The CD36 and SR-A/CD204 scavenger receptors fine-tune Staphylococcus aureus-stimulated cytokine production in mouse macrophages.

The occurring in SR-A/CD204- or CD36-deficient mice increased susceptibility to infections with Staphylococcus aureus (Sa) had traditionally been ascribed to the impairment of macrophage-mediated phagocytosis, which is, however, inconsistent with low effectiveness of unopsonized Sa killing within macrophages and redundant roles of both receptors in this process. We have found that Sa-stimulated cytokine production in mouse macrophages seems to be exclusively mediated by TLR2, mainly from within endosomes in response to Sa-derived lipoteichoic acid. By driving endocytic trafficking of TLR2 and its ligands through the clathrin-dependent pathway, CD36 and SR-A sensitize macrophages to activation by Sa as well as regulate the type and amount of cytokines produced. Additionally, upon direct Sa binding, both receptors autonomously generate anti-inflammatory signaling. Consequently, the delayed induction of acute inflammation in knockout mice may allow for the initial, uncontrolled multiplication of bacteria, stimulating excessive, septic shock-inducing production of inflammatory cytokines in later stages of infection.

Class A scavenger receptor-1/2 facilitates the uptake of bovine milk exosomes in murine bone marrow-derived macrophages and C57BL/6J mice.

Bovine milk exosomes (BMEs) are being explored in drug delivery despite their rapid elimination by macrophages. We aimed at identifying the BME transporter in murine bone marrow-derived macrophages (BMDMs). Fluorophore-labeled BMEs were used in transport studies in BMDMs from C57BL/6J and class A scavenger receptor type 1/2 (CASR-1/2) knockout mice and tissue accumulation in macrophage-depleted C57BL/6J mice. Parametric and nonparametric statistics tests for pairwise and multiple comparisons were used. Chemical inhibitors of phagocytosis by cytochalasin D led to a 69 ± 18% decrease in BME uptake compared with controls (P < 0.05), whereas inhibitors of endocytic pathways other than phagocytosis had a modest effect on uptake (P > 0.05). Inhibitors of class A scavenger receptors (CASRs) including CASR-1/2 caused a 70% decrease in BME uptake (P < 0.05). The uptake of BMEs by BMDMs from CASR-1/2 knockout mice was smaller by 58 ± 23% compared with wild-type controls (P < 0.05). Macrophage depletion by clodronate caused a more than 44% decrease in BME uptake in the spleen and lungs (P < 0.05), whereas the decrease observed in liver was not statistically significant. In conclusion, CASR-1/2 facilitates the uptake of BMEs in BMDMs and C57BL/6J mice.

Self-Maintenance of Cardiac Resident Reparative Macrophages Attenuates Doxorubicin-Induced Cardiomyopathy Through the SR-A1-c-Myc Axis.

RATIONALE: Doxorubicin-induced cardiomyopathy (DiCM) is a primary cause of heart failure and mortality in cancer patients, in which macrophage-orchestrated inflammation serves as an essential pathological mechanism. However, the specific roles of tissue-resident and monocyte-derived macrophages in DiCM remain poorly understood. OBJECTIVE: Uncovering the origins, phenotypes, and functions of proliferative cardiac resident macrophages and mechanistic insights into the self-maintenance of cardiac macrophage during DiCM progression. METHODS AND RESULTS: Mice were administrated with doxorubicin to induce cardiomyopathy. Dynamic changes of resident and monocyte-derived macrophages were examined by lineage tracing, parabiosis, and bone marrow transplantation. We found that the monocyte-derived macrophages primarily exhibited a proinflammatory phenotype that dominated the whole DiCM pathological process and impaired cardiac function. In contrast, cardiac resident macrophages were vulnerable to doxorubicin insult. The survived resident macrophages exhibited enhanced proliferation and conferred a reparative role. Global or myeloid specifically ablation of SR-A1 (class A1 scavenger receptor) inhibited proliferation of cardiac resident reparative macrophages and, therefore, exacerbated cardiomyopathy in DiCM mice. Importantly, the detrimental effect of macrophage SR-A1 deficiency was confirmed by transplantation of bone marrow. At the mechanistic level, we show that c-Myc (Avian myelocytomatosis virus oncogene cellular homolog), a key transcriptional factor for the SR-A1-P38-SIRT1 (Sirtuin 1) pathway, mediated the effect of SR-A1 in reparative macrophage proliferation in DiCM. CONCLUSIONS: The SR-A1-c-Myc axis may represent a promising target to treat DiCM through augmentation of cardiac resident reparative macrophage proliferation.

Macrophage MSR1 promotes the formation of foamy macrophage and neuronal apoptosis after spinal cord injury.

BACKGROUND: A sustained inflammatory response following spinal cord injury (SCI) contributes to neuronal damage, inhibiting functional recovery. Macrophages, the major participants in the inflammatory response, transform into foamy macrophages after phagocytosing myelin debris, subsequently releasing inflammatory factors and amplifying the secondary injury. Here, we assessed the effect of macrophage scavenger receptor 1 (MSR1) in phagocytosis of myelin debris after SCI and explained its possible mechanism. METHODS: The SCI model was employed to determine the critical role of MSR1 in phagocytosis of myelin debris in vivo. The potential functions and mechanisms of MSR1 were explored using qPCR, western blotting, and immunofluorescence after treating macrophages and RAW264.7 with myelin debris in vitro. RESULTS: In this study, we found improved recovery from traumatic SCI in MSR1-knockout mice over that in MSR1 wild-type mice. Furthermore, MSR1 promoted the phagocytosis of myelin debris and the formation of foamy macrophage, leading to pro-inflammatory polarization in vitro and in vivo. Mechanistically, in the presence of myelin debris, MSR1-mediated NF-κB signaling pathway contributed to the release of inflammatory mediators and subsequently the apoptosis of neurons. CONCLUSIONS: Our study elucidates a previously unrecognized role of MSR1 in the pathophysiology of SCI and suggests that its inhibition may be a new treatment strategy for this traumatic condition.

SR-A1 suppresses colon inflammation and tumorigenesis through negative regulation of NF-κB signaling.

Inflammatory bowel disease is characterized by chronic intestinal inflammatory disorders associated with increased risk of developing colorectal cancer. However, the detailed mechanisms are not fully understood. The aim of this study was to determine the effect of macrophage scavenger receptor class A1 (SR-A1), a pattern recognition receptor primarily expressed in macrophages, on colitis and clarify the underlying mechanisms. We found that SR-A1-/- mice had an aggravating dextran sodium sulfate-induced acute and recurring colitis. This action was associated with a robust activation of both canonical and noncanonical NF-κB signaling in the colon. Suppression of the noncanonical NF-κB signaling by SR-A1 may be via its interaction with TRAF3 in macrophages. Furthermore, the anti-inflammation effect of SR-A1 could inhibit occurrence of colitis-associated cancer in mice. These results, for the first time, demonstrate that SR-A1 as a suppressor for inflammatory bowel disease.

Roles of the Exogenous H2S-Mediated SR-A Signaling Pathway in Renal Ischemia/ Reperfusion Injury in Regulating Endoplasmic Reticulum Stress-Induced Autophagy in a Rat Model.

OBJECTIVE: This study aims to explore the effects of the exogenous hydrogen sulfide (H2S)-mediated scavenger receptor A (SR-A) signaling pathway on renal ischemia/reperfusion injury (IRI) by regulating endoplasmic reticulum (ER) stress-induced autophagy in rats. METHODS: A total of 48 normal Sprague-Dawley (SD) rats and SR-A knockout rats were selected and divided into six groups (n = 8): wild-type (WT) + sham, WT + ischemia-reperfusion (I/R), WT + I/R + NaHS, SR-A-/- + sham, SR-A-/- + I/R and SR-A-/- + I/R + NaHS. The concentrations of urinary protein, blood urea nitrogen (BUN), serum creatinine (SCR), malondialdehyde (MDA) and H2S in renal tissue were detected. qRT-PCR and Western blotting were used to detect the mRNA and protein levels of IL-6, TGF-ß, SR-A, LC3I, LC3II, P62, PERK, ATF6 and IRE1 pathway-related genes. A TUNEL assay was used to detect cell apoptosis. Electron microscopy was applied to observe the structure of renal autophagosomes. RESULTS: Compared with the WT + sham group, in the rates of the WT + I/R group, the urine volume, urinary protein, BUN, SCR and MDA concentrations, the mRNA and protein expression of IL-6, TGF-ß, LC3II/I, and ER stress pathway-related genes, the cell apoptosis index, and the number of autophagosomes were significantly increased 24 h after I/R, while P62 and SR-A protein expression and SOD and H2S concentrations were significantly decreased (all P < 0.05). The levels of renal injury, autophagy and ER stress pathway-related genes were decreased in the WT + I/R + NaHS group but were increased in the SR-A-/- + I/R group relative to the WT + I/R group. No significant differences were observed in the urine volume; the concentrations of urinary protein, BUN, SCR and MDA; the SOD activity; the mRNA and protein expression of IL-6, TGF-ß, SR-A, GRP78, SR-A, GPR94, ATF4, IRE1, XBP1, ATF6, and eIF2α; the cell apoptosis index; or the number of autophagosomes in rats of the SR-A-/- + I/R and SR-A-/- + I/R + NaHS groups (all P > 0.05). CONCLUSION: These results demonstrate that the exogenous H2S-mediated SR-A signaling pathway reduces renal IRI injury by up-regulating ER stress-induced autophagy in rats.

Complex formation with pentraxin-2 regulates factor X plasma levels and macrophage interactions.

Recently, we have identified scavenger receptor class A member I (SR-AI) as a receptor for coagulation factor X (FX), mediating the formation of an FX reservoir at the macrophage surface. Here, we demonstrate that the FX/SR-AI-complex comprises a third protein, pentraxin-2 (PTX2). The presence of PTX2 is essential to prevent internalization of FX by SR-AI, and the presence of FX is needed to interfere with internalization of PTX2. Binding studies showed that FX, SR-AI, and PTX2 independently bind to each other (KD,app: 0.2-0.7 µM). Surprisingly, immunoprecipitation experiments revealed that FX and PTX2 circulate as a complex in plasma, and complex formation involves the FX activation peptide. No binding of PTX2 to other vitamin K-dependent proteins was observed. Short hairpin RNA-mediated inhibition of PTX2 levels in mice resulted not only in reduced levels of PTX2, but also in similarly reduced FX levels. Moreover, PTX2 and FX levels were correspondingly reduced in SR-AI-deficient mice. Analysis of 71 human plasma samples uncovered a strong correlation between FX and PTX2 plasma levels. Furthermore, plasma samples of patients with reduced FX levels (congenital/acquired FX deficiency or after anti-vitamin K treatment) were characterized by concomitantly decreased PTX2 levels. In conclusion, we identified PTX2 as a novel partner for FX, and both proteins cooperate to prevent their SR-AI-mediated uptake by macrophages. Interestingly, their respective plasma levels are interdependent. These findings seem of relevance in perspective of ongoing clinical trials, in which plasma depletion of PTX2 is used as a therapeutical approach in the management of systemic amyloidosis.

Housing conditions modulate the severity of Mycoplasma pulmonis infection in mice deficient in class A scavenger receptor.

Mycoplasmosis is a frequent causative microbial agent of community-acquired pneumonia and has been linked to exacerbation of chronic obstructive pulmonary disease. The macrophage class A scavenger receptor (SRA) facilitates the clearance of noxious particles, oxidants, and infectious organisms by alveolar macrophages. We examined wildtype and SRA(-/-) mice, housed in either individually ventilated or static filter-top cages that were cycled with fresh bedding every 14 d, as a model of gene-environment interaction on the outcome of pulmonary Mycoplasma pulmonis infection. Intracage NH3 gas measurements were recorded daily prior to infection. Mice were intranasally infected with 1 × 10(7) cfu M. pulmonis UAB CT and evaluated at 3, 7, and 14 d after inoculation. Wildtype mice cleared 99.5% of pulmonary M. pulmonis by 3 d after infection but remained chronically infected through the study. SRA (-/-) mice were chronically infected with 40-fold higher mycoplasma numbers than were wildtype mice. M. pulmonis caused a chronic mixed inflammatory response that was accompanied with high levels of IL1ß, KC, MCP1, and TNFα in SRA(-/-) mice, whereas pulmonary inflammation in WT mice was represented by a monocytosis with elevation of IL1ß. Housing had a prominent influence on the severity and persistence of mycoplasmosis in SRA(-/-) mice. SRA(-/-) mice housed in static cages had an improved recovery and significant changes in surfactant proteins SPA and SPD compared with baseline levels. These results indicate that SRA is required to prevent chronic mycoplasma infection of the lung. Furthermore, environmental conditions may exacerbate chronic inflammation in M. pulmonis-infected SRA(-/-) mice.

Class A scavenger receptor deficiency augments angiotensin II-induced vascular remodeling.

Class A scavenger receptor (SR-A) is a multifunctional molecule that participates in macrophage-mediated inflammation. Here we evaluated the role of SR-A in angiotensin II (Ang II)-induced hypertensive vascular remodeling. Chronic infusion of Ang II leads to an increased systolic blood pressure both in SR-A knockout (SR-A(-/-)) and wild type (SR-A(+/+)) mice with no significant difference between these two groups. SR-A(-/-) hypertensive mice, however, exhibited a marked augmentation of arterial wall thickening and vascular cell proliferation compared with SR-A(+/+) hypertensive mice. M1 macrophage markers were increased whereas M2 macrophage markers were decreased in vascular tissues of SR-A(-/-) mice. Co-culture experiments revealed that more pro-inflammatory cytokines like TNF-α were produced by SR-A(-/-) peritoneal macrophages leading to a stronger proliferation of primary vascular smooth muscle cells in vitro. In addition, SR-A(-/-) macrophages were more prone to lipopolysaccharide-induced M1 differentiation while resisting interleukin-4-induced M2 differentiation. Importantly, transplantation of SR-A(-/-) bone marrow into SR-A(+/+) mice significantly augmented Ang II-induced vascular remodeling. These results show that SR-A is critical for Ang II-induced vascular remodeling by regulating macrophage polarization. Therefore, SR-A may be a useful therapeutic target for the intervention of hypertensive vascular remodeling.

Inflammatory stress induces statin resistance by disrupting 3-hydroxy-3-methylglutaryl-CoA reductase feedback regulation.

OBJECTIVE: The risk of cardiovascular disease is increased by up to 33 to 50× in chronic inflammatory states and convention doses of statins may not provide the same cardiovascular protection as in noninflamed patients. This study investigated whether the increase in 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCoA-R)-mediated cholesterol synthesis observed under inflammatory stress was resistant to the action of statins and if so, whether this was because of interference with the sterol regulatory element binding protein cleavage-activating protein pathway. APPROACH AND RESULTS: Inflammatory stress was induced by adding cytokines (interleukin-1ß, tumor necrosis factor-α, and interleukin-6) and lipopolysaccharides to vascular smooth muscle cells in vitro and by subcutaneous casein injection in apolipoprotein E/scavenger receptors class A/CD36 triple knockout mice in vivo. Inflammatory stress exacerbated cholesterol ester accumulation and was accompanied in vitro and in vivo by increased HMGCoA-R mRNA and protein expression mediated via activation of the sterol regulatory element binding protein cleavage-activating protein/sterol regulatory element binding protein-2 pathway. Atorvastatin reduced HMGCoA-R enzymatic activity and intracellular cholesterol synthesis in vitro. However, inflammatory stress weakened these suppressive effects. Atorvastatin at concentrations of 16 µmol/L inhibited HMGCoA-R activity by 50% in vascular smooth muscle cells, but the same concentration resulted in only 30% of HMGCoA-R activity in vascular smooth muscle cells in the presence of interleukin-1ß. Knocking down sterol regulatory element binding protein cleavage-activating protein prevented statin resistance induced by interleukin-1ß, and overexpression of sterol regulatory element binding protein cleavage-activating protein induced statin resistance even without inflammatory stress. In vivo, the amount of atorvastatin required to lower serum cholesterol and decrease aortic lipid accumulation rose from 2 to 10 mg/kg per day in the presence of inflammatory stress. CONCLUSIONS: Increased cholesterol synthesis mediated by HMGCoA-R under inflammatory stress may be one of the mechanisms for intracellular lipid accumulation and statin resistance.

Scavenger receptor A modulates the immune response to pulmonary Cryptococcus neoformans infection.

Scavenger receptors represent an important class of pattern recognition receptors shown to mediate both beneficial and detrimental roles in host defense against microbial pathogens. The role of the major macrophage scavenger receptor, scavenger receptor A (SRA), in the immune response against the pathogenic fungus, Cryptococcus neoformans, is unknown. To evaluate the role of SRA in anticryptococcal host defenses, SRA(+/+) mice and SRA(-/-) mice were infected intratracheally with C. neoformans. Results show that infection of SRA(-/-) mice resulted in a reduction in the pulmonary fungal burden at the efferent phase (3 wk) compared with SRA(+/+) mice. Improved fungal clearance in SRA(-/-) mice was associated with decreased accumulation of eosinophils and greater accumulation of CD4(+) T cells and CD11b(+) dendritic cells. Additional parameters were consistent with enhanced anticryptococcal immunity in the infected SRA(-/-) mice: 1) increased expression of the costimulatory molecules CD80 and CD86 by lung APCs, 2) decreased expression of Th2 cytokines (IL-4 and IL-13) and IL-10 in lung leukocytes and in cryptococcal Ag-pulsed splenocytes, 3) diminished IgE production in sera, and 4) increased hallmarks of classical pulmonary macrophage activation. These effects were preceded by increased expression of early pro-Th1 genes in pulmonary lymph nodes at the afferent phase (1 wk). Collectively, our data show that SRA can be exploited by C. neoformans to interfere with the early events of the afferent responses that support Th1 immune polarization. This results in amplification of Th2 arm of the immune response and subsequently impaired adaptive control of C. neoformans in the infected lungs.

Scara1 deficiency impairs clearance of soluble amyloid-ß by mononuclear phagocytes and accelerates Alzheimer's-like disease progression.

In Alzheimer's disease, soluble amyloid-ß causes synaptic dysfunction and neuronal loss. Receptors involved in clearance of soluble amyloid-ß are not known. Here we use short hairpin RNA screening and identify the scavenger receptor Scara1 as a receptor for soluble amyloid-ß expressed on myeloid cells. To determine the role of Scara1 in clearance of soluble amyloid-ß in vivo, we cross Scara1 null mice with PS1-APP mice, a mouse model of Alzheimer's disease, and generate PS1-APP-Scara1-deficient mice. Scara1 deficiency markedly accelerates Aß accumulation, leading to increased mortality. In contrast, pharmacological upregulation of Scara1 expression on mononuclear phagocytes increases Aß clearance. This approach is a potential treatment strategy for Alzheimer's disease.

Macrophage scavenger receptor a promotes tumor progression in murine models of ovarian and pancreatic cancer.

Alternatively activated macrophages express the pattern recognition receptor scavenger receptor A (SR-A). We demonstrated previously that coculture of macrophages with tumor cells upregulates macrophage SR-A expression. We show in this study that macrophage SR-A deficiency inhibits tumor cell migration in a coculture assay. We further demonstrate that coculture of tumor-associated macrophages and tumor cells induces secretion of factors that are recognized by SR-A on tumor-associated macrophages. We tentatively identified several potential ligands for the SR-A receptor in tumor cell-macrophage cocultures by mass spectrometry. Competing with the coculture-induced ligand in our invasion assay recapitulates SR-A deficiency and leads to similar inhibition of tumor cell invasion. In line with our in vitro findings, tumor progression and metastasis are inhibited in SR-A(-/-) mice in two in vivo models of ovarian and pancreatic cancer. Finally, treatment of tumor-bearing mice with 4F, a small peptide SR-A ligand able to compete with physiological SR-A ligands in vitro, recapitulates the inhibition of tumor progression and metastasis observed in SR-A(-/-) mice. Our observations suggest that SR-A may be a potential drug target in the prevention of metastatic cancer progression.

Progressive reactive lymphoid connective tissue disease and development of autoantibodies in scavenger receptor A5-deficient mice.

Scavenger receptor A5 (SCARA5) is a member of the class A scavenger receptors, with most similarity to SCARA1 (SR-A) and SCARA2 (MARCO), which are primarily expressed by macrophages and dendritic cells, in which they participate in clearance of various polyanionic macromolecules, pollution particles, and pathogens. The biological role of SCARA5 has been unknown. Herein, we show that SCARA5 is an endocytotic receptor whose ligand repertoire includes the typical scavenger receptor ligands, whole bacteria, and purified Gram-negative bacterial lipopolysaccharide. In contrast to expression of SCARA1 and SCARA2 in immune cells, SCARA5 is found in a subset of fibroblast-like cells in the interstitial stroma of most organs, with additional expression in the epithelial cells of testis and choroid plexus. SCARA5-null mice develop with age lymphoid cell accumulation in many organs, in particular the lungs, and show decreased endocytotic function in fibroblasts. Furthermore, about one-third of the mice develop antinuclear antibodies. These disturbances are reminiscent of those found in many human autoimmune connective tissue disorders, which suggests that defects in fibroblast SCARA5 can underlie some forms of autoimmune disease.

Scavenger receptor A deficiency accelerates cerebrovascular amyloidosis in an animal model.

Cerebrovascular amyloidosis caused by amyloid accumulation in blood vessel walls may lead to hemorrhagic stroke and cognitive impairment. Expression of TGF-ß1 under glial fibrillary acidic protein promoter in mice leads to age-related deposition of amyloid, including ß-amyloid (Aß), around cerebral blood vessels, leading to vascular pathology starting at age of 7 months. We have recently shown the important role of macrophages in clearing cerebrovascular amyloid. Scavenger receptor A (SRA) is a multi-ligand and multifunctional receptor expressed on macrophages, and it has been suggested to play a role in meditating phagocytosis of different types of antigens. We investigated the role of SRA in mediating cerebrovascular amyloid clearance. We bred TGF-ß1 mice with SRA(-/-) mice and discovered that TGF-ß1/SRA(-/-) mice showed cerebrovascular pathology at an earlier age (3 months) compared with TGF-ß1 mice. Furthermore, SRA deficiency in macrophages led to impaired clearing of congophilic cerebrovascular amyloid from amyloid precursor protein mouse model and led to reduced phagocytosis of both soluble and insoluble Aß in vivo as compared with macrophages from wild-type mice. Our findings demonstrate the important role of SRA in cerebrovascular amyloid pathology and suggest targeting SRA for future diagnostic and therapeutic approaches for cerebral amyloid angiopathy.

Scavenger receptor class a plays a central role in mediating mortality and the development of the pro-inflammatory phenotype in polymicrobial sepsis.

Sepsis is a frequent complication in critical illness. The mechanisms that are involved in initiation and propagation of the disease are not well understood. Scavenger receptor A (SRA) is a membrane receptor that binds multiple polyanions such as oxidized LDL and endotoxin. Recent studies suggest that SRA acts as a pattern recognition receptor in the innate immune response. The goal of the present study was to determine the role of SRA in polymicrobial sepsis. SRA deficient (SRA(-/-)) and C57BL/6JB/6J (WT) male mice were subjected to cecal ligation and puncture (CLP) to induce polymicrobial sepsis. NFκB activity, myeloperoxidase activity, and co-association of SRA with toll like receptor (TLR) 4 and TLR2 was analyzed in the lungs. Spleens were analyzed for apoptosis. Serum cytokines and chemokines were assayed. Blood and peritoneal fluid were cultured for aerobic and anaerobic bacterial burdens. Long-term survival was significantly increased in SRA(-/-) septic mice (53.6% vs. 3.6%, p < 0.05) when compared to WT mice. NFκB activity was 45.5% lower in the lungs of SRA(-/-) septic mice versus WT septic mice (p < 0.05). Serum levels of interleukin (IL)-5, IL-6, IL-10 and monocyte chemoattractant protein -1 were significantly lower in septic SRA(-/-) mice when compared to septic WT mice (p < 0.05). We found that SRA immuno-precipitated with TLR4, but not TLR2, in the lungs of WT septic mice. We also found that septic SRA(-/-) mice had lower bacterial burdens than WT septic mice. SRA deficiency had no effect on pulmonary neutrophil infiltration or splenocyte apoptosis during sepsis. We conclude that SRA plays a pivotal, and previously unknown, role in mediating the pathophysiology of sepsis/septic shock in a murine model of polymicrobial sepsis. Mechanistically, SRA interacts with TLR4 to enhance the development of the pro-inflammatory phenotype and mediate the morbidity and mortality of sepsis/septic shock.

Class A scavenger receptor deficiency exacerbates lung tumorigenesis by cultivating a procarcinogenic microenvironment in humans and mice.

RATIONALE: Genetic alterations on 8p22 have been implicated in multiple cancers, including lung cancer. In this region, genetic variants of the class A scavenger receptor (SR-A) gene have been associated with prostate cancer risk and have been highlighted as a potential susceptibility gene of cancer. OBJECTIVES: To determine whether common polymorphisms in the SR-A gene are associated with human lung cancer risk and to clarify the role of SR-A in lung carcinogenesis. METHODS: The relationship of three potentially functional polymorphisms (T-365C, T+25C, and Ala275Pro) in the SR-A gene with lung cancer risk was evaluated in 1287 lung cancer case subjects and 1261 control subjects from the Chinese population. At the same time, SR-A null mice were used to investigate its role in lung cancer development. MEASUREMENTS AND MAIN RESULTS: The T+25C polymorphism was independently associated with lung cancer risk and significantly correlated with decreased expression of SR-A. The decreased SR-A expression was also found in tumor tissues as compared with normal tissues. Depletion of SR-A boosted the growth and angiogenesis of implanted Lewis lung carcinoma in mice. The cancer-suppressing capability of SR-A was attributable to its expression in bone marrow-derived cells as evidenced by bone marrow transplantation. Further analysis revealed augmented expression of proangiogenic factors including matrix metalloproteinase-9 (MMP9) in SR-A-deficient mice, indicative of a more procarcinogenic microenvironment. Last, zoledronate, an MMP9 inhibitor, abrogated acceleration of tumor growth conferred by SR-A loss-of-function. CONCLUSIONS: Evidence from the population study and mouse model strongly indicates that SR-A may function as a tumor modulator to inhibit lung cancer growth through affecting the tumor microenvironment.

Expression of scavenger receptor A on antigen presenting cells is important for CD4+ T-cells proliferation in EAE mouse model.

BACKGROUND: Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) characterized by damage to the neuronal myelin sheath. One of the key effectors for inflammatory injury is the antigen-presenting cell (APC). The class A scavenger receptor (SRA), constitutively expressed by APCs, such as macrophages and dendritic cells in peripheral tissues and the CNS, was shown to play a role in the phagocytosis of myelin; however, the role of SRA in the development of experimental autoimmune encephalomyelitis (EAE) and autoimmune reaction in the periphery has not yet been studied. METHODS: We investigated EAE progression in wild-type (WT) vs. SRA-/- mice using clinical score measurements and characterized CNS pathology using staining. Furthermore, we assessed SRA role in mediating anti myelin pro-inflammatory response in cell cultures. RESULTS: We discovered that EAE progression and CNS demyelination were significantly reduced in SRA-/- mice compared to WT mice. In addition, there was a reduction of infiltrating peripheral immune cells, such as T cells and macrophages, in the CNS lesion of SRA-/- mice, which was associated with reduced astrogliosis. Immunological assessment showed that SRA deficiency resulted in significant reduction of pro-inflammatory cytokines that play a major role in EAE progression, such as IL-2, IFN-gamma, IL-17 and IL-6. Furthermore, we discovered that SRA-/- APCs showed impairments in activation and in their ability to induce pro-inflammatory CD4+ T cell proliferation. CONCLUSION: Expression of SRA on APCs is important for CD4+ T-cells proliferation in EAE mouse model. Further studies of SRA-mediated cellular pathways in APCs may offer useful insights into the development of MS and other autoimmune diseases, providing future avenues for therapeutic intervention.

Internalization of modified lipids by CD36 and SR-A leads to hepatic inflammation and lysosomal cholesterol storage in Kupffer cells.

BACKGROUND & AIMS: Non-alcoholic steatohepatitis (NASH) is characterized by steatosis and inflammation, which can further progress into fibrosis and cirrhosis. Recently, we demonstrated that combined deletion of the two main scavenger receptors, CD36 and macrophage scavenger receptor 1 (MSR1), which are important for modified cholesterol-rich lipoprotein uptake, reduced NASH. The individual contributions of these receptors to NASH and the intracellular mechanisms by which they contribute to inflammation have not been established. We hypothesize that CD36 and MSR1 contribute independently to the onset of inflammation in NASH, by affecting intracellular cholesterol distribution inside Kupffer cells (KCs). METHODS & RESULTS: Ldlr(-/-) mice were transplanted with wild-type (Wt), Cd36(-/-) or Msr1(-/-) bone marrow and fed a Western diet for 3 months. Cd36(-/-)- and Msr1(-/-)- transplanted (tp) mice showed a similar reduction in hepatic inflammation compared to Wt-tp mice. While the total amount of cholesterol inside KCs was similar in all groups, KCs of Cd36(-/-)- and Msr1(-/-)-tp mice showed increased cytoplasmic cholesterol accumulation, while Wt-tp mice showed increased lysosomal cholesterol accumulation. CONCLUSION: CD36 and MSR1 contribute similarly and independently to the progression of inflammation in NASH. One possible explanation for the inflammatory response related to expression of these receptors could be abnormal cholesterol trafficking in KCs. These data provide a new basis for prevention and treatment of NASH.

Deletion of scavenger receptor A protects mice from progressive nephropathy independent of lipid control during diet-induced hyperlipidemia.

Scavenger receptor A (SR-A) is a key transmembrane receptor in the endocytosis of lipids and contributes to the pathogenesis of atherosclerosis. To assess its role in hyperlipidemic chronic kidney disease, wild-type and SR-A-deficient (knockout) mice underwent uninephrectomy followed by either normal or high-fat diet. After 16 weeks of diet intervention, hyperlipidemic wild-type mice presented characteristic features of progressive nephropathy: albuminuria, renal fibrosis, and overexpression of transforming growth factor (TGF)-ß1/Smad. These changes were markedly diminished in hyperlipidemic knockout mice and attributed to reduced renal lipid retention, oxidative stress, and CD11c(+) cell infiltration. In vitro, overexpression of SR-A augmented monocyte chemoattractant protein-1 release and TGF-ß1/Smad activation in HK-2 cells exposed to oxidized low-density lipoprotein. SR-A knockdown prevented lipid-induced cell injury. Moreover, wild-type to knockout bone marrow transplantation resulted in renal fibrosis in uninephrectomized mice following 16 weeks of the high-fat diet. In contrast, knockout to wild-type bone marrow transplantation led to markedly reduced albuminuria, CD11c(+) cell infiltration, and renal fibrosis compared to wild-type to SR-A knockout or wild-type to wild-type bone marrow transplanted mice, without difference in plasma lipid levels. Thus, SR-A on circulating leukocytes rather than resident renal cells predominantly mediates lipid-induced kidney injury.