The effects of troglitazone on AMPK in HepG2 cells.

AMP-activated protein kinase (AMPK) is an enzyme crucial in cellular metabolism found to be inhibited in many metabolic diseases including type 2 diabetes. Thiazolidinediones (TZDs) are a class of anti-diabetic drug known to activate AMPK through increased phosphorylation at Thr172, however there has been no research to date on whether they have any effect on inhibition of AMPK's lesser known site of inhibition, Ser485/491. HepG2 cells were treated with troglitazone and phosphorylation of AMPK was found to increase at both Thr172 and Ser485 in a dose- and time-dependent manner. Treatment of HepG2 cells with insulin and PMA led to increases in p-AMPK Ser485 via Akt and PKD1 respectively; however these kinases were not found to be implicated in increases seen from troglitazone. Incubation with the other TZDs, rosiglitazone and pioglitazone, let to a minor increase in p-AMPK Ser485 phosphorylation as well as AMPK activity; however these findings were significantly less than those of troglitazone under equal conditions. These data suggest that the effects of troglitazone on AMPK are more complex than previously thought. Phosphorylation at sites of both activation and inhibition can occur in tandem, although the mechanism by which this occurs has not yet been elucidated.

Cell proliferation is reduced in the hippocampus in schizophrenia.

OBJECTIVE: The molecular and cellular basis of structural and functional abnormalities of the hippocampus found in schizophrenia is currently unclear. Postnatal neurogenesis contributes to hippocampal function in animal models and is correlated with hippocampal volume in primates. Reduced hippocampal cell proliferation has been previously reported in schizophrenia, which may contribute to hippocampal dysfunction. METHOD: We measured the cell proliferation marker, Ki67, in post-mortem hippocampal tissue from patients with schizophrenia (n = 10) and matched controls (n = 16). Ki67-labelled cells were counted within the dentate gyrus and hilus on sections taken from the anterior hippocampus. RESULTS: We replicated the finding of a significant reduction in Ki67+ cells/mm² in schizophrenia cases compared to controls (t24 = 2.1, p = 0.023). In our relatively small sample, we did not find a relationship between Ki67+ cells and age overall, or between Ki67 + cells and duration of illness or antipsychotic treatment in people with schizophrenia. CONCLUSION: Our results confirm that reduced hippocampal cell proliferation may be present in schizophrenia. Restoring hippocampal neurogenesis may be a potential therapeutic target for the treatment of hippocampal dysfunction in schizophrenia.

The effect of adolescent testosterone on hippocampal BDNF and TrkB mRNA expression: relationship with cell proliferation.

BACKGROUND: Testosterone attenuates postnatal hippocampal neurogenesis in adolescent male rhesus macaques through altering neuronal survival. While brain-derived neurotropic factor (BDNF)/ tyrosine kinase receptor B (TrkB) are critical in regulating neuronal survival, it is not known if the molecular mechanism underlying testosterone's action on postnatal neurogenesis involves changes in BDNF/TrkB levels. First, (1) we sought to localize the site of synthesis of the full length and truncated TrkB receptor in the neurogenic regions of the adolescent rhesus macaque hippocampus. Next, (2) we asked if gonadectomy or sex hormone replacement altered hippocampal BDNF and TrkB expression level in mammalian hippocampus (rhesus macaque and Sprague Dawley rat), and (3) if the relationship between BDNF/TrkB expression was altered depending on the sex steroid environment. RESULTS: We find that truncated TrkB mRNA+ cells are highly abundant in the proliferative subgranular zone (SGZ) of the primate hippocampus; in addition, there are scant and scattered full length TrkB mRNA+ cells in this region. Gonadectomy or sex steroid replacement did not alter BDNF or TrkB mRNA levels in young adult male rat or rhesus macaque hippocampus. In the monkey and rat, we find a positive correlation with cell proliferation and TrkB-TK+ mRNA expression, and this positive relationship was found only when sex steroids were present. CONCLUSIONS: We suggest that testosterone does not down-regulate neurogenesis at adolescence via overall changes in BDNF or TrkB expression. However, BDNF/TrkB mRNA appears to have a greater link to cell proliferation in the presence of circulating testosterone.

Evidence for reduced neurogenesis in the aging human hippocampus despite stable stem cell markers.

Reduced neurogenesis in the aging mammalian hippocampus has been linked to cognitive deficits and increased risk of dementia. We utilized postmortem human hippocampal tissue from 26 subjects aged 18-88 years to investigate changes in expression of six genes representing different stages of neurogenesis across the healthy adult lifespan. Progressive and significant decreases in mRNA levels of the proliferation marker Ki67 (MKI67) and the immature neuronal marker doublecortin (DCX) were found in the healthy human hippocampus over the lifespan. In contrast, expression of genes for the stem cell marker glial fibrillary acidic protein delta and the neuronal progenitor marker eomesodermin was unchanged with age. These data are consistent with a persistence of the hippocampal stem cell population with age. Age-associated expression of the proliferation and immature neuron markers MKI67 and DCX, respectively, was unrelated, suggesting that neurogenesis-associated processes are independently altered at these points in the development from stem cell to neuron. These data are the first to demonstrate normal age-related decreases at specific stages of adult human hippocampal neurogenesis.

Potential Role of Oestrogen Modulation in the Treatment of Neurocognitive Deficits in Schizophrenia.

Cognitive deficits are prevalent in schizophrenia, and these deficits represent a disabling aspect of the illness for which there are no current effective treatments. Recent work has shown that sex hormone levels correlate with brain activity and cognitive abilities differentially in patients with schizophrenia relative to healthy control groups. There is emerging evidence suggesting that oestrogen-based therapies may be useful in reversing the cognitive deficits associated with schizophrenia. To date, the results from clinical trials using oestrogen-based therapies to reverse cognitive impairment in schizophrenia have shown that the selective oestrogen receptor modulator raloxifene may be useful to improve attention, memory, learning and the associated brain activity in chronically ill men and women with schizophrenia or schizoaffective disorder. While these findings of cognitive enhancement with a selective oestrogen receptor modulator in people with schizophrenia are encouraging, additional studies will be required to replicate the initial results, assess the time frame of treatment effects, identify biomarkers in subsets of patients who may be more likely to optimally respond to treatment, and identify a more precise mechanism of action, which may include anti-inflammatory effects of oestrogen-based treatments.

Impacts of stress and sex hormones on dopamine neurotransmission in the adolescent brain.

RATIONALE: Adolescence is a developmental period of complex neurobiological change and heightened vulnerability to psychiatric illness. As a result, understanding factors such as sex and stress hormones which drive brain changes in adolescence, and how these factors may influence key neurotransmitter systems implicated in psychiatric illness, is paramount. OBJECTIVES: In this review, we outline the impact of sex and stress hormones at adolescence on dopamine neurotransmission, a signaling pathway which is critical to healthy brain function and has been implicated in psychiatric illness. We review normative developmental changes in dopamine, sex hormone, and stress hormone signaling during adolescence and throughout postnatal life, then highlight the interaction of sex and stress hormones and review their impacts on dopamine neurotransmission in the adolescent brain. RESULTS AND CONCLUSIONS: Adolescence is a time of increased responsiveness to sex and stress hormones, during which the maturing dopaminergic neural circuitry is profoundly influenced by these factors. Testosterone, estrogen, and glucocorticoids interact with each other and have distinct, brain region-specific impacts on dopamine neurotransmission in the adolescent brain, shaping brain maturation and cognitive function in adolescence and adulthood. Some effects of stress/sex hormones on cortical and subcortical dopamine parameters bear similarities with dopaminergic abnormalities seen in schizophrenia, suggesting a possible role for sex/stress hormones at adolescence in influencing risk for psychiatric illness via modulation of dopamine neurotransmission. Stress and sex hormones may prove useful targets in future strategies for modifying risk for psychiatric illness.

Rethinking schizophrenia in the context of normal neurodevelopment.

The schizophrenia brain is differentiated from the normal brain by subtle changes, with significant overlap in measures between normal and disease states. For the past 25 years, schizophrenia has increasingly been considered a neurodevelopmental disorder. This frame of reference challenges biological researchers to consider how pathological changes identified in adult brain tissue can be accounted for by aberrant developmental processes occurring during fetal, childhood, or adolescent periods. To place schizophrenia neuropathology in a neurodevelopmental context requires solid, scrutinized evidence of changes occurring during normal development of the human brain, particularly in the cortex; however, too often data on normative developmental change are selectively referenced. This paper focuses on the development of the prefrontal cortex and charts major molecular, cellular, and behavioral events on a similar time line. We first consider the time at which human cognitive abilities such as selective attention, working memory, and inhibitory control mature, emphasizing that attainment of full adult potential is a process requiring decades. We review the timing of neurogenesis, neuronal migration, white matter changes (myelination), and synapse development. We consider how molecular changes in neurotransmitter signaling pathways are altered throughout life and how they may be concomitant with cellular and cognitive changes. We end with a consideration of how the response to drugs of abuse changes with age. We conclude that the concepts around the timing of cortical neuronal migration, interneuron maturation, and synaptic regression in humans may need revision and include greater emphasis on the protracted and dynamic changes occurring in adolescence. Updating our current understanding of post-natal neurodevelopment should aid researchers in interpreting gray matter changes and derailed neurodevelopmental processes that could underlie emergence of psychosis.

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.