Abstract
Objectives
Macrophage polarization into pro-inflammatory M1 status is associated with the pathologic progression of adipose remodeling, while M2 polarization is linked with the resolution of inflammation. Urolithin A (UroA) is a gut metabolite derived from ellagic acid found in berries and nuts. Emerging evidence suggests UroA exerts anti-inflammatory function, but the underlying mechanism remains unknown. This study aims to test the hypothesis that UroA attenuates adipose inflammation by promoting M2 macrophage polarization.
Methods
To investigate the direct role of UroA in vitro, primary bone marrow-derived macrophages (BMDM) were stimulated with LPS for M1 polarization or IL-4/IL-13 for M2 polarization. Oxygen consumption rate was determined in BMDM by Seahorse extracellular flux analyzer. The anti-inflammatory role of UroA is validated by pro-IL-1β Gaussia luciferase (iGLuc) reporter assay and IL-1β secretion in J774 macrophages. Additionally, C57BL/6 mice were fed with a HF diet for 12 weeks along with UroA administration. The M1/M2 polarization status were examined in adipose tissue macrophages (ATM) and peritoneal macrophages by qPCR and protein markers.
Results
UroA treatment in BMDM in vitro significantly decreased Il-1β (P < 0.001), while increasing M2 markers of Arg1, Ch313 and Mgl2 (P < 0.01). UroA treatment suppressed NLRP3 inflammasome activation in J774 macrophages by decreasing iGLuc activity and IL-1β secretion in a dose-dependent manner. In vivo, UroA administration reduced HF-induced adipocyte hypertrophy, inflammatory markers, and ATM recruitment (P < 0.01) in the adipose tissue. Consistently, UroA suppressed M1 polarization but switched to M2 polarization in peritoneal macrophages, evidenced by decreased M1 signature genes of Cd11c, Tnf-α, Il-6, and Il-1β (P < 0.01), while elevated M2 markers of Ch313 and Mgl2 (P < 0.05). Lastly, UroA not only inhibits HF-driven pathogenic remodeling of adipose tissue, but also promote mitochondrial function and biogenesis.
Conclusions
UroA attenuates HF-driven pathologic remodeling of adipose tissue by favoring M2 macrophage polarization and augmenting mitochondrial function. Intake of UroA-producing foods may be a promising intervention strategy to mitigate obesity-mediated chronic inflammation and metabolic dysfunction.
Funding Sources
United States Department of Agriculture National Institute for Food and Agriculture.
Hyperhomocysteinemia Promotes Insulin Resistance and Adipose Tissue Inflammation in PCOS Mice Through Modulating M2 Macrophage Polarization via Estrogen Suppression
