Granulosa Cell Conditioned Medium Enhanced In Vitro Maturation and Developmental Potential of Mice Oocytes by Improving Mitochondrial Function, ATP Synthesis, and REDOX System

Abstract

Background: The aim of this study was to compare the effects of base medium supplemented with knock-out serum replacement (KSR; BMK group) or foetal bovine serum (FBS; BMF group) and granulosa cell conditioned medium (GCCM) prepared with KSR (CMK group) or FBS (CMF group) on in vitro maturation (IVM) of immature murine oocytes. Materials and Methods: In this experimental study, the BMF, BMK, CMF, and CMK media were assessed for lactate and pyruvate content, and total antioxidant capacity (TAC). Immature oocytes were cultured with these IVM media. Maturation rate [proportion of oocytes at metaphase II (MII) stage], mitochondrial membrane potential (MMP), ATP content, reactive oxygen species (ROS), and embryonic development following in vitro fertilisation (IVF) were evaluated in the cultured oocytes. Results: Immature oocytes cultured with BMK had the highest degeneration and lowest maturation rate (68.16% of MII-stage oocytes). The resultant in vitro-matured oocytes had the worst embryonic development (8.47% of blastocyst-stage embryos, P<0.05), which might be due to the low lactate content of this medium. Immature oocytes cultured in media that contained GCCM (CMF and CMK) had superior maturation rates (81.18 and 82.24% of MII-stage oocytes, respectively). The resultant in vitro-matured oocytes had higher mitochondrial activity and ATP, lower ROS and greater embryonic development (42.62 and 35.59% of blastocyst-stage embryos, respectively, P<0.05). This finding was probably related to the higher lactate content and antioxidant capacity of GCCM versus base medium. Conclusion: KSR was recognized as an unsuitable nutrient supplement for IVM of oocytes in mice, probably due to its lack of lactate. GCCM supplementation of IVM medium improved maturation rate, quality, and developmental potential of the in vitro-matured oocytes.