MSC-derived exosomal miR-140-3p improves cognitive dysfunction in sepsis-associated encephalopathy by HMGB1 and S-lactoylglutathione metabolism

MiRNAs in mesenchymal stem cells (MSCs)-derived exosome (MSCs-exo) play an important role in the treatment of sepsis. We explored the mechanism through which MSCs-exo influences cognitive impairment in sepsis-associated encephalopathy (SAE). Here, we show that miR-140-3p targeted Hmgb1. MSCs-exo plus miR-140-3p mimic (Exo) and antibiotic imipenem/cilastatin (ABX) improve survival, weight, and cognitive impairment in cecal ligation and puncture (CLP) mice. Exo and ABX inhibit high mobility group box 1 (HMGB1), IBA-1, interleukin (IL)-1β, IL-6, iNOS, TNF-α, p65/p-p65, NLRP3, Caspase 1, and GSDMD-N levels. In addition, Exo upregulates S-lactoylglutathione levels in the hippocampus of CLP mice. Our data further demonstrates that Exo and S-lactoylglutathione increase GSH levels in LPS-induced HMC3 cells and decrease LD and GLO2 levels, inhibiting inflammatory responses and pyroptosis. These findings suggest that MSCs-exo-mediated delivery of miR-140-3p ameliorates cognitive impairment in mice with SAE by HMGB1 and S-lactoylglutathione metabolism, providing potential therapeutic targets for the clinical treatment of SAE.

Irisin protects against sepsis-associated encephalopathy by suppressing ferroptosis via activation of the Nrf2/GPX4 signal axis

Sepsis-associated encephalopathy (SAE) is a common complication of severe sepsis. Irisin is a novel exercise-induced myokine involved in the regulation of adipose browning and thermogenesis. This study is designed to verify the existence of ferroptosis in the pathogenesis of SAE and demonstrate that irisin attenuated cognitive dysfunction in SAE mice via inhibition of hippocampus ferroptosis. A mouse SAE model was induced by cecal ligation and puncture (CLP) and in vitro model was established by LPS-stimulated hippocampus cells. Irisin were pre-treated in the models. We found that SAE triggered hippocampus ferroptosis, as evidenced by increasing ROS, iron content and MDA and reducing GSH level as well as altered ferroptosis-related protein (GPX4, ACSL4 and SLC7A11) expression, whereas irisin attenuated CLP-induced learning and memory dysfunction, neurologic severity score and hippocampus ferroptosis and microglial activation in SAE mice. However, the protective effect of irisin was eliminated by ferroptosis inducer Erastin. Consistently, irisin reduced ferroptosis and improved mitochondrial dysfunction in LPS-induced HT-22 cells, as evidenced by decreased lipid ROS and increased mitochondrial membrane potential. Furthermore, proteomics identified the differentially expressed proteins linked to ferroptosis in SAE. We also observed that irisin-mediated anti-ferroptosis was abolished by siRNA-Nrf2 or in Nrf2^-/- mice. Transwell assay revealed that irisin could prevent the recruitment and chemotaxis of microglial cells induced by ferroptotic hippocampal cells. In conclusion, irisin could ameliorate inflammatory microenvironment in SAE by suppressing hippocampus ferroptosis via the Nrf2/GPX4 signaling pathway.

Deficiency of cGAS signaling protects against sepsis-associated encephalopathy

Sepsis is a life-threatening inflammatory syndrome secondary to infection. Thanks to the advances of antibiotics and life-supporting techniques, the mortality of sepsis has been decreasing in recent decades. Nevertheless, sepsis-associated encephalopathy (SAE) is still common in septic patients, which promotes the mortality of septic patients and results in cognitive dysfunction in survivors. Full understanding and effective medicine in the treatment of SAE is currently scant. Here, we revealed a novel role of cGAS signaling in the pathogenesis of SAE. Deficiency of cGas significantly restored cognitive impairment in sepsis mice model. The restoration may attribute to the recovery of neo-neuron decline that associated with the decrease of activated microglia and astrocytes in the hippocampus of cGas-deficient mice. In addition, type I interferon (IFN) signaling, a downstream of cGAS pathway, was boosted in the hippocampus of septic mice, which was dramatically attenuated by deleting cGas. Moreover, administration of recombinant IFNβ markedly reversed the protection of ablation of cGas in the cognitive impairment in sepsis. Collectively, cGAS promotes the pathogenesis of SAE by up-regulating type I IFN signaling. Blocking cGAS may be a promising strategy for preventing encephalopathy in sepsis.

[Cognitive impairments relate to the expression of α7 nicotinic acetylcholinergic receptor (α7nAChR) and the proportion of M1/M2 microglia in the hippocampus of male mice with sepsis-associated encephalopathy]

Objective To investigate the cognitive differences between male and female mice with sepsis-associated encephalopathy (SAE) and its underlying mechanism. Methods The SAE model was induced by caecal ligation and puncture (CLP) in male and female mice aged from 6 to 8 weeks. The cognitive functions of the mice were evaluated by novel object recognition test and contextual fear conditioning test. The expression and distribution of α7 nicotinic acetylcholinergic receptor (α7nAChR) and the proportion of M2 microglia in hippocampus of SAE mice were detected by immunofluorescence staining, and the level of α7nAChR protein was detected by Western blot. Results The cognitive function of male SAE mice was significantly impaired, and the expression level of α7nAChR protein in hippocampus of male SAE mice decreased significantly compared with that of female SAE mice. At the same time, the proportion of M2 microglia in SAE male mice was significantly lower than that in female mice. Conclusion The expression level of α7nAChR protein in hippocampus of SAE male mice is significantly lower than that of SAE female mice, and the proportion of M2 microglia is relatively lower, which lead to the cognitive dysfunction of SAE male mice.

Hydrogen gas alleviates sepsis-induced neuroinflammation and cognitive impairment through regulation of DNMT1 and DNMT3a-mediated BDNF promoter IV methylation in mice

Sepsis-associated encephalopathy (SAE) can cause acute and long-term cognitive impairment and increase the mortality rate in sepsis patients, and we previously reported that 2% hydrogen gas (H2) inhalation has a therapeutic effect on SAE, but the underlying mechanism remains unclear. Dynamic DNA methylation, which catalyzed by DNA methyltransferases (DNMTs), is involved in the formation of synaptic plasticity and cognitive memory in the central nervous system. And brain-derived neurotrophic factor (BDNF), to be a key signaling component in activity-dependent synaptic plasticity, can be induced by neuronal activity accompanied by hypomethylation of its promoter IV. This study was designed to illustrate whether H2 can mediate SAE by alter the BDNF promoter IV methylation mediated by DNMTs. We established an SAE model by cecal ligation and perforation (CLP) in C57BL/6 mice. The Morris water maze test from the 4th to the 10th day after sham or CLP operations were used to evaluate mouse cognitive function. Hippocampal tissues were isolated at the 24 after sham or CLP surgery. Pro-inflammatory cytokines including tumor necrosis factor-α (TNF-α), Interleukin-6 (IL-6) and High Mobility Group Box 1 (HMGB1) were measured by enzyme-linked immunosorbent assay (ELISA). mRNA or protein levels of DNMTs (DNMT1, DNMT3a and DNMT3b), BDNF promoter IV and total BDNF were detected by RT-PCR and Western blot tests. Immunofluorescence staining were used to determine the expressions of DNMT1 and DNMT3a. The quantitative methylation analysis of the 11 CpG island of the promoter region of BDNF exon IV was determined using theAgena's MassARRAY EpiTYPER system. We found that 2% H2 inhalation can reduce pro-inflammatory factors, alleviate DNMT1, DNMT3a but not DNMT3b expression, make hypomethylation of BDNF promoter IV at 5 CpG sites, enhance the BDNF levels and then decrease escape latency but increase platform crossing times in septic mice. Our results suggest that 2% H2 inhalation may alleviate SAE through altering the regulation of BDNF promoter IV methylation which mediated by DNMT1 and DNMT3a in the hippocampus of septic mice.