Destabilization of the acrosome results in release of phospholipase A2 from human spermatozoa and subsequent formation of lysophospholipids

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Abstract
Phospholipase A(2) controls the phospholipid composition in spermatozoal membranes and is released from the acrosome of human spermatozoa. The extracellular phospholipase A(2) activity of human spermatozoa was determined by matrix-assisted laser desorption and ionization time-of-flight (MALDI-TOF) mass spectrometry after destabilization of acrosome by the calcium-ionophore calcimycin. MALDI-TOF mass spectrometry allowed the monitoring of changes in both substrate and products of spermatozoal phospholipase A(2) (PLA(2)) without the use of labelled phospholipids. The spermatozoal PLA(2) was characterized as a secretory one (sPLA(2)). Secretory PLA(2) exhibited a high substrate specificity for 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (PDPC), the most abundant spermatozoal phospholipid. A time- and cell number-dependent formation of the lysophospholipid PDPC was observed following incubation of extracellular medium of calcimycin-treated spermatozoa (CTS) with PDPC. Antibodies against sPLA(2), specific inhibitors of sPLA(2) and Ca(2+)-chelators could inhibit its generation. An antibody against lysophospholipase enhanced the lysoproduct concentration in the extracellular medium of CTS containing sPLA(2) because further metabolization of these products was blocked. The results demonstrated that destabilization of the acrosome is able to induce a release of secretory phospholipase A(2) from human spermatozoa with subsequent generation of lysophosphocholine in the surrounding of spermatozoa.