Regulation of MyD88 aggregation and the MyD88-dependent signaling pathway by sequestosome 1 and histone deacetylase 6

Pomalidomide promotes macrophage control of Mycobacterium tuberculosis via enhancing HDAC6-mediated autophagy

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a critical global health challenge. The development of new anti-tuberculosis drugs that can target the host immune system to clear intracellular Mtb is essential for TB control. Individuals known as resisters exhibit natural resistance to TB infection, offering a valuable model for exploring novel therapeutic targets. Our previous research has identified Histone Deacetylase 6 (HDAC6) as a key mediator of the innate immune responses in resisters against Mtb infection. In this study, we demonstrated that pomalidomide, an immunomodulatory drug, enhanced HDAC6 expression under Mtb infection and promoted autophagy and acidification of Mtb-containing phagosomes, thus reducing Mtb survival within macrophages. Importantly, pomalidomide enhanced autophagy in a manner dependent on HDAC6. Additionally, pomalidomide inhibited the production of pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6, and blocked the degradation of the key NF-κB pathway protein IκBα. In Mtb-infected mouse models, we observed that pomalidomide increased HDAC6 levels and autophagy-related gene expression in the lung of mice, reducing bacterial loads in the lung and spleen and alleviating inflammatory responses. In conclusion, our findings suggest that pomalidomide resists intracellular Mtb infection through HDAC6-mediated autophagy pathway, positioning it as a promising candidate for TB immunotherapy.

Targeting Immunoproteasome in Polarized Macrophages Ameliorates Experimental Emphysema Via Activating NRF1/2-P62 Axis and Suppressing IRF4 Transcription

Chronic obstructive pulmonary disease (COPD) stands as the prevailing chronic airway ailment, characterized by chronic bronchitis and emphysema. Current medications fall short in treatment of these diseases, underscoring the urgent need for effective therapy. Prior research indicated immunoproteasome inhibition alleviated various inflammatory diseases by modulating immune cell functions. However, its therapeutic potential in COPD remains largely unexplored. Here, an elevated expression of immunoproteasome subunits LMP2 and LMP7 in the macrophages isolated from mouse with LPS/Elastase-induced emphysema and polarized macrophages in vitro is observed. Subsequently, intranasal administration of the immunoproteasome-specific inhibitor ONX-0914 significantly mitigated COPD-associated airway inflammation and improved lung function in mice by suppressing macrophage polarization. Additionally, ONX-0914 capsulated in PLGA nanoparticles exhibited more pronounced therapeutic effect on COPD than naked ONX-0914 by targeting immunoproteasome in polarized macrophages. Mechanistically, ONX-0914 activated autophagy and endoplasmic reticulum (ER) stress are not attribute to the ONX-0914 mediated suppression of macrophage polarization. Intriguingly, ONX-0914 inhibited M1 polarization through the nuclear factor erythroid 2-related factor-1 (NRF1) and NRF2-P62 axis, while the suppression of M2 polarization is regulated by inhibiting the transcription of interferon regulatory factor 4 (IRF4). In summary, the findings suggest that targeting immunoproteasome in macrophages holds promise as a therapeutic strategy for COPD.

OTUD5 promotes the inflammatory immune response by enhancing MyD88 oligomerization and Myddosome formation

Myddosome is an oligomeric complex required for the transmission of inflammatory signals from TLR/IL1Rs and consists of MyD88 and IRAK family kinases. However, the molecular basis for the self-assemble of Myddosome proteins and regulation of intracellular signaling remains poorly understood. Here, we identify OTUD5 acts as an essential regulator for MyD88 oligomerization and Myddosome formation. OTUD5 directly interacts with MyD88 and cleaves its K11-linked polyubiquitin chains at Lys95, Lys231 and Lys250. This polyubiquitin cleavage enhances MyD88 oligomerization after LPS stimulation, which subsequently promotes the recruitment of downstream IRAK4 and IRAK2 to form Myddosome and the activation of NF-κB and MAPK signaling and production of inflammatory cytokines. Consistently, Otud5-deficient mice are less susceptible to LPS- and CLP-induced sepsis. Taken together, our findings reveal a positive regulatory role of OTUD5 in MyD88 oligomerization and Myddosome formation, which provides new sights into the treatment of inflammatory diseases.

Development of a tetrahydroindazolone-based HDAC6 inhibitor with in-vivo anti-arthritic activity

Histone deacetylase 6 (HDAC6) induces the expression of pro-inflammatory cytokines in macrophages; therefore, HDAC inhibitors may be beneficial for the treatment of macrophage-associated immune disorders and chronic inflammatory diseases, including atherosclerosis and rheumatoid arthritis. Structure-activity relationship studies were conducted on various phenyl hydroxamate HDAC6 inhibitors with indolone/indazolone-based bi- or tricyclic ring moieties as the cap group aiming to develop novel anti-arthritic drug candidates. Several compounds exhibited nanomolar activity and HDAC6 selectivity greater than 500-fold over HDAC1. Compound 21, a derivative with the tetrahydroindazolone cap group, is a potent HDAC6 inhibitor with an IC50 of 18 nM and 217-fold selectivity over HDAC1 and showed favorable oral bioavailability in animals. Compound 21 increases the acetylation level of tubulin without affecting histone acetylation in cutaneous T-cell lymphoma cells and inhibits TNF-α secretion in LPS-stimulated macrophage cells. The anti-arthritic effects of compound 21 were evaluated using a rat adjuvant-induced arthritis (AIA) model. Treatment with compound 21 significantly reduced the arthritis score, and combination treatment with methotrexate showed a synergistic effect in AIA models. We identified a novel HDAC6 inhibitor, compound 21, with excellent in vivo anti-arthritic efficacy, which can lead to the development of oral anti-arthritic drugs.

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.

Understanding the involvement of innate immunity and the Nrf2-NLRP3 axis on mitochondrial health in Parkinson's disease

Parkinson's disease (PD), a multifactorial movement disorder, is interlinked with numerous molecular pathways, including neuroinflammation, which is a critical factor in the development and progression of PD. Microglia play a central role in driving neuroinflammation through activation and overexpression of the M1 phenotype, which has a significant impact on mitochondria. Multiple regulators converge together, and among these, the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasomes have been implicated in transmitting inflammatory and deleterious components to the mitochondria. Nuclear factor erythroid 2-related factor 2 (Nrf2) regulates the NLRP3 inflammasome and acts as the saviour of the mitochondria. Together, the NLRP3-Nrf2 axis functions in regulating mitochondrial function in the case of PD. It regulates fundamental processes such as oxidative stress, mitochondrial respiratory function, and mitochondrial dynamics. In this review, we discuss the contributions that a variety of miRNAs make to the regulation of the NLRP3 inflammasome and Nrf2, which can be used to target this important axis and contribute to the preservation of mitochondrial integrity. This axis may prove to be a crucial target for extending the lives of Parkinson's patients by deferring neuroinflammatory damage to mitochondria.

Synthesis and biological evaluation of novel N-benzyltriazolyl-hydroxamate derivatives as selective histone deacetylase 6 inhibitors

Histone deacetylases (HDAC) regulate post-translational acetylation and the inhibition of these enzymes has emerged as an intriguing disease therapeutic. Among them, class IIb HDAC6 has the unique characteristic of mainly deacetylating cytoplasmic proteins, suggesting clinical applications for neurodegenerative diseases, inflammation, and cancer. In this study, we designed a novel N-benzyltriazolyl-hydroxamate scaffold based on the known HDAC6 inhibitors nexturastat A and tubastatin A. Among the 27 derivatives, 3-fluoro-4-((3-(2-fluorophenyl)-1H-1,2,4-triazol-1-yl)methyl)-N-hydroxybenzamide 4u (HDAC6 IC₅₀ = 7.08 nM) showed nanomolar HDAC6 inhibitory activity with 42-fold selectivity over HDAC1. Structure-activity relationship (SAR) and computational docking studies were conducted to optimize the triazole capping group. Docking analysis revealed that the capping group aligned with the conserved L1 pocket of HDAC6 and was associated with subtype selectivity. Overall, our study explored the triazole-based biaryl capping group and its substitution and orientation, suggesting a rationale for the design of HDAC6-selective inhibitors.

Acetylation licenses Th1 cell polarization to constrain Listeria monocytogenes infection

T helper 1 (Th1) immunity is typically viewed as a critical adaptation by vertebrates against intracellular pathogens. Identifying novel targets to enhance Th1 cell differentiation and function is increasingly important for anti-infection immunity. Here, through small-molecule screening focusing on epigenetic modifiers during the in vitro Th1 cell differentiation process, we identified that the selective histone deacetylase 6 (HDAC6) inhibitors ricolinostat and nexturastat A (Nex A) promoted Th1 cell differentiation. HDAC6-depleted mice exhibit elevation of Th1 cell differentiation, and decreased severity of Listeria monocytogenes infection. Mechanistically, HDAC6 directly deacetylated CBP-catalyzed acetylation of signal transducer and activator of transcription 4 (STAT4)-lysine (K) 667 via its enzymatic activity. Acetylation of STAT4-K667 is required for JAK2-mediated phosphorylation and activation of STAT4. Stat4K667R mutant mice lost the ability to normally differentiate into Th1 cells and developed severe Listeria infection. Our study identifies acetylation of STAT4-K667 as an essential signaling event for Th1 cell differentiation and defense against intracellular pathogen infections, and highlights the therapeutic potential of HDAC6 inhibitors for controlling intracellular pathogen infections.

The functions and effects of CUL3-E3 ligases mediated non-degradative ubiquitination

Ubiquitination of substrates usually have two fates: one is degraded by 26S proteasome, and the other is non-degradative ubiquitination modification which is associated with cell cycle regulation, chromosome inactivation, protein transportation, tumorigenesis, achondroplasia, and neurological diseases. Cullin3 (CUL3), a scaffold protein, binding with the Bric-a-Brac-Tramtrack-Broad-complex (BTB) domain of substrates recognition adaptor and RING-finger protein 1 (RBX1) form ubiquitin ligases (E3). Based on the current researches, this review has summarized the functions and effects of CUL3-E3 ligases mediated non-degradative ubiquitination.

CD11b suppresses TLR activation of nonclassical monocytes to reduce primary graft dysfunction after lung transplantation

Primary graft dysfunction (PGD) is the leading cause of postoperative mortality in lung transplant recipients and the most important risk factor for development of chronic lung allograft dysfunction. The mechanistic basis for the variability in the incidence and severity of PGD between lung transplant recipients is not known. Using a murine orthotopic vascularized lung transplant model, we found that redundant activation of Toll-like receptors 2 and 4 (TLR2 and -4) on nonclassical monocytes activates MyD88, inducing the release of the neutrophil attractant chemokine CXCL2. Deletion of Itgam (encodes CD11b) in nonclassical monocytes enhanced their production of CXCL2 and worsened PGD, while a CD11b agonist, leukadherin-1, administered only to the donor lung prior to lung transplantation, abrogated CXCL2 production and PGD. The damage-associated molecular pattern molecule HMGB1 was increased in peripheral blood samples from patients undergoing lung transplantation after reperfusion and induced CXCL2 production in nonclassical monocytes via TLR4/MyD88. An inhibitor of HMGB1 administered to the donor and recipient prior to lung transplantation attenuated PGD. Our findings suggest that CD11b acts as a molecular brake to prevent neutrophil recruitment by nonclassical monocytes following lung transplantation, revealing an attractive therapeutic target in the donor lung to prevent PGD in lung transplant recipients.

Diet-Induced High Serum Levels of Trimethylamine-N-oxide Enhance the Cellular Inflammatory Response without Exacerbating Acute Intracerebral Hemorrhage Injury in Mice

Trimethylamine-N-oxide (TMAO), an intestinal flora metabolite of choline, may aggravate atherosclerosis by inducing a chronic inflammatory response and thereby promoting the occurrence of cerebrovascular diseases. Knowledge about the influence of TMAO-related inflammatory response on the pathological process of acute stroke is limited. This study was designed to explore the effects of TMAO on neuroinflammation, brain injury severity, and long-term neurologic function in mice with acute intracerebral hemorrhage (ICH). We fed mice with either a regular chow diet or a chow diet supplemented with 1.2% choline pre- and post-ICH. In this study, we measured serum levels of TMAO with ultrahigh-performance liquid chromatography-tandem mass spectrometry at 24 h and 72 h post-ICH. The expression level of P38-mitogen-protein kinase (P38-MAPK), myeloid differentiation factor 88 (MyD88), high-mobility group box1 protein (HMGB1), and interleukin-1β (IL-1β) around hematoma was examined by western blotting at 24 h. Microglial and astrocyte activation and neutrophil infiltration were examined at 72 h. The lesion was examined on days 3 and 28. Neurologic deficits were examined for 28 days. A long-term choline diet significantly increased serum levels of TMAO compared with a regular diet at 24 h and 72 h after sham operation or ICH. Choline diet-induced high serum levels of TMAO did not enhance the expression of P38-MAPK, MyD88, HMGB1, or IL-1β at 24 h. However, it did increase the number of activated microglia and astrocytes around the hematoma at 72 h. Contrary to our expectations, it did not aggravate acute or long-term histologic damage or neurologic deficits after ICH. In summary, choline diet-induced high serum levels of TMAO increased the cellular inflammatory response probably by activating microglia and astrocytes. However, it did not aggravate brain injury or worsen long-term neurologic deficits. Although TMAO might be a potential risk factor for cerebrovascular diseases, this exploratory study did not support that TMAO is a promising target for ICH therapy.

Lower HDAC6 mRNA expression and promoter hypomethylation are associated with RA susceptibility

BACKGROUND/PURPOSE

Recent studies showed that Histone deacetylases 6 (HDAC6) inhibitors could improve arthritis in rheumatoid arthritis (RA) rodent models, whereas lower HDAC6 expression was observed in RA patients' synovial fibroblasts, raising the concerns to use HDAC6 inhibitors to treat RA patients. In the present study, we investigated the involvement of HDAC6 mRNA expression and promoter methylation in RA.

METHODS

The DNA and RNAs were extracted from the peripheral blood mononuclear cells (PBMCs) from 138 RA patients and 102 healthy controls. The pyrosequencing technique was used for promoter methylation analysis. The quantitative real-time polymerase chain reaction was used to determine the HDAC6 mRNA expression. The patients' clinical characteristics and disease biomarkers were recorded when blood sampling.

RESULTS

The HDAC6 mRNA expression was lower in the RA patients than controls (p = 0.001). The RA patients had significant hypomethylation of the HDAC6 promoter (p < 0.001). The HDAC6 promoter was hypo-methylated in the -229, -225, -144, and -142 CpG sites in RA patients (p < 0.05). Unexpectedly, promoter methylation and mRNA expression of the HDAC6 gene were positively associated (p < 0.001). The HDAC6 mRNA expression and promoter methylation status were associated with the risk of RA (p = 0.006 and 0.002, respectively). The inflammatory cytokines, TNF-α and IL-6, were significantly increased after HDAC6 knockdown in PMA-stimulated THP1 cells and SW982 cells (p < 0.05).

CONCLUSION

The HDAC6 mRNA expression and promoter methylation were lower in RA patients. Both HDAC6 mRNA expression level and promoter hypomethylation were associated the susceptibility of RA. HDAC6 inhibitors seem not proper for RA patients' treatment.

HDAC6 contributes to human resistance against Mycobacterium tuberculosis infection via mediating innate immune responses

Tuberculosis (TB), which is caused by Mycobacterium tuberculosis (Mtb), remains a major cause of morbidity and mortality worldwide. Increasing lines of evidence indicate that certain individuals, which are termed resisters, are naturally resistant to TB infection. The resister phenotype has been linked to host efficient innate immune responses, but the underlying mechanisms and the key immune factors remain unclear. Here, we find that upon Mtb infection, monocyte-derived macrophages (MDMs) from TB resisters exhibited distinctly higher production of TNF-α, IL-1β and IL-6, higher ratio of bacteria in acidic vacuoles, and lower intracellular bacterial loads, as compared to that from the healthy controls, individuals with latent TB infection, and TB patients. Such enhanced anti-Mtb immune capacity of macrophages from resisters largely depends on histone deacetylase 6 (HDAC6), whose expression is specifically maintained in MDMs from TB resisters during Mtb infection. Furthermore, we demonstrate that HDAC6 is required for acidification of Mtb-containing phagosomes in macrophages, thus controlling the intracellular survival of Mtb. Taken together, these findings unravel an indispensable role of HDAC6 in human innate resistance against Mtb infection, suggesting that HDAC6 may serve as a marker for individual TB risk as well as a novel host-directed anti-TB therapeutic target.

Metabolic syndrome and hidradenitis suppurativa: epidemiological, molecular, and therapeutic aspects

Hidradenitis suppurativa (HS) is a chronic, suppurative condition of the pilosebaceous unit. Patients suffering from HS demonstrate a molecular profile in keeping with a state of systemic inflammation and are often found to fit the criteria for a diagnosis of metabolic syndrome (MetS). In this paper, we review the literature with regards to established data on the prevalence of MetS in HS patients and revise the odds ratio of comorbid disease. Furthermore, we attempt to draw parallels between inflammatory pathways in HS and MetS and evaluate how convergences may explain the risk of comorbid disease, necessitating the need for multidisciplinary care.

Taming the Autophagy as a Strategy for Treating COVID-19

Currently, an efficient treatment for COVID-19 is still unavailable, and people are continuing to die from complications associated with SARS-CoV-2 infection. Thus, the development of new therapeutic approaches is urgently needed, and one alternative is to target the mechanisms of autophagy. Due to its multifaceted role in physiological processes, many questions remain unanswered about the possible advantages of inhibiting or activating autophagy. Based on a search of the literature in this field, a novel analysis has been made to highlight the relation between the mechanisms of autophagy in antiviral and inflammatory activity in contrast with those of the pathogenesis of COVID-19. The present analysis reveals a remarkable coincidence between the uncontrolled inflammation triggered by SARS-CoV-2 and autophagy defects. Particularly, there is conclusive evidence about the substantial contribution of two concomitant factors to the development of severe COVID-19: a delayed or absent type I and III interferon (IFN-I and IFN-III) response together with robust cytokine and chemokine production. In addition, a negative interplay exists between autophagy and an IFN-I response. According to previous studies, the clinical decision to inhibit or activate autophagy should depend on the underlying context of the pathological timeline of COVID-19. Several treatment options are herein discussed as a guide for future research on this topic.

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.

M-134, a novel HDAC6-selective inhibitor, markedly improved arthritic severity in a rodent model of rheumatoid arthritis when combined with tofacitinib

BACKGROUND

Although tofacitinib has shown highly significant efficacy for rheumatoid arthritis (RA), there are still a considerable number of patients that are non-responders owing to its limited effectiveness and various adverse effects. Thus, alternative options with better efficacy and lower toxicity are desired. Here, M-134, a recently developed HDAC6 inhibitor, was examined for its therapeutic potential when combined with tofacitinib in a rat model of RA.

METHODS

The single or combined administration of M-134 and tofacitinib was examined in complete Freund's adjuvant-induced arthritis (AIA) or collagen-induced arthritis (CIA) rodent models. To evaluate the therapeutic and adverse effects, the following factors were observed: macroscopic or microscopic scoring of all four paws; the expression of ICAM-1, VCAM-1, and IP-10 in the joints and that of various cytokines and chemokines in the plasma; the weight of the thymus and the liver; and changes in hematological enzymes.

RESULTS

Combination treatment showed strong synergistic effects as measured by the clinical score and histological changes, without adverse effects such as weight loss in the thymus and increased liver enzymes (ALT and AST). Additionally, it also reduced ICAM-1, VCAM-1, and IP-10 expression in the joints, and M-134 increased the efficacy of tofacitinib by regulating various cytokines, such as interleukin (IL)-1β, IL-17, and TNF-α, in the serum of AIA rats. Differences in the cytokine expression for each drug were found in the CIA model.

CONCLUSIONS

M-134 and tofacitinib combination therapy is a potential option for the treatment of RA through the regulation of cytokines, chemokines, and adhesion molecules.

Identification of putative phenotype-modifying genetic factors associated with phenotypic diversity in Brooke-Spiegler syndrome

Brooke-Spiegler syndrome (BSS, OMIM 605041) is a rare monogenic skin disease characterized by the development of skin appendage tumors caused by mutations in the cylindromatosis gene. We recently investigated a Hungarian and an Anglo-Saxon pedigrees affected by Brooke-Spiegler syndrome. Despite carrying the same disease-causing mutation (c.2806C>T, p.Arg936X) of the cylindromatosis (CYLD) gene, the affected family members of the two pedigrees exhibit striking differences in their phenotypes. To identify phenotype-modifying genetic factors, whole exome sequencing was performed and the data from the Hungarian and Anglo-Saxon BSS patients were compared. Three putative phenotype-modifying genetic variants were identified: the rs1053023 SNP of the signal transducer and activator of transcription 3 (STAT3) gene, the rs1131877 SNP of the tumor necrosis factor receptor-associated factor 3 (TRAF3) gene and the rs202122812 SNP of the neighbour of BRCA1 gene 1 (NBR1) gene. Our study contributes to the accumulating evidence for the clinical importance of phenotype-modifying genetic factors, which are potentially important for the elucidation of disease prognosis.

p62 is Negatively Implicated in the TRAF6-BECN1 Signaling Axis for Autophagy Activation and Cancer Progression by Toll-Like Receptor 4 (TLR4)

Toll-like receptors (TLRs) induce the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and autophagy through the TNF (Tumor necrosis factor) receptor-associated factor 6 (TRAF6)-evolutionarily conserved signaling intermediate in Toll pathways (ECSIT) and TRAF6-BECN1 signaling axes, respectively. Having shown that p62 negatively regulates Toll-like receptor 4 (TLR4)-mediated signaling via TRAF6-ECSIT signaling axis, we herein investigated whether p62 is functionally implicated in the TRAF6-BECN1 signaling axis, thereby regulating cancer cell migration and invasion. p62 interacted with TRAF6 and BECN1, to interrupt the functional associations required for TRAF6-BECN1 complex formation, leading to inhibitions of BECN1 ubiquitination and autophagy activation. Importantly, p62-deficient cancer cells, such as p62-knockdown (p62^KD) SK-HEP-1, p62^KD MDA-MB-231, and p62-knockout (p62^KO) A549 cells, showed increased activation of autophagy induced by TLR4 stimulation, suggesting that p62 negatively regulates autophagy activation. Moreover, these p62-deficient cancer cells exhibited marked increases in cell migration and invasion in response to TLR4 stimulation. Collectively, these results suggest that p62 is negatively implicated in the TRAF6-BECN1 signaling axis, thereby inhibiting cancer cell migration and invasion regulated by autophagy activation in response to TLR4 stimulation.

SPOP negatively regulates Toll-like receptor-induced inflammation by disrupting MyD88 self-association

Toll-like receptor (TLR) signaling pathways need to be tightly controlled to avoid excessive inflammation and unwanted damage to the host. Myeloid differentiation primary response gene 88 (MyD88) is a critical adaptor of TLR signaling. Here, we identified the speckle-type POZ protein (SPOP) as a MyD88-associated protein. SPOP was recruited to MyD88 following TLR4 activation. TLR4 activation also caused the translocation of SPOP from the nucleus to the cytoplasm. SPOP depletion promoted the aggregation of MyD88 and recruitment of the downstream signaling kinases IRAK4, IRAK1 and IRAK2. Consistently, overexpression of SPOP inhibited the TLR4-mediated activation of NF-κB and production of inflammatory cytokines, whereas SPOP depletion had the opposite effects. Furthermore, knockdown of SPOP increased MyD88 aggregation and inflammatory cytokine production upon TLR2, TLR7 and TLR9 activation. Our findings reveal a mechanism by which MyD88 is regulated and highlight a role for SPOP in limiting inflammatory responses.

p62 /SQSTM1 coding plasmid prevents age related macular degeneration in a rat model

P62/SQSTM1, a multi-domain protein that regulates inflammation, apoptosis, and autophagy, has been linked to age-related pathologies. For example, previously we demonstrated that administration of p62/SQSTM1-encoding plasmid reduced chronic inflammation and alleviated osteoporosis and metabolic syndrome in animal models. Herein, we built upon these findings to investigate effect of the p62-encoding plasmid on an age-related macular degeneration (AMD), a progressive neurodegenerative ocular disease, using spontaneous retinopathy in senescence-accelerated OXYS rats as a model. Overall, the p62DNA decreased the incidence and severity of retinopathy. In retinal pigment epithelium (RPE), p62DNA administration slowed down development of the destructive alterations of RPE cells, including loss of regular hexagonal shape, hypertrophy, and multinucleation. In neuroretina, p62DNA prevented gliosis, retinal thinning, and significantly inhibited microglia/macrophages migration to the outer retina, prohibiting their subretinal accumulation. Taken together, our results suggest that the p62DNA has a strong retinoprotective effect in AMD.

Histone deacetylase 6 regulates endothelial MyD88-dependent canonical TLR signaling, lung inflammation, and alveolar remodeling in the developing lung

Lung endothelial cell (EC) immune activation during bacterial sepsis contributes to acute lung injury and bronchopulmonary dysplasia in premature infants. The epigenetic regulators of sepsis-induced endothelial immune activation, lung inflammation, and alveolar remodeling remain unclear. Herein, we examined the role of the cytoplasmic histone deacetylase, HDAC6, in regulating EC Toll-like receptor 4 (TLR4) signaling and modulating sepsis-induced lung injury in a neonatal model of sterile sepsis. In human primary microvascular endothelial cells (HPMEC), lipopolysaccharide (LPS)-induced MAPK, IKK-β, and p65 phosphorylation as well as inflammatory cytokine expression were exaggerated with the HDAC6 inhibitor tubastatin A, and by dominant-negative HDAC6 with a mutated catalytic domain 2. Expression of HDAC6 wild-type protein suppressed LPS-induced myeloid differentiation primary response 88 (MyD88) acetylation, p65 (Lys³¹⁰) acetylation, MyD88/TNF receptor-associated factor 6 (TRAF6) coimmunoprecipitation, and proinflammatory TLR4 signaling in HPMEC. In a neonatal mouse model of sepsis, the HDAC6 inhibitor tubastatin A amplified lung EC TLR4 signaling and vascular permeability. HDAC6 inhibition augmented LPS-induced MyD88 acetylation, MyD88/TRAF6 binding, p65 acetylation, canonical TLR4 signaling, and inflammation in the developing lung. Sepsis-induced decreases in the fibroblast growth factors FGF2 and FGF7 and increase in matrix metalloproteinase-9 were worsened with HDAC6 inhibition, while elastin expression was equally suppressed. Exaggerated sepsis-induced acute lung inflammation observed with HDAC6 inhibition worsened alveolar simplification evidenced by increases in mean linear intercepts and decreased radial alveolar counts. Our studies reveal that HDAC6 is a constitutive negative regulator of cytoplasmic TLR4 signaling in EC and the developing lung. The therapeutic efficacy of augmenting HDAC6 activity in neonatal sepsis to prevent lung injury needs to be evaluated.

BANK1 interacts with TRAF6 and MyD88 in innate immune signaling in B cells

Evidence supports a possible role of BANK1 in innate immune signaling in B cells. In the present study, we investigated the interaction of BANK1 with two key mediators in interferon and inflammatory cytokine production, TRAF6 and MyD88. We revealed by coimmunoprecipitation (CoIP) analyses the binding of BANK1 with TRAF6 and MyD88, which were mediated by the BANK1 Toll/interleukin-1 receptor (TIR) domain. In addition, the natural BANK1–40C variant showed increased binding to MyD88. Next, we demonstrated in mouse splenic B cells that BANK1 colocalized with Toll-like receptor (TLR) 7 and TLR9 and that after stimulation with TLR7 and TLR9 agonists, the number of double-positive BANK1–TLR7, –TLR9, –TRAF6, and –MyD88 cells increased. Furthermore, we identified five TRAF6-binding motifs (BMs) in BANK1 and confirmed by point mutations and decoy peptide experiments that the C-terminal domain of BANK1-full-length (-FL) and the N-terminal domain of BANK1–Delta2 (-D2) are necessary for this binding. Functionally, we determined that the absence of the TIR domain in BANK1–D2 is important for its lysine (K)63-linked polyubiquitination and its ability to produce interleukin (IL)-8. Overall, our study describes a specific function of BANK1 in MyD88–TRAF6 innate immune signaling in B cells, clarifies functional differences between the two BANK1 isoforms and explains for the first time a functional link between autoimmune phenotypes including SLE and the naturally occurring BANK1–40C variant.

p62 Negatively Regulates TLR4 Signaling via Functional Regulation of the TRAF6-ECSIT Complex

Sequestosome 1 (SQSTM1, p62), a ubiquitin binding protein, plays a role in cell signaling, oxidative stress, and autophagy. However, its functional role in inflammatory signaling is controversial. Recent studies have shown that p62 is negatively implicated in inflammatory responses. But, the precise molecular mechanisms by which p62 regulates inflammatory responses remain unclear. In this study, we report on a new regulatory role for p62 in TLR4-mediated signaling. p62 overexpression led to the suppression of NF-κB activation and the production of pro-inflammatory cytokines, TNF-α, IL-6, and IL-1β in response to TLR4 stimulation. In contrast, p62^−/− mouse embryonic fibroblast (MEF) cells exhibited marked enhancement of NF-κB activation and production of pro-inflammatory cytokines by TLR4 stimulation, compared to p62^+/+ MEF cells. Additionally, the TLR4-induced activation of signal transduction was significantly augmented in p62^−/− MEF cells, indicating that p62 was negatively implicated in TLR4-mediated signaling. Biochemical studies revealed that p62 interacted with the internal domain of evolutionarily conserved signaling intermediate in Toll pathways (ECSIT), which is critical for associating with the TNF receptor associated factor 6 (TRAF6)-ECSIT complex to activate NF-κB in TLR4 signaling. Interestingly, p62-ECSIT interaction inhibited the interaction between TRAF6 and ECSIT and attenuated the ubiquitination of ECSIT. Furthermore, upon LPS challenge, the mortality of p62^−/− (p62-knockout) mice was markedly enhanced compared to p62^+/+ (p62 wild-type) mice. Taken together, our data demonstrate that p62 negatively regulated TLR4 signaling via functional regulation of the TRAF6-ECSIT complex.

Supramolecular Complexes in Cell Death and Inflammation and Their Regulation by Autophagy

Signaling activation is a tightly regulated process involving myriad posttranslational modifications such as phosphorylation/dephosphorylation, ubiquitylation/deubiquitylation, proteolytical cleavage events as well as translocation of proteins to new compartments within the cell. In addition to each of these events potentially regulating individual proteins, the assembly of very large supramolecular complexes has emerged as a common theme in signal transduction and is now known to regulate many signaling events. This is particularly evident in pathways regulating both inflammation and cell death/survival. Regulation of the assembly and silencing of these complexes plays important roles in immune signaling and inflammation and the fate of cells to either die or survive. Here we will give a summary of some of the better studied supramolecular complexes involved in inflammation and cell death, particularly with a focus on diseases caused by their autoactivation and the role autophagy either plays or may be playing in their regulation.

OmpA-like proteins of Porphyromonas gingivalis contribute to serum resistance and prevent Toll-like receptor 4-mediated host cell activation

Porphyromonas gingivalis possesses various abilities to evade and disrupt host immune responses, by which it acts as an important periodontal pathogen. P. gingivalis produces outer membrane protein A (OmpA)-like proteins (OmpALPs), Pgm6 and Pgm7, as major O-linked glycoproteins, but their pathological roles in P. gingivalis infection are largely unknown. Here, we report that OmpALP-deficient strains of P. gingivalis show an enhanced stimulatory activity in coculture with host cells. Such an altered ability of the OmpALP-deficient strains was found to be due to their impaired survival in coculture and the release of LPS from dead bacterial cells to stimulate Toll-like receptor 4 (TLR4). Further analyses revealed that the OmpALP-deficient strains were inviable in serum-containing media although they grew normally in the bacterial medium. The wild-type strain was able to grow in 90% normal human serum, while the OmpALP-deficient strains did not survive even at 5%. The OmpALP-deficient strains did not survive in heat-inactivated serum, but they gained the ability to survive and grow in proteinase K-treated serum. Of note, the sensitivity of the OmpALP-deficient strains to the bactericidal activity of human β-defensin 3 was increased as compared with the WT. Thus, this study suggests that OmpALPs Pgm6 and Pgm7 are important for serum resistance of P. gingivalis. These proteins prevent bacterial cell destruction by serum and innate immune recognition by TLR4; this way, P. gingivalis may adeptly colonize serum-containing gingival crevicular fluids and subgingival environments.

Investigation of interactions between TLR2, MyD88 and TIRAP by bioluminescence resonance energy transfer is hampered by artefacts of protein overexpression

Toll like receptors (TLRs) are important pattern recognition receptors that can detect pathogen and danger associated molecular patterns to initiate an innate immune response. TLR1 and 2 heterodimerize at the plasma membrane upon binding to triacylated lipopeptides from bacterial cell walls, or to the synthetic ligand Pam3CSK4. TLR1/2 dimers interact with adaptor molecules TIRAP and MyD88 to initiate a signalling cascade that leads to activation of key transcription factors, including NF-kB. Despite TLRs being extensively studied over the last two decades, the real-time kinetics of ligand binding and receptor activation remains largely unexplored. We aimed to study the kinetics of TLR activation and recruitment of adaptors, using TLR1/2 dimer interactions with adaptors MyD88 and TIRAP. Bioluminescence resonance energy transfer (BRET) allows detection of real-time protein-protein interactions in living cells, and was applied to study adaptor recruitment to TLRs. Energy transfer showed interactions between TLR2 and TIRAP, and between TLR2 and MyD88 only in the presence of TIRAP. Quantitative BRET and confocal microscopy confirmed that TIRAP is necessary for MyD88 interaction with TLR2. Furthermore, constitutive proximity between the proteins in the absence of Pam3CSK4 stimulation was observed with BRET, and was not abrogated with lowered protein expression, changes in protein tagging strategies, or use of the brighter NanoLuc luciferase. However, co-immunoprecipitation studies did not demonstrate constitutive interaction between these proteins, suggesting that the interaction observed with BRET likely represents artefacts of protein overexpression. Thus, caution should be taken when utilizing protein overexpression in BRET studies and in investigations of the TLR pathway.

Genistein and Myd88 Activate Autophagy in High Glucose-Induced Renal Podocytes In Vitro

BACKGROUND Renal podocyte damage plays a crucial role in the development of diabetic nephropathy. Genistein is derived from a leguminous plant, and MyD88 and TRIF are adaptor molecules in the Toll-like receptor (TLR) signaling pathway, which may play a role in autophagy. In this study, we utilized an in vitro high glucose (HG)-treated podocyte model to investigate the effects and underlying mechanisms of Genistein and MyD88 or TRIF siRNA induced autophagy and renal protection. MATERIAL AND METHODS An immortalized mouse podocyte cell line was treated with HG, Genistein, chloroquine, and/or transfected with specific Myd88 and TRIF siRNAs. The formation of autophagosomes and related autophagic vacuoles were monitored by transmission electron microscopy. The expression of autophagy-related factors and podocyte structure and functional markers, including LC3, p62, p-mTOR, synaptopodin, and nephrin, were measured by Western blot, and LC3 and p-mTOR expression were also assessed by immunofluorescence. RESULTS We showed that HG transiently (after 6-h exposure) induced expression of the autophagy activation marker LC3-II in podocytes. Genistein treatment induced autophagy in both normal and HG-treated podocytes through inactivating mTOR signaling. Moreover, Genistein protected podocytes against chloroquine in HG-cultured conditions in vitro by maintaining the level of autophagy-related proteins. In addition, MyD88 siRNA downregulated expression of autophagy-related proteins, whereas Genistein treatment reversed these effects. CONCLUSIONS This study demonstrated that Genistein-induced autophagy could be a potential treatment strategy for glomerular diseases.

Mass Spectrometry-based Structural Analysis and Systems Immunoproteomics Strategies for Deciphering the Host Response to Endotoxin

One cause of sepsis is systemic maladaptive immune response of the host to bacteria and specifically, to Gram-negative bacterial outer-membrane glycolipid lipopolysaccharide (LPS). On the host myeloid cell surface, proinflammatory LPS activates the innate immune system via Toll-like receptor-4/myeloid differentiation factor-2 complex. Intracellularly, LPS is also sensed by the noncanonical inflammasome through caspase-11 in mice and 4/5 in humans. The minimal functional determinant for innate immune activation is the membrane anchor of LPS called lipid A. Even subtle modifications to the lipid A scaffold can enable, diminish, or abolish immune activation. Bacteria are known to modify their LPS structure during environmental stress and infection of hosts to alter cellular immune phenotypes. In this review, we describe how mass spectrometry-based structural analysis of endotoxin helped uncover major determinations of molecular pathogenesis. Through characterization of LPS modifications, we now better understand resistance to antibiotics and cationic antimicrobial peptides, as well as how the environment impacts overall endotoxin structure. In addition, mass spectrometry-based systems immunoproteomics approaches can assist in elucidating the immune response against LPS. Many regulatory proteins have been characterized through proteomics and global/targeted analysis of protein modifications, enabling the discovery and characterization of novel endotoxin-mediated protein translational modifications.

HDAC6 controls innate immune and autophagy responses to TLR-mediated signalling by the intracellular bacteria Listeria monocytogenes

Recent evidence on HDAC6 function underlines its role as a key protein in the innate immune response to viral infection. However, whether HDAC6 regulates innate immunity during bacterial infection remains unexplored. To assess the role of HDAC6 in the regulation of defence mechanisms against intracellular bacteria, we used the Listeria monocytogenes (Lm) infection model. Our data show that Hdac6-/- bone marrow-derived dendritic cells (BMDCs) have a higher bacterial load than Hdac6+/+ cells, correlating with weaker induction of IFN-related genes, pro-inflammatory cytokines and nitrite production after bacterial infection. Hdac6-/- BMDCs have a weakened phosphorylation of MAPK signalling in response to Lm infection, suggesting altered Toll-like receptor signalling (TLR). Compared with Hdac6+/+ counterparts, Hdac6-/- GM-CSF-derived and FLT3L-derived dendritic cells show weaker pro-inflammatory cytokine secretion in response to various TLR agonists. Moreover, HDAC6 associates with the TLR-adaptor molecule Myeloid differentiation primary response gene 88 (MyD88), and the absence of HDAC6 seems to diminish the NF-κB induction after TLR stimuli. Hdac6-/- mice display low serum levels of inflammatory cytokine IL-6 and correspondingly an increased survival to a systemic infection with Lm. The impaired bacterial clearance in the absence of HDAC6 appears to be caused by a defect in autophagy. Hence, Hdac6-/- BMDCs accumulate higher levels of the autophagy marker p62 and show defective phagosome-lysosome fusion. These data underline the important function of HDAC6 in dendritic cells not only in bacterial autophagy, but also in the proper activation of TLR signalling. These results thus demonstrate an important regulatory role for HDAC6 in the innate immune response to intracellular bacterial infection.

MyD88 promotes myoblast fusion in a cell-autonomous manner

Myoblast fusion is an indispensable step for skeletal muscle development, postnatal growth, and regeneration. Myeloid differentiation primary response gene 88 (MyD88) is an adaptor protein that mediates Toll-like receptors and interleukin-1 receptor signaling. Here we report a cell-autonomous role of MyD88 in the regulation of myoblast fusion. MyD88 protein levels are increased during in vitro myogenesis and in conditions that promote skeletal muscle growth in vivo. Deletion of MyD88 impairs fusion of myoblasts without affecting their survival, proliferation, or differentiation. MyD88 regulates non-canonical NF-κB and canonical Wnt signaling during myogenesis and promotes skeletal muscle growth and overload-induced myofiber hypertrophy in mice. Ablation of MyD88 reduces myofiber size during muscle regeneration, whereas its overexpression promotes fusion of exogenous myoblasts to injured myofibers. Our study shows that MyD88 modulates myoblast fusion and suggests that augmenting its levels may be a therapeutic approach to improve skeletal muscle formation in degenerative muscle disorders.

Histone deacetylase 6 inhibitor ACY-1215 protects against experimental acute liver failure by regulating the TLR4-MAPK/NF-κB pathway

Histone deacetylase 6 (HDAC6) is considered a new target for anticancer, anti-inflammatory, and neurodegenerative treatment. ACY-1215 is a selective histone deacetylase 6 inhibitor, and it has been recognized as a potential anticancer and anti-inflammation drug. The aim of our study was to investigate whether ACY-1215 has protective effects on acute liver failure (ALF) in mice and explore its potential mechanism. Male C57/BL6 mice were divided into normal, model, and ACY-1215 groups. ACY-1215 (25mg/kg) and same amounts of saline were given to mice. After 2h, the ALF models were induced by lipopolysaccharide (LPS, 100μg/kg) combined with D-galactosamine (D-gal, 400mg/kg). All animals were killed after 24h. The expressions of HDAC6 were determined by western blotting and RT-PCR assay. The expression levels of inflammatory cytokines were detected by ELISA and RT-PCR. The protein expression of Toll-like receptor 4 (TLR4), mitogen-activated protein kinase (MAPK), and nuclear factor κB (NF-κB) species were determined by western blot. The mortality of mice with ALF induced by LPS and D-gal was significantly decreased by ACY-1215 pretreatment. Procedures to manage ALF caused adversely affected liver histology and function; this damage was repaired by pretreatment of ACY-1215. ACY-1215 treatment also attenuated the serum and messenger RNA levels of the proinflammatory cytokines. Pretreatment of ACY-1215 significantly decreased the protein expression of TLR4 and the activation of MAPK and NF-κB signalling pathways. ACY-1215 has potential therapeutic value in mice with ALF by directly inhibiting inflammatory response via regulation of the TLR4-MAPK/NF-kB pathway.

Structural basis of TIR-domain-assembly formation in MAL- and MyD88-dependent TLR4 signaling

Toll-like receptor (TLR) signaling is a key innate immunity response to pathogens. Recruitment of signaling adapters such as MAL (TIRAP) and MyD88 to the TLRs requires Toll/interleukin-1 receptor (TIR)-domain interactions, which remain structurally elusive. Here we show that MAL TIR domains spontaneously and reversibly form filaments in vitro. They also form cofilaments with TLR4 TIR domains and induce formation of MyD88 assemblies. A 7-Å-resolution cryo-EM structure reveals a stable MAL protofilament consisting of two parallel strands of TIR-domain subunits in a BB-loop-mediated head-to-tail arrangement. Interface residues that are important for the interaction are conserved among different TIR domains. Although large filaments of TLR4, MAL or MyD88 are unlikely to form during cellular signaling, structure-guided mutagenesis, combined with in vivo interaction assays, demonstrated that the MAL interactions defined within the filament represent a template for a conserved mode of TIR-domain interaction involved in both TLR and interleukin-1 receptor signaling.

Basal autophagy prevents autoactivation or enhancement of inflammatory signals by targeting monomeric MyD88

Autophagy, the processes of delivery of intracellular components to lysosomes, regulates induction of inflammation. Inducible macroautophagy degrades inflammasomes and dysfunctional mitochondria to downregulate inflammatory signals. Nonetheless, the effects of constitutive basal autophagy on inflammatory signals are largely unknown. Here, we report a previously unknown effect of basal autophagy. Lysosomal inhibition induced weak inflammatory signals in the absence of a cellular stimulus and in the presence of a nutrient supply, and their induction was impaired by MyD88 deficiency. During lysosomal inhibition, MyD88 was accumulated, and overabundant MyD88 autoactivated downstream signaling or enhanced TLR/IL-1R-mediated signaling. MyD88 is probably degraded via basal microautophagy because macroautophagy inhibitors, ATG5 deficiency, and an activator of chaperone-mediated autophagy did not affect MyD88. Analysis using a chimeric protein whose monomerization/dimerization can be switched revealed that monomeric MyD88 is susceptible to degradation. Immunoprecipitation of monomeric MyD88 revealed its interaction with TRAF6. In TRAF6-deficient cells, degradation of basal MyD88 was enhanced, suggesting that TRAF6 participates in protection from basal autophagy. Thus, basal autophagy lowers monomeric MyD88 expression, and thereby autoactivation of inflammatory signals is prevented. Given that impairment of lysosomes occurs in various settings, our results provide novel insights into the etiology of inflammatory signals that affect consequences of inflammation.

Role of p62 in the suppression of inflammatory cytokine production by adiponectin in macrophages: Involvement of autophagy and p21/Nrf2 axis

Adiponectin possesses potent anti-inflammatory properties. p62, an adaptor protein composed of multi-functional domain, is known to play a role in controlling inflammatory responses. In the present study, we examined the role of p62 in suppressing inflammatory cytokines produced by globular adiponectin (gAcrp) and the potential underlying mechanisms in macrophages. We demonstrated that gAcrp significantly increased p62 expression. Knockdown of p62 abrogated the suppressive effects of gAcrp on LPS-stimulated TNF-α and IL-1β expression and TRAF6/p38 MAPK pathway, indicating that p62 signaling is critical for suppressing inflammatory cytokines production by gAcrp. We next examined the role of p62 in gAcrp-induced autophagy activation, because autophagy has been shown to play a pivotal role in suppressing TNF-α. Herein, we observed that gene silencing of p62 prevented gAcrp-induced increases in autophagy-related genes and autophagosome formation. In addition, we found that Nrf2 knockdown prevented gAcrp-induced p62 expression, and p21 knockdown prevented Nrf2 induction, suggesting the role of p21/Nrf2 axis in gAcrp-induced p62 expression. Taken together, these findings imply that p62 signaling plays a crucial role in suppressing inflammatory cytokine production by globular adiponectin in macrophages, at least in part, through autophagy induction. Furthermore, the p21/Nrf2 signaling cascade contributes to p62 induction by globular adiponectin.

TLR3 downregulates expression of schizophrenia gene Disc1 via MYD88 to control neuronal morphology

Viral infection during fetal or neonatal stages increases the risk of developing neuropsychiatric disorders such as schizophrenia and autism spectrum disorders. Although neurons express several key regulators of innate immunity, the role of neuronal innate immunity in psychiatric disorders is still unclear. Using cultured neurons and in vivo mouse brain studies, we show here that Toll‐like receptor 3 (TLR3) acts through myeloid differentiation primary response gene 88 (MYD88) to negatively control Disrupted in schizophrenia 1 (Disc1) expression, resulting in impairment of neuronal development. Cytokines are not involved in TLR3‐mediated inhibition of dendrite outgrowth. Instead, TLR3 signaling suppresses expression of several psychiatric disorder‐related genes, including Disc1. The impaired dendritic arborization caused by TLR3 activation is rescued by MYD88 deficiency or DISC1 overexpression. In addition, TLR3 activation at the neonatal stage increases dendritic spine density, but narrows spine heads at postnatal day 21 (P21), suggesting a long‐lasting effect of TLR3 activation on spinogenesis. Our study reveals a novel mechanism of TLR3 in regulation of dendritic morphology and provides an explanation for how environmental factors influence mental health.

Increased VEGF-A promotes multiple distinct aging diseases of the eye through shared pathomechanisms

While increased VEGF‐A has been associated with neovascular age‐related macular degeneration (AMD), it is not known whether VEGF‐A may also promote other age‐related eye diseases. Here, we show that an increase in VEGF‐A is sufficient to cause multiple distinct common aging diseases of the eye, including cataracts and both neovascular and non‐exudative AMD‐like pathologies. In the lens, increased VEGF‐A induces age‐related opacifications that are associated with ERK hyperactivation, increased oxidative damage, and higher expression of the NLRP3 inflammasome effector cytokine IL‐1β. Similarly, increased VEGF‐A induces oxidative stress and IL‐1β expression also in the retinal pigment epithelium (RPE). Targeting NLRP3 inflammasome components or Il1r1 strongly inhibited not only VEGF‐A‐induced cataract formation, but also both neovascular and non‐exudative AMD‐like pathologies. Moreover, increased VEGF‐A expression specifically in the RPE was sufficient to cause choroidal neovascularization (CNV) as in neovascular AMD, which could be inhibited by RPE‐specific inactivation of Flk1, while Tlr2 inactivation strongly reduced CNV. These findings suggest a shared pathogenic role of VEGF‐A‐induced and NLRP3 inflammasome‐mediated IL‐1β activation for multiple distinct ocular aging diseases.

TLR Adaptor Protein MYD88 Mediates Sensitivity to HDAC Inhibitors via a Cytokine-Dependent Mechanism

Histone deacetylase (HDAC) inhibitors have proven useful therapeutic agents for certain hematologic cancers. However, HDAC inhibition causes diverse cellular outcomes, and identification of cancer-relevant pathways within these outcomes remains unresolved. In this study, we utilized an unbiased loss-of-function screen and identified the Toll-like receptor (TLR) adaptor protein MYD88 as a key regulator of the antiproliferative effects of HDAC inhibition. High expression of MYD88 exhibited increased sensitivity to HDAC inhibitors; conversely, low expression coincided with reduced sensitivity. MYD88-dependent TLR signaling controlled cytokine levels, which then acted via an extracellular mechanism to maintain cell proliferation and sensitize cells to HDAC inhibition. MYD88 activity was directly regulated through lysine acetylation and was deacetylated by HDAC6. MYD88 was a component of a wider acetylation signature in the ABC subgroup of diffuse large B-cell lymphoma, and one of the most frequent mutations in MYD88, L265P, conferred increased cell sensitivity to HDAC inhibitors. Our study defines acetylation of MYD88, which, by regulating TLR-dependent signaling to cytokine genes, influences the antiproliferative effects of HDAC inhibitors. Our results provide a possible explanation for the sensitivity of malignancies of hematologic origin to HDAC inhibitor-based therapy. Cancer Res; 76(23); 6975-87. ©2016 AACR.

γ-Glutamyltranspeptidase is an endogenous activator of Toll-like receptor 4-mediated osteoclastogenesis

Chronic inflammation-associated bone destruction, which is observed in rheumatoid arthritis (RA) and periodontitis, is mediated by excessive osteoclastogenesis. We showed previously that γ-glutamyltranspeptidase (GGT), an enzyme involved in glutathione metabolism, acts as an endogenous activator of such pathological osteoclastogenesis, independent of its enzymatic activity. GGT accumulation is clinically observed in the joints of RA patients, and, in animals, the administration of recombinant GGT to the gingival sulcus as an in vivo periodontitis model induces an increase in the number of osteoclasts. However, the underlying mechanisms of this process remain unclear. Here, we report that Toll-like receptor 4 (TLR4) recognizes GGT to activate inflammation-associated osteoclastogenesis. Unlike lipopolysaccharide, GGT is sensitive to proteinase K treatment and insensitive to polymyxin B treatment. TLR4 deficiency abrogates GGT-induced osteoclastogenesis and activation of NF-κB and MAPK signaling in precursor cells. Additionally, GGT does not induce osteoclastogenesis in cells lacking the signaling adaptor MyD88. The administration of GGT to the gingival sulcus induces increased osteoclastogenesis in wild-type mice, but does not induce it in TLR4-deficient mice. Our findings elucidate a novel mechanism of inflammation-associated osteoclastogenesis, which involves TLR4 recognition of GGT and subsequent activation of MyD88-dependent signaling.

Effects of aerobic training on markers of autophagy in the elderly

Autophagy is a molecular process essential for the maintenance of cellular homeostasis, which appears to (i) decline with age and (ii) respond to physical exercise. In addition, recent evidence suggests a crosstalk between autophagy and toll-like receptor (TLR)-associated inflammatory responses. This study assessed the effects of aerobic exercise training on autophagy and TLR signaling in older subjects. Twenty-nine healthy women and men (age, 69.7 ± 1.0 year) were randomized to a training (TG) or a control (CG) group. TG performed an 8-week aerobic training program, while CG followed their daily routines. Peripheral blood mononuclear cells were isolated from blood samples obtained before and after the intervention, and protein levels of protein 1 light chain 3 (LC3), sequestosome 1 (p62/SQSTM1), beclin-1, phosphorylated unc-51-like kinase (ULK-1), ubiquitin-like autophagy-related (Atg)12, Atg16, and lysosome-associated membrane protein (LAMP)-2 were measured. TLR2 and TLR4 signaling pathways were also analyzed. Peak oxygen uptake increased in TG after the intervention. Protein expression of beclin-1, Atg12, Atg16, and the LC3II/I ratio increased following the training program (p < 0.05), while expression of p62/SQSTM1 and phosphorylation of ULK-1 at Ser(757) were lower (p < 0.05). Protein content of TLR2, TLR4, myeloid differentiation primary response gen 88 (MyD88), and TIR domain-containing adaptor-inducing interferon (TRIF) were not significantly modified by exercise. The current data indicate that aerobic exercise training induces alterations in multiple markers of autophagy, which seem to be unrelated to changes in TLR2 and TLR4 signaling pathways. These results expand knowledge on exercise-induced autophagy adaptations in humans and suggest that the exercise type employed may be a key factor explaining the potential relationship between autophagy and TLR pathways.

A novel approach for emerging and antibiotic resistant infections: Innate defense regulators as an agnostic therapy

Innate Defense Regulators (IDRs) are short synthetic peptides that target the host innate immune system via an intracellular adaptor protein which functions at key signaling nodes. In this work, further details of the mechanism of action of IDRs have been discovered. The studies reported here show that the lead clinical IDR, SGX94, has broad-spectrum activity against Gram-negative and Gram-positive bacterial infections caused by intracellular or extracellular bacteria and also complements the actions of standard of care antibiotics. Based on in vivo and primary cell culture studies, this activity is shown to result from the primary action of SGX94 on tissue-resident cells and subsequent secondary signaling to activate myeloid-derived cells, resulting in enhanced bacterial clearance and increased survival. Data from non-clinical and clinical studies also show that SGX94 treatment modulates pro-inflammatory and anti-inflammatory cytokine levels, thereby mitigating the deleterious inflammatory consequences of innate immune activation. Since they act through host pathways to provide both broad-spectrum anti-infective capability as well as control of inflammation, IDRs are unlikely to be impacted by resistance mechanisms and offer potential clinical advantages in the fight against emerging and antibiotic resistant bacterial infections.

Methylation and gene expression of histone deacetylases 6 in systemic lupus erythematosus

AIM

The purpose of this study is to investigate the role of methylation in the histone deacetylases 6 (HDAC6) promoter and HDAC6 messenger RNA (mRNA) expression in the pathogenesis of systemic lupus erythematosus (SLE).

METHOD

Direct bisulfite-polymerase chain reaction (PCR) sequencing was performed to detect the HDAC6 promoter methylation in 33 patients with SLE and 35 healthy controls. The HDAC6 mRNA expression was measured in 93 SLE patients and 84 healthy controls by using the method of quantitative real-time PCR.

RESULTS

This study demonstrated that the methylation rates at HDAC6-680, -660 and -658 were significantly increased in the SLE patients compared with healthy controls (P = 0.041, 0.034 and 0.029, respectively). The SLE patients also had lower HDAC6 mRNA expression than the controls (P = 0.031). However, there was no significant difference in HDAC6 mRNA expression between patients with active and inactive SLE.

CONCLUSION

The SLE patients had higher methylation in the HDAC6 promoter and lower HDAC6 mRNA expression than the controls. These changes may be related to the susceptibility of SLE. However, they are not associated with the disease activity of SLE.

Novel Molecular Insights into Classical and Alternative Activation States of Microglia as Revealed by Stable Isotope Labeling by Amino Acids in Cell Culture (SILAC)-based Proteomics

Microglia, the resident immune cells of the brain, have been shown to display a complex spectrum of roles that span from neurotrophic to neurotoxic depending on their activation status. Microglia can be classified into four stages of activation, M1, which most closely matches the classical (pro-inflammatory) activation stage, and the alternative activation stages M2a, M2b, and M2c. The alternative activation stages have not yet been comprehensively analyzed through unbiased, global-scale protein expression profiling. In this study, BV2 mouse immortalized microglial cells were stimulated with agonists specific for each of the four stages and total protein expression for 4644 protein groups was quantified using SILAC-based proteomic analysis. After validating induction of the various stages through a targeted cytokine assay and Western blotting of activation states, the data revealed novel insights into the similarities and differences between the various states. The data identify several protein groups whose expression in the anti-inflammatory, pro-healing activation states are altered presumably to curtail inflammatory activation through differential protein expression, in the M2a state including CD74, LYN, SQST1, TLR2, and CD14. The differential expression of these proteins promotes healing, limits phagocytosis, and limits activation of reactive nitrogen species through toll-like receptor cascades. The M2c state appears to center around the down-regulation of a key member in the formation of actin-rich phagosomes, SLP-76. In addition, the proteomic data identified a novel activation marker, DAB2, which is involved in clathrin-mediated endocytosis and is significantly different between M2a and either M1 or M2b states. Western blot analysis of mouse primary microglia stimulated with the various agonists of the classical and alternative activation states revealed a similar trend of DAB2 expression compared with BV2 cells.

IRF7 in the Australian black flying fox, Pteropus alecto: evidence for a unique expression pattern and functional conservation

As the only flying mammal, bats harbor a number of emerging and re-emerging viruses, many of which cause severe diseases in humans and other mammals yet result in no clinical symptoms in bats. As the master regulator of the interferon (IFN)-dependent immune response, IFN regulatory factor 7 (IRF7) plays a central role in innate antiviral immunity. To explore the role of bat IRF7 in the regulation of the IFN response, we performed sequence and functional analysis of IRF7 from the pteropid bat, Pteropus alecto. Our results demonstrate that bat IRF7 retains the ability to bind to MyD88 and activate the IFN response despite unique changes in the MyD88 binding domain. We also demonstrate that bat IRF7 has a unique expression pattern across both immune and non-immune related tissues and is inducible by double-strand RNA. The broad tissue distribution of IRF7 may provide bats with an enhanced ability to rapidly activate the IFN response in a wider range of tissues compared to other mammals. The importance of IRF7 in antiviral activity against the bat reovirus, Pulau virus was confirmed by siRNA knockdown of IRF7 in bat cells resulting in enhanced viral replication. Our results highlight the importance of IRF7 in innate antiviral immunity in bats.

Interplay between HDAC6 and its interacting partners: essential roles in the aggresome-autophagy pathway and neurodegenerative diseases

Cytoplasmic localization and possession of two deacetylase domains and a ubiquitin-binding domain make histone deacetylase 6 (HDAC6) a unique histone deacetylase. HDAC6 interacts with a number of proteins in the cytoplasm. Some of these proteins can be deacetylated by HDAC6 deacetylase activity. Others can affect HDAC6 functions by modulating its catalytic activity or ubiquitin-binding capability. Over the last decade, HDAC6 has been shown to play important roles in the aggresome-autophagy pathway, which selectively targets on protein aggregates or damaged organelles for their accumulation and clearance in cells. HDAC6-interacting partners are integral components in this pathway with regard to their regulatory roles through interaction with HDAC6. The aggresome-autophagy pathway appears to be an attractive therapeutic target for the treatment of neurodegenerative diseases as accumulation of protein aggregates are hallmarks in these diseases. In the current review, I discuss the molecular details of how HDAC6 and its interacting partners regulate each individual step in the aggresome-autophagy pathway and also provide perspectives of how HDAC6 can be targeted in treating neurodegenerative diseases.