Disorders of the branched chain amino acid (BCAA) metabolism are the most common of the organic acidemias identified by newborn screening. The catabolism of leucine (LEU), isoleucine (ILE), and valine (VAL) begins through a set of common transporters and enzymes localized to the mitochondria. Thereafter, the pathways diverge. Four disorders in these pathways share enormous unmet needs for treatment: maple syrup urine disease (MSUD), and isovaleric (IVA), propionic (PA), and methylmalonic acidemias (MMA). This is a renewal application for a project with a long-term goal to characterize BCAA acid metabolism and its deficiencies. Significant progress has been made on each aim of the original project, and our results have provided unique opportunities to study novel therapies. This new application has three specific aims. Specific Specific Aim 1 is to continue characterization of the mitochondrial architecture of BCAA metabolism. Based on our data, I hypothesize that the catabolic enzymes of LEU and ILE/VAL comprise two separate metabolons within the mitochondrial matrix.
Specific Aim 1 a is to examine the physical interactions of BCKADH, IVDH, and 3MCC as a putative metabolon using STED and cryo-CLEM, and cryo-ET techniques.
Specific Aim 1 b is to examine the interactions of the enzymes involved in BCAA catabolism using protein cross linking and co- immunoprecipitation studies.
Specific Aim 2 is to identify novel small molecules to treat IVDH and BCKADH deficiency, either as substrate inhibitors or chemical chaperonins to improve folding of IVDH to restore partial flux through the leucine pathway. I hypothesize that small molecule inhibitors of BCAT will reduce accumulation of toxic intermediates of these disorders, while inhibitors of distal enzymes in the LEU pathway will induce accumulation of proximal substrates and stabilize mutant enzymes.
Specific Aim 2 a is to examine effects of a panel of BCAA catabolism inhibitors on IVDH and BCKADH stability and function in cells from patients with IVA and MSUD. I predict that these molecules will stabilize mutant IVDH and BCKADH proteins, making them compelling candidates for further preclinical drug development.
Specific Aim 2 b is to examine the effect of a BCAT inhibitor on flux through BCAA catabolism, and accumulation of toxic metabolites in cells from patients with IVA and MSUD. I predict that this compound will reduce accumulation of toxic metabolites in cells, identifying it as a potential therapy for IVA and MSUD.
Specific Aim 3 is to examine mitochondrial ETC and TCA cycle dysfunction in cells from patients with PA and MMA. I hypothesize that correction of such defects will allow development of therapeutic agents for these disorders.
Specific Aim 3 a is to examine the use of novel mitochondrial antioxidants to reverse secondary ETC dysfunction in cells from patients with MMA and PA.
Specific Aim 3 b is to examine the effect of restoring TCA cycle imbalance in cells from patients with PA and MMA on bioenergetic imbalance. I propose to study a set of novel synthetic anaplerotic agents in patient cells. I hypothesize that these compounds will be better than existing agent in reversing abnormalities.
Disorders of amino acid metabolism are identified by newborn screening and cause serious disease. This grant studies several of these disorders including isovaleric acidemia, maple syrup urine disease, propionic acidemia, and methylmalonic acidemia and attempt to identify promising new drugs to treat these disorders for clinical testing.
| Bloom, Kaitlyn; Mohsen, Al-Walid; Karunanidhi, Anuradha et al. (2018) Investigating the link of ACAD10 deficiency to type 2 diabetes mellitus. J Inherit Metab Dis 41:49-57 |
