Browsing by Author "Christman, John W."

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    Exosomal Transfer of DNA Methyl-Transferase mRNA Induces an Immunosuppressive Phenotype in Human Monocytes
    (Wolters Kluwer, 2022) Wisler, Jon R.; Singh, Kanhaiya; McCarty, Adara; Harkless, Ryan; Karpurapu, Manjula; Hernandez, Edward; Mukherjee, Debasmita; Abouhashem, Ahmed S.; Christman, John W.; Sen, Chandan K.; Surgery, School of Medicine
    Introduction: Survivors of sepsis exhibit persistent immunosuppression. Epigenetic events may be responsible for some of these immunosuppressive changes. During sepsis circulating exosomes contain large quantities of DNA methyltransferase (DNMT) mRNAs. We hypothesized that exosomes directly transfer DNMT mRNAs to recipient monocytes with resultant methylation events and immunosuppression. Methods: Exosomes containing DNMT mRNA were generated by stimulating monocytes with LPS. Confocal microscopy was used to determine uptake kinetics in the presence of pharmacologic inhibition. Expression and packaging of specific DNMT mRNA was controlled using DNMT siRNAs. Whole genome and gene specific methylation was assessed using bisulfite sequencing. Ingenuity pathway analysis was performed to determine the biological function of significance of differentially methylated regions. Results: Exosomes effectively transferred DNMT mRNA to recipient monocytes. Pharmacologic inhibition of exosome uptake prevented this increase in DNMT mRNA expression. Recipient monocytes exhibited hypermethylation changes and gene suppression. siRNAs decreased the packaging of DNMT mRNAs and prevented TNFα gene suppression, restoring immunocompetence. Conclusion: These data support a role for exosome-mediated transfer of DNMT mRNA with resultant methylation and gene silencing. Pharmacologic uptake inhibition or targeted siRNA mediated DNMT gene silencing prevented DNMT mRNA transfer and maintained the cell's ability to express TNFα in response to LPS. This highlights the potential therapeutic value of targeting these exosome-mediated epigenetic events to maintain the host immune response during sepsis.
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    Proteomic Pathway Analysis of Monocyte-Derived Exosomes during Surgical Sepsis Identifies Immunoregulatory Functions
    (Mary Ann Liebert, Inc., 2020-03) Wisler, Jon R.; Singh, Kanhaiya; Mccarty, Adara R.; Abouhashem, Ahmed Safwat Elsayed; Christman, John W.; Sen, Chandan K.; Surgery, School of Medicine
    Background: Patients with sepsis exhibit significant long-term immunosuppressive sequelae. Monocyte dysfunction is a hallmark of this damage. Circulating exosomes are an important mediator of the systemic signaling events that occur during the septic response; thus, we sought to characterize the contribution of circulating exosomes to the inflammatory process induced during sepsis Methods: Monocyte-derived exosomes were isolated from cultured monocytes from healthy adult donors via stimulation with lipopolysaccharide (LPS) or phosphate-buffered saline (PBS). The proteome was determined by capillary-liquid chromatography-nanospray tandem mass spectrometry (capillary-LC/NT/MS). Using pathway analysis, proteomic networks of exosomes derived from LPS-stimulated monocytes were compared with those isolated from patients with surgical sepsis. Naïve monocytes were then treated with these exosomes and stimulated with LPS to determine the effects on recipient-cell immune function. Results: Proteomic analysis demonstrated 18 differentially expressed proteins (17 down-regulated, one up-regulated) in sepsis-derived exosomes, with 15 differentially expressed proteins (14 down-regulated, one up-regulated) in the LPS-stimulated exosomes. Functional enrichment analysis demonstrated several down-regulated processes, including localization, biogenesis, and metabolic and cellular processes in addition to immune system processes. In LPS-stimulated macrophages, similar down-regulated processes were seen, including metabolic and cellular processes, as well as the response to stimulus. Cells treated with sepsis-derived exosomes or exosomes from LPS-stimulated monocytes demonstrated significant reductions in tumor necrosis factor (TNF)-α generation in response to LPS stimulation. Conclusions: Proteomic analysis of sepsis-derived exosomes and LPS-stimulated, macrophage-derived exosomes exhibited down-regulation of several important protein networks, including the immune response. In addition, human monocytes treated with exosomes from patients with sepsis or LPS-stimulated monocytes demonstrated significant reductions in TNF-α generation in response to LPS stimulation. These data suggest the contribution of circulating exosomes to systemic signaling and immunomodulation during sepsis.