(276) Effects of maternal liver abnormality on in vitro maturation of bovine oocytes

Yoshikazu Nagao^1,2, Shiori Ashibe², Yui Kobayashi², Shusuke Toishikawa², Mayuko Anazawa^1,2

¹United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, Tokyo, Japan

2University Farm, Utsunomiya University, Tochigi, Japan


Abstract Text:

It is known that variations in physiological conditions in female donors lead to differences in the developmental potential of oocytes in vitro. In cattle, for example, maternal liver function is known to influence oocyte and embryo quality; however, the detailed mechanisms underlying this association are not yet clear. Here, we examined whether maternal liver abnormalities in dairy cattle affect the in vitro maturation of oocytes by screening meiotic maturation, spindle morphology, actin filaments, and lysosomes.

Ovaries were obtained from Holstein dairy cows that had been slaughtered. An experienced veterinarian assessed the livers, and two groups of cows were established: a control group with normal livers (n=9), and a group with structural liver abnormalities, such as fatty liver, hepatitis, or liver degeneration (n=7). Cumulus–oocyte complexes (COCs) and follicular fluid (FF) were aspirated from the ovaries of each group in the laboratory. Samples of FF from each cow were analyzed for γ-glutamyl transpeptidase, which was confirmed to be lower than 50 IU/L in the control group and higher than 50 IU/L in the abnormal group . The two groups of COCs were subjected to in vitro culture, and examined for in vitro oocyte maturation rate, spindle morphology (area, width, and length) and chromosome alignment, cortical actin filament levels, and lysosome levels (metaphase II oocytes).

The results showed that the maturation rate (80.2%) was significantly lower in oocytes from the abnormal liver group as compared with the control group (90.8%; P < 0.05).  In contrast, the mean spindle area in oocytes from the abnormal group (50.4 ± 3.4 μm2) was significantly larger than that in control oocytes (40.8 ± 1.6 μm2; P< 0.05). Likewise, the mean spindle width was significantly larger in the abnormal group (8.8 ± 0.3 μm) than in the control group (7.8 ± 0.2 μm; P < 0.05). The proportion of cells with correctly aligned chromosomes was significantly lower in the abnormal group (48.0%) than in the control group (78.3%; P < 0.05). The number of cortical actin filaments in mature oocytes was significantly lower in the abnormal group (299.3 ± 3.7) than in the control group (314.7 ± 3.2; P < 0.05), while the number of lysosomes in mature oocytes was significantly higher in the abnormal group (1363.6±39.0 vs 1123.4 ± 26.3; P < 0.05).

In conclusion, our findings indicate that the quality of in vitro matured oocytes is lower in cattle with liver abnormalities than in healthy cattle, highlighting spindle morphology, actin filaments, and lysosomes as potential factors that influence the success of in vitro maturation.