Ski inhibits TGF-β/phospho-Smad3 signaling and accelerates hypertrophic differentiation in chondrocytes

miR-335-5p inhibits endochondral ossification by directly targeting SP1 in TMJ OA

OBJECTIVE

During the development of temporomandibular joint osteoarthritis, endochondral ossification is compromised which leads to condylar degeneration; miR-335-5p in endochondral ossification in osteoarthritic condylar cartilage tissue remains unclear.

METHODS

Up-regulated microRNA and its target gene were searched for endochondral ossification in osteoarthritis articular cartilage. The effect of increased or decreased miR-335-5p on endochondral ossification was evaluated by transfecting miR-335-5p mimics or miR-335-5p inhibitor in vitro in chondrocytes C28/I2. Finally, we injected the temporomandibular joint of rats intra-articularly with agomiR-335 in a unilateral anterior crossbite rat model to determine the in vivo regulation of miR-335.

RESULTS

After the onset of temporomandibular joint osteoarthritis, miR-335-5p levels were gradually up-regulated, whereas endochondral ossification-related genes were down-regulated in condylar cartilage specimens. Our results showed that miR-335 inhibited endochondral ossification after administration of a miR-335 antagonist into the temporomandibular joint articular cavity of a unilateral anterior crossbite rat model. AgomiR-335, a miR-335 agonist, inhibited matrix mineralization in fibrocartilage stem cells in vitro and then miR-335-5p negatively regulated chondrocyte activity by directly targeting SP1 via promoting transforming growth factor-β/Smad signalling.

CONCLUSION

miR-335-5p can significantly inhibit endochondral ossification; therefore, its inhibition may be beneficial for the treatment of temporomandibular joint osteoarthritis.

The roles and regulatory mechanisms of TGF-β and BMP signaling in bone and cartilage development, homeostasis and disease

Transforming growth factor-βs (TGF-βs) and bone morphometric proteins (BMPs) belong to the TGF-β superfamily and perform essential functions during osteoblast and chondrocyte lineage commitment and differentiation, skeletal development, and homeostasis. TGF-βs and BMPs transduce signals through SMAD-dependent and -independent pathways; specifically, they recruit different receptor heterotetramers and R-Smad complexes, resulting in unique biological readouts. BMPs promote osteogenesis, osteoclastogenesis, and chondrogenesis at all differentiation stages, while TGF-βs play different roles in a stage-dependent manner. BMPs and TGF-β have opposite functions in articular cartilage homeostasis. Moreover, TGF-β has a specific role in maintaining the osteocyte network. The precise activation of BMP and TGF-β signaling requires regulatory machinery at multiple levels, including latency control in the matrix, extracellular antagonists, ubiquitination and phosphorylation in the cytoplasm, nucleus-cytoplasm transportation, and transcriptional co-regulation in the nuclei. This review weaves the background information with the latest advances in the signaling facilitated by TGF-βs and BMPs, and the advanced understanding of their diverse physiological functions and regulations. This review also summarizes the human diseases and mouse models associated with disordered TGF-β and BMP signaling. A more precise understanding of the BMP and TGF-β signaling could facilitate the development of bona fide clinical applications in treating bone and cartilage disorders.

Leucine Supplementation Improves Diastolic Function in HFpEF by HDAC4 Inhibition

Heart failure with preserved ejection fraction (HFpEF) is a complex syndrome associated with a high morbidity and mortality rate. Leucine supplementation has been demonstrated to attenuate cardiac dysfunction in animal models of cachexia and heart failure with reduced ejection fraction (HFrEF). So far, no data exist on leucine supplementation on cardiac function in HFpEF. Thus, the current study aimed to investigate the effect of leucine supplementation on myocardial function and key signaling pathways in an established HFpEF rat model. Female ZSF1 rats were randomized into three groups: Control (untreated lean rats), HFpEF (untreated obese rats), and HFpEF_Leu (obese rats receiving standard chow enriched with 3% leucine). Leucine supplementation started at 20 weeks of age after an established HFpEF was confirmed in obese rats. In all animals, cardiac function was assessed by echocardiography at baseline and throughout the experiment. At the age of 32 weeks, hemodynamics were measured invasively, and myocardial tissue was collected for assessment of mitochondrial function and for histological and molecular analyses. Leucine had already improved diastolic function after 4 weeks of treatment. This was accompanied by improved hemodynamics and reduced stiffness, as well as by reduced left ventricular fibrosis and hypertrophy. Cardiac mitochondrial respiratory function was improved by leucine without alteration of the cardiac mitochondrial content. Lastly, leucine supplementation suppressed the expression and nuclear localization of HDAC4 and was associated with Protein kinase A activation. Our data show that leucine supplementation improves diastolic function and decreases remodeling processes in a rat model of HFpEF. Beneficial effects were associated with HDAC4/TGF-β1/Collagenase downregulation and indicate a potential use in the treatment of HFpEF.

Integrative Analysis Reveals the Diverse Effects of 3D Stiffness upon Stem Cell Fate

The origin of life and native tissue development are dependent on the heterogeneity of pluripotent stem cells. Bone marrow mesenchymal stem cells (BMMSCs) are located in a complicated niche with variable matrix stiffnesses, resulting in divergent stem cell fates. However, how stiffness drives stem cell fate remains unknown. For this study, we performed whole-gene transcriptomics and precise untargeted metabolomics sequencing to elucidate the complex interaction network of stem cell transcriptional and metabolic signals in extracellular matrices (ECMs) with different stiffnesses, and we propose a potential mechanism involved in stem cell fate decision. In a stiff (39~45 kPa) ECM, biosynthesis of aminoacyl-tRNA was up-regulated, and increased osteogenesis was also observed. In a soft (7~10 kPa) ECM, biosynthesis of unsaturated fatty acids and deposition of glycosaminoglycans were increased, accompanied by enhanced adipogenic/chondrogenic differentiation of BMMSCs. In addition, a panel of genes responding to the stiffness of the ECM were validated in vitro, mapping out the key signaling network that regulates stem cells' fate decisions. This finding of "stiffness-dependent manipulation of stem cell fate" provides a novel molecular biological basis for development of potential therapeutic targets within tissue engineering, from both a cellular metabolic and a biomechanical perspective.

Primary Cilia Direct Murine Articular Cartilage Tidemark Patterning Through Hedgehog Signaling and Ambulatory Load

Articular cartilage (AC) is essential for body movement but is highly susceptible to degenerative diseases and has poor self-repair capacity. To improve current subpar regenerative treatments, developmental mechanisms of AC should be clarified and, specifically, how its postnatal multizone organization is acquired. Primary cilia are cell surface organelles crucial for mammalian tissue morphogenesis. Although their importance for chondrocyte function is appreciated, their specific roles in postnatal AC morphogenesis remain unclear. To explore these mechanisms, we used a murine conditional loss-of-function approach (Ift88-flox) targeting joint-lineage progenitors (Gdf5Cre) and monitored postnatal knee AC development. Joint formation and growth up to juvenile stages were largely unaffected. However, mature AC (aged 2 months) exhibited disorganized extracellular matrix, decreased aggrecan and collagen II due to reduced gene expression (not increased catabolism), and marked reduction of AC modulus by 30%-50%. In addition, and unexpectedly, we discovered that tidemark patterning was severely disrupted, as was hedgehog signaling, and exhibited specificity based on regional load-bearing functions of AC. Interestingly, Prg4 expression was markedly increased in highly loaded sites in mutants. Together, our data provide evidence that primary cilia orchestrate postnatal AC morphogenesis including tidemark topography, zonal matrix composition, and ambulation load responses. © 2022 American Society for Bone and Mineral Research (ASBMR).

Identification of Transcription Factors Responsible for a Transforming Growth Factor-β-Driven Hypertrophy-like Phenotype in Human Osteoarthritic Chondrocytes

During osteoarthritis (OA), hypertrophy-like chondrocytes contribute to the disease process. TGF-β's signaling pathways can contribute to a hypertrophy(-like) phenotype in chondrocytes, especially at high doses of TGF-β. In this study, we examine which transcription factors (TFs) are activated and involved in TGF-β-dependent induction of a hypertrophy-like phenotype in human OA chondrocytes. We found that TGF-β, at levels found in synovial fluid in OA patients, induces hypertrophic differentiation, as characterized by increased expression of RUNX2, COL10A1, COL1A1, VEGFA and IHH. Using luciferase-based TF activity assays, we observed that the expression of these hypertrophy genes positively correlated to SMAD3:4, STAT3 and AP1 activity. Blocking these TFs using specific inhibitors for ALK-5-induced SMAD signaling (5 µM SB-505124), JAK-STAT signaling (1 µM Tofacitinib) and JNK signaling (10 µM SP-600125) led to the striking observation that only SB-505124 repressed the expression of hypertrophy factors in TGF-β-stimulated chondrocytes. Therefore, we conclude that ALK5 kinase activity is essential for TGF-β-induced expression of crucial hypertrophy factors in chondrocytes.

SKI knockdown suppresses apoptosis and extracellular matrix degradation of nucleus pulposus cells via inhibition of the Wnt/β-catenin pathway and ameliorates disc degeneration

This study aimed to determine the effects of SKI on interleukin (IL)-1β-induced apoptosis of nucleus pulposus (NP) cells, intervertebral disc degeneration (IDD), and the Wnt signaling pathway. NP tissue specimens of different Pfirrmann grades (II-V) were collected from patients with different grades of IDD. Real-time polymerase chain reaction and western blotting were used to compare SKI mRNA and protein expression in NP tissues from patients. Using the IL-1β-induced IDD model, NP cells were infected with lentivirus-coated si-SKI to downregulate the expression of SKI and treated with LiCl to evaluate the involvement of the Wnt/β-catenin signaling pathway. Western blotting, immunofluorescence, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were used to detect NP cell apoptosis, extracellular matrix (ECM) metabolism, and related protein expression changes in the Wnt/β-catenin signaling pathway. To investigate the role of SKI in vivo, a rat IDD model was established by needle puncture of the intervertebral disc. Rats were injected with lentivirus-coated si-SKI and evaluated by magnetic resonance imaging (MRI), and hematoxylin and eosin (HE) and safranin O staining. SKI expression positively correlated with the severity of human IDD. In the IL-1β-induced NP cell degeneration model, SKI expression increased significantly and reached a peak at 24 h. SKI knockdown protected against IL-1β-induced NP cell apoptosis and ECM degradation. LiCl treatment reversed the protective effects of si-SKI on NP cells. Furthermore, lentivirus-coated si-SKI injection partially reversed the NP tissue damage in the IDD model in vivo. SKI knockdown reduced NP cell apoptosis and ECM degradation by inhibiting the Wnt/β-catenin signaling pathway, ultimately protecting against IDD. Therefore, SKI may be an effective target for IDD treatment.

Strategies to Modulate the Redifferentiation of Chondrocytes

Because of the low self-healing capacity of articular cartilage, cartilage injuries and degenerations triggered by various diseases are almost irreversible. Previous studies have suggested that human chondrocytes cultured in vitro tend to dedifferentiate during the cell-amplification phase and lose the physiological properties and functions of the cartilage itself, which is currently a critical limitation in the cultivation of cartilage for tissue engineering. Recently, numerous studies have focused on the modulation of chondrocyte redifferentiation. Researchers discovered the effect of various conditions (extracellular environment, cell sources, growth factors and redifferentiation inducers, and gene silencing and overexpression) on the redifferentiation of chondrocytes during the in vitro expansion of cells, and obtained cartilage tissue cultured in vitro that exhibited physiological characteristics and functions that were similar to those of human cartilage tissue. Encouragingly, several studies reported positive results regarding the modulation of the redifferentiation of chondrocytes in specific conditions. Here, the various factors and conditions that modulate the redifferentiation of chondrocytes, as well as their limitations and potential applications and challenges are reviewed. We expect to inspire research in the field of cartilage repair toward the future treatment of arthropathy.

COMP and TSP-4: Functional Roles in Articular Cartilage and Relevance in Osteoarthritis

Osteoarthritis (OA) is a slow-progressing joint disease, leading to the degradation and remodeling of the cartilage extracellular matrix (ECM). The usually quiescent chondrocytes become reactivated and accumulate in cell clusters, become hypertrophic, and intensively produce not only degrading enzymes, but also ECM proteins, like the cartilage oligomeric matrix protein (COMP) and thrombospondin-4 (TSP-4). To date, the functional roles of these newly synthesized proteins in articular cartilage are still elusive. Therefore, we analyzed the involvement of both proteins in OA specific processes in in vitro studies, using porcine chondrocytes, isolated from femoral condyles. The effect of COMP and TSP-4 on chondrocyte migration was investigated in transwell assays and their potential to modulate the chondrocyte phenotype, protein synthesis and matrix formation by immunofluorescence staining and immunoblot. Our results demonstrate that COMP could attract chondrocytes and may contribute to a repopulation of damaged cartilage areas, while TSP-4 did not affect this process. In contrast, both proteins similarly promoted the synthesis and matrix formation of collagen II, IX, XII and proteoglycans, but inhibited that of collagen I and X, resulting in a stabilized chondrocyte phenotype. These data suggest that COMP and TSP-4 activate mechanisms to protect and repair the ECM in articular cartilage.

Apigenin attenuates TGF-β1-stimulated cardiac fibroblast differentiation and extracellular matrix production by targeting miR-155-5p/c-Ski/Smad pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Apigenin is a natural flavonoid compound present in chamomile (Matricaia chamomilla L.) from the Asteraceae family, which is used in the treatment of cardiovascular diseases by traditional healers, but its effects on differentiation and extracellular matrix (ECM) production of cardiac fibroblasts (CFs) induced by transforming growth factor beta 1 (TGF-β1) are poorly understood.

AIM OF THE STUDY

This study aimed to examine these effects and potential molecular mechanisms and to provide a new application of apigenin in the prevention and treatment of cardiac fibrosis.

MATERIALS AND METHODS

The TGF-β1-stimulated CFs or the combination of TGF-β1-stimulated and microRNA-155-5p (miR-155-5p) inhibitor- or mimic-transfected CFs were treated with or without apigenin. The expression levels of intracellular related mRNA and proteins were detected by real-time polymerase chain reaction and Western blot methods, respectively. The luciferase reporter gene containing cellular Sloan-Kettering Institute (c-Ski) wild or mutant type 3'-UTR was used and the luciferase activity was examined to verify the direct link of miR-155-5p and c-Ski.

RESULTS

After treatment of TGF-β1-stimulated CFs with 6-24 μM apigenin, the expression of c-Ski was increased, while levels of miR-155-5p, α-smooth muscle actin, collagen Ⅰ/Ⅲ, Smad2/3, and p-Smad2/3 were decreased. After transfection of CFs with the miR-155-5p inhibitor or mimic, the similar or inverse results were respectively observed as well. The combination of TGF-β1 and miR-155-5p inhibitor or mimic might cause an antagonistical or synergistic effect, respectively, and apigenin addition could enhance the effects of the inhibitor and antagonize the effects of the mimic. Luciferase reporter gene assay demonstrated that c-Ski was a direct target of miR-155-5p.

CONCLUSION

These findings suggested that apigenin could inhibit the differentiation and ECM production in TGF-β1-stimulated CFs, and its mechanisms might partly be attributable to the reduction of miR-155-5p expression and subsequent increment of c-Ski expression, which might result in the inhibition of Smad2/3 and p-Smad2/3 expressions.

Concise Review: The Regulatory Mechanism of Lysine Acetylation in Mesenchymal Stem Cell Differentiation

Nowadays, the use of MSCs has attracted considerable attention in the global science and technology field, with the self-renewal and multidirectional differentiation potential for diabetes, obesity treatment, bone repair, nerve repair, myocardial repair, and so on. Epigenetics plays an important role in the regulation of mesenchymal stem cell differentiation, which has become a research hotspot in the medical field. This review focuses on the role of lysine acetylation modification on the determination of MSC differentiation direction. During this progress, the recruitment of lysine acetyltransferases (KATs) and lysine deacetylases (KDACs) is the crux of transcriptional mechanisms in the dynamic regulation of key genes controlling MSC multidirectional differentiation.

A new mutational hotspot in the SKI gene in the context of MFS/TAA molecular diagnosis

SKI pathogenic variations are associated with Shprintzen-Goldberg Syndrome (SGS), a rare systemic connective tissue disorder characterized by craniofacial, skeletal and cardiovascular features. So far, the clinical description, including intellectual disability, has been relatively homogeneous, and the known pathogenic variations were located in two different hotspots of the SKI gene. In the course of diagnosing Marfan syndrome and related disorders, we identified nine sporadic probands (aged 2-47 years) carrying three different likely pathogenic or pathogenic variants in the SKI gene affecting the same amino acid (Thr180). Seven of these molecular events were confirmed de novo. All probands displayed a milder morphological phenotype with a marfanoid habitus that did not initially lead to a clinical diagnosis of SGS. Only three of them had learning disorders, and none had intellectual disability. Six out of nine presented thoracic aortic aneurysm, which led to preventive surgery in the oldest case. This report extends the phenotypic spectrum of variants identified in the SKI gene. We describe a new mutational hotspot associated with a marfanoid syndrome with no intellectual disability. Cardiovascular involvement was confirmed in a significant number of cases, highlighting the importance of accurately diagnosing SGS and ensuring appropriate medical treatment and follow-up.

Glucocorticoid Enhanced the Expression of Ski in Osteonecrosis of Femoral Head: The Effect on Adipogenesis of Rabbit BMSCs

Glucocorticoid (GC)-induced osteonecrosis has been considered as the most serious side effect in long-term or over-dose steroid therapy. The decreased bone mass and increased marrow fat tissue demonstrated that GC can destroy the normal differentiation of bone marrow mesenchymal stem cells (BMSCs), which accelerates adipogenesis but not osteogenesis. However, the underlying mechanisms are still unclear. Ski, an evolutionary conserved protein, is a multifunctional transcriptional regulator that involved in regulating signaling pathways associated with adipogenesis differentiation, but the concrete function remains unclear. In this work, we first established a methylprednisolone (MPS)-induced osteonecrosis of femoral head (ONFH) rabbit model, in which the expression of Ski, PPAR-γ, and FABP4 was up-regulated compared with control group, and then we induced the isolated BMSCs from rabbit with dexamethasone (Dex) in vitro and the results showed that the Ski expression was up-regulated by Dex in a dose- and time-dependent manner. Therefore, we demonstrated that the expression of Ski was up-regulated in glucocorticoid-related osteonecrosis disease in vivo and in vitro. Moreover, the adipogenesis differentiation capacity of BMSCs was enhanced after induced by Dex, which was identified by Oil Red O staining, and the up-regulated PPAR-γ and FABP4 expression. To further study the function of Ski in BMSC after induced by Dex, Ski specific small interfering RNA (Ski-siRNA) was used. Results showed that knockdown of Ski obviously decreased adipogenesis differentiation evident by Oil Red O staining, and the expression of PPAR-γ and FABP4 was down-regulated simultaneously. Collectively, our findings suggest that Ski increased significantly during glucocorticoid-induced adipogenic differentiation of BMSCs, and the expression level was consistent with adipogenic-related proteins including PPAR-γ and FABP4. Based on the above data, we believe that Ski might become a new molecule in the treatment of GC-induced ONFH and our study could provide a basis for further study on the detailed function of Ski in ONFH.

TGFβ/BMP Signaling Pathway in Cartilage Homeostasis

Cartilage homeostasis is governed by articular chondrocytes via their ability to modulate extracellular matrix production and degradation. In turn, chondrocyte activity is regulated by growth factors such as those of the transforming growth factor β (TGFβ) family. Members of this family include the TGFβs, bone morphogenetic proteins (BMPs), and growth and differentiation factors (GDFs). Signaling by this protein family uniquely activates SMAD-dependent signaling and transcription but also activates SMAD-independent signaling via MAPKs such as ERK and TAK1. This review will address the pivotal role of the TGFβ family in cartilage biology by listing several TGFβ family members and describing their signaling and importance for cartilage maintenance. In addition, it is discussed how (pathological) processes such as aging, mechanical stress, and inflammation contribute to altered TGFβ family signaling, leading to disturbed cartilage metabolism and disease.

Spatio-Temporal Expression and Functional Analysis of miR-206 in Developing Orofacial Tissue

BACKGROUND

Development of the mammalian palate is dependent on precise, spatiotemporal expression of a panoply of genes. MicroRNAs (miRNAs), the largest family of noncoding RNAs, function as crucial modulators of cell and tissue differentiation, regulating expression of key downstream genes.

OBSERVATIONS

Our laboratory has previously identified several developmentally regulated miRNAs, including miR-206, during critical stages of palatal morphogenesis. The current study reports spatiotemporal distribution of miR-206 during development of the murine secondary palate (gestational days 12.5-14.5).

RESULT AND CONCLUSION

Potential cellular functions and downstream gene targets of miR-206 were investigated using functional assays and expression profiling, respectively. Functional analyses highlighted potential roles of miR-206 in governing TGFß- and Wnt signaling in mesenchymal cells of the developing secondary palate. In addition, altered expression of miR-206 within developing palatal tissue of TGFß3-/- fetuses reinforced the premise that crosstalk between this miRNA and TGFß3 is crucial for secondary palate development.

Mir-29b promotes human aortic valve interstitial cell calcification via inhibiting TGF-β3 through activation of wnt3/β-catenin/Smad3 signaling

Herein, we hypothesized that pro-osteogenic MicroRNAs (miRs) could play functional roles in the calcification of the aortic valve and aimed to explore the functional role of miR-29b in the osteoblastic differentiation of human aortic valve interstitial cells (hAVICs) and the underlying molecular mechanism. Osteoblastic differentiation of hAVICs isolated from human calcific aortic valve leaflets obtained intraoperatively was induced with an osteogenic medium. Alizarin red S staining was used to evaluate calcium deposition. The protein levels of osteogenic markers and other proteins were evaluated using western blotting and/or immunofluorescence while qRT-PCR was applied for miR and mRNA determination. Bioinformatics and luciferase reporter assay were used to identify the possible interaction between miR-29b and TGF-β3. Calcium deposition and the number of calcification nodules were pointedly and progressively increased in hAVICs during osteogenic differentiation. The levels of osteogenic and calcification markers were equally increased, thus confirming the mineralization of hAVICs. The expression of miR-29b was significantly increased during osteoblastic differentiation. Furthermore, the osteoblastic differentiation of hAVICs was significantly inhibited by the miR-29b inhibition. TGF-β3 was markedly downregulated while Smad3, Runx2, wnt3, and β-catenin were significantly upregulated during osteogenic induction at both the mRNA and protein levels. These effects were systematically induced by miR-29b overexpression while the inhibition of miR-29b showed the inverse trends. Moreover, TGF-β3 was a direct target of miR-29b. Inhibition of miR-29b hinders valvular calcification through the upregulation of the TGF-β3 via inhibition of wnt/β-catenin and RUNX2/Smad3 signaling pathways.

The inhibitory roles of Ihh downregulation on chondrocyte growth and differentiation

The proliferative rate of chondrocytes affects bone elongation. Chondrocyte hypertrophy is required for endochondral bone formation as chondrocytes secrete factors required for osteoblast differentiation and maturation. Previous studies have demonstrated that the Indian hedgehog (Ihh) signaling pathway is a key regulator of skeletal development and homeostasis. The aim of the present study was to investigate the function of Ihh in chondrocyte proliferation and differentiation, as well as the underlying mechanisms. Ihh was knocked down in mouse chondrocyte cells using short hairpin RNA. Chondrocyte apoptosis and cell cycle arrest were assessed using flow cytometry and the results indicated that knockdown of Ihh significantly inhibited cell growth (P<0.05) and increased apoptosis (P<0.001) compared with negative control cells. Downregulation of Ihh also resulted in cell cycle arrest at G1 to S phase in chondrocytes. It was also observed that knockdown of Ihh decreased alkaline phosphatase activity and mineral deposition of chondrocytes. The inhibitory roles of Ihh downregulation on chondrocyte growth and differentiation may be associated with the transforming growth factor-β/mothers against decapentaplegic and osteoprotegerin/receptor activator of nuclear factor κB ligand signaling pathway. The results of the present study suggest that chondrocyte-derived Ihh is essential for maintaining bone growth plates and that manipulation of Ihh expression or its signaling components may be a novel therapeutic technique for the treatment of skeletal diseases, including achondroplasia.

TGF-β Stimulates Endochondral Differentiation after Denervation

Transforming growth factor beta (TGF-β) is a multifunctional protein that induces gene expression of cartilage-specific molecules, but its exact role in the process of chondrogenesis is unclear. Because recent studies suggest that TGF-β can facilitate chondrogenic precursor cells differentiating into chondrocytes, we sought to determine whether TGF-β prevents denervation-induced reduction of endochondral bone formation in an experimental model. Mice were treated daily with recombinant human TGF-β1 (rhTGF-β1) for 3 weeks. We found that rhTGF-β1 not only prevented denervation-induced reduction of gene expression of type II collagen, type X collagen, aggrecan, Indian hedgehog, and parathyroid hormone-related peptide, but also synergized endochondral differentiation. These results demonstrate that short-term systemic administration of TGF-β substantially prevents denervation-induced reduction of endochondral bone formation via stimulating endochondral differentiation. Potential therapeutic applications will be pursued in further studies that address the molecular biological mechanism of TGF-β on endochodral bone formation after denervation in animal models.

rAAV-mediated combined gene transfer and overexpression of TGF-β and SOX9 remodels human osteoarthritic articular cartilage

Direct administration of therapeutic candidate gene sequences using the safe and effective recombinant adeno-associated virus (rAAV) vectors is a promising strategy to stimulate the biologic activities of articular chondrocytes as an adapted tool to treat human osteoarthritic (OA) cartilage. In the present study, we developed a combined gene transfer approach based on the co-delivery of the pleiotropic transformation growth factor beta (TGF-β) with the specific transcription factor SOX9 via rAAV to human normal and OA chondrocytes in vitro and cartilage explants in situ in light of the mitogenic and pro-anabolic properties of these factors. Effective, durable co-overexpression of TGF-β and SOX9 significantly enhanced the levels of cell proliferation both in human normal and OA chondrocytes and cartilage explants over an extended period of time (21 days), while stimulating the biosynthesis of key matrix components (proteoglycans, type-II collagen) compared with control conditions (reporter lacZ gene transfer, absence of vector treatment). Of further note, expression of hypertrophic type-X collagen significantly decreased following co-treatment by the candidate vectors. The present findings show the value of combining the transfer and expression of potent candidate factors in human OA cartilage as a means to re-establish essential features of normal cartilage and counteract the pathological shift of homeostasis. These observations support the concept of developing dual therapeutic rAAV gene transfer strategies as future, adapted tools for the direct treatment of human OA. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:2181-2190, 2016.

Smad2 and Smad3 Regulate Chondrocyte Proliferation and Differentiation in the Growth Plate

TGFβs act through canonical and non-canonical pathways, and canonical signals are transduced via Smad2 and Smad3. However, the contribution of canonical vs. non-canonical pathways in cartilage is unknown because the role of Smad2 in chondrogenesis has not been investigated in vivo. Therefore, we analyzed mice in which Smad2 is deleted in cartilage (Smad2^CKO), global Smad3^-/- mutants, and crosses of these strains. Growth plates at birth from all mutant strains exhibited expanded columnar and hypertrophic zones, linked to increased proliferation in resting chondrocytes. Defects were more severe in Smad2^CKO and Smad2^CKO;Smad3^-/-(Smad2/3) mutant mice than in Smad3^-/- mice, demonstrating that Smad2 plays a role in chondrogenesis. Increased levels of Ihh RNA, a key regulator of chondrocyte proliferation and differentiation, were seen in prehypertrophic chondrocytes in the three mutant strains at birth. In accordance, TGFβ treatment decreased Ihh RNA levels in primary chondrocytes from control (Smad2^fx/fx) mice, but inhibition was impaired in cells from mutants. Consistent with the skeletal phenotype, the impact on TGFβ-mediated inhibition of Ihh RNA expression was more severe in Smad2^CKO than in Smad3^-/- cells. Putative Smad2/3 binding elements (SBEs) were identified in the proximal Ihh promoter. Mutagenesis demonstrated a role for three of them. ChIP analysis suggested that Smad2 and Smad3 have different affinities for these SBEs, and that the repressors SnoN and Ski were differentially recruited by Smad2 and Smad3, respectively. Furthermore, nuclear localization of the repressor Hdac4 was decreased in growth plates of Smad2^CKO and double mutant mice. TGFβ induced association of Hdac4 with Smad2, but not with Smad3, on the Ihh promoter. Overall, these studies revealed that Smad2 plays an essential role in the development of the growth plate, that both Smads 2 and 3 inhibit Ihh expression in the neonatal growth plate, and suggested they accomplish this by binding to distinct SBEs, mediating assembly of distinct repressive complexes.

The cartilage growth plate regulates the size and shape of nearly every skeletal element in the body. TGFβs are potent inducers of cartilage formation, but the mechanisms by which they transduce their signals in cartilage during development are poorly understood. Similarly, there is strong evidence that dysregulation of the TGFβ pathway increases the risk for osteoarthritis (OA) in humans, but the underlying mechanisms are unknown. TGFβs transduce their signals through a canonical pathway involving Smad2 and Smad3, and through several non-canonical pathways. However, the roles of canonical vs. noncanonical signaling are unknown in cartilage because the combined roles of Smad2 and Smad3 have not been determined. We generated mice lacking both Smad2 and Smad3 in cartilage in order to determine the role of canonical TGFβ signaling during embryonic development. We determined that Smad2 has a more prominent role than Smad3 in non-hypertrophic chondrocytes in the growth plate, and identified elevated levels of Ihh RNA in neonatal cartilage in Smad2 and Smad3 mutants. These findings may be important because Ihh is a vital regulator of cartilage proliferation and differentiation during cartilage development. More generally, the studies identify how Smad2 and Smad3 can regulate a common target gene through distinct mechanisms.

Unloading results in rapid loss of TGFβ signaling in articular cartilage: role of loading-induced TGFβ signaling in maintenance of articular chondrocyte phenotype?

OBJECTIVE

Recently it was shown that loading of articular cartilage explants activates TGFβ signaling. Here we investigated if in vivo chondrocytes express permanently high TGFβ signaling, and the consequence of the loss of compressive loading-mediated TGFβ signaling on chondrocyte function and phenotype.

METHOD

Bovine articular cartilage explants were collected within 10 min post mortem and stained immediately and after 30, 60 and 360 min for phosphorylated-Smad2, indicating active TGFβ signaling. Explants were unloaded for 48 h and subsequently repeatedly loaded with a compressive load of 3 MPa. In addition, explants were cultured unloaded for 2 weeks and the effect of loading or exogenous TGFβ on proteoglycan level and chondrocyte phenotype (Col10a1 mRNA expression) was analyzed.

RESULTS

Unloading of articular cartilage results in rapid loss of TGFβ signaling while subsequent compressive loading swiftly restored this. Loading and exogenous TGFβ enhanced expression of TGFβ1 and ALK5. Unloading of explants for 2 weeks resulted in proteoglycan loss and increased Col10a1 expression. Both loading and exogenous TGFβ inhibited elevated Col10a1 expression but not proteoglycan loss.

CONCLUSION

Our data might imply that in vivo regular physiological loading of articular cartilage leads to enduring TGFβ signaling and TGFβ-induced gene expression. We propose a hypothetical model in which loading activates a self-perpetuating system that prevents hypertrophic differentiation of chondrocytes and is crucial for cartilage homeostasis.

Bufalin inhibits proliferation of human gastric cancer MGC803 cells via TGFβ1/smad signaling pathways

AIM: To investigate whether TGFβ1/smad signaling pathways are involved in the effect of Bufalin on the proliferation of human gastric cancer MGC803 cells.

METHODS: Human gastric cancer MGC803 cells were treated with Bufalin. Cell proliferation was tested by MTT assay and Trypan blue assay. The content of TGFβ1 protein in culture medium treated with Bufalin was detected by ELISA. The expressions of cyclinD1, phosphorylated smad3 and smad4 was detected by Western blot.

RESULTS: Bufalin significantly reduced the viability of MGC803 cells in a dose-dependent manner, and there was a significant difference among different concentrations (F = 13.216, P = 0.002). The results of Trypan blue assay showed a similar trend (χ² = 9.667, P = 0.022). Compared with the control group, the expression of TGFβ1 protein in culture medium was decreased after the cells were treated with Bufalin (F = 36.455, P < 0.001), and the expression of P-smad3 and cyclinD1 protein in MGC803 cells was also decreased after the cells were treated with Bufalin (P < 0.05). However, the content of smad4 protein in MGC803 cells was increased after the application of Bufalin (P < 0.001).

CONCLUSION: Bufalin inhibits the proliferation of MGC803 cells via mechanisms possibly associated with inhibiting TGFβ1/smad signaling transduction pathways.

MiR-206 Attenuates Denervation-Induced Skeletal Muscle Atrophy in Rats Through Regulation of Satellite Cell Differentiation via TGF-β1, Smad3, and HDAC4 Signaling

Background

Denervation-induced skeletal muscle atrophy results in significant biochemical and physiological changes potentially leading to devastating outcomes including increased mortality. Effective treatments for skeletal muscle diseases are currently not available. Muscle-specific miRNAs, such as miR-206, play an important role in the regulation of muscle regeneration.

The aim of the present study was to examine the beneficial effects of miR-206 treatment during the early changes in skeletal muscle atrophy, and to study the underlying signaling pathways in a rat skeletal muscle atrophy model.

Material/Methods

The rat denervation-induced skeletal muscle atrophy model was established. miRNA-206 was overexpressed with or without TGF-β1 inhibitor in the rats. The mRNA and protein expression of HDAC4, TGF-β1, and Smad3 was determined by real-time PCR and western blot. The gastrocnemius muscle cross-sectional area and relative muscle mass were measured. MyoD1, TGF-β1, and Pax7 were determined by immunohistochemical staining.

Results

After sciatic nerve surgical transection, basic muscle characteristics, such as relative muscle weight, deteriorated continuously during a 2-week period. Injection of miR-206 (30 μg/rat) attenuated morphological and physiological deterioration of muscle characteristics, prevented fibrosis effectively, and inhibited the expression of TGF-β1 and HDAC4 as assessed 2 weeks after denervation. Moreover, miR-206 treatment increased the number of differentiating (MyoD1⁺/Pax7⁺) satellite cells, thereby protecting denervated muscles from atrophy. Interestingly, the ability of miR-206 to govern HDAC4 expression and to attenuate muscle atrophy was weakened after pharmacological blockage of the TGF-β1/Smad3 axis.

Conclusions

TGF-β1/Smad3 signaling pathway is one of the crucial signaling pathways by which miR-206 counteracts skeletal muscle atrophy by affecting proliferation and differentiation of satellite cells. miR-206 may be a potential target for development of a new strategy for treatment of patients with early denervation-induced skeletal muscle atrophy.

The transcription factors ZEB2 and T-bet cooperate to program cytotoxic T cell terminal differentiation in response to LCMV viral infection

The transcription factor T-bet is critical for cytotoxic T lymphocyte (CTL) differentiation, but it is unclear how it operates in a graded manner in the formation of both terminal effector and memory precursor cells during viral infection. We find that, at high concentrations, T-bet induced expression of Zeb2 mRNA, which then triggered CTLs to adopt terminally differentiated states. ZEB2 and T-bet cooperate to switch on a terminal CTL differentiation program, while simultaneously repressing genes necessary for central memory CTL development. Chromatin immunoprecipitation sequencing showed that a large proportion of these genes were bound by T-bet, and this binding was altered by ZEB2 deficiency. Furthermore, T-bet overexpression could not fully bypass ZEB2 function. Thus, the coordinated actions of T-bet and ZEB2 outline a novel genetic pathway that forces commitment of CTLs to terminal differentiation, thereby restricting their memory cell potential.

Histone Deacetylases in Bone Development and Skeletal Disorders

Histone deacetylases (Hdacs) are conserved enzymes that remove acetyl groups from lysine side chains in histones and other proteins. Eleven of the 18 Hdacs encoded by the human and mouse genomes depend on Zn(2+) for enzymatic activity, while the other 7, the sirtuins (Sirts), require NAD2(+). Collectively, Hdacs and Sirts regulate numerous cellular and mitochondrial processes including gene transcription, DNA repair, protein stability, cytoskeletal dynamics, and signaling pathways to affect both development and aging. Of clinical relevance, Hdacs inhibitors are United States Food and Drug Administration-approved cancer therapeutics and are candidate therapies for other common diseases including arthritis, diabetes, epilepsy, heart disease, HIV infection, neurodegeneration, and numerous aging-related disorders. Hdacs and Sirts influence skeletal development, maintenance of mineral density and bone strength by affecting intramembranous and endochondral ossification, as well as bone resorption. With few exceptions, inhibition of Hdac or Sirt activity though either loss-of-function mutations or prolonged chemical inhibition has negative and/or toxic effects on skeletal development and bone mineral density. Specifically, Hdac/Sirt suppression causes abnormalities in physiological development such as craniofacial dimorphisms, short stature, and bone fragility that are associated with several human syndromes or diseases. In contrast, activation of Sirts may protect the skeleton from aging and immobilization-related bone loss. This knowledge may prolong healthspan and prevent adverse events caused by epigenetic therapies that are entering the clinical realm at an unprecedented rate. In this review, we summarize the general properties of Hdacs/Sirts and the research that has revealed their essential functions in bone forming cells (e.g., osteoblasts and chondrocytes) and bone resorbing osteoclasts. Finally, we offer predictions on future research in this area and the utility of this knowledge for orthopedic applications and bone tissue engineering.

Protective Effect of Triptolide against Glomerular Mesangial Cell Proliferation and Glomerular Fibrosis in Rats Involves the TGF- β 1/Smad Signaling Pathway

Triptolide as a main active ingredient of Tripterygium wilfordii is known to be exerting anti-inflammatory, marked immunosuppressive, and podocyte-protective effects. In this study, we investigated the protective effect of triptolide in kidney disease. Rat glomerular mesangial cells were randomly divided into three groups: (1) control group, (2) TGF-β1 (10 μg/mL) group, and (3) triptolide group (triptolide 10 μg/L + TGF-β1 10 μg/L). Sixty male Sprague-Dawley rats were randomly divided into three groups: (1) control group, (2) chronic serum sickness glomerulonephritis model group, and (3) triptolide (0.2 mg/kg·d) group. Reverse transcription PCR was used to assess Ski and Smad3 mRNA expression in the mesangial cells and renal tissues. Western blotting was used to determine Ski and Smad3 protein expressions. Laser confocal fluorescence microscopy was used to observe the subcellular localization of Smad3 and Ski proteins in the mesangial cells. Triptolide inhibited the TGF-β1-induced proliferation of mesangial cells. It significantly upregulated Ski protein expression and downregulated Smad3 mRNA and protein expressions in a time-dependent manner. Laser confocal fluorescence microscopy detected high Smad3 fluorescence intensity in the cytoplasm and low Smad3 and high Ski fluorescence intensity in the nucleus. By upregulating Ski protein expression triptolide decreased the extent of fibrosis by affecting the TGF-β1/Smad3 signaling pathway.

The chondrocytic journey in endochondral bone growth and skeletal dysplasia

The endochondral bones of the skeleton develop from a cartilage template and grow via a process involving a cascade of chondrocyte differentiation steps culminating in formation of a growth plate and the replacement of cartilage by bone. This process of endochondral ossification, driven by the generation of chondrocytes and their subsequent proliferation, differentiation, and production of extracellular matrix constitute a journey, deviation from which inevitably disrupts bone growth and development, and is the basis of human skeletal dysplasias with a wide range of phenotypic severity, from perinatal lethality to progressively deforming. This highly coordinated journey of chondrocyte specification and fate determination is controlled by a myriad of intrinsic and extrinsic factors. SOX9 is the master transcription factor that, in concert with varying partners along the way, directs the different phases of the journey from mesenchymal condensation, chondrogenesis, differentiation, proliferation, and maturation. Extracellular signals, including bone morphogenetic proteins, wingless-related MMTV integration site (WNT), fibroblast growth factor, Indian hedgehog, and parathyroid hormone-related peptide, are all indispensable for growth plate chondrocytes to align and organize into the appropriate columnar architecture and controls their maturation and transition to hypertrophy. Chondrocyte hypertrophy, marked by dramatic volume increase in phases, is controlled by transcription factors SOX9, Runt-related transcription factor, and FOXA2. Hypertrophic chondrocytes mediate the cartilage to bone transition and concomitantly face a live-or-die situation, a subject of much debate. We review recent insights into the coordination of the phases of the chondrocyte journey, and highlight the need for a systems level understanding of the regulatory networks that will facilitate the development of therapeutic approaches for skeletal dysplasia.

c-Ski activates cancer-associated fibroblasts to regulate breast cancer cell invasion

Aberrant expression of c-Ski oncoprotein in some tumor cells has been shown to be associated with cancer development. However, the role of c-Ski in cancer-associated fibroblasts (CAFs) of tumor microenvironment has not been characterized. In the current study, we found that c-Ski is highly expressed in CAFs derived from breast carcinoma microenvironment and this CAF-associated c-Ski expression is associated with invasion and metastasis of human breast tumors. We showed that c-Ski overexpression in immortalized breast normal fibroblasts (NFs) induces conversion to breast CAFs by repressing p53 and thereby upregulating SDF-1 in NFs. SDF-1 treatment or p53 knockdown in NFs had similar effects on the activation of NFs as c-Ski overexpression. The c-Ski-activated CAFs show increased proliferation, migration, invasion and contraction compared with NFs. Furthermore, c-Ski-activated CAFs facilitated the migration and invasion of MDA-MB-231 breast cancer cells. Our data suggest that c-Ski is an important regulator in the activation of CAFs and may serve as a potential therapeutic target to block breast cancer progression.

In-frame mutations in exon 1 of SKI cause dominant Shprintzen-Goldberg syndrome

Shprintzen-Goldberg syndrome (SGS) is characterized by severe marfanoid habitus, intellectual disability, camptodactyly, typical facial dysmorphism, and craniosynostosis. Using family-based exome sequencing, we identified a dominantly inherited heterozygous in-frame deletion in exon 1 of SKI. Direct sequencing of SKI further identified one overlapping heterozygous in-frame deletion and ten heterozygous missense mutations affecting recurrent residues in 18 of the 19 individuals screened for SGS; these individuals included one family affected by somatic mosaicism. All mutations were located in a restricted area of exon 1, within the R-SMAD binding domain of SKI. No mutation was found in a cohort of 11 individuals with other marfanoid-craniosynostosis phenotypes. The interaction between SKI and Smad2/3 and Smad 4 regulates TGF-β signaling, and the pattern of anomalies in Ski-deficient mice corresponds to the clinical manifestations of SGS. These findings define SGS as a member of the family of diseases associated with the TGF-β-signaling pathway.