Caspase-3-dependent apoptosis in Escherichia coli-infected urothelium: involvement of inducible nitric oxide synthase

Abstract

To investigate if nitric oxide (NO) derived from inducible NO synthase (iNOS) regulates apoptosis and/or cell shedding in uroepithelial cells in vivo and in vitro, as bladder epithelial cells undergo shedding during urinary tract infection, which is considered a part of the host's defence and is thought to take place via an apoptotic pathway. Bladders and kidneys of mice infected with Escherichia coli were used to study caspase-3 immunoreactivity at different times after infection. Wild-type (E. coli 1177) and type-1 recombinant (E. coli PKL4) bacteria were used. iNOS-deficient mice were used to study the association of caspase-3 with iNOS. Isolated human uroepithelial cells were used to examine the effect of the NO donor DETA/NO and the peroxynitrite generator SIN-1 on caspase-3 activity and cell shedding in vitro. Many caspase-3 immunoreactive neutrophils were found soon after infection and some superficial bladder epithelial cells were also immunoreactive for caspase-3. Caspase-3 immunoreactivity was also detected in neutrophils and bladder epithelial cells of infected iNOS-deficient mice. There was no co-expression between iNOS- and caspase-3 in bladder epithelial cells. DETA/NO and SIN-1 did not stimulate caspase-3 activity or cell shedding in isolated human uroepithelial cells. Caspase-3 and iNOS are not co-expressed in uroepithelial cells and apoptosis is evident in the absence of iNOS. Exogenous NO did not induce apoptosis or cell shedding in isolated human uroepithelial cells.