In the present study, we investigated the role of binding immunoglobulin protein/glucose-regulated protein, 78-kDa (BIP/GRP78)-regulated endoplasmic reticulum (ER)-stress on meiotic maturation and cumulus cells expansion in porcine cumulus-oocyte complexes (COCs). Previously, it has been demonstrated that unfolded protein response (UPR)- related genes, such as molecules involved in ER-stress defense mechanisms, were expressed in matured oocytes and cumulus cells during in vitro maturation (IVM) of porcine oocytes. However, BIP/GRP78-mediated regulation of ER stress in porcine oocytes has not been reported. Firstly, we observed the effects of knockdown of BIP/GRP78 (an UPR initiation marker) using porcine-specific siRNAs (#909, #693, and #1570) on oocyte maturation. Among all siRNAs, siRNA #693 significantly reduced the protein levels of UPR marker proteins (BIP/GRP78, ATF4, and P90ATF6) in porcine COCs observed by Western blotting and immunofluorescence analysis. We also observed that the reduction of BIP/GRP78 levels by siRNA#693 significantly inhibited the meiotic maturation of oocytes (siRNA #693: 32.5±10.1% vs control: 77.8±5.3%). In addition, we also checked the effect of ER-stress inhibitors, tauroursodeoxycholic acid (TUDCA, 200 μM) and melatonin (0.1 μM), in BIP/ GRP78-knockdown oocytes. TUDCA and melatonin treatment could restore the expression levels of ER-stress marker proteins (BIP/GRP78, p-eIF2α, eIF2α, ATF4, and P90ATF6) in siRNA #693-transfected matured COCs. In conclusion, these results demonstrated that BIP/GRP78-mediated regulation of UPR signaling and ER stress plays an important role in in vitro maturation of porcine oocytes.

ABSTRACT
  INTRODUCTION
  MATERIALS AND METHODS
  RESULTS
  DISCUSSIONS
  REFERENCES

• Hyo-Jin Park(Dept. of Biotechnology, College of Engineering, Daegu University)
• Jae-Young Park(Dept. of Biotechnology, College of Engineering, Daegu University, Saewha Hospital, Dongnae)
• Jin-Woo Kim(Dept. of Biotechnology, College of Engineering, Daegu University)
• Seul-Gi Yang(Dept. of Biotechnology, College of Engineering, Daegu University)
• Jae-Min Jung(Dept. of Biotechnology, College of Engineering, Daegu University)
• Min-Ji Kim(Dept. of Biotechnology, College of Engineering, Daegu University)
• Joung Jun Park(Animal Reproduction & Biotechnology Center, Myung-Poom Hanwoo Consulting)
• Deog-Bon Koo(Dept. of Biotechnology, College of Engineering, Daegu University) Corresponding Author