Metabolomic Study of a Rat Model of Retinal Detachment

Abstract

Retinal detachment is a serious ocular disease leading to photoreceptor degeneration and vision loss. However, the mechanism of photoreceptor degeneration remains unclear. The aim of this study was to investigate the altered metabolism pathway and physiological changes after retinal detachment. Eight-week-old male SD rats were fed, and the model of retinal detachment was established by injecting hyaluronic acid into the retinal space. The rats were euthanized 3 days after RD, and the retinal tissues were sectioned for analysis. Untargeted lipid chromatography-mass spectrometry lipidomic was performed to analyze the metabolite changes. A total of 90 significant metabolites (34 in anionic and 56 in cationic models) were detected after retinal detachment. The main pathways were (1) histidine metabolism; (2) phenylalanine, tyrosine, and tryptophan biosynthesis; and (3) glycine, serine, and threonine metabolism. The key genes corresponding to each metabolic pathway were verified from the Gene Expression Omnibus (GEO) database of human retinal samples. The results indicated that the production of histamine by histidine decarboxylase from histidine reduced after RD (p < 0.05). Xanthine, hypoxanthine, guanine, and guanosine decreased after RD (p < 0.05). Decreased xanthine and hypoxanthine may reduce the antioxidant ability. The decreased guanosine could not provide enough sources for inosine monophosphate production. Tyrosine is an important neurotransmitter and was significantly reduced after RD (p < 0.05). Citrate was significantly reduced with the increase of ATP-citrate lyase enzyme (ACLY) (p < 0.05). We inferred that lipid oxidation might increase rather than lipid biogenesis. Thus, this study highlighted the main changes of metabolite and physiological process after RD. The results may provide important information for photoreceptor degeneration.

Keywords: amino acid; histamine; metabolomics; retina degeneration; retinal detachment.

Figure 1

Qualification of untargeted metabolomics analysis. (A,B) The PCA analysis of the included samples in both positive and negative models. (C,D) OPLS-DA score plots under the positive and negative models. (E,F) Permutation analysis plots of the OPLS-DA model under the positive and negative models.

Figure 2

Volcano plots of the untargeted metabolomics under the positive model (A) and the negative model (B) according to the criteria FC > 1.5 and p < 0.05.

Figure 3

Heatmap of the different metabolites under the positive model in untargeted metabolomics. The blue color indicates the lower relative level of each metabolite, and the red color stands for the higher relative level of each metabolite.

Figure 4

Heatmap of the different metabolites under the negative model in untargeted metabolomics. The blue color indicates the lower relative level of each metabolite, and the red color stands for the higher relative level of each metabolite.

Figure 5

KEGG pathway indicating the top 20 involved pathways of significantly changed metabolites under the positive model (A) and the negative model (B). The spot size stands for the compound number of metabolites, and the color stands for the p value.

Figure 6

The alternations of histidine metabolism and pathways. (A) The alternations in histidine metabolomics by untargeted metabolomics. (B) The gene alternations of the histidine metabolomic pathway after RD. (C) The summarized pathway of histidine metabolomics, 1 stands for histidine decarboxylase, L-histamine could be catalyzed by histidine decarboxylase, 2 stands for aldehyde dehydrogenase, histamine could be oxidated to imidazoleacetic acid and changed to Imidazol acetate by Aldehyde dehydrogenase, 3 stands for histamine N-methyltransgerase, released histamine is degraded to 1,4-methyl imidazoleacetic acid and it could be changed to 1,4-methylimidazol acetate by Aldehyde dehydrogenase.

Figure 7

The alternations of main metabolomics and related genes of metabolomics in the pathway. (A,B) The changes of purine and pyrimidine metabolism. (C) Gene change of IMPDH1 after RD. (D) The changes of phenylalanine, tyrosine, and tryptophan biosynthesis. (E,F) The changes of genes in tyrosine hydroxylase, phenylalanine hydroxylase, and tyrosinase-related protein1 after RD. (G) Gene change of ATP-citrate lyase enzyme after RD. (H) The changes of glycosylate and dicarboxylate metabolites after RD. (I) Gene alternations of phosphofructokinase 1 (PFK1) and pyruvate dehydrogenase 1 (PDH1) after RD.