Disrupted spermatogenesis in a metabolic syndrome model: the role of vitamin A metabolism in the gut-testis axis

Effects of chitosan on restoring spermatogenesis in mice: Insights from gut microbiota and multi-omics analysis

Chitosan, is a natural bio-based polymer with known prebiotic properties. However, its potential in the management of spermatogenic disorders remains largely unexplored. By utilizing a busulfan-treated mouse model and integrated multi-omics analysis, this study explored the potential mechanisms through which chitosan improves impaired spermatogenesis. The results showed that chitosan treatment can improve testicular function and significantly reshape the gut microbiota composition in busulfan-treated mice. Metabolomics revealed that docosahexaenoic acid (DHA) transport was significantly dysregulated in busulfan-treated mice, but chitosan reversed this dysfunction by modulating tight junction proteins and fatty acid transporters in the intestine. Fecal microbiota transplantation experiments further highlighted the critical role of gut microbiota in DHA transport and spermatogenesis. Additionally, DHA supplementation alleviated busulfan-induced ferroptosis in testicular tissues. Hence, owing to its prebiotic effects chitosan could serve as a novel therapeutic strategy for improving busulfan-induced spermatogenic disorders by restoring the homeostasis of the gut-testis axis.

Causal relationships between gut microbiota and male reproductive inflammation and infertility: Insights from Mendelian randomization

The study observed interactions between gut microbiota and male reproductive health, noting that the causal relationships were previously unclear. It aimed to explore the potential cause-and-effect relationship between gut bacteria and male reproductive problems such as inflammation, infertility, and sperm functionality, using a two-sample Mendelian randomization method to examine these connections. The analysis found that certain bacterial genera, such as Erysipelatoclostridium (0.71 [0.55-0.92]), Parasutterella (0.74 [0.57-0.96]), Ruminococcaceae UCG-009 (0.77 [0.60-0.98]), and Slackia (0.69 [0.49-0.96]), showed protective effects against prostatitis. In contrast, other genera like Faecalibacterium (1.59 [1.08-2.34]), Lachnospiraceae UCG004 (1.64 [1.15-2.34]), Odoribacter (1.68 [1.01-2.81]), Paraprevotella (1.28 [1.03-1.60]), and Sutterella (1.58 [1.13-2.19]) were detrimental. Additionally, causal relationships were identified between 2 genera and orchitis and epididymitis, 3 genera and male infertility, and 5 genera and abnormal spermatozoa. Further analysis of sperm-related proteins revealed causal associations between specific bacterial genera and proteins such as SPACA3, SPACA7, SPAG11A, SPAG11B, SPATA9, SPATA20, and ZPBP4. The results remained robust after sensitivity analysis and reverse Mendelian randomization analysis. The study concluded that specific bacterial genera have causal roles in reproductive inflammation, infertility, and sperm-associated proteins. This provides a novel strategy for the early diagnosis and identification of therapeutic targets in reproductive inflammation and infertility.

Gut-testis axis in roosters: Lactiplantibacillus plantarum supplementation improves reproductive performance

Probiotics are widely used in poultry farming and industry, as they offer numerous health and performance benefits for birds. Probiotic Lactobacilli maintain gut microbiota balance, aid nutrient utilization, boost the immune system, increase stress resistance and serve as antibiotic alternatives. However, their impact on male reproductive function is not yet fully understood. This study investigated the effect of a novel probiotic strain, Lactiplantibacillus plantarum SNI3 (LbSNI3), on the reproductive performance of roosters. Twenty adult roosters were used. LbSNI3 was administered orally (dose: 2 × 107 CFU/animal/day) for 7 weeks to half of the animals. Control birds (10) received sterile tap water vehicle. Ejaculate volume, sperm concentration, sperm motility, number of IPVL penetration holes and testosterone plasma concentration have been measured weekly. Testis weight, dimensions and histology have been determined at the end of the experiment. mRNA levels of select genes, involved in spermatogenesis and sperm motility, oxidative and steroid synthesis have been measured in the testis samples by qRT-PCR. Total antioxidant capacity, superoxide dismutase (SOD) enzyme activity and malondialdehyde (MDA) levels were also analyzed. LbSNI3 administration increased the ejaculate volume, sperm concentration and the number of penetration holes, resulting in a significant improvement in the reproductivity index. In contrast, testosterone levels were not statistically different in control versus LbSNI3-treated groups. At the end of the experiment, testis size, the area, and the lumen of seminiferous tubuli were increased in LbSNI3-treated roosters. The testicular expression of Gpx1, Sepw1, Dio2, Birc5 and Rec8 genes was elevated following oral administration of LbSNI3. Total antioxidant activity, SOD activity significantly increased, while MDA concentration decreased, indicating enhanced antioxidant capacity in the testis. LbSNI3 produces a bacterial metabolite, γ-glutamyl-glutamate, which enters the glutathione cycle and strengthens the testicular defense mechanisms against oxidative stress. In conclusion, oral administration of probiotic LbSNI3 enhances antioxidant defense mechanisms in the testis, leading to increased reproductive index in adult roosters. This effect may be mediated through the gut-testis axis and could be utilized to improve productivity in the livestock industry.

Long term exposure to multiple environmental stressors induces mitochondrial dynamics imbalance in testis: Insights from metabolomics and transcriptomics

Long-term exposure to adverse environment stressors (e.g. noise pollution, temperature, and crowding) impaired human health. However, research on the toxic effects of adverse environmental stressors on the male reproductive system is limited. This study employed integrated phenomics, metabolomics, and transcriptomics to investigate physiological disturbances in the testis of mice exposed to multiple adverse environmental stressors for two months. Phenotypic studies indicated that long-term environmental stimuli resulted in significant damage to the blood-testis barrier (BTB) and testes, evidenced by reduced testicular index, disrupted testicular tissue structure, abnormal tight junction protein expression, and spermatozoa abnormalities. Comprehensive multi-omics analysis revealed that long-term exposure to environmental stressors disrupted the BTB and testes, which was associated with mitochondrial metabolism disorders, including oxidative phosphorylation and fatty acid beta-oxidation, as well as glutathione and lipid metabolism alterations. Among these dysregulated pathways, significant alterations were observed in the critical regulators of mitochondrial fusion (MFN2) and fission (DRP1) within the BTB. Specifically, corticosterone treatment decreased tight junction protein expression, increased reactive oxygen species (ROS) levels, and impaired mitochondrial morphology and function, as evidenced by reduced mitochondrial membrane potential, elevated calcium ion concentration, and shortened mitochondrial length and network in vitro. Moreover, inhibiting DRP1 with Mdivi-1 or overexpressing MFN2 mitigated the corticosterone-induced reduction of tight junctions and mitochondrial dysregulation in TM4 cells. Collectively, maintaining mitochondrial homeostasis emerges as a promising strategy to alleviate the BTB and testicular injury induced by long-term exposure to multiple environmental stressors.

Deciphering the microbiome, lipopolysaccharides, and metabolome interplay: Unveiling putrescine's mechanism for enhancing sperm quality in heat-stressed boars

Global warming has added to concerns regarding declining male fertility due to high temperatures. As a metabolite of arginine, putrescine improves gut health and promotes testicular development in boar; however, its action in improving semen quality under heat stress is unknown. Therefore, we assessed the effect of putrescine on the semen quality of boars in a heat stress model. Results showed that putrescine ameliorated the heat stress-induced decline in semen quality and testosterone levels in boars, confirmed by sperm viability, immobility rate, and apoptosis levels. Fecal microbial 16S rRNA sequencing showed that heat stress induces intestinal microecological dysregulation triggering an increase in the serum lipopolysaccharide (LPS) levels and reducing boar semen quality. A negative correlation between the Lachnospiraceae_XPB1014_group and LPS-binding protein (LBP) levels was observed. The Lachnospiraceae_XPB1014_group was reduced significantly under heat stress, and its relative abundance significantly increased after putrescine diet, which reduced both LPS and LBP in the serum of heat-stressed boars. Heat stress also affected plasma amino acid metabolism, and the regulation of plasma metabolism by putrescine can be attributed to its effects on LPS and the LBP owing to the significantly correlation of both with multiple plasma differential metabolites. Putrescine is thus considered to inhibit the increased serum LPS by acting on intestinal microorganisms, particularly by increasing the relative abundance of the Lachnospiraceae_XPB1014_group, and further modulate plasma amino acid metabolism to improve the semen quality in heat-stressed boars.

Butyrate improves testicular spermatogenic dysfunction induced by a high-fat diet

Background

Obesity is closely associated with low male fertility and decreased sperm quality. Obesity is accompanied by an ecological imbalance in the gut microbiota, so it is of great significance to intervene in male infertility caused by obesity from the perspective of gut microbiota metabolites. This study aimed to evaluate the efficacy of butyrate in ameliorating obesity-induced spermatogenic dysfunction and to explore the potential molecular mechanisms.

Methods

This study explored the role of butyrate in recovering the dysfunctions of spermatogenesis caused by obesity by inducing an obese model of male mice with a high-fat diet (HFD). The effects of HFD and butyrate on testicular function were explored based on metabolomics.

Results

The results of the study showed that HFD caused a decrease in sperm count, a decrease in sperm motility, and an increase in sperm malformation rate in mice. After adding butyrate to the HFD, the various sperm indicators of mice were significantly improved. Through the analysis of metabolomics data from mouse testes, this study found that an HFD significantly altered the metabolic status of mice testes, involving multiple metabolic pathways. However, after adding butyrate, some metabolic characteristics tended to be similar to those of normal diet mice, and the steroid biosynthesis and primary bile acid biosynthesis pathways were significantly improved.

Conclusions

This study clarified the effect of butyrate on improving sperm quality, providing experimental evidence for the treatment of obesity-induced abnormal spermatogenesis with butyrate.

Gut microbiota and male fertility: A two-sample Mendelian randomization study

Previous studies have reported that alterations in gut microbiota composition are associated with male fertility. However, it is unclear and difficult to establish whether these associations reflect a causal relationship. We assessed genome-wide association study summary statistics for gut microbiota and male fertility to perform MR analysis. Independent single nucleotide polymorphisms closely associated with 211 gut bacterial taxa (N = 122,110) were identified as instrumental variables. The summary statistic data for male infertility (N = 733,479), abnormal spermatozoa (N = 209,921) and erectile dysfunction (N = 223,805) were obtained from the latest release from the FinnGen consortium as the outcome of interest. Two-sample MR was performed to evaluate the causal effect of gut microbiota on male fertility, including inverse-variance-weighted (IVW) method, weighted median method, MR-Egger, mode-based estimation and MR-PRESSO. A series of sensitivity analyses was performed to validate the robustness of the results. The robustness of the estimation was tested by a series of sensitivity analyses including Cochran's Q test, MR-Egger intercept analysis, leave-one-out analysis and funnel plot were used to assess the causal association. Combining the results from the discovery and replication stages, we identified 3 causal bacterial genus. Ruminiclostridm6 (OR = 0.537, 95%CI = 0.292-0.987, P = .045, PFDR = 0.234) was found to be closely associated with male infertility, and the decrease in its quantity increased the risk of male infertility. Decreased Prevotella9 (OR = 0.670, 95% CI = 0.452-0.992, P = .046, PFDR = 0.175) was found to be closely related to abnormal sperm. Lachnospiraceae NC2004 group (OR = 1.173, 95% CI = 1.008-1.366, P = .078, PFDR = 0.530) was found to be closely related to male erectile dysfunction, and there was a positive correlation between them. No heterogeneity and pleiotropy were detected. This study implied a causal relationship between the Ruminiclostridm6 genus, Prevotella9 genus, Lachnospiraceae NC2004 group genus and male fertility, thus providing novel insights into the gut microbiota-mediated development mechanism of ADs. Nevertheless, future studies are warranted to dissect the underlying mechanisms of specific bacterial taxa's role in the pathophysiology of male fertility.

Melatonin alleviates high temperature exposure induced fetal growth restriction via the gut-placenta-fetus axis in pregnant mice

INTRODUCTION

Global warming augments the risk of adverse pregnancy outcomes in vulnerable expectant mothers. Pioneering investigations into heat stress (HS) have predominantly centered on its direct impact on reproductive functions, while the potential roles of gut microbiota, despite its significant influence on distant tissues, remain largely unexplored. Our understanding of deleterious mechanisms of HS and the development of effective intervention strategies to mitigate the detrimental impacts are still limited.

OBJECTIVES

In this study, we aimed to explore the mechanisms by which melatonin targets gut microbes to alleviate HS-induced reproductive impairment.

METHODS

We firstly evaluated the alleviating effects of melatonin supplementation on HS-induced reproductive disorder in pregnant mice. Microbial elimination and fecal microbiota transplantation (FMT) experiments were then conducted to confirm the efficacy of melatonin through regulating gut microbiota. Finally, a lipopolysaccharide (LPS)-challenged experiment was performed to verify the mechanism by which melatonin alleviates HS-induced reproductive impairment.

RESULTS

Melatonin supplementation reinstated gut microbiota in heat stressed pregnant mice, reducing LPS-producing bacteria (Aliivibrio) and increasing beneficial butyrate-producing microflora (Butyricimonas). This restoration corresponded to decreased LPS along the maternal gut-placenta-fetus axis, accompanied by enhanced intestinal and placental barrier integrity, safeguarding fetuses from oxidative stress and inflammation, and ultimately improving fetal weight. Further pseudo-sterile and fecal microbiota transplantation trials confirmed that the protective effect of melatonin on fetal intrauterine growth under HS was partially dependent on gut microbiota. In LPS-challenged pregnant mice, melatonin administration mitigated placental barrier injury and abnormal angiogenesis via the inactivation of the TLR4/MAPK/VEGF signaling pathway, ultimately leading to enhanced nutrient transportation in the placenta and thereby improving the fetal weight.

CONCLUSION

Melatonin alleviates HS-induced low fetal weight during pregnancy via the gut-placenta-fetus axis, the first time highlighting the gut microbiota as a novel intervention target to mitigate the detrimental impact of global temperature rise on vulnerable populations.

Retinol metabolism signaling participates in microbiota-regulated fat deposition in obese mice

Obesity is a global pandemic threatening public health, excess fat accumulation and overweight are its characteristics. In this study, the interplay between gut microbiota and retinol metabolism in modulating fat accumulation was verified. We observed gut microbiota depletion reduced the body weight and the ratios of white adipose tissues (WATs) to body weight in high-fat diet (HFD) fed-mice. The kyoto encyclopedia of genes and genomes (KEGG) analysis and protein-protein interaction (PPI) network of RNA-seq results indicated that retinol metabolism signaling may be involved in the microbiota-regulated fat deposition. Furthermore, activated retinol metabolism signaling by all-trans retinoic acid (atRA) supplementation reduced body weight and WAT accumulation in obese mice. 16S rRNA gene sequencing of the ileal microbiota suggested that atRA supplementation increased the microbial diversity and induced the growth of beneficial bacteria including Parabacteroides, Bacteroides, Clostridium_XVIII, Bifidobacterium, Enterococcus, Bacillus, Leuconostoc, and Lactobacillus in obese mice. Spearman correlation showed that the microbiota altered by atRA were associated with body and WAT weights. Together, this study reveals the interaction between the gut microbiota and retinol metabolism signaling in regulating adipose accumulation and obesity. It is expected of this finding to provide new insights to prevent and develop therapeutic measures of obesity-related metabolic syndrome.

Lower Semen Quality Among Men in the Modern Era-Is There a Role for Diet and the Microbiome?

The prevalence of infertility is increasing worldwide; poor nutrition, increased sedentary lifestyles, obesity, stress, endocrine-disrupting chemicals, and advanced age of childbearing may contribute to the disruption of ovulation and influence oocyte and sperm quality and overall reproductive health. Historically, infertility has been primarily attributed to female factors, neglecting the importance of male fertility; this has resulted in an incomplete understanding of reproductive health. Male factors account for 40-50% of infertility cases. In half of these cases, the proximal cause for male infertility is unknown. Sperm contributes half of the nuclear DNA to the embryo, and its quality is known to impact fertilisation rates, embryo quality, pregnancy rates, risk of spontaneous miscarriage, de novo autosomal-dominant conditions, psychiatric and neurodevelopment conditions, and childhood diseases. Recent studies have suggested that both the microenvironment of the testes and diet quality may play an important role in fertility; however, there is limited research on the combination of these factors. This review summarises current known causes of male infertility and then focuses on the potential roles for diet and the seminal microbiome. Future research in this area will inform dietary interventions and health advice for men with poor semen quality, potentially alleviating the need for costly and invasive assisted reproduction treatments and allowing men to take an active role in the fertility conversation which has historically focussed on women individually.

Exploring the microbiome-gut-testis axis in testicular germ cell tumors

The microbiome-gut-testis axis has emerged as a significant area of interest in understanding testicular cancer, particularly testicular germ cell tumors (TGCTs), which represent the most common malignancy in young men. The interplay between the gut and testicular microbiomes is hypothesized to influence tumorigenesis and reproductive health, underscoring the complex role of microbial ecosystems in disease pathology. The microbiome-gut-testis axis encompasses complex interactions between the gut microbiome, systemic immune modulation, and the local microenvironment of the testis. Dysbiosis in the gut or testicular microbiomes may contribute to altered immune responses, inflammation, and hormonal imbalances, potentially playing a role in the pathogenesis of TGCTs. Concurrently, seminal microbiomes have been linked to variations in sperm quality, fertility potential, and possibly cancer susceptibility, underscoring the need for further evaluation. This review explores the emerging role of the microbiome-gut-testis axis in the context of testicular cancer, highlighting its implications for disease onset, progression, treatment efficacy, and toxicity. Identifying potential microbial biomarkers, followed by microbiota modulation to restore a balanced microbial community, might offer a novel supportive strategy for improving treatment efficacy in refractory TGCT patients while reducing chemotherapy-induced toxicity. We suggest a better understanding of the association between dysregulated microbial environments and TGCTs emphasizes potential pathways by which the gut microbiome might influence testicular cancer.

Microbiota contribute to regulation of the gut-testis axis in seasonal spermatogenesis

Seasonal breeding is an important adaptive strategy for animals. Recent studies have highlighted the potential role of the gut microbiota in reproductive health. However, the relationship between the gut microbiota and reproduction in seasonal breeders remains unclear. In this study, we selected a unique single food source animal, the flying squirrel (Trogopterus xanthipes), as a model organism for studying seasonal breeding. By integrating transcriptomic, metabolomic, and microbiome data, we comprehensively investigated the regulation of the gut-metabolism-testis axis in seasonal breeding. Here, we demonstrated a significant spermatogenic phenotype and highly active spermatogenic transcriptional characteristics in the testes of flying squirrels during the breeding season, which were associated with increased polyamine metabolism, primarily involving spermine and γ-amino butyric acid. Moreover, an enrichment of Ruminococcus was observed in the large intestine during the breeding season and may contribute to enhanced methionine biosynthesis in the gut. Similar changes in Ruminococcus abundance were also observed in several other seasonal breeders. These findings innovatively revealed that reshaping the gut microbiota regulates spermatogenesis in seasonal breeders through polyamine metabolism, highlighting the great potential of the gut-testis axis in livestock animal breeding and human health management.

Gut microbiota combined with metabolome dissects Fluorene-9-bisphenol exposure-induced male reproductive toxicity

A major alternative to bisphenol A (BPA), fluorene-9-bisphenol (BHPF) has been shown to cause multiorgan toxicity. However, its reproductive toxicity and the underlying biological mechanism remain largely unknown. Recently, changes in the gut microbiota and metablome caused by environmental contaminant exposure and their potential impact on male reproductive health have been of great concern. Therefore, we aimed to elucidate the underlying mechanism of BHPF-related fertility impairment by integrating metabolome and microbiome analysis. In the present study, we showed that BHPF exposure caused testicular dysfunction with impaired spermatogenesis and disrupted steroid hormone synthesis. Mechanistically, altered gut microbiota and metabolites were revealed by 16S rDNA sequencing and untargeted metabolomics analysis. Subsequent multi-omics combination analysis revealed a strong correlation between altered microbiota and lipid metabolites. We also found a strong relationship between lipid metabolites and sperm parameters such as sperm concentration, sperm motility, etc. Most importantly, these findings provide new insights into the mechanistic scenario underlying BHPF-induced fertility toxicity, that disrupted lipid metabolism caused by gut microbiota dysbiosis may be a reason for reproductive impairment caused by BHPF exposure.

Effects of environmental bisphenol S exposure on male rat reproductive health and gut-blood-testicular axis integrity

In this study, male Sprague-Dawley (SD) rats were exposed to bisphenol S (BPS) at environmentally relevant concentrations to investigate its reproductive toxicity and evaluate its effects on the gut-blood-testicular axis. After 28 days of exposure to BPS (0.05 and 20 mg/kg), the results showed a reduction in weight gain and the induction of reproductive toxicity in male rats, including decreased sperm parameters, lower sperm viability, and increased abnormal sperm density and mortality. These observations were made by counting with a hemocytometer under the optical microscope. 16S rRNA and untargeted metabolomic elucidated potential impacts on the gut-blood-testicular axis: BPS impaired the physical barrier, evoked inflammation, and resulted in dysbiosis of the gut microbiota. Additionally, BPS altered serum metabolites, including phosphatidic acid and diacylglycerol, which are involved in Fc gamma R-mediated phagocytosis and linked to inflammation. Furthermore, histopathological analysis, western blot (WB), enzyme-linked immunosorbent assay (ELISA), and immunofluorescence results showed that exposure to BPS led to testicular damage, inflammation, activation of the p38 and ERK MAPK pathways, and disruption of the blood-testis barrier (BTB). Collectively, these findings indicate that BPS impair the intestinal health, disrupt gut microbiome, and ultimately lead to reproductive dysfunction through the gut-blood-testicular axis.

Causal relationship between gut microbiota and androgenetic alopecia: A Mendelian randomization study

Recent studies have found a strong correlation between gut microbiota and the risk of skin diseases and proposed a "gut-skin axis." Androgenetic alopecia (AGA) is the most common type of alopecia, and androgen plays an important role in its pathogenesis. It has been found that the gut microbiome is closely related to androgens; however, whether this relationship is causal or merely coincidental remains uncertain. To address this issue, Mendelian randomization (MR) analysis was performed to explore the association between gut microbiota and AGA. Genome-wide association studies (GWAS) have compiled summary statistics of the gut microbiota, including 211 taxa (131 genera, 35 families, 20 orders, 16 classes, and 9 phyla), with data from MiBioGen's comprehensive study. We collected genetic associations with AGA from the IEU OpenGWAS project. We performed MR Analyses to assess the causal relationship between the genetically predicted gut microbiota and AGA. In order to verify the reliability of the findings, we systematically performed sensitivity analyses and heterogeneity tests and performed a heterogeneity test. MR Analysis provides important evidence for the causal relationship between genetically predicted gut microbiota and AGA. Lachnospiraceae UCG008 (OR = 0.939, 95%CI 0.175-0.775, P < .01), Oxalobacte (OR = 0.932, 95%CI 0.896-0.969, P < .01) would reduce the risk of AGA. Eubacterium rectale group (OR = 1.102, 95%CI 1.025-1.186, P < .01), Roseburia (OR = 1.183, 95%CI 1.048-1.336, P < .01) would increase the risk of AGA. Further sensitivity and heterogeneity analyses confirmed the robustness of these results. The results of this study indicate that there is a potential genetic susceptibility between gut microbiota and AGA, and screen out protective and risk factors. These results provide a theoretical basis for the prevention and treatment of AGA by regulating gut microbiota.

Gut Microbiota Regulates the Homeostasis of Dendritic Epidermal T Cells

Dendritic epidermal T cells (DETCs) are a γδ T cell subset residing in the skin epidermis. Although they have been known for decades, the fate of DETCs has largely remained enigmatic. Recent studies have highlighted the relationship between the gut microbiome and γδ T cells in various epithelial and non-epithelial tissues, such as the small intestine, lung, liver, gingiva, and testis. While the skin microbiota has been shown to impact skin γδ T cells, a direct relationship between the gut microbiota and DETCs remains unexplored. In this study, we investigated whether DETCs are regulated by the gut microbiota in the steady-state skin epidermis. We examined the occurrence of DETCs in Balb/c mice, which have a skin epidermis barely populated with DETCs, compared to C57BL/6 mice, under different housing conditions. Our findings reveal that local skin inflammation markedly increases DETC numbers in the ear epidermis of Balb/c mice and that DETCs are activated by environmental factors. Furthermore, an investigation of the gut microbiota under different housing conditions revealed distinct microbial compositions and functional profiles. Taken together, these results suggest a strong connection between DETCs and gut microbiota.

Gut microbiota modulation by L-Fucose as a strategy to alleviate Ochratoxin A toxicity on primordial follicle formation

In this study, we investigated the potential benefits of L-Fucose administration to pregnant mice exposed to Ochratoxin A (OTA), a widespread mycotoxin, producing ovarian damage in offspring. The results showed that administration of 3.5 μg/d OTA induced alterations in intestinal tissues and gut microbiota of pregnant mice, leading to heightened local and systemic inflammation. This inflammatory affected the ovaries of their 3 dpp offspring, in which elevated levels of LPS and ROS were found associated to significant decreased oocyte count and impaired primordial follicle assembly. Moreover, mRNA-Seq analysis showed significant changes in ovarian transcriptomes linked to various GO terms and KEGG pathways, notably ferroptosis, a recognized form of cell death observed. Interestingly, administration of 0.3 g/kg b. w. L-Fucose following OTA exposure mitigated these effects on intestinal tissues and gut microbiota in mothers and on the offspring's ovaries. Similar benefits were obtained by gut microbiota transplantation from L-Fucose-treated pregnant females into OTA-exposed mothers. These findings suggest that inflammatory impact of OTA on maternal intestine/gut can pass to the fetus causing offspring ovary defects and support the use of L-Fucose as adjuvant to counteract the adverse effects of mycotoxins on the gut microbiota, particularly reference to those affecting reproductive organs.

High-fat diet led to testicular inflammation and ferroptosis via dysbiosis of gut microbes

The disorder of gut microbiota has negative impact on male reproductive, and testicular damage is associated with obesity. However, the detailed mechanism of gut microbiota on the obesity-induced testis injury are still unknown. Therefore, we constructed a mouse model to investigate the effects of obesity on testis injury. In this study, we found that HFD-induced obesity could disorder gut microbiota homeostasis, which increased the abundance of Brevundimonas, Desulfovibrionaceae_unclassified and Ralstonia, ultimately leading to the overproduction of lipopolysaccharides (LPS). Meanwhile, HFD-feeding promoted intestinal permeability via inhibiting expression of tight junction proteins (ZO-1, Occludin and Claudin) and reducing excretion of mucus, leading to translocation of LPS. The over-accumulation of LPS in the bloodstream triggered an inflammatory response by activating TLR4/NF-κB pathway in testis. On the other hand, the gut microbiota produced-LPS also could induce ferroptosis in testis, as reflected by enhancing iron content and lipid peroxidation (MDA), as well as decreasing ferroptosis-related proteins, including GPX4, FTH1 and SLC1A11. Moreover, inhibition of LPS ligand (TLR4) with Resatorvid (TAK-242) alleviated obesity-induced testis injury through suppression of inflammation and ferroptosis. In conclusion, this study provides novel insights into the underlying mechanisms of obesity-related testis injury induced by gut microbiota disorder via the gut-testis axis, thus offering potential targets to counteract obesity-induced male reproductive disorder.

Association between gut microbiota and male infertility: a two-sample Mendelian randomization study

Previous research has confirmed the significant association between gut microbiota (GM) and male infertility (MI), but the causality between them remains unclear. This study aims to investigate the causal relationship between GM and MI using Mendelian randomization (MR) and provide supplementary information for the optimization of future randomized controlled trials (RCTs). Instrumental variables for 211 GM taxa were obtained from genome-wide association studies (GWAS), and inverse variance weighted (IVW) method was used as the main analysis method for two-sample MR analysis to assess the impact of GM on the risk of MI. Four methods were used to test for horizontal pleiotropy and heterogeneity of MR results to ensure the reliability of the MR findings. A total of 50 single-nucleotide polymorphisms (SNPs) closely related to GM were included, and ultimately identified 1 family and 4 general are causally associated with MI. Among them, Anaerotruncus (OR = 1.96, 95% CI 1.31-3.40, P = 0.016) is significantly associated with increased MI risk. Furthermore, we used four MR methods to evaluate the causality, and the results supported these findings. The leave-one-out analysis showed stable results with no instrumental variables exerting strong influence on the results. The causal direction indicated a positive effect, and the effects of heterogeneity and horizontal pleiotropy on the estimation of causal effect were minimized. We confirmed a causal relationship between GM taxa and MI, providing new insights into the mechanisms underlying GM-mediated MI.

Causal Link between Gut Microbiota and Infertility: A Two-sample Bidirectional Mendelian Randomization Study

OBJECTIVE

To investigate the associations of the gut microbiota with reproductive system diseases, including female infertility, male infertility, polycystic ovary syndrome (PCOS), primary ovarian failure, endometriosis, uterine fibroids, uterine polyps, sexual dysfunction, orchitis, and epididymitis.

METHODS

A two-sample bidirectional Mendelian randomization (MR) analysis was performed to evaluate the potential causal relationship between the composition of gut microbiota and infertility, along with associated diseases.

RESULTS

Sixteen strong causal associations between gut microbes and reproductive system diseases were identified. Sixty-one causal associations between gut microbes and reproductive system diseases were determined. The genus Eubacterium hallii was a protective factor against premature ovarian failure and a pathogenic factor of endometriosis. The genus Erysipelatoclostridium was the pathogenic factor of many diseases, such as PCOS, endometriosis, epididymitis, and orchitis. The genus Intestinibacter is a pathogenic factor of male infertility and sexual dysfunction. The family Clostridiaceae 1 was a protective factor against uterine polyps and a pathogenic factor of orchitis and epididymitis. The results of reverse causal association analysis revealed that endometriosis, orchitis, and epididymitis all led to a decrease in the abundance of bifidobacteria and that female infertility-related diseases had a greater impact on gut microbes than male infertility-related diseases did.

CONCLUSIONS

The findings from the MR analysis indicate that there is a bidirectional causal relationship between the gut microbiota and infertility as well as associated ailments. Compared with ovarian diseases, uterine diseases are more likely to lead to changes in women's gut microbiota. The findings of this research offer valuable perspectives on the mechanism and clinical investigation of reproductive system diseases caused by microorganisms.

Exploring the hypothetical links between environmental pollutants, diet, and the gut-testis axis: The potential role of microbes in male reproductive health

The gut system, commonly referred to as one of the principal organs of the human "superorganism," is a home to trillions of bacteria and serves an essential physiological function in male reproductive failures or infertility. The interaction of the endocrine-immune system and the microbiome facilitates reproduction as a multi-network system. Some recent studies that link gut microbiota to male infertility are questionable. Is the gut-testis axis (GTA) real, and does it affect male infertility? As a result, this review emphasizes the interconnected links between gut health and male reproductive function via changes in gut microbiota. However, a variety of harmful (endocrine disruptors, heavy metals, pollutants, and antibiotics) and favorable (a healthy diet, supplements, and phytoconstituents) elements promote microbiota by causing dysbiosis and symbiosis, respectively, which eventually modify the activities of male reproductive organs and their hormones. The findings of preclinical and clinical studies on the direct and indirect effects of microbiota changes on testicular functions have revealed a viable strategy for exploring the GTA-axis. Although the GTA axis is poorly understood, it may have potential ties to reproductive issues that can be used for therapeutic purposes in the future.

Activation of aryl hydrocarbon receptor protein promotes testosterone synthesis to alleviate abnormal spermatogenesis caused by cholestasis

In this study, we have investigated potential roles of cholestasis played in spermatogenesis in the cholestatic animal model generated by giving the mice DDC diet. The data showed that cholestasis jeopardized the testicular structure and function by downregulating the expressions of genes related to the androgen's synthesis. Mechanistically, the cholestasis disturbers the liver's tryptophan metabolism and its metabolites. These tryptophan metabolites including serotonin, 5-Hydroxyindoleacetic acid, 4-(2-Aminophenyl)-2,4-dioxobutanoic acid and Quinoline-4,8-diol were significantly reduced in the cholestatic mice model compared to their controlled counterparts. These tryptophan metabolites are the endogenous ligands of AHR and their levels are positively correlated to the expressions of genes related to the androgen's synthesis and AHR. Notably, supplementation of AHR ligand ITE promoted the expression of genes related to the testosterone synthesis and alleviated abnormal spermatogenesis. In addition, the bacteria that disturbed the tryptophan metabolism in cholestatic mice were identified by 16S rDNA sequencing and Spearman correlation analysis. Briefly, we have identified a cholestasis associated gut microbiota-testis axis. This axis is responsible for the cholestasis induced abnormal spermatogenesis and male reproductive dysfunction. Breaking vicious cycle of this axis may be a suitable strategy to prevent and treat the cholestasis associated male infertility.

Melatonin alleviates heat stress-induced spermatogenesis dysfunction in male dairy goats by regulating arachidonic acid metabolism mediated by remodeling the gut microbiota

BACKGROUND

Heat stress (HS) commonly occurring in summer has gradually become a factor threatening the reproductive performance of male dairy goats by reducing their fecundity. Despite the melatonin is applied to relieve HS, it is still unclear whether melatonin protects against reproductive damage induced by HS in dairy goats and how it works. The purpose of the present study is to evaluate the role of melatonin in alleviating HS-induced spermatogenesis dysfunction in male dairy goats and further explore its mechanism.

RESULTS

HS impaired spermatogenesis, sperm formation in the testes, and sperm maturation in the epididymis of dairy goats, resulting in decreased sperm quality. Melatonin rescued the decrease of sperm quality induced by HS via decreasing inflammatory and oxidative stress levels in testicular tissue and enhancing intercellular barrier function within the testes. Amplicon-based microbiota analysis revealed that despite gut microbiota differences between melatonin-treated dairy goats and NC dairy goats to some extent, melatonin administration tends to return the gut microbiota of male dairy goats under HS to the levels of natural control dairy goats. To explore whether the protective role of melatonin in sperm quality is mediated by regulating gut microbiota, fecal microbiota of HS dairy goats with or without melatonin treatment were transferred to HS mice, respectively. We found HS mice that had received fecal bacteria of HS dairy goats experienced serious testicular injury and dyszoospermia, while this phenomenon was ameliorated in HS mice that had received fecal bacteria of dairy goats treated with melatonin, indicating melatonin alleviates HS-induced spermatogenic damage in a microbiota dependent manner. We further found that the testicular tissue of both HS dairy goats and mice transplanted with HS dairy goat feces produced large amounts of arachidonic acid (AA)-related metabolites, which were closely associated with semen quality. Consistently, supplementation with AA has been shown to elevate the levels of inflammation and oxidative stress in the testicular tissue of mice, disrupting intercellular connections and ultimately leading to spermatogenic disorders.

CONCLUSION

This study has revealed that melatonin can effectively alleviate spermatogenic disorders in dairy goats caused by HS. This beneficial effect was primarily achieved through the modulation of gut microbiota, which subsequently inhibited the excessive synthesis of AA in testicular tissue. These discoveries are of great significance for preventing or improving the decline in male livestock reproductive performance caused by HS, enhancing the reproductive efficiency of elite male breeds, and ultimately improving the production efficiency of animal husbandry. Video Abstract.

Exosomes-mediated retinoic acid disruption: A link between gut microbiota depletion and impaired spermatogenesis

Gut microbiota symbiosis faces enormous challenge with increasing exposure to drugs such as environmental poisons and antibiotics. The gut microbiota is an important component of the host microbiota and has been proven to be involved in regulating spermatogenesis, but the molecular mechanism is still unclear. A male mouse model with gut microbiota depletion/dysbiosis was constructed by adding combined antibiotics to free drinking water, and reproductive parameters such as epididymal sperm count, testicular weight and paraffin sections were measured. Testicular transcriptomic and serum metabolomic analyses were performed to reveal the molecular mechanism of reproductive dysfunction induced by gut microbiota dysbiosis in male mice.This study confirms that antibiotic induced depletion of gut microbiota reduces sperm count in the epididymis and reduces germ cells in the seminiferous tubules in male mice. Further study showed that exosomes isolated from microbiota-depleted mice led to abnormally high levels of retinoic acid and decrease in the number of germ cells in the seminiferous tubules and sperm in the epididymis. Finally, abnormally high levels of retinoic acid was confirmed to disrupted meiotic processes, resulting in spermatogenesis disorders. This study proposed the concept of the gut microbiota-exosome-retinoic acid-testicular axis and demonstrated that depletion of the gut microbiota caused changes in the function of exosomes, which led to abnormal retinoic acid metabolism in the testis, thereby impairing meiosis and spermatogenesis processes.

The elusive male microbiome: revealing the link between the genital microbiota and fertility. Critical review and future perspectives

There is a growing focus on understanding the role of the male microbiome in fertility issues. Although research on the bacterial communities within the male reproductive system is in its initial phases, recent discoveries highlight notable variations in the microbiome's composition and abundance across distinct anatomical regions like the skin, foreskin, urethra, and coronary sulcus. To assess the relationship between male genitourinary microbiome and reproduction, we queried various databases, including MEDLINE (available via PubMed), SCOPUS, and Web of Science to obtain evidence-based data. The literature search was conducted using the following terms "gut/intestines microbiome," "genitourinary system microbiome," "microbiome and female/male infertility," "external genital tract microbiome," "internal genital tract microbiome," and "semen microbiome." Fifty-one relevant papers were analyzed, and eleven were strictly semen quality or male fertility related. The male microbiome, especially in the accessory glands like the prostate, seminal vesicles, and bulbourethral glands, has garnered significant interest because of its potential link to male fertility and reproduction. Studies have also found differences in bacterial diversity present in the testicular tissue of normozoospermic men compared to azoospermic suggesting a possible role of bacterial dysbiosis and reproduction. Correlation between the bacterial taxa in the genital microbiota of sexual partners has also been found, and sexual activity can influence the composition of the urogenital microbiota. Exploring the microbial world within the male reproductive system and its influence on fertility opens doors to developing ways to prevent, diagnose, and treat infertility. The present work emphasizes the importance of using consistent methods, conducting long-term studies, and deepening our understanding of how the reproductive tract microbiome works. This helps make research comparable, pinpoint potential interventions, and smoothly apply microbiome insights to real-world clinical practices.

Environmental Heat Stress Decreases Sperm Motility by Disrupting the Diurnal Rhythms of Rumen Microbes and Metabolites in Hu Rams

Heat stress (HS) has become a common stressor, owing to the increasing frequency of extreme high-temperature weather triggered by global warming, which has seriously affected the reproductive capacity of important livestock such as sheep. However, little is known about whether HS reduces sperm motility by inducing circadian rhythm disorders in rumen microorganisms and metabolites in sheep. In this study, the year-round reproduction of two-year-old Hu rams was selected, and the samples were collected in May and July 2022 at average environmental temperatures between 18.71 °C and 33.58 °C, respectively. The experiment revealed that the mean temperature-humidity index was 86.34 in July, indicating that Hu rams suffered from HS. Our research revealed that HS significantly decreased sperm motility in Hu rams. Microbiome analysis further revealed that HS reshaped the composition and circadian rhythm of rumen microorganisms, leading to the circadian disruption of microorganisms that drive cortisol and testosterone synthesis. Serum indicators further confirmed that HS significantly increased the concentrations of cortisol during the daytime and decreased the testosterone concentration at the highest body temperature. Untargeted metabolomics analysis revealed that the circadian rhythm of rumen fluid metabolites in the HS group was enriched by the cortisol and steroid synthesis pathways. Moreover, HS downregulated metabolites, such as kaempferol and L-tryptophan in rumen fluid and seminal plasma, which are associated with promotion of spermatogenesis and sperm motility; furthermore, these metabolites were found to be strongly positively correlated with Veillonellaceae_UCG_001. Overall, this study revealed the relationship between the HS-induced circadian rhythm disruption of rumen microorganisms and metabolites and sperm motility decline. Our findings provide a new perspective for further interventions in enhancing sheep sperm motility with regard to the circadian time scale.

The potential influence and intervention measures of gut microbiota on sperm: it is time to focus on testis-gut microbiota axis

As the global male infertility rate continues to rise, there is an urgent imperative to investigate the underlying causes of sustained deterioration in sperm quality. The gut microbiota emerges as a pivotal factor in host health regulation, with mounting evidence highlighting its dual influence on semen. This review underscores the interplay between the Testis-Gut microbiota axis and its consequential effects on sperm. Potential mechanisms driving the dual impact of gut microbiota on sperm encompass immune modulation, inflammatory responses mediated by endotoxins, oxidative stress, antioxidant defenses, gut microbiota-derived metabolites, epigenetic modifications, regulatory sex hormone signaling. Interventions such as probiotics, prebiotics, synbiotics, fecal microbiota transplantation, and Traditional natural herbal extracts are hypothesized to rectify dysbiosis, offering avenues to modulate gut microbiota and enhance Spermatogenesis and motility. Future investigations should delve into elucidating the mechanisms and foundational principles governing the interaction between gut microbiota and sperm within the Testis-Gut microbiota Axis. Understanding and modulating the Testis-Gut microbiota Axis may yield novel therapeutic strategies to enhance male fertility and combat the global decline in sperm quality.

A multi-omics approach reveals that lotus root polysaccharide iron ameliorates iron deficiency-induced testicular damage by activating PPARγ to promote steroid hormone synthesis

Iron deficiency is a common nutritional issue that seriously affects male reproductive health. Lotus root polysaccharide iron (LRPF), a novel nutritional supplement, may ameliorate the damage caused by iron deficiency, however, the mechanism is unclear. In this study, we comprehensively determined the benefits of LRPF on reproduction in iron-deficient mice by integrating transcriptomics, microbiomics and serum metabolomics. Microbiomics showed that LRPF could restore changes to the intestinal microbiota caused by iron deficiency. Metabolomics results showed that LRPF stabilised steroid hormone and fatty acid metabolism in iron-deficient mice, reduced the content of ethyl chrysanthemumate (EC) and ameliorated the reproductive impairment. The transcriptomic analysis showed that LRPF regulated steroid hormone synthesis and the peroxisome proliferator-activated receptor (PPAR) signalling pathway in iron-deficient mice. In vitro experiments showed that LRPF could promote steroid hormone synthesis in Leydig cells by activating PPARγ. In conclusion, this study highlights the advantage of LRPF to improve testicular development.

Effects of Interactions between Feeding Patterns and the Gut Microbiota on Pig Reproductive Performance

The feeding mode is an important factor affecting the reproductive performance of pigs. The composition and expression of the intestinal microbiota are closely related to the physiological and biochemical indicators of animals. Therefore, to explore the impact of different feeding patterns on the reproductive performance of pigs, this study collected reproductive performance data from 1607 Yorkshire pigs raised under different feeding patterns and conducted a fixed-effect variance analysis. Among them, 731 were in the artificial feeding (AM) group and 876 were in the feeding station feeding (SM) group. Additionally, 40 Yorkshire sows in the late gestation period were randomly selected from each feeding mode for intestinal microbiota analysis. The results of the analysis showed that, in the AM group, both the number of birth deformities (NBD) and the number of stillbirths (NSB) were significantly greater than they were in the SM group (p < 0.05). Additionally, the total number born (TNB) in the AM group was significantly lower than that in the SM group (p < 0.05). The results of the intestinal microbiota analysis revealed that at the phylum level, there were significant differences in nine bacterial taxa between the AM and SM groups (p < 0.05). At the genus level, the abundance of a variety of beneficial bacteria related to reproductive performance in the SM group was significantly greater than that in the AM group. Finally, fecal metabolomic analysis revealed that the contents of butyric acid, isovaleric acid, valeric acid, and isobutyric acid, which are associated with reproductive performance, in the feces of sows in the SM group were significantly higher than those in the AM group (p < 0.05). These results indicate that different feeding methods can affect the gut microbiota composition of Yorkshire pigs and further influence the reproductive performance of pigs through the gut microbiota-metabolic product pathway. The results of this study provide valuable insights for further exploring the relationships between feeding modes, intestinal microbial composition, and host phenotypes.

Assessing Fecal Microbial Diversity and Hormone Levels as Indicators of Gastrointestinal Health in Reintroduced Przewalski's Horses (Equus ferus przewalskii)

Diarrhea serves as a vital health indicator for assessing wildlife populations post-reintroduction. Upon release into the wild, wild animals undergo adaptation to diverse habitats and dietary patterns. While such changes prompt adaptive responses in the fecal microbiota, they also render these animals susceptible to gastrointestinal diseases, particularly diarrhea. This study investigates variations in fecal microorganisms and hormone levels between diarrhea-afflicted and healthy Przewalski's horses. The results demonstrate a significant reduction in the alpha diversity of the fecal bacterial community among diarrheal Przewalski's horses, accompanied by notable alterations in taxonomic composition. Firmicutes, Proteobacteria, and Bacteroidetes emerge as dominant phyla across all fecal samples, irrespective of health status. However, discernible differences in fecal bacterial abundance are observed between healthy and diarrhea-stricken individuals at the genus level, specifically, a diminished relative abundance of Pseudobutyrivibrio is observed. The majority of the bacteria that facilitate the synthesis of short-chain fatty acids, Christensenellaceae_R_7_group (Christensenellaceae), NK4A214_group (Ruminococcus), Lachnospiraceae_XPB1014_group (Lachnospiraceae), [Eubacterium]_coprostanoligenes_group (Eubacterium), Rikenellaceae_RC9_gut_group, Lachnospiraceae_AC2044_group (Lachnospiraceae), and Prevotellaceae_UcG_001 (Prevotella) are noted in diarrhea-affected Przewalski's horses, while Erysipelotrichaceae, Phoenicibacter, Candidatus_Saccharimonas (Salmonella), and Mogibacterium are present in significantly increased amounts. Moreover, levels of immunoglobulin IgA and cortisol are significantly elevated in the diarrhea group compared with the non-diarrhea group. Overall, this study underscores substantial shifts in fecal bacterial diversity, abundance, and hormone levels in Przewalski's horses during episodes of diarrhea.

Differential gene expression and gut microbiota composition in low-altitude and high-altitude goats

Previous studies have presented evidence suggesting that altitude exerts detrimental effects on reproductive processes, yet the underlying mechanism remains elusive. Our study employed two distinct goat breeds inhabiting low and high altitudes, and conducted a comparative analysis of mRNA profiles in testis tissues and the composition of gut microbiota. The results revealed a reduced testis size in high-altitude goats. RNA-seq analysis identified the presence of 214 differentially expressed genes (DEGs) in the testis. These DEGs resulted in a weakened immunosuppressive effect, ultimately impairing spermatogenesis in high-altitude goats. Additionally, 16S rDNA amplicon sequencing recognized statistically significant variations in the abundance of the genera Treponema, unidentified_Oscillospiraceae, Desulfovibrio, Butyricicoccus, Dorea, Parabacteroides between the two groups. The collective evidence demonstrated the gut and testis played a synergistic role in causing decreased fertility at high altitudes. Our research provides a theoretical basis for future investigations into the reproductive fitness of male goats.

Multi-Omics Reveals the Role of Arachidonic Acid Metabolism in the Gut-Follicle Axis for the Antral Follicular Development of Holstein Cows

In vitro embryonic technology is crucial for improving farm animal reproduction but is hampered by the poor quality of oocytes and insufficient development potential. This study investigated the relationships among changes in the gut microbiota and metabolism, serum features, and the follicular fluid metabolome atlas. Correlation network maps were constructed to reveal how the metabolites affect follicular development by regulating gene expression in granulosa cells. The superovulation synchronization results showed that the number of follicle diameters from 4 to 8 mm, qualified oocyte number, cleavage, and blastocyst rates were improved in the dairy heifers (DH) compared with the non-lactating multiparous dairy cows (NDC) groups. The gut microbiota was decreased in Rikenellaceae_RC9_gut_group, Alistipes, and Bifidobacterium, but increased in Firmicutes, Cyanobacteria, Fibrobacterota, Desulfobacterota, and Verrucomicrobiota in the NDC group, which was highly associated with phospholipid-related metabolites of gut microbiota and serum. Metabolomic profiling of the gut microbiota, serum, and follicular fluid further demonstrated that the co-metabolites were phosphocholine and linoleic acid. Moreover, the expression of genes related to arachidonic acid metabolism in granulosa cells was significantly correlated with phosphocholine and linoleic acid. The results in granulosa cells showed that the levels of PLCB1 and COX2, participating in arachidonic acid metabolism, were increased in the DH group, which improved the concentrations of PGD2 and PGF2α in the follicular fluid. Finally, the expression levels of apoptosis-related proteins, cytokines, and steroidogenesis-related genes in granulosa cells and the concentrations of steroid hormones in follicular fluid were determinants of follicular development. According to our results, gut microbiota-related phosphocholine and linoleic acid participate in arachidonic acid metabolism in granulosa cells through the gut-follicle axis, which regulates follicular development. These findings hold promise for enhancing follicular development and optimizing oocyte quality in subfertile dairy cows.

Impairment of oocyte quality caused by gut microbiota dysbiosis in obesity

Obesity poses risks to oocyte maturation and embryonic development in mice and humans, linked to gut microbiota dysbiosis and altered host metabolomes. However, it is unclear whether symbiotic gut microbes have a pivotal role in oocyte quality. In mouse models of fecal microbiota transplantation, we demonstrated aberrant meiotic apparatus and impaired maternal mRNA in oocytes, which is coincident with the poor developmental competence of embryos. Using metabolomics profiling, we discovered that the cytosine and cytidine metabolism was disturbed, which could account for the fertility defects observed in the high-fat diet (HFD) recipient mice. Additionally, cytosine and cytidine are closely related with gut microbiota dysbiosis, which is accompanied by a notable reduction of abundance of Christensenellaceae R-7 group in the HFD mice. In summary, our findings provided evidence that modifying the gut microbiota may be of value in the treatment of infertile female individuals with obesity.

Causal relationship between gut microbiota and male erectile dysfunction: a Mendelian randomization analysis

Background

Several observational studies have reported an association between gut microbiota and male erectile dysfunction (ED). However, it remains unclear whether there is a causal relationship between gut microbiota and male ED. Thus, we aimed to investigate the potential causal relationship between gut microbiota and male ED through Mendelian randomization (MR) analysis.

Objective

To assess the causal relationship between gut microbiota and male ED, we performed a two-sample MR analysis.

Methods

We obtained gut microbiota genome-wide association studies (GWAS) data from the MiBioGen consortium and publicly available GWAS data on male ED from the OPEN GWAS database. Subsequently, we performed a two-sample MR analysis to evaluate the causal relationship between gut microbiota and male ED. Finally, we performed sensitivity analysis, including Cochran's Q test, MR-Egger intercept analysis, MR-PRESSO, and leave-one-out analysis, to assess the level of heterogeneity and horizontal pleiotropy in the results.

Results

Our MR analysis revealed a negative causal relationship between the genus Ruminococcaceae UCG013 and male ED (OR = 0.761, 95% CI 0.626-0.926), while the family Lachnospiraceae, genus Lachnospiraceae NC2004 group, genus Oscillibacter, and genus Tyzzerella3 may be associated with an increased risk of male ED, with the highest risk observed for family Lachnospiraceae (OR = 1.264, 95% CI 1.063-1.504). Furthermore, sensitivity analysis confirmed the reliability of our positive findings.

Conclusion

Our MR analysis revealed a causal relationship between gut microbiota and male ED. This may contribute to a better understanding of the potential applications of gut microbiota in the occurrence and treatment of male ED.

Bidirectional Mendelian randomization to explore the causal relationships between the gut microbiota and male reproductive diseases

Gut bacteria might play an important role in male reproductive disorders, such as male infertility and sperm abnormalities; however, their causal role is unclear. Herein, Mendelian randomization (MR)-Egger, weighted median, inverse variance weighting, Simple mode, and Weighted mode were used to test the causal relationship between gut microbes and male reproductive diseases. The MR results were validated using various metrics. The MR results were also consolidated using reverse causality speculation, conducted using two-way MR analysis and Steiger filtering. Biological function was analysed using enrichment analyses. The results suggested that eight intestinal microflorae were causally associated with male infertility. The Eubacterium oxidoreducens group was associated with an increased risk of male infertility, while the family Bacteroidaceae was negatively associated with male reproductive diseases. Eight intestinal microflorae were causally associated with abnormal spermatozoa. The family Streptococcaceae was associated with a high risk of abnormal spermatozoa, whereas the family Porphyromonadaceae was associated with a low risk of abnormal spermatozoa. No pleiotropy was observed, this study identified a high correlation between the gut flora and the likelihood of male reproductive diseases. Future research will attempt to advance microbial-focused treatments for such diseases.

Advances in single-cell transcriptomics in animal research

Understanding biological mechanisms is fundamental for improving animal production and health to meet the growing demand for high-quality protein. As an emerging biotechnology, single-cell transcriptomics has been gradually applied in diverse aspects of animal research, offering an effective method to study the gene expression of high-throughput single cells of different tissues/organs in animals. In an unprecedented manner, researchers have identified cell types/subtypes and their marker genes, inferred cellular fate trajectories, and revealed cell‒cell interactions in animals using single-cell transcriptomics. In this paper, we introduce the development of single-cell technology and review the processes, advancements, and applications of single-cell transcriptomics in animal research. We summarize recent efforts using single-cell transcriptomics to obtain a more profound understanding of animal nutrition and health, reproductive performance, genetics, and disease models in different livestock species. Moreover, the practical experience accumulated based on a large number of cases is highlighted to provide a reference for determining key factors (e.g., sample size, cell clustering, and cell type annotation) in single-cell transcriptomics analysis. We also discuss the limitations and outlook of single-cell transcriptomics in the current stage. This paper describes the comprehensive progress of single-cell transcriptomics in animal research, offering novel insights and sustainable advancements in agricultural productivity and animal health.

Effects of microbiota-testis interactions on the reproductive health of male ruminants: A review

Ruminants are one of the world's economically important species, and their reproductive health is critical to the economic development of the livestock industry. In recent years, research on the relationship between microbiota and reproductive health has received much attention. Microbiota disruption affects the developmental health of the testes and epididymis, the male reproductive organs of the host, which in turn is related to sperm quality. Maintaining a stable microbiota protects the host from pathogens and increases breeding performance, which in turn promotes the economic development of animal husbandry. In addition, the effects and mechanisms of microbiota on reproduction were further explored. These findings support new approaches to improving and managing reproductive health in ruminants through the microbiota and facilitate further systematic exploration of microbiota-mediated reproductive impacts.

Effects of polycyclic aromatic hydrocarbons on the gut-testis axis

Polycyclic aromatic hydrocarbons (PAHs) are a large group of organic compounds which are comprised of two or more fused benzene rings. As a typical environmental pollutant, PAHs are widely distributed in water, soil, atmosphere and food. Despite extensive researches on the mechanisms of health damage caused by PAHs, especially their carcinogenic and mutagenic toxicity, there is still a lack of comprehensive summarization and synthesis regarding the mechanisms of PAHs on the gut-testis axis, which represents an intricate interplay between the gastrointestinal and reproductive systems. Thus, this review primarily focuses on the potential forms of interaction between PAHs and the gut microbiota and summarizes their adverse outcomes that may lead to gut microbiota dysbiosis, then compiles the possible mechanistic pathways on dysbiosis of the gut microbiota impairing the male reproductive function, in order to provide valuable insights for future research and guide further exploration into the intricate mechanisms underlying the impact of gut microbiota dysbiosis caused by PAHs on male reproductive function.

Understanding testicular single cell transcriptional atlas: from developmental complications to male infertility

Spermatogenesis is a multi-step biological process where mitotically active diploid (2n) spermatogonia differentiate into haploid (n) spermatozoa via regulated meiotic programming. The alarming rise in male infertility has become a global concern during the past decade thereby demanding an extensive profiling of testicular gene expression. Advancements in Next-Generation Sequencing (NGS) technologies have revolutionized our empathy towards complex biological events including spermatogenesis. However, despite multiple attempts made in the past to reveal the testicular transcriptional signature(s) either with bulk tissues or at the single-cell, level, comprehensive reviews on testicular transcriptomics and associated disorders are limited. Notably, technologies explicating the genome-wide gene expression patterns during various stages of spermatogenic progression provide the dynamic molecular landscape of testicular transcription. Our review discusses the advantages of single-cell RNA-sequencing (Sc-RNA-seq) over bulk RNA-seq concerning testicular tissues. Additionally, we highlight the cellular heterogeneity, spatial transcriptomics, dynamic gene expression and cell-to-cell interactions with distinct cell populations within the testes including germ cells (Gc), Sertoli cells (Sc), Peritubular cells (PTc), Leydig cells (Lc), etc. Furthermore, we provide a summary of key finding of single-cell transcriptomic studies that have shed light on developmental mechanisms implicated in testicular disorders and male infertility. These insights emphasize the pivotal roles of Sc-RNA-seq in advancing our knowledge regarding testicular transcriptional landscape and may serve as a potential resource to formulate future clinical interventions for male reproductive health.

Sleep deprivation causes gut dysbiosis impacting on systemic metabolomics leading to premature ovarian insufficiency in adolescent mice

Rationale: Currently, there are occasional reports of health problems caused by sleep deprivation (SD). However, to date, there remains a lack of in-depth research regarding the effects of SD on the growth and development of oocytes in females. The present work aimed to investigate whether SD influences ovarian folliculogenesis in adolescent female mice. Methods: Using a dedicated device, SD conditions were established in 3-week old female mice (a critical stage of follicular development) for 6 weeks and gut microbiota and systemic metabolomics were analyzed. Analyses were related to parameters of folliculogenesis and reproductive performance of SD females. Results: We found that the gut microbiota and systemic metabolomics were severely altered in SD females and that these were associated with parameters of premature ovarian insufficiency (POI). These included increased granulosa cell apoptosis, reduced numbers of primordial follicles (PmFs), correlation with decreased AMH, E2, and increased LH in blood serum, and a parallel increased number of growing follicles and changes in protein expression compatible with PmF activation. SD also reduced oocyte maturation and reproductive performance. Notably, fecal microbial transplantation from SD females into normal females induced POI parameters in the latter while niacinamide (NAM) supplementation alleviated such symptoms in SD females. Conclusion: Gut microbiota and alterations in systemic metabolomics caused by SD induced POI features in juvenile females that could be counteracted with NAM supplementation.

Gut-Derived Exosomes Mediate the Microbiota Dysbiosis-Induced Spermatogenesis Impairment by Targeting Meioc in Mice

Diseases like obesity and intestinal inflammation diseases are accompanied by dysbiosis of the gut microbiota (DSGM), which leads to various complications, including systemic metabolic disorders. DSGM reportedly impairs the fertility of male mice; however, the regulatory mechanism is unclear. Exosomes are molecular mediators of intercellular communication, but the regulation of spermatogenesis by non-reproductive tissue-originated exosomes remains unknown. The present study shows that DSGM altered the miRNA expression profile of mouse circulating exosomes and impaired spermatogenesis. Moreover, the single-cell sequencing results indicate that circulating exosomes from mice with DSGM impaired spermatogenesis, while circulating exosomes from wild mice improved spermatogenesis by promoting meiosis. Further study demonstrates that DSGM leads to abnormal upregulation of miR-211-5p in gut-derived circulating exosomes, which inhibited the expression of meiosis-specific with coiled-coil domain (Meioc) in the testes and impaired spermatogenesis by disturbing meiosis process. In summary, this study defines the important role of gut-derived exosomes in connecting the "gut-testis" axis.

Causal effect between gut microbiota and metabolic syndrome in European population: a bidirectional mendelian randomization study

BACKGROUND

Observational studies have reported that gut microbiota composition is associated with metabolic syndrome. However, the causal effect of gut microbiota on metabolic syndrome has yet to be confirmed.

METHODS

We performed a bidirectional Mendelian randomization study to investigate the causal effect between gut microbiota and metabolic syndrome in European population. Summary statistics of gut microbiota were from the largest available genome-wide association study meta-analysis (n = 13,266) conducted by the MiBioGen consortium. The summary statistics of outcome were obtained from the most comprehensive genome-wide association studies of metabolic syndrome (n = 291,107). The inverse-variance weighted method was applied as the primary method, and the robustness of the results was assessed by a series of sensitivity analyses.

RESULTS

In the primary causal estimates, Actinobacteria (OR = 0.935, 95% CI = 0.878-0.996, P = 0.037), Bifidobacteriales (OR = 0.928, 95% CI = 0.868-0.992, P = 0.028), Bifidobacteriaceae (OR = 0.928, 95% CI = 0.868-0.992, P = 0.028), Desulfovibrio (OR = 0.920, 95% CI = 0.869-0.975, P = 0.005), and RuminococcaceaeUCG010 (OR = 0.882, 95% CI = 0.803-0.969, P = 0.009) may be associated with a lower risk of metabolic syndrome, while Lachnospiraceae (OR = 1.130, 95% CI = 1.016-1.257, P = 0.025), Veillonellaceae (OR = 1.055, 95% CI = 1.004-1.108, P = 0.034) and Olsenella (OR = 1.046, 95% CI = 1.009-1.085, P = 0.015) may be linked to a higher risk for metabolic syndrome. Reverse MR analysis demonstrated that abundance of RuminococcaceaeUCG010 (OR = 0.938, 95% CI = 0.886-0.994, P = 0.030) may be downregulated by metabolic syndrome. Sensitivity analyses indicated no heterogeneity or horizontal pleiotropy.

CONCLUSIONS

Our Mendelian randomization study provided causal relationship between specific gut microbiota and metabolic syndrome, which might provide new insights into the potential pathogenic mechanisms of gut microbiota in metabolic syndrome and the assignment of effective therapeutic strategies.

Multiomics Reveals the Microbiota and Metabolites Associated with Sperm Quality in Rongchang Boars

In this study, we investigated the correlation between the composition and function of the gut microbiota and the semen quality of Rongchang boars. Significant differences in gut microbial composition between boars with high (group H) and low (group L) semen utilization rates were identified through 16S rRNA gene sequencing, with 18 differential microbes observed at the genus level. Boars with lower semen utilization rates exhibited a higher relative abundance of Treponema, suggesting its potential role in reducing semen quality. Conversely, boars with higher semen utilization rates showed increased relative abundances of Terrisporobacter, Turicibacter, Stenotrophomonas, Clostridium sensu stricto 3, and Bifidobacterium, with Stenotrophomonas and Clostridium sensu stricto 3 showing a significant positive correlation with semen utilization rates. The metabolomic analyses revealed higher levels of gluconolactone, D-ribose, and 4-pyridoxic acid in the H group, with 4 pyridoxic acid and D-ribose showing a significant positive correlation with Terrisporobacter and Clostridium sensu stricto 3, respectively. In contrast, the L group showed elevated levels of D-erythrose-4-phosphate, which correlated negatively with Bifidobacterium and Clostridium sensu stricto 3. These differential metabolites were enriched in the pentose phosphate pathway, vitamin B6 metabolism, and antifolate resistance, potentially influencing semen quality. These findings provide new insights into the complex interplay between the gut microbiota and boar reproductive health and may offer important information for the discovery of disease biomarkers and reproductive health management.

Heat stress-induced dysbiosis of the gut microbiota impairs spermatogenesis by regulating secondary bile acid metabolism in the gut

Heat stress (HS) poses a substantial challenge to livestock. Studies have demonstrated that HS reduces fertility and leads to gut microbiota dysbiosis in bulls. However, the impact of the gut microbiota on fertility in bulls during HS is still unclear. Our research revealed that HS exposure decreased semen quality in bulls, and fecal microbiota transplantation (FMT) from heat-stressed bulls to recipient mice resulted in a significant decrease in number of testicular germ cells and epididymal sperm. Untargeted metabolomics methodology and 16S rDNA sequencing conjoint analysis revealed that Akkermansia muciniphila (A. muciniphila) seemed to be a key bacterial regulator of spermatogenesis after HS exposure. Moreover, the research indicated that A. muciniphila regulated secondary bile acid metabolism by promoting the colonization of bile salt hydrolase (BSH)-metabolizing bacteria, leading to increase of retinol absorption in the host gut and subsequently elevation of testicular retinoic acid level, thereby improving spermatogenesis. This study sheds light on the relationship between HS-induced microbiota dysbiosis and spermatogenesis, offering a potential therapeutic approach for addressing bull spermatogenic dysfunction triggered by HS exposure.

The gut microbiota contributes to methamphetamine-induced reproductive toxicity in male mice

Methamphetamine (METH) is a psychostimulant drug belonging to the amphetamine-type stimulant class, known to exert male reproductive toxicity. Recent studies suggest that METH can disrupt the gut microbiota. Furthermore, the gut-testis axis concept has gained attention due to the potential link between gut microbiome dysfunction and reproductive health. Nonetheless, the role of the gut microbiota in mediating the impact of METH on male reproductive toxicity remains unclear. In this study, we employed a mouse model exposed to escalating doses of METH to assess sperm quality, testicular pathology, and reproductive hormone levels. The fecal microbiota transplantation method was employed to investigate the effect of gut microbiota on male reproductive toxicity. Transcriptomic, metabolomic, and microbiological analyses were conducted to explore the damage mechanism to the male reproductive system caused by METH. We found that METH exposure led to hormonal disorders, decreased sperm quality, and changes in the gut microbiota and testicular metabolome in mice. Testicular RNA sequencing revealed enrichment of several Gene Ontology terms associated with reproductive processes, as well as PI3K-Akt signaling pathways. FMT conveyed similar reproductive damage from METH-treated mice to healthy recipient mice. The aforementioned findings suggest that the gut microbiota plays a substantial role in facilitating the reproductive toxicity caused by METH, thereby highlighting a prospective avenue for therapeutic intervention in the context of METH-induced infertility.

Chronic exposure to tire rubber-derived contaminant 6PPD-quinone impairs sperm quality and induces the damage of reproductive capacity in male mice

It has been reported that N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q), a derivative of the tire antioxidant, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), exhibits acute toxicity towards organisms. However, the possible reproductive toxicity of 6PPD-Q in mammals has rarely been reported. In this study, the effects of 6PPD-Q on the reproductive toxicity of C57Bl/6 male mice were assessed after exposure to 6PPD-Q for 40 days at 4 mg/kg body weight (bw). Exposure to 6PPD-Q not only led to a decrease in testosterone levels but also adversely affected semen quality and in vitro fertilization (IVF) outcomes, thereby indicating impaired male fertility resulting from 6PPD-Q exposure. Additionally, transcriptomic and metabolomic analyses revealed that 6PPD-Q elicited differential expression of genes and metabolites primarily enriched in spermatogenesis, apoptosis, arginine biosynthesis, and sphingolipid metabolism in the testes of mice. In conclusion, our study reveals the toxicity of 6PPD-Q on the reproductive capacity concerning baseline endocrine disorders, sperm quality, germ cell apoptosis, and the sphingolipid signaling pathway in mice. These findings contribute to an enhanced understanding of the health hazards posed by 6PPD-Q to mammals, thereby facilitating the development of more robust safety regulations governing the utilization and disposal of rubber products.

Gut microbiota is involved in male reproductive function: a review

Globally, ~8%-12% of couples confront infertility issues, male-related issues being accountable for 50%. This review focuses on the influence of gut microbiota and their metabolites on the male reproductive system from five perspectives: sperm quality, testicular structure, sex hormones, sexual behavior, and probiotic supplementation. To improve sperm quality, gut microbiota can secrete metabolites by themselves or regulate host metabolites. Endotoxemia is a key factor in testicular structure damage that causes orchitis and disrupts the blood-testis barrier (BTB). In addition, the gut microbiota can regulate sex hormone levels by participating in the synthesis of sex hormone-related enzymes directly and participating in the enterohepatic circulation of sex hormones, and affect the hypothalamic-pituitary-testis (HPT) axis. They can also activate areas of the brain that control sexual arousal and behavior through metabolites. Probiotic supplementation can improve male reproductive function. Therefore, the gut microbiota may affect male reproductive function and behavior; however, further research is needed to better understand the mechanisms underlying microbiota-mediated male infertility.

Study on the correlation of supplementation with L-citrulline on the gastrointestinal flora and semen antifreeze performance of ram

INTRODUCTION

Cryopreservation of semen can give full play to the reproductive advantages of male animals. However, in actual production, due to the poor frost resistance of sheep semen and the low conception rate, the promotion of sheep frozen semen is greatly hindered. Therefore, it is urgent to improve the frost resistance of semen to improve the quality of frozen semen. At present, most studies on improving the quality of frozen semen are based on the improvement of semen dilutions, and few studies on improving the freezing resistance of ram semen by feeding functional amino acids.

METHODS

Therefore, 24 Turpan black rams were divided into high antifreeze group (HF) and a low antifreeze group (LF) Each of these groups was further randomly divided into control and experimental subgroups. The control subgroup was fed a basal diet, while the experimental subgroup received an additional 12 g/d of L-Cit supplementation based on the control group for a duration of 90 days.

RESULTS

The results showed that Following L-Cit supplementation, the experimental group demonstrated significantly elevated sperm density and VSL (Velocity of straight line), T-AOC, GSH-Px, and NO levels in fresh semen compared to the control group (P < 0.01). After thawing, the experimental group exhibited significantly higher levels of T-AOC, GSH-Px, and NO compared to the control group (P < 0.01). Additionally, the HFT group, after thawing frozen semen, displayed significantly higher HK1 protein expression compared to the control group. The number of spermatogonia, spermatocytes, and sperm cells in the HFT group was significantly higher than that in the HFC group. Moreover, 16S rRNA sequence analysis showed that Candidatus_Saccharimonas, Staphylococcus, Weissella, succinivbrionaceae_UcG_002, and Quinella were significantly enriched in the rumen of the HFT group, while Ureaplasma was significantly enriched in the HFC group. In the duodenum, Clostridiales_bacterium_Firm_14, Butyrivibrio, and Prevotellaceae_NK3831_group were significantly enriched in the HFT group, whereas Desulfovibrio and Quinella were significantly enriched in the HFC group.

DISCUSSION

Under the conditions employed in this study, L-Cit supplementation was found to enhance the intestinal flora composition in rams, thereby improving semen quality, enhancing the antifreeze performance of semen, and promoting the development of testicular spermatogenic cells.

Inflammatory cytokines may mediate the causal relationship between gut microbiota and male infertility: a bidirectional, mediating, multivariate Mendelian randomization study

Introduction

Studies have shown that the gut microbiota is associated with male infertility (MI). However, their causal relationship and potential mediators need more evidence to prove. We aimed to investigate the causal relationship between the gut microbiome and MI and the potential mediating role of inflammatory cytokines from a genetic perspective through a Mendelian randomization approach.

Methods

This study used data from genome-wide association studies of gut microbes (Mibiogen, n = 18, 340), inflammatory cytokines (NFBC1966, FYPCRS, FINRISK 1997 and 2002, n=13, 365), and male infertility (Finngen, n=120, 706) to perform two-way Mendelian randomization (MR), mediated MR, and multivariate MR(MVMR) analyses. In this study, the inverse variance weighting method was used as the primary analysis method, and other methods were used as supplementary analysis methods.

Results

In the present study, two gut microbes and two inflammatory cytokines were found to have a potential causal relationship with MI. Of the two gut microorganisms causally associated with male infertility, Anaerotruncus increased the risk of male infertility (odds ratio = 1.81, 95% confidence interval = 1.18-2.77, P = 0.0062), and Bacteroides decreased the risk of male infertility (odds ratio = 0.57, 95% confidence interval = 0.33-0.96, P = 0.0363). In addition, of the two inflammatory cytokines identified, hepatocyte growth factor(HGF) reduced the risk of male infertility (odds ratio = 0.50, 95% confidence interval = 0.35-0.71, P = 0.0001), Monocyte chemotactic protein 3 (MCP-3) increased the risk of male infertility (odds ratio = 1.28, 95% confidence interval = 1.03-1.61, P = 0.0039). Mediated MR analysis showed that HGF mediated the causal effect of Bacteroides on MI (mediated percentage 38.9%). Multivariate MR analyses suggest that HGF may be one of the pathways through which Bacteroides affects MI, with other unexplored pathways.

Conclusion

The present study suggests a causal relationship between specific gut microbiota, inflammatory cytokines, and MI. In addition, HGF may mediate the relationship between Bacteroides and MI.