Pirfenidone ameliorates pulmonary arterial pressure and neointimal remodeling in experimental pulmonary arterial hypertension by suppressing NLRP3 inflammasome activation

Pulmonary arterial hypertension (PAH) is a fatal disease characterized by increased pulmonary arterial pressure, inflammation, and neointimal remodeling of pulmonary arterioles. Serum levels of interleukin (IL)-1 beta and IL-18 are elevated in PAH patients and may enhance proinflammatory neointimal remodeling. NLRP3 inflammasome activation induces cleavage of the cytokines IL-1 beta and IL-18, required for their secretion. Pirfenidone (PFD), an antiflbrotic and anti-inflammatory drug, has been suggested to inhibit NLRP3 inflammasome activation. We hypothesized that PFD delays the progression of PAH by suppressing NLRP3 inflammasome activation. We assessed the effects of PFD treatment in a rat model for neointimal PAH induced by monocrotaline and aortocaval shunt using echocardiographic, hemodynamic, and vascular remodeling parameters. We measured inflammasome activation by NLRP3 immunostaining, Western blots for caspase-1, IL-1 beta and IL-18 cleavage, and macrophage IL-1 beta secretion. PFD treatment ameliorated pulmonary arterial pressure, pulmonary vascular resistance, and pulmonary vascular remodeling in PAH rats. In PAH rats, immunostaining of NLRP3 in pulmonary arterioles and caspase-1, IL-1 beta, and IL-18 cleavage in lung homogenates were increased compared to controls, reflecting NLRP3 inflammasome activation in vivo. PFD decreased IL-1 beta and IL-18 cleavage, as well as macrophage IL-1 beta secretion in vitro. Our studies show that PFD ameliorates pulmonary hemodynamics and vascular remodeling in experimental PAH. Although PFD did not affect all NLRP3 inflammasome parameters, it decreased IL-1 beta and IL-18 cleavage, the products of NLRP3 inflammasome activation that are key to its downstream effects. Our findings thus suggest a therapeutic benefit of PFD in PAH via suppression of NLRP3 inflammasome activation

Lymphatic vasculature mediates macrophage reverse cholesterol transport in mice

Reverse cholesterol transport (RCT) refers to the mobilization of cholesterol on HDL particles (HDL-C) from extravascular tissues to plasma, ultimately for fecal excretion. Little is known about how HDL-C leaves peripheral tissues to reach plasma. We first used 2 models of disrupted lymphatic drainage from skin — 1 surgical and the other genetic — to quantitatively track RCT following injection of [3H]-cholesterol–loaded macrophages upstream of blocked or absent lymphatic vessels. Macrophage RCT was markedly impaired in both models, even at sites with a leaky vasculature. Inhibited RCT was downstream of cholesterol efflux from macrophages, since macrophage efflux of a fluorescent cholesterol analog (BODIPY-cholesterol) was not altered by impaired lymphatic drainage. We next addressed whether RCT was mediated by lymphatic vessels from the aortic wall by loading the aortae of donor atherosclerotic Apoe-deficient mice with [2H]6-labeled cholesterol and surgically transplanting these aortae into recipient Apoe-deficient mice that were treated with anti-VEGFR3 antibody to block lymphatic regrowth or with control antibody to allow such regrowth. [2H]-Cholesterol was retained in aortae of anti–VEGFR3-treated mice. Thus, the lymphatic vessel route is critical for RCT from multiple tissues, including the aortic wall. These results suggest that supporting lymphatic transport function may facilitate cholesterol clearance in therapies aimed at reversing atherosclerosis

Cholesteryl ester transfer protein decreases high-density lipoprotein and severely aggravates atherosclerosis in APOE*3-Leiden mice

OBJECTIVE - The role of cholesteryl ester transfer protein (CETP) in the development of atherosclerosis is still undergoing debate. Therefore, we evaluated the effect of human CETP expression on atherosclerosis in APOE*3-Leiden (E3L) mice with a humanized lipoprotein profile. METHODS AND RESULTS - E3L mice were crossbred with human CETP transgenic mice. On a chow diet, CETP expression increased plasma total cholesterol (TC) (+43%; P<0.05). To evaluate the effects of CETP on the development of atherosclerosis, mice were fed a Western-type diet containing 0.25% cholesterol, leading to 4.3-fold elevated TC levels in both E3L and CETP.E3L mice (P<0.01). On both diets, CETP expression shifted the distribution of cholesterol from high-density lipoprotein (HDL) toward very-low-density lipoprotein (VLDL)/low-density lipoprotein (LDL). Moreover, plasma of CETP.E3L mice had reduced capacity (-3

Increased atherosclerosis in a mouse model of glycogen storage disease type 1a

Glycogen storage disease type 1a (GSD Ia) is an inborn error of carbohydrate metabolism. Despite severe hyperlipidemia, GSD Ia patients show limited atherogenesis compared to age-and-gender matched controls. Employing a GSD Ia mouse model that resembles the severe hyperlipidemia in patients, we here found increased atherogenesis in GSD Ia. These data provide a rationale for investigating atherogenesis in GSD Ia in a larger patient cohort.</p

Hepatocyte-specific glucose-6-phosphatase deficiency disturbs platelet aggregation and decreases blood monocytes upon fasting-induced hypoglycemia

International audienceObjective: Glycogen storage disease type 1a (GSD Ia) is a rare inherited metabolic disorder caused by mutations in the glucose-6-phosphatase (G6PC1) gene. When untreated, GSD Ia leads to severe fasting-induced hypoglycemia. Although current intensive dietary management aims to prevent hypoglycemia, patients still experience hypoglycemic events. Poor glycemic control in GSD Ia is associated with hypertriglyceridemia, hepatocellular adenoma and carcinoma, and also with an increased bleeding tendency of unknown origin.Methods: To evaluate the effect of glycemic control on leukocyte levels and coagulation in GSD Ia, we employed hepatocyte-specific G6pc1 deficient (L-G6pc-/-) mice under fed or fasted conditions, to match good or poor glycemic control in GSD Ia, respectively.Results: We found that fasting-induced hypoglycemia in L-G6pc-/- mice decreased blood leukocytes, specifically pro-inflammatory Ly6Chi monocytes, compared to controls. Refeeding reversed this decrease. The decrease in Ly6Chi monocytes was accompanied by an increase in plasma corticosterone levels and was prevented by the glucocorticoid receptor antagonist mifepristone. Further, fasting-induced hypoglycemia in L-G6pc-/- mice prolonged bleeding time in the tail vein bleeding assay, with reversal by refeeding. This could not be explained by changes in coagulation factors V, VII, or VIII, or von Willebrand factor. While the prothrombin and activated partial thromboplastin time, as well as total platelet counts were not affected by fasting-induced hypoglycemia in L-G6pc-/- mice, ADP-induced platelet aggregation was disturbed.Conclusions: These studies reveal a relationship between fasting-induced hypoglycemia, decreased blood monocytes, and disturbed platelet aggregation in L-G6pc-/- mice. While disturbed platelet aggregation likely accounts for the bleeding phenotype in GSD Ia, elevated plasma corticosterone decreases levels of pro-inflammatory monocytes. These studies highlight the necessity of maintaining good glycemic control in GSD Ia

Liver X receptors are required for thymic resilience and T cell output

The thymus is a primary lymphoid organ necessary for optimal T cell development. Here, we show that liver X receptors (LXRs)-a class of nuclear receptors and transcription factors with diverse functions in metabolism and immunity-critically contribute to thymic integrity and function. LXRαβ-deficient mice develop a fatty, rapidly involuting thymus and acquire a shrunken and prematurely immunoinhibitory peripheral T cell repertoire. LXRαβ's functions are cell specific, and the resulting phenotypes are mutually independent. Although thymic macrophages require LXRαβ for cholesterol efflux, thymic epithelial cells (TECs) use LXRαβ for self-renewal and thymocytes for negative selection. Consequently, TEC-derived LXRαβ protects against homeostatic premature involution and orchestrates thymic regeneration following stress, while thymocyte-derived LXRαβ limits cell disposal during negative selection and confers heightened sensitivity to experimental autoimmune encephalomyelitis. These results identify three distinct but complementary mechanisms by which LXRαβ governs T lymphocyte education and illuminate LXRαβ's indispensable roles in adaptive immunity

T cell cholesterol efflux suppresses apoptosis and senescence and increases atherosclerosis in middle aged mice

Atherosclerosis is a chronic inflammatory disease driven by hypercholesterolemia. During aging, T cells accumulate cholesterol, potentially affecting inflammation. However, the effect of cholesterol efflux pathways mediated by ATP-binding cassette A1 and G1 (ABCA1/ABCG1) on T cell-dependent age-related inflammation and atherosclerosis remains poorly understood. In this study, we generate mice with T cell-specific Abca1/Abcg1-deficiency on the low-density-lipoprotein-receptor deficient (Ldlr-/-) background. T cell Abca1/Abcg1-deficiency decreases blood, lymph node, and splenic T cells, and increases T cell activation and apoptosis. T cell Abca1/Abcg1-deficiency induces a premature T cell aging phenotype in middle-aged (12-13 months) Ldlr-/- mice, reflected by upregulation of senescence markers. Despite T cell senescence and enhanced T cell activation, T cell Abca1/Abcg1-deficiency decreases atherosclerosis and aortic inflammation in middle-aged Ldlr-/- mice, accompanied by decreased T cells in atherosclerotic plaques. We attribute these effects to T cell apoptosis downstream of T cell activation, compromising T cell functionality. Collectively, we show that T cell cholesterol efflux pathways suppress T cell apoptosis and senescence, and induce atherosclerosis in middle-aged Ldlr-/- mice

Myeloid cells regulate plasma LDL-cholesterol levels

Purpose of review Leukocytosis, elevated blood leukocyte levels, is associated with enhanced cardiovascular risk in humans. Hematopoietic stem and progenitor cells (HSPCs) drive leukocyte production in a process called hematopoiesis, which mainly occurs in the bone marrow, and under certain conditions also in other organs such as the spleen. Cholesterol accumulation in HSPCs enhances hematopoiesis, increasing levels of blood monocytes that infiltrate into atherosclerotic plaques. Although HSPC proliferation and monocytosis enhance atherogenesis in several studies, concomitant decreases in LDL-cholesterol levels have also been reported, associated with anti-atherogenic effects. This review focuses on the link between HSPC proliferation, leukocytosis, plasma LDL-cholesterol levels, and atherogenesis. Recent findings Recent studies have shown that an acute infection enhances cholesterol accumulation in HSPCs, driving HSPC proliferation, and leading to the expansion of myeloid cells (monocytes, neutrophils, and macrophages). Enhanced hematopoiesis is associated with low plasma LDL-cholesterol levels in animal models and humans, probably because of the increased number of myeloid cells that take up LDL-cholesterol. Despite low-plasma LDL-cholesterol levels, specific patient populations with enhanced hematopoiesis show increased cardiovascular risk. Summary Enhanced hematopoiesis and monocytosis may accelerate atherogenesis. Studies on these processes may lead to the identification of new therapeutic targets for cardiovascular diseases

Increased Systemic and Plaque Inflammation in ABCA1 Mutation Carriers With Attenuation by Statins

We previously demonstrated that subjects with functional ATP-binding cassette (ABC) A1 mutations have increased atherosclerosis, which has been attributed to the role of ABCA1 in reverse cholesterol transport. More recently, a proinflammatory effect of Abca1 deficiency was shown in mice, potentially contributing to atherogenesis. In this study, we investigated whether ABCA1 deficiency was associated with proinflammatory changes in humans. Thirty-one heterozygous, 5 homozygous ABCA1 mutation carriers, and 21 matched controls were studied. (18)Fluorodeoxyglucose positron emission tomography with computed tomographic scanning was performed in a subset of carriers and controls to assess arterial wall inflammation (target:background ratio). Heterozygous ABCA1 mutation carriers had a 20% higher target:background ratio than in controls (target:background ratio; P=0.008). In carriers using statins (n=7), target:background ratio was 21% reduced than in nonstatin users (n=7; P=0.03). We then measured plasma cytokine levels. Tumor necrosis factor α, monocyte chemoattractant protein-1, and interleukin-6 levels were increased in heterozygous and homozygous ABCA1 mutation carriers. We isolated monocytes from carriers and controls and measured inflammatory gene expression. Only TNFα mRNA was increased in monocytes from heterozygous ABCA1 mutation carriers. Additional studies in THP-1 macrophages showed that both ABCA1 deficiency and lipoprotein-deficient plasma from ABCA1 mutation carriers increased inflammatory gene expression. Our data suggest a proinflammatory state in ABCA1 mutation carriers as reflected by an increased positron emission tomography-MRI signal in nonstatin using subjects, and increased circulating cytokines. The increased inflammation in ABCA1 mutation carriers seems to be attenuated by statin