Effects of ionizing radiation on mesenchymal stromal cells of normal and leukemic bone marrow hematopoietic niches

Abstract

Background: Total body irradiation (TBI) followed by hematopoietic stem cell transplantation (HSCT) is a promising strategy to treat chemo-refractory acute myeloid leukemia (AML). Unfortunately, radiation-based transplantation is often insufficient to eradicate AML resulting in disease relapse. While HSCT supplies healthy donor-derived hematopoietic stem cells, the bone marrow (BM) hematopoietic niche remains patient-derived. The major cellular component of the hematopoietic niche is the mesenchymal stromal cell (MSC). We hypothesize that MSC function is abnormal in leukemic marrow and must be normalized following anti-leukemia therapy in order to prevent relapsed disease. The extent to which MSC function is altered in AML and following irradiation remains unknown but may be central to the success of TBI-based transplantation strategies. In this study, we have compared functional properties of MSCs from patients with AML and normal controls and tested the effects of high dose radiation on MSC function. Methods: Normal and AML-derived MSCs were treated with X-ray doses consistent with TBI protocols. Cells were compared based on CD marker expression, morphology, differentiation, cell proliferation and viability. Induction of DNA damage following irradiation was assessed using immunostaining for gH2A.X histone. Results: Both leukemic and irradiated cells demonstrated normal morphology and immunophenotypic profile. MSCs from AML patients had increased adipogenic and delayed osteogenic differentiation capacity and irradiation of healthy MSCs resulted in the same abnormal differentiation profile. AML-MSCs demonstrated decreased proliferation and increased necrosis. Irradiation decreased both normal and AML-MSC cell proliferation rates, had no effect on cell viability and induced extensive DNA damage as indicated by the presence of large foci of H2A.X histone. Conclusions: Taken together, AML-derived and irradiated MSCs demonstrated altered functional properties indicative of abnormal BM physiology. Therefore, strategies that normalize BM microenvironment prior to HSCT may be required.