Comparative study on the thermostability of collagen I of skin and bone: influence of posttranslational hydroxylation of prolyl and lysyl residues

Textural modification of Chinese traditional stewed pig trotter: Effect of acid or alkaline-induced degradation of collagen fibers

This study aimed to investigate the effects of acid or alkaline treatments on the textural properties of Chinese traditional stewed pig trotter in relation to the degradation of collagen fibers. Pig trotters were subjected to different pHs of 4, 5, 6, 7, and 8 and then stewed at 95°C for 60 min. Textural parameters (springiness, chewiness, hardness, and gumminess) of pig trotters and Raman spectroscopy, cross-links, decorin, and glycosaminoglycans contents of collagen fibers were assessed. The acid or alkaline treatments at pH 4, 5, 6, and 8 improved the textural properties evidenced by lower chewiness, hardness, and gumminess, and promoted the unfolding of the secondary structure evidenced by a loss of α-helix paralleled with an increase of random coil, as well as induced a breakage to the covalent cross-links evidenced by the reduction of cross-links, decorin, and glycosaminoglycans. This study thus concluded positive effects of acid or alkaline treatments on the textural modification of Chinese traditional stewed pig trotter in relation to the induced degradation of the collagen fibers.

The Thermal Stability of the Collagen Triple Helix Is Tuned According to the Environmental Temperature

Triple helix formation of procollagen occurs in the endoplasmic reticulum (ER) where the single-stranded α-chains of procollagen undergo extensive post-translational modifications. The modifications include prolyl 4- and 3-hydroxylations, lysyl hydroxylation, and following glycosylations. The modifications, especially prolyl 4-hydroxylation, enhance the thermal stability of the procollagen triple helix. Procollagen molecules are transported to the Golgi and secreted from the cell, after the triple helix is formed in the ER. In this study, we investigated the relationship between the thermal stability of the collagen triple helix and environmental temperature. We analyzed the number of collagen post-translational modifications and thermal melting temperature and α-chain composition of secreted type I collagen in zebrafish embryonic fibroblasts (ZF4) cultured at various temperatures (18, 23, 28, and 33 °C). The results revealed that thermal stability and other properties of collagen were almost constant when ZF4 cells were cultured below 28 °C. By contrast, at a higher temperature (33 °C), an increase in the number of post-translational modifications and a change in α-chain composition of type I collagen were observed; hence, the collagen acquired higher thermal stability. The results indicate that the thermal stability of collagen could be autonomously tuned according to the environmental temperature in poikilotherms.

Post-translational modifications in collagen type I of bone in a mouse model of aging

The fracture resistance of cortical bone and matrix hydration are known to decline with advanced aging. However, the underlying mechanisms remain poorly understood, and so we investigated levels of matrix proteins and post-translational modifications (PTM) of collagen I in extracts from the tibia of 6-mo. and 20-mo. old BALB/c mice (female and male analysis done separately). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis revealed that the levels of collagen I deamidation at specific asparagine (Asn) and glutamine (Gln) residues significantly increased with age. Other non-enzymatic PTMs such as carboxymethylation of lysine (CML) were detected as well, but the relative abundance did not vary with age. No significant age-related differences in the abundance of hydroxylysine glycosylation sites were found, but hydroxylation levels at a few of the numerous lysine and proline hydroxylation sites significantly changed by a small amount with age. We performed molecular modeling and dynamics (MD) simulations for three triple helical fragments representing collagen I regions with prominent age-dependent increases in deamidation as identified by LC-MS/MS of male extracts. These 3 fragments included deamidated Asn and Gln residues as follows: 1) an Asn⁴²⁸ site of the α2(I) chain in which deamidation levels increased from 4.4% at 6-mo. to 8.1% at 20-mo., 2) an Asn⁹⁸³ site of the α2(I) chain with a deamidation increase from 18.3% to 36.8% with age and an Asn¹⁰⁵² site of the α1(I) chain with consistent deamidation levels of ~60% across the age groups, and 3) a Gln⁴¹⁰ site of the α1(I) chain that went from no detectable deamidation at 6-mo. to 2.7% at 20-mo. and a neighboring Asn⁴²¹ site of the same chain with an age-related deamidation increase from 3.6% to 16.3%. The deamidation levels at these sites inversely correlated with an estimate of toughness determined from three-point bending tests of the femur mid-diaphysis. MD revealed that the sidechains become more negatively charged at deamidated sites and that deamidation alters hydrogen bonding with water along the collagen backbone while increasing water interactions with the aspartic and glutamic acid sidechains. Our findings suggest a new mechanism of the age-dependent reduction in the fracture resistance of cortical bone whereby deamidation of Asn and Glu residues redistributes bound water within collagen I triple helix.

Keratin Durability Has Implications for the Fossil Record: Results from a 10 Year Feather Degradation Experiment

Keratinous ‘soft tissue’ structures (i.e. epidermally derived and originally non-biomineralized), include feathers, skin, claws, beaks, and hair. Despite their relatively common occurrence in the fossil record (second only to bone and teeth), few studies have addressed natural degradation processes that must occur in all organic material, including those keratinous structures that are incorporated into the rock record as fossils. Because feathers have high preservation potential and strong phylogenetic signal, in the current study we examine feathers subjected to different burial environments for a duration of ~10 years, using transmission electron microscopy (TEM) and in situ immunofluorescence (IF). We use morphology and persistence of specific immunoreactivity as indicators of preservation at the molecular and microstructural levels. We show that feather keratin is durable, demonstrates structural and microstructural integrity, and retains epitopes suitable for specific antibody recognition in even the harshest conditions. These data support the hypothesis that keratin antibody reactivity can be used to identify the nature and composition of epidermal structures in the rock record, and to address evolutionary questions by distinguishing between alpha- (widely distributed) and beta- (limited to sauropsids) keratin.

Zebrafish Collagen Type I: Molecular and Biochemical Characterization of the Major Structural Protein in Bone and Skin

Over the last years the zebrafish imposed itself as a powerful model to study skeletal diseases, but a limit to its use is the poor characterization of collagen type I, the most abundant protein in bone and skin. In tetrapods collagen type I is a trimer mainly composed of two α1 chains and one α2 chain, encoded by COL1A1 and COL1A2 genes, respectively. In contrast, in zebrafish three type I collagen genes exist, col1a1a, col1a1b and col1a2 coding for α1(I), α3(I) and α2(I) chains. During embryonic and larval development the three collagen type I genes showed a similar spatio-temporal expression pattern, indicating their co-regulation and interdependence at these stages. In both embryonic and adult tissues, the presence of the three α(I) chains was demonstrated, although in embryos α1(I) was present in two distinct glycosylated states, suggesting a developmental-specific collagen composition. Even though in adult bone, skin and scales equal amounts of α1(I), α3(I) and α2(I) chains are present, the presented data suggest a tissue-specific stoichiometry and/or post-translational modification status for collagen type I. In conclusion, this data will be useful to properly interpret results and insights gained from zebrafish models of skeletal diseases.

Dinosaur peptides suggest mechanisms of protein survival

Eleven collagen peptide sequences recovered from chemical extracts of dinosaur bones were mapped onto molecular models of the vertebrate collagen fibril derived from extant taxa. The dinosaur peptides localized to fibril regions protected by the close packing of collagen molecules, and contained few acidic amino acids. Four peptides mapped to collagen regions crucial for cell-collagen interactions and tissue development. Dinosaur peptides were not represented in more exposed parts of the collagen fibril or regions mediating intermolecular cross-linking. Thus functionally significant regions of collagen fibrils that are physically shielded within the fibril may be preferentially preserved in fossils. These results show empirically that structure-function relationships at the molecular level could contribute to selective preservation in fossilized vertebrate remains across geological time, suggest a 'preservation motif', and bolster current concepts linking collagen structure to biological function. This non-random distribution supports the hypothesis that the peptides are produced by the extinct organisms and suggests a chemical mechanism for survival.

In vitro deposition of hydroxyapatite on cortical bone collagen stimulated by deformation-induced piezoelectricity

In the present work, we have studied the effect of the piezoelectricity of elastically deformed cortical bone collagen on surface using a biomimetic approach. The mineralization process induced as a consequence of the piezoelectricity effect was evaluated using scanning electron microscopy (SEM), thermally stimulated depolarization current (TSDC), and differential scanning calorimetry (DSC). SEM micrographs showed that mineralization occurred predominantly over the compressed side of bone collagen, due to the effect of piezoelectricity, when the sample was immersed in the simulated body fluid (SBF) in a cell-free system. The TSDC method was used to examine the complex collagen dielectric response. The dielectric spectra of deformed and undeformed collagen samples with different hydration levels were compared and correlated with the mineralization process followed by SEM. The dielectric measurements showed that the mineralization induced significant changes in the dielectric spectra of the deformed sample. DSC and TSDC results demonstrated a reduction of the collagen glass transition as the mineralization process advanced. The combined use of SEM, TSDC, and DSC showed that, even without osteoblasts present, the piezoelectric dipoles produced by deformed collagen can produce the precipitation of hydroxyapatite by electrochemical means, without a catalytic converter as occurs in classical biomimetic deposition.

Influence of different collagen species on physico-chemical properties of crosslinked collagen matrices

Collagen-based scaffolds are appealing products for the repair of cartilage defects using tissue engineering strategies. The present study investigated the species-related differences of collagen scaffolds with and without 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS)-crosslinking. Resistance against collagenase digestion, swelling ratio, amino acid sequence, shrinkage temperature, ultrastructural matrix morphology, crosslinking density and stress-strain characteristics were determined to evaluate the physico-chemical properties of equine- and bovine-collagen-based scaffolds. Three-factor ANOVA analysis revealed a highly significant effect of collagen type (p=0.0001), crosslinking (p=0.0001) and time (p=0.0001) on degradation of the collagen samples by collagenase treatment. Crosslinked equine collagen samples showed a significantly reduced swelling ratio compared to bovine collagen samples (p< 0.0001). The amino acid composition of equine collagen revealed a higher amount of hydroxylysine and lysine. Shrinkage temperatures of non-crosslinked samples showed a significant difference between equine (60 degrees C) and bovine collagen (57 degrees C). Three-factor ANOVA analysis revealed a highly significant effect of collagen type (p=0.0001), crosslinking (p=0.0001) and matrix condition (p=0.0001) on rupture strength measured by stress-strain analysis. The ultrastructure, the crosslinking density and the strain at rupture between collagen matrices of both species showed no significant differences. For tissue engineering purposes, the higher enzymatic stability, the higher form stability, as well as the lower risk of transmissible disease make the case for considering equine-based collagen. This study also indicates that results obtained for scaffolds based on a certain collagen species may not be transferable to scaffolds based on another, because of the differing physico-chemical properties.

Hyperthermic treatment of post-LASIK corneal striae

PURPOSE

To investigate the effect of hyperthermia for the treatment of long-standing corneal flap striae after laser in situ keratomileusis (LASIK).

SETTING

TLC Laser Eye Center, Garden City, New York, USA.

METHODS

Patients with visually significant flap striae at least 3 weeks post-LASIK were offered hyperthermic treatment. The central 6.0 mm of epithelium was removed from affected corneas, and the flaps were elevated. A striae removal spatula was heated to 65 degrees C in sterile water, and both sides of the flaps were mechanically massaged with the spatula for 5 to 10 minutes until the striae were visually reduced.

RESULTS

Thirty-six eyes of 34 patients were treated with hyperthermia to remove corneal striae. All patients had a clinical reduction in striae. The mean pretreatment best corrected visual acuity (BCVA) was 20/44, improving to 20/25 on follow-up (mean follow-up 16.4 months). Patients subjectively noted reduced haze and glare and no loss of BCVA. There were no serious flap complications.

CONCLUSION

Hyperthermic treatment is a safe, effective treatment option for corneal striae after LASIK.

Collagen and bone viscoelasticity: a dynamic mechanical analysis

The purpose of this study was to explore the effects of changes in Type I collagen on the viscoelasticity of bone. Bone coupons were heated at either 100 or 200 degrees C to induce the thermal denaturation of Type I collagen. Half of these specimens were rehydrated after heat treatment; the other half were tested in a dry condition. The degree of denatured collagen (DC%) was analyzed by a selective digestion technique with the use of alpha-chymotrypsin. Isothermal (37 degrees C) and variable temperature tests (scans from 35 to 200 degrees C) were performed with the use of a dynamic mechanical analyzer to evaluate changes in bone viscoelastic properties as a function of collagen damage, specifically, changes in the loss factor (tan delta) and storage modulus (E') were assessed. Significant collagen denaturation occurred only when bone was heated at 200 degrees C irrespective of the hydration condition. Also, DC% did not show a significant effect on tan delta. However, higher values of tan delta were observed in wet samples compared to dry specimens. The temperature-scan tests revealed that the hydration condition, but not DC%, significantly affected the behavior of tan delta. However, E' was not strongly influenced either by DC% or by water content. These results suggest that at a constant frequency the denaturation of collagen triple-helical molecules may have few effects on the viscoelasticity of bone, but moisture may play a prominent role in determining this property.

The role of collagen in determining bone mechanical properties

The hypothesis of this study was that collagen denaturation would lead to a significant decrease in the toughness of bone, but has little effect on the stiffness of bone. Using a heating model, effects of collagen denaturation on the biomechanical properties of human cadaveric bone were examined. Prior to testing, bone specimens were heat treated at varied temperatures (37-200 degrees C) to induce different degrees of collagen denaturation. Collagen denaturation and mechanical properties of bone were determined using a selective digestion technique and three-point bending tests, respectively. The densities and weight fractions of the mineral and organic phases in bone also were determined. A repeated measures analysis of variance showed that heating had a significant effect on the biomechanical integrity of bone, corresponding to the degree of collagen denaturation. The results of this study indicate that the toughness and strength of bone decreases significantly with increasing collagen denaturation, whereas the elastic modulus of bone is almost constant irrespective of collagen denaturation. These results suggest that the collagen network plays an important role in the toughness of bone, but has little effect on the stiffness of bone, thereby supporting the hypothesis of this study.

Thermal stability of bone collagen as an indicator of bone turnover in gonadectomized and multiparous rats

Previous findings indicate that the thermal stability of bone collagen is related to age. In this study, collagen from rat bone with reported different turnover rates was investigated. Cortical and trabecular bone from femur were obtained from intact, ovariectomized, orchidectomized and multiparous breeder rats. Thermal stabilities of fibrillar collagen in decalcified bone matrix and molecular collagen obtained by pepsin treatment were measured as shrinkage (Ts) and 'melting' temperature (Tm), respectively. Both Ts and Tm of cortical collagen from intact female rats decreased in parallel with age as previously found in male rats indicating that Ts and Tm measurements are interchangeable techniques in characterizing the thermal stability of bone collagen. Tm of trabecular collagen from intact rats decreased with age, however, with a decay only one-third of that for cortical collagen. The different rates possibly reflect different ages of collagen due to remodeling activity present in trabecular and minimal in cortical bone. Compared with control rats the Tm of trabecular collagen from gonadectomized and multiparous rats with a reported increased trabecular turnover rate was elevated, whereas only minor variations in Tm of cortical collagen were found. In conclusion, the thermal stability of bone collagen decreases with the age of the collagen. Increased bone turnover implies elevated thermal stability of bone collagen. Thus, thermal stability of bone collagen appears to be an indicator of bone turnover.

Three novel type I collagen mutations in osteogenesis imperfecta type IV probands are associated with discrepancies between electrophoretic migration of osteoblast and fibroblast collagen

In three cases of type IV osteogenesis imperfecta (OI), we identified unique point mutations in type I collagen alpha1(I) cDNA. In two cases, the appearance of dimers indicated the presence of cysteine substitutions in the alpha1(I) protein chain. Cyanogen bromide digestion localized these cross-links to CB8 and 3, respectively. In the third case, the overmodification pattern of the CNBr peptides was compatible with a substitution in the aa 123-402 region of either type I collagen chain. We identified a unique point mutation in each proband, which resulted in substitutions for glycine residues in a 300-aa region of the alpha1(I) helix, specifically, Gly to Ala at codon 220 (GGT-->GCT), Gly to Cys at codon 349 (GGT-->TGT) and Gly to Cys at codon 523 (GGT-->TGT). We compared each proband's fibroblast and osteoblast collagen directly, as well as with fibroblast and osteoblast controls. For all cases, the OI osteoblast collagen was more electrophoretically delayed than OI fibroblast collagen. In the patient with G349C, OI fibroblast and osteoblast collagen synthesized in the presence of alpha,alpha'-dipyridyl co-migrated on gels, demonstrating that the electrophoretic discrepancy resulted from differences in post-translational modification. Melting temperature curves for stability of the collagen helix yielded an identical Tm for control fibroblast and osteoblast collagen (41.2 degrees C). By contrast, for collagen with the gly349-->cys substitution, the Tm of the fibroblast collagen was 1 degree C lower than the Tm of the osteoblast collagen. These data indicate that the metabolism of mutant collagen might be cell-specific and has significant implications for understanding the phenotype/genotype correlations and the pathophysiology of OI.

Influence of neutral salts on the hydrothermal stability of acid-soluble collagen

The thermal stability of acid-soluble collagens was studied by circular dichroism (CD) spectroscopy. Adult bovine dermal collagen (BDC), rat-tail tendon collagen (RTC), and calf skin collagen (CSC) were compared. Despite some variability in amino acid composition and apparent molecular weight, the CD spectra for helical and unordered collagen structures were essentially the same for all the sources. The melting of these collagens occurs as a two-stage process characterized by a pretransition (Tp) followed by complete denaturation (Td). The characteristic temperatures vary with the source of the collagen; for mature collagens (BDC, RTC) Tp = 30 degrees C and Td = 36 degrees C, and for CSC Tp = 34 degrees C and Td = 40 degrees C. Neutral salts, NaCl or KCl, at low concentrations (0.02-0.2 M) appear to bind to the collagens and shift the thermal transitions of these collagens to lower temperatures.

Effect of collagen denaturation on the toughness of bone

The purpose of this study was to explore the relationship between the integrity of collagen and biomechanical properties of bone. In this study, age (range, 5-26 years old) and gender related changes in cortical bone samples from 33 baboon femurs (15 males and 18 females) were examined. The percentage of denatured collagen was determined using a selective digestion technique. The fracture toughness, elastic modulus, yield and ultimate strength, and energy to fracture of bone were determined in three-point bending configurations. The porosity and weight fractions of the mineral and organic phase also were measured. A two-way analysis of variance showed that age dependent changes were reflected primarily in the amount of denatured collagen, fracture toughness, energy to fracture, and elastic modulus, whereas gender had effects on the fracture toughness, elastic modulus, and porosity of bone. In addition, regression analyses indicated that the percentage of denatured collagen had an inverse correlation with the toughness of bone and a positive correlation with its elastic modulus, whereas mineral content had positive correlation with the strength and elastic modulus of bone. The results of this study suggest collagen influences the toughness of bone, whereas mineral content predominantly contributes to bone stiffness and strength.

Comparison of palmar aponeuroses from individuals with diabetes mellitus and Dupuytren's contracture

It is well known that Dupuytren's contracture is often associated with diabetes mellitus. Palmar fascia from individuals with diabetes mellitus and/or Dupuytren's contracture as well as controls were subjected to differential scanning calorimetry, biomechanical and biochemical analysis. The collagen denaturation temperature of the palmar aponeurosis from individuals with diabetes mellitus in the presence (71.0 degrees C) or absence of Dupuytren's contracture (70. 6 degrees C) was increased as compared with controls (68.5 degrees C), while this parameter was significantly reduced (about 3.5 degrees C) in contracture bands of Dupuytren's contracture. Stress relaxation experiments revealed that the viscous fraction was slightly reduced in diabetes mellitus (6.5%) vs. controls (8.3%), whereas in Dupuytren's contracture, irrespective of additional diabetes mellitus, a pronounced increase of this parameter was seen (36.5% vs. 24.5%) in the presence of diabetes mellitus. The time constants were significantly elevated by both disorders, this increase being more pronounced in Dupuytren's contracture. Taken together, these changes can be explained by increased cross-linking in diabetes mellitus, while in Dupuytren's contracture other structural changes, such as increased collagen type III content and loss of fascicular organization, play an additional role besides the finding of reduced cross linking.

Dynamic heat capacity changes of laser-irradiated type I collagen films

BACKGROUND AND OBJECTIVE

A common assumption made in the thermal response of biological materials due to laser irradiation is the constancy of the specific heat capacity at constant pressure, CP. In this investigation, CP of pure hydrated Type I collagen films is measured in time during laser irradiation.

STUDY DESIGN/MATERIALS AND METHODS

A Nd:YAG laser scanning calorimeter is developed and used to test the constant heat capacity assumption by monitoring transient, laser-induced thermal transitions in the collagen films.

RESULTS

Results of preliminary studies on the irreversible, laser induced thermal denaturation of collagen with heating rates of up to 110 K/sec show a broad CP transition that can attain large values (20 J/g K).

CONCLUSION

The magnitude of the CP change that occurs in response to laser irradiation shows that the assumption of a constant CP when modeling heat transport in tissues is not always valid.

Bone metabolism in spinal cord injured individuals and in others who have prolonged immobilisation. A review

Immobilisation or disuse is a condition known to be associated with a decrease in bone mass, osteopenia and in some people leading to osteoporosis with an increased risk of fractures. In this condition, previous histomorphometric and biochemical reports have shown an uncoupling between bone formation and resorption, but the exact sequence of the events resulting in bone loss is still not fully understood. In spinal cord injury for instance, the main finding soon after the onset is decreased osteoblastic activity associated with a dramatic increase in bone degradation. The overall consequence of these metabolic events is the development of a rapid and severe osteoporosis only observed in the paralysed part of the body associated with the loss of biomechanical strength and the biosynthesis of a structurally modified matrix which is unable to sustain normal mechanical stress. This situation dramatically increases the risk of fractures. The same uncoupling phenomenon has been described in healthy individuals who have been submitted to long duration bedrest and also in astronauts during spaceflight; but the timing, intensity and the metabolic subset may be different as these people do recover after cessation of the disuse period, which does not occur in paralysed patients. As new accurate and sensitive non-invasive techniques have become available recently to assess bone and connective tissue metabolism, more information is now available regarding bone loss in paralysed and/or immobilised individuals. These techniques should be definitely helpful in orientating new therapeutic trials with drugs and/or procedures intended to correct the musculoskeletal deleterious effects of disuse. This paper is therefore aimed at a review of bone metabolism in those with a severe spinal cord injury, or with a long duration of bedrest, or with loss of biomechanical function, or with actual or simulated spaceflight, in all instances using non-invasive techniques.

Collagen II from articular cartilage and annulus fibrosus. Structural and functional implication of tissue specific posttranslational modifications of collagen molecules

Collagen II was isolated and characterized from hyaline cartilage (articular cartilage) and fibro-cartilage (annulus fibrosus). Collagen II from the latter tissue has a substantially higher degree of hydroxylation and glycosylation than that isolated from articular cartilage. The higher degree of posttranslational modification was associated with a slower electrophoretic mobility, a greater resistance to mammalian collagenase digestion and a higher thermal stability. An increase of glycosylation accelerates the initial steps in fibril formation of collagen molecules but slows down the following lateral growth. The newly formed aggregates of collagen II from annulus fibrosus consisted of fibrils with a smaller diameter.

Fulvic acid supplementation and selenium deficiency disturb the structural integrity of mouse skeletal tissue. An animal model to study the molecular defects of Kashin-Beck disease

High concentrations of fulvic acid and selenium deficiency are the main causative factors of Kashin-Beck disease, an endemic, chronic and degenerative osteoarticular disorder found in China. In the search for an animal model of this disease, mice were exposed to these pathogenetic conditions for two generations and the collagen types from skin, bone and cartilage were analysed. The growth of the treated mice was slightly retarded, and the rate of reproduction was lower in animals maintained on a fulvic acid-supplemented and/or selenium-deficient diet. Irregular bone formation was seen by radiography and morphometry. Biochemical analysis indicated that lysine residues in collagen I from bone and in collagen II from cartilage were overmodified. The values of Hyl/(Hyl+Lys) in bone collagen alpha 1(I) chains from treated mice were about 0.434-0.484, i.e. substantially higher than that of the control (0.277). The values of this parameter for collagen II were 0.482 for control and 0.546-0.566 for treated mice. The melting temperature of collagen I from bones of treated mice was 1 degrees C lower than that of control collagen, indicating decreased thermal stability. The breakage point of the tibiae of treated mice occurred at a lower preload force than for controls, suggesting that the overmodified and thermally less stable collagen molecules are causally related to a lower mechanical strength of bones.