Rutin Attenuates Microglial Inflammatory Responses by Promoting M2-like Polarization via GDNF and SHH/GLI-1 Signaling and NLRP3 Inflammasome Inhibition

Introduction: Rutin is a heterocyclic flavonol glycoside found in plants like apples, citrus fruits and buckwheat, with demonstrated anti-inflammatory properties. However, the molecular mechanisms underlying rutin’s direct effects on microglia, the main immune effector cells in the central nervous system, are not fully understood. The SHH/GLI-1 pathway is a neuronal repair pathway that modulates microglial activity and cell proliferation. Objective: For better compression of the rutin anti-inflammatory effects, this work evaluated the action of rutin on SHH/GLI-1 regulation. Methodology: For this, primary cultures of microglia from postnatal P0–2 days Wistar rats were stimulated with LPS (1 µg/mL) and/or treated with rutin (0.5–1 µM). Microglia morphology was characterized by immunofluorescence for Iba1. Gene expression of cytokines, inflammasome, glial-derived neurotrophic factors (GDNFs), and Sonic Hedgehog and family zinc finger-1 (SHH/GLI) were evaluated by real-time qPCR. Result: The results demonstrated that rutin inhibited the LPS-induced inflammatory response in microglia regulating negatively TNF-alpha, IL-6, and NLR family pyrin domain-containing 3 (NLRP3) mRNA expression. In addition, rutin increased GDNF and SHH-GLI-1 mRNA expression. Furthermore, conditioned medium from rutin-treated microglia showed a protective effect on PC-12 cells against LPS-induced cytotoxicity, reducing cell death as measured by the propidium iodide test and preserving cell morphology. Conclusions: This is the first evidence of the effect of rutin in SHH-GLI-1 signaling, contributing to the understanding of its pharmacological mechanisms and potentially revealing new molecular targets for treatment of neuroinflammatory diseases.