Molecular definition and characterization of recombinant bovine CB8 and CB10: immunogenicity and arthritogenicity

Bioengineered Collagens

There is a great deal of interest in obtaining recombinant collagen as an alternative source of material for biomedical applications and as an approach for obtaining basic structural and biological information. However, application of recombinant technology to collagen presents challenges, most notably the need for post-translational hydroxylation of prolines for triple-helix stability. Full length recombinant human collagens have been successfully expressed in cell lines, yeast, and several plant systems, while collagen fragments have been expressed in E. coli. In addition, bacterial collagen-like proteins can be expressed in high yields in E. coli and easily manipulated to incorporate biologically active sequences from human collagens. These expression systems allow manipulation of biologically active sequences within collagen, which has furthered our understanding of the relationships between collagen sequences, structure and function. Here, recombinant studies on collagen interactions with cell receptors, extracellular matrix proteins, and matrix metalloproteinases are reviewed, and discussed in terms of their potential biomaterial and biomedical applications.

Effects of different crosslinking conditions on the chemical-physical properties of a novel bio-inspired composite scaffold stabilised with 1,4-butanediol diglycidyl ether (BDDGE)

Serious cartilage lesions (Outerbridge III, IV) may be successfully treated with a three-layered gradient scaffold made by magnesium-doped hydroxyapatite and type I collagen, manufactured through a bio-inspired process and stabilised by a reactive bis-epoxy (1,4-butanediol diglycidyl ether, BDDGE). Each layer was analysed to elucidate the effects of crosslinking variables (concentration, temperature and pH). The chemical stabilisation led to an homogeneous and aligned collagenous matrix: the fibrous structures switched to a laminar foils-based arrangement and organic phases acquired an highly coordinated 3D-organization. These morphological features were strongly evident when crosslinking occurred in alkaline solution, with BDDGE concentration of at least 1 wt%. The optimised crosslinking conditions did not affect the apatite nano-crystals nucleated into self-assembling collagen fibres. The present work allowed to demonstrate that acting on BDDGE reaction parameters might be an useful tool to control the chemical-physical properties of bio-inspired scaffold suitable to heal wide osteochondral defects, even through arthroscopic procedure.

A novel recombinant peptide containing only two T-cell tolerance epitopes of chicken type II collagen that suppresses collagen-induced arthritis

Immunotherapy of rheumatoid arthritis (RA) using oral-dosed native chicken or bovine type II collagen (nCII) to induce specific immune tolerance is an attractive strategy. However, the majority of clinical trials of oral tolerance in human diseases including RA in recent years have been disappointing. Here, we describe a novel recombinant peptide rcCTE1-2 which contains only two tolerogenic epitopes (CTE1 and CTE2) of chicken type II collagen (cCII). These are the critical T-cell determinants for suppression of RA that were first developed and used to compare its suppressive effects with ncCII on the collagen-induced arthritis (CIA) model. The rcCTE1-2 was produced using the prokaryotic pET expression system and purified by Ni-NTA His affinity chromatography. Strikingly, our results showed clearly that rcCTE1-2 was as efficacious as ncCII at the dose of 50 microg/kg/d. This dose significantly reduced footpad swelling, arthritic incidence and scores, and deferred the onset of disease. Furthermore, rcCTE1-2 of 50 microg/kg/d could lower the level of anti-nCII antibody in the serum of CIA animals, decrease Th1-cytokine INF-gamma level, and increase Th3-cytokine TGF-beta(1) produced level by spleen cells from CIA mice after in vivo stimulation with ncCII. Importantly, rcCTE1-2 was even more potent than native cCII, which was used in the clinic for RA. Equally importantly, the findings that the major T-cell determinants of cCII that are also recognized by H-2(b) MHC-restricted T cells have not previously been reported. Taken together, these results suggest that we have successfully developed a novel recombinant peptide rcCTE1-2 that can induce a potent tolerogenic response in CIA.

Pathogenesis of collagen-induced arthritis: modulation of disease by arthritogenic T-cell epitope location

Collagen-induced arthritis (CIA) is an animal model of human rheumatoid arthritis that can be induced in susceptible mice by immunization with type II collagen (CII) or with collagen fragments, including cyanogen bromide (CB) peptides. One susceptible mouse strain, B10.RIII (I-Ar), has previously been found to respond to two major T-cell determinants, namely CII 610-618 (GPAGTAGAR) within CB10 and CII 445-453 (GPAGPAGER) within CB8. Although CB10 contains the immunodominant determinant, it is not arthritogenic. Using recombinant techniques, the determinant within CB10 was mutated to rCB10(T614P,A617E), generating a recombinant CB10 that in effect contained the arthritogenic epitope. When used for immunization, rCB10(T614P,A617E) was arthritogenic. This suggested that the arthritogenic property was intrinsic to the epitope and unrelated to its position within the CII molecule. To test this hypothesis, additional mutants were generated. The wild-type T-cell epitope of CB10 was deleted from its natural position, and the 'arthritogenic' GPAGPAGER T-cell epitope was inserted into the C-terminal portion of the CB10 peptide. The resulting peptide induced arthritis in B10.RIII mice. Adding a second copy of the T-cell determinant to other sites within CB10, however, had varying results. A second T-cell epitope located at the C-terminus of rCB10 significantly increased the incidence and severity of arthritis, while determinants placed in other positions had little effect. These data indicate that the T-cell epitope has intrinsic arthritogenic properties, but there are positional and structural constraints that affect its arthritogenicity. Enhanced arthritis was associated with an increased T-cell proliferation to the peptides, an increase in the level of inflammatory cytokines, and higher levels of anti-CII immunoglobulin. These data suggest that the position and copy number of T-cell determinants also affect the overall immune T-cell responses.

Endoplasmic reticulum signaling as a determinant of recombinant protein expression

Generation of functional recombinant proteins requires efficient and undisturbed functioning of the ER-Golgi secretory pathway in host cells. In large-scale production, where target proteins are highly overexpressed, this pathway can be easily congested with unfolded or misfolded proteins. Accumulating evidence suggests that, in addition to responsibility for protein processing, ER is also an important signaling compartment and a sensor of cellular stress. Two ER responses have been described to arise from the overaccumulation of proteins: unfolded protein response (UPR) and ER overload response (EOR). UPR and EOR employ various mechanisms at the transcriptional and the translational levels to deal efficiently and appropriately with encountered stress. This review will outline the molecular bases of ER functioning and stress response, highlight the relevance of ER signaling to the large-scale cell culture productivity and discuss possible approaches to the improvement of the secretion capacities of recombinant cells.

Immunogenicity and arthritogenicity of recombinant CB10 in B10.RIII mice

Two major T cell determinants are recognized by I-Ar-specific T cells in CII, the immunodominant CII610-618 (GPAGT AGA R) within CB10 and the subdominant CII445-453 (GPAGP AGE R) within CB8. Although the determinants differ by only two residues, CB8 is capable of inducing collagen-induced arthritis (CIA), while CB10 is not. We, therefore, investigated the structural differences between the two determinants that are critical to inducing arthritis. When the CB10 determinant was mutated to that of CB8 using recombinant techniques, the resulting mutant rCB10T614P,A617E product became arthritogenic. Conversely, when the CB8 determinant was mutated to that of CB10, the resulting mutant CB8P449T,E452A was no longer arthritogenic. Comparison of the epitope specificity of the autoantibodies induced by wild-type CB10 and mutant rCB10T614P, A617E revealed no qualitative differences. T cells from mice immunized with either CB10 or mutant rCB10 produced predominantly Th1 cytokines when cultured with the immunizing Ag. In contrast, when cultured with mouse CII, T cells from mice immunized with the nonarthritogenic CB10 produced predominantly Th2 (IL-4 and IL-10) cytokines whereas the arthritogenic mutant rCB10 induced predominantly Th1 (IFN-gamma) cytokines. We conclude that the T cell cytokine response most critical for the induction of CIA is that induced against the corresponding homologous murine T cell determinant and, further, that the structural differences between the T cell determinants in CB8 and -10 are important in breaking self tolerance and inducing autoimmune response.