Biosynthesis of procollagen [(pro alpha 1 V)2 (pro alpha 2 V)] by chick tendon fibroblasts and procollagen (pro alpha 1 V)3 by hamster lung cell cultures

Collagen V localizes to pericellular sites during tendon collagen fibrillogenesis

During tendon development collagen fibrillogenesis occurs in extracellular micro-domains defined by the tenocytes. This permits cellular regulation of the extracellular steps involved in the tissue-specific matrix assembly required for function. The hypothesis tested here is that collagen V associates with the tenocyte surface where it functions in regulation of collagen assembly and cell-directed fibril deposition. The in vitro and in vivo data demonstrate that collagen V is a quantitatively minor component of the tendon. It is preferentially localized on the tenocyte surface as distinct foci in tendons and in cell culture. In vitro data indicate that this interaction with the tenocyte is not HSPG GAG-dependent. Collagen V is present as the mature, processed form, is absent from the media, and is a significant part of the detergent-insoluble cell layer, presumably as part of a membrane-associated complex. In contrast, procollagen I is not efficiently processed and is found predominantly in the culture media. Our data suggest that the regulatory role of collagen V requires collagen V to occupy a different cellular niche from the structural collagen I. In monolayer cultures, the conversion to the tissue form of collagen V and its deposition with the cell layer suggest efficient engagement of procollagen V with pericellular receptors and processing enzymes. The secretion of collagen I into the media and inefficient processing of procollagen I suggest reduced accessibility to these pericellular molecules due to disengagement from the cell surface. This all points to differential spatial localization of collagen V as a mechanism to optimize its regulatory roles during the cell-surface directed steps in tendon collagen fibril assembly.

Col V siRNA engineered tenocytes for tendon tissue engineering

The presence of uniformly small collagen fibrils in tendon repair is believed to play a major role in suboptimal tendon healing. Collagen V is significantly elevated in healing tendons and plays an important role in fibrillogenesis. The objective of this study was to investigate the effect of a particular chain of collagen V on the fibrillogenesis of Sprague-Dawley rat tenocytes, as well as the efficacy of Col V siRNA engineered tenocytes for tendon tissue engineering. RNA interference gene therapy and a scaffold free tissue engineered tendon model were employed. The results showed that scaffold free tissue engineered tendon had tissue-specific tendon structure. Down regulation of collagen V α1 or α2 chains by siRNAs (Col5α1 siRNA, Col5α2 siRNA) had different effects on collagen I and decorin gene expressions. Col5α1 siRNA treated tenocytes had smaller collagen fibrils with abnormal morphology; while those Col5α2 siRNA treated tenocytes had the same morphology as normal tenocytes. Furthermore, it was found that tendons formed by coculture of Col5α1 siRNA treated tenocytes with normal tenocytes at a proper ratio had larger collagen fibrils and relative normal contour. Conclusively, it was demonstrated that Col V siRNA engineered tenocytes improved tendon tissue regeneration. And an optimal level of collagen V is vital in regulating collagen fibrillogenesis. This may provide a basis for future development of novel cellular- and molecular biology-based therapeutics for tendon diseases.

Cloning of mouse type VII collagen reveals evolutionary conservation of functional protein domains and genomic organization

Type VII collagen is the major component of anchoring fibrils, attachment structures necessary for stable association of the dermal-epidermal basement membrane to the underlying dermis. The critical role of the anchoring fibrils in providing integrity to the cutaneous basement membrane zone is attested to by demonstration of mutations in the type VII collagen gene (COL7A1) in patients with dystrophic epidermolysis bullosa. To gain insight into the evolutionary conservation of the type VII collagen gene, in this study we have cloned the entire mouse type VII collagen cDNA and elucidated the intron-exon organization of the corresponding gene, Col7a1. The coding region of the cDNA consists of 8832 nucleotides encoding a polypeptide of 2944 amino acids with a calculated molecular mass of approximately 295 kDa. Computer analysis predicted the presence of an 18-amino acid signal peptide. Comparison of the deduced mouse alpha1(VII) collagen polypeptide with the corresponding human sequence indicated 84.7% identity and 90.4% homology at the amino acid level. In addition, the domain organization, including imperfections and interruptions within the collagenous domain consisting of Gly-X-Y repeat sequences, was highly conserved. The unit of evolutionary period between the full-length human and mouse polypeptides was calculated to be 6.5 million years, however, suggesting relatively rapid evolutionary divergence in comparison to other collagen genes. Elucidation of the intron-exon organization of the mouse Col7a1 gene revealed 118 distinct exons, the same number as present in the human gene. These data indicate a high degree of structural conservation between the human and mouse type VII collagen, supporting the critical role of this collagen as the major component of the anchoring fibrils.

Diversity in the processing events at the N-terminus of type-V collagen

The processing of human collagen type-V chains was studied using anti-peptide polyclonal antibodies raised against peptide sequences at the N-terminal non-triple-helical region of pro-alpha 1(V) and pro-alpha 2(V) chains. The anti-peptide polyclonal antibody raised against positions 48-57 of the N-terminal alpha 2(V) sequence recognized the mature form of the human alpha 2(V) chain extracted without any proteolytic treatment from several tissues in the presence of a mixture of protease inhibitors. It also recognized the pro-alpha 2(V) and pN-alpha 2(V) collagen chains secreted in the cell-culture media of the rhabdomyosarcoma A204 cell line. The pN-alpha 2(V) collagen chain from this cell line migrated during electrophoresis with the alpha 2(V) chain obtained from tissues. This demonstrates that the alpha 2(V) chain in tissues is incompletely processed and is present as the pN-alpha 2(V) collagen chain which lacks the C-propeptide. In comparison, an anti-peptide polyclonal antibody raised against residues at positions 284-299 of the N-terminal alpha 1(V) human sequence failed to recognize the mature form of the alpha 1(V) chain while it reacted with the pN-alpha 1(V) collagen chain form. These results suggest that the alpha 1(V) chain undergoes a processing event in the N-terminal region that involves the removal of at least the first 284 residues. Amino acid sequence analysis was performed on cyanogen-bromide-generated or trypsin-generated peptides of the two electrophoretic bands obtained for the tissue form of collagen V. The slower-migrating band corresponding to the intact alpha 1(V) chain gave, as expected, only sequences corresponding to the alpha 1(V) chain. However, the band previously considered to be the intact alpha 2(V) chain also gave sequences for the alpha 1(V) chain in addition to the alpha 2(V) chain. This result indicates the presence in tissue extracts of a further processed form of alpha 1(V) chain which migrates with the intact alpha 2(V) chain. On further analysis, we observed that the two bands of the tissue form of collagen V occurred in a 1:1 ratio whereas, after the pepsin digestion to remove non-collagenous regions, two bands were observed with an alpha 1(V)/alpha 2(V) chain ratio of 3:1. These results indicate that the alpha 1(V) chain exists in an additional stoichiometry, different from [alpha 1(V)]2 alpha 2(V).(ABSTRACT TRUNCATED AT 400 WORDS)

Immunoelectron microscopical evidence that type V collagen is a fibrillar collagen: importance for an aggregating capability of the preparation for reconstituting banding fibrils

Type V collagen has already been shown, in many immunohistochemical studies, to be widely distributed in connective tissues. Its supramolecular structure, however, has been unclear. We demonstrate that the major aggregates formed from type V collagen solution in vitro are fine fibrils with a D-periodic banding pattern. Further, by using the immunogold labeling method, we find that these fibrils react strongly with anti-type V collagen antibody. Electronmicroscopic examination showed three kinds of aggregate: fine fibrils with periodic banding pattern, fine fibrils without banding pattern, and non-fibrillar materials. Both striated and nonstriated fibrils, when incubated with rat polyclonal anti-human type V collagen IgG followed by incubation with 15 nm-gold conjugated goat anti-rat IgG, were labeled with colloidal gold. We conclude that type V can be classified as a fibrillar collagen. Also, from the present findings together with previous studies, we believe type V collagen may exist in vivo in various connective tissues as fine fibrils with a 67 nm-periodic banding pattern, by itself, or with type I or type III fibrillar collagen, being located between, and connecting the basal lamina and interstitial collagen fibers.

Covalent structure of collagen: amino acid sequence of three cyanogen bromide-derived peptides from human alpha 1(V) collagen chain

Type V collagen was prepared from human amnionic/chorionic membranes and separated into alpha 1(V) and alpha 2(V) polypeptide chains. The alpha 1(V) chain was digested with cyanogen bromide and nine peptides were obtained and purified. Three of the peptides, alpha 1(V)CB1, CB4, and CB7 having molecular weights of 5000, 8000, and 6000, respectively, were further analyzed by amino acid sequence analysis and thermolytic or tryptic digestions. CB1 contained 54 amino acids and identification of its complete sequence was aided by thermolysin digestion and isolation of two peptides, Th1 and Th2. CB4 contained 81 amino acids and sequence analysis of intact CB4 and five tryptic peptides provided us with its complete amino acid sequence. The peptide CB7 contained 67 amino acids and was cleaved into four tryptic peptides that were used for complete sequence analysis. The above results represent the first available covalent structure information on the alpha 1(V) collagen chain. These data enabled us to establish the location of these peptides within the helical structure of other collagen chains. CB4 was homologous to residues 66-145 in the collagen chain while CB1 represented residues 146-200 and CB7 was homologous with residues 201-269. This alignment was facilitated by identification of a helical collagen crossing site consisting of Hyl-Gly-His-Arg located at positions 87-90 in all collagen chains of this size thus far identified. Seventy-one percent homology (excluding Gly residues) was found between amino acids in this region of the alpha 1(XI) and of alpha 1(V) collagen chains while only 21 and 19% identity was calculated for the same region of alpha 2(V) and alpha 1(I) collagen chains, respectively.

Fractionation of type V collagen from carcinomatous and dysplasic breast in the presence of alkaline potassium chloride

A simple, one-step fractionation technique suitable for the finest quantitation of type V collagen from acidic mixtures of interstitial collagens is reported. The technique is based on the higher solubility of this collagen type in alkaline KCl-phosphate solution, and the purity of the sample has been monitored by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electron microscopic analyses. The latter reveal that the majority of the molecules are endowed with a thread portion and a terminal knob, and show a low tendency to originate ordered and reproducible polymers at low temperature.

Comparison of axial banding patterns in fibrils of type V collagen and type I collagen

Type V collagen and type I collagen were obtained from human placenta, essentially by salt fractionation. Precipitates were formed from mixed solutions of type V collagen and type I collagen in various ratios. They were incubated at 37 degrees C for 1 hour and negatively stained with 0.5% uranyl acetate (pH 4.4) at 37 degrees C. The specimens, seen by electron microscopy, were fibrils with a D-periodic banding pattern. Axial electron density profiles of collagen fibrils were obtained from selected electron micrographs by densitometric tracing. The slit width corresponded to 1.5 nm. The relative electron densities of overlap region vs. hole region were lower than 20% in fine fibrils containing a significant amount of type V collagen. It is suggested that the overlap region of such collagen fibrils may be loosely packed, being accessible to uranyl acetate, or the hole region may be filled by larger non-collagenous portions of type V collagen, resulting in loss of the light and dark alternation. Six to 8 white transverse lines were discerned per period and labeled consecutively with Arabic numerals. White lines 2 and 5 tended to merge with lines 1 and 4, respectively, in collagen fibrils formed from a solution containing a significant amount of type I collagen or pure type I collagen. The eight white lines corresponded to c2, c1, b2, b1, a4, a1, e1 and d with reference to their locations in the D-period. The locations of white lines in collagen fibrils which contain significant amount of type V collagen were identical with those in type I collagen fibrils. This is consistent with the primary structure that the axial distribution of charged amino acids in type V collagen is quite similar to that in type I collagen.

Localization of the alpha 3 (V) chain of type V collagen in human skin

Serum from goats immunized with human type V collagen chains that were cut out of polyacrylamide gels contained an antibody that recognized only type V collagen in an enzyme-linked immunoabsorbent assay and did not label laminin, fibronectin, or types I and IV collagen. Western blot analysis of the antibody showed that its determinant was the alpha 3 (V) chain of type V collagen. Indirect immunofluorescent staining of intact human skin with the antibody produced staining of the dermal blood vessels but not of the dermal-epidermal junction (DEJ). In contrast, both the dermal blood vessels and the DEJ were labeled by the antibody if the skin substrate was first split through the lamina lucida region of the DEJ by incubation in 1 M NaCl solution. Indirect immunoelectron microscopy confirmed the staining pattern found by immunofluorescence and defined the ultrastructural localization of type V collagen in skin. Type V collagen is localized within the DEJ to the lamina lucida region and polar aspects of the basal cell keratinocyte plasma membrane.

In vitro formation of hybrid fibrils of type V collagen and type I collagen. Limited growth of type I collagen into thick fibrils by type V collagen

Type V collagen and type I collagen were obtained from human placentas by pepsin treatment, followed by salt fractionation. The precipitates formed at 37 degrees C from a mixed solution of type V collagen and type I collagen, reacted with antibodies to either type V collagen or type I collagen. The precipitates seen by electron microscopy were fine flexible fibrils, with a D-periodic banding pattern. The average diameter of hybrid fibrils was smaller than 50 nm, when the proportion of type V collagen exceeded that of type I collagen. Type V collagen directly interacts with type I collagen in forming hybrid fibrils, resulting in limitation of the growth of type I collagen fibrils into thicker fibrils. We propose that the fibrils with a predominant type V collagen content may occur in the pericellular environment of various tissues, as a basic structure in connecting basal laminae with interstitial collagen fibrils.

In vitro formation of fine fibrils with a D-periodic banding pattern from type V collagen

Type V collagen was isolated from human placenta by limited pepsin treatment and purified by salt fractionation. A solution of type V collagen was dialyzed at 4 degrees C against phosphate-buffered saline or against 0.02 M Na2HPO4. Aggregates formed under these in vitro conditions from a pure type V collagen solution were examined by electron microscopy. The aggregates were fine flexible fibrils. The fibrils formed during incubation at 25 degrees C were of relatively uniform diameter, 34.8 +/- 9.1 nm and did not show an axial banding pattern. When the specimen was incubated at 37 degrees C, the fibrils were of slightly larger diameter, 38.2 +/- 9.1 nm and almost all the fibrils had the axial repeat pattern of 67 nm. The ability of type V collagen to form banding fibrils is discussed in relation in the localization of the collagen in tissues.

Biosynthesis of collagen

During the biosynthesis and assembly of collagen structures, disulfide links can serve several functions. During biosynthesis they successively stabilize intrapeptide folding and associations of three chains into one molecule. Studies on the refolding and reassociation of reduced and denatured carboxyl propeptides of procollagen I showed that successive interactions of folding and assembly are successively weaker. Disulfide bridges were reestablished within correctly refolded carboxyl propeptides. Rearrangements of disulfide bridges may occur during the processing of type V procollagen molecules as these collagens become incorporated into extracellular matrix. The basement membrane procollagen IV molecules become disulfide linked at each end into networks, and there are indications that further rearrangements of disulfide links may allow additional modulation.

Evidence that the collagen in the culture medium of Chinese hamster lung cells contains components related at the primary structural level to the alpha1(V) collagen chain

The collagenous protein synthesized by cultured Chinese hamster lung (CHL) cells and present in the culture medium has been isolated after limited pepsin digestion and differential salt precipitation. Molecular size analysis of this material indicates that the CHL cell medium collagen contains chains which exhibit an apparent molecular mass of approximately 85,000 Da. When chromatographed on CM-cellulose under denaturing conditions, the reduced and alkylated CHL cell medium collagen chains elute slightly after the human alpha1(I) chain but well before the pepsin-derived alpha1(V) chain, which is the constituent chain present in the CHL cell cellular matrix collagen. Analysis of the peptides derived by CNBr cleavage of the CHL medium collagen chains by chromatography on CM-cellulose reveals, however, that these chains contain peptides which correspond both in size and in chemical properties to those derived from the alpha1(V) collagen chain, but clearly lack two peptides (alpha1(V)-CB4 and alpha1(V)-CB5) which are normally present in pepsin-derived alpha1(V) chains. Furthermore, analysis of the CHL cell culture medium collagenous material obtained without pepsin digestion indicates the presence of collagenous chains that exhibit after reduction a molecular mass of approximately 160,000 Da, which is smaller than the proposed size of the pro alpha1(V) collagen chain. These results demonstrate that the collagenous protein present in the culture medium of CHL cells is directly related at the primary structural level to the alpha1(V) collagen chain, and it is postulated that this material represents the large fragment derived from a collagenase cleavage of the [pro alpha1(V)]3 molecules present in the cell layer. Furthermore, these results and previous reports indicate that the only identifiable genetic type of procollagen chain synthesized by this cloned cell line in culture corresponds to the pro alpha1(V) chain.

Protein disulphide-isomerase activity in various cells synthesizing collagen

A high correlation was found between the activities of protein disulphide isomerase and prolyl 4-hydroxylase when assayed in cells synthesizing various collagen types or the same type at markedly different rates. The highest activities of both enzymes were found in freshly isolated chick-embryo tendon and cartilage cells, intermediate activities in confluent cultures of human skin and lung fibroblasts and mouse 3T6 fibroblasts, and the lowest values in three human sarcoma cell lines, the difference in protein disulphide isomerase activity between the freshly isolated tendon cells and confluent simian-virus-40-transformed human lung fibroblasts being about 25-fold. All these differences are in good agreement with differences reported between the various cells in their rates of collagen synthesis. A great similarity was also found between the changes in the two enzyme activities measured per cell during the growth of 3T6 fibroblast cultures from the early logarithmic phase to the stationary phase. No correlation was found between protein disulphide isomerase activity and the type of collagen synthesized. The data suggest that protein disulphide isomerase may be involved in the formation of intra-chain and inter-chain disulphide bonds in procollagens, but there is no collagen type-related variation in this enzyme activity of a magnitude that would explain the marked differences in the rates of formation of inter-chain disulphide bonds between the various collagen types.

Nonhelical, fibronectin-binding basement-membrane collagen from endodermal cell culture

A novel method of affinity chromatography on insolubilized collagen-binding fragments of fibronectin was utilized to isolate a random-coil collagenous protein from culture media of mouse teratocarcinoma-derived endodermal cells. These cells also produced another collagenous protein, which did not bind to fibronectin but could be isolated by differential salt precipitation. The affinity-purified collagen differs from its conventionally isolated counterpart in that it is not triple-helical in structure, its polypeptides are not disulfide-crosslinked and it has affinity for fibronectin in its native state. Both collagens resemble previously characterized type IV basement-membrane collagens with respect to their amino acid composition, cyanogen bromide peptides, chain size, immunological reactivity and tissue localization. The random-coil collagen is directly active in promoting the attachment of some lines of cells, but for attachment of the endodermal cells addition of fibronectin is required. This suggests that the presence of nonhelical, fibronectin-binding collagen may have biological significance in the interaction of cells with the extracellular matrix.