Neuregulin-1 alpha, the underestimated molecule: emerging new roles in normal brain function and the pathophysiology of schizophrenia?

Neuroplastin in Neuropsychiatric Diseases

Molecular mechanisms underlying neuropsychiatric and neurodegenerative diseases are insufficiently elucidated. A detailed understanding of these mechanisms may help to further improve medical intervention. Recently, intellectual abilities, creativity, and amnesia have been associated with neuroplastin, a cell recognition glycoprotein of the immunoglobulin superfamily that participates in synapse formation and function and calcium signaling. Data from animal models suggest a role for neuroplastin in pathways affected in neuropsychiatric and neurodegenerative diseases. Neuroplastin loss or disruption of molecular pathways related to neuronal processes has been linked to various neurological diseases, including dementia, schizophrenia, and Alzheimer's disease. Here, we review the molecular features of the cell recognition molecule neuroplastin, and its binding partners, which are related to neurological processes and involved in learning and memory. The emerging functions of neuroplastin may have implications for the treatment of diseases, particularly those of the nervous system.

Inhibition of the Schizophrenia-Associated MicroRNA miR-137 Disrupts Nrg1α Neurodevelopmental Signal Transduction

Genomic studies have repeatedly associated variants in the gene encoding the microRNA miR-137 with increased schizophrenia risk. Bioinformatic predictions suggest that miR-137 regulates schizophrenia-associated signaling pathways critical to neural development, but these predictions remain largely unvalidated. In the present study, we demonstrate that miR-137 regulates neuronal levels of p55γ, PTEN, Akt2, GSK3β, mTOR, and rictor. All are key proteins within the PI3K-Akt-mTOR pathway and act downstream of neuregulin (Nrg)/ErbB and BDNF signaling. Inhibition of miR-137 ablates Nrg1α-induced increases in dendritic protein synthesis, phosphorylated S6, AMPA receptor subunits, and outgrowth. Inhibition of miR-137 also blocks mTORC1-dependent responses to BDNF, including increased mRNA translation and dendritic outgrowth, while leaving mTORC1-independent S6 phosphorylation intact. We conclude that miR-137 regulates neuronal responses to Nrg1α and BDNF through convergent mechanisms, which might contribute to schizophrenia risk by altering neural development.

Neuregulin1 alpha activates migration of neuronal progenitors expressing ErbB4

Deficits in neuronal migration during development in the central nervous system may contribute to psychiatric diseases. The ligand neuregulin1 (NRG1) and its receptor ErbB4 are genes conferring susceptibility to schizophrenia, playing a key role in the control of neuronal migration both during development and adulthood. Several NRG1 and ErbB4 isoforms were identified, which deeply differ in their characteristics. Here we focused on the four ErbB4 isoforms and the two NRG1 isoforms differing in their EGF-like domain, namely α and β. We hypothesized that these isoforms, which are differently regulated in schizophrenic patients, could play different roles in neuronal migration. Our hypothesis was strengthened by the observation that both NRG1α and NRG1β and the four ErbB4 isoforms are expressed in the medial and lateral ganglionic eminences and in the cortex during development in rat. We analysed in vitro the signal transduction pathways activated by the different ErbB4 isoforms following the treatment with soluble recombinant NRG1α or NRG1β and the ability to stimulate migration. Our data show that two ErbB4 isoforms, namely JMa-cyt2 and JMb-cyt1, following NRG1α and NRG1β treatment, strongly activate AKT phosphorylation, conferring high migratory activity to neuronal progenitors, thus demonstrating that both NRG1α and NRG1β can play a role in neuronal migration.

Human cell adhesion molecules: annotated functional subtypes and overrepresentation of addiction-associated genes

Human cell adhesion molecules (CAMs) are essential for proper development, modulation, and maintenance of interactions between cells and cell-to-cell (and matrix-to-cell) communication about these interactions. Despite the differential functional significance of these roles, there have been surprisingly few systematic studies to enumerate the universe of CAMs and identify specific CAMs in distinct functions. In this paper, we update and review the set of human genes likely to encode CAMs with searches of databases, literature reviews, and annotations. We describe likely CAMs and functional subclasses, including CAMs that have a primary function in information exchange (iCAMs), CAMs involved in focal adhesions, CAM gene products that are preferentially involved with stereotyped and morphologically identifiable connections between cells (e.g., adherens junctions, gap junctions), and smaller numbers of CAM genes in other classes. We discuss a novel proposed mechanism involving selective anchoring of the constituents of iCAM-containing lipid rafts in zones of close neuronal apposition to membranes expressing iCAM binding partners. We also discuss data from genetic and genomic studies of addiction in humans and mouse models to highlight the ways in which CAM variation may contribute to a specific brain-based disorder such as addiction. Specific examples include changes in CAM mRNA splicing mediated by differences in the addiction-associated splicing regulator RBFOX1/A2BP1 and CAM expression in dopamine neurons.