Early tyrosine phosphorylation events following adenosine A2A receptor in human neutrophils: identification of regulated pathways

Adenosine A2A receptor as a potential regulator of Mycobacterium leprae survival mechanisms: new insights into leprosy neural damage

Background

Leprosy is a chronic infectious disease caused by Mycobacterium leprae, which can lead to a disabling neurodegenerative condition. M. leprae preferentially infects skin macrophages and Schwann cells-glial cells of the peripheral nervous system. The infection modifies the host cell lipid metabolism, subverting it in favor of the formation of cholesterol-rich lipid droplets (LD) that are essential for bacterial survival. Although researchers have made progress in understanding leprosy pathogenesis, many aspects of the molecular and cellular mechanisms of host-pathogen interaction still require clarification. The purinergic system utilizes extracellular ATP and adenosine as critical signaling molecules and plays several roles in pathophysiological processes. Furthermore, nucleoside surface receptors such as the adenosine receptor A2AR involved in neuroimmune response, lipid metabolism, and neuron-glia interaction are targets for the treatment of different diseases. Despite the importance of this system, nothing has been described about its role in leprosy, particularly adenosinergic signaling (AdoS) during M. leprae-Schwann cell interaction.

Methods

M. leprae was purified from the hind footpad of athymic nu/nu mice. ST88-14 human cells were infected with M. leprae in the presence or absence of specific agonists or antagonists of AdoS. Enzymatic activity assays, fluorescence microscopy, Western blotting, and RT-qPCR analysis were performed. M. leprae viability was investigated by RT-qPCR, and cytokines were evaluated by enzyme-linked immunosorbent assay.

Results

We demonstrated that M. leprae-infected Schwann cells upregulated CD73 and ADA and downregulated A2AR expression and the phosphorylation of the transcription factor CREB (p-CREB). On the other hand, activation of A2AR with its selective agonist, CGS21680, resulted in: 1) reduced lipid droplets accumulation and pro-lipogenic gene expression; 2) reduced production of IL-6 and IL-8; 3) reduced intracellular M. leprae viability; 4) increased levels of p-CREB.

Conclusion

These findings suggest the involvement of the AdoS in leprosy neuropathogenesis and support the idea that M. leprae, by downmodulating the expression and activity of A2AR in Schwann cells, decreases A2AR downstream signaling, contributing to the maintenance of LD accumulation and intracellular viability of the bacillus.

Adenosine A2A Receptor Agonist, Polydeoxyribonucleotide Treatment Improves Locomotor Function and Thermal Hyperalgesia Following Neuropathic Pain in Rats

PURPOSE

Lithotomy position has been widely used in the various urologic surgery. Occasionally sensory and motor problems of the lower extremities are occurred due to the lithotomy position and these deficits may be related with sciatic nerve injury (SNI). Inflammatory process is a factor to induce functional impairment after SNI. Therefore, we evaluated the role of adenosine A2A receptor agonists, polydeoxyribonucleotide (PDRN) showing anti-inflammatory effect on locomotor function following SNI in rats.

METHODS

Sciatic nerve was compressed with surgical clips for 1 minute after exposing of right sciatic nerve. After 3 days of SNI, PDRN (2, 4, and 8 mg/kg) was applied to the damaged area of sciatic nerve once daily for 10 days. Walking track analysis was conducted for locomotor function and plantar test was performed for thermal pain sensitivity. Level of cyclic adenosine-3´,5´-monophosphate (cAMP) were measured using enzyme-linked immunosorbent assay. Western blot analysis was performed for tumor necrosis factor (TNF)-α, interleukin (IL)-1β, cAMP response element binding protein (CREP), vascular endothelial growth factor (VEGF). Immunofluorescence for neurofilament was also conducted.

RESULTS

Locomotor function was decreased and thermal pain sensitivity was increased by SNI. SNI enhanced proinflammatory cytokines' production, such as TNF-α and IL-1β, while suppressed CREP phosphorylation and cAMP level. SNI also reduced the expression of VEGF and neurofilaments. However, treatment with PDRN inhibited proinflammatory cytokines' production and upregulated CREP phosphorylation and cAMP expression. PDRN also enhanced the expression of VEGF and neurofilaments. As a result, PDRN improved locomotor function and alleviated thermal hyperalgesia after SNI.

CONCLUSION

PDRN has shown potential to be used as an effective treatment for neuropathic pain.

Adenosine receptor signalling in Alzheimer’s disease

Alzheimer’s disease (AD) is the most common dementia in the elderly and its increasing prevalence presents treatment challenges. Despite a better understanding of the disease, the current mainstay of treatment cannot modify pathogenesis or effectively address the associated cognitive and memory deficits. Emerging evidence suggests adenosine G protein-coupled receptors (GPCRs) are promising therapeutic targets for Alzheimer’s disease. The adenosine A₁ and A_2A receptors are expressed in the human brain and have a proposed involvement in the pathogenesis of dementia. Targeting these receptors preclinically can mitigate pathogenic β-amyloid and tau neurotoxicity whilst improving cognition and memory. In this review, we provide an accessible summary of the literature on Alzheimer’s disease and the therapeutic potential of A₁ and A_2A receptors. Although there are no available medicines targeting these receptors approved for treating dementia, we provide insights into some novel strategies, including allosterism and the targeting of oligomers, which may increase drug discovery success and enhance the therapeutic response.

Roflupram attenuates α-synuclein-induced cytotoxicity and promotes the mitochondrial translocation of Parkin in SH-SY5Y cells overexpressing A53T mutant α-synuclein

We have previously shown that inhibition of cAMP-specific 3',5'-cyclic phosphodiesterase 4 (PDE4) protects against cellular toxicity in neuronal cells. Since α-synuclein (α-syn) toxicity contributes to the neurodegeneration of Parkinson's disease (PD). The aim of this study was to explore the effects and mechanisms of PDE4 on α-syn-induced neuronal toxicity. Using mutant human A53T α-syn overexpressed SH-SY5Y cells, we found that PDE4B knockdown reduced cellular apoptosis. Roflupram (ROF, 20 μM), a selective PDE4 inhibitor, produced similar protective effects and restored the morphological alterations of mitochondria. Mechanistic studies identified that α-syn enhanced the phosphorylation of Parkin at Ser131, followed by the decreased mitochondrial translocation of Parkin. Whereas both PDE4B knockdown and PDE4 inhibition by ROF blocked the effects of α-syn on Parkin phosphorylation and mitochondrial translocation. Moreover, PDE4 inhibition reversed the increase in the phosphorylation of p38 mitogen-activated protein kinase (MAPK) induced by α-syn. ROF treatment also reduced the binding of p38 MAPK to Parkin. Consistently, overexpression of PDE4B blocked the roles of ROF on p38 MAPK phosphorylation, Parkin phosphorylation, and the subsequent mitochondrial translocation of parkin. Furthermore, PDE4B overexpression attenuated the protective role of ROF, as evidenced by reduced mitochondria membrane potential and increased cellular apoptosis. Interestingly, ROF failed to suppress α-syn-induced cytotoxicity in the presence of a protein kinase A (PKA) inhibitor H-89. Our findings indicate that PDE4 facilitates α-syn-induced cytotoxicity via the PKA/p38 MAPK/Parkin pathway in SH-SY5Y cells overexpressing A53T mutant α-synuclein. PDE4 inhibition by ROF is a promising strategy for the prevention and treatment of α-syn-induced neurodegeneration.

Adenosine and Inflammation: Here, There and Everywhere

Adenosine is a ubiquitous endogenous modulator with the main function of maintaining cellular and tissue homeostasis in pathological and stress conditions. It exerts its effect through the interaction with four G protein-coupled receptor (GPCR) subtypes referred as A1, A2A, A2B, and A3 adenosine receptors (ARs), each of which has a unique pharmacological profile and tissue distribution. Adenosine is a potent modulator of inflammation, and for this reason the adenosinergic system represents an excellent pharmacological target for the myriad of diseases in which inflammation represents a cause, a pathogenetic mechanism, a consequence, a manifestation, or a protective factor. The omnipresence of ARs in every cell of the immune system as well as in almost all cells in the body represents both an opportunity and an obstacle to the clinical use of AR ligands. This review offers an overview of the cardinal role of adenosine in the modulation of inflammation, showing how the stimulation or blocking of its receptors or agents capable of regulating its extracellular concentration can represent promising therapeutic strategies for the treatment of chronic inflammatory pathologies, neurodegenerative diseases, and cancer.

Dual Actions of A2A and A3 Adenosine Receptor Ligand Prevents Obstruction-Induced Kidney Fibrosis in Mice

Kidney fibrosis is the final outcome of chronic kidney disease (CKD). Adenosine plays a significant role in protection against cellular damage by activating four subtypes of adenosine receptors (ARs), A₁AR, A_2AAR, A_2BAR, and A₃AR. A_2AAR agonists protect against inflammation, and A₃AR antagonists effectively inhibit the formation of fibrosis. Here, we showed for the first time that LJ-4459, a newly synthesized dual-acting ligand that is an A_2AAR agonist and an A₃AR antagonist, prevents the progression of tubulointerstitial fibrosis. Unilateral ureteral obstruction (UUO) surgery was performed on 6-week-old male C57BL/6 mice. LJ-4459 (1 and 10 mg/kg) was orally administered for 7 days, started at 1 day before UUO surgery. Pretreatment with LJ-4459 improved kidney morphology and prevented the progression of tubular injury as shown by decreases in urinary kidney injury molecular-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL) excretion. Obstruction-induced tubulointerstitial fibrosis was attenuated by LJ-4459, as shown by a decrease in fibrotic protein expression in the kidney. LJ-4459 also inhibited inflammation and oxidative stress in the obstructed kidney, with reduced macrophage infiltration, reduced levels of pro-inflammatory cytokines, as well as reduced levels of reactive oxygen species (ROS). These data demonstrate that LJ-4459 has potential as a therapeutic agent against the progression of tubulointerstitial fibrosis.

Adenosine A2A receptor agonist polydeoxyribonucleotide ameliorates short-term memory impairment by suppressing cerebral ischemia-induced inflammation via MAPK pathway

Cerebral ischemia causes tissue death owing to occlusion of the cerebral blood vessels, and cerebral ischemia activates mitogen-activated protein kinase (MAPK) and induces secretion of pro-inflammatory cytokines. Adenosine A2A receptor agonist, polydeoxyribonucleotide (PDRN), suppresses the secretion of pro-inflammatory cytokines and exhibits anti-inflammatory effect. In the current study, the therapeutic effect of PDRN on cerebral ischemia was evaluated using gerbils. For the induction of cerebral ischemia, the common carotid arteries were exposed, and then aneurysm clips were used to occlude the common carotid arteries bilaterally for 7 minutes. In the PDRN-treated groups, the gerbils were injected intraperitoneally with 0.3 mL of saline containing 8 mg/kg PDRN, per a day for 7 days following cerebral ischemia induction. In order to confirm the participation of the adenosine A2A receptor in the effects mediated by PDRN, 8 mg/kg 7-dimethyl-1-propargylxanthine (DMPX), adenosine A2A receptor antagonist, was treated with PDRN. In the current study, induction of ischemia enhanced the levels of pro-inflammatory cytokines and increased phosphorylation of MAPK signaling factors in the hippocampus and basolateral amygdala. However, treatment with PDRN ameliorated short-term memory impairment by suppressing the production of pro-inflammatory cytokines and inactivation of MAPK signaling factors in cerebral ischemia. Furthermore, PDRN treatment enhanced the concentration of cyclic adenosine-3,5'-monophosphate (cAMP) as well as phosphorylation of cAMP response element-binding protein (p-CREB). Co-treatment of DMPX and PDRN attenuated the therapeutic effect of PDRN on cerebral ischemia. Based on these findings, PDRN may be developed as the primary treatment in cerebral ischemia.

Adenosine A2A Receptor Agonist Polydeoxyribonucleotide Alleviates Interstitial Cystitis-Induced Voiding Dysfunction by Suppressing Inflammation and Apoptosis in Rats

Background

Interstitial cystitis (IC) is a chronic disorder that indicates bladder-related pain or discomfort. Patients with IC often experience urination problems, such as urinary frequency and urgency, along with pain or discomfort in the bladder area. Therefore, new treatments based on IC etiology are needed. Polydeoxyribonucleotide (PDRN) is a biologic agonist of the adenosine A_2A receptor, and PDRN has anti-inflammatory effect and inhibits apoptosis. In the current study, the effect of PDRN on cyclophosphamide-induced IC animal model was investigated using rats.

Methodology

To induce the IC animal model, 75 mg/kg of cyclophosphamide was injected intraperitoneally once every 3 days for 10 days. The rats in the PDRN-treated groups were intraperitoneally injected with 0.5 mL physiological saline containing 8 mg/kg PDRN, once a day for 10 days after IC induction.

Results

Induction of IC by cyclophosphamide injection caused voiding dysfunction, bladder edema, and histological damage. Cyclophosphamide injection increased secretion of pro-inflammatory cytokines and enhanced apoptosis. In contrast, PDRN treatment alleviated voiding dysfunction, bladder edema, and histological damage. Secretion of pro-inflammatory cytokines and expressions of apoptotic factors were suppressed by PDRN treatment. These changes indicate that treatment with PDRN improves voiding function by ultimately promoting the repair of damaged bladder tissue.

Conclusion

The conclusion of this experiment suggests the possibility that PDRN could be used as an effective therapeutic agent for IC.

Polydeoxyribonucleotide Exerts Protective Effect Against CCl4-Induced Acute Liver Injury Through Inactivation of NF-κB/MAPK Signaling Pathway in Mice

Acute liver injury (ALI) causes life-threatening clinical problem, and its underlying etiology includes inflammation and apoptosis. An adenosine A_2A receptor agonist, polydeoxyribonucleotide (PDRN), exhibits anti-inflammatory and anti-apoptotic effects by inhibiting the secretion of pro-inflammatory cytokines. In the current study, the protective effect of PDRN against carbon tetrachloride (CCl₄)-induced ALI was investigated using mice. For the induction of ALI, mice received intraperitoneal injection of CCl₄ twice over seven days. Mice from the PDRN-treated groups received an intraperitoneal injection of 200 μL saline containing PDRN (8 mg/kg), once a day for seven days, starting on day 1 after the first CCl₄ injection. In order to confirm that the action of PDRN occurs through the adenosine A_2A receptor, 8 mg/kg 3,7-dimethyl-1-propargylxanthine (DMPX), an adenosine A_2A receptor antagonist, was treated with PDRN. Administration of CCl₄ impaired liver tissue and increased the liver index and histopathologic score. The expression of pro-inflammatory cytokines was increased, and apoptosis was induced by the administration of CCl₄. Administration of CCl₄ activated nuclear factor-kappa B (NF-κB) and facilitated phosphorylation of signaling factors in mitogen-activated protein kinase (MAPK). In contrast, PDRN treatment suppressed the secretion of pro-inflammatory cytokines and inhibited apoptosis. PDRN treatment inactivated NF-κB and suppressed phosphorylation of signaling factors in MAPK. As a result, liver index and histopathologic score were reduced by PDRN treatment. When PDRN was treated with DMPX, the anti-inflammatory and anti-apoptotic effect of PDRN disappeared. Therefore, PDRN can be used as an effective therapeutic agent for acute liver damage.

Adenosine-Induced NLRP11 in B Lymphoblasts Suppresses Human CD4+ T Helper Cell Responses

NLRP11 is a member of the PYD domain-containing, nucleotide-binding oligomerization-domain (NOD-) like receptor (NLR) family. The true stimulus of NLRP11 is still unclear to date, so the current study is built upon NLRP11 induction via adenosine stimulation and that activation can shape adaptive immune responses in a caspase-1-independent manner. We examined the regulation and mechanism of adenosine responsiveness via NLRP11 in human Daudi Burkitt's B lymphoma cells and their effects on human peripheral CD4⁺ T lymphocytes from healthy individuals. NLRP11 was significantly upregulated after induction with adenosine at both the mRNA and protein levels, which led to the interaction of endogenous NLRP11 with the ASC adaptor protein; however, this interaction did not result in the activation of the caspase-1 enzyme. Furthermore, cocultures of NLRP11-expressing Burkitt's lymphoma cells and naïve human peripheral CD4⁺ T lymphocytes had reduced IFN-γ and IL-17A production, whereas IL-13 and IL-10 cytokines did not change. Interestingly, IFN-γ and IL-17A were recovered after transfection of Burkitt's lymphoma cells with siRNAs targeting NLRP11. Concomitant with NLRP11 upregulation, we also exhibited that adenosine A_2B receptor signaling induced two phosphorylated downstream effectors, pErk1/2 and pAkt (Ser473), but not pAkt (Thr308). Taken together, our data indicate that adenosine is a negative regulator of Th1 and Th17 responses via NLRP11 in an inflammasome-independent manner.

Adenosine Receptors in Modulation of Central Nervous System Disorders

The ubiquitous signaling nucleoside molecule, adenosine is found in different cells of the human body to provide its numerous pharmacological role. The associated actions of endogenous adenosine are largely dependent on conformational change of the widely expressed heterodimeric G-protein-coupled A1, A2A, A2B, and A3 adenosine receptors (ARs). These receptors are well conserved on the surface of specific cells, where potent neuromodulatory properties of this bioactive molecule reflected by its easy passage through the rigid blood-brainbarrier, to simultaneously act on the central nervous system (CNS). The minimal concentration of adenosine in body fluids (30-300 nM) is adequate to exert its neuromodulatory action in the CNS, whereas the modulatory effect of adenosine on ARs is the consequence of several neurodegenerative diseases. Modulatory action concerning the activation of such receptors in the CNS could be facilitated towards neuroprotective action against such CNS disorders. Our aim herein is to discuss briefly pathophysiological roles of adenosine on ARs in the modulation of different CNS disorders, which could be focused towards the identification of potential drug targets in recovering accompanying CNS disorders. Researches with active components with AR modulatory action have been extended and already reached to the bedside of the patients through clinical research in the improvement of CNS disorders. Therefore, this review consist of recent findings in literatures concerning the impact of ARs on diverse CNS disease pathways with the possible relevance to neurodegeneration.

Polydeoxyribonucleotide ameliorates lipopolysaccharide-induced acute lung injury via modulation of the MAPK/NF-κB signaling pathway in rats

Acute lung injury (ALI) is characterized by disruption of the alveolar-capillary membrane resulting in pulmonary edema and accumulation of associated proteinaceous alveolar exudate. Initiation of ALI upregulates tumor necrosis factor-α (TNF-α), which activates nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinases (MAPK) that induce various pro-inflammatory mediators. Polydexyribonucleotide (PDRN) is an adenosine A_2A receptor agonist that exerts anti-inflammatory effects by suppressing the production of pro-inflammatory cytokines and apoptosis. We investigated the therapeutic efficiency of PDRN on ALI induced by lipopolysaccharide (LPS) in rats. ALI was induced by intratracheal instillation of LPS (5 mg/kg) in 200 μL saline. The PDRN treatment group received a single intraperitoneal injection of 500 μL saline including PDRN (8 mg/kg) 1 h after ALI induction. To confirm the involvement of the adenosine A_2A receptor in PDRN, 8 mg/kg 7-dimethyl-1-propargylxanthine (DMPX) was applied with PDRN treatment. Rats were then sacrificed 12 h after PDRN and DMPX treatments. Intratracheal administration of LPS caused lung tissue damage and significantly increased the lung injury scores and levels of pro-inflammatory cytokines, and apoptotic factors. In addition, MAPK/NF-κB signaling factors were increased by ALI initiation. PDRN treatment potently suppressed expressions of MAPK/NF-κB signaling factors compared to the PDRN + DMPX co-treated group. These alterations led to a reduction of pro-inflammatory cytokines, apoptotic factors, and NF-κB and MAPK signaling, which promoted the recovery of damaged lung tissue. PDRN therapy demonstrated therapeutic effects for LPS-induced ALI compared to the non-treated and DMPX-treated groups. Therefore, PDRN may be used as a therapy for initial treatment of ALI.

Evaluating the mucoprotective effect of polydeoxyribonucleotide against indomethacin-induced gastropathy via the MAPK/NF-κB signaling pathway in rats

Non-steroidal anti-inflammatory drugs (NSAIDs) cause gastric mucosal damage and gastric ulceration. Among the most commonly used NSAIDs, indomethacin upregulates mucosal tumor necrosis factor-α, which activates nuclear factor-kappa B (NF-κB), and mitogen-activated protein kinases (MAPK) to induce various pro-inflammatory mediators. Polydeoxyribonucleotide (PDRN) is an adenosine A_2A receptor agonist that exerts anti-inflammatory effects. In this study, we evaluated the efficacy of PDRN in the initial treatment of gastropathy against that of ecabet sodium and irsoglandin maleate, which are commonly used medications. The rats were administrated indomethacin once a day for 7 days after 24 h of fasting to induce gastropathy. Rats in the drug-treated groups were orally administrated 500 μl of distilled water containing the drug once daily for 7 days 1 h after indomethacin administration. Indomethacin administration caused mucosal damage and increased pro-inflammatory cytokine release. Both NF-κB and MAPK cascade factors were increased by indomethacin administration. PDRN therapy more potently suppressed the expressions of NF-κB and MAPK cascade factors compared to other drugs. The expression of cyclic adenosine-3',5'-monophosphate was also increased by PDRN treatment in the indomethacin-induced gastropathy rats. These changes led to a reduction in pro-inflammatory cytokines and apoptotic factors, which ultimately promote recovery of damaged gastric tissue. Therefore, PDRN may serve as a new therapeutic option in the initial treatment of NSAIDs-induced gastropathy.

PET Imaging of Adenosine Receptors in Diseases

Adenosine receptors (ARs) are a class of purinergic G-protein-coupled receptors (GPCRs). Extracellular adenosine is a pivotal regulation molecule that adjusts physiological function through the interaction with four ARs: A1R, A2AR, A2BR, and A3R. Alterations of ARs function and expression have been studied in neurological diseases (epilepsy, Alzheimer's disease, and Parkinson's disease), cardiovascular diseases, cancer, and inflammation and autoimmune diseases. A series of Positron Emission Tomography (PET) probes for imaging ARs have been developed. The PET imaging probes have provided valuable information for diagnosis and therapy of diseases related to alterations of ARs expression. This review presents a concise overview of various ARs-targeted radioligands for PET imaging in diseases. The most recent advances in PET imaging studies by using ARs-targeted probes are briefly summarized.

Adenosine signaling and the immune system: When a lot could be too much

Adenosine is increasingly recognized as a key mediator of the immune response. Signals delivered by extracellular adenosine are detected and transduced by G-protein-coupled cell-surface receptors, classified into four subtypes: A₁, A_2A, A_2B and A₃. These receptors, expressed virtually on all immune cells, modulate all aspects of immune/inflammatory responses. These immunoregulatory effects, which are mostly anti-inflammatory, contribute to the general tissue protective effects of adenosine and its receptors. In some instances, however, the effect of adenosine on the immune system is deleterious, as prolonged adenosine signaling can hinder anti-tumor and antibacterial immunity, thereby promoting cancer development and progression and sepsis, respectively.

A novel combination of astilbin and low-dose methotrexate respectively targeting A2AAR and its ligand adenosine for the treatment of collagen-induced arthritis

Methotrexate (MTX) is widely used for rheumatoid arthritis (RA) treatment with frequently serious adverse effects. Therefore, combination of low-dose MTX with other drugs is often used in clinic. In this study, we investigated the improvement of astilbin and low-dose MTX combination on collagen-induced arthritis in DBA/1J mice. Results showed that the clinic score, incidence rate, paw swelling, pathological changes of joints and rheumatoid factors were more alleviated in combination therapy than MTX or astilbin alone group. Elevated antibodies (IgG, IgG1, IgG2a, IgM and anti-collagen IgG) and pro-inflammatory cytokines (IL-1β, IL-6, TNF-α, IFN-γ and IL-17A) in serum were significantly inhibited, while anti-inflammatory cytokine, IL-10, was enhanced by combination therapy. Further studies indicated that combination therapy significantly decreased Th1 and Th17 cell differentiation and increased Treg cell differentiation. Mechanisms analysis demonstrated combination therapy greatly inhibited Con A-activated MAPK and inflammatory transcriptional signals. Moreover, MTX activated adenosine release and astilbin specifically up-regulated A_2A adenosine receptor (A_2AAR) expression simultaneously, which most probably contributed to the synergistic efficacy of combination therapy. ZM241385, a specific antagonist of A_2AAR, greatly blocked the effects of combination therapy on T cell functions and downstream pathways. All these findings suggest that astilbin is a valuable candidate for low-dose MTX combined therapy in RA via increasing A_2AAR/adenosine system and decreasing ERK/NFκB/STATs signals.

Role of negative regulation of immune signaling pathways in neutrophil function

Polymorphonuclear neutrophils (PMNs) play a critical role in host defense against infection and in the resolution of inflammation. However, immune responses mediated by PMN must be tightly regulated to facilitate elimination of invading pathogens without inducing detrimental inflammation and host tissue damage. Specific engagement of cell surface immunoreceptors by a diverse range of extracellular signals regulates PMN effector functions through differential activation of intracellular signaling cascades. Although mechanisms of PMN activation mediated via cell signaling pathways have been well described, less is known about negative regulation of PMN function by immune signaling cascades. Here, we provide an overview of immunoreceptor-mediated negative regulation of key PMN effector functions including maturation, migration, phagocytosis, reactive oxygen species release, degranulation, apoptosis, and NET formation. Increased understanding of mechanisms of suppression of PMN effector functions may point to possible future therapeutic targets for the amelioration of PMN-mediated autoimmune and inflammatory diseases.