Lysozyme 1 Inflamed CCR2+ Macrophages Promote Obesity-Induced Cardiac Dysfunction.

BACKGROUND: Macrophages are key players in obesity-associated cardiovascular diseases, which are marked by inflammatory and immune alterations. However, the pathophysiological mechanisms underlying macrophage's role in obesity-induced cardiac inflammation are incompletely understood. Our study aimed to identify the key macrophage population involved in obesity-induced cardiac dysfunction and investigate the molecular mechanism that contributes to the inflammatory response. METHODS: In this study, we used single-cell RNA-sequencing analysis of Cd45+CD11b+F4/80+ cardiac macrophages to explore the heterogeneity of cardiac macrophages. The CCR2+ (C-C chemokine receptor 2) macrophages were specifically removed by a dual recombinase approach, and the macrophage CCR2 was deleted to investigate their functions. We also performed cleavage under target and tagmentation analysis, chromatin immunoprecipitation-polymerase chain reaction, luciferase assay, and macrophage-specific lentivirus transfection to define the impact of lysozyme C in macrophages on obesity-induced inflammation. RESULTS: We find that the Ccr2 cluster undergoes a functional transition from homeostatic maintenance to proinflammation. Our data highlight specific changes in macrophage behavior during cardiac dysfunction under metabolic challenge. Consistently, inducible ablation of CCR2+CX3CR1+ macrophages or selective deletion of macrophage CCR2 prevents obesity-induced cardiac dysfunction. At the mechanistic level, we demonstrate that the obesity-induced functional shift of CCR2-expressing macrophages is mediated by the CCR2/activating transcription factor 3/lysozyme 1/NF-κB (nuclear factor kappa B) signaling. Finally, we uncover a noncanonical role for lysozyme 1 as a transcription activator, binding to the RelA promoter, driving NF-κB signaling, and strongly promoting inflammation and cardiac dysfunction in obesity. CONCLUSIONS: Our findings suggest that lysozyme 1 may represent a potential target for the diagnosis of obesity-induced inflammation and the treatment of obesity-induced heart disease.

Disruption of TIGAR-TAK1 alleviates immunopathology in a murine model of sepsis.

Macrophage-orchestrated inflammation contributes to multiple diseases including sepsis. However, the underlying mechanisms remain to be defined clearly. Here, we show that macrophage TP53-induced glycolysis and apoptosis regulator (TIGAR) is up-regulated in murine sepsis models. When myeloid Tigar is ablated, sepsis induced by either lipopolysaccharide treatment or cecal ligation puncture in male mice is attenuated via inflammation inhibition. Mechanistic characterizations indicate that TIGAR directly binds to transforming growth factor ß-activated kinase (TAK1) and promotes tumor necrosis factor receptor-associated factor 6-mediated ubiquitination and auto-phosphorylation of TAK1, in which residues 152-161 of TIGAR constitute crucial motif independent of its phosphatase activity. Interference with the binding of TIGAR to TAK1 by 5Z-7-oxozeaenol exhibits therapeutic effects in male murine model of sepsis. These findings demonstrate a non-canonical function of macrophage TIGAR in promoting inflammation, and confer a potential therapeutic target for sepsis by disruption of TIGAR-TAK1 interaction.

Major vault protein (MVP) suppresses aging- and estrogen deficiency-related bone loss through Fas-mediated apoptosis in osteoclasts.

Osteoclasts (OCs), derived from monocyte/macrophage lineage, are key orchestrators in bone remodeling. Targeting osteoclast apoptosis is a promising approach to cut down excessive osteoclast numbers, and thus slow down the rate of bone mass loss that inevitably occurs during aging. However, the therapeutic target of apoptosis in osteoclasts has not been fully studied. Our previous work generated Mvpf/fLyz2-Cre mice, conditionally depleting major vault protein (MVP) in monocyte lineage, and identified MVP as a bone protector for its negative role in osteoclastogenesis in vivo and in vitro. Here, we observed a notable decline of MVP in osteoclasts with aging in mice, encouraging us to further investigate the regulatory role of osteoclast MVP. Then, Mvpf/fLyz2-Cre mice were exploited in two osteoporosis contexts, aging and abrupt loss of estrogen, and we revealed that conditional knockout of MVP inhibited osteoclast apoptosis in vivo and in vitro. Moreover, we reported the interaction between MVP and death receptor Fas, and MVP-Fas signaling cascade was identified to positively regulate the apoptosis of osteoclasts, thus preventing osteoporosis. Collectively, our comprehensive discovery of MVP's regulatory role in osteoclasts provides new insight into osteoclast biology and therapeutic targets for osteoporosis.

Macrophage MVP regulates fracture repair by promoting M2 polarization via JAK2-STAT6 pathway.

OBJECTIVE: Major vault protein (MVP) is vital in various macrophage-related inflammatory diseases. However, the effects of MVP on macrophage polarization during fracture repair are still unknown. METHODS: We used Mvpflox/floxLyz2-Cre mice (myeloid-specific MVP gene knockout, abbreviated as MacKO) and Mvpflox/flox (abbreviated as MacWT) mice to compare their fracture healing phenotype. Next, we traced the changes in macrophage immune status in vivo and in vitro. We further explored the effects of MVP on osteogenesis and osteoclastogenesis. Finally, we re-expressed MVP in MacKO mice to confirm the role of MVP in fracture healing. RESULTS: The lack of MVP in macrophages impaired their transition from a pro-inflammatory to an anti-inflammatory phenotype during fracture repair. The increased secretion of pro-inflammatory cytokines by macrophages promoted their osteoclastic differentiation and impaired BMSC osteogenic differentiation, ultimately leading to impaired fracture repair in MacKO mice. Last, adeno-associated virus (AAV)-Mvp tibial injection significantly promoted fracture repair in MacKO mice. CONCLUSIONS: Our findings showed MVP has a previously unknown immunomodulatory role in macrophages during fracture repair. Targeting macrophage MVP may represent a novel therapeutic method for fracture treatment.

Macrophage scavenger receptor A1 antagonizes abdominal aortic aneurysm via upregulating IRG1.

AIMS: Abdominal aortic aneurysm (AAA) is a common, usually asymptomatic disease with high mortality and limited therapeutic options. Extensive extracellular matrix (ECM) fragmentation and transmural inflammation act as major pathological processes of AAA. However, the underlying regulatory mechanisms remain incompletely understood. Herein, we aimed to investigate the role of scavenger receptor A1 (SR-A1), a key pattern recognition receptor modulating macrophage activity, in pathogenesis of AAA. METHODS AND RESULTS: The AAA model was generated by administration of angiotensin II (Ang II) into apolipoprotein E knockout mice or peri-arterial application of calcium phosphate in C57BJ/6L mice. We found that SR-A1 was markedly down-regulated in the macrophages isolated from murine AAA aortas. Global or myeloid-specific ablation of SR-A1 aggravated vascular inflammation, loss of vascular smooth muscle cells and degradation of the extracellular matrix. These effects of SR-A1 deficiency on AAA development were mediated by suppressed immunoresponsive gene 1 (IRG1) and increased inflammatory response in macrophages. Mechanically, binding of SR-A1 with Lyn led to STAT3 phosphorylation and translocation into the nucleus, in which STAT3 promoted IRG1 transcription through directly binding to its promoter. Restoration of macrophage SR-A1 in SR-A1-deficient mice by bone marrow transplantation or administration of 4-octyl itaconate, the derivate of IRG1 product itaconate, could relieve murine AAA. CONCLUSION: Our study reveals a protective effect of macrophage SR-A1-STAT3-IRG1 axis against aortic aneurysm formation via inhibiting inflammation.

Major Vault Protein Prevents Atherosclerotic Plaque Destabilization by Suppressing Macrophage ASK1-JNK Signaling.

BACKGROUND: Macrophages are implicated in atherosclerotic plaque instability by inflammation and degradation of extracellular matrix. However, the regulatory mechanisms driving these macrophage-associated processes are not well understood. Here, we aimed to identify the plaque destabilization-associated cytokines and signaling pathways in macrophages. METHODS: The atherosclerotic models of myeloid-specific MVP (major vault protein) knockout mice and control mice were generated. Atherosclerotic instability, macrophage inflammatory signaling, and active cytokines released by macrophages were examined in vivo and in vitro by using cellular and molecular biological approaches. RESULTS: MVP deficiency in myeloid cells exacerbated murine plaque instability by increasing production of both MMP (matrix metallopeptidase)-9 and proinflammatory cytokines in artery wall. Mechanistically, expression of MMP-9 was mediated via ASK1 (apoptosis signal-regulating kinase 1)-MKK-4 (mitogen-activated protein kinase kinase 4)-JNK (c-Jun N-terminal kinase) signaling in macrophages. MVP and its α-helical domain could bind with ASK1 and inhibit its dimerization and phosphorylation. A 62 amino acid peptide (MVP-[686-747]) in the α-helical domain of MVP showed a crucial role in preventing macrophage MMP-9 production and plaque instability. CONCLUSIONS: MVP may act as an inhibitor for ASK1-JNK signaling-mediated MMP-9 production in macrophages and, thereby, attenuate unstable plaque formation. Our findings suggest that suppression of macrophage ASK1-JNK signaling may be a useful strategy antagonizing atherosclerotic diseases.

Serum amyloid A1 exacerbates hepatic steatosis via TLR4-mediated NF-κB signaling pathway.

OBJECTIVE: Chronic inflammatory response plays a prominent role in obesity-related nonalcoholic fatty liver disease (NAFLD). However, the intrahepatic triggering mechanism of inflammation remains obscure. This study aimed to elucidate the role of serum amyloid A1 (SAA1), an acute-phase response protein, in the obesity-induced hepatic inflammation and NAFLD. METHODS: Male mice were fed a high fat diet (HFD) for 16 weeks, and insulin resistance, hepatic steatosis, and inflammation in mice were monitored. Murine SAA1/2 was genetically manipulated to investigate the role of SAA1 in NAFLD. RESULTS: We found that SAA1 was increased in the NAFLD liver in both humans and mice. Knockout of SAA1/2 or knockdown of hepatic SAA1/2 promoted energy expenditure and alleviated HFD-induced metabolic disorder, hepatic steatosis, and inflammation. Endogenous overexpression of SAA1 in hepatocytes by adeno-associated virus 8 (AAV8) transfection aggravated overnutrition-associated gain of body weight, insulin resistance, hepatic lipid accumulation, and liver injury, which were markedly alleviated by knockout of murine toll-like receptor 4 (TLR4). Mechanistically, SAA1 directly bound with TLR4/myeloid differentiation 2 (MD2) to induce TLR4 internalization, leading to the activation of nuclear factor (NF)-κB signaling and production of both SAA1 and other inflammatory cytokines, including interleukin (IL)-6 and C-C chemokine ligand (CCL2) in hepatocytes. Administration of HFD mice with an AAV8-shRNA-SAA1/2 showed a therapeutic effect on hepatic inflammation and NAFLD progression. CONCLUSIONS: These results demonstrate that SAA1 triggers hepatic steatosis and intrahepatic inflammatory response by forming a SAA1/TLR4/NF-κB/SAA1 feedforward regulatory circuit, which, in turn, leads to NAFLD progression. SAA1 may act as a potential target for the disease intervention.

Major vault protein (MVP) negatively regulates osteoclastogenesis via calcineurin-NFATc1 pathway inhibition.

Rationale: Bone homeostasis is maintained by a balanced interplay of osteoblasts and osteoclasts. Osteoclasts are derived from monocyte/macrophage lineage. Major vault protein (MVP) is known to promote apoptosis and prevent metabolic diseases in macrophage. However, whether MVP is involved in osteoclastogenesis is unknown. Here, we identified an important function of MVP as a negative regulator of osteoclastogenesis and its therapeutic potential in preventing bone loss. Methods: Expression of MVP in osteoclasts was investigated in human tumor tissues with immunohistochemical staining. Next, we generated total body (Mvp-/- ) and monocyte-specific (Mvpf/fLyz2-Cre) MVP gene knockout mice to observe bone phenotype and osteoclastogenesis using micro-CT and bone histomorphometry. Moreover, we examined the effects of MVP on osteoclast differentiation, bone resorption, NFATc1 activation and calcium oscillations in vitro. Finally, we explored the clinical potential of targeting MVP in two osteoporosis mouse models and used an adeno-associated virus (AAV) gene to overexpress MVP locally in mice. Results: We found that Mvp-/- and Mvpf/fLyz2-Cre mice both exhibited osteoporosis-like phenotypes. MVP-deficiency also enhanced calcineurin-NFATc1 signaling and promoted NFATc1 activity, which led to enhanced osteoclastogenesis and bone resorption. Calcineurin inhibition using the small molecule inhibitor FK506 corrected the enhanced osteoclastogenesis in Mvpf/fLyz2-Cre group. Additionally, MVP reexpression in Mvpf/fLyz2-Cre group rescued calcineurin expression. MVP overexpression in wild-type mice prevented pathologic bone loss in mouse models of ovariectomized (OVX) and calvaria-adjacent lipopolysaccharide (LPS)-injected. Conclusions: Our data suggested that MVP negatively regulates osteoclast differentiation and bone resorption via inhibition of calcineurin-NFATc1 signaling. In osteoclast-related bone diseases such as osteoporosis, manipulation of MVP activity may be an attractive therapeutic target.

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.

Scavenger receptor A1 attenuates aortic dissection via promoting efferocytosis in macrophages.

Macrophage class A1 scavenger receptor (SR-A1) is a pattern recognition receptor with an anti-inflammatory feature in cardiovascular diseases. However, its role in acute aortic dissection (AD) is not known yet. Using an aortic dissection model in SR-A1-deficient mice and their wild type littermates, we found that SR-A1 deficiency aggravated beta-aminopropionitrile monofumarate induced thoracic aortic dilation, false lumen formation, extracellular matrix degradation, vascular inflammation and accumulation of apoptotic cells. These pathological changes were associated with an impaired macrophage efferocytosis mediated by tyrosine-protein kinase receptor Tyro3 in vitro and in vivo. SR-A1 could directly interact with Tyro3 and was required for Tyro3 phosphorylation to activate its downstream PI3K/Akt signaling pathway. Importantly, co-culture of SR-A1-/- macrophages with apoptotic Jurkat cells resulted in less devoured apoptotic cells accompanied by swelling mitochondria and damaged ATP generation, following poor IL-10 and robust TNF-α production. Deficiency of SR-A1 did not influence phagolysosome formation during the efferocytosis. Lentiviral overexpression of Tyro3 in SR-A1-/- macrophages induced restorative phagocytosis in vitro. Administration of Tyro3 agonist protein S could restore SR-A1-/- macrophages phagocytosis in vitro and in vivo. These findings suggest that SR-A1-Tyro3 axis in macrophages mitigate AD damage by promoting efferocytosis and inhibiting inflammation.

Major vault protein suppresses lung cancer cell proliferation by inhibiting STAT3 signaling pathway.

BACKGROUND: Major vault protein (MVP) is the major component of vault, a eukaryotic organelle involved in multiple cellular processes, and is important in multiple cellular processes and diseases including the drug resistance in cancer chemotherapies. However, the role of MVP in lung cancer remains unclear. METHODS: We examined MVP expression in 120 non-small cell lung cancer (NSCLC) tumors and matched normal tissues by immunohistochemistry. Its relationship with NSCLC prognosis was determined by investigating the patient cohort and analyzing the data from a published dataset consisting with more than 1900 lung cancer patients. We further performed shRNA-introduced knockdown of MVP in Lewis lung carcinoma (LLC) cells and examined its effects on the tumor formation in a xenograft mouse model and the tumor cell proliferation, apoptosis, and signal transduction in vitro. RESULTS: We found that MVP was up-regulated significantly in tumor tissues compared with the matched tumor-adjacent normal tissues. The increased expression of MVP in lung adenocarcinoma was associated with a better prognosis. Knockdown of MVP in LLC cells promoted xenografted lung cancer formation in mice, which was accompanied with accelerated tumor cell proliferation and suppressed cell apoptosis in vitro. Knockdown of MVP stimulated STAT3 phosphorylation, nuclear localization, and activation of JAK2 and RAF/MEK/ERK pathways in LLC cells. Administration of STAT3 inhibitor WP1066 could prevent MVP knockdown induced tumorigenesis. CONCLUSIONS: Our findings demonstrate that MVP may act as a lung tumor suppressor via inhibiting STAT3 pathway. MVP would be a potential target for novel therapies of lung adenocarcinoma.

Major vault protein suppresses obesity and atherosclerosis through inhibiting IKK-NF-κB signaling mediated inflammation.

Macrophage-orchestrated, low-grade chronic inflammation plays a pivotal role in obesity and atherogenesis. However, the underlying regulatory mechanisms remain incompletely understood. Here, we identify major vault protein (MVP), the main component of unique cellular ribonucleoprotein particles, as a suppressor for NF-κB signaling in macrophages. Both global and myeloid-specific MVP gene knockout aggravates high-fat diet induced obesity, insulin resistance, hepatic steatosis and atherosclerosis in mice. The exacerbated metabolic disorders caused by MVP deficiency are accompanied with increased macrophage infiltration and heightened inflammatory responses in the microenvironments. In vitro studies reveal that MVP interacts with TRAF6 preventing its recruitment to IRAK1 and subsequent oligomerization and ubiquitination. Overexpression of MVP and its α-helical domain inhibits the activity of TRAF6 and suppresses macrophage inflammation. Our results demonstrate that macrophage MVP constitutes a key constraint of NF-κB signaling thereby suppressing metabolic diseases.

Insulin Antagonizes LPS-Induced Inflammatory Responses by Activating SR-A1/ERK Axis in Macrophages.

Insulin is a key regulator of metabolism and inflammation in the body. However, the mechanism of the anti-inflammatory effect of insulin is not fully understood. In the present study, we investigated the role of the class A1 scavenger receptor (SR-A1), a prototypic member of the pattern recognition receptor family, in the insulin-mediated suppression of inflammatory responses in macrophages. Our murine in vivo studies show that insulin can attenuate lipopolysaccharide (LPS)-induced endotoxemia in a SR-A1-dependent manner, and this was consistent with our in vitro results which demonstrate that the SR-A1 is necessary for insulin to antagonize the LPS-induced inflammatory responses in macrophages. The effect of SR-A1 on the anti-inflammatory action of insulin might be associated with the activation of the extracellular signal-regulated kinases (ERK) signaling pathway in macrophages. Insulin could inhibit macrophage polarization to a pro-inflammatory phenotype via the SR-A1/ERK cascade. Collectively, our results suggest that SR-A1 may be a pivotal element for the anti-inflammation effect of insulin in macrophages.

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.

Scavenger Receptor A1 Prevents Metastasis of Non-Small Cell Lung Cancer via Suppression of Macrophage Serum Amyloid A1.

Mechanisms of cross-talk between tumor cells and tumor-associated macrophages (TAM), which drive metastasis, are not fully understood. Scavenger receptor A1 (SR-A1) expressed primarily in macrophages has been associated with lung tumorigenesis. In this study, we used population genetics, transcriptomics, and functional analyses to uncover how SR-A1 is involved in lung cancer and its prognosis. SR-A1 genetic variants were investigated for possible association with survival of advanced stage NSCLC patients in the Harvard Lung Cancer Study cohort. Two SNPs (rs17484273, rs1484751) in SR-A1 were associated significantly with poor overall survival in this cohort. Data from The Cancer Genome Atlas showed considerable downregulation of SR-A1 in lung tumor tissues. The association of SR-A1 with prognosis was validated in animal models in the context of lung cancer metastasis. Macrophages derived from mice genetically deficient for SR-A1 exhibited accelerated metastasis in a model of lung cancer. On the other hand, tumor cell seeding, migration, and invasion, as well as macrophage accumulation in lung cancer tissue, were enhanced in SR-A1-deficient mice. SR-A1 deletion upregulated serum amyloid A1 (SAA1) in macrophages via MAPK/IκB/NFκB signaling. SAA1 promoted tumor cell invasion and macrophage migration in vitro and in vivo, but these effects were blocked by administration of an anti-SAA1 antibody. Overall, our findings show how SR-A1 suppresses lung cancer metastasis by downregulating SAA1 production in TAMs. Cancer Res; 77(7); 1586-98. ©2017 AACR.

Class A Scavenger Receptor Exacerbates Osteoclastogenesis by an Interleukin-6-Mediated Mechanism through ERK and JNK Signaling Pathways.

Osteoclasts originate from bone marrow monocyte/macrophage lineage cells, which are important for bone health. Class A scavenger receptor (SR-A) is a multifunctional molecule that functions during differentiation of monocyte into macrophages and osteoclasts. To further characterize the role of SR-A in osteoclasts, we used the murine tooth movement model (TM) and the murine anterior cruciate ligament transection model of osteoarthritis (ACLT OA). In these two models the bones involved are of different origin and have different properties. Bone resorption was decreased in SR-A-/- mice compared to SR-A+/+ mice. Further evaluation showed that the number of multinucleated osteoclasts in SR-A-/- mice, compared to SR-A+/+ mice, was significantly decreased both in vivo and in vitro. The levels of interleukin-6 (IL-6) produced by osteoclasts were reduced in SR-A-/- mice compared to SR-A+/+ mice. In the in vitro marrow-derived osteoclast formation assay and in both mouse models, osteoclastogenesis was restored to normal in SR-A-/- mice by administration of recombinant murine IL-6. Moreover, neutralization of IL-6 reduced the number of osteoclasts formed in SR-A+/+ mice of TM model. Both extracellular signal-regulated kinase (ERK) and c-Jun N-terminal protein kinase (JNK), but not p38, signaling pathways were downregulated in receptor activator of nuclear factor-κB ligand (RANKL)-stimulated SR-A-/- osteoclasts. Importantly, when treated with either ERK or JNK inhibitor, the numbers of osteoclasts generated from RANKL-induced bone marrow derived-macrophages of SR-A+/+ mice, and their IL-6 production, were significantly decreased. This suggests that SR-A activates the ERK and JNK signaling pathways, and promotes production of IL-6 by osteoclasts to further stimulate osteoclast formation.

Miltefosine Suppresses Hepatic Steatosis by Activating AMPK Signal Pathway.

BACKGROUND AND PURPOSE: It has been accepted that AMPK (Adenosine monophosphate-activated protein kinase) activation exhibits many beneficial effects on glucolipid metabolism. Lysophosphatidylcholine (LPC) is an important lysophospholipid which can improve blood glucose levels in diabetic mice and attenuate inflammation by activating AMPK signal pathway in macrophages. Synthetic alkylphospholipids (ALPs), such as miltefosine, is used as an alternate of LPC for the clinical application. Here, we investigated whether miltefosine could have an impact on hepatic steatosis and related metabolic disorders. EXPERIMENTAL APPROACH: Mice were fed with high fat diet (HFD) for 16 weeks to generate an obese model. Next, the obese mice were randomly divided into three groups: saline-treated and miltefosine-treated (2.5 or 5 mg/kg/d) groups. Miltefosine was intraperitoneally administrated into mice for additional 4 weeks plus HFD treatment. KEY RESULTS: It was shown that miltefosine treatment could substantially improve glucose metabolism, prevented hepatic lipid accumulation, and inhibited liver inflammation in HFD-fed mice by activating AMPK signal pathway. In vitro, miltefosine stimulated AMPKα phosphorylation both in time and dose dependent manner and decreased lipid accumulation in liver cells. When a specific AMPK inhibitor compound C was used to treat mice, the antagonistic effects of miltefosine on HFD-induced mouse hyperlipidaemia and liver steatosis were abolished. Treatment with miltefosine also dramatically inhibited the HFD-induced liver inflammation in mice. CONCLUSIONS AND IMPLICATIONS: Here we demonstrated that miltefosine might be a new activator of AMPK signal pathway in vivo and in vitro and be useful for treatment of hepatic steatosis and related metabolic disorders.

Class A1 scavenger receptor modulates glioma progression by regulating M2-like tumor-associated macrophage polarization.

Macrophages enhance glioma development and progression by shaping the tumor microenvironment. Class A1 scavenger receptor (SR-A1), a pattern recognition receptor primarily expressed in macrophages, is up-regulated in many human solid tumors. We found that SR-A1 expression in 136 human gliomas was positively correlated with tumor grade (P<0.01), but not prognosis or tumor recurrence. SR-A1-expressing macrophages originated primarily from circulating monocytes attracted to tumor tissue, and were almost twice as numerous as resident microglia in glioma tissues (P<0.001). The effects of SR-A1 on glioma proliferation and invasion were assessed in vivo using an SR-A1-deficient murine orthotopic glioma model. SR-A1 deletion promoted M2-like tumor-associated macrophage (TAM) polarization in mice by activating STAT3 and STAT6, which resulted in robust orthotopic glioma proliferation and angiogenesis. Finally, we found that HSP70 might be an endogenous ligand that activates SR-A1-dependent anti-tumorigenic pathways in gliomas, although its expression does not appear informative for diagnostic purposes. Our findings demonstrate a relationship between TAMs, SR-A1 expression and glioma growth and provide new insights into the pathogenic role of TAMs in glioma.

A cross talk between class A scavenger receptor and receptor for advanced glycation end-products contributes to diabetic retinopathy.

In response to hyperglycemia in patients with diabetes, many signaling pathways contribute to the pathogenesis of diabetic complications, including diabetic retinopathy (DR). Excessive production of inflammatory mediators plays an important role in this process. Amadori-glycated albumin, one of the major forms of advanced glycated end-products, has been implicated in DR by inducing inflammatory responses in microglia/macrophages. Our goal was to delineate the potential cross talk between class A scavenger receptor (SR-A) and the receptor for advanced glycated end-product (RAGE) in the context of DR. We show here that SR-A ablation caused an exacerbated form of DR in streptozotocin-injected C57BL/6J mice as evidenced by fundus imaging and electroretinography. Immunohistochemical staining and RT-PCR assay indicated that there was augmented activation of proinflammatory macrophages with upregulated synthesis of proinflammatory mediators in the retina in Sr-a(-/-) mice. Overexpression of SR-A suppressed RAGE-induced mitogen-activated protein kinase (MAPK) signaling, whereas RAGE activation in macrophages favored a proinflammatory (M1) phenotype in the absence of SR-A. Mechanistic analysis on bone marrow-derived macrophages and HEK293 cell line revealed that SR-A interacted with and inhibited the phosphorylation of mitogen-activated protein kinase kinase 7, the major kinase in the RAGE-MAPK-NF-κB signaling, thereby leading to diminished secretion of proinflammatory cytokines. Our findings suggest that the antagonism between SR-A and RAGE contributes to the pathogenesis of DR by nurturing a disease-prone macrophage phenotype. Therefore, specific agonist that boosts SR-A signaling could potentially provide benefits in the prevention and/or intervention of DR.

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.