Data_Sheet_2_Human Brain and Blood N-Glycome Profiling in Alzheimer’s Disease and Alzheimer’s Disease-Related Dementias.docx

Glycosylation, the process of adding glycans (i.e., sugars) to proteins, is the most abundant post-translational modification. N-glycosylation is the most common form of glycosylation, and the N-glycan moieties play key roles in regulating protein functions and many other biological processes. Thus, identification and quantification of N-glycome (complete repertoire of all N-glycans in a sample) may provide new sources of biomarkers and shed light on health and disease. To date, little is known about the role of altered N-glycome in Alzheimer’s Disease and Alzheimer’s Disease-related Dementias (AD/ADRD). The current study included 45 older adults who had no cognitive impairment (NCI) at baseline, followed and examined annually, and underwent brain autopsy after death. During about 12-year follow-up, 15 developed mild cognitive impairment (MCI), 15 developed AD, and 15 remained NCI. Relative abundances of N-glycans in serum at 2 time points (baseline and proximate to death, ∼12.3 years apart) and postmortem brain tissue (dorsolateral prefrontal cortex) were quantified using MALDI-TOF-MS. Regression models were used to test the associations of N-glycans with AD/ADRD phenotypes. We detected 71 serum and 141 brain N-glycans, of which 46 were in common. Most serum N-glycans had mean fold changes less than one between baseline and proximate to death. The cross-tissue N-glycan correlations were weak. Baseline serum N-glycans were more strongly associated with AD/ADRD compared to change in serum N-glycans over time and brain N-glycans. The N-glycan associations were observed in both AD and non-AD neuropathologies. To our knowledge, this is the first comprehensive glycomic analysis in both blood and brain in relation to AD pathology. Our results suggest that altered N-glycans may serve as mechanistic biomarkers for early diagnosis and progression of AD/ADRD.

糖基化（Glycosylation）是指将聚糖（glycans，即糖类）缀合至蛋白质的过程，为丰度最高的蛋白质翻译后修饰（post-translational modification）类型。其中N-糖基化（N-glycosylation）是最为普遍的糖基化形式，N-聚糖结构单元（N-glycan moieties）在调控蛋白质功能及诸多生物学进程中发挥关键作用。因此，对N-糖组（N-glycome，即样本中全部N-聚糖的完整集合）进行鉴定与定量分析，有望发掘新型生物标志物（biomarkers），为健康与疾病研究提供新的洞察方向。

截至目前，学界对阿尔茨海默病及阿尔茨海默病相关痴呆（Alzheimer’s Disease and Alzheimer’s Disease-related Dementias，AD/ADRD）中N-糖组改变的调控作用仍知之甚少。本研究纳入45名基线期无认知障碍（no cognitive impairment，NCI）的老年受试者，对其开展年度随访与临床检查，并在受试者逝世后实施脑尸检。在为期约12年的随访周期内，15名受试者进展为轻度认知障碍（mild cognitive impairment，MCI），15名发展为阿尔茨海默病，剩余15名始终维持无认知障碍状态。

研究团队采用基质辅助激光解吸电离飞行时间质谱（MALDI-TOF-MS），对两个时间点——基线期与临终前（间隔约12.3年）采集的血清样本，以及尸检获取的背外侧前额叶皮层（dorsolateral prefrontal cortex）脑组织中的N-聚糖相对丰度进行定量检测。通过回归模型（regression models）分析N-聚糖与AD/ADRD表型（phenotypes）的关联。

本次研究共检出71种血清N-聚糖与141种脑组织N-聚糖，其中46种为两者共有。多数血清N-聚糖在基线期与临终前的平均折叠变化小于1。跨组织N-聚糖相关性较弱。相较于血清N-聚糖随时间的变化量以及脑组织N-聚糖，基线期血清N-聚糖与AD/ADRD的关联强度显著更高。上述N-聚糖关联现象在阿尔茨海默病与非阿尔茨海默病神经病理学改变中均有观测到。

据我们所知，本研究是首个针对血液与脑组织同时开展的、与阿尔茨海默病病理相关的全面糖组学分析。研究结果显示，N-聚糖的异常改变有望作为AD/ADRD早期诊断与病情进展的机制性生物标志物。