Gut microbiota mediates SREBP-1c-driven hepatic lipogenesis and steatosis in response to zero-fat high-sucrose diet

Abstract

Objectives: Sucrose-rich diets promote hepatic de novo lipogenesis (DNL) and steatosis through interactions with the gut microbiota. However, the role of sugar-microbiota dynamics in the absence of dietary fat remains unclear. This study aimed to investigate the effects of a high-sucrose, zero-fat diet (ZFD) on hepatic steatosis and host metabolism in conventionally raised (CONVR) and germ-free (GF) mice.

Methods: CONVR and GF mice were fed a ZFD, and hepatic lipid accumulation, gene expression, and metabolite levels were analyzed. DNL activity was assessed by measuring malonyl-CoA levels, expression of key DNL enzymes, and activation of the transcription factor SREBP-1c. Metabolomic analyses of portal vein plasma identified microbiota-derived metabolites linked to hepatic steatosis. To further examine the role of SREBP-1c, its hepatic expression was knocked down using antisense oligonucleotides in CONVR ZFD-fed mice.

Results: The gut microbiota was essential for sucrose-induced DNL and hepatic steatosis. In CONVR ZFD-fed mice, hepatic fat accumulation increased alongside elevated expression of genes encoding DNL enzymes, higher malonyl-CoA levels, and upregulation of SREBP-1c. Regardless of microbiota status, ZFD induced fatty acid elongase and desaturase gene expression and increased hepatic monounsaturated fatty acids. Metabolomic analyses identified microbiota-derived metabolites associated with hepatic steatosis. SREBP-1c knockdown in CONVR ZFD-fed mice reduced hepatic steatosis and suppressed fatty acid synthase expression.

Conclusions: Sucrose-microbiota interactions and SREBP-1c are required for DNL and hepatic steatosis in the absence of dietary fat. These findings provide new insights into the complex interplay between diet, gut microbiota, and metabolic regulation.

Keywords: Gut microbiota; Hepatic steatosis; High-sucrose diet; Metabolomics; SREBP-1c; Zero-fat diet; de novo lipogenesis.

Figure 1

The gut microbiota contributes to ZFD-induced steatosis. Mice were fed ZFD or chow diet for 3 weeks. (A) Body weight gain after diet intervention (n = 4–8/group). (B) Relative weight of EWAT and (C) liver (n = 7–12/group). (D–E) Representative micrographs of Oil Red O staining for neutral lipids. Scale bar = 200 μm. (F) Liver triglyceride-derived fatty acids and (G) relative amounts of SFA, MUFA, and PUFA (n = 3–7/group). (H) Hepatic gene expression determined by qRT-PCR (n = 3–8/group). (I) Liver concentrations of malonyl-CoA (n = 3–7/group). Significant p values for diet and colonization status were determined by two-way ANOVA with Tukey's multiple comparisons. Data are presented as mean ± SD. Abbreviations: CONVR – conventionally raised; GF – germ-free; ZFD – zero-fat diet; SFA – saturated fatty acids; MUFA – monounsaturated fatty acids; PUFA – polyunsaturated fatty acids; Srebf1 – sterol regulatory element binding transcription factor 1; Fasn – fatty acid synthase; Elovl6 – fatty acid elongase 6; Scd1 – stearoyl-Coenzyme A desaturase 1. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Figure 2

Interaction between ZFD and gut microbiota regulates hepatic lipid metabolism. RNA-seq analysis was performed on liver tissue from CONVR (n = 3/diet) and GF (n = 5/diet) mice fed ZFD or chow diet for 3 weeks. (A) Partial least squares (PLS) analysis of liver RNA-seq data, showing sample separation by microbiota status and diet. Each point represents an individual sample. Axes indicate variance explained by the first two PLS components. (B) Microbiota-induced gene regulation in mice fed ZFD (x-axis) or chow (y-axis). (C) Genes regulated by the interaction between diet and gut microbiota. Microbiota-induced regulation in mice fed ZFD (x-axis) or chow (y-axis). (D) Gene ontology categories enriched in subsets of genes located in quadrants Q1 and Q3 in panel (C). Statistical analysis was performed using a two-way ANOVA followed by Tukey's HSD post-hoc test. p-values were adjusted using false discovery rate (FDR) correction, and a corrected p-value <0.05 was considered statistically significant and are displayed in B and C. Abbreviations: CONVR – conventionally raised; GF – germ-free; ZFD – zero-fat diet.

Figure 3

Interaction between ZFD and gut microbiota regulates the portal vein metabolome. Analysis was performed on plasma from CONVR and GF mice fed ZFD or chow diet for 3 weeks (n = 5–6/group). (A) Partial least squares (PLS) analysis based on 536 compounds, showing sample separation by microbiota status and diet. Each point represents an individual sample. Axes indicate variance explained by the first two PLS components. (B) Microbiota-induced metabolite regulation in mice fed ZFD (x-axis) or chow (y-axis). (C) Metabolites regulated by the interaction between diet and gut microbiota. Microbiota-induced regulation in mice fed ZFD (x-axis) or chow (y-axis). Statistical analysis was performed using a two-way ANOVA followed by Tukey's HSD post-hoc test. p-values were adjusted using false discovery rate (FDR) correction, and a corrected p-value <0.05 was considered statistically significant and are displayed in B and C. Abbreviations: CONVR – conventionally raised; GF – germ-free; ZFD – zero-fat diet.

Figure 4

Srebf1 knockdown partially prevents ZFD-induced hepatic steatosis in CONVR mice. Mice were treated with Srebf1-specific ASO for 3 weeks and fed ZFD (n = 4–5/group). (A) Body weight gain, (B) relative EWAT weight, and (C) liver weight. (D) Representative micrographs of Oil Red O staining for neutral lipids. Scale bar = 200 μm. (E) Liver triglyceride-derived fatty acids and (F) relative amounts of SFA, MUFA, and PUFA. (G) Hepatic gene expression determined by qRT-PCR. Significant p values were determined by Student's t-test. Data are presented as mean ± SD. Abbreviations: Srebf1 – sterol regulatory element binding transcription factor 1; ASO – antisense oligonucleotide; SFA – saturated fatty acids; MUFA – monounsaturated fatty acids; PUFA – polyunsaturated fatty acids. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)