Browsing by Author "Pradhan, Kisha"

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    Development of Exhausted Memory Monocytes and Underlying Mechanisms
    Pradhan, Kisha; Yi, Ziyue; Geng, Shuo; Li, Liwu (2021-10-28)
    Pathogenic inflammation and immuno-suppression are cardinal features of exhausted monocytes increasingly recognized in septic patients and murine models of sepsis. However, underlying mechanisms responsible for the generation of exhausted monocytes have not been addressed. In this report, we examined the generation of exhausted primary murine monocytes through prolonged and repetitive challenges with high dose bacterial endotoxin lipopolysaccharide (LPS). We demonstrated that repetitive LPS challenges skew monocytes into the classically exhausted Ly6C(hi) population, and deplete the homeostatic non-classical Ly6C(lo) population, reminiscent of monocyte exhaustion in septic patients. scRNAseq analyses confirmed the expansion of Ly6C(hi) monocyte cluster, with elevation of pathogenic inflammatory genes previously observed in human septic patients. Furthermore, we identified CD38 as an inflammatory mediator of exhausted monocytes, associated with a drastic depletion of cellular NAD(+); elevation of ROS; and compromise of mitochondria respiration, representative of septic monocytes. Mechanistically, we revealed that STAT1 is robustly elevated and sustained in LPS-exhausted monocytes, dependent upon the TRAM adaptor of the TLR4 pathway. TRAM deficient monocytes are largely resistant to LPS-mediated exhaustion, and retain the non-classical homeostatic features. Together, our current study addresses an important yet less-examined area of monocyte exhaustion, by providing phenotypic and mechanistic insights regarding the generation of exhausted monocytes.
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    Dose-dependent effects of endotoxin on monocyte and the underlying mechanisms
    Pradhan, Kisha (Virginia Tech, 2022-01-24)
    Monocytes are dynamic innate immune cells that respond differently based upon the dose and duration of an infection. While super low dose endotoxin is found in chronic inflammatory diseases such as atherosclerosis, exposure to high dose endotoxin leads to sepsis. However, clear characterization of monocytes and the underlying mechanisms in these disease conditions is lacking. To elucidate the missing information, we conducted two different projects. In the first project, we investigated the role of super low dose endotoxin in polarizing monocytes to a prolonged low-grade inflammatory state with no resolution, disrupting homeostasis. This low grade inflammatory phenotype was confirmed by sustained induction of inflammatory mediators CD40 and CD11a. In addition, low grade inflammatory monocytes influence neighboring T cells by suppressing T cell regulatory functions. Mechanistically, we showed that the non-resolving inflammatory phenotypes in monocytes is dependent on non-traditional TLR4 adaptor called TRAM. In the second project, we focused on the effects of high dose endotoxin on monocyte phenotypes. We reported that high dose endotoxin give rise to a mix of both immunosuppressive and pathogenic inflammatory monocytes, leading to monocyte exhaustion. While thorough research is conducted to study the immunosuppressive monocytes and underlying long term effects, role of pathogenic inflammatory monocytes is not well addressed. Monocyte exhaustion leads to elevated levels of CD38, an inflammatory mediator, elevated ROS levels, depleted NAD+ and mitochondrial respiration. STAT1 and KLF4 are critical transcription factors in sustaining exhausted phenotypes. Indeed, TRAM adaptor molecule also mediates this exhaustion as TRAM deletion restores monocyte health. Taken together, our work defines novel monocyte phenotypes and mechanism in super-low dose or high dose endotoxin environments.
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    TICAM2-related pathway mediates neutrophil exhaustion
    Lin, RuiCi; Zhang, Yao; Pradhan, Kisha; Li, Liwu (2020-09-01)
    Pathogenic inflammation and immune suppression are the cardinal features that underlie the pathogenesis of severe systemic inflammatory syndrome and sepsis. Neutrophil exhaustion may play a key role during the establishment of pathogenic inflammation and immune suppression through elevated expression of inflammatory adhesion molecules such as ICAM1 and CD11b as well as immune-suppressors such as PD-L1. However, the mechanism of neutrophil exhaustion is not well understood. We demonstrated that murine primary neutrophils cultured in vitro with the prolonged lipopolysaccharides (LPS) stimulation can effectively develop an exhaustive phenotype resembling human septic neutrophils with elevated expression of ICAM1, CD11b, PD-L1 as well as enhanced swarming and aggregation. Mechanistically, we observed that TICAM2 is involved in the generation of neutrophil exhaustion, as TICAM2 deficient neutrophils have the decreased expression of ICAM1, CD11b, PD-L1, and the reduced aggregation following the prolonged LPS challenge as compared to wild type (WT) neutrophils. LPS drives neutrophil exhaustion through TICAM2 mediated activation of Src family kinases (SFK) and STAT1, as the application of SFK inhibitor Dasatinib blocks neutrophil exhaustion triggered by the prolonged LPS challenge. Functionally, TICAM2 deficient mice were protected from developing severe systemic inflammation and multi-organ injury following the chemical-induced mucosal damage. Together, our data defined a key role of TICAM2 in facilitating neutrophil exhaustion and that targeting TICAM2 may be a potential approach to treating the severe systemic inflammation.