Endoglin differentially regulates TGF-β-induced Smad2/3 and Smad1/5 signalling and its expression correlates with extracellular matrix production and cellular differentiation state in human chondrocytes

Collagen and Alginate Hydrogels Support Chondrocytes Redifferentiation In Vitro without Supplementation of Exogenous Growth Factors

Focal cartilage defects are a prevalent knee problem affecting people of all ages. Articular cartilage (AC) possesses limited healing potential, and osteochondral defects can lead to pain and long-term complications such as osteoarthritis. Autologous chondrocyte implantation (ACI) has been a successful surgical approach for repairing osteochondral defects over the past two decades. However, a major drawback of ACI is the dedifferentiation of chondrocytes during their in vitro expansion. In this study, we isolated ovine chondrocytes and cultured them in a two-dimensional environment for ACI procedures. We hypothesized that 3D scaffolds would support the cells' redifferentiation without the need for growth factors so we encapsulated them into soft collagen and alginate (col/alg) hydrogels. Chondrocytes embedded into the hydrogels were viable and proliferated. After 7 days, they regained their original rounded morphology (aspect ratio 1.08) and started to aggregate. Gene expression studies showed an upregulation of COL2A1, FOXO3A, FOXO1, ACAN, and COL6A1 (37, 1.13, 22, 1123, and 1.08-fold change expression, respectively) as early as day one. At 21 days, chondrocytes had extensively colonized the hydrogel, forming large cell clusters. They started to replace the degrading scaffold by depositing collagen II and aggrecan, but with limited collagen type I deposition. This approach allows us to overcome the limitations of current approaches such as the dedifferentiation occurring in 2D in vitro expansion and the necrotic formation in spheroids. Further studies are warranted to assess long-term ECM deposition and integration with native cartilage. Though limitations exist, this study suggests a promising avenue for cartilage repair with col/alg hydrogel scaffolds.

The interplay between biochemical mediators and mechanotransduction in chondrocytes: Unravelling the differential responses in primary knee osteoarthritis

In primary or idiopathic osteoarthritis (OA), it is unclear which factors trigger the shift of articular chondrocyte activity from pro-anabolic to pro-catabolic. In fact, there is a controversy about the aetiology of primary OA, either mechanical or inflammatory. Chondrocytes are mechanosensitive cells, that integrate mechanical stimuli into cellular responses in a process known as mechanotransduction. Mechanotransduction occurs thanks to the activation of mechanosensors, a set of specialized proteins that convert physical cues into intracellular signalling cascades. Moderate levels of mechanical loads maintain normal tissue function and have anti-inflammatory effects. In contrast, mechanical over- or under-loading might lead to cartilage destruction and increased expression of pro-inflammatory cytokines. Simultaneously, mechanotransduction processes can regulate and be regulated by pro- and anti-inflammatory soluble mediators, both local (cells of the same joint, i.e., the chondrocytes themselves, infiltrating macrophages, fibroblasts or osteoclasts) and systemic (from other tissues, e.g., adipokines). Thus, the complex process of mechanotransduction might be altered in OA, so that cartilage-preserving chondrocytes adopt a different sensitivity to mechanical signals, and mechanic stimuli positively transduced in the healthy cartilage may become deleterious under OA conditions. This review aims to provide an overview of how the biochemical exposome of chondrocytes can alter important mechanotransduction processes in these cells. Four principal mechanosensors, i.e., integrins, Ca2+ channels, primary cilium and Wnt signalling (canonical and non-canonical) were targeted. For each of these mechanosensors, a brief summary of the response to mechanical loads under healthy or OA conditions is followed by a concise overview of published works that focus on the further regulation of the mechanotransduction pathways by biochemical factors. In conclusion, this paper discusses and explores how biological mediators influence the differential behaviour of chondrocytes under mechanical loads in healthy and primary OA.

Endothelial Robo4 suppresses endothelial-to-mesenchymal transition induced by irradiation and improves hematopoietic reconstitution

Bone marrow ablation is routinely performed before hematopoietic stem cell transplantation (HSCT). Hematopoietic stem and progenitor cells (HSPCs) require a stable bone marrow microenvironment to expand and refill the peripheral blood cell pool after ablation. Roundabout guidance receptor 4 (Robo4) is a transmembrane protein exclusive to endothelial cells and is vital in preserving vascular integrity. Hence, the hypothesis is that Robo4 maintains the integrity of bone marrow endothelial cells following radiotherapy. We created an endothelial cell injury model with γ-radiation before Robo4 gene manipulation using lentiviral-mediated RNAi and gene overexpression techniques. We demonstrate that Robo4 and specific mesenchymal proteins (Fibronectin, Vimentin, αSma, and S100A4) are upregulated in endothelial cells exposed to irradiation (IR). We found that Robo4 depletion increases the expression of endoglin (CD105), an auxiliary receptor for the transforming growth factor (TGF-β) family of proteins, and promotes endothelial-to-mesenchymal transition (End-MT) through activation of both the canonical (Smad) and non-canonical (AKT/NF-κB) signaling pathways to facilitate Snail1 activation and its nuclear translocation. Endothelial Robo4 overexpression stimulates the expression of immunoglobulin-like adhesion molecules (ICAM-1 and VCAM-1) and alleviates irradiation-induced End-MT. Our coculture model showed that transcriptional downregulation of endothelial Robo4 reduces HSPC proliferation and increases HSC quiescence and apoptosis. However, Robo4 overexpression mitigated the damaged endothelium's suppressive effects on HSC proliferation and differentiation. These findings indicate that by controlling End-MT, Robo4 preserves microvascular integrity after radiation preconditioning, protects endothelial function, and lessens the inhibitory effect of damaged endothelium on hematopoietic reconstitution.

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.

The silencing of NREP aggravates OA cartilage damage through the TGF-β1/Smad2/3 pathway in chondrocytes

Background

Osteoarthritis (OA) is a common chronic degenerative joint disease. Due to the limited understanding of its complex pathological mechanism, there is currently no effective treatment that can alleviate or even reverse cartilage damage associated with OA. With improvement in public databases, researchers have successfully identified the key factors involved in the occurrence and development of OA through bioinformatics analysis. The aim of this study was to screen for the differentially expressed genes (DEGs) between the normal and OA cartilage through bioinformatics, and validate the function of the TGF-β1/Smad2/3 pathway-related neuron regeneration related protein (NREP) in the articular cartilage.

Methods

The DEGs between the cartilage tissues of OA patients and healthy controls were screened by bioinformatics, and functionally annotated by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. The expression levels of the DEG in human and murine OA cartilage was verified by reverse transcription-quantitative PCR (RT-qPCR), Western blotting and immunohistochemistry (IHC). RT-qPCR, Western-blotting, Cell Counting Kit-8(CCK8) and EdU assays were used to evaluate the effects of knocking down NREP in normal chondrocytes, and the molecular mechanisms were investigated by RT-qPCR, Western blotting and IHC.

Results

In this study, we identified NREP as a DEG in OA through bioinformatics analysis, and found that NREP was downregulated in the damaged articular cartilage of OA patients and mouse model with surgically-induced OA. In addition, knockdown of NREP in normal chondrocytes reduced their proliferative capacity, which is the pathological basis of OA. At the molecular level, knock-down of NREP inactivated the TGF-β1/Smad2/3 pathway, resulting in the downregulation of the anabolic markers Col2a1 and Sox9, and an increase in the expression of the catabolic markers MMP3 and MMP13.

Conclusion

NREP plays a key role in the progression of OA by regulating the TGF-β1/Smad2/3 pathway in chondrocytes, and warrants further study as a potential therapeutic target.

Scleral PERK and ATF6 as targets of myopic axial elongation of mouse eyes

Axial length is the primary determinant of eye size, and it is elongated in myopia. However, the underlying mechanism of the onset and progression of axial elongation remain unclear. Here, we show that endoplasmic reticulum (ER) stress in sclera is an essential regulator of axial elongation in myopia development through activation of both PERK and ATF6 axis followed by scleral collagen remodeling. Mice with lens-induced myopia (LIM) showed ER stress in sclera. Pharmacological interventions for ER stress could induce or inhibit myopia progression. LIM activated all IRE1, PERK and ATF6 axis, and pharmacological inhibition of both PERK and ATF6 suppressed myopia progression, which was confirmed by knocking down above two genes via CRISPR/Cas9 system. LIM dramatically changed the expression of scleral collagen genes responsible for ER stress. Furthermore, collagen fiber thinning and expression of dysregulated collagens in LIM were ameliorated by 4-PBA administration. We demonstrate that scleral ER stress and PERK/ATF6 pathway controls axial elongation during the myopia development in vivo model and 4-PBA eye drop is promising drug for myopia suppression/treatment.

Endoglin aggravates peritoneal fibrosis by regulating the activation of TGF-β/ALK/Smads signaling

Background: Peritoneal fibrosis (PF) is an intractable complication in patients on long-term peritoneal dialysis (PD). Transforming growth factor-β (TGF-β) is a key pro-fibrogenic factor involved in PD-associated PF, and endoglin, as a coreceptor for TGF-β, plays a role in balancing the TGF-β signaling pathway. Here, we investigated whether endoglin could be a potential therapeutic target for PF.

Methods:In vivo, we established PF model in SD rats by daily intraperitoneal injection of peritoneal dialysis fluids (PDF) containing 4.25% glucose for 6 weeks and downregulated endoglin expression by tail vein injection of AAV9-ENG on day 14 to assess the effect of endoglin on peritoneal morphology and markers related to fibrosis, angiogenesis, and epithelial-mesenchymal transition (EMT). In vitro, we treated human peritoneal mesothelial cells (HPMCs) transfected with ENG siRNA in high glucose medium to explore the potential mechanism of endoglin in PF.

Results: Compared to control group, continuous exposure to biologically incompatible PDF induced exacerbated PF, accompanied by a significant increase in endoglin expression. Conversely, knockdown of endoglin ameliorated peritoneal injury characterized by increased peritoneal thickening and collagen deposition, angiogenesis, as well as EMT. Consistently, HPMCs cultured in high glucose medium underwent the EMT process and exhibited over-expression of fibronectin, collagen type I, vascular endothelial growth factor (VEGF), whereas these aforementioned alterations were alleviated after ENG siRNA transfection. In addition, we also found that ENG siRNA inhibited TGF-β-induced phosphorylation of Smad2/3 and Smad1/5/9 in HPMCs treated with high glucose (HG).

Conclusion: Our findings confirmed for the first time that endoglin exacerbated PF by regulating the activation of TGF-β/ALK/Smads signaling, which will provide a novel potential therapeutic target in PF.

Endothelial Activin Receptor-Like Kinase 1 (ALK1) Regulates Myofibroblast Emergence and Peritubular Capillary Stability in the Early Stages of Kidney Fibrosis

Renal tubulo-interstitial fibrosis is characterized by the excessive accumulation of extracellular matrix (ECM) in the tubular interstitium during chronic kidney disease. The main source of ECM proteins are emerging and proliferating myofibroblasts. The sources of myofibroblasts in the renal tubular interstitium have been studied during decades, in which the epithelial contribution of the myofibroblast population through the epithelial-to-mesenchymal (EMT) process was assumed to be the major mechanism. However, it is now accepted that the EMT contribution is very limited and other mechanisms such as the proliferation of local resident fibroblasts or the transdifferentiation of endothelial cells seem to be more relevant. Activin receptor-like kinase 1 (ALK1) is a type I receptor which belongs to the transforming growth factor beta (TGF-β) superfamily, with a key role in tissue fibrosis and production of ECM by myofibroblast. Predominantly expressed in endothelial cells, ALK1 also plays an important role in angiogenesis and vessel maturation, but the relation of these processes with kidney fibrosis is not fully understood. We show that after 3 days of unilateral ureteral obstruction (UUO), ALK1 heterozygous mice (Alk1^+/−) display lower levels of kidney fibrosis associated to a lower number of myofibroblasts. Moreover, Alk1^+/− mice have a lower degree of vascular rarefaction, showing improved peritubular microvasculature after UUO. All these data suggest an important role of ALK1 in regulating vascular rarefaction and emergence of myofibroblasts.

Strontium Regulates the Proliferation and Differentiation of Isolated Primary Bovine Chondrocytes via the TGFβ/SMAD Pathway

The present study evaluated the effects of strontium (Sr) on proliferation and differentiation of chondrocytes isolated from dairy cows, and whether Sr exerts its effects via transforming growth factor β (TGFβ) signaling. The chondrocytes were isolated from patellar cartilage from newborn Holstein bull calves (n = 3, 1 day old, 38.0 ± 2.8 kg, fasting) within 15 min after euthanasia, and treated with different concentrations of Sr (0, 0.1, 1, and 10 μg/ml, as SrCl₂·6H₂O). After pretreatment with or without activin receptor-like kinase 5 (ALK5) inhibitor (10 μM SB-505124) for 4 h, chondrocytes were incubated with Sr for another 4 h. Overall effects of Sr were evaluated relative to NaCl as the control. In contrast, the 1 μg/ml Sr-treated group served as the control to determine effects of preincubating with SB-505124. Western blot and qRT-PCR were used for measuring expression of proliferation-, differentiation-, and TGFβ1-responsive factors. Data were analyzed using one-way ANOVA in GraphPad Prism 7.0. Incubation with all doses of Sr increased TGFβ1/ALK5-induced SMAD3 phosphorylation, and at 10 μg/ml it inhibited ALK1-induced SMAD1/5/9 phosphorylation. Expression of mRNA and protein of the proliferation-responsive factors type Ⅱ Collagen α1 (COL2A1) and aggrecan (ACAN) was induced by Sr at 1 μg/ml. In contrast, Sr at 10 μg/ml inhibited the expression of differentiation-responsive factors type Ⅹ Collagen α1 (COL10A1) and secreted phosphoprotein 1 (SPP1), and at 1 μg/ml it had the same effect on alkaline phosphatase (ALPL) mRNA and protein levels. Cells were stained with PI/RNase Staining buffer to assess cell cycle activity using flow-cytometry. Incubation with Sr at 1 and 10 μg/ml induced an increase in the number of cells in the S-phase, leading to an increase in the proliferation index. Incubation with SB-505124 inhibited phosphorylation of SMAD3. Abundance of ACAN and COL2A1 mRNA and protein was lower when cells were pre-incubated with SB-505124. Overall, data indicated that Sr promotes proliferation and inhibits differentiation of primary chondrocytes by directing TGFβ1 signaling towards SMAD3 phosphorylation rather than SMAD1/5/9 phosphorylation. Whether these effects occur in vivo remains to be determined and could impact future application of Sr as an experimental tool in livestock.

Krüppel-like factors in bone biology

The krüppel-like factor (KLF) family is a group of zinc finger transcription factors and contributes to different cellular processes such as differentiation, proliferation, migration, and apoptosis. While different studies show the roles of this family in skeletal development-specifically in chondrocyte and osteocyte development and bone homeostasis-there are few reviews summarizing their importance. To fill this gap, this review discusses current knowledge on different functions of the KLF family during skeletal development, including their roles in stem cell maintenance and differentiation, cell apoptosis, and cell cycle. To understand the importance of the KLF family, we also review genotype-phenotype correlations in different animal models. We also discuss how KLF proteins function through different signaling pathways and display their paramount importance in skeletal development. To highlight their roles in cartilage- or bone-related cells, we also use single-cell RNA sequencing publicly available data on mouse hindlimb. We also challenge our knowledge of how the KLF family is epigenetically regulated-e.g., using DNA methylation, histone modifications, and noncoding RNAs-during chondrocyte and osteocyte development.

Transcriptome Analysis Reveals Novel Genes Associated with Cartilage Degeneration in Posttraumatic Osteoarthritis Progression

OBJECTIVE

The current therapeutic strategy for posttraumatic osteoarthritis (PTOA) focuses on early intervention to attenuate disease progression, preserve joint function, and defer joint replacement timing. Sequential transcriptomic changes of articular cartilage in a rat model were investigated to explore the molecular mechanism in early PTOA progression.

DESIGN

Anterior cruciate ligament transection and medial meniscectomy (ACLT + MMx)-induced PTOA model was applied on male Wistar rats. Articular cartilages were harvested at time 0 (naïve), 2 week, and 4 weeks after surgery. Affymetrix Rat genome 230 2.0 array was utilized to analyze the gene expression changes of articular cartilages.

RESULTS

We identified 849 differentially expressed genes (DEGs) at 2 weeks and 223 DEGs at 4 weeks post-ACLT + MMx surgery compared with time 0 (naïve group). Gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed to gain further insights from these DEGs. 22 novel genes and 1 novel KEGG pathway (axon guidance) in cartilage degeneration of osteoarthritis were identified. Axon guidance molecules-Gnai1, Sema4d, Plxnb1, and Srgap2 commonly dysregulated in PTOA progression. Gnai1 gene showed a concordant change in protein expression by immunohistochemistry staining.

CONCLUSIONS

Our study identified 22 novel dysregulated genes and axon guidance pathway associated with articular cartilage degeneration in PTOA progression. These findings provide the potential candidates of biomarkers and therapeutic targets for further investigation.

Role of the hippo signaling pathway in the extracellular matrix degradation of chondrocytes induced by fluoride exposure

To identify the role of the Hippo signaling pathway in the extracellular matrix degradation of chondrocytes induced by fluoride exposure. Environmental response genes (ERGs) of bone injury induced by fluoride exposure were obtained from the Comparative Toxicogenomics Database, and annotated by STRING for KEGG pathway enrichment analysis. The CCK-8 kit was used to measure the proliferation of ATDC5 cells. The malondialdehyde (MDA), total antioxidant capacity (T-AOC), total superoxide dismutase (T-SOD), and glutathione peroxidase (GSH-PX) levels in ATDC5 cells were measured using oxidative stress detection kit. Western blot analysis was used to measure the p-MST1/2, p-LATS1/2, and p-YAP/YAP1 expression levels in the Hippo pathway and the COL2A1, ACAN and MMP13 expression levels in the cartilage matrix. Localizations of YAP1 and COL2A1 proteins in chondrocytes were performed using cell immunofluorescence. Continuous data from the multiple groups were compared using one-way analysis of variance, and then the differences between groups were tested with Dunnett's t-test, with the test level α = 0.05. The 145 ERGs of bone injury induced by fluoride exposure were identified, and KEGG enrichment analysis revealed Hippo signaling pathways significantly related to bone injury. A CCK-8 assay revealed that the viability of the ATDC5 cells was significantly decreased with increased fluorine concentration. The MDA content in 20 mg/L sodium fluoride (NaF) exposure group was significantly higher than that in the control group, the T-SOD, T-AOC and GSH-PX activities in 15 and 20 mg/L NaF exposure groups were significantly lower than those in the control group (P < 0.05). Western blot results showed the protein levels of p-MST1/2, p-LATS1/2 and p-YAP1 in 15 and 20 mg/L NaF exposure groups were significantly lower than those in the control group, while the YAP1 protein level in 20 mg/L NaF group was significantly higher than that in the control group. The COL2A1 and ACAN proteins in 20 mg/L NaF group were significantly decreased, while the MMP13 protein level in 15 and 20 mg/L NaF groups were significantly increased (P < 0.05). It was observed that the expression of YAP1 protein expression level in the cytoplasm decreased with the increased fluoride exposure, whereas that the expression level of YAP1 protein in the nucleus increased. Fluoride inhibited the proliferation of ATDC5 cells, induced oxidative stress, inhibited the activity of the Hippo pathway, and eventually led to cartilage matrix degradation.

Impact of donor nutritional balance on the growth and development of mesenchymal stem cells from caprine umbilical cord Wharton´s jelly

Mesenchymal stem cells (MSCs) from the umbilical cord (UC) have aroused considerable interest. However, little is known about the maternal effect on these cells. The aim of this study was to verify the impact of the nutritional status of donor goats on the growth and differentiation of MSCs from the UC. At parturition, 19 goats were grouped based on their low or high body mass index (low BMI, LBMI, n = 9; and high BMI, HBMI, n = 10). UCs were collected during delivery and Wharton's jelly (WJ) fragments cultured. WJ-MSCs were differentiated into osteocytes, adipocytes, chondrocytes, and the population doubling time (PDT) was determined. Samples of WJ-MSCs were also used to verify the expression of the CD90, CD73, CD34, CD45, and CD105 genes. Media used for WJ-MSC primary cultures were analyzed using near-infrared spectroscopy. The lag phase was 7.5 ± 0.6 days and the entire culture took 26.7 ± 1.3 days, with a cell proliferation rate of 8.500 cells/day. The mean PDT from subculture was 30.0 ± 0.7 h. The CD105 gene was sub-expressed in LBMI, and the spectra of the spent media from the second to fourth day of WJ-MSC primary culture were segregated into negative scores by multivariate analysis. We conclude that, in goats, the nutritional balance of the donor did not affect the in vitro growth of MSCs derived from the UC. However, the molecular profile observed in the low BMI group suggests that the use of MSCs for therapeutic purposes should be considered more carefully.

Fluid shear stress generates a unique signaling response by activating multiple TGFβ family type I receptors in osteocytes

Bone is a dynamic tissue that constantly adapts to changing mechanical demands. The transforming growth factor beta (TGFβ) signaling pathway plays several important roles in maintaining skeletal homeostasis by both coupling the bone‐forming and bone‐resorbing activities of osteoblasts and osteoclasts and by playing a causal role in the anabolic response of bone to applied loads. However, the extent to which the TGFβ signaling pathway in osteocytes is directly regulated by fluid shear stress (FSS) is unknown, despite work suggesting that fluid flow along canaliculi is a dominant physical cue sensed by osteocytes following bone compression. To investigate the effects of FSS on TGFβ signaling in osteocytes, we stimulated osteocytic OCY454 cells cultured within a microfluidic platform with FSS. We find that FSS rapidly upregulates Smad2/3 phosphorylation and TGFβ target gene expression, even in the absence of added TGFβ. Indeed, relative to treatment with TGFβ, FSS induced a larger increase in levels of pSmad2/3 and Serpine1 that persisted even in the presence of a TGFβ receptor type I inhibitor. Our results show that FSS stimulation rapidly induces phosphorylation of multiple TGFβ family R‐Smads by stimulating multimerization and concurrently activating several TGFβ and BMP type I receptors, in a manner that requires the activity of the corresponding ligand. While the individual roles of the TGFβ and BMP signaling pathways in bone mechanotransduction remain unclear, these results implicate that FSS activates both pathways to generate a downstream response that differs from that achieved by either ligand alone.

Endoglin in the Spotlight to Treat Cancer

A spotlight has been shone on endoglin in recent years due to that fact of its potential to serve as both a reliable disease biomarker and a therapeutic target. Indeed, endoglin has now been assigned many roles in both physiological and pathological processes. From a molecular point of view, endoglin mainly acts as a co-receptor in the canonical TGFβ pathway, but also it may be shed and released from the membrane, giving rise to the soluble form, which also plays important roles in cell signaling. In cancer, in particular, endoglin may contribute to either an oncogenic or a non-oncogenic phenotype depending on the cell context. The fact that endoglin is expressed by neoplastic and non-neoplastic cells within the tumor microenvironment suggests new possibilities for targeted therapies. Here, we aimed to review and discuss the many roles played by endoglin in different tumor types, as well as the strong evidence provided by pre-clinical and clinical studies that supports the therapeutic targeting of endoglin as a novel clinical strategy.

Endoglin Level Is Critical for Cartilage Tissue Formation In Vitro by Passaged Human Chondrocytes

Transforming growth factor beta (TGFβ) signaling is required for in vitro chondrogenesis. In animal models of osteoarthritis (OA), TGFβ receptor alterations are detected in chondrocytes in severe OA cartilage. It is not known whether such changes are dependent on the grade of human OA and if they affect chondrogenesis. Thus, the purpose of this study was to determine if human OA chondrocytes obtained from low-grade or high-grade disease could form cartilage tissue and to assess the role of the co-receptors, endoglin (ENG) and TGFβ receptor 3 (TGFBRIII), in the regulation of this tissue generation in vitro. We hypothesized that the grade of OA disease would not affect the ability of cells to form cartilage tissue and that the TGFβ co-receptor, ENG, would be critical to regulating tissue formation. Chondrocytes isolated from low-grade OA or high-grade OA human articular cartilage (AC) were analyzed directly (P0) or passaged in monolayer to P2. Expression of the primary TGFβ receptor ALK5, and the co-receptors ENG and TGFβRIII, was assessed by image flow cytometry. To assess the ability to form cartilaginous tissue, cells were placed in three-dimensional culture at high density and cultured in chondrogenic media containing TGFβ3. ENG knockdown was used to determine its role in regulating tissue formation. Overall, grade-specific differences in expression of ALK5, ENG, and TGFβRIII in primary or passaged chondrocytes were not detected; however, ENG expression increased significantly after passaging. Despite the presence of ALK5, P0 cells did not form cartilaginous tissue. In contrast, P2 cells derived from low-grade and high-grade OA AC formed hyaline-like cartilaginous tissues of similar quality. Knockdown of ENG in P2 cells inhibited cartilaginous tissue formation compared to controls indicating that the level of ENG protein expression is critical for in vitro chondrogenesis by passaged articular chondrocytes. This study demonstrates that it is not the grade of OA, but the levels of ENG in the presence of ALK5 that influences the ability of human passaged articular chondrocytes to form cartilaginous tissue in vitro in 3D culture. This has implications for cartilage repair therapies. Impact statement These findings are important clinically, given the limited availability of osteoarthritis (OA) cartilage tissue. Being able to use cells from all grades of OA will increase our ability to obtain sufficient cells for cartilage repair. In addition, it is possible that endoglin (ENG) levels, in the presence of ALK5 expression, may be suitable to use as biomarkers to identify cells able to produce cartilage.

The complexity of TGFβ/activin signaling in regeneration

The role of transforming growth factor β TGFβ/activin signaling in wound repair and regeneration is highly conserved in the animal kingdom. Various studies have shown that TGF-β/activin signaling can either promote or inhibit different aspects of the regeneration process (i.e., proliferation, differentiation, and re-epithelialization). It has been demonstrated in several biological systems that some of the different cellular responses promoted by TGFβ/activin signaling depend on the activation of Smad-dependent or Smad-independent signal transduction pathways. In the context of regeneration and wound healing, it has been shown that the type of R-Smad stimulated determines the different effects that can be obtained. However, neither the possible roles of Smad-independent pathways nor the interaction of the TGFβ/activin pathway with other complex signaling networks involved in the regenerative process has been studied extensively. Here, we review the important aspects concerning the TGFβ/activin signaling pathway in the regeneration process. We discuss data regarding the role of TGF-β/activin in the most common animal regenerative models to demonstrate how this signaling promotes or inhibits regeneration, depending on the cellular context.

Toward Regulatory Effects of Curcumin on Transforming Growth Factor-Beta Across Different Diseases: A Review

Immune response, proliferation, migration and angiogenesis are juts a few of cellular events that are regulated by transforming growth factor-β (TGF-β) in cells. A number of studies have documented that TGF-β undergoes abnormal expression in different diseases, e.g., diabetes, cancer, fibrosis, asthma, arthritis, among others. This has led to great fascination into this signaling pathway and developing agents with modulatory impact on TGF-β. Curcumin, a natural-based compound, is obtained from rhizome and roots of turmeric plant. It has a number of pharmacological activities including antioxidant, anti-inflammatory, anti-tumor, anti-diabetes and so on. Noteworthy, it has been demonstrated that curcumin affects different molecular signaling pathways such as Wnt/β-catenin, Nrf2, AMPK, mitogen-activated protein kinase and so on. In the present review, we evaluate the potential of curcumin in regulation of TGF-β signaling pathway to corelate it with therapeutic impacts of curcumin. By modulation of TGF-β (both upregulation and down-regulation), curcumin ameliorates fibrosis, neurological disorders, liver disease, diabetes and asthma. Besides, curcumin targets TGF-β signaling pathway which is capable of suppressing proliferation of tumor cells and invading cancer cells.

Association between gene polymorphisms of TGF-β and Smad3 and susceptibility to arthritis: a meta-analysis

OBJECTIVES

This meta-analysis was performed to investigate the associations between single-nucleotide polymorphisms (SNPs) in the TGF- β and Smad3 genes and arthritis.

METHODS

A meta-analysis was performed in STATA 14.0, with publication bias and meta-regression analysis. All types of arthritis were included, and subgroup analyses were performed to interpret variations among different types of arthritis.

RESULTS

Twenty-two qualified studieswere selected to analyze the pooled accuracy, and 4 SNP sites were involved. The analysis of the TGFB1 SNP rs1800470 showed an association with arthritis in allelic (P = 0.011), homozygous (P = 0.034) and recessive (P = 0.021) genetic models. The analysis of the TGFB1 SNP rs1800471 demonstrated a close association with rheumatoid arthritis (RA) in homozygous (P = 0.000, 95%) and recessive (P = 0.008) models. The analysis of the SMAD3 SNP rs12901499 revealed a close association with osteoarthritis (OA) in the allelic (P = 0.001) model.

CONCLUSION

This research showed that genetic variants of the TGF-β pathway impact arthritis. The polymorphisms rs1800470, rs1800471 and rs12901499 were correlated with a higher prevalence of arthritis.

Mechanotransduction pathways in the regulation of cartilage chondrocyte homoeostasis

Mechanical stress plays a critical role in cartilage development and homoeostasis. Chondrocytes are surrounded by a narrow pericellular matrix (PCM), which absorbs dynamic and static forces and transmits them to the chondrocyte surface. Recent studies have demonstrated that molecular components, including perlecan, collagen and hyaluronan, provide distinct physical properties for the PCM and maintain the essential microenvironment of chondrocytes. These physical signals are sensed by receptors and molecules located in the cell membrane, such as Ca²⁺ channels, the primary cilium and integrins, and a series of downstream molecular pathways are involved in mechanotransduction in cartilage. All mechanoreceptors convert outside signals into chemical and biological signals, which then regulate transcription in chondrocytes in response to mechanical stresses. This review highlights recent progress and focuses on the function of the PCM and cell surface molecules in chondrocyte mechanotransduction. Emerging understanding of the cellular and molecular mechanisms that regulate mechanotransduction will provide new insights into osteoarthritis pathogenesis and precision strategies that could be used in its treatment.

The effects of inhibiting the activation of hepatic stellate cells by lignan components from the fruits of Schisandra chinensis and the mechanism of schisanhenol

Liver fibrosis is a pathological manifestation induced by chronic liver injury and may cause cirrhosis and liver cancer with the chronic progression of fibrosis. During the onset and progression of liver fibrosis, the activation of hepatic stellate cells (HSCs) is the core mechanism for the secretion of many extracellular matrices to induce fibrosis. Lignans are reportedly the main effective components of Schisandra chinensis with good anti-fibrosis effects. In this study, we compared the inhibiting effects of the seven lignan components from S. chinensis on HSC activation. We found that the seven lignans inhibited the activation of human HSCs (LX-2) in various degrees. Among all lignans, schisanhenol showed the best effect in inhibiting the activation of LX-2 with a dose-effect relationship. Sal also inhibited the phosphorylations of Smad1, Smad2, Smad3, extracellular regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), p38, and nuclear transcription factor-κB (NF-κB), as well as downregulated Smad4. All these findings suggested that schisanhenol may ameliorate liver fibrosis by inhibiting the transforming growth factor β (TGF-β)/Smad and mitogen-activated protein kinase (MAPK) signaling pathways. Remarkably, schisanhenol may be a potential anti-liver fibrosis drug and warrants further research.

Non-canonical (non-SMAD2/3) TGF-β signaling in fibrosis: Mechanisms and targets

Transforming growth factor (TGF)-β uses several intracellular signaling pathways besides canonical ALK5-Smad2/3 signaling to regulate a diverse array of cellular functions. Several of these so-called non-canonical (non-Smad2/3) pathways have been implicated in the pathogenesis of fibrosis and may therefore represent targets for therapeutic intervention. This review summarizes our current knowledge on the mechanisms of non-canonical TGF-β signaling in fibrosis, the potential molecular targets and the use of agonists/antagonists for therapeutic intervention.

Biomarker expression related to chondromatosis in the temporomandibular joint

Background: Synovial chondromatosis is usually detected at a late stage based on free bodies in joint space. The purpose of this study was to identify biomarkers for cell proliferation and chondrogenesis in the primary stage of synovial chondromatosis in the temporomandibular joint (TMJ).Clinical Presentation: A 67-year-old female was referred for right side TMJ pain. Magnetic resonance imaging (MRI) findings suggested an intra-joint space lesion, but no free bodies were observed intraoperatively. Pathological examination led to diagnosis of Milgram stage 1 synovial chondromatosis. Biomarkers related to mesenchymal stem cells (MSCs), cell proliferation, and chondrogenesis were observed in immunohistopathological examination of specimens.Clinical Relevance: The findings suggest that MSCs with chondrogenic potential and growth activity are present at the start of cartilage formation in the synovial membrane. These cells may be the origin of disease. Those findings improve understanding of the etiology and disease progression of synovial chondromatosis in the TMJ.

Bioreactor-Controlled Physoxia Regulates TGF-β Signaling to Alter Extracellular Matrix Synthesis by Human Chondrocytes

Culturing articular chondrocytes under physiological oxygen tension exerts positive effects on their extracellular matrix synthesis. The underlying molecular mechanisms which enhance the chondrocytic phenotype are, however, still insufficiently elucidated. The TGF-β superfamily of growth factors, and the prototypic TGF-β isoforms in particular, are crucial in maintaining matrix homeostasis of these cells. We employed a feedback-controlled table-top bioreactor to investigate the role of TGF-β in microtissues of human chondrocytes over a wider range of physiological oxygen tensions (i.e., physoxia). We compared 1%, 2.5%, and 5% of partial oxygen pressure (pO₂) to the ‘normoxic’ 20%. We confirmed physoxic conditions through the induction of marker genes (PHD3, VEGF) and oxygen tension-dependent chondrocytic markers (SOX9, COL2A1). We identified 2.5% pO₂ as an oxygen tension optimally improving chondrocytic marker expression (ACAN, COL2A1), while suppressing de-differentiation markers (COL1A1,COL3A1). Expression of TGF-β isoform 2 (TGFB2) was, relatively, most responsive to 2.5% pO₂, while all three isoforms were induced by physoxia. We found TGF-β receptors ALK1 and ALK5 to be regulated by oxygen tension on the mRNA and protein level. In addition, expression of type III co-receptors betaglycan and endoglin appeared to be regulated by oxygen tension as well. R-Smad signaling confirmed that physoxia divergently regulated phosphorylation of Smad1/5/8 and Smad2/3. Pharmacological inhibition of canonical ALK5-mediated signaling abrogated physoxia-induced COL2A1 and PAI-1 expression. Physoxia altered expression of hypertrophy markers and that of matrix metalloproteases and their activity, as well as expression ratios of specific proteins (Sp)/Krüppel-like transcription factor family members SP1 and SP3, proving a molecular concept of ECM marker regulation. Keeping oxygen levels tightly balanced within a physiological range is important for optimal chondrocytic marker expression. Our study provides novel insights into transcriptional regulations in chondrocytes under physoxic in vitro conditions and may contribute to improving future cell-based articular cartilage repair strategies.

Pathological mechanisms and therapeutic outlooks for arthrofibrosis

Arthrofibrosis is a fibrotic joint disorder that begins with an inflammatory reaction to insults such as injury, surgery and infection. Excessive extracellular matrix and adhesions contract pouches, bursae and tendons, cause pain and prevent a normal range of joint motion, with devastating consequences for patient quality of life. Arthrofibrosis affects people of all ages, with published rates varying. The risk factors and best management strategies are largely unknown due to a poor understanding of the pathology and lack of diagnostic biomarkers. However, current research into the pathogenesis of fibrosis in organs now informs the understanding of arthrofibrosis. The process begins when stress signals stimulate immune cells. The resulting cascade of cytokines and mediators drives fibroblasts to differentiate into myofibroblasts, which secrete fibrillar collagens and transforming growth factor-β (TGF-β). Positive feedback networks then dysregulate processes that normally terminate healing processes. We propose two subtypes of arthrofibrosis occur: active arthrofibrosis and residual arthrofibrosis. In the latter the fibrogenic processes have resolved but the joint remains stiff. The best therapeutic approach for each subtype may differ significantly. Treatment typically involves surgery, however, a pharmacological approach to correct dysregulated cell signalling could be more effective. Recent research shows that myofibroblasts are capable of reversing differentiation, and understanding the mechanisms of pathogenesis and resolution will be essential for the development of cell-based treatments. Therapies with significant promise are currently available, with more in development, including those that inhibit TGF-β signalling and epigenetic modifications. This review focuses on pathogenesis of sterile arthrofibrosis and therapeutic treatments.

Increased TGF-β and BMP Levels and Improved Chondrocyte-Specific Marker Expression In Vitro under Cartilage-Specific Physiological Osmolarity

During standard expansion culture (i.e., plasma osmolarity, 280 mOsm) human articular chondrocytes dedifferentiate, making them inappropriate for autologous chondrocyte implantation to treat cartilage defects. Increasing the osmolarity of culture media to physiological osmolarity levels of cartilage (i.e., 380 mOsm), increases collagen type II (COL2A1) expression of human articular chondrocytes in vitro, but the underlying molecular mechanism is not fully understood. We hypothesized that TGF-β superfamily signaling may drive expression of COL2A1 under physiological osmolarity culture conditions. Human articular chondrocytes were cultured in cytokine-free medium of 280 or 380 mOsm with or without siRNA mediated TGF-β2 knockdown (RNAi). Expression of TGF-β isoforms, and collagen type II was evaluated by RT-qPCR and immunoblotting. TGF-β2 protein secretion was evaluated using ELISA and TGF-β bioactivity was determined using an established reporter assay. Involvement of BMP signaling was investigated by culturing human articular chondrocytes in the presence or absence of BMP inhibitor dorsomorphin and BMP bioactivity was determined using an established reporter assay. Physiological cartilage osmolarity (i.e., physosmolarity) most prominently increased TGF-β2 mRNA expression and protein secretion as well as TGF-β bioactivity. Upon TGF-β2 isoform-specific knockdown, gene expression of chondrocyte marker COL2A1 was induced. TGF-β2 RNAi under physosmolarity enhanced TGF-β bioactivity. BMP bioactivity increased upon physosmotic treatment, but was not related to TGF-β2 RNAi. In contrast, dorsomorphin inhibited COL2A1 mRNA expression in human articular chondrocytes independent of the osmotic condition. Our data suggest a role for TGF-β superfamily member signaling in physosmolarity-induced mRNA expression of collagen type II. As physosmotic conditions favor the expression of COL2A1 independent of our manipulations, contribution of other metabolic, post-transcriptional or epigenetic factors cannot be excluded in the underlying complex and interdependent regulation of marker gene expression. Dissecting these molecular mechanisms holds potential to further improve future cell-based chondral repair strategies.

A dual role of TGF-β in human osteoclast differentiation mediated by Smad1 versus Smad3 signaling

TGF-β1 is highly expressed in the synovial tissue of patients with rheumatoid arthritis and is known as a cytokine that plays an important role in tissue repair and immune cell regulation. However, the role of TGF-β1 is still unclear in osteoclastogenesis. In this study, we examined the effect of TGF-β1 on osteoclast differentiation and the underlying mechanism using healthy human peripheral blood monocytes. TGF-β1 was found to inhibit osteoclast differentiation and decrease the expression of osteoclast-specific genes such as acid phosphatase 5, tartrate resistant and cathepsin K. Levels of NFAT1, an important transcription factor in osteoclastogenesis, were also reduced. In addition, TGF-β1 suppressed receptor activator of NF-κB (RANK) ligand-induced NF-κB and p38 MAPK signaling. Inhibition of osteoclast differentiation by TGF-β1 was reversed by 1 μM SB431542 (an inhibitor of ALK4/5/7), which inhibited TGF-β1-induced phosphorylation of SMAD1, but not that of SMAD3. TGF-β1 also restricted RANK expression, and this was partially reversed by 1 μM SB431542. In contrast, the inhibition of SMAD3 by SIS3 (an inhibitor of SMAD3) reduced the osteoclast formation. TGF-β1 has both inhibitory and stimulatory effects on human osteoclast differentiation, and that these opposing functions are mediated by SMAD1 and SMAD3 signaling, respectively.

Association between SMAD3 gene polymorphisms and osteoarthritis risk: a systematic review and meta-analysis

Objective

Several studies have been performed to investigate the association between SMAD3 gene polymorphism and osteoarthritis (OA), but the results were inconclusive. This study aims to determine whether SMAD3 polymorphism is associated with risk of OA.

Method

A comprehensive literature search in PubMed, Embase, and ISI Web of Science for relevant studies was performed. After extracting data from eligible studies, we chose the fixed or random effect model according to the heterogeneity test. Estimation of publication bias and sensitivity analysis were conducted to confirm the stability of this meta-analysis.

Results

In total, 10 studies from 6 articles with 5093 OA patients and 5699 controls were enrolled in this meta-analysis. The combined results revealed significant association between SMAD3 rs12901499 polymorphism and the risk of OA (allele model: OR 1.21, 95% CI 1.07–1.38). Subgroup analysis revealed that G allele increased the risk of OA in Caucasians, but not in Asians (allele model: Caucasians: OR 1.31, 95% CI 1.18–1.44; Asians: OR 1.24, 95% CI 0.95–1.61). And the pooled results revealed significant association between SMAD3 rs12901499 polymorphism and both knee and hip OA (knee OA: OR 1.18, 95% CI 1.04–1.34; hip OA: OR 1.31, 95% CI 1.18–1.44).

Conclusion

The current meta-analysis revealed that the G variant of SMAD3 rs12901499 polymorphism increased the risk of OA in Caucasians. Further well-designed studies with larger sample size in different ethnic populations are required to confirm these results.

Electronic supplementary material

The online version of this article (10.1186/s13018-018-0939-2) contains supplementary material, which is available to authorized users.

SMAD3 gene rs12901499 polymorphism increased the risk of osteoarthritis

A growing body of evidence suggested that smad family member 3 gene rs12901499 polymorphism was associated with the risk of osteoarthritis. However, the results of previous studies were conflicting. In the present study, we assessed whether smad family member 3 gene rs12901499 polymorphism was associated with the risk of osteoarthritis by the meta-analysis. We searched in the databases of PubMed, Embase, and CNKI. Pooled odds ratios and 95% confidence intervals were calculated. Seven papers involving 11 studies (5344 cases and 9080 controls) analyzed the association between smad family member 3 gene rs12901499 polymorphism and osteoarthritis risk. This meta-analysis confirmed that smad family member 3 gene rs12901499 polymorphism increased the risk of osteoarthritis. Stratification analysis of ethnicity found that rs12901499 polymorphism increased the risk of osteoarthritis among both Asians and Caucasians [G vs A: Asians, OR and 95%CI, 1.34(1.07, 1.69), P=0.012; Caucasians, OR and 95%CI, 1.21(1.13, 1.29), P<0.001]. In addition, subgroup analysis by type of osteoarthritis revealed that smad family member 3 gene rs12901499 polymorphism was correlated with the increased risk of hip osteoarthritis, but not associated with knee osteoarthritis. Sensitivity analysis did not draw different findings. In conclusion, this meta-analysis indicates that smad family member 3 gene rs12901499 polymorphism increased the risk of osteoarthritis.

Differential Role of Transforming Growth Factor-beta in an Osteoarthritic or a Healthy Joint

Transforming growth factor-β (TGF-β) is a cytokine that plays an important role in both normal joints and joints affected by osteoarthritis (OA), the most common joint disease. However, the role of this pleiotropic cytokine in a normal healthy joint is very different from its role in an OA joint. In a normal synovial joint, active TGF-β is only present after joint loading and only for a short period. In contrast, permanent and high levels of active TGF-β are detected in OA joints. Due to this difference in levels and exposure period of joint cells to active TGF-β, the function of TGF-β is strikingly different in normal and OA joints. The consequences of this difference in TGF-β levels on joint homeostasis and pathological changes in OA joints are discussed in this review.

Endoglin in human liver disease and murine models of liver fibrosis-A protective factor against liver fibrosis

BACKGROUND & AIMS

Liver fibrosis is the outcome of chronic liver injury. Transforming growth factor-β (TGF-β) is a major profibrogenic cytokine modulating hepatic stellate cell (HSC) activation and extracellular matrix homeostasis. This study analyses the effect of Endoglin (Eng), a TGF-β type III auxiliary receptor, on fibrogenesis in two models of liver injury by HSC-specific endoglin deletion.

METHODS

Eng expression was measured in human and murine samples of liver injury. After generating GFAP^Cre(+) Eng^ΔHSC mice, the impact of Endoglin deletion on chronic liver fibrosis was analysed. For in vitro analysis, Eng^flox/flox HSCs were infected with Cre-expressing virus to deplete Endoglin and fibrogenic responses were analysed.

RESULTS

Endoglin is upregulated in human liver injury. The receptor is expressed in liver tissues and mesenchymal liver cells with much higher abundance of the L-Eng splice variant. Comparing GFAP^Cre(-) Eng^f/f to GFAP^Cre(+) Eng^ΔHSC mice in toxic liver injury, livers of GFAP^Cre(+) Eng^ΔHSC mice showed 39.9% (P < .01) higher Hydroxyproline content compared to GFAP^Cre(-) Eng^f/f littermates. Sirius Red staining underlined these findings, showing 58.8% (P < .05) more Collagen deposition in livers of GFAP^Cre(+) Eng^ΔHSC mice. Similar results were obtained in mice subjected to cholestatic injury.

CONCLUSION

Endoglin isoforms are differentially upregulated in liver samples of patients with chronic and acute liver injury. Endoglin deficiency in HSC significantly aggravates fibrosis in response to injury in two different murine models of liver fibrosis and increases α-SMA and fibronectin expression in vitro. This suggests that Endoglin protects against fibrotic injury, likely through modulation of TGF-β signalling.

Endoglin haploinsufficiency is associated with differential regulation of extracellular matrix production during skin fibrosis and cartilage repair in mice

Transforming growth factor (TGF)-β is a multifunctional growth factor with potent pro-fibrotic effects. Endoglin is a TGF-β co-receptor that strongly regulates TGF-β signaling in a variety of cell types. Although aberrant regulation of TGF-β signaling is known to play a key role in fibrotic diseases such as scleroderma and impaired cartilage repair, the significance of endoglin function in regulating these processes is poorly understood. Here we examined whether endoglin haploinsufficiency regulates extracellular (ECM) protein expression and fibrotic responses during bleomycin induced skin fibrosis and surgically induced osteoarthritis, using endoglin-heterozygous (Eng+/-) mice and wild-type (Eng+/+) littermates. Skin fibrosis was induced by injecting mice intradermally with bleomycin or vehicle. Osteoarthritis was induced surgically by destabilization of medial meniscus. Dermal thickness, cartilage integrity and ECM protein expression were then determined. Eng+/- mice subjected to bleomycin challenge show a marked decrease in dermal thickness (P < 0.005) and reduced collagen content and decreased collagen I, fibronectin, alpha-smooth muscle actin levels as compared to Eng+/+ mice, both under basal and bleomycin treated conditions. Eng+/- mice undergoing surgically induced osteoarthritis show no differences in the degree of cartilage degradation, as compared to Eng+/+ mice, although chondrocytes isolated from Eng^+/- display markedly enhanced collagen II levels. Our findings suggest that endoglin haploinsufficiency in mice ameliorates bleomycin-induced skin fibrosis suggesting that endoglin represents a pro-fibrotic factor in the mouse skin. However, endoglin haploinsufficiency does not protect these mice from surgically indiced cartilage degradation, demonstrating differential regulation of endoglin action during skin and cartilage repair.

The TGFβ pathway is a key player for the endothelial-to-hematopoietic transition in the embryonic aorta

The embryonic aorta produces hematopoietic stem and progenitor cells from a hemogenic endothelium localized in the aortic floor through an endothelial to hematopoietic transition. It has been long proposed that the Bone Morphogenetic Protein (BMP)/Transforming Growth Factor ß (TGFß) signaling pathway was implicated in aortic hematopoiesis but the very nature of the signal was unknown. Here, using thorough expression analysis of the BMP/TGFß signaling pathway members in the endothelial and hematopoietic compartments of the aorta at pre-hematopoietic and hematopoietic stages, we show that the TGFß pathway is preferentially balanced with a prominent role of Alk1/TgfßR2/Smad1 and 5 on both chicken and mouse species. Functional analysis using embryonic stem cells mutated for Acvrl1 revealed an enhanced propensity to produce hematopoietic cells. Collectively, we reveal that TGFß through the Alk1/TgfßR2 receptor axis is acting on endothelial cells to produce hematopoiesis.

Association between Single Nucleotide Polymorphisms of SMAD3 and BMP5 with the Risk of Knee Osteoarthritis

INTRODUCTION

The role of genetic factors influencing osteoarthritis (OA) susceptibility is well documented and several candidate genes have been identified to be associated with it. Among these genes are Bone Morphogenetic Protein 5 (BMP5) and Smad family member 3 (SMAD3), all involved in Transforming Growth Factor (TGF) signaling pathway. The knee is the commonly affected joint, and knee OA has an especially high prevalence in Asian population.

AIM

To investigate associations between Single Nucleotide Polymorphisms (SNPs) rs12901499 in SMAD3 and rs921126 in the BMP5 gene with knee OA susceptibility in and around Lucknow, Uttar Pradesh, India.

MATERIALS AND METHODS

SNPs rs12901499 in SMAD3 and rs921126 in BMP5 were genotyped in patients with knee OA and age- sex matched OA-free controls from our population. A total of 450 patients with knee OA and 458 controls were enrolled in the study. Venous blood samples were obtained from all cases as well as controls for PCR-RFLP (Polymerase Chain Reaction- Restriction Fragment Length Polymorphism). Data was collected and entered in excel sheets. Statistical analyses of the data were performed using statistical software package SPSS version 16.0. Chi-square, Student's t-test and logistic regression tests were used to analyse the data.

RESULTS

GA and GG genotypes of both SNPs (rs12901499 and rs921126), and variant G, were associated with a significantly increased risk of knee OA. A significantly increased risk of knee OA was associated with the genotype GG and GA of rs12901499 (p < 0.03 and p <0.004 respectively) and rs921126 (p< 0.0001 and p<0.001 respectively) compared with the AA genotype. In addition, those bearing at least one G allele (GG + GA) had a significantly increased risk of knee OA compared with those without the G allele (AA) in rs921126 (p< 0.0001). However, in rs12901499, significant association with the risk of knee OA was not found (p<0.4). On age and gender based stratification, the association between the risk of OA and rs921126 GG mutant compared with AA homozygotes was strong in both gender (adjusted OR= 2.93 for male and 2.25 for female) and in those aged >55 years (adjusted OR= 3.4), similarly in rs12901499, GG mutant compared with AA homozygote was strong in female (adjusted OR= 1.5) and in those aged >55 years (adjusted OR= 1.5).

CONCLUSION

The results showed that both in SMAD3 rs12901499 and BMP5 921126, G allele is significantly associated with knee OA. A to G change and variant G genotype may contribute to knee OA risk in our study population of Lucknow.

Crosstalk between Smad2/3 and specific isoforms of ERK in TGF-β1-induced TIMP-3 expression in rat chondrocytes

This study investigated the roles of ERK1 and ERK2 in transforming growth factor‐β1 (TGF‐β1)‐induced tissue inhibitor of metalloproteinases‐3 (TIMP‐3) expression in rat chondrocytes, and the specific roles of ERK1 and ERK2 in crosstalk with Smad2/3 were investigated to demonstrate the molecular mechanism of ERK1/2 regulation of TGF‐β1 signalling. To examine the interaction of specific isoforms of ERK and the Smad2/3 signalling pathway, chondrocytes were infected with LV expressing either ERK1 or ERK2 siRNA and stimulated with or without TGF‐β1. At indicated time‐points, TIMP‐3 expression was determined by real‐time PCR and Western blotting; p‐Smad3, nuclear p‐Smad3, Smad2/3, p‐ERK1/2 and ERK1/2 levels were assessed. And then, aggrecan, type II collagen and the intensity of matrix were examined. TGF‐β1‐induced TIMP‐3 expression was significantly inhibited by ERK1 knock‐down, and the decrease in TIMP‐3 expression was accompanied by a reduction of p‐Smad3 in ERK1 knock‐down cells. Knock‐down of ERK2 had no effect on neither TGF‐β1‐induced TIMP‐3 expression nor the quantity of p‐Smad3. Moreover, aggrecan, type II collagen expression and the intensity of matrix were significantly suppressed by ERK1 knock‐down instead of ERK2 knock‐down. Taken together, ERK1 and ERK2 have different roles in TGF‐β1‐induced TIMP‐3 expression in rat chondrocytes. ERK1 instead of ERK2 can regulate TGF‐β/Smad signalling, which may be the mechanism through which ERK1 regulates TGF‐β1‐induced TIMP‐3 expression.

Overexpression of CD109 in the Epidermis Differentially Regulates ALK1 Versus ALK5 Signaling and Modulates Extracellular Matrix Synthesis in the Skin

Transforming growth factor-β (TGF-β) is a multifunctional growth factor involved in many physiological processes including wound healing and inflammation. Excessive TGF-β signaling in the skin has been implicated in fibrotic skin disorders such as keloids and scleroderma. We previously identified CD109 as a TGF-β co-receptor and inhibitor of TGF-β signaling and have shown that transgenic mice overexpressing CD109 in the epidermis display decreased scarring. In certain cell types, in addition to the canonical type I receptor, ALK5, which activates Smad2/3, TGF-β can signal through another type I receptor, ALK1, which activates Smad1/5. Here we demonstrate that ALK1 is expressed and co-localizes with CD109 in mouse keratinocytes and that mice overexpressing CD109 in the epidermis display enhanced ALK1-Smad1/5 signaling but decreased ALK5-Smad2/3 signaling, TGF-β expression, and extracellular matrix production in the skin when compared with wild-type littermates. Furthermore, treatment with conditioned media from isolated keratinocytes or epidermal explants from CD109 transgenic mouse skin leads to a decrease in extracellular matrix production in mouse skin fibroblasts. Taken together, our findings suggest that CD109 differentially regulates TGF-β-induced ALK1-Smad1/5 versus ALK5-Smad2/3 pathways, leading to decreased extracellular matrix production in the skin and that epidermal CD109 expression regulates dermal function through a paracrine mechanism.

Transforming Growth Factor β1 (TGF-β1) Activates Hepcidin mRNA Expression in Hepatocytes

The hepatic hormone hepcidin is the master regulator of systemic iron homeostasis. Its expression level is adjusted to alterations in iron levels, inflammatory cues, and iron requirements for erythropoiesis. Bone morphogenetic protein 6 (BMP6) contributes to the iron-dependent control of hepcidin. In addition, TGF-β1 may stimulate hepcidin mRNA expression in murine hepatocytes and human leukocytes. However, receptors and downstream signaling proteins involved in TGF-β1-induced hepcidin expression are still unclear. Here we show that TGF-β1 treatment of mouse and human hepatocytes, as well as ectopic expression of TGF-β1 in mice, increases hepcidin mRNA levels. The hepcidin response to TGF-β1 depends on functional TGF-β1 type I receptor (ALK5) and TGF-β1 type II receptor (TβRII) and is mediated by a noncanonical mechanism that involves Smad1/5/8 phosphorylation. Interestingly, increasing availability of canonical Smad2/3 decreases TGF-β1-induced hepcidin regulation, whereas the BMP6-hepcidin signal was enhanced, indicating a signaling component stoichiometry-dependent cross-talk between the two pathways. Although ALK2/3-dependent hepcidin activation by BMP6 can be modulated by each of the three hemochromatosis-associated proteins: HJV (hemojuvelin), HFE (hemochromatosis protein), and TfR2 (transferrin receptor 2), these proteins do not control the ALK5-mediated hepcidin response to TGF-β1. TGF-β1 mRNA levels are increased in mouse models of iron overload, indicating that TGF-β1 may contribute to hepcidin synthesis under these conditions. In conclusion, these data demonstrate that a complex regulatory network involving TGF-β1 and BMP6 may control the sensing of systemic and/or hepatic iron levels.

Expression of CD90 decreases with progression of synovial chondromatosis in the temporomandibular joint

OBJECTIVES

The aim of the present study was to investigate the factors that contribute to the progression of synovial chondromatosis in the temporomandibular joint (TMJ).

METHODS

The authors investigated the expression of CD105 and CD90 in specimens from 17 patients with synovial chondromatosis in the TMJ, using immunohistochemical staining, and expression of CD105 and CD90 in cartilaginous nodules was scored semiquantitatively.

RESULTS

The expression of CD105 and CD90 was found in almost all the cases. In particular, the expression of CD90 in cartilaginous nodules significantly decreased with the progression of synovial chondromatosis.

DISCUSSION

The factors that determine progression of synovial chondromatosis are not fully understood. The results of this study suggest that CD90 may play an important role in the progression of synovial chondromatosis in the TMJ.

CD105 promotes chondrogenesis of synovium-derived mesenchymal stem cells through Smad2 signaling

Mesenchymal stem cells (MSCs) are considered to be suitable for cell-based tissue regeneration. Expressions of different cell surface markers confer distinct differentiation potential to different sub-populations of MSCs. Understanding the effect of cell surface markers on MSC differentiation is essential to their targeted application in different tissues. Although CD105 positive MSCs possess strong chondrogenic capacity, the underlying mechanisms are not clear. In this study, we observed a considerable heterogeneity with respect to CD105 expression among MSCs isolated from synovium. The CD105(+) and CD105(-) synovium-derived MSCs (SMSCs) were sorted to compare their differentiation capacities and relative gene expressions. CD105(+) subpopulation had higher gene expressions of AGG, COL II and Sox9, and showed a stronger affinity for Alcian blue and immunofluorescent staining for aggrecan and collagenase II, as compared to those in CD105(-) cells. However, no significant difference was observed with respect to gene expressions of ALP, Runx2, LPL and PPARγ. CD105(+) SMSCs showed increased levels of Smad2 phosphorylation, while total Smad2 levels were similar between the two groups. There was no difference in activation of Smad1/5. These results were further confirmed by CD105-knockdown in SMSCs. Our findings suggest a stronger chondrogenic potential of CD105(+) SMSCs in comparison to that of CD105(-) SMSCs and that CD105 enhances chondrogenesis of SMSCs by regulating TGF-β/Smad2 signaling pathway, but not Smad1/5. Our study provides a better understanding of CD105 with respect to chondrogenic differentiation.

Leucine-rich α-2-glycoprotein promotes TGFβ1-mediated growth suppression in the Lewis lung carcinoma cell lines

Leucine-rich α2-glycoprotein (LRG) is an approximately 50-kDa glycoprotein that has been found to be elevated in the sera of patients with several types of cancer. LRG directly binds to transforming growth factor beta 1 (TGFβ1) and modulates TGFβ1 signaling in endothelial cells; however, the precise function of LRG in cancer remains unclear. This study aimed to investigate the role of LRG in cancer. Lewis lung carcinoma (LLC) cells hardly expressed LRG. The growth of LLC tumors allografted in the LRG knockout (KO) mice was significantly increased compared with wild-type (WT) mice. Conversely, overexpression of LRG significantly inhibited the growth of LLC tumors in WT mice. In the presence of LRG, TGFβ1 significantly inhibited the proliferation of LLC cells and human hepatocellular carcinoma Hep3B cells in vitro by inducing apoptosis via the potent activation of smad2 and its downstream signaling pathway. Furthermore, administration of a TGFβR1 inhibitor (SB431542) significantly enhanced the growth of LLC tumors in WT mice compared with LRG KO mice via inhibition of apoptosis. We propose that LRG potentiates the effect of TGFβ1 in cancer cells whose growth is suppressed in the presence of TGFβ1.

TGF-β signalling in tumour associated macrophages

Tumour associated macrophages (TAM) represent an important component of tumour stroma. They develop under the influence of tumour microenvironment where transforming growth factor (TGF)β is frequently present. Activities of TAM regulated by TGFβ stimulate proliferation of tumour cells and lead to tumour immune escape. Despite high importance of TGFβ-induction of TAM activities till now our understanding of the mechanism of this induction is limited. We have previously developed a model of type 2 macrophages (M2) resembling certain properties of TAM. We established that in M2 TGFβRII is regulated on the level of subcellular sorting by glucocorticoids. Further studies revealed that in M2 with high levels of TGFβRII on the surface TGFβ activates not only its canonical Smad2/3-mediated signaling, but also Smad1/5-mediated signaling, what is rather typical for bone morphogenetic protein (BMP) stimulation. Complexity of macrophage populations, however, allows assumption that TGFβ signalling may function in different ways depending on the functional state of the cell. To understand the peculiarities of TGFβ signalling in human TAMs experimental systems using primary cells have to be developed and used together with the modern mathematical modelling approaches.

Glucocorticoids modify effects of TGF-β1 on multidrug resistance in the fetal blood-brain barrier

Transforming growth factor-β1 (TGF-β1) increases P-glycoprotein (P-gp; encoded by Abcb1) activity in fetal brain endothelial cells (BECs). P-gp is important for fetal brain protection against xenobiotics including synthetic glucocorticoids (sGC). We hypothesized that antenatal sGC would modify P-gp responsiveness to TGF-β1 in fetal BECs. Pregnant guinea pigs were treated with dexamethasone or vehicle (N = 5/group) on gestational day (GD) 48-49 and BECs derived on GD50. In BECs from control fetuses, TGF-β1 increased Abcb1 mRNA and P-gp function, by approximately 5-fold and 55% respectively, as well as tight junction function. In contrast, TGF-β1 had no effect on these parameters in BECs from sGC-exposed fetuses. Moreover, levels of TGF-β1 responsive gene, Smad7, were increased 3-fold in BECs from control fetuses after TGF-β1 but not in sGC-exposed fetuses. In conclusion, antenatal sGC alters responsiveness to TGF-β1 in fetal BECs. This study has identified novel mechanisms by which TGF-β1 and sGC modulate fetal brain protection against xenobiotics and other P-gp substrates.

Restriction of spontaneous and prednisolone-induced leptin production to dedifferentiated state in human hip OA chondrocytes: role of Smad1 and β-catenin activation

OBJECTIVE

The aetiology of OA is not fully understood although several adipokines such as leptin are known mediators of disease progression. Since leptin levels were increased in synovial fluid compared to serum in OA patients, it was suggested that joint cells themselves could produce leptin. However, exact mechanisms underlying leptin production by chondrocytes are poorly understood. Nevertheless, prednisolone, although displaying powerful anti-inflammatory properties has been recently reported to be potent stimulator of leptin and its receptor in OA synovial fibroblasts. Therefore, we investigated, in vitro, spontaneous and prednisolone-induced leptin production in OA chondrocytes, focusing on transforming growth factor-β (TGFβ) and Wnt/β-catenin pathways.

DESIGN

We used an in vitro dedifferentiation model, comparing human freshly isolated hip OA chondrocytes cultivated in monolayer during 1 day (type II, COL2A1 +; type X, COL10A1 + and type I collagen, COL1A1 -) or 14 days (COL2A1 -; COL10A1 - and COL1A1+).

RESULTS

Leptin expression was not detected in day1 OA chondrocytes whereas day14 OA chondrocytes produced leptin, significantly increased with prednisolone. Activin receptor-like kinase 1 (ALK1)/ALK5 ratio was shifted during dedifferentiation, from high ALK5 and phospho (p)-Smad2 expression at day1 to high ALK1, endoglin and p-Smad1/5 expression at day14. Moreover, inactive glycogen synthase kinase 3 (GSK3) and active β-catenin were only found in dedifferentiated OA chondrocytes. Smad1 and β-catenin but not endoglin stable lentiviral silencing led to a significant decrease in leptin production by dedifferentiated OA chondrocytes.

CONCLUSIONS

Only dedifferentiated OA chondrocytes produced leptin. Prednisolone markedly enhanced leptin production, which involved Smad1 and β-catenin activation.

Tendon progenitor cells in injured tendons have strong chondrogenic potential: the CD105-negative subpopulation induces chondrogenic degeneration

To study the cellular mechanism of the tendon repair process, we used a mouse Achilles tendon injury model to focus on the cells recruited to the injured site. The cells isolated from injured tendon 1 week after the surgery and uninjured tendons contained the connective tissue progenitor populations as determined by colony-forming capacity, cell surface markers, and multipotency. When the injured tendon-derived progenitor cells (inTPCs) were transplanted into injured Achilles tendons, they were not only integrated in the regenerating area expressing tenogenic phenotype but also trans-differentiated into chondrogenic cells in the degenerative lesion that underwent ectopic endochondral ossification. Surprisingly, the micromass culture of the inTPCs rapidly underwent chondrogenic differentiation even in the absence of exogenous bone morphogenetic proteins or TGFβs. The cells isolated from human ruptured tendon tissues also showed connective tissue progenitor properties and exhibited stronger chondrogenic ability than bone marrow stromal cells. The mouse inTPCs contained two subpopulations one positive and one negative for CD105, a coreceptor of the TGFβ superfamily. The CD105-negative cells showed superior chondrogenic potential in vitro and induced larger chondroid degenerative lesions in mice as compared to the CD105-positive cells. These findings indicate that tendon progenitor cells are recruited to the injured site of tendons and have a strong chondrogenic potential and that the CD105-negative population of these cells would be the cause for chondroid degeneration in injured tendons. The newly identified cells recruited to the injured tendon may provide novel targets to develop therapeutic strategies to facilitate tendon repair.

TGF-β/BMP proteins as therapeutic targets in renal fibrosis. Where have we arrived after 25 years of trials and tribulations?

The understanding of renal fibrosis in chronic kidney disease (CKD) remains as a challenge. More than 10% of the population of developed countries suffer from CKD. Proliferation and activation of myofibroblasts and accumulation of extracellular matrix proteins are the main features of kidney fibrosis, a process in which a large number of cytokines are involved. Targeting cytokines responsible for kidney fibrosis development might be an important strategy to face the problem of CKD. The increasing knowledge of the signaling pathway network of the transforming growth factor beta (TGF-β) superfamily members, such as the profibrotic cytokine TGF-β1 or the bone morphogenetic proteins (BMPs), and their involvement in the regulation of kidney fibrosis, has stimulated numerous research teams to look for potential strategies to inhibit profibrotic cytokines or to enhance the anti-fibrotic actions of other cytokines. The consequence of all these studies is a better understanding of all these canonical (Smad-mediated) and non-canonical signaling pathways. In addition, the different receptors involved for signaling of each cytokine, the different combinations of type I-type II receptors, and the presence and function of co-receptors that can influence the biological response have been also described. However, are these studies leading to suitable strategies to block the appearance and progression of kidney fibrosis? In this review, we offer a critical perspective analyzing the achievements using the most important strategies developed up till now: TGF-β antibodies, chemical inhibitors of TGF-β receptors, miRNAs and signaling pathways and BMP agonists with a potential role as therapeutic molecules against kidney fibrosis.

¹⁸F-FPRGD₂ PET/CT imaging of musculoskeletal disorders

OBJECTIVE

This work reports on musculoskeletal uptake of ¹⁸F-FPRGD₂, targeting the integrin αvβ3, in patients who had undergone ¹⁸F-FPRGD₂ positron emission tomography combined with computed tomography (PET/CT) for oncologic purposes.

METHODS

Whole-body ¹⁸F-FPRGD₂ PET/CT images of 62 cancer patients were retrospectively reviewed to detect foci of musculoskeletal ¹⁸F-FPRGD₂ uptake. For 37 patients, a FDG PET/CT performed in clinical settings was available. In each joint with an abnormal uptake, the maximum standardized uptake value (SUVmax) was estimated.

RESULTS

A total of 260 musculoskeletal foci of ¹⁸F-FPRGD₂ uptake were detected. Most common sites of uptake were joints and discs (n = 160; 61.5%), entheses (osteotendinous and osteoligamentous junctions; n = 55; 21.2%) and recent fractures (n = 18; 6.9%). In addition, 27 (10.4%) miscellaneous foci were detected. Out of the 146 lesions for which a FDG PET was available, 63% showed both ¹⁸F-FPRGD₂ and FDG uptake, 33.6% did not show FDG avidity and 3.4% showed only FDG uptake. The uptake intensity of the 92 lesions positive with ¹⁸F-FPRGD₂ and FDG was similar with both radiopharmaceuticals, but the target-to-background (blood pool or muscle) ratios were significantly higher with ¹⁸F-FPRGD₂ than with FDG (p < 0.0001).

CONCLUSION

The ¹⁸F-FPRGD₂ uptake in joints, spine degenerative diseases and tendons was highly prevalent in our population. Up to one-third of ¹⁸F-FPRGD₂ foci showed no FDG uptake suggesting that ¹⁸F-FPRGD₂ signal may not be related to inflammatory angiogenesis only.

Gene-gene interactions between TGF-β/Smad3 signalling pathway polymorphisms affect susceptibility to knee osteoarthritis

OBJECTIVE

Transforming growth factor/Smad family member 3 (TGF)-β/Smad3 signalling is essential for maintaining articular cartilage. A relationship between the genetic variants of TGF-β itself, TGF-β signalling and binding molecules, and osteoarthritis (OA) has been reported. Although variants of candidate genes have become prime targets for genetic analysis, their detailed interplay has not been documented. Our goal was to establish whether single nucleotide polymorphisms (SNPs) of TGF-β1, TGF-βRI, Smad3 and tissue inhibitor of metalloproteinases 3 (TIMP3), and their interactions, are associated with knee OA.

DESIGN

We performed a case-control association study and genotyped 518 knee patients with OA and 468 healthy controls. All participants were genotyped for TGF-β1 (rs1800469C/T), TGF-βRI (rs1590A/G), Smad3 (rs12901499A/G and rs6494629T/C), and TIMP3 (rs715572G/A and rs1962223G/C) polymorphisms by polymerase chain reaction-restriction fragment length polymorphism analysis. Multifactor dimensionality reduction (MDR) was used to identify gene-gene interactions.

RESULTS

Significant associations were observed for TIMP3 rs715572G/A polymorphisms in knee patients with OA and healthy individuals. The GA heterozygote in TIMP3 (rs715572G/A) was significantly associated with OA (p=0.007). Patient stratification using the Kellgren-Lawrence grading scale showed significant differences in TIMP3 rs715572G/A genotypes between grade 4 knee OA and controls. By MDR analysis, a two-locus model (Smad3 rs6494629T/C and TIMP3 rs715572G/A) of gene-gene interaction was the best for predicting knee OA risk, and its maximum testing accuracy was 57.55% and maximum cross-validation consistency was 10/10.

CONCLUSIONS

TIMP3 rs715572G/A is a candidate protective gene for severe knee OA. Gene-gene interactions between Smad3 rs6494629T/C and TIMP3 rs715572G/A polymorphisms may play more important protective roles in knee OA.