Person:

Subburaju, Sivan

Recent studies of the hippocampus have suggested that a network of genes is associated with the regulation of the (GAD_{67}) (GAD1) expression and may play a role in c-amino butyric acid (GABA) dysfunction in schizophrenia (SZ) and bipolar disorder (BD). To obtain a more detailed understanding of how (GAD_{67}) regulation may result in GABAergic dysfunction, we have developed an in vitro model in which GABA cells are differentiated from the hippocampal precursor cell line, HiB5. Growth factors, such as PDGF, and BDNF, regulate the GABA phenotype by inducing the expression of (GAD_{67}) and stimulating the growth of cellular processes, many with growth cones that form appositions with the cell bodies and processes of other (GAD_{67})-positive cells. These changes are associated with increased expression of acetylated tubulin, microtubule-associated protein 2 (MAP2) and the post-synaptic density protein 95 (PSD95). The addition of BDNF, together with PDGF, increases the levels of mRNA and protein for (GAD_{67}), as well as the high affinity GABA uptake protein, GAT1. These changes are associated with increased concentrations of GABA in the cytoplasm of "differentiated" HiB5 neurons. In the presence of (Ca^{2+}) and (K^+), newly synthesized GABA is released extracellularly. When the HiB5 cells appear to be fully differentiated, they also express (GAD_{65}), parvalbumin and calbindin, and GluR subtypes as well as HDAC1, DAXX, PAX5, Runx2, associated with (GAD_{67}) regulation. Overall, these results suggest that the HiB5 cells can differentiate into functionally mature GABA neurons in the presence of gene products that are associated with (GAD_{67}) regulation in the adult hippocampus.

Identification of 108 genomic regions significantly associated with schizophrenia risk by the Psychiatric Genomics Consortium was a milestone for the field, and much work is now focused on determining the mechanism of risk associated with each locus. Within these regions, we investigated variability of DNA methylation, a low-level cellular phenotype closely linked to genotype, in two highly similar cellular populations sampled from the human hippocampus, to draw inferences about the elaboration of genotype to phenotype within these loci enriched for schizophrenia risk. DNA methylation was assessed with the Illumina HumanMethylation450 BeadArray in tissue laser-microdissected from the stratum oriens of subfield CA1 or CA2/3, regions having unique connectivity with intrinsic and extrinsic fiber systems within the hippocampus. Samples consisted of postmortem human hippocampus tissue from eight schizophrenia patients, eight bipolar disorder patients, and eight healthy control subjects. Within these genomic regions, we observed far greater difference in methylation patterns between circuit locations within subjects than in a single subregion between subjects across diagnostic groups, demonstrating the complexity of genotype to phenotype elaboration across the diverse circuitry of the human brain.

The cerebral cortex is essential for integration and processing of information that is required for most behaviors. The exquisitely precise laminar organization of the cerebral cortex arises during embryonic development when neurons migrate successively from ventricular zones to coalesce into specific cortical layers. While radial glia act as guide rails for projection neuron migration, pre-formed vascular networks provide support and guidance cues for GABAergic interneuron migration. This study provides novel conceptual and mechanistic insights into this paradigm of vascular-neuronal interactions, revealing new mechanisms of GABA and its receptor-mediated signaling via embryonic forebrain endothelial cells. With the use of two new endothelial cell specific conditional mouse models of the GABA pathway (Gabrb3ΔTie2-Cre and VgatΔTie2-Cre), we show that partial or complete loss of GABA release from endothelial cells during embryogenesis results in vascular defects and impairs long-distance migration and positioning of cortical interneurons. The downstream effects of perturbed endothelial cell-derived GABA signaling are critical, leading to lasting changes to cortical circuits and persistent behavioral deficits. Furthermore, we illustrate new mechanisms of activation of GABA signaling in forebrain endothelial cells that promotes their migration, angiogenesis and acquisition of blood-brain barrier properties. Our findings uncover and elucidate a novel endothelial GABA signaling pathway in the CNS that is distinct from the classical neuronal GABA signaling pathway and shed new light on the etiology and pathophysiology of neuropsychiatric diseases, such as autism spectrum disorders, epilepsy, anxiety, depression and schizophrenia.

Intrinsic defects within blood vessels from the earliest developmental time points can directly contribute to psychiatric disease origin. Our work has shown that pre-formed vascular networks autonomously regulate key events during brain development, such as neurogenesis and neuronal migration. Vascular deficits and abnormalities in blood vessels emerging at prenatal stages will persist in the adult brain with direct consequences for blood flow and behavior. Therefore, rescue of abnormal prenatal angiogenesis is pivotal for the rescue of brain development and is a vital aspect for preventing the origin of psychiatric disease. Here we show for the first time, that nicotinamide adenine dinucleotide (NAD+), administered during a critical window of prenatal development in a pre-clinical model of psychiatric disease, results in synergistic repair of impaired angiogenesis and normalization of brain development, thus preventing the acquisition of abnormal behavioral symptoms. The prenatal NAD+ treatment stimulated extensive cellular and molecular changes in endothelial cells, and restored blood vessel formation, GABAergic neuronal development, and forebrain morphology by recruiting an alternate pathway for cellular repair, via new transcriptional mechanisms and purinergic receptor signaling. It rescued the lost neuro-vascular interactions, by restoring endothelial cell-derived GABA, a valuable guidance cue for the long-distance migration of GABAergic interneurons to their final destination in the embryonic forebrain. This rescue of forebrain angiogenesis in the prenatal period was of a permanent and irreversible nature, and significantly improved blood flow in the adult brain. A multi-faceted behavioral phenotype that included stress, anxiety, depression, sociability and cognition were completely cured in this psychiatric disease model. Our findings illustrate a novel and powerful role for NAD+ in sculpting vascular networks during prenatal brain development that has profound implications for rescuing brain blood flow with long lasting consequences for mental health outcome.