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

WNT Signaling Factors as Potential Synovial Inflammation Moderators in Patients with Hip Osteoarthritis

Background: The main feature of osteoarthritis (OA) is the deterioration of articular cartilage, but numerous studies have demonstrated the role of synovial inflammation in the early stages of the disease, leading to further progression of OA. The WNT signaling pathway is involved in numerous activities in joint tissue, but there is a lack of evidence considering the role of WNT in OA synovitis. Our research aims to investigate the expression of WNT Family Member 5A/B (WNT5A/B), β-catenin, acetyl-α-tubulin, Dishevelled-1 (DVL-1), and Inversin (INV) in the synovial membrane of osteoarthritis (OA) hips. Methods: The immunohistochemical expressions of the aforementioned proteins in the synovial membrane were analyzed and compared with samples of control group participants with fractured femoral necks. Results: The immunoexpression of acetyl-α-tubulin was significantly increased in the intima (p < 0.0001) and subintima (p < 0.0001) of the group with OA compared with the intima and subintima of the control group. At the same time, acetyl-α-tubulin was also more highly expressed in the intima of the OA group than in the subintima of the OA group (p < 0.05); we found the same expression pattern in the control group (p < 0.0001). The differential analysis of the GEO dataset did not show significant differences between the osteoarthritis (OA) and control groups in the expression of TUBA1A. β-catenin was significantly increased in the subintima (p < 0.01) of the group with OA compared to the subintima of the control group. WNT expression has significantly higher positivity in the subintima than in the intima, especially in the control group (p < 0.01). WNT5A and WNT5B were significantly down-regulated in OA compared to the control in the differential analysis of the GEO dataset. The expression of INV and DVL-1 in our study and the differential analysis of the GEO dataset did not differ significantly between the osteoarthritis (OA) and control groups. Conclusions: Based on our results, we suggest that acetyl-α-tubulin and β-catenin might be involved in synovial membrane inflammation in OA and serve as potential therapeutic targets.

HDAC6-Mediated FoxO1 Acetylation And Phosphorylation Control Periodontal Inflammatory Responses

Post-translational modifications (PTMs) are critical regulators of protein function and cellular signaling. While histone deacetylation by histone deacetylases (HDACs) is well established, the role of specific HDACs in modulating non-histone protein PTMs, particularly in an infectious context, is poorly understood. Here, we reveal a pivotal role for HDAC6 in orchestrating periodontal inflammation through its dual regulatory effects on FoxO1 acetylation and phosphorylation. Using Porphyromonas gingivalis , a key periodontal pathogen, as a model pathogen, we observed that infection induces HDAC6 activation, driving inflammatory responses via modulating FoxO1 activity. HDAC6 depletion increased FoxO1 acetylation and phosphorylation, leading to its cytoplasmic sequestration and subsequent suppression of FoxO1- mediated pro-inflammatory cytokine production in macrophages. Mechanistically, HDAC6 deficiency not only directly enhances the acetylation of FoxO1 but also upregulates the expression of Rictor, a critical component of the mTORC2 complex, thereby promoting Akt phosphorylation and subsequently FoxO1 phosphorylation. This results in its cytoplasmic retention and attenuated inflammatory transcriptional activity. Functional studies demonstrated that HDAC6 depletion suppressed the production of key inflammatory mediators, including TNFα, IL-6, IL-12p40, and MIP-2, while promoting macrophage polarization toward anti-inflammatory M2 phenotypes. In vivo , using oral gavage infection and ligature-induced mouse periodontitis models, HDAC6 deficiency significantly reduced inflammatory cell infiltration in gingival tissues and protected against alveolar bone loss. These findings establish HDAC6 as a central regulator of periodontal inflammation, acting through the coordinated modulation of FoxO1 acetylation and phosphorylation. Beyond its role in oral pathology, HDAC6 may serve as a promising therapeutic target for managing inflammatory diseases linked to immune dysregulation.

Histone deacetylase inhibition mitigates cognitive deficits and astrocyte dysfunction induced by amyloid-β (Aβ) oligomers

BACKGROUND AND PURPOSE

Inhibitors of histone deacetylases (iHDACs) are promising drugs for neurodegenerative diseases. We have evaluated the therapeutic potential of the new iHDAC LASSBio-1911 in Aβ oligomer (AβO) toxicity models and astrocytes, key players in neuroinflammation and Alzheimer's disease (AD).

EXPERIMENTAL APPROACH

Astrocyte phenotype and synapse density were evaluated by flow cytometry, Western blotting, immunofluorescence and qPCR, in vitro and in mice. Cognitive function was evaluated by behavioural assays using a mouse model of intracerebroventricular infusion of AβO.

KEY RESULTS

LASSBio-1911 modulates reactivity and synaptogenic potential of cultured astrocytes and improves synaptic markers in cultured neurons and in mice. It prevents AβO-triggered astrocytic reactivity in mice and enhances the neuroprotective potential of astrocytes. LASSBio-1911 improves behavioural performance and rescues synaptic and memory function in AβO-infused mice.

CONCLUSION AND IMPLICATIONS

These results contribute to unveiling the mechanisms underlying astrocyte role in AD and provide the rationale for using astrocytes as targets to new drugs for AD.

Novel mechanistic study of HDAC6 regulation of rheumatoid arthritis via CMA: exploring potential therapeutic targets

Objective

Rheumatoid arthritis (RA) is a systemic autoimmune disease. Its pathogenesis has not yet been clarified, so it is urgent to explore therapeutic targets. Here, we clarified the role of HDAC6 in the mechanism of action of RA through mediating chaperone-mediated autophagy (CMA) to provide a clinical treatment of RA.

Methods

We used rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS) and collagen-induced arthritis mice (CIA mice) as models of RA and pharmacological inhibitors as well as genetic interference with adeno-associated viruses to reduce the expression of HDAC6. We explored the influence of CAY10603 on RA-FLS proliferation and inflammation, as well as the expression of proteins related to the CMA signaling pathway. CIA model was constructed using DBA/1J mice. Arthritis symptoms in CIA mice were evaluated, and the expression and localization of CMA-related proteins in mouse ankle joints were examined.

Results

CAY10603 inhibited proliferation as well as the level of the molecular chaperone autophagy in RA-FLS. HDAC6 shRNA significantly reduced the clinical signs of arthritis in CIA mice, as did the expression of HDAC6 in the serum and ankle synovial tissues of CIA mice. Finally, it significantly inhibited the level of Hsc70 and LAMP-2A, which are involved in the CMA signaling pathway, in ankle joint tissues.

Conclusion

Downregulation of HDAC6 may inhibit CMA and thereby ameliorate RA.

[68 Ga]Ga-FAPI-04 PET/CT may be a predictor for early treatment response in rheumatoid arthritis

BACKGROUND

The identification of biomarkers predicting the treatment response of rheumatoid arthritis (RA) is important. [68 Ga]Ga-FAPI-04 showed markedly increased uptake in the joints of patients with RA. The purpose of this study is to investigate whether [68 Ga]Ga-FAPI-04 PET/CT can be a predictor of treatment response in RA.

RESULTS

Nineteen patients diagnosed with RA in the prospective cohort study were finally enrolled. Both total synovitis uptake (TSU) and metabolic synovitis volume (MSV) in [68 Ga]Ga-FAPI-04 and [18F]FDG PET/CT of the responders were significantly higher than those in non-responders according to Clinical Disease Activity Index (CDAI) and Simplified Disease Activity Index (SDAI) response criteria at 3-months' follow-up (P < 0.05). The PET joint count (PJC) detected in [68 Ga]Ga-FAPI-04 and [18F]FDG PET/CT were also significantly higher in CDAI responders than non-responders (P = 0.016 and 0.045, respectively). The clinical characteristics of disease activity at baseline did not show significant difference between the responders and non-responders, except CRP (P = 0.035 and 0.033 in CDAI and SDAI response criteria, respectively). The baseline PJCFAPI, TSUFAPI and MSVFAPI > cutoff values in [68 Ga]Ga-FAPI-04 PET/CT successfully discriminated CDAI and SDAI responders and non-responders at 3-months' follow-up.

CONCLUSION

[68 Ga]Ga-FAPI-04 uptake at baseline were significantly higher in early responders than those in non-responders. Trial registration ClinicalTrials. NCT04514614. Registered 13 August 2020, https://register.

CLINICALTRIALS

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Deacetylation of Histones and Non-histone Proteins in Inflammatory Diseases and Cancer Therapeutic Potential of Histone Deacetylase Inhibitors

Epigenetic changes play an important role in the pathophysiology of autoimmune diseases such as allergic asthma, multiple sclerosis, lung diseases, diabetes, cystic fibrosis, atherosclerosis, rheumatoid arthritis, and COVID-19. There are three main classes of epigenetic alterations: post-translational modifications of histone proteins, control by non-coding RNA and DNA methylation. Since histone modifications can directly affect chromatin structure and accessibility, they can regulate gene expression levels. Abnormal expression and activity of histone deacetylases (HDACs) have been reported in immune mediated diseases. Increased acetylated levels of lysine residues have been suggested to be related to the overexpression of inflammatory genes. This review focuses on the effect of HDAC modifications on histone and non-histone proteins in autoimmune diseases. Furthermore, we discuss the potential therapeutic effect of HDAC inhibitors (HDACi) used in these diseases.

Efficacy of HDAC inhibitors and epigenetic modulation in the amelioration of synovial inflammation, cellular invasion, and bone erosion in rheumatoid arthritis pathogenesis

Rheumatoid arthritis (RA), an auto-immune disorder affected 1 % of the population around the globe. The pathophysiology of RA is highly concerted process including synovial hyperplasia, pannus formation, bone erosion, synovial cell infiltration in joints, and cartilage destruction. However, recent reports suggest that epigenetics play a pivotal role in the formation and organization of immune response in RA. Particularly, altered DNA methylation and impaired microRNA (miRNA) were detected in several immune cells of RA patients, such as T regulatory cells, fibroblast-like synoviocytes, and blood mononuclear cells. All these processes can be reversed by regulating the ubiquitous or tissue-based expression of histone deacetylases (HDACs) to counteract and terminate them. Hence, HDAC inhibitors (HDACi) could serve as highly potent anti-inflammatory regulators in the uniform amelioration of inflammation. Therefore, this review encompasses the information mainly focussing on the epigenetic modulation in RA pathogenesis and the efficacy of HDACi as an alternative therapeutic option for RA treatment. Overall, these studies have reported the targeting of HDAC1, 2 & 6 molecules would attenuate synoviocyte inflammation, cellular invasion, and bone erosion. Further, the inhibitors such as trichostatin A, suberoyl bis-hydroxamic acid, suberoyl anilide hydroxamic acid, and other compounds are found to attenuate synovial inflammatory immune response, clinical arthritis score, paw swelling, bone erosion, and cartilage destruction. Insight to view this, more clinical studies are required to determine the efficacy of HDACi in RA treatment and to unravel the underlying molecular mechanisms.

HDAC6 inhibition: a significant potential regulator and therapeutic option to translate into clinical practice in renal transplantation

Histone deacetylase 6 (HDAC6), an almost exclusively cytoplasmic enzyme, plays an essential role in many biological processes and exerts its deacetylation-dependent/independent effects on a variety of target molecules, which has contributed to the flourishing growth of relatively isoform-specific enzyme inhibitors. Renal transplantation (RT) is one of the alternatively preferred treatments and the most cost-effective treatment approaches for the great majority of patients with end-stage renal disease (ESRD). HDAC6 expression and activity have recently been shown to be increased in kidney disease in a number of studies. To date, a substantial amount of validated studies has identified HDAC6 as a pivotal modulator of innate and adaptive immunity, and HDAC6 inhibitors (HDAC6i) are being developed and investigated for use in arrays of immune-related diseases, making HDAC6i a promising therapeutic candidate for the management of a variety of renal diseases. Based on accumulating evidence, HDAC6i markedly open up new avenues for therapeutic intervention to protect against oxidative stress-induced damage, tip the balance in favor of the generation of tolerance-related immune cells, and attenuate fibrosis by inhibiting multiple activations of cell profibrotic signaling pathways. Taken together, we have a point of view that targeting HDAC6 may be a novel approach for the therapeutic strategy of RT-related complications, including consequences of ischemia-reperfusion injury, induction of immune tolerance in transplantation, equilibrium of rejection, and improvement of chronic renal graft interstitial fibrosis after transplantation in patients. Herein, we will elaborate on the unique function of HDAC6, which focuses on therapeutical mechanism of action related to immunological events with a general account of the tantalizing potential to the clinic.

New Targets and Strategies for Rheumatoid Arthritis: From Signal Transduction to Epigenetic Aspect

Rheumatoid arthritis (RA) is a chronic autoimmune disease that can lead to joint damage and even permanent disability, seriously affecting patients' quality of life. At present, the complete cure for RA is not achievable, only to relieve the symptoms to reduce the pain of patients. Factors such as environment, genes, and sex can induce RA. Presently, non-steroidal anti-inflammatory drugs, DRMADs, and glucocorticoids are commonly used in treating RA. In recent years, some biological agents have also been applied in clinical practice, but most have side effects. Therefore, finding new mechanisms and targets for treating RA is necessary. This review summarizes some potential targets discovered from the perspective of epigenetics and RA mechanisms.

CX-4945 inhibits fibroblast-like synoviocytes functions through the CK2-p53 axis to reduce rheumatoid arthritis disease severity

Fibroblast-like synoviocytes (FLS) mediate many pathological processes in rheumatoid arthritis (RA), including pannus formation, bone erosion, and inflammation. RA FLS have unique aggressive phenotypes and exhibit several tumor cell-like characteristics, including hyperproliferation, excessive migration and invasion. Casein kinase 2 (CK2) is reportedly overexpressed in numerous tumor types, and targeted inhibition of CK2 has therapeutic benefits for tumors. However, the expression level of CK2 and its functions in RA FLS remain unclear. Herein, we aimed to elucidate whether CK2 is responsible for the aggressive phenotypes of RA FLS and whether targeted therapy can alleviate the severity of RA. We found that CK2 subunits were elevated in RA FLS compared with osteoarthritis FLS, and the activity of CK2 also markedly increased in RA FLS. Targeted inhibition of CK2 using CX-4945 suppressed RA FLS proliferation through cell cycle arrest. Cell migration and invasion were also inhibited by CX-4945 treatment. Moreover, CX-4945 reduced Interleukin-6 (IL-6), CC motif chemokine ligand 2 (CCL2) and Matrix metalloproteinase-3 (MMP-3) secretion in RA FLS. Further proteomic investigation revealed that p53 signaling pathway significantly changes after CX-4945 treatment in RA FLS. The siRNA-mediated p53 knockdown partly abolished the anti-proliferation and reduced IL-6, MMP-3 secretion effects of CX-4945. Furthermore, CX-4945 administration alleviates arthritis severity in CIA mice. Collectively, our results demonstrated the abnormal elevation of CK2 and its positive association with abnormal phenotypes in RA FLS. Our novel findings suggest the possible therapeutic potential of CX-4945 for RA.

Epigenetic modifications of inflammation in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a common cause of joint-related chronic disability in elderly individuals worldwide. It seriously impacts the quality of life and inflicts a substantial social and economic burden. The pathological mechanisms underlying IDD have not been fully revealed, leading to less satisfactory clinical treatment outcomes. More studies are urgently needed to reveal its precise pathological mechanisms. Numerous studies have revealed that inflammation is closely related to various pathological processes of IDD, including the continuous loss of extracellular matrix, cell apoptosis, and senescence, indicating the important role of inflammation in the pathological mechanism of IDD. Epigenetic modifications affect the functions and characteristics of genes mainly through DNA methylation, histone modification, non-coding RNA regulation, and other mechanisms, thus having a major effect on the survival state of the body. Recently, the role of epigenetic modifications in inflammation during IDD has been attracting research interest. In this review, we summarize the roles of different types of epigenetic modifications in inflammation during IDD in recent years, to improve our understanding of the etiology of IDD and to transform basic research strategy into a clinically effective treatment for joint-related chronic disability in elderly individuals.

Selectivity of Hydroxamate- and Difluoromethyloxadiazole-Based Inhibitors of Histone Deacetylase 6 In Vitro and in Cells

Histone deacetylase 6 (HDAC6) is a unique member of the HDAC family of enzymes due to its complex domain organization and cytosolic localization. Experimental data point toward the therapeutic use of HDAC6-selective inhibitors (HDAC6is) for use in both neurological and psychiatric disorders. In this article, we provide side-by-side comparisons of hydroxamate-based HDAC6is frequently used in the field and a novel HDAC6 inhibitor containing the difluoromethyl-1,3,4-oxadiazole function as an alternative zinc-binding group (compound 7). In vitro isotype selectivity screening uncovered HDAC10 as a primary off-target for the hydroxamate-based HDAC6is, while compound 7 features exquisite 10,000-fold selectivity over all other HDAC isoforms. Complementary cell-based assays using tubulin acetylation as a surrogate readout revealed approximately 100-fold lower apparent potency for all compounds. Finally, the limited selectivity of a number of these HDAC6is is shown to be linked to cytotoxicity in RPMI-8226 cells. Our results clearly show that off-target effects of HDAC6is must be considered before attributing observed physiological readouts solely to HDAC6 inhibition. Moreover, given their unparalleled specificity, the oxadiazole-based inhibitors would best be employed either as research tools in further probing HDAC6 biology or as leads in the development of truly HDAC6-specific compounds in the treatment of human disease states.

Fibroblast heterogeneity: Keystone of tissue homeostasis and pathology in inflammation and ageing

Fibroblasts, derived from the embryonic mesenchyme, are a diverse array of cells with roles in development, homeostasis, repair, and disease across tissues. In doing so, fibroblasts maintain micro-environmental homeostasis and create tissue niches by producing a complex extracellular matrix (ECM) including various structural proteins. Although long considered phenotypically homogenous and functionally identical, the emergence of novel technologies such as single cell transcriptomics has allowed the identification of different phenotypic and cellular states to be attributed to fibroblasts, highlighting their role in tissue regulation and inflammation. Therefore, fibroblasts are now recognised as central actors in many diseases, increasing the need to discover new therapies targeting those cells. Herein, we review the phenotypic heterogeneity and functionality of these cells and their roles in health and disease.

Targeting fibroblast-like synoviocytes in rheumatoid arthritis

Fibroblast-like synoviocytes (FLS) are mesenchymal-derived cells that play an important role in the physiology of the synovium by producing certain components of the synovial fluid and articular cartilage. In rheumatoid arthritis (RA), however, fibroblasts become a key driver of synovial inflammation and joint damage. Because of this, there has been recent interest in FLS as a therapeutic target in RA to avoid side effects such as systemic immune suppression associated with many existing RA treatments. In this review, we describe how approved treatments for RA affect FLS signaling and function and discuss the effects of investigational FLS-targeted drugs for RA.

Targeted inhibition of the GRK2/HIF-1α pathway is an effective strategy to alleviate synovial hypoxia and inflammation

G-protein coupled receptor (GPCR) kinases (GRKs) and hypoxia-inducible factor-1α (HIF-1α) play key roles in rheumatoid arthritis (RA). Several studies have demonstrated that HIF-1α expression is positively regulated by GRK2, suggesting its posttranscriptional effects on HIF-1α. In this study, we review the role of HIF-1α and GRK2 in RA pathophysiology, focusing on their proinflammatory roles in immune cells and fibroblast-like synoviocytes (FLS).We then introduce several drugs that inhibit GRK2 and HIF-1α, and briefly outline their molecular mechanisms. We conclude by presenting gaps in knowledge and our prospects for the pharmacological potential of targeting these proteins and the relevant downstream signaling pathways.Future research is warranted and paramount for untangling these novel and promising roles for GRK2 and HIF-1α in RA.

Tofacitinib enhances IGF1 via inhibiting STAT6 transcriptionally activated-miR-425-5p to ameliorate inflammation in RA-FLS

Rheumatoid arthritis (RA) is a systemic autoimmune disease, which has been reported closely associated with the dysfunction of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway. This study aims to explore the potential therapeutic effect of Tofacitinib, a putative JAK/STAT inhibitor, in RA. Tofacitinib suppressed proliferation and accelerated apoptosis of rheumatoid arthritis synovial fibroblasts (RA-FLS) as confirmed by CCK-8, EdU and Western blot assays. Tofacitinib significantly inhibited expression of pro-inflammatory factors including tumor necrosis factor-α (TNF-α), vascular endothelial growth factor A, matrix metalloproteinase 1, matrix metalloproteinase 3, interleukin-6 and interferon gamma in RA-FLS cells. mechanistically, tofacitinib decreased signal transducer and activator of transcription 6 (STAT6), which transcriptionally activates miR-425-5p, and thus increased insulin like growth factor 1 (IGF1) expression, a target of miR-425-5p in RA-FLS. Overexpression of STAT6 restored the expression of pro-inflammatory factors and proliferation inhibited by Tofacitinib in RA-FLS. Overall, Tofacitinib exerted inhibitory effect on proliferation and inflammation of RA-FLS through modulating STAT6/miR-425-5p/IGF1 signal axis. These findings shed light on the novel strategies for improving RA.

Synovial fibroblasts as potential drug targets in rheumatoid arthritis, where do we stand and where shall we go?

Fibroblast-like synoviocytes or synovial fibroblasts (FLS) are important cellular components of the inner layer of the joint capsule, referred to as the synovial membrane. They can be found in both layers of this synovial membrane and contribute to normal joint function by producing extracellular matrix components and lubricants. However, under inflammatory conditions like in rheumatoid arthritis (RA), they may start to proliferate, undergo phenotypical changes and become central elements in the perpetuation of inflammation through their direct and indirect destructive functions. Their importance in autoimmune joint disorders makes them attractive cellular targets, and as mesenchymal-derived cells, their inhibition may be carried out without immunosuppressive consequences. Here, we aim to give an overview of our current understanding of the target potential of these cells in RA.

Mitochondrial Dysfunction and Oxidative Stress in Rheumatoid Arthritis

Control of excessive mitochondrial oxidative stress could provide new targets for both preventive and therapeutic interventions in the treatment of chronic inflammation or any pathology that develops under an inflammatory scenario, such as rheumatoid arthritis (RA). Increasing evidence has demonstrated the role of mitochondrial alterations in autoimmune diseases mainly due to the interplay between metabolism and innate immunity, but also in the modulation of inflammatory response of resident cells, such as synoviocytes. Thus, mitochondrial dysfunction derived from several danger signals could activate tricarboxylic acid (TCA) disruption, thereby favoring a vicious cycle of oxidative/mitochondrial stress. Mitochondrial dysfunction can act through modulating innate immunity via redox-sensitive inflammatory pathways or direct activation of the inflammasome. Besides, mitochondria also have a central role in regulating cell death, which is deeply altered in RA. Additionally, multiple evidence suggests that pathological processes in RA can be shaped by epigenetic mechanisms and that in turn, mitochondria are involved in epigenetic regulation. Finally, we will discuss about the involvement of some dietary components in the onset and progression of RA.

Epigenetic Regulation in the Pathogenesis of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease. The etiology of RA remains undetermined and the pathogenesis is complex. There remains a paucity of ideal therapeutic drugs and treatment strategies. The epigenetic modifications affect and regulate the function and characteristics of genes through mechanisms, including DNA methylation, histone modification, chromosome remodeling, and RNAi, thereby exerting a significant impact on the living state of the body. Recently, the phenomenon of epigenetic modification in RA has garnered growing research interest. The application of epigenetically modified methods is the frontier field in the research of RA pathogenesis. This review highlights the research on the pathogenesis of RA based on epigenetic modification in the recent five years, thereby suggesting new methods and strategies for the diagnosis and treatment of RA.

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.