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AimsIn spite of current medical treatment approaches, mortality of chronic heart failure (HF) remains high and novel treatment modalities are thus urgently needed. A recent theory proposes a possible impact of the intestinal microbiome on the incidence and clinical course of heart failure. This study sought to systematically investigate, if there are specific changes of the intestinal microbiome in heart failure patients.Methods and resultsThe intestinal microbiome of 20 patients with heart failure with reduced ejection fraction due to ischemic or dilated cardiomyopathy was investigated by applying high‐throughput sequencing of the bacterial 16S rRNA gene. Microbial profiles were compared to those of matched controls in which heart failure was ruled out by clinical assessment and NT‐proBNP serum levels (n = 20). According to the Shannon diversity index (which measures the intra‐individual alpha‐diversity) based on the distribution of operational taxonomic units (OTUs), HF cases showed a nominally significantly lower diversity index compared to controls (P nom. = 0.01), and testing for genera abundance showed a tendency towards a decreased alpha diversity of HF patients. Beta‐diversity measures (inter‐individual diversity) revealed a highly significant separation of HF cases and controls, (e.g. P weighted UniFracv = 0.004). Assessing the individual abundance of core measurable microbiota (CMM), a significant decrease of Coriobacteriaceae, Erysipelotrichaceae and Ruminococcaceae was observed on the family level. In line with that, Blautia, Collinsella, uncl. Erysipelotrichaceae and uncl. Ruminococcaceae showed a significant decrease in HF cases compared to controls on the genus level.ConclusionsHeart failure patients showed a significantly decreased diversity of the intestinal microbiome as well as a downregulation of key intestinal bacterial groups. Our data point to an altered intestinal microbiome as a potential player in the pathogenesis and progression of heart failure.

Enteric infections with attaching/effacing lesion-inducing bacterial pathogens are a worldwide health problem. A murine infection model with one such pathogen, Citrobacter rodentium, was used to elucidate the importance of the pleiotropic immune regulator, IL-6, in the pathogenesis of infection. IL-6 was strongly induced in colonic epithelial cells and macrophages upon C. rodentium infection and was required for effective host defense, because mice lacking IL-6 failed to control bacterial numbers 2–3 wk after infection and exhibited increased mortality. IL-6 was not needed for mounting effective T and B cell responses to the pathogens, nor was it important for induction of IFN-γ or TNF-α, cytokines involved in host defense against the bacteria, or the antibacterial effector, NO. Instead, IL-6 played a key role in mucosal protection, since its absence was associated with marked infection-induced apoptosis in the colonic epithelium and subsequent ulcerations. Cell culture studies confirmed that IL-6 protected colon epithelial cells directly against inducible apoptosis, which was accompanied by increased expression of an array of genes encoding antiapoptotic proteins, including Bcl-xL, Mcl-1, cIAP-2, and Bcl-3. Ulcerations appeared to be pathogenetically important, because bacteria localized preferentially to those regions, and chemically induced colonic ulcerations promoted bacterial colonization. Furthermore, blood components likely present in ulcer exudates, particularly alanine, asparagine, and glycine, promoted bacterial growth. Thus, IL-6 is an important regulator of host defense against C. rodentium by protecting the mucosa against ulcerations which can act as a microbial niche for the bacteria.

Hypomorphic mutations in the DNA repair enzyme RNase H2 cause the neuroinflammatory autoimmune disorder Aicardi-Goutières syndrome (AGS). Endogenous nucleic acids are believed to accumulate in patient cells and instigate pathogenic type I interferon expression. However, the underlying nucleic acid species amassing in the absence of RNase H2 has not been established yet. Here, we report that murine RNase H2 knockout cells accumulated cytosolic DNA aggregates virtually indistinguishable from micronuclei. RNase H2-dependent micronuclei were surrounded by nuclear lamina and most of them contained damaged DNA. Importantly, they induced expression of interferon-stimulated genes (ISGs) and co-localized with the nucleic acid sensor cGAS. Moreover, micronuclei associated with RNase H2 deficiency were cleared by autophagy. Consequently, induction of autophagy by pharmacological mTOR inhibition resulted in a significant reduction of cytosolic DNA and the accompanied interferon signature. Autophagy induction might therefore represent a viable therapeutic option for RNase H2-dependent disease. Endogenous retroelements have previously been proposed as a source of self-nucleic acids triggering inappropriate activation of the immune system in AGS. We used human RNase H2-knockout cells generated by CRISPR/Cas9 to investigate the impact of RNase H2 on retroelement propagation. Surprisingly, replication of LINE-1 and Alu elements was blunted in cells lacking RNase H2, establishing RNase H2 as essential host factor for the mobilisation of endogenous retrotransposons.