Fiona Grüninger

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 Alzheimers disease brain correlates closely with disease progression. Tau immunotherapy has therefore been proposed as a new therapeutic approach to Alzheimers 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 Alzheimers disease-like tau pathology in a triple transgenic mouse model of Alzheimers 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.

Human napsin A: expression, immunochemical detection, and tissue localization

A novel aspartic proteinase, called napsin, has recently been found in human and mouse. Due to high similarity with cathepsin D a structural model of human napsin A could be built. Based on this model a potential epitope SFYLNRDPEEPDGGE has been identified, which was used to immunize rabbits. The resulting antibody was employed in monitoring the expression of recombinant human napsin A in HEK293 cell line. Western blot analysis confirmed the specificity of the antibody and showed that human napsin A is expressed as a single chain protein with the molecular weight of approximately 38 kDa. Immunohistochemical studies revealed high expression levels of napsin A in human kidney and lung but low expression in spleen.

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

IntroductionThe 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.ResultsFAD, 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.ConclusionTaken 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.

Invited review: Drug development for tauopathies

Many different approaches to treating tauopathies are currently being explored, with a few compounds already in clinical development (including small molecules such as anti‐aggregation compound LMTX and active vaccines AADvac1 and ACI‐35). This review aims to summarize the status of the clinical candidates and to highlight the emerging areas of research that hold promise for drug development. Tau is post‐translationally modified in several different ways (phosphorylated, acetylated, glycosylated and truncated). The extent of these modifications can be manipulated to influence tau aggregation state and pathogenesis and the enzymes involved provide tractable targets for drug intervention. In addition, modulation of tau expression levels is an attractive therapeutic approach. Finally, the recently described prion‐like spreading of tau between cells opens up novel avenues from the tau drug development perspective. The review compares the merits of small‐molecule and antibody‐based therapies and emphasizes the need for amenable clinical biomarkers for drug development, particularly PET imaging.

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-bret/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.