Investigation of Cumulus Cell Factors Associated With Embryo Development and Pregnancy Outcome in Human IVF

Recent evidence suggests that the expression of some candidate genes in cumulus cells (CC) have the potential to serve as markers of oocyte quality. The aims of this study were: 1) to validate a multiplex quantitative polymerase chain reaction (QPCR) method to measure four genes simultaneously in extracts from individual CC and; 2) to investigate the relationships in individual cumulus-oocyte-complexes (COC) amongst the expression levels of a range of candidate genes (N=8) from individual CC, the numbers of CC per COC and developmental indicators (good blastocyst development and live birth outcome) of the associated oocytes following in vitro fertilization (IVF) with intra-cytoplasmic sperm injection (ICSI). Sixty eight women were recruited for this study following approval from NZ Multi-Regional Ethics Committee and classified into four research groups: young and healthy women (<38 years, N=25), young women with polycystic ovarian syndrome (<38 years, N=11), young with diminished ovarian reserve (<38 years, N=12) and older and healthy women (≥40 years, N=20). Following exogenous rFSH-assisted ovarian stimulation, 608 COC were collected and subjected to ICSI. Oocyte and embryo quality, and pregnancy outcomes were recorded. Expression levels of the following candidate genes HAS2, FSHR, SLC2A4 (GLUT4), ALCAM, SFRP2, VCAN, NRP1 and PR in CC extracts from individual COC were measured by TaqMan QPCR and normalized against the house-keeping gene, RPL19. The numbers of CC from individual COC were calculated from RPL19 expression levels plotted against a standard curve of CC number. These results were then assessed against the outcomes of the associated oocytes following ICSI. HAS2, FSHR, ALCAM, VCAN, NRP1 and PR mRNA were detectable in most samples (98.5%) whereas those for SLC2A4 and SFRP2 were generally undetectable. The minimum number of CC required for QPCR was estimated to be ~70. The mean levels of FSHR mRNA were up-regulated in young women with PCOS compared to those in the other two groups of women <38y. Expression levels of HAS2 across all four groups of women were correlated to both biological (age, basal serum FSH and serum AMH) and treatment (amount of rFSH used for stimulation, follicle numbers and COC retrieved) variables. Investigations related to oocyte development in young and healthy women showed that 1) mean mRNA levels of VCAN, HAS2 and PR were higher (P=0.002, P<0.05, P<0.05, respectively) in CC associated with oocytes that resulted in good quality blastocysts and those of VCAN were higher (P<0.05) in CC associated with oocytes that resulted in a live birth, compared with those with developmental failure. However, the expression levels of all measurable candidate genes were highly variable for individual CC from COC from each woman. Indeed, 99.7% of individual COC were different in CC mRNA levels and cell composition. The application of a ranking method to score the relative CC mRNA levels of selected candidate genes from each COC recovered from individual women was evaluated. This approach demonstrated a predictive power of 80% efficiency for selecting good quality oocytes (at least one), whilst requiring the insemination of no more than three oocytes in any treatment cycle. Furthermore, this selection method resulted in a pregnancy and live birth rate of 60 and 52% respectively (N=25 women). This outcome is similar to that achieved when all metaphase II (MII) oocytes are inseminated. In conclusion, this study has validated a multiplex QPCR method to quantify the expression levels of four genes in CC of individual human COC simultaneously using as few as 70 cells. Moreover, that there is sufficient cDNA so that many more candidate genes can be measured in the same extract. From the knowledge of the mRNA levels of at least four genes, VCAN, FSHR, HAS2 and PR in CC, it is possible to improve upon existing biological indicators the potential to predict good blastocyst formation and a successful pregnancy outcome. It is concluded that the application of a multiplex QPCR approach to assess the expression levels of a limited number of marker genes in CC can be used to select the best oocytes for successful pregnancy outcomes.