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Telias M, Segal M, Ben-Yosef D. Immature Responses to GABA in Fragile X Neurons Derived from Human Embryonic Stem Cells. Front Cell Neurosci 2016; 10:121. [PMID: 27242433 PMCID: PMC4864171 DOI: 10.3389/fncel.2016.00121] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2016] [Accepted: 04/26/2016] [Indexed: 01/10/2023] Open
Abstract
Fragile X Syndrome (FXS) is the most common form of inherited cognitive disability. However, functional deficiencies in FX neurons have been described so far almost exclusively in animal models. In a recent study we found several functional deficits in FX neurons differentiated in-vitro from human embryonic stem cells (hESCs), including their inability to fire repetitive action potentials, and their lack of synaptic activity. Here, we investigated the responses of such neurons to pulse application of the neurotransmitter GABA. We found two distinct types of responses to GABA and sensitivity to the GABA-A receptor antagonist bicuculline; type 1 (mature) characterized by non-desensitized responses to GABA as well as a high sensitivity to bicuculline, and type 2 (immature) which are desensitized to GABA and insensitive to bicuculline. Type 1 responses were age-dependent and dominant in mature WT neurons. In contrast, FX neurons expressed primarily type 2 phenotype. Expression analysis of GABA-A receptor subunits demonstrated that this bias in human FX neurons was associated with a significant alteration in the expression pattern of the GABA-A receptor subunits α2 and β2. Our results indicate that FMRP may play a role in the development of the GABAergic synapse during neurogenesis. This is the first demonstration of the lack of a mature response to GABA in human FX neurons and may explain the inappropriate synaptic functions in FXS.
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Affiliation(s)
- Michael Telias
- Wolfe PGD-Stem Cell Lab, Racine IVF Unit, Tel-Aviv Sourasky Medical Center, Lis Maternity HospitalTel-Aviv, Israel; Department of Cell and Developmental Biology, Sackler Medical School, Tel-Aviv UniversityTel-Aviv, Israel
| | - Menahem Segal
- Department of Neurobiology, The Weizmann Institute of Science Rehovot, Israel
| | - Dalit Ben-Yosef
- Wolfe PGD-Stem Cell Lab, Racine IVF Unit, Tel-Aviv Sourasky Medical Center, Lis Maternity HospitalTel-Aviv, Israel; Department of Cell and Developmental Biology, Sackler Medical School, Tel-Aviv UniversityTel-Aviv, Israel
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Broek JAC, Lin Z, de Gruiter HM, van 't Spijker H, Haasdijk ED, Cox D, Ozcan S, van Cappellen GWA, Houtsmuller AB, Willemsen R, de Zeeuw CI, Bahn S. Synaptic vesicle dynamic changes in a model of fragile X. Mol Autism 2016; 7:17. [PMID: 26933487 PMCID: PMC4772588 DOI: 10.1186/s13229-016-0080-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2016] [Accepted: 02/20/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Fragile X syndrome (FXS) is a single-gene disorder that is the most common heritable cause of intellectual disability and the most frequent monogenic cause of autism spectrum disorders (ASD). FXS is caused by an expansion of trinucleotide repeats in the promoter region of the fragile X mental retardation gene (Fmr1). This leads to a lack of fragile X mental retardation protein (FMRP), which regulates translation of a wide range of messenger RNAs (mRNAs). The extent of expression level alterations of synaptic proteins affected by FMRP loss and their consequences on synaptic dynamics in FXS has not been fully investigated. METHODS Here, we used an Fmr1 knockout (KO) mouse model to investigate the molecular mechanisms underlying FXS by monitoring protein expression changes using shotgun label-free liquid-chromatography mass spectrometry (LC-MS(E)) in brain tissue and synaptosome fractions. FXS-associated candidate proteins were validated using selected reaction monitoring (SRM) in synaptosome fractions for targeted protein quantification. Furthermore, functional alterations in synaptic release and dynamics were evaluated using live-cell imaging, and interpretation of synaptic dynamics differences was investigated using electron microscopy. RESULTS Key findings relate to altered levels of proteins involved in GABA-signalling, especially in the cerebellum. Further exploration using microscopy studies found reduced synaptic vesicle unloading of hippocampal neurons and increased vesicle unloading in cerebellar neurons, which suggests a general decrease of synaptic transmission. CONCLUSIONS Our findings suggest that FMRP is a regulator of synaptic vesicle dynamics, which supports the role of FMRP in presynaptic functions. Taken together, these studies provide novel insights into the molecular changes associated with FXS.
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Affiliation(s)
- Jantine A C Broek
- Cambridge Centre for Neuropsychiatric Research, Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | - Zhanmin Lin
- Department of Neurosciences, Erasmus MC, Rotterdam, The Netherlands
| | | | - Heleen van 't Spijker
- Cambridge Centre for Neuropsychiatric Research, Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | - Elize D Haasdijk
- Department of Neurosciences, Erasmus MC, Rotterdam, The Netherlands
| | - David Cox
- Cambridge Centre for Neuropsychiatric Research, Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | - Sureyya Ozcan
- Cambridge Centre for Neuropsychiatric Research, Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | | | | | - Rob Willemsen
- Department of Clinical Genetics, Erasmus MC, Rotterdam, The Netherlands
| | - Chris I de Zeeuw
- Department of Neurosciences, Erasmus MC, Rotterdam, The Netherlands.,Netherlands Institute for Neurosciences, Royal Academy for Arts and Sciences, Amsterdam, The Netherlands
| | - Sabine Bahn
- Cambridge Centre for Neuropsychiatric Research, Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK.,Department of Neurosciences, Erasmus MC, Rotterdam, The Netherlands
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Advancing drug discovery for neuropsychiatric disorders using patient-specific stem cell models. Mol Cell Neurosci 2016; 73:104-15. [PMID: 26826498 DOI: 10.1016/j.mcn.2016.01.011] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Revised: 01/22/2016] [Accepted: 01/25/2016] [Indexed: 12/17/2022] Open
Abstract
Compelling clinical, social, and economic reasons exist to innovate in the process of drug discovery for neuropsychiatric disorders. The use of patient-specific, induced pluripotent stem cells (iPSCs) now affords the ability to generate neuronal cell-based models that recapitulate key aspects of human disease. In the context of neuropsychiatric disorders, where access to physiologically active and relevant cell types of the central nervous system for research is extremely limiting, iPSC-derived in vitro culture of human neurons and glial cells is transformative. Potential applications relevant to early stage drug discovery, include support of quantitative biochemistry, functional genomics, proteomics, and perhaps most notably, high-throughput and high-content chemical screening. While many phenotypes in human iPSC-derived culture systems may prove adaptable to screening formats, addressing the question of which in vitro phenotypes are ultimately relevant to disease pathophysiology and therefore more likely to yield effective pharmacological agents that are disease-modifying treatments requires careful consideration. Here, we review recent examples of studies of neuropsychiatric disorders using human stem cell models where cellular phenotypes linked to disease and functional assays have been reported. We also highlight technical advances using genome-editing technologies in iPSCs to support drug discovery efforts, including the interpretation of the functional significance of rare genetic variants of unknown significance and for the purpose of creating cell type- and pathway-selective functional reporter assays. Additionally, we evaluate the potential of in vitro stem cell models to investigate early events of disease pathogenesis, in an effort to understand the underlying molecular mechanism, including the basis of selective cell-type vulnerability, and the potential to create new cell-based diagnostics to aid in the classification of patients and subsequent selection for clinical trials. A number of key challenges remain, including the scaling of iPSC models to larger cohorts and integration with rich clinicopathological information and translation of phenotypes. Still, the overall use of iPSC-based human cell models with functional cellular and biochemical assays holds promise for supporting the discovery of next-generation neuropharmacological agents for the treatment and ultimately prevention of a range of severe mental illnesses.
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