells. STHdhQ7/Q7 and STHdhQ111/Q111 neuronal cells were used to model wild-type and HD neurons, respectively. We determined that STHdhQ111/Q111 cells were hypersensitive to pro-inflammatory factors secreted by microglia, and that TNF was required to induce neuronal death. Microglia-mediated neuronal death could be effectively halted through the use of JAK-STAT or TNF inhibitors which supported the requirement for TNF as well as IFNγ in the process of secondary neurotoxicity. Further data derived from human HD patients as well as HD mice were suggestive of enhanced receptor density for TNF (TNFR1) and IFNγ (IFNGR) which could sensitize the HD brain to these cytokines. This highlights several potential mechanisms by which microglia may induce neuronal death and suggests that these mechanisms may be upregulated in the brain of HD patients.

In Vitro Assessment of the Neuroprotective Effects of Pomegranate (Punica granatum L.) Polyphenols Against Tau Phosphorylation, Neuroinflammation, and Oxidative Stress

BACKGROUND

Oxidative stress and chronic inflammation, at both the systemic and the central level, are critical early events in atherosclerosis and Alzheimer's disease (AD).

PURPOSE

To investigate the oxidative stress-, inflammation-, and Tau-phosphorylation-lowering effects of pomegranate polyphenols (PPs) (punicalagin, ellagic acid, peel, and aril extracts).

METHODS

We used flow cytometry to quantify the protein expression of proinflammatory cytokines (IL-1β) and anti-inflammatory mediators (IL-10) in THP-1 macrophages, as well as M1/M2 cell-specific marker (CD86 and CD163) expression in human microglia HMC3 cells. The IL-10 protein expression was also quantified in U373-MG human astrocytes. The effect of PPs on human amyloid beta 1-42 (Aβ1-42)-induced oxidative stress was assessed in the microglia by measuring ROS generation and lipid peroxidation, using 2',7'-dichlorofluorescein diacetate (DCFH-DA) and thiobarbituric acid reactive substance (TBARS) tests, respectively. Neuronal viability and cell apoptotic response to Aβ1-42 toxicity were assayed using the MTT (3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide) assay and the annexin-V-FITC apoptosis detection kit, respectively. Finally, flow cytometry analysis was also performed to evaluate the ability of PPs to modulate Aβ1-42-induced Tau-181 phosphorylation (pTau-181).

RESULTS

Our data indicate that PPs are significantly (p < 0.05) effective in countering Aβ1-42-induced inflammation through increasing the anti-inflammatory cytokines (IL-10) in U373-MG astrocytes and THP1 macrophages and decreasing proinflammatory marker (IL-1β) expression in THP1 macrophages. The PPs were also significantly (p < 0.05) effective in inducing the phenotypic transition of THP-1 macrophages and microglial cells from M1 to M2 by decreasing CD86 and increasing CD163 surface receptor expression. Moreover, our treatments have a significant (p < 0.05) beneficial impact on oxidative stress, illustrated in the reduction in TBARS and ROS generation. Our treatments have significant (p < 0.05) cell viability improvement capacities and anti-apoptotic effects on human H4 neurons. Furthermore, our results suggest that Aβ1-42 significantly (p < 0.05) increases pTau-181. This effect is significantly (p < 0.05) attenuated by arils, peels, and punicalagin and drastically reduced by the ellagic acid treatment.

CONCLUSION

Overall, our results attribute to PPs anti-inflammatory, antioxidant, anti-apoptotic, and anti-Tau-pathology potential. Future studies should aim to extend our knowledge of the potential role of PPs in Aβ1-42-induced neurodegeneration, particularly concerning its association with the tauopathy involved in AD.

Loss of C1q alters the auditory brainstem response

Neural circuits in the auditory brainstem compute interaural time and intensity differences used to determine the locations of sound sources. These circuits display features that are specialized for these functions. The projection from the ventral cochlear nucleus (VCN) to the medial nucleus of the trapezoid (MNTB) body travels along highly myelinated fibers and terminates in the calyx of Held. This monoinnervating synapse emerges during development as multiple inputs are eliminated. We previously demonstrated that elimination of microglia with a colony stimulating factor-1 inhibitor results in impaired synaptic pruning so that multiple calyceal terminals reside on principal cells of MNTB. This inhibitor also resulted in impaired auditory brainstem responses (ABRs), with elevated thresholds and increased peak latencies. Loss of the microglial fractalkine receptor, CX3CR1, decreased peak latencies in the ABR. The mechanisms underlying these effects are not known. One prominent microglial signaling pathway involved in synaptic pruning and plasticity during development and aging is the C1q-initiated compliment cascade. Here we investigated the classical complement pathway initiator, C1q, in auditory brainstem maturation. We found that C1q expression is detected in the MNTB by the first postnatal week. C1q levels increased with age and were detected within microglia and surrounding the soma of MNTB principal neurons. Loss of C1q did not affect microglia-dependent calyceal pruning. Excitatory and inhibitory synaptic markers in the MNTB and LSO were not altered with C1q deletion. ABRs showed that C1q KO mice had normal hearing thresholds but shortened peak latencies. Altogether this study uncovers the developmental time frame of C1q expression in the sound localization pathway and shows a subtle functional consequence of C1q knockdown.

GSP1-111 Modulates the Microglial M1/M2 Phenotype by Inhibition of Toll-like Receptor 2: A Potential Therapeutic Strategy for Depression

Neuroinflammation plays a vital role in neurodegenerative diseases and neuropsychiatric disorders, and microglia and astrocytes chiefly modulate inflammatory responses in the central nervous system (CNS). Toll-like receptors (TLRs), which are expressed in neurons, astrocytes, and microglia in the CNS, are critical for innate immune responses; microglial TLRs can regulate the activity of these cells, inducing protective or harmful effects on the surrounding cells, including neurons. Therefore, regulating TLRs in microglia may be a potential therapeutic strategy for neurological disorders. We examined the protective effects of GSP1-111, a novel synthetic peptide for inhibiting TLR signaling, on neuroinflammation and depression-like behavior. GSP1-111 decreased TLR2 expression and remarkably reduced the mRNA expression of inflammatory M1-phenotype markers, including tumor necrosis factor (TNF)α, interleukin (IL)-1β, and IL-6, while elevating that of the M2 phenotype markers, Arg-1 and IL-10. In vivo, GSP1-111 administration significantly decreased the depression-like behavior induced by lipopolysaccharide (LPS) in a forced swim test and significantly reduced the brain levels of M1-specific inflammatory cytokines (TNFα, IL-1β, and IL-6). GSP1-111 prevented the LPS-induced microglial activation and TLR2 expression in the brain. Accordingly, GSP1-111 prevented inflammatory responses and induced microglial switching of the inflammatory M1 phenotype to the protective M2 phenotype. Thus, GSP1-111 could prevent depression-like behavior by inhibiting TLR2. Taken together, our results suggest that the TLR2 pathway is a promising therapeutic target for depression, and GSP1-111 could be a novel therapeutic candidate for various neurological disorders.

Huanshaodan regulates microglial glucose metabolism reprogramming to alleviate neuroinflammation in AD mice through mTOR/HIF-1α signaling pathway

Abnormal glucose metabolism in microglial is closely associated with Alzheimer's disease (AD). Reprogramming of microglial glucose metabolism is centered on regulating the way in which microglial metabolize glucose to alter microglial function. Therefore, reprogramming microglial glucose metabolism is considered as a therapeutic strategy for AD. Huanshaodan (HSD) is a Chinese herbal compound which shows significant efficacy in treating AD, however, the precise mechanism by which HSD treats AD remains unclear. This study is aim to investigate whether HSD exerts anti-AD effects by regulating the metabolic reprogramming of microglial through the mTOR/HIF-1α signaling pathway. SAMP8 mice and BV2 cells were used to explore the alleviative effect of HSD on AD and the molecular mechanism in vivo and in vitro. The pharmacodynamic effects of HSD was evaluated by behavioral tests. The pathological deposition of Aβ in brain of mice was detected by immunohistochemistry. ELISA method was used to measure the activity of HK2 and the expression of PKM2, IL-6 and TNF-α in hippocampus and cortex tissues of mice. Meanwhile, proteins levels of p-mTOR, mTOR, HIF-1α, CD86, Arg1 and IL-1β were detected by Western-blot. LPS-induced BV2 cells were treated with HSD-containing serum. The analysis of the expression profiles of the CD86 and CD206 markers by flow cytometry allows us to distinguish the BV2 polarization. Glucose, lactic acid, ATP, IL-6 and TNF-α levels, as well as lactate dehydrogenase and pyruvate dehydrogenase activities were evaluated in the BV2. Western-blot analysis was employed to detect mTOR, p-mTOR, HIF-1α and IL-1β levels in BV2. And the mTOR agonist MHY1485 (MHY) was chosen to reverse validate. In this study, it is found that HSD improved cognitive impairment in SAMP8 mice and reduced Aβ deposition, suppressed the levels of glycolysis and neuroinflammation in mice. In LPS-induced BV2 cells, HSD also regulated glycolysis and neuroinflammation, and suppressed the mTOR/HIF-1α signaling pathway. More importantly, these effects were reversed by MHY. It is demonstrated that HSD regulated microglial glucose metabolism reprogramming by inhibiting the mTOR/HIF-1α signaling pathway, alleviated neuroinflammation, and exerted anti-AD effects. This study provided scientific evidence for the clinical application of HSD for treating AD.

Hofbauer cells and fetal brain microglia share transcriptional profiles and responses to maternal diet-induced obesity

Maternal immune activation is associated with adverse offspring neurodevelopmental outcomes, many mediated by in utero microglial programming. As microglia remain inaccessible throughout development, identification of noninvasive biomarkers reflecting fetal brain microglial programming could permit screening and intervention. We used lineage tracing to demonstrate the shared ontogeny between fetal brain macrophages (microglia) and fetal placental macrophages (Hofbauer cells) in a mouse model of maternal diet-induced obesity, and single-cell RNA-seq to demonstrate shared transcriptional programs. Comparison with human datasets demonstrated conservation of placental resident macrophage signatures between mice and humans. Single-cell RNA-seq identified common alterations in fetal microglial and Hofbauer cell gene expression induced by maternal obesity, as well as sex differences in these alterations. We propose that Hofbauer cells, which are easily accessible at birth, provide insights into fetal brain microglial programs and may facilitate the early identification of offspring vulnerable to neurodevelopmental disorders.

Microglia in Glioblastomas: Molecular Insight and Immunotherapeutic Potential

Glioblastoma (GBM) is one of the most aggressive and devastating primary brain tumors, with a median survival of 15 months following diagnosis. Despite the intense treatment regimen which routinely includes maximal safe neurosurgical resection followed by adjuvant radio- and chemotherapy, the disease remains uniformly fatal. The poor prognosis associated with GBM is multifactorial owing to factors such as increased proliferation, angiogenesis, and metabolic switching to glycolytic pathways. Critically, GBM-mediated local and systemic immunosuppression result in inadequate immune surveillance and ultimately, tumor-immune escape. Microglia-the resident macrophages of the central nervous system (CNS)-play crucial roles in mediating the local immune response in the brain. Depending on the specific pathological cues, microglia are activated into either a pro-inflammatory, neurotoxic phenotype, known as M1, or an anti-inflammatory, regenerative phenotype, known as M2. In either case, microglia secrete corresponding pro- or anti-inflammatory cytokines and chemokines that either promote or hinder tumor growth. Herein, we review the interplay between GBM cells and resident microglia with a focus on contemporary studies highlighting the effect of GBM on the subtypes of microglia expressed, the associated cytokines/chemokines secreted, and ultimately, their impact on tumor pathogenesis. Finally, we explore how understanding the intricacies of the tumor-immune landscape can inform novel immunotherapeutic strategies against this devastating disease.

Benefits of bone marrow mesenchymal stem cells compared to their conditioned medium in valproic acid-induced autism in rats

BACKGROUND

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by repetitive behaviors, a limited range of activities, and deficiencies in social communications. Bone marrow mesenchymal stem cells (BM-MSCs), which secrete factors that stimulate surrounding microenvironment, and BM-MSCs conditioned medium (BM-MSCs-CM), which contains cell-secreted products, have been speculated to hold potential as a therapy for ASD. This study aimed to compare the therapeutic effects of BM-MSCs and BM-MSCs-CM on behavioral and microglial changes in an animal model of autism induced by valproic acid (VPA).

METHODS AND RESULTS

Pregnant Wistar rats were administered by VPA at a dose of 600 mg/kg at 12.5 days post-conception. After birth, male pups were included in the study. At 6 weeks of age, one group of rats received intranasal administration of BM-MSCs, while another group received BM-MSCs-CM. The rats were allowed to recover for 2 weeks. Behavioral tests, quantitative real-time polymerase chain reaction (qRT-PCR), and immunohistochemistry were performed. Both BM-MSCs and BM-MSCs-CM administration significantly improved some behavioral deficits. Furthermore, these treatments notably reduced Iba-1 marker associated with microgliosis. Additionally, there was a significant reduction in the expression of pro-inflammatory cytokines IL-1β and IL-6, and an increase in the levels of the anti-inflammatory cytokine IL-10 in rats administered by BM-MSCs and BM-MSCs-CM.

CONCLUSIONS

Post-developmental administration of BM-MSCs and BM-MSCs-CM can ameliorate prenatal neurodevelopmental deficits, restore cognitive and social behaviors, and modulate microglial and inflammatory markers. Results indicated that the improvement rate was higher in the BM-MSCs group than BM-MSCs-CM group.

Role of microglia in brain development after viral infection

Microglia are immune cells in the brain that originate from the yolk sac and enter the developing brain before birth. They play critical roles in brain development by supporting neural precursor proliferation, synaptic pruning, and circuit formation. However, microglia are also vulnerable to environmental factors, such as infection and stress that may alter their phenotype and function. Viral infection activates microglia to produce inflammatory cytokines and anti-viral responses that protect the brain from damage. However, excessive or prolonged microglial activation impairs brain development and leads to long-term consequences such as autism spectrum disorder and schizophrenia spectrum disorder. Moreover, certain viruses may attack microglia and deploy them as "Trojan horses" to infiltrate the brain. In this brief review, we describe the function of microglia during brain development and examine their roles after infection through microglia-neural crosstalk. We also identify limitations for current studies and highlight future investigated questions.

Hofbauer cells and fetal brain microglia share transcriptional profiles and responses to maternal diet-induced obesity

Maternal immune activation is associated with adverse offspring neurodevelopmental outcomes, many mediated by in utero microglial programming. As microglia remain inaccessible throughout development, identification of noninvasive biomarkers reflecting fetal brain microglial programming could permit screening and intervention. We used lineage tracing to demonstrate the shared ontogeny between fetal brain macrophages (microglia) and fetal placental macrophages (Hofbauer cells) in a mouse model of maternal diet-induced obesity, and single-cell RNA-seq to demonstrate shared transcriptional programs. Comparison with human datasets demonstrated conservation of placental resident macrophage signatures between mice and humans. Single-cell RNA-seq identified common alterations in fetal microglial and Hofbauer cell gene expression induced by maternal obesity, as well as sex differences in these alterations. We propose that Hofbauer cells, which are easily accessible at birth, provide novel insights into fetal brain microglial programs, and may facilitate the early identification of offspring vulnerable to neurodevelopmental disorders in the setting of maternal exposures.

Changes of optical coherence tomographic hyperreflective foci in rhegmatogenous retinal detachment patients after successful surgery

PURPOSE

To assess the changes of hyperreflective foci (HRF) in rhegmatogenous retinal detachment (RRD) patients after successful reattachment surgery.

METHODS

Twenty-nine macula-off RRD eyes with successful reattachment surgery were retrospectively analyzed. Optical coherence tomography (OCT) was used to image macular regions and measure HRF in outer retina and inner retina at 0.5, 1, 3, 6, 12 months after surgery. The relationships between HRF and photoreceptor layer status, visual outcomes were evaluated.

RESULTS

After retinal reattachment, HRF mainly distributed at the location where external limiting membrane (ELM) or inner and outer segment (IS/OS) line was disrupted. The HRF numbers in outer and inner retina were greater in eyes with discontinuous IS/OS line than eyes with continuous IS/OS line (all p<0.05). In the outer retina,  HRF increased in the initial three months after retinal reattachment, and then decreased gradually after 3 months (p<0.05). The HRF number in the outer retina at postoperative 0.5 months was associated with favorable visual outcomes at 6 and 12 months (r=-0.487,  p =0.025; r=-0.626,  p=0.005, respectively), nevertheless, the HRF number at 3 months was correlated with poor visual results at 6 and 12 months (r=0.441,  p =0.017; r=0.477,  p=0.019, respectively).

CONCLUSION

HRF mainly occurred near the site where ELM or IS/OS line was injured after retinal reattachment. In the outer retina, the number of HRF gradually increased in the first 3 months and then gradually decreased. The early appearance of HRF in the outer retina was associated with a good visual prognosis, while the late appearance may suggest a less favorable visual outcome.

Hofbauer cell function in the term placenta associates with adult cardiovascular and depressive outcomes

Pathological placental inflammation increases the risk for several adult disorders, but these mediators are also expressed under homeostatic conditions, where their contribution to adult health outcomes is unknown. Here we define an inflammation-related expression signature, primarily expressed in Hofbauer cells of the term placenta and use expression quantitative trait loci to create a polygenic score (PGS) predictive of its expression. Using this PGS in the UK Biobank we conduct a phenome-wide association study, followed by Mendelian randomization and identify protective, sex-dependent effects of the placental module on cardiovascular and depressive outcomes. Genes differentially regulated by intra-amniotic infection and preterm birth are over-represented within the module. We also identify aspirin as a putative modulator of this inflammation-related signature. Our data support a model where disruption of placental Hofbauer cell function, due to preterm birth or prenatal infection, contributes to the increased risk of depression and cardiovascular disease observed in these individuals.

Global m6A methylation and gene expression patterns in human microglial HMC3 cells infected with HIV-1

N6-methyladenosine (m6A) methylation of human immunodeficiency virus type 1 (HIV-1) RNA regulates viral replication, and the m6A of host RNA is affected by HIV-1 infection, but its global pattern and function are still unclear. In this study, we report that the number and position of m6A peaks in huge genes of human microglial HMC3 cells were modulated by a single cycle HIV-1 pseudotyped with VSV-G envelope glycoprotein infection using methylated RNA immunoprecipitation sequencing (MeRIP-seq). A conjoint analysis of MeRIP-seq and high-throughput sequencing for mRNA (RNA-seq) explored four groups of clearly classified genes, including 45 hyper-up (m6A-mRNA), 45 hyper-down, 120 hypo-up, and 54 hypo-down genes, in HIV-1 infected cells compared to uninfected ones. KEGG pathway analysis showed that these genes were mainly enriched in the Wnt and TNF signaling pathway, and cytokine-cytokine receptor interaction, which might be related to the immune response in HMC3 cells. And some of these genes might be associated with the pathway of axon guidance and neuroactive ligan-receptor interaction, which affect the neuronal state. However, the cognitive disorders caused by HIV-1 is associated with inflammatory changes that have not yet been well clarified. Furthermore, we confirmed the expression and m6A levels of four genes using RT-PCR and MeRIP-qPCR. Similar to the sequencing results, the expressions of these genes were significantly upregulated by HIV-1 infection. And the m6A level of IL-6 was downregulated, and those of HLA-B, CFB, and OLR1 were upregulated. These results suggest that HIV-1-induced changes in gene expression may be achieved through the regulation of methylation. Our study revealed the global m6A methylation and gene expression patterns under HIV-1 infection in human microglia, which might provide clues for understanding the interaction between HIV-1 and host cells and the cognitive disorders caused by HIV-1.

Understanding the diversity and dynamics of in vivo efferocytosis: Insights from the fly embryo

The clearance of dead and dying cells, termed efferocytosis, is a rapid and efficient process and one that is critical for organismal health. The extraordinary speed and efficiency with which dead cells are detected and engulfed by immune cells within tissues presents a challenge to researchers who wish to unravel this fascinating process, since these fleeting moments of uptake are almost impossible to catch in vivo. In recent years, the fruit fly (Drosophila melanogaster) embryo has emerged as a powerful model to circumvent this problem. With its abundance of dying cells, specialist phagocytes and relative ease of live imaging, the humble fly embryo provides a unique opportunity to catch and study the moment of cell engulfment in real-time within a living animal. In this review, we explore the recent advances that have come from studies in the fly, and how live imaging and genetics have revealed a previously unappreciated level of diversity in the efferocytic program. A variety of efferocytic strategies across the phagocytic cell population ensure efficient and rapid clearance of corpses wherever death is encountered within the varied and complex setting of a multicellular living organism.

Early diagnosis of retinal neurovascular injury in diabetic patients without retinopathy by quantitative analysis of OCT and OCTA

AIMS

To quantitatively analyze and compare the differences in retinal neurovascular units (NVUs) between healthy individuals and patients with type 2 diabetes mellitus (DM) by optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) techniques and to determine the value of this technique for the early diagnosis of retinal neurovascular damage in patients with diabetes mellitus without retinopathy (NDR).

METHODS

This observational case‒control study was conducted from July 1, 2022, to November 30, 2022, at the outpatient ophthalmology clinic of the Affiliated Hospital of Shandong University of Traditional Chinese Medicine. All subjects underwent baseline data entry and mean thickness of the peripapillary retinal nerve fiber layer (pRNFL), the thickness of each retinal layer in the macula 3 × 3 mm, and vascular density (VD) examination.

RESULTS

The study included 35 healthy individuals and 48 patients with DM. The retinal VD as well as partial pRNFL, macular nerve fiber layer (NFL), and macular ganglion cell layer (GCL) thickness in DM patients exhibited significantly lower VD in the DM group than in the control group (p < 0.05). Age and disease duration of DM patients showed a negative trend with pRNFL thickness, macular NFL thickness, macular GCL thickness, and VD. However, a positive trend was observed between DM duration and partial inner nuclear layer (INL) thickness. Moreover, there was a positive correlation between macular NFL and GCL thickness and VD for the most part, while a negative correlation was shown between INL temporal thickness and DVC-VD. pRNFL-TI and GCL-superior thickness were screened as two variables in the analysis of the predictors of retinal damage in DM according to the presence or absence of DM. The AUCs were 0.765 and 0.673, respectively. By combining the two indicators for diagnosis, the model predicted prognosis with an AUC of 0.831. In the analysis of retinal damage indicators associated with the duration of DM, after regression logistic analysis according to the duration of DM within 5 years and more than 5 years, the model incorporated two indicators, DVC-VD and pRNFL-N thickness, and the AUCs were 0.764 and 0.852, respectively. Combining the two indicators for diagnosis, the AUC reached 0.925.

CONCLUSIONS

Retinal NVU may have been compromised in patients with DM without retinopathy. Basic clinical information and rapid noninvasive OCT and OCTA techniques are useful for the quantitative assessment of retinal NVU prognosis in patients with DM without retinopathy.

Prenatally VPA exposure is likely to cause autistic-like behavior in the rats offspring via TREM2 down-regulation to affect the microglial activation and synapse alterations

Microglial dysfunction has been reported in the valproic acid (VPA)-induced autism spectrum disorder (ASD) rat models. However, how does prenatal VPA exposure affect microglia remains to be elucidated. The triggering receptor expressed on myeloid cells 2 (TREM2) is revealed to be implicated in a range of microglia functions. However, reports on the association between TREM2 and VPA-induced ASD rat models are scarce. Our results showed that prenatal VPA exposure induced autistic-like behaviors, downregulated the levels of TREM2, up-regulated microglial activation, dysregulated microglial polarization, and altered synapse in offspring. TREM2 overexpression partly ameliorated microglia dysfunction and autistic-like behaviors in prenatal VPA-exposed rats. Our findings demonstrated that prenatally VPA exposure is likely to cause autistic-like behavior in the rat offspring via TREM2 down-regulation to affect the microglial activation, microglial polarization and synaptic pruning of microglia for the first time.

An overview of hyperbaric oxygen preconditioning against ischemic stroke

Ischemic stroke (IS) has become the second leading cause of morbidity and mortality worldwide, and the prevention of IS should be given high priority. Recent studies have indicated that hyperbaric oxygen preconditioning (HBO-PC) may be a protective nonpharmacological method, but its underlying mechanisms remain poorly defined. This study comprehensively reviewed the pathophysiology of IS and revealed the underlying mechanism of HBO-PC in protection against IS. The preventive effects of HBO-PC against IS may include inducing antioxidant, anti-inflammation, and anti-apoptosis capacity; activating autophagy and immune responses; upregulating heat shock proteins, hypoxia-inducible factor-1, and erythropoietin; and exerting protective effects upon the blood-brain barrier. In addition, HBO-PC may be considered a safe and effective method to prevent IS in combination with stem cell therapy. Although the benefits of HBO-PC on IS have been widely observed in recent research, the implementation of this technique is still controversial due to regimen differences. Transferring the results to clinical application needs to be taken carefully, and screening for the optimal regimen would be a daunting task. In addition, whether we should prescribe an individualized preconditioning regimen to each stroke patient needs further exploration.

Inflammation and the Potential Implication of Macrophage-Microglia Polarization in Human ASD: An Overview

Autism spectrum disorder (ASD) is a heterogeneous collection of neurodevelopmental disorders, difficult to diagnose and currently lacking treatment options. The possibility of finding reliable biomarkers useful for early identification would offer the opportunity to intervene with treatment strategies to improve the life quality of ASD patients. To date, there are many recognized risk factors for the development of ASD, both genetic and non-genetic. Although genetic and epigenetic factors may play a critical role, the extent of their contribution to ASD risk is still under study. On the other hand, non-genetic risk factors include pollution, nutrition, infection, psychological states, and lifestyle, all together known as the exposome, which impacts the mother's and fetus's life, especially during pregnancy. Pathogenic and non-pathogenic maternal immune activation (MIA) and autoimmune diseases can cause various alterations in the fetal environment, also contributing to the etiology of ASD in offspring. Activation of monocytes, macrophages, mast cells and microglia and high production of pro-inflammatory cytokines are indeed the cause of neuroinflammation, and the latter is involved in ASD's onset and development. In this review, we focused on non-genetic risk factors, especially on the connection between inflammation, macrophage polarization and ASD syndrome, MIA, and the involvement of microglia.

Developmental and functional relationships between hypothalamic tanycytes and embryonic radial glia

The hypothalamus is a key regulator of several homeostatic processes, such as circadian rhythms, energy balance, thirst, and thermoregulation. Recently, the hypothalamic third ventricle has emerged as a site of postnatal neurogenesis and gliogenesis. This hypothalamic neural stem potential resides in a heterogeneous population of cells known as tanycytes, which, not unlike radial glia, line the floor and ventrolateral walls of the third ventricle and extend a long process into the hypothalamic parenchyma. Here, we will review historical and recent data regarding tanycyte biology across the lifespan, focusing on the developmental emergence of these diverse cells from embryonic radial glia and their eventual role contributing to a fascinating, but relatively poorly characterized, adult neural stem cell niche.

Synapse Dysfunctions in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic neuroinflammatory disease of the central nervous system (CNS) affecting nearly three million humans worldwide. In MS, cells of an auto-reactive immune system invade the brain and cause neuroinflammation. Neuroinflammation triggers a complex, multi-faceted harmful process not only in the white matter but also in the grey matter of the brain. In the grey matter, neuroinflammation causes synapse dysfunctions. Synapse dysfunctions in MS occur early and independent from white matter demyelination and are likely correlates of cognitive and mental symptoms in MS. Disturbed synapse/glia interactions and elevated neuroinflammatory signals play a central role. Glutamatergic excitotoxic synapse damage emerges as a major mechanism. We review synapse/glia communication under normal conditions and summarize how this communication becomes malfunctional during neuroinflammation in MS. We discuss mechanisms of how disturbed glia/synapse communication can lead to synapse dysfunctions, signaling dysbalance, and neurodegeneration in MS.

Serum complement proteins rather than inflammatory factors is effective in predicting psychosis in individuals at clinical high risk

Immunological/inflammatory factors are implicated in the development of psychosis. Complement is a key driver of inflammation; however, it remains unknown which factor is better at predicting the onset of psychosis. This study aimed to compare the alteration and predictive performance of inflammation and complement in individuals at clinical high risk (CHR). We enrolled 49 individuals at CHR and 26 healthy controls (HCs). Twenty-five patients at CHR had converted to psychosis (converter) by the 3-year follow-up. Inflammatory cytokines, including interleukin (IL)-1β, 6, 8, 10, tumor necrosis factor-alpha (TNF-alpha), macrophage colony-stimulating factor levels, and complement proteins (C1q, C2, C3, C3b, C4, C4b, C5, C5a, factor B, D, I, H) were measured by enzyme-linked immunosorbent assay at baseline. Except for TNF- alpha, none of the inflammatory cytokines reached a significant level in either the comparison of CHR individuals and HC or between CHR-converters and non-converters. The C5, C3, D, I, and H levels were significantly lower (C5, p = 0.006; C3, p = 0.009; D, p = 0.026; I, p = 0.016; H, p = 0.019) in the CHR group than in the HC group. Compared to non-converters, converters had significantly lower levels of C5 (p = 0.012) and C5a (p = 0.007). None of the inflammatory factors, but many complement factors, showed significant correlations with changes in general function and symptoms. None of the inflammatory markers, except for C5a and C5, were significant in the discrimination of conversion outcomes in CHR individuals. Our results suggest that altered complement levels in the CHR population are more associated with conversion to psychosis than inflammatory factors. Therefore, an activated complement system may precede the first-episode of psychosis and contribute to neurological pathogenesis at the CHR stage.

Once induced, it lasts for a long time: the structural and molecular signatures associated with depressive-like behavior after neonatal immune activation

Adverse factors such as stress or inflammation in the neonatal period can affect the development of certain brain structures and have negative delayed effects throughout the lifespan of an individual, by reducing cognitive abilities and increasing the risk of psychopathologies. One possible reason for these delayed effects is the neuroinflammation caused by neonatal immune activation (NIA). Neuroinflammation can lead to disturbances of neurotransmission and to reprogramming of astroglial and microglial brain cells; when combined, the two problems can cause changes in the cytoarchitecture of individual regions of the brain. In addition, neuroinflammation may affect the hypothalamic-pituitary-adrenal (HPA) axis and processes of oxidative stress, thereby resulting in higher stress reactivity. In our review, we tried to answer the questions of whether depressive-like behavior develops after NIA in rodents and what the molecular mechanisms associated with these disorders are. Most studies indicate that NIA does not induce depressive-like behavior in a steady state. Nonetheless, adult males (but not females or adolescents of both sexes) with experience of NIA exhibit marked depressive-like behavior when exposed to aversive conditions. Analyses of molecular changes have shown that NIA leads to an increase in the amount of activated microglia and astroglia in the frontal cortex and hippocampus, an increase in oxidative-stress parameters, a change in stress reactivity of the HPA axis, and an imbalance of cytokines in various regions of the brain, but not in blood plasma, thus confirming the local nature of the inflammation. Therefore, NIA causes depressive-like behavior in adult males under aversive testing conditions, which are accompanied by local inflammation and have sex- and age-specific effects.

The biological alterations of synapse/synapse formation in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a common complication caused by sepsis, and is responsible for increased mortality and poor outcomes in septic patients. Neurological dysfunction is one of the main manifestations of SAE patients. Patients may still have long-term cognitive impairment after hospital discharge, and the underlying mechanism is still unclear. Here, we first outline the pathophysiological changes of SAE, including neuroinflammation, glial activation, and blood-brain barrier (BBB) breakdown. Synapse dysfunction is one of the main contributors leading to neurological impairment. Therefore, we summarized SAE-induced synaptic dysfunction, such as synaptic plasticity inhibition, neurotransmitter imbalance, and synapses loss. Finally, we discuss the alterations in the synapse, synapse formation, and mediators associated with synapse formation during SAE. In this review, we focus on the changes in synapse/synapse formation caused by SAE, which can further understand the synaptic dysfunction associated with neurological impairment in SAE and provide important insights for exploring appropriate therapeutic targets of SAE.

Effects of various mRNA-LNP vaccine doses on neuroinflammation in BALB/c mice

It has been proven that mRNA vaccines are highly effective against the COVID-19 outbreak, and low prevalence of side effects has been shown. However, there are still many gaps in our understanding of the biology and biosafety of nucleic acids as components of lipid nanoparticles (LNPs) most often used as a system for inctracellular delivery of mRNA-based vaccines. It is known that LNPs cause severe injection site inflammation, have broad biodistribution profiles, and are found in multiple tissues of the body, including the brain, after administration. The role of new medications with such pharmacokinetics in inflammation developing in inaccessible organs is poorly understood. The study was aimed to assess the effects of various doses of mRNA-LNP expressing the reporter protein (0, 5, 10, and 20 μg of mRNA encoding the firefly luciferase) on the expression of neuroinflammation markers (Tnfα, Il1β, Gfap, Aif1) in the prefrontal cortex and hypothalamus of laboratory animals 4, 8, and 30 h after the intramuscular injection of LNP nanoemulsion. It was shown that mRNA-LNP vaccines in a dose of 10–20 μg of mRNA could enhance Aif1 expression in the hypothalamus 8 h after vaccination, however, no such differences were observed after 30 h. It was found that the Gfap, l11β, Tnfα expression levels in the hypothalamus observed at different times in the experimental groups were different. According to the results, mRNA-LNPs administered by the parenteral route can stimulate temporary activation of microglia in certain time intervals in the dose-dependent and site specific manner.

Increased production of inflammatory cytokines and activation of microglia in the fetal brain of preeclamptic mice induced by angiotensin II

Preeclampsia (PE) is a hypertensive obstetric disorder with poor prognosis for both the mother and offspring. Infants born to mothers with PE are known to be at increased risk of developing higher brain dysfunction, such as autism. However, how maternal PE can affect the environment in the fetal brain has not been fully elucidated. Here, we examined the impact of PE on the fetal brain in a mouse model of PE induced by angiotensin II (Ang II), focusing on changes in the inflammatory condition. We confirmed that pregnant mice which were continuously administered Ang II exhibited PE phenotypes, including high blood pressure, proteinuria, and fetal growth restriction. Quantitative RT-PCR analysis demonstrated that the brain of fetuses on embryonic day 17.5 (E17.5) in the Ang II-administered pregnant mice showed increased expression of cytokines, interleukin (IL)- 6, IL-17a, tumor necrosis factor-α, interferon-γ, IL-12, IL-4, and IL-10. Immunohistochemical analysis over a wide area, from the tip of the frontal lobe to the posterior cerebral end, on E17.5 revealed that the microglia in the fetal brain of the Ang II-administered group displayed higher solidity and circularity than those of the control group, indicating that the microglia had transformed to an amoeboid morphology and were activated. Our findings suggest that maternal PE may cause altered inflammatory conditions in the fetal brain, which might be associated with the pathological mechanism connecting maternal PE and brain dysfunction in the offspring.

Microglia have limited influence on early prion pathogenesis, clearance, or replication

Microglia (MG) are critical to host defense during prion infection, but the mechanism(s) of this neuroprotection are poorly understood. To better examine the influence of MG during prion infection, we reduced MG in the brains of C57BL/10 mice using PLX5622 and assessed prion clearance and replication using multiple approaches that included bioassay, immunohistochemistry, and Real-Time Quaking Inducted Conversion (RT-QuIC). We also utilized a strategy of intermittent PLX5622 treatments to reduce MG and allow MG repopulation to test whether new MG could alter prion disease progress. Lastly, we investigated the influence of MG using tga20 mice, a rapid prion model that accumulates fewer pathological features and less PrPres in the infected brain. In C57BL/10 mice we found that MG were excluded from the inoculation site early after infection, but Iba1 positive infiltrating monocytes/macrophage were present. Reducing MG in the brain prior to prion inoculation did not increase susceptibility to prion infection. Short intermittent treatments with PLX5622 in prion infected C57BL/10 mice after 80 dpi were unsuccessful at altering the MG population, gliosis, or survival. Additionally, MG depletion using PLX5622 in tga20 mice had only a minor impact on prion pathogenesis, indicating that the presence of MG might be less important in this fast model with less prion accumulation. In contrast to the benefits of MG against prion disease in late stages of disease, our current experiments suggest MG do not play a role in early prion pathogenesis, clearance, or replication.

The dual function of microglial polarization and its treatment targets in ischemic stroke

Stroke is the leading cause of disability and death worldwide, with ischemic stroke occurring in ~5% of the global population every year. Recently, many studies have been conducted on the inflammatory response after stroke. Microglial/macrophage polarization has a dual function and is critical to the pathology of ischemic stroke. Microglial/macrophage activation is important in reducing neuronal apoptosis, enhancing neurogenesis, and promoting functional recovery after ischemic stroke. In this review, we investigate the physiological characteristics and functions of microglia in the brain, the activation and phenotypic polarization of microglia and macrophages after stroke, the signaling mechanisms of polarization states, and the contribution of microglia to brain pathology and repair. We summarize recent advances in stroke-related microglia research, highlighting breakthroughs in therapeutic strategies for microglial responses after stroke, thereby providing new ideas for the treatment of ischemic stroke.

Microglial control of neuronal development via somatic purinergic junctions

Microglia, the resident immune cells of the brain, play important roles during development. Although bi-directional communication between microglia and neuronal progenitors or immature neurons has been demonstrated, the main sites of interaction and the underlying mechanisms remain elusive. By using advanced methods, here we provide evidence that microglial processes form specialized contacts with the cell bodies of developing neurons throughout embryonic, early postnatal, and adult neurogenesis. These early developmental contacts are highly reminiscent of somatic purinergic junctions that are instrumental for microglia-neuron communication in the adult brain. The formation and maintenance of these junctions is regulated by functional microglial P2Y12 receptors, and deletion of P2Y12Rs disturbs proliferation of neuronal precursors and leads to aberrant cortical cytoarchitecture during development and in adulthood. We propose that early developmental formation of somatic purinergic junctions represents an important interface for microglia to monitor the status of immature neurons and control neurodevelopment.

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.

Artificial gravity partially protects space-induced neurological deficits in Drosophila melanogaster

Spaceflight poses risks to the central nervous system (CNS), and understanding neurological responses is important for future missions. We report CNS changes in Drosophila aboard the International Space Station in response to spaceflight microgravity (SFμg) and artificially simulated Earth gravity (SF1g) via inflight centrifugation as a countermeasure. While inflight behavioral analyses of SFμg exhibit increased activity, postflight analysis displays significant climbing defects, highlighting the sensitivity of behavior to altered gravity. Multi-omics analysis shows alterations in metabolic, oxidative stress and synaptic transmission pathways in both SFμg and SF1g; however, neurological changes immediately postflight, including neuronal loss, glial cell count alterations, oxidative damage, and apoptosis, are seen only in SFμg. Additionally, progressive neuronal loss and a glial phenotype in SF1g and SFμg brains, with pronounced phenotypes in SFμg, are seen upon acclimation to Earth conditions. Overall, our results indicate that artificial gravity partially protects the CNS from the adverse effects of spaceflight.

Changes in microglia during drug treatment of stroke

Microglia are the main immune cells in the brain and the first defense barrier of the nervous system. Microglia play a complex role in the process of stroke. A growing number of studies focus on the mechanism of action of drugs functions and how to regulate microglia. Therefore, we talk about the pathophysiological mechanisms of stroke and elaborate on the microglia signaling pathways of drug action in stroke models and how these drugs play a role in stroke treatment in this review. Understanding how drugs modulate proinflammatory and anti-inflammatory responses of microglia may be critical to implementing therapeutic strategies using immune interventions in stroke.

Nerve Growth Factor Promotes Retinal Neurovascular Unit Repair: A Review

Purpose: The purpose of this paper is to investigate how the imbalance of neurogenic factor (NGF) and its precursor (pro-NGF) mediates structural and functional impairment of retinal neurovascular unit (RNVU) that plays a role in retinal degenerative diseases.Methods: A literature search of electronic databases was performed.Results: The pro-apoptotic effect of pro-NGF and the pro-growth effect of NGF are essential for the pathological and physiological activities of RNVU. Studies show that NGF-based treatment of retinal degenerative diseases, including glaucoma, age-related macular degeneration, retinitis pigmentosa, and diabetic retinopathy, has achieved remarkable efficacy.Conclusions: RNVU plays a complex and multifaceted role in retinal degenerative diseases. The exploration of the differential signaling expression of proNGF-NGF homeostasis under physiological and pathological conditions, and the corresponding pathological processes induced by its regulation, has prompted us to focus on earlier retinal neuroprotective therapeutic strategies to prevent retinal degenerative diseases.

Prenatal psychological or metabolic stress increases the risk for psychiatric disorders: the "funnel effect" model

Adverse stressful experiences in utero can redirect fetal brain development, ultimately leading to increased risk for psychiatric disorders. Obesity during pregnancy can have similar effects as maternal stress, affecting mental health in the offspring. In order to explain how similar outcomes may originate from different prenatal conditions, we propose a "funnel effect" model whereby maternal psychological or metabolic stress triggers the same evolutionarily conserved response pathways, increasing vulnerability for psychopathology. In this context, the placenta, which is the main mother-fetus interface, appears to facilitate such convergence, re-directing "stress" signals to the fetus. Characterizing converging pathways activated by different adverse environmental conditions is fundamental to assess the emergence of risk signatures of major psychiatric disorders, which might enable preventive measures in risk populations, and open up new diagnostics, and potentially therapeutic approaches for disease prevention and health promotion already during pregnancy.

Overview of myelin, major myelin lipids, and myelin-associated proteins

Myelin is a modified cell membrane that forms a multilayer sheath around the axon. It retains the main characteristics of biological membranes, such as lipid bilayer, but differs from them in several important respects. In this review, we focus on aspects of myelin composition that are peculiar to this structure and differentiate it from the more conventional cell membranes, with special attention to its constituent lipid components and several of the most common and important myelin proteins: myelin basic protein, proteolipid protein, and myelin protein zero. We also discuss the many-fold functions of myelin, which include reliable electrical insulation of axons to ensure rapid propagation of nerve impulses, provision of trophic support along the axon and organization of the unmyelinated nodes of Ranvier, as well as the relationship between myelin biology and neurologic disease such as multiple sclerosis. We conclude with a brief history of discovery in the field and outline questions for future research.

Modulation of retinoid-X-receptors differentially regulates expression of apolipoprotein genes apoc1 and apoeb by zebrafish microglia

Transcriptome analyses performed in both human and zebrafish indicate strong expression of Apoe and Apoc1 by microglia. Apoe expression by microglia is well appreciated, but Apoc1 expression has not been well-examined. PPAR/RXR and LXR/RXR receptors appear to regulate expression of the apolipoprotein gene cluster in macrophages, but a similar role in microglia in vivo has not been studied. Here, we characterized microglial expression of apoc1 in the zebrafish central nervous system (CNS) in situ and demonstrate that in the CNS, apoc1 expression is unique to microglia. We then examined the effects of PPAR/RXR and LXR/RXR modulation on microglial expression of apoc1 and apoeb during early CNS development using a pharmacological approach. Changes in apoc1 and apoeb transcripts in response to pharmacological modulation were quantified by RT-qPCR in whole heads, and in individual microglia using hybridization chain reaction (HCR) in situ hybridization. We found that expression of apoc1 and apoeb by microglia were differentially regulated by LXR/RXR and PPAR/RXR modulating compounds, respectively, during development. Our results also suggest RXR receptors could be involved in endogenous induction of apoc1 expression by microglia. Collectively, our work supports the use of zebrafish to better understand regulation and function of these apolipoproteins in the CNS.

Summary: Here we investigate expression of two apolipoprotein genes by microglia in the zebrafish model during normal development, and in contexts of pharmacological manipulations that target candidate regulatory receptors.

Molecular neuroimaging of inflammation in HIV

People with HIV now have near-normal life expectancies due to the success of effective combination antiretroviral therapy (cART). Following cART initiation, immune recovery occurs, and opportunistic diseases become rare. Despite this, high rates of non-infectious comorbidities persist in treated people with HIV, hypothesized to be related to persistent immuno-activation. One such comorbidity is cognitive impairment, which may partly be driven by ongoing neuro-inflammation in otherwise effectively treated people with HIV. In order to develop therapeutic interventions to address neuro-inflammation in effectively treated people with HIV, a deeper understanding of the pathogenic mechanisms driving persistent neuro-inflammatory responses and the ability to better characterize and measure neuro-inflammation in the central nervous system is required. This review highlights recent advances in molecular neuroimaging techniques which have the potential to assess neuro-inflammatory responses within the central nervous system in HIV disease. Proton magnetic resonance spectroscopy (1H-MRS) has been utilized to assess neuro-inflammatory responses since early in the HIV pandemic and shows promise in recent studies assessing different antiretroviral regimens. 1H-MRS is widely available in both resource-rich and some resource-constrained settings and is relatively inexpensive. Brain positron emission tomography (PET) imaging using Translocator Protein (TSPO) radioligands is a rapidly evolving field; newer TSPO-radioligands have lower signal-to-noise ratio and have the potential to localize neuro-inflammation within the brain in people with HIV. As HIV therapeutics evolve, people with HIV continue to age and develop age-related comorbidities including cognitive disorders. The use of novel neuroimaging modalities in the field is likely to advance in order to rapidly assess novel therapeutic interventions and may play a role in future clinical assessments.

The immune system and autism spectrum disorder: association and therapeutic challenges

Autism spectrum disorder (ASD) is a neurodevelopmental disorder, affecting communication and behavior. Historically, ASD had been described as a purely psychiatric disorder with genetic factors playing the most critical role. Recently, a growing body of literature has been emphasizing the importance of environmental and immunological factors in its pathogenesis, with the autoimmune process attracting the most attention. This study provides a review of the autoimmune involvement in the pathogenesis of ASD. The\r\nmicrobiome, the representative of the innate immune system in the central nervous system (CNS), plays a critical role in triggering inflammation. Besides, a bidirectional communicational pathway between the CNS and the intestine called the gut‑brain‑axis is linked to the development of ASD. Moreover, the higher plasma level of pro‑inflammatory cytokines in ASD patients and the higher prevalence of autoimmune disorders in the first‑degree family members of affected persons are other clues of the immune system involvement in\r\nthe pathogenesis of ASD. Furthermore, some anti‑inflammatory drugs, including resveratrol and palmitoylethanolamide have shown promising effects by relieving the manifestations of ASD. Although considerable advances have been made in elucidating the role of autoimmunity in the ASD pathogenesis, further studies with stronger methodologies are needed to apply the knowledge to the definitive treatment of ASD.

Innate immune responses after stimulation with Toll-like receptor agonists in ex vivo microglial cultures and an in vivo model using mice with reduced microglia

Background

Past experiments studying innate immunity in the central nervous system (CNS) utilized microglia obtained from neonatal mouse brain, which differ developmentally from adult microglia. These differences might impact our current understanding of the role of microglia in CNS development, function, and disease.

Methods

Cytokine protein secretion was compared in ex vivo P3 and adult microglial cultures after exposure to agonists for three different toll-like receptors (TLR4, lipopolysaccharide [LPS]; TLR7, imiquimod [IMQ]; and TLR9, CpG Oligodeoxynucleotide [CpG-ODN] 1585). In addition, changes in inflammatory gene expression in ex vivo adult microglia in response to the TLR agonists was assessed. Furthermore, in vivo experiments evaluated changes in gene expression associated with inflammation and TLR signaling in brains of mice with or without treatment with PLX5622 to reduce microglia.

Results

Ex vivo adult and P3 microglia increased cytokine secretion when exposed to TLR4 agonist LPS and to TLR7 agonist IMQ. However, adult microglia decreased expression of numerous genes after exposure to TLR 9 agonist CpG-ODN 1585. In contrast, in vivo studies indicated a core group of inflammatory and TLR signaling genes increased when each of the TLR agonists was introduced into the CNS. Reducing microglia in the brain led to decreased expression of various inflammatory and TLR signaling genes. Mice with reduced microglia showed extreme impairment in upregulation of genes after exposure to TLR7 agonist IMQ.

Conclusions

Cultured adult microglia were more reactive than P3 microglia to LPS or IMQ exposure. In vivo results indicated microglial influences on neuroinflammation were agonist specific, with responses to TLR7 agonist IMQ more dysregulated in mice with reduced microglia. Thus, TLR7-mediated innate immune responses in the CNS appeared more dependent on the presence of microglia. Furthermore, partial responses to TLR4 and TLR9 agonists in mice with reduced microglia suggested other cell types in the CNS can compensate for their absence.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02240-w.

The multifactorial roles of microglia and macrophages in the maintenance and progression of glioblastoma

The functional characteristics of glial cells, in particular microglia, have attained considerable importance in several diseases, including glioblastoma, the most hostile and malignant type of intracranial tumor. Microglia performs a highly significant role in the brain's inflammatory response mechanism. They exhibit anti-tumor properties via phagocytosis and the activation of a number of different cytotoxic substances. Some tumor-derived factors, however, transform these microglial cells into immunosuppressive and tumor-supportive, facilitating survival and progression of tumorigenic cells. Glioma-associated microglia and/or macrophages (GAMs) accounts for a large proportion of glioma infiltrating cells. Once within the tumor, GAMs exhibit a distinct phenotype of initiation that subsequently supports the growth and development of tumorigenic cells, angiogenesis and stimulates the infiltration of healthy brain regions. Interventions that suppress or prohibit the induction of GAMs at the tumor site or attenuate their immunological activities accommodating anti-tumor actions are likely to exert positive impact on glioblastoma treatment. In the present paper, we aim to summarize the most recent knowledge of microglia and its physiology, as well as include a very brief description of different molecular factors involved in microglia and glioblastoma interplay. We further address some of the major signaling pathways that regulate the baseline motility of glioblastoma progression. Finally, we discussed a number of therapeutic approaches regarding glioblastoma treatment.

CD22 Blockage Restores Age-Related Impairments of Microglia Surveillance Capacity

Microglia, the innate immune cells of the brain, are essential for maintaining homeostasis by their ramified, highly motile processes and for orchestrating the immune response to pathological stimuli. They are implicated in several neurodegenerative diseases like Alzheimer's and Parkinson's disease. One commonality of these diseases is their strong correlation with aging as the highest risk factor and studying age-related alterations in microglia physiology and associated signaling mechanism is indispensable for a better understanding of age-related pathomechanisms. CD22 has been identified as a modifier of microglia phagocytosis in a recent study, but not much is known about the function of CD22 in microglia. Here we show that CD22 surface levels are upregulated in aged versus adult microglia. Furthermore, in the amyloid mouse model PS2APP, Aβ-containing microglia also exhibit increased CD22 signal. To assess the impact of CD22 blockage on microglia morphology and dynamics, we have established a protocol to image microglia process motility in acutely prepared brain slices from CX3CR1-GFP reporter mice. We observed a significant reduction of microglial ramification and surveillance capacity in brain slices from aged versus adult mice. The age-related decrease in surveillance can be restored by antibody-mediated CD22 blockage in aged mice, whereas surveillance in adult mice is not affected by CD22 inhibition. Moreover to complement the results obtained in mice, we show that human iPSC-derived macrophages exhibit an increased phagocytic capacity upon CD22 blockage. Downstream analysis of antibody-mediated CD22 inhibition revealed an influence on BMP and TGFβ associated gene networks. Our results demonstrate CD22 as a broad age-associated modulator of microglia functionality with potential implications for neurodegenerative disorders.

Comparison of inflammatory, nutrient, and neurohormonal indicators in patients with schizophrenia, bipolar disorder and major depressive disorder

Psychiatric disorders are severe, debilitating conditions with unknown etiology and are commonly misdiagnosed, when based solely on clinical interviews, because of overlapping symptoms and similar familial patterns. Until now, no valid and objective biomarkers have been used to diagnose and differentiate between psychiatric disorders. We compared clinically tested serum indicators in terms of inflammation (C-reactive protein, complement proteins C3 and C4, and serum Immunoglobulins A, M, and G), nutrients (homocysteine, folate, and vitamin B12), and neurohormones (adrenocorticotropic hormone and cortisol) in patients with schizophrenia (SCZ, n = 1659), bipolar disorder (BD, n = 1901), and major depressive disorder (MDD, n = 1521) to investigate potential biomarkers. A receiver operating characteristic (ROC) curve was used to analyze the diagnostic potential of these analytes. We found that compared with MDD, serum levels of C-reactive protein, C3, C4, and homocysteine were higher in SCZ and BD groups, and folate and vitamin B12 were lower in SCZ and BD groups. In contrast with BD, adrenocorticotropic hormone and cortisol increased in patients with MDD. Although ROC analysis suggested that they were not able to effectively distinguish between the three, these biological indicators showed different patterns in the three disorders. As such, more specific biomarkers should be explored in the future.

Minocycline attenuation of rat corpus callosum abnormality mediated by low-dose lipopolysaccharide-induced microglia activation

Background

Microglia are resident innate immune cells in the brain, and activation of these myeloid cells results in secretion of a variety of pro-inflammatory molecules, leading to the development of neurodegenerative disorders. Lipopolysaccharide (LPS) is a widely used experimental stimulant in microglia activation. We have previously shown that LPS produced microglia activation and evoked detectable functional abnormalities in rat corpus callosum (CC) in vitro. Here, we further validated the effects of low-dose LPS-induced microglia activation and resultant white matter abnormality in the CC in an animal model and examined its attenuation by an anti-inflammatory agent minocycline.

Methods

Twenty-four SD rats were divided randomly into three groups and intra-peritoneally injected daily with saline, LPS, and LPS + minocycline, respectively. All animals were subject to MRI tests 6 days post-injection. The animals were then sacrificed to harvest the CC tissues for electrophysiology, western blotting, and immunocytochemistry. One-way ANOVA with Tukey’s post-test of all pair of columns was employed statistical analyses.

Results

Systemic administration of LPS produced microglial activation in the CC as illustrated by Iba-1 immunofluorescent staining. We observed that a large number of Iba-1-positive microglial cells were hyper-ramified with hypertrophic somata or even amoeba like in the LPS-treated animals, and such changes were significantly reduced by co-administration of minocycline. Electrophysiological recordings of axonal compound action potential (CAP) in the brain slices contained the CC revealed an impairment on the CC functionality as detected by a reduction in CAP magnitude. Such an impairment was supported by a reduction of fast axonal transportation evidenced by β-amyloid precursor protein accumulation. These alterations were attenuated by minocycline, demonstrating minocycline reduction of microglia-mediated interruption of white matter integrity and function in the CC.

Conclusions

Systemic administration of LPS produced microglia activation in the CC and resultant functional abnormalities that were attenuated by an anti-inflammatory agent minocycline.