Reduced Expression of SARM in Mouse Spleen during Polymicrobial Sepsis

Toll-like receptor 2 deficiency relieves splenic immunosuppression during sepsis

Immunosuppression is associated with long-term mortality during sepsis. However, the underlying mechanism of immunosuppression remains poorly understood. Toll-like receptor 2 (TLR2) contributes to sepsis pathogenesis. We sought to determine the role of TLR2 in immunosuppression in the spleen during polymicrobial sepsis. Using an experimental model of polymicrobial sepsis induced by cecal ligation and puncture (CLP), we measured the expression of inflammatory cytokines and chemokines in spleen 6 and 24 h after CLP to evaluate the immune response, and compared the expression of inflammatory cytokines and chemokines, apoptosis, and intracellular ATP production in spleen of wild-type (WT) and TLR2-deficient (TLR2^-/-) mice 24 h after CLP. We found that pro-inflammatory cytokines and chemokines, such as TNF-α and IL-1β peaked 6 h after CLP, while IL-10, an anti-inflammatory cytokine, peaked 24 h after CLP in the spleen. At this later time point, TLR2^-/- mice presented decreased levels of IL-10 and decreased caspase 3 activation but no significant difference in intracellular ATP production in spleen compared to WT mice. Our data imply that TLR2 has a pronounced effect on sepsis-induced immunosuppression in spleen.

Longitudinal and simultaneous profiling of 11 modes of cell death in mouse retina post-optic nerve injury

Retinal ganglion cell (RGC) death is a critical pathological trigger leading to irreversible visual impairment and blindness after optic nerve (ON) injury. Yet, there is still no effective clinical treatment to rescue RGC death after ON injury. Understanding the involvement of different modes of cell death post-ON injury could facilitate the development of targeting treatments against RGC death. Herein we aimed to characterize the regulation of 11 modes of cell death simultaneously and longitudinally in mouse retina post-ON injury. The number of RGCs gradually decreased from Day 3-14 in mice post-ON injury. Increase in the apoptosis (cleaved caspase-3), autolysis (cleaved cathespin B) and pyroptosis (cleaved caspase-1) marker expression in the retina began at Day 3 post-ON injury. Meanwhile, the markers for autophagy (Atg7 and Becn1) and phagocytosis (Mfge8 and Mertk) were downregulated from Day 1 to Day 5. Additionally, the expression of ferroptosis marker (4-hydroxynonenal) was upregulated from Day 7 to Day 14 post-ON injury following the early reduction of Gpx4. Yet, the reduction of parthanatos, sarmoptosis, and mitochondrial permeable transition could be related to autophagy and apoptosis. The markers for necroptosis did not show significant changes post-ON injury. In summary, this study revealed that the activation of apoptosis, autolysis, pyroptosis and ferroptosis, together with the early downregulation of autophagy and phagocytosis, are the major modes of cell death involved in the RGC death post-ON injury. Simultaneously targeting multiple modes of cell death at different time courses could be a potential treatment approach against RGC death for traumatic optic neuropathy.

Aloe-Emodin Suppresses Oxidative Stress and Inflammation via a PI3K-Dependent Mechanism in a Murine Model of Sepsis

Background

This study was designed to assess the impact of aloe-emodin (AE) on oxidative stress and inflammation in a murine model of LPS-induced sepsis. In addition, the mechanistic basis for anti-inflammatory and antioxidant activity was assessed.

Methods

Male ICR mice received an intraperitoneal injection of LPS (10 mg/kg), and the preventive properties of AE (80 or 150 mg/kg) on these mice were assessed by monitoring spleen index, and levels of inflammatory and oxidative stress-related factors. Peripheral blood TNF-α and IL-6 levels were assessed via ELISA kits, while changes in hepatic SOD and GSH-Px levels were assessed using appropriate biochemical kits. Splenic PI3K, AKT, and mTOR levels were assessed via qPCR and western blotting.

Results

Relative to animals in the LPS model group, those in the AE treatment groups exhibited reduced spleen index, decreased inflammatory cytokine levels, and improved SOD and GSH-Px activity in liver tissues. Splenic PI3K, Akt, and mTOR levels were also reduced in response to AE treatment.

Conclusions

These findings indicated that AE can alleviate sepsis-related tissue damage, inflammation, and oxidative stress, at least in part by suppressing the PI3K/Akt/mTOR signaling pathway. These results offer a clinical basis for the use of AE to treat sepsis and associated diseases.

Therapeutic Potential of Extracellular Vesicles for Sepsis Treatment

Sepsis is a deadly condition lacking a specific treatment despite decades of research. This has prompted the exploration of new approaches, with extracellular vesicles (EVs) emerging as a focal area. EVs are nanosized, cell-derived particles that transport bioactive components (i.e., proteins, DNA, and RNA) between cells, enabling both normal physiological functions and disease progression depending on context. In particular, EVs have been identified as critical mediators of sepsis pathophysiology. However, EVs are also thought to constitute the biologically active component of cell-based therapies and have demonstrated anti-inflammatory, anti-apoptotic, and immunomodulatory effects in sepsis models. The dual nature of EVs in sepsis is explored here, discussing their endogenous roles and highlighting their therapeutic properties and potential. Related to the latter component, prior studies involving EVs from mesenchymal stem/stromal cells (MSCs) and other sources are discussed and emerging producer cells that could play important roles in future EV-based sepsis therapies are identified. Further, how methodologies could impact therapeutic development toward sepsis treatment to enhance and control EV potency is described.

Splenectomy provides protective effects against CLP-induced sepsis by reducing TRegs and PD-1/PD-L1 expression

The role of the spleen in sepsis is still controversial. Therefore, we investigated the effect of the spleen on sepsis-induced immune dysfunction in C57BL/6 mice subjected to caecal ligation and puncture (CLP). Changes in different immune cells and apoptotic cells in the spleen and peripheral blood were observed 4, 24 and 48 h after CLP. Then, we determined that 48 h following CLP was the most significant period of immunosuppression. Next, we divided the mice into four groups: control, CLP, CLP + spx (splenectomy 48 h after CLP) and spx + CLP (splenectomy surgery two weeks before CLP). Compared with the CLP mice, the CLP + spx and spx + CLP mice had improved survival rates and organ injuries, increased expression of inflammatory factors, a decreased proportion of regulatory T cells (Tregs), and reduced expression of the genes involved in the programmed cell death 1 and its ligand 1 (PD1-PDL1) pathway in immune cells and T-cell immunoglobulin-mucin domain 3 (Tim 3) and Galectin9 in the liver and lungs after 72 h in late-phase sepsis. In addition, the expression of PD-1 was significantly reduced in T cells in spx + CLP mice, and the expression of PD-L1 in myeloid-derived suppressor cells (MDSCs) was reduced in the CLP + spx group, especially in macrophages. These findings suggested that splenectomy could protect septic mice from exhaustion of immune cells by reducing the proliferation of Treg cells and expression of the PD-1/PD-L1 axis in immune cells during the immunosuppressive stage of sepsis. Splenectomy could also reduce liver and lung injuries possibly via the Tim 3 and/or Galectin-9 axis. The spleen is an important regulator of the occurrence and development of sepsis, which provides a new perspective to improve the prognosis of sepsis by regulating the spleen.

Toll-like receptors in sepsis-associated cytokine storm and their endogenous negative regulators as future immunomodulatory targets

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Sepsis infects more than 48.9 million people world-wide, with 19.7 million deaths.

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Cytokine storm plays a significant role in sepsis, along with severe COVID-19.

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TLR signaling pathways plays a crucial role in generating the cytokine storm.

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Endogenous negative regulators of TLR signaling are crucial to regulate cytokine storm.

Cytokine storm generates during various systemic acute infections, including sepsis and current pandemic called COVID-19 (severe) causing devastating inflammatory conditions, which include multi-organ failure or multi-organ dysfunction syndrome (MODS) and death of the patient. Toll-like receptors (TLRs) are one of the major pattern recognition receptors (PRRs) expressed by immune cells as well as non-immune cells, including neurons, which play a crucial role in generating cytokine storm. They recognize microbial-associated molecular patterns (MAMPs, expressed by pathogens) and damage or death-associate molecular patterns (DAMPs; released and/expressed by damaged/killed host cells). Upon recognition of MAMPs and DAMPs, TLRs activate downstream signaling pathways releasing several pro-inflammatory mediators [cytokines, chemokines, interferons, and reactive oxygen and nitrogen species (ROS or RNS)], which cause acute inflammation meant to control the pathogen and repair the damage. Induction of an exaggerated response due to genetic makeup of the host and/or persistence of the pathogen due to its evasion mechanisms may lead to severe systemic inflammatory condition called sepsis in response to the generation of cytokine storm and organ dysfunction. The activation of TLR-induced inflammatory response is hardwired to the induction of several negative feedback mechanisms that come into play to conclude the response and maintain immune homeostasis. This state-of-the-art review describes the importance of TLR signaling in the onset of the sepsis-associated cytokine storm and discusses various host-derived endogenous negative regulators of TLR signaling pathways. The subject is very important as there is a vast array of genes and processes implicated in these negative feedback mechanisms. These molecules and mechanisms can be targeted for developing novel therapeutic drugs for cytokine storm-associated diseases, including sepsis, severe COVID-19, and other inflammatory diseases, where TLR-signaling plays a significant role.