Dramatic and concerted conformational changes enable rhodocetin to block α2β1 integrin selectively

Study on the mechanism of magnesium calcium alloys/mineralized collagen composites mediating macrophage polarization to promote bone repair

Magnesium-based composites are a focal point in biomaterials research. However, the rapid degradation rate of magnesium alloys does not align with the healing time of bone tissue. Additionally, the host reaction caused by magnesium implantation hampers its full osteogenic potential. To maintain an appropriate microenvironment, it is important to enhance both corrosion resistance and osteogenic activity of the magnesium matrix. In this study, a composite scaffold composed of mineralized collagen and magnesium alloy was utilized to investigate the regulatory effect of mineralized collagen on mouse macrophages and evaluate its impact on mouse bone marrow mesenchymal stem cells in terms of osteogenesis, immune response, and macrophage-induced osteogenic differentiation. This experiment examined the biocompatibility of mouse bone marrow mesenchymal stem cells and macrophage-induced osteogenic differentiation in vitro, and examined the expression levels of relevant pathways proteins. Magnesium calcium alloys/mineralized collagen exhibited extensive spreading, facilitated by broad and abundant pseudopodia that firmly adhered them to the material surface and promoted growth and pseudopodia formation. The findings revealed that magnesium calcium alloy/mineralized collagen scaffold materials induced osteogenic differentiation mainly through M2 polarization of macrophages. This effect was mainly mediated by promoting the integrin α2β1-FAK-ERK1/2 signaling pathways and inhibiting the RANK signaling pathways.

pH-regulated single cell migration

Over the last two decades, extra- and intracellular pH have emerged as fundamental regulators of cell motility. Fundamental physiological and pathological processes relying on appropriate cell migration, such as embryonic development, wound healing, and a proper immune defense on the one hand, and autoimmune diseases, metastatic cancer, and the progression of certain parasitic diseases on the other, depend on surrounding pH. In addition, migrating single cells create their own localized pH nanodomains at their surface and in the cytosol. By this means, the migrating cells locally modulate their adhesion to, and the re-arrangement and digestion of, the extracellular matrix. At the same time, the cytosolic nanodomains tune cytoskeletal dynamics along the direction of movement resulting in concerted lamellipodia protrusion and rear end retraction. Extracellular pH gradients as found in wounds, inflamed tissues, or the periphery of tumors stimulate directed cell migration, and long-term exposure to acidic conditions can engender a more migratory and invasive phenotype persisting for hours up to several generations of cells after they have left the acidic milieu. In the present review, the different variants of pH-dependent single cell migration are described. The underlying pH-dependent molecular mechanisms such as conformational changes of adhesion molecules, matrix protease activity, actin (de-)polymerization, and signaling events are explained, and molecular pH sensors stimulated by H+ signaling are presented.

High throughput identification of human monoclonal antibodies and heavy-chain-only antibodies to treat snakebite

Snakebite envenoming is a priority Neglected Tropical Disease that causes an estimated 81,000-135,000 fatalities each year. The development of a new generation of safer, affordable, and accessible antivenom therapies is urgently needed. With this goal in mind, rigorous characterisation of the specific toxins in snake venom is key to generating novel therapies for snakebite. Monoclonal antibodies directed against venom toxins are emerging as potentially strong candidates in the development of new snakebite diagnostics and treatment. Venoms comprise many different toxins of which several are responsible for their pathological effects. Due to the large variability of venoms within and between species, formulations of combinations of human antibodies are proposed as the next generation antivenoms. Here a high-throughput screening method employing antibody-based ligand fishing of venom toxins in 384 filter-well plate format has been developed to determine the antibody target/s The approach uses Protein G beads for antibody capture followed by exposure to a full venom or purified toxins to bind their respective ligand toxin(s). This is followed by a washing/centrifugation step to remove non-binding toxins and an in-well tryptic digest. Finally, peptides from each well are analysed by nanoLC-MS/MS and subsequent Mascot database searching to identify the bound toxin/s for each antibody under investigation. The approach was successfully validated to rapidly screen antibodies sourced from hybridomas, derived from venom-immunised mice expressing either regular human antibodies or heavy-chain-only human antibodies (HCAbs).

Single-cell Expression Atlas Reveals Cell Heterogeneity in the Creeping Fat of Crohn's Disease

BACKGROUND

Creeping fat (CrF) has been recognized to play a positive role in Crohn's disease (CD) progression, yet the cellular compositions within mesenteric adipose tissue (MAT) and their potential mechanism in CrF formation are poorly understood.

METHODS

Analysis of 10X single-cell RNA sequencing was performed on 67 064 cells from 3 pairs of surgically resected samples of CrF and their uninvolved MAT. The results were validated in another cohort with 6 paired MAT samples by immunofluorescence.

RESULTS

All samples manifested excellent consistency and repeatability in our study, and 10 cell types from the transcriptome atlas, including 20 clusters, were identified. In CrF, a specific vascular endothelial cell subpopulation highly expressing lipoprotein lipase was first identified, with a significantly increased proportion. This vascular endothelial cell subpopulation manifested robust peroxisome proliferator-activated receptor γ (PPARγ) transcription activity and an upregulated PPAR signaling pathway and was involved in lipid metabolism and the antibacterial response. A novel fibroblast subpopulation (FC3) with remarkable GREM1 and RFLNB expression was identified and validated to predominantly accumulate in the CrF. The FC3 was annotated as inflammation-associated fibroblasts, which are characterized by inflammatory responses and the regulation of Smad phosphorylation related to intestinal fibrosis. The trajectory of fibroblasts revealed their pro-inflammatory and profibrotic conversion tendency during CrF formation with corresponding gene dynamics. Additionally, we unprecedently dissected the different origins and functions of 6 macrophage subclusters within the myeloid compartment.

CONCLUSIONS

Our results uncover the cellular heterogeneity in the MAT of CD and the role of these various cellular compositions in CrF development. This comprehensive understanding of CrF provides future directions for in-depth research on and potential targets for MAT-based treatment.

Understanding collagen interactions and their targeted regulation by novel drugs

Introduction: Among protein and fibers in the extracellular matrix (ECM), collagen is the most copious and widely employed in cosmetic, food, pharmaceutical, and biomedical industries due to its extensive biocompatible and versatile properties. In the last years, the knowledge about functions of collagens increased and expanded dramatically. Once considered only crucial for the ECM scaffolding and mechanotransduction, additional functional roles have now been ascribed to the collagen superfamily which are defined by other recently discovered domains, supramolecular assembly and receptors.Areas covered: Given the importance of each step in the collagen biosynthesis, folding and signaling, medicinal chemists have explored small molecules, peptides, and monoclonal antibodies to modulate enzymes, receptors and interactions with the physiological ligands of collagen. These compounds were also explored toward diseases and pathological conditions. The authors discuss this providing their expert perspectives on the subject area.Expert opinion: Understanding collagen protein properties and its interactome is beneficial for therapeutic drug design. Nevertheless, compounds targeting collagen-based interactome suffered from the presence of different isoforms for each target and the lack of specific 3D crystal structures able to guide properly drug design.

Insight into the LFA-1/SARS-CoV-2 Orf7a Complex by Protein-Protein Docking, Molecular Dynamics, and MM-GBSA Calculations

In the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) genome, open reading frames (ORFs) encode for viral accessory proteins. Among these, Orf7a structurally resembles the members of the immunoglobulin (Ig) superfamily and intracellular adhesion molecules (ICAMs), in particular. ICAMs are involved in integrin binding through lymphocyte function-associated antigen 1 (LFA-1). Based on such considerations and on previous findings on SARS-CoV, it has been postulated that the formation of the LFA-1/Orf7a complex could contribute to SARS-CoV-2 infectivity and pathogenicity. With the current work, we aim at providing insight into this macromolecular assembly, taking advantage of the recently reported SARS-CoV-2 Orf7a structure. Protein-protein docking, molecular dynamics (MD) simulations, and a Molecular Mechanical-Generalized Born Surface Area (MM-GBSA)-based stage were enrolled to provide refined models.

Effect of magnesium ions/Type I collagen promote the biological behavior of osteoblasts and its mechanism

Type I collagen (Col I) is a main component of extracellular matrix (ECM). Its safety, biocompatibility, hydrophilicity and pyrogen immunogenicity make it suitable for tissues engineering applications. Mg²⁺ also control a myriad of cellular processes, including the bone development by enhancing the attachment and differentiation of osteoblasts and accelerating mineralization to enhance bone healing. In our studies, Mg²⁺ bind collagen to promote the proliferation and differentiation of osteoblasts through the expression of integrins and downstream signaling pathways. In order to clarify the biological behavior effect of 10 mM Mg²⁺/Col I coating, we performed 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), alkaline phosphatase (ALP), 4′6-diamidino-2-phenylindole (DAPI), Alizarin red staining and Rhodamine B-isothiocyanate (RITC)-labeled phalloidin experiments and found that 10 mM Mg²⁺ group, Col I-coating group, 10 mM Mg²⁺/Col I-coating group, respectively, promoted the proliferation and differentiation of osteoblasts, especially 10 mM Mg²⁺/Col I-coating group. We detected the mRNA expression of osteogenic-related genes (Runx2, ALP and OCN, OPN and BMP-2) and the protein expression of signaling pathway (integrin α2, integrin β1, FAK and ERK1/2), these results indicated that 10 mM Mg²⁺/Col I coating play an critical role in up-regulating the MC3T3-E1 cells activity. The potential mechanisms of this specific performance may be through activating via integrin α2β1-FAK-ERK1/2 protein-coupled receptor pathway.

Structurally Robust and Functionally Highly Versatile-C-Type Lectin (-Related) Proteins in Snake Venoms

Snake venoms contain an astounding variety of different proteins. Among them are numerous C-type lectin family members, which are grouped into classical Ca²⁺- and sugar-binding lectins and the non-sugar-binding snake venom C-type lectin-related proteins (SV-CLRPs), also called snaclecs. Both groups share the robust C-type lectin domain (CTLD) fold but differ in a long loop, which either contributes to a sugar-binding site or is expanded into a loop-swapping heterodimerization domain between two CLRP subunits. Most C-type lectin (-related) proteins assemble in ordered supramolecular complexes with a high versatility of subunit numbers and geometric arrays. Similarly versatile is their ability to inhibit or block their target molecules as well as to agonistically stimulate or antagonistically blunt a cellular reaction triggered by their target receptor. By utilizing distinct interaction sites differentially, SV-CLRPs target a plethora of molecules, such as distinct coagulation factors and receptors of platelets and endothelial cells that are involved in hemostasis, thrombus formation, inflammation and hematogenous metastasis. Because of their robust structure and their high affinity towards their clinically relevant targets, SV-CLRPs are and will potentially be valuable prototypes to develop new diagnostic and therapeutic tools in medicine, provided that the molecular mechanisms underlying their versatility are disclosed.

Structural Aspects of Carbohydrate Recognition Mechanisms of C-Type Lectins

Carbohydrate recognition is an essential function occurring in all living organisms. Lectins are carbohydrate-binding proteins and are classified into several families. In mammals, Ca²⁺-dependent C-type lectins, such as β-galactoside-binding galectin and sialic acid-binding siglec, play crucial roles in the immune response and homeostasis. C-type lectins are abundant and diverse in animals. Their immunological activities include lymphocyte homing, pathogen recognition, and clearance of apoptotic bodies. C-type lectin domains are composed of 110-130 amino acid residues with highly conserved structural folds. Remarkably, individual lectins can accept a wide variety of sugar ligands and can distinguish subtle structural differences in closely related ligands. In addition, several C-type lectin-like proteins specifically bind to carbohydrate ligands in Ca²⁺-independent ways. The accumulated 3D structural evidence clarifies the unexpected structural versatility of C-type lectins underlying the variety of ligand binding modes. In this issue, we focus on the structural aspects of carbohydrate recognition mechanisms of C-type lectins and C-type lectin-like proteins.

Snake venom components in medicine: From the symbolic rod of Asclepius to tangible medical research and application

Both mythologically and logically, snakes have always fascinated man. Snakes have attracted both awe and fear not only because of the elegant movement of their limbless bodies, but also because of the potency of their deadly venoms. Practically, in 2017, the world health organization (WHO) listed snake envenomation as a high priority neglected disease, as snakes inflict up to 2.7 million poisonous bites, around 100.000 casualties, and about three times as many invalidities on man. The venoms of poisonous snakes are a cocktail of potent compounds which specifically and avidly target numerous essential molecules with high efficacy. The individual effects of all venom toxins integrate into lethal dysfunctions of almost any organ system. It is this efficacy and specificity of each venom component, which after analysis of its structure and activity may serve as a potential lead structure for chemical imitation. Such toxin mimetics may help in influencing a specific body function pharmaceutically for the sake of man's health. In this review article, we will give some examples of snake venom components which have spurred the development of novel pharmaceutical compounds. Moreover, we will provide examples where such snake toxin-derived mimetics are in clinical use, trials, or consideration for further pharmaceutical exploitation, especially in the fields of hemostasis, thrombosis, coagulation, and metastasis. Thus, it becomes clear why a snake captured its symbolic place at the Asclepius rod with good reason still nowadays.

Titration ELISA as a Method to Determine the Dissociation Constant of Receptor Ligand Interaction

The dissociation constant describes the interaction between two partners in the binding equilibrium and is a measure of their affinity. It is a crucial parameter to compare different ligands, e.g., competitive inhibitors, protein isoforms and mutants, for their binding strength to a binding partner. Dissociation constants are determined by plotting concentrations of bound versus free ligand as binding curves. In contrast, titration curves, in which a signal that is proportional to the concentration of bound ligand is plotted against the total concentration of added ligand, are much easier to record. The signal can be detected spectroscopically and by enzyme-linked immunosorbent assay (ELISA). This is exemplified in a protocol for a titration ELISA that measures the binding of the snake venom-derived rhodocetin to its immobilized target domain of α2β1 integrin. Titration ELISAs are versatile and widely used. Any pair of interacting proteins can be used as immobilized receptor and soluble ligand, provided that both proteins are pure, and their concentrations are known. The difficulty so far has been to determine the dissociation constant from a titration curve. In this study, a mathematical function underlying titration curves is introduced. Without any error-prone graphical estimation of a saturation yield, this algorithm allows processing of the raw data (signal intensities at different concentrations of added ligand) directly by mathematical evaluation via non-linear regression. Thus, several titration curves can be recorded simultaneously and transformed into a set of characteristic parameters, among them the dissociation constant and the concentration of binding-active receptor, and they can be evaluated statistically. When combined with this algorithm, titration ELISAs gain the advantage of directly presenting the dissociation constant. Therefore, they may be used more efficiently in the future.