Unique proteomic fingerprints of human cumulus cells correlate with embryo morphology

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OBJECTIVE: The ability to non-invasively screen for oocyte competence would assist not only in selecting which oocytes to inseminate, but also in improving embryo selection in human IVF. Several studies have shown that specific gene changes in cumulus cells (CCs) can be correlated with various measures of IVF outcome. However, it is the proteins produced by gene transcripts that realize biological function. This study investigated the CC proteome of individual human oocytes and their relationship to embryonic development. DESIGN: Proteomic analysis of human CCs. MATERIALS AND METHODS: Infertile couples (n=8) undergoing IVF treatment donated CCs with consent, following oocyte retrieval. CCs were trimmed and approximately 100 cells per individual oocyte (n=30) were extracted in lysis buffer and processed prior to analysis using surface enhanced laser desorption ionization time-of-flight mass spectrometry to determine a cumulus cell proteomic fingerprint. Oocytes were cultured separately with embryo assessment performed on days 3 and 5. The following groups were analyzed; oocytes that failed to fertilize (n=8), cleavage stage arrest embryos (n=8) and developing blastocysts (n=14). RESULTS: Unique CC proteomic fingerprints were consistently generated according to embryo morphology. Statistical analysis revealed a novel CC profile based on the inclusion of five proteins across the range of 7.5-16.5 kDa to be differentially expressed across embryos of different morphologies (P < 0.01). In particular, the CC proteomic fingerprint of developing blastocysts displayed higher expression of all five proteins. Oocytes that did not fertilize exhibited the lowest levels of expression, whilst embryos that arrested during the cleavage stage showed higher expression than unfertilized oocytes but lower compared to developing blastocysts (P < 0.01). A potential candidate ID for the 16.5kDa biomarker is presenilin-2, involved in cell division, differentiation and modulation of intracellular calcium signaling. CONCLUSIONS: This study has shown that like certain aspects of the CC genome, its proteome also correlates to morphological characteristics of resulting embryos. Oocytes which subsequently developed to blastocyst exhibit a unique CC proteomic fingerprint with significantly higher expression of a novel panel of proteins that could form the basis of a non-invasive assay to determine oocyte and embryo developmental competence. Additionally, this approach of protein analysis could improve our understanding of oogenesis.