Omega-3 PUFAs Suppress IL-1β-Induced Hyperactivity of Immunoproteasomes in Astrocytes

Emilia Zgorzynska,Barbara Dziedzic,Monika Markiewicz,Anna Walczewska

doi:10.3390/ijms22115410

Abstract

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.

Highlights

Pre-incubation of astrocytes with DHA reduced the expression of β1i and β5i by 30% and 32% (Figure 2C,D), respectively, as well as the β1i/ β1 and β5i/β5 ratios by about a half, compared to the group treated with IL-1β without pretreatment with DHA (Figure 2E,F)
Eicosapentaenoic acid, likewise DHA, lowered the mRNA levels of β1i and β5i (p < 0.05), in cells treated with IL-1β without fatty acids pretreatment, the β5i/β5 ratio was 3.16, while in cells incubated with the same concentration of DHA and EPA, it was reduced to 1.63 (p < 0.01)
We have recently reported that DHA inhibits the activity of NF-κB and AP-1 transcription factors in astrocytes stimulated with IL-1β [10]

Summary

Introduction

The immunoproteasome (iP), a key regulator of innate and adaptive immune responses [1], is a specialized, pro-inflammatory cytokine- and oxidative stress-induced form of the constitutive proteasome, significantly upregulated in immunological cells, especially in the antigen-presenting cells [2]. The β1, β2 and β5 subunits of 20S core constitutive proteasome are replaced by their inducible counterparts, i.e., iβ1/LMP2, iβ2/MECL1 and iβ5/LMP7 creating the iP, which possesses stronger than constitutive proteasome chymotrypsin-like activity in cleaving proteins, after hydrophobic amino acids [2]. Further study has revealed that the activation of iP occurs in glia and nerve cells in response to amyloid-β and in post-mortem brains of patients with Alzheimer’s disease [3]. An abundant increase in iPs levels has been reported in the damaged retina and brain [4]

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Results

Conclusion