Alzheimer's-disease-related protein in geriatric schizophrenic patients with cognitive impairment

Biomarkers of neurodegeneration in schizophrenia: systematic review and meta-analysis

QUESTION

Does neurodegenerative disease underlie the increased rate of dementia observed in older people with schizophrenia? Several studies have reported a higher prevalence of dementia in people with schizophrenia compared with the general population. This may reflect a higher risk of developing neurodegenerative diseases such as vascular dementia or Alzheimer's disease (AD). Alternatively, this may reflect non-pathological, age-related cognitive decline in a population with low cognitive reserve.

STUDY SELECTION AND ANALYSIS

We reviewed papers that compared postmortem findings, hippocampal MRI volume or cerebrospinal fluid (CSF) markers of AD, between patients with schizophrenia with evidence of cognitive impairment (age ≥45 years) with controls. We subsequently performed a meta-analysis of postmortem studies that compared amyloid-β plaques (APs) or neurofibrillary tangles (NFTs) in cognitively impaired patients with schizophrenia to normal controls or an AD group.

FINDINGS

No studies found a significant increase of APs or NFTs in cognitively impaired patients with schizophrenia compared with controls. All postmortem studies that compared APs or NFTs in patients with schizophrenia to an AD group found significantly more APs or NFTs in AD. No studies found a significant differences in CSF total tau or phosphorylated tau between patients with schizophrenia and controls. The two studies which compared CSF Aβ42 between patients with schizophrenia and controls found significantly decreased CSF Aβ42 in schizophrenia compared with controls. Hippocampal volume findings were mixed.

CONCLUSIONS

Studies have not found higher rates of AD-related pathology in cognitively impaired individuals with schizophrenia compared with controls. Higher rates of dementia identified in population studies may reflect a lack of specificity in clinical diagnostic tools used to diagnose dementia.

Altered fucosyltransferase expression in the superior temporal gyrus of elderly patients with schizophrenia

Glycosylation is a post-translational modification that is an essential element in cell signaling and neurodevelopmental pathway regulation. Glycan attachment can influence the tertiary structure and molecular interactions of glycosylated substrates, adding an additional layer of regulatory complexity to functional mechanisms underlying central cell biological processes. One type of enzyme-mediated glycan attachment, fucosylation, can mediate glycoprotein and glycolipid cell surface expression, trafficking, secretion, and quality control to modulate a variety of inter- and intracellular signaling cascades. Building on prior reports of glycosylation abnormalities and evidence of dysregulated glycosylation enzyme expression in schizophrenia, we examined the protein expression of 5 key fucose-modifying enzymes: GDP-fucose:protein O-fucosyltransferase 1 (POFUT1), GDP-fucose:protein O-fucosyltransferase 2 (POFUT2), fucosyltransferase 8 (FUT8), fucosyltransferase 11 (FUT11), and plasma α-l-fucosidase (FUCA2) in postmortem superior temporal gyrus of schizophrenia (N=16) and comparison (N=14) subjects. We also used the fucose binding protein, Aleuria aurantia lectin (AAL), to assess α-1,6-fucosylated N-glycoprotein abundance in the same subjects. In schizophrenia, we found increased expression of POFUT2, a fucosyltransferase uniquely responsible for O-fucosylation of thrombospondin-like repeat domains that is involved in a non-canonical endoplasmic reticulum quality control pathway. We also found decreased expression of FUT8 in schizophrenia. Given that FUT8 is the only α-1,6-fucosyltransferase expressed in mammals, the concurrent decrease in AAL binding in schizophrenia, particularly evident for N-glycoproteins in the ~52-58kDa and ~60-70kDa molecular mass ranges, likely reflects a consequence of abnormal FUT8 expression in the disorder. Dysregulated FUT8 and POFUT2 expression could potentially explain a variety of molecular abnormalities in schizophrenia.

Haloperidol inactivates AMPK and reduces tau phosphorylation in a tau mouse model of Alzheimer's disease

INTRODUCTION

The use of antipsychotic medications in Alzheimer's disease has been associated with an increased risk of mortality in clinical trials. However, an older postmortem literature suggests that those with schizophrenia treated in an era of exclusively conventional antipsychotic medications had a surprisingly low incidence of tau pathology. No previously published studies have investigated the impact of conventional antipsychotic exposure on tau outcomes in a tau mouse model of AD.

METHODS

In two experiments, transgenic rTg (tauP301L) 4510 tau mice were treated with either haloperidol or vehicle and phosphotau epitopes were quantified using high-sensitivity tau ELISA.

RESULTS

After treatments of 2 and 6 week's duration, mice treated with haloperidol evidenced a significant reduction in tau phosphorylation associated with an inactivation of the tau kinase AMPK.

DISCUSSION

The data suggest that D2 receptor blockade reduces tau phosphorylation in vivo. Future studies are necessary to investigate the impact of this reduction on tau neuropathology.

Neuronal Nicotinic Acetylcholine Receptors: Involvement in Alzheimer’s Disease and Schizophrenia

Nicotinic acetylcholine receptors (nAChRs) play a role in a variety of diseases of the central nervous system including Alzheimer's disease (AD) and schizophrenia. There is great interest in evaluating disease-related nAChR changes, and pharmacological treatment of nAChR deficits is a promising therapy. In AD, 7 nAChRs remain relatively stable, contrasting to 4 2 nAChRs that are lost in substantial numbers. -amyloid, a major neuropathology in AD, blocks 4 2 and 7 nAChRs. Agonists selective to 7 nAChRs are neuroprotective against amyloid. Paradoxically, 7 nAChRs may function as receptors for -amyloid. These results indicate 7 nAChR antagonists may be appropriate therapy in AD. In schizophrenia, 7 nAChRs are significantly reduced in hippocampus and neocortex. The exceptionally high rate of smoking in schizophrenics is likely a form of self-medication. Therapy with 7 nAChR agonists relieves some schizophrenic symptoms. Despite disparities in etiology and symptomatology, AD and schizophrenia share a target for therapeutic intervention— 7 nAChRs.

Abnormal subcellular localization of GABAA receptor subunits in schizophrenia brain

Inhibitory neurotransmission is primarily mediated by γ-aminobutyric acid (GABA) activating synaptic GABA type A receptors (GABA(A)R). In schizophrenia, presynaptic GABAergic signaling deficits are among the most replicated findings; however, postsynaptic GABAergic deficits are less well characterized. Our lab has previously demonstrated that although there is no difference in total protein expression of the α1-6, β1-3 or γ2 GABA(A)R subunits in the superior temporal gyrus (STG) in schizophrenia, the α1, β1 and β2 GABA(A)R subunits are abnormally N-glycosylated. N-glycosylation is a posttranslational modification that has important functional roles in protein folding, multimer assembly and forward trafficking. To investigate the impact that altered N-glycosylation has on the assembly and trafficking of GABA(A)Rs in schizophrenia, this study used western blot analysis to measure the expression of α1, α2, β1, β2 and γ2 GABA(A)R subunits in subcellular fractions enriched for endoplasmic reticulum (ER) and synapses (SYN) from STG of schizophrenia (N = 16) and comparison (N = 14) subjects and found evidence of abnormal localization of the β1 and β2 GABA(A)R subunits and subunit isoforms in schizophrenia. The β2 subunit is expressed as three isoforms at 52 kDa (β2(52 kDa)), 50 kDa (β2(50 kDa)) and 48 kDa (β2(48 kDa)). In the ER, we found increased total β2 GABA(A)R subunit (β2(ALL)) expression driven by increased β2(50 kDa), a decreased ratio of β(248 kDa):β2(ALL) and an increased ratio of β2(50 kDa):β2(48 kDa). Decreased ratios of β1:β2(ALL) and β1:β2(50 kDa) in both the ER and SYN fractions and an increased ratio of β2(52 kDa):β(248 kDa) at the synapse were also identified in schizophrenia. Taken together, these findings provide evidence that alterations of N-glycosylation may contribute to GABAergic signaling deficits in schizophrenia by disrupting the assembly and trafficking of GABA(A)Rs.

Pattern of memory compromise in chronic geriatric schizophrenia, frontotemporal dementia and normal geriatric controls

OBJECTIVE

The purpose of this study was to explore whether memory deficits in schizophrenia are attributable to poor organisation/encoding during initial learning vs. memory decay.

METHODS

Subjects included geriatric schizophrenia/schizoaffective disorders [SSD; n = 37; age = 59.92 (55-74); education = 11.70 (7-18)]; frontotemporal dementia [FTD; n = 41; age = 76.59 (64-83); education = 14.61 (12-20)] and geriatric controls [n = 107; age = 70.97 (55-93); education = 13.76 (6-20)]. Subjects were administered the Wechsler Memory Scale, Third Edition and discrepancy scores between immediate and delayed subtests/indices were used to explore possible differences between groups in pattern of impairment.

RESULTS

Significant differences were found between groups on age/education and these variables were related to several outcome measures. Gender was not related to diagnostic group and there were no gender differences on study variables. There were differences between the SSD subjects on several variables, with the schizoaffective subjects performing worse despite equivalence on global cognitive function, living status and chronicity. Seven one-way between-subjects ANCOVAs compared groups on discrepancy scores. RESULTS failed to suggest differences between groups on immediate-delayed memory discrepancy scores (p > 0.05). Subsequent analyses revealed differences in percentage retention scores between SSD and FTD on the faces subtest (p = 0.040), with SSD retaining greater information over time.

CONCLUSION

RESULTS failed to show distinctions between groups on pattern of memory impairment when using discrepancy comparisons. However, an analysis examining percentage retention scores revealed better maintenance of non-contextual visual information over time in SSD. Findings may suggest deficits in immediate encoding rather than memory decay for some types of memory ability among geriatric SSD. Our failure to document group differences when using discrepancy comparisons may be attributable to relative similarity in pattern between groups or the limited sensitivity of this technique.

Neuropsychological functioning in elderly patients with schizophrenia and Alzheimer's disease

Cognitive functioning was compared in elderly patients with schizophrenia, elderly patients with probable Alzheimer's disease (AD), and matched healthy controls using a brief neuropsychological battery. Both schizophrenia and AD patients demonstrated marked impairment as compared to controls, with the profile of neuropsychological deficits in both disorders appearing remarkably similar. Only visual confrontation naming, verbal delayed recall, and rate of forgetting (i.e. savings score) significantly differentiated between the two patient groups, with AD patients showing poorer overall recall and more rapid forgetting of verbal information over delay. In addition, schizophrenia subjects showed a significantly greater deficit in visual confrontation naming than the AD group. The relationship of neuropsychological function and clinical symptoms of schizophrenia subjects was also examined. Results showed that word list learning, delayed recall, and rate of forgetting correlated most strongly with positive and negative symptoms. Recent neuropathological studies have indicated abnormalities in specific subfields of the hippocampal formation in schizophrenia that are also severely affected in AD. Though the specific histopathology of the two disorders differs, abnormalities in the common sites may underlie the common neuropsychological profile.

Cellular and molecular neuropathology of the parahippocampal region in schizophrenia

The entorhinal cortex, subiculum, and hippocampus have been regions of great interest in both clinical and neuropathological investigations of schizophrenia. Postmortem studies have identified numerous abnormalities, although many remain controversial or unconfirmed. Among the cellular and molecular neuropathological findings are (1) abnormal cytoarchitecture of the entorhinal cortex characterized by poorly formed layer II neuron clusters and laminar disorganization; (2) normal neuron density but smaller neuron size in the superficial lamina of the entorhinal cortex and subiculum; (3) abnormal expression of the microtubule-associated protein MAP2 in the entorhinal cortex and subiculum; (4) aberrant glutamatergic and catecholaminergic innervation of the entorhinal cortex; (5) abnormal mRNA expression of various transcription factors, ion channels, and neurosecretory pathway-related proteins in entorhinal stellate neurons; and (6) an absence of any neurodegeneration. Altogether, these findings suggest that aberrant neurodevelopmental processes play a key role in the pathobiology of schizophrenia and provide a neuroanatomic basis for understanding many of the clinical and neuropsychological abnormalities in the disorder.

Absence of neurodegeneration in the thalamus and caudate of elderly patients with schizophrenia

The cognitive and functional deterioration observed in many 'poor-outcome' patients with schizophrenia suggests an ongoing neurodegenerative process. Diagnostic neuropathologic studies have excluded known neurodegenerative diseases as the cause of this dementia, and in a previous quantitative investigation of neurodegeneration and neural injury in this population we found no abnormalities in the cerebral cortex. However, it is possible that the deterioration observed in these patients could be due to subcortical neurodegenerative processes. Neurodegeneration and neural injury in the caudate nucleus and mediodorsal nucleus of the thalamus were investigated in a postmortem study of 11 prospectively accrued, clinically well-characterized elderly people with schizophrenia, 11 elderly control subjects with no neuropsychiatric illness, and 12 subjects with Alzheimer's disease. Traditional and immunohistochemical staining and unbiased computerized counting methods were used to quantify common markers of neurodegeneration and neural injury (neuron loss, neurofibrillary tangles, astrocytosis, microgliosis). No statistically significant differences were found between schizophrenia and control subjects for the densities of any markers. There is no evidence that abnormal neurodegeneration occurs in these two important subcortical structures.

Comparison of A68 levels in Alzheimer diseased and non-Alzheimer's diseased brain by two ALZ50 based methods

A total of 61 human brain specimens were analyzed with both ELISA and Western Blot using the ALZ50 monoclonal antibody. The brain specimens included: Alzheimer's Disease (AD, n=31), AD/Down's (n=2), Normal (n=14), Parkinson's Disease (n=7), Huntington's chorea (n=2), Wernicke-Korsakov's Encephalopathy (n=3), and Motor Neuron Disease (n=2). The non-AD cases (n=28) had no detectable A68 by ELISA, and showed no A68 bands by Western blot. The AD cases (n=33), all were positive for A68 by the ELISA, but only 31 of 33 had visible A68 band by Western blot. Additionally, a method for solubilization of A68 is reported.

Cognition and neuropathology in schizophrenia

Clinical, neuropsychological and neuropathological avenues of research have advanced in concert to increase our understanding of schizophrenia. Progress in four general areas of investigation will be reviewed: (i) fronto-temporal-limbic dysfunction; (ii) abnormal connectivity or 'miswiring'; (iii) aberrant neurodevelopment; and (iv) neurodegeneration and neural injury. The challenge for post-mortem research is to identify the molecular pathways in which abnormalities culminate in the highly diverse features of the disorder. Candidate pathways must be able to account for the developmental and deteriorative clinical profiles and the global and focal neuropsychological deficits, as well as the various patho-anatomical abnormalities that indicate aberrant cytoarchitecture and connectivity in the absence of neurodegeneration or other obvious evidence of postmaturational neural injury.

Autopsy study of Alzheimer's disease brain pathology in schizophrenia

The brains of 125 schizophrenic patients (DSM-IV criteria) without other major diseases likely to affect brain morphology were examined at autopsy in our hospital for an evaluation of the number of neurofibrillary tangles (NFT) and senile plaques (SP) as indicators of the incidence of Alzheimer's disease (AD) brain pathology. The clinical degree of dementia and the presence or absence of delirium and Parkinsonism were determined in a review of the patients' charts. No significant difference in the degree of AD brain pathology between the 12 schizophrenics more than 75 years old and 12 age-matched normal controls was present. We conclude that AD pathology seems to be no more frequent among schizophrenic patients than in the normal population, and that the severe cognitive impairment observed in schizophrenics is based on neither neuronal degeneration nor neuronal loss like that occurring in AD. We believe that future morphological studies of cognitive impairments in schizophrenics will require a more detailed investigation at the receptor level.

No neuropathologic evidence for an increased frequency of Alzheimer's disease among elderly schizophrenics

BACKGROUND

There is currently controversy as to the frequency of Alzheimer's disease (AD) in elderly persons with schizophrenia. Several studies have reported an increased frequency of AD in elderly schizophrenics, whereas others have found no increase. This issue is important because it has been hypothesized that medications used to treat schizophrenia may exacerbate AD histopathology.

METHODS

We examined autopsy cases from a state psychiatric hospital and a Veterans Affairs medical center. Charts were reviewed on 166 subjects to determine if the history warranted a DSM-IV diagnosis of schizophrenia. All subjects had complete gross and microscopic neuropathologic evaluations, which were reviewed for evidence of Alzheimer's disease.

RESULTS

Retrospective chart review identified 51 subjects over the age of 55 who met DSM-IV criteria for schizophrenia (mean age = 71.7 years, SD = 8.6, range 56-95 years). Of these 51, only I met neuropathologic criteria for AD, a frequency of 2%.

CONCLUSIONS

The frequency of subjects meeting neuropathologic criteria for Alzheimer's disease in our sample of schizophrenics was equal to or less than that found in the general population. Because institutionalized populations may contain an excess of elderly schizophrenic patients with severe behavioral pathologies, which may in turn reflect the presence of neurodegenerative processes such as Alzheimer's disease, our results may actually overestimate the frequency of Alzheimer's in the entire schizophrenic population. The frequency of Alzheimer's disease in the elderly with schizophrenia may be less than that in the general population.

Developmental trajectory and disease progression in schizophrenia: the conundrum, and insights from a 12-year prospective study in the Monaghan 101

Though conceptualised originally as a deteriorating disorder, some contemporary studies have been interpreted as challenging these foundations; more radically, it has been proposed that schizophrenia may be a 'static encephalopathy' of neurodevelopmental origin. The argument offered here is that schizophrenia is indeed a neurodevelopmental disorder, but that this is not in itself antithetical to later disease progression. Rather, the onset of psychosis may reflect the maturationally-mediated triggering of an active disease process that is associated with progressive deterioration unless attenuated by antipsychotic drugs. A developmental trajectory is proposed to link first or early second trimester dysplasia to the chronic course of the illness; from this, it is argued that schizophrenia is inherently a progressive disorder but that antipsychotic drugs may act to ameliorate this progressive component and thus confer on the disease course some of the characteristics of a 'static encephalopathy'. The 'true' natural history of an illness cannot be determined from studies in treated populations.

Neuropeptide deficits in schizophrenia vs. Alzheimer's disease cerebral cortex

Neuropeptide concentrations were determined in the postmortem cerebral cortex from 19 cognitive-impaired schizophrenics, 4 normal elderly subjects, 4 multi-infarct dementia (MID) cases, and 13 Alzheimer's disease (AD) patients. Only AD patients met criteria for AD. The normal elderly and MID cases were combined into one control group. Somatostatin concentrations were reduced in both schizophrenia and AD. Neuropeptide Y concentrations were reduced only in schizophrenia, and corticotropin-releasing hormone concentrations were primarily reduced in AD. Concentrations of vasoactive intestinal polypeptide and cholecystokinin also were reduced in schizophrenia, although not as profoundly as somatostatin or neuropeptide Y. In AD, cholecystokinin and vasoactive intestinal peptide were unchanged. Neuropeptide deficits in schizophrenics were more pronounced in the temporal and frontal lobes than in the occipital lobe. The mechanisms underlying these deficits in schizophrenia and AD are likely distinct. In schizophrenia, a common neural element, perhaps the cerebral cortical gaba-aminobutyric acid (GABA)-containing neuron, may underlie these deficits.