Effect of paternal aging and vitrification on mitochondrial DNA copy number and telomere length of mouse blastocysts

In this study, we examined the effects of paternal aging on the mitochondrial DNA copy number (mt-cn), telomere length (TL), and gene expression in mouse embryos. The effects of vitrification on the mt-cn and TL of the embryos derived from young and aged male parents (YF and AF, respectively) were examined. C57BL/6N male mice were used for embryo production at 13-23 and 50-55 weeks of age. Two-cell stage embryos were collected from the oviducts of superovulated female mice (8-15 weeks old) and cultured for 24 h until the 8-cell stage, followed by embryo vitrification. Fresh and vitrified-warmed embryos were incubated for 2 days until the blastocyst stage, and mt-cn and TL were investigated. The cell-free mitochondrial DNA copy number (cf-mt-cn) in the spent culture medium (SCM) of the embryos was then investigated. RNA sequencing of blastocysts revealed that metabolic pathways, including oxidative phosphorylation and mTOR pathways, were enriched in differentially expressed genes. The mt-cn and TL of AF-derived blastocysts were lower and shorter, respectively, than those of YF-derived blastocysts. Paternal aging did not affect the blastocyst rate after vitrification. Vitrification of the 8-cell stage embryos did not affect the mt-cn of the blastocysts. However, it increased the cf-mt-cn (cell-free mt-cn) in the SCM of both YF- and AF-derived embryos. Vitrification did not affect the TL of either YF- or AF-derived embryos. Thus, paternal aging affected the mt-cn and TL of the embryos, but vitrification did not affect these parameters in either age groups.

Aging affects gene expression in spermatids of Brown Norway rats

The effects of aging on the reproductive health of men and the consequences for their offspring are becoming more widely recognized. Correlative epidemiological studies examining paternal age and offspring health suggest there are more frequent occurrences of genetic disorders in the children of older fathers. Given the genetic basis for paternal age-related disorders, we aim to characterize gene expression in developing germ cells. Round spermatids (RS) were collected from young (mean = 5.3 months) and aged (mean = 19.5 months) Brown Norway rats, representative of humans aged 20-30 years and 55+ years, respectively. Gene expression data were obtained by mRNA sequencing (n = 5), and were analysed for differential expression. Sequencing data display 211 upregulated and 9 downregulated transcripts in RS of aged rats, compared to young (log2FC >1, p < 0.05). Transcripts with increased expression are involved in several processes including sperm motility/morphology, sperm-egg binding, capacitation, and epigenetic inheritance. In addition, there are numerous dysregulated transcripts that regulate germ cell epigenetic marks and Sertoli-germ cell binding and communication. These results show an overall increase in RS gene expression with age, with spermatogenic functions being perturbed. Taken together, these findings help identify the genetic origin of the fertility, germ cell niche, and epigenetic effects observed with advanced paternal aging.

Paternal aging impacts mitochondrial DNA content and telomere length in mouse embryos

Mitochondrial DNA (mtDNA) copy number and telomere length (TL) in blastocysts derived from the same male mice at young (10-19-week-old) and aged (40-49-week-old) time points and mtDNA and TL in the hearts of offspring derived from young and aged male mice were examined. Paternal aging correlated with reduced mtDNA and TL in blastocysts. mtDNA and TL were significantly correlated, which was also observed in bovine blastocysts. Moreover, mtDNA in the heart of offspring was reduced in male mice with paternal aging. In conclusion, paternal aging affects embryonic mtDNA and TL, potentially impacting their offspring.

Risk of Neurodevelopmental Disease by Paternal Aging: A Possible Influence of Epigenetic Alteration in Sperm

Sincethe theory of DOHaD has been thrown in the spotlight, most attention has focused on environmental effects of the uterus on developing embryos/fetuses. However, the ontogenesis traces back to gametogenesis. Compared to oogenesis, spermatogenesis goes through far more cell divisions and is therefore more prone to genetic variation and epigenetic alterations. This article will mainly discuss recent findings about the effects of the advanced paternal age on the next generation, in relation to the onset of psychiatric disorders such as autism spectrum disorder. We would like to advocate for further exploration on the DOHaD theory in a wider view.