Oxidized ATP decreases beta-actin expression and intracellular superoxide concentrations in RBA-2 type-2 astrocytes independently of P2X7 receptor

Techniques for evaluating the ATP-gated ion channel P2X7 receptor function in macrophages and microglial cells

Resident macrophages are tissue-specific innate immune cells acting as sentinels, constantly patrolling their assigned tissue to maintain homeostasis, and quickly responding to pathogenic invaders or molecular danger signals molecules when necessary. Adenosine triphosphate (ATP), when released to the extracellular medium, acts as a danger signal through specific purinergic receptors. Interaction of ATP with the purinergic receptor P2X7 activates macrophages and microglial cells in different pathological conditions, triggering inflammation. The highly expressed P2X7 receptor in these cells induces cell membrane permeabilization, inflammasome activation, cell death, and the production of inflammatory mediators, including cytokines and nitrogen and oxygen-reactive species. This review explores the techniques to evaluate the functional and molecular aspects of the P2X7 receptor, particularly in macrophages and microglial cells. Polymerase chain reaction (PCR), Western blotting, and immunocytochemistry or immunohistochemistry are essential for assessing gene and protein expression in these cell types. Evaluation of P2X7 receptor function involves the use of ATP and selective agonists and antagonists and diverse techniques, including electrophysiology, intracellular calcium measurements, ethidium bromide uptake, and propidium iodide cell viability assays. These techniques are crucial for studying the role of P2X7 receptors in immune responses, neuroinflammation, and various pathological conditions. Therefore, a comprehensive understanding of the functional and molecular aspects of the P2X7 receptor in macrophages and microglia is vital for unraveling its involvement in immune modulation and its potential as a therapeutic target. The methodologies presented and discussed herein offer valuable tools for researchers investigating the complexities of P2X7 receptor signaling in innate immune cells in health and disease.

Carboxymethyl-chitosan attenuates inducible nitric oxide synthase and promotes interleukin-10 production in rat chondrocytes

Osteoarthritis (OA) is a common age-related degenerative joint disease, which is caused by the breakdown of joint cartilage and the underlying bone. Carboxymethyl (CM)-chitosan is a soluble derivative of chitosan that has similar physicochemical properties to the extracellular proteoglycans identified in hyaline cartilage. Previous studies have demonstrated that CM-chitosan serves a protective role in a rabbit OA model. The aim of the present study was to investigate the effect of CM-chitosan on NO production and inflammation through its upregulation of interleukin (IL)-10, and the activation of the janus kinase (JAK)/signal transducer and activator of transcription (STAT)/suppressor of cytokine signaling (SOCS) signaling pathway. In the present study primary rat chondrocytes were induced to inflammation with 2 µg/ml lipopolysaccharide. The cells were subsequently subjected to increasing concentrations of CM-chitosan (50, 100 and 200 µg/ml) and the relative mRNA and protein expression of inducible nitric oxide synthase (iNOS), IL-10, JAK1, STAT3 and SOCS3 were measured by RT-qPCR and western blot analysis respectively. The results revealed that CM-chitosan attenuated inflammation by significantly reducing iNOS expression and upregulating the anti-inflammatory cytokine IL-10 in a dose-dependent manner (P<0.05). The expression of JAK1, STAT3 and SOCS3 were also significantly upregulated by CM-chitosan (all P<0.05). The protective role of CM-chitosan against NO production was due to its upregulation of IL-10 and its activation of the JAK/STAT/SOCS signaling pathway.

Periodate-oxidized ATP modulates macrophage functions during infection with Leishmania amazonensis

Previously, we showed that treating macrophages with ATP impairs the intracellular growth of Leishmania amazonensis, and that the P2X7 purinergic receptor is overexpressed during leishmaniasis. In the present study, we directly evaluated the effect of periodate-oxidized ATP (oATP) on parasite control in Leishmania-infected macrophages. We found that oATP impaired the attachment/entrance of L. amazonensis promastigotes to C57BL/6 mouse macrophages in a P2X7 receptor-independent manner, as macrophages from P2X7(-/-) mice were similarly affected. Although oATP directly inhibited the growth of axenic promastigotes in culture, promoted rapid ultrastructural alterations, and impaired Leishmania internalization by macrophages, it did not affect intracellular parasite multiplication. Upon infection, phagosomal acidification was diminished in oATP-treated macrophages, accompanied by reduced endosomal proteolysis. Likewise, MHC class II molecules expression and ectoATPase activity was decreased by oATP added to macrophages at the time of parasite infection. These inhibitory effects were not due to a cytotoxic effect, as no additional release of lactate dehydrogenase was detected in culture supernatants. Moreover, the capacity of macrophages to produce nitric oxide and reactive oxygen species was not affected by the presence of oATP during infection. We conclude that oATP directly affects extracellular parasite integrity and macrophage functioning.

Roles of P2X7 receptor in glial and neuroblastoma cells: the therapeutic potential of P2X7 receptor antagonists

Recently, one of the P2 purinergic receptors, the P2X(7) receptor, has been extensively studied in nervous system and important functions have been revealed in both astrocytes and microglia. Stimulation of the receptors induces a sustained and nondesensitized increase in intracellular Ca(2+) concentration ([Ca(2+)](i)). In astrocytes purinergic receptors primarily regulate neurotransmission by inducing gliotransmitters release whereas in microglia the receptors stimulate the processing and release of proinflammation cytokines such as interleukin-1 and are thereby involved in inflammation and neurodegeneration. Thus, P2X(7) receptors are considered not only to exert physiological functions but also mediate cell death. P2X(7) receptors have also been identified in various cancer cells and in neuroblastoma cells. In these cells, the P2X(7) receptor-mediated sustained Ca(2+) signal is important in maintaining cellular viability and growth. Accordingly, these findings not only lead to a better understanding of roles of the receptor but also prompt the development of more potent, selective and safer P2X(7) selective antagonists. These emerging antagonists bring new hope in the treatment of inflammatory-induced neurodegenerative diseases as well as neuroblastoma.

Functional decreases in P2X7 receptors are associated with retinoic acid-induced neuronal differentiation of Neuro-2a neuroblastoma cells

Neuro-2a (N2a) cells are derived from spontaneous neuroblastoma of mouse and capable to differentiate into neuronal-like cells. Recently, P2X7 receptor has been shown to sustain growth of human neuroblastoma cells but its role during neuronal differentiation remains unexamined.We characterized the role of P2X7 receptors in the retinoic acid (RA)-differentiated N2a cells. RA induced N2a cells differentiation into neurite bearing and neuronal specific proteins, microtubule-associated protein 2 (MAP2) and neuronal specific nuclear protein (NeuN), expressing neuronal-like cells. Interestingly, the RA-induced neuronal differentiation was associated with decreases in the expression and function of P2X7 receptors. Functional inhibition of P2X7 receptors by P2X7 receptor selective antagonists, 5'-triphosphate, periodate-oxidized 2',3'-dialdehyde ATP (oATP), brilliant blue G (BBG) or A438079 induced neurite outgrowth. In addition, RA and oATP treatment stimulated the expression of neuron-specific class III beta-tubulin (TuJ1), and knockdown of P2X7 receptor expression by siRNA induced neurite outgrowth. To elucidate the possible mechanism, we found the levels of basal intracellular Ca2+ concentrations ([Ca2+]i) were decreased in either RA- or oATP-differentiated or P2X7receptor knockdown N2a cells. Simply cultured N2a cells in low Ca2+ medium induced a 2-fold increase in neurite length. Treatment of N2a cells with ATP hydrolase apyrase and the P2X7 receptors selective antagonist oATP or BBG decreased cell viability and cell number. Nevertheless, oATP but not BBG decreased cell proliferation and cell cycle progression. These results suggest for the first time that decreases in expression/function of P2X7 receptors are involved in neuronal differentiation.We provide additional evidence shown that the ATP release-activated P2X7 receptor is important in maintaining cell survival of N2a neuroblastoma cells.

Effects of extracellular ATP on bovine lung endothelial and epithelial cell monolayer morphologies, apoptoses, and permeabilities

Pneumonia in cattle is an important disease both economically and in terms of animal welfare. Recent evidence in other species has shown ATP to be an important modulator of inflammation in the lung, where it is released by activated alveolar macrophages and damaged lung cells. Whether ATP serves a similar process during infection in the bovine lung is unknown. In the present study, we examined the effects of ATP treatment on the morphology, apoptosis, and permeability of bovine pulmonary epithelial (BPE) cells and bovine pulmonary microvascular endothelial cells (BPMEC). Monolayers of BPE cells underwent striking morphological changes when exposed to ATP that included separation of the cells. Neither BPE cells nor BPMEC exhibited increased apoptosis in response to ATP. BPE cell and BPMEC monolayers displayed virtually identical increases in permeability when exposed to ATP, with a 50% change occurring within the first hour of exposure. Both cell types contained mRNA for the P2X(7) receptor, a known receptor for ATP. In BPE cells, but not BPMEC, the change in permeability in response to ATP was reversed by the addition of a P2X(7) receptor antagonist. If similar permeability changes occur in vivo, they could be a factor in vascular leakage into lung airspaces during pneumonia.

Stimulated efflux of amino acids and glutathione from cultured hippocampal slices by omission of extracellular calcium: likely involvement of connexin hemichannels

Omission of extracellular Ca(2+) for 15 min from the incubation medium of cultured hippocampal slices stimulated the efflux of glutathione, phosphoethanolamine, hypotaurine, and taurine. The efflux was reduced by several blockers of gap junctions, i.e. carbenoxolone, flufenamic acid, and endothelin-1, and by the connexin43 hemichannel blocking peptide Gap26 but was unchanged by the P2X(7) receptor inhibitor oxidized ATP, a pannexin1 hemichannel blocking peptide and an inactive analogue of carbenoxolone. Pretreatment of the slices with the neurotoxin N-methyl-d -aspartate left the efflux by Ca(2+) omission unchanged, indicating that the stimulated efflux primarily originated from glia. Elevated glutamate efflux was detected when Ca(2+) omission was combined with the glutamate uptake blocker l-trans-pyrrolidine-2,4-dicarboxylate and when both Ca(2+) and Mg(2+) were omitted from the medium. Omission of Ca(2+) for 15 min alone did not induce delayed toxicity, but in combination with blocked glutamate uptake, significant cell death was observed 24 h later. Our results indicate that omission of extracellular Ca(2+) stimulates efflux of glutathione and specific amino acids including glutamate via opening of glial hemichannels. This type of efflux may have protective functions via glutathione efflux but can aggravate toxicity in situations when glutamate reuptake is impaired, such as following a stroke.