Immunohistochemical characterization of sonic hedgehog and its downstream signaling molecules during human penile development

The role of sonic hedgehog homologue signal pathway in hypospadias aetiology

INTRODUCTION

Hypospadias is one of the most common congenital anomalies of the male genitalia. Sonic hedgehog homologue (SHH) signalling pathway is believed to be involved in the development of the male genital system.

OBJECTIVE

In this clinical prospective study, the role of the SHH pathway in hypospadias aetiology was investigated.

STUDY DESIGN

In this study, 200 healthy children (boys without hypospadias, control group), 118 patients (boys with distal hypospadias) and 82 patients (boys with proximal hypospadias) of age 0-16 years were included. The expression of the genes suppressor of fused protein (SUFU), SHH, protein patched homologue (PTCH; PTCH1 and PTCH2), glioma-associated oncogene homologue (GLI; GLI1, GLI2, GLI3 and GLI4), smoothened, frizzled-class receptor (SMO) and serine/threonine-protein kinase 36 (STK36) that are involved in SHH pathway were investigated. Furthermore, polymorphism analyses of GLI2, SHH and PTCH1 genes were performed. The history of hypospadias in the first and second-degree relatives of the patients in boys with distal hypospadias and boys with proximal hypospadias was inquired.

RESULTS

Ten patients in the boys with distal hypospadias and twenty patients in the boys with proximal hypospadias had a history of hypospadias in first or second-degree relatives (p < 0.05). There was a significant decrease in mRNA expressions of SHH and PTCH1 genes in boys with proximal hypospadias compared to boys without hypospadias (p < 0.05). Besides, a significant decrease in mRNA fold-change of GLI2 gene was detected in boys with both distal hypospadias and proximal hypospadias compared to boys without hypospadias (p < 0.05). In contrast, there was no significant difference in the mRNA fold-changes of PTCH2, SUFU, GLI1, GLI3, GLI4, SMO and STK36 genes among the groups. Moreover, there were no significant differences in the frequencies of variant genotypes and alleles rs735557, rs12711538 and rs4848632 (GLI2 gene), rs104894049 (SHH gene) and rs41313327 (PTCH1 gene) (p > 0.05).

DISCUSSION

SHH expression is required for the growth and differentiation of the genital bulge. Developmental defects in the external genital organs were demonstrated in mice with SHH deletion. It has been demonstrated that SHH mainly plays a role in the formation of sinusoid morphology of the penis. In the present study, although SHH and PTCH gene expressions were found to be decreased only in the penile tissues of proximal hypospadias, GLI2 gene expression was decreased in penile tissues of boys with both distal hypospadias and boys with proximal hypospadias.

CONCLUSION

Genes involved in the SHH pathway might play a role in the aetiology of hypospadias. Furthermore, there is a correlation between molecular defects in this pathway and severity of hypospadias.

Hedgehog signal disruption, gonadal dysgenesis and reproductive disorders: Is there a link to endocrine disrupting chemicals?

Developmental exposure to chemicals that can disrupt sex hormone signaling may cause a broad spectrum of reproductive disorders. This is because reproductive development is tightly regulated by steroid sex hormones. Consequently, non-animal screening methods currently used to test chemicals for potential endocrine disrupting activities typically include steroidogenesis and nuclear receptor assays. In many cases there is a correlation between in vitro and in vivo data examining endocrine disruption, for example between blocked androgen receptor activity and feminized male genitals. However, there are many examples where there is poor, or no, correlation between in vitro data and in vivo effect outcomes in rodent studies, for various reasons. One possible, and less studied, reason for discordance between in vitro and in vivo data is that the mechanisms causing the in vivo effects are not covered by those typically tested for in vitro. This knowledge gap must be addressed if we are to elaborate robust testing strategies that do not rely on animal experimentation. In this review, we highlight the Hedgehog (HH) signaling pathway as a target for environmental chemicals and its potential implications for reproductive disorders originating from early life exposure. A central proposition is that, by disrupting HH signal transduction during critical stages of mammalian development, the endocrine cells of the testes or ovaries fail to develop normally, which ultimately will lead to disrupted sex hormone synthesis and sexual development in both sexes. If this is the case, then such mechanism must also be included in future test strategies aimed at eliminating chemicals that may cause reproductive disorders in humans.

Expression patterns of Fgf8 and Shh in the developing external genitalia of Suncus murinus

Reciprocal epithelial–mesenchymal interactions and several signalling pathways regulate the development of the genital tubercle (GT), an embryonic primordium of external genitalia. The morphology of the adult male external genitalia of the Asian house musk shrew Suncus murinus (hereafter, laboratory name: suncus) belonging to the order Eulipotyphla (the former order Insectivora or Soricomorpha) differs from those of mice and humans. However, the developmental process of the suncus GT and its regulatory genes are unknown. In the present study, we explored the morphological changes and gene expression patterns during the development of the suncus GT. Morphological observations suggested the presence of common (during the initial outgrowth) and species-specific (during the sexual differentiation of GT) developmental processes of the suncus GT. In gene expression analysis, fibroblast growth factor 8 (Fgf8) and sonic hedgehog (Shh), an indicator and regulator of GT development in mice respectively, were found to be expressed in the cloacal epithelium and the developing urethral epithelium of the suncus GT. This pattern of expression specifically in GT epithelium is similar to that observed in the developing mouse GT. Our results indicate that the mechanism of GT formation regulated by the FGF and SHH signalling pathways is widely conserved in mammals.

The Genetic and Environmental Factors Underlying Hypospadias

Hypospadias results from a failure of urethral closure in the male phallus and affects 1 in 200-300 boys. It is thought to be due to a combination of genetic and environmental factors. The development of the penis progresses in 2 stages: an initial hormone-independent phase and a secondary hormone-dependent phase. Here, we review the molecular pathways that contribute to each of these stages, drawing on studies from both human and mouse models. Hypospadias can occur when normal development of the phallus is disrupted, and we provide evidence that mutations in genes underlying this developmental process are causative. Finally, we discuss the environmental factors that may contribute to hypospadias and their potential immediate and transgenerational epigenetic impacts.

EVC gene polymorphisms and risks of isolated hypospadias - a preliminary study

Introduction

Hypospadias has a complex etiology with both genetic and environmental factors contributing to the condition. Urogenital abnormalities including hypospadias, are found in 22% of cases with Ellis van Creveld syndrome (EvC). Mutations in the EVC gene can cause major and minor anomalies, which form phenotypes that partially overlap with those present in EvC.

The aim of this study was to evaluate the association between nucleotide variants of the EVC gene and the risk of hypospadias.

Material and methods

Four single nucleotide polymorphisms (SNPs) of the EVC gene (rs3774856, rs2302075, rs1383180, rs7680768) were taken under investigation in 96 patients with isolated hypospadias and 284 matched controls. Genotyping of all polymorphisms was carried out by PCR and followed by appropriate restriction enzyme digestion (PCR-RFLP).

Results

Individuals homozygous for the SNP rs2302075 (p.Thr449Lys) showed an elevated risk for hypospadias. Haplotypes containing the rs2302075 variant also revealed modest associations with hypospadias, which did not survive multiple testing corrections. None of the other tested EVC polymorphisms displayed significant association with the risk of hypospadias, either in dominant or recessive inheritance models.

Conclusions

The results of this study suggest that polymorphic variants of the EVC gene do not substantially contribute to the risk of hypospadias based on our study population. However, further studies should help to clarify the relationship between polymorphisms of EVC and hypospadias.

Molecular mechanisms of external genitalia development

External genitalia development occurs through a combination of hormone independent, hormone dependent, and endocrine pathways. Perturbation of these pathways can lead to abnormal external genitalia development. We review human and animal mechanisms of normal and abnormal external genitalia development, and we evaluate abnormal mechanisms that lead to hypospadias. We also discuss recent laboratory findings that further our understanding of animal models of hypospadias.

Aetiology of hypospadias: a systematic review of genes and environment

BACKGROUND

Hypospadias is a common congenital malformation of the male external genitalia. Most cases have an unknown aetiology, which is probably a mix of monogenic and multifactorial forms, implicating both genes and environmental factors. This review summarizes current knowledge about the aetiology of hypospadias.

METHODS

Pubmed was used to identify studies on hypospadias aetiology published between January 1995 and February 2011. Reference lists of the selected manuscripts were also searched to identify additional studies, including those published before 1995.

RESULTS

The search provided 922 articles and 169 articles were selected for this review. Studies screening groups of patients with hypospadias for single gene defects found mutations in WT1, SF1, BMP4, BMP7, HOXA4, HOXB6, FGF8, FGFR2, AR, HSD3B2, SRD5A2, ATF3, MAMLD1, MID1 and BNC2. However, most investigators are convinced that single mutations do not cause the majority of isolated hypospadias cases. Indeed, associations were found with polymorphisms in FGF8, FGFR2, AR, HSD17B3, SRD5A2, ESR1, ESR2, ATF3, MAMLD1, DGKK, MID1, CYP1A1, GSTM1 and GSTT1. In addition, gene expression studies indentified CTGF, CYR61 and EGF as candidate genes. Environmental factors consistently implicated in hypospadias are low birthweight, maternal hypertension and pre-eclampsia, suggesting that placental insufficiency may play an important role in hypospadias aetiology. Exogenous endocrine-disrupting chemicals have the potential to induce hypospadias but it is unclear whether human exposure is high enough to exert this effect. Other environmental factors have also been associated with hypospadias but, for most, the results are inconsistent.

CONCLUSIONS

Although a number of contributors to the aetiology of hypospadias have been identified, the majority of risk factors remain unknown.