Mitochondrial Fusion and Leber’s Hereditary Optic Neuropathy mtDNA Point Mutations Cause Altered Nuclear Gene Expression

Abstract

Abstract: : Purpose: To understand the mechanism of LHON which is caused by inherited mitochondrial mutations. Methods: Affymetrix-based microarray of cells fused with LHON mitochondria. Results: Mutations in mitochondrial DNA-encoded subunits (mtDNA positions 11778, 3460, 14484) of Complex I of the Electron Transport Chain cause Leber’s Hereditary Optic Neuropathy (LHON). Currently the mechanism by which these mutations cause optic neurodegeneration are not known. We have utilized microarray analysis of cytoplasmic-hybrid (cybrid) cells, (Osteosarcoma and Ntera 2/D1 [NT2]) that were created by fusing cells which lack mtDNA with mitochondria from LHON patients. Total RNA was isolated from these cells to identify changes in gene expression in cells bearing LHON mitochondria. Using the Affymetrix microarray U-95 platform, and the Dchip statistical analysis package. Conclusions: We observed that the fusion process itself alters the gene expression profile of cybrid cell lines, and in fact about half of the differences between mutant and control cells were accounted for by the fusion process itself. These include genes involved in mitochondrial oxidative phosphorylation, gene regulation, apoptosis, cytoskeletal maintenance, neural development, and the oxidative stress response. By studing how LHON mutations affect global gene expression we hope to better understand the mechanism behind the degeneration of the optic nerve and subsequent blindness in patients.

Keywords: genetics • neuro-ophthalmology: optic nerve • mitochondria