Osteoarthritis (OA) is characterised by the deterioration of cartilage in the joints and pain. We hypothesise that semaphorin‐3A (sema‐3A), a chemorepellent for sensory nerves, plays a role in joint ...degradation and pain. We used the mechanical joint loading (MJL) model of OA to investigate sema‐3A expression in the joint and examine its association with the development of OA and pain. We also analyse its effect on chondrocyte differentiation using the ATDC5 cell line. We demonstrate that sema‐3A is present in most tissues in the healthy joint and its expression increases in highly innervated tissues, such as cruciate ligaments, synovial lining and subchondral bone, in loaded compared to nonloaded control joints. In contrast, sema‐3A expression in cartilage was decreased in the severe OA induced by the application of high loads. There was a significant increase in circulating sema‐3A, 6 weeks after MJL compared to the nonloaded mice. mRNA for sema‐3A and its receptor Plexin A1 were upregulated in the dorsal root ganglia of mice submitted to MJL. These increases were supressed by zoledronate, an inhibitor of bone pain. Sema‐3A was expressed at all stages of Chondrocyte maturation and, when added exogenously, stimulated expression of markers of chondrocyte differentiation. This indicates that sema‐3A could affect joint tissues distinctively during the development of OA. In highly innervated joint tissues, sema‐3A could control innervation and/or induce pain‐associated neuronal changes. In cartilage, sema‐3A could favour its degeneration by modifying chondrocyte differentiation.
Significance statement
Semaphorin‐3A (sema‐3A) is an axon guidance molecule previously shown to play a role in neural ingrowth and vascularisation during degeneration of tissues. We investigated its expression in tissues of the mouse joint and examined changes in expression with the development of osteoarthritis (OA). We show that sema‐3A expression is increased in highly innervated joint tissues with OA and may control innervation in these tissues. In contrast, sema‐3A expression in cartilage decreases with the severity of OA. We also demonstrate using a chondrocytic cell line that sema‐3A stimulates expression of markers of chondrocyte differentiation and may play a role in cartilage degeneration.
Background & Aims
Bone marrow (BM) cells may transdifferentiate into or fuse with organ parenchymal cells. BM therapy shows promise in murine models of cirrhosis, and clinical trials of bone marrow ...stem cell therapy for organ healing are underway. However, the BM may contribute to scar-forming myofibroblasts in various organs including the liver. We have studied this axis of regeneration and scarring in murine models of cirrhosis, including an assessment of the temporal and functional contribution of the BM-derived myofibroblasts.
Methods
Female mice were lethally irradiated and received male BM transplants. Carbon tetrachloride or thioacetamide was used to induce cirrhosis. BM-derived cells were tracked through in situ hybridization for the Y chromosome. BM transplants from 2 strains of transgenic mice were used to detect intrahepatic collagen production.
Results
In the cirrhotic liver, the contribution of BM to parenchymal regeneration was minor (0.6%); by contrast, the BM contributed significantly to hepatic stellate cell (68%) and myofibroblast (70%) populations. These BM-derived cells were found to be active for collagen type 1 transcription in 2 independent assays and could influence the fibrotic response to organ injury. These BM-derived myofibroblasts did not occur through cell fusion between BM-derived cells and indigenous hepatic cells but, instead, originated largely from the BM’s mesenchymal stem cells.
Conclusions
The BM contributes functionally and significantly to liver fibrosis and is a potential therapeutic target in liver fibrosis. Clinical trials of BM cell therapy for liver regeneration should be vigilant for the possibility of enhanced organ fibrosis.
Alkaptonuria (AKU) is caused by homogentisate 1,2‐dioxygenase deficiency that leads to homogentisic acid (HGA) accumulation, ochronosis and severe osteoarthropathy. Recently, nitisinone treatment, ...which blocks HGA formation, has been effective in AKU patients. However, a consequence of nitisinone is elevated tyrosine that can cause keratopathy. The effect of tyrosine and phenylalanine dietary restriction was investigated in nitisinone‐treated AKU mice, and in an observational study of dietary intervention in AKU patients. Nitisinone‐treated AKU mice were fed tyrosine/phenylalanine‐free and phenylalanine‐free diets with phenylalanine supplementation in drinking water. Tyrosine metabolites were measured pre‐nitisinone, post‐nitisinone, and after dietary restriction. Subsequently an observational study was undertaken in 10 patients attending the National Alkaptonuria Centre (NAC), with tyrosine >700 μmol/L who had been advised to restrict dietary protein intake and where necessary, to use tyrosine/phenylalanine‐free amino acid supplements. Elevated tyrosine (813 μmol/L) was significantly reduced in nitisinone‐treated AKU mice fed a tyrosine/phenylalanine‐free diet in a dose responsive manner. At 3 days of restriction, tyrosine was 389.3, 274.8, and 144.3 μmol/L with decreasing phenylalanine doses. In contrast, tyrosine was not effectively reduced in mice by a phenylalanine‐free diet; at 3 days tyrosine was 757.3, 530.2, and 656.2 μmol/L, with no dose response to phenylalanine supplementation. In NAC patients, tyrosine was significantly reduced (P = .002) when restricting dietary protein alone, and when combined with tyrosine/phenylalanine‐free amino acid supplementation; 4 out of 10 patients achieved tyrosine <700 μmol/L. Tyrosine/phenylalanine dietary restriction significantly reduced nitisinone‐induced tyrosinemia in mice, with phenylalanine restriction alone proving ineffective. Similarly, protein restriction significantly reduced circulating tyrosine in AKU patients.
Dear editor, On April 1st 2012, NHS England Highly Specialised Services (HSS) commissioned the National Alkaptonuria Service for adults in the Department of Clinical Biochemistry & Metabolic Medicine ...at the Royal Liverpool University Hospital. 1 The service is called the Robert Gregory National Alkaptonuria Centre (NAC) in memory of the alkaptonuria (AKU) patient who founded the Alkaptonuria Society (AKUS) in 2003.The AKUS is embedded in the NAC and crucial to its functioning and success, ensuring patients are at the centre of the service. The NAC has generated new knowledge about AKU and its management (Table S1); with a few examples being prevalent cataract before and after nitisinone, nitisinone-associated vitiligo, characterising spine and joint disease and demonstrating lack of cognitive impairment during nitisinone therapy of adults with AKU. 8–11 The NAC permitted research collaboration between the NAC and the University of Liverpool, allowing cutting edge research into AKU to be pioneered and carried out with examples including development of conditional mouse models of AKU including liver and kidney knockouts in which new therapies are tested such as tyrosine-reducing therapies, as well as enzyme replacement therapies involving gene and mRNA administration. 12 A new mechanism of joint damage in AKU was developed and found to apply in osteoarthritis. 13 Unachieved goals and further challenges: ...we have developed an assay system using the MitraTM sampling device, which offers a more user-friendly and robust alternative. 14 Preliminary feedback from patients has been positive and we are in the process of integrating this into the patient pathway.
Objective
Cartilage destruction in osteoarthritis (OA) is mediated mainly by matrix metalloproteinases (MMPs) and ADAMTS. The therapeutic candidature of targeting aggrecanases has not yet been ...defined in joints in which spontaneous OA arises from genetic susceptibility, as in the case of the STR/Ort mouse, without a traumatic or load‐induced etiology. In addition, we do not know the long‐term effect of aggrecanase inhibition on bone. We undertook this study to assess the potential aggrecanase selectivity of a variant of tissue inhibitor of metalloproteinases 3 (TIMP‐3), called ‐1ATIMP‐3, on spontaneous OA development and bone formation in STR/Ort mice.
Methods
Using the background of STR/Ort mice, which develop spontaneous OA, we generated transgenic mice that overexpress ‐1ATIMP‐3, either ubiquitously or conditionally in chondrocytes. ‐1ATIMP‐3 has an extra alanine at the N‐terminus that selectively inhibits ADAMTS but not MMPs. We analyzed a range of OA‐related measures in all mice at age 40 weeks.
Results
Mice expressing high levels of ‐1ATIMP‐3 were protected against development of OA, while those expressing low levels were not. Interestingly, we also found that high levels of ‐1ATIMP‐3 transgene overexpression resulted in increased bone mass, particularly in females. This regulation of bone mass was at least partly direct, as adult mouse primary osteoblasts infected with ‐1ATIMP‐3 in vitro showed elevated rates of mineralization.
Conclusion
The results provide evidence that ‐1ATIMP‐3–mediated inhibition of aggrecanases can protect against cartilage degradation in a naturally occurring mouse model of OA, and they highlight a novel role that aggrecanase inhibition may play in increased bone mass.
Osteoporosis is the most common age‐related metabolic bone disorder, which is characterized by low bone mass and deterioration in bone architecture, with a propensity to fragility fractures. The best ...treatment for osteoporosis relies on stimulation of osteoblasts to form new bone and restore bone structure, however, anabolic therapeutics are few and their use is time restricted. Here, we report that Syndecan‐3 increases new bone formation through enhancement of WNT signaling in osteoblasts. Young adult Sdc3−/− mice have low bone volume, reduced bone formation, increased bone marrow adipose tissue, increased bone fragility, and a blunted anabolic bone formation response to mechanical loading. This premature osteoporosis‐like phenotype of Sdc3−/− mice is due to delayed osteoblast maturation and impaired osteoblast function, with contributing increased osteoclast‐mediated bone resorption. Indeed, overexpressing Sdc3 in osteoblasts using the Col1a1 promoter rescues the low bone volume phenotype of the Sdc3−/− mice, and also increases bone volume in WT mice. Mechanistically, SDC3 enhances canonical WNT signaling in osteoblasts through stabilization of Frizzled 1, making SDC3 an attractive target for novel bone anabolic drug development.
Background & Aims Recent studies have reported that bone marrow (BM)-derived cells migrating into fibrotic liver tissue exhibit a myofibroblast-like phenotype and may participate in the progression ...of liver fibrosis. However, their contribution to collagen production has not been fully verified yet. We revisited this issue by using 2 mechanistically distinct liver fibrosis models introduced into transgenic collagen reporter mice and their BM recipients. Methods BM of wild-type mice was replaced by cells obtained from transgenic animals harboring tissue-specific enhancer/promoter sequences of α2(I) collagen gene ( COL1A2 ) linked to enhanced green fluorescent protein (EGFP) or firefly luciferase (LUC) gene. Liver fibrosis was introduced into those mice by repeated carbon tetrachloride injections or ligation of the common bile duct. Activation of COL1A2 promoter was assessed by confocal microscopic examination detecting EGFP signals and luciferase assays of liver homogenates. Results The tissue-specific COL1A2 enhancer/promoter was activated in hepatic stellate cells following a single carbon tetrachloride injection or during primary culture on plastic. A large number of EGFP-positive collagen-expressing cells were observed in liver tissue of transgenic COL1A2/EGFP mice in both liver fibrosis models. In contrast, there were few EGFP-positive BM-derived collagen-producing cells detected in fibrotic liver tissue of COL1A2/EGFP recipients. Luciferase assays of liver tissues from COL1A2/LUC-recipient mice further indicated that BM-derived cells produced little collagen in response to fibrogenic stimuli. Conclusions By using a specific and sensitive experimental system, which detects exclusively BM-derived collagen-producing cells, we conclude an unexpectedly limited role of BM-derived cells in collagen production during hepatic fibrogenesis.
Laminins (LMs) are essential components of all basement membranes where they regulate an extensive array of tissue functions. Alternative splicing from the laminin α3 gene produces a non‐laminin but ...netrin‐like protein, Laminin N terminus α31 (LaNt α31). LaNt α31 is widely expressed in intact tissue and is upregulated in epithelial cancers and during wound healing. In vitro functional studies have shown that LaNt α31 can influence numerous aspects of epithelial cell behavior via modifying matrix organization, suggesting a new model of laminin auto‐regulation. However, the function of this protein has not been established in vivo. Here, a mouse transgenic line was generated using the ubiquitin C promoter to drive inducible expression of LaNt α31. When expression was induced at embryonic day 15.5, LaNt α31 transgenic animals were not viable at birth, exhibiting localized regions of erythema. Histologically, the most striking defect was widespread evidence of extravascular bleeding across multiple tissues. Additionally, LaNt α31 transgene expressing animals exhibited kidney epithelial detachment, tubular dilation, disruption of the epidermal basal cell layer and of the hair follicle outer root sheath, and ~50% reduction of cell numbers in the liver, associated with depletion of hematopoietic erythrocytic foci. These findings provide the first in vivo evidence that LaNt α31 can influence tissue morphogenesis.
Objective
The excessive deposition of extracellular matrix, including type I collagen, is a key aspect in the pathogenesis of connective tissue diseases such as systemic sclerosis (SSc; scleroderma). ...To further our understanding of the mechanisms governing the dysregulation of type I collagen production in SSc, we investigated the role of the activator protein 1 (AP‐1) family of transcription factors in regulating COL1A2 transcription.
Methods
The expression and nuclear localization of AP‐1 family members (c‐Jun, JunB, JunD, Fra‐1, Fra‐2, and c‐Fos) were examined by immunohistochemistry and Western blotting in dermal biopsy specimens and explanted skin fibroblasts from patients with diffuse cutaneous SSc and healthy controls. Gene activation was determined by assessing the interaction of transcription factors with the COL1A2 enhancer using transient transfection of reporter gene constructs, electrophoretic mobility shift assays, chromatin immunoprecipitation analysis, and RNA interference involving knockdown of individual AP‐1 family members. Inhibition of fibroblast mammalian target of rapamycin (mTOR), Akt, and glycogen synthase kinase 3β (GSK‐3β) signaling pathways was achieved using small‐molecule pharmacologic inhibitors.
Results
Binding of JunB to the COL1A2 enhancer was observed, with its coalescence directed by activation of gene transcription through the proximal promoter. Knockdown of JunB reduced enhancer activation and COL1A2 expression in response to transforming growth factor β. In SSc dermal fibroblasts, increased mTOR/Akt signaling was associated with inactivation of GSK‐3β, leading to blockade of JunB degradation and, thus, constitutively high expression of JunB.
Conclusion
In patients with SSc, the accumulation of JunB resulting from altered mTOR/Akt signaling and a failure of proteolytic degradation underpins the aberrant overexpression of type I collagen. These findings identify JunB as a potential target for antifibrotic therapy in SSc.
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