Clinton Turner

Elevation of brain glucose and polyol-pathway intermediates with accompanying brain-copper deficiency in patients with Alzheimer’s disease: metabolic basis for dementia

Impairment of brain-glucose uptake and brain-copper regulation occurs in Alzheimer’s disease (AD). Here we sought to further elucidate the processes that cause neurodegeneration in AD by measuring levels of metabolites and metals in brain regions that undergo different degrees of damage. We employed mass spectrometry (MS) to measure metabolites and metals in seven post-mortem brain regions of nine AD patients and nine controls, and plasma-glucose and plasma-copper levels in an ante-mortem case-control study. Glucose, sorbitol and fructose were markedly elevated in all AD brain regions, whereas copper was correspondingly deficient throughout (all P < 0.0001). In the ante-mortem case-control study, by contrast, plasma-glucose and plasma-copper levels did not differ between patients and controls. There were pervasive defects in regulation of glucose and copper in AD brain but no evidence for corresponding systemic abnormalities in plasma. Elevation of brain glucose and deficient brain copper potentially contribute to the pathogenesis of neurodegeneration in AD.

Distribution of PSA-NCAM in normal, Alzheimer’s and Parkinson’s disease human brain

Polysialated neural cell adhesion molecule (PSA-NCAM) is a membrane bound glycoprotein widely expressed during nervous system development. While commonly described in the neurogenic niches of the adult human brain, there is limited evidence of its distribution in other brain regions. PSA-NCAM is an important regulator of cell-cell interactions and facilitates cell migration and plasticity. Recent evidence suggests these functions may be altered in neurodegenerative diseases such as Alzheimers (AD) and Parkinsons disease (PD). This study provides a detailed description of the PSA-NCAM distribution throughout the human brain and quantitatively compares the staining load in cortical regions and sub-cortical structures between the control, AD and PD brain. Our results provide evidence of widespread, yet specific, PSA-NCAM expression throughout the human brain including regions devoid of PSA-NCAM in the rodent brain such as the caudate nucleus (CN) and cerebellum (CB). We also detected a significant reduction in PSA-NCAM load in the entorhinal cortex (EC) of cases that was inversely correlated with hyperphosphorylated tau load. These results demonstrate that PSA-NCAM-mediated structural plasticity may not be limited to neurogenic niches and is conserved in the aged brain. We also provide evidence that PSA-NCAM is reduced in the EC, a region severely affected by AD pathology.

String Vessel Formation is Increased in the Brain of Parkinson Disease

BACKGROUND String vessels are collapsed basement membrane without endothelium and have no function in circulation. String vessel formation contributes to vascular degeneration in Alzheimer disease. By comparing to age-matched control cases we have recently reported endothelial degeneration in brain capillaries of human Parkinson disease (PD). OBJECTIVE Current study evaluated changes of basement membrane of capillaries, string vessel formation and their association with astrocytes, blood-brain-barrier integrity and neuronal degeneration in PD. METHODS Brain tissue from human cases of PD and age-matched controls was used. Immunohistochemical staining for collagen IV, GFAP, NeuN, tyrosine hydroxylase, fibrinogen and Factor VIII was evaluated by image analysis in the substantia nigra, caudate nucleus and middle frontal gyrus. RESULTS While the basement-membrane-associated vessel density was similar between the two groups, the density of string vessels was significantly increased in the PD cases, particularly in the substantia nigra. Neuronal degeneration was found in all brain regions. Astrocytes and fibrinogen were increased in the caudate nuclei of PD cases compared with control cases. CONCLUSIONS Endothelial degeneration and preservation of basement membrane result in an increase of string vessel formation in PD. The data may suggest a possible role for cerebral hypoperfusion in the neuronal degeneration characteristic of PD, which needs further investigation. Elevated astrocytosis in the caudate nucleus of PD cases could be associated with disruption of the blood-brain barrier in this brain region.

Multimodal molecular analysis of astroblastoma enables reclassification of most cases into more specific molecular entities

Astroblastoma is a rare and controversial glioma with variable clinical behavior. The diagnosis currently rests on histologic findings of a circumscribed glioma with astroblastomatous pseudorosettes and vascular hyalinization. Immunohistochemical studies have suggested different oncogenic drivers, such as BRAF p.V600E, but very few cases have been studied using genome‐wide methodologies. Recent genomic profiling identified a subset of CNS embryonal tumors with astroblastoma‐like morphology that harbored MN1 gene fusions, termed “CNS high‐grade neuroepithelial tumors with MN1 alteration” (CNS‐HGNET‐MN1). To further characterize the genetic alterations that drive astroblastomas, we performed targeted next‐generation sequencing (NGS) of 500 cancer‐associated genes in a series of eight cases. We correlated these findings with break‐apart fluorescence in situ hybridization (FISH) analysis of the MN1 locus and genome‐wide DNA methylation profiling. Four cases showed MN1 alteration by FISH, including two pediatric cases that lacked other pathogenic alterations, and two adult cases that harbored other cancer‐associated gene mutations or copy number alterations (eg, CDKN2A/B homozygous deletion, TP53, ATM and TERT promoter mutations). Three of these cases grouped with the CNS‐HGNET‐MN1 entity by methylation profiling. Two of four MN1 intact cases by FISH showed genetic features of either anaplastic pleomorphic xanthoastrocytoma (BRAF p.V600E mutation, CDKN2A/B homozygous deletion and TERT promoter mutation) or IDH‐wildtype glioblastoma (trisomy 7, monosomy 10, CDK4 amplification and TP53, NRAS and TERT promoter mutations) and these cases had an aggressive clinical course. Two clinically indolent cases remained unclassifiable despite multimodal molecular analysis. We conclude that astroblastoma histology is not specific for any entity including CNS‐HGNET‐MN1, and that additional genetic characterization should be considered for astroblastomas, as a number of these tumors likely contain a methylation profile or genetic alterations that suggest classification as other tumor entities. Our heterogeneous molecular findings help to explain the clinical unpredictability of astroblastoma.

Impaired expression of GABA transporters in the human Alzheimer’s disease hippocampus, subiculum, entorhinal cortex and superior temporal gyrus

Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the brain and plays an important role in regulating neuronal excitability. GABA reuptake from the synapse is dependent on specific transporters - mainly GAT-1, GAT-3 and BGT-1 (GATs). This study is the first to show alterations in the expression of the GATs in the Alzheimers disease (AD) hippocampus, entorhinal cortex and superior temporal gyrus. We found a significant increase in BGT-1 expression associated with AD in all layers of the dentate gyrus, in the stratum oriens of the CA2 and CA3 and the superior temporal gyrus. In AD there was a significant decrease in GAT-1 expression in the entorhinal cortex and superior temporal gyrus. We also found a significant decrease in GAT-3 immunoreactivity in the stratum pyramidale of the CA1 and CA3, the subiculum and entorhinal cortex. These observations indicate that the expression of the GATs shows brain-region- and layer-specific alterations in AD, suggesting a complex activation pattern of different GATs during the course of the disease.

C9ORF72 and UBQLN2 mutations are causes of amyotrophic lateral sclerosis in New Zealand: a genetic and pathologic study using banked human brain tissue.

Amyotrophic lateral sclerosis (ALS) is a devastatin g neurodegenerative disease which causes progressive and eventually fatal loss of motor func tio . Here we describe genetic and pathological characterisation of brain tissue banked from 19 ALS patients over nearly 20 years at the Department of Anatomy and the Centre for Brain Research, Unive rs ty of Auckland, New Zealand. We screened for mutations in SOD1, TARDBP, FUS, and C9ORF72 genes, and for neuropathology caused by phosphorylated TDP-43, dipeptide repeats and ubiqui lin. We identified two cases with C9ORF72 repeat expansions. Both harboured phosphorylated TD P-43 and dipeptide repeat inclusions. We show that dipeptide repeat inclusions can incorporate or occur independently of ubiquilin. We also identified one case with a UBQLN2 mutation, which showed phosphorylated TDP-43 and characteristic ubiquilin protein inclusions. This i s the first study of ALS genetics in New Zealand, adding New Zealand to the growing list of countries in which C9ORF72 repeat expansion and UBQLN2 mutations are detected in ALS cases.

Neurochemical Characterization of PSA-NCAM+ Cells in the Human Brain and Phenotypic Quantification in Alzheimer’s Disease Entorhinal Cortex

Polysialylated neural cell adhesion molecule (PSA-NCAM) is widely expressed in the adult human brain and facilitates structural remodeling of cells through steric inhibition of intercellular NCAM adhesion. We previously showed that PSA-NCAM immunoreactivity is decreased in the entorhinal cortex in Alzheimers disease (AD). Based on available evidence, we hypothesized that a loss of PSA-NCAM+ interneurons may underlie this reduction. PSA-NCAM expression by interneurons has previously been described in the human medial prefrontal cortex. Here we used postmortem human brain tissue to provide further evidence of PSA-NCAM+ interneurons throughout the human hippocampal formation and additional cortical regions. Furthermore, PSA-NCAM+ cell populations were assessed in the entorhinal cortex of normal and AD cases using fluorescent double labeling and manual cell counting. We found a significant decrease in the number of PSA-NCAM+ cells per mm2 in layer II and V of the entorhinal cortex, supporting our previous description of reduced PSA-NCAM immunoreactivity. Additionally, we found a significant decrease in the proportion of PSA-NCAM+ cells that co-labeled with NeuN and parvalbumin, but no change in the proportion that co-labeled with calbindin or calretinin. These results demonstrate that PSA-NCAM is expressed by a variety of interneuron populations throughout the brain. Furthermore, that loss of PSA-NCAM expression by NeuN+ cells predominantly contributes to the reduced PSA-NCAM immunoreactivity in the AD entorhinal cortex.

Metal concentrations and distributions in the human olfactory bulb in Parkinson’s disease

In Parkinson’s disease (PD), the olfactory bulb is typically the first region in the body to accumulate alpha-synuclein aggregates. This pathology is linked to decreased olfactory ability, which becomes apparent before any motor symptoms occur, and may be due to a local metal imbalance. Metal concentrations were investigated in post-mortem olfactory bulbs and tracts from 17 human subjects. Iron (p < 0.05) and sodium (p < 0.01) concentrations were elevated in the PD olfactory bulb. Combining laser ablation inductively coupled plasma mass spectrometry and immunohistochemistry, iron and copper were evident at very low levels in regions of alpha-synuclein aggregation. Zinc was high in these regions, and free zinc was detected in Lewy bodies, mitochondria, and lipofuscin of cells in the anterior olfactory nucleus. Increased iron and sodium in the human PD olfactory bulb may relate to the loss of olfactory function. In contrast, colocalization of free zinc and alpha-synuclein in the anterior olfactory nucleus implicate zinc in PD pathogenesis.

Merosin-deficient congenital muscular dystrophy: A novel homozygous mutation in the laminin-2 gene

Merosin deficient congenital muscular dystrophy (MDC1A) is an autosomal recessive disorder characterized by mutations in the LAMA2 gene at chromosome 6q22-23. This gene spans 65 exons and encodes the α2 chain subunit of laminin-2. A variety of deletions, missense, nonsense and splice site mutations have been described in the LAMA2 gene, with resultant MDC1A. We describe a novel LAMA2 homozygous sequence variant in a Samoan patient with MDC1A and confirm its pathogenic effect with merosin immunohistochemistry on skeletal muscle biopsy. The likely effect of the sequence variant is modeled using in silico analysis.

GABAA receptor subunit expression changes in the human Alzheimer's disease hippocampus, subiculum, entorhinal cortex and superior temporal gyrus

Gamma‐aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system. GABA type A receptors (GABAARs) are severely affected in Alzheimers disease (AD). However, the distribution and subunit composition of GABAARs in the AD brain are not well understood. This is the first comprehensive study to show brain region‐ and cell layer‐specific alterations in the expression of the GABAAR subunits α1‐3, α5, β1‐3 and γ2 in the human AD hippocampus, entorhinal cortex and superior temporal gyrus. In late‐stage AD tissue samples using immunohistochemistry we found significant alteration of all investigated GABAARs subunits except for α3 and β1 that were well preserved. The most prominent changes include an increase in GABAAR α1 expression associated with AD in all layers of the CA3 region, in the stratum (str.) granulare and hilus of the dentate gyrus. We found a significant increase in GABAAR α2 expression in the str. oriens of the CA1‐3, str. radiatum of the CA2,3 and decrease in the str. pyramidale of the CA1 region in AD cases. In AD there was a significant increase in GABAAR α5 subunit expression in str. pyramidale, str. oriens of the CA1 region and decrease in the superior temporal gyrus. We also found a significant decrease in the GABAAR β3 subunit immunoreactivity in the str. oriens of the CA2, str. granulare and str. moleculare of the dentate gyrus. In conclusion, these findings indicate that the expression of the GABAAR subunits shows brain region‐ and layer‐specific alterations in AD, and these changes could significantly influence and alter GABAAR function in the disease.