BMP-2 treatment of C3H10T1/2 mesenchymal cells blocks MMP-9 activity during chondrocyte commitment

Fibroblast Growth Factor 9 (FGF9) negatively regulates the early stage of chondrogenic differentiation

Fibroblast growth factor signaling is essential for mammalian bone morphogenesis and growth, involving membranous ossification and endochondral ossification. FGF9 has been shown to be an important regulator of endochondral ossification; however, its role in the early differentiation of chondrocytes remains unknown. Therefore, in this study, we aimed to determine the role of FGF9 in the early differentiation of chondrogenesis. We found an increase in FGF9 expression during proliferating chondrocyte hypertrophy in the mouse growth plate. Silencing of FGF9 promotes the growth of ATDC5 cells and promotes insulin-induced differentiation of ATDC5 chondrocytes, which is due to increased cartilage matrix formation and type II collagen (col2a1) and X (col10a1), Acan, Ihh, Mmp13 gene expression. Then, we evaluated the effects of AKT, GSK-3β, and mTOR. Inhibition of FGF9 significantly inhibits phosphorylation of AKT and GSK-3β, but does not affected the activation of mTOR. Furthermore, phosphorylation of inhibited AKT and GSK-3β was compensated using the AKT activator SC79, and differentiation of ATDC5 cells was inhibited. In conclusion, our results indicate that FGF9 acts as an important regulator of early chondrogenesis partly through the AKT/GSK-3β pathway.

Destroy to Rebuild: The Connection Between Bone Tissue Remodeling and Matrix Metalloproteinases

Bone is a dynamic organ that undergoes constant remodeling, an energetically costly process by which old bone is replaced and localized bone defects are repaired to renew the skeleton over time, thereby maintaining skeletal health. This review provides a general overview of bone’s main players (bone lining cells, osteocytes, osteoclasts, reversal cells, and osteoblasts) that participate in bone remodeling. Placing emphasis on the family of extracellular matrix metalloproteinases (MMPs), we describe how: (i) Convergence of multiple protease families (including MMPs and cysteine proteinases) ensures complexity and robustness of the bone remodeling process, (ii) Enzymatic activity of MMPs affects bone physiology at the molecular and cellular levels and (iii) Either overexpression or deficiency/insufficiency of individual MMPs impairs healthy bone remodeling and systemic metabolism. Today, it is generally accepted that proteolytic activity is required for the degradation of bone tissue in osteoarthritis and osteoporosis. However, it is increasingly evident that inactivating mutations in MMP genes can also lead to bone pathology including osteolysis and metabolic abnormalities such as delayed growth. We argue that there remains a need to rethink the role played by proteases in bone physiology and pathology.

BMP-2 restoration aids in recovery from liver fibrosis by attenuating TGF-β1 signaling

Transforming growth factor-β (TGF-β) plays a central role in hepatic fibrogenesis. This study investigated the function and mechanism of bone morphogenetic protein-2 (BMP-2) in regulation of hepatic fibrogenesis. BMP-2 expression in fibrotic liver was measured in human tissue microarray and mouse models of liver fibrosis induced by bile duct ligation surgery or carbon tetrachloride administration. Adenovirus-mediated BMP-2 gene delivery was used to test the prophylactic effect on liver fibrosis. Primary hepatic stellate cells (HSC), HSC-T6 and clone-9 cell lines were used to study the interplay between BMP-2 and TGF-β1. Hepatic BMP-2 was localized in parenchymal hepatocytes and activated HSCs and significantly decreased in human and mouse fibrotic livers, showing an opposite pattern of hepatic TGF-β1 contents. BMP-2 gene delivery alleviated the elevations of serum hepatic enzymes, cholangiocyte marker CK19, HSC activation markers, and liver fibrosis in both models. Mechanistically, exogenous TGF-β1 dose dependently reduced BMP-2 expression, whereas BMP-2 significantly suppressed expression of TGF-β and its cognate type I and II receptor peptides, as well as the induced Smad3 phosphorylation levels in primary mouse HSCs. Aside from its suppressive effects on cell proliferation and migration, BMP-2 treatment prominently attenuated the TGF-β1-stimulated α-SMA and fibronectin expression, and reversed the TGF-β1-modulated epithelial-to-mesenchymal transition marker expression in mouse HSCs. The mutual regulation between BMP-2 and TGF-β1 signaling axes may constitute the anti-fibrogenic mechanism of BMP-2 in the pathogenesis of liver fibrosis. BMP-2 may potentially serve as a novel therapeutic target for treatment of liver fibrosis.

BIO alleviated compressive mechanical force-mediated mandibular cartilage pathological changes through Wnt/β-catenin signaling activation

Osteoarthritis induced by compressive mechanical force is characterized by decreased chondrocyte proliferation and degradation of the ECM. To examine underlying mechanisms of the pathological changes of mandibular cartilage induced by compressive mechanical force, an established animal model was used to examine Wnt signaling activation by glycogen synthase kinase-3 beta (GSK3β) inhibitor 6-Bromoindirubin-3'-oxime (BIO) injection in vivo. Histological changes in mandibular cartilage were assessed via hematoxylin & eosin (HE), masson, and alcian blue staining. Immunohistochemistry and real-time PCR were performed to evaluate activation of the Wnt signaling pathway and chondrocytes proliferation markers. Chondrocytes apoptosis was examined by TUNEL staining. During the compressive mechanical force loading-mediated process, Wnt signaling was largely inhibited, which showed the inhibited expression of β-catenin and the increased expression of GSK-3β. The expression of chondrocytes proliferation markers Ki67, and proliferating cell nuclear antigen (PCNA) also decreased. With BIO injection, the Wnt signaling was restored and the proliferation of mandibular chondrocytes was also increased in the late stage (7 days) of compressive mechanical force loading. Finally, the decreasing mandibular cartilage thickness, the degradation of extracellular matrix, and the erosion of bone trabecula were subsequently restored. Also, the changes of extracellular matrix markers such as collagen II and collagen X, matrix metalloproteases, and inflammatory cytokines were reversed followed by the injection of BIO. In summary, compressive mechanical force decreased endogenously Wnt signaling, leading to impaired proliferation in chondrocytes and degradation in cartilage matrix. Restoration of Wnt signaling largely recovered the proliferation defects and alleviated the pathological changes of mandibular cartilage. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1228-1237, 2018.

Inactivation of glycogen synthase kinase-3β up-regulates β-catenin and promotes chondrogenesis

This study aimed to investigate whether inhibition of glycogen synthase kinase-3β (GSK-3β) could promote chondrocytes proliferation. The expression pattern of GSK-3β was firstly determined by immunohistochemistry (IHC) in normal mouse. Tibias were then isolated and cultured for 6 days. The tibias were treated with dimethylsulfoxide (control) or GSK-3 inhibitor SB415286 (SB86). Length of tibias was measured until 6 days after treatment. These bones were either stained with alcian blue/alizarin red or analyzed by IHC. In addition, GSK-3β and β-catenin were analyzed by Western blot. Finally, cartilage-specific GSK-3β deletion mice (KO) were generated. Efficiency of GSK-3β deletion was determined through Western blot and IHC. After treated by inhibitor SB86, the overall length of growth plate was not changed. However, growth of tibia in SB86 group was increased by 31 %, the length of resting and proliferating was increased 13 % (P < 0.01), whereas the length of hypertrophic was decreased by 57 % (P < 0.01). Besides, the mineralized length was found to be significant longer than the control group (P < 0.05). In KO mice, growth plate and calvaria tissue both exhibit significant reduction of GSK-3β (P < 0.05) whereas the lengths of tibias in KO were almost same compared with control mice. Finally, an increase amount of β-catenin protein was observed in SB86 (P < 0.05). In addition, significantly increased β-catenin was also found in the growth plate of KO mice (P < 0.05). Inhibition of GSK-3 could promote longitudinal growth of bone through increasing bone formation. Besides, the inactivation of GSK-3β could lead to enhancing β-catenin, therefore promote chondrocytes proliferation.

Inhibition of Gsk3β in cartilage induces osteoarthritic features through activation of the canonical Wnt signaling pathway

OBJECTIVE

In the past years, the canonical Wnt/β-catenin signaling pathway has emerged as a critical regulator of cartilage development and homeostasis. In this pathway, glycogen synthase kinase-3β (GSK3β) down-regulates transduction of the canonical Wnt signal by promoting degradation of β-catenin. In this study we wanted to further investigate the role of Gsk3β in cartilage maintenance.

DESIGN

Therefore, we have treated chondrocytes ex vivo and in vivo with GIN, a selective GSK3β inhibitor.

RESULTS

In E17.5 fetal mouse metatarsals, GIN treatment resulted in loss of expression of cartilage markers and decreased chondrocyte proliferation from day 1 onward. Late (3 days) effects of GIN included cartilage matrix degradation and increased apoptosis. Prolonged (7 days) GIN treatment resulted in resorption of the metatarsal. These changes were confirmed by microarray analysis showing a decrease in expression of typical chondrocyte markers and induction of expression of proteinases involved in cartilage matrix degradation. An intra-articular injection of GIN in rat knee joints induced nuclear accumulation of β-catenin in chondrocytes 72 h later. Three intra-articular GIN injections with a 2 days interval were associated with surface fibrillation, a decrease in glycosaminoglycan expression and chondrocyte hypocellularity 6 weeks later.

CONCLUSIONS

These results suggest that, by down-regulating β-catenin, Gsk3β preserves the chondrocytic phenotype, and is involved in maintenance of the cartilage extracellular matrix. Short term β-catenin up-regulation in cartilage secondary to Gsk3β inhibition may be sufficient to induce osteoarthritis-like features in vivo.