Immunophenotypic changes of human articular chondrocytes during monolayer culture reflect bona fide dedifferentiation rather than amplification of progenitor cells

In this study, a time-course comparison of human articular chondrocytes (HAC) and bone marrow-derived mesenchymal stem cells (MSC) immunophenotype was performed in order to determine similarities/differences between both cell types during monolayer culture, and to identify HAC surface markers indicative of dedifferentiation. Our results show that dedifferentiated HAC can be distinguished from MSC by combining CD14, CD90, and CD105 expression, with dedifferentiated HAC being CD14+/CD90bright/CD105dim and MSC being CD14-/CD90dim/CD105bright. Surface markers on MSC showed little variation during the culture, whereas HAC showed upregulation of CD90, CD166, CD49c, CD44, CD10, CD26, CD49e, CD151, CD51/61, and CD81, and downregulation of CD49a, CD54, and CD14. Thus, dedifferentiated HAC appear as a bona fide cell population rather than a small population of MSC amplified during monolayer culture. While most of the HAC surface markers showed major changes at the beginning of the culture period (Passage 1-2), CD26 was upregulated and CD49a downregulated at later stages of the culture (Passage 3-4). To correlate changes in HAC surface markers with changes in extracellular matrix gene expression during monolayer culture, CD14 and CD90 mRNA levels were combined into a new differentiation index and compared with the established differentiation indices based on the ratios of mRNA levels of collagen type II to I (COL2/COL1) and of aggrecan to versican (AGG/VER). A correlation of CD14/CD90 ratio at the mRNA and protein level with the AGG/VER ratio during HAC dedifferentiation in monolayer culture validated CD14/CD90 as a new membrane and mRNA based HAC differentiation index.

Mesenchymal progenitor cell markers in human articular cartilage: normal distribution and changes in osteoarthritis

INTRODUCTION: Recent findings suggest that articular cartilage contains mesenchymal progenitor cells. The aim of this study was to examine the distribution of stem cell markers (Notch-1, Stro-1 and VCAM-1) and of molecules that modulate progenitor differentiation (Notch-1 and Sox9) in normal adult human articular cartilage and in osteoarthritis (OA) cartilage. METHODS: Expression of the markers was analyzed by immunohistochemistry (IHC) and flow cytometry. Hoechst 33342 dye was used to identify and sort the cartilage side population (SP). Multilineage differentiation assays including chondrogenesis, osteogenesis and adipogenesis were performed on SP and non-SP (NSP) cells. RESULTS: A surprisingly high number (>45%) of cells were positive for Notch-1, Stro-1 and VCAM-1 throughout normal cartilage. Expression of these markers was higher in the superficial zone (SZ) of normal cartilage as compared to the middle zone (MZ) and deep zone (DZ). Non-fibrillated OA cartilage SZ showed reduced Notch-1 and Sox9 staining frequency, while Notch-1, Stro-1 and VCAM-1 positive cells were increased in the MZ. Most cells in OA clusters were positive for each molecule tested. The frequency of SP cells in cartilage was 0.14 +/- 0.05% and no difference was found between normal and OA. SP cells displayed chondrogenic and osteogenic but not adipogenic differentiation potential. CONCLUSIONS: These results show a surprisingly high number of cells that express putative progenitor cell markers in human cartilage. In contrast, the percentage of SP cells is much lower and within the range of expected stem cell frequency. Thus, markers such as Notch-1, Stro-1 or VCAM-1 may not be useful to identify progenitors in cartilage. Instead, their increased expression in OA cartilage implicates involvement in the abnormal cell activation and differentiation process characteristic of OA.

BMP-2 induces the expression of chondrocyte-specific genes in bovine synovium-derived progenitor cells cultured in three-dimensional alginate hydrogel

OBJECTIVE: According to recent reports, the synovial membrane may contain mesenchymal stem cells with the potential to differentiate into chondrocytes under appropriate conditions. In order to assess the usefulness of synovium-derived progenitor cells for the purposes of cartilage tissue engineering, we explored their requirements for the expression of chondrocyte-specific genes after expansion in vitro. DESIGN: Mesenchymal progenitor cells were isolated from the synovial membranes of bovine shoulder joints and expanded in two-dimensions on plastic surfaces. They were then seeded either as micromass cultures or as single cells within alginate gels, which were cultured in serum-free medium. Under these three-dimensional conditions, chondrogenesis is known to be supported and maintained. Cell cultures were exposed either to bone morphogenetic protein-2 (BMP-2) or to isoforms of transforming growth factor-beta (TGF-beta). The levels of mRNA for Sox9, collagen types I and II and aggrecan were determined by RT-PCR. RESULTS: When transferred to alginate gel cultures, the fibroblast-like synovial cells assumed a rounded form. BMP-2, but not isoforms of TGF-beta, stimulated, in a dose-dependent manner, the production of messenger RNAs (mRNAs) for Sox9, type II collagen and aggrecan. Under optimal conditions, the expression levels of cartilage-specific genes were comparable to those within cultured articular cartilage chondrocytes. However, in contrast to cultured articular cartilage chondrocytes, synovial cells exposed to BMP-2 continued to express the mRNA for alpha1(I) collagen. CONCLUSIONS: This study demonstrates that bovine synovium-derived mesenchymal progenitor cells can be induced to express chondrocyte-specific genes. However, the differentiation process is not complete under the chosen conditions. The stimulation conditions required for full transformation must now be delineated.

Novel cell-free strategy for therapeutic angiogenesis: in vitro generated conditioned medium can replace progenitor cell transplantation

BACKGROUND: Current evidence suggests that endothelial progenitor cells (EPC) contribute to ischemic tissue repair by both secretion of paracrine factors and incorporation into developing vessels. We tested the hypothesis that cell-free administration of paracrine factors secreted by cultured EPC may achieve an angiogenic effect equivalent to cell therapy. METHODOLOGY/PRINCIPAL FINDINGS: EPC-derived conditioned medium (EPC-CM) was obtained from culture expanded EPC subjected to 72 hours of hypoxia. In vitro, EPC-CM significantly inhibited apoptosis of mature endothelial cells and promoted angiogenesis in a rat aortic ring assay. The therapeutic potential of EPC-CM as compared to EPC transplantation was evaluated in a rat model of chronic hindlimb ischemia. Serial intramuscular injections of EPC-CM and EPC both significantly increased hindlimb blood flow assessed by laser Doppler (81.2+/-2.9% and 83.7+/-3.0% vs. 53.5+/-2.4% of normal, P<0.01) and improved muscle performance. A significantly increased capillary density (1.62+/-0.03 and 1.68+/-0.05/muscle fiber, P<0.05), enhanced vascular maturation (8.6+/-0.3 and 8.1+/-0.4/HPF, P<0.05) and muscle viability corroborated the findings of improved hindlimb perfusion and muscle function. Furthermore, EPC-CM transplantation stimulated the mobilization of bone marrow (BM)-derived EPC compared to control (678.7+/-44.1 vs. 340.0+/-29.1 CD34(+)/CD45(-) cells/1x10(5) mononuclear cells, P<0.05) and their recruitment to the ischemic muscles (5.9+/-0.7 vs. 2.6+/-0.4 CD34(+) cells/HPF, P<0.001) 3 days after the last injection. CONCLUSIONS/SIGNIFICANCE: Intramuscular injection of EPC-CM is as effective as cell transplantation for promoting tissue revascularization and functional recovery. Owing to the technical and practical limitations of cell therapy, cell free conditioned media may represent a potent alternative for therapeutic angiogenesis in ischemic cardiovascular diseases.

Bone-marrow derived progenitor cells are associated with psychosocial determinants of health after controlling for classical biological and behavioral cardiovascular risk factors

BACKGROUND: Circulating progenitor cells have been implicated with maintaining vascular integrity. Low counts are found in adults with high cardiovascular risk and are associated with impaired endothelial function. It remains unknown whether psychosocial risk factors are independently related to counts of circulating progenitor cells. METHODS: We investigated a random sample of 468 adult industrial employees (mean age 41.2 years, 89% men) of Caucasian origin. Cardiovascular risk factors (blood pressure, LDL, HDL and C-reactive protein), health behavior (smoking, alcohol and physical exercise), psychological variables (effort-reward imbalance social support, negative affectivity) and interaction terms served as predictors of circulating progenitor cells (CD34+ CD31dim) as enumerated by flow-cytometry. FINDINGS: Psychosocial variables were independently associated with progenitor cell counts. The association with risk factors increased with age (explained variance in 18-36 year olds R(2)=0.17, p=0.55; age 36.1-46 R(2)=0.32, p=0.001; age>46 R(2)=0.27, p<0.001). Data revealed a shift from a larger association between behavioral and psychosocial variables and cell counts to a stronger association between biological variables and cell counts in older individuals. A significant interaction was observed between smoking and effort-reward imbalance in middle-aged subjects, those with both risk factors present had lower cell counts. In older employees, the interaction between biological risk factors and smoking was related to lower cell counts. INTERPRETATION: In working middle-aged and older men, psychosocial risk factors were related to circulating counts of progenitor cells. Smoking interacted negatively with psychosocial risk factors (middle-aged men) or with biological risk factors (older employees).

3D scaffolds co-seeded with human endothelial progenitor and mesenchymal stem cells: evidence of prevascularisation within 7 days

Blood supply is a critical issue in most tissue engineering approaches for large defect healing. As vessel ingrowth from surrounding tissues is proven to be insufficient, current strategies are focusing on the neo-vascularisation process. In the present study, we developed an in vitro pre-vascularised construct using 3D polyurethane (PU) scaffolds, based on the association of human Endothelial Progenitor Cells (EPC, CD34+ and CD133+) with human Mesenchymal Stem Cells (MSC). We showed the formation of luminal tubular structures in the co-seeded scaffolds as early as day 7 in culture. These tubular structures were proven positive for endothelial markers von Willebrand Factor and PECAM-1. Of special significance in our constructs is the presence of CD146-positive cells, as a part of the neovasculature scaffolding. These cells, coming from the mesenchymal stem cells population (MSC or EPC-depleted MSC), also expressed other markers of pericyte cells (NG2 and αSMA) that are known to play a pivotal function in the stabilisation of newly formed pre-vascular networks. In parallel, in co-cultures, osteogenic differentiation of MSCs occurred earlier when compared to MSCs monocultures, suggesting the close cooperation between the two cell populations. The presence of angiogenic factors (from autologous platelet lysates) in association with osteogenic factors seems to be crucial for both cell populations' cooperation. These results are promising for future clinical applications, as all components (cells, growth factors) can be prepared in an autologous way.

Identification and isolation of small CD44-negative mesenchymal stem/progenitor cells from human bone marrow using elutriation and polychromatic flow cytometry

The method of isolation of bone marrow (BM) mesenchymal stem/stromal cells (MSCs) is a limiting factor in their study and therapeutic use. MSCs are typically expanded from BM cells selected on the basis of their adherence to plastic, which results in a heterogeneous population of cells. Prospective identification of the antigenic profile of the MSC population(s) in BM that gives rise to cells with MSC activity in vitro would allow the preparation of very pure populations of MSCs for research or clinical use. To address this issue, we used polychromatic flow cytometry and counterflow centrifugal elutriation to identify a phenotypically distinct population of mesenchymal stem/progenitor cells (MSPCs) within human BM. The MSPC activity resided within a population of rare, small CD45⁻CD73⁺CD90⁺CD105⁺ cells that lack CD44, an antigen that is highly expressed on culture-expanded MSCs. In culture, these MSPCs adhere to plastic, rapidly proliferate, and acquire CD44 expression. They form colony forming units-fibroblast and are able to differentiate into osteoblasts, chondrocytes, and adipocytes under defined in vitro conditions. Their acquired expression of CD44 can be partially downregulated by treatment with recombinant human granulocyte-colony stimulating factor, a response not found in BM-MSCs derived from conventional plastic adherence methods. These observations indicate that MSPCs within human BM are rare, small CD45⁻CD73⁺CD90⁺CD105⁺ cells that lack expression of CD44. These MSPCs give rise to MSCs that have phenotypic and functional properties that are distinct from those of BM-MSCs purified by plastic adherence.

Creatine supports propagation and promotes neuronal differentiation of inner ear progenitor cells

Long-term propagation of inner ear-derived progenitor/stem cells beyond the third generation and differentiation into inner ear cell types has been shown to be feasible, but challenging. We investigated whether the known neuroprotective guanidine compound creatine (Cr) promotes propagation of inner ear progenitor/stem cells as mitogen-expanded neurosphere cultures judged from the formation of spheres over passages. In addition, we studied whether Cr alone or in combination with brain-derived neurotrophic factor (BDNF) promotes neuronal differentiation of inner ear progenitors. For this purpose, early postnatal rat spiral ganglia, utricle, and organ of Corti-derived progenitors were grown as floating spheres in the absence (controls) or presence of Cr (5 mM) from passage 3 onward. Similarly, dissociated sphere-derived cultures were differentiated for 14 days in the presence or absence of Cr (5 mM) and spiral ganglia sphere-derived cultures in a combination of Cr with the neurotrophin BDNF (50 ng/ml). We found that the cumulative total number of spheres over all passages was significantly higher after Cr supplementation as compared with controls in all the three inner ear cultures. In contrast, sphere sizes were not affected by the administration of Cr. Administration of Cr during differentiation of spiral ganglia cells resulted in a significantly higher density of β-III-tubulin-positive cells compared with controls, whereas densities of myosin VIIa-positive cells in cultures of utricle and organ of Corti were not affected by the treatment. Importantly, a combination of Cr with the neurotrophin BDNF resulted in further significantly increased densities of β-III-tubulin-positive cells in cultures of spiral ganglia cells as compared with single treatments. In sum, Cr promoted continuing propagation of rat inner ear-derived progenitor cells and supported specifically in combination with BDNF the differentiation of neuronal cell types from spiral ganglion-derived spheres.