Activation of the transcription factor FosB/activating protein-1 (AP-1) is a prominent downstream signal of the extracellular nucleotide receptor P2RX7 in monocytic and osteoblastic cells

Comparative Analysis of Differentially Expressed Genes in Chondrocytes from Rats Exposed to Low Selenium and T-2 Toxin

The aim of this study was to construct rat models of environmental risk factors for Kashin-Beck disease (KBD) with low selenium and T-2 toxin levels and to screen the differentially expressed genes (DEGs) between the rat models exposed to environmental risk factors. The Se-deficient (SD) group and T-2 toxin exposure (T-2) group were constructed. Knee joint samples were stained with hematoxylin-eosin, and cartilage tissue damage was observed. Illumina high-throughput sequencing technology was used to detect the gene expression profiles of the rat models in each group. Gene Ontology (GO) functional enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) signaling pathway enrichment analysis were performed and five differential gene expression results were verified by quantitative real-time polymerase chain reaction (qRT‒PCR). A total of 124 DEGs were identified from the SD group, including 56 upregulated genes and 68 downregulated genes. A total of 135 DEGs were identified in the T-2 group, including 68 upregulated genes and 67 downregulated genes. The DEGs were significantly enriched in 4 KEGG pathways in the SD group and 9 KEGG pathways in the T-2 group. The expression levels of Dbp, Pc, Selenow, Rpl30, and Mt2A were consistent with the results of transcriptome sequencing by qRT‒PCR. The results of this study confirmed that there were some differences in DEGs between the SD group and the T-2 group and provided new evidence for further exploration of the etiology and pathogenesis of KBD.

CD_99 G1 neutrophils modulate osteogenic differentiation of mesenchymal stem cells in the pathological process of ankylosing spondylitis

OBJECTIVES

This study aimed to identify the types and heterogeneity of cells within the spinal enthesis and investigate the underlying mechanisms of osteogenesis.

METHODS

Single-cell RNA sequencing was used to identify cell populations and their gene signatures in the spinal enthesis of five patients with ankylosing spondylitis (AS) and three healthy individuals. The transcriptomes of 40 065 single cells were profiled and divided into 7 clusters: neutrophils, monocytic cells, granulomonocytic progenitor_erythroblasts, T cells, B cells, plasma cells and stromal cells. Real-time quantitative PCR, immunofluorescence, flow cytometry, osteogenesis induction, alizarin red staining, immunohistochemistry, short hairpin RNA and H&E staining were applied to validate the bioinformatics analysis.

RESULTS

Pseudo-time analysis showed two differentiation directions of stromal cells from the mesenchymal stem cell subpopulation MSC-C2 to two Cxcl12-abundant-reticular (CAR) cell subsets, Osteo-CAR and Adipo-CAR, within which three transcription factors, C-JUN, C-FOS and CAVIN1, were highly expressed in AS and regulated the osteogenesis of mesenchymal stem cells. A novel subcluster of early-stage neutrophils, CD99_G1, was elevated in AS. The proinflammatory characteristics of monocyte dendritic cell progenitor-recombinant adiponectin receptor 2 monocytic cells were explored. Interactions between Adipo-CAR cells, CD99_G1 neutrophils and other cell types were mapped by identifying ligand-receptor pairs, revealing the recruitment characteristics of CD99_G1 neutrophils by Adipo-CAR cells and the pathogenesis of osteogenesis induced in AS.

CONCLUSIONS

Our results revealed the dynamics of cell subpopulations, gene expression and intercellular interactions during AS pathogenesis. These findings provide new insights into the cellular and molecular mechanisms of osteogenesis and will benefit the development of novel therapeutic strategies.

Phasic regulation of the ATP/P2X7 receptor signaling pathway affects the function of antigen-presenting cells in experimental autoimmune uveitis

Purinergic ligand-gated ion channel 7 receptor (P2X7R) is a purine type P2 receptor that is expressed on a variety of immune cells. Recent studies have shown that P2X7R signaling is required to trigger an immune response, and P2X7R antagonist-oxidized ATP (oxATP) effectively blocks P2X7R activation. In this study, we investigated the effect of phasic regulation of the ATP/P2X7R signaling pathway on antigen-presenting cells (APCs) by constructing an experimental autoimmune uveitis (EAU) disease model. Our results demonstrated that APCs isolated from the 1st, 4th, 7th and 11th days of EAU presented antigen function and could stimulate the differentiation of naive T cells. Moreover, after stimulation by ATP and BzATP (a P2X7R agonist), antigen presentation, promoting differentiation and inflammation were enhanced. The regulation of the Th17 cell response was significantly stronger than that of the Th1 cell response. In addition, we verified that oxATP blocked the P2X7R signaling pathway on APCs, attenuated the effect of BzATP, and significantly improved the adoptive transfer EAU induced by antigen-specific T cells cocultured with APCs. Our results demonstrated that at an early stage of EAU, the ATP/P2X7R signaling pathway regulation of APCs was time dependent, and the treatment of EAU could be achieved by intervening in P2X7R function on APCs.

Genome-wide expression analysis reveals different heat shock responses in indigenous (Bos indicus) and crossbred (Bos indicus X Bos taurus) cattle

Environmental heat stress in dairy cattle leads to poor health, reduced milk production and decreased reproductive efficiency. Multiple genes interact and coordinate the response to overcome the impact of heat stress. The present study identified heat shock regulated genes in the peripheral blood mononuclear cells (PBMC). Genome-wide expression patterns for cellular stress response were compared between two genetically distinct groups of cattle viz., Hariana (B. indicus) and Vrindavani (B. indicus X B. taurus). In addition to major heat shock response genes, oxidative stress and immune response genes were also found to be affected by heat stress. Heat shock proteins such as HSPH1, HSPB8, FKB4, DNAJ4 and SERPINH1 were up-regulated at higher fold change in Vrindavani compared to Hariana cattle. The oxidative stress response genes (HMOX1, BNIP3, RHOB and VEGFA) and immune response genes (FSOB, GADD45B and JUN) were up-regulated in Vrindavani whereas the same were down-regulated in Hariana cattle. The enrichment analysis of dysregulated genes revealed the biological functions and signaling pathways that were affected by heat stress. Overall, these results show distinct cellular responses to heat stress in two different genetic groups of cattle. This also highlight the long-term adaptation of B. indicus (Hariana) to tropical climate as compared to the crossbred (Vrindavani) with mixed genetic makeup (B. indicus X B. taurus).

ATP ion channel P2X purinergic receptors in inflammation response

Different studies have confirmed that P2X purinergic receptors play a key role in inflammation. Activation of P2X purinergic receptors can release inflammatory cytokines and participate in the progression of inflammatory diseases. In an inflammatory microenvironment, cells can release a large amount of ATP to activate P2X receptors, open non-selective cation channels, activate multiple intracellular signaling, release multiple inflammatory cytokines, amplify inflammatory response. While P2X4 and P2X7 receptors play an important role in the process of inflammation. P2X4 receptor can mediate the activation of microglia involved in neuroinflammation, and P2X7 receptor can mediate different inflammatory cells to mediate the progression of tissue-wide inflammation. At present, the role of P2X receptors in inflammatory response has been widely recognized and affirmed. Therefore, in this paper, we discussed the role of P2X receptors-mediated inflammation. Moreover, we also described the effects of some antagonists (such as A-438079, 5-BDBD, A-804598, A-839977, and A-740003) on inflammation relief by antagonizing the activities of P2X receptors.

P2X7 receptor in inflammation and pain

Different studies have confirmed P2X7 receptor-mediated inflammatory mediators play a key role in the development of pain. P2X7 receptor activation can induce the development of pain by mediating the release of inflammatory mediators. In view of the fact that P2X7 receptor is expressed in the nervous system and immune system, it is closely related to the stability and maintenance of the nervous system function. ATP activates P2X7 receptor, opens non-selective cation channels, activates multiple intracellular signaling, releases multiple inflammatory cytokines, and induces pain. At present, the role of P2X7 receptor in inflammatory response and pain has been widely recognized and affirmed. Therefore, in this paper, we discussed the pathological mechanism of P2X7 receptor-mediated inflammation and pain, focused on the internal relationship between P2X7 receptor and pain. Moreover, we also described the effects of some antagonists on pain relief by inhibiting the activities of P2X7 receptor. Thus, targeting to inhibit activation of P2X7 receptor is expected to become another potential target for the relief of pain.

Function of the P2X7 receptor in hematopoiesis and leukemogenesis

Adenosine triphosphate (ATP) accumulates at tissue injury and inflammation sites. The P2X7 receptor is an ATP-gated ion channel known for its cytotoxic activity. However, P2X7 receptors also play important roles in the growth of cancer and the immune regulation. Functional P2X7 receptor is widely expressed in murine and human hematopoietic stem cells and their lineages, including monocytes, macrophages, mast cells, and B or T lymphocytes, and participates in various physiological and pathologic activities. Therefore, it is not surprising that the P2X7 receptor is important for the normal hematopoiesis and leukemogenesis. Here, we summarize the biological functions of P2X7 receptor during both normal hematopoiesis and leukemogenesis. In particular, we found that ATP levels are dramatically increased in the leukemic bone marrow niche and the fates of leukemia-initiating cells of acute myeloid leukemia are tightly controlled by P2X7 expression and ATP-P2X7-mediated signaling pathways. These findings strongly indicate that the P2X7 receptor may be considered a potential biomarker of hematological malignancies in bone marrow niches, and its antagonists may be useful for the leukemia treatment in addition to the traditional chemotherapy.

Expression profiling of cultured podocytes exposed to nephrotic plasma reveals intrinsic molecular signatures of nephrotic syndrome

BACKGROUND

Nephrotic syndrome (NS) is a common renal disorder in children attributed to podocyte injury. However, children with the same diagnosis have markedly variable treatment responses, clinical courses, and outcomes, suggesting molecular heterogeneity.

PURPOSE

This study aimed to explore the molecular responses of podocytes to nephrotic plasma to identify specific genes and signaling pathways differentiating various clinical NS groups as well as biological processes that drive injury in normal podocytes.

METHODS

Transcriptome profiles from immortalized human podocyte cell line exposed to the plasma of 8 subjects (steroidsensitive nephrotic syndrome [SSNS], n=4; steroid-resistant nephrotic syndrome [SRNS], n=2; and healthy adult individuals [control], n=2) were generated using microarray analysis.

RESULTS

Unsupervised hierarchical clustering of global gene expression data was broadly correlated with the clinical classification of NS. Differential gene expression (DGE) analysis of diseased groups (SSNS or SRNS) versus healthy controls identified 105 genes (58 up-regulated, 47 down-regulated) in SSNS and 139 genes (78 up-regulated, 61 down-regulated) in SRNS with 55 common to SSNS and SRNS, while the rest were unique (50 in SSNS, 84 genes in SRNS). Pathway analysis of the significant (P≤0.05, -1≤ log2 FC ≥1) differentially expressed genes identified the transforming growth factor-β and Janus kinase-signal transducer and activator of transcription pathways to be involved in both SSNS and SRNS. DGE analysis of SSNS versus SRNS identified 2,350 genes with values of P≤0.05, and a heatmap of corresponding expression values of these genes in each subject showed clear differences in SSNS and SRNS.

CONCLUSION

Our study observations indicate that, although podocyte injury follows similar pathways in different clinical subgroups, the pathways are modulated differently as evidenced by the heatmap. Such transcriptome profiling with a larger cohort can stratify patients into intrinsic subtypes and provide insight into the molecular mechanisms of podocyte injury.

Lgr4 Governs a Pro-Inflammatory Program in Macrophages to Antagonize Post-Infarction Cardiac Repair

RATIONALE

Macrophages are critically involved in wound healing following myocardial infarction (MI). Lgr4, a member of LGR (leucine-rich repeat-containing G protein-coupled receptor) family, is emerging as a regulator of macrophage-associated immune responses. However, the contribution of Lgr4 to macrophage phenotype and function in the context of MI remains unclear.

OBJECTIVE

To determine the role of macrophage Lgr4 in MI and to dissect the underlying mechanisms.

METHODS AND RESULTS

During early inflammatory phase of MI, infarct macrophages rather than neutrophils expressed high level of Lgr4. Macrophage-specific Lgr4 knockout mice had no baseline cardiovascular defects but manifested improved heart function, modestly reduced infarct size, decreased early mortality due to cardiac rupture, and ameliorated adverse remodeling after MI. Improved outcomes in macrophage-specific Lgr4 knockout mice subjected to MI were associated with mitigated ischemic injury and optimal infarct healing, as determined by reduction of cardiac apoptosis in the peri-infarct zone, attenuation of local myocardial inflammatory response, decrease of matrix metalloproteinase expression in the infarct, enhancement of angiogenesis, myofibroblast proliferation, and collagen I deposition in reparative granulation tissue as well as formation of collagen-rich scar. More importantly, macrophage-specific Lgr4 knockout infarcts had reduced numbers of infiltrating leukocytes and inflammatory macrophages but harbored abundant reparative macrophage subsets. Lgr4-null infarct macrophages exhibited a less inflammatory transcriptional signature. These findings were further supported by transcriptomic profiling data showing repression of multiple pathways and broad-spectrum genes associated with proinflammatory responses in macrophage-specific Lgr4 knockout infarcts. Notably, we discovered that Lgr4-mediated functional phenotype programing in infarct macrophages was at least partly attributed to regulation of AP (activator protein)-1 activity. We further demonstrated that the synergistic effects of Lgr4 on AP-1 activation in inflammatory macrophages occurred via enhancing CREB (cAMP response element-binding protein)-mediated c-Fos, Fosl1, and Fosb transactivation.

CONCLUSIONS

Together, our data highlight the significance of Lgr4 in governing proinflammatory phenotype of infarct macrophages and postinfarction repair.

Adult mesenchymal stem cells: is there a role for purine receptors in their osteogenic differentiation?

The role played by mesenchymal stem cells (MSCs) in contributing to adult tissue homeostasis and damage repair thanks to their differentiation capabilities has raised a great interest, mainly in bone regenerative medicine. The growth/function of these undifferentiated cells of mesodermal origin, located in specialized structures (niches) of differentiated organs is influenced by substances present in this microenvironment. Among them, ancestral and ubiquitous molecules such as adenine-based purines, i.e., ATP and adenosine, may be included. Notably, extracellular purine concentrations greatly increase during tissue injury; thus, MSCs are exposed to effects mediated by these agents interacting with their own receptors when they act/migrate in vivo or are transplanted into a damaged tissue. Here, we reported that ATP modulates MSC osteogenic differentiation via different P2Y and P2X receptors, but data are often inconclusive/contradictory so that the ATP receptor importance for MSC physiology/differentiation into osteoblasts is yet undetermined. An exception is represented by P2X7 receptors, whose expression was shown at various differentiation stages of bone cells resulting essential for differentiation/survival of both osteoclasts and osteoblasts. As well, adenosine, usually derived from extracellular ATP metabolism, can promote osteogenesis, likely via A2B receptors, even though findings from human MSCs should be implemented and confirmed in preclinical models. Therefore, although many data have revealed possible effects caused by extracellular purines in bone healing/remodeling, further studies, hopefully performed in in vivo models, are necessary to identify defined roles for these compounds in favoring/increasing the pro-osteogenic properties of MSCs and thereby their usefulness in bone regenerative medicine.

To Inhibit or Enhance? Is There a Benefit to Positive Allosteric Modulation of P2X Receptors?

The family of ligand-gated ion channels known as P2X receptors were discovered several decades ago. Since the cloning of the seven P2X receptors (P2X1-P2X7), a huge research effort has elucidated their roles in regulating a range of physiological and pathophysiological processes. Transgenic animals have been influential in understanding which P2X receptors could be new therapeutic targets for disease. Furthermore, understanding how inherited mutations can increase susceptibility to disorders and diseases has advanced this knowledge base. There has been an emphasis on the discovery and development of pharmacological tools to help dissect the individual roles of P2X receptors and the pharmaceutical industry has been involved in pushing forward clinical development of several lead compounds. During the discovery phase, a number of positive allosteric modulators have been described for P2X receptors and these have been useful in assigning physiological roles to receptors. This review will consider the major physiological roles of P2X1-P2X7 and discuss whether enhancement of P2X receptor activity would offer any therapeutic benefit. We will review what is known about identified compounds acting as positive allosteric modulators and the recent identification of drug binding pockets for such modulators.

P2X7 Interactions and Signaling - Making Head or Tail of It

Extracellular adenine nucleotides play important roles in cell-cell communication and tissue homeostasis. High concentrations of extracellular ATP released by dying cells are sensed as a danger signal by the P2X7 receptor, a non-specific cation channel. Studies in P2X7 knockout mice and numerous disease models have demonstrated an important role of this receptor in inflammatory processes. P2X7 activation has been shown to induce a variety of cellular responses that are not usually associated with ion channel function, for example changes in the plasma membrane composition and morphology, ectodomain shedding, activation of lipases, kinases, and transcription factors, as well as cytokine release and apoptosis. In contrast to all other P2X family members, the P2X7 receptor contains a long intracellular C-terminus that constitutes 40% of the whole protein and is considered essential for most of these effects. So far, over 50 different proteins have been identified to physically interact with the P2X7 receptor. However, few of these interactions have been confirmed in independent studies and for the majority of these proteins, the interaction domains and the physiological consequences of the interactions are only poorly described. Also, while the structure of the P2X7 extracellular domain has recently been resolved, information about the organization and structure of its C-terminal tail remains elusive. After shortly describing the structure and assembly of the P2X7 receptor, this review gives an update of the identified or proposed interaction domains within the P2X7 C-terminus, describes signaling pathways in which this receptor has been involved, and provides an overlook of the identified interaction partners.

Characterization of Gene Expression Phenotype in Amyotrophic Lateral Sclerosis Monocytes

Importance

Amyotrophic lateral sclerosis (ALS) is a common adult-onset neurodegenerative disease characterized by selective loss of upper and lower motor neurons. Patients with ALS have persistent peripheral and central inflammatory responses including abnormally functioning T cells and activated microglia. However, much less is known about the inflammatory gene profile of circulating innate immune monocytes in these patients.

Objective

To characterize the transcriptomics of peripheral monocytes in patients with ALS.

Design, Setting, and Participants

Monocytes were isolated from peripheral blood of 43 patients with ALS and 22 healthy control individuals. Total RNA was extracted from the monocytes and subjected to deep RNA sequencing, and these results were validated by quantitative reverse transcription polymerase chain reaction.

Main Outcomes and Measures

The differential expressed gene signatures of these monocytes were identified using unbiased RNA sequencing strategy for gene expression profiling.

Results

The demographics between the patients with ALS (mean [SD] age, 58.8 [1.57] years; 55.8% were men and 44.2% were women; 90.7% were white, 4.65% were Hispanic, 2.33% were black, and 2.33% were Asian) and control individuals were similar (mean [SD] age, 57.6 [2.15] years; 50.0% were men and 50.0% were women; 90.9% were white, none were Hispanic, none were black, and 9.09% were Asian). RNA sequencing data from negative selected monocytes revealed 233 differential expressed genes in ALS monocytes compared with healthy control monocytes. Notably, ALS monocytes demonstrated a unique inflammation-related gene expression profile, the most prominent of which, including IL1B, IL8, FOSB, CXCL1, and CXCL2, were confirmed by quantitative reverse transcription polymerase chain reaction (IL8, mean [SE], 1.00 [0.18]; P = .002; FOSB, 1.00 [0.21]; P = .009; CXCL1, 1.00 [0.14]; P = .002; and CXCL2, 1.00 [0.11]; P = .01). Amyotrophic lateral sclerosis monocytes from rapidly progressing patients had more proinflammatory DEGs than monocytes from slowly progressing patients.

Conclusions and Relevance

Our data indicate that ALS monocytes are skewed toward a proinflammatory state in the peripheral circulation and may play a role in ALS disease progression, especially in rapidly progressing patients. This increased inflammatory response of peripheral immune cells may provide a potential target for disease-modifying therapy in patients with ALS.

P2X7Rs are involved in cell death, growth and cellular signaling in primary human osteoblasts

The ionotropic ATP-gated P2X7 receptor (P2X7R) is involved in the regulation of many physiological functions including bone metabolism. Several studies on osteoblasts from rodents and human osteoblast-like cell lines have addressed the expression and function of P2X7R on these bone-forming cells however; its role in human primary osteoblasts has not yet been reported. The aim of this study was to assess the expression of the P2X7R in bone marrow-derived stromal cells and in primary human trabecular osteoblasts and to determine the function in bone formation and cell signaling. We report that osteoblasts derived from human trabecular explants express a functional P2X7R capable of agonist-induced increase in intracellular calcium concentration and a positive permeability to fluorescent dyes. These osteoblasts are fully differentiated cells with alkaline phosphatase activity and the ability to form mineralized nodules. We show that the transcriptional regulation of osteoblastic markers can be modulated by P2X7R activity or blockade thereby influencing the differentiation, proliferation and bone matrix formation by these primary human osteoblasts. Finally, we demonstrate that the P2X7R is involved in propagation of mechanically-induced intercellular signaling in addition to the known mechanisms involving calcium signaling via P2Y2 receptors and gap junction.

Transcriptome Profiling Reveals Disruption of Innate Immunity in Chronic Heavy Ethanol Consuming Female Rhesus Macaques

It is well established that heavy ethanol consumption interferes with the immune system and inflammatory processes, resulting in increased risk for infectious and chronic diseases. However, these processes have yet to be systematically studied in a dose and sex-dependent manner. In this study, we investigated the impact of chronic heavy ethanol consumption on gene expression using RNA-seq in peripheral blood mononuclear cells isolated from female rhesus macaques with daily consumption of 4% ethanol available 22hr/day for 12 months resulting in average ethanol consumption of 4.3 g/kg/day (considered heavy drinking). Differential gene expression analysis was performed using edgeR and gene enrichment analysis using MetaCore™. We identified 1106 differentially expressed genes, meeting the criterion of ≥ two-fold change and p-value ≤ 0.05 in expression (445 up- and 661 down-regulated). Pathway analysis of the 879 genes with characterized identifiers showed that the most enriched gene ontology processes were "response to wounding", "blood coagulation", "immune system process", and "regulation of signaling". Changes in gene expression were seen despite the lack of differences in the frequency of any major immune cell subtype between ethanol and controls, suggesting that heavy ethanol consumption modulates gene expression at the cellular level rather than altering the distribution of peripheral blood mononuclear cells. Collectively, these observations provide mechanisms to explain the higher incidence of infection, delay in wound healing, and increase in cardiovascular disease seen in subjects with Alcohol use disorder.

microRNA targeting of the P2X7 purinoceptor opposes a contralateral epileptogenic focus in the hippocampus

The ATP-gated ionotropic P2X7 receptor (P2X7R) modulates glial activation, cytokine production and neurotransmitter release following brain injury. Levels of the P2X7R are increased in experimental and human epilepsy but the mechanisms controlling P2X7R expression remain poorly understood. Here we investigated P2X7R responses after focal-onset status epilepticus in mice, comparing changes in the damaged, ipsilateral hippocampus to the spared, contralateral hippocampus. P2X7R-gated inward currents were suppressed in the contralateral hippocampus and P2rx7 mRNA was selectively uploaded into the RNA-induced silencing complex (RISC), suggesting microRNA targeting. Analysis of RISC-loaded microRNAs using a high-throughput platform, as well as functional assays, suggested the P2X7R is a target of microRNA-22. Inhibition of microRNA-22 increased P2X7R expression and cytokine levels in the contralateral hippocampus after status epilepticus and resulted in more frequent spontaneous seizures in mice. The major pro-inflammatory and hyperexcitability effects of microRNA-22 silencing were prevented in P2rx7^−/− mice or by treatment with a specific P2X7R antagonist. Finally, in vivo injection of microRNA-22 mimics transiently suppressed spontaneous seizures in mice. The present study supports a role for post-transcriptional regulation of the P2X7R and suggests therapeutic targeting of microRNA-22 may prevent inflammation and development of a secondary epileptogenic focus in the brain.

Purinergic P2Y2 Receptor Control of Tissue Factor Transcription in Human Coronary Artery Endothelial Cells: NEW AP-1 TRANSCRIPTION FACTOR SITE AND NEGATIVE REGULATOR

We recently reported that the P2Y2 receptor (P2Y2R) is the predominant nucleotide receptor expressed in human coronary artery endothelial cells (HCAEC) and that P2Y2R activation by ATP or UTP induces dramatic up-regulation of tissue factor (TF), a key initiator of the coagulation cascade. However, the molecular mechanism of this P2Y2R-TF axis remains unclear. Here, we report the role of a newly identified AP-1 consensus sequence in the TF gene promoter and its original binding components in P2Y2R regulation of TF transcription. Using bioinformatics tools, we found that a novel AP-1 site at -1363 bp of the human TF promoter region is highly conserved across multiple species. Activation of P2Y2R increased TF promoter activity and mRNA expression in HCAEC. Truncation, deletion, and mutation of this distal AP-1 site all significantly suppressed TF promoter activity in response to P2Y2R activation. EMSA and ChIP assays further confirmed that upon P2Y2R activation, c-Jun, ATF-2, and Fra-1, but not the typical c-Fos, bound to the new AP-1 site. In addition, loss-of-function studies using siRNAs confirmed a positive transactivation role of c-Jun and ATF-2 but unexpectedly revealed a strong negative role of Fra-1 in P2Y2R-induced TF up-regulation. Furthermore, we found that P2Y2R activation promoted ERK1/2 phosphorylation through Src, leading to Fra-1 activation, whereas Rho/JNK mediated P2Y2R-induced activation of c-Jun and ATF-2. These findings reveal the molecular basis for P2Y G protein-coupled receptor control of endothelial TF expression and indicate that targeting the P2Y2R-Fra-1-TF pathway may be an attractive new strategy for controlling vascular inflammation and thrombogenicity associated with endothelial dysfunction.

Control of bone development by P2X and P2Y receptors expressed in mesenchymal and hematopoietic cells

Bone development and homeostasis require the interplay between several cell types, including mesenchymal osteoblasts and osteocytes, as well as hematopoietic osteoclasts. Recent evidence suggests that cell proliferation, differentiation and apoptosis of both mesenchymal and hematopoietic stem cells, which are fundamental for tissue regeneration and treatment of degenerative diseases, are controlled by P2 receptors (i.e., P2X and P2Y receptors). Both types of P2 receptors are versatile transducers of diverse signals activated by extracellular nucleotides like ATP that are released in response to tissue injury, infection or shear stress. The P2X family of receptors has been shown to mediate multiple signaling events including the influx of calcium, activation of mitogen activated protein kinases (MAPKs) and induction of AP-1 family members known to regulate bone development. Support for the significance of P2X7 in regulating bone development and homeostasis has been provided by several studies focusing on animal models and single nucleotide polymorphisms. P2 receptors are functionally expressed in both bone forming osteoblasts and bone resorbing osteoclasts, while recent findings also suggest that these receptors translate mechanical stimuli in osteocytes. Their ability to respond to external nucleotide analogs renders these cell surface proteins excellent targets for skeletal regenerative therapies. This overview summarizes mechanisms by which nucleotide receptors control skeletal cells and contribute to bone tissue development remodeling and repair.

P2X7 receptors: role in bone cell formation and function

The role of the P2X7 receptor (P2X7R) is being explored with intensive interest in the context of normal bone physiology, bone-related diseases and, to an extent, bone cancer. In this review, we cover the current understanding of P2X7R regulation of bone cell formation, function and survival. We will discuss how the P2X7R drives lineage commitment of undifferentiated bone cell progenitors, the vital role of P2X7R activation in bone mineralisation and its relatively unexplored role in osteocyte function. We also review how P2X7R activation is imperative for osteoclast formation and its role in bone resorption via orchestrating osteoclast apoptosis. Variations in the gene for the P2X7R (P2RX7) have implications for P2X7R-mediated processes and we review the relevance of these genetic variations in bone physiology. Finally, we highlight how targeting P2X7R may have therapeutic potential in bone disease and cancer.

The P2X7 receptor channel: recent developments and the use of P2X7 antagonists in models of disease

The P2X7 receptor is a trimeric ATP-gated cation channel found predominantly, but not exclusively, on immune cells. P2X7 activation results in a number of downstream events, including the release of proinflammatory mediators and cell death and proliferation. As such, P2X7 plays important roles in various inflammatory, immune, neurologic and musculoskeletal disorders. This review focuses on the use of P2X7 antagonists in rodent models of neurologic disease and injury, inflammation, and musculoskeletal and other disorders. The cloning and characterization of human, rat, mouse, guinea pig, dog, and Rhesus macaque P2X7, as well as recent observations regarding the gating and permeability of P2X7, are discussed. Furthermore, this review discusses polymorphic and splice variants of P2X7, as well as the generation and use of P2X7 knockout mice. Recent evidence for emerging signaling pathways downstream of P2X7 activation and the growing list of negative and positive modulators of P2X7 activation and expression are also described. In addition, the use of P2X7 antagonists in numerous rodent models of disease is extensively summarized. Finally, the use of P2X7 antagonists in clinical trials in humans and future directions exploring P2X7 as a therapeutic target are described.

Differential expression of AP-1 proteins in human myometrium after spontaneous term labour onset

OBJECTIVES

The aims of this study were (i) to determine the localisation of activator protein (AP)-1 family members (cFos, FosB, cJun, JunB and JunD) in human myometrium; and (ii) to determine the effect of human term labour on the expression of AP-1 family of transcription factors in myometrium.

STUDY DESIGN

This localised the AP-1 family members cFos, FosB, cJun, JunB and JunD in human myometrium was performed by immunohistochemistry. The effect of term labour on the expression of these family members at the mRNA and protein level was assessed by qRT-PCR and Western blotting, respectively. The effect of pro-inflammatory stimuli on AP-1 transcriptional activity was assessed using a luciferase assay in primary human myometrial cells.

RESULTS

Immunohistochemical expression of cFos, FosB, cJun, JunB and JunD were all present in human myometrial tissue and displayed cytoplasmic staining. FosB and JunD also displayed nuclear staining. Term labour was associated with an increase in cFos and JunB mRNA and protein expression. On the other hand, JunD mRNA and protein expression was decreased with labour. FosB mRNA was increased with labour, but there was no change at the protein level. There was no change in cJun mRNA or protein expression. AP-1 transcriptional activity was increased in human myometrial cells by the pro-inflammatory cytokine TNF-α. There was, however, no effect of the bacterial products lipopolysaccharide (LPS; TLR4 ligand), iE-DAP (NOD1 ligand), MDP (NOD2 ligand), FSL-1 (TLR2 ligand) or flagellin (TLR5 ligand) on AP-1 transcriptional activity.

CONCLUSION

This study shows that human labour is associated with changes in AP-1 family members. Further studies are required to determine the exact role of the AP-1 family members in myometrium.

Purinergic signalling in the musculoskeletal system

It is now widely recognised that extracellular nucleotides, signalling via purinergic receptors, participate in numerous biological processes in most tissues. It has become evident that extracellular nucleotides have significant regulatory effects in the musculoskeletal system. In early development, ATP released from motor nerves along with acetylcholine acts as a cotransmitter in neuromuscular transmission; in mature animals, ATP functions as a neuromodulator. Purinergic receptors expressed by skeletal muscle and satellite cells play important pathophysiological roles in their development or repair. In many cell types, expression of purinergic receptors is often dependent on differentiation. For example, sequential expression of P2X5, P2Y1 and P2X2 receptors occurs during muscle regeneration in the mdx model of muscular dystrophy. In bone and cartilage cells, the functional effects of purinergic signalling appear to be largely negative. ATP stimulates the formation and activation of osteoclasts, the bone-destroying cells. Another role appears to be as a potent local inhibitor of mineralisation. In osteoblasts, the bone-forming cells, ATP acts via P2 receptors to limit bone mineralisation by inhibiting alkaline phosphatase expression and activity. Extracellular ATP additionally exerts significant effects on mineralisation via its hydrolysis product, pyrophosphate. Evidence now suggests that purinergic signalling is potentially important in several bone and joint disorders including osteoporosis, rheumatoid arthritis and cancers. Strategies for future musculoskeletal therapies might involve modulation of purinergic receptor function or of the ecto-nucleotidases responsible for ATP breakdown or ATP transport inhibitors.

Nucleotide receptor P2RX7 stimulation enhances LPS-induced interferon-β production in murine macrophages

Stimulation of P2RX(7) with extracellular ATP potentiates numerous LPS-induced proinflammatory events, including cytokine induction in macrophages, but the molecular mechanisms underlying this process are not well defined. Although P2RX(7) ligation has been proposed to activate several transcription factors, many of the LPS-induced mediators affected by P2RX(7) activation are not induced by P2RX(7) agonists alone, suggesting a complementary role for P2RX(7) in transcriptional regulation. Type I IFN production, whose expression is tightly controlled by multiple transcription factors that form an enhanceosome, is critical for resistance against LPS-containing bacteria. The effect of purinergic receptor signaling on LPS-dependent type I IFN is unknown and would be of great relevance to a diverse array of inflammatory conditions. The present study demonstrates that stimulation of macrophages with P2RX(7) agonists substantially enhances LPS-induced IFN-β expression, and this enhancement is ablated in macrophages that do not express functional P2RX(7) or when the MAPK MEK1/2 pathways are inhibited. Potentiation of LPS-induced IFN-β expression following P2RX(7) stimulation is likely transcriptionally regulated, as this enhancement is observed at the IFN-β promoter level. Furthermore, P2RX(7) stimulation is able to increase the phosphorylation and subsequent IFN-β promoter occupancy of IRF-3, a transcription factor that is critical for IFN-β transcription by TLR agonists. This newly discovered role for P2RX(7) in IFN regulation may have implications in antimicrobial defense, which has been linked to P2RX(7) activation in other studies.

The C-terminus of human nucleotide receptor P2X7 is critical for receptor oligomerization and N-linked glycosylation

Background

The P2X₇ receptor binds extracellular ATP to mediate numerous inflammatory responses and is considered a potential biomarker and therapeutic target for diverse inflammatory and neurological diseases. P2X₇ contains many single nucleotide polymorphisms, including several mutations located within its intracellular C-terminal trafficking domain. Mutations within the trafficking domain result in attenuated receptor activity and cell surface presentation, but the mechanisms by which amino acid changes within this region promote altered P2X₇ function have not been elucidated.

Methods and Results

We analyzed the amino acid sequence of P2X₇ for any potential trafficking signals and found that P2X₇ contains putative Arg-X-Arg ER retention sequences. Alanine substitutions near or within these sequences were constructed, and we determined that single mutation of R574 and R578 but not R576 or K579 attenuates P2X₇-stimulated activation of ERK1/2 and induction of the transcription factors FosB and ΔFosB. We found that mutation of R578 within the trafficking domain to the naturally occurring Gln substitution disrupts P2X₇ localization at the plasma membrane and results in R578Q displaying a higher apparent molecular weight in comparison to wild-type receptor. We used the glycosidase endoglycosidase H to determine that this difference in mass is due in part to the R578Q mutant possessing a larger mass of oligosaccharides, indicative of improper N-linked glycosylation addition and/or trimming. Chemical cross-linking experiments were also performed and suggest that the R578Q variant also does not form trimers as well as wild-type receptor, a function required for its full activity.

Conclusions

These data demonstrate the distal C-terminus of P2X₇ is important for oligomerization and post-translational modification of the receptor, providing a mechanism by which mutations in the trafficking domain disrupt P2X₇ activity and localization at the plasma membrane.

Dynamic redistribution of paxillin in bovine osteoblasts stimulated with adenosine 5'-triphosphate

Exposure to extracellular 5′-adenosine triphosphate (ATP) is known to induce membrane blebbing. In this study, we investigated the subcellular distribution of the cytoskeletal adaptor protein paxillin in primary bovine osteoblasts upon stimulation with ATP. Cells expressing a fusion protein of green fluorescent protein (GFP) and paxillin were followed by time-lapse video-microscopy after stimulation with 100 μM ATP. Within 100 s, GFP-paxillin became incorporated in numerous de novo formed focal aggregates localized at the cell periphery. The assembly of individual paxillin-containing aggregates occurred with a mean half-life time of <60 s, whereas their disassembly lasted twice as long. Despite the ongoing presence of ATP, the formation of paxillin aggregates was self-limiting within 25 min. Paxillin clustering was preceded by a transient rise in cytoplasmic calcium transients, which peaked already 20 s after adding ATP. The high mobility of paxillin was confirmed by measuring the dissociation rate of GFP-paxillin at mature focal adhesions, demonstrating the presence of a highly mobile fraction with a mean recovery half-life of 8.2 ± 1.2 s, followed by a slower phase (53 ± 20 s). Thus, both the exchange of paxillin at mature focal adhesions and the increase in intracellular calcium concentrations upon ATP stimulation are very rapid processes, which override the time course of ATP-induced paxillin membrane clustering by one to two orders of magnitude. Our data demonstrate that the transient recruitment of paxillin in membrane protuberances is based on the high intracytoplasmic mobility of unbound paxillin molecules and their rapid focal accumulation.

P2X7 Receptor Function in Bone-Related Cancer

Modulation of tumor microenvironment by different mediators is central in determining neoplastic formation and progression. Among these molecules extracellular ATP is emerging as a good candidate in promoting cell growth, neovascularization, tumor-host interactions, and metastatization. This paper summarizes recent findings on expression and function of P2X7 receptor for extracellular ATP in primary and metastatic bone cancers. Search of mRNA expression microchip databases and literature analysis demonstrate a high expression of P2X7 in primary bone tumors as well as in other malignancies such as multiple myeloma, neuroblastoma, breast, and prostate cancer. Evidence that P2X7 triggers NFATc1, PI3K/Akt, ROCK, and VEGF pathways in osteoblasts promoting either primary tumor development or osteoblastic lesions is also reported. Moreover, P2X7 receptor is involved in osteoclast differentiation, RANKL expression, matrix metalloproteases and cathepsin secretion thus promoting bone resorption and osteolytic lesions. Taken together these data point to a pivotal role for the P2X7 receptor in bone cancer biology.

Purinergic receptors influence the differentiation of human mesenchymal stem cells

Adult stem cells, including adipose tissue-derived mesenchymal stem cells (MSCs) or ectomesenchymal dental follicle cells (DFCs), attract considerable attention for their potential to differentiate into lineages, which are of major interest in the field of Regenerative Medicine. Purinergic receptors exert a wide range of biological actions in many cell and tissue types through extracellular nucleotides. Little is known about P2 receptors in adult stem cells and changes in their expression levels during differentiation. All known P2 receptors have been investigated, and a variety of P2X and P2Y receptor subtypes were detected in MSCs. Studies investigating intracellular calcium levels on receptor stimulation demonstrated that the found P2 receptors are metabolically active. Interestingly, up- or downregulation of several P2 receptor subtypes at gene and protein level was observed during adipogenic and osteogenic differentiation, and the effect on differentiation was directly influenced by both the application of agonists/antagonists and apyrase-induced nucleotide cleavage. Here, we show for the first time that the combination of several P2 receptors plays a role in the differentiation of adult stem cells. The expression pattern of the P2 receptors, as well as their fate in differentiation, varies in stem cells of mesenchymal origin if compared with stem cells of ectomesenchymal origin. The subtypes P2X6, P2Y4, and P2Y14 seem to be pivotal regulators in MSC commitment, as they are regulated in both adipogenic and osteogenic differentiation of adipose tissue-derived stem cells and DFCs. These findings provide new insights into the differentiation processes and might reveal novel options to influence stem cell fate in future applications.

AP-1 protein induction during monopoiesis favors C/EBP: AP-1 heterodimers over C/EBP homodimerization and stimulates FosB transcription

AP-1 proteins heterodimerize via their LZ domains to bind TGACGTCA or TGACTCA, whereas C/EBPs dimerize to bind ATTGCGCAAT. We demonstrate that intact C/EBPα also heterodimerizes with c-Jun or c-Fos to bind a hybrid DNA element, TGACGCAA, or more weakly to TGATGCAA. A 2:1 ratio of c-Jun:C/EBPα or c-Fos:C/EBPα was sufficient for preferential binding. Semiquantitative Western blot analysis indicates that the summation of c-Jun, JunB, and c-Fos levels in differentiating myeloid cells is similar to or exceeds the entirety of C/EBPα and C/EBPβ, indicating the feasibility of heterodimer formation. Induction of AP-1 proteins during monocytic differentiation favored formation of C/EBP:AP-1 heterodimers, with C/EBPα homodimers more evident during granulopoiesis. Approximately 350 human and 300 murine genes contain the TGACGCAA motif between -2 kb and +1 kb of their transcription start sites. We focused on the murine Fosb promoter, which contains a C/EBP:AP-1 cis element at -56 and -253, with the hFOSB gene containing an identical site at -253 and a 1-bp mismatch at -56. C/EBPα:AP-1 heterodimers bound either site preferentially in a gel-shift assay, C/EBPα:c-Fos ER fusion proteins induced endogenous Fosb mRNA but not in the presence of CHX, C/EBP and AP-1 proteins bound the endogenous Fosb promoter, mutation of the -56 cis element reduced reporter activity fivefold, and endogenous FosB protein was expressed preferentially during monopoiesis versus granulopoiesis. Increased expression of Jun/Fos proteins elevates C/EBP:AP-1 heterodimer formation to potentially activate novel sets of genes during monopoiesis and potentially during other biologic processes.

Transcriptional control mechanisms associated with the nucleotide receptor P2X7, a critical regulator of immunologic, osteogenic, and neurologic functions

The nucleotide receptor P2X(7) is an attractive therapeutic target and potential biomarker for multiple inflammatory and neurologic disorders, and it is expressed in several immune, osteogenic, and neurologic cell types. Aside from its role in the nervous system, it is activated by ATP released at sites of tissue damage, inflammation, and infection. Ligand binding to P2X(7) stimulates many cell responses, including calcium fluxes, MAPK activation, inflammatory mediator release, and apoptosis. Much work has centered on P2X(7) action in cell death and mediator processing (e.g., pro-interleukin-1 cleavage by the inflammasome), but the contribution of P2X(7) to transcriptional regulation is less well defined. This review will focus on the growing evidence for the importance of nucleotide-mediated gene expression, highlight several animal models, human genetic, and clinical studies that support P2X(7) as a therapeutic target, and discuss the latest developments in anti-P2X(7) clinical trials.