Cell Surface CD36 Protein in Monocyte/Macrophage Contributes to Phagocytosis during the Resolution Phase of Ischemic Stroke in Mice

Comprehensive immune modulation mechanisms of Angong Niuhuang Wan in ischemic stroke: Insights from mass cytometry analysis

BACKGROUND

Angong Niuhuang Wan (AGNHW, ), is a classical medicinal formula in Traditional Chinese Medicine (TCM) that has been appreciated for its neuroprotective properties in ischemic cerebral injuries, yet its intricate mechanisms remain only partially elucidated.

AIMS

This study leverages advanced Mass cytometry (CyTOF) to analyze AGNHW's multifaceted immunomodulation effects in-depth, emphasizing previously underexplored areas.

RESULTS

AGNHW mitigated monocyte-derived macrophages (MoDM) infiltration in the brain, distinguishing its effects on those from microglia. While the vehicle group exhibited elevated inflammatory markers like CD4, CD8a, and CD44 in ischemic brains, the AGNHW-treated group attenuated their expressions, indicating AGNHW's potential to temper the post-ischemic inflammatory response. Systemically, AGNHW modulated fundamental immune cell dynamics, notably augmenting CD8+ T cells, B cells, monocytes, and neutrophil counts in the peripheral blood under post-stroke conditions. Intracellularly, AGNHW exhibited its targeted modulation of the signaling pathways, revealing a remarked inhibition of key markers like IκBα, indicating potential suppression of inflammatory responses in ischemic brain injuries.

CONCLUSION

This study offers a comprehensive portrait of AGNHW's immunomodulation effects on ischemic stroke, illuminating its dual sites of action-both cerebral and systemic-and its nuanced modulation of cellular and molecular dynamics.

Interplay of CD36, autophagy, and lipid metabolism: insights into cancer progression

CD36, a scavenger receptor B2 that is dynamically distributed between cell membranes and organelle membranes, plays a crucial role in regulating lipid metabolism. Abnormal CD36 activity has been linked to a range of metabolic disorders, such as obesity, nonalcoholic fatty liver disease, insulin resistance and cardiovascular disease. CD36 undergoes various modifications, including palmitoylation, glycosylation, and ubiquitination, which greatly affect its binding affinity to various ligands, thereby triggering and influencing various biological effects. In the context of tumors, CD36 interacts with autophagy to jointly regulate tumorigenesis, mainly by influencing the tumor microenvironment. The central role of CD36 in cellular lipid homeostasis and recent molecular insights into CD36 in tumor development indicate the applicability of CD36 as a therapeutic target for cancer treatment. Here, we discuss the diverse posttranslational modifications of CD36 and their respective roles in lipid metabolism. Additionally, we delve into recent research findings on CD36 in tumors, outlining ongoing drug development efforts targeting CD36 and potential strategies for future development and highlighting the interplay between CD36 and autophagy in the context of cancer. Our aim is to provide a comprehensive understanding of the function of CD36 in both physiological and pathological processes, facilitating a more in-depth analysis of cancer progression and a better development and application of CD36-targeting drugs for tumor therapy in the near future.

Human monocyte subtype expression of neuroinflammation and regeneration-related genes is linked to age and sex

Stroke is a leading cause of disability and the third cause of death. The immune system plays an essential role in post-stroke recovery. After an ischemic stroke, monocytes infiltrate the injured brain tissue and can exacerbate or mitigate the damage. Ischemic stroke is more prevalent in the aged population, and the aging brain exhibits an altered immune response. There are also sex disparities in ischemic stroke incidence, outcomes, and recovery, and these differences may be hormone-driven and determined by genetic and epigenetic factors. Here, we studied whether human peripheral blood monocyte subtype (classical, intermediate, and non-classical) expression of neuronal inflammation- and regeneration-related genes depends on age and sex. A FACS analysis of blood samples from 44 volunteers (male and female, aged 28 to 98) showed that in contrast to other immune cells, the proportion of natural killer cells increased in females. The proportion of B-cells decreased in both sexes with age, and subtypes of monocytes were not linked to age or sex. Gene expression analysis by qPCR identified several genes differentially correlating with age and sex within different monocyte subtypes. Interestingly, ANXA1 and CD36 showed a consistent increase with aging in all monocytes, specifically in intermediate (CD36) and intermediate and non-classical (ANXA1) subtypes. Other genes (IL-1β, S100A8, TNFα, CD64, CD33, TGFβ1, TLR8, CD91) were differentially changed in monocyte subtypes with increased aging. Most age-dependent gene changes were differentially expressed in female monocytes. Our data shed light on the nuanced interplay of age and sex in shaping the expression of inflammation- and regeneration-related genes within distinct monocyte subtypes. Understanding these dynamics could pave the way for targeted interventions and personalized approaches in post-stroke care, particularly for the aging population and individuals of different sexes.

Brain Maturation as a Fundamental Factor in Immune-Neurovascular Interactions in Stroke

Injuries in the developing brain cause significant long-term neurological deficits. Emerging clinical and preclinical data have demonstrated that the pathophysiology of neonatal and childhood stroke share similar mechanisms that regulate brain damage, but also have distinct molecular signatures and cellular pathways. The focus of this review is on two different diseases-neonatal and childhood stroke-with emphasis on similarities and distinctions identified thus far in rodent models of these diseases. This includes the susceptibility of distinct cell types to brain injury with particular emphasis on the role of resident and peripheral immune populations in modulating stroke outcome. Furthermore, we discuss some of the most recent and relevant findings in relation to the immune-neurovascular crosstalk and how the influence of inflammatory mediators is dependent on specific brain maturation stages. Finally, we comment on the current state of treatments geared toward inducing neuroprotection and promoting brain repair after injury and highlight that future prophylactic and therapeutic strategies for stroke should be age-specific and consider gender differences in order to achieve optimal translational success.

Monocyte-related cytokines/chemokines in cerebral ischemic stroke

AIMS

Ischemic stroke is one of the leading causes of death worldwide and the most common cause of disability in Western countries. Multiple mechanisms contribute to the development and progression of ischemic stroke, and inflammation is one of the most important mechanisms.

DISCUSSION

Ischemia induces the release of adenosine triphosphate/reactive oxygen species, which activates immune cells to produce many proinflammatory cytokines that activate downstream inflammatory cascades to induce fatal immune responses. Research has confirmed that peripheral blood immune cells play a vital role in the immunological cascade after ischemic stroke. The role of monocytes has received much attention among numerous peripheral blood immune cells. Monocytes induce their effects by secreting cytokines or chemokines, including CCL2/CCR2, CCR4, CCR5, CD36, CX3CL1/CX3CR1, CXCL12(SDF-1), LFA-1/ICAM-1, Ly6C, MMP-2/9, NR4A1, P2X4R, P-selectin, CD40L, TLR2/4, and VCAM-1/VLA-4. Those factors play important roles in the process of monocyte recruitment, migration, and differentiation.

CONCLUSION

This review focuses on the function and mechanism of the cytokines secreted by monocytes in the process of ischemic stroke and provides novel targets for treating cerebral ischemic stroke.

Exogenous heat shock proteins HSPA1A and HSPB1 regulate TNF-α, IL-1β and IL-10 secretion from monocytic cells

Endogenous molecules, such as heat shock proteins (HSP), can function as danger signals when released into the extracellular environment in response to cell stress, where they elicit an immune response such as cytokine secretion. There has also been some suggestion that contamination of exogenous HSPs with lipopolysaccharide (LPS) may be responsible for these effects. This study investigates the effects of exogenous HSPA1A and HSPB1 on the activation of immune cells and the resulting secretion of cytokines, which are involved in inflammatory responses. To address whether exogenous HSPs can directly activate cytokine secretion, naïve U937 cells, differentiated U937 cells and peripheral blood mononuclear cells (PBMCs) were treated with either exogenously applied HSPA1A or HSPB1 and then secreted IL-1β, TNF-α and IL-10 were measured by ELISA. Both HSPs were able to induce a dose-dependent increase in IL-10 secretion from naïve U937 cells and dose-dependent IL-1β, TNF-α and IL-10 secretion were also observed in differentiated U937 cells and PBMCs. We also observed that CD14 affects the secretion levels of IL-1β, TNF-α and IL-10 from cells in response to exogenous HSP treatment. In addition, HSPA1A and HSPB1 were shown to interact with CD14, CD36 and CD11b extracellular receptor proteins. Several approaches used in this study indicate that HSP-induced cytokine secretion is largely independent of any contaminating LPS in the samples.

Single-cell multi-omics topic embedding reveals cell-type-specific and COVID-19 severity-related immune signatures

The advent of single-cell multi-omics sequencing technology makes it possible for researchers to leverage multiple modalities for individual cells and explore cell heterogeneity. However, the high-dimensional, discrete, and sparse nature of the data make the downstream analysis particularly challenging. Here, we propose an interpretable deep learning method called moETM to perform integrative analysis of high-dimensional single-cell multimodal data. moETM integrates multiple omics data via a product-of-experts in the encoder and employs multiple linear decoders to learn the multi-omics signatures. moETM demonstrates superior performance compared with six state-of-the-art methods on seven publicly available datasets. By applying moETM to the scRNA + scATAC data, we identified sequence motifs corresponding to the transcription factors regulating immune gene signatures. Applying moETM to CITE-seq data from the COVID-19 patients revealed not only known immune cell-type-specific signatures but also composite multi-omics biomarkers of critical conditions due to COVID-19, thus providing insights from both biological and clinical perspectives.

Regulators of phagocytosis as pharmacologic targets for stroke treatment

Stroke, including ischemic and hemorrhagic stroke, causes massive cell death in the brain, which is followed by secondary inflammatory injury initiated by disease-associated molecular patterns released from dead cells. Phagocytosis, a cellular process of engulfment and digestion of dead cells, promotes the resolution of inflammation and repair following stroke. However, professional or non-professional phagocytes also phagocytose stressed but viable cells in the brain or excessively phagocytose myelin sheaths or prune synapses, consequently exacerbating brain injury and impairing repair following stroke. Phagocytosis includes the smell, eating and digestion phases. Notably, efficient phagocytosis critically depends on phagocyte capacity to take up dead cells continually due to the limited number of phagocytes vs. dead cells after injury. Moreover, phenotypic polarization of phagocytes occurring after phagocytosis is also essential to the proresolving and prorepair properties of phagocytosis. Much has been learned about the molecular signals and regulatory mechanisms governing the sense and recognition of dead cells by phagocytes during the smell and eating phase following stroke. However, some key areas remain extremely understudied, including the mechanisms involved in digestion regulation, continual phagocytosis and phagocytosis-induced phenotypic switching following stroke. Here, we summarize new discoveries related to the molecular mechanisms and multifaceted effects of phagocytosis on brain injury and repair following stroke and highlight the knowledge gaps in poststroke phagocytosis. We suggest that advancing the understanding of poststroke phagocytosis will help identify more biological targets for stroke treatment.

Leishmania major drives host phagocyte death and cell-to-cell transfer depending on intracellular pathogen proliferation rate

The virulence of intracellular pathogens relies largely on the ability to survive and replicate within phagocytes but also on release and transfer into new host cells. Such cell-to-cell transfer could represent a target for counteracting microbial pathogenesis. However, our understanding of the underlying cellular and molecular processes remains woefully insufficient. Using intravital 2-photon microscopy of caspase-3 activation in the Leishmania major-infected (L. major-infected) live skin, we showed increased apoptosis in cells infected by the parasite. Also, transfer of the parasite to new host cells occurred directly without a detectable extracellular state and was associated with concomitant uptake of cellular material from the original host cell. These in vivo findings were fully recapitulated in infections of isolated human phagocytes. Furthermore, we observed that high pathogen proliferation increased cell death in infected cells, and long-term residency within an infected host cell was only possible for slowly proliferating parasites. Our results therefore suggest that L. major drives its own dissemination to new phagocytes by inducing host cell death in a proliferation-dependent manner.

The Role of CD36 in Cancer Progression and Its Value as a Therapeutic Target

Cluster of differentiation 36 (CD36) is a cell surface scavenger receptor that plays critical roles in many different types of cancer, notably breast, brain, and ovarian cancers. While it is arguably most well-known for its fatty acid uptake functions, it is also involved in regulating cellular adhesion, immune response, and apoptosis depending on the cellular and environmental contexts. Here, we discuss the multifaceted role of CD36 in cancer biology, such as its role in mediating metastasis, drug resistance, and immune evasion to showcase its potential as a therapeutic target. We will also review existing approaches to targeting CD36 in pre-clinical studies, as well as discuss the only CD36-targeting drug to advance to late-stage clinical trials, VT1021. Given the roles of CD36 in the etiology of metabolic disorders, such as atherosclerosis, diabetes, and non-alcoholic fatty liver disease, the clinical implications of CD36-targeted therapy are wide-reaching, even beyond cancer.

Targeting foam cell formation to improve recovery from ischemic stroke

Inflammation is a crucial part of the healing process after an ischemic stroke and is required to restore tissue homeostasis. However, the inflammatory response to stroke also worsens neurodegeneration and creates a tissue environment that is unfavorable to regeneration for several months, thereby postponing recovery. In animal models, inflammation can also contribute to the development of delayed cognitive deficits. Myeloid cells that take on a foamy appearance are one of the most prominent immune cell types within chronic stroke infarcts. Emerging evidence indicates that they form as a result of mechanisms of myelin lipid clearance becoming overwhelmed, and that they are a key driver of the chronic inflammatory response to stroke. Therefore, targeting lipid accumulation in foam cells may be a promising strategy for improving recovery. The aim of this review is to provide an overview of current knowledge regarding inflammation and foam cell formation in the brain in the weeks and months following ischemic stroke and identify targets that may be amenable to therapeutic intervention.

Endothelial cell CD36 mediates stroke-induced brain injury via BBB dysfunction and monocyte infiltration in normal and obese conditions

CD36 expressed in multiple cell types regulates inflammation, vascular function, and innate immunity. Specifically, CD36 in microvascular endothelial cells (ECs) signals to elicit inflammation and causes EC death. This study investigated roles for EC-CD36 on acute stroke pathology in normal and obese conditions. Obesity induced by a high-fat diet (HD) selectively increased CD36 expression in ECs, not in monocytes/macrophages, in the post-ischemic brain. Mice deficient CD36 in ECs (ECCD36-/-) showed reduced injury size and vascular permeability in normal conditions. While control mice fed a HD developed obesity and aggravated stroke injury, ECCD36-/- mice were resistant to develop an obesity phenotype. Subjecting ECCD36-/- mice to stroke resulted in reduced injury size and BBB disruption. Moreover, the mice had reduced MCP-1 and CCR2 gene expression, resulting in reduced monocyte trafficking with improved survival and acute motor function. Reduced MCP-1 and CCR2 expression was still evident in ECCD36-/- mice subjected to severe stroke, suggesting that monocyte trafficking is an infarct-independent metabolic effect associated with specific EC-CD36 deletion. Our findings demonstrate the importance of EC-CD36 in developing vascular comorbidities and suggest that targeting EC-CD36 is a potential preventative strategy to normalize vascular risk factors, leading to improved acute stroke outcomes.

Single-cell multi-omic topic embedding reveals cell-type-specific and COVID-19 severity-related immune signatures

The advent of single-cell multi-omics sequencing technology makes it possible for re-searchers to leverage multiple modalities for individual cells and explore cell heterogeneity. However, the high dimensional, discrete, and sparse nature of the data make the downstream analysis particularly challenging. Most of the existing computational methods for single-cell data analysis are either limited to single modality or lack flexibility and interpretability. In this study, we propose an interpretable deep learning method called multi-omic embedded topic model (moETM) to effectively perform integrative analysis of high-dimensional single-cell multimodal data. moETM integrates multiple omics data via a product-of-experts in the encoder for efficient variational inference and then employs multiple linear decoders to learn the multi-omic signatures of the gene regulatory programs. Through comprehensive experiments on public single-cell transcriptome and chromatin accessibility data (i.e., scRNA+scATAC), as well as scRNA and proteomic data (i.e., CITE-seq), moETM demonstrates superior performance compared with six state-of-the-art single-cell data analysis methods on seven publicly available datasets. By applying moETM to the scRNA+scATAC data in human bone marrow mononuclear cells (BMMCs), we identified sequence motifs corresponding to the transcription factors that regulate immune gene signatures. Applying moETM analysis to CITE-seq data from the COVID-19 patients revealed not only known immune cell-type-specific signatures but also composite multi-omic biomarkers of critical conditions due to COVID-19, thus providing insights from both biological and clinical perspectives.

Murine macrophage-based iNos reporter reveals polarization and reprogramming in the context of breast cancer

As part of the first line of defense against pathogens, macrophages possess the ability to differentiate into divergent phenotypes with varying functions. The process by which these cells change their characteristics, commonly referred to as macrophage polarization, allows them to change into broadly pro-inflammatory (M1) or anti-inflammatory (M2) subtypes, and depends on the polarizing stimuli. Deregulation of macrophage phenotypes can result in different pathologies or affect the nature of some diseases, such as cancer and atherosclerosis. Therefore, a better understanding of macrophage phenotype conversion in relevant models is needed to elucidate its potential roles in disease. However, there are few existing probes to track macrophage changes in multicellular environments. In this study, we generated an eGFP reporter cell line based on inducible nitric oxide synthase (iNos) promoter activity in RAW264.7 cells (RAW:iNos-eGFP). iNos is associated with macrophage activation to pro-inflammatory states and decreases in immune-suppressing ones. We validated the fidelity of the reporter for iNos following cytokine-mediated polarization and confirmed that reporter and parental cells behaved similarly. RAW:iNos-eGFP cells were then used to track macrophage responses in different in vitro breast cancer models, and their re-education from anti- to pro-inflammatory phenotypes via a previously reported pyrimido(5,4-b)indole small molecule, PBI1. Using two mouse mammary carcinoma cell lines, 4T1 and EMT6, effects on macrophages were assessed via conditioned media, two-dimensional/monolayer co-culture, and three-dimensional spheroid models. While conditioned media derived from 4T1 or EMT6 cells and monolayer co-cultures of each cancer cell line with RAW:iNos-eGFP cells all resulted in decreased fluorescence, the trends and extents of effects differed. We also observed decreases in iNos-eGFP signal in the macrophages in co-culture assays with 4T1- or EMT6-based spheroids. We then showed that iNos production is enhanced in these cancer models using PBI1, tracking increased fluorescence. Collectively, this work demonstrates that this reporter-based approach provides a facile means to study macrophage responses in complex, multicomponent environments. Beyond the initial studies presented here, this platform can be used with a variety of in vitro models and extended to in vivo applications with intravital imaging.

Activation of TRPV1 receptor facilitates myelin repair following demyelination via the regulation of microglial function

The transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel that is activated by capsaicin (CAP), the main component of chili pepper. Despite studies in several neurological diseases, the role of TRPV1 in demyelinating diseases remains unknown. Herein, we reported that TRPV1 expression was increased within the corpus callosum during demyelination in a cuprizone (CPZ)-induced demyelination mouse model. TRPV1 deficiency exacerbated motor coordinative dysfunction and demyelination in CPZ-treated mice, whereas the TRPV1 agonist CAP improved the behavioral performance and facilitated remyelination. TRPV1 was predominantly expressed in Iba1+ microglia/macrophages in human brain sections of multiple sclerosis patients and mouse corpus callosum under demyelinating conditions. TRPV1 deficiency decreased microglial recruitment to the corpus callosum, with an associated increase in the accumulation of myelin debris. Conversely, the activation of TRPV1 by CAP enhanced the recruitment of microglia to the corpus callosum and potentiated myelin debris clearance. Using real-time live imaging we confirmed an increased phagocytic function of microglia following CAP treatment. In addition, the expression of the scavenger receptor CD36 was increased, and that of the glycolysis regulators Hif1a and Hk2 was decreased. We conclude that TRPV1 is an important regulator of microglial function in the context of demyelination and may serve as a promising therapeutic target for demyelinating diseases such as multiple sclerosis.

Prognostic significance of spleen shear wave elastography and dispersion in patients with heart failure: the crucial role of cardio-splenic axis

INTRODUCTION

The interaction between the heart and spleen plays a crucial role among cardiac and multiple organ networks, particularly in heart failure (HF). Ultrasound shear wave imaging is a non-invasive technology capable of quantifying tissue quality, but its significance in the spleen in patients with HF is poorly understood.

METHODS AND RESULTS

This prospective observational study enrolled hospitalized 232 patients with HF undergoing abdominal ultrasonography. We used shear wave elastography (SWE) to assess spleen tissue elasticity and shear wave dispersion (SWD) to assess spleen tissue viscosity. Clinical, echocardiography, right heart catheterization, and outcome data were collected. Spleen SWE was negatively correlated with right ventricular fractional area change (R =  - 0.180, P = 0.039), but not with right-sided pressure or congestion indices. When patients were divided into three groups based on tertile values of splenic parameters, Kaplan-Meier analysis demonstrated that patients with the highest spleen SWE and SWD had lower event-free survival rates from cardiac deaths and decompensated HF over a median 494-days follow-up period (P < 0.0001 and P < 0.0001, respectively). In a multivariable Cox proportional hazard model, both spleen SWE and SWD were independently associated with increased risks of adverse cardiac events (hazard ratio, 4.974 and 1.384; P = 0.003 and P < 0.0001). Mechanistically, we evaluated mRNA expressions of CD36, a monocyte/macrophage-associated molecule, in peripheral leukocytes, and found that enhanced spleen stiffness was associated with the upregulation of CD36 expressions.

CONCLUSION

Share wave imaging of the spleen is useful for stratifying the prognosis of HF patients and may suggest a role of the cardio-splenic axis in HF pathogenies.

Protective effects of an electrophilic metabolite of docosahexaenoic acid on UVB-induced oxidative cell death, dermatitis, and carcinogenesis

Docosahexaenoic acid (DHA), a representative omega-3 (ω-3) polyunsaturated fatty acids, undergoes metabolism to produce biologically active electrophilic species. 17-Oxo-DHA is one such reactive metabolite generated from DHA by cyclooxygenase-2 and dehydrogenase in activated macrophages. The present study was aimed to investigate the effects of 17-oxo-DHA on ultraviolet B (UVB)-induced oxidative stress, inflammation, and carcinogenesis in mouse skin. UVB-induced epidermal cell death was ameliorated by topically applied 17-oxo-DHA. Topical application of 17-oxo-DHA onto hairless mouse skin inhibited UVB-induced phosphorylation of the proinflammatory transcription factor, STAT3 on tyrosine 705 (Tyr705). The 17-oxo-DHA treatment also reduced the levels of oxidative stress markers, 4-hydroxynonenal-modified protein, malondialdehyde, and 8-oxo-2'-deoxyguanosine. The protective effects of 17-oxo-DHA against oxidative damage in UVB-irradiated mouse skin were associated with activation of Nrf2. 17-Oxo-DHA enhanced the engulfment of apoptotic JB6 cells by macrophages, which was related to the increased expression of the scavenger receptor CD36. The 17-oxo-DHA-mediated potentiation of efferocytic activity of macrophages was attenuated by the pharmacologic inhibition or knockout of Nrf2. The pretreatment with 17-oxo-DHA reduced the UVB-induced skin carcinogenesis and tumor angiogenesis. It was also confirmed that 17-oxo-DHA treatment significantly inhibited the phosphorylation of the Tyr705 residue of STAT3 and decreased the expression of its target proteins in cutaneous papilloma. In conclusion, 17-oxo-DHA protects against UVB-induced oxidative cell death, dermatitis, and carcinogenesis. These effects were associated with inhibition of STAT3-mediated proinflammatory signaling and also activation of Nrf2 with subsequent upregulation of antioxidant and anti-inflammatory gene expression.

Macrophage scavenger receptors: Tumor support and tumor inhibition

Tumor-associated macrophages (TAMs) are a heterogeneous population of myeloid cells that constitute up to 50% of the cell mass of human tumors. TAMs interact with the components of the tumor microenvironment (TME) by using scavenger receptors (SRs), a large superfamily of multifunctional receptors that recognize, internalize and transport to the endosomal/lysosomal pathway apoptotic cells, cytokines, matrix molecules, lipid modified lipoproteins and other unwanted-self ligands. In our review, we summarized state-of-the art for the role of macrophage scavenger receptors in tumor development and their significance as cancer biomarkers. In this review we focused on functional activity of TAM-expressing SRs in animal models and in patients, and summarized the data for different human cancer types about the prognostic significance of TAM-expressed SRs. We discussed the role of SRs in the regulation of cancer cell biology, cell-cell and cell-matrix interaction in TME, immune status in TME, angiogenesis, and intratumoral metabolism. Targeting of tumor-promoting SRs can be a promising therapeutic approach in anti-cancer therapy. In our review we provide evidence for both tumor supporting and tumor inhibiting functions of scavenger receptors expressed on TAMs. We focused on the key differences in the prognostic and functional roles of SRs that are specific for cancer types. We highlighted perspectives for inhibition of tumor-promoting SRs in anti-cancer therapy.

Identification of crucial genes that induce coronary atherosclerosis through endothelial cell dysfunction in AMI-identifying hub genes by WGCNA

OBJECTIVE

To identify the most relevant genes of cardiovascular disease in acute myocardial infarction patients using weighted gene co-expression network analysis (WGCNA).

METHODS

The microarray dataset of GSE66360 was downloaded from the Gene Expression Omnibus (GEO) website. The differential genes with adjusted P < 0.05 and |log2 fold change (FC)| > 0.5 were included in the analysis. The weighed gene co-expression network analysis (WGCNA) was used to build a gene co-expression network and identify the most significant module. Cytoscape was used to filter the hub genes. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed for the hub genes. The key genes were defined as having high statistical and biological significance.

RESULTS

A total of 4751 differentially expressed genes (DEGs) were screened from the dataset. The purple module had the highest significance in AMI. There were 47 hub genes identified from the module. The GO terms "amyloid beta protein metabolism" and "carbohydrate metabolism" and the KEGG terms "phagosome-related pathways" and "Staphylococcus aureus-associated pathways" were the pathways strongly enriched in AMI. Fatty acid translocase cluster of differentiation (CD36), formyl peptide receptor type 2 (FPR2), integrin subunit alpha M (ITGAM), and oxidized low density lipoprotein receptor 1 (OLR1) were considered key genes in AMI.

CONCLUSION

Our research suggested that the underlying mechanism was related to inflammation and lipid formation. The hub genes identified were CD36, FPR2, ITGAM, and OLR1.

CD36-Fatty Acid-Mediated Metastasis via the Bidirectional Interactions of Cancer Cells and Macrophages

Tumour heterogeneity refers to the complexity of cell subpopulations coexisting within the tumour microenvironment (TME), such as proliferating tumour cells, tumour stromal cells and infiltrating immune cells. The bidirectional interactions between cancer and the surrounding microenvironment mark the tumour survival and promotion functions, which allow the cancer cells to become invasive and initiate the metastatic cascade. Importantly, these interactions have been closely associated with metabolic reprogramming, which can modulate the differentiation and functions of immune cells and thus initiate the antitumour response. The purpose of this report is to review the CD36 receptor, a prominent cell receptor in metabolic activity specifically in fatty acid (FA) uptake, for the metabolic symbiosis of cancer-macrophage. In this review, we provide an update on metabolic communication between tumour cells and macrophages, as well as how the immunometabolism indirectly orchestrates the tumour metastasis.

Roles of peripheral immune cells in the recovery of neurological function after ischemic stroke

Stroke is a leading cause of mortality and long-term disability worldwide, with limited spontaneous repair processes occurring after injury. Immune cells are involved in multiple aspects of ischemic stroke, from early damage processes to late recovery-related events. Compared with the substantial advances that have been made in elucidating how immune cells modulate acute ischemic injury, the understanding of the impact of the immune system on functional recovery is limited. In this review, we summarized the mechanisms of brain repair after ischemic stroke from both the neuronal and non-neuronal perspectives, and we review advances in understanding of the effects on functional recovery after ischemic stroke mediated by infiltrated peripheral innate and adaptive immune cells, immune cell-released cytokines and cell-cell interactions. We also highlight studies that advance our understanding of the mechanisms underlying functional recovery mediated by peripheral immune cells after ischemia. Insights into these processes will shed light on the double-edged role of infiltrated peripheral immune cells in functional recovery after ischemic stroke and provide clues for new therapies for improving neurological function.

Kinetics of monocyte subpopulations during experimental cerebral malaria and its resolution in a model of late chloroquine treatment

Cerebral malaria (CM) is one of the most severe forms of malaria and is a neuropathology that can lead to death. Monocytes have been shown to accumulate in the brain microvasculature at the onset of neurological symptoms during CM. Monocytes have a remarkable ability to adapt their function to their microenvironment from pro-inflammatory to resolving activities. This study aimed to describe the behavior of monocyte subpopulations during infection and its resolution. C57BL/6 mice were infected with the Plasmodium berghei ANKA strain and treated or not with chloroquine (CQ) on the first day of the onset of neurological symptoms (day 6) for 4 days and followed until day 12 to mimic neuroinflammation and its resolution during experimental CM. Ly6C monocyte subpopulations were identified by flow cytometry of cells from the spleen, peripheral blood, and brain and then quantified and characterized at different time points. In the brain, the Ly6C^int and Ly6C^low monocytes were associated with neuroinflammation, while Ly6C^hi and Ly6C^int were mobilized from the peripheral blood to the brain for resolution. During neuroinflammation, CD36 and CD163 were both involved via splenic monocytes, whereas our results suggest that the low CD36 expression in the brain during the neuroinflammation phase was due to degradation. The resolution phase was characterized by increased expressions of CD36 and CD163 in blood Ly6C^low monocytes, a higher expression of CD36 in the microglia, and restored high expression levels of CD163 in Ly6C^hi monocytes localized in the brain. Thus, our results suggest that increasing the expressions of CD36 and CD163 specifically in the brain during the neuroinflammatory phase contributes to its resolution.

Neutrophil heterogeneity in complement C1q expression associated with sepsis mortality

Sepsis is a life-threatening systemic inflammatory condition causing approximately 11 million annual deaths worldwide. Although key hyperinflammation-based organ dysfunctions that drive disease pathology have been recognized, our understanding of the factors that predispose patients to septic mortality is limited. Due to the lack of reliable prognostic measures, the development of appropriate clinical management that improves patient survival remains challenging. Here, we discovered that a subpopulation of CD49chigh neutrophils with dramatic upregulation of the complement component 1q (C1q) gene expression arises during severe sepsis. We further found that deceased septic patients failed to maintain C1q protein expression in their neutrophils, whereas septic survivors expressed higher levels of C1q. In mouse sepsis models, blocking C1q with neutralizing antibodies or conditionally knocking out C1q in neutrophils led to a significant increase in septic mortality. Apoptotic neutrophils release C1q to control their own clearance in critically injured organs during sepsis; thus, treatment of septic mice with C1q drastically increased survival. These results suggest that neutrophil C1q is a reliable prognostic biomarker of septic mortality and a potential novel therapeutic target for the treatment of sepsis.

Phagocytosis converts infiltrated monocytes to microglia-like phenotype in experimental brain ischemia

BACKGROUND

Monocyte-derived macrophages (MDMs) and microglia elicit neural inflammation and clear debris for subsequent tissue repair and remodeling. The role of infiltrating MDMs in the injured brain, however, has been controversial due to overlapping antigen expression with microglia. In this study, we define the origin and function of MDMs in cerebral ischemia.

METHODS

Using adoptive transfer of GFP+ splenocytes into adult asplenic mice subjected to transient middle cerebral artery occlusion, we compared the role of CD11b+/CD45+/NK1.1-/Ly6G- MDMs and microglia in the ischemic brain. The phagocytic activities of MDMs and microglia were measured by the uptake of fluorescent beads both in vivo with mice infused with GFP+ splenocytes and ex vivo with cultures of isolated brain immune cells.

RESULTS

Stroke induced an infiltration of MDMs [GFP+] into the ipsilateral hemisphere at acute (3 days) and sub-acute phases (7 days) of post-stroke. At 7 days, the infiltrating MDMs contained both CD45High and CD45Low subsets. The CD45High MDMs in the injured hemisphere exhibited a significantly higher proliferation capacity (Ki-67 expression levels) as well as higher expression levels of CD11c when compared to CD45Low MDMs. The CD45High and CD45Low MDM subsets in the injured hemisphere were approximately equal populations, indicating that CD45High MDMs infiltrating the ischemic brain changes their phenotype to CD45Low microglia-like phenotype. Studies with fluorescent beads reveal high levels of MDM phagocytic activity in the post-stroke brain, but this phagocytic activity was exclusive to post-ischemic brain tissue and was not detected in circulating monocytes. By contrast, CD45Low microglia-like cells had low levels of phagocytic activity when compared to CD45High cells. Both in vivo and ex vivo studies also show that the phagocytic activity in CD45High MDMs is associated with an increase in the CD45Low/CD45High ratio, indicating that phagocytosis promotes MDM phenotype conversion.

CONCLUSIONS

This study demonstrates that MDMs are the predominant phagocytes in the post-ischemic brain, with the CD45High subset having the highest phagocytic activity levels. Upon phagocytosis, CD45High MDMs in the post-ischemic brain adopt a CD45Low phenotype that is microglia-like. Together, these studies reveal key roles for MDMs and their phagocytic function in tissue repair and remodeling following cerebral ischemia.

Inflammatory Responses After Ischemic Stroke

Ischemic stroke generates an immune response that contributes to neuronal loss as well as tissue repair. This is a complex process involving a range of cell types and effector molecules and impacts tissues outside of the CNS. Recent reviews address specific aspects of this response, but several years have passed and important advances have been made since a high-level review has summarized the overall state of the field. The present review examines the initiation of the inflammatory response after ischemic stroke, the complex impacts of leukocytes on patient outcome, and the potential of basic science discoveries to impact the development of therapeutics. The information summarized here is derived from broad PubMed searches and aims to reflect recent research advances in an unbiased manner. We highlight valuable recent discoveries and identify gaps in knowledge that have the potential to advance our understanding of this disease and therapies to improve patient outcomes.

Interactions between the Autonomic Nervous System and the Immune System after Stroke

Acute stroke is one of the leading causes of morbidity and mortality worldwide. Stroke-induced immune-inflammatory response occurs in the perilesion areas and the periphery. Although stroke-induced immunosuppression may alleviate brain injury, it hinders brain repair as the immune-inflammatory response plays a bidirectional role after acute stroke. Furthermore, suppression of the systemic immune-inflammatory response increases the risk of life-threatening systemic bacterial infections after acute stroke. Therefore, it is essential to explore the mechanisms that underlie the stroke-induced immune-inflammatory response. Autonomic nervous system (ANS) activation is critical for regulating the local and systemic immune-inflammatory responses and may influence the prognosis of acute stroke. We review the changes in the sympathetic and parasympathetic nervous systems and their influence on the immune-inflammatory response after stroke. Importantly, this article summarizes the mechanisms on how ANS regulates the immune-inflammatory response through neurotransmitters and their receptors in immunocytes and immune organs after stroke. To facilitate translational research, we also discuss the promising therapeutic approaches modulating the activation of the ANS or the immune-inflammatory response to promote neurologic recovery after stroke. © 2022 American Physiological Society. Compr Physiol 12:3665-3704, 2022.

Delayed Infiltration of Peripheral Monocyte Contributes to Phagocytosis and Transneuronal Degeneration in Chronic Stroke

BACKGROUND

Mononuclear phagocytes, including monocyte-derived macrophages (MDMs) and microglia, contribute to infarct development as well as tissue repair in the postischemic brain. Here, we identify the origin and function of MDMs in the brain during poststroke repair processes.

METHODS

Adult mice were subjected to transient middle cerebral artery occlusion. Longitudinal brain atrophy and secondary degeneration were evaluated during acute to recovery phases of stroke. Adoptive transfer of GFP+ splenocytes into asplenic mice was used to distinguish MDMs from resident microglia. Fluorescence beads were injected into stroked animals to examine phagocytic function.

RESULTS

Progressive atrophy and neuronal degeneration in remote regions were observed in chronic stroke, which also was accompanied by MDM infiltration into the ipsilateral hemisphere. Compared with microglia, MDMs had significantly higher phagocytic activity. MDM trafficking and phagocytosis was spatiotemporally regulated with acute and prolonged infiltration into infarcted tissue, as well as delayed entry in remote areas such as the thalamus and substantia nigra.

CONCLUSIONS

The stepwise and long-lasting involvement of MDMs at multiple poststroke stages shows that MDMs have a role in progressive stroke-induced injury and repair processes. These findings suggest that manipulating monocyte entry at different stroke stages may be an effective immune-based strategy to limit injury propagation in chronic stroke.

Ejection of damaged mitochondria and their removal by macrophages ensure efficient thermogenesis in brown adipose tissue

Recent findings have demonstrated that mitochondria can be transferred between cells to control metabolic homeostasis. Although the mitochondria of brown adipocytes comprise a large component of the cell volume and undergo reorganization to sustain thermogenesis, it remains unclear whether an intercellular mitochondrial transfer occurs in brown adipose tissue (BAT) and regulates adaptive thermogenesis. Herein, we demonstrated that thermogenically stressed brown adipocytes release extracellular vesicles (EVs) that contain oxidatively damaged mitochondrial parts to avoid failure of the thermogenic program. When re-uptaken by parental brown adipocytes, mitochondria-derived EVs reduced peroxisome proliferator-activated receptor-γ signaling and the levels of mitochondrial proteins, including UCP1. Their removal via the phagocytic activity of BAT-resident macrophages is instrumental in preserving BAT physiology. Depletion of macrophages in vivo causes the abnormal accumulation of extracellular mitochondrial vesicles in BAT, impairing the thermogenic response to cold exposure. These findings reveal a homeostatic role of tissue-resident macrophages in the mitochondrial quality control of BAT.

Mechanisms of neuroinflammation in hydrocephalus after intraventricular hemorrhage: a review

Intraventricular hemorrhage (IVH) is a significant cause of morbidity and mortality in both neonatal and adult populations. IVH not only causes immediate damage to surrounding structures by way of mass effect and elevated intracranial pressure; the subsequent inflammation causes additional brain injury and edema. Of those neonates who experience severe IVH, 25-30% will go on to develop post-hemorrhagic hydrocephalus (PHH). PHH places neonates and adults at risk for white matter injury, seizures, and death. Unfortunately, the molecular determinants of PHH are not well understood. Within the past decade an emphasis has been placed on neuroinflammation in IVH and PHH. More information has come to light regarding inflammation-induced fibrosis and cerebrospinal fluid hypersecretion in response to IVH. The aim of this review is to discuss the role of neuroinflammation involving clot-derived neuroinflammatory factors including hemoglobin/iron, peroxiredoxin-2 and thrombin, as well as macrophages/microglia, cytokines and complement in the development of PHH. Understanding the mechanisms of neuroinflammation after IVH may highlight potential novel therapeutic targets for PHH.

Stroke induces disease-specific myeloid cells in the brain parenchyma and pia

Inflammation triggers secondary brain damage after stroke. The meninges and other CNS border compartments serve as invasion sites for leukocyte influx into the brain thus promoting tissue damage after stroke. However, the post-ischemic immune response of border compartments compared to brain parenchyma remains poorly characterized. Here, we deeply characterize tissue-resident leukocytes in meninges and brain parenchyma and discover that leukocytes respond differently to stroke depending on their site of residence. We thereby discover a unique phenotype of myeloid cells exclusive to the brain after stroke. These stroke-associated myeloid cells partially resemble neurodegenerative disease-associated microglia. They are mainly of resident microglial origin, partially conserved in humans and exhibit a lipid-phagocytosing phenotype. Blocking markers specific for these cells partially ameliorates stroke outcome thus providing a potential therapeutic target. The injury-response of myeloid cells in the CNS is thus compartmentalized, adjusted to the type of injury and may represent a therapeutic target.

Erythrophagocytosis by Microglia/Macrophage in Intracerebral Hemorrhage: From Mechanisms to Translation

Intracerebral hemorrhage (ICH) is a devastating condition characterized by hematoma related mass effect. Microglia/macrophage (M φ) are rapidly recruited in order to remove the red blood cells through erythrophagocytosis. Efficient erythrophagocytosis can detoxify hemolytic products and facilitate neurological recovery after ICH. The underlying mechanisms include modulation of inflammatory response and oxidative stress, among others. It is a dynamic process mediated by a cascade of signal transduction, including “find-me” signals, “eat-me” signals and a set of phagocytotic receptors-ligand pairs that may be exploited as therapeutic targets. This review summarizes mechanistic signaling pathways of erythrophagocytosis and highlights the potential of harnessing M φ-mediated phagocytosis for ICH treatment.

The Intriguing Role of TLR Accessory Molecules in Cardiovascular Health and Disease

Activation of Toll like receptors (TLR) plays an important role in cardiovascular disease development, progression and outcomes. Complex TLR mediated signaling affects vascular and cardiac function including tissue remodeling and repair. Being central components of both innate and adaptive arms of the immune system, TLRs interact as pattern recognition receptors with a series of exogenous ligands and endogenous molecules or so-called danger associated molecular patterns (DAMPs) that are released upon tissue injury and cellular stress. Besides immune cells, a number of structural cells within the cardiovascular system, including endothelial cells, smooth muscle cells, fibroblasts and cardiac myocytes express TLRs and are able to release or sense DAMPs. Local activation of TLR-mediated signaling cascade induces cardiovascular tissue repair but in a presence of constant stimuli can overshoot and cause chronic inflammation and tissue damage. TLR accessory molecules are essential in guiding and dampening these responses toward an adequate reaction. Furthermore, accessory molecules assure specific and exclusive TLR-mediated signal transduction for distinct cells and pathways involved in the pathogenesis of cardiovascular diseases. Although much has been learned about TLRs activation in cardiovascular remodeling, the exact role of TLR accessory molecules is not entirely understood. Deeper understanding of the role of TLR accessory molecules in cardiovascular system may open therapeutic avenues aiming at manipulation of inflammatory response in cardiovascular disease. The present review outlines accessory molecules for membrane TLRs that are involved in cardiovascular disease progression. We first summarize the up-to-date knowledge on TLR signaling focusing on membrane TLRs and their ligands that play a key role in cardiovascular system. We then survey the current evidence of the contribution of TLRs accessory molecules in vascular and cardiac remodeling including myocardial infarction, heart failure, stroke, atherosclerosis, vein graft disease and arterio-venous fistula failure.

Scavenger receptor CD36 governs recruitment of myeloid cells to the blood-CSF barrier after stroke in neonatal mice

Background

Ischemic stroke induces the activation and recruitment of peripheral leukocytes to the injured brain. These cells can infiltrate the brain through multiple routes, either by penetrating blood–brain barrier or via blood–CSF barriers at the meninges or the choroid plexus (CP). We previously showed that myeloid cell trafficking via the CP occurs early after neonatal arterial stroke and modulates injury. CD36 is a receptor that mediates function of endothelial cells and cells of the monocyte lineage under various neurodegenerative conditions and can influence brain injury after neonatal stroke. Here we asked whether CD36 impacts injury by altering leukocyte trafficking through the CP in neonatal mice subjected to transient middle cerebral artery occlusion (tMCAO).

Methods

In neonatal mice with intact or globally disrupted CD36 signalling (CD36 KO), we characterized the phenotypes of myeloid cells by flow cytometry and the underlying gene expression signatures in the CPs contralateral and ipsilateral to tMCAO by RNA sequencing analyses, focussing on early post-reperfusion time window.

Results

Flow cytometry in the isolated CPs revealed that CD36 mediates stepwise recruitment of myeloid cells to the CP ipsilateral to tMCAO early after reperfusion, with a predominant increase first in inflammatory monocyte subsets and neutrophils followed by patrolling monocytes. RNA sequencing analyses demonstrated marked changes in gene expression in the CP ipsilateral compared to the CP contralateral to tMCAO in wild type mice. Changes were further modified by lack of CD36, including distinction in several clusters of genes involved in inflammatory, metabolic and extracellular matrix signalling in the CP ipsilateral to tMCAO.

Conclusion

Altogether, our data suggest cooperation between blood–CSF–brain interface via the CP through CD36-mediated signalling following neonatal stroke with a key role for inflammatory monocytes and neutrophils.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02388-z.

The Role of Microglial Phagocytosis in Ischemic Stroke

Microglia are the resident immune cells of the central nervous system that exert diverse roles in the pathogenesis of ischemic stroke. During the past decades, microglial polarization and chemotactic properties have been well-studied, whereas less attention has been paid to phagocytic phenotypes of microglia in stroke. Generally, whether phagocytosis mediated by microglia plays a beneficial or detrimental role in stroke remains controversial, which calls for further investigations. Most researchers are in favor of the former proposal currently since efficient clearance of tissue debris promotes tissue reconstruction and neuronal network reorganization in part. Other scholars propose that excessively activated microglia engulf live or stressed neuronal cells, which results in neurological deficits and brain atrophy. Upon ischemia challenge, the microglia infiltrate injured brain tissue and engulf live/dead neurons, myelin debris, apoptotic cell debris, endothelial cells, and leukocytes. Cell phagocytosis is provoked by the exposure of "eat-me" signals or the loss of "don^'t eat-me" signals. We supposed that microglial phagocytosis could be initiated by the specific "eat-me" signal and its corresponding receptor on the specific cell type under pathological circumstances. In this review, we will summarize phagocytic characterizations of microglia after stroke and the potential receptors responsible for this programmed biological progress. Understanding these questions precisely may help to develop appropriate phagocytic regulatory molecules, which are promoting self-limiting inflammation without damaging functional cells.

Lipid scavenging macrophages and inflammation

Macrophages are professional phagocytes, indispensable for maintenance of tissue homeostasis and integrity. Depending on their resident tissue, macrophages are exposed to highly diverse metabolic environments. Adapted to their niche, they can contribute to local metabolic turnover through metabolite uptake, conversion, storage and release. Disturbances in tissue homeostasis caused by infection, inflammation or damage dramatically alter the local milieu, impacting macrophage activation status and metabolism. In the case of persisting stimuli, defective macrophage responses ensue, which can promote tissue damage and disease. Especially relevant herein are disbalances in lipid rich environments, where macrophages are crucially involved in lipid uptake and turnover, preventing lipotoxicity. Lipid uptake is to a large extent facilitated by macrophage expressed scavenger receptors that are dynamically regulated and important in many metabolic diseases. Here, we review the receptors mediating lipid uptake and summarize recent findings on their role in health and disease. We further highlight the underlying pathways driving macrophage lipid acquisition and their impact on myeloid metabolic remodelling.

Leukotriene D4 Upregulates Oxidized Low-Density Lipoprotein Receptor 1 and CD36 to Enhance Oxidized LDL Uptake and Phagocytosis in Macrophages Through Cysteinyl Leukotriene Receptor 1

Endothelial permeability, leukocyte attachment, and unregulated oxidized LDL (oxLDL) uptake by macrophages leading to the formation of foam cells are all vital in the initiation and progression of atherosclerosis. During inflammation, several inflammatory mediators regulate this process through the expression of distinct oxLDL binding cell surface receptors on macrophages. We have previously shown that Leukotriene D4 (LTD4) promotes endothelial dysfunction, increasing endothelial permeability and enhancing TNFα-mediated attachment of monocytes to endothelium, which hints at its possible role in atherosclerosis. Here we analyzed the effect of LTD4 on macrophage function. Macrophages mainly express CysLT1R and flux calcium in response to LTD4. Further, LTD4 potentiates phagocytosis in macrophages as revealed by the uptake of zymosan particles. Notably, LTD4 augmented macrophage phagocytosis and oxLDL uptake which is sensitive to MK-571 [Montelukast (MK)], a CysLT1R-specific antagonist. Mechanistically, LTD4 upregulated two receptors central to foam cell formation, oxidized low-density lipoprotein receptor-1 (OLR1/LOX-1), and CD36 in a time and dose-dependent manner. Finally, LTD4 enhanced the secretion of chemokines MCP-1 and MIP1β. Our results suggest that LTD4 contributes to atherosclerosis either through driving foam cell formation or recruitment of immune cells or both. CysLT1R antagonists are safely being used in the treatment of asthma, and the findings from the current study suggest that these can be re-purposed for the treatment of atherosclerosis.

How cytosolic compartments play safeguard functions against neuroinflammation and cell death in cerebral ischemia

Ischemic stroke is the second leading cause of mortality and disability globally. Neuronal damage following ischemic stroke is rapid and irreversible, and eventually results in neuronal death. In addition to activation of cell death signaling, neuroinflammation is also considered as another pathogenesis that can occur within hours after cerebral ischemia. Under physiological conditions, subcellular organelles play a substantial role in neuronal functionality and viability. However, their functions can be remarkably perturbed under neurological disorders, particularly cerebral ischemia. Therefore, their biochemical and structural response has a determining role in the sequel of neuronal cells and the progression of disease. However, their effects on cell death and neuroinflammation, as major underlying mechanisms of ischemic stroke, are still not understood. This review aims to provide a comprehensive overview of the contribution of each organelle on these pathological processes after ischemic stroke.

Atypical antipsychotic drugs deregulate the cholesterol metabolism of macrophage-foam cells by activating NOX-ROS-PPARγ-CD36 signaling pathway

BACKGROUND

Clinical reports indicate that schizophrenia patients taking atypical antipsychotic drugs suffer from metabolism diseases including atherosclerosis. However, the mechanisms underlying the detrimental effect of atypical antipsychotic drugs on atherosclerosis remain to be explored.

METHODS

In this study, we used apolipoprotein E-deficient (apoe^-/-) hyperlipidemic mice and apoe^-/-cd36^-/- mice to investigate the underlying mechanism of atypical antipsychotic drugs on atherosclerosis and macrophage-foam cells.

RESULTS

In vivo studies showed that genetic deletion of cd36 gene ablated the pro-atherogenic effect of olanzapine in apoe^-/- mice. Moreover, in vitro studies revealed that genetic deletion or siRNA-mediated knockdown of cd36 or pharmacological inhibition of CD36 prevented atypical antipsychotic drugs-induced oxLDL accumulation in macrophages. Additionally, olanzapine and clozapine activated NADPH oxidase (NOX) to generate reactive oxygen species (ROS) which upregulated the activity of peroxisome proliferator-activated receptor γ (PPARγ) and subsequently elevated CD36 expression. Inhibition of NOX activity, ROS production or PPARγ activity suppressed CD36 expression and abolished the detrimental effects of olanzapine and clozapine on oxLDL accumulation in macrophages.

CONCLUSION

Collectively, our results suggest that atypical antipsychotic drugs exacerbate atherosclerosis and macrophage-foam cell formation by activating the NOX-ROS-PPARγ-CD36 pathway.

Increased CD47 and MHC Class I Inhibitory Signals Expression in Senescent CD1 Primary Mouse Lung Fibroblasts

Cellular senescence is more than a proliferative arrest in response to various stimuli. Senescent cells (SC) participate in several physiological processes, and their adequate removal is essential to maintain tissue and organism homeostasis. However, SC accumulation in aging and age-related diseases alters the tissue microenvironment leading to deterioration. The immune system clears the SC, but the specific scenarios and mechanisms related to recognizing and eliminating them are unknown. Hence, we aimed to evaluate the existence of three regulatory signals of phagocytic function, CD47, major histocompatibility complex class I (MHC-I), and calreticulin, present in the membrane of SC. Therefore, primary fibroblasts were isolated from CD1 female mice lungs, and stress-induced premature senescence (SIPS) was induced with hydrogen peroxide. Replicative senescence (RS) was used as a second senescent model. Our results revealed a considerable increment of CD47 and MHC-I in RS and SIPS fibroblasts. At the same time, no significant changes were found in calreticulin, suggesting that those signals might be associated with evading immune system recognition and thus averting senescent cells clearance.

Gene therapy for Alzheimer's disease targeting CD33 reduces amyloid beta accumulation and neuroinflammation

Neuroinflammation is a key contributor to the pathology of Alzheimer's disease (AD). CD33 (Siglec-3) is a transmembrane sialic acid-binding receptor on the surface of microglial cells. CD33 is upregulated on microglial cells from post-mortem AD patient brains, and high levels of CD33 inhibit uptake and clearance of amyloid beta (Aβ) in microglial cell cultures. Furthermore, knockout of CD33 reduces amyloid plaque burden in mouse models of AD. Here, we tested whether a gene therapy strategy to reduce CD33 on microglia in AD could decrease Aβ plaque load. Intracerebroventricular injection of an adeno-associated virus (AAV) vector-based system encoding an artificial microRNA targeting CD33 (miRCD33) into APP/PS1 mice reduced CD33 mRNA and TBS-soluble Aβ40 and Aβ42 levels in brain extracts. Treatment of APP/PS1 mice with miRCD33 vector at an early age (2 months) was more effective at reducing Aβ plaque burden than intervening at later times (8 months). Furthermore, early intervention downregulated several microglial receptor transcripts (e.g. CD11c, CD47 and CD36) and pro-inflammatory activation genes (e.g. Tlr4 and Il1b). Marked reductions in the chemokine Ccl2 and the pro-inflammatory cytokine Tnfα were observed at the protein level in the brain of APP/PS1 mice treated with miRCD33 vector. Overall, our data indicate that CD33 is a viable target for AAV-based knockdown strategies to reduce AD pathology. One Sentence Summary: A gene therapy approach for Alzheimer's disease using adeno-associated virus vector-based knockdown of CD33 reduced amyloid beta accumulation and neuroinflammation.

Gene expression during THP-1 differentiation is influenced by vitamin D3 and not vibrational mechanostimulation

Background

In injury or infection, monocytes migrate into the affected tissues from circulation and differentiate into macrophages which are subsequently involved in the inflammatory responses. Macrophage differentiation and activation have been studied in response to multiple chemokines and cytokines. However, mechanical, and physical stimuli can also influence macrophage differentiation, activation, cytokine production, and phagocytic activity.

Methods

In this study the macrophage differentiation from THP-1 monocytes was assessed upon the stimulation with 1,25-dihydroxyvitamin D3 and 1,000 Hz vibrations, using qPCR for quantification of transcript expression. Vitamin D binds the vitamin D receptor (VDR) and subsequently modulates the expression of a variety of genes in monocytes. The effects of the 1,000 Hz vibrational stimulation, and the combined treatment of vitamin D3 and 1000 Hz vibrations were unknown. The differentiation of macrophages was assessed by looking at transcription of macrophage markers (e.g., CD14, CD36), antigen presenting molecules (e.g., HLA-DRA), transcription factors (e.g., LEF-1, TCF7L2), and mechanosensors (e.g., PIEZO1 and PKD2).

Results

The results showed that vitamin D3 induced THP-1 macrophage differentiation, which was characterized by upregulation of CD14 and CD36, downregulation of HLA-DRA, upregulation of the PKD2 (TRPP2), and an inverse relationship between TCF7L2 and LEF-1, which were upregulated and downregulated respectively. The 1,000 Hz vibrations were sensed from the cells which upregulated PIEZO1 and TCF3, but they did not induce expression of genes that would indicate macrophage differentiation. The mRNA transcription profile in the cells stimulated with the combined treatment was comparable to that of the cells stimulated by the vitamin only. The 1,000 Hz vibrations slightly weakened the effect of the vitamin for the regulation of CD36 and HLA-DMB in the suspension cells, but without causing changes in the regulation patterns. The only exception was the upregulation of TCF3 in the suspension cells, which was influenced by the vibrations. In the adherent cells, the vitamin D3 cancelled the upregulating effect of the 1,000 Hz vibrations and downregulated TCF3. The vitamin also cancelled the upregulation of PIEZO1 gene by the 1,000 Hz vibrations in the combined treatment.

Conclusion

The mechanical stimulation with 1,000 Hz vibrations resulted in upregulation of PIEZO1 in THP-1 cells, but it did not affect the differentiation process which was investigated in this study. Vitamin D3 induced THP-1 macrophage differentiation and could potentially influence M2 polarization as observed by upregulation of CD36 and downregulation of HLA-DRA. In addition, in THP-1 cells undergoing the combined stimulation, the gene expression patterns were influenced by vitamin D3, which also ablated the effect of the mechanical stimulus on PIEZO1 upregulation.

Macrophage phagocytosis after spinal cord injury: when friends become foes

After spinal cord injury (SCI), macrophages can exert either beneficial or detrimental effects depending on their phenotype. Aside from their critical role in inflammatory responses, macrophages are also specialized in the recognition, engulfment, and degradation of pathogens, apoptotic cells, and tissue debris. They promote remyelination and axonal regeneration by removing inhibitory myelin components and cellular debris. However, excessive intracellular presence of lipids and dysregulated intracellular lipid homeostasis result in the formation of foamy macrophages. These develop a pro-inflammatory phenotype that may contribute to further neurological decline. Additionally, myelin-activated macrophages play a crucial role in axonal dieback and retraction. Here, we review the opposing functional consequences of phagocytosis by macrophages in SCI, including remyelination and regeneration versus demyelination, degeneration, and axonal dieback. Furthermore, we discuss how targeting the phagocytic ability of macrophages may have therapeutic potential for the treatment of SCI.

Role of microglial and endothelial CD36 in post-ischemic inflammasome activation and interleukin-1β-induced endothelial activation

Cerebral ischemia is associated with an acute inflammatory response that contributes to the resulting injury. The innate immunity receptor CD36, expressed in microglia and endothelium, and the pro-inflammatory cytokine interleukin-1β (IL-1β) are involved in the mechanisms of ischemic injury. Since CD36 has been implicated in activation of the inflammasome, the main source of IL-1β, we investigated whether CD36 mediates brain injury through the inflammasome and IL-1β. We found that active caspase-1, a key inflammasome component, is decreased in microglia of CD36-deficient mice subjected to transient middle cerebral artery occlusion, an effect associated with a reduction in brain IL-1β. Conditional deletion of CD36 either in microglia or endothelium reduced ischemic injury in mice, attesting to the pathogenic involvement of CD36 in both cell types. Application of an ischemic brain extract to primary brain endothelial cell cultures from wild type (WT) mice induced IL-1β-dependent endothelial activation, reflected by increases in the cytokine colony stimulating factor-3, a response markedly attenuated in CD36-deficient endothelia. Similarly, the increase in colony stimulating factor-3 induced by recombinant IL-1β was attenuated in CD36-deficient compared to WT endothelia. We conclude that microglial CD36 is a key determinant of post-ischemic IL-1β production by regulating caspase-1 activity, whereas endothelial CD36 is required for the full expression of the endothelial activation induced by IL-1β. The data identify microglial and endothelial CD36 as critical upstream components of the acute inflammatory response to cerebral ischemia and viable putative therapeutic targets.

Distinct peripheral blood monocyte and neutrophil transcriptional programs following intracerebral hemorrhage and different etiologies of ischemic stroke

Understanding cell-specific transcriptome responses following intracerebral hemorrhage (ICH) and ischemic stroke (IS) will improve knowledge of the immune response to brain injury. Transcriptomic profiles of 141 samples from 48 subjects with ICH, different IS etiologies, and vascular risk factor controls were characterized using RNA-seq in isolated neutrophils, monocytes and whole blood. In both IS and ICH, monocyte genes were down-regulated, whereas neutrophil gene expression changes were generally up-regulated. The monocyte down-regulated response to ICH included innate, adaptive immune, dendritic, NK cell and atherosclerosis signaling. Neutrophil responses to ICH included tRNA charging, mitochondrial dysfunction, and ER stress pathways. Common monocyte and neutrophil responses to ICH included interferon signaling, neuroinflammation, death receptor signaling, and NFAT pathways. Suppressed monocyte responses to IS included interferon and dendritic cell maturation signaling, phagosome formation, and IL-15 signaling. Activated neutrophil responses to IS included oxidative phosphorylation, mTOR, BMP, growth factor signaling, and calpain proteases-mediated blood-brain barrier (BBB) dysfunction. Common monocyte and neutrophil responses to IS included JAK1, JAK3, STAT3, and thrombopoietin signaling. Cell-type and cause-specific approaches will assist the search for future IS and ICH biomarkers and treatments.

Zeb2 Is a Regulator of Astrogliosis and Functional Recovery after CNS Injury

The astrocytic response to injury is characterized on the cellular level, but our understanding of the molecular mechanisms controlling the cellular processes is incomplete. The astrocytic response to injury is similar to wound-healing responses in non-neural tissues that involve epithelial-to-mesenchymal transitions (EMTs) and upregulation in ZEB transcription factors. Here we show that injury-induced astrogliosis increases EMT-related genes expression, including Zeb2, and long non-coding RNAs, including Zeb2os, which facilitates ZEB2 protein translation. In mouse models of either contusive spinal cord injury or transient ischemic stroke, the conditional knockout of Zeb2 in astrocytes attenuates astrogliosis, generates larger lesions, and delays the recovery of motor function. These findings reveal ZEB2 as an important regulator of the astrocytic response to injury and suggest that astrogliosis is an EMT-like process, which provides a conceptual connection for the molecular and cellular similarities between astrogliosis and wound-healing responses in non-neural tissue.

CD36 deficiency reduces chronic BBB dysfunction and scar formation and improves activity, hedonic and memory deficits in ischemic stroke

Ameliorating blood-brain barrier disruption and altering scar formation dynamics are potential strategies that may improve post-stroke recovery. CD36 is a class B scavenger receptor that plays a role in innate immunity, inflammation and vascular dysfunction and regulates post-stroke injury, neovascularization, reactive astrogliosis and scar formation. By subjecting WT and CD36KO mice to different MCAo occlusion durations to generate comparable acute lesion sizes, we addressed the role of CD36 in BBB dysfunction, scar formation and recovery. The majority of stroke recovery studies primarily focus on motor function. Here, we employed an extensive behavioral test arsenal to evaluate psychological and cognitive endpoints. While not evident during the acute phase, CD36 deficient mice displayed significantly attenuated BBB leakage and scar formation at three months after stroke compared to wild-type littermates. Assessment of motor (open field, rotarod), anxiety (plus maze, light-dark box), depression (forced swim, sucrose preference) and memory tests (water maze) revealed that CD36 deficiency ameliorated stroke-induced behavioral impairments in activity, hedonic responses and spatial learning and strategy switching. Our findings indicate that CD36 contributes to stroke-induced BBB dysfunction and scar formation in an injury-independent manner, as well as to the chronic motor and neurophysiological deficits in chronic stroke.

CD36 - A novel molecular target in the neurovascular unit

CD36 is an integral membrane protein primarily known for its function as a fatty acid transporter, yet also playing other biological roles from lipid metabolism to inflammation modulation. These pleiotropic effects are explained by the existence of multiple different ligands and the extensive distribution in numerous cell types. Moreover, the receptor is related to various pathologies and it may prove to be a good target for prospective therapeutic strategies. In the neurovascular unit (NVU), CD36 is expressed in cells like microglia, microvascular endothelial cells, astrocytes and neurons. In the normal brain, CD36 was proven to be involved in phagocytosis of apoptotic cells, oro‐sensory detection of dietary lipids, and fatty acid transport across the blood brain barrier (BBB). CD36 was also acknowledged as a potentially important player in central nervous system (CNS) disorders, such as Alzheimer Disease‐associated vascular dysfunction and oxidative stress and the neuroinflammatory response in stroke. Despite continuous efforts, the therapeutic arsenal for such diseases is still scarce and there is an increasing interest in discovering new molecular targets for more specific therapeutic approaches. In this review, we summarize the role of CD36 in the normal function of the NVU and in several CNS disorders, focusing on the dysregulation of the NVU and the potential therapeutic modulation.

Microglia-derived interleukin-10 accelerates post-intracerebral hemorrhage hematoma clearance by regulating CD36

Hematoma size after intracerebral hemorrhage (ICH) significantly affects patient outcome. However, our knowledge of endogenous mechanisms that underlie hematoma clearance and the potential role of the anti-inflammatory cytokine interleukin-10 (IL-10) is limited. Using organotypic hippocampal slice cultures and a collagenase-induced ICH mouse model, we investigated the role of microglial IL-10 in phagocytosis ex vivo and hematoma clearance in vivo. In slice culture, exposure to hemoglobin induced IL-10 expression in microglia and enhanced phagocytosis that depended on IL-10-regulated expression of CD36. Following ICH, IL-10-deficient mice had more severe neuroinflammation, brain edema, iron deposition, and neurologic deficits associated with delayed hematoma clearance. Intranasal administration of recombinant IL-10 accelerated hematoma clearance and improved neurologic function. Additionally, IL-10-deficient mice had weakened in vivo phagocytic ability owing to decreased expression of microglial CD36. Moreover, loss of IL-10 significantly increased monocyte-derived macrophage infiltration and enhanced brain inflammation in vivo. These results indicate that IL-10 regulates microglial phagocytosis and monocyte-derived macrophage infiltration after ICH and that CD36 is a key phagocytosis effector regulated by IL-10. Leveraging the innate immune response to ICH by augmenting IL-10 signaling may provide a useful strategy for accelerating hematoma clearance and improving neurologic outcome in clinical translation studies.

Microarray investigation of glycan remodeling during macrophage polarization reveals α2,6 sialic acid as an anti-inflammatory indicator

Glycosylation is a widely occurring posttranslational modification. Here, we applied a quick, convenient and high-throughput strategy (lectin array) to investigate the variation in glycans on different macrophage subtypes derived from THP-1 and RAW264.7 cells. For THP-1 cells, there were more significant differences in the glycan on M2 macrophages compared to the other two subtypes. In contrast, M1 macrophages exhibited more significant glycan remodeling than the other subtypes for the RAW264.7 cell line. The response of the lectins which recogonize the N-glycan and α2,6 sialic acid was higher during polarization into anti-inflammatory phase (THP-1 derived M2 subtypes), and lower in pro-inflammatory phase (RAW264.7 M1 subtypes). The regulation of several α2,6 sialyltransferase genes was coincident with the regulation of the α2,6 sialic acid on the two cell lines. The lectin response and glycosyltranferase gene expression confirmed that α2,6 sialic acid showed higher expression in the anti-inflammatory phase. This indicated that α2,6 sialic acid was a potential indicator for the anti-inflammatory response.