Targeted deletion of Minpp1 provides new insight into the activity of multiple inositol polyphosphate phosphatase in vivo.

Multiple inositol polyphosphate phosphatase (Minpp1) metabolizes inositol 1,3,4,5,6-pentakisphosphate (InsP(5)) and inositol hexakisphosphate (InsP(6)) with high affinity in vitro. However, Minpp1 is compartmentalized in the endoplasmic reticulum (ER) lumen, where access of enzyme to these predominantly cytosolic substrates in vivo has not previously been demonstrated. To gain insight into the physiological activity of Minpp1, Minpp1-deficient mice were generated by homologous recombination. Tissue extracts from Minpp1-deficient mice lacked detectable Minpp1 mRNA expression and Minpp1 enzyme activity. Unexpectedly, Minpp1-deficient mice were viable, fertile, and without obvious defects. Although Minpp1 expression is upregulated during chondrocyte hypertrophy, normal chondrocyte differentiation and bone development were observed in Minpp1-deficient mice. Biochemical analyses demonstrate that InsP(5) and InsP(6) are in vivo substrates for ER-based Minpp1, as levels of these polyphosphates in Minpp1-deficient embryonic fibroblasts were 30 to 45% higher than in wild-type cells. This increase was reversed by reintroducing exogenous Minpp1 into the ER. Thus, ER-based Minpp1 plays a significant role in the maintenance of steady-state levels of InsP(5) and InsP(6). These polyphosphates could be reduced below their natural levels by aberrant expression in the cytosol of a truncated Minpp1 lacking its ER-targeting N terminus. This was accompanied by slowed cellular proliferation, indicating that maintenance of cellular InsP(5) and InsP(6) is essential to normal cell growth. Yet, depletion of cellular inositol polyphosphates during erythropoiesis emerges as an additional physiological activity of Minpp1; loss of this enzyme activity in erythrocytes from Minpp1-deficient mice was accompanied by upregulation of a novel, substitutive inositol polyphosphate phosphatase.

A rapid method for labelling CD4+ T cells with ultrasmall paramagnetic iron oxide nanoparticles for magnetic resonance imaging that preserves proliferative, regulatory and migratory behaviour in vitro.

A number of techniques have been developed to track the migration of T cells in vivo, but they all suffer significant shortcomings, including the examination of selected organs rather than the organism as a whole--thus precluding longitudinal studies--or limitations imposed by poor spatial resolution and the application of ionizing radiation. By conjugating the HIV tat peptide to ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles in a reaction yielding a mean valence of 45, a magnetic resonance (MR) contrast agent was synthesised that allowed T cells to be efficiently labelled within just 5 min. The USPIO nanoparticles were incorporated into both the cytoplasm and nucleus of labelled cells, which retained normal in vitro proliferative responses to a polyclonal stimulus; suppressive responses mediated by labelled CD4(+) CD25(+) regulatory T cells; chemotactic responses to the chemokine CXCL-12; and transmigration of an activated endothelial monolayer. We believe that this rapid, efficient and essentially non-toxic approach to labelling both murine and human T cells for MRI holds considerable promise, paving the way for the wider immunological application of this exciting technology.

Malocclusion model of temporomandibular joint osteoarthritis in mice with and without receptor for advanced glycation end products.

OBJECTIVE: This study has two aims: 1. Validate a non-invasive malocclusion model of mouse temporomandibular joint (TMJ) osteoarthritis (OA) that we developed and 2. Confirm role of inflammation in TMJ OA by comparing the disease in the presence and absence of the receptor for advanced glycation end products (RAGE). DESIGN: The malocclusion procedure was performed on eight week old mice, either wild type (WT) or without RAGE. RESULTS: We observed TMJ OA at two weeks post-misalignment/malocclusion. The modified Mankin score used for the semi-quantitative assessment of OA showed an overall significantly higher score in mice with malocclusion compared to control mice at all times points (2, 4, 6 and 8 weeks). Mice with malocclusion showed a decrease in body weight by the first week after misalignment but returned to normal weight for their ages during the following weeks. The RAGE knock out (KO) mice had statistically lower modified Mankin scores compared to WT mice of the same age. The RAGE KO mice had statistically lower levels of Mmp-13 and HtrA1 but higher Tgf-ß1, as measured by immunohistochemistry, compared to WT mice at eight weeks post malocclusion. CONCLUSIONS: We demonstrate an inexpensive, efficient, highly reproducible and non-invasive model of mouse TMJ OA. The mechanical nature of the malocclusion resembles the natural development of TMJ OA in humans, making this an ideal model in future studies that aim to elucidate the pathogenesis of the disease leading to the discovery of a treatment. The RAGE plays a role in mouse TMJ OA.

BMP-6 is an autocrine stimulator of chondrocyte differentiation.

While parathyroid hormone-related protein (PTHrP) has been characterized as an important negative regulator of chondrocyte maturation in the growth plate, the autocrine or paracrine factors that stimulate chondrocyte maturation are not well characterized. Cephalic sternal chondrocytes were isolated from 13-day embryos, and the role of bone morphogenetic protein-6 (BMP-6) as a positive regulator of chondrocyte maturation was examined in monolayer cultures. Progressive maturation, which was accelerated in the presence of ascorbate, occurred in the cultures. During maturation, the cultures expressed high levels of BMP-6 mRNA which preceded the induction of type X collagen mRNA. Treatment of the cultures with PTHrP (10(-7) M) at the time of plating completely abolished BMP-6 and type X collagen mRNA expression. Removal of PTHrP after 6 days was followed by the rapid (within 24 h) expression of BMP-6 and type X collagen mRNA, with BMP-6 again preceding type X collagen expression. The addition of exogenous BMP-6 (100 ng/ml) to the cultures accelerated the maturation process both in the presence and absence of ascorbate and resulted in the highest levels of type X collagen. When exogenous BMP-6 was added to PTHrP containing cultures, maturation occurred with the expression of high levels of type X collagen, despite the presence of PTHrP in the cultures. Furthermore, BMP-6 did not stimulate expression of its own mRNA in the PTHrP treated cultures, but it did stimulate the expression of Indian hedgehog (Ihh) mRNA. These latter findings suggest that while PTHrP directly inhibits BMP-6, it indirectly regulates Ihh expression through BMP-6. Other phenotypic changes associated with chondrocyte differentiation were also stimulated by BMP-6, including increased alkaline phosphatase activity and decreased proliferation. The results suggest that BMP-6 is an autocrine factor that initiates chondrocyte maturation and that PTHrP may prevent maturation by inhibiting the expression of BMP-6.

Smad2 and 3 mediate transforming growth factor-beta1-induced inhibition of chondrocyte maturation.

Transforming growth factor-beta (TGF-beta) is a multifunctional regulator of a variety of cellular functions, including proliferation, differentiation, matrix synthesis, and apoptosis. In growth plate chondrocytes, TGF-beta slows the rate of maturation. Because the current paradigm of TGF-beta signaling involves Smad proteins as downstream regulators of target genes, we have characterized their role as mediators of TGF-beta effects on chondrocyte maturation. Both Smad2 and 3 translocated to the nucleus upon TGF-beta1 signaling, but not upon BMP-2 signaling. Cotransfection experiments using the TGF-beta responsive and Smad3 sensitive p3TP-Lux luciferase reporter demonstrated that wild-type Smad3 potentiated, whereas dominant negative Smad3 inhibited TGF-beta1 induced luciferase activity. To confirm the role of Smad2 and 3 as essential mediators of TGF-beta1 effects on chondrocyte maturation, we overexpressed both wild-type and dominant negative Smad2 and 3 in virally infected chondrocyte cultures. Overexpression of both wild-type Smad2 and 3 potentiated the inhibitory effect of TGF-beta on chondrocyte maturation, as determined by colx and alkaline phosphatase activity, whereas dominant negative Smad2 and 3 blocked these effects. Wild-type and dominant negative forms of Smad3 had more pronounced effects than Smad2. Our results define Smad2 and 3 as key mediators of the inhibitory effect of TGF-beta1 signaling on chondrocyte maturation.

Somatic mutation and germline variants of MINPP1, a phosphatase gene located in proximity to PTEN on 10q23.3, in follicular thyroid carcinomas.

Various genes have been identified to play a role in the pathogenesis of follicular thyroid tumors. Cowden syndrome is the only known familial syndrome with an increased risk of both follicular thyroid adenoma (FA) and carcinoma (FTC). Germline mutations in the tumor suppressor gene PTEN, which encodes a dual-specificity phosphatase, have been found in up to 80% of patients with Cowden syndrome suggesting a role of PTEN in the pathogenesis of follicular thyroid tumors. Although somatic intragenic mutations in PTEN, which maps to 10q23.3, are rarely found in follicular tumors, loss of heterozygosity (LOH) of markers within 10q22-24 occurs in about 25%. Recently, another phosphatase gene, MINPP1, has been localized to 10q23.3. MINPP1 has the ability to remove 3-phosphate from inositol phosphate substrates, a function that overlaps that of PTEN. Because of this overlapping function with PTEN and the physical location of MINPP1 to a region with frequent LOH in follicular thyroid tumors, we considered it to be an excellent candidate gene that could contribute to the pathogenesis of follicular thyroid tumors. We analyzed DNA from tumor and corresponding normal tissue from 23 patients with FA and 15 patients with FTC for LOH and mutations at the MINPP1 locus. LOH was identified in four malignant and three benign tumors. One of these FTCs with LOH was found to harbor a somatic c.122C > T or S41L mutation. We also found two germline sequence variants, c.809A > G (Q270R) and IVS3 + 34T > A. The c.809A > G variant was found in only one patient with FA but not in patients with FTC or normal controls. More interestingly, IVS3 + 34T > A was found in about 15% of FA cases and normal controls but not in patients with FTC. These results suggest a role for MINPP1 in the pathogenesis of at least a subset of malignant follicular thyroid tumors, and MINPP1 might act as a low penetrance predisposition allele for FTC.

Cloning of the chick BMP1/Tolloid cDNA and expression in skeletal tissues.

The astacin-related metalloproteases Bone Morphogenetic Protein-1 (BMP1) and Tolloid possess multiple functions in the maturation of extracellular matrices containing fibrillar collagens. We are interested in developing an in-vitro model system to study the role of BMP1 and Tolloid in chondrocytes and osteoblasts. Cloning of the cDNAs for chick BMP1 and Tolloid reveals that the two gene products are more than 80% identical to their human and mouse homologs and are similarly derived from the same genetic locus. Anti-BMP1/Tolloid antibodies have been developed, and detect two proteins of 80 and 116kDa. Chick BMP1 and Tolloid message and proteins are found in a variety of embryonic and juvenile tissues, including chondrocytes and osteoblasts. Tolloid message and protein are generally less abundant than BMP1 message; this discrepancy is greatest in growth plate chondrocytes. Tolloid protein is more tightly bound than BMP1 to the extracellular matrix produced by cultured osteoblasts. The Chordin gene is also expressed in chondrocytes and osteoblasts, suggesting that BMP1 and Tolloid influence BMP signaling as well as matrix maturation during skeletogenesis.

Differential regulation of type-II and type-X collagen synthesis by parathyroid hormone-related protein in chick growth-plate chondrocytes.

Parathyroid hormone-related protein is a critical autocrine regulator of endochondral ossification in the growth plate, as demonstrated by the severe disruption of growth-plate structure and function in parathyroid hormone-related protein-deficient transgenic mice. In the present study, the effects of parathyroid hormone-related protein on the synthesis of collagen mRNA and protein were studied in short-term cultures of isolated chick growth-plate chondrocytes. Parathyroid hormone-related protein selectively inhibits type-X collagen protein synthesis with no significant effect on type-II collagen protein synthesis. These effects were present in all maturationally distinct populations of chondrocytes separated by countercurrent centrifugal elutriation. In cultures of resting chondrocytes, the onset of type-X collagen expression was inhibited, while the synthesis of type-X collagen was decreased in cultures of hypertrophic chondrocytes. Synthesis of type-II and type-X collagen mRNA was examined by nonradioactive in situ hybridization with synthetic oligonucleotide cDNA probes, and the level of expression was quantified using digital image analysis. Dose-dependent suppression of type-X collagen gene expression by parathyroid hormone-related protein was observed, with no significant effect on type-II collagen mRNA detected. The results were confirmed by analysis of Northern blots of total chondrocyte mRNA. These experiments demonstrated differential transcriptional regulation of type-II and type-X collagen, with selective suppression of type-X collagen expression, by parathyroid hormone-related protein in growth-plate chondrocytes. In addition, excellent agreement was found between traditional protein and mRNA analyses and microscopic digital image analysis techniques, supporting the use of this convenient and sensitive assay method. Parathyroid hormone-related protein inhibits chondrocyte maturation and is known to stimulate proliferation, suggesting that this autocrine factor may function to regulate premature hypertrophy in the growth plate.

Bone morphogenetic protein-7 in growth-plate chondrocytes: regulation by retinoic acid is dependent on the stage of chondrocyte maturation.

Although the bone morphogenetic proteins stimulate chondrogenesis, little is known regarding their expression and regulation in growth-plate chondrocytes. The expression of bone morphogenetic protein-7 was examined in chick growth-plate chondrocyte cultures. Low basal levels of bone morphogenetic protein-7 mRNA and protein expression were stimulated by increasing doses of all-trans retinoic acid, a metabolite of vitamin A. The addition of 10 microM retinoic acid resulted in approximately a 6-fold increase in bone morphogenetic protein-7 mRNA levels. In contrast, other growth regulators, including basic fibroblast growth factor, transforming growth factor-beta, vitamin D, bone morphogenetic protein-6, bone morphogenetic protein-7, and parathyroid hormone-related peptide, did not alter bone morphogenetic protein-7 transcript levels. The increase in bone morphogenetic protein-7 transcripts, although present at 6 hours, was maximal following a 12-hour exposure to retinoic acid. Retinoic acid induction of bone morphogenetic protein-7 transcript levels was dependent on protein synthesis because the induction could be blocked by cyclohexamide. In maturationally distinct subpopulations of chondrocytes separated by countercurrent centrifugal elutriation, retinoic acid markedly induced bone morphogenetic protein-7 mRNA levels in the least differentiated chondrocytes but had no effect in the most terminally differentiated hypertrophic chondrocytes. Immunohistochemical localization of bone morphogenetic protein-7 demonstrates its expression throughout the developing and adolescent growth plate consistent with the constitutive pattern of expression seen in isolated chondrocytes. The addition of exogenous bone morphogenetic protein-7 to chondrocyte cultures stimulated maturation in undifferentiated chondrocyte populations. The data support a role for bone morphogenetic protein-7 as an autocrine regulator of chondrocyte maturation in the growth plate. Regulation of bone morphogenetic protein-7 by retinoic acid may be important in normal growth and development as well as in pathologic conditions of an excess or deficiency of vitamin A.

Interleukin-10 inhibits cytokine synthesis in monocytes stimulated by titanium particles: evidence of an anti-inflammatory regulatory pathway.

The anti-inflammatory mediator interleukin-10 was investigated as a potential inhibitor of proinflammatory cytokine release in human peripheral blood monocytes activated with titanium particles. It inhibited the secretion of both tumor necrosis factor-alpha and interleukin-6 in a dose-dependent manner, with complete inhibition observed at 2 ng/ml. Co-culture experiments were performed to determine whether this cytokine may have functional importance as an inhibitor of the inflammatory response. When unstimulated lymphocytes and monocytes were co-cultured with titanium-stimulated monocytes, they significantly suppressed the secretion of both interleukin-6 and tumor necrosis factor-alpha. The inhibitory effect of these co-cultured cells could be partially blocked with the addition of an interleukin-10 neutralizing antibody. Interleukin-10 levels were measured in monocyte cultures treated with titanium particles as well as in fresh monocyte cultures treated with conditioned medium from titanium-stimulated monocytes. The latter experiments demonstrated marked stimulation of interleukin-10 secretion in conditioned medium-treated cultures, an effect that was related to the presence of tumor necrosis factor-alpha in the conditioned medium. The addition of titanium to conditioned medium-treated cultures markedly reduced the secretion of interleukin-10, suggesting that the most responsive cells are unstimulated monocytes exposed to agents released from activated monocytes. Altogether, the expression and responsiveness to interleukin-10 suggest a potential role for anti-inflammatory cytokines in regulation of the inflammatory response to wear debris.

BMP signaling stimulates chondrocyte maturation and the expression of Indian hedgehog.

Mutant BMP receptors were transfected into cultured embryonic upper sternal chrondrocytes using retroviral vectors to determine if BMP signaling is required for chondrocyte maturation and the expression of a key regulatory molecule, Indian hedgehog (Ihh). Chondrocytes infected with replication competent avian retroviruses (RCAS) viruses carrying constitutive active (CA) BMPR-IA and BMPR-IB had enhanced expression of type X collagen and Ihh mRNA. Addition of PTHrP, a known inhibitor of chondrocyte maturation, abolished the expression of type X collagen, BMP-6, and Ihh mRNAs in control cells. In contrast, PTHrP treated cultures infected with of CA BMPR-IA or CA BMPR-IB had low levels of BMP-6 and type X collagen, but high levels of Ihh expression. Although dominant negative (DN) BMPR-IA had no effect, DN BMPR-IB inhibited the expression of type X collagen and BMP-6, and decreased alkaline phosphatase activity, even in the presence of exogenously added BMP-2 and BMP-6. DN BMPR-IB also completely blocked Ihh expression. Overall, the effect of DN BMPR-IB mimicked the effects of PTHrP. To determine if there is an autocrine role for the BMPs in chondrocyte maturation, the cultures were treated with noggin and follistatin, molecules that bind BMP-2/-4 and BMP-6/-7, respectively. While noggin and follistatin inhibited the effects of recombinant BMP-2 and BMP-6, respectively, they had only minimal effects on the spontaneous maturation of chondrocytes in culture, suggesting that more than one subgroup of BMPs regulates chondrocyte maturation. The results demonstrate that: (i) BMP signaling stimulates chondrocyte maturation; (ii) BMP signaling increases Ihh expression independent of maturational effects; and (iii) BMP signaling can partially overcome the inhibitory effects of PTHrP on maturation.

Modulation of the production of cytokines in titanium-stimulated human peripheral blood monocytes by pharmacological agents. The role of cAMP-mediated signaling mechanisms.

Cytokines secreted by activated macrophages play a role in the development of osteolysis adjacent to prosthetic joints. To determine whether the synthesis of cytokines can be inhibited by pharmacological agents, we studied the role of the cAMP-protein kinase A signal transduction pathway in the synthesis of interleukin-6 and tumor necrosis factor-alpha and examined the effect of potential pharmacological regulators of this pathway in human peripheral blood monocytes stimulated with titanium particles. Dibutyryl cAMP enhanced the synthesis of interleukin-6 by titanium-stimulated monocytes and resulted in a marked increase (maximum, seventyfold) in the synthesis of interleukin-6 even in the absence of titanium particles. However, the active analogs (agonists) of cAMP, dibutyryl cAMP and Sp cAMP, inhibited the production of tumor necrosis factor-alpha by titanium-stimulated monocytes (the maximum effects resulted in complete inhibition), while the cAMP antagonist, Rp cAMP, enhanced the production of tumor necrosis factor-alpha. Additional agents that alter the intracellular levels of cAMP were examined for their effects on the synthesis of cytokines. Prostaglandins E1 and E2 were potent inhibitors of the synthesis of tumor necrosis factor-alpha but stimulated the synthesis of interleukin-6. In contrast, indomethacin enhanced the stimulatory effects of titanium particles on tumor necrosis factor-alpha, resulting in a more than threefold increase in the maximum levels of tumor necrosis factor-alpha. Phosphodiesterase inhibitors, such as isobutyryl methylxanthine and pentoxifylline, which increase intracellular levels of cAMP, caused a decrease in the production of tumor necrosis factor-alpha and an increase in the production of interleukin-6. In contrast, the fluoroquinolone antibiotic ciprofloxacin, which is also a phosphodiesterase inhibitor, caused a dose-dependent inhibition of the synthesis of both tumor necrosis factor-alpha and interleukin-6 by titanium-stimulated monocytes, suggesting that ciprofloxacin suppresses the synthesis of interleukin-6 through a mechanism that is independent of cAMP.

Increased levels of tumor necrosis factor-alpha and interleukin-6 protein and messenger RNA in human peripheral blood monocytes due to titanium particles.

Cytokines produced by macrophages in the periprosthetic membranes surrounding joint replacements have been implicated as causal agents in osteolysis and prosthetic loosening. The present study characterizes the response of human peripheral blood monocytes to titanium particles. Monocytes were obtained from volunteers and blood that had been donated to the American Red Cross and were cultured in the presence of titanium particles (one to three micrometers in diameter). There were consistent dose-dependent increases in the production of TNF-alpha (tumor necrosis factor-alpha) and IL-6 (interleukin-6) protein, with the greatest stimulation generally observed with a concentration of 6 x 10(5) to 6 x 10(6) particles of titanium per milliliter. The level of TNF-alpha was the greatest (fifty to 1000 times greater than the control level) after eight hours of exposure to titanium particles; the level of IL-6 was two to five times greater than the control level after sixteen hours of exposure. These increases were similar to those observed after stimulation with lipopolysaccharide and depended on de novo synthesis rather than on release from intracellular stores. The production of TNF-alpha was inhibited in a dose-dependent manner by the translational inhibitor cycloheximide and the transcriptional inhibitor actinomycin D, indicating the requirement for both mRNA (messenger RNA) and protein synthesis for the induction of cytokine synthesis by titanium particles. Although the increase in the levels of cytokine mRNA in response to titanium was rapid (thirty to ninety minutes), the increase in the level of TNF-alpha mRNA preceded that of IL-6 mRNA. The level of TNF-alpha mRNA was the greatest at ninety minutes and the level of IL-6 mRNA was the greatest at three hours. After stimulation with titanium particles, the level of TNF-alpha mRNA was increased as much as fivefold and the level of IL-6 mRNA, as much as twelvefold.

Neonatal cranial ultrasound interpretation: a clinical audit.

OBJECTIVE: To assess the abilities of doctors to interpret neonatal cranial ultrasound scans. DESIGN AND SETTING: High resolution scanned images of six important neonatal cranial ultrasound abnormalities were posted as a questionnaire to the 59 neonatal units in the North and South Thames regions. RESULTS: Forty two questionnaires were returned (71%). Currently 56% of those interpreting cranial ultrasound scans are neonatal registrars, 27% are consultant paediatricians or neonatologists, and 17% are radiologists. The response rate from registrars was excellent (97%), but it was poor from consultant paediatric (38%) and radiological (40%) staff. The mean accurate identification of cerebral abnormalities was only 59% (range 45-71%). Only 44% of the neonatal registrars, compared with nearly all the consultant staff, have had any formal training in cranial ultrasonography. CONCLUSIONS: The data highlight the current accuracy of neonatal cranial ultrasound scan reporting in the Greater London region and have important implications for clinical services and research studies. Doctors who are responsible for interpreting neonatal cranial ultrasound scans should have formal training and supervision, and more formal reporting would improve and maintain standards. The findings raise significant doubts about the accuracy of local interpretation of cranial ultrasound scans in multicentre research studies.

Mutation induction by 365-nm radiation and far-ultraviolet light in Escherichia coli strains differing in near- and far-ultraviolet light sensitivity.

The his-4 locus derived from Escherichia coli strain AB1157 has been transduced into 4 E. coli strains that exhibit all 4 possible combinations of genes controlling sensitivity to near-ultraviolet light (nur versus nur+) and far-ultraviolet light (uvrA6 versus uvrA+). The 4 strains exhibited the predicted sensitivity to 254-nm radiation based on the sensitivity of the parent strains from which they were derived and the frequency of his+ mutations predicted from experiments with AB1157 from which the his-4 locus was derived. When the 4 strains were treated with 365-nm radiation, they exhibited the predicted sensitivity based on the near-ultraviolet light sensitivity of the strains from which they were derived while his+ mutations were undetectable with the 4 strains as well as with strain AB1157. When treated with 365-nm radiation, cells of a WP2s strain (a derivative of B/r transduced to his-4) plated on semi-enriched medium prepared with casamino acids did not yield induced mutations, whereas plating on semi-enriched medium prepared with nutrient broth did yield mutants at both the his-4 and trp loci at frequencies at least an order of magnitude lower than that observed with far-ultraviolet light. The induction of nutritionally independent mutants by 365-nm radiation is strongly dependent on the supplement used for semi-enrichment. When compared at equivalent survival levels, mutant frequencies are significantly less following 365-nm radiation when compared with far-ultraviolet radiation.

Osteoarthritis in temporomandibular joint of Col2a1 mutant mice.

OBJECTIVE: Col2a1 gene mutations cause premature degeneration of knee articular cartilage in disproportionate micromelia (Dmm) and spondyloepiphesial dysplasia congenita (sedc) mice. The present study analyses the temporomandibular joint (TMJ) in Col2a1 mutant mice in order to provide an animal model of TMJ osteoarthritis (OA) that may offer better understanding of the progression of this disease in humans. DESIGN: Dmm/+ mice and controls were compared at two, six, nine and 12 months. Craniums were fixed, processed to paraffin sections, stained with Safranin-O/Fast Green, and analysed with light microscopy. OA was quantified using a Mankin scoring procedure. Unfolded protein response (UPR) assay was performed and immunohistochemistry (IHC) was used to assay for known OA biomarkers. RESULTS: Dmm/+ TMJs showed fissuring of condylar cartilage as early as 6 months of age. Chondrocytes were clustered, leaving acellular regions in the matrix. Significant staining of HtrA1, Ddr2 and Mmp-13 was observed in Dmm/+ mice (p<0.01). We detected upregulation of the UPR in knee but not TMJ. CONCLUSIONS: Dmm/+ mice are subject to early-onset OA in the TMJ. We observed upregulation of biomarkers and condylar cartilage degradation concomitant with OA. An upregulated UPR may exacerbate the onset of OA. The Dmm/+ mouse TMJ is a viable model for the study of the progression of OA in humans.