High density lipoprotein-induced endothelial nitric-oxide synthase activation is mediated by Akt and MAP kinases.
ABSTRACT High density lipoprotein (HDL) activates endothelial nitric-oxide synthase (eNOS), leading to increased production of the antiatherogenic molecule NO. A variety of stimuli regulate eNOS activity through signaling pathways involving Akt kinase and/or mitogen-activated protein (MAP) kinase. In the present study, we investigated the role of kinase cascades in HDL-induced eNOS stimulation in cultured endothelial cells and COS M6 cells transfected with eNOS and the HDL receptor, scavenger receptor B-I. HDL (10-50 microg/ml, 20 min) caused eNOS phosphorylation at Ser-1179, and dominant negative Akt inhibited both HDL-mediated phosphorylation and activation of the enzyme. Phosphoinositide 3-kinase (PI3 kinase) inhibition or dominant negative PI3 kinase also blocked the phosphorylation and activation of eNOS by HDL. Studies with genistein and PP2 showed that the nonreceptor tyrosine kinase, Src, is an upstream stimulator of the PI3 kinase-Akt pathway in this paradigm. In addition, HDL activated MAP kinase through PI3 kinase, and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase inhibition fully attenuated eNOS stimulation by HDL without affecting Akt or eNOS Ser-1179 phosphorylation. Conversely, dominant negative Akt did not alter HDL-induced MAP kinase activation. These results indicate that HDL stimulates eNOS through common upstream, Src-mediated signaling, which leads to parallel activation of Akt and MAP kinases and their resultant independent modulation of the enzyme.
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ABSTRACT: The question of whether the distinct isoforms of the family of enzymes phosphoinositide 3-kinases (PI3Ks) play redundant roles within a cell or whether they control distinct cellular processes or distinct steps within the same cellular process has gained considerable importance in the recent years due to the development of inhibitors able to selectively target individual isoforms. It is important to understand whether inhibition of one PI3K can result in compensatory effect from other isoform(s) and therefore whether strategies aimed at simultaneously blocking more than one PI3K may be needed. In this study we investigated the relative contribution of distinct PI3K isoforms to endothelial cells (EC) functions specifically regulated by the sphingolipid sphingosine-1-phosphate (S1P) and by high density lipoproteins (HDL), the major carrier of S1P in human plasma. Here we show that a co-ordinated action of different PI3Ks is required to tightly regulate remodelling of EC on Matrigel, a process dependent on cell proliferation, apoptosis and migration. The contribution of each isoform to this process appears to be distinct, with the class II enzyme PI3K-C2β and the class IB isoform p110γ mainly regulating the S1P- and HDL-dependent EC migration and PI3K-C2α primarily controlling EC survival. Data further indicate that PI3K-C2β and p110γ control distinct steps involved in cell migration supporting the hypothesis that different PI3Ks regulate distinct cellular processes.PLoS ONE 01/2013; 8(1):e53808. · 4.09 Impact Factor
Article: Molecular mechanisms of vascular effects of High-density lipoprotein: alterations in cardiovascular disease.[show abstract] [hide abstract]
ABSTRACT: Low high-density lipoprotein (HDL)-cholesterol levels are associated with an increased risk of coronary artery disease (CAD) and myocardial infarction, which has triggered the hypothesis that HDL, in contrast to low-density lipoprotein (LDL), acts as an anti-atherogenic lipoprotein. Moreover, experimental studies have identified potential anti-atherogenic properties of HDL, including promotion of macrophage cholesterol efflux and direct endothelial-protective effects of HDL, such as stimulation of endothelial nitric oxide production and repair, anti-apoptotic, anti-inflammatory and anti-thrombotic properties. Studies in gene-targeted mice, however, have also indicated that increasing HDL-cholesterol plasma levels can either limit (e.g. apolipoprotein A-I) or accelerate (e.g. Scavenger receptor class B type I) atherosclerosis. Moreover, vascular effects of HDL have been observed to be heterogenous and are altered in patients with CAD or diabetes, a condition that has been termed 'HDL dysfunction'. These alterations in biological functions of HDL may need to be taken into account for HDL-targeted therapies and considering raising of HDL-cholesterol levels alone is likely not sufficient in this respect. It will therefore be important to further determine, which biological functions of HDL are critical for its anti-atherosclerotic properties, as well as how these can be measured and targeted.EMBO Molecular Medicine 03/2012; 4(4):251-68. · 10.33 Impact Factor
Article: Regulation of adipocyte autophagy - The potential anti-obesity mechanism of high density lipoprotein and ApolipoproteinA-I.[show abstract] [hide abstract]
ABSTRACT: Obesity is reaching epidemic worldwide and is risk factor for cardiovascular disease and type 2 diabetes. Although plasma high density lipoprotein (HDL) and apolipoprotein A-I (apoA-I) are inversely correlated to obesity, whether HDLs have anti-obesity effect remains unclear until a recent study reporting the direct anti-obesity effect of apoA-I and its mimetic peptide. However, the mechanism is not fully understood. Increasing adipose energy expenditure through attainment of brown adipocyte phenotype in white adipose tissue is considered a potential strategy to combat obesity. Specific inhibition of autophagy in adipose tissue is associated with reduced adiposity which is attributed to the attainment of brown adipocyte phenotype in white adipose tissue and the increased energy expenditure. HDL and apoA-I could activate PI3K-Akt-mTORC1 signaling which negatively regulates autophagy. The links between HDL/apoA-I and autophagy brings a new understanding on the anti-obesity effect of HDL and apoA-I.Lipids in Health and Disease 10/2012; 11:131. · 2.17 Impact Factor