Phloretin suppresses neuroinflammation by autophagy-mediated Nrf2 activation in macrophages

Dany Bylemans,Sam Vanherle,Annick Boeykens,Elien Grajchen,Saadia Kerdine-Römer,Elien Wouters,Melanie Loix,Jerome J A Hendriks,Kévin Hardonnière,Tess Dierckx,Jeroen F J Bogie,Mansour Haidar

doi:10.1186/s12974-021-02194-z

Abstract

BackgroundMacrophages play a dual role in neuroinflammatory disorders such as multiple sclerosis (MS). They are involved in lesion onset and progression but can also promote the resolution of inflammation and repair of damaged tissue. In this study, we investigate if and how phloretin, a flavonoid abundantly present in apples and strawberries, lowers the inflammatory phenotype of macrophages and suppresses neuroinflammation.MethodsTranscriptional changes in mouse bone marrow-derived macrophages upon phloretin exposure were assessed by bulk RNA sequencing. Underlying pathways related to inflammation, oxidative stress response and autophagy were validated by quantitative PCR, fluorescent and absorbance assays, nuclear factor erythroid 2–related factor 2 (Nrf2) knockout mice, western blot, and immunofluorescence. The experimental autoimmune encephalomyelitis (EAE) model was used to study the impact of phloretin on neuroinflammation in vivo and confirm underlying mechanisms.ResultsWe show that phloretin reduces the inflammatory phenotype of macrophages and markedly suppresses neuroinflammation in EAE. Phloretin mediates its effect by activating the Nrf2 signaling pathway. Nrf2 activation was attributed to 5′ AMP-activated protein kinase (AMPK)-dependent activation of autophagy and subsequent kelch-like ECH-associated protein 1 (Keap1) degradation.ConclusionsThis study opens future perspectives for phloretin as a therapeutic strategy for neuroinflammatory disorders such as MS.Trial registrationNot applicable.

Highlights

Macrophages play a dual role in neuroinflammatory disorders such as multiple sclerosis (MS)
Findings show that phloretin activates nuclear factor erythroid 2–related factor 2 (Nrf2) and suppresses the inflammatory phenotype of macrophages
By using high-resolution Airyscan confocal microscopy combined with colocalization analysis, we show that phloretin stimulates the interaction of p62 and kelch-like ECH-associated protein 1 (Keap1), as demonstrated by an increased value of the colocalization parameter (Pearson’s coefficient) in phloretin-treated Bone marrow-derived macrophages (BMDMs) (Fig. 5A, B)

Summary

Introduction

Macrophages play a dual role in neuroinflammatory disorders such as multiple sclerosis (MS) They are involved in lesion onset and progression but can promote the resolution of inflammation and repair of damaged tissue. We investigate if and how phloretin, a flavonoid abundantly present in apples and strawberries, lowers the inflammatory phenotype of macrophages and suppresses neuroinflammation. Phloretin is a glucose transporter (GLUT) inhibitor, a feature that affects the phenotype of macrophages since macrophage activation is fueled by GLUT [25, 26]. Overall, these characteristics make phloretin a promising compound to modulate the phenotype of macrophages and neuroinflammation

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Discussion

Conclusion