Anatomical Transcriptome Atlas of the Male Mouse Reproductive System During Aging

Reproductive Ageing: Current insights and a potential role of NAD in the reproductive health of aging fathers and their children

In brief

In light of the increasing age of first-time fathers, this article summarizes the current scientific knowledge base on reproductive aging in the male, including sperm quality and health impacts for the offspring. The emerging role of NAD decline in reproductive aging is highlighted.

Abstract

Over the past decades, the age of first-time fathers has been steadily increasing due to socio-economic pressures. While general mechanisms of aging are subject to intensive research, male reproductive aging has remained an understudied area, and the effects of increased age on the male reproductive system are still only poorly understood, despite new insights into the potential dire consequences of advanced paternal age for the health of their progeny. There is also growing evidence that reproductive aging is linked to overall health in men, but this review mainly focuses on pathophysiological consequences of old age in men, such as low sperm count and diminished sperm genetic integrity, with an emphasis on mechanisms underlying reproductive aging. The steady decline of NAD levels observed in aging men represents one of the emerging concepts in that regard. Because it offers some mechanistic rationale explaining the effects of old age on the male reproductive system, some of the NAD-dependent functions in male reproduction are briefly outlined in this review. The overview also provides many questions that remain open about the basic science of male reproductive aging.

Exposure to female olfactory cues hastens reproductive ageing and increases mortality when mating in male mice

Theories of ageing predict that investment in reproduction will trade-off against survival and later-life reproduction. Recent evidence from invertebrates suggests that just perceiving cues of a potential mate's presence can reduce lifespan, particularly in males, and that activation of neuroendocrine reward pathways associated with mating can alleviate these effects. Whether similar effects occur in vertebrates remains untested. We tested whether exposure to olfactory cues from the opposite sex would influence mortality and reproductive senescence in male mice. We observed that males exposed to female olfactory cues from middle- to old age (from 10 to 24 months of age) showed reduced late-life fertility, irrespective of whether they had also been allowed to mate with females earlier in life. Males that were exposed to female odours in conjunction with mating also showed an increased mortality rate across the exposure period, indicating that olfactory cues from females can increase male mortality in some environments. Our results show that exposure to female odours can influence reproductive ageing and mortality in male mice, highlighting that sensory perception of mates may be an important driver of life-history trade-offs in mammals.

Effect of feeding corn silage on semen quality and spermatogenesis of bulls

Bovine reproduction, including male fertility traits like semen quality, are influenced by a variety of different factors like breed, nutrition, environment, and feeding management. Diet in a crucial determinant, and in this regard although corn silage is generally considered to be a favorable roughage for fattening meat type breeds, it tends to have a negative impact on semen quality. In the current study, alfalfa hay was substituted by corn silage as a roughage source in the diet of bulls to investigate its effects on the fertility of breeding bulls. A feeding trail spanning 140 days was conducted, with semen collection occurring twice a week commencing 60 days after the start of trial. Semen quality parameters, serum antioxidant indexes, sex hormone content in semen, rumen microflora, and sperm transcriptome were characterized. Feeding corn silage enhanced host antioxidant capacity, significantly decreased spermatozoal motility and increased sperm deformity rate in bulls. Furthermore, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) content in semen were significantly decreased (P < 0.05), and the inhibin B (INHB) content was significantly increased (P < 0.01). Feeding corn silage led to significant changes in the diversity of rumen microbiota of cattle at the phylum and genus levels, some of which were significantly correlated with semen quality. Subsequent RNA sequencing indicated that DHH and PITHD1, two genes related to sperm and reproductive development, were differentially expressed, and enrichment analysis also identified several pathways and biological functions relevant to sperm development and reproduction. These results indicate that feeding corn silage modulates semen quality via different pathways. Firstly, corn silage metabolites likely affect the secretion of INHB through the testicular capillaries, which affects semen quality by regulating genes involved in spermatogenesis. Secondly, low lignin content in silage corn appears to reduce abundance of rumen flora that are positively correlated with semen quality. Overall, results indicate that feeding bulls corn silage as the primary source of forage could negatively impact semen quality and may not be appropriate as the primary roughage of forage for breeding bulls.

Human Umbilical Cord Mesenchymal Stem Cell-Derived Exosomes Rescue Testicular Aging

BACKGROUND

Testicular aging is associated with diminished fertility and certain age-related ailments, and effective therapeutic interventions remain elusive. Here, we probed the therapeutic efficacy of exosomes derived from human umbilical cord mesenchymal stem cells (hUMSC-Exos) in counteracting testicular aging.

METHODS

We employed a model of 22-month-old mice and administered intratesticular injections of hUMSC-Exos. Comprehensive analyses encompassing immunohistological, transcriptomic, and physiological assessments were conducted to evaluate the effects on testicular aging. Concurrently, we monitored alterations in macrophage polarization and the oxidative stress landscape within the testes. Finally, we performed bioinformatic analysis for miRNAs in hUMSC-Exos.

RESULTS

Our data reveal that hUMSC-Exos administration leads to a marked reduction in aging-associated markers and cellular apoptosis while promoting cellular proliferation in aged testis. Importantly, hUMSC-Exos facilitated the restoration of spermatogenesis and elevated testosterone synthesis in aged mice. Furthermore, hUMSC-Exos could attenuate inflammation by driving the phenotypic shift of macrophages from M1 to M2 and suppress oxidative stress by reduced ROS production. Mechanistically, these efficacies against testicular aging may be mediated by hUMSC-Exos miRNAs.

CONCLUSIONS

Our findings suggest that hUMSC-Exos therapy presents a viable strategy to ameliorate testicular aging, underscoring its potential therapeutic significance in managing testicular aging.

Hyperhomocysteinemia lowers serum testosterone concentration via impairing testosterone production in Leydig cells

Hyperhomocysteinemia (HHcy) plays a salient role in male infertility. However, whether HHcy interferes with testosterone production remains inconclusive. Here, we reported a lower serum testosterone level in HHcy mice. Single-cell RNA sequencing revealed that genes related to testosterone biosynthesis, together with nuclear receptor subfamily 5 group A member 1 (Nr5a1), a key transcription factor for steroidogenic genes, were downregulated in the Leydig cells (LCs) of HHcy mice. Mechanistically, Hcy lowered trimethylation of histone H3 on lysine 4 (H3K4me3), which was bound on the promoter region of Nr5a1, resulting in downregulation of Nr5a1. Intriguingly, we identified an unknown cell cluster annotated as Macrophage-like Leydig cells (McLCs), expressing both LCs and macrophages markers. In HHcy mice, McLCs were shifted toward pro-inflammatory phenotype and thus promoted inflammatory response in LC. Betaine supplementation rescued the downregulation of NR5A1 and restored the serum testosterone level in HHcy mice. Overall, our study highlights an etiological role of HHcy in LCs dysfunction.

Exploring biomarkers of premature ovarian insufficiency based on oxford nanopore transcriptional profile and machine learning

Premature ovarian insufficiency (POI) is a reproductive endocrine disorder characterized by infertility and perimenopausal syndrome, with a highly heterogeneous genetic etiology and its mechanism is not fully understood. Therefore, we utilized Oxford Nanopore Technology (ONT) for the first time to characterize the full-length transcript profile, and revealed biomarkers, pathway and molecular mechanisms for POI by bioinformatics analysis and machine learning. Ultimately, we identified 272 differentially expressed genes, 858 core genes, and 25 hub genes by analysis of differential expression, gene set enrichment, and protein-protein interactions. Seven candidate genes were identified based on the intersection features of the random forest and Boruta algorithm. qRT-PCR results indicated that COX5A, UQCRFS1, LCK, RPS2 and EIF5A exhibited consistent expression trends with sequencing data and have potential as biomarkers. Additionally, GSEA analysis revealed that the pathophysiology of POI is closely associated with inhibition of the PI3K-AKT pathway, oxidative phosphorylation and DNA damage repair, as well as activation of inflammatory and apoptotic pathways. Furthermore, we emphasize that downregulation of respiratory chain enzyme complex subunits and inhibition of oxidative phosphorylation pathways play crucial roles in the pathophysiology of POI. In conclusion, our utilization of long-read sequencing has refined the annotation information within the POI transcriptional profile. This valuable data provides novel insights for further exploration into molecular regulatory networks and potential biomarkers associated with POI.

Transcriptome profiling of the initial segment and proximal caput of mouse epididymis

Background

The proximal region of the mouse epididymis plays a pivotal role in sperm transport, sperm maturation, and male fertility. Several studies have focused on segment-dependent gene expression of the mouse epididymis through high-throughput sequencing without the precision of the microdissection.

Methods and results

Herein, we isolated the initial segment (IS) and proximal caput (P-caput) by physical microdissection using an Lcn9-cre; Rosa26tdTomato mouse model. We defined the transcriptome changes of caput epididymis by RNA sequencing (RNA-seq), which identified 1,961 genes that were abundantly expressed in the IS and 1,739 genes that were prominently expressed in the P-caput. In addition, we found that many differentially expressed genes (DEGs) were predominantly or uniquely expressed in the epididymis and region-specific genes were highly associated with transport, secretion, sperm motility, fertilization, and male fertility.

Conclusion

Thus, this study provides an RNA-seq resource to identify region-specific genes in the caput epididymis. The epididymal-selective/specific genes are potential targets for male contraception and may provide new insights into understanding segment-specific epididymal microenvironment-mediated sperm transport, maturation, and male fertility.

Single-cell RNA sequencing reveals the local cell landscape in mouse epididymal initial segment during aging

BACKGROUND

Morphological and functional alterations in aging reproductive organs result in decreased male fertility. The epididymis functions as the transition region for post-testicular sperm maturation. And we have previously demonstrated that the epididymal initial segment (IS), a region of the reproductive tract essential for sperm maturation and capacitation, undergoes considerable histological changes and chronic immune activation in mice during aging. However, the local aging-associated cellular and molecular changes in the aged epididymal IS are poorly understood.

RESULTS

We conducted single-cell RNA sequencing analysis on the epididymal IS of young (3-month-old) and old (21-month-old) mice. In total, 10,027 cells from the epididymal IS tissues of young and old mice were obtained and annotated. The cell composition, including the expansion of a principal cell subtype and Ms4a4b^HiMs4a6b^Hi T cells, changed with age. Aged principal cells displayed multiple functional gene expression changes associated with acrosome reaction and sperm maturation, suggesting an asynchronous process of sperm activation and maturation during epididymal transit. Meanwhile, aging-related altered pathways in immune cells, especially the "cell chemotaxis" in Cx3cr1^Hi epididymal dendritic cells (eDCs), were identified. The monocyte-specific expression of chemokine Ccl8 increased with age in eDCs. And the aged epididymal IS showed increased inflammatory cell infiltration and cytokine secretion. Furthermore, cell-cell communication analysis indicated that age increased inflammatory signaling in the epididymal IS.

CONCLUSION

Contrary to the general pattern of lower immune responses in the male proximal genital tract, we revealed an inflammaging status in mouse epididymal initial segment. These findings will allow future studies to enable the delay of male reproductive aging via immune regulation.