Chronic
neuroinflammation is thought to potentiate medial temporal lobe (MTL)
atrophy and memory decline in
Alzheimer's disease (AD). It has become increasingly important to find novel immunological
biomarkers of
neuroinflammation or other processes that can track AD development and progression. Our study explored which pro- or anti-inflammatory cerebrospinal fluid (CSF)
biomarkers best predicted AD neuropathology over 24months. Using
Alzheimer's Disease Neuroimaging Initiative data (N=285), CSF inflammatory
biomarkers from mass spectrometry and multiplex panels were screened using stepwise regression, followed up with 50%/50% model retests for validation.
Neuronal Pentraxin 2 (NPTX2) and Chitinase-3-like-protein-1 (C3LP1),
biomarkers of glutamatergic synaptic plasticity and microglial activation respectively, were the only consistently significant
biomarkers selected. Once these
biomarkers were selected, linear mixed models were used to analyze their baseline and longitudinal associations with bilateral MTL volume, memory decline, global cognition, and established AD
biomarkers including CSF
amyloid and tau. Higher baseline NPTX2 levels corresponded to less MTL
atrophy [R2=0.287, p<0.001] and substantially less memory decline [R2=0.560, p<0.001] by month 24. Conversely, higher C3LP1 modestly predicted more MTL
atrophy [R2=0.083, p<0.001], yet did not significantly track memory decline over time. In conclusion, NPTX2 is a novel pro-inflammatory
cytokine that predicts AD-related outcomes better than any immunological
biomarker to date, substantially accounting for brain
atrophy and especially memory decline. C3LP1 as the microglial
biomarker, by contrast, performed modestly and did not predict longitudinal memory decline. This research may advance the current understanding of AD etiopathogenesis, while expanding early diagnostic techniques through the use of novel pro-inflammatory
biomarkers, such as NPTX2. Future studies should also see if NPTX2 causally affects MTL morphometry and memory performance.