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Osteoclasts (OCLs) are specialized cells responsible for physiological bone resorption and as well as pathologic bone loss. In addition to unique ability to resorb bone, OCLs also play potential role in the mobilization of hematopoietic progenitor cells from bone marrow, particularly under various stress stimuli(e.g. hypoxia, injury or inflammation). We investigated effect of activated OCLs on the stem niche whether lead to mobilization of hematopoietic progenitors under liver specific injury, which was established in our previous acute liver disease study. We exposed mice to stress situation by inducing liver injury with CCl4 or combination of additional injecting of RANKL to activate OCLs, and compared the effect on the mobilization of hematopoietic progenitor cells from the BM. To investigate OCLs involved mechanism underlying mobilization, we induced activated OCLs from RAW 264.7 cell line through stimulation with RANKL and quantified the level of stem cell niche component, SDF-1 on the osteblasts and CXCR4 on the bone marrow cells(BMCs), after culturing with supernatants from activated OCLs. As a result, Under the stress situation in vivo, the mobilized hematopoietic progenitor cells were significantly increased after RANKL treatment under liver specific injury. Moreover, we found that functional OCLs cleaved SDF-1α on the osteoblasts and increased CXCR4 expression on the BMCs in vitro. These results suggest that OCLs might be involved in alteration of the interaction between SDF-1 and CXCR4 leading to mobilization of hematopoietic progenitor cells from the BM.

Acute Graft-versus-Host Disease (GVHD) remains a major complication after allogeneic hematopoietic cell transplantation (HCT). Several publications show a potential benefit of human MSCs for the treatment of refractory GVHD; however, their cellular fate and distribution remain unclear. We set out to develop an animal model that can be used to study the effect of MSCs on GVHD. GVHD was induced by transplantating C3H/he or C57BL/6 donor bone marrow cells (5 × 106) and CD3+ spleen cells (1 × 106) into lethally irradiated BALB/c recipient mice. C3H/10T1/2 cell lines were transfected with a pcDNA3.1-luciferase construct (luc-MSCs). Bioluminescence of these cells was measured (IVIS-Xenogen system) after treatment with luciferin, showing a linear increase of photon emission with rising cell numbers. To track these cells in vivo, groups of mice were injected with various dose luc-MSCs per animal and imaged with bioluminescence imaging at various time points. After transplantation, mice were monitored daily for weight and survival. Differences in symptom severity were compared using a clinical GVHD scoring system. We conclude that this mouse model can be used to study the effects of MSCs on acute GVHD and the described bioluminescence technology provides a sensitive and safe tool for the repeated in vivo tracking of infused luc-MSCs in GVHD target organs.

PURPOSE: It has been known that MSCs have the capability of regenerating organs, as well as modulating immune function. Recent studies suggest that the vitamin A metabolite, ATRA is capable of promoting anti‐inflammatory Treg cell differentiation. With this, we analyzed expressional changes of CD4+CD25+Foxp3+Tregs with mice injected MSCs and/or ATRA.METHOD: MSCs (1×106) prepared from C57BL/6 mice bone marrow were adoptively transferred into syngenic mice via a tail vein. After one day, the MSCs injected mice were I.P. immunized with OVA (100 μg/mouse) and Alum (1 mg). After immunization, ATRA (10 mg/kg) was I.P. injected everyday. Two weeks after postimmunization, we obtained spleen cells and measured Treg cells related markers of CD4, CD25, Foxp3 and cytokine pofiles of IL‐10, IL‐4, IL‐12 and IFN‐r by flow cytometry analysis.RESULTS: Compared to the group that did not undergo MSCs transplantation, the group that received transplantation showed to have a high expression of Foxp3 within the spleen cells, and more so with ATRA‐treatment. Also, expressions of IL‐4 and IL‐10 were higher in the group with that received transplantation and more so in the ATRA‐treated group.CONCLUSION: MSCs and ATRA treatment might have immunomodulatory effet in immunized mice through the up‐regulation of Foxp3 and IL‐10 expression.