Junlan Huang

Genetic inhibition of fibroblast growth factor receptor 1 in knee cartilage attenuates the degeneration of articular cartilage in adult mice

OBJECTIVE Fibroblast growth factor (FGF) family members are involved in the regulation of articular cartilage homeostasis. The aim of this study was to investigate the function of FGF receptor 1 (FGFR-1) in the development of osteoarthritis (OA) and its underlying mechanisms. METHODS FGFR-1 was deleted from the articular chondrocytes of adult mice in a cartilage-specific and tamoxifen-inducible manner. Two OA models (aging-associated spontaneous OA, and destabilization-induced OA), as well as an antigen-induced arthritis (AIA) model, were established and tested in Fgfr1-deficient and wild-type (WT) mice. Alterations in cartilage structure and the loss of proteoglycan were assessed in the knee joints of mice of either genotype, using these 3 arthritis models. Primary chondrocytes were isolated and the expression of key regulatory molecules was assessed quantitatively. In addition, the effect of an FGFR-1 inhibitor on human articular chondrocytes was examined. RESULTS The gross morphologic features of Fgfr1-deficient mice were comparable with those of WT mice at both the postnatal and adult stages. The articular cartilage of 12-month-old Fgfr1-deficient mice displayed greater aggrecan staining compared to 12-month-old WT mice. Fgfr1 deficiency conferred resistance to the proteoglycan loss induced by AIA and attenuated the development of cartilage destruction after surgically induced destabilization of the knee joint. The chondroprotective effect of FGFR-1 inhibition was largely associated with decreased expression of matrix metalloproteinase 13 (MMP-13) and up-regulation of FGFR-3 in mouse and human articular chondrocytes. CONCLUSION Disruption of FGFR-1 in adult mouse articular chondrocytes inhibits the progression of cartilage degeneration. Down-regulation of MMP-13 expression and up-regulation of FGFR-3 levels may contribute to the phenotypic changes observed in Fgfr1-deficient mice.

Inactivation of Vhl in Osteochondral Progenitor Cells Causes High Bone Mass Phenotype and Protects Against Age‐Related Bone Loss in Adult Mice

Previous studies have shown that disruption of von Hippel–Lindau gene (Vhl) coincides with activation of hypoxia‐inducible factor α (HIFα) signaling in bone cells and plays an important role in bone development, homeostasis, and regeneration. It is known that activation of HIF1α signaling in mature osteoblasts is central to the coupling between angiogenesis and bone formation. However, the precise mechanisms responsible for the coupling between skeletal angiogenesis and osteogenesis during bone remodeling are only partially elucidated. To evaluate the role of Vhl in bone homeostasis and the coupling between vascular physiology and bone, we generated mice lacking Vhl in osteochondral progenitor cells (referred to as Vhl cKO mice) at postnatal and adult stages in a tamoxifen‐inducible manner and changes in skeletal morphology were assessed by micro–computed tomography (µCT), histology, and bone histomorphometry. We found that mice with inactivation of Vhl in osteochondral progenitor cells at the postnatal stage largely phenocopied that of mice lacking Vhl in mature osteoblasts, developing striking and progressive accumulation of cancellous bone with increased microvascular density and bone formation. These were accompanied with a significant increase in osteoblast proliferation, upregulation of differentiation marker Runx2 and osteocalcin, and elevated expression of vascular endothelial growth factor (VEGF) and phosphorylation of Smad1/5/8. In addition, we found that Vhl deletion in osteochondral progenitor cells in adult bone protects mice from aging‐induced bone loss. Our data suggest that the VHL‐mediated signaling in osteochondral progenitor cells plays a critical role in bone remodeling at postnatal/adult stages through coupling osteogenesis and angiogenesis.

FGFR3 Deficiency Causes Multiple Chondroma-like Lesions by Upregulating Hedgehog Signaling.

Most cartilaginous tumors are formed during skeletal development in locations adjacent to growth plates, suggesting that they arise from disordered endochondral bone growth. Fibroblast growth factor receptor (FGFR)3 signaling plays essential roles in this process; however, the role of FGFR3 in cartilaginous tumorigenesis is not known. In this study, we found that postnatal chondrocyte-specific Fgfr3 deletion induced multiple chondroma-like lesions, including enchondromas and osteochondromas, adjacent to disordered growth plates. The lesions showed decreased extracellular signal-regulated kinase (ERK) activity and increased Indian hedgehog (IHH) expression. The same was observed in Fgfr3-deficient primary chondrocytes, in which treatment with a mitogen-activated protein kinase (MEK) inhibitor increased Ihh expression. Importantly, treatment with an inhibitor of IHH signaling reduced the occurrence of chondroma-like lesions in Fgfr3-deficient mice. This is the first study reporting that the loss of Fgfr3 function leads to the formation of chondroma-like lesions via downregulation of MEK/ERK signaling and upregulation of IHH, suggesting that FGFR3 has a tumor suppressor-like function in chondrogenesis.

Conditional Deletion of Fgfr3 in Chondrocytes leads to Osteoarthritis-like Defects in Temporomandibular Joint of Adult Mice

Osteoarthritis (OA) in the temporomandibular joint (TMJ) is a common degenerative disease in adult, which is characterized by progressive destruction of the articular cartilage. To investigate the role of FGFR3 in the homeostasis of TMJ cartilage during adult stage, we generated Fgfr3f/f; Col2a1-CreERT2 (Fgfr3 cKO) mice, in which Fgfr3 was deleted in chondrocytes at 2 months of age. OA-like defects were observed in Fgfr3 cKO TMJ cartilage. Immunohistochemical staining and quantitative real-time PCR analyses revealed a significant increase in expressions of COL10, MMP13 and AMAMTS5. In addition, there was a sharp increase in chondrocyte apoptosis at the Fgfr3 cKO articular surface, which was accompanied by a down-regulation of lubricin expression. Importantly, the expressions of RUNX2 and Indian hedgehog (IHH) were up-regulated in Fgfr3 cKO TMJ. Primary Fgfr3 cKO chondrocytes were treated with IHH signaling inhibitor, which significantly reduced expressions of Runx2, Col10, Mmp13 and Adamts5. Furthermore, the IHH signaling inhibitor partially alleviated OA-like defects in the TMJ of Fgfr3 cKO mice, including restoration of lubricin expression and improvement of the integrity of the articular surface. In conclusion, our study proposes that FGFR3/IHH signaling pathway plays a critical role in maintaining the homeostasis of TMJ articular cartilage during adult stage.

Loss of Vhl in cartilage accelerated the progression of age-associated and surgically induced murine osteoarthritis.

OBJECTIVE To investigate the role of Vhl in maintaining the integrity of articular cartilage and in the development of experimental osteoarthritis (OA). METHOD Histology of articular cartilage and subchondral bone in both Vhl cKO and WT mice were analyzed by histopathology and micro-CT. Articular cartilage destruction and proteoglycan loss were scored in aged (12-month-old) mice as well as in mice with surgically induced OA. Apoptosis of cartilage in age-related and surgically induced OA was detected with TUNEL assay. Expressions of von Hippel-Lindau (VHL), Fas, LC-3, HIF-1α, HIF-2α, p-mTOR and MMP-13 in the knee joints were analyzed by immunostaining. RESULTS No gross differences in cartilage were observed between Vhl cKO and WT mice at age 4 months. However, Vhl cKO mice displayed accelerated age-associated spontaneous OA and surgically induced OA. Cartilage destruction and proteoglycan loss were observed in the absence of Vhl. In addition, inactivation of Vhl resulted in up-regulation of HIF-2α and increased chondrocyte apoptosis and decreased expression of autophagy during OA development. Immunohistochemical staining also showed that Vhl deficiency led to increased expression of Fas, p-mTOR and MMP-13, and those genes were associated with cell apoptosis, autophagy and cartilage matrix breakdown, respectively. CONCLUSION Loss of Vhl in adult articular cartilage is associated with earlier dysregulation of cartilage homeostasis, characterized by an increased chondrocyte apoptosis, compromised chondrocyte autophagy, and an accelerated age-related and surgery-induced OA development. These results highlight the novel role of Vhl in maintaining joint homeostasis and OA development.

A novel fibroblast growth factor receptor 1 inhibitor protects against cartilage degradation in a murine model of osteoarthritis.

The attenuated degradation of articular cartilage by cartilage-specific deletion of fibroblast growth factor receptor 1 (FGFR1) in adult mice suggests that FGFR1 is a potential target for treating osteoarthritis (OA). The goal of the current study was to investigate the effect of a novel non-ATP-competitive FGFR1 inhibitor, G141, on the catabolic events in human articular chondrocytes and cartilage explants and on the progression of cartilage degradation in a murine model of OA. G141 was screened and identified via cell-free kinase-inhibition assay. In the in vitro study, G141 decreased the mRNA levels of catabolic markers ADAMTS-5 and MMP-13, the phosphorylation of Erk1/2, JNK and p38 MAPK, and the protein level of MMP-13 in human articular chondrocytes. In the ex vivo study, proteoglycan loss was markedly reduced in G141 treated human cartilage explants. For the in vivo study, intra-articular injection of G141 attenuated the surgical destabilization of the medial meniscus (DMM) induced cartilage destruction and chondrocyte hypertrophy and apoptosis in mice. Our data suggest that pharmacologically antagonize FGFR1 using G141 protects articular cartilage from osteoarthritic changes, and intra-articular injection of G141 is potentially an effective therapy to alleviate OA progression.

Fibroblast Growth Factor Receptor 3 Inhibits Osteoarthritis Progression in the Knee Joints of Adult Mice.

Fibroblast growth factor (FGF) signaling is involved in articular cartilage homeostasis. This study was undertaken to investigate the role and mechanisms of FGF receptor 3 (FGFR‐3) in the pathogenesis of osteoarthritis (OA) caused by surgery and aging in mice.

Efficient multi-site-directed mutagenesis directly from genomic template

In this article, the traditional multi-site-directed mutagenesis method based on overlap extension PCR was improved specifically for complicated templates, such as genomic sequence or complementary DNA. This method was effectively applied for multi-site-directed mutagenesis directly from mouse genomic DNA, as well as for combination, deletion or insertion of DNA fragments.

Anemonin attenuates osteoarthritis progression through inhibiting the activation of IL-1β/NF-κB pathway

The osteoarthritis (OA) progression is now considered to be related to inflammation. Anemonin (ANE) is a small natural molecule extracted from various kinds of Chinese traditional herbs and has been shown to inhibiting inflammation response. In this study, we examined whether ANE could attenuate the progression of OA via suppression of IL‐1β/NF‐κB pathway activation. Destabilization of the medial meniscus (DMM) was performed in 10‐week‐old male C57BL/6J mice. ANE was then intra‐articularly injected into joint capsule for 8 and 12 weeks. Human articular chondrocytes and cartilage explants challenged with interleukin‐1β (IL‐1β) were treated with ANE. We found that ANE delayed articular cartilage degeneration in vitro and in vivo. In particular, proteoglycan loss and chondrocyte hypertrophy were significantly decreased in ANE ‐treated mice compared with vehicle‐treated mice. ANE decreased the expressions of matrix metalloproteinase‐13 (MMP13), A disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS5), collagen X (Col X) while increasing Aggrecan level in murine with DMM surgery. ANE treatment also attenuated proteoglycan loss in human cartilage explants treated with IL‐1β ex vivo. ANE is a potent protective molecule for OA; it delays OA progression by suppressing ECM loss and chondrocyte hypertrophy partially by suppressing IL‐1β/NF‐κB pathway activation.

A novel FGFR1-binding peptide attenuates the degeneration of articular cartilage in adult mice

OBJECTIVE We previously reported that genetic ablation of (Fibroblast Growth Factors Receptors) FGFR1 in knee cartilage attenuates the degeneration of articular cartilage in adult mice, which suggests that FGFR1 is a potential targeting molecule for osteoarthritis (OA). Here, we identified R1-P1, an inhibitory peptide for FGFR1 and investigated its effect on the pathogenesis of OA in mice induced by destabilization of medial meniscus (DMM). DESIGN Binding ability between R1-P1 and FGFR1 protein was evaluated by enzyme-linked immuno sorbent assay (ELISA) and molecular docking. Alterations in cartilage were evaluated histologically. The expression levels of molecules associated with articular cartilage homeostasis and FGFR1 signaling were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR), Western blotting and immunohistochemistry (IHC). The chondrocyte apoptosis was detected by terminal-deoxynucleoitidyl transferase mediated nick end labeling (TUNEL) assay. RESULTS R1-P1 had highly binding affinities to human FGFR1 protein, and efficiently inhibited extracellular signal-regulated kinase (ERK)1/2 pathway in mouse primary chondrocytes. In addition, R1-P1 attenuated the IL-1β induced significant loss of proteoglycan in full-thickness cartilage tissue from human femur head. Moreover, this peptide can significantly restore the IL-1β mediated loss of proteoglycan and type II collagen (Col II) and attenuate the expression of matrix metalloproteinase-13 (MMP13) in mouse primary chondrocytes. Finally, intra-articular injection of R1-P1 remarkably attenuated the loss of proteoglycan and the destruction of articular cartilage and decreased the expressions of extracellular matrix (ECM) degrading enzymes and apoptosis in articular chondrocytes of mice underwent DMM surgery. CONCLUSIONS R1-P1, a novel inhibitory peptide for FGFR1, attenuates the degeneration of articular cartilage in adult mice, which is a potential leading molecule for the treatment of OA.