Koehler, H. | bioRxiv Science

bioRxiv2024

Caspase-8 activity mediates TNFα production and restricts Coxiella burnetii replication during murine macrophage infection

Coxiella burnetii is an obligate intracellular bacteria which causes the global zoonotic disease Q Fever. Treatment options for infection are limited, and development of novel therapeutic strategies requires a greater understanding of how C. burnetii interacts with immune signaling. Cell death responses are known to be manipulated by C. burnetii, but the role of caspase-8, a central regulator of multiple cell death pathways, has not been investigated. In this research, we studied bacterial manipulation of caspase-8 signaling and the significance of caspase-8 to C. burnetii infection, examining bacterial replication, cell death induction, and cytokine signaling. We measured caspase, RIPK, and MLKL activation in C. burnetii-infected TNF/CHX-treated THP-1 macrophage-like cells and TNF/ZVAD-treated L929 cells to assess apoptosis and necroptosis signaling. Additionally, we measured C. burnetii replication, cell death, and TNF induction over 12 days in RIPK1-kinase-dead, RIPK3-kinase-dead, or RIPK3-kinase-dead-caspase-8-/- BMDMs to understand the significance of caspase-8 and RIPK1/3 during infection. We found that caspase-8 is inhibited by C. burnetii, coinciding with inhibition of apoptosis and increased susceptibility to necroptosis. Furthermore, C. burnetii replication was increased in BMDMs lacking caspase-8, but not in those lacking RIPK1/3 kinase activity, corresponding with decreased TNF production and reduced cell death. As TNF is associated with the control of C. burnetii, this lack of a TNF response may allow for the unchecked bacterial growth we saw in caspase-8-/- BMDMs. This research identifies and explores caspase-8 as a key regulator of C. burnetii infection, opening novel therapeutic doors.

microbiology↗

bioRxiv2023

Viral genomic features predict orthopoxvirus reservoir hosts

Orthopoxviruses (OPVs), including the causative agents of smallpox and mpox have led to devastating outbreaks in human populations worldwide. However, the discontinuation of smallpox vaccination, which also provides cross-protection against related OPVs, has diminished global immunity to OPVs more broadly. We apply machine learning models incorporating both host ecological and viral genomic features to predict likely reservoirs of OPVs. We demonstrate that incorporating viral genomic features in addition to host ecological traits enhanced the accuracy of potential OPV host predictions, highlighting the importance of host-virus molecular interactions in predicting potential host species. We identify hotspots for geographic regions rich with potential OPV hosts in parts of southeast Asia, equatorial Africa, and the Amazon, revealing high overlap between regions predicted to have a high number of potential OPV host species and those with the lowest smallpox vaccination coverage, indicating a heightened risk for the emergence or establishment of zoonotic OPVs. Our findings can be used to target wildlife surveillance, particularly related to concerns about mpox establishment beyond its historical range.

microbiology↗

bioRxiv2022

The host-directed therapeutic imatinib mesylate accelerates immune responses to Mycobacterium marinum infection and limits pathology associated with granulomas

Mycobacterial infections, including those caused by members of the mycobacterium tuberculosis complex [MTC] and Nontuberculous mycobacteria [NTM], can induce widespread morbidity and mortality in people. Mycobacterial infections cause both a delayed immune response, which limits rate of bacterial clearance, and formation of granulomas, which contain bacterial spread, but also contribute to lung damage, fibrosis, and morbidity. Granulomas also limit access of antibiotics to bacteria, which may facilitate development of resistance. MTC members resistant to some or all antibiotics are estimated to account for a third of deaths from tuberculosis [TB], and newly developed antibiotics have already engendered resistance, pointing to the need for new therapeutic approaches. Imatinib mesylate, a cancer drug used to treat chronic myelogenous leukemia [CML] that targets Abl and related tyrosine kinases, is a possible host-directed therapeutic [HDT] for mycobacterial infections, including TB. Here, we use the murine Mycobacterium marinum [Mm] infection model, which forms quantifiable granulomas on the tails, in conjunction with transcriptomic analysis of the tail lesions. The data indicate that imatinib induces gene signatures indicative of immune activation at early time points post infection that resemble those seen at later ones, suggesting that imatinib accelerates but does not substantially alter anti-mycobacterial immune responses. Moreover, focusing on the TNF pathway, which is induced by imatinib, we show that imatinib promotes cell survival in infected bone marrow-derived macrophages [BMDMs] in a manner that depends on caspase 8. Moreover, imatinib limits formation and growth of granulomas, an effect abrogated in mice lacking caspase 8. These data provide evidence for the utility of imatinib as an HDT for mycobacterial infections in accelerating immune responses, and limiting pathology associated with granulomas, and thus mitigating post-treatment morbidity. Author SummaryMycobacterial infections remain an important cause of morbidity and mortality in humans; for example, Mycobacterium tuberculosis [Mtb], the cause of tuberculosis [TB], kills [~]1.5 million and newly infects [~]10 million each year. Although most people effectively combat mycobacterial infections, treatment is compromised in at-risk individuals by an indolent immune response and chronic inflammation, which results in granulomas that encase the bacteria and limit spread. Granulomas also contribute to tissue damage and limit access of antibiotics to bacteria, which engenders resistance. We proposed using imatinib mesylate, a host directed therapeutic [HDT], against mycobacteria. Imatinib, a cancer therapeutic that inhibits Abl and related tyrosine kinases, alters intracellular transit of bacteria during infection. Using systems biology approaches in conjunction with murine infections with Mycobacterium marinum, a close genetic relative of Mtb that forms tail granulomas, we report that imatinib does not fundamentally alter the anti-mycobacteria immune response, but rather accelerates it. In addition, imatinib limits granuloma formation and growth, an effect abrogated in mice lacking caspase 8. These data highlight imatinib as a possible HDT for mycobacterial infections including TB with the capacity to augment the immune response in at-risk individuals, and limit granuloma growth, thereby limiting tissue damage.

immunology↗