The effect of lipopolysaccharide on enhanced inflammatory process with age: Modulation of NF-κB

Abstract

Oxidative stress is thought to be a causative factor for age-related damage in a wide variety of cellular constituents that can lead to dysfunction and various pathological conditions, including the inflammatory process. At the molecular level, the redox-sensitive transcription factor, NF-κB plays a key role in the regulation of the inflammatory process, along with cytokines, cyclooxygenase-2 (COX-2), and inducible nitric oxide synthase (iNOS). We studied the mechanism underlying the modulation of the inflammatory reaction with age by investigating NF-κB activation and the expression of COX-2, iNOS, and cytokines genes in hepatic tissues isolated from young and old rats. We expanded our investigation of these factors in rats injected with the inflammatory activator, lipopolysaccharide (LPS). Data showed that NF-κB activity was up-regulated with age and was further enhanced by LPS injection, indicating an increased susceptibility and sensitivity to the inflammatory stimulus with age. To explore further the molecular events leading to NF-κB activation, we investigated the inhibitory component of NF-κB complex, IκB. Cytosolic IκBα, but not IκBβ, was significantly decreased in both old and LPS-treated rats, signifying the enhanced migration of cytosolic NF-κB complex into the nucleus following dissociation from the inhibitor. The appearance of the polypeptide, p65, as determined in the nucleus, corresponded with the change in IκBα, providing further supporting evidence for the molecular process involved in NF-κB activation. Our additional investigation of two proinflammatory-related enzymes, COX-2 and iNOS, and three cytokines, interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α, clearly showed aged-related increases, in corroboration with the NF-κB activation. Our results demonstrated that LPS injection caused the enhanced gene expression of inducible proinflammatory proteins, COX-2 and iNOS through NF-κB activation.