Targeting STAT6-mediated synovial macrophage activation improves pain in experimental knee osteoarthritis

BACKGROUND

Pain from osteoarthritis (OA) is one of the top causes of disability worldwide, but effective treatment is lacking. Nociceptive factors are released by activated synovial macrophages in OA, but depletion of synovial macrophages paradoxically worsens inflammation and tissue damage in previous studies. Rather than depleting macrophages, we hypothesized that inhibiting macrophage activation may improve pain without increasing tissue damage. We aimed to identify key mechanisms mediating synovial macrophage activation and test the role of STAT signaling in macrophages on pain outcomes in experimental knee OA.

METHODS

We induced experimental knee OA in rats via knee destabilization surgery, and performed RNA sequencing analysis on sorted synovial tissue macrophages to identify macrophage activation mechanisms. Liposomes laden with STAT1 or STAT6 inhibitors, vehicle (control), or clodronate (depletion control) were delivered selectively to synovial macrophages via serial intra-articular injections up to 12 weeks after OA induction. Treatment effects on knee and hindpaw mechanical pain sensitivity were measured during OA development, along with synovitis, cartilage damage, and synovial macrophage infiltration using histopathology and immunofluorescence. Lastly, crosstalk between drug-treated synovial tissue and articular chondrocytes was assessed in co-culture.

RESULTS

The majority of pathways identified by transcriptomic analyses in OA synovial macrophages involve STAT signaling. As expected, macrophage depletion reduced pain, but increased synovial tissue fibrosis and vascularization. In contrast, STAT6 inhibition in macrophages led to marked, sustained improvements in mechanical pain sensitivity and synovial inflammation without worsening synovial or cartilage pathology. During co-culture, STAT6 inhibitor-treated synovial tissue had minimal effects on healthy chondrocyte gene expression, whereas STAT1 inhibitor-treated synovium induced changes in numerous cartilage turnover-related genes.

CONCLUSION

These results suggest that STAT signaling is a major mediator of synovial macrophage activation in experimental knee OA. STAT6 may be a key mechanism mediating the release of nociceptive factors from macrophages and the development of mechanical pain sensitivity. Whereas therapeutic depletion of macrophages paradoxically increases inflammation and fibrosis, blocking STAT6-mediated synovial macrophage activation may be a novel strategy for OA-pain management without accelerating tissue damage.

Inhibition of IL-4/STAT6/IRF4 signaling reduces the epithelial-mesenchymal transition in eosinophilic chronic rhinosinusitis with nasal polyps

BACKGROUND

Previous studies have shown that epithelial-to-mesenchymal transition (EMT) in nasal epithelial cells is critical for tissue remodeling of chronic rhinosinusitis with nasal polyps (CRSwNP). However, the precise mechanism underlying the EMT remains poorly understood. This study aimed to investigate the role of interleukin-4 (IL-4)/signal transducer and activator of transcription 6 (STAT6)/interferon regulatory factor 4 (IRF4) signaling pathway on EMT in eosinophilic CRSwNP.

METHODS

We performed quantitative real-time polymerase chain reaction, immunohistochemistry, immunofluorescent staining, and Western blotting to evaluate the expression of STAT6, IRF4, and EMT markers in sinonasal mucosal samples. Effects of IL-4-induced EMT were determined using primary human nasal epithelial cells (hNECs) from patients with eosinophilic CRSwNP. Wound scratch assay, cell morphology, Western blotting, and immunofluorescence cytochemistry were performed to evaluate EMT, and EMT-related markers. Next, human THP-1 monocytic cells were stimulated by phorbolate-12-myristate-13-acetate to differentiate into M0 and were subsequently polarized into M1 with lipopolysaccharide and interferon-γ, M2 with IL-4. The markers of the macrophage phenotype were assessed by Western blotting. The co-culture system was built to explore the interaction between macrophages (THP-1 cells) and hNECs. After co-culture with M2 macrophages, EMT-related markers of primary hNECs were evaluated by immunofluorescence cytochemistry and Western blotting. Enzymelinked immunosorbent assays were used to detect transforming growth factor beta 1 (TGF-β1) in THP-1-derived supernatants.

RESULTS

STAT6 and IRF4 mRNA and protein expression were significantly upregulated in both eosinophilic and noneosinophilic nasal polyps compared with control tissues. The expression of STAT6 and IRF4 in eosinophilic nasal polyps was higher than those in noneosinophilic nasal polyps. STAT6 and IRF4 were not only expressed in epithelial cells but also in macrophages. The number of STAT6⁺CD68⁺ cells and IRF4⁺CD68⁺ cells in eosinophilic nasal polyps was higher than those in noneosinophilic nasal polyps and control tissues. EMT was enhanced in eosinophilic CRSwNP compared to the healthy controls and noneosinophilic CRSwNP. IL-4-stimulated human nasal epithelial cells exhibited EMT characteristics. The hNECs co-cultured with M2 macrophages demonstrated high levels of EMT-related markers. The TGF-β1 level was significantly induced by IL-4 and elevated (M2) rather than control macrophages. The inhibition of STAT6 by AS1517499 reduced the expression of IRF4 in epithelial cells and macrophages and counteracted IL-4-induced EMT in epithelial cells.

CONCLUSION

In eosinophilic nasal polyps, IL-4 induces STAT6 signaling to upregulate IRF4 expression in epithelial cells and macrophages. IL-4 promotes EMT of hNECs through the STAT6/IRF4 signaling pathway. IL-4-induced M2 macrophages enhanced EMT of hNECs. Inhibition of STAT6 can downregulate the expression of IRF4 and suppress the EMT process, thus providing a new strategy for the treatment of nasal polyps.

Cadmium inhibits signal transducer and activator of transcription 6 leading to pancreatic β cell apoptosis

The toxic heavy metal cadmium has been proven to cause pancreatic dysfunction and lead to the development of DM. However, the underlying mechanisms have not been completely elucidated. Here, we investigated the effects of cadmium on the pancreatic β cell line MIN6 and explored the underlying mechanisms. The Cell Counting Kit-8 (CCK8) assay and flow cytometry were used to determine cell viability and apoptosis in MIN6 cells. The expression levels of signal transducer and activator of transcription 6 (STAT6) were assessed by western blotting. We further assessed the effects of cadmium on the function of pancreatic β cells under high glucose levels using enzyme-linked immunosorbent assay (ELISA) and western blotting. Insulin secretion and expression were decreased by cadmium in MIN6 cells. In addition, cadmium suppressed cell viability and promoted apoptosis of MIN6 cells, downregulated insulin secretion and genesis of MIN6 cells under high glucose conditions, while inhibiting STAT6. Furthermore, after treatment with IL-4, the activator of STAT6, the MIN6 cell viability suppression and apoptosis promotion effect caused by cadmium were blocked. In conclusion, cadmium inhibits pancreatic β cell MIN6 growth by regulating the activation of STAT6. Our findings reveal a new mechanism of cadmium toxicity in pancreatic β cells.

[Effect of acupuncture and moxibustion at "Feishu""Dazhui"and "Fengmen"on the expression of CC chemokine ligand 1 and CC chemokine receptor 8 in lung tissue of rats with asthma]

OBJECTIVE

To investigate the protein expression of CC chemokine ligand 1 (CCL1) and CC chemokine receptor 8 (CCR8) in the lung tissue of rats and the mechanism of acupuncture and moxibustion at "Feishu"(BL13), "Dazhui" (GV14) and "Fengmen"(BL12) in the treatment of asthma.

METHODS

Sprague-Dawley rats were randomly divided into blank， model, acupuncture and moxibustion groups，n=10 in each group. Ovalbumin sensitization via intraperitoneal injection was performed to establish a model of asthma. The rats in the acupuncture group and the moxibustion group were given acupuncture for 20 min or circling moxibustion for 10 min at BL13, GV14 and BL12, once a day for 7 days. H.E. staining was used to observe the morphological changes of lung tissue. Real-time fluorescence quantitative PCR was used to measure the mRNA expression of signal transducer and activator of transcription 6 (STAT6) in lung tissue and immunohistochemistry was used to measure the protein expression of CCL1 and CCR8 in lung tissue.

RESULTS

H.E. staining showed that the rats in the blank group had regular bronchial lumens and alveolar arrangement, with no inflammatory cell infiltration and aggregation around the bronchi; the rats in the model group had the infiltration and aggregation of a large number of inflammatory cells around the bronchi, stenosis of bronchial lumens, wall thickening, and alveolar structural disorder; compared with the model group, the acupuncture group and the moxibustion group had lower degrees of inflammatory cell infiltration and aggregation around the bronchi, stenosis of bronchial lumens, and wall thickening, as well as regular alveolar arrangement. The model group had significantly higher protein expression of CCL1 and CCR8 and mRNA expression of STAT6 than the blank group (P<0.05), and the acupuncture group and the moxibustion group had significantly lower protein expression of CCL1 and CCR8 and mRNA expression of STAT6 (P<0.05).

CONCLUSION

Acupuncture and moxibustion can intervene against airway inflammation by inhibiting the protein expression of CCL1 and CCR8 and STAT6 signal transduction in lung tissue, which may be one of the mechanisms of acupuncture and moxibustion in the treatment of asthma.

Functions of the Signal Transducer and Activator of Transcription 6 in a Behavioral Animal Model of Depression

AIMS

Depression is one of the most common inflammatory and mental disorders. Signal transducer and activator of transcription 6 (STAT6) plays a crucial role in the pathology of mental disorders as well as inflammatory diseases.

METHODS

Here we determined the role of STAT6 in the pathogenesis of depression using STAT6-deficient mice in a forced swimming test.

RESULTS

The immobility time was significantly decreased in STAT6-deficient mice compared to wild-type mice without alteration of locomotor activity. STAT6-deficient mice exhibited a significantly enhancing dopamine and 5-hydroxytryptamine (5-HT, serotonin) in brain. In addition, the expression of serotonin transporter in the hippocampus was markedly downregulated in STAT6-deficient mice. These results provide the first evidence that STAT6 affects depressive-like behavior through downregulating monoamines, including dopamine and 5-HT in the hippocampus of brain.

CONCLUSIONS

In conclusion, identification of STAT6 signaling pathways on depression might open new perspectives for antidepressant therapies.

Ameliorative effect of atractylenolide III in the mast cell proliferation induced by TSLP

Atractylenolide III (ATL-III) is an active compound of Atractylodes lancea, which has been widely used for the treatment of cancer. Cancer is closely connected with inflammation, and many anti-inflammatory agents are also used to treat cancer. We investigated the influence of ATL-III on thymic stromal lymphopoietin (TSLP)-induced inflammatory reactions. Pretreatment with ATL-III suppressed murine double minute 2 levels and promoted p53 levels in TSLP-treated human mast cell, HMC-1 cells. Mast cell proliferation increased by TSLP or IL-3 stimulation was significantly decreased by ATL-III pretreatment. Interleukin (IL)-13 and phosphorylated signal transducer and activator of transcription 3, 5, and 6 levels in TSLP-treated HMC-1 cells were also decreased by ATL-III pretreatment. In addition, ATL-III decreased the TSLP-induced production of proinflammatory cytokines (IL-6, IL-1β, tumor necrosis factor-α, and IL-8). ATL-III decreased the levels of Bcl2 and procaspase-3 and increased caspase-3 activation and cleaved PARP levels. Furthermore, ATL-III decreased TSLP-induced mast cell proliferation and the production of inflammatory cytokine by LAD2 cells. Taken together, these findings suggest that ATL-III plays a useful role as an anti-inflammatory agent and should be viewed as a potential anti-cancer agent.

Interleukin-13 stimulates MUC5AC expression via a STAT6-TMEM16A-ERK1/2 pathway in human airway epithelial cells

Transmembrane protein 16A (TMEM16A), a channel underlying the calcium-activated chloride channel (CaCC) currents, has been shown to be a key regulator of mucus overproduction in airway epithelial cells. However, the precise molecular mechanism involved in the TMEM16A-mediated mucus secretion remains unclear. In the present study, we inquired into a novel signaling mechanism for TMEM16A driving mucin 5AC (MUC5AC) production in human airway epithelial cells. Following treatment for 24-48h with type 13 interleukin (IL-13), an upregulation of TMEM16A expression in both mRNA and protein levels was observed in human bronchial epithelial cell line (HBE16), while signal transducer and activator of transcription 6 (STAT6) inhibition could decrease this elevated expression, suggesting that the regulation of TMEM16A expression by IL-13 was via a STAT6-based transcriptional mechanism. Further investigation of the HBE16 cells revealed that TMEM16A knockdown or specific chloride channel inhibitor T16Ainh-A01 could suppress the CaCC currents and consequently reduce the extracellular regulated kinase (ERK1/2) phosphorylation, accompanying a dramatical decrease in MUC5AC expression. Moreover, pretreated with PD98059, an inhibitor of ERK1/2, the HB16 cells showed a remarkable diminution in TMEM16A-mediated MUC5AC expression. Altogether, STAT6-TMEM16A-ERK1/2 signal pathway and TMEM16A channel activity are required for the IL-13-induced TMEM16A mediated mucus production.

Inhibition of MDM2 expression by rosmarinic acid in TSLP-stimulated mast cell

Rosmarinic acid (RA) has an anti-inflammatory property while thymic stromal lymphopoietin (TSLP) has an important role in mast cell-mediated inflammatory responses. Thus, the aim of this study was to determine the regulatory effect of RA in TSLP-stimulated human mast cell line, HMC-1 cells, and short ragweed pollen-induced allergic conjunctivitis mouse model. As a result, we found that RA significantly decreased the TSLP-induced mast cell proliferation and murine double minute (MDM) 2 expression. RA significantly decreased the levels of interleukin (IL)-13 and phosphorylated the signal transducer and activation of transcription 6 in the TSLP-stimulated HMC-1 cells. RA induced the increment of p53 levels, caspase-3 activation, and poly-ADP-ribose polymerase cleavage and the reduction of the procaspase-3 and Bcl2. RA significantly reduced the production of tumor necrosis factor-α, IL-1β, and IL-6 on the TSLP-stimulated HMC-1 cells. In addition, RA significantly reduced the levels of IgE, IL-4, and TSLP in the short ragweed pollen-induced allergic conjunctivitis mouse model. In conclusion, the results of the study suggest that RA has a significant anti-inflammatory effect on TSLP-induced inflammatory reactions. These effects of RA are likely to be mediated through inhibiting the MDM2 increased by TSLP.

E3 ubiquitin ligase Cbl-b suppresses human ORMDL3 expression through STAT6 mediation

Orosomucoid 1-Like Protein 3 (ORMDL3) is an asthma candidate gene and Casitas B lineage lymphoma b (Cbl-b), an E3 ubiquitin ligase, is a critical factor in maintaining airway immune tolerance. However, the association of Cbl-b with ORMDL3 for asthma is unclear. Here, we show that expression of ORMDL3 is significantly increased and shows a strong linear correlation with decreased Cbl-b in the peripheral blood of recurrent wheeze patients. To elucidate the molecular mechanisms underlying this correlation, we identified that Cbl-b suppressed the transcriptional activity and mRNA expression of ORMDL3 in vivo. Further investigation showed that phosphorylation of signal transducer and activator of transcription 6 (STAT6) was induced by interleukin 4 bound to the ORMDL3 promoter, while Cbl-b reduced the phosphorylation of STAT6. Our results show that Cbl-b suppresses human ORMDL3 expression through STAT6.

Association of STAT6 genetic variants with childhood atopic dermatitis in Taiwanese population

BACKGROUND

Atopic dermatitis (AD) is the single most common allergic disease in children. STAT6 has been noted as a hub molecule in IL-4 mediated response and AD pathogenesis. However, the association between STAT6 genetic variants and childhood AD has never been thoroughly examined.

OBJECTIVE

We investigate the association between STAT6 genetic variants and childhood AD risk in Taiwanese population.

METHODS

We used data from the Han Chinese in Beijing genome panel of International HapMap Project and the Taiwan Children Health Study cohort to investigate the association of STAT6 genetic variants and childhood AD risks. Four tagged SNPs were selected from HapMap database and rs324011 was most significantly associated with childhood AD. Subsequently, deep sequencing around rs324011 and unconditional/conditional logistic models were applied.

RESULTS

rs324011 showed statistical significance for the occurrence of childhood AD (OR: 1.23; 95% CI: 1.01-1.51) and rs167769 showed borderline statistical significance (OR: 1.21; 95% CI: 0.99-1.49). Likelihood ratio tests revealed that haplotypes (rs167769/rs324011) were associated with childhood AD (global p=0.0018). T alleles of two STAT6 intron2 SNPs, rs324011 and rs167769, increased STAT6 promoter activity significantly in luciferase reporter assay.

CONCLUSION

T allele of rs324011 in STAT6 would increase the risk of AD occurrence in children. Haplotypes of rs324011/rs167769 were also significantly associated with childhood AD in Taiwanese population.

Rapid desensitization induces internalization of antigen-specific IgE on mouse mast cells

BACKGROUND

Rapid desensitization transiently prevents severe allergic reactions, allowing administration of life-saving therapies in previously sensitized patients. However, the mechanisms underlying successful rapid desensitization are not fully understood.

OBJECTIVES

We sought to investigate whether the mast cell (MC) is an important target of rapid desensitization in mice sensitized to exhibit IgE-dependent passive systemic anaphylaxis in vivo and to investigate the antigen specificity and underlying mechanisms of rapid desensitization in our mouse model.

METHODS

C57BL/6 mice (in vivo) or primary isolated C57BL/6 mouse peritoneal mast cells (PMCs; in vitro) were passively sensitized with antigen-specific anti-2,4-dinitrophenyl IgE, anti-ovalbumin IgE, or both. MCs were exposed over a short period of time to increasing amounts of antigen (2,4-dinitrophenyl-human serum albumin or ovalbumin) in the presence of extracellular calcium in vitro or by means of intravenous administration to sensitized mice in vivo before challenging the mice with or exposing the PMCs to optimal amounts of specific or irrelevant antigen.

RESULTS

Rapidly exposing mice or PMCs to progressively increasing amounts of specific antigen inhibited the development of antigen-induced hypothermia in sensitized mice in vivo and inhibited antigen-induced PMC degranulation and prostaglandin D2 synthesis in vitro. Such MC hyporesponsiveness was induced antigen-specifically and was associated with a significant reduction in antigen-specific IgE levels on MC surfaces.

CONCLUSIONS

Rapidly exposing MCs to progressively increasing amounts of antigen can both enhance the internalization of antigen-specific IgE on the MC surface and also desensitize these cells in an antigen-specific manner in vivo and in vitro.

IL-13 receptor α2 contributes to development of experimental allergic asthma

BACKGROUND

IL-13 receptor α2 (IL-13Rα2) binds IL-13 with high affinity and modulates IL-13 responses. There are soluble and membrane forms of IL-13Rα2 generated by alternative splicing in mice, but human subjects express only the membrane form of IL-13Rα2 (memIL-13Rα2).

OBJECTIVE

We determined the role of memIL-13Rα2 in the development of allergic inflammation in mouse models of asthma.

METHODS

IL-13Rα2-deficient and memIL-13Rα2 lung epithelium-specific transgenic mice were challenged with house dust mite (HDM). Airway hyperresponsiveness (AHR) and inflammation were assessed based on the airway pressure-time index, bronchoalveolar lavage (BAL) cell counts, and lung histology. Mucus production was determined by means of periodic acid-Schiff staining of lung sections, Western blot analysis of chloride channel calcium activated 3 (CLCA3) expression in lung homogenates, and ELISA of Muc5ac in BAL fluid. The expression of cytokines and chemokines was determined by using RT-quantitative PCR.

RESULTS

In IL-13Rα2-deficient mice AHR and airway inflammation were attenuated compared with levels seen in wild-type mice after HDM challenge. Lung epithelial overexpression of memIL-13Rα2 in the IL-13Rα2-deficient mice reconstituted AHR and inflammation to levels similar to those observed in HDM-challenged wild-type mice. Mucus production was attenuated in lungs from HDM-treated IL-13Rα2-deficient mice, whereas lung epithelial overexpression of memIL-13Rα2 increased mucus production. Lung epithelial overexpression of memIL-13Rα2 had no effect on levels of the soluble form of IL-13Rα2 in serum or BAL fluid and did not affect IL-13-dependent signal transducer and activator of transcription 6 activation in the lungs.

CONCLUSION

These data collectively support a distinct role for memIL-13Rα2 in the lung and suggest that memIL-13Rα2 might contribute to allergic inflammation.

An association study of the signal transducer and activator of transcription 6 gene with periodic psychosis

OBJECTIVE

Recent molecular and genetic investigations have suggested that the current nosology for major psychiatric disorders, based on the "two-entities-principal" is not accurate with respect to clinical observations; patient groups that do not fit to the current operative diagnostic boundaries are readily identified. We aimed to perform an investigation of the signal transducer and activator of transcription 6 (STAT6) gene (located on 12q13), which has an important role in the apoptotic cascade, with patients suffering from periodic psychosis.

METHODS

Genetic association study has been employed for the current work. Investigated six tag-SNPs were chosen from Hapmap database.

RESULTS

Among six tag-SNPs, one marker (rs10783813), located in the STAT6 gene, showed modest association (p<0.05), although no marker or haplotype block showed association after Bonferroni's correction.

CONCLUSION

Future studies will reveal the etiological role of STAT6, and of other genes of the apoptotic cascade, in major psychiatric disorders.