α-linolenic Acid Regulates Macrophages NF-κB/NLRP3 Signal Pathway via Binding GPR120 to Inhibit Inflammation in Type 2 Diabetes
Authors: Liu Yuanyuan , Guo Mixue , Li Yiwei , Wang Ting , Ren Yi , Wang Rui , Jiang Xin , Zhang Xiaoxia , Wang Hao 
Published: May 2022

Abstract
Background
Type 2 diabetes mellitus (T2DM) is one of the metabolic diseases that increasingly common worldwide. Recent studies confirm that chronic low-grade inflammation is closely associated with metabolic syndromes, and anti-inflammatory therapy is a potential approach for treating T2DM. Accumulating evidence suggests that G-protein coupled receptor 120 (GPR120) activation is a feasible solution to ameliorating chronic inflammation and improving glucolipid metabolism. α-linolenic acid (ALA) has proved to benefit for chronic metabolic diseases. However, the triggering mechanisms of ALA alleviated the inflammation in T2DM by enhancing the expression of GPR120 are still ill-understood. In this study, we investigated the anti-inflammatory potential of ALA in T2DM and uncovered the underlying mechanisms.
Methods
In vivo, SD rats were randomly allocated into 4 groups: pair-fed (PF) with corn oil (CO) group (PF/CO), DM with CO group (DM/CO), PF with ALA group (PF/ALA), DM with ALA group (DM/ALA). A diabetic rat model was generated by a single intraperitoneal injection of streptozotocin-nicotinamide (STZ-NA). Each group was fed diet with or without ALA. In vitro, lipopolysaccharide (LPS) stimulated RAW264.7 mouse macrophages cellular inflammation model was established. The effect of ALA on liver macrophages (Mψs) in T2DM rat was measured by immunofluorescence (IF). The concentrations of TNF-α, IL-6, IL-1β, IL-18 and IL-10 in RAW264.7 cell culture supernatants were analyzed with ELISA kits. The protein expressions of GPR120, β-arrestin2, NLRP3, caspase-1, TLR-4 and NF-κB signaling pathway were investigated with western blot analysis. Furthermore, LPS-induced RAW264.7 cells were treated with AH7614, the GPR120 antagonist, to confirm the effect of ALA dependent on GPR120.
Results
It was shown that the expression of liver Mψs was significantly attenuated in DM/ALA group compared with that in the DM/CO group. In addition, ALA decreased the levels of proinflammatory cytokines (TNF-α, IL-6, IL-1β and IL-18) and increased the levels of anti-inflammatory cytokines (IL-10) in LPS-induced RAW264.7 mouse macrophages. Moreover, ALA markedly inhibited the up-regulation of Toll-like receptor 4 (TLR4), the activation of nuclear factor kappa B (NF-κB) and the expression of the inflammasome components such as NOD-like receptor protein 3 (NLRP3) and caspase-1 in LPS-stimulated RAW264.7 cells. Of note, our observations indicated that expressions of GPR120 and β-arrestin2 were enhanced by the treatment with ALA, suggesting that GPR120 and subsequent recruited β-arrestin2 participated in anti-inflammatory effect. Intriguingly, blocked with GPR120 antagonist, AH7614, the inhibitory effects of ALA on inflammation and TLR4/NF-κB pathway activity in LPS-stimulated RAW264.7 mouse macrophages were weakened.
Conclusion
Collectively, ALA suppressed NF-κB signal pathway and NLRP3 inflammasome activation of macrophage by binding to the GPR120 receptor to ameliorate T2DM.