Vinculin transmits high-level integrin tensions that are dispensable for focal adhesion formation

Esophageal Reconstruction with Myogenesis-Inducing Gene Transfected Mesenchymal Stem Cell-Seeded Film with Leaf-Stacked Structure

In the domain of tissue engineering and regenerative medicine, artificial replacements have been developed as viable options for esophageal reconstruction and serve as alternatives to traditional surgical procedures. Restoration of smooth muscle functionality is crucial in esophageal regeneration. We evaluated the efficacy of esophageal reconstructions in an animal model, using tissue-engineered films with a leaf-stacked structure (FLSS), seeded with mesenchymal stem cells (MSCs), which were genetically modified with myogenic genes. Esophageal partial defects were variously reconstructed in animals (n = 8 per group, except the no-implantation group), categorized as (1) normal rats; (2) rats implanted with naked FLSS; (3) rats implanted with FLSS with MSCs; (4) rats implanted using FLSS with myogenesis-inducing gene transfected MSCs; and (5) rats without implantation at the defect site (n = 3). The FLSS exhibited appropriate mechanical characteristics for transplantation. Successful repair of esophageal defects was observed with significantly enhanced epithelial regeneration in the MSC-seeded FLSS group compared to that in the naked FLSS group. Moreover, smooth muscle regeneration was notably higher in the FLSS with myogenesis-inducing gene transfected MSCs than in the group without myogenic gene transfection. The myogenesis-inducing gene-transfected MSC-seeded FLSS group showed a tendency toward increased smooth muscle regeneration, this indicates that FLSS with myogenesis-inducing genes transfected MSC may contribute positively to the maintenance of function in the reconstructed esophagus.

Live-cell imaging of single integrin tensions with minimal background fluorescence noise

One powerful method for studying cell mechanobiology is to monitor receptor-mediated forces at the single-molecule level in live cells. Hairpin DNA labeled with a quencher-dye pair has been used as a tension probe (TP) to image cellular forces in real time. The TP emits fluorescence when cellular forces unfold the DNA hairpin and de-quench the dye, thereby converting the force signal into fluorescence. However, when applied to monitor cellular forces at the single-molecule level, the TP often suffers from background fluorescent spots (BFSs) due to nonquenched dyes, which interfere with molecular force imaging and analysis. In this work, we identified that the BFSs are primarily caused by missing quenchers in some TP constructs and surface-adsorbed dye-labeled DNA strands. To address these issues, we developed a double-quencher TP (dqTP) and incorporated Tween-20 treatment during surface preparation. These two simple strategies reduced the BFS level by 10-fold, significantly improving the signal/background ratio for single molecular force imaging. We demonstrated the performance of dqTP by monitoring the temporal dynamics of integrin tensions in platelets and HeLa cells, showing that single integrin tensions remain stable for at least 100 s in wild-type HeLa cells. In contrast, with vinculin knocked out, a subpopulation of integrin tensions, especially at cell peripheral regions, exhibited molecular force fluctuations with an average force duration shorter than 10 s. Overall, this work provides a convenient and practical approach to significantly reduce BFS levels on TP surfaces, offering a nearly false-signal-free platform for monitoring single-molecule forces in live cells.

Synergistic enhancement of angiogenesis and osseointegration in 3D-printed porous polyetheretherketone scaffolds using biomimetic coatings of bone morphogenetic protein-2/fibronectin

This study explored a novel modification method for porous polyetheretherketone (PEEK) implants using a biomimetic coating to achieve synergistic enhancement of vascularization and bone regeneration. Inspired by the natural extracellular matrix (ECM) structure (consists of growth factors and matrix proteins), a biomimetic dual-factor coating capable of releasing bone morphogenetic protein-2 (BMP-2) and fibronectin (FN) was coated on the surface of 3D-printed porous PEEK scaffolds using polydopamine (PDA) as a binder. Experiments conducted with MC3T3-E1 cells or HUVECs in co-culture with scaffolds revealed that the biomimetic coating not only synergically promoted cell migration, adhesion and proliferation, but also enhanced angiogenesis and osteogenic differentiation simultaneously in vivo. The synergistic effect is attributed to the crosstalks between intracellular signaling pathways of FN and BMP-2, as well as the sustained release on account of their combination mitigates explosive release and degradation of BMP-2. Overall, this study designed a novel biomimetic coating modified PEEK scaffolds and confirmed the synergistic mechanism of the scaffolds on osteogenic differentiation and angiogenesis for the first time. These insights have significant implications for the clinical transformation of PEEK dental implants.

Unravelling molecular mechanobiology using DNA-based fluorogenic tension sensors

Investigations of the biological system have revealed many principles that govern regular life processes. Recently, the analysis of tiny mechanical forces associated with many biological processes revealed their significance in understanding biological functions. Consequently, this piqued the interest of researchers, and a series of technologies have been developed to understand biomechanical cues at the molecular level. Notable techniques include single-molecule force spectroscopy, traction force microscopy, and molecular tension sensors. Well-defined double-stranded DNA structures could possess programmable mechanical characteristics, and hence, they have become one of the central molecules in molecular tension sensor technology. With the advancement of DNA technology, DNA or nucleic acid-based robust tension sensors offer the possibility of understanding mechanobiology in the bulk to single-molecule level range with desired spatiotemporal resolution. This review presents a comprehensive account of molecular tension sensors with a special emphasis on DNA-based fluorogenic tension sensors. Along with a detailed discussion on irreversible and reversible DNA-based tension sensors and their application in super-resolution microscopy, a discussion on biomolecules associated with cellular mechanotransduction and key findings in the field are included. This review ends with an elaborate discussion on the current challenges and future prospects of molecular tension sensors.

Biomimetic concentric microgrooved titanium surfaces influence bone marrow-derived mesenchymal stem cell osteogenic differentiation via H3K4 trimethylation epigenetic regulation

Material surface micromorphology can modulate cellular behavior and promote osteogenic differentiation through cytoskeletal rearrangement. Bone reconstruction requires precise regulation of gene expression in cells, a process governed by epigenetic mechanisms such as histone modifications, DNA methylation, and chromatin remodeling. We constructed osteon-mimetic concentric microgrooved titanium surfaces with different groove sizes and cultured bone marrow-derived mesenchymal stem cells (BMSCs) on the material surfaces to study how they regulate cell biological behavior and osteogenic differentiation through epigenetics. We found that the cells arranged in concentric circles along the concentric structure in the experimental group, and the concentric microgrooved surface did not inhibit cell proliferation. The results of a series of osteogenic differentiation experiments showed that the concentric microgrooves facilitated calcium deposition and promoted osteogenic differentiation of the BMSCs. Concentric microgrooved titanium surfaces that were 30 μm wide and 10 μm deep promoted osteogenic differentiation of BMSC by increasing WDR5 expression via H3K4 trimethylation upregulation.

Develop Tandem Tension Sensor to Gauge Integrin-Transmitted Molecular Forces

DNA-based tension sensors have innovated the imaging and calibration of mechanosensitive receptor-transmitted molecular forces, such as integrin tensions. However, these sensors mainly serve as binary reporters, only indicating if molecular forces exceed one predefined threshold. Here, we have developed tandem tension sensor (TTS), which comprises two consecutive force-sensing units, each with unique force detection thresholds and distinct fluorescence spectra, thereby enabling the quantification of molecular forces with dual reference levels. With TTS, we revealed that vinculin is not required for transmitting integrin tensions at approximately 10 pN (piconewtons) but is essential for elevating integrin tensions beyond 20 pN in focal adhesions (FAs). Such high tensions have emerged during the early stage of FA formation. TTS also successfully detected changes in integrin tensions in response to disrupted actin formation, inhibited myosin activity, and tuned substrate elasticity. We also applied TTS to examine integrin tensions in platelets and revealed two force regimes, with integrin tensions surpassing 20 pN at cell central regions and 13-20 pN integrin tensions at the cell edge. Overall, TTS, especially the construct consisting of a hairpin DNA (13 pN opening force) and a shearing DNA (20 pN opening force), stands as a valuable tool for the quantification of receptor-transmitted molecular forces within living cells.

DNA-based ForceChrono probes for deciphering single-molecule force dynamics in living cells

Understanding cellular force transmission dynamics is crucial in mechanobiology. We developed the DNA-based ForceChrono probe to measure force magnitude, duration, and loading rates at the single-molecule level within living cells. The ForceChrono probe circumvents the limitations of in vitro single-molecule force spectroscopy by enabling direct measurements within the dynamic cellular environment. Our findings reveal integrin force loading rates of 0.5-2 pN/s and durations ranging from tens of seconds in nascent adhesions to approximately 100 s in mature focal adhesions. The probe's robust and reversible design allows for continuous monitoring of these dynamic changes as cells undergo morphological transformations. Additionally, by analyzing how mutations, deletions, or pharmacological interventions affect these parameters, we can deduce the functional roles of specific proteins or domains in cellular mechanotransduction. The ForceChrono probe provides detailed insights into the dynamics of mechanical forces, advancing our understanding of cellular mechanics and the molecular mechanisms of mechanotransduction.

Vinculin is essential for sustaining normal levels of endogenous forces at cell-cell contacts

Transmission of cell-generated (i.e., endogenous) tension at cell-cell contacts is crucial for tissue shape changes during morphogenesis and adult tissue repair in tissues such as epithelia. E-cadherin-based adhesions at cell-cell contacts are the primary means by which endogenous tension is transmitted between cells. The E-cadherin-β-catenin-α-catenin complex mechanically couples to the actin cytoskeleton (and thereby the cell's contractile machinery) both directly and indirectly. However, the key adhesion constituents required for substantial endogenous force transmission at these adhesions in cell-cell contacts are unclear. Due to the role of α-catenin as a mechanotransducer that recruits vinculin at cell-cell contacts, we expected α-catenin to be essential for sustaining normal levels of force transmission. Instead, using the traction force imbalance method to determine the inter-cellular force at a single cell-cell contact between cell pairs, we found that it is vinculin that is essential for sustaining normal levels of endogenous force transmission, with absence of vinculin decreasing the inter-cellular tension by over 50%. Our results constrain the potential mechanical pathways of force transmission at cell-cell contacts and suggest that vinculin can transmit forces at E-cadherin adhesions independent of α-catenin, possibly through β-catenin. Furthermore, we tested the ability of lateral cell-cell contacts to withstand external stretch and found that both vinculin and α-catenin are essential to maintain cell-cell contact stability under external forces.

Thy-1 (CD90)-regulated cell adhesion and migration of mesenchymal cells: insights into adhesomes, mechanical forces, and signaling pathways

Cell adhesion and migration depend on the assembly and disassembly of adhesive structures known as focal adhesions. Cells adhere to the extracellular matrix (ECM) and form these structures via receptors, such as integrins and syndecans, which initiate signal transduction pathways that bridge the ECM to the cytoskeleton, thus governing adhesion and migration processes. Integrins bind to the ECM and soluble or cell surface ligands to form integrin adhesion complexes (IAC), whose composition depends on the cellular context and cell type. Proteomic analyses of these IACs led to the curation of the term adhesome, which is a complex molecular network containing hundreds of proteins involved in signaling, adhesion, and cell movement. One of the hallmarks of these IACs is to sense mechanical cues that arise due to ECM rigidity, as well as the tension exerted by cell-cell interactions, and transduce this force by modifying the actin cytoskeleton to regulate cell migration. Among the integrin/syndecan cell surface ligands, we have described Thy-1 (CD90), a GPI-anchored protein that possesses binding domains for each of these receptors and, upon engaging them, stimulates cell adhesion and migration. In this review, we examine what is currently known about adhesomes, revise how mechanical forces have changed our view on the regulation of cell migration, and, in this context, discuss how we have contributed to the understanding of signaling mechanisms that control cell adhesion and migration.

Hydrogel-based molecular tension fluorescence microscopy for investigating receptor-mediated rigidity sensing

Extracellular matrix (ECM) rigidity serves as a crucial mechanical cue impacting diverse biological processes. However, understanding the molecular mechanisms of rigidity sensing has been limited by the spatial resolution and force sensitivity of current cellular force measurement techniques. Here we developed a method to functionalize DNA tension probes on soft hydrogel surfaces in a controllable and reliable manner, enabling molecular tension fluorescence microscopy for rigidity sensing studies. Our findings showed that fibroblasts respond to substrate rigidity by recruiting more force-bearing integrins and modulating integrin sampling frequency of the ECM, rather than simply overloading the existing integrin-ligand bonds, to promote focal adhesion maturation. We also demonstrated that ECM rigidity positively regulates the pN force of T cell receptor-ligand bond and T cell receptor mechanical sampling frequency, promoting T cell activation. Thus, hydrogel-based molecular tension fluorescence microscopy implemented on a standard confocal microscope provides a simple and effective means to explore detailed molecular force information for rigidity-dependent biological processes.

Development of a Ratiometric Tension Sensor Exclusively Responding to Integrin Tension Magnitude in Live Cells

Integrin tensions are critical for cell mechanotransduction. By converting force to fluorescence, molecular tension sensors image integrin tensions in live cells with a high resolution. However, the fluorescence signal intensity results collectively from integrin tension magnitude, tension dwell time, integrin density, sensor accessibility, and so forth, making it highly challenging to specifically monitor the molecular force level of integrin tensions. Here, a ratiometric tension sensor (RTS) was developed to exclusively monitor the integrin tension magnitude. The RTS consists of two tension-sensing units that are coupled in series and always subject to the same integrin tension. These two units are activated by tension to fluoresce in separate spectra and with different activation rates. The ratio of their activation probabilities, reported by fluorescence ratiometric measurement, is solely determined by the local integrin tension magnitude. RTS responded sensitively to the variation of integrin tension magnitude in platelets and focal adhesions due to different cell plating times, actomyosin inhibition, or vinculin knockout. At last, RTS confirmed that integrin tension magnitude in platelets and focal adhesions decreases monotonically with the substrate rigidity, verifying the rigidity dependence of integrin tensions in live cells and suggesting that integrin tension magnitude could be a key biomechanical factor in cell rigidity sensing.