Abstract
Backgrounds: We have reported bone marrow regeneration using adipose-derived stem cells (ASCs) since 2003. In our study using mice, we showed that not only bone matrix but also bone marrow could be regenerated subcutaneously in vivo. Transplanted ASCs proliferated and differentiated into osteoblasts in micropores on the surface of scaffolds made of hydroxyapatites (HA). We have not yet obtained incontrovertible proof that the ASCs differentiated into hematopoietic cells. However, we could regenerate a subcutaneous microenvironment in which hematopoietic cells survived, which may lead to new treatments for fibrotic bone marrow diseases, such as idiopathic myelofibrosis and osteopetrosis.
Purposes: In this report, we examined the optimal shapes of scaffolds for bone and bone marrow regeneration using ASCs.
Methods: Taking advantage of homogeneously marked cells from green fluorescent protein (GFP) transgenic mice, ASCs were isolated from the inguinal fat pads of GFP transgenic mice. ASCs were cultured in vitro and after three passages were seeded into the small pores of scaffolds of various shapes made of HA. The ASC-containing scaffolds were then subsequently implanted into immunocompetent mice subcutaneously. Two months later, the scaffolds were extirpated for histological, immunohistochemical and flow cytometry analyses.
Results: Histological examination showed that the pores were filled with bone matrix and that the bone marrow was composed of adipocytes, hematopoietic cells, and vasculatures. Bone marrow regeneration on small, thin scaffolds of high porosity was better than on other scaffolds. Immunohistochemical analysis confirmed that the GFP+ ASCs that had differentiated into osteoblasts were composed of bone matrix. Flow cytometry analyses showed that the bone marrow was composed of blood cells, including populations of monocytes, lymphocytes and granulocytes.
Conclusions: Bone marrow engineering has great potential for hematopoietic disease therapy. The regeneration of the hematopoietic system using ASCs might be useful in the future for treating hematopoietic stem cell diseases such as leukemia as well as fibrotic bone marrow diseases. We plan to continue looking for suitable scaffolds and methods for bone and bone marrow regeneration using ASCs.
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