(330) Effects of liver function on gene expression in cumulus cells and oocyte development potential in fattened Japanese black cattle

Mayuko Anazawa1,2; Shiori Ashibe 2; Yoshikazu Nagao 1,2

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

2University Farm, Utsunomiya University, Tochigi, Japan

Abstract Text:

The nutritional status of females affects their oocyte fertility, and both low energy status and obesity negatively affect reproductive function. On the one hand, we previously reported that liver disease caused by low energy status is associated with reduced oocyte fertility in dairy cows. On the other hand, excess energy intake and obesity induce fatty liver and cirrhosis. Because liver function is closely related to ovarian function, we considered that impaired liver function due to obesity might also affect oocyte quality, although the detailed mechanism underlying obesity is unknown. Among various breeds of cattle, the Japanese black cow has the highest capacity for fat production; therefore, we considered it a suitable model for studying the impacts of obesity in large animals. Here, we examined the effects of obesity-associated liver disease on gene expression in periovarian cumulus cells (CC) and early oocyte developmental potential in fattened Japanese black cattle.

Japanese black cattle at the slaughterhouse were classified as fattened cattle for meat or non-fattened cattle for breeding. Cumulus-oocyte complexes (COCs) and follicular fluid (FF) were aspirated from small follicles in the ovaries of individual cows and the concentration of γ-glutamyl transpeptidase (γ-GTP) in each FF sample was immediately measured. Fattened cattle whose livers were completely discarded due to liver disease diagnosed by the veterinarian in the slaughterhouse, and whose γ-GTP concentration in FF was higher than 50 IU/L were classified as having liver disease (LD) and included in the LD group (n=11). Non-fattened cattle with healthy livers and whose γ-GTP concentration in FF was less than 50 IU/L were included in the control group (n=12). Mitochondrial (Mt) membrane potential and reactive oxygen species (ROS) levels in oocytes were measured by fluorescent staining. CCs were collected from COs before in vitro maturation at a site close to the oocyte, and the levels of IGF-1R, IRS1/2, and EGFR mRNA in CCs were quantified by real-time PCR. Each group of COCs was subjected to in vitro culture, and the number of morphologically high-quality oocytes, cleavage rate, and rate of blastocyst development were recorded.

The results showed that oocyte Mt activity was lower and ROS content was higher in the LD group than in the control group (P < 0.05). In addition, levels of IGF-1R, IRS2, and EGFR mRNA in CCs were lower in the LD group (P < 0.05). Furthermore, the rate of good oocytes (60.1% vs 49.2%) and the rates of blastocyst development (27.6% vs 14.3%) were lower in the LD group than in the control group (P < 0.05).
Collectively, the findings indicate that γ-GTP levels in FF are raised, oocyte ROS levels are increased, and Mt activity is decreased in obesity-induced liver disease. They also suggest that metabolic abnormalities associated with liver disease reduce the gene expression of receptors essential for oocyte development in CCs. In conclusion, these factors and their associated mechanisms may play a role in the reduced oocyte development potential caused by obesity.