The cytokine IL‐1β transiently enhances P2X₇ receptor expression and function in human astrocytes

Abstract

Extracellular nucleotide di-and triphosphates such as ATP and ADP mediate their effects through purinergic P2 receptors belonging to either the metabotropic P2Y or the ionotropic P2X receptor family. The P2X 7 R is a unique member of the P2X family, which forms a pore in response to ligand stimulation, regulating cell permeability, cytokine release, and/or apoptosis. This receptor is also unique in that its affinity for the ligand benzoyl-benzoyl ATP (BzATP) is at least 10-fold greater than that of ATP. Primary human fetal astrocytes in culture express low-levels of P2X 7 R mRNA and protein, and BzATP induces only a slight influx in intracellular calcium [Ca 2+ ] i , with little demonstrable effect on gene expression or pore formation in these cells. We now show that, following treatment with the proinflammatory cytokine IL-1β, BzATP induces a robust rise in [Ca 2+ ] i with agonist and antagonist profiles indicative of the P2X 7 R. IL-1β also induced the formation of membrane pores as evidenced by the uptake of YO-PRO-1 (375 Da). Quantitative real-time PCR demonstrated transient upregulation of P2X 7 R mRNA in IL-1β-treated cells, while FACS analysis indicated a similar upregulation of P2X 7 R protein at the cell membrane. In multiple sclerosis lesions, immunoreactivity for the P2X 7 R was demonstrated on reactive astrocytes in autopsy brain tissues. In turn, P2X 7 R stimulation increased the production of IL-1-induced nitric oxide synthase activity by astrocytes in culture. These studies suggest that signaling via the P2X 7 R may modulate the astrocytic response to inflammation in the human central nervous system.

Interleukin-1β affects calcium signaling and in vitro cell migration of astrocyte progenitors

“…Given that Rac is primarily involved in lamelipodia protrusion at the leading edge (Bokoch, 2005;Barber and Welch, 2006), reduced activity of P2Y 1 R is expected to attenuate cell migration. Clearly, further studies are necessary to evaluate such hypothesis and to elucidate whether the deactivating effect of IL-1β on Rho GTPase seen in mature astrocytes (John et al, 2004) is also effective in reducing astrocyte progenitor cell migration, independently of P2Y 1 R. Nevertheless, because the effects of IL-1β on the activity of P2 receptors reported in the present study are very similar to what has been previously reported for mature astrocytes, i.e., decreased response to agonists of P2Y 1 receptors (Scemes, 2008) and increased response of P2X 7 receptors (Narcisse et al, 2005), it is likely that astrocyte progenitors acquire in early stages of CNS development, the ability to fully respond to IL-1β.…”

“…This is based on our current and previous studies showing that neither the P2X 7 R agonist BzATP (this study) nor its antagonist KN-62 (Scemes et al, 2003) had an impact on progenitor cell migration. Although the P2X 7 receptors have been proposed to be a component of the inflammatory response in astrocytes (Narcisse et al, 2005), and a contributor to pathogenic Ca 2+ entry (Yeung et al, 2006), and cell death (Zhang et al, 2005;Wang et al, 2004), further studies are needed to disclose the impact of these ionotropic receptors on neural progenitor cell (patho) physiology.…”

“…Because purinergic receptor expression and activity can be modulated by pro-inflammatory cytokines (John et al, 1999;Narcisse et al, 2005;Scemes, 2008), we evaluated the effects of conditioned medium of activated microglia (CM), as well as those induced by interleukin-1β (IL-1β) and tumor necrosis factor-α (TNFα) on astrocyte progenitor cell migration and calcium signaling. Our results indicate that, similarly to the effects of conditioned medium of activated microglia, the pro-inflammatory cytokine IL-1β, but not TNFα reduced the rate of in vitro progenitor cell migration.…”

P2X7Receptors Mediate ATP Release and Amplification of Astrocytic Intercellular Ca2+Signaling

“…Moreover, a recent study performed on two P2X 7 Ϫ/Ϫ mouse lines indicated that, at least in the hippocampus of healthy mouse brains, these receptors are either not expressed or are expressed at undetectable levels (Sim et al, 2004), suggesting that they are unlikely candidates for gliotransmitter release under physiological situations. In contrast, under pathological conditions such as during inflammation, ischemia, spreading depression, and trauma, when upregulation of these receptors, changes in extracellular cation composition, and increased extracellular ATP levels have been reported (Kraig and Nicholson, 1978;Harris and Symon, 1984;Nilsson et al, 1993;Le Feuvre et al, 2002;Guerra et al, 2003;Narcisse et al, 2005), the participation of P2X 7 R might be expected to exacerbate the extent of cell damage. Indeed, evidence for the participation of P2X 7 R in the regulation of extracellular transmitter levels was provided from studies showing that ATP-evoked glutamate efflux from neuronal and non-neuronal cells was greatly attenuated in P2X 7 R-null hippocampal slices (Papp et al, 2004) and from those showing that P2X 7 R antagonists greatly attenuated the extent of cell damage after acute spinal cord traumatic injury (Wang et al, 2004).…”

Expression, signaling, and function of P2X7 receptors in bone

“…Additional studies are needed to examine whether expression of P2X7 is regulated and how such regulation might contribute to bone cell function. In this regard, exposure to certain stimuli has been found to enhance P2X7 expression in various cell types [89][90][91]. On the other hand, high concentrations of ATP appear to mediate internalization of P2X7 in osteoclast-like cells [59].…”