System level changes in gene expression in maturing bladder mucosa

Purpose: Bladder problems clinically present early in life as birth defects that often lead to kidney failure and late in life as overactive bladder, incontinence and related disorders. We investigated the transcriptome of mouse bladder mucosa at juvenile and adult stages by microarray to identify the pathways associated with normal, healthy growth and maturation. We hypothesized that understanding these pathways could be key to achieving bladder regeneration or reawakening normal function in the elderly population.

Materials and methods: RNA was isolated from the mucosa at 3, 6, 20 and 30 weeks postnatally. Affymetrix® Mouse 430 v2 arrays were used to profile the expression of approximately 45,000 genes. The software program Statistical Analysis of Microarrays was used to identify genes that significantly changed during the time course.

Results: No genes were significantly up-regulated during maturation. However, 66 well annotated genes demonstrated a statistically significant downward trend, of which 10 of 10 were confirmed by quantitative polymerase chain reaction. The main functions affected by age were transcription, regulation of cellular processes, neurogenesis, blood vessel development and cell differentiation. Notable genes included collagens, Mmp2, SPARC and several transcription factors, including Crebbp, Runx1, Klf9, Mef2c, Nrp1, Pex1 and Tcf4. These molecules were indirectly regulated by inferred Tgfb1 and Egf growth factors. Analysis of gene promoter regions for overrepresented upstream transcription factor binding sites identified specificity protein 1 and epidermal growth factor receptor-specific transcription factor as potentially major transcriptional regulators driving maturation related changes.

Conclusions: These findings identify a coherent set of genes that appear to be down-regulated during urothelial maturation. These genes may represent an attractive target for bladder regeneration or for treating age related loss of function.