The impact of maternal cigarette smoke exposure on the male germline (#131)
Cigarette smoke is a well known cocktail of reproductive toxicants which is particularly harmful to both foetal and neonatal germ cells. Despite this notoriety, recent studies suggest that over 36.9% of Australian mothers under the age of 25 smoke during pregnancy, highlighting the need for further research into how maternal smoking impacts offspring fertility. To do this we exposed pregnant mice to mainstream cigarette smoke via direct inhalation during the gestational/weaning period to mimic human exposure, and examined the effects of maternal smoking on male offspring testicular development and fertility. Histomorphological analysis revealed significantly reduced seminiferous tubule counts and surface area (p<0.05) in postnatal day 3, 6, 12, and 21 testes. Caspase activity and DNA damage were also detected in gonocytes and early/late stage spermatocytes during weaning, but were absent in spermatogonial cells. Abnormal testicular development persisted into early adulthood, with 8 week old males having significantly reduced testes size, tubule diameter, and abnormal tubular organisation. Microarray analysis of adult testis revealed 104 genes were significantly altered >1.3-fold (p<0.05) as a consequence of maternal smoke exposure. Bioinformatics identified a reduced expression in genes associated with spermatocyte and spermatid development (Akap4, Odf2, and Ybx2), and an increase in markers of oxidative stress (Gstm1, Gpx3, and Txnip) and testosterone production (Cyp17a1, Cyp11a1, and Acly). Adult offspring also had significantly reduced sperm counts (-1.5 fold) and motility (-1.8 fold), increased head and tail abnormalities (-2 fold), and a decreased capacity to interact with the zona pellucida (-2 fold) and oolemma membrane (-1.9 fold). Our results demonstrate that maternal cigarette smoke exposure during the gestational/weaning period causes gonocyte and meiotic germ cell apoptosis in the neonatal testis. Abnormalities persist in the young adult characterised by reduced germ cell number, dysfunctional spermatocyte/spermatid development, and the production of abnormal spermatozoa with a reduced capacity for fertilisation.