Dysregulation of lipid metabolism appears to be associated with the reduced daily weight gain observed in goat kids fed with milk replacer feeding
Evaluating the effect of milk replacer on the growth performance of goat kids, we found that there was no significant difference in body weight between BM and MR groups on 0 d, 14 d and 28 d after delivery, however, Goats in the BM group gained weight significantly faster than those in the MR group, where kids in the BM group gained 104.64 g/d per day compared to 69.00 g/d in the MR group (P > 0.05; Fig. 1B). Compared with BM kids, stress-related indicators showed a highly significant increase in serum concentrations of Cor, Cort, HIF-α and DAO in the MR group (P < 0.001; Fig S1A), indicators related to pro-inflammation showed a highly significant increase in serum concentrations of IL-1β, IL-6 and TNF-α in the MR group, and a significant decrease in IL-10, an indicator related to anti-inflammation (P < 0.01; Fig S1B), consistent with immune-related indicators including IgA, IgG and IgM showed a similar pattern of decrease (P < 0.01; Fig S1B). The serum Glu index was also significantly decreased in the MR group (P < 0.05; Fig. 1C). To clearly clarify the effect of milk replacer feeding on lipid metabolism in kids, a TC, TG and NEFA indictor were measured in serum and liver samples and revealed that milk replacer feeding treatment decreased TC and NEFA concentrations (P < 0.05; Fig. 1E-F), and no significant effect on TG concentrations in serum and liver (P > 0.05; Fig. 1D). Taken together, these results revealed that milk replacer feeding attenuates weight gain of kids and the lipid metabolism associated with it.
Colonic epithelial lipid transport-related genes profile is influenced by milk replacer feeding
To further investigate the impact of milk replacer feeding on the expression profile of colonic epithelial lipid transport-related genes. We performed transcriptome sequencing using goat colonic epithelium samples. A total of 97.42 Gb clean data was obtained using RNA-seq of 10 colonic epithelium samples, with an average of 668,563,298 high-quality paired reads produced per sample. The alignment rate to the Capra hircus reference genome exceeded 94%. In total, 672 differentially expressed genes (DEGs) were screened, of which 403 were upregulated, and 269 were downregulated (Fig. 2A; Table S4). Among them, genes such as ABCG8, ABCG5, SCTR, SCT, CCL25, PRAP1, FABP2, RBP2, APOC3, SLC5A12, CLDN19, SLC2A2, SLC13A4, LOC102172669, LOC102181858, LOC102186942 and LOC102186759 were significantly upregulated in the MR group. In contrast, the genes AQP5, OSR2, HOXD10, MRAP2, KRT4 and KRT6A were significantly downregulated in the MR group (|log2FC| ≥ 1 and P-adjust < 0.05; Fig. 2B). Among them, this DEGs mainly enriched in cholesterol metabolism pathway (involved in APOC3, ABCG8, SOAT2 and ABCG5), steroid hormone biosynthesis pathway, bile secretion pathway (involved in SCT, ABCG8, LOC102181069, ABCG5 and SCTR), fat digestion and absorption pathway (involved in FABP2, ABCG8 and ABCG5), insulin secretion pathway (involved in CREB3L3, SLC2A2 and PDX1) and PPAR signaling pathway (involved in FABP2 and APOC3) (Fig. 2C). They were also enriched in 336 Gene Ontology (GO) categories, mainly including negative regulation of cholesterol transport, negative regulation of sterol transport, negative regulation of intestinal lipid absorption, negative regulation of intestinal cholesterol absorption, and negative regulation of intestinal phytosterol absorption (Fig. S2A). Based on the functional enrichment analysis network, the significantly enriched pathways mainly involve downstream pathways related to negative regulation of cholesterol transport (Fig. S2B). Taken together, milk replacer feeding significantly upregulates the expression of genes associated with negative regulation of lipid metabolism in the colon, leading to lipid dysfunction in goat kids.
Milk replacer feeding altered the colonic microbiota and potential function in goat kids
To further investigate the effects of milk replacer feeding treatment on gut microbial composition and function in goat kids and the correlation between the colon microbes with lipid metabolism. The variety of the bacteria in the colon was examined in the two groups. According to the Shannon and Chao index, the MR group generally had less alpha diversity at the species level than the BM group (P = 0.02, Fig. S2A). Principal coordinate analysis (PCoA) at species level showed a clear separation of microbial community structure between the two groups (ANOSIM, r = 0.996, P = 0.001, Fig. 3A). We also analyzed variations in microbial communities between the two groups at the phylum level, and we found that the abundance of Firmicutes was significantly lower in the MR groups than in the BM group. In contrast, the abundance of Actinobacteria was significantly higher in the MR groups than in the BM group (Fig. 3B). At the genus level, the abundance of Megamonas, Bifidobacterium, Prevotella, and Parabacteroides were significantly increased in the MR group (P < 0.05, Fig. S2B), however, the abundance of Clostridium, Subdoligranulum, Faecalibacterium, Eubacterium and Lachnoclostridium were significantly decreased in the MR group (P < 0.05, Fig. S2B). Using linear discriminate analysis effect size (LEfSe) analysis to identify additional key signature species, it was discovered that MR goats had significantly higher levels of Bacteroides plebeius CAG 211, Lactobacillus mucosae, Bacteroides coprocola CAG 162, Bifidobacterium longum, Prevotella sp 109, Ruminococcus gnavus CAG 126, and Megamonas funiformis CAG 377 (LDA > 3.5, Fig. 3C; Table S5), and BM goats had significantly higher levels of Bacteroides vulgatus, Subdoligranulum variabile, Faecalibacterium prausnitzii, Ruminococcaceae bacterium AM2, Flavonifractor plautii, Clostridia bacterium UC5.1-1D1, Eubacterium desmolans, Staphylococcus sp CAG 324, Lactobacillus reuteri, Pseudoflavonifractor capillosus, and Butyricimonas virosa (LDA > 3.5, Fig. 3C). Further analysis of the differences in colonic microbial interaction networks between the two groups revealed that the MR group formed an interaction network with core species including Bacteroides plebeius, Escherichia coli, Bacteroides finegoldii, Bacteroides coprophilus, Parabacteroides distasonis, Olsenella sp. DNF00959, Ruminococcaceae bacterium GD1, Sutterella wadsworthensis, and Blautia sp. KLE 1732 (Degree Centrality > 0.45; Fig. S4), while the BM group formed an interaction network with core species including Clostridia bacterium UC5.1-1D1, Eubacterium desmolans, [Ruminococcus] gnavus, Lactobacillus amylovorus, Alistipes sp. HGB5, Alistipes finegoldii, Firmicutes bacterium CAG:424, Clostridium sp. ATCC BAA-442, and Blautia sp. KLE 1732 (Degree Centrality > 0.45; Fig. S4). This further confirms the influence of milk replacer feeding on the core structure of colonic microbiota.
At the functional level, the microbiota in the MR group was mainly enriched in pathways related to ‘starch and sucrose metabolism’, ‘fructose and mannose metabolism’, ‘biosynthesis of amino acids’, ‘phenylpropanoid biosynthesis’, ‘oxidative phosphorylation’, and ‘beta-Lactam resistance’, while the microbiota in the BM group was mainly enriched in ‘ABC transporters’, ‘pyruvate metabolism’, ‘aminoacyl-tRNA biosynthesis’, and ‘amino sugar and nucleotide sugar metabolism’ (Fig. 3F). Further analysis of the differences in the abundance of CAZyme genes encoding carbohydrate enzymes in the colonic microbiota revealed that, compared to the BM group, the MR group showed significantly upregulated enzyme gene expression related to the synthesis of glucose from butyrate (Fig. 3D), as well as enzymes involved in the degradation of L-Leucine, L-Valine, and L-Isoleucine, which are precursors for Gluconeogenesis, TCA cycle, and Fatty acid synthesis (Fig. 3E). This further confirms that disturbances in the core structure of colonic microbiota caused by milk replacer feeding may potentially affect the host's absorption and utilization of energy and lipid nutrients.
The correlations between the level of serum triglyceride (TG) and cholesterol (TC) and liver triglyceride, cholesterol and free fatty acid (NEFA) and changes in microbial abundance were evaluated by Spearman’s correlation analysis. We found that liver cholesterol and liver free fatty acid concentrations positive correlated with Clostridia_bacterium_UC5.1-1D1, Eubacterium desmolans, Flavonifractor plautii, Ruminococcaceae_bacterium_AM2, Faecalibacterium prausnitzii, Lactobacillus reuteri and Subdoligranulum variabile, negatively correlated with Bacteroides_plebeius_CAG:211, Bacteroides coprocola, Bacteroides plebeius. Besides, Bacteroides fragilis abundance positively correlated with liver NEFA, [Ruminococcus] gnavus negatively correlated with liver cholesterol concentrations, and Butyricimonas virosa positively correlated with liver cholesterol concentrations (Fig. 3G). In conclusion, these results indicated that the changes in colonic microbial composition and function during milk replacer feeding may potentially impact the host's lipid metabolism capabilities.
Milk replacer feeding affect the colonic content lipid metabolism pathways in goat kids
We analysed the effect of milk replacer feeding on differential metabolites in the colonic contents of goat kids using an LC-ESI-MS/MS system. A total of 272 metabolites were significantly altered in the MR group compared to the BM group, of which 56 metabolites were significantly downregulated and 216 metabolites were significantly upregulated (Table S6). Interesting, 44 metabolites were undetectable in the BM group, while they exhibited a high abundance in the MR group, primarily including carnitine and fatty acid-like compounds (Rs-mevalonic acid, salicylaldehyde, 3-hydroxypicolinic acid, nicotinuric acid, and 3-hydroxyhippuric acid) (Fig. 4A; Table S6). Furthermore, 15 metabolites were exclusively abundant in the BM group and were not detectable in the MR group, mainly belonging to the bile acid class (lithocholic acid, hododeoxycholic acid, glycine deoxycholic acid, and deoxycholic acid) (Fig. 4B). We further calculated Spearman’s rho coefficients between the DEG and colonic luminal metabolites, and coefficients greater than 0.8 with a P-value < 0.05 were considered significant. We found that the lipid metabolism genes ABCG5、ABCG8、SCTR、SCT was positively correlated with the metabolites choline, spermidine, acetaminophen, glycocholic acid, glutathione, DL-carnitine and cyclic amp involved in the bile acid secretion pathway and negatively correlated with deoxycholic acid and lithocholic acid. LOC102172669, LOC102186942, LOC102181858 and LOC102186759 genes was positively correlated with the metabolites LTE4, 19(S)-HETE, 5,6-DiHETrE and 20-HETE involved in the arachidonic acid metabolism pathway and negatively correlated with 15-deoxy-δ-12,14-PGJ2 (Fig. 4C).
To further analyze the correlation between differential metabolites and distinct colonic microbiota, Spearman’s coefficients between differential microbial and metabolites were then calculated, and coefficients greater than 0.8 with a P-value < 0.05 were considered significant. Interestingly, we found Bacteroides coprocola abundance positively correlated with carnitine C13:0 Isomer1, glycine linoleate, 2-methylbutyroylcarnitine, DL-carnitine, Cis-9,10-epoxystearic acid, punicic acid, linoleic acid C18:2N6C, carnitine C18:2-OH and O-phosphorylethanolamine involved in the FA. Ruminococcus_gnavus_CAG:126 abundance positively correlated with carnitine. Among the metabolites of oxidized lipid, Bacteroides_plebeius_CAG:211 positively correlated with 9,10-EpOME, 12,13-EpOME, 9,10-DiHOME, 12,13-DiHOME and 6-keto-PGF1α. Lactobacillus_reuteri, Megamonas_funiformis and Bacteroides_dorei negatively correlated with 9-HOTrE, 13(R)-HODE, 20-HETE and 9-HpODE. Lactobacillus_reuter positively correlated with glycine deoxycholic acid. Faecalibacterium_prausnitzii, Pseudoflavonifractor_capillosus, Ruminococcaceae_bacterium_D16, Eubacterium_desmolans and Subdoligranulum_variabile positively correlated with β-murine, taurodeoxycholic acid, deoxycholic acid and glycine deoxycholic acid involved in the bile acids. Ruminococcus_gnavus_CAG:126 negatively correlated with hododeoxycholic acid and lithocholic acid (Fig. 4D). These findings indicated that colon microbiota reshaping induced by milk replacer feeding leads to a deficiency in colonic secretion of certain secondary bile acids.
Milk replacer feeding affect the serum metabolism pathways in goat kids
Untargeted metabolome profiles were generated on goat serum samples using an LC-ESI-MS/MS system to assess the effect of milk replacer on differential metabolites in serum. We found 39 metabolites were significantly downregulated, and 20 metabolites were significantly upregulated in MR group (Fig. 5A; Table S7). Among them, 1,7-Dimethylxanthine, 9-HpODE, Lysope 14:0, 13-oxoODE, octapentaenoic acid, 9(S)-HpOTrE, 5,6-EET and 5,6-DiHETrE were the top 10 upregulated metabolites in the MR group. Lithocholic acid, carnitine C17:0, β-murine, urocanic acid, glycyl-L-proline, 1,2-dioctanoyl PC, 23-deoxydeoxycholic acid, 5-HETrE, capric acid (C10:0) and linoleylethanolamide were the top 10 downregulated metabolites in the MR group. Interestingly, we found that some metabolites were in high relative abundance in the BM group such as urocanic acid, 1,2-dioctanoyl PC, 5-HETrE, capric acid C10:0, linoleylethanolamide and 6-hydroxynicotinic acid, while phenylpyruvic acid, 1,7-Dimethylxanthine, 5,6-EET, methanesulfonic acid, tetracosaenoic acid and hydrocinnamic acid were in high abundance in the MR group (Fig. 5B-C; Table S7).
The KEGG compound database generated the KEGG enrichment to describe the effect of milk replacer on these responsive metabolites and revealed that the ‘arachidonic acid metabolism’, ‘Biosynthesis of unsaturated fatty acids’, ‘Cholesterol Metabolism’, ‘Fatty acid biosynthesis’, ‘Fatty acid degradation’, ‘Fatty acid elongation’, ‘Fatty acid Metabolism’, ‘Linoleic acid metabolism’, and ‘alpha − Linolenic acid metabolism’ were the most significantly affected pathways (Fig. 5D). The metabolic pathways significantly downregulated were ‘fatty acid elongation’, ‘fatty acid metabolism’ and ‘epithelial cell signaling in helicobacter pylori infection’ in the MR group (Fig. 5E). This further corroborates that milk replacer feeding significantly disrupts the concentrations of metabolites involved in lipid metabolism in the serum, thereby impacting the host's lipid metabolism capacity.
Formula feeding affect the lipid metabolism profile is transferable by IMT
To validate the causal relationship between milk replacer feeding-induced colonic microbiota disruption and host lipid metabolism, we transferred the colon microbiota from BM and MR group to bacterial-restricted SPF C57/6J mice (Fig. 6A). Compared with BM_IMT mice, the weight of MR_IMT mice decreased from day 12 of transplantation, and the weight difference between the two groups was significant at day 20 of transplantation (Fig. 6B). The organ indexes of liver and spleen of BM_IMT and MR_IMT mice showed no significant difference (Fig. 6C). To clarify the causal relationship between hindgut microbes and lipid metabolism in goat, we evaluated the effects of microbiota on lipid metabolism ability of mice. The levels of TC, TG and NEFA indictor were measured in serum and liver samples and revealed that MR_IMT group significantly decreased TC concentrations in liver and NEFA concentrations in serum and liver compared with the BM_IMT group but no significant effect on TG concentration in serum and liver (Fig. 6D-G). The mRNA expression level of genes associated with lipid metabolism in the NC, Ab, BM_IMT and MR_IMT treatment groups was further investigated. There was a significant increase in the mRNA expression of ABCG5, ABCG8 and FABP2 in the MR_IMT group, while the mRNA expression of RBP2 and APOC3 showed no significant difference (Fig. 6H).
We conducted 16S rRNA gene sequencing to examine the colon bacteria composition to confirm that fecal transplantation modulates the gut microbiota. Our results indicated that α-diversity (via Chao and Pd Index) and β-diversity were not significantly different in the BM_IMT and MR_IMT group (Fig. S5A-B). At the genus level, the abundance of Bacteroides, Colidextribacter, Parabacteroides and Escherichia-Shigella were enriched in the MR_IMT group, while u_f_Eggerthellaceae and Holdemania were enriched in the BM_IMT group (Fig. S5C). The ASV-level analysis showed that the relative abundance of ASV131 (Bacteroidaceae), ASV266 (Lachnospiraceae) were detected in the BM_IMT group. Moreover, the relative abundance of ASV398 (Muribaculaceae), ASV94 (Muribaculaceae), ASV6 (Muribaculaceae), ASV233 (Clostridia_UCG-014), ASV472 (Clostridia_vadinBB60), ASV993 (Sutterellaceae), ASV383 (Sutterellaceae) were not identified in the BM_IMT group (Fig. S5D). These results causally confirm that milk replacer feeding-induced colonic microbiota disruption is associated with a phenomenon that can affect the host's lipid metabolism capacity, with potential cross-species implications.