An N-glycan Tissue Atlas of Multiple Tissue Types and a Focus on DCIS

Abstract

N-glycosylation is an abundant post-translational modification of most cell-surface proteins and is critical to many cellular functions. Each organ has its own distinct N-glycome which often becomes altered in disease states, especially cancer, and serve as some of the best clinical biomarkers. However, N-glycan atlasing is far from complete, both in general tissues and specific diseases, such as ductal carcinoma in situ (DCIS). DCIS is a pre-invasive, highly prevalent breast cancer with very low chances of progressing to invasive ductal carcinoma (IDC) yet is treated aggressively with no current method to predict progression. To address these issues, I used N-glycan-targeted MALDI mass spectrometry imaging for two specific aims: 1) generating a reference database of N-glycans for matched normal and tumor tissue types and 2) identifying the N-glycome of DCIS and determining differences between pure DCIS and DCIS that has progressed into IDC as well as between primary DCIS lesions with known outcomes. In Aim 1, N-glycomes of fifteen tissue types and their respective cancers were profiled. It was found that oligomannose N-glycans and core fucosylated multiantennary N-glycans were more abundant in most cancers, and exceptions to these patterns were identified. Individual N-glycans of various kinds were significantly altered in cancer for each tissue type. Overall patterns demonstrated reduction of tissue-specific N-glycosylation patterns in corresponding cancers. Sialylation and core fucosylation were also profiled in depth. For Aim 2, the profiling methods of Aim 1 were applied to DCIS to examine differences between un-progressed and progressed DCIS as well as primary lesions with known outcomes. N-glycans colocalizing to DCIS were identified and oligomannose structures were prominent among these. Several N-glycans were determined to be significant between pure DCIS and DCIS in IDC and between DCIS that did and did not eventually progress into IDC. Gene expression of N-glycosylation-related genes was also analyzed, indicating increased branching and decreased glycoprotein quality control in DCIS that would later progress. These findings offer valuable wide-scale information for normal and cancerous tissues and DCIS, indicating potential biomarker candidates for DCIS progression and serving as a reference for future studies and potential diagnostic applications of MALDI-MSI