AAA-ATPase p97 suppresses apoptotic and autophagy-associated cell death in rheumatoid arthritis synovial fibroblasts

The histone acetyl transferases CBP and p300 regulate stress response pathways in synovial fibroblasts at transcriptional and functional levels

The activation of stress response pathways in synovial fibroblasts (SF) is a hallmark of rheumatoid arthritis (RA). CBP and p300 are two highly homologous histone acetyl transferases and writers of activating histone 3 lysine 27 acetylation (H3K27ac) marks. Furthermore, they serve as co-factors for transcription factors and acetylate many non-histone proteins. Here we showed that p300 but not CBP protein expression was down regulated by TNF and 4-hydroxynonenal, two factors that mimic inflammation and oxidative stress in the synovial microenvironment. We used existing RNA-sequencing data sets as a basis for a further in-depth investigation of individual functions of CBP and p300 in regulating different stress response pathways in SF. Pathway enrichment analysis pointed to a profound role of CBP and/ or p300 in regulating stress response-related gene expression, with an enrichment of pathways associated with oxidative stress, hypoxia, autophagy and proteasome function. We silenced CBP or p300, and performed confirmatory experiments on transcriptome, protein and functional levels. We have identified some overlap of CBP and p300 target genes in the oxidative stress response pathway, however, with several genes being regulated in opposite directions. The majority of stress response genes was regulated by p300, with a specific function of p300 in regulating hypoxia response genes and genes encoding proteasome subunits. Silencing of p300 suppressed proteasome enzymatic activities. CBP and p300 regulated autophagy on transcriptome and functional levels. Whereas CBP was indispensable for autophagy synthesis, silencing of p300 affected late-stage autophagy. In line with impaired autophagy and proteasome function, poly-ubiquitinated proteins accumulated after silencing of p300.

Inhibitors of the ATPase p97/VCP: From basic research to clinical applications

Protein homeostasis deficiencies underlie various cancers and neurodegenerative diseases. The ubiquitin-proteasome system (UPS) and autophagy are responsible for most of the protein degradation in mammalian cells and, therefore, represent attractive targets for cancer therapy and that of neurodegenerative diseases. The ATPase p97, also known as VCP, is a central component of the UPS that extracts and disassembles its substrates from various cellular locations and also regulates different steps in autophagy. Several UPS- and autophagy-targeting drugs are in clinical trials. In this review, we focus on the development of various p97 inhibitors, including the ATPase inhibitors CB-5083 and CB-5339, which reached clinical trials by demonstrating effective anti-tumor activity across various tumor models, providing an effective alternative to targeting protein degradation for cancer therapy. Here, we provide an overview of how different p97 inhibitors have evolved over time both as basic research tools and effective UPS-targeting cancer therapies in the clinic.

Anti-inflammatory effect of baicalin in rats with adjuvant arthritis and its autophagy- related mechanism

BACKGROUND:

It has been found that baicalin have anti-inflammatory effects since it reduces the elevated levels of pro-inflammatory cytokines. Meanwhile, it has also been shown that baicalin brings positive effects against rheumatoid arthritis (RA). However, little is observed on its beneficial effects on adjuvant arthritis.

OBJECTIVE:

To consider the anti-inflammatory influence of baicalin on adjuvant arthritis rats and its related autophagy mechanism.

METHODS:

In this research, there are six groups of rats, each has 10 rats in it. These groups are normal group (normal saline), model group (normal saline), dexamethasone group (0.125 mg/kg dexamethasone), low-dose baicalin group (50 mg/kg baicalin), medium-dose baicalin group (100 mg/kg baicalin) and high-dose baicalin group (200 mg/kg baicalin). The degrees of adjuvant-induced swelling in rats’ feet were measured every 4 days and the arthritis scores were calculated every 7 days. The inflamed joint tissues were taken after rats were sacrificed. The rat’ joints showed pathological changes, which were observed by HE staining. The relative expression levels of inflammatory factors IL-6, IL-1, IL-17, TNF-α, COX2, and COX1 in the rats’ snovial tissues were detected by RT-PCR. As for the expression levels of autophagy markers Beclin1, Atg5, Atg7, Atg12, microtubule-associated protein-light chain3-II (LC3-II), Bcl-2, and Bax in the synovial tissue, they were discoverd by Western blot.

RESULTS:

Baicalin could significantly inhibit the inflammatory response of adjuvant arthritis rats.

CONCLUSIONS:

RT-PCR studies showed that the different doses of baicalin could inhibit the expression of TNF-a, IL-6, IL-1, IL-17, COX2 and COX1 in the synovial tissue (P< 0.05 or P< 0.01). Western blot studies showed that the different doses of baicalin could reduce the expression of Atg5, Atg7, Atg12, LC3-II, Beclin1 and Bcl-2 proteins, and increase the expression of Bax proteins in the synovial tissue.

New potential therapeutic approaches targeting synovial fibroblasts in rheumatoid arthritis

Synovial cells play a key role in joint destruction during chronic inflammation. In particular, activated synovial fibroblasts (SFs) undergo intrinsic alterations leading to an aggressive phenotype mediating cartilage destruction and bone erosion in rheumatoid arthritis (RA). Recent research has revealed a number of targets to control arthritogenic changes in SFs. Therefore, identification of SF phenotypes, control of epigenetic changes, modulation of cellular functions, or regulation of the activity of cation channels and different signaling pathways has been investigated. Although many of these approaches have shown efficacy in vitro and in animal models of RA, further research is needed to select the most relevant targets for drug development. This review is focused on the role of SFs as a potential strategy to discover novel therapeutic targets in RA aimed at preserving joint architecture and function.

TNF induces glycolytic shift in fibroblast like synoviocytes via GLUT1 and HIF1A

TNF is a central cytokine in the pathogenesis of rheumatoid arthritis (RA). Elevated level of TNF causes local inflammation that affects immune cells and fibroblast-like synoviocytes (FLS). Nowadays, only 20–30% of patients experience remission after the standard of care therapy—antibodies against TNF. Interestingly, responders show reduced levels of GLUT1 and GAPDH, highlighting a potential link to cellular metabolism. The aim of the study was to investigate whether TNF directly affects the metabolic phenotype of FLS. Real-time respirometry displayed TNF-induced upregulation of glycolysis along with a modest increase of oxidative phosphorylation in FLS from healthy donors. In addition, TNF stimulation enhanced HIF1A and GLUT1 expression. The upregulation of HIF1A and GLUT1 reflects their enriched level in FLS from RA patients (RA-FLS). The inhibition of TAK1, HIF1a and hexokinase deciphered the importance of TNF/TAK1/HIF1A/glycolysis signaling axis. To prove that inhibition of glycolysis reduced the pathogenic phenotype, we showed that 2-deoxyglucose, a hexokinase inhibitor, partially decreased secretion of RA biomarkers. In summary, we identified a direct role of TNF on glycolytic reprogramming of FLS and confirmed the potency of immunometabolism for RA. Further studies are needed to evaluate the therapeutic impact especially regarding non-responder data.

Inhibition of histone deacetylase 6 suppresses inflammatory responses and invasiveness of fibroblast-like-synoviocytes in inflammatory arthritis

Background

To investigate the effects of inhibiting histone deacetylase (HDAC) 6 on inflammatory responses and tissue-destructive functions of fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA).

Methods

FLS from RA patients were activated with interleukin (IL)-1β in the presence of increasing concentrations of M808, a novel specific HDAC6 inhibitor. Production of ILs, chemokines, and metalloproteinases (MMPs) was measured in ELISAs. Acetylation of tubulin and expression of ICAM-1 and VCAM-1 were assessed by Western blotting. Wound healing and adhesion assays were performed. Cytoskeletal organization was visualized by immunofluorescence. Finally, the impact of HDAC6 inhibition on the severity of arthritis and joint histology was examined in a murine model of adjuvant-induced arthritis (AIA).

Results

HDAC6 was selectively inhibited by M808. The HDAC6 inhibitor suppressed the production of MMP-1, MMP-3, IL-6, CCL2, CXCL8, and CXCL10 by RA-FLS in response to IL-1β. Increased acetylation of tubulin was associated with decreased migration of RA-FLS. Inhibiting HDAC6 induced cytoskeletal reorganization in RA-FLS by suppressing the formation of invadopodia following activation with IL-1β. In addition, M808 tended to decrease the expression of ICAM-1 and VCAM-1. In the AIA arthritis model, M808 improved the clinical arthritis score in a dose-dependent manner. Also, HDAC6 inhibition was associated with less severe synovial inflammation and joint destruction.

Conclusion

Inhibiting HDAC6 dampens the inflammatory and destructive activity of RA-FLS and reduces the severity of arthritis. Thus, targeting HDAC6 has therapeutic potential.

Autophagy Activation by Resveratrol Reduces Severity of Experimental Rheumatoid Arthritis

SCOPE

Previous work reported that dietary supplementation with resveratrol lowers synovial hyperplasia, inflammatory and oxidative damage in an antigen-induced arthritis (AIA) model. Here, it is investigated whether resveratrol can regulate the abnormal synovial proliferation by inducing autophagy and controlling the associated inflammatory response.

METHODS AND RESULTS

Animals treated with resveratrol 8 weeks before AIA induction show the highest significant signal for microtubule-associated protein 1 light chain 3 by confocal microscopy. Besides, resveratrol significantly reduces p62 expression, but it does not increase the signal of beclin-1. Also, active caspase-3 expression, as well as poly(ADP-ribose) polymerase, is upregulated in the AIA group, and is significantly reduced in resveratrol-treated AIA group. Resveratrol also mitigates angiopoietin-1 and vascular endothelial growth factor signals. Finally, resveratrol significantly reduces the serum levels of IL-1β, C reactive protein, and prostaglandin E2, as well as nuclear factor κB synovial tissue expression, which shows a significant correlation with p62 expression.

CONCLUSION

Dietary supplementation with resveratrol induces the noncanonical autophagy pathway and limits the cross-talk with inflammation, which in consequence modulates the synovial hyperplasia. Preventive strategies that incorporate dietary intervention with resveratrol may offer a potential therapeutic alternative to drugs to influence the risk of rheumatoid arthritis and influence its course.

Astragalus polysaccharides inhibits cell growth and pro-inflammatory response in IL-1β-stimulated fibroblast-like synoviocytes by enhancement of autophagy via PI3K/AKT/mTOR inhibition

The hyperplastic growth of rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLSs) and inflammatory response are pathological hallmarks of RA. It has been reported that Astragalus polysaccharides (APS) possess appreciable anti-inflammatory activity against adjuvant-induced arthritis. Nevertheless, little is known about the role and detailed mechanism underlying the therapeutic effects of APS in RA. This study demonstrated that administration of APS dose-dependently impaired cell viability, increased cell apoptosis by decreasing Bcl-2 expression, increasing Bax expression and Caspase3 activity in IL-1β-stimulated RSC-364 cells and RA-FLS. Simultaneously, IL-1β-induced production of pro-inflammatory cytokines IL-6 and TNF-α was significantly decreased after APS treatment. Furthermore, preconditioning with APS dramatically enhanced autophagy activity by increasing Beclin-1 and LC3II/LC3I expression coupled with decreasing p62 expression and augmenting the number of LC3 puncta in IL-1β-stimulated RSC-364 cells. More importantly, autophagy inhibitor 3-methyladenine (3-MA) partly abolished APS-triggered inhibitory effects on cell growth and production of pro-inflammatory cytokines. APS also repressed the activation of PI3K/Akt/mTOR signaling pathway in IL-1β-stimulated RSC-364 cells. Moreover, treatment with insulin-like growth factor-1 (IGF-1), an activator of PI3K/Akt signaling, partly reversed the therapeutic effects of APS in IL-1β-stimulated RSC-364 cells. Collectively, we concluded that APS might attenuate the pathological progression of RA by exerting the pro-apoptotic and anti-inflammatory effects in IL-1β-stimulated FLSs by regulating the PI3K/AKT/mTOR-autophagy pathway.

Autophagy inhibitor regulates apoptosis and proliferation of synovial fibroblasts through the inhibition of PI3K/AKT pathway in collagen-induced arthritis rat model

BACKGROUND AND OBJECTIVE

Mounting studies have illustrated an important role of autophagy in various diseases, but few studies have reported its contribution to rheumatoid arthritis (RA) and the underlying mechanism was largely unknown. This study aimed to investigate whether autophagy inhibitors could regulate apoptosis and proliferation through PI3K/AKT pathway in RA.

METHODS

RA animal model was established by collagen induction. General observations and degree of joint swelling were observed. Inflammatory response, cell survival related factors and apoptosis were also detected in synovial fibroblasts. In addition, cultured rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS) were subjected to TNF-α treatment in vitro, and TNF-α induced cell autophagy, synovial cell proliferation and apoptosis were detected. Moreover, cell cycle and cytokine secretion protein, along with the above parameters, were analyzed.

RESULTS

Results from the animal model showed that autophagy inhibitors attenuated inflammatory reaction and synovial hyperplasia, while promoted synovial fibroblasts apoptosis. Meanwhile, inhibition of autophagy promoted cell apoptosis and reversed cell proliferation in vitro, also blocked cell in the G2/M arrest and reduced the S phase cells. Furthermore, we observed that inhibition of PI3K/AKT pathway reversed TNF-α mediated autophagy and cytokine secretion.

CONCLUSION

autophagy inhibitors could mitigate inflammation response, inhibiting RA-FLS cell proliferation while promoting cell apoptosis by the PI3K/AKT pathway.