Metabolomic signatures and microbial community profiling of depressive rat model induced by adrenocorticotrophic hormone

Abstract

Background: Adrenocorticotrophic hormone (ACTH)-treatment rat model has been utilized as a widely accepted model of treatment-resistant depression. Metabolomic signatures represent the pathophysiological phenotype of diseases. Recent studies in gut microbiota and metabolomics analysis revealed the dramatic role of microbiome in psychoneurological system diseases, but still, the mechanisms underlying gut microbiome-host interaction remain unclear.

Methods: Male Wistar rats were s.c. injection of ACTH fragment 1-24 for 14 days to induce treatment-resistant depression. Depression-related behavioral tests, analysis of serum monoamine neurotransmitters and hypothalamic-pituitary-adrenal (HPA) axis-related hormones were determined for assessment of ACTH-induced depression rat model. A gas chromatography-time-of-flight mass spectrometer based urinary metabolomic signatures integrated 16S rRNA sequence analysis based gut microbial profiling was performed, as well as Spearman's correlation coefficient analysis was used to manifest the covariation between the differential urinary metabolites and gut microbiota of genus level.

Results: Chronic injection of ACTH-induced depression-like phenotype (increased immobility time in forced swimming test and tail suspension test) was accompanied by peripheral serotonin down-regulation and HPA axis overactivation (ACTH and corticosterone up-regulation). Urinary metabolomics analysis indicated that pyruvic acid, L-threonine, mannitol, D-gluconic acid, 4-hydroxybenzoic acid, D-arabitol, myo-inositol and ascorbic acid levels were reduced in ACTH-treated rats' urine, while hippurate level was elevated. In addition, microbial community profiling revealed bacterial enrichment (e.g. Ruminococcus, Klebsiella) and reduction (e.g. Akkermansia, Lactobacillus) in the ACTH-induced depression rat model. Correlation analysis showed that Akkermansia and Lactobacillus were closely relevant to metabolites myo-inositol and hippurate, which were included in host inositol phosphate metabolism, and phenylalanine, tyrosine and tryptophan biosynthesis.

Conclusions: Depression rat model induced by ACTH is associated with disturbance of pyruvate metabolism, ascorbate and aldarate metabolism, inositol phosphate metabolism, glycine, serine and threonine metabolism, and glycolysis or gluconeogenesis, as well as changes in microbial community structure. Gut microbiota may participate in the mediation of systemic metabolomic changes in ACTH-induced depression model. Therefore, integrated metabolomic signatures and gut microbial community profiling would provide a basis for further studies on the pathogenesis of depression.

Keywords: Depression; Gut microbiota; HPA axis; Metabolomics.

Fig. 1

Urinary metabolic profiling (n = 6). PCA score plot (a), V-plots (b, VIP > 1.0), and heat map (c) of the differential metabolites in ACTH group and Control group

Fig. 2

Pathway analysis of urinary metabolites using Metaboanalyst (impact factor ≥ 0.1). (1) Ascorbate and aldarate metabolism; (2) glycine, serine and threonine metabolism; (3) glycolysis or gluconeogenesis; (4) pyruvate metabolism; (5) inositol phosphate metabolism

Fig. 3

Perturbed metabolic pathways and altered urinary metabolites in ACTH-treated rats. Red labeled metabolites were up-regulated, and blue labeled metabolites were down-regulated. Blue blocks represented disturbed metabolic pathways

Fig. 4

a The partial least squares discriminant analysis (PLS-DA) of the microbial community for ACTH group (in green) and Control group (in red), n = 6. b The fecal microbial structures at the phylum level for ACTH group and Control group, different colors represent different microbe at phylum level, n = 6. c LEfSe analysis of gut microbiota for ACTH group and Control group, n = 6. The abundances of taxa from phylum to genus levels were compared between the two groups. Taxa enriched in ACTH group are indicated by a negative LDA score (green), and taxa enriched in Control group have a positive LDA score (red). Only taxa of an LDA significant threshold of 3.0 were shown

Fig. 5

The relevance between the gut microbiota of genus level and the differential urinary metabolites. a Spearman’s correlation heat map: red indicates positive correlation, while blue indicates negative correlation. The deeper color means the greater correlation (*P < 0.05). b The gut microbiota of genus level, predicted by metabolic variation (|r| > 0.3), is labeled with a similarity value. Lines connecting with metabolites show the direction of relevance to each genus of microbe with the red (positive) or blue (negative) lines