Novel Mouse Model of Myocardial Infarction, Plaque Rupture, and Stroke Shows Improved Survival With Myeloperoxidase Inhibition.

BACKGROUND: Thromboembolic events, including myocardial infarction (MI) or stroke, caused by the rupture or erosion of unstable atherosclerotic plaques are the leading cause of death worldwide. Although most mouse models of atherosclerosis develop lesions in the aorta and carotid arteries, they do not develop advanced coronary artery lesions. Moreover, they do not undergo spontaneous plaque rupture with MI and stroke or do so at such a low frequency that they are not viable experimental models to study late-stage thrombotic events or to identify novel therapeutic approaches for treating atherosclerotic disease. This has stymied the development of more effective therapeutic approaches for reducing these events beyond what has been achieved with aggressive lipid lowering. Here, we describe a diet-inducible mouse model that develops widespread advanced atherosclerosis in coronary, brachiocephalic, and carotid arteries with plaque rupture, MI, and stroke. METHODS: We characterized a novel mouse model with a C-terminal mutation in the scavenger receptor class B, type 1 (SR-BI), combined with Ldlr knockout (designated SR-BI∆CT/∆CT/Ldlr-/-). Mice were fed Western diet (WD) for 26 weeks and analyzed for MI and stroke. Coronary, brachiocephalic, and carotid arteries were analyzed for atherosclerotic lesions and indices of plaque stability. To validate the utility of this model, SR-BI∆CT/∆CT/Ldlr-/- mice were treated with the drug candidate AZM198, which inhibits myeloperoxidase, an enzyme produced by activated neutrophils that predicts rupture of human atherosclerotic lesions. RESULTS: SR-BI∆CT/∆CT/Ldlr-/- mice show high (>80%) mortality rates after 26 weeks of WD feeding because of major adverse cardiovascular events, including spontaneous plaque rupture with MI and stroke. Moreover, WD-fed SR-BI∆CT/∆CT/Ldlr-/- mice displayed elevated circulating high-sensitivity cardiac troponin I and increased neutrophil extracellular trap formation within lesions compared with control mice. Treatment of WD-fed SR-BI∆CT/∆CT/Ldlr-/- mice with AZM198 showed remarkable benefits, including >90% improvement in survival and >60% decrease in the incidence of plaque rupture, MI, and stroke, in conjunction with decreased circulating high-sensitivity cardiac troponin I and reduced neutrophil extracellular trap formation within lesions. CONCLUSIONS: WD-fed SR-BI∆CT/∆CT/Ldlr-/- mice more closely replicate late-stage clinical events of advanced human atherosclerotic disease than previous models and can be used to identify and test potential new therapeutic agents to prevent major adverse cardiac events.

Induced Endothelial Cell Cycle Arrest Prevents Arteriovenous Malformations in Hereditary Hemorrhagic Telangiectasia.

BACKGROUND: Distinct endothelial cell cycle states (early G1 versus late G1) provide different "windows of opportunity" to enable the differential expression of genes that regulate venous versus arterial specification, respectively. Endothelial cell cycle control and arteriovenous identities are disrupted in vascular malformations including arteriovenous shunts, the hallmark of hereditary hemorrhagic telangiectasia (HHT). To date, the mechanistic link between endothelial cell cycle regulation and the development of arteriovenous malformations (AVMs) in HHT is not known. METHODS: We used BMP (bone morphogenetic protein) 9/10 blocking antibodies and endothelial-specific deletion of activin A receptor like type 1 (Alk1) to induce HHT in Fucci (fluorescent ubiquitination-based cell cycle indicator) 2 mice to assess endothelial cell cycle states in AVMs. We also assessed the therapeutic potential of inducing endothelial cell cycle G1 state in HHT to prevent AVMs by repurposing the Food and Drug Administration-approved CDK (cyclin-dependent kinase) 4/6 inhibitor (CDK4/6i) palbociclib. RESULTS: We found that endothelial cell cycle state and associated gene expressions are dysregulated during the pathogenesis of vascular malformations in HHT. We also showed that palbociclib treatment prevented AVM development induced by BMP9/10 inhibition and Alk1 genetic deletion. Mechanistically, endothelial cell late G1 state induced by palbociclib modulates the expression of genes regulating arteriovenous identity, endothelial cell migration, metabolism, and VEGF-A (vascular endothelial growth factor A) and BMP9 signaling that collectively contribute to the prevention of vascular malformations. CONCLUSIONS: This study provides new insights into molecular mechanisms leading to HHT by defining how endothelial cell cycle is dysregulated in AVMs because of BMP9/10 and Alk1 signaling deficiencies, and how restoration of endothelial cell cycle control may be used to treat AVMs in patients with HHT.

Endocannabinoid biosynthetic enzymes regulate pain response via LKB1-AMPK signaling.

Diacylglycerol lipase-beta (DAGLß) serves as a principal 2-arachidonoylglycerol (2-AG) biosynthetic enzyme regulating endocannabinoid and eicosanoid metabolism in immune cells including macrophages and dendritic cells. Genetic or pharmacological inactivation of DAGLß ameliorates inflammation and hyper-nociception in preclinical models of pathogenic pain. These beneficial effects have been assigned principally to reductions in downstream proinflammatory lipid signaling, leaving alternative mechanisms of regulation largely underexplored. Here, we apply quantitative chemical- and phospho-proteomics to find that disruption of DAGLß in primary macrophages leads to LKB1-AMPK signaling activation, resulting in reprogramming of the phosphoproteome and bioenergetics. Notably, AMPK inhibition reversed the antinociceptive effects of DAGLß blockade, thereby directly supporting DAGLß-AMPK crosstalk in vivo. Our findings uncover signaling between endocannabinoid biosynthetic enzymes and ancient energy-sensing kinases to mediate cell biological and pain responses.

A New Autosomal Myh11-CreERT2 Smooth Muscle Cell Lineage Tracing and Gene Knockout Mouse Model-Brief Report.

BACKGROUND: The Myh11 promoter is extensively used as a smooth muscle cell (SMC) Cre-driver and is regarded as the most restrictive and specific promoter available to study SMCs. Unfortunately, in the existing Myh11-CreERT2 mouse, the transgene was inserted on the Y chromosome precluding the study of female mice. Given the importance of including sex as a biological variable and that numerous SMC-based diseases have a sex-dependent bias, the field has been tremendously limited by the lack of a model to study both sexes. Here, we describe a new autosomal Myh11-CreERT2 mouse (referred to as Myh11-CreERT2-RAD), which allows for SMC-specific lineage tracing and gene knockout studies in vivo using both male and female mice. METHODS: A Myh11-CreERT2-RAD transgenic C57BL/6 mouse line was generated using bacterial artificial chromosome clone RP23-151J22 modified to contain a Cre-ERT2 after the Myh11 start codon. Myh11-CreERT2-RAD mice were crossed with 2 different fluorescent reporter mice and tested for SMC-specific labeling by flow cytometric and immunofluorescence analyses. RESULTS: Myh11-CreERT2-RAD transgene insertion was determined to be on mouse chromosome 2. Myh11-CreERT2-RAD fluorescent reporter mice showed Cre-dependent, tamoxifen-inducible labeling of SMCs equivalent to the widely used Myh11-CreERT2 mice. Labeling was equivalent in both male and female Cre+ mice and was limited to vascular and visceral SMCs and pericytes in various tissues as assessed by immunofluorescence. CONCLUSIONS: We generated and validated the function of an autosomal Myh11-CreERT2-RAD mouse that can be used to assess sex as a biological variable with respect to the normal and pathophysiological functions of SMCs.

Smooth muscle cell FTO regulates contractile function.

The fat mass and obesity gene (FTO) is a N6-methyladenosine RNA demethylase that was initially linked by Genome-wide association studies to increased rates of obesity. Subsequent studies have revealed multiple mass-independent effects of the gene, including cardiac myocyte contractility. We created a mouse with a conditional and inducible smooth muscle cell deletion of Fto (Myh11 Cre+ Ftofl/fl) and did not observe any changes in mouse body mass or mitochondrial metabolism. However, the mice had significantly decreased blood pressure (hypotensive), despite increased heart rate and sodium, and significantly increased plasma renin. Remarkably, the third-order mesenteric arteries from these mice had almost no myogenic tone or capacity to constrict to smooth muscle depolarization or phenylephrine. Microarray analysis from Fto-/--isolated smooth muscle cells demonstrated a significant decrease in serum response factor (Srf) and the downstream effectors Acta2, Myocd, and Tagln; this was confirmed in cultured human coronary arteries with FTO siRNA. We conclude Fto is an important component to the contractility of smooth muscle cells.NEW & NOTEWORTHY We show a key role for the fat mass obesity (FTO) gene in regulating smooth muscle contractility, possibly by methylation of serum response factor (Srf).

BAFF antagonism via the BAFF receptor 3 binding site attenuates BAFF 60-mer-induced classical NF-κB signaling and metabolic reprogramming of B cells.

Human recombinant B cell activating factor (BAFF) is secreted as 3-mers, which can associate to form 60-mers in culture supernatants. However, the presence of BAFF multimers in humans is still debated and it is incompletely understood how BAFF multimers activate the B cells. Here, we demonstrate that BAFF can exist as 60-mers or higher order multimers in human plasma. In vitro, BAFF 60-mer strongly induced the transcriptome of B cells which was partly attenuated by antagonism using a soluble fragment of BAFF receptor 3. Furthermore, compared to BAFF 3-mer, BAFF 60-mer strongly induced a transient classical and prolonged alternate NF-κB signaling, glucose oxidation by both aerobic glycolysis and oxidative phosphorylation, and succinate utilization by mitochondria. BAFF antagonism selectively attenuated classical NF-κB signaling and glucose oxidation. Altogether, our results suggest critical roles of BAFF 60-mer and its BAFF receptor 3 binding site in hyperactivation of B cells.

SMC-Derived Hyaluronan Modulates Vascular SMC Phenotype in Murine Atherosclerosis.

[Figure: see text].

Multiple cell types contribute to the atherosclerotic lesion fibrous cap by PDGFRß and bioenergetic mechanisms.

Stable atherosclerotic plaques are characterized by a thick, extracellular matrix-rich fibrous cap populated by protective ACTA2+ myofibroblast (MF)-like cells, assumed to be almost exclusively derived from smooth muscle cells (SMCs). Herein, we show that in murine and human lesions, 20% to 40% of ACTA2+ fibrous cap cells, respectively, are derived from non-SMC sources, including endothelial cells (ECs) or macrophages that have undergone an endothelial-to-mesenchymal transition (EndoMT) or a macrophage-to-mesenchymal transition (MMT). In addition, we show that SMC-specific knockout of the Pdgfrb gene, which encodes platelet-derived growth factor receptor beta (PDGFRß), in Apoe-/- mice fed a Western diet for 18 weeks resulted in brachiocephalic artery lesions nearly devoid of SMCs but with no changes in lesion size, remodelling or indices of stability, including the percentage of ACTA2+ fibrous cap cells. However, prolonged Western diet feeding of SMC Pdgfrb-knockout mice resulted in reduced indices of stability, indicating that EndoMT- and MMT-derived MFs cannot compensate indefinitely for loss of SMC-derived MFs. Using single-cell and bulk RNA-sequencing analyses of the brachiocephalic artery region and in vitro models, we provide evidence that SMC-to-MF transitions are induced by PDGF and transforming growth factor-ß and dependent on aerobic glycolysis, while EndoMT is induced by interleukin-1ß and transforming growth factor-ß. Together, we provide evidence that the ACTA2+ fibrous cap originates from a tapestry of cell types, which transition to an MF-like state through distinct signalling pathways that are either dependent on or associated with extensive metabolic reprogramming.

Probing the substitution pattern of indole-based scaffold reveals potent and selective sphingosine kinase 2 inhibitors.

Elevated levels of sphingosine 1-phosphate (S1P) and increased expression of sphingosine kinase isoforms (SphK1 and SphK2) have been implicated in a variety of disease states including cancer, inflammation, and autoimmunity. Consequently, the S1P signaling axis has become an attractive target for drug discovery. Selective inhibition of either SphK1 or SphK2 has been demonstrated to be effective in modulating S1P levels in animal models. While SphK1 inhibitors have received much attention, the development of potent and selective SphK2 inhibitors are emerging. Previously, our group reported a SphK2 naphthalene-based selective inhibitor, SLC5081308, which displays approximately 7-fold selectivity for hSphK2 over hSphK1 and has a SphK2 Ki value of 1.0 µM. To improve SphK2 potency and selectivity, we designed, synthesized, and evaluated a series of indole-based compounds derived from SLC5081308. After investigating substitution patterns around the indole ring, we discovered that 1,5-disubstitution promoted optimal binding in the SphK2 substrate binding site and subsequent inhibition of enzymatic activity. Our studies led to the identification of SLC5101465 (6r, SphK2 Ki = 90 nM, >110 fold selective for SphK2 over SphK1). Molecular modeling studies revealed key nonpolar interactions with Val308, Phe548, His556, and Cys533 and hydrogen bonds with both Asp211 and Asp308 as responsible for the high SphK2 inhibition and selectivity.

Adaptive thermogenesis in brown adipose tissue involves activation of pannexin-1 channels.

OBJECTIVE: Brown adipose tissue (BAT) is specialized in thermogenesis. The conversion of energy into heat in brown adipocytes proceeds via stimulation of ß-adrenergic receptor (ßAR)-dependent signaling and activation of mitochondrial uncoupling protein 1 (UCP1). We have previously demonstrated a functional role for pannexin-1 (Panx1) channels in white adipose tissue; however, it is not known whether Panx1 channels play a role in the regulation of brown adipocyte function. Here, we tested the hypothesis that Panx1 channels are involved in brown adipocyte activation and thermogenesis. METHODS: In an immortalized brown pre-adipocytes cell line, Panx1 currents were measured using patch-clamp electrophysiology. Flow cytometry was used for assessment of dye uptake and luminescence assays for adenosine triphosphate (ATP) release, and cellular temperature measurement was performed using a ratiometric fluorescence thermometer. We used RNA interference and expression plasmids to manipulate expression of wild-type and mutant Panx1. We used previously described adipocyte-specific Panx1 knockout mice (Panx1Adip-/-) and generated brown adipocyte-specific Panx1 knockout mice (Panx1BAT-/-) to study pharmacological or cold-induced thermogenesis. Glucose uptake into brown adipose tissue was quantified by positron emission tomography (PET) analysis of 18F-fluorodeoxyglucose (18F-FDG) content. BAT temperature was measured using an implantable telemetric temperature probe. RESULTS: In brown adipocytes, Panx1 channel activity was induced either by apoptosis-dependent caspase activation or by ß3AR stimulation via a novel mechanism that involves Gßγ subunit binding to Panx1. Inactivation of Panx1 channels in cultured brown adipocytes resulted in inhibition of ß3AR-induced lipolysis, UCP-1 expression, and cellular thermogenesis. In mice, adiponectin-Cre-dependent genetic deletion of Panx1 in all adipose tissue depots resulted in defective ß3AR agonist- or cold-induced thermogenesis in BAT and suppressed beigeing of white adipose tissue. UCP1-Cre-dependent Panx1 deletion specifically in brown adipocytes reduced the capacity for adaptive thermogenesis without affecting beigeing of white adipose tissue and aggravated diet-induced obesity and insulin resistance. CONCLUSIONS: These data demonstrate that Gßγ-dependent Panx1 channel activation is involved in ß3AR-induced thermogenic regulation in brown adipocytes. Identification of Panx1 channels in BAT as novel thermo-regulatory elements downstream of ß3AR activation may have therapeutic implications.

Modulation of PKM activity affects the differentiation of TH17 cells.

Small molecules that promote the metabolic activity of the pyruvate kinase isoform PKM2, such as TEPP-46 and DASA-58, limit tumorigenesis and inflammation. To understand how these compounds alter T cell function, we assessed their therapeutic activity in a mouse model of T cell-mediated autoimmunity that mimics multiple sclerosis (MS). TH17 cells are believed to orchestrate MS pathology, in part, through the production of two proinflammatory cytokines: interleukin-17 (IL-17) and GM-CSF. We found that both TEPP-46 and DASA-58 suppressed the development of IL-17-producing TH17 cells but increased the generation of those producing GM-CSF. This switch redirected disease pathology from the spinal cord to the brain. In addition, we found that activation of PKM2 interfered with TGF-ß1 signaling, which is necessary for the development of TH17 and regulatory T cells. Collectively, our data clarify the therapeutic potential of PKM2 activators in MS-like disease and how these agents alter T cell function.

Macrophage metabolic adaptation to heme detoxification involves CO-dependent activation of the pentose phosphate pathway.

Heme is an essential cofactor for numerous cellular functions, but release of free heme during hemolysis results in oxidative tissue damage, vascular dysfunction, and inflammation. Macrophages play a key protective role in heme clearance; however, the mechanisms that regulate metabolic adaptations that are required for effective heme degradation remain unclear. Here we demonstrate that heme loading drives a unique bioenergetic switch in macrophages, which involves a metabolic shift from oxidative phosphorylation toward glucose consumption. Metabolomic and transcriptional analysis of heme-loaded macrophages revealed that glucose is funneled into the pentose phosphate pathway (PPP), which is indispensable for efficient heme detoxification and is required to maintain redox homeostasis. We demonstrate that the metabolic shift to the PPP is controlled by heme oxygenase-dependent generation of carbon monoxide (CO). Finally, we show that PPP upregulation occurs in vivo in organ systems central to heme clearance and that PPP activity correlates with heme levels in mouse sickle cell disease (SCD). Together, our findings demonstrate that metabolic adaptation to heme detoxification in macrophages requires a shift to the PPP that is induced by heme-derived CO, suggesting pharmacologic targeting of macrophage metabolism as a novel therapeutic strategy to improve heme clearance in patients with hemolytic disorders.

Loss of Endothelial FTO Antagonizes Obesity-Induced Metabolic and Vascular Dysfunction.

RATIONALE: Increasing prevalence of obesity and its associated risk with cardiovascular diseases demands a better understanding of the contribution of different cell types within this complex disease for developing new treatment options. Previous studies could prove a fundamental role of FTO (fat mass and obesity-associated protein) within obesity; however, its functional role within different cell types is less understood. OBJECTIVES: We identify endothelial FTO as a previously unknown central regulator of both obesity-induced metabolic and vascular alterations. METHODS AND RESULTS: We generated endothelial Fto-deficient mice and analyzed the impact of obesity on those mice. While the loss of endothelial FTO did not influence the development of obesity and dyslipidemia, it protected mice from high-fat diet-induced glucose intolerance and insulin resistance by increasing AKT (protein kinase B) phosphorylation in endothelial cells and skeletal muscle. Furthermore, loss of endothelial FTO prevented the development of obesity-induced hypertension by preserving myogenic tone in resistance arteries. In Fto-deficient arteries, microarray analysis identified upregulation of L-Pgds with significant increases in prostaglandin D2 levels. Blockade of prostaglandin D2 synthesis inhibited the myogenic tone protection in resistance arteries of endothelial Fto-deficient mice on high-fat diet; conversely, direct addition of prostaglandin D2 rescued myogenic tone in high-fat diet-fed control mice. Myogenic tone was increased in obese human arteries with FTO inhibitors or prostaglandin D2 application. CONCLUSIONS: These data identify endothelial FTO as a previously unknown regulator in the development of obesity-induced metabolic and vascular changes, which is independent of its known function in regulation of obesity.

Regioisomer-independent quantification of fatty acid oxidation products by HPLC-ESI-MS/MS analysis of sodium adducts.

Despite growing acknowledgement of the role of oxidized fatty acids (oxFA) as cellular signaling molecules and in the pathogenesis of disease, developing methods to measure these species in biological samples has proven challenging. Here we describe a novel method utilizing HPLC-ESI-MS/MS to identify and quantify multiple full-length oxFA species in a regioisomer-independent manner without the need for time-consuming sample preparation or derivatization. Building on recent progress in the characterization of FA and their oxidation products by MS/MS, we employed positive-ion ionization by measuring sodium adducts in conjunction with Differential Energy Qualifier Ion Monitoring to unequivocally verify the presence of the hydroperoxide, hydroxide, and ketone oxidation products of linoleic and arachidonic acid. Our HPLC method achieved separation of these oxidized species from their unoxidized counterparts while maintaining regioisomer-independent elution, allowing quantification over a 5 log10 range with a lower limit of quantification of 0.1 picomoles. With a simple sample preparation and a runtime as low as 11 minutes, our method allows the rapid and facile detection and measurement of full-length oxFA in biological samples. We believe this approach will allow for new insight and further investigation into the role of oxFA in metabolic disease.

Efferocytosis induces a novel SLC program to promote glucose uptake and lactate release.

Development and routine tissue homeostasis require a high turnover of apoptotic cells. These cells are removed by professional and non-professional phagocytes via efferocytosis1. How a phagocyte maintains its homeostasis while coordinating corpse uptake, processing ingested materials and secreting anti-inflammatory mediators is incompletely understood1,2. Here, using RNA sequencing to characterize the transcriptional program of phagocytes actively engulfing apoptotic cells, we identify a genetic signature involving 33 members of the solute carrier (SLC) family of membrane transport proteins, in which expression is specifically modulated during efferocytosis, but not during antibody-mediated phagocytosis. We assessed the functional relevance of these SLCs in efferocytic phagocytes and observed a robust induction of an aerobic glycolysis program, initiated by SLC2A1-mediated glucose uptake, with concurrent suppression of the oxidative phosphorylation program. The different steps of phagocytosis2-that is, 'smell' ('find-me' signals or sensing factors released by apoptotic cells), 'taste' (phagocyte-apoptotic cell contact) and 'ingestion' (corpse internalization)-activated distinct and overlapping sets of genes, including several SLC genes, to promote glycolysis. SLC16A1 was upregulated after corpse uptake, increasing the release of lactate, a natural by-product of aerobic glycolysis3. Whereas glycolysis within phagocytes contributed to actin polymerization and the continued uptake of corpses, lactate released via SLC16A1 promoted the establishment of an anti-inflammatory tissue environment. Collectively, these data reveal a SLC program that is activated during efferocytosis, identify a previously unknown reliance on aerobic glycolysis during apoptotic cell uptake and show that glycolytic by-products of efferocytosis can influence surrounding cells.

Macrophage phenotype and bioenergetics are controlled by oxidized phospholipids identified in lean and obese adipose tissue.

Adipose tissue macrophages (ATMs) adapt their metabolic phenotype either to maintain lean tissue homeostasis or drive inflammation and insulin resistance in obesity. However, the factors in the adipose tissue microenvironment that control ATM phenotypic polarization and bioenergetics remain unknown. We have recently shown that oxidized phospholipids (OxPL) uniquely regulate gene expression and cellular metabolism in Mox macrophages, but the presence of the Mox phenotype in adipose tissue has not been reported. Here we show, using extracellular flux analysis, that ATMs isolated from lean mice are metabolically inhibited. We identify a unique population of CX3CR1neg/F4/80low ATMs that resemble the Mox (Txnrd1+HO1+) phenotype to be the predominant ATM phenotype in lean adipose tissue. In contrast, ATMs isolated from obese mice had characteristics typical of the M1/M2 (CD11c+CD206+) phenotype with highly activated bioenergetics. Quantifying individual OxPL species in the stromal vascular fraction of murine adipose tissue, using targeted liquid chromatography-mass spectrometry, revealed that high fat diet-induced adipose tissue expansion led to a disproportional increase in full-length over truncated OxPL species. In vitro studies showed that macrophages respond to truncated OxPL species by suppressing bioenergetics and up-regulating antioxidant programs, mimicking the Mox phenotype of ATMs isolated from lean mice. Conversely, full-length OxPL species induce proinflammatory gene expression and an activated bioenergetic profile that mimics ATMs isolated from obese mice. Together, these data identify a redox-regulatory Mox macrophage phenotype to be predominant in lean adipose tissue and demonstrate that individual OxPL species that accumulate in adipose tissue instruct ATMs to adapt their phenotype and bioenergetic profile to either maintain redox homeostasis or to promote inflammation.

Novel Role of IL (Interleukin)-1ß in Neutrophil Extracellular Trap Formation and Abdominal Aortic Aneurysms.

OBJECTIVE: Neutrophils promote experimental abdominal aortic aneurysm (AAA) formation via a mechanism that is independent from MMPs (matrix metalloproteinases). Recently, we reported a dominant role of IL (interleukin)-1ß in the formation of murine experimental AAAs. Here, the hypothesis that IL-1ß-induced neutrophil extracellular trap formation (NETosis) promotes AAA was tested. APPROACH AND RESULTS: NETs were identified through colocalized staining of neutrophil, Cit-H3 (citrullinated histone H3), and DNA, using immunohistochemistry. NETs were detected in human AAAs and were colocalized with IL-1ß. In vitro, IL-1RA attenuated IL-1ß-induced NETosis in human neutrophils. Mechanistically, IL-1ß treatment of isolated neutrophils induced nuclear localization of ceramide synthase 6 and synthesis of C16-ceramide, which was inhibited by IL-1RA or fumonisin B1, an inhibitor of ceramide synthesis. Furthermore, IL-1RA or fumonisin B1 attenuated IL1-ß-induced NETosis. In an experimental model of murine AAA, NETs were detected at a very early stage-day 3 of aneurysm induction. IL-1ß-knockout mice demonstrated significantly lower infiltration of neutrophils to aorta and were protected from AAA. Adoptive transfer of wild-type neutrophils promoted AAA formation in IL-1ß-knockout mice. Moreover, treatment of wild-type mice with Cl-amidine, an inhibitor NETosis, significantly attenuated AAA formation, whereas, treatment with deoxyribonuclease, a DNA digesting enzyme, had no effect on AAA formation. CONCLUSIONS: Altogether, the results suggest a dominant role of IL-1ß-induced NETosis in AAA formation.

cGAS drives noncanonical-inflammasome activation in age-related macular degeneration.

Geographic atrophy is a blinding form of age-related macular degeneration characterized by retinal pigmented epithelium (RPE) death; the RPE also exhibits DICER1 deficiency, resultant accumulation of endogenous Alu-retroelement RNA, and NLRP3-inflammasome activation. How the inflammasome is activated in this untreatable disease is largely unknown. Here we demonstrate that RPE degeneration in human-cell-culture and mouse models is driven by a noncanonical-inflammasome pathway that activates caspase-4 (caspase-11 in mice) and caspase-1, and requires cyclic GMP-AMP synthase (cGAS)-dependent interferon-ß production and gasdermin D-dependent interleukin-18 secretion. Decreased DICER1 levels or Alu-RNA accumulation triggers cytosolic escape of mitochondrial DNA, which engages cGAS. Moreover, caspase-4, gasdermin D, interferon-ß, and cGAS levels were elevated in the RPE in human eyes with geographic atrophy. Collectively, these data highlight an unexpected role of cGAS in responding to mobile-element transcripts, reveal cGAS-driven interferon signaling as a conduit for mitochondrial-damage-induced inflammasome activation, expand the immune-sensing repertoire of cGAS and caspase-4 to noninfectious human disease, and identify new potential targets for treatment of a major cause of blindness.

Macrophages sensing oxidized DAMPs reprogram their metabolism to support redox homeostasis and inflammation through a TLR2-Syk-ceramide dependent mechanism.

OBJECTIVE: Macrophages control tissue homeostasis and inflammation by sensing and responding to environmental cues. However, the metabolic adaptation of macrophages to oxidative tissue damage and its translation into inflammatory mechanisms remains enigmatic. METHODS: Here we identify the critical regulatory pathways that are induced by endogenous oxidation-derived DAMPs (oxidized phospholipids, OxPL) in vitro, leading to formation of a unique redox-regulatory metabolic phenotype (Mox), which is strikingly different from conventional classical or alternative macrophage activation. RESULTS: Unexpectedly, metabolomic analyses demonstrated that Mox heavily rely on glucose metabolism and the pentose phosphate pathway (PPP) to support GSH production and Nrf2-dependent antioxidant gene expression. While the metabolic adaptation of macrophages to OxPL involved transient suppression of aerobic glycolysis, it also led to upregulation of inflammatory gene expression. In contrast to classically activated (M1) macrophages, Hif1α mediated expression of OxPL-induced Glut1 and VEGF but was dispensable for Il1ß expression. Mechanistically, we show that OxPL suppress mitochondrial respiration via TLR2-dependent ceramide production, redirecting TCA metabolites to GSH synthesis. Finally, we identify spleen tyrosine kinase (Syk) as a critical downstream signaling mediator that translates OxPL-induced effects into ceramide production and inflammatory gene regulation. CONCLUSIONS: Together, these data demonstrate the metabolic and bioenergetic requirements that enable macrophages to translate tissue oxidation status into either antioxidant or inflammatory responses via sensing OxPL. Targeting dysregulated redox homeostasis in macrophages could therefore lead to novel therapies to treat chronic inflammation.