L-carnitine treatment during oocyte maturation improves in vitro development of cloned pig embryos by influencing intracellular glutathione synthesis and embryonic gene expression
The objective of this study was to examine the effect of L-carnitine treatment during in vitro maturation (IVM) of immature pig (Sus scrofa) oocytes. Specifically, the effects of L-carnitine treatment on nuclear maturation and oocyte intracellular glutathione (GSH) levels, embryonic development after parthenogenetic activation (PA) and somatic cell nuclear transfer (SCNT), and gene expression levels in SCNT pig embryos were determined. During IVM culture, immature oocytes were either treated or not treated with 10 mM L-carnitine. L-carnitine treatment did not improve the nuclear maturation of oocytes but significantly increased intracellular GSH levels, which led to a reduction of reactive oxygen species (ROS) levels in IVM oocytes. Oocytes treated with L-carnitine showed higher (P<0.05) rates of blastocyst formation after PA (39.4% vs. 27.1%) and SCNT (23.2% vs. 14.9%) compared with untreated oocytes. SCNT embryos that were derived from L-carnitine-treated oocytes showed increased (P<0.05) expression levels of DNMT1, PCNA, FGFR2, and POU5F1 mRNA compared with control embryos. Treatment of recipient oocytes with L-carnitine increased (P<0.05) the expression of both BAX and p-Bcl-xl mRNA in SCNT blastocysts. However, the increase was more prominent in BAX than in p-Bcl-xl mRNA. Our results demonstrate that L-carnitine treatment during IVM improves the developmental competence of SCNT embryos. This effect is probably due to increased intracellular GSH synthesis in recipient ooplasts, which reduces ROS levels, and the stimulation of nuclear reprogramming via increased expression of POU5F1 and transcription factors.