The human endometrium must be receptive for successful embryo implantation to occur. To achieve receptivity, the endometrium undergoes a variety of morphological and molecular changes during a woman’s menstrual cycle. Secretion of some proteins found within uterine fluid is cyclic and may be indicative of receptivity or a woman’s fertility status. A 2D-DIGE study showed differential expression of protease inhibitor alpha-2-macroglobulin (A2M) isoforms between fertile and infertile women, and phase of menstrual cycle, arising from post-translational modifications i.e. glycosylation. Specific glycoforms of A2M and their use as biomarkers of endometrial receptivity has not previously been investigated.
We hypothesised that specific A2M glycoforms may be differentially expressed according to fertility status and phase of menstrual cycle, and may serve as biomarkers of endometrial receptivity. Our aim was to identify protein glycoforms that discriminate fertile and infertile, receptive and non-receptive endometrium.
An array of 21 lectins was used to investigate glycoform distribution of A2M in uterine lavage; collected during proliferative and secretory phases, from fertile and infertile women (n=6/group). Lectins showing the most promising differences between these groups were examined further using an A2M-lectin Luminex assay. The influence of hormone treatment on A2M glycoform expression by endometrial epithelial cell lines was investigated.
The A2M glycoform distribution was altered between fertile and infertile, proliferative and secretory phases. LEL binding glycoform was significantly lower (p<0.05) in infertile women during the proliferative phase. DBA and GSL-I binding glycoforms were significantly (p<0.05) altered between phases of the menstrual cycle and were significantly lower (p<0.05) in infertile women during the mid-secretory phase. Endometrial cell lines showed a different glycoform distribution compared to uterine lavage.
Specific glycoforms of A2M may be useful biomarkers of endometrial receptivity and fertility status. Additionally, cancer cell lines may not provide an accurate representation of protein glycoform expression.