Prolonged gestation, elevated preparturitional plasma progesterone and reproductive aging in C57BL/6J mice

Effect of reproductive ageing on pregnant mouse uterus and cervix

KEY POINTS

Older pregnant women have a greater risk of operative delivery, still birth and post-term induction. This suggests that maternal age can influence the timing of birth and processes of parturition. We have found that increasing maternal age in C57BL/6J mice is associated with prolongation of gestation and length of labour. Older pregnant mice also had delayed progesterone withdrawal and impaired myometrial function. Uterine ageing and labour dysfunction should be investigated further in older primigravid women.

ABSTRACT

Advanced maternal age (≥35 years) is associated with increased rates of operative delivery, stillbirth and post-term labour induction. The physiological causes remain uncertain, although impaired myometrial function has been implicated. To investigate the hypothesis that maternal age directly influences successful parturition, we assessed the timing of birth and fetal outcome in pregnant C57BL/6J mice at 3 months (young) and 5 months (intermediate) vs. 8 months (older) of age using infrared video recording. Serum progesterone profiles, myometrium and cervix function, and mitochondrial electron transport chain complex enzymatic activities were also examined. Older pregnant mice had a longer mean gestation and labour duration (P < 0.001), as well as reduced litter size (P < 0.01) vs. 3-month-old mice. Older mice did not exhibit the same decline in serum progesterone concentrations as younger mice. Cervical tissues from older mice were more distensible than younger mice (P < 0.05). Oxytocin receptor and connexin-43 mRNA expression were reduced in the myometrium from 8-month-old vs. 3-month-old mice (P < 0.05 and P < 0.01 respectively) in tandem with more frequent but shorter duration spontaneous myometrial contractions (P < 0.05) and an attenuated contractile response to oxytocin. Myometrial mitochondrial copy number was reduced in older mice, although there were no age-induced changes to the enzymatic activities of the mitochondrial electron transport chain complexes. In conclusion, 8-month-old mice provide a useful model of reproductive ageing. The present study has identified potential causes of labour dysfunction amenable to investigation in older primigravid women.

Mucosal inflammation at the respiratory interface: a zebrafish model

Inflammatory diseases of the respiratory system such as asthma and chronic obstructive pulmonary disease are increasing globally and remain poorly understood conditions. Although attention has long focused on the activation of type 1 and type 2 helper T cells of the adaptive immune system in these diseases, it is becoming increasingly apparent that there is also a need to understand the contributions and interactions between innate immune cells and the epithelial lining of the respiratory system. Cigarette smoke predisposes the respiratory tissue to a higher incidence of inflammatory disease, and here we have used zebrafish gills as a model to study the effect of cigarette smoke on the respiratory epithelium. Zebrafish gills fulfill the same gas-exchange function as the mammalian airways and have a similar structure. Exposure to cigarette smoke extracts resulted in an increase in transcripts of the proinflammatory cytokines TNF-α, IL-1β, and MMP9 in the gill tissue, which was at least in part mediated via NF-κB activation. Longer term exposure of fish for 6 wk to cigarette smoke extract resulted in marked structural changes to the gills with lamellar fusion and mucus cell formation, while signs of inflammation or fibrosis were absent. This shows, for the first time, that zebrafish gills are a relevant model for studying the effect of inflammatory stimuli on a respiratory epithelium, since they mimic the immunopathology involved in respiratory inflammatory diseases of humans.

An extensive genetic program occurring during postnatal growth in multiple tissues

Mammalian somatic growth is rapid in early postnatal life but then slows and eventually ceases in multiple tissues. We hypothesized that there exists a postnatal gene expression program that is common to multiple tissues and is responsible for this coordinate growth deceleration. Consistent with this hypothesis, microarray analysis identified more than 1600 genes that were regulated with age (1 vs. 4 wk) coordinately in kidney, lung, and heart of male mice, including many genes that regulate proliferation. As examples, we focused on three growth-promoting genes, Igf2, Mest, and Peg3, that were markedly down-regulated with age. In situ hybridization revealed that expression occurred in organ-specific parenchymal cells and suggested that the decreasing expression with age was due primarily to decreased expression per cell rather than a decreased number of expressing cells. The declining expression of these genes was slowed during hypothyroidism and growth inhibition (induced by propylthiouracil at 0-5 wk of age) in male rats, suggesting that the normal decline in expression is driven by growth rather than by age per se. We conclude that there exists an extensive genetic program occurring during postnatal life. Many of the involved genes are regulated coordinately in multiple organs, including many genes that regulate cell proliferation. At least some of these are themselves apparently regulated by growth, suggesting that, in the embryo, a gene expression pattern is established that allows for rapid somatic growth of multiple tissues, but then, during postnatal life, this growth leads to negative-feedback changes in gene expression that in turn slow and eventually halt somatic growth, thus imposing a fundamental limit on adult body size.

Anti-aging effects of nanpao, a kampo medicine, on reproductive functions in female rats

The improvement effect of nanpao, a kampo medicine, on the age-related decline in reproductive function was evaluated in female rats given the test drug for a long-term period. Young rats were allocated to the cesarean section and natural delivery groups to examine reproductive performance (young rat groups). Five-month-old rats were allocated to the 3 groups (aged rat groups): 1--control and 2--nanpao-treated groups. They were given orally in a dose of 0, 30 or 100mg/kg/day of the test drug, respectively. In aged rats, the first mating experiment was initiated at week 21 of dosing to evaluate reproductive performance by natural delivery and the second mating experiment at week 31 of dosing was evaluated by cesarean section. In the first and second mating experiments, various reproductive functions decreased in aged rats as compared to the young rats. On the other hand, loss of regular estrous cycles, decreases in delivery and pregnancy rates and mean fetal weights were inhibited in the treated groups as compared to the control group. In addition, decreases in the numbers of mean live offspring and fetuses were inhibited in the 100 mg/kg/day group. In conclusion, nanpao maintained normal embryo-foetal development in female rats.

A phenotype for the α7 nicotinic acetylcholine receptor null mutant

The alpha7 nicotinic acetylcholine receptor (nAChR) is heavily expressed in the mammalian brain. On a molecular level, the alpha7 nAChR may have a diversity of functions, but it is not known if these molecular events translate into phenotypes. The null mutant mouse is viable and generally normal. Here, we report a phenotype for the alpha7 nAChR null mutant mouse. The alpha7 nAChR is obligatory for the synchronization of an important biological rhythm, the female estrous cycle. The female null mutant mouse has asynchronous estrous cycles and a reduced number of surviving pups. Female null mutants also demonstrate a reliable diversity in phenotype, suggesting an interaction between environment and gene expression. Real-time RT-PCR measurements of the alpha7 mRNA expression in reproductive tissues of wild-type mice suggest that the ovulatory dysfunction in null mutants is probably central in origin.

Infertility in transgenic female mice with human growth hormone expression: evidence for luteal failure

Introduction of the human growth hormone (hGH) gene fused with mouse metallothionein I promoter into domestic mice leads to ectopic synthesis of hGH, marked stimulation of somatic growth, and female sterility. Transgenic females (produced by mating transgenic males to normal females) mated but failed to become pregnant or pseudopregnant as evidenced by the recurrence of vaginal plugs every 5-7 days. Daily injections of 1 mg progesterone, starting on day 1 postcoitum (p.c.), maintained pregnancy, suggesting that the sterility of these animals is due to inadequate luteal function. In ovariectomized female transgenic mice, median eminence (ME) turnover of dopamine (DA) was increased, and plasma prolactin (PRL) levels were reduced, presumably because of the known lactogenic activity of hGH in rodents. From these observations we suspected that either 1) the corpora lutea of these animals are unresponsive to lactogenic hormones, or 2) hGH by stimulating tuberoinfundibular dopaminergic (TIDA) neurons interferes with the increase in PRL release that normally follows mating and this, in turn, leads to luteal failure. To distinguish between these possibilities, transgenic females were treated with PRL-secreting ectopic pituitary transplants from normal females of the same strain on day 1 p.c. Eight of ten treated females became pregnant and delivered litters. We conclude that infertility of transgenic female mice with hGH expression is due to activation of the TIDA system, suppression of endogenous PRL release, and luteal deficiency.

Aging and responses to toxins in female reproductive functions

Reproductive senescence in laboratory rodents has been well characterized using vaginal smear analysis, a relatively simple and inexpensive technique to monitor changes in estrous cyclicity. Although some differences exist, laboratory animal models are available to study most aspects of age-related changes in human reproductive physiology (4,13). Thus presumptive reproductive toxins can be tested on laboratory rodents using the qualitative and quantitative parameters for estrous cyclicity described here to assess damage. Before implementing such tests, however, certain limitations must be considered. Quantitative changes in estrous cycles, for example, cycle length distribution, which indicate more subtle impairments in reproductive function, require more refined data analysis. In particular, baseline data for at least one month is required before exposure to the presumptive toxin. In addition, the period of maximum cycling regularity is fairly short (three to four months duration) so long-term exposures to presumptive toxins would not be applicable. Longer term exposure (greater than or equal to six months) would be permissible if qualitative changes in cyclicity (i.e., acyclic vs. cyclic) were the dependent variable used to assess toxicity. Finally, if other parameters of reproductive function (e.g., fertility, litter size) are used to assess reproductive toxicity, we urge that cycling characteristics of the offspring be carefully monitored to assess possible cryptic damage to later neuroendocrine functions that occurred to the fetuses in utero.

Aging and uterine growth during implantation in C57BL/6J mice

Uterine growth during implantation was compared in C57BL/6J mice aged 3-7 mo vs. 11-12 mo. All mice had given birth to at least one previous litter. Older mice had smaller uteri during early gestation (3 to 10 days post coitum) as measured by DNA content, although wet weight and protein were generally similar in both age groups. However, there were no age effects on uterine growth during implantation, as measured by the increments of DNA, as well as protein and wet weight per implantation site (decidual swelling) on days 6-10. These data are discussed in terms of the major increase in fetal death and resorptions in older mice subsequently observed by day 12-13. Larger age-related impairment of the artificially-induced decidual response is also considered. We conclude that impairments of the artificially induced decidual response do not predict the extent of decidual responses during pregnancy in aging mice.