A Genetic Animal Model for Bladder Dysfunction Associated with Type 2 Diabetes
Zongwei Wang, M.D., PhD1, Maryrose Sullivan, PhD2, Zhiyong Cheng, PhD3, Morris White, PhD3, Pablo Gomery, M.D.1, Aria F. Olumi, M.D.1.
1Massachusetts General Hospital, Boston, MA, USA, 2West Roxbury VA, Boston, MA, USA, 3Children's Hospital, Boston, MA, USA.
BACKGROUND: Type 2 diabetes mellitus (DM2) stems from insulin resistance and affects 7% of the US population. Lower urinary tract dysfunction is one of the major urologic complications associated with DM2, and the patients present with detrusor overactivity or detrusor underactivity. Although diabetic bladder dysfunction affects up to 80% of patients with DM2 its underlying pathophysiology is poorly understood. Here, we demonstrate a genetic mouse model with DM2 with conditional knockout of insulin receptor substrates 1 & 2 (Irs1, Irs2), which mimic the diabetic lower urinary tract dysfunction in humans.
METHODS: Conditional hepatocyte knockout Irs1/Irs2 mice were created by generating albumin -Cre mice using the C57/BL6 and 129Sv genetic background. Basal glucose levels were evaluated in 1-week old through 30-week old mice. Glucose stimulation was carried out in mice at 6-8 weeks of age. Bladder of mice at 6, 10, 14 and 20 weeks of age were harvested and bladder muscle strips were analyzed for spontaneous contraction, and stimulated by electricity, carbachol or KCl. Western blot analyses were carried out to assess expression of phosphorylated myosin light chain (pMLC) protein.
RESULTS: Irs1/Irs2 double knockout (DKO) mice developed type 2 diabetes with hyperglycemia after 5 weeks of age and remained hyperglycemic through age 30 weeks. Abnormal glucose stimulation tests were detected in Irs1/Irs2 mice compared to control mice. Bladder of 6-week and 10-week old mice demonstrated overactivity compared to controls by spontaneous contraction and electrical field stimulation assays (p<0.001). However, bladder of 14-week and 20-week old Irs1/Irs2 DKO mice demonstrated underactivity compared to controls (p<0.05). Carbachol and KCl stimulation studies demonstrated similar findings where 6-week old and 10-week old Irs1/Irs2 DKO bladders were overactive, whereas 14-week and 20-week old DKO bladders were underactive compared to controls (p<0.01). The pMLC protein in the bladder was highly expressed in 6 and 10 week old mice, and significantly reduced in 20-week old mice, which correlates with the over- and underactivities observed in Irs1/Irs2 DKO bladders.
CONCLUSIONS: Pathophysiology of bladder dysfunction in type 2 diabetes is poorly understood. Irs1/Irs2 DKO mice develop insulin resistant diabetes. Lower urinary tract dysfunctions in Irs1/Irs2 DKO bladders are associated with overactivity in early/mid life of the mice, and underactivity in late adult life. Irs1/Irs2 DKO mice are a good model to evaluate the molecular alterations associated with bladder dysfunction in type 2 insulin resistant diabetes.