Itaconate alleviates anesthesia/surgery-induced cognitive impairment by activating a Nrf2-dependent anti-neuroinflammation and neurogenesis via gut-brain axis.

BACKGROUND: Postoperative cognitive dysfunction (POCD) is a common neurological complication of anesthesia and surgery in aging individuals. Neuroinflammation has been identified as a hallmark of POCD. However, safe and effective treatments of POCD are still lacking. Itaconate is an immunoregulatory metabolite derived from the tricarboxylic acid cycle that exerts anti-inflammatory effects by activating the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. In this study, we investigated the effects and underlying mechanism of 4-octyl itaconate (OI), a cell-permeable itaconate derivative, on POCD in aged mice. METHODS: A POCD animal model was established by performing aseptic laparotomy in 18-month-old male C57BL/6 mice under isoflurane anesthesia while maintaining spontaneous ventilation. OI was intraperitoneally injected into the mice after surgery. Primary microglia and neurons were isolated and treated to lipopolysaccharide (LPS), isoflurane, and OI. Cognitive function, neuroinflammatory responses, as well as levels of gut microbiota and their metabolites were evaluated. To determine the mechanisms underlying the therapeutic effects of OI in POCD, ML385, an antagonist of Nrf2, was administered intraperitoneally. Cognitive function, neuroinflammatory responses, endogenous neurogenesis, neuronal apoptosis, and Nrf2/extracellular signal-related kinases (ERK) signaling pathway were evaluated. RESULTS: Our findings revealed that OI treatment significantly alleviated anesthesia/surgery-induced cognitive impairment, concomitant with reduced levels of the neuroinflammatory cytokines IL-1ß and IL-6, as well as suppressed activation of microglia and astrocytes in the hippocampus. Similarly, OI treatment inhibited the expression of IL-1ß and IL-6 in LPS and isoflurane-induced primary microglia in vitro. Intraperitoneal administration of OI led to alterations in the gut microbiota and promoted the production of microbiota-derived metabolites associated with neurogenesis. We further confirmed that OI promoted endogenous neurogenesis and inhibited neuronal apoptosis in the hippocampal dentate gyrus of aged mice. Mechanistically, we observed a decrease in Nrf2 expression in hippocampal neurons both in vitro and in vivo, which was reversed by OI treatment. We found that Nrf2 was required for OI treatment to inhibit neuroinflammation in POCD. The enhanced POCD recovery and promotion of neurogenesis triggered by OI exposure were, at least partially, mediated by the activation of the Nrf2/ERK signaling pathway. CONCLUSIONS: Our findings demonstrate that OI can attenuate anesthesia/surgery-induced cognitive impairment by stabilizing the gut microbiota and activating Nrf2 signaling to restrict neuroinflammation and promote neurogenesis. Boosting endogenous itaconate or supplementation with exogenous itaconate derivatives may represent novel strategies for the treatment of POCD.

Seasonal advance of intense tropical cyclones in a warming climate.

Intense tropical cyclones (TCs), which often peak in autumn1,2, have destructive impacts on life and property3-5, making it crucial to determine whether any changes in intense TCs are likely to occur. Here, we identify a significant seasonal advance of intense TCs since the 1980s in most tropical oceans, with earlier-shifting rates of 3.7 and 3.2 days per decade for the Northern and Southern Hemispheres, respectively. This seasonal advance of intense TCs is closely related to the seasonal advance of rapid intensification events, favoured by the observed earlier onset of favourable oceanic conditions. Using simulations from multiple global climate models, large ensembles and individual forcing experiments, the earlier onset of favourable oceanic conditions is detectable and primarily driven by greenhouse gas forcing. The seasonal advance of intense TCs will increase the likelihood of intersecting with other extreme rainfall events, which usually peak in summer6,7, thereby leading to disproportionate impacts.

[Effect of M1 microglia-derived exosomal microRNA-20a-5p on neuronal injury after oxygen-glucose deprivation and restoration injury].

OBJECTIVE: To investigate the effect of M1 microglia-derived exosomes (M1-exo) on neuronal injury after oxygen-glucose deprivation and restoration, and to explore its mechanism. METHODS: The mouse microglia BV2 cells grown in logarithmic growth phase were added with 100 µg/L liposolysaccharide (LPS) and 20 µg/L interferon-γ (IFN-γ) to induce the polarization of microglia into M1 phenotype. M1 microglia were identified by Western blotting, quantitative real-time polymerase chain reaction (qPCR) and immunofluorescence. The supernatant of M1 microglia was collected, and exosomes were extracted by ExoQuick-TCTM kit. The morphology of exosomes were observed by transmission electron microscope and nanoparticle tracking analysis (NTA), and the expression of characteristic proteins CD9 and CD63 of exosomes were detected by Western blotting. The well-growing mouse neuroblastoma N2a cells were divided into six groups: the cells in group C were conventionally-cultured; and the cells in group O were subjected to oxygen-glucose deprivation for 3 hours followed by restoration of oxygen-glucose supply 24 hours to establish the model of oxygen-glucose deprivation and restoration injury; and the N2a cells in group E were co-cultured with M1-exo 24 hours after oxygen-glucose deprivation 3 hours; NC group, M group and I group constructed negative control, overexpression and knockdown of microRNA-20a-5p (miR-20a-5p) M1-exo, respectively. The succession of transfection was detected by qPCR and N2a cells in group NC, group M and group I were co-cultured with such transfected M1-exo for 24 hours after oxygen-glucose deprivation 3 hours. Cell viability were detected by cell counting kit-8 (CCK-8) assay, cell apoptosis were detected by flow cytometry, and the expression of miR-20a-5p were detected by qPCR. RESULTS: Compared with M0 microglia, the fluorescence intensity and mRNA and protein expressions of CD32 and inducible nitric oxide synthase (iNOS), specific markers of M1 microglia, were increased [CD32 (fluorescence intensity): 36.919±1.541 vs. 3.533±0.351, CD32 mRNA (2-ΔΔCt): 4.887±0.031 vs. 1.003±0.012, CD32/ß-actin: 2.663±0.219 vs. 1.000±0.028; iNOS (fluorescence intensity): 29.513±1.197 vs. 7.933±0.378, iNOS mRNA (2-ΔΔCt): 4.829±0.177 vs. 1.000±0.016, iNOS/ß-actin: 1.991±0.035 vs. 1.000±0.045; all P < 0.01], indicating M1 microglia were successfully activated. Under electron microscopy, M1-exo had round or oval vesicular bodies with obvious membranous structures, with diameters ranging from 100 nm. Western blotting showed that the exosomes expressed specific CD63 and CD9 proteins. Compared with group C, the cell viability was decreased, the apoptosis rate and the expression of miR-20a-5p were significantly increased in group O [cell viability (A value): 0.540±0.032 vs. 1.001±0.014, apoptosis rate: (19.857±0.910)% vs. (13.508±0.460)%, miR-20a-5p (2-ΔΔCt): 5.508±0.291 vs. 1.033±0.101, all P < 0.01]. Compared with O group, cell viability was decreased, apoptosis rate and the expression of miR-20a-5p were increased in group E [cell viability (A value): 0.412±0.029 vs. 0.540±0.032, apoptosis rate: (31.802±0.647)% vs. (19.857±0.910)%, miR-20a-5p (2-ΔΔCt): 8.912±0.183 vs. 5.508±0.291, all P < 0.01], indicating that M1 microglia-derived exosomes further aggravated the damage of N2a cells after oxygen-glucose deprivation and restoration. Compared with group E, cell viability was decreased, apoptosis rate and the expression of miR-20a-5p were increased in group M [cell viability (A value): 0.311±0.028 vs. 0.412±0.029, apoptosis rate: (36.343±0.761)% vs. (31.802±0.647)%, miR-20a-5p (2-ΔΔCt): 32.348±0.348 vs. 8.912±0.183, all P < 0.01]; and the cell viability was increased, apoptosis rate and the expression of miR-20a-5p were decreased in group I [cell viability (A value): 0.498±0.017 vs. 0.412±0.029, apoptosis rate: (26.437±0.793)% vs. (31.802±0.647)%, miR-20a-5p (2-ΔΔCt): 6.875±0.219 vs. 8.912±0.183, all P < 0.01]. There was no significant difference in cell viability, apoptosis rate and the expression of miR-20a-5p between group E and group NC. CONCLUSIONS: M1 microglia-derived exosomes aggravate the injury of neurons after oxygen and glucose deprivation and reoxygenation, which may be related to miR-20a-5p carried by M1-exo.