Mechanism and role of high density lipoprotein-induced activation of AMP-activated protein kinase in endothelial cells

Ligand-dependent interactions between SR-B1 and S1PR1 in macrophages and atherosclerotic plaques

HDLs carry sphingosine-1-phosphate (S1P) and stimulate signaling pathways in different cells including macrophages and endothelial cells, involved in atherosclerotic plaque development. HDL signaling via S1P relies on the HDL receptor scavenger receptor class B, type I (SR-B1) and the sphingosine-1-phosphate receptor 1 (S1PR1), which interact when both are heterologously overexpressed in the HEK293 cell line. In this study, we set out to test if SR-B1 and S1PR1 interacted in primary murine macrophages in culture and atherosclerotic plaques. We used knock-in mice that endogenously expressed S1PR1 tagged with eGFP-(S1pr1eGFP/eGFP mice), combined with proximity ligation analysis to demonstrate that HDL stimulates the physical interaction between SR-B1 and S1PR1 in primary macrophages, that this is dependent on HDL-associated S1P and can be blocked by an inhibitor of SR-B1's lipid transfer activity or an antagonist of S1PR1. We also demonstrate that a synthetic S1PR1-selective agonist, SEW2871, stimulates the interaction between SR-B1 and S1PR1 and that this was also blocked by an inhibitor of SR-B1's lipid transport activity. Furthermore, we detected abundant SR-B1/S1PR1 complexes in atherosclerotic plaques of S1pr1eGFP/eGFP mice that also lacked apolipoprotein E. Treatment of mice with the S1PR1 antagonist, Ex26, for 12 h disrupted the SR-B1-S1PR1 interaction in atherosclerotic plaques. These findings demonstrate that SR-B1 and S1PR1 form ligand-dependent complexes both in cultured primary macrophages and within atherosclerotic plaques in mice and provide mechanistic insight into how SR-B1 and S1PR1 participate in mediating HDL signaling to activate atheroprotective responses in macrophages.

High-density lipoprotein protects vascular endothelial cells from indoxyl sulfate insults through its antioxidant ability

Chronic kidney disease (CKD) patients have a high risk of cardiovascular disease. Indoxyl sulfate (IS) is a uremic toxin that has been shown to inhibit nitric oxide production and cause cell senescence by inducing oxidative stress. High-density lipoprotein (HDL) has a protective effect on the cardiovascular system; however, its impacts on IS-damaged endothelial cells are still unknown. This study aimed to explore the effects of exogenous supplement of HDL on vascular endothelial cells in a uremia-mimic environment. Tube formation, migration, adhesion, and senescence assays were used to evaluate the cell function of human aortic endothelial cells (HAECs). Reactive oxygen species generation was measured by using Amplex red assay. L-NAME and MCI186 were used as a nitric oxide synthase inhibitor and a free radical scavenger, respectively. HDL exerted anti-inflammatory and antioxidant effects via HIF-1α/HO-1 activation and IL-1β/TNF-α/IL-6 inhibition in IS-stimulated HAECs. HDL improved angiogenesis ability through upregulating Akt/eNOS/VEGF/SDF-1 in IS-stimulated HAECs. HDL decreased endothelial adhesiveness via downregulating VCAM-1 and ICAM-1 in IS-stimulated HAECs. Furthermore, HDL reduced cellular senescence via upregulating SIRT1 and downregulating p53 in IS-stimulated HAECs. Importantly, the above beneficial effects of HDL were mainly due to its antioxidant ability. In conclusion, HDL exerted a comprehensive protective effect on vascular endothelial cells against damage from IS through its antioxidant ability. The results of this study might provide a theoretical basis for potential HDL supplementation in CKD patients with endothelial damage.

The Role of Obesity, Inflammation and Sphingolipids in the Development of an Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a local dilatation of the vessel equal to or exceeding 3 cm. It is a disease with a long preclinical period commonly without any symptoms in its initial stage. Undiagnosed for years, aneurysm often leads to death due to vessel rupture. The basis of AAA pathogenesis is inflammation, which is often associated with the excess of adipose tissue, especially perivascular adipose tissue, which synthesizes adipocytokines that exert a significant influence on the formation of aneurysms. Pro-inflammatory cytokines such as resistin, leptin, and TNFα have been shown to induce changes leading to the formation of aneurysms, while adiponectin is the only known compound that is secreted by adipose tissue and limits the development of aneurysms. However, in obesity, adiponectin levels decline. Moreover, inflammation is associated with an increase in the amount of macrophages infiltrating adipose tissue, which are the source of matrix metalloproteinases (MMP) involved in the degradation of the extracellular matrix, which are an important factor in the formation of aneurysms. In addition, an excess of body fat is associated with altered sphingolipid metabolism. It has been shown that among sphingolipids, there are compounds that play an opposite role in the cell: ceramide is a pro-apoptotic compound that mediates the development of inflammation, while sphingosine-1-phosphate exerts pro-proliferative and anti-inflammatory effects. It has been shown that the increase in the level of ceramide is associated with a decrease in the concentration of adiponectin, an increase in the concentration of TNFα, MMP-9 and reactive oxygen species (which contribute to the apoptosis of vascular smooth muscle cell). The available data indicate a potential relationship between obesity, inflammation and disturbed sphingolipid metabolism with the formation of aneurysms; therefore, the aim of this study was to systematize the current knowledge on the role of these factors in the pathogenesis of abdominal aortic aneurysm.

High-density lipoproteins and immune response: A review

High-density lipoproteins (HDLs) are heterogeneous lipoproteins that modify their composition and functionality depending on physiological or pathological conditions. The main roles of HDL are cholesterol efflux, and anti-inflammatory and antioxidant functions. These functions can be compromised under pathological conditions. HDLs play a role in the immune system as anti-inflammatory molecules but when inflammation occurs, HDLs change their composition and carry pro-inflammatory cargo. Hence, many molecular intermediates that influence inflammatory microenvironments and cell signaling pathways can modulate HDLs structural modification and function. This review provides a comprehensive assessment of the importance of HDL composition and anti-inflammatory function in the onset and progression of atherosclerotic cardiovascular diseases. On the other hand, immune cell activation during progression of atheroma plaque formation can be influenced by HDLs through HDL-derived cholesterol depletion from lipid rafts and through HDL interaction with HDL receptors expressed on T and B lymphocytes. Cholesterol efflux is mediated by HDL receptors located in lipid rafts in peripheral cells, which undergo membrane structural modifications, and interferes with subsequent molecules interactions or intracellular signaling cascades. Regarding antigen-presentation cells such as macrophages or dendritic cells, HDL function may then modulate lymphocytes activation in immune response. Our review also contributes to the understanding of the effects exerted by HDLs in signal transduction associated to our immune cell population during chronic diseases progression.

Lipid regulation of NLRP3 inflammasome activity through organelle stress

Inflammation driven by the NLRP3 inflammasome in macrophages is an important contributor to chronic metabolic diseases that affect growing numbers of individuals. Many of these diseases involve the pathologic accumulation of endogenous lipids or their oxidation products, which can activate NLRP3. Other endogenous lipids, however, can inhibit the activation of NLRP3. The intracellular mechanisms by which these lipids modulate NLRP3 activity are now being identified. This review discusses emerging evidence suggesting that organelle stress, particularly involving mitochondria, lysosomes, and the endoplasmic reticulum, may be key in lipid-induced modification of NLRP3 inflammasome activity.

Omentin-1: Protective impact on ischemic stroke via ameliorating atherosclerosis

Omentin-1, a newly identified adipokine, has recently been revealed as a novel biomarker for ischemic stroke (IS). Low circulating omentin-1 levels could indicate a high risk of IS, and elevated omentin-1 levels exert a favorable impact on cerebral ischemia. Furthermore, omentin-1 has anti-atherosclerotic, anti-inflammatory, and cardiovascular protective capabilities through the intracellular Akt/AMP-activated protein kinase (AMPK)/ nuclear factor-κB (NF-κB) and certain protein kinase (ERK, JNK, and p38) signaling pathways. Omentin-1 also alleviates endothelial cell dysfunction, improves revascularization via the Akt-endothelial nitric-oxide synthase (eNOS) regulatory axis, promotes endothelium-dependent vasodilation through endothelium-derived NO in an eNOS fashion, and inhibits VSMC proliferation by means of AMPK/ERK signaling pathways, VSMC migration via inactivation of the NADPH oxidase (NOX)/ROS/p38/HSP27 pathways and artery calcification via the PI3K-Akt pathway. These findings indicate that omentin-1 may be a negative mediator of IS. Pharmacologically, several lines of clinical evidence indicate that metformin and statins could elevate omentin-1 levels, although the specific mechanism has not been precisely delineated until now. This study is the first to summarize the comprehensive mechanisms between omentin-1 and atherosclerosis and to review the shielding effect of omentin-1 on IS. We shed light on omentin-1 as a novel therapeutic target for combating IS.

Endothelial Cell Receptors in Tissue Lipid Uptake and Metabolism

Lipid uptake and metabolism are central to the function of organs such as heart, skeletal muscle, and adipose tissue. Although most heart energy derives from fatty acids (FAs), excess lipid accumulation can cause cardiomyopathy. Similarly, high delivery of cholesterol can initiate coronary artery atherosclerosis. Hearts and arteries-unlike liver and adrenals-have nonfenestrated capillaries and lipid accumulation in both health and disease requires lipid movement from the circulation across the endothelial barrier. This review summarizes recent in vitro and in vivo findings on the importance of endothelial cell receptors and uptake pathways in regulating FAs and cholesterol uptake in normal physiology and cardiovascular disease. We highlight clinical and experimental data on the roles of ECs in lipid supply to tissues, heart, and arterial wall in particular, and how this affects organ metabolism and function. Models of FA uptake into ECs suggest that receptor-mediated uptake predominates at low FA concentrations, such as during fasting, whereas FA uptake during lipolysis of chylomicrons may involve paracellular movement. Similarly, in the setting of an intact arterial endothelial layer, recent and historic data support a role for receptor-mediated processes in the movement of lipoproteins into the subarterial space. We conclude with thoughts on the need to better understand endothelial lipid transfer for fuller comprehension of the pathophysiology of hyperlipidemia, and lipotoxic diseases such as some forms of cardiomyopathy and atherosclerosis.

Phenolic Substances in Foods and Anticarcinogenic Properties: A Public Health Perspective

The interest in polyphenols from vegetable sources has been progressively increased because of the demonstrated correlation between their abundance in certain foods or food preparations of traditional importance and heritage, and the answer of anti-inflammatory strategies in hospitalized patients in the presence of polypehnol-rich foods (as a complementary therapy). Consequently, research involving the accessory role of polyphenols as anti-tumoral aids have been carried out with the aim of finding new additional strategies. The purpose of this paper to evaluate the role of phenolic compounds in foods with reference to health effects for human beings. The importance of these molecules has been evaluated by the health and safety perspectives in terms of: fight to cardiovascular diseases; prevention of chronic-degenerative disorders; general antioxidant properties; and anticarcinogenic features. Moreover, the role of polyphenols-rich foods as anticancer agents has been discussed with relation to two distinct "action plans" on the public hygiene level: the promotion of human health on the one side (for non-hospitalized and normal subjects), and reliable contrasting strategies in cancer patients.

Role of cholesterol homeostasis and its efflux pathways in cancer progression

Tumor cells show high avidity for cholesterol in order to support their inherent nature to divide and proliferate. This results in the rewiring of cholesterol homeostatic pathways by influencing not only de novo synthesis but also uptake or efflux pathways of cholesterol. Recent findings have pointed towards the importance of cholesterol efflux in tumor pathogenesis. Cholesterol efflux is the first and foremost step in reverse cholesterol transport and any perturbation in this pathway may lead to the accumulation of intracellular cholesterol, thereby altering the cellular equilibrium. This review addresses the different mechanisms of cholesterol efflux from the cell and highlights their role and regulation in context to tumor development. There are four different routes by which cholesterol can be effluxed from the cell namely, 1) passive diffusion of cholesterol to mature HDL particles, 2) SR-B1 mediated facilitated diffusion, 3) Active efflux to apo A1 via ABCA1 and 4) ABCG1 mediated efflux to mature HDL. These molecular players facilitating cholesterol efflux are engaged in a complex interplay with different signaling pathways. Thus, an understanding of the efflux pathways, their regulation and cross-talk with signaling molecules may provide novel prognostic markers and therapeutic targets to combat the onset of carcinogenesis.

Trained Circulating Monocytes in Atherosclerosis: Ex Vivo Model Approach

Inflammation is one of the key processes in the pathogenesis of atherosclerosis. Numerous studies are focused on the local inflammatory processes associated with atherosclerotic plaque initiation and progression. However, changes in the activation state of circulating monocytes, the main components of the innate immunity, may precede the local events. In this article, we discuss tolerance, which results in decreased ability of monocytes to be activated by pathogens and other stimuli, and training, the ability of monocyte to potentiate the response to pathological stimuli, and their relation to atherosclerosis. We also present previously unpublished results of the experiments that our group performed with monocytes/macrophages isolated from atherosclerosis patients. Our data allow assuming the existence of relationship between the formation of monocyte training and the degree of atherosclerosis progression. The suppression of trained immunity ex vivo seems to be a perspective model for searching anti-atherogenic drugs.

The PI3K/Akt pathway is not a main driver in HDL-mediated cell protection

High-density lipoproteins (HDLs) can protect cells against a variety of death-inducing stresses. This is often accompanied by activation of the anti-apoptotic Akt kinase but whether this activation mediates the protective functions of HDLs is still unclear. In this study, we evaluated the roles of PI3K/Akt signaling in endoplasmic reticulum (ER) stress- and starvation-induced cell death using pharmacological and genetic approaches to gain a better understanding of the relationship between Akt- and HDL-mediated protection. Three cell models were used for this purpose, a primary endothelial cell line, an insulinoma cell line and a colon adenocarcinoma cell line. Our results show that HDLs indeed elicited mild Akt activation in all the tested cellular models. PI3K is one of the main upstream proteins involved in Akt stimulation. In the three cellular models, LY294002, a PI3K inhibitor, only slightly blunted HDLs protection, indicating that HDLs induce PI3K-independent cell protection. Furthermore, genetic ablation or silencing of Akt did not abolish the protective effects of HDLs. This study demonstrates that the PI3K-Akt signaling pathway is not the main mediator of the cell protective functions of HDLs. Further investigation is therefore needed to identify the intrinsic mechanism of HDL-mediated cell protection.

Sphingosine-1-phosphate promotes barrier-stabilizing effects in human microvascular endothelial cells via AMPK-dependent mechanisms

Breakdown of the endothelial barrier is a critical step in the development of organ failure in severe inflammatory conditions such as sepsis. Endothelial cells from different tissues show phenotypic variations which are often neglected in endothelial research. Sphingosine-1-phosphate (S1P) and AMP-dependent kinase (AMPK) have been shown to protect the endothelium and phosphorylation of AMPK by S1P was shown in several cell types. However, the role of the S1P-AMPK interrelationship for endothelial barrier stabilization has not been investigated. To assess the role of the S1P-AMPK signalling axis in this context, we established an in vitro model allowing real-time monitoring of endothelial barrier function in human microvascular endothelial cells (HMEC-1) and murine glomerular endothelial cells (GENCs) with the electric cell-substrate impedance sensing (ECIS™) system. Following the disruption of the cell barrier by co-administration of LPS, TNF-α, IL-1ß, IFN-γ, and IL-6, we demonstrated self-recovery of the disrupted barrier in HMEC-1, while the barrier remained compromised in GENCs. Under physiological conditions we observed a rapid phosphorylation of AMPK in HMEC-1 stimulated with S1P, but not in GENCs. Consistently, S1P enhanced the basal endothelial barrier in HMEC-1 exclusively. siRNA-mediated knockdown of AMPK in HMEC-1 led to a less pronounced barrier enhancement. Thus we present evidence for a functional role of AMPK in S1P-mediated barrier stabilization in HMEC-1 and we provide insight into cell-type specific differences of the S1P-AMPK-interrelationship, which might influence the development of interventional strategies targeting endothelial barrier dysfunction.

Metformin inhibits visceral allodynia and increased gut permeability induced by stress in rats

BACKGROUND AND AIM

Metformin has been shown to have anti-cytokine property. Lipopolysaccharide (LPS)-induced or repeated water avoidance stress (WAS)-induced visceral allodynia and increased gut permeability were pro-inflammatory cytokine-dependent responses, which were considered to be animal models of irritable bowel syndrome (IBS). We hypothesized that metformin improves symptoms in the patients with IBS by attenuating these visceral changes and tested the hypothesis in rats.

METHODS

The threshold of the visceromotor response induced by colonic balloon distention was measured. Colonic permeability was determined in vivo by quantifying the absorbed Evans blue for 15 min spectrophotometrically.

RESULTS

Subcutaneously injected LPS (1 mg/kg) reduced the threshold of visceromotor response, and metformin (5-50 mg/kg for 3 days) intraperitoneally attenuated this response in a dose-dependent manner. Repeated WAS (1 h daily for 3 days) induced visceral allodynia, which was also blocked by metformin. The antinociceptive effect of metformin on the LPS-induced allodynia was reversed by compound C, an adenosine monophosphate-activated protein kinase inhibitor or N^G -nitro-L-arginine methyl ester, a nitric oxide synthesis inhibitor but not modified by naloxone. Additionally, it was blocked by sulpiride, a dopamine D2 receptor antagonist, but domperidone, a peripheral dopamine D2 receptor antagonist, did not alter it. Metformin also blocked the LPS-induced or repeated WAS-induced increased colonic permeability.

CONCLUSIONS

Metformin attenuated the visceral allodynia and increased gut permeability in animal IBS models. These actions may be evoked via activation of adenosine monophosphate-activated protein kinase, nitric oxide, and central dopamine D2 pathways. These results indicate the possibility that metformin can be useful for treating IBS.

Role of AMPK in atherosclerosis via autophagy regulation

Atherosclerosis is characterized by the accumulation of lipids and deposition of fibrous elements in the vascular wall, which is the primary cause of cardiovascular diseases. Adenosine monophosphate-activated protein kinase (AMPK) is a metabolic sensor of energy metabolism that regulates multiple physiological processes, including lipid and glucose metabolism and the normalization of energy imbalances. Overwhelming evidence indicates that AMPK activation markedly attenuates atherosclerosis development. Autophagy inhibits cell apoptosis and inflammation and promotes cholesterol efflux and efferocytosis. Physiological autophagy is essential for maintaining normal cardiovascular function. Increasing evidence demonstrates that autophagy occurs in developing atherosclerotic plaques. Emerging evidence indicates that AMPK regulates autophagy via a downstream signaling pathway. The complex relationship between AMPK and autophagy has attracted the attention of many researchers because of this close relationship to atherosclerosis development. This review demonstrates the role of AMPK and autophagy in atherosclerosis. An improved understanding of this interrelationship will create novel preventive and therapeutic strategies for atherosclerosis.

VEGFR2 is activated by high-density lipoproteins and plays a key role in the proangiogenic action of HDL in ischemia

High-density lipoproteins augment hypoxia-induced angiogenesis by inducing the key angiogenic vascular endothelial growth factor A (VEGFA) and total protein levels of its receptor 2 (VEGFR2). The activation/phosphorylation of VEGFR2 is critical for mediating downstream, angiogenic signaling events. This study aimed to determine whether reconstituted high-density lipoprotein (rHDL) activates VEGFR2 phosphorylation and the downstream signaling events and the importance of VEGFR2 in the proangiogenic effects of rHDL in hypoxia. In vitro, rHDL increased VEGFR2 activation and enhanced phosphorylation of downstream, angiogenic signaling proteins ERK1/2 and p38 MAPK in hypoxia. Incubation with a VEGFR2-neutralizing antibody attenuated rHDL-induced phosphorylation of VEGFR2, ERK1/2, p38 MAPK, and tubule formation. In a murine model of ischemia-driven neovascularization, rHDL infusions enhanced blood perfusion and augmented capillary and arteriolar density. Infusion of a VEGFR2-neutralizing antibody ablated those proangiogenic effects of rHDL. Circulating Sca1⁺/CXCR4⁺ angiogenic progenitor cell levels, important for neovascularization in response to ischemia, were higher in rHDL-infused mice 3 d after ischemic induction, but that did not occur in mice that also received the VEGFR2-neutralizing antibody. In summary, VEGFR2 has a key role in the proangiogenic effects of rHDL in hypoxia/ischemia. These findings have therapeutic implications for angiogenic diseases associated with an impaired response to tissue ischemia.-Cannizzo, C. M., Adonopulos, A. A., Solly, E. L., Ridiandries, A., Vanags, L. Z., Mulangala, J., Yuen, S. C. G., Tsatralis, T., Henriquez, R., Robertson, S., Nicholls, S. J., Di Bartolo, B. A., Ng, M. K. C., Lam, Y. T., Bursill, C. A., Tan, J. T. M. VEGFR2 is activated by high-density lipoproteins and plays a key role in the proangiogenic action of HDL in ischemia.

Rhizoma Coptidis and Berberine as a Natural Drug to Combat Aging and Aging-Related Diseases via Anti-Oxidation and AMPK Activation

Aging is the greatest risk factor for human diseases, as it results in cellular growth arrest, impaired tissue function and metabolism, ultimately impacting life span. Two different mechanisms are thought to be primary causes of aging. One is cumulative DNA damage induced by a perpetuating cycle of oxidative stress; the other is nutrient-sensing adenosine monophosphate-activated protein kinase (AMPK) and rapamycin (mTOR)/ ribosomal protein S6 (rpS6) pathways. As the main bioactive component of natural Chinese medicine rhizoma coptidis (RC), berberine has recently been reported to expand life span in Drosophila melanogaster, and attenuate premature cellular senescence. Most components of RC including berberine, coptisine, palmatine, and jatrorrhizine have been found to have beneficial effects on hyperlipidemia, hyperglycemia and hypertension aging-related diseases. The mechanism of these effects involves multiple cellular kinase and signaling pathways, including anti-oxidation, activation of AMPK signaling and its downstream targets, including mTOR/rpS6, Sirtuin1/ forkhead box transcription factor O3 (FOXO3), nuclear factor erythroid-2 related factor-2 (Nrf2), nicotinamide adenine dinucleotide (NAD⁺) and nuclear factor-κB (NF-κB) pathways. Most of these mechanisms converge on AMPK regulation on mitochondrial oxidative stress. Therefore, such evidence supports the possibility that rhizoma coptidis, in particular berberine, is a promising anti-aging natural product, and has pharmaceutical potential in combating aging-related diseases via anti-oxidation and AMPK cellular kinase activation.

Differential expression of osteopontin, and osteoprotegerin mRNA in epicardial adipose tissue between patients with severe coronary artery disease and aortic valvular stenosis: association with HDL subclasses

BACKGROUND

Previous studies suggest a relationship of the epicardial adipose tissue (EAT) with progression and calcification of the atherosclerotic plaque; however, it is unknown if this tissue expresses genes that may participate on these processes and if the expression of these genes is regulated by high-density lipoprotein (HDL) subclasses.

METHODS

To explore this possibility, we determined the mRNA expression by qPCR of a pro-calcifying gene (osteopontin (OPN)), and two anti-calcifying genes (osteoprotegerin (OPG) and osteonectin (ON)), in biopsies of EAT obtained from 15 patients with coronary artery disease (CAD) determined by angiography, and 15 patients with diagnostic of aortic valve stenosis but without CAD as control group. We determined the distribution and composition of HDL subclasses by electrophoresis and their statistical relationship with the gene expression in EAT.

RESULTS

EAT from CAD patients showed a higher expression level of OPN and OPG than control group, whereas ON expression was similar between groups. Large HDL subclasses were cholesterol-poor in CAD patients as estimated by the cholesterol-to-phospholipid ratio. A linear regression model showed an independent association of OPN expression with HDL3a-cholesterol, and OPG expression with the relative proportion of HDL3b protein. Logistic analysis determined that OPN expression was positively associated with the presence of atherosclerotic plaque CONCLUSION: OPN, ON, and OPG genes are transcribed in EAT; to the exception of ON, the level of expression was different in CAD patients and control group, and correlated with some HDL subclasses, suggesting a new role of these lipoproteins.

Energy sensing pathways: Bridging type 2 diabetes and colorectal cancer?

The recently rapid increase of obesity and type 2 diabetes mellitus has caused great burden to our society. A positive association between type 2 diabetes and risk of colorectal cancer has been reported by increasing epidemiological studies. The molecular mechanism of this connection remains elusive. However, type 2 diabetes may result in abnormal carbohydrate and lipid metabolism, high levels of circulating insulin, insulin growth factor-1, and adipocytokines, as well as chronic inflammation. All these factors could lead to the alteration of energy sensing pathways such as the AMP activated kinase (PRKA), mechanistic (mammalian) target of rapamycin (mTOR), SIRT1, and autophagy signaling pathways. The resulted impaired SIRT1 and autophagy signaling pathway could increase the risk of gene mutation and cancer genesis by decreasing genetic stability and DNA mismatch repair. The dysregulated mTOR and PRKA pathway could remodel cell metabolism during the growth and metastasis of cancer in order for the cancer cell to survive the unfavorable microenvironment such as hypoxia and low blood supply. Moreover, these pathways may be coupling metabolic and epigenetic alterations that are central to oncogenic transformation. Further researches including molecular pathologic epidemiologic studies are warranted to better address the precise links between these two important diseases.

High density lipoprotein promoting proliferation and migration of type II alveolar epithelial cells during inflammation state

BACKGROUND

To investigate the effect and mechanism of high density lipoprotein (HDL) on type II alveolar epithelial cells during inflammation state.

METHODS

The original generation of type II alveolar epithelial cells were separated in rats and treated with PBS/LPS/HDL/HDL + LPS. To observe the proliferation and migration of type II alveolar epithelial cells with bromodeoxyuridine(BrdU) assay, transwell assay and wound healing experiments. In addition, western blot detected the expression of TP-binding cassette transporter A1 (ABCA1), cystic fibrosis transmembrane conductance regulator (CFTR) and the phosphorylation of AKT/extracellular signal-regulated kinase(ERK)/mitogen-activated protein kinase(MAPK). Enzyme-linked immunosorbent assay (ELISA) tested the secretion of tumor necrosis factor a(TNF-a)/interleukin 1a(IL-1a)/IL-6.

RESULTS

HDL promoted the proliferation (↑17%, p < 0.001 HDL+ LPS vs. LPS) and migration (wounding healing: ↑93%, p < 0.001 HDL+ LPS vs. LPS; transwell migration: ↑154%, p < 0.001 HDL+ LPS vs. LPS) of type II alveolar epithelial cells. Furthermore, HDL increased the phosphorylation of MAPK, but not AKT/ERK. And HDL decreased the secretion of TNF-a (↓46%, p < 0.01 HDL+ LPS vs. LPS) and IL-1a (↓45%, p < 0.001 HDL+ LPS vs. LPS), but not IL-6. In addition, HDL up-regulated the expression of ABCAI (↑99%, p < 0.001 HDL vs. CON) and down-regulated the expression of CFTR (↓25%, p < 0.05 HDL vs. CON) in type II alveolar epithelial cells.

CONCLUSIONS

HDL increases the phosphorylation of MAPK, which promotes the proliferation and migration of type II alveolar epithelial cells. And it decreased the secretion of TNF-a/IL-1a and the expression of CFTR. All these suggest that HDL plays an important role in anti-inflammatory effect in inflammation state of lung.

S1P in HDL promotes interaction between SR-BI and S1PR1 and activates S1PR1-mediated biological functions: calcium flux and S1PR1 internalization

HDL normally transports about 50-70% of plasma sphingosine 1-phosphate (S1P), and the S1P in HDL reportedly mediates several HDL-associated biological effects and signaling pathways. The HDL receptor, SR-BI, as well as the cell surface receptors for S1P (S1PRs) may be involved partially and/or completely in these HDL-induced processes. Here we investigate the nature of the HDL-stimulated interaction between the HDL receptor, SR-BI, and S1PR1 using a protein-fragment complementation assay and confocal microscopy. In both primary rat aortic vascular smooth muscle cells and HEK293 cells, the S1P content in HDL particles increased intracellular calcium concentration, which was mediated by S1PR1. Mechanistic studies performed in HEK293 cells showed that incubation of cells with HDL led to an increase in the physical interaction between the SR-BI and S1PR1 receptors that mainly occurred on the plasma membrane. Model recombinant HDL (rHDL) particles formed in vitro with S1P incorporated into the particle initiated the internalization of S1PR1, whereas rHDL without supplemented S1P did not, suggesting that S1P transported in HDL can selectively activate S1PR1. In conclusion, these data suggest that S1P in HDL stimulates the transient interaction between SR-BI and S1PRs that can activate S1PRs and induce an elevation in intracellular calcium concentration.

SR-BI: Linking Cholesterol and Lipoprotein Metabolism with Breast and Prostate Cancer

Studies have demonstrated the significant role of cholesterol and lipoprotein metabolism in the progression of cancer. The SCARB1 gene encodes the scavenger receptor class B type I (SR-BI), which is an 82-kDa glycoprotein with two transmembrane domains separated by a large extracellular loop. SR-BI plays an important role in the regulation of cholesterol exchange between cells and high-density lipoproteins. Accordingly, hepatic SR-BI has been shown to play an essential role in the regulation of the reverse cholesterol transport pathway, which promotes the removal and excretion of excess body cholesterol. In the context of atherosclerosis, SR-BI has been implicated in the regulation of intracellular signaling, lipid accumulation, foam cell formation, and cellular apoptosis. Furthermore, since lipid metabolism is a relevant target for cancer treatment, recent studies have focused on examining the role of SR-BI in this pathology. While signaling pathways have initially been explored in non-tumoral cells, studies with cancer cells have now demonstrated SR-BI's function in tumor progression. In this review, we will discuss the role of SR-BI during tumor development and malignant progression. In addition, we will provide insights into the transcriptional and post-transcriptional regulation of the SCARB1 gene. Overall, studying the role of SR-BI in tumor development and progression should allow us to gain useful information for the development of new therapeutic strategies.

Insulin Resistance Prevents AMPK-induced Tau Dephosphorylation through Akt-mediated Increase in AMPKSer-485 Phosphorylation

Metabolic syndrome (MetS) is a cluster of cardiovascular risk factors including obesity, diabetes, and dyslipidemia, and insulin resistance (IR) is the central feature of MetS. Recent studies suggest that MetS is a risk factor for Alzheimer disease (AD). AMP-activated kinase (AMPK) is an evolutionarily conserved fuel-sensing enzyme and a key player in regulating energy metabolism. In this report, we examined the role of IR on the regulation of AMPK phosphorylation and AMPK-mediated Tau phosphorylation. We found that AMPK(Ser-485), but not AMPK(Thr-172), phosphorylation is increased in the cortex of db/db and high fat diet-fed obese mice, two mouse models of IR. In vitro, treatment of human cortical stem cell line (HK-5320) and primary mouse embryonic cortical neurons with the AMPK activator, 5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR), induced AMPK phosphorylation at both Thr-172 and Ser-485. AMPK activation also triggered Tau dephosphorylation. When IR was mimicked in vitro by chronically treating the cells with insulin, AICAR specifically induced AMPK(Ser-485), but not AMPK(Thr-172), hyperphosphorylation whereas AICAR-induced Tau dephosphorylation was inhibited. IR also resulted in the overactivation of Akt by AICAR treatment; however, preventing Akt overactivation during IR prevented AMPK(Ser-485) hyperphosphorylation and restored AMPK-mediated Tau dephosphorylation. Transfection of AMPK(S485A) mutant caused similar results. Therefore, our results suggest the following mechanism for the adverse effect of IR on AD pathology: IR → chronic overactivation of Akt → AMPK(Ser-485) hyperphosphorylation → inhibition of AMPK-mediated Tau dephosphorylation. Together, our results show for the first time a possible contribution of IR-induced AMPK(Ser-485) phosphorylation to the increased risk of AD in obesity and diabetes.

Sphingosine-1-Phosphate Is a Novel Regulator of Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Activity

The cystic fibrosis transmembrane conductance regulator (CFTR) attenuates sphingosine-1-phosphate (S1P) signaling in resistance arteries and has emerged as a prominent regulator of myogenic vasoconstriction. This investigation demonstrates that S1P inhibits CFTR activity via adenosine monophosphate-activated kinase (AMPK), establishing a potential feedback link. In Baby Hamster Kidney (BHK) cells expressing wild-type human CFTR, S1P (1μmol/L) attenuates forskolin-stimulated, CFTR-dependent iodide efflux. S1P's inhibitory effect is rapid (within 30 seconds), transient and correlates with CFTR serine residue 737 (S737) phosphorylation. Both S1P receptor antagonism (4μmol/L VPC 23019) and AMPK inhibition (80μmol/L Compound C or AMPK siRNA) attenuate S1P-stimluated (i) AMPK phosphorylation, (ii) CFTR S737 phosphorylation and (iii) CFTR activity inhibition. In BHK cells expressing the ΔF508 CFTR mutant (CFTRΔF508), the most common mutation causing cystic fibrosis, both S1P receptor antagonism and AMPK inhibition enhance CFTR activity, without instigating discernable correction. In summary, we demonstrate that S1P/AMPK signaling transiently attenuates CFTR activity. Since our previous work positions CFTR as a negative S1P signaling regulator, this signaling link may positively reinforce S1P signals. This discovery has clinical ramifications for the treatment of disease states associated with enhanced S1P signaling and/or deficient CFTR activity (e.g. cystic fibrosis, heart failure). S1P receptor/AMPK inhibition could synergistically enhance the efficacy of therapeutic strategies aiming to correct aberrant CFTR trafficking.

Characterization of Imidazopyridine Compounds as Negative Allosteric Modulators of Proton-Sensing GPR4 in Extracellular Acidification-Induced Responses

G protein-coupled receptor 4 (GPR4), previously proposed as the receptor for sphingosylphosphorylcholine, has recently been identified as the proton-sensing G protein-coupled receptor (GPCR) coupling to multiple intracellular signaling pathways, including the G_s protein/cAMP and G₁₃ protein/Rho. In the present study, we characterized some imidazopyridine compounds as GPR4 modulators that modify GPR4 receptor function. In the cells that express proton-sensing GPCRs, including GPR4, OGR1, TDAG8, and G2A, extracellular acidification stimulates serum responsive element (SRE)-driven transcriptional activity, which has been shown to reflect Rho activity, with different proton sensitivities. Imidazopyridine compounds inhibited the moderately acidic pH-induced SRE activity only in GPR4-expressing cells. Acidic pH-stimulated cAMP accumulation, mRNA expression of inflammatory genes, and GPR4 internalization within GPR4-expressing cells were all inhibited by the GPR4 modulator. We further compared the inhibition property of the imidazopyridine compound with psychosine, which has been shown to selectively inhibit actions induced by proton-sensing GPCRs, including GPR4. In the GPR4 mutant, in which certain histidine residues were mutated to phenylalanine, proton sensitivity was significantly shifted to the right, and psychosine failed to further inhibit acidic pH-induced SRE activation. On the other hand, the imidazopyridine compound almost completely inhibited acidic pH-induced action in mutant GPR4. We conclude that some imidazopyridine compounds show specificity to GPR4 as negative allosteric modulators with a different action mode from psychosine, an antagonist susceptible to histidine residues, and are useful for characterizing GPR4-mediated acidic pH-induced biological actions.

Drug-subphenotype interactions for cancer in type 2 diabetes mellitus

On the basis of data obtained from a prospective cohort of Chinese patients with type 2 diabetes mellitus (T2DM), we discuss cancer subphenotypes (risk factors) in patients with T2DM, which can lead to drug-cancer subphenotype interactions. These subphenotypes include HDL cholesterol levels <1.0 mmol/l, co-occurrence of LDL cholesterol levels <2.8 mmol/l and triglyceride levels <1.7 mmol/l, and co-occurrence of LDL cholesterol levels <2.8 mmol/l and albuminuria. The increased risk of cancer associated with low levels of HDL cholesterol, low LDL cholesterol levels plus low triglyceride levels, and low levels of LDL cholesterol plus albuminuria can be reduced by treatment with metformin, renin-angiotensin system (RAS) inhibitors and statins, respectively. Mechanistic studies support the hypothesis that dysregulation of the 5'-AMP-activated protein kinase pathway and crosstalk between the RAS and insulin-like growth factor 1-cholesterol pathways create a cancer-promoting milieu in patients with T2DM. These findings highlight that in Chinese individuals, multiple pathways are implicated in the link between T2DM and cancer, which can generate multiple subphenotypes as well as drug-subphenotype interactions.

Signal transduction by HDL: agonists, receptors, and signaling cascades

Numerous epidemiologic studies revealed that high-density lipoprotein (HDL) is an important risk factor for coronary heart disease. There are several well-documented HDL functions such as reversed cholesterol transport, inhibition of inflammation, or inhibition of platelet activation that may account for the atheroprotective effects of this lipoprotein. Mechanistically, these functions are carried out by a direct interaction of HDL particle or its components with receptors localized on the cell surface followed by generation of intracellular signals. Several HDL-associated receptor ligands such as apolipoprotein A-I (apoA-I) or sphingosine-1-phosphate (S1P) have been identified in addition to HDL holoparticles, which interact with surface receptors such as ATP-binding cassette transporter A1 (ABCA1); S1P receptor types 1, 2, and 3 (S1P1, S1P2, and S1P3); or scavenger receptor type I (SR-BI) and activate intracellular signaling cascades encompassing kinases, phospholipases, trimeric and small G-proteins, and cytoskeletal proteins such as actin or junctional protein such as connexin43. In addition, depletion of plasma cell cholesterol mediated by ABCA1, ATP-binding cassette transporter G1 (ABCG1), or SR-BI was demonstrated to indirectly inhibit signaling over proinflammatory or proliferation-stimulating receptors such as Toll-like or growth factor receptors. The present review summarizes the current knowledge regarding the HDL-induced signal transduction and its relevance to athero- and cardioprotective effects as well as other physiological effects exerted by HDL.

HDL and endothelial protection

High-density lipoproteins (HDLs) represent a family of particles characterized by the presence of apolipoprotein A-I (apoA-I) and by their ability to transport cholesterol from peripheral tissues back to the liver. In addition to this function, HDLs display pleiotropic effects including antioxidant, anti-apoptotic, anti-inflammatory, anti-thrombotic or anti-proteolytic properties that account for their protective action on endothelial cells. Vasodilatation via production of nitric oxide is also a hallmark of HDL action on endothelial cells. Endothelial cells express receptors for apoA-I and HDLs that mediate intracellular signalling and potentially participate in the internalization of these particles. In this review, we will detail the different effects of HDLs on the endothelium in normal and pathological conditions with a particular focus on the potential use of HDL therapy to restore endothelial function and integrity.

High-density lipoprotein: a novel target for antirestenosis therapy

Restenosis is an integral pathological process central to the recurrent vessel narrowing after interventional procedures. Although the mechanisms for restenosis are diverse in different pathological conditions, endothelial dysfunction, inflammation, vascular smooth muscle cell (SMC) proliferation, and myofibroblasts transition have been thought to play crucial role in the development of restenosis. Indeed, there is an inverse relationship between high-density lipoprotein (HDL) levels and risk for coronary heart disease (CHD). However, relatively studies on the direct assessment of HDL effect on restenosis are limited. In addition to involvement in the cholesterol reverse transport, many vascular protective effects of HDL, including protection of endothelium, antiinflammation, antithrombus actions, inhibition of SMC proliferation, and regulation by adventitial effects may contribute to the inhibition of restenosis, though the exact relationships between HDL and restenosis remain to be elucidated. This review summarizes the vascular protective effects of HDL, emphasizing the potential role of HDL in intimal hyperplasia and vascular remodeling, which may provide novel prophylactic and therapeutic strategies for antirestenosis.

Atheroprotective role of high-density lipoprotein (HDL)-associated sphingosine-1-phosphate (S1P)

Numerous epidemiological studies documented an inverse relationship between plasma high-density lipoprotein (HDL) cholesterol levels and the extent of atherosclerotic disease. However, clinical interventions targeting HDL cholesterol failed to show clinical benefits with respect to cardiovascular risk reduction, suggesting that HDL components distinct from cholesterol may account for anti-atherogenic effects attributed to this lipoprotein. Sphingosine-1-phosphate (S1P)-a lysosphingolipid exerting its biological activity via binding to specific G protein-coupled receptors and regulating a wide array of biological responses in a variety of different organs and tissues including the cardiovascular system-has been identified as an integral constituent of HDL particles. In the present review, we discuss current evidence from epidemiological studies, experimental approaches in vitro, and animal models of atherosclerosis, suggesting that S1P contributes to atheroprotective effects exerted by HDL particles.

OxLDL induces endothelial dysfunction and death via TRAF3IP2: inhibition by HDL3 and AMPK activators

Oxidized low-density lipoprotein (oxLDL) induces endothelial cell death through the activation of NF-κB and AP-1 pathways. TRAF3IP2 is a redox-sensitive cytoplasmic adapter protein and an upstream regulator of IKK/NF-κB and JNK/AP-1. Here we show that oxLDL-induced death in human primary coronary artery endothelial cells (ECs) was markedly attenuated by the knockdown of TRAF3IP2 or the lectin-like oxLDL receptor 1 (LOX-1). Further, oxLDL induced Nox2/superoxide-dependent TRAF3IP2 expression, IKK/p65 and JNK/c-Jun activation, and LOX-1 upregulation, suggesting a reinforcing mechanism. Similarly, the lysolipids present in oxLDL (16:0-LPC and 18:0-LPC) and minimally modified LDL also upregulated TRAF3IP2 expression. Notably, whereas native HDL3 reversed oxLDL-induced TRAF3IP2 expression and cell death, 15-lipoxygenase-modified HDL3 potentiated its proapoptotic effects. The activators of the AMPK/Akt pathway, adiponectin, AICAR, and metformin, attenuated superoxide generation, TRAF3IP2 expression, and oxLDL/TRAF3IP2-mediated EC death. Further, both HDL3 and adiponectin reversed oxLDL/TRAF3IP2-dependent monocyte adhesion to endothelial cells in vitro. Importantly, TRAF3IP2 gene deletion and the AMPK activators reversed oxLDL-induced impaired vasorelaxation ex vivo. These results indicate that oxLDL-induced endothelial cell death and dysfunction are mediated via TRAF3IP2 and that native HDL3 and the AMPK activators inhibit this response. Targeting TRAF3IP2 could potentially inhibit progression of atherosclerotic vascular diseases.

Dietary polyphenols regulate endothelial function and prevent cardiovascular disease

Vascular endothelial cell (EC) dysfunction strongly induces development of cardiovascular and cerebrovascular diseases. Epidemiologic studies demonstrated a preventative effect of dietary polyphenols toward cardiovascular disease. In studies using cultured vascular ECs, polyphenols were recognized to regulate nitric oxide and endothelin-1 (ET-1) production. Furthermore, epigallocatechin-3-gallate inhibited the expression of adhesion molecules by a signaling pathway that is similar to that of high-density lipoprotein and involves induction of Ca(2+)/calmodulin-dependent kinase II, liver kinase B, and phosphatidylinositol 3-kinase expression. The effects of polyphenols on ECs include antioxidant activity and enhancement of the expression of several protective proteins, including endothelial nitric oxide synthase and paraoxonase 1. However, the observed effects of dietary polyphenols in vitro do not always translate to an in vivo setting. As such, there are many questions concerning their physiological mode of action. In this review, we discuss research on the effect of dietary polyphenols on cardiovascular disease and their protective effect on EC dysfunction.

AMPK activation--protean potential for boosting healthspan

AMP-activated kinase (AMPK) is activated when the cellular (AMP+ADP)/ATP ratio rises; it therefore serves as a detector of cellular "fuel deficiency." AMPK activation is suspected to mediate some of the health-protective effects of long-term calorie restriction. Several drugs and nutraceuticals which slightly and safely impede the efficiency of mitochondrial ATP generation-most notably metformin and berberine-can be employed as clinical AMPK activators and, hence, may have potential as calorie restriction mimetics for extending healthspan. Indeed, current evidence indicates that AMPK activators may reduce risk for atherosclerosis, heart attack, and stroke; help to prevent ventricular hypertrophy and manage congestive failure; ameliorate metabolic syndrome, reduce risk for type 2 diabetes, and aid glycemic control in diabetics; reduce risk for weight gain; decrease risk for a number of common cancers while improving prognosis in cancer therapy; decrease risk for dementia and possibly other neurodegenerative disorders; help to preserve the proper structure of bone and cartilage; and possibly aid in the prevention and control of autoimmunity. While metformin and berberine appear to have the greatest utility as clinical AMPK activators-as reflected by their efficacy in diabetes management-regular ingestion of vinegar, as well as moderate alcohol consumption, may also achieve a modest degree of health-protective AMPK activation. The activation of AMPK achievable with any of these measures may be potentiated by clinical doses of the drug salicylate, which can bind to AMPK and activate it allosterically.

HDLs protect the MIN6 insulinoma cell line against tunicamycin-induced apoptosis without inhibiting ER stress and without restoring ER functionality

HDLs protect pancreatic beta cells against apoptosis induced by several endoplasmic reticulum (ER) stressors, including thapsigargin, cyclopiazonic acid, palmitate and insulin over-expression. This protection is mediated by the capacity of HDLs to maintain proper ER morphology and ER functions such as protein folding and trafficking. Here, we identified a distinct mode of protection exerted by HDLs in beta cells challenged with tunicamycin (TM), a protein glycosylation inhibitor inducing ER stress. HDLs were found to inhibit apoptosis induced by TM in the MIN6 insulinoma cell line and this correlated with the maintenance of a normal ER morphology. Surprisingly however, this protective response was neither associated with a significant ER stress reduction, nor with restoration of protein folding and trafficking in the ER. These data indicate that HDLs can use at least two mechanisms to protect beta cells against ER stressors. One that relies on the maintenance of ER function and one that operates independently of ER function modulation. The capacity of HDLs to activate several anti-apoptotic pathways in beta cells may explain their ability to efficiently protect these cells against a variety of insults.

Anti-allergic and anti-inflammatory effects of bakkenolide B isolated from Petasites japonicus leaves

AIMS OF THE STUDY

To elucidate the anti-allergic and anti-inflammatory effects of Petasites genus, we studied the effects of several compounds isolated from Petasites japonicas leaves.

MATERIALS AND METHODS

Bakkenolide B was isolated from Petasites japonicus leaves. Antigen-induced degranulation was measured in RBL-2H3 mast cells by measuring β-hexosamidase activity. Induction of inducible nitric oxide synthase and cyclooxygenase 2 was measured by Western blotting in peritoneal macrophages. Ovalbumin-induced asthma model was used for in vivo efficacy test of bakkanolide B.

RESULTS

We found that bakkenolide B, a major component of the leaves, concentration-dependently inhibited RBL-2H3 mast cell degranulation. Bakkenolide B also inhibited the gene inductions of inducible nitric oxide synthase and cyclooxygenase 2 in mouse peritoneal macrophages. Furthermore, in an ovalbumin-induced asthma model, bakkenolide B strongly inhibited the accumulation of eosinophils, macrophages, and lymphocytes to bronchoalveolar lavage fluid.

CONCLUSION

Bakkenolide B has suppressive properties for allergic and inflammatory responses and may be utilized as a potent agent for the treatment of asthma.

Laminar shear stress upregulates endothelial Ca²⁺-activated K⁺ channels KCa2.3 and KCa3.1 via a Ca²⁺/calmodulin-dependent protein kinase kinase/Akt/p300 cascade

In endothelial cells (ECs), Ca²⁺-activated K⁺ channels KCa2.3 and KCa3.1 play a crucial role in the regulation of arterial tone via producing NO and endothelium-derived hyperpolarizing factors. Since a rise in intracellular Ca²⁺ levels and activation of p300 histone acetyltransferase are early EC responses to laminar shear stress (LS) for the transcriptional activation of genes, we examined the role of Ca²⁺/calmodulin-dependent kinase kinase (CaMKK), the most upstream element of a Ca²⁺/calmodulin-kinase cascade, and p300 in LS-dependent regulation of KCa2.3 and KCa3.1 in ECs. Exposure to LS (15 dyn/cm²) for 24 h markedly increased KCa2.3 and KCa3.1 mRNA expression in cultured human coronary artery ECs (3.2 ± 0.4 and 45 ± 10 fold increase, respectively; P < 0.05 vs. static condition; n = 8-30), whereas oscillatory shear (OS; ± 5 dyn/cm² × 1 Hz) moderately increased KCa3.1 but did not affect KCa2.3. Expression of KCa2.1 and KCa2.2 was suppressed under both LS and OS conditions, whereas KCa1.1 was slightly elevated in LS and unchanged in OS. Inhibition of CaMKK attenuated LS-induced increases in the expression and channel activity of KCa2.3 and KCa3.1, and in phosphorylation of Akt (Ser473) and p300 (Ser1834). Inhibition of Akt abolished the upregulation of these channels by diminishing p300 phosphorylation. Consistently, disruption of the interaction of p300 with transcription factors eliminated the induction of these channels. Thus a CaMKK/Akt/p300 cascade plays an important role in LS-dependent induction of KCa2.3 and KCa3.1 expression, thereby regulating EC function and adaptation to hemodynamic changes.

Endothelial lipase is a critical determinant of high-density lipoprotein-stimulated sphingosine 1-phosphate-dependent signaling in vascular endothelium

OBJECTIVE

In addition to an extensively characterized role of high-density lipoprotein (HDL) in reverse cholesterol transport, bioactive lipids bound to HDL can also exert diverse vascular effects. Despite this, integration of HDL action in the vasculature with pathways that metabolize HDL and release bioactive lipids has been much less explored. The effects of HDL on endothelial cells are mediated in part by HDL-associated sphingosine 1-phosphate (S1P), which binds to S1P1 receptors and promotes activation of endothelial NO synthase (eNOS) and the kinase Akt. In these studies, we characterized the role of endothelial lipase (EL) in the control of endothelial signaling and biology, including those mediated by HDL-associated S1P.

APPROACH AND RESULTS

HDL-induced angiogenesis in aortic rings from EL-deficient (EL(-/-)) mice was markedly decreased compared with wild-type controls. In cultured endothelial cells, small interfering RNA-mediated knockdown of EL abrogated HDL-promoted endothelial cell migration and tube formation. Small interfering RNA-mediated EL knockdown also attenuated HDL-induced phosphorylation of eNOS(1179) and Akt(473). S1P stimulation restored HDL-induced endothelial migration and Akt/eNOS phosphorylation that had been blocked by small interfering RNA-mediated EL knockdown. HDL-induced endothelial cell migration and Akt/eNOS phosphorylation were completely inhibited by the S1P1 antagonist W146 but not by the S1P3 antagonist CAY10444.

CONCLUSIONS

EL is a critical determinant of the effects of HDL on S1P-mediated vascular responses and acts on HDL to promote activation of S1P1, leading to Akt/eNOS phosphorylation and subsequent endothelial migration and angiogenesis. The role of EL in HDL-associated S1P effects provides new insights into EL action, the responses seen through EL and HDL interaction, and S1P signaling.

Regulation of signal transduction by HDL

High density lipoprotein (HDL) cholesterol has direct effects on numerous cell types that influence cardiovascular and metabolic health. These include endothelial cells, vascular smooth-muscle cells, leukocytes, platelets, adipocytes, skeletal muscle myocytes, and pancreatic β cells. The effects of HDL or apoA-I, its major apolipoprotein, occur through the modulation of intracellular calcium, oxygen-derived free-radical production, numerous kinases, and enzymes, including endothelial nitric-oxide synthase (eNOS). ApoA-I and HDL also influence gene expression, particularly genes encoding mediators of inflammation in vascular cells. In many paradigms, the change in intracellular signaling occurs as a result of cholesterol efflux, with the cholesterol acceptor methyl-β-cyclodextrin often invoking responses identical to HDL or apoA-I. The ABC transporters ABCA1 and ABCG1 and scavenger receptor class B, type I (SR-BI) frequently participate in the cellular responses. Structure-function relationships are emerging for signal initiation by ABCA1 and SR-BI, with plasma membrane cholesterol binding by the C-terminal transmembrane domain of SR-BI uniquely enabling it to serve as a sensor of changes in membrane cholesterol. Further investigation of the processes underlying HDL and apoA-I modulation of intracellular signaling will potentially reveal new prophylactic and therapeutic strategies to optimize both cardiovascular and metabolic health.

Epigallocatechin 3-gallate inhibits 7-ketocholesterol-induced monocyte-endothelial cell adhesion

7-Ketocholesterol (7KC) induces monocytic adhesion to endothelial cells, and induces arteriosclerosis while high-density lipoprotein (HDL) inhibits monocytic adhesion to the endothelium. Epigallocatechin 3-gallate (EGCG) was found to have a protective effect against arteriosclerosis. Therefore, the purpose of this study was to examine the possible HDL-like mechanisms of EGCG in endothelial cells by investigating whether EGCG inhibits 7KC-induced monocyte-endothelial cell adhesion by activating HDL-dependent signal transduction pathways. 7KC and/or EGCG were added to human endothelial cells (ISO-HAS), and the adhesion of pro-monocytic U937 cells was examined. The expression of genes associated with HDL effects such as Ca(2+)/calmodulin-dependent kinase II (CaMKKII), liver kinase B (LKD1), PSD-95/Dlg/ZO-1 kinase 1 (PDZK1), phosphatidylinositol 3-kinase (PI3K), intercellular adhesion molecule-1 (ICAM-1), monocyte chemotactic protein-1 (MCP-1), and endothelial nitric oxide synthase (eNOS) was examined by RT-PCR, and ICAM-1 protein expression was evaluated by western blot (WB). Production of reactive oxygen species (ROS) was examined with H2DCFDA. 7KC significantly induced adhesion of U937 cells to human endothelial cells while significantly increasing gene expressions of ICAM-1 and MCP-1 and decreasing eNOS and CaMKKII gene expressions. EGCG inhibited 7KC-induced monocytic adhesion to endothelial cells, and induced expression of eNOS and several genes involved in the CaMKKII pathway. Stimulation of endothelial cells with EGCG produced intracellular ROS, whereas treatment with N-acetylcysteine (NAC) blocked EGCG-induced expression of eNOS and CaMKKII. These results suggest that inhibition of monocyte-endothelial cell adhesion by EGCG is associated with CaMKKII pathway activation by ROS. Inhibition of 7KC-induced monocyte-endothelial cell adhesion induced by EGCG may function similarly to HDL.

Immunometabolism of AMPK in insulin resistance and atherosclerosis

Obesity leads to insulin resistance and atherosclerosis, which precede Type 2 diabetes and cardiovascular disease. Immunometabolism addresses how metabolic and inflammatory pathways converge to maintain health and a contemporary problem is determining how obesity-induced inflammation precipitates chronic diseases such as insulin resistance and atherosclerosis. AMP-activated protein kinase (AMPK) is an important serine/threonine kinase well known for regulating metabolic processes and maintaining energy homeostasis. However, both metabolic and immunological AMPK-mediated effects play a role in disease. Pro-inflammatory mediators suppress AMPK activity and hinder lipid oxidation. In addition, AMPK activation curbs inflammation by directly inhibiting pro-inflammatory signaling pathways and limiting the build-up of specific lipid intermediates that elicit immune responses. In the context of obesity and chronic disease, these reciprocal responses involve both immune and metabolic cells. Therefore, the immunometabolism of AMPK-mediated processes and therapeutics should be considered in atherosclerosis and insulin resistance.

The sphingosine-1-phosphate analog FTY720 reduces muscle ceramide content and improves glucose tolerance in high fat-fed male mice

FTY720 is a sphingosine-1-phosphate analog that has been shown to inhibit ceramide synthesis in vitro. Because ceramide accumulation in muscle is associated with insulin resistance, we aimed to examine whether FTY720 would prevent muscle ceramide accumulation in high fat-fed mice and subsequently improve glucose homeostasis. Male C57Bl/6 mice were fed either a chow or high fat-diet (HFD) for 6 wk, after which they were treated with vehicle or FTY720 (5 mg/kg) daily for a further 6 wk. The ceramide content of muscle was examined and insulin action was assessed. Whereas the HFD increased muscle ceramide, this was prevented by FTY720 treatment. This was not associated with alterations in the expression of genes involved in sphingolipid metabolism. Interestingly, the effects of FTY720 on lipid metabolism were not limited to ceramide because FTY720 also prevented the HFD-induced increase in diacylglycerol and triacylglycerol in muscle. Furthermore, the increase in CD36 mRNA expression induced by fat feeding was prevented in muscle of FTY720-treated mice. This was associated with an attenuation of the HFD-induced increase in palmitate uptake and esterification. In addition, FTY720 improved glucose homeostasis as demonstrated by a reduction in plasma insulin, an improvement in whole-body glucose tolerance, an increase in insulin-stimulated glucose uptake, and Akt phosphorylation in muscle. In conclusion, FTY720 exerts beneficial effects on muscle lipid metabolism that prevent lipid accumulation and improve glucose tolerance in high fat-fed mice. Thus, FTY720 and other compounds that target sphingosine-1-phosphate signaling may have therapeutic potential in treating insulin resistance.

HDL functionality

PURPOSE OF REVIEW

HDL cholesterol concentration is inversely correlated with cardiovascular disease and has a wide range of functions involved in many systems. The purpose of this review is to summarize HDL functionality, its relevance to atherosclerosis and factors affecting HDL functions.

RECENT FINDINGS

The contribution of HDL to reverse cholesterol transport may not be as great as first envisaged. However, it still plays an important role in cholesterol efflux from peripheral tissues. The capacity of HDL to promote cellular cholesterol efflux in an ex-vivo model has been reported to correlate more closely with carotid intima-media thickness than HDL cholesterol concentration. Recently, a variety of other functions of HDL have been described including antimicrobial, antioxidant, antiglycation, anti-inflammatory, nitric oxide--inducing, antithrombotic and antiatherogenic activity and immune modulation as well as a potential role in glucose homeostasis, diabetes pathophysiology and complications.

SUMMARY

HDL has a wide range of functions some of which are independent of its cholesterol content. Its cargo of apolipoproteins, various proteins and phospholipids contributes most to its various functions. These functions are affected by a number of genetic, physiological and pathological factors.

β-carotene reverses the IL-1β-mediated reduction in paraoxonase-1 expression via induction of the CaMKKII pathway in human endothelial cells

Interleukin-1 beta (IL-1β) induces endothelial dysfunction and reduces nitric oxide (NO) production. IL-1β also enhances adhesion molecule expression and induces arteriosclerosis. Conversely, high-density lipoprotein (HDL) induces endothelial NO synthase (eNOS), paraoxonase-1 (PON-1) activity, and maintains vascular health. Diet-derived β-carotene prevents arteriosclerosis, but its mode of action is not understood. The purpose of this study was to examine the HDL-like mechanisms of β-carotene in endothelial cells. We added IL-1β and/or β-carotene to cultured human endothelial cells and examined its effects on the regulation of HDL signal transduction pathways using RT-PCR, real-time PCR, Western blot (WB), and endothelial-U937 adhesion analysis. IL-1β decreased the expression of Ca2+/calmodulin-dependent kinase II (CaMKII), eNOS, PON-1, phosphatidylinositol 3-kinase (PI3K), PSD-95/Dlg/ZO-1 (PZK1), and liver kinase B1 (LKB1). Conversely, it increased the expression of intercellular adhesion molecule-1 (ICAM-1), and monocyte chemoattractant protein 1 (MCP-1). In contrast, β-carotene increased the expression of CaMKKII, PI3K, PZK1, LKB1, eNOS, PON-1, and reduced the expression of ICAM-1 and MCP-1. β-carotene also induced phospho-AMP-activated protein kinase (p-AMPK), phospho-eNOS and PON-1 proteins. Importantly, β-carotene upregulated the IL-1β-mediated decrease of CaMKKII, PZK1, LKB1, eNOS and PON-1. β-carotene inhibited IL-1β-mediated cell adhesion of U937 to endothelial cells. The effect of β-carotene was reversed by a CaMKK inhibitor, STO-609. These findings indicate that β-carotene regulates the expression of PON-1, eNOS and adhesion molecules via CaMKK pathway activation. β-carotene may contribute to the functional maintenance of vascular endothelial cells in a manner similar to HDL, protecting them against stimuli such as IL-1β.

Fenofibrate increases high-density lipoprotein and sphingosine 1 phosphate concentrations limiting abdominal aortic aneurysm progression in a mouse model

There are currently no acceptable treatments to limit progression of abdominal aortic aneurysm (AAA). Increased serum concentrations of high-density lipoprotein (HDL) are associated with reduced risk of developing an AAA. The present study aimed to assess the effects of fenofibrate on aortic dilatation in a mouse model of AAA. Male low-density lipoprotein receptor-deficient (Ldlr(-/-)) mice were maintained on a high-fat diet for 3 weeks followed by 6 weeks of oral administration of vehicle or fenofibrate. From 14 to 18 weeks of age, all mice were infused with angiotensin II (AngII). At 18 weeks of age, blood and aortas were collected for assessment of serum lipoproteins, aortic pathology, aortic Akt1 and endothelial nitric oxide synthase (eNOS) activities, immune cell infiltration, eNOS and inducible NOS (iNOS) expression, sphingosine 1 phosphate (S1P) receptor status, and apoptosis. Mice receiving fenofibrate had reduced suprarenal aortic diameter, reduced aortic arch Sudan IV staining, higher serum HDL levels, increased serum S1P concentrations, and increased aortic Akt1 and eNOS activities compared with control mice. Macrophages, T lymphocytes, and apoptotic cells were less evident and eNOS, iNOS, and S1P receptors 1 and 3 were up-regulated in aortas from mice receiving fenofibrate. The present findings suggest that fenofibrate antagonizes AngII-induced AAA and atherosclerosis by up-regulating serum HDL and S1P levels, with associated activation of NO-producing enzymes and reduction of aortic inflammation.

The role of cholesterol efflux in mechanisms of endothelial protection by HDL

PURPOSE OF REVIEW

HDL and their main apolipoprotein (apo) constituent apoA-I are antiatherogenic. This has been predominantly attributed to the ability of apoA-I/HDL to efflux cholesterol from macrophages within atherosclerotic plaques. It is now emerging that a number of the protective properties of HDL may be due to their effects on the endothelium.

RECENT FINDINGS

In addition to their well characterized anti-inflammatory and antioxidant effects, apoA-I and HDL regulate several other key biological pathways known to preserve endothelial function and promote vascular repair. The ATP-binding cassette (ABC) transporters ABCA1 and ABCG1, and the scavenger receptor B type 1 mediate multiple intracellular signaling pathways as well as the efflux of cholesterol and/or oxysterols in response to apoA-I/HDL. Although cholesterol efflux triggers a host of signaling events in endothelial cells, there is evidence that some of the beneficial actions of HDL may occur independently of efflux.

SUMMARY

Current data suggest that in endothelial cells ABCA1 and ABCG1 mediate the activation of intracellular signaling pathways primarily through the efflux of cholesterol and oxysterols to apoA-I/HDL. Interaction between HDL and scavenger receptor B type 1 initiates the greatest number of known signaling pathways and there is evidence that some of these are activated independent of efflux.