Oxidant driven signaling pathways during diabetes: role of Rac1 and modulation of protein kinase activity in mouse urinary bladder

BACKGROUND: Urinary bladder dysfunction is a complication in diabetes but the mechanisms involved are undefined. Here, we investigated roles of oxidative stress and oxidant driven signaling pathways in a murine model of diabetes, with an emphasis on urothelial vs. smooth muscle regional changes. METHODS: Mice were dosed with streptozotocin (150 mg/kg) or vehicle and studied at 5 weeks. Functional changes were assessed by in vitro cystometry. Immunohistochemical methods and automated digital imaging was used for morphometric and histochemical analysis of bladder tissue regions. RESULTS: We detected significant increases in protein 3-nitrotyrosine in both urothelium and smooth muscle regions during diabetes, demonstrating an increased prevalence of reactive nitrogen species. In light of nitric oxide synthase (NOS) isoforms as potential contributors to increased protein nitration, all three NOS isoforms were studied; region specific increases in NOS1 (urothelium and smooth muscle), NOS2 (urothelium only) but no alterations in NOS3 isoform were detected during diabetes. In contrast, p21-Rac1 (coordinating protein of NADPH oxidase) was significantly increased only in smooth muscle (diabetic vs. controls). We also investigated phosphorylation of ERK, JNK, p38 and Akt using immunohistochemical techniques; each of these was increased during diabetes but with different distributions in the two major regions of bladder tissues viz the smooth muscle and urothelium. CONCLUSIONS: The STZ mouse model of diabetes exhibits bladder dysfunction and structural changes similar to human. Reactive nitrogen species formation occurs in this setting and region specific assessments also revealed that urothelial changes and smooth muscle changes are discrete with respect to mechanisms of reactive nitrogen species (increased production of NO vs. superoxide anion) and activation of oxidant related stress signaling pathways.