The role of TGFbetas and Sox9 during limb chondrogenesis

Rho kinase-dependent activation of SOX9 in chondrocytes

OBJECTIVE

The transcription factor SOX9 directly regulates the expression of the major proteoglycans and collagens comprising the cartilage extracellular matrix. The DNA binding activity and cellular localization of SOX9 is controlled through posttranslational modifications, including phosphorylation. The activity of Rho kinase (ROCK) has profound effects on the actin cytoskeleton, and these effects are instrumental in determining the phenotype and differentiation of chondrocytes. However, the mechanisms linking ROCK to altered chondrocyte gene expression remain unknown. The purpose of the present study was to test for a direct interaction between ROCK and SOX9.

METHODS

Human SW1353 chondrosarcoma cells were transfected with constructs coding for RhoA, ROCK, Lim kinase, and SOX9. The interaction between ROCK and SOX9 was tested on purified proteins, and was verified within a cellular context using induced overexpression and activation of the Rho pathway. The effects of SOX9 transcriptional activation were quantified with a luciferase reporter plasmid containing SOX9 binding sites from the COL2A1 enhancer element.

RESULTS

SOX9 was found to contain a consensus phosphorylation site for ROCK. In vitro, ROCK directly phosphorylated SOX9 at Ser(181), and the overexpression of ROCK or the activation of the RhoA pathway in SW1353 chondrosarcoma cells increased SOX9(Ser181) phosphorylation. ROCK caused a dose-dependent increase in the transcription of a SOX9-luciferase reporter construct, and increased phosphorylation and nuclear accumulation of SOX9 protein in response to transforming growth factor beta treatment and mechanical compression.

CONCLUSION

These results demonstrate a new interaction that directly links ROCK to increased cartilage matrix production via activation of SOX9 in response to mechanical and growth factor stimulation.

Human stanniocalcin-1 or -2 expressed in mice reduces bone size and severely inhibits cranial intramembranous bone growth

Stanniocalcin-1 (STC1) and -2 (STC2) are highly related, secreted, homodimeric glycoproteins that are significantly upregulated by different forms of stress including high phosphate levels. Transgenic mice that constitutively express either human STC1 or STC2 exhibit intra-uterine growth restriction and permanent post-natal growth retardation. STC1 is expressed in chondrocytic and osteoblastic cells during murine development and can enhance differentiation of calvarial cells in culture. Therefore, there is mounting evidence that stanniocalcins (STCs) modulate bone development in vivo. To further define the effects of stanniocalcins on skeletal development, we performed a series of measurements on components of the axial, appendicular, and cranial skeleton in transgenic and wildtype mice. We show that skeletal growth is retarded and that the intramembranous bones of the cranium exhibit a particularly severe delay in suture closure. The posterior frontal suture remains patent throughout the lifetime of human STC1 and STC2 transgenic mice. We did not observe significant effects on chondrogenesis: however, calvarial cells exhibited reduced viability, proliferation and delayed differentiation, indicating that developing osteoblasts are particularly sensitive to the levels of STCs. Given the evidence linking STC1 to cellular phosphate homeostasis, we assessed the expression of a variety of phosphate regulators in transgenic and wildtype calvarial cells and found significantly lower levels of Mepe, Dmp1, Sfrp4 in transgenic cells without a change in Pit1 or Pit2. Collectively these data support a direct regulatory role for STCs in osteoblasts and suggest that overexposure to these factors inhibits normal skeletal development without significant changes in patterning.

The Effects of TWEAK, Fn14, and TGF-beta1 on Degeneration of Human Intervertebral Disc

OBJECTIVE

The purpose of this study is to explain the effect and reciprocal action among tumor necrosis factor (TNF) like weak inducer of apoptosis (TWEAK), fibroblast growth factor-inducible 14 (Fn14), and transforming growth factor-beta1 (TGF-beta1) on degeneration of human intervertebral disc (IVD).

METHODS

Human intervertebral disc tissues and cells were cultured with Dulbecco's Modified Eagle's Medium/Nutrient F-12 Ham (DMEM/F-12) media in 37, 5% CO(2) incubator. When IVD tissues were cultured with TWEAK, Fn14 that is an antagonistic receptor for TWEAK and TGF-beta1, the level of sulfated glycosaminoglycan (sGAG) was estimated by dimethyl methyleneblue (DMMB) assay and sex determining region Y (SRY)-box 9 (Sox9) and versican messenger ribonucleic acid (mRNA) levels were estimated by reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

When human IVD tissue was cultured for nine days, the sGAG content was elevated in proportion to culture duration. The sGAG was decreased significantly by TWEAK 100 ng/mL, however, Fn14 500 ng/mL did not change the sGAG production of IVD tissue. The Fn14 increased versican and Sox9 mRNA levels decreased with TWEAK in IVD tissue TGF-beta1 20 ng/mL elevated the sGAG concentration 40% more than control. The sGAG amount decreased with TWEAK was increased with Fn14 or TGF-beta1 but the result was insignificant statistically. TGF-beta1 increased the Sox9 mRNA expression to 180% compared to control group in IVD tissue. Sox9 and versican mRNA levels decreased by TWEAK were increased with TGF-beta1 in primary cultured IVD cells, however, Fn14 did not show increasing effect on Sox9 and versican.

CONCLUSION

This study suggests that TWEAK would act a role in intervertebral disc degeneration through decreasing sGAG and the mRNA level of versican and Sox9.

Smad3 prevents beta-catenin degradation and facilitates beta-catenin nuclear translocation in chondrocytes

Our previous study demonstrated that transforming growth factor (TGF)-beta activates beta-catenin signaling through Smad3 interaction with beta-catenin in chondrocytes. In the present studies, we further investigated the detailed molecular mechanism of the cross-talk between TGF-beta/Smad3 and Wnt/beta-catenin signaling pathways. We found that C-terminal Smad3 interacted with both the N-terminal region and the middle region of beta-catenin protein in a TGF-beta-dependent manner. Both Smad3 and Smad4 were required for the interaction with beta-catenin and protected beta-catenin from an ubiquitin-proteasome-dependent degradation. In addition, the formation of the Smad3-Smad4-beta-catenin protein complex also mediated beta-catenin nuclear translocation. This Smad3-mediated regulatory mechanism of beta-catenin protein stability enhanced the activity of beta-catenin to activate downstream target genes during chondrogenesis. Our findings demonstrate a novel mechanism between TGF-beta and Wnt/beta-catenin signaling pathways during chondrocyte development.

Enhancement of chondrogenesis of human adipose derived stem cells in a hyaluronan-enriched microenvironment

Microenvironment plays a critical role in guiding stem cell differentiation. We investigated the enhancing effect of a hyaluronan (HA)-enriched microenvironment on human adipose derived stem cell (hADSC) chondrogenesis for articular cartilage tissue engineering. The hADSCs were obtained from patients undergoing hip replacement. HA-coated wells and HA-modified poly-(lactic-co-glycolic acid) (HA/PLGA) scaffolds were used as the HA-enriched microenvironment. The mRNA expressions of chondrogenic (SOX-9, aggrecan and collagen type II), fibrocartilage (collagen type I), and hypertrophic (collagen type X) marker genes were quantified by real-time polymerase chain reaction. Sulfated glycosaminoglycan (sGAG) deposition was detected by Alcian blue, safranin-O staining, and dimethylmethylene blue (DMMB) assays. Localized collagen type II was detected by immunohistochemistry. The hADSCs cultured in HA-coated wells (0.005-0.5 mg/cm(2)) showed enhanced aggregation and mRNA expressions (SOX-9, collagen type II, and aggrecan) after 24h, and sGAG content was also significantly increased after 9 days of culture. The HA-modified PLGA did not change the cell adherence and viability of hADSCs. The mRNA expressions of chondrogenic marker genes were significantly enhanced in hADSCs cultured in HA/PLGA rather than those cultured in the PLGA scaffold after 1, 3, and 5 days of culture. The hADSCs cultured in HA/PLGA produced higher levels of sGAG and collagen type II, compared to those in the PLGA scaffold after 4 weeks of cultures. Our results suggest that HA-enriched microenvironment induces chondrogenesis in hADSCs, which may be beneficial in articular cartilage tissue engineering.

Arginine methyltransferase CARM1/PRMT4 regulates endochondral ossification

Background

Chondrogenesis and subsequent endochondral ossification are processes tightly regulated by the transcription factor Sox9 (SRY-related high mobility group-Box gene 9), but molecular mechanisms underlying this activity remain unclear. Here we report that coactivator-associated arginine methyltransferase 1 (CARM1) regulates chondrocyte proliferation via arginine methylation of Sox9.

Results

CARM1-null mice display delayed endochondral ossification and decreased chondrocyte proliferation. Conversely, cartilage development of CARM1 transgenic mice was accelerated. CARM1 specifically methylates Sox9 at its HMG domain in vivo and in vitro. Arg-methylation of Sox9 by CARM1 disrupts interaction of Sox9 with beta-catenin, regulating Cyclin D1 expression and cell cycle progression of chondrocytes.

Conclusion

These results establish a role for CARM1 as an important regulator of chondrocyte proliferation during embryogenesis.

Sox9, more than a marker of the outer root sheath: spatiotemporal expression pattern during human cutaneous embryogenesis

BACKGROUND

The sex-determining gene Sox9 was recently unexpectedly found to have an essential role in outer root sheath differentiation. It was also characterized as a general marker of basal cell carcinoma. Herein, we describe its spatiotemporal expression pattern outside the hair follicle during human cutaneous embryogenesis.

METHODS

We examined immunohistochemically samples from embryonic and fetal human skin for the expression of SOX9 using standard techniques. For comparison reasons, we also included scalp skin from adults.

RESULTS

SOX9 is expressed in the developing nail organ, eccrine glands, blood vessels and melanocytes/melanoblasts. In the nail organ, the nail bed but not the nail matrix was immunoreactive for SOX9. In plantar skin, SOX9 specifically labels the evolving eccrine glands but not the interfollicular keratinocytes.

CONCLUSIONS

The distinctive expression pattern of SOX9 during human cutaneous embryogenesis indicates a key role in skin homeostasis that includes but goes beyond its role in outer root sheath differentiation. Studying immunohistochemical markers in developing human skin has the potential to further our understanding of adult skin physiology and to deepen our concepts especially of the histogenesis of adnexal tumors (including those of the nail unit) and the relationship of the various adnexal structures to each other.

Chondrogenic and osteogenic differentiations of human bone marrow-derived mesenchymal stem cells on a nanofibrous scaffold with designed pore network

The utilization of 3D scaffolds and stem cells is a promising approach to solve the problem of bone and cartilage tissue shortage and to construct osteochondral (cartilage/bone composite) tissues. In this study, 3D highly porous nanofibrous (NF) poly(L-lactic acid) (PLLA) scaffolds fabricated using a phase separation technique were seeded with multi-potent human bone marrow-derived mesenchymal stem cells (hMSCs) and the constructs were induced along osteogenic and chondrogenic development routes in vitro. Histological analysis and calcium content quantification showed that NF scaffolds supported in vitro bone differentiation. SEM observation showed an altered shape for cells cultured on an NF matrix compared with those on smooth films. Consistent with the morphological change, the gene expression of early chondrogenic commitment marker Sox-9 was enhanced on the NF matrix. NF scaffolds were then used to support long-term in vitro 3D cartilaginous development. It was found that in the presence of TGF-beta1, cartilage tissue developed on PLLA NF scaffolds, with the cartilage-specific gene expressed, glycosaminoglycan and type II collagen accumulated, and typical cartilage morphology formed. These findings suggest that NF scaffolds can support both bone and cartilage development and are excellent candidate scaffolds for osteochondral defect repair.

Morphogenetic and regulatory mechanisms during developmental chondrogenesis: new paradigms for cartilage tissue engineering

Cartilage is the first skeletal tissue to be formed during embryogenesis leading to the creation of all mature cartilages and bones, with the exception of the flat bones in the skull. Therefore, errors occurring during the process of chondrogenesis, the formation of cartilage, often lead to severe skeletal malformations such as dysplasias. There are hundreds of skeletal dysplasias, and the molecular genetic etiology of some remains more elusive than of others. Many efforts have aimed at understanding the morphogenetic event of chondrogenesis in normal individuals, of which the main morphogenetic and regulatory mechanisms will be reviewed here. For instance, many signaling molecules that guide chondrogenesis--for example, transforming growth factor-beta, bone morphogenetic proteins, fibroblast growth factors, and Wnts, as well as transcriptional regulators such as the Sox family--have already been identified. Moreover, extracellular matrix components also play an important role in this developmental event, as evidenced by the promotion of the chondrogenic potential of chondroprogenitor cells caused by collagen II and proteoglycans like versican. The growing evidence of the elements that control chondrogenesis and the increasing number of different sources of progenitor cells will, hopefully, help to create tissue engineering platforms that could overcome many developmental or degenerative diseases associated with cartilage defects.

Early tissue patterning recreated by mouse embryonic fibroblasts in a three-dimensional environment

Cellular self-organization studies have been mainly focused on models such as Volvox, the slime mold Dictyostelium discoideum, and animal (metazoan) embryos. Moreover, animal tissues undergoing regeneration also exhibit properties of embryonic systems such as the self-organization process that rebuilds tissue complexity and function. We speculated that the recreation in vitro of the biological, biophysical, and biomechanical conditions similar to those of a regenerative milieu could elicit the intrinsic capacity of differentiated cells to proceed to the development of a tissue-like structure. Here we show that, when primary mouse embryonic fibroblasts are cultured in a soft nanofiber scaffold, they establish a cellular network that causes an organized cell contraction,proliferation, and migration that ends in the formation of a symmetrically bilateral structure with a distinct central axis. A subset of mesodermal genes (brachyury, Sox9, Runx2) is upregulated during this morphogenetic process. The expression of brachyury was localized first at the central axis, extending then to both sides of the structure. The spontaneous formation of cartilage-like tissue mainly at the paraxial zone followed expression ofSox9 and Runx2. Because cellular self-organization is an intrinsic property of the tissues undergoing development,this model could lead to new ways to consider tissue engineering and regenerative medicine.

Suppression of chondrogenesis by Id helix-loop-helix proteins in murine embryonic orofacial tissue

Inhibitors of differentiation (Id) proteins are helix-loop-helix (HLH) transcription factors lacking a DNA-binding domain. Id proteins modulate cell proliferation, apoptosis and differentiation in embryonic/fetal tissue. Perturbation of any of these processes in cells of the developing orofacial region results in orofacial anomalies. Chondrogenesis, a process integral to normal orofacial ontogenesis, is known to be modulated, in part, by Id proteins. In the present study, the mRNA and protein expression patterns of Id1, Id2, Id3 and Id4 were examined in developing murine orofacial tissue in vivo, as well as in murine embryonic maxillary mesenchymal cells in vitro. The functional role of Ids during chondrogenesis was also explored in vitro. Results reveal that cells derived from developing murine orofacial tissue (1) express Id1, Id2, Id3 and Id4 mRNAs and proteins on each of gestational days 12-14, (2) express all four Id proteins in a developmentally regulated manner, (3) undergo chondrogenesis and express genes encoding various chondrogenic marker proteins (e.g. Runx2, Type X collagen, Sox9) when cultured under micromass conditions and (4) can have their chondrogenic potential regulated via alteration of Id protein function through overexpression of a basic HLH factor. In summary, results from the current report reveal for the first time the expression of all four Id proteins in cells derived from developing murine orofacial tissue, and demonstrate a functional role for the Ids in regulating the ability of these cells to undergo chondrogenesis.

MicroRNAs and micromanaging the skeleton in disease, development and evolution

MicroRNAs (miRNAs) are short, non-protein-encoding RNAs that effect post-transcriptional gene regulation by targeting messenger RNAs. miRNAs are associated with specific human diseases and help regulate development. Here we review recent advances in understanding the roles of miRNAs in skeletal malformations, including cleft palate, and in the evolution of skeletal morphologies. We propose the hypothesis that evolutionary variation in miRNA expression patterns or structural variation in miRNA binding sites in messenger RNAs can help explain the evolution of craniofacial variation among species, the development of human craniofacial disease and physiological changes leading to osteopenia that increases with ageing.

Differential gene expression associated with postnatal equine articular cartilage maturation

Background

Articular cartilage undergoes an important maturation process from neonate to adult that is reflected by alterations in matrix protein organization and increased heterogeneity of chondrocyte morphology. In the horse, these changes are influenced by exercise during the first five months of postnatal life. Transcriptional profiling was used to evaluate changes in articular chondrocyte gene expression during postnatal growth and development.

Methods

Total RNA was isolated from the articular cartilage of neonatal (0–10 days) and adult (4–5 years) horses, subjected to one round of linear RNA amplification, and then applied to a 9,367-element equine-specific cDNA microarray. Comparisons were made with a dye-swap experimental design. Microarray results for selected genes (COL2A1, COMP, P4HA1, TGFB1, TGFBR3, TNC) were validated by quantitative polymerase chain reaction (qPCR).

Results

Fifty-six probe sets, which represent 45 gene products, were up-regulated (p < 0.01) in chondrocytes of neonatal articular cartilage relative to chondrocytes of adult articular cartilage. Conversely, 586 probe sets, which represent 499 gene products, were up-regulated (p < 0.01) in chondrocytes of adult articular cartilage relative to chondrocytes of neonatal articular cartilage. Collagens, matrix-modifying enzymes, and provisional matrix non-collagenous proteins were expressed at higher levels in the articular cartilage of newborn foals. Those genes with increased mRNA abundance in adult chondrocytes included leucine-rich small proteoglycans, matrix assembly, and cartilage maintenance proteins.

Conclusion

Differential expression of genes encoding matrix proteins and matrix-modifying enzymes between neonates and adults reflect a cellular maturation process in articular chondrocytes. Up-regulated transcripts in neonatal cartilage are consistent with growth and expansion of the articular surface. Expression patterns in mature articular cartilage indicate a transition from growth to homeostasis, and tissue function related to withstanding shear and weight-bearing stresses.

Mechanical modulation of osteochondroprogenitor cell fate

Mesenchymal cells are natural tissue builders. They exhibit an extraordinary capacity to metamorphize into differentiated cells, using extrinsic spatial and temporal inputs and intrinsic algorithms, as well as to build and adapt their own habitat. In addition to providing a habitat for osteoprogenitor cells, tissues of the skeletal system provide mechanical support and protection for the multiple organs of vertebrate organisms. This review examines the role of mechanics on determination of cell fate during pre-, peri- and postnatal development of the skeleton as well as during tissue genesis and repair in postnatal life. The role of cell mechanics is examined and brought into context of intrinsic cues during mesenchymal condensation. Remarkable new insights regarding structure function relationships in mesenchymal stem cells, and their influence on determination of cell fate are integrated in the context of de novo tissue generation and postnatal repair. Key differences in the formation of osteogenic and chondrogenic condensations are discussed in relation to direct intramembranous and indirect endochondral ossification. New approaches are discussed to elucidate and exploit extrinsic cues to generate tissues in the laboratory and in the clinic.

The Relation Between Sox9, TGF-beta1, and Proteoglycan in Human Intervertebral Disc Cells

OBJECTIVE

The aim of this study is to elucidate the effects of transforming growth factor-beta (TGF-beta)1 and L-ascorbic acid on proteoglycan synthesis, and the relationship between Sox9, proteoglycan, and TGF-beta1 in intervertebral disc cells.

METHODS

Human intervertebral disc tissue was sequentially digested to 0.2% pronase and 0.025% collagenase in DMEM/F-12 media and extracted cells were cultured in 37, 5% CO(2) incubator. When intervertebral disc cells were cultured with TGF-beta1 or L-ascorbic acid, the production level of sulfated glycosaminoglycan (sGAG) was estimated by dimethyl methyleneblue (DMMB) assay. The changes of Sox9 mRNA and protein levels via TGF-beta1 were detected by RT-PCR and Western blot analysis in each.

RESULTS

The amount of sGAG was increased with the lapse of time during incubation, and sGAG content of pellet cultured cells was much larger than monolayer culture. When primary cultured intervertebral disc cells in monolayer and pellet cultures were treated by TGF-beta1 20 ng, sGAG content of experimental group was increased significantly compared to control group in both cultures. L-Ascorbic acid of serial concentrations (50-300 ug/ml) increased sGAG content of mono layer cultured intervertebral disc cells significantly in statistics. The co-treatment of TGF-beta1 and L-ascorbic acid increased more sGAG production than respective treatment. After treating with TGF-beta1, Sox9 mRNA and protein expression rates were significantly increased in disc cells compared with the control group.

CONCLUSION

This study suggests that TGF-beta1 would increase sulfated glycosaminoglycan (sGAG) and other proteoglycans such as versican by elevating Sox9 mRNA and protein expressions in order.

Sparc (Osteonectin) functions in morphogenesis of the pharyngeal skeleton and inner ear

Sparc (Osteonectin), a matricellular glycoprotein expressed by many differentiated cells, is a major non-collagenous constituent of vertebrate bones. Recent studies indicate that Sparc expression appears early in development, although its function and regulation during embryogenesis are largely unknown. We cloned zebrafish sparc and investigated its role during development, using a mo rpholino antisense oligonucleotide-based knockdown approach. Consistent with its strong expression in the otic vesicle and developing pharyngeal cartilages, knockdown of Sparc function resulted in specific inner ear and cartilage defects that are highlighted by changes in gene expression, morphology and behavior. We rescued the knockdown phenotypes by co-injecting sparc mRNA, providing evidence that the knockdown phenotype is due specifically to impairment of Sparc function. A comparison of the phenotypes of Sparc knockdown and known zebrafish mutants with similar defects places Sparc downstream of sox9 in the genetic network that regulates development of the pharyngeal skeleton and inner ear of vertebrates.

Ectopic SOX9 mediates extracellular matrix deposition characteristic of organ fibrosis

Appropriate temporospatial expression of the transcription factor SOX9 is important for normal development of a wide range of organs. Here, we show that when SOX9 is expressed ectopically, target genes become expressed that are associated with disease. Histone deacetylase inhibitors in clinical trials for cancer therapy induced SOX9 expression via enhanced recruitment of nuclear factor Y (NF-Y) to CCAAT elements in the SOX9 proximal promoter. The effect of histone deacetylase inhibitors could be elicited in cells that normally lack SOX9, such as hepatocytes. In human fetal hepatocytes, this aberrant induction of SOX9 protein caused ectopic expression of COL2A1 and COMP1 that encode extracellular matrix (ECM) components normally associated with chondrogenesis. Previously, ectopic expression of this "chondrogenic" profile has been implicated in vascular calcification. More broadly, inappropriate ECM deposition is a hallmark of fibrosis. We demonstrated that induction of SOX9 expression also occurred during activation of fibrogenic cells from the adult liver when the transcription factor was responsible for expression of the major component of fibrotic ECM, type 1 collagen. These combined data identify new aspects in the regulation of SOX9 expression. They support a role for SOX9 beyond normal development as a transcriptional regulator in the pathology of fibrosis.

Effects of hydrostatic pressure on cytoskeleton and BMP-2, TGF-beta, SOX-9 production in rat temporomandibular synovial fibroblasts

OBJECTIVE

Recent experimental evidence has suggested that pressure may play an important role in the pathogenesis of arthritic diseases such as temporomandibular disorders (TMDs), rheumatic diseases and osteoarthritis. This study examines the effects of hydrostatic pressure (HP) on cytoskeleton and protein production of bone morphogenetic protein-2 (BMP-2), transforming growth factor-beta (TGF-beta) and the SRY HMG box related gene 9 (SOX-9) in synovial fibroblasts (SFs) of rat temporomandibular joint (TMJ).

METHODS

SFs derived from rat TMJ were grown to confluence in Dulbecco's modified Eagle medium supplemented with 15% fetal calf serum. The monolayer of SFs was subjected to different HPs (0, 30, 60, and 90kPa) by an in-house designed pressure chamber for 12h. Changes of cell morphology were observed by fluorescent microscope. Production of TGF-beta, BMP-2 and SOX-9 was examined by immunocytochemical assay and western blot.

RESULTS

Compared with the untreated control, the cellular actin configuration of SFs became elongated and more intense F-actin stress fiber staining was observed after HP loading. Exposure of SFs to HP for 12h resulted in significant up-regulation of BMP-2 by 46, 54, and 66% at 30, 60, and 90kPa, respectively, whilst TGF-beta increased by 11, 19, and 28% at 30, 60, and 90kPa, respectively. HP also induced the increase of SOX-9 by 72% at 30kPa and 83% at 60kPa, but only 54% at 90kPa.

CONCLUSIONS

The obtained data suggest that HP induced the alteration of cytoskeleton and bone-morphogenetic-related proteins' production of SFs, which may influence the pathological condition of TMDs.