Simulated Bladder Pressure Stimulates Human Bladder Smooth Muscle Cell Proliferation via the PI3K/SGK1 Signaling Pathway

Abstract

A mechanical stimulus on detrusor tissue is critical to bladder outlet obstruction progression and functional bladder tissue engineering. A hypothesis is that mechanical stimulus triggers human bladder smooth muscle cell proliferation. To help better understand this relationship of bladder function to growth at the cellular level we used a novel method of applying cyclic hydrodynamic pressure that simulates the bladder cycle to cell cultures. We detected the proliferation response of human bladder smooth muscle cells (4310, ScienCell™) to different pressures as well as the signal transduction mechanism of this process. Human bladder smooth muscle cells cultured in scaffolds underwent 4 pressures (0, 100, 200 and 300 cm H(2)O) for 24 hours, as controlled by a BioDynamic® bioreactor. We then used flow cytometry to examine cell cycle distribution, and polymerase chain reaction and immunoblot to quantify SGK1 and AKT expression and activation in each group. SGK1 was silenced in human bladder smooth muscle cells using small interfering RNA to validate the role of SGK1 in mediating pressure induced cell proliferation. Compared with the 0 cm H(2)O control group, human bladder smooth muscle cells in the 200 and 300 cm H(2)O groups showed increased cell proliferation. SGK1 expression and activity were also increased while AKT, another downstream signal of PI3K, did not change significantly. SGK1 silencing abolished the increases in cell proliferation induced by pressure. To our knowledge we provide the first report of cyclic hydrodynamic pressure stimulating the proliferation of human bladder smooth muscle cells cultured in scaffolds. The signal transduction mechanism for this process is involved with the PI3K/SGK1 and not the PI3K/AKT signaling pathway.