Abstract
The identification of multipotent adipose-derived stromal cells (ASC) has raised hope that tissue regeneration approaches established with bone-marrow-derived stromal cells (BMSC) can be reproduced with a cell-type that is far more accessible in large quantities. Recent detailed comparisons, however, revealed subtle functional differences between ASC and BMSC, stressing the concept of a common mesenchymal progenitor existing in a perivascular niche across all tissues. Focussing on bone and cartilage repair, this review summarises recent in vitro and in vivo studies aiming towards tissue regeneration with ASC. Advantages of good accessibility, high yield and superior growth properties are counterbalanced by an inferiority of ASC to form ectopic bone and stimulate long-bone healing along with their less pronounced osteogenic and angiogenic gene expression signature. Hence, particular emphasis is placed on establishing whether stem cell activity of ASC is so far proven and relevant for successful osteochondral regeneration, or whether trophic activity may largely determine therapeutic outcome.
Highlights
Established strategies for cartilage and bone repair, such as autologous chondrocyte transplantation (ACT) (Ref. 1) and bone grafting (Ref. 2), have reached broad clinical application and yield satisfactory results due to continuous improvement
Repair strategies that are based on autologous bone-marrow-derived stromal cells (BMSC) do not circumvent these problems, but harvesting bone marrow from the iliac crest is generally judged as less invasive (Ref. 4)
The discovery that multipotent stromal cells can be isolated from lipoaspirates (Ref. 5) and that the number of adherent cells in an equal volume of adipose tissue exceeds the content of bone marrow aspirate by about 300-fold (Refs 6, 7, 8) challenged the assumption that bone marrow would be the most appropriate source for cellbased therapies of skeletal injuries and diseases
Summary
Established strategies for cartilage and bone repair, such as autologous chondrocyte transplantation (ACT) (Ref. 1) and bone grafting (Ref. 2), have reached broad clinical application and yield satisfactory results due to continuous improvement. Similar adipogenic in vitro differentiation capacities of Reduced osteogenic gene expression adipose and bone marrow-derived cells were signature in ASC reported (Refs 52, 69, 70), but no study. Beyond their reduced performance in osteochondral in vitro differentiation assays, ASC showed no intrinsic osteochondral in vivo differentiation potential and, seem to possess no skeletal stem cell properties as seen with BMSC, providing a strong argument for fundamental functional differences regarding their use for in vivo osteochondral repair. Since nonclonal cells are widely used for tissue regeneration, the benefit of enhanced availability of ASC, appears currently to be balanced by an enhanced need for inductive conditions via timely and intensive in vitro culture efforts, if their physical contribution to the new skeletal tissue is desired
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