Kidneys are one of the major oxygen consuming organs in the human body, utilizing 10% of the oxygen used in cellular respiration. As such, mitochondriopathies are increasingly recognized as cause for hereditary kidney diseases, and play critical roles in the pathogenesis of glomerulosclerosis, tubular abnormalities and progression of renal failure. In addition, many gene mutations are associated with increased energy demand and oxidative stress. Thus, understanding mitochondriopathies may provide novel strategies to maintain cellular homeostasis in hereditary disease. In contrast to most mitochondrial proteins, which are encoded on nuclear DNA, the core subunits of the proton pumping respiratory chain complexes are encoded on a single circular mitochondrial genome located in the matrix. Mitochondrial DNA depletion syndromes are characterized by severely decreased mitochondrial DNA copy numbers and consequently insufficient synthesis of respiratory chain components essential for mitochondrial function. Mutations of the mitochondrial inner membrane protein Mpv17/Sym1 cause mitochondrial DNA depletion, leading to nephrotic syndrome and renal failure. However, the function of Mpv17/Sym1 is unclear and therefore the role of Mpv17/Sym1 in the pathogenesis of renal diseases remains unknown. Similar to nuclear DNA the mitochondrial genome is bound to several proteins constituting the mitochondrial nucleoid. Major unsolved questions in mitochondrial biology are the composition of mitochondrial DNA nucleoids and the identification of the anchor for mitochondrial DNA at the inner membrane. To understand the mitochondrial DNA depletion syndromes and the maintenance and inheritance of mitochondrial DNA, two complementary approaches are proposed. As a bottom up approach the mitochondrial DNA depletion syndrome disease gene MPV17/SYM1 will be analyzed. Identification of interaction partners, metabolomic analysis of mutant mitochondria and quantitative mitochondrial mutant cell proteomics will be employed to characterize the role of Mpv17/Sym1. As a top down approach the protein interaction network for mitochondrial DNA nucleoid proteins will by determined by protein affinity isolation with PCR mediated verification, to define the composition and membrane association of the mitochondrial genome. The goal of this project is the molecular analysis of mitochondrial DNA inheritance and its involvement in the pathogenesis of hereditary kidney diseases.