Lewis, Jada

AbstractBackgroundPathological aging (PA) patients are individuals that are cognitively normal prior to death but have abundant and widespread amyloid‐β (Aβ) deposits. These individuals typically have few cored amyloid deposits with variable levels of diffuse parenchymal deposits and/or vascular deposits. There is little or no inflammatory reaction, neuritic pathology or neurofibrillary tangles in the cortex. Previously, we have shown that total Aβ levels in PA brain lysates were similar to the levels in Alzheimer’s disease (AD) brain lysates, with overlap in the length of the Aβ peptides that were deposited and no major differences in SDS‐stable Aβ oligomeric assemblies. Despite these similarities, it is unclear whether PA represents a prodromal phase of AD or if the amyloid pathology of PA patients represents a less pathogenic variant. To explore this idea, we examined the seeding capacity of AD and PA brain homogenates to induce Aβ deposition and to secondarily induce tau pathology.MethodWe determined the seeding capacity of two AD, four PA and two control brain homogenates in transgenic mice expressing APPswe/ind with and without Tau‐P301L by intracerebral injection at neonatal day 0. At either 6, 9, 12 or 18 months, we assessed Aβ deposition and neurofibrillary pathology in all 4 genotypes by immunohistochemical and biochemical methods. Furthermore we examined the seeding activity of human AD brain lysates in brain slice cultures from APP/Tau transgenic mice.ResultIn our newborn mouse injections, we observed widespread Aβ seeding as evidenced by accelerated onset of diffuse parenchymal Aβ deposition that was largely proportional to the burden of parenchyma deposits in patient brains. In all cases, high levels of pial deposition were observed and Aβ42 was the predominant peptide deposited. Tau pathology was not induced in any animal, and with the absence of neuritic plaques there was no induction of tau positive neurites.ConclusionThis study provides evidence that the Aβ conformers associated with diffuse Aβ deposits in the brains of cognitively normal individuals possess seeding activities similar to those found in the brains of AD patients. The findings are consistent with the idea that pathological aging is on a continuum with AD.

Abstract Tau is a microtubule-associated protein that promotes polymerization and stabilization of microtubules. It is the major component of fibrillary neuronal and glial inclusions in Alzheimer's disease (AD) and the tauopathies. An autosomal dominant familial tauopathy, frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17), has been shown to be caused by pathogenic tau mutations. Neuropathologic features of FTDP-17 are filamentous tau aggregates in neurons and glia. Previous transgenic mice carrying the normal human tau gene developed motor neuron disease and had dystrophic axons, but no neurofibrillary tangles (NFT). In this report we describe ultrastructural features of NFT in transgenic mice carrying a mutant human tau gene. The mice were generated with a tau cDNA containing exon 1, 4, 5, 7, 9, 10, 11-13, intron 13 and exon 14, driven by the mouse prion promoter (MoPrP) and containing the most common FTDP-17 mutation, P301L. The transgenic construct was generated by ligating the P301L tau cDNA with the mouse prion promoter.

Progranulin is a mediator of development, tumorigenesis and wound repair. Mutations in the gene for progranulin cause frontotemporal dementia. Little is known about the role of progranulin in the nervous system. The cleavage products of progranulin, granulins, were first isolated from granule‐enriched fractions of human and equine neutrophils and from rat bone marrow. Immunohistochemistry of granulin has been reported in macrophages or monocytes. Here we use a post‐embedding immunogold labeling method to ultrastructurally localize progranulin in mouse and human tissue. Bone marrow from mouse femoral bone was fixed in 4% paraformaldehyde. Human choroid plexus and a brain abscess were obtained from autopsy brains fixed in formalin. Tissues were dehydrated in ethanols, infiltrated and embedded in LR White resin. Thin sections were collected on Formvar‐coated nickel grids and incubated with antibodies to mouse or human progranulin, followed by gold‐conjugated secondary antibodies. In all tissues progranulin was localized to secretory granules and vesicles in neutrophils and macrophages. Labeled granules had morphological features of secretory granules. They were membrane‐bound vesicles with pale to optically dense contents and ranged from 200 to 500 microns in diameter. This is the first report of the ultrastructural localization of progranulin to mouse and human neutrophils and macrophages in normal and inflammatory conditions, including neuroinflammatory disorders.

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.