Anatomical location and redistribution of G protein-coupled estrogen receptor-1 during the estrus cycle in mouse kidney and specific binding to estrogens but not aldosterone

Prior studies have linked renoprotective effects of estrogens to G-protein-coupled estrogen receptor-1 (GPER-1) and suggest that aldosterone may also activate GPER-1. Here, the role of GPER-1 in murine renal tissue was further evaluated by examining its anatomical distribution, subcellular distribution and steroid binding specificity. Dual immunofluorescent staining using position-specific markers showed that GPER-1 immunoreactivity primarily resides in distal convoluted tubules and the Loop of Henle (stained with Tamm-Horsfall Protein-1). Lower GPER-1 expression was observed in proximal convoluted tubules marked with megalin, and GPER-1 was not detected in collecting ducts. Plasma membrane fractions prepared from whole kidney tissue or HEK293 cells expressing recombinant human GPER-1 (HEK-GPER-1) displayed high-affinity, specific [(3)H]-17β-estradiol ([(3)H]-E2) binding, but no specific [(3)H]-aldosterone binding. In contrast, cytosolic preparations exhibited specific binding to [(3)H]-aldosterone but not to [(3)H]-E2, consistent with the subcellular distribution of GPER-1 and mineralocorticoid receptor (MR) in these preparations. Aldosterone and MR antagonists, spironolactone and eplerenone, failed to compete for specific [(3)H]-E2 binding to membranes of HEK-GPER-1 cells. Furthermore, aldosterone did not increase [(35)S]-GTP-γS binding to membranes of HEK-GPER-1 cells, indicating that it is not involved in G protein signaling mediated through GPER-1. During the secretory phases of the estrus cycle, GPER-1 is upregulated on cortical epithelia and localized to the basolateral surface during proestrus and redistributed intracellularly during estrus. GPER-1 is down-modulated during luteal phases of the estrus cycle with significantly less receptor on the surface of renal epithelia. Our results demonstrate that GPER-1 is associated with specific estrogen binding and not aldosterone binding and that GPER-1 expression is modulated during the estrus cycle which may suggest a physiological role for GPER-1 in the kidney during reproduction.

Incidence and nature of testicular toxicity findings in pharmaceutical development

BACKGROUND

Testicular toxicity (TT) is a sporadic and challenging issue in pharmaceutical drug development. Efforts to develop TT screening assays or biomarkers have been overshadowed by consortium efforts to predict drug-induced toxicities such as hepatic injury, which are encountered more frequently.

METHODS

To gauge the current state of the field and to prioritize future TT activities, the International Life Sciences Institute-Health and Environmental Sciences Institute Developmental and Reproductive Toxicology (DART) Technical Committee sponsored a survey to better understand the incidence and nature of TT findings encountered during drug development.

RESULTS

Highlights from the 16 survey respondents include: (1) Although preclinical TT was encountered relatively infrequently, half of the participants observed repeated problems with TT during pharmaceutical development, (2) despite control measures such as use of sexually mature animals to diminish confounding effects of spurious lesions, interpretation of TT remains a challenge, (3) "traditional" evaluation tools such as hormonal monitoring and newer approaches such as -omics are utilized to investigate testicular changes, and (4) an understanding of the risk and relevance of TT findings is achieved through joint consideration of factors such as species specificity, potential mode of action, and safety margins.

CONCLUSIONS

TT remains a relatively uncommon but persistent challenge in pharmaceutical development. Although current preclinical TT approaches appear to be effective in limiting the occurrence of pharmaceutical candidate attrition in clinical trials, improved biomarker or screening platforms would allow companies to identify TT at an earlier stage, thus decreasing the time and resources expended on safety evaluation of pharmaceutical candidates.

Effects of in utero exposure to Bisphenol A or diethylstilbestrol on the adult male reproductive system

The objective of this study was to determine whether in utero exposure to Bisphenol A (BPA) induced reproductive tract abnormalities in the adult male testis. Using the C57/Bl6 mouse, we examined sex-organ weights, anogenital distance, and testis histopathology in adult males exposed in utero via oral gavage to sesame oil, 50 µg/kg BPA, 1000 µg/kg BPA, or 2 µg/kg diethylstilbestrol (DES) as a positive control from gestational days 10 to 16. No changes in sperm production or germ cell apoptosis were observed in adult testes after exposure to either chemical. Adult mRNA levels of genes associated with sexual maturation and differentiation, GATA4 and ID2, were significantly lower only in DES-exposed testes. In summary, the data indicate no gross alterations in spermatogenesis after in utero exposure to BPA or DES. At the molecular level, in utero exposure to DES, but not BPA, leads to decreased mRNA expression of genes associated with Sertoli cell differentiation.

Developmental toxicity testing for safety assessment: new approaches and technologies

The ILSI Health and Environmental Sciences Institute's Developmental and Reproductive Toxicology Technical Committee held a 2-day workshop entitled "Developmental Toxicology-New Directions" in April 2009. The fourth session of this workshop focused on new approaches and technologies for the assessment of developmental toxicology. This session provided an overview of the application of genomics technologies for developmental safety assessment, the use of mouse embryonic stem cells to capture data on developmental toxicity pathways, dynamical cell imaging of zebrafish embryos, the use of computation models of development pathways and systems, and finally, high-throughput in vitro approaches being utilized by the EPA ToxCast program. Issues discussed include the challenges of anchoring in vitro predictions to relevant in vivo endpoints and the need to validate pathway-based predictions with targeted studies in whole animals. Currently, there are 10,000 to 30,000 chemicals in world-wide commerce in need of hazard data for assessing potential health risks. The traditional animal study designs for assessing developmental toxicity cannot accommodate the evaluation of this large number of chemicals, requiring that alternative technologies be utilized. Though a daunting task, technologies are being developed and utilized to make that goal reachable.

Cross-talk between the Akt and NF-kappaB signaling pathways inhibits MEHP-induced germ cell apoptosis

Phthalates are ubiquitous contaminants that target the testis during in utero and postnatal development. The PI3K/Akt and nuclear factor kappa B (NF-kappaB) signaling pathways have been implicated in germ cell survival following testicular injury. Here we observe that Akt kinase activity increases in the testes of postnatal day 28 wild-type mice following exposure to 500 mg/kg mono-(2-ethylhexyl) phthalate (MEHP), and that loss of Akt1 results in the premature onset of germ cell apoptosis. To further determine the basis for this sensitivity, we investigated the potential for cross-talk between the PI3K/Akt and NF-kappaB signaling pathways. We found a twofold increase in Akt1-dependent phosphorylation of the I kappaB alpha subunit following exposure to 500 mg/kg MEHP and decreased levels of the total I kappaB alpha protein. Examination of the expression of the NF-kappaB subunits, p50 and p65, in Akt1 wild-type testes following MEHP exposure revealed a twofold increase in p50 mRNA at 6 h. Interestingly, in Akt1-deficient testes, basal expression of both the p50 and p65 subunits was elevated 1.6- and 4-fold, respectively. This was due, at least in part, to increased levels of oxidative stress as measured by both superoxide anion formation and increased expression of SMAC/DIABLO, a proapoptotic mitochondrial protein. In wild-type testes, MEHP-induced Akt1-dependent transcription of the antiapoptotic mitochondrial target gene, Bcl-xL. Together, these results indicate that Akt1 plays a role in the initial protection of germ cells following MEHP-induced germ cell apoptosis and that this response is partially mediated by cross-talk with the NF-kappaB signaling pathway and an increased sensitivity to oxidative stress.

Akt1 suppresses radiation-induced germ cell apoptosis in vivo

Radiation exposure is a well-characterized germ cell injury model leading to cell cycle arrest or apoptosis. The serine-threonine kinase, Akt1, has been implicated in inhibiting cell death induced by different stimuli including growth factor withdrawal, cell cycle discordance, DNA damage, and loss of cell adhesion. However, the in vivo relevance of this prosurvival pathway has not been explored in the testis. To evaluate a protective role for Akt1 in the testis in vivo, we examined the incidence of apoptosis in Akt1-deficient mice after radiation-induced germ cell injury. We found that Akt kinase activity increases in the testes of wild-type mice after ionizing radiation, and that loss of Akt1 results in an earlier onset of germ cell apoptosis and enhanced sensitivity of mitotic spermatogonia to ionizing radiation. At both the mRNA and protein level, neither Akt2 nor Akt3 expression were induced in the absence of Akt1. These data demonstrate an important survival function governed by Akt1 and, to a lesser extent, Akt2 in the survival of germ cells after radiation-induced testicular injury. In addition, the results point to a role for Fas ligand in the regulation of this response.

The mammalian SIR2alpha protein has a role in embryogenesis and gametogenesis

The yeast Sir2p protein has an essential role in maintaining telomeric and mating type genes in their transcriptionally inactive state. Mammalian cells have a very large proportion of their genome inactive and also contain seven genes that have regions of homology with the yeast sir2 gene. One of these mammalian genes, sir2alpha, is the presumptive mammalian homologue of the yeast sir2 gene. We set out to determine if sir2alpha plays a role in mammalian gene silencing by creating a strain of mice carrying a null allele of sir2alpha. Animals carrying two null alleles of sir2alpha were smaller than normal at birth, and most died during the early postnatal period. In an outbred background, the sir2alpha null animals often survived to adulthood, but both sexes were sterile. We found no evidence for failure of gene silencing in sir2alpha null animals, suggesting that either SIR2alpha has a different role in mammals than it does in Saccharomyces cerevisiae or that its role in gene silencing in confined to a small subset of mammalian genes. The phenotype of the sir2alpha null animals suggests that the SIR2alpha protein is essential for normal embryogenesis and for normal reproduction in both sexes.

FISH studies of the sperm of fathers of paternally derived cases of trisomy 21: no evidence for an increase in aneuploidy

Paternal nondisjunction accounts for approximately 5% of cases of trisomy 21. To test the hypothesis that, in some such cases, the fathers might be predisposed to meiotic nondisjunction, we utilized fluorescence in situ hybridization (FISH) to screen for aneuploidy in sperm. We analyzed sperm samples from ten males with a trisomy 21 offspring of paternal origin. Among these individuals, the overall frequency of disomy 21 was 0.15%, comparable to estimates of disomy 21 in the general male population. Furthermore, none of the ten fathers of trisomy 21 individuals had significantly elevated levels of disomic sperm. Thus, our results provide no evidence that the occurrence of a trisomy 21 conceptus of paternal origin imparts an increased risk of trisomy in subsequent pregnancies.

Quo vadis photorespiration: a tale of two aldolases

An O2-consuming side reaction of D-ribulose 1,5-bisphosphate carboxylase causes photorespiration in plants. This reaction may be an inevitable consequence of the enzyme's inability to protect its ene-diolate reaction intermediate from O2, a notion that is supported by the failure of persistent efforts to eliminate selectively its oxygenase activity by genetic manipulation. We have examined two a1dolases with similar ene-diolate intermediates, L-rhamnulose 1-phosphate aldolase and L-fuculose 1-phosphate aldolase. The former enzyme has an oxygenase activity, while the latter does not, suggesting that the reaction with O2 is not inevitable.

Alteration of cell cycle kinase complexes in human papillomavirus E6- and E7-expressing fibroblasts precedes neoplastic transformation

Expression of viral oncoproteins results in the loss of cell cycle checkpoint control and the accumulation of chromosomal abnormalities. Expression of both human papillomavirus type 16 oncoproteins, E6 and E7, in normal human fibroblasts completely dissociates p21 and proliferating cell nuclear antigen from the quarternary cyclin-cyclin-dependent kinase (CDK) complexes present in normal cells, causes disruption of the cyclin D-CDK4 complex and replacement with a CDK4-p16 complex, and leaves binary complexes of cyclin B1-CDC2 and cyclin A-CDK2 intact. These results are identical to those observed in fully transformed cells. The expression of the individual oncoproteins dramatically affects the association of proliferating cell nuclear antigen into the complexes while leaving the total cellular levels unaltered. Expression of low-risk human papillomavirus has no effect on cyclin complexes. These findings provide evidence for the gross alteration of cyclin-CDK complexes in preneoplastic cells and links this alteration to the loss of genomic stability.