Microgel iron oxide nanoparticles for tracking human fetal mesenchymal stem cells through magnetic resonance imaging

A comparison of bioreactors for culture of fetal mesenchymal stem cells for bone tissue engineering

Bioreactors provide a dynamic culture system for efficient exchange of nutrients and mechanical stimulus necessary for the generation of effective tissue engineered bone grafts (TEBG). We have shown that biaxial rotating (BXR) bioreactor-matured human fetal mesenchymal stem cell (hfMSC) mediated-TEBG can heal a rat critical sized femoral defect. However, it is not known whether optimal bioreactors exist for bone TE (BTE) applications. We systematically compared this BXR bioreactor with three most commonly used systems: Spinner Flask (SF), Perfusion and Rotating Wall Vessel (RWV) bioreactors, for their application in BTE. The BXR bioreactor achieved higher levels of cellularity and confluence (1.4-2.5x, p < 0.05) in large 785 mm(3) macroporous scaffolds not achieved in the other bioreactors operating in optimal settings. BXR bioreactor-treated scaffolds experienced earlier and more robust osteogenic differentiation on von Kossa staining, ALP induction (1.2-1.6×, p < 0.01) and calcium deposition (1.3-2.3×, p < 0.01). We developed a Micro CT quantification method which demonstrated homogenous distribution of hfMSC in BXR bioreactor-treated grafts, but not with the other three. BXR bioreactor enabled superior cellular proliferation, spatial distribution and osteogenic induction of hfMSC over other commonly used bioreactors. In addition, we developed and validated a non-invasive quantitative micro CT-based technique for analyzing neo-tissue formation and its spatial distribution within scaffolds.

Superparamagnetic iron oxide nanoparticles labeling of bone marrow stromal (mesenchymal) cells does not affect their "stemness"

Superparamagnetic iron oxide nanoparticles (SPION) are increasingly used to label human bone marrow stromal cells (BMSCs, also called “mesenchymal stem cells”) to monitor their fate by in vivo MRI, and by histology after Prussian blue (PB) staining. SPION-labeling appears to be safe as assessed by in vitro differentiation of BMSCs, however, we chose to resolve the question of the effect of labeling on maintaining the “stemness” of cells within the BMSC population in vivo. Assays performed include colony forming efficiency, CD146 expression, gene expression profiling, and the “gold standard” of evaluating bone and myelosupportive stroma formation in vivo in immuncompromised recipients. SPION-labeling did not alter these assays. Comparable abundant bone with adjoining host hematopoietic cells were seen in cohorts of mice that were implanted with SPION-labeled or unlabeled BMSCs. PB+ adipocytes were noted, demonstrating their donor origin, as well as PB+ pericytes, indicative of self-renewal of the stem cell in the BMSC population. This study confirms that SPION labeling does not alter the differentiation potential of the subset of stem cells within BMSCs.

Cartilage repair using hyaluronan hydrogel-encapsulated human embryonic stem cell-derived chondrogenic cells

Human embryonic stem cells (hESCs) have the potential to offer a virtually unlimited source of chondrogenic cells for use in cartilage repair and regeneration. We have recently shown that expandable chondrogenic cells can be derived from hESCs under selective growth factor-responsive conditions. In this study, we explore the potential of these hESC-derived chondrogenic cells to produce an extracellular matrix (ECM)-enriched cartilaginous tissue construct when cultured in hyaluronic acid (HA)-based hydrogel, and further investigated the long-term reparative ability of the resulting hESC-derived chondrogenic cell-engineered cartilage (HCCEC) in an osteochondral defect model. We hypothesized that HCCEC can provide a functional template capable of undergoing orderly remodeling during the repair of critical-sized osteochondral defects (1.5 mm in diameter, 1 mm depth into the subchondral bone) in a rat model. In the process of repair, we observed an orderly spatial-temporal remodeling of HCCEC over 12 weeks into osteochondral tissue, with characteristic architectural features including a hyaline-like neocartilage layer with good surface regularity and complete integration with the adjacent host cartilage and a regenerated subchondral bone. By 12 weeks, the HCCEC-regenerated osteochondral tissue resembled closely that of age-matched unoperated native control, while only fibrous tissue filled in the control defects which left empty or treated with hydrogel alone. Here we demonstrate that transplanted hESC-derived chondrogenic cells maintain long-term viability with no evidence of tumorigenicity, providing a safe, highly-efficient and practical strategy of applying hESCs for cartilage tissue engineering.

More insight into mesenchymal stem cells and their effects inside the body

IMPORTANCE OF THE FIELD

The pan-tissue existence and multipotency of differentiation make mesenchymal stem cells (MSCs) an attractive source of cells as tissue repair cells, seeds of engineered tissue, vehicles for gene therapy or in combination to promote tissue regeneration in wound healing and disease recovery.

AREAS COVERED IN THIS REVIEW

This review focuses on recent understanding on MSC's basic biological characteristics and the mechanisms underlying the therapeutic effects of MSCs in vivo.

WHAT THE READER WILL GAIN

The gene expression profiles for mRNA, protein, microRNA and cell surface marker of MSCs are summarized. Special attention is given to miRNA expression and its relationship with the characteristics of MSCs. The mechanisms of therapeutic effects of MSCs are attributed to their ability to migrate along chemokine gradients, differentiate into tissue-specific cells, enhance angiogenesis of wound tissue and regulate immune response. As examples, a detailed description is given on the regeneration of functional sweat glands on burned skin as well as neural cells in middle cerebral artery occlusion (MCAO) animals upon MSC transplantation.

TAKE HOME MESSAGE

Based on current data, although limited, the mesenchymal-epithelial transition is proposed to be one of the important ways for MSCs to participate tissue repair.

Nanotechnology for treatment of stroke and spinal cord injury

The use of nanotechnology in cell therapy and tissue engineering offers promising future perspectives for brain and spinal cord injury treatment. Stem cells have been shown to selectively target injured brain and spinal cord tissue and improve functional recovery. To allow cell detection, superparamagnetic iron-oxide nanoparticles can be used to label transplanted cells. MRI is then a suitable method for the in vivo tracking of grafted cells in the host organism. CNS, and particularly spinal cord, injury is accompanied by tissue damage and the formation of physical and biochemical barriers that prevent axons from regenerating. One aspect of nanomedicine is the development of biologically compatible nanofiber scaffolds that mimic the structure of the extracellular matrix and can serve as a permissive bridge for axonal regeneration or as a drug-delivery system. The incorporation of biologically active epitopes and/or the utilization of these scaffolds as stem cell carriers may further enhance their therapeutic efficacy.

The use of microgel iron oxide nanoparticles in studies of magnetic resonance relaxation and endothelial progenitor cell labelling

In vivo tracking of stem cells after transplantation is crucial for understanding cell-fate and therapeutic efficacy. By labelling stem cells with magnetic particles, they can be tracked by Magnetic Resonance Imaging (MRI). We previously demonstrated that microgel iron oxide nanoparticle (MGIO) provide superior tracking sensitivity over commercially available particles. Here, we describe the synthesis of MGIO and report on their morphology, hydrodynamic diameters (87-766 nm), iron oxide weight content (up to 82%) and magnetization characteristics (M(s)=52.9 Am(2)/kg, M(R)=0.061 Am(2)/kg and H(c)=0.672 A/m). Their MR relaxation characteristics are comparable to those of theoretical models and represent the first such correlation between model and real particles of varying diameters. A labelling study of primary endothelial progenitor cells also confirms that MGIO is an efficient label regardless of cell type. The facile synthesis of MGIO makes it a useful tool for the studying of relaxation induced by magnetic particles and cellular tracking by MRI.

Neo-vascularization and bone formation mediated by fetal mesenchymal stem cell tissue-engineered bone grafts in critical-size femoral defects

Tissue-engineered bone grafts (TEBG) require highly osteogenic cell sources for use in fracture repair applications. Compared to other sources of mesenchymal stem cells (MSC), human fetal MSC (hfMSC) have recently been shown to be more proliferative and osteogenic. We studied the functional performance of hfMSC-mediated TEBG in 7 mm rat femoral critical-sized bone defects (CSD). Dynamically-cultured and osteogenically-primed hfMSC seeded onto macroporous poly-epsilon-caprolactone tri-calcium phosphate scaffolds were transplanted into CSDs. After 12 weeks, hfMSC-mediated TEBG induced 2.1x more new bone formation (43.3+/-10.5 vs. 21.0+/-7.4 mm(3), p<0.05), with greater compact and woven bone, and a 9.8x increase in stiffness (3.9+/-1.7 vs. 0.4+/-0.3 mNm/degree, p<0.05) compared to acellular scaffolds, such that only animals transplanted with TEBG underwent full fracture repair of the CSD. Although hfMSC survived for <4 weeks, by 4 weeks they were associated with a 3.9x larger vasculature network in the defect area (35.2+/-11.1 vs. 6.5+/-3.6 mm(3)p<0.05), suggesting an important role for hfMSC in the promotion of neo-vasculogenesis. We speculate that hfMSC-mediated healing of the CSD by stimulating neo-vascularization through as yet undetermined mechanisms. This proof-of-principle study demonstrates the utility of primitive MSC for bone regeneration, and may be of relevance to vascularization in other areas of regenerative medicine.