Pneumolysin is responsible for differential gene expression and modifications in the epigenetic landscape of primary monocyte derived macrophages

Abstract

14 15 2 16 Abstract: 17 Epigenetic modifications regulate gene expression in the host response to a 18 diverse range of pathogens. The extent and consequences of epigenetic modification 19 during macrophage responses to Streptococcus pneumoniae, and the role of 20 pneumolysin, a key Streptococcus pneumoniae virulence factor, in influencing these 21 responses, are currently unknown. To investigate this, we infected human monocyte 22 derived macrophages (MDMs) with Streptococcus pneumoniae and addressed 23 whether pneumolysin altered the epigenetic landscape and the associated acute 24 macrophage transcriptional response using a combined transcriptomic and proteomic 25 approach. Transcriptomic analysis identified 503 genes that were differentially 26 expressed in a pneumolysin-dependent manner in these samples. Pathway analysis 27 highlighted the involvement of transcriptional responses to core innate responses to 28 pneumococci including modules associated with metabolic pathways activated in 29 response to infection, oxidative stress responses and NFB, NOD-like receptor and 30 TNF signalling pathways. Quantitative proteomic analysis confirmed pneumolysin-31 regulated protein expression, early after bacterial challenge, in representative 32 transcriptional modules associated with innate immune responses. In parallel, 33 quantitative mass spectrometry identified global changes in the relative abundance of 34 histone post translational modifications (PTMs) upon pneumococcal challenge. We 35 identified an increase in the relative abundance of H3K4me1, H4K16ac and a 36 decrease in H3K9me2 and H3K79me2 in a PLY-dependent fashion. We confirmed 37 that pneumolysin blunted early transcriptional responses involving TNF-α and IL-6 38 expression. Vorinostat, a histone deacetylase inhibitor, similarly downregulated TNF 39 production, reprising the pattern observed with pneumolysin. In conclusion, 40 widespread changes in the macrophage transcriptional response are regulated by 3 41 pneumolysin and are associated with global changes in histone PTMs. Modulating 42 histone PTMs can reverse pneumolysin-associated transcriptional changes 43 influencing innate immune responses, suggesting that epigenetic modification by 44 pneumolysin plays a role in dampening the innate responses to pneumococci. 45 46 Author summary: 47 Pneumolysin is a toxin that contributes to how Streptococcus pneumoniae, the 48 leading cause of pneumonia, causes disease. In this study, the toxin alters gene 49 expression in immune cells called macrophages, one of the first lines of defence 50 against bacteria at sites of infection. Modulation involved multiple immune responses, 51 including generation of chemical signals coordinating responses in immune cells 52 termed cytokines. In addition, changes were observed in histone proteins that are 53 involved in controlling gene expression in the cell. Pneumolysin reduced early54 production of the cytokine TNF-α and a medicine vorinostat that modifies these 55 'epigenetic' histone modifications had a similar affec...

Host-informed therapies for the treatment of pneumococcal pneumonia

“…Both canonical nonselective autophagy and noncanonical autophagy observed in phagocytic cells (LAP) are vital defense systems against engulfed S. pneumoniae, contributing to rapid phagosome delivery to lysosomes and efficient bacterial killing [68][69][70][71]. To avoid clearance by these mechanisms, S. pneumoniae engages in autophagy evasion strategies when inside the phagosome.…”