Genetic screening of patients with bladder exstrophy epispadias complex

Abstract

Bladder Exstrophy Epispadias Complex (BEEC) is a serious congenital anomaly. Babies affected are born with an exposed bladder, and leak urine continually. The high incidence among the offspring, siblings and identical twins of BEEC patients suggests a genetic etiology. We previously showed that TP63 is a candidate gene of this disorder. There are two main isoforms, TAP63 and ΔNP63, and ΔNp63 is expressed predominantly in the murine bladder epithelium. Notably, p63-/- mice developed a condition similar to BEEC. In addition, the p63-/- mutation led to an increase in apoptosis, decrease in cell proliferation and absence of smooth muscle development in the bladder. We found that ΔNP63 expression is reduced in BEEC patients’ bladders, whereas TAP63 expression is increased. Although, no mutations were found in P63 coding sequence, we did identify In/del polymorphisms in the ΔNP63 promoter that were associated with significantly increased risk of BEEC. The analysis of the TAP63 promoter region for possible mutations did not reveal any variants that might contribute to the risk of BEEC. Study of the literature showed that p63 acts upstream of Perp, and that Perp and desmosomes co-localize in the plasma membrane to form a desmosomal adhesive assembly complex to maintain tissue integrity. These findings about p63, Perp and Desmosome lead to a new hypothesis that the TP63>PERP>Desmosome pathway may play a major role in BEEC pathogenesis. In order to determine the functional significance of the pathway, mutation screening was carried out in PERP and DSP exons and promoters. Although several common SNPs were found in DSP and PERP coding regions, no rare, potentially causative variants were identified. Interestingly, as part of this study, bacterial DNA contamination was found in buccal DNA which can be a major component of buccal-derived DNA samples. This has significant implications for other studies using buccal DNA for genetic analysis. To further explore the role of epigenetic regulation in BEEC pathogenesis, ChIP analysis with Histone antibody (H3k4me3 and H3K27ac) and a high throughput sequencing (ChIP-seq) was carried out in normal human urothelial cells. Our genome wide mapping of H3K4me3 and H3K27ac enrichment, and also the overlapping regions of these histone modifications with TP63 binding, showed that intron 1 of PERP and DSP are candidate loci for BEEC pathogenesis. De novo motif searches on H3K4me3 and H3K27ac enriched regions have identified significant enrichment of IRF2 and SCL transcription factor, respectively. IRF2 recruits RELA in the nucleus to activate NFƙB complex, which in turn expresses cell adhesion molecules and maintains epithelial integrity during development via IRF-RELA-NFƙB signalling pathway. SCL acts via the SHH pathway to induce mesenchyme development, which in turn is involved in epithelial-mesenchymal interaction in the development of bladder smooth muscle via SCL-SHH pathway. Based on our epigenetic findings, we have speculated the significant involvement of the IRF-RELA-NFƙB and SCL-SHH pathways in the aetiology of BEEC. Overall, this research will lead to a better understanding of BEEC pathogenesis. Moreover, the epigenetic data will be a valuable resource for future BEEC studies, in order to better determine the role of genetic and epigenetic variation in BEEC pathogenesis.