Activation of protein kinase C inhibits the secretion of platelet-activating factor acetylhydrolase by human decidual macrophages

Abstract

Background and Aims: Platelet activating factor (PAF), a potent phospholipid mediator, has been implicated in a number of reproductive processes through ovulation to parturition. To clarify the regulatory mechanism of PAF metabolism in the decidua, we have investigated the effect of activation of protein kinase C (PKC) on the secretion of PAF-acetylhydrolase (PAF-AH), a PAF-inactivating enzyme, by human decidual macrophages. Methods: Decidual macrophage populations were isolated from human decidua by using enzymic digestion, Ficoll-Paque centrifugation, or flow cytometric sorting. The cells were treated with a PKC activator (TPA), H-7, dibutyryl cyclic adenosine monophosphate (AMP), Bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, tetra (acetoxymethyl)-ester (BAPTA/AM) and/or nifedipine. The activity of PAF-AH secreted in the culture medium was assayed. Results: The PKC activator, TPA, inhibited the PAF-AH secretion by decidual cells in a dose-dependent manner. The TPA also decreased the enzyme secretion by flow cytometrically purified macrophages. The inhibitory effect of TPA was blocked by a PKC inhibitor, H-7. Protein kinase A (PKA) activation by dibutyryl cyclic AMP was without effect on the enzyme secretion. Calcium channel blockers, BAPTA/AM and nifedipine had no effect on the PAF-AH secretion. Conclusion: It is suggested that the TPA-induced inhibition of PAF-AH secretion may be mediated, in part, by a PKC-dependent signal transduction, and that activation of PKC may result in the increase in the local concentration of PAF in the decidua because of its inhibitory effect on the PAF-AH secretion by decidual macrophages. (Reprod Med Biol 2003; 2: 121-126).

Keywords: decidua; parturition; platelet‐activating factor acetylhydrolase; protein kinase C; signal transduction.

Figure 1

Effect of 12‐O‐tetradecanoylphobol 13‐acetate (TPA) on the platelet activating factor‐acetylhydrolase (PAF‐AH) secretion by decidual cells. Cells were treated with various concentrations of TPA on day 0 and cultured for 6 days. The PAF‐AH activity in the medium was assayed. Results are expressed as percentage of the enzyme activity of a non‐treated control.

Figure 2

Flow cytometric analysis of purified decidual macrophages. For flow cytometric analysis, 1 × 10⁶ decidual cells were labeled with fluorescein‐conjugated anti‐CD14 mouse monoclonal antibody. Macrophages purified flow cytometrically using a flow cytometric cell sorter were analyzed.