The cell/microenvironment interface is the starting point of integrin-mediated mechanotransduction, but many details of mechanotransductive signal integration remain elusive due to the complexity of the involved (extra)cellular structures, such as the glycocalyx. We used nano-bio-interfaces reproducing the complex nanotopographical features of the extracellular matrix to analyse the glycocalyx impact on PC12 cell mechanosensing at the nanoscale (e.g., by force spectroscopy with functionalised probes). Our data demonstrates that the glycocalyx configuration affects spatio-temporal nanotopography-sensitive mechanotransductive events at the cell/microenvironment interface. Opposing effects of major glycocalyx removal were observed, when comparing flat and specific nanotopographical conditions. The excessive retrograde actin flow speed and force loading are strongly reduced on certain nanotopographies upon strong reduction of the native glycocalyx, while on the flat substrate we observe the opposite trend. Our results highlight the importance of the glycocalyx configuration in a molecular clutch force loading-dependent cellular mechanism for mechanosensing of microenvironmental nanotopographical features. Graphical Abstract

During wound healing, fibroblasts undergo radical processes that impact their phenotype and behavior. They are activated, recruited to the injury site, assume a contractile phenotype, and secrete extracellular matrix proteins to orchestrate tissue repair. Thus, fibroblast responses require dynamic changes in cytoskeleton assembly and organization, adhesion morphology, and force generation. At the same time, fibroblasts experience changes in environmental stiffness during tissue wounding and healing. Although cells are generally known to use their adhesion-contraction machinery to sense microenvironmental stiffness, little is known about how stiffness affects the fibroblast phenotypical transition and behavior in wound healing. Here we demonstrate that stiffness plays a deterministic role in determining fibroblast phenotype, surprisingly even overruling the classical TGF-β-mediated stimulation. By combining morphometric analysis, traction force microscopy, and single-cell migration analysis, we show that environmental stiffness primes the cytoskeletal and mechanical responses of fibroblasts, strongly modulating their morphology, force generation, and migration behavior. Our study, therefore, points to the importance of tissue stiffness as a key mechanobiological regulator of fibroblast behavior, thus serving as a potential target for controlling tissue repair.

The switching of the fibroblast phenotype to myofibroblast is a hallmark of a wide variety of tissue pathologies. This phenotypical switch is known to be influenced not only by humoral factors such as TGF-β, but also by mechanical and physical cues in the cellular environment, and is accompanied by distinctive changes in cell morphology. However, the causative link between these cues, the concomitant morphological changes, and the resulting phenotypic switch remain elusive. Here, we use protein micropatterning to spatially control dermal fibroblast adhesion without invoking exogenous mechanical changes and demonstrate that varying the spatial configuration of focal adhesions (FAs) is sufficient to direct fibroblast phenotype. We further developed an automated morphometry analysis pipeline, which revealed FA eccentricity as the primary determinant of cell-state positioning along the spectrum of fibroblast phenotype. Moreover, linear fibronectin patterns that constrain the FAs were found to promote a further phenotype transition, characterized by dispersed expression of alpha-smooth muscle actin, pointing to an interesting possibility of controlling fibroblast phenotype beyond the canonical fibroblast–myofibroblast axis. Together, our study reveals that the spatial configuration of adhesion to the cellular microenvironment is a key factor governing fibroblast morphotype and phenotype, shedding new light on fibroblast phenotype regulation.

In the event of disease or injury, restoration of the native organization of cells and extracellular matrix is crucial for regaining tissue functionality. In the cornea, a highly organized collagenous tissue, keratocytes can align along the anisotropy of the physical microenvironment, providing a blueprint for guiding the organization of the collagenous matrix. Inspired by this physiological process, anisotropic contact guidance cues have been employed to steer the alignment of keratocytes as a first step to engineer in vitro cornea-like tissues. Despite promising results, two major hurdles must still be overcome to advance the field. First, there is an enormous design space to be explored in optimizing cellular contact guidance in three dimensions. Second, the role of contact guidance cues in directing the long-term deposition and organization of extracellular matrix proteins remains unknown. To address these challenges, here we combined two microengineering strategies—UV-based protein patterning (2D) and two-photon polymerization of topographies (2.5D)—to create a library of anisotropic contact guidance cues with systematically varying height (H, 0 µm ≤ H ≤ 20 µm) and width (W, 5 µm ≤ W ≤ 100 µm). With this unique approach, we found that, in the short term (24 h), the orientation and morphology of primary human fibroblastic keratocytes were critically determined not only by the pattern width, but also by the height of the contact guidance cues. Upon extended 7-day cultures, keratocytes were shown to produce a dense, fibrous collagen network along the direction of the contact guidance cues. Moreover, increasing the heights also increased the aligned fraction of deposited collagen and the contact guidance response of cells, all whilst the cells maintained the fibroblastic keratocyte phenotype. Our study thus reveals the importance of dimensionality of the physical microenvironment in steering both cellular organization and the formation of aligned, collagenous tissues.

The cell/microenvironment interface is the starting point of integrin-mediated mechanotransduction, but many details of mechanotransductive signal integration remain elusive due to the complexity of the involved (extra)cellular structures, such as the glycocalyx. We used nano-bio-interfaces reproducing the complex nanotopographical features of the extracellular matrix to analyse the glycocalyx impact on PC12 cell mechanosensing at the nanoscale ( e.g ., by force spectroscopy with functionalised probes). Our data demonstrates that the glycocalyx configuration affects spatio-temporal nanotopography-sensitive mechanotransductive events at the cell/microenvironment interface. Opposing effects of glycocalyx removal were observed, when comparing flat and specific nanotopographical conditions. The excessive retrograde actin flow speed and force loading are strongly reduced on certain nanotopographies upon removal of the native glycocalyx, while on the flat substrate we observe the opposite trend. Our results highlight the importance of the glycocalyx configuration in a molecular clutch force loading-dependent cellular mechanism for mechanosensing of microenvironmental nanotopographical features.

During wound healing, fibroblasts undergo radical processes that impact their phenotype and behavior. They are activated, recruited to the injury site, assume a contractile phenotype, and secrete extracellular matrix proteins to orchestrate tissue repair. Thus, fibroblasts response require dynamic changes in cytoskeleton assembly and organization, adhesion morphology, and force generation. At the same time, fibroblasts experience changes in environmental stiffness during tissue wounding and healing. Although cells are generally known to use their adhesion–contraction machinery to sense microenvironmental stiffness, little is known about how stiffness affects the fibroblast phenotypical transition and behavior in wound healing. Here we demonstrate that stiffness plays a deterministic role in determining fibroblast phenotype, surprisingly even overruling the classical TGF-β-mediated stimulation. By combining morphometric analysis, traction force microscopy, and single-cell migration analysis, we show that environmental stiffness primes the cytoskeletal and mechanical responses of fibroblasts, strongly modulating their morphology, force generation, and migration behavior. Our study, therefore, points to the importance of tissue stiffness as a key mechanobiological regulator of fibroblast behavior, thus serving as a potential target for controlling tissue repair.