The Effects of Palmitate on Hepatic Insulin Resistance Are Mediated by NADPH Oxidase 3-derived Reactive Oxygen Species through JNK and p38MAPK Pathways

Abstract

Elevated plasma free fatty acid (FFA) levels in obesity may play a pathogenic role in the development of insulin resistance. However, molecular mechanisms linking FFA to insulin resistance remain poorly understood. Oxidative stress acts as a link between FFA and hepatic insulin resistance. NADPH oxidase 3 (NOX3)-derived reactive oxygen species (ROS) may mediate the effect of TNF-␣ on hepatocytes, in particular the drop in cellular glycogen content. In the present study, we define the critical role of NOX3-derived ROS in insulin resistance in db/db mice and HepG2 cells treated with palmitate. The db/db mice displayed increased serum FFA levels, excess generation of ROS, and upregulation of NOX3 expression, accompanied by increased lipid accumulation and impaired glycogen content in the liver. Similar results were obtained from palmitate-treated HepG2 cells. The exposure of palmitate elevated ROS production and NOX3 expression and, in turn, increased gluconeogenesis and reduced glycogen content in HepG2 cells. We found that palmitate induced hepatic insulin resistance through JNK and p38 MAPK pathways, which are rescued by siRNA-mediated NOX3 reduction. In conclusion, our data demonstrate a critical role of NOX3-derived ROS in palmitate-induced insulin resistance in hepatocytes, indicating that NOX3 is the predominant source of palmitate-induced ROS generation and that NOX3-derived ROS may drive palmitate-induced hepatic insulin resistance through JNK and p38 MAPK pathways.

Free Fatty Acids Shift Insulin-induced Hepatocyte Proliferation towards CD95-dependent Apoptosis

“…Saturated FFAs rapidly trigger generation of ROS, which may explain JNK activation. Mitochondria (34,35) and NADPH oxidase were discussed as predominant sources of palmitate-induced ROS generation in the liver (36,37). The FFA-induced JNK signal directs activated EGFR from proliferative signaling toward association with CD95 and proapoptotic signaling.…”

miR-200s Contribute to Interleukin-6 (IL-6)-induced Insulin Resistance in Hepatocytes

“…Therefore, the results of the microarray need to be further validated by real-time PCR. These in vivo observations suggest that (24). In addition, NCTC 1469 cells were treated with different concentrations of IL-6 (10, 20, and 40 ng/ml) for different times (12,24, and 48 h) to induce insulin resistance (data not shown).…”

“…These in vivo observations suggest that (24). In addition, NCTC 1469 cells were treated with different concentrations of IL-6 (10, 20, and 40 ng/ml) for different times (12,24, and 48 h) to induce insulin resistance (data not shown). The treatment of 10 ng/ml IL-6 for 24 h was chosen for the following experiments.…”

RNASET2 is required for ROS propagation during oxidative stress-mediated cell death

“…13 Similarly, whereas engagement of the endoplasmic reticulum (ER) stress machinery or generation of reactive oxygen species (ROS) can serve adaptive or productive signaling functions in response to lipid overload, extreme ER and oxidative stress engage cell death pathways. [14][15][16][17] The importance of oxidative stress in the pathophysiological response to substrate excess is underscored by observation that treatment with chemical antioxidants and overexpression of ROS-scavenging enzymes mitigates against lipotoxic cell death and against diabetic complications in animal models. [18][19][20][21] To identify critical mediators of lipotoxic cell death, our laboratory has focused on characterizing genes identified through a loss-of-function genetic screen in mammalian fibroblasts.…”