Histone deacetylase 6 negatively regulates NLRP3 inflammasome activation

Mechanisms and therapeutic strategies for NLRP3 degradation via post-translational modifications in ubiquitin-proteasome and autophagy lysosomal pathway

The NLRP3 inflammasome is crucial for immune responses. However, its overactivation can lead to severe inflammatory diseases, underscoring its importance as a target for therapeutic intervention. Although numerous inhibitors targeting NLRP3 exist, regulating its degradation offers an alternative and promising strategy to suppress its activation. The degradation of NLRP3 is primarily mediated by the proteasomal and autophagic pathways. The review not only elaborates on the traditional concepts of ubiquitination and NLRP3 degradation but also investigates the important roles of indirect regulatory modifications, such as phosphorylation, acetylation, ubiquitin-like modifications, and palmitoylation-key post-translational modifications (PTMs) that influence NLRP3 degradation. Additionally, we also discuss the potential targets that may affect NLRP3 degradation during the proteasomal and autophagic pathways. By unraveling these complex regulatory mechanisms, the review aims to enhance the understanding of NLRP3 regulation and its implications for developing therapeutic strategies to combat inflammatory diseases.

Indole-3-Aldehyde alleviates lung inflammation in COPD through activating Aryl Hydrocarbon Receptor to inhibit HDACs/NF-κB/NLRP3 signaling pathways

Indole-3-aldehyde (I3A) is an intestinal microbial metabolite that regulates inflammation in various inflammatory diseases; however, its role in chronic obstructive pulmonary disease (COPD) remains unclear. This study aimed to investigate the anti-inflammatory effects and molecular mechanisms of I3A in COPD. We constructed in vivo models using cigarette smoke (CS)-stimulated mice and in vitro models using cigarette smoke extract (CSE)-stimulated MH-S cells. The results demonstrated that I3A significantly alleviated bronchial obstruction in mice with COPD and reduced the expression of inflammatory factors such as TNF-α, IL-1β, and IL-6. Additionally, I3A decreased the levels of matrix metalloproteinases MMP2, MMP12, and inhibited the NF-κB p65/NLRP3 pathways. Further investigation revealed that I3A inhibited NF-κB activity by suppressing p65 phosphorylation and nuclear translocation in CSE-stimulated MH-S cells. The activation of the NF-κB and NLRP3 signaling pathways is mediated by histone deacetylase 5 (HDAC5) and HDAC6, both of which are inhibited by I3A. Subsequent experiments indicated that aryl hydrocarbon receptor (AHR) knockdown attenuated the inhibitory effect of I3A on pro-inflammatory cytokines and the HDACs/NF-κB/NLRP3 signaling pathways, highlighting the dependence of I3A's anti-inflammatory effects on the AHR receptor. KEY MESSAGES: I3A effectively reduced lung inflammation in COPD mice by inhibiting the NF-κB pathway. In CSE-stimulated MH-S cells, I3A suppressed p65 phosphorylation and nuclear translocation, thereby inhibiting NF-κB activity. The activation of the NF-κB/NLRP3 pathways by HDAC5 and HDAC6 was diminished by I3A. Through the activation of the AHR receptor, I3A suppressed the activities of HDAC5/6, leading to a decrease in inflammatory factor levels.

HDAC10 switches NLRP3 modification from acetylation to ubiquitination and attenuates acute inflammatory diseases

BACKGROUND

The NOD-like receptor protein (NLRP)3 inflammasome is at the signaling hub center to instigate inflammation in response to pathogen infection or oxidative stress, and its tight control is pivotal for immune defense against infection while avoiding parallel intensive inflammatory tissue injury. Acetylation of NLRP3 is critical for the full activation of NLRP3 inflammasome, while the precise regulation of the acetylation and deacetylation circuit of NLRP3 protein remained to be fully understood.

METHODS

The interaction between histone deacetylase 10 (HDAC10) and NLRP3 was detected by immunoprecipitation and western blot in the HDAC10 and NLRP3 overexpressing cells. The role of HDAC10 in NLRP3 inflammasome activation was measured by immunofluorescence, real-time PCR and immunoblotting assay in peritoneal macrophages and bone marrow-derived macrophages after the stimulation with LPS and ATP. To investigate the role of HDAC10 in NLRP3-involved inflammatory diseases, the Hdac10 knockout (Hdac10-/-) mice were used to construct the LPS-induced acute endotoxemia model and folic acid-induced acute tubular necrosis model. Tissue injury level was analyzed by hematoxylin and eosin staining, and the serum level of IL-1β was measured by enzyme-linked immunosorbent assay (ELISA). The conservative analysis and immunoprecipitation assay were performed to screen the precise catalytic site regulated by HDAC10 responsible for the switching from the acetylation to ubiquitination of NLRP3.

RESULTS

Here we demonstrated that HDAC10 directly interacted with NLRP3 and induced the deacetylation of NLRP3, thus leading to the inhibition of NLRP3 inflammasome and alleviation of NLRP3 inflammasome-mediated acute inflammatory injury. Further investigation demonstrated that HDAC10 directly induced the deacetylation of NLRP3 at K496 residue, thus switching NLRP3 acetylation to the ubiquitination modification, resulting in the proteasomal degradation of NLRP3 protein. Thus, this study identified HDAC10 as a new eraser for NLRP3 acetylation, and HDAC10 attenuated NLRP3 inflammasome involved acute inflammation via directly deacetylating NLRP3.

CONCLUSIONS

This study indicated that HDAC10 switched NLRP3 modification from acetylation to ubiquitination and attenuated acute inflammatory diseases, thus it provided a potential therapeutic strategy for NLRP3 inflammasome-associated diseases by targeting HDAC10.

Modified Danzhi XiaoyaoSan inhibits neuroinflammation via regulating TRIM31/NLRP3 inflammasome in the treatment of CUMS depression

The NLRP3 inflammasome is critically involved in the development of depression. The E3 ubiquitin ligase TRIM31 negatively regulates this process by promoting the degradation of NLRP3 through the ubiquitin-proteasome pathway. Modified Danzhi Xiaoyaosan (MDZXYS) has shown good therapeutic effect in both preclinical and clinical depression treatments, yet the underlying mechanisms of its antidepressant effects are not fully understood. In the present study, we aimed to explore the antidepressant mechanisms of MDZXYS, focusing on NLRP3 activation and ubiquitin-mediated degradation. We employed rats with depression induced by chronic unpredictable mild stress (CUMS) and conducted various behavioral tests, including the sucrose preference, forced swimming, and open field tests. Neuronal damage in CUMS-treated rats was assessed using Nissl staining. We measured proinflammatory cytokine levels using ELISA kits and analyzed NLRP3/TRIM31 protein expression via Western blotting and immunofluorescence staining. Our results disclosed that MDZXYS reversed CUMS-induced depression-like behaviors in rats, reduced proinflammatory cytokine levels (IL-1β), and ameliorated neuronal damage in the prefrontal cortex. Additionally, CUMS activated the NLRP3 inflammasome in the prefrontal cortex and upregulated the protein expression of TRIM31. After MDZXYS administration, the expression of NLRP3 inflammasome-associated proteins was reduced, while the expression level of TRIM31 was further increased. Through co-localized immunofluorescence staining, we observed a significant elevation in the co-localization expression of NLRP3 and TRIM31 in the prefrontal cortex of the MDZXYS group. These findings suggest that inhibiting NLRP3 inflammasome-mediated neuroinflammation by modulating the TRIM31signaling pathway may underlie the antidepressant effects of MDZXYS, and further support targeting NLRP3 as a novel approach for the prevention and treatment of depression.

Advanced Progress of Histone Deacetylases in Rheumatic Diseases

Rheumatic disease is a disease which is not yet fully clarified to etiology and also involved in a local pathological injury or systemic disease. With the continuous improvement of clinical medical research in recent years, the development process of rheumatic diseases has been gradually elucidated; with the intensely study of epigenetics, it is realized that environmental changes can affect genetics, among which histone acetylation is one of the essential mechanisms in epigenetics. Histone deacetylases (HDACs) play an important role in regulating gene expression in various biological processes, including differentiation, development, stress response, and injury. HDACs are involved in a variety of physiological processes and are promising drug targets in various pathological conditions, such as cancer, cardiac and neurodegenerative diseases, inflammation, metabolic and immune disorders, and viral and parasitic infections. In this paper, we reviewed the roles of HDACs in rheumatic diseases in terms of their classification and function.

Groebke Blackburn Bienaymé-mediated multi-component synthesis of selective HDAC6 inhibitors with anti-inflammatory properties

Histone deacetylases (HDACs) are a class of enzymes that cleave acyl groups from lysine residues of histone and non-histone proteins. There are 18 human HDAC isoforms with different cellular targets and functions. Among them, HDAC6 was found to be overexpressed in different types of cancer. However, when used in monotherapy, HDAC6 inhibition by selective inhibitors fails to show pronounced anti-cancer effects. The HDAC6 enzyme also addresses non-histone proteins like α-tubulin and cortactin, making it important for cell migration and angiogenesis. Recently, the NLRP3 inflammasome was identified as an important regulator of inflammation and immune responses and, importantly, HDAC6 is critically involved the activation of the inflammasome. We herein report the design, synthesis and biological evaluation of a library of selective HDAC6 inhibitors. Starting from the previously published crystal structure of MAIP-032 in complex with CD2 of zHDAC6, we performed docking studies to evaluate additional possible interactions of the cap group with the L1-loop pocket. Based on the results we synthesized 13 novel HDAC6 inhibitors via the Groebke-Blackburn-Bienaymé three component reaction as the key step. Compounds 8k (HDAC1 IC50: 5.87 μM; HDAC6 IC50: 0.024 μM; selectivity factor (SF1/6): 245) and 8m (HDAC1 IC50: 3.07 μM; HDAC6 IC50: 0.026 μM; SF1/6: 118) emerged as the most potent and selective inhibitors of HDAC6 and outperformed the lead structure MAIP-032 (HDAC1 IC50: 2.20 μM; HDAC6 IC50: 0.058 μM; SF1/6: 38) both in terms of inhibitory potency and selectivity. Subsequent immunoblot analysis confirmed the high selectivity of 8k and 8m for HDAC6 in a cellular environment. While neither 8k and 8m nor the selectivity HDAC6 inhibitor tubastatin A showed antiproliferative effects in the U-87 MG glioblastoma cell line, compound 8m attenuated cell migration significantly in wound healing assays in U-87 MG cells. Moreover, in macrophages compounds 8k and 8m demonstrated significant inhibition of LPS-induced IL1B mRNA expression and TNF release. These findings suggest that our imidazo[1,2-a]pyridine-capped HDAC6 inhibitors may serve as promising candidates for the development of drugs to effectively treat NLRP3 inflammasome-driven inflammatory diseases.

HDAC6/aggresome processing pathway importance for inflammasome formation is context-dependent

The inflammasome is a large multiprotein complex that assembles in the cell cytoplasm in response to stress or pathogenic infection. Its primary function is to defend the cell and promote the secretion of pro-inflammatory cytokines, including IL-1β and IL-18. Previous research has shown that in immortalized bone marrow-derived macrophages (iBMDMs) inflammasome assembly is dependent on the deacetylase HDAC6 and the aggresome processing pathway (APP), a cellular pathway involved in the disposal of misfolded proteins. Here we used primary BMDMs from mice in which HDAC6 is ablated or impaired and found that inflammasome activation was largely normal. We also used human peripheral blood mononuclear cells and monocyte cell lines expressing a synthetic protein blocking the HDAC6-ubiquitin interaction and impairing the APP and found that inflammasome activation was moderately affected. Finally, we used a novel HDAC6 degrader and showed that inflammasome activation was partially impaired in human macrophage cell lines with depleted HDAC6. Our results therefore show that HDAC6 importance in inflammasome activation is context-dependent.

Construction of a molecular inflammatory predictive model with histone modification-related genes and identification of CAMK2D as a potential response signature to infliximab in ulcerative colitis

Background

Ulcerative colitis (UC) is a lifelong inflammatory disease affecting the rectum and colon with numerous treatment options that require an individualized treatment plan. Histone modifications regulate chromosome structure and gene expression, resulting in effects on inflammatory and immune responses. However, the relationship between histone modification-related genes and UC remains unclear.

Methods

Transcriptomic data from GSE59071 and GSE66407 were obtained from the Gene Expression Omnibus (GEO), encompassing colonic biopsy expression profiles of UC patients in inflamed and non-inflamed status. Differentially expressed gene (DEG) analyses, functional enrichment analyses, weighted gene co-expression network analysis (WGCNA), and random forest were performed to identify histone modification-related core genes associated with UC inflammation. Features were screened through the least absolute shrinkage and selection operator (LASSO) and support vector machine-recursive feature elimination (SVM-RFE), establishing a molecular inflammatory predictive model using logistic regression. The model was validated in the GSE107499 dataset, and the performance of the features was assessed using receiver operating characteristic (ROC) and calibration curves. Immunohistochemistry (IHC) staining of colonic biopsy tissues from UC patients treated with infliximab was used to further confirm the clinical application value. Univariate logistic regression on GSE14580 highlighted features linked to infliximab response.

Results

A total of 253 histone modification-related DEGs were identified between inflammatory and non-inflammatory patients with UC. Seven key genes (IL-1β, MSL3, HDAC7, IRF4, CAMK2D, AUTS2, and PADI2) were selected using WGCNA and random forest. Through univariate logistic regression, three core genes (CAMK2D, AUTS2, and IL-1β) were further incorporated to construct the molecular inflammatory predictive model. The area under the curve (AUC) of the model was 0.943 in the independent validation dataset. A significant association between CAMK2D protein expression and infliximab response was observed, which was validated in another independent verification set of GSE14580 from the GEO database.

Conclusion

The molecular inflammatory predictive model based on CAMK2D, AUTS2, and IL-1β could reliably distinguish the mucosal inflammatory status of UC patients. We further revealed that CAMK2D was a predictive marker of infliximab response. These findings are expected to provide a new evidence base for personalized treatment and management strategies for UC patients.

Small molecule inhibitors of NLRP3 inflammasome and GSK-3β in the management of traumatic brain injury: A review

Traumatic brain injury (TBI) is a debilitating mental condition which causes physical disability and morbidity worldwide. TBI may damage the brain by direct injury that subsequently triggers a series of neuroinflammatory events. The activation of NLRP3 inflammasome and dysregulated host immune system has been documented in various neurological disorders such as TBI, ischemic stroke and multiple sclerosis. The activation of NLRP3 post-TBI increases the production of pro-inflammatory cytokines and caspase-1, which are major drivers of neuroinflammation and apoptosis. Similarly, GSK-3β regulates apoptosis through tyrosine kinase and canonical Wnt signalling pathways. Thus, therapeutic targeting of NLRP3 inflammasome and GSK-3β has emerged as promising strategies for regulating the post-TBI neuroinflammation and neurobehavioral disturbances. In this review, we discuss the identification & development of several structurally diverse and pharmacologically interesting small molecule inhibitors for targeting the NLRP3 inflammasome and GSK-3β in the management of TBI.

Knockdown of HDAC6 alleviates ventricular remodeling in experimental dilated cardiomyopathy via inhibition of NLRP3 inflammasome activation and promotion of cardiomyocyte autophagy

Histone deacetylases (HDACs) has been implicated in cardiac diseases, while the role of HDAC6 in dilated cardiomyopathy (DCM) remains obscure. The in silico analyses predicted potential association of HDAC6 with autophagy-related genes and DCM. Thus, we evaluated the functional relevance of HDAC6 in DCM in vivo and in vitro. We developed a rat model in vivo and a cell model in vitro by doxorubicin (DOX) induction to simulate DCM. HDAC6 expression was determined in myocardial tissues of DCM rats. DCM rats exhibited elevated HDAC6 mRNA and protein expression as compared to sham-operated rats. We knocked HDAC6 down and/or overexpressed NLRP3 in vivo and in vitro to characterize their roles in cardiomyocyte autophagy. It was established that shRNA-mediated HDAC6 silencing augmented cardiomyocyte autophagy and suppressed NLRP3 inflammasome activation, thus ameliorating cardiac injury in myocardial tissues of DCM rats. Besides, in DOX-injured cardiomyocytes, HDAC6 silencing also diminished NLRP3 inflammasome activation and cell apoptosis but enhanced cell autophagy, whereas ectopic NLRP3 expression negated the effects of HDAC6 silencing. Since HDAC6 knockdown correlates with enhanced cardiomyocyte autophagy and suppressed NLRP3 inflammasome activation through an interplay with NLRP3, it is expected to be a potential biomarker and therapeutic target for DCM. 1. HDAC6 was up-regulated in DCM rats. 2. HDAC6 knockdown promoted cardiomyocyte autophagy to relieve cardiac dysfunction. 3. HDAC6 knockdown inhibited NLRP3 inflammasome and promoted cardiomyocyte autophagy. 4. Silencing HDAC6 promoted autophagy and repressed apoptosis in cardiomyocytes. 5. This study provides novel therapeutic targets for DCM.

Pharmacological inhibition of HDAC6 suppresses NLRP3 inflammasome-mediated IL-1β release

The nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing protein 3 (NLRP3) inflammasome is an important regulator of inflammation and immune responses. Histone deacetylase 6 (HDAC6) has been implicated in the assembly and activation of the NLRP3 inflammasome in mouse cells, however, the role in human immune cells remains poorly understood. Here, we investigated the effect of HDAC6 deficiency on NLRP3-mediated interleukin (IL)-1β release using proteolysis targeting chimeras (PROTAC) technology. We designed an HDAC6 PROTAC (A6) composed of the pan-HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) and the E3 ligase ligand thalidomide and a control PROTAC (non-degrading control, nc-A6) that binds to HDAC6 but lacks the ability to induce HDAC6 degradation. A6 but not nc-A6 reduced HDAC6 levels in THP-1 macrophages without affecting cell viability. PROTAC A6 and nc-A6 significantly reduced the release of IL-1β in a concentration-dependent manner, suggesting that HDAC6 deficiency is not necessary for inhibition of NLRP3 inflammasome-mediated IL-1β release. We found that inhibition of the catalytic domain with HDAC inhibitor SAHA or the specific HDAC6 inhibitor tubastatin A is sufficient to reduce IL-1β release indicating that the enzymatic activity of HDAC6 is critical for NLRP3 inflammasome function. Mechanistically, the observed effects of HDAC6 inhibition on NLRP3-mediated inflammatory responses could be attributed to its interaction with Toll-like receptor (TLR) signaling. Tubastatin A did not affect IL-1β levels when added after TLR-mediated priming. Collectively, our findings indicate that HDAC6 inhibitors show potent anti-inflammatory activity and suppress IL-1β release by human macrophages, independent of NLRP3 assembly and activation.

Histone deacetylase 6's function in viral infection, innate immunity, and disease: latest advances

In the family of histone-deacetylases, histone deacetylase 6 (HDAC6) stands out. The cytoplasmic class IIb histone deacetylase (HDAC) family is essential for many cellular functions. It plays a crucial and debatable regulatory role in innate antiviral immunity. This review summarises the current state of our understanding of HDAC6's structure and function in light of the three mechanisms by which it controls DNA and RNA virus infection: cytoskeleton regulation, host innate immune response, and autophagy degradation of host or viral proteins. In addition, we summed up how HDAC6 inhibitors are used to treat a wide range of diseases, and how its upstream signaling plays a role in the antiviral mechanism. Together, the findings of this review highlight HDAC6's importance as a new therapeutic target in antiviral immunity, innate immune response, and some diseases, all of which offer promising new avenues for the development of drugs targeting the immune response.

New insights into the non-enzymatic function of HDAC6

Histone deacetylase 6 (HDAC6) is a class IIb histone deacetylase that contains two catalytic domains and a zinc-finger ubiquitin binding domain (ZnF-UBP) domain. The deacetylation function of HDAC6 has been extensively studied with common substrates such as α-tubulin, cortactin, and Hsp90. Apart from its deacetylase activity, HDAC6 ZnF-UBP binds to unanchored ubiquitin of specific sequences and serves as a carrier for transporting aggregated proteins. As a result, aggresomes are formed and protein degradation is facilitated by the autophagy-lysosome pathway. This HDAC6-dependent microtubule transport can be used by cells to assemble and activate inflammasomes, which play a critical role in immune regulation. Even viruses can benefit from the carrier of HDAC6 to assist in uncoating their surfaces during their infection cycle. However, HDAC6 is also capable of blocking virus invasion and replication in a non-enzymatic manner. Given these non-enzymatic functions, HDAC6 is closely associated with various diseases, including neurodegeneration, inflammasome-associated diseases, cancer, and viral infections. Small molecule inhibitors targeting the ubiquitin binding pocket of HDAC6 have been investigated. In this review, we focus on mechanisms in non-enzymatic functions of HDAC6 and discuss the rationality and prospects of therapeutic strategies by intervening the activation of HDAC6 ZnF-UBP in concrete diseases.

The lysosomal Ragulator complex activates NLRP3 inflammasome in vivo via HDAC6

The cellular activation of the NLRP3 inflammasome is spatiotemporally orchestrated by various organelles, but whether lysosomes contribute to this process remains unclear. Here, we show the vital role of the lysosomal membrane-tethered Ragulator complex in NLRP3 inflammasome activation. Deficiency of Lamtor1, an essential component of the Ragulator complex, abrogated NLRP3 inflammasome activation in murine macrophages and human monocytic cells. Myeloid-specific Lamtor1-deficient mice showed marked attenuation of NLRP3-associated inflammatory disease severity, including LPS-induced sepsis, alum-induced peritonitis, and monosodium urate (MSU)-induced arthritis. Mechanistically, Lamtor1 interacted with both NLRP3 and histone deacetylase 6 (HDAC6). HDAC6 enhances the interaction between Lamtor1 and NLRP3, resulting in NLRP3 inflammasome activation. DL-all-rac-α-tocopherol, a synthetic form of vitamin E, inhibited the Lamtor1-HDAC6 interaction, resulting in diminished NLRP3 inflammasome activation. Further, DL-all-rac-α-tocopherol alleviated acute gouty arthritis and MSU-induced peritonitis. These results provide novel insights into the role of lysosomes in the activation of NLRP3 inflammasomes by the Ragulator complex.

Extracellular vesicles from Listeria monocytogenes-infected dendritic cells alert the innate immune response

Communication through cell-cell contacts and extracellular vesicles (EVs) enables immune cells to coordinate their responses against diverse types of pathogens. The function exerted by EVs in this context depends on the proteins and nucleic acids loaded into EVs, which elicit specific responses involved in the resolution of infection. Several mechanisms control protein and nucleic acid loading into EVs; in this regard, acetylation has been described as a mechanism of cellular retention during protein sorting to exosomes. HDAC6 is a deacetylase involved in the control of cytoskeleton trafficking, organelle polarity and cell migration, defense against Listeria monocytogenes (Lm) infection and other immune related functions. Here, we show that the protein content of dendritic cells (DCs) and their secreted EVs (DEVs) vary during Lm infection, is enriched in proteins related to antiviral functions compared to non-infected cells and depends on HDAC6 expression. Analyses of the post-translational modifications revealed an alteration of the acetylation and ubiquitination profiles upon Lm infection both in DC lysates and DEVs. Functionally, EVs derived from infected DCs upregulate anti-pathogenic genes (e.g. inflammatory cytokines) in recipient immature DCs, which translated into protection from subsequent infection with vaccinia virus. Interestingly, absence of Listeriolysin O in Lm prevents DEVs from inducing this anti-viral state. In summary, these data underscore a new mechanism of communication between bacteria-infected DC during infection as they alert neighboring, uninfected DCs to promote antiviral responses.

Specific epigenetic regulators serve as potential therapeutic targets in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF), a disorder observed mostly in older human beings, is characterised by chronic and progressive lung scarring leading to an irreversible decline in lung function. This health condition has a dismal prognosis and the currently available drugs only delay but fail to reverse the progression of lung damage. Consequently, it becomes imperative to discover improved therapeutic compounds and their cellular targets to cure IPF. In this regard, a number of recent studies have targeted the epigenetic regulation by histone deacetylases (HDACs) to develop and categorise antifibrotic drugs for lungs. Therefore, this review focuses on how aberrant expression or activity of Classes I, II and III HDACs alter TGF-β signalling to promote events such as epithelial-mesenchymal transition, differentiation of activated fibroblasts into myofibroblasts, and excess deposition of the extracellular matrix to propel lung fibrosis. Further, this study describes how certain chemical compounds or dietary changes modulate dysregulated HDACs to attenuate five faulty TGF-β-dependent profibrotic processes, both in animal models and cell lines replicating IPF, thereby identifying promising means to treat this lung disorder.

Epigenetic and transcriptional regulation of innate immunity in cancer

Innate immune cells participate in the detection of tumor cells via complex signaling pathways mediated by pattern-recognition receptors, such as Toll-like receptors (TLR) and NOD-like receptors (NLR). These pathways are finely tuned via multiple mechanisms, including epigenetic regulation. It is well established that hematopoietic progenitors generate innate immune cells that can regulate cancer cell behavior, and the disruption of normal hematopoiesis in pathologic states may lead to altered immunity and the development of cancer. In this review, we discuss the epigenetic and transcriptional mechanisms that underlie the initiation and amplification of innate immune signaling in cancer. We also discuss new targeting possibilities for cancer control that exploit innate immune cells and signaling molecules, potentially heralding the next generation of immunotherapy.

The Role of HDAC6 in Autophagy and NLRP3 Inflammasome

Autophagy fights against harmful stimuli and degrades cytosolic macromolecules, organelles, and intracellular pathogens. Autophagy dysfunction is associated with many diseases, including infectious and inflammatory diseases. Recent studies have identified the critical role of the NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasomes activation in the innate immune system, which mediates the secretion of proinflammatory cytokines IL-1β/IL-18 and cleaves Gasdermin D to induce pyroptosis in response to pathogenic and sterile stimuli. Accumulating evidence has highlighted the crosstalk between autophagy and NLRP3 inflammasome in multifaceted ways to influence host defense and inflammation. However, the underlying mechanisms require further clarification. Histone deacetylase 6 (HDAC6) is a class IIb deacetylase among the 18 mammalian HDACs, which mainly localizes in the cytoplasm. It is involved in two functional deacetylase domains and a ubiquitin-binding zinc finger domain (ZnF-BUZ). Due to its unique structure, HDAC6 regulates various physiological processes, including autophagy and NLRP3 inflammasome, and may play a role in the crosstalk between them. In this review, we provide insight into the mechanisms by which HDAC6 regulates autophagy and NLRP3 inflammasome and we explored the possibility and challenges of HDAC6 in the crosstalk between autophagy and NLRP3 inflammasome. Finally, we discuss HDAC6 inhibitors as a potential therapeutic approach targeting either autophagy or NLRP3 inflammasome as an anti-inflammatory strategy, although further clarification is required regarding their crosstalk.

NLRP3 Ubiquitination-A New Approach to Target NLRP3 Inflammasome Activation

In response to diverse pathogenic and danger signals, the cytosolic activation of the NLRP3 (NOD-, LRR-, and pyrin domain-containing (3)) inflammasome complex is a critical event in the maturation and release of some inflammatory cytokines in the state of an inflammatory response. After activation of the NLRP3 inflammasome, a series of cellular events occurs, including caspase 1-mediated proteolytic cleavage and maturation of the IL-1β and IL-18, followed by pyroptotic cell death. Therefore, the NLRP3 inflammasome has become a prime target for the resolution of many inflammatory disorders. Since NLRP3 inflammasome activation can be triggered by a wide range of stimuli and the activation process occurs in a complex, it is difficult to target the NLRP3 inflammasome. During the activation process, various post-translational modifications (PTM) of the NLRP3 protein are required to form a complex with other components. The regulation of ubiquitination and deubiquitination of NLRP3 has emerged as a potential therapeutic target for NLRP3 inflammasome-associated inflammatory disorders. In this review, we discuss the ubiquitination and deubiquitination system for NLRP3 inflammasome activation and the inhibitors that can be used as potential therapeutic agents to modulate the activation of the NLRP3 inflammasome.

Mitochondrial Arrest on the Microtubule Highway-A Feature of Heart Failure and Diabetic Cardiomyopathy?

A pathophysiological consequence of both type 1 and 2 diabetes is remodelling of the myocardium leading to the loss of left ventricular pump function and ultimately heart failure (HF). Abnormal cardiac bioenergetics associated with mitochondrial dysfunction occurs in the early stages of HF. Key factors influencing mitochondrial function are the shape, size and organisation of mitochondria within cardiomyocytes, with reports identifying small, fragmented mitochondria in the myocardium of diabetic patients. Cardiac mitochondria are now known to be dynamic organelles (with various functions beyond energy production); however, the mechanisms that underpin their dynamism are complex and links to motility are yet to be fully understood, particularly within the context of HF. This review will consider how the outer mitochondrial membrane protein Miro1 (Rhot1) mediates mitochondrial movement along microtubules via crosstalk with kinesin motors and explore the evidence for molecular level changes in the setting of diabetic cardiomyopathy. As HF and diabetes are recognised inflammatory conditions, with reports of enhanced activation of the NLRP3 inflammasome, we will also consider evidence linking microtubule organisation, inflammation and the association to mitochondrial motility. Diabetes is a global pandemic but with limited treatment options for diabetic cardiomyopathy, therefore we also discuss potential therapeutic approaches to target the mitochondrial-microtubule-inflammatory axis.

Modulatory mechanisms of NLRP3: Potential roles in inflammasome activation

The NLRP3 inflammasome regulates innate immune and inflammatory responses by promoting pro-inflammatory cytokines such as IL-18 and IL-1β. NLRP3 is one of the main factors restricting the activation of the inflammasome, which is closely related to the abundance and localization of NLRP3. A substantial number of studies have focused on specifically targeting NLRP3 to develop inhibitors against NLRP3 inflammasome. Here, we succinctly review the regulation of NLRP3 expression at DNA/chromosome, transcriptional, post-transcriptional, and translation levels. These are critical for the fine regulation of the NLRP3 inflammasome.

HDAC6 mediates an aggresome-like mechanism for NLRP3 and pyrin inflammasome activation

Inflammasomes are supramolecular complexes that play key roles in immune surveillance. This is accomplished by the activation of inflammatory caspases, which leads to the proteolytic maturation of interleukin 1β (IL-1β) and pyroptosis. Here, we show that nucleotide-binding domain, leucine-rich repeat, and pyrin domain-containing protein 3 (NLRP3)- and pyrin-mediated inflammasome assembly, caspase activation, and IL-1β conversion occur at the microtubule-organizing center (MTOC). Furthermore, the dynein adapter histone deacetylase 6 (HDAC6) is indispensable for the microtubule transport and assembly of these inflammasomes both in vitro and in mice. Because HDAC6 can transport ubiquitinated pathological aggregates to the MTOC for aggresome formation and autophagosomal degradation, its role in NLRP3 and pyrin inflammasome activation also provides an inherent mechanism for the down-regulation of these inflammasomes by autophagy. This work suggests an unexpected parallel between the formation of physiological and pathological aggregates.

Role of Epigenetics in the Regulation of Immune Functions of the Skin

This review is intended to illuminate the emerging understanding of epigenetic modifications that regulate both adaptive and innate immunity in the skin. Host defense of the epidermis and dermis involves the interplay of many cell types to enable homeostasis; tolerance to the external environment; and appropriate response to transient microbial, chemical, and physical insults. To understand this process, the study of cutaneous immunology has focused on immune responses that reflect both adaptive learned and genetically programmed innate defense systems. However, recent advances have begun to reveal that epigenetic modifications of chromatin structure also have a major influence on the skin immune system. This deeper understanding of how enzymatic changes in chromatin structure can modify the skin immune system and may explain how environmental exposures during life, and the microbiome, lead to both short-term and long-term changes in cutaneous allergic and other inflammatory processes. Understanding the mechanisms responsible for alterations in gene and chromatin structure within skin immunocytes could provide key insights into the pathogenesis of inflammatory skin diseases that have thus far evaded understanding by dermatologists.

Inflammation and Inflammasomes: Pros and Cons in Tumorigenesis

Over the past decade, it has been well established that tumorigenesis is affected by chronic inflammation. During this event, proinflammatory cytokines are produced by numerous types of cells, such as fibroblasts, endothelial cells, macrophages, and tumor cells, and are able to promote the initiation, progression, and metastasis of different types of cancer. When persistent inflammation occurs, activation of inflammasome complexes is initiated, leading to its assembly and further activation of caspase, production of proinflammatory cytokines, and pyroptosis induction. The function of this multiprotein complex is not only to reassure inflammation and to promote cell death, through caspase activity, but also has been identified to have significant contributions during tumorigenesis and cancer development. So far, many efforts have been made in order to extend the knowledge of inflammasome implications and how its components could be targeted as therapeutic agents. Additionally, microRNAs (miRNAs), evolutionary conserved noncoding molecules, have emerged as pivotal players during numerous biological events by regulating gene and protein expression. Therefore, dysregulations of miRNA expressions have been correlated with inflammation during tumor development. In this review, we aim to highlight the dual role of inflammasomes and proinflammatory cytokines during carcinogenesis paired with the distinguished effects of miRNAs upon inflammation cascades during tumor growth and progression.

HDAC6 Mediates Poly (I:C)-Induced TBK1 and Akt Phosphorylation in Macrophages

Macrophages are derived from monocytes in the bone marrow and play an important role in anti-viral innate immune responses. Macrophages produce cytokines such as interferons and IL-10 upon viral infection to modulate anti-viral immune responses. Type I interferons (IFNs) promote anti-viral defense. IL-10 is a suppressor cytokine that down-regulates anti-viral immune responses. HDAC6 is a tubulin deacetylase that can modulate microtubule dynamics and microtubule-mediated cell signaling pathways. In the present study, we investigated the potential role of HDAC6 in macrophage anti-viral responses by examining poly (I:C)-induced IFN-β and IL-10 production in mouse bone marrow-derived macrophages (BMDMs). We also investigated the role of HDAC6 in poly (I:C)-induced anti-viral signaling such as TBK1, GSK-3β, and Akt activation in mouse BMDMs. Our data showed that HDAC6 deletion enhanced poly (I:C)-induced INF-β expression in macrophages by up-regulating TBK1 activity and eliminating the inhibitory regulation of GSK-3β. Furthermore, HDAC6 deletion inhibited poly (I:C)-induced suppressor cytokine IL-10 production in the BMDMs, which was associated with the inhibition of Akt activation. Our results suggest that HDAC6 modulates IFN-β and IL-10 production in macrophages through its regulation of TBK1, GSK-3β, and Akt signaling. HDAC6 could act as a suppressor of anti-viral innate immune responses in macrophages.

Functional Inhibition of Host Histone Deacetylases (HDACs) Enhances in vitro and in vivo Anti-mycobacterial Activity in Human Macrophages and in Zebrafish

The rapid and persistent increase of drug-resistant Mycobacterium tuberculosis (Mtb) infections poses increasing global problems in combatting tuberculosis (TB), prompting for the development of alternative strategies including host-directed therapy (HDT). Since Mtb is an intracellular pathogen with a remarkable ability to manipulate host intracellular signaling pathways to escape from host defense, pharmacological reprogramming of the immune system represents a novel, potentially powerful therapeutic strategy that should be effective also against drug-resistant Mtb. Here, we found that host-pathogen interactions in Mtb-infected primary human macrophages affected host epigenetic features by modifying histone deacetylase (HDAC) transcriptomic levels. In addition, broad spectrum inhibition of HDACs enhanced the antimicrobial response of both pro-inflammatory macrophages (Mϕ1) and anti-inflammatory macrophages (Mϕ2), while selective inhibition of class IIa HDACs mainly decreased bacterial outgrowth in Mϕ2. Moreover, chemical inhibition of HDAC activity during differentiation polarized macrophages into a more bactericidal phenotype with a concomitant decrease in the secretion levels of inflammatory cytokines. Importantly, in vivo chemical inhibition of HDAC activity in Mycobacterium marinum-infected zebrafish embryos, a well-characterized animal model for tuberculosis, significantly reduced mycobacterial burden, validating our in vitro findings in primary human macrophages. Collectively, these data identify HDACs as druggable host targets for HDT against intracellular Mtb.

Control of the inflammasome by the ubiquitin system

Inflammation is the body's response to danger. One of the first immune cell types to encounter danger is the macrophage. Macrophages sense danger signals such as extracellular ATP or bacterial toxins, derived from tissue damage or infection, and initiate the activation of an intracellular molecular complex called the inflammasome. The inflammasome consists of a cytosolic pattern recognition receptor, an adaptor molecule ASC (apoptosis-associated speck-like protein containing a CARD) and the protease caspase-1. Assembly of the complex leads to the cleavage and activation of caspase-1 that triggers processing and release of the cytokines interleukin (IL)-1β and IL-18, and ultimately cell death via the process of pyroptosis. The ability to sense and respond to danger appropriately is critical for maintaining immune homeostasis. Dysregulation of inflammasomes contributes to the progression of chronic diseases prevalent in the ageing population, such as Alzheimer's disease, COPD and metabolic disease; hence, it is critical that activation of the inflammatory response and inflammasome activation are tightly regulated. Post-translational modifications (PTMs) such as ubiquitination have recently emerged as important regulators of inflammasome assembly. However, the mechanisms by which PTMs regulate the inflammasome are still not understood. This review aims to summarize our knowledge to date on how the ubiquitin system controls inflammasome activation and where this area of research is heading.

The Post-amyloid Era in Alzheimer's Disease: Trust Your Gut Feeling

The amyloid hypothesis, the assumption that beta-amyloid toxicity is the primary cause of neuronal and synaptic loss, has been the mainstream research concept in Alzheimer's disease for the past two decades. Currently, this model is quietly being replaced by a more holistic, “systemic disease” paradigm which, like the aging process, affects multiple body tissues and organs, including the gut microbiota. It is well-established that inflammation is a hallmark of cellular senescence; however, the infection-senescence link has been less explored. Microbiota-induced senescence is a gradually emerging concept promoted by the discovery of pathogens and their products in Alzheimer's disease brains associated with senescent neurons, glia, and endothelial cells. Infectious agents have previously been associated with Alzheimer's disease, but the cause vs. effect issue could not be resolved. A recent study may have settled this debate as it shows that gingipain, a Porphyromonas gingivalis toxin, can be detected not only in Alzheimer's disease but also in the brains of older individuals deceased prior to developing the illness. In this review, we take the position that gut and other microbes from the body periphery reach the brain by triggering intestinal and blood-brain barrier senescence and disruption. We also surmise that novel Alzheimer's disease findings, including neuronal somatic mosaicism, iron dyshomeostasis, aggressive glial phenotypes, and loss of aerobic glycolysis, can be explained by the infection-senescence model. In addition, we discuss potential cellular senescence targets and therapeutic strategies, including iron chelators, inflammasome inhibitors, senolytic antibiotics, mitophagy inducers, and epigenetic metabolic reprograming.

MicroRNA Post-transcriptional Regulation of the NLRP3 Inflammasome in Immunopathologies

Inflammation has a crucial role in protection against various pathogens. The inflammasome is an intracellular multiprotein signaling complex that is linked to pathogen sensing and initiation of the inflammatory response in physiological and pathological conditions. The most characterized inflammasome is the NLRP3 inflammasome, which is a known sensor of cell stress and is tightly regulated in resting cells. However, altered regulation of the NLRP3 inflammasome is found in several pathological conditions, including autoimmune disease and cancer. NLRP3 expression was shown to be post-transcriptionally regulated and multiple miRNA have been implicated in post-transcriptional regulation of the inflammasome. Therefore, in recent years, miRNA based post-transcriptional control of NLRP3 has become a focus of much research, especially as a potential therapeutic approach. In this review, we provide a summary of the recent investigations on the role of miRNA in the post-transcriptional control of the NLRP3 inflammasome, a key regulator of pro-inflammatory IL-1β and IL-18 cytokine production. Current approaches to targeting the inflammasome product were shown to be an effective treatment for diseases linked to NLRP3 overexpression. Although utilizing NLRP3 targeting miRNAs was shown to be a successful therapeutic approach in several animal models, their therapeutic application in patients remains to be determined.

PARP inhibition by olaparib alleviates chronic asthma-associated remodeling features via modulating inflammasome signaling in mice

Despite the reported role of poly(ADP-ribose) polymerase (PARP) in asthma inflammation, its contribution during remodeling is not clearly known. The main aim of the current investigation was to examine the potential of olaparib, a pharmacological inhibitor of PARP against airway remodeling using an ovalbumin (OVA)-based murine model of chronic asthma. The results demonstrated that post-challenge olaparib treatment (5 mg/kg i.p., 30 min after OVA exposure) for six weeks (3 days/week) attenuates inflammation, mucus production, and collagen deposition in lungs. Additionally, olaparib blunted the protein expression of STAT-6 and GATA-3 considerably along with a modest reduction in p65-NF-κB phosphorylation. Furthermore, olaparib normalized the OVA-induced redox imbalance as reflected by data on reactive oxygen species, malondialdehyde, protein carbonyls, and reduced glutathione/oxidized glutathione ratio. Interestingly, the protection offered by olaparib was further linked with the altered level of NLRP3 inflammasome-mediated IL-1β release and consequent expression of its downstream targets matrix metalloproteinase-9 and transforming growth factor beta. Suppressed collagen deposition in the lungs correlates well with the reduced expression of vimentin upon olaparib treatment. Finally, olaparib restored the expression of histone deacetylase 2, a steroid-responsive element in asthma. Overall, results suggest that olaparib prevents OVA-induced airway inflammation as well as remodeling via modulating inflammasome signaling in mice. © 2019 IUBMB Life, 1-11, 2019.

Opportunities for future therapeutic interventions for hyperoxaluria: targeting oxidative stress

INTRODUCTION

Oxalate is a toxic byproduct of metabolism and is normally produced in quantities easily removed from the body. However, under specific circumstances oxalate production is increased resulting in deposition of calcium oxalate (CaOx) crystals in the kidneys as well as other organs causing inflammation and injury. Excessive buildup of crystal deposits in the kidneys causes eventual loss of renal function requiring renal transplantation. Areas covered: Cellular exposure to CaOx crystals induces the production of reactive oxygen species (ROS) with the involvement of renin-angiotensin aldosterone system (RAAS), mitochondria, and NADPH oxidase. Inflammasomes are activated and pro-inflammatory cytokines, such as IL-1β and IL-18 are produced. We reviewed results of experimental and clinical studies of crystal renal epithelial cell interactions with emphasis on cellular injury and ROS production. Expert opinion: Treatment should depend upon the level of hyperoxaluria and whether it is associated with CaOx crystal deposition. Persistent low grade or intermittent hyperoxaluria can be treated with antioxidants, free radical scavengers. Hyperoxaluria associated with CaOx crystal deposition will require administration of angiotensin II receptor blockers, and NADPH oxidase or NLRP3 inflammasome inhibitors. DASH-style diet will be beneficial in both cases.

Rusty Microglia: Trainers of Innate Immunity in Alzheimer's Disease

Alzheimer's disease, the most common form of dementia, is marked by progressive cognitive and functional impairment believed to reflect synaptic and neuronal loss. Recent preclinical data suggests that lipopolysaccharide (LPS)-activated microglia may contribute to the elimination of viable neurons and synapses by promoting a neurotoxic astrocytic phenotype, defined as A1. The innate immune cells, including microglia and astrocytes, can either facilitate or inhibit neuroinflammation in response to peripherally applied inflammatory stimuli, such as LPS. Depending on previous antigen encounters, these cells can assume activated (trained) or silenced (tolerized) phenotypes, augmenting or lowering inflammation. Iron, reactive oxygen species (ROS), and LPS, the cell wall component of gram-negative bacteria, are microglial activators, but only the latter can trigger immune tolerization. In Alzheimer's disease, tolerization may be impaired as elevated LPS levels, reported in this condition, fail to lower neuroinflammation. Iron is closely linked to immunity as it plays a key role in immune cells proliferation and maturation, but it is also indispensable to pathogens and malignancies which compete for its capture. Danger signals, including LPS, induce intracellular iron sequestration in innate immune cells to withhold it from pathogens. However, excess cytosolic iron increases the risk of inflammasomes' activation, microglial training and neuroinflammation. Moreover, it was suggested that free iron can awaken the dormant central nervous system (CNS) LPS-shedding microbes, engendering prolonged neuroinflammation that may override immune tolerization, triggering autoimmunity. In this review, we focus on iron-related innate immune pathology in Alzheimer's disease and discuss potential immunotherapeutic agents for microglial de-escalation along with possible delivery vehicles for these compounds.

Diabetic Nephropathy: a Tangled Web to Unweave

Diabetic nephropathy (DN) is currently the leading cause of end-stage renal disease globally. Given the increasing incidence of diabetes, many experts hold the view that DN will eventually progress toward pandemic proportions. Whilst hyperglycaemia-induced vascular dysfunction is the primary initiating mechanism in DN, its progression is also driven by a heterogeneous set of pathological mechanisms, including oxidative stress, inflammation and fibrosis. Current treatment strategies for DN are targeted against the fundamental dysregulation of glycaemia and hypertension. Unfortunately, these standards of care can delay but do not prevent disease progression or the significant emotional, physical and financial costs associated with this disease. As such, there is a pressing need to develop novel therapeutics that are both effective and safe. Set against the genomic era, numerous potential target pathways in DN have been identified. However, the clinical translation of basic DN research has been met with a number of challenges. Moreover, the notion of DN as a purely vascular disease is outdated and it has become clear that DN is a multi-dimensional, multi-cellular condition. The review will highlight the current therapeutic approaches for DN and provide an insight into how the inherent complexity of DN is shaping the research pathways toward the development and clinical translation of novel therapeutic strategies.

NLRP3: A promising therapeutic target for autoimmune diseases

NLRP3, a member of nucleotide-binding domain-(NOD) like receptor family, can be found in large varieties of immune and non-immune cells. Upon activation, the NLRP3, apoptosis-associated speck-like protein (ASC) and pro-caspase-1 would assemble into a multimeric protein, called the NLRP3 inflammasome. Then the inflammasome promotes inflammation (through specific cleavage and production of bioactive IL-1β and IL-18) and pyroptotic cell death. Previous studies have indicated the importance of NLRP3 in regulating innate immunity. Recently, numerous studies have revealed their significance in autoimmune diseases, such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), systemic sclerosis (SSc) and inflammatory bowel disease (IBD). In this review, we will briefly discuss the biological features of NLRP3 and summarize the recent progression of the involvement of NLRP3 in the development and pathogenesis of autoimmune diseases, as well as its clinical implications and therapeutic potential.

An update on cell intrinsic negative regulators of the NLRP3 inflammasome

Inflammasomes are multimeric protein complexes that promote inflammation (through specific cleavage and production of bioactive IL-1β and IL-18) and pyroptotic cell death. The central role of inflammasomes in combating infection and maintaining homeostasis has been studied extensively. Although inflammasome-mediated inflammation and cell death are vital to limit pathogenic insults and to promote wound healing/tissue regeneration, unchecked/uncontrolled inflammation, and cell death can cause cytokine storm, tissue damage, autoinflammatory and autoimmune diseases, and even death in the afflicted individuals. NLRP3 is one of the major cytosolic sensors that assemble an inflammasome. Given the adverse consequences of uncontrolled inflammasome activation, our immune system has developed tiered mechanisms to inhibit NLRP3 inflammasome activation. In this review, we highlight and discuss recent advances and our current understanding of mechanisms by which NLRP3 inflammasome can be negatively regulated.

Tubastatin ameliorates pulmonary fibrosis by targeting the TGFβ-PI3K-Akt pathway

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive and fatal disease. Histone deacetylase 6 (HDAC6) alters function and fate of various proteins via deacetylation of lysine residues, and is implicated in TGF-β1-induced EMT (epithelial-mesenchymal transition). However, the role of HDAC6 in pulmonary fibrosis is unknown.

METHODS

HDAC6 expression in IPF and control lungs was assessed by quantitative real-time PCR (qRT-PCR) and immunoblots. Lung fibroblasts were treated with TGF-β1 ± HDAC6 inhibitors (Tubacin, Tubastatin, ACY1215, or MC1568), and fibrotic markers such as type I collagen were assessed using qRT-PCR and immunoblots. Mice were treated with bleomycin (oropharyngeal aspiration; single dose) ± Tubastatin (intraperitoneally injection; daily for 21 days), and lung collagen expression was gauged using immunoblots and trichrome staining. In a separate experiment, HDAC6 wild-type (WT) and knockout (KO) mice were administered bleomycin, and lungs were evaluated in the same manner.

RESULTS

HDAC6 expression was deregulated in IPF lungs. Among the HDAC6 inhibitors tested, only Tubastatin significantly repressed TGF-β1-induced expression of type-1 collagen in lung fibroblasts, and this finding was coupled with decreased Akt phosphorylation and increased Akt-PHLPP (PH domain and Leucine rich repeat Protein Phosphatase) association. Tubastatin repressed TGF-β1-induced S6K phosphorylation, HIF-1α expression, and VEGF expression. Tubastatin also repressed TGF-β1-induced inhibition of LC3B-II (a marker of autophagosome formation). In bleomycin-treated mouse lungs, HDAC6 expression was increased, and Tubastatin repressed type-1 collagen expression. However, in HDAC6 KO mice, bleomycin-induced type-1 collagen expression was not repressed compared to WT mice. Knockdown of HDAC6, as well as HDAC10, another potential Tubastatin target, did not inhibit TGF-β1-induced collagen expression in lung fibroblasts.

CONCLUSIONS

HDAC6 expression is altered during lung fibrogenesis. Tubastatin represses TGF-β1-induced collagen expression, by diminishing Akt phosphorylation and regulating downstream targets such as HIF-1α-VEGF axis and autophagy. Tubastatin-treated WT mice are protected against bleomycin-induced fibrosis, but HDAC6 KO mice are not. Our data suggest that Tubastatin ameliorates pulmonary fibrosis, by targeting the TGFβ-PI3K-Akt pathway, likely via an HDAC6-independent mechanism.

Ubiquitin-Modifying Enzymes and Regulation of the Inflammasome

Ubiquitin and ubiquitin-modifying enzymes play critical roles in a wide variety of intracellular signaling pathways. Inflammatory signaling cascades downstream of TNF, TLR agonists, antigen receptor cross-linking, and cytokine receptors, all rely on ubiquitination events to direct subsequent immune responses. In the past several years, inflammasome activation and subsequent signal transduction have emerged as an excellent example of how ubiquitin signals control inflammatory responses. Inflammasomes are multiprotein signaling complexes that ultimately lead to caspase activation and release of the interleukin-1 (IL-1) family members, IL-1β and IL-18. Inflammasome activation is critical for the host's defense against pathogens, but dysregulation of inflammasomes may contribute to the pathogenesis of multiple diseases. Ultimately, understanding how various ubiquitin interacting proteins control inflammatory signaling cascades could provide new pathways for therapeutic intervention. Here we review specific ubiquitin-modifying enzymes and ubiquitination events that orchestrate inflammatory responses, with an emphasis on the NLRP3 inflammasome.

Inflammasomes, the cardinal pathology mediators are activated by pathogens, allergens and mutagens: A critical review with focus on NLRP3

Inflammation is a pivotal defense system of body. Unfortunately, when homeostasis falters, the same inflammatory mechanism acts as a double-edged sword, and turns offensive, paving the path for a broad array of pathologies. A multi-protein complex termed as inflammasome perceives the PAMPs (pathogen associated molecular patterns) and DAMPs (danger associated molecular patterns), executing immune responses. This activation predominantly encompasses the elaboration of effector cytokines IL-1β, IL-18, and the cysteine proteases (caspase 1 and 11). Extensive study on an inflammasome NLRP3 has revealed its role in the onset and progression of pathogenic, metabolic, autoimmune, neural, and geriatric diseases. In this regard, this inflammasome's immune activation mechanisms and inhibition strategies have been discussed. Through this rigorous literature analysis, the superficial diversity between pathogens/allergens and mutagens, and NLRP3 activity towards them has been emphasized. Though there is a scope for inhibition of aberrant inflammasomes, including that of NLRP3, given their complexity and unpredictability, prevention of their activation by lifestyle correction has been suggested.

Inflammasome Priming in Sterile Inflammatory Disease

The inflammasome is a cytoplasmic protein complex that processes interleukins (IL)-1β and IL-18, and drives a form of cell death known as pyroptosis. Oligomerization of this complex is actually the second step of activation, and a priming step must occur first. This involves transcriptional upregulation of pro-IL-1β, inflammasome sensor NLRP3, or the non-canonical inflammasome sensor caspase-11. An additional aspect of priming is the post-translational modification of particular inflammasome constituents. Priming is typically accomplished in vitro using a microbial Toll-like receptor (TLR) ligand. However, it is now clear that inflammasomes are activated during the progression of sterile inflammatory diseases such as atherosclerosis, metabolic disease, and neuroinflammatory disorders. Therefore, it is time to consider the endogenous factors and mechanisms that may prime the inflammasome in these conditions.

Ubiquitin in Influenza Virus Entry and Innate Immunity

Viruses are obligatory cellular parasites. Their mission is to enter a host cell, to transfer the viral genome, and to replicate progeny whilst diverting cellular immunity. The role of ubiquitin is to regulate fundamental cellular processes such as endocytosis, protein degradation, and immune signaling. Many viruses including influenza A virus (IAV) usurp ubiquitination and ubiquitin-like modifications to establish infection. In this focused review, we discuss how ubiquitin and unanchored ubiquitin regulate IAV host cell entry, and how histone deacetylase 6 (HDAC6), a cytoplasmic deacetylase with ubiquitin-binding activity, mediates IAV capsid uncoating. We also discuss the roles of ubiquitin in innate immunity and its implications in the IAV life cycle.

Molecular Basis of Acute Cystitis Reveals Susceptibility Genes and Immunotherapeutic Targets

Tissue damage is usually regarded as a necessary price to pay for successful elimination of pathogens by the innate immune defense. Yet, it is possible to distinguish protective from destructive effects of innate immune activation and selectively attenuate molecular nodes that create pathology. Here, we identify acute cystitis as an Interleukin-1 beta (IL-1β)-driven, hyper-inflammatory condition of the infected urinary bladder and IL-1 receptor blockade as a novel therapeutic strategy. Disease severity was controlled by the mechanism of IL-1β processing and mice with intact inflammasome function developed a moderate, self-limiting form of cystitis. The most severe form of acute cystitis was detected in mice lacking the inflammasome constituents ASC or NLRP-3. IL-1β processing was hyperactive in these mice, due to a new, non-canonical mechanism involving the matrix metalloproteinase 7- (MMP-7). ASC and NLRP-3 served as transcriptional repressors of MMP7 and as a result, Mmp7 was markedly overexpressed in the bladder epithelium of Asc^-/- and Nlrp3^-/- mice. The resulting IL-1β hyper-activation loop included a large number of IL-1β-dependent pro-inflammatory genes and the IL-1 receptor antagonist Anakinra inhibited their expression and rescued susceptible Asc^-/- mice from bladder pathology. An MMP inhibitor had a similar therapeutic effect. Finally, elevated levels of IL-1β and MMP-7 were detected in patients with acute cystitis, suggesting a potential role as biomarkers and immunotherapeutic targets. The results reproduce important aspects of human acute cystitis in the murine model and provide a comprehensive molecular framework for the pathogenesis and immunotherapy of acute cystitis, one of the most common infections in man.

Infections continue to threaten human health as pathogenic organisms outsmart available therapies with remarkable genetic versatility. Fortunately, microbial versatility is matched by the flexibility of the host immune system which provide a rich source of novel therapeutic concepts. Emerging therapeutic solutions include substances that strengthen the immune system rather than killing the bacteria directly. Selectivity is a concern, however, as boosting of the antibacterial immune response may cause collateral tissue damage. This study addresses how the host response to urinary bladder infection causes acute cystitis and how this response can be attenuated in patients who suffer from this very common condition. We identify the cytokine Interleukin-1 beta (IL-1β) as a key immune response determinant in acute cystitis and successfully treat mice with severe acute cystitis by inhibiting IL-1β or the enzyme MMP-7 that processes IL-1β to its active form. Finally, we detect elevated levels of these molecules in urine samples from patients with cystitis, suggesting clinical relevance and a potential role of IL-1β and MMP-7 both as therapeutic targets and as biomarkers of infection. These findings provide a much needed, molecular framework for the pathogenesis and treatment of acute cystitis.

Deubiquitinases: Novel Therapeutic Targets in Immune Surveillance?

Inflammation is a protective response of the organism to tissue injury or infection. It occurs when the immune system recognizes Pathogen-Associated Molecular Patterns (PAMPs) or Damage-Associated Molecular Pattern (DAMPs) through the activation of Pattern Recognition Receptors. This initiates a variety of signalling events that conclude in the upregulation of proinflammatory molecules, which initiate an appropriate immune response. This response is tightly regulated since any aberrant activation of immune responses would have severe pathological consequences such as sepsis or chronic inflammatory and autoimmune diseases. Accumulative evidence shows that the ubiquitin system, and in particular ubiquitin-specific isopeptidases also known as deubiquitinases (DUBs), plays crucial roles in the control of these immune pathways. In this review we will give an up-to-date overview on the role of DUBs in the NF-κB pathway and inflammasome activation, two intrinsically related events triggered by activation of the membrane TLRs as well as the cytosolic NOD and NLR receptors. Modulation of DUB activity by small molecules has been proposed as a way to control dysregulation or overactivation of these key players of the inflammatory response. We will also discuss the advances and challenges of a potential use of DUBs as therapeutic targets in inflammatory pathologies.