P1‐355: Mechanistic studies of antibody mediated clearance of tau aggregates using an ex vivo brain slice model

Abstract

Recent studies have shown that immunotherapy clears amyloid beta (Aβ) plaques and reduces Aβ levels in mouse models of Alzheimer's disease (AD), as well as in AD patients. Tangle pathology is also relevant for the neurodegeneration in AD, and our studies have shown that active immunization with an AD related phospho-tau peptide reduces aggregated tau within the brain and slows the progression of tauopathy-induced behavioral impairments. Thus, clearance of neurofibrillary tangles and/or their precursors may reduce synaptic and neuronal loss associated with AD and other tauopathies. So far the mechanisms involved in antibody-mediated clearance of tau pathology are yet to be elucidated. In this study we have used a mouse brain slice model to examine the uptake and localization of FITC labeled anti-tau antibodies. Confocal microscopy analysis showed that the FITC labeled anti-tau antibody co-stained with phosphorylated tau, had a perinuclear appearance and co-localized with markers of the endosomal/lysosomal pathway. Additionally, tau and FITC-IgG were found together in an enriched lysosome fraction. In summary, antibodymediated clearance of intracellular tau aggregates appears to occur via the lysosomal pathway.

Antibody Uptake into Neurons Occurs Primarily via Clathrin-dependent Fcγ Receptor Endocytosis and Is a Prerequisite for Acute Tau Protein Clearance

“…Importantly, this indicates that antibody-mediated Tau clearance takes place primarily within neurons. Previous data from our laboratory showed that antibodies were present in neurons of treated ani-mals and that the treatment resulted in clearance of phosphoTau but not total Tau (10), which we subsequently confirmed in other studies (11,12,19). Together, these prior studies suggest involvement of intracellular Tau antibodies in Tau clearance, and we now show in the primary Tg JNPL3 neuronal model that this pathway is necessary for removal of Tau.…”

“…Recent results from our group have shown that Tau antibodies not only co-localize with intraneuronal pathological Tau but also with endosomal/lysosomal pathway markers (10,19). Sim-ilar findings have been observed by others utilizing antibodies for ␣-synuclein and A␤ (20 -22).…”

“…As with the slices, a significant decrease in 4E6G7 uptake was observed in primary JNPL3 neurons at the 0.5, 5, and 10 g/ml (n ϭ 6 wells per group) doses of Fc block (19,43, and 53% decreases, respectively, p ϭ 0.01, 0.006, and 0.008) (Fig. 9B), 125 I-4E6G7 and increasing concentrations of Fc block (anti-CD16/CD32, Fc␥II/III).…”

“…B, primary neurons (n ϭ 6 wells per group) from JNPL3 pups were also incubated with Fc block and 125 I-4E6G7. The 1, 5, and 10 g/ml antibody concentrations significantly reduced uptake (19,43, and 53%, respectively, p ϭ 0.01, 0.006, and 0.008). As with slice cultures, incubation with Fc␥ I antibodies did not significantly affect uptake at any dose.…”

Opportunities for Conformation-Selective Antibodies in Amyloid-Related Diseases

“…For a number of years tau was considered to be purely intracellular. Sigurdsson et al reported antibodies inside neurons and proposed that antibody-mediated clearance of intracellular tau aggregates follows the lysosomal pathway [74,75]. Further studies have revealed that tau antibody uptake into neurons correlates well with tau levels.…”