An insight into pluripotency and cellular aging through glycan analysis

All kinds of cells from all kinds of organisms (i.e., animals, plants, fungi and bacteria) are covered by a dense layer of glycans. The origin of glycans or carbohydrates is not known^[1], however, the above fact implies that they are widely and closely associated with various biological phenomena based on cellular communications, which include development, differentiation, morphogenesis, carcinogenesis, immunity and infection. It is also notable that glycoproteins, one of existing forms of glycans (i.e., glycoconjugates) are generally synthesized in lumen sites of endoplasmic reticulum and the following Golgi apparatus, distinct from cytoplasmic proteins, which are not subjected to glycosylation, a major event of posttranslational modifications. In fact, glycan structures largely depend on a series of (e.g., >200 in human) glycol-genes, which are defined as genes involved in glycan synthesis (e.g., glycosyltransferases, sulfotransferases, nucleotide sugar transporters), of which expressions differ under different conditions. Because expression of each glycol-gene differs in different cell types (e.g., biological origin, tissue) and states (e.g., developmental stage, malignancy), glycans can be a good marker for cell typing (e.g., SSEA-1) and serum diagnosis (e.g., cancer biomarker such as CA19-9). However, glycan preparation as well as its analysis and total understanding are much more difficult compared with other major disciplines like genomics and proteomics. As a result, most of nonglycoscientists tend to hesitate glycomics, i.e., "glycophobia". Nevertheless, glycoscience is a very important field of life science, particularly in the future, without which many remaining issues will not be solved. In this plenary lecture, a novel approach to glycan profiling^[2] and its applications to biomarker investigation and regenerative medicine^[3] will be described.