Elevated hydrostatic pressure stimulates ATP release which mediates activation of the NLRP3 inflammasome via P2X4 in rat urothelial cells

Abstract

Partial bladder outlet obstruction (pBOO) is a prevalent urological condition commonly accompanied by increased intravesical pressure, inflammation, and fibrosis. Studies have demonstrated that pBOO results in increased NLRP3 inflammasome and caspase-1 activation and that ATP is released from urothelial cells in response to elevated pressure. In the present study, we investigated the role of elevated pressure in triggering caspase-1 activation via purinergic receptors activation in urothelial cells. Rat urothelial cell line, MYP3 cells, was subjected to hydrostatic pressures of 15 cmH2O for 60 min, or 40 cmH2O for 1 min to simulate elevated storage and voiding pressure conditions, respectively. ATP concentration in the supernatant media and intracellular caspase-1 activity in cell lysates were measured. Pressure experiments were repeated in the presence of antagonists for purinergic receptors to determine the mechanism for pressure-induced caspase-1 activation. Exposure of MYP3 cells to both pressure conditions resulted in an increase in extracellular ATP levels and intracellular caspase-1 activity. Treatment with P2X7 antagonist led to a decrease in pressure-induced ATP release by MYP3 cells, while P2X4 antagonist had no effect but both antagonists inhibited pressure-induced caspase-1 activation. Moreover, when MYP3 cells were treated with extracellular ATP (500 µM), P2X4 antagonist inhibited ATP-induced caspase-1 activation, but not P2X7 antagonist. We concluded that pressure-induced extracellular ATP in urothelial cells is amplified by P2X7 receptor activation and ATP-induced-ATP release. The amplified ATP signal then activates P2X4 receptors, which mediate activation of the caspase-1 inflammatory response.