Allergic sensitization increases the amount of extracellular ATP hydrolyzed by guinea pig leukocytes

Abstract

Increased levels of ATP have been found in the bronchoalveolar lavage of patients with asthma, and subjects with this disease, but not healthy subjects, develop bronchospasm after nebulization with ATP. Because the main mechanism for controlling the noxious effects of extracellular ATP is its enzymatic hydrolysis, we hypothesized that allergic sensitization is accompanied by a decreased functioning of such hydrolysis. In the present study, peripheral blood leukocytes from sensitized and non-sensitized guinea pigs were used for determining the extracellular metabolism (as assessed by inorganic phosphate production) of ATP, ADP, AMP, or adenosine, and for detecting possible changes in the expression (qPCR and Western blot) of major ectonucleotidases (NTPDase1, NTPDase3, and NPP1) and purinoceptors (P2X 1 , P2X 7 , P2Y 4 , and P2Y 6 ). Contrary to our hypothesis, we found that leukocytes from allergic animals produced higher amounts of inorganic phosphate after stimulation with ATP and ADP, as compared with leukocytes from non-sensitized animals. Although at first glance, this result suggested that sensitization caused higher efficiency of ectonucleotidases, their mRNA and protein expressions were unaffected. On the other hand, after sensitization, we found a significant increase in the protein expression of P2X 7 and P2Y 4 , two purinoceptors known to be responsible for ATP release after activation. We concluded that allergic sensitization increased the amount of ATP hydrolyzed by ectonucleotidases, the latter probably not due to the enhanced efficiency of its enzymatic breakdown, but rather due to an increased release of endogenous ATP or other nucleotides, partly mediated by enhanced expression or P2X 7 and P2Y 4 receptors.

Extracellular Adenosine Diphosphate Stimulates CXCL10-Mediated Mast Cell Infiltration Through P2Y1 Receptor to Aggravate Airway Inflammation in Asthmatic Mice

“…Initial experimental results revealed that the expression of extracellular ADP was relatively high in the BALF of patients with asthma and the expression of P2Y1 receptor was highly expressed in the lung tissues of asthmatic patients. Consistently, a previous study has also shown that the extracellular ATP level is increased in the BALF of patients with asthma ( Chavez et al, 2019 ). Another study demonstrated that extracellular ADP can activate NLRP3 inflammasome to aggravate microglial inflammation in combination with ATP by acting on the P2Y12 receptor ( Suzuki et al, 2020 ).…”

Enhancement of Mast Cell Degranulation Mediated by Purinergic Receptors’ Activation and PI3K Type δ

“…Physiological agonist/agonist receptor systems require a given nondegraded agonist present at its cognate receptor site. The sensitivity to purinergic agonists at PR sites is thus influenced by the expression and activity of ectonucleotidases on the cell surface (59,60). It follows that the "right" purinergic agonist at the "right" purinergic cell surface receptor in the "right" permissive ectonucleotidases environment must "line up" in aggregate to result in effective WAS-induced enhancement mediated by P2Y11R's activation in LAD2 cells.…”

Enhancement of Mast Cell Degranulation Mediated by Purinergic Receptor Activation and PI3K(δ)

“…The sensitivity to effects of purinergic agonists at purinergic receptor sites is thus influenced by the expression and activity of ectonucleotidases on cells' surface. 49,50 It follows that the "right" purinergic agonist at the "right" purinergic cell surface receptor in the "right" permissive ectonucleotidases environment must "line up" in aggregate to result in effective WAS enhancement in the case of P2Y11 and LAD2 cells. This also means that higher cell surface expression of ectonucleotidases (e.g.…”