Mechanotransduction is a context-dependent activator of TGF-β signaling in mesenchymal stem cells

We previously found that surface topographies induce the expression of the Scxa gene, encoding Scleraxis in tenocytes. Because Scxa is a TGF-β responsive gene, we investigated the link between mechanotransduction and TGF-β signaling. We discovered that mesenchymal stem cells exposed to both micro-topographies and TGF-β2 display synergistic induction of SMAD phosphorylation and transcription of the TGF-β target genes SCXA, a-SMA, and SOX9. Pharmacological perturbations revealed that Rho/ROCK/SRF signaling is required for this synergistic response. We further found an activation of the early response genes SRF and EGR1 during the early adaptation phase on micro-topographies, which coincided with higher expression of the TGF-β type-II receptor gene. Of interest, PKC activators Prostratin and Ingenol-3, known for inducing actin reorganization and activation of serum response elements, were able to mimic the topography-induced TGF-β response. These findings provide novel insights into the convergence of mechanobiology and TGF-β signaling, which can lead to improved culture protocols and therapeutic applications

Micro-topographies induce epigenetic reprogramming and quiescence in human mesenchymal stem cells

Biomaterials can control cell and nuclear morphology. Since the shape of the nucleus influences chromatin architecture, gene expression, and cell identity, surface topography can control cell phenotype. This study explores how surface topography influences nuclear morphology, histone modifications, and expression of histone-associated proteins through advanced histone mass spectrometry and microarray analysis. We found that nuclear confinement is associated with loss of both histone acetylation and nucleoli abundance, while pathway analysis revealed a substantial reduction in gene expression associated with chromosome organization. In light of previous observations where we found a decrease in proliferation and metabolism induced by micro-topographies, we connect these findings with a quiescent phenotype in mesenchymal stem cells, as further shown by a reduction of ribosomal proteins and the maintenance of multipotency on micro-topographies after long-term culture conditions. Furthermore, this influence of micro-topographies on nuclear morphology and proliferation was reversible, as shown by a full return of proliferation when re-cultured on a flat surface. Our findings provide novel insights on how biophysical signaling influences nuclear organization and subsequent cellular phenotype