Effects of reactive γ‐ketoaldehydes formed by the isoprostane pathway (isoketals) and cyclooxygenase pathway (levuglandins) on proteasome function

Abstract

Oxidative stress can impair proteasome function, both of which are features of neurodegenerative diseases. Inhibition of proteasome function leads to protein accumulation and cell death. We discovered recently the formation of highly reactive g-ketoaldehydes, isoketals (IsoKs), and neuroketals (NeuroKs) as products of the isoprostane and neuroprostane pathways of free radical-induced lipid peroxidation that are analogous to cyclooxygenase-derived levuglandins (LGs). Because aldehydes that are much less reactive than IsoKs have been shown to inhibit proteasome function, we explored the ability of the proteasome to degrade IsoK-adducted proteins/peptides and the effect of IsoK and IsoK-adducted proteins/peptides on proteasome function. Adduction of IsoK to model proteasome substrates significantly reduced their rate of degradation by the 20S proteasome. The ability of IsoK to inhibit proteasome function directly was observed only at very high concentrations. However, at much lower concentrations, an IsoK-adducted protein (ovalbumin) and peptide (Ab1-40) significantly inhibited chymotrypsin-like activity of the 20S proteasome. Moreover, incubation of IsoK with P19 neuroglial cultures dose-dependently inhibited proteasome activity (IC50 = 330 nM) and induced cell death (LC50 = 670 nM). These findings suggest that IsoKs/NeuroKs/LGs can inhibit proteasome activity and, if overproduced, may have relevance to the pathogenesis of neurodegenerative diseases.

Molecular Basis for the Direct Inhibition of AP-1 DNA Binding by 15-Deoxy-Δ12,14-prostaglandin J2

“…The observations that 15d-PGJ 2 -induced c-Jun cross-linking occurs in the presence of 0.5 mM DTT and is resistant to reducing agents suggest that this effect could also occur in the presence of the cellular antioxidant defenses. It is known that oxidative stress-induced lipid peroxidation can give rise to reactive lipid aldehydes that may induce protein cross-linking and aggregation, a process that impairs protein degradation and has important implications in the pathophysiology of inflammatory and neurodegenerative diseases (38). Thus, it would be interesting to explore whether protein cross-linking by 15d-PGJ 2 or related cyPG could contribute to protein aggregation in pathophysiological settings.…”

Levuglandinyl Adducts of Proteins Are Formed via a Prostaglandin H2 Synthase-dependent Pathway after Platelet Activation

“…Considerable information on other lipid adducts of proteins indicates that they may alter processes such as localization, degradation, or function (13). As an example specific to the levuglandins, formation of levuglandinyl adducts on proteins significantly reduces their clearance by the 20 S proteasome (14). Also, the initial species of the levuglandinyl adducts are known to be highly reactive.…”

Reactive gamma-ketoaldehydes as novel activators of hepatic stellate cells in vitro

“…In addition, IsoLGs induce protein crosslinks and oligomerization at concentrations at least 100-fold lower than those required for 4-HNE to promote the same degree of crosslinking [14,17]. The formation of IsoLGs protein adducts may result in loss of function, formation of neo-antigens, and inhibition of proteasome function [18].…”

“…Other cellular consequences of IsoLGs exposure include increased expression of pro-inflammatory cytokines and adhesion molecules [20], and cell death [18,22].…”

“…Mechanistically, in other cell types, IsoLG act primarily by forming adducts to Longato 14 protein, lipids or nucleic acids [41]. Notably, IsoLG-adducted proteins are poor substrates for proteosomal degradation and the proteasome itself can be functionally impaired following IsoLG exposure [18]. We then thought that some of the effects observed in HSC could be mediated by induction of autophagy, an alternative pathway to the ubiquitin-proteasome system to remove damaged proteins and organelles [42,43].…”