Exploratory Mass Spectrometry of Cerebrospinal Fluid from Persons with Autopsy-Confirmed LATE-NC

Common neuropathologies associated with dementia include Alzheimer's disease neuropathologic change (ADNC) and limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC). Biofluid proteomics provides a window into the pathobiology of dementia and the information from biofluid tests may help guide clinical management. Participants (n = 29) had been autopsied and had antemortem CSF draws in a longitudinal cohort of older adults at the University of Kentucky AD Research Center. Cases were designated as LATE-NC + if they had LATE-NC stage > 1 (n = 9); the remaining 20 cases were designated LATE-NC-. This convenience sample of CSF specimens was analyzed in two separate processes: From one group, aliquots were depleted of highly abundant proteins using affinity spin columns. Tryptic digests of sample proteins were subjected to liquid chromatographic separation and mass spectrometry. Relative quantification was performed using Sciex software. Peptides referent to a total of 949 proteins were identified in the samples depleted of abundant proteins, and 820 different proteins were identified in the non-depleted samples. When the Bonferroni/false-discovery statistical correction was applied to account for having made multiple comparison tests, only 4 proteins showed differential expression (LATE-NC + vs LATE-NC-) in the non-depleted samples (RBP4, MIF, IGHG3, and ITM2B). Post hoc western blots confirmed that RBP4 expression was higher in the LATE-NC + cases at the group level. In summary, an exploratory assessment of proteomes of autopsy-confirmed LATE-NC and non-LATE-NC CSF did not demonstrate a clear-cut proteomic fingerprint that distinguished the two groups. There was, however, an increase in RBP4 protein levels in CSF from LATE-NC cases.