The estimation of the role of AKT1 in GABA transmission and cognitive functions using Akt1 mutant mice and P19 cell culture
Date Issued
2014
Date
2014
Author(s)
Chang, Chia-Yuan
Abstract
Schizophrenia is a serve mental disorder with 1% prevalence comprising positive, negative and cognitive symptoms. There are two important fields in the study of schizophrenia: the etiology of disorder and the discovery/development of potential antipsychotic drugs. Accumulating evidence suggests that AKT1 and GABA (A) receptor were both candidate genes of schizophrenia. The reduction of GABA system was reported in the postmortem tissue of some schizophrenic patients. For clarifying the cause effect between specific biological components and cognitive functions, gene knockout mice provide a feasible approach for elucidating causal relationships between susceptibility gene(s) and related functions. Taking advantage of knockout (homozygous) mice, we study causality between Akt1gene and GABA-related function in study 1. We found that ~50% reduction of parvalbumin-positive interneurons, a subpopulation GABAergic interneurons, was found in hippocampus of female Akt1 knockout mice but no difference was found in calretinin-positive interneurons. A reduction of GABA (A) receptors subunit, β2 subunit, was also oobserved on plasma membrane of hippocampal neurons. Interestingly, Akt1 knockout female mice further displayed impaired hippocampal oscillation power and behavioral deficits in hippocampus related cognitive functions (especially in Y-maze task and Morris water maze). Our data in study 1 suggest that Akt1 deficiency resulted in the alteration of specific GABA synapse which might lead up to the impairment of hippocampus-dependent cognitive functions in female Akt1 knockout mice. In contrast to Akt1 homologous mutant mice, the use of Akt1 heterozygous (HET) mutant mice offers a more feasible tool to mimic human subjects with a genetic deficiency of AKT1 and to evaluate drug effects in vivo. In study 2, female Akt1 heterozygous mice were used to evaluate the rescue effect of valproate, the GABA function facilitator, on the behavioral deficits in Tail suspension test (TST) and Y-maze task. Our result revealed that female Akt1 HET mice only displayed impairment in TST but not in Y-maze. Such impairment can be rescued by chronic injections of valproate. In study 3, to minimize time spent on mouse breeding and to reduce potential compensatory effect in mutant mouse models, a cell culture model was developed as a high-throughput platform for in vitro drug screening. The in vitro model using Ascl1 to differentiate P19 embryonal carcinoma cells into neurons was established and AKT1/2 inhibitor resulted in a reduction of neurite outgrowth and neuron differentiation. Taking advantage of this model, the rescue effects of lithium on the neurite outgrowth in DIV 3 and the expression of GABAergic neuron in DIV 5 were examined. Our data revealed a 40% reduction of GAD67-positive neurons and a 60% reduction of parvalbumin-positive neurons in neurons treated with AKT1/2 inhibitor. The AKT 1/2 inhibitor also resulted in a 60% reduction of the neurite length in DIV 3. Importantly, the reduction of neurite outgrowth observed in AKT inhibitor-treated neurons can be rescued by the treatment of lithium. Taken together, these findings suggest that the deficiency of Akt1 has a causal-effect on the alteration of GABAergic systems which can resulted in the impairment of GABA-related hippocampal functions in Akt1 mutant female mice. Lithium and valproate might have some therapeutic potentials in the development of treatments for Akt1-related GABAergic impairments.
Subjects
AKT1
GABA
Akt1 基因剔除小鼠
Akt1 HET小鼠
P19 細胞株
parvalbumin
海馬迴
神經震盪
鋰鹽
valproate
神經元軸突
懸尾作業
Y型迷津
莫氏水迷津
SDGs
Type
thesis
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