Binding of the chemokine CXCL12α to its natural extracellular matrix ligand heparan sulfate enables myoblast adhesion and facilitates cell motility

The chemokine CXCL12α is a potent chemoattractant that guides the migration of muscle precursor cells (myoblasts) during myogenesis and muscle regeneration. To study how the molecular presentation of chemokines influences myoblast adhesion and motility, we designed multifunctional biomimetic surfaces as a tuneable signalling platform that enabled the response of myoblasts to selected extracellular cues to be studied in a well-defined environment. Using this platform, we demonstrate that CXCL12α, when presented by its natural extracellular matrix ligand heparan sulfate (HS), enables the adhesion and spreading of myoblasts and facilitates their active migration. In contrast, myoblasts also adhered and spread on CXCL12α that was quasi-irreversibly surface-bound in the absence of HS, but were essentially immotile. Moreover, co-presentation of the cyclic RGD peptide as integrin ligand along with HS-bound CXCL12α led to enhanced spreading and motility, in a way that indicates cooperation between CXCR4 (the CXCL12α receptor) and integrins (the RGD receptors). Our findings reveal the critical role of HS in CXCL12α induced myoblast adhesion and migration. The biomimetic surfaces developed here hold promise for mechanistic studies of cellular responses to different presentations of biomolecules. They may be broadly applicable for dissecting the signalling pathways underlying receptor cross-talks, and thus may guide the development of novel biomaterials that promote highly specific cellular responses

A fluorogenic monolayer to detect the co-immobilization of peptides that combine cartilage targeting and regeneration

Strategies to generate platforms combining tissue targeting and regeneration properties are in great demand in the regenerative medicine field. Here we employ an approach to directly visualize the immobilization of cysteine-terminated peptides on a novel fluorogenic surface. Peptides with relevant biological properties, CLPLGNSH and CLRGRYW, were synthesized to function as peptide binders to transforming growth factor (TGF)-β1 and collagen type II (CII). The selective immobilization of the peptides was directly detected using a fluorogenic surface. Adhered proteins were confined to patterns of these peptides matching with the fluorogenic areas. These results show that the fluorogenic signal can be used to detect the chemo-selective immobilization of non-fluorescent biomolecules and to correlate the cell response with the patterned peptides. After analyzing the sequence specificity and cross-reactivity of the binding of TGF-β1 and CII to the respective peptide regions employing immunofluorescence assays, both peptides were co-immobilized in a step-wise process as detected by the fluorogenic surface. TGF-β1 and CII could be self-sorted from a mixture in a regio-selective manner resulting in a bi-functional protein platform. Surfaces of CLPLGNSH pre-loaded with TGF-β1 showed excellent bioactivity in combination with human articular chondrocytes (HACs) and stimulated expression of chondrogenic marker

Viscoelastic properties of vimentin originate from nonequilibrium conformational changes

Structure and dynamics of living matter rely on design principles fundamentally different from concepts of traditional material science. Specialized intracellular filaments in the cytoskeleton permit living systems to divide, migrate, and grow with a high degree of variability and durability. Among the three filament systems, microfilaments, microtubules, and intermediate filaments (IFs), the physical properties of IFs and their role in cellular mechanics are the least well understood. We use optical trapping of individual vimentin filaments to investigate energy dissipation, strain history dependence, and creep behavior of stretched filaments. By stochastic and numerical modeling, we link our experimental observations to the peculiar molecular architecture of IFs. We find that individual vimentin filaments display tensile memory and are able to dissipate more than 70% of the input energy. We attribute these phenomena to distinct nonequilibrium folding and unfolding of a helices in the vimentin monomers constituting the filaments

Reversible and oriented immobilization of ferrocene-modified proteins

Adopting supramolecular chemistry for immobilization of proteins is an attractive strategy that entails reversibility and responsiveness to stimuli. The reversible and oriented immobilization and micropatterning of ferrocene-tagged yellow fluorescent proteins (Fc-YFPs) onto ß-cyclodextrin (ßCD) molecular printboards was characterized using surface plasmon resonance (SPR) spectroscopy and fluorescence microscopy in combination with electrochemistry. The proteins were assembled on the surface through the specific supramolecular host–guest interaction between ßCD and ferrocene. Application of a dynamic covalent disulfide lock between two YFP proteins resulted in a switch from monovalent to divalent ferrocene interactions with the ßCD surface, yielding a more stable protein immobilization. The SPR titration data for the protein immobilization were fitted to a 1:1 Langmuir-type model, yielding KLM = 2.5 × 105 M–1 and Ki,s = 1.2 × 103 M–1, which compares favorably to the intrinsic binding constant presented in the literature for the monovalent interaction of ferrocene with ßCD self-assembled monolayers. In addition, the SPR binding experiments were qualitatively simulated, confirming the binding of Fc-YFP in both divalent and monovalent fashion to the ßCD monolayers. The Fc-YFPs could be patterned on ßCD surfaces in uniform monolayers, as revealed using fluorescence microscopy and atomic force microscopy measurements. Both fluorescence microscopy imaging and SPR measurements were carried out with the in situ capability to perform cyclic voltammetry and chronoamperometry. These studies emphasize the repetitive desorption and adsorption of the ferrocene-tagged proteins from the ßCD surface upon electrochemical oxidation and reduction, respectively