Proteome profiling identifies a link between the mitochondrial pathways and host-microbial sensor ELMO1 following...

The host EnguLfment and cell MOtility protein 1 (ELMO1) is a cytosolic microbial sensor that facilitates bacterial sensing, internalization, clearance, and inflammatory responses. We have shown previously that ELMO1 binds bacterial effector proteins, including pathogenic effectors from Salmonella and controls host innate immune signaling. To understand the ELMO1-regulated host pathways, we have performed liquid chromatography Multinotch MS3-Tandem Mass Tag (TMT) multiplexed proteomics to determine the global quantification of proteins regulated by ELMO1 in macrophages during Salmonella infection. Comparative proteome analysis of control and ELMO1-depleted murine J774 macrophages after Salmonella infection quantified more than 7000 proteins with a notable enrichment in mitochondrial-related proteins. Gene ontology enrichment analysis revealed 19 upregulated and 11 downregulated proteins exclusive to ELMO1-depleted cells during infection, belonging to mitochondrial functions, metabolism, vesicle transport, and the immune system. By assessing the cellular energetics via Seahorse analysis, we found that Salmonella infection alters mitochondrial metabolism, shifting it from oxidative phosphorylation to glycolysis. Importantly, these metabolic changes are significantly influenced by the depletion of ELMO1. Furthermore, ELMO1 depletion resulted in a decreased ATP rate index following Salmonella infection, indicating its importance in counteracting the effects of Salmonella on immunometabolism. Among the proteins involved in mitochondrial pathways, mitochondrial fission protein DRP1 was significantly upregulated in ELMO1-depleted cells and in ELMO1-KO mice intestine following Salmonella infection. Pharmacological Inhibition of DRP1 revealed the link of the ELMO1-DRP1 pathway in regulating the pro-inflammatory cytokine TNF-α following infection. The role of ELMO1 has been further characterized by a proteome profile of ELMO1-depleted macrophage infected with SifA mutant and showed the involvement of ELMO1-SifA on mitochondrial function, metabolism and host immune/defense responses. Collectively, these findings unveil a novel role for ELMO1 in modulating mitochondrial functions, potentially pivotal in modulating inflammatory responses.

Host microbial sensing is critical in infection and inflammation. Among these sensors, ELMO1 has emerged as a key regulator, finely tuning innate immune signaling and discriminating between pathogenic and non-pathogenic bacteria through interactions with microbial effectors like SifA of Salmonella . In this study, we employed Multinotch MS3-Tandem Mass Tag (TMT) multiplexed proteomics to determine the proteome alterations mediated by ELMO1 in macrophages following WT and SifA mutant Salmonella infection. Our findings highlight a substantial enrichment of host proteins associated with metabolic pathways and mitochondrial functions. Notably, we validated the mitochondrial fission protein DRP1 that is upregulated in ELMO1-depleted macrophages and in ELMO1 knockout mice intestine after infection. Furthermore, we demonstrated that Salmonella -induced changes in cellular energetics are influenced by the presence of ELMO1. This work shed light on a possible novel link between mitochondrial dynamics and microbial sensing in modulating immune responses.