Effects of the A(-115)G variant on CREB1 promoter activity in two brain cell lines: Interactions with gonadal steroids

Differential hippocampal gene expression and pathway analysis in an etiology-based mouse model of major depressive disorder

We have recently reported the creation and initial characterization of an etiology-based recombinant mouse model of a severe and inherited form of Major Depressive Disorder (MDD). This was achieved by replacing the corresponding mouse DNA sequence with a 6-base DNA sequence from the human CREB1 promoter that is associated with MDD in individuals from families with recurrent, early-onset MDD (RE-MDD). In the current study, we explored the effect of the pathogenic Creb1 allele on gene expression in the mouse hippocampus, a brain region that is altered in structure and function in MDD. Mouse whole-genome profiling was performed using the Illumina MouseWG-6 v2.0 Expression BeadChip microarray. Univariate analysis identified 269 differentially-expressed genes in the hippocampus of the mutant mouse. Pathway analyses highlighted 11 KEGG pathways: the phosphatidylinositol signaling system, which has been widely implicated in MDD, Bipolar Disorder, and the action of mood stabilizers; gap junction and long-term potentiation, which mediate cognition and memory functions often impaired in MDD; cardiac muscle contraction, insulin signaling pathway, and three neurodegenerative brain disorders (Alzheimer's, Parkinson's, and Huntington's Diseases) that are associated with MDD; ribosome and proteasome pathways affecting protein synthesis/degradation; and the oxidative phosphorylation pathway that is key to energy production. These findings illustrate the merit of this congenic C57BL/6 recombinant mouse as a model of RE-MDD, and demonstrate its potential for highlighting molecular and cellular pathways that contribute to the biology of MDD. The results also inform our understanding of the mechanisms that underlie the comorbidity of MDD with other disorders.

Alterations of brain anatomy in mouse model of MDD created by replacement of homologous mouse DNA sequence with an illness-associated 6-base human CREB1 promoter sequence

We have recently reported the creation and initial characterization of an etiology-based recombinant mouse model of a severe and inherited form of Major Depressive Disorder (MDD). This was achieved by replacing the corresponding mouse DNA sequence with a 6-base DNA sequence from the human CREB1 promoter that is associated with the development of MDD in men and women from families identified by probands with recurrent, early-onset MDD (RE-MDD). Individuals in these families are also at increased risk for childhood developmental disorders and late life neurodegenerative disorders. The current study used three-dimensional magnetic resonance microscopy (3D-MRM) to determine the effect of the resulting humanized mutation of the mouse Creb1 gene on the anatomy of the mouse brain. Homozygous mutant mice manifested prominent increases in the volume and surface area of the lateral ventricles, as well as reduced volume of the anterior corpus callosum, compared to age/sex-matched wild-type mice. No significant genotype effects were observed on the volume or surface area of total brain, or several brain regions sometimes observed to be abnormal in human depression, including hippocampus, amygdala, or striatum. These findings suggest that at least some forms of MDD result from abnormal brain development produced by inherited genetic variants.

Inhibition of phosphodiesterase-4 promotes oligodendrocyte precursor cell differentiation and enhances CNS remyelination

The increasing effectiveness of new disease-modifying drugs that suppress disease activity in multiple sclerosis has opened up opportunities for regenerative medicines that enhance remyelination and potentially slow disease progression. Although several new targets for therapeutic enhancement of remyelination have emerged, few lend themselves readily to conventional drug development. Here, we used transcription profiling to identify mitogen-activated protein kinase (Mapk) signalling as an important regulator involved in the differentiation of oligodendrocyte progenitor cells (OPCs) into oligodendrocytes. We show in tissue culture that activation of Mapk signalling by elevation of intracellular levels of cyclic adenosine monophosphate (cAMP) using administration of either dibutyryl-cAMP or inhibitors of the cAMP-hydrolysing enzyme phosphodiesterase-4 (Pde4) enhances OPC differentiation. Finally, we demonstrate that systemic delivery of a Pde4 inhibitor leads to enhanced differentiation of OPCs within focal areas of toxin-induced demyelination and a consequent acceleration of remyelination. These data reveal a novel approach to therapeutic enhancement of remyelination amenable to pharmacological intervention and hence with significant potential for translation.

Developmental effects of tobacco smoke exposure during human embryonic stem cell differentiation are mediated through the transforming growth factor-β superfamily member, Nodal

While the pathologies associated with in utero smoke exposure are well established, their underlying molecular mechanisms are incompletely understood. We differentiated human embryonic stem cells in the presence of physiological concentrations of tobacco smoke and nicotine. Using post hoc microarray analysis, quantitative PCR, and immunoblot analysis, we demonstrated that tobacco smoke has lineage- and stage-specific effects on human embryonic stem cell differentiation, through both nicotine-dependent and -independent pathways. We show that three major stem cell pluripotency/differentiation pathways, Notch, canonical Wnt, and transforming growth factor-β, are affected by smoke exposure, and that Nodal signaling through SMAD2 is specifically impacted by effects on Lefty1, Nodal, and FoxH1. These events are associated with upregulation of microRNA-302a, a post-transcriptional silencer of Lefty1. The described studies provide insight into the mechanisms by which tobacco smoke influences fetal development at the cellular level, and identify specific transcriptional, post-transcriptional, and signaling pathways by which this likely occurs.

Cell Models for the Study of Sex Steroid Hormone Neurobiology

To date many aspects of neurons and glia biology remain elusive, due in part to the cellular and molecular complexity of the brain. In recent decades, cell models from different brain areas have been established and proven invaluable toward understanding this complexity. In the field of steroid hormone neurobiology, an important question is: what is the profile of steroid hormone receptor expression in these specific cell lines? Currently, a clear summary of such receptor profiling is lacking. For this reason, we summarized in this review the expression of estrogen, progesterone, and androgen receptors in several widely used cell lines (glial and neuronal) derived from the forebrain and midbrain, based on our own data and that from the literature. Such information will aid in the selection of specific cell lines used to test hypotheses related to the biology of estrogens, progestins, and/or androgens.

No evidence of non-homologous insertions in mouse model of MDD created by replacement of homologous mouse DNA sequence with pathogenic 6-base human CREB1 promoter sequence

We have recently reported the creation and initial characterization of the first etiology-based recombinant mouse model of major depressive disorder (MDD). This was achieved by replacing the corresponding mouse DNA sequence with a 6-base DNA sequence from the human CREB1 promoter that is associated with the development of MDD in families identified by probands with recurrent, early-onset MDD. The current study explored whether the desired homologous recombination event at the mouse Creb1 gene that resulted in the creation of the mouse model was also accompanied by insertions of the targeting vector at unintended non-homologous locations in the mouse genome. No evidence of insertions of targeting vector sequence was observed at regions other than the mouse Creb1 gene.

Replacement of homologous mouse DNA sequence with pathogenic 6-base human CREB1 promoter sequence creates murine model of major depressive disorder

Major depressive disorder (MDD) is a leading cause of disability worldwide. Families with recurrent, early-onset MDD (RE-MDD), a severe, familial form of MDD, have provided an important resource for identifying and characterizing genetic variants that confer susceptibility to MDD and related disorders. Previous studies identified a rare, highly penetrant A(-115)G transition within the human CREB1 promoter that reduced promoter activity in vitro and was associated with depressive disorders in RE-MDD families. The development of an etiology-based recombinant animal model for MDD would facilitate the advancement of our limited understanding of the pathophysiology of MDD, as well as the development of improved treatments. Here we report the construction and initial characterization of a congenic mutant C57BL/6NTac mouse model that carries the human pathogenic sequence at the homologous position of the mouse Creb1 promoter. The recombinant strain exhibited decreases in reproductive capacity and pup survival that may be related to increased infant mortality observed in RE-MDD families; enlargement of the cerebral ventricles; reduced levels of CREB protein in the mouse cerebral cortex, as predicted from transfection experiments employing the pathogenic human CREB1 promoter; and alterations in two standardized behavioral tests, the forced swim and marble burying tests. These initial findings support the pathogenicity of the human A(-115)G promoter variant, and invite further characterization of this etiology-based recombinant animal model for MDD. Human promoter variants that have highly penetrant effects on disease expression provide an attractive opportunity for creating etiology-based mouse models of human diseases, with minimal disruption of the mouse genome.