Autonomic Regulation of Voltage-Gated Cardiac Ion Channels

Altering voltage-gated ion channel currents, by changing channel number or voltage-dependent kinetics, regulates the propagation of action potentials along the plasma membrane of individual cells and from one cell to its neighbors. Functional increases in the number of cardiac sodium channels (Na_V1.5) at the myocardial sarcolemma are accomplished by the regulation of caveolae by β adrenergically stimulated G-proteins. We demonstrate that Na_V1.5, Ca_V1.2a, and K_V1.5 channels specifically localize to isolated caveolar membranes, and to punctate regions of the sarcolemma labeled with caveolin-3. In addition, we show that Na_V1.5, Ca_V1.2a, and K_V1.5 channel antibodies label the same subpopulation of isolated caveolae. Plasma membrane sheet assays demonstrate that Na_V1.5, Ca_V1.2a, and K_V1.5 cluster with caveolin-3. This may have interesting implications for the way in which adrenergic pathways alter the cardiac action potential morphology and the velocity of the excitatory wave.     

C-reactive protein promotes atherosclerosis by increasing LDL transcytosis across endothelial cells

Background and Purpose

The retention of plasma low-density lipoprotein (LDL) particles in subendothelial space following transcytosis across the endothelium is the initial step of atherosclerosis. Whether or not C-reactive protein (CRP) can directly affect the transcytosis of LDL is not clear. Here we have examined the effect of CRP on transcytosis of LDL across endothelial cells and have explored the underlying mechanisms.

Experimental Approach

Effects of CRP on transcytosis of FITC-labelled LDL were examined with human umbilical vein endothelial cells and venous rings in vitro and, in vivo, ApoE^-/- mice. Laser scanning confocal microscopy, immunohistochemistry and Oil Red O staining were used to assay LDL.

Key Results

CRP increased transcytosis of LDL. An NADPH oxidase inhibitor, diphenylene iodonium, and the reducing agent, dithiothreitol partly or completely blocked CRP-stimulated increase of LDL transcytosis. The PKC inhibitor, bisindolylmaleimide I and the Src kinase inhibitor, PP2, blocked the trafficking of the molecules responsible for transcytosis. Confocal imaging analysis revealed that CRP stimulated LDL uptake by endothelial cells and vessel walls. In ApoE^-/- mice, CRP significantly promoted early changes of atherosclerosis, which were blocked by inhibitors of transcytosis.

Conclusions and Implications

CRP promoted atherosclerosis by directly increasing the transcytosis of LDL across endothelial cells and increasing LDL retention in vascular walls. These actions of CRP were associated with generation of reactive oxygen species, activation of PKC and Src, and translocation of caveolar or soluble forms of the N-ethylmaleimide-sensitive factor attachment protein.     

Caveolin-1 expression is maintained in rat and human astroglioma cell lines

Caveolin-1 is the principal structural and functional component of caveolae, a plasmalemmal compartment that has been proposed to sequester lipid and protein components that participate in transmembrane signal transduction processes. Multiple studies reveal a reduction in the expression level of caveolin-1 mRNA and protein in many carcinomas as well as transformed cells. The human caveolin-1 gene is localized to a suspected tumor suppressor locus (7q31.1). Collectively, these data have been taken to imply that caveolin-1 may function in a tumor suppressor capacity. To determine if a reduction in the expression level of caveolin-1 mRNA and protein accompanied the transformation of astrocytes, we undertook studies of two transformed rat astroglial cell lines, C6 and DI TNC(1), as well as several cell lines derived from human glioblastoma tumors: T98G, U87MG, U118MG, U138MG, and U373MG. Ultrastructural, immunolocalization, immunoblot, and Northern blot analyses demonstrated that caveolin-1 message and protein were expressed in all rat and human glioma cells. The localization pattern, buoyant density, and detergent-insolubility property of caveolin-1 protein were indistinguishable from that determined for nontransformed type 1 astrocytes in culture. Nucleotide sequence analyses of caveolin-1 cDNAs indicate that mutations are not present in the caveolin-1 sequence in any of the glioma cell types. Taken together with previous analyses, these data indicate that, at least for astrocytes, the process of transformation in and of itself is not solely sufficient to reduce the level of caveolin-1 expression, and that caveolin-1 expression in and of itself is not solely sufficient to prevent the acquisition of a transformed phenotype.     

内皮细胞caveolae,caveolin-1的生理功能

Caveolae是一种直径为50~100nm的细胞质膜表面特异性内陷结构。Caveolin-1是一个相对分子质量为21×103~24×103的完整膜蛋白,是组成caveolae的主要蛋白质成分。它们富含于多种类型的细胞内,其中内皮细胞是含量最丰富的细胞类型之一。内皮细胞caveolae与caveolin-1在物质转运、内皮组织通透性、动脉粥样硬化发生发展以及信号转导过程中发挥着重要的调节作用。     

The MAP kinase pathway mediates transcytosis induced by TNF-alpha in an in vitro blood-brain barrier model

Cerebral capillary endothelial cells constitute the blood-brain barrier (BBB). In these highly specialized cells, transcellular transports rarely occur, and the presence of tight junctions between them leads to a low paracellular permeability. In order to understand the functions of this barrier, an in vitro model of the BBB has been developed and consists in a co-culture of primary cerebral capillary endothelial cells and glial cells. When these endothelial cells are subjected to an inflammatory agent, such as tumor necrosis factor-alpha (TNF-alpha), in vitro BBB permeability is increased, as indicated by the increase in holotransferrin transcytosis. However, no significant change in the paracellular permeability is observed. In order to understand the molecular mechanisms that underlie these transcytosis processes, we investigated the implication of the mitogen-activated protein kinase (MAPK) signalling pathway, as TNF-alpha is known to activate this kinase family. In the present study, an increase in the activation of p42-44 MAPK is observed after TNF-alpha treatment. Holotransferrin transcytosis as well as p42-44 MAPK activation are inhibited after addition of a p42-44 MAPK pathway inhibitor (UO126) during TNF-alpha challenge. These data suggest that the MAPK pathway is involved in the transcytosis regulation in endothelial cells from an in vitro BBB model.     

小窝蛋白-1与特发性肺纤维化

小窝蛋白作为小窝膜内的支架蛋白,能够组织和浓缩特异性的脂质,修饰信号转导分子以及负性调控许多信号转导通路和生物过程。生物体内小窝蛋白表达异常可引起疾病,特发性肺纤维化就是其中一种。大量研究表明,小窝蛋白-1在特发性肺纤维化发病过程中表达明显下调,大大降低了其对多条信号传导通路如TGF-β/SMAD、ERK/MAPK、JNK/MAPK和PKC等的负性调控作用,进而导致肺泡上皮细胞损伤、成纤维细胞增殖及表型转化、细胞外基质(ECM)重塑,加速了肺纤维化发病进程。因此该文就小窝蛋白-1在特发性肺纤维化中的作用进行了综述。     

Induction of apoptosis by the ginsenoside Rh2 by internalization of lipid rafts and caveolae and inactivation of Akt

Background and purpose:

Lipid rafts and caveolae are membrane microdomains with important roles in cell survival signalling involving the Akt pathway. Cholesterol is important for the structure and function of these microdomains. The ginsenoside Rh2 exhibits anti-tumour activity. Because Rh2 is structurally similar to cholesterol, we investigated the possibility that Rh2 exerted its anti-tumour effect by modulating rafts and caveolae.

Experimental approach:

A431 cells (human epidermoid carcinoma cell line) were treated with Rh2 and the effects on cell apoptosis, raft localization and Akt activation measured. We also examined the effects of over-expression of Akt and active-Akt on Rh2-induced cell death.

Key results:

Rh2 induced apoptosis concentration- and time-dependently. Rh2 reduced the levels of rafts and caveolae in the plasma membrane and increased their internalization. Furthermore, Akt activity was decreased and consequently, Akt-dependent phosphorylation of Bad, a pro-survival protein, was decreased whereas the pro-apoptotic proteins, Bim and Bax, were increased upon Rh2 treatment. Unlike microdomain internalization induce by cholesterol depletion, Rh2-mediated internalization of rafts and caveolae was not reversed by cholesterol addition. Also, cholesterol addition did not restore Akt activation or rescue cells from Rh2-induced cell death. Rh2-induced cell death was attenuated in MDA-MB-231 cells over-expressing either wild-type or dominant-active Akt.

Conclusions and implications:

Rh2 induced internalization of rafts and caveolae, leading to Akt inactivation, and ultimately apoptosis. Because elevated levels of membrane rafts and caveolae, and Akt activation have been correlated with cancer development, internalization of these microdomains by Rh2 could potentially be used as an anti-cancer therapy.     

Ultrastructural changes in prostate cells during hormone-induced canine prostatic hyperplasia

Benign prostatic hyperplasia is a prevalent disease that has received relatively little attention in spite of its morbidity and remarkable social impact. There are few animal models of prostatic hyperplasia. The dog is the only species, along with humans, in which prostatic hyperplasia develops spontaneously and almost universally with age. The aim of the present study has been to compare the ultrastructural findings in a model of experimentally induced canine prostatic hyperplasia with those of the spontaneously developed changes in untreated dogs. An experimental group of 5 male beagle dogs were castrated and treated with combined steroids (3 weekly doses for over 30 weeks). Prostate samples were surgically obtained every 42 days (experimental stages 0 through 6). The control group consisted of 3 noncastrated dogs that were treated with vehicle and in which samples were taken only at stages 0, 1, 4, and 6. Changes in the control groups were similar but of lower intensity compared to those of the experimental groups. In luminal cells, crowding with papillary projections, prominent, branching microvilli, and abundant, often compartmentalized granules were observed. The most striking change was the previously unreported finding of caveolae in basal cells. They were mostly located in the basal aspect of basal cells and were more prominent in the experimental group and in advanced stages of treatment. These ultrastructural findings have not been previously reported in canine or human prostatic hyperplasia and merit further research. The model of experimentally induced canine prostatic hyperplasia provides an adequate setting for the understanding of this disease.