Paramita Chakrabarty - US grants

Title: APOE as a modifier of prion-like spread in dementia Abstract: The overall objective of this multidisciplinary project is to test the hypothesis that relative to APOE2 or APOE3, APOE4 facilitates the seeding and spread of misfolded A?, tau, and ?-synuclein (?Syn). Inheritance of an APOE4 allele increases the risk of developing Alzheimer's disease (AD) dramatically. Most studies suggest that the primary mechanism by APOE increases the risk for AD is by modulating the deposition of A? peptide. However, there are studies that suggest APOE may also directly modulate the phosphorylation and misfolding of tau. Although APOE genotype is not recognized as a risk factor allele for the pure ?Syn-opathies, such as Parkinson's disease (PD) the presence of an APOE4 allele has been shown to increase risk of dementia in PD by some studies. In vitro, APOE can directly modulate the aggregation of ?Syn. Somewhat surprisingly, although the first descriptions of A? seeding in mice were reported more than 10 years ago and various human APOE models have been available for many years, there have been no studies of how APOE genotype may modulate seeding of A?. Similarly, there has been no study of how APOE genotype may influence tau or ?Syn seeding. We now propose three Aims to conduct a thorough and systematic assessment of how different isoforms of human APOE impact the prion-like seeding of A?, tau and ?Syn, with focus on assessing whether different APOE isoform may interact with these aggregating proteins to produce distinct strains of misfolded A?, tau, or ?Syn. Aim 1 will determine the relative ability of APOE2, APOE3 and APOE4 to support the seeding of A? pathology, and whether APOE isoform modulates the strain characteristics of the seeded A? aggregates. Aim 2 will determine whether ApoE genotype influences the severity or spread of CNS tau pathology. Aim 3 will determine the impact of ApoE genotype on the seeding and transmission of ?Syn. Collectively, these studies will produce a unique repertoire of animal models and provide the first assessment of whether different human ApoE isoforms may be influencing that pathogenesis of AD and DLB by modulating the prion-like seeding of amyloid, tauopathy, and ?-Synopathy.

Progressive accumulation of intracellular inclusions of ?-synuclein protein in the nervous system is a characteristic feature of Lewy Body diseases which is part of a spectrum of sporadic and hereditary neurodegenerative diseases termed ?- synucleinopathies. The definitive involvement of ?-synuclein in the etiology of these disorders was established by the findings that mutations in ?-synuclein can directly cause Lewy body dementia. Many studies suggest that the progressive spread of ?-synuclein pathology in the peripheral nervous system and the brain occurs through direct ?-synuclein transmission between cells. However, there is a major gap in our understanding of the epigenetic factors that modulate such prionoid properties of ?-synuclein. Our preliminary data suggests that ?-synuclein is an immunogenic protein and that additional factors, such as activation of cellular immunity, may contribute to the prionoid propagation of peripherally administered exogenous ?-synuclein to the CNS of mice. To provide novel insights into immune-mediated mechanisms involved in induction of CNS ?-synuclein inclusion pathology following peripheral challenge with exogenous ?-synuclein, we have assembled a team of experienced investigators with diverse and unique expertise in ?-synuclein proteostasis and neuroimmune regulation. In Aim 1, we will determine whether inflammatory preconditioning of peripheral immune milieu exacerbates induction and CNS transmission of ?-synuclein pathology following peripheral challenge with exogenous ?- synuclein fibrils. In Aim 2, we will test whether the prionoid properties of ?-synuclein fibrils is suppressed in two independent lines of immunodeficient ?-synuclein transgenic mice. Our study will inform us on the interplay between ?- synuclein seeding and propagation and cellular immunity. We expect our study to be highly translational as it will clarify 1) potential interactions between ?-synuclein and cellular immunity and further help us 2) devise preventive immunobiotherapies strategies to slow down intercellular ?-synuclein pathogenesis in the future.

The goal of our proposal is to determine the role of the master regulatory cytokine, Interleukin 10 (IL10), in regulating proteostasis in mouse models of Alzheimer?s disease (AD) in an Apolipoprotein E (ApoE) isoform dependent manner. Our proposal addresses two key questions that are relevant to understanding of AD pathogenesis: (1) how does immune pathways interact with and modulate the function of AD risk genes, such as APOE and (2) can we harness this knowledge to disrupt the IL-10/APOE axis and achieve therapeutic benefits in AD-relevant mouse models? Our preliminary data has shown that the anti-inflammatory cytokine Interleukin (IL)-10, has unexpected negative effect on A? and tau proteostasis in transgenic mouse models of AD. This demonstrates a complex interplay between innate immunity and proteostasis in AD type neurodegenerative diseases, an interaction we call immunoproteostasis. The mechanism(s) underlying such immunoproteostasis leading to neurodegenerative pathology in AD remain unknown; studying the mechanisms underlying immunoproteostasis can enable us to design immunobiotherapies targeting such signaling pathways. We have observed that overexpression of IL-10 in APP transgenic mice worsens A? plaque pathology and cognitive functions via an ApoE-dependent mechanism. Mechanistically, we could attribute the negative effects of IL-10 on A? proteostasis to synergistic effects of decreased A? phagocytosis by microglia, increased endogenous ApoE expression and enhanced accumulation of ApoE in insoluble amyloid plaques. In our study, the increased level of insoluble ApoE was plaque-associated, consistent with mouse ApoE functioning as a pathological chaperone for A? aggregates. Blocking IL-10 signaling using the soluble decoy receptor against IL-10 abrogated this effect and reduced brain amyloid plaque burden. We observed similar ApoE dependent effects on tau proteostasis following IL-10 overexpression in two independent mouse models of tauopathy. Essentially, IL-10 accelerated tauopathy and reduced time to survival in JNPL3 mice; it also promoted forebrain neurodegeneration and tauopathy in the rTg4510 mice. While this was an unexpected phenotype, we provide preliminary data that ApoE specifically interacts with fibrillar tau in a cell free system, which could partially explain the proteostasis, though other mechanisms, such as autophagy inhibition also need to be considered. Guided by these robust preliminary data, we will undertake the following specific aims: Aim 1. Assess whether APOE genotype affects IL10-induced proteostasis in APP mice and evaluate whether interaction of human APOE isoforms with A? aggregates alters microglial clearance of insoluble A?. We will test the effects of IL- 10 immunoproteostasis on amyloid plaque deposition in an APP transgenic mouse expressing human APOE protein (2 or 3 or 4) and provide mechanistic insights into APOE-dependent microglial uptake and clearance of aggregated A?. We expect that promoting expression of the protective APOE2 isoform will have beneficial effects while APOE4 induction will have harmful effects. Aim2. Determine the effects of an AAV-delivered soluble IL-10 receptor decoy (sIL10R1) strategy in APP, tau and non- transgenic mice. Given that IL-10 worsens proteostasis and AD-relevant phenotype in mouse models of A? and tau, herein, we will test the efficacy of a decoy receptor strategy against IL-10. By blocking IL-10 signaling, we expect the decoy receptor strategy to be a potentially translatable disease modifying therapy against both A? and tau proteostasis. Aim3. Replicate and extend our studies of IL-10 overexpression as a driver of tau pathology. Herein, using the AAV toolkit, and systems biology approach, we propose to reproduce our observations of IL-10/APOE-dependent proteostasis phenotype in a well-controlled and behaviorally-characterized tau transgenic cohort and further provide insights into possible mechanisms underlying such amyloidogenic properties of the IL-10/APOE axis. The strength of this proposal lies in the teamwork between a new investigator with continuing commitment to studying the neuroimmune axis in mouse models of AD and an established investigator with experience in creating transgenic AD mouse models. We expect that this proposal will enhance our knowledge of the complex immune signaling cascades in AD proteostasis and uncover translatable immune decoy receptor strategies targeting APOE-regulated proteostasis.