miR‐214‐3p and NCKAP1: A microglial functional dimension of Alzheimer's progression

Abstract INTRODUCTION Biological Alzheimer's disease (AD) pathology does not fully explain the marked heterogeneity in clinical severity or progression. We investigated whether patient‐derived induced microglia‐like cell (iMG) profiles capture a functional dimension of AD progression beyond conventional plasma biomarkers. METHODS We studied 114 participants comprising amyloid‐negative healthy controls ( n = 18) and amyloid‐positive AD‐continuum groups (cognitively unimpaired, n = 2; mild cognitive impairment, n = 18; AD dementia, n = 76). Plasma biomarkers, patient‐derived iMG phagocytic function, and molecular markers were measured from the same blood draw. Longitudinal clinical follow‐up was available in 102 participants, and paired baseline/follow‐up blood samples were analyzed in a longitudinal biomarker cohort ( n = 38). RESULTS iMG phagocytic capacity progressively declined across the AD continuum, accompanied by reduced NCK‐associated protein 1 (NCKAP1) expression and the strongest association with plasma glial fibrillary acidic protein (GFAP). Baseline NCKAP1 primarily reflected current cognitive impairment, whereas plasma miR‐214‐3p independently predicted faster cognitive decline beyond plasma tau phosphorylated at threonine 217 (p‐tau217), GFAP, neurofilament light chain (NfL), age, and baseline cognition. Within amyloid‐positive AD dementia, plasma miR‐214‐3p identified rapidly progressive disease and substantially improved prognostic discrimination beyond conventional plasma biomarkers. Longitudinally, declining NCKAP1 and increasing plasma miR‐214‐3p tracked the rate of cognitive deterioration, whereas plasma p‐tau217, GFAP, and NfL changed over time but did not track disease tempo. DISCUSSION Patient‐derived iMG profiling identifies microglial phagocytic dysfunction as a complementary functional dimension of AD progression beyond conventional plasma biomarkers. Longitudinal microglial dynamics tracked disease tempo more closely than conventional plasma pathology markers and may help interpret biological‐clinical discordance, supporting biologically informed staging, prognosis, and patient stratification in AD.