Transdifferentiation of Hematopoietic Stem Cells (HSC) into a–Smooth Muscle Actin (aSMA ) Expressing Cells Unlikely Occurs in vivo

Abstract

Abstract: : Purpose: Although the role of endothelial precursor cells of bone marrow origin in angiogenesis has been well established, little is known about the origin of vascular smooth muscle cells. Recently, some studies have suggested that bone marrow HSCs might give rise to other tissue types including smooth muscle cells. However, this is still extremely controversial. In this study, we have investigated the potential of bone marrow stem cells to generate αSMA expressing cells by utilizing αSMA–GFP mice. Methods: The chimeric mice that carry αSMA–GFP transgene in bone marrow cells were created by bone marrow transplantation from αSMA–GFP mice. The differentiation of transplanted stem cells into αSMA expressing cells was examined by flow cytometry and fluorescent microscopy combined with cell culture of bone marrow stromal cells, retinal capillary pericytes and renal glomerular mesangial cells. Results: A small population of GFP⁺ bone marrow cells was detectable in αSMA–GFP mice. Bone marrow stromal cells from αSMA–GFP mice also displayed the high levels of GFP expression in vitro, suggesting bone marrow contains a stromal progenitor that develops αSMA expressing cells. PCR analysis displayed the GFP transgene in both bone marrow cells and peripheral mononuclear cells of wild–type mice received bone marrow transplant from αSMA–GFP mice, suggesting the successful reconstitution of hematopoiesis by transplanted stem cells in αSMA–GFP chimeras. However, no GFP⁺ cells were detected in bone marrow of αSMA–GFP chimeras. The αSMA expressing bone marrow stromal cells, capillary pericytes and glomerular mesangial cells also displayed no GFP expression. To further confirm the evidence from αSMA–GFP chimeras, another chimeric mouse was created with Tie2–GFP mice that carries GFP gene under the control of endothelial specific Tie2 promoter. Tie2–GFP mice also contained a small population of GFP⁺ bone marrow cells, and this Tie2–GFP⁺ cell population was clearly detectable in Tie2–GFP chimeras. Conclusions: Bone marrow contains a stromal progenitor for αSMA expressing cells. However, this progenitor is not transplantable in systemic bone marrow transplantation. The data also suggest that the developmental plasticity of HSCs is strictly limited. HSCs are unlikely to give rise to αSMA expressing progeny.

Keywords: retinal neovascularization • diabetic retinopathy • vascular cells