Constitutively released adenosine diphosphate regulates proplatelet formation by human megakaryocytes.

BACKGROUND: The interaction of adenosine diphosphate with its P2Y(1) and P2Y(12) receptors on platelets is important for platelet function. However, nothing is known about adenosine diphosphate and its function in human megakaryocytes. DESIGN AND METHODS: We studied the role of adenosine diphosphate and P2Y receptors on proplatelet formation by human megakaryocytes in culture. RESULTS: Megakaryocytes expressed all the known eight subtypes of P2Y receptors, and constitutively released adenosine diphosphate. Proplatelet formation was inhibited by the adenosine diphosphate scavengers apyrase and CP/CPK by 60-70% and by the P2Y(12) inhibitors cangrelor and 2-MeSAMP by 50-60%, but was not inhibited by the P2Y(1) inhibitor MRS 2179. However, the active metabolites of the anti-P2Y(12) drugs, clopidogrel and prasugrel, did not inhibit proplatelet formation. Since cangrelor and 2-MeSAMP also interact with P2Y(13), we hypothesized that P2Y(13), rather than P2Y(12) is involved in adenosine diphosphate-regulated proplatelet formation. The specific P2Y(13) inhibitor MRS 2211 inhibited proplatelet formation in a concentration-dependent manner. Megakaryocytes from a patient with severe congenital P2Y(12) deficiency showed normal proplatelet formation, which was inhibited by apyrase, cangrelor or MRS 2211 by 50-60%. The platelet count of patients with congenital delta-storage pool deficiency, who lack secretable adenosine diphosphate, was significantly lower than that of patients with other platelet function disorders, confirming the important role of secretable adenosine diphosphate in platelet formation. CONCLUSIONS: This is the first demonstration that adenosine diphosphate released by megakaryocytes regulates their function by interacting with P2Y(13). The clinical relevance of this not previously described physiological role of adenosine diphosphate and P2Y(13) requires further exploration.