In ageing tissues, long-lived extracellular matrix (ECM) proteins are susceptible to the accumulation of structural damage due to diverse mechanisms including glycation, oxidation and protease cleavage. Peptide location fingerprinting (PLF) is a new mass spectrometry (MS) analysis technique capable of identifying proteins exhibiting structural differences in complex proteomes. PLF applied to published young and aged intervertebral disc (IVD) MS datasets (posterior, lateral and anterior regions of the annulus fibrosus), identified 268 proteins with age-related structural differences. For several ECM assemblies (collagens I, II and V and aggrecan), these differences were markedly conserved between degeneration-prone (posterior and lateral) and resistant (anterior) regions. Significant differences in peptide yields, observed within collagen I, II and V α-chains (COL1A2, COL2A1, COL5A1), were located within their triple helical regions and/or cleaved C-terminal propeptides, indicating potential accumulation of damage and impaired maintenance in ageing. Several proteins (COL5A1, COL2A1 and aggrecan) also exhibited tissue region (lateral)-specific differences in structure between aged and young, suggesting that some ageing mechanisms may act locally within tissues. This study not only provides evidence of age-related changes in ECM protein structures which are tissue-region specific, but also highlights the ability of PLF to identify potential protein biomarkers of localised tissue remodelling.

Background: This paper investigates the statistical relationship between bilingualism and the Onset Age (OA) of AD and MCI across a clinical sample, consisting of 580 Alzheimer's Disease (AD) subjects and 1264 Mild Cognitive Impairment (MCI) subjects, via a statistical analysis conducted on the sample retrieved from the Alzheimer's Disease Neuroimaging Initiative (ADNI) dataset. Method: To investigate whether bilingualism has any correlation with the OAs of AD or MCI subjects, our study leverages the full potential of the ADNI dataset, a dataset that covers both the OA and the bilingualism status of both the AD and MCI subjects. Prior to performing any meaningful statistical analysis, a regression model and a probabilistic model were developed in parallel to fill in the missing OA and bilingualism values. A simple least-square regression model that consists of an independent variable of registered age for Mini-Mental State Examination (MMSE) score was used to estimate the OA of the AD and MCI subjects in the ADNI dataset. After filling in the missing OA values, the number of subjects relevant for the statistical analysis increased from 816 (AD: 371, MCI: 445) to 1844 (AD: 580, MCI: 1264), which greatly enlarged the representation of the AD and MCI sample in the ADNI population. With increased sample size, a novel probabilistic classification model was introduced to infer an ADNI subject’s bilingualism when relevant demographic information and deterministic outcome were not readily available from the ADNI dataset. The weighted average OA for the bilinguals and the monolinguals was then computed, where the weights for the probabilistic labels were assigned based on the percentage of bilingualism in the general US population. Finally, a statistical analysis was performed to test whether any statistically significant correlation exists between the OA and the bilingualism of the AD and MCI subjects within the ADNI dataset. Findings: Our preliminary study demonstrates no significant statistical difference between the OA of the bilinguals and the monolinguals within the ADNI dataset. Thus, the monolingual speakers within the ADNI dataset do not statistically manifest earlier onset, as compared to the bilingual speakers, which is slightly inconsistent with some earlier statistical findings that bilingual speakers enjoy certain distinctive advantages, such as late onset of AD, as compared to monolingual counterparts.