In Vitro Characterization of Human Mesenchymal Stem Cells Isolated from Different Tissues with a Potential to Promote Complex Bone Regeneration.

Bone tissue regeneration is a major, worldwide medical need, and several strategies have been developed to support the regeneration of extensive bone defects, including stem cell based bone grafts. In addition to the application of stem cells with high osteogenic potential, it is important to maintain proper blood flow in a bone graft to avoid inner graft necrosis. Mesenchymal stem cells (MSCs) may form both osteocytes and endothelial cells; therefore we examined the combined in vitro osteogenic and endothelial differentiation capacities of MSCs derived from adipose tissue, Wharton's jelly, and periodontal ligament. Based on a detailed characterization presented here, MSCs isolated from adipose tissue and periodontal ligament may be most appropriate for generating vascularized bone grafts.

ABCG2 is a selectable marker for enhanced multilineage differentiation potential in periodontal ligament stem cells.

Periodontal ligament stem cells (PDLSCs) provide an important source for tissue regeneration and may become especially useful in the formation of osteogenic seeds. PDLSCs can be cultured, expanded, and differentiated in vitro; thus, they may be applied in the long-term treatment of the defects in the dental regions. Here we studied numerous potential markers allowing the selection of human PDLSCs with a maximum differentiation potential. We followed the expression of the ATP-binding cassette subfamily G member 2 (ABCG2) membrane transporter protein and isolated ABCG2-expressing cells by using a monoclonal antibody, recognizing the transporter at the cell surface in intact cells. The expression of the ABCG2 protein, corresponding to the so-called side-population phenotype in various tissue-derived stem cells, was found to be a useful marker for the selection of PDLSCs with enhanced osteogenic, chondrogenic, and adipogenic differentiation. These findings may have important applications in achieving efficient dental tissue regeneration by using stem cells from extracted teeth.

A novel cyclic RGD-containing peptide polymer improves serum-free adhesion of adipose tissue-derived mesenchymal stem cells to bone implant surfaces.

Seeding of bone implants with mesenchymal stem cells (MSCs) may promote osseointegration and bone regeneration. However, implant material surfaces, such as titanium or bovine bone mineral, fail to support rapid and efficient attachment of MSCs, especially under serum-free conditions that may be desirable when human applications or tightly controlled experiments are envisioned. Here we demonstrate that a branched poly[Lys(Ser(i)-DL-Ala(m))] polymer functionalized with cyclic arginyl-glycyl-aspartate, when immobilized by simple adsorption to tissue culture plastic, surgical titanium alloy (Ti6Al4V), or Bio-Oss(®) bovine bone substitute, significantly accelerates serum-free adhesion and enhances seeding efficiency of human adipose tissue-derived MSCs. Moreover, when exposed to serum-containing osteogenic medium, MSCs survived and differentiated on the peptide-coated scaffolds. In summary, the presented novel polypeptide conjugate can be conveniently used for coating various surfaces, and may find applications whenever quick and efficient seeding of MSCs is required to various scaffolds in the absence of serum.

Combined introduction of Bmi-1 and hTERT immortalizes human adipose tissue-derived stromal cells with low risk of transformation.

Adipose tissue-derived stromal cells (ASCs) are increasingly being studied for their usefulness in regenerative medicine. However, limited life span and donor-dependent variation of primary cells such as ASCs present major hurdles to controlled and reproducible experiments. We therefore aimed to establish immortalized ASC cell lines that provide steady supply of homogeneous cells for in vitro work while retain essential features of primary cells. To this end, combinations of human telomerase reverse transcriptase (hTERT), murine Bmi-1, and SV40 large T antigen (SV40T) were introduced by lentiviral transduction into ASCs. The resulting cell lines ASC(hTERT), ASC(Bmi-1), ASC(Bmi-1+hTERT) and ASC(SV40T+hTERT) were tested for transgene expression, telomerase activity, surface immunomarkers, proliferation, osteogenic and adipogenic differentiation, karyotype, tumorigenicity, and cellular senescence. All cell lines have maintained expression of characteristic surface immunomarkers, and none was tumorigenic. However, ASC(Bmi-1) had limited replicative potential, while the rapidly proliferating ASC(SV40T+hTERT) acquired chromosomal aberrations, departed from MSC phenotype, and lost differentiation capacity. ASC(hTERT) and ASC(hTERT+Bmi-1), on the other hand, preserved all essential MSC features and did not senesce after 100 population doublings. Notably, a subpopulation of ASC(hTERT) also acquired aberrant karyotype and showed signs of transformation after long-term culture. In conclusion, hTERT alone was sufficient to extend the life span of human ASC, but ASC(hTERT) are prone to transformation during extensive subculturing. The combination of Bmi-1 and hTERT successfully immortalized human ASCs without significantly perturbing their phenotype or biological behavior.

Positional identity of murine mesenchymal stem cells resident in different organs is determined in the postsegmentation mesoderm.

Although mesenchymal stem cells (MSCs) of distinct tissue origin have a large number of similarities and differences, it has not been determined so far whether tissue-resident MSCs are the progenies of one ancestor cell lineage or the results of parallel cell developmental events. Here we compared the expression levels of 177 genes in murine MSCs derived from adult and juvenile bone marrow and adult adipose tissue, as well as juvenile spleen, thymus, and aorta wall by quantitative real-time polymerase chain reaction and the results were partially validated at protein level. All MSC lines uniformly expressed a large set of genes including well-known mesenchymal markers, such as α-smooth muscle actin, collagen type I α-chain, GATA6, Mohawk, and vimentin. In contrast, pluripotency genes and the early mesodermal marker T-gene were not expressed. On the other hand, different MSC lines consistently expressed distinct patterns of Hox genes determining the positional identity of a given cell population. Moreover, MSCs of different origin expressed a few other transcription factors also reflecting their topological identity and so the body segment or organ to which they normally contributed in vivo: (1) thymus-derived cells specifically expressed Tbx5 and Pitx2; (2) spleen-derived MSCs were characterized with Tlx1 and Nkx2.5; (3) Pitx1 designated femoral bone marrow cells and (4) En2 appeared in aorta wall-derived MSCs. Thus, MSCs exhibited topographic identity and memory even after long-term cultivation in vitro. On the basis of these results, we suggest that postnatal MSCs isolated from different anatomical sites descend from precursor cells developing in the postsegmentation mesoderm.