Figure 5. Butyrate treatment promotes gut mucin, protecting against the adverse effects of old microbiota on leaky gut and inflammation.

(A–C) Old FCM reduced mucin accumulation (PAS [blue] staining) (A) and Muc2 expression in both CMT93 cells (B) and enteroids (C), and butyrate treatment (6 mM) attenuated the decrease. The original magnification of these images was 4×. (D–F) Butyrate (2%) feeding in drinking water significantly reduced leaky gut (FITC-dextran leakage from gut to blood) (D) and increased Muc2 expression in the ileum (E) and fecal mucin content (F) of mice receiving old FMT (green) compared with controls not treated with butyrate (grey). Their gut recovered to the point that it resembled that of the young FMT recipient controls (blue). (G–M) Similarly, old FMT-induced inflammation (Il1b, Il6, and Tnfa) in ileum (G) and brain (H) along with behavioral abnormalities, such as cognitive dysfunction (I), depression (J and K), and anxiety (L and M), were significantly reduced in butyrate-treated old FMT recipient mice (green) compared with controls (gray), until their condition resembled that of young FMT recipients (blue). All the values represent the mean of 5–8 animals or 3–4 independent replicates for each group in the cell and enteroid experiments, repeated 2–3 times, and error bars represent the standard error of means. Statistical significance was determined using 2-tailed Student’s t test or 1- or 2-way ANOVA, as applicable, and P values *^,#P < 0.05, **P < 0.01, and ***^,###P < 0.001 are statistically significant.