SOX11 contributes to the regulation of GDF5 in joint maintenance

Hox gene activity directs physical forces to differentially shape chick small and large intestinal epithelia

Hox transcription factors play crucial roles in organizing developmental patterning across metazoa, but how these factors trigger regional morphogenesis has largely remained a mystery. In the developing gut, Hox genes help demarcate identities of intestinal subregions early in embryogenesis, which ultimately leads to their specialization in both form and function. Although the midgut forms villi, the hindgut develops sulci that resolve into heterogeneous outgrowths. Combining mechanical measurements of the embryonic chick intestine and mathematical modeling, we demonstrate that the posterior Hox gene HOXD13 regulates biophysical phenomena that shape the hindgut lumen. We further show that HOXD13 acts through the transforming growth factor β (TGF-β) pathway to thicken, stiffen, and promote isotropic growth of the subepithelial mesenchyme-together, these features lead to hindgut-specific surface buckling. TGF-β, in turn, promotes collagen deposition to affect mesenchymal geometry and growth. We thus identify a cascade of events downstream of positional identity that direct posterior intestinal morphogenesis.

Synergistic effects of biological stimuli and flexion induce microcavities promote hypertrophy and inhibit chondrogenesis during in vitro culture of human mesenchymal stem cell aggregates

Interzone/cavitation are key steps in early stage joint formation that have not been successfully developed in vitro. Further, current models of endochondral ossification, an important step in early bone formation, lack key morphology morphological structures such as microcavities found during development in vivo. This is possibly due to the lack of appropriate strategies for incorporating chemical and mechanical stimuli that are thought to be involved in joint development. We designed a bioreactor system and investigated the synergic effect of chemical stimuli (chondrogenesis-inducing [CIM] and hypertrophy-inducing medium [HIM]) and mechanical stimuli (flexion) on the growth of human mesenchymal stem cells (hMSCs) based linear aggregates under different conditions over 4 weeks of perfusion culture. Computational studies were used to evaluate tissue stress qualitatively. After harvesting, both Safranin-O and hematoxylin & eosin (H&E) staining histology demonstrated microcavity structures and void structures in the region of higher stresses for tissue aggregates cultured only in HIM under flexion. In comparison to either HIM treatment or flexion only, increased glycosaminoglycan (GAG) content in the extracellular matrix (ECM) at this region indicates the morphological change resembles the early stage of joint cavitation; while decreased type II collagen (Col II), and increased type X collagen (Col X) and vascular endothelial growth factor (VEGF) with a clear boundary in the staining section indicates it resembles the early stage of ossification. Further, cell alignment analysis indicated that cells were mostly oriented toward the direction of flexion in high-stress region only in HIM under flexion, resembling cell morphology in both joint cavitation and hypertrophic cartilage in growth plate. Collectively, our results suggest that flexion and HIM inhibit chondrogenesis and promote hypertrophy and development of microcavities that resemble the early stage of joint cavitation and endochondral ossification. We believe the tissue model described in this work can be used to develop in vitro models of joint tissue for applications such as pathophysiology and drug discovery.

A Functional Single-Nucleotide Polymorphism Upstream of the Collagen Type III Gene Is Associated with Catastrophic Fracture Risk in Thoroughbred Horses

Fractures caused by bone overloading are a leading cause of euthanasia in Thoroughbred racehorses. The risk of fatal fracture has been shown to be influenced by both environmental and genetic factors but, to date, no specific genetic mechanisms underpinning fractures have been identified. In this study, we utilised a genome-wide polygenic risk score to establish an in vitro cell system to study bone gene regulation in horses at high and low genetic risk of fracture. Candidate gene expression analysis revealed differential expression of COL3A1 and STAT1 genes in osteoblasts derived from high- and low-risk horses. Whole-genome sequencing of two fracture cases and two control horses revealed a single-nucleotide polymorphism (SNP) upstream of COL3A1 that was confirmed in a larger cohort to be significantly associated with fractures. Bioinformatics tools predicted that this SNP may impact the binding of the transcription factor SOX11. Gene modulation demonstrated SOX11 is upstream of COL3A1, and the region binds to nuclear proteins. Furthermore, luciferase assays demonstrated that the region containing the SNP has promoter activity. However, the specific effect of the SNP depends on the broader genetic background of the cells and suggests other factors may also be involved in regulating COL3A1 expression. In conclusion, we have identified a novel SNP that is significantly associated with fracture risk and provide new insights into the regulation of the COL3A1 gene.

HOXA10 promotes Gdf5 expression in articular chondrocytes

Growth differentiation factor 5 (GDF5), a BMP family member, is highly expressed in the surface layer of articular cartilage. The GDF5 gene is a key risk locus for osteoarthritis and Gdf5-deficient mice show abnormal joint development, indicating that GDF5 is essential in joint development and homeostasis. In this study, we aimed to identify transcription factors involved in Gdf5 expression by performing two-step screening. We first performed microarray analyses to find transcription factors specifically and highly expressed in the superficial zone (SFZ) cells of articular cartilage, and isolated 11 transcription factors highly expressed in SFZ cells but not in costal chondrocytes. To further proceed with the identification, we generated Gdf5-HiBiT knock-in (Gdf5-HiBiT KI) mice, by which we can easily and reproducibly monitor Gdf5 expression, using CRISPR/Cas9 genome editing. Among the 11 transcription factors, Hoxa10 clearly upregulated HiBiT activity in the SFZ cells isolated from Gdf5-HiBiT KI mice. Hoxa10 overexpression increased Gdf5 expression while Hoxa10 knockdown decreased it in the SFZ cells. Moreover, ChIP and promoter assays proved the direct regulation of Gdf5 expression by HOXA10. Thus, our results indicate the important role played by HOXA10 in Gdf5 regulation and the usefulness of Gdf5-HiBiT KI mice for monitoring Gdf5 expression.

The association of growth differentiation factor 5 rs143383 gene polymorphism with osteoarthritis: a systematic review and meta-analysis

BACKGROUND

Osteoarthritis (OA) is caused by a complex set of pathophysiological factors. The genetic factors involved in the occurrence and progress of the disease have been widely discussed by scholars. It was found that growth differentiation factor 5 (GDF5) gene polymorphisms may be linked to OA susceptibility, which has been controversial and needs to be further confirmed by an updated meta-analysis.

OBJECTIVES

We examined the association between GDF5 rs143383 single nucleotide polymorphism (SNP) and OA susceptibility.

METHODS

All relevant articles that met the criteria are retrieved and included, and the search deadline is June 2022. The allele frequencies and different genotype frequencies of GDF5 rs143383 loci in each study were extracted and statistically analyzed by R4.1.3 software, and the different genetic models were analyzed based on their odds ratio (OR) and 95% confidence interval (CI).

RESULTS

The meta-analysis explained that GDF5 rs143383 SNP was crucial correlated with OA in all patients with OA of knee, hip and hand. The codominant gene model in the whole crowd (OR = 1.17, 95% CI 1.07-1.27, P < 0.01) enlightened that OA was vitally associated with GDF5 gene polymorphism. At the same time, we did a subgroup analysis based on ethnicity. The codominant gene model (OR = 1.31, 95% CI 1.12-1.53, P < 0.01) in Asian population, the codominant homozygote model (OR = 1.28, 95% CI 1.14-1.43), codominant heterozygote gene model (OR = 1.12, 95% CI 1.01-1.23, P = 0.02), and dominant gene model (OR = 1.19, 95% CI 1.09-1.31, P < 0.01) in Caucasian are analyzed by subgroup analysis. It means that there is a momentous relationship between the GDF5rs143383 gene polymorphism and OA, especially among Caucasians. In addition, we also discussed different types of OA separately and discover that the GDF5rs143383 gene polymorphism was relevant for knee osteoarthritis (KOA) and hand osteoarthritis, and it was more significant in the Caucasian population. But due to the high heterogeneity in hip osteoarthritis, it could not be accurately concluded. Furthermore, we also analyzed the osteoarthritis of different genders and found that the GDF5 rs143383 SNP was associated with both men and women and was still significant in the Caucasian population.

CONCLUSION

We found a close association between osteoarthritis and GDF5rs143383SNP in this study. From the analysis of each group, we got the same conclusion in KOA and hand OA, but which need further verification in hip OA. Considering gender, we found a close relationship between GDF5 rs143383 SNP and OA of the knee, hip and hand, both for men and women. This conclusion is more obvious in Caucasian people.

Sox, Fox, and Lmx1b binding sites differentially regulate a Gdf5-Associated regulatory region during elbow development

Introduction: The articulating ends of limb bones have precise morphology and asymmetry that ensures proper joint function. Growth differentiation factor 5 (Gdf5) is a secreted morphogen involved in cartilage and bone development that contributes to the architecture of developing joints. Dysregulation of Gdf5 results in joint dysmorphogenesis often leading to progressive joint degeneration or osteoarthritis (OA). The transcription factors and cis-regulatory modules (CRMs) that regulate Gdf5 expression are not well characterized. We previously identified a Gdf5-associated regulatory region (GARR) that contains predicted binding sites for Lmx1b, Osr2, Fox, and the Sox transcription factors. These transcription factors are recognized factors involved in joint morphogenesis and skeletal development. Methods: We used in situ hybridization to Gdf5, Col2A1, and the transcription factors of interest in developing chicken limbs to determine potential overlap in expression. We further analyzed scRNA-seq data derived from limbs and knees in published mouse and chicken datasets, identifying cells with coexpression of Gdf5 and the transcription factors of interest. We also performed site-directed mutatgenesis of the predicted transcription factor binding sites in a GARR-reporter construct and determined any change in activity using targeted regional electroporation (TREP) in micromass and embryonic chicken wing bioassays. Results: Gdf5 expression overlapped the expression of these transcription factors during joint development both by in situ hybridization (ISH) and scRNA-seq analyses. Within the GARR CRM, mutation of two binding sites common to Fox and Sox transcripstion factors reduced enhancer activity to background levels in micromass cultures and in ovo embryonic chicken wing bioassays, whereas mutation of two Sox-only binding sites caused a significant increase in activity. These results indicate that the Fox/Sox binding sites are required for activity, while the Sox-only sites are involved in repression of activity. Mutation of Lmx1b binding sites in GARR caused an overall reduction in enhancer activity in vitro and a dorsal reduction in ovo. Despite a recognized role for Osr2 in joint development, disruption of the predicted Osr2 site did not alter GARR activity. Conclusion: Taken together, our data indicates that GARR integrates positive, repressive, and asymmetrical inputs to fine-tune the expression of Gdf5 during elbow joint development.

Tanshinone I alleviates steroid-induced osteonecrosis of femoral heads and promotes angiogenesis: in vivo and in vitro studies

BACKGROUND

The impaired blood supply to the bones is an important pathological feature of steroid-induced osteonecrosis of the femoral head (SIONFH). Danshen is a Chinese herb that shows therapeutic effects on SIONFH, but the effects of one of its major bioactive constituents, Tanshinone I (TsI), on SIONFH remain unknown. Here, we evaluated the effects of TsI on SIONFH, particularly focusing on its effects on angiogenesis, in in vivo and in vitro research.

METHODS

SIONFH was induced in Sprague-Dawley rats by an intramuscular injection of methylprednisolone (40 mg/kg) in combination with an intraperitoneal injection of lipopolysaccharide (20 μg/kg). Morphological alterations of the femoral head were observed by dual-energy X-ray absorptiometry and HE staining. Western blot, qRT-PCR, and immunohistochemical/immunofluorescence staining were used to determine gene expression.

RESULTS

TsI (10 mg/kg) alleviated bone loss and rescued the expression of angiogenesis-related molecules (CD31, VWF, VEGF, and VEGFR2) in the femoral heads of SIONFH rats. Notably, TsI rescued the down-regulated expression of SRY-box transcription factor 11 (SOX11) in CD31⁺ endothelial cells in the femoral heads of SIONFH rats. In vitro studies showed that TsI preserved the dexamethasone-harmed angiogenic property (migration and tube formation) of human umbilical vein cells (EA.hy926), suppressed dexamethasone-induced cell apoptosis, reduced pro-apoptotic proteins (cytosolic cytochrome C, Bax, and caspase 3/9) and increased anti-apoptotic protein Bcl-2, whereas silencing of SOX11 reversed these beneficial effects.

CONCLUSIONS

This study demonstrates that TsI alleviates SIONFH and promotes angiogenesis by regulating SOX11 expression. Our work would provide new evidence for the application of TsI to treat SIONFH.

SOXC Transcription Factors as Diagnostic Biomarkers and Therapeutic Targets for Arthritis

Osteoarthritis (OA) and rheumatoid arthritis (RA) are two common disorders that disrupt the quality of life of millions of people. These two chronic diseases cause damage to the joint cartilage and surrounding tissues of more than 220 million people worldwide. Sex-determining region Y-related (SRY) high-mobility group (HMG) box C, SOXC, is a superfamily of transcription factors that have been recently shown to be involved in various physiological and pathological processes. These include embryonic development, cell differentiation, fate determination, and autoimmune diseases, as well as carcinogenesis and tumor progression. The SOXC superfamily includes SOX4, SOX11, and SOX12, all have a similar DNA-binding domain, i.e., HMG. Herein, we summarize the current knowledge about the role of SOXC transcription factors during arthritis progression and their potential utilization as diagnostic biomarkers and therapeutic targets. The involved mechanistic processes and signaling molecules are discussed. SOX12 appears to have no role in arthritis, however SOX11 is dysregulated and promotes arthritic progression according to some studies but supports joint maintenance and protects cartilage and bone cells according to others. On the other hand, SOX4 upregulation during OA and RA was documented in almost all studies including preclinical and clinical models. Molecular details have indicated that SOX4 can autoregulate its own expression besides regulating the expression of SOX11, a characteristic associated with the transcription factors that protects their abundance and activity. From analyzing the currently available data, SOX4 seems to be a potential diagnostic biomarker and therapeutic target of arthritis.

Growth differentiation factor 5 in cartilage and osteoarthritis: A possible therapeutic candidate

Growth differentiation factor 5 (GDF-5) is essential for cartilage development and homeostasis. The expression and function of GDF-5 are highly associated with the pathogenesis of osteoarthritis (OA). OA, characterized by progressive degeneration of joint, particularly in cartilage, causes severe social burden. However, there is no effective approach to reverse the progression of this disease. Over the past decades, extensive studies have demonstrated the protective effects of GDF-5 against cartilage degeneration and defects. Here, we summarize the current literature describing the role of GDF-5 in development of cartilage and joints, and the association between the GDF-5 gene polymorphisms and OA susceptibility. We also shed light on the protective effects of GDF-5 against OA in terms of direct GDF-5 supplementation and modulation of the GDF-5-related signalling. Finally, we discuss the current limitations in the application of GDF-5 for the clinical treatment of OA. This review provides a comprehensive insight into the role of GDF-5 in cartilage and emphasizes GDF-5 as a potential therapeutic candidate in OA.

Erythropoietin enhances meniscal regeneration and prevents osteoarthritis formation in mice

Osteoarthritis (OA) is a leading cause of pain and disability, and knee is the most commonly afflicted joint. Meniscal tear due to injury or degeneration is an established factor for OA pathogenesis. Previous studies have demonstrated that meniscectomy does not reduce the OA incidence. We hypothesized that enhancing meniscal regeneration may prevent OA formation and progression. We first investigated the developmental pattern of mouse meniscus. Knee joint samples were collected at embryonic stages as well as after birth for histological and immunohistochemical studies. The results showed that meniscal cells underwent active proliferation and apoptosis at embryonic day 19.5 and Day 1 after birth. Collagen I (Col-1) is a major type of matrix protein in matured meniscus. Meniscal cells isolated from 3-month-old mice were used to examine the effect of selected factors on the molecules related to cell proliferation, angiogenesis, inflammation, extracellular matrix proteins and matrix degradation enzymes. Overall assessment indicated that EPO had optimal effect on meniscal regeneration. An organ culture system of mouse meniscus was established to test the effect of EPO on in vitro cultured menisci. EPO upregulated the expression of Col-1, Col-2 and VEGF-A, and downregulated the expression of MMP-13. Finally, we established a mouse model of meniscus injury induced OA (MIO), and mice were subjected to PBS or EPO treatments. The results demonstrated that EPO enhanced meniscal repair and prevented OA formation. EPO may become an effective Disease Modifying Osteoarthritis Drug and may be used for early treatment for meniscal injury to prevent OA progression.

Genetic and Mechanical Regulation of Intestinal Smooth Muscle Development

The gastrointestinal tract is enveloped by concentric and orthogonally aligned layers of smooth muscle; however, an understanding of the mechanisms by which these muscles become patterned and aligned in the embryo has been lacking. We find that Hedgehog acts through Bmp to delineate the position of the circumferentially oriented inner muscle layer, whereas localized Bmp inhibition is critical for allowing formation of the later-forming, longitudinally oriented outer layer. Because the layers form at different developmental stages, the muscle cells are exposed to unique mechanical stimuli that direct their alignments. Differential growth within the early gut tube generates residual strains that orient the first layer circumferentially, and when formed, the spontaneous contractions of this layer align the second layer longitudinally. Our data link morphogen-based patterning to mechanically controlled smooth muscle cell alignment and provide a mechanistic context for potentially understanding smooth muscle organization in a wide variety of tubular organs.

Site-Dependent Lineage Preference of Adipose Stem Cells

Adult stem cells have unique properties in both proliferation and differentiation preference. In this study, we hypothesized that adipose stem cells have a depot-dependent lineage preference. Four rabbits were used to provide donor-matched adipose stem cells from either subcutaneous adipose tissue (ScAT) or infrapatellar fat pad (IPFP). Proliferation and multi-lineage differentiation were evaluated in adipose stem cells from donor-matched ScAT and IPFP. RNA sequencing (RNA-seq) and proteomics were conducted to uncover potential molecular discrepancy in adipose stem cells and their corresponding matrix microenvironments. We found that stem cells from ScAT exhibited significantly higher proliferation and adipogenic capacity compared to those from donor-matched IPFP while stem cells from IPFP displayed significantly higher chondrogenic potential compared to those from donor-matched ScAT. Our findings are strongly endorsed by supportive data from transcriptome and proteomics analyses, indicating a site-dependent lineage preference of adipose stem cells.

Role of Signal Transduction Pathways and Transcription Factors in Cartilage and Joint Diseases

Osteoarthritis and rheumatoid arthritis are common cartilage and joint diseases that globally affect more than 200 million and 20 million people, respectively. Several transcription factors have been implicated in the onset and progression of osteoarthritis, including Runx2, C/EBPβ, HIF2α, Sox4, and Sox11. Interleukin-1 β (IL-1β) leads to osteoarthritis through NF-ĸB, IκBζ, and the Zn²⁺-ZIP8-MTF1 axis. IL-1, IL-6, and tumor necrosis factor α (TNFα) play a major pathological role in rheumatoid arthritis through NF-ĸB and JAK/STAT pathways. Indeed, inhibitory reagents for IL-1, IL-6, and TNFα provide clinical benefits for rheumatoid arthritis patients. Several growth factors, such as bone morphogenetic protein (BMP), fibroblast growth factor (FGF), parathyroid hormone-related protein (PTHrP), and Indian hedgehog, play roles in regulating chondrocyte proliferation and differentiation. Disruption and excess of these signaling pathways cause genetic disorders in cartilage and skeletal tissues. Fibrodysplasia ossificans progressive, an autosomal genetic disorder characterized by ectopic ossification, is induced by mutant ACVR1. Mechanistic target of rapamycin kinase (mTOR) inhibitors can prevent ectopic ossification induced by ACVR1 mutations. C-type natriuretic peptide is currently the most promising therapy for achondroplasia and related autosomal genetic diseases that manifest severe dwarfism. In these ways, investigation of cartilage and chondrocyte diseases at molecular and cellular levels has enlightened the development of effective therapies. Thus, identification of signaling pathways and transcription factors implicated in these diseases is important.

Regulation of Gdf5 expression in joint remodelling, repair and osteoarthritis

Growth and Differentiation Factor 5 (GDF5) is a key risk locus for osteoarthritis (OA). However, little is known regarding regulation of Gdf5 expression following joint tissue damage. Here, we employed Gdf5-LacZ reporter mouse lines to assess the spatiotemporal activity of Gdf5 regulatory sequences in experimental OA following destabilisation of the medial meniscus (DMM) and after acute cartilage injury and repair. Gdf5 expression was upregulated in articular cartilage post-DMM, and was increased in human OA cartilage as determined by immunohistochemistry and microarray analysis. Gdf5 expression was also upregulated during cartilage repair in mice and was switched on in injured synovium in prospective areas of cartilage formation, where it inversely correlated with expression of the transcriptional co-factor Yes-associated protein (Yap). Indeed, overexpression of Yap suppressed Gdf5 expression in chondroprogenitors in vitro. Gdf5 expression in both mouse injury models required regulatory sequence downstream of Gdf5 coding exons. Our findings suggest that Gdf5 upregulation in articular cartilage and synovium is a generic response to knee injury that is dependent on downstream regulatory sequence and in progenitors is associated with chondrogenic specification. We propose a role for Gdf5 in tissue remodelling and repair after injury, which may partly underpin its association with OA risk.

Tanshinone I Inhibits IL-1β-Induced Apoptosis, Inflammation And Extracellular Matrix Degradation In Chondrocytes CHON-001 Cells And Attenuates Murine Osteoarthritis

Background

Osteoarthritis (OA) is a prevalent degenerative joint disease, which was characterized by inflammation and cartilage degradation. Accumulating evidence has demonstrated that Tanshinone I has an anti-inflammatory effect in various diseases. However, the efficacy of Tanshinone I as an anti-inflammatory agent in OA remains unclear. This study aimed to explore the role of Tanshinone I on OA both in vitro and in vivo.

Methods

CHON-001 cells were treated with IL-1β (10 ng/mL) for 72 hrs to induce OA model in vitro. Meanwhile, CHON-001 cells were pre-treated with 20 μM Tanshinone I for 24 hrs and then stimulated with IL-1β (10 ng/mL) for 72 hrs. CCK-8, immunofluorescence and flow cytometry assays were used to detect the viability, proliferation and apoptosis in CHON-001 cells, respectively. Western blotting assay was used to detect the levels of collagen II, aggrecan, MMP-13, cleaved caspase 1, Gasdermin D, SOX11 and p-NF-κB in CHON-001 cells. In addition, the mouse model of OA was built by anterior cruciate ligament transection (ACLT) in the right knee. Meanwhile, the mice were administrated with 10 or 30 mg/kg Tanshinone I for 8 weeks. Safranin-O/Fast Green staining was used to assess cartilage destruction in a mouse model of OA.

Results

In this study, IL-1β significantly induced apoptosis, extracellular matrix degradation and inflammatory response in CHON-001 cells. Tanshinone I significantly inhibited IL-1β-induced apoptosis in CHON-001 cells. In addition, the IL-1β-induced collagen II, aggrecan degradation, SOX11 downregulation, and MMP-13 and p-NF-κB upregulation in CHON-001 cells were notably reversed by Tanshinone I treatment. Moreover, Tanshinone I alleviated cartilage destruction and synovitis and reduced OARSI scores and subchondral bone thickness in a mouse model of OA.

Conclusion

Our findings showed that Tanshinone I could alleviate the progression of OA in vitro and in vivo. These results demonstrated that Tanshinone I might be regarded as a promising therapeutic agent for the treatment of OA.

Roles and regulation of SOX transcription factors in skeletogenesis

SOX transcription factors participate in the specification, differentiation and activities of many cell types in development and beyond. The 20 mammalian family members are distributed into eight groups based on sequence identity, and while co-expressed same-group proteins often have redundant functions, different-group proteins typically have distinct functions. More than a handful of SOX proteins have pivotal roles in skeletogenesis. Heterozygous mutations in their genes cause human diseases, in which skeletal dysmorphism is a major feature, such as campomelic dysplasia (SOX9), or a minor feature, such as LAMSHF syndrome (SOX5) and Coffin-Siris-like syndromes (SOX4 and SOX11). Loss- and gain-of-function experiments in animal models have revealed that SOX4 and SOX11 (SOXC group) promote skeletal progenitor survival and control skeleton patterning and growth; SOX8 (SOXE group) delays the differentiation of osteoblast progenitors; SOX9 (SOXE group) is essential for chondrocyte fate maintenance and differentiation, and works in cooperation with SOX5 and SOX6 (SOXD group) and other types of transcription factors. These and other SOX proteins have also been proposed, mainly through in vitro experiments, to have key roles in other aspects of skeletogenesis, such as SOX2 in osteoblast stem cell self-renewal. We here review current knowledge of well-established and proposed skeletogenic roles of SOX proteins, their transcriptional and non-transcriptional actions, and their modes of regulation at the gene, RNA and protein levels. We also discuss gaps in knowledge and directions for future research to further decipher mechanisms underlying skeletogenesis in health and diseases and identify treatment options for skeletal malformation and degeneration diseases.

Sox4 is involved in osteoarthritic cartilage deterioration through induction of ADAMTS4 and ADAMTS5

Osteoarthritis is a common disease in joint cartilages. Because the molecular pathogenesis of osteoarthritis remains elusive, early diagnostic markers and effective therapeutic agents have not been developed. To understand the molecular mechanisms, we attempted to identify transcription factors involved in the onset of osteoarthritis. Microarray analysis of mouse articular cartilage cells indicated that retinoic acid, a destructive stimulus in articular cartilage, up-regulated expression of sex-determining region Y-box (Sox)4, a SoxC family transcription factor, together with increases in Adamts4 and Adamts5, both of which are aggrecanases of articular cartilages. Overexpression of Sox4 induced a disintegrin-like and metallopeptidase with thrombospondin type 4 and 5 motif (ADAMTS4 and ADAMTS5, respectively) expression in chondrogenic cell lines C3H10T1/2 and SW1353. In addition, luciferase reporter and chromatin immunoprecipitation assays showed that Sox4 up-regulated ADAMTS4 and Adamts5 gene promoter activities by binding to their gene promoters. Another SoxC family member, Sox11, evoked similar effects. To evaluate the roles of Sox4 and Sox11 in articular cartilage destruction, we performed organ culture experiments using mouse femoral head cartilages. Sox4 and Sox11 adenovirus infections caused destruction of articular cartilage associated with increased Adamts5 expression. Finally, SOX4 and SOX11 mRNA expression was increased in cartilage of patients with osteoarthritis compared with nonosteoarthritic subjects. Thus, Sox4, and presumably Sox11, are involved in osteoarthritis onset by up-regulating ADAMTS4 and ADAMTS5.-Takahata, Y., Nakamura, E., Hata, K., Wakabayashi, M., Murakami, T., Wakamori, K., Yoshikawa, H., Matsuda, A., Fukui, N., Nishimura, R. Sox4 is involved in osteoarthritic cartilage deterioration through induction of ADAMTS4 and ADAMTS5.

BMP14 induces tenogenic differentiation of bone marrow mesenchymal stem cells in vitro

Bone marrow mesenchymal stem cells (BMSCs) are pluripotent cells, which have the capacity to differentiate into various types of mesenchymal cell phenotypes, including osteoblasts, chondroblasts, myoblasts and tendon fibroblasts (TFs). The molecular mechanism for tenogenic differentiation of BMSCs is still unknown. The present study investigated the effects of bone morphogenetic protein (BMP) 14 on BMSC differentiation in vitro. It was revealed that BMP14 significantly increased the expression of tendon markers (scleraxis and tenomodulin) at the mRNA and protein level, which led to the upregulation of sirtuin 1 (Sirt1) expression. The gain or loss of Sirt1 function may promote or inhibit tenogenic differentiation by deacetylating the peroxisome proliferator-activated receptor (PPAR)-γ. BMP14 also triggered the phosphorylation of c-Jun N-terminal kinase (JNK) and Smad1; overexpression of Sirt1 significantly increased the phosphorylation and knockdown of Sirt1 significantly decreased the phosphorylation. The inhibition of JNK and Smad significantly increased the acetylation of PPARγ and inhibited the expression of tenogenic differentiation markers. These results suggest that BMP14 may induce the tenogenic differentiation of BMSCs via the Sirt1-JNK/Smad1-PPARγ signaling pathway. The present study provided a cellular and molecular basis for the development of novel therapeutic strategies for tendon healing.

Sox11 gene disruption causes congenital anomalies of the kidney and urinary tract (CAKUT)

Congenital abnormalities of the kidney and the urinary tract (CAKUT) belong to the most common birth defects in human, but the molecular basis for the majority of CAKUT patients remains unknown. Here we show that the transcription factor SOX11 is a crucial regulator of kidney development. SOX11 is expressed in both mesenchymal and epithelial components of the early kidney anlagen. Deletion of Sox11 in mice causes an extension of the domain expressing Gdnf within rostral regions of the nephrogenic cord and results in duplex kidney formation. On the molecular level SOX11 directly binds and regulates a locus control region of the protocadherin B cluster. At later stages of kidney development, SOX11 becomes restricted to the intermediate segment of the developing nephron where it is required for the elongation of Henle's loop. Finally, mutation analysis in a cohort of patients suffering from CAKUT identified a series of rare SOX11 variants, one of which interferes with the transactivation capacity of the SOX11 protein. Taken together these data demonstrate a key role for SOX11 in normal kidney development and may suggest that variants in this gene predispose to CAKUT in humans.

Genetics of patella hypoplasia/agenesis

The patella is a sesamoid bone, crucial for knee stability. When absent or hypoplastic, recurrent knee subluxations, patellofemoral dysfunction and early gonarthrosis may occur. Patella hypoplasia/agenesis may be isolated or observed in syndromic conditions, either as the main clinical feature (Nail-patella syndrome, small patella syndrome), as a clue feature which can help diagnosis assessment, or as a background feature that may be disregarded. Even in the latter, the identification of patella anomalies is important for an appropriate patient management. We review the clinical characteristics of these rare diseases, provide guidance to facilitate the diagnosis and discuss how the genes involved could affect patella development.

Transcriptome comparison of meniscus from patients with and without osteoarthritis

OBJECTIVE

To assess the impact of osteoarthritis (OA) on the meniscus by comparing transcripts and biological processes in the meniscus between patients with and without OA.

DESIGN

RNA microarrays were used to identify transcripts differentially expressed (DE) in meniscus obtained from 12 OA and 12 non-OA patients. The non-OA specimens were obtained at the time of arthroscopic partial meniscectomy. Real-time PCR was performed on selected transcripts. Biological processes and gene-networking was examined computationally. Transcriptome signatures were mapped with 37 OA-related transcripts to evaluate how meniscus gene expression relates to that of OA cartilage.

RESULTS

We identified 168 transcripts significantly DE between OA (75 elevated, 93 repressed) and non-OA samples (≥1.5-fold). Among these, CSN1S1, COL10A1, WIF1, and SPARCL1 were the most prominent transcripts elevated in OA meniscus, POSTN and VEGFA were most highly repressed in OA meniscus. Transcripts elevated in OA meniscus represented response to external stimuli, cell migration and cell localization while those repressed in OA meniscus represented histone deacetylase activity (related to epigenetics) and skeletal development. Numerous long non-coding RNAs (lncRNAs) were DE between the two groups. When segregated by OA-related transcripts, two distinct clustering patterns appeared: OA meniscus appeared to be more inflammatory while non-OA meniscus exhibited a "repair" phenotype.

CONCLUSIONS

Numerous transcripts with potential relevance to the pathogenesis of OA are DE in OA and non-OA meniscus. These data suggest an involvement of epigenetically regulated histone deacetylation in meniscus tears as well as expression of lncRNAs. Patient clustering based on transcripts related to OA in articular cartilage confirmed distinct phenotypes between injured (non-OA) and OA meniscus.

Identification of novel genes in aging osteoblasts using next-generation sequencing and bioinformatics

During the aging process, impaired osteoblastic function is one key factor of imbalanced bone formation and age-related bone loss. The aim of this study is to explore the differentially expressed genes in normal and aged osteoblasts and to identify genes potentially involved in age-related alteration in bone physiology. Based on next generation sequencing and bioinformatics analysis, 12 differentially expressed microRNAs and 22 differentially expressed genes were identified. Up-regulation of miR-204-5p was validated in an array of osteoporotic hip fracture in the Gene Expression Omnibus database (GSE74209). The putative targets for miR-204-5p were Kruppel-like factor 7 (KLF7) and SRY-box 11 (SOX11). Ingenuity Pathway Analysis identified SOX11, involved in osteoarthritis pathway and differentiation of osteoblasts, together with miR-204-5p, a potential upstream regulator, suggesting the critical role of miR-204-5p-SOX11 regulation in the aging process of human bones. In addition, as semaphorin 3A (SEMA3A) and ephrin type-A receptor 5 (EPHA5) were involved in nervous system related biological functions, we postulated a potential linkage between SEMA3A, EPHA5 and development of neurogenic heterotopic ossification. Our findings implicate new candidate genes in the diagnosis of geriatric musculoskeletal disorders, and provide novel insights that may contribute to the elaboration of new biomarkers for neurogenic heterotopic ossification.

The Good the Bad and the Ugly of Glycosaminoglycans in Tissue Engineering Applications

High sulfation, low cost, and the status of heparin as an already FDA- and EMA- approved product, mean that its inclusion in tissue engineering (TE) strategies is becoming increasingly popular. However, the use of heparin may represent a naïve approach. This is because tissue formation is a highly orchestrated process, involving the temporal expression of numerous growth factors and complex signaling networks. While heparin may enhance the retention and activity of certain growth factors under particular conditions, its binding 'promiscuity' means that it may also inhibit other factors that, for example, play an important role in tissue maintenance and repair. Within this review we focus on articular cartilage, highlighting the complexities and highly regulated processes that are involved in its formation, and the challenges that exist in trying to effectively engineer this tissue. Here we discuss the opportunities that glycosaminoglycans (GAGs) may provide in advancing this important area of regenerative medicine, placing emphasis on the need to move away from the common use of heparin, and instead focus research towards the utility of specific GAG preparations that are able to modulate the activity of growth factors in a more controlled and defined manner, with less off-target effects.

BMP signaling controls buckling forces to modulate looping morphogenesis of the gut

Looping of the initially straight embryonic gut tube is an essential aspect of intestinal morphogenesis, permitting proper placement of the lengthy small intestine within the confines of the body cavity. The formation of intestinal loops is highly stereotyped within a given species and results from differential-growth-driven mechanical buckling of the gut tube as it elongates against the constraint of a thin, elastic membranous tissue, the dorsal mesentery. Although the physics of this process has been studied, the underlying biology has not. Here, we show that BMP signaling plays a critical role in looping morphogenesis of the avian small intestine. We first exploited differences between chicken and zebra finch gut morphology to identify the BMP pathway as a promising candidate to regulate differential growth in the gut. Next, focusing on the developing chick small intestine, we determined that Bmp2 expressed in the dorsal mesentery establishes differential elongation rates between the gut tube and mesentery, thereby regulating the compressive forces that buckle the gut tube into loops. Consequently, the number and tightness of loops in the chick small intestine can be increased or decreased directly by modulation of BMP activity in the small intestine. In addition to providing insight into the molecular mechanisms underlying intestinal development, our findings provide an example of how biochemical signals act on tissue-level mechanics to drive organogenesis, and suggest a possible mechanism by which they can be modulated to achieve distinct morphologies through evolution.

Lmx1b-targeted cis-regulatory modules involved in limb dorsalization

Lmx1b is a homeodomain transcription factor responsible for limb dorsalization. Despite striking double-ventral (loss-of-function) and double-dorsal (gain-of-function) limb phenotypes, no direct gene targets in the limb have been confirmed. To determine direct targets, we performed a chromatin immunoprecipitation against Lmx1b at E12.5 followed by next generation sequencing (ChIP-seq). Nearly 84% (n=617) of the Lmx1b-bound genomic intervals (LBIs) identified overlap with chromatin regulatory marks indicative of potential cis-regulatory modules (PCRMs). In addition, 73 LBIs mapped to known CRMs active during limb development. We compared Lmx1b-bound PCRMs to genes differentially expressed by Lmx1b and found 292 PCRMs within 1 Mb of 254 Lmx1b-regulated genes. Gene ontologic analysis suggests that Lmx1b targets extracellular matrix production, bone/joint formation, axonal guidance, vascular development, cell proliferation and cell movement. We validated the functional activity of a PCRM associated with joint-related Gdf5 that provides a mechanism for Lmx1b-mediated joint modification and a PCRM associated with Lmx1b that suggests a role in autoregulation. This is the first report to describe genome-wide Lmx1b binding during limb development, directly linking Lmx1b to targets that accomplish limb dorsalization.

Heads, Shoulders, Elbows, Knees, and Toes: Modular Gdf5 Enhancers Control Different Joints in the Vertebrate Skeleton

Synovial joints are crucial for support and locomotion in vertebrates, and are the frequent site of serious skeletal defects and degenerative diseases in humans. Growth and differentiation factor 5 (Gdf5) is one of the earliest markers of joint formation, is required for normal joint development in both mice and humans, and has been genetically linked to risk of common osteoarthritis in Eurasian populations. Here, we systematically survey the mouse Gdf5 gene for regulatory elements controlling expression in synovial joints. We identify separate regions of the locus that control expression in axial tissues, in proximal versus distal joints in the limbs, and in remarkably specific sub-sets of composite joints like the elbow. Predicted transcription factor binding sites within Gdf5 regulatory enhancers are required for expression in particular joints. The multiple enhancers that control Gdf5 expression in different joints are distributed over a hundred kilobases of DNA, including regions both upstream and downstream of Gdf5 coding exons. Functional rescue tests in mice confirm that the large flanking regions are required to restore normal joint formation and patterning. Orthologs of these enhancers are located throughout the large genomic region previously associated with common osteoarthritis risk in humans. The large array of modular enhancers for Gdf5 provide a new foundation for studying the spatial specificity of joint patterning in vertebrates, as well as new candidates for regulatory regions that may also influence osteoarthritis risk in human populations.

Joints, such as the hip and knee, are crucial for support and locomotion in animals, and are the frequent sites of serious human diseases such as arthritis. The Growth and differentiation factor 5 (Gdf5) gene is required for normal joint formation, and has been linked to risk of common arthritis in Eurasians. Here, we surveyed the mouse gene for the regulatory information that controls Gdf5's expression pattern in stripes at sites of joint formation. The gene does not have a single regulatory sequence that drives expression in all joints. Instead, Gdf5 has multiple different control sequences that show striking specificity for joints in the head, vertebral column, shoulder, elbow, wrist, hip, knee, and digits. Rescue experiments show that multiple control sequences are required to restore normal joint formation in Gdf5 mutants. The joint control sequences originally found in mice are also present in humans, where they are marked as active regions during fetal development and post-natal life, and map to a large region associated with arthritis risk in human populations. Regulatory variants in the human GDF5 control sequences can now be studied for their potential role in altering joint development or disease risk at particular locations in the skeleton.

Articular cartilage and joint development from embryogenesis to adulthood

Within each synovial joint, the articular cartilage is uniquely adapted to bear dynamic compressive loads and shear forces throughout the joint's range of motion. Injury and age-related degeneration of the articular cartilage often lead to significant pain and disability, as the intrinsic repair capability of the tissue is extremely limited. Current surgical and biological treatment options have been unable to restore cartilage de novo. Before successful clinical cartilage restoration strategies can be developed, a better understanding of how the cartilage forms during normal development is essential. This review focuses on recent progress made towards addressing key questions about articular cartilage morphogenesis, including the origin of synovial joint progenitor cells, postnatal development and growth of the tissue. These advances have provided novel insight into fundamental questions about the developmental biology of articular cartilage, as well as potential cell sources that may participate in joint response to injury.

SOXC Genes and the Control of Skeletogenesis

The SOXC group of transcription factors, composed of SOX4, SOX11, and SOX12, has evolved to fulfill key functions in cell fate determination. Expressed in many types of progenitor/stem cells, including skeletal progenitors, SOXC proteins potentiate pathways critical for cell survival and differentiation. As skeletogenesis unfolds, SOXC proteins ensure cartilage primordia delineation by amplifying canonical WNT signaling and antagonizing the chondrogenic action of SOX9 in perichondrium and presumptive articular joint cells. They then ensure skeletal elongation by inducing growth plate formation via enabling non-canonical WNT signaling. Human studies have associated SOX4 with bone mineral density and fracture risk in osteoporotic patients, and SOX11 with Coffin-Siris, a syndrome that includes skeletal dysmorphism. Meanwhile, in vitro and mouse studies have suggested important cell-autonomous roles for SOXC proteins in osteoblastogenesis. We here review current knowledge and gaps in understanding of SOXC protein functions, with an emphasis on the skeleton and possible links to osteoporosis.

Regulation of mouse chondrocyte differentiation by CCAAT/enhancer-binding proteins

CCAAT/enhancer-binding protein (C/EBP) β regulates chondrocyte differentiaion and proliferation during endochondral ossification. However, expression and function of other C/EBP family members in chondrocytes have not been fully understood. To understand the comprehensive regulation of chondrocyte differentiation by C/EBPs, we initially examined their expression levels. Among four members (C/EBPα, C/EBPβ, C/EBPδ and C/EBPε) with transactivation domain, expression of Cebpb and Cebpd was abundant compared to Cebpa, while Cebpe was hardly expressed in mouse isolated chondrocytes. Doxycycline (DOX)-inducible overexpression of each of the three C/EBPs (C/EBPα, C/EBPβ and C/EBPδ) in ATDC5 cells suppressed expressions of early differentiation markers including Col2a1, aggrecan and Sox9, enhanced those of late differentiation markers including Mmp13, Vegfa and Col10a1, and decelerated cell proliferation, indicating their overlapped functions in chondrocytes. In contrast, DOX-inducible overexpression of A-CEBP, which exerts a dominant-negative effect against all C/EBPs, increased expressions of early differentiation markers and decreased those of late differentiation markers. Finally, microarray and gene ontology analyses showed that A-CEBP altered many genes related with various events or tissues such as skeletal development, cartilage, cell cycle, inflammation and apoptosis. In conclusion, C/EBPα, C/EBPβ and C/EBPδ regulate proliferation and differentiation of chondrocytes and possibly is involved with apoptosis and inflammation. C/EBPs may play a variety of roles in the homeostasis of joint cartilage under physiological and pathological conditions.

SOXC proteins amplify canonical WNT signaling to secure nonchondrocytic fates in skeletogenesis

In skeletogenic mesenchyme, SOXC proteins enter the APC–Axin destruction complex to inhibit β-catenin phosphorylation by GSK3 and thereby synergize with canonical WNT signaling to inhibit chondrogenesis.

Canonical WNT signaling stabilizes β-catenin to determine cell fate in many processes from development onwards. One of its main roles in skeletogenesis is to antagonize the chondrogenic transcription factor SOX9. We here identify the SOXC proteins as potent amplifiers of this pathway. The SOXC genes, i.e., Sox4, Sox11, and Sox12, are coexpressed in skeletogenic mesenchyme, including presumptive joints and perichondrium, but not in cartilage. Their inactivation in mouse embryo limb bud caused massive cartilage fusions, as joint and perichondrium cells underwent chondrogenesis. SOXC proteins govern these cells cell autonomously. They replace SOX9 in the adenomatous polyposis coli–Axin destruction complex and therein inhibit phosphorylation of β-catenin by GSK3. This inhibition, a crucial, limiting step in canonical WNT signaling, thus becomes a constitutive event. The resulting SOXC/canonical WNT-mediated synergistic stabilization of β-catenin contributes to efficient repression of Sox9 in presumptive joint and perichondrium cells and thereby ensures proper delineation and articulation of skeletal primordia. This synergy may determine cell fate in many processes besides skeletogenesis.

Genesis and morphogenesis of limb synovial joints and articular cartilage

Limb synovial joints are intricate structures composed of articular cartilage, synovial membranes, ligaments and an articular capsule. Together, these tissues give each joint its unique shape, organization and biomechanical function. Articular cartilage itself is rather complex and organized in distinct zones, including the superficial zone that produces lubricants and contains stem/progenitor cells. For many years there has been great interest in deciphering the mechanisms by which the joints form and come to acquire such unique structural features and diversity. Decades ago, classic embryologists discovered that the first overt sign of joint formation at each prescribed limb site was the appearance of a dense and compact population of mesenchymal cells collectively called the interzone. Work carried out since then by several groups has provided evidence that the interzone cells actively participate in joint tissue formation over developmental time. This minireview provides a succinct but comprehensive description of the many important recent advances in this field of research. These include studies using various conditional reporter mice to genetically trace and track the origin, fate and possible function of joint progenitor cells; studies on the involvement and roles in signaling pathways and transcription factors in joint cell determination and functioning; and studies using advanced methods of gene expression analyses to uncover novel genetic determinants of joint formation and diversity. The overall advances are impressive, and the findings are not only of obvious interest and importance but also have major implications in the conception of future translational medicine tools to repair and regenerate defective, overused or aging joints.

Sox11 is required to maintain proper levels of Hedgehog signaling during vertebrate ocular morphogenesis

Ocular coloboma is a sight-threatening malformation caused by failure of the choroid fissure to close during morphogenesis of the eye, and is frequently associated with additional anomalies, including microphthalmia and cataracts. Although Hedgehog signaling is known to play a critical role in choroid fissure closure, genetic regulation of this pathway remains poorly understood. Here, we show that the transcription factor Sox11 is required to maintain specific levels of Hedgehog signaling during ocular development. Sox11-deficient zebrafish embryos displayed delayed and abnormal lens formation, coloboma, and a specific reduction in rod photoreceptors, all of which could be rescued by treatment with the Hedgehog pathway inhibitor cyclopamine. We further demonstrate that the elevated Hedgehog signaling in Sox11-deficient zebrafish was caused by a large increase in shha transcription; indeed, suppressing Shha expression rescued the ocular phenotypes of sox11 morphants. Conversely, over-expression of sox11 induced cyclopia, a phenotype consistent with reduced levels of Sonic hedgehog. We screened DNA samples from 79 patients with microphthalmia, anophthalmia, or coloboma (MAC) and identified two novel heterozygous SOX11 variants in individuals with coloboma. In contrast to wild type human SOX11 mRNA, mRNA containing either variant failed to rescue the lens and coloboma phenotypes of Sox11-deficient zebrafish, and both exhibited significantly reduced transactivation ability in a luciferase reporter assay. Moreover, decreased gene dosage from a segmental deletion encompassing the SOX11 locus resulted in microphthalmia and related ocular phenotypes. Therefore, our study reveals a novel role for Sox11 in controlling Hedgehog signaling, and suggests that SOX11 variants contribute to pediatric eye disorders.

De novo SOX11 mutations cause Coffin-Siris syndrome

Coffin-Siris syndrome (CSS) is a congenital disorder characterized by growth deficiency, intellectual disability, microcephaly, characteristic facial features and hypoplastic nails of the fifth fingers and/or toes. We previously identified mutations in five genes encoding subunits of the BAF complex, in 55% of CSS patients. Here we perform whole-exome sequencing in additional CSS patients, identifying de novo SOX11 mutations in two patients with a mild CSS phenotype. sox11a/b knockdown in zebrafish causes brain abnormalities, potentially explaining the brain phenotype of CSS. SOX11 is the downstream transcriptional factor of the PAX6-BAF complex, highlighting the importance of the BAF complex and SOX11 transcriptional network in brain development.