Chicco 2016c Abstract MitoFit Science Camp 2016

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Investigating the mechanism of cardiac mitochondrial respiratory impairment in Barth Syndrome.
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Adam Chicco

Chicco AJ, Le CH, Benage LG, Prenni JE, Heuberger AL (2016)

Event: MitoFit Science Camp 2016 Kuehtai AT

Barth Syndrome (3-methylglutaconic aciduria type II; BTHS) is a childhood onset cardioskeletal myopathy that results from mutations in the tafazzin gene encoding a phospholipid transacylase responsible for remodeling cardiolipin in the inner mitochondrial membrane. Cardiolipin is known to be required for optimal function and assembly of respiratory supercomplexes in the inner membrane, but precisely how loss of tafazzin function impairs mitochondrial respiratory function leading to BTHS is unclear. We utilized high-resolution respirometry (HHR) with a variety of substrate combinations to investigate the sites of cardiac mitochondrial dysfunction in the tafazzin shRNA (Taz) mouse model of BTHS, which exhibits ~90% tafazzin deficiency and cardiolipin abnormalities characteristic of BTHS in humans.

Initial HRR studies revealed 50% lower rates of Complex I (CI)-linked OXPHOS respiration in Taz mitochondria compared to wild-type (WT) controls using pyruvate & malate as substrates, while succinate (CII)-supported OXPHOS and maximal enzymatic capacities of complexes I, II-IV and IV were only suppressed by 12-20%. Surprisingly, CI-linked OXPHOS supported by glutamate & malate was 50% higher in Taz, approximating rates of maximal pyruvate-supported OXPHOS in WT, arguing against CI as a primary site of OXPHOS limitation in Taz. To investigate fatty acid-supported OXPHOS, long- (16:0; palmitate) and medium-chain (8:0; octanoate) fatty acids were supplied bound to carnitine (CPT1-independent) or CoA (CPT1-dependent) to address effects on mitochondrial fatty acid transport, activation and acyl-CoA dehydrogenase isozyme-specific function [1].

Results demonstrated significant impairment of respiration supported by both medium and long-chain acyl-carnitines in Taz compared to WT mitochondria, which was blunted when palmitoyl-CoA & carnitine were used as substrates. Interestingly, metabolomic analysis of cardiac tissues revealed an 41% decrease in pantothenic acid that corresponded to a similar loss of mitochondrial CoA content in Taz compared to WT hearts. To test the hypothesis that CoA deficiency limits pyruvate and fatty acid oxidation in Taz, mitochondria were pre-incubated with 100 μM CoA to restore levels prior to repeating HRR experiments with pyruvate or palmitoylcarnitine (& malate). This increased CoA content in both Taz and WT mitochondria and partially rescued OXPHOS supported by substrates to near WT levels, despite having no significant effect on OXPHOS rates with either substrate in WT.


O2k-Network Lab: US CO Fort Collins Chicco AJ


Labels: MiParea: Respiration, mt-Medicine  Pathology: Myopathy 

Organism: Mouse  Tissue;cell: Heart 


Regulation: Substrate  Coupling state: OXPHOS  Pathway: F, N, S, CIV, Other combinations  HRR: Oxygraph-2k  Event: D2  MitoFit Science Camp 2016 

Affiliations

1-Depts. Biomedical Sci, 2-Cell Mol Biol, 3-Biochem Mol Biol, Colorado State Univ, Fort Collins, USA, CO. - Adam.Chicco@colostate.edu

Abstract continued

Taken together, our studies suggest a contributory role of CoA deficiency in Taz-deficient cardiac mitochondrial dysfunction, with potential implications for future study and treatment of BTHS. More broadly, these results highlight the value of comprehensive mitochondrial respirometry and enzyme analysis as means of defining sites of OXPHOS impairment in mitochondrial pathologies as established by Hoppel [2], and the importance of considering the metabolic pathways of respiratory substrates upstream of their associated sites of entry to electron transfer-pathway. In particular, comparison of OXPHOS rates obtained with glutamate versus pyruvate, which are often used interchangeably as CI substrates, might reveal important insights relevant to the mechanisms of mitochondrial adaptation in health and disease.

References

  1. Raja V, Greenberg ML (2014) The functions of cardiolipin in cellular metabolism-potential modifiers of the Barth syndrome phenotype. Chem Phys Lipids 179:49.
  2. Puchowicz MA, Varnes ME, Cohen BH, Friedman NR, Kerr DS, Hoppel CL (2004) Oxidative phosphorylation analysis: assessing the integrated functional activity of human skeletal muscle mitochondria--case studies. Mitochondrion 4:377.