Apoptosis in human cumulus cells in relation to maturation stage and cleavage of the corresponding oocyte

Abstract

The purpose of this study was to determine the incidence of apoptosis in cumulus cells, and correlate these findings with the maturation stage, fertilization rate and embryo score of the corresponding oocyte, in couples undergoing ICSI due to a male factor. The study group consisted of 21 couples where ICSI was performed. The total number of oocyte-cumulus complexes retrieved was 164. Sperm samples were assessed according to the WHO manual, morphology according to the strict criteria and for the presence of apoptosis. The degree of apoptotic DNA fragmentation was determined using the free 3'OH DNA termini in situ with chemically labeled and unlabeled nucleotides. The study was blinded for the technician involved in the assessments of apoptosis in the cumulus cells, apoptosis and morphology in spermatozoa. Ovarian hyperstimulation was carried out according to a long down regulation protocol using GnRH, recFSH and hCG. A maximum of 3 embryos were transferred on day 2 after ICSI. This study demonstrated that the incidence of apoptosis was significantly higher in cumulus cells from germinal vesicle and metaphase I oocytes compared to cumulus cells from metaphase II oocytes (p<0.0001). Non-fertilized metaphase II oocytes showed significantly higher incidence of apoptosis in cumulus cells compared to fertilized metaphase II oocytes (p=0.0082). Furthermore, apoptosis in spermatozoa had an impact on the embryo score (p=0.0087). Comparing apoptosis in cumulus cells with maturity of the corresponding oocytes, a significantly higher degree was found related to immature oocytes. Apoptosis in cumulus cells from human metaphase II oocytes impaired the fertilization rate. The degree of fragmentation in the embryo might be correlated to apoptosis in the spermatozoa.