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P-selectin, and not E-selectin, negatively regulates murine megakaryocytopoiesis
Naheed Banu1, Shalom Avraham, Hava Karsenty Avraham
1Division of Experimental Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, 4 Blackfan Circle, Boston, MA 02115, USA.
Abstract:
To assess the role of P-selectin and E-selectin in megakaryocytopoiesis, in vitro assays were performed in animal models deficient in both adhesion receptors. There was a significantly greater number of IL-3-responsive megakaryocyte progenitors CFU (CFU-MK) and an increase in immature megakaryoblasts in response to IL-6 in the P-selectin-null mice compared with the wild-type controls. Furthermore, P-selectin-null mice showed a greater number of CFU-MK colonies derived from CD34(+) cells in response to IL-3 or IL-3 plus stem cell factor. A significant shift in baseline ploidy with a reduction in 8N cells and an increase in 32N cells was also observed in the P-selectin-null mice. Secretion of the inhibitory growth factor TGF-beta1 and not TGF-beta2 was significantly lower in the supernatants of cultures containing bone marrow cells from P-selectin-deficient mice as compared with those from the wild-type control bone marrow cells. No differences in the responsiveness of murine CFU-MK, immature megakaryocytes, or 5-fluorouracil-selected stem cells to cytokines were observed in E-selectin-null mice as compared with the control mice. These studies indicate that the absence of P-selectin, and not E-selectin, resulted in an altered adhesion environment with subsequent expansion of megakaryocyte progenitors and immature megakaryoblasts, enhanced secretion of TGF-beta1, and apparent increased responsiveness to inflammatory cytokines.
Insights
P-selectin deficiency in mice enhances megakaryocyte progenitor growth and alters cell ploidy, suggesting a role in megakaryocytopoiesis. E-selectin deficiency showed no significant impact on these processes.
Area of Science:
- Hematology
- Cell Biology
- Immunology
Background:
- Megakaryocytopoiesis is crucial for platelet production.
- Selectins (P-selectin and E-selectin) are adhesion molecules involved in cell trafficking and immune responses.
- The specific roles of P-selectin and E-selectin in megakaryocytopoiesis remain incompletely understood.
Purpose of the Study:
- To investigate the distinct roles of P-selectin and E-selectin in megakaryocytopoiesis.
- To determine how the absence of these selectins affects megakaryocyte progenitor proliferation and differentiation.
Main Methods:
- In vitro assays using animal models deficient in P-selectin and/or E-selectin.
- Quantification of megakaryocyte progenitors (CFU-MK) and immature megakaryoblasts.
- Analysis of cellular ploidy and cytokine secretion (TGF-beta1, TGF-beta2).
Main Results:
- P-selectin-null mice exhibited significantly increased IL-3-responsive megakaryocyte progenitors (CFU-MK) and IL-6-responsive immature megakaryoblasts.
- P-selectin deficiency led to enhanced CFU-MK colony formation from CD34+ cells and a shift in baseline ploidy (reduced 8N, increased 32N cells).
- Lower secretion of TGF-beta1 was observed in P-selectin-deficient bone marrow cultures; E-selectin deficiency had no significant effect.
Conclusions:
- The absence of P-selectin, but not E-selectin, significantly alters the adhesion environment, promoting megakaryocyte progenitor expansion and immature megakaryoblast proliferation.
- P-selectin deficiency is associated with altered TGF-beta1 secretion and potentially increased responsiveness to inflammatory cytokines during megakaryocytopoiesis.
- These findings highlight P-selectin as a key regulator in megakaryocytopoiesis, influencing progenitor expansion and differentiation pathways.