Type I collagen is thermally unstable at body temperature

The Bone Extracellular Matrix as an Ideal Milieu for Cancer Cell Metastases

Bone is a preferential site for cancer metastases, including multiple myeloma, prostate, and breast cancers.The composition of bone, especially the extracellular matrix (ECM), make it an attractive site for cancer cell colonization and survival. The bone ECM is composed of living cells embedded within a matrix composed of both organic and inorganic components. Among the organic components, type I collagen provides the tensile strength of bone. Inorganic components, including hydroxyapatite crystals, are an integral component of bone and provide bone with its rigidity. Under normal circumstances, two of the main cell types in bone, the osteoblasts and osteoclasts, help to maintain bone homeostasis and remodeling through cellular communication and response to biophysical signals from the ECM. However, under pathological conditions, including osteoporosis and cancer, bone remodeling is dysregulated. Once in the bone matrix, disseminated tumor cells utilize normal products of bone remodeling, such as collagen type I, to fuel cancer cell proliferation and lesion outgrowth. Models to study the complex interactions between the bone matrix and metastatic cancer cells are limited. Advances in understanding the interactions between the bone ECM and bone metastatic cancer cells are necessary in order to both regulate and prevent metastatic cancer cell growth in bone.

Streptococcal Collagen-like Protein 1 Binds Wound Fibronectin: Implications in Pathogen Targeting

Group A Streptococcus (GAS) infections are responsible for significant morbidity and mortality worldwide. The outlook for an effective global vaccine is reduced because of significant antigenic variation among GAS strains worldwide. Other challenges in GAS therapy include the lack of common access to antibiotics in developing countries, as well as allergy to and treatment failures with penicillin and increasing erythromycin resistance in the industrialized world. At the portal of entry, GAS binds to newly deposited extracellular matrix, which is rich in cellular fibronectin isoforms with extra domain A (EDA, also termed EIIIA) via the surface adhesin, the streptococcal collagen-like protein 1 (Scl1). Recombinant Scl1 constructs, derived from diverse GAS strains, bind the EDA loop segment situated between the C and C' β-strands. Despite the sequence diversity in Scl1 proteins, multiple sequence alignments and secondary structure predictions of Scl1 variants, as well as crystallography and homology modeling studies, point to a conserved mechanism of Scl1-EDA binding. We propose that targeting this interaction may prevent the progression of infection. A synthetic cyclic peptide, derived from the EDA C-C' loop, binds to recombinant Scl1 with a micromolar dissociation constant. This review highlights the current concept of EDA binding to Scl1 and provides incentives to exploit this binding to treat GAS infections and wound colonization.

Principles and development of collagen-mediated tissue fusion induced by laser irradiation

The mechanism underlying tissue fusion mediated by laser irradiation remains unclear. We clarify the mechanisms underlying laser-mediated tissue fusion using a novel model. Microscopic examinations of morphological changes within the adventitia of a bovine carotid artery and a collagen sheet prepared from bovine dermis showed collagen fibril bundle loosening and collagen fibre swelling following heating at 46 °C. An incised bovine carotid artery covered with a collagen sheet to which pressure and laser heat of 40 °C–52 °C were applied created a structure that was pressure resistant to >300 mmHg. Microscopic analyses of the irradiation site showed collagen fibril interdigitation. Hence, low-temperature laser-mediated tissue fusion causes collagen fibril bundles to loosen and swell, and crimping causes the fibres to intertwine. As the temperature declines, the loosened and swollen fibrils and fibres tighten, and collagen fibre interdigitation is completed. This technology could be applied to fuse tissues during surgery.

Structure and Dynamics of Collagen Hydration Water from Molecular Dynamics Simulations: Implications of Temperature and Pressure

Dynamics of water molecules in hydrated collagen plays an important role in determining the structural and functional properties of collagenous tissues. Experimental results suggest that collagen-bridging water molecules exhibit dynamic and thermodynamic properties of one-dimensional ice. However, molecular dynamics (MD) studies performed to date have failed to identify icelike water bridges. It has been hypothesized that this discrepancy is due to the experimental measurements and computational MD analysis having been performed on very different systems: complete tissues with large-scale collagen fiber assemblies and individual tropocollagen fragments, respectively. In this work, we explore ways of emulating a tissuelike macromolecular environment in MD simulations of hydrated collagen without increasing the size of the system to computationally prohibitive levels. We have investigated the effects of temperature and pressure on the dynamics of a small hydrated tropocollagen fragment. The occupancy and bond energies of interchain hydrogen bonds were relatively insensitive to temperature, suggesting that they play a key role in the stability of the collagen triple helix. The lifetimes of water bridges lengthened with decreasing temperature, but even at 280 K, no bridging water molecules exhibited icelike dynamics. We discuss the implications of these findings for the ability to emulate tissuelike conditions in hydrated collagen.

Tension in fibrils suppresses their enzymatic degradation - A molecular mechanism for 'use it or lose it'

Tissue homeostasis depends on a balance of synthesis and degradation of constituent proteins, with turnover of a given protein potentially regulated by its use. Extracellular matrix (ECM) is predominantly composed of fibrillar collagens that exhibit tension-sensitive degradation, which we review here at different levels of hierarchy. Past experiments and recent proteomics measurements together suggest that mechanical strain stabilizes collagen against enzymatic degradation at the scale of tissues and fibrils whereas isolated collagen molecules exhibit a biphasic behavior that depends on load magnitude. Within a Michaelis-Menten framework, collagenases at constant concentration effectively exhibit a low activity on substrate fibrils when the fibrils are strained by tension. Mechanisms of such mechanosensitive regulation are surveyed together with relevant interactions of collagen fibrils with cells.

Biomimetic Properties of Force-Spun PHBV Membranes Functionalised with Collagen as Substrates for Biomedical Application

The force-spinning process parameters (i.e., spin speed, spinneret-collector distance, and polymer concentration), optimised and characterised in previous work by this group, allowed the rapid fabrication of large quantities of high surface area poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) polymeric fibre membranes. This paper examined the potential application for force-spun PHBV fibres functionalised with type I collagen for tissue regeneration applications. PHBV fibre scaffolds provide a biologically suitable substrate to guide the regeneration of dermal tissues, however, have poor cellular adhesion properties. The grafting of collagen type-I to PHBV fibres demonstrated improved cell adhesion and growth in Neo-NHDF (neonatal human dermal fibroblasts) fibroblasts. The examination of fibre morphology, thermal properties, collagen content, and degradability was used to contrast the physicochemical properties of the PHBV and PHBV-Collagen fibres. Biodegradation models using phosphate buffered saline determined there was no appreciable change in mass over the course of 6 weeks; a Sirius Red assay was performed on degraded samples, showing no change in the quantity of collagen. Cell metabolism studies showed an increase in cell metabolism on conjugated samples after three and 7 days. In addition, in vitro cytocompatibility studies demonstrated superior cell activity and adhesion on conjugated samples over 7 days.

MMP-9 selectively cleaves non-D-banded material on collagen fibrils with discrete plasticity damage in mechanically-overloaded tendon

The mechanical properties of tendon are due to the properties and arrangement of its collagen fibril content. Collagen fibrils are highly-organized supermolecular structures with a periodic banding pattern (D-band) indicative of the geometry of molecular organization. Following mechanical overload of whole tendon, collagen fibrils may plastically deform at discrete sites along their length, forming kinks, and acquiring a fuzzy, non-D-banded, outer layer (shell). Termed discrete plasticity, such non-uniform damage to collagen fibrils suggests localized cellular response at the fibril level during subsequent repair/replacement. Matrix metallo-proteinases (MMPs) are enzymes which act upon the extracellular matrix, facilitating cell mobility and playing important roles in wound healing. A sub-group within this family are the gelatinases, MMP-2 and MMP-9, which selectively cleave denatured collagen molecules. Of these two, MMP-9 is specifically upregulated during the initial stages of tendon repair. This suggests a singular function in damage debridement. Using atomic force microscopy (AFM), a novel fibril-level enzymatic assay was employed to assess enzymatic removal of material by trypsin and MMP-9 from individual fibrils which were: (i) untreated, (ii) partially heat denatured, (iii) or displaying discrete plasticity damaged after repeated mechanical overload. Both enzymes removed material from heat denatured and discrete plasticity-damaged fibrils; however, only MMP-9 demonstrated the selective removal of non-D-banded material, with greater removal from more damaged fibrils. The selectivity of MMP-9, coupled with documented upregulation, suggests a likely mechanism for the in vivo debridement of individual collagen fibrils, following tendon overload injury, and prior to deposition of new collagen.

Processing of collagen based biomaterials and the resulting materials properties

Collagen, the most abundant extracellular matrix protein in animal kingdom belongs to a family of fibrous proteins, which transfer load in tissues and which provide a highly biocompatible environment for cells. This high biocompatibility makes collagen a perfect biomaterial for implantable medical products and scaffolds for in vitro testing systems. To manufacture collagen based solutions, porous sponges, membranes and threads for surgical and dental purposes or cell culture matrices, collagen rich tissues as skin and tendon of mammals are intensively processed by physical and chemical means. Other tissues such as pericardium and intestine are more gently decellularized while maintaining their complex collagenous architectures. Tissue processing technologies are organized as a series of steps, which are combined in different ways to manufacture structurally versatile materials with varying properties in strength, stability against temperature and enzymatic degradation and cellular response. Complex structures are achieved by combined technologies. Different drying techniques are performed with sterilisation steps and the preparation of porous structures simultaneously. Chemical crosslinking is combined with casting steps as spinning, moulding or additive manufacturing techniques. Important progress is expected by using collagen based bio-inks, which can be formed into 3D structures and combined with live cells. This review will give an overview of the technological principles of processing collagen rich tissues down to collagen hydrolysates and the methods to rebuild differently shaped products. The effects of the processing steps on the final materials properties are discussed especially with regard to the thermal and the physical properties and the susceptibility to enzymatic degradation. These properties are key features for biological and clinical application, handling and metabolization.

A pendant peptide endows a sunscreen with water-resistance

Ultraviolet light causes skin cancer. Salicylic acid and other molecular filters absorb damaging radiation but are washed away readily. Conjugation to a collagen mimetic peptide is shown to retain salicylic acid on collagen-containing skin surrogates after repeated washing. This strategy, which is highly modular, could enhance the water-resistance of sunscreens.

Collagen glycosylation

Despite the ubiquity of collagens in the animal kingdom, little is known about the biology of the disaccharide Glc(α1-2)Gal(β1-O) bound to hydroxylysine across collagens from sponges to mammals. The extent of collagen glycosylation varies by the types of collagen, with basement membrane collagen type IV being more glycosylated than fibrillar collagens. Beyond true collagens, proteins including collagen domains such as the complement protein 1Q and the hormone adiponectin also feature glycosylated hydroxylysine. Collagen glycosylation is initiated in the endoplasmic reticulum by the galactosyltransferases COLGALT1 and COLGALT2. Mutations in the COLGALT1 gene cause cerebral small vessel abnormality and porencephaly, which are common in collagen type IV deficiency. Beyond the strongly conserved Glc(α1-2)Gal(β1-O) glycan, additional forms of collagen glycosylation have been described in the deep-sea worm Riftia pachyptila and in the giant virus Mimivirus, thereby suggesting that further forms of collagen glycosylation are likely to be identified in the future.

The effect of colostrum intake on osteoprotegerin and bone metabolic markers in the blood of newborn calves during the first week of life

The aim of this study was to elucidate the bone metabolic status after taking colostrum in newborn calves. Fourteen neonatal calves were randomly allocated to two groups fed either unheated or heated (60°C, 30 min) colostrum three times on the first day (2 l every 10 hr; 6 l in total). Heat treatment on colostrum was to reduce the bone metabolic markers assumed as heat-sensitive. The concentrations of four bone metabolic markers (the enzymes from bone cells or the bone collagen fragments) and a bone protective protein, osteoprotegerin (OPG), were measured in the blood of calves during a week after the birth and in the colostrum. The colostral concentrations of four bone metabolic markers were reduced by heating. Then those circulatory markers peaked after colostrum intake in the calves fed unheated colostrum; whereas those fed heated colostrum did not show such changes. However, the plasma tartrate resistant acid phosphatase 5b (TRAP5b) activity was transiently increased after taking colostrum in both groups. Meanwhile, heating did not decrease colostral OPG and there was no significant rise in the serum OPG concentrations after the first colostrum intake in both groups. The study revealed that the blood concentrations of studied bone metabolic markers depended on those colostral values except for TRAP5b. Based on the plasma TRAP5b changes, accelerated formation of premature osteoclast cells may be induced by colostrum intake. Meanwhile, colostral OPG absorption is less likely to impact on its circulating levels.

3D mapping of native extracellular matrix reveals cellular responses to the microenvironment

Cells and extracellular matrix (ECM) are mutually interdependent: cells guide self-assembly of ECM precursors, and the resulting ECM architecture supports and instructs cells. Though bidirectional signaling between ECM and cells is fundamental to cell biology, it is challenging to gain high-resolution structural information on cellular responses to the matrix microenvironment. Here we used cryo-scanning transmission electron tomography (CSTET) to reveal the nanometer- to micron-scale organization of major fibroblast ECM components in a native-like context, while simultaneously visualizing internal cell ultrastructure including organelles and cytoskeleton. In addition to extending current models for collagen VI fibril organization, three-dimensional views of thick cell regions and surrounding matrix showed how ECM networks impact the structures and dynamics of intracellular organelles and how cells remodel ECM. Collagen VI and fibronectin were seen to distribute in fundamentally different ways in the cell microenvironment and perform distinct roles in supporting and interacting with cells. This work demonstrates that CSTET provides a new perspective for the study of ECM in cell biology, highlighting labeled extracellular elements against a backdrop of unlabeled but morphologically identifiable cellular features with nanometer resolution detail.

The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development

Collagen is the oldest and most abundant extracellular matrix protein that has found many applications in food, cosmetic, pharmaceutical, and biomedical industries. First, an overview of the family of collagens and their respective structures, conformation, and biosynthesis is provided. The advances and shortfalls of various collagen preparations (e.g., mammalian/marine extracted collagen, cell-produced collagens, recombinant collagens, and collagen-like peptides) and crosslinking technologies (e.g., chemical, physical, and biological) are then critically discussed. Subsequently, an array of structural, thermal, mechanical, biochemical, and biological assays is examined, which are developed to analyze and characterize collagenous structures. Lastly, a comprehensive review is provided on how advances in engineering, chemistry, and biology have enabled the development of bioactive, 3D structures (e.g., tissue grafts, biomaterials, cell-assembled tissue equivalents) that closely imitate native supramolecular assemblies and have the capacity to deliver in a localized and sustained manner viable cell populations and/or bioactive/therapeutic molecules. Clearly, collagens have a long history in both evolution and biotechnology and continue to offer both challenges and exciting opportunities in regenerative medicine as nature's biomaterial of choice.

Incorporation of hydroxyproline in bacterial collagen from Streptococcus pyogenes

Bacterial collagen-like proteins differ from vertebrate collagens in that they do not contain hydroxyproline, which is seen as a characteristic of the vertebrate collagens, and which provides a significant contribution to the stability of the collagen triple-helix at body temperature. Despite this difference, the bacterial collagens are stable at around body temperature through inclusion of other stabilising sequence elements. Another difference is the lack of aggregation, and certain vertebrate collagen binding domains that can be introduced into the bacterial sequence lack full function when hydroxyproline is absent. In the present study we have demonstrated that a simple method utilising co-translational incorporation during fermentation can be used to incorporate hydroxyproline into the recombinant bacterial collagen. The presence and amount of hydroxyproline incorporation was shown by amino acid analysis and by mass spectrometry. A small increase in thermal stability was observed using circular dichroism spectroscopy. STATEMENT OF SIGNIFICANCE: Recombinant bacterial collagens provide a new opportunity for biomedical materials as they are readily produced in large quantity in E. coli. Unlike animal collagens, they are stable without the need for inclusion of a secondary modification system for hydroxyproline incorporation. In animal collagens, however, introduction of hydroxyproline is essential for stability and is also important for functional molecular interactions within the mammalian extracellular matrix. The present study has shown that hydroxyproline can be readily introduced into recombinant S. pyogenes bacterial collagen through direct co-translational incorporation of this modified imino acid during expression using the codons for proline in the introduced gene construct. This hydroxylation further improves the stability of the collagen and is available to enhance any introduced molecular functions.

Substitutions for arginine at position 780 in triple helical domain of the α1(I) chain alter folding of the type I procollagen molecule and cause osteogenesis imperfecta

OI is a clinically and genetically heterogeneous disorder characterized by bone fragility. More than 90% of patients are heterozygous for mutations in type I collagen genes, COL1A1 and COL1A2, and a common mutation is substitution for an obligatory glycine in the triple helical Gly-X-Y repeats. Few non-glycine substitutions in the triple helical domain have been reported; most result in Y-position substitutions of arginine by cysteine. Here, we investigated leucine and cysteine substitutions for one Y-position arginine, p.Arg958 (Arg780 in the triple helical domain) of proα1(I) chains that cause mild OI. We compared their effects with two substitutions for glycine located in close proximity. Like substitutions for glycine, those for arginine reduced the denaturation temperature of the whole molecule and caused asymmetric posttranslational overmodification of the chains. Circular dichroism and increased susceptibility to cleavage by MMP1, MMP2 and catalytic domain of MMP1 revealed significant destabilization of the triple helix near the collagenase cleavage site. On a cellular level, we observed slower triple helix folding and intracellular collagen retention, which disturbed the Endoplasmic Reticulum function and affected matrix deposition. Molecular dynamic modeling suggested that Arg780 substitutions disrupt the triple helix structure and folding by eliminating hydrogen bonds of arginine side chains, in addition to preventing HSP47 binding. The pathogenic effects of these non-glycine substitutions in bone are probably caused mostly by procollagen misfolding and its downstream effects.

How electrostatic networks modulate specificity and stability of collagen

One-quarter of the 28 types of natural collagen exist as heterotrimers. The oligomerization state of collagen affects the structure and mechanics of the extracellular matrix, providing essential cues to modulate biological and pathological processes. A lack of high-resolution structural information limits our mechanistic understanding of collagen heterospecific self-assembly. Here, the 1.77-Å resolution structure of a synthetic heterotrimer demonstrates the balance of intermolecular electrostatics and hydrogen bonding that affects collagen stability and heterospecificity of assembly. Atomistic simulations and mutagenesis based on the solved structure are used to explore the contributions of specific interactions to energetics. A predictive model of collagen stability and specificity is developed for engineering novel collagen structures.

Elastic compliance of fibrillar assemblies in type I collagen

Fibrillary assemblies of Type I collagen find important applications in tissue engineering and as matrices for biophysical studies. The mechanical and structural properties of these structures are governed by factors such as protein concentration, temperature, pH and ionic strength. This study reports on an impedance based analysis of the elastic compliance of fibrillary assemblies of Type I collagen using quartz crystal microbalance with dissipation (QCM-D) at a fundamental frequency of 5 MHz and overtones (n = 3,5,7,9,11). Here, In situ partial fibrillation of the adsorbing collagen followed by its fibrillary assemblies on hydrophilic gold coated quartz surface have been crosslinked using Gallic acid (GA), Chromium (III) gallate (Cr-GA), Catechin (Cat), Tetrakis(hydroxymethyl)phosphonium sulfate (THPS) and Oxazolidine (Ox). This approach allows direct comparison of how viscoelastic properties track the structural evolution of the fiber and network length scales. The collagen crosslinking shows significant positive impact on the protein's mechanical behaviour and on the type of crosslinking agents used. The elastic modulus increases as collagen <GA < THPS < Cr-GA < Cat < Ox. Atomic force microscopic studies on the adsorbed collagen after cross linking confirmed the presence of fibrous assemblies. The results indicate stabilization and reinforcement through strong physical entanglement between the molecules of collagen as well as chemical interaction between collagen matrix and fibrils during cross linking. The elastic compliance evaluated from ΔDissipation/Δfreq. from QCM-D showed that cross linking with GA, Cr-GA and Ox resulted in flexible fibrillary network while agents like THPS and Cat showed elastic moduli similar to that of pure collagen. Results suggest that optimal collagen-crosslinking agent ratio and degree of crosslinking of collagen can help tailor the mechanical properties for specific applications in design of bio-materials of these composites.

Synthesis and characterization of a photocleavable collagen-like peptide

A 34-amino acid long collagen-like peptide rich in proline, hydroxyproline, and glycine, and with four photoreactive N-acyl-7-nitroindoline units incorporated into the peptide backbone was synthesized by on-resin fragment condensation. Its circular dichroism supports a stable triple helix structure. The built-in photochemical function enables the decomposition of the peptide into small peptide fragments by illumination with UV light of 350 nm in aqueous solution. Illumination of a thin film of the peptide, or a thin film of a photoreactive amino acid model compound containing a 5-bromo-7-nitroindoline moiety, with femtosecond laser light at 710 nm allows for the creation of well-resolved micropatterns. The cytocompatibility of the peptide was demonstrated using human mesenchymal stem cells and mouse embryonic fibroblasts. Our data show that the full-length peptide is cytocompatible as it can support cell growth and maintain cell viability. In contrast, the small peptide fragments created by photolysis are somewhat cytotoxic and therefore less cytocompatible. These data suggest that biomimetic collagen-like photoreactive peptides could potentially be used for growing cells in 2D micropatterns based on patterns generated by photolysis prior to cell growth.

Recombinant collagen scaffolds as substrates for human neural stem/progenitor cells

Adhesion to the microenvironment profoundly affects stem cell functions, including proliferation and differentiation, and understanding the interaction of stem cells with the microenvironment is important for controlling their behavior. In this study, we investigated the effects of the integrin binding epitopes GFOGER and IKVAV (natively present in collagen I and laminin, respectively) on human neural stem/progenitor cells (hNSPCs). To test the specificity of these epitopes, GFOGER or IKVAV were placed within the context of recombinant triple-helical collagen III engineered to be devoid of native integrin binding sites. HNSPCs adhered to collagen that presented GFOGER as the sole integrin-binding site, but not to IKVAV-containing collagen. For the GFOGER-containing collagens, antibodies against the β1 integrin subunit prevented cellular adhesion, antibodies against the α1 subunit reduced cell adhesion, and antibodies against α2 or α3 subunits had no significant effect. These results indicate that hNSPCs primarily interact with GFOGER through the α1β1 integrin heterodimer. These GFOGER-presenting collagen variants also supported differentiation of hNSPCs into neurons and astrocytes. Our findings show, for the first time, that hNSPCs can bind to the GFOGER sequence, and they provide motivation to develop hydrogels formed from recombinant collagen variants as a cell delivery scaffold. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1363-1372, 2018.

An efficient combination of BEST and NUS methods in multidimensional NMR spectroscopy for high throughput analysis of proteins

Application of Non Uniform Sampling (NUS) along with Band-selective Excitation Short-Transient (BEST) NMR experiments has been demonstrated for obtaining the important residue-specific atomic level backbone chemical shift values in short durations of time. This application has been demonstrated with both well-folded (ubiquitin) and unfolded (α-synuclein) proteins alike. With this strategy, the experiments required for determining backbone chemical shifts can be performed very rapidly, i.e., in ∼2 hours of spectrometer time, and this data can be used to calculate the backbone folds of proteins using well established algorithms. This will be of great value for structural proteomic investigations on one hand, where the speed of structure determination is a limiting factor and for application in the study of slow kinetic processes involving proteins, such as fibrillization, on the other hand.

Application of NUS along with BEST NMR experiments has been demonstrated for obtaining the important residue-specific atomic level backbone chemical shift values in short durations of time.

Lower temperatures reduce type I interferon activity and promote alphaviral arthritis

Chikungunya virus (CHIKV) belongs to a group of mosquito-borne alphaviruses associated with acute and chronic arthropathy, with peripheral and limb joints most commonly affected. Using a mouse model of CHIKV infection and arthritic disease, we show that CHIKV replication and the ensuing foot arthropathy were dramatically reduced when mice were housed at 30°C, rather than the conventional 22°C. The effect was not associated with a detectable fever, but was dependent on type I interferon responses. Bioinformatics analyses of RNA-Seq data after injection of poly(I:C)/jetPEI suggested the unfolded protein response and certain type I interferon responses are promoted when feet are slightly warmer. The ambient temperature thus appears able profoundly to effect anti-viral activity in the periphery, with clear consequences for alphaviral replication and the ensuing arthropathy. These observations may provide an explanation for why alphaviral arthropathies are largely restricted to joints of the limbs and the extremities.

Matrix metalloproteinase collagenolysis in health and disease

The proteolytic processing of collagen (collagenolysis) is critical in development and homeostasis, but also contributes to numerous pathologies. Mammalian interstitial collagenolytic enzymes include members of the matrix metalloproteinase (MMP) family and cathepsin K. While MMPs have long been recognized for their ability to catalyze the hydrolysis of collagen, the roles of individual MMPs in physiological and pathological collagenolysis are less defined. The use of knockout and mutant animal models, which reflect human diseases, has revealed distinct collagenolytic roles for MT1-MMP and MMP-13. A better understanding of temporal and spatial collagen processing, along with the knowledge of the specific MMP involved, will ultimately lead to more effective treatments for cancer, arthritis, cardiovascular conditions, and infectious diseases. This article is part of a Special Issue entitled: Matrix Metalloproteinases edited by Rafael Fridman.

Fabrication of tough poly(ethylene glycol)/collagen double network hydrogels for tissue engineering

In this study, a series of poly(ethylene glycol)/collagen (PEG/Col) double network (DN) hydrogel is fabricated from PEG and Col. Results of the compressive strength test indicate that the strength and toughness of these DN hydrogels are significantly enhanced. The fracture strength of PEG/Col DN hydrogels increases by 9- to 12-fold compared with that of PEG single network (SN) hydrogel, and by 36- to 48-fold compared with that of Col SN hydrogel. Taking advantage of both PEG and Col building blocks, the PEG/Col DN hydrogels possess a strengthened skeleton. Moreover, the water-storage capability and favorable biocompatibility of Col are effectively maintained. Given that the DN hydrogels can provide the appropriate environment for the adhesion, growth, and proliferation of MC3T3-E1 cells, PEG/Col DN hydrogels have potential as a load-bearing tissue repair material. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 192-200, 2018.

Novel transparent collagen film patch derived from duck's feet for tympanic membrane perforation

To increase healing rate of tympanic membrane (TM) perforations, patching procedure has been commonly conducted. Biocompatible, biodegradable patching materials which is not limited across cultures is needed. The authors evaluated the effectiveness of novel transparent duck's feet collagen film (DCF) patch in acute traumatic TM perforation. This procedure was compared with spontaneous healing and paper patching. Cell proliferation features were observed in paper and DCF patches. Forty-eight TMs of 24 rats were used for animal experiment, perforations were made on each TMs, and divided into three groups according to treatment modality. Sixteen were spontaneously healed, 16 were paper patched and 16 were DCF patched. The gross and histological healing results were analyzed. Both paper and DCF patch showed no cytotoxicity, but cell proliferations were more active in DCF than paper in early stage. In animal study, the healing of TM perforations were completed within 14 days in all three groups, but found to be faster in DCF patch group than paper patch or spontaneous healing group. The DCF patches were transparent and size of DCF patches were gradually decreased, so there were no need to remove the DCF patches to check the wound status or after the completion of healing. According to this result, authors concluded that DCF patch is transparent, biocompatible and biodegradable material, and can induce fast healing in acute traumatic TM perforations.

Circular Dichroism Spectroscopy of Collagen Fibrillogenesis: A New Use for an Old Technique

Type-I collagen assembles in a stepwise, hierarchic fashion from the folding of the triple helix to the assembly of fibrils into fibers. The mature assembled fibers are crucial for tissue structure and mechanics, cell interactions, and other functions in vivo. Although triple helix folding can be followed with the use of optical methods such as circular dichroism (CD) spectroscopy, fibrillogenesis is typically measured by alternative methods such as turbidity, rheology, and microscopy. Together, these approaches allow for investigation of the mechanical properties and architectures of collagen-based scaffolds and excised tissues. Herein, we demonstrate that CD spectroscopy, a technique that is used primarily to evaluate the secondary structure of proteins, can also be employed to monitor collagen fibrillogenesis. Type-I collagen suspensions demonstrated a strong, negative ellipticity band between 204 and 210 nm under conditions consistent with fibrillogenesis. Deconvolution of CD spectra before, during, and after fibrillogenesis identified a unique fibril spectrum distinct from triple helix and random coil conformations. The ability to monitor multiple states of collagen simultaneously in one experiment using one modality provides a powerful platform for studying this complex assembly process and the effects of other factors, such as collagenases, on fibrillogenesis and degradation.

Collagen Type I Alpha 2 (COL1A2) Polymorphism Contributes to Intracranial Aneurysm Susceptibility: A Meta-Analysis

Background

COL1A2, which encodes collagen type I alpha2, has long been suggested to be a potential positional and functional candidate gene for intracranial aneurysm. We performed a meta-analysis to assess the association between COL1A2 rs42524 polymorphism and the risk of intracranial aneurysm.

Material/Methods

We conducted a systematic search for relevant literature from the following databases up to 22 July 2016: PubMed, Embase, Web of Science, and China National Knowledge Infrastructure. The strength of association between gene and disease was estimated using odds ratios (ORs) with 95% confidence intervals (CIs) under 5 genetic models.

Results

A total of 6 qualified studies were enrolled in this meta-analysis. Pooling results indicated a significant association between COL1A2 rs42524 polymorphism and intracranial aneurysm risk under 4 genetic models (C vs. G: OR=1.74, 95%CI=1.34–2.26; GC vs. GG: OR=1.81, 95%CI=1.37–2.41; CC+GC vs. GG: OR=1.74, 95%CI=1.28–2.36; CC vs. GC+GG: OR=1.76, 95%CI=1.02–3.04). This association was still robust when stratified by ethnicity, intracranial aneurysm type, or Hardy-Weinberg Equilibrium, which was stronger in Asian than in Caucasians. No publication bias was observed.

Conclusions

This meta-analysis suggests COL1A2 rs42524 is a significant risk factor for IA susceptibility, with an especially strong effect in Asian people. Further larger-scale epidemiological studies among different ethnicities are warranted to confirm our findings.

Blocking collagen fibril formation in injured knees reduces flexion contracture in a rabbit model

Post-traumatic joint contracture is a frequent orthopaedic complication that limits the movement of injured joints, thereby severely impairing affected patients. Non-surgical and surgical treatments for joint contracture often fail to improve the range of motion. In this study, we tested a hypothesis that limiting the formation of collagen-rich tissue in the capsules of injured joints would reduce the consequences of the fibrotic response and improve joint mobility. We targeted the formation of collagen fibrils, the main component of fibrotic deposits formed within the tissues of injured joints, by employing a relevant rabbit model to test the utility of a custom-engineered antibody. The antibody was delivered directly to the cavities of injured knees in order to block the formation of collagen fibrils produced in response to injury. In comparison to the non-treated control, mechanical tests of the antibody-treated knees demonstrated a significant reduction of flexion contracture. Detailed microscopic and biochemical studies verified that this reduction resulted from the antibody-mediated blocking of the assembly of collagen fibrils. These findings indicate that extracellular processes associated with excessive formation of fibrotic tissue represent a valid target for limiting post-traumatic joint stiffness. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1038-1046, 2017.

Molecular level detection and localization of mechanical damage in collagen enabled by collagen hybridizing peptides

Mechanical injury to connective tissue causes changes in collagen structure and material behaviour, but the role and mechanisms of molecular damage have not been established. In the case of mechanical subfailure damage, no apparent macroscale damage can be detected, yet this damage initiates and potentiates in pathological processes. Here, we utilize collagen hybridizing peptide (CHP), which binds unfolded collagen by triple helix formation, to detect molecular level subfailure damage to collagen in mechanically stretched rat tail tendon fascicle. Our results directly reveal that collagen triple helix unfolding occurs during tensile loading of collagenous tissues and thus is an important damage mechanism. Steered molecular dynamics simulations suggest that a likely mechanism for triple helix unfolding is intermolecular shearing of collagen α-chains. Our results elucidate a probable molecular failure mechanism associated with subfailure injuries, and demonstrate the potential of CHP targeting for diagnosis, treatment and monitoring of tissue disease and injury.

Collagen denaturation is thought to occur during tissue mechanical damage, but its role in damage initiation is still unclear. Here, the authors use a collagen hybridizing peptide to provide insights into the molecular mechanisms leading to collagen unfolding during tendon mechanical stretch.

Peptide-drug conjugates as effective prodrug strategies for targeted delivery

Peptide-drug conjugates (PDCs) represent an important class of therapeutic agents that combine one or more drug molecules with a short peptide through a biodegradable linker. This prodrug strategy uniquely and specifically exploits the biological activities and self-assembling potential of small-molecule peptides to improve the treatment efficacy of medicinal compounds. We review here the recent progress in the design and synthesis of peptide-drug conjugates in the context of targeted drug delivery and cancer chemotherapy. We analyze carefully the key design features in choosing the peptide sequence and linker chemistry for the drug of interest, as well as the strategies to optimize the conjugate design. We highlight the recent progress in the design and synthesis of self-assembling peptide-drug amphiphiles to construct supramolecular nanomedicine and nanofiber hydrogels for both systemic and topical delivery of active pharmaceutical ingredients.

Collagen-like proteins of pathogenic streptococci

The collagen domain, which is defined by the presence of the Gly-X-Y triplet repeats, is amongst the most versatile and widespread known structures found in proteins from organisms representing all three domains of life. The streptococcal collagen-like (Scl) proteins are widely present in pathogenic streptococci, including Streptococcus pyogenes, S. agalactiae, S. pneumoniae, and S. equi. Experiments and bioinformatic analyses support the hypothesis that all Scl proteins are homotrimeric and cell wall-anchored. These proteins contain the rod-shaped collagenous domain proximal to cell surface, as well as a variety of outermost non-collagenous domains that generally lack predicted functions but can be grouped into one of six clusters based on sequence similarity. The well-characterized Scl1 proteins of S. pyogenes show a dichotomous switch in ligand binding between human tissue and blood environments. In tissue, Scl1 adhesin specifically recognizes the wound microenvironment, promotes adhesion and biofilm formation, decreases bacterial killing by neutrophil extracellular traps, and modulates S. pyogenes virulence. In blood, ligands include components of complement and coagulation-fibrinolytic systems, as well as plasma lipoproteins. In all, the Scl proteins signify a large family of structurally related surface proteins, which contribute to the ability of streptococci to colonize and cause diseases in humans and animals.

Fibrillar Collagens

Fibrillar collagens (types I, II, III, V, XI, XXIV and XXVII) constitute a sub-group within the collagen family (of which there are 28 types in humans) whose functions are to provide three-dimensional frameworks for tissues and organs. These networks confer mechanical strength as well as signalling and organizing functions through binding to cellular receptors and other components of the extracellular matrix (ECM). Here we describe the structure and assembly of fibrillar collagens, and their procollagen precursors, from the molecular to the tissue level. We show how the structure of the collagen triple-helix is influenced by the amino acid sequence, hydrogen bonding and post-translational modifications, such as prolyl 4-hydroxylation. The numerous steps in the biosynthesis of the fibrillar collagens are reviewed with particular attention to the role of prolyl 3-hydroxylation, collagen chaperones, trimerization of procollagen chains and proteolytic maturation. The multiple steps controlling fibril assembly are then discussed with a focus on the cellular control of this process in vivo. Our current understanding of the molecular packing in collagen fibrils, from different tissues, is then summarized on the basis of data from X-ray diffraction and electron microscopy. These results provide structural insights into how collagen fibrils interact with cell receptors, other fibrillar and non-fibrillar collagens and other ECM components, as well as enzymes involved in cross-linking and degradation.

Evolutionary trend toward kinetic stability in the folding trajectory of RNases H

Proper folding of proteins is critical to producing the biological machinery essential for cellular function. The rates and energetics of a protein's folding process, which is described by its energy landscape, are encoded in the amino acid sequence. Over the course of evolution, this landscape must be maintained such that the protein folds and remains folded over a biologically relevant time scale. How exactly a protein's energy landscape is maintained or altered throughout evolution is unclear. To study how a protein's energy landscape changed over time, we characterized the folding trajectories of ancestral proteins of the ribonuclease H (RNase H) family using ancestral sequence reconstruction to access the evolutionary history between RNases H from mesophilic and thermophilic bacteria. We found that despite large sequence divergence, the overall folding pathway is conserved over billions of years of evolution. There are robust trends in the rates of protein folding and unfolding; both modern RNases H evolved to be more kinetically stable than their most recent common ancestor. Finally, our study demonstrates how a partially folded intermediate provides a readily adaptable folding landscape by allowing the independent tuning of kinetics and thermodynamics.