Targeting the pathological tau N368 fragment: A pharmacological perspective on a novel immunotherapy for Alzheimer's disease.

Alzheimer's disease (AD) is the most prevalent dementia, and while anti-Aβ immunotherapies have recently been approved, their modest clinical benefits underscore an urgent need for strategies targeting tau pathology, which correlates more closely with cognitive decline. Asparagine endopeptidase (AEP) generates a pathological tau fragment by cleaving tau at N368 residue (Tau N368). This fragment drives neurodegeneration through dual mechanisms: it promotes toxic aggregation and directly antagonizes BDNF/TrkB neurotrophic signaling. Clinically, the cerebrospinal fluid (CSF) Tau N368/total-tau ratio has emerged as a promising biomarker that appears to accurately reflects neocortical tau burden and cognitive impairment, though prospective validation is needed. From a pharmacological perspective, a Tau N368-specific monoclonal antibody has demonstrated robust preclinical efficacy in mouse models, substantially reducing tau pathology, restoring neurotrophic signaling, and improving cognitive deficits in two AD mouse models. This review provides a comprehensive pharmacological analysis of the AEP-Tau N368 axis. We examine its molecular mechanisms, critically evaluate its role as a candidate biomarker with potential pharmacodynamic utility, and assess the preclinical proof-of-concept for targeted immunotherapy while acknowledging the need for independent replication and addressing translational challenges. By situating this approach within the broader landscape of failed tau-targeted trials, we discuss remaining opportunities and translational challenges, including brain penetration, patient stratification, and combination strategies that position Tau N368 as a candidate for further pharmacological development in AD and related tauopathies.