Abstract Body

BIN1, a member of the BAR adaptor protein family, is a significant LOAD risk factor. BIN1 is expressed to varying degrees in oligodendrocytes, neurons, and microglia. The BIN1 gene undergoes complex alternative splicing to generate tissue- and cell-type-specific as well as ubiquitous isoforms. LOAD is characterized by a decrease in the levels of the longest neuronal BIN1 isoform 1. We have characterized BIN1 expression using a series of cell-type-specific conditional knockout mice. Neuronal BIN1 localizes to the synapses, and the loss of neuronal BIN1 expression in mice leads to reduced hippocampal synapse density. These knockout mice show deficits in presynaptic release probability and altered neurotransmitter vesicle dynamics in CA1 excitatory synapses and have spatial learning and memory impairment. However, neuronal BIN1 does not appear to contribute to beta-amyloid pathogenesis in AD. Our recent studies show that the loss of neuronal BIN1 expression significantly lowers the survival of mice with tau pathology. BIN1 has been mechanistically linked to Tau pathology based on its ability to bind to Tau in the cytosol and also BIN1’s function in endocytosis to limit extracellular Tau uptake and pathology propagation in cultured neurons. Finally, we have characterized microglial BIN1 expression and isoform diversity. Currently, we are investigating the normal and disease-associated functions of BIN1 in microglia using cultured microglia and conditional knockout mice. Thus, we conclude that BIN1 plays a non-redundant role in presynaptic regulation and synaptic physiology, which are relevant to Alzheimer’s disease, and BIN1 may have additional functions in microglia.

Abstract Body

The study of the long preclinical phase of Alzheimer's disease, characterized by the presence of amyloid plaques and sometimes neuronal tangles without dementia symptoms, is extremely important as this is the time that therapeutics might be most effective.

We will discuss in this talk how amyloid plaques induce a progressing cellular reaction which involves astroglia, microglia and oligodendrocytes and stresses neurons, leading to abnormal phosphorylation of Tau and of kinases involved in necroptosis. The cellular phase affects mouse neurons differently from human neurons, which appear much more sensitive to this insult. We discuss our single cell trancriptomic and spatial transcriptomic analyses of this cellular reaction and the use of humanized chimeric mouse models to study the disease.

Abstract Body

Neuroinflammation, characterized by the activation of microglia and astrocytes, contributes to the onset and progression of various neurodegenerative diseases including Parkinson's disease (PD). Microglial activation has long been considered to be a key event in prolonged neuroinflammation. However, it remains largely unknown whether and how astrocytes modulate immune signals and contribute to neurodegeneration. Here, we show that the transcription factor early B cell factor 1 (EBF1) is both required and sufficient for an astrocyte-driven inflammatory response. Mice deficient in either Ebf1 or its downstream effector, regulator of G-protein signaling 5 (RGS5), displayed marked reduction in the production of proinflammatory mediators, with a simultaneous attenuation in dopaminergic neuron degeneration, following exposure to lipopolysaccharide. Astrocytic Rgs5 modulates neuroinflammatory response through long non-coding RNA growth-arrest stress 5 (GAS5) and discoidin domain-containing receptor 2 (DDR2)-mediated production of inflammatory mediators and ADAMTS-regulated extracellular matrix remodeling. Our data suggest that the EBF1-RGS5 signaling axis is a critical determinant for astrocyte activation in vivo, and is a new candidate for the strategic targeting of astrocyte-driven neuroinflammation and associated neurodegenerative diseases such as PD.

Abstract Body

TSPO PET studies suggest that In Alzheimer's disease (AD) there is a biphasic inflammatory trajectory. In prodromal AD (β-amyloid positive MCI) high levels of activated microglia are seen that subsequently decline. However, MCI cases with low baseline amyloid which later rises show rising inflammation in this earlier disease phase. These microglia may have a protective phenotype which fails. In late prodromal AD cases, where β-amyloid load is high and tau tangle load is rising, a second rise in inflammation is now seen. At this stage both tau load and inflammation levels independently cinfluence cognitive status while amyloid load shows no significant correlation. The inflammatory process has now switched to becoming neurotoxic and may drive AD progression. In Parkinson's disease there has been no evidence of an initial protective inflammatory phase. Prodromal cases of PD (GBA and LRRK2 gene mutation carriers and idiopathic REM Sleep Behaviour Disorder cases) show microglial activation in substantia nigra and icortical association areas targeted by Lewy body pathology. 30% of GBA and a majority of LRRK2 and RBD cases develop PD or dementia with Lewy bodies and microglial activation becomes widespread. Huntington's disease gene carriers show prodromal striatal and cortical microglial activation which increases as cases become symptomatic. In summary, in most neurodegenerations microglial activation appears to be toxic in nature from onset and therapeutic strategies should target its suppression. The exception is AD where initially β-amyloid deposition excites a protective microglial phenotype which then fails and is replaced by toxic microglia as tau tangle load rises.

Abstract Body

Alzheimer’s disease (AD) is characterized by the accumulation of Aβ (A) and tau (T) as well as neuroinflammatory changes, characterized by reactive astrocytes and activated microglia. It has been proposed that reactive astrocytosis is an early event in the disease process. We aimed to test this hypothesis by assessing Aβ and tau, brain volumetrics and reactive astrocytosis, in young (YCN) and elderly cognitively unimpaired controls (OCN), mild cognitive impaired (MCI) and AD patients. Given that reactive astrocytes overexpress monoamine oxidase-B (MAO-B) in the outer mitochondrial membrane, we used the novel MAO-B PET tracer ¹⁸F-SMBT-1, to assess reactive astrocytosis, in addition to Aβ (NAV4694) and tau (MK6240) imaging

SMBT-1 is a highly selectively and reversibly binding tracer for MAO-B, with high entry into the brain yielding high contrast images, that does not bind to Aβ or tau, follows the reported regional brain distribution of MAO-B, and captured the known MAO-B increases with age. When compared to A-T-OCN, SMBT-1 binding was significantly higher in several cortical regions in A+T+MCI and AD patients and also, and most importantly, in A+T-OCN. When all groups were considered together, SMBT-1 was highly correlated with Aβ, slightly less with tau, but was not significantly associated with cognitive performance.

SMBT-1 is a highly selective F-18 MAO-B tracer with a pharmacokinetic and binding profile of a suitable surrogate marker of reactive astrocytosis. The addition of early markers of reactive astrocytosis to Aβ and tau will likely allow better characterization and prognosis of healthy individuals at risk of developing AD.

Aims

There are many genetic risk factors that impact the risk of Alzheimer’s disease (AD). One of the most influential risk factors is Apolipoprotein E (APOE), a cholesterol and lipid transporter in the brain. Studies show that ApoE isoforms have differing effects on AD pathologies. ApoE has also been shown to impact microglial activation and the neuroinflammatory response to AD pathologies in animal models.

Methods

We used the Human Neuroinflammation NanoString panel identified the neuroinflammatory RNA profile in the superior medial temporal gyrus and cerebellar regions of age and sex matched individuals with the following genotypes and pathology: APOE-e3/3-AD; APOE-e4/4-AD; and APOE-e3/3-control. Results were analyzed with NanoStringDiff followed by additional statistical analysis. In a separate subsample, we used NanoString Digital Spatial Profiling to investigate protein levels of inflammatory markers on fixed tissue surrounding AD pathology in APOE-e3 and APOE-e4 subjects

Results

Significant gene expression changes were found in pathways associated with AD in APOE-e3 individuals. However, APOE-e4/4-AD and APOE-e3/3-control, showed no significant differences, suggesting that APOE-e4/4-AD individuals potentially have an impaired inflammatory response. We compared APOE-e3/3-AD and APOE-e4/4-AD to identify isoform-associated effects with AD pathology and found significant changes. DSP was used to verify these findings and also suggests APOE4 individuals have an altered inflammatory phenotype.

Conclusions

Our results suggest APOE-e3 individuals respond to AD pathology compared to non-AD individuals. Our results indicate that APOE-e4 individuals have an impaired inflammatory response and cannot produce an appropriate response to the pathology. These findings highlight the importance of accounting for APOE isoforms in studies when investigating inflammatory mechanisms of AD.

Aims

Alzheimer's disease (AD) is a devastating neurodegenerative disease. Despite intensive research, all current therapeutic attempts have failed, highlighting the need for new therapeutic approaches. While most research traditionally attributed cognitive impairment to neuronal damage, recent studies have highlighted the role of non-neuronal cells, mainly the brain innate-immune cells, the microglia. However, the contribution of non-immune glial cells remains elusive. Oligodendrocytes are the central nervous system myelin-forming cells and are crucial for proper neuronal signaling and brain function. However, little is known about their fate in AD. In our study, we aimed to reveal cellular heterogeneity among non-immune glia, and particularly oligodendrocytes, in AD.

Methods

To this end, we used the 5xFAD model of AD and performed single cell RNA-sequencing, bulk RNA-sequencing, computational meta-analysis and immunofluorescence stainings.

Results

We found that oligodendrocytes are the most affected cell type and unveiled a novel oligodendrocyte cell-state, which we termed ‘Disease-associated OLigodendrocytes’ (DOLs). DOLs were found exclusively in the AD mouse brains, spatially associated with amyloid-beta plaques and increased with disease progression. DOL signature points at possible interactions with the immune system and immune-related signaling, plaque propagation, and blood-brain-barrier interference. Meta-analysis across other neuroinflammatory and neurodegenerative conditions revealed a conserved oligodendrocyte response similar to DOLs. Bulk RNA-sequencing of oligodendrocytes following different stimulations revealed partial similarity between DOL signature and oligodendrocyte response to inflammatory cues and neuronal death.

Conclusions

Overall, this study demonstrates that oligodendrocytes have a common response to neuroinflammation and neurodegeneration, which can serve as a potential therapeutic target in multiple pathologies.

Aims

Alzheimer’s disease (AD) is the most common form of dementia in the elderly, for which there is no cure. Efficient treatment development requires a) knowledge on early mechanisms and b) tools that allow follow up of disease and treatment effects in a clinically translational way. Disruptions of large-scale functional brain networks occur early on in mouse models of amyloid pathology¹. Calcium imaging studies show aberrant calcium activity in neurons at this stage, as well as in astrocytes ². This means that early deficits of astrocytes could contribute to functional network disruptions and even to disease progression. We aim at investigating the role of astrocytes as potential targets for treatment development in the APP^NLF/NLF mouse model.

Methods

We applied chemogenetic and other viral vector approaches to increase or decrease calcium signalling in astrocytes in 3 months old APP^NLF/NLF and APP^NL/NL mice, i.e. before amyloid plaques deposition. We assessed the effects of these modulations using, among others, resting-state functional Magnetic Resonance Imaging (rsfMRI), a clinically translational tool.

Results

Our results show that before amyloid deposition, APP^NLF/NLF mice display hypersynchrony of functional networks involving the cingulate and retrosplenial areas, which are important for many cognitive functions and are also affected in AD patients. Interestingly, increasing or decreasing calcium signalling in astrocytes affects these functional network disruptions differently.

Conclusions

Our results suggest that astrocytes are involved in early functional network disruptions and could be a potential target for treatment development.

1. Shah et al., Alzheimers Dement. 2016;12(9)

2. Kuchibhotla et al., Science (80). 2009;323(5918)