P2X₁-initiated p38 signalling enhances thromboxane A₂-induced platelet secretion and aggregation

Summary

ATP released by activated platelets can serve as a positive feedback machinery to amplify platelet responses by activating P2X₁ receptors. It has, however, not been defined how P2X₁ activities influence thromboxane A₂ (TXA₂)-stimulated platelet functional responses. Our aim was to elaborate the molecular mechanisms of P2X₁ engagements in TXA₂-induced platelet secretion and aggregation. P2X₁ inhibition by 1 µM NF449 inhibited platelet P-selectin expression induced by a low concentration of the TXA₂ analogue U46619 (0.3 µM) (32.0 ± 2.0% vs 43.4 ± 3.0%; n=5; p<0.05). p38 inhibition by SB203580, but not ERK inhibition by U0126, elicited a similar inhibition by NF499. The combination of NF449 and SB203580 provided, however, no additive effects. U46619-induced platelet aggregation was similarly decreased by NF449 and SB203580 alone or incombination, and by P2×1 pre-desensitisation with α,β-Me-ATP. U46619 caused rapid and reversible P2×1-dependent p38 phosphorylation. However, the P2X₁-p38 pathway mainly enhanced mild platelet activation by U46619, because α,β-Me-ATP supplementation or p38 blockade had no effect on intense platelet activation induced by a higher concentration of U46619 (3 µM). In conclusion, P2×1 activation, via p38 signalling, potentiates platelet activation initiated by low doses of U46619. Hence, the P2X₁-induced p38 signalling promotes more robust platelet activation in response to mild platelet stimuli.

Keywords

Platelets - ATP - P2X₁ - p38 - thromboxane A₂

^* These authors contributed equally to the study.

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