Animal models of human mitochondrial DNA mutations

Abstract

Background: Mutations in mitochondrial DNA (mtDNA) cause a variety of pathologic states in human patients. Development of animal models harboring mtDNA mutations is crucial to elucidating pathways of disease and as models for preclinical assessment of therapeutic interventions.

Scope of review: This review covers the knowledge gained through animal models of mtDNA mutations and the strategies used to produce them. Animals derived from spontaneous mtDNA mutations, somatic cell nuclear transfer (SCNT), nuclear translocation of mitochondrial genes followed by mitochondrial protein targeting (allotopic expression), mutations in mitochondrial DNA polymerase gamma, direct microinjection of exogenous mitochondria, and cytoplasmic hybrid (cybrid) embryonic stem cells (ES cells) containing exogenous mitochondria (transmitochondrial cells) are considered.

Major conclusions: A wide range of strategies have been developed and utilized in attempts to mimic human mtDNA mutation in animal models. Use of these animals in research studies has shed light on mechanisms of pathogenesis in mitochondrial disorders, yet methods for engineering specific mtDNA sequences are still in development.

General significance: Research animals containing mtDNA mutations are important for studies of the mechanisms of mitochondrial disease and are useful for the development of clinical therapies. This article is part of a Special Issue entitled Biochemistry of Mitochondria.

Figure 1

Creation of Cybrid Cells via Somatic Cell Nuclear Transfer (SCNT). Somatic Cell Nuclear Transfer (SCNT) is performed by transferring a nucleus isolated from a somatic cell (or the intact somatic cell) into an enucleated zygote. This technology was developed and used to produce both homoplasmic and heteroplasmic cybrid models.

Figure 2

Nuclear Expression and Subsequent Mitochondrial Transport of a Recombinant Mitochondrial Gene (Allotopic Expression). Allotopic expression of a mitochondrial gene occurs as the coding sequence is engineered to contain nuclear codons and is cloned downstream of a mitochondrial transport signal (MTS). The transgenic construct integrates into the nuclear genome, is transcribed in the nucleus, and translated in the cytoplasm. The nascent protein is translocated to the mitochondria via the MTS. In this manner, mtDNA mutations can be modeled via production of recombinant, allotopically expressed mtDNA genes.

Figure 3

Microinjection of Exogenous Mitochondria into Mouse Zygotes. Exogenous mitochondria (light colored) microinjected directly into the cytoplasm of a pronuclear stage mouse embryo containing endogenous mitochondria results in creation of a heteroplasmic state within the developing embryo and resulting mice.

Figure 4

Creation of Cybrid Cells via Cell Fusion. Cytoplasmic hybrid (cybrid) cells are produced when a ρ⁰ cell (devoid of mtDNA) is fused with an enucleated cytoplast. The resulting cell derives its nuclear genome from the ρ⁰ cell and its mitochondrial genome from the cytoplast. The use of murine embryonic stem (ES) cells as mitochondrial donor cells has led to the creation of transmitochondrial mouse models.

Figure 5

Hypothesized Suboptimal Protein Interactions in Respiratory Complexes through Xenomitochondrial Cybrid Modeling. Suboptimal protein-protein interactions between respiratory subunits of divergent species are hypothesized to lead to mitochondrial dysfunction in murine xenomitochondrial cybrids.