Discrete Role for Cytosolic Phospholipase A2α in Platelets

Abstract

Among several different types of phospholipase A2 (PLA2), cytosolic PLA2 (cPLA2)α and group IIA (IIA) secretory PLA2 (sPLA2) have been studied intensively. To determine the discrete roles of cPLA2α in platelets, we generated two sets of genetically engineered mice (cPLA2α−/−/sPLA2-IIA−/− and cPLA2α−/−/sPLA2-IIA+/+) and compared their platelet function with their respective wild-type C57BL/6J mice (cPLA2α+/+/sPLA2-IIA−/−) and C3H/HeN (cPLA2α+/+/sPLA2-IIA+/+). We found that cPLA2α is needed for the production of the vast majority of thromboxane (TX)A2 with collagen stimulation of platelets. In cPLA2α-deficient mice, however, platelet aggregation in vitro is only fractionally decreased because small amounts of TX produced by redundant phospholipase enzymes sufficiently preserve aggregation. In comparison, adenosine triphosphate activation of platelets appears wholly independent of cPLA2α and sPLA2-IIA for aggregation or the production of TX, indicating that these phospholipases are specifically linked to collagen receptors. However, the lack of high levels of TX limiting vasoconstriction explains the in vivo effects seen: increased bleeding times and protection from thromboembolism. Thus, cPLA2α plays a discrete role in the collagen-stimulated production of TX and its inhibition has a therapeutic potential against thromboembolism, with potentially limited bleeding expected.

Interactions of 12‐lipoxygenase with phospholipase A2isoforms following platelet activation through the glycoprotein VI collagen receptor

“…Our observations suggest a critical role for cPLA 2 in providing substrate to the p12‐LOX also. This is in agreement with a recent study which showed that deletion of cPLA 2 causes 80% reduction in serum 12‐HETE levels, although in mice this metabolite will not exclusively originate from platelet 12‐LOX, as 12/15‐LOX will also be a significant source [18].…”

Group VIB Calcium-Independent Phospholipase A2 (iPLA2γ) Regulates Platelet Activation, Hemostasis and Thrombosis in Mice

“…PLA 2 plays a central role in platelet activation by hydrolysis of membrane phospholipids in response to a variety of stimuli. Previous studies have shown that, among several different PLA 2 enzymes, cPLA 2 α is critical for platelet activation, even though other PLA 2 (s) may also be involved [10] . The present study has revealed that iPLA 2 γ, one of the Ca 2+ -independent intracellular PLA 2 enzymes, represents the missing link; it is also responsible for stimulus-dependent AA release and functions as a key enzyme in platelet aggregation in vitro and thrombus formation in vivo .…”

“…Bleeding time was assessed according to a previously reported method [10] . In brief, 8∼9-wks of age male mice were restrained in the upright position and their tails were transected 5 mm proximal from the tip.…”

“…AA production in platelets is dependent on cPLA 2 α but not on sPLA 2 -IIA [9] . A functional deficiency of cPLA 2 α diminished platelet aggregatory and secretory responses to collagen [10] . cPLA 2 α-deficient mice have prolonged bleeding times and are resistant to thromboembolism induced by injection of a mixture of ADP and collagen, indicating a role of this enzyme in platelet adhesive and hemostatic functions.…”

Function, Activity, and Membrane Targeting of Cytosolic Phospholipase A2ζ in Mouse Lung Fibroblasts

“…However, eicosanoid production is not completely ablated in the cPLA 2 ␣ knock-out mouse indicating a role for other PLA 2 s in mediating arachidonic acid release (23,24). We previously isolated mouse lung fibroblasts (MLF) from cPLA 2 ␣ wild type and knock-out mice and demonstrated a primary role for cPLA 2 ␣ in mediating arachidonic acid release and prostaglandin E 2 (PGE 2 ) production (25).…”