The chemistry and structure of collagen

Improvement of collagen self-assembly and thermal stability in the presence of trehalose

Trehalose, as a compatible osmolyte, can stabilize collagen and is beneficial to the self-assembly and mechanical properties of its products.

An integrated approach to investigate age-related modifications of morphological, mechanical and structural properties of type I collagen

The main propose of this study is to characterize the impact of chronological aging on mechanical, structural, biochemical, and morphological properties of type I collagen. We have developed an original approach combining a stress-strain measurement device with a portable Raman spectrometer to enable simultaneous measurement of Raman spectra during stress vs strain responses of young adult, adult and old rat tail tendon fascicles (RTTFs). Our data showed an increase in all mechanical properties such as Young's modulus, yield strength, and ultimate tensile strength with aging. At the molecular level, Raman data revealed that the most relevant frequency shift was observed at 938 cm^-1 in Old RTTFs, which is assigned to the C-C. This suggested a long axis deformation of the peptide chains in Old RTTFs during tensile stress. In addition, the intensity of the band at 872 cm^-1, corresponding to hydroxyproline decreased for young adult RTTFs and increased for the adult ones, while it remained unchanged for Old RTTFs during tensile stress. The amide III band (1242 and 1265 cm^-1) as well as the band ratios I₁₆₃₁/ I₁₆₆₃ and I₁₆₄₅ / I₁₆₆₃ responses to tensile stress were depending on mechanical phases (toe, elastic and plastic). The quantification of advanced glycation end-products by LC-MS/MS and spectrofluorometry showed an increase in their content with aging. This suggested that the accumulation of such products was correlated to the alterations observed in the mechanical and molecular properties of RTTFs. Analysis of the morphological properties of RTTFs by SHG combined with CT-FIRE software revealed an increase in length and straightness of collagen fibers, whereas their width and wavy fraction decreased. Our integrated study model could be useful to provide additional translational information to monitor progression of diseases related to collagen remodeling in musculoskeletal disorders. STATEMENT OF SIGNIFICANCE: Type I collagen is the major component of the extracellular matrix. Its architectural and structural organization plays an important role in the mechanical properties of many tissues at the physiological and pathological levels. The objective of this work is to develop an integrated approach to bring a new insight on the impact of chronological aging on the structural organization and mechanical properties of type I collagen. We combined a portable Raman spectrometer with a mechanical tensile testing device in order to monitor in real time the changes in the Raman fingerprint of type I collagen fibers during the mechanical stress. Raman spectroscopy allowed the identification of the type I collagen bonds that were affected by mechanical stress in a differential manner with aging.

Reconstruction of a Demineralized Dentin Matrix via Rapid Deposition of CaF2 Nanoparticles In Situ Promotes Dentin Bonding

Dentin bonding based on a wet-bonding technique is the fundamental technique used daily in clinics for tooth-restoration fixation and clinical treatment of tooth-related diseases. Limited bonding durability led by insufficient adhesive infiltration in the demineralized dentin (DD) matrix is the biggest concern in contemporary adhesive dentistry. This study proposes that the highly hydrated noncollagenous protein (NCP)-formed interfacial microenvironment of the DD matrix is the root cause of this problem. Meanwhile, the endogenous phosphate groups of the NCPs are used as pseudonuclei to rapidly induce the formation of amorphous CaF₂ nanoparticles in situ in the interfacial microenvironment. The DD matrix is thus reconstructed into a novel porous structure. It markedly facilitates the infiltration of dentin adhesives in the DD matrix and also endows the DD matrix with anticollapsing capability when water evaporates. Whether using a wet-bonding or air-drying mode, the bonding effectiveness is greatly promoted, with the 12 month bonding strength being about twice that of the corresponding control groups. This suggests that the nanoreinforced DD matrix eliminates the dependence of bonding effectiveness on the moisture status of the DD surface controlled only by experiences of dentists. Consequently, this bonding strategy not only greatly improves bonding durability but also overcomes the technical sensitivity of bonding operations of the total-etched bonding pattern. This exhibits the potential to promote dentin bonding and is of great significance to dentistry.

Intermolecular channels direct crystal orientation in mineralized collagen

The mineralized collagen fibril is the basic building block of bone, and is commonly pictured as a parallel array of ultrathin carbonated hydroxyapatite (HAp) platelets distributed throughout the collagen. This orientation is often attributed to an epitaxial relationship between the HAp and collagen molecules inside 2D voids within the fibril. Although recent studies have questioned this model, the structural relationship between the collagen matrix and HAp, and the mechanisms by which collagen directs mineralization remain unclear. Here, we use XRD to reveal that the voids in the collagen are in fact cylindrical pores with diameters of ~2 nm, while electron microscopy shows that the HAp crystals in bone are only uniaxially oriented with respect to the collagen. From in vitro mineralization studies with HAp, CaCO₃ and γ-FeOOH we conclude that confinement within these pores, together with the anisotropic growth of HAp, dictates the orientation of HAp crystals within the collagen fibril.

Non-natural 3-Arylmorpholino-β-amino Acid as a PPII Helix Inducer

A new non-natural β-amino acid, named 3-Ar-β-Morph, was designed and synthesized via a regio- and diastereoselective Pd-catalyzed C(sp3)H-arylation of the corresponding 2S,6S-(6-methoxymorpholin-2-yl)carboxylic acid, readily available from glucose. According to the computational prevision and confirmed by IR and NMR data, the insertion of 3-Ar-β-Morph in a model foldamer represents a way to stabilize a PPII-like helix through the presence of two γ-turns, secondary structure motifs induced by the morpholine ring, and the trans-tertiary amide bond.

The predominant roles of the sequence periodicity in the self-assembly of collagen-mimetic mini-fibrils

Collagen fibrils represent a unique case of protein folding and self‐association. We have recently successfully developed triple‐helical peptides that can further self‐assemble into collagen‐mimetic mini‐fibrils. The 35 nm axially repeating structure of the mini‐fibrils, which is designated the d‐period, is highly reminiscent of the well‐known 67 nm D‐period of native collagens when examined using TEM and atomic force spectroscopy. We postulate that it is the pseudo‐identical repeating sequence units in the primary structure of the designed peptides that give rise to the d‐period of the quaternary structure of the mini‐fibrils. In this work, we characterize the self‐assembly of two additional designed peptides: peptide Col877 and peptide Col108rr. The triple‐helix domain of Col877 consists of three pseudo‐identical amino acid sequence units arranged in tandem, whereas that of Col108rr consists of three sequence units identical in amino acid composition but different in sequence. Both peptides form stable collagen triple helices, but only triple helices Col877 self‐associate laterally under fibril forming conditions to form mini‐fibrils having the predicted d‐period. The Co108rr triple helices, however, only form nonspecific aggregates having no identifiable structural features. These results further accentuate the critical involvement of the repeating sequence units in the self‐assembly of collagen mini‐fibrils; the actual amino acid sequence of each unit has only secondary effects. Collagen is essential for tissue development and function. This novel approach to creating collagen‐mimetic fibrils can potentially impact fundamental research and have a wide range of biomedical and industrial applications.

Distributions: The Importance of the Chemist's Molecular View for Biological Materials

Characterization of materials with biological applications and assessment of physiological effects of therapeutic interventions are critical for translating research to the clinic and preventing adverse reactions. Analytical techniques typically used to characterize targeted nanomaterials and tissues rely on bulk measurement. Therefore, the resulting data represent an average structure of the sample, masking stochastic (randomly generated) distributions that are commonly present. In this Perspective, we examine almost 20 years of work our group has done in different fields to characterize and control distributions. We discuss the analytical techniques and statistical methods we use and illustrate how we leverage them in tandem with other bulk techniques. We also discuss the challenges and time investment associated with taking such a detailed view of distributions as well as the risks of not fully appreciating the extent of heterogeneity present in many systems. Through three case studies showcasing our research on conjugated polymers for drug delivery, collagen in bone, and endogenous protein nanoparticles, we discuss how identification and characterization of distributions, i.e., a molecular view of the system, was critical for understanding the observed biological effects. In all three cases, data would have been misinterpreted and insights missed if we had only relied upon spatially averaged data. Finally, we discuss how new techniques are starting to bridge the gap between bulk and molecular level analysis, bringing more opportunity and capacity to the research community to address the challenges of distributions and their roles in biology, chemistry, and the translation of science and engineering to societal challenges.

Collagen structure: new tricks from a very old dog

The main features of the triple helical structure of collagen were deduced in the mid-1950s from fibre X-ray diffraction of tendons. Yet, the resulting models only could offer an average description of the molecular conformation. A critical advance came about 20 years later with the chemical synthesis of sufficiently long and homogeneous peptides with collagen-like sequences. The availability of these collagen model peptides resulted in a large number of biochemical, crystallographic and NMR studies that have revolutionized our understanding of collagen structure. High-resolution crystal structures from collagen model peptides have provided a wealth of data on collagen conformational variability, interaction with water, collagen stability or the effects of interruptions. Furthermore, a large increase in the number of structures of collagen model peptides in complex with domains from receptors or collagen-binding proteins has shed light on the mechanisms of collagen recognition. In recent years, collagen biochemistry has escaped the boundaries of natural collagen sequences. Detailed knowledge of collagen structure has opened the field for protein engineers who have used chemical biology approaches to produce hyperstable collagens with unnatural residues, rationally designed collagen heterotrimers, self-assembling collagen peptides, etc. This review summarizes our current understanding of the structure of the collagen triple helical domain (COL×3) and gives an overview of some of the new developments in collagen molecular engineering aiming to produce novel collagen-based materials with superior properties.

Water scaffolding in collagen: Implications on protein dynamics as revealed by solid-state NMR

Solid-state NMR studies of collagen samples of various origins confirm that the amplitude of collagen backbone and sidechain motions increases significantly on increasing the water content. This conclusion is supported by the changes observed in three different NMR observables: (i) the linewidth dependence on the 1H decoupling frequency; (ii) 13C CSA changes for the peptide carbonyl groups, and (iii) dephasing rates of 1H-13C dipolar couplings. In particular, a nearly threefold increase in motional amplitudes of the backbone librations about C-Cα or N-Cα bonds was found on increasing the added water content up to 47 wt%D2 O. On the basis of the frequencies of NMR observables involved, the timescale of the protein motions dependent on the added water content is estimated to be of the order of microseconds. This estimate agrees with that from wideline T2(1)H NMR measurements. Also, our wideline 1H NMR measurements revealed that the timescale of the microsecond motions in proteins reduces significantly on increasing the added water content, i.e., an ∼15-fold increase in protein motional frequencies is observed on increasing the added water content to 45 wt% D2 O. The observed changes in collagen dynamics is attributed to the increase in water translational diffusion on increasing the amount of added water, which leads to more frequent "bound water/free water" exchange on the protein surface, accompanied by the breakage and formation of new hydrogen bonds with polar functionalities of protein.

A perspective on structural and computational work on collagen

Collagen is the single most abundant protein in the extracellular matrix in the animal kingdom, with remarkable structural and functional diversity and regarded one of the most useful biomaterials.

Fibrous proteins: At the crossroads of genetic engineering and biotechnological applications

Fibrous proteins, such as silk, elastin and collagen are finding broad impact in biomaterial systems for a range of biomedical and industrial applications. Some of the key advantages of biosynthetic fibrous proteins compared to synthetic polymers include the tailorability of sequence, protein size, degradation pattern, and mechanical properties. Recombinant DNA production and precise control over genetic sequence of these proteins allows expansion and fine tuning of material properties to meet the needs for specific applications. We review current approaches in the design, cloning, and expression of fibrous proteins, with a focus on strategies utilized to meet the challenges of repetitive fibrous protein production. We discuss recent advances in understanding the fundamental basis of structure-function relationships and the designs that foster fibrous protein self-assembly towards predictable architectures and properties for a range of applications. We highlight the potential of functionalization through genetic engineering to design fibrous protein systems for biotechnological and biomedical applications.

Structure and Biophysical Properties of a Triple-Stranded Beta-Helix Comprising the Central Spike of Bacteriophage T4

Gene product 5 (gp5) of bacteriophage T4 is a spike-shaped protein that functions to disrupt the membrane of the target cell during phage infection. Its C-terminal domain is a long and slender β-helix that is formed by three polypeptide chains wrapped around a common symmetry axis akin to three interdigitated corkscrews. The folding and biophysical properties of such triple-stranded β-helices, which are topologically related to amyloid fibers, represent an unsolved biophysical problem. Here, we report structural and biophysical characterization of T4 gp5 β-helix and its truncated mutants of different lengths. A soluble fragment that forms a dimer of trimers and that could comprise a minimal self-folding unit has been identified. Surprisingly, the hydrophobic core of the β-helix is small. It is located near the C-terminal end of the β-helix and contains a centrally positioned and hydrated magnesium ion. A large part of the β-helix interior comprises a large elongated cavity that binds palmitic, stearic, and oleic acids in an extended conformation suggesting that these molecules might participate in the folding of the complete β-helix.

d-Glucose based syntheses of β-hydroxy derivatives of l-glutamic acid, l-glutamine, l-proline and a dihydroxy pyrrolidine alkaloid

The β-hydroxy derivatives of l-glutamic acid, l-glutamine and l-proline, useful for peptide/protein studies, were synthesized starting from d-glucose.

Polymers in cell encapsulation from an enveloped cell perspective

In the past two decades, many polymers have been proposed for producing immunoprotective capsules. Examples include the natural polymers alginate, agarose, chitosan, cellulose, collagen, and xanthan and synthetic polymers poly(ethylene glycol), polyvinyl alcohol, polyurethane, poly(ether-sulfone), polypropylene, sodium polystyrene sulfate, and polyacrylate poly(acrylonitrile-sodium methallylsulfonate). The biocompatibility of these polymers is discussed in terms of tissue responses in both the host and matrix to accommodate the functional survival of the cells. Cells should grow and function in the polymer network as adequately as in their natural environment. This is critical when therapeutic cells from scarce cadaveric donors are considered, such as pancreatic islets. Additionally, the cell mass in capsules is discussed from the perspective of emerging new insights into the release of so-called danger-associated molecular pattern molecules by clumps of necrotic therapeutic cells. We conclude that despite two decades of intensive research, drawing conclusions about which polymer is most adequate for clinical application is still difficult. This is because of the lack of documentation on critical information, such as the composition of the polymer, the presence or absence of confounding factors that induce immune responses, toxicity to enveloped cells, and the permeability of the polymer network. Only alginate has been studied extensively and currently qualifies for application. This review also discusses critical issues that are not directly related to polymers and are not discussed in the other reviews in this issue, such as the functional performance of encapsulated cells in vivo. Physiological endocrine responses may indeed not be expected because of the many barriers that the metabolites encounter when traveling from the blood stream to the enveloped cells and back to circulation. However, despite these diffusion barriers, many studies have shown optimal regulation, allowing us to conclude that encapsulated grafts do not always follow nature's course but are still a possible solution for many endocrine disorders for which the minute-to-minute regulation of metabolites is mandatory.

Tendon's ultrastructure

The structure of a tendon is an important example of complexity of ECM three-dimensional organization. The extracellular matrix (ECM) is a macromolecular network with both structural and regulatory functions. ECM components belong to four major types of macromolecules: the collagens, elastin, proteoglycans, and noncollagenous glycoproteins. Tendons are made by a fibrous, compact connective tissue that connect muscle to bone designed to transmit forces and withstand tension during muscle contraction. Here we show the ultrastructural features of tendon's components.

Type I collagen self-assembly: the roles of substrate and concentration

Collagen molecules, self-assembled into macroscopic hierarchical tissue networks, are the main organic building block of many biological tissues. A particularly common and important form of this self-assembly consists of type I collagen fibrils, which exhibit a nanoscopic signature, D-periodic gap/overlap spacing, with a distribution of values centered at approximately 67 nm. In order to better understand the relationship between type I collagen self-assembly and D-spacing distribution, we investigated surface-mediated collagen self-assembly as a function of substrate and incubation concentration. Collagen fibril assembly on phlogopite and muscovite mica as well as fibrillar gel coextrusion in glass capillary tubes all exhibited D-spacing distributions similar to those commonly observed in biological tissues. The observation of D-spacing distribution by self-assembly of type I collagen alone is significant as it eliminates the necessity to invoke other preassembly or postassembly hypotheses, such as variation in the content of collagen types, enzymatic cross-linking, or other post-translational modifications, as mechanistic origins of D-spacing distribution. The D-spacing distribution on phlogopite mica is independent of type I collagen concentration, but on muscovite mica D-spacing distributions showed increased negative skewness at 20 μg/mL and higher concentrations. Tilted D-spacing angles were found to correlate with decreased D-spacing measurements, an effect that can be removed with a tilt angle correction, resulting in no concentration dependence of D-spacing distribution on muscovite mica. We then demonstrated that tilted D-spacing is uncommon in biological tissues and it does not explain previous observations of low D-spacing values in ovariectomized dermis and bone.

Type I collagen D-spacing in fibril bundles of dermis, tendon, and bone: bridging between nano- and micro-level tissue hierarchy

Fibrillar collagens in connective tissues are organized into complex and diverse hierarchical networks. In dermis, bone, and tendon, one common phenomenon at the micrometer scale is the organization of fibrils into bundles. Previously, we have reported that collagen fibrils in these tissues exhibit a 10 nm width distribution of D-spacing values. This study expands the observation to a higher hierarchical level by examining fibril D-spacing distribution in relation to the bundle organization. We used atomic force microscopy imaging and two-dimensional fast Fourier transform analysis to investigate dermis, tendon, and bone tissues. We found that, in each tissue type, collagen fibril D-spacings within a single bundle were nearly identical and frequently differ by less than 1 nm. The full 10 nm range in D-spacing values arises from different values found in different bundles. The similarity in D-spacing was observed to persist for up to 40 μm in bundle length and width. A nested mixed model analysis of variance examining 107 bundles and 1710 fibrils from dermis, tendon, and bone indicated that fibril D-spacing differences arise primarily at the bundle level (∼76%), independent of species or tissue types.

Effects of avocado and soya bean lipidic non-saponifiables on the components of skin connective tissue after topical application in the hairless rat: biophysical and biomechanical determination

Synopsis The non-saponifiable lipidic fractions of avocado and soya bean applied percutaneously to hairless rats for 15 days had been shown to produce biochemical modifications of dermal connective tissue components: increases of soluble collagen and of the ratio soluble collagen/insoluble collagen. In this present study, we tried to show whether these biochemical modifications could be confirmed by biophysical analytical methods and could affect the biochemical properties of the skin. The experiments were carried out on three groups of rats treated by application to the dorsal skin, either with 0.9% NaCl (control), or sweet almond oil (vehicle), or with a mixture of 2/3 soya bean and 1/3 avocado in solution at 5% of sweet almond oil (treated group). After 15 days treatment, the rats were killed and the skin of the treated area dissected. X-ray diffraction diagrams were recorded by varying the position of previously dried samples in controlled conditions. Results indicated that the vehicle decreased the orientation degree of collagen fibres, acting on their reticulation. The addition of the non-saponifiable fraction did not significantly add to the vehicle effect. The study of thermostability of the cutaneous collagen by differential scanning calorimetry showed that non-saponifiables increased the slope of the rise of temperature of denaturation. The quantity of heat absorbed during the denaturation (enthalpy variation) reached around 0.04 J mg(-1) of collagen in the control groups and did not exceed 0.03 J mg(-1) of collagen in the treated ones. Taken in conjunction with previous work it is probable that the non-saponifiables increase the proportion of soluble collagen. The elasticity of whole skin, determined by a static method using an Instron exten-siometer was significantly modified by treatment with non-saponifiables. They produced a decrease of the elasticity module. These results correspond to a decrease of collagen reticulation degree.

Fibrillar structure and elasticity of hydrating collagen: a quantitative multiscale approach

It is well known that hydration of collagenous tissues leads to their swelling, as well as to softening of their elastic behavior. However, it is much less clear which microstructural and micromechanical "rules" are involved in this process. Here, we develop a theoretical approach cast in analytical mathematical formulations, which is experimentally validated by a wealth of independent tests on collagenous tissues, such as X-ray diffraction, vacuum drying, mass measurements, and Brillouin light scattering. The overall emerging picture is the following: air-drying leaves water only in the gap zones between the triple-helical collagen molecules; upon re-hydration, the extrafibrillar space is established at volumes directly proportional to the hydration-induced swelling of the (micro) fibrils, until the maximum equatorial distance between the long collagen molecules is reached. Thereafter, the volume of the fibrils stays constant, and only the extrafibrillar volume continues to grow. At all these hydration stages, the elastic behavior is governed by the same, hydration-invariant mechanical interaction pattern of only two, interpenetrating mechanical phases: transversely isotropic molecular collagen and isotropic water (or empty pores in the vacuum-dried case).

Recent advances in the use of serological bone formation markers to monitor callus development and fracture healing

The failure of an osseous fracture to heal, or the development of a nonunion, is common; however, current diagnostic measures lack the capability of early and reliable detection of such events. Analyses of radiographic imaging and clinical examination, in combination, remain the gold standard for diagnosis; however, these methods are not reliable for early detection. Delayed diagnosis of a nonunion is costly from both the patient and treatment standpoints. In response, repeated efforts have been made to identify bone metabolic markers as diagnostic or prognostic tools for monitoring bone healing. Thus far, the evidence regarding a correlation between the kinetics of most bone metabolic markers and nonunion is very limited. With the aim of classifying the role of biological pathways of bone metabolism and of understanding bone conditions in the development of osteoporosis, advances have been made in our knowledge of the molecular basis of bone remodeling, fracture healing, and its failure. Procollagen type I amino-terminal propeptide has been shown to be a reliable bone formation marker in osteoporosis therapy and its kinetics during fracture healing has been recently described. In this article, we suggest that procollagen type I amino-terminal propeptide presents a good opportunity for early detection of nonunion. We also review the role and potential of serum PINP, as well as other markers, as indications of fracture healing.

Lineage restriction of human hepatic stem cells to mature fates is made efficient by tissue-specific biomatrix scaffolds

Current protocols for differentiation of stem cells make use of multiple treatments of soluble signals and/or matrix factors and result typically in partial differentiation to mature cells with under- or overexpression of adult tissue-specific genes. We developed a strategy for rapid and efficient differentiation of stem cells using substrata of biomatrix scaffolds, tissue-specific extracts enriched in extracellular matrix, and associated growth factors and cytokines, in combination with a serum-free, hormonally defined medium (HDM) tailored for the adult cell type of interest. Biomatrix scaffolds were prepared by a novel, four-step perfusion decellularization protocol using conditions designed to keep all collagen types insoluble. The scaffolds maintained native histology, patent vasculatures, and ≈1% of the tissue's proteins but >95% of its collagens, most of the tissue's collagen-associated matrix components, and physiological levels of matrix-bound growth factors and cytokines. Collagens increased from almost undetectable levels to >15% of the scaffold's proteins with the remainder including laminins, fibronectins, elastin, nidogen/entactin, proteoglycans, and matrix-bound cytokines and growth factors in patterns that correlate with histology. Human hepatic stem cells (hHpSCs), seeded onto liver biomatrix scaffolds and in an HDM tailored for adult liver cells, lost stem cell markers and differentiated to mature, functional parenchymal cells in ≈1 week, remaining viable and with stable mature cell phenotypes for more than 8 weeks.

CONCLUSION

Biomatrix scaffolds can be used for biological and pharmaceutical studies of lineage-restricted stem cells, for maintenance of mature cells, and, in the future, for implantable, vascularized engineered tissues or organs.

Structure and dynamics of water in native and tanned collagen fibers: Effect of crosslinking

The influence of crosslinking on the hydration structure of collagen has been investigated. Nuclear magnetic resonance, dielectric relaxation and thermoporometry were used to investigate water structure in native and crosslinked collagen fibers on both wet and dried specimen. Measurements reveal the influence of different chemical treatments on the transverse relaxation time and polarization of the collagen fibers. The frequency dependence of dielectric constant of collagen fibers displays an induction behavior on low frequencies. Bound water constrained in collagen fibers seems to provide signatures for changes induced by crosslinking agents on the pore diameter and distribution in collagen fibers. A correlation of transverse relaxation time of water in dry and wet states presented in this study presents an experimental tool for examining the differences in efficacy of crosslinking agents. Changes in the dielectric relaxation, dynamics of water structure and hydroporometric structure of collagen are dependent on the nature of crosslinking material.

Storage conditions do not have detrimental effect on allograft collagen or scaffold performance

Musculoskeletal allografts are a valuable alternative to autograft tissue in orthopaedic surgeries. However, the effects of the allografts' storage history on the collagen and subsequent allograft scaffold properties are unknown. In this study, we hypothesized that freezing and refrigeration of allografts for 1 week would alter the biologic performance and mechanical properties of the allograft collagen. Allograft collagen was characterized by SDS-PAGE migration pattern, amino acid profile and measured denaturation. Scaffolds made from allograft collagen were evaluated for fibroblast proliferation, platelet activation and scaffold retraction. Collagen gelation kinetics (elastic and inelastic moduli and the viscous-elastic transition point) were also evaluated. Fibroblast proliferation, platelet activation and scaffold retraction results showed only minor, though statistically significant, differences between the storage groups. In addition, there were no significant differences in rheological properties or collagen biochemistry. In conclusion, this study suggests that freezing or refrigeration for 1 week does not appear to have any detrimental effect on the mechanical properties and biologic performance of the collagen within allografts.

Identification of the first prokaryotic collagen sequence motif that mediates binding to human collagen receptors, integrins alpha2beta1 and alpha11beta1

Many pathogenic bacteria interact with human integrins to enter host cells and to augment host colonization. Group A Streptococcus (GAS) employs molecular mimicry by direct interactions between the cell surface streptococcal collagen-like protein-1 (Scl1) and the human collagen receptor, integrin alpha2beta1. The collagen-like (CL) region of the Scl1 protein mediates integrin-binding, although, the integrin binding motif was not defined. Here, we used molecular cloning and site-directed mutagenesis to identify the GLPGER sequence as the alpha2beta1 and the alpha11beta1 binding motif. Electron microscopy experiments mapped binding sites of the recombinant alpha2-integrin-inserted domain to the GLPGER motif of the recombinant Scl (rScl) protein. rScl proteins and a synthetic peptide harboring the GLPGER motif mediated the attachment of C2C12-alpha2+myoblasts expressing the alpha2beta1 integrin as the sole collagen receptor. The C2C12-alpha11+myoblasts expressing the alpha11beta1 integrin also attached to GLPGER-harboring rScl proteins. Furthermore, the C2C12-alpha11+cells attached to rScl1 more efficiently than C2C12-alpha2+cells, suggesting that the alpha11beta1 integrin may have a higher binding affinity for the GLPGER sequence. Human endothelial cells and dermal fibroblasts adhered to rScl proteins, indicating that multiple cell types may recognize and bind the Scl proteins via their collagen receptors. This work is a stepping stone toward defining the utilization of collagen receptors by microbial collagen-like proteins that are expressed by pathogenic bacteria.

Melanoma associated spongiform scleropathy: characterization, biochemical and immunohistochemical studies

SUMMARY

Melanoma associated spongiform scleropathy (MASS) is a non-inflammatory scleral change with a spongiotic morphology seen in association with uveal melanoma. MASS is seen as whitish spindle shaped areas within the sclera that is adjacent to and in contact with a choroidal or ciliary body melanoma. This change can be seen as small scattered lesions in the inner scleral layers or as extensive areas along the whole extent of contact between the tumour and the sclera and involves most of the scleral thickness. MASS changes of different grades of severity were seen in 38% of 363 melanoma eyes investigated. The presence of MASS showed a statistical correlation with age. A significant high incidence of MASS was found in old age groups. This might due to the fact that MASS needs a longer period of contact between the tumour and the sclera to develop. It is also possible that age-related changes of the extracellular matrix might alter its response to melanoma produced factors leading to the development of MASS. The development of MASS and its severity are influenced by the extent of contact between the tumour and the sclera. This is supported by the significant statistical relation between the largest basal diameter of the tumours and the severity of MASS. Statistical correlation was found between MASS and scleral and extrascleral tumour extension. More than 90% of 82 specimens that showed tumour extension were associated with MASS. A biochemical analysis of scleral samples taken from areas with severe MASS showed a significant reduction of the main amino acids of collagen type I, which is the main scleral collagen. The amounts of total scleral proteins were significantly reduced. This scleral protein reduction is associated with an increase in glycosaminoglycans. These findings indicate a collagen degradation process. Immunohistochemical studies were performed to investigate the expression of matrix metalloproteinases (MMPs). In situ hybridization showed a significantly more frequent and more intense expression of MMP-2 by scleral fibroblasts in areas with MASS compared with areas without MASS. This was also seen by immunohistochemical staining. Similar high frequency and intense expression of MMP-2 were seen in tumour infiltrating macrophages. The results of biochemical and immunohistochemical studies indicate a collagen degradation process. This degradation may be the result of the proteolytic enzyme MMP-2 expressed by scleral fibroblasts under the effect of tumour humeral factors and/or tumour infiltrating macrophages. This scleral degradation results in fragmentation of the scleral collagen fibrils. This along with the accumulation of water in the sclera, as a result of the increase in the production of glycosaminoglycans, results in increase of scleral thickness in MASS areas and forms the histopathological picture of MASS. The scleral degradation may facilitate tumour invasion and may explain the statistical relation between MASS and scleral tumour invasion. MASS was found in a few of the eyes that had received pre-enucleation radiation. The possible explanation is that radiation might cause destruction of scleral fibroblasts reducing their ability to produce MMP-2, thus decreasing the development of MASS. No relation between MASS and survival was found. This is probably explained by the fact that the main cause of death due to uveal melanoma is distant metastasis. MASS changes are found to be associated with local tumour invasion but not statistically correlated to survival.

Triple-helical peptides: an approach to collagen conformation, stability, and self-association

Peptides have been an integral part of the collagen triple-helix structure story, and have continued to serve as useful models for biophysical studies and for establishing biologically important sequence-structure-function relationships. High resolution structures of triple-helical peptides have confirmed the basic Ramachandran triple-helix model and provided new insights into the hydration, hydrogen bonding, and sequence dependent helical parameters in collagen. The dependence of collagen triple-helix stability on the residues in its (Gly-X-Y)(n) repeating sequence has been investigated by measuring melting temperatures of host-guest peptides and an on-line collagen stability calculator is now available. Although the presence of Gly as every third residue is essential for an undistorted structure, interruptions in the repeating (Gly-X-Y)(n) amino acid sequence pattern are found in the triple-helical domains of all nonfibrillar collagens, and are likely to play a role in collagen binding and degradation. Peptide models indicate that small interruptions can be incorporated into a rod-like triple-helix with a highly localized effect, which perturbs hydrogen bonds and places the standard triple-helices on both ends out of register. In contrast to natural interruptions, missense mutations which replace one Gly in a triple-helix domain by a larger residue have pathological consequences, and studies on peptides containing such Gly substitutions clarify their effect on conformation, stability, and folding. Recent studies suggest peptides may also be useful in defining the basic principles of collagen self-association to the supramolecular structures found in tissues.

Micro/nanostructured polymeric systems for biomedical and pharmaceutical applications

This review provides an outline of the polymeric micro/nanostructured advanced systems that are suited for the controlled and targeted administration of, specifically, nonconventional drugs. The contribution of new trends in drug-delivery technology is focused on two major parts, dealing with brief surveys of: the biodegradable/bioerodible polymeric systems used in the formulation of micro/nanoparticles and techniques used in the preparation of micro/nanoparticles for their biomedical application in cancer treatment specifically, in inflammation pathologies, as oxygen carriers (blood substitutes) and in tissue-engineering practice. A small discussion of the future perspectives of the described systems is also given.