Attenuation Of NF-κB Signaling Research Articles

The Protective Effect of Glucosamine on Cardiac Function Following Trauma Hemorrhage: Downregulation of cardiac NF‐κB signaling

Administration of glucosamine (GlcN) following trauma-hemorrhage (TH) increased tissue levels of O-linked N-acetylglucosamine (GlcNAc) attenuated circulating proinflammatory cytokines TNF-α and IL-6, and improved cardiac function. However, the mechanism(s) by which increased O-GlcNAc levels improve recovery and decrease the inflammatory response is unclear. Therefore, the goal of this study was to determine if the beneficial effect of GlcN was mediated by downregulation of NF-κB signaling pathway following TH. Fasted male rats were subject to TH by bleeding to a mean arterial blood pressure of 40 mmHg for 90 minutes followed by 60 minutes resuscitation; GlcN (2.5mls, 150mM) or vehicle (2.5mls normal saline) were administered mid-way through resuscitation. Two hours later mean arterial pressure, heart rate and ±dp/dt were recorded and tissues harvested. Consistent with our earlier study GlcN improved cardiac function at the end of resuscitation. In hearts from vehicle treated rats, there were increased levels of intercellular adhesion molecule 1 protein (ICAM1), IκB-α phosphorylation, nuclear NF-κB protein and increased NF-κB nuclear DNA binding activity compared to sham controls. GlcN treatment significantly decreased ICAM1 expression, IκB-α phosphorylation, nuclear NF-κB expression and NF-κB DNA binding activity. Thus, GlcN administration during resuscitation attenuated NF-κB signaling pathway in the heart and this may contribute to the protection associated with increased protein O-GlcNAc levels. (Supported by NIH grants R01 HL076165-03 and R37 GM39519).

Distinctive Antioxidant and Antiinflammatory Effects of Flavonols

The antioxidant and antiinflammatory effects of flavonols have been suggested to be structure-related. Results revealed that selected flavonols, including fisetin (F), kaempferol (K), morin (MO), myricetin (MY), and quercetin (Q), exhibited distinctive free radical scavenging properties against different kinds of free radicals. The H donation (DPPH bleaching) potential was Q > F approximately equals MY > MO > K, indicating that the presence of a 3',4'-catechol moiety in the B ring correlated with high activity. The 4'-OH in the B ring was suggested to be important for reducing xanthing/xanthine oxidase-generated superoxide; while an additional OH moiety on the ortho sites (3' or 5') attenuated the effect as the observed inhibitory potency was K approximately equals MO > Q > F > MY. The relative inhibitory effect for Fenton-mediated hydroxyl radical was K approximately equals MO approximately equals Q > F > MY. This result implies the involvement of 4-keto, 5-OH region in Fe++ chelating and the negative effect of pyrogallol moiety in the B ring. Similar to the inhibitory activity against a N-formyl-methionyl-leucyl-phenylalanine (f-MLP)-stimulated oxidative burst in human polymorphonuclear neutrophils (PMN), our result showed that the structural peculiarity of the di-OH in the B ring obviously rendered F, Q, and MO more potent as ROS inhibitors than MY and K, which have tri- and mono-OH in the B ring, respectively. All of the previous data indicated that the structure prerequisite to reinforce the free radical scavenging activity varies with the type of free radical. We further analyzed the effects of flavonols on nitric oxide (NO) production in endotoxin-stimulated murine macrophages, RAW264.7 cells. Results showed that all flavonols (up to 10 microM) inhibited NO production without exerting detectable cytotoxicity. F, K, and Q dose-dependently repressed iNOS mRNA expression and prostaglandin E2 (PGE2) production, in part through an attenuating NF-kappaB signaling pathway. This result indicates that flavonols, despite structural similarity, have different antioxidant and antiinflammatory effects.

Yersinia virulence factor YopJ acts as a deubiquitinase to inhibit NF-κB activation

The bacterial pathogens of the genus Yersinia, the causative agents of plague, septicemia, and gastrointestinal syndromes, use a type III secretion system to inject virulence factors into host target cells. One virulence factor, YopJ, is essential for the death of infected macrophages and can block host proinflammatory responses by inhibiting both the nuclear factor κB (NF-κB) and mitogen-activated protein kinase pathways, which might be important for evasion of the host immune response and aid in establishing a systemic infection. Here, we show that YopJ is a promiscuous deubiquitinating enzyme that negatively regulates signaling by removing ubiquitin moieties from critical proteins, such as TRAF2, TRAF6, and IκBα. In contrast to the cylindromatosis tumor suppressor CYLD, which attenuates NF-κB signaling by selectively removing K63-linked polyubiquitin chains that activate IκB kinase, YopJ also cleaves K48-linked chains and thereby inhibits proteasomal degradation of IκBα. YopJ, but not a catalytically inactive YopJ mutant, promoted deubiquitination of cellular proteins and cleaved both K48- and K63-linked polyubiquitin. Moreover, an in vitro assay was established to demonstrate directly the deubiquitinating activity of purified YopJ.