odendaal4

Coenzyme A (CoA) is a vital cofactor involved in 8-10% of all metabolic reactions in human cells. Different inherited enzyme deficiencies in which the oxidation of acyl-CoAs is hampered have been hypothesised to share a phenotype characterised by toxic accumulation of acyl-CoA and a concomitant decline in free CoA (CoASH) levels, whereby CoASH becomes limiting for other metabolic reactions. This is referred to as CoASH sequestration. There is, however, limited experimental evidence for this hypothesis. Using a combination of approaches, we test this hypothesis in medium-chain acyl-CoA dehydrogenase deficiency (MCADD), the most common deficiency of mitochondrial fatty acid oxidation (mFAO), under energetic stress. Both in vitro MCAD-knockout (KO) HepG2 cells and a kinetic model of mFAO showed decreased CoASH, elevated medium-chain acyl-CoA, and decreased long-chain acyl-CoA levels. MCAD-KO mice exposed to fasting and cold as energetic stressors had a significantly increased total CoA pool and increased expression of CoA biosynthetic enzymes in the liver, indicative of an upregulated CoA biosynthesis. Expression of carnitine acyltransferases and acyl-CoA thioesterases, enzymes that liberate CoASH from acyl-CoAs, was also upregulated, suggesting an adaptive response of CoA metabolism to decreased CoASH. Finally, computational model simulations showed that a combination of elevated total CoA and thioesterase activity led to normalisation of both CoASH and medium-chain acyl-CoA levels. Together, the results provide the first evidence for the CoA sequestration hypothesis in MCADD. The observed adaptation of CoA metabolism under energetic stress may act as a compensatory response that counteracts CoASH depletion and accumulation of toxic medium-chain acyl-CoAs.