Type II secretory phospholipase A₂binds to ischemic flip-flopped cardiomyocytes and subsequently induces cell death

Abstract

Type II secretory phospholipase A2 (sPLA2) is a cardiovascular risk factor. We recently found depositions of sPLA2 in the necrotic center of infarcted human myocardium and normally appearing cardiomyocytes adjacent to the border zone. The consequences of binding of sPLA2 to ischemic cardiomyocytes are not known. To explore a potential effect of sPLA2 on ischemic cardiomyocytes at a cellular level we used an in vitro model. The cardiomyocyte cell line H9c2 or adult cardiomyocytes were isolated from rabbits that were incubated with sPLA2 in the presence of metabolic inhibitors to mimic ischemia-reperfusion conditions. Cell viability was established with the use of annexin V and propidium iodide or 7-aminoactinomycin D. Metabolic inhibition induced an increase of the number of flip-flopped cells, including a population that did not stain with propidium iodide and that was caspase-3 negative. sPLA2 bound to the flip-flopped cells, including those negative for caspase-3. sPLA2 binding induced cell death in these latter cells. In addition, sPLA2 potentiated the binding of C-reactive protein (CRP) to these cells. We conclude that by binding to flip-flopped cardiomyocytes, including those that are caspase-3 negative and presumably reversibly injured, sPLA2 may induce cell death and tag these cells with CRP.

Annexin A5 Scintigraphy of Forearm as a Novel In Vivo Model of Skeletal Muscle Preconditioning in Humans

“…16,17,19,22 Our observation is in agreement, however, with reversible availability of externalized phosphatidylserines in response to mild hypoxia or ischemia as has been reported by others. 21,23,24 Alternatively, one might argue that targeting of Annexin A5 in our experiments is driven mainly by reactive hyperemia. Although this concept provides an explanation for the lack of uptake of Annexin A5 when injected 1 hour after reperfusion, it does not explain why Annexin A5 targeting was prevented by ischemic preconditioning or adenosine infusion.…”

Inhibition of type 2A secretory phospholipase A2 reduces death of cardiomyocytes in acute myocardial infarction

“…As a result, the anionic phospholipids phosphatidylserine and phosphatidylethanolamine, which under normal conditions are kept within the inner plasma membrane leaflet, are exposed in the outer membrane leaflet, a process called flip-flop [6]. We and others have shown that this flip-flop can be reversible [7,8]. However, during reperfusion the inflammatory mediator type IIA secretory-type phospholipase A 2 (sPLA 2 -IIA) was shown to bind to and to induce death in these flip-flopped cardiomyocytes [4,8,9].…”

“…We and others have shown that this flip-flop can be reversible [7,8]. However, during reperfusion the inflammatory mediator type IIA secretory-type phospholipase A 2 (sPLA 2 -IIA) was shown to bind to and to induce death in these flip-flopped cardiomyocytes [4,8,9]. sPLA 2 -IIA is a 14 kDa acute-phase protein that catalyses the hydrolysis of cellular phospholipids to liberate nonesterified fatty acids [10].…”

“…This binding of CRP then induces binding and activation of complement, resulting in further tissue damage [12]. In addition sPLA 2 -IIA can not only induce cell death via CRP and complement activation, but also via a direct cytotoxic effect, independent of other inflammatory mediators [8].…”

“…We further hypothesized that inhibition of sPLA 2 -IIA would not impair wound healing after AMI, since sPLA 2 -IIA inhibition would protect the reversibly damaged cardiomyocytes, while the irreversibly damaged cardiomyocytes would still be cleared from the myocardium independent of sPLA 2 -IIA [8]. In this study, we therefore analyzed the effect of PX-18 on membrane flip-flop (reversibly damaged and/or apoptotic cells), both in vitro and in vivo in a rat AMI model.…”