Generation of Mitochondrial-nuclear eXchange Mice via Pronuclear Transfer

Increased Diabetes Complications in a Mouse Model of Oxidative Stress Due to 'Mismatched' Mitochondrial DNA

Associations between chronic diabetes complications and mitochondrial dysfunction represent a subject of major importance, given the diabetes pandemic and high personal and socioeconomic costs of diabetes and its complications. Modelling diabetes complications in inbred laboratory animals is challenging due to incomplete recapitulation of human features, but offer mechanistic insights and preclinical testing. As mitochondrial-based oxidative stress is implicated in human diabetic complications, herein we evaluate diabetes in a unique mouse model that harbors a mitochondrial DNA from a divergent mouse species (the 'xenomitochondrial mouse'), which has mild mitochondrial dysfunction and increased oxidative stress. We use the streptozotocin-induced diabetes model with insulin supplementation, with 20-weeks diabetes. We compare C57BL/6 mice and the 'xenomitochondrial' mouse, with measures of heart and kidney function, histology, and skin oxidative stress markers. Compared to C57BL/6 mice, the xenomitochondrial mouse has increased diabetic heart and kidney damage, with cardiac dysfunction, and increased cardiac and renal fibrosis. Our results show that mitochondrial oxidative stress consequent to divergent mtDNA can worsen diabetes complications. This has implications for novel therapeutics to counter diabetes complications, and for genetic studies of risk, as mtDNA genotypes may contribute to clinical outcomes.

Dissecting the Roles of the Nuclear and Mitochondrial Genomes in a Mouse Model of Autoimmune Diabetes

Mitochondria, the organelles responsible for generating ATP in eukaryotic cells, have been previously implicated as a contributor to diabetes. However, mitochondrial proteins are encoded by both nuclear DNA (nDNA) and mtDNA. In order to better understand the relative contribution of each of these genomes to diabetes, a chimeric mitochondrial-nuclear exchange (MNX) mouse was created via pronuclear transfer carrying nDNA from a strain susceptible to type 1 diabetes (NOD/ShiLtJ) and mtDNA from nondiabetic C57BL/6J mice. Inheritance of the resulting heteroplasmic mtDNA mixture was then tracked across multiple generations, showing that offspring heteroplasmy generally followed that of the mother, with occasional large shifts consistent with an mtDNA bottleneck in the germ line. In addition, survival and incidence of diabetes in MNX mice were tracked and compared with those in unaltered NOD/ShiLtJ control mice. The results indicated improved survival and a delay in diabetes onset in the MNX mice, demonstrating that mtDNA has a critical influence on disease phenotype. Finally, enzyme activity assays showed that the NOD/ShiLtJ mice had significant hyperactivity of complex I of the electron transport chain relative to MNX mice, suggesting that a particular mtDNA variant (m.9461T>C) may be responsible for disease causation in the original NOD/ShiLtJ strain.

ARTICLE HIGHLIGHTS

Mitochondria have been previously implicated in diabetes, but the specific genetic factors remain unclear. To better understand the contributions of mitochondrial genes in nuclear DNA (nDNA) versus mtDNA, we created mitochondrial-nuclear exchange (MNX) mice carrying nDNA from a diabetic strain and mtDNA from nondiabetic mice. Long-term tracking of MNX mice showed occasional large shifts in heteroplasmy consistent with an mtDNA bottleneck in the germ line. In addition, the MNX mice showed improved survival and delayed incidence of diabetes relative to the unaltered diabetic mice, which appeared to be linked to the activity of respiratory complex I.

Mitochondrial Transfer to Host Cells from Ex Vivo Expanded Donor Hematopoietic Stem Cells

Mitochondrial dysfunction is observed in various conditions, from metabolic syndromes to mitochondrial diseases. Moreover, mitochondrial DNA (mtDNA) transfer is an emerging mechanism that enables the restoration of mitochondrial function in damaged cells. Hence, developing a technology that facilitates the transfer of mtDNA can be a promising strategy for the treatment of these conditions. Here, we utilized an ex vivo culture of mouse hematopoietic stem cells (HSCs) and succeeded in expanding the HSCs efficiently. Upon transplantation, sufficient donor HSC engraftment was attained in-host. To assess the mitochondrial transfer via donor HSCs, we used mitochondrial-nuclear exchange (MNX) mice with nuclei from C57BL/6J and mitochondria from the C3H/HeN strain. Cells from MNX mice have C57BL/6J immunophenotype and C3H/HeN mtDNA, which is known to confer a higher stress resistance to mitochondria. Ex vivo expanded MNX HSCs were transplanted into irradiated C57BL/6J mice and the analyses were performed at six weeks post transplantation. We observed high engraftment of the donor cells in the bone marrow. We also found that HSCs from the MNX mice could transfer mtDNA to the host cells. This work highlights the utility of ex vivo expanded HSC to achieve the mitochondrial transfer from donor to host in the transplant setting.

Mitochondrial haplotype modulates genome expression and mitochondrial structure/function in cardiomyocytes following volume overload

Mitochondrial DNA (mtDNA) haplotype regulates mitochondrial structure/function and reactive oxygen species in aortocaval fistula (ACF) in mice. Here, we unravel the mitochondrial haplotype effects on cardiomyocyte mitochondrial ultrastructure and transcriptome response to ACF in vivo. Phenotypic responses and quantitative transmission electron microscopy (TEM) and RNA sequence at 3 days were determined after sham surgery or ACF in vivo in cardiomyocytes from wild-type (WT) C57BL/6J (C57n:C57mt) and C3H/HeN (C3Hn:C3Hmt) and mitochondrial nuclear exchange mice (C57n:C3Hmt or C3Hn:C57mt). Quantitative TEM of cardiomyocyte mitochondria C3HWT hearts have more electron-dense compact mitochondrial cristae compared with C57WT. In response to ACF, mitochondrial area and cristae integrity are normal in C3HWT; however, there is mitochondrial swelling, cristae lysis, and disorganization in both C57WT and MNX hearts. Tissue analysis shows that C3HWT hearts have increased autophagy, antioxidant, and glucose fatty acid oxidation-related genes compared with C57WT. Comparative transcriptomic analysis of cardiomyocytes from ACF was dependent upon mtDNA haplotype. C57mtDNA haplotype was associated with increased inflammatory/protein synthesis pathways and downregulation of bioenergetic pathways, whereas C3HmtDNA showed upregulation of autophagy genes. In conclusion, ACF in vivo shows a protective response of C3Hmt haplotype that is in large part driven by mitochondrial nuclear genome interaction.NEW & NOTEWORTHY The results of this study support the effects of mtDNA haplotype on nuclear gene expression in cardiomyocytes. Currently, there is no acceptable therapy for volume overload due to mitral regurgitation. The findings of this study could suggest that mtDNA haplotype activates different pathways after ACF warrants further investigations on human population of heart disease from different ancestry backgrounds.

Roles of mitochondrial genetics in cancer metastasis

The contributions of mitochondria to cancer have been recognized for decades. However, the focus on the metabolic role of mitochondria and the diminutive size of the mitochondrial genome compared to the nuclear genome have hindered discovery of the roles of mitochondrial genetics in cancer. This review summarizes recent data demonstrating the contributions of mitochondrial DNA (mtDNA) copy-number variants (CNVs), somatic mutations, and germline polymorphisms to cancer initiation, progression, and metastasis. The goal is to summarize accumulating data to establish a framework for exploring the contributions of mtDNA to neoplasia and metastasis.

Mitochondrial genome variations, mitochondrial-nuclear compatibility, and their association with metabolic diseases

Two genomes regulate the energy metabolism of eukaryotic cells: the nuclear genome, which codes for most cellular proteins, and the mitochondrial genome, which, together with the nuclear genome, coregulates cellular bioenergetics. Therefore, mitochondrial genome variations can affect, directly or indirectly, all energy-dependent cellular processes and shape the metabolic state of the organism. This review provides a current and up-to-date overview on how codependent these two genomes are, how they appear to have coevolved, and how variations within the mitochondrial genome might be associated with the manifestation of metabolic diseases. This review summarizes and structures results obtained from epidemiological studies that identified links between mitochondrial haplogroups and individual risks for developing obesity and diabetes. This is complemented by findings on the compatibility of mitochondrial and nuclear genomes and cellular bioenergetic fitness, which have been acquired from well-controlled studies in conplastic animal models. These elucidate, more mechanistically, how single-nucleotide variants can influence cellular metabolism and physiology. Overall, it seems that certain mitochondrial genome variations negatively affect mitochondrial-nuclear compatibility and are statistically linked with the onset of metabolic diseases, whereas, for others, greater uncertainty exists, and additional research into this exciting field is required.

Conplastic strains for identification of retrograde effects of mitochondrial dna variation on cardiometabolic traits in the spontaneously hypertensive rat

Mitochondrial retrograde signaling is a pathway of communication from mitochondria to the nucleus. Recently, natural mitochondrial genome (mtDNA) polymorphisms (haplogroups) received increasing attention in the pathophysiology of human common diseases. However, retrograde effects of mtDNA variants on such traits are difficult to study in humans. The conplastic strains represent key animal models to elucidate regulatory roles of mtDNA haplogroups on defined nuclear genome background. To analyze the relationship between mtDNA variants and cardiometabolic traits, we derived a set of rat conplastic strains (SHR-mtBN, SHR-mtF344 and SHR-mtLEW), harboring all major mtDNA haplotypes present in common inbred strains on the nuclear background of the spontaneously hypertensive rat (SHR). The BN, F344 and LEW mtDNA differ from the SHR in multiple amino acid substitutions in protein coding genes and also in variants of tRNA and rRNA genes. Different mtDNA haplotypes were found to predispose to various sets of cardiometabolic phenotypes which provided evidence for significant retrograde effects of mtDNA in the SHR. In the future, these animals could be used to decipher individual biochemical components involved in the retrograde signaling.

Mito-Mendelian interactions alter in vivo glucose metabolism and insulin sensitivity in healthy mice

The regulation of euglycemia is essential for human health with both chronic hypoglycemia and hyperglycemia having detrimental effects. It is well documented that the incidence of type 2 diabetes increases with age and exhibits racial disparity. Interestingly, mitochondrial DNA (mtDNA) damage also accumulates with age and its sequence varies with geographic maternal origins (maternal race). From these two observations, we hypothesized that mtDNA background may contribute to glucose metabolism and insulin sensitivity. Pronuclear transfer was used to generate mitochondrial-nuclear eXchange (MNX) mice to directly test this hypothesis, by assessing physiologic parameters of glucose metabolism in nuclear isogenic C57BL/6J mice harboring either a C57BL/6J (C57ⁿ:C57^mt wild type-control) or C3H/HeN mtDNA (C57ⁿ:C3H^mt-MNX). All mice were fed normal chow diets. MNX mice were significantly leaner, had lower leptin levels, and were more insulin sensitive, with lower modified Homeostatic Model Assessment of Insulin Resistance (mHOMA-IR) values and enhanced insulin action when compared with their control counterparts. Further interrogation of muscle insulin signaling revealed higher phosphorylated Akt/total Akt ratios in MNX animals relative to control, consistent with greater insulin sensitivity. Overall, these results are consistent with the hypothesis that different mtDNA combinations on the same nuclear DNA (nDNA) background can significantly impact glucose metabolism and insulin sensitivity in healthy mice.NEW & NOTEWORTHY Different mitochondrial DNAs on the same nuclear genetic background can significantly impact body composition, glucose metabolism, and insulin sensitivity in healthy mice.

Possible role of the mitochondrial genome in the pathogenesis of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenic renal disease in adults and is due to heterozygous germ line variants in either PKD1, PKD2 or rarely other genes. It is characterized by marked intra-familial disease variability suggesting that other genetic and/or environmental factors are involved in determining the lifetime course ADPKD. Recently, research indicates that polycystin-mediated mitochondrial dysfunction and metabolic re-programming contributes to the progression of ADPKD. Although biochemical abnormalities have gained the most interest, variants in the mitochondrial genome could be one of the mechanisms underlying the phenotypic variability in ADPKD. This narrative review aims to evaluate the role of the mitochondrial genome in the pathogenesis of APDKD.

University of Alabama at Birmingham Nathan Shock Center: comparative energetics of aging

The UAB Nathan Shock Center focuses on comparative energetics and aging. Energetics, as defined for this purpose, encompasses the causes, mechanisms, and consequences of the acquisition, storage, and use of metabolizable energy. Comparative energetics is the study of metabolic processes at multiple scales and across multiple species as it relates to health and aging. The link between energetics and aging is increasingly understood in terms of dysregulated mitochondrial function, altered metabolic signaling, and aberrant nutrient responsiveness with increasing age. The center offers world-class expertise in comprehensive, integrated energetic assessment and analysis from the level of the organelle to the organism and across species from the size of worms to rats as well as state-of-the-art data analytics. The range of services offered by our three research cores, (1) The Organismal Energetics Core, (2) Mitometabolism Core, and (3) Data Analytics Core, is described herein.

Mechanisms of breast cancer metastasis

Invasive breast cancer tends to metastasize to lymph nodes and systemic sites. The management of metastasis has evolved by focusing on controlling the growth of the disease in the breast/chest wall, and at metastatic sites, initially by surgery alone, then by a combination of surgery with radiation, and later by adding systemic treatments in the form of chemotherapy, hormone manipulation, targeted therapy, immunotherapy and other treatments aimed at inhibiting the proliferation of cancer cells. It would be valuable for us to know how breast cancer metastasizes; such knowledge would likely encourage the development of therapies that focus on mechanisms of metastasis and might even allow us to avoid toxic therapies that are currently used for this disease. For example, if we had a drug that targeted a gene that is critical for metastasis, we might even be able to cure a vast majority of patients with breast cancer. By bringing together scientists with expertise in molecular aspects of breast cancer metastasis, and those with expertise in the mechanical aspects of metastasis, this paper probes interesting aspects of the metastasis cascade, further enlightening us in our efforts to improve the outcome from breast cancer treatments.

An evolutionary, or "Mitocentric" perspective on cellular function and disease

The incidence of common, metabolic diseases (e.g. obesity, cardiovascular disease, diabetes) with complex genetic etiology has been steadily increasing nationally and globally. While identification of a genetic model that explains susceptibility and risk for these diseases has been pursued over several decades, no clear paradigm has yet been found to disentangle the genetic basis of polygenic/complex disease development. Since the evolution of the eukaryotic cell involved a symbiotic interaction between the antecedents of the mitochondrion and nucleus (which itself is a genetic hybrid), we suggest that this history provides a rational basis for investigating whether genetic interaction and co-evolution of these genomes still exists. We propose that both mitochondrial and Mendelian, or "mito-Mendelian" genetics play a significant role in cell function, and thus disease risk. This paradigm contemplates the natural variation and co-evolution of both mitochondrial and nuclear DNA backgrounds on multiple mitochondrial functions that are discussed herein, including energy production, cell signaling and immune response, which collectively can influence disease development. At the nexus of these processes is the economy of mitochondrial metabolism, programmed by both mitochondrial and nuclear genomes.

Unlocking the Secrets of Mitochondria in the Cardiovascular System: Path to a Cure in Heart Failure—A Report from the 2018 National Heart, Lung, and Blood Institute Workshop

Mitochondria have emerged as a central factor in the pathogenesis and progression of heart failure, and other cardiovascular diseases, as well, but no therapies are available to treat mitochondrial dysfunction. The National Heart, Lung, and Blood Institute convened a group of leading experts in heart failure, cardiovascular diseases, and mitochondria research in August 2018. These experts reviewed the current state of science and identified key gaps and opportunities in basic, translational, and clinical research focusing on the potential of mitochondria-based therapeutic strategies in heart failure. The workshop provided short- and long-term recommendations for moving the field toward clinical strategies for the prevention and treatment of heart failure and cardiovascular diseases by using mitochondria-based approaches.

Mitochondrial Haplotype of the Host Stromal Microenvironment Alters Metastasis in a Non-cell Autonomous Manner

Mitochondria contribute to tumor growth through multiple metabolic pathways, regulation of extracellular pH, calcium signaling, and apoptosis. Using the Mitochondrial Nuclear Exchange (MNX) mouse models, which pair nuclear genomes with different mitochondrial genomes, we previously showed that mitochondrial SNPs regulate mammary carcinoma tumorigenicity and metastatic potential in genetic crosses. Here, we tested the hypothesis that polymorphisms in stroma significantly affect tumorigenicity and experimental lung metastasis. Using syngeneic cancer cells (EO771 mammary carcinoma and B16-F10 melanoma cells) injected into wild-type and MNX mice (i.e., same nuclear DNA but different mitochondrial DNA), we showed mt-SNP-dependent increases (C3H/HeN) or decreases (C57BL/6J) in experimental metastasis. Superoxide scavenging reduced experimental metastasis. In addition, expression of lung nuclear-encoded genes changed specifically with mt-SNP. Thus, mitochondrial-nuclear cross-talk alters nuclear-encoded signaling pathways that mediate metastasis via both intrinsic and extrinsic mechanisms. SIGNIFICANCE: Stromal mitochondrial polymorphisms affect metastatic colonization through reactive oxygen species and mitochondrial-nuclear cross-talk.

Mitochondrial genetics cooperate with nuclear genetics to selectively alter immune cell development/trafficking

The nuclear genome drives differences in immune cell populations and differentiation potentials, in part regulated by changes in metabolism. Despite this connection, the role of mitochondrial DNA (mtDNA) polymorphisms (SNP) in this process has not been examined. Using mitochondrial nuclear exchange (MNX) mice, we and others have shown that mtDNA strongly influences varying aspects of cell biology and disease. Based upon an established connection between mitochondria and immune cell polarization, we hypothesized that mtDNA SNP alter immune cell development, trafficking, and/or differentiation. Innate and adaptive immune cell populations were isolated and characterizated from the peritoneum and spleen. While most differences between mouse strains are regulated by nuclear DNA (nDNA), there are selective changes that are mediated by mtDNA differences (e.g., macrophage (CD11c) differentiation), These findings highlight how nuclear-mitochondrial crosstalk may alter pathology and physiology via regulation of specific components of the immune system.

Mitochondrial polymorphisms contribute to aging phenotypes in MNX mouse models

Many inbred strains of mice develop spontaneous tumors as they age. Recent awareness of the impacts of mitochondrial DNA (mtDNA) on cancer and aging has inspired developing a mitochondrial-nuclear exchange (MNX) mouse model in which nuclear DNA is paired with mitochondrial genomes from other strains of mouse. MNX mice exhibit mtDNA influences on tumorigenicity and metastasis upon mating with transgenic mice. However, we also wanted to investigate spontaneous tumor phenotypes as MNX mice age. Utilizing FVB/NJ, C57BL/6J, C3H/HeN, and BALB/cJ wild-type inbred strains, previously documented phenotypes were observed as expected in MNX mice with the same nuclear background. However, aging nuclear matched MNX mice exhibited decreased occurrence of mammary tumors in C3H/HeN mice containing C57BL/6J mitochondria compared to wild-type C3H/HeN mice. Although aging tumor phenotypes appear to be driven by nuclear genes, evidence suggesting that some differences are modified by the mitochondrial genome is presented.

Roles of the mitochondrial genetics in cancer metastasis: not to be ignored any longer

Mitochondrial DNA (mtDNA) encodes for only a fraction of the proteins that are encoded within the nucleus, and therefore has typically been regarded as a lesser player in cancer biology and metastasis. Accumulating evidence, however, supports an increased role for mtDNA impacting tumor progression and metastatic susceptibility. Unfortunately, due to this delay, there is a dearth of data defining the relative contributions of specific mtDNA polymorphisms (SNP), which leads to an inability to effectively use these polymorphisms to guide and enhance therapeutic strategies and diagnosis. In addition, evidence also suggests that differences in mtDNA impact not only the cancer cells but also the cells within the surrounding tumor microenvironment, suggesting a broad encompassing role for mtDNA polymorphisms in regulating the disease progression. mtDNA may have profound implications in the regulation of cancer biology and metastasis. However, there are still great lengths to go to understand fully its contributions. Thus, herein, we discuss the recent advances in our understanding of mtDNA in cancer and metastasis, providing a framework for future functional validation and discovery.

The second genome: Effects of the mitochondrial genome on cancer progression

The role of genetics in cancer has been recognized for centuries, but most studies elucidating genetic contributions to cancer have understandably focused on the nuclear genome. Mitochondrial contributions to cancer pathogenesis have been documented for decades, but how mitochondrial DNA (mtDNA) influences cancer progression and metastasis remains poorly understood. This lack of understanding stems from difficulty isolating the nuclear and mitochondrial genomes as experimental variables, which is critical for investigating direct mtDNA contributions to disease given extensive crosstalk exists between both genomes. Several in vitro and in vivo models have isolated mtDNA as an independent variable from the nuclear genome. This review compares and contrasts different models, their advantages and disadvantages for studying mtDNA contributions to cancer, focusing on the mitochondrial-nuclear exchange (MNX) mouse model and findings regarding tumor progression, metastasis, and other complex cancer-related phenotypes.

Mitochondrial - nuclear genetic interaction modulates whole body metabolism, adiposity and gene expression in vivo

We hypothesized that changes in the mitochondrial DNA (mtDNA) would significantly influence whole body metabolism, adiposity and gene expression in response to diet. Because it is not feasible to directly test these predictions in humans we used Mitochondrial-Nuclear eXchange mice, which have reciprocally exchanged nuclear and mitochondrial genomes between different Mus musculus strains. Results demonstrate that nuclear-mitochondrial genetic background combination significantly alters metabolic efficiency and body composition. Comparative RNA sequencing analysis in adipose tissues also showed a clear influence of the mtDNA on regulating nuclear gene expression on the same nuclear background (up to a 10-fold change in the number of differentially expressed genes), revealing that neither Mendelian nor mitochondrial genetics unilaterally control gene expression. Additional analyses indicate that nuclear-mitochondrial genome combination modulates gene expression in a manner heretofore not described. These findings provide a new framework for understanding complex genetic disease susceptibility.

Inter-individual variation in adaptations to endurance and resistance exercise training: genetic approaches towards understanding a complex phenotype

Exercise training which meets the recommendations set by the National Physical Activity Guidelines ensues a multitude of health benefits towards the prevention and treatment of various chronic diseases. However, not all individuals respond well to exercise training. That is, some individuals have no response, while others respond poorly. Genetic background is known to contribute to the inter-individual (human) and -strain (e.g., mice, rats) variation with acute exercise and exercise training, though to date, no specific genetic factors have been identified that explain the differential responses to exercise. In this review, we provide an overview of studies in human and animal models that have shown a significant contribution of genetics in acute exercise and exercise training-induced adaptations with standardized endurance and resistance training regimens, and further describe the genetic approaches which have been used to demonstrate such responses. Finally, our current understanding of the role of genetics and exercise is limited primarily to the nuclear genome, while only a limited focus has been given to a potential role of the mitochondrial genome and its interactions with the nuclear genome to predict the exercise training-induced phenotype(s) responses. We therefore discuss the mitochondrial genome and literature that suggests it may play a significant role, particularly through interactions with the nuclear genome, in the inherent ability to respond to exercise.

Understanding Mitochondrial Polymorphisms in Cancer

Alterations in mitochondrial DNA (mtDNA) were once thought to be predominantly innocuous to cell growth. Recent evidence suggests that mtDNA undergo naturally occurring alterations, including mutations and polymorphisms, which profoundly affect the cells in which they appear and contribute to a variety of diseases, including cardiovascular disease, diabetes, and cancer. Furthermore, interplay between mtDNA and nuclear DNA has been found in cancer cells, necessitating consideration of these complex interactions for future studies of cancer mutations and polymorphisms. In this issue of Cancer Research, Vivian and colleagues utilize a unique mouse model, called Mitochondrial Nuclear eXchange mice, that contain the nuclear DNA from one inbred mouse strain, and the mtDNA from a different inbred mouse strain to examine the genome-wide nuclear DNA methylation and gene expression patterns of brain tissue. Results demonstrated there were alterations in nuclear DNA expression and DNA methylation driven by mtDNA. These alterations may impact disease pathogenesis. In light of these results, in this review, we highlight alterations in mtDNA, with a specific focus on polymorphisms associated with cancer susceptibility and/or prognosis, mtDNA as cancer biomarkers, and considerations for investigating the role of mtDNA in cancer progression for future studies. Cancer Res; 77(22); 6051-9. ©2017 AACR.

Mitochondrial Haplotype Alters Mammary Cancer Tumorigenicity and Metastasis in an Oncogenic Driver-Dependent Manner

Using a novel mouse model, a mitochondrial-nuclear exchange model termed MNX, we tested the hypothesis that inherited mitochondrial haplotypes alter primary tumor latency and metastatic efficiency. Male FVB/N-Tg(MMTVneu)202Mul/J (Her2) transgenic mice were bred to female MNX mice having FVB/NJ nuclear DNA with either FVB/NJ, C57BL/6J, or BALB/cJ mtDNA. Pups receiving the C57BL/6J or BALB/cJ mitochondrial genome (i.e., females crossed with Her2 males) showed significantly (P < 0.001) longer tumor latency (262 vs. 293 vs. 225 days), fewer pulmonary metastases (5 vs. 7 vs. 15), and differences in size of lung metastases (1.2 vs. 1.4 vs. 1.0 mm diameter) compared with FVB/NJ mtDNA. Although polyoma virus middle T-driven tumors showed altered primary and metastatic profiles in previous studies, depending upon nuclear and mtDNA haplotype, the magnitude and direction of changes were not the same in the HER2-driven mammary carcinomas. Collectively, these results establish mitochondrial polymorphisms as quantitative trait loci in mammary carcinogenesis, and they implicate distinct interactions between tumor drivers and mitochondria as critical modifiers of tumorigenicity and metastasis. Cancer Res; 77(24); 6941-9. ©2017 AACR.

Mitochondrial Genomic Backgrounds Affect Nuclear DNA Methylation and Gene Expression

Mitochondrial DNA (mtDNA) mutations and polymorphisms contribute to many complex diseases, including cancer. Using a unique mouse model that contains nDNA from one mouse strain and homoplasmic mitochondrial haplotypes from different mouse strain(s)-designated Mitochondrial Nuclear Exchange (MNX)-we showed that mtDNA could alter mammary tumor metastasis. Because retrograde and anterograde communication exists between the nuclear and mitochondrial genomes, we hypothesized that there are differential mtDNA-driven changes in nuclear (n)DNA expression and DNA methylation. Genome-wide nDNA methylation and gene expression were measured in harvested brain tissue from paired wild-type and MNX mice. Selective differential DNA methylation and gene expression were observed between strains having identical nDNA, but different mtDNA. These observations provide insights into how mtDNA could be altering epigenetic regulation and thereby contribute to the pathogenesis of metastasis. Cancer Res; 77(22); 6202-14. ©2017 AACR.