Fig 2: RT-qPCR validation of mRNA expression levels of key enzymes and transporters in glutamatergic and monoaminergic pathways in the EC of mice after CRS exposure. ß-actin and GAPDH were used to normalize the expression levels of genes in control group and CRS group. (A) The mRNA expression levels of SERT, AADC, MAOA, TPH1, TPH2, NET and COMT in monoaminergic pathway were examined by RT-qPCR. (B) The mRNA expression levels of GAD1, EAAT2, GLUL, SNAT1, GLS and VGLUT1 in glutamatergic pathway were tested in both groups through RT-qPCR. (* P<0.05, ** P<0.01, *** P<0.001; n=6-8 mice per group).

Fig 3: Effects of TMAO on BV2 cells.A Effects of TMAO on proliferation of BV2 cells, measured using the MTT assay. B Expression of MAOA, MAOB, COMT, AChE, AMP, CHRNA1, and CHRNB1 in TMAO- damaged BV2 cells. C Expression of circNF1-419 and circ_0001239 in TMAO- damaged BV2 cells. D Expression of circNF1-419 and circ_0001239 in Kombucha tea-treated mice. E Ratio of abundance of Bifidobacterium species and Lactobacillus species was imbalanced in mice fed a HSHF diet and in AD-like mice. Data are the mean ± SD of more than five independent experiments (and three independent experiments when using western blotting). *p < 0.05 and **p < 0.01 vs. the model group by one-way ANOVA, followed by the Holm–Sidak test.

Fig 4: Western blot analysis of protein expression levels of key enzymes and transporters in glutamatergic and monoaminergic pathways in the EC of mice after CRS exposure. ß-actin and GAPDH were used to normalize the expression levels of proteins in control group and CRS group. (A) The protein expression levels of SERT, TH, AADC, MAOA and VMAT2 in monoaminergic pathway were examined by western blott (* P<0.05, n=6-7 mice per group). (B) The protein expression levels of GAD1, EAATT2, GLUL and SNAT1 in glutamatergic pathway were analyzed in both groups. (* P<0.05; n=6-7 mice per group).

Fig 5: MAOA decreases the levels of cellular 5-HT to suppress anti-ferroptotic role of 5-HT. A) Tumor volumes of B16F10 xenograft in C57BL/6 mice (n = 5) supplemented with 5-HT (10 mg kg-1) or IKE (40 mg kg-1). B) Representative images of B16F10 xenograft in C57BL/6 mice (n = 5) supplemented with 5-HT (10 mg kg-1) or IKE (40 mg kg-1). C) Tumor weight of B16F10 xenograft in C57BL/6 mice (n = 5) supplemented with 5-HT (10 mg kg-1) or IKE (40 mg kg-1). D) DPPH assay to test the ability of 5-HT (10 µm) as radical trapping agent, fer-1 (10 µm), lipro-1 (10 µm), and Vitamin E (10 µm) as positive controls. E) Representative autoxidation of STY-BODIPY (1 µm)-embedded liposomes of egg phosphatidylcholine lipids (1 mm, ˜100-nm particle size) suspended in PBS, initiated by 0.2 mm DTUN containing lipro-1 (2.5 µm) or 5-HT for the indicated concentrations. F) Dose-dependent toxicity of RSL3 induced cell death in Be2C cells with or without 5-HT treatment. Cell viability was assessed 24 h thereafter using CCK8. G) Western blot analysis of DDC, MAOA, and MAOB levels in a panel of cancer cells lines. H) Western blot analysis showed that MAOA is undetectable in Be2C MAOA-/- clones. I) LC-MS based quantitative metabolomics of cellular 5-HT in Be2C WT and MAOA KO cells with or without 5-HT (10 µm) treatment. J) Cell death and K) lipid peroxidation measurement of Be2C WT and MAOA KO cells treated with RSL3 (5 µm) and 5-HT (10 µm) for 12 h. L) Western blot analysis of MAOA in Be2C MAOA-/- cells transfected with empty or MAOA vector. M) Cell viability of Be2C MAOA-/- cells transfected with empty or MAOA vector treated with RSL3 (5 µm) for 12 h. N) Dot plot depicting the relevance of the signal intensity of MAOA and 4-HNE IHC staining in the indicated kidney renal clear cell carcinoma samples.