Developmental Exposure of Mice to Dioxin Promotes Transgenerational Testicular Inflammation and an Increased Risk of Preterm Birth in Unexposed Mating Partners

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin, commonly known as dioxin) is a ubiquitous environmental contaminant and known endocrine disruptor. Using a mouse model, we previously found that adult female mice exposed in utero to TCDD (F1 generation) as well as multiple subsequent generations (F2-F4) exhibited reduced fertility and an increased incidence of spontaneous preterm birth. Additional studies revealed that male F1 mice with a similar in utero/developmental TCDD exposure also exhibited diminished fertility and conferred an increased risk of preterm birth to their unexposed mating partners. Herein, we extend these previous observations, reporting that reduced fertility in male F1 mice is linked to testicular inflammation which coincides with apoptosis of developing spermatocytes, sub-fertility and an increased risk of preterm birth in their unexposed mating partners. Significantly, in the absence of additional toxicant exposure, testicular inflammation and reduced fertility persisted in F2 and F3 males and their control mating partners also frequently exhibited spontaneous preterm birth. Although a steady, global decline in male fertility has been noted over the last few decades, the reasons for these changes have not been firmly established. Likewise, the PTB rate in the U.S. and other countries has paralleled industrial development, suggesting a possible relationship between environmental toxicant exposure and adverse pregnancy outcomes. Most current clinical strategies to prevent preterm birth are focused solely on the mother and have yielded limited benefits. In contrast, our studies strongly suggest that the preconception testicular health of the father is a critical determinant of pregnancy outcomes in mice. Future clinical studies should examine the potential contribution of the male to gestation length in women and whether efforts to reduce the incidence of preterm birth should be initiated in both parents prior to pregnancy

Hexavalent Chromium Disrupts Oocyte Development in Rats by Elevating Oxidative Stress, DNA Double-Strand Breaks, Microtubule Disruption, and Aberrant Segregation of Chromosomes

Environmental and occupational exposure to hexavalent chromium, Cr(VI), causes female reproductive failures and infertility. Cr(VI) is used in more than 50 industries and is a group A carcinogen, mutagenic and teratogenic, and a male and female reproductive toxicant. Our previous findings indicate that Cr(VI) causes follicular atresia, trophoblast cell apoptosis, and mitochondrial dysfunction in metaphase II (MII) oocytes. However, the integrated molecular mechanism of Cr(VI)-induced oocyte defects is not understood. The current study investigates the mechanism of Cr(VI) in causing meiotic disruption of MII oocytes, leading to oocyte incompetence in superovulated rats. Postnatal day (PND) 22 rats were treated with potassium dichromate (1 and 5 ppm) in drinking water from PND 22–29 and superovulated. MII oocytes were analyzed by immunofluorescence, and images were captured by confocal microscopy and quantified by Image-Pro Plus software, Version 10.0.5. Our data showed that Cr(VI) increased microtubule misalignment (~9 fold), led to missegregation of chromosomes and bulged and folded actin caps, increased oxidative DNA (~3 fold) and protein (~9–12 fold) damage, and increased DNA double-strand breaks (~5–10 fold) and DNA repair protein RAD51 (~3–6 fold). Cr(VI) also induced incomplete cytokinesis and delayed polar body extrusion. Our study indicates that exposure to environmentally relevant doses of Cr(VI) caused severe DNA damage, distorted oocyte cytoskeletal proteins, and caused oxidative DNA and protein damage, resulting in developmental arrest in MII oocytes

TUNEL staining in adult testis of control, F1, F2 and F3 males.

<p>TUNEL staining was minimal in control testis (A), but prominent in tissues from F1, F2 and F3 males (B–D). Semi-quantitative analysis of TUNEL staining is shown in E. Compared to control samples, <i>p</i><0.01 for all toxicant exposed mice. Results are representative of at least 6 animals per group and from ≥3 more litters/group. Original magnification, 200x. <b>Inset</b>: Primary antibody omitted using the same tissue shown in Panel D.</p

ELISA of PGE₂ in whole testis of adult control, F1, F2 and F3 males.

<p>Only low levels of PGE₂ were detected in the testis of all control animals. In mice with a toxicant exposure history, there was a clear trend toward increased expression of PGE₂; however, production of this prostaglandin was highly variable and did not reach significance (compared to control: F1, <i>p</i> = 0.07; F2, <i>p</i> = 0.10; F3, <i>p</i> = 0.16). N = 6 for all groups.</p

Light microscopy of normal and abnormal murine spermatozoa.

<p>All spermatozoa were classified by standard morphologic assessment. Normal spermatozoan (A); common tail defects (B–E); acrosome defect (F); misshapen head (G); mid-piece defects (H, I) and decapitated sperm (J). Magnification, 1000x.</p