Downregulation of P2X₇ receptor expression in rat oligodendrocyte precursor cells after hypoxia ischemia

Abstract

Oligodendrocyte precursor cells (OPCs) are the predominant oligodendrocyte-lineage stage in the cerebral hemispheres of neonatal rat. Prior studies have shown that OPCs are highly vulnerable to hypoxic-ischemic injury, yet the mechanisms are not well understood. P2X 7 receptor (P2X 7 R) is an ATP-gated ion channel that has unusual properties and plays very complex roles in a variety of neuropathologic conditions. However, little is known about the involvement of P2X 7 R in OPCs development and injury. The present study was aimed at examining the presence of P2X 7 R in OPCs and evaluating the change of the receptor expression after hypoxia ischemia. Using Immunofluorescence, RT-PCR, and western blot analysis, we demonstrated that OPCs expressed P2X 7 R in vitro and in vivo. Activation of P2X 7 R in OPCs in response to 3 0 -O-(4-benzoyl) benzoyl-ATP (BzATP) led to an increased mobilization of intracellular calcium [Ca 21 ]i, formation of large pores and cell death. These functional responses were sensitive to pretreatment of cells with the P2X 7 R antagonist, Brilliant Blue G (BBG, 100 nM), which was a selective antagonist for P2X 7 R in nanomole range. A decrease in P2X 7 R expression was observed in cultured OPCs after exposure to oxygen-glucose deprivation (OGD) for 2 h in vitro. Using a neonatal hypoxic-ischemic injury model in postnatal 3 rats, the similar downregulation was also detected in ischemic cerebral cortex, subcortical white matter and hippocampus compared with sham operation controls. In conclusion, the present data demonstrated that OPCs expressed functional P2X 7 R. The post-ischemic downregulation of P2X 7 R suggested a role for this receptor in the pathophysiology of hypoxic-ischemic brain injury. V V C

P2X7 receptors in cerebral ischemia

“…However, inconsistent with most reports that P2X 7 R expression is increased in response to OGD in vitro or MCAO in vivo, Wang et al showed decreased expression of P2X 7 Rs in cultured oligodendrocyte precursor cells, the predominant oligodendrocyte-lineage stage in the cerebral hemispheres of the neonatal rat, after exposure to OGD for 2 h in vitro, and in a neonatal hypoxic-ischemic injury model in 3-day-old rats [14] . More recently, Zeng et al reported that OGD decreases P2X 7 R expression and modulates GSK-3β phosphorylation in radial glial clone L2.3 cells, and BzATP (a selective agonist of the P2X 7 R) induces L2.3 cell death in a dose-and time-dependent manner [27] .…”

“…Under normal conditions, P2X 7 Rs are widespread on the membranes of neurons, astrocytes, microglia, oligodendrocytes, and oligodendrocyte precursor cells, as well as Schwann cells [14,[25][26][27] , unlike the localization of P2X [1][2][3][4][5][6] receptor subtypes, which is mainly on the membranes of neurons [28] . They are especially abundant on microglia that are in a physiologically resting state, [20] , and play protective roles such as host defense and tissue repair [28] against neuronal damage [29] , suggesting that P2X 7 Rs are involved in immune functions and inflammatory responses [13] .…”

“…Seven distinct ionotropic P2X (P2X [1][2][3][4][5][6][7] and eight distinct metabotropic P2Y receptor subunits (P2Y 1,2,4,6,[11][12][13][14], classified by electrophysiological properties and their amino-acid sequence homology, have been cloned from mammals [4] .…”

“…Most indicate that up-regulation or overactivation of P2X 7 Rs aggravate the brain tissue damage and sensorimotor deficit through several mechanisms such as Ca 2+ overload which induces excitotoxic neuronal death or apoptosis, and receptor antagonists play a protective role [1,4,[9][10][11][12] . However, a few reports are contradictory [13,14] .…”

Intertwining extracellular nucleotides and their receptors with Ca2+in determining adult neural stem cell survival, proliferation and final fate

“…All these data, obtained in several models of disease, suggest that P2X7R contributes to damage exacerbation; however, it has also been reported that the expression of P2X7R was downregulated in OPC cultures and in ischaemic cerebral cortex, subcortical white matter and hippocampus in a paradigm of perinatal hypoxia-ischaemia, probably in an attempt to prevent the excessive receptor stimulation in the early stages of damage [99].…”