Cryptic epitopes and functional diversity in extracellular proteins

Superior low-immunogenicity of tilapia type I collagen based on unique secondary structure with single calcium binding motif over terrestrial mammals by inhibiting activation of DC intracellular Ca2+-mediated STIM1-Orai1/NF-кB pathway

The reason for low- or non-immunogenicity of fish collagens is still in doubt, which, to some extent, bottlenecks their production and clinical application as biomaterials. Employing bovine or porcine type I collagens (BCI or PCI) as controls in this paper, we intensively investigate the influence of tilapia type I collagens (TCI) on the function of dendritic cells (DCs) and T cells. From bio-informatic analyses, as well as data obtained in vitro and in vivo, we find the variations in amino acid sequences lead to only one calcium binding motif in the secondary structure of TCI, compared with three in BCI or PCI. So when TCI (together with the minor amount of Ca²⁺ they take) are uptaken, intracellular [Ca²⁺] remains stable and DCs maintain immature. On the contrary, those that have uptaken PCI or BCI experience not only increased [Ca²⁺] in the plasma but also phosphorylation of p65, resulting in activation of STIM1-Orai1/NF-кB signaling pathway and DC maturation. We fully prove our results on mice models, with no obvious cellular and humoral immune reactions. Our study primarily reveal the underlying mechanisms why TCI, different from BCI or PCI, show almost non-immunogenicity. Our findings are of great importance for the promotion and wide application of TCI in biomedicine.

Secreted Protein Acidic and Rich in Cysteine: Metabolic and Homeostatic Properties beyond the Extracellular Matrix Structure

An extracellular matrix (ECM) is a network of numerous macromolecules that represents the cellular structural support involved in key biofunctions such as signal transduction and cellular adhesion. In addition, ECM-associated proteins interact with ECM and with other endogenous structures and molecules to control cellular growth, structural modifications, cellular migration, etc. Among the ECM-associated proteins, secreted protein acidic and rich in cysteine (SPARC) is a protein that is known to be expressed when tissues change. Herein, we put a spotlight on selected, metabolic and homeostatic properties beyond the known properties of ECM and SPARC. Importantly, the synchronization of the metabolic and structural implications of SPARC and the ECM would indicate an adaptation of the metabolism to meet the needs of the changes that the tissues undergo. Highlighting such properties would have important applications in diverse fields that include therapeutics, metabolics, and pathogenesis.

Single-Molecule Assay for Proteolytic Susceptibility: Force-Induced Collagen Destabilization

Force plays a key role in regulating dynamics of biomolecular structure and interactions, yet techniques are lacking to manipulate and continuously read out this response with high throughput. We present an enzymatic assay for force-dependent accessibility of structure that makes use of a wireless mini-radio centrifuge force microscope to provide a real-time readout of kinetics. The microscope is designed for ease of use, fits in a standard centrifuge bucket, and offers high-throughput, video-rate readout of individual proteolytic cleavage events. Proteolysis measurements on thousands of tethered collagen molecules show a load-enhanced trypsin sensitivity, indicating destabilization of the triple helix.

Age-Associated Changes in Estrogen Receptor Ratios Correlate with Increased Female Susceptibility to Coxsackievirus B3-Induced Myocarditis

Sexual bias is a hallmark in various diseases. This review evaluates sexual dimorphism in clinical and experimental coxsackievirus B3 (CVB3) myocarditis, and how sex bias in the experimental disease changes with increased age. Coxsackieviruses are major causes of viral myocarditis, an inflammation of the heart muscle, which is more frequent and severe in men than women. Young male mice infected with CVB3 develop heart-specific autoimmunity and severe myocarditis. Females infected during estrus (high estradiol) develop T-regulatory cells and when infected during diestrus (low estradiol) develop autoimmunity similar to males. During estrus, protection depends on estrogen receptor alpha (ERα), which promotes type I interferon, activation of natural killer/natural killer T cells and suppressor cell responses. Estrogen receptor beta has opposing effects to ERα and supports pro-inflammatory immunity. However, the sexual dimorphism of the disease is significantly ameliorated in aged animals when old females become as susceptible as males. This correlates to a selective loss of the ERα that is required for immunosuppression. Therefore, sex-associated hormones control susceptibility in the virus-mediated disease, but their impact can alter with the age and physiological stage of the individual.