Characterization of transferrin glycopeptide structures in human cerebrospinal fluid

Transferrin in cerebrospinal fluid (CSF) exists as a mixture of silao and asialoglycoforms believed to originate from liver and brain respectively. We have previously shown that alteration in the asialoglycoform pattern could be an indication of certain anomalies in the central nervous system. Additionally, CSF asialo-transferrin has been shown to be a reliable marker to assess cerebrospinal leakage in head trauma. Therefore, the CSF transferrin glycoform pattern could be a useful diagnostic and prognostic tool. In this study we sought to characterize, in-depth, the transferrin glycovariants in cerebrospinal fluid using a combination of two-dimensional gel electrophoresis and high precision mass spectrometry analysis. Cerebrospinal fluid transferrin was detected as multiple spots (seven major spots) with different isoelectric points and slight shift in apparent molecular mass. High resolution (>60,000) and high accuracy (<3 ppm error) mass spectrometry analysis revealed that each spot had a unique glycopeptide signature. MSn analysis enabled characterization of the glycan structure directly from the in-gel digested spots. The multiple spots detected for cerebrospinal fluid transferrin were mainly due to heterogeneity of di-antennary and tri-antennary glycans harboring a varying number of terminal N-acetylneuraminic acids and the existence of a high mannose and high N-acetylhexosamine glycosylated species.

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► Cerebrospinal fluid transferrin exists as a mixture of sialo and asialoglycoforms.
► Cerebrospinal fluid asialo-transferrin is a specific brain-type and does not normally occur in blood.
► Altered glycosylation patterns in cerebrospinal fluid transferrin is indicative of neurodegenerative diseases.