Collagen: an overview

Constructing networks for comparison of collagen types

Collagens are structural proteins that are predominantly found in the extracellular matrix of multicellular animals, where they are mainly responsible for the stability and structural integrity of various tissues. All collagens contain polypeptide strands (α-chains). There are several types of collagens, some of which differ significantly in form, function, and tissue specificity. Because of their importance in clinical research, they are grouped into subdivisions, the so-called collagen families, and their sequences are often analysed. However, problems arise with highly homologous sequence segments. To increase the accuracy of collagen classification and prediction of their functions, the structure of these collagens and their expression in different tissues could result in a better focus on sequence segments of interest. Here, we analyse collagen families with different levels of conservation. As a result, clusters with high interconnectivity can be found, such as the fibrillar collagens, the COL4 network-forming collagens, and the COL9 FACITs. Furthermore, a large cluster between network-forming, FACIT, and COL28a1 α-chains is formed with COL6a3 as a major hub node. The formation of clusters also signifies, why it is important to always analyse the α-chains and why structural changes can have a wide range of effects on the body.

Osteocytes Influence on Bone Matrix Integrity Affects Biomechanical Competence at Bone-Implant Interface of Bioactive-Coated Titanium Implants in Rat Tibiae

Osseointegration is a prerequisite for the long-term success of implants. Titanium implants are preferred for their biocompatibility and mechanical properties. Nonetheless, the need for early and immediate loading requires enhancing these properties by adding bioactive coatings. In this preclinical study, extracellular matrix properties and cellular balance at the implant/bone interface was examined. Polyelectrolyte multilayers of chitosan and gelatin or with chitosan and Hyaluronic acid fabricated on titanium alloy using a layer-by-layer self-assembly process were compared with native titanium alloy. The study aimed to histologically evaluate bone parameters that correlate to the biomechanical anchorage enhancement resulted from bioactive coatings of titanium implants in a rat animal model. Superior collagen fiber arrangements and an increased number of active osteocytes reflected a significant improvement of bone matrix quality at the bone interface of the chitosan/gelatin-coated titan implants over chitosan/hyaluronic acid-coated and native implants. Furthermore, the numbers and localization of osteoblasts and osteoclasts in the reparative and remodeling phases suggested a better cellular balance in the chitosan/Gel-coated group over the other two groups. Investigating the micro-mechanical properties of bone tissue at the interface can elucidate detailed discrepancies between different promising bioactive coatings of titanium alloys to maximize their benefit in future medical applications.

Main and Minor Types of Collagens in the Articular Cartilage: The Role of Collagens in Repair Tissue Evaluation in Chondral Defects

Several collagen subtypes have been identified in hyaline articular cartilage. The main and most abundant collagens are type II, IX and XI collagens. The minor and less abundant collagens are type III, IV, V, VI, X, XII, XIV, XVI, XXII, and XXVII collagens. All these collagens have been found to play a key role in healthy cartilage, regardless of whether they are more or less abundant. Additionally, an exhaustive evaluation of collagen fibrils in a repaired cartilage tissue after a chondral lesion is necessary to determine the quality of the repaired tissue and even whether or not this repaired tissue is considered hyaline cartilage. Therefore, this review aims to describe in depth all the collagen types found in the normal articular cartilage structure, and based on this, establish the parameters that allow one to consider a repaired cartilage tissue as a hyaline cartilage.

Advances in Plant-Derived Scaffold Proteins

Scaffold proteins form critical biomatrices that support cell adhesion and proliferation for regenerative medicine and drug screening. The increasing demand for such applications urges solutions for cost effective and sustainable supplies of hypoallergenic and biocompatible scaffold proteins. Here, we summarize recent efforts in obtaining plant-derived biosynthetic spider silk analogue and the extracellular matrix protein, collagen. Both proteins are composed of a large number of tandem block repeats, which makes production in bacterial hosts challenging. Furthermore, post-translational modification of collagen is essential for its function which requires co-transformation of multiple copies of human prolyl 4-hydroxylase. We discuss our perspectives on how the GAANTRY system could potentially assist the production of native-sized spider dragline silk proteins and prolyl hydroxylated collagen. The potential of recombinant scaffold proteins in drug delivery and drug discovery is also addressed.

Protein Adductomics: Analytical Developments and Applications in Human Biomonitoring

Proteins contain many sites that are subject to modification by electrophiles. Detection and characterisation of these modifications can give insights into environmental agents and endogenous processes that may be contributing factors to chronic human diseases. An untargeted approach, utilising mass spectrometry to detect modified amino acids or peptides, has been applied to blood proteins haemoglobin and albumin, focusing in particular on the N-terminal valine residue of haemoglobin and the cysteine-34 residue in albumin. Technical developments to firstly detect simultaneously multiple adducts at these sites and then subsequently to identify them are reviewed here. Recent studies in which the methods have been applied to biomonitoring human exposure to environmental toxicants are described. With advances in sensitivity, high-throughput handling of samples and robust quality control, these methods have considerable potential for identifying causes of human chronic disease and of identifying individuals at risk.

Tissue loading and microstructure regulate the deformation of embedded nerve fibres: predictions from single-scale and multiscale simulations

Excessive deformation of nerve fibres (axons) in the spinal facet capsular ligaments (FCLs) can be a cause of pain. The axons are embedded in the fibrous extracellular matrix (ECM) of FCLs, so understanding how local fibre organization and micromechanics modulate their mechanical behaviour is essential. We constructed a computational discrete-fibre model of an axon embedded in a collagen fibre network attached to the axon by distinct fibre-axon connections. This model was used to relate the axonal deformation to the fibre alignment and collagen volume concentration of the surrounding network during transverse, axial and shear deformations. Our results showed that fibre alignment affects axonal deformation only during transverse and axial loading, but higher collagen volume concentration results in larger overall axonal strains for all loading cases. Furthermore, axial loading leads to the largest stretch of axonal microtubules and induces the largest forces on axon's surface in most cases. Comparison between this model and a multiscale continuum model for a representative case showed that although both models predicted similar averaged axonal strains, strain was more heterogeneous in the discrete-fibre model.

Corneal regenerative medicine

Recently, regenerative medicine has become a highlighted field because it has great potential to induce a paradigm shift of supportive conventional therapy into definitive treatment. The cornea is the avascular, transparent, dome-shaped outermost layer of the eyeball, and it consists of three layers: epithelium, stroma, and endothelium. Conventional corneal transplantation, known as keratoplasty, has two main problems, a donor shortage and immunological rejection. Therefore, regenerative medicine has been applied to overcome these challenges. Regenerative medicine involving the corneal epithelium has been clinically applied, along with an understanding of corneal epithelial stem cell biology, earlier than that of the corneal stroma or endothelium. Thus, the effectiveness and safety of cultivated corneal or oral mucosal epithelial cell sheet transplantation have been reported by many researchers. Clinical studies on regenerative medicine for corneal stroma or endothelium have begun after basic and nonclinical study. Translational research has been performed to make corneal regenerative medicine a universal therapy. This article reviews corneal regenerative medicine.

Determination of the glycosaminoglycan and collagen contents in tissue samples by high-resolution 1H NMR spectroscopy after DCl-induced hydrolysis

The determination of the collagen and glycosaminoglycan (GAG) contents of native and particularly bioengineered tissues is of considerable interest because the collagen-to-GAG ratio determines the water content of the tissue, which is crucial regarding its mechanical properties. (1)H NMR spectroscopy subsequent to the hydrolysis of the sample by aqueous 6 M DCl at 353 K is used to determine the GAG and collagen contents simultaneously. Under these strongly acidic conditions the biopolymers of the extracellular matrix, collagen, and GAG are fragmented into their individual monomers, that is, free amino acids from collagen and monosaccharides from the polymer repeat units of GAGs. The amino acid amount can be easily determined in the presence of an internal standard by (1)H NMR spectroscopy because amino acids proved to be stable under acidic conditions. The carbohydrates are subject to charring in the presence of concentrated DCl, but glucosamine and galactosamine were found to be sufficiently stable for quantification under the chosen conditions.

Influence of glycosaminoglycan identity on vocal fold fibroblast behavior

Poly(ethylene glycol) (PEG) hydrogels have recently begun to be studied for the treatment of scarred vocal fold lamina propria due, in part, to their tunable mechanical properties, resistance to fibroblast-mediated contraction, and ability to be polymerized in situ. However, pure PEG gels lack intrinsic biochemical signals to guide cell behavior and generally fail to mimic the frequency-dependent viscoelastic response critical to normal superficial lamina propria function. Recent results suggest that incorporation of viscoelastic bioactive substances, such as glycosaminoglycans (GAGs), into PEG networks may allow these gels to more closely approach the mechanical responses of normal vocal fold lamina propria while also stimulating desired vocal fold fibroblast behaviors. Although a number of vocal fold studies have examined the influence of hyaluronan (HA) on implant mechanics and vocal fold fibroblast responses, the effects of other GAG types have been relatively unexplored. This is significant, since recent studies have suggested that chondroitin sulfate C (CSC) and heparan sulfate (HS) are substantially altered in scarred lamina propria. The present study was therefore designed to evaluate the effects of CSC and HS incorporation on the mechanical response of PEG gels and vocal fold fibroblast behavior relative to HA. As with PEG-HA, the viscoelasticity of PEG-CSC and PEG-HS gels more closely approached that of the normal vocal fold lamina propria than pure PEG hydrogels. In addition, collagen I deposition and fibronectin production were significantly higher in CSC than in HA gels, and levels of the myofibroblast marker smooth muscle α-actin (SM α-actin) were greater in CSC and HS gels than in HA gels. Since collagen I, fibronectin, and SM α-actin are generally elevated in scarred lamina propria these results suggest that CSC and HS may be undesirable for vocal fold implants relative to HA. Investigation of various signaling intermediates indicated that alterations in NFκB-p50, NFκB-p65, or pERK1/2 levels may underlie the observed differences among the PEG-GAG gels.

Hydroxylation of recombinant human collagen type I alpha 1 in transgenic maize co-expressed with a recombinant human prolyl 4-hydroxylase

Background

Collagens require the hydroxylation of proline (Pro) residues in their triple-helical domain repeating sequence Xaa-Pro-Gly to function properly as a main structural component of the extracellular matrix in animals at physiologically relevant conditions. The regioselective proline hydroxylation is catalyzed by a specific prolyl 4-hydroxylase (P4H) as a posttranslational processing step.

Results

A recombinant human collagen type I α-1 (rCIα1) with high percentage of hydroxylated prolines (Hyp) was produced in transgenic maize seeds when co-expressed with both the α- and β- subunits of a recombinant human P4H (rP4H). Germ-specific expression of rCIα1 using maize globulin-1 gene promoter resulted in an average yield of 12 mg/kg seed for the full-length rCIα1 in seeds without co-expression of rP4H and 4 mg/kg seed for the rCIα1 (rCIα1-OH) in seeds with co-expression of rP4H. High-resolution mass spectrometry (HRMS) analysis revealed that nearly half of the collagenous repeating triplets in rCIα1 isolated from rP4H co-expressing maize line had the Pro residues changed to Hyp residues. The HRMS analysis determined the Hyp content of maize-derived rCIα1-OH as 18.11%, which is comparable to the Hyp level of yeast-derived rCIα1-OH (17.47%) and the native human CIa1 (14.59%), respectively. The increased Hyp percentage was correlated with a markedly enhanced thermal stability of maize-derived rCIα1-OH when compared to the non-hydroxylated rCIα1.

Conclusions

This work shows that maize has potential to produce adequately modified exogenous proteins with mammalian-like post-translational modifications that may be require for their use as pharmaceutical and industrial products.

Regulation of smooth muscle cell phenotype by glycosaminoglycan identity

The retention of lipoproteins in the arterial intima is an initial event in early atherosclerosis and occurs, in part, through interactions between negatively charged glycosaminoglycans (GAGs) and the positively charged residues of apolipoproteins. Smooth muscle cells (SMCs) which infiltrate into the lipoprotein-enriched intima have been observed to transform into lipid-laden foam cells. This phenotypic switch is associated with SMC acquisition of a macrophage-like capacity to phagocytose lipoproteins and/or of an adipocyte-like capacity to synthesize fatty acids de novo. The aim of the present work was to explore the impact of GAG identity on SMC foam cell formation using a scaffold environment intended to be mimetic of early atherosclerosis. In these studies, we focused on chondroitin sulfate C (CSC), dermatan sulfate (DS), and an intermediate molecular weight hyaluronan (HAIMW, ∼400 kDa), the levels and/or distribution of each of which are significantly altered in atherosclerosis. DS hydrogels were associated with greater SMC phagocytosis of apolipoprotein B than HAIMW gels. Similarly, only SMCs in DS constructs maintained increased expression of the adipocyte marker A-FABP relative to HAIMW gels over 35 days of culture. The increased SMC foam cell phenotype in DS hydrogels was reflected in a corresponding decrease in SMC myosin heavy chain expression in these constructs relative to HAIMW gels at day 35. In addition, this DS-associated increase in foam cell formation was mirrored in an increased SMC synthetic phenotype, as evidenced by greater levels of collagen type I and glucose 6-phosphate dehydrogenase in DS gels than in HAIMW gels. Combined, these results support the increasing body of literature that suggests a critical role for DS-bearing proteoglycans in early atherosclerosis.

The collagen family

Collagens are the most abundant proteins in mammals. The collagen family comprises 28 members that contain at least one triple-helical domain. Collagens are deposited in the extracellular matrix where most of them form supramolecular assemblies. Four collagens are type II membrane proteins that also exist in a soluble form released from the cell surface by shedding. Collagens play structural roles and contribute to mechanical properties, organization, and shape of tissues. They interact with cells via several receptor families and regulate their proliferation, migration, and differentiation. Some collagens have a restricted tissue distribution and hence specific biological functions.

Production of a non-triple helical collagen alpha chain in transgenic silkworms and its evaluation as a gelatin substitute for cell culture

We generated transgenic silkworms that synthesized human type I collagen alpha1 chain [alpha1(I) chain] in the middle silk glands and secreted it into cocoons. The initial content of the recombinant alpha1(I) chain in the cocoons of the transgenic silkworms was 0.8%. The IE1 gene, a trans-activator from the baculovirus, was introduced into the transgenic silkworm to increase the content of the chain. We also generated silkworms homozygous for the transgenes. These manipulations increased the alpha1(I) chain content to 8.0% (4.24 mg per cocoon). The alpha1(I) chain was extracted and purified from the cocoons using a very simple method. The alpha1(I) chain contained no hydroxyprolines due to the absence of prolyl-hydroxylase activity in the silk glands. Circular dichroism analysis showed that the secondary structure of the alpha1(I) chain is similar to that of denatured type I collagen, demonstrating the absence of the triple helical structure. Human skin fibroblasts were seeded on the alpha1(I) chain-coated dishes. The cells attached and spread, although at decreased chain concentrations the spreading rate was lower than that of the collagen and gelatin. Cynomolgus monkey embryonic stem cells cultured on the alpha1(I) chain-coated dishes maintained an undifferentiated state after 30 passages, and their pluripotency was confirmed by teratoma formation in severe combined immunodeficient mice. These results show that the recombinant human alpha1(I) chain is a promising candidate biomaterial as a high-quality and safe gelatin substitute for cell culture.

Inorganic-organic hybrid scaffolds for osteochondral regeneration

Ligament graft failure frequently results from poor integration of the replacement tissue with associated bone. Thus, the ability to regenerate the bone-ligament osteochondral interface would be advantageous in ligament reconstruction. At the osteochondral interface, the tissue transitions from a bone-like matrix to fibrocartilage. Therefore, a scaffold which promotes a spatially regulated transition in cell behavior from osteoblast-like to chondrocyte-like would be desirable. Previous research indicates that addition of inorganic components to organic scaffolds can enhance the deposition of bone-like matrix by associated osteoblasts. We therefore reasoned that a gradient in the inorganic content of a hybrid inorganic-organic scaffold may induce an osteochondral-like transition in cell phenotype and matrix production. To test this hypothesis, hydrogels were prepared from poly(ethylene glycol) (PEG) and star poly(dimethylsiloxane) (PDMS(star)). As anticipated, both the matrix deposition and phenotype of encapsulated osteoblasts varied with scaffold inorganic content, although the directionality of this modulation was contrary to expectation. Specifically, osteoblasts appeared to transdifferentiate into chondrocyte-like cells with increasing scaffold inorganic content, as indicated by increased chondroitin sulfate and collagen type II production and by upregulation of sox9, a transcription factor associated with chondrocytic differentiation. Furthermore, the deposition of bone-like matrix (collagen type I, calcium phosphate, and osteocalcin) decreased with increasing PDMS(star) content. The resistance of the PDMS(star)-PEG scaffolds to protein adsorption and/or the changes in gel modulus/mesh structure accompanying PDMS(star) incorporation may underlie the unexpected increase in chondrocytic phenotype with increasing inorganic content. Combined, the present results indicate that PDMS(star)-PEG hybrid gels may prove promising for osteochondral regeneration. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

Purification and characterization of a transgenic corn grain-derived recombinant collagen type I alpha 1

Corn offers advantages as a transgenic host for producing recombinant proteins required at large volumes (1,000's of tons per year) and low cost (less than US$50/kg) by generating them as co-products of biorefining. We describe the purification and characterization of a corn grain-derived mammalian structural protein having such market characteristics: a full length recombinant collagen type I alpha 1 (rCI alpha 1) chain. Material properties of interest are gelation behavior, which would depend on as yet unverified ability of corn to carry out post-translational prolyl hydroxylation and formation of triple helical conformation. The starting material was grain where the expression of rCI alpha 1 had been directed by an embryo-specific promoter. Purification consisted of extraction at low pH followed by membrane and chromatographic steps to isolate rCI alpha 1 for characterization. The amino acid composition and immunoreactivity of CI alpha 1 was similar to that of an analogous native human CI alpha 1 and to rCI alpha 1 produced by the yeast Pichia pastoris. Tandem mass spectrometry confirmed the primary sequence of the corn-derived rCI alpha 1 with 46% coverage. Fragments of the rCI alpha 1 chains were also observed, possibly caused by endogenous plant proteases. The corn-derived rCI alpha 1 had a low level of prolyl hydroxylation (approximately 1% versus 11%) relative to animal-derived CI alpha 1 and folded into its characteristic triple-helical structure as indicated by its resistance to pepsin digestion below its melting temperature of 26(o)C. The 29 amino acid foldon fused to the C-terminus to initiate triple helix formation was not cleaved from the rCI alpha 1 chains, but could be removed by pepsin treatment.

Production of a recombinant full-length collagen type I alpha-1 and of a 45-kDa collagen type I alpha-1 fragment in barley seeds

Recombinant DNA technology can be used to design and express collagen and gelatin-related proteins with predetermined composition and structure. Barley seed was chosen as a production host for a recombinant full-length collagen type I alpha1 (rCIa1) and a related 45-kDa rCIa1 fragment. The transgenic barley seeds were shown to accumulate both the rCIa1 and the 45-kDa rCIa1 fragment. Even when the amount of the rCIa1 was just above the detection threshold, this work using rCIa1 as a model demonstrated for the first time that barley seed can be used as a production system for collagen-related structural proteins. The 45-kDa rCI1a fragment expression, targeted to the endoplasmic reticulum, was controlled by three different promoters (a constitutive maize ubiquitin, seed endosperm-specific rice glutelin and germination-specific barley alpha-amylase fusion) to compare their effects on rCIa1 accumulation. Highest accumulation of the 45-kDa rCIa1 was obtained with the glutelin promoter (140 mg/kg seed), whereas the lowest accumulation was obtained with the alpha-amylase promoter. To induce homozygosity for stable 45-kDa rCIa1 production in the transgenic lines, doubled haploid (DH) progeny was generated through microspore culture. The 45-kDa rCIa1 expression levels achieved from the best DH lines were 13 mg/kg dry seeds under the ubiquitin promoter and 45 mg/kg dry seeds under the glutelin promoter. Mass spectroscopy and amino acid composition analysis of the purified 45-kDa rCIa1 fragment revealed that a small percent of prolines were hydroxylated with no additional detectable post-translational modifications.

Lamina propria cellularity and collagen composition: an integrated assessment of structure in humans

OBJECTIVES

In this study, we quantitatively examined cell density, collagen types I and III, and regional variations in collagen fiber thickness and orientation in the human midmembranous vocal fold lamina propria (LP).

METHODS

Lamina propria samples were solubilized with proteinase K or with cyanogen bromide. Cell density was assessed in proteinase K digests by measuring DNA and normalizing it to tissue total protein. Collagen types I and III were quantified by enzyme-linked immunosorbent assay-based detection of collagen type-specific peptides generated by cyanogen bromide digestion. In addition, LP total collagen was determined by measuring sample hydroxyproline levels. Variations in collagen fiber thickness and orientation with LP region were evaluated by examining picrosirius red-stained LP sections with circularly polarized light.

RESULTS

The mean (+/-SEM) cell density in the LP and associated epithelium was approximately 0.57 +/- 0.09 million cells per milligram of tissue total protein. Collagen type III composed an average of 34% to 40% of LP total collagen. Quantitative histology indicated that the superficial LP contained an average of 70% thin, 26% intermediate, and 4% thick collagen fibers. This is in contrast to the intermediate and deep LPs, each of which contained less than 25% thin and more than 50% thick collagen fibers. The angular deviations in collagen fiber orientation were relatively large and were similar in magnitude across all LP layers.

CONCLUSIONS

The total cell density of the LP and associated epithelium was intermediate between that of hyaline cartilage and dermis. The ratio of collagen type III to total collagen in the LP was similar to that of highly elastic lung parenchyma and roughly twice that of the comparatively less-elastic dermis. The average thickness of collagen fibers increased markedly with increasing LP depth, and the relatively large angular deviations in fiber orientation appeared to correspond in part to the crimped nature of LP collagen fibers.

Procollagen Alpha 1 Type I: A Potential Aide in Histopathological Grading of Glioma

Collagen type I production has been shown to play a role in malignant transformation. We examined procollagen type I expression in brain tumors and with histopathological grading. Expression levels of procollagen alpha 1 type 1 were determined in 5 glioma cell lines by RT-PCR, Northern, and Western blot analysis. In addition, 41 primary brain tumors and 2 metastatic lung cancers to the brain were examined by PCR. Of the 5 glioma cell line analyzed, 3 (glioma 1, SW-1783 and U-118) expressed procollagen alpha 1 type I and were sensitive to vitamin D3 (VD3). In contrast, 2 of the cell lines (U-373 and T-98G) lacked procollagen alpha 1 type 1 expression. In patients' samples, 14 of 15 anaplastic and low grade gliomas expressed procollagen alpha 1 type I, and 12 of the 14 expressed high levels. In contrast, only 12 of 21 high grade gliomas from patients expressed procollagen alpha 1 type1 and among these, only 4 of the 12 expressed high levels. Thus, there is an inversed correlation between procollagen alpha 1 type 1 expression and histopathological grading (R2=- 0.56, p=0.0005). Our data suggest that procollagen alpha 1 type I expression occurs more commonly in intermediate and low grade gliomas and may assist in histopathological grading.

A comparative analysis of the collagen type and distribution in the trabecular meshwork, sclera, lamina cribrosa and the optic nerve in the human eye

A theory has been advanced (Tengroth et al 1984) that one common factor might be involved in the pathogenesis of chronic open angle glaucoma. The mechanical properties of the collagen could be one such factor. To characterize the collagen composition of the critical structures in cases with chronic open angle glaucoma i.e. the trabecular meshwork and the lamina cribrosa in the human eye, the following investigations were performed. Using immunoperoxidase technique and type specific antibodies to the genetically distinct collagen types I, III, IV and procollagen I along with the major non collagen proteins in the extracellular matrix laminin and fibronectin a light microscopic study was undertaken on the trabecular meshwork, cornea, sclera, lamina cribrosa and the optic nerve of the human eye. Furthermore biochemical analysis was performed on the collagen associated aminoacids hydroxyproline (Hyp), hydroxylysine (Hyl) and prolin (Pro) from microdissected samples of trabecular meshwork, sclera, lamina cribrosa and optic nerve. Both the immunohistological and the biochemical findings suggested similarities in the collagen composition between the trabecular meshwork and the lamina cribrosa. The immunohistochemical findings showed stronger staining of type III and IV in the trabecular meshwork and lamina cribrosa as compared to sclera or cornea while the opposite was true for type I and procollagen I. Fibronectin and laminin were present in both the trabecular meshwork and lamina cribrosa. These findings were in agreement with the amino acid analysis when the Hyp/Hyl ratio was calculated for each sample.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of a 44-kDa recombinant collagen I alpha 1 fragment from corn grain

This paper demonstrates that a fibrous, repetitive amino acid sequence collagen-related protein, a 44-kDa fragment of human collagen I alpha 1 (CIalpha1), was expressed in corn grain molecularly equivalent to that produced in recombinant yeast. The recombinant CIalpha1 was extracted and purified from early generation plants having low levels of recombinant protein accumulation. It was selectively extracted at low pH and purified by ion exchange and gel filtration chromatography, resulting in a 44-kDa CIalpha1 with >70% purity and 60% recovery. The N-terminal sequence, amino acid composition, and immunoreactivity closely matched those of an analogous 44-kDa CIalpha1 fragment produced by the yeast Pichia . The corn-derived 44-kDa CIalpha1 had an intact protein mass of 44088 Da, which is within 0.2% of the mass calculated from the expected sequence. Tandem mass spectrometry confirmed the primary sequence with 78% coverage. The amino acid composition analysis indicated a low level of prolyl hydroxylation. Glycoprotein staining revealed no glycosylation.

Influence of hydrogel mechanical properties and mesh size on vocal fold fibroblast extracellular matrix production and phenotype

Current clinical management of vocal fold (VF) scarring produces inconsistent and often suboptimal results. Researchers are investigating a number of alternative treatments for VF lamina propria (LP) scarring, including designer implant materials for functional LP regeneration. In the present study, we investigate the effects of the initial scaffold elastic modulus and mesh size on encapsulated VF fibroblast (VFF) extracellular matrix (ECM) production toward rational scaffold design. Poly(ethylene glycol) diacrylate (PEGDA) hydrogels were selected for this study since their material properties, including mechanical properties, mesh size, degradation rate and bioactivity, can be tightly controlled and systematically modified. Porcine VFF were encapsulated in four PEGDA hydrogels with degradation half lives of approximately 25 days, but with initial elastic compressive moduli and mesh sizes ranging from approximately 30 to 100kPa and from approximately 9 to 27nm, respectively. After 30 days of static culture, VFF ECM production and phenotype in each formulation was assessed biochemically and histologically. Sulfated glycosaminoglycan synthesis increased in similar degree with both increasing initial modulus and decreasing initial mesh size. In contrast, elastin production decreased with increasing initial modulus but increased with decreasing initial mesh size. Both collagen deposition and the induction of a myofibroblastic phenotype depended strongly on initial mesh size but appeared largely unaffected by variations in initial modulus. The present results indicate that scaffold mesh size warrants further investigation as a critical regulator of VFF ECM synthesis. Furthermore, this study validates a systematic and controlled approach for analyzing VFF response to scaffold properties, which should aid in rational scaffold selection/design.

Ultrastructural and histochemical study of collagen fibres types I and III in the venom gland of Bothrops jararaca during secretory cycle

Fragments of snake (Bothrops jararaca) venom gland were analysed by light and transmission electron microscopy in order to characterize the changes in collagen fibres types I and III in the intertubular gland septa during the secretory cycle. The snakes were sacrificed at 45 days (unmilked group), 6 h, 4 and 8 days after manual extraction of the venom. The fragments were fixed, processed according to standard histologic technique for embedding in paraffin, and stained with haematoxylin-eosin and Gomori's trichrome and submitted to Gomori's silver impregnation technique and picrosirius-polarization method. For transmission electron microscopy the fragments were fixed and processed for embedding in Spurr's medium. At the 45th day (the gland at rest), when the secretory activity was at a minimum, the septa were narrow and filled with densely packed collagen fibrils. At 6 h, the septa were enlarged and exhibited wide spaces filled with finely granular Alcian Blue-positive material. Until the 8th day, the septa were narrower and the histologic aspect resembled that of the gland at rest. The results demonstrated structural modifications in the glandular septa according to the different periods of the secretory cycle. These modifications can be associated with the transformation in the secretory epithelium during the venom synthesis cycle.

The biodegradability of poly(Pro-Hyp-Gly) synthetic polypeptide and the promotion of a dermal wound epithelialization using a poly(Pro-Hyp-Gly) sponge

Collagens are widely used in medical applications, but animal-derived collagens have several drawbacks, such as low thermal stability, nonspecific cell attachment, and susceptibility to contamination by infectious pathogens, such as prions, which may transfect humans. We have previously reported the chemical synthesis of polypeptides consisting of a Pro-Hyp-Gly sequence and the high thermostability of their triple-helical structure. To clarify the biomaterial characteristics of the poly(Pro-Hyp-Gly) polypeptide, we assessed its biodegradability and its capability for skin regeneration. Eight weeks after implantation, a poly(Pro-Hyp-Gly) freeze-dried sponge embedded subcutaneously into a rat dorsal area degraded at the same rate as Terudermis, which is made from bovine type I atelocollagen and is used as an artificial dermis. Surprisingly, compared with Terudermis, the poly(Pro-Hyp-Gly) sponge significantly promoted epithelialization of a full-thickness wound on a rabbit's ear pad. This chemically synthesized polypeptide may be useful as a scaffold for tissue engineering and tissue regeneration.

Effect of Umbelliferone on Tail Tendon Collagen and Haemostatic Function in Streptozotocin-Diabetic Rats

Diabetes mellitus is known to affect collagen in various tissues. Umbelliferone (7-hydroxycoumarin), a natural antioxidant and benzopyrone, is found in golden apple (Aegle marmelos Correa) and bitter orange (Citrus aurantium). Plant-derived phenolic coumarins have been shown to act as dietary antioxidants. In this study, we have investigated the influence of umbelliferone on collagen content and its effects on the tail tendon in streptozotocin-diabetic rats. Male albino Wistar rats (180-200 g) were made diabetic by intraperitoneal administration of streptozotocin (40 mg/kg). Normal and diabetic rats were treated with umbelliferone for 45 days. Diabetic rats had increased glucose and decreased insulin levels. Tail tendons of diabetic rats had increased total collagen, glycation and fluorescence, and decreased levels of neutral, acid and pepsin-soluble collagens. We have studied the effect of umbelliferone on haemostatic function because umbelliferone is also a coumarin derivative like the anticoagulant, warfarin. Diabetic rats had a significant decrease in prothrombin, clotting and bleeding time, and treatment with umbelliferone made these parameters almost normal. Our results show that umbelliferone controls glycaemia and has a beneficial effect on collagen content and its properties, i.e. collagen related parameters, in the tail tendon, which indicates recovery from the risk (recovery of animals from the risk of complications) of collagen-mediated diabetic polyneuropathy and diabetic nephropathy.

Lysyl hydroxylase 2 is a specific telopeptide hydroxylase, while all three isoenzymes hydroxylate collagenous sequences

Lysyl hydroxylase (LH), with three isoenzymes in vertebrates, catalyzes the formation of hydroxylysine by acting on -X-Lys-Gly- triplets in the collagenous domains of proteins of the collagen superfamily and also in -X-Lys-Ala- or -X-Lys-Ser- sequences in the telopeptides located at the ends of the polypeptide chains in some fibril-forming collagens. The hydroxylysine residues are essential for the stability of collagen crosslinks and act as carbohydrate attachment sites. The extent of lysine hydroxylation varies between collagen types, between tissues in the same collagen type and in certain diseases, suggesting that the LH isoenzymes may have different substrate specificities. We studied here the hydroxylation of synthetic peptides representing various hydroxylation sites in type I and IV collagens by purified recombinant LHs in vitro and of a recombinant full-length type I procollagen chain coexpressed with each LH in insect cells. All three LHs hydroxylated peptides representing collagenous sequences of type I and IV collagens, although with different K(m) and V(max) values. Furthermore, all three hydroxylated the collagenous domain of the coexpressed type I procollagen chain to a similar extent. None of the isoenzymes hydroxylated peptides representing the N and C telopeptides of type I collagen, but LH2, unlike the other two isoenzymes, hydroxylated the N telopeptide in the coexpressed procollagen chain. Hydroxylation of the telopeptide lysines by LH2 thus occurs only in the context of a long peptide. These data provide the first direct evidence that LH2 is a specific telopeptide hydroxylase, while all three LHs act on collagenous sequences.

Fluorescence spectroscopy and birefringence of molecular changes in maturing rat tail tendon

Tissue remodeling during maturation, wound healing, and response to vascular stress involves molecular changes of collagen and elastin in the extracellular matrix (ECM). Two optical techniques are effective for investigating these changes--laser-induced fluorescence (LIF) spectroscopy and polarizing microscopy. LIF spectroscopy integrates the signal from both elastin and collagen cross-linked structure, whereas birefringence is a measure of only collagen. Our purpose is (1) to evaluate the rat tail tendon (RTT) spectroscopy against data from purified extracted protein standards and (2) to correlate the two optical techniques in the study of RTT and skin. Spectra from tissue samples from 27 male rats and from extracted elastin and collagen were obtained using LIF spectroscopy (357 nm). Birefringence was measured on 5-mum histological sections of the same tissue. Morphometric analysis reveals that elastin represents approximately 10% of tendon volume and contributes to RTT fluorescence. RTT maximum fluorescence emission intensity (FEI(max)), which includes collagen and elastin, increases with animal weight (R(2)=0.64). Birefringence, when plotted against weight, increases to a plateau (nonlinear correlation: R(2)=0.90), tendon having greater birefringence than skin. LIF spectroscopy and collagen fiber birefringence are shown to provide complementary measurements of molecular structure (tendon birefringence versus FEI(max) at R(2)=0.60).

Distribution of collagen types I, III, and V in pregnant mouse endometrium

Decidualization in mice comprises a deep remodeling of extracellular matrix (ECM) components of the endometrium. In a previous biochemical study we showed that collagen types I and III are present in both pregnant and nonpregnant mouse endometrium, whereas collagen type V is expressed exclusively after the onset of decidualization. The distribution of collagen types in the pregnant mouse endometrium and possible changes of these molecular types in the different regions of the decidua is, however, not known. Using immunofluorescence and confocal microscopy we showed the presence of collagen types I, III, and V in the endometrial stroma of implantation and interimplantation sites from days 5 to 8 of pregnancy in the mouse. Collagen type III was chiefly expressed in the implantation sites and was the only collagen type to be present in the materno-fetal interface on the day of the embryo implantation. However, collagen type I was the predominant collagen in the interimplantation sites. Collagen type V was weakly expressed in the nondecidualized stroma during all periods but was expressed in larger amounts in the decidualized areas on day 7 of pregnancy, simultaneously with the accumulation of thick collagen fibrils in the same region. The highest immunofluorescence labeling for the three types of collagen was observed on day 7 when the antimesometrial decidual tissue achieved its greatest development. These data support previous studies that showed an intense ECM remodeling of the mouse endometrial stroma during the beginning of pregnancy. This outstanding remodeling may be important to stabilize placental anchorage.

Physiologic pulsatile flow bioreactor conditioning of poly(ethylene glycol)-based tissue engineered vascular grafts

Mechanical conditioning represents a potential means to enhance the biochemical and biomechanical properties of tissue engineered vascular grafts (TEVGs). A pulsatile flow bioreactor was developed to allow shear and pulsatile stimulation of TEVGs. Physiological 120 mmHg/80 mmHg peak-to-trough pressure waveforms can be produced at both fetal and adult heart rates. Flow rates of 2 mL/sec, representative of flow through small diameter blood vessels, can be generated, resulting in a mean wall shear stress of approximately 6 dynes/cm(2) within the 3 mm ID constructs. When combined with non-thrombogenic poly(ethylene glycol) (PEG)-based hydrogels, which have tunable mechanical properties and tailorable biofunctionality, the bioreactor represents a flexible platform for exploring the impact of controlled biochemical and biomechanical stimuli on vascular graft cells. In the present study, the utility of this combined approach for improving TEVG outcome was investigated by encapsulating 10T-1/2 mouse smooth muscle progenitor cells within PEG-based hydrogels containing an adhesive ligand (RGDS) and a collagenase degradable sequence (LGPA). Constructs subjected to 7 weeks of biomechanical conditioning had significantly higher collagen levels and improved moduli relative to those grown under static conditions.

Generation of hybrid transgenic silkworms that express Bombyx mori prolyl-hydroxylase alpha-subunits and human collagens in posterior silk glands: Production of cocoons that contained collagens with hydroxylated proline residues

Prolyl 4-hydroxylase (P4H) is a heterotetramer enzyme consisting of alpha-subunits (P4Halpha) and beta-subunits (P4Hbeta), and is required for collagen biosynthesis. Previously, we generated transgenic silkworms that produced human type III collagen fragments (mini-collagens) in the posterior silk gland (PSG). However, prolyl 4-hydroxylation did not occur on the mini-collagens, because in spite of an abundant expression of P4Hbeta in PSGs, P4Halpha expression was quite low there, thus resulting in an insufficient activity of P4H. In this study we aimed at generating hybrid transgenic silkworms whose PSGs are capable of producing mini-collagens and enough P4H for their prolyl 4-hydroxylation. Isolated PSGs were bombarded with fibroin L-chain gene promoter-driven vectors containing Bombyx mori P4Halpha (BmP4Halpha) cDNAs and were transplanted into the hemolymphatic cavity. The P4H activity in the PSG cells significantly increased, indicating that the expressed BmP4Halpha formed active tetramers with endogenous BmP4Hbeta. Using germ-line transgenesis technology, silkworms were generated that synthesized BmP4Halpha in PSG cells. The P4H activity in the transgenic silkworms was 130-fold higher than that of wild-type counterparts. Finally, we generated hybrid transgenic silkworms that expressed cDNAs of both BmP4Halpha and mini-collagen in PSG cells. They spun cocoons that contained mini-collagens whose appropriate proline residues had been adequately hydroxylated.

Quantitative and comparative studies of the vocal fold extracellular matrix II: collagen

OBJECTIVES

This study examines the collagen content and turnover in the midmembranous vocal fold laminae propriae (LPs) of humans, dogs, pigs, and ferrets.

METHODS

The LP collagen levels were assessed by quantifying tissue hydroxyproline. Quantitative histology allowed evaluation of the collagen content in specific LP regions. Several collagen types and two markers of collagen turnover were examined immunohistochemically.

RESULTS

Collagen made up 43.4% +/- 2.6% of human LP total protein (TP), with men having approximately 30% higher collagen content than women (p < .024). The collagen levels in pigs (52.6% +/- 1.9% of TP) and ferrets (29.8% +/- 3.7% of TP), but not that in dogs (45.3% +/- 1.2% of TP), varied significantly from that in humans (pigs, p < .016; ferrets, p < .011). Quantitative histology indicated marked interspecies differences in total collagen distribution. Collagen types I, III, and IV were detected in the LP, and spatially complex staining patterns were observed for the two markers of collagen turnover studied.

CONCLUSIONS

The collagen content of the human LP is approximately 60% to 70% of that of human dermis. Although canine LP collagen levels are most similar to those of humans, quantitative histology indicates that the collagen distribution of the human LP is best matched by the porcine LP. Collagen types I and III seem to be the dominant LP collagens. Spatial variations in collagen turnover appear to exist that may contribute to normal LP physiology.

Monocyte chemoattractant protein 1 released from glycosaminoglycans mediates its profibrotic effects in systemic sclerosis via the release of interleukin-4 from T cells

OBJECTIVE

Monocyte chemoattractant protein 1 (MCP-1; CCL2) has been implicated in the pathogenesis of fibrotic diseases and is up-regulated in patients with systemic sclerosis (SSc). The aim of the present study was to examine the mechanisms by which MCP-1 mediates its profibrotic effects in the setting of SSc.

METHODS

The expression of receptors for MCP-1 on dermal fibroblasts was analyzed by real-time polymerase chain reaction and fluorescence-activated cell sorting. The ability of extracellular matrix proteins to bind and release MCP-1 was quantified by enzyme-linked immunosorbent assay. Th0 cells were isolated using a magnetic-activated cell sorting system and were stimulated twice in the presence of MCP-1. The synthesis of collagen was measured using the Sircol collagen assay kit.

RESULTS

The glycosaminoglycan chondroitin sulfate, but not fibronectin or collagens, bound and released MCP-1 in a time-dependent manner. MCP-1 that was released from chondroitin sulfate induced the differentiation of interleukin-4 (IL-4)-producing T cells in a dose-dependent manner. In turn, dermal fibroblasts from patients with SSc expressed IL-4 receptor, and stimulation with IL-4 significantly increased the production of collagen in dermal fibroblasts. In contrast, CCR2a and CCR2b, as well as D6 and US28 (other potential receptors of MCP-1), were not detectable in SSc and normal fibroblasts, and their expression was not induced by platelet-derived growth factor, IL-1beta, or IL-4. In addition, MCP-1 had no direct effects on collagen production by fibroblasts.

CONCLUSION

MCP-1 has no direct effects on dermal fibroblasts but contributes to fibrosis in patients with SSc by inducing the differentiation of IL-4-producing T cells. Because MCP-1 has both proinflammatory and profibrotic effects, pharmacologic targeting of MCP-1 could be a promising therapeutic approach in SSc.

Synthesis of poly(Pro-Hyp-Gly)(n) by direct poly-condensation of (Pro-Hyp-Gly)(n), where n=1, 5, and 10, and stability of the triple-helical structure

Pro-Hyp-Gly is a characteristic amino acid sequence found in fibrous collagens, and (Pro-Hyp-Gly)(10), which has been widely used as a collagen-model peptide, forms a stable triple-helical structure. Here, we synthesized polypeptides consisting of the Pro-Hyp-Gly sequence by direct poly-condensation of (Pro-Hyp-Gly)(n), where n=1, 5, and 10, using 1-hydroxybenzotriazole and 1-ethyl-3-(3-dimethyl-aminopropyl)-carbodiimide hydrochloride in both phosphate buffer (pH=7.4) and dimethylsulfoxide (DMSO) solutions for 48 h at 20 degrees C. The reaction of (Pro-Hyp-Gly)(5) and (Pro-Hyp-Gly)(10) in DMSO successfully gave polypeptides with molecular weights over 10,000, whereas low molecular weight products were obtained by reaction in phosphate buffer (pH=7.4). In contrast, Pro-Hyp-Gly at a concentration of 50 mg/mL in phosphate buffer (pH=7.4) gave polypeptides with molecular weights over 10,000. The Fourier transform infrared (FTIR) and (1)H nuclear magnetic resonance (NMR) spectra of poly(Pro-Hyp-Gly)(10) revealed that the polymerization of (Pro-Hyp-Gly)(10) described in this report had no side reactions. Each polypeptide obtained shows a collagen-like triple-helical structure, and the triple-helical structures of poly(Pro-Hyp-Gly) and poly(Pro-Hyp-Gly)(10) were stable up to T=80 degrees C, which suggests that the high molecular weight promotes stability of the triple-helical structure, in addition to the high Hyp content. Furthermore, transmission electron microscopy (TEM) observations show that poly(Pro-Hyp-Gly)(10) aggregates to form nanofiber-like structures about 10 nm in width, which suggests that a Pro-Hyp-Gly repeating sequence contains enough information for triple-helix formation, and for subsequent nanofiber-like structure formation.

Relevance of Posttranslational Modifications for the Arthritogenicity of Type II Collagen

To establish the role of posttranslational modification in modulating the immune response to collagen, recombinant human type II collagen (rCII) was produced using a yeast expression system (rCII(pic)) and a baculovirus expression system (rCII(bac)). The biosynthesis of CII requires extensive posttranslational modification including the hydroxylation of prolyl and lysyl residues and glycosylation of selected hydroxylysyl residues. Amino acid analyses indicated that the rCII(bac) was adequately hydroxylated at prolyl residues but underhydroxylated at lysyl residues and underglycosylated compared with tissue-derived CII, whereas rCII(pic) was adequately hydroxylated at prolyl residues but unhydroxylated at lysyl residues and had no glycosylation. When DBA/1 mice were immunized with rCII, rCII(pic) induced a lower incidence of arthritis than tissue-derived CII, whereas rCII(bac) induced an intermediate level of arthritis. The severity of the arthritis was significantly lower in mice immunized with rCII(pic) compared with mice immunized with tissue-derived CII, whereas that of rCII(bac) was intermediate. These data indicate that the degree of lysine hydroxylation and glycosylation plays a role in the induction of arthritis. The recombinant collagens were then compared with tissue-derived CII when given as i.v. or oral tolerogens to suppress arthritis. Both recombinant collagens were less potent than tissue-derived CII, and this decrease in arthritis was associated with a decrease in Ab response to CII. These data suggest that the degree of glysosylation affects the immune response to CII, so that underglycosylated CII is less effective in the induction of arthritis and in its ability to suppress collagen-induced arthritis.

Periurethral connective tissue status of postmenopausal women with genital prolapse with and without stress incontinence

OBJECTIVE

Connective tissue consists mainly of collagen and structural glycoproteins and is considered an important factor of the supportive structures of the genitourinary region. Few data have been published as yet with respect to the role of connective tissue in pelvic floor relaxation and genuine stress incontinence (GSI). We compared periurethral connective tissue structures between continent and incontinent postmenopausal women with genital prolapse.

METHODS

Twenty-nine women underwent pelvic floor reconstructive surgery (anterior colporrhaphy: n = 29, sacrospinous fixation: n = 12), with biopsies obtained from the periurethral region. Fifteen patients and 14 women were incontinent and continent, respectively. Tissue samples were investigated for localization and distribution of collagen (types I, III, IV, V, VI) and glycoproteins (fibronectin, laminin, vitronectin) using immunofluorescent microscopic techniques.

RESULTS

Collagen types I, III, IV, V, and VI were found in all tissue samples. Compared with the continent women, the tissue samples of the incontinent women showed a significantly weaker immunohistochemical staining of type I, III, and VI collagen. No difference in staining patterns of collagen type IV and V, fibronectin, and laminin was observed between the two groups. Intact vitronectin was found in the periurethral tissues of all the continent women, whereas this glycoprotein was either absent or fragmented in the incontinent women.

CONCLUSIONS

Our results indicate an altered metabolism of connective tissue in the periurethral region with a significant decrease of collagen and vitronectin expression in postmenopausal women with pelvic floor relaxation with and without GSI.

Triosidines: novel Maillard reaction products and cross-links from the reaction of triose sugars with lysine and arginine residues

The role of the highly reactive triose sugars glyceraldehyde and glyceraldehyde-3-phosphate in protein cross-linking and other amino acid modifications during the Maillard reaction was investigated. From the incubation of glyceraldehyde with N (alpha)-acetyl-L-lysine and N (alpha)-acetyl-L-arginine, we isolated four new Maillard reaction pyridinium compounds named 'triosidines'. Two of them, 'lys-hydroxy-triosidine' [1-(5-amino-5-carboxypentyl)-3-[(5-amino-5-carboxypentylamino)methyl]-5-hydroxypyridinium] and 'arg-hydroxy-triosidine' [2-(4-amino-4-carboxybutylamino)-8-(5-amino-5-carboxypentyl)-6-hydroxy-3,4-dihydro-pyrido[2,3-d]pyrimidin-8-ium] are fluorescent, UV-active Lys-Lys and Lys-Arg cross-links respectively. Their structures were identified by NMR and MS. In addition, two UV-active lysine adducts, 'trihydroxy-triosidine' [1-(5-amino-5-carboxypentyl)-3,4-dihydroxy-5-(hydroxymethyl)pyridinium] and 'triosidine carbaldehyde' [1-(5-amino-5-carboxypentyl)-3-formylpyridinium] were tentatively identified by MS. All structures involve six sugar-derived carbons as part of the heterocyclic ring. Of the two novel cross-links, only arg-hydroxy-triosidine was formed by glyceraldehyde-3-phosphate, an intermediate metabolite of the glycolytic pathway. Lys-hydroxy-triosidine and arg-hydroxy-triosidine were detected in human and porcine corneas treated with glyceraldehyde. The HPLC-fluorescence identification was confirmed by MS. Triosidines were also formed from dihydroxyacetone, a widely used artificial sun-tanning agent. Triosidines are expected to be useful tools in tissue engineering, where the utilization of highly reactive sugars is needed to stabilize the loose matrix. In addition, they are expected to be present in selected biological conditions, such as on consumption of a high fructose diet, and syndromes associated with high glyceraldehyde excretion, such as Fanconi Syndrome, fructose-1,6-diphosphatase deficiency and tyrosinaemia.

High-level production of human type I collagen in the yeast Pichia pastoris

Four human genes, two of them encoding the proalpha1 and proalpha2 chains of type I procollagen and two of them the two types of subunit of prolyl 4-hydroxylase (4-PH), were integrated into the genome of Pichia pastoris. The proalpha1 and proalpha2 chains expressed formed type I procollagen molecules with the correct 2:1 chain ratio, and the 4-PH subunits formed an active enzyme tetramer that fully hydroxylated the proalpha chains. Chains lacking their N but not C propeptides formed pCcollagen molecules with the 2:1 chain ratio and, surprisingly, the expression levels of pCcollagen were 1.5-3-fold relative to those of procollagen. Both types of molecule could be converted by pepsin treatment to collagen molecules that formed native-type fibrils in vitro. The expression levels obtained for the pCcollagen using only single copies of each of the four genes and a 2 l fermenter ranged up to 0.5 g/l, indicating that it should be possible to optimize this system for high-level production of recombinant human type I collagen for numerous medical applications.

A deficiency of cysteine impairs fibrillin-1 deposition: implications for the pathogenesis of cystathionine beta-synthase deficiency

Cystathionine beta-synthase (CBS) deficiency is an inborn error of amino acid metabolism that has pleiotropic manifestations and is commonly called "homocystinuria." The features include skeletal, ocular, and vascular defects, some of which are reminiscent of those found in Marfan syndrome (MFS). Because of the spectrum of clinical effects, the pathogenesis of homocystinuria has long been thought to involve the extracellular matrix (ECM), and the condition has been classified as a heritable disorder of connective tissue. Because of the superficial similarities with MFS, we and others (Pyeritz, in McKusicks Heritable Disorders of Connective Tissue, St. Louis, Mosby-Year Book Inc., 5th ed., pp 137-178, 1993; Pyeritz, in Principles and Practice of Medical Genetics, New York, Churchill Livingstone, 3rd ed., pp 1027-1066, 1997; Mudd, Levy, and Skovby, in The Metabolic and Molecular Bases of Inherited Disease, New York, McGraw-Hill Publishing Co., 7th ed., pp 1279-1327, 1995) have speculated how CBS deficiency might affect fibrillin-1, the protein altered in MFS. For example, the altered plasma concentrations of homocysteine and/or cysteine in patients with CBS deficiency may hinder fibrillin-1 synthesis, deposition, or both. When arterial smooth muscle cells were cultured under conditions of cysteine deficiency, fibrillin-1 deposition into the ECM was greatly diminished as revealed by immunocytochemistry. Excessive homocysteine, in contrast, had little, if any, effect on fibrillin-1 deposition. When cysteine concentrations were returned to normal, the smooth muscle cells began to accumulate a matrix rich in fibrillin-1. Type I collagen, the major matrix component synthesized by these smooth muscle cells, was not reduced by low cysteine concentrations nor high homocysteine concentrations. These results demonstrate that a deficiency of cysteine and subsequent inhibition of fibrillin-1 accumulation in CBS deficient patients may be at least partly responsible for their phenotype, and suggest that maintenance of normal plasma cyst(e)ine levels may be an important therapeutic goal.

Production of recombinant human type I procollagen homotrimer in the mammary gland of transgenic mice

The large scale production of recombinant collagen for use in biomaterials requires an efficient expression system capable of processing a large (> 400 Kd) multisubunit protein requiring post-translational modifications. To investigate whether the mammary gland of transgenic animals fulfills these requirements, transgenic mice were generated containing the alpha S1-casein mammary gland-specific promoter operatively linked to 37 Kb of the human alpha 1(I) procollagen structural gene and 3' flanking region. The frequency of transgenic lines established was 12%. High levels of soluble triple helical homotrimeric [(alpha 1)3] type I procollagen were detected (up to 8 mg/ml) exclusively in the milk of six out of 9 lines of lactating transgenic mice. The transgene-derived human procollagen chains underwent efficient assembly into a triple helical structure. Although proline or lysine hydroxylation has never been described for any milk protein, procollagen was detected with these post-translational modifications. The procollagen was stable in milk; minimal degradation was observed. These results show that the mammary gland is capable of expressing a large procollagen gene construct, efficiently assembling the individual polypeptide chains into a stable triple helix, and secreting the intact molecule into the milk.

Influence of Fibrillar Collagen Structure on the Mechanisms of Platelet Thrombus Formation Under Flow

We have used real-time video microscopy to study the mechanisms of platelet adhesion to type I collagen fibrils of distinct structure exposed to flowing blood. Electron microscopy analysis by surface replication demonstrated morphological differences between acid-insoluble fibrils, displaying a regularly repeating striated pattern (banded collagen), and acid-soluble fibrils generated by pepsin treatment of insoluble collagen, smaller in size with a helical configuration (nonbanded collagen). These structural differences proved to be related to the role of platelet integrin 2β1 in stabilizing adhesion to collagen under a variety of flow conditions. Blocking 2β1 function with a monoclonal antibody had no effect on platelet adhesion to insoluble type I collagen coated at high density on a glass surface, whereas there was an absolute dependence of 2β1 function for the initial permanent arrest of platelets and subsequent thrombus formation on pepsin-solubilized type I collagen under the same conditions. In contrast, reconstituted, banded fibrils prepared from pepsin-solubilized type I collagen supported platelet adhesion and thrombus development even when platelet 2β1 function was blocked, a process that was greatly accelerated by pre-exposure of this substrate to autologous plasma under flow. These results implicate a collagen receptor(s) on platelets other than 2β1 that can selectively engage domains in banded, but not nonbanded type I collagen when 2β1 function is blocked. In addition, collagen structure may regulate the extent and affinity of the binding under flow of plasma components such as von Willebrand factor and/or other IIbβ3 ligands.

The determination of von Willebrand factor activity by collagen binding assay

A new collagen binding assay has been developed for the determination of the functional activity of human von Willebrand factor based on the following principle: pepsin-digested type III collagen from human placenta was covalently immobilized on a microtitre plate. Binding of collagen to the microtitre plate was carried out in neutral phosphate buffer within 1 h. A collagen concentration of 3 micrograms mL-1 was sufficient to achieve optimal coating. After drying, the coated microtitre plates remained stable for months without losing their vWF-binding properties and could be incorporated into a ready-to-use kit. The suitability of various types of collagen for use in this assay was evaluated by simulating the binding of vWF to collagen immobilized on the microtitre plate by using surface plasmon resonance technology with collagen immobilized on a sensor chip. vWF was most effectively bound to pepsin-digested type III collagen from human placenta. The assay thus comprises the following steps: (1) serial dilutions of a vWF reference preparation and vWF-containing samples are prepared and bound to a microtitre plate which is precoated with collagen; (2) vWF is detected with a polyclonal antibody; (3) the substrate reaction is photometrically measured with an ELISA reader. This test is highly specific and sensitive for vWF (detection limit: 10 ng mL-1). The collagen binding activity measured corresponds to the degree of multimerization of vWF. The high sensitivity and the short time needed to carry it out may make it useful for clinical diagnosis and for the measurement of the functional activity of vWF in factor concentrates. In certain applications it may represent a suitable replacement for the ristocetin cofactor assay.

Effect of curcumin on the advanced glycation and cross-linking of collagen in diabetic rats

A close association between increased oxidative stress and hyperglycemia has been postulated to contribute significantly to the accelerated accumulation of advanced glycation end products (AGEs) and the cross-linking of collagen in diabetes mellitus. In the present work, we report the influence of curcumin, an efficient antioxidant, on the level of AGEs and the cross-linking of collagen in diabetic rats. Diabetic rats were given curcumin (200 mg/kg body wt) orally for a duration of 8 weeks. The antioxidant status in serum and the level of AGEs, cross-linking and browning of collagen in tail tendons and skin were investigated. The oxidative stress observed in diabetic rats was reduced significantly by curcumin administration. Nonenzymic antioxidants such as vitamin C, vitamin E, and glutathione were maintained at near normal values in curcumin-treated diabetic animals. Similarly, the accumulation of lipid peroxidation products in diabetic serum was reduced significantly by curcumin. Accelerated accumulation of AGE-collagen in diabetic animals, as detected by ELISA, was prevented by curcumin. Extensive cross-linking of collagen in the tail tendon and skin of diabetic animals was also prevented to a greater extent by curcumin treatment. A correlation between the level of AGEs and collagen cross-linking was noted, suggesting the involvement of advanced glycation in cross-linking. It was also noted that the preventive effect of curcumin on the advanced glycation and cross-linking of collagen was more pronounced than its therapeutic effect. However, the Maillard reaction fluorescence in both tail and skin collagen remained unaltered by curcumin. This study confirms the significance of free radicals in the accumulation of AGEs and cross-linking of collagen in diabetes. It supports curcumin administration for the prevention of AGE-induced complications of diabetes mellitus.