Cartilage oligomeric matrix protein associates with granulin-epithelin precursor (GEP) and potentiates GEP-stimulated chondrocyte proliferation

Collagen II regulates chondroycte integrin expression profile and differentiation

Collagen II is the major fibril-forming collagen in cartilage. Complete absence of collagen II in mice is not compatible with life and in humans mutations in the COL2A1 gene lead to osteochondrodysplasias with diverse phenotypes. However, mechanistic studies on how chondrocytes respond to a lack of collagen II in their extracellular matrix are limited. Primary mouse chondrocytes were isolated from knee joints of newborn mice and transfected with siRNA targeting Col2α1 to suppress collagen II expression. The expression of integrin receptors and matrix proteins was investigated by RT-PCR and immunoblots. The localization of matrix components was evaluated by immunostaining. Signaling pathways and the differentiation state of chondrocytes was monitored by RT-PCR and flow cytometry. We demonstrate that in the absence of collagen II chondrocytes start to produce collagen I. Some binding partners of collagen II are partially lost from the matrix while other proteins, e.g. COMP, were still found associated with the newly formed collagen network. The lack of collagen II induced changes in the expression profile of integrins. Further, we detected alterations in the Indian hedgehog/parathyroid hormone-related protein (Ihh/PTHrP) pathway that were accompanied by changes in the differentiation state of chondrocytes. Collagen II seems not to be essential for chondrocyte survival in culture but it plays an important role in maintaining chondrocyte differentiation. We suggest that a crosstalk between extracellular matrix and cells via integrins and the Ihh/PTHrP pathway is involved in regulating the differentiation state of chondrocytes.

Antioxidant and anti-inflammatory agents mitigate pathology in a mouse model of pseudoachondroplasia

Pseudoachondroplasia (PSACH), a severe short-limb dwarfing condition, results from mutations that cause misfolding of the cartilage oligomeric matrix protein (COMP). Accumulated COMP in growth plate chondrocytes activates endoplasmic reticulum stress, leading to inflammation and chondrocyte death. Using a MT-COMP mouse model of PSACH that recapitulates the molecular and clinical PSACH phenotype, we previously reported that oxidative stress and inflammation play important and unappreciated roles in PSACH pathology. In this study, we assessed the ability of antioxidant and anti-inflammatory agents to affect skeletal and cellular pathology in our mouse model of PSACH. Treatment of MT-COMP mice with aspirin or resveratrol from birth to P28 decreased mutant COMP intracellular retention and chondrocyte cell death, and restored chondrocyte proliferation. Inflammatory markers associated with cartilage degradation and eosinophils were present in the joints of untreated juvenile MT-COMP mice, but were undetectable in treated mice. Most importantly, these treatments resulted in significantly increased femur length. This is the first and only therapeutic approach shown to mitigate both the chondrocyte and long-bone pathology of PSACH in a mouse model and suggests that reducing inflammation and oxidative stress early in the disease process may be a novel approach to treat this disorder.

Intra-articular transplantation of atsttrin-transduced mesenchymal stem cells ameliorate osteoarthritis development

Osteoarthritis (OA) remains an intractable clinical challenge. Few drugs are available for reversing this degenerative disease, although some promising candidates have performed well in preclinical studies. Tumor necrosis factor α (TNFα) has been identified as a crucial effector modulating OA pathogenesis. This study aimed to investigate the therapeutic effects of Atsttrin, a novel TNFα blocker, on OA treatment. We developed genetically modified mesenchymal stem cells (MSCs) that expressed recombinant Atsttrin (named as MSC-Atsttrin). Expression levels of ADAMTS-5, MMP13, and iNOS of human chondrocytes were analyzed when cocultured with MSC-GFP/Atsttrin. OA animal models were induced by anterior cruciate ligament transection, and MSC-GFP/Atsttrin were injected into the articular cavity 1 week postsurgery. The results showed that MSC-Atsttrin significantly suppressed TNFα-driven up-regulation of matrix proteases and inflammatory factors. Intra-articular injection of MSC-Atsttrin prevented the progression of degenerative changes in the surgically induced OA mouse model. Additionally, levels of detrimental matrix hydrolases were significantly diminished. Compared with nontreated OA samples at 8 weeks postsurgery, the percentages of MMP13- and ADAMTS-5-positive cells were significantly reduced from 91.33% ± 9.87% to 24.33% ± 5.7% (p < .001) and from 91.33% ± 7.1% to 16.67% ± 3.1% (p < .001), respectively. Our results thus indicated that suppression of TNFα activity is an effective strategy for OA treatment and that intra-articular injection of MSCs-Atsttrin could be a promising therapeutic modality.

Progranulin knockout accelerates intervertebral disc degeneration in aging mice

Intervertebral disc (IVD) degeneration is a common degenerative disease, yet much is unknown about the mechanisms during its pathogenesis. Herein we investigated whether progranulin (PGRN), a chondroprotective growth factor, is associated with IVD degeneration. PGRN was detectable in both human and murine IVD. The levels of PGRN were upregulated in murine IVD tissue during aging process. Loss of PGRN resulted in an early onset of degenerative changes in the IVD tissue and altered expressions of the degeneration-associated molecules in the mouse IVD tissue. Moreover, PGRN knockout mice exhibited accelerated IVD matrix degeneration, abnormal bone formation and exaggerated bone resorption in vertebra with aging. The acceleration of IVD degeneration observed in PGRN null mice was probably due to the enhanced activation of NF-κB signaling and β-catenin signaling. Taken together, PGRN may play a critical role in homeostasis of IVD, and may serve as a potential molecular target for prevention and treatment of disc degenerative diseases.

Progranulin protects against osteoarthritis through interacting with TNF-α and β-Catenin signalling

OBJECTIVE

Progranulin (PGRN) was previously isolated as an osteoarthritis (OA)-associated growth factor. Additionally, PGRN was found to play a therapeutic role in inflammatory arthritis mice models through antagonising tumour necrosis factor α (TNF-α). This study was aimed at investigating the role of PGRN in degradation of cartilage and progression of OA.

METHODS

Progression of OA was analysed in both spontaneous and surgically induced OA models in wild type and PGRN-deficient mice. Cartilage degradation and OA were evaluated using Safranin O staining, immunohistochemistry and ELISA. Additionally, mRNA expression of degenerative factors and catabolic markers known to be involved in cartilage degeneration in OA were analysed. Furthermore, the anabolic effects and underlying mechanisms of PGRN were investigated by in vitro experiments with primary chondrocytes.

RESULTS

Here, we found that deficiency of PGRN led to spontaneous OA-like phenotype in 'aged' mice. Additionally, PGRN-deficient mice exhibited exaggerated breakdown of cartilage structure and OA progression, while local delivery of recombinant PGRN protein attenuated degradation of cartilage matrix and protected against OA development in surgically induced OA models. Furthermore, PGRN activated extracellular signal-regulated kinases (ERK) 1/2 signalling and elevated the levels of anabolic biomarkers in human chondrocyte, and the protective function of PGRN was mediated mainly through TNF receptor 2. Additionally, PGRN suppressed inflammatory action of TNF-α and inhibited the activation of β-Catenin signalling in cartilage and chondrocytes.

CONCLUSIONS

Collectively, this study provides new insight into the pathogenesis of OA, and also presents PGRN as a potential target for the treatment of joint degenerative diseases, including OA.

Pseudoachondroplasia/COMP - translating from the bench to the bedside

Pseudoachondroplasia (PSACH) is a skeletal dysplasia characterized by disproportionate short stature, small hands and feet, abnormal joints and early onset osteoarthritis. PSACH is caused by mutations in thrombospondin-5 (TSP-5, also known as cartilage oligomeric matrix protein or COMP), a pentameric extracellular matrix protein primarily expressed in chondrocytes and musculoskeletal tissues. The thrombospondin gene family is composed of matricellular proteins that associate with the extracellular matrix (ECM) and regulate processes in the matrix. Mutations in COMP interfere with calcium-binding, protein conformation and export to the extracellular matrix, resulting in inappropriate intracellular COMP retention. This accumulation of misfolded protein is cytotoxic and triggers premature death of chondrocytes during linear bone growth, leading to shortened long bones. Both in vitro and in vivo models have been employed to study the molecular processes underlying development of the PSACH pathology. Here, we compare the strengths and weaknesses of current mouse models of PSACH and discuss how the resulting phenotypes may be translated to clinical therapies.

Regulation of chondrocyte differentiation by IRE1α depends on its enzymatic activity

Bone morphogenetic protein 2(BMP2) is known to activate unfolded protein response (UPR) signal molecules in chondrogenesis. Inositol-requiring enzyme-1α (IRE1α),as one of three unfolded protein sensors in UPR signaling pathways, can be activated during ER stress. However, the influence on IRE1α in chondrocyte differentiation has not yet been elucidated. Here we present evidence demonstrating that overexpression of IRE1α inhibits chondrocyte differentiation, as revealed by reduced expression of collagen II (ColII), Sox9, collagen X (ColX), matrix metalloproteinase 13 (MMP-13), Indian hedgehog (IHH), Runx2 and enhanced expression of parathyroid hormone-related peptide (PTHrP). Furthermore, IRE1α-mediated inhibition of chondrogenesis depends on its enzymatic activity, since its point mutant lacking enzymatic activity completely loses this activity. The RNase and Kinase domains of IRE1α C-terminal are necessary for its full enzymatic activity and inhibition of chondrocyte differentiation. Mechanism studies demonstrate that granulin-epithelin precursor(GEP), a growth factor known to stimulate chondrogenesis, induced IRE1α expression in chondrogenesis. The expression of IRE1α is depended on GEP signaling, and IRE1α expression is hardly detectable in GEP(-/-) embryos. In addition, IRE1α inhibits GEP-mediated chondrocyte differentiation as a negative regulator. Altered expression of IRE1α in chondrocyte hypertrophy was accompanied by altered levels of IHH and PTHrP. Collectively, IRE1α may be a novel regulator of chondrocyte differentiation by 1) inhibition GEP-mediated chondrocyte differentiation as a negative regulator; 2) promoting IHH/PTHrP signaling.

IRE1a constitutes a negative feedback loop with BMP2 and acts as a novel mediator in modulating osteogenic differentiation

Bone morphogenetic protein 2 (BMP2) is known to activate unfolded protein response (UPR) signaling molecules, such as BiP (IgH chain-binding protein), PERK (PKR-like ER-resistant kinase), and IRE1α. Inositol-requiring enzyme-1a (IRE1a), as one of three unfolded protein sensors in UPR signaling pathways, can be activated during ER stress. Granulin-epithelin precursor (GEP) is an autocrine growth factor that has been implicated in embryonic development, tissue repair, tumorigenesis, and inflammation. However, the influence on IRE1a in BMP2-induced osteoblast differentiation has not yet been elucidated. Herein we demonstrate that overexpression of IRE1a inhibits osteoblast differentiation, as revealed by reduced activity of alkaline phosphatase (ALP) and osteocalcin; however, knockdown of IRE1a via the RNAi approach stimulates osteoblastogenesis. Mechanistic studies revealed that the expression of IRE1a during osteoblast was a consequence of JunB transcription factor binding to several AP1 sequence (TGAG/CTCA) in the 5'-flanking regulatory region of the IRE1a gene, followed by transcription. In addition, GEP induces IRE1a expressions and this induction of IRE1a by GEP depends on JunB. Furthermore, IRE1a inhibition of GEP-induced osteoblastogenesis relies on JunB. Besides, GEP is required for IRE1a inhibition of BMP2-induced bone formation. Collectively, these findings demonstrate that IRE1a negatively regulates BMP2-induced osteoblast differentiation and this IRE1a inhibition effect depends on GEP growth factor. Thus, IRE1a, BMP2, GEP growth factor, and JunB transcription factor form a regulatory loop and act in concert in the course of osteoblastogenesis.

XBP1S, a BMP2-inducible transcription factor, accelerates endochondral bone growth by activating GEP growth factor

We previously reported that transcription factor XBP1S binds to RUNX2 and enhances chondrocyte hypertrophy through acting as a cofactor of RUNX2. Herein, we report that XBP1S is a key downstream molecule of BMP2 and is required for BMP2-mediated chondrocyte differentiation. XBP1S is up-regulated during chondrocyte differentiation and demonstrates the temporal and spatial expression pattern during skeletal development. XBP1S stimulates chondrocyte differentiation from mesenchymal stem cells in vitro and endochondral ossification ex vivo. In addition, XBP1S activates granulin-epithelin precursor (GEP), a growth factor known to stimulate chondrogenesis, and endogenous GEP is required, at least in part, for XBP1S-stimulated chondrocyte hypertrophy, mineralization and endochondral bone formation. Furthermore, XBP1S enhances GEP-stimulated chondrogenesis and endochondral bone formation. Collectively, these findings demonstrate that XBP1S, a BMP2-inducible transcription factor, positively regulates endochondral bone formation by activating GEP chondrogenic growth factor.

Establishment of a surgically-induced model in mice to investigate the protective role of progranulin in osteoarthritis

Destabilization of medial meniscus (DMM) model is an important tool for studying the pathophysiological roles of numerous arthritis associated molecules in the pathogenesis of osteoarthritis (OA) in vivo. However, the detailed, especially the visualized protocol for establishing this complicated model in mice, is not available. Herein we took advantage of wildtype and progranulin (PGRN)-/- mice as examples to introduce a protocol for inducing DMM model in mice, and compared the onset of OA following establishment of this surgically induced model. The operations performed on mice were either sham operation, which just opened joint capsule, or DMM operation, which cut the menisco-tibial ligament and caused destabilization of medial meniscus. Osteoarthritis severity was evaluated using histological assay (e.g. Safranin O staining), expressions of OA-associated genes, degradation of cartilage extracellular matrix molecules, and osteophyte formation. DMM operation successfully induced OA initiation and progression in both wildtype and PGRN-/- mice, and loss of PGNR growth factor led to a more severe OA phenotype in this surgically induced model.

The role of PGRN in musculoskeletal development and disease

Progranulin (PGRN) is a growth factor that has been implicated in wound healing, inflammation, infection, tumorigenesis, and is most known for its neuroprotective and proliferative properties in neurodegenerative disease. This pleiotropic growth factor has been found to be a key player and regulator of a diverse spectrum of multi-systemic functions. Its critical anti-inflammatory role in rheumatoid arthritis and other inflammatory disease models has allowed for the propulsion of research to establish its significance in musculoskeletal diseases, including inflammatory conditions involving bone and cartilage pathology. In this review, we aim to elaborate on the emerging role of PGRN in the musculoskeletal system, reviewing its particular mechanisms described in various musculoskeletal diseases, with special focus on osteoarthritis and inflammatory joint disease patho-mechanisms and potential therapeutic applications of PGRN and its derivatives in these and other musculoskeletal diseases.

Identification, prioritization, and evaluation of glycoproteins for aggressive prostate cancer using quantitative glycoproteomics and antibody-based assays on tissue specimens

Prostate cancer is highly heterogeneous in nature; while the majority of cases are clinically insignificant, some cases are lethal. Currently, there are no reliable screening methods for aggressive prostate cancer. Since most established serum and urine biomarkers are glycoproteins secreted or leaked from the diseased tissue, the current study seeks to identify glycoprotein markers specific to aggressive prostate cancer using tissue specimens. With LC-MS/MS glycoproteomic analysis, we identified 350 glycopeptides with 17 being altered in aggressive prostate cancer. ELISA assays were developed/purchased to evaluate four candidates, that is, cartilage oligomeric matrix protein (COMP), periostin, membrane primary amine oxidase (VAP-1), and cathepsin L, in independent tissue sets. In agreement with the proteomic analysis, we found that COMP and periostin expressions were significantly increased in aggressive prostate tumors while VAP-1 expression was significantly decreased in aggressive tumor. In addition, the expression of these proteins in prostate metastases also follows the same pattern observed in the proteomic analysis. This study provides a workflow for biomarker discovery, prioritization, and evaluation of aggressive prostate cancer markers using tissue specimens. Our data suggest that increase in COMP and periostin and decrease in VAP-1 expression in the prostate may be associated with aggressive prostate cancer.

The promotion of bone healing by progranulin, a downstream molecule of BMP-2, through interacting with TNF/TNFR signaling

Endochondral ossification plays a key role in the bone healing process, which requires normal cartilage callus formation. Progranulin (PGRN) growth factor is known to enhance chondrocyte differentiation and endochondral ossification during development, yet whether PGRN also plays a role in bone regeneration remains unknown. In this study we established surgically-induced bone defect and ectopic bone formation models based on genetically-modified mice. Thereafter, the bone healing process of those mice was analyzed through radiological assays including X-ray and micro CT, and morphological analysis including histology and immunohistochemistry. PGRN deficiency delayed bone healing, while recombinant PGRN enhanced bone regeneration. Moreover, PGRN was required for BMP-2 induction of osteoblastogenesis and ectopic bone formation. Furthermore, the role of PGRN in bone repair was mediated, at least in part, through interacting with TNF-α signaling pathway. PGRN-mediated bone formation depends on TNFR2 but not TNFR1, as PGRN promoted bone regeneration in deficiency of TNFR1 but lost such effect in TNFR2 deficient mice. PGRN blocked TNF-α-induced inflammatory osteoclastogenesis and protected BMP-2-mediated ectopic bone formation in TNF-α transgenic mice. Collectively, PGRN acts as a critical mediator of the bone healing process by constituting an interplay network with BMP-2 and TNF-α signaling, and this represents a potential molecular target for treatment of fractures, especially under inflammatory conditions.

Progranulin deficiency exaggerates, whereas progranulin-derived Atsttrin attenuates, severity of dermatitis in mice

PGRN and its derived engineered protein, Atsttrin, were reported to antagonize TNFα and protect against inflammatory arthritis [Tang, W. et al. (2011) The growth factor progranulin binds to TNF receptors and is therapeutic against inflammatory arthritis in mice. Science 332 (6028) 478-484]. Here we found that PGRN level was also significantly elevated in skin inflammation. PGRN-/- mice exhibited more severe inflammation following induction of oxazolone (OXA). In contrast, recombinant Atsttrin protein effectively attenuated inflammation in mice dermatitis model. In addition, the protective role of PGRN and Atsttrin in dermatitis was probably due to their inhibition on NF-κB signaling. Collectively, PGRN, especially its derived engineered protein, Atsttrin, may represent a potential molecular target for prevention and treatment of inflammatory skin diseases.

Insights into the role of progranulin in immunity, infection, and inflammation

PGRN, a pleiotrophic growth factor, is known to play an important role in the maintenance and regulation of the homeostatic dynamics of normal tissue development, proliferation, regeneration, and the host-defense response and therefore, has been widely studied in the fields of infectious diseases, wound healing, tumorigenesis, and neuroproliferative and degenerative diseases. PGRN has also emerged as a multifaceted immune-regulatory molecule through regulating the signaling pathways known to be critical for immunology, especially TNF/TNFR signaling. In this review, we start with updates about the interplays of PGRN with ECM proteins, proteolytic enzymes, inflammatory cytokines, and cell-surface receptors, as well as various pathophysiological processes involved. We then review the data supporting an emerging role of PGRN in the fields of the "Cubic of I", namely, immunity, infection, and inflammation, with special focus on its regulation of autoimmune syndromes. We conclude with insights into the immunomodulating, anti-inflammatory, therapeutic potential of PGRN in treating diseases with an inflammatory etiology in a vast range of medical specialties.

Negative effects of ADAMTS-7 and ADAMTS-12 on endplate cartilage differentiation

The roles of ADAMTS-7 and ADAMTS-12 in disc degeneration have not been previously examined. The purpose of this study was to examine the expression of ADAMTS-7 and ADAMTS-12 in the endplate cells isolated from patients with degenerative disc disease and to see whether they are associated with the pathological change of endplate. Sixty-four degenerated lumbar endplate specimens were obtained from the patients with degenerative disc disease categorized as type Modic I or II in magnetic resonance imaging (MRI) and 12 nondegenerative specimens as control (vertebra burst fracture patients without degenerative change in MRI) during surgical procedures. The expression of ADAMTS-7 and ADAMTS-12 was examined by real-time PCR and Western blotting. A statistically significant increase in mRNA expression of ADAMTS-7 and ADAMTS-12 was observed in the endplate cells in degenerative discs compared with nondegenerative discs. The corresponding protein levels of ADAMTS-7 and ADAMTS-12 had the same expression patterns. Moreover, ADAMTS-7 and ADAMTS-12 down-regulated the expression of Col II, Sox9, and Col X the marker genes for chondrogenesis. Our results indicate that ADAMTS-7 and ADAMTS-12 appear to be potent negative regulators of endplate cartilage development.

Identification and characterization of tropomyosin 3 associated with granulin-epithelin precursor in human hepatocellular carcinoma

BACKGROUND AND AIM

Granulin-epithelin precursor (GEP) has previously been reported to control cancer growth, invasion, chemo-resistance, and served as novel therapeutic target for cancer treatment. However, the nature and characteristics of GEP interacting partner remain unclear. The present study aims to identify and characterize the novel predominant interacting partner of GEP using co-immunoprecipitation and mass spectrometry.

METHODS AND RESULTS

Specific anti-GEP monoclonal antibody was used to capture GEP and its interacting partner from the protein extract of the liver cancer cells Hep3B. The precipitated proteins were analyzed by SDS-PAGE, followed by mass spectrometry and the protein identity was demonstrated to be tropomyosin 3 (TPM3). The interaction has been validated in additional cell models using anti-TPM3 antibody and immunoblot to confirm GEP as the interacting partner. GEP and TPM3 expressions were then examined by real-time quantitative RT-PCR in clinical samples, and their transcript levels were significantly correlated. Elevated TPM3 levels were observed in liver cancer compared with the adjacent non-tumorous liver, and patients with elevated TPM3 levels were shown to have poor recurrence-free survival. Protein expression of GEP and TPM3 was observed only in the cytoplasm of liver cancer cells by immunohistochemical staining.

CONCLUSIONS

TPM3 is an interacting partner of GEP and may play an important role in hepatocarcinogenesis.

XBP1S protects cells from ER stress-induced apoptosis through Erk1/2 signaling pathway involving CHOP

The mammalian unfolded protein response (UPR) protects the cell against the stress of misfolded proteins in the endoplasmic reticulum (ER), and the transcription factor X-box binding protein 1 spliced (XBP1S), a regulator of the UPR, is known to be important for ER stress (ERS)-mediated apoptosis and cell growth, but the molecular mechanism underlying these processes remains unexplored. Here, we report that knockdown of XBP1S by an siRNA silencing approach increased the expression of ERS-associated molecules. The overexpression of XBP1S stimulated, whereas its knockdown inhibited, cell proliferation in chondrocytes and chondrosarcoma cells; in addition, overexpression of XBP1S inhibited, while its repression enhanced, ERS-mediated apoptosis in chondrocytes and chondrosarcoma cells. Furthermore, XBP1S-mediated inhibition of apoptosis in response to ERS is through the Erk1/2 signaling pathway and down-regulation CHOP transcription factor. CHOP is one of the key downstream molecules known to be involved in ERS-mediated apoptosis. Collectively, these findings reveal a novel critical role of XBP1S in ERS-mediated apoptosis and the molecular mechanisms involved.

GEP constitutes a negative feedback loop with MyoD and acts as a novel mediator in controlling skeletal muscle differentiation

Granulin-epithelin precursor (GEP) is an autocrine growth factor that has been implicated in embryonic development, tissue repair, tumorigenesis, and inflammation. Here we report that GEP was expressed in skeletal muscle tissue and its level was differentially altered in the course of C2C12 myoblast fusion. The GEP expression during myoblast fusion was a consequence of MyoD transcription factor binding to several E-box (CANNTG) sequences in the 5'-flanking regulatory region of GEP gene, followed by transcription. Recombinant GEP potently inhibited myotube formation from C2C12 myoblasts whereas the knockdown of endogenous of GEP via a siRNA approach accelerated the fusion of myoblasts to myotubes. Interestingly, the muscle fibers of GEP knockdown mice were larger in number but noticeably smaller in size when compared to the wild-type. Mechanistic studies revealed that during myoblast fusion, the addition of GEP led to remarkable reductions in the expressions of muscle-specific transcription factors, including MyoD. In addition, the regulation of myotube formation by GEP is mediated by the anti-myogenic factor JunB, which is upregulated following GEP stimulation. Thus, GEP growth factor, JunB, and MyoD transcription factor form a regulatory loop and act in concert in the course of myogenesis.

Analysis of cartilage oligomeric matrix protein and matrix metalloproteinase-9 in cerebrospinal fluid of miniature dachshund with intervertebral disc herniation

We evaluated whether the cerebrospinal fluid (CSF) concentration of cartilage oligomeric matrix protein (COMP) is related to disease severity, prognosis and matrix metalloproteinase (MMP)-9 activity of the CSF in miniature dachshund with intervertebral disc herniation. Samples were obtained from 23 patients and 6 normal dogs, and all patients received hemilaminectomy. Twenty dogs recovered successfully and 3 of 11 dogs without deep nociception had MMP-9 activity in the CSF and an unsuccessful outcome. The COMP levels from patients were significantly higher than those from normal dogs. MMP-9 activity and neurological severity were not related to the COMP levels. However, the COMP levels from 3 unsuccessful cases that had MMP-9 activity were significantly lower than those from all recovered cases and/or successful cases without deep nociception. Concerning severe cases, increased proteolytic activity might affect the COMP concentration and prognosis due to MMP-9 associated deleterious effects.

D469del-COMP retention in chondrocytes stimulates caspase-independent necroptosis

Mutations in the cartilage oligomeric matrix protein gene (COMP) cause pseudoachondroplasia (PSACH). This dysplasia results from the intracellular retention of mutant COMP protein and premature death of growth-plate chondrocytes. Toward better understanding of these underlying mechanisms, we examined D469del-COMP activation of the unfolded protein response and cell death pathways in rat chondrosarcoma cells. Using an inducible expression system, we examined the effects of D469del-COMP retention after 4 days of mRNA expression and then 5 days without inducing agent. Retention of D469del-COMP stimulated Chop (Ddit3) and Gadd34 (Ppp1r15a) and triggered reactivation of protein translation that exacerbated intracellular retention. High levels of Nox4 and endoplasmic reticulum receptor stress-inducible Ero1β generated reactive oxygen species, causing oxidative stress. Increased expression of Gadd genes and presence of γH2AX indicated that DNA damage was occurring. The presence of cleaved apoptosis inducing factor (tAIF) and the absence of activated caspases indicated that retention of D469del-COMP triggers cell death in chondrocytes by necroptosis, a caspase-independent programmed necrosis. Loss of growth-plate chondrocytes by necroptosis was also found in our pseudoachondroplasia mouse model. These results suggest a model in which D469del-COMP expression induces persistent endoplasmic reticulum stress, oxidative stress, and DNA damage, thus priming chondrocytes for necroptosis. We define for the first time the precise mechanisms underlying D469del-COMP pathology in pseudoachondroplasia and suggest that oxidative stress and AIF may be promising therapeutic targets.

Systemic transplantation of human adipose-derived stem cells stimulates bone repair by promoting osteoblast and osteoclast function

Systemic transplantation of adipose-derived stem cells (ASCs) is emerging as a novel therapeutic option for functional recovery of diverse damaged tissues. This study investigated the effects of systemic transplantation of human ASCs (hASCs) on bone repair. We found that hASCs secrete various bone cell-activating factors, including hepatocyte growth factor and extracellular matrix proteins. Systemic transplantation of hASCs into ovariectomized mice induced an increased number of both osteoblasts and osteoclasts in bone tissue and thereby prevented bone loss. We also observed that conditioned medium from hASCs is capable of stimulating proliferation and differentiation of osteoblasts via Smad/extracellular signal-regulated kinase (ERK)/JNK (c-jun NH₂-terminal kinase) activation as well as survival and differentiation of osteoclasts via ERK/JNK/p38 activation in vitro. Overall, our findings suggest that paracrine factors secreted from hASCs improve bone repair and that hASCs can be a valuable tool for use in osteoporosis therapy.

Modified yeast-two-hybrid system to identify proteins interacting with the growth factor progranulin

Progranulin (PGRN), also known as granulin epithelin precursor (GEP), is a 593-amino-acid autocrine growth factor. PGRN is known to play a critical role in a variety of physiologic and disease processes, including early embryogenesis, wound healing, inflammation, and host defense. PGRN also functions as a neurotrophic factor, and mutations in the PGRN gene resulting in partial loss of the PGRN protein cause frontotemporal dementia. Our recent studies have led to the isolation of PGRN as an important regulator of cartilage development and degradation. Although PGRN, discovered nearly two decades ago, plays crucial roles in multiple physiological and pathological conditions, efforts to exploit the actions of PGRN and understand the mechanisms involved have been significantly hampered by our inability to identify its binding receptor(s). To address this issue, we developed a modified yeast two-hybrid (MY2H) approach based on the most commonly used GAL4 based 2-hybrid system. Compared with the conventional yeast two-hybrid screen, MY2H dramatically shortens the screen process and reduces the number of false positive clones. In addition, this approach is reproducible and reliable, and we have successfully employed this system in isolating the binding proteins of various baits, including ion channel, extracellular matrix protein, and growth factor. In this paper, we describe this MY2H experimental procedure in detail using PGRN as an example that led to the identification of TNFR2 as the first known PGRN-associated receptor.

Chop (Ddit3) is essential for D469del-COMP retention and cell death in chondrocytes in an inducible transgenic mouse model of pseudoachondroplasia

Cartilage oligomeric matrix protein (COMP), a secreted glycoprotein synthesized by chondrocytes, regulates proliferation and type II collagen assembly. Mutations in the COMP gene cause pseudoachondroplasia and multiple epiphyseal dysplasia. Previously, we have shown that expression of D469del-COMP in transgenic mice causes intracellular retention of D469del-COMP, thereby recapitulating pseudoachondroplasia chondrocyte pathology. This inducible transgenic D469del-COMP mouse is the only in vivo model to replicate the critical cellular and clinical features of pseudoachondroplasia. Here, we report developmental studies of D469del-COMP-induced chondrocyte pathology from the prenatal period to adolescence. D469del-COMP retention was limited prenatally and did not negatively affect the growth plate until 3 weeks after birth. Results of immunostaining, transcriptome analysis, and qRT-PCR suggest a molecular model in which D469del-COMP triggers apoptosis during the first postnatal week. By 3 weeks (when most chondrocytes are retaining D469del-COMP), inflammation, oxidative stress, and DNA damage contribute to chondrocyte cell death by necroptosis. Importantly, by crossing the D469del-COMP mouse onto a Chop null background (Ddit3 null), thereby eliminating Chop, the unfolded protein response was disrupted, thus alleviating both D469del-COMP intracellular retention and premature chondrocyte cell death. Chop therefore plays a significant role in processes that mediate D469del-COMP retention. Taken together, these results suggest that there may be an optimal window before the induction of significant D469del-COMP retention during which endoplasmic reticulum stress could be targeted.

Immunohistochemical analysis of cartilage-derived retinoic acid-sensitive protein (CD-RAP)/melanoma inhibitory activity (MIA) in murine, canine, bovine and equine cerebrospinal tissues

Cartilage-derived retinoic acid-sensitive protein (CD-RAP)/melanoma inhibitory activity (MIA), which appears abundantly in hypertrophic cartilage at the stage of endochondral ossification, is also detected in cerebrospinal fluid (CSF) following spinal cord injury. In this study, the localization of the CD-RAP/MIA molecule in normal tissues of the spine and brain obtained from mice, rats, dogs, cattle and horses was examined using immunohistochemistry with a specific antibody. The positive signals of CD-RAP/MIA were found at nerve cells in the spinal cords of all species and were especially strong at cerebellar Purkinje cells. The results suggested that CD-RAP/MIA included in normal cerebrospinal tissues could be a biomarker associated with tissue injuries, as the molecules might flow into the CSF.

A novel form of chondrocyte stress is triggered by a COMP mutation causing pseudoachondroplasia

Pseudoachondroplasia (PSACH) results from mutations in cartilage oligomeric matrix protein (COMP) and the p.D469del mutation within the type III repeats of COMP accounts for approximately 30% of PSACH. To determine disease mechanisms of PSACH in vivo, we introduced the Comp D469del mutation into the mouse genome. Mutant animals were normal at birth but grew slower than their wild-type littermates and developed short-limb dwarfism. In the growth plates of mutant mice chondrocyte columns were reduced in number and poorly organized, while mutant COMP was retained within the endoplasmic reticulum (ER) of cells. Chondrocyte proliferation was reduced and apoptosis was both increased and spatially dysregulated. Previous studies on COMP mutations have shown mutant COMP is co-localized with chaperone proteins, and we have reported an unfolded protein response (UPR) in mouse models of PSACH-MED (multiple epiphyseal dysplasia) harboring mutations in Comp (T585M) and Matn3, Comp etc (V194D). However, we found no evidence of UPR in this mouse model of PSACH. In contrast, microarray analysis identified expression changes in groups of genes implicated in oxidative stress, cell cycle regulation, and apoptosis, which is consistent with the chondrocyte pathology. Overall, these data suggest that a novel form of chondrocyte stress triggered by the expression of mutant COMP is central to the pathogenesis of PSACH.

Progranulin: a growth factor, a novel TNFR ligand and a drug target

Progranulin (PGRN) is abundantly expressed in epithelial cells, immune cells, neurons, and chondrocytes, and reportedly contributes to tumorigenesis. PGRN is a crucial mediator of wound healing and tissue repair. PGRN also functions as a neurotrophic factor and mutations in the PGRN gene resulting in partial loss of the PGRN protein cause frontotemporal dementia. PGRN has been found to be a novel chondrogenic growth factor and to play an important role in cartilage development and inflammatory arthritis. Although research has shown that PGRN exhibits anti-inflammatory properties, the details about the exact molecular pathway of such effects, and, in particular, the PGRN binding receptor, have not been identified so far. Recently, researchers have shown that PGRN binds to tumor necrosis factor (TNF)-receptors (TNFR), interfering with the interaction between TNFα and TNFR. They further demonstrated that mice deficient in PGRN are susceptible to collagen-induced arthritis, an experimental model of rheumatoid arthritis, and that administration of PGRN reversed the arthritic process. An engineered protein made of three PGRN fragments (Atsttrin), displayed selective TNFR binding and was more active than natural PGRN. Both PGRN and Atsttrin prevented inflammation in various arthritis mouse models and inhibited TNFα-induced intracellular signaling pathways. Thus, PGRN is a key regulator of inflammation and it may mediate its anti-inflammatory effects, at least in part, by blocking TNF binding to its receptors. As we discuss here, TNFR-based interventions may both stimulate and suppress the growth of cancer cells, and the same may be true in analogy for Atsttrin as a new player.

Increased interleukin-1β gene expression in peripheral blood leukocytes is associated with increased pain and predicts risk for progression of symptomatic knee osteoarthritis

OBJECTIVE

To evaluate whether gene expression profiles could serve as biomarkers of symptomatic knee osteoarthritis (OA) by examining gene expression profiles in peripheral blood leukocytes (PBLs) from patients with OA compared with those from non-OA controls, and to determine whether candidate genomic biomarkers (PBL expression of inflammatory genes) predict an increased risk of disease progression in patients with symptomatic radiographic knee OA.

METHODS

Three independent cohorts of patients with knee OA and non-OA control subjects were studied. Two cohorts (a learning cohort and a validation cohort) were recruited at New York University Hospital for Joint Diseases (NYUHJD), and 1 cohort (a validation cohort) was recruited at Duke University Medical Center. PBL gene expression was assessed using Affymetrix microarray and was confirmed by quantitative polymerase chain reaction (qPCR). Radiographic progression at 2 years was assessed in 86 patients.

RESULTS

We identified 173 genes that were significantly up-regulated or down-regulated (≥1.5-fold change) in OA PBLs, at a false discovery rate of 5%. Cluster analysis revealed 2 distinct subgroups among the patients with OA: those in whom the expression of interleukin-1β (IL-1β) was increased ≥2-fold compared with controls, and those in whom the expression of IL-1β was comparable with that in controls. Overexpression of IL-1β in these OA subclasses was validated using qPCR in all 3 cohorts. Patients with the inflammatory "IL-1β signature" had higher pain scores and decreased function and were at higher risk of radiographic progression of OA.

CONCLUSION

PBLs from patients with symptomatic knee OA display a characteristic transcriptome profile. Moreover, increased expression of IL-1β identifies a subset of patients with OA who have increased pain and are at higher risk of radiographic progression of OA.

Structure, function, and mechanism of progranulin; the brain and beyond

Mutation of human GRN, the gene encoding the secreted glycoprotein progranulin, results in a form of frontotemporal lobar degeneration that is characterized by the presence of ubiquitinated inclusions containing phosphorylated and cleaved fragments of the transactivation response element DNA-binding protein-43. This has stimulated interest in understanding the role of progranulin in the central nervous system, and in particular, how this relates to neurodegeneration. Progranulin has many roles outside the brain, including regulation of cellular proliferation, survival, and migration, in cancer, including cancers of the brain, in wound repair, and inflammation. It often acts through the extracellular signal-regulated kinase and phopshatidylinositol-3-kinases pathways. The neurobiology of progranulin has followed a similar pattern with proposed roles for progranulin (PGRN) in the central nervous system as a neuroprotective agent and in neuroinflammation. Here we review the structure, biology, and mechanism of progranulin action. By understanding PGRN in a wider context, we may be better able to delineate its roles in the normal brain and in neurodegenerative disease.

Cellular effects of progranulin in health and disease

Progranulin is a fascinating multifunctional protein, which has been implicated in cell growth, wound repair, tumorigenesis, inflammation, neurodevelopment, and more recently in neurodegeneration. The mechanism of action of this protein is still largely unknown, but the knowledge about the cellular effects on various cell types is expanding. In the current review, we will summarize what is known about the cell biology of progranulin. A better understanding of the biology of progranulin will impact diverse areas of research.

Proepithelin stimulates growth plate chondrogenesis via nuclear factor-kappaB-p65-dependent mechanisms

Proepithelin, a previously unrecognized growth factor in cartilage, has recently emerged as an important regulator for cartilage formation and function. In the present study, we provide several lines of evidences in proepithelin-mediated induction of cell proliferation, differentiation, and apoptosis in the metatarsal growth plate. Proepithelin-mediated stimulation of metatarsal growth and growth plate chondrogenesis was neutralized by pyrrolidine dithiocarbamate, a known NF-κB inhibitor. In rat growth plate chondrocytes, proepithelin induced NF-κB-p65 nuclear translocation, and nuclear NF-κB-p65 initiated its target gene cyclin D1 to regulate chondrocyte functions. The inhibition of NF-κB-p65 expression and activity (by p65 short interfering RNA (siRNA) and pyrrolidine dithiocarbamate, respectively) in chondrocytes reversed the proepithelin-mediated induction of cell proliferation and differentiation and the proepithelin-mediated prevention of cell apoptosis. Moreover, the inhibition of the phosphatidylinositol 3-kinase and Akt abolished the effects of proepithelin on NF-κB activation. Finally, using siRNA and antisense strategies, we demonstrated that endogenously produced proepithelin by chondrocytes is important for chondrocyte growth in serum-deprived conditions. These results support the hypothesis that the induction of NF-κB activity of in growth plate chondrocytes is critical in proepithelin-mediated growth plate chondrogenesis and longitudinal bone growth.

Progranulin: a promising therapeutic target for rheumatoid arthritis

Progranulin (PGRN) is an autocrine growth factor with multiple functions. This review provides updates about the interplays of PGRN with extracellular matrix proteins, proteolytic enzymes, inflammatory cytokines, and cell surface receptors in cartilage and arthritis, with a special focus on the interaction between PGRN and TNF receptors (TNFR) and its implications in inflammatory arthritis. The paper also highlights Atsttrin, an engineered protein composed of three PGRN fragments that prevents inflammation in several inflammatory arthritis models. Identification of PGRN as a ligand of TNFR and an antagonist of TNFα signaling, together with the discovery of Atsttrin, not only betters our understanding of the pathogenesis of arthritis, but also provides new therapeutic interventions for various TNFα-mediated pathologies and conditions, including rheumatoid arthritis.

The growth factor progranulin binds to TNF receptors and is therapeutic against inflammatory arthritis in mice

The growth factor progranulin (PGRN) has been implicated in embryonic development, tissue repair, tumorigenesis, and inflammation, but its receptors remain unidentified. We report that PGRN bound directly to tumor necrosis factor receptors (TNFRs) and disturbed the TNFα-TNFR interaction. PGRN-deficient mice were susceptible to collagen-induced arthritis, and administration of PGRN reversed inflammatory arthritis. Atsttrin, an engineered protein composed of three PGRN fragments, exhibited selective TNFR binding. PGRN and Atsttrin prevented inflammation in multiple arthritis mouse models and inhibited TNFα-activated intracellular signaling. Collectively, these findings demonstrate that PGRN is a ligand of TNFR, an antagonist of TNFα signaling, and plays a critical role in the pathogenesis of inflammatory arthritis in mice. They also suggest new potential therapeutic interventions for various TNFα-mediated pathologies and conditions, including rheumatoid arthritis.

GEP, a local growth factor, is critical for odontogenesis and amelogenesis

Granulin epithelin precursor (GEP) is a new growth factor that functions in brain development, chondrogenesis, tissue regeneration, tumorigenesis, and inflammation. The goal of this study was to study whether GEP was critical for odontogenesis and amelogenesis both in vivo and in vitro. The in situ hybridization and immunohistochemistry data showed that GEP was expressed in both odontoblast and ameloblast cells postnatally. Knockdown of GEP by crossing U6-ploxPneo-GEP and Sox2-Cre transgenic mice led to a reduction of dentin thickness, an increase in predentin thickness, and a reduction in mineral content in enamel. The in vitro application of recombinant GEP up-regulated molecular markers important for odontogenesis (DMP1, DSPP, and ALP) and amelogenesis (ameloblastin, amelogenin and enamelin). In conclusion, both the in vivo and the in vivo data support an important role of GEP in tooth formation during postnatal development.

Granulin-epithelin precursor binds directly to ADAMTS-7 and ADAMTS-12 and inhibits their degradation of cartilage oligomeric matrix protein

OBJECTIVE

To determine 1) whether a protein interaction network exists between granulin-epithelin precursor (GEP), ADAMTS-7/ADAMTS-12, and cartilage oligomeric matrix protein (COMP); 2) whether GEP interferes with the interactions between ADAMTS-7/ADAMTS-12 metalloproteinases and COMP substrate, including the cleavage of COMP; 3) whether GEP affects tumor necrosis factor alpha (TNFalpha)-mediated induction of ADAMTS-7/ADAMTS-12 expression and COMP degradation; and 4) whether GEP levels are altered during the progression of arthritis.

METHODS

Yeast two-hybrid, in vitro glutathione S-transferase pull-down, and coimmunoprecipitation assays were used to 1) examine the interactions between GEP, ADAMTS-7/ADAMTS-12, and COMP, and 2) map the binding sites required for the interactions between GEP and ADAMTS-7/ADAMTS-12. Immunofluorescence cell staining was performed to visualize the subcellular localization of GEP and ADAMTS-7/ADAMTS-12. An in vitro digestion assay was employed to determine whether GEP inhibits ADAMTS-7/ADAMTS-12-mediated digestion of COMP. The role of GEP in inhibiting TNFalpha-induced ADAMTS-7/ADAMTS-12 expression and COMP degradation in cartilage explants was also analyzed.

RESULTS

GEP bound directly to ADAMTS-7 and ADAMTS-12 in vitro and in chondrocytes, and the 4 C-terminal thrombospondin motifs of ADAMTS-7/ADAMTS-12 and each granulin unit of GEP mediated their interactions. Additionally, GEP colocalized with ADAMTS-7 and ADAMTS-12 on the cell surface of chondrocytes. More importantly, GEP inhibited COMP degradation by ADAMTS-7/ADAMTS-12 in a dose-dependent manner through 1) competitive inhibition through direct protein-protein interactions with ADAMTS-7/ADAMTS-12 and COMP, and 2) inhibition of TNFalpha-induced ADAMTS-7/ADAMTS-12 expression. Furthermore, GEP levels were significantly elevated in patients with either osteoarthritis or rheumatoid arthritis.

CONCLUSION

Our observations demonstrate a novel protein-protein interaction network between GEP, ADAMTS-7/ADAMTS-12, and COMP. Furthermore, GEP is a novel specific inhibitor of ADAMTS-7/ADAMTS-12-mediated COMP degradation and may play a significant role in preventing the destruction of joint cartilage in arthritis.

Thrombospondins and novel TSR-containing proteins, R-spondins, regulate bone formation and remodeling

Thrombospondins (TSPs) are a family of five secreted multimeric matricellular proteins that share homology in the type II and III repeats and carboxy-terminal region. Type I repeats, also known as properdin or thrombospondin repeats (TSRs), are found in TSP1/2, but not TSP3-5. A variety of other secreted proteins contain TSRs, including the novel extracellular molecules, R-spondins. TSP family and many TSR-containing proteins, including R-spondins, are highly expressed in skeletal tissues during development and postnatal. TSP2 regulates the osteoblast lineage, influencing bone mass and geometry, as well as response to fracture healing, ovariectomy, and mechanical loading. Compound knockout mice of TSPs have revealed important mechanistic insights. TSP1/2 knockout mice have craniofacial dysmorphism, and TSP1/3/5 compound knockout mice display growth plate abnormalities. R-spondins promote osteoblast differentiation and R-spondin-2 deficiency results in skeletal developmental defects. Overall, TSP and other TSR molecules influence multiple aspects of bone development and remodeling.

The role of ADAMTSs in arthritis

The ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family consists of 19 proteases. These enzymes are known to play important roles in development, angiogenesis and coagulation; dysregulation and mutation of these enzymes have been implicated in many disease processes, such as inflammation, cancer, arthritis and atherosclerosis. This review briefly summarizes the structural organization and functional roles of ADAMTSs in normal and pathological conditions, focusing on members that are known to be involved in the degradation of extracellular matrix and loss of cartilage in arthritis, including the aggrecanases (ADAMTS-4 and ADAMTS-5), ADAMTS-7 and ADAMTS-12, the latter two are associated with cartilage oligomeric matrix protein (COMP), a component of the cartilage extracellular matrix (ECM). We will discuss the expression pattern and the regulation of these metalloproteinases at multiple levels, including their interaction with substrates, induction by pro-inflammatory cytokines, protein processing, inhibition (e.g., TIMP-3, alpha-2-macroglobulin, GEP), and activation (e.g., syndecan-4, PACE-4).

Interaction between cartilage oligomeric matrix protein and extracellular matrix protein 1 mediates endochondral bone growth

In an effort to define the biological functions of COMP, a functional genetic screen was performed. This led to the identification of extracellular matrix protein 1 (ECM1) as a novel COMP-associated partner. COMP directly binds to ECM1 both in vitro and in vivo. The EGF domain of COMP and the C-terminus of ECM1 mediate the interaction between them. COMP and ECM1 colocalize in the growth plates invivo. ECM1 inhibits chondrocyte hypertrophy, matrix mineralization, and endochondral bone formation, and COMP overcomes the inhibition by ECM1. In addition, COMP-mediated neutralization of ECM1 inhibition depends on their interaction, since COMP largely fails to overcome the ECM1 inhibition in the presence of the EGF domain of COMP, which disturbs the association of COMP and ECM1. These findings provide the first evidence linking the association of COMP and ECM1 and the biological significance underlying the interaction between them in regulating endochondral bone growth.

Granulin epithelin precursor: a bone morphogenic protein 2-inducible growth factor that activates Erk1/2 signaling and JunB transcription factor in chondrogenesis

Granulin epithelin precursor (GEP) has been implicated in development, tissue regeneration, tumorigenesis, and inflammation. Herein we report that GEP stimulates chondrocyte differentiation from mesenchymal stem cells in vitro and endochondral ossification ex vivo, and GEP-knockdown mice display skeleton defects. Similar to bone morphogenic protein (BMP) 2, application of the recombinant GEP accelerates rabbit cartilage repair in vivo. GEP is a key downstream molecule of BMP2, and it is required for BMP2-mediated chondrocyte differentiation. We also show that GEP activates chondrocyte differentiation through Erk1/2 signaling and that JunB transcription factor is one of key downstream molecules of GEP in chondrocyte differentiation. Collectively, these findings reveal a novel critical role of GEP growth factor in chondrocyte differentiation and the molecular events both in vivo and in vitro.

The granulin gene family: from cancer to dementia

The growth factor progranulin (PGRN) regulates cell division, survival, and migration. PGRN is an extracellular glycoprotein bearing multiple copies of the cysteine-rich granulin motif. With PGRN family members in plants and slime mold, it represents one of the most ancient of the extracellular regulatory proteins still extant in modern animals. PRGN has multiple biological roles. It contributes to the regulation of early embryogenesis, to adult tissue repair and inflammation. Elevated PGRN levels often occur in cancers, and PGRN immunotherapy inhibits the growth of hepatic cancer xenografts in mice. Recent studies have demonstrated roles for PGRN in neurobiology. An autosomal dominant mutation in GRN, the gene for PGRN, leads to neuronal atrophy in the frontal and temporal lobes, resulting in the disease frontotemporal lobar dementia. In this review we will discuss current knowledge of the multifaceted biology of PGRN.

Cartilage oligomeric matrix protein in canine spinal cord appears in the cerebrospinal fluid associated with intervertebral disc herniation

STUDY DESIGN

Cerebrospinal fluid (CSF) from dogs with intervertebral disc herniation (IVDH) were analyzed using a specific antibody against cartilage oligomeric matrix protein (COMP). Immunolocalization and genetic expression of COMP were also examined in the spinal cords of mouse, rat, and dog.

OBJECTIVE

To investigate the hypothesis that COMP is present in CSF of dogs with IVDH, and the clinical relevance of COMP expression in CSF as a potential biomarker of spinal cord injury.

SUMMARY OF BACKGROUND DATA

In dog IVDH, diagnostic imaging is useful for determining the spinal cord compression, but less useful for assessment of traumatic degeneration. Aggrecan, a well-known component of cartilage matrix, is increased in CSF from cases of neural damage and inflammation of the spinal cord.

METHODS

CSF from the cisterna magna (C-CSF) and the lumbar spine (L-CSF) of 19 dogs with IVDH and 5 normal dogs were analyzed using inhibition enzyme-linked immunosorbent assay (ELISA) and immunoblotting with an antibody cross-reactive with dog COMP. Samples of normal spinal cord from mouse, rat, and dog were also prepared for immunohistochemistry and in situ hybridization.

RESULTS

ELISA values were significantly higher for L-CSF than for C-CSF in dogs with IVDH, whereas there was no significant difference between them in normal dogs. Immunoblots of L-CSF samples revealed positive bands of approximately 500 kDa in 6 cases of IVDH (positive cases), but no signal in negative cases. ELISA values were significantly higher in the positive cases than in the negative cases. Both COMP protein and mRNA were present at high levels in the gray matter of the spinal cord in all species.

CONCLUSION

In dog IVDH, release of COMP from the spinal cord in association with injury may lead to COMP accumulation in L-CSF posterior to the site of disc extrusion, and therefore might be a predictive marker of spinal cord injury.

An inducible cartilage oligomeric matrix protein mouse model recapitulates human pseudoachondroplasia phenotype

Cartilage oligomeric matrix protein (COMP) is a pentameric extracellular protein expressed in cartilage and other musculoskeletal tissues. Mutations in the COMP gene cause pseudoachondroplasia (PSACH), a severe dwarfing condition that has a growth plate chondrocyte pathology. PSACH is characterized by intracellular retention of COMP and other extracellular matrix (ECM) proteins, which form an ordered matrix within large rough endoplasmic reticulum cisternae. This accumulation is cytotoxic and causes premature chondrocyte cell death, thereby depleting chondrocytes needed for normal long bone growth. Research to define the underlying molecular mechanisms of PSACH has been hampered by the lack of a suitable model system. In this study, we achieved robust expression of human mutant (MT) or wild-type (WT) COMP in mice by using a tetracycline-inducible promoter. Normal growth plate distribution of ECM proteins was observed in 1-month-old WT-COMP and C57BL\6 control mice. In contrast, the structure of the MT-COMP growth plate recapitulated the findings of human PSACH growth plate morphology, including (1) retention of ECM proteins, (2) intracellular matrix formation in the rER cisternae, and (3) increased chondrocyte apoptosis. Therefore, we have generated the first mouse model to show extensive intracellular retention of ECM proteins recapitulating the human PSACH disease process at the cellular level.

The emerging roles of ADAMTS-7 and ADAMTS-12 matrix metalloproteinases

The a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) comprise a family of secreted zinc metalloproteinases with a precisely ordered modular organization. These enzymes play an important role in the turnover of extracellular matrix proteins in various tissues and their dysregulation has been implicated in disease-related processes such as arthritis, atherosclerosis, cancer, and inflammation. ADAMTS-7 and ADAMTS-12 share a similar domain organization to each other and form a subgroup within the ADAMTS family. Emerging evidence suggests that ADAMTS-7 and ADAMTS-12 may play an important role in the development and pathogenesis of various kinds of diseases. In this review, we summarize what is currently known about the roles of these two metalloproteinases, with a special focus on their involvement in chondrogenesis, endochondral ossification, and the pathogenesis of arthritis, atherosclerosis, and cancer. The future study of ADAMTS-7 and ADAMTS-12, as well as the molecules with which they interact, will help us to better understand a variety of human diseases from both a biological and therapeutic standpoint.

ADAMTS-7, a direct target of PTHrP, adversely regulates endochondral bone growth by associating with and inactivating GEP growth factor

ADAMTS-7, a metalloproteinase that belongs to ADAMTS family, is important for the degradation of cartilage extracellular matrix proteins in arthritis. Herein we report that ADAMTS-7 is upregulated during chondrocyte differentiation and demonstrates the temporal and spatial expression pattern during skeletal development. ADAMTS-7 potently inhibits chondrocyte differentiation and endochondral bone formation, and this inhibition depends on its proteolytic activity. The cysteine-rich domain of ADAMTS-7 is required for its interaction with the extracellular matrix, and the C-terminal four-thrombospondin motifs are necessary for its full proteolytic activity and inhibition of chondrocyte differentiation. ADAMTS-7 is an important target of canonical PTHrP signaling, since (i) PTHrP induces ADAMTS-7, (ii) ADAMTS-7 is downregulated in PTHrP null mutant (PTHrP-/-) growth plate chondrocytes, and (iii) blockage of ADAMTS-7 almost abolishes PTHrP-mediated inhibition of chondrocyte hypertrophy and endochondral bone growth. ADAMTS-7 associates with granulin-epithelin precursor (GEP), an autocrine growth factor that has been implicated in tissue regeneration, tumorigenesis, and inflammation. In addition, ADAMTS-7 acts as a new GEP convertase and neutralizes GEP-stimulated endochondral bone formation. Collectively, these findings demonstrate that ADAMTS-7, a direct target of PTHrP signaling, negatively regulates endochondral bone formation by associating with and inactivating GEP chondrogenic growth factor.