Time-dependent urinary bladder remodeling in the streptozotocin-induced diabetic rat model

Urinary bladder dysfunction and remodeling are well-recognized phenomena in diabetes but detailed assessments of tissue morphological changes have not been conducted. We studied time-dependent morphological changes in bladders from diabetic rats (streptozotocin model) and evaluated the usefulness of automated digital imaging technology as an unbiased, reproducible, and convenient method for the bladder morphometric analysis. Urinary bladders were isolated from diabetic (3 days, 2 weeks or 5 weeks after single injection of streptozotocin, 65 mg/kg) or control rats (0 or 5 weeks) and were processed for histochemical evaluations (hematoxylin/cosin and Mason's trichrome staining). Digital image analysis was used to quantify equatorial cross-sectional areas of bladder tissue and lumen, as well as relative prevalence of the three primary tissue components viz. smooth muscle, urothelium, and extracellular matrix. Digital imaging and color segmentation provided reliable and unbiased evaluations of the bladder tissue sections. Progressive increases in total bladder tissue and lumen area were observed in the diabetic animals relative to controls (p<0.05), demonstrating classic hypertrophy and dilation. Prevalence of smooth muscle and urothelium (% of total tissue) both increased significantly, but collagen content decreased. Average bladder wall thickness and urothelium thickness were unchanged. Bladder remodeling during experimental diabetes is associated with time-dependent chamber dilation and increased tissue mass. Changes in bladder wall composition also occurred in a time-dependent manner, most notably increased smooth muscle and urothelium and decreased collagen prevalence. Furthermore, automated digital imaging technologies provide an unbiased, reproducible, and convenient method for detailed morphometric analysis of bladder tissues.