# CSF Proteome Analysis of p‐Tau181 and Other Alzheimer's Disease Biomarkers Identifies Autotaxin–Lysophosphatidic Acid Signaling as Potential Therapeutic Targets

## TL;DR

This study identifies proteins linked to Alzheimer's disease biomarkers in cerebrospinal fluid, highlighting autotaxin–lysophosphatidic acid signaling as a potential therapeutic target.

## Contribution

The study identifies autotaxin (ENPP2) and lysophosphatidic acid signaling as novel therapeutic targets for Alzheimer's disease.

## Key findings

- 41 CSF proteins were significantly associated with p-tau181 levels, including PLD3, APOE, and OSTP being increased, and ENPP2 and CERU being decreased.
- ENPP2 expression was reduced in AD and amyloidosis, and LPA administration mitigated Aβ42-induced changes in zebrafish.
- Pathways related to axon development and axonogenesis were enriched among proteins associated with p-tau181 levels.

## Abstract

We investigated the relationship between the cerebrospinal fluid (CSF) proteome in Alzheimer's disease (AD) and the clinical and biomarker‐assisted diagnoses, and with CSF biomarker levels of AD.

CSF was collected in 500 individuals of non‐Hispanic white, African Americans, and Caribbean Hispanic individuals from Dominican Republic and New York City. CSF biomarkers of AD were measured including p‐tau181, Aβ40, Aβ42, total‐tau, neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP). CSF was depleted of abundant proteins followed by precipitation, cysteine reduction/alkylation, and proteolytic cleavage by trypsin. Peptides were measured using a Q Exactive HF mass spectrometer (Thermo Scientific). Association of individual and co‐abundant modules of proteins were tested with the clinical diagnosis of AD, as well as biologically defined AD pathological process based on CSF p‐tau181 and other biomarker levels. Results from replicated in 397 participants from the Accelerated Medicine Partnership‐Alzheimer's Disease CSF cohort and significantly associated proteins were functionally validated in postmortem human brains and zebrafish models.

CSF levels of 41 proteins were significantly associated with p‐tau181 levels after multiple testing correction. Notably phospholipase D3 (PLD3, p = 2.41E‐09), APOE (p = 4.25e‐08) and osteopontin (OSTP, p = 1.4E‐16) were increased and autotaxin (ENPP2, p =  8.39E‐09) and ceruloplasmin (CERU, p = 2.72E‐07) were decreased among individuals with high p‐tau181 levels. These proteins were also associated with CSF Aβ42/Aβ40 ratio and total Tau levels but not with NfL. OSTP was also associated with CSF levels of GFAP (p = 1.32e‐05). We did not identify any protein association with clinical AD. Among proteins associated with p‐tau181 levels, pathways related to axon development (p = 2.4E‐12), axonogenesis (p = 1.45E‐11) and regulation of axonogenesis (p = 5.1E‐09) were enriched. Immunostaining on postmortem human and zebrafish brains found that ENPP2 expression reduces significantly with AD and amyloidosis, respectively. LPA administration into the zebrafish CSF mitigated Aβ42‐induced vascular, neural, and glial changes.

Unbiased profiling of circulating CSF proteins identified key proteins associated with β‐amyloid and phosphorylated tau pathology. Biologically based diagnostic criteria may aid in the identification of unique pathogenic mechanisms.