Cells Sensing Mechanical Cues: Stiffness Influences the Lifetime of Cell–Extracellular Matrix Interactions by Affecting the Loading Rate

Abstract

The question of how cells sense substrate mechanical cues has gained increasing attention among biologists. By introducing contour-based data analysis to single-cell force spectroscopy, we identified a loading-rate threshold for the integrin α2β1-DGEA bond beyond which a dramatic increase in bond lifetime was observed. On the basis of mechanical cues (elasticity or topography), the effective spring constant of substrates k is mapped to the loading rate r under actomyosin pulling speed v, which, in turn, affects the lifetime of the integrin-ligand bond. Additionally, downregulating v with a low-dose blebbistatin treatment promotes the neuronal lineage specification of mesenchymal stem cells on osteogenic stiff substrates. Thus, sensing of the loading rate is central to how cells sense mechanical cues that affect cell-extracellular matrix interactions and stem cell differentiation.

Integrin endocytosis on elastic substrates mediates mechanosensing

“…The substrate elasticity determines the effective spring constant of substrates and the loading rate under actomyosin pulling speed on integrin α2β1-DGEA bond, which in turn affects the lifetime of the integrin ligand bond. (Jiang et al, 2015) The present work also showed that down regulating actomyosin pulling speed by a low dose blebbistatin treatment markedly enhanced internalization of both integrin 1 and 2, suggesting that not only integrin α2β1, but also integrin 1β1 is loading rate sensitive (Fig.S4). Thus the loading rate-stiffening property of the integrin is crucial for collagen-coated soft substrate promoting internalization.…”

“…(Du et al, 2011;Zu et al, 2015). Our more recent research shows a threshold of the loading rate on integrin α2β1-DGEA bond, the specific binding site of integrin α2β1 on collagen I, beyond which a dramatic increase of the bond lifetime was seen.…”

“…We have previously demonstrated that integrin β1 was internalized with bone morphogenetic protein 3 receptor IA (BMPR1A) in stem cells grown on a collagen I-coated soft substrate, thereby inducing the neurogenic differentiation of the stem cells (Du et al, 2011;Zu et al, 2015). Our more recent research shows a threshold of the loading rate on integrin α2β1-DGEA bond, beyond which a dramatic increase of the bond lifetime was seen.…”

“…The 1 integrin neutralizing antibody blocked Nestin and Map2 expression and reduced the level of NFL (Fig 8). In addition, we have previously demonstrated that inhibiting caveolin-1 by siRNA blocks the neuronal differentiation in BMMSCs on soft substrate (Du et al, 2011); integrin binds to bone morphogenesis protein receptor IA (BMPR1A), thus BMPR1A and integrin are internalized together (Zu et al, 2015), resulting in a down-regulation of BMP-Smad pathway. Taken together, these results suggest that increased integrin internalization has sound impact on cell differentiation.…”

“…Our more recent research shows a threshold of the loading rate on integrin α2β1-DGEA bond, beyond which a dramatic increase of the bond lifetime was seen. When compared to the stiff substrate, the soft one presents a lower effective spring constant of substrates and a lower loading rate on integrin α2β1-DGEA bond, which in turn results in a low lifetime of the integrin-ligand bond (Jiang et al, 2015). According to the reports from independent groups, the rupture of integrins results in a caveolae-mediated endocytosis of integrin (del Pozo et al, 2004;del Pozo et al, 2005).…”