Modulation of cartilage proteoglycan metabolism by LIF binding protein

TRPV4 differentially controls inflammatory cytokine networks during static and dynamic compression of the intervertebral disc

Background

The ion channel transient receptor potential vanilloid 4 (TRPV4) critically transduces mechanical forces in the IVD, and its inhibition can prevent IVD degeneration due to static overloading. However, it remains unknown whether different modes of loading signals through TRPV4 to regulate the expression of inflammatory cytokines. We hypothesized that TRPV4 signaling is essential during static and dynamic loading to mediate homeostasis and mechanotransduction.

Methods

Mouse functional spine units were isolated and either cyclically compressed for 5 days (1 Hz, 1 h, 10% strain) or statically compressed (24 h, 0.2 MPa). Conditioned media were monitored at 6 h, 24 h, 2 days, and 5 days, with and without TRPV4 inhibition. Effects of TRPV4 activation was also evaluated without loading. The media was analyzed for a panel of 44 cytokines using a microbead array and then a correlative network was constructed to explore the regulatory relationships during loading and TRPV4 inhibition. After the loading regimen, the IVDs were evaluated histologically for degeneration.

Results

Activation of TRPV4 led to an increase interleukin-6 (IL-6) family of cytokines (IL-6, IL-11, IL-16, and leukemia inhibitory factor [LIF]) and decreased the T-cell (CCL3, CCL4, CCL17, CCL20, CCL22, and CXCL10) and monocyte (CCL2 and CCL12) recruiting chemokines by the IVD. Dynamic and static loading each provoked unique chemokine correlation networks. The inhibition of TRPV4 during dynamic loading dysregulated the relationship between LIF and other cytokines, while the inhibition of TRPV4 during static loading disrupted the connectivity of IL-16 and VEGFA.

Conclusions

We demonstrated that TRPV4 critically mediates the cytokine production following dynamic and static loading. The activation of TRPV4 upregulated a diverse set of cytokines that may suppress the chemotaxis of T-cells and monocytes, implicating the role of TRPV4 in maintaining the immune privilege of healthy IVD.

Transcriptome dynamics of long noncoding RNAs and transcription factors demarcate human neonatal, adult, and human mesenchymal stem cell-derived engineered cartilage

The engineering of a native-like articular cartilage (AC) is a long-standing objective that could serve the clinical needs of millions of patients suffering from osteoarthritis and cartilage injury. An incomplete understanding of the developmental stages of AC has contributed to limited success in this endeavor. Using next generation RNA sequencing, we have transcriptionally characterized two critical stages of AC development in humans-that is, immature neonatal and mature adult, as well as tissue-engineered cartilage derived from culture expanded human mesenchymal stem cells. We identified key transcription factors (TFs) and long noncoding RNAs (lncRNAs) as candidate drivers of the distinct phenotypes of these tissues. AGTR2, SCGB3A1, TFCP2L1, RORC, and TBX4 stand out as key TFs, whose expression may be capable of reprogramming engineered cartilage into a more expandable and neonatal-like cartilage primed for maturation into biomechanically competent cartilage. We also identified that the transcriptional profiles of many annotated but poorly studied lncRNAs were dramatically different between these cartilages, indicating that lncRNAs may also be playing significant roles in cartilage biology. Key neonatal-specific lncRNAs identified include AC092818.1, AC099560.1, and KC877982. Collectively, our results suggest that tissue-engineered cartilage can be optimized for future clinical applications by the specific expression of TFs and lncRNAs.

In VitroEvaluation of Leukemia Inhibitory Factor Receptor Antagonists as Candidate Therapeutics for Inflammatory Arthritis

Leukemia inhibitory factor (LIF) and oncostatin M (OSM) are found in appreciable concentrations in synovial fluid from patients with rheumatoid arthritis (RA) but not osteoarthritis. Accordingly, both are potential therapeutic targets in inflammatory diseases of the joints. Several LIF antagonists have been developed. They have the capacity to inhibit the biologic activities of not only LIF but also other interleukin-6 (IL-6) subfamily cytokines, including OSM. Both LIF and OSM share the same receptor, which is part of a cytokine receptor super family in which the glycoprotein 130 (gp130) subunit is a common constituent. The aim of this study was to evaluate the antagonistic potentials of two LIF mutants, LIF05 and MH35-BD. Both are mutant forms of human LIF with reduced affinity for gp130 and greater LIF receptor (LIFR) binding affinity. The results, using Ba/F3 cell proliferation assay, acute-phase protein (haptoglobin) induction analysis in HepG2 human hepatoma cells, a porcine cartilage glycosaminoglycan release assessment for proteoglycan degradation, and a collagen release assay, show that these antagonists inhibit relevant LIF, OSM, and other IL-6 subfamily cytokines in vitro albeit with differential potencies and have, therefore, therapeutic potential for treatment of RA and perhaps other diseases.

Expression of galanin and galanin receptor-1 in normal bone and during fracture repair in the rat

The neuropeptide galanin (GAL) has recognized physiological actions in the nervous system and other tissues, but there is no documented evidence of GAL influencing normal or pathological bone metabolism. GAL expression, however, is upregulated in central and peripheral nerves following axotomy and is known to influence neural regeneration. Thus, severance of skeletal-associated nerves during fracture could similarly increase local GAL concentrations and thereby influence fracture healing. The initial aim of this study was therefore to identify the presence of GAL in normal bone and/or fracture callus by assessing the concentration and cellular localization of GAL in intact and/or fractured rat rib, using radioimmunoassay and immunohistochemistry, respectively. Groups of Sprague-Dawley rats (13 weeks old) had their left sixth ribs surgically fractured or underwent sham surgery and then calluses and nonfractured rib samples were analyzed at 1 and 2 weeks postsurgery (n = 5-6 per group). Low (basal) concentrations of GAL were detected in control ribs, whereas at 1 and 2 weeks postfracture, callus samples contained markedly increased levels of peptide ( approximately 32- and 18-fold increase, respectively, relative to controls; P < 0.01), revealing a strong upregulation during bone healing. Plasma GAL concentrations were also increased at 2 weeks postfracture (P < 0.005). In normal (nonfractured) rib, minimal levels of GAL-like immunoreactivity (LI) were present in cortical bone, periosteum, endosteum, and surrounding skeletal muscle. In costal cartilage plates, intense GAL-LI was present in all chondrocytes of the hypertrophic zone and in a population of chondrocytes in the reserve zone. GAL-LI was not present, however, in chondrocytes in the proliferative zone of costal cartilage or skeletal muscle fibers. In fracture callus, levels of GAL-LI were moderate to intense in osteoprogenitor cells and osteoblasts, in some chondrocytes, and in cartilaginous, osseous, and periosteal matrices. Subsequent studies revealed the presence of galanin receptor-1-like immunoreactivity (GALR1-LI) in most cell types shown to contain GAL-LI, although the distribution of GALR1-LI was more extensive in reserve zone chondrocytes than that of GAL-LI; and GALR1-LI also appeared in late proliferative zone chondrocytes of costal cartilage. In summary, GAL concentrations were significantly increased in fracture callus and plasma of rats that underwent rib fracture. In addition, GAL- and GALR1-LI was also detected in specific cells and structures within costal cartilage, bone, and fracture callus. These results strongly implicate GAL in aspects of cartilage growth plate physiology and fracture repair, possibly acting in an autocrine/paracrine fashion via GALR1.

Murine oncostatin M stimulates mouse synovial fibroblasts in vitro and induces inflammation and destruction in mouse joints in vivo

Oncostatin M (OSM) is a multifunctional cytokine, a member of the interleukin-6/leukemia inhibitory factor (IL-6/LIF) family, that can regulate a number of connective-tissue cell types in vitro including cartilage and synovial tissue-derived fibroblasts, however its role in joint inflammation in vivo is not clear. We have analyzed murine OSM (muOSM) activity in vitro and in vivo in mouse joint tissue, to determine the potential role of this cytokine in local joint inflammation and pathology. The effects of muOSM and other IL-6/LIF cytokines on mouse synovial fibroblast cultures were assessed in vitro and showed induction of monocyte chemotactic protein-1, interleukin-6, and tissue inhibitor metalloproteinase-1, as well as enhancement of colony growth in soft agarose culture. Other IL-6/LIF cytokines including IL-6, LIF, or cardiotrophin-1, did not have such effects when tested at relatively high concentrations (20 ng/ml). To assess effects of muOSM in articular joints in vivo, we used recombinant adenovirus expressing muOSM cDNA (AdmuOSM) and injected purified recombinant virus (10(6) to 10(8) pfu) intra-articularly into the knees of various mouse strains. Histological analysis revealed dramatic alterations in the synovium but not in synovium of knees treated with the control virus Ad-dl70 or knees treated with Adm-IL-6 encoding biologically active murine IL-6. AdmuOSM effects were characterized by increases in the synovial cell proliferation, infiltration of mononuclear cells, and increases in extracellular matrix deposition that were evident at day 4, but much more marked at days 7, 14, and 21 after administration. The synovium took on characteristics similar to pannus and appeared to contact and invade cartilage. Collectively, these results provide good evidence that OSM regulates synovial fibroblast function differently than other IL-6-type cytokines, and can induce a proliferative invasive phenotype of synovium in vivo in mice on overexpression. We suggest that OSM may contribute to pathology in arthritis.

Leukemia-inhibitory factor-neuroimmune modulator of endocrine function

Leukemia-inhibitory factor (LIF) is a pleiotropic cytokine expressed by multiple tissue types. The LIF receptor shares a common gp130 receptor subunit with the IL-6 cytokine superfamily. LIF signaling is mediated mainly by JAK-STAT (janus-kinase-signal transducer and activator of transcription) pathways and is abrogated by the SOCS (suppressor-of cytokine signaling) and PIAS (protein inhibitors of activated STAT) proteins. In addition to classic hematopoietic and neuronal actions, LIF plays a critical role in several endocrine functions including the utero-placental unit, the hypothalamo-pituitary-adrenal axis, bone cell metabolism, energy homeostasis, and hormonally responsive tumors. This paper reviews recent advances in our understanding of molecular mechanisms regulating LIF expression and action and also provides a systemic overview of LIF-mediated endocrine regulation. Local and systemic LIF serve to integrate multiple developmental and functional cell signals, culminating in maintaining appropriate hormonal and metabolic homeostasis. LIF thus functions as a critical molecular interface between the neuroimmune and endocrine systems.

Soluble glycoprotein 130 (gp130) attenuates OSM- and LIF-induced cartilage proteoglycan catabolism

Oncostatin M (OSM) and leukaemia inhibitory factor (LIF) exhibit pleiotropic biological activities and share many structural and genetic features. The two cytokines bind with high affinity to the same receptor (LIF/OSM receptor), which consists of the LIF receptor alpha chain (LIFRalpha) and the signal transduction unit gp130. A soluble form of the beta chain of the receptor complex called soluble gp130 (sgp130) has been cloned. In this study, we sought to determine whether recombinant sgp130 or anti-gp130 Ab could attenuate the resorption of proteoglycans induced by OSM and LIF in articular cartilage explants. The results show that at high concentrations sgp130 is capable of attenuating both LIF and OSM mediated resorption. In contrast, anti-gp130 Ab selectively inhibited the stimulation of proteoglycan (PG) release by OSM, albeit minimally. The failure of anti-gp130 to attenuate LIF stimulated PG resorption may be due to the normal interaction of LIF with LIFRalpha and unfettered heterodimerization of LIFRalpha with gp130 in the presence of the antibody. The results indicate that sgp130 and anti-gp130 can modulate cartilage PG metabolism in vitro. Whether sgp130 may have therapeutic activity in models of arthritis or indeed in arthritic diseases remains to be determined.

Oncostatin M induces leukocyte infiltration and cartilage proteoglycan degradation in vivo in goat joints

OBJECTIVE

To evaluate the effect of intraarticular injections of recombinant human oncostatin M (rHuOSM) in the goat joint.

METHODS

One milliliter of endotoxin-free normal saline (vehicle) containing either 40 ng, 200 ng, or 1,000 ng of rHuOSM was injected into the right radiocarpal joints (RCJs) of 12 male angora goats, while the left RCJs were injected with an equivalent volume of vehicle alone. In subsequent studies, the right and left RCJs of 8 male angora goats were injected with 200 ng of rHuOSM, and 1 hour later, the right RCJs were injected with either 5 microg of recombinant murine leukemia inhibitory factor binding protein (rMuLBP) or 1 mg of recombinant human interleukin-1 receptor antagonist (rHuIL-1Ra) in 1 ml of vehicle, while the left RCJs received 1 ml of vehicle alone. Goat joints were examined for clinical features of inflammation, and synovial fluid (SF) was aspirated on day 0 (before injection) and at days 2 and 6 postinjection.

RESULTS

Injections of rHuOSM stimulated dose-dependent increases in the carpal:metacarpal ratio, SF volume, and SF leukocyte numbers, and stimulated dose-dependent decreases in the cartilage proteoglycan (PG) content ex vivo and PG synthesis. No significant changes were observed in the control joints that received saline alone, or between RCJs that were injected with 200 ng rHuOSM followed by 5 microg rMuLBP and RCJs that were injected with 200 ng of rHuOSM alone, except in respect to synovial fluid keratan sulfate concentrations, where a modest statistically significant reduction was observed in the joints injected with the combination of rHuOSM and rMuLPB. In contrast, RCJs injected with 200 ng rHuOSM followed by 1 mg of rHuIL-1Ra had significantly lower SF volumes (P<0.0001) and a significantly higher rate of ex vivo PG synthesis (P<0.0001).

CONCLUSION

These results indicate that rHuOSM stimulates inflammation and modulates cartilage PG metabolism in vivo. Some of the effects of rHuOSM in vivo appear to be due, in part, to elaboration of IL-1. Even at very high doses, however, the rHuIL-1Ra did not attenuate OSM-mediated cartilage PG resorption. Thus, OSM has the potential to contribute to synovitis in vivo and can stimulate cartilage PG resorption in vivo, independent of IL-1.

Leukemia inhibitory factor is an autocrine survival factor for Schwann cells

Schwann cells play a major role in promoting nerve survival and regeneration after injury. Their activities include providing neurotrophic factors and increasing the production of extracellular matrix components and cell surface adhesion molecules to promote axon regeneration. Following nerve transection, leukemia inhibitory factor (LIF) is up-regulated by Schwann cells at the injury site. LIF receptors are also up-regulated at the nerve injury site, but their cellular localization and function have not been fully characterized. We demonstrate that Schwann cells express mRNAs for LIF and the LIF receptor components LIF receptor subunit beta and glycoprotein 130 in vitro. We also show that although LIF is not required for the genesis of Schwann cells, it can potentiate the survival of differentiated Schwann cells in the context of neuregulin support. Not only does exogenous LIF promote survival under these conditions, but addition of the soluble LIF receptor (LIF binding protein) and anti-LIF antibodies significantly reduced cell survival, suggesting that LIF exerts autocrine effects. These results suggest that Schwann cell survival following nerve injury is potentially modulated by LIF.