Impact of oxidative stress in aged mouse oocytes on calcium oscillations at fertilization

Abstract

In vivo post-ovulatory aging of oocytes significantly affects the development of oocytes and embryos. Also, oocyte aging alters the regulation of the intracellular calcium concentration, thus affecting Ca(2+) oscillations in fertilized oocytes. Because reactive oxygen species (ROS) are known to significantly perturb Ca(2+) homeostasis mainly through direct effects on the machinery involved in intracellular Ca(2+) storage, we hypothesized that the poor development of aged oocytes that may have been exposed to oxidative stress for a prolonged time might arise from impaired Ca(2+)-oscillation-dependent signaling. The fertilization rates of aged oocytes and of fresh oocytes treated with 100 microM hydrogen peroxide (H(2)O(2)) for 10 min were significantly lower than that of fresh oocytes. Comparing within the fertilized oocytes, blastocyst formation was decreased while embryo fragmentation was increased similarly in the aged and H(2)O(2)-treated fresh oocytes. The frequency of Ca(2+) oscillations was significantly increased whereas the amplitude of individual Ca(2+) transients was lowered in the aged and H(2)O(2)-treated fresh oocytes. The rates of rise and decline in individual Ca(2+) transients were decreased in these oocytes, indicating impaired Ca(2+) handling. When lipid peroxidation was assessed using 4,4-difluoro-5-(4-phenyl-1,3-buttadienyl)-4-bora-3a, 4a-diaza-s-indacene-3-undecanoic acid (C11-BODIPY) in unfertilized oocytes placed in a 5% CO(2) in air atmosphere, the green fluorescence (indicating lipid peroxidation) increased faster in the aged oocytes than in the fresh oocytes. Furthermore, the green fluorescence in the aged oocytes was already approximately 20 times higher than that in the fresh oocytes at the beginning of the measurements. These findings support the idea that Ca(2+) oscillations play a key role in the development of fertilized aged oocytes.

Deficit of mitochondria-derived ATP during oxidative stress impairs mouse MII oocyte spindles

“…The data from the present study further reinforce the fact that normal mitochondria function is essential to maintaining the integrity of the MT network and meiotic apparatus including spindles [23,31]. As a source of ROS, mitochondria is meanwhile a well-known vulnerable target of ROS and its responses to oxidative stress have been investigated in various fields, especially in studying oocytes and embryos during apoptosis, fertility and development [32][33][34], supporting the theory that free oxygen radicals induce aging [35][36][37]. Our present results demonstrate that dysfunction of oocytic mitochondria, which is directly caused by oxidants via opening mitochondrial PTPs, may further impair the ability of oocytes to form normal meiotic apparatuses.…”

Inhibition of c-Jun N-terminal kinase (JNK) suppresses porcine oocyte ageing in vitro

“…ROS induce apoptosis not only by activating JNK and the subsequent release of cytochrome c from mitochondria, but also through endoplasmic reticulum (ER) (He et al, 2008) which is closely related to maintaining intracellular calcium homeostasis . Increased ROS level affects calcium signalling and leads to the increase of cytoplasmic concentration of calcium cations (Takahashi et al, 2003).…”

In vitro aging of porcine oocytes

“…The spontaneous parthenogenetic activation of in vitro aged pig oocytes could be due to this mode of MPF inactivation. But it could also be due to the destruction of cycline B induced by changes in intracellular calcium levels, because the intracellular calcium signalling is significantly altered in aged oocytes (Takahashi et al, 2000(Takahashi et al, , 2003.…”

“…The fragmentation of aged oocytes is generally thought to be the result of apoptosis (Perez and Tilly, 1997;Perez et al, 1999). This is not surprising because it is well known that the apoptosis is induced by changes in intracellular calcium levels (Orrenius et al, 2003) and that calcium signalling is severely disturbed in aged oocytes (Takahashi et al, 2000(Takahashi et al, , 2003.…”