Sperm Telomere Length Research Articles

Sperm telomere length: Diagnostic and prognostic biomarker in male infertility (Review)

Telomere length is an important biomarker in a number of diseases, including male infertility. A decreased telomere length has been reported in several diseases and telomere shortening may occur due to aging, decreased telomerase activity, oxidative stress or cell division. In recent years, several studies have indicated that males with infertility have a shorter sperm telomere length than fertile males. Sperm telomere shortening is associated with male infertility through several mechanisms, including the apoptosis of spermatozoa, decreased motility, low sperm count, incorrect chromosomal pairing and movement during meiosis, and failed fertilization. The aim of this review was to compile current findings on sperm telomere length and discuss findings to compare sperm from infertile males with that of fertile males. Several studies reported shortening of sperm telomeres associated with infertility. Thus, sperm telomere length can be used as biomarker for the diagnosis and prognosis of male infertility, since fertile males have longer telomeres and the length decreases with age. However, there is no specific telomere length that is set as standard/recommended length.

Comparison of Sperm Telomere Length between Two Sperm Selection Procedures: Density Gradient Centrifugation and Zeta Potential.

BackgroundTelomeres are particular sequences of DNA located at the end of the eukaryotic chromosomes that are essential for genome integrity. Telomere length in spermatozoa differs among males, as well as spermatozoa. Also, decreased telomere length in spermatozoa of infertile men is associated with the reduction of fertility potential and embryo quality. Density gradient centrifugation (DGC) and swim-up are useful techniques for separation of spermatozoa with longer telomeres. Also, the selection of sperm based on surface negative electric charge or “Zeta potential”, can separate high percentage of spermatozoa with intact chromatin compared to DGC alone, and also the combination of DGC-Zeta can improve clinical outcomes of infertile men candidate for intracytoplasmic sperm injection (ICSI). Therefore, we compared sperm telomere length and DNA fragmentation between two sperm preparation procedures, namely DGC and zeta potential.Materials and MethodsIn this experimental study, we assessed sperm telomere length and DNA fragmentation by quantitative real-time polymerase chain reaction (PCR) and TUNEL assay methods, respectively. The spermatozoa were obtained from infertile men with normozoospermia between September 2017 and December 2017 and prepared either by DGC or zeta potential methods. Sperm telomere length was expressed as relative and absolute units.ResultsCompared with washed semen samples or control, no significant (P>0.05) difference was observed in the mean relative or absolute sperm telomere length when the two methods DGC or zeta potential were compared. However, the mean percentage of DNA fragmentation was significantly (P<0.05) lower in spermatozoa prepared by DGC or zeta potential methods than spermatozoa obtained from control samples.ConclusionThis is the first study that compared the effect of DGC and zeta potential as the sperm preparation methods on sperm telomere length. It seems that both methods can select sperm population with high DNA integrity and the same sperm telomeres length.

Testing for paternal influences on offspring telomere length in a human cohort in the Philippines.

Telomeres, emerging biomarkers of aging, are comprised of DNA repeats located at chromosomal ends that shorten with cellular replication and age in most human tissues. In contrast, spermatocyte telomeres lengthen with age. These changes in telomere length (TL) appear to be heritable, as older paternal ages of conception (PAC) predict longer offspring TL. Mouse-model studies raise questions about the potential for effects of paternal experiences on human offspring TL, as they suggest that smoking, inflammation, DNA damage, and stressors all shorten sperm TL. Here, we examined whether factors from the paternal environment predict offspring TL as well as interact with PAC to predict offspring TL. Using data from the Philippines, we tested if smoking, psychosocial stressors, or shorter knee height (a measure of early life adversity) predict shorter offspring TL. We also tested if these interacted with PAC in predicting offspring TL. While we did not find the predicted associations, we observed a trend toward fathers with shorter knee height having offspring with longer TL. In addition, we found that knee height interacted with PAC to predict offspring TL. Specifically, fathers with shorter knee heights showed a stronger positive effect of PAC on offspring TL. While the reasons for these associations remain uncertain, shorter knee height is characteristic of earlier puberty. Since spermatocyte TL increases with the production of sperm, we speculate that individuals with earlier puberty, and its concomitant commencement of production of sperm, had more time to accumulate longer sperm telomeres.

Associations of sperm telomere length with semen parameters, clinical outcomes and lifestyle factors in human normozoospermic samples.

Many studies have demonstrated that lifestyle factors can affect sperm quality and fertility. Sperm telomere length (STL) has been reported as potential biomarker or sperm quality. However, no studies have investigated how lifestyle factors can affect STL and associated clinical outcomes. The purpose of this manuscript is to investigate any association between STL with lifestyle factors, semen parameters and clinical outcomes. Sperm telomere length was measured using real-time PCR in normozoospermic male partners (n=66) of couples undergoing ART treatment. Each participant also completed a detailed questionnaire about general lifestyle. Linear regression univariate analysis and ANCOVA were performed to respectively determine correlations between STL and study parameters or identify statistically significant differences in STL while controlling for age, BMI and other factors. Using a linear regression model, STL is positively correlated with in vitro fertilization success (n=65, r = 0.37, P = .004) but not with embryo cleavage rates and post-implantation clinical outcomes including gestational age-adjusted birth weight. No associations were observed between STL and sperm count, concentration or progressive motility. We further found that STL did not associate age, BMI, health or lifestyle factors. In somatic cells, the rate of telomere shortening is influenced by a number of lifestyle factors such as smoking, diet and occupation. However, little is known about how lifestyle factors affect STL and subsequently reproductive outcome. Out data suggest that STL might have an important role mechanistically for fertilization rate regardless of sperm parameters and lifestyle factors. The results of this study demonstrate that STL is associated with in vitro fertilization rates, but not with semen parameters nor lifestyle factors. Further investigations are warranted to identify the potential variation of STL overtime to clarify its significance as a potential biomarker in ART.

The association between sperm telomere length, cardiorespiratory fitness and exercise training in humans

Telomeres protect genomic integrity and shorten in somatic cells due to the end replication problem. Sperm telomeres are, however, longer in older individuals and linked to semen quality. Exercise training may attenuate age-related telomere shortening in somatic cells, but the influence of exercise on sperm telomeres is unknown. Mature sperm from 34 healthy men were isolated by density gradient centrifugation and telomere length was assessed by qPCR. No significant correlations were observed between telomere length, fitness or exercise performance. Inter-individual variation in sperm telomere length responses to a 6-wk vigorous exercise training intervention (ΔT/S ratio range: −0.49 to 0.87) and a strong correlation between improvements in fitness and sperm telomere lengthening were revealed (r = 0.87, p < 0.001). These preliminary data suggest exercise training may regulate sperm telomere length and should encourage larger studies to explore the implications this may have on the health of the next generation.

The Impact of Lifestyle on Sperm Telomere Length and Telomerase Activity in Men Undergoing IVF Treatments

The Impact of Lifestyle on Sperm Telomere Length and Telomerase Activity in Men Undergoing IVF Treatments

Sperm Telomere Length in Men with Normal and Abnormal semen Parameters. A Pilot Study

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Older paternal ages and grandpaternal ages at conception predict longer telomeres in human descendants.

Telomere length (TL) declines with age in most human tissues, and shorter TL appears to accelerate senescence. By contrast, men's sperm TL is positively correlated with age. Correspondingly, in humans, older paternal age at conception (PAC) predicts longer offspring TL. We have hypothesized that this PAC effect could persist across multiple generations, and thereby contribute to a transgenerational genetic plasticity that increases expenditures on somatic maintenance as the average age at reproduction is delayed within a lineage. Here, we examine TL data from 3282 humans together with PAC data across four generations. In this sample, the PAC effect is detectable in children and grandchildren. The PAC effect is transmitted through the matriline and patriline with similar strength and is characterized by a generational decay. PACs of more distant male ancestors were not significant predictors, although statistical power was limited in these analyses. Sensitivity analyses suggest that the PAC effect is linear, not moderated by offspring age, or maternal age, and is robust to controls for income, urbanicity and ancestry. These findings show that TL reflects the age at the reproduction of recent male matrilineal and patrilineal ancestors, with an effect that decays across generations.

Reduced sperm telomere length in individuals with varicocele is associated with reduced genomic integrity

Varicocele, defined as enlarged varicose veins in the scrotum, is the most common identifiable cause of male infertility. There are significant correlations between oxidative stress and varicocele-related infertility due to testicular hyperthermia, which can result in low sperm function. In addition, recent excessive oxidative stress can affect sperm telomere length and integrity of sperm DNA. Therefore, we assessed sperm telomere length as a potential marker of paternal genome integrity and leukocyte telomere length as an internal control (real-time PCR), along with sperm chromatin status (TUNEL and chromomycin A3 assay), and lipid peroxidation (Bodipy probe) in 18 infertile men with grade II or III varicocele, and 20 fertile men. Means of sperm parameters, sperm and leukocyte telomere length were significantly lower, while means of sperm DNA fragmentation, protamine deficiency, and lipid peroxidation were significantly higher in infertile men with varicocele compared to fertile men. Therefore, shortened telomere length in sperm and leukocytes is likely associated with increased oxidative stress related to the state of varicocele, which also accounts for increase in sperm DNA fragmentation. Thus, assessment of leukocyte telomere length could be taken as an indicator of antioxidant capacity in an individual, which also affects sperm function.

Epigenetic inheritance of telomere length in wild birds.

Telomere length (TL) predicts health and survival across taxa. Variation in TL between individuals is thought to be largely of genetic origin, but telomere inheritance is unusual, because zygotes already express a TL phenotype, the TL of the parental gametes. Offspring TL changes with paternal age in many species including humans, presumably through age-related TL changes in sperm, suggesting an epigenetic inheritance mechanism. However, present evidence is based on cross-sectional analyses, and age at reproduction is confounded with between-father variation in TL. Furthermore, the quantitative importance of epigenetic TL inheritance is unknown. Using longitudinal data of free-living jackdaws Corvus monedula, we show that erythrocyte TL of subsequent offspring decreases with parental age within individual fathers, but not mothers. By cross-fostering eggs, we confirmed the paternal age effect to be independent of paternal age dependent care. Epigenetic inheritance accounted for a minimum of 34% of the variance in offspring TL that was explained by paternal TL. This is a minimum estimate, because it ignores the epigenetic component in paternal TL variation and sperm TL heterogeneity within ejaculates. Our results indicate an important epigenetic component in the heritability of TL with potential consequences for offspring fitness prospects.

Evaluation of sperm telomere length in infertile men with failed/low fertilization after intracytoplasmic sperm injection

Telomeres are non-coding, repetitive DNA sequences (TTAGGG repeats) that play an important role in maintaining genome integrity. Unlike in somatic cells, telomere length in spermatozoa increases with male age and is considered as a molecular marker of sperm quality. The aetiology of failed fertilization following intracytoplasmic sperm injection (ICSI) is multifactorial; perhaps one of the reasons for this failure in these individuals is shortened sperm telomere length. This study therefore aimed to assess sperm telomere length in addition to DNA damage, lipid peroxidation and protamine deficiency in infertile men with previously failed/low fertilization post-ICSI. Semen samples were obtained from infertile men with previous failed/low fertilization rates (n = 10). Chromatin integrity (chromomycin A3 staining and TUNEL assay), lipid peroxidation (BODIPY probe) and telomere length (real-time PCR) for semen samples from these men were compared with samples obtained from fertile individuals (n=10). The results showed significantly higher mean values for sperm DNA damage, lipid peroxidation and reduced telomere length in spermatozoa of infertile men with previous failed/low fertilization compared with fertile individuals (P<0.05). Failed/low fertilization rates could be related to oxidative stress resulting in short telomere length, and also increased sperm chromatin damage and lipid peroxidation. From literature sources, shortened telomere length may lead to detachment of chromosomes from the nuclear membrane, the consequences of which are defects in the process of spermatogenesis, pronuclei formation, and delayed or arrested cell cycle post-ICSI.

Shedding light into the relevance of telomeres in human reproduction and male factor infertility†.

Sperm telomere length (STL) is a promising new parameter for sperm quality analysis that may elucidate the molecular mechanisms underlying the idiopathic cases of male factor infertility, which represent almost half of all the male factor infertility cases worldwide. Telomeres consist of nucleoprotein structures present at the ends of eukaryotic chromosomes, whose protective functions maintain the genomic stability. Their role in reproduction includes an active intervention during gametogenesis, fertilization, and preimplantation embryo development. In consonance, studies have shown that compromised telomere homeostasis is associated with male infertility. Since critically short telomeres have their function affected, assessing STL may be a fast and economic method for sperm quality analysis and expectantly contribute to improve the success of fertility treatments. This hypothesis is supported by several reports associating STL with seminal parameters, sperm genome integrity, and clinical outcomes. However, there are other studies in the literature that do not demonstrate these associations. Additionally, it is still not clear whether the lengthening mechanisms of telomeres occurring during early embryo development resume the inherited telomere length. Further research is essential to clarify the suitability of STL as a biomarker for male infertility, before it could be routinely implemented in medically assisted reproduction centers. Understanding the molecular mechanisms underlying STL function and dynamics will provide us new insights into the origins of male infertility and a possible new useful tool as an outcome predictor for assisted reproduction.

Links between parental life histories of wild salmon and the telomere lengths of their offspring.

The importance of parental contributions to offspring development and subsequent performance is self-evident at a genomic level; however, parents can also affect offspring fitness by indirect genetic and environmental routes. The life history strategy that an individual adopts will be influenced by both genes and environment; and this may have important consequences for offspring. Recent research has linked telomere dynamics (i.e., telomere length and loss) in early life to future viability and longevity. Moreover, a number of studies have reported a heritable component to telomere length across a range of vertebrates, although the effects of other parental contribution pathways have been far less studied. Using wild Atlantic salmon with different parental life histories in an experimental split-brood invitro fertilization mating design and rearing the resulting families under standardized conditions, we show that there can be significant links between parental life history and offspring telomere length (studied at the embryo and fry stage). Maternal life history traits, in particular egg size, were most strongly related to offspring telomere length at the embryonic stage, but then became weaker through development. In contrast, paternal life history traits, such as the father's growth rate in early life, had a greater association in the later stages of offspring development. However, offspring telomere length was not significantly related to either maternal or paternal age at reproduction, nor to paternal sperm telomere length. This study demonstrates both the complexity and the importance of parental factors that can influence telomere length in early life.

Sperm telomere length in donor samples is not related to ICSI outcome.

Variations in sperm telomere length (STL) have been associated with altered sperm parameters, poor embryo quality, and lower pregnancy rates, but for normozoospermic men, STL relevance in IVF/ICSI is still uncertain. Moreover, in all studies reported so far, each man's STL was linked to the corresponding female partner characteristics. Here, we study STL in sperm donor samples, each used for up to 12 women, in order to isolate and determine the relationship between STL and reproductive outcomes. Relative STL was determined by qPCR in 60 samples used in a total of 676 ICSI cycles. Univariable and multivariable statistical analyses were used to study the STL effect on fertilization rate; embryo morphology; biochemical, clinical, and ongoing pregnancy rates; and live birth (LB) rates. The average STL value was 4.5 (relative units; SD 1.9; range 2.4-14.2). Locally weighted scatterplot smoothing regression and the rho-Spearman test did not reveal significant correlations between STL and the outcomes analyzed. STL was not different between cycles resulting or not in pregnancy and LB (Mann-Whitney U test, p > 0.05). No significant effect of STL on reproductive outcomes was found, with the OR for each unit increase in STL (95% CI) of 0.94 (0.86-1-04), 0.99 (0.9-1.09), 0.98 (0.89-1.09), and 0.93 (0.8-1.06) for biochemical, clinical, and ongoing pregnancy and LB, respectively. The multilevel analysis confirmed that the effect of STL on fertilization; biochemical, clinical, and ongoing pregnancy; and LB was not significant (p > 0.05). After addressing STL independently from female variables, results show that STL measurement is not useful to predict reproductive outcomes in ICSI cycles using donor semen.

Genomic fragmentation and extrachromosomal telomeric repeats impact assessment of telomere length in human spermatozoa: quantitative experiments and systematic review.

Can differences in DNA isolation alter assessment of sperm telomere length (spTL) and do they account for conflicting results in the literature on spTL and male fertility? DNA isolation methods preferentially include or exclude short, extrachromosomal (EC) telomere-specific sequences that alter spTL measurements, and are responsible for a proportion of the disparity observed between investigations. The relationship between spTL and male fertility has become an active area of research. The results across investigations, however, have been discordant, generating a need to critically evaluate the existing body of knowledge to guide future investigations. Quantitative experiments determined the effect of DNA isolation on the integrity of sperm DNA and measures of spTL, while a systematic analysis of the current literature evaluated the effect of DNA isolation and study design on experimental outcomes. Two DNA isolation methods were compared: Genomic Tips which isolate 'High Molecular Weight' (HMW) DNA exclusively, and QIAamp® DNA Mini which isolates 'Total' genomic DNA irrespective of size. DNA quality was assessed via field inversion gel electrophoresis (FIGE) and spTL was measured via terminal restriction fragment analysis. In addition, major databases in medicine, health and the life sciences were subject to a targeted search, and results were independently screened according to defined exclusion/inclusion criterion. Findings from primary articles were analyzed for concordance and study designs were compared across six moderator variables (sample size, participant age, fertility status, semen fraction, telomere population and type of analysis). HMW DNA spTL was significantly longer than spTL measured from total DNA (P < 0.01), indicating that Total DNA contained short, EC telomeric repeats that shifted downstream assessment towards shorter spTL. HMW DNA spTL reflected the length of intact, chromosomal telomeres. Major findings on spTL showed the greatest concordance amongst studies that implemented HMW DNA isolation prior to spTL assessment. Studies that utilized Total DNA varied in concordance, but outcomes were similar if (i) a comparative analysis was applied or (ii) a sample size threshold of 81 was achieved for correlative analysis. Chromosomal and EC telomeric DNA were distinguished based on outcomes of HMW DNA isolation and size. Further experiments are required to determine the nature and function of these two types of telomeric sequences. This study reveals a dramatic impact of upstream DNA processing and study design on measurements of spTL, which accounts for conflicting results in the literature. Future assessments of spTL should incorporate independent detection of chromosomal and EC telomeric DNA and specific experimental planning. This study was funded by CReATe Fertility Centre, Toronto, Ontario, Canada. The authors have declared no conflict of interest. N/A.

Effects of Highly Polluted Environment on Sperm Telomere Length: A Pilot Study.

High environmental pressure may impair male fertility by affecting sperm quality, but the real effect remains controversial. Herein, we assessed the influence of environmental exposure on telomere length (TL) in both leukocytes (LTL) and sperm cells (STL). A pilot biomonitoring study was conducted in 112 clinically healthy, normospermic men living in various areas of Campania region (South of Italy) with high (n = 57, High Group) or low (n = 55, Low Group) environmental pressure. TL analysis was assessed by quantitative real time-PCR. STL was not significantly correlated with either age (p = 0.6) or LTL (p = 0.7), but was significantly longer in the High Group compared with the Low Group (p = 0.04). No significant difference was observed between leukocyte TL in the High or Low Group. Our results showed that male residents in areas with high environment exposure had a significant increase in STL. This finding supports the view that the human semen is a sentinel biomarker of environmental exposure.

Intergenerational Transmission of Paternal Epigenetic Marks: Mechanisms Influencing Susceptibility to Post-Concussion Symptomology in a Rodent Model

Epigenetic transmission of phenotypic variance has been linked to paternal experiences prior to conception and during perinatal development. Previous reports indicate that paternal experiences increase phenotypic heterogeneity and may contribute to offspring susceptibility to post-concussive symptomology. This study sought to determine if epigenetic tags, specifically DNA methylation of promoter regions, are transmitted from rodent fathers to their sons. Using MethyLight, promoter methylation of specific genes involved in recovery from concussion and brain plasticity were analyzed in sperm and brain tissue. Promoter methylation in sperm differed based on paternal experience. Differences in methylation were often identified in both the sperm and brain tissue obtained from their sons, demonstrating transmission of epigenetic tags. For certain genes, methylation in the sperm was altered following a concussion suggesting that a history of brain injury may influence paternal transmission of traits. As telomere length is paternally inherited and linked to neurological health, this study examined paternally derived differences in telomere length, in both sperm and brain. Telomere length was consistent between fathers and their sons, and between brain and sperm, with the exception of the older fathers. Older fathers exhibited increased sperm telomere length, which was not evident in sperm or brain of their sons.

Shorter sperm telomere length in association with exposure to polycyclic aromatic hydrocarbons: Results from the MARHCS cohort study in Chongqing, China and in vivo animal experiments

It has been well demonstrated that polycyclic aromatic hydrocarbons (PAHs) can cause reproductive toxicity, and shorter telomere length in sperm may be one of the factors causing male infertility. However, whether exposure to PAHs is associated with sperm telomere length (STL) has never been evaluated. The present study aimed to assess the potential association between PAHs exposure and STL, and to explore potential biomarkers that may predict the effects of low-level exposure to PAHs on human sperm. Questionnaires and biological samples were collected from 666 volunteers participating in the Male Reproductive Health in Chongqing College Students (MARHCS) cohort study in 2014. Semen parameters were measured for 656 participants, while urinary PAH metabolites, STL and sperm apoptosis were successfully measured for 492, 444 and 628 participants, respectively. The linear regression analysis revealed that increased levels of urinary 1-hydroxypyrene (1-OHPyr) and 1-hydroxynapthalene (1-OHNap) were associated with decreased STL (−0.385; 95% CI, −0.749, −0.021 for 1-OHPyr; and −0.079; 95% CI, −0.146, −0.011 for 1-OHNap). The significant negative associations remained after adjusting for potential confounders. However, no significant associations were observed between urinary PAH metabolites and semen quality or sperm apoptosis. We also administrated rats with benzo[a]pyrene (B[a]P; 0, 1, 5, and 10mg/kg) for 4weeks and found shorter STL and decreased telomerase expression in germ cells in a dose-dependent manner. In conclusion, environmental exposure to some PAHs may be associated with decreased human STL, and the in vivo animal results also demonstrate the adverse effects of B[a]P on telomere of male germ cells.

Effect of paternal overweight or obesity on IVF treatment outcomes and the possible mechanisms involved.

Leukocyte telomere lengths (LTLs) are shorter in obese compared with normal weight people. However, it is not known whether sperm telomere length (STL) is related to obesity. The aim of the study was to evaluate the impact of men’s body mass index (BMI) on STL, embryo quality, and clinical outcomes in couples undergoing IVF. In total, 651 couples were recruited, including 345 men with a normal BMI and 306 men with an overweight BMI (normal BMI group: 20–25 kg/m2; overweight BMI group: >28 kg/m2). We found that couples with male’s BMI over 28 kg/m2 exhibited a significantly lower fertilization rate, good-quality embryo rate and clinical pregnancy rate compared to their normal BMI counterparts. The mean STL in the overweight BMI group was also significantly shorter than that of the normal BMI group. The results also showed that individuals with higher BMI had higher ROS (Reactive oxygen species) content and sperm DNA fragmentation rate when compared with normal BMI individuals. Mitochondrial activity was also lower in the overweight BMI group than in the normal BMI group. This is the first report to find that STL is shorter in overweight/obese men, which may account for their poorer treatment outcomes in IVF cycles.

Investigation of sperm telomere length as a potential marker of paternal genome integrity and semen quality

Recent studies have reported shorter sperm telomere length (STL) in men with idiopathic infertility. The aim of this study was to measure STL in semen samples from men to evaluate whether STL variation is associated with chromosomal abnormality, DNA fragmentation, traditional semen parameters, IVF outcome, or all four factors. A significant correlation between telomere length and diploidy was observed (P = 0.037). Additionally, STL was found to be positively associated with sperm count (P = 0.006); oligospermic samples had particularly short telomeres (0.9 ± 0.1 versus 1.4 ± 0.1; P = 0.0019). The results confirmed a link between sperm DNA fragmentation and aneuploidy, previously proposed (P = 0.009). A negative relationship was demonstrated between sperm concentration and aneuploidy and Sperm DNA framentation (P = 0.03, P < 0.0001, respectively). For a subset of 51 of the 73 sperm samples used for fertilization, IVF outcomes were known. A total of 17.6% of these samples had atypical STLs. None of these samples produced an ongoing pregnancy. In contrast, the pregnancy rate for samples that had STLs in the normal range was 35.7% (P = 0.044). In conclusion, STL has potential as a fast and inexpensive form of sperm quality assessment.