Structural basis of homo- and heterotrimerization of collagen I

Active synthesis of type I collagen homotrimer in Dupuytren's fibrosis is unaffected by anti-TNF-α treatment

Dupuytren's disease is a common fibroproliferative disease of the palmar fascia of the hand, with advanced cases treated surgically. Anti-TNF injection has undergone phase 2 trials and may be effective in slowing early-stage disease progression. Here we sought to determine how new synthesis of type I collagen in Dupuytren's differs from normal palmar fascia samples and to analyze the role of TNF in aberrant collagen synthesis. Model nonfibrotic but fibrous connective tissues were used to analyze active type I collagen protein synthesis in development, aging, and degenerative disease, where it was restricted to early development and ruptured tissue. Dupuytren's tissue was shown to actively synthesize type I collagen, including abnormal type I collagen homotrimer. TNF-α reduced COL1A2 gene expression only in the presence of serum in 2D cell culture and had opposing effects on collagen protein production in the presence or absence of serum. TNF-α had only limited effects in 3D tendon-like constructs. Anti-TNF did not reduce type I collagen synthesis in 3D tendon-like constructs or prevent type I collagen homotrimer synthesis in Dupuytren's tissue. Hence, modulation of the TNF-α pathway in Dupuytren's disease is unlikely to prevent the pathological collagen accumulation that is characteristic of fibrosis.

Hierarchical Assemblies of Collagen-Mimetic Peptides: From a Fundamental Understanding to Developing Biomaterials

Collagen is the most abundant protein in animals and crucial for maintaining the structural and functional integrity of the extracellular matrix. Its primary structure consists of ∼300 repeats of the Xaa-Yaa-Gly triplet, where Xaa and Yaa are often proline (Pro) and 4-(R)-hydroxyproline (Hyp) residues, respectively. Collagen is fundamentally a right-handed triple helix that undergoes self-association, forming complex supramolecular structures in the body. Despite extensive study, the detailed mechanisms behind its higher-order assembly remain unclear due to challenges in its purification and the extensive post-translational modifications that it undergoes. To better understand the molecular aspects of collagen's complex structure, researchers developed collagen-mimetic peptides (CMPs)─short peptides composed of 7-17 Xaa-Yaa-Gly triplets─easily synthesized in the laboratory. Over the years, research on CMPs has provided significant insights into the formation and stability of the collagen triple helix. However, creating multihierarchical self-assembled structures beyond the triple helix remains challenging. Recently, various strategies such as covalent linkages, salt-bridge interactions, incorporation of hydrophobic groups, metal-coordinated assembly, and coassembly with foreign partners have been employed to design higher-order CMP assemblies. These innovations have led to the creation of fibers, 2D sheets, wires, and spherical micelles. This progress has paved the way for the rational design of novel peptide-based biomaterials, which may offer advantages over animal-derived collagen, including the absence of potential allergens and contaminants. This review highlights recent advancements in CMP assembly design, discussing the principles, challenges, and prospects of these biomaterials in clinical applications.

Collagen remodeling-mediated signaling pathways and their impact on tumor therapy

In addition to their traditional roles in maintaining tissue morphology and organ development, emerging evidence suggests that collagen (COL) remodeling-referring to dynamic changes in the quantity, stiffness, arrangements, cleavage states, and homo-/hetero-trimerization of COLs-serves as a key signaling mechanism that governs tumor growth and metastasis. COL receptors act as switches, linking various forms of COL remodeling to different cell types during cancer progression, including cancer cells, immune cells, and cancer-associated fibroblasts. In this review, we summarize recent findings on the signaling pathways mediated by COL arrangement, cleavage, and trimerization states (both homo- and hetero-), as well as the roles of the primary COL receptors-integrin, DDR1/2, LAIR-1/2, MRC2, and GPVI-in cancer progression. We also discuss the latest therapeutic strategies targeting COL fragments, cancer-associated fibroblasts, and COL receptors, including integrins, DDR1/2, and LAIR1/2. Understanding the pathways modulated by COL remodeling and COL receptors in various pathological contexts will pave the way for developing new precision therapies.

Metalloproteomic analysis of hemophilic arthropathy synovial tissue: insights into metal overload and pathogenesis

BACKGROUND

Hemophilic arthropathy (HA) is a joint disease characterized by local iron overload stemming from erythrocyte rupture and closely linked to synovial lesions. However, the precise molecular characteristics of clinical HA synovial samples remain to be defined.

OBJECTIVES

To gain insight into HA synovial tissue lesions, we utilized a metalloprotein strategy to compare the metal and protein spectra of HA with those of osteoarthritis and rheumatoid arthritis.

METHODS

We collected synovial samples from patients with HA, osteoarthritis, and rheumatoid arthritis. Tissue metal and protein profiles were obtained by metallomics and proteomics, respectively. Finally, metalloproteomics strategies compared metal content, proteins, metalloproteins, and the life processes involved.

RESULTS

Our metallomics analysis revealed an explicit increase in heavy metal content, particularly arsenic and mercury, in HA synovial samples. Through proteomics, we delineated specific metalloproteins and identified correlations between metals and pathways.

CONCLUSION

These findings yield valuable insights into the pathogenesis of HA and offer potential therapeutic targets for conditions characterized by iron overload.

Production of recombinant human type I collagen homotrimers in CHO cells and their physicochemical and functional properties

Collagen is the most abundant protein in human and mammalian structures and is a component of the mammalian extracellular matrix (ECM). Recombinant collagen is a suitable alternative to native collagen extracted from animal tissue for various biomaterials. However, due to the limitations of the expression system, most recombinant collagens are collagen fragments and lack triple helix structures. In this study, Chinese hamster ovary (CHO) cells were used to express the full-length human type I collagen α1 chain (rhCol1α1). Moreover, Endo180 affinity chromatography and pepsin were used to purify pepsin-soluble rhCol1α1 (PSC1). The amino acid composition of PSC1 was closer to that of native human type I collagen, and PSC1 contained 9.1 % hydroxyproline. Analysis of the CD spectra and molecular weight distribution results revealed that PSC1 forms a stable triple helix structure that is resistant to pepsin hydrolysis and has some tolerance to MMP1, MMP2 and MMP8 hydrolysis. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) revealed that PSC1 can self-assemble into fibers at a concentration of 1 mg/ml; moreover, PSC1 can promote the proliferation and migration of NIH 3T3 cells. In conclusion, our data suggest that PSC1 is a highly similar type of recombinant collagen that may have applications in biomaterials and other medical fields.

An outcome-defining role for the triple-helical domain in regulating collagen-I assembly

Collagens are the foundational component of diverse tissues, including skin, bone, cartilage, and basement membranes, and are the most abundant protein class in animals. The fibrillar collagens are large, complex, multidomain proteins, all containing the characteristic triple helix motif. The most prevalent collagens are heterotrimeric, meaning that cells express at least two distinctive procollagen polypeptides that must assemble into specific heterotrimer compositions. The molecular mechanisms ensuring correct heterotrimeric assemblies are poorly understood - even for the most common collagen, type-I. The longstanding paradigm is that assembly is controlled entirely by the ~30 kDa globular C-propeptide (C-Pro) domain. Still, this dominating model for procollagen assembly has left many questions unanswered. Here, we show that the C-Pro paradigm is incomplete. In addition to the critical role of the C-Pro domain in templating assembly, we find that the amino acid sequence near the C terminus of procollagen's triple-helical domain plays an essential role in defining procollagen assembly outcomes. These sequences near the C terminus of the triple-helical domain encode conformationally stabilizing features that ensure only desirable C-Pro-mediated trimeric templates are committed to irreversible triple-helix folding. Incorrect C-Pro trimer assemblies avoid commitment to triple-helix formation thanks to destabilizing features in the amino acid sequences of their triple helix. Incorrect C-Pro assemblies are consequently able to dissociate and search for new binding partners. These findings provide a distinctive perspective on the mechanism of procollagen assembly, revealing the molecular basis by which incorrect homotrimer assemblies are avoided and setting the stage for a deeper understanding of the biogenesis of this ubiquitous protein.

Selective Excitation of the 1Lα State of Tryptophan in Collagen-like Peptides Can Reveal the Formation of a Heterotrimer

Fluorescence emission from tryptophan residues has been often used to probe the protein structure due to its transition dipole moment sensitivity to the local environment. We report the fluorescence study of a collagen-like peptide heterotrimer modified with the tryptophan in the X position (X-Y-Gly) n that shows the diminished fluorescence in a homotrimer versus a heterotrimer when the 1Lα state is selectively excited. This behavior is only observed in folded peptides, below the helix-to-coil transition temperature, and can be explained by long-range interactions between the tryptophans located on different strands within the triple helix, not by the change in the local environment. Our results suggest that tryptophan homotransfer is possible at distances much longer than the R 0 (0.5-0.7 nm) previously estimated. These observations imply that the energy transfer between the 1Lα states of proximal tryptophans can be facilitated by constraining their rotation by the helix and, thus, can be employed as a reporter of heterotrimer formation in biosensors.

Functional and Structural Properties of Type V Collagen from the Skin of the Shortbill Spearfish (Tetrapturus angustirostris)

Type V collagen is considered to be a crucial minor collagen in fish skin with unique physiological functions. In this research, the cDNAs of three procollagens (Tacol5a1, Tacol5a2, and Tacol5a3) in type V collagen were cloned from the skin of shortbill spearfish (Tetrapturus angustirostris). The open reading frames (ORFs) of Tacol5a1, Tacol5a2, and Tacol5a3 contained 5991, 4485, and 5607 bps, respectively, encoding 1997, 1495, and 1869 amino acid residues. Each of the deduced amino acid sequences of procollagens contained a signal peptide and a fibrillar collagen C-terminal domain (COLFI). A conserved thrombospondin-like N-terminal domain (TSPN) was found at the N-terminus of Tacol5a1 and 5a3 procollagens, whereas a von Willebrand factor (VWC) was found at the N-terminus of Tacol5a2 procollagen. Tacol5a1, Tacol5a2, and Tacol5a3 had their theoretical isoelectric points of 5.06, 6.75, and 5.76, respectively, and predicted molecular weights of 198,435.60, 145,058.48, and 189,171.18, respectively. The phylogenetic tree analysis revealed that Tacol5a1 of shortbill spearfish clustered with that of yellow perch (Perca flavescens) instead of broadbill swordfish (Xiphias gladius). In addition, type V collagen was extracted from the shortbill spearfish skin. The in silico method demonstrated that shortbill spearfish type V collagen has a high potential for angiotensin-converting enzyme (ACE) inhibition activity (79.50%), dipeptidyl peptidase IV inhibition (74.91%) activity, and antithrombotic activity (46.83%). The structural clarification and possible functional investigation in this study provide the foundation for the applications of exogenous type V collagen derived from fish sources.

Spike 1 trimer, a nanoparticle vaccine against porcine epidemic diarrhea virus induces protective immunity challenge in piglets

Porcine epidemic diarrhea virus (PEDV) is considered the cause for porcine epidemic diarrhea (PED) outbreaks and hefty losses in pig farming. However, no effective commercial vaccines against PEDV mutant strains are available nowadays. Here, we constructed three native-like trimeric candidate nanovaccines, i.e., spike 1 trimer (S1-Trimer), collagenase equivalent domain trimer (COE-Trimer), and receptor-binding domain trimer (RBD-Trimer) for PEDV based on Trimer-Tag technology. And evaluated its physical properties and immune efficacy. The result showed that the candidate nanovaccines were safe for mice and pregnant sows, and no animal death or miscarriage occurred in our study. S1-Trimer showed stable physical properties, high cell uptake rate and receptor affinity. In the mouse, sow and piglet models, immunization of S1-Trimer induced high-level of humoral immunity containing PEDV-specific IgG and IgA. S1-Trimer-driven mucosal IgA responses and systemic IgG responses exhibited high titers of virus neutralizing antibodies (NAbs) in vitro. S1-Trimer induced Th1-biased cellular immune responses in mice. Moreover, the piglets from the S1-Trimer and inactivated vaccine groups displayed significantly fewer microscopic lesions in the intestinal tissue, with only one and two piglets showing mild diarrhea. The viral load in feces and intestines from the S1-Trimer and inactivated vaccine groups were significantly lower than those of the PBS group. For the first time, our data demonstrated the protective efficacy of Trimer-Tag-based nanovaccines used for PEDV. The S1-Trimer developed in this study was a competitive vaccine candidate, and Trimer-Tag may be an important platform for the rapid production of safe and effective subunit vaccines in the future.

Glycosylation Modulates the Structure and Functions of Collagen: A Review

Collagens are fundamental constituents of the extracellular matrix and are the most abundant proteins in mammals. Collagens belong to the family of fibrous or fiber-forming proteins that self-assemble into fibrils that define their mechanical properties and biological functions. Up to now, 28 members of the collagen superfamily have been recognized. Collagen biosynthesis occurs in the endoplasmic reticulum, where specific post-translational modification-glycosylation-is also carried out. The glycosylation of collagens is very specific and adds β-d-galactopyranose and β-d-Glcp-(1→2)-d-Galp disaccharide through β-O-linkage to hydroxylysine. Several glycosyltransferases, namely COLGALT1, COLGALT2, LH3, and PGGHG glucosidase, were associated the with glycosylation of collagens, and recently, the crystal structure of LH3 has been solved. Although not fully understood, it is clear that the glycosylation of collagens influences collagen secretion and the alignment of collagen fibrils. A growing body of evidence also associates the glycosylation of collagen with its functions and various human diseases. Recent progress in understanding collagen glycosylation allows for the exploitation of its therapeutic potential and the discovery of new agents. This review will discuss the relevant contributions to understanding the glycosylation of collagens. Then, glycosyltransferases involved in collagen glycosylation, their structure, and catalytic mechanism will be surveyed. Furthermore, the involvement of glycosylation in collagen functions and collagen glycosylation-related diseases will be discussed.

Analysis of Homo- and Heterotriple Helix Formation of Collagen Model Peptides and Evaluation of Their Stability in a Biological Environment

Self-assembled materials have attracted attention and have been extensively studied because the reversibility of noncovalent interactions allows them to possess various properties, such as stimulus responsiveness and self-healing. Collagen model peptides have an amino acid sequence characteristic of the triple helix region of collagen and exhibit repeatable triple helix formation. Many studies of their applications have used homotrimers, and although some studies on heterotrimers have been reported, few have clarified the details. If the characteristics of heterotrimers can be revealed, they are expected to be applied as new self-assembled materials. In this study, we analyzed the detailed self-assembling properties of hetero- and homohelices formed by (proline-proline-glycine)10 (PPG)10 and (proline-hydroxyproline-glycine)10 (POG)10 to evaluate the potential of the helices for biomedical application. Fluorescein isothiocyanate-labeled (PPG)10 (F(PPG)10) and (POG)10 (F(POG)10) were synthesized to analyze the heterotriple helix formation using concentration quenching based on triple helix formation. When (PPG)10 was added to F(POG)10, the fluorescence intensity did not reach a plateau, while the fluorescence intensity reached about 100% in the other pairs such as (POG)10-F(POG)10, (PPG)10-F(PPG)10, and (POG)10-F(PPG)10. The critical triple helix formation concentration was 7 μM for the heterotrimer prepared under 1:2 mixing conditions of (PPG)10 and (POG)10, 320 μM for [(PPG)10]3, and 4 μM for [(POG)10]3, indicating that the triple helix formation concentration of the heterotrimer is almost half that of [(POG)10]3 but 45 times higher than [(PPG)10]3. Furthermore, the heterotrimer formed at 37 °C was stable after 5 days, which was the same as [(POG)10]3. These results suggest that heterotrimers have different association properties from homotrimers and are expected to be applied in nanotechnology and biomaterials as new self-assembled materials.

Dynamic changes in mitral valve extracellular matrix, tissue mechanics and function in a mouse model of Marfan syndrome

OBJECTIVE

Mouse models of Marfan syndrome (MFS) with Fibrillin 1 (Fbn1) variant C1041G exhibit cardiovascular abnormalities, including myxomatous valve disease (MVD) and aortic aneurism, with structural extracellular matrix (ECM) dysregulation. In this study, we examine the structure-function-mechanics relations of the mitral valve related to specific transitions in ECM composition and organization in progressive MVD in MFS mice from Postnatal day (P)7 to 1 year-of-age.

APPROACH AND RESULTS

Mechanistic links between mechanical forces and biological changes in MVD progression were examined in Fbn1C1041G/+ MFS mice. By echocardiography, mitral valve dysfunction is prevalent at 2 months with a decrease in cardiac function at 6 months, followed by a preserved cardiac function at 12 months. Mitral valve (MV) regurgitation occurs in a subset of mice at 2-6 months, while progressive dilatation of the aorta occurs from 2 to 12 months. Mitral valve tissue mechanical assessments using a uniaxial Permeabilizable Fiber System demonstrate decreased stiffness of MFS MVs at all stages. Histological and microscopic analysis of ECM content, structure, and fiber orientation demonstrate that alterations in ECM mechanics, composition, and organization precede functional abnormalities in Fbn1C1041G/+MFS MVs. At 2 months, ECM abnormalities are detected with an increase in proteoglycans and decreased stiffness of the mitral valve. By 6-12 months, collagen fiber remodeling is increased with abnormal fiber organization in MFS mitral valve leaflets. At the same time, matrifibrocyte gene expression characteristic of collagen-rich connective tissue is increased, as detected by RNA in situ hybridization and qPCR. Together, these studies demonstrate early prevalence of proteoglycans at 2 months followed by upregulation of collagen structure and organization with age in MVs of MFS mice.

CONCLUSIONS

Altogether, our data indicate dynamic regulation of mitral valve structure, tissue mechanics, and function that reflect changes in ECM composition, organization, and gene expression in progressive MVD. Notably, increased collagen fiber organization and orientation, potentially dependent on increased matrifibrocyte cell activity, is apparent with altered mitral valve mechanics and function in aging MFS mice.

Isolation of type I collagen homotrimer from human placenta with LC-MS monitoring of the α1(I)/α2(I) chain ratio

The general molecular form of type I collagen is heterotrimer consisting of two α1(I) chains and one α2(I) chain. However, α111(I) homotrimer is rarely observed in vivo, especially in pathological tissues such as cancer. Here we utilized a previously developed LC-MS method that can accurately and sensitively quantitate α1(I) and α2(I) chains to distinguish type I collagen homotrimer from human placenta. By monitoring with the LC-MS method, the α1(I)/α2(I) chain ratio was found to be high in the supernatant of salt precipitation with >2.8 M NaCl at neutral pH. Type I collagen homotrimer was successfully isolated using optimized sequential salt fractionation and confirmed to show previously reported features of the homotrimer, including high thermal stability and overmodification. These data clearly indicate that placental tissue contains α111(I) homotrimer. Our LC-MS method can sensitively detect the rare form of type I collagen and can help understand its physiological and pathological significance.

Col1a2-Deleted Mice Have Defective Type I Collagen and Secondary Reactive Cardiac Fibrosis with Altered Hypertrophic Dynamics

RATIONALE

The adult cardiac extracellular matrix (ECM) is largely comprised of type I collagen. In addition to serving as the primary structural support component of the cardiac ECM, type I collagen also provides an organizational platform for other ECM proteins, matricellular proteins, and signaling components that impact cellular stress sensing in vivo.

OBJECTIVE

Here we investigated how the content and integrity of type I collagen affect cardiac structure function and response to injury.

METHODS AND RESULTS

We generated and characterized Col1a2-/- mice using standard gene targeting. Col1a2-/- mice were viable, although by young adulthood their hearts showed alterations in ECM mechanical properties, as well as an unanticipated activation of cardiac fibroblasts and induction of a progressive fibrotic response. This included augmented TGFβ activity, increases in fibroblast number, and progressive cardiac hypertrophy, with reduced functional performance by 9 months of age. Col1a2-loxP-targeted mice were also generated and crossed with the tamoxifen-inducible Postn-MerCreMer mice to delete the Col1a2 gene in myofibroblasts with pressure overload injury. Interestingly, while germline Col1a2-/- mice showed gradual pathologic hypertrophy and fibrosis with aging, the acute deletion of Col1a2 from activated adult myofibroblasts showed a loss of total collagen deposition with acute cardiac injury and an acute reduction in pressure overload-induce cardiac hypertrophy. However, this reduction in hypertrophy due to myofibroblast-specific Col1a2 deletion was lost after 2 and 6 weeks of pressure overload, as fibrotic deposition accumulated.

CONCLUSIONS

Defective type I collagen in the heart alters the structural integrity of the ECM and leads to cardiomyopathy in adulthood, with fibroblast expansion, activation, and alternate fibrotic ECM deposition. However, acute inhibition of type I collagen production can have an anti-fibrotic and anti-hypertrophic effect.

Tcf20 deficiency is associated with increased liver fibrogenesis and alterations in mitochondrial metabolism in mice and humans

BACKGROUND & AIMS

Transcription co-activator factor 20 (TCF20) is a regulator of transcription factors involved in extracellular matrix remodelling. In addition, TCF20 genomic variants in humans have been associated with impaired intellectual disability. Therefore, we hypothesized that TCF20 has several functions beyond those described in neurogenesis, including the regulation of fibrogenesis.

METHODS

Tcf20 knock-out (Tcf20-/- ) and Tcf20 heterozygous mice were generated by homologous recombination. TCF20 gene genotyping and expression was assessed in patients with pathogenic variants in the TCF20 gene. Neural development was investigated by immufluorescense. Mitochondrial metabolic activity was evaluated with the Seahorse analyser. The proteome analysis was carried out by gas chromatography mass-spectrometry.

RESULTS

Characterization of Tcf20-/- newborn mice showed impaired neural development and death after birth. In contrast, heterozygous mice were viable but showed higher CCl4 -induced liver fibrosis and a differential expression of genes involved in extracellular matrix homeostasis compared to wild-type mice, along with abnormal behavioural patterns compatible with autism-like phenotypes. Tcf20-/- embryonic livers and mouse embryonic fibroblast (MEF) cells revealed differential expression of structural proteins involved in the mitochondrial oxidative phosphorylation chain, increased rates of mitochondrial metabolic activity and alterations in metabolites of the citric acid cycle. These results parallel to those found in patients with TCF20 pathogenic variants, including alterations of the fibrosis scores (ELF and APRI) and the elevation of succinate concentration in plasma.

CONCLUSIONS

We demonstrated a new role of Tcf20 in fibrogenesis and mitochondria metabolism in mice and showed the association of TCF20 deficiency with fibrosis and metabolic biomarkers in humans.

3D Bioprinting of Hyaline Articular Cartilage: Biopolymers, Hydrogels, and Bioinks

The musculoskeletal system, consisting of bones and cartilage of various types, muscles, ligaments, and tendons, is the basis of the human body. However, many pathological conditions caused by aging, lifestyle, disease, or trauma can damage its elements and lead to severe disfunction and significant worsening in the quality of life. Due to its structure and function, articular (hyaline) cartilage is the most susceptible to damage. Articular cartilage is a non-vascular tissue with constrained self-regeneration capabilities. Additionally, treatment methods, which have proven efficacy in stopping its degradation and promoting regeneration, still do not exist. Conservative treatment and physical therapy only relieve the symptoms associated with cartilage destruction, and traditional surgical interventions to repair defects or endoprosthetics are not without serious drawbacks. Thus, articular cartilage damage remains an urgent and actual problem requiring the development of new treatment approaches. The emergence of biofabrication technologies, including three-dimensional (3D) bioprinting, at the end of the 20th century, allowed reconstructive interventions to get a second wind. Three-dimensional bioprinting creates volume constraints that mimic the structure and function of natural tissue due to the combinations of biomaterials, living cells, and signal molecules to create. In our case-hyaline cartilage. Several approaches to articular cartilage biofabrication have been developed to date, including the promising technology of 3D bioprinting. This review represents the main achievements of such research direction and describes the technological processes and the necessary biomaterials, cell cultures, and signal molecules. Special attention is given to the basic materials for 3D bioprinting-hydrogels and bioinks, as well as the biopolymers underlying the indicated products.

Classification of osteogenesis imperfecta: Importance for prophylaxis and genetic counseling

Osteogenesis imperfecta (OI) is a genetically heterogeneous monogenic disease characterized by decreased bone mass, bone fragility, and recurrent fractures. The phenotypic spectrum varies considerably ranging from prenatal fractures with lethal outcomes to mild forms with few fractures and normal stature. The basic mechanism is a collagen-related defect, not only in synthesis but also in folding, processing, bone mineralization, or osteoblast function. In recent years, great progress has been made in identifying new genes and molecular mechanisms underlying OI. In this context, the classification of OI has been revised several times and different types are used. The Sillence classification, based on clinical and radiological characteristics, is currently used as a grading of clinical severity. Based on the metabolic pathway, the functional classification allows identifying regulatory elements and targeting specific therapeutic approaches. Genetic classification has the advantage of identifying the inheritance pattern, an essential element for genetic counseling and prophylaxis. Although genotype-phenotype correlations may sometimes be challenging, genetic diagnosis allows a personalized management strategy, accurate family planning, and pregnancy management decisions including options for mode of delivery, or early antenatal OI treatment. Future research on molecular pathways and pathogenic variants involved could lead to the development of genotype-based therapeutic approaches. This narrative review summarizes our current understanding of genes, molecular mechanisms involved in OI, classifications, and their utility in prophylaxis.

Potential implications of the glycosylation patterns in collagen α1(I) and α2(I) chains for fibril assembly and growth

O-Glycosylation of hydroxylysine (Hyl) in collagen occurs at an early stage of biosynthesis before the triple-helix has formed. This simple post-translational modification (PTM) of lysine by either a galactosyl or glucosylgalactosyl moiety is highly conserved in collagens and depends on the species, type of tissue and the collagen amino acid sequence. The structural/functional reason why only specific lysines are modified is poorly understood, and has led to increased efforts to map the sites of PTMs on collagen sequences from different species and to ascertain their potential role in vivo. To investigate this, we purified collagen type I (Col1) from the skins of four animals, then used mass spectrometry and proteomic techniques to identify lysines that were oxidised, galactosylated, glucosylgalactosylated, or glycated in its mature sequence. We found 18 out of the 38 lysines in collagen type Iα1, (Col1A1) and 7 of the 30 lysines in collagen type Iα2 (Col1A2) were glycosylated. Six of these modifications had not been reported before, and included a lysine involved in crosslinking collagen molecules. A Fourier transform analysis of the positions of the glycosylated hydroxylysines showed they display a regular axial distribution with the same d-period observed in collagen fibrils. The significance of this finding in terms of the assembly of collagen molecules into fibrils and of potential restrictions on the growth of the collagen fibrils is discussed.

A novel chlorin e6 derivative-mediated photodynamic therapy STBF-PDT reverses photoaging via the TGF-β pathway

OBJECTIVE

Photoaging is characterized by wrinkles in the skin and the deterioration of the skin barrier function, mainly caused by long-term exposure to ultraviolet (UV) radiation. Photodynamic therapy (PDT) has been shown to treat photoaging. The novel photosensitizer ShengTaiBuFen(STBF) is a derived substance of Chlorin e6(Ce6) that can exert photodynamic effects directly. In this study, we investigated the availability and the mechanism of STBF-PDT in the treatment of photoaging.

METHODS

Fluorophotometer was used to determine therapeutic parameters for in vivo experiments. Camera photographs, dermoscopy, HE and Masson staining, skin pH, trans epidermal water loss (TEWL), epidermal water content, and sebum testing were used together to evaluate the results of the treatment. Dark toxicity and therapeutic parameters for in vitro experiments were determined by CCK8 analysis. Scratch assay was used to identify the cell migration of STBF-PDT on HaCaT cells. qPCR and Western blot were used to evaluate the TGF-β/Smad signaling pathway in human dermal fibroblast (HDF) cells.

RESULTS

We investigated the optimal STBF concentration and time of incubation in vivo and in vitro experiments. STBF-PDT improved the skin phenotype of photoaged mice. The skin of photoaged mice treated with 80 J/cm² STBF-PDT became smooth, while skin flakes were reduced. The epidermis of STBF-PDT-treated mice was thinner, and the cells were neatly arranged, with increased dermal collagen. In vitro, STBF-PDT promoted the migration of HaCaT cells below a light dose of 0.1 J/cm². HDF cells co-cultured with HaCaT cells treated with low-dose STBF-PDT showed activation of the TGF-β pathway.

CONCLUSION

As a novel photosensitizer, STBF-mediated low-dose PDT could reverse photoaging via the TGF-β pathway.

Tendon properties in a mouse model of severe osteogenesis imperfecta

PURPOSE/AIM OF THE STUDY

Osteogenesis imperfecta is a heritable bone disorder that is usually caused by mutations in collagen type I encoding genes. The impact of such mutations on tendons, a structure with high collagen type I content, remains largely unexplored. We hypothesized that tendon properties are abnormal in the context of a mutation affecting collagen type I. The main purpose of the study was to assess the anatomical, mechanical, and material tendon properties of Col1a1^Jrt/+ mice, a model of severe dominant OI.

MATERIALS AND METHODS

The Flexor Digitorum Longus (FDL) tendon of Col1a1^Jrt/+ mice and wild-type littermates (WT) was assessed with in vitro mechanical testing.

RESULTS

The results showed that width and thickness of FDL tendons were about 40% larger in WT (p < 0.01) than in Col1a1^Jrt/+ mice, whereas the cross-sectional area was 138% larger (p < 0.001). The stiffness, peak- and yield-force were between 160% and 194% higher in WT vs. Col1a1^Jrt/+ mice. The material properties did not show significant differences between mouse strains with differences <15% between WT and Col1a1^Jrt/+ (p > 0.05). Analysis of the Achilles tendon collagen showed no difference between mice strains for the content but collagen solubility in acetic acid was 66% higher in WT than in Col1a1^Jrt/+ (p < 0.001).

CONCLUSIONS

This study shows that the FDL tendon of Col1a1^Jrt/+ mice has reduced mechanical properties but apparently normal material properties. It remains unclear whether the tendon phenotype of Col1a1^Jrt/+ mice is secondary to muscle weakness or a direct effect of the Col1a1 mutation or a combination of both.

Identification of the Collagen Types Essential for Mammalian Breast Acinar Structures

Modeling human breast tissue architecture is essential to study the pathophysiological conditions of the breast. We report that normal mammary epithelial cells grown in human breast extracellular matrix (ECM) hydrogel formed acini structurally similar to those of human and pig mammary tissues. Type I, II, III and V collagens were commonly identified in human, pig, and mouse breast ECM. Mammary epithelial cells formed acini on certain types or combinations of the four collagens at normal levels of breast tissue elasticity. Comparison of the collagen species in mouse normal breast and breast tumor ECM revealed common and distinct sets of collagens within the two types of tissues. Elevated expression of collagen type I alpha 1 chain (Col1a1) was found in mouse and human breast cancers. Collagen type XXV alpha 1 chain (Col25a1) was identified in mouse breast tumors but not in normal breast tissues. Our data provide strategies for modeling human breast pathophysiological structures and functions using native tissue-derived hydrogels and offer insight into the potential contributions of different collagen types in breast cancer development.

Molecular Characteristics and Promoter Analysis of Porcine COL1A1

COL1A1 encodes the type I collagen α1 chain, which shows the highest abundance among members of the collagen family and is widely expressed in different mammalian cells and tissues. However, its molecular characteristics are not completely elucidated. In this study, the molecular profiles of COL1A1 and characteristics of the COL1A1 protein were investigated using a promoter activity assay and multiple bioinformatics tools. The results showed that the 5' flanking region of porcine COL1A1 contained two CpG islands, five core promoter sequences, and twenty-six transcription factor-binding sites. In the luciferase assay, the upstream 294 bp region of the initiation codon of COL1A1 showed the highest activity, confirming that this section is the core region of the porcine COL1A1 promoter. Bioinformatic analysis revealed that COL1A1 is a negatively charged, hydrophilic secreted protein. It does not contain a transmembrane domain and is highly conserved in humans, mice, sheep, and pigs. Protein interaction analysis demonstrated that the interaction coefficient of COL1A1 with COL1A2, COL3A1, ITGB1, and ITGA2 was greater than 0.9, suggesting that this protein plays a crucial role in collagen structure formation and cell adhesion. These results provide a theoretical basis for further investigation of the functions of porcine COL1A1.

Collagen synthesis in the skin: genetic and epigenetic aspects

One of the most important functions of the skin, mechanical, is provided by collagen fibers and their interaction with other elements of the extracellular matrix. Synthesis of collagen fibers is a complex multistep process. At each stage, disturbances may occur, leading, as a result, to a decrease in the mechanical properties of the connective tissue. In clinical practice, disorders of collagen synthesis are manifested through increased skin laxity and looseness and premature aging. In addition to the clinical presentation, it is important for the cosmetologist and dermatologist to understand the etiology and pathogenesis of collagenopathies. The present review summarizes and systematizes available information about the role of genetic and epigenetic factors in the synthesis of collagen fibers in the skin. Understanding the etiology of collagen synthesis disorders can allow doctors to prescribe pathogenetically grounded treatment with the most effective results and minimize adverse reactions.

Collagen (I) homotrimer potentiates the osteogenesis imperfecta (oim) mutant allele and reduces survival in male mice

The osteogenesis imperfecta murine (oim) model with solely homotrimeric (α1)3 type I collagen, owing to a dysfunctional α2(I) collagen chain, has a brittle bone phenotype, implying that the (α1)2(α2)1 heterotrimer is required for physiological bone function. Here, we comprehensively show, for the first time, that mice lacking the α2(I) chain do not have impaired bone biomechanical or structural properties, unlike oim homozygous mice. However, Mendelian inheritance was affected in male mice of both lines, and male mice null for the α2(I) chain exhibited age-related loss of condition. Compound heterozygotes were generated to test whether gene dosage was responsible for the less-severe phenotype of oim heterozygotes, after allelic discrimination showed that the oim mutant allele was not downregulated in heterozygotes. Compound heterozygotes had impaired bone structural properties compared to those of oim heterozygotes, albeit to a lesser extent than those of oim homozygotes. Hence, the presence of heterotrimeric type I collagen in oim heterozygotes alleviates the effect of the oim mutant allele, but a genetic interaction between homotrimeric type I collagen and the oim mutant allele leads to bone fragility.

LARP6 Regulates Keloid Fibroblast Proliferation, Invasion, and Ability to Synthesize Collagen

Keloid is a skin fibroproliferative disease currently having no uniformly successful treatment. The lesion is composed of actively proliferating and collagen-overproducing fibroblasts. LARP6 is an RNA-binding protein able to regulate collagen synthesis in fibroblasts and to promote proliferation and invasion of tumor cells. To explore LARP6's likely functions in keloid pathogenesis, we performed immunohistochemistry staining on human keloid tissues and discovered markedly upregulated LARP6 expression in lesion fibroblasts compared with that of normal skin and hypertrophic scar tissues. In addition, the keloid tissue‒derived fibroblasts showed constitutive upregulation of LARP6 expression as well as significantly upregulated mRNA and protein expressions of type I collagen and enhanced cell proliferation and invasive behavior in cell culture system. Intriguingly, LARP6 knockdown by targeting with small interfering RNAs significantly inhibited type I collagen expression, proliferation, and invasion capability of keloid tissue‒derived fibroblasts relative to that of normal skin‒ and hypertrophic scar‒derived fibroblasts and control keloid tissue‒derived fibroblasts that were transfected with a scrambled small interfering RNA. In conclusion, the abnormally upregulated expression of LARP6 in fibroblasts may play an important role in the growth and invasive behavior of keloid lesions.

Using sequence data to predict the self-assembly of supramolecular collagen structures

Collagen fibrils are the major constituents of the extracellular matrix, which provides structural support to vertebrate connective tissues. It is widely assumed that the superstructure of collagen fibrils is encoded in the primary sequences of the molecular building blocks. However, the interplay between large-scale architecture and small-scale molecular interactions makes the ab initio prediction of collagen structure challenging. Here, we propose a model that allows us to predict the periodic structure of collagen fibers and the axial offset between the molecules, purely on the basis of simple predictive rules for the interaction between amino acid residues. With our model, we identify the sequence-dependent collagen fiber geometries with the lowest free energy and validate the predicted geometries against the available experimental data. We propose a procedure for searching for optimal staggering distances. Finally, we build a classification algorithm and use it to scan 11 data sets of vertebrate fibrillar collagens, and predict the periodicity of the resulting assemblies. We analyzed the experimentally observed variance of the optimal stagger distances across species, and find that these distances, and the resulting fibrillar phenotypes, are evolutionary well preserved. Moreover, we observed that the energy minimum at the optimal stagger distance is broad in all cases, suggesting a further evolutionary adaptation designed to improve the assembly kinetics. Our periodicity predictions are not only in good agreement with the experimental data on collagen molecular staggering for all collagen types analyzed, but also for synthetic peptides. We argue that, with our model, it becomes possible to design tailor-made, periodic collagen structures, thereby enabling the design of novel biomimetic materials based on collagen-mimetic trimers.

Mechanism of integrin activation by talin and its cooperation with kindlin

Talin-induced integrin binding to extracellular matrix ligands (integrin activation) is the key step to trigger many fundamental cellular processes including cell adhesion, cell migration, and spreading. Talin is widely known to use its N-terminal head domain (talin-H) to bind and activate integrin, but how talin-H operates in the context of full-length talin and its surrounding remains unknown. Here we show that while being capable of inducing integrin activation, talin-H alone exhibits unexpectedly low potency versus a constitutively activated full-length talin. We find that the large C-terminal rod domain of talin (talin-R), which otherwise masks the integrin binding site on talin-H in inactive talin, dramatically enhances the talin-H potency by dimerizing activated talin and bridging it to the integrin co-activator kindlin-2 via the adaptor protein paxillin. These data provide crucial insight into the mechanism of talin and its cooperation with kindlin to promote potent integrin activation, cell adhesion, and signaling.

Prokaryotic Collagen-Like Proteins as Novel Biomaterials

Collagens are the major structural component in animal extracellular matrices and are critical signaling molecules in various cell-matrix interactions. Its unique triple helical structure is enabled by tripeptide Gly-X-Y repeats. Understanding of sequence requirements for animal-derived collagen led to the discovery of prokaryotic collagen-like protein in the early 2000s. These prokaryotic collagen-like proteins are structurally similar to mammalian collagens in many ways. However, unlike the challenges associated with recombinant expression of mammalian collagens, these prokaryotic collagen-like proteins can be readily expressed in E. coli and are amenable to genetic modification. In this review article, we will first discuss the properties of mammalian collagen and provide a comparative analysis of mammalian collagen and prokaryotic collagen-like proteins. We will then review the use of prokaryotic collagen-like proteins to both study the biology of conventional collagen and develop a new biomaterial platform. Finally, we will describe the application of Scl2 protein, a streptococcal collagen-like protein, in thromboresistant coating for cardiovascular devices, scaffolds for bone regeneration, chronic wound dressing and matrices for cartilage regeneration.

Expanding the clinical spectrum of COL2A1 related disorders by a mass like phenotype

MASS phenotype is a connective tissue disorder clinically overlapping with Marfan syndrome and caused by pathogenic variants in FBN1. We report four patients from three families presenting with a MASS-like phenotype consisting of tall stature, arachnodactyly, spinal deformations, dural ectasia, pectus and/or feet deformations, osteoarthritis, and/or high arched palate. Gene panel sequencing was negative for FBN1 variants. However, it revealed likely pathogenic missense variants in three individuals [c.3936G > T p.(Lys1312Asn), c.193G > A p.(Asp65Asn)] and a missense variant of unknown significance in the fourth patient [c.4013G > A p.(Ser1338Asn)] in propeptide coding regions of COL2A1. Pathogenic COL2A1 variants are associated with type II collagenopathies comprising a remarkable clinical variablility. Main features include skeletal dysplasia, ocular anomalies, and auditory defects. A MASS-like phenotype has not been associated with COL2A1 variants before. Thus, the identification of likely pathogenic COL2A1 variants in our patients expands the phenotypic spectrum of type II collagenopathies and suggests that a MASS-like phenotype can be assigned to various hereditary disorders of connective tissue. We compare the phenotypes of our patients with related disorders of connective tissue and discuss possible pathomechanisms and genotype–phenotype correlations for the identified COL2A1 variants. Our data recommend COL2A1 sequencing in FBN1-negative patients suggestive for MASS/Marfan-like phenotype (without aortopathy).

The Regulation of Collagen Processing by miRNAs in Disease and Possible Implications for Bone Turnover

This article describes several recent examples of miRNA governing the regulation of the gene expression involved in bone matrix construction. We present the impact of miRNA on the subsequent steps in the formation of collagen type I. Collagen type I is a main factor of mechanical bone stiffness because it constitutes 90-95% of the organic components of the bone. Therefore, the precise epigenetic regulation of collagen formation may have a significant influence on bone structure. We also describe miRNA involvement in the expression of genes, the protein products of which participate in collagen maturation in various tissues and cancer cells. We show how non-collagenous proteins in the extracellular matrix are epigenetically regulated by miRNA in bone and other tissues. We also delineate collagen mineralisation in bones by factors that depend on miRNA molecules. This review reveals the tissue variability of miRNA regulation at different levels of collagen maturation and mineralisation. The functionality of collagen mRNA regulation by miRNA, as proven in other tissues, has not yet been shown in osteoblasts. Several collagen-regulating miRNAs are co-expressed with collagen in bone. We suggest that collagen mRNA regulation by miRNA could also be potentially important in bone metabolism.

Heterologous expression, fermentation strategies and molecular modification of collagen for versatile applications

Collagen is a kind of high macromolecular protein with unique tissue distribution and distinctive functions in the body. At present, most collagen products are extracted from the tissues and organs of mammals or marine fish. However, this method exhibits several disadvantages, including low efficiency and serious waste generation, which makes it difficult to meet the current market demand. With the rapid development of synthetic biology and the deepening of high-density fermentation technology, the collagen preparation by biosynthesis strategy emerges as the times require. Co-expression with the proline hydroxylase gene can solve the problem of non-hydroxylated collagen, but the yield may be affected. Therefore, improving the expression through molecular modification and dynamic regulation of synthesis is an entry point for future research. Due to the defects in certain properties of the natural collagen, modification of properties would be benefit for meeting the requirements of practical application. In this paper, in-depth investigations on recombinant expression, fermentation, and modification studies of collagen are conducted. Also, it summarizes the research progress of collagen in food, medicine, and beauty industry in recent years. Furthermore, the future development trend and application prospect of collagen are discussed, which would provide guidance for its preparation and application.

Comprehensive RNA sequencing in primary murine keratinocytes and fibroblasts identifies novel biomarkers and provides potential therapeutic targets for skin-related diseases

BACKGROUND

Keratinocytes and fibroblasts represent the major cell types in the epidermis and dermis of the skin and play a significant role in maintenance of skin homeostasis. However, the biological characteristics of keratinocytes and fibroblasts remain to be elucidated. The purpose of this study was to compare the gene expression pattern between keratinocytes and fibroblasts and to explore novel biomarker genes so as to provide potential therapeutic targets for skin-related diseases such as burns, wounds, and aging.

METHODS

Skin keratinocytes and fibroblasts were isolated from newborn mice. To fully understand the heterogeneity of gene expression between keratinocytes and fibroblasts, differentially expressed genes (DEGs) between the two cell types were detected by RNA-seq technology. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the known genes of keratinocytes and fibroblasts and verify the RNA-seq results.

RESULTS

Transcriptomic data showed a total of 4309 DEGs (fold-change > 1.5 and q-value < 0.05). Among them, 2197 genes were highly expressed in fibroblasts and included 10 genes encoding collagen, 16 genes encoding transcription factors, and 14 genes encoding growth factors. Simultaneously, 2112 genes were highly expressed in keratinocytes and included 7 genes encoding collagen, 14 genes encoding transcription factors, and 8 genes encoding growth factors. Furthermore, we summarized 279 genes specifically expressed in keratinocytes and 33 genes specifically expressed in fibroblasts, which may represent distinct molecular signatures of each cell type. Additionally, we observed some novel specific biomarkers for fibroblasts such as Plac8 (placenta-specific 8), Agtr2 (angiotensin II receptor, type 2), Serping1 (serpin peptidase inhibitor, clade G, member 1), Ly6c1 (lymphocyte antigen 6 complex, locus C1), Dpt (dermatopontin), and some novel specific biomarkers for keratinocytes such as Ly6a (lymphocyte antigen 6 complex, locus A) and Lce3c (late cornified envelope 3C), Ccer2 (coiled-coil glutamate-rich protein 2), Col18a1 (collagen, type XVIII, alpha 1) and Col17a1 (collagen type XVII, alpha 1). In summary, these data provided novel identifying biomarkers for two cell types, which can provide a resource of DEGs for further investigations.

Genetic and Epigenetic Aspects of Skin Collagen Fiber Turnover and Functioning

One of the most important functions of the skin, i.e., protection from mechanical damage, is ensured by collagen fibers and their interaction with other elements in the extracellular matrix. Collagen fiber turnover is a complex multi-stage process. At each stage, a disruption may occur, leading to a decrease in the mechanical properties of the connective tissue. Clinically, collagen formation disorders manifest themselves as increased flabbiness and looseness of the skin and as early signs of facial aging. In addition to the clinical picture, it is important for cosmetologists and dermatologists to understand the etiology and pathogenesis of collagenopathies. In our review, we summarized and systematized the available information concerning the role of genetic and epigenetic factors in skin collagen fiber turnover. Furthermore, we focused on the functions of different types of collagens present in the skin. Understanding the etiology of impaired collagen formation can allow doctors to prescribe pathogenetically based treatments, achieve the most effective results, and minimize adverse reactions.

Hypusinated eIF5A is required for the translation of collagen

Translation of mRNAs that encode peptide sequences with consecutive prolines (polyproline) requires the conserved and essential elongation factor eIF5A to facilitate the formation of peptide bonds. It has been shown that, upon eIF5A depletion, yeast ribosomes stall in polyproline motifs, but also in tripeptide sequences that combine proline with glycine and charged amino acids. Mammalian collagens are enriched in putative eIF5A-dependent Pro-Gly-containing tripeptides. Here, we show that depletion of active eIF5A in mouse fibroblasts reduced collagen type I α1 chain (Col1a1) content, which concentrated around the nuclei. Moreover, it provoked the upregulation of endoplasmic reticulum (ER) stress markers, suggesting retention of partially synthesized collagen 1 (Col1) in the ER. We confirmed that eIF5A is needed for heterologous collagen synthesis in yeast and, using a double luciferase reporter system, showed that eIF5A depletion interrupts translation at Pro-Gly collagenic motifs. A dramatically lower level of Col1a1 protein was also observed in functional eIF5A-depleted human hepatic stellate cells treated with the profibrotic cytokine TGF-β1. In sum, our results show that collagen expression requires eIF5A and imply its potential as a target for regulating collagen production in fibrotic diseases.

Collagen's enigmatic, highly conserved N-glycan has an essential proteostatic function

Intracellular procollagen folding begins at the protein's C-terminal propeptide (C-Pro) domain, which initiates triple-helix assembly and defines the composition and chain register of fibrillar collagen trimers. The C-Pro domain is later proteolytically cleaved and excreted from the body, while the mature triple helix is incorporated into the extracellular matrix. The procollagen C-Pro domain possesses a single N-glycosylation site that is widely conserved in all the fibrillar procollagens across humans and diverse other species. Given that the C-Pro domain is removed once procollagen folding is complete, the N-glycan might be presumed to be important for folding. Surprisingly, however, there is no difference in the folding and secretion of N-glycosylated versus non-N-glycosylated collagen type-I, leaving the function of the N-glycan unclear. We hypothesized that the collagen N-glycan might have a context-dependent function, specifically, that it could be required to promote procollagen folding only when proteostasis is challenged. We show that removal of the N-glycan from misfolding-prone C-Pro domain variants does indeed cause serious procollagen and ER proteostasis defects. The N-glycan promotes folding and secretion of destabilized C-Pro variants by providing access to the ER's lectin-based chaperone machinery. Finally, we show that the C-Pro N-glycan is actually critical for the folding and secretion of even wild-type procollagen under ER stress conditions. Such stress is commonly incurred during development, wound healing, and other processes in which collagen production plays a key role. Collectively, these results establish an essential, context-dependent function for procollagen's previously enigmatic N-glycan, wherein the carbohydrate moiety buffers procollagen folding against proteostatic challenge.

Lumbar Scheuermann's disease found in a patient with osteogenesis imperfecta (OI) caused by a heterozygous mutation in COL1A2 (c.4048G > A): a case report

Background

Osteogenesis imperfecta (OI) is a heterogeneous connective tissue disorder characterized by increased bone fragility and a series of extraskeletal manifestations. Approximately 90 % of OI cases are caused by type I collagen variants encoded by the collagen type I alpha 1 (COL1A1) or type I alpha 2 (COL1A2) gene. Lumbar Scheuermann’s disease is an atypical type of Scheuermann’s disease accompanied by Schmorl’s nodes and irregular endplates but without pronounced kyphosis. Although the etiology of Scheuermann’s disease is unclear, genetic and environmental factors are likely.

Case presentation

Here, we report a 32-year-old male patient who experienced multiple brittle fractures. Gene sequencing revealed a heterozygous mutation, c.4048G > A (p.G1350S), in the COL1A2 gene, and the patient was diagnosed with OI. Magnetic resonance imaging of his thoracolumbar spine revealed multiple Schmorl’s nodes.

Conclusions

This is the first reported case of OI coexisting with the spinal presentation of Scheuermann’s disease. It is speculated that the COL1A2 gene mutation might be an underlying novel genetic cause of Scheuermann’s disease. In conclusion, this case demonstrates the relationship between Scheuermann’s disease and OI for the first time and enriches the genotype-phenotype spectrum of OI.

Collagen Biosynthesis, Processing, and Maturation in Lung Ageing

In addition to providing a macromolecular scaffold, the extracellular matrix (ECM) is a critical regulator of cell function by virtue of specific physical, biochemical, and mechanical properties. Collagen is the main ECM component and hence plays an essential role in the pathogenesis and progression of chronic lung disease. It is well-established that many chronic lung diseases, e.g., chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) primarily manifest in the elderly, suggesting increased susceptibility of the aged lung or accumulated alterations in lung structure over time that favour disease. Here, we review the main steps of collagen biosynthesis, processing, and turnover and summarise what is currently known about alterations upon lung ageing, including changes in collagen composition, modification, and crosslinking. Recent proteomic data on mouse lung ageing indicates that, while the ER-resident machinery of collagen biosynthesis, modification and triple helix formation appears largely unchanged, there are specific changes in levels of type IV and type VI as well as the two fibril-associated collagens with interrupted triple helices (FACIT), namely type XIV and type XVI collagens. In addition, levels of the extracellular collagen crosslinking enzyme lysyl oxidase are decreased, indicating less enzymatically mediated collagen crosslinking upon ageing. The latter contrasts with the ageing-associated increase in collagen crosslinking by advanced glycation endproducts (AGEs), a result of spontaneous reactions of protein amino groups with reactive carbonyls, e.g., from monosaccharides or reactive dicarbonyls like methylglyoxal. Given the slow turnover of extracellular collagen such modifications accumulate even more in ageing tissues. In summary, the collective evidence points mainly toward age-induced alterations in collagen composition and drastic changes in the molecular nature of collagen crosslinks. Future work addressing the consequences of these changes may provide important clues for prevention of lung disease and for lung bioengineering and ultimately pave the way to novel targeted approaches in lung regenerative medicine.

Genetic analysis in Japanese patients with osteogenesis imperfecta: Genotype and phenotype spectra in 96 probands

BACKGROUND

Osteogenesis imperfecta (OI) is a rare connective-tissue disorder characterized by bone fragility. Approximately 90% of all OI cases are caused by variants in COL1A1 or COL1A2. Additionally, IFITM5 variants are responsible for the unique OI type 5. We previously analyzed COL1A1/2 variants in 22 Japanese families with OI through denaturing high-performance liquid chromatography screening, but our detection rate was low (41%).

METHODS

To expand the genotype-phenotype correlations, we performed a genetic analysis of COL1A1/2 and IFITM5 in 96 non-consanguineous Japanese OI probands by Sanger sequencing.

RESULTS

Of these individuals, 54, 41, and 1 had type 1 (mild), type 2-4 (moderate-to-severe), and type 5 phenotypes, respectively. In the mild group, COL1A1 nonsense and splice-site variants were prevalent (n = 30 and 20, respectively), but there were also COL1A1 and COL1A2 triple-helical glycine substitutions (n = 2 and 1, respectively). In the moderate-to-severe group, although COL1A1 and COL1A2 glycine substitutions were common (n = 14 and 18, respectively), other variants were also detected. The single case of type 5 had the characteristic c.-14C>T variant in IFITM5.

CONCLUSION

These results increase our previous detection rate for COL1A1/2 variants to 99% and provide insight into the genotype-phenotype correlations in OI.

Dual-LC PSHG microscopy for imaging collagen type I and type II gels with pixel-resolution analysis

Collagen of type I (Col I) and type II (Col II) are critical for cartilage and connective tissues in the human body, and several diseases may alter their properties. Assessing the identification and quantification of fibrillar collagen without biomarkers is a challenge. Advancements in non-invasive polarization-resolved second-harmonic generation (PSHG) microscopy have provided a method for the non-destructive investigation of collagen molecular level properties. Here we explored an alternative polarization modulated approach, dual-LC PSHG, that is based on two liquid crystal devices (Liquid crystal polarization rotators, LPRs) operating simultaneously with a laser scanning SHG microscope. We demonstrated that this more accessible technology allows the quick and accurate generation of any desired linear and circular polarization state without any mechanical parts. This study demonstrates that this method can aid in improving the ability to quantify the characteristics of both types of collagen, including pitch angle, anisotropy, and circular dichroism analysis. Using this approach, we estimated the effective pitch angle for Col I and Col II to be 49.7° and 51.6°, respectively. The effective peptide pitch angle for Col II gel was first estimated and is similar to the value obtained for Col I gel in the previous studies. Additionally, the difference of the anisotropy parameter of both collagen type gels was assessed to be 0.293, which reflects the different type molecular fibril assembly. Further, our work suggests a potential method for monitoring and differentiating different collagen types in biological tissues, especially cartilage or connective tissue.

Type I collagen deletion in αSMA+ myofibroblasts augments immune suppression and accelerates progression of pancreatic cancer

Stromal desmoplastic reaction in pancreatic ductal adenocarcinoma (PDAC) involves significant accumulation of type I collagen (Col1). However, the precise molecular and mechanistic contribution of Col1 in PDAC progression remains unknown. Activated pancreatic stellate cells/αSMA+ myofibroblasts are major contributors of Col1 in the PDAC stroma. We use a dual-recombinase genetic mouse model of spontaneous PDAC to delete Col1 specifically in myofibroblasts. This results in significant reduction of total stromal Col1 content and accelerates the emergence of PanINs and PDAC, decreasing overall survival. Col1 deletion leads to Cxcl5 upregulation in cancer cells via SOX9. Increase in Cxcl5 is associated with recruitment of myeloid-derived suppressor cells and suppression of CD8+ T cells, which can be attenuated with combined targeting of CXCR2 and CCR2 to restrain accelerated PDAC progression in the setting of stromal Col1 deletion. Our results unravel the fundamental role of myofibroblast-derived Co1l in regulating tumor immunity and restraining PDAC progression.

Quality Control of Procollagen in Cells

Collagen is the most abundant protein in mammals. A unique feature of collagen is its triple-helical structure formed by the Gly-Xaa-Yaa repeats. Three single chains of procollagen make a trimer, and the triple-helical structure is then folded in the endoplasmic reticulum (ER). This unique structure is essential for collagen's functions in vivo, including imparting bone strength, allowing signal transduction, and forming basement membranes. The triple-helical structure of procollagen is stabilized by posttranslational modifications and intermolecular interactions, but collagen is labile even at normal body temperature. Heat shock protein 47 (Hsp47) is a collagen-specific molecular chaperone residing in the ER that plays a pivotal role in collagen biosynthesis and quality control of procollagen in the ER. Mutations that affect the triple-helical structure or result in loss of Hsp47 activity cause the destabilization of procollagen, which is then degraded by autophagy. In this review, we present the current state of the field regarding quality control of procollagen.

Cultivation of human skin cells under physiological oxygen concentration modulates expression of skin significant genes and response to hydroxy acids

Physiological oxygen concentration (physioxia) ranges from 1 to 8% in human tissues while many researchers cultivate mammalian cells under an atmospheric concentration of 21% (hyperoxia). Oxygen is one of the significant gases which functions in human cells including energy production in mitochondria, metabolism in peroxidase, and transcription of various genes in company with HIF (Hypoxia-inducible factors) in the nucleus. Thus, mammalian cell culture should be deliberated on the oxygen concentration to mimic in vivo physiology. Here, we studied if the cultivation of human skin cells under physiological conditions could affect skin significant genes in barrier functions and dermal matrix formation. We further examined that some representative active ingredients in dermatology such as glycolic acid, gluconolactone, and salicylic acid work in different ways depending on the oxygen concentration. Taken together, we present the importance of oxygen concentration in skin cell culture for proper screening of novel ingredients as well as the mechanistic study of skin cell regulation.

A trimeric human angiotensin-converting enzyme 2 as an anti-SARS-CoV-2 agent

Effective intervention strategies are urgently needed to control the COVID-19 pandemic. Human angiotensin-converting enzyme 2 (ACE2) is a membrane-bound carboxypeptidase that forms a dimer and serves as the cellular receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). ACE2 is also a key negative regulator of the renin-angiotensin system that modulates vascular functions. We report here the properties of a trimeric ACE2 ectodomain variant, engineered using a structure-based approach. The trimeric ACE2 variant has a binding affinity of ~60 pM for the spike protein of SARS‑CoV‑2 (compared with 77 nM for monomeric ACE2 and 12-22 nM for dimeric ACE2 constructs), and its peptidase activity and the ability to block activation of angiotensin II receptor type 1 in the renin-angiotensin system are preserved. Moreover, the engineered ACE2 potently inhibits SARS‑CoV‑2 infection in cell culture. These results suggest that engineered, trimeric ACE2 may be a promising anti-SARS-CoV-2 agent for treating COVID-19.

Homozygous HESX1 and COL1A1 Gene Variants in a Boy with Growth Hormone Deficiency and Early Onset Osteoporosis

We report on a patient born to consanguineous parents, presenting with Growth Hormone Deficiency (GHD) and osteoporosis. SNP-array analysis and exome sequencing disclosed long contiguous stretches of homozygosity and two distinct homozygous variants in HESX1 (Q6H) and COL1A1 (E1361K) genes. The HESX1 variant was described as causative in a few subjects with an incompletely penetrant dominant form of combined pituitary hormone deficiency (CPHD). The COL1A1 variant is rare, and so far it has never been found in a homozygous form. Segregation analysis showed that both variants were inherited from heterozygous unaffected parents. Present results further elucidate the inheritance pattern of HESX1 variants and recommend assessing the clinical impact of variants located in C-terminal propeptide of COL1A1 gene for their potential association with rare recessive and early onset forms of osteoporosis.

Collagen Mimetic Peptides

Since their first synthesis in the late 1960s, collagen mimetic peptides (CMPs) have been used as a molecular tool to study collagen, and as an approach to develop novel collagen mimetic biomaterials. Collagen, a major extracellular matrix (ECM) protein, plays vital roles in many physiological and pathogenic processes. Applications of CMPs have advanced our understanding of the structure and molecular properties of a collagen triple helix-the building block of collagen-and the interactions of collagen with important molecular ligands. The accumulating knowledge is also paving the way for developing novel CMPs for biomedical applications. Indeed, for the past 50 years, CMP research has been a fast-growing, far-reaching interdisciplinary field. The major development and achievement of CMPs were documented in a few detailed reviews around 2010. Here, we provided a brief overview of what we have learned about CMPs-their potential and their limitations. We focused on more recent developments in producing heterotrimeric CMPs, and CMPs that can form collagen-like higher order molecular assemblies. We also expanded the traditional view of CMPs to include larger designed peptides produced using recombinant systems. Studies using recombinant peptides have provided new insights on collagens and promoted progress in the development of collagen mimetic fibrillar self-assemblies.

Prolyl and lysyl hydroxylases in collagen synthesis

Collagens are the most abundant proteins in the extracellular matrix. They provide a framework to build organs and tissues and give structural support to make them resistant to mechanical load and forces. Several intra- and extracellular modifications are needed to make functional collagen molecules, intracellular post-translational modifications of proline and lysine residues having key roles in this. In this article, we provide a review on the enzymes responsible for the proline and lysine modifications, that is collagen prolyl 4-hydroxylases, 3-hydroxylases and lysyl hydroxylases, and discuss their biological functions and involvement in diseases.

Collagen: quantification, biomechanics, and role of minor subtypes in cartilage

Collagen is a ubiquitous biomaterial in vertebrate animals. Although each of its 28 subtypes contributes to the functions of many different tissues in the body, most studies on collagen or collagenous tissues have focussed on only one or two subtypes. With recent developments in analytical chemistry, especially mass spectrometry, significant advances have been made toward quantifying the different collagen subtypes in various tissues; however, high-throughput and low-cost methods for collagen subtype quantification do not yet exist. In this Review, we introduce the roles of collagen subtypes and crosslinks, and describe modern assays that enable a deep understanding of tissue physiology and disease states. Using cartilage as a model tissue, we describe the roles of major and minor collagen subtypes in detail; discuss known and unknown structure-function relationships; and show how tissue engineers may harness the functional characteristics of collagen to engineer robust neotissues.

A trimeric human angiotensin-converting enzyme 2 as an anti-SARS-CoV-2 agent in vitro

Effective intervention strategies are urgently needed to control the COVID-19 pandemic. Human angiotensin-converting enzyme 2 (ACE2) is a carboxypeptidase that forms a dimer and serves as the cellular receptor for SARS-CoV-2. It is also a key negative regulator of the renin-angiotensin system (RAS), conserved in mammals, which modulates vascular functions. We report here the properties of a trimeric ACE2 variant, created by a structure-based approach, with binding affinity of ~60 pM for the spike (S) protein of SARS-CoV-2, while preserving the wildtype peptidase activity as well as the ability to block activation of angiotensin II receptor type 1 in the RAS. Moreover, the engineered ACE2 potently inhibits infection of SARS-CoV-2 in cell culture. These results suggest that engineered, trimeric ACE2 may be a promising anti-SARS-CoV-2 agent for treating COVID-19.