Characterization of thromboxane A₂ receptor signaling in developing rat oligodendrocytes: Nuclear receptor localization and stimulation of myelin basic protein expression

The present work investigates the role of thromboxane A₂ (TXA₂) receptors in the development of oligodendrocytes (OLGs), The results demonstrate that the proteins of the TXA₂ signaling pathway, i.e., cyclooxygenase (COX-1), TXA₂ synthase (TS), and TXA₂ receptor (TPR) are expressed in the developing rat brain during myelination. Furthermore, culture of OLG progenitor cells (OPCs) revealed that the expression levels of these proteins as well as TXA₂ synthesis increase during OLG maturation. Separate studies established that activation of TPRs by the agonist U46619 increases intracellular calcium in both OPCs and OLGs as visualized by digital fluorescence imaging. Immunocytochemical staining demonstrated that TPRs are localized in the plasma membrane and perinuclear compartments in OPCs. However, during OLG differentiation, TPRs shift their localization pattern and also become associated with the nuclear compartment. This shift to nuclear localization was confirmed by biochemical analysis in cultured cells and by immunocytochemical analysis in developing rat brain. Finally, it was found that U46619 activation of TPRs in maturing OLGs resulted in enhanced myelin basic protein (MBP) expression. Alternatively, inhibition of endogenous TPR signaling led to reduced MBP expression. Furthermore, TPR-mediated MBP expression was found to be associated with increased transcription from the MBP promoter using a MBP-luciferase reporter. Collectively, these findings suggest a novel TPR signaling pathway in OLGs and a potential role for this signaling during OLG maturation and myelin production.