, showed that hypoxic conditions during expansion culture of human BMSCs resulted in improved chondrogenesis even under normoxic conditions. While it has been shown that normoxia isolated and expanded non-human and human BMSCs undergo enhanced chondrogenic differentiation under hypoxic conditions, it is unknown whether human BMSCs isolated and expanded under hypoxia are predisposed towards improved subsequent chondrogenesis regardless of the oxygen tension. However, it is not clear whether hypoxia isolated and propagated ovine BMSCs would have similarly displayed improved chondrogenesis had they been differentiated under hypoxic conditions. Moreover, it was demonstrated that ovine BMSCs isolated and expanded under hypoxic conditions and subsequent chondrogenic differentiation under normoxia displayed an enhanced chondrogenic phenotype compared to their counterparts after normoxia mediated isolation and expansion. Ovine BMSCs have been isolated and propagated under hypoxia (5% O 2) and shown to increase in proliferation rate relative to cells expanded under normoxia. investigated chondrogenesis on commercially acquired human BMSCs that lacked initial isolation and cell expansion culture history prior to further cell propagation under normoxia and subsequent chondrogenic differentiation under normoxia and hypoxia for their studies hypoxia enhanced BMSC chondrogenic differentiation potential. investigated osteogenic differentiation of BMSCs after hypoxia mediated expansion, while the study of Martin-Rendon et al.
While these studies demonstrated the effect of hypoxia on human BMSC expansion in vitro, the downstream effect of hypoxic conditions during isolation and expansion on human BMSCs' chondrogenic differentiation capacity was unexplored. Accordingly, human BMSCs showed enhanced proliferative activity under hypoxic (1.5% to 3% O 2) conditions relative to normoxia. In agreement with this observation, hypoxic (3% O 2) conditions have been reported to favor the multi-potentiality of a subpopulation of human bone marrow stromal cells over osteogenic differentiation.
While it is practiced within the art that human BMSCs are isolated after initial cell adherence to tissue culture plastic ware and subsequent cell expansion under normal mammalian conditions of air containing 21% oxygen tension (normoxia), there is increasing evidence that BMSCs are adapted to limiting metabolic conditions. Since the first published report of Friedenstein and co-workers, describing the isolation and expansion of an adherent and spindle-shaped population of cells from whole human bone marrow aspirates, little has changed in the methodology of isolation and expansion of BMSCs. Thus, in vitro culture expansion is a requisite for increasing cell numbers for research and clinical applications. Human BMSCs have been estimated to account for a mere 0.001% to 0.01% of the total bone marrow mononuclear cells (MNCs) in the stromal compartment of bone marrow. The reason for this is unclear but may be related to hypertrophic differentiation or the lack of a consensus on how human BMSCs are to be cultured for reproducible and optimal chondrogenic differentiation. While there has been much study related to the potential of BMSCs to form cartilaginous tissue, there has been a limited number of reports of the implantation of human BMSCs for cartilage repair. Thus, there is interest in other cell sources for cartilage repair.Īdherent bone marrow stromal cells or bone marrow mesenchymal stromal cells (BMSCs) have received much interest for cartilage repair because of their multipotent capacity to differentiate into different cell types including chondrocytes. Furthermore, there is evidence that the matrix-forming capacity of expanded chondrocytes is compromised due to de-differentiation processes. However, there is some evidence of progressive degenerative changes in the joint using this technique. Cell-based strategies using culture expanded autologous chondrocytes from non-loading regions of articular cartilage are currently used to treat focal cartilage defects. If left untreated, cartilage defects progressively lead to more extensive lesions and, ultimately, require joint arthroplasty.
Unfortunately, articular cartilage has a very limited capacity to repair after injury. Articular cartilage covers the end of long bones in articulating joints where it provides near frictionless movement.