Developmental mechanisms and experimental models to understand forebrain malformative diseases

Spatiotemporal Changes of Cerebral Monocarboxylate Transporter 8 Expression

Background: Mutations of monocarboxylate transporter 8 (MCT8), a thyroid hormone (TH)-specific transmembrane transporter, cause a severe neurodevelopmental disorder, the Allan-Herndon-Dudley syndrome. In MCT8 deficiency, TH is not able to reach those areas of the brain where TH uptake depends on MCT8. Currently, therapeutic options for MCT8-deficient patients are missing, as TH treatment is not successful in improving neurological deficits. Available data on MCT8 protein and transcript levels indicate complex expression patterns in neural tissue depending on species, brain region, sex, and age. However, information on human MCT8 expression is still scattered and additional efforts are needed to map sites of MCT8 expression in neurovascular units and neural tissue. This is of importance because new therapeutic strategies for this disease are urgently needed. Methods: To identify regions and time windows of MCT8 expression, we used highly specific antibodies against MCT8 to perform immunofluorescence labeling of postnatal murine brains, adult human brain tissue, and human cerebral organoids. Results: Qualitative and quantitative analyses of murine brain samples revealed stable levels of MCT8 protein expression in endothelial cells of the blood-brain barrier (BBB), choroid plexus epithelial cells, and tanycytes during postnatal development. Conversely, the neuronal MCT8 protein expression that was robustly detectable in specific brain regions of young mice strongly declined with age. Similarly, MCT8 immunoreactivity in adult human brain tissue was largely confined to endothelial cells of the BBB. Recently, cerebral organoids emerged as promising models of human neural development and our first analyses of forebrain-like organoids revealed MCT8 expression in early neuronal progenitor cell populations. Conclusions: With respect to MCT8-deficient conditions, our analyses not only strongly support the contention that the BBB presents a lifelong barrier to TH uptake but also highlight the need to decipher the TH transport role of MCT8 in early neuronal cell populations in more detail. Improving the understanding of the spatiotemporal expression in latter barriers will be critical for therapeutic strategies addressing MCT8 deficiency in the future.

Ybx1 fine-tunes PRC2 activities to control embryonic brain development

Chromatin modifiers affect spatiotemporal gene expression programs that underlie organismal development. The Polycomb repressive complex 2 (PRC2) is a crucial chromatin modifier in executing neurodevelopmental programs. Here, we find that PRC2 interacts with the nucleic acid-binding protein Ybx1. In the mouse embryo in vivo, Ybx1 is required for forebrain specification and restricting mid-hindbrain growth. In neural progenitor cells (NPCs), Ybx1 controls self-renewal and neuronal differentiation. Mechanistically, Ybx1 highly overlaps PRC2 binding genome-wide, controls PRC2 distribution, and inhibits H3K27me3 levels. These functions are consistent with Ybx1-mediated promotion of genes involved in forebrain specification, cell proliferation, or neuronal differentiation. In Ybx1-knockout NPCs, H3K27me3 reduction by PRC2 enzymatic inhibitor or genetic depletion partially rescues gene expression and NPC functions. Our findings suggest that Ybx1 fine-tunes PRC2 activities to regulate spatiotemporal gene expression in embryonic neural development and uncover a crucial epigenetic mechanism balancing forebrain-hindbrain lineages and self-renewal-differentiation choices in NPCs.

Maternal hyperglycemia disturbs neocortical neurogenesis via epigenetic regulation in C57BL/6J mice

Offspring of mothers with hyperglycemia during pregnancy have a higher incidence of long-term neuropsychiatric disorders than offspring from a normal pregnancy, indicating that neocortical neurogenesis might be affected by maternal hyperglycemia. A paucity of study evaluating the effects of hyperglycemia on neocortical neurogenetic differentiation of neural stem cells, and the mechanism remains unclear. We sought to investigate the the roles and possible molecular mechanism of maternal hyperglycemia on neocortical neurogenetic differentiation of neural stem cells. We established a mouse model of a hyperglycemic pregnancy to study effects of intrauterine exposure to maternal hyperglycemia on neocortical neurogenesis. We observed morphological changes in the neocortex and detected the neurogenetic differentiation of neural stem cells in offspring affected by high glucose levels. We investigated the regulatory network between epigenetic modification and transcription factors in differentiated neural stem cells under hyperglycemic conditions. Maternal hyperglycemia disturbs neocortical lamination in some non-malformed offspring. Our results suggested that hyperglycemia altered the early-born neuron fate and the distribution of newborn neurons in deep layers by promoting the earlier differentiation of neural stem cells. Altered histone acetylation and its regulation on the transcription of proneural genes might be correlated to the disrupted differentiation of neural stem cells and altered distribution of newborn projection neurons in the neocortex. Our data raised the possibility that maternal hyperglycemia in pregnancy disturbs the laminar distribution of neocortical projection neurons in some non-malformed offspring via epigenetic regulation on neural stem cell differentiation and the birthdate of neocortical neurons.

Maternal thyroid hormones are transcriptionally active during embryo-foetal development: results from a novel transgenic mouse model

Even though several studies highlighted the role of maternal thyroid hormones (THs) during embryo-foetal development, direct evidence of their interaction with embryonic thyroid receptors (TRs) is still lacking. We generated a transgenic mouse model ubiquitously expressing a reporter gene tracing TH action during development. We engineered a construct (TRE2×) containing two TH-responsive elements controlling the expression of the LacZ reporter gene, which encodes β-galactosidase (β-gal). The specificity of the TRE2× activation by TH was evaluated in NIH3T3 cells by cotransfecting TRE2× along with TRs, retinoic or oestrogen receptors in the presence of their specific ligands. TRE2× transgene was microinjected into the zygotes, implanted in pseudopregnant BDF1 (a first-generation (F1) hybrid from a cross of C57BL/6 female and a DBA/2 male) mice and transgenic mouse models were developed. β-gal expression was assayed in tissue sections of transgenic mouse embryos at different stages of development. In vitro, TRE2× transactivation was observed only following physiological T3 stimulation, mediated exclusively by TRs. In vivo, β-gal staining, absent until embryonic day 9.5-10.5 (E9.5-E10.5), was observed as early as E11.5-E12.5 in different primordia (i.e. central nervous system, sense organs, intestine, etc.) of the TRE2× transgenic embryos, while the foetal thyroid function (FTF) was still inactive. Immunohistochemistry for TRs essentially colocalized with β-gal staining. No β-gal staining was detected in embryos of hypothyroid transgenic mice. Importantly, treatment with T3 in hypothyroid TRE2× transgenic mice rescued β-gal expression. Our results provide in vivo direct evidence that during embryonic life and before the onset of FTF, maternal THs are transcriptionally active through the action of embryonic TRs. This model may have clinical relevance and may be employed to design end-point assays for new molecules affecting THs action.

Esquizofrenia: uma doença inflamatória?

OBJETIVO: Neste estudo, o objetivo foi revisar o papel de um possível processo inflamatório na gênese da esquizofrenia. MÉTODO: Foram selecionados os trabalhos publicados em revistas indexadas nas bases de dados Lilacs e MedLine, sob os unitermos "esquizofrenia", "inflamação" e "estresse oxidativo", nos últimos 10 anos até dezembro de 2009, nos idiomas inglês e português. Foram excluídos os artigos que tratavam de aspectos fisiopatológicos da doença fora do interesse da psiquiatria. RESULTADOS: Sessenta e um artigos foram selecionados. Doze abordavam o envolvimento do estresse oxidativo na esquizofrenia, nove tratavam de alterações no sistema imunológico de pacientes esquizofrênicos, dezesseis da infecção pré-natal como desencadeador da doença e sete mostravam a ação antioxidante e anti-inflamatória de fármacos antipsicóticos. CONCLUSÃO: Os estudos enfatizam o envolvimento do sistema imunológico (isto é, interleucinas e ação anti-inflamatória dos antipsicóticos), das infecções, do estresse oxidativo e da função mitocondrial na fisiopatologia da esquizofrenia. Portanto, esses novos achados são importantes para a melhor compreensão e, consequentemente, a elaboração de terapias mais específicas e eficazes no combate dessa doença mental.

Longitudinal brain changes in early-onset psychosis

Progressive losses of cortical gray matter volumes and increases in ventricular volumes have been reported in patients with childhood-onset schizophrenia (COS) during adolescence. Longitudinal studies suggest that the rate of cortical loss seen in COS during adolescence plateaus during early adulthood. Patients with first-episode adolescent-onset schizophrenia show less marked progressive changes, although the number of studies in this population is small. Some studies show that, although less exaggerated, progressive changes are also present in nonschizophrenia early-onset psychosis. The greater loss of brain tissue seen in COS, even some years after the first episode, as compared to adolescent- or adult-onset schizophrenia may be due to variables such as sample bias (more severe, treatment refractory sample of childhood-onset patients studied), a process uniquely related to adolescent development in COS, differential brain effects of drug treatment in this population, clinical outcome, or interactions among these variables. Findings from both cross-sectional studies of first-episode patients and longitudinal studies in COS and adolescent onset support the concept of early-onset schizophrenia as a progressive neurodevelopmental disorder with both early and late developmental abnormalities. Future studies should look for correlates at a cellular level and for pathophysiological explanations of volume changes in these populations. The association of risk genes involved in circuitries associated with schizophrenia and their relationship to developmental trajectories is another promising area of future research.