Exploratory Analysis of Autophagy–Lysosomal Pathway Proteins in Dermal Fibroblasts as Potential Peripheral Biomarkers for Alzheimer’s Disease: A Pilot Study

<b>Background/Objectives:</b> Alzheimer's disease (AD) is characterized by accumulation of abnormal intracellular substances and autophagy-lysosomal pathway (ALP) dysfunction. While current diagnostic methods rely on cerebrospinal fluid biomarkers and neuroimaging, minimally invasive peripheral biomarkers are needed. Dermal fibroblasts could serve as accessible reporters of AD-related molecular changes. This exploratory pilot study investigated whether ALP-associated proteins in patient-derived fibroblasts could serve as potential peripheral biomarkers for AD diagnosis. <b>Methods:</b> We analyzed dermal fibroblasts from 9 AD patients (amyloid Positron emission tomography (PET)-positive) and 9 age-matched controls (amyloid PET-negative). Comprehensive immunoblot analysis assessed expression profiles of 16 AD- and ALP-associated proteins. Autophagic flux and lysosomal function were evaluated using bafilomycin A1 treatment and LysoTracker staining. Diagnostic performance was assessed through receiver operating characteristic (ROC) curve analysis and multivariable logistic regression. <b>Results:</b> AD fibroblasts showed significantly reduced Beta-site APP cleaving enzyme 1 (BACE1) (<i>p</i> = 0.022) and elevated Tax1-binding protein 1 (TAX1BP1) (<i>p</i> = 0.035) expression. BCL2-associated athanogene proteins 2 (BAG2) and OPTN demonstrated consistent directional changes across patients. Preliminary ROC analysis showed promising performance for protein combinations, with BAG2 + OPTN achieving Area under the curve (AUC) = 0.963 (sensitivity 77.8%, specificity 88.9%). Integration with Apolipoprotein E4 (<i>APOE4</i>) status further enhanced diagnostic accuracy (<i>APOE4</i> + BACE1: AUC = 0.914). Notably, baseline autophagic flux and lysosomal acidification were preserved, suggesting pathway-specific rather than systemic ALP dysfunction. <b>Conclusions:</b> This exploratory study provides preliminary evidence that dermal fibroblast-derived ALP proteins show disease-associated alterations in AD and may represent potential peripheral biomarkers. However, given the small sample size (<i>n</i> = 18) and lack of independent validation, these findings require confirmation in larger multi-center cohorts before clinical translation.