Targeting histone deacetylase activity in rheumatoid arthritis and asthma as prototypes of inflammatory disease: should we keep our HATs on?

Cellular activation, proliferation and survival in chronic inflammatory diseases is regulated not only by engagement of signal trans-duction pathways that modulate transcription factors required for these processes, but also by epigenetic regulation of transcription factor access to gene promoter regions. Histone acetyl trans-ferases coordinate the recruitment and activation of transcription factors with conformational changes in histones that allow gene promoter exposure. Histone deacetylases (HDACs) counteract histone acetyl transferase activity through the targeting of both histones as well as nonhistone signal transduction proteins important in inflammation. Numerous studies have indicated that depressed HDAC activity in patients with inflammatory airway diseases may contribute to local proinflammatory cytokine production and diminish patient responses to corticosteroid treatment. Recent observations that HDAC activity is depressed in rheumatoid arthritis patient synovial tissue have predicted that strategies restoring HDAC function may be therapeutic in this disease as well. Pharmacological inhibitors of HDAC activity, however, have demonstrated potent therapeutic effects in animal models of arthritis and other chronic inflammatory diseases. In the present review we assess and reconcile these outwardly paradoxical study results to provide a working model for how alterations in HDAC activity may contribute to pathology in rheumatoid arthritis, and highlight key questions to be answered in the preclinical evaluation of compounds modulating these enzymes

Histone deacetylase inhibitors suppress rheumatoid arthritis fibroblast-like synoviocyte and macrophage IL-6 production by accelerating mRNA decay

Background Histone deacetylase inhibitors (HDACi) display potent therapeutic efficacy in animal models of arthritis and suppress inflammatory cytokine production in rheumatoid arthritis (RA) synovial macrophages and tissue. Objectives To determine the molecular mechanisms contributing to the suppressive effects of HDACi on RA synovial cell activation, using interleukin 6 (IL-6) regulation as a model. Methods RA fibroblast-like synoviocytes (FLS) and healthy donor macrophages were treated with IL-1 beta, tumour necrosis factor (TNF)alpha, lipopolysaccharide or polyinosinic: polycytidylic acid (poly(I:C)) in the absence or presence of the HDACi trichostatin A (TSA) or ITF2357 (givinostat). IL-6 production and mRNA expression was measured by ELISA and quantitative PCR (qPCR), respectively. Protein acetylation and the activation of intracellular signalling pathways were assessed by immunoblotting. The DNA-binding activity of nuclear factor kappa B (NF kappa B) and activator protein 1 (AP-1) components was measured by ELISA-based assays. Results HDACi (0.25-1.0 mu M) suppressed RA FLS IL-6 production induced by IL-1 beta, TNF alpha and Toll-like receptor ligands. Phosphorylation of mitogen-activated protein kinases and inhibitor of kappa B alpha (I kappa B alpha) following IL-1 beta stimulation were unaffected by HDACi, as were AP-1 composition and binding activity, and c-Jun induction. TSA induced a significant reduction in nuclear retention of NF kappa B in FLS 24 h after IL-1 beta stimulation, but this did not reduce NF kappa B transcriptional activity or correlate temporally with reductions in IL-6 mRNA accumulation. HDACi significantly reduced the stability of IL-6 mRNA in FLS and macrophages. Conclusions Our study identifies a novel, shared molecular mechanism by which HDACi can disrupt inflammatory cytokine production in RA synovial cells, namely the promotion of mRNA decay, and suggests that targeting HDAC activity may be clinically useful in suppressing inflammation in R

Histone deacetylases in RA: epigenetics and epiphenomena

Reduced synovial expression of histone deacetylases (HDACs) is proposed to contribute to pathology in rheumatoid arthritis (RA) by enhancing histone-dependent access of transcription factors to promoters of inflammatory genes. In the previous issue of Arthritis Research & Therapy, Kawabata and colleagues provided independent evidence that HDAC activity is increased in the synovium and fibroblast-like synoviocytes (FLSs) of patients with RA and is paralleled by increased HDAC1 expression and synovial tumor necrosis factor-alpha (TNFα) production. Remarkably, stimulation of RA FLSs with TNFα specifically increases HDAC activity and HDAC1 expression, suggesting that changes in synovial HDAC activity and expression may be secondary to local inflammatory status

Selective involvement of ERK and JNK mitogen-activated protein kinases in early rheumatoid arthritis (1987 ACR criteria compared to 2010 ACR/EULAR criteria): a prospective study aimed at identification of diagnostic and prognostic biomarkers as well as therapeutic targets

Objectives To investigate the expression and activation of mitogen-activated protein kinases in patients with early arthritis who are disease-modifying antirheumatic drug (DMARD) naive. Methods A total of 50 patients with early arthritis who were DMARD naive (disease duration <1 year) were prospectively followed and diagnosed at baseline and after 2 years for undifferentiated arthritis (UA), rheumatoid arthritis (RA) (1987 American College of Rheumatology (ACR) and 2010 ACR/European League Against Rheumatism (EULAR) criteria), or spondyloarthritis (SpA). Synovial biopsies obtained at baseline were examined for expression and phosphorylation of p38, extracellular signal regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) by immunohistochemistry and digital analysis. Synovial tissue mRNA expression was measured by quantitative PCR (qPCR). Results ERK and JNK activation was enhanced at inclusion in patients meeting RA criteria compared to other diagnoses. JNK activation was enhanced in patients diagnosed as having UA at baseline who eventually fulfilled 1987 ACR RA criteria compared to those who remained UA, and in patients with RA fulfilling 2010 ACR/EULAR criteria at baseline. ERK and JNK activation was enhanced in patients with RA developing progressive joint destruction. JNK activation in UA predicted 1987 ACR RA classification criteria fulfilment (R-2=0.59, p=0.02) after follow-up, and disease progression in early arthritis (R-2=0.16, p <0.05). Enhanced JNK activation in patients with persistent disease was associated with altered synovial expression of extracellular matrix components and CD44. Conclusions JNK activation is elevated in RA before 1987 ACR RA classification criteria are met and predicts development of erosive disease in early arthritis, suggesting JNK may represent an attractive target in treating RA early in the disease proces

A Rac1 inhibitory peptide suppresses antibody production and paw swelling in the murine collagen-induced arthritis model of rheumatoid arthritis

Introduction: The Rho family GTPase Rac1 regulates cytoskeletal rearrangements crucial for the recruitment, extravasation and activation of leukocytes at sites of inflammation. Rac1 signaling also promotes the activation and survival of lymphocytes and osteoclasts. Therefore, we assessed the ability of a cell-permeable Rac1 carboxy-terminal inhibitory peptide to modulate disease in mice with collagen-induced arthritis (CIA). Methods: CIA was induced in DBA/1 mice, and in either early or chronic disease, mice were treated three times per week by intraperitoneal injection with control peptide or Rac1 inhibitory peptide. Effects on disease progression were assessed by measurement of paw swelling. Inflammation and joint destruction were examined by histology and radiology. Serum levels of anti-collagen type II antibodies were measured by enzyme-linked immunosorbent assay. T-cell phenotypes and activation were assessed by fluorescence-activated cell sorting analysis. Results were analyzed using Mann-Whitney U and unpaired Student t tests. Results: Treatment of mice with Rac1 inhibitory peptide resulted in a decrease in paw swelling in early disease and to a lesser extent in more chronic arthritis. Of interest, while joint destruction was unaffected by Rac1 inhibitory peptide, anti-collagen type II antibody production was significantly diminished in treated mice, in both early and chronic arthritis. Ex vivo, Rac1 inhibitory peptide suppressed T-cell receptor/CD28-dependent production of tumor necrosis factor a, interferon. and interleukin-17 by T cells from collagen-primed mice, and reduced induction of ICOS and CD154, T-cell costimulatory proteins important for B-cell help. Conclusions: The data suggest that targeting of Rac1 with the Rac1 carboxy-terminal inhibitory peptide may suppress T-cell activation and autoantibody production in autoimmune disease. Whether this could translate into clinically meaningful improvement remains to be show

The Small Gtpase, Rap1, Mediates Cd31-Induced Integrin Adhesion

Integrin-mediated leukocyte adhesion is a critical aspect of leukocyte function that is tightly regulated by diverse stimuli, including chemokines, antigen receptors, and adhesion receptors. How cellular signals from CD31 and other adhesion amplifiers are integrated with those from classical mitogenic stimuli to regulate leukocyte function remains poorly understood. Here, we show that the cytoplasmic tail of CD31, an important integrin adhesion amplifier, propagates signals that induce T cell adhesion via β1 (VLA-4) and β2 (LFA-1) integrins. We identify the small GTPase, Rap1, as a critical mediator of this effect. Importantly, CD31 selectively activated the small Ras-related GTPase, Rap1, but not Ras, R-Ras, or Rap2. An activated Rap1 mutant stimulated T lymphocyte adhesion to intercellular adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM), as did the Rap1 guanine nucleotide exchange factor C3G and a catalytically inactive mutant of RapGAP. Conversely, negative regulators of Rap1 signaling blocked CD31-dependent adhesion. These findings identify a novel important role for Rap1 in regulating ligand-induced cell adhesion and suggest that Rap1 may play a more general role in coordinating adhesion-dependent signals during leukocyte migration and extravasation. Our findings also suggest an alternative mechanism, distinct from interference with Ras-proximal signaling, by which Rap1 might mediate transformation reversion

Expanding Thurston Maps

We study the dynamics of Thurston maps under iteration. These are branched covering maps $f$ of 2-spheres $S^2$ with a finite set $\mathop{post}(f)$ of postcritical points. We also assume that the maps are expanding in a suitable sense. Every expanding Thurston map $f\: S^2 \to S^2$ gives rise to a type of fractal geometry on the underlying sphere $S^2$. This geometry is represented by a class of \emph{visual metrics} $\varrho$ that are associated with the map. Many dynamical properties of the map are encoded in the geometry of the corresponding {\em visual sphere}, meaning $S^2$ equipped with a visual metric $\varrho$. For example, we will see that an expanding Thurston map is topologically conjugate to a rational map if and only if $(S^2, \varrho)$ is quasisymmetrically equivalent to the Riemann sphere $\widehat{\mathbf{C}}$. We also obtain existence and uniqueness results for $f$-invariant Jordan curves $\mathcal{C}\subset S^2$ containing the set $\mathop{post}(f)$. Furthermore, we obtain several characterizations of Latt\`{e}s maps

Histone modifications underlie monocyte dysregulation in patients with systemic sclerosis, underlining the treatment potential of epigenetic targeting.

Background and objective S ystemic sclerosis (SSc) is a severe autoimmune disease, in which the pathogenesis is dependent on both genetic and epigenetic factors. Altered gene expression in SSc monocytes, particularly of interferon (IFN)-responsive genes, suggests their involvement in SSc development. We investigated the correlation between epigenetic histone marks and gene expression in SSc monocytes. Methods C hromatin immunoprecipitation followed by sequencing (ChIPseq) for histone marks H3K4me3 and H3K27ac was performed on monocytes of nine healthy controls and 14 patients with SSc. RNA sequencing was performed in parallel to identify aberrantly expressed genes and their correlation with the levels of H3K4me3 and H3K27ac located nearby their transcription start sites. ChIP-qPCR assays were used to verify the role of bromodomain proteins, H3K27ac and STATs on IFNresponsive gene expression. Results 1046 and 534 genomic loci showed aberrant H3K4me3 and H3K27ac marks, respectively, in SSc monocytes. The expression of 381 genes was directly and significantly proportional to the levels of such chromatin marks present near their transcription start site. Genes correlated to altered histone marks were enriched for immune, IFN and antiviral pathways and presented with recurrent binding sites for IRF and STAT transcription factors at their promoters. IFN\u3b1 induced the binding of STAT1 and STAT2 at the promoter of two of these genes, while blocking acetylation readers using the bromodomain BET family inhibitor JQ1 suppressed their expression. Conclusion SS c monocytes have altered chromatin marks correlating with their IFN signature. Enzymes modulating these reversible marks may provide interesting therapeutic targets to restore monocyte homeostasis to treat or even prevent SSc

Association of MicroRNA-618 Expression With Altered Frequency and Activation of Plasmacytoid Dendritic Cells in Patients With Systemic Sclerosis

Objective. Plasmacytoid dendritic cells (PDCs) are a critical source of type I interferons (IFNs) that can contribute to the onset and maintenance of autoimmunity. Molecular mechanisms leading to PDC dysregulation and a persistent type I IFN signature are largely unexplored, especially in patients with systemic sclerosis (SSc), a disease in which PDCs infiltrate fibrotic skin lesions and produce higher levels of IFN alpha than those in healthy controls. This study was undertaken to investigate potential microRNA (miRNA)-mediated epigenetic mechanisms underlying PDC dysregulation and type I IFN production in SSc.Methods. We performed miRNA expression profiling and validation in highly purified PDCs obtained from the peripheral blood of 3 independent cohorts of healthy controls and SSc patients. Possible functions of miRNA-618 (miR-618) on PDC biology were identified by overexpression in healthy PDCs.Results. Expression of miR-618 was up-regulated in PDCs from SSc patients, including those with early disease who did not present with skin fibrosis. IFN regulatory factor 8, a crucial transcription factor for PDC development and activation, was identified as a target of miR-618. Overexpression of miR-618 reduced the development of PDCs from CD34+ cells in vitro and enhanced their ability to secrete IFN alpha, mimicking the PDC phenotype observed in SSc patients.Conclusion. Up-regulation of miR-618 suppresses the development of PDCs and increases their ability to secrete IFN alpha, potentially contributing to the type I IFN signature observed in SSc patients. Considering the importance of PDCs in the pathogenesis of SSc and other diseases characterized by a type I IFN signature, miR-618 potentially represents an important epigenetic target to regulate immune system homeostasis in these conditions