I. Endothelial mitochondrial dysfunction in the development of heart failure

Professor Aleksandra Trifunovic

Rationale and aims

Endothelial cell (EC) dysfunction crucially contributes to the development of impaired coronary and systemic perfusion as well as reduced exercise capacity in patients with HF. The key determinants in endothelial dysfunction are reduced levels of NO and abundant formation of ROS within the vascular wall. Recent studies have suggested that endothelial mitochondria are centrally involved in maintaining the fine regulatory balance between mitochondrial calcium concentration, ROS production, and NO availability. In comparison with other cell types with higher energy requirements, mitochondria content in ECs is modest, making up only 2-6% of total cell volume. The low content of mitochondria indicates that they are likely to serve as critical signaling organelles in the endothelium. The role of mitochondria in vascular smooth muscle cells (VSMCs) is even less understood. Similar to ECs, mitochondria contribute only modestly to the VSMC bioenergetics. Nevertheless, mitochondrial dysfunction, and particularly mitochondrial DNA damage, has recently been associated to atherosclerosis. The historical view that in atherosclerosis, aberrant proliferation of VSMCs promotes plaque formation, but that VSMCs in advanced plaques are beneficial by, e.g. preventing rupture of the fibrous cap, has recently also been challenged. This project aims to determine the role of endothelial mitochondria in the development of HF.

Current state of research and own preliminary work

Figure 1: Model of endothelial cell Dars2-deficiency and experimental approach to assess the role of mitochondrial dysfunction in heart failure.

To this end, we have recently developed an EC-specific model of mitochondrial dysfunction where we have abolished mitochondrial protein synthesis by deleting the DARS2 gene (Mitochondrial Aspartyl-tRNA synthase) specifically in ECs by using the EC-specific, tamoxifen-inducible Cre-line (EndSCL-CreERT). Thus, we can now precisely time the blockage of mitochondrial respiration and vary the level of damage we induce (Figure 1).

Experimental approach and work program

In this project, we will analyze the hearts of Dars2loxP/loxP;+/EndSCL-CreERT mice in normal conditions and after ischemia/reperfusion injury. The analysis will include in vivo analysis of cardiac functional parameters utilizing echocardiography and magnetic resonance imaging combined with different histological, immune-histochemical, and enzymatic stainings on heart cross-sections, as well as analysis of markers of cardiac hypertrophy, mitochondrial dysfunction, and adaptive stress response. To further understand the role of endothelial mitochondria in the development of HF during aging, we will use mtDNA mutator mice – the mouse model for mitochondrial dysfunction-induced premature aging. We have previously shown that these mice develop heart hypertrophy over time. Using a mtDNA mutator mice background, we will now block mitochondrial EC function in a similar way as proposed earlier (with EndSCL-CreERT), and then follow the development of cardiac phenotypes over time. We will also mirror these proposed experiments using Dars2loxP/loxP;+/EndSCL-CreERT mice. The analysis of these mouse models will allow us to precisely determine the role of EC mitochondrial function in HF and its progression with age.

Potential future therapeutic implications

Strong mitochondrial dilated cardiomyopathy and diminished respiration can be alleviated by the loss of mitochondrial matrix protease CLPP, opening a new avenue for novel therapeutic intervention in mitochondrial diseases.

Added value through collaborations within the CCRC

This project is intimately related to other projects of this initiative and will benefit greatly from collaborations with the groups of V. Rudolph and S. Rosenkranz, which will allow us to pursue the experiments of ischemia/reperfusion and systemic vascular dysfunction as well as to analyze cardiac function in vivo. This project critically depends on the services provided by Proteomics (C. Freese / M. Krüger) and Histopathology (A. Quaas / R. Büttner) core facilities and, in the future, we also anticipate the need for services from the Functional Genomics core facility (P. Nürnberg). We will also collaborate with J. Brüning and S. Rosenkranz on their respective projects providing expertise in analysis of mitochondrial dysfunction.

General research interest

Mitochondria are the main energy producing stations within our cells. Over three decades ago Hartman was one of the first to propose that mitochondria play a central role in ageing. The initial theory suggested that ageing, as well as the associated degenerative diseases, could be attributed to the deleterious effects of reactive oxygen species (ROS) on various cell compartments. The fact that the mitochondrial electron transport chain is the major site of production of reactive oxygen species has lead to the suggestion that mitochondria are a prime target for oxidative damage and hence the mitochondrial theory of ageing, a correlate of the free radical theory. This idea is intellectually very appealing, as mitochondria are the only organelles in animal cells that possess their own DNA, mtDNA, localized in the physical proximity to the respiratory chain, allowing irreversible damage to be introduced. The mitochondrial theory of ageing is based around the idea that mitochondrial DNA (mtDNA) mutations accumulate progressively during life and are directly responsible for a respiratory chain dysfunction that leads to an impaired bioenergetic homeostasis and an enhanced production of free oxygen radicals.

Recently, we have made a considerable progress in understanding basic role of acquired mtDNA mutations in ageing by generating the mtDNA mutator mice. The creation of mtDNA-mutator mice has provided the first direct evidence that accelerating mtDNA mutation rate can result in premature ageing, consistent with the view that loss of mitochondrial function is a major causal factor in ageing. Furthermore, we showed that there is no direct connection between increased mtDNA mutation load and elevated ROS production, arguing against a direct role of oxidative stress in the ageing process.

The main focus of our group is to understand the role of mitochondrial (dys)function in the determination of longevity. We are also interested in understanding molecular mechanisms by which mitochondria contribute to development and progression of age-associated diseases. We are studying these complex aspects of mitochondrial biology using two different model systems: transgenic mice and a roundworm, Caenorhabditis elegans.

Professor Aleksandra Trifunovic

Date of birth            May 19, 1971
Address                   CECAD at the Institute for Genetics
                              University of Cologne
                              Zülpicher Str. 47a, 50674 Cologne
E-mail:                   aleksandra.trifunovic@uk-koeln.de

Position                   Independent Group Leader

Education

1989-1994               BSc in Biology, Faculty of Biology, University of Belgrade, Yugoslavia

1994-1998               Magister in Molecular Biology and Biochemistry at
                               the Institute of Molecular Genetics and Genetic Engineering
                               (IMGGE), University of Belgrade, Yugoslavia

1998-2000               PhD in Molecular Biology and Biochemistry at IMGGE,
                               University of Belgrade, Yugoslavia

Research Career   

2009 - 2014               Independent Research Group Leader on Tenure track at the
                                 Cologne Excellence Cluster: Cellular Stress responses
                                 in Aging-Associated Diseases (CECAD),
                                 University of Cologne, Germany

2006-2011                 Independent Junior Group Leader/Assistant Professor -
                                 position financed by Swedish Research Counsel. The
                                 position was located at the Department of Laboratory
                                 Medicine, Karolinska Institute, Stockholm, Sweden

2005-2006                 Research Assistant, financed by fellowship from Loo and
                                 Hans Ostermans Stiftelse. The position was located at the
                                 Department of Laboratory Medicine, Karolinska Institute,
                                 Stockholm, Sweden.

2000 –2005               Postdoctoral fellow, laboratory of Prof Nils-Göran Larsson,
                                 Department of Molecular Medicine and Department of
                                 Medical Nutrition, Karolinska Institute, Stockholm, Sweden

Service to Scientific Community and Honours

Since 2012                       Visiting Professor, Medical School, Belgrade University,
                                       Serbia

Since 2011                       Editorial board member Frontiers in Science

Since 2010                       Member of the Scientific Committee for 8th and 9th
                                       European Meeting on Mitochondrial Pathology

Since 2008                       Member of the Organizing Committee for FEBS/EMBO
                                       Course Mitochondria in life, death and disease

2007                                Young Investigator award Jaensson Foundation