Proteomic analysis in Alzheimer’s disease and other dementias: a focus on sex-specific differences

BACKGROUND: Fluid protein studies in cerebrospinal fluid (CSF) and plasma have provided important insights into neurodegenerative dementias; however, there is a limited investigation of sex-related differences and cross-biofluid relationships. In Alzheimer's disease (AD), Lewy body dementia (LBD), and frontotemporal dementia (FTD), large-scale, sex-stratified analyses of paired CSF and plasma samples remain scarce. Using the multiplex and ultrasensitive capabilities of NULISAseq™ technology, this study aims to characterize sex- and disease-specific proteomic alterations associated with Central Nervous System (CNS) pathology to explore underlying mechanisms. METHODS: CSF and plasma samples from 359 individuals with AD, LBD, FTD, and cognitively healthy controls were analyzed using the NULISAseq™ CNS Disease Panel 120. Differential protein expression analyses were conducted across diagnoses and stratified by sex, adjusting for relevant covariates. Spearman's correlation analyses were performed to assess concordance between CSF and plasma protein levels. All statistical analyses were conducted in R v4.4.3. RESULTS: Differential protein expression analyses across diagnoses revealed two potential transdiagnostic biomarkers: ICAM1 in CSF and ANXA5 in plasma, showing consistent increases across AD, LBD, and FTD. Sex-stratified analyses in CSF showed modest changes, including higher CCL26, ANXA5, and IL10 in females with AD, and higher IL9, PRDX6, and CX3CL1 in males with AD. In LBD, females exhibited upregulation of ACHE, SFRP1, POSTN in both CSF and plasma. NPTX1 was identified as a potential CSF biomarker for FTD, showing downregulation particularly in males. In contrast, analyses stratified by sex in plasma displayed a larger number of proteins across all dementias, with females showing a higher number of upregulated inflammation-related proteins predominantly involved in cytokine signaling. Overall cross-fluid correlations were restricted to a small subset of proteins, indicating compartment-specific regulation. CONCLUSIONS: This study represents a large-scale, sex-stratified proteomic analysis of CSF and plasma across major neurodegenerative dementias using NULISAseq™ technology. The findings highlight sex-dependent biomarker patterns, particularly in plasma, and underscore the importance of incorporating sex as a biological variable in dementia research. Future studies should validate candidate proteins in independent cohorts, investigate their functional and mechanistic roles, and assess their utility for biomarker development and sex-tailored therapeutic strategies.