Histone deacetylase inhibitors impair antibacterial defenses of macrophages

Histone deacetylases (HDACs) control gene expression by deacetylating histones and nonhistone proteins. HDAC inhibitors (HDACi) are powerful anticancer drugs that exert anti-inflammatory and immunomodulatory activities. We recently reported a proof-of-concept study demonstrating that HDACi increase susceptibility to bacterial infections in vivo. Yet, still little is known about the effects of HDACi on antimicrobial innate immune defenses. Here we show that HDACi belonging to different chemical classes inhibit at multiple levels the response of macrophages to bacterial infection. HDACi reduce the phagocytosis and the killing of Escherichia coli and Staphylococcus aureus by macrophages. In line with these findings, HDACi decrease the expression of phagocytic receptors and inhibit bacteria-induced production of reactive oxygen and nitrogen species by macrophages. Consistently, HDACi impair the expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits and inducible nitric oxide synthase. These data indicate that HDACi have a strong impact on critical antimicrobial defense mechanisms in macrophages.     

Regulation of innate immune responses by Toll-like receptors

Innate immune response in Drosophila is mediated by signaling through Toll receptors. In mammals, Toll-like receptors (TLRs), comprising a large family, recognize a specific pattern of microbial components. So far, the roles of TLR2, TLR4, TLR5, TLR6, and TLR9 have been revealed. The recognition of microbial components by TLRs leads to activation of innate immunity, which provokes inflammatory responses and finally the development of adaptive immunity. The inflammatory response depends on a TLR-mediated MyD88-dependent cascade. However, there seems to exist additional cascades in TLR signaling. In the case of TLR4 signaling, an MyD88-independent pathway is now being characterized. In addition to the activation of innate immune responses, TLR-mediated signaling leads to suppression of the activity of innate immune cells, represented by "lipopolysaccharide (LPS) tolerance". Progress in elucidating the molecular mechanisms for LPS tolerance has been made through the analysis of TLR-mediated signaling pathways. Thus, the activity for innate immune responses is known to be finely regulated by TLRs.     

Toll-like receptor-initiated testicular innate immune responses in mouse Leydig cells

The testis is an immunoprivileged site, where the local cell-initiated testicular innate immune responses play a crucial role in defense against microbial infections. Mechanisms modulating the testicular cell-built defense system remain to be clarified. In this article, we demonstrate that Leydig cells, a major cell population in the testicular interstitium, initiate innate immunity through the activation of Toll-like receptors (TLRs). Several TLRs are expressed in mouse Leydig cells; among these, TLR3 and TLR4 are expressed at relatively high levels compared with other TLR members. Both TLR3 and TLR4 can be activated by their agonists (polyinosinic:polycytidylic acid and lipopolysaccharide) in Leydig cells and subsequently induce the production of inflammatory factors, such as IL-1β, IL-6, TNF-α, and type 1 interferons (IFN) (IFN-α and IFN-β). Notably, the activation of TLR3 and TLR4 suppresses steroidogenesis by Leydig cells. Further, we provide evidence that Axl and Mer receptor tyrosine kinases are expressed in Leydig cells and regulate TLR-mediated innate immune responses negatively. Data presented here describe a novel function of Leydig cells in eliciting testicular innate immune responses that should contribute to the protection of the testis from microbial infections.     

Toll样受体介导小鼠原代肝细胞产生的天然免疫应答及其对乙型肝炎病毒复制的抑制作用

目的 探讨肝细胞的Toll样受体(TLR)信号途径及其诱导的抗病毒免疫应答.方法 分离野生型C57BL/6小鼠的原代肝细胞,定量逆转录-聚合酶链反应法检测TLR的表达.分别用TLR 1～9配体刺激肝细胞并收集细胞上清液.酶联免疫吸附法检测细胞上清液内的细胞因子.病毒保护实验检测细胞上清液的抗脑膜炎心肌炎病毒因子,并将细胞上清液与HBV-Met细胞共孵育,用Southern blot法检测其对HBV复制的抑制效应.结果 原代肝细胞能表达TLR 1～9.与其TLR表达谱相应的,肝细胞在TLR1～9配体的刺激下均可以产生炎性细胞因子(肿瘤坏死因子α和白细胞介素6),而仅在TLR1、TLR3、TLR7和TLR9配体刺激下可产生I型干扰素(干扰素α和干扰素β).在病毒保护实验中,TLR3和TLR7的配体可以刺激肝细胞产生大量的抗脑膜炎心肌炎病毒效应分子;而TLR1、TLR3和TLR4配体直接刺激的肝细胞上清液,以及TLR3、TLR7和TLR9配体转染刺激的肝细胞上清液,都能有效抑制HBV的复制.结论 小鼠原代肝细胞有独特的TLR信号途径,并能通过TLR配体的激活产生抑制HBV复制的效应.这一发现对于制定基于TLR的抗肝脏靶向性病毒的治疗措施有指导意义.     

The dipeptidylpeptidase‐IV inhibitors sitagliptin,vildagliptin and saxagliptin do not impair innate and adaptive immune responses

Inhibitors of dipeptidylpeptidase IV (DPP‐IV) represent a novel class of frequently used anti‐diabetic drugs. In addition to its function in metabolic regulation, DPP‐IV also plays a role in the immune system. Whether the DPP‐IV inhibitors sitagliptin, vildagliptin or saxagliptin impair immune responses is, however, currently unknown. Here, we investigated the effect of these agents on both innate and adaptive immunity. We found that the DPP‐IV inhibitors did not affect the innate immune response induced by Toll‐like receptor (TLR) ligands, as cytokine secretion and induction of co‐stimulatory molecules by human blood mononuclear cells was not impaired. Furthermore, proliferation of T cells and suppressive function of regulatory T cells was preserved. Mice treated with vildagliptin showed normal cytokine production, immune cell activation and lymphocyte trafficking upon TLR activation. Thus, crucial immunological parameters remain unaffected upon treatment with DPP‐IV inhibitors, a fact that is reassuring with respect to safety of these drugs.     

Histone deacetylase inhibitors reduce polyglutamine toxicity

Polyglutamine diseases include at least nine neurodegenerative disorders, each caused by a CAG repeat expansion in a different gene. Accumulation of mutant polyglutamine-containing proteins occurs in patients, and evidence from cell culture and animal experiments suggests the nucleus as a site of pathogenesis. To understand the consequences of nuclear accumulation, we created a cell culture system with nuclear-targeted polyglutamine. In our system, cell death can be mitigated by overexpression of full-length cAMP response element binding protein (CREB)-binding protein (CBP) or its amino-terminal portion alone. CBP is one of several histone acetyltransferases sequestered by polyglutamine inclusions. We found histone acetylation to be reduced in cells expressing mutant polyglutamine. Reversal of this hypoacetylation, which can be achieved either by overexpression of CBP or its amino terminus or by treatment with deacetylase inhibitors, reduced cell loss. These findings suggest that nuclear accumulation of polyglutamine can lead to altered protein acetylation in neurons and indicate a novel therapeutic strategy for polyglutamine disease.     

The role of Toll-like receptors and MyD88 in innate immune responses

Toll-like receptors (TLRs) are phylogenetically conserved receptors that recognize pathogen associated molecular patterns (PAMPS). We previously generated mice lacking TLR2 and TLR4 and showed the differential role of TLR2 and TLR4 in microbial recognition. TLR4 functions as the transmembrane component of the lipopolysaccharide (LPS) receptor, while TLR2 recognizes peptidoglycan from Gram-positive bacteria and lipoprotein. We also generated mice lacking MyD88, an adaptor involved in IL-1R/TLR signalings. The responses to a variety of bacterial components were completely abrogated in MyD88-deficient cells. However, unlike the signaling mediated by other bacterial components such as lipoprotein and bacterial DNA, activation of NF-kappaB and MAP kinases was induced in response to LPS even in the absence of MyD88, which indicates the existence of a MyD88-independent pathway. We have recently found that the MyD88-independent pathway is involved in LPS-induced maturation of dendritic cells (DCs).     

Toll样受体介导的天然免疫应答与常见病原体肺部感染之间的关系

Toll样受体家族是近年来发现的一类在宿主固有免疫及获得性免疫中起到关键作用的蛋白受体.越来越多的研究表明,Toll样受体与多种机体感染有关,包括肺部感染.本文就Toll样受体在肺部感染发病机制中的作用进行综述.     

HCV innate immune responses

Hepatitis C virus (HCV) establishes a persistent infection in more than 70% of infected individuals. This striking ability to evade the powerful innate immune system results from viral interference occurring at several levels of the interferon (IFN) system. There is strong evidence from cell culture experiments that HCV can inhibit the induction of IFNβ by cleaving important proteins in the virus sensory pathways of cells such as MAVS and TRIF. There is also evidence that HCV interferes with IFNα signaling through the Jak-STAT pathway, and that HCV proteins target IFN effector systems such as protein kinase R (PKR). These in vitro findings will have to be confirmed in clinical trials investigating the molecular mechanisms of HCV interference with the innate immune system in liver samples.     

Elevated CO2 suppresses specific Drosophila innate immune responses and resistance to bacterial infection

Elevated CO₂ levels (hypercapnia) frequently occur in patients with obstructive pulmonary diseases and are associated with increased mortality. However, the effects of hypercapnia on non-neuronal tissues and the mechanisms that mediate these effects are largely unknown. Here, we develop Drosophila as a genetically tractable model for defining non-neuronal CO₂ responses and response pathways. We show that hypercapnia significantly impairs embryonic morphogenesis, egg laying, and egg hatching even in mutants lacking the Gr63a neuronal CO₂ sensor. Consistent with previous reports that hypercapnic acidosis can suppress mammalian NF-κB-regulated innate immune genes, we find that in adult flies and the phagocytic immune-responsive S2* cell line, hypercapnia suppresses induction of specific antimicrobial peptides that are regulated by Relish, a conserved Rel/NF-κB family member. Correspondingly, modest hypercapnia (7–13%) increases mortality of flies inoculated with E. faecalis, A. tumefaciens, or S. aureus. During E. faecalis and A. tumefaciens infection, increased bacterial loads were observed, indicating that hypercapnia can decrease host resistance. Hypercapnic immune suppression is not mediated by acidosis, the olfactory CO₂ receptor Gr63a, or by nitric oxide signaling. Further, hypercapnia does not induce responses characteristic of hypoxia, oxidative stress, or heat shock. Finally, proteolysis of the Relish IκB-like domain is unaffected by hypercapnia, indicating that immunosuppression acts downstream of, or in parallel to, Relish proteolytic activation. Our results suggest that hypercapnic immune suppression is mediated by a conserved response pathway, and illustrate a mechanism by which hypercapnia could contribute to worse outcomes of patients with advanced lung disease, who frequently suffer from both hypercapnia and respiratory infections.     

Toll样受体介导的抗乙型肝炎病毒的固有免疫

在抗感染免疫过程中,特别是病毒感染早期,固有免疫应答具有重要意义。固有免疫系统发挥防御作用的关键是对病原体的识别,Toll样受体（TLRs）作为固有免疫的重要组分之一,通过配体识别、信号转导、免疫分子活化等环节启动固有免疫并调节获得性免疫。本文就近年来TLRs介导的固有免疫抗乙型肝炎病毒感染的作用和相关的免疫调节机制进行综述     

Innate immunity of the human newborn: distinct cytokine responses to LPS and other Toll-like receptor agonists

Human newborns are at increased risk of microbial invasion and display diminished responses to many vaccines indicating a functional immaturity of the immune system at birth. Such altered immune reactivity may reflect the demands of in utero existence, including the need to avoid potentially harmful inflammatory immune reactions. Despite normal basal expression of Toll-like receptors and membrane CD14, innate immune responses of neonatal mononuclear cells to lipopolysaccharide are characterized by markedly reduced release of the pro-inflammatory Th1-polarizing cytokines TNF-alpha and interferon-gamma with relative preservation of anti-inflammatory Th2-polarizing cytokines. Differences between newborns and adults with respect to TLR-induced TNF-alpha release extend to a range of TLR agonists, including bacterial lipopeptides, and are due to differences in soluble factors present in blood plasma. Soluble factors in neonatal blood plasma suppress TLR-induced TNF-alpha release from monocytes and efforts to identify and characterize these inhibitors are on-going. Such altered immunity to TLR agonists is likely to alter both innate and adaptive immune responses in newborns profoundly. Definition of the mechanisms underlying distinct neonatal immunity promises to identify novel ways to prevent and treat infection in this relatively high-risk population.     

Histone deacetylase inhibitors in the treatment for multiple myeloma

Histone lysine acetylation is regulated by both histone deacetylases (HDACs) and histone acetyl transferases. Inhibition of deacetylases induces hyperacetylate of target proteins and has a crucial role in the epigenetic regulation of gene expression mediating cell survival and proliferation. Therefore, HDAC inhibitors have emerged as novel therapeutic agents for cancers, including multiple myeloma (MM). Recent studies revealed that HDAC inhibitors trigger hyperacetylation of not only histones, but also non-histone proteins regulating cell growth and survival, revealing the complexity of mechanism of action of HDAC inhibitors. Many HDAC inhibitors have already shown significant anti-MM activities in preclinical studies and are under evaluation in clinical trials.