INTRODUCTION:

Aminoacyl tRNA synthetases (ARSs) are central and indispensable enzymes facilitating protein synthesis by shuttling amino acids to tRNA molecules. The vital importance of ARSs is exemplified by the embryonic lethality resulting from their knockout in vivo. We aimed to identify the metabolite transported by SLC25A47, a unique mitochondrial carrier specific to hepatocytes. To achieve this goal, we implemented a commercially available hepatocyte-specific knockout mouse model of Slc25a47. Unexpectedly, the genomic recombination of the Slc25a47 locus, in this mouse model, induces a knockdown of the cytosolic tryptophanyl tRNA synthetase (Wars1), found in the same locus (hereafter referred to as the Slc25a47-Wars1 locus).

METHODS:

To delineate the effects associated with Wars1, we employed a co-injection protocol wherein Slc25a47-Wars1^lox/lox mice were administered AAV8_Cre to induce gene locus recombination. Concomitantly, mice were injected with either Slc25a47 or Wars1 enabling us to segregate the phenotypic outcomes attributable to Wars1. The injected viruses were under the human alpha-1 anti-trypsin promoter, which made the expression hepatocyte-specific. C57BL/6J mice were fed either tryptophan-deficient, methionine-deficient, or amino acid-sufficient diets. Body weight was collected twice per week, and an oral glucose and an insulin tolerance test were performed. Significance was determined using Two-way ANOVA followed by Tukey’s post-hoc correction, n=9 mice for the rescue experiment and n=10 mice for the special diet were tested. qPCR analysis of inflammation and fibrosis markers was performed on n=6 mice, and statistical significance was determined using One-way ANOVA followed by Tukey's post-hoc correction.

RESULTS:

The knockdown of Wars1 in hepatocytes induced a hypermetabolic phenotype, reflected by reduced body weight, improved glucose tolerance, and insulin sensitivity. When we compared these phenotypes with tryptophan-deficient and methionine-deficient feeding, we found that Wars1 knockdown in hepatocytes was sufficient to recapitulate the whole-body phenotypes of these amino acid-deprived diets. However, the better metabolic health came at a high cost for the liver, as inflammation and fibrosis were observed after Wars1 knockdown.

CONCLUSIONS:

These findings underscore the significance of amino acid incorporation into protein, particularly within hepatocytes, in governing whole-body homeostasis. Further investigation is warranted to elucidate the central role of hepatocytes and amino acid metabolism in metabolic diseases.