Restraint stress of male mice induces apoptosis in spermatozoa and spermatogenic cells: role of the FasL/Fas system†

The association between greenspace exposure and sperm quality: A retrospective cohort study focusing on sperm kinematics and the influence of buffer settings

BACKGROUND

While previous studies have suggested a potential link between greenspace and semen quality, the effect of greenspace exposure on sperm kinematics, as well as the impact of greenspace estimation scales, remains underexplored.

OBJECTIVES

This study aimed to examine the association between greenspace exposure and sperm kinematics, and to determine whether this relationship varies across different greenspace estimation scales.

METHODS

We conducted a retrospective longitudinal study of 5025 semen measurements from 1674 sperm donors recruited by the Sichuan Provincial Human Sperm Bank (SHSB) between June 2019 and December 2021. Greenspace exposure was estimated using the Normalized Difference Vegetation Index (NDVI) for four buffer zones (250 m, 500 m, 1,000 m, and 2000 m) centred on the geocoded residential addresses. Linear mixed-effects models and restricted cubic spline models (knots = 4) were used to assess the associations between greenspace exposure and both conventional semen parameters and sperm kinematic parameters across all buffer zones.

RESULTS

A non-linear association between NDVI-500m and progressive motility was observed for conventional semen parameters (P non-linear = 0.018). For sperm kinematics, NDVI-500m could be associated with multiple kinematic measures (VCL: % change = 1.81, 95% CI: 0.72, 2.91; VAP: % change = 2.57, 95% CI: 1.46, 3.70; VSL: % change = 3.37, 95% CI: 2.11, 4.66; LIN: % change = 1.51, 95% CI: 0.82, 2.21; STR: % change = 0.83, 95% CI: 0.44, 1.23; WOB: % change = 0.69, 95% CI: 0.35, 1.04; BCF: % change = 1.82, 95% CI: 0.97, 2.68), and significant non-linear associations were found between NDVI-500m and LIN (P non-linear = 0.011), STR (P non-linear = 0.015), WOB (P non-linear = 0.012), and ALH (P non-linear <0.001). Regarding the impact of greenspace estimation scales, smaller buffer zones exhibited stronger non-linear relationships for conventional semen parameters, whereas larger buffer zones revealed more pronounced non-linear relationships for sperm kinematics. There was a stable and significant linear association between greenspace exposure and sperm kinematics during the 70-90 days before ejaculation (spermatocytogenesis). PM2.5 and PM10 attenuated the negative effect of greenspace exposure on IM at a buffer scale of 250 m, while enhanced the positive effect of greenspace on kinematics at all scales.

CONCLUSIONS

Greenspace exposure were significantly associated with sperm kinematics, with the strength and nature of these associations varying by buffer scale. 70-90 days before ejaculation (spermatocytogenesis) was the window of susceptibility for greenspace exposures at all buffer scales. As PM2.5 and PM10 increased, increasing levels of greenspace can improve sperm kinematics more significantly. These findings support the beneficial effect of greenspace on male fertility, and underscore the importance of considering greenspace buffer zones in urban planning to optimize health benefits effectively.

Chronic psychological stress induces testicular oxidative stress affecting reproductive behavior in rats

The inhibitory effect of chronic psychological stress on reproductive behavior is widely recognized since long. However, the biological mechanisms underlying these effects, especially the cellular biology of the testicular cells, have not been fully investigated. This study aimed to investigate the effects of chronic psychological stress on rat reproductive behavior and its correlation with testicular cell damage and oxidative stress. The results showed that chronic psychological stress led to a decline in the preference scores of male rats for female rats and caused damage to the testicular tissue structure. Subcellular structures were particularly affected in the chronic psychological stress rats. Furthermore, the levels of MDA, NO, and NOS in testicular cells substantially increased under chronic psychological stress conditions. In conclusion, male reproductive behavioral disorders induced by chronic psychological stress are potentially linked to oxidative damage in testicular tissue.

Chronic unpredictable stress disturbs the blood-testis barrier affecting sperm parameters in mice

RESEARCH QUESTION

Does chronic stress affect the key proteins and sperm parameters of the blood-testis barrier (BTB)?

DESIGN

C57Bl/6 mice were divided into two groups: a non-treated control group and a chronic unpredictable stress (CUS) applied group. The stress status of the animals was confirmed with behavioural tests. Histopathologic evaluation was conducted by haematoxylin and eosin staining and electron microscope. Malondialdehyde, corticosterone and testosterone levels were evaluated in peripheral blood. Expression levels of BTB proteins, namely zonula occludens-1 (ZO-1), claudin-11 (CLDN11) and clathrin in Sertoli cells, were assessed by Western blotting and immunofluorescence techniques. Sperm samples were collected from cauda epididymis, and sperm parameters analysed.

RESULTS

The stress model was confirmed by behavioural tests. Histopathological evaluation of the testes demonstrated a mild degeneration in seminiferous tubules. Malondialdehyde (P = 0.008) and corticosterone levels increased (P = 0.004) and testosterone levels decreased (P = 0.005) in the CUS group. Electron microscopic evaluation confirmed the damage in BTB integrity in the CUS group. Western blot analysis showed that ZO-1 and CLDN11 levels were significantly decreased, although clathrin levels were unchanged. Although sperm concentration and total motility rate were not significantly different between the groups, progressive motility (P = 0.03), normal sperm morphology (P = 0.04), chromatin integrity (toluidine blue) (P = 0.002) and the acrosomal reaction rate (P = 0.002) were significantly decreased, and acrosomal abnormality rate was dramatically increased (P = 0.04) in the CUS group.

CONCLUSIONS

In mice, CUS disrupted BTB integrity and impaired sperm parameters. A decrease in ZO-1 and CLDN11 expression levels may be proposed as the causative factor.

Restraint stress and elevation of corticotrophin-releasing hormone in female mice impair oocyte competence through activation of the tumour necrosis factor α (TNF-α) system

Studies have observed that restraint stress (RS) and the associated elevation in corticotrophin-releasing hormone (CRH) impair oocyte competence by triggering apoptosis of ovarian cells but the underlying mechanisms are largely unclear. Although one study demonstrated that RS and CRH elevation triggered apoptosis in ovarian cells and oocytes via activating Fas/FasL signalling, other studies suggested that RS might damage cells by activating other pathways as well as Fas signalling. The objective of this study was to test whether RS and CRH elevation impairs oocytes by activating tumour necrosis factor α (TNF-α) signalling. Our invivo experiments showed that RS applied during oocyte prematuration significantly increased expression of TNF-α and its receptor (TNFR1) while inducing apoptosis in both oocytes and mural granulosa cells (MGCs). Invitro treatment of MGCs with CRH significantly increased their apoptotic percentages and levels of TNF-α and TNFR1 expression. Invitro knockdown by interfering RNA, invivo knockout of the TNF-α gene or injection of TNF-α antagonist etanercept significantly relieved the adverse effects of RS and CRH on apoptosis of MGCs and/or the developmental potential and apoptosis of oocytes. The results suggest that RS and CRH elevation in females impair oocyte competence through activating TNF-α signalling and that a TNF-α antagonist might be adopted to ameliorate the adverse effects of psychological stress on oocytes.

Restraint stress of male mice triggers apoptosis in spermatozoa and spermatogenic cells via activating the TNF-α system

Studies have indicated that psychological stress impairs human fertility and that various stressors can induce apoptosis of testicular cells. However, the mechanisms by which psychological stress on males reduces semen quality and stressors induce apoptosis in testicular cells are largely unclear. Using a psychological (restraint) stress mouse model, we tested whether male psychological stress triggers apoptosis of spermatozoa and spermatogenic cells through activating tumour necrosis factor (TNF)-α signalling. Wild-type or TNF-α-/- male mice were restrained for 48 h before examination for apoptosis and expression of TNF-α and TNF receptor 1 (TNFR1) in spermatozoa, epididymis, seminiferous tubules and spermatogenic cells. The results showed that male restraint significantly decreased fertilization rate and mitochondrial membrane potential, while increasing levels of malondialdehyde, active caspase-3, TNF-α and TNFR1 in spermatozoa. Male restraint also increased apoptosis and expression of TNF-α and TNFR1 in caudae epididymides, seminiferous tubules and spermatogenic cells. Sperm quality was also significantly impaired when spermatozoa were recovered 35 days after male restraint. The restraint-induced damage to spermatozoa, epididymis and seminiferous tubules was significantly ameliorated in TNF-α-/- mice. Furthermore, incubation with soluble TNF-α significantly reduced sperm motility and fertilizing potential. Taken together, the results demonstrated that male psychological stress induces apoptosis in spermatozoa and spermatogenic cells through activating the TNF-α system and that the stress-induced apoptosis in spermatogenic cells can be translated into impaired quality in future spermatozoa.