Pathophysiological mechanisms of grey matter morphometry changes in preclinical Alzheimer’s disease

Abstract

AbstractBackgroundThe biological mechanisms underlying structural brain changes in early Alzheimer’s disease (AD) are not well understood. Combining a wide selection of biomarkers of AD pathology, synaptic dysfunction, neuroaxonal injury, and neuroinflammation, and examining their effects on grey matter (GM) changes may provide a deeper understanding of the multifactorial nature of AD. We aimed to identify biological components of key fluid biomarkers predictive of longitudinal GM changes in cognitively unimpaired adults.MethodWe studied 322 cognitively unimpaired individuals from the ALFA+ cohort (Table1) with available longitudinal MRI and cerebrospinal fluid (CSF) biomarkers of β‐amyloid (Aβ42/40), phospho‐tau (p‐tau181), neurogranin, neurofilament light chain (NfL), total‐tau, α‐synuclein, glial fibrillary acidic protein (GFAP), chitinase‐3‐like protein‐1 (YKL‐40), soluble triggering receptor expressed on myeloid cells‐2 (sTREM2), S100 calcium‐binding protein B (S100B), and interleukin‐6 measured using the Roche NeuroToolKit immunoassays. Pairwise longitudinal registration analysis was performed using SPM12 to calculate Jacobian determinant maps. Next, we performed partial least‐squares analysis to determine the optimal number of CSF biomarker components and tested their association with GM volume changes by AT (Amyloid‐Tau) stage.ResultFour distinct biomarker components (C1‐4) were identified (Figure1). C1 was driven by moderate contributions from several biomarkers, particularly markers of core AD pathology and neurodegeneration, which were strongly associated with temporal lobe atrophy in A+T‐ individuals. C2 represented mainly Aβ pathology and, to a lesser extent, axonal damage and astrogliosis that contributed to a decrease in GM volume, especially in the hippocampus in A‐T‐ participants, while showing strong correlations with volume increases in medial frontal regions in A+T+ participants. C3 loading was associated with greater frontoparietal atrophy, especially in A+T+ individuals, and consisted of microglial activation together with Aβ pathology but in the absence of reactive astrogliosis. Lastly, C4, reflecting mostly microglial activation alone, was also strongly associated with frontoparietal atrophy, particularly in A+T+ participants.ConclusionOur results suggest important contributions of Aβ pathology, neuroaxonal damage, and microglial activation to GM morphometry changes in the earliest stages of the AD continuum. Atrophy patterns differed depending on the underlying pathological drivers and on A and T positivity, showing stronger correlations with increasing disease severity; however, volumetric increases were also observed.