CARD9 as a potential target in cardiovascular disease

Regulatory roles of CARD9-BCL10-Rac1 (CBR) signalome in islet β-cell function in health and metabolic stress: Is there room for MALT1?

It is widely accepted that pancreatic islet β-cell failure and the onset of type 2 diabetes (T2DM) constitute an intricate interplay between the genetic expression of the disease and a host of intracellular events including increased metabolic (oxidative, endoplasmic reticulum) stress under the duress of glucolipotoxicity. Emerging evidence implicates unique roles for Caspase Recruitment Domain containing protein 9 (CARD9) in the onset of metabolic diseases, including obesity and insulin resistance. Mechanistically, CARD9 has been implicated in the regulation of p38MAPK and NFkB signaling pathways culminating in cellular dysfunction. Several regulatory factors, including B-cell lymphoma/leukemia 10 (BCL10) have been identified as modulators of CARD9 function in multiple cell types. Despite this evidence on regulatory roles of CARD9-BCL10 signalome in the onset of various pathological states, putative roles of this signaling module in islet β-cell dysfunction in metabolic stress remain less understood. This brief review is aimed at highlighting roles for CARD9 in islet β-cell function under acute (physiological insulin secretion) and long-term (cell dysfunction) exposure to glucose. Emerging roles of other signaling proteins, such as Rac1, BCL10 and MALT1 as contributors to CARD9 signaling in the islet β-cells are also reviewed. Potential avenues for future research toward the development of novel therapeutics for the prevention CARD9-BCL10-Rac1 (CBR) signalome-induced β-cell defects under metabolic stress are discussed.

Regulatory Roles of Histone Deacetylation in Metabolic Stress-Induced Expression of Caspase Recruitment Domain-Containing Protein 9 (CARD9) in Pancreatic β-Cells

CARD9, a scaffolding protein, has been implicated in the pathogenesis of metabolic diseases, including obesity and diabetes. We recently reported novel roles for CARD9 in islet β-cell dysregulation under duress of gluco (HG)- and glucolipotoxic (GLT) stress. CARD9 expression was also increased in β-cells following exposure to HG and GLT stress. The current study is aimed at understanding the putative roles of histone deacetylation in HG- and GLT-induced expression of CARD9. Using two structurally distinct inhibitors of histone deacetylases (HDACs), namely trichostatin (TSA) and suberoylanilide hydroxamic acid (SAHA), we provide the first evidence to suggest that the increased expression of CARD9 seen under duress of HG and GLT stress is under the regulatory control of histone deacetylation. Interestingly, the expression of protein kinase Cδ (PKCδ), a known upstream regulator of CARD9 activation, is also increased under conditions of metabolic stress. However, it is resistant to TSA and SAHA, suggesting that it is not regulated via histone deacetylation. Based on these data, we propose that targeting the appropriate HDACs, which mediate the expression (and function) of CARD9, might be the next step to further enhance our current understanding of the roles of CARD9 in islet dysfunction under metabolic stress and diabetes.

Time-dependent Effects of Moderate- and High-intensity Exercises on Myocardial Transcriptomics

The heart is a highly adaptable organ that responds to changes in functional requirements due to exposure to internal and external stimuli. Physical exercise has unique stimulatory effects on the myocardium in both healthy individuals and those with health disorders, where the effects are primarily determined by the intensity and recovery time of exercise. We investigated the time-dependent effects of different exercise intensities on myocardial transcriptional expression in rats. Moderate intensity exercise induced more differentially expressed genes in the myocardium than high intensity exercise, while 16 differentially expressed genes were down-regulated by moderate intensity exercise but up-regulated by high intensity exercise at 12 h post- exercise. Both Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis indicated that moderate intensity exercise specifically regulated gene expression related to heart adaptation, energy metabolism, and oxidative stress, while high intensity exercise specifically regulated gene expression related to immunity, inflammation, and apoptosis. Moreover, there was increased expression of Tbx5, Casq1, Igsf1, and Ddah1 at all time points after moderate intensity exercise, while there was increased expression of Card9 at all time points after high intensity exercise. Our study provides a better understanding of the intensity dependent effects of physical exercise of the molecular mechanisms of cardiac adaptation to physical exercise.

CARD9 Mediates Pancreatic Islet Beta-Cell Dysfunction Under the Duress of Hyperglycemic Stress

BACKGROUND/AIMS

Published evidence implicates Caspase recruitment domain containing protein 9 (CARD9) in innate immunity. Given its recently suggested roles in obesity and insulin resistance, we investigated its regulatory role(s) in the onset of islet beta cell dysfunction under chronic hyperglycemic (metabolic stress) conditions.

METHODS

Islets from mouse pancreas were isolated by the collagenase digestion method. Expression of CARD9 was suppressed in INS-1 832/13 cells by siRNA transfection using the DharmaFect1 reagent. The degree of activation of Rac1 was assessed by a pull-down assay kit. Interactions between CARD9, RhoGDIβ and Rac1 under metabolic stress conditions were determined by co-immunoprecipitation assay. The degree of phosphorylation of stress kinases was assessed using antibodies directed against phosphorylated forms of the respective kinases.

RESULTS

CARD9 expression is significantly increased following exposure to high glucose, not to mannitol (both at 20 mM; 24 hrs.) in INS-1 832/13 cells. siRNA-mediated knockdown of CARD9 significantly attenuated high glucose-induced activation of Rac1 and phosphorylation of p38MAPK and p65 subunit of NF-κB (RelA), without significantly impacting high glucose-induced effects on JNK1/2 and ERK1/2 activities. CARD9 depletion also suppressed high glucose-induced CHOP expression (a marker for endoplasmic reticulum stress) in these cells. Co-immunoprecipitation studies revealed increased association between CARD9-RhoGDIβ and decreased association between RhoGDIβ-Rac1 in cells cultured under high glucose conditions.

CONCLUSION

Based on these data, we conclude that CARD9 regulates activation of Rac1-p38MAPK-NFκB signaling pathway leading to functional abnormalities in beta cells under metabolic stress conditions.

CARD9 Signaling, Inflammation, and Diseases

Caspase-recruitment domain 9 (CARD9) protein is expressed in many cells especially in immune cells, and is critically involved in the function of the innate and adaptive immune systems through extensive interactions between CARD9 and other signaling molecules including NF-κB and MAPK. CARD9-mediated signaling plays a central role in regulating inflammatory responses and oxidative stress through the productions of important cytokines and chemokines. Abnormalities of CARD9 and CARD9 signaling or CARD9 mutations or polymorphism are associated with a variety of pathological conditions including infections, inflammation, and autoimmune disorders. This review focuses on the function of CARD9 and CARD9-mediated signaling pathways, as well as interactions with other important signaling molecules in different cell types and the relations to specific disease conditions including inflammatory diseases, infections, tumorigenesis, and cardiovascular pathologies.

Annual reports on hypertension research 2020

In 2020, 199 papers were published in Hypertension Research. Many excellent papers have contributed to progress in research on hypertension. Here, our editorial members have summarized eleven topics from published work and discussed current topics in depth. We hope you enjoy our special feature, Annual Reports on Hypertension Research.

CARD9 mediates glucose-stimulated insulin secretion in pancreatic beta cells

Caspase recruitment domain containing protein 9 (CARD9) plays key regulatory role(s) in innate and adaptive immune responses. Recent evidence implicates CARD9 in the onset of metabolic diseases including insulin resistance. However, potential contributory roles of CARD9 in glucose-stimulated insulin secretion (GSIS) remain unknown. Herein, we report that CARD9 is expressed in human islets, rat islets, mouse islets and clonal INS-1 832/13 cells. Subcellularly, CARD9 is predominantly cytosolic (~75%) in INS-1 832/13 cells. siRNA-mediated depletion of CARD9 expression significantly (~50%) suppressed GSIS in INS-1 832/13 cells. Interestingly, glucose-induced activation of Rac1, a small G-protein, which is a requisite for GSIS to occur, is unaffected in CARD9-si transfected cells, suggesting that CARD9-mediates GSIS in a Rac1-independent fashion. Furthermore, insulin secretion promoted by KCl or mastoparan (a global G protein activator), remained resistant to CARD9 depletion in INS-1 832/13 cells. In addition, pharmacological inhibition (BRD5529) of interaction between CARD9 and TRIM62, its ubiquitin ligase, exerted no significant effects on GSIS. Lastly, depletion of CARD9 prevented glucose-induced p38, not ERK1/2 phosphorylation in beta cells. Based on these observations, we propose that CARD9 might regulate GSIS via a Rac1-independent and p38-dependent signaling module.

The roles of the inhibitory autophagy regulator Rubicon in the heart: A new therapeutic target to prevent cardiac cell death

Autophagy contributes to the maintenance of cardiac homeostasis. The level of autophagy is dynamically altered in heart disease. Although autophagy is a promising therapeutic target, only a few selective autophagy activator candidates have been reported thus far. Rubicon is one of the few endogenous negative regulators of autophagy and a potential target for autophagy-inducing therapeutics. Rubicon was initially identified as a component of the Class III PI3K complex, and it has multiple functions, not only in canonical autophagy but also in endosomal trafficking and inflammatory responses. This review summarizes the molecular action of Rubicon in canonical and noncanonical autophagy. We discuss the roles of Rubicon in cardiac stress and the therapeutic potential of Rubicon in cardiac diseases through its modulation of autophagy.

Inhibition of MyD88 by LM8 Attenuates Obesity-Induced Cardiac Injury

Obesity-induced cardiomyopathy involves chronic and sustained inflammation. The toll-like receptor 4 (TLR4) signaling pathway can associate innate immunity with obesity. Myeloid differentiation primary response 88 (MyD88), an indispensable downstream adaptor molecule of TLR4, has been reported to mediate obesity complications. However, whether inhibition of MyD88 can mitigate obesity-induced heart injury remains unclear. LM8, a new MyD88 inhibitor, exhibits prominent anti-inflammatory activity in lipopolysaccharide-treated macrophages. In this study, the protective effects of LM8 on a high-fat diet (HFD)-induced heart injury were assessed in a mouse model of obesity. As suggested from the achieved results, LM8 treatment alleviated HFD-induced pathological and functional damages of the heart in mice. Meantime, the treatment of mice with LM8 could significantly inhibit myocardial hypertrophy, fibrosis, inflammatory cytokines expression, and inflammatory cell infiltration induced by HFD. Besides, LM8 administration inhibited the formation of MyD88/TLR4 complex, phosphorylation of ERK, and activation of nuclear factor-κB induced by HFD. According to the achieved results, MyD88 inhibitor LM8 ameliorated obesity-induced heart injury by inhibiting MyD88-ERK/nuclear factor-κB dependent cardiac inflammatory pathways. Furthermore, targeting MyD88 might be a candidate of a therapeutic method to treat obesity-induced heart injury.

Zinc homeostasis plays an important role in the prevention of obesity-induced cardiac inflammation, remodeling and dysfunction

Obesity often leads to cardiovascular diseases, such as obesity-related cardiac hypertrophy (ORCH), due to chronic cardiac inflammation. Zinc is structurally and functionally essential for many transcription factors, therefore it not only has anti-inflammatory and anti-oxidative stress functions, but also has insulin-like function, however, its role in the development of obesity-associated cardiac pathogenesis and the potentially underlying mechanism(s) remains unclear. This review aims to summarize the available evidence on the role of zinc homeostasis in the prevention of ORCH. It was recently reported that when four-week old mice were fed either high fat diet (HFD) or normal diet containing deficient, adequate or supplemented zinc, HFD induced obesity and ORCH along with increased phosphorylation of p38 MAPK and increased expression of B-cell lymphoma/ leukemia 10 (BCL10) and caspase recruitment domain family member 9 (CARD9). These effects were further aggravated by zinc deficiency and significantly alleviated by zinc supplementation. Mechanistically administration of a p38 MAPK specific inhibitor in HFD-fed mice for 3 months did not affect HFD-induced obesity and increased expression of BCL10 and CARD9, but completely abolished HFD/obesity-induced cardiac hypertrophy and inflammation. In cultured cardiomyocytes, inhibition of BCL10 expression by siRNA prevented palmitate-induced increased p38 MAPK activation and atrial natriuretic peptide expression. Deletion of metallothionein abolished the protective effect of zinc on palmitate-induced up-regulation of BCL10 and phospho-p38 MAPK. Taken together with other recent studies, we concluded that HFD and zinc deficiency synergistically induce ORCH by increasing oxidative stress-mediated activation of BCL10/CARD9/p38 MAPK signaling. Zinc supplementation ameliorates ORCH through activation of metallothionein to repress oxidative stress-activated BCL10 expression and p38 MAPK activation.

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.

The Role of CARD9 in Metabolic Diseases

Caspase recruitment domain containing protein 9 (CARD9) is an adaptor protein that plays a critical role in pattern recognition receptors (PRRs)-mediated activation of NF-?B and mitogen-activated protein kinase (MAPK). This elicits initiation of the pro-inflammatory cytokines and leads to inflammatory responses, which has been recognized as a critical contributor to chronic inflammation. Current researches demonstrate that CARD9 is strongly associated with metabolic diseases, such as obesity, insulin resistance, atherosclerosis and so on. In this review, we summarize CARD9 signaling pathway and the role of CARD9 in metabolic diseases.

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.

Deletion of hematopoietic Dectin-2 or CARD9 does not protect against atherosclerotic plaque formation in hyperlipidemic mice

Inflammatory reactions activated by pattern recognition receptors (PRRs) on the membrane of innate immune cells play an important role in atherosclerosis. Whether the PRRs of the C-type lectin receptor (CLR) family including Dectin-2 may be involved in the pathogenesis of atherosclerosis remains largely unknown. Recently, the CLR-adaptor molecule caspase recruitment domain family member 9 (CARD9) has been suggested to play a role in cardiovascular pathologies as it provides the link between CLR activation and transcription of inflammatory cytokines as well as immune cell recruitment. We therefore evaluated whether hematopoietic deletion of Dectin-2 or CARD9 reduces inflammation and atherosclerosis development. Low-density lipoprotein receptor (Ldlr)-knockout mice were transplanted with bone marrow from wild-type, Dectin-2- or Card9-knockout mice and fed a Western-type diet containing 0.1% (w/w) cholesterol. After 10 weeks, lipid and inflammatory parameters were measured and atherosclerosis development was determined. Deletion of hematopoietic Dectin-2 or CARD9 did not influence plasma triglyceride and cholesterol levels. Deletion of hematopoietic Dectin-2 did not affect atherosclerotic lesion area, immune cell composition, ex vivo cytokine secretion by peritoneal cells or bone marrow derived macrophages. Unexpectedly, deletion of hematopoietic CARD9 increased atherosclerotic lesion formation and lesion severity. Deletion of hematopoietic CARD9 did also not influence circulating immune cell composition and peripheral cytokine secretion. Besides a tendency to a reduced macrophage content within these lesions, plasma MCP-1 levels decreased upon WTD feeding. Deletion of hematopoietic Dectin-2 did not influence atherosclerosis development in hyperlipidemic mice. The absence of CARD9 unexpectedly increased atherosclerotic lesion size and severity, suggesting that the presence of CARD9 may protect against initiation of atherosclerosis development.

Picomolar zinc binding modulates formation of Bcl10-nucleating assemblies of the caspase recruitment domain (CARD) of CARD9

The caspase recruitment domain-containing protein 9 (CARD9)-B-cell lymphoma/leukemia 10 (Bcl10) signaling axis is activated in myeloid cells during the innate immune response to a variety of diverse pathogens. This signaling pathway requires a critical caspase recruitment domain (CARD)-CARD interaction between CARD9 and Bcl10 that promotes downstream activation of factors, including NF-κB and the mitogen-activated protein kinase (MAPK) p38. Despite these insights, CARD9 remains structurally uncharacterized, and little mechanistic understanding of its regulation exists. We unexpectedly found here that the CARD in CARD9 binds to Zn²⁺ with picomolar affinity-a concentration comparable with the levels of readily accessible Zn²⁺ in the cytosol. NMR solution structures of the CARD9-CARD in the apo and Zn²⁺-bound states revealed that Zn²⁺ has little effect on the ground-state structure of the CARD; yet the stability of the domain increased considerably upon Zn²⁺ binding, with a concomitant reduction in conformational flexibility. Moreover, Zn²⁺ binding inhibited polymerization of the CARD9-CARD into helical assemblies. Here, we also present a 20-Å resolution negative-stain EM (NS-EM) structure of these filamentous assemblies and show that they adopt a similar helical symmetry as reported previously for filaments of the Bcl10 CARD. Using both bulk assays and direct NS-EM visualization, we further show that the CARD9-CARD assemblies can directly template and thereby nucleate Bcl10 polymerization, a capacity considered critical to propagation of the CARD9-Bcl10 signaling cascade. Our findings indicate that CARD9 is a potential target of Zn²⁺-mediated signaling that affects Bcl10 polymerization in innate immune responses.

The essential function of CARD9 in diet-induced inflammation and metabolic disorders in mice

Inflammation and metabolic disorder are common pathophysiological conditions, which play a vital role in the development of obesity and type 2 diabetes. The purpose of this study was to explore the effects of caspase recruitment domain (CARD) 9 in the high fat diet (HFD)‐treated mice and attempt to find a molecular therapeutic target for obesity development and treatment. Sixteen male CARD9^−/− and corresponding male WT mice were fed with normal diet or high fat diet, respectively, for 12 weeks. Glucose tolerance, insulin resistance, oxygen consumption and heat production of the mice were detected. The CARD9/MAPK pathway‐related gene and protein were determined in insulin‐responsive organs using Western blotting and quantitative PCR. The results showed that HFD‐induced insulin resistance and impairment of glucose tolerance were more severe in WT mice than that in the CARD9^−/− mice. CARD9 absence significantly modified O₂ consumption, CO₂ production and heat production. CARD9^−/− mice displayed the lower expression of p38 MAPK, JNK and ERK when compared to the WT mice in both HFD‐ and ND‐treated groups. HFD induced the increase of p38 MAPK, JNK and ERK in WT mice but not in the CARD9^−/− mice. The results indicated that CARD9 absence could be a vital protective factor in diet‐induced obesity via the CARD9/MAPK pathway, which may provide new insights into the development of gene knockout to improving diet‐induced obesity and metabolism disorder.

Molecular and physiological roles of the adaptor protein CARD9 in immunity

CARD9 is a caspase recruitment domain-containing signaling protein that plays a critical role in innate and adaptive immunity. It has been widely demonstrated that CARD9 adaptor allows pattern recognition receptors to induce NF-κB and MAPK activation, which initiates a “downstream” inflammation cytokine cascade and provides effective protection against microbial invasion, especially fungal infection. Here our aim is to update existing paradigms and summarize the most recent findings on the CARD9 signaling pathway, revealing significant mechanistic insights into the pathogenesis of CARD9 deficiency. We also discuss the effect of CARD9 genetic mutations on the in vivo immune response, and highlight clinical advances in non-infection inflammation.