Lipoapoptosis induced by saturated free fatty acids stimulates monocyte migration: a novel role for Pannexin1 in liver cells.

Recruitment of monocytes in the liver is a key pathogenic feature of hepatic inflammation in nonalcoholic steatohepatitis (NASH), but the mechanisms involved are poorly understood. Here, we studied migration of human monocytes in response to supernatants obtained from liver cells after inducing lipoapoptosis with saturated free fatty acids (FFA). Lipoapoptotic supernatants stimulated monocyte migration with the magnitude similar to a monocyte chemoattractant protein, CCL2 (MCP-1).

Pannexin1 contributes to pathophysiological ATP release in lipoapoptosis induced by saturated free fatty acids in liver cells.

Hepatocyte lipoapoptosis induced by saturated free fatty acids (FFA) contributes to hepatic inflammation in lipotoxic liver injury, and the cellular mechanisms involved have not been defined. Recent studies have shown that apoptosis in nonhepatic cells stimulates ATP release via activation of pannexin1 (panx1), and extracellular ATP functions as a proinflammatory signal for recruitment and activation of the inflammatory cells. However, it is not known whether lipoapoptosis stimulates ATP release in liver cells.

Increased phosphoenolpyruvate carboxykinase gene expression and steatosis during hepatitis C virus subgenome replication: role of nonstructural component 5A and CCAAT/enhancer-binding protein β.

Chronic hepatitis C virus (HCV) infection greatly increases the risk for type 2 diabetes and nonalcoholic steatohepatitis; however, the pathogenic mechanisms remain incompletely understood. Here we report gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) transcription and associated transcription factors are dramatically up-regulated in Huh.8 cells, which stably express an HCV subgenome replicon.

Evidence for sustained ATP release from liver cells that is not mediated by vesicular exocytosis.

Extracellular ATP regulates many important cellular functions in the liver by stimulating purinergic receptors. Recent studies have shown that rapid exocytosis of ATP-enriched vesicles contributes to ATP release from liver cells. However, this rapid ATP release is transient, and ceases in ~30 s after the exposure to hypotonic solution.

Copper inhibits P2Y(2)-dependent Ca(2+) signaling through the effects on thapsigargin-sensitive Ca(2+) stores in HTC hepatoma cells.

Purinergic P2Y(2) G-protein coupled receptors play a key role in the regulation of hepatic Ca(2+) signaling by extracellular ATP. The concentration of copper in serum is about 20muM. Since copper accumulates in the liver in certain disease states, the purpose of these studies was to assess the effects of copper on P2Y(2) receptors in a model liver cell line.

5-Nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) stimulates cellular ATP release through exocytosis of ATP-enriched vesicles.

Cells release ATP in response to physiologic stimuli. Extracellular ATP regulates a broad range of important cellular functions by activation of the purinergic receptors in the plasma membrane. The purpose of these studies was to assess the role of vesicular exocytosis in cellular ATP release.

Evidence for AMPK-dependent regulation of exocytosis of lipoproteins in a model liver cell line.

5'-AMP-activated kinase (AMPK) plays a key role in the regulation of cellular lipid metabolism. The contribution of vesicular exocytosis to this regulation is not known. Accordingly, we studied the effects of AMPK on exocytosis and intracellular lipid content in a model liver cell line.

Characterization of ionotrophic purinergic receptors in hepatocytes.

Unlabelled: Ionotrophic purinergic (P2X) receptors function as receptor-gated cation channels, where agonist binding leads to opening of a nonselective cation pore permeable to both Na(+) and Ca(2+). Based on evidence that extracellular adenosine 5'-triphosphate (ATP) stimulates glucose release from liver, these studies evaluate whether P2X receptors are expressed by hepatocytes and contribute to ATP-dependent calcium signaling and glucose release. Studies were performed in isolated hepatocytes from rats and mice and hepatoma cells from humans and rats.

Emerging roles of chloride channels in human diseases.

In the past decade, there has been remarkable progress in understanding of the roles of Cl(-) channels in the development of human diseases. Genetic studies in humans have identified mutations in the genes encoding Cl(-) channels which lead to a loss of Cl(-) channel activity. These mutations are responsible for the development of a variety of deleterious diseases in muscle, kidney, bone and brain including myotonia congenita, dystrophia myotonica, cystic fibrosis, osteopetrosis and epilepsy.

Inhibition of cellular responses to insulin in a rat liver cell line. A role for PKC in insulin resistance.

The initial response of liver cells to insulin is mediated through exocytosis of Cl- channel-containing vesicles and a subsequent opening of plasma membrane Cl- channels. Intracellular accumulation of fatty acids leads to profound defects in metabolism, and is closely associated with insulin resistance. It is not known whether the activity of Cl- channels is altered in insulin resistance and by which mechanisms.

Vesicular exocytosis contributes to volume-sensitive ATP release in biliary cells.

Extracellular ATP is a potent autocrine/paracrine signal that regulates a broad range of liver functions through activation of purinergic receptors. In biliary epithelium, increases in cell volume stimulate ATP release through a phosphoinositide 3-kinase (PI3-kinase)-dependent mechanism. Because PI3-kinase also regulates vesicular exocytosis, the purpose of these studies was to determine whether volume-stimulated vesicular exocytosis contributes to cellular ATP release.

Volume-sensitive tyrosine kinases regulate liver cell volume through effects on vesicular trafficking and membrane Na+ permeability.

In liver cells, the influx of Na+ mediated by nonselective cation (NSC) channels in the plasma membrane contributes importantly to regulation of cell volume. Under basal conditions, channels are closed; but both physiologic (e.g.

Exocytosis in bovine chromaffin cells: studies with patch-clamp capacitance and FM1-43 fluorescence.

In response to physiological stimuli, neuroendocrine cells secrete neurotransmitters through a Ca(2+)-dependent fusion of secretory granules with the plasma membrane. We studied insertion of granules in bovine chromaffin cells using capacitance as a measure of plasma membrane area and fluorescence of a membrane marker FM1-43 as a measure of exocytosis. Intracellular dialysis with [Ca(2+)] (1.

Cholangiocytes exhibit dynamic, actin-dependent apical membrane turnover.

The present studies of cholangiocytes used complementary histological, biochemical, and electrophysiological methods to identify a dense population of subapical vesicles, quantify the rates of vesicular trafficking, and assess the contribution of the actin cytoskeleton to membrane trafficking. FM 1-43 fluorescence measured significant basal rates of total exocytosis (1.33 +/- 0.

Heterotrimeric G-proteins activate Cl- channels through stimulation of a cyclooxygenase-dependent pathway in a model liver cell line.

Circulating hormones produce rapid changes in the Cl(-) permeability of liver cells through activation of plasma membrane receptors coupled to heterotrimeric G-proteins. The resulting effects on intracellular pH, membrane potential, and Cl(-) content are important contributors to the overall metabolic response. Consequently, the purpose of these studies was to evaluate the mechanisms responsible for G-protein-mediated changes in membrane Cl(-) permeability using HTC hepatoma cells as a model.