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J Biol Chem. 2016 Dec 9;291(50):26126-26137. Epub 2016 Oct 25.

Natural and Induced Mitochondrial Phosphate Carrier Loss: DIFFERENTIAL DEPENDENCE OF MITOCHONDRIAL METABOLISM AND DYNAMICS AND CELL SURVIVAL ON THE EXTENT OF DEPLETION.

Author information

1
From the MitoCare Center for Imaging Research and Diagnostics, Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, erin.seifert@jefferson.edu.
2
From the MitoCare Center for Imaging Research and Diagnostics, Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107.
3
Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, and.
4
Division of Clinical and Metabolic Genetics, Hospital for Sick Children and Department of Paediatrics, University of Toronto, Toronto, Ontario M5G 1X8, Canada.
5
From the MitoCare Center for Imaging Research and Diagnostics, Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, gyorgy.hajnoczky@jefferson.edu.

Abstract

The relevance of mitochondrial phosphate carrier (PiC), encoded by SLC25A3, in bioenergetics is well accepted. However, little is known about the mechanisms mediating the cellular impairments induced by pathological SLC25A3 variants. To this end, we investigated the pathogenicity of a novel compound heterozygous mutation in SLC25A3 First, each variant was modeled in yeast, revealing that substituting GSSAS for QIP within the fifth matrix loop is incompatible with survival on non-fermentable substrate, whereas the L200W variant is functionally neutral. Next, using skin fibroblasts from an individual expressing these variants and HeLa cells with varying degrees of PiC depletion, PiC loss of ∼60% was still compatible with uncompromised maximal oxidative phosphorylation (oxphos), whereas lower maximal oxphos was evident at ∼85% PiC depletion. Furthermore, intact mutant fibroblasts displayed suppressed mitochondrial bioenergetics consistent with a lower substrate availability rather than phosphate limitation. This was accompanied by slowed proliferation in glucose-replete medium; however, proliferation ceased when only mitochondrial substrate was provided. Both mutant fibroblasts and HeLa cells with 60% PiC loss showed a less interconnected mitochondrial network and a mitochondrial fusion defect that is not explained by altered abundance of OPA1 or MFN1/2 or relative amount of different OPA1 forms. Altogether these results indicate that PiC depletion may need to be profound (>85%) to substantially affect maximal oxphos and that pathogenesis associated with PiC depletion or loss of function may be independent of phosphate limitation when ATP requirements are not high.

KEYWORDS:

confocal microscopy; energy metabolism; live cell imaging; mitochondria; mitochondrial disease; mitochondrial dynamics; mitochondrial transport

PMID:
27780865
PMCID:
PMC5207081
DOI:
10.1074/jbc.M116.744714
[Indexed for MEDLINE]
Free PMC Article

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