Projects I and II seek to elucidate the mechanisms underlying heterogeneity of AD+aSyn/LBD, hypothesizing that different biochemically and milieu-influenced strains formed by misfolded aSyn underlie the spectrum represented by AD+aSyn and LBD compared with the more virulent MSA aSyn stain (see Figure 1).
Projects III and IV complement these first two Projects by focusing on patient-oriented studies of LBD and AD to examine clinical and pathological heterogeneity with multimodal clinical, genetic, and biomarker assessments, with follow up to autopsy which will reveal those patients with AD+aSyn versus pure AD (AD-aSyn). Together, these Projects will advance more precise approaches to understanding AD+aSyn and LBD.
For a closer look at the science behind these projects, view the full U19 Overall:
Project I Leader: Virginia M.-Y Lee, PhD
The diversity of misfolded aSyn pathology in AD+aSyn/LBD/MSA supports the aSyn strain hypothesis wherein pathological aSyn adopts different conformations that account for disease in these disorders. Since aSyn pathology progressively spreads in brains of AD+aSyn/LBD/MSA patients, we propose the strain transmission hypothesis to explain the heterogeneity of these disorders and the spreading of pathological aSyn.
For more on Project I, click the title above.
Projects I and II have advanced beyond the use of Tg mice and synthetic aSyn PFFs to study the spread of pathological aSyn in (wild type) WT mice for modelling AD+aSyn and LBD versus MSA using aSyn strains isolated from AD+aSyn, LBD and MSA brains characterized genetically and neuropathologically by Core C from patients followed by Core B and studied in Projects III and IV.
We demonstrated the existence of human brain-derived aSyn strains through the analyses of pathological aSyn isolated from AD+aSyn and LBD brains harboring abundant LNs/LBs (aSyn-LB) and MSA brains with abundant GCIs (aSyn-GCI).1 We showed that aSyn-LB (from AD+aSyn and LBD brains) and aSyn-GCI from MSA brains are conformationally and biologically distinct, and that aSyn-GCI is ~1,000-fold more potent than aSyn-LB in seeding pathological aSyn aggregation. Moreover, other recent studies suggest the intracellular environment plays a deterministic role in aSyn strain specification.1
Going forward, we will identify the determinants of cell type specificities for AD+aSyn and LBD brain derived aSyn-LB compared to MSA brain derived aSyn-GCI strains and elucidate mechanisms for the templated propagation of these and other aSyn strains we uncover. This will include cryo-electron microscopy (Cryo-EM) studies with Vera Moiseenkova-Bell, PhD, the new Director of the Beckham Center for Cryo-EM launched in May 2019 in which we will collaborate on these Cryo-EM studies of brain derived aSyn stains.
Project I works closely with all U19 Center Cores/Projects, especially Project II, to provide LB-aSyn and GCI-aSyn strains for strain-specific transmission studies in mouse models.
Project II Leader: Kelvin Luk, PhD
In Project II, we test the hypothesis that pathological aSyn in AD+aSyn, PD, PDD and DLB (i.e., LBD) brains represent the emergence and spread of different aSyn strains in neurons to form LBs and LNs. We compare these strains to each other and with aSyn strains in MSA brain derived GCI-aSyn strains.
Co-Investigator: Virginia M.-Y. Lee, PhD
For more on Project II, click the title above.
Testing this hypothesis will advance understanding of if/how distinct aSyn strains drive clinical and pathological heterogeneity in these diverse synucleinopathies. Since dementia in PDD and DLB frequently is accompanied by AD pathology (aSyn+AD), we will test the hypothesis that aSyn strains from AD+aSyn and LBD brains (aSyn-LB) induce Aβ and tau pathologies compared to pathological aSyn from MSA brains (aSyn-GCI) which rarely show comorbid AD.
Project II works closely with all U19 Center Cores/Projects to determine if aSyn-LB and aSyn-GCI strains differentially induce pathological aSyn in neurons versus glia as well as recruit AD-like plaque and tangle pathology following intracerebral injections into Tg mice that model Aβ plaque and/or tau pathologies compared to WT and transgenic (Tg) mice that model MSA-like GCIs.
These studies will open up new pathways to explore how LB versus GCI aSyn strains contribute to the distinct and heterogeneous clinical and pathological features of AD+aSyn/LBD versus MSA as well as interact with AD pathologies.
Project III Leader: David Irwin, MD
Our recent autopsy studies of a large number of clinically diagnosed PDD and DLB patients showed that aSyn pathology, when accompanied by tau and Aβ co-pathology (i.e. aSyn+AD), is relatively more abundant in cortex than striatum and associates with more rapid clinical decline as well as more cognitive difficulties.142 In contrast, aSyn pathology consistent with LBD but without AD pathology (i.e. aSyn-AD) is equally abundant in cortex and striatum, and patients have longer survival with less cognitive difficulties. In our living cohort, we also found that LBD patients with abnormal CSF Aβ1-42, consistent with likely aSyn+AD, have greater MRI cortical atrophy and cognitive difficulties while patients with normal CSF Aβ, consistent with likely pure aSyn (i.e. aSyn-AD), have more prominent striatal atrophy with less cognitive, but greater motor, difficulties.
Co-Investigators: Phil Cook, Corey McMillan, Daniel Weintraub, David Wolk, Paul Yuskevich
For more on Project III, click the title above.
In Project III, we build on these findings with all the U19 Cores to study the nature and anatomic distribution of ND pathologies and associated aSyn strains, and examine the corresponding clinical, cognitive, and anatomic features of LBD versus AD during life. This will be done by collaborating with Core C through pathologic evaluation of LBD and AD using a validated digital histology (DHist) approach with superior sensitivity to quantify the anatomic distribution of aSyn, Aβ and tau pathology in a 2X2 design comparing LBD (aSyn-AD, aSyn+AD) and AD (AD-aSyn, AD+aSyn), relate these pathologies to antemortem clinical features from Core B as well as with Project IV, and use digital microscopy methods (DHist) to assess monoclonal antibodies (mAbs) characterized by Projects I and II to correlate aSyn strains defined in these Projects with human pathology in aSyn-AD vs. AD+aSyn. We also compare aSyn+AD with pure AD (i.e. AD-aSyn), and expect different anatomic distributions of pathology and corresponding clinical differences that are related to specific aSyn strains.
We extend these studies into living patients with autopsy-validated CSF to define likely pathology in aSyn-AD vs. aSyn+AD, and AD-aSyn vs. AD+aSyn. Using cross-sectional and longitudinal multimodal structural MRI, we study the spread of cerebral atrophy and examine associated cognitive decline in executive, language, memory and spatial domains. We expect to find relatively different patterns of progressive atrophy and related cognitive impairments depending on likely aSyn+AD pathology compared to pure aSyn (i.e. aSyn-AD) pathology, and compare these to pure AD pathology (i.e. AD-aSyn) and AD+aSyn pathology.
We will also relate the anatomic and cognitive profiles to aSyn strains in CSF from Project IV. These multimodal studies will elucidate how aSyn pathology is modified by Aβ and tau co-pathology in aSyn+AD versus AD+aSyn and pure AD, identify related clinical phenotypes, assess the contribution of aSyn strains to pathologic and clinical heterogeneity of AD and LBD, and improve diagnosis and prognosis as treatments emerge for these conditions.
Project IV Leader: Alice Chen-Plotkin, MD
To tackle the problem of heterogeneity of PD/PDD/DLB compared to AD+aSyn in a manner that is likely to yield both biological insight and practical tools, Project IV will develop biochemical and genetic biomarkers of differential PD/PDD cognitive progression. In the past 5 years, we have collected DNA and baseline biofluids from ~400 Penn LBD and AD+aSyn patients assessed on an annual/biennial schedule with motor and cognitive measures. We have generated data suggesting that multiple plasma-based biochemical markers predict differential cognitive progression, as reflected by change in the Mattis Dementia Rating Scale-2 (DRS-2). While some baseline biochemical biomarkers predict subsequent decline along both motor and cognitive trajectories, others are selectively informative with respect to motor or cognitive outcomes.
Co-Investigators: Rizwan Akhtar and Dan Weintraub
For more on Project IV, click the title above.
We now propose to confirm our Penn-discovered, NINDS funded PD Biomarker Program (PDBP)-replicated lead proteins in additional cohorts of PD/PDD/AD+aSyn patients, and to develop assays that can translate into clinical or clinical trial use. We will additionally relate common genetic variants to expression levels of top biomarker candidates using (1) publicly available resources such as the Genotype-Tissue Expression (GTEx) project to perform expression quantitative trait locus (eQTL) analyses, and (2) Penn-based datasets of genome-wide genotyping and protein profiling in the same patients to conduct protein quantitative trait locus (pQTL) analyses. We will test the hypothesis that genetic variants nominated through these eQTL and pQTL analyses will predict progression in LBD using cohorts at Penn and elsewhere. Finally, we will use antibodies to the aSyn strains defined in Projects I and II to develop biomarker assays to characterize biofluids from our Penn cohort to test the hypothesis that distinct aSyn strains result in differential development of cognitive features in clinical PD/PDD/DLB and AD+aSyn patients.
Finally, all of the Penn U19 Center investigators worked very closely together to design and formulate the research plan described in this application by pursuing NIA research priorities in “Recommendations of the Alzheimer's disease-related dementias conference”,13 and especially the priorities that address AD and RD including LBD (DLB and PDD), as well as the new guidelines on the biological definition of AD.14-17 We incorporate these NIA recommendations in each of the Projects and Cores of the U19 Center, while all Project and Center investigators also deliberately designed the plans for interacting closely and frequently across all the Projects and Cores to ensure that all Center investigators interact synergistically with a very deliberate common purpose to implement the goals of the U19 Center (see Fig. 5 of the Overall – linked below). In addition, we will implement a unique U19 data and biosample sharing program described in the full Overall and in Core A in partnership with our U19 NIA Program Officer, Austin Yang.