NADPH Oxidase 2-Derived Reactive Oxygen Species Mediate FFAs-Induced Dysfunction and Apoptosis of β-Cells via JNK, p38 MAPK and p53 Pathways

Abstract

Dysfunction of β-cell is one of major characteristics in the pathogenesis of type 2 diabetes. The combination of obesity and type 2 diabetes, characterized as ‘diabesity’, is associated with elevated plasma free fatty acids (FFAs). Oxidative stress has been implicated in the pathogenesis of FFA-induced β-cell dysfunction. However, molecular mechanisms linking between reactive oxygen species (ROS) and FFA-induced β-cell dysfunction and apoptosis are less clear. In the present study, we test the hypothesis that NOX2-derived ROS may play a critical role in dysfunction and apoptosis of β-cells induced by FFA. Our results show that palmitate and oleate (0.5 mmol/L, 48 h) induced JNK activation and AKT inhibition which resulted in decreased phosphorylation of FOXO1 following nuclear localization and the nucleocytoplasmic translocation of PDX-1, leading to the reducing of insulin and ultimately dysfunction of pancreatic NIT-1 cells. We also found that palmitate and oleate stimulated apoptosis of NIT-1 cells through p38MAPK, p53 and NF-κB pathway. More interestingly, our data suggest that suppression of NOX2 may restore FFA-induced dysfunction and apoptosis of NIT-1 cells. Our findings provide a new insight of the NOX2 as a potential new therapeutic target for preservation of β-cell mass and function.

The p66Shc redox adaptor protein is induced by saturated fatty acids and mediates lipotoxicity-induced apoptosis in pancreatic beta cells

“…FA-induced beta cell apoptosis involves a variety of signalling mechanisms, including endoplasmic reticulum (ER) stress induction [4], mitochondrial dysfunction [5], activation of specific intracellular kinases such as the members of the mitogen-activated protein kinase (MAPK) family c-Jun N-terminal kinase (JNK) and p38 MAPK [6,7] and protein kinase C (PKC)δ [8], and peroxisome-generated reactive oxygen species (ROS) [7,9]. The tumour suppressor protein p53 is also implicated in FA-induced beta cell apoptosis [7,10], since both palmitate and oleate were shown to stimulate apoptosis of NIT-1 beta cells through p53 [7], and p53 inhibition was found to be involved in growth factor-dependent promotion of beta cell survival via Akt/protein kinase B [10].…”

“…The tumour suppressor protein p53 is also implicated in FA-induced beta cell apoptosis [7,10], since both palmitate and oleate were shown to stimulate apoptosis of NIT-1 beta cells through p53 [7], and p53 inhibition was found to be involved in growth factor-dependent promotion of beta cell survival via Akt/protein kinase B [10]. However, p53 signalling in the context of beta cell lipotoxicity is still poorly defined.…”

Capsaicin attenuates palmitate-induced expression of macrophage inflammatory protein 1 and interleukin 8 by increasing palmitate oxidation and reducing c-Jun activation in THP-1 (human acute monocytic leukemia cell) cells

“…Intracellular signaling by FFAs involves the activities of multiple kinases, including p38; JNK2/3; and, perhaps, more specifically, JNK and c-Jun [28,33]. The activation of JNK and p38 is stimulated by inflammatory responses.…”

“…Other studies have shown that palmitate induces ROS generation in various cells such as skeletal muscle cells [13], THP-1 monocytes [12], pancreatic islet cells [38], and adipocytes [39] mainly through the activation of the NADPH (nicotinamide adenine dinucleotide phosphate) oxidase system [12]; they may also be formed as by-products of mitochondrial oxidative phosphorylation [37]. These ROS stimulate JNK activation [28] and induce mitochondrial dysfunction [15]. To determine if anti-inflammatory effect of capsaicin was related to reduced ROS levels, we tested whether capsaicin would reduce ROS production in palmitate-treated cells using the fluorescent probe DCFDA (2′,7′-dichlorodihydrofluorescein diacetate, acetyl ester).…”

“…Inside the cell, acyl-CoA synthetase acts on palmitate to produce palmitoyl-CoA, which is metabolized by the mitochondria or is used to produce lipid mediators such as DAG and ceramide in lipid synthesis pathways; DAG is known to activate several kinases that mediate stress signals, including JNK, p38, NF-κB, and PKC [15,28]. To determine whether palmitate could regulate these signaling pathways in THP-1 cells, THP-1 cells were treated with 200 μmol/L palmitate for different periods; and the phosphorylated forms of JNK, p38, extracellular signalrelated kinase, and NF-κB were examined on immunoblots.…”