Necroptosis, which is mediated by RIP1/RIP3/MLKL (receptor-interacting protein kinase 1/receptor-interacting protein kinase 3/mixed lineage kinase domain-like protein) signaling, is a critical process in the development of acute ischemic stroke. However, it is unclear precisely how necroptosis promotes the pathogenesis of acute ischemic stroke. In this experimental study in mice, we investigated how necroptosis loss-of-function mice, RIP1 kinase-dead mice, RIP3-deficiency mice, and MLKL-deficiency mice could be protected against cerebral injury after acute ischemic stroke. Insoluble RIP1, RIP3, and MLKL were all detected in the infarct area of the study mice, indicating activation of necroptosis. Two types of RIP1 kinase-dead mutant mice (Rip1 ^K45A/K45A or Rip1 ^Δ/Δ) were used to show that catalytically-inactive RIP1 can decrease the infarct volume and improve neurological function after MCAO/R (middle cerebral artery occlusion/reperfusion). Both Rip3 ^−/− mice and Mlkl ^−/− mice were protected against acute ischemic stroke. In addition, necroptosis loss-of-function mice showed less inflammatory responses in the infarct area. Therefore, necroptosis and its accompanying inflammatory response can lead to acute injury following ischemia stroke. Our study provides new insight into the pathogenetic mechanisms of acute ischemic stroke, and suggests potential therapeutic targets for neuroprotection.

Sepsis-associated encephalopathy (SAE) is a severe neurological condition caused by sepsis, and presents with symptoms ranging from delirium and coma to long-term cognitive dysfunction. SAE is acknowledged as a widespread brain impairment characterized by the activation of microglia. However, the specific pathological mechanisms that drive this activation are still not clearly understood. Growth differentiation factor 15 (GDF15) levels have been noted to be considerably increased in patients with sepsis, where they are linked to disease severity and can independently predict short- and long-term mortality risk. Serum levels of GDF15 have also been negatively associated with gray matter volume and predict cognitive impairment in older individuals. However, the impact of GDF15 on sepsis-induced cognitive and memory impairments, as well as the mechanisms behind these effects, are poorly understood. To examine the role of GDF15 in SAE, a sepsis model was created in adult C57BL/6J mice using intraperitoneal administration of lipopolysaccharide (LPS). GDF15 levels in plasma and cerebrospinal fluid were measured by ELISA. The anti-GDF15 monoclonal antibody ponsegromab was injected intracerebroventricularly before modeling, and cognitive and memory functions of the septic mice were assessed using fear-conditioning and novel object recognition tests. Microglial activation and phagocytosis were evaluated using immunofluorescence and Golgi staining. Additionally, an in vitro investigation of LPS-stimulated microglia was conducted to evaluate the impacts of GDF15 on inflammatory cytokine productions and microglial phagocytic activity. Mechanisms were explored using RNA sequencing, qPCR, western blotting, flow cytometry, and immunofluorescence assays. In the cerebrospinal fluid of septic mice, levels of GDF15 were notably elevated after intraperitoneal injection of LPS. Lateral ventricular injection of the anti-GDF15 antibody alleviated both cognitive and memory impairment in the septic mice, together with microglial activation and phagocytosis in the hippocampus, thereby protecting against synaptic loss. The levels of GDF15 were elevated in the brains of septic mice. Targeting GDF15 with an anti-GDF15 antibody was found to improve sepsis-induced cognitive and memory impairment by reducing the microglial inflammatory response and phagocytosis. These results indicate that GDF15 could serve as an important therapeutic target for treating SAE.

Rationale: Hosts defend against viral infection by sensing viral pathogen-associated molecular patterns and activating antiviral innate immunity through TBK1-IRF3 signaling. However, the underlying molecular mechanism remains unclear.

Acute lung injury (ALI) is characterized by dramatic lung inflammation and alveolar epithelial cell death. Although protein kinase R (PKR) (double-stranded RNA-activated serine/threonine kinase) has been implicated in inflammatory response to bacterial cell wall components, whether it plays roles in lipopolysaccharide (LPS)-induced ALI remains unclear. This study was aimed to reveal whether and how PKR was involved in LPS-induced ALI pathology and the potential effects of its specific inhibitor, C16 (C₁₃H₈N₄OS). During the experiment, mice received C16 (100 or 500 ug/kg) intraperitoneally 1 h before intratracheal LPS instillation. Then, whole lung lavage was collected for analysis of total protein levels and proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and IL-6. The lungs were tested for Western blot, transferase-mediated dUTP nick-end labeling (TUNEL) stain and immunohistochemistry. Results showed that PKR phosphorylation increased significantly after LPS instillation. Furthermore, PKR specific inhibition attenuated LPS-induced lung injury (hematoxylin and eosin stain), reduced lung protein permeability (total protein levels in whole lung lavage) and suppressed proinflammatory cytokines (TNF-α, IL-1β and IL-6) and lung apoptosis (TUNEL stain and caspase3 activation). Moreover, mechanism-study showed that C16 significantly suppressed I kappa B kinase (IKK)/I kappa B alpha (IκBα)/NF-κB signaling pathway after LPS challenge. These findings suggested that PKR inhibition ameliorated LPS-induced lung inflammation and apoptosis in mice by suppressing NF-κB signaling pathway.