Abstract
If fertilization of matured oocyte does not occur, unfertilized oocyte undergoes aging, resulting in a time-dependent reduction of the oocyte’s quality. The aging of porcine oocytes can lead to apoptosis. Carbon monoxide (CO), a signal molecule produced by the heme oxygenase (HO), possesses cytoprotective and anti-apoptotic effects that have been described in somatic cells. However, the effects of CO in oocytes have yet to be investigated. By immunocytochemistry method we detected that both isoforms of heme oxygenase (HO-1 and HO-2) are present in the porcine oocytes. Based on the morphological signs of oocyte aging, it was found that the inhibition of both HO isoforms by Zn-protoporphyrin IX (Zn-PP IX) leads to an increase in the number of apoptotic oocytes and decrease in the number of intact oocytes during aging. Contrarily, the presence of CO donors (CORM-2 or CORM-A1) significantly decrease the number of apoptotic oocytes while increasing the number of intact oocytes. We also determined that CO donors significantly decrease the caspase-3 (CAS-3) activity. Our results suggest that HO/CO contributes to the sustaining viability through regulation of apoptosis during in vitro aging of porcine oocytes.
Highlights
In most mammals, a mature oocyte is in the stage of the metaphase of the second meiotic division, when it awaits fertilization
Heme oxygenase isoforms are present in porcine oocyte during in vitro aging The objective of the experiment was to localize heme oxygenase (HO)-1 and HO-2 in meiotically mature porcine oocytes (MII) and oocytes exposed to in vitro aging for the period of 24, 48 and 72 h
In comparison with meiotically matured oocytes, in oocytes aged 24 h the expression of HO-1 increased by 2.2 ± 0.2 times, aged 48 h increased by 3.5 ± 0.3 times and aged 72 h increased by 6.7 ± 1.3 times (Fig. 4A)
Summary
A mature oocyte is in the stage of the metaphase of the second meiotic division, when it awaits fertilization. If the fertilization does not occur within the time referred to as a ‘temporal window for optimal fertilization’ (Fissore et al, 2002; Goud et al, 2005), a time-dependent decrease in oocyte quality takes place, which is referred to as post-ovulatory oocyte aging (Fissore et al, 2002; Miao et al, 2009; Lord & Aitken, 2013). As well as in other mammals, the aging process takes place in both in vivo and in vitro conditions (Petrová et al, 2004; Petrová et al, 2009). The negative effects of aging include premature exocytosis of cortical granules (Szollosi, 1971), structural changes of the zona pellucida (Xu et al, 1997), the decrease of the fertilizing capability
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