Nrf2, a PPARγ alternative pathway to promote CD36 expression on inflammatory macrophages: implication for malaria

The role of Nrf2 signaling in parasitic diseases and its therapeutic potential

In response to invading parasites, one of the principal arms of innate immunity is oxidative stress, caused by reactive oxygen species (ROS). However, oxidative stresses play dual functions in the disease, whereby free radicals promote pathogen removal, but they can also trigger inflammation, resulting in tissue injuries. A growing body of evidence has strongly supported the notion that nuclear factor erythroid 2-related factor 2 (NRF) signaling is one of the main antioxidant pathways to combat this oxidative burst against parasites. Given the important role of NRF2 in oxidative stress, in this review, we investigate the activation mechanism of the NRF2 antioxidant pathway in different parasitic diseases, such as malaria, leishmaniasis, trypanosomiasis, toxoplasmosis, schistosomiasis, entamoebiasis, and trichinosis.

Targeted macrophage phagocytosis by Irg1/itaconate axis improves the prognosis of intracerebral hemorrhagic stroke and peritonitis

BACKGROUND

Macrophages are innate immune cells whose phagocytosis function is critical to the prognosis of stroke and peritonitis. cis-aconitic decarboxylase immune-responsive gene 1 (Irg1) and its metabolic product itaconate inhibit bacterial infection, intracellular viral replication, and inflammation in macrophages. Here we explore whether itaconate regulates phagocytosis.

METHODS

Phagocytosis of macrophages was investigated by time-lapse video recording, flow cytometry, and immunofluorescence staining in macrophage/microglia cultures isolated from mouse tissue. Unbiased RNA-sequencing and ChIP-sequencing assays were used to explore the underlying mechanisms. The effects of Irg1/itaconate axis on the prognosis of intracerebral hemorrhagic stroke (ICH) and peritonitis was observed in transgenic (Irg1flox/flox; Cx3cr1creERT/+, cKO) mice or control mice in vivo.

FINDINGS

In a mouse model of ICH, depletion of Irg1 in macrophage/microglia decreased its phagocytosis of erythrocytes, thereby exacerbating outcomes (n = 10 animals/group, p < 0.05). Administration of sodium itaconate/4-octyl itaconate (4-OI) promoted macrophage phagocytosis (n = 7 animals/group, p < 0.05). In addition, in a mouse model of peritonitis, Irg1 deficiency in macrophages also inhibited phagocytosis of Staphylococcus aureus (n = 5 animals/group, p < 0.05) and aggravated outcomes (n = 9 animals/group, p < 0.05). Mechanistically, 4-OI alkylated cysteine 155 on the Kelch-like ECH-associated protein 1 (Keap1), consequent in nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) and transcriptional activation of Cd36 gene. Blocking the function of CD36 completely abolished the phagocytosis-promoting effects of Irg1/itaconate axis in vitro and in vivo.

INTERPRETATION

Our findings provide a potential therapeutic target for phagocytosis-deficiency disorders, supporting further development towards clinical application for the benefit of stroke and peritonitis patients.

FUNDING

The National Natural Science Foundation of China (32070735, 82371321 to Q. Li, 82271240 to F. Yang) and the Beijing Natural Science Foundation Program and Scientific Research Key Program of Beijing Municipal Commission of Education (KZ202010025033 to Q. Li).

Transcription Factor NRF2 in Shaping Myeloid Cell Differentiation and Function

NFE2-related factor 2 (NRF2) is a master transcription factor (TF) that coordinates key cellular homeostatic processes including antioxidative responses, autophagy, proteostasis, and metabolism. The emerging evidence underscores its significant role in modulating inflammatory and immune processes. This chapter delves into the role of NRF2 in myeloid cell differentiation and function and its implication in myeloid cell-driven diseases. In macrophages, NRF2 modulates cytokine production, phagocytosis, pathogen clearance, and metabolic adaptations. In dendritic cells (DCs), it affects maturation, cytokine production, and antigen presentation capabilities, while in neutrophils, NRF2 is involved in activation, migration, cytokine production, and NETosis. The discussion extends to how NRF2's regulatory actions pertain to a wide array of diseases, such as sepsis, various infectious diseases, cancer, wound healing, atherosclerosis, hemolytic conditions, pulmonary disorders, hemorrhagic events, and autoimmune diseases. The activation of NRF2 typically reduces inflammation, thereby modifying disease outcomes. This highlights the therapeutic potential of NRF2 modulation in treating myeloid cell-driven pathologies.

Sulforaphane Inhibits Foam Cell Formation and Atherosclerosis via Mechanisms Involving the Modulation of Macrophage Cholesterol Transport and the Related Phenotype

Sulforaphane (SFN), an isothiocyanate, is one of the major dietary phytochemicals found in cruciferous vegetables. Many studies suggest that SFN can protect against cancer and cardiometabolic diseases. Despite the proposed systemic and local vascular protective mechanisms, SFN's potential to inhibit atherogenesis by targeting macrophages remains unknown. In this study, in high fat diet fed ApoE-deficient (ApoE^-/-) mice, oral SFN treatment improved dyslipidemia and inhibited atherosclerotic plaque formation and the unstable phenotype, as demonstrated by reductions in the lesion areas in both the aortic sinus and whole aorta, percentages of necrotic cores, vascular macrophage infiltration and reactive oxygen species (ROS) generation. In THP-1-derived macrophages, preadministration SFN alleviated oxidized low-density lipoprotein (ox-LDL)-induced lipid accumulation, oxidative stress and mitochondrial injury. Moreover, a functional study revealed that peritoneal macrophages isolated from SFN-treated mice exhibited attenuated cholesterol influx and enhanced apolipoprotein A-I (apoA-I)- and high-density lipoprotein (HDL)-mediated cholesterol efflux. Mechanistic analysis revealed that SFN supplementation induced both intralesional and intraperitoneal macrophage phenotypic switching toward high expression of nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1) and ATP-binding cassette subfamily A/G member 1 (ABCA1/G1) and low expression of peroxisome proliferator-activated receptor γ (PPARγ) and cluster of differentiation 36 (CD36), which was further validated by the aortic protein expression. These results suggest that the regulation of macrophages' cholesterol transport and accumulation may be mainly responsible for SFN's potential atheroprotective properties, and the regulatory mechanisms might involve upregulating ABCA1/G1 and downregulating CD36 via the modulation of PPARγ and Nrf2.

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.

Sinigrin in combination with artesunate provides protection against lethal murine malaria via falcipain-3 inhibition and immune modulation

Plant-derived antimalarials are indispensable for malaria treatment and a platform for new drugs. The present study explores sinigrin, for malaria using in vitro, in silico and in vivo strategies and the immune response generated after administration. The compound exhibited promising activity against chloroquine (CQ)-resistant (RKL-9) IC₅₀ 5.14 μg/mL and CQ-sensitive (3D7) IC₅₀ 5.47 μg/mL strains of P. falciparum and was safe in both in vitro (CC₅₀ > 640 μg/mL) and in vivo (LD₅₀ > 2 g/kg) toxicity studies. In addition, virtual screening showed hydrogen bonding, hydrophobic and van der Waals interactions with amino acid residues of 3BPM (falcipain-3). In vivo studies revealed promising antimalarial activity of sinigrin (200 mg/kg) with 87.44% chemo-suppression on day 5 and significantly (p < 0.0001) enhanced the mean survival time (21 ± 4.74 days) in contrast to the infected control (5.4 ± 1.14 days). In combination therapy, sinigrin (100 mg/kg and 200 mg/kg) augmented the efficacy of artesunate (AS 50 mg/kg) with 100% survival and no recrudescence. These observations are further corresponded and supported by DLC, NO production, cytokine analysis, biochemical and histopathological studies. Treatment with the combination resulted in a regulated interplay of immune cells and cytokines aiding in parasite clearance in addition to its specific inhibitory activity. We report the antimalarial activity of sinigrin first time with best D-score against falcipain-3. These findings highlight sinigrin as a HIT molecule, which may potentially be used in drug and vaccine development approaches.

Leishmania Parasites Differently Regulate Antioxidant Genes in Macrophages Derived From Resistant and Susceptible Mice

Macrophage-Leishmania interactions are central to parasite growth and disease outcome. Macrophages have developed various strategies to fight invaders, including oxidative burst. While some microorganisms seem to survive and even thrive in an oxidative environment, others are susceptible and get killed. To counter oxidative stress, macrophages switch the expressions of cytoprotective and detoxifying enzymes, which are downstream targets of the nuclear factor erythroid 2-related factor 2 (Nrf2), to enhance cell survival. We have explored the transcription of NRF2 and of its target genes and compared the effect of the parasite on their transcription in bone marrow-derived macrophages (BMdMs) from Leishmania-resistant and Leishmania-susceptible mice. While heme oxygenase 1 (HO-1) transcription is independent of the genetic background, the transcription of glutathione reductase (Gsr) and of cysteine/glutamate exchange transporter (Slc7a11), involved in glutathione accumulation, was differentially regulated in BMdMs from both mouse strains. We also show that, except for HO-1, known to favor the survival of the parasite, the transcription of the selected genes, including Gsr, CD36, and catalase (CAT), was actively repressed, if not at all time points at least at the later ones, by the parasite, especially in Balb/c BMdMs. Consistent with these results, we found that the silencing of NRF2 in this study increases the survival and multiplication of the parasite.

Transcription Factors Interplay Orchestrates the Immune-Metabolic Response of Leishmania Infected Macrophages

Leishmaniasis is a group of heterogenous diseases considered as an important public health problem in several countries. This neglected disease is caused by over 20 parasite species of the protozoa belonging to the Leishmania genus and is spread by the bite of a female phlebotomine sandfly. Depending on the parasite specie and the immune status of the patient, leishmaniasis can present a wide spectrum of clinical manifestations. As an obligate intracellular parasite, Leishmania colonize phagocytic cells, mainly the macrophages that orchestrate the host immune response and determine the fate of the infection. Once inside macrophages, Leishmania triggers different signaling pathways that regulate the immune and metabolic response of the host cells. Various transcription factors regulate such immune-metabolic responses and the associated leishmanicidal and inflammatory reaction against the invading parasite. In this review, we will highlight the most important transcription factors involved in these responses, their interactions and their impact on the establishment and the progression of the immune response along with their effect on the physiopathology of the disease.

Dengue Virus Targets Nrf2 for NS2B3-Mediated Degradation Leading to Enhanced Oxidative Stress and Viral Replication

Dengue virus (DENV) is a mosquito-borne virus that infects upward of 300 million people annually and has the potential to cause fatal hemorrhagic fever and shock. While the parameters contributing to dengue immunopathogenesis remain unclear, the collapse of redox homeostasis and the damage induced by oxidative stress have been correlated with the development of inflammation and progression toward the more severe forms of disease. In the present study, we demonstrate that the accumulation of reactive oxygen species (ROS) late after DENV infection (>24 hpi) resulted from a disruption in the balance between oxidative stress and the nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent antioxidant response. The DENV NS2B3 protease complex strategically targeted Nrf2 for degradation in a proteolysis-independent manner; NS2B3 licensed Nrf2 for lysosomal degradation. Impairment of the Nrf2 regulator by the NS2B3 complex inhibited the antioxidant gene network and contributed to the progressive increase in ROS levels, along with increased virus replication and inflammatory or apoptotic gene expression. By 24 hpi, when increased levels of ROS and antiviral proteins were observed, it appeared that the proviral effect of ROS overcame the antiviral effects of the interferon (IFN) response. Overall, these studies demonstrate that DENV infection disrupts the regulatory interplay between DENV-induced stress responses, Nrf2 antioxidant signaling, and the host antiviral immune response, thus exacerbating oxidative stress and inflammation in DENV infection.IMPORTANCE Dengue virus (DENV) is a mosquito-borne pathogen that threatens 2.5 billion people in more than 100 countries annually. Dengue infection induces a spectrum of clinical symptoms, ranging from classical dengue fever to severe dengue hemorrhagic fever or dengue shock syndrome; however, the complexities of DENV immunopathogenesis remain controversial. Previous studies have reported the importance of the transcription factor Nrf2 in the control of redox homeostasis and antiviral/inflammatory or death responses to DENV. Importantly, the production of reactive oxygen species and the subsequent stress response have been linked to the development of inflammation and progression toward the more severe forms of the disease. Here, we demonstrate that DENV uses the NS2B3 protease complex to strategically target Nrf2 for degradation, leading to a progressive increase in oxidative stress, inflammation, and cell death in infected cells. This study underlines the pivotal role of the Nrf2 regulatory network in the context of DENV infection.

Tanshinone IIA attenuates atherosclerosis via inhibiting NLRP3 inflammasome activation

Tanshinone IIA (Tan IIA) possesses potent anti-atherogenic function, however, the underlying pharmacological mechanism remains incompletely understood. Previous studies suggest that oxidized LDL (oxLDL)-induced NLRP3 (NOD-like receptor (NLR) family, pyrin domain-containing protein 3) inflammasome activation in macrophages plays a vital role in atherogenesis. Whether the anti-atherogenic effect of Tan IIA relies on the inhibition of the NLRP3 inflammasome has not been investigated before. In this study, we found that Tan IIA treatment of high-fat diet fed ApoE-/- mice significantly attenuated NLRP3 inflammasome activation in vivo. Consistently, Tan IIA also potently inhibited oxLDL-induced NLRP3 inflammasome activation in mouse macrophages. Mechanically, Tan IIA inhibited NF-κB activation to downregulate pro-interleukin (IL) -1β and NLRP3 expression, and decreased oxLDL-induced expression of lectin-like oxidized LDL receptor-1 (LOX-1) and cluster of differentiation 36 (CD36), thereby attenuating oxLDL cellular uptake and subsequent induction of mitochondrial and lysosomal damage - events that promote the NLRP3 inflammasome assembly. Through regulating both the inflammasome 'priming' and 'activation' steps, Tan IIA potently inhibited oxLDL-induced NLRP3 inflammasome activation, thereby ameliorating atherogenesis.

CD36-mediated uptake of myelin debris by macrophages and microglia reduces neuroinflammation

Background

The presence of foamy macrophages and microglia containing intracellular myelin remnants is a pathological hallmark of neurodegenerative disorders such as multiple sclerosis (MS). Despite the importance of myelin internalization in affecting both central nervous system repair and neuroinflammation, the receptors involved in myelin clearance and their impact on the phagocyte phenotype and lesion progression remain to be clarified.

Methods

Flow cytometry, quantitative PCR, and immunohistochemistry were used to define the mRNA and protein abundance of CD36 in myelin-containing phagocytes. The impact of CD36 and nuclear factor erythroid 2–related factor 2 (NRF2) on the phagocytic and inflammatory features of macrophages and microglia was assessed using a pharmacological CD36 inhibitor (sulfo-N-succinimidyl oleate) and Nrf2^−/− bone marrow-derived macrophages. Finally, the experimental autoimmune encephalomyelitis (EAE) model was used to establish the impact of CD36 inhibition on neuroinflammation and myelin phagocytosis in vivo.

Results

Here, we show that the fatty acid translocase CD36 is required for the uptake of myelin debris by macrophages and microglia, and that myelin internalization increased CD36 expression through NRF2. Pharmacological inhibition of CD36 promoted the inflammatory properties of myelin-containing macrophages and microglia in vitro, which was paralleled by a reduced activity of the anti-inflammatory lipid-sensing liver X receptors and peroxisome proliferator-activated receptors. By using the EAE model, we provide evidence that CD36 is essential for myelin debris clearance in vivo. Importantly, CD36 inhibition markedly increased the neuroinflammatory burden and disease severity in the EAE model.

Conclusion

Altogether, we show for the first time that CD36 is crucial for clearing myelin debris and suppressing neuroinflammation in demyelinating disorders such as MS.

Comparative study of the effects of ziram and disulfiram on human monocyte-derived macrophage functions and polarization: involvement of zinc

Ziram, a zinc dithiocarbamate is widely used worldwide as a fungicide in agriculture. In order to investigate ziram-induced changes in macrophage functions and polarization, human monocytes-derived macrophages in culture were treated with ziram at 0.01-10 μmol.L^-1 for 4-24 h. To characterize zinc involvement in these changes, we also determined the effects of disulfiram alone (dithiocarbamate without zinc) or in co-incubation with ZnSO₄. We have shown that ziram and disulfiram at 0.01 μmol.L^-1 increased zymosan phagocytosis. In contrast, ziram at 10 μmol.L^-1 completely inhibited this phagocytic process, the oxidative burst triggered by zymosan and the production of TNF-α, IL-1β, IL-6, and CCL2 triggered by LPS. Disulfiram had the same effects on these macrophages functions only when combined with zinc (10 μmol.L^-1). In contrast, at 10 μmol.L^-1 ziram and zinc associated-disulfiram induced expression of several antioxidants genes HMOX1, SOD2, and catalase, which could suggest the induction of oxidative stress. This oxidative stress could be involved in the increase in late apoptosis induced by ziram (10 μmol.L^-1) and zinc associated-disulfiram. Concerning gene expression profiles of membrane markers of macrophage polarization, ziram at 10 μmol.L^-1 had two opposite effects. It inhibited the gene expression of M2 markers (CD36, CD163) in the same way as the disulfiram-zinc co-treatment. Conversely, ziram induced gene expression of other M2 markers CD209, CD11b, and CD16 in the same way as treatment with zinc alone. Disulfiram-zinc association had no significant effects on these markers. These results taken together show that ziram via zinc modulates macrophages to M2-like anti-inflammatory phenotype which is often associated with various diseases.

Severe Fever with Thrombocytopenia Syndrome Virus NSs Interacts with TRIM21 To Activate the p62-Keap1-Nrf2 Pathway

Nuclear factor erythroid 2-related factor 2 (Nrf2) dissociates from its inhibitor, Keap1, upon stress signals and subsequently induces an antioxidant response that critically controls the viral life cycle and pathogenesis. Besides intracellular Fc receptor function, tripartite motif 21 (TRIM21) E3 ligase plays an essential role in the p62-Keap1-Nrf2 axis pathway for redox homeostasis. Specifically, TRIM21-mediated p62 ubiquitination abrogates p62 oligomerization and sequestration activity and negatively regulates the Keap1-Nrf2-mediated antioxidant response. A number of viruses target the Nrf2-mediated antioxidant response to generate an optimal environment for their life cycle. Here we report that a nonstructural protein (NSs) of severe fever with thrombocytopenia syndrome virus (SFTSV) interacts with and inhibits TRIM21 to activate the Nrf2 antioxidant signal pathway. Mass spectrometry identified TRIM21 to be a binding protein for NSs. NSs bound to the carboxyl-terminal SPRY subdomain of TRIM21, enhancing p62 stability and oligomerization. This facilitated p62-mediated Keap1 sequestration and ultimately increased Nrf2-mediated transcriptional activation of antioxidant genes, including those for heme oxygenase 1, NAD(P)H quinone oxidoreductase 1, and CD36. Mutational analysis found that the NSs-A46 mutant, which no longer interacted with TRIM21, was unable to increase Nrf2-mediated transcriptional activation. Functionally, the NS wild type (WT), but not the NSs-A46 mutant, increased the surface expression of the CD36 scavenger receptor, resulting in an increase in phagocytosis and lipid uptake. A combination of reverse genetics and assays with Ifnar ^-/- mouse models revealed that while the SFTSV-A46 mutant replicated similarly to wild-type SFTSV (SFTSV-WT), it showed weaker pathogenic activity than SFTSV-WT. These data suggest that the activation of the p62-Keap1-Nrf2 antioxidant response induced by the NSs-TRIM21 interaction contributes to the development of an optimal environment for the SFTSV life cycle and efficient pathogenesis.IMPORTANCE Tick-borne diseases have become a growing threat to public health. SFTSV, listed by the World Health Organization as a prioritized pathogen, is an emerging phlebovirus, and fatality rates among those infected with this virus are high. Infected Haemaphysalis longicornis ticks are the major source of human SFTSV infection. In particular, the recent spread of this tick to over 12 states in the United States has increased the potential for outbreaks of this disease beyond Far East Asia. Due to the lack of therapies and vaccines against SFTSV infection, there is a pressing need to understand SFTSV pathogenesis. As the Nrf2-mediated antioxidant response affects viral life cycles, a number of viruses deregulate Nrf2 pathways. Here we demonstrate that the SFTSV NSs inhibits the TRIM21 function to upregulate the p62-Keap1-Nrf2 antioxidant pathway for efficient viral pathogenesis. This study not only demonstrates the critical role of SFTSV NSs in viral pathogenesis but also suggests potential future therapeutic approaches to treat SFTSV-infected patients.

Hepatocyte-specific Nrf2 deficiency mitigates high-fat diet-induced hepatic steatosis: Involvement of reduced PPARγ expression

Non-alcoholic fatty liver disease (NAFLD) is an emerging global disease with increasing prevalence. However, the mechanism of NAFLD development is not fully understood. To elucidate the cell-specific role of nuclear factor erythroid-derived 2-like 2 (NRF2) in the pathogenesis of NAFLD, we utilized hepatocyte- and macrophage-specific Nrf2-knockout [Nrf2(L)-KO and Nrf2(Mϕ)-KO] mice to examine the progress of NAFLD induced by high-fat diet (HFD). Compared to Nrf2-LoxP littermates, Nrf2(L)-KO mice showed less liver enlargement, milder inflammation and less hepatic steatosis after HFD feeding. In contrast, Nrf2(Mϕ)-KO mice displayed no significant difference in HFD-induced hepatic steatosis from Nrf2-LoxP control mice. Mechanistic investigations revealed that Nrf2 deficiency in hepatocytes dampens the expression of peroxisome proliferator-activated receptor γ (PPARγ) and its downstream lipogenic genes in the liver and/or primary hepatocytes induced by HFD and palmitate exposure, respectively. While PPARγ agonists augmented PPARγ expression and its transcriptional activity in primary hepatocytes in a NRF2-dependent manner, forced overexpression of PPARγ1 or γ2 distinctively reversed the decreased expression of their downstream genes fatty acid binding protein 4, lipoprotein lipase and/or fatty acid synthase caused by Nrf2 deficiency. We conclude that NRF2-dependent expression of PPARγ in hepatocytes is a critical initiating process in the development of NAFLD, suggesting that inhibition of NRF2 specifically in hepatocytes may be a valuable approach to prevent the disease.

Glucose negatively affects Nrf2/SKN-1-mediated innate immunity in C. elegans

High glucose levels negatively affect immune response. However, the underlying mechanisms are not well understood. Upon infection, the round worm C. elegans induces multiple gene transcription programs, including the Nrf2/SKN-1-mediated detoxification program, to activate the innate immunity. In this study, we find that high glucose conditions inhibit the SKN-1-mediated immune response to Salmonella typhimurium, exacerbate the infection and greatly decrease survival. The effect of glucose shows specificity to SKN-1 pathway, as UPR^mit and UPR^ER that are known to be induced by infection, are not affected. Hyper-activation of SKN-1 by wdr-23 RNAi restores partly the immune response and increases the survival rate in response to S. typhimurium. In all, our study reveals a molecular pathway responsible for glucose’s negative effect on innate immunity, which could help to better understand diseases associated with hyperglycemia.

Targeting Foam Cell Formation in Atherosclerosis: Therapeutic Potential of Natural Products

Foam cell formation and further accumulation in the subendothelial space of the vascular wall is a hallmark of atherosclerotic lesions. Targeting foam cell formation in the atherosclerotic lesions can be a promising approach to treat and prevent atherosclerosis. The formation of foam cells is determined by the balanced effects of three major interrelated biologic processes, including lipid uptake, cholesterol esterification, and cholesterol efflux. Natural products are a promising source for new lead structures. Multiple natural products and pharmaceutical agents can inhibit foam cell formation and thus exhibit antiatherosclerotic capacity by suppressing lipid uptake, cholesterol esterification, and/or promoting cholesterol ester hydrolysis and cholesterol efflux. This review summarizes recent findings on these three biologic processes and natural products with demonstrated potential to target such processes. Discussed also are potential future directions for studying the mechanisms of foam cell formation and the development of foam cell-targeted therapeutic strategies.

Changes in monocyte subsets are associated with clinical outcomes in severe malarial anaemia and cerebral malaria

Monocytes are plastic heterogeneous immune cells involved in host-parasite interactions critical for malaria pathogenesis. Human monocytes have been subdivided into three populations based on surface expression of CD14 and CD16. We hypothesised that proportions and phenotypes of circulating monocyte subsets can be markers of severity or fatality in children with malaria. To address this question, we compared monocytes sampled in children with uncomplicated malaria, severe malarial anaemia, or cerebral malaria. Flow cytometry was used to distinguish and phenotype monocyte subsets through CD14, CD16, CD36 and TLR2 expression. Data were first analysed by univariate analysis to evaluate their link to severity and death. Second, multinomial logistic regression was used to measure the specific effect of monocyte proportions and phenotypes on severity and death, after adjustments for other variables unrelated to monocytes. Multivariate analysis demonstrated that decreased percentages of non-classical monocytes were associated with death, suggesting that this monocyte subset has a role in resolving malaria. Using univariate analysis, we also showed that the role of non-classical monocytes involves a mostly anti-inflammatory profile and the expression of CD16. Further studies are needed to decipher the functions of this sub-population during severe malaria episodes, and understand the underlying mechanisms.

Monocyte-derived dendritic cells in malaria

The pathogenesis of malaria is a multifactorial syndrome associated with a deleterious inflammatory response that is responsible for many of the clinical manifestations. While dendritic cells (DCs) play a critical role in initiating acquired immunity and host resistance to infection, they also play a pathogenic role in inflammatory diseases. In our recent studies, we found in different rodent malaria models that the monocyte-derived DCs (MO-DCs) become, transiently, a main DC population in spleens and inflamed non-lymphoid organs. These studies suggest that acute infection with Plasmodium berghei promotes the differentiation of splenic monocytes into inflammatory monocytes (iMOs) and thereafter into MO-DCs that play a pathogenic role by promoting inflammation and tissue damage. The recruitment of MO-DCs to the lungs and brain are dependent on expression of CCR4 and CCR5, respectively, and expression of respective chemokine ligands in each organ. Once they reach the target organ the MO-DCs produce the CXCR3 ligands (CXCL9 and CXCL10), recruit CD8⁺ T cells, and produce toxic metabolites that play an important role in the development of experimental cerebral malaria (ECM) and acute respiratory distress syndrome (ARDS).

Nrf2 downregulates zymosan-induced neutrophil activation and modulates migration

Polymorphonuclear neutrophils (PMNs) are the first line of defense against pathogens and their activation needs to be tightly regulated in order to limit deleterious effects. Nrf2 (Nuclear factor (erythroïd-derived 2)-like 2) transcription factor regulates oxidative stress and/or represses inflammation in various cells such as dendritic cells or macrophages. However, its involvement in PMN biology is still unclear. Using Nrf2 KO mice, we thus aimed to investigate the protective role of Nrf2 in various PMN functions such as oxidative burst, netosis, migration, cytokine production and phagocytosis, mainly in response to zymosan. We found that zymosan induced Nrf2 accumulation in PMNs leading to the upregulation of some target genes including Hmox-1, Nqo1 and Cat. Nrf2 was able to decrease zymosan-induced PMN oxidative burst; sulforaphane-induced Nrf2 hyperexpression confirmed its implication. Tnfα, Ccl3 and Cxcl2 gene transcription was decreased in zymosan-stimulated Nrf2 KO PMNs, suggesting a role for Nrf2 in the regulation of proinflammatory cytokine production. However, Nrf2 was not involved in phagocytosis. Finally, spontaneous migration of Nrf2 KO PMNs was lower than that of WT PMNs. Moreover, in response to low concentrations of CXCL2 or CXCL12, Nrf2 KO PMN migration was decreased despite similar CXCR2 and CXCR4 expression and ATP levels in PMNs from both genotypes. Nrf2 thus seems to be required for an optimal migration. Altogether these results suggest that Nrf2 has a protective role in several PMN functions. In particular, it downregulates their activation in response to zymosan and is required for an adequate migration.

Organic dust, causing both oxidative stress and Nrf2 activation, is phagocytized by bronchial epithelial cells

Inhalation of organic dust (OD) from swine confinement facilities leads to pulmonary inflammation, airway hyperresponsiveness, and oxidative stress. In mice, pretreatment with a hydroxyl radical scavenger prevents airway inflammation and airway hyperresponsiveness (AHR) induced by OD exposure. We sought to determine a mechanism by which OD could induce oxidative stress in bronchial epithelial cells. Human bronchial epithelial cells (BEAS-2B or NHBE) were treated with various concentrations of OD, followed by evaluation of intracellular oxidative stress using 2',7'-dichlorofluorescein diacetate (DCFDA). After stimulation with OD, gene expression of antioxidant genes was assessed by real-time quantitative PCR followed by quantification of Nrf2 nuclear translocation using a luciferase reporter assay. Phagocytic markers (CD36 and CD68) were analyzed by FACS. Cells were treated with an actin inhibitor, cytochalasin D, before OD exposure and evaluated for Nrf2 nuclear translocation and DCFDA. Mice were pretreated with sulforaphane, the Nrf2 activator, before OD exposure and evaluated for pulmonary inflammation and airway reactivity. OD induced a time- and concentration-dependent increase in DCFDA. mRNA expression levels of Nrf2-dependent genes and Nrf2 nuclear translocation were increased after OD exposure. OD exposure increased the expression of CD68 and CD36. Cytochalasin D prevented oxidative stress and Nrf2 nuclear translocation after OD. Pretreatment with sulforaphane prevented OD-induced inflammation and AHR while increasing the uptake of OD in bronchial epithelial cells. Bronchial epithelial cells can phagocytose OD, resulting in an increase in endogenous oxidative stress. Nrf2-dependent mechanisms mediate the antioxidant response to OD.

CD36 signaling in vascular redox stress

Scavenger receptor CD36 is a multifunctional membrane protein that promotes thrombosis in conditions of oxidative stress such as metabolic disorders including dyslipidemia, diabetes mellitus, and chronic inflammation. In these conditions, specific reactive oxidant species are generated that are context and cell dependent. In the vasculature, CD36 signaling in smooth muscle cells and endothelial cells promotes generation of reactive oxygen species, genetic downregulation of antioxidant genes, and impaired smooth muscle and endothelial function. In hematopoietic cells, CD36 signaling enhances platelet dysfunction thus decreasing the threshold for platelet activation and accelerating arterial thrombosis, whereas in macrophages, CD36 promotes lipid-laden foam cell formation and atherosclerosis. These clinically significant processes are mediated through complex redox regulated signaling mechanisms that include Src-family kinases, MAP kinases and other downstream effectors. We provide an overview of CD36 signaling in vascular redox stress highlighting the role in oxidant generation in vascular and hematopoietic cells, but with special emphasis on platelets and dyslipidemia.

Nrf2 Involvement in Chemical-Induced Skin Innate Immunity

Exposure to certain chemicals disturbs skin homeostasis. In particular, protein-reactive chemical contact sensitizers trigger an inflammatory immune response resulting in eczema and allergic contact dermatitis. Chemical sensitizers activate innate immune cells which orchestrate the skin immune response. This involves oxidative and inflammatory pathways. In parallel, the Nrf2/Keap1 pathway, a major ubiquitous regulator of cellular oxidative and electrophilic stress is activated in the different skin innate immune cells including epidermal Langerhans cells and dermal dendritic cells, but also in keratinocytes. In this context, Nrf2 shows a strong protective capacity through the downregulation of both the oxidative stress and inflammatory pathways. In this review we highlight the important role of Nrf2 in the control of the innate immune response of the skin to chemical sensitizers.

Lipid Uptake by Alveolar Macrophages Drives Fibrotic Responses to Silica Dust

Silicosis is a common occupational disease and represents a significant contributor to respiratory morbidity and mortality worldwide. Lipid-laden macrophages, or foam cells, are observed in the lungs of patients with silicosis but the mechanisms mediating their formation remain poorly understood. In this study, we sought to elucidate the mechanisms by which silica promotes foam cell formation in the lung, and to determine whether uptake of lipids alone is sufficient to drive TGF-β production by alveolar macrophages. Consistent with previous reports, we found that foam cells were markedly increased in the lungs of patients with silicosis and that these findings associated with both higher levels of intracellular lipid levels (oxidized LDL, ox-LDL) and elevated transcript levels for the lipid scavenger receptor CD36 and the nuclear receptor PPARγ. Employing a rat alveolar macrophage cell line, we found that exposure to silica dust or ox-LDL alone had a modest effect on the induction of foam cell formation and only silica was capable of inducing the production of TGF-β. In contrast, foam cell formation and TGF-β production were both dramatically increased when cells were exposed to a combination of silica dust and ox-LDL. Moreover, we found that these endpoints were markedly attenuated by either blocking CD36 or inhibiting the activity of PPARγ. Altogether, our findings suggest that foam cell formation and TGF-β production are driven by the simultaneous uptake of silica and lipids in alveolar macrophages and that strategies aimed at blocking lipid uptake by alveolar macrophages might be effective in ameliorating fibrotic responses to silica in the lung.

microRNA-27a and microRNA-146a SNP in cerebral malaria

Background

During Plasmodium falciparum infection, microRNA expression alters in brain tissue of mice with cerebral malaria compared to noninfected controls. MicroRNA regulates gene expression post‐transcriptionally to influence biological processes. Cerebral malaria pathology caused mainly by the immunological disorder. We hypothesize that single‐nucleotide polymorphism in a microRNA influences microRNA biogenesis or target gene recognition and altering susceptibility to cerebral malaria.

Methods

We performed a literature search based on immunological mechanism and applied microRNA‐related single‐nucleotide polymorphisms database to examine candidate microRNA SNPs possibly responsible for cerebral malaria. MicroRNA‐27a and microRNA‐146a are supposed to involve in cerebral malaria pathology. To assess the relationship of microRNA SNP to cerebral malaria outcome, we performed TaqMan Genotyping Assays in 110 cerebral malaria and 207 uncomplicated malaria cases for three candidate microRNA SNPs (rs895819 of microRNA‐27a, rs57095329 and rs2910164 of microRNA‐146a).

Results

Our study detected no significant difference in genotype and allele frequency of individual microRNA SNPs as well as in haplotypes of microRNA‐146a between these two groups of malaria patients in Thailand. Hardy–Weinberg disequilibrium of rs57095329 in the cerebral malaria group showed a heterozygous excess which might be due to natural selection.

Conclusion

Our data supported that the candidate microRNA SNPs have no major role to develop cerebral malaria.

Monocyte phagocytosis of malaria β-haematin in the presence of artemisinin, amodiaquine, chloroquine, doxycycline, primaquine, pyrimethamine and quinine

The intraerythrocytic malaria parasite digests haemoglobin to provide amino acids for metabolism and releases toxic haem that is sequestered into haemozoin, a non-toxic, insoluble, crystalline pigment. Following erythrocyte rupture, haemozoin is released into circulation and phagocytosed by monocytes. Phagocytosed haemozoin and antimalarial drugs have both been reported to modulate monocyte functions. This study determined the effects of therapeutic concentrations of seven antimalarial drugs; amodiaquine, artemisinin, chloroquine, doxycycline, primaquine, pyrimethamine and quinine, on the phagocytosis of β-haematin (synthetic haemozoin) by two monocytic cell lines, J774A.1 and U937, and human peripheral blood mononuclear cells. A novel spectrophotometric method based on the absorbance (O.D 400 nm) of alkali/SDS treated monocytes containing β-haematin was developed to complement counting phagocytosis with microscopy. The method has potential use for the large scale screening of monocyte phagocytic activity. Artemisinin, quinine, primaquine and pyrimethamine activated β-haematin phagocytosis by 12% or more, whereas amodiaquine, chloroquine and doxycyline inhibited β-haematin phagocytosis. In contrast, antimalarial drugs had minimal inhibitory effects on the phagocytosis of latex beads with only quinine resulting in more than 20% inhibition. Antimalarial drugs appear to alter monocyte phagocytic activity which has implications for the treatment, pathogenicity and adjunct therapies for malaria.

nSMase2 (Type 2-Neutral Sphingomyelinase) Deficiency or Inhibition by GW4869 Reduces Inflammation and Atherosclerosis in Apoe-/- Mice

OBJECTIVE

Atherosclerosis is a chronic multifactorial and inflammatory disease of large and medium arteries and the leading cause of cardiovascular diseases worldwide. The aim of this study was to investigate whether and how the nSMase2 (type 2-neutral sphingomyelinase), a key enzyme of sphingolipid metabolism, may contribute to the development of atherosclerotic lesions.

APPROACH AND RESULTS

The role of nSMase2 in atherosclerosis was investigated in Apoe^-/-;Smpd3^fro/fro mice, mutant for nSMase2, and in Apoe^-/-;Smpd3^+/+ mice intraperitoneally injected with GW4869, a pharmacological nSMase2 inhibitor. The defect or inhibition of nSMase2 resulted in a reduction of atherosclerotic lesions and a decrease in macrophage infiltration and lipid deposition, although cholesterolemia remained unchanged. nSMase2 inhibition decreased the inflammatory response of murine endothelial cells to oxLDL (oxidized low-density lipoprotein), as assessed by the significant reduction of MCP-1 (monocyte chemoattractant protein 1), ICAM-1 (intercellular adhesion molecule-1), and VCAM-1 (vascular cell adhesion molecule-1) mRNA expressions and macrophage recruitment. Likewise, in RAW264.7 or in macrophages isolated from Apoe^-/-/Smpd3^fro/fro or Apoe^-/-/Smpd3^+/+ mice stimulated by lipopolysaccharides, nSMase2 inhibition resulted in a decrease in the expression of inflammatory molecules. Mechanistically, the anti-inflammatory response resulting from nSMase2 inhibition involves Nrf2 (nuclear factor [erythroid-derived 2]-like 2 or NF-E2-related factor-2) activation in both endothelial cells and macrophages, as assessed by the lack of protective effect of GW4869 in endothelial cells silenced for Nrf2 by small interfering RNAs, and in lipopolysaccharide-stimulated macrophages issued from Nrf2-KO mice.

CONCLUSIONS

The genetic deficiency or inhibition of nSMase2 strongly decreases the development of atherosclerotic lesions in Apoe^-/- mice, by reducing inflammatory responses through a mechanism involving the Nrf2 pathway. Inhibitors of nSMase2 may, therefore, constitute a novel approach to slow down atherosclerosis progression.

Targeting the 15-keto-PGE2-PTGR2 axis modulates systemic inflammation and survival in experimental sepsis

Sepsis is a systemic inflammation accompanied by multi-organ dysfunction due to microbial infection. Prostaglandins and their metabolites have long been studied for their importance in regulating the innate immune response. 15-keto-PGE2 (15k-PGE₂) is a prostaglandin E2 (PGE₂) metabolite, whose further processing is catalyzed by prostaglandin reductase 2 (PTGR2). We showed disruption of the Ptgr2 gene in mice improves the survival rate under both LPS- and cecum ligation/puncture (CLP)-induced experimental sepsis. Knockdown of PTGR2 showed significant accumulation of intracellular 15k-PGE₂ in activated macrophages. Both PTGR2 knockdown and exogenous treatment with 15k-PGE₂ resulted in reduced pro-inflammatory cytokines production in LPS-stimulated RAW264.7 cells or bone marrow-derived macrophages (BMDM). The same treatment in RAW264.7 and BMDM also led to increased levels of the anti-oxidative transcription factor, Nuclear factor (erythroid-2) related factor-2 (NRF2), augmented anti-oxidant response element (ARE)-mediated reporter activity and upregulated expression of the corresponding anti-oxidant genes. 15k-PGE₂ further demonstrated modification to Kelch-like ECH-associated protein 1 (Keap1), a negative regulator of Nrf2, at cysteine 288 (Cys288) site post-translationally. Finally, 15k-PGE₂-treated mice were found to be more resistant to experimental sepsis. Taken together, our study affirms the significance of PTGR2 and 15k-PGE₂ in mitigating inflammatory responses and suggests a novel anti-oxidative and anti-inflammatory therapy for sepsis through targeting PTGR2 and administering15k-PGE₂.

Haematoma scavenging in intracerebral haemorrhage: from mechanisms to the clinic

The products of erythrocyte lyses, haemoglobin (Hb) and haem, are recognized as neurotoxins and the main contributors to delayed cerebral oedema and tissue damage after intracerebral haemorrhage (ICH). Finding a means to efficiently promote absorption of the haemolytic products (Hb and haem) around the bleeding area in the brain through stimulating the function of the body's own garbage cleaning system is a novel clinical challenge and critical for functional recovery after ICH. In this review, available information of the brain injury mechanisms underlying ICH and endogenous haematoma scavenging system is provided. Meanwhile, potential intervention strategies are discussed. Intracerebral blood itself has ‘toxic’ effects beyond its volume effect after ICH. Haptoglobin–Hb–CD163 as well as haemopexin–haem–LRP1 is believed to be the most important endogenous scavenging pathway which participates in blood components resolution following ICH. PPARγ–Nrf2 activates the aforementioned clearance pathway and then accelerates haematoma clearance. Meanwhile, the scavenger receptors as novel targets for therapeutic interventions to treat ICH are also highlighted.

Collaborative Power of Nrf2 and PPARγ Activators against Metabolic and Drug-Induced Oxidative Injury

Mammalian cells have evolved a unique strategy to protect themselves against oxidative damage induced by reactive oxygen species (ROS). Especially, two transcription factors, nuclear factor erythroid 2p45-related factor 2 (Nrf2) and peroxisome proliferator-activated receptor γ (PPARγ), have been shown to play key roles in establishing this cellular antioxidative defense system. Recently, several researchers reported ameliorating effects of pharmacological activators for these Nrf2 and PPARγ pathways on the progression of various metabolic disorders and drug-induced organ injuries by oxidative stress. In this review, general features of Nrf2 and PPARγ pathways in the context of oxidative protection will be summarized first. Then, a number of successful applications of natural and synthetic Nrf2 and PPARγ activators to the alleviation of pathological and drug-related oxidative damage will be discussed later.

Nuclear protein HMGN2 attenuates pyocyanin-induced oxidative stress via Nrf2 signaling and inhibits Pseudomonas aeruginosa internalization in A549 cells

Pyocyanin (PCN, 1-hydroxy-5-methyl-phenazine) is one of the most essential virulence factors of Pseudomonas aeruginosa (PA) to cause various cytotoxic effects in long-term lung infectious diseases, however the early effect of this bacterial toxin during PA infection and subsequent autonomous immune response in host cells have not been fully understood yet. Our results display that early onset of PCN stimulates Pseudomonas aeruginosa PAO1 adhesion and invasion in A549 cells via ROS production. Non-histone nuclear protein HMGN2 is found to be involved in the regulation of PCN-induced oxidative stress by promoting intracellular ROS clearance. Mechanistically, HMGN2 facilitates nuclear translocation of transcription factor Nrf2 upon PCN stimulation and in turn elevates antioxidant gene expression. We also found that actin cytoskeleton dynamics is targeted by ROS, which is to be exploited by PAO1 for host cell internalization. HMGN2 regulates actin skeleton rearrangement in both PCN-dependent and independent manners and specifically attenuates PCN-mediated PAO1 infection via ROS elimination. These results uncover a novel link between nuclear protein HMGN2 and Nrf2-mediated cellular redox circumstance and suggest roles of HMGN2 in autonomous immune response to PA infection.

Establishment of a novel mouse model for pioglitazone-induced skeletal muscle injury

Skeletal muscle (SKM) injury is one of the major safety concerns in risk assessment for drug development. However, no appropriate pre-clinical animal model exists to evaluate drug-induced SKM injury except that caused by fibrates and statins. Thiazolidinedione, a PPARγ agonistic drug for type 2 diabetes mellitus, is widely used clinically but can induce adverse effects such as hepatotoxicity and SKM injury, as has been reported in recent decades. Moreover, thiazolidinedione-induced SKM injury has only been reported in humans, and no evidence of SKM injury has been observed in rodents. To establish a drug-induced SKM injury mouse model, we administered pioglitazone with a glutathione biosynthesis inhibitor, L-buthionine-S,R-sulfoximine, to C57BL/6J mice for 2days and subsequently observed prominent increases in plasma aspartate aminotransferase and creatinine phosphokinase, which were associated with SKM lesions. Furthermore, plasma miR-206 (SKM-specific microRNA) level was significantly increased, whereas plasma miR-208 (heart-specific microRNA) was not detected, indicating that pioglitazone specifically caused SKM, not cardiac, injury. Furthermore, we revealed that pioglitazone-induced SKM injury was caused by oxidative stress that was independent of the PPARγ agonistic effect. This study demonstrated for the first time that the glutathione-depleted C57BL/6J mouse is a novel model for assessing drug-induced SKM injury in drug development.

Tim-3 inhibits macrophage control of Listeria monocytogenes by inhibiting Nrf2

T cell immunoglobulin mucin-3 (Tim-3) is an immune checkpoint inhibitor and its dysregulation has been related to T cell tolerance and many immune disorders, such as tumors and infection tolerance. However, the physiopathology roles of Tim-3 in innate immunity remain elusive. Here, we demonstrate that Tim-3 inhibits macrophage phagocytosis of L. monocytogenes by inhibiting the nuclear erythroid 2-related factor 2 (Nrf2) signaling pathway and increases bacterial burden. Tim-3 signaling promotes Nrf2 degradation by increasing its ubiquitination and, as a result, decreasing its nuclear translocation. CD36 and heme oxygenase-1 (HO-1), two downstream molecules in the Tim-3-Nrf2 signaling axis, are involved in the Tim-3- mediated immune evasion of L. monocytogenes both in vitro and in vivo. We here identified new mechanisms by which Tim-3 induces infection tolerance. By modulating the Tim-3 pathway, we demonstrate the feasibility of manipulating macrophage function as a potent tool for treating infectious diseases, such as Listeria infection.

High-density lipoprotein from subjects with coronary artery disease promotes macrophage foam cell formation: role of scavenger receptor CD36 and ERK/MAPK signaling

Although high-density lipoprotein is atheroprotective, it can become dysfunctional in chronic inflammatory conditions and increase cardiovascular risk. We previously demonstrated that HDL from subjects with documented coronary artery disease is dysfunctional and is pro-oxidant/proinflammatory in macrophages. Here we examined the influence of dysfunctional/proinflammatory HDL (piHDL) on lipid accumulation in human macrophages, in comparison to functional HDL (nHDL). Exposure of macrophages to piHDL, in contrast to nHDL, resulted in oxidative stress and marked uptake of lipids from piHDL, leading to the formation of foam cell phenotype as noted by oil red O staining with concomitant increase in total cellular cholesterol content. Using western blotting, we identified that piHDL profoundly upregulated the expression of scavenger receptor CD36 and suppressed the expression of ABCG1 and SRB1 in macrophages, thereby facilitating cholesterol influx capacity of macrophages. We then identified that CD36 did not act alone, indeed it was activated in macrophages along with ERK/MAPK, in response to piHDL, which in turn led to lipid accumulation as well as proinflammatory response via activation of NFkB and subsequent release of proinflammatory markers-TNF-ά and MMP-9. These effects were confirmed using pharmacological inhibitors for either CD36 or ERK/MAPK. Furthermore, piHDL treatment moderately activated PPAR-γ and Nrf2, the known regulators of CD36 in macrophages, suggesting that the two forms of HDL differentially regulate CD36 expression. Taken together, the results demonstrate that a novel CD36-ERK/MAPK-dependent mechanism is involved in macrophage lipid accumulation by piHDL, there by revealing the importance of functional deficiency in HDL and its potential link to atherogenesis.

Antioxidant defense of Nrf2vspro-inflammatory system of NF-κB during the amoebic liver infection in hamster

Entamoeba histolyticais the causative agent of amoebic liver abscess (ALA), which course with an uncontrolled inflammation and nitro-oxidative stresses, although it is well known that amoeba has an effective defence mechanisms against this toxic environment, the underlying molecular factors responsible for progression of tissue damage remain largely unknown. The purpose of the present study was to determine during the acute stage of ALA in hamsters, the involvement of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and nuclear factor-kappa B (NF-κB), which are activated in response to oxidative stress. From 12 h post-infection the ALA was visible, haematoxylin-eosin and Masson's trichrome stains were consistent with these observations, and alanine aminotransferase, alkaline phosphatase and γ-glutamyl transpeptidase serum activities were increased too. At 48 h after infection, liver glycogen content was significantly reduced. Western blot analyses showed that 4-Hydroxy-2-nonenal peaked at 12 h, while glycogen synthase kinase-3β, cleaved caspase-3, pNF-κB, interleukin-1β and tumour necrosis factor-α were overexpressed from 12 to 48 h post-infection. Otherwise, Nrf2 and superoxide dismutase-1, decreased at 48 h and catalase declined at 36 and 48 h. Furthermore, heme oxygenase-1 was increased at 12 and 24 h and decreased to normal levels at 36 and 48 h. These findings suggest for the first time that the host antioxidant system of Nrf2 is influenced during ALA.

LPA/PKD-1-FoxO1 Signaling Axis Mediates Endothelial Cell CD36 Transcriptional Repression and Proangiogenic and Proarteriogenic Reprogramming

OBJECTIVE

CD36 is a scavenger and antiangiogenic receptor that is important in atherothrombotic diseases, diabetes mellitus, cancer, and obesity. Lysophosphatidic acid, a phospholipid signaling mediator, abolishes endothelial cell responses to antiangiogenic proteins containing thrombospondin type 1 homology domains by downregulating endothelial CD36 transcription via protein kinase D1 (PKD-1) signaling. We aimed to understand mechanisms by which lysophosphatidic acid-mediated angiogenic signaling is integrated to regulate CD36 transcription and endothelial cell function via a nuclear transcriptional complex.

APPROACH AND RESULTS

Microvascular endothelial cells expressing CD36 were used for studying angiogenic signaling and CD36 transcription. Gene transfection and transduction, RT-qPCR, avidin-biotin-conjugated DNA-binding assay, chromatin immunoprecipitation assay, co-immunoprecipitation, proximal ligation assay, and immunofluorescence microscopy showed that lysophosphatidic acid-mediated CD36 transcriptional repression involved PKD-1 signaling mediated formation of forkhead box protein O1-histone deacetylase 7 complex in the nucleus. Unexpectedly, turning off CD36 transcription initiated reprogramming microvascular endothelial cells to express ephrin B2, a critical molecular signature involved in angiogenesis and arteriogenesis. Spheroid-based angiogenesis and in vivo Matrigel angiogenesis assays indicated that angiogenic branching morphogenesis and in vivo angiogenesis were dependent on PKD-1 signaling. A mouse tumor angiogenesis model revealed enhanced PKD-1 signaling and expression of ephrin B2 and smooth muscle actin in neovessels of Lewis Lung Carcinomas, along with low-CD36 expression or CD36 deficiency.

CONCLUSIONS

Lysophosphatidic acid/PKD-1 signaling leads to nuclear accumulation of histone deacetylase 7, where it interacts with forkhead box protein O1 to suppress endothelial CD36 transcription and mediates silencing of antiangiogenic switch, resulting in proangiogenic and proarteriogenic reprogramming. Targeting this signaling cascade could be a novel approach for ischemic cardiovascular disease and cancer.

Anti-TNF certolizumab pegol induces antioxidant response in human monocytes via reverse signaling

BACKGROUND

Anti TNF drugs have been widely used in rheumatoid arthritis (RA) but only 70 to 80 % of patients respond to this therapy. Exploring the mode of action of anti-TNF drugs remains important in order to improve the efficiency of the treatment and enhance our knowledge of inflammation. TNF-α exists as classical soluble cytokine as well as transmembrane protein (tmTNF-α). Evidence suggests that tmTNF-α can induce reverse signaling. In the present study, we have explored consequences of reverse signaling in human monocytes using certolizumab pegol (CZP).

METHODS

Monocytes were purified from healthy blood donors and were incubated with CZP. Nuclear translocation of Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) was evaluated by wide-field microscopy and cell fractionation. Heme oxygenase 1 (HO-1) was assessed by RT-qPCR and western blot. Monocytes were stimulated with lipopolysaccharide (LPS). IL-1β was quantitated by RT-qPCR. Reactive oxygen species (ROS) were evaluated by flow cytometry using the H2DCFDA fluorescent marker.

RESULTS

CZP induced rapid minimal ROS production and Nrf2 nuclear translocation. This was followed by HO-1 mRNA and protein production. IL-1β induction by LPS was inhibited at the mRNA and protein level. At a later time-point, CZP was able to counteract the strong production of ROS induced by LPS. Reverse signaling was suggested by short kinetics of Nrf2 translocation, extensive washing of CZP and the use of anti-TNF-Rs antibodies.

CONCLUSION

Our data suggest a novel mechanism of ROS modulation by CZP. This observation sheds new light on the function of reverse signaling and on potential mechanisms of action of anti-TNF drugs.

The immunological balance between host and parasite in malaria

Coevolution of humans and malaria parasites has generated an intricate balance between the immune system of the host and virulence factors of the parasite, equilibrating maximal parasite transmission with limited host damage. Focusing on the blood stage of the disease, we discuss how the balance between anti-parasite immunity versus immunomodulatory and evasion mechanisms of the parasite may result in parasite clearance or chronic infection without major symptoms, whereas imbalances characterized by excessive parasite growth, exaggerated immune reactions or a combination of both cause severe pathology and death, which is detrimental for both parasite and host. A thorough understanding of the immunological balance of malaria and its relation to other physiological balances in the body is of crucial importance for developing effective interventions to reduce malaria-related morbidity and to diminish fatal outcomes due to severe complications. Therefore, we discuss in this review the detailed mechanisms of anti-malarial immunity, parasite virulence factors including immune evasion mechanisms and pathogenesis. Furthermore, we propose a comprehensive classification of malaria complications according to the different types of imbalances.

Recruited monocytes modulate malaria-induced lung injury through CD36-mediated clearance of sequestered infected erythrocytes

Pulmonary complications occur in a significant percentage of adults and children during the course of severe malaria. The cellular and molecular innate immune mechanisms that limit the extent of pulmonary inflammation and preserve lung function during severe Plasmodium infections remain unclear. In particular, the contributions to pulmonary complications by parasitized erythrocyte sequestration and subsequent clearance from the lung microvasculature by immune cells have not been clearly defined. We used the Plasmodium berghei ANKA-C57BL/6 mouse model of severe malaria to investigate the mechanisms governing the nature and extent of malaria-associated lung injury. We have demonstrated that sequestration of infected erythrocytes on postcapillary endothelial surfaces results in acute lung injury and the rapid recruitment of CCR2(+)CD11b(+)Ly6C(hi) monocytes from the circulation. These recruited cells remain in the lungs as monocyte-derived macrophages and are instrumental in the phagocytic clearance of adherent Plasmodium berghei-infected erythrocytes. In contrast, alveolar macrophages do not play a significant role in the clearance of malaria-infected cells. Furthermore, the results obtained from Ccr2(-/-), Cd36(-/-), and CD36 bone marrow chimeric mice showed that sequestration in the absence of CD36-mediated phagocytic clearance by monocytes leads to exaggerated lung pathologic features. In summary, our data indicate that the intensity of malaria-induced lung pathologic features is proportional to the steady-state levels of Plasmodium-infected erythrocytes adhering to the pulmonary vasculature. Moreover, the present work has defined a major role of recruited monocytes in clearing infected erythrocytes from the pulmonary interstitium, thus minimizing lung damage.

Dichotomous roles for externalized cardiolipin in extracellular signaling: Promotion of phagocytosis and attenuation of innate immunity

Among the distinct molecular signatures present in the mitochondrion is the tetra-acylated anionic phospholipid cardiolipin, a lipid also present in primordial, single-cell bacterial ancestors of mitochondria and multiple bacterial species today. Cardiolipin is normally localized to the inner mitochondrial membrane; however, when cardiolipin becomes externalized to the surface of dysregulated mitochondria, it promotes inflammasome activation and stimulates the elimination of damaged or nonfunctional mitochondria by mitophagy. Given the immunogenicity of mitochondrial and bacterial membranes that are released during sterile and pathogen-induced trauma, we hypothesized that cardiolipins might function as "eat me" signals for professional phagocytes. In experiments with macrophage cell lines and primary macrophages, we found that membranes with mitochondrial or bacterial cardiolipins on their surface were engulfed through phagocytosis, which depended on the scavenger receptor CD36. Distinct from this process, the copresentation of cardiolipin with the Toll-like receptor 4 (TLR4) agonist lipopolysaccharide dampened TLR4-stimulated production of cytokines. These data suggest that externalized, extracellular cardiolipins play a dual role in host-host and host-pathogen interactions by promoting phagocytosis and attenuating inflammatory immune responses.

Nrf2-driven CD36 and HO-1 gene expression in circulating monocytes correlates with favourable clinical outcome in pregnancy-associated malaria

Background

Pregnancy-associated malaria (PAM) constitutes one of the most severe forms of malaria infection leading to fetal growth restriction and high risk of infant death. The severity of the pathology is largely attributed to the recruitment of monocytes and macrophages in the placenta which is evidenced by dysregulated inflammation found in placental blood. Importantly, CD36⁺ monocytes/macrophages are also thought to participate in the tight control of the pro- and anti-inflammatory responses following Plasmodium detection through elimination of apoptotic cells and malaria-infected erythrocytes, internalization and recycling of oxidized forms of low-density lipoprotein and collaboration with TLR2 in pro-inflammatory response. Interestingly, previous work demonstrated that CD36 expression was upregulated on inflammatory macrophages following stimulation of the Nrf2 transcription factor, whilst the PPARγ pathway was inhibited and non-functional in the same inflammatory conditions. This current study examined the possible role of Nrf2-driven gene expression, CD36 and Haem-Oxygenase-1 (HO-1), in PAM clinical outcomes.

Methods

Clinical data and biological samples including peripheral blood mononuclear cells were collected from 27 women presenting PAM. Polychromatic flow cytometry was used to characterize innate immune cell subpopulations and quantify CD36 protein expression level on monocytes. mRNA levels of CD36, PPARγ, Nrf2 and HO-1 were determined by qPCR and related to clinical outcomes. Finally, the capacity of monocytes to modulate CD36 expression upon rosiglitazone or sulforaphane treatment, two respective PPARγ or Nrf2 activators, was also investigated.

Results

The CD36 receptor, mostly expressed by CD14⁺ circulating monocytes, statistically correlated with increased infant birth weights. Interestingly, mRNA levels of the transcription factor Nrf2 and the enzyme HO-1 also correlated with lower parasitaemia and increased infant birth weight, while PPARγ mRNA levels did not. Finally, monocytes isolated from low infant birth weight pregnant women were capable of up-regulating CD36 via the Nrf2 pathway ex vivo.

Conclusions

Altogether these results suggest that Nrf2-driven CD36 and HO-1 expression on innate immune cells could contribute to a protective and detoxifying mechanism during PAM. More powered and mechanistical studies are however needed to strengthen the conclusions of this study.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-015-0888-8) contains supplementary material, which is available to authorized users.

Nrf2 as a master regulator of tissue damage control and disease tolerance to infection

Damage control refers to those actions made towards minimizing damage or loss. Depending on the context, these can range from emergency procedures dealing with the sinking of a ship or to a surgery dealing with severe trauma or even to an imaginary company in Marvel comics, which repairs damaged property arising from conflicts between super heroes and villains. In the context of host microbe interactions, tissue damage control refers to an adaptive response that limits the extent of tissue damage associated with infection. Tissue damage control can limit the severity of infectious diseases without interfering with pathogen burden, conferring disease tolerance to infection. This contrasts with immune-driven resistance mechanisms, which although essential to protect the host from infection, can impose tissue damage to host parenchyma tissues. This damaging effect is countered by stress responses that confer tissue damage control and disease tolerance to infection. Here we discuss how the stress response regulated by the transcription factor nuclear factor-erythroid 2-related factor 2 (Nrf2) acts in such a manner.

LRH-1 mediates anti-inflammatory and antifungal phenotype of IL-13-activated macrophages through the PPARγ ligand synthesis

Liver receptor homologue-1 (LRH-1) is a nuclear receptor involved in the repression of inflammatory processes in the hepatointestinal tract. Here we report that LRH-1 is expressed in macrophages and induced by the Th2 cytokine IL-13 via a mechanism involving STAT6. We show that loss-of-function of LRH-1 in macrophages impedes IL-13-induced macrophage polarization due to impaired generation of 15-HETE PPARγ ligands. The incapacity to generate 15-HETE metabolites is at least partially caused by the compromised regulation of CYP1A1 and CYP1B1. Mice with LRH-1-deficient macrophages are, furthermore, highly susceptible to gastrointestinal and systemic Candida albicans infection. Altogether, these results identify LRH-1 as a critical component of the anti-inflammatory and fungicidal response of alternatively activated macrophages that acts upstream from the IL-13-induced 15-HETE/PPARγ axis.

CD36 upregulation mediated by intranasal LV-NRF2 treatment mitigates hypoxia-induced progression of Alzheimer's-like pathogenesis

AIMS

There is extensive evidence that oxidative stress induces cellular dysfunction in the brain and plays a critical role in Alzheimer's disease (AD) pathogenesis. Hypoxia increases factors involved in oxidative stress injury and contributes to the onset and progression of AD. Nuclear factor erythroid 2-related factor 2 (NRF2), a major component regulating antioxidant response, is attenuated in the AD brain. Importantly, NRF2 directly regulates the alternative first exons of CD36, an important participant in oxidative and inflammatory processes. To explore the effects of hypoxia-induced deterioration of AD-like pathogenesis and investigate the correlation between hypoxia-induced NRF2 signal alterations and CD36 expression, we examined the NRF2 signaling, CD36, and oxidative stress events in hypoxia-treated APPswe/PSEN1dE9 (APP/PS1) mice brain.

RESULTS

We observed that hypoxia treatment increased oxidative stress, exacerbated inflammation, and aggravated learning defects in aged APP/PS1 mice. Microglia from hypoxia-treated mice brain exhibited marked reduction in CD36 expression and inhibition of β-amyloid (Aβ) degradation. Accordingly, hypoxia treatment caused a decrease in transactivation of NRF2 target genes in the aging mouse brain. Intranasal administration with a lentiviral vector encoding human NRF2 increased CD36 expression, ameliorated the weak antioxidant response triggered by hypoxia, diminished Aβ deposition, and improved spatial memory defects.

INNOVATION

In this study, we demonstrated for the first time that NRF2 intranasal treatment-induced increases of CD36 could enhance Aβ clearance in AD transgenic mouse.

CONCLUSION

These results suggest that targeting NRF2-mediated CD36 expression might provide a beneficial intervention for cognitive impairment and oxidative stress in AD progression.

Cleaning up after ICH: the role of Nrf2 in modulating microglia function and hematoma clearance

As a consequence of intracerebral hemorrhage (ICH), blood components enter brain parenchyma causing progressive damage to the surrounding brain. Unless hematoma is cleared, the reservoirs of blood continue to inflict injury to neurovascular structures and blunt the brain repair processes. Microglia/macrophages (MMΦ) represent the primary phagocytic system that mediates the cleanup of hematoma. Thus, the efficacy of phagocytic function by MMΦ is an essential step in limiting ICH-mediated damage. Using primary microglia to model red blood cell (main component of hematoma) clearance, we studied the role of transcription factor nuclear factor-erythroid 2 p45-related factor 2 (Nrf2), a master-regulator of antioxidative defense, in the hematoma clearance process. We showed that in cultured microglia, activators of Nrf2 (i) induce antioxidative defense components, (ii) reduce peroxide formation, (iii) up-regulate phagocytosis-mediating scavenger receptor CD36, and (iv) enhance red blood cells (RBC) phagocytosis. Through inhibiting Nrf2 or CD36 in microglia, by DNA decoy or neutralizing antibody, we documented the important role of Nrf2 and CD36 in RBC phagocytosis. Using autologous blood injection ICH model to measure hematoma resolution, we showed that Nrf2 activator, sulforaphane, injected to animals after the onset of ICH, induced CD36 expression in ICH-affected brain and improved hematoma clearance in rats and wild-type mice, but expectedly not in Nrf2 knockout (KO) mice. Normal hematoma clearance was impaired in Nrf2-KO mice. Our experiments suggest that Nrf2 in microglia play an important role in augmenting the antioxidative capacity, phagocytosis, and hematoma clearance after ICH.

Plasmodium and mononuclear phagocytes

Plasmodium, the causative agent of malaria, initially multiplies inside liver cells and then in successive cycles inside erythrocytes, causing the symptoms of the disease. In this review, we discuss interactions between the extracellular and intracellular forms of the Plasmodium parasite and innate immune cells in the mammalian host, with a special emphasis on mononuclear phagocytes. We overview here what is known about the innate immune cells that interact with parasites, mechanisms used by the parasite to evade them, and the protective or detrimental contribution of these interactions on parasite progression through its life cycle and pathology in the host.

Leishmanicidal compounds and potent PPARγ activators from Renealmia thyrsoidea (Ruiz & Pav.) Poepp. & Endl

ETHNOPHARMACOLOGICAL RELEVANCE

Leaves and rhizomes of Renealmia thyrsoidea (Ruiz & Pav.) Poepp. & Endl. traditionally used in the Yanesha pharmacopoeia to treat skin infections such as leishmaniasis ulcers, or to reduce fever were chemically investigated to identify leishmanicidal compounds, as well as PPARγ activators.

METHODS

Compounds were isolated through a bioassay-guided fractionation and their structures were determined via detailed spectral analysis. The viability of Leishmania amazonensis axenic amastigotes was assessed by the reduction of tetrazolium salt (MTT), the cytotoxicity on macrophage was evaluated using trypan blue dye exclusion method, while the percentage of infected macrophages was determined microscopically in the intracellular macrophage-infected assay. The CD36, mannose receptor (MR) and dectin-1 mRNA expression on human monocytes-derived macrophages was evaluated by quantitative real-time PCR.

RESULTS

Six sesquiterpenes (1-6), one dihydrobenzofuranone (7) and four flavonoids (8-11) were isolated from the leaves. Alongside, two flavonoids (12-13) and five diarylheptanoids (14-18) were identified in the rhizomes. Leishmanicidal activity against Leishmania amazonensis axenic amastigotes was evaluated for all compounds. Compounds 6, 7, and 11, isolated from the leaves, showed to be the most active derivatives. Diarylheptanoids 14-18 were also screened for their ability to activate PPARγ nuclear receptor in macrophages. Compounds 17 and 18 bearing a Michael acceptor moiety strongly increased the expression of PPARγ target genes such as CD36, Dectin-1 and mannose receptor (MR), thus revealing interesting immunomodulatory properties.

CONCLUSIONS

Phytochemical investigation of Renealmia thyrsoidea has led to the isolation of leishmanicidal compounds from the leaves and potent PPARγ activators from the rhizomes. These results are in agreement with the traditional uses of the different parts of Renealmia thyrsoidea.

Lipid storage by adipose tissue macrophages regulates systemic glucose tolerance

Proinflammatory pathways in adipose tissue macrophages (ATMs) can impair glucose tolerance in obesity, but ATMs may also be beneficial as repositories for excess lipid that adipocytes are unable to store. To test this hypothesis, we selectively targeted visceral ATMs in obese mice with siRNA against lipoprotein lipase (LPL), leaving macrophages within other organs unaffected. Selective silencing of ATM LPL decreased foam cell formation in visceral adipose tissue of obese mice, consistent with a reduced supply of fatty acids from VLDL hydrolysis. Unexpectedly, silencing LPL also decreased the expression of genes involved in fatty acid uptake (CD36) and esterification in ATMs. This deficit in fatty acid uptake capacity was associated with increased circulating serum free fatty acids. Importantly, ATM LPL silencing also caused a marked increase in circulating fatty acid-binding protein-4, an adipocyte-derived lipid chaperone previously reported to induce liver insulin resistance and glucose intolerance. Consistent with this concept, obese mice with LPL-depleted ATMs exhibited higher hepatic glucose production from pyruvate and glucose intolerance. Silencing CD36 in ATMs also promoted glucose intolerance. Taken together, the data indicate that LPL secreted by ATMs enhances their ability to sequester excess lipid in obese mice, promoting systemic glucose tolerance.