Transcriptomic and Metabolomic Studies Reveal That Toll-like Receptor 2 Has a Role in Glucose-Related Metabolism in Unchallenged Zebrafish Larvae (Danio rerio)

SIMPLE SUMMARY: Toll-like receptor 2 (TLR2) has been demonstrated to participate in the progression of some metabolic disorders due to its role as a pro-inflammatory trigger. However, whether TLR2 plays a role in mediating metabolism under an unchallenged condition is still unknown. Therefore, we utilized zebrafish larvae as an in vivo model to investigate the metabolic control functions of TLR2 through transcriptomic and metabolomic approaches at a whole-organism level. We found that the concentration of glucose, lactate, succinate, and malate is higher in a tlr2 mutant which is associated with lower expression of genes involved in the glycolysis and gluconeogenesis pathways. These results demonstrate that tlr2 plays a role in controlling glucose metabolism homeostasis. ABSTRACT: Toll-like receptors (TLRs) have been implicated in the regulation of various metabolism pathways, in addition to their function in innate immunity. Here, we investigate the metabolic function of TLR2 in a larval zebrafish system. We studied larvae from a tlr2 mutant and the wild type sibling controls in an unchallenged normal developmental condition using transcriptomic and metabolomic analyses methods. RNAseq was used to evaluate transcriptomic differences between the tlr2 mutant and wild-type control zebrafish larvae and found a signature set of 149 genes to be significantly altered in gene expression. The expression level of several genes was confirmed by qPCR analyses. Gene set enrichment analysis (GSEA) revealed differential enrichment of genes between the two genotypes related to valine, leucine, and isoleucine degradation and glycolysis and gluconeogenesis. Using (1)H nuclear magnetic resonance (NMR) metabolomics, we found that glucose and various metabolites related with glucose metabolism were present at higher levels in the tlr2 mutant. Furthermore, we confirmed that the glucose level is higher in tlr2 mutants by using a fluorometric assay. Therefore, we have shown that TLR2, in addition to its function in immunity, has a function in controlling metabolism during vertebrate development. The functions are associated with transcriptional regulation of various enzymes involved in glucose metabolism that could explain the different levels of glucose, lactate, succinate, and malate in larvae of a tlr2 mutant.