Decreased iPLA2γ expression induces lipid peroxidation and cell death and sensitizes cells to oxidant-induced apoptosis

Abstract

Our previous studies showed that renal proximal tubular cells (RPTC) express Ca 21 -independent phospholipase A 2 g (iPLA 2 g) in endoplasmic reticulum (ER) and mitochondria and that iPLA 2 g prevents and/or repairs lipid peroxidation induced by oxidative stress. Our present studies determined the importance of iPLA 2 g in mitochondrial and cell function using an iPLA 2 g-specific small hairpin ribonucleic acid (shRNA) adenovirus. iPLA 2 g expression and activity were decreased in the ER by 24 h and in the mitochondria by 48 h compared with scrambled shRNA adenovirus-treated cells. Lipid peroxidation was elevated by 2-fold at 24 h and remained elevated through 72 h in cells with decreased iPLA 2 g. Using electrospray ionization-mass spectrometry, primarily phosphatidylcholines and phosphatidylethanolamines were increased in iPLA 2 g-shRNA-treated cells. At 48 h after exposure to the iPLA 2 g shRNA, uncoupled oxygen consumption was inhibited by 25% and apoptosis was observed at 72 and 96 h. RPTC with decreased iPLA 2 g expression underwent apoptosis when exposed to a nonlethal concentration of the oxidant tert-butyl hydroperoxide (TBHP). Exposure of control cells to a nonlethal concentration of TBHP induced iPLA 2 g expression in RPTC. These results suggest that iPLA 2 g is required for the prevention and repair of basal lipid peroxidation and the maintenance of mitochondrial function and viability, providing further evidence for a cytoprotective role for iPLA 2 g from oxidative stress.

Calcium-independent Phospholipase A2γ Enhances Activation of the ATF6 Transcription Factor during Endoplasmic Reticulum Stress

“…In renal proximal tubular cells, iPLA 2 ␥ removes oxidized phospholipids from the ER membrane during oxidative stress; thus, iPLA 2 ␥ may act to repair damaged lipids or prevent lipid peroxidation during oxidative stress (4). Consistent with these results, iPLA 2 ␥ knockdown in renal cells increased lipid peroxidation and induced apoptosis (6). Conversely, inhibition of microsomal iPLA 2 ␥ in rabbit renal proximal tubular cells during cisplatin-induced apoptosis reduced apoptosis markers, indicating that iPLA 2 ␥ contributes to apoptosis (7).…”

“…Up-regulation of such genes potentially enhances the chaperoning capacity of a cell, thereby alleviating adverse effects of protein misfolding and reducing cytotoxicity. Furthermore, it should also be considered that mechanisms other than ATF6 activation at the ER could contribute to iPLA 2 ␥ cytoprotection; for example, the action of iPLA 2 ␥ could involve reducing lipid peroxidation (4,6). In GECs, a portion of iPLA 2 ␥ was localized at the mitochondria (11).…”

Genetic Ablation of Calcium-independent Phospholipase A2γ Leads to Alterations in Hippocampal Cardiolipin Content and Molecular Species Distribution, Mitochondrial Degeneration, Autophagy, and Cognitive Dysfunction

“…Considering that both eicosanoids and lysolipids mediate multiple cellular signaling pathways, the observed neurologic pathologies due to iPLA 2 ␥ ablation are not unanticipated and likely result from the accumulation of lipid substrates for iPLA 2 ␥ within the mitochondria. Alterations in mitochondrial membrane composition are likely associated with compromised mitochondrial function analogous to mitochondrial function observed in adenoviral-mediated short hairpin RNA iPLA 2 ␥ knockdown previously demonstrated in renal proximal tubular cells (47).…”

Complement-mediated Activation of Calcium-independent Phospholipase A2γ

“…During oxidative stress, an ER-associated iPLA 2 in renal proximal tubular cells (iPLA 2 ␥) recognizes, cleaves, and removes oxidized phospholipids from the ER membrane (25); thus, iPLA 2 ␥ may act to repair or prevent lipid peroxidation during oxidative stress (25). Another study demonstrated that expression of shRNA against iPLA 2 ␥ increased lipid peroxidation and induced apoptosis in renal cells (26). iPLA 2 is involved in signal transduction pathways that include mitogen-activated protein kinase (MAPK) p38, epidermal growth factor (EGF) receptor, the tumor suppressor gene, p53, and cell cycle-regulator, p21 (27).…”