Male reproductive system and antioxidants in oxidative stress induced by hypobaric hypoxia

Effects of Reactive Oxygen and Nitrogen Species on Male Fertility

Significance: In recent decades, male fertility has been severely reduced worldwide. The causes underlying this decline are multifactorial, and include, among others, genetic alterations, changes in the microbiome, and the impact of environmental pollutants. Such factors can dysregulate the physiological levels of reactive species of oxygen (ROS) and nitrogen (RNS) in the patient, generating oxidative and nitrosative stress that impairs fertility. Recent Advances: Recent studies have delved into other factors involved in the dysregulation of ROS and RNS levels, such as diet, obesity, persistent infections, environmental pollutants, and gut microbiota, thus leading to new strategies to solve male fertility problems, such as consuming prebiotics to regulate gut flora or treating psychological conditions. Critical Issues: The pathways where ROS or RNS may be involved as modulators are still under investigation. Moreover, the extent to which treatments can rescue male infertility as well as whether they may have side effects remains, in most cases, to be elucidated. For example, it is known that prescription of antioxidants to treat nitrosative stress can alter sperm chromatin condensation, which makes DNA more exposed to ROS and RNS, and may thus affect fertilization and early embryo development. Future Directions: The involvement of extracellular vesicles, which might play a crucial role in cell communication during spermatogenesis and epididymal maturation, and the relevance of other factors such as sperm epigenetic signatures should be envisaged in the future.

Cascading effects of hypobaric hypoxia on the testis: insights from a single-cell RNA sequencing analysis

Most mammals tolerate exposure to hypobaric hypoxia poorly as it may affect multiple regulatory mechanisms and inhibit cell proliferation, promote apoptosis, limit tissue vascularization, and disrupt the acid-base equilibrium. Here, we quantified the functional state of germ cell development and demonstrated the interaction between the germ and somatic cells via single-cell RNA sequencing (scRNA-seq). The present study elucidated the regulatory effects of hypobaric hypoxia exposure on germ cell formation and sperm differentiation by applying enrichment analysis to genomic regions. Hypobaric hypoxia downregulates the genes controlling granule secretion and organic matter biosynthesis, upregulates tektin 1 (TEKT1) and kinesin family member 2C (KIF2C), and downregulates 60S ribosomal protein 11 (RPL11) and cilia- and flagella-associated protein 206 (CFAP206). Our research indicated that prosaposin-G protein-coupled receptor 37 (PSAP-GPR37) ligands mediate the damage to supporting cells caused by hypobaric hypoxic exposure. The present work revealed that hypoxia injures peritubular myoid (PTM) cells and spermatocytes in the S phase. It also showed that elongating spermatids promote maturation toward the G2 phase and increase their functional reserve for sperm-egg binding. The results of this study provide a theoretical basis for future investigations on prophylactic and therapeutic approaches toward protecting the reproductive system against the harmful effects of hypobaric hypoxic exposure.

Fertility Impairment after Trekking at High Altitude: A Proof of Mechanisms on Redox and Metabolic Seminal Changes

Many authors described negative but reversible effects of high-altitude hypoxic exposure on animal and human fertility in terms of sperm concentration, function, and biochemical alterations. The aim of this study was to evaluate the acute and chronic effects of high-altitude exposure on classical sperm parameters, redox status, and membrane composition in a group of travellers. Five healthy Italian males, all lowlanders not accustomed to the altitude, were evaluated after 19 days-trekking through low, moderate, and high altitudes in the Himalayas. Sperm samples were collected before (Pre), 10 days after (Post), and 70 days after the end of the expedition (Follow-up). Sperm concentration, cholesterol and oxysterol membrane content, and redox status were measured. Hypoxic trek led to a significant reduction in sperm concentration (p < 0.001, η2p = 0.91), with a reduction from Pre to Post (71.33 ± 38.81 to 60.65 ± 34.63 × 106/mL) and a further reduction at Follow-up (to 37.13 ± 39.17 × 106/mL). The seminal volume was significantly affected by the hypoxic trek (p = 0.001, η2p = 0.75) with a significant reduction from Pre to Post (2.86 ± 0.75 to 1.68 ± 0.49 mL) and with partial recovery at Follow-up (to 2.46 ± 0.45 mL). Moreover, subjects had an increase in ROS production (+86%), and a decrease in antioxidant capacity (−37%) in the Post period with partial recovery at Follow-up. These results integrated the hormonal response on thyroid function, hypothalamus−pituitary−gonadal axis, and the prolactin/cortisol pathways previously reported. An uncontrolled ROS production, rather than a compromised antioxidant activity, was likely the cause of impaired sperm quality. The reduction in fertility status observed in this study may lie in an evolutionary Darwinian explanation, i.e., limiting reproduction due to the “adaptive disadvantage” offered by the combined stressors of high-altitude hypoxia and daily physical exercise.

Hypobaric hypoxia exposure alters transcriptome in mouse testis and impairs spermatogenesis in offspring

Male fertility relies on continual and robust spermatogenesis. Environmental hypoxia adversely affects reproductive health in humans and animal studies provide compelling evidences that hypoxia impairs spermatogenesis in directly exposed individuals. However, a detail examination of hypoxia induced changes in testicular gene expression is still lacking and spermatogenesis in offspring of hypoxia exposed animals of awaits investigation. In this study, a hypobaric hypoxic chamber was used to simulate hypoxic conditions in mice and effects of hypoxia on spermatogenesis, fertility and testicular gene expression were evaluated. The results showed that hypoxia exposure reduced the number of undifferentiated spermatogonia but did not change the regenerative capacity of spermatogonial stem cells (SSCs) after transplantation. Hypoxia significantly increased the percent of abnormal sperm and these defects were recovered 2 months after returning to the normoxia. Transcriptome analysis of testicular tissues from control and hypoxia treated animals revealed that 766 genes were up-regulated and 965 genes were down-regulated. Surprisingly, expressions of genes that regulate epigenetic modifications were altered, indicating hypoxia-induced damage to spermatogenesis may be intergenerational. Indeed, animals that were sired by hypoxia exposed males exhibited impaired spermatogenesis. Together, these findings suggest that hypoxia exposure alters testicular gene expression and causes long-lasting damage to spermatogenesis.

Effects of chronic intermittent hypobaric hypoxia on prostate-specific antigen (PSA) in Chilean miners

OBJECTIVE

The aim was to determine the effects of chronic intermittent hypobaric hypoxia (CIHH) on prostate-specific antigen (PSA) levels in Chilean miners who work at different altitudes.

METHODS

A cross-sectional study was conducted between April and July 2019. Miners from five mines (N=338) at different altitudes were evaluated. We recorded sociodemographic, working and altitude information. Haemoglobin oxygen saturation (SaO2) and haemoglobin (Hb) were measured in situ, while PSA and testosterone were analysed at a low level. Linear mixed-effect models were used to evaluate the association between PSA level and two CIHH exposures: composite CIHH (with four descriptors) and ChileStd-CIHH (CIHH Chilean standard; based on the Chilean technical guide for occupational exposure to CIHH). All models were adjusted by age, body mass index and day of the work the samples were taken.

RESULTS

Highest and lowest PSA levels were found in mines ≥3000 m above sea level (mine 3: median=0.75, IQR=-0.45; mine 4: median=0.46, IQR=-0.35). In the multilevel models, the wider altitude difference between mining operation and camp showed lower PSA levels (model D: βPSA=-0.93 ng/mL, βlogPSA=-0.07, p<0001), adjusted for other CIHH descriptors, SaO2, Hb and testosterone. The descriptors of composite CIHH explained better PSA variations than ChileStd-CIHH (model D: marginal R2=0.090 vs model A: marginal R2=0.016).

CONCLUSIONS

Occupational health regulations and high altitude medicine should consider these results as initial evidence on the inclusion of new descriptors for CIHH and the possible effect of this exposure on PSA levels in this male-dominated occupational sector.

iTRAQ-based proteomic analysis of sperm reveals candidate proteins that affect the quality of spermatozoa from boars on plateaus

Background

Tibetan pigs (TP) exhibit heritable adaptations to their hypoxic environments as a result of natural selection. However, candidate proteins that affect the sperm quality of boars on plateaus have not yet been clearly investigated.

Methods

In this study, to reveal the candidate proteins that affect the quality of spermatozoa of boars on plateaus, we analyzed the sperm quality using computer-assisted semen analysis (CASA) system and reactive oxygen species (ROS) levels. We also compared the proteomes of sperm proteomes between TP and Yorkshire pigs (YP) raised at high altitudes using the isobaric tags for relative and absolute quantitation (iTRAQ) in combination with the liquid chromatography-tandem mass spectrometry (LC–MS/MS) proteomic method, and confirmed the relative expression levels of the four proteins by western blotting.

Results

The sperm quality of the TP was superior to that of the YP on plateaus. Of the 1,555 quantified proteins, 318 differentially expressed proteins (DEPs) were identified. Gene ontology (GO) analysis revealed that the DEPs were predominantly associated with the sorbitol metabolic process, removal of superoxide radicals, cellular response to superoxide, response to superoxide and regulation of the mitotic spindle assembly. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were mainly enriched in pathways involved in the regulation of the actin cytoskeleton, glutathione metabolism, oxidative phosphorylation, and estrogen signaling. Based on the protein–protein interaction (PPI) network analysis, we identified 8 candidate proteins (FN1, EGF, HSP90B1, CFL1, GPX4, NDUFA6, VDAC2, and CP) that might play important roles and affect the sperm quality of boars on plateaus. Moreover, the relative expression levels of four proteins (CFL1, EGF, FN1, and GPX4) were confirmed by western blot analysis.

Conclusions

Our study revealed 8 candidate proteins (FN1, EGF, HSP90B1, CFL1, GPX4, NDUFA6, VDAC2, and CP) that affect the sperm quality of boar on plateaus and provide a reference for further studies on improving sperm quality and the molecular breeding of boars on plateaus.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12953-021-00177-9.

Effects of leptin on HPG axis and reproductive function in male rat in simulated altitude of 5500 m hypoxia environment

High altitude hypobaric hypoxia environment impairs male's reproductive function. Leptin is an adipose tissue-derived hormone which regulates body weight homeostasis. Its receptor (LepR) has been found in all levels of male reproductive axis, indicating that it can affect male reproductive system in a direct or (and) indirect way. However, the role of leptin signaling in hypobaric hypoxia induced male reproductive dysfunction remains to be elucidated. In this study, we investigated the changes of leptin levels in male SD rats in stimulated altitude of 5500 m hypobaric hypoxia environment and their effects on the hypothalamus-pituitary-gonad axis (HPG axis). A hypoxia animal model was established using a hypobaric hypoxia chamber. Rats were divided randomly into 1, 7, 14, 28-day hypoxia group, recovery group (14 days hypoxia+14 days normoxia) and their control groups. Hypoxia groups displayed obvious changes of testicular and epididymis index compared to control groups. The total number of sperm and sperm motility rate decreased dramatically, while sperm deformity rate increased in hypoxia groups. The flow cytometry analysis showed that the percentage of haploid in 1-day, 7-day and 28-day hypoxia groups increased while the proportion of diploid decreased in 14-day and 28-day hypoxia group. TUNEL staining showed that the testis cells apoptosis index (AI) of hypoxia groups increased significantly, and the apoptosis of cells mainly focus on spermatogonia and spermatocytes. The expression of GnRH in hypothalamus decreased dramatically under hypoxia condition, accompanied with the reduction of serum testosterone (T) level in 1-day and 28-day hypoxia groups and free-testosterone level (FT) in 1-day and 14-day hypoxia groups. Importantly, ELISA analysis showed that serum leptin level decreased in 7-day hypoxia groups and acylated-ghrelin, gastrin also changed, accompanying with reduction of LepR in hypothalamus in hypoxia groups. Immunohistochemical staining exhibited increased leptin and LepR in testis under hypobaric hypoxia conditions. Our results suggested that simulated high altitude hypobaric hypoxia environment decreased male reproductive function, depressed HPG axis activity and altered the serum concentration of hormones related to food intake in adult male rats. Additionally, hypobaric hypoxia induced the leptin-LepR expression in adult male rats' testis, suggesting leptin-LepR signaling may mediate hypoxia-induced impairment in male rats' reproductive system.

Immigrant reproductive dysfunction facilitates ecological speciation

The distributions of species are not only determined by where they can survive - they must also be able to reproduce. Although immigrant inviability is a well-established concept, the fact that immigrants also need to be able to effectively reproduce in foreign environments has not been fully appreciated in the study of adaptive divergence and speciation. Fertilization and reproduction are sensitive life-history stages that could be detrimentally affected for immigrants in non-native habitats. We propose that "immigrant reproductive dysfunction" is a hitherto overlooked aspect of reproductive isolation caused by natural selection on immigrants. This idea is supported by results from experiments on an externally fertilizing fish (sand goby, Pomatoschistus minutus). Growth and condition of adults were not affected by non-native salinity whereas males spawning as immigrants had lower sperm motility and hatching success than residents. We interpret these results as evidence for local adaptation or acclimation of sperm, and possibly also components of paternal care. The resulting loss in fitness, which we call "immigrant reproductive dysfunction," has the potential to reduce gene flow between populations with locally adapted reproduction, and it may play a role in species distributions and speciation.

Effects of Arctium lappa on Cadmium-Induced Damage to the Testis and Epididymis of Adult Wistar Rats

The protective role of Arctium lappa (AL) on the testes of rats acutely exposed to cadmium (Cd) was tested. The rats were randomly divided into a control group (C-group) and three major experimental groups, which were further subdivided into minor groups (n = 6) according to the experimental period (7 or 56 days). The C-group was subdivided into C-7 and C-56 [receiving a single saline solution, intraperitoneal (i.p.), on the first day]; the AL-group, AL-7, and AL-56, received AL extract (300 mg/kg/daily); the Cd group, Cd-7 and Cd-56, received a single i.p. dose of CdCl2 (1.2 mg/kg body weight (BW)) on the first day; the CdAL group, CdAL-7 and CdAL-56, received the same Cd dose, followed by AL extract. Water or AL extract was administered daily by gavage. After either 7 or 56 days, the testis and accessory glands were removed after whole-body perfusion. Exposure to Cd and CdAL decreased the weight of the testis and epididymis, the gonadosomatic index, seminiferous tubular (ST) diameter, and ST volumetric proportion, and increased the volumetric proportion of interstitium after 56 days. In the epididymis caput, the tubular volumetric proportion decreased along with an increase of interstitial volumetric proportion and epithelium height after 56 days. The alterations observed were less severe only after 7 days. A progressive testicular damage resulted mainly in tubules lined only by Sertoli cells. The sperm number and cell debris decreased in the epididymis. We demonstrated that the testicular damage induced by single acute i.p. exposure to Cd occurred despite the daily oral intake of AL extract.

Sperm forward motility is negatively affected by short-term exposure to altitude hypoxia

Human exposure to altitude is a model to study the role of oxygen in different areas of physiology and pathophysiology. The aim of this study was to evaluate whether a short exposure to hypoxia (5 days) combined with exercise, at altitude ranging from 900 m above sea level to 5895 m above sea level (Kilimanjaro Expedition) can modify seminal and reproductive hormonal parameter levels in human beings. During the ascent, blood oxygen saturation at 3.848 m above sea level was found to be decreased when compared to sea level (P < 0.02). The sperm forward motility at sea level after the expedition showed a significant reduction ​​(P < 0.02). There were no changes in other seminal parameters among those compared. Determination of the hormonal plasma concentrations showed that baseline values of follicle-stimulating hormone, total testosterone, prolactin and oestradiol were unchanged at sea level after the hypoxic experience, with respect to baseline values at sea level. On the other hand, luteinising hormone levels after altitudes trekking significantly increased compared to levels before the expedition (P < 0.05). Because of the short-term exposure, we can assume that the reduced forward motility described here may result from the effects of the acute altitude hypoxia on spermatozoa during the epididymal transit where they mature acquiring their motility.

Protective effects of polyunsatutared fatty acids supplementation against testicular damage induced by intermittent hypobaric hypoxia in rats

BACKGROUND

Intermittent hypobaric hypoxia (IHH) induces changes in the redox status and structure in rat testis. These effects may be present in people at high altitudes, such as athletes and miners. Polyunsaturated fatty acids (PUFA) can be effective in counteracting these oxidative modifications due to their antioxidants properties. The aim of the work was to test whether PUFA supplementation attenuates oxidative damage in testis by reinforcing the antioxidant defense system. The animals were divided into four groups (7 rats per group): normobaric normoxia (~750 tor; pO2 156 mmHg; Nx); Nx + PUFA, supplemented with PUFA (DHA: EPA = 3:1; 0.3 g kg(-1) of body weight per day); hypoxic hypoxia (~428 tor; pO2 90 mmHg; Hx) and, Hx + PUFA. The hypoxic groups were exposed in 4 cycles to 96 h of HH followed by 96 h of normobaric normoxia for 32 days. Total antioxidant capacity (FRAP) and lipid peroxidation (malondialdehyde, MDA) in plasma and reduced (GSH)/oxidized glutathione (GSSG) ratio, tissue lipid peroxidation (TBARS) and antioxidant enzymes activity were assessed at the end of the study in testis. Also, SIRTUIN 1 and HIF-1 protein expression in testis were determined.

RESULTS

IHH increased lipid peroxidation in plasma and HIF-1 protein levels in testis. In addition, IHH reduced FRAP levels in plasma, antioxidant enzymes activities and SIRTUIN 1 protein levels in testis. PUFA supplementation attenuated these effects, inducing the increases in FRAP, in the antioxidant enzymes activity and HIF-1 levels.

CONCLUSIONS

These results suggest that the IHH model induces a prooxidant status in plasma and testis. The molecular protective effect of PUFA may involve the induction of an antioxidant mechanism.