A sweet view of reproduction.

CONCEPTIONS A sweet view of reproduction In recent years, the advent of ‘omics’ has permitted large- scale molecular comparisons of cells, tissues, and secretions under different conditions. In reproductive medicine, ovarian and breast cancer, endometriosis, infertility, and failed implantation contribute signiﬁcantly to the global burden of diseases. Much focus has been given to genomic markers used to generate molecular signatures of cells and organs, but more than 50% of expressed proteins are further modiﬁed by cotranscriptional and posttranscriptional events, which may not be reﬂected in altered gene expression proﬁles alone. The availability of newer secretomic technologies is aimed at recognizing diagnostic biomarkers in human body ﬂuids in the hope of identifying disease markers. Much of the focus has been on proteomics, particularly with the recent advances in mass spectrometry instrumentation that have enabled identiﬁcation and quantiﬁcation of proteins abundance between normal and disease states. The last two decades have also seen signiﬁcant improve- ments in the feasibility of glycan (oligo- and polysaccharides attached to glycoconjugates such as glycolipids, glycoproteins, and proteoglycans) analyses based on mass spectrometry. Gly- comic proﬁling allows both the monosaccharide composition analysis of tissue samples and the detailed proﬁling of different classes of glycans. It is now possible to gain important knowl- edge about the identity and abundance of glycoconjugates from even very limited biologic samples. As it turns out, all living cells are coated by a thick glycocalyx (sugar coat) consisting of complex oligo- and polysaccharides attached to glycoproteins and glycolipids. Some glycoproteins, such as mucins on epithelia (including endometrium), are 50% to 80% glycan by mass. Unlike protein synthesis, glycosylation is not a template- driven process but rather results from sequential actions of cotranslationally and posttranslationally active enzymes in the endoplasmic reticulum and Golgi apparatus of cells. The same protein can have radically different biological effects based on the glycan modiﬁcation that is added. Glycosylation plays an important role in diverse protein functions, commu- nication between the cell and its environment, immune recognition and response, inﬂammation, and tissue and or- gan development (1). Changes in glycoprotein moieties result in altered biological function and have been observed in can- cer, diabetes, rheumatoid arthritis, and cardiovascular- immunologic-congenital-infectious disorders. In women with ovarian cancer, a decrease in galactosylation of IgG and an increase in sialyl Lewis X, with an increased half- life and decreased apoptosis rate of cells, have been seen (2). Glycomic proﬁling allows both the monosaccharide composition analysis of tissue samples and the detailed proﬁling of different classes of glycans (N- and O-glycans) released from the proteins to which they are attached as well as glycosaminoglycans and glycolipids in vivo. In breast cancer, certain N-glycans have been found as highly probable biomarkers of the disease, and alterations in the plasma N- glycome in patients with endometriosis suggests a potential marker of endometriosis. The surface of gametes is no exception. Sperm have a particularly thick glycocalyx, and oocytes have a polysaccha- VOL. - NO. - / - 2015 ride (hyaluronic acid) matrix that surrounds the egg and its complex mesh of zona pellucida glycoprotein heteropoly- mers, which bear species-speciﬁc glycans (3). Furthermore, seminal ﬂuid and uterine secretions contain large amounts of secreted glycoconjugates such as glycodelin, which carry sex-speciﬁc modiﬁcations. Moreover, the immune environ- ment of the female reproductive tract includes antibodies targeting glycans on sperm surface glycoproteins, such as CD52 with sperm-speciﬁc glycans. Sperm also achieve strong immune evasion by being coated with highly sialylated gly- copeptides such as b-defensin-126 (4). Glycoproteins secreted by the female also vary across the reproductive cycle (e.g., cervical mucin) and along the reproductive tract; for example, glycodelin has different glycoforms in the uterus, the oviduct, and the cumulus. Furthermore, mammalian sperm carry neur- aminidases that modify their sialic acids during capacitation, and inhibition of their activity in vitro can compromise capacitation and sperm-zona pellucida binding in mice (5). Given the important roles of glycoconjugates for many biological recognition processes, including fertilization, devel- opment, inﬂammation, and immunity, the inclusion of glyco- biological analyses (glycomics) will be crucial to provide an integrated view combined with genomic, proteomic, metabolo- mic, and lipidomics (all the -omics) and to improve our under- standing of key determinants in human reproduction. Steven R. Lindheim, M.D., M.M.M. a Pascal Gagneux, Ph.D. b a Department of Obstetrics and Gynecology, Boonshoft School of Medicine, Wright State University, Dayton, Ohio; and b Division of Comparative Pathology and Medicine, Department of Pathology, University of California, San Diego, California http://dx.doi.org/10.1016/j.fertnstert.2015.06.009 You can discuss this article with its authors and with other ASRM members at http://fertstertforum.com/lindheims-sweet-view- reproduction/ Use your smartphone to scan this QR code and connect to the discussion forum for this article now.* * Download a free QR code scanner by searching for “QR scanner” in your smartphone’s app store or app marketplace. REFERENCES Varki A. Biological roles of oligosaccharides: all of the theories are correct. Glycobiology 1993;3:97–130. Qian Y, Wang Y, Zhang X, Zhou L, Zhang Z, Xu J, et al. Quantitative analysis of serum IgG galactosylation assists differential diagnosis of ovarian cancer. J Proteome Res 2013;12:4046–55. Tecle E, Gagneux P. Sugar-coated sperm: unraveling the function of the mammalian sperm glycocalyx. Mol Reprod Dev 2015 Jun 9; http:// dx.doi.org/10.1002/mrd.22500. [Epub ahead of print]. Tollner TL, Bevins CL, Cherr GN. Multifunctional glycoprotein DEFB126—a curious story of defensin-clad spermatozoa. Nat Rev Urol 2012;9:365–75. Ma F, Wu D, Deng L, Secrest P, Zhao J, Varki N, et al. Sialidases on mammalian sperm mediate deciduous sialylation during capacitation. J Biol Chem 2012;