Discovery of Orally Available and Brain Penetrant AEP Inhibitors.

Alzheimer's Disease (AD) is the most widespread form of dementia, with one of the pathological hallmarks being the formation of neurofibrillary tangles (NFTs). These tangles consist of phosphorylated Tau fragments. Asparagine endopeptidase (AEP) is a key Tau cleaving enzyme that generates aggregation-prone Tau fragments. Inhibition of AEP to reduce the level of toxic Tau fragment formation could represent a promising therapeutic strategy. Here, we report the first orthosteric, selective, orally bioavailable, and brain penetrant inhibitors with an irreversible binding mode. We outline the development of the series starting from reversible molecules and demonstrate the link between inhibition of AEP and reduction of Tau N368 fragment both in vitro and in vivo.

Increased G3BP2-Tau interaction in tauopathies is a natural defense against Tau aggregation.

Many RNA-binding proteins (RBPs), particularly those associated with RNA granules, promote pathological protein aggregation in neurodegenerative diseases. Here, we demonstrate that G3BP2, a core component of stress granules, directly interacts with Tau and inhibits Tau aggregation. In the human brain, the interaction of G3BP2 and Tau is dramatically increased in multiple tauopathies, and it is independent of neurofibrillary tangle (NFT) formation in Alzheimer's disease (AD). Surprisingly, Tau pathology is significantly elevated upon loss of G3BP2 in human neurons and brain organoids. Moreover, we found that G3BP2 masks the microtubule-binding region (MTBR) of Tau, thereby inhibiting Tau aggregation. Our study defines a novel role for RBPs as a line of defense against Tau aggregation in tauopathies.

Identification and characterization of a MAPT-targeting locked nucleic acid antisense oligonucleotide therapeutic for tauopathies.

Tau is a microtubule-associated protein (MAPT, tau) implicated in the pathogenesis of tauopathies, a spectrum of neurodegenerative disorders characterized by accumulation of hyperphosphorylated, aggregated tau. Because tau pathology can be distinct across diseases, a pragmatic therapeutic approach may be to intervene at the level of the tau transcript, as it makes no assumptions to mechanisms of tau toxicity. Here we performed a large library screen of locked-nucleic-acid (LNA)-modified antisense oligonucleotides (ASOs), where careful tiling of the MAPT locus resulted in the identification of hot spots for activity in the 3' UTR. Further modifications to the LNA design resulted in the generation of ASO-001933, which selectively and potently reduces tau in primary cultures from hTau mice, monkey, and human neurons. ASO-001933 was well tolerated and produced a robust, long-lasting reduction in tau protein in both mouse and cynomolgus monkey brain. In monkey, tau protein reduction was maintained in brain for 20 weeks post injection and corresponded with tau protein reduction in the cerebrospinal fluid (CSF). Our results demonstrate that LNA-ASOs exhibit excellent drug-like properties and sustained efficacy likely translating to infrequent, intrathecal dosing in patients. These data further support the development of LNA-ASOs against tau for the treatment of tauopathies.

Region-specific permeability of the blood-brain barrier upon pericyte loss.

The blood-brain barrier (BBB) regulates differing needs of the various brain regions by controlling transport of blood-borne components from the neurovascular circulation into the brain parenchyma. The mechanisms underlying region-specific transport across the BBB are not completely understood. Previous work showed that pericytes are key regulators of BBB function. Here we investigated whether pericytes influence BBB permeability in a region-specific manner by analysing the regional permeability of the BBB in the pdgf-b ret/ret mouse model of pericyte depletion. We show that BBB permeability is heterogeneous in pdgf-b ret/ret mice, being significantly higher in the cortex, striatum and hippocampus compared to the interbrain and midbrain. However, we show that this regional heterogeneity in BBB permeability is not explained by local differences in pericyte coverage. Region-specific differences in permeability were not associated with disruption of tight junctions but may result from changes in transcytosis across brain endothelial cells. Our data show that certain brain regions are able to maintain low BBB permeability despite substantial pericyte loss and suggest that additional, locally-acting mechanisms may contribute to control of transport.

Trafficking of Endogenous Immunoglobulins by Endothelial Cells at the Blood-Brain Barrier.

The Blood-Brain Barrier (BBB) restricts access of large molecules to the brain. The low endocytic activity of brain endothelial cells (BECs) is believed to limit delivery of immunoglobulins (IgG) to the brain parenchyma. Here, we report that endogenous mouse IgG are localized within intracellular vesicles at steady state in BECs in vivo. Using high-resolution quantitative microscopy, we found a fraction of endocytosed IgG in lysosomes. We observed that loss of pericytes (key components of the BBB) in pdgf-b(ret/ret) mice affects the intracellular distribution of endogenous mouse IgG in BECs. In these mice, endogenous IgG was not detected within lysosomes but instead accumulate at the basement membrane and brain parenchyma. Such IgG accumulation could be due to reduced lysosomal clearance and increased sorting to the abluminal membrane of BECs. Our results suggest that, in addition to low uptake from circulation, IgG lysosomal degradation may be a downstream mechanism by which BECs further restrict IgG access to the brain.

Autophagic and lysosomal defects in human tauopathies: analysis of post-mortem brain from patients with familial Alzheimer disease, corticobasal degeneration and progressive supranuclear palsy.

INTRODUCTION: The accumulation of insoluble proteins within neurons and glia cells is a pathological hallmark of several neurodegenerative diseases. Abnormal aggregation of the microtubule-associated protein tau characterizes the neuropathology of tauopathies, such as Alzheimer disease (AD), corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP). An impairment of the lysosomal degradation pathway called macroautophagy, hereafter referred to as autophagy, could contribute to the accumulation of aggregated proteins. The role of autophagy in neurodegeneration has been intensively studied in the context of AD but there are few studies in other tauopathies and it is not known if defects in autophagy is a general feature of tauopathies. In the present study, we analysed autophagic and lysosomal markers in human post-mortem brain samples from patients with early-onset familial AD (FAD) with the APP Swedish mutation (APPswe), CBD and PSP and control individuals. RESULTS: FAD, CBD and PSP patients displayed an increase in LC3-positive vesicles in frontal cortex, indicating an accumulation of autophagic vesicles. Moreover, using double-immunohistochemistry and in situ proximity ligation assay, we observed colocalization of hyperphosphorylated tau with the autophagy marker LC3 in FAD, CBD and PSP patients but not in control individuals. Increased levels of the lysosomal marker LAMP1 was detected in FAD and CBD, and in addition Cathepsin D was diffusely spread in the cytoplasm in all tauopathies suggesting an impaired lysosomal integrity. CONCLUSION: Taken together, our results indicate an accumulation of autophagic and lysosomal markers in human brain tissue from patients with primary tauopathies (CBD and PSP) as well as FAD, suggesting a defect of the autophagosome-lysosome pathway that may contribute to the development of tau pathology.

Neuronal uptake of tau/pS422 antibody and reduced progression of tau pathology in a mouse model of Alzheimer's disease.

The severity of tau pathology in Alzheimer's disease brain correlates closely with disease progression. Tau immunotherapy has therefore been proposed as a new therapeutic approach to Alzheimer's disease and encouraging results have been obtained by active or passive immunization of tau transgenic mice. This work investigates the mechanism by which immunotherapy can impact tau pathology. We demonstrate the development of Alzheimer's disease-like tau pathology in a triple transgenic mouse model of Alzheimer's disease and show that tau/pS422 is present in membrane microdomains on the neuronal cell surface. Chronic, peripheral administration of anti-tau/pS422 antibody reduces the accumulation of tau pathology. The unequivocal presence of anti-tau/pS422 antibody inside neurons and in lysosomes is demonstrated. We propose that anti-tau/pS422 antibody binds to membrane-associated tau/pS422 and that the antigen-antibody complexes are cleared intracellularly, thereby offering one explanation for how tau immunotherapy can ameliorate neuronal tau pathology.