P2X7 Receptor-Dependent Cell Death Is Modulated during Murine T Cell Maturation and Mediated by Dual Signaling Pathways

Abstract

Extracellular ATP causes apoptosis and/or necrosis of the hemopoietic lineage through the activation of P2X7 receptors. In this study, we investigated P2X7 receptor-mediated cell death during murine T cell maturation. The expression level and activity of P2X7 receptors, as measured by induction of cell death and pore formation, were higher in splenocytes than thymocytes. Flow cytometric analysis revealed that cell shrinkage was induced by activation of the P2X7 receptor in murine lymphocytes and the responding cells were T cells. Splenic T cells were more responsive than their thymic counterpart. These observations indicate that the system of P2X7 receptor-mediated cell death in T cells could be modulated during T cell maturation. Furthermore, decreased extracellular Cl− suppressed ATP-induced cell shrinkage in splenocytes without inhibiting ERK1/2 phosphorylation, which is reported to mediate necrotic cell death. Treatment with U0126 (a MEK inhibitor) suppressed ATP-induced ERK1/2 phosphorylation without inhibiting cell shrinkage. Moreover, decreased extracellular Cl− and treatment with U0126 suppressed ATP-induced cell death. These observations indicate that the activation of P2X7 receptor leads to T cell death by two independent pathways, one of which is cell shrinkage dependent and the other of which involves the phosphorylation of ERK1/2. In conclusion, we demonstrate increasing P2X7 receptor activity during T cell maturation and the existence of two essential pathways in P2X7 receptor-mediated T cell death. Our findings suggest that ATP-induced cell death of peripheral T lymphocytes is important in P2X7 receptor-regulated immune responses.

ATP release from non-excitable cells

“…These data are contradicted by results showing that osteoblasts release the same amount of ATP by fluid shear stress, regardless of whether they express P2X 7 receptors or not [85]. It is noteworthy that the P2X 7 receptor in several cell types is associated with the induction of necrosis and apoptosis [86]. This could inevitably cause nucleotide release by a cell death mechanism and may confound the interpretation of a more direct P2X 7 receptor-mediated mechanism.…”

Microglia Proliferation Is Controlled by P2X7 Receptors in a Pannexin-1-Independent Manner during Early Embryonic Spinal Cord Invasion

“…Another consequence of the interaction of P2X7R with Panx1 is their induction of cell death (Locovei et al, 2007). In that respect, immature T-cells are less sensitive to cell death evoked by P2X7R activation when compared with mature T-cells (Tsukimoto et al, 2006). A lack of coupling between P2X7R and Panx1 in embryonic microglia may prevent this detrimental effect without affecting other P2X7R functions.…”

Purinergic signaling in inflammatory cells: P2 receptor expression, functional effects, and modulation of inflammatory responses

“…When secreted by cytotoxic T cells towards the target cell, ATP may contribute to the death of the target cell, while secretion of ATP by T helper cells toward the antigen-presenting cell may modulate the action of lymphokines by involving purinergic receptors or ectoprotein kinases [174]. Similarly, Blanchard et al provided evidence that ATP is released from cytotoxic T cells during antigen presentation, and that IFN-γ-activated macrophages underwent necrosis [173].Besides the induction of cell death in the cytotoxic T lympocytes' target cells, also the T cells themselves are reported to undergo ATP-mediated cell death [175]. Unlike cytotoxic T cells and T helper cells, it is the T regulatory cells that are reported to be particularly sensitive to undergo cell death accompanied by CD62L shedding in response to ATP [176,177].…”