Scavenger Receptor CD36 Research Articles

Reduced angiogenesis and delayed endochondral ossification in CD163-/- mice highlights a role of M2 macrophages during bone fracture repair.

While recent studies showed that macrophages are critical for bone fracture healing, and lack of M2 macrophages have been implicated in models of delayed union, functional roles for specific M2 receptors have yet to be defined. Moreover, the M2 scavenger receptor CD163 has been identified as a target to inhibit sepsis following implant-associated osteomyelitis, but potential adverse effects on bone healing during blockage therapy have yet to be explored. Thus, we investigated fracture healing in C57BL/6 versus CD163-/- mice using a well-established closed, stabilized, mid-diaphyseal femur fracture model. While gross fracture healing in CD163-/- mice was similar to that of C57BL/6, plain radiographs revealed persistent fracture gaps in the mutant mice on Day 14, which resolved by Day 21. Consistently, 3D vascular micro-CT demonstrated delayed union on Day 21, with reduced bone volume (74%, 61%, and 49%) and vasculature (40%, 40%, and 18%) compared to C57BL/6 on Days 10, 14, and 21 postfracture, respectively (p < 0.01). Histology confirmed large amounts of persistent cartilage in CD163-/- versus C57BL/6 fracture callus on Days 7 and 10 that resolves over time, and immunohistochemistry demonstrated deficiencies in CD206+ M2 macrophages. Torsion testing of the fractures confirmed the delayed early union in CD163-/- femurs, which display decreased yield torque on Day 21, and a decreased rigidity with a commensurate increase in rotation at yield on Day 28 (p < 0.01). Collectively, these results demonstrate that CD163 is required for normal angiogenesis, callus formation, and bone remodeling during fracture healing, and raise potential concerns about CD163 blockade therapy.

Abstract 2881: Investigating cholesterol transfer between macrophages and prostate cancer cells

Abstract Background: Androgens stimulate androgen receptor (AR) signaling, driving prostate cancer (PC) cell proliferation and progression. Androgen deprivation therapy (ADT) effectively treats primary disease, but 20-30% of patients relapse after ~5 years, resulting in castration-resistant prostate cancer (CRPC), which has limited treatment options. We have previously shown in a murine model of CRPC that macrophages promote AR signaling in CRPC and that depleting tumor macrophages extends survival in response to ADT with Lupron. This correlates with reduced androgen levels in macrophage-depleted tumors and the ability of macrophages to transfer cholesterol, the anabolic precursor of androgens, to prostate cancer cells. However, the mechanism by which this transfer occurs, and whether cholesterol exchange mediates resistance to ADT, is currently unknown. Methods: To assess cholesterol transfer from macrophages to cancer cells, we established a culture system involving prostate cancer cell lines and either the RAW264.7 macrophage cell line or bone marrow-derived macrophages (BMDMs). Macrophages were pre-loaded with cholesterol using fluorescently labeled low-density lipoprotein (LDL) and were co-cultured or placed in a transwell system with tumor cells for 24 hours. Cholesterol transfer was then measured by flow cytometry. Results: Fluorescent signal from LDL was detected in 50-70% of tumor cells after 24 hours of co-culture. Cell contact was required for cholesterol transfer, as no fluorescence was detected in prostate cancer cells during transwell experiments. Macrophages were also able to internalize and transfer acetylated LDL, which is poorly taken up by tumor cells compared to unmodified LDL. Macrophage polarization with interleukin-4 did not impact cholesterol transfer and uptake of acetylated LDL occurred independently of the scavenger receptor CD36. The scavenger receptor SR-B1, which is often upregulated in prostate cancer cells, was dispensable for transfer, as knocking out SR-B1 via CRISPR/Cas9 in cancer cell lines did not reduce LDL uptake. Conclusion: Cholesterol transfer between macrophages and prostate cancer cells occurs in a contact-dependent manner, independently of the scavenger receptors most commonly associated with cholesterol accumulation. Citation Format: Olabisi Osunmakinde, Brian Ruffell. Investigating cholesterol transfer between macrophages and prostate cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2881.

Assessment of the Macrophage Scavenger Receptor CD163 in Mediating Glaesserella parasuis Infection of Host Cells.

The macrophage CD163 surface glycoprotein is a member of the SRCR family class B, which has been identified as the key trigger in host-pathogen interactions, but its specific roles in sensing Glaesserella parasuis (G. parasuis) infection are largely unknown. Here, we investigated porcine CD163 in mediating the adhesion and immune response of G. parasuis using in vitro host-bacteria interaction models. CD163-overexpressing Chinese hamster ovary K1 cells (CHO-K1) showed obvious subcellular localization in the cytoplasm, especially in the cytomembrane. Although detection using scanning electron microscopy (SEM) confirmed the bacterial adhesion, there was no significant difference in the adhesion of G. parasuis to CHO-K1 cells between the presence and absence of CD163. In addition, similar results were observed in 3D4/21 cells. Meanwhile, bindings of G. parasuis to nine synthetic peptides, the bacterial binding motifs within SRCR domains of CD163, were weak based on a solid-phase adhesion assay and agglutination assay. Moreover, CD163 had no effect on the expression of G. parasuis-induced inflammatory cytokines (IL-6, INF-γ, IL-10, IL-4 and TGF-β) in CHO-K1 cells. In conclusion, these findings indicate that porcine CD163 plays a minor role in sensing G. parasuis infection.

OxLDL sensitizes platelets for increased formation of extracellular vesicles capable of finetuning macrophage gene expression

Platelet extracellular vesicles (PEVs) generated upon platelet activation may play a role in inflammatory pathologies such as atherosclerosis. Oxidized low-density lipoprotein (oxLDL), a well-known contributor to atherogenesis, activates platelets and presensitizes them for activation by other agonists. We studied the effect of oxLDL on the secretion, composition, and inflammatory functions of PEVs using contemporary EV analytics. Platelets were activated by co-stimulation with thrombin (T) and collagen (C) ± oxLDL and characterized by high-resolution flow cytometry, nanoparticle tracking analysis, proximity extension assay, western blot, and electron microscopy. The effect of PEVs on macrophage differentiation and functionality was examined by analyzing macrophage surface markers, cytokine secretion, and transcriptome. OxLDL upregulated TC-induced formation of CD61+, P-selectin+ and phosphatidylserine+ PEVs. Blocking the scavenger receptor CD36 significantly suppressed the oxLDL+TC-induced PEV formation, and HDL caused a slight but detectable suppression. The inflammatory protein cargo differed between the PEVs from stimulated and unstimulated platelets. Both oxLDL+TC- and TC-induced PEVs enhanced macrophage HLA-DR and CD86 expression and decreased CD11c expression as well as secretion of several cytokines. Pathways related to cell cycle and regulation of gene expression, and immune system signaling were overrepresented in the differentially expressed genes between TC PEV -treated vs. control macrophages and oxLDL+TC PEV -treated vs. control macrophages, respectively. In conclusion, we speculate that oxLDL and activated platelets contribute to proatherogenic processes by increasing the number of PEVs that provide an adhesive and procoagulant surface, contain inflammatory mediators, and subtly finetune the macrophage gene expression.

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.

CD36 neutralisation blunts TLR2-IRF7 but not IRF3 pathway in neonatal mouse brain and immature human microglia following innate immune challenge

Innate immune response in neonatal brain is associated with a robust microglial activation and induction of Toll-like Receptors (TLRs). To date, the role of the scavenger receptor CD36 in TLRs modulation, particularly TLR2 signaling, has been well established in adult brain. However, the crosstalk between TLR4, TLR2 and CD36 and its immunogenic influence in the neonatal brain remains unclear. In this study, using a CD36 blocking antibody (anti-CD36) at post-natal day 8, we evaluated the response of neonates to systemic endotoxin (lipopolysaccharide; LPS) challenge. We visualized the TLR2 response by bioluminescence imaging using the transgenic mouse model bearing the dual reporter system luciferase/green fluorescent protein under transcriptional control of a murine TLR2 promoter. The anti-CD36 treatment modified the LPS induced inflammatory profile in neonatal brains, causing a significant decrease in inflammatory cytokine levels and the TLR2 and TLR3 mediated signalling.The interferon regulatory factor 3 (IRF3) pathway remained unaffected. Treatment of the LPS-challenged human immature microglia with anti-CD36 induced a marked decrease in TLR2/TLR3 expression levels while TLR4 and IRF3 expression was not affected, suggesting the shared CD36 regulatory mechanisms in human and mouse microglia. Collectively, our results indicate that blocking CD36 alters LPS-induced inflammatory profile of mouse and human microglia, suggesting its role in fine-tuning of neuroinflammation.

Expression of scavenger receptors CD163, CD204, and CD206 on macrophages in patients with pulmonary tuberculosis

The aim of the study was to evaluate the expression of scavenger receptors (CD163, CD204, CD206) on macrophages in patients with pulmonary tuberculosis, depending on the clinical form of the disease and sensitivity of the pathogen to anti-tuberculosis drugs.Materials and methods. 64 patients with pulmonary tuberculosis (TB) were examined: 26 patients with disseminated pulmonary tuberculosis (DTB) and 38 patients with infiltrative pulmonary tuberculosis (ITB). Of these, 42 patients secreted Mycobacterium tuberculosis (MBT) sensitive to basic antituberculosis drugs (ATBD), and 22 patients secreted MBT resistant to first-line anti-TB drugs. Material for the study was venous blood. To isolate monocytes from the whole blood in order to transform them into macrophages, Ficoll density gradient centrifugation with a density of 1.077 g / cm3 was used followed by immunomagnetic separation of CD14+ cells. Monocytes were cultured in the X-VIVO 10 medium with gentamicin and phenol red with the addition of macrophage colony-stimulating factor (M-CSF) (5 ng / ml) at a concentration of 1×106 cells / ml with stimulators: interleukin (IL)-4 (10 ng / ml) and interferon (IFN) γ (100 ng / ml). Immunophenotyping of macrophages was performed using monoclonal antibodies to CD163, CD204, and CD206 on the Beckman Coulter CytoFLEX LX Flow Cytometer. The analysis of the obtained data was carried out using the CytExpert 2.0 software. The results were analyzed using statistical methods.Results. Switching the phenotype of macrophages from the M1-like proinflammatory phenotype to M2-like antiinflammatory one contributes to the chronic course of pulmonary TB, dissemination, and persistence of infection. In the present study, we analyzed the features of the expression of CD163, CD204, and CD206 scavenger receptors on macrophages in patients with pulmonary TB. An increase in the number of macrophages carrying markers of the M2 subpopulation (CD163, CD204, and CD206) on their surface was noted, regardless of the clinical form of pulmonary TB and drug resistance of M. tuberculosis.Conclusion. Studying the mechanisms underlying M1 or M2 activation of macrophages is necessary for a deeper understanding of the immunopathogenesis of TB and the role of innate immunity cells in protecting the body from mycobacteria. The analysis of the expression of scavenger receptors CD163, CD204, and CD206 on macrophages allowed to conclude that, in pulmonary TB, especially in patients with drug resistant M. tuberculosis and infiltrative TB, regulatory mechanisms that suppress the activation of innate immunity are implemented together with polarization of macrophage differentiation towards the M2 phenotype. It may be the cause of immune deficiency induced by the pathogen.

CD36 promotes tubular ferroptosis by regulating the ubiquitination of FSP1 in acute kidney injury

Reactive oxidative species (ROS) production-driven ferroptosis plays a role in acute kidney injury (AKI). However, its exact molecular mechanism is poorly understood. Scavenger receptor CD36 has important roles in oxidizing lipids, lipid accumulation, metabolic syndrome, and insulin resistance in chronic kidney disease, but its roles remain unexplored in AKI. The present study investigated the role and mechanism of CD36 in regulating proximal tubular cell ferroptosis and AKI. The expression of CD36 was found to be significantly up-regulated in AKI renal tissues and correlated with renal function, which might serve as an independent biomarker for AKI patients. Moreover, in adult mice subjected to AKI, deletion of CD36 (CD36−/−) induced tubular cell ROS accumulation, ferroptosis activation, and renal injury. Mechanistically, combining LC-MS/MS, co-IP, and ubiquitination analyses revealed that CD36 could specifically bind to ferroptosis suppressor protein 1 (FSP1) and regulate its ubiquitination at sites K16 and K24, leading to FSP1 degradation and progression of ferroptosis in AKI. The present results emphasize a novel mechanism of CD36 in cisplatin-induced AKI. The discovery of the special CD36 roles in promoting ferroptosis and AKI development by regulating the ubiquitination of FSP1 in proximal tubular cells may be potential therapeutic targets for AKI. Moreover, CD36 may play a key role in the progression of AKI. Therefore, targeting CD36 may provide a promising treatment option for AKI.

Mesenchymal Stem Cells Therapy Led to the Improvement of Spatial Memory in Rats with Alzheimer's disease Through Changing the Expression of LncRNA TUSC7/ miR-449a/ PPARγ and CD36 Genes in the Brain Tissue.

Mesenchymal stem cells (MSCs) have the ability to phagocytize amyloid beta (Aβ) plaques and lower inflammation through the activity of microglia. Peroxisome proliferator-activated receptor gamma (PPARγ) is a protein involved in reducing inflammation through the activity of microglia and the phagocytosis of Aβ plaques by scavenger receptor CD36, in this study, the effect of MSCs therapy on memory function and plaques was investigated. A total of 24 adult male Wistar rats were randomly divided into three groups:1) the control group, 2) the Aβ-treated group (Alzheimer's disease (AD)), and 3) the MSC-treated group (AD + MSC). After the treatment with Aβ and MSCs, western blotting and real-time polymerase chain reaction (PCR) techniques were used to assess protein and gene expression levels, respectively. MSCs improved spatial learning and memory in the AD group (p ≤0.05). The expression levels of PPARγ, lncRNA TUSC7, and CD36 genes were significantly elevated in the group receiving MSCs compared to the AD group (p≤0.0001). Also, the expression level of miR-449a significantly decreased in the AD + MSC group (p≤0.0001). Moreover, western blot analysis revealed that PPARγ and CD36 protein levels were enhanced in the AD + MSC group compared to the AD group (p≤0.0001). MSC treatment led to the positive regulation of the PPARγ gene and its protein expression by ncRNAs, which could have a beneficial impact on CD36 protein levels, and subsequently, reduce the number of plaques in the cell recipient.

Assessment of Haptoglobin 2-2 Genotype in Type 2 Diabetes and Cardiovascular Patients in North Indian Population: A Case-control Study

Introduction: Haptoglobin (Hp), an acute phase protein, is a plasma inflammatory marker. It is important in both infectious and non infectious illnesses. When intravascular haemolysis occurs, the dead red blood cells are discharged into the circulation and link to Hp to form the haemoglobin (Hb)-haptoglobin (Hb-Hp) complex that is recognised by the macrophage scavenger receptor CD163. The Hp1 and Hp2 are its two alleles. The Hp2 is formed by a partial duplication of the Hp1 gene. The Hp1 has five exons, but Hp2 has seven exons owing to the duplication of Hp1 third and fourth exon. There are three genotypes of Hp: Hp1-1, Hp2-1, and Hp2-2. The encoded products of genotypes are attached to haemoglobin with varying degrees of affinity: Hp1-1 has the most affinity, Hp2-1 has medium affinity, and Hp2-2 has the lowest affinity. Hp allelic and genotypic variation differs amongst populations and different geographic regions of the world. Aim: To study the haptoglobin 2-2 genotype in type 2 diabetes and cardiovascular patients in north Indian population. Materials and Methods: It was a case-control study and a total of 200 participants were recruited randomly including 50 participants of type 2 Diabetes Mellitus (DM), 50 participants of Cardiovascular Disorders (CVD), 50 participants with Cardiovascular Disorders With type 2 Diabetes Mellitus (CVDWDM) and 50 normal healthy controls from Punjab Institute of Medical Sciences (PIMS) Hospital and clinics and Aashirwad laboratory of Jalandhar, Punjab, India in February 2021 to January 2022. Anthropometric variables were determined by using standard methods and biochemical parameters were measured by commercial available kits. Allele specific Polymerase Chain Reaction (PCR) or Amplification Refractory Mutation System (ARMS) PCR was used to detect Hp genotypes. Data were represented as mean±Standard Deviation and the statistical difference i.e. p&lt;0.05 between all parameters was determined by using the Mann-Whitney U test. Results: Anthropometric parameters i.e. Body Mass Index (BMI) was found to be statistically significant in CVDWDM as compared to CVD, N and T2DM i.e. p=0.023, p=0.01 and p=0.014. Waist Circumference (WC) was found to be statistically significant in CVDWDM as compared to CVD, N and T2DM i.e. p=0.02, p=0.013 and p=0.012 and Hip Circumference (HC) was found to be statistically significant in CVDWDM as compared to CVD, N and T2DM i.e. p=0.02, p=0.017 and p=0.014. However, Apolipoprotein A1 mean value was found to be higher and statistically significant i.e. p=0.03 in Type 2 Diabetes Mellitus (T2DM) as compared to healthy participants. Triglycerides mean value was increased in T2DM as compared to CVD, CVD as compared to N and CVDWDM as compared to healthy controls (p-value=0.012,0.04,0.015, respectively). The findings had shown that a 349 bp band was detected in patients with T2DM, CVD and CVDWDM, implying that the Hp2-2 genotypes were observed but not in healthy controls. Conclusion: The study finds that people with DM, CVD, or CVDWDM all have a 349bp band. It means that the genotypes of the Hp2-2 allele were found in patients of diabetes, CVD and diabetics with CVD but not in the healthy individuals.

Obese Patients With Nonalcoholic Fatty Liver Disease Have an Increase in Soluble Plasma CD163 and a Concurrent Decrease in Hepatic Expression of CD163.

Macrophages play an important role in the development of nonalcoholic fatty liver disease (NAFLD) and its progression to nonalcoholic steatohepatitis (NASH). In this study, we investigated the hepatic expression of the macrophage scavenger receptor CD163 and the plasma level of its shed soluble form (sCD163) in patients with obesity and NASH, non-NASH NAFLD (NAFL), or healthy livers (no NAFLD). Paired liver biopsies and plasma samples were collected from 61 patients with obesity (body mass index ≥35). Hepatic expression of CD163 was analyzed by immunohistochemistry and data-independent acquisition mass spectrometry, whilst plasma levels of sCD163 were determined by enzyme-linked immunosorbent assay and data-independent acquisition mass spectrometry. NAFLD stage and activity were assessed using the Kleiner fibrosis and NASH Clinical Research Network (NAS-CRN) scoring system. sCD163 turned out as a promising predictor of NASH with an area under the receiver-operating characteristic curve of 0.78 [0.65;0.92] (P= .0008). sCD163 increased with more severe NAFLD both in univariate (odds ratio [OR]= 3.31[1.80;6.11], P < .001) and multivariable ordinal logistic regression adjusting for NAFLD risk factors (OR= 2.02 [1.03;3.97], P= .042). On the other hand, hepatic expression of CD163 was negatively associated with more severe NAFLD in univariate ordinal logistic regression determined by immunohistochemistry (OR= 0.91[0.84;0.98], P= .015) and proteomics (OR= 0.13[0.02;0.80], P= .028). Taking NAFLD risk factors into account, hepatic expression of CD163 was only associated with the fibrosis stage (OR= 0.01 [0.0003;0.21], P= .004). Accordingly, hepatic CD163 surface expression and sCD163 were negatively correlated (rho=-0.478, P= .0001). An increased plasma sCD163 and a concurrent decreased hepatic expression of CD163 are strongly associated with NAFLD in obese patients.

The Past and Present Lives of the Intraocular Transmembrane Protein CD36.

Cluster of differentiation 36 (CD36) belongs to the B2 receptors of the scavenger receptor class B family, which is comprised of single-chain secondary transmembrane glycoproteins. It is present in a variety of cell types, including monocytes, macrophages, microvascular endothelial cells, adipocytes, hepatocytes, platelets, skeletal muscle cells, kidney cells, cardiomyocytes, taste bud cells, and a variety of other cell types. CD36 can be localized on the cell surface, mitochondria, endoplasmic reticulum, and endosomes, playing a role in lipid accumulation, oxidative stress injury, apoptosis, and inflammatory signaling. Recent studies have found that CD36 is expressed in a variety of ocular cells, including retinal pigment epithelium (RPE), retinal microvascular endothelial cells, retinal ganglion cells (RGC), Müller cells, and photoreceptor cells, playing an important role in eye diseases, such as age-related macular degeneration (AMD), diabetic retinopathy (DR), and glaucoma. Therefore, a comprehensive understanding of CD36 function and downstream signaling pathways is of great significance for the prevention and treatment of eye diseases. This article reviews the molecular characteristics, distribution, and function of scavenger receptor CD36 and its role in ophthalmology in order to deepen the understanding of CD36 in eye diseases and provide new ideas for treatment strategies.

Lipid Handling Protein Gene Expression in Colorectal Cancer: CD36 and Targeting miRNAs

The reprogramming of lipid metabolism has been highlighted in colorectal cancer (CRC) studies, suggesting a critical role for the scavenger receptor CD36 and fatty acid synthase (FASN) in this malignancy. In this study, we analyzed the gene expression levels of CD36, FASN, the cell surface glypican 4 (GPC4), and the two transporters SLC27A3 and SLC27A4 in 39 paired tumoral and peritumoral tissues from patients with CRC compared with 18 normal colonic mucosae. Moreover, the levels of seven miRNAs targeting CD36 and most of the analyzed genes were evaluated. We found a significant impairment of the expression of all the analyzed genes except GPC4 as well as the differential expression of miR-16-5p, miR-26b-5p, miR-107, miR-195-5p, and miR-27a-3p in the colonic mucosa of CRC patients. Interestingly, CD36 and miR-27a-3p were downregulated and upregulated, respectively, in tumoral tissues compared to peritumoral and control tissues, with a significant negative correlation in the group of patients developing lymph node metastasis. Our results sustain the relationship between CRC and fatty acid metabolism and emphasize the importance of related miRNAs in developing new therapeutic strategies.

CD36-A Host Receptor Necessary for Malaria Parasites to Establish and Maintain Infection.

Plasmodium falciparum-infected erythrocytes (PfIEs) present P. falciparum erythrocyte membrane protein 1 proteins (PfEMP1s) on the cell surface, via which they cytoadhere to various endothelial cell receptors (ECRs) on the walls of human blood vessels. This prevents the parasite from passing through the spleen, which would lead to its elimination. Each P. falciparum isolate has about 60 different PfEMP1s acting as ligands, and at least 24 ECRs have been identified as interaction partners. Interestingly, in every parasite genome sequenced to date, at least 75% of the encoded PfEMP1s have a binding domain for the scavenger receptor CD36 widely distributed on host endothelial cells and many other cell types. Here, we discuss why the interaction between PfIEs and CD36 is optimal to maintain a finely regulated equilibrium that allows the parasite to multiply and spread while causing minimal harm to the host in most infections.

Botanical Antcin K Alleviates High-Fat Damage in Palm Acid Oil-Treated Vascular Endothelial Cells and Macrophages.

Lipid metabolism disorder is the most critical risk factor for atherosclerosis, and the process involves lipid deposition in the arterial intima. In Taiwan, antcin K, an active triterpenoid from the fruiting bodies of Antrodia camphorata, has been considered a potential lipid-lowering agent. Despite this, the possible therapeutic mechanisms of antcin K remain unclear. To explore the crucial role of botanical antcin K in reducing atherosclerotic plaque, we used SVEC4-10 vascular endothelial cells and RAW264.7 macrophages with palm acid oil-induced high-fat damage as our cell models. Our results showed through using the DPPH assay that antcin K had excellent free radical scavenging ability. Antcin K treatment can significantly alleviate the high-fat damage and reduce the levels of inflammatory factors of TNF-α and IL-1β in vascular endothelial cells and macrophages, as shown through MTT assay and ELISA. Furthermore, antcin K treatment can effectively enhance migration ability and clear lipid deposition in macrophages, as shown by using cell migration assay and oil red O staining. When stained with immunofluorescence, antcin K was shown to significantly decrease the expression of adhesion molecules of vascular cell adhesion molecule 1 (VCAM-1) in vascular endothelial cells involved in monocyte migration and inflammation. Antcin K not only reduced the expression of the CD36 scavenger receptor but also augmented the expression of Kruppel-like factor 4 (KLF4) transcription factor in macrophages, which inhibits the transformation of macrophages into foam cells underlying the pathological process of atherosclerosis. Taking our findings into account, we suggested that botanical antcin K could have therapeutic potential for the treatment of atherosclerosis.

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.

NLRP3 mediates atheromatous plaque macrophage proliferation

Abstract Background Macrophage accumulation in atherosclerotic plaques drives disease progression largely dependent on in situ proliferation. We previously reported that systemic cholesterol lowering or reduced modified lipoprotein uptake supress atheromatous plaque macrophage proliferation. In this work we investigate the intracellular mediators of macrophage proliferation. Methods and results Macrophages deficient in scavenger receptors CD36 or Msr1 and impaired in cholesterol-rich lipoprotein uptake, proliferated less compared to control macrophages in the same plaque exposed to the same lipid levels in a LDLR-deficient bone marrow irradiation mixed chimera model. Proliferation of plaque macrophages deficient in the intracellular cholesterol sensor LXR was not impaired, however. As modified LDL uptake can activate the NLRP3 inflammasome, we generated mixed bone marrow knockout chimeras for components of the inflammasome. NLRP3 but not Caspase-1 or interleukin-1 receptor deficient macrophages proliferated 35% less compared to NLRP3-expressing macrophages in the same plaque in vivo. These results were confirmed in NLRP3-deficient oxLDL stimulated macrophages in vitro. In line, NLRP3 inhibition of human carotid artery plaque cultures suppressed human plaque macrophage proliferation and reduced inflammasome-dependent IL-1b secretion. However, IL-1b supplementation did not restore local macrophage proliferation in accord with our findings in IL-1 receptor deficient murine plaque macrophages. Conclusion We identified a novel role for NLRP3, independent of the canonical Caspase-1–IL-1b inflammasome pathway, in mediating macrophage proliferation in atherosclerotic plaques in mice and men representing a druggable target. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): DFG

CD36-mediated metabolic crosstalk between tumor cells and macrophages affects liver metastasis

Liver metastasis is highly aggressive and treatment-refractory, partly due to macrophage-mediated immune suppression. Understanding the mechanisms leading to functional reprogramming of macrophages in the tumor microenvironment (TME) will benefit cancer immunotherapy. Herein, we find that the scavenger receptor CD36 is upregulated in metastasis-associated macrophages (MAMs) and deletion of CD36 in MAMs attenuates liver metastasis in mice. MAMs contain more lipid droplets and have the unique capability in engulfing tumor cell-derived long-chain fatty acids, which are carried by extracellular vesicles. The lipid-enriched vesicles are preferentially partitioned into macrophages via CD36, that fuel macrophages and trigger their tumor-promoting activities. In patients with liver metastases, high expression of CD36 correlates with protumoral M2-type MAMs infiltration, creating a highly immunosuppressive TME. Collectively, our findings uncover a mechanism by which tumor cells metabolically interact with macrophages in TME, and suggest a therapeutic potential of targeting CD36 as immunotherapy for liver metastasis.

S5.3d How mitochondrial complex I proteins in Candida albicans moderate phagocytosis and the production of pro-inflammatory cytokines in murine macrophages and dendritic cells

S5.3 Cellular pleomorphism and fungal virulence, September 22, 2022, 3:00 PM - 4:30 PM ObjectivesInhibition of respiration in Candida albicans impairs its colonization in the host tissues and causes avirulence in a murine vascular candidiasis model. Accordingly, blockage of the mitochondrial electron transport chain (ETC) of C. albicans by respiratory inhibitors promotes phagocytosis by increasing exposure of glucan which could be due to the mannan reduction. In our model, we have reported that 85% mannan reduction in goa1Δ, a deletion mutant of an ETC Complex I (CI) regulator, oppositely decreased phagocytosis. To understand such a difference, we broaden our investigation with three CI respiratory subunit mutants, which are either fungal-specific (nuo1Δ and nuo2Δ) or broadly conserved subunits (ndh51Δ) for cell wall analysis and innate immune responses.MethodsWe characterized mutant cell wall defects in these mutants, then analyzed their respective survival in macrophages. Fungal internalization into macrophages was visualized under fluorescent microscopy and live-cell imaging and analyzed through flow cytometry analysis. Cytokine production in dendritic cells (DCs) infected by fungal cells was measured by xMAP technology and the transcriptional profiles of murine macrophages-infected by different mutants were compared.ResultsWe find that phosphopeptidomannan (PPM) reduction in goa1Δ and nuo1Δ and phospholipomannan (PLM) reduction in nuo2Δ correlate with massive inhibition of cytokine. PPM loss in nuo1Δ or goa1Δ fails to promote phagocytosis but promotes opsonized neutrophil killing. The cause of PPM insufficiency results from reduced phosphorylation of the Cek1 MAPK in goa1Δ and nuo1Δ. In contrast other three mutants, phagocytosis and cytokine production of ndh51Δ more resemble WT cells, which have shown an ∼ 30% glucan reduction due to a defective Mek1 MAPK response. The divergent immune responses to these CI mutants are shown at the transcriptional level in infected macrophages. We noted that those well-characterized host receptors such as dectins and TLR2/4 for PPM, PLM, and glucan ligands are not significantly affected at 1 h post-infection. However, the scavenger receptor CD36, integrin ICAM, and growth factor receptors are downregulated along with a generally downregulated endocytosis and antigen processing/presentation. In addition, the host metabolic processes, oxidative stress-induced senescence, apoptosis, and signaling pathways such as Ras1/Erk5, the cAMP/CREB, and TLR9 pathway, are each individually affected in the host cells.ConclusionWe speculate that mitochondrial signals of fungal origin may also be sensed by the host immune cells to coordinate the immune responses together with cell replication and metabolism during the early stage of infection.

CD163-Expressing Porcine Macrophages Support NADC30-like and NADC34-like PRRSV Infections.

Porcine reproductive and respiratory syndrome virus (PRRSV) has a strict cell tropism. In addition to the primary alveolar macrophages, PRRSV is strictly cytotropic to African green monkey kidney cells, such as MARC-145 cells; however, MARC-145 cells are not infected by most NADC30-like and NADC34-like PRRSV strains. The essential scavenger receptor CD163 has been proved to mediate productive infection of PRRSV in various non-permissive cell lines. In this study, we systematically tested the porcine CD163 stably expressing 3D4/21 cells for infections with various PRRSV strains. The results showed that the porcine CD163-expressing macrophages support the infections of PRRSV2 of lineages 1, 5, and 8, as evidenced by Western blotting, immunofluorescence assay, quantitative PCR, and virus titration assay. Considering the current prevalence of NADC30-like and NADC34-like PRRSV2 of lineage 1 in China, the CD163-expressing macrophages are very useful for PRRSV research and disease management.