Rip2 deficiency leads to increased atherosclerosis despite decreased inflammation

The Role of Cdc42 in the Insulin and Leptin Pathways Contributing to the Development of Age-Related Obesity

Age-related obesity significantly increases the risk of chronic diseases such as type 2 diabetes, cardiovascular diseases, hypertension, and certain cancers. The insulin-leptin axis is crucial in understanding metabolic disturbances associated with age-related obesity. Rho GTPase Cdc42 is a member of the Rho family of GTPases that participates in many cellular processes including, but not limited to, regulation of actin cytoskeleton, vesicle trafficking, cell polarity, morphology, proliferation, motility, and migration. Cdc42 functions as an integral part of regulating insulin secretion and aging. Some novel roles for Cdc42 have also been recently identified in maintaining glucose metabolism, where Cdc42 is involved in controlling blood glucose levels in metabolically active tissues, including skeletal muscle, adipose tissue, pancreas, etc., which puts this protein in line with other critical regulators of glucose metabolism. Importantly, Cdc42 plays a vital role in cellular processes associated with the insulin and leptin signaling pathways, which are integral elements involved in obesity development if misregulated. Additionally, a change in Cdc42 activity may affect senescence, thus contributing to disorders associated with aging. This review explores the complex relationships among age-associated obesity, the insulin-leptin axis, and the Cdc42 signaling pathway. This article sheds light on the vast molecular web that supports metabolic dysregulation in aging people. In addition, it also discusses the potential therapeutic implications of the Cdc42 pathway to mitigate obesity since some new data suggest that inhibition of Cdc42 using antidiabetic drugs or antioxidants may promote weight loss in overweight or obese patients.

RIP2 Knockdown Attenuates Vascular Smooth Muscle Cells Activation via Negative Regulating Myocardin Expression

BACKGROUND

RIP2 is an adaptor protein contributing to the activation of nuclear factor-κB induced by TNF receptor-associated factor (TRAF) and nucleotide oligomerization domain (NOD)-dependent signaling implicated in innate and adaptive immune response. Beyond regulation of immunity, we aimed to elucidate the role of RIP2 in vascular smooth muscle cell (VSMC) phenotypic modulation.

METHODS AND RESULTS

In the current study, we observed that RIP2 showed an increased expression in VSMCs with PDGF-BB stimulation in a dose-dependent manner. Knockdown of RIP2 expression mediated by adenovirus dramatically accelerated the expression of VSMC-specific differentiation genes induced by PDGF-BB. Silencing of RIP2 inhibited proliferative and migratory ability of VSMCs. Additionally, we demonstrated that RIP2 knockdown can promoted myocardin expression. Furthermore, RIP2 inhibition also can attenuate the formation of intimal hyperplasia.

CONCLUSIONS

These findings suggested that RIP2 played an important role in regulation of VSMCs differentiation, migration, and proliferation that may due to affect myocardin expression. Our results indicated that RIP2 may be a novel therapeutic target for intimal hyperplasia.

Assessment and management of the heightened risk for atherosclerotic cardiovascular events in patients with lupus erythematosus or dermatomyositis

For patients with lupus erythematosus (LE) or dermatomyositis (DM), there is an urgent need to address a heightened risk of clinical events, chiefly heart attacks and strokes, caused by atherosclerotic cardiovascular disease (ASCVD). Patients with LE or DM frequently exhibit high levels of conventional risk factors for ASCVD events, particularly dyslipoproteinemia and hypertension; an amplified burden of atherosclerotic plaques; and increased age- and sex-adjusted rates of ASCVD events compared with the general population. The rate of ASCVD events exceeds what would be expected from conventional risk factors, suggesting that disease-specific autoimmune processes exacerbate specific, known pathogenic steps in atherosclerosis. Importantly, despite their heightened risk, patients with LE or DM are often undertreated for known causative agents and exacerbators of ASCVD. Herein, we propose an approach to assess and manage the heightened risk of ASCVD events in patients with LE or DM. Our approach is modeled in large part on established approaches to patients with diabetes mellitus or stage 3 or 4 chronic kidney disease, which are well-studied conditions that also show heightened risk for ASCVD events and have been explicitly incorporated into standard clinical guidelines for ASCVD. Based on the available evidence, we conclude that patients with LE or DM require earlier and more aggressive screening and management of ASCVD. We suggest that physicians consider implementing multipliers of conventional risk calculators to trigger earlier initiation of lifestyle modifications and medical therapies in primary prevention of ASCVD events, employ vascular imaging to quantify the burden of subclinical plaques, and treat to lower lipid targets using statins and newer therapies, such as PCSK9 inhibitors, that decrease ASCVD events in nonautoimmune cohorts. More clinical vigilance is needed regarding surveillance, prevention, risk modification, and treatment of dyslipidemias, hypertension, and smoking in patients with LE or DM. All of these goals are achievable.

Gut microbiota-based vaccination engages innate immunity to improve blood glucose control in obese mice

Objective

Obesity and diabetes increase circulating levels of microbial components derived from the gut microbiota. Individual bacterial factors (i.e., postbiotics) can have opposing effects on blood glucose.

Methods

We tested the net effect of gut bacterial extracts on blood glucose in mice using a microbiota-based vaccination strategy.

Results

Male and female mice had improved glucose and insulin tolerance five weeks after a single subcutaneous injection of a specific dose of a bacterial extract obtained from the luminal contents of the upper small intestine (SI), lower SI, or cecum. Injection of mice with intestinal extracts from germ-free mice revealed that bacteria were required for a microbiota-based vaccination to improve blood glucose control. Vaccination of Nod1^−/−, Nod2^−/−, and Ripk2^−/− mice showed that each of these innate immune proteins was required for bacterial extract injection to improve blood glucose control. A microbiota-based vaccination promoted an immunoglobulin-G (IgG) response directed against bacterial extract antigens, where subcutaneous injection of mice with the luminal contents of the lower SI elicited a bacterial extract-specific IgG response that is compartmentalized to the lower SI of vaccinated mice. A microbiota-based vaccination was associated with an altered microbiota composition in the lower SI and colon of mice. Lean mice only required a single injection of small intestinal-derived bacterial extract, but high fat diet (HFD)-fed, obese mice required prime-boost bacterial extract injections for improvements in blood glucose control.

Conclusions

Subversion of the gut barrier by vaccination with a microbiota-based extract engages innate immunity to promote long-lasting improvements in blood glucose control in a dose-dependent manner.

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Subcutaneous injection of gut bacterial extracts improved blood glucose control in mice.

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Microbiota-based vaccination engaged NOD1-NOD2-RIPK2 to alter blood glucose.

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Microbiota-based vaccination promoted a proximal gut IgG response.

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Microbiota-based vaccination altered the composition of the gut microbiome.

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Obese mice required prime-boost injections to improve blood glucose control.

RIPK1 Expression Associates With Inflammation in Early Atherosclerosis in Humans and Can Be Therapeutically Silenced to Reduce NF-κB Activation and Atherogenesis in Mice

BACKGROUND

Chronic activation of the innate immune system drives inflammation and contributes directly to atherosclerosis. We previously showed that macrophages in the atherogenic plaque undergo RIPK3 (receptor-interacting serine/threonine-protein kinase 3)-MLKL (mixed lineage kinase domain-like protein)-dependent programmed necroptosis in response to sterile ligands such as oxidized low-density lipoprotein and damage-associated molecular patterns and that necroptosis is active in advanced atherosclerotic plaques. Upstream of the RIPK3-MLKL necroptotic machinery lies RIPK1 (receptor-interacting serine/threonine-protein kinase 1), which acts as a master switch that controls whether the cell undergoes NF-κB (nuclear factor κ-light-chain-enhancer of activated B cells)-dependent inflammation, caspase-dependent apoptosis, or necroptosis in response to extracellular stimuli. We therefore set out to investigate the role of RIPK1 in the development of atherosclerosis, which is driven largely by NF-κB-dependent inflammation at early stages. We hypothesize that, unlike RIPK3 and MLKL, RIPK1 primarily drives NF-κB-dependent inflammation in early atherogenic lesions, and knocking down RIPK1 will reduce inflammatory cell activation and protect against the progression of atherosclerosis.

METHODS

We examined expression of RIPK1 protein and mRNA in both human and mouse atherosclerotic lesions, and used loss-of-function approaches in vitro in macrophages and endothelial cells to measure inflammatory responses. We administered weekly injections of RIPK1 antisense oligonucleotides to Apoe^-/- mice fed a cholesterol-rich (Western) diet for 8 weeks.

RESULTS

We find that RIPK1 expression is abundant in early-stage atherosclerotic lesions in both humans and mice. Treatment with RIPK1 antisense oligonucleotides led to a reduction in aortic sinus and en face lesion areas (47.2% or 58.8% decrease relative to control, P<0.01) and plasma inflammatory cytokines (IL-1α [interleukin 1α], IL-17A [interleukin 17A], P<0.05) in comparison with controls. RIPK1 knockdown in macrophages decreased inflammatory genes (NF-κB, TNFα [tumor necrosis factor α], IL-1α) and in vivo lipopolysaccharide- and atherogenic diet-induced NF-κB activation. In endothelial cells, knockdown of RIPK1 prevented NF-κB translocation to the nucleus in response to TNFα, where accordingly there was a reduction in gene expression of IL1B, E-selectin, and monocyte attachment.

CONCLUSIONS

We identify RIPK1 as a central driver of inflammation in atherosclerosis by its ability to activate the NF-κB pathway and promote inflammatory cytokine release. Given the high levels of RIPK1 expression in human atherosclerotic lesions, our study suggests RIPK1 as a future therapeutic target to reduce residual inflammation in patients at high risk of coronary artery disease.

CARD9 mediates T cell inflammatory response in Coxsackievirus B3-induced acute myocarditis

Cardiac inflammation in Coxsackievirus B3 (CVB3)-induced myocarditis is a consequence of viral-related cardiac injury and immune response. Caspase-associated recruitment domain 9 (CARD9) is a critical adaptor protein involved in transduction of signals from various innate pattern recognition receptors. In this study, the role of CARD9 in acute viral myocarditis was evaluated. CARD9^-/- and C57BL/6 mice were infected with CVB3. On day 7 postinfection, myocardial tissue and blood samples were collected and examined. After CARD9 knockout, mRNA and protein levels of transforming growth factor-β(TGF-β), interleukin-17A(IL-17A), and CARD domain of B-cell CLL/lymphoma 10(BCL-10) in the myocardium were markedly lower in CARD9^-/- mice than in C57BL/6 mice with CVB3-induced viral myocarditis. This trend was similar for the pathological scores for inflammation and serum levels of cytokines interleukin-6(IL-6), interleukin-10(IL-10), interferon -γ(IFN-γ), TGF-β, and IL-17A. These results suggest that the CARD9-mediated secretion of pro-inflammatory cytokines plays an important role in the immune response to acute viral myocarditis.

Receptor-interacting protein kinase 2 (RIPK2) and nucleotide-binding oligomerization domain (NOD) cell signaling inhibitors based on a 3,5-diphenyl-2-aminopyridine scaffold

Receptor-interacting protein kinase 2 (RIPK2) is a key mediator of nucleotide-binding oligomerization domain (NOD) cell signaling that has been implicated in various chronic inflammatory conditions. A new class of RIPK2 kinase/NOD signaling inhibitors based on a 3,5-diphenyl-2-aminopyridine scaffold was developed. Several co-crystal structures of RIPK2•inhibitor complexes were analyzed to provide insights into inhibitor selectivity versus the structurally related activin receptor-like kinase 2 (ALK2) demonstrating that the inhibitor sits deeper in the hydrophobic binding pocket of RIPK2 perturbing the orientation of the DFG motif. In addition, the structure-activity relationship study revealed that in addition to anchoring to the hinge and DFG via the 2-aminopyridine and 3-phenylsulfonamide, respectively, appropriate occupancy of the region between the gatekeeper and the αC-helix provided by substituents in the 4- and 5-positions of the 3-phenylsulfonamide were necessary to achieve potent NOD cell signaling inhibition. For example, compound 18t (e.g. CSLP37) displayed potent biochemical RIPK2 kinase inhibition (IC₅₀ = 16 ± 5 nM), >20-fold selectivity versus ALK2 and potent NOD cell signaling inhibition (IC₅₀ = 26 ± 4 nM) in the HEKBlue assay. Finally, in vitro ADME and pharmacokinetic characterization of 18t further supports the prospects of the 3,5-diphenyl-2-aminopyridine scaffold for the generation of in vivo pharmacology probes of RIPK2 kinase and NOD cell signaling functions.

CARD9 promotes autophagy in cardiomyocytes in myocardial ischemia/reperfusion injury via interacting with Rubicon directly

Autophagy in cardiomyocyte is involved in myocardial ischemia/reperfusion (M-I/R) injury. Caspase recruitment domain-containing protein 9 (CARD9) plays a critical role in cardiovascular diseases (CVDs) such as hypertension and cardiac fibrosis. However, its role in autophagy following M-I/R injury is yet to be fully elucidated. Here, we found that CARD9 expression increased in M-I/R mouse hearts, and in H9c2 or neonatal rat ventricular myocytes (NRVMs) in response to hypoxia/reoxygenation (H/R) or H₂O₂. CARD9^-/- mice exhibited a significant cardiac dysfunction following M-I/R injury (30 min of left ascending coronary (LAD) ischemia and 12 h of reperfusion) compared to wild-type (WT) mice. CARD9 deletion impaired autophagy during M-I/R in vivo and in vitro, evidenced by decrease of microtubule-associated protein 1 light chain 3 (LC3) lipidation and p62 accumulation. Conversely, CARD9 overexpression increased autophagic flux as indicated by enhanced expression of LC3 II/LC3 I and a reduction in p62. The protective effect of CARD9 on cardiomyocytes against H/R-induced oxidative stress was abolished by treatment with autophagy inhibitors, 3-methyladenine (3-MA) or Bafilomycin A1(BafA1). CARD9 interacted with RUN domain Beclin-1-interacting cysteine-rich-containing (Rubicon), a negative regulator of autophagy, and enhanced UV-irradiation-resistance-associated gene (UVRAG)-Beclin1-phosphatidylinositol 3-kinase catalytic subunit type 3 (PI3KC3) interaction and UVRAG-Vps16-mediated Rab7 activation to promote autophagosome formation, maturation, and endocytosis. Ablation of Rubicon by siRNA effectively prevented the detrimental effect of CARD9 knockdown on cardiomyocytes. These results suggest that CARD9 has protective effects on the myocardium against M-I/R injury by activating autophagy and restoring autophagic flux in vivo and in vitro.

CARD9 inhibits mitochondria-dependent apoptosis of cardiomyocytes under oxidative stress via interacting with Apaf-1

Cardiomyocyte apoptosis is known to contribute to myocardial ischemia/reperfusion (I/R) injury. Caspase recruitment domain-containing protein 9 (CARD9) play a role in cardiac fibrosis and dysfunction. However, the role of CARD9 in apoptosis of cardiomyocytes in myocardial I/R injury and its underlying mechanisms are still unclear. In this study, CARD9 expression was found to increase in H9c2 cells in response to hydrogen peroxide. Loss of CARD9 significantly increased caspase-3 activation and cardiomyocyte death following oxidative stress in vitro. Conversely, CARD9 overexpression decreased apoptosis as evidenced by a reduction in caspase-3 activation and the apoptotic rate. The caspase recruitment domain (CARD) of CARD9 was necessary for the protective effect of CARD9 against oxidative stress in cardiomyocytes. CARD9 suppressed the activation of caspase-9 by interacting with Apaf-1 via its CARD domain in H9c2 cells exposed to H₂O₂. Ablation of caspase-9 activity by z-lehd-fmk effectively prevented the detrimental effect of CARD9 deficiency on cardiomyocytes. Wild-type (WT) and CARD9^-/- mice were subjected to 30 min of left ascending coronary (LAD) ischemia and 12 h of reperfusion. TdT-mediated dUTP nick end labeling (TUNEL) staining analysis showed that CARD9^-/- mice exhibited a significantly higher number of apoptotic-positive cells after myocardial I/R injury than the WT mice. These results suggest that CARD9 protects cardiomyocytes from apoptosis by interacting with Apaf-1 and interfering with apoptosome formation following myocardial I/R injury in vivo and in vitro.

RIPK2-Mediated Autophagy and Negatively Regulated ROS-NLRP3 Inflammasome Signaling in GMCs Stimulated with High Glucose

Background

Hyperglycemia plays a vital role in diabetic nephropathy (DN); autophagy and its potential upregulator receptor-interacting protein kinase 2 (RIPK2) are associated with ROS, which play a potential role in regulating NLRP3, and may be involved in inflammation in DN.

Aim

In this study, we aimed to explore the mechanisms mediated by RIPK2 in autophagy and the relationship with ROS-NLRP3 of DN, by investigating the levels of RIPK2 and autophagy in glomerular mesangial cells (GMCs) stimulated with high glucose.

Material and Methods

GMCs were divided into the following groups: normal group (NC), high glucose group (HG), and RIPK2 siRNA group. RIPK2, LC3, caspase1, and IL-1β levels were measured by western blotting and RT-PCR. Autophagosomes were measured by GFP-RFP-LC3; ROS were detected by DCFH-DA.

Results

High glucose upregulated RIPK2 and LC3 in GMCs during short periods (0-12 h) (p < 0.01), while RIPK2 and LC3 were significantly downregulated in the long term (12-72 h) (p < 0.01); these changes were positively correlated with glucose concentration (p < 0.01). In addition, levels of ROS, caspase1, and IL-1β increased in a time- and dose-dependent manner in the high glucose group, even with an increased expression of LC3 (p < 0.01). However, LC3 expression decreased in the siRIPK2 group, while levels of ROS, caspase1, and IL-1β increased (p < 0.01).

Conclusions

Autophagy was activated by high glucose at short time periods but was inhibited in the long term, demonstrating a dual role for high glucose in autophagy of GMCs. RIPK2 regulates ROS-NLRP3 inflammasome signaling through autophagy and may be involved in the pathogenesis of DN.

T-Cell-Intrinsic Receptor Interacting Protein 2 Regulates Pathogenic T Helper 17 Cell Differentiation

Receptor interacting protein 2 (RIP2) plays a role in sensing intracellular pathogens, but its function in T cells is unclear. We show that RIP2 deficiency in CD4+ T cells resulted in chronic and severe interleukin-17A-mediated inflammation during Chlamydia pneumoniae lung infection, increased T helper 17 (Th17) cell formation in lungs of infected mice, accelerated atherosclerosis, and more severe experimental autoimmune encephalomyelitis. While RIP2 deficiency resulted in reduced conventional Th17 cell differentiation, it led to significantly enhanced differentiation of pathogenic (p)Th17 cells, which was dependent on RORα transcription factor and interleukin-1 but independent of nucleotide oligomerization domain (NOD) 1 and 2. Overexpression of RIP2 resulted in suppression of pTh17 cell differentiation, an effect mediated by its CARD domain, and phenocopied by a cell-permeable RIP2 CARD peptide. Our data suggest that RIP2 has a T cell-intrinsic role in determining the balance between homeostatic and pathogenic Th17 cell responses.

Vimentin deficiency in macrophages induces increased oxidative stress and vascular inflammation but attenuates atherosclerosis in mice

The aim was to clarify the role of vimentin, an intermediate filament protein abundantly expressed in activated macrophages and foam cells, in macrophages during atherogenesis. Global gene expression, lipid uptake, ROS, and inflammation were analyzed in bone-marrow derived macrophages from vimentin-deficient (Vim-/-) and wild-type (Vim+/+) mice. Atherosclerosis was induced in Ldlr-/- mice transplanted with Vim-/- and Vim+/+ bone marrow, and in Vim-/- and Vim+/+ mice injected with a PCSK9 gain-of-function virus. The mice were fed an atherogenic diet for 12-15 weeks. We observed impaired uptake of native LDL but increased uptake of oxLDL in Vim-/- macrophages. FACS analysis revealed increased surface expression of the scavenger receptor CD36 on Vim-/- macrophages. Vim-/- macrophages also displayed increased markers of oxidative stress, activity of the transcription factor NF-κB, secretion of proinflammatory cytokines and GLUT1-mediated glucose uptake. Vim-/- mice displayed decreased atherogenesis despite increased vascular inflammation and increased CD36 expression on macrophages in two mouse models of atherosclerosis. We demonstrate that vimentin has a strong suppressive effect on oxidative stress and that Vim-/- mice display increased vascular inflammation with increased CD36 expression on macrophages despite decreased subendothelial lipid accumulation. Thus, vimentin has a key role in regulating inflammation in macrophages during atherogenesis.

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. We now report that Akt3 constitutively suppresses macropinocytosis in macrophages through a novel WNK1/SGK1/Cdc42 pathway. Mechanistic studies have demonstrated that the lack of Akt3 expression in murine and human macrophages results in increased expression of with-no-lysine kinase 1 (WNK1), which, in turn, leads to increased activity of serum and glucocorticoid-inducible kinase 1 (SGK1). SGK1 promotes expression of the Rho family GTPase Cdc42, a positive regulator of actin assembly, cell polarization, and pinocytosis. Individual suppression of WNK1 expression, SGK1, or Cdc42 activity in Akt3-deficient macrophages rescued the phenotype. These results demonstrate that Akt3 is a specific negative regulator of macropinocytosis in macrophages.

Receptor-interacting protein 2 (RIP2) gene polymorphisms are associated with increased risk of subclinical atherosclerosis and clinical and metabolic parameters. The Genetics of Atherosclerotic Disease (GEA) Mexican study

The receptor-interacting protein 2 (Rip2) is a serine/threonine kinase involved in multiple nuclear factor-κB (NFκB) activation pathways and is a key regulator of cellular lipid metabolism and cardiovascular disease. The aim of the present study was to evaluate the role of RIP2 gene polymorphisms as susceptibility markers for subclinical atherosclerosis (SA). Using an informatics analysis, four RIP2 gene polymorphisms with predicted functional effects (rs2293808, rs43133, rs431264, and rs16900627) were selected. The polymorphisms were genotyped in 405 individuals with SA (calcium score>0 assessed by computed tomography) and 1099 controls (calcium score=0). Clinical, anthropometric, tomographic and biochemical traits were measured. The association between the RIP2 polymorphisms and SA was evaluated using logistic regression analyses. Pair wise linkage disequilibrium (LD, D') estimations between polymorphisms and haplotype reconstruction were performed with Haploview version 4:1. Under different models adjusted by age, gender, body mass index, hypertension, diabetes mellitus, smoking habit, total cholesterol, HDL-cholesterol, LDL-cholesterol and triglyceride levels, rs43133 (OR=1.43, 95% CI: 1.05-1.94, P=0.022), and rs16900627 (OR=1.59, 95% CI: 1.00-2.54, P_dom=0.048 and OR=1.60, 95% CI: 1.05-2.54, P_add=0.028) were associated with increased risk of developing SA. Moreover, rs2293808, and rs431264 were associated with clinical or metabolic parameters in SA individuals and in healthy controls. The four polymorphisms were in high linkage disequilibrium and the GAAG haplotype was associated with increased risk of developing SA (OR=1.47, P=0.027). This study shows for the first time, that RIP2 polymorphisms are associated with increased risk of SA and with some clinical and metabolic parameters.

CARD9 as a potential target in cardiovascular disease

Systemic inflammation and localized macrophage infiltration have been implicated in cardiovascular pathologies, including coronary artery disease, carotid atherosclerosis, heart failure, obesity-associated heart dysfunction, and cardiac fibrosis. Inflammation induces macrophage infiltration and activation and release of cytokines and chemokines, causing tissue dysfunction by instigating a positive feedback loop that further propagates inflammation. Cytosolic adaptor caspase recruitment domain family, member 9 (CARD9) is a protein expressed primarily by dendritic cells, neutrophils, and macrophages, in which it mediates cytokine secretion. The purpose of this review is to highlight the role of CARD9 as a potential target in inflammation-related cardiovascular pathologies.

Regulatory role of CARD3 in left ventricular remodelling and dysfunction after myocardial infarction

Caspase activation and recruitment domain 3 (CARD3) is a caspase recruitment domain (CARD)-containing serine/threonine kinase and plays a pivotal role in apoptosis, immunity, tissue development and proliferation. To date, the causal relationship between CARD3 and myocardial infarction (MI) remains largely unexplored. This study aimed to identify the functional significance of CARD3 in the regulation of cardiac remodelling after MI and the underlying mechanisms of its effects. The levels of CARD3 expression were up-regulated in failing human and mouse post-infarction hearts. In addition, CARD3-knockout (KO) mice and transgenic mice overexpressing CARD3 in the heart were then generated and subjected to MI. Compared with wild-type (WT) control mice, CARD3-KO mice developed smaller infarct sizes, improved survival rates, and preserved left ventricle (LV) function after MI. Significantly, CARD3-KO hearts had less cardiomyocyte apoptosis and inflammatory cell infiltration in the infarct border zone. Attenuated LV remodelling was also observed in the KO hearts following MI, with reduced cardiac hypertrophy and fibrosis. Conversely, CARD3 overexpression resulted in the opposite MI-induced phenotype. Similar results were observed in ex vivo-cultured neonatal rat cardiomyocytes exposed to hypoxia. Mechanistically, we discovered that the CARD3-mediated detrimental effects of MI were associated with the activation of the NF-κB and p38 signalling cascades. Taken together, these data demonstrate that CARD3 serves as a novel positive modulator of ventricular remodelling after MI via the regulation of the NF-κB and p38 signalling. Thus, CARD3 may be a promising therapeutic target for the treatment of heart failure after MI.

HMGB1 release triggered by the interaction of live retinal cells and uveitogenic T cells is Fas/FasL activation-dependent

Background

It is not clear how invading autoreactive T cells initiate the pathogenic process inside the diseased organ in T cell-mediated organ-specific autoimmune disease. In experimental autoimmune uveitis (EAU) induced by adoptive transfer of interphotoreceptor retinoid-binding protein (IRBP)-specific T cells in mice, we have previously reported that intraocular inflammation was initiated by infiltrating IRBP-specific T cells that directly interacted with retinal cells and resulted in the active release of high mobility group box 1 (HMGB1), an important member of damage associate molecular patterns (DAMPs). Furthermore, blockade of HMGB1 in our murine model reduced intraocular inflammation via suppression of IRBP-specific T cell functions. These results have demonstrated that HMGB1 is an early and critical mediator of induction of intraocular inflammation. The present study identified the cell surface molecule that triggers HMGB1 secretion.

Methods

Retinal explants from Fas-deficient (Fas^lpr) and wild-type (Wt) C57BL/6 (B6) mice were cultured with activated IRBP 1–20 peptide-specific T cells or with a Fas-activating antibody (Jo2), and then the level of HMGB1 in culture supernatants were detected by ELISA. In addition, released HMGB1 was examined in the eye of Fas^lpr and Wt mice after IRBP-specific T cell transfer. Uveitis was evaluated in the IRBP-specific T cell transferred Fas^lpr mice after recombinant HMGB1 was restored within the eye and in the IRBP-specific T cell transferred Wt mice after they were treated with a Fas antagonist (Met12).

Results

In contrast to retinal explants from Wt mice, those from Fas^lpr mice did not release HMGB1 after exposure to IRBP-specific T cells or to Jo2. The release of HMGB1 by Wt retinal explants was suppressed by Met 12. Moreover, after IRBP-specific T cell injection, Fas^lpr mice did not release HMGB1 in the eye or develop EAU, but intravitreous injection of HMGB1 resulted in intraocular inflammation. Finally, tEAU in Wt mice was attenuated by local treatment with Met 12. Unlike HMGB1, Fas-induced IL-1 and IL-18 were not essential for tEAU induction.

Conclusion

Our results show that interaction of retinal cells with infiltrating uveitogenic T cells leads to rapid release of HMGB1 via the Fas/FasL inflammatory signaling pathway.

CARD3 deficiency protects against colitis through reduced epithelial cell apoptosis

BACKGROUND

Caspase activation and recruitment domain 3 (CARD3) is a 61-kDa protein kinase. Recent evidence shows the importance of CARD3 in the immune response and inflammatory diseases. To elucidate its impact on inflammatory bowel disease, we studied the effects of the loss of CARD3 in the acute dextran sodium sulfate-induced colitis.

METHODS

Colitis was induced by administration of dextran sodium sulfate to wild-type and CARD3 mice. Colon tissues were analyzed.

RESULTS

CARD3 mice were less susceptible to the development of colitis than wild-type controls as determined by weight loss, disease activity, colon histology, neutrophil infiltration, and cytokine expression. Reduced susceptibility of CARD3 mice to colitis was closely related to increased density of colonic epithelial cells relative to wild-type controls, which was because of decreased levels of apoptosis that resulted in enhanced epithelial barrier function. Finally, CARD3 levels were increased in intestinal tissue from patients with IBD.

CONCLUSIONS

These results imply a role for CARD3 as a positive regulator of intestinal epithelial cell apoptosis in the inflamed colon. Genetic loss of CARD3 is protective against colitis through decreased epithelial cell apoptosis and consequent enhancement of intestinal epithelial barrier function. Thus, targeted CARD3 inhibition may represent a new therapeutic approach in IBD.

Activation of an innate immune receptor, Nod1, accelerates atherogenesis in Apoe-/- mice

Atherosclerosis is essentially a vascular inflammatory process in the presence of an excess amount of lipid. We have recently reported that oral administration of a nucleotide-binding oligomerization domain (Nod)-1 ligand, FK565, induced vascular inflammation in vivo. No studies, however, have proven the association between Nod1 and atherosclerosis in vivo. To investigate a potential role of NOD1 in atherogenesis, we orally administered FK565 to apolipoprotein E knockout (Apoe(-/-)) mice for 4 wk intermittently and performed quantification of atherosclerotic lesions in aortic roots and aortas, immunohistochemical analyses, and microarray-based gene expression profiling of aortic roots. FK565 administration accelerated the development of atherosclerosis in Apoe(-/-) mice, and the effect was dependent on Nod1 in non-bone marrow origin cells by bone marrow transplantation experiments. Immunohistochemical studies revealed the increases in the accumulation of macrophages and CD3 T cells within the plaques in aortic roots. Gene expression analyses of aortic roots demonstrated a marked upregulation of the Ccl5 gene during early stage of atherogenesis, and the treatment with Ccl5 antagonist significantly inhibited the acceleration of atherosclerosis in FK565-administered Apoe(-/-) mice. Additionally, as compared with Apoe(-/-) mice, Apoe and Nod1 double-knockout mice showed reduced development of atherosclerotic lesions from the early stage as well as their delayed progression and a significant reduction in Ccl5 mRNA levels at 9 wk of age. Data in the present study show that the Nod1 signaling pathway in non-bone marrow-derived cells contributes to the development of atherosclerosis.

Loss of One Copy of Zfp148 Reduces Lesional Macrophage Proliferation and Atherosclerosis in Mice by Activating p53

Rationale:

Cell proliferation and cell cycle control mechanisms are thought to play central roles in the pathogenesis of atherosclerosis. The transcription factor Zinc finger protein 148 (Zfp148) was shown recently to maintain cell proliferation under oxidative conditions by suppressing p53, a checkpoint protein that arrests proliferation in response to various stressors. It is established that inactivation of p53 accelerates atherosclerosis, but whether increased p53 activation confers protection against the disease remains to be determined.

Objective:

We aimed to test the hypothesis that Zfp148 deficiency reduces atherosclerosis by unleashing p53 activity.

Methods and Results:

Mice harboring a gene-trap mutation in the Zfp148 locus ( Zfp148 gt/+ ) were bred onto the apolipoprotein E ( Apoe ) –/– genetic background and fed a high-fat or chow diet. Loss of 1 copy of Zfp148 markedly reduced atherosclerosis without affecting lipid metabolism. Bone marrow transplantation experiments revealed that the effector cell is of hematopoietic origin. Peritoneal macrophages and atherosclerotic lesions from Zfp148 gt/+ Apoe –/– mice showed increased levels of phosphorylated p53 compared with controls, and atherosclerotic lesions contained fewer proliferating macrophages. Zfp148 gt/+ Apoe –/– mice were further crossed with p53-null mice ( Trp53 –/– [the gene encoding p53]). There was no difference in atherosclerosis between Zfp148 gt/+ Apoe –/– mice and controls on a Trp53 +/– genetic background, and there was no difference in levels of phosphorylated p53 or cell proliferation.

Conclusions:

Zfp148 deficiency increases p53 activity and protects against atherosclerosis by causing proliferation arrest of lesional macrophages, suggesting that drugs targeting macrophage proliferation may be useful in the treatment of atherosclerosis.

Innate immune receptor NOD2 promotes vascular inflammation and formation of lipid-rich necrotic cores in hypercholesterolemic mice

Atherosclerosis is an inflammatory disease associated with the activation of innate immune TLRs and nucleotide-binding oligomerization domain-containing protein (NOD)-like receptor pathways. However, the function of most innate immune receptors in atherosclerosis remains unclear. Here, we show that NOD2 is a crucial innate immune receptor influencing vascular inflammation and atherosclerosis severity. 10-week stimulation with muramyl dipeptide (MDP), the NOD2 cognate ligand, aggravated atherosclerosis, as indicated by the augmented lesion burden, increased vascular inflammation and enlarged lipid-rich necrotic cores in Ldlr(-/-) mice. Myeloid-specific ablation of NOD2, but not its downstream kinase, receptor-interacting serine/threonine-protein kinase 2, restrained the expansion of the lipid-rich necrotic core in Ldlr(-/-) chimeric mice. In vitro stimulation of macrophages with MDP enhanced the uptake of oxidized low-density lipoprotein and impaired cholesterol efflux in concordance with upregulation of scavenger receptor A1/2 and downregulation of ATP-binding cassette transporter A1. Ex vivo stimulation of human carotid plaques with MDP led to increased activation of inflammatory signaling pathways p38 MAPK and NF-κB-mediated release of proinflammatory cytokines. Altogether, this study suggests that NOD2 contributes to the expansion of the lipid-rich necrotic core and promotes vascular inflammation in atherosclerosis.

RIP kinases: key decision makers in cell death and innate immunity

Innate immunity represents the first line of defence against invading pathogens. It consists of an initial inflammatory response that recruits white blood cells to the site of infection in an effort to destroy and eliminate the pathogen. Some pathogens replicate within host cells, and cell death by apoptosis is an important effector mechanism to remove the replication niche for such microbes. However, some microbes have evolved evasive strategies to block apoptosis, and in these cases host cells may employ further countermeasures, including an inflammatory form of cell death know as necroptosis. This review aims to highlight the importance of the RIP kinase family in controlling these various defence strategies. RIP1 is initially discussed as a key component of death receptor signalling and in the context of dictating whether a cell triggers a pathway of pro-inflammatory gene expression or cell death by apoptosis. The molecular and functional interplay of RIP1 and RIP3 is described, especially with respect to mediating necroptosis and as key mediators of inflammation. The function of RIP2, with particular emphasis on its role in NOD signalling, is also explored. Special attention is given to emphasizing the physiological and pathophysiological contexts for these various functions of RIP kinases.

Translational studies of A20 in atherosclerosis and cardiovascular disease

Cardiovascular disease (CVD) is the biggest killer in the Western World despite significant advances in understanding its molecular underpinnings. Chronic inflammation, the classical hallmark of atherogenesis is thought to play a key pathogenic role in the development of atherosclerotic lesions from initiation of fatty streaks to plaque rupture. Over-representation of mostly pro-inflammatory nuclear factor kappa B (NF-kappaB) target genes within atherosclerotic lesions has led to the common-held belief that excessive NF-kappaB activity promotes and aggravates atherogenesis. However, mouse models lacking various proteins involved in NF-kappaB signaling have often resulted in conflicting findings, fueling additional investigations to uncover the molecular involvement of NF-kappaB and its target genes in atherogenesis. In this chapter we will review the role of the NF-kappaB-regulated, yet potent NF-kappaB inhibitory and anti-inflammatory gene A20/TNFAIP3 in atherogenesis, and highlight the potential use of its atheroprotective properties for the prevention and treatment of cardiovascular diseases.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Cholesteryl esters accumulate in the heart in a porcine model of ischemia and reperfusion

Myocardial ischemia is associated with intracellular accumulation of lipids and increased depots of myocardial lipids are linked to decreased heart function. Despite investigations in cell culture and animal models, there is little data available on where in the heart the lipids accumulate after myocardial ischemia and which lipid species that accumulate. The aim of this study was to investigate derangements of lipid metabolism that are associated with myocardial ischemia in a porcine model of ischemia and reperfusion. The large pig heart enables the separation of the infarct area with irreversible injury from the area at risk with reversible injury and the unaffected control area. The surviving myocardium bordering the infarct is exposed to mild ischemia and is stressed, but remains viable. We found that cholesteryl esters accumulated in the infarct area as well as in the bordering myocardium. In addition, we found that expression of the low density lipoprotein receptor (LDLr) and the low density lipoprotein receptor-related protein 1 (LRP1) was up-regulated, suggesting that choleteryl ester uptake is mediated via these receptors. Furthermore, we found increased ceramide accumulation, inflammation and endoplasmatic reticulum (ER) stress in the infarcted area of the pig heart. In addition, we found increased levels of inflammation and ER stress in the myocardium bordering the infarct area. Our results indicate that lipid accumulation in the heart is one of the metabolic derangements remaining after ischemia, even in the myocardium bordering the infarct area. Normalizing lipid levels in the myocardium after ischemia would likely improve myocardial function and should therefore be considered as a target for treatment.

Inflammatory mediator profiling reveals immune properties of chemotactic gradients and macrophage mediator production inhibition during thioglycollate elicited peritoneal inflammation

Understanding of spatiotemporal profiling of inflammatory mediators and their associations with MΦ accumulation is crucial to elucidate the complex immune properties. Here, we used murine thioglycollate elicited peritonitis to determine concentrations of 23 inflammatory mediators in peritoneal exudates and plasma before (day 0) and after (days 1 and 3) thioglycollate administration to peritoneal cavities; these mediators included TNF-α, FGF-9, IFN-γ, IP-10, RANTES, IL-1α, IL-6, IL-7, IL-10, IL-11, IL-12p70, IL-17A, lymphotactin, OSM, KC/GRO, SCF, MIP-1β, MIP-2, TIMP-1, VEGF-A, MCP-1, MCP-3, and MCP-5. Our results showed that concentrations of most mediators in exudates and plasma reached peak levels on day 1 and were significantly reduced on day 3. Conversely, MΦ numbers started to increase on day 1 and reached peak levels on day 3. Moreover, LPS treatment in vitro significantly induced mediator productions in cell culture media and lysates from MΦ isolated on day 3. Our results also showed that on day 0, concentrations of many mediators in plasma were higher than those in exudates, whereas on day 1, the trend was reversed. Overall, the findings from thioglycollate elicited peritonitis reveal that reversible chemotactic gradients between peritoneal exudates and blood exist in basal and inflamed conditions and the inflammatory mediator production in vivo is disassociated with macrophage accumulation during inflammation resolution.

The SYK side of TLR4: signalling mechanisms in response to LPS and minimally oxidized LDL

Spleen tyrosine kinase (SYK) is the best known for its involvement in immune receptor signalling, mediated by binding of SYK tandem Src-homology 2 domains to tandem phosphotyrosine in immunoreceptor tyrosine-based activation motifs (ITAMs). ITAM adaptors or ITAM-containing receptor tails mediate signalling from B- and T-cell receptors, Fc receptors and many C-type lectins, including dectin-1. Recent data point to constitutive binding of SYK to the cytoplasmic domain of toll-like receptor-4 (TLR4). This SYK-TLR4 binding increases upon TLR4 dimerization and phosphorylation, and SYK plays a prominent role in TLR4 signalling in response to LPS in neutrophils and monocytes. SYK also plays an important role in TLR4-mediated macrophage responses to minimally oxidized low-density lipoprotein (mmLDL), which is a form of oxidized LDL relevant to development of human atherosclerosis. Interestingly, mmLDL-induced effects in macrophages, which occur via TLR4, are predominantly MyD88 independent. This unmasks the role of the SYK branch of TLR4 signalling, which mediates modest cytokine release via activation of AP-1 transcription and robust reactive oxygen species generation and cytoskeletal rearrangements. The latter results in extensive membrane ruffling and macropinocytosis, leading to lipoprotein uptake and foam cell formation, a hallmark of atherosclerotic lesions. Because inhibitors of SYK activity, such as fostamatinib, are in advanced clinical trials for rheumatoid arthritis and other autoimmune diseases, understanding the role of SYK in signalling via TLR4 is of immediate importance. This signalling pathway seems to be particularly important in TLR4 activation by host-derived, damage-associated molecular pattern ligands, such as mmLDL, relevant to development of atherosclerosis and other chronic inflammatory diseases.

CARD3 deficiency exacerbates diet-induced obesity, hepatosteatosis, and insulin resistance in male mice

Caspase activation and recruitment domain 3 (CARD3) is a 61-kDa protein kinase with an N-terminal serine/threonine kinase domain and a C-terminal CARD. Previous research on the function of CARD3 has focused on its role in the immune response and inflammatory diseases. Obesity is now a worldwide health problem and is generally recognized as an inflammatory disease. Unexpectedly, we found that CARD3 expression was lower during obesity. In this study, we explored the biological and genetic bases of obesity using CARD3-knockout (KO) and wild-type (WT) mice fed a high-fat diet (HFD) for 24 weeks. We demonstrate that KO mice were more obese than their WT littermates, and KO mice exhibited obvious visceral fat accumulation and liver weight gains after 24 weeks of HFD feeding. We also observed more severe hepatosteatosis in KO mice compared with the WT controls. Hepatic steatosis in the HFD-fed KO mice was linked to a significant increase in the expression of key lipogenic and cholesterol synthesis enzymes, whereas the expression of the enzymes involves in β-oxidation was dramatically reduced. Furthermore, we confirmed the repression of AMP-activated protein kinase signaling and activation of the endoplasmic reticulum stress response. Fatty liver impaired the global glucose and lipid metabolism, which further exacerbated the insulin resistance associated with the repression of Akt signaling and up-regulated systemic inflammation through the M1/M2 (pro- and anti-inflammation) type switch and the activation of the nuclear factor-κB pathway. Our studies demonstrate the crucial role of CARD3 in metabolism and indicate that CARD3 deficiency promotes the diet-induced phenotype of type 2 diabetes.

Targeting GGTase-I activates RHOA, increases macrophage reverse cholesterol transport, and reduces atherosclerosis in mice

BACKGROUND

Statins have antiinflammatory and antiatherogenic effects that have been attributed to inhibition of RHO protein geranylgeranylation in inflammatory cells. The activity of protein geranylgeranyltransferase type I (GGTase-I) is widely believed to promote membrane association and activation of RHO family proteins. However, we recently showed that knockout of GGTase-I in macrophages activates RHO proteins and proinflammatory signaling pathways, leading to increased cytokine production and rheumatoid arthritis. In this study, we asked whether the increased inflammatory signaling of GGTase-I-deficient macrophages would influence the development of atherosclerosis in low-density lipoprotein receptor-deficient mice.

METHODS AND RESULTS

Aortic lesions in mice lacking GGTase-I in macrophages (Pggt1b▵/▵) contained significantly more T lymphocytes than the lesions in controls. Surprisingly, however, mean atherosclerotic lesion area in Pggt1b▵/▵ mice was reduced by ≈60%. GGTase-I deficiency reduced the accumulation of cholesterol esters and phospholipids in macrophages incubated with minimally modified and acetylated low-density lipoprotein. Analyses of GGTase-I-deficient macrophages revealed upregulation of the cyclooxygenase 2-peroxisome proliferator-activated-γ pathway and increased scavenger receptor class B type I- and CD36-mediated basal and high-density lipoprotein-stimulated cholesterol efflux. Lentivirus-mediated knockdown of RHOA, but not RAC1 or CDC42, normalized cholesterol efflux. The increased cholesterol efflux in cultured cells was accompanied by high levels of macrophage reverse cholesterol transport and slightly reduced plasma lipid levels in vivo.

CONCLUSIONS

Targeting GGTase-I activates RHOA and leads to increased macrophage reverse cholesterol transport and reduced atherosclerosis development despite a significant increase in inflammation.

Apolipoprotein B100 autoimmunity and atherosclerosis - disease mechanisms and therapeutic potential

PURPOSE OF REVIEW

Adaptive immune responses have been shown to play an important role in the atherosclerotic disease process and both pathogenic and protective immunity has been identified. Apolipoprotein (apo) B100 appears to be a key antigen and novel therapies modulating immune responses against apo B100 have shown promising results in experimental models. This review will discuss recent developments in the mechanistic understanding of apo B100 autoimmunity and approaches taken to use this knowledge for development of novel therapies.

RECENT FINDINGS

It has recently been shown that not only apo B100 modified by oxidation but also nonmodified apo B100 is targeted by autoimmune responses. This implies that a corresponding set of regulatory T cells with the same antigen specificity must exist and that these cells under normal circumstances are able to prevent autoimmunity against LDL. Recent studies also suggest that the atheroprotective effect of apo B100 peptide immunization acts by re-enforcing the activity of such cells.

SUMMARY

These novel findings suggest that aggravation of plaque inflammation may occur as a result of a local loss of tolerance against LDL in the plaque due to insufficient activity of regulatory T cells. Restoration of lost tolerance represents an interesting novel approach for treatment of cardiovascular disease.