Molecular Bases of Disease
Intracellular pathogen Leishmania intervenes in iron loading into ferritin by cleaving chaperones in host macrophages as an iron acquisition strategy
Iron (Fe) sequestration is one of the most important strategies of the host to control the growth and survival of invading pathogens. Ferritin (Ft) plays a pivotal role in the sequestration mechanism of mammalian hosts by storing Fe. Recent evidence suggests that poly(rC)-binding proteins (PCBPs) act as chaperones for loading Fe into Ft. Incidentally, modulation of host PCBPs in respect to storing Fe in Ft during any infection remains unexplored. Among PCBPs, PCBP1 and PCBP2 are present in every cell type and involved in interacting with Ft for Fe loading.GPNMB plays a protective role against obesity-related metabolic disorders by reducing macrophage inflammatory capacity
Obesity is a global health problem that is often related to cardiovascular and metabolic diseases. Chronic low-grade inflammation in white adipose tissue (WAT) is a hallmark of obesity. Previously, during a search for differentially expressed genes in WAT of obese mice, we identified glycoprotein nonmetastatic melanoma protein B (GPNMB), of which expression was robustly induced in pathologically expanded WAT. Here, we investigated the role of GPNMB in obesity-related metabolic disorders utilizing GPNMB-deficient mice.Disrupting phosphatase SHP2 in macrophages protects mice from high-fat diet-induced hepatic steatosis and insulin resistance by elevating IL-18 levels
Chronic low-grade inflammation plays an important role in the pathogenesis of type 2 diabetes. Src homology 2 domain-containing tyrosine phosphatase-2 (SHP2) has been reported to play diverse roles in different tissues during the development of metabolic disorders. We previously reported that SHP2 inhibition in macrophages results in increased cytokine production. Here, we investigated the association between SHP2 inhibition in macrophages and the development of metabolic diseases. Unexpectedly, we found that mice with a conditional SHP2 knockout in macrophages (cSHP2-KO) have ameliorated metabolic disorders.The USP14–NLRC5 pathway inhibits titanium particle–induced osteolysis in mice by suppressing NF-κB and PI3K/AKT activities
Total hip arthroplasty (THA) is a widely-used surgical intervention for treating patients with end-stage degenerative and inflammatory osteoarthropathy. However, wear particles from the artificial titanium joint can induce osteolysis, limiting the long-term survivorship of THA. Monocyte/macrophage lineage cells are the key players in the response to wear particles, and the proinflammatory NF-κB and phosphoinositide 3-kinase (PI3K)–AKT Ser/Thr kinase (AKT)-signaling pathways have been shown to be the most important contributors to wear particle–induced osteolysis.Moonlighting matrix metalloproteinase substrates: Enhancement of proinflammatory functions of extracellular tyrosyl-tRNA synthetase upon cleavage
Tyrosyl-tRNA synthetase ligates tyrosine to its cognate tRNA in the cytoplasm, but it can also be secreted through a noncanonical pathway. We found that extracellular tyrosyl-tRNA synthetase (YRS) exhibited proinflammatory activities. In addition to acting as a monocyte/macrophage chemoattractant, YRS initiated signaling through Toll-like receptor 2 (TLR2) resulting in NF-κB activation and release of tumor necrosis factor α (TNFα) and multiple chemokines, including MIP-1α/β, CXCL8 (IL8), and CXCL1 (KC) from THP1 monocyte and peripheral blood mononuclear cell–derived macrophages.Myeloid Acat1/Soat1 KO attenuates pro-inflammatory responses in macrophages and protects against atherosclerosis in a model of advanced lesions
Cholesterol esters are a key ingredient of foamy cells in atherosclerotic lesions; their formation is catalyzed by two enzymes: acyl-CoA:cholesterol acyltransferases (ACATs; also called sterol O-acyltransferases, or SOATs) ACAT1 and ACAT2. ACAT1 is present in all body cells and is the major isoenzyme in macrophages. Whether blocking ACAT1 benefits atherosclerosis has been under debate for more than a decade. Previously, our laboratory developed a myeloid-specific Acat1 knockout (KO) mouse (Acat1−M/−M), devoid of ACAT1 only in macrophages, microglia, and neutrophils.The tumor suppressor RASSF1A modulates inflammation and injury in the reperfused murine myocardium
Inflammation is a central feature of cardiovascular disease, including myocardial infarction and heart failure. Reperfusion of the ischemic myocardium triggers a complex inflammatory response that can exacerbate injury and worsen heart function, as well as prevent myocardial rupture and mediate wound healing. Therefore, a more complete understanding of this process could contribute to interventions that properly balance inflammatory responses for improved outcomes. In this study, we leveraged several approaches, including global and regional ischemia/reperfusion (I/R), genetically modified mice, and primary cell culture, to investigate the cell type–specific function of the tumor suppressor Ras association domain family member 1 isoform A (RASSF1A) in cardiac inflammation.Inflammasome inhibition blocks cardiac glycoside cell toxicity
Chronic heart failure and cardiac arrhythmias have high morbidity and mortality, and drugs for the prevention and management of these diseases are a large part of the pharmaceutical market. Among these drugs are plant-derived cardiac glycosides, which have been used by various cultures over millennia as both medicines and poisons. We report that digoxin and related compounds activate the NLRP3 inflammasome in macrophages and cardiomyocytes at concentrations achievable during clinical use. Inflammasome activation initiates the maturation and release of the inflammatory cytokine IL-1β and the programmed cell death pathway pyroptosis in a caspase-1–dependent manner.Oxidation of methionine residues in human apolipoprotein A-I generates a potent pro-inflammatory molecule
Amyloid deposits of apolipoprotein A-I (apoA-I) and inflammation are common in atherosclerotic arteries. In this study, we investigated the interplay between oxidation of apoA-I methionine residues (Met(O)-ApoA-I), a known amyloidogenic modification of apoA-I, and the inflammatory response of immune cells. Soluble pre-fibrillar Met(O)-ApoA-I, but not apoA-I, induced intracellular accumulation of pro-interleukin (IL)-1β and secretion of the pro-inflammatory cytokines tumor necrosis factor α (TNFα) and IL-6 in mouse bone marrow–derived macrophages (BMDMs) and human primary monocytes.RORγ regulates the NLRP3 inflammasome
RAR-related orphan receptor γ (RORγ) is a nuclear receptor that plays an essential role in the development of T helper 17 (Th17) cells of the adaptive immune system. The NLRP3 inflammasome is a component of the innate immune system that processes interleukin (IL)-1β into a mature cytokine. Elevated activity of the NLRP3 inflammasome contributes to the progression of an array of inflammatory diseases. Bone marrow–derived macrophages (BMDMs) isolated from RORγ-null mice displayed reduced capacity to secrete IL-1β, and they also displayed a reduction in Nlrp3 and Il1b gene expression.The signaling protein Wnt5a promotes TGFβ1-mediated macrophage polarization and kidney fibrosis by inducing the transcriptional regulators Yap/Taz
M2 macrophage polarization is known to underlie kidney fibrosis. We previously reported that most of the members of the Wnt family of signaling proteins are induced in fibrotic kidneys. Dysregulation of the signaling protein Wnt5a is associated with fibrosis, but little is known about the role of Wnt5a in regulating M2 macrophage activation that results in kidney fibrosis. Here, using murine Raw 264.7 cells and bone marrow–derived macrophages, we found that Wnt5a enhanced transforming growth factor β1 (TGFβ1)-induced macrophage M2 polarization as well as expression of the transcriptional regulators Yes-associated protein (Yap)/transcriptional coactivator with PDZ-binding motif (Taz).c-Myc is a novel Leishmania virulence factor by proxy that targets the host miRNA system and is essential for survival in human macrophages
Leishmania species are intracellular protozoan pathogens that have evolved to successfully infect and deactivate host macrophages. How this deactivation is brought about is not completely understood. Recently, microRNAs (miRNAs) have emerged as ubiquitous regulators of macrophage gene expression that contribute to shaping the immune responses to intracellular pathogens. Conversely, several pathogens have evolved the ability to exploit host miRNA expression to manipulate host-cell phenotype. However, very little is known about the mechanisms used by intracellular pathogens to drive changes in host-cell miRNA abundance.Protease-activated receptor 1 inhibits cholesterol efflux and promotes atherogenesis via cullin 3–mediated degradation of the ABCA1 transporter
Although signaling of thrombin via its receptor protease-activated receptor 1 (Par1) is known to occur in atherothrombosis, its link to the actual pathogenesis of this condition is less clear. To better understand the role of thrombin–Par1 signaling in atherosclerosis, here we have studied their effects on cellular cholesterol efflux in mice. We found that by activating Par1 and cullin 3–mediated ubiquitination and degradation of ABC subfamily A member 1 (ABCA1), thrombin inhibits cholesterol efflux in both murine macrophages and smooth muscle cells.Myeloperoxidase-derived oxidants damage artery wall proteins in an animal model of chronic kidney disease–accelerated atherosclerosis
Increased myeloperoxidase (MPO) levels and activity are associated with increased cardiovascular risk among individuals with chronic kidney disease (CKD). However, a lack of good animal models for examining the presence and catalytic activity of MPO in vascular lesions has impeded mechanistic studies into CKD-associated cardiovascular diseases. Here, we show for the first time that exaggerated atherosclerosis in a pathophysiologically relevant CKD mouse model is associated with increased macrophage-derived MPO activity.Signaling between pancreatic β cells and macrophages via S100 calcium-binding protein A8 exacerbates β-cell apoptosis and islet inflammation
Chronic low-grade inflammation in the pancreatic islets is observed in individuals with type 2 diabetes, and macrophage levels are elevated in the islets of these individuals. However, the molecular mechanisms underlying the interactions between the pancreatic β cells and macrophages and their involvement in inflammation are not fully understood. Here, we investigated the role of S100 calcium-binding protein A8 (S100A8), a member of the damage-associated molecular pattern molecules (DAMPs), in β-cell inflammation.Countervailing, time-dependent effects on host autophagy promote intracellular survival of Leishmania
Autophagy is essential for cell survival under stress and has also been implicated in host defense. Here, we investigated the interactions between Leishmania donovani, the main etiological agent of visceral leishmaniasis, and the autophagic machinery of human macrophages. Our results revealed that during early infection—and via activation of the Akt pathway—Leishmania actively inhibits the induction of autophagy. However, by 24 h, Leishmania switched from being an inhibitor to an overall inducer of autophagy.Inflammatory responses induce an identity crisis of alveolar macrophages, leading to pulmonary alveolar proteinosis
Pulmonary alveolar proteinosis (PAP) is a severe respiratory disease characterized by dyspnea caused by accumulation of surfactant protein. Dysfunction of alveolar macrophages (AMs), which regulate the homeostasis of surfactant protein, leads to the development of PAP; for example, in mice lacking BTB and CNC homology 2 (Bach2). However, how Bach2 helps prevent PAP is unknown, and the cell-specific effects of Bach2 are undefined. Using mice lacking Bach2 in specific cell types, we found that the PAP phenotype of Bach2-deficient mice is due to Bach2 deficiency in more than two types of immune cells.C1q/TNF-related protein 6 (CTRP6) links obesity to adipose tissue inflammation and insulin resistance
Obesity is associated with chronic low-grade inflammation, and metabolic regulators linking obesity to inflammation have therefore received much attention. Secreted C1q/TNF-related proteins (CTRPs) are one such group of regulators that regulate glucose and fat metabolism in peripheral tissues and modulate inflammation in adipose tissue. We have previously shown that expression of CTRP6 is up-regulated in leptin-deficient mice and, conversely, down-regulated by the anti-diabetic drug rosiglitazone.CD14 is a key mediator of both lysophosphatidic acid and lipopolysaccharide induction of foam cell formation
Macrophage uptake of oxidized low-density lipoprotein (oxLDL) plays an important role in foam cell formation and the pathogenesis of atherosclerosis. We report here that lysophosphatidic acid (LPA) enhances lipopolysaccharide (LPS)-induced oxLDL uptake in macrophages. Our data revealed that both LPA and LPS highly induce the CD14 expression at messenger RNA and protein levels in macrophages. The role of CD14, one component of the LPS receptor cluster, in LPA-induced biological functions has been unknown.Autophagy downstream of endosomal Toll-like receptor signaling in macrophages is a key mechanism for resistance to Leishmania major infection
Leishmaniasis is caused by protozoan parasites of the genus Leishmania. In mammalians, these parasites survive and replicate in macrophages and parasite elimination by macrophages is critical for host resistance. Endosomal Toll-like receptors (TLRs) have been shown to be crucial for resistance to Leishmania major in vivo. For example, mice in the resistant C57BL/6 genetic background that are triple-deficient for TLR3, -7, and -9 (Tlr3/7/9−/−) are highly susceptible to L. major infection. Tlr3/7/9−/− mice are as susceptible as mice deficient in MyD88 or UNC93B1, a chaperone required for appropriate localization of endosomal TLRs, but the mechanisms are unknown.Increased levels of Gab1 and Gab2 adaptor proteins skew interleukin-4 (IL-4) signaling toward M2 macrophage-driven pulmonary fibrosis in mice
M2-polarized macrophages, also known as alternatively activated macrophages, have long been associated with pulmonary fibrosis; however, the mechanism has not been fully defined. Gab1 and Gab2 proteins belong to the Gab family of adaptors and are integral components of the signal specificity in response to various extracellular stimuli. In this report, we found that levels of both Gab1 and Gab2 were elevated in M2-polarized macrophages isolated from bleomycin-induced fibrotic lungs. In vitro Gab1/2 deficiency in bone marrow-derived macrophages abrogated IL-4–mediated M2 polarization.Akt3 kinase suppresses pinocytosis of low-density lipoprotein by macrophages via a novel WNK/SGK1/Cdc42 protein pathway
Fluid-phase pinocytosis of LDL by macrophages is regarded as a novel promising target to reduce macrophage cholesterol accumulation in atherosclerotic lesions. The mechanisms of regulation of fluid-phase pinocytosis in macrophages and, specifically, the role of Akt kinases are poorly understood. We have found previously that increased lipoprotein uptake via the receptor-independent process in Akt3 kinase-deficient macrophages contributes to increased atherosclerosis in Akt3−/− mice. The mechanism by which Akt3 deficiency promotes lipoprotein uptake in macrophages is unknown.AMP-activated protein kinase α1 promotes atherogenesis by increasing monocyte-to-macrophage differentiation
Monocyte-to-macrophage differentiation, which can be initiated by physiological or atherogenic factors, is a pivotal process in atherogenesis, a disorder in which monocytes adhere to endothelial cells and subsequently migrate into the subendothelial spaces, where they differentiate into macrophages and macrophage-derived foam cells and cause atherosclerotic lesions. However, the monocyte-differentiation signaling pathways that are activated by atherogenic factors are poorly defined. Here we report that the AMP-activated protein kinase α1 (AMPKα1) in monocytes promotes atherosclerosis by increasing monocyte differentiation and survival.Mycobacterium tuberculosis EsxL inhibits MHC-II expression by promoting hypermethylation in class-II transactivator loci in macrophages
Mycobacterium tuberculosis is known to modulate the host immune responses to facilitate its persistence inside the host cells. One of the key mechanisms includes repression of class-II transactivator (CIITA) and MHC-II expression in infected macrophages. However, the precise mechanism of CIITA and MHC-II down-regulation is not well studied. M. tuberculosis 6-kDa early secretory antigenic target (ESAT-6) is a known potent virulence and antigenic determinant. The M. tuberculosis genome encodes 23 such ESAT-6 family proteins.Protein arginine methyltransferase 1 modulates innate immune responses through regulation of peroxisome proliferator-activated receptor γ-dependent macrophage differentiation
Arginine methylation is a common posttranslational modification that has been shown to regulate both gene expression and extranuclear signaling events. We recently reported defects in protein arginine methyltransferase 1 (PRMT1) activity and arginine methylation in the livers of cirrhosis patients with a history of recurrent infections. To examine the role of PRMT1 in innate immune responses in vivo, we created a cell type-specific knock-out mouse model. We showed that myeloid-specific PRMT1 knock-out mice demonstrate higher proinflammatory cytokine production and a lower survival rate after cecal ligation and puncture.
