A luminescence-based reporter to study tau secretion reveals overlapping mechanisms for the release of healthy and pathological tau.

In Alzheimer's disease, tau pathology is thought to spread via a prion-like manner along connected neuronal networks. For this to occur, the usually cytosolic tau protein must be secreted via an unconventional mechanism prior to uptake into the connected neuron. While secretion of healthy and pathological tau has been documented, it remains under-investigated whether this occurs via overlapping or distinct processes. Here, we established a sensitive bioluminescence-based assay to assess mechanisms underlying the secretion of pseudohyperphosphorylated and wild-type tau in cultured murine hippocampal neurons. We found that under basal conditions, both wild-type and mutant tau are secreted, with mutant tau being more robustly secreted. Pharmacological stimulation of neuronal activity led to a modest increase of wild-type and mutant tau secretion, whereas inhibition of activity had no effect. Interestingly, inhibition of heparin sulfate proteoglycan (HSPG) biosynthesis drastically decreased secretion of both wild-type and mutant tau without affecting cell viability. This shows that native and pathological tau share release mechanisms; both activity-dependent and non-activity-dependent secretion of tau is facilitated by HSPGs.

Co-culture of Murine Neurons Using a Microfluidic Device for The Study of Tau Misfolding Propagation.

The deposition of misfolded, aggregated tau protein is a hallmark of several neurodegenerative diseases, collectively termed "tauopathies". Tau pathology spreads throughout the brain along connected pathways in a prion-like manner. The process of tau pathology propagation across circuits is a focus of intense research and has been investigated in vivo in human post-mortem brain and in mouse models of the diseases, in vitro in diverse cellular systems including primary neurons, and in cell free assays using purified recombinant tau protein. Here we describe a protocol that takes advantage of a minimalistic neuronal circuit arrayed within a microfluidic device to follow the propagation of tau misfolding from a presynaptic to a postsynaptic neuron. This assay allows high-resolution imaging as well as individual manipulation of the releasing and receiving neuron, and is therefore beneficial for investigating the propagation of tau and other misfolded proteins in vitro.

Exploring Erythrocytes as Blood Biomarkers for Alzheimer's Disease.

Peripheral biomarkers for dementia are few and far between. Despite research into blood plasma/serum biomarkers for dementia diagnostics, there is a lack of information on erythrocytes and their vast proteomes as potential biomarkers. This review identifies a number of relevant and potentially promising erythrocyte biomarkers for various subtypes of dementia. These include erythrocyte morphology, oxidative stress, and erythrocyte membrane proteins such as the glucose transporter (GLUT-1), amyloid-ß, IgG, Hsp90, calpain-1, and band 3 protein. Of those proteins identified Hsp90, amyloid-ß, calpain-1 and band 3 show the most promise as pre-clinical biomarkers. However, the most intriguing aspect of erythrocytes is their changed morphology in dementia. The altered morphology not only could be used as a diagnostic biomarker but may be crucial in early pathogenesis of the disease. Further work must be done to establish the pathological connection between the periphery and central disease processes.

Effects of environmental enrichment on white matter glial responses in a mouse model of chronic cerebral hypoperfusion.

BACKGROUND: This study was designed to explore the beneficial effects of environmental enrichment (EE) on white matter glial changes in a mouse model of chronic cerebral hypoperfusion induced by bilateral common carotid artery stenosis (BCAS). METHODS: A total of 74 wild-type male C57BL/6J mice underwent BCAS or sham surgery. One week after surgery, the mice were randomly assigned into three different groups having varied amounts of EE-standard housing with no EE conditions (std), limited exposure with 3 h EE a day (3 h) and full-time exposure to EE (full) for 12 weeks. At 16 weeks after BCAS surgery, behavioural and cognitive function were assessed prior to euthanasia. Brain tissues were analysed for the degree of gliosis including morphological changes in astrocytes and microglia. RESULTS: Chronic cerebral hypoperfusion (or BCAS) increased clasmatodendrocytes (damaged astrocytes) with disruption of aquaporin-4 immunoreactivity and an increased degree of microglial activation/proliferation. BCAS also impaired behavioural and cognitive function. These changes were significantly attenuated, by limited exposure compared to full-time exposure to EE. CONCLUSIONS: Our results suggest that moderate or limited exposure to EE substantially reduced glial damage/activation. Our findings also suggest moderate rather than continuous exposure to EE is beneficial for patients with subcortical ischaemic vascular dementia characterised by white matter disease-related inflammation.