Irradiation increased mRNA transcripts of hematopoiesis-related molecules in bone marrow-derived mesenchymal stem cells

[Speaker] Keigo Amari:1
[Co-author] Reina Kume:1, Mako Tomogane:1, Ryosuke Wakabayashi:1, Yuki Toda:1, Kazuyuki Takata:1, Eishi Ashihara:1
1:Department of Clinical and Translational Physiology, Kyoto Pharmaceutical University, Japan

[INTRODUCTION] Hematopoietic stem cells (HSCs) are multipotent stem cells with abilities of self-renewal and differentiation into blood cells. HSCs reside in a specialized microenvironment within the bone marrow (BM), which is called "HSC niche." HSC niche regulates the quiescence, proliferation, and differentiation of HSCs by adhesion molecules and cytokines. HSC transplantation (HSCT) is used to cure patients diagnosed with hematological and autoimmune diseases. To eradicate normal and malignant cells, total-body irradiation is conducted for myeloablative preconditioning, followed by HSC infusion. Total-body irradiation affects HSC niche such as mesenchymal stem cells (MSCs) as well as hematopoietic cells. However, the influence on capacity of supporting hematopoiesis by MSCs after irradiation remains unclear. Therefore, to elucidate the contribution of MSCs to hematopoiesis after irradiation, we investigated the effects of irradiation on mouse BM-derived MSCs.
[METHODS] MSCs were isolated from the BM of 6- to 8-wk-old C57Bl/6 mice. A purified population of MSCs was obtained by changing medium every eight hours to remove hematopoietic cells. After irradiation at doses of 3 or 7 Gy, we examined the change of proliferation ability with trypan blue staining and osteogenic differentiation ability with alizarin red staining. Additionally, we examined the influence on expression of hematopoiesis-related molecules to determine the capacity of supporting hematopoiesis by quantitative RT-PCR (qRT-PCR).
[RESULTS and DISCUSSION] First, isolated cells from BM cells were evaluated by flow cytometry and osteogenic differentiation. Isolated MSCs expressed CD105, not CD45. Irradiation suppressed MSCs proliferation in a dose-dependent manner. But, irradiation didn't alter the osteogenic differentiation ability in MSCs. Furthermore, mRNA expression levels of hematopoiesis-related cytokine such as Kitl, Thpo, Flt3l, Il6 and adhesion molecule such as Cxcl12, Vcam1 increased in irradiated MSCs. These results suggested that irradiated MSCs could promote engraftment and expansion of infused HSCs in HSCT.
[CONCLUSION] Total-body irradiation for HSCT has only been focused on the reduction hematopoietic cells so far. Our results revealed that irradiated MSCs increased mRNA expression levels of hematopoiesis-related molecules. In conclusion, it is suggested that irradiation of MSCs can give significant effects for promoting adhesion and expansion of infused HSCs in HSCT.
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