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Esophageal adenocarcinoma (EAC) is a highly aggressive malignancy that is characterized by resistance to chemotherapy and a poor clinical outcome. The overexpression of the receptor tyrosine kinase AXL is frequently associated with unfavorable prognosis in EAC. Although it is well documented that AXL mediates cancer cell invasion as a downstream effector of epithelial-to-mesenchymal transition, the precise molecular mechanism underlying this process is not completely understood. Herein, we demonstrate for the first time that AXL mediates cell invasion through the regulation of lysosomes peripheral distribution and cathepsin B secretion in EAC cell lines. Furthermore, we show that AXL-dependent peripheral distribution of lysosomes and cell invasion are mediated by extracellular acidification, which is potentiated by AXL-induced secretion of lactate through AKT-NF-κB-dependent MCT-1 regulation. Our novel mechanistic findings support future clinical studies to evaluate the therapeutic potential of the AXL inhibitor R428 (BGB324) in highly invasive EAC.
Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.
Before insulin can stimulate glucose uptake in muscle, it must be delivered to skeletal muscle (SkM) through the microvasculature. Insulin delivery is determined by SkM perfusion and the rate of movement of insulin across the capillary endothelium. The endothelium therefore plays a central role in regulating insulin access to SkM. Nitric oxide (NO) is a key regulator of endothelial function and stimulates arterial vasodilation, which increases SkM perfusion and the capillary surface area available for insulin exchange. The effects of NO on transendothelial insulin efflux (TIE), however, are unknown. We hypothesized that acute reduction of endothelial NO would reduce TIE. However, intravital imaging of TIE in mice revealed that reduction of NO by l--nitro-l-arginine methyl ester (l-NAME) enhanced the rate of TIE by ∼30% and increased total extravascular insulin delivery. This accelerated TIE was associated with more rapid insulin-stimulated glucose lowering. Sodium nitroprusside, an NO donor, had no effect on TIE in mice. The effects of l-NAME on TIE were not due to changes in blood pressure alone, as a direct-acting vasoconstrictor (phenylephrine) did not affect TIE. These results demonstrate that acute NO synthase inhibition increases the permeability of capillaries to insulin, leading to an increase in delivery of insulin to SkM.
© 2018 by the American Diabetes Association.
Two genes encode the Na -K -2Cl cotransporters, NKCC1 and NKCC2, that mediate the tightly coupled movement of 1Na , 1K , and 2Cl across the plasma membrane of cells. Na -K -2Cl cotransport is driven by the chemical gradient of the three ionic species across the membrane, two of them maintained by the action of the Na /K pump. In many cells, NKCC1 accumulates Cl above its electrochemical potential equilibrium, thereby facilitating Cl channel-mediated membrane depolarization. In smooth muscle cells, this depolarization facilitates the opening of voltage-sensitive Ca channels, leading to Ca influx, and cell contraction. In immature neurons, the depolarization due to a GABA-mediated Cl conductance produces an excitatory rather than inhibitory response. In many cell types that have lost water, NKCC is activated to help the cells recover their volume. This is specially the case if the cells have also lost Cl . In combination with the Na /K pump, the NKCC's move ions across various specialized epithelia. NKCC1 is involved in Cl -driven fluid secretion in many exocrine glands, such as sweat, lacrimal, salivary, stomach, pancreas, and intestine. NKCC1 is also involved in K -driven fluid secretion in inner ear, and possibly in Na -driven fluid secretion in choroid plexus. In the thick ascending limb of Henle, NKCC2 activity in combination with the Na /K pump participates in reabsorbing 30% of the glomerular-filtered Na . Overall, many critical physiological functions are maintained by the activity of the two Na -K -2Cl cotransporters. In this overview article, we focus on the functional roles of the cotransporters in nonpolarized cells and in epithelia. © 2018 American Physiological Society. Compr Physiol 8:871-901, 2018.
Copyright © 2018 American Physiological Society. All rights reserved.
Islet β cells from newborn mammals exhibit high basal insulin secretion and poor glucose-stimulated insulin secretion (GSIS). Here we show that β cells of newborns secrete more insulin than adults in response to similar intracellular Ca concentrations, suggesting differences in the Ca sensitivity of insulin secretion. Synaptotagmin 4 (Syt4), a non-Ca binding paralog of the β cell Ca sensor Syt7, increased by ∼8-fold during β cell maturation. Syt4 ablation increased basal insulin secretion and compromised GSIS. Precocious Syt4 expression repressed basal insulin secretion but also impaired islet morphogenesis and GSIS. Syt4 was localized on insulin granules and Syt4 levels inversely related to the number of readily releasable vesicles. Thus, transcriptional regulation of Syt4 affects insulin secretion; Syt4 expression is regulated in part by Myt transcription factors, which repress Syt4 transcription. Finally, human SYT4 regulated GSIS in EndoC-βH1 cells, a human β cell line. These findings reveal the role that altered Ca sensing plays in regulating β cell maturation.
Copyright © 2018 Elsevier Inc. All rights reserved.
BACKGROUND - Our aim was to evaluate lipid trafficking and inflammatory response of macrophages exposed to lipoproteins from subjects with moderate to severe chronic kidney disease (CKD), and to investigate the potential benefits of activating cellular cholesterol transporters via liver X receptor (LXR) agonism.
METHODS - LDL and HDL were isolated by sequential density gradient ultracentrifugation of plasma from patients with stage 3-4 CKD and individuals without kidney disease (HDL and HDL, respectively). Uptake of LDL, cholesterol efflux to HDL, and cellular inflammatory responses were assessed in human THP-1 cells. HDL effects on inflammatory markers (MCP-1, TNF-α, IL-1β), Toll-like receptors-2 (TLR-2) and - 4 (TLR-4), ATP-binding cassette class A transporter (ABCA1), NF-κB, extracellular signal regulated protein kinases 1/2 (ERK1/2) were assessed by RT-PCR and western blot before and after in vitro treatment with an LXR agonist.
RESULTS - There was no difference in macrophage uptake of LDL isolated from CKD versus controls. By contrast, HD was significantly less effective than HDL in accepting cholesterol from cholesterol-enriched macrophages (median 20.8% [IQR 16.1-23.7] vs control (26.5% [IQR 19.6-28.5]; p = 0.008). LXR agonist upregulated ABCA1 expression and increased cholesterol efflux to HDL of both normal and CKD subjects, although the latter continued to show lower efflux capacity. HDL increased macrophage cytokine response (TNF-α, MCP-1, IL-1β, and NF-κB) versus HDL. The heightened cytokine response to HDL was further amplified in cells treated with LXR agonist. The LXR-augmentation of inflammation was associated with increased TLR-2 and TLR-4 and ERK1/2.
CONCLUSIONS - Moderate to severe impairment in kidney function promotes foam cell formation that reflects impairment in cholesterol acceptor function of HDL. Activation of cellular cholesterol transporters by LXR agonism improves but does not normalize efflux to HDL. However, LXR agonism actually increases the pro-inflammatory effects of HDL through activation of TLRs and ERK1/2 pathways.
OBJECTIVE - Hepatocyte deletion of estrogen receptor alpha (LKO-ERα) worsens fatty liver, dyslipidemia, and insulin resistance in high-fat diet fed female mice. However, whether or not hepatocyte ERα regulates reverse cholesterol transport (RCT) in mice has not yet been reported.
METHODS AND RESULTS - Using LKO-ERα mice and wild-type (WT) littermates fed a Western-type diet, we found that deletion of hepatocyte ERα impaired in vivo RCT measured by the removal of H-cholesterol from macrophages to the liver, and subsequently to feces, in female mice but not in male mice. Deletion of hepatocyte ERα decreased the capacity of isolated HDL to efflux cholesterol from macrophages and reduced the ability of isolated hepatocytes to accept cholesterol from HDL ex vivo in both sexes. However, only in female mice, LKO-ERα increased serum cholesterol levels and increased HDL particle sizes. Deletion of hepatocyte ERα increased adiposity and worsened insulin resistance to a greater degree in female than male mice. All of the changes lead to a 5.6-fold increase in the size of early atherosclerotic lesions in female LKO-ERα mice compared to WT controls.
CONCLUSIONS - Estrogen signaling through hepatocyte ERα plays an important role in RCT and is protective against lipid retention in the artery wall during early stages of atherosclerosis in female mice fed a Western-type diet.
Published by Elsevier GmbH.
Before insulin can stimulate myocytes to take up glucose, it must first move from the circulation to the interstitial space. The continuous endothelium of skeletal muscle (SkM) capillaries restricts insulin's access to myocytes. The mechanism by which insulin crosses this continuous endothelium is critical to understand insulin action and insulin resistance; however, methodological obstacles have limited understanding of endothelial insulin transport in vivo. Here, we present an intravital microscopy technique to measure the rate of insulin efflux across the endothelium of SkM capillaries. This method involves development of a fully bioactive, fluorescent insulin probe, a gastrocnemius preparation for intravital microscopy, an automated vascular segmentation algorithm, and the use of mathematical models to estimate endothelial transport parameters. We combined direct visualization of insulin efflux from SkM capillaries with modeling of insulin efflux kinetics to identify fluid-phase transport as the major mode of transendothelial insulin efflux in mice. Model-independent experiments demonstrating that insulin movement is neither saturable nor affected by insulin receptor antagonism supported this result. Our finding that insulin enters the SkM interstitium by fluid-phase transport may have implications in the pathophysiology of SkM insulin resistance as well as in the treatment of diabetes with various insulin analogs.
Aquaporins (AQPs), by playing essential roles in the maintenance of ocular lens homeostasis, contribute to the establishment and maintenance of the overall optical properties of the lens over many decades of life. Three aquaporins, AQP0, AQP1 and AQP5, each with distinctly different functional properties, are abundantly and differentially expressed in the different regions of the ocular lens. Furthermore, the diversity of AQP functionality is increased in the absence of protein turnover by age-related modifications to lens AQPs that are proposed to alter AQP function in the different regions of the lens. These regional differences in AQP functionality are proposed to contribute to the generation and directionality of the lens internal microcirculation; a system of circulating ionic and fluid fluxes that delivers nutrients to and removes wastes from the lens faster than could be achieved by passive diffusion alone. In this review, we present how regional differences in lens AQP isoforms potentially contribute to this microcirculation system by highlighting current areas of investigation and emphasizing areas where future work is required.
The liver is a critical hub for numerous physiological processes. These include macronutrient metabolism, blood volume regulation, immune system support, endocrine control of growth signaling pathways, lipid and cholesterol homeostasis, and the breakdown of xenobiotic compounds, including many current drugs. Processing, partitioning, and metabolism of macronutrients provide the energy needed to drive the aforementioned processes and are therefore among the liver's most critical functions. Moreover, the liver's capacities to store glucose in the form of glycogen, with feeding, and assemble glucose via the gluconeogenic pathway, in response to fasting, are critical. The liver oxidizes lipids, but can also package excess lipid for secretion to and storage in other tissues, such as adipose. Finally, the liver is a major handler of protein and amino acid metabolism as it is responsible for the majority of proteins secreted in the blood (whether based on mass or range of unique proteins), the processing of amino acids for energy, and disposal of nitrogenous waste from protein degradation in the form of urea metabolism. Over the course of evolution this array of hepatic functions has been consolidated in a single organ, the liver, which is conserved in all vertebrates. Developmentally, this organ arises as a result of a complex differentiation program that is initiated by exogenous signal gradients, cellular localization cues, and an intricate hierarchy of transcription factors. These processes that are fully developed in the mature liver are imperative for life. Liver failure from any number of sources (e.g. viral infection, overnutrition, or oncologic burden) is a global health problem. The goal of this primer is to concisely summarize hepatic functions with respect to macronutrient metabolism. Introducing concepts critical to liver development, organization, and physiology sets the stage for these functions and serves to orient the reader. It is important to emphasize that insight into hepatic pathologies and potential therapeutic avenues to treat these conditions requires an understanding of the development and physiology of specialized hepatic functions.
Copyright © 2017 Elsevier Ltd. All rights reserved.
Mitochondrial dysfunction is elevated in very early stages of Alzheimer's disease and exacerbates oxidative stress, which contributes to disease pathology. Mitochondria were isolated from 4-month-old wild-type mice, transgenic mice carrying the APP and PSEN1 mutations, mice with decreased brain and mitochondrial ascorbate (vitamin C) via heterozygous knockout of the sodium dependent vitamin C transporter (SVCT2) and transgenic APP/PSEN1 mice with heterozygous SVCT2 expression. Mitochondrial isolates from SVCT2 mice were observed to consume less oxygen using high-resolution respirometry, and also exhibited decreased mitochondrial membrane potential compared to wild type isolates. Conversely, isolates from young (4 months) APP/PSEN1 mice consumed more oxygen, and exhibited an increase in mitochondrial membrane potential, but had a significantly lower ATP/ADP ratio compared to wild type isolates. Greater levels of reactive oxygen species were also produced in mitochondria isolated from both APP/PSEN1 and SVCT2 mice compared to wild type isolates. Acute administration of ascorbate to mitochondria isolated from wild-type mice increased oxygen consumption compared with untreated mitochondria suggesting ascorbate may support energy production. This study suggests that both presence of amyloid and ascorbate deficiency can contribute to mitochondrial dysfunction, even at an early, prodromal stage of Alzheimer's disease, although occurring via different pathways. Ascorbate may, therefore, provide a useful preventative strategy against neurodegenerative disease, particularly in populations most at risk for Alzheimer's disease in which stores are often depleted through mitochondrial dysfunction and elevated oxidative stress.
Copyright © 2017 Elsevier Inc. All rights reserved.