MicroRNA-140 Suppresses Human Chondrocytes Hypertrophy by Targeting SMAD1 and Controlling the Bone Morphogenetic Protein Pathway in Osteoarthritis

Background

This study aimed to investigate the expression levels and relationship of bone morphogenetic proteins (BMPs) signaling molecules and microRNA-140 (miR-140) in human osteoarthritis (OA) chondrocytes.

Matrix metalloproteinases and aggrecanases cleave aggrecan in different zones of normal cartilage but colocalize in the development of osteoarthritic lesions in STR/ort mice

Objective

To map aggrecan cleavage by matrix metalloproteinases (MMPs) and aggrecanases in normal murine tibial articular cartilage (CBA strain) and in the development of spontaneous osteoarthritis (OA) in the STR/ort mouse and to assess the influence of sex hormone status on these conditions in gonadectomized STR/ort mice.

Methods

The distributions of neoepitopes of aggrecan generated by MMP (VDIPEN) and aggrecanase (NITEGE) cleavage were investigated by immunohistochemistry.

Results

VDIPEN neoepitope was detected mainly in the pericellular matrix of deep‐zone chondrocytes in normal tibial cartilage from STR/ort and CBA mice. In early OA, VDIPEN immunostaining also localized to the pericellular matrix of chondrocytes at the site of the lesion. With increasing severity of OA lesions, VDIPEN immunostaining was also detected in the interterritorial matrix, close to the site of the lesion. In contrast, NITEGE mapped most strongly to the pericellular matrix of upper‐zone chondrocytes in normal tibial cartilage. As with VDIPEN, NITEGE was strongly expressed in the pericellular matrix at the site of early OA lesions. With advancing OA, NITEGE colocalized with VDIPEN in both the pericellular and interterritorial matrices of chondrocytes adjacent to OA lesions and in those of the deep zones. Hormone status did not appear to influence the development of OA or the distribution of aggrecan neoepitopes in STR/ort mice.

Conclusion

MMP‐ and aggrecanase‐generated neoepitopes map predominantly to different regions in normal murine tibial cartilage. However, both groups of enzymes generate increased amounts of neoepitopes in pericellular and interterritorial matrix adjacent to histopathologic lesions of OA. Aggrecan degradation and the development of OA appear to be independent of sex hormone status in this model.

     

Bone morphogenetic protein and transforming growth factor β inhibitory Smads 6 and 7 are expressed in human adult normal and osteoarthritic cartilage in vivo and are differentially regulated in vitro by interleukin‐1β

Objective

Bone morphogenetic protein (BMP) and transforming growth factor β (TGFβ) are potent anabolic factors in adult articular chondrocytes. In this study, we investigated whether intracellular inhibitors of BMP and TGFβ signaling, inhibitory Smad6 (I‐Smad6) and I‐Smad7, are expressed in articular chondrocytes in normal and osteoarthritic (OA) cartilage, and whether their expression shows a correlation with the anabolic activity of OA chondrocytes in vivo and after interleukin‐1β (IL‐1β) stimulation in vitro.

Methods

RNA isolated directly from normal and OA human knee cartilage as well as from cultured articular chondrocytes was analyzed by (quantitative) polymerase chain reaction technology. Immunolocalization of the I‐Smads was performed on tissue sections and compared with the anabolic cellular activity as documented by in situ hybridization experiments for aggrecan and type II collagen.

Results

Both Smad6 and Smad7 were expressed in all samples of normal and OA cartilage. Immunostaining (including confocal microscopy) confirmed the presence of Smad6 and Smad7 in the majority of normal and degenerated articular chondrocytes; localization was mostly cytoplasmic. No correlation between expression of the main anabolic genes and expression of the I‐Smads was found. In cultured articular chondrocytes, stimulation with IL‐1β showed up‐regulation of Smad7, whereas Smad6 was down‐regulated.

Conclusion

Both Smad6 and Smad7 are expressed in adult human articular chondrocytes. The primarily cytoplasmic localization suggests permanent activation of the I‐Smads in articular cartilage in vivo. No evidence was found that up‐regulation or down‐regulation of I‐Smads in OA cartilage correlates directly with the anabolic (or catabolic) activity of articular chondrocytes. The regulation in chondrocytes of Smad6 and Smad7 expression by IL‐1β suggests a potentially important role of IL‐1β signaling in chondrocytes, via indirect influencing of the BMP/TGFβ signaling cascade.

     

Dkk‐1 expression in chondrocytes inhibits experimental osteoarthritic cartilage destruction in mice

Objective

Dkk is a family of canonical Wnt antagonists with 4 members (Dkk‐1, Dkk‐2, Dkk‐3, and Dkk‐4). We undertook this study to explore the roles of Dkk‐1 and Dkk‐2 in osteoarthritic (OA) cartilage destruction in mice.

Methods

Expression of Dkk and other catabolic factors was determined at the messenger RNA and protein levels in human and mouse OA cartilage. Experimental OA in mice was induced by destabilization of the medial meniscus (DMM) or by intraarticular injection of Epas1 adenovirus (AdEPAS‐1). The role of Dkk in OA pathogenesis was examined by intraarticular injection of AdDkk‐1 or by using chondrocyte‐specific Dkk1 (Col2a1‐Dkk1)–transgenic mice and Dkk2 (Col2a1‐Dkk2)–transgenic mice. Primary culture mouse chondrocytes were also treated with recombinant Dkk proteins.

Results

We found opposite patterns of Dkk1 and Dkk2 expression in human and mouse experimental OA cartilage: Dkk1 was up‐regulated and Dkk2 was down‐regulated. Overexpression of Dkk1 by intraarticular injection of AdDkk‐1 significantly inhibited DMM‐induced experimental OA. DMM‐induced OA was also significantly inhibited in Col2a1‐Dkk1–transgenic mice compared with their wild‐type littermates. However, Col2a1‐Dkk2–transgenic mice showed no significant difference in OA pathogenesis. Wnt‐3a, which activates the canonical Wnt pathway, induced Mmp13 and Adamts4 expression in primary culture chondrocytes, an effect that was significantly inhibited by Dkk‐1 pretreatment or Dkk1 overexpression.

Conclusion

Our findings indicate that expression of Dkk1, but not Dkk2, in chondrocytes inhibits OA cartilage destruction. The protective effect of Dkk‐1 appears to be associated with its capacity to inhibit Wnt‐mediated expression of catabolic factors, such as Mmp13, providing evidence that Dkk‐1 might serve as a therapeutic target for OA treatment.

     

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.

     

Catabolic stress induces features of chondrocyte senescence through overexpression of caveolin 1: Possible involvement of caveolin 1–induced down‐regulation of articular chondrocytes in the pathogenesis of osteoarthritis

Objective

Articular chondrocyte senescence is responsible, at least in part, for the increased incidence of osteoarthritis (OA) with increased age. Recently, it was suggested that caveolin 1, a 21–24‐kd membrane protein, participates in premature cellular senescence. Caveolin 1 is the principal structural component of caveolae, vesicular invaginations of the plasma membrane. This study was undertaken to investigate whether the catabolic factors oxidative stress and interleukin‐1β (IL‐1β) induce features of premature senescence of articular chondrocytes through up‐regulation of caveolin 1 expression.

Methods

Caveolin 1 expression was investigated in human OA cartilage by real‐time polymerase chain reaction and in rat OA cartilage by immunohistologic analysis. We studied whether IL‐1β and H₂O₂ induce caveolin 1 expression in OA chondrocytes and analyzed the relationship between cellular senescent phenotypes and caveolin 1 expression in human chondrocytes.

Results

In human and rat OA articular cartilage, caveolin 1 positivity was associated with cartilage degeneration. Both IL‐1β and H₂O₂ up‐regulated caveolin 1 messenger RNA and protein levels, and both treatments induced marked expression of senescent phenotypes: altered cellular morphology, cell growth arrest, telomere erosion, and specific senescence‐associated β‐galactosidase activity. Caveolin 1 overexpression induced p38 MAPK activation and impaired the ability of chondrocytes to produce type II collagen and aggrecan. In contrast, down‐regulation of caveolin 1 with antisense oligonucleotide significantly inhibited the features of chondrocyte senescence induced by catabolic factors. Caveolin 1 induction and stresses with both IL‐1β and H₂O₂ up‐regulated p53 and p21 and down‐regulated phosphorylated retinoblastoma (Rb), suggesting that the p53/p21/Rb phosphorylation pathway, as well as prolonged p38 MAPK activation, may mediate the features of chondrocyte senescence induced by stress.

Conclusion

Our findings suggest that IL‐1β and oxidative stress induce features of premature senescence in OA chondrocytes, mediated, at least in part, by stress‐induced caveolin 1 expression. This indicates that caveolin 1 plays a role in the pathogenesis of OA via promotion of chondrocyte down‐regulation.

     

Mitochondrial dysfunction in osteoarthritis is associated with down‐regulation of superoxide dismutase 2

Objective

Superoxide dismutase 2 (SOD2) is down‐ regulated in osteoarthritis (OA). This study was undertaken to investigate the functional effects of this down‐regulation in the context of oxidative damage and mitochondrial dysfunction.

Methods

Lipid peroxidation in articular cartilage from OA patients and from lesion‐free control subjects with femoral neck fracture was assessed by measuring malondialdehyde levels using the thiobarbituric acid reactive substances assay. Long‐range polymerase chain reaction amplification and a mitochondrial DNA (mtDNA) strand break assay were used to investigate the presence of somatic large‐scale mtDNA rearrangements in cartilage. Microscale oxygraphy was used to explore possible changes in mitochondrial respiratory activity between OA and control chondrocytes. RNA interference was used to determine the effects of SOD2 depletion on lipid peroxidation, mtDNA damage, and mitochondrial respiration.

Results

OA cartilage had higher levels of lipid peroxidation compared to control cartilage, and lipid peroxidation was similarly elevated in SOD2‐depleted chondrocytes. SOD2 depletion led to a significant increase in mtDNA strand breaks in chondrocytes, but there was no notable difference in the level of strand breaks between OA and control chondrocytes. Furthermore, only very low levels of somatic, large‐scale mtDNA rearrangements were identified in OA cartilage. OA chondrocytes showed less spare respiratory capacity (SRC) and higher proton leak compared to control chondrocytes. SOD2‐depleted chondrocytes also showed less SRC and higher proton leak.

Conclusion

This is the first study to analyze the effects of SOD2 depletion in human articular chondrocytes in terms of changes to oxidation and mitochondrial function. The findings indicate that SOD2 depletion in chondrocytes leads to oxidative damage and mitochondrial dysfunction, suggesting that SOD2 down‐regulation is a potential contributor to the pathogenesis of OA.

     

Developmental and osteoarthritic changes in Col6a1‐knockout mice: Biomechanics of type VI collagen in the cartilage pericellular matrix

Objective

Chondrocytes, the sole cell type in articular cartilage, maintain the extracellular matrix (ECM) through a homeostatic balance of anabolic and catabolic activities that are influenced by genetic factors, soluble mediators, and biophysical factors such as mechanical stress. Chondrocytes are encapsulated by a narrow tissue region termed the “pericellular matrix” (PCM), which in normal cartilage is defined by the exclusive presence of type VI collagen. Because the PCM completely surrounds each cell, it has been hypothesized that it serves as a filter or transducer for biochemical and/or biomechanical signals from the cartilage ECM. The present study was undertaken to investigate whether lack of type VI collagen may affect the development and biomechanical function of the PCM and alter the mechanical environment of chondrocytes during joint loading.

Methods

Col6a1^−/− mice, which lack type VI collagen in their organs, were generated for use in these studies. At ages 1, 3, 6, and 11 months, bone mineral density (BMD) was measured, and osteoarthritic (OA) and developmental changes in the femoral head were evaluated histomorphometrically. Mechanical properties of articular cartilage from the hip joints of 1‐month‐old Col6a1^−/−, Col6a1^+/−, and Col6a1^+/+ mice were assessed using an electromechanical test system, and mechanical properties of the PCM were measured using the micropipette aspiration technique.

Results

In Col6a1^−/− and Col6a1^+/− mice the PCM was structurally intact, but exhibited significantly reduced mechanical properties as compared with wild‐type controls. With age, Col6a1^−/− mice showed accelerated development of OA joint degeneration, as well as other musculoskeletal abnormalities such as delayed secondary ossification and reduced BMD.

Conclusion

These findings suggest that type VI collagen has an important role in regulating the physiology of the synovial joint and provide indirect evidence that alterations in the mechanical environment of chondrocytes, due to either loss of PCM properties or Col6a1^−/−‐derived joint laxity, can lead to progression of OA.

     

Osteoarthritic chondrocyte–secreted morphogens induce chondrogenic differentiation of human mesenchymal stem cells

Objective

The potential of stem cells to repair compromised cartilage tissue, such as in osteoarthritis (OA), depends strongly on how transplanted cells respond to factors secreted from the residing OA chondrocytes. This study was undertaken to determine the effect of morphogenetic signals from OA chondrocytes on chondrogenic differentiation of human mesenchymal stem cells (MSCs).

Methods

The effect of OA chondrocyte–secreted morphogens on chondrogenic differentiation of human MSCs was evaluated using a coculture system involving both primary and passaged OA chondrocytes. The findings were compared against findings for human MSCs cultured in OA chondrocyte–conditioned medium. Gene expression analysis, biochemical assays, and immunofluorescence staining were used to characterize the chondrogenic differentiation of human MSCs. Mass spectrometry analysis was used to identify the soluble factors. Numerical analysis was carried out to model the concentration profile of soluble factors within the human MSC–laden hydrogels.

Results

The human MSCs cocultured with primary OA chondrocytes underwent chondrogenic differentiation even in the absence of growth factors; however, the same effect could not be mimicked using OA chondrocyte–conditioned medium or expanded cells. Additionally, the cocultured environment down‐regulated hypertrophic differentiation of human MSCs. Mass spectrometry analysis demonstrated cell–cell communication and chondrocyte phenotype–dependent effects on cell‐secreted morphogens.

Conclusion

The experimental findings, along with the results of the numerical analysis, suggest a crucial role of soluble morphogens and their local concentrations in the differentiation pattern of human MSCs in a 3‐dimensional environment. The concept of using a small number of chondrocytes to promote chondrogenic differentiation of human MSCs while preventing their hypertrophic differentiation could be of great importance in formulating effective stem cell–based cartilage repair.

     

Nonsteroidal antiinflammatory drugs and prostaglandin E2 modulate the synthesis of osteoprotegerin and RANKL in the cartilage of patients with severe knee osteoarthritis

Objective

Although the osteoprotegerin (OPG)/RANK/RANKL system is the main modulator of bone remodeling, it remains unclear whether it is regulated in cartilage during osteoarthritis (OA). The aim of this study was to examine whether nonsteroidal antiinflammatory drug (NSAID) treatment modulates the synthesis of OPG and RANKL in the cartilage of patients with OA, and to investigate whether prostaglandin E₂ (PGE₂) modifies this system in human OA chondrocytes in culture.

Methods

A 3‐month clinical trial was carried out in 20 patients with severe knee OA, all of whom were scheduled to undergo knee replacement surgery. Ten of these patients were treated with celecoxib, and the other 10 patients, who did not want to be treated, served as the control group. After surgery, cartilage was processed for molecular biology studies. We also used human OA chondrocytes to examine the effects of PGE₂ on OPG/RANKL synthesis, examining which surface receptors were affected by PGE₂.

Results

In patients with OA, celecoxib decreased RANKL synthesis in the cartilage, thereby increasing the OPG:RANKL ratio. In human OA chondrocytes in culture, PGE₂ elicited a dose‐ and time‐dependent increase in the synthesis of RANKL, the extent of which was greater than that of OPG. Confocal microscopy revealed that PGE₂ induced RANKL transport to the cell membrane. Only EP2/EP4 agonists reproduced the effects of PGE₂ on OPG and RANKL induction.

Conclusion

Long‐term NSAID treatment inhibited the resorptive signal synthesized by chondrocytes. In vitro, PGE₂ regulated the expression and release of these key mediators of bone metabolism by articular chondrocytes. The role of OPG/RANK/RANKL in OA cartilage metabolism is still unknown, although the synthesis of these proteins would enable the cartilage to control the activity of subchondral bone cells.

     

Parathyroid hormone 1–34 inhibits terminal differentiation of human articular chondrocytes and osteoarthritis progression in rats

Objective

Parathyroid hormone 1–34 (PTH[1–34]), a parathyroid hormone analog, shares the same receptor, PTH receptor 1, with parathyroid hormone–related peptide (PTHrP). This study was undertaken to address the hypothesis that PTH(1–34) inhibits terminal differentiation of articular chondrocytes and in turn suppresses the progression of osteoarthritis (OA).

Methods

We studied the effect of PTH(1–34) on human articular chondrocytes with azacytidine (azaC)–induced terminal differentiation in vitro and on papain‐induced OA in the knee joints of rats. In the in vitro study, we measured the levels of messenger RNA for SOX9, aggrecan, type II collagen, type X collagen, alkaline phosphatase (AP), Indian hedgehog (IHH), Bcl‐2, and Bax by real‐time polymerase chain reaction, levels of glycosaminoglycan (GAG) by dimethylmethylene blue assay, and rate of apoptosis by TUNEL staining. In the in vivo study, we evaluated the histologic changes in GAG, type II collagen, type X collagen, and chondrocyte apoptosis in the articular cartilage of rat knees.

Results

AzaC induced terminal differentiation of human chondrocytes, including down‐regulation of aggrecan, type II collagen, and GAG and up‐regulation of type X collagen, alkaline phosphatase, and IHH. Apoptosis was reversed by 3–10 days of treatment with 10 nM PTH(1–34). SOX9 expression was not changed by either azaC or PTH(1–34) treatment. Bcl‐2 and Bax were up‐regulated on day 10 and day 14, respectively, after azaC induction of terminal differentiation, but PTH(1–34) treatment did not reverse this effect. Furthermore, PTH(1–34) treatment reversed papain‐induced OA changes (decreasing GAG and type II collagen, and increasing type X collagen and chondrocyte apoptosis) in the knee joints of rats.

Conclusion

Our findings indicate that PTH(1–34) inhibits the terminal differentiation of human articular chondrocytes in vitro and inhibits progression of OA in rats in vivo, and may be used to treat OA.