Short/Branched Chain Acyl CoA Dehydrogenase Deficiency: a newborn screening disorder and a novel therapeutic target

Introduction

The metabolism of branched chain amino acids (isoleucine, valine and leucine) is tightly regulated, and responds to anabolic and catabolic signals in the cell. These amino acids can either be oxidatively degraded in the mitochondria to provide energy for the cell, alternatively be used as precursors to synthesize new proteins, or also form branched-chain fatty acids with yet enigmatic function(s). The importance of the branched chain amino acid metabolism is illustrated by the association to various diseases: (i) inefficient degradation underlies the inborn metabolic disease Maple Syrup Urine Disease); (ii) reprogramming of the metabolism is a hallmark of pancreatic cancer and glioblastoma; (iii) type-2 diabetes and insulin resistance correlates with inefficient degradation of branched-chain amino acids. This metabolic pathway is therefore a very interesting therapeutic target, and at the Department of Medical Biochemistry, Oslo University Hospital and University of Oslo, we are currently establishing pharmacological inhibitors for several key enzymes in this pathway, to develop future therapies for diseases associated to this pathway.

The Short/Branched Chain Acyl CoA Dehydrogenase (ACADSB) is a mitochondrial flavin-containing enzyme that catalyzes the reduction of 2-methylbutanoyl-CoA to 2-methylbut-2-enoyl CoA in the degradation of isoleucine. Inborn defects of this enzyme causes Short Chain Acyl CoA Dehydrogenase Deficiency, a rare metabolic disease with variable penetrance in newborn children. We believe the reason for the different pathology is due to individual variability in alternative routes for isoleucine degradation. In order to test this, we will investigate the enzymatic activity of recombinant ACADSB towards different substrates and inhibitors and characterize metabolites associated to the degradation of alloisoleucine.

Aim of project
The aim of this project is understand how isoleucine derivates are processed by ACADSB, and determine how intermediates in the isoleucine metabolism accumulates in vivo.

Project plan
The project will consist of the following tasks and methods:

1. Express recombinant human ACADSB using E coli as host and purify enzyme by protein chromatography
2. Structure determination of ACADSB/substrate complexes by X-ray crystallography, and enzymatic characterization of the recombinant enzyme  by spectrophotometric analyses
3. Supply recombinant enzyme with mitochondrial fractions to reconstitute branched-chain degradation in vitro.
4. Perform mass spectrometry-based metabolic tracing of isotope-labelled isoleucine to map metabolism in vivo

Organisation / collaboration

This project will be a joint project between group leaders Bjørn Dalhus, Katja Elgstøen and Lars Eide at the Department of Medical Biochemistry, University of Oslo and Oslo University Hospital. See research group pages:

https://www.ous-research.no/dalhus; https://www.ous-research.no/elgstoen; https://www.ous-research.no/home/larseide;

Internal supervisor is Hans-Petter Hersleth (https://www.mn.uio.no/ibv/personer/vit/hphersle)