Manufacturing Flagship, Commonwealth Scientific and Industrial Research Organization, Melbourne, Victoria, Australia.
Australian Regenerative Medicine Institute, Monash University, Melbourne, Australia.
Stem Cells. 2015 Jul;33(7):2351-7. doi: 10.1002/stem.2038. Epub 2015 May 15.
Factor V (FV) and factor X (FX) activate and complex to form prothrombinase which subsequently cleaves prothrombin (PT), converting it to active thrombin. Thrombin cleaved osteopontin (tcOPN) contains a cryptic binding site for α4 β1 and α9 β1 integrins. We have previously shown that hematopoietic stem cells (HSC) bind to tcOPN via this site resulting in a decrease in their proliferation and differentiation. Therefore, tcOPN and the factors required for its generation are important components of the HSC niche. Herein we show mature megakaryocytes (MM, ≥8N) contain FV, FX, and PT mRNA and protein. Furthermore, we show 8N, 16N, 32N, and 64N MM all release the required factors to enable thrombin cleavage of OPN. Importantly, mice devoid of the myeloproliferative leukemia protein (Mpl), c-Mpl(-/-) mice, contain only approximately 10% of normal megakaryocyte numbers, showed significantly reduced FX and tcOPN protein levels in endosteal bone marrow (BM). In addition, WT hematopoietic progenitors and HSC showed reduced homing to the BM of c-Mpl(-/-) mice. This is the first report identifying MM as a key cellular component in the production of tcOPN in situ, allowing the BM microenvironment to self regulate HSC biology via tcOPN.
凝血因子 V（FV）和凝血因子 X（FX）激活并形成复合物，形成凝血酶原酶，随后该酶裂解凝血酶原（PT），将其转化为活性凝血酶。凝血酶裂解骨桥蛋白（tcOPN）包含一个针对α4β1和α9β1整合素的隐蔽结合位点。我们之前已经表明，造血干细胞（HSC）通过该位点与 tcOPN 结合，导致其增殖和分化减少。因此，tcOPN 和生成它所需的因子是 HSC 龛位的重要组成部分。在此，我们表明成熟巨核细胞（MM，≥8N）含有 FV、FX 和 PT mRNA 和蛋白。此外，我们表明 8N、16N、32N 和 64N MM 均释放所需的因子以实现 OPN 的凝血酶裂解。重要的是，缺乏骨髓增生性白血病蛋白（Mpl）的小鼠（c-Mpl(-/-) 小鼠）的巨核细胞数量仅约为正常数量的 10%，在内质骨骨髓（BM）中显示出 FX 和 tcOPN 蛋白水平显著降低。此外，WT 造血祖细胞和 HSC 显示出向 c-Mpl(-/-) 小鼠 BM 的归巢减少。这是首次报道 MM 作为原位产生 tcOPN 的关键细胞成分，允许 BM 微环境通过 tcOPN 自我调节 HSC 生物学。
