Effects of calcium-free ageing on ethanol-induced activation and developmental potential of mouse oocytes.

Although ethanol treatment is widely used to activate oocytes, the underlying mechanisms are largely unclear. Roles of intracellular calcium stores and extracellular calcium in ethanol-induced activation (EIA) of oocytes remain to be verified, and whether calcium-sensing receptor (CaSR) is involved in EIA is unknown. This study showed that calcium-free ageing (CFA) in vitro significantly decreased intracellular stored calcium (sCa) and CaSR expression, and impaired EIA, spindle/chromosome morphology and developmental potential of mouse oocytes. Although EIA in oocytes with full sCa after ageing with calcium does not require calcium influx, calcium influx is essential for EIA of oocytes with reduced sCa after CFA. Furthermore, the extremely low EIA rate in oocytes with CFA-downregulated CaSR expression and the fact that inhibiting CaSR significantly decreased the EIA of oocytes with a full complement of CaSR suggest that CaSR played a significant role in the EIA of ageing oocytes. In conclusion, CFA impaired EIA and the developmental potential of mouse oocytes by decreasing sCa and downregulating CaSR expression. Because mouse oocytes routinely treated for activation (18 h post hCG) are equipped with a full sCa complement and CaSR, the present results suggest that, while calcium influx is not essential, CaSR is required for the EIA of oocytes.

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 induces apoptosis in spermatozoa and spermatogenic cells: role of the FasL/Fas system†.

The mechanisms by which psychological stress impairs semen quality are largely unknown. By using a restraint-stressed mouse model, we studied the role of the FasL/Fas system in psychological stress-induced apoptosis of spermatozoa and spermatogenic cells. Male mice were restrained for 48 h before examination for sperm fertilizing potential and for apoptosis and FasL/Fas expression in spermatozoa, spermatogenetic cells/seminiferous tubules, and caudae epididymides. The results showed that the male restraint reduced motility, fertilization rates, and mitochondrial membrane potential while increasing apoptosis and Fas expression in spermatozoa. Restraint also facilitated apoptosis and FasL/Fas expression in spermatogenic cells/seminiferous tubules and caudae epididymides. The restraint-induced apoptosis in spermatozoa and spermatogenic cells was significantly ameliorated in gld mice that harbor a loss-of-function mutation in FasL. However, incubation with FasL did not affect sperm motility and apoptosis, while incubation with tumor necrosis factor (TNF)-α did. The epididymis of the gld mice produced significantly less TNF-α and TNF-related apoptosis-inducing ligand (TRAIL) than that of wild-type mice did after male restraint. Thus, the results confirmed that the FasL/Fas system played an important role in the psychological stress-induced apoptosis of spermatozoa and spermatogenic cells and that FasL triggered sperm apoptosis in epididymis dependently through promoting TNF-α and TRAIL secretion.