Anterior hippocampus in schizophrenia pathogenesis: molecular evidence from a proteome study.

OBJECTIVE: The purpose of the present study was to identify differentially expressed proteins in the anterior and posterior hippocampus of brains of schizophrenia patients compared to neurologically healthy controls. METHOD: Proteins extracted from fresh frozen post-mortem posterior and anterior hippocampus for nine schizophrenia and nine control individuals, and seven schizophrenia and seven control individuals, respectively, were screened for differential expression using 2-D gel electrophoresis and mass spectrometry. RESULTS: A significantly larger number of protein spots were differentially expressed in the anterior (n = 43) compared to the posterior (n = 16) hippocampus, representing 34 and 14 unique proteins, respectively. These proteins are involved in cytoskeleton structure and function, neurotransmission and mitochondrial function. CONCLUSION: Based on the aberrant protein expression profiles, the anterior hippocampus appears to be more involved in schizophrenia pathogenesis than the posterior hippocampus. Furthermore, consistent with previous findings, we found molecular evidence to support abnormal neuronal cytoarchitecture and function, neurotransmission and mitochondrial function in the schizophrenia hippocampus.

Differential gene expression in the hippocampus of the Df1/+ mice: a model for 22q11.2 deletion syndrome and schizophrenia.

Genes and a 3-Mb deletion mapping to human chromosome 22q11.2 have been implicated in 22q11.2 deletion syndrome (22q11.2DS) and schizophrenia. The Df1 heterozygous (Df1/+) mice, a model for 22q11.2DS, display specific deficits in hippocampus-dependent learning and memory and impaired sensorimotor gating, abnormalities observed in patients with schizophrenia and 22q11.2DS. In light of the analogous behavioral abnormalities observed between the Df1/+ mice and 22q11.2DS and schizophrenia respectively, particularly in association with the 22q11.2 deletion, the Df1/+ mice are suitable for investigating the molecular changes that may underlie the cognitive deficits and behavioral abnormalities arising as a result of this deletion. Hence we applied microarray technology to identify such molecular changes in the hippocampus at the transcript level. Twelve genes mapping to the deleted region were reliably identified as expressed in the hippocampus by microarray analysis. 159 other differentially expressed genes/ESTs were also identified. Thus far differential expression of fifteen of these genes involved in signal transduction, synaptic plasticity, neuronal differentiation, microtubule assembly and ubiquitin pathway relevant to hippocampus mediated function have been confirmed by real-time PCR. Of particular interest is the decreased expression (32%) of calmodulin 1, encoding a calcium-dependent protein involved in the calmodulin-calcineurin regulated pathway implicated in learning and memory.

COMT Val108/158 Met modifies mismatch negativity and cognitive function in 22q11 deletion syndrome.

BACKGROUND: Microdeletions at 22q11.2 greatly increase the risk of schizophrenia in early adulthood (relative risk approximately 25-30). We hypothesized that before the onset of schizophrenia, individuals with 22q11DS would manifest specific cognitive and neurophysiological anomalies (endophenotypes) in common with individuals at high risk for schizophrenia in the general population. We further predicted that the catechol-O-methyltransferase Val(108/158)Met polymorphism, located within the deleted chromosomal segment, would modify the severity of endophenotypic features. METHODS: 22q11DS adolescents and young adults (aged 13-21) were compared with age- and IQ-matched control subjects on measures that are associated with risk of idiopathic schizophrenia. RESULTS: 22q11DS subjects displayed poorer verbal working memory and expressive language performance than control subjects. Auditory mismatch negativity (MMN) event-related potentials were reduced at frontal electrodes but were intact at temporal sites. Presence of the COMT(108/158)Met allele on the single intact chromosome 22 was associated with more marked MMN amplitude reduction and poorer neuropsychological performance. Neither COMT Val(108/158)Met allele influenced psychiatric symptoms. CONCLUSIONS: 22q11DS is associated with neurodevelopmental characteristics that are similar to idiopathic schizophrenia. The COMT Val(108/158)Met polymorphism modifies the severity of endophenotypes for schizophrenia, indicating that impaired catecholamine regulation contributes to neuropsychiatric risk in 22q11DS.

Lack of change in markers of presynaptic terminal abundance alongside subtle reductions in markers of presynaptic terminal plasticity in prefrontal cortex of schizophrenia patients.

BACKGROUND: Reduced synaptic connectivity in frontal cortex may contribute to schizophrenia symptoms. While altered messenger RNA (mRNA) and protein expression of various synaptic genes have been found, discrepancies between studies mean a generalizable synaptic pathology has not been identified. METHODS: We determined if mRNAs encoding presynaptic proteins enriched in inhibitory (vesicular gamma-aminobutyric acid transporter [VGAT] and complexin 1) and/or excitatory (vesicular glutamate transporter 1 [VGluT1] and complexin 2) terminals are altered in the dorsolateral prefrontal cortex of subjects with schizophrenia (n = 37 patients, n = 37 control subjects). We also measured mRNA expression of markers associated with synaptic plasticity/neurite outgrowth (growth associated protein 43 [GAP43] and neuronal navigators [NAVs] 1 and 2) and mRNAs of other synaptic-associated proteins previously implicated in schizophrenia: dysbindin and vesicle-associated membrane protein 1 (VAMP1) mRNAs using quantitative polymerase chain reaction. RESULTS: No significant changes in complexin 1, VGAT, complexin 2, VGluT1, dysbindin, NAV2, or VAMP1 mRNA expression were found; however, expression of mRNAs associated with plasticity/cytoskeletal modification (GAP43 and NAV1) was reduced in schizophrenia. Although dysbindin mRNA did not differ in schizophrenia compared with control subjects, dysbindin mRNA positively correlated with GAP43 and NAV1 in schizophrenia but not in control subjects, suggesting low levels of dysbindin may be linked to reduced plasticity in the disease state. No relationships between three dysbindin genetic polymorphisms previously associated with dysbindin mRNA levels were found. CONCLUSIONS: A reduction in the plasticity of synaptic terminals supports the hypothesis that their reduced modifiability may contribute to neuropathology and working memory deficits in schizophrenia.

Developmental patterns of doublecortin expression and white matter neuron density in the postnatal primate prefrontal cortex and schizophrenia.

Postnatal neurogenesis occurs in the subventricular zone and dentate gyrus, and evidence suggests that new neurons may be present in additional regions of the mature primate brain, including the prefrontal cortex (PFC). Addition of new neurons to the PFC implies local generation of neurons or migration from areas such as the subventricular zone. We examined the putative contribution of new, migrating neurons to postnatal cortical development by determining the density of neurons in white matter subjacent to the cortex and measuring expression of doublecortin (DCX), a microtubule-associated protein involved in neuronal migration, in humans and rhesus macaques. We found a striking decline in DCX expression (human and macaque) and density of white matter neurons (humans) during infancy, consistent with the arrival of new neurons in the early postnatal cortex. Considering the expansion of the brain during this time, the decline in white matter neuron density does not necessarily indicate reduced total numbers of white matter neurons in early postnatal life. Furthermore, numerous cells in the white matter and deep grey matter were positive for the migration-associated glycoprotein polysialiated-neuronal cell adhesion molecule and GAD65/67, suggesting that immature migrating neurons in the adult may be GABAergic. We also examined DCX mRNA in the PFC of adult schizophrenia patients (n = 37) and matched controls (n = 37) and did not find any difference in DCX mRNA expression. However, we report a negative correlation between DCX mRNA expression and white matter neuron density in adult schizophrenia patients, in contrast to a positive correlation in human development where DCX mRNA and white matter neuron density are higher earlier in life. Accumulation of neurons in the white matter in schizophrenia would be congruent with a negative correlation between DCX mRNA and white matter neuron density and support the hypothesis of a migration deficit in schizophrenia.

Expression of interneuron markers in the dorsolateral prefrontal cortex of the developing human and in schizophrenia.

OBJECTIVE: The onset of schizophrenia symptoms in late adolescence implies a neurodevelopmental trajectory for the disease. Indeed, the γ-aminobutyric acid (GABA) inhibitory system shows protracted development, and GABA-ergic deficits are widely replicated in postmortem schizophrenia studies. The authors examined expression of several interneuron markers across postnatal human development and in schizophrenia to assess whether protracted development of certain interneuron subpopulations may be associated with a particular vulnerability in schizophrenia. METHOD: RNA was extracted postmortem from dorsolateral prefrontal cortex of individuals from age 6 weeks to 49 years (N=68) and from a cohort of normal comparison subjects and schizophrenia patients (N=74, 37 pairs). Expression levels of parvalbumin, cholecystokinin, somatostatin, neuropeptide Y, calretinin, calbindin, and vasoactive intestinal peptide were measured by quantitative reverse transcription-polymerase chain reaction. Changes in calretinin protein levels were examined by Western blot. RESULTS: Interneuron marker genes followed one of three general expression profiles: either increasing (parvalbumin, cholecystokinin) or decreasing (somatostatin, calretinin, neuropeptide Y) in expression over postnatal life, with the most dramatic changes seen in the first few years before reaching a plateau; or increasing to peak expression in the toddler years before decreasing (calbindin, vasoactive intestinal peptide). mRNA expression of all genes, with the exception of calbindin (which increased), showed a reduction (8%-31%) in schizophrenia. Somatostatin showed the most dramatic reduction (31%) in schizophrenia. CONCLUSIONS: It appears that a heterogeneous population of interneurons is implicated in schizophrenia. Further studies are needed to determine whether specific interneuron subpopulations are altered or whether common or distinct upstream pathways are responsible for interneuron deficits in schizophrenia.

Abnormal pathways in the genu of the corpus callosum in schizophrenia pathogenesis: a proteome study.

Abnormalities within the corpus callosum (CC) have been identified in schizophrenia brains and are thought to affect inter-hemispheric communication, which in-turn is postulated to underlie some schizophrenia symptoms. Furthermore, hemisphere asymmetry of fractional anisotropy, detected by diffusion tensor imaging, left-higher-than-right- has been observed in normal individuals in the CC genu. This asymmetry is significantly reduced in the left CC genu of first-episode and chronic schizophrenia subjects. We examined the protein expression profile of the CC genu, including the profiles from the left and right hemisphere, in schizophrenia brains compared to controls using two-dimensional gel electrophoresis and mass spectrometry techniques. Proteins involved in cytoskeletal structure and function, neuroprotective function and energy metabolism were identified as differentially expressed, suggesting these proteins may underlie abnormal CC genu structure and function. Proteins in these functional categories also displayed different expression levels in the left CC genu compared to the right in both control and schizophrenia brains and therefore may be involved in normal CC asymmetry and reduced asymmetry in schizophrenia individuals. This initial pool of protein candidates and abnormal functional pathways opens up avenues for further investigation of molecular mechanisms involving the CC in schizophrenia pathogenesis and symptoms.

Quasi-linkage: a confounding factor in linkage analysis of complex diseases?

Human linkage analysis is based on the assumption that unlinked genomic loci, particularly loci located on non-homologous chromosomes, segregate independently during meiosis. An exception to this rule is the phenomenon of quasi-linkage (QL) that describes the non-random segregation of non-homologous chromosomes, which can undermine the basic concept of linkage. Molecular mechanisms of QL are not clear; however, observations in mice and plants suggest a possible affinity between non-homologous chromosomal regions containing repetitive or like sequences. QL has not been investigated in humans. As QL may generate false linkages in genome scans of complex diseases, we sought to determine whether genomic loci detected in such genome scans exhibit QL. A number of individual markers showing linkage to schizophrenia, asthma, multiple sclerosis, inflammatory bowel disease and type-1 diabetes were tested for QL in a pairwise linkage analysis against all other markers exhibiting evidence for linkage in each specific study. The Marshfield genotype dataset of eight CEPH families was used for this purpose. The best QL lod scores generated from the analysis were within the range of the "lukewarm" lod scores reported in the majority of linkage studies for complex disorders. In addition, we performed a genome-wide QL analysis on the Marshfield family database which detected eight QL lod scores >6. The replication of the best Marshfield QL scores was performed using the deCODE families and although none of the eight pairs demonstrated independent evidence for QL, three pairs generated maximal lod scores of 0.11, 0.3, and 1.51. In conclusion, although complex disease relevant markers did not produce high QL lod scores, the general phenomenon of QL in humans cannot be excluded and potentially can be a confounding factor in genetic studies of complex traits.