Giasson, Benoit I.

Abstract Human neurodegenerative diseases can be characterized as disorders of protein aggregation. As a key player in cellular autophagy and the ubiquitin proteasome system, p62 may represent an effective immunohistochemical target, as well as mechanistic operator, across neurodegenerative proteinopathies. In this study, 2 novel mouse-derived monoclonal antibodies 5G3 and 2A5 raised against residues 360–380 of human p62/sequestosome-1 were characterized via immunohistochemical application upon human tissues derived from cases of C9orf72-expansion spectrum diseases, Alzheimer disease, progressive supranuclear palsy, Lewy body disease, and multiple system atrophy. 5G3 and 2A5 reliably highlighted neuronal dipeptide repeat, tau, and α-synuclein inclusions in a distribution similar to a polyclonal antibody to p62, phospho-tau antibodies 7F2 and AT8, and phospho-α-synuclein antibody 81A. However, antibodies 5G3 and 2A5 consistently stained less neuropil structures, such as tau neuropil threads and Lewy neurites, while 2A5 marked fewer glial inclusions in progressive supranuclear palsy. Both 5G3 and 2A5 revealed incidental astrocytic tau immunoreactivity in cases of Alzheimer disease and Lewy body disease with resolution superior to 7F2. Through their unique ability to highlight specific types of pathological deposits in neurodegenerative brain tissue, these novel monoclonal p62 antibodies may provide utility in both research and diagnostic efforts.

Abstract Understanding the biological functions of tau variants can illuminate differential etiologies of Alzheimer’s disease (AD) and primary tauopathies. Though the end-stage neuropathological attributes of AD and primary tauopathies are similar, the etiology and behavioral outcomes of these diseases follow unique and divergent trajectories. To study the divergent physiological properties of tau variants on a uniform immunogenetic background, we created somatic transgenesis CNS models of tauopathy utilizing neonatal delivery of adeno-associated viruses expressing wild-type (WT) or mutant tau in non-transgenic mice. We selected four different tau variants—WT tau associated with AD, P301L mutant tau associated with frontotemporal dementia (FTD), S320F mutant tau associated with Pick’s disease and a combinatorial approach using P301L/S320F mutant tau. CNS-targeted expression of WT and P301L mutant tau results in robust tau hyperphosphorylation without tangle pathology, gradually developing age-progressive memory deficits. In contrast, the S320F variant, especially in combination with P301L, produces an AD-type tangle pathology, focal neuroinflammation and memory impairment on an accelerated time scale. Using the doubly mutated P301L/S320F tau variant, we demonstrate that combining different mutations can have an additive effect on neuropathologies and associated co-morbidities, possibly hinting at involvement of unique functional pathways. Importantly, we also show that overexpression of wild-type tau as well as an FTD-associated tau variant can lead to cognitive deficits even in the absence of tangles. Together, our data highlights the synergistic neuropathologies and associated cognitive and synaptic alterations of the combinatorial tau variant leading to a robust model of tauopathy.

It has been challenging to produce ex vivo models of the inclusion pathologies that are hallmark pathologies of many neurodegenerative diseases. Using three-dimensional mouse brain slice cultures (BSCs), we have developed a paradigm that rapidly and robustly recapitulates mature neurofibrillary inclusion and Lewy body formation found in Alzheimer’s and Parkinson’s disease, respectively. This was achieved by transducing the BSCs with recombinant adeno-associated viruses (rAAVs) that express α-synuclein or variants of tau. Notably, the tauopathy BSC model enables screening of small molecule therapeutics and tracking of neurodegeneration. More generally, the rAAV BSC “toolkit” enables efficient transduction and transgene expression from neurons, microglia, astrocytes, and oligodendrocytes, alone or in combination, with transgene expression lasting for many months. These rAAV-based BSC models provide a cost-effective and facile alternative to in vivo studies, and in the future can become a widely adopted methodology to explore physiological and pathological mechanisms related to brain function and dysfunction.

There is considerable interest in harnessing innate immunity to treat Alzheimer’s disease (AD). Here, we explore whether a decoy receptor strategy using the ectodomain of select TLRs has therapeutic potential in AD. AAV-mediated expression of human TLR5 ectodomain (sTLR5) alone or fused to human IgG4 Fc (sTLR5Fc) results in robust attenuation of amyloid β (Aβ) accumulation in a mouse model of Alzheimer-type Aβ pathology. sTLR5Fc binds to oligomeric and fibrillar Aβ with high affinity, forms complexes with Aβ, and blocks Aβ toxicity. Oligomeric and fibrillar Aβ modulates flagellin-mediated activation of human TLR5 but does not, by itself, activate TLR5 signaling. Genetic analysis shows that rare protein coding variants in human TLR5 may be associated with a reduced risk of AD. Further, transcriptome analysis shows altered TLR gene expression in human AD. Collectively, our data suggest that TLR5 decoy receptor–based biologics represent a novel and safe Aβ-selective class of biotherapy in AD.

Hyperphosphorylation and aggregation of tau are observed in multiple neurodegenerative diseases termed tauopathies. Tau has also been implicated in the pathogenesis of Parkinson's disease (PD) and parkinsonisms. Some PD patients with mutations in the leucine‐rich repeat kinase 2 (LRRK2) gene exhibit tau pathology. Mutations in LRRK2 are a major risk factor for PD, but LRRK2 protein function remains unclear. The most common mutation, G2019S, is located in the kinase domain of LRRK2 and enhances kinase activity in vitro. This suggests that the kinase activity of LRRK2 may underlie its cellular toxicity. Recently, in vitro studies have suggested a direct interaction between tubulin‐bound tau and LRRK2 that results in tau phosphorylation at one identified site. Here we present data suggesting that microtubules (MTs) enhance LRRK2‐mediated tau phosphorylation at three different epitopes. We also explore the effect of divalent cations as catalytic cofactors for G2019S LRRK2‐mediated tau phosphorylation and show that manganese does not support kinase activity but inhibits the efficient ability of magnesium to catalyze LRRK2‐mediated phosphorylation of tau. These results suggest that cofactors such as MTs and cations in the cellular milieu have an important impact on LRRK2‐tau interactions and resultant tau phosphorylation. © 2015 Wiley Periodicals, Inc.