Oligodendrocyte-type-2 astrocyte (O-2A) progenitor cells express glutamine synthetase: developmental and cell type-specific regulation

Abstract

Glutamine synthetase (GS), the enzyme that catalyses glutamine synthesis from glutamate and ammonia, plays a central role in the detoxification of brain ammonia.¹ In the central nervous system (CNS), GS also subserves additional important functions such as regulating glutamate, GABA and amino acid metabolism.² Oligodendrocytes (OL) form the myelin sheath in the central nervous system (CNS) and are essential for efficient propagation of nerve impulses. In culture, OL arise from bipotential O-2A progenitor cells. These O-2A cells give rise to type-2 astrocytes in the presence of serum. GS is expressed in mature glial cells^3–7 in vivo and in vitro, but it is unknown whether GS is present in glial progenitors. In addition, a comparison of the GS expression level among the various types of glial cells has never been done in vitro. The current study investigates in vitro GS expression levels in O-2A progenitors, astrocytes and OL. We demonstrate that the GS gene is expressed in O-2A progenitors and is expressed at different levels in each cultured glial cell type. GS also is stimulated during OL developmental maturation. Thus, the GS gene is expressed in O-2A cells and is regulated in a developmental and macroglial cell type-specific manner.