Adhesion,proliferation, and differentiation of mesenchymal stem cells on RGD nanopatterns of varied nanospacings

The present report is an extension of our preceding publication in Biomaterials (2013) entitled “Effect of RGD nanospacing on differentiation of stem cells.” Cell-adhesive peptide arginine-glycine-aspartate (RGD) was nanopatterned on a non-fouling poly(ethylene glycol) (PEG) hydrogel, and mesenchymal stem cells (MSCs) derived from rat bone marrow were cultured on the patterned surfaces at nanospacings from 37 to 124 nm. Cell adhesion parameters such as spreading areas varied with RGD nanospacings significantly. The differences were well observed at both the first and eighth days, which confirmed the persistence of this nanospacing effect on our nanopatterns. The proliferation rate also varied with the nanospacings. Osteogenic and adipogenic inductions were undertaken, and a significant influence of RGD nanospacing on stem cell differentiation was found. The effect on differentiation cannot be simply interpreted by differences in cell adhesion and proliferation. We further calculated the fractions of single, coupled, and multiple cells on those nanopatterns, and ruled out the possibility that the extent of cell-cell contact determined the different differentiation fractions. Accordingly, we reinforced the idea that RGD nanospacing might directly influence stem cell differentiation.     

New tools for labeling silica in living diatoms

Silicon biomineralization is a widespread mechanism found in several kingdoms that concerns both unicellular and multicellular organisms. As a result of genomic and molecular tools, diatoms have emerged as a good model for biomineralization studies and have provided most of the current knowledge on this process. However, the number of techniques available to study its dynamics at the cellular level is still rather limited. Here, new probes were developed specifically to label the pre-existing or the newly synthesized silica frustule of several diatoms species. It is shown that the LysoTracker Yellow HCK-123, which can be used to visualize silica frustules with common filter sets, presents an enhanced signal-to-noise ratio and allows details of the frustules to be imaged without of the use of ionophores. It is also demonstrated that methoxysilane derivatives can be coupled to fluorescein-5-isothiocyanate (FITC) to preferentially label the silica components of living cells. The coupling of labeling procedures might help to address the challenging question of the process of frustule exocytosis.