The Expression of Functional Dopamine and Serotonin Receptors on Megakaryocytes

Monoamine dopamine (DA) and serotonin (5-HT) can affect the functions of many cells including platelets. Our previous studies have shown that 5-HT has potent effects on promoting megakaryopoiesis and platelet formation (Yang et al, Stem Cells, 2007; 2014). In this study, our hypothesis is that both DA and 5-HT receptors may have the development expression on platelets, megakaryocytes (MK) and hematopoietic stem cells (HSCs). The expression of DA receptors: DA1, DA2 and 5-HT receptors: 5-HT2A, 2B and 2C on these hematopoietic cells, and the effect of DA and 5-HT on the cell proliferation and apoptosis were investigated using RT-PCR, flow cytometry, immunofluorescence staining, annexin V, JC-1 and caspase-3 assay. Our results showed that dopamine DA1, DA2 receptors, 5-HT2A, 2B and 2C receptors were identified on human platelets, MK and HSCs using RT-PCR method. Using flow cytometry with monoclonal antibodies, these receptors were also identified on human platelets and MK. But these receptors expressed on human HSCs at a low levels. The expression of the five receptors were further confirmed on human bone marrow MK and HSC by using immunofluorescence staining. The functions of receptors were further studied in human MK and HSCs. DA at a low dose induced cell differention, but at a high dose induced cell apoptosis. This effect could be reduced by DA2 receptor blocker L-Sulpiride (L-SULP). In the other hand, 5-HT had an anti-apoptotic effect in MK cells. 5-HT also stimulated CFU-MK formation, this effect was reduced by 5-HT2R antagonist ketanserin. 5-HT also enhanced Akt phosphorylation, while addition of ketanserin compromised the 5-HT effect. 5-HT-driven MK effect was likely mediated via 5-HT2R and p-Akt. A higher number of proplatelet bearing MK was also detected in 5-HT-treated. Polymerization F-actin level was higher in 5-HT group. Adding ketanserin/PD98059, the intensity was reduced. Treated with 5-HT for 30 minutes ERK1/2 was activated. The adding of ketanserin/PD98059 to 5-HT cultures nullified the 5-HT effect. This effect was likely mediated via 5HT2R, p-ERK1/2, which leads to F-actin reorganization and proplatelet formation. This study demonstrated that the expression of DA and 5-HT functional receptors on human platelets, MKs and HSCs. DA and 5-HT may be involved in the regulation of thrombopoiesis.