Hypoxia induced amoeboid microglial cell activation in postnatal rat brain is mediated by ATP receptor P2X4

Fan Li,Liang He,Lei Wang,Ji-Wei Li,Zhen Dai,Min Gong,Shu-Qing Li,Rui Feng

doi:10.1186/1471-2202-12-111

Abstract

BackgroundActivation of amoeboid microglial cells (AMC) and its related inflammatory response have been linked to the periventricular white matter damage after hypoxia in neonatal brain. Hypoxia increases free ATP in the brain and then induces various effects through ATP receptors. The present study explored the possible mechanism in ATP induced AMC activation in hypoxia.ResultsWe first examined the immunoexpression of P2X4, P2X7 and P2Y12 in the corpus callosum (CC) and subependyma associated with the lateral ventricles where both areas are rich in AMC. Among the three purinergic receptors, P2X4 was most intensely expressed. By double immunofluorescence, P2X4 was specifically localized in AMC (from P0 to P7) but the immunofluorescence in AMC was progressively diminished with advancing age (P14). It was further shown that P2X4 expression was noticeably enhanced in P0 day rats subjected to hypoxia and killed at 4, 24, 72 h and 7 d versus their matching controls by double labeling and western blotting analysis. P2X4 expression was most intense at 7 d whence the inflammatory response was drastic after hypoxia. We then studied the association of P2X4 with cytokine release in AMC after hypoxic exposure. In primary microglial cells exposed to hypoxia, IL-1β and TNF-α protein levels were up-regulated. Blockade of P2X4 receptor with 2', 3'-0-(2, 4, 6-Trinitrophenyl) adenosine 5'-triphosphate, a selective P2X1-7 blocker resulted in partial suppression of IL-1β (24% vs hypoxic group) and TNF-α expression (40% vs hypoxic group). However, pyridoxal phosphate-6-azo (benzene-2, 4-disulfonic acid) tetrasodium salt hydrate, a selective P2X1-3, 5-7 blocker did not exert any significant effect on the cytokine expression.ConclusionsIt is concluded that P2X4 which is constitutively expressed by AMC in postnatal rats was enhanced in hypoxia. Hypoxia induced increase in IL-1β and TNF-α expression was reversed by 2', 3'-0-(2, 4, 6-Trinitrophenyl) adenosine 5'-triphosphate suggesting that P2X4 mediates ATP induced AMC activation and its production of proinflammatory cytokines.

Highlights

Activation of amoeboid microglial cells (AMC) and its related inflammatory response have been linked to the periventricular white matter damage after hypoxia in neonatal brain
AMC activation in hypoxia is followed by inflammatory response affecting the axons and oligodendrocytes [4], but the underlying mechanism leading to AMC activation has remained uncertain
There was a total coincidence between OX-42 and P2X4 in the AMC either in the corpus callosum (CC) (Figure 1Ba-c) or subventricular zone (SVZ) (Figure 1Ca-c)

Summary

Introduction

Activation of amoeboid microglial cells (AMC) and its related inflammatory response have been linked to the periventricular white matter damage after hypoxia in neonatal brain. Hypoxia increases free ATP in the brain and induces various effects through ATP receptors. It has been reported recently that the preponderant amoeboid microglial cells (AMC) and their activation is associated with the periventricular white matter damage (PWMD) in neonatal brain after hypoxia [3,4]. It has been reported that ATP elicits discrete currents of P2X4R on microglia/macrophages [14] In the latter, P2X4 receptors are involved in microglial activity in some pathological conditions. The above studies strongly suggest that P2X4 expression in microglial cells/macrophages may take part in the inflammatory response in injuries of the central nervous system

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