Fig 2: The effects of TAK-242 on depressive-like behaviors, and proinflammatory cytokine mRNA expression evoked by Mrp8/14. TAK-242 was administrated (IP) 30 min before the ICV injection of the Mrp8/14 heterodimer. a, b TAK-242 could alleviate the depressive-like behavior induced by Mrp8/14 (n = 7–10 mice/group). c, d The phosphorylation of NF-?B p65 evoked by Mrp14 was decreased after TAK-242 treatment (n = 4 mice/group). e The mRNA expression of proinflammatory cytokines and IBA-1 induced by Mrp8/14 was reduced by TAK-242 administration (n = 6–8 mice/group). *p < 0.05, **p < 0.01, ***p < 0.001 vs vehicle group. #p < 0.05, ##p < 0.01 vs Mrp8/14 group

Fig 3: Changes in behavioral performance, cytokine expression, and TLR4/NF-?B signaling in response to recombinant proteins. After treatment with recombinant Mrp8, Mrp14, or Mrp8/14, depressive-like behaviors were determined by the sucrose preference test and tail suspension test (TST). a Both Mrp14- and Mrp8/14-treated mice exhibited reduced sucrose preference compared with the vehicle group (n = 10 mice/group). b All of the three recombinant proteins could extend the immobility time in TST compared with vehicle treatment (n = 5–6 mice/group). c The results of RT-PCR of the mRNA changes of proinflammatory cytokines and IBA-1 in the hippocampus. n = 4–5 mice/group for TNF-a, IL-6, and IBA-1, n = 3–5 mice/group for IL-1ß. d–i Western blot analyses showed that hippocampal TLR4/NF-?B signaling was activated after these protein treatments, while the RAGE protein was not significantly changed among these groups (n = 4 mice/group). *p < 0.05, **p < 0.01, ***p < 0.001 between two indicated groups. The data are presented as the mean ± SEM

Fig 4: Mrp8/14-induced BV2 microglia activation was alleviated by a TLR4 inhibitor (TAK-242). Cells were administrated with TAK-242 for 30 min before treatment of Mrp8/14 heterodimer. a The iNOS protein level was reduced in Mrp8/14 + TAK-242 group compared with Mrp8/14 group (n = 4 per group). b The iNOS mRNA level was reduced in Mrp8/14 + TAK-242 group compared with Mrp8/14 group (n = 3–4 per group). c The production of nitric oxide (NO) induced by Mrp8/14 was decreased when pretreatment of TAK-242 (n = 3–4 per group). d The representative photos exhibited that the production of reactive oxygen species (ROS) induced by Mrp8/14 was reduced when pretreatment of TAK-242. *p < 0.05, **p < 0.01, ***p < 0.001 between two indicated groups

Fig 5: CUMS induced depressive-like phenotypes and upregulated the expression of Mrp8 and Mrp14 in the hippocampus and serum. a After 4-week chronic unpredictable mild stress (CUMS), mice had a lower body weight than control mice (n = 14–15 mice/group). b, c CUMS resulted in depressive-like behavior, including decreased sucrose preference (n = 10 mice/group) and increased immobility time in tail suspension test (TST) (n = 10 mice/group). d, e Protein levels of Mrp8 (d) and Mrp14 (e) were slightly but statistically significantly increased in the serum of CUMS-exposed mice (n = 10–11 mice/group). f Representative images of western blot. Proteins were extracted from the hippocampus. g, h The quantitative analyses revealed that both Mrp8 (n = 3 mice/group) and Mrp14 (n = 3 mice/group) were increased in the hippocampus of stress mice. *p < 0.05, **p < 0.01 between two groups