Oxidative Stress Is Associated with Telomere Interaction Impairment and Chromatin Condensation Defects in Spermatozoa of Infertile Males

Molecular mechanisms of aging and anti-aging strategies

Aging is a complex and multifaceted process involving a variety of interrelated molecular mechanisms and cellular systems. Phenotypically, the biological aging process is accompanied by a gradual loss of cellular function and the systemic deterioration of multiple tissues, resulting in susceptibility to aging-related diseases. Emerging evidence suggests that aging is closely associated with telomere attrition, DNA damage, mitochondrial dysfunction, loss of nicotinamide adenine dinucleotide levels, impaired macro-autophagy, stem cell exhaustion, inflammation, loss of protein balance, deregulated nutrient sensing, altered intercellular communication, and dysbiosis. These age-related changes may be alleviated by intervention strategies, such as calorie restriction, improved sleep quality, enhanced physical activity, and targeted longevity genes. In this review, we summarise the key historical progress in the exploration of important causes of aging and anti-aging strategies in recent decades, which provides a basis for further understanding of the reversibility of aging phenotypes, the application prospect of synthetic biotechnology in anti-aging therapy is also prospected.

Is telomere length a biomarker of sperm quality? A systematic review and meta-analysis of observational studies

BACKGROUND

Telomeres are essential for the integrity of chromosome ends during cell division and their involvement in different processes linked to aging has been established. These chromosome components are involved in spermatogenesis and seem to play an important role in fertilization and embryo development. Telomere length is shortened with each cell division. Recently, short sperm telomere length has been proposed as a potential biomarker of male infertility.

OBJECTIVES

To conduct a systematic review and meta-analysis of studies exploring the association between spermatozoa and/or leukocyte telomere length with sperm quality parameters and different infertility conditions.

MATERIAL AND METHODS

A systematic review and meta-analysis was conducted with studies from Medline-PUBMED and Cochrane Library databases until May 2022. Eligible studies included cohort, cross-sectional and case-control studies, and telomere length in spermatozoa and/or leukocytes cells was defined as the exposure. Semen quality parameters or infertility conditions (e.g., oligozoospermia, asthenozoospermia, teratozoospermia, or other spermatogenic impairment combinations) were defined as the outcomes.

RESULTS

Twenty-three observational studies were included. In the qualitative analysis, high heterogeneity was observed between studies regarding the associations between telomere length and semen parameters in different normozoospermic/fertile and oligozoospermic/infertile populations. In the meta-analysis, spermatozoa and leukocyte telomere length were shorter in infertile individuals than in fertile individuals (mean difference [95% confidence interval]: -1.43 [-1.66 to -1.21], p-value <0.001 and -1.67 [-2.02 to -1.31], p-value <0.001, respectively). Moreover, in terms of sperm telomere length, these differences were also significant between individuals with a normal seminogram and individuals with a low quantity of spermatozoa in the ejaculate (-0.97 [-1.32, -0.61], p-value <0.001).

CONCLUSION

The current systematic review and meta-analysis suggests the potential role of spermatozoa or leukocyte telomere length as a reliable biomarker of semen quality, which may help distinguish between infertility conditions beyond the routine semen analysis.

Sperm telomere length in male-factor infertility and reproduction

The underlying reasons for male-factor infertility are often unknown. 30% of all men have unexplained semen analysis abnormalities. Moreover, 15%-40% of infertile men have normal semen analyses. There have been increasing efforts to identify causes and associations that may explain idiopathic male-factor infertility. Telomeres have become an area of considerable interest in the field because of the essential roles they have in cellular division and genome integrity. Research to date most consistently supports that men with infertility have shorter sperm telomere length (STL); however, associations between shorter STL and meaningful reproductive health outcomes are less consistent. There is a major need for additional studies to better identify the role of STL in male reproductive health and use the information to improve the counseling and treatment of couples with idiopathic male-factor infertility.

Freezing Does Not Alter Sperm Telomere Length despite Increasing DNA Oxidation and Fragmentation

Correlations were reported between sperm telomere length (STL) and male fertility, sperm DNA fragmentation, and oxidation. Sperm freezing is widely used for assisted reproductive techniques, fertility preservation, and sperm donation. However, its impact on STL remains unknown. For this study, semen surplus from patients who underwent routine semen analysis were used. The impact of slow freezing on STL was analyzed by performing qPCR before and after freezing. Sperm populations with different STL were evaluated using Q-FISH. The relationship between sperm DNA oxidation, DNA fragmentation, and STL was assessed in fresh and frozen sperm samples. No significant impact of slow freezing on STL was observed, neither measured by qPCR nor Q-FISH. However, Q-FISH allowed for the distinguishing of sperm populations with different STLs within individual sperm samples. Slow freezing induced different STL distributions for some of the analyzed sperm samples, but no correlation was found between STL and sperm DNA fragmentation or oxidation. Slow freezing does not alter STL despite increasing sperm DNA oxidation and fragmentation. As STL alterations could be transmitted to offspring, the lack of impact of the slow freezing method on STL ensures the safety of this procedure.

Male Germ Cell Telomeres and Chemical Pollutants

In recent decades, male infertility has been correlated with the shortening of sperm telomeres. Telomeres regulate the reproductive lifespan by mediating the synapsis and homologous recombination of chromosomes during gametogenesis. They are composed of thousands of hexanucleotide DNA repeats (TTAGGG) that are coupled to specialized shelterin complex proteins and non-coding RNAs. Telomerase activity in male germ cells ensures that the telomere length is maintained at maximum levels during spermatogenesis, despite telomere shortening due to DNA replication or other genotoxic factors such as environmental pollutants. An emerging body of evidence has associated an exposure to pollutants with male infertility. Although telomeric DNA may be one of the important targets of environmental pollutants, only a few authors have considered it as a conventional parameter for sperm function. The aim of this review is to provide comprehensive and up-to-date data on the research carried out so far on the structure/function of telomeres in spermatogenesis and the influence of environmental pollutants on their functionality. The link between pollutant-induced oxidative stress and telomere length in germ cells is discussed.

Telomere Length and Telomerase Activity of Granulosa Cells and Follicular Fluid in Women Undergoing In Vitro Fertilization

This study aimed to evaluate the interrelationship between telomere length, telomerase activity and oxidative DNA damage in patients undergoing in vitro fertilization (IVF). This single-center, observational clinical study comprised 102 unselected, consecutive patients with various infertility diagnoses. Granulosa cells (GCs) and follicular fluid (FF) were analyzed simultaneously for telomere functions and for the marker of oxidative DNA damage, 8-hydroxy-2-deoxyguanosine (8-OHdG). An Absolute Human Telomere Lengths Quantification qPCR Assay kit and Telomerase Activity Quantification qPCR Assay kit (Nucleotestbio, Budapest, Hungary), as well as an 8-OHdG ELISA kit (Abbexa Ltd., Cambridge, United Kingdom) were used for analyses. Similar telomere lengths were found in GCs and FF, however telomerase activity was markedly depressed, while 8-OHdG levels were markedly elevated in FF compared with those in GCs (p < 0.01). Telomere lengths were independent of telomerase activity both in GCs and FF. However, GC 8-OHdG was inversely related to telomerase activity in GCs and FF (p < 0.05). Importantly, 8-OHdG levels both in GCs and FF had significant negative impact on the number of the retrieved and MII oocytes (p < 0.01), whereas FF 8-OHdG was negatively related further to the number of fertilized oocytes and blastocysts (p < 0.01). In conclusion, we could not confirm the direct association of telomere function and reproductive potential. However, oxidative DNA damage, as mainly reflected by 8-OHdG, adversely affected early markers of IVF outcome and clinical pregnancies.

Functional association between telomeres, oxidation and mitochondria

Prior research has substantiated the vital role of telomeres in human fertility. Telomeres are prerequisites for maintaining the integrity of chromosomes by preventing the loss of genetic material following replication events. Little is known about the association between sperm telomere length and mitochondrial capacity involving its structure and functions. Mitochondria are structurally and functionally distinct organelles that are located on the spermatozoon's midpiece. Mitochondria produce adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS), which is necessary for sperm motility and generate reactive oxygen species (ROS). While a moderate concentration of ROS is critical for egg-sperm fusion, and fertilization, excessive ROS generation is primarily related to telomere shortening, sperm DNA fragmentation, and alterations in the methylation pattern leading to male infertility. This review aims to highlight the functional connection between mitochondria biogenesis and telomere length in male infertility, as mitochondrial lesions have a damaging impact on telomere length, leading both to telomere lengthening and reprogramming of mitochondrial biosynthesis. Furthermore, it aims to shed light on how both inositol and antioxidants can positively affect male fertility.

Oxidative Stress and Nuclear Reprogramming: A Pilot Study of the Effects of Reactive Oxygen Species on Architectural and Epigenetic Landscapes

Cell genome integrity is continuously threatened by various sources, both endogenous and exogenous. Oxidative stress causes a multitude of damages, severely affecting cell viability, fidelity of genetic information inheritance, and determining profound alterations in gene expression. Epigenetics represents a major form of gene expression modulation, influencing DNA accessibility to transcription factors and the overall nuclear architecture. When assessing the stress-induced epigenome reprogramming, widely diffused biochemical and molecular approaches commonly fail to incorporate analyses such as architectural chromatin alterations and target molecules precise spatial localization. Unveiling the significance of the nuclear response to the oxidative stress, as well as the functional effects over the chromatin organization, may reveal targets and strategies for approaches aiming at limiting the impact on cellular stability. For these reasons, we utilized potassium bromate treatment, a stressor able to induce DNA damages without altering the cellular microenvironment, hence purely modeling nuclear oxidative stress. By means of high-resolution techniques, we described profound alterations in DNA and histone epigenetic modifications and in chromatin organization in response to the reactive oxygen species.

Spectrum of sperm mtDNA deletions in men exposed to industrial air pollution

Sperm mtDNA status can serve as a molecular marker of oxidative stress and environmental exposure. High levels of air pollution may be associated with increased mitochondrial DNA (mtDNA) deletion rates in sperm. We compared the length spectra of sperm mtDNA deletions in semen samples collected from city policemen exposed to traffic and industrial air pollution in two seasons with different levels of air pollution. We used long-range PCR to amplify a fragment of mtDNA (8066 bp) frequently affected by deletions, visualized the PCR products by gel electrophoresis, and analysed aberrant bands corresponding to deleted mtDNA, using gel documentation software. The predominance of undeleted sperm mtDNA was accompanied by a variety of shorter PCR product lengths in the vast majority of sperm samples, in both seasons. Sperm mtDNA molecules and bands corresponding to long deletions were more frequently detected than shorter deletions, in both seasons. We did not detect any difference in the total number of electrophoretic bands corresponding to deleted sperm mtDNA and in the number of deleted sperm mtDNA molecules between the two seasons. In our study, air pollution during sperm maturation did not induce formation of large mtDNA deletions detectable by long PCR and gel electrophoresis (>1 kb) in maturing sperm mtDNA.

Oxidative Stress Markers and Sperm DNA Fragmentation in Men Recovered from COVID-19

SARS-CoV-2 negatively affects semen characteristics, impairs various biochemical processes in seminal fluid and within spermatogenic cells ultimately leading to male fertility decline. However, the distinct mechanisms, in particular, the role of oxidative stress on the consequences of coronavirus infection, have not been well investigated, which is the purpose of the present study. The standard semen parameters, its pro- and antioxidant system state, as well as the level of sperm DNA fragmentation, were assessed in 17 semen samples of men five months after the coronavirus infection and in 22 age-matched control patients. We determined that the DNA fragmentation rate negatively correlated with the period after coronavirus recovery, as well as seminal fluid superoxide dismutase activity and uric acid level. It was demonstrated that COVID-19 is not always associated with increased DNA fragmentation, allowing them to be considered as two independent factors. Thus, the most significant changes were noted in the samples of men after COVID-19 and abnormal TUNEL results: increased round cell number, decreased seminal fluid's nitrotyrosine level, and total antioxidant capacity and Zn, as well as an increased 8-hydroxy-2'-deoxyguanosine level within spermatozoa. The data obtained indicate that increased DNA fragmentation and diminished semen quality in men can be the result of an imbalance in semen pro- and antioxidant components after COVID-19.

Arsenic, Oxidative Stress and Reproductive System

Infertility is a severe medical problem and is considered a serious global public health issue affecting a large proportion of humanity. Oxidative stress is one of the most crucial factors involved in infertility. Recent studies indicate that the overproduction of reactive oxygen species (ROS) or reactive nitrogen species (RNS) may cause damage to the male and female reproductive systems leading to infertility. Low amounts of ROS and RNS are essential for the normal functioning of the male and female reproductive systems, such as sperm motility, acrosome reaction, interactions with oocytes, ovulation, and the maturation of follicles. Environmental factors such as heavy metals can cause reproductive dysfunction in men and women through the overproduction of ROS and RNS. It is suggested that oxidative stress caused by arsenic is associated with male and female reproductive disorders such as through the alteration in sperm counts and motility, decreased sex hormones, dysfunction of the testis and ovary, as well as damage to the processes of spermatogenesis and oogenesis. This review paper highlights the relationship between arsenic-induced oxidative stress and the prevalence of infertility, with detailed explanations of potential underlying mechanisms.

Antioxidants and Male Infertility

Oxidative stress has been associated with decreased sperm quality and male infertility [...].

Association between sperm mitochondrial DNA copy number and deletion rate and industrial air pollution dynamics

The effects of air pollution on men's reproductive health can be monitored by evaluating semen quality and sperm DNA damage. We used real-time PCR to analyse the effects of air pollution on sperm mitochondrial DNA copy number (mtDNAcn) and deletion (mtDNAdel) rates in semen samples collected from 54 men in two seasons with different levels of industrial and traffic air pollution. MtDNAdel rates were significantly higher following the high exposure period and were positively correlated with mtDNAcn. However, we did not find any difference in mtDNAcn between the two seasons. MtDNAcn was positively correlated with the DNA fragmentation index and the rates of sperm with chromatin condensation defects, previously assessed by sperm chromatin structure assay, and negatively correlated with sperm concentration, progressive motility, viability, and normal morphology. This indicates that mtDNAcn is more closely associated with male fertility than mtDNAdel rates. In contrast, mtDNAdel might be a more sensitive biomarker of air pollution exposure in urban industrial environments.

The Role of ROS as a Double-Edged Sword in (In)Fertility: The Impact of Cancer Treatment

Simple Summary

Tumor cells are highly resistant to oxidative stress, but beyond a certain threshold, it may lead to apoptosis/necrosis. Thus, induced loss of redox balance can be a strategy used in anticancer therapies. However, the effectiveness of drugs contrasts with unknown mechanisms involved in the loss of fertility. Considering that cancer patients’ life expectancy is increasing, it raises concerns about the unknown adverse effects. Therefore, new strategies should be pursued alongside explaining to the patients their options regarding the reproduction side effects.

Abstract

Tumor cells are highly resistant to oxidative stress resulting from the imbalance between high reactive oxygen species (ROS) production and insufficient antioxidant defenses. However, when intracellular levels of ROS rise beyond a certain threshold, largely above cancer cells’ capacity to reduce it, they may ultimately lead to apoptosis or necrosis. This is, in fact, one of the molecular mechanisms of anticancer drugs, as most chemotherapeutic treatments alter redox homeostasis by further elevation of intracellular ROS levels or inhibition of antioxidant pathways. In traditional chemotherapy, it is widely accepted that most therapeutic effects are due to ROS-mediated cell damage, but in targeted therapies, ROS-mediated effects are mostly unknown and data are still emerging. The increasing effectiveness of anticancer treatments has raised new challenges, especially in the field of reproduction. With cancer patients’ life expectancy increasing, many aiming to become parents will be confronted with the adverse effects of treatments. Consequently, concerns about the impact of anticancer therapies on reproductive capacity are of particular interest. In this review, we begin with a short introduction on anticancer therapies, then address ROS physiological/pathophysiological roles in both male and female reproductive systems, and finish with ROS-mediated adverse effects of anticancer treatments in reproduction.

Kastor and Polluks polypeptides encoded by a single gene locus cooperatively regulate VDAC and spermatogenesis

Although several long noncoding RNAs (lncRNAs) have recently been shown to encode small polypeptides, those in testis remain largely uncharacterized. Here we identify two sperm-specific polypeptides, Kastor and Polluks, encoded by a single mouse locus (Gm9999) previously annotated as encoding a lncRNA. Both Kastor and Polluks are inserted in the outer mitochondrial membrane and directly interact with voltage-dependent anion channel (VDAC), despite their different amino acid sequences. Male VDAC3-deficient mice are infertile as a result of reduced sperm motility due to an abnormal mitochondrial sheath in spermatozoa, and deficiency of both Kastor and Polluks also severely impaired male fertility in association with formation of a similarly abnormal mitochondrial sheath. Spermatozoa lacking either Kastor or Polluks partially recapitulate the phenotype of those lacking both. Cooperative function of Kastor and Polluks in regulation of VDAC3 may thus be essential for mitochondrial sheath formation in spermatozoa and for male fertility.

A number of testes-specific lncRNAs have been annotated but their roles remain largely unexplored. Here the authors identify two small peptides encoded by the lncRNA Gm9999, Kastor and Polluks, both of which are required for male fertility in mice.

Relationships of Telomere Homeostasis with Oxidative Stress and Cardiac Dysfunction in Human Ischaemic Hearts

Although the roles of telomeres and oxidative stress in ischaemic cardiomyopathy (ICM) are known, mechanisms of telomere homeostasis and their relationship with oxidative stress are incompletely understood. We performed two RNA-seq analyses (mRNA n = 23; ncRNA n = 30) and protein validation on left ventricles of explanted hearts from ICM and control subjects. We observed dysregulation of the shelterin and cohesin complexes, which was related to an increase in the response to cellular oxidative stress. Moreover, we found alterations at mRNA level in the mechanisms of telomeric DNA repair. Specifically, increased RAD51D mRNA levels were correlated with left ventricular diameters. RAD51D protein levels were unaltered, however, and were inversely corelated with the miR-103a-3p upregulation. We also observed the overexpression of lncRNAs (TERRA and GUARDIN) involved in telomere protection in response to stress and alterations in their regulatory molecules. Expression of the TERRA transcription factor ATF7 was correlated with superoxide dismutase 1 expression and left ventricular diameters. The levels of GUARDIN and its transcription factor FOSL2 were correlated with those of catalase. Therefore, we showed specific alterations in the mechanisms of telomeric DNA repair and protection, and these alterations are related to an increase in the response mechanisms to oxidative stress and cardiac dysfunction in ICM.

Genetic Association in the Maintenance of the Mitochondrial Microenvironment and Sperm Capacity

Sperm motility is one of the major determinants of male fertility. Since sperm need a great deal of energy to support their fast movement by active metabolism, they are thus extremely vulnerable to oxidative damage by the reactive oxygen species (ROS) and other free radicals generated as byproducts in the electron transport chain. The present study is aimed at understanding the impact of a mitochondrial oxidizing/reducing microenvironment in the etiopathology of male infertility. We detected the mitochondrial DNA (mtDNA) 4,977 bp deletion in human sperm. We examined the gene mutation of ATP synthase 6 (ATPase6 m.T8993G) in ATP generation, the gene polymorphisms of uncoupling protein 2 (UCP2, G-866A) in the uncoupling of oxidative phosphorylation, the role of genes such as manganese superoxide dismutase (MnSOD, C47T) and catalase (CAT, C-262T) in the scavenging system in neutralizing reactive oxygen species, and the role of human 8-oxoguanine DNA glycosylase (hOGG1, C1245G) in 8-hydroxy-2′-deoxyguanosine (8-OHdG) repair. We found that the sperm with higher motility were found to have a higher mitochondrial membrane potential and mitochondrial bioenergetics. The genotype frequencies of UCP2 G-866A, MnSOD C47T, and CAT C-262T were found to be significantly different among the fertile subjects, the infertile subjects with more than 50% motility, and the infertile subjects with less than 50% motility. A higher prevalence of the mtDNA 4,977 bp deletion was found in the subjects with impaired sperm motility and fertility. Furthermore, we found that there were significant differences between the occurrences of the mtDNA 4,977 bp deletion and MnSOD (C47T) and hOGG1 (C1245G). In conclusion, the maintenance of the mitochondrial redox microenvironment and genome integrity is an important issue in sperm motility and fertility.