Bipartite mechanism for laminin-integrin interactions: Identification of the integrin-binding site in LG domains of the laminin α chain

Multifunctional and bioinspired titanium surface with multilayer nanofilms for novel dental implant applications

Introduction: Smart multifunctional surfaces targeting intricate biological events or versatile therapeutic strategies are imminent to achieve long-term transmucosal implant success. Methods: This study used dopamine (DA), graphene oxide (GO), and type IV collagen (COL-IV) to construct multilayer nanofilms (DGCn) based on their universal adhesive and biomimetic properties to design a versatile and bioactive titanium implant. The characterization of DGCn on different titanium surfaces was performed, and its loading capacity, release profile, in situ gene delivery, and in vitro biological properties were preliminarily evaluated. Results: Our results demonstrate that hydrogenated TiO2 nanotubes (H) provide a better platform for the DGCn coating than machined Ti and air-TiO2 nanotubes. The H-DGC10 displayed the most stable surface with excellent loading capacity, sustained-release profile, and in situ gene transfection efficiency; this could be due to the high specific surface area of H and GO, as well as the functional groups in H, DA, and GO. Moreover, the H-DGC10 exhibited good biocompatibility for human oral epithelial cells and promoted the expression of integrin β4 and laminin 332, both being hemidesmosome-related proteins. Discussion: Our findings suggest that H-DGCn can be designed as a smart multifunctional interface for titanium implants to achieve long-term transmucosal implant success and aid in versatile therapeutic strategies.

Perception and response of skeleton to mechanical stress

Mechanical stress stands as a fundamental factor in the intricate processes governing the growth, development, morphological shaping, and maintenance of skeletal mass. The profound influence of stress in shaping the skeletal framework prompts the assertion that stress essentially births the skeleton. Despite this acknowledgment, the mechanisms by which the skeleton perceives and responds to mechanical stress remain enigmatic. In this comprehensive review, our scrutiny focuses on the structural composition and characteristics of sclerotin, leading us to posit that it serves as the primary structure within the skeleton responsible for bearing and perceiving mechanical stress. Furthermore, we propose that osteocytes within the sclerotin emerge as the principal mechanical-sensitive cells, finely attuned to perceive mechanical stress. And a detailed analysis was conducted on the possible transmission pathways of mechanical stress from the extracellular matrix to the nucleus.

Visualization of basement membranes by a nidogen-based fluorescent reporter in mice

Basement membranes (BMs) are thin, sheet-like extracellular structures that cover the basal side of epithelial and endothelial tissues and provide structural and functional support to adjacent cell layers. The molecular structure of BMs is a fine meshwork that incorporates specialized extracellular matrix proteins. Recently, live visualization of BMs in invertebrates demonstrated that their structure is flexible and dynamically rearranged during cell differentiation and organogenesis. However, the BM dynamics in mammalian tissues remain to be elucidated. We developed a mammalian BM imaging probe based on nidogen-1, a major BM-specific protein. Recombinant human nidogen-1 fused with an enhanced green fluorescent protein (Nid1-EGFP) retains its ability to bind to other BM proteins, such as laminin, type IV collagen, and perlecan, in a solid-phase binding assay. When added to the culture medium of embryoid bodies derived from mouse ES cells, recombinant Nid1-EGFP accumulated in the BM zone of embryoid bodies, and BMs were visualized in vitro. For in vivo BM imaging, a knock-in reporter mouse line expressing human nidogen-1 fused to the red fluorescent protein mCherry (R26-CAG-Nid1-mCherry) was generated. R26-CAG-Nid1-mCherry showed fluorescently labeled BMs in early embryos and adult tissues, such as the epidermis, intestine, and skeletal muscles, whereas BM fluorescence was unclear in several other tissues, such as the lung and heart. In the retina, Nid1-mCherry fluorescence visualized the BMs of vascular endothelium and pericytes. In the developing retina, Nid1-mCherry fluorescence labeled the BM of the major central vessels; however, the BM fluorescence were hardly observed in the peripheral growing tips of the vascular network, despite the presence of endothelial BM. Time-lapse observation of the retinal vascular BM after photobleaching revealed gradual recovery of Nid1-mCherry fluorescence, suggesting the turnover of BM components in developing retinal blood vessels. To the best of our knowledge, this is the first demonstration of in vivo BM imaging using a genetically engineered mammalian model. Although R26-CAG-Nid1-mCherry has some limitations as an in vivo BM imaging model, it has potential applications in the study of BM dynamics during mammalian embryogenesis, tissue regeneration, and pathogenesis.

Structural mechanism of laminin recognition by integrin

Recognition of laminin by integrin receptors is central to the epithelial cell adhesion to basement membrane, but the structural background of this molecular interaction remained elusive. Here, we report the structures of the prototypic laminin receptor α6β1 integrin alone and in complex with three-chain laminin-511 fragment determined via crystallography and cryo-electron microscopy, respectively. The laminin-integrin interface is made up of several binding sites located on all five subunits, with the laminin γ1 chain C-terminal portion providing focal interaction using two carboxylate anchor points to bridge metal-ion dependent adhesion site of integrin β1 subunit and Asn189 of integrin α6 subunit. Laminin α5 chain also contributes to the affinity and specificity by making electrostatic interactions with large surface on the β-propeller domain of α6, part of which comprises an alternatively spliced X1 region. The propeller sheet corresponding to this region shows unusually high mobility, suggesting its unique role in ligand capture.

Linker Protein Repair of LAMA2 Dystrophic Neuromuscular Basement Membranes

An understanding of basement membrane (BM) assembly at a molecular level provides a foundation with which to develop repair strategies for diseases with defects of BM structure. As currently understood, laminins become anchored to cell surfaces through receptor-mediated interactions and polymerize. This provisional matrix binds to proteoglycans, nidogens and type IV collagen to form a mature BM. Identification of BM binding domains and their binding targets has enabled investigators to engineer proteins that link BM components to modify and improve their functions. This approach is illustrated by the development of two linker proteins to repair the LAMA2-deficient muscular dystrophy (LAMA2-MD). Dystrophy-causing mutations of the LAMA2 gene product (Lmα2) disrupt the BM molecular architecture, destabilizing it. In a mild ambulatory type of the dystrophy, α2LN mutations in laminin-211 prevents polymerization. In the more common and severe non-ambulatory type (MDC1A), an absent Lmα2 subunit is replaced by the naturally occurring Lmα4 subunit that is normally largely confined to the microvasculature. The compensatory laminin, however, is a poor substitute because it neither polymerizes nor binds adequately to the anchoring receptor α-dystroglycan. A chimeric laminin-binding protein called αLNNd enables laminins with defective or absent αLN domains to polymerize while another engineered protein, miniagrin (mag), promotes efficient α-dystroglycan receptor-binding in otherwise weakly adhesive laminins. Alone, αLNNd enables Lm211 with a self-assembly defect to polymerize and was used to ameliorate a mouse model of the ambulatory dystrophy. Together, these linker proteins alter Lm411 such that it both polymerizes and binds αDG such that it properly assembles. This combination was used to ameliorate a mouse model of the non-ambulatory dystrophy in which Lm411 replaced Lm211 as seen in the human disease. Collectively, these studies pave the way for the development of somatic gene delivery of repair proteins for treatment of LAMA2-MD. The studies further suggest a more general approach of linker-protein mediated repair in which a variety of existing BM protein domains can be combined together to stabilize BMs in other diseases.