Homing and differentiation of mesenchymal stem cells delivered intravenously to ischemic myocardium in vivo: a time-series study

Granulocyte-colony stimulating factor increases donor mesenchymal stem cells in bone marrow and their mobilization into peripheral circulation but does not repair dystrophic heart after bone marrow transplantation

BACKGROUND

Hereditary disordered cardiac muscle could be replaced with intact cardiomyocytes derived from genetically intact bone marrow (BM)-derived stem cells.

METHODS AND RESULTS

Cardiomyopathic mice with targeted mutation of delta-sarcoglycan gene underwent intra-BM-BM transplantation (IBM-BMT) from transgenic mice expressing green fluorescence protein. The host BM and the peripheral blood were completely reconstituted by donor-derived hematopoietic cells by IBM-BMT. Treatment with granulocyte-colony stimulating factor (G-CSF) markedly increased donor-derived mesenchymal stem cells (MSC) in the BM and their mobilization into the peripheral blood after IBM-BMT. Treatment with isoproterenol (iso) for 7 days caused myocardial damage and left ventricular (LV) dysfunction in the cardiomyopathic mice. Co-treatment with iso and G-CSF increased donor BM cell recruitment to the heart and temporarily improved LV function in the cardiomyopathic mice with or without IBM-BMT. However, the cardiac muscle was not replaced with donor BM-derived cardiomyocytes in the cardiomyopathic mice with or without IBM-BMT, and this was associated with no improvement of LV function of mice aged 20 weeks.

CONCLUSIONS

These results suggest that G-CSF enhances engraftment of donor MSC in the BM and their mobilization into the peripheral circulation after IBM-BMT but MSC recruited to the heart do not differentiate into cardiomyocytes and do not repair the dystrophic heart.

Mobilization of mesenchymal stem cells by granulocyte colony-stimulating factor in rats with acute myocardial infarction

PURPOSE

Intravenous delivery of mesenchymal stem cells (MSCs), a noninvasive strategy for myocardial repair after acute myocardial infarction (MI), is limited by the low percentage of MSCs migration to the heart. The purpose of this study was to test whether granulocyte colony-stimulating factor (G-CSF) would enhance the colonization of intravenously infused MSCs in damaged heart in a rat model of acute MI.

METHODS

After induction of anterior MI, Sprague-Dawley rats were randomized to receive: (1) saline (n=9); (2) MSCs (n=15); and (3) MSCs plus G-CSF (50 microg/kg/day for 5 consecutive days, n=13).

RESULTS

Flow cytometry revealed that G-CSF slightly increased surface CXCR4 expression on MSCs in vitro. After completion of G-CSF administration, MSCs showed a significantly lower colonization in bone marrow and a trend toward higher localization in the infarcted myocardium. At 3 months, vessel density in the infarct region of heart was significantly increased in MSCs group and trended to increase in MSCs+G-CSF group. However, echocardiographic and hemodynamic parameters, including left ventricular (LV) end-diastolic diameters, ejection fraction, and +/-dP/dtmax, were not statistically different. Morphological analysis showed that infarct size and collagen content were similar in the three groups. Immunohistochemistry revealed that the combined therapy accelerated endothelial recovery of the blood vessels in the ischemic myocardium. However, myocardial regeneration resulting from MSCs differentiation was not observed.

CONCLUSIONS

G-CSF enhanced the migration of systemically delivered MSCs from bone marrow to infarcted heart. However, the beneficial effect of this kind of migration is limited, as cardiac function did not improve.

Mobilization of endothelial progenitor cells in fracture healing and distraction osteogenesis

INTRODUCTION

Fracture healing and distraction osteogenesis (DO) are unique postnatal bone formation processes, and neovascularization is critically required for successful bone regeneration. We investigated endothelial progenitor cell (EPC) mobilization during bone regeneration, and the possible contribution of EPCs to increased vascularization and new bone formation, especially in DO.

METHODS

Mouse tibia fracture and rat tibia DO models were used in this study. The proportion of EPCs among the peripheral and splenic mononuclear cells (MNCs) was determined by examining the endothelial lineage staining characteristics and EPC cell surface markers. Messenger RNA expression of molecules related to EPC mobilization and homing at the fracture site were analyzed by ribonuclease protection assay and reverse-transcription polymerase chain reaction. In the rat tibia DO model, we measured blood flow during DO, and determined the distribution of ex vivo-expanded and intravenously-infused EPCs.

RESULTS

The proportion of EPCs among the peripheral and splenic MNCs increased after fracture, peaked on post-fracture day 3, and returned to basal levels during the healing period. Messenger RNA expression of EPC mobilizing cytokines such as vascular endothelial growth factor (VEGF), stem cell factor, monocyte chemoattractant protein-1, and stromal cell-derived factor-1, were upregulated at the fracture callus. The plasma VEGF levels peaked prior to the increase in the EPC proportion. Adhesion molecules involved in EPC homing were expressed at the fracture callus. In the DO model, the temporal pattern of the increase in the EPC proportion was similar to that in the fracture healing model, but the EPC proportion increased again during the distraction and consolidation phases. The distraction gap was relatively ischemic during the distraction phase and blood flow increased profusely later in the consolidation phase. The number of EPCs homing to the bone regeneration site in the DO model correlated with the number of transplanted EPCs in a dose-dependent manner.

CONCLUSIONS

These findings suggest that signals from the bone regeneration site mobilize EPCs from the bone marrow into the peripheral circulation. Increased EPC mobilization and homing may contribute to neovascularization and thus to new bone formation in fracture healing and DO.

The dependence of in vivo stable ectopic chondrogenesis by human mesenchymal stem cells on chondrogenic differentiation in vitro

In vivo niche plays an important role in determining the fate of implanted mesenchymal stem cells (MSCs) by directing committed differentiation. An inappropriate in vivo niche can also alter desired ultimate fate of exogenous MSCs even they are in vitro induced to express a specific phenotype before in vivo implantation. Studies have shown that in vitro chondrogenically differentiated MSCs are apt to lose their phenotype and fail to form stable cartilage in subcutaneous environment. We hypothesized that failure of maintaining the phenotype of induced MSCs in subcutaneous environment is due to the insufficient chondrogenic differentiation in vitro and fully differentiated MSCs can retain their chondrocyte-like phenotype and form stable ectopic cartilage. To test this hypothesis, extended in vitro chondrogenic induction and cartilage formation were carried out before implantation. Human bone marrow stem cells (hBMSCs) were seeded onto polylactic acid coated polyglycolic acid scaffolds. The cell-scaffold constructs were chondrogenically induced from 4 to 12 weeks for in vitro chondrogenesis, and then implanted subcutaneously into nude mice for 12 or 24 weeks. The engineered cartilages were evaluated by gross view, glycosaminoglycan content measurement, and histological staining before and after implantation. Histological examination showed typical cartilage structure formation after 8 weeks of induction in vitro. However, part of the constructs became ossified after implantation when in vitro induction lasted 8 weeks or less time. In contrast, those induced for 12 weeks in vitro could retain their cartilage structure after in vivo implantation. These results indicate that a fully differentiated stage achieved by extended chondrogenic induction in vitro is necessary for hBMSCs to form stable ectopic chondrogenesis in vivo.

Targeted migration of mesenchymal stem cells modified with CXCR4 gene to infarcted myocardium improves cardiac performance

With the goal of devising a non-invasive cell therapy for cardiac repair that may be well tolerated by patients with myocardial infarction (MI), this study evaluated the efficacy of intravenous infusion of genetically modified mesenchymal stem cells (MSCs) overexpressing CXC chemokine receptor 4 (CXCR4). CXCR4 is the cognate receptor for stromal-derived factor-1 (SDF-1), a chemokine required for homing of progenitor cells to ischemic tissues. In this study, retrovirally transduced MSCs constitutively expressing CXCR4 (CXCR4-MSCs) were delivered intravenously 24 hours after coronary occlusion/reperfusion in rats. When compared with untransduced MSCs, CXCR4-MSCs homed in toward the infarct region of the myocardium in greater numbers. In the CXCR4-MSC-treated animals, echocardiographic imaging 30 days after MI showed a decrease in anterior wall thinning and good preservation of left ventricular (LV) chamber dimensions, whereas the animals treated with saline or unmodified MSCs showed significant remodeling. Histochemical analysis showed a decrease in collagen I/III ratio in the infarcted wall of CXCR4-MSC-treated animals, thereby suggesting improved chamber compliance. Assessment revealed post-MI recovery of LV function in the CXCR4-MSC-treated animals, whereas LV function remained depressed in the saline and MSC-treated animals. In summary, intravenous delivery of genetically modified MSCs expressing CXCR4 may be a useful, non-invasive, and safe therapeutic strategy for post-infarction myocardial repair.

The interactions between brain microvascular endothelial cells and mesenchymal stem cells under hypoxic conditions

The purpose of the present study was to investigate the interactions between brain microvascular endothelial cells (BMEC) and mesenchymal stem cells (MSC) under hypoxic conditions. Primary cultured human bone marrow MSC and rat BMEC were isolated, cultured and identified. Vascular endothelial growth factor (VEGF) and matrix metalloproteinase-9 (MMP-9) were detected in the conditioned media of BMEC and MSC under normal and hypoxic conditions using ELISA. MSC differentiation was analyzed using flow cytometry and fluorescence immunocytochemistry. Transendothelial electrical resistance (TEER) techniques were employed to measure changes in permeability across the BMEC monolayer. Under hypoxic conditions, the concentration of VEGF and MMP-9 in the conditioned media increased significantly, with greater levels in the MSC than the BMEC media. Primary MSC did not express vWF and Flk-1. MSC were co-cultured with BMEC under hypoxic conditions 5 days later. MSC expressing Flk-1 accounted for 23.64+/-2.50% (n=6, P<0.001) of the total number of cells. Interestingly, some Flk-1 positive cells began to coexpress vWF simultaneously. Under hypoxic conditions, MSC conditioned media significantly enhanced the proliferation and migration of BMEC. In addition, MSC decreased the TEER of the BMEC monolayer (lowest values: 50.5+/-2.6% of the original), which could partially be inhibited by both anti-VEGF antibody and MMP-9 inhibitor. These data indicate that under hypoxic conditions BMEC induce MSC to differentiate into endothelial cells, and MSC enhance the proliferation and migration of BMEC through paracrine functions, while simultaneously increasing the permeability of the BMEC monolayer.

Direct mechanical measurement of geodesic structures in rat mesenchymal stem cells

During numerous biological processes, cell adhesion, cell migration and cell spreading are vital. These basic biological functions are regulated by the interaction of cells with their extracellular environment. To examine the morphology and mechanical changes occurring in mesenchymal stem cells cultured on a mechanically rigid substrate, atomic force microscopy and fluorescence microscopy were employed. Investigations of the cells revealed both linear and geodesic F-actin configurations. No particular cell characteristics or intra-cellular location were implicated in the appearance of the geodesic structures. However, the length of time the cells were cultured on the substrate correlated with the percentage appearance of the geodesic structures. Calculating energy dissipation from cell images acquired by dynamic mode atomic force microscopy, it was observed that the vertices of the geodesic structures had significantly higher energy dissipation compared to the linear F-actin and the glass. This supports work by Lazarides [J. Cell Biol. 68, 202-219 (1976)], who postulated that the vertices of these geodesic structures should have a greater flexibility. Our results also support predictions based on the microfilament tensegrity model. By understanding the basic principles of cell ultrastructure and cell mechanics in relation to different extracellular environments, a better understanding of physiological and pathological process will be elicited.

Bone marrow cell-mediated cardiovascular repair: potential of combined therapies

Recent evidence indicates that bone-marrow cells (BMCs) can contribute to the healing process of the injured cardiovascular system via the chemokine receptor CXCR4/SDF-1, thymosin beta(4) and integrin alpha(4)beta(1) molecular pathways. During tissue ischemia overwhelming numbers of detrimental oxygen radicals are generated, and therefore treatment with antioxidants and L-arginine, the precursor of nitric oxide (NO), could induce beneficial effects beyond those achieved by BMC transplantation alone. Recent studies have reported that BMCs have enhanced neovascularization capacity in cotreatment with alpha-tocopherol (vitamin E), ascorbic acid (vitamin C) and L-arginine. Moreover, BMC therapy can be combined with gene therapy. Clinical trials employing BMCs in the treatment of cardiovascular diseases have been completed with mixed or positive results, and several trials are ongoing. Here, we discuss the clinical potential of BMC transplantation alone and in combined therapy that aims to restore organ vascularization and function. We also consider the mechanisms of mobilization, differentiation and incorporation of BMCs.