Collagen genes: mutations affecting collagen structure and expression

The Role of Membrane-Type 1 Matrix Metalloproteinase-Substrate Interactions in Pathogenesis

A protease is an enzyme with a proteolytic activity that facilitates the digestion of its substrates. Membrane-type I matrix metalloproteinase (MT1-MMP), a member of the broader matrix metalloproteinases (MMP) family, is involved in the regulation of diverse cellular activities. MT1-MMP is a very well-known enzyme as an activator of pro-MMP-2 and two collagenases, MMP-8 and MMP-13, all of which are essential for cell migration. As an anchored membrane enzyme, MT1-MMP has the ability to interact with a diverse group of molecules, including proteins that are not part of the extracellular matrix (ECM). Therefore, MT1-MMP can regulate various cellular activities not only by changing the extra-cellular environment but also by regulating cell signaling. The presence of both intracellular and extra-cellular portions of MT1-MMP can allow it to interact with proteins on both sides of the cell membrane. Here, we reviewed the MT1-MMP substrates involved in disease pathogenesis.

The Circular RNA CircCOL1A1 Functions as a miR-149-5p Sponge to Regulate the Formation of Superior-Quality Brush Hair via the CMTM3/AR Axis

Superior-quality brush hair, also called Type III hair, can be obtained only from the cervical spine region of skin tissues of Yangtze River Delta white goats. The formation of superior-quality brush hair is controlled by a series of critical genes and related signaling pathways. Circular RNAs (circRNAs) are ubiquitous endogenous noncoding RNAs that regulate many biological and physiological processes in mammals. However, little is known about the potential regulatory role of circRNAs in superior-quality brush hair formation. Here, we analyzed circRNA sequencing data from cervical spine region skin tissues of normal-quality brush hair goats and superior-quality brush hair goats and then selected and identified the differentially expressed circRNA circCOL1A1. To investigate the regulatory role and mechanism of action of circCOL1A1, goat hair follicle stem cells (gHFSCs) were cultured and treated with a circCOL1A1 overexpression plasmid and small-interfering RNAs (siRNAs). Functional assays showed that circCOL1A1 knockdown promoted the proliferation and differentiation of gHFSCs cultured in vitro but inhibited stem cell apoptosis, whereas overexpression of circCOL1A1 suppressed stem cell proliferation and differentiation and induced apoptosis. Bioinformatics analysis combined with dual-luciferase reporter assays and RNA binding protein immunoprecipitation (RIP) verified that, mechanistically, circCOL1A1 could bind miR-149-5p directly and then relieve its inhibitory effect on CMTM3 to further control the CMTM3/AR axis. Collectively, our results reveal a novel regulatory pathway for the formation of superior-quality brush hair and indicate that circCOL1A1 plays a role in gHFSC growth and superior-quality brush hair formation by targeting the miR-149-5p/CMTM3/AR axis.

Bioinformatic and experimental analyses of key biomarkers in pancreatic cancer

The present study aimed to screen the key genes in pancreatic cancer and to explore the pathogenesis of pancreatic cancer. A total of three expression profiling datasets (GSE28735, GSE16515 and GSE15471) associated with pancreatic cancer were retrieved from the public gene chip database. The differentially expressed genes (DEGs) were screened by GEO2R and subjected to Gene Ontology (GO) and signaling pathway enrichment analysis. Furthermore, a protein interaction network was constructed. The GEPIA online database was used to screen for genes that affect the prognosis of pancreatic cancer. Finally, cell functional experiments were performed on the selected key genes. A total of 72 DEGs were identified, including 52 upregulated and 20 downregulated genes. Enrichment analysis revealed roles of the DEGs in endodermal cell differentiation, cell adhesion, extracellular matrix-receptor interaction and PI3K-Akt signaling pathway. In total, 10 key nodal genes were identified, including integrin subunit α 2 (ITGA2), ITGB6 and collagen α 1 chain 1. Through survival analysis, two genes with an impact on the prognosis of pancreatic cancer were identified, namely ITGA2 and ITGB6. Silencing of ITGB6 in a pancreatic cancer cell line significantly suppressed cell proliferation and induced cell cycle arrest at G2/M phase. The identified key genes and signaling pathways may help to deepen the understanding of the molecular mechanisms involved in pancreatic cancer and provide a theoretical basis to develop novel therapies.

Cancer-Associated Fibroblasts Modulate Transcriptional Signatures Involved in Proliferation, Differentiation and Metastasis in Head and Neck Squamous Cell Carcinoma

Simple Summary

Cancer-associated fibroblasts (CAFs) are the major cellular component of the tumor microenvironment and have been shown to stimulate tumor growth, epithelial-to-mesenchymal transition (EMT), invasion, and radio-resistance. Radio-resistance leading to disease relapse is one of the major challenges in long-term survival and outcome in head and neck squamous cell carcinoma (HNSCC). Therefore, it is essential to search for predictive markers and new targets for treatment using clinically relevant in vitro tumor models. We show that CAFs alter the expression of HNSCC tumor cell genes, many of which are associated with proliferation, differentiation, and metastasis. Moreover, the expression pattern of selected CAF-regulated genes differed between HNSCC tumor tissue and the adjacent non-tumoral tissue. Two CAF-regulated genes, MMP9 and FMOD, were found to be associated with overall survival (OS) in patients treated with radiotherapy.

Abstract

Cancer-associated fibroblasts (CAFs) are known to increase tumor growth and to stimulate invasion and metastasis. Increasing evidence suggests that CAFs mediate response to various treatments. HNSCC cell lines were co-cultured with their patient-matched CAFs in 2D and 3D in vitro models, and the tumor cell gene expression profiles were investigated by cDNA microarray and qRT-PCR. The mRNA expression of eight candidate genes was examined in tumor biopsies from 32 HNSCC patients and in five biopsies from normal oral tissue. Differences in overall survival (OS) were tested with Kaplan–Meier long-rank analysis. Thirteen protein coding genes were found to be differentially expressed in tumor cells co-cultured with CAFs in 2D and 81 in 3D when compared to tumor cells cultured without CAFs. Six of these genes were upregulated both in 2D and 3D (POSTN, GREM1, BGN, COL1A2, COL6A3, and COL1A1). Moreover, two genes upregulated in 3D, MMP9 and FMOD, were significantly associated with the OS. In conclusion, we demonstrated in vitro that CAF-derived signals alter the tumor cell expression of multiple genes, several of which are associated with differentiation, epithelial-to-mesenchymal transition (EMT) phenotype, and metastasis. Moreover, six of the most highly upregulated genes were found to be overexpressed in tumor tissue compared to normal tissue.

Methods for the Construction of Collagen-Based Triple-Helical Peptides Designed as Matrix Metalloproteinase Inhibitors

The triple-helical structure of collagen has been accurately reproduced in numerous chemical and recombinant model systems. Triple-helical peptides have found application for dissecting collagen-stabilizing forces, isolating receptor and protein binding sites in collagen, evaluating collagen-mediated cell signaling activities, mechanistic examination of collagenolytic proteases, and developing novel biomaterials and drug delivery vehicles. Due to their inherent stability to general proteolysis, triple-helical peptides present an opportunity as in vivo inhibitory agents. The present chapter provides methods for the construction of collagen-based triple-helical peptides designed as matrix metalloproteinase inhibitors.

Matrix metalloproteinase collagenolysis in health and disease

The proteolytic processing of collagen (collagenolysis) is critical in development and homeostasis, but also contributes to numerous pathologies. Mammalian interstitial collagenolytic enzymes include members of the matrix metalloproteinase (MMP) family and cathepsin K. While MMPs have long been recognized for their ability to catalyze the hydrolysis of collagen, the roles of individual MMPs in physiological and pathological collagenolysis are less defined. The use of knockout and mutant animal models, which reflect human diseases, has revealed distinct collagenolytic roles for MT1-MMP and MMP-13. A better understanding of temporal and spatial collagen processing, along with the knowledge of the specific MMP involved, will ultimately lead to more effective treatments for cancer, arthritis, cardiovascular conditions, and infectious diseases. This article is part of a Special Issue entitled: Matrix Metalloproteinases edited by Rafael Fridman.

Drug-induced Physeal Abnormalities in Preclinical Toxicity Studies

Most toxic physeal changes are characterized microscopically by altered chondrocyte development, proliferation, or maturation in the growth plate and eventually result in disordered appositional bone growth. Many therapeutic drugs directly or indirectly target proteins involved in chondrocytic differentiation and maturation pathways, so toxic physeal injury has become increasingly common in preclinical toxicologic pathology. While physeal dysplasia has been associated with several different drug classes including bisphosphonates, vascular endothelial growth factor receptor inhibitors, fibroblast growth factor receptor inhibitors, transforming growth factor beta receptor inhibitors, and vascular targeting agents, physeal changes often share similar morphologic features including thickening and disorganization of the hypertrophic layer, increased numbers of hypertrophic chondrocytes, altered mineralization of endochondral ossification, and/or increased thickness of subphyseal bone. Knowledge of genetic and nutritional diseases affecting bone growth has been important in helping to determine which specific target drugs may be affecting that could result in toxic physeal lesions. A pathophysiologic mechanism for most physeal toxicants has been determined in detail using a variety of investigative techniques. However, due to the signaling cross talk and the tight regulation required for chondrocyte maturation in the physis, several growth factor pathways are likely to be affected simultaneously with pharmacologic disruption of physeal homeostasis and inhibition of one factor necessary for chondrocyte function often affects others.

Identification of COL1A1 and COL1A2 as candidate prognostic factors in gastric cancer

Background

The role of type I collagen, composed of collagen type I alpha 1 (COL1A1) and collagen type I alpha 2 (COL1A2), has been studied in several cancers. However, the expression of COL1A1 and COL1A2 in malignant, premalignant, and normal gastric tissues and their clinical significances in gastric cancer have not been elucidated.

Methods

Real-time quantitative PCR was performed in 55 malignant, 27 premalignant, and 19 normal tissues to measure COL1A1 and COL1A2 messenger RNA (mRNA) expression, and the correlations between COL1A1 and COL1A2 expression and clinicopathological parameters and patients’ survival rate were analyzed.

Results

We found that COL1A1 mRNA expression was significantly upregulated in premalignant and malignant tissues than in normal tissues, whereas COL1A2 mRNA expression was significantly higher in malignant tissues than in premalignant and normal tissues. Moreover, COL1A1 expression was unrelated to clinicopathological parameters, while COL1A2 expression was positively related to tumor size and depth of invasion. Besides, higher COL1A1 and COL1A2 expression levels were related to lower overall survival.

Conclusions

We find that COL1A1 might have its potential as a monitoring factor to screen early gastric cancer, and COL1A1 and COL1A2 might predict poor clinical outcomes in gastric cancer patients.

Development of somites and their derivatives in amphioxus, and implications for the evolution of vertebrate somites

Background

Vertebrate somites are subdivided into lineage compartments, each with distinct cell fates and evolutionary histories. Insights into somite evolution can come from studying amphioxus, the best extant approximation of the chordate ancestor. Amphioxus somites have myotome and non-myotome compartments, but development and fates of the latter are incompletely described. Further, while epithelial to mesenchymal transition (EMT) is important for most vertebrate somitic lineages, amphioxus somites generally have been thought to remain entirely epithelial. Here, we examined amphioxus somites and derivatives, as well as extracellular matrix of the axial support system, in a series of developmental stages by transmission electron microscopy (TEM) and in situ hybridization for collagen expression.

Results

The amphioxus somite differentiates medially into myotome, laterally into the external cell layer (a sub-dermal mesothelium), ventrally into a bud that forms mesothelia of the perivisceral coelom, and ventro-medially into the sclerotome. The sclerotome forms initially as a monolayered cell sheet that migrates between the myotome and the notochord and neural tube; subsequently, this cell sheet becomes double layered and encloses the sclerocoel. Other late developments include formation of the fin box mesothelia from lateral somites and the advent of isolated fibroblasts, likely somite derived, along the myosepta. Throughout development, all cells originating from the non-myotome regions of somites strongly express a fibrillar collagen gene, ColA, and thus likely contribute to extracellular matrix of the dermal and axial connective tissue system.

Conclusions

We provide a revised model for the development of amphioxus sclerotome and fin boxes and confirm previous reports of development of the myotome and lateral somite. In addition, while somite derivatives remain almost entirely epithelial, limited de-epithelialization likely converts some somitic cells into fibroblasts of the myosepta and dermis. Ultrastructure and collagen expression suggest that all non-myotome somite derivatives contribute to extracellular matrix of the dermal and axial support systems. Although amphioxus sclerotome lacks vertebrate-like EMT, it resembles that of vertebrates in position, movement to surround midline structures and into myosepta, and contribution to extracellular matrix of the axial support system. Thus, many aspects of the sclerotome developmental program evolved prior to the origin of the vertebrate mineralized skeleton.

Stabilization of collagen-model, triple-helical peptides for in vitro and in vivo applications

The triple-helical structure of collagen has been accurately reproduced in numerous chemical and recombinant model systems. Triple-helical peptides and proteins have found application for dissecting collagen-stabilizing forces, isolating receptor- and protein-binding sites in collagen, mechanistic examination of collagenolytic proteases, and development of novel biomaterials. Introduction of native-like sequences into triple-helical constructs can reduce the thermal stability of the triple-helix to below that of the physiological environment. In turn, incorporation of nonnative amino acids and/or templates can enhance triple-helix stability. We presently describe approaches by which triple-helical structure can be modulated for use under physiological or near-physiological conditions.

The molecular chaperone Hsp47 is essential for cartilage and endochondral bone formation

Heat shock protein 47 kDa (Hsp47) is considered as a molecular chaperone essential for the correct folding of type I and type IV procollagen in the ER. However, the function of Hsp47 for other types of procollagen and its importance for chondrogenesis have never been elucidated. To examine the function of Hsp47 in cartilage formation and endochondral ossification, we conditionally inactivated the Hsp47 gene in chondrocytes using Hsp47 floxed mice and mice carrying a chondrocyte-specific Col2a1-Cre transgene. Hsp47 conditional null mutant mice died just before or shortly after birth, and exhibited severe generalized chondrodysplasia and bone deformities with lower levels of type II and type XI collagen. Second-harmonic generation (SHG) analysis and electron microscopy revealed the accumulation of misaligned type I collagen molecules in the intervertebral discs and a substantial decrease in type II collagen fibers, respectively. Whole-mount skeletal staining showed no calcified region in the vertebral bodies of sacral vertebrae, and revealed that the endochondral bones were severely twisted and shortened. These results demonstrate that Hsp47 is indispensable for well-organized cartilage and normal endochondral bone formation.

Synthesis and biological applications of collagen-model triple-helical peptides

Triple-helical peptides (THPs) have been utilized as collagen models since the 1960s. The original focus for THP-based research was to unravel the structural determinants of collagen. In the last two decades, virtually all aspects of collagen structural biochemistry have been explored with THP models. More specifically, secondary amino acid analogs have been incorporated into THPs to more fully understand the forces that stabilize triple-helical structure. Heterotrimeric THPs have been utilized to better appreciate the contributions of chain sequence diversity on collagen function. The role of collagen as a cell signaling protein has been dissected using THPs that represent ligands for specific receptors. The mechanisms of collagenolysis have been investigated using THP substrates and inhibitors. Finally, THPs have been developed for biomaterial applications. These aspects of THP-based research are overviewed herein.

TGF-β1and TNF-α are involved in the transcription of type I collagen α2gene in soleus muscle atrophied by mechanical unloading

The aim of this study was to examine the effect of hindlimb suspension (HS) on the expressions of COL1A2 (type I collagen α2chain) mRNA and its regulatory factors, transforming growth factors (TGF)-β1, -β2, and -β3, phosphorylated Smad3, and tumor necrosis factor-α (TNF-α) in rat hindlimb muscles. Forty-eight male Wistar rats (age, 5 wk) were randomly assigned to HS for 1, 3, 7, and 14 days and control ( n = 6 for each). During the exposure to HS, COL1A2 mRNA expression decreased in the soleus muscle at day 3 and recovered to control level at day 7. The content of TNF-α, one of the negative regulatory factors for COL1A2, increased from day 3 until day 14. On the other hand, the contents of TGF-β1, TGF-β3, and Smad3, positive regulatory factors for COL1A2, increased at day 7. The in situ hybridization for COL1A2 and the immunohistochemistry of TGF-β1and TNF-α revealed their expressions around nerve-related tissues, including muscle spindles and connective tissue sheath. The results indicate that the transcriptional activity of COL1A2 in the soleus muscle initially decreases in response to unloading through an increase in TNF-α production; thereafter, it returns toward normal level through the activated TGF-β/Smad pathway.

Induction of Endothelial Cell Activation by a Triple Helical α2β1 Integrin Ligand, Derived from Type I Collagen α1(I)496–507

Endothelial cell activation involves the elevated expression of cell adhesion molecules, chemoattractants, chemokines, and cytokines. These expression profiles may be regulated by integrin-mediated cell signaling pathways. In the current study, an alpha2beta1 integrin triple helical peptide ligand derived from type I collagen residues alpha1(I)496-507 was examined for induction of human aortic endothelial cell (HAEC) activation. In addition, a "miniextracellular matrix" composed of a mixture of the alpha1(I)496-507 ligand and a second, alpha-helical ligand incorporating the endothelial cell proliferating region of SPARC (secreted protein acidic and rich in cysteine) was studied for induction of HAEC activation. Following HAEC adhesion to alpha1(I)496-507, mRNA expression of E-selectin-1, vascular and intercellular cell adhesion molecules-1, and monocytic chemoattractant protein-1 was stimulated, whereas that of endothelin-1 was inhibited. Enzyme-linked immunosorbent assay analysis demonstrated that E-selectin-1 and monocytic chemoattractant protein-1 expression was also stimulated, whereas endothelin-1 protein expression diminished. Engagement of the alpha2beta1 integrin initiated a HAEC response similar to that of tumor necrosis factor-alpha-induced HAECs but was not sufficient to induce an inflammatory response. Addition of the SPARC119-122 region had only a slight effect on HAEC activation. Other cell-extracellular matrix interactions appear to be required to elicit an inflammatory response. The alpha2beta1 integrin specific triple helical peptide ligand described herein represents a more general in vitro model system by which gene expression and protein production profiles induced by binding to a single cellular receptor type can be quantified.

Transforming growth factor-beta isoforms differently stimulate proalpha2 (I) collagen gene expression during wound healing process in transgenic mice

The role of many growth factors and cytokines in the process of wound healing has been intensively investigated in recent two decades. Among them, transforming growth factor-betas (TGF-betas) are well known to have a potent stimulatory effect on collagen synthesis as shown in various in vivo experimental systems. In the present study, we examined the effects of various growth factors on the promoter activity of the proalpha2 (I) collagen gene (COL1A2) during the wound healing process. For this purpose, we utilized transgenic mice harboring the -17 kb promoter sequence of the mouse COL1A2 linked to either a firefly luciferase or a bacterial beta-galactosidase gene. These mice exhibited normal phenotypic expression and the wound healing process was not impaired. Full thickness wounds were made by punch biopsy. We examined the effects of TGF-beta1, -beta2, -beta3, basic fibroblast growth factor, platelet-derived growth factor, and connective tissue growth factor by applying them locally to the open wound every 2 days. Among the growth factors examined, all of the three isoforms of TGF- exhibited a more potent stimulatory effect on COL1A2 promoter activity than did other factors. In addition, while TGF-beta1 and -beta2 significantly increased the number of fibroblasts which were positive for X-Gal staining, TGF-beta3 treatment did not change the number of beta-galactosidase expressing cells. Accumulation of collagen fibers was observed to the same extent in the mice treated with TGF-beta1 and those with TGF-beta3. These findings suggest that TGF-beta1 and -beta3 have similar but not identical regulatory mechanisms of COL1A2 expression, and that their pathophysiological roles in wound healing might be different from each other.

Ultrastructural aspects of connective tissue in hereditary gingival fibromatosis

OBJECTIVE

The purpose of this study was to analyze the ultrastructure of gingival connective tissue from patients in one family affected by hereditary gingival fibromatosis (HGF).

STUDY DESIGN

Electron microscopic examination was performed with gingival tissue from 10 patients from a Brazilian family with 132 members. Fifty of 96 persons at risk for this disorder were affected, which is consistent with an autosomal dominant pattern of inheritance.

RESULTS

The extracellular matrix showed flocculent material and collagen fibrils with structural abnormalities and variation in diameter. Increased numbers of oxytalan fibers were identified; however, elastic fibers were rare in the analyzed areas.

CONCLUSIONS

The structural alterations found in HGF appear similar to those described in certain other heritable collagen disorders, suggesting that HGF should be included in the group of hereditary diseases in which connective tissue alterations have a distinct pattern, in contrast to reactive fibrotic gingival enlargements with no genetic component.

A five-base pair deletion in the sedlin gene causes spondyloepiphyseal dysplasia tarda in a six-generation Arkansas kindred

A six-generation kindred from Arkansas with X-linked recessive spondyloepiphyseal dysplasia tarda (SEDT) was investigated by genetic linkage and mutation analysis. SEDT had been mapped on the X-chromosome (Xp22.2), and the clinical and radiographic evolution of this kindred had been published. Linkage analysis proved informative for all five polymorphic markers tested, and DXS987 and DXS16 co-segregated with the Arkansas kindred (peak logarithm of the odds scores, 3.54 and 3.36, respectively). Subsequently, dinucleotide deletion in a new gene designated "sedlin" was reported to cause SEDT in three families. In an affected man and obligate carrier woman in the Arkansas kindred, we found a 5-bp deletion in exon 5 of sedlin. The defect causes a frameshift, resulting in eight missense amino acids and premature termination. The 5-bp deletion was then demonstrated to segregate with SEDT in the four living generations, including eight affected males and nine obligate carrier females. Furthermore, the deletion was identified in four females who potentially were heterozygous carriers for SEDT. The mutation was not detected in the two young sons of the consultand (believed to be a carrier because of her subtle radiographic skeletal changes and then shown to have the deletion), but they were too young for x-ray diagnosis Identification of a defect in sedlin in this SEDT kindred enables carrier detection and presymptomatic diagnosis and reveals an important role for this gene in postnatal endochondral bone formation.

X-linked recessive spondyloepiphyseal dysplasia tarda. Clinical and radiographic evolution in a 6-generation kindred and review of the literature

We characterize the clinical and radiographic evolution of X-linked recessive spondyloepiphyseal dysplasia tarda (SEDT) in a 6-generation kindred from Arkansas (SEDT(AK)). Our observations show the natural progression of SEDT(AK) and enable carrier detection by radiographic study. We find that, SEDT(AK) manifests as a postnatal defect. Affected hemizygous males can have radiographically normal vertebrae at birth. The pathogenesis seems to involve a developmental disturbance in endochondral bone formation that is reflected most dramatically in vertebrae by a radiographically inapparent ring apophysis. This defect leads to distinctive malformation of the anterior margins of the lumbar vertebrae during childhood. Subsequently, there is degeneration of intervertebral discs and destruction of spinal facet joints. In the femur, the head, neck, and distal condyles are abnormally shaped and become distorted so that osteoarthritis of the hip is not uncommon. Obligate carrier females heterozygous for the SEDT(AK) gene defect demonstrate several similar but more subtle skeletal abnormalities beginning in early adult life. These women seem to be troubled frequently by arthralgia by middle age. The cumulative findings in SEDT(AK) implicate a defect in a gene at Xp22.2-22.1 that engenders a relatively mild disturbance in endochondral bone formation, especially in the axial skeleton. Accounts of large, well-characterized SEDT kindreds remain essential to appreciate fully any interfamily variability of disease expression and to understand better the pathogenesis of the SEDT defect on the X chromosome.

Stickler-like syndrome due to a dominant negative mutation in the COL2A1 gene

The type II collagenopathies include a wide spectrum of phenotypes ranging from mild spondylo epiphyseal dysplasia (SED) to severe achondrogenesis/hypochondrogenesis. Several attempts have been made at providing phenotype-genotype correlations in this group of disorders. In this report we discuss a South African family in which four members have a phenotype resembling Stickler syndrome type 1. Ocular problems and conductive deafness predominate, while skeletal changes resemble those of a mild form of multiple epiphyseal dysplasia (MED). In distinction to the classical form of Stickler syndrome, the affected persons have stubby digits. DNA analysis of the exons of the COL2A1 gene documented a C-T transversion in exon 39, resulting in an Arg704Cys substitution in the triple helical domain of the type II collagen peptide; this nontermination mutation may be indicative of further heterogeneity in the Stickler group of disorders or of a new syndrome amongst the type II collagenopathies.

A potent far-upstream enhancer in the mouse pro alpha 2(I) collagen gene regulates expression of reporter genes in transgenic mice

We have identified three DNase I-hypersensitive sites in chromatin between 15 and 17 kb upstream of the mouse pro alpha 2 (I) collagen gene. These sites were detected in cells that produce type I collagen but not in cells that do not express these genes. A construction containing the sequences from -17 kb to +54 bp of the mouse pro alpha 2 (I) collagen gene, cloned upstream of either the Escherichia coli beta-galactosidase or the firefly luciferase reporter gene, showed strong enhancer activity in transgenic mice when compared with the levels seen previously in animals harboring shorter promoter fragments. Especially high levels of expression of the reporter gene were seen in dermis, fascia, and the fibrous layers of many internal organs. High levels of expression could also be detected in some osteoblastic cells. When various fragments of the 5' flanking sequences were cloned upstream of the 350-bp proximal pro alpha 2(I) collagen promoter linked to the lacZ gene, the cis-acting elements responsible for enhancement were localized in the region between -13.5 and -19.5 kb, the same region that contains the three DNase I-hypersensitive sites. Moreover, the DNA segment from -13.5 to -19.5 kb was also able to drive the cell-specific expression of a 220-bp mouse pro alpha 1(I) collagen promoter, which is silent in transgenic mice. Hence, our data suggest that a far-upstream enhancer element plays a role in regulating high levels of expression of the mouse pro alpha 2(I) collagen gene.

Molecular genetic basis of the human chondrodysplasias

Considerable progress has been made in delineating the molecular genetic basis of the human chondrodysplasias. Two genes emerge as harboring mutations found in patients with the most common disorders. Mutations in the type II collagen gene account for most spondyloepiphyseal dysplasia and spondyloepiphyseal dysplasia-like clinical disorders, whereas mutations in the fibroblast growth factor receptor 3 gene are responsible for achondroplasia, thanatophoric dysplasia, and hypochondroplasia. A substantial portion of remaining patients have mutations of the genes encoding cartilage oligomeric matrix protein or diastrophic dysplasia sulfate transporter.

An ultrastructural and immunogold localization study of proteoglycans associated with the osteocytes of fetal bone in osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a rare, heterogeneous, inherited connective tissue disorder frequently caused by abnormalities of type I collagen. It is characterized by bone fragility, osteopenia, and progressive skeletal deformities. Electron microscopy of three OI type II fetal bone samples revealed numerous large osteocyte lacunae. In addition, there was a perilacunar osteoid-like band of collagen surrounding the osteocytes, which was unmineralized and morphologically unusual. Furthermore, large osteocyte lacunae contained fine particles and filamentous material similar to the expected ultrastructural appearance of proteoglycans. More detailed examination was carried out using histochemical and immunogold localization of proteoglycans at light and ultrastructural levels. These tests and the use of electron probe X-ray microanalysis confirmed that the material in the osteocyte lacunae was proteoglycan. In contrast, in the age- and site-matched normal fetal bone, all the osteocyte lacunae appeared negative for proteoglycan. Proteoglycans are regarded as inhibitors of calcification. Our observation of substantial amounts of proteoglycan in abnormally enlarged osteocytic lacunae of some OI fetal bone suggests association with the abnormal bone of this particular subtype of OI type II.

Nuclear retention of COL1A1 messenger RNA identifies null alleles causing mild osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heritable connective tissue disorder characterized by bone fragility. Most cases of severe OI result from mutations in the coding region of the COL1A1 or COL1A2 genes yielding an abnormal collagen alpha chain. In contrast, many patients with mild OI show evidence of a null allele due to a premature stop mutation in the mutant RNA transcript. We have previously described a null allele arising from a splice donor mutation where the transcript containing the included intron was sequestered in the nucleus. Here we demonstrate that transcripts from null alleles arising from premature stop mutations are also present in the nucleus and absent in the cytoplasm. Using reverse transcriptase-PCR and single-strand conformational polymorphism of COL1A1 mRNA from patients with mild OI, we describe three patients with distinct null producing mutations identified from the mutant transcript within the nuclear compartment. A fourth patient with a Gly--->Arg expressed point mutation exhibits the mutant transcript in both compartments. Defining the distribution of allelic variants of COL1A1 mRNA in the nuclear and cytoplasmic compartments gives further insight into cell biology of OI and provides a strategy for investigating potential causes of a null allele.

Perspectives on the synthesis and application of triple-helical, collagen-model peptides

Collagens can be distinguished from other proteins based on their triple-helical structure. Synthetic peptide models have been developed to better understand the triple helix structurally and to evaluate the triple helix as a recognition element for biological processes. Associated triple-helical peptides were first designed and assembled by solid-phase methodology in the late 1960s. Such peptides were used for triple-helical structural characterization by CD, nmr, and ir spectroscopies, and x-ray crystallography, and for studying the structural preferences of hydroxylases. In the late 1970s, methods were developed for covalently linking the three strands of triple-helical peptides. One benefit of "branched" peptides was the enhancement of triple-helical thermal stability. The incorporation of specific collagen sequences into thermally stable synthetic triple helices in the early 1990s has allowed for the mechanistic investigation of collagen-mediated cell adhesion and platelet aggregation. In time, discriminatory therapeutics may result from the continued exploration and further understanding of the biological effects of collagen primary, secondary, and tertiary structures via triple-helical peptide models.

Extracellular matrix stoichiometry in osteoblasts from patients with osteogenesis imperfecta

In previous work, we compared the steady-state levels of specific matrix components in human bone cells derived from patients with osteogenesis imperfecta (OI) to those of age-matched controls. A remarkable finding was the observation that there was a reduction not only in the total levels of collagen, but also in osteonectin and three proteoglycans (a large chondroitin sulfate proteoglycan, biglycan, and decorin). This pattern was observed in patients with and without detectable collagen defects. More recent analysis of extracellular matrix composition have yielded that, compared with age-matched controls, bone cells from OI patients produced higher steady-state levels of fibronectin and thrombospondin. The percentage of these two proteins incorporated into the cell layer pool was also higher in OI than in age-matched controls. In addition, the steady-state levels of hyaluronan and a heparan sulfate proteoglycan were analyzed in both OI and age-matched controls. Although the total (medium + cell layer) steady-state levels of hyaluronan were reduced by 1/3, the percentage of the hyaluronan in the cell layer pool of patients with OI increased between 100-250% of age-matched control. Thus the matrix elaborated by human OI bone cells is not only quantitatively different but also qualitatively distinct from that of age-matched controls. Not only have specific bone cell matrix components (collagen, osteonectin, the large chondroitin sulfate proteoglycan, biglycan, and decorin) been found to be present in reduced levels in OI bone cells, but some matrix components (thrombospondin, fibronectin, and hyaluronan) have also been found to be present in elevated levels in the matrix of OI cells.(ABSTRACT TRUNCATED AT 250 WORDS)