Metabolomic analysis of small intestinal mucosa of SERT KO mice reveals alterations in microbial related metabolites
Authors: Calzadilla Nathan , Qazi Aisha , Sharma Anchal , Comiskey Shane , Eathara Abhijith , Goldberg Zachary , Suarez Ricardo , Saksena Seema , Dudeja Pradeep , Alrefai Waddah , Gill Ravinder 
Published: May 2023

Serotonin (5-HT) regulates intestinal functions such as electrolyte secretion, absorption, blood flow, and motility. 5-HT availability is primarily controlled by the serotonin transporter (SERT), a 12 transmembrane domain transporter that removes extracellular 5-HT through a Na+/Cl- dependent process. SERT KO mice show anxiety like behavior, irritable bowel syndrome like phenotype, metabolic syndrome upon aging, and increased susceptibility to intestinal inflammation, albeit the underlying mechanisms are not yet fully understood. Our previous studies have shown that SERT KO mice exhibit gut microbial dysbiosis and changes in metabolic functions of intestinal microbiome that strongly correlate with altered lipid metabolism gene pathways in the ileum. However, the identity of the key gut microbial metabolites altered in SERT KO small intestinal mucosa that may contribute to its pleiotropic phenotype are not known. Methods: Ileal mucosa from WT (n = 7) and SERT KO (n = 6) C57BL/6J (7-9 wks M) was collected for metabolomic analysis by “Metabolon.” Microbial-related metabolites were determined with MetOrigin. Welch’s t-test (p < 0.05) was used. Results: Our study identified differentially altered metabolites (110 decreased, 65 increased) in ileal mucosa of SERT KO mice. MetOrigin analysis identified 21 altered microbial-related metabolites in SERT KO mice. Interestingly, biopterin, a cofactor involved in the synthesis of 5-HT, was decreased in the absence of SERT. Additionally, lanosterol, a cholesterol precursor and equol, an antioxidative isoflavone derivative, were significantly decreased. Of note, tryptophan metabolites indoleacetylglycine, kynurenate, and xanthurenate were decreased in the ileal mucosa of mice lacking SERT, suggesting decreased tryptophan catabolism in intestinal epithelial cells. Tryptophan metabolism along the kynurenine (kynurenate precursor) pathway has been shown to be anti-inflammatory, offering clues into the pre-inflammatory nature of SERT deficiency. Our analysis also identified 37 altered host/microbial co-metabolized compounds. In the glycolytic pathway, there were decreases in phenylpyruvate and glucose-6-phosphate, indicating impaired energy metabolism in SERT deficiency. Significantly altered nucleotide metabolites in SERT KO mice included increases in purine (adenosine, AMP, inosine, IMP, guanosine, and guanine) and pyrimidine (uridine, 5,6-dihydrouracil, and 5’-CMP) abundance, suggesting increased nucleotide breakdown in the absence of SERT. Several diacylglycerols, which have been shown to play essential roles in regulating innate and adaptive immunity, were abundant in SERT KO mucosa. Conclusion: Our study, for the first time, characterized the small intestinal mucosal metabolic profile in response to SERT deficiency, with the identification of microbial-influenced metabolic alterations in pathways important for energy metabolism, nucleotide utilization, immune regulation and antioxidative function. NIH/NIDDK R01DK 098170 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.