Mitochondrial Haplotypes Influence Metabolic Traits in Porcine Transmitochondrial Cybrids

2015 
The mitochondrial genome plays an essential role in energy production, and involves the control of many cell functions including oxidative phosphorylation (OXPHOS), reactive oxygen species (ROS) production, thermogenesis, cellular calcium homeostasis and regulation of apoptosis. The mitochondrial DNA (mtDNA) variation was reported in association with a wide spectrum of human traits, either as specific mutations or deletions leading to metabolic and developmental disorders, or as multiple factors in complex traits, including diseases, athletic performance, body fat mass, metabolic traits and lifespan of humans and other vertebrates1,2,3. In farm animals, mtDNA variations were reported in association with complex traits in pigs4,5, cattle6,7,8, chickens9, ducks10 and donkeys11. However, the phenotypic effects of variations in the mitochondrial genome were difficult to isolate owing to confounding variation in the nuclear genome, epigenetic phenomena, and environmental factors. Few animal models have been available for directly investigating the effect of mtDNA variations on complex metabolic phenotypes in vivo until the creation of transmitochondrial cybrids12. The transmitochondrial cybrid is the fusion of a cytoplast (enucleated cell) to an intact cell (often ρ0) to produce a single cell with mixed mitochondrial populations13,14. The cybrid allows characterization of the biochemical phenotypes of cell lines, and this approach also provides a uniform nuclear background for studies using cytoplasts made from different individuals, eliminating confounding nuclear variables15. In this study, we isolated somatic cells from three pig breeds representing different mitochondrial genome haplotypes: Lantang (C0), Xiang (C1) and Large White (C2). Their mitochondrial DNAs and variations were then characterized. Transmitochondrial cybrids were generated by mitochondria: nuclear transfer using C0 nuclei and mitochondria of either C1 or C2 plasma (schematic diagram see Fig. 1). Using cybrids, mitochondrial respiratory capacity (ATP content and SDH activity) and oxidative stress (ROS production) were compared as measures of energy metabolism. The aim of this study was to shed light on the influences of mitochondrial haplotype by creating an in vivo cellular model. The model would allow separation of phenotypic changes resulting from mitochondrial genome variation from confounding influences imparted by nuclear gene expression, epigenetic phenomena and environmental factors. This study provides the first evidence detailing the mtDNA effect on targeted biochemical traits in pig cells. Figure 1 Schematic representation of the porcine cybrid construction.
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