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Functional metabotropic glutamate receptors are expressed in oligodendrocyte progenitor cells
Karen Luyt1, Aniko Varadi, Elek Molnar
1MRC Centre for Synaptic Plasticity, Department of Anatomy, University of Bristol, Bristol, UK.
Abstract:
We investigated the expression of metabotropic glutamate receptor (mGluR) isoforms in CG-4 rodent oligodendroglial progenitor cells (OPC) and rat brain oligodendrocytes. Our RT-PCR analysis detected mRNAs for mGluR3 and mGluR5 isoforms in OPCs. Although neurons express both mGluR5a and mGluR5b splice variants, only mGluR5a was identified in OPCs. Antibodies to mGluR2/3 and mGluR5 detected the corresponding receptor proteins in immunoblots of OPC membrane fractions. Furthermore, immunocytochemical analysis identified mGluR5 in oligodendrocyte marker O4-positive OPCs. The expression of mGluR5 was also demonstrated in oligodendrocyte marker (O4 and O1) positive cells in white matter of postnatal 4- and 7-day-old rat brain sections using immunofluorescent double labelling and confocal microscopy. The mGluR5 receptor function was assessed in CG-4 OPCs with fura-2 microfluorometry. Application of the mGluR1/5 specific agonist (S)-3,5-dihydroxyphenylglycine (DHPG) induced calcium oscillations, which were inhibited by the selective mGluR5 antagonist 2-methyl-6-(phenylethynyl) pyridine hydrochloride (MPEP). The DHPG induced calcium oscillations required Ca2+ release from intracellular stores. In OPCs the group II mGluR agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV) decreased forskolin-stimulated cAMP synthesis, indicating the presence of functional mGluR3. The newly identified mGluR3 and mGluR5a may be involved in the differentiation of oligodendrocytes, myelination and the development of white matter damage.
Insights
This study identified metabotropic glutamate receptor 3 (mGluR3) and mGluR5a in oligodendroglial progenitor cells (OPCs). These receptors may play roles in oligodendrocyte differentiation and white matter development.
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Oligodendrocytes are crucial for central nervous system myelination.
- Metabotropic glutamate receptors (mGluRs) are implicated in neuronal function, but their role in oligodendrocytes is less understood.
Purpose of the Study:
- To investigate the expression and function of mGluR isoforms in oligodendroglial progenitor cells (OPCs) and mature oligodendrocytes.
- To determine the potential involvement of identified mGluRs in oligodendrocyte development and white matter integrity.
Main Methods:
- RT-PCR to detect mGluR mRNA expression in CG-4 OPCs.
- Immunoblotting and immunocytochemistry to confirm receptor protein presence in OPCs and rat brain sections.
- Fura-2 microfluorometry to assess mGluR5 function via calcium signaling.
- Measurement of cAMP synthesis to evaluate functional mGluR3 activity.
Main Results:
- mGluR3 and mGluR5a mRNA were detected in CG-4 OPCs.
- mGluR5 protein was localized to OPCs and oligodendrocytes in rat brain white matter.
- Activation of mGluR5 by DHPG induced calcium oscillations in OPCs, dependent on intracellular calcium release.
- The mGluR3 agonist DCG-IV inhibited forskolin-stimulated cAMP synthesis in OPCs, indicating functional mGluR3.
Conclusions:
- OPCs express functional mGluR3 and mGluR5a receptors.
- These mGluRs may be involved in oligodendrocyte differentiation, myelination processes, and the pathogenesis of white matter damage.