Investigating Mechanisms of Neuronal Migration in the Zebrafish Embryo

The construction of the brain architecture and its complex neuronal circuitry are coordinated processes. Cortical development is dependent on timely production and correct migration of neurons from proliferative regions. Cortical development involves a set of complex events which includes cell proliferation, migration and differentiation. Disruption in any of these processes can lead to cortical malformations. This thesis investigated different aspects of neuronal migration during development using the zebrafish embryo as a model. We chose to investigate three models of neuronal migration. In our first model we investigated the role of the basement membranes in neuronal development using the laminin β1 zebrafish mutant grumpy (gup). We demonstrate that laminin β1 mutants display a decrease in the width of the ventricular space, a marked reduction in size of the forebrain, and ectopic FBMNs, resembling features of cobblestone (COB) Lissencephaly. We also attempted to identify an uncharacterised gup mutation. Previous studies has implicated the hydroxymethylglutaryl co-enzyme A reductase pathway in motor neuron and oligodendrocyte precursor cell migration. In our second model, we investigated the role of the HMGCoAR pathway in forebrain development of zebrafish embryos. Our data suggests the requirement of prenylation, in particular gernaylgeranylation, downstream to the HMGCoAR pathway, is required for correct neuronal positioning and ventricular space morphogenesis in the forebrain. FE65 null mouse model has previously been shown to display defects in basement membrane assembly, neuronal migration, and patterning of the cortex, thus highlighting the importance of FE65 proteins in development. In our third model we hypothesised that FE65 maintains integrity of the basement membrane in the zebrafish, and a loss of function will disrupt neuronal development. Knockdown of FE65 using antisense oligonucleotides morpholinos display defects in neuronal specification and axonal projections in the forebrain, which can be rescued by knocking down p53, suggesting that p53 may be a downstream target of FE65 signalling

A novel SNCA E83Q mutation in a case of dementia with Lewy bodies and atypical frontotemporal lobar degeneration

In this case report, we discuss a patient presenting with parkinsonism followed by a non-amnestic dementia with aphasic clinical features, as well as frontal dysexecutive syndrome. There was a family history of dementia with an autopsy diagnosis of "Pick's disease" in the proband's father. Neuroimaging of the patient revealed focal and severe temporal lobe and lesser frontoparietal lobe atrophy. At autopsy, there was severe frontotemporal lobar degeneration. Histologic evaluation revealed an absence of tau or transactivation response DNA-binding protein of 43 kDa (TDP) pathology but rather severe Lewy body deposition in the affected cortices. Genetic phenotyping revealed a novel missense mutation (p.E83Q) in exon 4 of the gene encoding α-synuclein (SNCA). This case study presents a patient with a novel SNCA E83Q mutation associated with widespread Lewy body pathology with prominent severe atrophy of the frontotemporal lobes and corresponding cognitive impairment

White Matter Hyperintensities in Vascular Contributions to Cognitive Impairment and Dementia (VCID): Knowledge Gaps and Opportunities

White matter hyperintensities (WMHs) are frequently seen on brain magnetic resonance imaging scans of older people. Usually interpreted clinically as a surrogate for cerebral small vessel disease, WMHs are associated with increased likelihood of cognitive impairment and dementia (including Alzheimer\u27s disease [AD]). WMHs are also seen in cognitively healthy people. In this collaboration of academic, clinical, and pharmaceutical industry perspectives, we identify outstanding questions about WMHs and their relation to cognition, dementia, and AD. What molecular and cellular changes underlie WMHs? What are the neuropathological correlates of WMHs? To what extent are demyelination and inflammation present? Is it helpful to subdivide into periventricular and subcortical WMHs? What do WMHs signify in people diagnosed with AD? What are the risk factors for developing WMHs? What preventive and therapeutic strategies target WMHs? Answering these questions will improve prevention and treatment of WMHs and dementia

Frequency of LATE neuropathologic change across the spectrum of Alzheimer’s disease neuropathology: combined data from 13 community-based or population-based autopsy cohorts

Limbic-predominant age-related TDP-43 encephalopathy neuropathologic change (LATE-NC) and Alzheimer’s disease neuropathologic change (ADNC) are each associated with substantial cognitive impairment in aging populations. However, the prevalence of LATE-NC across the full range of ADNC remains uncertain. To address this knowledge gap, neuropathologic, genetic, and clinical data were compiled from 13 high-quality community- and population-based longitudinal studies. Participants were recruited from United States (8 cohorts, including one focusing on Japanese–American men), United Kingdom (2 cohorts), Brazil, Austria, and Finland. The total number of participants included was 6196, and the average age of death was 88.1 years. Not all data were available on each individual and there were differences between the cohorts in study designs and the amount of missing data. Among those with known cognitive status before death (n = 5665), 43.0% were cognitively normal, 14.9% had MCI, and 42.4% had dementia—broadly consistent with epidemiologic data in this age group. Approximately 99% of participants (n = 6125) had available CERAD neuritic amyloid plaque score data. In this subsample, 39.4% had autopsy-confirmed LATE-NC of any stage. Among brains with “frequent” neuritic amyloid plaques, 54.9% had comorbid LATE-NC, whereas in brains with no detected neuritic amyloid plaques, 27.0% had LATE-NC. Data on LATE-NC stages were available for 3803 participants, of which 25% had LATE-NC stage > 1 (associated with cognitive impairment). In the subset of individuals with Thal Aβ phase = 0 (lacking detectable Aβ plaques), the brains with LATE-NC had relatively more severe primary age-related tauopathy (PART). A total of 3267 participants had available clinical data relevant to frontotemporal dementia (FTD), and none were given the clinical diagnosis of definite FTD nor the pathological diagnosis of frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP). In the 10 cohorts with detailed neurocognitive assessments proximal to death, cognition tended to be worse with LATE-NC across the full spectrum of ADNC severity. This study provided a credible estimate of the current prevalence of LATE-NC in advanced age. LATE-NC was seen in almost 40% of participants and often, but not always, coexisted with Alzheimer’s disease neuropathology

Impact of multiple pathologies on the threshold for clinically overt dementia

Longitudinal clinical-pathological studies have increasingly recognized the importance of mixed pathologies (the coexistence of one or more neurodegenerative and cerebrovascular disease pathologies) as important factors in the development of Alzheimer's disease (AD) and other forms of dementia. Older persons with AD pathology, often have concomitant cerebrovascular disease pathologies (macroinfarcts, microinfarcts, atherosclerosis, arteriolosclerosis, cerebral amyloid angiopathy) as well as other concomitant neurodegenerative disease pathologies (Lewy bodies, TDP-43, hippocampal sclerosis). These additional pathologies lower the threshold for clinical diagnosis of AD. Many of these findings from pathologic studies, especially for CVD, have been confirmed using sophisticated neuroimaging technologies. In vivo biomarker studies are necessary to provide an understanding of specific pathologic contributions and time course relationships along the spectrum of accumulating pathologies. In this review, we provide a clinical-pathological perspective on the role of multiple brain pathologies in dementia followed by a review of the available clinical and biomarker data on some of the mixed pathologies

Association of TDP-43 Pathology With Domain-specific Literacy in Older Persons

Background Low health and financial literacy may be an early behavioral manifestation of cognitive impairment, dementia, and accumulating Alzheimer’s pathology. However, there are limited studies investigating the behavioral features associated with hyperphosphorylated transactive response DNA-binding protein-43 (TDP-43), a common age-related pathology, and even fewer studies investigating the neurobiological basis underlying low literacy in aging. Objective To test the hypothesis that TDP-43 pathology is associated with lower literacy. Methods Data came from 293 community-based older persons who were enrolled in two ongoing studies of aging. Participants completed literacy and cognitive assessments, consented to brain donation, and underwent detailed neuropathological evaluation for AD and TDP-43. Linear regression models assessed the association of TDP-43 with literacy after adjusting for demographics, and AD pathology. Post-hoc pairwise comparisons examined whether the level of literacy differed by TDP-43 stage. Results TDP-43 pathology was associated with lower literacy (estimate=−3.16; SE=0.86; p<0.001), above and beyond demographics and AD pathology, and this association persisted even after additionally adjusting for global cognition (estimate=−1.53; SE=0.74; p=0.038). Further, literacy was lower among persons with neocortical TDP-43 pathology compared to those without TDP-43 pathology. Conclusion TDP-43 pathology is associated with lower health and financial literacy in old age, above and beyond AD pathology

Atherosclerosis and Hippocampal Volumes in Older Adults: The Role of Age and Blood Pressure

Background Lower hippocampal volume is associated with late‐life cognitive decline and is an important, but nonspecific marker for clinical Alzheimer's dementia. Cerebrovascular disease may also be associated with hippocampal volume. Here we study the role of intracranial large vessel disease (atherosclerosis) in association with hippocampal volume and the potential role of age, average late‐life blood pressure across all visits, and other factors (sex, apolipoprotein ε4 [APOE ε4], and diabetes). Methods and Results Data came from 765 community‐based older people (91 years old on average at death; 72% women), from 2 ongoing clinical‐pathologic cohort studies. Participants completed baseline assessment, annual standardized blood pressure measurements, vascular risk assessment for diabetes, and blood draws to determine APOE genotype, and at death, brains were removed and underwent ex vivo magnetic resonance imaging and neuropathologic evaluation for atherosclerosis pathology and other cerebrovascular and neurodegenerative pathologies. Linear regression models examined the association of atherosclerosis and hippocampal to hemisphere volume ratio and whether age at death, blood pressure, and other factors modified associations. In linear regression models adjusted for demographics and neurodegenerative and other cerebrovascular pathologies, atherosclerosis severity was associated with a lower hippocampal to hemisphere volume ratio. In separate models, we found the effect of atherosclerosis on the ratio of hippocampal to hemisphere volume was attenuated among advanced age at death or having higher systolic blood pressure (interaction terms P≤0.03). We did not find confounding or interactions with sex, diabetes, or APOE ε4. Conclusions Atherosclerosis severity is associated with lower hippocampal volume, independent of neurodegenerative and other cerebrovascular pathologies. Higher systolic blood pressures and advanced age attenuate associations

Ex-vivo quantitative susceptibility mapping of human brain hemispheres.

Ex-vivo brain quantitative susceptibility mapping (QSM) allows investigation of brain characteristics at essentially the same point in time as histopathologic examination, and therefore has the potential to become an important tool for determining the role of QSM as a diagnostic and monitoring tool of age-related neuropathologies. In order to be able to translate the ex-vivo QSM findings to in-vivo, it is crucial to understand the effects of death and chemical fixation on brain magnetic susceptibility measurements collected ex-vivo. Thus, the objective of this work was twofold: a) to assess the behavior of magnetic susceptibility in both gray and white matter of human brain hemispheres as a function of time postmortem, and b) to establish the relationship between in-vivo and ex-vivo gray matter susceptibility measurements on the same hemispheres. Five brain hemispheres from community-dwelling older adults were imaged ex-vivo with QSM on a weekly basis for six weeks postmortem, and the longitudinal behavior of ex-vivo magnetic susceptibility in both gray and white matter was assessed. The relationship between in-vivo and ex-vivo gray matter susceptibility measurements was investigated using QSM data from eleven older adults imaged both antemortem and postmortem. No systematic change in ex-vivo magnetic susceptibility of gray or white matter was observed over time postmortem. Additionally, it was demonstrated that, gray matter magnetic susceptibility measured ex-vivo may be well modeled as a linear function of susceptibility measured in-vivo. In conclusion, magnetic susceptibility in gray and white matter measured ex-vivo with QSM does not systematically change in the first six weeks after death. This information is important for future cross-sectional ex-vivo QSM studies of hemispheres imaged at different postmortem intervals. Furthermore, the linear relationship between in-vivo and ex-vivo gray matter magnetic susceptibility suggests that ex-vivo QSM captures information linked to antemortem gray matter magnetic susceptibility, which is important for translation of ex-vivo QSM findings to in-vivo

Ex-vivo magnetic susceptibility as a function of in-vivo magnetic susceptibility.

<p>Plot of regional gray matter magnetic susceptibility values measured ex-vivo as a function of the corresponding susceptibility values measured in-vivo in the same hemispheres, for all hemispheres of Dataset 2. Each point in the scatter plot represents a single gray matter brain region of a single hemisphere. Ex-vivo magnetic susceptibility values shown in the plot have been corrected for the effects of lower temperature during ex-vivo imaging [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0188395#pone.0188395.ref004" target="_blank">4</a>].</p

Postmortem brain hemisphere in imaging container.

<p>Example of a participant’s brain hemisphere submerged in formaldehyde solution.</p