Hydrolyzed fish collagen induced chondrogenic differentiation of equine adipose tissue-derived stromal cells

Adipose-derived stromal cells (ADSCs) are multipotent cells which, in the presence of appropriate stimuli, can differentiate into various lineages such as the osteogenic, adipogenic and chondrogenic. In this study, we investigated the effect of transforming growth factor beta 1 (TGF-β1) in comparison to hydrolyzed fish collagen in terms of the chondrogenic differentiation potential of ADSCs. ADSCs were isolated from subcutaneous fat of horses by liposuction. Chondrogenesis was investigated using a pellet culture system. The differentiation medium was either supplemented with TGF-β1 (5 ng/ml) or fish collagen (0.5 mg/ml) for a 3 week period. After the 3 weeks in vitro differentiation, RT-PCR and histological staining for proteoglycan synthesis and type II collagen were performed to evaluate the degree of chondrogenic differentiation and the formation of cartilaginous extracellular matrix (ECM). The differentiation of ADSCs induced by TGF-β1 showed a high expression of glycosaminoglycan (GAG). Histological analysis of cultures stimulated by hydrolyzed fish collagen demonstrated an even higher GAG expression than cultures stimulated under standard conditions by TGF-β1. The expression of cartilage-specific type II collagen and Sox9 was about the same in both stimulated cultures. In this study, chondrogenesis was as effectively induced by hydrolyzed fish collagen as it was successfully induced by TGF-β1. These findings demonstrated that hydrolyzed fish collagen alone has the potential to induce and maintain ADSCs-derived chondrogenesis. These results support the application of ADSCs in equine veterinary tissue engineering, especially for cartilage repair.     

Analysis of collagen expression during chondrogenic induction of human bone marrow mesenchymal stem cells

Adult mesenchymal stem cells (MSCs) are currently being investigated as an alternative to chondrocytes for repairing cartilage defects. As several collagen types participate in the formation of cartilage-specific extracellular matrix, we have investigated their gene expression levels during MSC chondrogenic induction. Bone marrow MSCs were cultured in pellet in the presence of BMP-2 and TGF-β3 for 24 days. After addition of FGF-2, at the fourth passage during MSC expansion, there was an enhancing effect on specific cartilage gene expression when compared to that without FGF-2 at day 12 in pellet culture. A switch in expression from the pre-chondrogenic type IIA form to the cartilage-specific type IIB form of the collagen type II gene was observed at day 24. A short-term addition of FGF-2 followed by a treatment with BMP-2/TGF-β3 appears sufficient to accelerate chondrogenesis with a particular effect on the main cartilage collagens.     

FGF-2 increases osteogenic and chondrogenic differentiation potentials of human mesenchymal stem cells by inactivation of TGF-β signaling

Human mesenchymal stem cells (hMSCs) are able to self-replicate and differentiate into a variety of cell types including osteoblasts, chondrocytes, adipocytes, endothelial cells, and muscle cells. It was reported that fibroblast growth factor-2 (FGF-2) increased the growth rate and multidifferentiation potentials of hMSCs. In this study, we investigated the genes involved in the promotion of osteogenic and chondrogenic differentiation potentials of hMSCs in the presence of FGF-2. hMSCs were maintained in the medium with FGF-2. hMSCs were harvested for the study of osteogenic or chondrogenic differentiation potential after 15 days’ culture. To investigate osteogenic differentiation, the protein levels of alkaline phosphatase (ALP) and the mRNA expression levels of osteocalcin were measured after the induction of osteogenic differentiation. Moreover, the investigation for chondrogenic differentiation was performed by measuring the mRNA expression levels of type II and type X collagens after the induction of chondrogenic differentiation. The expression levels of ALP, type II collagen, and type X collagen of hMSCs cultured with FGF-2 were significantly higher than control. These results suggested that FGF-2 increased osteogenic and chondrogenic differentiation potentials of hMSCs. Furthermore, microarray analysis was performed after 15 days’ culture in the medium with FGF-2. We found that the overall insulin-like growth factor-I (IGF-I) and transforming growth factor-β (TGF-β) signaling pathways were inactivated by FGF-2. These results suggested that the inactivation of IGF-I and TGF-β signaling promotes osteogenic and chondrogenic differentiation potential of hMSCs in the presence of FGF-2.     

Alpha-smooth muscle actin expression and structure integrity in chondrogenesis of human mesenchymal stem cells

The expression of alpha-smooth muscle actin (SMA) by human mesenchymal stem cells (hMSCs) during chondrogenesis was investigated by the use of pellet culture. Undifferentiated hMSCs expressed low but detectable amounts of SMA and the addition of transforming growth factor β1 (TGF-β1) to the culture medium increased SMA expression in a dose-dependent manner. Differentiation in pellet culture was rapidly induced in the presence of TGF-β1 and was accompanied by the development of annular layers at the surface of the pellet. These peripheral layers lacked expression of glycosaminoglycan and type II collagen during early differentiation. Progress in differentiation increased the synthesis of glycosaminoglycan and type II collagen and the expression of SMA in these layers. Double-staining for type II collagen and SMA by immunofluorescence demonstrated the differentiation of hMSCs into cells positive for these two proteins. The addition of cytochalasin D, a potent inhibitor of the polymerization of actin microfilaments, caused damage to the structural integrity and surface smoothness of the chondrogenic pellets. The SMA-positive cells in the peripheral layers of the chondrogenic pellets mimic those within the superficial layer of articular cartilage and are speculated to play a major role in cartilage development and maintenance.This work was supported by grants R92-001-1 and R92-001-2 from the Veterans General Hospital, Taipei, and grant NSC-92-2314-B-075-022 from the National Science Council, Taiwan.     

Regulation of osteogenic and chondrogenic differentiation of mesenchymal stem cells in PEG-ECM hydrogels

Bone-marrow-derived mesenchymal stem cells (MSCs) are candidates for regeneration applications in musculoskeletal tissue such as cartilage and bone. Various soluble factors in the form of growth factors and cytokines have been widely studied for directing the chondrogenic and osteogenic differentiation of MSCs, but little is known about the way that the composition of extracellular matrix (ECM) components in three-dimensional microenvironments plays a role in regulating the differentiation of MSCs. To define whether ECM components influence the regulation of osteogenic and chondrogenic differentiation by MSCs, we encapsulated MSCs in poly-(ethylene glycol)-based (PEG-based) hydrogels containing exogenous type I collagen, type II collagen, or hyaluronic acids (HA) and cultured them for up to 6 weeks in chondrogenic medium containing transforming growth factor-β1 (10 ng/ml) or osteogenic medium. Actin cytoskeleton organization and cellular morphology were strongly dependent on which ECM components were added to the PEG-based hydrogels. Additionally, chondrogenic differentiation of MSCs was marginally enhanced in collagen-matrix-based hydrogels, whereas osteogenic differentiation, as measured by calcium accumulation, was induced in HA-containing hydrogels. Thus, the microenvironments created by exogenous ECM components seem to modulate the fate of MSC differentiation.     

Oxygen tension regulates the osteogenic, chondrogenic and endochondral phenotype of bone marrow derived mesenchymal stem cells

The local oxygen tension is a key regulator of the fate of mesenchymal stem cells (MSCs). The objective of this study was to investigate the effect of a low oxygen tension during expansion and differentiation on the proliferation kinetics as well as the subsequent osteogenic and chondrogenic potential of MSCs. We first hypothesised that expansion in a low oxygen tension (5% pO(2)) would improve both the subsequent osteogenic and chondrogenic potential of MSCs compared to expansion in a normoxic environment (20% pO(2)). Furthermore, we hypothesised that chondrogenic differentiation in a low oxygen environment would suppress hypertrophy of MSCs cultured in both pellets and hydrogels used in tissue engineering strategies. MSCs expanded at 5% pO(2) proliferated faster forming larger colonies, resulting in higher cell yields. Expansion at 5% pO(2) also enhanced subsequent osteogenesis of MSCs, whereas differentiation at 5% pO(2) was found to be a more potent promoter of chondrogenesis than expansion at 5% pO(2). Greater collagen accumulation, and more intense staining for collagen types I and X, was observed in pellets maintained at 20% pO(2) compared to 5% pO(2). Both pellets and hydrogels stained more intensely for type II collagen when undergoing chondrogenesis in a low oxygen environment. Differentiation at 5% pO(2) also appeared to inhibit hypertrophy in both pellets and hydrogels, as demonstrated by reduced collagen type X and Alizarin Red staining and alkaline phosphatase activity. This study demonstrates that the local oxygen environment can be manipulated in vitro to either stabilise a chondrogenic phenotype for use in cartilage repair therapies or to promote hypertrophy of cartilaginous grafts for endochondral bone repair strategies.     

软骨寡聚基质蛋白过表达对BMP-2诱导骨髓间充质干细胞分化的影响

目的：研究软骨寡聚基质蛋白（cartilage oligomeric matrix protein,COMP）过表达对BMP-2诱导骨髓间充质干细胞成骨及成软骨分化的影响。方法：BMP-2诱导骨髓间充质干细胞分化,通过脂质体转染含人COMP基因的质粒使骨髓间充质干细胞过表达COMP,采用实时定量PCR和Western blotting分析COMP基因过表达、成骨相关基因Ⅰ型胶原、RUNX2、骨钙蛋白以及成软骨相关基因Ⅱ型胶原、SOX9、蛋白聚糖、X型胶原的表达变化;通过茜素红染色观察成骨终末阶段矿化结节的生成情况,阿利新蓝染色观察细胞基质蛋白多糖的合成情况。结果：质粒转染后骨髓间充质干细胞COMP基因蛋白和mRNA表达水平显著提高（P<0.05）。COMP基因过表达后,成骨标记基因RUNX2、Ⅰ型胶原（Col1a1）mRNA水平均显著低于对照组（P<0.05）,RUNX2、骨钙蛋白（Osteocalcin）蛋白表达水平明显低于对照组（P<0.05）,而成软骨标记基因SOX9、蛋白聚糖（Aggrecan）mRNA水平均显著高于对照组（P<0.05）,SOX9、Ⅱ型胶原（Col2a1）蛋白表达均明显多于对照组（P<0.05）。细胞成骨茜素红染色弱于对照组,而阿利新蓝染色强于对照组。过表达组细胞X型胶原（Col10a1）基因表达显著低于对照组（P<0.05）,结论：骨髓间充质干细胞COMP基因过表达可抑制BMP-2诱导其成骨分化,促进骨髓间充质干细胞成软骨分化,并抑制软骨细胞的成熟肥大,为软骨组织工程研究提供新的方向。     

Adenoviral transduction of hTGF-β1 enhances the chondrogenesis of bone marrow derived stromal cells

TGF-β1 plays a necessary and important role in the induction of chondrogenic differentiation of bone marrow stromal cells (BMSCs). In this study, porcine BMSCs were infected with a replication-deficient adenovirus expression vector carrying the hTGF-β1 gene. The transduced BMSCs were cultured as pelleted micromasses in vitro for 21 days, seeded onto disk-shaped PGA scaffolds for 3 days and subsequently implanted into the subcutaneous tissue of mice. BMSCs transduced with AdhTGF-β1 expressed and secreted more hTGF-β1 protein in vitro than those of the control group. Histological and immunohistological examination of the pellets revealed robust chondrogenic differentiation. Tissues made from cells transduced with AdhTGF-β1 exhibited neocartilage formation after 3 weeks in vivo. The neocartilage occupied 42 ± 5% of the total tissue volume which was significantly greater than that of the control group. Furthermore, there was extensive staining for sulfated proteoglycans and type II collagen in the AdhTGF-β1 group compared to controls, and quantification of GAG content showed significantly greater amounts of GAG in experimental groups. The results demonstrate that transfer of hTGF-β1 into BMSCs via adenoviral transduction can induce chondrogenic differentiation in vitro and enhance chondrogenesis in vivo.     

TGF-β1 and serum both stimulate contraction but differentially affect apoptosis in 3D collagen gels

Apoptosis of fibroblasts may be key for the removal of cells following repair processes. Contraction of three-dimensional collagen gels is a model of wound healing and remodeling. Here two potent inducers of contraction, TGF-β1 and fetal calf serum (FCS) were evaluated for their effect on fibroblast apoptosis in contracting collagen gels. Human fetal lung fibroblasts were cultured in floating type I collagen gels, exposed to TGF-β1 or FCS, and allowed to contract for 5 days. Apoptosis was evaluated using TUNEL and confirmed by DNA content profiling. Both TGF-β1 and serum significantly augmented collagen gel contraction. TGF-β1 also increased apoptosis assessed by TUNEL positivity and DNA content analysis. In contrast, serum did not affect apoptosis. TGF-β1 induction of apoptosis was associated with augmented expression of Bax, a pro-apoptotic member of the Bax/Bcl-2 family, inhibition of Bcl-2, an anti-apoptotic member of the same family, and inhibition of both cIAP-1 and XIAP, two inhibitors of the caspase cascade. Serum was associated with an increase in cIAP-1 and Bcl-2, anti-apoptotic proteins. Interestingly, serum was also associated with an apparent increase in Bax, a pro-apoptotic protein. Blockade of Smad3 with either siRNA or by using murine fibroblasts deficient in Smad3 resulted in a lack of TGF-β induction of augmented contraction and apoptosis. Contraction induced by different factors, therefore, may be differentially associated with apoptosis, which may be related to the persistence or resolution of the fibroblasts that accumulate following injury.     

Chondrogenic differentiation of amniotic fluid-derived stem cells

For regenerating damaged articular cartilage, it is necessary to identify an appropriate cell source that is easily accessible, can be expanded to large numbers, and has chondrogenic potential. Amniotic fluid-derived stem (AFS) cells have recently been isolated from human and rodent amniotic fluid and shown to be highly proliferative and broadly pluripotent. The purpose of this study was to investigate the chondrogenic potential of human AFS cells in pellet and alginate hydrogel cultures. Human AFS cells were expanded in various media conditions, and cultured for three weeks with growth factor supplementation. There was increased production of sulfated glycosaminoglycan (sGAG) and type II collagen in response to transforming growth factor-β (TGF-β) supplementation, with TGF-β1 producing greater increases than TGF-β3. Modification of expansion media supplements and addition of insulin-like growth factor-1 during pellet culture further increased sGAG/DNA over TGF-β1 supplementation alone. Compared to bone marrow-derived mesenchymal stem cells, the AFS cells produced less cartilaginous matrix after three weeks of TGF-β1 supplementation in pellet culture. Even so, this study demonstrates that AFS cells have the potential to differentiate along the chondrogenic lineage, thus establishing the feasibility of using these cells for cartilage repair applications.     

Transient down-regulation of cbfa1/Runx2 by RNA interference in murine C3H10T1/2 mesenchymal stromal cells delays in vitro and in vivo osteogenesis, but does not overtly affect chondrogenesis

In order to ensure that MSCs designed for in vivo cartilage repair do not untowardly differentiate into osteoblasts and mineralize in situ, we tested whether siRNA-induced suppression of cbfa1/Runx2 affected the osteogenic and chondrogenic differentiation potential of the murine cell line C3H10T1/2. Anti-cbfa1/Runx2 siRNA decreased the levels of cbfa1/Runx2 mRNA and protein by 65-80%, and also markedly reduced the expression of osteoblast-related genes such as Dlx5, osterix, collagen type I, alkaline phosphatase (AP), osteocalcin, SPARC/osteonectin and osteopontin, leading to a temporal expression of AP enzyme activity and mineralization potential delayed by at least some 7-9 days. Furthermore, siRNA-transfected cells, grown under chondrogenic conditions did not display biologically significant changes in the expression of aggrecan, collagen type II or type X, or histology when grown in micropellets or monolayer cultures. Finally, when cells were propagated in osteogenic medium and injected into the tibial muscles of SCID mice, no overtly mineralized bone tissue emerged. These experiments indicate that a major transient reduction of cbfa1/Runx2 expression in MSCs is sufficient to delay osteoblastic differentiation, both in vitro and in vivo, while chondrogenesis seemed to be sustained.     

Chondrogenic differentiation of bovine bone marrow mesenchymal stem cells (MSCs) in different hydrogels: influence of collagen type II extracellular matrix on MSC chondrogenesis

Bone marrow mesenchymal stem cells (MSCs) are candidate cells for cartilage tissue engineering. This is due to their ability to undergo chondrogenic differentiation after extensive expansion in vitro and stimulation with various biomaterials in three-dimensional (3-D) systems. Collagen type II is one of the major components of the hyaline cartilage and plays a key role in maintaining chondrocyte function. This study aimed at analyzing the MSC chondrogenic response during culture in different types of extracellular matrix (ECM) with a focus on the influence of collagen type II on MSC chondrogenesis. Bovine MSCs were cultured in monolayer as well as in alginate and collagen type I and II hydrogels, in both serum free medium and medium supplemented with transforming growth factor (TGF) beta1. Chondrogenic differentiation was detected after 3 days of culture in 3-D hydrogels, by examining the presence of glycosaminoglycan and newly synthesized collagen type II in the ECM. Differentiation was most prominent in cells cultured in collagen type II hydrogel, and it increased in a time-dependent manner. The expression levels of the of chondrocyte specific genes: sox9, collagen type II, aggrecan, and COMP were measured by quantitative "Real Time" RT-PCR, and genes distribution in the hydrogel beads were localized by in situ hybridization. All genes were upregulated by the presence of collagen, particularly type II, in the ECM. Additionally, the chondrogenic influence of TGF beta1 on MSCs cultured in collagen-incorporated ECM was analyzed. TGF beta1 and dexamethasone treatment in the presence of collagen type II provided more favorable conditions for expression of the chondrogenic phenotype. In this study, we demonstrated that collagen type II alone has the potential to induce and maintain MSC chondrogenesis, and prior interaction with TGF beta1 to enhance the differentiation.     

Chondrogenesis of human periosteum-derived progenitor cells in atelocollagen

Periosteum-derived progenitor cells (PDPCs) could be differentiated into cartilage using atelocollagen as a carrier and in the presence of transforming growth factor-β3 (TGF-β3). Chondrogenesis was verified by RT-PCR and Western blotting. Expression of the type II collagen mRNA was found from the differentiated PDPCs in atelocollagen 3 weeks after chondrogenic induction. The chondrogenic potential of the PDPCs was also verified by histochemical staining for type II collagen protein. Increased production of glycosaminoglycan shows that the PDPCs in atelocollagen could differentiate into chondrocytes under a chondrogenic environment. PDPCs can therefore be used as a cell source for cell-based therapies targeted toward the articular cartilage of the knee.     

Transforming growth factor-beta 1 in adipose derived stem cells conditioned medium is a dominant paracrine mediator determines hyaluronic acid and collagen expression profile

Conditioned medium from adipose derived stem cells (ADSC-CM) stimulates both collagen synthesis and migration of fibroblasts, and accelerates wound healing in vivo. Recently, the production and secretion of growth factors has been identified as an essential function of adipose-derived stem cells (ADSCs). However, the main soluble factor of ADSC-CM which mediates paracrine effects and its underlying mechanism has not been elucidated yet. In this study, we considered transforming growth factor-beta1 (TGF-β1) as a strong candidate for paracrine effect of ADSC-CM and investigated collagen synthesis and hyaluronic acid synthase (HAS) expression. After ADSC-CM addition, collagen type I, type III, HAS and hyaluronic acid (HA) expressions on human dermal fibroblasts (HDFs) were evaluated. Furthermore, to clarify effects of TGF-β1 as a paracrine mediator, TGF-β1 antibody and external supplementary TGF-β1 were treated to HDFs. Collagens type I, type III, HAS-1 and HAS-2 mRNA expressions of HDFs were greatly increased by ADSC-CM treatment, however there was no change in TGF-β1 antibody treated HDFs compared with non-treated control. These results strongly demonstrate that TGF-β1 plays an important role as a paracrine mediator of ECM synthesis. The fact that TGF-β1 contained in ADSC-CM not only accelerates collagen deposition but also increase hyaluronic acid synthesis of HDFs through HAS-1 and HAS-2 expression was also elucidated in this study. Therefore, ADSC-CM shows promise for the treatment of cutaneous wounds and accelerates granulation formation during healing process.     

Dose dependent effect of C-type natriuretic peptide signaling in glycosaminoglycan synthesis during TGF-β1 induced chondrogenic differentiation of mesenchymal stem cells

Recent investigations credited important roles to C-type natriuretic peptide (CNP) signaling during chondrogenesis. This study investigated the putative role of CNP in transforming growth factor (TGF)-β1 induced in vitro chondrogenic differentiation of mesenchymal stem cells (MSCs) in pellet culture. MSCs were derived from human trabecular bone and were characterized on the basis of their cell surface antigens and adipogenic, osteogenic, and chondrogenic differentiation potential. TGF-β1 induced chondrogenic differentiation and glycosaminoglycan (GAG) synthesis was analyzed on the basis of basic histology, collagen type II, Sox 9 and aggrecan expressions, and Alcian blue staining. Results revealed that human trabecular bone-derived MSCs express CNP and NPR-B analyzed on the basis of RT-PCR and immunohistochemistry. In pellet cultures of MSCs TGF-β1 successfully induced chondrogenic differentiation and GAG synthesis. RT-PCR analyses of both CNP and NPR-B during this process revealed an activation of this signaling pathway in response to TGF-β1. Similar cultures induced with TGF-β1 and treated with different doses of CNP showed that CNP supplementation at 10^?8 and 10^?7 M concentrations significantly increased GAG synthesis in a dose dependent manner, whereas at 10^?6 M concentration this stimulatory effect was diminished. In conclusion, CNP/NPR-B signaling pathway is activated during TGF-β1 induced chondrogenic differentiation of human trabecular bone-derived MSCs and may strongly be involved in GAG synthesis during this process. This effect is likely to be a dose-dependent effect.     

Dose-Response of Superparamagnetic Iron Oxide Labeling on Mesenchymal Stem Cells Chondrogenic Differentiation: A Multi-Scale In Vitro Study

Aim

The aim of this work was the development of successful cell therapy techniques for cartilage engineering. This will depend on the ability to monitor non-invasively transplanted cells, especially mesenchymal stem cells (MSCs) that are promising candidates to regenerate damaged tissues.

Methods

MSCs were labeled with superparamagnetic iron oxide particles (SPIO). We examined the effects of long-term labeling, possible toxicological consequences and the possible influence of progressive concentrations of SPIO on chondrogenic differentiation capacity.

Results

No influence of various SPIO concentrations was noted on human bone marow MSC viability or proliferation. We demonstrated long-term (4 weeks) in vitro retention of SPIO by human bone marrow MSCs seeded in collagenic sponges under TGF-β1 chondrogenic conditions, detectable by Magnetic Resonance Imaging (MRI) and histology. Chondrogenic differentiation was demonstrated by molecular and histological analysis of labeled and unlabeled cells. Chondrogenic gene expression (COL2A2, ACAN, SOX9, COL10, COMP) was significantly altered in a dose-dependent manner in labeled cells, as were GAG and type II collagen staining. As expected, SPIO induced a dramatic decrease of MRI T2 values of sponges at 7T and 3T, even at low concentrations.

Conclusions

This study clearly demonstrates (1) long-term in vitro MSC traceability using SPIO and MRI and (2) a deleterious dose-dependence of SPIO on TGF-β1 driven chondrogenesis in collagen sponges. Low concentrations (12.5–25 µg Fe/mL) seem the best compromise to optimize both chondrogenesis and MRI labeling.     

The role of BMP‐7 in chondrogenic and osteogenic differentiation of human bone marrow multipotent mesenchymal stromal cells in vitro

This study addresses the role of bone morphogenetic protein‐7 (BMP‐7) in chondrogenic and osteogenic differentiation of human bone marrow multipotent mesenchymal stromal cells (BM MSCs) in vitro. BM MSCs were expanded and differentiated in the presence or absence of BMP‐7 in monolayer and three‐dimensional cultures. After 3 days of stimulation, BMP‐7 significantly inhibited MSC growth in expansion cultures. When supplemented in commonly used induction media for 7–21 days, BMP‐7 facilitated both chondrogenic and osteogenic differentiation of MSCs. This was evident by specific gene and protein expression analyses using real‐time PCR, Western blot, histological, and immunohistochemical staining. BMP‐7 supplementation appeared to enhance upregulation of lineage‐specific markers, such as type II and type IX collagens (COL2A1, COL9A1) in chondrogenic and secreted phosphoprotein 1 (SPP1), osteocalcin (BGLAP), and osterix (SP7) in osteogenic differentiation. BMP‐7 in the presence of TGF‐β3 induced superior chondrocytic proteoglycan accumulation, type II collagen, and SOX9 protein expression in alginate and pellet cultures compared to either factor alone. BMP‐7 increased alkaline phosphatase activity and dose‐dependently accelerated calcium mineralization of osteogenic differentiated MSCs. The potential of BMP‐7 to promote adipogenesis of MSCs was restricted under osteogenic conditions, despite upregulation of adipocyte gene expression. These data suggest that BMP‐7 is not a singular lineage determinant, rather it promotes both chondrogenic and osteogenic differentiation of MSCs by co‐ordinating with initial lineage‐specific signals to accelerate cell fate determination. BMP‐7 may be a useful enhancer of in vitro differentiation of BM MSCs for cell‐based tissue repair. J. Cell. Biochem. 109: 406–416, 2010. © 2009 Wiley‐Liss, Inc.