Functional consequences of CD36 downregulation by TLR signals

Naoxueshu oral liquid promotes hematoma absorption by targeting CD36 in M2 microglia via TLR4/MyD88/NF-κB signaling pathway in rats with intracerebral hemorrhage

ETHNOPHARMACOLOGICAL RELEVANCE

Intracerebral hemorrhage (ICH) is a major public health issue that leads to elevated rates of death and disability and has few proven treatments. Naoxueshu oral liquid (NXS), a TCM patent drug, is widely used in patients with ICH. Although a series of clinical studies have confirmed the efficacy and safety of NXS, the underlying mechanism of hematoma absorption is unclear.

AIM OF THE STUDY

Our work aimed to elucidate the effect and mechanism of NXS on hematoma absorption in rats with ICH.

MATERIALS AND METHODS

Induction of ICH model in the rats with intracerebral injection of collagenase VII, followed by treatment with NXS and Edaravone as a control neuroprotection medication. Neural functional recovery was assessed using mNSS, foot fault test, corner test, forelimb grip-traction test, and adhesive removal test. Hematoma absorption was assessed by the spectrophotometric hemoglobin assay with Drabkin's reagent. The protein expression of CD36, M2 microglia marker (CD206 and YM-1) and TLR4/MyD88/NF-κB pathway related proteins were determined by Western blot and immunofluorescence.

RESULTS

NXS could significantly ameliorate the ICH recovery of neural and locomotor function as well as reduce hemorrhage volume. NXS could increase the expression of CD36 expressed in M2 microglia and promote M2 microglia polarization. Simultaneously, NXS significantly suppressed protein expressions of TLR4, MyD88, and NF-κB following ICH in rats. The results indicated that lipopolysaccharide (LPS), TLR4 specific agonist, could partially reverse the change in ICH rats administrated with NXS.

CONCLUSIONS

NXS promotes hematoma absorption by targeting CD36 expression in M2 microglia via TLR4/MyD88/NF-κB signaling pathway in rats with ICH. Collectively, current research provides a novel theoretical basis for the clinical application of NXS.

Pathogenic role of S100 proteins in psoriasis

Psoriasis is a chronic inflammatory skin disease. The histopathological features of psoriasis include excessive proliferation of keratinocytes and infiltration of immune cells. The S100 proteins are a group of EF-hand Ca2+-binding proteins, including S100A2, -A7, -A8/A9, -A12, -A15, which expression levels are markedly upregulated in psoriatic skin. These proteins exert numerous functions such as serving as intracellular Ca2+ sensors, transduction of Ca2+ signaling, response to extracellular stimuli, energy metabolism, and regulating cell proliferation and apoptosis. Evidence shows a crucial role of S100 proteins in the development and progress of inflammatory diseases, including psoriasis. S100 proteins can possibly be used as potential therapeutic target and diagnostic biomarkers. This review focuses on the pathogenic role of S100 proteins in psoriasis.

Pro-Inflammatory Alterations of Circulating Monocytes in Latent Tuberculosis Infection

Background

Latent tuberculosis infection (LTBI) has been associated with increased cardiovascular risk. We investigated the activation and pro-inflammatory profile of monocytes in individuals with LTBI and their association with coronary artery disease (CAD).

Methods

Individuals 40-70 years old in Lima, Peru, underwent QuantiFERON-TB testing to define LTBI, completed a coronary computed tomography angiography to evaluate CAD, and provided blood for monocyte profiling using flow cytometry. Cells were stimulated with lipopolysaccharide to assess interleukin-6 (IL-6) and tumor necrosis factor (TNF)-α responses.

Results

The clinical characteristics of the LTBI (n = 28) and non-LTBI (n = 41) groups were similar. All monocyte subsets from LTBI individuals exhibited higher mean fluorescence intensity (MFI) of CX3CR1 and CD36 compared with non-LTBI individuals. LTBI individuals had an increased proportion of nonclassical monocytes expressing IL-6 (44.9 vs 26.9; P = .014), TNF-α (62.3 vs 35.1; P = .014), and TNF-α⁺IL-6⁺ (43.2 vs 36.6; P = .042). Among LTBI individuals, CAD was associated with lower CX3CR1 MFI on classical monocytes and lower CD36 MFI across all monocyte subsets. In multivariable analyses, lower CD36 MFI on total monocytes (b = -0.17; P = .002) and all subsets remained independently associated with CAD in LTBI.

Conclusions

Individuals with LTBI have distinct monocyte alterations suggestive of an exacerbated inflammatory response and tissue migration. Whether these alterations contribute to cardiovascular disease pathogenesis warrants further investigation.

Investigation on the potential targets of Astragaloside IV against intracerebral hemorrhage based on network pharmacology and experimental validation

Intracerebral hemorrhage (ICH) is a life-threatening type of stroke that affects millions of individuals worldwide. Astragaloside IV (AS-IV), the main bioactive ingredient in Radix Astragali, has been linked to a variety of pharmacologic actions, including stroke. However, the effects and potential mechanisms of AS-IV on hematoma absorption after ICH are still unknown. The study aims to identify potential targets and regulation mechanisms of AS-IV on hematoma absorption after ICH. Network pharmacology, molecular docking, pharmacodynamic study, and western blot were used in this study to explore the potential mechanisms. The results showed that AS-IV could improve the hematoma absorption and neurological outcomes in collagenase VII induced rat ICH models. Molecular docking results had shown that PI3K and AKT were the potential targets of AS-IV against ICH. The experimental validation showed that AS-IV could reduce phosphorylation expression of PI3K and AKT, thereby inhibiting the NF-κB and increasing CD36 expression. This study demonstrated that AS-IV could play a critical role on hematoma absorption after ICH by regulating the PI3K/AKT signaling pathway and promoting CD36 phagocytosis, which provided a new thought for the drug development of ICH.

The Early Immune Response of Lymphoid and Myeloid Head-Kidney Cells of Rainbow Trout (Oncorhynchus mykiss) Stimulated with Aeromonas salmonicida

The teleost head kidney is a highly relevant immune organ, and myeloid cells play a major role in this organ’s innate and adaptive immune responses. Because of their complexity, the early phases of the innate immune reaction of fish against bacteria are still poorly understood. In this study, naïve rainbow trout were stimulated with inactivated A. salmonicida and sampled at 12 h, 24 h and 7 d poststimulation. Cells from the head kidney were magnetically sorted with a monoclonal antibody mAB21 to obtain one (MAb21-positive) fraction enriched with myeloid cells and one (MAb21-negative) fraction enriched with lymphocytes and thrombocytes. The gene expression pattern of the resulting cell subpopulations was analysed using a panel of 43 immune-related genes. The results show an overall downregulation of the complement pathway and cytokine production at the considered time points. Some of the selected genes may be considered as parameters for diagnosing bacterial furunculosis of rainbow trout.

Phenotypic and Functional Consequences of PLT Binding to Monocytes and Its Association with Clinical Features in SLE

Platelets (PLTs) can modulate the immune system through the release of soluble mediators or through interaction with immune cells. Monocytes are the main immune cells that bind with PLTs, and this interaction is increased in several inflammatory and autoimmune conditions, including systemic lupus erythematosus (SLE). Our aim was to characterize the phenotypic and functional consequences of PLT binding to monocytes in healthy donors (HD) and in SLE and to relate it to the pathogenesis of SLE. We analyzed the phenotypic and functional features of monocytes with non-activated and activated bound PLTs by flow cytometry. We observed that monocytes with bound PLTs and especially those with activated PLTs have an up-regulated HLA-DR, CD86, CD54, CD16 and CD64 expression. Monocytes with bound PLTs also have an increased capacity for phagocytosis, though not for efferocytosis. In addition, monocytes with bound PLTs have increased IL-10, but not TNF-α, secretion. The altered phenotypic and functional features are comparable in SLE and HD monocytes and in bound PLTs. However, the percentages of monocytes with bound PLTs are significantly higher in SLE patients and are associated with undetectable levels of anti-dsDNA antibodies and hematuria, and with normal C3 and albumin/creatinine levels. Our results suggest that PLTs have a modulatory influence on monocytes and that this effect may be highlighted by an increased binding of PLTs to monocytes in autoimmune conditions.

White Adipose Tissue Surface Expression of LDLR and CD36 is Associated with Risk Factors for Type 2 Diabetes in Adults with Obesity

OBJECTIVE

Human conditions with upregulated receptor uptake of low-density lipoproteins (LDL) are associated with diabetes risk, the reasons for which remain unexplored. LDL induce metabolic dysfunction in murine adipocytes. Thus, it was hypothesized that white adipose tissue (WAT) surface expression of LDL receptor (LDLR) and/or CD36 is associated with WAT and systemic metabolic dysfunction. Whether WAT LDLR and CD36 expression is predicted by plasma lipoprotein-related parameters was also explored.

METHODS

This was a cross-sectional analysis of 31 nondiabetic adults (BMI > 25 kg/m² ) assessed for WAT surface expression of LDLR and CD36 (immunohistochemistry), WAT function, WAT and systemic inflammation, postprandial fat metabolism, and insulin resistance (IR; hyperinsulinemic-euglycemic clamp).

RESULTS

Fasting WAT surface expression of LDLR and CD36 was negatively associated with WAT function (³ H-triglyceride storage, r = -0.45 and -0.66, respectively) and positively associated with plasma IL-1 receptor antagonist (r = 0.64 and 0.43, respectively). Their expression was suppressed 4 hours postprandially, and reduced LDLR was further associated with IR (M/I_clamp , r = 0.61 women, r = 0.80 men). Plasma apolipoprotein B (apoB)-to-PCSK9 ratio predicted WAT surface expression of LDLR and CD36, WAT dysfunction, WAT NLRP3 inflammasome priming and disrupted cholesterol-sensing genes, and systemic IR independent of sex and body composition.

CONCLUSIONS

Higher fasting and lower postprandial WAT surface expression of LDLR and CD36 is associated with WAT dysfunction, systemic inflammation, and IR in adults with overweight/obesity, anomalies that are predicted by higher plasma apoB-to-PCSK9 ratio.

CD36 in Alzheimer's Disease: An Overview of Molecular Mechanisms and Therapeutic Targeting

CD36 is a membrane protein with wide distribution in the human body, is enriched in the monocyte-macrophage system and endothelial cells, and is involved in the cellular uptake of long chain fatty acids (LCFA) and oxidized low-density lipoproteins. It is also a scavenger receptor, binding hydrophobic amyloid fibrils found in the Alzheimer's disease (AD) brain. In neurobiology research, it has been mostly studied in relationship with chronic ischemia and stroke, but it was also related to amyloid clearance by microglial phagocytosis. In AD animal models, amyloid binding to CD36 has been consistently correlated with a pro-inflammatory response. Therapeutic approaches have two main focuses: CD36 blockade with monoclonal antibodies or small molecules, which is beneficial in terms of the inflammatory milieu, and upregulation of CD36 for increased amyloid clearance. The balance of the two approaches, centered on microglia, is poorly understood. Furthermore, CD36 evaluation in AD clinical studies is still at a very early stage and there is a gap in the knowledge regarding the impact of LCFA on AD progression and CD36 expression and genetic phenotype. This review summarizes the role played by CD36 in the pathogenic amyloid cascade and explore the translatability of preclinical data towards clinical research.

Effects of β2/aβ2 on oxLDL-induced CD36 activation in THP-1 macrophages

AIMS

β2-glycoprotein I/anti-β2-glycoprotein I antibody complex (β2/aβ2) could promote oxLDL-induced endothelial inflammation through Toll-like receptor 4 (TLR4), therefore accelerates atherosclerosis in patients with anti-phospholipid syndrome (APS). However, effects of β2/aβ2 and TLR4 on oxLDL-induced CD36 activation in macrophages remain to be elucidated and are currently under investigation.

MATERIALS AND METHODS

THP-1 macrophages with or without the pre-treatment of TAK-242, a TLR4 inhibitor, were treated with RPMI 1640, oxLDL, oxLDL+β2/aβ2 or oxLDL + LPS.CD36 expression and subsequent intracellular lipid accumulation, cholesterol-transportation-related proteins (ACAT1, ABCG1 and ABCA1) expression, inflammatory cytokines (IL-1β, TNF-α and IL-6) secretion, focal adhesion kinases (FAK) activation and matrix metalloproteinases (MMP-2 and MMP-9) expression by these THP-1 macrophages were evaluated. Moreover, effects of TLR4 on oxLDL+β2/aβ2-induced peroxisome proliferators-activated receptor-γ (PPAR-γ) expression and CD36 translocation have also been observed.

KEY FINDINGS

Compared with oxLDL-treated ones, CD36 expression, intracellular lipid accumulation and FAK activation were inhibited, whereas the levels of inflammatory cytokines and MMPs were upregulated in THP-1 macrophages treated with oxLDL+β2/aβ2 (p < 0.05). Moreover, observed differences between oxLDL-treated and oxLDL+β2/aβ2-treated THP-1 macrophages could be reversed by TAK-242 pre-treatment (p < 0.05). Furthermore, oxLDL+β2/aβ2 promoted PPAR-γ expression and CD36 cytoplasmic translocation in THP-1 macrophages, these effects could also be attenuated by TAK-242 (p < 0.05).

SIGNIFICANCE

Through a TLR4 dependent manner, β2/aβ2 inhibited oxLDL-induced CD36 expression, lipid accumulation and FAK activation, while promoted inflammatory cytokines and MMPs expression in THP-1 macrophages, indicating the novel dual roles played by β2/aβ2 in APS-related atherosclerosis.

Resistin-Inhibited Neural Stem Cell-Derived Astrocyte Differentiation Contributes to Permeability Destruction of the Blood-Brain Barrier

Neuroinflammation is an important part of the development of neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's and amyotrophic lateral sclerosis. Inflammatory factors destroy the balance of the microenvironment, which results in changes in neural stem cell differentiation and proliferation behaviour. However, the mechanism underlying inflammatory factor-induced NSC behavioural changes is not clear. Resistin is a proinflammatory and adipogenic factor and is involved in several human pathology processes. The neural stem cell microenvironment changes when the concentration of resistin in the brain during an inflammatory response disease increases. In the present study, we explored the effect and mechanism of resistin on the proliferation and differentiation of neural stem cells. We found that intracerebroventricular injection of resistin induced a decrease in GFAP-positive cells in mice by influencing NSC differentiation. Resistin significantly decreased TEER and increased permeability in an in vitro blood-brain barrier model, which is consistent with the results of an HBMEC-astrocyte coculture system. Resistin-inhibited astrocyte differentiation is mediated through TLR4 on neural stem cells. To our knowledge, this is the first study reporting the effect of resistin on neural stem cells. Our findings shed light on resistin-involved neural stem cell degeneration mechanisms.

S100A12-CD36 axis: A novel player in the pathogenesis of atherosclerosis?

S100A12 is a member of the S100 family of EF-hand calcium-binding proteins and have a variety of intracellular and extracellular activities. It exerts its proinflammatory effects by binding to the receptor for advanced glycation end products (RAGE) and Toll-like receptor 4 (TLR4). CD36 is a class B scavenger receptor that acts as a fatty acid transporter. Both S100A12 and CD36 are implicated in vascular inflammation and atherosclerosis. It has recently been demonstrated that S100A12 binds with high affinity to CD36. On the other hand, RAGE and TLR4 play a key role in the regulation of CD36 expression. These observations point to the fact that S100A12 is an interesting molecular target for the development of therapeutics. This Cytokine stimulus will focus on the possible mechanisms of S100A12-CD36 axis in the pathogenesis of atherosclerosis.

Modulators of microglial activation and polarization after intracerebral haemorrhage

Intracerebral haemorrhage (ICH) is the most lethal subtype of stroke but currently lacks effective treatment. Microglia are among the first non-neuronal cells on the scene during the innate immune response to ICH. Microglia respond to acute brain injury by becoming activated and developing classic M1-like (proinflammatory) or alternative M2-like (anti-inflammatory) phenotypes. This polarization implies as yet unrecognized actions of microglia in ICH pathology and recovery, perhaps involving microglial production of proinflammatory or anti-inflammatory cytokines and chemokines. Furthermore, alternatively activated M2-like microglia might promote phagocytosis of red blood cells and tissue debris, a major contribution to haematoma clearance. Interactions between microglia and other cells modulate microglial activation and function, and are also important in ICH pathology. This Review summarizes key studies on modulators of microglial activation and polarization after ICH, including M1-like and M2-like microglial phenotype markers, transcription factors and key signalling pathways. Microglial phagocytosis, haematoma resolution, and the potential crosstalk between microglia and T lymphocytes, neurons, astrocytes, and oligodendrocytes in the ICH brain are described. Finally, the clinical and translational implications of microglial polarization in ICH are presented, including the evidence that therapeutic approaches aimed at modulating microglial function might mitigate ICH injury and improve brain repair.

CSF-1 regulates the function of monocytes in Crohn's disease patients in remission

During the flare-ups of Crohn’s disease (CD) patients, circulating leukocytes actively migrate toward the inflamed sites. During the remission, the lack of symptoms does not necessarily imply immunological remission. To decipher inflammatory mechanisms still operating during CD remission, we compared the expression of chemokine receptors on monocytes from CD and healthy donors (HD), and how these differences could modulate monocyte maturation and cytokine production. Flow cytometry analysis showed a higher expression of CCR5 on monocytes from CD patients than those from HD after 24 h. This CCR5 upregulation was associated with the spontaneous production of CSF-1 and IL-10. The higher expression of CCR5 on CD monocytes increased their migratory pattern in response to CCL5. Signaling through CCR5/CCL5 increased CD163 and HLA-DR expression and diminished TLR4-induced TNF-α and IL-6 secretion during monocyte differentiation. When we analyzed clinical parameters, patients treated with azathioprine had the highest CSF-1 levels and CCR5 expression. Our results suggest that monocytes from CD patients in remission produced high levels of CSF-1 that upregulate CCR5 expression. Consequently, monocytes differentiated in these conditions had a characteristic phenotype and lower production of inflammatory cytokines. The treatment with azathioprine could be responsible for this anti-inflammatory profile of monocytes.

Inactivation of Rab11a GTPase in Macrophages Facilitates Phagocytosis of Apoptotic Neutrophils

The timely and efficient clearance of apoptotic neutrophils by macrophages (efferocytosis) is required for the resolution of inflammation and tissue repair, but the regulatory mechanisms remain unclear. In this study, we investigated the role of the small GTPase Ras-related protein in brain (Rab)11a in regulating efferocytosis, and on this basis the resolution of inflammatory lung injury. We observed that apoptotic neutrophil feeding induced a rapid loss of Rab11a activity in bone marrow-derived macrophages and found that depletion of Rab11a in macrophages by small interfering RNA dramatically increased the phagocytosis of apoptotic neutrophils compared with control cells. Additionally, overexpression of wild-type Rab11a inhibited macrophage efferocytosis, whereas overexpression of dominant-negative Rab11a (Rab11a S25N) increased the clearance of apoptotic neutrophils. Rab11a knockdown also increased the surface level of CD36 in macrophages, but it reduced cell surface expression of a disintegrin and metalloproteinase (ADAM) 17. Depletion of ADAM17 rescued the decreased surface CD36 expression found in macrophages overexpressing wild-type Rab11a. Also, blockade of CD36 abolished the augmented efferocytosis seen in Rab11a-depleted macrophages. In mice challenged with endotoxin, intratracheal instillation of Rab11a-depleted macrophages reduced neutrophil count in bronchoalveolar lavage fluid, increased the number of macrophages containing apoptotic neutrophils, and prevented inflammatory lung injury. Thus, Rab11a inactivation in macrophages as a result of apoptotic cell binding initiates phagocytosis of apoptotic neutrophils via the modulation of ADAM17-mediated CD36 cell surface expression. Our results raise the possibility that inhibition of Rab11a activity in macrophages is a promising strategy for activating the resolution of inflammatory lung injury.

Effects of Porphyromonas gingivalis lipopolysaccharide on the expression of key genes involved in cholesterol metabolism in macrophages

INTRODUCTION

Cardiovascular diseases are positively correlated with periodontal disease. However, the molecular mechanisms linking atherosclerosis and periodontal infection are not clear. This study aimed to determine whether Porphyromonas gingivalis lipopolysaccharide (Pg-LPS) altered the expression of genes regulating cholesterol metabolism in macrophages in the presence of low-density lipoprotein (LDL).

MATERIAL AND METHODS

THP-1-derived macrophages were exposed to different concentrations (0.1, 1, 10 µg/ml) of LPS in the presence of 50 µg/ml native LDL. Macrophages were also incubated with 1 µg/ml LPS for varying times (0, 24, 48, or 72 h) in the presence of native LDL. Foam cell formation was determined by oil red O staining and cholesterol content quantification. CD36, lectin-like oxidized LDL receptor-1 (LOX-1), ATP-binding cassette G1 (ABCG1), and acetyl CoA acyltransferase 1 (ACAT1) expression levels were measured by western blot and qRT-PCR.

RESULTS

Foam cell formation was induced in a time- and concentration-dependent manner as assessed by both morphological and biochemical criteria. Pg-LPS caused downregulation of CD36 and ABCG1 but upregulation of ACAT1, while LOX-1 expression was not affected (p = 0.137).

CONCLUSIONS

Pg-LPS appears to be an important link in the development of atherosclerosis by mechanisms targeting cholesterol homeostasis, namely, excess cholesterol ester formation via ACAT1 and reduced cellular cholesterol efflux via ABCG1.

CD36 regulates lipopolysaccharide-induced signaling pathways and mediates the internalization of Escherichia coli in cooperation with TLR4 in goat mammary gland epithelial cells

The scavenger receptor CD36 is involved in pathogen recognition, phagocytosis, and pathogen-induced signaling. This study investigated the relationship between CD36 and TLR4 in modifying lipopolysaccharide (LPS)-induced signaling pathways and mediating Escherichia coli (E. coli) endocytosis in primary goat mammary epithelial cells (pGMECs). The manipulation of CD36 expression significantly influenced TLR4 and nuclear factor kappa B (NF-κB) mRNA expression in pGMECs stimulated with LPS for 12 h. NF-κB and activator protein-1 (AP-1) activity was regulated by the manipulation of CD36 expression in LPS-induced pGMECs. However, CD36-mediated AP-1 activation occurred primarily through c-Jun N-terminal kinase (c-JNK). Adaptor proteins and proinflammatory cytokines were also involved in these signaling pathways and acted by regulating CD36 expression in LPS-stimulated cells. Moreover, CD36 cooperated with TLR4 in TLR4-mediated phagocytosis following E. coli simulation, but this complex was not induced by LPS treatment. Our study is the first to illuminate CD36 as a scavenger receptor in ruminants. Additionally, this study indicates that CD36 plays a vital role in the LPS-induced activation of downstream signaling cascades and mediates E. coli phagocytosis via TLR4 in pGMECs, which offers a novel treatment strategy for mastitis.

Microglial Polarization and Inflammatory Mediators After Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is a subtype of stroke with high mortality and morbidity. When a diseased artery within the brain bursts, expansion and absorption of the resulting hematoma trigger a series of reactions that cause primary and secondary brain injury. Microglia are extremely important for removing the hematoma and clearing debris, but they are also a source of ongoing inflammation. This article discusses the role of microglial activation/polarization and related inflammatory mediators, such as Toll-like receptor 4, matrix metalloproteinases, high-mobility group protein box-1, nuclear factor erythroid 2-related factor 2, heme oxygenase, and iron, in secondary injury after ICH and highlights the potential targets for ICH treatment.

Prostaglandin E2 receptor subtype 2 regulation of scavenger receptor CD36 modulates microglial Aβ42 phagocytosis

Recent studies underline the potential relevance of microglial innate immune activation in Alzheimer disease. Primary mouse microglia that lack prostaglandin E2 receptor subtype 2 (EP2) show decreased innate immune-mediated neurotoxicity and increased amyloid β (Aβ) peptide phagocytosis, features that were replicated in vivo. Here, we tested the hypothesis that scavenger receptor CD36 is an effector of EP2-regulated Aβ phagocytosis. CD36 expression was 143-fold greater in mouse primary microglia than in primary astrocytes. Three different means of suppressing EP2 signaling increased and an agonist of EP2 decreased CD36 expression in primary wild-type microglia. Activation of Toll-like receptor (TLR) 3, TLR4, and TLR7, but not TLR2 or TLR9, reduced primary microglial CD36 transcription and cell surface CD36 protein and reduced Aβ42 phagocytosis as well. At each step, the effects of innate immune activation on CD36 were reversed by at least 50% by an EP2 antagonist, and this partial rescue of microglia Aβ42 phagocytosis was largely mediated by CD36 activity. Finally, we showed in hippocampus of wild-type mice that innate immune activation suppressed CD36 expression by an EP2-dependent mechanism. Taken together with results of others that found brain clearance of Aβ peptides and behavioral improvements mediated by CD36 in mice, regulation of CD36-mediated Aβ phagocytosis by suppression of EP2 signaling may provide a new approach to suppressing some aspects of Alzheimer disease pathogenesis.

The effect of albumin on podocytes: the role of the fatty acid moiety and the potential role of CD36 scavenger receptor

Evidence is emerging that podocytes are able to endocytose proteins such as albumin using kinetics consistent with a receptor-mediated process. To date the role of the fatty acid moiety on albumin uptake kinetics has not been delineated and the receptor responsible for uptake is yet to be identified. Albumin uptake studies were carried out on cultured human podocytes exposed to FITC-labelled human serum albumin either carrying fatty acids (HSA+FA) or depleted of them (HSA-FA). Receptor-mediated endocytosis of FITC-HSA+FA over 60 min was 5 times greater than that of FITC-HSA-FA. 24h exposure of podocytes to albumin up-regulated nephrin expression and induced the activation of caspase-3. These effects were more pronounced in response to HSA-FA. Individually, anti-CD36 antibodies had no effect upon endocytosis of FITC-HSA. However, a cocktail of 2 antibodies reduced uptake by nearly 50%. Albumin endocytosis was enhanced in the presence of the CD36 specific inhibitor sulfo-N-succinimidyl oleate (SSO) while knock-down of CD36 using CD36siRNA had no effect on uptake. These data suggest that receptor-mediated endocytosis of albumin by podocytes is regulated by the fatty acid moiety, although, some of the detrimental effects are induced independently of it. CD36 does not play a direct role in the uptake of albumin.

CD36-mediated hematoma absorption following intracerebral hemorrhage: negative regulation by TLR4 signaling

Promoting hematoma absorption is a novel therapeutic strategy for intracerebral hemorrhage (ICH); however, the mechanism of hematoma absorption is unclear. The present study explored the function and potential mechanism of CD36 in hematoma absorption using in vitro and in vivo ICH models. Hematoma absorption in CD36-deficient ICH patients was examined. Compared with patients with normal CD36 expression, CD36-deficient ICH patients had slower hematoma adsorption and aggravated neurologic deficits. CD36 expression in perihematomal tissues in wild-type mice following ICH was increased, whereas the hematoma absorption in CD36(-/-) mice was decreased. CD36(-/-) mice also showed aggravated neurologic deficits and increased TNF-α and IL-1β expression levels. The phagocytic capacity of CD36(-/-) microglia for RBCs was also decreased. Additionally, the CD36 expression in the perihematoma area after ICH in TLR4(-/-) and MyD88(-/-) mice was significantly increased, and hematoma absorption was significantly promoted, which was significantly inhibited by an anti-CD36 Ab. In vitro, TNF-α and IL-1β significantly inhibited the microglia expression of CD36 and reduced the microglia phagocytosis of RBCs. Finally, the TLR4 inhibitor TAK-242 upregulated CD36 expression in microglia, promoted hematoma absorption, increased catalase expression, and decreased the H2O2 content. These results suggested that CD36 mediated hematoma absorption after ICH, and TLR4 signaling inhibited CD36 expression to slow hematoma absorption. TLR4 inhibition could promote hematoma absorption and significantly improve neurologic deficits following ICH.

Human embryonic epidermis contains a diverse Langerhans cell precursor pool

Despite intense efforts, the exact phenotype of the epidermal Langerhans cell (LC) precursors during human ontogeny has not been determined yet. These elusive precursors are believed to migrate into the embryonic skin and to express primitive surface markers, including CD36, but not typical LC markers such as CD1a, CD1c and CD207. The aim of this study was to further characterize the phenotype of LC precursors in human embryonic epidermis and to compare it with that of LCs in healthy adult skin. We found that epidermal leukocytes in first trimester human skin are negative for CD34 and heterogeneous with regard to the expression of CD1c, CD14 and CD36, thus contrasting the phenotypic uniformity of epidermal LCs in adult skin. These data indicate that LC precursors colonize the developing epidermis in an undifferentiated state, where they acquire the definitive LC marker profile with time. Using a human three-dimensional full-thickness skin model to mimic in vivo LC development, we found that FACS-sorted, CD207(-) cord blood-derived haematopoietic precursor cells resembling foetal LC precursors but not CD14(+)CD16(-) blood monocytes integrate into skin equivalents, and without additional exogenous cytokines give rise to cells that morphologically and phenotypically resemble LCs. Overall, it appears that CD14(-) haematopoietic precursors possess a much higher differentiation potential than CD14(+) precursor cells.

HIV-1 Nef impairs key functional activities in human macrophages through CD36 downregulation

Monocytes and macrophages utilize the class A and B scavenger receptors to recognize and perform phagocytosis of invading microbes before a pathogen-specific immune response is generated. HIV-1 Nef protein affects the innate immune system impairing oxidative burst response and phagocytic capacity of macrophages. Our data show that exogenous recombinant myristoylated Nef protein induces a marked CD36 downregulation in monocytes from Peripheral Blood Mononuclear Cells, in Monocyte-Derived Macrophages (MDMs) differentiated by cytokines and in MDMs contained in a mixed culture obtained expanding PBMCs under Human Erythroid Massive Amplification condition. Under the latter culture condition we identify three main populations after 6 days of expansion: lymphocytes (37.8±14.7%), erythroblasts (46.7±6.1%) and MDMs (15.7±7.5%). The Nef addition to the cell culture significantly downregulates CD36 expression in MDMs, but not in erythroid cells. Furthermore, CD36 inhibition is highly specific since it does not modify the expression levels of other MDM markers such as CD14, CD11c, CD86, CD68, CD206, Toll-like Receptor 2 and Toll-like Receptor 4. Similar results were obtained in MDMs infected with VSV-G pseudotyped HIV-1-expressing Nef. The reduced CD36 membrane expression is associated with decrease of correspondent CD36 mRNA transcript. Furthermore, Nef-induced CD36 downregulation is linked to both impaired scavenger activity with reduced capability to take up oxidized lipoproteins and to significant decreased phagocytosis of fluorescent beads and GFP-expressing Salmonella tiphymurium. In addition we observed that Nef induces TNF-α release in MDMs. Although these data suggest a possible involvement of TNF-α in mediating Nef activity, our results exclude a possible relationship between Nef-induced TNF-α release and Nef-mediated CD36 downregulation. The present work shows that HIV-1 Nef protein may have a role in the strategies elaborated by HIV-1 to alter pathogen disease outcomes, by modulating CD36 expression in macrophages, favoring the onset of opportunistic infections in HIV-1 infected people.

The effect of high intensity interval exercise on postprandial triacylglycerol and leukocyte activation--monitored for 48 h post exercise

Postprandial phenomenon are thought to contribute to atherogenesis alongside activation of the immune system. A single bout of high intensity interval exercise attenuates postprandial triacylglycerol (TG), although the longevity and mechanisms underlying this observation are unknown. The aims of this study were to determine whether this attenuation in postprandial TG remained 2 days after high intensity interval exercise, to monitor markers of leukocyte activation and investigate the underlying mechanisms. Eight young men each completed two three day trials. On day 1: subjects rested (Control) or performed 5 x 30 s maximal sprints (high intensity interval exercise). On day 2 and 3 subjects consumed high fat meals for breakfast and 3 h later for lunch. Blood samples were taken at various times and analysed for TG, glucose and TG-rich lipoprotein (TRL)-bound LPL-dependent TRL-TG hydrolysis (LTTH). Flow cytometry was used to evaluate granulocyte, monocyte and lymphocyte CD11b and CD36 expression. On day 2 after high intensity interval exercise TG area under the curve was lower (P<0.05) (7.46±1.53 mmol/l/7h) compared to the control trial (9.47±3.04 mmol/l/7h) with no differences during day 3 of the trial. LTTH activity was higher (P<0.05) after high intensity interval exercise, at 2 hours of day 2, compared to control. Granulocyte, monocyte and lymphocyte CD11b expression increased with time over day 2 and 3 of the study (P<0.0001). Lymphocyte and monocyte CD36 expression decreased with time over day 2 and 3 (P<0.05). There were no differences between trials in CD11b and CD36 expression on any leukocytes. A single session of high intensity interval exercise attenuated postprandial TG on day 2 of the study, with this effect abolished by day 3.The reduction in postprandial TG was associated with an increase in LTTH. High intensity interval exercise had no effect on postprandial responses of CD11b or CD36.

Unilateral once daily milking locally induces differential gene expression in both mammary tissue and milk epithelial cells revealing mammary remodeling

Once daily milking reduces milk yield, but the underlying mechanisms are not yet fully understood. Local regulation due to milk stasis in the tissue may contribute to this effect, but such mechanisms have not yet been fully described. To challenge this hypothesis, one udder half of six Holstein dairy cows was milked once a day (ODM), and the other twice a day (TDM). On the 8th day of unilateral ODM, mammary epithelial cells (MEC) were purified from the milk using immunomagnetic separation. Mammary biopsies were harvested from both udder halves. The differences in transcript profiles between biopsies from ODM and TDM udder halves were analyzed by a 22k bovine oligonucleotide array, revealing 490 transcripts that were differentially expressed. The principal category of upregulated transcripts concerned mechanisms involved in cell proliferation and death. We further confirmed remodeling of the mammary tissue by immunohistochemistry, which showed less cell proliferation and more apoptosis in ODM udder halves. Gene expression analyzed by RT-qPCR in MEC purified from milk and mammary biopsies showed a common downregulation of six transcripts (ABCG2, FABP3, NUCB2, RNASE1 and 5, and SLC34A2) but also some discrepancies. First, none of the upregulated transcripts in biopsies varied in milk-purified MEC. Second, only milk-purified MEC showed significant LALBA downregulation, which suggests therefore that they correspond to a mammary epithelial cell subpopulation. Our results, obtained after unilateral milking, suggest that cell remodeling during ODM is due to a local effect, which may be triggered by milk accumulation.

TRIF mediates Toll-like receptor 2-dependent inflammatory responses to Borrelia burgdorferi

TRIF is an adaptor molecule important in transducing signals from intracellularly signaling Toll-like receptor 3 (TLR3) and TLR4. Recently, TLR2 was found to signal from intracellular compartments. Using a synthetic ligand for TLR2/1 heterodimers, as well as Borrelia burgdorferi, which is a strong activator of TLR2/1, we found that TLR2 signaling can utilize TRIF. Unlike TRIF signaling by other TLRs, TLR2-mediated TRIF signaling is dependent on the presence of another adaptor molecule, MyD88. However, unlike MyD88 deficiency, TRIF deficiency does not result in diminished control of infection with B. burgdorferi in a murine model of disease. This appears to be due to the effects of MyD88 on phagocytosis via scavenger receptors, such as MARCO, which are not affected by the loss of TRIF. In mice, TRIF deficiency did have an effect on the production of inflammatory cytokines, suggesting that regulation of inflammatory cytokines and control of bacterial growth may be uncoupled, in part through transduction of TLR2 signaling through TRIF.