Helen M. Chao

The Effect of Social Stress on Hippocampal Gene Expression

The housing of male and female rats in a visible burrow system in which a dominance hierarchy is established and interactions between animals can be monitored provides an effective method by which the behavioral and neuroendocrine effects of social stress can be examined. In this social system, subordinate male rats exhibit plasma corticosterone levels that appear to be chronically elevated relative to the dominant rats in the colonies and compared to singly housed controls. Previous studies have indicated that in the hippocampus adrenal steroids negatively regulate the expression of the mRNAs encoding the glucocorticoid receptor (GR), the mineralocorticoid receptor (MR), and the growth-associated protein GAP-43, while the preproenkephalin (ppENK) mRNA is positively regulated by glucocorticoids. This study examined the effect of social stress and the resulting sustained increase in steroid levels in the subordinate animals on gene expression in the hippocampus. The results indicated that GR, MR, and GAP-43 mRNAs were decreased in subordinate rats relative to controls, in the CA1 region of the hippocampus, while ppENK mRNA was unaffected. No statistically significant differences in mRNA expression were observed in other hippocampal subfields. These findings suggest that the social stress encountered by the subordinate rats in this burrow environment elicits changes in hippocampal gene expression that are consistent with their regulation by adrenal steroids.

BDNF Val66Met variant and age of onset in schizophrenia.

Brain‐derived neurotrophic factor (BDNF) has been advanced as a candidate gene for schizophrenia by virtue of its effects on neurotransmitter systems that are dysregulated in psychiatric disorder and its involvement in the response to antipsychotic drugs. The extensively examined BDNF gene Val66Met (or rs6265) variant has been associated with schizophrenia, and studies have linked this polymorphism to brain morphology, cognitive function, and psychiatric symptoms in schizophrenia. Moreover the BDNF Val66Met variant has been reported to be associated with age of onset in schizophrenia. Genotyping of African‐American subjects with schizophrenia for five BDNF coding region single nucleotide polymorphisms revealed variance only at the Val66Met allele. The results of statistical analyses indicate a relationship between the BDNF Val66Met genotype and the ages of first psychiatric hospitalization and first schizophrenia symptoms.

Early involvement of synapsin III in neural progenitor cell development in the adult hippocampus

Synapsin III is a synaptic vesicle‐associated protein that is expressed in cells of the subgranular layer of the hippocampal dentate gyrus, a brain region known to sustain substantial levels of neurogenesis into adulthood. Here we tested the hypothesis that synapsin III plays a role in adult neurogenesis with synapsin III knockout and wild‐type mice. Immunocytochemistry of the adult hippocampal dentate gyrus revealed that synapsin III colocalizes with markers of neural progenitor cell development (nestin, PSA‐NCAM, NeuN, and Tuj1) but did not colocalize with markers of mitosis (Ki67 and PCNA). Because neurogenesis consists of a number of stages, the proliferation, survival, and differentiation of neural progenitor cells were systematically quantitated in the hippocampal dentate gyrus of adult synapsin III knockout and wild‐type mice. We found a 30% decrease in proliferation and a 55% increase in survival of neural progenitor cells in synapsin III knockout mice. We also observed a 6% increase in the number of neural progenitor cells that differentiated into neurons. No difference in the volume of the dentate gyrus was observed between synapsin III knockout and wild‐type mice. Collectively, our results demonstrate a novel role for synapsin III in regulating the proliferation of neural progenitor cells in the adult hippocampal dentate gyrus. These findings suggest a distinct function for this synaptic vesicle protein, in addition to its role in neurotransmission. J. Comp. Neurol. 507:1860–1870, 2008.

Evidence for a Tetrahydrobiopterin Deficit in Schizophrenia

Tetrahydrobiopterin (BH4) is a vital cofactor maintaining availability of the amine neurotransmitters [dopamine (DA), noradrenaline (NA), and serotonin (5-HT)], regulating the synthesis of nitric oxide (NO) by nitric oxide synthase (NOS), and stimulating and modulating the glutamatergic system (directly and indirectly). These BH4 properties and their potential relevance to schizophrenia led us to investigate the hypothesis of a study group (healthy controls, n = 37; schizophrenics, n = 154) effect on fasting plasma total biopterin levels (a measure of BH4). Study analysis showed a highly significant deficit of total biopterins for the schizophrenic sample after partialling out the effects of potential confounds of gender, age, ethnicity, neuroleptic use history and dose of current use, 24-hour dietary phenylalanine/protein ratio (a dietary variable relevant to BH4 synthesis), and plasma phenylalanine (which stimulates BH4 synthesis). A mean decrement of 34% in plasma total biopterins for schizophrenics from control values supports clinical relevance for the finding. In a subsample (21 controls and 23 schizophrenics), sequence analysis was done of the GTP cyclohydrolase I feedback regulatory gene and no mutations were found in the coding region of the gene. A deficiency of BH4 could lead to hypofunction of the systems of DA, NA, 5-HT, NOS/NO, and glutamate, all of which have been independently implicated in schizophrenia psychopathology. Further, evidence has been accumulating which implicates the critical interdependence of these neurotransmitter systems in schizophrenia; this concept, along with the present study finding of a biopterin deficit, suggests that further study of the BH4 system in schizophrenia is warranted and desirable.

Phenylalanine hydroxylase gene in psychiatric patients: screening and functional assay of mutations

BACKGROUND Reports relating phenylalanine kinetics and metabolism to psychiatric disorders led us to undertake the comprehensive screening of the phenylalanine hydroxylase (PAH) coding region and functional testing of discovered mutations in a sample of psychiatric patients and healthy control subjects. METHODS Genomic DNA from psychiatric patients and control subjects was assayed for sequence variants in all PAH coding regions and splice junctions. In vivo functional analysis of mutations was conducted by assessing the kinetics and conversion to tyrosine of a standardized phenylalanine dose and by measuring fasting pterin levels. RESULTS A known missense mutation was observed in a schizoaffective subject, and a novel missense mutation was discovered in four subjects with schizophrenia and one normal subject. The schizoaffective patient heterozygous for the known A403V mutation showed the lowest rate of phenylalanine kinetics and lowest conversion to tyrosine in the patient sample. The four schizophrenic patients heterozygous for the novel K274E mutation showed significantly decreased phenylalanine kinetics, reduced conversion to tyrosine, and increased synthesis of the PAH cofactor tetrahydrobiopterin compared with schizophrenic subjects without the mutation. CONCLUSIONS The study findings suggest that larger scale studies are warranted to test the relationship of the PAH genotype with a psychiatric phenotype.

Investigation of the phenylalanine hydroxylase gene and tardive dyskinesia.

Phenylketonuria (PKU), an inborn error of phenylalanine metabolism, has been shown to be a risk factor for tardive dyskinesia (TD). In male psychiatric patients there was a significant relationship between TD and measures of plasma phenylalanine following ingestion of a standardized phenylalanine dose that was indicative of higher brain availability of phenylalanine in patients with TD. In addition, a medical food formulation consisting of branched chain amino acids, which compete with phenylalanine for transport across the blood–brain barrier, has been demonstrated to be an efficacious treatment for TD. Cumulatively these findings suggested that TD was related to phenylalanine metabolism and thus that sequence variants in the gene for phenylalanine hydroxylase (PAH), the rate‐limiting enzyme in the catabolism of phenylalanine, could be associated with TD susceptibility. Genetic screening of PAH in a group of 123 psychiatric patients revealed ten sequence polymorphisms and two mutations, but none appeared to be a significant risk factor for TD.

CA1 pyramidal neuron gene expression mosaics in the Ts65Dn murine model of Down syndrome and Alzheimer's disease following maternal choline supplementation

Although there are changes in gene expression and alterations in neuronal density and afferent inputs in the forebrain of trisomic mouse models of Down syndrome (DS) and Alzheimers disease (AD), there is a lack of systematic assessments of gene expression and encoded proteins within individual vulnerable cell populations, precluding translational investigations at the molecular and cellular level. Further, no effective treatment exists to combat intellectual disability and basal forebrain cholinergic neurodegeneration seen in DS. To further our understanding of gene expression changes before and following cholinergic degeneration in a well‐established mouse model of DS/AD, the Ts65Dn mouse, we assessed RNA expression levels from CA1 pyramidal neurons at two adult ages (∼6 months of age and ∼11 months of age) in both Ts65Dn and their normal disomic (2N) littermates. We further examined a therapeutic intervention, maternal choline supplementation (MCS), which has been previously shown to lessen dysfunction in spatial cognition and attention, and have protective effects on the survival of basal forebrain cholinergic neurons in the Ts65Dn mouse model. Results indicate that MCS normalized expression of several genes in key gene ontology categories, including synaptic plasticity, calcium signaling, and AD‐associated neurodegeneration related to amyloid‐beta peptide (Aβ) clearance. Specifically, normalized expression levels were found for endothelin converting enzyme‐2 (Ece2), insulin degrading enzyme (Ide), Dyrk1a, and calcium/calmodulin‐dependent protein kinase II (Camk2a), among other relevant genes. Single population expression profiling of vulnerable CA1 pyramidal neurons indicates that MCS is a viable therapeutic for long‐term reprogramming of key transcripts involved in neuronal signaling that are dysregulated in the trisomic mouse brain which have translational potential for DS and AD.