Research Article

Topoisomerase 1 inhibition suppresses inflammatory genes and protects from death by inflammation

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Science  27 May 2016:
Vol. 352, Issue 6289, aad7993
DOI: 10.1126/science.aad7993

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Unwinding DNA and unleasing inflammation

Fighting infections often comes with collateral damage, which sometimes can be deadly. For instance, in septic shock, the overwhelming release of inflammatory mediators drives multi-organ failure. Rialdi et al. now report a potential new therapeutic target for controlling excessive inflammation: the DNA unwinding enzyme topoisomerase I (Top1) (see the Perspective by Pope and Medzhitov). Upon infection, Top1 specifically localizes to the promoters of pathogen-induced genes and promotes their transcription by helping to recruit RNA polymerase II. Pharmacological inhibition of Top1 in a therapeutic setting increased survival in several mouse models of severe microbially induced inflammation.

Science, this issue p. 10.1126/science.aad7993; see also p. 1058

Structured Abstract

INTRODUCTION

Infection causes inflammation, which contributes to pathogen clearance and organismal survival. The balance between the intensity and resolution of an inflammatory response is key for the fitness of the organism. Sepsis, for example, is a life-threatening condition caused by an excessive host response to infection, which in turn leads to multi-organ failure and death. Worldwide, millions of people each year succumb to sepsis. With an overall mortality rate of 20 to 50%, sepsis is the 10th leading cause of death (more than HIV and breast cancer) in the United States, according to the Centers for Disease Control and Prevention. Estimates indicate that 250,000 to 500,000 people die from sepsis annually in the United States. Children and the elderly are especially vulnerable to sepsis; it is the most common cause of death in infants and children. Childhood pneumonia, often caused by virus-bacteria co-infection, leads to septic shock and lung destruction. This occurs after bacterial invasion even in the presence of an appropriate antibiotic therapy. Finding remedies to treat sepsis and diseases associated with detrimental acute inflammatory reactions is thus pivotal for humankind.

RATIONALE

We reasoned that if excessive inflammation in response to infection leads to lethal consequences, dampening inflammation could be advantageous for the host. At least two strategies could be used to suppress inflammatory responses associated with infection. One is indirect and targets the pathogen (antibiotics). The second one, which we used, directly acts on the host response itself. In such a strategy, the suppression of acute inflammation would bypass the fatal outcome associated with overt inflammation and would “buy time” to allow the host immune response to eliminate the pathogen. After microbial invasion, many steps could be targeted between the early phases of the cellular response (sensing of the pathogen and signal transduction) and the information flow from DNA to RNA to proteins that act as inflammatory mediators (i.e., cytokines). We decided to identify and chemically inhibit cellular factors that act at the DNA (chromatin) level and play a primary role in activating the expression of inflammatory genes.

RESULTS

We found that chemical inhibition of topoisomerase 1 (Top1), an enzyme that unwinds DNA, suppresses the expression of infection-induced genes with little to no effect on housekeeping gene expression and without cellular damage. In vitro, depletion or chemical inhibition of Top1 in epithelial cells and macrophages suppresses the host response against influenza and Ebola viruses as well as bacterial products. At the mechanistic level, as shown by chemical genetics and epigenetic approaches, Top1 inhibition primarily suppresses RNA polymerase II (RNAPII) activity at pathogen-associated molecular pattern (PAMP)–induced genes. These genes require SWI/SNF chromatin remodeling for activation and display unique genetic and epigenetic features, such as the presence of IRF3 binding sites, low basal levels of RNAPII, histone H3 Lys27 acetylation marks, DNA hypersensitivity, and CpG islands. This gene “signature” of specificity was also validated using public data sets. In vivo, Top1 inhibition therapy rescued 70 to 90% mortality caused by exacerbated inflammation in three mouse models: acute bacteria infection, liver failure, and virus-bacteria co-infection. Strikingly, one to three doses of inhibitors were sufficient for the protective effect in all models, without overt side effects.

CONCLUSION

The inflammatory immune response against microbes is essential in protecting us against infections. In some cases, such as highly pathogenic and pandemic infections, the organism turns against itself and responds too acutely, with an excessive inflammation that can have fatal consequences. Our results suggest that a therapy based on Top1 inhibition could save millions of people affected by sepsis, pandemics, and many congenital deficiencies associated with acute inflammatory episodes and “cytokine storms.”

CREDIT: RYGER/SHUTTERSTOCK

Abstract

The host innate immune response is the first line of defense against pathogens and is orchestrated by the concerted expression of genes induced by microbial stimuli. Deregulated expression of these genes is linked to the initiation and progression of diseases associated with exacerbated inflammation. We identified topoisomerase 1 (Top1) as a positive regulator of RNA polymerase II transcriptional activity at pathogen-induced genes. Depletion or chemical inhibition of Top1 suppresses the host response against influenza and Ebola viruses as well as bacterial products. Therapeutic pharmacological inhibition of Top1 protected mice from death in experimental models of lethal inflammation. Our results indicate that Top1 inhibition could be used as therapy against life-threatening infections characterized by an acutely exacerbated immune response.

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