Overactivation Of NLRP3 Inflammasome Research Articles

Predictable chronic mild stress promotes recovery from LPS-induced depression

Clinical depression is frequently comorbid with chronic inflammatory disease, and neuroinflammation is currently proposed as a key mechanism in major depressive disorders. Different from unpredictable chronic stress, which is a well-established animal model for depression, predictable chronic mild stress (PCMS), a routine stress experienced in day-to-day life, has been demonstrated to improve mood and memory. In the present study, we assess the effects of PCMS (5 min of daily restrain stress for 4 weeks) on depressive-like behavior, neuroinflammation, oxidative stress, and pyrin domain containing three (NLRP3) activation in hippocampus of mice subjected to peripheral immune challenge by lipopolysaccharide (LPS). We found that PCMS facilitated the recovery from LPS-induced depressive- or anxiety-like behavior. Concurrent with the reversal of abnormal behavioral changes, PCMS suppressed LPS-induced proinflammatory cytokine expression, microglia activation, and oxidative stress in hippocampus. Correspondingly, PCMS inhibited LPS-induced overactivation of NLRP3 inflammasome components (NLRP3, ASC, and Caspase-1), and interleukin 1 beta (IL-1β) maturation. Nrf2 (nuclear factor (erythroid-derived 2)-like 2) signaling was demonstrated to inhibit NLRP3 inflammasome overactivation and oxidative stress. PCMS activated Nrf2 signaling and inhibited thioredoxin (Trx)-interacting protein (TXNIP) expression in LPS-treated mice. Collectively, present data suggest that PCMS, contrary to severe and uncontrolled stress, alleviated impairments of the Nrf2-TXNIP-Trx system and may contribute to inflammatory brain damage and the imbalance of cellular redox homeostasis in depressed mice. This study provides a mechanistic link to the resilience of PCMS to LPS-induced behavioral deficits.

Abstract WP150: Autophagy Regulates NLRP3 Inflammasome in Cerebral Ischemia With Comorbid Stress: A Protective Mechanism of Progesterone

Introduction: Exposure to stress primes microglia and the NLRP3 inflammasome, resulting in an exaggerated inflammatory response to a secondary insult such as stroke. NLRP3-mediated inflammation can be regulated by the autophagic removal of inflammasome activators, components, or cytokines. We hypothesized that progesterone (PROG), a neuroprotective neurosteroid, would enhance autophagy in a rodent model of cerebral ischemia combined with stress, and in an in vitro inflammasome assay. Methods: Adult male rats were exposed to social defeat stress for 8 days and then subjected to global ischemia. PROG (8 mg/Kg) was administered 2 and 6 h after occlusion, then daily for 7 days. At 7 and 14 days post-ischemia, hippocampi were dissected and autophagic flux was evaluated by western blot using LC3-II and p62 as indicators. To activate the NLRP3 inflammasome in vitro , cultured primary mouse microglia were primed with 1 ug/mL LPS for 2 h prior to stimulation with 5 mM ATP (a classical inflammasome activator) for 1h, and concomitantly treated with PROG. IL-1b production was measured by ELISA, while LC3 puncta were detected by immunofluorescence. Results: After social defeat, no changes in LC3-II levels were observed, but p62 levels slightly decreased. Global ischemia impaired autophagy as evidenced by decreased LC3 and p62 levels compared to non-ischemic controls. Stressed ischemic animals showed lower LC3 and p62 levels than ischemic animals. Notably, PROG enhanced autophagy, LC3 levels were increased and p62 reduced in both stressed and non-stressed ischemic animals. LPS and ATP synergized in compromising microglial autophagy and worsened IL-1b production. LPS-primed microglia treated with PROG showed enhanced autophagy, a larger number of LC3 puncta, and reduced IL-1b production compared to untreated controls. PROG’s beneficial effects were blocked by 3-methyladenine, an autophagy inhibitor. We conclude that PROG reduced the neurotoxic potential of primed microglia via autophagy, and attenuated NLRP3 inflammasome overactivation. These findings provide new insight into the mechanisms underlying PROG’s protective effects on the excessive inflammatory response, particularly important for improving outcome in stroke patients with comorbid stress.

Astragaloside IV attenuates cognitive impairments induced by transient cerebral ischemia and reperfusion in mice via anti-inflammatory mechanisms

Astragaloside IV (AS-IV) is the main active component isolated from the traditional Chinese medicinal herb Astragalus membranaceus. Studies have demonstrated that AS-IV has neuroprotective effects in cerebral ischemic models. In this study, we aimed to investigate the effects of AS-IV on memory impairment induced by transient cerebral ischemia and reperfusion in mice, as well as the associated signaling mechanisms. Severe memory deficits were induced by bilateral common carotid artery occlusion (BCCAO) in mice as indicated in the Morris water maze test in this study. Oral administration of AS-IV (10 and 20mg/kg, once per day, started 7days before surgery and continued for 7days after surgery) significantly attenuated memory impairment and neuroinflammation. Moreover, AS-IV treatment significantly reduced the expression of toll-like receptor-4 (TLR4) and its downstream adaptor proteins, including myeloid differentiation primary response gene 88 (MyD88), toll/interleukin-1 receptor-domain containing adaptor-inducing interferon-β (TRIF) and tumour necrosis factor receptor associated factor-6 (TRAF6), and subsequently inhibited NF-κB phosphorylation. It is well-known that cerebral ischemia and reperfusion injury enhances the formation of reactive oxygen species (ROS) and further neuroinflammation. Importantly, we found that AS-IV suppressed NLRP3 inflammasome activation by controlling ROS production. In addition, AS-IV markedly reduced overactivation of microglia and the overexpression of inflammatory cytokines in the hippocampus compared with the transient cerebral ischemia and reperfusion group. These results suggest that AS-IV might possess neuroprotective effects against transient cerebral ischemia and reperfusion partly through its anti-inflammatory effects by inhibiting TLR4 signaling pathway and NLRP3 inflammasome overactivation.