Does the small GTPase Rac1 has a role on bladder dysfunction in streptozotocin-induced diabetic rats?

AS Evcim1, S Cilaker Micili2, M Karaman3, G Erbil2, E Guneli3, S Gidener1, M Gumustekin1. 1Dokuz Eylul University School of Medicine, Department of Pharmacology, Izmir, 35340, Turkey, 2Dokuz Eylul University School of Medicine, Department of Histology Embriology, Izmir, 35340, Turkey, 3Dokuz Eylul University School of Medicine, Department of Laboratory Animal Science, Izmir, 35340, Turkey

In addition to endothelial dysfunction, smooth muscle contraction or regulatory protein abnormalities have been shown to induce diabetes-related changes in diabetic animal models. The aim of this study was to investigate the role of small GTPase Rac1 on diabetic bladder dysfunction because of its roles in the contraction of smooth muscle and urothelial function.

In streptozotocin-induced diabetic rat model, control, diabetic and insulin-treated diabetic groups were performed. Urinary bladder detrusor muscle strips were suspended in organ baths at the end of 8-12 weeks after STZ injection. In either the absence and presence of Rac1 inhibitor NSC 23766 (0.1, 1 and 10 µM), carbachol (CCh) (10-9-10-4 M) dose-response curves were obtained. Experiments were repeated in the presence of indomethacin (5x10-7 M) for evaluation effects of prostaglandins which are released from urothelium. In paraffin-embedded sections of the urinary bladder neck, diabetes-related histopathological changes and Rac1 expressions were evaluated by hematoxylin eosin staining and immunohistochemical staining respectively.

CCh produced dose-dependent contractile responses in all experimental groups. In diabetic and insulin-treated diabetic groups, contractile responses to CCh were higher than those of the control group (p<0.001). In the presence of Rac1 inhibitor NSC-23766, CCh-induced contractions were decreased significantly in all groups (p<0.001), but the inhibition in diabetic and insulin-treated diabetic group were higher than those of the control group. When compared to control group the significantly differences were observed in the presence of 0.1 µM NSC 23766 in diabetic group (p<0.001) and in the presence of 0.1 ve 10 µM NSC 23766 in insulin-treated diabetic group (p<0.001). NSC 23766 inhibited the CCh contractions in a dose-independent manner, in all groups.

Indomethacin significantly inhibited CCh-induced contractions in all groups (p<0.001), but there were not any significant differences among groups. Indomethacin didn’t potentiate the inhibitory effects of the small GTPase Rac1.

In hematoxylin eosin staining, bladder wall thickness was increased in diabetic and insulin-treated diabetic groups compared to control group (p<0.001). The immunohistochemical expressions of Rac1 were increased in all strata of urinary bladder in diabetic and insulin-treated diabetic groups compared to control group and there was statistically significant increase in lamina propria and tunica muscularis in diabetic group compared to insulin-treated diabetic group (p<0.05).

In the presence of NSC 23766, the inhibition of CCh-induced contractions in diabetic and insulin-treated diabetic group were higher than those of the control group. Therefore small GTPase Rac1 may play a role on bladder dysfunction in diabetes. Increased Rac1 expressions were found in diabetic and insulin-treated diabetic groups, Rac1 mediated effects may be due to its increased expression. Insulin therapy didn’t improve the inhibitory effects of small GTPase Rac1 in diabetic group. These results suggest that need an additional treatments to insulin in diabetes-associated bladder dysfunction. At this point further studies are needed for promising therapies that target the small GTPase Rac1 in the bladder dysfunction in diabetes.

Keywords: diabetes mellitus, urinary bladder, rat, small GTPase, Rac1, insulin