The effect of conditioned media on mouse oocytes ultrastructure following in vitro maturation

Abstract

Optimizing the culture condition and vitrification process during in vitro maturation (IVM) of oocyte has been controversial. This study aimed to evaluate the effect conditioned medium (CM) enriched with human mesenchymal stem cells (hUCM) derived from bone marrow and umbilical cord blood on the ultrastructure of immature mouse oocytes during IVM. Three hundred ninety-two germinal vesicle (GV) oocytes were obtained from mouse ovaries. They were divided into fresh IVM (fIVM) and vitrified IVM (vIVM) groups and cultivated in either alpha Minimum Essential Medium (α-MEM) (control) or CMs supplemented with supernatants derived from cultures of bone marrow or umbilical cord mesenchyme stem cells (MSCs). Then the maturation rate was evaluated in the experimental groups. Twelve in vivo fresh mature oocytes were randomly obtained from uterine tubes as the control group. Finally, 43 matured IVM oocytes were randomly selected for ultra-structural evaluations using transmission electron microscopy (TEM). Oocyte maturation rates were significantly higher in fIVM than vIVM groups. The highest maturation rate was observed in the fIVM umbilical cord MSCs while the lowest rate was related to α-MEM vIVM (86.44% vs 72.72%). There was an increase in the number of mitochondria–vesicle (MV) complexes in IVM groups. Also, the distribution of cortical granules showed the highest decline in α-MEM vIVM groups. The highest aggregations of mitochondria–SER (M-SER) were observed in fIVM umbilical cords. Oolemma had an irregular border with small microvilli in vIVM groups. The Zona pellucida was darker in the vIVM than fIVM groups. In conclusion, umbilical cord MSCs showed a superior efficacy than bone marrow cells for supporting oocyte maturation and conserving its ultrastructure.