ProfessorGlenda Halliday

Frontotemporal dementia and motor neurodegenerative syndromes

This program of research facilitates and enhances collaboration between internationally-recognised leaders working on the clinical, pathological and biological characteristics of frontotemporal dementia and motor neurodegenerative syndromes. Frontotemporal and motor neurodegeneration cause a group of disorders identified by distinct clinical signs and symptoms, and/or specific histopathologies. These disorders are generally rapidly progressing (median survival 1-3 years from diagnosis), cause behavioural, language or motor deficits (often in combination), and together are a leading cause of dementia (particularly in people aged <65 years). They are unified by the focal and selective nature of the neurodegeneration, which largely occurs in association with the abnormal aggregation of one of three distinct proteins (tau, TDP43, FUS) in neurons and/or glia. For most patients their clinical presentations relate to the brain region affected rather than the underlying proteinopathy. This program unites the diverse research of the investigators to focus on crucial, understudied research areas; 1) the pathogenesis and selectivity of degeneration; 2) the characterisation and mechanisms of disease progression, 3) differences in toxicity of the proteins involved, 4) the development of in vivo biomarkers to detect the different proteinopathies, and 5) novel treatment approaches.

Non-Alzheimer’s disease degenerative dementias: Identifying prodromal genetic/familial phenotypes, modifying factors, and protein variations involved in progression

Background: Non-Alzheimer's disease (AD) dementias, including those overlapping with AD, occur in more than 50% of dementia patients. In those without overlapping AD, most have pathology consistent with a frontotemporal dementia (FTD) syndrome, motor neuron disease (MND) or Lewy body disease, including Parkinson’s disease (LBD). Clinical diagnostic schemas for dementia largely identify individuals with advanced disease, at a point where disease modifying therapies will be less effective. In 2014, diagnostic criteria for preclinical AD were defined to allow better therapeutic targeting. A similar approach is required for the non-AD dementias.

Need: Identification of preclinical forms of FTD and LBD is required, in addition to identifying the different protein species involved in the various non-AD phenotypes for therapeutic targeting.

Strategy:

1) Screen well-defined Australian cohorts of FTD, MND and LBD to recruit and study families with genetic forms of these disorders (presymptomatic and symptomatic mutation carriers to be compared with non-carriers)

2) phenotype clinical, imaging (structural & amyloid/tau) and biological fluid (blood, saliva, urine, CSF) proteins and determine patterns of change over time

3) identify propagation/progression of the proteinopathies and biomarker validation

4) assess modifying factors

5) database all information

6) develop preclinical/early clinical diagnostic criteria

Diagnostic and prognostic precision medicine for behavioral variant frontotemporal dementia

The behavioural variant of frontotemporal dementia (bvFTD) is a common cause of early-onset dementia with heterogeneity in underlying pathology, genetics, and natural course, demanding a customized approach to predict individual prognosis and develop personalized treatments. BvFTD is often mistaken for a primary psychiatric disorder (PPD), causing substantial diagnostic delay of up to 6 years on average. Unlike with Alzheimer’s disease, reliable in vivo biomarkers for FTD are not available yet. Recent research attention has been on genetic FTD (now known to differ pathologically and often clinically); however, the critical challenge is how to diagnose non-familial forms of bvFTD (which accounts for 80% of all cases) early in the disease course and therefore distinguish it from late-onset psychiatric disorders that may mimic bvFTD, in order to deliver relevant interventions and treatments. The creation of a diagnostic and prognostic model of sporadic bvFTD is highly needed and crucial to enable performing precision medicine. All members of our multidisciplinary consortium have a strong track record in bvFTD research. We selected the most promising results of our ongoing research, including neuropsychological and social cognitive markers; neuroimaging- based classifiers; serum neurofilaments, plasma neuronal derived exosome signatures, and cell free DNA. In this project, we will combine cohorts from several countries into a comprehensive retrospective discovery cohort to examine the above-mentioned markers focusing on sporadic cases and PPD, in addition to a large number of pathologically confirmed bvFTD and PPD cases. We will further collect a deeply phenotyped prospective multi-national cohort to validate these markers, in addition to collecting postmortem cases of clinically less well-defined bvFTD / PPD cases. We will use statistical modeling to create the best diagnostic and prognostic model for non-familial forms of bvFTD and PPD. As a subgoal we aim to determine underlying FTD pathology within the sporadic bvFTD group, to enable eventual patient stratification. Our project will contribute towards an early and accurate bvFTD identification, that is crucial for trial enrolment, whereas early PPD identification will lead to the appropriate psychiatric treatments. Our results will increase the ability to predict rate of progression in sporadic bvFTD and other patients presenting with behavioral changes, that is pivotal for patient stratification, trial design and personalized treatments.

Towards treatments for non-Alzheimer neurodegenerative diseases by establishing their biology from presymptomatic to terminal stages

My research aims toadvance basic knowledge, develop diagnostic markers and identify treatment targets for the different molecular pathologies(abnormal tau, alpha-synuclein, TDP-43)underlying non-Alzheimer neurodegenerative diseases at different stages (preclinical, with mild impairments, following disease conversion) because these syndromes are under-recognised but highly prevalent and more rapidly lethal than Alzheimer’s disease. I will particularly focus on determining early biomarkers by collecting peripheral tissues (eg. blood, skin, saliva) through longitudinal studies that I lead. These tissues will be sampled and tested serially in pre-symptomatic genetic and mildly affected prodromic cohorts with risk factors for these major molecular pathologies and compared to biological samples in those meeting clinical criteria for disease, or controls without disease. Validation of any underlying molecular changes will be assessed in brain tissue collected with consent after death. Brain tissue will also be used to determine targetable cellular factors (particularly RNAs and pathological protein 'strains') in all types of brain regions (severely, mildly, unaffected) in each diseased individual. This will identify the earliest as well as later pathobiological changes in the different molecular subtypes known (4 tau, 3 alpha-synuclein, 4 TDP-43). Cells from blood and skin tissue will be used to determine if there are any easily-accessible peripheral cells with similar subtype changes. Unbiased 'omic' analyses of fluids and tissue homogenates will determine targetable biomarkers that differentiate these diseases from each other and from Alzheimer’s disease.This research program will develop new early preclinical diagnostic tools and methods for identifying the underlying pathobiology of these diseases, and determine currently unknown but targetable RNA dysfunction that develops and progresses.

Astroglial contribution to the development of alpha-synucleinopathy reveals novel therapeutic and monitor approach to Parkinson’s disease

In addition to neuronalalpha-synuclein, astroglia are the other major cell type that has increased non-fibrillara-synuclein in disease affected brain regions in Parkinson’s disease (PD). Recent studies show that with advanced age, astrocyte specific genes are the most susceptible to expression changes in a region-specific manner, and that environmental agents directly modulate transcriptional programs of astrocytes. Both age and environmental factors are significant risk factors for PD in that astrocyte is potentially critical to the onset of PD rather than a bystander. Our preliminary studies in PD brain tissue have found that astrocytes react toa-synuclein in unique ways in different brain regions, indicating a diversity of responses in different astrocytic populations. Therefore, interventions targeting astroglial pathways may need to be astrocyte subtype and stage dependent, the essential questions to be answered in this proposal. We hypothesise that key protein/s involved in astrocyte pathways (induction factors for A1 inflammatory phenotype, compensatory neuroprotective proteins, and PARK related proteins) will be associated with increaseda-synuclein in different astrocyte subtypes. In this project, we aim to determine which astrocyte subtypes and pathways are the earliest involved. There have been technical barriers to studying astrocytes in the human brain due to their dynamic and regional heterogeneity. To overcome this, we will incorporate tissue array to the traditional histology methods, which allows discerning early astrocyte events by experimentally defined critical changes in different astroglia populations in different brain regions at different stages of PD. The results will provide fundamental information required for understanding the involvement of astrocytes in PD pathogenesis, which is necessary for the selection of potential treatment targets within the optimal intervene windows and biomarkers to monitor these disease aspects.

Elucidating the biological differences between distinct fibrillar and non-fibrillar alpha-synuclein inclusions in human stem-cell models

Alzheimer’s disease (AD) and AD related dementias (ADRD) are unpreventable, incurable and remain poorly understood. Their hallmark pathology consists of misfolded proteins in characteristic “inclusions” within subsets of neurons and glial cells of the brain. Misfolding of the membrane-­associated protein α-­synuclein (αS) is central to ADRD. Inclusions rich in αS in cortical and dopaminergic (DA) neurons are the hallmark lesions of dementia with Lewy bodies (DLB) and Parkinson disease with dementia (PDD). But αS inclusions are also found in >50% of AD cases, correlating with cognitive decline and frequently colocalizing with tau pathology. αS pathology is strikingly heterogeneous and poorly understood. Common αS pathology comprises vesicle-­rich “pale bodies” (PBs), amyloid-­rich Lewy bodies (LBs), or combinations of these. PBs have indeed been discussed as precursors of LBs, but what gives rise to PBs and how they may convert into LBs remains enigmatic. The ultrastructural features of PBs and LBs parallel enormous interest in the field in both amyloid and vesicle-­trafficking pathologies in PD. In experimental settings, the seeding of neurons with pre-­formed fibrils leads to LB-­like amyloid aggregates. These aggregates can under certain conditions spread and self-­template in adjacent cells. Different amyloid fiber conformers (“strains”) lead to different patterns of neurodegeneration, with differing levels of phosphorylated αS and tau. Human genetic studies have repeatedly implicated perturbed vesicle trafficking and (membrane) lipid homeostasis as a fundamental and unifying feature in disparate forms of ADRD. We hypothesize that altered cellular, and especially lipid, microenvironments can trigger αS amyloid formation and the development of different strains and pathologies. An increasing body of evidence, including work from our groups, indeed suggests that αS toxicity and aggregation can be modulated by altering cellular fatty acid (FA) saturation or sphingolipid (SL) composition through manipulation of glucocerebrosidase (GBA) and stearoyl-­coA desaturase (SCD), respectively. We propose to dissect the influence of these pathways on PB and LB formation and transition in the most disease-­relevant patient-­derived induced pluripotent stem cell (iPSC) models. Importantly, we will employ patient brain-­derived “seed” as the most relevant trigger for neuronal αS aggregation. The use of both patient-­specific cell types and misfolded protein conformers will allow us to capture “in the dish” both sides of the toxic equation in neurodegeneration. We recognize the importance, but also the limitations, of postmortem end-­stage pathology in delineating disease mechanisms, and propose to establish cross-­correlation between in vitro assays, human induced pluripotent stem cell (iPSC) models and postmortem brain tissue. We will focus on iPSCs derived from patients with familial and sporadic synucleinopathies that are matched to postmortem brain, including cases with concomitant levels of AD (β-­amyloid and tau) pathology. Our approaches not only promise to shed light on the formation and consequences of amyloid strains in ADRD, but will also point at potential interventions centered around the transient interaction of αS with lipid membranes.

An in vivo approach to elucidate the pathobiology of Parkinson's disease associated genes using human diseased neurons

Mutations and/or deletions in specific genes result in a high probability of developing Parkinson’s Disease (PD), suggesting a critical role for these genes in the health and survival of specific cells. Curiously, it is not yet clear how, or which specific types of brain cells are functionally impacted by genetic mutations to generate neuronal loss that defines PD. This project is built on the premise that patient-derived cells from genetic forms of PD, studied in the environment of the living brain over time, will provide a unique paradigm to reveal temporal, spatial and cellular components of disease pathobiology. We will use patient inducedd pluripotent stemcells (iPSCs) derived from two known genetic causes of PD – namely cells generated from patients with loss of parkin function (PRKN KO iPSCs) and those that have been obtained from patients with disease-causing mutations in SNCA. Notably, these genetic forms have distinctly different presentations. Complete loss of Parkin function causes an autosomal recessive parkinsonism – invariably seen as an early onset PD with a more benign and motor-dominant clinical course where the neurodegeneration is predominantly restricted to catecholaminergic cells in the brain and typically lacks protein aggregates. At the cellular level, we know that the Parkin deficiency causes mitochondrial defects in cells with severe consequences to their survival. In contrast, point mutations in SNCA cause an autosomal dominant disease, have wide-spread pathology with high aggregate burden, involve not only the monoaminergic cells but also other neuronal systems e.g., the cortical region in the brain, and often times present with non-motor symptoms such as dementia, although the phenotype can be variable between mutation carriers. Importantly, different from Parkin cases, SNCA mutations are thought to impact on the lysosomal degradation pathway, which consequently pushes the cells into a state of dysfunction and degeneration. Here we propose to use patient-derived iPSCs from the three genetically defined iPSC line for each of the two target genes and demonstrate that neurons and astrocytes generated from these cells and grafted in nude-mice will present with deficiencies impacting on their overall survival and function. Furthermore, we will show that SNCA mutation bearing cortical cells are hit as hard, and just like dopamine neurons, present with abnormally processed aggregated alpha-synuclein protein causing the cells to become dysfunctional and potentially die within the course of in vivo follow-up period. We think this property will not be shared with the PRKN cases, where we expect to find a selective vulnerability of dopaminergic cells and astrocytes over cortical neurons. Our analysis will include not only an array of histological and biochemical end-points known to be informative in assessing the human tissue from the respective genetic cases but also transcriptomics analysis of individual mature neurons after long-term in vivo follow-up making our findings unique and highly novel. Furthermore, we will not only compare each line to an appropriate control (where relevant and possible also isogenic cells) making our results more robust and reliable. This approach will give us an additional opportunity to insert PRKN and GBA mutations in isogenic corrected SNCA lines and investigate whether resulting phenotype will be similar to the original lines. We know that the 3 SNCA iPSC lines available from the PPMI study cohorts have highly variable phenotypic presentation (one early-onset disease, a second with late onset and a third from an asymptomatic individual). Based on the hypothesized divergence in the causal pathogenic events, it is tempting to speculate that insertion of PRKN gene mutations in corrected SNCA lines might not replicate the same phenotypic distinction, while on the other hand, insertion of GBA mutation, where the pathogenic pathway converges at the level of lysosomal function might in fact reproduce the different phenotypes.