Formation of recombinant triple-helical [alpha 1(IV)]2 alpha 2(IV) collagen molecules in CHO cells

Status and developmental trends in recombinant collagen preparation technology

Recombinant collagen is a pivotal topic in foundational biological research and epitomizes the application of critical bioengineering technologies. These technological advancements have profound implications across diverse areas such as regenerative medicine, organ replacement, tissue engineering, cosmetics and more. Thus, recombinant collagen and its preparation methodologies rooted in genetically engineered cells mark pivotal milestones in medical product research. This article provides a comprehensive overview of the current genetic engineering technologies and methods used in the production of recombinant collagen, as well as the conventional production process and quality control detection methods for this material. Furthermore, the discussion extends to foresee the strides in physical transfection and magnetic control sorting studies, envisioning an enhanced preparation of recombinant collagen-seeded cells to further fuel recombinant collagen production.

Collagen- and hyaluronic acid-based hydrogels and their biomedical applications

Hydrogels have been widely investigated in biomedical fields due to their similar physical and biochemical properties to the extracellular matrix (ECM). Collagen and hyaluronic acid (HA) are the main components of the ECM in many tissues. As a result, hydrogels prepared from collagen and HA hold inherent advantages in mimicking the structure and function of the native ECM. Numerous studies have focused on the development of collagen and HA hydrogels and their biomedical applications. In this extensive review, we provide a summary and analysis of the sources, features, and modifications of collagen and HA. Specifically, we highlight the fabrication, properties, and potential biomedical applications as well as promising commercialization of hydrogels based on these two natural polymers.

Bioprinting of Collagen: Considerations, Potentials, and Applications

Collagen is the most abundant extracellular matrix protein that is widely used in tissue engineering (TE). There is little research done on printing pure collagen. To understand the bottlenecks in printing pure collagen, it is imperative to understand collagen from a bottom-up approach. Here it is aimed to provide a comprehensive overview of collagen printing, where collagen assembly in vivo and the various sources of collagen available for TE application are first understood. Next, the current printing technologies and strategy for printing collagen-based materials are highlighted. Considerations and key challenges faced in collagen printing are identified. Finally, the key research areas that would enhance the functionality of printed collagen are presented.

Advances in Plant-Derived Scaffold Proteins

Scaffold proteins form critical biomatrices that support cell adhesion and proliferation for regenerative medicine and drug screening. The increasing demand for such applications urges solutions for cost effective and sustainable supplies of hypoallergenic and biocompatible scaffold proteins. Here, we summarize recent efforts in obtaining plant-derived biosynthetic spider silk analogue and the extracellular matrix protein, collagen. Both proteins are composed of a large number of tandem block repeats, which makes production in bacterial hosts challenging. Furthermore, post-translational modification of collagen is essential for its function which requires co-transformation of multiple copies of human prolyl 4-hydroxylase. We discuss our perspectives on how the GAANTRY system could potentially assist the production of native-sized spider dragline silk proteins and prolyl hydroxylated collagen. The potential of recombinant scaffold proteins in drug delivery and drug discovery is also addressed.

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.

Frequency of COL4A3/COL4A4 mutations amongst families segregating glomerular microscopic hematuria and evidence for activation of the unfolded protein response. Focal and segmental glomerulosclerosis is a frequent development during ageing

Familial glomerular hematuria(s) comprise a genetically heterogeneous group of conditions which include Alport Syndrome (AS) and thin basement membrane nephropathy (TBMN). Here we investigated 57 Greek-Cypriot families presenting glomerular microscopic hematuria (GMH), with or without proteinuria or chronic kidney function decline, but excluded classical AS. We specifically searched the COL4A3/A4 genes and identified 8 heterozygous mutations in 16 families (28,1%). Eight non-related families featured the founder mutation COL4A3-p.(G1334E). Renal biopsies from 8 patients showed TBMN and focal segmental glomerulosclerosis (FSGS). Ten patients (11.5%) reached end-stage kidney disease (ESKD) at ages ranging from 37-69-yo (mean 50,1-yo). Next generation sequencing of the patients who progressed to ESKD failed to reveal a second mutation in any of the COL4A3/A4/A5 genes, supporting that true heterozygosity for COL4A3/A4 mutations predisposes to CRF/ESKD. Although this could be viewed as a milder and late-onset form of autosomal dominant AS, we had no evidence of ultrastructural features or extrarenal manifestations that would justify this diagnosis. Functional studies in cultured podocytes transfected with wild type or mutant COL4A3 chains showed retention of mutant collagens and differential activation of the unfolded protein response (UPR) cascade. This signifies the potential role of the UPR cascade in modulating the final phenotype in patients with collagen IV nephropathies.

Evidence for activation of the unfolded protein response in collagen IV nephropathies

Thin-basement-membrane nephropathy (TBMN) and Alport syndrome (AS) are progressive collagen IV nephropathies caused by mutations in COL4A3/A4/A5 genes. These nephropathies invariably present with microscopic hematuria and frequently progress to proteinuria and CKD or ESRD during long-term follow-up. Nonetheless, the exact molecular mechanisms by which these mutations exert their deleterious effects on the glomerulus remain elusive. We hypothesized that defective trafficking of the COL4A3 chain causes a strong intracellular effect on the cell responsible for COL4A3 expression, the podocyte. To this end, we overexpressed normal and mutant COL4A3 chains (G1334E mutation) in human undifferentiated podocytes and tested their effects in various intracellular pathways using a microarray approach. COL4A3 overexpression in the podocyte caused chain retention in the endoplasmic reticulum (ER) that was associated with activation of unfolded protein response (UPR)-related markers of ER stress. Notably, the overexpression of normal or mutant COL4A3 chains differentially activated the UPR pathway. Similar results were observed in a novel knockin mouse carrying the Col4a3-G1332E mutation, which produced a phenotype consistent with AS, and in biopsy specimens from patients with TBMN carrying a heterozygous COL4A3-G1334E mutation. These results suggest that ER stress arising from defective localization of collagen IV chains in human podocytes contributes to the pathogenesis of TBMN and AS through activation of the UPR, a finding that may pave the way for novel therapeutic interventions for a variety of collagenopathies.

Expression, Purification and Characterization of Recombinant Human Gelatin in Pichia pastoris

Based on the idiographic character of collagenous domain of human type III collagen, a recombinant human gelatin monomeric gene (gel) was designed and synthesized. All hydrophobic amino acids (proline excluded) were replaced by hydrophilic amino acids to improve the hydrophilic properties, and the codons encoding amino acids were optimized according to Pichia pastoris bias usage. Then a recombinant human gelatin expression vector pPIC9KG6 containing six monomeric genes ligated in the same orientation was constructed successfully. After verificated the validity of construction by DNA sequencing, the recombinant vector pPIC9KG6 was electroporated into the Pichia pastoris GS115, and Mut+ pPIC9KG6 transformants were selected on the basis of G418 resistance. Then a high-level expression strain was picked up from transformants by analyzing their recombinant protein expression levels. SDS-PAGE analysis of cell lysate and fermentation supernatant of the high-level expression strain showed that recombinant human gelatin can be expressed intracellularly and secreted expression, and its expression level reaches 16.06 g per liter. Secreted recombinant human gelatin was purified from fermentation supernatant by gel filtration chromatography. By UV spectroscopy and FTIR and SEM, it was confirmed that purified recombinant human gelatin is similar to animal-derived gelatin in protein structure.

The collagen V homotrimer [alpha1(V)](3) production is unexpectedly favored over the heterotrimer [alpha1(V)](2)alpha2(V) in recombinant expression systems

Collagen V, a fibrillar collagen with important functions in tissues, assembles into distinct chain associations. The most abundant and ubiquitous molecular form is the heterotrimer [α1(V)]₂α2(V). In the attempt to produce high levels of recombinant collagen V heterotrimer for biomedical device uses, and to identify key factors that drive heterotrimeric chain association, several cell expression systems (yeast, insect, and mammalian cells) have been assayed by cotransfecting the human proα1(V) and proα2(V) chain cDNAs. Suprisingly, in all recombinant expression systems, the formation of [α1(V)]₃ homotrimers was considerably favored over the heterotrimer. In addition, pepsin-sensitive proα2(V) chains were found in HEK-293 cell media indicating that these cells lack quality control proteins preventing collagen monomer secretion. Additional transfection with Hsp47 cDNA, encoding the collagen-specific chaperone Hsp47, did not increase heterotrimer production. Double immunofluorescence with antibodies against collagen V α-chains showed that, contrary to fibroblasts, collagen V α-chains did not colocalized intracellularly in transfected cells. Monensin treatment had no effect on the heterotrimer production. The heterotrimer production seems to require specific machinery proteins, which are not endogenously expressed in the expression systems. The different constructs and transfected cells we have generated represent useful tools to further investigate the mechanisms of collagen trimer assembly.

Effect of glycine substitutions on alpha5(IV) chain structure and structure-phenotype correlations in Alport syndrome

The phenotype variety caused by glycine substitutions in alpha5(IV) chain in X-linked Alport syndrome (XLAS) prompted the complexity of structure changes of alpha5(IV) chain that was little to know now. In this study, we expressed a domain of alpha5(IV) chain containing different glycine substitutions (G1015V and G1030S, respectively) which were revealed in two XLAS pedigrees with different phenotype severities and the corresponding domain of a control in Escherichia coli. The recombinant proteins were characterized by immunoblot and mass spectrometry and analyzed the secondary structure by using circular dichroism (CD) spectroscopy. CD analysis showed that the recombinant protein containing G1015V mutation identified in the pedigree of juvenile-onset XLAS exhibited 12.9% alpha-helix that was not found in the control recombinant protein. The spectrum of the recombinant protein containing G1030S mutation identified in the pedigree of adult-onset XLAS was slightly different from that of the control, that is, mostly with the random coil and the beta-sheet, while without alpha-helix. These results demonstrated that two kinds of glycine substitutions, although in the same domain of alpha5(IV) chain, displayed the distinctly different secondary structures. The changes of the secondary structure could explain the phenotypic diversities of XLAS, which would be hardly understood solely by analyzing genomic DNA or mRNA of alpha5(IV) chain.

Characterization of assembly of recombinant type IV collagen α3, α4, and α5 chains in transfected cell strains

BACKGROUND

Alport syndrome is caused by mutations in type IV collagen alpha3, alpha4, and alpha5 genes. Immunohistochemical analyses of kidney sections from normal individuals and Alport syndrome patients have suggested that the alpha3(IV), alpha4(IV), and alpha5(IV) chains form a heterotrimer in the glomerular basement membrane (GBM) and that a defect in any one of the chains disrupts the assembly of the three chains, resulting in Alport syndrome.

METHODS

We established stable transformants of HEK293 cells that expressed mouse alpha3(IV) and/or alpha4(IV) and/or alpha5(IV) chains. Using cell extracts and culture media of these cells, experiments were performed to determine whether or not the alpha3(IV) and alpha4(IV) chains were coimmunoprecipitated with the alpha5(IV) chain. Moreover, we examined complex formation of mutant alpha5(IV) chain containing either a deletion or substitution mutation with the alpha3(IV) and alpha4(IV) chains.

RESULTS

The established cell strains were named according to their transfected alpha(IV) chains. The alpha3(IV) and alpha4(IV) chains were coimmunoprecipitated with the alpha5(IV) chain in alpha345 cells but not in alpha35 and alpha45 cells. These chains were not coimmunoprecipitated with the alpha5(IV) chain, which lacked either a collagenous domain or NC1 domain. The ability of the alpha5(IV) chain with either a G1182R or C1573R substitution, corresponding to previously reported mutations in Alport syndrome patients, to form a complex with alpha3(IV) and alpha4(IV) chains was diminished.

CONCLUSION

The findings indicate that alpha3(IV), alpha4(IV), and alpha5(IV) chains form a complex, which is a heterotrimer, and that a defect in complex formation might be one of the molecular mechanisms underlying the pathogenesis of Alport syndrome.

Transfer of the alpha 5(IV) collagen chain gene to smooth muscle restores in vivo expression of the alpha 6(IV) collagen chain in a canine model of Alport syndrome

X-linked Alport syndrome is a progressive renal disease caused by mutations in the COL4A5 gene, which encodes the alpha 5(IV) collagen chain. As an initial step toward gene therapy for Alport syndrome, we report on the expression of recombinant alpha 5(IV) collagen in vitro and in vivo. A full-length cDNA-encoding canine alpha 5(IV) collagen was cloned and expressed in vitro by transfection of HEK293 cells that synthesize the alpha1(IV) and alpha2(IV), but not the alpha 3(IV) to alpha 6(IV) collagen chains. By Northern blotting, an alpha 5(IV) mRNA transcript of 5.2 kb was expressed and the recombinant protein was detected by immunocytochemistry. The chain was secreted into the medium as a 190-kd monomer; no triple helical species were detected. Transfected cells synthesized an extracellular matrix containing the alpha1(IV) and alpha2(IV) chains but the recombinant alpha 5(IV) chain was not incorporated. These findings are consistent with the concept that the alpha 5(IV) chain requires one or more of the alpha 3(IV), alpha 4(IV), or alpha 6(IV) chains for triple helical assembly. In vivo studies were performed in dogs with X-linked Alport syndrome. An adenoviral vector containing the alpha 5(IV) transgene was injected into bladder smooth muscle that lacks both the alpha 5(IV) and alpha 6(IV) chains in these animals. At 5 weeks after injection, there was expression of both the alpha 5(IV) and alpha 6(IV) chains by smooth muscle cells at the injection site in a basement membrane distribution. Thus, this recombinant alpha 5(IV) chain is capable of restoring expression of a second alpha(IV) chain that requires the presence of the alpha 5(IV) chain for incorporation into collagen trimers. This vector will serve as a useful tool to further explore gene therapy for Alport syndrome.

Biosynthesis of alpha2(IV) and alpha1(IV) chains of collagen IV and interactions with matrix metalloproteinase-9

In vitro binding studies with latent matrix metalloproteinase-9 (pro-MMP-9) have revealed the existence of nondisulfide-bonded alpha2(IV) chains on the cell surface capable of forming a high-affinity complex with the enzyme. Here we investigated the biosynthesis and cellular distribution of alpha2(IV) and alpha1(IV) chains in breast epithelial (MCF10A and MDA-MB-231) and fibrosarcoma (HT1080) cells by pulse-chase analysis followed by immunoprecipitation with chain-specific monoclonal antibodies (mAb). These studies showed that whereas the alpha1(IV) chain remained in the intracellular compartment, nondisulfide-bonded alpha2(IV) chains were secreted into the media in a stable form. Consistently, only alpha2(IV) was detected on the cell surface by surface biotinylation or indirect immunofluorescence. In agreement with the pulse-chase analysis, media subjected to co-precipitation experiments with pro-MMP-9 or pro-MMP-9-affinity chromatography followed by immunoblotting with chain-specific mAbs resulted in the detection of alpha2(IV). A preferential secretion of nondisulfide-bonded alpha2(IV) chains was also observed in CHO-K1 cells transiently transfected with full-length mouse alpha2(IV) or alpha (IV) cDNAs. However, a complex of mouse alpha1(IV) with pro-MMP-9 was coprecipitated with exogenous enzyme from lysates of CHO-K1 cells transfected with mouse alpha1(IV), suggesting that under overexpression conditions the enzyme can also interact with the alpha1 (IV) chain. Collectively, these studies further demonstrate the interactions of pro-MMP-9 with collagen IV chains and a unique processing and targeting of nondisulfide-bonded alpha2(IV) chains that may play a role in the surface/matrix association of pro-MMP-9.

Goodpasture antigen: expression of the full-length alpha3(IV) chain of collagen IV and localization of epitopes exclusively to the noncollagenous domain

BACKGROUND

Tissue injury in Goodpasture (GP) syndrome (rapidly progressive glomerular nephritis and pulmonary hemorrhage) is mediated by antibasement membrane antibodies that are targeted to the alpha3(IV) chain of type IV collagen, one of five alpha(IV) chains that occur in the glomerular basement membrane. GP antibodies are known to bind epitopes within the carboxyl terminal noncollagenous domain (NC1) of the alpha3(IV) chain, termed the GP autoantigen. Whether epitopes also exist in the 1400-residue collagenous domain is unknown because studies to date have focused solely on the NC1 domain. A knowledge of GP epitopes is important for the understanding of the etiology and pathogenesis of the disease and for the development of therapeutic strategies.

METHODS

A cDNA construct was prepared for the full-length human alpha3(IV) chain. The construct was stably transfected into human embryonic kidney 293 cells. The purified full-length r-alpha3(IV) chain was characterized by electrophoresis and electron microscopy. The capacity of this chain for binding of GP antibodies from five patients was compared with that of the human r-alpha3(IV)NC1 domain by competitive enzyme-linked immunosorbent assay.

RESULTS

The r-alpha3(IV) chain was secreted from 293 cells as a single polypeptide chain that did not spontaneously undergo assembly into a triple-helical molecule. An analysis of GP-antibody binding to the full-length r-alpha3(IV) chain showed binding exclusively to the globular NC1 domain.

CONCLUSION

The full-length human alpha3(IV) chain possesses the capacity to bind GP autoantibodies. The epitope(s) is found exclusively on the nontriple-helical NC1 domain of the alpha3(IV) chain, indicating the presence of specific immunogenic properties. The alpha3(IV) chain alone does not spontaneously undergo assembly into a triple-helical homotrimeric molecule, suggesting that coassembly with either the alpha4(IV) and/or the alpha5(IV) chain may be required for triple-helix formation.

Characterization of human type X procollagen and its NC-1 domain expressed as recombinant proteins in HEK293 cells

Type X collagen is a short-chain, network-forming collagen found in hypertrophic cartilage in the growth zones of long bones, vertebrae, and ribs. To obtain information about the structure and assembly of mammalian type X collagen, we generated recombinant human type collagen X by stable expression of full-length human alpha1(X) cDNA in the human embryonal kidney cell line HEK293 and the fibrosarcoma cell line HT1080. Stable clones were obtained secreting recombinant human type X collagen (hrColX) in amounts of 50 microg/ml with alpha1(X)-chains of apparent molecular mass of 75 kDa. Pepsin digestion converted the native protein to a molecule migrating as one band at 65 kDa, while bands of 55 and 43 kDa were generated by trypsin digestion. Polyclonal antibodies prepared against purified hrColX reacted specifically with type X collagen in sections of human fetal growth cartilage. Circular dichroism spectra and trypsin/chymotrypsin digestion experiments of hrColX at increasing temperatures indicated triple helical molecules with a reduced melting temperature of 31 degrees C as a result of partial underhydroxylation. Ultrastructural analysis of hrColX by rotary shadowing demonstrated rodlike molecules with a length of 130 nm, assembling into aggregates via the globular noncollagenous (NC)-1 domains as reported for chick type X collagen. NC-1 domains generated by collagenase digestion of hrColX migrated as multimers of apparent mass of 40 kDa on SDS-polyacrylamide gel electrophoresis, even after reduction and heat denaturation, and gave rise to monomers of 18-20 kDa after treatment with trichloroacetic acid. The NC-1 domains prepared by collagenase digestion comigrated with NC-1 domains prepared as recombinant protein in HEK293 cells, both in the multimeric and monomeric form. These studies demonstrate the potential of the pCMVsis expression system to produce recombinant triple helical type X collagens in amounts sufficient for further studies on its structural and functional domains.