Liver X receptor agonist GW3965 protects against sepsis by promoting myeloid derived suppressor cells apoptosis in mice

Eliminating myeloid-derived suppressor cells alleviates immunosuppression and reduces susceptibility to secondary infections in a two-hit sepsis model

Myeloid-derived suppressor cells (MDSCs) are known for their immunosuppressive effects on both innate and adaptive immunity, particularly targeting T cells, and they undergo continuous expansion during sepsis. However, the pathophysiological significance of MDSCs in sepsis-induced immunosuppression remains to be fully elucidated. In this study, we investigated the dynamic changes in MDSCs during sepsis and their contribution to sepsis-induced immunosuppression using a clinically relevant "two-hit" sepsis model. Our findings revealed that mice surviving cecal ligation and puncture (CLP) exhibited a significant accumulation and enhanced activity of MDSCs, which correlated with sepsis-related immune paralysis, impaired bacterial clearance, and heightened susceptibility to secondary infections. Importantly, administration of the liver X receptor (LXR) agonist GW3965 at the late stage of sepsis significantly restored immune function, decreased susceptibility to secondary infections, enhanced bacterial clearance, and improved prognosis by eliminating MDSCs. These results highlight the pivotal role of MDSCs in the development of sepsis-associated immunosuppression and indicate that targeting MDSCs could be a promising therapeutic approach to mitigate immunosuppression in sepsis.

HDL Nanodiscs Loaded with Liver X Receptor Agonist Decreases Tumor Burden and Mediates Long-term Survival in Mouse Glioma Model

Glioblastoma multiforme (GBM) is a highly aggressive primary brain tumor with a 5-year survival rate of 7%. Previous studies have shown that GBM tumors have a reduced capacity to produce cholesterol and instead depend on the uptake of cholesterol produced by astrocytes. To target cholesterol metabolism to induce cancer cell death, synthetic high-density lipoprotein (sHDL) nanodiscs delivering Liver-X-Receptor (LXR) agonists and CpG oligonucleotides for targeting GBM are investigated. LXR agonists synergize with sHDL nanodiscs by increasing the expression of the ABCA1 cholesterol efflux transporter, resulting in further depletion of cholesterol reserves within tumors, and CpG oligonucleotides are established adjuvants used in cancer immunotherapy that work through the toll-like receptor 9 pathway. In the present study, treatment with GW-CpG-sHDL nanodiscs increases the expression of cholesterol efflux transporters on murine GL261 cells leading to enhanced cholesterol removal. Experiments in GL261-tumor-bearing mice reveal combining GW-CpG-sHDL nanodiscs with radiation (IR) therapy significantly increases median survival compared to GW-CpG-sHDL or IR alone. Furthermore, 66% of long-term survivors from the GW-CpG-sHDL +IR treatment group show no tumor tissue when rechallenged.

CD47-amyloid-β-CD74 signaling triggers adaptive immunosuppression in sepsis

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. However, how this dysregulation occurs remains to be elucidated. In this study, we use single-cell RNA sequencing (scRNA-seq) and conventional RNA-seq to analyze the immune landscape of sepsis and observe that adaptive immunity is acutely and strongly suppressed. This systemic immunosuppression occurs not only in the peripheral blood but also in all other immune compartments, including the spleen, lymph nodes, and bone marrow. Clinical data show that these adaptive immunity-related genes may have the potential to be used to distinguish patients with sepsis from those with common infections. CD47 is found to play a pivotal role in this immunosuppression by inducing the production of amyloid-β (Aβ), which interacts with CD74 on B cells, leading to B-cell suppression and subsequent adaptive immunosuppression. Blocking CD47-Aβ signaling significantly reduces organ injury and improves the survival rate of septic mice by restoring phagocytic cell functions and alleviating B-cell suppression and adaptive immunosuppression.

HDL Nanodiscs Loaded with Liver X Receptor Agonist Decreases Tumor Burden and Mediates Long-term Survival in Mouse Glioma Model

Glioblastoma multiforme (GBM) is highly aggressive primary brain tumor with a 5-year survival rate of 7%. Previous studies have shown that GBM tumors have a reduced capacity to produce cholesterol and instead depend on the uptake of cholesterol produced by astrocytes. To target cholesterol metabolism to induce cancer cell death, synthetic high-density lipoprotein (sHDL) nanodiscs delivering Liver-X-Receptor (LXR) agonists and CpG oligonucleotides for targeting GBM were investigated. LXR agonists synergize with sHDL nanodiscs by increasing the expression of the ABCA1 cholesterol CpG oligonucleotides are established adjuvants used in cancer immunotherapy that work through the toll-like receptor 9 pathway. In the present study, treatment with GW-CpG-sHDL nanodiscs increased the expression of cholesterol efflux transporters on murine GL261 cells leading to enhanced cholesterol removal. Experiments in GL261-tumor-bearing mice revealed combining GW-CpG-sHDL nanodiscs with radiation (IR) therapy significantly increases median survival compared to GW-CpG-sHDL or IR alone. Furthermore, 66% of long-term survivors from the GW-CpG-sHDL +IR treatment group showed no tumor tissue when rechallenged.

Diethylhexyl phthalate induces immune dysregulation and is an environmental immune disruptor

Diethylhexyl phthalate (DEHP) is the most abundant phthalate compound in the environment, and has been linked with multiple human diseases. The immune system is closely associated with the occurrence and progression of various diseases. However, minimal research has addressed the impact of DEHP on the immune system. In this study, single-cell RNA sequencing was performed using spleen tissue of mice to comprehensively determine alterations of the immune system in response to DEHP. The results showed that DEHP exposure reduced the absolute number of peripheral white blood cells (WBCs), including lymphocytes, monocytes, eosinophils, basophils, and neutrophils in mice. In addition, scRNA-seq analyses showed that inflammatory signaling and the expression of heat shock proteins (HSPs) were reduced in all peripheral immune cell populations. Furthermore, we established a mice cecal ligation and puncture (CLP) model, and showed that DEHP exacerbated sepsis-induced immunosuppression and organ damage. These results suggest that DEHP is an environmental immune disruptor that undermines the immune system, exacerbating acute infections and organ damage. Our findings offer a novel perspective on the hazards of DEHP to human health.

A critical role for HNF4α in polymicrobial sepsis-associated metabolic reprogramming and death

In sepsis, limited food intake and increased energy expenditure induce a starvation response, which is compromised by a quick decline in the expression of hepatic PPARα, a transcription factor essential in intracellular catabolism of free fatty acids. The mechanism upstream of this PPARα downregulation is unknown. We found that sepsis causes a progressive hepatic loss-of-function of HNF4α, which has a strong impact on the expression of several important nuclear receptors, including PPARα. HNF4α depletion in hepatocytes dramatically increases sepsis lethality, steatosis, and organ damage and prevents an adequate response to IL6, which is critical for liver regeneration and survival. An HNF4α agonist protects against sepsis at all levels, irrespectively of bacterial loads, suggesting HNF4α is crucial in tolerance to sepsis. In conclusion, hepatic HNF4α activity is decreased during sepsis, causing PPARα downregulation, metabolic problems, and a disturbed IL6-mediated acute phase response. The findings provide new insights and therapeutic options in sepsis.

The role of trained immunity in sepsis

Sepsis is defined as a life-threatening organ dysfunction syndrome caused by dysregulated host response to infection, characterized by a systemic inflammatory response to infection. The use of antibiotics, fluid resuscitation, and organ support therapy has limited prognostic benefit in patients with sepsis, and its incidence is not diminishing, which is attracting increased attention in medicine. Sepsis remains one of the most debilitating and expensive illnesses. One of the main reasons of septic mortality is now understood to be disruption of immune homeostasis. Immunotherapy is revolutionizing the treatment of illnesses in which dysregulated immune responses play a significant role. This "trained immunity", which is a potent defense against infection regardless of the type of bacteria, fungus, or virus, is attributed to the discovery that the innate immune cells possess immune memory via metabolic and epigenetic reprogramming. Here we reviewed the immunotherapy of innate immune cells in sepsis, the features of trained immunity, and the relationship between trained immunity and sepsis.

Protective effect of omega-3 polyunsaturated fatty acids on sepsis via the AMPK/mTOR pathway

CONTEXT

Sepsis is a systemic inflammatory response caused by infection, with high morbidity and mortality. Omega-3 polyunsaturated fatty acids (ω-3 PUFAs) have reported biological activities.

OBJECTIVE

This study explored the signaling pathways through which ω-3 PUFAs protect against sepsis-induced multiorgan failure.

MATERIALS AND METHODS

Septic Sprague-Dawley (SD) rat model was established by the cecum ligation perforation (CLP) method. Rats were divided into control, sham, model, parenteral ω-3 PUFAs (0.5 g/kg) treatment, ω-3 PUFAs (0.5 g/kg) + AMPK inhibitor Compound C (30 mg/kg) treatment, and ω-3 PUFAs (0.5 g/kg) + mTOR activator MHY1485 (10 mg/kg) treatment groups. The serum inflammatory cytokines were measured using ELISA. Organ damage-related markers cTnI, CK, CK-MB, Cr, BUN, ALT, and AST were measured using an automated chemical analyzer. The AMPK/mTOR pathway in liver, kidney, and myocardial tissues was detected using western blot and qRT-PCR methods.

RESULTS

CLP treatment enhanced the secretion of pro-inflammatory cytokines and multi-organ related markers, along with increased p-AMPK/AMPK ratio (from 0.47 to 0.87) and decreased p-mTOR/mTOR ratio (from 0.33 to 0.12) in rats. The inflammation response and multi-organ injury induced by CLP treatment could be partially counteracted by 0.5 g/kg parenteral ω-3 PUFA treatment. The activated AMPK/mTOR pathway in CLP-induced rats was further promoted. Finally, Compound C and MHY1485 could reverse the effects of parenteral ω-3 PUFA treatment on sepsis rats.

DISCUSSION AND CONCLUSION

ω-3 PUFAs ameliorated sepsis development by activating the AMPK/mTOR pathway, serving as a potent therapeutic agent for sepsis. Further in vivo studies may validate potential clinical use.

MDSCs in sepsis-induced immunosuppression and its potential therapeutic targets

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. In sepsis, a complicated immune response is initiated, which varies over time with sustained excessive inflammation and immunosuppression. Identifying a promising way to orchestrate sepsis-induced immunosuppression is a challenge. Myeloid-derived suppressor cells (MDSCs) comprise pathologically activated neutrophils and monocytes with potent immunosuppressive activity. They play an important part in inhibiting innate and adaptive immune responses, and have emerged as part of the immune response in sepsis. MDSCs numbers are persistently high in sepsis patients, and associated with nosocomial infections and other adverse clinical outcomes. However, their characteristics and functional mechanisms during sepsis have not been addressed fully. Our review sheds light on the features and suppressive mechanism of MDSCs. We also review the potential applications of MDSCs as biomarkers and targets for clinical treatment of sepsis.