Free Fatty Acids Induce JNK-dependent Hepatocyte Lipoapoptosis

Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 05/2006; 281(17):12093-101. DOI: 10.1074/jbc.M510660200
Source: PubMed


Elevated serum free fatty acids (FFAs) and hepatocyte lipoapoptosis are features of non-alcoholic fatty liver disease. However, the mechanism by which FFAs mediate lipoapoptosis is unclear. Because JNK activation is pivotal in both the metabolic syndrome accompanying non-alcoholic fatty liver disease and cellular apoptosis, we examined the role of JNK activation in FFA-induced lipoapoptosis. Multiple hepatocyte cell lines and primary mouse hepatocytes were treated in culture with monounsaturated fatty acids and saturated fatty acids. Despite equal cellular steatosis, apoptosis and JNK activation were greater during exposure to saturated versus monounsaturated FFAs. Inhibition of JNK, pharmacologically as well as genetically, reduced saturated FFA-mediated hepatocyte lipoapoptosis. Cell death was caspase-dependent and associated with mitochondrial membrane depolarization and cytochrome c release indicating activation of the mitochondrial pathway of apoptosis. JNK-dependent lipoapoptosis was associated with activation of Bax, a known mediator of mitochondrial dysfunction. As JNK can activate Bim, a BH3 domain-only protein capable of binding to and activating Bax, its role in lipoapoptosis was also examined. Small interfering RNA-targeted knock-down of Bim attenuated both Bax activation and cell death. Collectively the data indicate that saturated FFAs induce JNK-dependent hepatocyte lipoapoptosis by activating the proapoptotic Bcl-2 proteins Bim and Bax, which trigger the mitochondrial apoptotic pathway.

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    • "The clinical importance of NASH is related to its capacity to evolve in liver cirrhosis and cancer [4]. The principal risk factor for the development of NASH is insulin resistance [5] [6] [7] that increases lipolysis and releases free fatty acids (FFA) causing liver injury [8] [9] [10] by excessive liver lipid accumulation. Oversupply of free fatty acids induces an increase in mitochondrial H 2 O 2 production that, in turn, oxidizes mitochondrial membranes and regulates activity of uncoupling protein 2 and carnitine palmitoyl transferase 1 [11]. "
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    ABSTRACT: Liver steatosis can evolve to steatohepatitis (NASH) through a series of biochemical steps related to oxidative stress in hepatocytes. Antioxidants, such as silybin, have been proposed as a treatment of patients with nonalcoholic fatty liver disease (NAFLD) and NASH. In this study, we evaluated, in patients with histologically documented NASH, the oxidant/antioxidant status and lipid "fingerprint" in the serum of NASH patients, both in basal conditions and after 12 months of treatment with silybin-based food integrator Realsil (RA). The oxidant/antioxidant status analysis showed the presence of a group of patients with higher basal severity of disease (NAS scores 4.67 ± 2.5) and a second group corresponding to borderline NASH (NAS scores = 3.8 ± 1.5). The chronic treatment with RA changed the NAS score in both groups that reached the statistical significance only in group 2, in which there was also a significant decrease of serum lipid peroxidation. The lipidomic profile showed a lipid composition similar to that of healthy subjects with a restoration of the values of free cholesterol, lysoPC, SM, and PC only in group 2 of patients after treatment with RA. Conclusion. These data suggest that lipidomic and/or oxidative status of serum from patients with NASH could be useful as prognostic markers of response to an antioxidant treatment.
    Full-text · Article · Jun 2014 · Oxidative medicine and cellular longevity
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    • "Influences of saturated fatty acids, as typified by palmitate, may account for the liver cell damage which contributes to developing NASH, characterized by saturated FFA-induced lipotoxicity [8], lipoapoptosis [12] and insulin resistance [13]. Inflammation may also be a major cause of NASH. "
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    ABSTRACT: Background Polyunsaturated fatty acids (PUFAs) may protect against metabolic diseases. Although the benefits of the n-3 family of PUFA have been well investigated in nonalcoholic steatohepatitis (NASH), little is known about the effect of the n-6 family. This study examined the effect of linoleate, a member of the n-6 family, on regulation of the palmitate-induced inflammatory cytokine interleukin-8 (IL8) in hepatocytes. Methods Huh7 cells and HepG2 cells were cultured with and without free fatty acid treatment (palmitate and linoleate, alone or in combination, 100–1000 μM). Inflammatory pathways, lipid accumulation, apoptosis and cell viability were monitored. Results Dose- and time-related changes of IL8 mRNA expression were examined and 9 h treatment with 500 μM palmitate showed the greatest elevation of IL8. Co-treatment with 500 μM palmitate and 400 μM linoleate significantly suppressed IL8 production below that with palmitate alone in both cells (both mRNA and protein). A quantitative measurement for lipid accumulation showed no significant difference between palmitate-treated cells (1.69 ± 0.21), linoleate-treated cells (1.61 ± 0.16) and palmitate and linoleate-treated cells (1.73 ± 0.22, NS, n = 7). The co-treatment with 400 μM linoleate inhibited phospho-c-Jun N-terminal kinase (pJNK) activation and IkBα reduction caused by 500 μM palmitate treatment. Treatment with 400 μM linoleate alone led to IL8 production (5.48 fold change), similar to co-treatment, with no influence on the expression of pJNK/IkBα. The cell viability was similar between treatment with 500 μM palmitate and with both 500 μM palmitate and 400 μM linoleate, showing no significant changes in the expression of cleaved caspase-3. Conclusions Linoleate is a potent regulator of the proinflammatory cytokine IL8 via the JNK and nuclear factor kappa B pathways that are involved in the pathophysiology of NASH, suggesting a future recommendation of dietary management.
    Full-text · Article · May 2014 · Lipids in Health and Disease
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    • "The cytotoxic response to elevated fatty acids appears to be specific to or made more severe by long-chain saturated fatty acids [8] [9] [10] [11]. In hepatocytes, saturated fatty acids promote endoplasmic reticulum (ER) stress and apoptosis [11] [12], both of which are characteristic features of NAFLD [13] [14]. The toxic effects of saturated fatty acids may be due to their inability, relative to unsaturated fatty acids, to be esterified and incorporated into triglyceride [7, 15–17]. "
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    ABSTRACT: Liver specific deletion of the tumor suppressor phosphatase and tensin homologue deleted on chromosome 10 (PTEN) induces steatosis and hypersensitivity to insulin. Saturated fatty acids, which induce endoplasmic reticulum stress and cell death, appear to increase PTEN, whereas unsaturated fatty acids which do not induce endoplasmic reticulum stress or cell death reduce this protein. In the present study, the role of PTEN in saturated fatty acid-induced cytotoxicity was examined in H4IIE and HepG2 liver cells. Palmitate and stearate increased the expression of PTEN, whereas the unsaturated fatty acids, oleate and linoleate, reduced PTEN expression in both cell types. SiRNA-mediated knockdown of PTEN did not increase liver cell triglyceride stores or reduce palmitate- or stearate-mediated ER stress or apoptosis. These results suggest that PTEN does not play a significant role in saturated fatty acid-induced cytotoxicity in these liver cell models and in the absence of insulin.
    Full-text · Article · Apr 2013 · Journal of nutrition and metabolism
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