Background: Interstitial cystitis/bladder pain syndrome is a debilitating inflammatory bladder disease with currently unknown etiology. We determined the expression of calcium-independent phospholipase A2β (iPLA2β) and iPLA2γ isoforms in cultured immortalized urothelial cells isolated from normal or IC/BPS patient bladders.
Materials and methods: Immunoblot analysis was used to determine the iPLA2 isoform expression in immortalized urothelial cells isolated from normal and IC/BPS patients. iPLA2 activity was measured using a radiometric assay with (16:0, [3H]18:1) plasmenylcholine as substrate. Platelet-activating factor (PAF) accumulation was determined by labeling cells with [3H] acetic acid. Adherence of polymorphonuclear leukocytes (PMN) to urothelial cells was determined by measuring myeloperoxidase (MPO) activity.
Results: We identified the two predominant mammalian iPLA2 isoforms, iPLA2β and iPLA2γ, in immortalized urothelial cells. IC/BPS urothelial cells demonstrated a decrease in iPLA2γ and an increase in iPLA2β immunoprotein when compared to normal cells. Selective pharmacologic inhibition demonstrated that the majority of iPLA2 activity in normal urothelium represents iPLA2γ whereas that in IC/BPS urothelium is iPLA2β. Greater PAF production and PMN adherence was observed in tryptase-stimulated IC/BPS urothelial cells when compared to normal urothelial cells. In both normal and IC/BPS urothelial cells, increased PAF production and PMN adherence was completely blocked when tryptase-stimulated cells were pretreated with (S)-bromoenol lactone (BEL) to inhibit iPLA2β. PMN adherence was blocked when PMNs were pretreated with ginkgolide B to block the PAF-receptor (PAFR).
Conclusions: Urothelial cells derived from IC/BPS origin exhibit a redistribution of iPLA2 isoforms with iPLA2β being predominately expressed compared to normal urothelial cells. The redistribution of iPLA2β, increased PAF production and increased PMN adherence may represent a mechanism whereby IC/BPS patients' exhibit increased susceptibility to bladder inflammation.
Keywords: Inflammation, platelet-activating factor, PMN adherence, urothelial cells