Epoxyeicosatrienoic acids pretreatment improves amyloid β-induced mitochondrial dysfunction in cultured rat hippocampal astrocytes

Abstract

Amyloid-β (Aβ) has long been implicated as a causative protein in Alzheimer's disease. Cellular Aβ accumulation is toxic and causes mitochondrial dysfunction, which precedes clinical symptoms of Alzheimer's disease pathology. In the present study, we explored the possible use of epoxyeicosatrienoic acids (EETs), epoxide metabolites of arachidonic acid, as therapeutic target against Aβ-induced mitochondrial impairment using cultured neonatal hippocampal astrocytes. Inhibition of endogenous EET production by a selective epoxygenase inhibitor, MS-PPOH, caused a greater reduction in mitochondrial membrane potential in the presence of Aβ (1, 10 μM) exposure versus absence of Aβ. MS-PPOH preincubation also aggravated Aβ-induced mitochondrial fragmentation. Preincubation of the cells with either 14,15- or 11,12-EET prevented this mitochondrial depolarization and fragmentation. EET pretreatment also further improved the reduction observed in mitochondrial oxygen consumption in the presence of Aβ. Preincubation of the cells with EETs significantly improved cellular respiration under basal condition and in the presence of the protonophore, carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP). The uncoupling of ATP synthase from the electron transfer chain that occurred in Aβ-treated cells was also prevented by preincubation with EETs. Lastly, cellular reactive oxygen species production, a hallmark of Aβ toxicity, also showed significant reduction in the presence of EETs. We have previously shown that Aβ reduces EET synthesis in rat brain homogenates and cultured hippocampal astrocytes and neurons (Sarkar P, Narayanan J, Harder DR. Differential effect of amyloid beta on the cytochrome P450 epoxygenase activity in rat brain. Neuroscience 194: 241-249, 2011). We conclude that reduction of endogenous EETs may be one of the mechanisms through which Aβ inflicts toxicity and thus supplementing the cells with exogenous EETs improves mitochondrial dynamics and prevents metabolic impairment.

Novel function of ceramide for regulation of mitochondrial ATP release in astrocytes

“…Fragmentation led to about 50% reduction in mitochondrial length, aspect ratio, and form factor (Fig. 1B-D), consistent with previous studies showing similar effects of amyloid on mitochondrial morphology (64). As an alternative approach to deplete cells of ceramide we used the ceramide synthase (CerS) inhibitor Fumonisin B1 (FB1), which also protected astrocytes from mitochondrial fragmentation (Supplemental Fig.…”

“…Mitochondrial morphology was analyzed using standard protocols for quantitation of mitochondrial length (L), aspect ratio (L/W), and form factor (P 2 /4πA) as previously described (64).…”

14,15-EET promotes mitochondrial biogenesis and protects cortical neurons against oxygen/glucose deprivation-induced apoptosis

“…On the other hand, ischemia inhibits the expressions of PGC1a, NRF-1 and TFAM, and then reduces mitochondrial biogenesis [10,13]. Recent studies report that the physiological role of EETs is linked to the function of mitochondria, for instance, EETs protect mitochondrial functions by limiting ROS generation and reducing the loss of mitochondrial membrane potential, as well as preserving ATP synthesis in astrocyte, H9c2 cell and carcinoma cell line [14][15][16]. Based on the above data, we hypothesized that 14,15-EET may exert neuroprotective effect on cortical neurons against OGD-induced apoptosis by enhancing the biogenesis and function of mitochondria.…”

The Pharmacology of the Cytochrome P450 Epoxygenase/Soluble Epoxide Hydrolase Axis in the Vasculature and Cardiovascular Disease

“…Similarly, EETs have been linked to a decrease in the Ca 2+ accumulation associated with anoxia-reoxygenation as well as the maintenance of the cardiac myocyte mitochondrial potential (Batchu et al, 2012a,b). In cancer cells and astrocytes, 11,12-EET attenuated reactive oxygen species generation, loss of mitochondrial function, and caspase activation induced by toxic stimuli the antileukemia drug arsenic trioxide Sarkar et al, 2014). On the other hand, 11,12-EET was found to acutely reduce the mitochondrial potential in pulmonary smooth muscle 1130 Fleming cells by promoting the association of the BKa and BKb1 subunits on the mitochondrial membrane, ultimately leading to the depolarization and contraction of pulmonary artery smooth muscle cells (Loot et al, 2012).…”