Accelerated and increased joint damage in young mice with global inactivation of mitogen-inducible gene 6 after ligament and meniscus injury

Gene 33/Mig6/ERRFI1, an Adapter Protein with Complex Functions in Cell Biology and Human Diseases

Gene 33 (also named Mig6, RALT, and ERRFI1) is an adapter/scaffold protein with a calculated molecular weight of about 50 kD. It contains multiple domains known to mediate protein–protein interaction, suggesting that it has the potential to interact with many cellular partners and have multiple cellular functions. The research over the last two decades has confirmed that it indeed regulates multiple cell signaling pathways and is involved in many pathophysiological processes. Gene 33 has long been viewed as an exclusively cytosolic protein. However, recent evidence suggests that it also has nuclear and chromatin-associated functions. These new findings highlight a significantly broader functional spectrum of this protein. In this review, we will discuss the function and regulation of Gene 33, as well as its association with human pathophysiological conditions in light of the recent research progress on this protein.

Overexpression of MIG-6 in the cartilage induces an osteoarthritis-like phenotype in mice

BACKGROUND

Osteoarthritis (OA) is the most common form of arthritis and characterized by degeneration of the articular cartilage. Mitogen-inducible gene 6 (Mig-6) has been identified as a negative regulator of the epidermal growth factor receptor (EGFR). Cartilage-specific Mig-6 knockout (KO) mice display increased EGFR signaling, an anabolic buildup of the articular cartilage, and formation of chondro-osseous nodules. Since our understanding of the EGFR/Mig-6 network in the cartilage remains incomplete, we characterized mice with cartilage-specific overexpression of Mig-6 in this study.

METHODS

Utilizing knee joints from cartilage-specific Mig-6-overexpressing (Mig-6over/over) mice (at multiple time points), we evaluated the articular cartilage using histology, immunohistochemical staining, and semi-quantitative histopathological scoring (OARSI) at multiple ages. MicroCT analysis was employed to examine skeletal morphometry, body composition, and bone mineral density.

RESULTS

Our data show that cartilage-specific Mig-6 overexpression did not cause any major developmental abnormalities in the articular cartilage, although Mig-6over/over mice have slightly shorter long bones compared to the control group. Moreover, there was no significant difference in bone mineral density and body composition in any of the groups. However, our results indicate that Mig-6over/over male mice show accelerated cartilage degeneration at 12 and 18 months of age. Immunohistochemistry for SOX9 demonstrated that the number of positively stained cells in Mig-6over/over mice was decreased relative to controls. Immunostaining for MMP13 appeared increased in areas of cartilage degeneration in Mig-6over/over mice. Moreover, staining for phospho-EGFR (Tyr-1173) and lubricin (PRG4) was decreased in the articular cartilage of Mig-6over/over mice.

CONCLUSION

Overexpression of Mig-6 in the articular cartilage causes no major developmental phenotype; however, these mice develop earlier OA during aging. These data demonstrate that Mig-6/EGFR pathways are critical for joint homeostasis and might present a promising therapeutic target for OA.

ERRFI1 Inhibits Proliferation and Inflammation of Nucleus Pulposus and Is Negatively Regulated by miR-2355-5p in Intervertebral Disc Degeneration

STUDY DESIGN

In vivo and in vitro studies of the role of miR-2355-5p and its possible targets in intervertebral disc degeneration (IVDD).

OBJECTIVE

To elucidate the regulatory role of miR-2355-5p in IVDD and the underlying mechanisms.

SUMMARY OF BACKGROUND DATA

IVDD, which is caused by multiple factors, is the main cause of lower back pain with or without extremity pain. However, the underlying cellular mechanisms of IVDD pathogenesis are not well elucidated. Cell hyper-proliferation, inflammation, and epidermal growth factor receptor activation have been implicated in IVDD. Up-regulated miR-2355-5p level was identified to associate with IVDD. ERRFI1 (the product of mitogen-inducible gene 6 [MIG6]) was known to inhibit epidermal growth factor receptor activation.

METHODS

We monitored the expression of miR-2355-5p and ERRFI1 in IVDD tissues and lipopolysaccharides (LPS)-treated nucleus pulposus (NP) cells. We explored the effects of ERFFI1 on NP cells proliferation and LPS-induced pro-inflammatory cytokines production. We searched the targets of miR-2355-5p and explored the effects of miR-2355-5p on NP cells proliferation and cytokines production.

RESULTS

We identified the up-regulation of miR-2355-5p and down-regulation of ERFFI1 in IVDD samples and LPS-treated NP cells. ERFFI1 inhibited NP cells proliferation and LPS-induced pro-inflammatory cytokine production. MiR-2355-5p targeted ERFFI1 and negatively regulated ERFFI1 expression. MiR-2355-5p regulated IVDD by targeting ERFFI1.

CONCLUSION

MiR-2355-5p negatively regulated ERFFI1 and prevented the effects of ERRFI1 on inhibiting NP cells proliferation and inflammation.

LEVEL OF EVIDENCE

N/A.

RIPK1 suppresses apoptosis mediated by TNF and caspase-3 in intervertebral discs

BACKGROUND

Low back pain has become a serious social and economic burden and the leading cause of disability worldwide. Among a variety of pathophysiological triggers, intervertebral disc (IVD) degeneration plays a primary underlying role in causing such pain. Specifically, multiple independent endplate changes have been implicated in the initiation and progression of IVD degeneration.

METHODS

In this study, we built a signaling network comprising both well-characterized IVD pathology-associated proteins as well as some potentially correlated proteins that have been associated with one or more of the currently known pathology-associated proteins. We then screened for the potential IVD degeneration-associated proteins using patients' normal and degenerative endplate specimens. Short hairpin RNAs for receptor interacting serine/threonine kinase 1 (RIPK1) were constructed to examine the effects of RIPK1 knockdown in primary chondrocyte cells and in animal models of caudal vertebra intervertebral disc degeneration in vivo.

RESULTS

RIPK1 was identified as a potential IVD degeneration-associated protein based on IVD pathology-associated signaling networks and the patients' degenerated endplate specimens. Construction of the short hairpin RNAs was successful, with short-term RIPK1 knockdown triggering inflammation in the primary chondrocytes, while long-term knockdown triggered apoptosis through cleavage of the caspase 3 pathway, down-regulated NF-κB and mitogen-activating protein kinase (MAPK)s cascades, and decreased cell survival and inflammation. Animal models of caudal vertebra intervertebral disc degeneration further demonstrated that apoptosis was induced by up-regulation of tumor necrosis factor (TNF) accompanied by down-regulation of NF-κB and MAPKs cascades that are dependent on caspase and RIPK1.

CONCLUSIONS

These results provide proof-of-concept for developing novel therapies to combat IVD degeneration through interfering with RIPK1-mediated apoptosis signaling pathways especially in patients with RIPK1 abnormality.

EGFR Signaling: Friend or Foe for Cartilage?

Recent studies using genetically modified mice, pharmacological approaches, and human samples have highlighted an important role for the epidermal growth factor receptor (EGFR), selected ligands, and downstream components in endochondral bone formation and joint homeostasis. Although most data demonstrate an important function of this pathway in endochondral ossification and articular cartilage growth, conflicting results on its role in osteoarthritis have been reported. In some contexts, inactivation of EGFR signaling has been shown to protect joints from surgically induced osteoarthritis, whereas in others, similar manipulations worsened joint pathology. The current review summarizes recent studies of cartilage EGFR signaling in long bone development and diseases, provides potential explanations for the reported discrepancies, and suggests directions for future work to clarify the potential of this pathway as target for osteoarthritis treatment. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

A Macaca Fascicularis Knee Osteoarthritis Model Developed by Modified Hulth Combined with Joint Scratches

BACKGROUND Osteoarthritis is a common degenerative disease of joints, and animal models have important significance in the investigation of this disease. The aim of this study was to develop a better method for developing osteoarthritis models in primates by comparing the modified Hulth score combined with joint scratches modeling method with others. MATERIAL AND METHODS We randomly divided 15 young male Macaca fascicularis and 3 old male Macaca fascicularis into 6 groups (n=3). Knee osteoarthritis (KOA) models were developed with different methods: modified Hulth combined with joint scratches (Group A), modified Hulth (Group B), Hulth (Group C), spontaneous models (Group D); sham-operated (Group E), and blank control (Group F). Morphology and pathology of knee joints were observed at the 8th week after surgery. The levels of WBC, IL-1b, and TGF-b1 in synovial fluid were detected by ELISA. The levels of COL-II, ACAN, and MMP-13 in articular cartilage were examined by RT-qPCR and Western blot. RESULTS In Brittberg and modified Mankin score, Group A was higher than B (P<0.05) and lower than C (P<0.05), and there was no statistically significant difference between Group A and D (P>0.05). Except for Group E and F, the differences were statistically significant among others in WBC, IL-1β, and TGF-β1 (P<0.05). COL-II and ACAN decreased and MMP-13 increased, and there was no significant difference between Groups A and D (P>0.05) or between Groups E and F (P>0.05). There were statistically significant differences among other groups (P<0.05). CONCLUSIONS The models developed by modified Hulth combined with joint scratches were the closet to spontaneous models at the 8th week after surgery.

Multiscale characterization of the mineral phase at skeletal sites of breast cancer metastasis

Skeletal metastases, the leading cause of death in advanced breast cancer patients, depend on tumor cell interactions with the mineralized bone extracellular matrix. Bone mineral is largely composed of hydroxyapatite (HA) nanocrystals with physicochemical properties that vary significantly by anatomical location, age, and pathology. However, it remains unclear whether bone regions typically targeted by metastatic breast cancer feature distinct HA materials properties. Here we combined high-resolution X-ray scattering analysis with large-area Raman imaging, backscattered electron microscopy, histopathology, and microcomputed tomography to characterize HA in mouse models of advanced breast cancer in relevant skeletal locations. The proximal tibial metaphysis served as a common metastatic site in our studies; we identified that in disease-free bones this skeletal region contained smaller and less-oriented HA nanocrystals relative to ones that constitute the diaphysis. We further observed that osteolytic bone metastasis led to a decrease in HA nanocrystal size and perfection in remnant metaphyseal trabecular bone. Interestingly, in a model of localized breast cancer, metaphyseal HA nanocrystals were also smaller and less perfect than in corresponding bone in disease-free controls. Collectively, these results suggest that skeletal sites prone to tumor cell dissemination contain less-mature HA (i.e., smaller, less-perfect, and less-oriented crystals) and that primary tumors can further increase HA immaturity even before secondary tumor formation, mimicking alterations present during tibial metastasis. Engineered tumor models recapitulating these spatiotemporal dynamics will permit assessing the functional relevance of the detected changes to the progression and treatment of breast cancer bone metastasis.

Using mouse models to investigate the pathophysiology, treatment, and prevention of post-traumatic osteoarthritis

Post-traumatic osteoarthritis (PTOA) is defined by its development after joint injury. Factors contributing to the risk of PTOA occurring, the rate of progression, and degree of associated disability in any individual, remain incompletely understood. What constitutes an "OA-inducing injury" is not defined. In line with advances in the traumatic brain injury field, we propose the scope of PTOA-inducing injuries be expanded to include not only those causing immediate structural damage and instability (Type I), but also those without initial instability/damage from moderate (Type II) or minor (Type III) loading severity. A review of the literature revealed this full spectrum of potential PTOA subtypes can be modeled in mice, with 27 Type I, 6 Type II, and 4 Type III models identified. Despite limitations due to cartilage anatomy, joint size, and bio-fluid availability, mice offer advantages as preclinical models to study PTOA, particularly genetically modified strains. Histopathology was the most common disease outcome, cartilage more frequently studied than bone or synovium, and meniscus and ligaments rarely evaluated. Other methods used to examine PTOA included gene expression, protein analysis, and imaging. Despite the major issues reported by patients being pain and biomechanical dysfunction, these were the least commonly measured outcomes in mouse models. Informative correlations of simultaneously measured disease outcomes in individual animals, was rarely done in any mouse PTOA model. This review has identified knowledge gaps that need to be addressed to increase understanding and improve prevention and management of PTOA. Preclinical mouse models play a critical role in these endeavors. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:424-439, 2017.

RNA-binding protein SAMD4 regulates skeleton development through translational inhibition of Mig6 expression

Protein translation regulation has essential roles in inflammatory responses, cancer initiation and the pathogenesis of several neurodegenerative disorders. However, the role of the regulation of protein translation in mammalian skeleton development has been rarely elaborated. Here we report that the lack of the RNA-binding protein sterile alpha motif domain containing protein 4 (SAMD4) resulted in multiple developmental defects in mice, including delayed bone development and decreased osteogenesis. Samd4-deficient mesenchymal progenitors exhibit impaired osteoblast differentiation and function. Mechanism study demonstrates that SAMD4 binds the Mig6 mRNA and inhibits MIG6 protein synthesis. Consistent with this, Samd4-deficient cells have increased MIG6 protein level and knockdown of Mig6 rescues the impaired osteogenesis in Samd4-deficient cells. Furthermore, Samd4-deficient mice also display chondrocyte defects, which is consistent with the regulation of MIG6 protein level by SAMD4. These findings define SAMD4 as a previously unreported key regulator of osteoblastogenesis and bone development, implying that regulation of protein translation is an important mechanism governing skeletogenesis and that control of protein translation could have therapeutic potential in metabolic bone diseases, such as osteoporosis.

Context-specific protection of TGFα null mice from osteoarthritis

Transforming growth factor alpha (TGFα) is a growth factor involved in osteoarthritis (OA). TGFα induces an OA-like phenotype in articular chondrocytes, by inhibiting matrix synthesis and promoting catabolic factor expression. To better understand TGFα’s potential as a therapeutic target, we employed two in vivo OA models: (1) post-traumatic and (2) aging related OA. Ten-week old and six-month old male Tgfa null mice and their heterozygous (control) littermates underwent destabilization of the medial meniscus (DMM) surgery. Disease progression was assessed histologically using the Osteoarthritis Research Society International (OARSI) scoring system. As well, spontaneous disease progression was analyzed in eighteen-month-old Tgfa null and heterozygous mice. Ten-week old Tgfa null mice were protected from OA progression at both seven and fourteen weeks post-surgery. No protection was seen however in six-month old null mice after DMM surgery, and no differences were observed between genotypes in the aging model. Thus, young Tgfa null mice are protected from OA progression in the DMM model, while older mice are not. In addition, Tgfa null mice are equally susceptible to spontaneous OA development during aging. Thus, TGFα might be a valuable therapeutic target in some post-traumatic forms of OA, however its role in idiopathic disease is less clear.

Disturbed cartilage and joint homeostasis resulting from a loss of mitogen-inducible gene 6 in a mouse model of joint dysfunction

OBJECTIVE

Mitogen-inducible gene 6 (MIG-6) regulates epidermal growth factor receptor (EGFR) signaling in synovial joint tissues. Whole-body knockout of the Mig6 gene in mice has been shown to induce osteoarthritis and joint degeneration. To evaluate the role of chondrocytes in this process, Mig6 was conditionally deleted from Col2a1-expressing cell types in the cartilage of mice.

METHODS

Bone and cartilage in the synovial joints of cartilage-specific Mig6-deleted (knockout [KO]) mice and control littermates were compared. Histologic staining and immunohistochemical analyses were used to evaluate joint pathology as well as the expression of key extracellular matrix and regulatory proteins. Calcified tissue in synovial joints was assessed by micro-computed tomography (micro-CT) and whole-skeleton staining.

RESULTS

Formation of long bones was found to be normal in KO animals. Cartilage thickness and proteoglycan staining of articular cartilage in the knee joints of 12-week-old KO mice were increased as compared to controls, with higher cellularity throughout the tissue. Radiopaque chondro-osseous nodules appeared in the knees of KO animals by 12 weeks of age and progressed to calcified bone-like tissue by 36 weeks of age. Nodules were also observed in the spine of 36-week-old animals. Erosion of bone at ligament entheses was evident by 12 weeks of age, by both histologic and micro-CT assessment.

CONCLUSION

MIG-6 expression in chondrocytes is important for the maintenance of cartilage and joint homeostasis. Dysregulation of EGFR signaling in chondrocytes results in anabolic activity in cartilage, but erosion of ligament entheses and the formation of ectopic chondro-osseous nodules severely disturb joint physiology.