High-fat diet mainly loaded gut microbiome diversity
To determine the impact of SD and HFD-induced obesity on the baseline composition of the gut microbiome, fecal samples were collected, and shotgun metagenome sequencing was performed for taxonomic profiling and functional analysis. To calculate inter-group dissimilarity (beta-diversity), we computed the Bray-Curtis dissimilarity, and unweighted and weighted Unifrac. Beta-diversity-based principal coordinate analysis plots (Fig. 1b and Supplementary Fig. 2) showed a strong distinction by diet. This means that diets had a greater impact on gut microbial diversity than that of sleep variables. In the permutational multivariate analysis of variance test (Fig. 2c), diet showed a significant effect, but sleep did not cause significant differences between the groups (Fig. 1C).
At the phylum level, the Firmicutes/Bacteroidetes (F/B) ratio is significantly associated with intestinal homeostasis 22. The HFD significantly increased the microbiota F/B ratio by increasing the content of Firmicutes; in contrast, SD decreased the F/B ratio, but the difference was not statistically significant (Tables 1 and 2). Figure 1D shows the intragroup diversity (alpha diversity) expressed using the Shannon index. The HFD decreased alpha diversity while SD increased alpha diversity, but these changes were not statistically significant. At the genus level, the HFD decreased the relative abundance of the genera Prevotella and Muribaculum and increased that of Lactococcus. SD increased the abundance of Firmicutes (Fig. 1E and 1F).
Predictive metabolomic profiling of gut microbiota following sleep deprivation and consumption of a high-fat diet
Gut microbiota composition was then examined at the species level. Figure 2A shows the diverse compositions of the bacterial species within each group. The HFD reduced the relative abundance of Muribaculum intestinale and Prevotella MGM1 and MGM2 and increased the abundance of Anaerotruncus colihominis and Lactococcus lactis. When compared to that in the control (EC + SCD group), Muribaculaceae bacteria DSM 103720 abundance increased in the SD + SCD group but not in the SD + HFD group. When SD and an HFD were combined, Ileibacterium valens was a key player (Fig. 2B). Principal component analysis (PCA) ordination plots of the relative abundance of species indicated the main drivers of each principal component (Fig. 2C).
The gut microbiota is an important part of host digestion, and this process results in hundreds of microbial metabolites 23. Recent findings suggest that there is a bidirectional link between the brain and intestine, the so-called gut-brain axis (GBA); microbial metabolites are major mediators of this communication 23–25. To understand the metabolic effects of sleep and diet, we performed strain-level functional pathway-enriched pathway analysis (Fig. 2D). Among the enriched pathways, inosin-5’-phosphate (5’-IMP) biosynthesis-related strains were significantly increased in the SD + HFD group compared to those in the other groups.
Transcriptome analysis of mouse large intestine after sleep deprivation and consumption of a high-fat diet
Next, to compare the effects of sleep and diet on the gut transcriptome, we performed RNA-seq analysis of the large intestine of mice from the EC + SCD, EC + HFD, SD + SCD, and SD + HFD groups. PCA was performed to reveal the major stress on the gut transcriptome between sleep and diet. Figure 3A depicts the results. Unlike the gut microbiota, which was mostly affected by diet, the gut transcriptome was primarily affected by sleep. In a DEG analysis (Fig. 3B), 90 genes were upregulated, and 26 genes were downregulated in the SD + SCD group compared to those in the EC + SCD group. Gasdermin C-like 2 (Gsdmcl2), chymase 1 (Cma1), solute carrier family 37 member 2 (Slc37a2), Alpha-2,8-sialyltransferase 8E (St8sia5), and gasdermin C4 (Gsdmc4) genes were the top five upregulated DEGs (based on P-value). Stress-associated endoplasmic reticulum protein 1 (Serp1), death-associated protein 1(Dap), transmembrane protein 35A (Tmem35a), ubiquitin-like modifier enzyme 5 (Uba5), and bone gamma-carboxyglutamate protein 3 (Bglap3) were the top five downregulated DEGs (based on P-value). In the HFD group, only 11 genes were upregulated, and 23 genes were downregulated (SD + HFD vs. EC + HFD). The Serp1 gene was also one of the top five downregulated genes in the SD + HFD group compared to that in the EC + HFD group (Fig. 3B).
Gsdmcl2, Cma1, Slc37a2, and St8sia5 were downregulated in the SD + HFD group compared to those in the EC + SCD group, but were upregulated in the SD + SCD group compared to those in the EC + SCD group (Fig. 3B). After SD, the tumor protein D52-like 1 (Tpd52l1), cellular communication network factor 3 (Ccn3), and UDP-GlcNAc:betaGal beta-1,3-N-acetylglucosaminyltransfera 9 (B3gnt9) genes were downregulated in both SCD- and HFD-fed mice (Supplementary Fig. 3).
The KEGG enrichment analysis indicated that DEGs between the SD + SCD and EC + SCD groups were enriched in digestive system-related pathways, including “Pancreatic secretion” and “Protein digestion and absorption” (Fig. 3C). The DEGs between the SD + HFD and EC + HFD groups were enriched in nucleic acid metabolism-related and lipid metabolism-related pathways (Fig. 3C and 3D). Figure 3E shows the common GO terms related to SD. The nutrient metabolism-related terms, including “carbohydrate biosynthetic process,” “fatty acid metabolic process,” and “glycoprotein biosynthetic process,” and immune system-related terms, including “cytokine-mediated signaling pathway,” “leukocyte migration,” and “macrophage-derived foam cell differentiation,” were highly enriched in both the SCD and HFD conditions after SD (Fig. 3E).
Using DEGs among the four groups, we performed heatmap clustering analysis. Figure 3F shows a heatmap of GO terms based on the DEGs in each cluster. Cluster A, which was composed of DEGs in the EC + HFD group, included immune system-related GO terms such as “leukocyte proliferation,” “lymphocyte proliferation,” and “regulation of mononuclear cell proliferation.” Cluster D, which was composed of DEGs in the EC + SCD group, included DNA replication-related genes (Fig. 3F).
Neuroinflammatory changes in the brain after sleep deprivation and consumption of a high-fat diet
To identify neuroinflammatory changes associated with SD or an HFD in the brain, we employed a nanoString neuroinflammation panel 26, which covers 770 genes related to neuroinflammation in the brain. Figure 4A shows volcano plots of the DEGs between each group. Under the SCD, cathepsin S (Ctss), endothelial cell adhesion molecule (Esam), and minichromosome maintenance complex component 6 (Mcm6) were the top three upregulated genes, and aspartate beta-hydroxylase (Asph), ribosomal protein S (Rps21), and BRCA-associated RING domain 1 (Bard1) were the top three downregulated genes after SD. The mcm6, C-C motif chemokine ligand 4 (CCl4), and interleukin 1 receptor kinase 3 (Irak3) genes were upregulated in the EC + HFD group compared to those in the EC + SCD group (Fig. 4A).
Using DEGs from the four groups, we compared the expression patterns in each group. In the SD + HFD group, Fc epsilon receptor 1 g (Fcer1g), growth arrest and DNA damage inducible alpha (Gadd45a), and RAS like proto-oncogene B (Ralb) gene expression was significantly increased compared to that in the other groups (Fig. 4B). Figure 4C shows the DEGs between each group and their roles in neuroinflammation. Under the SCD, five genes related to adaptive immune response, three genes related to microglial function, and three genes related to the cell cycle were differentially expressed after SD. Under the HFD, two genes related to cytokine signaling, two genes related to the innate immune response, and three genes related to microglial function were differentially expressed after SD. Adaptive immune response-related genes did not show significant differences between the SD + HFD and EC + HFD groups. Sialic acid-binding Ig-like lectin 1 (Siglec1), a marker for active neuroinflammation 27, was highly expressed in the SD + HFD group compared to that in the SD + SCD group. Compared with that in the EC + SCD group, the SD + HFD group had the highest number of DEGs (Fig. 4A). These genes were related to inflammation, neuropathology, and microglial function (Fig. 4D).
Integration analysis of gut microbiome and host gene expression
To identify the main factors that mediate the microbiota-gut-brain interactions, we performed multi-omics factor analysis (MOFA) by integrating microbiome and gene expression data 28,29. Figure 5A displays the four determinants discovered by the factor analysis. Among the four factors, factors 1 and 2 showed effective discriminating values (Fig. 5A and Supplementary Fig. 4). The variable with the largest weight in factors 1 and 2 was from the microbiome layer. Prevotella sp. MGM1 in factor 1 and Bacteroides satori in factor 2 showed the highest weight in this analysis (Fig. 5B and Supplementary Fig. 5).
To determine the main driver of the microbiota-gut-brain interactions, we performed factor analysis. MOFA2 revealed that the major feature of factors 1 and 2 was gut bacteria (Fig. 5 and Supplementary Fig. 5). This suggests that the main driver of microbiota-gut-brain interactions with SD and an HFD is the gut microbiome. Notably, the SRSF3 genes in the gut showed significant negative correlations with factors 1 and 2. According to recent studies, SRSF3 suppresses tumorigenesis 54 and inhibits cellular senescence 55. Thus, reduced SRSF3 expression might be an important contributor to gastrointestinal dysfunction caused by SD and an HFD.
Our study had several limitations. First, we performed an MOFA based on microbiome and transcriptome data. Further evidence, such as the blood metabolome and gut proteome, is required to substantiate our conclusions. Second, we only tested adult male mice. As a result, sex differences and aging were not reflected in our study.
In summary, our study revealed novel associations between the gut microbiota and host responses after SD and diet-induced obesity. Obesity with SD has deleterious effects on gut and brain health. We discovered that the gut microbiota may be the primary driver of microbiota-gut-brain interactions, and 5'-IMP may be an essential microbial metabolite that facilitates gut-brain communication. These findings imply that healing gut dysbiosis may be a viable therapeutic target for enhancing sleep quality and curing obesity-related dysfunction.