Nome del progetto:
The mitochondrial respiratory chain: unveiling its biogenesis and its regulation to develop novel therapeutic approaches for fatal infantile mitochondrial diseases.
Dr. Leonardo Salviati.
Inizio progetto – Fine progetto: 01/05/2013 – 31/12/2016
Budget: 500.000 €
BACKGROUND AND RATIONALE
Mitochondria are central to the life and death of cells because they control crucial cellular pathways such as the production of ATP through the RC, calcium homeostasis, and apoptosis. The RC is comprised of five different enzymatic complexes and two electron carriers, cytochrome c and coenzyme Q. RC enzyme complexes interact to form RC supercomplexes, the functional unit of the RC. CoQ is a small lipophylic molecule synthesised in mitochondria by a specific set of enzymes encoded by COQ genes. These proteins form a multienzyme complex that we discovered interacts with RC supercomplexes. This interaction is necessary for efficient CoQ biosynthesis. Mutations in COQ genes cause primary CoQ Deficiency a severe and often fatal mitochondrial disorder which affects mostly newborns or young children. It presents with encephalomyopathy and nephropathy. We have demonstrated that oral supplementation is an effective treatment for the disease. CoQ deficiency is a secondary phenomenon in many other conditions not directly related to the biosynthesis of CoQ, such as primary defects of the RC. Treatment is helpful also for these conditions.
Cytochrome c oxidase (COX), is complex IV of the RC, and is the enzyme that allows cells to utilize oxygen for respiration. It is comprised of 14 protein subunits (an 11th nuclear subunit was identified this month) and of different prosthetic groups and requires a large set of ancillary proteins for its assembly. This process and its regulation in mammalian cells are still incompletely understood. Mutations in COX assembly genes result in COX deficiency, usually manifesting as a severe childhood encephalomyopathies. At least 10 COX assembly genes are involved in the metabolism of copper. We have shown that supplementation with copper may rescue COX deficiency in case of mutations in these genes, opening a therapeutic option for some of these patients.
DESCRIPTION OF THE PROJECT
The purpose of this project is to follow up on the results obtained during the current project funded by CARIPARO and to pursue different lines of research focused on mitochondrial pathophysiology. We will focus on four independent (but closely related) aims: 1) To refine the characterization of the structure of the CoQ biosynthetic complex and its relationships with other mitochondrial structures. 2) To generate and characterize a mouse model lacking COQ4, a key component of the CoQ biosynthetic complex. 3) To study the role of copper chaperones in the biogenesis of COX. 4) Study the regulation of COQ biosynthesis and of COX assembly.
In the first specific aim we will clarify the physical and functional relationships that we have found to exist between the RC complexes, the enzymes involved in CoQ biosynthesis, and other mitochondrial proteins. This will be crucial to understand the bases of secondary deficiencies. To address these issue will employ both cell lines and different models (yeast, C. elegans and Zebrafish).
In the second specific aim we will develop a mouse model of COQ4 defects, a gene we have found in patients with CoQ deficiency that is critical for the assembly of the CoQ biosynthetic complex, and the rate limiting factor in CoQ synthesis. These animals will be essential to unveil the pathophysiology of the disease and to optimize current therapeutic protocols.
In the third specific aim we will focus on the copper chaperones involved in the COX assembly process. Again we will employ different models in order to understand the role of the different genes involved in this pathway, and test copper supplementation in animal models.
In the fourth aim we will study the effectors (kinases/phosphatase) that regulate CoQ biosynthesis and COX assembly, and characterize a patient with a novel defect in the regulation of CoQ biosynthesis.
Overall, these studies will provide us with invaluable information on some central aspects of mitochondrial pathophysiology. The confirmation of the close physical and functional link between enzymes implicated in different mitochondrial processes (RC, CoQ biosynthesis, and mitochondrial dynamics), will dramatically impact our understanding of mitochondrial homeostasis in normal conditions or in disease. Moreover, the information gained in the different WP will be essential to optimize the treatments for these terrible disorders, and to develop new therapeutic strategies based on the modulation of the pathways that regulate biogenesis of the RC. The ability to modulate RC biogenesis could also be important to counteract the Warburg effect in cancer cells.