SDF-1/CXCR4 axis and megakaryocyte-derived growth factors after irradiation. (A) Semiquantitative RT-PCR analyses of SDF-1 and CXCR4 expression in BM cells flushed from mice in the TBI and nonirradiated control groups (n = 3 per group). The negative control (Neg, without template) is shown in the middle lane. (B) Comparison of SDF-1 and CXCR4 expression levels (calculated relative to GAPDH levels and reported as mean percentages ± SD) in irradiated versus nonirradiated control mice. Increase of SDF-1 expression and the decrease of CXCR4 expression in the irradiated groups are both significant (P = .03 and P = .003, respectively). (C) Comparison of the SDF-1 protein level measured by ELISA in irradiated versus nonirradiated control mice (n = 3 per group; P = .008). (D top) Immunohistochemical staining (red) confirming an increase of SDF-1 levels in osteoblasts (, left panel) and megakaryocytes () after 48 hours after TBI vs nonirradiated control mice (middle panel). Bone (Bo) from a TBI mouse stained using an isotype primary antibody was used as control (right panel). (Bottom) In contrast to SDF-1, the CXCR4 levels decreased at 48 hours after TBI and remained localized into the osteoblasts () and in the surviving megakaryocytes (). Controls and isotype-stained sections as described for SDF-1. Scale bar represents 50 μm. (E) Semiquantitative RT-PCR analyses of TGF-β1, PGDF-β, and bFGF in BM cells flushed from mice in the TBI and nonirradiated control groups (n = 3). The negative control (Neg, without template) is shown in the middle lane. (F) Levels of PGDF-β and bFGF, but not TGF-β1, calculated relative to GAPDH levels and reported as mean percentages (± SD), were significantly higher in the TBI group (P = .006, P = .02, P > .05, respectively).