Faculty Bibliography

Complex physiological and behavioral traits, including neurological and psychiatric disorders, often associate with distributed anatomical variation. This paper introduces a global metric, called morphometricity, as a measure of the anatomical signature of different traits. Morphometricity is defined as the proportion of phenotypic variation that can be explained by macroscopic brain morphology. We estimate morphometricity via a linear mixed-effects model that uses an anatomical similarity matrix computed based on measurements derived from structural brain MRI scans. We examined over 3,800 unique MRI scans from nine large-scale studies to estimate the morphometricity of a range of phenotypes, including clinical diagnoses such as Alzheimer's disease, and nonclinical traits such as measures of cognition. Our results demonstrate that morphometricity can provide novel insights about the neuroanatomical correlates of a diverse set of traits, revealing associations that might not be detectable through traditional statistical techniques.

Introduction Abnormal changes in the neurovascular architecture are associated with numerous conditions including tumors, Alzheimer's disease, and diabetes. Pre-clinical mouse models are invaluable in our understanding, diagnosis and treatment of such conditions, but we have yet to see a longitudinal assessment of neurovascular changes in wild type (WT) control mice. Contrast enhanced-magnetic resonance angiography (CE-MRA) utilizes an exogenous contrast agent to study neurovasculature clinically and pre-clinically with little hemodynamic-dependence. Here, we implemented 3D in vivo CE-MRA to longitudinally study the neurovasculature of aging WT mice. This study provides insight into the normal aging process in WT mice and could serve as a baseline for future studies of neurovascular disease models. Materials and Methods Gadolinium (Gd)-bound micelles were synthesized to serve as a blood pool agent via a previously described thin-film method¹ combining Gd-DPTA, polyethylene glycol, and Rhodamine B-bound lipids. Assessment of size, relaxivity, and plasma half-life confirmed the imaging potential of this compound. Gd-micelles were administered via femoral injection into female WT C57BL/6 mice; the most widely used inbred strain for models of human disease². Twentyseven micelle-administered mice were imaged between ages 2-to-26 months (mo). A subset of mice was aged and imaged at 2-4mo, 14-16mo, and 24-26mo to assess variability in neurovascular changes of individual mice. Angiograms were acquired on a 7-Tesla Bruker micro-MRI system with an 87-minute (100mum) ³ isotropic resolution scan. Neurovascular analysis was applied to anatomically identifiable regions following brain alignment with software by the Mouse Imaging Center (Toronto, Canada)3 and tools developed by the Montreal Neurological Institute (Montreal, Canada). Neurovascular changes were quantified using intensity-based vascular thresholding and segmentation (see figure). Results Quantification of the whole brain showed a significant decrease in detectable neurovasculature between the 2-4mo and 14-16mo groups (p<0.01, one-way ANOVA plus Bonferroni test). A reduction was again seen in the second year of aging. We also quantified the neurovascular changes of the cortex, circle of willis, and sagittal midline and found a significant reduction during the first year of aging and further reduction in the second year. However, the hippocampus showed no significant neurovascular changes. Conclusion Gd micelle-enhanced MRA allowed for the detection of an overall decline in the neurovascular volume of aging C57BL/6 mice. To our knowledge, this is the first report of an age-dependent neurovascular reduction in longitudinally monitored WT animals. These unexpected results stress the need to establish a baseline using control animals of the same background when studying transgenic models of neurovascular diseases. Such reductions may also explain age-dependent changes in cerebral blood flow and function. (Figure Presented)

Depressive symptoms are frequently seen in patients with dementia and mild cognitive impairment (MCI). Evidence suggests that there may be a link between current depressive symptoms and Alzheimer disease (AD)-associated pathological changes, such as an increase in cortical amyloid-β (Aβ). However, limited in vivo studies have explored the relationship between current depressive symptoms and cortical Aβ in patients with MCI and AD. Our study, using a large sample of 455 patients with MCI and 153 patients with AD from the Alzheimer's disease Neuroimaging Initiatives, investigated whether current depressive symptoms are related to cortical Aβ deposition. Depressive symptoms were assessed using the Geriatric Depression Scale and Neuropsychiatric Inventory-depression/dysphoria. Cortical Aβ was quantified using positron emission tomography with the Aβ probe(18)F-florbetapir (AV-45).(18)F-florbetapir standardized uptake value ratio (AV-45 SUVR) from the frontal, cingulate, parietal, and temporal regions was estimated. A global AV-45 SUVR, defined as the average of frontal, cingulate, precuneus, and parietal cortex, was also used. We observed that current depressive symptoms were not related to cortical Aβ, after controlling for potential confounds, including history of major depression. We also observed that there was no difference in cortical Aβ between matched participants with high and low depressive symptoms, as well as no difference between matched participants with the presence and absence of depressive symptoms. The association between depression and cortical Aβ deposition does not exist, but the relationship is highly influenced by stressful events in the past, such as previous depressive episodes, and complex interactions of different pathways underlying both depression and dementia.

PURPOSE/OBJECTIVE:Posterior cingulate cortex (PCC) hypometabolism as measured by FDG PET is an indicator of Alzheimer's disease (AD) in prodromal stages, such as in mild cognitive impairment (MCI), and has been found to be closely associated with hippocampus atrophy in AD dementia. We studied the effects of local and remote atrophy and of local amyloid load on the PCC metabolic signal in patients with different preclinical and clinical stages of AD. METHODS:We determined the volume of the hippocampus and PCC grey matter based on volumetric MRI scans, PCC amyloid load based on AV45 PET, and PCC metabolism based on FDG PET in 667 subjects participating in the Alzheimer's Disease Neuroimaging Initiative spanning the range from cognitively normal ageing through prodromal AD to AD dementia. RESULTS:In cognitively normal individuals and those with early MCI, PCC hypometabolism was exclusively associated with hippocampus atrophy, whereas in subjects with late MCI it was associated with both local and remote effects of atrophy as well as local amyloid load. In subjects with AD dementia, PCC hypometabolism was exclusively related to local atrophy. CONCLUSION/CONCLUSIONS:Our findings suggest that the effects of remote pathology on PCC hypometabolism decrease and the effects of local pathology increase from preclinical to clinical stages of AD, consistent with a progressive disconnection of the PCC from downstream cortical and subcortical brain regions.

The immune response is highly active in Alzheimer's disease (AD). Identification of genetic risk contributed by immune genes to AD may provide essential insight for the prognosis, diagnosis, and treatment of this neurodegenerative disease. In this study, we performed a genetic screening for AD-related top immune genes identified in Europeans in a Chinese cohort, followed by a multiple-stage study focusing on Complement Factor H (CFH) gene. Effects of the risk SNPs on AD-related neuroimaging endophenotypes were evaluated through magnetic resonance imaging scan, and the effects on AD cerebrospinal fluid biomarkers (CSF) and CFH expression changes were measured in aged and AD brain tissues and AD cellular models. Our results showed that the AD-associated top immune genes reported in Europeans (CR1, CD33, CLU, and TREML2) have weak effects in Chinese, whereas CFH showed strong effects. In particular, rs1061170 (P(meta)=5.0 × 10(-4)) and rs800292 (P(meta)=1.3 × 10(-5)) showed robust associations with AD, which were confirmed in multiple world-wide sample sets (4317 cases and 16 795 controls). Rs1061170 (P=2.5 × 10(-3)) and rs800292 (P=4.7 × 10(-4)) risk-allele carriers have an increased entorhinal thickness in their young age and a higher atrophy rate as the disease progresses. Rs800292 risk-allele carriers have higher CSF tau and Aβ levels and severe cognitive decline. CFH expression level, which was affected by the risk-alleles, was increased in AD brains and cellular models. These comprehensive analyses suggested that CFH is an important immune factor in AD and affects multiple pathological changes in early life and during disease progress.

Protein misfolding, mitochondrial dysfunction and oxidative stress are common pathomechanisms that underlie neurodegenerative diseases. In prion disease, central to these processes is the post-translational transformation of cellular prion protein (PrPc) to the aberrant conformationally altered isoform; PrPSc. This can trigger oxidative reactions and impair mitochondrial function by increasing levels of peroxynitrite, causing damage through formation of hydroxyl radicals or via nitration of tyrosine residues on proteins. The 6 member Peroxiredoxin (Prdx) family of redox proteins are thought to be critical protectors against oxidative stress via reduction of H2O2, hydroperoxides and peroxynitrite. In our in vitro studies cellular metabolism of SK-N-SH human neuroblastoma cells was significantly decreased in the presence of H2O2 (oxidative stressor) or CoCl2 (cellular hypoxia), but was rescued by treatment with exogenous Prdx6, suggesting that its protective action is in part mediated through a direct action. We also show that CoCl2-induced apoptosis was significantly decreased by treatment with exogenous Prdx6. We proposed a redox regulator role for Prdx6 in regulating and maintaining cellular homeostasis via its ability to control ROS levels that could otherwise accelerate the emergence of prion-related neuropathology. To confirm this, we established prion disease in mice with and without astrocyte-specific antioxidant protein Prdx6, and demonstrated that expression of Prdx6 protein in Prdx6 Tg ME7-animals reduced severity of the behavioural deficit, decreased neuropathology and increased survival time compared to Prdx6 KO ME7-animals. We conclude that antioxidant Prdx6 attenuates prion-related neuropathology, and propose that augmentation of endogenous Prdx6 protein represents an attractive adjunct therapeutic approach for neurodegenerative diseases. Lay Summary Alzheimer's and prion diseases are characterized by accumulation and deposition of misfolded proteins. In prion disease parallel with loss of subsets of nerve cells is an increase in non-neuronal cells (astrocytes) that can impact on their homeostasis. These astrocytes produce peroxiredoxin-6 (Prdx6), a protective antioxidant protein constituent of specific pathways that are activated in response to the misfolding insult and could be highly beneficial to both neuronal and non-neuronal cells. We proposed a redox regulator role for Prdx6 in regulating and maintaining normal cell function via its ability to control the cell stressors, which would contribute to amelioration of prion pathology. To confirm this we generated diseased animals with and without Prdx6 protein. Upon onset of pathology we tested the animals behaviourally, and showed that there was improvement of behavioural deficit and rescue of survival in animals with Prdx6 (Prdx6 Tg) compared to animals without Prdx6 (Prdx6 KO). Neuropathology was attenuated in the brains of Prdx6KO animals compared to Prdx6 Tg animals with disease. Furthermore application of exogenous Prdx6 rescued toxicity due to a chemical inducer of oxidative stress and a chemical inducer of cellular hypoxia in cell culture. We contend that augmentation of endogenous Prdx6 protein represents an attractive adjunct therapeutic approach for acute and chronic degenerative diseases.

Accumulation of ss-amyloid (Ass) in the brain is essential to Alzheimer inverted question marks disease (AD) pathogenesis. Carriers of the apolipoprotein E (APOE) inverted question mark4 allele demonstrate greatly increased AD risk and enhanced brain Ass deposition. In contrast, APOE inverted question mark2 allele carries show reduced AD risk, later age of disease onset, and lesser Ass accumulation. However, it remains elusive whether the apoE2 isoform exerts truly protective effect against Ass pathology or apoE2 plays deleterious role albeit less pronounced than the apoE4 isoform. Here, we characterized APPSW/PS1dE9/APOE inverted question mark2-TR (APP/E2) and APPSW/PS1dE9/APOE inverted question mark4-TR (APP/E4) mice, with targeted replacement (TR) of the murine Apoe for human inverted question mark2 or inverted question mark4 alleles, and used these models to investigate effects of pharmacological inhibition of the apoE/Ass interaction on Ass deposition and neuritic degeneration. APP/E2 and APP/E4 mice replicate differential effect of human apoE isoforms on Ass pathology with APP/E4 mice showing a several-fold greater load of Ass plaques, insoluble brain Ass levels, Ass oligomers, and density of neuritic plaques than APP/E2 mice. Furthermore, APP/E4 mice, but not APP/E2 mice, exhibit memory impairment on object recognition and radial arm maze tests. Between the age of 6 and 10 months APP/E2 and APP/E4 mice received treatment with Ass12-28P, a non-toxic, synthetic peptide homologous to the apoE binding motif within the Ass sequence, which competitively blocks the apoE/Ass interaction. In both lines, the treatment significantly reduced brain Ass accumulation, co-accumulation of apoE within Ass plaques, and neuritic degeneration, and prevented memory deficit in APP/E4 mice. These results indicate that both apoE2 and apoE4 isoforms contribute to Ass deposition and future therapies targeting the apoE/Ass interaction could produce favorable outcome in APOE inverted question mark2 and inverted question mark4 allele carriers.