Luteolin modulates macrophage phenotypic switching via the AMPK-PPARγ pathway to alleviate ulcerative colitis in mice

Ethnopharmacological relevance: Lonicerae japonicae flos (LJF), the dried flower bud or newly bloomed flower of Lonicera japonica Thunb., is widely used in Traditional Chinese medicine (TCM), exhibiting anti-inflammatory and immune-enhancing properties. Luteolin (Lut) is a major bioactive component of LJF, demonstrating a regulatory role in immune disorders. However, the specific role of Lut in regulating macrophage-mediated intestinal inflammation and its underlying molecular mechanisms have not yet been fully explored.

Aim of the study: This study was designed to explore whether Lut alleviates Ulcerative colitis (UC) in mice and to elucidate its underlying mechanism in intestinal inflammation.

Materials and methods: Mice were administered Dextran sodium sulfate (DSS) for 7 d to establish a UC model, followed by oral administration of Lut (12.5, 25, and 50 mg/kg body weight). RNA-sequencing (RNA-Seq) was used to screen signaling pathways. RAW264.7 cells were cultured and treated with Lut (6.25, 12.5, and 25 μM) and lipopolysaccharide (LPS, 1 μg/mL) for 24 h. To examine the role of the AMP-activated protein kinase (AMPK)/Peroxisome Proliferator-activated Receptor γ (PPARγ) signaling pathway, the cells were treated with compound C (an AMPK Inhibitor) and GW9662 (a PPARγ Antagonist).

Results: Lut suppressed the inflammation of DSS-induced colitis in vivo, attenuated DSS-induced clinical man-ifestations, reversed colon length reduction, and reduced histological injury. Lut induced a shift in the macrophage phenotype from classical (M1) to alternative (M2) by suppressing M1 marker gene expression and enhancing M2 marker gene expression following DSS or LPS induction. RNA-seq revealed that PPARγ was involved in the regulation of macrophages by Lut. Furthermore, the polarization effect of Lut on macrophages was shown to be mediated through the AMPK-PPARγ signaling pathway.

Conclusion: These findings indicate that Lut effectively ameliorates UC in mice through the activation of the AMPK-PPARγ signaling pathway, leading to the inhibition of macrophage M1 polarization and promotion of M2 polarization. This study provides insight into future research on the utilization of Lut-rich TCM dietary supplements as a prophylactic treatment strategy in the prevention of UC.

AMPK-PPARγ pathway; Inflammatory bowel disease; Luteolin; Macrophage polarization.