Collagen fibrillogenesis: a mechanism of structural biology

Cutaneous wound healing after treatment with plant-derived human recombinant collagen flowable gel

Chronic wounds, particularly diabetic ulcers, represent a main public health concern with significant costs. Ulcers often harbor an additional obstacle in the form of tunneled or undermined wounds, requiring treatments that can reach the entire wound tunnel, because bioengineered grafts are typically available only in a sheet form. While collagen is considered a suitable biodegradable scaffold material, it is usually extracted from animal and human cadaveric sources, and accompanied by potential allergic and infectious risks. The purpose of this study was to test the performance of a flowable gel made of human recombinant type I collagen (rhCollagen) produced in transgenic tobacco plants, indicated for the treatment of acute, chronic, and tunneled wounds. The performance of the rhCollagen flowable gel was tested in an acute full-thickness cutaneous wound-healing rat model and compared to saline treatment and two commercial flowable gel control products made of bovine collagen and cadaver human skin collagen. When compared to the three control groups, the rhCollagen-based gel accelerated wound closure and triggered a significant jumpstart to the healing process, accompanied by enhanced re-epithelialization. In a cutaneous full-thickness wound pig model, the rhCollagen-based flowable gel induced accelerated wound healing compared to a commercial product made of bovine tendon collagen. By day 21 post-treatment, 95% wound closure was observed with the rhCollagen product compared to 68% closure in wounds treated with the reference product. Moreover, rhCollagen treatment induced an early angiogenic response and induced a significantly lower inflammatory response than in the control group. In summary, rhCollagen flowable gel proved to be efficacious in animal wound models and is expected to be capable of reducing the healing time of human wounds.

Inhibition of Enzyme Activities and the Antiwrinkle Effect of Polyphenol Isolated from the Persimmon Leaf (Diospyros kaki folium) on Human Skin

BACKGROUND

Many studies have been conducted to find a natural material that has high biologic functions for human skin without any side effects. Persimmon leaf has a substantial amount of tannins in different forms; therefore, it was selected as a target material.

OBJECTIVE

The biosynthesis rate of the collagen was also investigated to clarify the beneficial functions for the human skin.

METHODS

Persimmon leaves were obtained, extracted with 80% ethanol, and isolated into PFs I, II, and III after column chromatography using a Sephadex LH-20 column followed by thin-layer chromatography.

RESULTS

The xanthine oxidase inhibition effect of both PFs II and III was over 40% at a 100 ppm concentration. PF II, containing higher flavonoids levels, had a significantly higher tyrosinase inhibition than that of PF III. Collagenase inhibition was 16.3 and 8.1% for PF III and PF II, respectively, at 100 ppm. On the other hand, elastase inhibition activity was significantly higher in PF II than PF III. Collagen biosynthesis rates of PF III were over 25% from a 1 to 10 ppm concentration. Consequently, PFs isolated from the persimmon leaf can be used as natural materials or additives for human skin owing to their beneficial biologic functions, including the antiwrinkle effect and the inhibition of skin problems, for food or cosmetic compositions.

Synthesis and maturation of type I and type III collagens in endometrial adenocarcinoma

OBJECTIVE

The structure and distribution of type I and type III collagens in the extracellular matrix of malignant endometrium was evaluated for their roles in the development and progression of this neoplasm.

STUDY DESIGN

Collagen synthesis and deposition in endometrial adenocarcinomas was determined by immunohistochemical analysis of type I and type III procollagen and verified by computer-assisted morphometry and in situ hybridization.

RESULTS

In the stroma of well-differentiated adenocarcinomas increased intracellular collagen synthesis was observed in fibroblastic cells as well as increased extracellular formation of newly synthesized type I and type III procollagen. Collagen maturation was also rapid. In moderately differentiated tumors, destruction and dissolution occurred around invading islets, concomitantly with decreased deposits of both collagens, despite increases in corresponding mRNAs. In poorly differentiated neoplasms, solid epithelial islets coexisted with sparse and distinctly collagen-positive stroma. Poorly differentiated neoplasms also contained tumor cells exhibiting intracellular collagen staining as well as in situ hybridization signals. In highly malignant papillary adenocarcinomas, the tumor cells induced distinctly increased collagen synthesis and deposition of newly synthesized collagen but not the mature cross-linked protein.

CONCLUSIONS

In malignancy, compression of surrounding stroma and a fibroproliferative response with increased collagen synthesis and deposition may prevent tumor growth. In more advanced lesions, stromal dissolution may permit tumor spread and in highly malignant lesions an abnormal stroma may promote neoplasm progression.

Identification, characterization and localization of three proteins expressed by the porcine oviduct

At estrus, the oviduct undergoes endocrine-induced changes which provide an essential microenvironment for maturation of gametes, fertilization and embryonic development. Several oviduct expressed proteins which interact with gametes or embryos, including the oviduct-specific, estrogen-dependent glycoprotein (OGP), have been identified and characterized. The objective of the present study was to identify, characterize and localize other proteins expressed by the porcine oviduct during estrus that may function in an autocrine or paracrine manner to enhance fertilization and embryonic development. Oviducts were collected during the estrous cycle or early pregnancy, flushed and divided into functional segments, and portions of the infundibulum, ampulla and isthmus were fixed for immunocytochemical analysis or cultured. Culture media was semi-purified by heparin-agarose affinity chromatography, proteins were transferred to polyvinylidene fluoride (PVDF) membrane after two-dimensional (2D)-SDS-PAGE and three different proteins were identified, excised and subjected to N-terminal amino acid analysis. These proteins were identified as complement component C3b, the carboxy-terminal propeptide of alpha 1 (III) procollagen (PIIICP), and the heavy chain variable region of IgA. Electrophoresis and fluorography of media from Days 0 to 12 of early pregnancy or the estrous cycle revealed both spatial and temporal expression of C3b and IgA heavy chain but not PIIICP by the oviduct. Further, all three proteins were identified in oviduct fluid by electrophoresis, immunoblot or immunoprecipitation analysis. Complement component C3b and IgA heavy chain were immunolocalized in all three oviduct segments on all days; however, temporal and spatial differences were demonstrated. Staining was greater in the infundibulum and during estrus for all three identified proteins. In summary, three proteins expressed by the oviduct at estrus and during early pregnancy were identified; characterization and localization suggest they may play a critical role in protecting the luminal environment, participating in ECM remodeling and gamete interactions.

Trimerization of the amino propeptide of type IIA procollagen using a 14-amino acid sequence derived from the coiled-coil neck domain of surfactant protein D

The folding of a collagen triple helix usually requires the presence of additional sequences that contribute to the association and correct alignment of the collagen chains. We recently reported that the C-terminal neck and lectin domains of a collagenous C-type lectin, rat pulmonary surfactant protein D (SP-D), are sufficient to drive the trimerization of a heterologous type IIA procollagen amino propeptide sequence. However, the conformation of the resulting trimeric IIA propeptide and the specific contributions of the SP-D sequence to trimerization were not elucidated. In the present study, we show that trimerization of the fusion protein is associated with correct folding of the collagen helix within the IIA propeptide domain (as assessed by circular dichroism) and that the constituent chains are hydroxylated. Chemical cross-linking and analytical ultracentrifugation showed that the IIA amino-propeptide retains its trimeric configuration even after proteolytic removal of the SP-D domains. By contrast, IIA amino-propeptides synthesized without fusion to the neck or lectin domains are assembled exclusively as monomers. To localize the trimerization sequence, mutant chimeric cDNA constructs were designed containing premature termination codons within the coiled-coil neck domain. A short, 14-amino acid sequence corresponding to the first two heptad repeats of the neck domain was sufficient to drive the trimeric association of the IIA amino-propeptide alpha-chains. However, deletion of the collagen domain resulted in the secretion of monomers. These studies demonstrate that two heptad repeats are sufficient for trimeric association of the propeptide but indicate that cooperative interactions between the coiled-coil and collagen domains are required for the formation of a stable helix.

Semiquantitative analysis of collagen types in the hypertrophied left ventricle

Cardiac fibrosis is a characteristic feature of left ventricular hypertrophy. The aim of this study was to develop a simple and accurate method to analyse collagen accumulation, taking into account the variation in cardiac muscle fibre orientation and nonuniform collagen distribution. This technique was used to determine the amount and types of collagen that accumulate during pressure overload cardiac hypertrophy. These data were correlated with myocyte size, and with the diastolic stress-strain relationship of the intact myocardium. Myocyte size was significantly increased in the hypertrophied hearts, compared with age and sex matched controls (control 363 +/- 25 microm2 vs experimental 244 +/- 12 microm2; mean +/- S.E., P < 0.05). No overall collagen accumulation was observed in the hypertrophied hearts, but a significant increase in collagen I was found with a reduction in the amount of collagen III in experimental animals. Since no increase in diastolic stiffness of the hearts was observed, these results indicate that an increase in the overall collagen content of the heart, rather than the upregulation of a specific type, may be necessary to cause diastolic dysfunction.

Immuno-electron-microscopic localization of types III pN-collagen and IV collagen, laminin and tenascin in developing and adult human spleen

The distribution of the extracellular matrix proteins types III pN-collagen and IV collagen, laminin and tenascin was investigated in fetal, infant, and adult human spleens by using immuno-electron microscopy. The presence of type III pN-collagen was assessed by using an antibody against the aminoterminal propeptide of type III procollagen. All the proteins other than type III pN-collagen were found in reticular fibers throughout development. In the white pulp of the fetus aged 16 gestational weeks, only an occasional type III pN-collagen-containing fibril was present, although type III pN-collagen was abundant in the reticular fibers of the red pulp. Conversely, in adults, most of the reticular fibers of the white pulp, but not of the red pulp, were immunoreactive for type III pN-collagen. Ring fibers, the basement membranes of venous sinuses, were well developed in both infant and adult spleens. The first signs of their formation could be seen as a discontinuous basement membrane, which was immunoreactive for type IV collagen, laminin, and tenascin in the fetus aged 20 gestational weeks. Intracytoplasmic immunoreactivity for all the proteins studied was visible in the mesenchymal cells of the fetus aged 16 gestational weeks and in the reticular cells of the older fetuses, which also showed labeling for type IV collagen and laminin in the endothelial cells. The results suggest that proteins of the extracellular matrix are produced by these stationary cells.

Dilated cardiomyopathy is associated with an increase in the type I/type III collagen ratio: a quantitative assessment

OBJECTIVES

The aim of this study was to quantify total collagen and the type I/type III collagen ratio and their localization in hearts with dilated cardiomyopathy.

BACKGROUND

Patients with dilated cardiomyopathy have an increase in intramyocardial fibrillar collagen. Types I and III are the main constituents and have different physical properties that may affect cardiac compliance.

METHODS

Nineteen hearts with dilated cardiomyopathy were studied (17 cardiac explants, 2 hearts obtained at autopsy) and compared with reference hearts. Total collagen was determined by hydroxyproline analysis. Collagen types I and III were analyzed using the cyanogen bromide method and immunohistochemical analysis followed by microdensitophotometric quantification. Localization of collagen types I and III was established at the light and electron microscopic levels. Immunoelectron microscopy provided information regarding their localization.

RESULTS

Total collagen and the collagen type I/type III ratio were increased in hearts with dilated cardiomyopathy (p < 0.05). Electron microscopy showed a diffuse increase in collagen fibrils in the endomysium; the perimysium showed an inhomogeneous increase. Collagen fibrils were thicker, and fibrous long-spacing collagen occurred in the endomysium. Immunoelectron microscopic findings confirmed an increase in type I collagen.

CONCLUSIONS

Hearts with dilated cardiomyopathy have a statistically significant increase in the collagen type I/type III ratio. The changes occur in the endomysium and perimysium, although with differences in distribution. These changes in intramyocardial collagen may be clinically relevant because they may affect cardiac rigidity and, therefore, eventually may render the heart less compliant. Further studies are needed to evaluate at what point in the course of the disease these changes appear.

The hepatic extracellular matrix. I. Components and distribution in normal liver

The unique nature of the hepatic extracellular matrix (ECM) is predicated by the special configuration of the space of Disse. Whereas other epithelial organs have two basement membranes (BM) and a substantial ECM interposed between endothelial and epithelial cells, the liver lobule has no BM and only an attenuated ECM, consisting mostly of fibronectin, some collagen type I, and minor quantities of types III, IV, V, and VI. This configuration, together with the abundant fenestrations and gaps of the sinusoidal endothelial cells, seems ideally suited to facilitate the rapid bidirectional exchange of macromolecules normally taking place between plasma and hepatocytes. During organogenesis, the liver anlage is vascularized by continuous capillaries with BM, but by day 13.5 of development (in the rat) the vessels in the immediate proximity of hepatocytes become fenestrated, lacking specialized junctions and BM, suggesting that the hepatocytes produce signals capable of modulating the endothelial phenotype. In regeneration, hepatocyte proliferation precedes vascular proliferation resulting in the formation of hepatocyte clusters that, temporarily, lack sinusoids. Eventually, vascular proliferation follows and the normal hepatocyte-vascular relationships are restored. During this period laminin synthesis by Ito cells is prominent. As soon as hepatocytes become stable, secretion of the sinusoid phenotype-maintaining factors resumes and laminin synthesis and secretion terminates. The interplay between extracellular matrix and liver cells is essential for normal homeostasis and its modification results in deranged hepatic function.

Developmental changes in the type I procollagen processing pathway in chick-embryo cornea

Type I procollagen processing in chick-embryo corneas was studied at days 12, 14 and 17 of development. Pulse-chase experiments and electrophoretic analysis of salt-soluble extracts showed developmental changes in the processing pathway. A kinetic model was fitted to the data to determine rate constants for processing of both N- and C-propeptides. Data for pro alpha 1(I)-chain processing and pro alpha 2(I)-chain processing were fitted separately (where pro means procollagen). Between days 12 and 17 the relative flux through the pC-collagen (procollagen chain lacking the N-propeptide) and pN-collagen (procollagen chain lacking the C-propeptide) pathways increased approx. 4-fold. Pro alpha 1(I) chains and pro alpha 2(I) chains were processed by slightly different routes. Variations in the rate constants were compared with electron-microscopic measurements of collagen fibril diameters at each stage of development. Diameters increased by less than 10% over the period from 12 to 17 days. It was concluded that fibril diameters are relatively insensitive to the pathway of procollagen processing in the salt-soluble pool.

Distribution of laminin and types IV and III collagen in fetal, infant and adult human spleens

The immunohistochemical distribution of the basement membrane (BM) proteins, laminin and type IV collagen, and interstitial type III collagen was investigated in 12 fetal spleens at the 15th-38th gestational weeks (g.w.) and in spleens of 8 infants from term to 4 years. The results were compared with the distribution of the same proteins in adult human spleen. BM proteins were found to be abundantly present in the red pulp of all spleens during the whole of development. The content of type III collagen gradually decreased with advancing age and, in adult spleen, there were only occasional positively staining fibers in Billroth's cords. This finding indicates that the composition of reticular fibers in the red pulp of spleen is different from the reticular fibers elsewhere in lymphoreticular tissue. Early signs of ring fiber formation in the walls of venous sinuses were detectable at the 15th-19th g.w., although their more complete development occurred relatively late from the 36th g.w. onwards. Ring fibers contained both laminin and type IV collagen in all the investigated spleens. They never stained for type III collagen. The developing white pulp was positive for BM proteins, but showed no staining for type III collagen at the 15th g.w. At later ages, the white pulp stained similarly for both BM proteins and type III collagen.

Extracellular matrix of the skin: 50 years of progress

The extracellular connective tissue matrix of the skin is a complex aggregate of distinct collagenous and non-collagenous components. Optimal quantities and delicate interactions of these components are necessary to maintain normal physiologic properties of skin. This overview summarizes the progress made in understanding the normal biology and biochemistry of the extracellular matrix, and will highlight cutaneous diseases with underlying molecular defects in the structure and expression of extracellular matrix components.

Localization of the expression of types I, III, and IV collagen, TGF-beta 1 and c-fos genes in developing human calvarial bones

Total RNA extracted from developing calvarial bones of 15- to 18-week human fetuses was studied by Northern hybridization: in addition to high levels of type I collagen mRNAs, the presence of mRNAs for type III and type IV collagen, TGF-beta and c-fos was observed. In situ hybridization of sections containing calvarial bone, overlying connective tissues, and skin was employed to identify the cells containing these mRNAs. Considerable variation was observed in the distribution of pro alpha 1(I) collagen mRNA in osteoblasts: the amount of the mRNA in cells at or near the upper surface of calvarial bone was distinctly greater than that in cells at the lower surface, indicating the direction of bone growth. High levels of type I collagen mRNAs were also detected in fibroblasts of periosteum, dura mater, and skin. Type III collagen mRNA revealed a considerably different distribution: the highest levels were detected in upper dermis, lower levels were seen in fibroblasts of the periosteum and the fibrous mesenchyme between bone spiculas, and none was seen in osteoblasts. Type IV collagen mRNAs were only observed in the endothelial cells of blood capillaries. Immunohistochemical localization of type III and IV collagens agreed well with these observations. The distribution of TGF-beta mRNA resembled that of type I collagen mRNA. In addition, high levels of TGF-beta mRNA were observed in osteoclasts of the calvarial bone. These cells, responsible for bone resorption, were also found to contain high levels of c-fos mRNA. Production of TGF-beta by osteoclasts and its activation by the acidic environment could form a link between bone resorption and new matrix formation.

Systemic scleroderma. Clinical and pathophysiologic aspects

Systemic scleroderma is a generalized disease of connective tissue involving mainly the skin, the gastrointestinal tract, the lungs, the heart, and the kidneys. It can be present in different forms, of which acroscleroderma, with limited cutaneous and extracutaneous involvement, and diffuse scleroderma within a more rapid progression are most characteristic. Circulating antibodies against antinucleolar antigens are present in most patients with systemic scleroderma. They are helpful for establishing a classification and for determining the prognosis of the disease; their involvement in the pathogenesis, however, is still unclear. Alterations of the blood vessels and induction of fibroblasts by potent mediators are thought to play an important role in the early phase of scleroderma. Therefore early diagnosis is required, which then can initiate vasoactive therapy. In patients with systemic scleroderma, who also suffer from additional myositis, interstitial lung diseases, or arthritis, anti-inflammatory treatment with prednisolone and azathioprine is suggested. Development and progression of fibrosis cannot yet be influenced sufficiently. Only D-penicillamine affecting cross-linking of collagen has been widely used in scleroderma and has some beneficial effect.

Comparative structural studies of reconstituted and native type I and type II collagen fibrils by low-angle X-ray diffraction

Acid-soluble and pepsin-soluble type I collagen from calf skin and pepsin-soluble type II collagen from bovine articular cartilage were precipitated in fibrillar form by various methods. Reconstituted native-like fibrils were analysed by low-angle X-ray diffraction, and the patterns were compared with those obtained with native type I (rat tail tendon) and type II fibrils (bovine articular cartilage). For both orientated and disorientated forms of these samples, we measured the ratio of the first/third-order intensities of the meridional diffraction peaks which are associated with the gap-filling. The values obtained with the reconstituted native-like fibrils (types I and II) were double and 20-times the values, respectively, measured for rat tail tendon and bovine articular cartilage. These differences reflect the extent of specific interactions of other components (proteoglycans) at the gap level along the collagen fibrils in the two tissues.