Identification of calcium-independent phospholipase A₂γ in mitochondria and its role in mitochondrial oxidative stress

Abstract

Oxidant-induced lipid peroxidation and cell death mediate pathologies associated with ischemia-reperfusion and inflammation. Our previous work in rabbit renal proximal tubular cells (RPTC) demonstrated that inhibition of Ca(2+)-independent phospholipase A(2) (iPLA(2)) potentiates oxidant-induced lipid peroxidation and necrosis, implicating iPLA(2) in phospholipid repair. This study was conducted to identify a RPTC mitochondrial PLA(2) and determine the role of PLA(2) in oxidant-induced mitochondrial dysfunction. iPLA(2) activity was detected in Percoll-purified rabbit renal cortex mitochondria (RCM) and in isolated mitochondrial inner membrane fractions from rabbit and human RCM. Immunoblot analysis and inhibitor sensitivity profiles revealed that iPLA(2)gamma is the RCM iPLA(2) activity. RCM iPLA(2) activity was enhanced in the presence of ATP and was blocked by the PKCepsilon V1-2 inhibitor. Oxidant-induced mitochondrial lipid peroxidation and swelling were accelerated by pretreatment with R-BEL, but not S-BEL. Furthermore, oxidant treatment of isolated RCM resulted in decreased iPLA(2)gamma activity. These results reveal that RCM iPLA(2) is iPLA(2)gamma, RCM iPLA(2)gamma is regulated by phosphorylation by PKCepsilon, iPLA(2)gamma protects RCM from oxidant-induced lipid peroxidation and dysfunction, and that a strategy to preserve or enhance iPLA(2)gamma activity may be of therapeutic benefit.

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

“…In GECs, a portion of iPLA 2 ␥ was localized at the mitochondria (11). Thus, by analogy to its action in kidney cortical preparations, iPLA 2 ␥ may protect GEC mitochondria from oxidant-induced lipid peroxidation and dysfunction (37).…”

Complement-mediated Activation of Calcium-independent Phospholipase A2γ

“…iPLA 2 ␥ Localizes at the ER and Mitochondria-The expression and localization of iPLA 2 isoforms varies considerably among different cell types, and the role of iPLA 2 may be determined by the isoform present in a specific cell or organelle (43). We examined the localization of M1 GFP-iPLA 2 ␥ WT in stably transfected GECs.…”

“…2). iPLA 2 ␥ may protect renal cortical mitochondria from oxidant-induce lipid peroxidation and dysfunction (43). Thus, in the presence of oxidized phospholipid acyl chains, iPLA 2 ␥ may hydrolyze damaged acyl chains and allow for reesterification with normal fatty acids, thereby repairing mitochondrial membrane phospholipids.…”

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

“…The iPLA 2 family consists of at least seven members, with different isoforms being localized to different subcellular compartments, each displaying PLA 2 activity in the absence of Ca 21 (1). PLA 2 is reported to perform diverse functions, including generation of signaling molecules [e.g., arachidonic acid (2), membrane remodeling (3), and protection or repair of membranes from oxidative damage (4)(5)(6)]. In support of a protective role for PLA 2 , PLA 2 has been hypothesized to participate in the removal of oxidized fatty acids from biological membranes to maintain membrane integrity (7).…”