Bone Marrow Derived Mesenchymal Stem Cells and Radiation Response: a Kinetic Study of Gene Response Using Microarray Analysis.

Abstract 4575

Mesenchymal Stem cells (MSC) are an important radiosensitive component of the so called hematopoietic stem cell niche. Importantly this supportive microenvironment influences the stem cell repopulation capacity as well as the quiescent/non proliferative state of hematopoietic cells. Senescence is considered as a major process in MSC response following irradiation. However, other studies have reported in mice the reduction of the pool of bone marrow mesenchymal stem/progenitor cells following TBI independently of senescence. An altered osteoblastic differentiation was pointed out in these studies. Furthermore, MSC have been shown to be involved in the repair of ionizing radiation damage of distant epithelial sites which requires adherence genes mitigation. The aim of this study was to clarify some of these points using an in vitro model of irradiation and short term culture.

Briefly, confluent human BM-MSC were irradiated at the dose of 2.5 Gy (dose rate: 95 cGy.min^-1) and immediately put into culture (Minimum essential medium supplemented with 10% FCS and 10 μg/ml of ciprofloxacin, penicillin and streptomycin). Six, 12, 24, 48 and 72 hours after irradiation, cells were harvested and lysed. Total RNAs were purified using the automatic Qiacube system (Qiagen,Courtaboeuf, France) and processed on DNA microarray scanner (Agilent technologies Inc.) according to supplier's recommendations. Data were analyzed with GeneSpring GX Expresion Analysis software version 10.0 (Agilent) in order to identify the transduction pathways involved.

No apoptosis was observed during this short term incubation. Among other genes we identified plasminogen activator inhibitor 1 (PAI-1) as a factor highly upregulated after irradiation, in addition to CD151. This is in accordance with MSC response to nutrient-poor, hypoxic stress environment (Copland et al, Stem cells 2009). As MSC are radiosensitive cells, this may indicate that PAI impacts MSC survival through the mitigation of their adhesiveness to surrounding matrices. As PAI-1 is an important factor involved in the balance of blood coagulation and fibrinolysis as well as in the regulation of angiogenesis, one may speculate the consequences of PAI-1 release from MSC on blood homeostasis. Work is going on to describe the main response target genes. This could allow us to identify therapeutic strategies based on ex-vivo or in vivo manipulation of MSC in a purpose of tissue remodelling.