Lactococcus petauri LZys1 modulates gut microbiota, diminishes ileal FXR-FGF15 signaling, and regulates hepatic function

Abstract

Recent studies have indicated that Lactococcus petauri LZys1 (L. petauri LZys1), isolated from healthy human feces, exhibits a promising probiotic profile in vitro. However, its impact on the physiological status of the host in vivo remains uncertain. The objective of our study was to investigate the effects and mechanisms of orally administering L. petauri LZys1 on gut microbiota and liver function in mice. We administered L. petauri LZys1 through daily oral gavage to C57BL/6 male mice. Subsequently, we analyzed changes in gut microbiota composition using 16S rRNA sequencing and quantified alterations in hepatic-intestinal bile acid (BA) profile. Serum biochemical parameters were assessed to evaluate liver function. Our findings revealed that L. petauri LZys1 led to an increase in body weight, liver mass, and serum aminotransferase levels. Oral administration altered the gut microbiota composition, resulting in reduced diversity and abundance of intestinal bacteria. Additionally, the profiles of BAs were suppressed across organs, associated with the downregulation of the ileum's farnesoid X receptor (FXR)/fibroblast growth factor 15 (FGF15) signaling pathway. The decrease in circulating FGF15 mediated the downregulation of hepatic fibroblast growth factor receptor 4 (FGFR4)/FXR, disrupting BA metabolism and fatty acid oxidation. Our findings suggest that L. petauri LZys1 may impact liver function by influencing the gut microbiota-mediated ileal FXR-FGF15 axis and inhibiting hepatic bile acid metabolism.

Importance: This work elucidated the impact of L. petauri LZys1 on host gut microbiota metabolism and hepatic physiological metabolism. We observed that L. petauri LZys1 administration induced liver weight gain and biochemical parameters changes, in addition to a altered gut microbiota and suppressed bile acid (BA) profiles. Furthermore, we propose that changes in liver status are related to the enterohepatic farnesoid X receptor-fibroblast growth factor axis, which alters bile acid metabolism and disrupts liver function. The above findings suggest that attention should be paid to the effect of probiotics on liver function.

Keywords: FGF15; FXR; Lactococcus petauri LZys1; gut microbiota; liver function.

Fig 1

L. petauri LZys1 regulates liver function. (A) The weight changes at the start (0 week) and end (8 weeks) of the L. petauri LZys1 administration. (B) Body composition analysis after 8 weeks. The OGTT curves (C) and their area under the curves (D) are presented for both the LZys1 group and the control group. (E) The liver mass of the LZys1 group and the control group after 8 weeks. (F) The ratio of liver mass to body weight. Serum biochemical indicators including triglyceride (G), cholesterol (H), HDL (I), cholinesterase (J), ALT (K), ALP (L), AST (M), and ALB (N). Data (A, B, D–N) are expressed as mean ± SEM and were analyzed using two-sample t-test, *P < 0.05. Number of samples is six per group.

Fig 2

L. petauri LZys1 induces the dysbiosis of the gut microbiota. The Ace index (A), Chao index (B), Simpson index (C), and Shannon index (D) of the gut microbiota in LZys1 and control mice. (E) Principal coordinates analysis on the basis of Bray-Curtis dissimilarity of the LZys1 and control groups. (F) Bacterial composition at the genus level. (G) Bacterial composition at the phylum level. (H) The LEfSe analysis between the LZys1 and control groups. (I) The differences between groups at the genus level using the Wilcoxon rank-sum test. The 95% CIs were calculated by the method of bootstrap. Data (A, B, C, D, F, G) are expressed as mean ± SEM and compared by two-sample t-test, *P < 0.05; **P < 0.01. Number of samples is six per group.

Fig 3

L. petauri LZys1 alters BA metabolism. (A) The total amount of BAs in the ileum of the LZys1 and control groups. (B) The ratio of secondary BAs and primary BAs in the ileum. (C) The amount of the conjugated BAs in the ileum. (D) The amount of the unconjugated BAs in the ileum. (E) The significantly different BA components between the LZys1 and control groups in the ileum. (F) The total amount of BAs in cecal contents of the LZys1 and control groups. (G) The ratio of secondary BAs and primary BAs in cecal contents. (H) The total amount of BAs in the liver. (I) The ratio of unconjugated BAs and conjugated BAs in the liver. Data (A–I) are expressed as mean ± SEM and compared by two-sample t-test; *P 0.05, **P < 0.01. Number of samples is five per group.

Fig 4

Alteration in gut microbiota associates with BA metabolism. (A) Heatmap exhibiting Spearman correlation coefficient between gut microbiota and different BA components of the LZys1 and control groups in the ileum. (B) Heatmap exhibiting Spearman correlation coefficient between gut microbiota and the ratio of unconjugated BAs and conjugated BAs in the liver. *P < 0.05, **P < 0.01. The number of samples is five per group.

Fig 5

L. petauri LZys1 decreases ileal-derived circulating FGF15 and downregulates hepatic FGFR4-FXR-mediated BA metabolism and fatty acid oxidation. (A) The expression levels of genes associated with the FXR/FGF15 pathway in the ileum, normalized to β-actin (n = 5, per group). (B) Serum FGF15 concentration (n = 4, per group). (C) Expression of genes associated with the FXR/FGF15 pathway in the liver, normalized to β-actin (n = 6, per group). (D) Representative Western blot images illustrating the level of FGFR4 and FXR protein in the liver (n = 6, per group). (E) The relative grayscale values of Western blot images in (D). (F) The expression of genes associated with BA secretion and synthesis of the conjugated BAs in the liver, normalized to β-actin (n = 6, per group). (G) The expression of genes associated with oxidation of fatty acids in the liver, normalized to β-actin (n = 6, per group). (H) The expression of profibrotic growth factors and proinflammatory cytokine genes in the liver, normalized to β-actin (n = 6, per group). Data (A–H) are expressed as mean ± SEM and compared by two-sample t-test. *P < 0.05, **P < 0.01.

Fig 6

L. petauri LZys1 modulates gut microbiota, diminishes ileal FXR-FGF15 signaling, and regulates hepatic function.