ANIMAL

Adverse effect of IL-6 on the in vitro maturation of porcine oocytes

Young-Joo Yi1,*   Adikari Arachchige Dilki Indrachapa  Adikari1   Seung-Tae Moon1   Jung-Min Heo2   Sang-Myeong Lee3   

1Department of Agricultural Education, College of Education, Sunchon National University, Suncheon 57922, Korea
2Department of Animal Science and Biotechnology, Chungnam National University, Daejeon 34134, Korea
3Laboratory of Veterinary Virology, College of Veterinary Medicine, Chungbuk National University, Cheongju 28644, Korea

Abstract

Cytokines are protein mediators that possess the ability to assist cell-to-cell communication in immune system-related activities. In general, pathogen endotoxins activate the release of inflammatory mediators, and with time, there is an increase in the cytokine levels in the body. Interleukin (IL)-6 mediates the acute-phase inflammatory response, and elevated IL-6 levels have been reported in peritoneal fluids of women with pelvic inflammation and endometriosis, thereby associating it with oocyte quality and infertility. To overcome subfertility or infertility in humans and animals, the present study was done to examine the effect of recombinant IL-6 on porcine oocytes matured in vitro and subsequently to determine the fertilization rate and embryo development. Porcine oocytes were incubated with varying concentrations of IL-6 (0 - 2 µg·mL-1) for 44 h followed by in vitro fertilization and culturing of the oocytes. The oocytes or embryos were fixed with 3.7% paraformaldehyde (PFA) and stained with fluorescence dyes, and the meiotic spindle, chromosome organization, fertilization status and embryo development were subsequently assessed under a fluorescence microscope. We observed induction of an abnormal meiotic spindle alignment in the oocytes incubated with IL-6 compared to the control oocytes incubated without IL-6. Moreover, significantly decreased fertilization rates and embryo development were observed for oocytes incubated with IL-6 (p < 0.05). Thus, an increased IL-6 level during oocyte maturation could be associated with fertilization failure due to an aberrant chromosomal alignment and a disruption of the cortical granules. Taken together, our results indicate that successful assisted reproduction can be achieved by controlling the levels of inflammatory cytokines.

Figures & Tables

Fig. 1. Representative patterns of cortical granule (CGs) migration and meiotic spindle formation in oocytes matured in the absence (A-A”’ and B-B”’; absence [W/O]) or presence (C-C”’ and D-D”’) of 1 μg·mL interleukin-6 (IL-6) during maturation (IVM). DNA: 4’6’-diamidino-2- phenylindole (DAPI) (blue), cortical granules (CGs): FITC-conjugated agglutinin (LCA) (green), spindle: ß-tubulin (red). A-A”’ and C-C”’: × 400, B-B”’ and D-D”’: × 1,000 magnification.