Surface expression of CXCR4 in unrestricted somatic stem cells and its regulation by growth factors. Cell Biol Int. 2010;34:687-692. [PMID: 20196768 DOI: 10.1042/cbi20090415]

Preconditioning strategies for improving the survival rate and paracrine ability of mesenchymal stem cells in acute kidney injury

Acute kidney injury (AKI) is a common, severe emergency case in clinics, with high incidence, significant mortality and increased costs. Despite development in the understanding of its pathophysiology, the therapeutic choices are still confined to dialysis and renal transplantation. Considering their antiapoptotic, immunomodulatory, antioxidative and pro‐angiogenic effects, mesenchymal stem cells (MSCs) may be a promising candidate for AKI management. Based on these findings, some clinical trials have been performed, but the results are contradictory (NCT00733876, NCT01602328). The low engraftment, poor survival rate, impaired paracrine ability and delayed administration of MSCs are the four main reasons for the limited clinical efficacy. Investigators have developed a series of preconditioning strategies to improve MSC survival rates and paracrine ability. In this review, by summarizing these encouraging studies, we intend to provide a comprehensive understanding of various preconditioning strategies on AKI therapy and improve the prognosis of AKI patients by regenerative medicine.

Novel preconditioning strategies for enhancing the migratory ability of mesenchymal stem cells in acute kidney injury

Acute kidney injury (AKI) remains a worldwide public health issue due to its increasing incidence, significant mortality, and lack of specific target-orientated therapy. Developments in mesenchymal stem cell (MSC) research make MSCs a promising candidate for AKI management but relevant clinical trials show confusing results (NCT00733876, NCT01602328). One primary cause of the limited therapeutic effect may result from poor engraftment of transplanted cells. To solve this problem, investigators have developed a series of preconditioning strategies to improve MSC engraftment in animal AKI models. In this review, we summarize these previous studies, providing an integrated and updated view of different preconditioning strategies aimed at promoting the therapeutic effect of MSCs in AKI patients.

Enhanced Homing of CXCR-4 Modified Bone Marrow-Derived Mesenchymal Stem Cells to Acute Kidney Injury Tissues by Micro-Bubble-Mediated Ultrasound Exposure

Although the curative effects of bone marrow stromal cells (BMSCs) for acute kidney injury (AKI) have been recognized, their in vivo reparative capability is limited by the low levels of targeted homing and retention of intravenous injected cells. Stromal cell-derived factor-1 (SDF-1) plays an important role in stem cell homing and retention through interaction with its specific functional receptor, CXCR4, which is presumably related to the poor homing in AKI therapy. However, most of the functional CXCR4 chemokine receptors are lost upon in vitro culturing. Ultrasound-targeted micro-bubble destruction (UTMD) has become one of the most promising strategies for the targeted delivery of drugs and genes. To improve BMSC homing to AKI kidneys, we isolated and cultured rat BMSCs to third passage and enhanced CXCR-4 transfection efficiency in vitro by applying UTMD and polyethylenimine. Transwell migration assay showed that the migration ability of CXCR4-modified BMSCs was nine-fold higher than controls. Then, mercuric chloride-induced AKI rats were injected with transfected BMSCs through their tail veins. We showed that enhanced homing and retention of BMSCs were observed in the CXCR-4 modified group compared with other groups at 1, 2 and 3 d post-treatment. Collectively, our data indicated that UTMD was an effective method to increase BMSCs' engraftment to AKI kidney tissues by increasing CXCR-4 expression.

Administration of BMSCs with muscone in rats with gentamicin-induced AKI improves their therapeutic efficacy

The therapeutic action of bone marrow-derived mesenchymal stem cells (BMSCs) in acute kidney injury (AKI) has been reported by several groups. However, recent studies indicated that BMSCs homed to kidney tissues at very low levels after transplantation. The lack of specific homing of exogenously infused cells limited the effective implementation of BMSC-based therapies. In this study, we provided evidence that the administration of BMSCs combined with muscone in rats with gentamicin-induced AKI intravenously, was a feasible strategy to drive BMSCs to damaged tissues and improve the BMSC-based therapeutic effect. The effect of muscone on BMSC bioactivity was analyzed in vitro and in vivo. The results indicated that muscone could promote BMSC migration and proliferation. Some secretory capacity of BMSC still could be improved in some degree. The BMSC-based therapeutic action was ameliorated by promoting the recovery of biochemical variables in urine or blood, as well as the inhibition of cell apoptosis and inflammation. In addition, the up-regulation of CXCR4 and CXCR7 expression in BMSCs could be the possible mechanism of muscone amelioration. Thus, our study indicated that enhancement of BMSCs bioactivities with muscone could increase the BMSC therapeutic potential and further developed a new therapeutic strategy for the treatment of AKI.

Hypoxic preconditioning with cobalt of bone marrow mesenchymal stem cells improves cell migration and enhances therapy for treatment of ischemic acute kidney injury

Mesenchymal stem cell (MSC) administration is known to enhance the recovery of the kidney following injury. Here we tested the potential of hypoxic-preconditioned-MSC transplantation to enhance the efficacy of cell therapy on acute kidney injury (AKI) by improving MSC migration to the injured kidney. Cobalt was used as hypoxia mimetic preconditioning (HMP). MSC were subjected to HMP through 24 h culture in 200 µmol/L cobalt. Compared to normoxia cultured MSC (NP-MSC), HMP significantly increased the expression of HIF-1α and CXCR4 in MSC and enhanced the migration of MSC in vitro. This effect was lost when MSC were treated with siRNA targeting HIF-1α or CXCR4 antagonist. SPIO labeled MSC were administered to rats with I/R injury followed immediately by magnetic resonance imaging. Imaging clearly showed that HMP-MSC exhibited greater migration and a longer retention time in the ischemic kidney than NP-MSC. Histological evaluation showed more HMP-MSC in the glomerular capillaries of ischemic kidneys than in the kidneys receiving NP-MSC. Occasional tubules showed iron labeling in the HMP group, while no tubules had iron labeling in NP group, indicating the possibility of tubular transdifferentiation after HMP. These results were also confirmed by fluorescence microscopy study using CM-DiI labeling. The increased recruitment of HMP-MSC was associated with reduced kidney injury and enhanced functional recovery. This effect was also related to the increased paracrine action by HMP-MSC. Thus we suggest that by enhancing MSC migration and prolonging kidney retention, hypoxic preconditioning of MSC may be a useful approach for developing AKI cell therapy.

Genetic modification of mesenchymal stem cells to overexpress CXCR4 and CXCR7 does not improve the homing and therapeutic potentials of these cells in experimental acute kidney injury

The therapeutic potential of bone marrow mesenchymal stem cells (MSCs) in kidney failure has been examined in some studies. However, recent findings indicate that after transplantation, these cells home to kidneys at very low levels. Interaction of stromal derived factor-1 (SDF-1) with its receptor, CXCR4, is of pivotal importance in migration and homing. Recently, CXCR7 has also been recognized as another SDF-1 receptor that interacts with CXCR4 and modulates its functions. In this study, CXCR4 and CXCR7 were separately and simultaneously overexpressed in BALB/c bone marrow MSCs by using a lentiviral vector system and the homing and renoprotective potentials of these cells were evaluated in a mouse model of cisplatin-induced acute kidney injury. Using flow cytometry, immunohistochemistry, and real-time PCR methods for detection of GFP-labeled MSCs, we found that although considerably entrapped in lungs, native MSCs home very rarely to kidneys and bone marrow and this rate cannot be significantly affected by CXCR4 and/or CXCR7 upregulation. Transplantation of neither native nor genetically engineered MSCs ameliorated kidney failure. We concluded that overexpression of CXCR4 and CXCR7 receptors in murine MSCs cannot improve the homing and therapeutic potentials of these cells and it can be due to severe chromosomal abnormalities that these cells bear during ex vivo expansion.

Modeling SDF-1-induced mobilization in leukemia cell lines

The stromal cell-derived factor 1 (SDF-1) is essential for circulation, homing, and retention of hematopoietic stem cells in the bone marrow. Present evidence indicates that this factor might play an important role in leukemia cells as well. The aim of this study is to present a model of SDF-1-induced mobilization using leukemia cell lines. CXCR4 expression was compared in Kasumi-1, Jurkat, HL-60, KG-1a, and K562 cells by flow cytometry and Western blot. Migration was analyzed with Transwell assays, and adhesive cell-cell interaction was quantified with a standardized adhesion assay and flow cytometry. CXCR4 was expressed by all leukemic cell lines analyzed, although surface expression of this receptor was found in Kasumi-1 and Jurkat cells only. Correspondingly, SDF-1α effects on migration and cell-cell adhesion were observed in Kasumi-1 and Jurkat cells only, and this could be blocked by AMD3100 in a reversible manner. We have provided evidence that SDF-1α acts as a chemotactic and chemokinetic agent. In addition, surface expression of integrin-β2, activated leukocyte cell adhesion molecule and N-cadherin decreased after stimulation with SDF-1α. SDF-1α affects cell-cell adhesion and migration only in leukemia cells on which the CXCR4 receptor is present on the surface. An SDF-1 gradient is not necessarily required to induce migration, as chemokinesis can also occur. Upon stimulation with SDF-1, CXCR4 promotes modifications on the surface pattern of adhesion molecules, which have an influence on adhesion and migration.

Physiological and pathological role of local and immigrating colonic stem cells

The latest avenue of research is revealing the existence of and role for the colonic stem cells in the physiological renewal of the mucosa and in pathological circumstances where they have both positive and negative effects. In the case of human colon, different levels of stem cell compartments exist. First, the crypt epithelial stem cells, which have a role in the normal crypt epithelial cell dynamics and in colorectal carcinogenesis. Close to the crypts, the second layer of stem cells can be found; the local subepithelial stem cell niche, including the pericryptic subepithelial myofibroblasts that regulate the epithelial cell differentiation and have a crucial role in cancer progression and chronic inflammation-related fibrosis. The third level of stem cell compartment is the immigrating bone-marrow-derived stem cells, which have an important role in wound healing after severe mucosal inflammation, but are also involved in cancer invasion. This paper focuses on stem cell biology in the context of physiological and pathological processes in the human colon.

Electrospun nanofiber-based regeneration of cartilage enhanced by mesenchymal stem cells

Application of biomaterials in combination with stem cells is a novel tissue engineering approach to regenerate cartilage. The objective of this study was to investigate the potential of poly(vinyl alcohol)/polycaprolactone (PVA/PCL) nanofiber scaffolds seeded with rabbit bone marrow-mesenchymal stem cell (BM-MSC) for cartilage tissue engineering in vitro and in vivo. We tested the biocompatibility and mechanical properties of nanofibrous scaffolds using scanning electron microscope, MTT assay, and tensile measurements. The capacity of MSC for chondrogenic differentiation on scaffolds was examined using reverse transcription-polymer chain reaction and immunostaining. For in vivo assessments, PVA/PCL nanofiber scaffolds with or without MSC were implanted into rabbit full-thickness cartilage defects. To evaluate cartilage regeneration, semi-quantitative grading and histological analysis were performed. Our results showed that PVA/PCL scaffolds supported the proliferation and chondrogenic differentiation of MSC in vitro. Moreover, the animals treated with cell-seeded PVA/PCL scaffolds showed improved healing of defects compared with untreated control and those which received cell-free scaffolds. Our findings suggest that PVA/PCL scaffolds incorporated with MSC can serve as a suitable graft for articular cartilage reconstruction.

Dormant phase and multinuclear cells: two key phenomena in early culture of murine bone marrow mesenchymal stem cells

Special features of mesenchymal stem cells (MSCs) have made them a popular tool in cell therapy and tissue engineering. Although mouse animal models and murine MSCs are common tools in this field, our understanding of the effect of in vitro expansion on the behavior of these cells is poor and controversial. In addition, in comparison to human, isolation of MSCs from mouse has been reported to be more difficult and some unexplained features such as heterogeneity and slow growth rate in the culture of these cells have been observed. Here we followed mouse bone marrow MSCs for >1 year after isolation and examined the effect of expansion on changes in morphology, growth kinetics, plasticity, and chromosomal structure during in vitro culture. Shortly after isolation, the growth rate of the cells decreased until they stopped dividing and entered a dormant state. In this state the size of the cells increased and they became multinuclear. These large multinuclear cells then gave origin to small mononuclear cells, which after a while resumed proliferation and could be expanded immortally. The immortal cells had diminished plasticity and were aneuploid but could not form tumors in nude mice. These results suggest that mouse bone marrow MSCs bear several modifications when expanded in vitro, and therefore, the interpretation of the data obtained with these cells should be done more cautiously.

Nanohydroxyapatite-coated electrospun poly(l-lactide) nanofibers enhance osteogenic differentiation of stem cells and induce ectopic bone formation

A combination of calcium phosphates with nanofibrous scaffolds holds promising potential for bone tissue engineering applications. In this study, nanohydroxyapatite (n-HA) was coated on the plasma-treated surface of electrospun poly(l-lactide) (PLLA) nanofibers and the capacity of fabricated scaffolds for bone formation was investigated in vitro using human cord blood derived unrestricted somatic stem cells (USSC) under osteogenic induction and in vivo after subcutaneous implantation. PLLA and n-HA-coated PLLA (n-HA/PLLA) scaffolds exhibited a nanofibrous structure with interconnected pores and suitable mechanical properties. These scaffolds were also shown to support attachment, spreading, and proliferation of USSC, as shown by their flattened normal morphology and MTT assay. During osteogenic differentiation, significantly higher values of ALP activity, biomineralization, and bone-related gene expression were observed on n-HA/PLLA compared to PLLA scaffolds. Subsequently, these markers were measured in higher amounts in USSC on PLLA nanofibers compared to TCPS. According to the in vivo results, ossification and formation of trabeculi was observed in the n-HA/PLLA scaffold compared to PLLA. Taking together, it was shown that nanofibrous structure enhanced osteogenic differentiation of USSC. Furthermore, surface-coated n-HA stimulated the effect of nanofibers on the orientation of USSC toward osteolineage. In addition, the n-HA/PLLA electrospun scaffold showed the capacity for ectopic bone formation in the absence of exogenous cells.