Sepsis-associated encephalopathy (SAE) is a common complication that leads to long-term cognitive impairments and increased mortality in sepsis survivors. The mechanisms underlying this complication remain unclear and an effective intervention is lacking. Accumulating evidence suggests the nucleotide-binding domain-like receptor protein3 (NLRP3)/caspase-1 pathway is involved in several neurodegenerative diseases. Thus, we hypothesized that the NLRP3/caspase-1 pathway is involved in NLRP3-mediated pyroptosis, maturation and release of inflammatory cytokines, and cognitive deficits in SAE. We used the NLRP3 inhibitor MCC950 and the caspase-1 inhibitor Ac-YVAD-CMK to study the role of the NLRP3/caspase-1 pathway in pyroptosis and cognitive deficits in a mouse model of SAE. Mice were randomly assigned to one of six groups: sham+saline, sham+MCC950, sham+Ac-YVAD-CMK, cecal ligation and puncture (CLP)+saline, CLP+MCC950, and CLP+Ac-YVAD-CMK. Surviving mice underwent behavioral tests or had hippocampal tissues collected for histochemical analysis and biochemical assays. Our results show that CLP-induced hippocampus-dependent memory deficits are accompanied by increased NLRP3 and caspase-1 positive cells, and augmented protein levels of NLRP3, caspase-1, gasdermin-D, and pro-inflammatory cytokines in the hippocampus. In addition, administration of MCC950 or Ac-YVAD-CMK rescues cognitive deficits and ameliorates increased hippocampal NLRP3-mediated neuronal pyroptosis and pro-inflammatory cytokines. Our results suggest that the NLRP3/caspase-1 pathway-induced pyroptosis mediates cognitive deficits in a mouse model of SAE.

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Sepsis-associated encephalopathy induces cognitive dysfunction via mechanisms that commonly involve neuroinflammation and synaptic plasticity impairment of the hippocampus. The β2-adrenoceptor (β2-AR) is a G-protein coupled receptor that regulates immune response and synaptic plasticity, whereas its dysfunction has been implicated in various neurodegenerative diseases. Thus, we hypothesized abnormal β2-AR signaling is involved in sepsis-induced cognitive impairment. In the present study, C57BL/6 mice were subjected to cecal ligation and puncture (CLP) to mimic the clinical human sepsis-associated encephalopathy. The levels of hippocampal β2-AR, proinflammatory cytokines tumor necrosis factor (TNF-α), interleukin-1β (IL-1β), IL-6, cAMP-response element binding protein (CREB), brain derived neurotrophic factor (BDNF), post-synaptic density protein 95 (PSD95), and NMDA receptor 2 B subtypes (GluN2B) were determined at 6, 12, 24 h and 7 and 16 days after CLP. For the interventional study, mice were treated with β2-AR agonist clenbuterol in two ways: early treatment (immediately following CLP) and delayed treatment (on the 8th day following CLP). Neurobehavioral performances were assessed by open field and fear conditioning tests. Here, we found that hippocampal β2-AR expression was significantly decreased starting from 12 h and persisted until 16 days following CLP. Besides, sepsis mice also exhibited increasing neuroinflammation, down-regulated CREB/BDNF, decreasing PSD95 and GluN2B expression, and displayed hippocampus-dependent cognitive impairments. Notably, early clenbuterol treatment alleviated sepsis-induced cognitive deficits by polarizing microglia toward an anti-inflammatory phenotype, reducing proinflammatory cytokines including IL-1β, TNF-α, and up-regulating CREB/BDNF, PSD95, and GluN2B. Intriguingly, delayed clenbuterol treatment also improved cognitive impairments by normalization of hippocampal CREB/BDNF, PSD95, and GluN2B. In summary, our results support the beneficial effects of both early and delayed clenbuterol treatment, which suggests that activation of β2-AR has a translational value in sepsis-associated organ dysfunction including cognitive impairments.