Effect of aging on spontaneous and induced mouse testicular germ cell apoptosis

Starvation-induced autophagy modulates spermatogenesis and sperm quality in Nile tilapia

Spermatogenesis is a finely regulated process that involves the interaction of several cellular mechanisms to ensure the proper development and maturation of germ cells. This study assessed autophagy contribution and its relation to apoptosis in fish spermatogenesis during starvation. To that end, Nile tilapia males were subjected to 0 (control), 7, 14, 21, and 28 days of starvation to induce autophagy. Testes samples were obtained for analyses of spermatogenesis by histology, electron microscopy, immunohistochemistry, and western blotting. Sperm quality was assessed using a computer-assisted sperm analysis (CASA) system. Data indicated a significant reduction in gonadosomatic index, seminiferous tubule area, and spermatozoa proportion in fish subject to starvation compared to the control group. Immunoblotting revealed a reduction of Bcl2 and Beclin 1 associated with increased Bax and Caspase-3, mainly after 21 and 28 days of starvation. LC3 and P62 indicated reduced autophagic flux in these starvation times. Immunolabeling for autophagic and apoptotic proteins occurred in all development stages of the germ cells, but protein expression varied throughout starvation. Beclin 1 and Cathepsin D decreased while Bax and Caspase-3 increased in spermatocytes, spermatids, and spermatozoa after 21 and 28 days. Autophagic and lysosomal proteins colocalization indicated the fusion of autophagosomes with lysosomes and lysosomal degradation in spermatogenic cells. The CASA system indicated reduced sperm motility and velocity in animals subjected to 21 and 28 days of starvation. Altogether, the data support autophagy acting at different spermatogenesis stages in Nile tilapia, with decreased autophagy and increased apoptosis after 21 and 28 days of starvation, which results in a decrease in the spermatozoa number and sperm quality.

Testicular aging, male fertility and beyond

Normal spermatogenesis and sperm function are crucial for male fertility. The effects of healthy testicular aging and testicular premature aging on spermatogenesis, sperm function, and the spermatogenesis microenvironment cannot be ignored. Compared with younger men, the testis of older men tends to have disturbed spermatogenic processes, sperm abnormalities, sperm dysfunction, and impaired Sertoli and Leydig cells, which ultimately results in male infertility. Various exogenous and endogenous factors also contribute to pathological testicular premature aging, such as adverse environmental stressors and gene mutations. Mechanistically, Y-chromosomal microdeletions, increase in telomere length and oxidative stress, accumulation of DNA damage with decreased repair ability, alterations in epigenetic modifications, miRNA and lncRNA expression abnormalities, have been associated with impaired male fertility due to aging. In recent years, the key molecules and signaling pathways that regulate testicular aging and premature aging have been identified, thereby providing new strategies for diagnosis and treatment. This review provides a comprehensive overview of the underlying mechanisms of aging on spermatogenesis. Furthermore, potential rescue measures for reproductive aging have been discussed. Finally, the inadequacy of testicular aging research and future directions for research have been envisaged to aid in the diagnosis and treatment of testicular aging and premature aging.

Effects of starvation and refeeding cycles on spermatogenesis and sex steroids in the Nile tilapia Oreochromis niloticus

Food restriction is part of the life cycle of many fish species; however, nutritional deficiency may negatively influence gametogenesis and gonadal maturation. The aim of this study was to evaluate the effects of food restriction on the spermatogenesis of Nile tilapia. For this, adult males were submitted to starvation and refeeding cycles (alternating periods of starvation and feeding) for 7, 14, 21, and 28 days. After 7 days of starvation, glycaemic and lipid levels were significantly reduced, followed by reduction of plasma testosterone (T) and 11-ketotestosterone (11-KT). In addition, reduced proliferation of spermatogonia and increased apoptosis of spermatocytes, spermatids, and spermatozoa was observed in starvation groups. In the refeeding groups, the sex steroids and the proportion of germ cells had no significant alterations compared to the control group, except for spermatozoa. In this sense, the present study suggests that starvation after 7 days progressively reduces T and 11-TK, resulting in damage to the production of spermatogenic cells, while refeeding may delay spermatogenesis but does not lead to testicular impairment.

Vitamin D3 regulates apoptosis and proliferation in the testis of D-galactose-induced aged rat model

The age-associated imbalances between proliferation and apoptosis lead to impaired spermatogenesis and infertility. The age-associated decline in vitamin D3 levels has been reported and suggested the anti-aging potential of vitamin D3. However, the age-associated decline levels of vitamin D3 has not been studied in relation to the testicular activity. Thus, we investigated the effect of vitamin D3 on the expression of testicular proliferation markers, apoptotic markers, antioxidants system and oxidative stress in a D-gal-induced aged rat model. The present study investigated the levels of vitamin D3 and AGE in serum and testes along with the expression of the AGE-receptor (AGER) in the testis. Vitamin D3 treatment significantly increases cell proliferation and decreases apoptosis in a D-gal-induced aged rat testis. Furthermore, vitamin D3 significantly decreases oxidative stress in aged rat testis by improving the antioxidant defense systems. The expression of AGER was down-regulated by vitamin D3 treatment in aged testis. The circulating and intra-testicular AGE was higher in aged groups, however, only circulating vitamin D3 levels decreased in aged groups. The immunolocalization of VDR showed increased immunostaining in the testis by vitamin D3 treatment. Thus, it can be concluded that vitamin D3 delays testicular senescence by regulating proliferation and apoptosis.

Mitochondrial adaptations evoked with exercise are associated with a reduction in age-induced testicular atrophy in Fischer-344 rats

Mitochondrial dysfunction in various tissues has been associated with numerous conditions including aging. In testes, aging induces atrophy and a decline in male reproductive function but the involvement of mitochondria is not clear. The purpose of this study was to examine whether the mitochondrial profile differed with (1) aging, and (2) 10-weeks of treadmill exercise training, in the testes of young (6 month) and old (24 month) Fischer-344 (F344) animals. Old animals exhibited significant atrophy (30 % decline; P < 0.05) in testes compared to young animals. However, relative mitochondrial content was not reduced with age and this was consistent with the lack of change in the mitochondrial biogenesis regulator protein, peroxisome proliferator-activated receptor gamma coactivator 1-alpha and its downstream targets nuclear respiratory factor-1 and mitochondrial transcription factor A. No effect was observed in the pro- or anti-apoptotic proteins, Bax and Bcl-2, respectively, but age increased apoptosis inducing factor levels. Endurance training induced beneficial mitochondrial adaptations that were more prominent in old animals including greater increases in relative mtDNA content, biogenesis/remodeling (mitofusin 2), antioxidant capacity (mitochondrial superoxide dismutase) and lower levels of phosphorylated histone H2AX, an early marker of DNA damage (P < 0.05). Importantly, these exercise-induced changes were associated with an attenuation of testes atrophy in older sedentary animals (P < 0.05). Our results indicate that aging-induced atrophy in testes may not be associated with changes in relative mitochondrial content and key regulatory proteins and that exercise started in late-life elicits beneficial changes in mitochondria that may protect against age-induced testicular atrophy.

High prevalence of isolated sperm DNA damage in infertile men with advanced paternal age

BACKGROUND

Sperm DNA damage is associated with male infertility, lower pregnancy rates and pregnancy loss.

OBJECTIVE

The primary aim of our study was to evaluate the prevalence of sperm DNA damage in younger and older men with normozoospermia.

DESIGN, SETTING AND PARTICIPANTS

We obtained semen from 277 consecutive non-azoospermic men presenting for sperm DNA testing.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The main outcome measures included sperm % DNA fragmentation index (%DFI, using sperm chromatin structure assay), sperm concentration, motility and morphology, and, paternal age.

RESULTS AND LIMITATIONS

Sperm % DFI was positively correlated with paternal age (r = 0.20, P < 0.001) and inversely correlated % progressive motility (r = -0.16, P = 0.01). Sperm %DFI was significantly higher in older (≥40 years) compared to younger (<40 years) normozoospermic men (17 ± 13 vs. 12 ± 8, respectively P = 0.008), whereas, sperm concentration, progressive motility and morphology were not significantly different in these two groups. Moreover, the prevalence of high levels of sperm DNA damage (>30 % DFI) was significantly higher in older compared to younger normozoospermic men (17 % vs. 3 %, respectively, P < 0.001).

CONCLUSION

The data indicate that a conventional semen analysis can often fail to detect a defect in spermatogenesis (high %DFI) in older men and suggest that infertile couples with advanced paternal age, including those with normal semen parameters, should consider sperm DNA testing as part of the couple evaluation.

Lifelong running reduces oxidative stress and degenerative changes in the testes of mice

Regular exercise can counteract the adverse effects of aging on the musculoskeletal and cardiovascular systems. In males, the normal aging process is associated with reductions in testosterone production and impaired spermatogenesis, but the underlying mechanisms and their potential modification by exercise are unknown. Here, we report that lifelong regular exercise (running) protects the testes against the adverse effects of advancing age, and that this effect of running is associated with decreased amounts of oxidative damage to proteins, lipids, and DNA in spermatogenic and Leydig cells. Six-month-old male mice were divided into a sedentary group and a group that ran an average of 1.75 km/day, until the mice reached the age of 20 months. Seminiferous tubules of runners exhibited a full complement of cells at different stages of the spermatogenic process and a clear central lumen with large numbers of spermatozoa, in contrast to sedentary mice that exhibited disorganized spermatogenic cells and lacked spermatocytes in a central lumen. Levels of protein carbonyls, nitrotyrosine, lipid peroxidation products, and oxidatively modified DNA were significantly greater in spermatogenic and Leydig cells of sedentary mice compared with runners. These findings suggest that lifelong regular exercise suppresses aging of testes by a mechanism that involves reduced oxidative damage to spermatogenic and Leydig cells.

Spontaneous mutagenesis is enhanced in Apex heterozygous mice

Germ line DNA directs the development of the next generation and, as such, is profoundly different from somatic cell DNA. Spermatogenic cells obtained from young adult lacI transgenic mice display a lower spontaneous mutant frequency and greater in vitro base excision repair activity than somatic cells and tissues obtained from the same mice. However, spermatogenic cells from old lacI mice display a 10-fold higher mutant frequency. This increased spontaneous mutant frequency occurs coincidentally with decreased in vitro base excision repair activity for germ cell and testicular extracts that in turn corresponds to a decreased abundance of AP endonuclease. To directly test whether a genetic diminution of AP endonuclease results in increased spontaneous mutant frequencies in spermatogenic cell types, AP endonuclease heterozygous (Apex(+/-)) knockout mice were crossed with lacI transgenic mice. Spontaneous mutant frequencies were significantly elevated (approximately twofold) for liver and spleen obtained from 3-month-old Apex(+/-) lacI(+) mice compared to frequencies from Apex(+/+) lacI(+) littermates and were additionally elevated for somatic tissues from 9-month-old mice. Spermatogenic cells from 9-month-old Apex(+/-) lacI(+) mice were significantly elevated twofold compared to levels for 9-month-old Apex(+/+) lacI(+) control mice. These data indicate that diminution of AP endonuclease has a significant effect on spontaneous mutagenesis in somatic and germ line cells.

Paternal transmission of genetic damage: findings in animals and humans

The concept that mutations can be induced in the male germ-line and result in adverse effects in the offspring has achieved only limited acceptance despite considerable theoretical appeal. This is partly because fetal malformations are generally perceived to be induced solely as a result of maternally mediated events during gestation and partly because the low incidence of the end-points concerned make experimental approaches costly and time-consuming. Nonetheless, a substantial body of work relating to the hypothesis has accumulated in the last 20 years, which has never been reviewed in its entirety. A consideration of the available evidence indicates that preconceptional paternal exposure to mutagens (particularly radiation, cyclophosphamide and ethylnitrosourea) can indeed, under certain conditions, have adverse effects on offspring. The results suggest two principal mechanisms by which such effects may be induced: the induction of germ-line genomic instability or the suppression of germ cell apoptosis.