Background
Methylmalonic acidemia (MMA) and propionic acidemia (PA) are related disorders of mitochondrial propionate metabolism, caused by defects in methylmalonyl-CoA mutase (MUT) and propionyl-CoA carboxylase (PCC), respectively. These biochemical defects lead to a complex cascade of downstream metabolic abnormalities, and identification of these abnormal pathways has important implications for understanding disease pathophysiology. Using a multi-omics approach in cellular models of MMA and PA, we identified serine and thiol metabolism as important areas of metabolic dysregulation.
Conclusion
We identified abnormal serine metabolism as a novel area of cellular dysfunction in MMA and PA, thus introducing a potential new target for therapeutic investigation.
Methods
We performed global proteomic analysis of fibroblasts and untargeted metabolomics analysis of plasma from individuals with MMA to identify novel pathways of dysfunction. We probed these novel pathways in CRISPR-edited, MUT and PCCA null HEK293 cell lines via targeted metabolomics, gene expression analysis, and flux metabolomics tracing utilization of 13C-glucose.
Results
Proteomic analysis of fibroblasts identified upregulation of multiple proteins involved in serine synthesis and thiol metabolism including: phosphoserine amino transferase (PSAT1), cystathionine beta synthase (CBS), and mercaptopyruvate sulfurtransferase (MPST). Metabolomics analysis of plasma revealed significantly increased levels of cystathionine and glutathione, central metabolites in thiol metabolism. CRISPR-edited MUT and PCCA HEK293 cells recapitulate primary defects of MMA and PA and have upregulation of transcripts associated with serine and thiol metabolism including PSAT1. 13C-glucose flux metabolomics in MUT and PCCA null HEK293 cells identified increases in serine de novo biosynthesis, serine transport, and abnormal downstream TCA cycle utilization.