Total Body Irradiation Is Permissive for Mesenchymal Stem Cell-Mediated New Bone Formation Following Local Transplantation

Abstract

Skeletal injury is a major clinical challenge accentuated by the decrease of bone marrow-derived mesenchymal stem/stromal cells (BMSCs) with age or disease. Numerous experimental and clinical studies have revealed that BMSCs hold great promise for regenerative therapies due to their direct osteogenic potential and indirect trophic/ paracrine actions. Increasing evidence suggests that stromal cell-derived factor-1 (SDF-1) is involved in modulating the host response to the injury. Common problems with BMSC therapy include poor cell engraftment, which can be addressed by total body irradiation (TBI) prior to transplantation. In this study, we tested the hypothesis that direct tibial transplantation of BMSCs drives endogenous bone formation in a dose-dependent manner, which is enhanced by TBI, and investigated the potential role of SDF-1 in facilitating these events. We found that TBI is permissive for transplanted BMSCs to engraft and contribute to new bone formation. Bone marrow (BM) interstitial fluid analysis revealed no differences of SDF-1 splice variants in irradiated animals compared to controls, despite the increased mRNA and protein levels expressed in whole BM cells. This correlated with increased dipeptidyl peptidase IV activity and the failure to induce chemotaxis of BMSCs in vitro. We found increased mRNA expression levels of the major SDF-1-cleaving proteases in whole BM cells from irradiated animals suggesting distinct spatial differences within the BM in which SDF-1 may play different autocrine and paracrine signaling roles beyond the immediate cell surface microenvironment.

Mesenchymal stem cell expression of stromal cell‐derived factor‐1β augments bone formation in a model of local regenerative therapy

“…8,39 This dose has been shown to result in 0% survival after 30 days in untreated mice. 40 The next day, lethally irradiated mice were anesthetized with 2% isoflourane and transplanted with 6.0 × 10 6 cells/ml of rescuing whole BM, obtained from femora and tibiae of donor litter mates, supplemented with 1% diprotin A to enhance BM cell engraftment 8,39,41 (Peptide Institute, Osaka, Japan) by injection into the retro-orbital sinus.…”

“…8,21 Briefly, Tet-Off BMSCs were plated and treated as above. After 24 h, the media were collected and cell lysates prepared in Complete Lysis-M EDTA-free buffer containing protease inhibitors (Roche Diagnostics, Indianapolis, IN).…”

“…8 The scanner was equipped with a 50 kV, 800 μA X-ray tube and a 1.3 megapixel CCD coupled to a scintillator. Four tibiae were placed in a plastic sample holder with the long axes oriented parallel to the image plane and scanned in air using 18 μm isotropic voxels, 400 ms integration time, 0.5° rotation step, 360° rotation, and frame averaging of 5.…”

“…To that end, it appears reasonable that indirect actions of implanted BMSCs may be as important in bone tissue regeneration as their direct osteogenic potential, which could lead to novel therapeutic approaches in the treatment of musculoskeletal diseases and injuries. 7,8 …”

“…8 Here, we tested the hypothesis that SDF-1β, expressed at high levels in genetically engineered Tet-Off-SDF-1β BMSCs, 21 augments endogenous bone formation in a model of direct intramedullary tibial transplantation.…”