Bile acid-CoA:amino acid N-acyltransferase gene knockout alters early life development, the gut microbiome and reveals unusual bile acid conjugates in mice

Abstract

Bile acids are steroid detergents in bile that contribute to fat absorption, cell signaling and microbiome interactions in mammals. The final step in their synthesis is amino acid conjugation with either glycine or taurine to a cholic acid or chenodeoxycholic acid backbone in the liver by the enzyme bile acid-CoA:amino acid N-acyltransferase (BAAT). Here, we describe the microbial, chemical, and physiological consequences of BAAT gene deletion in mice. BAAT-/- mice were underweight after weaning but quickly exhibited catch-up growth. At 3-weeks-of-age, KO animals had increased phospholipid excretion and decreased subcutaneous fat pad mass, glycogen staining in hepatocytes and vitamin A stores in the liver, but these phenotypes were less marked in adulthood. Their bile acid (BA) pool was highly altered throughout the 8-weeks of life but was not completely devoid of conjugated BAs. These animals had 27-fold lower amounts of taurine-conjugated BAs than wildtype in their liver, but similar concentrations of glycine-conjugated BAs and higher microbially-conjugated BAs. The BA pool in BAAT-/- was enriched in a variety of unusual bile acids that were putatively sourced from cysteamine conjugation with subsequent oxidation and methylation of the sulfur group to mimic taurine. KO mice also had an altered microbiome, but most strongly in the first 3-weeks, indicating bile acid conjugation is important for proper microbiome development during the postnatal period. Finally, antibiotic treatment increased taurine, glycine, and the unusually conjugated BAs in BAAT-/- animals, indicating the microbiome was not the likely source of the conjugation. Instead, BA conjugation in KO animals was likely derived from the peroxisomal acyltransferases ACNAT1 and ACNAT2, which are duplications of BAAT in the mouse genome, but inactivated in humans. This study demonstrates that BA conjugation is important for early life development in mice and is facilitated by other host or microbial enzymes besides BAAT in a manner that results in molecular mimics of taurine that may rescue pathological phenotypes.

Comparison of Cosine, Modified Cosine, and Neutral Loss Based Spectrum Alignment For Discovery of Structurally Related Molecules

“…Our lab has recently discovered many new bile acids, for which the MS/MS spectra have been made available as an open access resource. − Additionally, we have collected MS/MS data on a historical library of previously determined bile acids. Although other studies have reported the recent discovery of new bile acids as well, − unfortunately these could not be included in the current analysis as the corresponding MS/MS data are not publicly available yet. Because our continued study of bile acids has given us a deep understanding of this subset of molecules, we can further analyze these data to understand how specific modifications influence spectrum similarity (Figure ).…”

Comparison of Cosine, Modified Cosine, and Neutral Loss Based Spectrum Alignment For Discovery of Structurally Related Molecules

“…[26][27][28][29][30] Additionally, we have collected MS/MS data on a historical library of previously determined bile acids. Although other studies have reported the recent discovery of new bile acids as well, [31][32][33][34][35][36] unfortunately these could not be included in the current analysis as the corresponding MS/MS data are not publicly available yet. Because our continued study of bile acids has given us a deep understanding of this subset of molecules, we can further analyze these data to understand how specific modifications influence spectrum similarity (Figure 5).…”

Biliatresone treatment of pregnant mice causes changes in bile metabolism and liver inflammation in their offspring

“…Interestingly, a recent study found that glycine conjugation in mice does not decrease after BAAT knock down, suggesting that alternate pathways are available for glycine conjugation in mice. These could include microbial bile conjugation as well as conjugation mediated by the peroxisomal acyltransferases ACNAT1 and ACNAT2 [23]. It is unknown whether any these pathways are affected by biliatresone exposure.…”