Characterization of human type II procollagen and collagen-specific antibodies and their application to the study of human type II collagen processing and ultrastructure

Development of a rapid, efficient, and reusable magnetic bead-based immunocapture system for recombinant human procollagen type II isolation from yeast fermentation broth

Recombinant collagen production, especially using yeasts as expression systems, could represent a promising alternative over traditional extractive methods from animal sources, offering controllable, scalable, and high-quality products. Monitoring the efficiency and efficacy of procollagen/collagen expression, especially in the initial fermentation phases, can be difficult and time consuming, as biological matrices necessitate purification and commonly used analytical methods are only partially informative. We propose a straightforward, efficient, and reusable immunocapture system able to specifically isolate human procollagen type II from fermentation broths and to release it in few experimental steps. A recovered sample allows for a detailed characterization providing information on structural identity and integrity, which can strongly support the monitoring of fermentation processes. The immunocapture system relies on the use of protein A-coated magnetic beads which have been functionalized and cross-linked with a human anti-procollagen II antibody (average immobilization yield of 97.7%) to create a stable and reusable support for the specific procollagen fishing. We set up the binding and release conditions ensuring specific and reproducible binding with a synthetic procollagen antigen. The absence of non-specific interaction with the support and binding specificity was demonstrated, and the latter was also confirmed by a peptide mapping epitope study in reversed-phase liquid chromatography high-resolution mass spectrometry (RP-LC-HRMS). The bio-activated support proved to be reusable and stable over 21 days from the initial use. Finally, the system was successfully tested on a raw yeast fermentation sample to provide a proof of concept of the applicability within recombinant collagen production.

Clinical outcome of autologous chondrocyte implantation is correlated with infrared spectroscopic imaging-derived parameters

OBJECTIVE

To investigate whether Fourier transform infrared imaging spectroscopy (FT-IRIS), a modality based on molecular vibrations, is a viable alternative to histology and immunohistochemistry (IHC) for assessment of tissue quality and patient clinical outcome.

METHODS

Osteochondral biopsies were obtained from patients (9-65 months post-surgery) who underwent an autologous chondrocyte implantation (ACI) procedure to repair a cartilage defect (N = 14). The repair tissue was evaluated histologically by OsScore grading, for the presence of types I and II collagen by IHC, and for proteoglycan (PG) distribution and collagen quality parameters by FT-IRIS. Patient clinical outcome was assessed by the Lysholm score.

RESULTS

Improvement in Lysholm score occurred in 79% of patients. IHC staining showed the presence of types I and II collagen in all samples, with a greater amount of collagen type II in the deep zone. The amount and location of immunostaining for type II collagen correlated to the FT-IRIS-derived parameters of relative PG content and collagen helical integrity. In addition, the improvement in Lysholm score post-ACI correlated positively with the OsScore, type II collagen (IHC score) and FT-IRIS-determined parameters. Regression models for the relation between improvement in Lysholm score and either OsScore, IHC area score or the FT-IRIS parameters all reached significance (p < 0.01). However, the FT-IRIS model was not significantly improved with inclusion of the OsScore and IHC score parameters.

CONCLUSION

Demonstration of the correlation between FT-IRIS-derived molecular parameters of cartilage repair tissue and patient clinical outcome lays the groundwork for translation of this methodology to the clinical environment to aid in the management of cartilage disorders and their treatment.

Transcriptional inhibition of type I collagen gene expression in scleroderma fibroblasts by the antineoplastic drug ecteinascidin 743

We previously showed that COL1A1 expression is up-regulated at the transcriptional level in systemic sclerosis (SSc) fibroblasts and that the CCAAT-binding factor (CBF) is involved in this increased expression. Ecteinascidin 743 (ET-743) is a chemotherapeutic agent that binds with sequence specificity to the minor groove of DNA and inhibits CBF-mediated transcriptional activation of numerous genes. Therefore, we examined the effects of ET-743 on the increased COL1A1 expression in SSc fibroblasts. The drug caused a potent and dose-dependent inhibition of type I collagen biosynthesis, which reached 70-90% at 700 pM without affecting cell viability. The same drug concentration caused 60-80% reduction in COL1A1 mRNA levels. The stability of the corresponding transcripts was not affected. In vitro nuclear transcription assays demonstrated a 54% down-regulation of COL1A1 transcription. Transient transfections with COL1A1 promoter constructs containing the specific CBF binding sequence into SSc cells previously treated with 700 pM ET-743 failed to show an effect on COL1A1 promoter activity. Furthermore, ET-743 did not affect the binding of CBF or Sp1 transcription factors to their cognate COL1A1 elements. However, treatment with 700 pM ET-743 of stably transfected NIH 3T3 cells expressing a human type II procollagen gene under the control of the human COL1A1 promoter caused a greater than 50% reduction in the production of type II procollagen and a similar decrease in the corresponding type II procollagen transcripts. These results indicate that ET-743 is a potent inhibitor of COL1A1 transcription. However, this effect cannot be explained by a direct effect on CBF binding to the COL1A1 promoter. Although the exact mechanisms responsible for the transcriptional inhibition of COL1A1 by ET-743 are not apparent, our observations suggest that the drug may be an effective agent to decrease collagen overproduction in SSc and other fibrotic diseases.

Glucosamine sulfate modulates the levels of aggrecan and matrix metalloproteinase-3 synthesized by cultured human osteoarthritis articular chondrocytes

OBJECTIVE

The functional integrity of articular cartilage is determined by a balance between chondrocyte biosynthesis of extracellular matrix and its degradation. In osteoarthritis (OA), the balance is disturbed by an increase in matrix degradative enzymes and a decrease in biosynthesis of constitutive extracellular matrix molecules, such as collagen type II and aggrecan. In this study, we examined the effects of the sulfate salt of glucosamine (GS) on the mRNA and protein levels of the proteoglycan aggrecan and on the activity of matrix metalloproteinase (MMP)-3 in cultured human OA articular chondrocytes.

DESIGN

Freshly isolated chondrocytes were obtained from knee cartilage of patients with OA. Levels of aggrecan and MMP-3 were determined in culture media by employing Western blots after incubation with GS at concentrations ranging from 0.2 to 200 microM. Zymography (casein) was performed to confirm that effects observed at the protein level were reflected at the level of enzymatic activity. Northern hybridizations were used to examine effects of GS on levels of aggrecan and MMP-3 mRNA. Glycosaminoglycan (GAG) assays were performed on the cell layers to determine levels of cell-associated GAG component of proteoglycans.

RESULTS

Treatment of OA chondrocytes with GS (1.0-150 microM) resulted in a dose-dependent increase in aggrecan core protein levels, which reached 120% at 150 microM GS. These effects appeared to be due to increased expression of the corresponding gene as indicated by an increase in aggrecan mRNA levels in response to GS. MMP-3 levels decreased (18-65%) as determined by Western blots. Reduction of MMP-3 protein was accompanied by a parallel reduction in enzymatic activity. GS caused a dose-dependent increase (25-140%) in cell-associated GAG content. Chondrocytes obtained from 40% of OA patients failed to respond to GS.

CONCLUSIONS

The results indicate that GS can stimulate mRNA and protein levels of aggrecan core protein and, at the same time, inhibit production and enzymatic activity of matrix-degrading MMP-3 in chondrocytes from OA articular cartilage. These results provide a cogent molecular mechanism to support clinical observations suggesting that GS may have a beneficial effect in the prevention of articular cartilage loss in some patients with OA.

Regulation of type-II collagen gene expression during human chondrocyte de-differentiation and recovery of chondrocyte-specific phenotype in culture involves Sry-type high-mobility-group box (SOX) transcription factors

During ex vivo growth as monolayer cultures, chondrocytes proliferate and undergo a process of de-differentiation. This process involves a change in morphology and a change from expression of chondrocyte-specific genes to that of genes that are normally expressed in fibroblasts. Transfer of the monolayer chondrocyte culture to three-dimensional culture systems induces the cells to re-acquire a chondrocyte-specific phenotype and produce a cartilaginous-like tissue in vitro. We investigated mechanisms involved in the control of the de-differentiation and re-differentiation process in vitro. De-differentiated chondrocytes re-acquired their chondrocyte-specific phenotype when cultured on poly-(2-hydroxyethyl methacrylate) (polyHEMA) as assayed by morphology, reverse transcriptase PCR of chondrocyte-specific mRNA, Western-blot analysis and chondrocyte-specific promoter activity. Essentially, full recovery of the chondrocyte-specific phenotype was observed when cells that had been cultured for 4 weeks on plastic were transferred to culture on polyHEMA. However, after subsequent passages on plastic, the phenotype recovery was incomplete or did not occur. The activity of a gene reporter construct containing the promoter and enhancer from the human type-II collagen gene (COL2A1) was modulated by the culture conditions, so that its transcriptional activity was repressed in monolayer cultures and rescued to some extent when the cells were switched to polyHEMA cultures. The binding of Sry-type high-mobility-group box (SOX) transcription factors to the enhancer region was modulated by the culture conditions, as were the mRNA levels for SOX9. A transfected human type-II collagen reporter construct was activated in de-differentiated cells by ectopic expression of SOX transcription factors. These results underscore the overt change in phenotype that occurs when chondrocytes are cultured as monolayers on tissue-culture plastic substrata.

Stable transfection of human fetal chondrocytes with a type II procollagen minigene: expression of the mutant protein and alterations in the structure of the extracellular matrix in vitro

OBJECTIVE

To perform stable transfections of human chondrocytes under conditions that allow the maintenance of the chondrocyte-specific phenotype, and to examine the effects of the stable transfection of a mutated type II procollagen gene (COL2A1) on the structure of the cartilaginous extracellular matrix produced in vitro.

METHODS

A type II procollagen minigene that lacks exons 16-27 was stably transfected into human fetal epiphyseal chondrocytes in vitro. Expression of the minigene was detected by reverse transcriptase-polymerase chain reaction, and the encoded protein was identified by Western blot with a human type II collagen-specific antibody. The cartilaginous extracellular matrix produced by the cultured transfected chondrocytes was characterized using histochemical staining, polarized light microscopy analysis, and transmission electron microscopy.

RESULTS

A shortened type II collagen encoded by the transfected minigene was biosynthesized and produced in the cultures of transfected cells. Histologic analyses demonstrated a more dense, negatively charged cartilaginous matrix in control cultures. In contrast, COL2A1 minigene-transfected cultures were more cellular, were populated with cells of irregular shape and less-chondrocytic appearance, contained abundant intracellular dense granules, and were surrounded by a less-dense matrix. Polarized light microscopy and transmission electron microscopy revealed a well-organized collagen fibrillar matrix in untransfected, control chondrocyte cultures, while the matrix in the transfected cultures was less birefringent and contained numerous truncated collagen fibrils.

CONCLUSION

The findings illustrate the feasibility of gene transfer into human fetal chondrocytes under conditions that allow the preservation of their specific phenotype, and also shed light on the function of type II collagen in the maintenance of the structural integrity of articular cartilage matrix.

Restoration of normal bone development by human homologue of collagen type II (COL2A1) gene in Col2a1 null mice

Development of the vertebrate skeleton is a highly complex process in which collagen type II plays a vital role in the formation of long bones via endochondral ossification. Collagen type II, which is encoded by a single COL2A1/ Col2a1 gene, is the most abundant structural protein in the cartilage matrix, where it undergoes complex interactions with several other proteins. The sequence of mature collagen type II chains, each with about 1,100 amino acids, is conserved between different mammalian species. There are 37 amino acid positions that are different between mouse and human collagen type II. Previously, we have demonstrated that transgenic mice, in which Col2a1 gene is knocked out, exhibit a lethal phenotype due to the absence of endochondral bone formation. To investigate whether the biological role of collagen type II is conserved between the species, human COL2A1 gene was expressed in Col2a1 null mice by crossing with transgenic mice in which human COL2A1 gene was integrated. The collagen type II from human gene rescued the lethal phenotype in null mice, indicating that the biological function of collagen type II is conserved between human and mouse. The animals exhibited normal endochondral bone formation and a normal growth plate in tibio-tarsal joint. Chondrocytes isolated from the cartilage of these mice secreted human protein, suggesting that the animals incorporated heterologous protein to form cartilage which is essentially "humanized." The animals reached puberty and produced normal progeny. A completely normal phenotype in newborns indicates that human COL2A1 gene is expressed properly both temporally and spatially. These animals may be useful to generate models to study the effect of COL2A1 mutations on skeletal development in humans by introducing mutated gene constructs either into embryos or by crossing with transgenic animals with COL2A1 mutations.

Detection and characterization of Sp1 binding activity in human chondrocytes and its alterations during chondrocyte dedifferentiation

We have detected DNA binding activity for a synthetic oligonucleotide containing an Sp1 consensus sequence in nuclear extracts from human chondrocytes. Changes in the levels of Sp1 oligonucleotide binding activity were examined in nuclear extracts from freshly isolated human chondrocytes, from chondrocytes that had been cultured under conditions that allowed the maintenance of a chondrocyte-specific phenotype on plastic dishes coated with the hydrogel poly(2-hydroxyethyl methacrylate), and from chondrocytes induced to dedifferentiate into fibroblast-like cells by passage in monolayer culture on plastic substrata. It was observed that Sp1 binding was 2-3-fold greater in nuclear extracts from dedifferentiated chondrocytes than in nuclear extracts from either freshly isolated chondrocytes or from cells cultured in suspension. The Sp1 binding activity was specific, since it was competed by unlabeled Sp1 but not by AP1 or AP2. The addition of a polyclonal antibody against Sp1 to nuclear extracts from freshly isolated chondrocytes or to extracts isolated from chondrocytes cultured in monolayer decreased the binding of Sp1 by approximately 85%. However, when the same experiment was carried out with nuclear extracts prepared from cells cultured on poly(2-hydroxyethyl methacrylate)-coated plates, only a very slight inhibition of Sp1 binding was observed. When fragments of the COL2A1 promoter containing putative Sp1 binding sites amplified by polymerase chain reaction were examined, it was found that the amounts of DNA-protein complex formed with nuclear extracts from dedifferentiated chondrocytes were 2-3-fold greater than the amounts formed with nuclear extracts from freshly isolated chondrocytes or from cells cultured in suspension. Quantitation of DNA binding activity by titration experiments demonstrated that nuclear extracts from fibroblast-like cells contained approximately 2-fold greater Sp-1 specific binding activity than nuclear extracts from chondrocytes. The direct role of Sp1 in type II collagen gene transcription was demonstrated by co-transfection experiments of COL2A1 promoter-CAT constructs in Drosophila Schneider line L2 cells that lack Sp1 homologs. This is the first demonstration of Sp1 binding activity in human chondrocytes and of differences in Sp1 DNA binding activity between differentiated and dedifferentiated chondrocytes.