Dehydroascorbic acid reduction in several tissues and cultured hepatocytes of the chicken

Linoleic acid stimulates gluconeogenesis via Ca2+/PLC, cPLA2, and PPAR pathways through GPR40 in primary cultured chicken hepatocytes

Fatty acids serve vital functions as sources of energy, building materials for cellular structures, and modulators of physiological responses. Therefore, this study examined the effect of linoleic acid on glucose production and its related signal pathways in primary cultured chicken hepatocytes. Linoleic acid (double-unsaturated, long chain) increased glucose production in a dose (≥10−4 M)- and time (≥8 h)-dependent manner. Both oleic acid (monounsaturated, long chain) and palmitic acid (saturated, long chain) also increased glucose production, whereas caproic acid (saturated, short chain) failed to increase glucose production. Linoleic acid increased G protein-coupled receptor 40 (GPR40; also known as free fatty acid receptor-1) protein expression and glucose production that was blocked by GPR40-specific small interfering RNA. Linoleic acid increased intracellular calcium concentration, which was blocked by EGTA (extracellular calcium chelator)/BAPTA-AM (intracellular calcium chelator), U-73122 (phospholipase C inhibitor), nifedipine, or methoxyverapamil (L-type calcium channel blockers). Linoleic acid increased cytosolic phospholipase A2 (cPLA2) phosphorylation and the release of [3H]-labeled arachidonic acid. Moreover, linoleic acid increased the level of cyclooxygenase-2 (COX-2) protein expression, which stimulated the synthesis of prostaglandin E2 (PGE2). The increase in PGE2 production subsequently stimulated peroxisome proliferator-activated receptor (PPAR) expression, and MK-886 (PPAR-α antagonist) and GW-9662 (PPAR-δ antagonist) inhibited glucose-6-phosphatase and phosphoenolpyruvate carboxykinase. In addition, linoleic acid-induced glucose production was blocked by inhibition of extracellular and intracellular calcium, cPLA2, COX-2, or PPAR pathways. In conclusion, linoleic acid promoted glucose production via Ca2+/PLC, cPLA2/COX-2, and PPAR pathways through GPR40 in primary cultured chicken hepatocytes.

High glucose induced translocation of Aquaporin8 to chicken hepatocyte plasma membrane: involvement of cAMP, PI3K/Akt, PKC, MAPKs, and microtubule

Aquaporin8 (AQP8) is a transmembrane water channel that is found mainly in hepatocytes. The direct involvement of AQP8 in high glucose condition has not been established. Therefore, this study examined the effects of high glucose on AQP8 and its related signal pathways in primary cultured chicken hepatocytes. High glucose increased the movement of AQP8 from the intracellular membrane to plasma membrane in a 30 mM glucose concentration and in a time- (> or =10 min) dependent manner. On the other hand, 30 mM mannitol did not affect the translocation of AQP8, which suggested the absence of osmotic effect. Thirty millimolar glucose increased intracellular cyclic adenosine 3, 5-monophosphate (cAMP) level. Moreover, high glucose level induced Akt phosphorylation, protein kinase C (PKC) activation, p44/42 mitogen-activated protein kinases (MAPKs), p38 MAPK, and c-jun NH2-terminal kinase (JNK) phosphorylation. On the other hand, inhibition of each pathway by SQ 22536 (adenylate cyclase inhibitor), LY 294002 (PI3-K phosphatidylinositol 3-kinase inhibitor), Akt inhibitor, staurosporine (PKC inhibitor), PD 98059 (MEK inhibitor), SB 203580 (p38 MAPK inhibitor), or SP 600125 (JNK inhibitor) blocked 30 mM glucose-induced AQP8 translocation, respectively. In addition, inhibition of microtubule movement with nocodazole blocked high glucose-induced AQP8 translocation. High glucose level also increased the level of kinesin light chain and dynein protein expression. In conclusion, high glucose level stimulates AQP8 via cAMP, PI3-K/Akt, PKC, and MAPKs pathways in primary cultured chicken hepatocytes.

Estradiol-17beta protects against hypoxia-induced hepatocyte injury through ER-mediated upregulation of Bcl-2 as well as ER-independent antioxidant effects

Although many previous studies have suggested that estrogen functions as a cytoprotective agent under oxidative stress conditions, the underlying mechanism by which this effect is exerted remains to be elucidated. This study assessed the effects of estradiol-17beta (E(2)) (10(-8) M) on hypoxia-induced cell injury and its related signaling in primary cultured chicken hepatocytes. Hypoxic conditions were found to augment the level of DNA damage and to reduce cell viability and the level of [(3)H]-thymidine incorporation, and these phenomena were prevented through treatment with E(2). Hypoxia also increased caspase-3 expression, but showed no evidence of an influence on the expression of Bcl-2. However, E(2) induced an increase in the level of Bcl-2 expression under hypoxic conditions and reduced the level of caspase-3 expression. The effects of E(2) on Bcl-2 and caspase expression were blocked by ICI 182780 (E(2) receptor (ER) antagonist, 10(-7) M). In addition, hypoxia resulted in an increase in the intracellular reactive oxygen species (ROS) generated. These effects were blocked by E(2), but not by E(2)-BSA and ICI 182780. Hypoxia also activated p38 mitogen-activated protein kinase (MAPK), c-JUN N-terminal kinase/stress-activated protein kinase (JNK/SAPK) and nuclear factor-kappaB (NF-kappaB). These effects were blocked by E(2), but not by ICI 182780. The inhibition of p38 MAPK and JNK/SAPK blocked NF-kappaB activation. In conclusion, E(2) was found to protect against hypoxia-induced cell injury in chicken hepatocytes through ER-mediated upregulation of Bcl-2 expression and through reducing the activity of ROS-dependent p38 MAPK, JNK/SAPK and NF-kappaB.

Effect of EGF on [3H]-thymidine incorporation and cell cycle regulatory proteins in primary cultured chicken hepatocytes: Involvement of Ca2+/PKC and MAPKs

The reported studies on the metabolism in chicken hepatocytes in comparison with those of mammals are quite different. Therefore, this study examined the effect of EGF on DNA synthesis along with its related signal cascades in primary cultured chicken hepatocytes. EGF stimulated DNA synthesis in a dose (> or =10 ng/ml)-dependent manner, which correlated with the increase in CDK-2 and CDK-4 expression. The EGF-induced increase in [3H]-thymidine incorporation was blocked by AG 1478 (an EGF receptor tyrosine kinase antagonist), genistein, and herbimycin A (tyrosine kinase inhibitors), suggesting a role in the activation and tyrosine phosphorylation of the EGF receptor. In addition, the EGF-induced stimulation of [3H]-thymidine incorporation was prevented by staurosporine, H-7, or bisindolylmaleimide I (protein kinase C inhibitors), suggesting a role of PKC. In addition, PD 98059 (a MEK inhibitor), SB 203580 (a p38 MAPK inhibitor), and SP 600125 (a JNK inhibitor) blocked the EGF-induced stimulation of [3H]-thymidine incorporation and CDK-2/4 expression. Indeed, EGF increased the translocation of PKC from the cytosol to the membrane fraction, and increased the activation of p44/42 MAPK, p38 MAPK, and JNK. Moreover, EGF increased the CDK-2, CDK-4, cyclin D1, and cyclin E expression levels but decreased the p21 and p27 expression levels. These EGF-induced increases were blocked by an EGF receptor antagonist, tyrosine kinase inhibitors, PKC inhibitors, and MAPKs inhibitors. In conclusion, EGF stimulates DNA synthesis of primary cultured chicken hepatocytes via Ca2+/PKC and the MAPKs signaling pathways.

EGF-induced inhibition of glucose transport is mediated by PKC and MAPK signal pathways in primary cultured chicken hepatocytes

EGF is a regulator of a wide variety of processes in various cell systems. Hepatocytes are important sites in the body's metabolism and function. Glucose transporter 2 (GLUT2) is a major transporter that is expressed strongly in hepatocytes. Therefore, this study examined the effect of EGF on GLUT2 and its related signal cascades in primary cultured chicken hepatocytes. EGF decreased [(3)H]deoxyglucose uptake in a dose- and time-dependent manner (>10 ng/ml, 2 h). AG-1478 (an EGF receptor antagonist) and genistein and herbimycin A (tyrosine kinase inhibitors) blocked the EGF-induced decrease in [(3)H]deoxyglucose uptake, which correlated with the GLUT2 expression level. In addition, the EGF-induced decrease in GLUT2 protein expression was inhibited by staurosporine, H-7, or bisindolylmaleimide I (PKC inhibitors), PD-98059 (a MEK inhibitor), SB-203580 (a p38 MAPK inhibitor), and SP-600125 (a JNK inhibitor), suggesting a role of both PKC and MAPKs (p44/42 MAPK, p38 MAPK, and JNK). In particular, EGF increased the translocation of PKC isoforms (PKC-alpha, -beta(1), -gamma, -delta, and -zeta) from the cytosol to the membrane fraction and increased the activation of p44/42 MAPK, p38 MAPK, and JNK. Moreover, PKC inhibitors blocked the EGF-induced phosphorylation of three MAPKs. In conclusion, EGF decreases the GLUT2 expression level via the PKC-MAPK signal cascade in chicken hepatocytes.