Extracellular ATP signaling and clinical relevance

Purine and purinergic receptors in health and disease

Purines and purinergic receptors are widely distributed throughout the human body. Purine molecules within cells play crucial roles in regulating energy metabolism and other cellular processes, while extracellular purines transmit signals through specific purinergic receptors. The ubiquitous purinergic signaling maintains normal neural excitability, digestion and absorption, respiratory movement, and other complex physiological activities, and participates in cell proliferation, differentiation, migration, and death. Pathological dysregulation of purinergic signaling can result in the development of various diseases, including neurodegeneration, inflammatory reactions, and malignant tumors. The dysregulation or dysfunction of purines and purinergic receptors has been demonstrated to be closely associated with tumor progression. Compared with other subtypes of purinergic receptors, the P2X7 receptor (P2X7R) exhibits distinct characteristics (i.e., a low affinity for ATP, dual functionality upon activation, the mediation of ion channels, and nonselective pores formation) and is considered a promising target for antitumor therapy, particularly in patients with poor response to immunotherapy This review summarizes the physiological and pathological significance of purinergic signaling and purinergic receptors, analyzes their complex relationship with tumors, and proposes potential antitumor immunotherapy strategies from tumor P2X7R inhibition, tumor P2X7R overactivation, and host P2X7R activation. This review provides a reference for clinical immunotherapy and mechanism investigation.

Intracellular energy production and distribution in hypoxia

The hydrolysis of ATP is the primary source of metabolic energy for eukaryotic cells. Under physiological conditions, cells generally produce more than sufficient levels of ATP to fuel the active biological processes necessary to maintain homeostasis. However, mechanisms underpinning the distribution of ATP to subcellular microenvironments with high local demand remain poorly understood. Intracellular distribution of ATP in normal physiological conditions has been proposed to rely on passive diffusion across concentration gradients generated by ATP producing systems such as the mitochondria and the glycolytic pathway. However, subcellular microenvironments can develop with ATP deficiency due to increases in local ATP consumption. Alternatively, ATP production can be reduced during bioenergetic stress during hypoxia. Mammalian cells therefore need to have the capacity to alter their metabolism and energy distribution strategies to compensate for local ATP deficits while also controlling ATP production. It is highly likely that satisfying the bioenergetic requirements of the cell involves the regulated distribution of ATP producing systems to areas of high ATP demand within the cell. Recently, the distribution (both spatially and temporally) of ATP-producing systems has become an area of intense investigation. Here, we review what is known (and unknown) about intracellular energy production and distribution and explore potential mechanisms through which this targeted distribution can be altered in hypoxia, with the aim of stimulating investigation in this important, yet poorly understood field of research.

Effects of Modified Glucosamine on the Chondrogenic Potential of Circulating Stem Cells under Experimental Inflammation

Glucosamine (GlcN) is a glycosaminoglycan (GAGs) constituent in connective tissues. It is naturally produced by our body or consumed from diets. In the last decade, in vitro and in vivo trials have demonstrated that the administration of GlcN or its derivates has a protective effect on cartilage when the balance between catabolic and anabolic processes is disrupted and cells are no longer able to fully compensate for the loss of collagen and proteoglycans. To date, these benefits are still controversial because the mechanism of action of GlcN is not yet well clarified. In this study, we have characterized the biological activities of an amino acid (AA) derivate of GlcN, called DCF001, in the growth and chondrogenic induction of circulating multipotent stem cells (CMCs) after priming with tumor necrosis factor-alpha (TNFα), a pleiotropic cytokine commonly expressed in chronic inflammatory joint diseases. In the present work, stem cells were isolated from the human peripheral blood of healthy donors. After priming with TNFα (10 ng/mL) for 3 h, cultures were treated for 24 h with DCF001 (1 μg/mL) dissolved in a proliferative (PM) or chondrogenic (CM) medium. Cell proliferation was analyzed using a Corning^® Cell Counter and trypan blue exclusion technique. To evaluate the potentialities of DCF001 in counteracting the inflammatory response to TNFα, we measured the amount of extracellular ATP (eATP) and the expression of adenosine-generating enzymes CD39/CD73, TNFα receptors, and NF-κB inhibitor IκBα using flow cytometry. Finally, total RNA was extracted to perform a gene expression study of some chondrogenic differentiation markers (COL2A1, RUNX2, and MMP13). Our analysis has shed light on the ability of DCF001 to (a) regulate the expression of CD39, CD73, and TNF receptors; (b) modulate eATP under differentiative induction; (c) enhance the inhibitory activity of IκBα, reducing its phosphorylation after TNFα stimulation; and (d) preserve the chondrogenic potentialities of stem cells. Although preliminary, these results suggest that DCF001 could be a valuable supplement for ameliorating the outcome of cartilage repair interventions, enhancing the efficacy of endogenous stem cells under inflammatory stimuli.

Metabolic reprogramming through mitochondrial biogenesis drives adenosine anti-inflammatory effects: new mechanism controlling gingival fibroblast hyper-inflammatory state

Introduction

Fibroblasts are the dominant stromal cells in the gingival lamina propria with a well-established relevance in regulation of inflammation, and in innate immunity. This is exemplified by their hypersecretion of CXCL8, enhancing leukocyte infiltration in chronic and sustained inflammatory conditions. We have previously shown adenosine to be a key metabolic nucleoside that regulates stromal inflammation, but the underlying mechanisms linking adenosine to the metabolic status of fibroblasts and to the resultant inflammatory response are unclear. This study examined, by seahorse real-time cell metabolic analysis, the bioenergetics of the stromal fibroblast response to extracellular adenosine and IL-1β, focusing on CXCL8 secretion by primary human gingival fibroblasts (HGF).

Methods

Markers of the glycolytic pathway and mitochondrial biogenesis were tracked through immunoblot. Further, the influence of adenosine on mitochondrial accumulation was measured by uptake of MitoTracker Red fluorescent probe and assessment of the role of FCCP (a mitochondrial uncoupler) in CXCL8 secretion and mitochondrial accumulation.

Results

Our results show that the anti-inflammatory response of HGF to extracellular adenosine, typified by reduced CXCL8 secretion, is mediated by mitochondrial oxidative phosphorylation, reflected in higher oxygen consumption rate (OCR). In the presence of IL-1β, adenosine-treated cells induced higher ATP production, basal respiration and proton leak compared to IL-1β without adenosine. Surprisingly, adenosine had no additional effect on the IL-1β-induced higher glycolysis rate demonstrated by the extracellular acidification rate (ECAR). In addition, the higher OCR in adenosine-stimulated cells was not due to the mitochondrial fuel dependency or capacity, but due to an increase in mitochondrial biogenesis and accumulation in the cells with concomitant decrease in mitophagy-required p-PINK1 marker. We detected the accumulation of functional mitochondria with increased activation of the AMPK/SIRT1/PGC-1α pathway. The adenosine-induced uptake of MitoTracker was abrogated by PGC-1α inhibition with SR-12898. In addition, the adenosine effects on reduced CXCL8 were ablated by treatment with FCCP, a potent uncoupler of mitochondrial oxidative phosphorylation.

Conclusion

Our findings reveal a key role for mitochondrial bioenergetics in regulation of CXCL8-mediated inflammation by HGF through the adenosine/AMPK/SIRT1/PGC-1α axis. Therapeutically targeting this pathway in gingival fibroblasts might be a promising future strategy to modulate stromal-mediated sustained hyper-inflammatory responses.

cGAMP the travelling messenger

2'3'-cGAMP is a key molecule in the cGAS-STING pathway. This cyclic dinucleotide is produced by the cytosolic DNA sensor cGAS in response to the presence of aberrant dsDNA in the cytoplasm which is associated with microbial invasion or cellular damage. 2'3'-cGAMP acts as a second messenger and activates STING, the central hub of DNA sensing, to induce type-I interferons and pro-inflammatory cytokines necessary for responses against infection, cancer or cellular stress. Classically, detection of pathogens or danger by pattern recognition receptors (PRR) was thought to signal and induce the production of interferon and pro-inflammatory cytokines in the cell where sensing occurred. These interferon and cytokines then signal in both an autocrine and paracrine manner to induce responses in neighboring cells. Deviating from this dogma, recent studies have identified multiple mechanisms by which 2'3'-cGAMP can travel to neighboring cells where it activates STING independent of DNA sensing by cGAS. This observation is of great importance, as the cGAS-STING pathway is involved in immune responses against microbial invaders and cancer while its dysregulation drives the pathology of a wide range of inflammatory diseases to which antagonists have been elusive. In this review, we describe the fast-paced discoveries of the mechanisms by which 2'3'-cGAMP can be transported. We further highlight the diseases where they are important and detail how this change in perspective can be applied to vaccine design, cancer immunotherapies and treatment of cGAS-STING associated disease.

P2X4 receptor modulates gut inflammation and favours microbial homeostasis in colitis

BACKGROUND

Inflammatory bowel disease (IBD) is a non-specific chronic inflammatory disease of the intestine. In addition to genetic susceptibility, environmental factors and dysregulated host immunity, the gut microbiota is implicated in the pathogenesis of Crohn's disease (CD) or ulcerative colitis (UC), the two primary types of IBD. The P2X4 receptor has been demonstrated to have a crucial role in preventing infection, inflammation, and organ damage. However, it remains unclear whether the P2X4 receptor affects IBD and the underlying mechanisms.

METHODS

Colitis was induced in mice administrated with dextran sodium sulphate (DSS). 16S rDNA sequencing was used to analyze the gut microbiota in knockout and wild-type mice. Clinical and histopathological parameters were monitored throughout the disease progression.

RESULTS

Gene Expression Omnibus analysis showed the downregulation of P2RX4 (P2rx4) expression in colonic tissues from patients or mice with IBD. However, its expression at the protein levels was upregulated on day 4 or 6 and then downregulated on day 7 in C57BL/6 mice treated with DSS. Gene ablation of P2rx4 aggravated DSS-induced colitis accompanying gut microbiota dysbiosis in mice. Moreover, P2X4 receptor-positive modulator ivermectin alleviated colitis and corrected dysregulated microbiota in wild-type C57BL/6 mice. Further antibiotic-treated gut microbiota depletion, cohousing experiment, and fecal microbiota transplantation proved that gut microbiota dysbiosis was associated with the aggravation of colitis in the mouse model initiated by P2rx4.

CONCLUSIONS

Our findings elaborate on an unrevealed etiopathophysiological mechanism by which microbiota dysbiosis induced by the P2X4 receptor influences the development of colitis, indicating that the P2X4 receptor represents a promising target for treating patients with CD and UC.

The ATP-dependent Pathways and Human Diseases

Adenosine triphosphate (ATP) is one of the most important molecules of life, present both inside the cells and extracellularly. It is an essential building block for nucleic acids biosynthesis and crucial intracellular energy storage. However, one of the most interesting functions of ATP is the role of a signaling molecule. Numerous studies indicate the involvement of ATP-dependent pathways in maintaining the proper functioning of individual tissues and organs. Herein, the latest data indicating the ATP function in the network of intra- and extracellular signaling pathways including purinergic signaling, MAP kinase pathway, mTOR and calcium signaling are collected. The main ATP-dependent processes maintaining the proper functioning of the nervous, cardiovascular and immune systems, as well as skin and bones, are summarized. The disturbances in the ATP amount, its cellular localization, or interaction with target elements may induce pathological changes in signaling pathways leading to the development of serious diseases. The impact of an ATP imbalance on the development of dangerous health dysfunctions such as neurodegeneration diseases, cardiovascular diseases (CVDs), diabetes mellitus, obesity, cancers and immune pathogenesis are discussed here.

P2X7 receptor activation impairs antitumour activity of natural killer cells

BACKGROUND AND PURPOSE

A high number of intratumoural infiltrating natural killer (NK) cells is associated with better survival in several types of cancer, constituting an important first line of defence against tumours. Hypoxia in the core of solid tumours induces cellular stress and ATP release into the extracellular space where it triggers purinergic receptor activation on tumour-associated immune cells. The aim of this study was to assess whether activation of the purinergic receptor P2X7 by extracellular ATP plays a role in the NK cells antitumour activity.

EXPERIMENTAL APPROACH

We carried out in vitro experiments using purified human NK cells triggered through P2X7 by extracellular ATP. NK cell killing activity against the tumour target cells K562 was studied by means of NK cytotoxicity assays. Likewise, we designed a subcutaneous solid tumour in vivo mouse model.

KEY RESULTS

In this study we found that human NK cells, expressing a functional plasma membrane P2X7, acquired an anergic state after ATP treatment, which impaired their antitumour activity and decreased IFN-γ secretion. This effect was reversed by specific P2X7 antagonists and pretreatment with either IL-2 or IL-15. Furthermore, genetic P2rx7 knockdown resulted in improved control of tumour size by NK cells. In addition, IL-2 therapy restored the ability of NK cells to diminish the size of tumours.

CONCLUSIONS AND IMPLICATIONS

Our results show that P2X7 activation represents a new mechanism whereby NK cells may lose antitumour effectiveness, opening the possibility of generating modified NK cells lacking P2X7 but with improved antitumour capacity.

A Novel Oxidative Phosphorylation-Associated Gene Signature for Prognosis Prediction in Patients with Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a common type of malignant tumor with high morbidity and mortality. The oxidative phosphorylation (OXPHOS) metabolic pathway produces adenosine triphosphate (ATP) by delivering electrons to transmembrane protein complexes in the mitochondria. This research was dedicated to identifying an OXPHOS-associated signature for the assessment of prognosis of HCC patients. A total of 371 HCC patients from the Cancer Genome Atlas (TCGA) and 231 HCC patients from the International Cancer Genome Consortium (ICGC) with RNA expression data and clinical data were employed as construction and validation cohorts, respectively. The least absolute shrinkage and selection operator (LASSO) Cox regression was applied to establish a multigene signature in the TCGA cohort, and the ICGC cohort was used for validation. The prognostic value of the risk signature was evaluated using univariate and multivariate Cox regression, Kaplan–Meier curves, and receiver operating characteristic (ROC) curves. The potential enrichment of biological functions was investigated using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. Meanwhile, we analyzed the correlation between the risk score and the tumor microenvironment (TME). A five-gene signature including ATP6V0B, ATP6V1C1, ATP6V1E1, TIMM9, and UQCRH was identified by LASSO Cox regression to classify patients into low- and high-risk groups. ROC curve analysis indicated that the five-gene signature is a prospective prognostic factor in HCC patients. Univariate and multivariate Cox regression analyses demonstrated that the risk score was an independent prognostic factor for overall survival (OS). Functional analysis showed that differentially expressed genes (DEGs) between the low- and high-risk groups were enriched in mitosis and the cell cycle pathway. In addition, the five-gene signature was associated with innate immune cell infiltration, immune subtypes, and tumor stemness. A novel OXPHOS-associated gene signature can be used for prognostic prediction for patients with HCC.

Lysophosphatidylcholine induces adenosine release from macrophages via TRPM7-mediated mitochondrial activation

Even though macrophages have the potential to harm tissues through excessive release of inflammatory mediators, they play protective roles to maintain tissue integrity. In this study, we hypothesized that lysophosphatidylcholine (LPC), via G2A and A2B receptors, puts brakes on macrophages by the induction of adenosine release which could contribute to termination of inflammation. Mechanistically, LPC-induced PGE2 production followed by the activation of cAMP/protein kinase A (PKA) pathway which results in the activation of LKB1/AMPK signaling pathway leading to increasing Mg2+ influx concomitantly with an increase in mitochondrial membrane potential (MMP, Δψm) and ATP production. Then, ATP is converted to adenosine intracellularly followed by efflux via ENT1. In a parallel pathway, LPC-induced elevation of cytosolic calcium was essential for adenosine release, and Ca2+/calmodulin signaling cooperated with PKA to regulate ENT1 permeation to adenosine. Pharmacological blockade of TRPM7 and antisense treatment suppressed LPC-induced adenosine release and magnesium influx in bone marrow-derived macrophages (BMDMs). Moreover, LPC suppressed LPS-induced phosphorylation of connexin-43, which may counteract TLR4-mediated inflammatory response. Intriguingly, we found LPC increased netrin-1 production from BMDMs. Netrin-1 induces anti-inflammatory signaling via A2B receptor. In the presence of adenosine deaminase which removes adenosine in the medium, the chemotaxis of macrophages toward LPC was significantly increased. Hypoxia and metabolic acidosis are usually developed in a variety of inflammatory situations such as sepsis. We found LPC augmented hypoxia- or acidosis-induced adenosine release from BMDMs. These results provide evidence of LPC-induced brake-like action on macrophages by adenosine release via cellular magnesium signaling.

The roles of nucleotide signaling and platelets in inflammation

Nucleotides and platelets have been associated with a wide range of activities that affect the host inflammatory response. The main goal of this study is to examine the roles of nucleotide signaling and platelets in inflammation. The study analysis entailed conducting a systematic search to identify relevant articles in PsycINFO, PubMed, Web of Science, and CINAHL. The evidence gathered from the identified articles shows the roles of nucleotides and platelets in inflammation. In the extracellular environment, nucleotides act as signaling molecules that can activate nucleotide receptors to promote inflammation. Inflammation is an essential process through which the innate immune system responds to pathogens, microbes, and damage-associated molecular patterns. Moreover, research evidence shows that the mechanisms through which platelets affect inflammatory responses and regulate hemostasis are the same. The roles of nucleotides and platelets in inflammation have been explored in several studies worldwide. Although platelets and nucleotides have unique structures, both of them influence the host response to pathogens and tumors. Analysis of platelets and nucleotides will offer valuable insight for the development of new treatments for infectious and inflammatory diseases.

Regulatory T Cells in acute and chronic human Chikungunya infection

Chikungunya virus (CHIKV) infection generates strong immune responses that are associated with the disease pathophysiology. Regulatory T cells (Treg-cluster of differentiation (CD)-4⁺CD25^highforkhead box P3 (FOXP3⁺)) are essential for the induction and maintenance of peripheral tolerance. Thus, they play key roles in determining the patient prognosis by preventing excessive immune responses via different suppression immune mechanisms. However, the regulatory mechanisms involved in human CHIKV infection are still poorly understood. Here, we characterize for the first time the Treg cell molecule-associated-mechanism during acute and chronic human Chikungunya disease. Here, we assessed the Treg cell population and molecule-associated mechanism in the peripheral blood samples of acute and chronic patients with Chikungunya. Our results indicate that CHIKV infection is associated with reduced frequency of Tregs, along with the impaired expression and production of Treg functional markers, including CD39, CD73, perforin, granzyme, programmed death 1 (PD-1), cytotoxic T lymphocyte antigen (CTLA)-4, and transforming growth factor (TGF)-β. This observation suggests that Treg cells possess poor regulatory capacity in both acute and chronic phases of the disease. Taken together, these data provide significant evidence that the imbalanced response of Treg cells plays an essential role in establishing the pathogenesis of Chikungunya.

In vitro biosynthesis of ATP from adenosine and polyphosphate

Adenosine triphosphate (ATP) acts as a crucial energy currency in vivo, and it is a widely used energy and/or phosphate donor for enzyme-catalyzed reactions in vitro. In this study, we established an in vitro multi-enzyme cascade system for ATP production. Using adenosine and inorganic polyphosphate (polyP) as key substrates, we combined adenosine kinase and two functionally distinct polyphosphate kinases (PPKs) in a one-pot reaction to achieve chain-like ATP regeneration and production. Several sources of PPK were screened and characterized, and two suitable PPKs were selected to achieve high rates of ATP production. Among these, Sulfurovum lithotrophicum PPK (SlPPK) exhibited excellent activity over a wide pH range (pH 4.0-9.0) and synthesized ATP from ADP using short-chain polyP. Furthermore, it had a half-life > 155.6 h at 45 °C. After optimizing the reaction conditions, we finally carried out the coupling-catalyzed reaction with different initial adenosine concentrations of 10, 20, and 30 mM. The highest yields of ATP were 76.0, 70.5, and 61.3%, respectively.

P2X Receptor-Dependent Modulation of Mast Cell and Glial Cell Activities in Neuroinflammation

Localisation of mast cells (MCs) at the abluminal side of blood vessels in the brain favours their interaction with glial cells, neurons, and endothelial cells, resulting in the activation of these cells and the release of pro-inflammatory mediators. In turn, stimulation of glial cells, such as microglia, astrocytes, and oligodendrocytes may result in the modulation of MC activities. MCs, microglia, astrocytes, and oligodendrocytes all express P2X receptors (P2XRs) family members that are selectively engaged by ATP. As increased concentrations of extracellular adenosine 5′-triphosphate (ATP) are present in the brain in neuropathological conditions, P2XR activation in MCs and glial cells contributes to the control of their communication and amplification of the inflammatory response. In this review we discuss P2XR-mediated MC activation, its bi-directional effect on microglia, astrocytes and oligodendrocytes and role in neuroinflammation.

Hypoxia-inducible factor-1alpha protects the liver against ischemia-reperfusion injury by regulating the A2B adenosine receptor

Hepatic ischemia-reperfusion injury (IRI) is an inevitable complication associated with liver surgical procedures, and its pathological process remains elusive. Therefore, the present study investigated the role and mechanism of hypoxia-inducible factor-1alpha (HIF-1α) in hepatic IRI. Here, we constructed rat models with hepatic IRI and BRL-3A cell models with hypoxia/reoxygenation (H/R) insult. The extent of liver injury was assayed by measuring serum ALT/AST levels and performing H&E staining; the levels of SOD, MDA, MPO, IL-6 and TNF-α were determined using commercial kits; apoptosis was detected using the TUNEL assay and flow cytometry; and the expression of HIF-1α/A2BAR signaling-related molecules and apoptosis-associated indicators was detected using Western blotting or qRT-PCR. The expression level of HIF-1α was significantly upregulated in the liver of rats subjected to IRI, as well as in BRL-3A cells treated with H/R. HIF-1α overexpression exerted a protective effect on hepatic IRI or H/R insult by reducing serum aminotransferase levels and hepatic necrosis, inhibiting inflammation and apoptosis of hepatocytes, and alleviating oxidative stress. In contrast, inhibition of HIF-1α expression exacerbated hepatic injury induced by IR or H/R. Mechanistically, the expression level of A2BAR was markedly increased during hepatic IRI or H/R insult. Moreover, A2BAR expression increased with HIF-1α upregulation and decreased with HIF-1α downregulation. Importantly, inhibition of A2BAR signaling abolished HIF-1α overexpression-mediated hepatoprotection. Taken together, HIF-1α exerts protective effects on hepatic IRI by attenuating liver necrosis, the inflammatory response, oxidative stress and apoptosis, and its mechanism may be related to the upregulation of A2BAR signaling.

Surface AMP deaminase 2 as a novel regulator modifying extracellular adenine nucleotide metabolism

Adenine nucleotides represent crucial immunomodulators in the extracellular environment. The ectonucleotidases CD39 and CD73 are responsible for the sequential catabolism of ATP to adenosine via AMP, thus promoting an anti-inflammatory milieu induced by the "adenosine halo". AMPD2 intracellularly mediates AMP deamination to IMP, thereby both enhancing the degradation of inflammatory ATP and reducing the formation of anti-inflammatory adenosine. Here, we show that this enzyme is expressed on the surface of human immune cells and its predominance may modify inflammatory states by altering the extracellular milieu. Surface AMPD2 (eAMPD2) expression on monocytes was verified by immunoblot, surface biotinylation, mass spectrometry, and immunofluorescence microscopy. Flow cytometry revealed enhanced monocytic eAMPD2 expression after TLR stimulation. PBMCs from patients with rheumatoid arthritis displayed significantly higher levels of eAMPD2 expression compared with healthy controls. Furthermore, the product of AMPD2-IMP-exerted anti-inflammatory effects, while the levels of extracellular adenosine were not impaired by an increased eAMPD2 expression. In summary, our study identifies eAMPD2 as a novel regulator of the extracellular ATP-adenosine balance adding to the immunomodulatory CD39-CD73 system.

Synthesis, In-vitro evaluation and molecular docking studies of oxoindolin phenylhydrazine carboxamides as potent and selective inhibitors of ectonucleoside triphosphate diphosphohydrolase (NTPDase)

Members of the ectonucleoside triphosphate diphosphohydrolases (NTPDases) constitute the major family of enzymes responsible for the maintenance of extracellular levels of nucleotides and nucleosides by catalyzing the hydrolysis of nucleoside triphosphate (NTP) and nucleoside diphosphates (NDP) to nucleoside monophosphate (NMP). Although, NTPDase inhibitors can act as potential drug candidates for the treatment of various diseases, there is lack of potent as well as selective inhibitors of NTPDases. The current study describes the synthesis of a number of carboxamide derivatives that were tested on recombinant human (h) NTPDases. The most promising inhibitors were 2h (h-NTPDase1, IC₅₀: 0.12 ± 0.03 µM), 2d (h-NTPDase2, IC₅₀: 0.15 ± 0.01 µM) and 2a (h-NTPDase3, IC₅₀: 0.30 ± 0.04 µM; h-NTPDase8, IC₅₀: 0.16 ± 0.02 µM). Four compounds (2e, 2f, 2g and 2h) were associated with the selective inhibition of h-NTPDase1 while 2b was identified as a selective h-NTPDase3 inhibitor. Considering the importance of NTPDase3 in the regulation of insulin release, the NTPDase3 inhibitors were further investigated to elucidate their role in the insulin release. The obtained data suggested that compound 2a was actively participating in regulating the insulin release without producing any effect on NTPDase3 mRNA. Moreover, the most potent inhibitors were docked within the active site of respective enzyme and the observed interactions were in compliance with in vitro results. Hence, these compounds can be used as pharmacological tool to further investigate the role of NTPDase3 coupled to insulin release.

An interplay of resource availability, population size and mutation rate potentiates the evolution of metabolic signaling

Background

Asexually reproducing populations of single cells evolve through mutation, natural selection, and genetic drift. Environmental conditions in which the evolution takes place define the emergent fitness landscapes. In this work, we used Avida—a digital evolution framework—to uncover a hitherto unexplored interaction between mutation rates, population size, and the relative abundance of metabolizable resources, and its effect on evolutionary outcomes in small populations of digital organisms.

Results

Over each simulation, the population evolved to one of several states, each associated with a single dominant phenotype with its associated fitness and genotype. For a low mutation rate, acquisition of fitness by organisms was accompanied with, and dependent on, an increase in rate of genomic replication. At an increased mutation rate, phenotypes with high fitness values were similarly achieved through enhanced genome replication rates. In addition, we also observed the frequent emergence of suboptimal fitness phenotype, wherein neighboring organisms signaled to each other information relevant to performing metabolic tasks. This metabolic signaling was vital to fitness acquisition and was correlated with greater genotypic and phenotypic heterogeneity in the population. The frequency of appearance of signaling populations increased with population size and with resource abundance.

Conclusions

Our results reveal a minimal set of environment–genotype interactions that lead to the emergence of metabolic signaling within evolving populations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01782-0.

Induction of osteogenesis in bone tumour cells by purine-conjugated zinc-hydroxyapatite

This study aimed to improve the biocompatibility and osteogenic property of hydroxyapatite (HAP). So HAP nanoparticles were doped with zinc (Zn), and their surface was modified with a purine nucleotide, guanosine 5′-triphosphate (GTP). GTP-loaded nanoparticles (GTP@ZnHAP) were characterised by field emission scanning electron microscopy, Fourier transform infrared, thermogravimetric analysis, zeta potential and ultraviolet–visible spectroscopy. Biological experiments revealed that GTP@ZnHAP nanoparticles were internalised by the cells, inhibiting tumour cell (osteoblast-like cells, Saos-2) expansion with an efficiency more than that observed for ZnHAP nanoparticles and GTP alone. Furthermore, Saos-2 cells were committed to differentiate into the normal osteoblast cells under the influence of GTP@ZnHAP nanoparticles demonstrated by the quantitative assessment of bone-related protein expression (Runx2 and osteocalcin) and cell morphological changes. Moreover, high-performance liquid chromatography analyses disclosed a significant enhancement of intracellular GTP content in GTP@ZnHAP-treated cells, proposing perturbation of intracellular nucleotide equilibrium during the process of osteogenesis induced by GTP@ZnHAP nanoparticles. Overall, GTP@ZnHAP exhibits a better synergistic effect on the modulation of cell growth and induction of osteogenic differentiation in osteosarcoma cells than ZnHAP nanoparticles and GTP alone do. Therefore, GTP@ZnHAP may be regarded as a promising biomaterial for the treatment of bone-related diseases.

Functionalized Oxoindolin Hydrazine Carbothioamide Derivatives as Highly Potent Inhibitors of Nucleoside Triphosphate Diphosphohydrolases

Ectonucleoside triphosphate diphosphohydrolases (NTPDases) are ectoenzymes that play an important role in the hydrolysis of nucleoside triphosphate and diphosphate to nucleoside monophosphate. NTPDase1, -2, -3 and -8 are the membrane bound members of this enzyme family that are responsible for regulating the levels of nucleotides in extracellular environment. However, the pathophysiological functions of these enzymes are not fully understood due to lack of potent and selective NTPDase inhibitors. Herein, a series of oxoindolin hydrazine carbothioamide derivatives is synthesized and screened for NTPDase inhibitory activity. Four compounds were identified as selective inhibitors of h-NTPDase1 having IC₅₀ values in lower micromolar range, these include compounds 8b (IC₅₀ = 0.29 ± 0.02 µM), 8e (IC₅₀ = 0.15 ± 0.009 µM), 8f (IC₅₀ = 0.24 ± 0.01 µM) and 8l (IC₅₀ = 0.30 ± 0.03 µM). Similarly, compound 8k (IC₅₀ = 0.16 ± 0.01 µM) was found to be a selective h-NTPDase2 inhibitor. In case of h-NTPDase3, most potent inhibitors were compounds 8c (IC₅₀ = 0.19 ± 0.02 µM) and 8m (IC₅₀ = 0.38 ± 0.03 µM). Since NTPDase3 has been reported to be associated with the regulation of insulin secretion, we evaluated our synthesized NTPDase3 inhibitors for their ability to stimulate insulin secretion in isolated mice islets. Promising results were obtained showing that compound 8m potently stimulated insulin secretion without affecting the NTPDase3 gene expression. Molecular docking studies of the most potent compounds were also carried out to rationalize binding site interactions. Hence, these compounds are useful tools to study the role of NTPDase3 in insulin secretion.

Extracellular ATP: A Feasible Target for Cancer Therapy

Adenosine triphosphate (ATP) is one of the main biochemical components of the tumor microenvironment (TME), where it can promote tumor progression or tumor suppression depending on its concentration and on the specific ecto-nucleotidases and receptors expressed by immune and cancer cells. ATP can be released from cells via both specific and nonspecific pathways. A non-regulated release occurs from dying and damaged cells, whereas active release involves exocytotic granules, plasma membrane-derived microvesicles, specific ATP-binding cassette (ABC) transporters and membrane channels (connexin hemichannels, pannexin 1 (PANX1), calcium homeostasis modulator 1 (CALHM1), volume-regulated anion channels (VRACs) and maxi-anion channels (MACs)). Extracellular ATP acts at P2 purinergic receptors, among which P2X7R is a key mediator of the final ATP-dependent biological effects. Over the years, P2 receptor- or ecto-nucleotidase-targeting for cancer therapy has been proposed and actively investigated, while comparatively fewer studies have explored the suitability of TME ATP as a target. In this review, we briefly summarize the available evidence suggesting that TME ATP has a central role in determining tumor fate and is, therefore, a suitable target for cancer therapy.

Development of Anthraquinone Derivatives as Ectonucleoside Triphosphate Diphosphohydrolase (NTPDase) Inhibitors With Selectivity for NTPDase2 and NTPDase3

Ectonucleoside triphosphate diphosphohydrolases (NTPDases) catalyze the hydrolysis of nucleoside tri- and di-phosphates to mono-phosphates. The products are subsequently hydrolyzed by ecto-5′-nucleotidase (ecto-5′-NT) to nucleosides. NTPDase inhibitors have potential as novel drugs, e.g., for the treatment of inflammation, neurodegenerative diseases, and cancer. In this context, a series of anthraquinone derivatives structurally related to the anthraquinone dye reactive blue-2 (RB-2) was synthesized and evaluated as inhibitors of human NTPDases utilizing a malachite green assay. We identified several potent and selective inhibitors of human NTPDase2 and -3. Among the most potent NTPDase2 inhibitors were 1-amino-4-(9-phenanthrylamino)-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate (20, PSB-16131, IC₅₀ of 539 nM) and 1-amino-4-(3-chloro-4-phenylsulfanyl)phenylamino-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate (48, PSB-2020, IC₅₀ of 551 nM). The most potent NTPDase3 inhibitors were 1-amino-4-[3-(4,6-dichlorotriazin-2-ylamino)-4-sulfophenylamino]-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate (42, PSB-1011, IC₅₀ of 390 nM) and 1-amino-4-(3-carboxy-4-hydroxyphenylamino)-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate (33, PSB-2046, IC₅₀ of 723 nM). The best NTPDase2 inhibitor 20 showed a non-competitive inhibition type, while the NTPDase3 inhibitor 42 behaved as a mixed-type inhibitor. These potent compounds were found to be selective vs. other NTPDases. They will be useful tools for studying the roles of NTPDase2 and -3 in physiology and under pathological conditions.

Nonesterified free fatty acids enhance the inflammatory response in renal tubules by inducing extracellular ATP release

In proteinuric renal diseases, excessive plasma nonesterified free fatty acids bound to albumin can leak across damaged glomeruli to be reabsorbed by renal proximal tubular cells and cause inflammatory tubular cells damage by as yet unknown mechanisms. The present study was designed to investigate these mechanisms induced by palmitic acid (PA; one of the nonesterified free fatty acids) overload. Our results show that excess PA stimulates ATP release through the pannexin 1 channel in human renal tubule epithelial cells (HK-2), increasing extracellular ATP concentration approximately threefold compared with control. The ATP release is dependent on caspase-3/7 activation induced by mitochondrial reactive oxygen species. Furthermore, extracellular ATP aggravates PA-induced monocyte chemoattractant protein-1 secretion and monocyte infiltration of tubular cells, enlarging the inflammatory response in both macrophages and HK-2 cells via the purinergic P2X7 receptor-mammalian target of rapamycin-forkhead box O1-thioredoxin-interacting protein/NOD-like receptor protein 3 inflammasome pathway. Hence, PA increases mitochondrial reactive oxygen species-induced ATP release and inflammatory stress, which cause a "first hit," while ATP itself is a "second hit" in amplifying the renal tubular inflammatory response. Thus, inhibition of ATP release or the purinergic P2X7 receptor may be an approach to reduce renal inflammation and improve renal function.

Gap Junctions and Breast Cancer Dormancy

Breast cancer (BC) relapse, despite clinical advancement, remains one of the biggest issues in the field. Intercellular communication, specifically via connexin (Cx)-mediated gap junctions (GJs), play a key role in the long-term survival of these, treatment-resistant breast cancer stem cells (CSCs), allowing for relapse. Both basic and clinical evidence reveal dual roles for GJs, in tumor suppression, generally referred to as dormancy, and progression and metastasis. GJ intercellular communication (GJIC) can be mediated by multiple types of Cxs, depending on the organ to which the BC cells metastasize. This review expands on the differential expression of Cx-mediated GJIC between CSCs and niche cells within a given microenvironment.

Purinergic signaling and gene expression of purinoceptors in the head kidney of the silver catfish Rhamdia quelen experimentally infected by Flavobacterium columnare

The head kidney is a lymphoid immune organ that plays a key role in the immune and inflammatory responses of teleost fish. It is associated with immunoglobulin G production and differentiation of B cells. The presence of a multi-enzymatic complex found anchored in the plasma membrane makes the head kidney an important purinergic-dependent tissue. Purinergic signaling has been associated with these responses under pathological conditions via regulation of extracellular adenosine triphosphate (ATP), the main damage molecular associated pattern agent released during bacterial infections. The aim of this study was to determine whether purinergic signaling is a pathway associated with impairment of immune responses in silver catfish (Rhamdia quelen) experimentally infected by Flavobacterium columnare, as well as to evaluate the role of P2 purine receptors in this response. Triphosphate diphosphohydrolase (NTPDase) activity in the head kidney was significantly lower in silver catfish experimentally-infected F. columnare 72 h post-infection (hpi) than in the control group, while no significant difference was observed with respect NTPDase activity on adenosine diphosphate, as well as on 5'-nucleotidase and adenosine deaminase activities. Extracellular ATP levels were significantly higher in the head kidney of experimentally-infected fish than in the control group at 72 hpi. Finally, p2ry11 and p2rx3 purine receptor levels were significantly higher in experimentally-infected fish than in the control group at 72 hpi. We conclude that purinergic signaling in the head kidney of silver catfish infected by F. columnare creates a pro-inflammatory profile that may contribute to impairment of immune and inflammatory responses via reduction of ATP hydrolysis and its accumulation in the extracellular milieu, accompanied by upregulation of p2ry11 and p2rx3 purine receptors, leading to pro-inflammatory status.

ATP-Diphosphohydrolases in Parasites: Localization, Functions and Recent Developments in Drug Discovery

ATP-diphosphohydrolases (EC 3.6.1.5), also known as ATPDases, NTPases, NTPDases, EATPases or apyrases, are enzymes that hydrolyze a variety of nucleoside tri- and diphosphates to their respective nucleosides, being their activities dependent on the presence of divalent cations, such as calcium and magnesium. Recently, ATP-diphosphohydrolases were identified on the surface of several parasites, such as Trypanosoma sp, Leishmania sp and Schistosoma sp. In parasites, the activity of ATPdiphosphohydrolases has been associated with the purine recuperation and/or as a protective mechanism against the host organism under conditions that involve ATP or ADP, such as immune responses and platelet activation. These proteins have been suggested as possible targets for the development of new antiparasitic drugs. In this review, we will comprehensively address the main aspects of the location and function of ATP-diphosphohydrolase in parasites. Also, we performed a detailed research in scientific database of recent developments in new natural and synthetic inhibitors of the ATPdiphosphohydrolases in parasites.

Mesenchymal stem/stromal cells-derived IL-6 promotes nasopharyngeal carcinoma growth and resistance to cisplatin via upregulating CD73 expression

Previous studies have implicated the important role of mesenchymal stem/stromal cells (MSCs) within tumor microenvironment (TME) in the pathogenesis and progression of nasopharyngeal carcinoma (NPC), but the potential mechanisms are still unclear. Herein, we showed that an elevated IL-6 level was positively correlated with elevated expression of CD73 in TME of NPC. NPC specimens with an IL-6^highCD73^high phenotype showed higher expression levels of gp80, gp130, p-STAT3, MMP-9 and α-SMA, and clinically, a poorer prognosis than those with an IL-6^lowCD73^low phenotype. We found that stimulation with conditioned media derived from IL-6 gene knocked out MSC (MSC^IL6KO-CM) down-regulated the expression of CD73, IL-6, gp80, p-STAT3, and proliferative cell nuclear antigen (PCNA) in CNE-2 NPC cells. Meanwhile, NPC cells co-cultured with MSC^IL6KO-CM were more sensitive to cisplatin than those co-cultured with MSC-CM. Additionally, MSC-derived IL-6 transcriptionally upregulated CD73 expression via activating STAT3 signaling pathway in NPC cells. In summary, our findings suggest that MSCs promote NPC progression and chemoresistance by upregulation of CD73 expression via activating STAT3 signaling pathway.

Experimental listeriosis: A study of purinergic and cholinergic inflammatory pathway

The cholinergic, purinergic and oxidative stress systems were related to nervous system damage in some pathologies, as well as being involved in pro-inflammatory and anti-inflammatory pathways. The objective was to investigate changes in purinergic, cholinergic systems and oxidative stress related to the neuropathology of listeriosis. Gerbils were used as experimental models. The animals were divided in two groups: control and infected. The animals were orally infected with 5 × 10⁸ CFU/animal of the pathogenic strain of Listeria monocytogenes. Collected of material was 6 and 12th days post-infection (PI). Infected animals showed moderate mixed inflammatory infiltrates in the liver. The spleen and brain was used for PCR analyses, confirming infection by L. monocytogenes. Increase in number of total leukocytes because of an increase in lymphocytes in infected (P < 0.001). ATP and ADP hydrolysis by NTPDase was lower at 6 and 12th days PI in infected animals than in the control group. ADA (adenosine deaminase) activity was higher on the 6th day PI (P < 0.05) and decreased on the 12th day PI (P < 0.05) in infected animals. AChE (acetylcholinesterase) activity did not differ between groups on the 6th day PI; however, activity decreased in infected group on the 12th day PI (P < 0.05). On the 12th day PI, an increase of oxygen-reactive species levels and lower catalase and superoxide dismutase activities in the infected group was observed, characterizing a situation of cerebral oxidative stress. The inflammatory and oxidative mechanisms are present in listeriosis in asymptomatic animals, and that ectonucleotidases and cholinesterase's are involved in immunomodulation.

Chemotherapy-Induced Tumor Cell Death at the Crossroads Between Immunogenicity and Immunotolerance: Focus on Acute Myeloid Leukemia

In solid tumors and hematological malignancies, including acute myeloid leukemia, some chemotherapeutic agents, such as anthracyclines, have proven to activate an immune response via dendritic cell-based cross-priming of anti-tumor T lymphocytes. This process, known as immunogenic cell death, is characterized by a variety of tumor cell modifications, i.e., cell surface translocation of calreticulin, extracellular release of adenosine triphosphate and pro-inflammatory factors, such as high mobility group box 1 proteins. However, in addition to with immunogenic cell death, chemotherapy is known to induce inflammatory modifications within the tumor microenvironment, which may also elicit immunosuppressive pathways. In particular, DCs may be driven to acquire tolerogenic features, such as the overexpression of indoleamine 2,3-dioxygensase 1, which may ultimately hamper anti-tumor T-cells via the induction of T regulatory cells. The aim of this review is to summarize the current knowledge about the mechanisms and effects by which chemotherapy results in both activation and suppression of anti-tumor immune response. Indeed, a better understanding of the whole process underlying chemotherapy-induced alterations of the immunological tumor microenvironment has important clinical implications to fully exploit the immunogenic potential of anti-leukemia agents and tune their application.

Biomaterial-Based Metabolic Regulation in Regenerative Engineering

Recent advances in cell metabolism studies have deepened the appreciation of the role of metabolic regulation in influencing cell behavior during differentiation, angiogenesis, and immune response in the regenerative engineering scenarios. However, the understanding of whether the intracellular metabolic pathways could be influenced by material-derived cues remains limited, although it is now well appreciated that material cues modulate cell functions. Here, an overview of how the regulation of different aspect of cell metabolism, including energy homeostasis, oxygen homeostasis, and redox homeostasis could contribute to modulation of cell function is provided. Furthermore, recent evidence demonstrating how material cues, including the release of inherent metabolic factors (e.g., ions, regulatory metabolites, and oxygen), tuning of the biochemical cues (e.g., inherent antioxidant properties, cell adhesivity, and chemical composition of nanomaterials), and changing in biophysical cues (topography and surface stiffness), may impact cell metabolism toward modulated cell behavior are discussed. Based on the resurgence of interest in cell metabolism and metabolic regulation, further development of biomaterials enabling metabolic regulation toward dictating cell function is poised to have substantial implications for regenerative engineering.

CD73 Rather Than CD39 Is Mainly Involved in Controlling Purinergic Signaling in Calcified Aortic Valve Disease

The study aimed to compare composition of peripheral blood T-cell subsets and assess their surface expression of CD39 and CD73 ectonucleotidases in patients with severe and moderate aortic stenosis (AS) as well as to evaluate involvement of T-cell-mediated immune processes in valve calcification. The study was performed with 38 patients suffering from severe calcified aortic stenosis (SAS), 33 patients with MAS, and 30 apparently healthy volunteers (HVs). The relative distribution and percentage of T-cell subsets expressing CD39 and CD73 were evaluated by flow cytometry. T helper (Th) and cytotoxic T-cell subsets (Tcyt) were identified by using CD3, CD4, and CD8 antibodies. Regulatory T cells (Tregs) were characterized by the expression of CD3, CD4, and high IL-2R alpha chain (CD25high) levels. CD45R0 and CD62L were used to assess differentiation stage of Th, Tcyt, and Treg subsets. It was found that MAS and SAS patients differed in terms of relative distribution of Tcyt and absolute number of Treg. Moreover, the absolute number of Tcyt and terminally differentiated CD45RA-positive effector T-cells (TEMRA) subset was significantly higher in SAS vs. MAS patients and HVs. However, the absolute and relative number of naïve Th and the absolute number of Treg were significantly higher in MAS vs. SAS patients; the relative number of naïve Tregs was significantly (p < 0.01) decreased in SAS patients. It was shown that CD73 expression was significantly higher in SAS vs. MAS patients noted in all EM, CM, TEMRA, and naïve Th cell subsets. However, only the latter were significantly increased (p = 0.003) in patients compared with HVs. SAS vs. MAS patients were noted to have significantly higher percentage of CD73+ EM Tcyt (p = 0.006) and CD73+ CM Tcyt (p = 0.002). The expression of CD73 in patients significantly differed in all three Treg populations such as EM (p = 0.049), CM (p = 0.044), and naïve (p < 0.001). No significant differences in CD39 expression level was found in MAS and SAS patients compared with the HV group. Overall, the data obtained demonstrated that purinergic signaling was involved in the pathogenesis of aortic stenosis and calcification potentially acting via various cell types, wherein among enzymes, degrading extracellular ATP CD73 rather than CD39 played a prominent role.

Extracellular ATP activates P2X7R-NF-κB (p65) pathway to promote the maturation of bone marrow-derived dendritic cells of mice

The maturation state of dendritic cell (DC) plays an important role in immune activities. Previously we had found that NF-κB (p65) pathway could promote DC maturation and subsequent immune effects. But the upstream mechanism of this pathway was still unclear. Extracellular adenosine triphosphate (ATP) activating its receptor P2X7R has recently been considered as the fourth signal to activate T lymphocytes. Here we aimed to find out the connection between P2X7R and NF-κB (p65) pathway in DC maturation. Results showed that the expression of P2X7R and the intracellular ATP levels were increased along with the maturation of DC. P2X7R agonist stimulated the morphological changes of DCs into the appearance of mature DCs, and promoted the expression of NF-κB (p65), as well as the release of IFN-γ and IL-12. Whereas, P2X7R inhibitor had the opposite influences. Co-immunoprecipitation assay confirmed the binding of P2X7R and NF-κB (p65). Our study suggested that extracellular ATP could promote DC maturation and release of inflammatory cytokines through the binding of P2X7R and NF-κB (p65). This is the first study to show the P2X7R-NF-κB (p65) pathway in DC. Interference with this pathway may be able to regulate immune responses in areas like infectious diseases, inflammation, transplantation, tumor and autoimmune diseases. In addition, intracellular ATP level could be a new indicator of the maturation state of DC.

Extracellular nucleotides and nucleosides as signalling molecules

Extracellular nucleotides, mainly ATP, but also ADP, UTP, UDP and UDP-sugars, adenosine, and adenine base participate in the "purinergic signalling" pathway, an ubiquitous system of cell-to-cell communication. Fundamental pathophysiological processes such as tissue homeostasis, wound healing, neurodegeneration, immunity, inflammation and cancer are modulated by purinergic signalling. Nucleotides can be released from cells via unspecific or specific mechanisms. A non-regulated nucleotide release can occur from damaged or dying cells, whereas exocytotic granules, plasma membrane-derived microvesicles, membrane channels (connexins, pannexins, calcium homeostasis modulator (CALHM) channels and P2X7 receptor) or specific ATP binding cassette (ABC) transporters are involved in the controlled release. Four families of specific receptors, i.e. nucleotide P2X and P2Y receptors, adenosine P1 receptors, and the adenine-selective P0 receptor, and several ecto- nucleotidases are essential components of the "purinergic signalling" pathway. Thanks to the activity of ecto-nucleotidases, ATP (and possibly other nucleotides) are degraded into additional messenger molecules with specific action. The final biological effects depend on the type and amount of released nucleotides, their modification by ecto-nucleotidases, and their possible cellular re-uptake. Overall, these processes confer a remarkable level of selectivity and plasticity to purinergic signalling that makes this network one of the most relevant extracellular messenger systems in higher organisms.

Regulation of the Immune Response by the Inflammatory Metabolic Microenvironment in the Context of Allotransplantation

Antigen challenge induced by allotransplantation results in the activation of T and B cells, followed by their differentiation and proliferation to mount an effective immune response. Metabolic fitness has been shown to be crucial for supporting the major shift from quiescent to active immune cells and for tuning the immune response. Metabolic reprogramming includes regulation of the balance between glycolysis and mitochondrial respiration processes. Recent research has shed new light on the functions served by the end products of metabolism such as lactate, acetate, and ATP. At enhanced local concentrations, these metabolites have complex effects in which they not only induce T and B cell responses, cell mobility, and cytokine secretion but also favor the resolution of inflammation by promoting regulatory functions. Such mechanisms are instrumental in the context of the immune response in transplantation, not only to protect the graft and/or eliminate cells targeting it but also to maintain cell homeostasis per se. Metabolic adaptation thus plays an instrumental role on the outcome of the cellular and humoral responses. This, of course, raises the possibility of drugs that would interfere in these metabolic pathways to control the immune response but also highlights the risk that some drugs may perturb this metabolism and cell homeostasis and be deleterious for graft outcome. This review focuses on how metabolic alterations of the local immune microenvironment regulate the immune response and the impact of metabolic manipulation in allotransplantation.

The Emerging Link Between the Complement Cascade and Purinergic Signaling in Stress Hematopoiesis

Innate immunity plays an important role in orchestrating the immune response, and the complement cascade (ComC) is a major component of this ancient defense system, which is activated by the classical-, alternative-, or mannan-binding lectin (MBL) pathways. However, the MBL-dependent ComC-activation pathway has been somewhat underappreciated for many years; recent evidence indicates that it plays a crucial role in regulating the trafficking of hematopoietic stem/progenitor cells (HSPCs) by promoting their egress from bone marrow (BM) into peripheral blood (PB). This process is initiated by the release of danger-associated molecular patterns (DAMPs) from BM cells, including the most abundant member of this family, adenosine triphosphate (ATP). This nucleotide is well known as a ubiquitous intracellular molecular energy source, but when secreted becomes an important extracellular nucleotide signaling molecule and mediator of purinergic signaling. What is important for the topic of this review, ATP released from BM cells is recognized as a DAMP by MBL, and the MBL-dependent pathway of ComC activation induces a state of "sterile inflammation" in the BM microenvironment. This activation of the ComC by MBL leads to the release of several potent mediators, including the anaphylatoxins C5a and _desArgC5a, which are crucial for egress of HSPCs into the circulation. In parallel, as a ligand for purinergic receptors, ATP affects mobilization of HSPCs by activating other pro-mobilizing pathways. This emerging link between the release of ATP, which on the one hand is an activator of the MBL pathway of the ComC and on the other hand is a purinergic signaling molecule, will be discussed in this review. This mechanism plays an important role in triggering defense mechanisms in response to tissue/organ injury but may also have a negative impact by triggering autoimmune disorders, aging of HSPCs, induction of myelodysplasia, and graft-versus-host disease after transplantation of histoincompatible hematopoietic cells.

Effective Combination Adjuvants Engage Both TLR and Inflammasome Pathways To Promote Potent Adaptive Immune Responses

The involvement of innate receptors that recognize pathogen- and danger-associated molecular patterns is critical to programming an effective adaptive immune response to vaccination. The synthetic TLR4 agonist glucopyranosyl lipid adjuvant (GLA) synergizes with the squalene oil-in-water emulsion (SE) formulation to induce strong adaptive responses. Although TLR4 signaling through MyD88 and TIR domain-containing adapter inducing IFN-β are essential for GLA-SE activity, the mechanisms underlying the synergistic activity of GLA and SE are not fully understood. In this article, we demonstrate that the inflammasome activation and the subsequent release of IL-1β are central effectors of the action of GLA-SE, as infiltration of innate cells into the draining lymph nodes and production of IFN-γ are reduced in ASC^-/- animals. Importantly, the early proliferation of Ag-specific CD4⁺ T cells was completely ablated after immunization in ASC^-/- animals. Moreover, numbers of Ag-specific CD4⁺ T and B cells as well as production of IFN-γ, TNF-α, and IL-2 and Ab titers were considerably reduced in ASC^-/-, NLRP3^-/-, and IL-1R^-/- mice compared with wild-type mice and were completely ablated in TLR4^-/- animals. Also, extracellular ATP, a known trigger of the inflammasome, augments Ag-specific CD4⁺ T cell responses, as hydrolyzing it with apyrase diminished adaptive responses induced by GLA-SE. These data thus demonstrate that GLA-SE adjuvanticity acts through TLR4 signaling and NLRP3 inflammasome activation to promote robust Th1 and B cell responses to vaccine Ags. The findings suggest that engagement of both TLR and inflammasome activators may be a general paradigm for induction of robust CD4 T cell immunity with combination adjuvants such as GLA-SE.