(1) Background: Despite the existence of well-established, CSF-based biomarkers such as amyloid-β and phosphorylated-tau, the pathways involved in the pathophysiology of Alzheimer’s disease (AD) remain an active area of research. (2) Methods: We measured 3072 proteins in CSF samples of AD-biomarker positive mild cognitive impairment (MCI) participants (n = 38) and controls (n = 48), using the Explore panel of the Olink proximity extension assay (PEA). We performed group comparisons, association studies with diagnosis, age, and APOE ε4 status, overrepresentation analysis (ORA), and gene set enrichment analysis (GSEA) to determine differentially expressed proteins and dysregulated pathways. (3) Results: GSEA results demonstrated an enrichment of granulocyte-related and chemotactic pathways (core enrichment proteins: ITGB2, ITGAM, ICAM1, SELL, SELP, C5, IL1A). Moreover, some of the well-replicated, differentially expressed proteins in CSF included: ITGAM, ITGB2, C1QA, TREM2, GFAP, NEFL, MMP-10, and a novel tau-related marker, SCRN1. (4) Conclusion: Our results highlight the upregulation of neuroinflammatory pathways, especially chemotactic and granulocyte recruitment in CSF of early AD patients.

Background Normal cognitive aging is accompanied by molecular changes in the brain and periphery, but the specific proteomic and peptide-level alterations remain poorly defined. This study aimed to characterize age-related protein and peptide modifications by analyzing matched cerebrospinal fluid (CSF) and plasma samples from cognitively normal individuals. Methods Mass spectrometry was used to profile the proteome and peptide-level data of CSF and plasma samples from young (n = 52; mean age 29 ± 5.9 years; 4% male) and older (n = 40; mean age 69 ± 6.3 years; 48% male) adults. Differential abundance analysis, gene set enrichment, and weighted correlation network analyses were performed to identify age-associated pathways. Protein cleavage, alternative splicing, and phosphorylation events were examined to capture post-translational modifications linked to aging. Results In CSF, aging is associated with significant upregulation of extracellular matrix (ECM) components, coagulation, and inflammatory pathways. In plasma, the insulin-like growth factor-1 (IGF-1) signaling pathway is notably downregulated. Peptide-level analysis reveals novel alternative cleavage and phosphorylation patterns in key proteins involved in lipid metabolism, ECM structure, axonogenesis, and synaptic activity, including APP, APOE, COL4A2, NRXN1, and NRCAM. These findings highlight distinct and compartment-specific molecular changes that occur with aging. Conclusions This study provides a comprehensive proteomic and peptide-level landscape of normal cognitive aging, identifying both protein-level shifts and novel age-associated cleavage and phosphorylation events.

Given the persistent challenge of differentiating idiopathic Normal Pressure Hydrocephalus (iNPH) from similar clinical entities, we conducted an in-depth proteomic study of cerebrospinal fluid (CSF) in 28 shunt-responsive iNPH patients, 38 Mild Cognitive Impairment (MCI) due to Alzheimer’s disease, and 49 healthy controls. Utilizing the Olink Explore 3072 panel, we identified distinct proteomic profiles in iNPH that highlight significant downregulation of synaptic markers and cell-cell adhesion proteins. Alongside vimentin and inflammatory markers upregulation, these results suggest ependymal layer and transependymal flow dysfunction. Moreover, downregulation of multiple proteins associated with congenital hydrocephalus (e.g., L1CAM, PCDH9, ISLR2, ADAMTSL2, and B4GAT1) points to a possible shared molecular foundation between congenital hydrocephalus and iNPH. Through orthogonal partial least squares discriminant analysis (OPLS-DA), a panel comprising 13 proteins has been identified as potential diagnostic biomarkers of iNPH, pending external validation. These findings offer novel insights into the pathophysiology of iNPH, with implications for improved diagnosis.