A molecular ensemble in the rER for procollagen maturation

Pathobiology of the crystalline lens in Stickler syndrome

PURPOSE

The Stickler syndromes are a group of connective tissue disorders characterised by congenital myopia, giant retinal tear and retinal detachment, cleft palate, hearing loss and premature arthropathy. Patients with Stickler syndrome are also susceptible to abnormalities of the crystalline lens. Since neither type II or type XI collagen (those typically affected in the vast majority of Stickler patients) are highly expressed in the lens, this observational cohort study explores potential alternative mechanisms to explain why patients frequently exhibit such unusual but characteristic types of cataract.

METHODS

Author observations drawn from a cohort of over 1,800 patients with genetically confirmed Stickler syndrome.

RESULTS

3 distinct lens pathologies were identified. Firstly, a congenital quadrantic lamellar opacity. This can be present in both type 1 (COL2A1) and type 2 (COL11A1) Stickler syndrome. Secondly, early onset Pantone 557 C blue-green nuclear cataract. Thirdly, congenital lens coloboma associated with localised zonule deficiency.

CONCLUSIONS

The characteristic quadrantic lamellar lens opacity can be helpful in alerting to the possible diagnosis, particularly in sub-groups with an ocular-only phenotype. Temporal and spatial signalling pathways shared embryologically by both the developing vitreous body and crystalline lens suggest an ancillary role of the fibrillar collagens in cell signalling beyond their basic structural function. A common pathway of TGFb/BMP super-family dysregulation may be shared with allied disorders associated with both retinal detachment and cataract as well as the pathobiology linking retinal detachment and cataract in the population at large. Congenital lens coloboma associated with localised zonule deficiency can increase the difficulty and risks of cataract surgery. Strategies to mitigate such risks are presented.

Setrusumab for the treatment of osteogenesis imperfecta: 12-month results from the phase 2b asteroid study

Osteogenesis imperfecta (OI) is a rare genetic disorder commonly caused by variants of the type I collagen genes COL1A1 and COL1A2. OI is associated with increased bone fragility, bone deformities, bone pain, and reduced growth. Setrusumab, a neutralizing antibody to sclerostin, increased areal bone mineral density (aBMD) in a 21-week phase 2a dose escalation study. The phase 2b Asteroid (NCT03118570) study evaluated the efficacy and safety of setrusumab in adults. Adults with a clinical diagnosis of OI type I, III, or IV, a pathogenic variant in COL1A1/A2, and a recent fragility fracture were randomized 1:1:1:1 to receive 2, 8, or 20 mg/kg setrusumab doses or placebo by monthly intravenous infusion during a 12-mo treatment period. Participants initially randomized to the placebo group were subsequently reassigned to receive setrusumab 20 mg/kg open label. Therefore, only results from the 2, 8, and 20 mg/kg double-blind groups are presented herein. The primary endpoint of Asteroid was change in distal radial trabecular volumetric bone mineral density (vBMD) from baseline at month 12, supported by changes in high-resolution peripheral quantitative computed tomography micro-finite element (microFE)-derived bone strength. A total of 110 adults were enrolled with similar baseline characteristics across treatment groups. At 12 mo, there was a significant increase in mean (SE) failure load in the 20 mg/kg group (3.17% [1.26%]) and stiffness in the 8 (3.06% [1.70%]) and 20 mg/kg (3.19% [1.29%]) groups from baseline. There were no changes in radial trabecula vBMD (p>05). Gains in failure load and stiffness were similar across OI types. There were no significant differences in annualized fracture rates between doses. Two adults in the 20 mg/kg group experienced related serious adverse reactions. Asteroid demonstrated a beneficial effect of setrusumab on estimates of bone strength across the different types of OI and provides the basis for additional phase 3 evaluation.

HSP47 in human diseases: Navigating pathophysiology, diagnosis and therapy

Heat shock protein 47 (HSP47) is a chaperone protein responsible for regulating collagen maturation and transport, directly impacting collagen synthesis levels. Aberrant HSP47 expression or malfunction has been associated with collagen-related disorders, most notably fibrosis. Recent reports have uncovered new functions of HSP47 in various cellular processes. Hsp47 dysregulation in these alternative roles has been linked to various diseases, such as cancer, autoimmune and neurodegenerative disorders, thereby highlighting its potential as both a diagnostic biomarker and a therapeutic target. In this review, we discuss the pathophysiological roles of HSP47 in human diseases, its potential as a diagnostic tool, clinical screening techniques and its role as a target for therapeutic interventions.

ColPTMScape: An open access knowledge base for tissue-specific collagen PTM maps

Collagen is a key component of the extracellular matrix (ECM). In the remodeling of ECM, a remarkable variation in collagen post-translational modifications (PTMs) occurs. This makes collagen a potential target for understanding extracellular matrix remodeling during pathological conditions. Over the years, scientists have gathered a huge amount of data about collagen PTM during extracellular matrix remodeling. To make such information easily accessible in a consolidated space, we have developed ColPTMScape (https://colptmscape.iitmandi.ac.in/), a dedicated knowledge base for collagen PTMs. The identified site-specific PTMs, quantitated PTM sites, and PTM maps of collagen chains are deliverables to the scientific community, especially to matrix biologists. Through this knowledge base, users can easily gain information related to the difference in the collagen PTMs across different tissues in different organisms.

Collagen fibril formation at the plasma membrane occurs independently from collagen secretion

Collagen fibrils are the primary supporting scaffold of vertebrate tissues but how they are assembled is unclear. Here, using CRISPR-tagging of type I collagen and SILAC labelling, we elucidate the cellular mechanism for the spatiotemporal assembly of collagen fibrils, in cultured fibroblasts. Our findings reveal multifaceted trafficking of collagen, including constitutive secretion, intracellular pooling, and plasma membrane-directed fibrillogenesis. Notably, we differentiate the processes of collagen secretion and fibril assembly and identify the crucial involvement of endocytosis in regulating fibril formation. By employing Col1a1 knockout fibroblasts we demonstrate the incorporation of exogenous collagen into nucleation sites at the plasma membrane through these recycling mechanisms. Our study sheds light on the assembly process and its regulation in health and disease. Mass spectrometry data are available via ProteomeXchange with identifier PXD036794.

HTRA1-driven detachment of type I collagen from endoplasmic reticulum contributes to myocardial fibrosis in dilated cardiomyopathy

BACKGROUND

The aberrant secretion and excessive deposition of type I collagen (Col1) are important factors in the pathogenesis of myocardial fibrosis in dilated cardiomyopathy (DCM). However, the precise molecular mechanisms underlying the synthesis and secretion of Col1 remain unclear.

METHODS AND RESULTS

RNA-sequencing analysis revealed an increased HtrA serine peptidase 1 (HTRA1) expression in patients with DCM, which is strongly correlated with myocardial fibrosis. Consistent findings were observed in both human and mouse tissues by immunoblotting, quantitative reverse transcription polymerase chain reaction (qRT-PCR), immunohistochemistry, and immunofluorescence analyses. Pearson's analysis showed a markedly positive correlation between HTRA1 level and myocardial fibrosis indicators, including extracellular volume fraction (ECV), native T1, and late gadolinium enhancement (LGE), in patients with DCM. In vitro experiments showed that the suppression of HTRA1 inhibited the conversion of cardiac fibroblasts into myofibroblasts and decreased Col1 secretion. Further investigations identified the role of HTRA1 in promoting the formation of endoplasmic reticulum (ER) exit sites, which facilitated the transportation of Col1 from the ER to the Golgi apparatus, thereby increasing its secretion. Conversely, HTRA1 knockdown impeded the retention of Col1 in the ER, triggering ER stress and subsequent induction of ER autophagy to degrade misfolded Col1 and maintain ER homeostasis. In vivo experiments using adeno-associated virus-serotype 9-shHTRA1-green fluorescent protein (AAV9-shHTRA1-GFP) showed that HTRA1 knockdown effectively suppressed myocardial fibrosis and improved left ventricular function in mice with DCM.

CONCLUSIONS

The findings of this study provide valuable insights regarding the treatment of DCM-associated myocardial fibrosis and highlight the therapeutic potential of targeting HTRA1-mediated collagen secretion.

Designing collagens to shed light on the multi-scale structure-function mapping of matrix disorders

Collagens are the most abundant structural proteins in the extracellular matrix of animals and play crucial roles in maintaining the structural integrity and mechanical properties of tissues and organs while mediating important biological processes. Fibrillar collagens have a unique triple helix structure with a characteristic repeating sequence of (Gly-X-Y)n. Variations within the repetitive sequence can cause misfolding of the triple helix, resulting in heritable connective tissue disorders. The most common variations are single-point missense mutations that lead to the substitution of a glycine residue with a bulkier amino acid (Gly → X). In this review, we will first discuss the importance of collagen's triple helix structure and how single Gly substitutions can impact its folding, structure, secretion, assembly into higher-order structures, and biological functions. We will review the role of "designer collagens," i.e., synthetic collagen-mimetic peptides and recombinant bacterial collagen as model systems to include Gly → X substitutions observed in collagen disorders and investigate their impact on structure and function utilizing in vitro studies. Lastly, we will explore how computational modeling of collagen peptides, especially molecular and steered molecular dynamics, has been instrumental in probing the effects of Gly substitutions on structure, receptor binding, and mechanical stability across multiple length scales.

A STRP-ed definition of Structured Tandem Repeats in Proteins

Tandem Repeat Proteins (TRPs) are a class of proteins with repetitive amino acid sequences that have been studied extensively for over two decades. Different features at the level of sequence, structure, function and evolution have been attributed to them by various authors. And yet many of its salient features appear only when looking at specific subclasses of protein tandem repeats. Here, we attempt to rationalize the existing knowledge on Tandem Repeat Proteins (TRPs) by pointing out several dichotomies. The emerging picture is more nuanced than generally assumed and allows us to draw some boundaries of what is not a "proper" TRP. We conclude with an operational definition of a specific subset, which we have denominated STRPs (Structural Tandem Repeat Proteins), which separates a subclass of tandem repeats with distinctive features from several other less well-defined types of repeats. We believe that this definition will help researchers in the field to better characterize the biological meaning of this large yet largely understudied group of proteins.

Expanding the genetic and clinical spectrum of osteogenesis imperfecta: identification of novel rare pathogenic variants in type I collagen-encoding genes

Introduction

Osteogenesis imperfecta (OI) is a clinically and genetically heterogeneous skeletal disorder. The majority of affected cases are attributed to autosomal dominant pathogenic variants (PVs) found in the COL1A1 and COL1A2 genes, which encode type I collagen. However, PVs in other genes involved in collagen posttranslational modification, processing, crosslinking, osteoblast differentiation, and bone mineralization have also been associated with OI.

Methods

In this study, we present the results of next-generation sequencing (NGS) analysis using a custom panel of 11 genes known to be associated with OI. This clinical study enrolled a total of 10 patients, comprising 7 male and 3 female patients from 7 families, all from the Puglia Region in South Italy, providing a detailed overview of their age, gender, family history, OI type, and non-skeletal features.

Results

The genetic analysis revealed 5 PVs in the COL1A1 gene and 2 PVs in the COL1A2 gene. Importantly, three of these PVs have not been previously reported in the literature. These include two novel heterozygous frameshift PVs in COL1A1 (c.2890_2893del and c.3887del) and one novel heterozygous missense PV in COL1A2 (c.596G>T).

Discussion

The identification of these previously unreported PVs expands the variant spectrum of the COL1A1 and COL1A2 genes and may have implications for accurate diagnosis, genetic counselling, and potential therapeutic interventions in affected individuals and their families.

Local Net Charge State of Collagen Triple Helix Is a Determinant of FKBP22 Binding to Collagen III

Mutations in the FKBP14 gene encoding the endoplasmic reticulum resident collagen-related proline isomerase FK506 binding protein 22 kDa (FKBP22) result in kyphoscoliotic Ehlers-Danlos Syndrome (EDS), which is characterized by a broad phenotypic outcome. A plausible explanation for this outcome is that FKBP22 participates in the biosynthesis of subsets of collagen types: FKBP22 selectively binds to collagens III, IV, VI, and X, but not to collagens I, II, V, and XI. However, these binding mechanisms have never been explored, and they may underpin EDS subtype heterogeneity. Here, we used collagen Toolkit peptide libraries to investigate binding specificity. We observed that FKBP22 binding was distributed along the collagen helix. Further, it (1) was higher on collagen III than collagen II peptides and it (2) was correlated with a positive peptide charge. These findings begin to elucidate the mechanism by which FKBP22 interacts with collagen.

Busulfan-induced hepatic sinusoidal endothelial cell injury: Modulatory role of pirfenidone for therapeutic purposes

Transplantation conditioning using Busulfan has been known to cause hepatotoxicity, which has great individual differences. Some have mild symptoms like the increase of hepatic drug-metabolizing enzyme, while others may have very serious ones, like hepatic sinusoidal obstruction syndrome. However, simply controlling the exposure of Busulfan may not effectively prevent or reduce the occurrence of hepatic sinusoidal obstruction syndrome. The occurrence of hepatic sinusoid obstruction syndrome is closely related to hepatic sinusoidal endothelial cells (HSECs). The objective of this study is to investigate the potential protective effect of Pirfenidone against Busulfan-induced damage to hepatic sinusoidal endothelial cells and to preliminarily explore the mechanisms underlying this protective effect. Our results indicate that Pirfenidone has a great protective effect on the injury induced by Busulfan. In addition, Busulfan increased the relative mRNA expression of transforming growth factor-β1 (TGF-β1), collagen and tissue inhibitor of metalloproteinase-1 in HSECs. After pretreatment with Pirfenidone, the expression level of TGF-β1 was down-regulated. Mechanically, Pirfenidone primarily improves liver fibrosis by inhibiting collagen formation and hepatic stellate cell activation, thereby providing a protective effect on HSECs damaged by Busulfan. Therefore, Pirfenidone may reduce the hepatotoxicity caused by transplantation conditioning regimens based on Busulfan.

Cell differentiation and matrix organization are differentially affected during bone formation in osteogenesis imperfecta zebrafish models with different genetic defects impacting collagen type I structure

Osteogenesis imperfecta (OI) is a family of rare heritable skeletal disorders associated with dominant mutations in the collagen type I encoding genes and recessive defects in proteins involved in collagen type I synthesis and processing and in osteoblast differentiation and activity. Historically, it was believed that the OI bone phenotype was only caused by abnormal collagen type I fibrils in the extracellular matrix, but more recently it became clear that the altered bone cell homeostasis, due to mutant collagen retention, plays a relevant role in modulating disease severity in most of the OI forms and it is correlated to impaired bone cell differentiation. Despite in vitro evidence, in vivo data are missing. To better understand the physiopathology of OI, we used two zebrafish models: Chihuahua (Chi/+), carrying a dominant p.G736D substitution in the α1 chain of collagen type I, and the recessive p3h1-/-, lacking prolyl 3-hydroxylase (P3h1) enzyme. Both models share the delay of collagen type I folding, resulting in its overmodification and partial intracellular retention. The regeneration of the bony caudal fin of Chi/+ and p3h1-/- was employed to investigate the impact of abnormal collagen synthesis on bone cell differentiation. Reduced regenerative ability was evident in both models, but it was associated to impaired osteoblast differentiation and osteoblastogenesis/adipogenesis switch only in Chi/+. On the contrary, reduced osteoclast number and activity were found in both models during regeneration. The dominant OI model showed a more detrimental effect in the extracellular matrix organization. Interestingly, the chemical chaperone 4-phenylbutyrate (4-PBA), known to reduce cellular stress and increase collagen secretion, improved bone formation only in p3h1-/- by favoring caudal fin growth without affecting bone cell markers expression. Taken together, our in vivo data proved the negative impact of structurally abnormal collagen type I on bone formation but revealed a gene mutation-specific effect on bone cell differentiation and matrix organization in OI. These, together with the distinct ability to respond to the chaperone treatment, underline the need for precision medicine approaches to properly treat the disease.

Seasonal Molecular Difference in Fibrillar Collagen Extracts Derived from the Marine Sponge Chondrosia reniformis (Nardo, 1847) and Their Impact on Its Derived Biomaterials

Chondrosia reniformis (Nardo, 1847) is a marine sponge of high biotechnological interest both for its natural compound content and for its peculiar collagen, which is suitable for the production of innovative biomaterials in the form, for instance, of 2D membranes and hydrogels, exploitable in the fields of tissue engineering and regenerative medicine. In this study, the molecular and chemical-physical properties of fibrillar collagen extracted from specimens collected in different seasons are studied to evaluate the possible impact of sea temperature on them. Collagen fibrils were extracted from sponges harvested by the Sdot Yam coast (Israel) during winter (sea temperature: 17 °C) and during summer (sea temperature: 27 °C). The total AA composition of the two different collagens was evaluated, together with their thermal stability and glycosylation level. The results showed a lower lysyl-hydroxylation level, lower thermal stability, and lower protein glycosylation level in fibrils extracted from 17 °C animals compared to those from 27 °C animals, while no differences were noticed in the GAGs content. Membranes obtained with fibrils deriving from 17 °C samples showed a higher stiffness if compared to the 27 °C ones. The lower mechanical properties shown by 27 °C fibrils are suggestive of some unknown molecular changes in collagen fibrils, perhaps related to the creeping behavior of C. reniformis during summer. Overall, the differences in collagen properties gain relevance as they can guide the intended use of the biomaterial.

Upregulation of GLT25D1 in Hepatic Stellate Cells Promotes Liver Fibrosis via the TGF-β1/SMAD3 Pathway In Vivo and In vitro

BACKGROUND AND AIMS

Collagen β(1-O) galactosyltransferase 25 domain 1 (GLT25D1) is associated with collagen production and glycosylation, and its knockout in mice results in embryonic death. However, its role in liver fibrosis remains elusive, particularly in hepatic stellate cells (HSCs), the primary collagen-producing cells associated with liver fibrogenesis. Herein, we aimed to elucidate the role of GLT25D1 in HSCs.

METHODS

Bile duct ligation (BDL)-induced mouse liver fibrosis models, primary mouse HSCs (mHSCs), and transforming growth factor beta 1 (TGF-β1)-stimulated LX-2 human hepatic stellate cells were used in in vivo and in vitro studies. Stable LX-2 cell lines with either GLT25D1 overexpression or knockdown were established using lentiviral transfection. RNA-seq was performed to investigate the genomic differences. HPLC-MS/MS were used to identify glycosylation sites. Scanning electronic microscopy (SEM) and second-harmonic generation/two-photon excited fluorescence (SHG/TPEF) were used to image collagen fibril morphology.

RESULTS

GLT25D1 expression was upregulated in nonparenchymal cells in human cirrhotic liver tissues. Meanwhile, its knockdown attenuated collagen deposition in BDL-induced mouse liver fibrosis and inhibited mHSC activation. GLT25D1 was overexpressed in activated versus quiescence LX-2 cells and regulated in vitro LX-2 cell activation, including proliferation, contraction, and migration. GLT25D1 also significantly increased liver fibrogenic gene and protein expression. GLT25D1 upregulation promoted HSC activation and enhanced collagen expression through the TGF-β1/SMAD signaling pathway. Mass spectrometry showed that GLT25D1 regulated the glycosylation of collagen in HSCs, affecting the diameter of collagen fibers.

CONCLUSIONS

Collectively, the upregulation of GLT25D1 in HSCs promoted the progression of liver fibrosis by affecting HSCs activation and collagen stability.

Rgp1 contributes to craniofacial cartilage development and Rab8a-mediated collagen II secretion

Rgp1 was previously identified as a component of a guanine nucleotide exchange factor (GEF) complex to activate Rab6a-mediated trafficking events in and around the Golgi. While the role of Rgp1 in protein trafficking has been examined in vitro and in yeast, the role of Rgp1 during vertebrate embryogenesis and protein trafficking in vivo is unknown. Using genetic, CRISPR-induced zebrafish mutants for Rgp1 loss-of-function, we found that Rgp1 is required for craniofacial cartilage development. Within live rgp1-/- craniofacial chondrocytes, we observed altered movements of Rab6a+ vesicular compartments, consistent with a conserved mechanism described in vitro. Using transmission electron microscopy (TEM) and immunofluorescence analyses, we show that Rgp1 plays a role in the secretion of collagen II, the most abundant protein in cartilage. Our overexpression experiments revealed that Rab8a is a part of the post-Golgi collagen II trafficking pathway. Following loss of Rgp1, chondrocytes activate an Arf4b-mediated stress response and subsequently respond with nuclear DNA fragmentation and cell death. We propose that an Rgp1-regulated Rab6a-Rab8a pathway directs secretion of ECM cargoes such as collagen II, a pathway that may also be utilized in other tissues where coordinated trafficking and secretion of collagens and other large cargoes is required for normal development and tissue function.

EPHB4-RASA1-Mediated Negative Regulation of Ras-MAPK Signaling in the Vasculature: Implications for the Treatment of EPHB4- and RASA1-Related Vascular Anomalies in Humans

Ephrin receptors constitute a large family of receptor tyrosine kinases in mammals that through interaction with cell surface-anchored ephrin ligands regulate multiple different cellular responses in numerous cell types and tissues. In the cardiovascular system, studies performed in vitro and in vivo have pointed to a critical role for Ephrin receptor B4 (EPHB4) as a regulator of blood and lymphatic vascular development and function. However, in this role, EPHB4 appears to act not as a classical growth factor receptor but instead functions to dampen the activation of the Ras-mitogen activated protein signaling (MAPK) pathway induced by other growth factor receptors in endothelial cells (EC). To inhibit the Ras-MAPK pathway, EPHB4 interacts functionally with Ras p21 protein activator 1 (RASA1) also known as p120 Ras GTPase-activating protein. Here, we review the evidence for an inhibitory role for an EPHB4-RASA1 interface in EC. We further discuss the mechanisms by which loss of EPHB4-RASA1 signaling in EC leads to blood and lymphatic vascular abnormalities in mice and the implications of these findings for an understanding of the pathogenesis of vascular anomalies in humans caused by mutations in EPHB4 and RASA1 genes. Last, we provide insights into possible means of drug therapy for EPHB4- and RASA1-related vascular anomalies.

Assessment of Collagen in Translational Models of Lung Research

The extracellular matrix (ECM) plays an important role in lung health and disease. Collagen is the main component of the lung ECM, widely used for the establishment of in vitro and organotypic models of lung disease, and as scaffold material of general interest for the field of lung bioengineering. Collagen also is the main readout for fibrotic lung disease, where collagen composition and molecular properties are drastically changed and ultimately result in dysfunctional "scarred" tissue. Because of the central role of collagen in lung disease, quantification, determination of molecular properties, and three-dimensional visualization of collagen is important for both development and characterization of translational models of lung research. In this chapter, we provide a comprehensive overview on the various methodologies currently available for quantification and characterization of collagen including their detection principles, advantages, and disadvantages.

Zebrafish Tric-b is required for skeletal development and bone cells differentiation

INTRODUCTION

Trimeric intracellular potassium channels TRIC-A and -B are endoplasmic reticulum (ER) integral membrane proteins, involved in the regulation of calcium release mediated by ryanodine (RyRs) and inositol 1,4,5-trisphosphate (IP₃Rs) receptors, respectively. While TRIC-A is mainly expressed in excitable cells, TRIC-B is ubiquitously distributed at moderate level. TRIC-B deficiency causes a dysregulation of calcium flux from the ER, which impacts on multiple collagen specific chaperones and modifying enzymatic activity, leading to a rare form of osteogenesis imperfecta (OI Type XIV). The relevance of TRIC-B on cell homeostasis and the molecular mechanism behind the disease are still unknown.

RESULTS

In this study, we exploited zebrafish to elucidate the role of TRIC-B in skeletal tissue. We demonstrated, for the first time, that tmem38a and tmem38b genes encoding Tric-a and -b, respectively are expressed at early developmental stages in zebrafish, but only the latter has a maternal expression. Two zebrafish mutants for tmem38b were generated by CRISPR/Cas9, one carrying an out of frame mutation introducing a premature stop codon (tmem38b^-/- ) and one with an in frame deletion that removes the highly conserved KEV domain (tmem38b^{Δ120-7/Δ120-7} ). In both models collagen type I is under-modified and partially intracellularly retained in the endoplasmic reticulum, as described in individuals affected by OI type XIV. Tmem38b^-/- showed a mild skeletal phenotype at the late larval and juvenile stages of development whereas tmem38b^{Δ120-7/Δ120-7} bone outcome was limited to a reduced vertebral length at 21 dpf. A caudal fin regeneration study pointed towards impaired activity of osteoblasts and osteoclasts associated with mineralization impairment.

DISCUSSION

Our data support the requirement of Tric-b during early development and for bone cell differentiation.

Extracellular matrix stiffness-The central cue for skin fibrosis

Skin fibrosis is a physiopathological process featuring the excessive deposition of extracellular matrix (ECM), which is the main architecture that provides structural support and constitutes the microenvironment for various cellular behaviors. Recently, increasing interest has been drawn to the relationship between the mechanical properties of the ECM and the initiation and modulation of skin fibrosis, with the engagement of a complex network of signaling pathways, the activation of mechanosensitive proteins, and changes in immunoregulation and metabolism. Simultaneous with the progression of skin fibrosis, the stiffness of ECM increases, which in turn perturbs mechanical and humoral homeostasis to drive cell fate toward an outcome that maintains and enhances the fibrosis process, thus forming a pro-fibrotic "positive feedback loop". In this review, we highlighted the central role of the ECM and its dynamic changes at both the molecular and cellular levels in skin fibrosis. We paid special attention to signaling pathways regulated by mechanical cues in ECM remodeling. We also systematically summarized antifibrotic interventions targeting the ECM, hopefully enlightening new strategies for fibrotic diseases.

Extraction and characterization of collagen from the skin of Amazonian freshwater fish pirarucu

The need to fully exploit fishing resources due to increasing production and consequent waste generation requires research to promote the sustainability of the fishing industry. Fish waste from the industry is responsible for relevant environmental contamination. However, these raw materials contain high amounts of collagen and other biomolecules, being attractive due to their industrial and biotechnological applicability. Thus, to reduce the waste from pirarucu (Arapaima gigas) processing, this study aimed to obtain collagen from pirarucu skin tissue. The extraction process used 0.05 M sodium hydroxide, 10% butyl alcohol, and 0.5 M acetic acid, with extraction temperature of 20°C. The obtained yield was 27.8%, and through sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), it was determined that the collagen obtained was type I. This study showed that collagen solubility was highest at pH 3 and the lowest solubility was at concentrations of 3% sodium chloride. The denaturation temperature of collagen was 38.1°C, and its intact molecular structure was observed using the Fourier transform infrared spectrophotometry technique with an absorption radius of 1. The results showed that it was possible to obtain collagen from pirarucu skin at 20°C, which has the typical characteristics of commercial type I collagen. In conclusion, the procedures used may be considered to be an interesting alternative for collagen extraction, a new product obtained from the processing of fish waste.

Lysyl hydroxylase 3-mediated post-translational modifications are required for proper biosynthesis of collagen α1α1α2(IV)

Collagens are the most abundant proteins in the body and among the most biosynthetically complex. A molecular ensemble of over 20 endoplasmic reticulum resident proteins participates in collagen biosynthesis and contributes to heterogeneous post-translational modifications. Pathogenic variants in genes encoding collagens cause connective tissue disorders, including osteogenesis imperfecta, Ehlers-Danlos syndrome, and Gould syndrome (caused by mutations in COL4A1 and COL4A2), and pathogenic variants in genes encoding proteins required for collagen biosynthesis can cause similar but overlapping clinical phenotypes. Notably, pathogenic variants in lysyl hydroxylase 3 (LH3) cause a multisystem connective tissue disorder that exhibits pathophysiological features of collagen-related disorders. LH3 is a multifunctional collagen-modifying enzyme; however, its precise role(s) and substrate specificity during collagen biosynthesis has not been defined. To address this critical gap in knowledge, we generated LH3 KO cells and performed detailed quantitative and molecular analyses of collagen substrates. We found that LH3 deficiency severely impaired secretion of collagen α1α1α2(IV) but not collagens α1α1α2(I) or α1α1α1(III). Amino acid analysis revealed that LH3 is a selective LH for collagen α1α1α2(IV) but a general glucosyltransferase for collagens α1α1α2(IV), α1α1α2(I), and α1α1α1(III). Importantly, we identified rare variants that are predicted to be pathogenic in the gene encoding LH3 in two of 113 fetuses with intracranial hemorrhage-a cardinal feature of Gould syndrome. Collectively, our findings highlight a critical role of LH3 in α1α1α2(IV) biosynthesis and suggest that LH3 pathogenic variants might contribute to Gould syndrome.

Rosemary Extract-Induced Autophagy and Decrease in Accumulation of Collagen Type I in Osteogenesis Imperfecta Skin Fibroblasts

Osteogenesis imperfecta (OI) is a heterogeneous connective tissue disease mainly caused by structural mutations in type I collagen. Mutant collagen accumulates intracellularly, causing cellular stress that has recently been shown to be phenotype-related. Therefore, the aim of the study was to search for potential drugs reducing collagen accumulation and improving OI fibroblast homeostasis. We found that rosemary extract (RE), which is of great interest to researchers due to its high therapeutic potential, at concentrations of 50 and 100 µg/mL significantly reduced the level of accumulated collagen in the fibroblasts of four patients with severe and lethal OI. The decrease in collagen accumulation was associated with RE-induced autophagy as was evidenced by an increase in the LC3-II/LC3-I ratio, a decrease in p62, and co-localization of type I collagen with LC3-II and LAMP2A by confocal microscopy. The unfolded protein response, activated in three of the four tested cells, and the level of pro-apoptotic markers (Bax, CHOP and cleaved caspase 3) were attenuated by RE. In addition, the role of RE-modulated proteasome in the degradation of unfolded procollagen chains was investigated. This study provides new insight into the beneficial effects of RE that may have some implications in OI therapy targeting cellular stress.

HypDB: A functionally annotated web-based database of the proline hydroxylation proteome

Proline hydroxylation (Hyp) regulates protein structure, stability, and protein-protein interaction. It is widely involved in diverse metabolic and physiological pathways in cells and diseases. To reveal functional features of the Hyp proteome, we integrated various data sources for deep proteome profiling of the Hyp proteome in humans and developed HypDB (https://www.HypDB.site), an annotated database and web server for Hyp proteome. HypDB provides site-specific evidence of modification based on extensive LC-MS analysis and literature mining with 14,413 nonredundant Hyp sites on 5,165 human proteins including 3,383 Class I and 4,335 Class II sites. Annotation analysis revealed significant enrichment of Hyp on key functional domains and tissue-specific distribution of Hyp abundance across 26 types of human organs and fluids and 6 cell lines. The network connectivity analysis further revealed a critical role of Hyp in mediating protein-protein interactions. Moreover, the spectral library generated by HypDB enabled data-independent analysis (DIA) of clinical tissues and the identification of novel Hyp biomarkers in lung cancer and kidney cancer. Taken together, our integrated analysis of human proteome with publicly accessible HypDB revealed functional diversity of Hyp substrates and provides a quantitative data source to characterize Hyp in pathways and diseases.

Golgin Subfamily A Member 5 Is Essential for Production of Extracellular Matrix Proteins during TGF-β1-Induced Periodontal Ligament-Fibroblastic Differentiation

Human periodontal ligament stem cells (hPDLSCs) can be differentiated into periodontal ligament- (PDL-) fibroblastic progenitors by treatment with low concentrations of transforming growth factor beta 1 (TGF-β1). Although much is known about the profibrotic effects of TGF-β1, the molecular mechanisms mediating the activation of fibroblasts in periodontal ligament-fibroblastic differentiation are not well known. Our study was to investigate the mechanism of the fibroblastic process in the periodontal ligament differentiation of hPDLSCs through the discovery of novel markers. One of the monoclonal antibodies previously established through decoy immunization was the anti-LG11 antibody, which recognized Golgi subfamily A member 5 (GOLGA5) as a PDL-fibroblastic progenitor-specific antigen. GOLGA5/LG11 was significantly upregulated in TGF-β1-induced PDL-fibroblastic progenitors and accumulated in the PDL region of the tooth root. GOLGA5 plays a role in vesicle tethering and docking between the endoplasmic reticulum and the Golgi apparatus. siRNA-mediated depletion of endogenous GOLGA5 upregulated in TGF-β1-induced PDL-fibroblastic progenitors resulted in downregulation of representative PDL-fibroblastic markers and upregulation of osteoblast markers. When the TGF-β1 signaling pathway was blocked or GOLGA5 was depleted by siRNA, the levels of extracellular matrix (ECM) proteins, such as type I collagen and fibronectin, decreased in PDL-fibroblastic progenitors. In addition, Golgi structures in the perinuclear region underwent fragmentation under these conditions. These results suggest that GOLGA5/LG11 is a PDL-fibroblastic marker with functional importance in ECM protein production and secretion, which are important processes in PDL-fibroblastic differentiation.

Molecular Basis of Pathogenic Variants in the Fibrillar Collagens

The fibrillar collagen family is comprised of the quantitatively major types I, II and III collagens and the quantitatively minor types V and XI. These form heterotypic collagen fibrils (composed of more than a single collagen type) where the minor collagens have a regulatory role in controlling fibril formation and diameter. The structural pre-requisites for normal collagen biosynthesis and fibrillogenesis result in many places where this process can be disrupted, and consequently a wide variety of phenotypes result when pathogenic changes occur in these fibrillar collagen genes. Another contributing factor is alternative splicing, both naturally occurring and as the result of pathogenic DNA alterations. This article will discuss how these factors should be taken into account when assessing DNA sequencing results from a patient.

Collagen misfolding mutations: the contribution of the unfolded protein response to the molecular pathology

Mutations in collagen genes cause a broad range of connective tissue pathologies. Structural mutations that impact procollagen assembly or triple helix formation and stability are a common and important mutation class. How misfolded procollagens engage with the cellular proteostasis machinery and whether they can elicit a cytotoxic unfolded protein response (UPR) is a topic of considerable research interest. Such interest is well justified since modulating the UPR could offer a new approach to treat collagenopathies for which there are no current disease mechanism-targeting therapies. This review scrutinizes the evidence underpinning the view that endoplasmic reticulum stress and chronic UPR activation contributes significantly to the pathophysiology of the collagenopathies. While there is strong evidence that the UPR contributes to the pathology for collagen X misfolding mutations, the evidence that misfolding mutations in other collagen types induce a canonical, cytotoxic UPR is incomplete. To gain a more comprehensive understanding about how the UPR amplifies to pathology, and thus what types of manipulations of the UPR might have therapeutic relevance, much more information is needed about how specific misfolding mutation types engage differentially with the UPR and downstream signaling responses. Most importantly, since the capacity of the proteostasis machinery to respond to collagen misfolding is likely to vary between cell types, reflecting their functional roles in collagen and extracellular matrix biosynthesis, detailed studies on the UPR should focus as much as possible on the actual target cells involved in the collagen pathologies.

FK506-Binding Protein 11 Is a Novel Plasma Cell-Specific Antibody Folding Catalyst with Increased Expression in Idiopathic Pulmonary Fibrosis

Antibodies are central effectors of the adaptive immune response, widespread used therapeutics, but also potentially disease-causing biomolecules. Antibody folding catalysts in the plasma cell are incompletely defined. Idiopathic pulmonary fibrosis (IPF) is a fatal chronic lung disease with increasingly recognized autoimmune features. We found elevated expression of FK506-binding protein 11 (FKBP11) in IPF lungs where FKBP11 specifically localized to antibody-producing plasma cells. Suggesting a general role in plasma cells, plasma cell-specific FKBP11 expression was equally observed in lymphatic tissues, and in vitro B cell to plasma cell differentiation was accompanied by induction of FKBP11 expression. Recombinant human FKBP11 was able to refold IgG antibody in vitro and inhibited by FK506, strongly supporting a function as antibody peptidyl-prolyl cis-trans isomerase. Induction of ER stress in cell lines demonstrated induction of FKBP11 in the context of the unfolded protein response in an X-box-binding protein 1 (XBP1)-dependent manner. While deficiency of FKBP11 increased susceptibility to ER stress-mediated cell death in an alveolar epithelial cell line, FKBP11 knockdown in an antibody-producing hybridoma cell line neither induced cell death nor decreased expression or secretion of IgG antibody. Similarly, antibody secretion by the same hybridoma cell line was not affected by knockdown of the established antibody peptidyl-prolyl isomerase cyclophilin B. The results are consistent with FKBP11 as a novel XBP1-regulated antibody peptidyl-prolyl cis-trans isomerase and indicate significant redundancy in the ER-resident folding machinery of antibody-producing hybridoma cells.

Nonpermissive skin environment impairs nerve regeneration in diabetes via Sec31a

OBJECTIVE

Although the microenvironment for peripheral nerve regeneration is permissive, such a mechanism is defective in diabetes, and the molecular mediators remain elusive. This study aimed to (1) investigate the relationship between skin innervation and collagen pathology in diabetic neuropathy and to (2) clarify the molecular alterations that occur in response to hyperglycemia and their effects on axon regeneration.

METHODS

We addressed this issue using two complementary systems: (1) human skin from patients with diabetic neuropathy and to (2) a coculture model of human dermal fibroblasts (HDFs) with rat dorsal root ganglia neurons in the context of intrinsic neuronal factor and extrinsic microenvironmental collagen and its biosynthetic pathways.

RESULTS

In diabetic neuropathy, the skin innervation of intraepidermal nerve fiber density (IENFd), a measure of sensory nerve degeneration, was reduced with similar expression of a growth associated protein 43, a marker of nerve regeneration. In contrast, the content and packing of collagen in the diabetic skin became more rigid than the control skin. Sec31a, a protein that regulates the collagen biosynthetic pathway, was upregulated and inversely correlated with IENFd. In the cell model, activated HDFs exposed to high-glucose medium enhanced the expression of Sec31a and collagen I through the activation of transforming growth factor β, a profibrotic molecule. Sec31a upregulation impaired neurite outgrowth. This effect was reversed by silencing Sec31a expression and neurite outgrowth was resumed.

INTERPRETATION

The current study provides evidence that Sec31a plays a key role in inhibiting nerve regeneration in diabetic neuropathy. This article is protected by copyright. All rights reserved.

Traf2 and NCK Interacting Kinase Is a Critical Regulator of Procollagen I Trafficking and Hepatic Fibrogenesis in Mice

Hepatic fibrosis is driven by deposition of matrix proteins following liver injury. Hepatic stellate cells (HSCs) drive fibrogenesis, producing matrix proteins, including procollagen I, which matures into collagen I following secretion. Disrupting intracellular procollagen processing and trafficking causes endoplasmic reticulum stress and stress-induced HSC apoptosis and thus is an attractive antifibrotic strategy. We designed an immunofluorescence-based small interfering RNA (siRNA) screen to identify procollagen I trafficking regulators, hypothesizing that these proteins could serve as antifibrotic targets. A targeted siRNA screen was performed using immunofluorescence to detect changes in intracellular procollagen I. Tumor necrosis factor receptor associated factor 2 and noncatalytic region of tyrosine kinase-interacting kinase (TNIK) was identified and interrogated in vitro and in vivo using the TNIK kinase inhibitor NCB-0846 or RNA interference-mediated knockdown. Our siRNA screen identified nine genes whose knockdown promoted procollagen I retention, including the serine/threonine kinase TNIK. Genetic deletion or pharmacologic inhibition of TNIK through the small molecule inhibitor NCB-0846 disrupted procollagen I trafficking and secretion without impacting procollagen I expression. To investigate the role of TNIK in liver fibrogenesis, we analyzed human and murine livers, finding elevated TNIK expression in human cirrhotic livers and increased TNIK expression and kinase activity in both fibrotic mouse livers and activated primary human HSCs. Finally, we tested whether inhibition of TNIK kinase activity could limit fibrogenesis in vivo. Mice receiving NCB-0846 displayed reduced CCl₄ -induced fibrogenesis compared to CCl₄ alone, although α-smooth muscle actin levels were unaltered. Conclusions: Our siRNA screen effectively identified TNIK as a key kinase involved in procollagen I trafficking in vitro and hepatic fibrogenesis in vivo.

PDIA3/ERp57 promotes a matrix-rich secretome that stimulates fibroblast adhesion through CCN2

The matricellular glycoprotein thrombospondin1 (TSP1) has complex roles in the extracellular matrix and at cell surfaces, but relatively little is known about its intracellular associations prior to secretion. To search for novel intracellular interactions of TSP1 in situ, we carried out a biotin ligase-based TSP1 interactome screen and identified protein disulphide isomerase A3 (PDIA3/ERp57) as a novel candidate binding protein. In validation, TSP1 and PDIA3 were established to bind in vitro and to colocalise in the endoplasmic reticulum of human dermal fibroblasts (HDF). Loss of PDIA3 function, either by pharmacological inhibition in HDF or in Pdia3^-/- mouse embryo fibroblasts (Pdia3^-/-MEF), led to alterations in the composition of cell-derived ECM, involving changed abundance of fibronectin and TSP1, and was correlated with reduced cell spreading, altered organisation of F-actin and reduced focal adhesions. These cellular phenotypes of Pdia3^-/-MEF were normalised by exposure to conditioned medium (WTCM) or extracellular matrix (WTECM) from wild-type (WT)-MEF. Rescue depended on PDIA3 activity in WT-MEF, and was not prevented by immunodepletion of fibronectin. Heparin-binding proteins in WTCM were found to be necessary for rescue. Comparative quantitative tandem-mass-tag proteomics and functional assays on the heparin-binding secretomes of WT-MEF and Pdia3^-/- MEF identified multiple ECM and growth factor proteins to be down-regulated in the CM of Pdia3^-/- MEF. Of these, CCN2 was identified to be necessary for the adhesion-promoting activity of WTCM on Pdia3^-/- MEF and to bind TSP1. Thus, PDIA3 coordinates fibroblast production of an ECM-rich, pro-adhesive microenvironment, with implications for PDIA3 as a translational target.

New mechanistic insights to PLOD1-mediated human vascular disease

Heritable thoracic aortic disease and familial thoracic aortic aneurysm/dissection are important causes of human morbidity/mortality, most without identifiable genetic cause. In a family with familial thoracic aortic aneurysm/dissection, we identified a missense p. (Ser178Arg) variant in PLOD1 segregating with disease, and evaluated PLOD1 enzymatic activity, collagen characteristics and in human aortic vascular smooth muscle cells, studied the effect on function. Comparison with homologous PLOD3 enzyme indicated that the pathogenic variant may affect the N-terminal glycosyltransferase domain, suggesting unprecedented PLOD1 activity. In vitro assays demonstrated that wild-type PLOD1 is capable of processing UDP-glycan donor substrates, and that the variant affects the folding stability of the glycosyltransferase domain and associated enzymatic functions. The PLOD1 substrate lysine was elevated in the proband, however the enzymatic product hydroxylysine and total collagen content was not different, albeit despite collagen fibril narrowing and preservation of collagen turnover. In VSMCs overexpressing wild-type PLOD1, there was upregulation in procollagen gene expression (secretory function) which was attenuated in the variant, consistent with loss-of-function. In comparison, si-PLOD1 cells demonstrated hypercontractility and upregulation of contractile markers, providing evidence for phenotypic switching. Together, the findings suggest that the PLOD1 product is preserved, however newly identified glucosyltransferase activity of PLOD1 appears to be affected by folding stability of the variant, and is associated with compensatory vascular smooth muscle cells phenotypic switching to support collagen production, albeit with less robust fibril girth. Future studies should focus on the impact of PLOD1 folding/variant stability on the tertiary structure of collagen and ECM interactions.

Compression Fractures and Partial Phenotype Rescue With a Low Phosphorus Diet in the Chihuahua Zebrafish Osteogenesis Imperfecta Model

Osteogenesis imperfecta (OI) is a group of heritable disorders affecting bone and other connective tissues. Dominant OI forms are mainly caused by mutations in collagen type I. Patients suffer from skeletal deformities, fractures of long bones and vertebral compression fractures from early childhood onward. Altered collagen structure and excess mineralisation are the main causes for the bone phenotype. The Chihuahua (Chi/+) zebrafish has become an important model for OI. Given that reduced dietary phosphorus (P) intake reduces the bone mineral content and promotes bone matrix formation in teleosts, including zebrafish, we tested whether a low dietary P (LP) intake mitigates the OI phenotype in the Chi/+ model. To answer this question, we characterised the Chi/+ vertebral column phenotype at a morphological, cellular and subcellular level. We present the first description of vertebral compression fractures in Chi/+ and assess the effects of LP diet on the Chi/+ phenotype (Chi/+_LP). Compared to untreated Chi/+, two months of LP dietary treatment decreases vertebral deformities in the abdominal region and reduces shape variation of caudal vertebral bodies to a condition more similar to wild type (WT). At the histological level, the osteoid layer, covering the bone at the vertebral body endplates in WT zebrafish, is absent in Chi/+, but it is partially restored with the LP diet. Whole mount-stained specimens and histological sections show various stages of vertebral compression fractures in Chi/+ and Chi/+_LP animals. Both Chi/+ and Chi/+_LP show abundant osteoclast activity compared to WT. Finally, the ultrastructure analysis of WT, Chi/+ and Chi/+_LP shows Chi/+ and Chi/+_LP osteoblasts with enlarged endoplasmic reticulum cisternae and a high protein content, consistent with intracellular retention of mutated collagen. Nevertheless, the secreted collagen in Chi/+_LP appears better organised concerning fibre periodicity compared to Chi/+. Our findings suggest that a reduced mineral content of Chi/+ bone could explain the lower frequency of vertebral column deformities and the restored shape of the vertebral bodies in Chi/+_LP animals. This, together with the improved quality of the bone extracellular matrix, suggests that two months of reduced dietary P intake can alleviate the severe bone phenotype in Chi/+ zebrafish.

Fighting the Fiber: Targeting Collagen in Lung Fibrosis

Organ fibrosis is characterized by epithelial injury and aberrant tissue repair, where activated effector cells, mostly fibroblasts and myofibroblasts, excessively deposit collagen into the extracellular matrix. Fibrosis frequently results in organ failure and has been estimated to contribute to at least one third of all global deaths. Also lung fibrosis, in particular idiopathic pulmonary fibrosis (IPF), is a fatal disease with rising incidence worldwide. As current treatment options targeting fibrogenesis are insufficient, there is an urgent need for novel therapeutic strategies. During the last decade, several studies have proposed to target intra- and extracellular components of the collagen biosynthesis, maturation, and degradation machinery. This includes intra- and extracellular targets directly acting on collagen gene products, but also such that anabolize essential building blocks of collagen, in particular glycine and proline biosynthetic enzymes. Collagen, however, is a ubiquitous molecule in the body and fulfils essential functions as a macromolecular scaffold, growth factor reservoir, and receptor binding site in virtually every tissue. This review summarizes recent advances and future directions in this field. Evidence for the proposed therapeutic targets and where they currently stand in terms of clinical drug development for treatment of fibrotic disease is provided. The drug targets are furthermore discussed in light of (1) specificity for collagen biosynthesis, maturation and degradation, and (2) specificity for disease-associated collagen. As therapeutic success and safety of these drugs may largely depend on targeted delivery, different strategies for specific delivery to the main effector cells and to the extracellular matrix are discussed.

Basic Structure, Physiology, and Biochemistry of Connective Tissues and Extracellular Matrix Collagens

The physiology of connective tissues like tendons and ligaments is highly dependent upon the collagens and other such extracellular matrix molecules hierarchically organized within the tissues. By dry weight, connective tissues are mostly composed of fibrillar collagens. However, several other forms of collagens play essential roles in the regulation of fibrillar collagen organization and assembly, in the establishment of basement membrane networks that provide support for vasculature for connective tissues, and in the formation of extensive filamentous networks that allow for cell-extracellular matrix interactions as well as maintain connective tissue integrity. The structures and functions of these collagens are discussed in this chapter. Furthermore, collagen synthesis is a multi-step process that includes gene transcription, translation, post-translational modifications within the cell, triple helix formation, extracellular secretion, extracellular modifications, and then fibril assembly, fibril modifications, and fiber formation. Each step of collagen synthesis and fibril assembly is highly dependent upon the biochemical structure of the collagen molecules created and how they are modified in the cases of development and maturation. Likewise, when the biochemical structures of collagens or are compromised or these molecules are deficient in the tissues - in developmental diseases, degenerative conditions, or injuries - then the ultimate form and function of the connective tissues are impaired. In this chapter, we also review how biochemistry plays a role in each of the processes involved in collagen synthesis and assembly, and we describe differences seen by anatomical location and region within tendons. Moreover, we discuss how the structures of the molecules, fibrils, and fibers contribute to connective tissue physiology in health, and in pathology with injury and repair.

Noncanonical ER-Golgi trafficking and autophagy of endogenous procollagen in osteoblasts

Secretion and quality control of large extracellular matrix proteins remain poorly understood and debated, particularly transport intermediates delivering folded proteins from the ER to Golgi and misfolded ones to lysosomes. Discrepancies between different studies are related to utilization of exogenous cargo, off-target effects of experimental conditions and cell manipulation, and identification of transport intermediates without tracing their origin and destination. To address these issues, here we imaged secretory and degradative trafficking of type I procollagen in live MC3T3 osteoblasts by replacing a region encoding N-propeptide in endogenous Col1a2 gDNA with GFP cDNA. We selected clones that produced the resulting fluorescent procollagen yet had normal expression of key osteoblast and ER/cell stress genes, normal procollagen folding, and normal deposition and mineralization of extracellular matrix. Live-cell imaging of these clones revealed ARF1-dependent transport intermediates, which had no COPII coat and delivered procollagen from ER exit sites (ERESs) to Golgi without stopping at ER-Golgi intermediate compartment (ERGIC). It also confirmed ERES microautophagy, i.e., lysosomes engulfing ERESs containing misfolded procollagen. Beyond validating these trafficking models for endogenous procollagen, we uncovered a probable cause of noncanonical cell stress response to procollagen misfolding. Recognized and retained only at ERESs, misfolded procollagen does not directly activate the canonical UPR, yet it disrupts the ER lumen by blocking normal secretory export from the ER.

Cotranslational prolyl hydroxylation is essential for flavivirus biogenesis

Viral pathogens are an ongoing threat to public health worldwide. Analysing their dependence on host biosynthetic pathways could lead to effective antiviral therapies1. Here we integrate proteomic analyses of polysomes with functional genomics and pharmacological interventions to define how enteroviruses and flaviviruses remodel host polysomes to synthesize viral proteins and disable host protein production. We find that infection with polio, dengue or Zika virus markedly modifies polysome composition, without major changes to core ribosome stoichiometry. These viruses use different strategies to evict a common set of translation initiation and RNA surveillance factors from polysomes while recruiting host machineries that are specifically required for viral biogenesis. Targeting these specialized viral polysomes could provide a new approach for antiviral interventions. For example, we find that both Zika and dengue use the collagen proline hydroxylation machinery to mediate cotranslational modification of conserved proline residues in the viral polyprotein. Genetic or pharmacological inhibition of proline hydroxylation impairs nascent viral polyprotein folding and induces its aggregation and degradation. Notably, such interventions prevent viral polysome remodelling and lower virus production. Our findings delineate the modular nature of polysome specialization at the virus-host interface and establish a powerful strategy to identify targets for selective antiviral interventions.

Imaging of type I procollagen biosynthesis in cells reveals biogenesis in highly organized bodies; Collagenosomes

Mechanistic aspects of type I procollagen biosynthesis in cells are poorly understood. To provide more insight into this process we designed a system to directly image type I procollagen biogenesis by co-expression of fluorescently labeled full size procollagen α1(I) and one α2(I) polypeptides. High resolution images show that collagen α1(I) and α2(I) polypeptides are produced in coordination in discrete structures on the ER membrane, which we termed the collagenosomes. Collagenosomes are disk shaped bodies, 0.5-1 μM in diameter and 200-400 nm thick, in the core of which folding of procollagen takes place. Collagenosomes are intimately associated with the ER membrane and their formation requires intact translational machinery, suggesting that they are the sites of nascent procollagen biogenesis. Collagenosomes show little co-localization with the COPII transport vesicles, which export type I procollagen from the ER, suggesting that these two structures are distinct. LARP6 is the protein which regulates translation of type I collagen mRNAs. The characteristic organization of collagenosomes depends on binding of LARP6 to collagen mRNAs. Without LARP6 regulation, collagenosomes are poorly organized and the folding of α1(I) and α2(I) polypeptides into procollagen in their cores is diminished. This indicates that formation of collagenosomes is dependent on regulated translation of collagen mRNAs. In live cells the size, number and shape of collagenosomes show little change within several hours, suggesting that they are stable structures of type I procollagen biogenesis. This is the first report of structural organization of type I collagen biogenesis in collagenosomes, while the fluorescent reporter system based on simultaneous imaging of both type I collagen polypeptides will enable the detailed elucidation of their structure and function.

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.

Histopathology of osteogenesis imperfecta bone. Supramolecular assessment of cells and matrices in the context of woven and lamellar bone formation using light, polarization and ultrastructural microscopy

Diaphyseal long bone cortical tissue from 30 patients with lethal perinatal Sillence II and progressively deforming Sillence III osteogenesis imperfecta (OI) has been studied at multiple levels of structural resolution. Interpretation in the context of woven to lamellar bone formation by mesenchymal osteoblasts (MOBLs) and surface osteoblasts (SOBLs) respectively demonstrates lamellar on woven bone synthesis as an obligate self-assembly mechanism and bone synthesis following the normal developmental pattern but showing variable delay in maturation caused by structurally abnormal or insufficient amounts of collagen matrix. The more severe the variant of OI is, the greater the persistence of woven bone and the more immature the structural pattern; the pattern shifts to a structurally stronger lamellar arrangement once a threshold accumulation for an adequate scaffold of woven bone has been reached. Woven bone alone characterizes lethal perinatal variants; variable amounts of woven and lamellar bone occur in progressively deforming variants; and lamellar bone increasingly forms rudimentary and then partially compacted osteons not reaching full compaction. At differing levels of microscopic resolution: lamellar bone is characterized by short, obliquely oriented lamellae with a mosaic appearance in progressively deforming forms; polarization defines tissue conformations and localizes initiation of lamellar formation; ultrastructure of bone forming cells shows markedly dilated rough endoplasmic reticulum (RER) and prominent Golgi bodies with disorganized cisternae and swollen dispersed tubules and vesicles, structural indications of storage disorder/stress responses and mitochondrial swelling in cells with massively dilated RER indicating apoptosis; ultrastructural matrix assessments in woven bone show randomly oriented individual fibrils but also short pericellular bundles of parallel oriented fibrils positioned obliquely and oriented randomly to one another and in lamellar bone show unidirectional fibrils that deviate at slight angles to adjacent bundles and obliquely oriented fibril groups consistent with twisted plywood fibril organization. Histomorphometric indices, designed specifically to document woven and lamellar conformations in normal and OI bone, establish ratios for: i) cell area/total area X 100 indicating the percentage of an area occupied by cells (cellularity index) and ii) total area/number of cells (pericellular matrix domains). Woven bone is more cellular than lamellar bone and OI bone is more cellular than normal bone, but these findings occur in a highly specific fashion with values (high to low) encompassing OI woven, normal woven, OI lamellar and normal lamellar conformations. Conversely, for the total area/number of cells ratio, pericellular matrix accumulations in OI woven are smallest and normal lamellar largest. Since genotype-phenotype correlation is not definitive, interposing histologic/structural analysis allowing for a genotype-histopathologic-phenotype correlation will greatly enhance understanding and clinical management of OI.

Type I and type V procollagen triple helix uses different subsets of the molecular ensemble for lysine posttranslational modifications in the rER

Collagen is the most abundant protein in humans. It has a characteristic triple-helix structure and is heavily posttranslationally modified. The complex biosynthesis of collagen involves processing by many enzymes and chaperones in the rough endoplasmic reticulum. Lysyl hydroxylase 1 (LH1) is required to hydroxylate lysine for cross-linking and carbohydrate attachment within collagen triple helical sequences. Additionally, a recent study of prolyl 3-hydroxylase 3 (P3H3) demonstrated that this enzyme may be critical for LH1 activity; however, the details surrounding its involvement remain unclear. If P3H3 is an LH1 chaperone that is critical for LH1 activity, P3H3 and LH1 null mice should display a similar deficiency in lysyl hydroxylation. To test this hypothesis, we compared the amount and location of hydroxylysine in the triple helical domains of type V and I collagen from P3H3 null, LH1 null, and wild-type mice. The amount of hydroxylysine in type V collagen was reduced in P3H3 null mice, but surprisingly type V collagen from LH1 null mice contained as much hydroxylysine as type V collagen from wild-type mice. In type I collagen, our results indicate that LH1 plays a global enzymatic role in lysyl hydroxylation. P3H3 is also involved in lysyl hydroxylation, particularly at cross-link formation sites, but is not required for all lysyl hydroxylation sites. In summary, our study suggests that LH1 and P3H3 likely have two distinct mechanisms to recognize different collagen types and to distinguish cross-link formation sites from other sites in type I collagen.

Defining the Extracellular Matrix of Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of childhood with a propensity to metastasize. Current treatment for patients with RMS includes conventional systemic chemotherapy, radiation therapy, and surgical resection; nevertheless, little to no improvement in long term survival has been achieved in decades-underlining the need for target discovery and new therapeutic approaches to targeting tumor cells or the tumor microenvironment. To evaluate cross-species sarcoma extracellular matrix production, we have used murine models which feature knowledge of the myogenic cell-of-origin. With focus on the RMS/undifferentiated pleomorphic sarcoma (UPS) continuum, we have constructed tissue microarrays of 48 murine and four human sarcomas to analyze expression of seven different collagens, fibrillins, and collagen-modifying proteins, with cross-correlation to RNA deep sequencing. We have uncovered that RMS produces increased expression of type XVIII collagen alpha 1 (COL18A1), which is clinically associated with decreased long-term survival. We have also identified significantly increased RNA expression of COL4A1, FBN2, PLOD1, and PLOD2 in human RMS relative to normal skeletal muscle. These results complement recent studies investigating whether soft tissue sarcomas utilize collagens, fibrillins, and collagen-modifying enzymes to alter the structural integrity of surrounding host extracellular matrix/collagen quaternary structure resulting in improved ability to improve the ability to invade regionally and metastasize, for which therapeutic targeting is possible.

Dynamically remodeled hepatic extracellular matrix predicts prognosis of early-stage cirrhosis

Liver cirrhosis remains major health problem. Despite the progress in diagnosis of asymptomatic early-stage cirrhosis, prognostic biomarkers are needed to identify cirrhotic patients at high risk developing advanced stage disease. Liver cirrhosis is the result of deregulated wound healing and is featured by aberrant extracellular matrix (ECM) remodeling. However, it is not comprehensively understood how ECM is dynamically remodeled in the progressive development of liver cirrhosis. It is yet unknown whether ECM signature is of predictive value in determining prognosis of early-stage liver cirrhosis. In this study, we systematically analyzed proteomics of decellularized hepatic matrix and identified four unique clusters of ECM proteins at tissue damage/inflammation, transitional ECM remodeling or fibrogenesis stage in carbon tetrachloride-induced liver fibrosis. In particular, basement membrane (BM) was heavily deposited at the fibrogenesis stage. BM component minor type IV collagen α5 chain expression was increased in activated hepatic stellate cells. Knockout of minor type IV collagen α5 chain ameliorated liver fibrosis by hampering hepatic stellate cell activation and promoting hepatocyte proliferation. ECM signatures were differentially enriched in the biopsies of good and poor prognosis early-stage liver cirrhosis patients. Clusters of ECM proteins responsible for homeostatic remodeling and tissue fibrogenesis, as well as basement membrane signature were significantly associated with disease progression and patient survival. In particular, a 14-gene signature consisting of basement membrane proteins is potent in predicting disease progression and patient survival. Thus, the ECM signatures are potential prognostic biomarkers to identify cirrhotic patients at high risk developing advanced stage disease.

Aberrant binding of mutant HSP47 affects posttranslational modification of type I collagen and leads to osteogenesis imperfecta

Heat shock protein 47 (HSP47), encoded by the SERPINH1 gene, is a molecular chaperone essential for correct folding of collagens. We report a homozygous p.(R222S) substitution in HSP47 in a child with severe osteogenesis imperfecta leading to early demise. p.R222 is a highly conserved residue located within the collagen interacting surface of HSP47. Binding assays show a significantly reduced affinity of HSP47-R222S for type I collagen. This altered interaction leads to posttranslational overmodification of type I procollagen produced by dermal fibroblasts, with increased glycosylation and/or hydroxylation of lysine and proline residues as shown by mass spectrometry. Since we also observed a normal intracellular folding and secretion rate of type I procollagen, this overmodification cannot be explained by prolonged exposure of the procollagen molecules to the modifying hydroxyl- and glycosyltransferases, as is commonly observed in other types of OI. We found significant upregulation of several molecular chaperones and enzymes involved in procollagen modification and folding on Western blot and RT-qPCR. In addition, we showed that an imbalance in binding of HSP47-R222S to unfolded type I collagen chains in a gelatin sepharose pulldown assay results in increased binding of other chaperones and modifying enzymes. The elevated expression and binding of this molecular ensemble to type I procollagen suggests a compensatory mechanism for the aberrant binding of HSP47-R222S, eventually leading to overmodification of type I procollagen chains. Together, these results illustrate the importance of HSP47 for proper posttranslational modification and provide insights into the molecular pathomechanisms of the p.(R222S) alteration in HSP47, which leads to a severe OI phenotype.

Heat shock protein 47 (HSP47) is essential for correct collagen folding. We report a homozygous p.(R222S) substitution in HSP47 in a child with severe osteogenesis imperfecta. The highly conserved p.R222 residue is located within the collagen interacting surface and HSP47-R222S shows a significantly reduced affinity for type I collagen. This altered interaction leads to posttranslational overmodification of type I procollagen. In contrast to other types of OI, this overmodification is not caused by prolonged exposure of procollagen to modifying enzymes, since the intracellular folding rate of type I procollagen appears to be normal. We show significant upregulation of several molecular chaperones and collagen-modifying enzymes and increased binding of several of these molecules to unfolded type I collagen chains upon abnormal HSP47-R222S binding. This suggests a compensatory mechanism for aberrant HSP47-R222S binding, eventually leading to overmodification of type I procollagen chains, and underscores the importance of HSP47 for proper posttranslational modification.

Tunnels for Protein Export from the Endoplasmic Reticulum

The functions of coat protein complex II (COPII) coats in cargo packaging and the creation of vesicles at the endoplasmic reticulum are conserved in eukaryotic protein secretion. Standard COPII vesicles, however, cannot handle the secretion of metazoan-specific cargoes such as procollagens, apolipoproteins, and mucins. Metazoans have thus evolved modules centered on proteins like TANGO1 (transport and Golgi organization 1) to engage COPII coats and early secretory pathway membranes to engineer a novel mode of cargo export at the endoplasmic reticulum.

4-Phenylbutyric acid enhances the mineralization of osteogenesis imperfecta iPSC-derived osteoblasts

Osteogenesis imperfecta (OI) is a heritable brittle bone disease mainly caused by mutations in the two type I collagen genes. Collagen synthesis is a complex process including trimer formation, glycosylation, secretion, extracellular matrix (ECM) formation, and mineralization. Using OI patient-derived fibroblasts and induced pluripotent stem cells (iPSCs), we investigated the effect of 4-phenylbutyric acid (4-PBA) on collagen synthesis to test its potential as a new treatment for OI. Endoplasmic reticulum (ER) retention of type I collagen was observed by immunofluorescence staining in OI patient-derived fibroblasts with glycine substitution and exon skipping mutations. Liquid chromatography-mass spectrometry analysis revealed excessive glycosylation of secreted type I collagen at the specific sites in OI cells. The misfolding of the type I collagen triple helix in the ECM was demonstrated by the incorporation of heat-dissociated collagen hybridizing peptide in OI cells. Type I collagen was produced excessively by OI fibroblasts with a glycine mutation, but this excessive production was normalized when OI fibroblasts were cultured on control fibroblast-derived ECM. We also found that mineralization was impaired in osteoblasts differentiated from OI iPSCs. In summary, treatment with 4-PBA normalizes the excessive production of type I collagen, reduces ER retention, partially improves misfolding of the type I collagen helix in ECM, and improves osteoblast mineralization. Thus, 4-PBA may improve not only ER retention, but also type I collagen synthesis and mineralization in human cells from OI patients.

Activation of Src family kinase ameliorates secretory trafficking in mutant prion protein cells

Fatal familial insomnia (FFI), genetic Creutzfeldt-Jakob disease (gCJD), and Gerstmann-Sträussler-Scheinker (GSS) syndrome are neurodegenerative disorders linked to prion protein (PrP) mutations. The pathogenic mechanisms are not known, but increasing evidence points to mutant PrP misfolding and retention in the secretory pathway. We previously found that the D178N/M129 mutation associated with FFI accumulates in the Golgi of neuronal cells, impairing post-Golgi trafficking. In this study we further characterized the trafficking defect induced by the FFI mutation and tested the 178N/V129 variant linked to gCJD and a nine-octapeptide repeat insertion associated with GSS. We used transfected HeLa cells, embryonic fibroblasts and primary neurons from transgenic mice, and fibroblasts from carriers of the FFI mutation. In all these cell types, the mutant PrPs showed abnormal intracellular localizations, accumulating in the endoplasmic reticulum (ER) and Golgi. To test the efficiency of the membrane trafficking system, we monitored the intracellular transport of the temperature-sensitive vesicular stomatite virus glycoprotein (VSV-G), a well-established cargo reporter, and of endogenous procollagen I (PC-I). We observed marked alterations in secretory trafficking, with VSV-G accumulating mainly in the Golgi complex and PC-I in the ER and Golgi. A redacted version of mutant PrP with reduced propensity to misfold did not impair VSV-G trafficking, nor did artificial ER or Golgi retention of wild-type PrP; this indicates that both misfolding and intracellular retention were required to induce the transport defect. Pharmacological activation of Src family kinase (SFK) improved intracellular transport, suggesting that mutant PrP impairs secretory trafficking through corruption of SFK-mediated signaling.

Transcription factor EB‑mediated autophagy promotes dermal fibroblast differentiation and collagen production by regulating endoplasmic reticulum stress and autophagy‑dependent secretion

Autophagy is reported to be involved in the formation of skin hypertrophic scar (HTS). However, the role of autophagy in the process of fibrosis remains unclear, therefore an improved understanding of the molecular mechanisms associated with autophagy may accelerate the development of effective therapeutic strategies against HTS. The present study evaluated the roles of autophagy mediated by transcription factor EB (TFEB), a pivotal regulator of lysosome biogenesis and autophagy, in transforming growth factor-β1 (TGF-β1)-induced fibroblast differentiation and collagen production. Fibroblasts were treated with TGF-β1, TGF-β1 + tauroursodeoxycholic acid (TUDCA) or TGF-β1 + TFEB-small interfering RNA (siRNA). TGF-β1 induced phenotypic transformation of fibro-blasts, as well as collagen synthesis and secretion in fibroblasts in a dose-dependent manner. Western blotting and immuno-fluorescence analyses demonstrated that TGF-β1 upregulated the expression of autophagy-related proteins through the endoplasmic reticulum (ER) stress pathway, whereas TUDCA reversed TGF-β1-induced changes. Reverse transcription-quantitative PCR (RT-qPCR), western blotting and RFP-GFP-LC3 double fluorescence analyses demonstrated that knockdown of TFEB by TFEB-siRNA decreased autophagic flux, upregulated the expression of proteins involved in the apoptotic pathway, such as phosphorylated-α subunit of eukaryotic initiation factor 2, C/EBP homologous protein and cysteinyl aspartate specific proteinase 3, and also downregulated the expression of α-smooth muscle actin and collagen I (COL I) in fibroblasts. Immunofluorescence confocal analyses and enzyme-linked immunosorbent assay indicated that TGF-β1 increased the colocalization of COL I with lysosomal-associated membrane protein 1 and Ras-related protein Rab-8A, a marker of secretory vesicles, in fibroblasts, as well as the secretion of pro-COL Iα1 in culture supernatants. Meanwhile, these effects were abolished by TFEB knockdown. The present results suggested that autophagy reduced ER stress, decreased cell apoptosis and maintained fibroblast activation not only through degradation of misfolded or unfolded proteins, but also through promotion of COL I release from the autolysosome to the extracellular environment.

RASA1-driven cellular export of collagen IV is required for the development of lymphovenous and venous valves in mice

RASA1, a negative regulator of Ras-MAPK signaling, is essential for the development and maintenance of lymphatic vessel valves. However, whether RASA1 is required for the development and maintenance of lymphovenous valves (LVV) and venous valves (VV) is unknown. In this study, we show that induced disruption of Rasa1 in mouse embryos did not affect initial specification of LVV or central VV, but did affect their continued development. Similarly, a switch to expression of a catalytically inactive form of RASA1 resulted in impaired LVV and VV development. Blocked development of LVV was associated with accumulation of the basement membrane protein, collagen IV, in LVV-forming endothelial cells (EC), and could be partially or completely rescued by MAPK inhibitors and drugs that promote collagen IV folding. Disruption of Rasa1 in adult mice resulted in venous hypertension and impaired VV function that was associated with loss of EC from VV leaflets. In conclusion, RASA1 functions as a negative regulator of Ras signaling in EC that is necessary for EC export of collagen IV, thus permitting the development of LVV and the development and maintenance of VV.

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.