INVESTIGATIVE UROLOGY

Microarray analysis of exstrophic human bladder smooth muscle
Hipp J, Andersson KE, Kwon TG, Kwak EK, Yoo J, Atala A
Department of Urology, Wake Forest Institute for Regenerative Medicine, Wake Forest University, Winston-Salem, NC, USA
BJU Int. 2008; 101: 100-5

• Objective: To compare the genetic profiles of ‘healthy’ bladder smooth muscle cells (SMCs) and exstrophic SMCs (ESMCs) to identify genes that are over- and under-expressed in ESMCs, thus providing a molecular evaluation of the quality and therapeutic potential of ESMC tissue.
• Patients, Material and Methods: Classical bladder exstrophy is a rare disorder, occurring in 1 in 30,000 live births. Studies have shown that exstrophic bladders are developmentally immature at birth. After surgical closure, the bladder typically undergoes abnormal remodelling (such as over-expression of collagen III) throughout early development. We hypothesized that the predominant genetic differences between normal SMCs and ESMCs are in the developmental genes. This hypothesis was tested by the use of microarray analysis. Bladder SM biopsies were taken from ‘healthy’ subjects undergoing bladder surgeries for other conditions (for example, urinary reflux) and patients with bladder exstrophy. Cells were expanded in vitro, and total RNA was isolated and hybridized to the Affymetrix U133A GeneChip (Affymetrix Inc., Santa Clara, CA, USA) by the Wake Forest University School of Medicine Affymetrix core facility, using standard protocols.
• Results: We created a genetic signature consisting of 961 genes that are over-expressed and 432 genes that are under-expressed in ESMCs. Analysis of these signatures identified an over-expression of inflammatory genes and an under-expression of developmental genes.
• Conclusion: Our data is in concordance with previous studies and histological data showing that ESMCs are developmentally immature relative to healthy bladder SM. The clinical implication of the ESMC genetic signature is that it provides a list of targets that can be (i) manipulated ex vivo and/or in vivo to induce differentiation (the completion of development) and (ii) used as biomarkers to explain the variability of the clinical symptoms after surgical closure.
  
  
• Editorial Comment
  This is another pioneer study from this group of investigators, which opened new windows on understanding and treatment of bladder exstrophy-epispadias complex (BEEC).
  The authors used the microarray technique to identify the global genetic differences between bladder exstrophic smooth muscle cells (ESMCs) and normal bladder smooth muscle (SM) cells from patients who underwent surgery for other conditions (not age matched). The authors were able to create a genetic signature consisting of 961 genes that were over-expressed and 432 genes that were under-expressed in ESMCs.
  The analysis of these signatures identified an over-expression of inflammatory genes and an under-expression of developmental genes.
  The authors emphasized that the data on inflammatory genes shows the importance of keeping the bladder sterile after birth and would argue that an antibiotic should be given after birth. Also, the authors think that it is important to note any possible pathogen exposure before surgery as a way to identify patients that can potentially be at greater risk of complications, such as retention of inflammatory gene expression after in vitro expansion and fibrotic tissue that could be identified during development. The data on inflammatory over-expression could also explain why some patients have symptoms during childhood and others are asymptomatic. Concerning the inflammatory issue, the authors demonstrated the importance of keeping the bladder sterile after birth and argued that an antibiotic should be given after birth. They also think that it is important to note any possible pathogen exposure before surgery as a way to identify patients that can potentially be at greater risk of complications.
  Concerning developmen, the present microarray analysis shows that ESMCs are developmentally immature relative to healthy SMCs. This issue was already demonstrated previously, nevertheless, the present data is data is original because it gives a molecular explanation, identifying the presence of key developmental pathways such as IL-6 and Wnt. This is further validated by the under-expression data set, which was comprised of several biosynthetic processes.

Dr. Francisco J.B. Sampaio
Full-Professor and Chair, Urogenital Research Unit
State University of Rio de Janeiro
Rio de Janeiro, RJ, Brazil