Systemic toxicity in hepatic Propionyl-CoA Carboxylase deficiency

Inborn errors in Propionyl-CoA Carboxylase (Pcca/b) cause life threatening propionic acidemia. To understand the contribution of mitochondrial propionyl-CoA metabolism to cellular and systemic metabolic dysfunction, we generated inducible and tissue-specific knockout (KO) mouse models of Pcca. Adult inducible loss of Pcca results in acute metabolic decompensation resembling the inborn error. The liver-specific loss of Pcca largely recapitulates this in a sexually dimorphic manner. Propionate and pyruvate converge in the TCA cycle as major anaplerotic substrates. Paradoxically, the simultaneous KO of Pyruvate Carboxylase (Pcx) rescues the lethality of liver-specific Pcca KO male mice. Most metabolites suspected as deleterious in propionic acidemia are exacerbated in Pcca;Pcx double KO mice with the noted exception of methylcitrate suggesting the centrality of this metabolite to systemic toxicity. These data clarify relevant toxic biomarkers and suggest that rebalancing hepatic TCA cycle metabolism as critical to mitigate the adverse effects of alternative propionyl-CoA metabolism.