Tissue-specific and differential expression of alternatively spliced alpha 1(II) collagen mRNAs in early human embryos

Proteomic interrogation of the meninges reveals the molecular identities of structural components and regional distinctions along the CNS axis

The meninges surround the brain and spinal cord, affording physical protection while also serving as a niche of neuroimmune activity. Though possessing stromal qualities, its complex cellular and extracellular makeup has yet to be elaborated, and it remains unclear whether the meninges vary along the neuroaxis. Hence, studies were carried-out to elucidate the protein composition and structural organization of brain and spinal cord meninges in normal, adult Biozzi ABH mice. First, shotgun, bottom-up proteomics was carried-out. Prominent proteins at both brain and spinal levels included Type II collagen and Type II keratins, representing extracellular matrix (ECM) and cytoskeletal categories, respectively. While the vast majority of total proteins detected was shared between both meningeal locales, more were uniquely detected in brain than in spine. This pattern was also seen when total proteins were subdivided by cellular compartment, except in the case of the ECM category where brain and spinal meninges each had near equal number of unique proteins, and Type V and type III collagen registered exclusively in the spine. Quantitative analysis revealed differential expression of several collagens and cytoskeletal proteins between brain and spinal meninges. High-resolution immunofluorescence and immunogold-scanning electronmicroscopy on sections from whole brain and spinal cord - still encased within bone -identified major proteins detected by proteomics, and highlighted their association with cellular and extracellular elements of variously shaped arachnoid trabeculae. Western blotting aligned with the proteomic and immunohistological analyses, reinforcing differential appearance of proteins in brain vs spinal meninges. Results could reflect regional distinctions in meninges that govern protective and/or neuroimmune functions.

Presence of type IIB procollagen in mouse articular cartilage and growth plate is revealed by immuno-histochemical analysis with a novel specific antibody

Type II collagen is the major fibrillar collagen in cartilage. It is synthesized in the form of precursors (procollagens) containing N- and C-terminal propeptides. The two main isoforms of type II procollagen protein are type IIA and type IIB procollagens, generated in a developmentally regulated manner by differential splicing of the primary gene transcript. Isoform IIA contains exon 2 and is produced mainly by chondroprogenitor cells while isoform IIB lacks exon 2 and is produced by differentiated chondrocytes. Thus, expression of IIA and IIB isoforms are reliable markers for identifying the differentiation status of chondrocytes but their biological function in the context of skeletal development is still not yet fully understood. Specific antibodies against IIA and IIB procollagen isoforms are already available. In this study, a synthetic peptide spanning the junction between exon 1 and exon 3 of the murine sequence was used as an immunogen to generate a novel rabbit polyclonal antibody directed against procollagen IIB. Characterization of this antibody by Western-blotting analysis of murine cartilage extracts and ELISA tests demonstrated its specificity to the type IIB isoform. Furthermore, by immunohistochemical studies, this antibody allowed the detection of procollagen IIB in embryonic cartilage as well as in articular cartilage and growth plate of young adult mice. Interestingly, this is the first antibody that has allowed the detection of procollagen IIB at both the intra- and extracellular level. This antibody therefore represents an interesting new tool for monitoring the spatial and temporal distribution of IIB isoforms in skeletal tissues of mouse models and for tracking the trafficking and processing of type IIB procollagen.

Chondrocyte Tsc1 controls cranial base bone development by restraining the premature differentiation of synchondroses

Cranial base bones are formed through endochondral ossification. Synchondroses are growth plates located between cranial base bones that facilitate anterior-posterior growth of the skull. Coordinated proliferation and differentiation of chondrocytes in cranial base synchondroses is essential for cranial base bone growth. Herein, we report that constitutive activation of the mechanistic target of rapamycin complex 1 (mTORC1) signaling via Tsc1 (Tuberous sclerosis 1) deletion in chondrocytes causes abnormal skull development with decreased size and rounded shape. In contrast to decreased anterior-posterior growth of the cranial base, mutant mice also exhibited significant expansion of cranial base synchondroses including the intersphenoid synchondrosis (ISS) and the spheno-occipital synchondrosis (SOS). Cranial base synchondrosis expansion in TSC1-deficient mice was accounted for by an expansion of the resting zone due to increased cell number and size without alteration in cell proliferation. Furthermore, our data showed that mTORC1 activity is inhibited in the resting and proliferating zone chondrocytes of wild type mice, and Tsc1 deletion activated mTORC1 signaling of the chondrocytes in the resting zone area. Consequently, the chondrocytes in the resting zone of TSC1-deficient mice acquired characteristics generally attributed to pre-hypertrophic chondrocytes including high mTORC1 activity, increased cell size, and increased expression level of PTH1R (Parathyroid hormone 1 receptor) and IHH (Indian hedgehog). Lastly, treatment with rapamycin, an inhibitor of mTORC1, rescued the abnormality in synchondroses. Our results established an important role for TSC1-mTORC1 signaling in regulating cranial base bone development and showed that chondrocytes in the resting zone of synchondroses are maintained in an mTORC1-inhibitory environment.

Biochemical and immuno-histochemical localization of type IIA procollagen in annulus fibrosus of mature bovine intervertebral disc

For next generation tissue-engineered constructs and regenerative medicine to succeed clinically, the basic biology and extracellular matrix composition of tissues that these repair techniques seek to restore have to be fully determined. Using the latest reagents coupled with tried and tested methodologies, we continue to uncover previously undetected structural proteins in mature intervertebral disc. In this study we show that the “embryonic” type IIA procollagen isoform (containing a cysteine-rich amino propeptide) was biochemically detectable in the annulus fibrosus of both calf and mature steer caudal intervertebral discs, but not in the nucleus pulposus where the type IIB isoform was predominantly localized. Specifically, the triple-helical type IIA procollagen isoform immunolocalized in the outer margins of the inner annulus fibrosus. Triple helical processed type II collagen exclusively localized within the inter-lamellae regions and with type IIA procollagen in the intra-lamellae regions. Mass spectrometry of the α1(II) collagen chains from the region where type IIA procollagen localized showed high 3-hydroxylation of Proline-944, a post-translational modification that is correlated with thin collagen fibrils as in the nucleus pulposus. The findings implicate small diameter fibrils of type IIA procollagen in select regions of the annulus fibrosus where it likely contributes to the organization of collagen bundles and structural properties within the type I-type II collagen transition zone.

A novel deep intronic COL2A1 mutation in a family with early-onset high myopia/ocular-only Stickler syndrome

PURPOSE

To identify the genetic defect causing early-onset high myopia (eoHM)/ocular-only Stickler syndrome (ocular-STL) in a large Chinese family.

METHODS

Genomic DNA and clinical data from a four-generation family with eoHM/ocular-STL were collected. Whole-exome sequencing was performed on one affected member in initial screening. Linkage scan based on microsatellite markers was carried out initially from candidate loci associated with autosomal dominant eoHM and Stickler syndrome. Sanger sequencing was used to detect potential variants. The pathogenicity of candidate variants was evaluated using mini genes ex vivo.

RESULTS

Eight patients and five unaffected members in the family participated in the study, in which the patients had high myopia with other variable ocular phenotypes but without extraocular abnormalities. Whole exome sequencing did not detect any potential pathogenic variant in all genes known to associate with the disease. The eoHM/ocular-STL in the family was mapped to markers around COL2A1 by candidate loci linkage scan, with a maximum lod score of 3.31 for D12S1590 at θ = 0. A novel deep intronic variant, c.86-50C > G in intron 1 of COL2A1, was detected by Sanger sequencing and co-segregated with eoHM/ocular-STL in the family. Ex vivo splicing test using mini genes confirmed that the variant created a new splicing acceptor 49 bp before the canonical splicing site of exon 2, resulted in addition of 49 bp fragment in the transcript (from c.86-49 to c.86-1) and premature termination.

CONCLUSIONS

Linkage study, bioinformatics prediction, and ex vivo transcript analysis suggest a novel deep intronic variant adjacent to 5-prime of exon 2 of COL2A1, affecting exon 2 splicing, as a potential cause of ocular-STL in a large family. To our knowledge, this is the first report of an intronic variant around exon 2 as a cause of ocular-STL while a series of variants in the coding region of exon 2, a dispensable alternative-splicing exon for extraocular tissues, in COL2A1 have been reported to cause Stickler syndrome-related ocular phenotype alone.

Early onset of disc degeneration in SM/J mice is associated with changes in ion transport systems and fibrotic events

Intervertebral disc degeneration (IDD) causes back pain and sciatica, affecting quality of life and resulting in high economic/social burden. The etiology of IDD is not well understood. Along with aging and environmental factors, genetic factors also influence the onset, progression and severity of IDD. Genetic studies of risk factors for IDD using human cohorts are limited by small sample size and low statistical power. Animal models amenable to genetic and functional studies of IDD provide desirable alternatives. Despite differences in size and cellular content as compared to human intervertebral discs (IVDs), the mouse is a powerful model for genetics and assessment of cellular changes relevant to human biology. Here, we provide evidence for early onset disc degeneration in SM/J relative to LG/J mice with poor and good tissue healing capacity respectively. In the first few months of life, LG/J mice maintain a relatively constant pool of notochordal-like cells in the nucleus pulposus (NP) of the IVD. In contrast, chondrogenic events are observed in SM/J mice beginning as early as one-week-old, with progressive fibrotic changes. Further, the extracellular matrix changes in the NP are consistent with IVD degeneration. Leveraging on the genomic data of two parental and two recombinant inbred lines, we assessed the genetic contribution to the NP changes and identified processes linked to the regulation of ion transport systems. Significantly, "transport" system is also in the top three gene ontology (GO) terms from a comparative proteomic analysis of the mouse NP. These findings support the potential of the SM/J, LG/J and their recombinant inbred lines for future genetic and biological analysis in mice and validation of candidate genes and biological relevance in human cohort studies. The proteomic data has been deposited to the ProteomeXchange Consortium via the PRIDE [1] partner repository with the dataset identifier PXD008784.

Activation of mTORC1 in chondrocytes does not affect proliferation or differentiation, but causes the resting zone of the growth plate to become disordered

There are several pitfalls associated with research based on transgenic mice. Here, we describe our interpretation and analysis of mTORC1 activation in growth plate chondrocytes and compare these to a recent publication (Yan et al., Nature Communications 2016, 7:11151). Both laboratories employed TSC1-floxed mice crossed with collagen type 2-driven Cre (Col2-Cre), but drew substantially different conclusions. It was reported that activation of mechanistic target of rapamycin complex 1 (mTORC1) via Tsc1 ablation promotes the hypertrophy of growth plate chondrocytes, whereas we observe only disorganization in the resting zone, with no effect on chondrocyte hypertrophy or proliferation. Here, we present our data and discuss the differences in comparison to the earlier phenotypic characterization of TSC1 ablation in cartilage. Importantly, we detect Col2-Cre activity in non-cartilaginous tissues (including the brain) and discuss it in relation to other studies reporting non-cartilaginous expression of collagen alpha(1) II. Altogether, we conclude that mouse phenotypes following genetic ablation using Col2-Cre should be interpreted with care. We also conclude that activation of mTORC1 by TSC1 ablation in postnatal chondrocytes with inducible Col2-Cre (Col2-CreERt) leads to disorganization of the resting zone but causes no changes in chondrocyte proliferation or differentiation.

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Ablation of Tsc1 using Col2-Cre causes severe developmental abnormalities.

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Col2-Cre is not specific to chondrocytes during early development.

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Mice develop normally when Tsc1 is ablated in chondrocytes postnatally.

Genome-wide association study identifies COL2A1 locus involved in the hand development failure of Kashin-Beck disease

Kashin-Beck disease (KBD) is a chronic osteochondropathy. The pathogenesis of growth and development failure of hand of KBD remains elusive now. In this study, we conducted a two-stage genome-wide association study (GWAS) of palmar length-width ratio (LWR) of KBD, totally including 493 study subjects. Affymetrix Genome Wide Human SNP Array 6.0 was applied for genome-wide SNP genotyping of 90 KBD patients. Association analysis was conducted by PLINK. Imputation analysis was performed by IMPUTE against the reference panel of the 1000 genome project. Two SNPs were selected for replication in an independent validation sample of 403 KBD patients. In the discovery GWAS, significant association was observed between palmar LWR and rs2071358 of COL2A1 gene (P value = 4.68 × 10⁻⁸). In addition, GWAS detected suggestive association signal at rs4760608 of COL2A1 gene (P value = 1.76 × 10⁻⁴). Imputation analysis of COL2A1 further identified 2 SNPs with association evidence for palmar LWR. Replication study observed significant association signals at both rs2071358 (P value = 0.017) and rs4760608 (P value = 0.002) of COL2A1 gene. Based on previous and our study results, we suggest that COL2A1 was a likely susceptibility gene involved in the hand development failure of KBD.

Extracellular matrix microarrays to study inductive signaling for endoderm specification

During tissue development, stem and progenitor cells are faced with fate decisions coordinated by microenvironmental cues. Although insights have been gained from in vitro and in vivo studies, the role of the microenvironment remains poorly understood due to the inability to systematically explore combinations of stimuli at a large scale. To overcome such restrictions, we implemented an extracellular matrix (ECM) array platform that facilitates the study of 741 distinct combinations of 38 different ECM components in a systematic, unbiased and high-throughput manner. Using embryonic stem cells as a model system, we derived definitive endoderm progenitors and applied them to the array platform to study the influence of ECM, including the interactions of ECM with growth factor signaling, on the specification of definitive endoderm cells towards the liver and pancreas fates. We identified ECM combinations that influence endoderm fate decisions towards these lineages, and demonstrated the utility of this platform for studying ECM-mediated modifications to signal activation during liver specification. In particular, defined combinations of fibronectin and laminin isoforms, as well as combinations of distinct collagen subtypes, were shown to influence SMAD pathway activation and the degree of hepatic differentiation. Overall, our systematic high-throughput approach suggests that ECM components of the microenvironment have modulatory effects on endoderm differentiation, including effects on lineage fate choice and cell adhesion and survival during the differentiation process. This platform represents a robust tool for analyzing effects of ECM composition towards the continued improvement of stem cell differentiation protocols and further elucidation of tissue development processes.

STATEMENT OF SIGNIFICANCE

Cellular microarrays can provide the capability to perform high-throughput investigations into the role of microenvironmental signals in a variety of cell functions. This study demonstrates the utility of a high-throughput cellular microarray approach for analyzing the effects of extracellular matrix (ECM) in liver and pancreas differentiation of endoderm progenitor cells. Despite an appreciation that ECM is likely involved in these processes, the influence of ECM, particularly combinations of matrix proteins, had not been systematically explored. In addition to the identification of relevant ECM compositions, this study illustrates the capability of the cellular microarray platform to be integrated with a diverse range of cell fate measurements, which could be broadly applied towards the investigation of cell fate regulation in other tissue development and disease contexts.

Hsp90 and hepatobiliary transformation during sea lamprey metamorphosis

BACKGROUND

Biliary atresia (BA) is a human infant disease with inflammatory fibrous obstructions in the bile ducts and is the most common cause for pediatric liver transplantation. In contrast, the sea lamprey undergoes developmental BA with transient cholestasis and fibrosis during metamorphosis, but emerges as a fecund adult. Therefore, sea lamprey liver metamorphosis may serve as an etiological model for human BA and provide pivotal information for hepatobiliary transformation and possible therapeutics.

RESULTS

We hypothesized that liver metamorphosis in sea lamprey is due to transcriptional reprogramming that dictates cellular remodeling during metamorphosis. We determined global gene expressions in liver at several metamorphic landmark stages by integrating mRNA-Seq and gene ontology analyses, and validated the results with real-time quantitative PCR, histological and immunohistochemical staining. These analyses revealed that gene expressions of protein folding chaperones, membrane transporters and extracellular matrices were altered and shifted during liver metamorphosis. HSP90, important in protein folding and invertebrate metamorphosis, was identified as a candidate key factor during liver metamorphosis in sea lamprey. Blocking HSP90 with geldanamycin facilitated liver metamorphosis and decreased the gene expressions of the rate limiting enzyme for cholesterol biosynthesis, HMGCoA reductase (hmgcr), and bile acid biosynthesis, cyp7a1. Injection of hsp90 siRNA for 4 days altered gene expressions of met, hmgcr, cyp27a1, and slc10a1. Bile acid concentrations were increased while bile duct and gall bladder degeneration was facilitated and synchronized after hsp90 siRNA injection.

CONCLUSIONS

HSP90 appears to play crucial roles in hepatobiliary transformation during sea lamprey metamorphosis. Sea lamprey is a useful animal model to study postembryonic development and mechanisms for hsp90-induced hepatobiliary transformation.

Cartilage collagen type II seromarker patterns in axial spondyloarthritis and psoriatic arthritis: associations with disease activity, smoking and HLA-B27

The aim of the study was to assess the possible association between type II collagen turnover seromarkers and disease profile in patients with axial spondyloarthritis (SpA) and psoriatic arthritis (PsA). Outpatients with axial SpA (n = 110) or PsA (n = 101) underwent clinical examination including disease activity measures and HLA-B27 typing. The procollagen IIA N-terminal peptide (PIIANP) and a matrix metalloproteinase-generated type II collagen fragment (C2M) were quantified in serum by ELISA. C2M was higher in SpA than in controls, 0.41 versus 0.36 ng/ml (p = 0.004), while PIIANP did not differ between patients and healthy subjects, 2252 versus 2142 ng/ml (p = 0.13). However, DMARD-naïve SpA patients had higher PIIANP, 2461 ng/ml (p = 0.01) and C2M, 0.44 ng/ml (p = 0.0007) levels than controls, and PIIANP correlated with CRP (ρ = 0.34). C2M was lower in SpA smokers, 0.36 ng/ml versus non-smokers, 0.43 ng/ml (p = 0.02), while PIIANP was higher in HLA-B27 positive, 2312 ng/ml versus negative patients, 2021 ng/ml (p = 0.03). In PsA, PIIANP and C2M did not differ between patients and controls, but PIIANP was elevated in patients not receiving DMARDs, 2726 ng/ml. In PsA, PIIANP and C2M did not differ according to smoking and HLA-B27. Cartilage degradation assessed by C2M is increased in SpA irrespective of treatment but not in PsA. Cartilage synthesis reflected by PIIANP is increased in untreated SpA and PsA. PIIANP correlates with CRP in SpA while not in PsA. In DMARD-naïve SpA but not in PsA, HLA-B27 positivity and smoking are associated with a chondro-proliferative metabolic pattern.

Alternative Splicing Shapes the Phenotype of a Mutation in BBS8 To Cause Nonsyndromic Retinitis Pigmentosa

Bardet-Biedl syndrome (BBS) is a genetic disorder affecting multiple systems and organs in the body. Several mutations in genes associated with BBS affect only photoreceptor cells and cause nonsyndromic retinitis pigmentosa (RP), raising the issue of why certain mutations manifest as a systemic disorder whereas other changes in the same gene affect only a specific cell type. Here, we show that cell-type-specific alternative splicing is responsible for confining the phenotype of the A-to-G substitution in the 3' splice site of BBS8 exon 2A (IVS1-2A>G mutation) in the BBS8 gene to photoreceptor cells. The IVS1-2A>G mutation leads to missplicing of BBS8 exon 2A, producing a frameshift in the BBS8 reading frame and thus eliminating the protein specifically in photoreceptor cells. Cell types other than photoreceptors skip exon 2A from the mature BBS8 transcript, which renders them immune to the mutation. We also show that the splicing of Bbs8 exon 2A in photoreceptors is directed exclusively by redundant splicing enhancers located in the adjacent introns. These intronic sequences are sufficient for photoreceptor-cell-specific splicing of heterologous exons, including an exon with a randomized sequence.

Alternative splicing of type II procollagen: IIB or not IIB?

Over two decades ago, two isoforms of the type II procollagen gene (COL2A1) were discovered. These isoforms, named IIA and IIB, are generated in a developmentally-regulated manner by alternative splicing of exon 2. Chondroprogenitor cells synthesize predominantly IIA isoforms (containing exon 2) while differentiated chondrocytes produce mainly IIB transcripts (devoid of exon 2). Importantly, this IIA-to-IIB alternative splicing switch occurs only during chondrogenesis. More recently, two other isoforms have been reported (IIC and IID) that also involve splicing of exon 2; these findings highlight the complexities involving regulation of COL2A1 expression. The biological significance of why different isoforms of COL2A1 exist within the context of skeletal development and maintenance is still not completely understood. This review will provide current knowledge on COL2A1 isoform expression during chondrocyte differentiation and what is known about some of the mechanisms that control exon 2 alternative splicing. Utilization of mouse models to address the biological significance of Col2a1 alternative splicing in vivo will also be discussed. From the knowledge acquired to date, some new questions and concepts are now being proposed on the importance of Col2a1 alternative splicing in regulating extracellular matrix assembly and how this may subsequently affect cartilage and endochondral bone quality and function.

Changes in type II procollagen isoform expression during chondrogenesis by disruption of an alternative 5' splice site within Col2a1 exon 2

This study describes a new mechanism controlling the production of alternatively spliced isoforms of type II procollagen (Col2a1) in vivo. During chondrogenesis, precursor chondrocytes predominantly produce isoforms containing alternatively spliced exon 2 (type IIA and IID) while Col2a1 mRNA devoid of exon 2 (type IIB) is the major isoform produced by differentiated chondrocytes. We previously identified an additional Col2a1 isoform containing a truncated exon 2 and premature termination codons in exon 6 (type IIC). This transcript is produced by utilization of another 5' splice site present in exon 2. To determine the role of this IIC splicing event in vivo, we generated transgenic mice containing silent knock-in mutations at the IIC 5' splice site (Col2a1-mIIC), thereby inhibiting production of IIC transcripts. Heterozygous and homozygous knock-in mice were viable and display no overt skeletal phenotype to date. However, RNA expression profiles revealed that chondrocytes in cartilage from an age range of Col2a1-mIIC mice produced higher levels of IIA and IID mRNAs and decreased levels of IIB mRNAs throughout pre-natal and post-natal development, when compared to chondrocytes from littermate control mice. Immunofluorescence analyses showed a clear increase in expression of embryonic type II collagen protein isoforms (i.e. containing the exon 2-encoded cysteine-rich (CR) protein domain) in cartilage extracellular matrix (ECM). Interestingly, at P14, P28 and P56, expression of embryonic Col2a1 isoforms in Col2a1-mIIC mice persisted in the pericellular domain of the ECM in articular and growth plate cartilage. We also show that persistent expression of the exon 2-encoded CR domain in the ECM of post-natal cartilage tissue may be due, in part, to the embryonic form of type XI collagen (the α3 chain of which is also encoded by the Col2a1 gene). In conclusion, expression of the Col2a1 IIC splice form may have a regulatory function in controlling alternative splicing of exon 2 to generate defined proportions of IIA, IID and IIB procollagen isoforms during cartilage development. Future studies will involve ultrastructural and biomechanical analysis of the collagen ECM to determine the effects of persistent mis-expression of embryonic collagen isoforms in mature cartilage tissue.

A unique tool to selectively detect the chondrogenic IIB form of human type II procollagen protein

Type II collagen, the major fibrillar collagen of cartilage, is synthesized as precursor forms (procollagens) containing N- and C-terminal propeptides. Three splice variants are thought to be translated to produce procollagen II isoforms (IIA/D and IIB) which differ in their amino propeptide parts. The IIA and IID are transient embryonic isoforms that include an additional cysteine-rich domain encoded by exon 2. The IIA and IID transcripts are co-expressed during chondrogenesis then decline and the IIB isoform is the only one expressed and synthesized in fully differentiated chondrocytes. Additionally, procollagens IIA/D can be re-expressed by dedifferentiating chondrocytes and in osteoarthritic cartilage. Therefore, it is an important point to determine which isoform(s) is (are) synthesized in vivo in normal and pathological situations and in vitro, to fully assess the phenotype of cells producing type II collagen protein. Antibodies directed against the cysteine-rich extra domain found in procollagens IIA and IID are already available but antibodies detecting only the chondrogenic IIB form of type II procollagen were missing so far. A synthetic peptide encompassing the junction between exon 1 and exon 3 of the human sequence was used as immunogen to produce rabbit polyclonal antibodies to procollagen IIB. After affinity purification on immobilized peptide their absence of crossreaction with procollagens IIA/D and with the fibrillar procollagens I, III and V was demonstrated by Western blotting. These antibodies were used to reveal at the protein level that the treatment of dedifferentiated human chondrocytes by bone morphogenic protein (BMP)-2 induces the synthesis of the IIB (chondrocytic) isoform of procollagen II. In addition, immunohistochemical staining of bovine cartilage demonstrates the potential of these antibodies in the analysis of the differential spatiotemporal distribution of N-propeptides of procollagens IIA/D and IIB during normal development and in pathological situations.

Transcriptional regulation of the alpha-1 type II collagen gene by nuclear factor B/p65 and Sox9 in the chondrocytic phenotype of uterine carcinosarcomas

Uterine carcinosarcomas (U-CSs) are considered monoclonal in origin, but little is known about the mechanisms for establishment of heterologous sarcomatous components. Here, we examine the functional roles of nuclear factor κB (NF-κB)/p65 and Sox9 in the transcriptional regulation of alpha-1 type II collagen (COL2A1), a hallmark of chondrogenesis, during morphologic change in the direction of the chondrocytic phenotype. In 32 cases of U-CS, both phosphorylated p65 and Sox9 expression were colocalized in Col2A1-positive sarcomatous components, particularly in cartilaginous elements, with strongly positive correlation (ρ = 0.72, P = .005). A positive association of Col2A1 expression between protein (immunohistochemistry) and messenger RNA (in situ hybridization) assays was evident in sarcomatous components, whereas 9 cases also showed distinct positive signals for the messenger RNA without protein expression in carcinomatous elements, probably through a posttranscriptional and/or posttranslational modulation mechanism. In the Ishikawa endometrial cancer line, overexpression of p65 could activate transcription of COL2A1 promoter-intron reporters through binding to specific NF-κB sites in the first intron, along with up-regulation of Sox9. Exogenous induction of Sox9 also caused an increase in transcription of COL2A1, in contrast to a repression of the p65-mediated COL2A1 transcription, suggesting the existence of a negative feedback loop. These data, therefore, suggest that NF-κB/p65 signaling, as well as Sox9, may contribute to changes in the morphology of U-CS cells toward the chondrocytic phenotype through modulation of COL2A1 transcription.

Disruption of the developmentally-regulated Col2a1 pre-mRNA alternative splicing switch in a transgenic knock-in mouse model

The present study describes the generation of a knock-in mouse model to address the role of type II procollagen (Col2a1) alternative splicing in skeletal development and maintenance. Alternative splicing of Col2a1 precursor mRNA is a developmentally-regulated event that only occurs in chondrogenic tissue. Normally, chondroprogenitor cells synthesize predominantly exon 2-containing mRNA isoforms (type IIA and IID) while Col2a1 mRNA devoid of exon 2 (type IIB) is the major isoform produced by differentiated chondrocytes. Another isoform, IIC, has also been identified that contains a truncated exon 2 and is not translated into protein. The biological significance of this IIA/IID to IIB splicing switch is not known. Utilizing a splice site targeting knock-in approach, a 4 nucleotide mutation was created to convert the 5' splice site of Col2a1 exon 2 from a weak, non-consensus sequence to a strong, consensus splice site. This resulted in apparent expression of only the IIA mRNA isoform, as confirmed in vitro by splicing of a type II procollagen mini-gene containing the 5' splice site mutation. To test the splice site targeting approach in vivo, homozygote mice engineered to retain IIA exon 2 (Col2a1(+ex2)) were generated. Chondrocytes from hindlimb epiphyseal cartilage of homozygote mice were shown to express only IIA mRNA and protein at all pre- and post-natal developmental stages analyzed (E12.5, E16.5, P0, P3, P7, P14, P28 and P70). As expected, type IIB procollagen was the major isoform produced in wild type cartilage at all post-natal time points. Col2a1(+ex2) homozygote mice are viable, appear healthy and display no overt phenotype to date. However, research is currently underway to investigate the biological consequence of persistent expression of the exon 2-encoded conserved cysteine-rich domain in post-natal skeletal tissues.

Characterization of tissue-specific and developmentally regulated alternative splicing of exon 64 in the COL5A1 gene

The COL5A1 gene, a member of the clade B fibrillar collagen gene family, was recently shown to contain two alternatively spliced exons (64A and 64B) that encode 23 amino acids in the carboxyl-terminal propeptide. The two are identical in length, very similar in sequence, and used in a mutually exclusive fashion because of the small intron that separates them. Each COL5A1 allele uses both exons, but a given transcript will contain only one of the two exons. The sequences in other species are highly conserved at the amino acid level. The expression profile of the two isoforms was determined from analysis of RNA levels in a panel of murine tissues. While both isoforms were found in all tissues studied, actively proliferating tissues (liver, lung) used isoform B more often, while a less mitotically active tissue, brain, had a higher proportion of exon 64A. The high degree of conservation between the two exons is consistent with a regional genomic duplication. The presence of the two isoforms as far back as pufferfish (tetraodon) implies an important functional significance. The exact role determined by the two sequences is not known, but involvement in the determination of chain composition of mature type V collagen or regulation of cell activity is possible, given the differences in tissue distribution.

Loss of procollagen IIA from the anterior mesendoderm disrupts the development of mouse embryonic forebrain

Morphogenesis of the mammalian forebrain is influenced by the patterning activity of signals emanating from the anterior mesendoderm. In this study, we show that procollagen IIA (IIA), an isoform of the cartilage extracellular matrix protein encoded by an alternatively spliced transcript of Col2a1, is expressed in the prechordal plate and the anterior definitive endoderm. In the absence of IIA activity, the null mutants displayed a partially penetrant phenotype of loss of head tissues, holoprosencephaly, and loss of mid-facial structures, which is associated with reduced sonic hedgehog (Shh) expression in the prechordal mesoderm. Genetic interaction studies reveal that IIA function in forebrain and face development does not involve bone morphogenetic protein receptor 1A (BMPR1A)- or NODAL-mediated signaling activity.

Uncoupling of collagen II metabolism in newly diagnosed, untreated rheumatoid arthritis is linked to inflammation and antibodies against cyclic citrullinated peptides

OBJECTIVE

To investigate the relationship between markers of collagen II synthesis and degradation with disease activity measures, autoantibodies, and radiographic outcomes in a 4-year protocol on patients with early rheumatoid arthritis (RA) who are naïve to disease-modifying antirheumatic drugs.

METHODS

One hundred sixty patients with newly diagnosed, untreated RA entered the Cyclosporine, Methotrexate, Steroid in RA (CIMESTRA) trial. Disease activity and radiograph status were measured at baseline and 4 years. The N-terminal propeptide of collagen IIA (PIIANP) and the cross-linked C-telopeptide of collagen II (CTX-II) were quantified at baseline by ELISA. PIIANP was also assayed at 2 and 4 years. Anticyclic citrullinated peptide (anti-CCP) was recorded at baseline. An uncoupling index for cartilage collagen metabolism was calculated from PIIANP and CTX-II measurements.

RESULTS

PIIANP was low at diagnosis and 4 years on (p < 0.001), irrespective of treatment and disease activity. PIIANP was lowest in anti-CCP positive patients (p = 0.006), and there was a negative correlation between PIIANP and anti-CCP titers (rho = -0.25, p 0.002). CTX-II was increased (p < 0.001) and correlated positively with disease activity and radiographic progression, but not with anti-CCP (p = 0.93). The uncoupling index was not superior to CTX-II in predicting radiographic changes.

CONCLUSION

These results suggest that cartilage collagen formation and degradation are unbalanced when RA is diagnosed. The different associations of collagen II anabolism (PIIANP) and collagen II degradation (CTX-II) with anti-CCP, synovitis, and radiographic progression indicate that at this early stage of RA, cartilage collagen degradation is mainly driven by synovitis, while anti-CCP antibodies may interfere with cartilage regeneration by inhibiting collagen IIA formation. Trial registration j.nr NCT00209859.

Circadian pattern and the effect of standardized physical exercise on procollagen IIA N-peptide (PIIANP) in rheumatoid arthritis at different stages and in healthy individuals

BACKGROUND

Variant collagen IIA is re-expressed in diseased cartilage. Low procollagen IIA N-peptide (PIIANP) levels in serum have recently been reported in rheumatoid arthritis (RA). We investigated circadian rhythmicity and effect of physical activity on PIIANP in early and longstanding RA and in healthy subjects.

METHODS

Patients with early and longstanding RA and controls were included. Fasting and serial blood samples were collected during 24 h. PIIANP response to physical activity was studied before and serially after standardized exercise.

RESULTS AND CONCLUSION

In RA at different stages and healthy individuals, PIIANP exhibited no circadian rhythmicity, and PIIANP in serum was not influenced by physical activity.

BMP-2 and TGF-beta1 differentially control expression of type II procollagen and alpha 10 and alpha 11 integrins in mouse chondrocytes

Bone morphogenetic protein (BMP)-2 and transforming growth factor (TGF)-beta1 are multifunctional cytokines both proposed as stimulants for cartilage repair. Thus it is crucial to closely examine and compare their effects on the expression of key markers of the chondrocyte phenotype, at the gene and protein level. In this study, the expression of alpha 10 and alpha 11 integrin subunits and the IIA/IIB spliced forms of type II procollagen have been monitored for the first time in parallel in the same in vitro model of mouse chondrocyte dedifferentiation/redifferentiation. We demonstrated that TGF-beta1 stimulates the expression of the non-chondrogenic form of type II procollagen, IIA isoform, and of a marker of mesenchymal tissues, i.e. the alpha 11 integrin subunit. On the contrary, BMP-2 stimulates the cartilage-specific form of type II procollagen, IIB isoform, and a specific marker of chondrocytes, i.e. the alpha 10 integrin subunit. Collectively, our results demonstrate that BMP-2 has a better capability than TGF-beta1 to stimulate chondrocyte redifferentiation and reveal that the relative expressions of type IIB to type IIA procollagens and alpha 10 to alpha 11 integrin subunits are good markers to define the differentiation state of chondrocytes. In addition, adenoviral expression of Smad6, an inhibitor of BMP canonical Smad signaling, did not affect expression of total type II procollagen or the ratio of type IIA and type IIB isoforms in mouse chondrocytes exposed to BMP-2. This result strongly suggests that signaling pathways other than Smad proteins are involved in the effect of BMP-2 on type II procollagen expression.

The developmental roles of the extracellular matrix: beyond structure to regulation

Cells in multicellular organisms are surrounded by a complex three-dimensional macromolecular extracellular matrix (ECM). This matrix, traditionally thought to serve a structural function providing support and strength to cells within tissues, is increasingly being recognized as having pleiotropic effects in development and growth. Elucidation of the role that the ECM plays in developmental processes has been significantly advanced by studying the phenotypic and developmental consequences of specific genetic alterations of ECM components in the mouse. These studies have revealed the enormous contribution of the ECM to the regulation of key processes in morphogenesis and organogenesis, such as cell adhesion, proliferation, specification, migration, survival, and differentiation. The ECM interacts with signaling molecules and morphogens thereby modulating their activities. This review considers these advances in our understanding of the function of ECM proteins during development, extending beyond their structural capacity, to embrace their new roles in intercellular signaling.

Bone morphogenetic protein-2 stimulates chondrogenic expression in human nasal chondrocytes expanded in vitro

Articular cartilage contains an extracellular matrix with characteristic macromolecules such as type II collagen. Because this tissue is avascular and mature chondrocytes do not proliferate, cartilage lesions have a limited capacity for healing after trauma. Autologous chondrocyte implantation (ACI) is widely used for the treatment of patients with focal damage to articular cartilage. However, this method faces a major issue: dedifferentiation of chondrocytes occurs during the long-term culture necessary for mass cell production. The aim of this study was to determine if the step of cell amplification required for ACI could benefit from the use of bone morphogenetic protein (BMP)-2, a potent regulator of chondrogenic expression. Chondrocytes were isolated from human nasal cartilage, a hyaline cartilage like articular cartilage and were serially cultured in monolayers. After one, two or three passages, BMP-2 was used to evaluate the chondrogenic potential of the dedifferentiated chondrocytes, at the gene and protein level. We found that BMP-2 can reactivate the program of chondrogenic expression in dedifferentiated chondrocytes. To gain insight into the molecular mechanisms involved in the responsiveness of chondrocytes to BMP-2, we examined the phosphorylation of Smad proteins and the interaction of the Sry-type high-mobility-group box (Sox) transcription factors with the cartilage-specific enhancer of the type II procollagen gene. Our results show that BMP-2 acts by stimulating Smad phosphorylation and by enhancing DNA-binding of the Sox transcription factors to the specific enhancer of the type II procollagen gene. Thus, this study reveals the potential use of BMP-2 as a stimulatory agent in conventional ACI strategies.

Col2-Cre recombinase is co-expressed with endogenous type II collagen in embryonic renal epithelium and drives development of polycystic kidney disease following inactivation of ciliary genes

Here we report on the severe defects in renal epithelium induced by the transgenic Col2-Cre line used previously for skeletal tissue-specific gene targeting. We demonstrate that conditional ablation of the Kif3a or Pkd1 genes encoding primary cilium/intraflagellar transport-associated proteins using type II collagen-specific Cre transgenic strain results in a severe form of polycystic kidney disease in mice. We detect Col2-Cre recombinase expression in kidney epithelium, which reflects expression of the endogenous Col1alpha(II) gene in the embryonic renal tubules. We determine the exon 2-containing splice variant of the Col1alpha(II) gene as a major transcript expressed in kidney. Furthermore, the confocal immunocytochemical analysis demonstrates deposition of the type II collagen within the mesenchymal-epithelial renal tissue interfaces and its co-localization with the basement membrane marker collagen IV during embryonic kidney morphogenesis.

Gene expression patterns underlying proximal-distal skeletal segmentation in late-stage zebrafish, Danio rerio

Timing and pattern of expression of ten candidate segmentation genes or gene pairs were reviewed or examined in developing median fins of late-stage zebrafish, Danio rerio. We found a general correspondence in timing and pattern of expression between zebrafish fin radial segmentation and tetrapod joint development, suggesting that molecular mechanisms underlying radial segmentation have been conserved over 400 million years of evolution. Gene co-expression during segmentation (5.5-6.5 mm SL) is similar between tetrapods and zebrafish: bmp2b, bmp4, chordin, and gdf5 in interradial mesenchyme and ZS; bapx1, col2a1, noggin3, and sox9a in chondrocytes. Surprisingly, wnt9a is not expressed in the developing median fins, though wnt9b is detected. In contrast to all other candidate segmentation genes we examined, bapx1 is not expressed in the caudal fin, which does not segment. Together, these data suggest a scenario of gene interactions underlying radial segmentation based on the patterns and timing of candidate gene expression.

Missense and nonsense mutations in the alternatively-spliced exon 2 ofCOL2A1cause the ocular variant of Stickler syndrome

Stickler syndrome type I (STL1) is a phenotypically heterogeneous disorder characterized by ocular and extraocular features. It is caused by null-allele mutations in the COL2A1 gene that codes for procollagen II. COL2A1 precursor mRNA undergoes alternative splicing, resulting in two isoforms, a long form including exon 2 (type IIA isoform) and a short form excluding exon 2 (type IIB isoform). The short form is predominantly expressed by differentiated chondrocytes in adult cartilage, and the long form in chondroprogenitor cells during early development and in the vitreous of the eye, which is the only adult tissue containing procollagen IIA. Recent evidence indicates that due to the tissue-specific expression of these two isoforms, premature termination codon mutations in exon 2 cause Stickler syndrome with minimal or no extraocular manifestations. We describe here two mutations in exon 2 of COL2A1 in three patients with predominantly ocular Stickler syndrome: Cys64Stop in two patients, and a novel structural mutation, Cys57Tyr, in one patient. RT-PCR of total lymphoblast RNA from one patient with the Cys64Stop mutation revealed that only the normal allele of the IIA form was present, indicating that the mutation resulted either in complete loss of the allele by nonsense-mediated mRNA decay or by skipping of exon 2 via nonsense-mediated altered splicing, resulting in production of the type IIB isoform. The results of COL2A1 minigene expression studies suggest that both Cys64Stop and Cys57Tyr alter positive cis regulatory elements for splicing, resulting in a lower IIA:IIB ratio.

Expression of two novel alternatively spliced COL2A1 isoforms during chondrocyte differentiation

Alternative splicing of the type II procollagen gene (COL2A1) is developmentally regulated during chondrogenesis. Type IIA procollagen (+ exon 2) is synthesized by chondroprogenitor cells while type IIB procollagen (- exon 2) is synthesized by differentiated chondrocytes. Here, we report expression of two additional alternatively spliced COL2A1 isoforms during chondrocyte differentiation of bone marrow-derived mesenchymal stem cells (MSCs). One isoform, named IIC, contains only the first 34 nucleotides of exon 2 by the use of an alternative 5' splice site, resulting in a premature termination codon and possible nonsense-mediated decay of IIC mRNA. Low levels of the IIC isoform were detected by RT-PCR and Southern analysis of COL2A1 cDNA amplified from differentiating rabbit and human MSCs. A second novel transcript, named IID, arises by the use of another 5' alternative splice site in intron 2. The IID isoform contains exon 2 plus 3 nucleotides, resulting in the insertion of an additional amino acid. The IID isoform was co-expressed with the IIA isoform during chondrogenesis, and was approximately one-third as abundant. Deletion of the IIC alternative 5' splice site from a COL2A1 mini-gene construct resulted in a significant increase in the IIA:IIB ratio. A mutant mini-gene that inhibited production of the IID isoform, however, had differential effects on the production of the IIA and IIB isoforms: this was apparently related to the differentiation status of the cell type used. These data suggest that COL2A1 mRNA abundance and other aspects of chondrocyte differentiation may be regulated by the use of these previously undetermined alternative splice sites.

Differential Expression Pattern of Extracellular Matrix Molecules During Chondrogenesis of Mesenchymal Stem Cells from Bone Marrow and Adipose Tissue

Adipose-derived adult stem cells (ADASCs) or bone marrow-derived mesenchymal stem cells (BMSCs) are considered as alternative cell sources for cell-based cartilage repair due to their ability to produce cartilage-specific matrix. This article addresses the differential expression pattern of extracellular matrix (ECM) molecules in BMSCs or ADASCs following chondrogenic differentiation. Human BMSCs or ADASCs were encapsulated in alginate and cultured in TGF-beta1-containing medium for 2 or 3 weeks. Chondrospecific mRNA expression was analyzed and alternative splicing of alpha(1)-procollagen type II mRNA was monitored via reverse transcriptase-polymerase chain reaction (RT-PCR). Corresponding ECM synthesis was demonstrated using immunohistochemistry. After chondroinduction, expression of collagen type II, type X, COMP and aggrecan mRNA was 3-15-fold higher than in ADASCs. The type IIA splicing form of alpha(1)-procollagen type II was expressed in both populations, and the type IIB splicing form was exclusively detected in BMSCs. In response to TGF-beta, collagen type II and X were secreted more strongly by BMSCs than by ADASCs. BMSCs express a more mature phenotype than ADASCs after chondroinduction. TGF-beta1 induces alternative splicing of the alpha(1)-procollagen type II transcript in BMSCs, but not in ADASCs. These findings may direct the development of a cell-specific culture environment either to prevent hypertrophy in BMSCs or to promote chondrogenic maturation in ADASCs.

Mechanical compressive loading stimulates the activity of proximal region of human COL2A1 gene promoter in transfected chondrocytes

Previous studies have demonstrated that the mechanical compressive loading affects the biosynthesis of chondrocytes seeded in three dimensional scaffolds. In this study, the level of type II collagen mRNA expression was increased by a continuous dynamic compression at 10% compressive strain and 0.1 Hz in chondrocytes seeded in a biodegradable, elastomeric scaffold, poly(L-lactide-co-epsilon-caprolactone) (PLCL). To further examine this molecular mechanism, the promoter region of COL2A1 gene, which is encoding type II collagen, was analyzed using rabbit chondrocytes transfected with luciferase reporter vectors containing the 5'-flanking regions of human COL2A1 gene. A deletion mutant analysis revealed that the most active short promoter in response to continuous dynamic compression is in the region between -509 and -109 base pairs, where the transcription factor Sp1 is located. Additionally, an mRNA decay experiment using transcription inhibitor actinomycin D demonstrated that dynamic compression do not stabilize type II collagen mRNA. Our results indicate that mechanical compression increases the level of type II mRNA expression by transcriptional activation possibly through the Sp1 binding sites residing in the proximal region of the COL2A1 gene promoter.

Kinetics of tamoxifen-regulated Cre activity in mice using a cartilage-specific CreERT to assay temporal activity windows along the proximodistal limb skeleton

Cartilage differentiation occurs over a broad time range from early embryonic development, when the mesenchymal condensations that give rise to cartilage models for future bone first appear, and continuing through adult life, when there is ongoing maintenance of articular joint surfaces and re-activation of cartilage formation after fracture. The chondrogenic response also figures in the pathogenesis of degenerative and inflammatory joint diseases. We have generated a transgenic line expressing tamoxifen-dependent Cre recombinase that gives efficient recombination in the chondrogenic lineage, both during embryogenesis and postnatally, and provides a valuable tool for analysis of gene function selectively in chondrogenic cells using conditional genetic approaches. Because the cartilage model of the limb skeleton forms progressively in a proximodistal order during discrete, well-defined time periods, evaluation of the spatial extent of tamoxifen-induced recombination along the limb axis during these time windows has also enabled us to examine the pharmacokinetics of single-dose tamoxifen injections during pregnancy.

Alternative splicing of type II procollagen exon 2 is regulated by the combination of a weak 5' splice site and an adjacent intronic stem-loop cis element

Alternative splicing of the type II procollagen gene (COL2A1) is developmentally regulated during chondrogenesis. Chondroprogenitor cells produce the type IIA procollagen isoform by splicing (including) exon 2 during pre-mRNA processing, whereas differentiated chondrocytes synthesize the type IIB procollagen isoform by exon 2 skipping (exclusion). Using a COL2A1 mini-gene and chondrocytes at various stages of differentiation, we identified a non-classical consensus splicing sequence in intron 2 adjacent to the 5' splice site, which is essential in regulating exon 2 splicing. RNA mapping confirmed this region contains secondary structure in the form of a stem-loop. Mutational analysis identified three cis elements within the conserved double-stranded stem region that are functional only in the context of the natural weak 5' splice site of exon 2; they are 1) a uridine-rich enhancer element in all cell types tested except differentiated chondrocytes; 2) an adenine-rich silencer element, and 3) an enhancer cis element functional in the context of secondary structure. This is the first report identifying key cis elements in the COL2A1 gene that modulate the cell type-specific alternative splicing switch of exon 2 during cartilage development.

Collagens and collagen-related matrix components in the human and mouse eye

The three-dimensional structure of the eye plays an important role in providing a correct optical environment for vision. Much of this function is dependent on the unique structural features of ocular connective tissue, especially of the collagen types and their supramolecular structures. For example, the organization of collagen fibrils is largely responsible for transparency and refraction of cornea, lens and vitreous body, and collagens present in the sclera are largely responsible for the structural strength of the eye. Phylogenetically, most of the collagens are highly conserved between different species, which suggests that collagens also share similar functions in mice and men. Despite considerable differences between the mouse and the human eye, particularly in the proportion of the different tissue components, the difficulty of performing systematic histologic and molecular studies on the human eye has made mouse an appealing alternative to studies addressing the role of individual genes and their mutations in ocular diseases. From a genetic standpoint, the mouse has major advantages over other experimental animals as its genome is better known than that of other species and it can be manipulated by the modern techniques of genetic engineering. Furthermore, it is easy, quick and relatively cheap to produce large quantities of mice for systematic studies. Thus, transgenic techniques have made it possible to study consequences of specific mutations in genes coding for structural components of ocular connective tissues in mice. As these changes in mice have been shown to resemble those in human diseases, mouse models are likely to provide efficient tools for pathogenetic studies on human disorders affecting the extracellular matrix. This review is aimed to clarify the role of collagenous components in the mouse and human eye with a closer look at the new findings of the collagens in the cartilage and the eye, the so-called "cartilage collagens".

Solution structure and dynamics of a prototypical chordin-like cysteine-rich repeat (von Willebrand Factor type C module) from collagen IIA

Chordin-like cysteine-rich (CR) repeats (also referred to as von Willebrand factor type C (VWC) modules) have been identified in approximately 200 extracellular matrix proteins. These repeats, named on the basis of amino acid conservation of 10 cysteine residues, have been shown to bind members of the transforming growth factor-beta (TGF-beta) superfamily and are proposed to regulate growth factor signaling. Here we describe the intramolecular disulfide bonding, solution structure, and dynamics of a prototypical chordin-like CR repeat from procollagen IIA (CR(ColIIA)), which has been previously shown to bind TGF-beta1 and bone morphogenetic protein-2. The CR(ColIIA) structure manifests a two sub-domain architecture tethered by a flexible linkage. Initial structures were calculated using RosettaNMR, a de novo prediction method, and final structure calculations were performed using CANDID within CYANA. The N-terminal region contains mainly beta-sheet and the C-terminal region is more irregular with the fold constrained by disulfide bonds. Mobility between the N- and C-terminal sub-domains on a fast timescale was confirmed using NMR relaxation measurements. We speculate that the mobility between the two sub-domains may decrease upon ligand binding. Structure and sequence comparisons have revealed an evolutionary relationship between the N-terminal sub-domain of the CR module and the fibronectin type 1 domain, suggesting that these domains share a common ancestry. Based on the previously reported mapping of fibronectin binding sites for vascular endothelial growth factor to regions containing fibronectin type 1 domains, we discuss the possibility that this structural homology might also have functional relevance.

Spontaneous differentiation of mesenchymal stem cells obtained from fetal rat circulation

Mesenchymal stem cells (MSCs) are thought to be multipotential, capable of differentiating into multiple lineages. We attempted to characterize rat cells derived from fetal circulating blood (FCBCs) that displayed a fibroblastic morphology and differentiated into osteoblastic and chondrocytic lineages. Notably, they differentiated into a chondrocyte-specific phenotype on plastic culture dishes in medium supplemented only with 10% fetal bovine serum (FBS) without the use of a three-dimensional culture substrate. Bone marrow-derived cells did not convey such phenotypic expression under the same conditions. The characteristic features of these cells were analyzed by reverse transcription polymerase chain reaction, immunohistological and von Kossa staining, and by immuno-dot blotting. In one population, expression of collagen types II and X was detected in differentiated cells at the same levels as observed in chondrocytes derived from rat rib cartilage. In another population, parathyroid hormone receptor, alkaline phosphatase, and osteocalcin were also expressed at levels almost equal to those observed in long bone-derived osteoblasts. After 3 weeks in culture, extensively condensed cell masses, stained with anti-type II collagen antibody, could be distinguished histologically from small, multilayered, von Kossa-positive nodules, which stained with anti-osteocalcin, but not with anti-type II collagen antibody. In addition, the FCBCs differentiated into adipogenic cells in the presence of methyl-isobutyl xanthine, dexamethasone, insulin, and indomethacin. These cells expressed PPARgamma2 mRNA and accumulated lipid vesicles detectable by Oil red-O staining. Our findings suggest that FCBCs have the potential to readily differentiate into multiple lineages and that they are distinct from mesenchymal stem cells derived from bone marrow or circulating blood from more mature and adults in their spontaneous differentiation in the absence of specific factors such as transforming growth factor-beta (TGF-beta) or dexamethasone, or a three-dimensional culture environment.

Expression of collagen type I and type II in consecutive stages of human osteoarthritis

In normal hyaline cartilage the predominant collagen type is collagen type II along with its associated collagens, for example, types IX and XI, produced by normal chondrocytes. In contrast, investigations have demonstrated that in vitro a switch from collagen type II to collagen type I occurs. Some authors have detected collagen type I in osteoarthritic cartilage also in vivo, especially in late stages of osteoarthritis, while others have not. In the light of these diverging results, we have attempted to elucidate which type of collagen, type I and/or type II, is synthesized in the consecutive stages of human osteoarthritis. We performed in situ hybridization and immunohistochemistry with cartilage tissue samples from patients suffering from various stages of osteoarthritis. Furthermore, we quantitated our results on the gene expression of collagen type I and type II with the help of real-time PCR. We found that with the progression of the disease not only collagen type II, but also increasing amounts of collagen type I mRNA were produced. This supports the conclusion that collagen type I gradually becomes one of the factors involved in the pathogenesis of osteoarthritis.

Expression patterns of cartilage collagens and Sox9 during mouse heart development

A majority of congenital heart defects are due to abnormal development of the valves and membranous septa, i.e., connective tissue components of the heart. During development, an interesting feature of cardiac connective tissue is transient expression of collagens typical for cartilage. To better understand the role of these collagens in the heart, we have performed a systematic study on the temporospatial expression of type II and IX collagen isoforms during mouse heart development employing northern hybridization and RNase protection assay. The mRNAs for alpha1(II) and alpha1(IX) collagens were expressed transiently between embryonic days 10.5 and 14.5 in embryonic mouse heart. RNase protection assays revealed that for both transcripts the embryonic ("prechondrogenic") variants of the alternatively spliced mRNA isoforms dominated. Immunohistochemistry demonstrated that type IIA collagen and Sox9, its key transcriptional regulator, were expressed in the epithelial-mesenchymal areas of the developing heart, with partially overlapping patterns particularly in valvular and septal regions. In addition, Sox9 expression was detected widely in the developing heart. These observations support the hypothesis that cartilage collagens, especially the long isoform of type II collagen, participate in the morphogenesis of cardiac valves and septa.

Alternative splicing of type II procollagen pre-mRNA in chondrocytes is oppositely regulated by BMP-2 and TGF-beta1

Type II collagen is the major protein of cartilage and is synthesized as a procollagen in two forms (IIA and IIB), generated by differential splicing of the gene primary transcript. Previous studies have indicated that only type IIB is expressed in differentiated chondrocytes. Here, we examined the effects of bone morphogenetic protein (BMP)-2 and transforming growth factor (TGF)-beta1 on the expression of IIA and IIB forms expressed in de-differentiated chondrocytes grown in monolayer. Our results demonstrate that BMP-2 favors expression of type IIB whereas TGF-beta1 potentiates expression of type IIA induced by subculture. These observations reveal the specific capability of BMP-2 to reverse the de-differentiation state of chondrocytes.

Type II and type IX collagen transcript isoforms are expressed during mouse testis development

Mutations in the transcription factor SOX9 give rise to campomelic dysplasia, a syndrome characterized by skeletal abnormalities and XY sex reversal. Sox9 is expressed at sites of chondrogenesis and in the developing testis, and, thus, it plays a role in two overtly different pathways of differentiation. Previous studies have identified the gene for type II collagen, Col2a1, as a target of Sox9 in mouse chondrocytes and implicated Col9a3 as a Sox9 target in testis. Using differential expression analysis combined with reverse transcription-polymerase chain reaction and whole-mount in situ hybridization, we have identified nonchondrocytic collagen transcript isoforms that are expressed in the early male mouse gonad. Male-specific, gonadal expression of nonchondrocytic Col2a1 was first seen at 11.5 days postcoitum (dpc) and was undetectable by 13.5 dpc. This was accompanied by increasing expression of nonchondrocytic Col9a1, Col9a2, and Col9a3, first detected at 11.5 dpc. Expression was analyzed in testes that had been depleted of germ cells by the cytotoxic drug busulfan. These studies showed Col9a3 and Col2a1 to be expressed in Sertoli cells within the developing testis cords. Nonchondrocytic type II collagen contains a cysteine-rich domain that has been shown to bind members of the transforming growth factor beta superfamily of signaling molecules. Thus, this interaction may play a role in the morphogenesis and differentiation of the testis.

Expression of Sox9 and type IIA procollagen during ocular development and aging in transgenic Del1 mice with a mutation in the type II collagen gene

PURPOSE

To study the expression and distribution of transcription factor Sox9 and type IIA procollagen in the developing and aging eyes of normal and transgenic Dell mice carrying pro(alpha)1(II) collagen transgenes with a short deletion mutation, which cause ocular abnormalities in this mouse line.

METHODS

The eyes of Del1 mice were studied on embryonic days E14.5, E16.5 and E18.5, and at the ages of 4 and nine months, using their nontransgenic littermates as controls. Sox9 and pro(alpha)1(IIA) collagen were detected by RNase protection assay and immunohistochemistry.

RESULTS

RNase protection assay revealed Sox9 transcripts in the eyes of Del1 and control mice during development and aging. The mRNA for type IIA procollagen had a similar temporal expression pattern. On embryonic days E14.5, E16.5 and E18.5, Sox9 was located by immunohistochemistry in the nuclei and type IIA procollagen in the extracellular space of the developing retina. During growth and aging, the ocular expression of Sox9 mRNA and the immunohistochemical reaction for Sox9 antibody diminished, concomitant with the reduction in type II procollagen mRNA. However, at the age of nine months, levels of Sox9 and type IIA procollagen mRNAs were higher in the degenerating eyes of Del1 and control mice.

CONCLUSIONS

The similarities in the temporo-spatial distribution of Sox9 and type IIA procollagen suggest that this transcription factor is involved in the activation of type II collagen expression in the eye, as has been demonstrated in prechondrogenic mesenchyme and immature cartilage. The increased production of Sox9 and type IIA procollagen in the aging retina and vitreous is analogous to degenerating articular cartilage where attempted tissue repair has also been observed.

Radial perivascular retinal degeneration: a key to the clinical diagnosis of an ocular variant of Stickler syndrome with minimal or no systemic manifestations

PURPOSE

To identify the genetic defect and present the ocular and extraocular findings in a large pedigree of predominantly ocular Stickler syndrome.

DESIGN

Observational case series.

METHODS

An eight-generation pedigree with hereditary retinal detachments was retrospectively and prospectively studied. Clinical information was obtained by medical records, telephone interviews, medical questionnaires, detailed ophthalmologic examinations, physical examinations, and personal observations. Linkage analysis of the COL2A1 gene was performed on 21 family members, and mutation analysis was performed on three family members.

RESULTS

The pedigree consisted of 100 affected individuals. The ocular findings, frequently bilateral, consisted of radial perivascular retinal degeneration (RPRD) (100%), vitreous syneresis (100%), high myopia (76%), retinal detachment (65%), presenile cataract development (occurring before 50 years of age; 78%), and glaucoma (18%). Most (70%) of the retinal detachments occurred between 4 and 18 years of age. Extraocular manifestations, characteristic for Stickler syndrome, were detected in only four of 100 (4%) affected individuals. Linkage analysis with COL2A1 flanking markers showed evidence for linkage to the COL2A1 locus. The COL2A1 gene analysis identified a mutation converting a codon TGC for cysteine(86) to a premature termination codon in the alternatively spliced exon 2.

CONCLUSIONS

A variant of Stickler syndrome, caused by mutations in exon 2 of COL2A1, may present in families with all of the ocular findings and no clinically identifiable extraocular findings associated with Stickler syndrome. The predominant ocular findings are a congenitally abnormal vitreous and an acquired radial perivascular retinal degeneration that may lead to complicated childhood and adult retinal detachment.

Uncoupling of type II collagen synthesis and degradation predicts progression of joint damage in patients with knee osteoarthritis

OBJECTIVE

The hallmark of osteoarthritis (OA) is the loss of articular cartilage. This loss arises from an imbalance between cartilage synthesis and cartilage degradation over a variable period of time. The aims of this study were to investigate the rates of these processes in patients with knee OA using two new molecular markers and to investigate whether the combined use of these markers could predict the progression of joint damage evaluated by both radiography and arthroscopy of the joints during a period of 1 year.

METHODS

Seventy-five patients with medial knee OA (51 women, 24 men; mean +/- SD age 63 +/- 8 years, mean +/- SD disease duration 4.8 +/- 5.2 years) were studied prospectively. At baseline, we measured serum levels of N-propeptide of type IIA procollagen (PIIANP) and urinary excretion of C-terminal crosslinking telopeptide of type II collagen (CTX-II) as markers of type II collagen synthesis and degradation, respectively. Joint space width (JSW) on radiography and medial chondropathy at arthroscopy (assessed using a 100-mm visual analog scale [VAS]) were measured in all patients at baseline and in 52 patients at 1 year. Progression of joint destruction was defined as a decrease of > or =0.5 mm in JSW on radiography and as increased chondropathy (an increase in the VAS score of >8.0 units) between the baseline and 1-year evaluations.

RESULTS

At baseline, compared with 58 healthy age- and sex-matched controls, patients with knee OA had decreased serum levels of PIIANP (20 ng/ml versus 29 ng/ml; P < 0.001) and increased urinary excretion of CTX-II (618 ng/mmole creatinine [Cr] versus 367 ng/mmole Cr; P < 0.001). The highest discrimination between OA patients and controls was obtained by combining PIIANP and CTX-II in an uncoupling index (Z score CTX-II - Z score PIIANP), which yielded a mean Z score of 2.9 (P < 0.0001). Increased baseline values in the uncoupling index were associated with greater progression of joint damage evaluated either by changes in JSW (r = -0.46, P = 0.0016) or by VAS score (r = 0.36, P = 0.014). Patients with both low levels of PIIANP (less than or equal to the mean - 1 SD in controls) and high levels of CTX-II (greater than or equal to the mean + 1 SD in controls) had an 8-fold more rapid progression of joint damage than other patients (P = 0.012 and P < 0.0001 as assessed by radiography and arthroscopy, respectively) and had relative risks of progression of 2.9 (95% confidence interval [95% CI] 0.80-11.1) and 9.3 (95% CI 2.2-39) by radiography and arthroscopy, respectively.

CONCLUSION

Patients with knee OA are characterized by an uncoupling of type II collagen synthesis and degradation which can be detected by assays for serum PIIANP and urinary CTX-II. The combination of these two new markers could be useful for identifying knee OA patients at high risk for rapid progression of joint damage.

Functions of transforming growth factor-beta family type I receptors and Smad proteins in the hypertrophic maturation and osteoblastic differentiation of chondrocytes

We investigated the effects of bone morphogenetic protein (BMP)-2, a member of the transforming growth factor-beta superfamily, on the regulation of the chondrocyte phenotype, and we identified signaling molecules involved in this regulation. BMP-2 triggers three concomitant responses in mouse primary chondrocytes and chondrocytic MC615 cells. First, BMP-2 stimulates expression or synthesis of type II collagen. Second, BMP-2 induces expression of molecular markers characteristic of pre- and hypertrophic chondrocytes, such as Indian hedgehog, parathyroid hormone/parathyroid hormone-related peptide receptor, type X collagen, and alkaline phosphatase. Third, BMP-2 induces osteocalcin expression, a specific trait of osteoblasts. Constitutively active forms of transforming growth factor-beta family type I receptors and Smad proteins were overexpressed to address their role in this process. Activin receptor-like kinase (ALK)-1, ALK-2, ALK-3, and ALK-6 were able to reproduce the hypertrophic maturation of chondrocytes induced by BMP-2. In addition, ALK-2 mimicked further the osteoblastic differentiation of chondrocytes induced by BMP-2. In the presence of BMP-2, Smad1, Smad5, and Smad8 potentiated the hypertrophic maturation of chondrocytes, but failed to induce osteocalcin expression. Smad6 and Smad7 impaired chondrocytic expression and osteoblastic differentiation induced by BMP-2. Thus, our results indicate that Smad-mediated pathways are essential for the regulation of the different steps of chondrocyte and osteoblast differentiation and suggest that additional Smad-independent pathways might be activated by ALK-2.