Catabolism of Branched Chain Amino Acids Contributes Significantly to Synthesis of Odd-Chain and Even-Chain Fatty Acids in 3T3-L1 Adipocytes

Abstract

The branched chain amino acids (BCAA) valine, leucine and isoleucine have been implicated in a number of diseases including obesity, insulin resistance, and type 2 diabetes mellitus, although the mechanisms are still poorly understood. Adipose tissue plays an important role in BCAA homeostasis by actively metabolizing circulating BCAA. In this work, we have investigated the link between BCAA catabolism and fatty acid synthesis in 3T3-L1 adipocytes using parallel 13C-labeling experiments, mass spectrometry and model-based isotopomer data analysis. Specifically, we performed parallel labeling experiments with four fully 13C-labeled tracers, [U-13C]valine, [U-13C]leucine, [U-13C]isoleucine and [U-13C]glutamine. We measured mass isotopomer distributions of fatty acids and intracellular metabolites by GC-MS and analyzed the data using the isotopomer spectral analysis (ISA) framework. We demonstrate that 3T3-L1 adipocytes accumulate significant amounts of even chain length (C14:0, C16:0 and C18:0) and odd chain length (C15:0 and C17:0) fatty acids under standard cell culture conditions. Using a novel GC-MS method, we demonstrate that propionyl-CoA acts as the primer on fatty acid synthase for the production of odd chain fatty acids. BCAA contributed significantly to the production of all fatty acids. Leucine and isoleucine contributed at least 25% to lipogenic acetyl-CoA pool, and valine and isoleucine contributed 100% to lipogenic propionyl-CoA pool. Our results further suggest that low activity of methylmalonyl-CoA mutase and mass action kinetics of propionyl-CoA on fatty acid synthase result in high rates of odd chain fatty acid synthesis in 3T3-L1 cells. Overall, this work provides important new insights into the connection between BCAA catabolism and fatty acid synthesis in adipocytes and underscores the high capacity of adipocytes for metabolizing BCAA.

Function and evolution of specialized endogenous lipids in toothed whales

“…BCFA are derived from the catabolism of branched-chain amino acids (BCAA) (Morii and and valine (i-12:0), respectively, and (E) isopalmitic alcohol is a fatty alcohol (i-16:0alc) derived via the valine pathway, common to most acoustic fat bodies. Kaneda, 1982;Brosnan and Brosnan, 2006;Crown et al, 2015). Most amino acids are degraded in the liver; however, BCAA (i.e.…”

“…Most amino acids are degraded in the liver; however, BCAA (i.e. leucine, valine and isoleucine) are poorly metabolized by the liver and instead are degraded in muscle and adipose tissue (Rosenthal et al, 1974;Crown et al, 2015). According to Brosnan and Brosnan (2006), the three BCAA are catabolized simultaneously because the first two degradation enzymes are common, especially the one that is rate-limiting (Shimomura et al, 2001; see Fig.…”

“…The second, and flux-limiting, step is via the branch chain keto-acid dehydrogenase complex, which converts each α-keto acid into its corresponding acyl-CoA: isobutyryl-CoA (valine), α-methylbutyryl-CoA (isoleucine) and isovaleryl-CoA (leucine). These three acyl-CoAs are then processed by their respective dehydrogenase enzymes to another set of intermediates, and after additional enzyme reactions the final products are propionyl-CoA (valine and isoleucine), acetylCoA (isoleucine and leucine) and acetoacetate (leucine) (see Brosnan and Brosnan, 2006;Newgard, 2012;Crown et al, 2015). In adipose tissue, propionyl-CoA is then used for the synthesis of odd-numbered fatty acid chains and acetyl-CoA is the precursor for even-numbered fatty acid chains, both via elongation (Crown et al, 2015).…”

“…These three acyl-CoAs are then processed by their respective dehydrogenase enzymes to another set of intermediates, and after additional enzyme reactions the final products are propionyl-CoA (valine and isoleucine), acetylCoA (isoleucine and leucine) and acetoacetate (leucine) (see Brosnan and Brosnan, 2006;Newgard, 2012;Crown et al, 2015). In adipose tissue, propionyl-CoA is then used for the synthesis of odd-numbered fatty acid chains and acetyl-CoA is the precursor for even-numbered fatty acid chains, both via elongation (Crown et al, 2015). Toothed whales have modified these pathways, particularly in their cranial acoustic fats, to deposit large quantities of isobutylCoA and isovaleryl-CoA-derived fatty acids (Fig.…”

Amino acid biosynthetic routes as drug targets for pulmonary fungal pathogens: what is known and why do we need to know more?

“…Cryptococcal leucine biosynthesis from 2-ketoisovalerate, a biosynthetic pathway absent in humans and requiring the isopropylmalate dehydrogenase Leu1 is required for full virulence in an intranasal murine model of cryptococcosis but remains untested in a cerebrospinal model [30]. Interestingly, branched chain amino acids are precursors for fatty acid synthesis [31,32], which is an essential and quite unexplored field in fungi. For A. fumigatus, the pathogenicity of aroM, metH and cysB;mecA null mutants awaits further validation in systemic infection, and an argEF mutant, of the arginine biosynthesis pathway, which showed decreased virulence in an insect model of infection [33] remains to be tested in animals.…”