Impact of diabetes mellitus on bladder uroepithelial cells

Abstract

Diabetic bladder dysfunction (DBD), a prevalent complication of diabetes mellitus (DM), is characterized by a broad spectrum of symptoms including urinary urgency, frequency, and incontinence. As DBD is commonly diagnosed late, it is important to understand the chronic impact of DM on bladder tissues. While changes in bladder smooth muscle and innervation have been reported in diabetic patients, the impact of DM on the specialized epithelial lining of the urinary bladder, the urothelium (UT), is largely unknown. Quantitative polymerase chain reaction analysis and electron microscopy were used to evaluate UT gene expression and cell morphology 3, 9, and 20 wk following streptozotocin (STZ) induction of DM in female Sprague-Dawley rats compared with age-matched control tissue. Desquamation of superficial (umbrella) cells was noted at 9 wk DM, indicating a possible breach in barrier function. One causative factor may be metabolic burden due to chronic hyperglycemia, suggested by upregulation of the polyol pathway and glucose transport genes in DM UT. While superficial UT repopulation occurred by 20 wk DM, the phenotype was different, with significant upregulation of receptors associated with UT mechanosensation (transient receptor potential vanilloid subfamily member 1; TRPV1) and UT autocrine/paracrine signaling (acetylcholine receptors AChR-M2 and -M3, purinergic receptors P2X(2) and P2X(3)). Compromised barrier function and alterations in UT mechanosensitivity and cell signaling could contribute to bladder instability, hyperactivity, and altered bladder sensation by modulating activity of afferent nerve endings, which appose the urothelium. Our results show that DM impacts urothelial homeostasis and may contribute to the underlying mechanisms of DBD.

Fig. 1.

Transmission electron microscopic analysis of streptozotocin-treated and control rat bladder urothelium. Rats were untreated (A–C) or 3 wk (D–F), 9 wk (G–I), and 20 wk DM (J–L). The location of the junctional complex between adjacent umbrella cells is circled. In E and F, arrowheads show hinge areas. A, D, G, and J show the three urothelial cell layers: and basel (BC), intermediate (IC), and umbrella (UC). B and C, E and F, H and I, K and L are respectively corresponding stepwise higher magnifications focusing on the umbrella cells. 9 wk DM tissue in G and H and I exhibits dramatic defects in UC morphology, such as fewer discoidal- or fusiform-shaped vesicle (DCV). In G, the asterisk marks an UC that lacks underlying ICs or BCs and has an apical protrusion/dome (marked with an arrowhead). The IC marked with a black dot extends deep into the submucosa. The arrow in G cell debris. J–L from 20 wk DM tissue exhibit normal/unperturbed morphology, similar to A–C from control/untreated tissue and D–F, from 3 wk DM tissue. Images were processed as described in materials and methods.

Fig. 2.

Scanning electron microscopic (SEM) analysis of control and streptozotocin (STZ)-treated rat bladder urothelium. SEM was performed to examine the three-dimensional morphology of the surface of the urothelium in control/untreated rats (A–C) or STZ-diabetic rats at 3 wk (D–F), 9 wk (G–I), and 20 wk (J–L) postonset of STZ-induced DM. D–F reveal signs of barrier pathophysiology at 3 wk DM tissue, not apparent in TEM (discussed in the results). G–I show compromised barrier morphology in 9 wk DM tissue. The asterisk in G shows a region where an UC has dissociated, revealing the underlying intermediate cells. The arrows in H indicate regions where the plasma membrane is disrupted. A higher magnification view of the boxed area is shown in the inset. Scale bar is equal to 10 μm. J–L from 20 wk DM tissue show unperturbed/normal morphology of the apical surface of the UCs, similar to A–C, from control/untreated tissue. DUC, dissociating umbrella cell; H, hinge; ZM, zippered apical membrane. Images were processed as described in materials and methods.

Fig. 3.

Temporal impact of DM on UT gene expression at: 3 wk (A); 9 wk (B), and 20 wk (C). Genes were grouped into four categories: glucose metabolism (open bars); cell survival and proliferation (hatched bars); cell-signaling receptors (closed bars); cell stress and cell death (apoptosis) (dotted bars). Values are expressed as fold change in gene expression relative to age-matched control values (black bars); n = 4–5; ANOVA, *P < 0.05 or **P < 0.005. See text for abbreviations.