Introduction: Cell-material interactions are fundamental in biomaterial sciences and cell biology. How matrix stiffness influences stem cell differentiation is one of the key topics[1]. It has been widely accepted that stiff matrix prefers the osteogenic differentiation and soft matrix is beneficial for the adipogenic differentiation. However, our recent experiments led to results apparently not fully consistent with the above common knowledge. The presentation will report the phenomenon and give an interpretation.
Materials and Methods: We generated arrays of arginine-glycine-aspartate (RGD) peptide on poly(ethylene glycol) (PEG) hydrogel. The RGD peptide can trigger specific cell adhesion via conjugation with integrin, its receptor in cell membrane, and the PEG hydrogel can resist nonspecific cell adhesion. The decoration was accomplished using a unique material technique[2],[3]. PEG hydrogels were formed by free radical polymerization of PEG macromers, and the matrix stiffness could be adjusted by chainlength and concentration of the macromers[4].
Mesenchymal stem cells (MSCs) were derived from bone marrow of rats. Osteogenic and adipogenic induction media were added. After about one week, ALP and oil-droplet stainings were made to character osteogenic and adipogenic differentiation, respectively.
Results and Discussion: We confirmed that matrix stiffness did influence extents of differentiation. However, while relatively stiff hydrogel is, as expected, beneficial for osteogenesis, it is, unexpectedly, also beneficial for adipogenesis. We hypothesized that the interplay between cell adhesion and cell differentiation might account for the “abnormal” phenomenon, and cell-cell contact of MSCs on relatively stiff matrix due to more cell spreading might be the underlying reason of the enhanced adipogenesis, since it has been known that cell-cell contact favors adipogenesis[5],[6].
In order to confirm our interpretation, we then cultured and induced MSCs of a very low seeding density and thus avoid significant cell-cell contact. Then all of the results became normal.
Conclusion: Matrix stiffness regulates stem cell differentiation. Cell fat in an in vitro two dimensional culturing and induction is decided by the interplay of cell adhesion and cell differentiation. Cell-cell contact and cell density should also be taken into consideration when one interprets the results of stem cell differentiation on matrixes of varied stiffness.
References:
[1] Xiang Yao, Rong Peng, Jiandong Ding, Cell-material interactions revealed via material techniques of surface patterning, Adv. Mater., 25(37), 5257–5286 (2013)
[2] Rong Peng, Xiang Yao, Jiandong Ding, Effect of cell anisotropy on differentiation of stem cells on micropatterned surfaces through the controlled single cell adhesion, Biomaterials, 32, 8048-8057 (2011)
[3] Xuan Wang, Shiyu Li, Ce Yan, Peng Liu, Jiandong Ding, Fabrication of RGD micro/nanopattern and corresponding study of stem cell differentiation, Nano Lett., 15(3), 1457–1467 (2015)
[4] Kai Ye, Xuan Wang, Luping Cao, Shiyu Li, Zhenhua Li, Lin Yu, Jiandong Ding, Matrix stiffness and nanoscale spatial organization of cell-adhesive ligands direct stem cell fate, Nano Lett., 15(7), 4720-4729 (2015)
[5] Jiang Tang, Rong Peng, Jiandong Ding, The regulation of stem cell differentiation by cell-cell contact on micropatterned material surfaces, Biomaterials, 31, 2470–2476 (2010)
[6] Rong Peng, Xiang Yao, Bin Cao, Jian Tang, Jiandong Ding, The effect of culture conditions on the adipogenic and osteogenic inductions of mesenchymal stem cells on micropatterned surfaces, Biomaterials, 33, 6008-6019 (2012)