5-HT是调控thrombopoietin合成的调节子？

Thrombopoietin (TPO) is a major cytokine for megakaryopoiesis and platelet production. It is synthesized by liver, kidney and bone marrow stromal cells. However, how to regulate TPO production is still unclear. At present, it was found that liver and kidneys produce TPO consistently. And a proportion of total TPO is produced by stromal cells in the bone marrow and their TPO mRNA production is sensitive to factors produced by platelets and thus also linked to platelet number.   The mechanism of action remains unknown. Since serotonin (5-HT) can be released from the active platelets when the body undergoing bleeding or stress, it may functions as an essential hormonal mediator regulating TPO production...Here, we hypothesized that 5-HT exerts its effect through the binding of 5-HT 2 receptors, regulating TPO production in bone marrowl stromal cells (MSCs). In this study, we will test our hypothesis though three objectives:(1)To identify the expression of 5-HT2 receptors on MSCs of bone marrow;（2） To determine the role of 5-HT2 receptors and Erk1/2 signaling on TPO released from MSCs at mRNA and protein levels; (3)To investigate the impact of 5-HT on the production of TPO mRNA and protein contained within the MSCs –derived microparticles (MPs). Furthermore, the relationship between the plasma levels of 5-HT and TPO, and the expression of MSCs TPO mRNA of bone marrow in 5-HTR2b Knock-out mouse model will be studied...Results from this study may show that 5-HT stimulates TPO production from MSCs in both dissociative and MP-bounded form, which will help us to understand the physiological regulation of TPO production.

血小板生成素TPO生成调控是尚未解决的科学问题。目前认为肝肾产生TPO基本恒定，骨髓产生TPO可调节，但机制不清楚。我们基于对5-HT在调控巨核细胞系造血的原创性工作（Stem Cells，2007；2014）提出出血应激时血小板激活释出5-HT，作用于骨髓基质细胞（MSCs）5-HT2型受体，激活Erk1/2通路，在转录水平调控TPO生成之假说。本研究将验证：（1）MSCs表达5-HT2型受体，5-HT通过5-HT2型受体对MSCs发挥作用；（2）5-HT激活5-HT2受体和Erk1/2通路，在转录水平调节TPO合成；（3）5-HT促进微粒（MPs）释放和增加MPs中TPO含量。上述目标完成后，制作5-HTR2b Knock-out小鼠模型，进一步验证体外结果。本研究将证明血小板源性5-HT是否是TPO合成的调节子，为解答如何调控TPO的生成和指导临床使用TPO有重要的科学意义。

骨髓间充质细胞（MSCs）是骨髓造血微环境的重要组成部分，为血液细胞的生长和分化提供细胞支持和多种细胞因子。研究者认为，骨髓间充质细胞在外源性因素的影响下反馈调节骨髓TPO的合成和分泌，并且认为血小板分泌的因子可能参与了该调节过程。骨髓TPO的生成可能是由循环中血小板的某种感受机制触发的，但是具体机制仍不明确。循环中大部分的5-HT储存于血小板的致密颗粒中，血小板激活后会释放出大量的5-HT。有研究证实，5-HT既能促进巨核细胞的增殖和减少其凋亡，还能促进骨髓基质细胞成纤维细胞集落形成单位（CFU-F）的形成，其机制还不明确。5-HT对骨髓间充质细胞TPO的合成是否有影响，以及其机制是什么？因此，本研究提出假说：在创伤出血应激等情况下，血小板激活释放出5-HT，5-HT作用于微环境中骨髓间充质细胞，通过5-HT2受体，激活STAT3通路，增加TPO的生成。. 我们的研究发现，血小板来源的5-HT促进创伤性小鼠模型中TPO的产生；体外试验中，5-HT明显促进MSCs中TPO mRNA和蛋白的合成，其机制是通过5-HT2B受体，促进STAT3的磷酸化，并能够增加MSCs微粒的释放及微粒中TPO的含量。此外，我们证实5-HT通过FAK/Rho A/ROCK信号通路及调控F-actin重组调控微粒的释放。. 由于如何调节血小板生长因子 TPO 的产生是尚未解决的科学问题，希望本研究能够提供更多有助于解决该生理学问题的证据；5-HT是一种神经递质，目前的研究结果将有助于阐明神经系统可能通过神经递质在调节造血中的作用。