Adenosine from a biologic source regulates neutrophil extracellular traps (NETs)

Abstract

Neutrophil extracellular traps (NETs) are implicated in autoimmune, thrombotic, malignant, and inflammatory diseases; however, little is known of their endogenous regulation under basal conditions. Inflammatory effects of neutrophils are modulated by extracellular purines such as adenosine (ADO) that is inhibitory or ATP that generally up‐regulates effector functions. In order to evaluate the effects of ADO on NETs, human neutrophils were isolated from peripheral venous blood from healthy donors and stimulated to make NETs. Treatment with ADO inhibited NET production as quantified by 2 methods: SYTOX green fluorescence and human neutrophil elastase (HNE)‐DNA ELISA assay. Specific ADO receptor agonist and antagonist were tested for their effects on NET production. The ADO 2A receptor (A2AR) agonist CSG21680 inhibited NETs to a similar degree as ADO, whereas the A2AR antagonist ZM241385 prevented ADO's NET‐inhibitory effects. Additionally, CD73 is a membrane bound ectonucleotidase expressed on mesenchymal stromal cells (MSCs) that allows manipulation of extracellular purines in tissues such as bone marrow. The effects of MSCs on NET formation were evaluated in coculture. MSCs reduced NET formation in a CD73‐dependent manner. These results imply that extracellular purine balance may locally regulate NETosis and may be actively modulated by stromal cells to maintain tissue homeostasis.

Adenosine Signaling in Autoimmune Disorders

“…Finally, A 3 ARs are involved in the formation and extension of filipodia-like projections in neutrophils, as shown by the selective agonist 2-chloro-N 6 -(3-iodobenzyl)-adenosine-5 -N-methyluronamide (Cl-IB-MECA), thus improving bacterial phagocytosis and chemotaxis [18]. Interestingly, Ado signaling is involved in the formation of the so-called Neutrophil Extracellular Traps (NETs), which are chromatin filaments coated with pro-inflammatory and effector molecules released by neutrophils into the extracellular space in response to inflammatory triggers [19]. NETs formation has the main role of containing pathogen spreading, but it has been also linked to autoimmune disorders, since their bioactive molecules can directly damage the extracellular matrix and amplify the immune response.…”

“…NETs formation has the main role of containing pathogen spreading, but it has been also linked to autoimmune disorders, since their bioactive molecules can directly damage the extracellular matrix and amplify the immune response. In this scenario, Ado has proven its ability to reduce NETs formation and the excessive so-called "NETosis", mostly via activation of A 2A ARs, thus contributing to down-regulate NET pro-inflammatory activity, and to counteract the development of autoimmunity [19].…”

The adenosinergic pathway in mesenchymal stem cell fate and functions

“…In their studies, Abbasi et al 210,211 showed that BM‐MSCs treated with caffeine at low to moderate concentrations promoted neutrophil survival, besides, to increase the phagocytosis and production of reactive oxygen species (ROS), when compared to MSCs not treated. Similarly, the CD73 inhibition in BM‐MSCs impairs the production of extracellular Ado and significantly reduces neutrophils' maturation and modulatory abilities 212 . Although these findings offer new insights into the immunomodulatory effects from MSCs through the adenosinergic pathway, the mechanism underlying these effects needs to be further clarified.…”

Candida Extracellular Nucleotide Metabolism Promotes Neutrophils Extracellular Traps Escape

“…The purinergic signaling system involves the release of ATP and adenosine to the extracellular milieu during cellular disturbances, both important controllers of the immune cell functions ( Burnstock and Verkhratsky, 2009 ; Antonioli et al., 2013 ; Virgilio and Vuerich, 2015 ; Cekic and Linden, 2016 ). In neutrophils, ATP induces neutrophil activation, but the accumulation of adenosine through extracellular ATP degradation can lead to considerable inhibitory and anti-inflammatory effects ( Antonioli et al., 2013 ; Xu et al., 2019 ). In addition, several studies reveal that this sequential dephosphorylation of ATP into adenosine (ATP > ADP > AMP > adenosine) is under control of ectonucleotidases, cell surface-located enzymes.…”