Comparison of mouse and human ankles and establishment of mouse ankle osteoarthritis models by surgically-induced instability

OBJECTIVE

Prevalence of ankle osteoarthritis (OA) is lower than that of knee OA, however, the molecular mechanisms underlying the difference remain unrevealed. In the present study, we developed mouse ankle OA models for use as tools to investigate pathophysiology of ankle OA and molecular characteristics of ankle cartilage.

DESIGN

We anatomically and histologically examined ankle and knee joints of C57BL/6 mice, and compared them with human samples. We examined joints of 8-week-old and 25-month-old mice. For experimental models, we developed three different ankle OA models: a medial model, a lateral model, and a bilateral model, by resection of respective structures. OA severity was evaluated 8 weeks after the surgery by safranin O staining, and cartilage degradation in the medial model was sequentially examined.

RESULTS

Anatomical and histological features of human and mouse ankle joints were comparable. Additionally, the mouse ankle joint was more resistant to cartilage degeneration with aging than the mouse knee joint. In the medial model, the tibiotalar joint was markedly affected while the subtalar joint was less degenerated. In the lateral model, the subtalar joint was mainly affected while the tibiotalar joint was less altered. In the bilateral model, both joints were markedly degenerated. In the time course of the medial model, TdT-mediated dUTP nick end labeling (TUNEL) staining and Adamts5 expression were enhanced at early and middle stages, while Mmp13 expression was gradually increased during the OA development.

CONCLUSION

Since human and mouse ankles are comparable, the present models will contribute to ankle OA pathophysiology and general cartilage research in future.

Transcriptional induction of SOX9 by NF-kappaB family member RelA in chondrogenic cells

OBJECTIVE

Although SOX9 is a key molecule for chondrogenic differentiation, little is known about the upstream signal. The present study attempted to identify transcription factors to induce SOX9 expression and examined the mechanism.

METHODS

Sequences of about 1 kb of 5'-end flanking regions were compared between human and mouse SOX9 genes. In vivo localization was examined by immunohistochemistry in the limb cartilage of fetal mice. Promoter activities of the SOX9, SOX6, and type II collagen (COL2A1) genes were determined in human non-chondrogenic HeLa cells and mouse chondrogenic ATDC5 cells transfected with a luciferase-reporter gene containing the promoter fragments. Protein-DNA binding was examined by electrophoretic mobility shift and chromatin immunoprecipitation assays. The chondrogenic differentiation was assessed by endogenous SOX9, SOX6, and COL2A1 mRNA levels, and by Alcian blue staining and alkaline phosphatase activity.

RESULTS

Among transcription factors whose binding motifs were identified in the highly-conserved regions between human and mouse SOX9 promoters, a nuclear factor kappa B (NF-kappaB) member RelA strongly activated the promoter activity. RelA and SOX9 were co-localized in the limb cartilage. Deletion, mutagenesis, and tandem-repeat analyses identified the core region responsive to RelA at the NF-kappaB binding motif to be around -250bp of the human SOX9 promoter, and this was confirmed to show specific binding to RelA. RelA induced the chondrogenic differentiation parameters in HeLa and ATDC5 cells.

CONCLUSION

We have identified RelA as a transcriptional factor for SOX9 induction and chondrogenic differentiation via binding to an NF-kappaB binding motif in the SOX9 promoter.

Osteoarthritis development in novel experimental mouse models induced by knee joint instability

OBJECTIVE

Although osteoarthritis (OA) is induced by accumulated mechanical stress to joints, little is known about the underlying molecular mechanism. To apply approaches from mouse genomics, this study created experimental mouse OA models by producing instability in the knee joints.

METHODS

The models were of four types: severe, moderate, mild, and medial, depending on the severity and direction of instability imposed by combinations of ligament transection and menisectomy. OA development was evaluated by X-ray and histology by Safranin-O staining, and quantified using our original gradings. Expressions of type II, IX and X collagens and matrix metalloproteinase (MMP)-2, -3, -9 and -13 were further examined by immunohistochemistry and in situ hybridization (ISH).

RESULTS

The severe, moderate and mild models exhibited OA development in the posterior tibial cartilage. The severe model showed cartilage destruction at 2 weeks and osteophyte formation at 4-8 weeks after surgery; however, the mild model showed only a partial cartilage destruction at 8 weeks. The grading confirmed that the OA disorders progressed depending on the severity of joint instability. In the medial model, the OA development in the medial tibial cartilage was similar to that in the posterior cartilage of the mild model. Among the collagens and MMPs, type X collagen and MMP-13 were markedly induced and colocalized in the early stage OA cartilage.

CONCLUSION

We established four types of mouse models exhibiting various speeds of OA progression. By applying a mouse genomics approach to the models, molecular backgrounds in various stages of OA development can be clarified.

The parathyroid hormone-related protein and Indian hedgehog feedback loop in the growth plate

Normal development of the growth plate requires coordinated proliferation and differentiation of chondrocytes and osteoblasts. In previous work, we have shown that Indian hedgehog (IHH), produced by prehypertrophic and hypertrophic chondrocytes, stimulates production of parathyroid hormone-related protein (PTHrP) by perichondrial and early chondrocytic cells. PTHrP then maintains chondrocytes in a proliferative, less differentiated state. Because this less differentiated state delays the production of IHH, IHH and PTHrP may participate in a negative feedback loop that synchronizes and determines the pace of differentiation of chondrocytes in the growth plate. To establish the roles of physiological levels of PTHrP and IHH, we have now injected PTH/PTHrP receptor (-/-) embryonic stem (ES) cells into normal blastocysts to generate mice with chimeric growth plates. The PTH/PTHrP receptor cells leave the proliferative cycle and differentiate prematurely in the middle of the normal proliferative columns. The columns of wild-type cells are longer than normal and the adjacent bone collar is also longer than normal. Patterns of gene expression and the use of chimeras using PTH/PTHrP receptor (-/-); IHH (-/-) ES cells suggest that modified patterns of IHH and PTHrP synthesis explain these abnormalities. Thus, IHH is a master regulator of both chondrocyte and osteoblast differentiation.

Parathyroid hormone-related peptide and Indian hedgehog

Normal endochondral bone development requires temporal and spatial coordination of various cell types. Parathyroid hormone-related peptide and Indian hedgehog interact with each other and form a feedback loop that plays a major role in this coordination. Defects in the signalling of either of the two molecules cause severe bone malformations.

Parathyroid hormone-related peptide (PTHrP) induces parietal endoderm formation exclusively via the type I PTH/PTHrP receptor

A number of studies suggest a role for PTHrP and the classical PTH/PTHrP receptor (type I) in one of the first differentiation processes in mouse embryogenesis, i.e. the formation of parietal endoderm (PE). We previously reported that although in type I receptor (-/-) embryos PE formation seemed normal, the embryos were smaller from at least day 9.5 p.c. and 60% had died before day 12.5 p.c. Here we show that the observed growth defect commences even earlier, at day 8.5 p.c. Using two novel antibodies, we show that the expression of the type I receptor protein at this stage is confined to extraembryonic endoderm only. In addition, we show that large amounts of PTHrP protein are present in the adjacent trophoblast giant cells, suggesting a paracrine interaction of PTHrP and the type I PTH/PTHrP receptor in PE formation. The involvement in PE differentiation of other recently described receptors for PTHrP would explain a possible redundancy for the type I receptor in PE formation. However, deletion of the type I PTH/PTHrP receptor in ES cells by homologous recombination completely prevents PTHrP-induced PE differentiation. Based upon these observations, we propose that PTHrP and the type I PTH/PTHrP receptor, although not required for the initial formation of PE, are required for its proper differentiation and/or functioning.

The interaction between Ku antigen and REF1 protein mediates negative gene regulation by extracellular calcium

Through the specific binding of a negative calcium-responsive element to its binding protein in response to extracellular Ca (Ca2+e), negative calcium-responsive element-bearing genes, such as the human parathyroid hormone gene, are negatively regulated by Ca2+e. The Ku antigen mediated negative gene regulation by Ca2+e by interacting with a redox factor protein, REF1. Although sequence-nonspecific DNA binding activity of the Ku antigen has been well characterized, the mechanism of its sequence-specific DNA binding remained obscure. Here, we report that the specific binding of the Ku antigen to another protein, REF1, leads to DNA-protein complex formation with a novel sequence specificity and thereby regulates gene expression.

A redox factor protein, ref1, is involved in negative gene regulation by extracellular calcium

A rise in extracellular calcium (Ca2+e) suppresses not only secretion of parathyroid hormone (PTH) but also expression of the PTH gene to ensure constant plasma Ca2+ level. A nuclear protein(s) in a wide variety of cells bound to the specific DNA elements (negative Ca2+ responsive elements, nCaREs) in the human PTH gene in sequence-specific and Ca2+e concentration-dependent manners. Our Southwestern cloning revealed that a redox factor protein (ref1), which was known to activate several transcription factors via alterations of their redox state, belonged to an nCaRE binding protein. The level of ref1 mRNA as well as of its protein was elevated by an increase in Ca2+e concentration. In gel shift assay, anti-ref1 antibody eliminated formation of the nCaRE-protein complex. We also found that there was another protein(s) interacting with nCaREs and ref1. Further, experiments with an antisense-ref cDNA expression vector introduced into cultured cells suggested that DNA (nCaRE)-ref1 interaction led to Ca2+e-mediated transcriptional suppression. Thus, it is concluded that ref1 possesses transcription repressor activity in addition to its function as a transcriptional auxiliary protein.

A patient with protein-losing enteropathy associated with systemic lupus erythematosus

A 46-year-old woman previously diagnosed as having systemic lupus erythematosus presented with severe hypoalbuminemia and anasarca. She was demonstrated to have protein-losing enteropathy without any other active symptoms of SLE. Her bowel habit was normal and endoscopic examination revealed non-specific colitis and a small ulcer in the duodenum. Serum biochemistry showed an abnormal profile of the serum protein, including severe hyperlipoproteinemia and hyperfibrinogenemia. The process of protein-losing was not selective in terms of the molecular size. All of these symptoms and the abnormalities in laboratory data were improved by corticosteroid therapy.