Nrf2 is a basic region leucine-zipper transcription factor that plays a pivotal role in the coordinated gene expression of antioxidant and detoxifying enzymes, promoting cell survival in adverse environmental or defective metabolic conditions. After synthesis, Nrf2 is arrested in the cytoplasm by the Kelch-like ECH-associated protein 1 suppressor (Keap1) leading Nrf2 to ubiquitin-dependent degradation. One Nrf2 activation mechanism relies on disconnection from the Keap1 homodimer through the oxidation of cysteine at specific sites of Keap1. Free Nrf2 enters the nucleus, dimerizes with small musculoaponeurotic fibrosarcoma proteins (sMafs), and binds to the antioxidant response element (ARE) sequence of the target genes. Since oxidative stress, next to neuroinflammation and mitochondrial dysfunction, is one of the hallmarks of neurodegenerative pathologies, a molecular intervention into Nrf2/ARE signaling and the enhancement of the transcriptional activity of particular genes are targets for prevention or delaying the onset of age-related and inherited neurogenerative diseases. In this study, we review evidence for the Nrf2/ARE-driven pathway dysfunctions leading to various neurological pathologies, such as Alzheimer’s, Parkinson’s, and Huntington’s diseases, as well as amyotrophic lateral sclerosis, and the beneficial role of natural and synthetic molecules that are able to interact with Nrf2 to enhance its protective efficacy.

Background: Astrocytes are responsible for a broad range of functions that maintain homeostasis in the brain. However, their response to the pro-inflammatory cytokines released by activated microglia in various neurological pathologies may exacerbate neurodegenerative processes. Accumulating evidence suggests that omega-3 docosahexaenoic fatty acid (DHA) has an anti-inflammatory effect in various cell cultures studies and in a variety of neurological disorders. In this study we examined the mechanism involved in the inhibition of the pro-inflammatory response by DHA in astrocytes treated with IL-1β. Methods and results: Activation of the transcription factors NF-κB and AP-1 was measured in IL-1β-treated primary astrocytes incubated with various concentrations of DHA. COX-2 and iNOS protein expression was determined by Western blot, and TNF-α and IL-6 secretion was measured using ELISA-based assays. DHA treatment inhibited translocation of p65NF-κB to the nucleus, significantly lowered p65NF-κB protein level and fluorescence of p65NF-κB in the nucleus, reduced dose-dependently IκB protein phosphorylation, and the binding of the AP-1 transcription factor members (c-Jun/c-Fos) to the specific TPA-response element (TRE) of DNA. In addition, the expression of pro-inflammatory COX-2 and iNOS proteins was downregulated and TNF-α and IL-6 secretion was also reduced. Conclusions: These results indicate that DHA is a powerful factor that reduces the pro-inflammatory response in astrocytes. Consequently, successful introduction of DHA into the astrocyte membranes can attenuate neuroinflammation, which is a key factor of age-related neurodegenerative disorders.

The role of immunoproteasome (iP) in astroglia, the cellular component of innate immunity, has not been clarified. The results so far indicate that neuroinflammation, a prominent hallmark of Alzheimer’s disease, strongly activates the iP subunits expression. Since omega-3 PUFAs possess anti-inflammatory and pro-resolving activity in the brain, we investigated the effect of DHA and EPA on the gene expression of constitutive (β1 and β5) and inducible (iβ1/LMP2 and iβ5/LMP7) proteasome subunits and proteasomal activity in IL-1β-stimulated astrocytes. We found that both PUFAs downregulated the expression of IL-1β-induced the iP subunits, but not the constitutive proteasome subunits. The chymotrypsin-like activity was inhibited in a dose-dependent manner by DHA, and much strongly in the lower concentration by EPA. Furthermore, we established that C/EBPα and C/EBPβ transcription factors, being the cis-regulatory element of the transcription complex, frequently activated by inflammatory mediators, participate in a reduction in the iP subunits’ expression. Moreover, the expression of connexin 43 the major gap junction protein in astrocytes, negatively regulated by IL-1β was markedly increased in PUFA-treated cells. These findings indicate that omega-3 PUFAs attenuate inflammation-induced hyperactivity of iPs in astrocytes and have a beneficial effect on preservation of interastrocytic communication by gap junctions.

Background/Aims: Microglial cells play a crucial role in the development of neuroinflammation in response to harmful stimuli, such as infection, ischemia or injury. Their chronic activation, however, is associated with a progression of neurodegenerative diseases. Therefore, looking for potential factors limiting microglial activation, the effect of docosahexaenoic acid (DHA) on the inflammatory response and TREM2-dependent phagocytic activity in microglia was investigated. Methods: In LPS-induced primary microglia preincubated with DHA, or without preincubation the expression of ATF3 and TREM2 genes and TREM2, Syk, Akt proteins were determined by RT-PCR and WB, respectively. Cell viability was assayed by MTT and cytokine and chemokine expression was determined by the Proteome Profiler assay. Moreover, the phagocytic activity of microglia was assayed using immunofluorescence. Results: We found that DHA significantly increased the expression of ATF3 , and decreased the levels of CINC-1, CINC-2αβ, CINC-3 chemokines, IL-1α and IL-1β cytokines, and ICAM-1 adhesion protein. Additionally, preincubation of microglia with DHA resulted in increased Src/Syk kinases activation associated with increased phagocytic microglia activity. Conclusion: These findings indicate that DHA efficiently inhibits ATF3-dependent release of proinflammatory mediators and enhances phagocytic activity of microglia. The study provides a new mechanism of DHA action in reactive microglia, which may help limit neuronal damage caused by the pro-inflammatory milieu in the brain.