European Society of Biomechanics S.M. Perren Award 2012: The external mechanical environment can override the influence of local substrate in determining stem cell fate

Abstract

The aim of this study was to explore how cell-matrix interactions and extrinsic mechanical signals interact to determine stem cell fate in response to transforming growth factor-β3 (TGF-β3). Bone marrow derived mesenchymal stem cells (MSCs) were seeded in agarose and fibrin hydrogels and subjected to dynamic compression in the presence of different concentrations of TGF-β3. Markers of chondrogenic, myogenic and endochondral differentiation were assessed. MSCs embedded within agarose hydrogels adopted a spherical cell morphology, while cells directly adhered to the fibrin matrix and took on a spread morphology. Free-swelling agarose constructs stained positively for chondrogenic markers, with MSCs appearing to progress towards terminal differentiation as indicated by mineral staining. MSC seeded fibrin constructs progressed along an alternative myogenic pathway in long-term free-swelling culture. Dynamic compression suppressed differentiation toward any investigated lineage in both fibrin and agarose hydrogels in the short-term. Given that fibrin clots have been shown to support a chondrogenic phenotype in vivo within mechanically loaded joint defect environments, we next explored the influence of long term (42 days) dynamic compression on MSC differentiation. Mechanical signals generated by this extrinsic loading ultimately governed MSC fate, directing MSCs along a chondrogenic pathway as opposed to the default myogenic phenotype supported within unloaded fibrin clots. In conclusion, this study demonstrates that external cues such as the mechanical environment can override the influence specific substrates, scaffolds or hydrogels have on determining mesenchymal stem cell fate. The temporal data presented in this study highlights the importance of considering how MSCs respond to extrinsic mechanical signals in the long term.3

Engineering osteochondral constructs through spatial regulation of endochondral ossification

“…The subcutaneous environment differs in a number of notable ways to the orthotopic environment. Mechanical cues, absent in the subcutaneous environment, such as hydrostatic pressure [59][60] and dynamic compression [61][62] have been shown to play a role in regulating the endochondral phenotype of MSCs as well as matrix production [63].…”

Engineering cartilage or endochondral bone: A comparison of different naturally derived hydrogels

“…2), may explain the large accumulation in sGAG during culture in chondrogenic conditions. Unlike alginate, fibrin permits cell mediated integrin binding [33] and a more spread MSC morphology [34], which in turn may support robust osteogenic [35] and/or endochondral differentiation. This may explain why in contrast to alginate and chitosan constructs, which calcified preferentially around their periphery upon culture in hypertrophic conditions, fibrin constructs facilitated a homogenous deposition of calcium in vitro while accumulating the highest levels of calcium when normalized by % wet weight.…”

 

“…Thorpe et al [16] isolated bovine chondrocytes ( 6×10 6 ), which were seeded into rhCII gels (rhCII-cell) and subsequently injected subcutaneously into the back of nude mice. The results demonstrated that extra cellular matrix stained heavily with toluidine blue and had strongly positive collagen type II immunohistochemical staining.…”

“…In repairing cartilage defects, there appears an evidence that fibrin is not as useful as other well developed hydrogels, [16] because bone marrow mesenchymal stem cells (BMSCs) and adipose derived stem cells (ADSCs) showed a diminished chondrogenic potential when encapsulated in fibrin. [16,33,34] Therefore, we need further functionalize this versatile injectable hydrogel system to optimize for cartilage repair therapies.…”

“…[16,33,34] Therefore, we need further functionalize this versatile injectable hydrogel system to optimize for cartilage repair therapies. Articular cartilage extracellular matrix-derived materials have been previously used to fabricate cartilage grafts with promising results.…”