Drugs Modulating CD4+ T Cells Blood-Brain Barrier Interaction in Alzheimer's Disease

Factors regulating the differences in frequency of infiltration of Th17 and Treg of the blood-brain barrier

Controlling CD4+ immune cell infiltration of the brain is a leading aim in designing therapeutic strategies for a range of neuropathological disorders such as multiple sclerosis, Alzheimer's disease, and depression. CD4+ T cells are a highly heterogeneous and reprogrammable family, which includes various distinctive cell types such as Th17, Th1, and Treg cells. Interestingly Th17 and Treg cells share a related transcriptomic profile, where the TGFβ-SMADS pathway plays a fundamental role in regulating the differentiation of both of these cell types. However, Th17 could be highly pathogenic and was shown to promote inflammation in various neuropathological disorders. Conversely, Treg is anti-inflammatory and is known to inhibit Th17. It could be noticed that Th17 frequencies of infiltration of the blood-brain barrier in various neurological disorders are significantly upregulated. However, Treg infiltration numbers are significantly low. The reasons behind these contradicting observations are still unknown. In this perspective, we propose that the difference in the T-cell receptor repertoire diversity, diapedesis pathways, chemokine expression, and mechanical properties of these two cell types could be contributing to answering this intriguing question.

Combined analysis of single-cell and bulk RNA sequencing reveals the expression patterns of circadian rhythm disruption in the immune microenvironment of Alzheimer's disease

Background

Circadian rhythm disruption (CRD) represents a critical contributor to the pathogenesis of Alzheimer's disease (AD). Nonetheless, how CRD functions within the AD immune microenvironment remains to be illustrated.

Methods

Circadian rhythm score (CRscore) was utilized to quantify the microenvironment status of circadian disruption in a single-cell RNA sequencing dataset derived from AD. Bulk transcriptome datasets from public repository were employed to validate the effectiveness and robustness of CRscore. A machine learning-based integrative model was applied for constructing a characteristic CRD signature, and RT-PCR analysis was employed to validate their expression levels.

Results

We depicted the heterogeneity in B cells, CD4⁺ T cells, and CD8⁺ T cells based on the CRscore. Furthermore, we discovered that CRD might be strongly linked to the immunological and biological features of AD, as well as the pseudotime trajectories of major immune cell subtypes. Additionally, cell-cell interactions revealed that CRD was critical in the alternation of ligand-receptor pairs. Bulk sequencing analysis indicated that the CRscore was found to be a reliable predictive biomarker in AD patients. The characteristic CRD signature, which included 9 circadian-related genes (CRGs), was an independent risk factor that accurately predicted the onset of AD. Meanwhile, abnormal expression of several characteristic CRGs, including GLRX, MEF2C, PSMA5, NR4A1, SEC61G, RGS1, and CEBPB, was detected in neurons treated with Aβ1-42 oligomer.

Conclusion

Our study revealed CRD-based cell subtypes in the AD microenvironment at single-cell level and proposed a robust and promising CRD signature for AD diagnosis. A deeper knowledge of these mechanisms may provide novel possibilities for incorporating "circadian rhythm-based anti-dementia therapies" into the treatment protocols of individualized medicine.

The Role of CD4+ T Cells in the Immunotherapy of Brain Disease by Secreting Different Cytokines

Upon different stimulation, naïve CD4⁺ T cells differentiate into various subsets of T helper (Th) cells, including Th1, Th2, Th17, and Tregs. They play both protective and pathogenic roles in the central nervous system (CNS) by secreting different cytokines. Failure of the homeostasis of the subgroups in the CNS can result in different brain diseases. Recently, immunotherapy has drawn more and more attention in the therapy of various brain diseases. Here, we describe the role of different CD4⁺ T cell subsets and their secreted cytokines in various brain diseases, as well as the ways in which by affecting CD4⁺ T cells in therapy of the CNS diseases. Understanding the role of CD4⁺ T cells and their secreted cytokines in the immunotherapy of brain disease will provide new targets and therapeutics for the treatment of brain disease. The role of CD4 + T cell subtypes in different diseases and their associated regulatory genes, proteins, and enzymes. CD4 + T cell subtypes play both protective (green) and pathogenic (red) roles in different brain diseases. The immune regulatory effects of CD4 + T cells and their subtypes are promoted or inhibited by different genes, proteins, and enzymes.

Identification of mRNA expression biomarkers associated with epilepsy and response to valproate with co-expression analysis

Purpose

Valproate (VPA) resistance was reported to be an important predictor of intractable epilepsy. We conducted this study to identify candidate biomarkers in peripheral blood correlated with VPA resistance.

Methods

The microarray dataset (GSE143272) was downloaded from the Gene Expression Omnibus database. Weighted gene co-expression network analysis (WGCNA) was performed to construct co-expression modules and obtain the most prominent module associated with VPA resistance. Differentially expressed genes (DEGs) between VPA-responsive and VPA-resistant patients were obtained using the “Limma” package in R. The intersections between the most prominent module and DEGs were identified as target genes. Metascape was performed to discover the possible involved pathways of the target genes. GeneCards database was used to know the function of each target gene.

Results

All genes in the GSE143272 were divided into 24 different modules. Among these modules, the darkred module showed a pivotal correlation with VPA resistance. A total of 70 DEGs between VPA-responsive and VPA-resistant patients were identified. After taking the intersection, 25 target genes were obtained. The 25 target genes were significantly enriched in T cell receptor recognition, T cell receptor signaling pathway, regulation of T cell activation, cytokine–cytokine receptor interaction, and in utero embryonic development. Half of the target genes (CD3D, CD3G, CXCR3, CXCR6, GATA3, GZMK, IL7R, LIME1, SIRPG, THEMIS, TRAT1, and ZNF683) were directly involved in the T cell development, migration, and activation signaling pathway.

Conclusion

We identified 25 target genes prominently associated with VPA resistance, which could be potential candidate biomarkers for epilepsy resistance in peripheral blood. The peripheral blood T cells may play a crucial role in VPA resistance. Those genes and pathways might become therapeutic targets with clinical usefulness in the future.

Adera2.0: A Drug Repurposing Workflow for Neuroimmunological Investigations Using Neural Networks

Drug repurposing in the context of neuroimmunological (NI) investigations is still in its primary stages. Drug repurposing is an important method that bypasses lengthy drug discovery procedures and focuses on discovering new usages for known medications. Neuroimmunological diseases, such as Alzheimer's, Parkinson's, multiple sclerosis, and depression, include various pathologies that result from the interaction between the central nervous system and the immune system. However, the repurposing of NI medications is hindered by the vast amount of information that needs mining. We previously presented Adera1.0, which was capable of text mining PubMed for answering query-based questions. However, Adera1.0 was not able to automatically identify chemical compounds within relevant sentences. To challenge the need for repurposing known medications for neuroimmunological diseases, we built a deep neural network named Adera2.0 to perform drug repurposing. The workflow uses three deep learning networks. The first network is an encoder and its main task is to embed text into matrices. The second network uses a mean squared error (MSE) loss function to predict answers in the form of embedded matrices. The third network, which constitutes the main novelty in our updated workflow, also uses a MSE loss function. Its main usage is to extract compound names from relevant sentences resulting from the previous network. To optimize the network function, we compared eight different designs. We found that a deep neural network consisting of an RNN neural network and a leaky ReLU could achieve 0.0001 loss and 67% sensitivity. Additionally, we validated Adera2.0's ability to predict NI drug usage against the DRUG Repurposing Hub database. These results establish the ability of Adera2.0 to repurpose drug candidates that can shorten the development of the drug cycle. The workflow could be download online.

Sex differences in the genetic architecture of cognitive resilience to Alzheimer's disease

Approximately 30% of elderly adults are cognitively unimpaired at time of death despite the presence of Alzheimer's disease neuropathology at autopsy. Studying individuals who are resilient to the cognitive consequences of Alzheimer's disease neuropathology may uncover novel therapeutic targets to treat Alzheimer's disease. It is well established that there are sex differences in response to Alzheimer's disease pathology, and growing evidence suggests that genetic factors may contribute to these differences. Taken together, we sought to elucidate sex-specific genetic drivers of resilience. We extended our recent large scale genomic analysis of resilience in which we harmonized cognitive data across four cohorts of cognitive ageing, in vivo amyloid PET across two cohorts, and autopsy measures of amyloid neuritic plaque burden across two cohorts. These data were leveraged to build robust, continuous resilience phenotypes. With these phenotypes, we performed sex-stratified [n (males) = 2093, n (females) = 2931] and sex-interaction [n (both sexes) = 5024] genome-wide association studies (GWAS), gene and pathway-based tests, and genetic correlation analyses to clarify the variants, genes and molecular pathways that relate to resilience in a sex-specific manner. Estimated among cognitively normal individuals of both sexes, resilience was 20-25% heritable, and when estimated in either sex among cognitively normal individuals, resilience was 15-44% heritable. In our GWAS, we identified a female-specific locus on chromosome 10 [rs827389, β (females) = 0.08, P (females) = 5.76 × 10-09, β (males) = -0.01, P(males) = 0.70, β (interaction) = 0.09, P (interaction) = 1.01 × 10-04] in which the minor allele was associated with higher resilience scores among females. This locus is located within chromatin loops that interact with promoters of genes involved in RNA processing, including GATA3. Finally, our genetic correlation analyses revealed shared genetic architecture between resilience phenotypes and other complex traits, including a female-specific association with frontotemporal dementia and male-specific associations with heart rate variability traits. We also observed opposing associations between sexes for multiple sclerosis, such that more resilient females had a lower genetic susceptibility to multiple sclerosis, and more resilient males had a higher genetic susceptibility to multiple sclerosis. Overall, we identified sex differences in the genetic architecture of resilience, identified a female-specific resilience locus and highlighted numerous sex-specific molecular pathways that may underly resilience to Alzheimer's disease pathology. This study illustrates the need to conduct sex-aware genomic analyses to identify novel targets that are unidentified in sex-agnostic models. Our findings support the theory that the most successful treatment for an individual with Alzheimer's disease may be personalized based on their biological sex and genetic context.

Th17 cells and inflammation in neurological disorders: Possible mechanisms of action

Neurological disorders (NDs) are one of the leading causes of global death. A sustained neuroinflammatory response has been reported to be associated with the pathogenesis of multiple NDs, including Parkinson’s disease (PD), multiple sclerosis (MS), Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), and major depressive disorder (MDD). Accumulating evidence shows that the recruitment of abundant lymphocytes in the central nervous system may contribute to promoting the development and progress of inflammation in neurological disorders. As one subset of T lymphocytes, CD4⁺ T cells have a critical impact on the inflammation of neurological disorders. T helper (Th) 17 is one of the most studied CD4⁺ Th subpopulations that produces cytokines (e.g., IL-17A, IL-23, IL-21, IL-6, and IFN-γ), leading to the abnormal neuroinflammatory response including the excessive activation of microglia and the recruitment of other immune cell types. All these factors are involved in several neurological disorders. However, the possible mechanisms of Th17 cells and their associated cytokines in the immunopathology of the abovementioned neurological disorders have not been clarified completely. This review will summarize the mechanisms by which encephalitogenic inflammatory Th17 cells and their related cytokines strongly contribute to chronic neuroinflammation, thus perpetuating neurodegenerative processes in NDs. Finally, the potential therapeutic prospects of Th17 cells and their cytokines in NDs will also be discussed.

An Update on the Evolutionary History of Bregs

The relationship between the evolutionary history and the differentiation of Bregs is still not clear. Bregs were demonstrated to possess a regulatory effect on B cells. Various subsets of Bregs have been identified including T2-MZP, MZ, B10, IL10-producing plasma cells, IL10 producing plasmablasts, immature IL10 producing B cells, TIM1, and Br1. It is known that B cells have evolved during fish emergence. However, the origin of Bregs is still not known. Three main models have been previously proposed to describe the origin of Bregs, the first known as single–single (SS) suggests that each type of Bregs subpopulation has emerged from a single pre-Breg type. The second model (single–multi) (SM) assumes that a single Bregs gave rise to multiple types of Bregs that in turn differentiated to other Breg subpopulations. In the third model (multi–multi) (MM), it is hypothesized that Bregs arise from the nearest B cell phenotype. The link between the differentiation of cells and the evolution of novel types of cells is known to follow one of three evolutionary patterns (i.e., homology, convergence, or concerted evolution). Another aspect that controls differentiation and evolution processes is the principle of optimization of energy, which suggests that an organism will always use the choice that requires less energy expenditure for survival. In this review, we investigate the evolution of Breg subsets. We studied the feasibility of Breg origination models based on evolution and energy constraints. In conclusion, our review indicates that Bregs are likely to have evolved under a combination of SM–MM models. This combination ensured successful survival in harsh conditions by following the least costly differentiation pathway, as well as adapting to changing environmental conditions.

The role of Th17 cells/IL-17A in AD, PD, ALS and the strategic therapy targeting on IL-17A

Neurodegenerative diseases are a group of disorders characterized by progressive loss of certain populations of neurons, which eventually lead to dysfunction. These diseases include Alzheimer’s disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS). Immune pathway dysregulation is one of the common features of neurodegeneration. Recently, there is growing interest in the specific role of T helper Th 17 cells and Interleukin-17A (IL-17A), the most important cytokine of Th 17 cells, in the pathogenesis of the central nervous system (CNS) of neurodegenerative diseases. In the present study, we summarized current knowledge about the function of Th17/IL-17A, the physiology of Th17/IL-17A in diseases, and the contribution of Th17/IL-17A in AD, PD, and ALS. We also update the findings on IL-17A-targeting drugs as potentially immunomodulatory therapeutic agents for neurodegenerative diseases. Although the specific mechanism of Th17/IL-17A in this group of diseases is still controversial, uncovering the molecular pathways of Th17/IL-17A in neurodegeneration allows the identification of suitable targets to modulate these cellular processes. Therapeutics targeting IL-17A might represent potentially novel anti-neurodegeneration drugs.

Cellular Immune Signal Exchange From Ischemic Stroke to Intestinal Lesions Through Brain-Gut Axis

As a vital pivot for the human circulatory system, the brain-gut axis is now being considered as an important channel for many of the small immune molecules’ transductions, including interleukins, interferons, neurotransmitters, peptides, and the chemokines penetrating the mesentery and blood brain barrier (BBB) during the development of an ischemic stroke (IS). Hypoxia-ischemia contributes to pituitary and neurofunctional disorders by interfering with the molecular signal release and communication then providing feedback to the gut. Suffering from such a disease on a long-term basis may cause the peripheral system’s homeostasis to become imbalanced, and it can also lead to multiple intestinal complications such as gut microbiota dysbiosis (GMD), inflammatory bowel disease (IBD), necrotizing enterocolitis (NEC), and even the tumorigenesis of colorectal carcinoma (CRC). Correspondingly, these complications will deteriorate the cerebral infarctions and, in patients suffering with IS, it can even ruin the brain’s immune system. This review summarized recent studies on abnormal immunological signal exchange mediated polarization subtype changes, in both macrophages and microglial cells as well as T-lymphocytes. How gut complications modulate the immune signal transduction from the brain are also elucidated and analyzed. The conclusions drawn in this review could provide guidance and novel strategies to benefit remedies for both IS and relative gut lesions from immune-prophylaxis and immunotherapy aspects.

Polysaccharide from Ganoderma lucidum alleviates cognitive impairment in a mouse model of chronic cerebral hypoperfusion by regulating CD4+CD25+Foxp3+ regulatory T cells

Ganoderma lucidum (G. lucidum) is a kind of edible and medicinal mushroom. G. lucidum polysaccharide-1 (GLP-1) is one of the polysaccharides purified from crude GLP. Chronic cerebral hypoperfusion (CCH) as the common pathological basis of various forms of dementia is an important cause of cognitive impairment. In this study, a step-down test was used to evaluate the cognitive ability of CCH mice. Flow cytometry was used to detect the proportion of CD4⁺CD25⁺Foxp3⁺ regulatory T (Foxp3⁺Treg) cells. ELISA analysis and western blot analysis were used to detect the transforming growth factor-β1 (TGF-β1) and Interleukin-10 (IL-10) levels that Foxp3⁺Treg cells secreted. Metabolomic analysis based on gas chromatography-mass spectrometry (GC-MS) was used to evaluate the effect of GLP-1 on dysfunctional metabolism caused by inflammation. Results indicate that GLP-1 exhibited an alleviating cognitive impairment effect on CCH mice. The mechanism was related to GLP-1 by increasing Foxp3⁺Treg cell levels to increase levels of IL-10 and TGF-β1 and regulate abnormal energy metabolism. These findings could provide preliminary results to exploit G. lucidum as a health care product or functional food for the adjuvant therapy of cognitive impairment of CCH.

Ganoderic Acid A To Alleviate Neuroinflammation of Alzheimer's Disease in Mice by Regulating the Imbalance of the Th17/Tregs Axis

Ganoderic acid A (GAA) is a kind of lanostane-type triterpenoid isolated from Ganoderma lucidum. Imbalance of the Th17/Tregs axis exists in the progress of neuroinflammation of Alzheimer's disease (AD). In this study, the alleviating neuroinflammatory effect of GAA on d-galactose mice was studied from the aspect of regulating the imbalance of the Th17/Tregs axis. The Morris water maze test was used to evaluate the cognitive ability of AD mice. Flow cytometry was used to detect the percentages of IL-17A, IL-17F, IL-21, IL-22, and CD4⁺CD25⁺Foxp3⁺ in peripheral blood. Transmission electron microscopy was used to assess the cerebral mitochondrial ultrastructure. Metabolomic analysis based on gas chromatography-mass spectrometry was used to evaluate the mitochondrial dysfunction metabolism. Western blot analysis was used to detect the protein expressions of cytokines secreted by Th17 cells and Treg cells in the brain. As the results show, GAA has an alleviating neuroinflammatory effect on AD mice via regulating the imbalance of the Th17/Tregs axis. The potential mechanism was related to inhibition of the JAK/STAT signaling pathway induced by Th17 cells and enhancement of the mitochondrial oxidative phosphorylation by regulating Treg cells, thereby improving mitochondrial dysfunction of AD mice.

Alterations in T-Cell Transcription Factors and Cytokine Gene Expression in Late-Onset Alzheimer's Disease

BACKGROUND

Late-onset Alzheimer's disease (LOAD) is associated with many environmental and genetic factors. The effect of systemic inflammation on the pathogenesis of neurodegenerative diseases such as AD has been strongly suggested. T helper cells (Th) are one of the important components of the immune system and can easily infiltrate the brain in pathological conditions. The development of each Th-subset depends on the production of unique cytokines and their main regulator.

OBJECTIVE

This study aimed to compare the mRNA levels of Th-related genes derived from peripheral blood mononuclear cells of LOAD patients with control. Also, the identification of the most important Th1/Th2 genes and downstream pathways that may be involved in the pathogenesis of AD was followed by computational approaches.

METHODS

This study invloved 30 patients with LOAD and 30 non-demented controls. The relative expression of T-cell cytokines (IFN-γ, TNF-α, IL-4, and IL-5) and transcription factors (T-bet and GATA-3) were assessed using real-time PCR. Additionally, protein-protein interaction (PPI) was investigated by gene network construction.

RESULTS

A significant decrease at T-bet, IFN-γ, TNF-α, and GATA-3 mRNA levels was detected in the LOAD group, compared to the controls. However, there was no significant difference in IL-4 or IL-5 mRNA levels. Network analysis revealed a list of the highly connected protein (hubs) related to mitogen-activated protein kinase (MAPK) signaling and Th17 cell differentiation pathways.

CONCLUSION

The findings point to a molecular dysregulation in Th-related genes, which can promising in the early diagnosis or targeted interventions of AD. Furthermore, the PPI analysis showed that upstream off-target stimulation may involve MAPK cascade activation and Th17 axis induction.

Dexmedetomidine alleviates cognitive impairment by reducing blood-brain barrier interruption and neuroinflammation via regulating Th1/Th2/Th17 polarization in an experimental sepsis model of mice

Clinical studies have shown that dexmedetomidine (DEX) reduces mortality and inflammation in patients with sepsis, and ameliorates cognitive decline in both postoperative and critical care patients. This study aims to explain the neuroprotective effects provided by DEX in mice with cecal ligation and puncture (CLP)-induced polymicrobial sepsis. Mice were treated with DEX intraperitoneally three times every two hours after CLP. The survival rate, body weight, and clinical scores were recorded each day. Morris water maze (MWM) and fear conditioning tests were used to evaluate cognitive function. Blood brain barrier (BBB) permeability, hippocampal inflammation, hippocampal neural apoptosis, and T helper (Th) cell subgroups were assessed. Furthermore, Atipamezole was used to verify that the potential neuroprotective effects in the sepsis-associated encephalopathy (SAE) were mediated by DEX. Compared with the Sham group, CLP mice showed significant cognitive impairment, BBB interruption, excessive neuroinflammation, and neuronal apoptosis. These detrimental effects of CLP were attenuated by DEX. Furthermore, we found that DEX corrects peripheral Th1/Th2/Th17 shift and reduces proinflammatory cytokines in the hippocampus. Additionally, atipamezole prevented DEX's protective effect. Taken together, DEX alleviates cognitive impairments by reducing blood-brain barrier interruption and neuroinflammation by regulating Th1/Th2/Th17 polarization.

Cellular and molecular influencers of neuroinflammation in Alzheimer's disease: Recent concepts & roles

Alzheimer's disease (AD), an extremely common neurodegenerative disorder of the older generation, is one of the leading causes of death globally. Besides the conventional hallmarks i.e. Amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs), neuroinflammation also serves as a major contributing factor in the pathogenesis of AD. There are mounting evidences to support the fundamental role of cellular (microglia, astrocytes, mast cells, and T-cells) and molecular (cytokines, chemokines, caspases, and complement proteins) influencers of neuroinflammation in producing/promoting neurodegeneration and dementia in AD. Genome-wide association studies (GWAS) have revealed the involvement of various single nucleotide polymorphisms (SNPs) of genes related to neuroinflammation with the risk of developing AD. Modulating the release of the neuroinflammatory molecules and targeting their relevant mechanisms may have beneficial effects on the onset, progress and severity of the disease. Here, we review the distinct role of various mediators and modulators of neuroinflammation that impact the pathogenesis and progression of AD as well as incite further research efforts for the treatment of AD through a neuroinflammatory approach.

JKAP, Th1 cells, and Th17 cells are dysregulated and inter-correlated, among them JKAP and Th17 cells relate to cognitive impairment progression in Alzheimer's disease patients

BACKGROUND

JNK pathway-associated phosphatase (JKAP) is engaged in Alzheimer's disease (AD) pathology via regulating immune response, cluster of differentiation 4 positive (CD4⁺) T cell differentiation, inflammation, and phosphorylated tau (p-tau). This study aimed to investigate its clinical value serving as a biomarker for AD.

METHODS

Fifty AD patients, 50 Parkinson's disease (PD) patients, and 50 controls (patients with non-degenerative neurological diseases with normal cognition) were enrolled. Their β-protein 42 (Aβ42), total tau (t-tau), p-tau, and Mini-Mental State Examination (MMSE) scale were assessed. Furthermore, JKAP in serum and T-help type 1 (Th1) and T-help type 17 (Th17) cells in CD4⁺ T cells were measured.

RESULTS

JKAP level was lower, while Th17 cell proportion (but not Th1 cell proportion) was higher in AD patients compared with PD patients and controls (all P < 0.01). Besides, JKAP level negatively correlated with both Th1 (r =  - 0.306, P = 0.030) and Th17 (r =  - 0.380, P = 0.006) cell proportions in AD patients but not PD patients and controls. Furthermore, in AD patients, JKAP positively correlated with Aβ42 (r = 0.307, P = 0.030) and MMSE score (r = 0.350, P = 0.013) while negatively correlated with p-tau (r =  - 0.280, P = 0.048); Th17 cell proportion negatively associated with Aβ42 (r =  - 0.281, P = 0.048) and MMSE score (r =  - 0.366, P = 0.009). Notably, JKAP was negatively related to 1-year (r =  - 0.297, P = 0.038) and 2-year MMSE decline (r =  - 0.304, P = 0.048); Th17 cell proportion was positively linked with 1-year (r = 0.392; P = 0.008), 2-year (r = 0.482, P = 0.001), and 3-year (r = 0.365, P = 0.013) MMSE decline.

CONCLUSION

JKAP, Th1 cells, and Th17 cells are dysregulated and inter-correlated; among them, JKAP and Th17 cells relate to cognitive impairment progression in AD patients.

Investigation of Evolutionary History and Origin of the Tre1 Family Suggests a Role in Regulating Hemocytes Cells Infiltration of the Blood-Brain Barrier

Simple Summary

Understanding the evolutionary association between immune cells and the blood–brain barrier (BBB) is vital to develop therapeutic approaches. In Drosophila, glial cells form the BBB that regulates the access of hemocytes to the brain. It is still not known which diapedesis route hemocytes cells follow. In vertebrates, paracellular migration is dependent on PECAM1, while transcellular migration is dependent on the expression of CAV1. The drosophila genome lacks both genes. The Tre1 family (Tre1, moody, and Dmel_CG4313) contribute to regulating transepithelial migration in Drosophila. However, its evolutionary history is not known. We performed phylogenetic analysis to reconstruct the evolutionary history of the Tre1 family. We found Dmel_CG4313 only in insects. Tre1 exists only in invertebrates and is highly conserved. moody evolutionary history is more spread as it appears from Cnidaria up to mammals and is less conserved. The Tre1 family origin seems to be related to opsins. We have identified an SH3 motif in Tre1, moody, and Dmel_CG4313. SH3 regulates actin movement in a Rho-dependent manner in PECAM1. Our results suggest that the Tre1 family could be playing an important role in paracellular diapedesis in Drosophila. Thus, targeting the Tre1 family could help us regulate access to the brain.

Abstract

Understanding the evolutionary relationship between immune cells and the blood–brain barrier (BBB) is important to devise therapeutic strategies. In vertebrates, immune cells follow either a paracellular or a transcellular pathway to infiltrate the BBB. In Drosophila, glial cells form the BBB that regulates the access of hemocytes to the brain. However, it is still not known which diapedesis route hemocytes cells follow. In vertebrates, paracellular migration is dependent on PECAM1, while transcellular migration is dependent on the expression of CAV1. Interestingly Drosophila genome lacks both genes. Tre1 family (Tre1, moody, and Dmel_CG4313) play a diverse role in regulating transepithelial migration in Drosophila. However, its evolutionary history and origin are not yet known. We performed phylogenetic analysis, together with HH search, positive selection, and ancestral reconstruction to investigate the Tre1 family. We found that Tre1 exists in Mollusca, Arthropoda, Ambulacraria, and Scalidophora. moody is shown to be a more ancient protein and it has existed since Cnidaria emergence and has a homolog (e.g., GPCR84) in mammals. The third family member (Dmel_CG4313) seems to only exist in insects. The origin of the family seems to be related to the rhodopsin-like family and in particular family α. We found that opsin is the nearest receptor to have a common ancestor with the Tre1 family that has diverged in sponges. We investigated the positive selection of the Tre1 family using PAML. Tre1 seems to have evolved under negative selection, whereas moody has evolved during positive selection. The sites that we found under positive selection are likely to play a role in the speciation of function in the case of moody. We have identified an SH3 motif, in Tre1 and, moody and Dmel_CG4313. SH3 is known to play a fundamental role in regulating actin movement in a Rho-dependent manner in PECAM1. Our results suggest that the Tre1 family could be playing an important role in paracellular diapedesis in Drosophila.

Identifying the Main Functional Pathways Associated with Cognitive Resilience to Alzheimer's Disease

Understanding the mechanisms involved in cognitive resilience in Alzheimer’s disease (AD) represents a promising strategy to identify novel treatments for dementia in AD. Previous findings from our group revealed that the study of aged-Tg2576 cognitive resilient individuals is a suitable tool for this purpose. In the present study, we performed a transcriptomic analysis using the prefrontal cortex of demented and resilient Tg2576 transgenic AD mice. We have been able to hypothesize that pathways involved in inflammation, amyloid degradation, memory function, and neurotransmission may be playing a role on cognitive resilience in AD. Intriguingly, the results obtained in this study are suggestive of a reduction of the influx of peripheral immune cells into the brain on cognitive resilient subjects. Indeed, CD4 mRNA expression is significantly reduced on Tg2576 mice with cognitive resilience. For further validation of this result, we analyzed CD4 expression in human AD samples, including temporal cortex and peripheral blood mononuclear cells (PBMC). Interestingly, we have found a negative correlation between CD4 mRNA levels in the periphery and the score in the Mini-Mental State Exam of AD patients. These findings highlight the importance of understanding the role of the immune system on the development of neurodegenerative diseases and points out to the infiltration of CD4⁺ cells in the brain as a key player of cognitive dysfunction in AD.

Interleukins and Interleukin Receptors Evolutionary History and Origin in Relation to CD4+ T Cell Evolution

Understanding the evolution of interleukins and interleukin receptors is essential to control the function of CD4+ T cells in various pathologies. Numerous aspects of CD4+ T cells’ presence are controlled by interleukins including differentiation, proliferation, and plasticity. CD4+ T cells have emerged during the divergence of jawed vertebrates. However, little is known about the evolution of interleukins and their origin. We traced the evolution of interleukins and their receptors from Placozoa to primates. We performed phylogenetic analysis, ancestral reconstruction, HH search, and positive selection analysis. Our results indicated that various interleukins’ emergence predated CD4+ T cells divergence. IL14 was the most ancient interleukin with homologs in fungi. Invertebrates also expressed various interleukins such as IL41 and IL16. Several interleukin receptors also appeared before CD4+ T cells divergence. Interestingly IL17RA and IL17RD, which are known to play a fundamental role in Th17 CD4+ T cells first appeared in mollusks. Furthermore, our investigations showed that there is not any single gene family that could be the parent group of interleukins. We postulate that several groups have diverged from older existing cytokines such as IL4 from TGFβ, IL10 from IFN, and IL28 from BCAM. Interleukin receptors were less divergent than interleukins. We found that IL1R, IL7R might have diverged from a common invertebrate protein that contained TIR domains, conversely, IL2R, IL4R and IL6R might have emerged from a common invertebrate ancestor that possessed a fibronectin domain. IL8R seems to be a GPCR that belongs to the rhodopsin-like family and it has diverged from the Somatostatin group. Interestingly, several interleukins that are known to perform a critical function for CD4+ T cells such as IL6, IL17, and IL1B have gained new functions and evolved under positive selection. Overall evolution of interleukin receptors was not under significant positive selection. Interestingly, eight interleukin families appeared in lampreys, however, only two of them (IL17B, IL17E) evolved under positive selection. This observation indicates that although lampreys have a unique adaptive immune system that lacks CD4+ T cells, they could be utilizing interleukins in homologous mode to that of the vertebrates’ immune system. Overall our study highlights the evolutionary heterogeneity within the interleukins and their receptor superfamilies and thus does not support the theory that interleukins evolved solely in jawed vertebrates to support T cell function. Conversely, some of the members are likely to play conserved functions in the innate immune system.

Paracellular and Transcellular Leukocytes Diapedesis Are Divergent but Interconnected Evolutionary Events

Infiltration of the endothelial layer of the blood-brain barrier by leukocytes plays a critical role in health and disease. When passing through the endothelial layer during the diapedesis process lymphocytes can either follow a paracellular route or a transcellular one. There is a debate whether these two processes constitute one mechanism, or they form two evolutionary distinct migration pathways. We used artificial intelligence, phylogenetic analysis, HH search, ancestor sequence reconstruction to investigate further this intriguing question. We found that the two systems share several ancient components, such as RhoA protein that plays a critical role in controlling actin movement in both mechanisms. However, some of the key components differ between these two transmigration processes. CAV1 genes emerged during Trichoplax adhaerens, and it was only reported in transcellular process. Paracellular process is dependent on PECAM1. PECAM1 emerged from FASL5 during Zebrafish divergence. Lastly, both systems employ late divergent genes such as ICAM1 and VECAM1. Taken together, our results suggest that these two systems constitute two different mechanical sensing mechanisms of immune cell infiltrations of the brain, yet these two systems are connected. We postulate that the mechanical properties of the cellular polarity is the main driving force determining the migration pathway. Our analysis indicates that both systems coevolved with immune cells, evolving to a higher level of complexity in association with the evolution of the immune system.

What has single-cell RNA sequencing revealed about microglial neuroimmunology?

The use of single-cell RNA sequencing (scRNA-seq) in microglial research is increasing rapidly. The basic workflow of this approach consists of isolating single cells, followed by sequencing. scRNA-seq is capable of examining microglial heterogeneity on a cellular level. However, the results gained from applying this technique suffer from discrepancies due to differences between applied methods characteristics such as the number of cells sequenced and the depth of sequencing. This review aims to shed more light on the recent developments that happened in this field and how they are related to the methods used. To do that, we track the progress and limitations of various scRNA-seq methods currently available. The review then summarizes the current knowledge gained using scRNA-seq in the field of microglia, including novel subpopulations associated with function and development under homeostasis as well during several pathological conditions such as Alzheimer, lipopolysaccharide response, and HIV in relation to the methods employed. Our review points out that despite major developments found using this technique, current scRNA-seq methods suffer from high cost, low yields, and nonstandardization of generated data. Additional development of scRNA-seq methods will raise our awareness of microglia's heterogeneity and plasticity under healthy and pathological conditions.