pH-dependent mechanisms of disease caused by TBC1D24 mutations
Awardee: Dennis Brown
Institution: Massachusetts General Hospital
Grant Amount: $60,000.00
Funding Period: February 1, 2024 - January 31, 2025
Summary:
There are several lines of evidence, both from genetics and protein-protein interaction studies that there is an important physiological link between Tbc1d24 and a molecular proton pump, called V-ATPase. The major function of the V-ATPase is to pump acid (in the form of protons) into small vesicles inside the cell, such as synaptic vesicles and lysosomes. A low, acidic pH within these vesicles is required for their normal function, in particular neurotransmitter loading of synaptic vesicle in neurons or degradation of various molecules in lysosomes. In addition, proper pH gradients are required for efficient intracellular vesicle trafficking and recycling of proteins, telling them where to go inside a cell, which is extremely important at neuronal synapses. V-ATPase is not a single protein, but a protein complex, consisting of 13 core proteins, or subunits. While severe mutations in V-ATPase subunit genes causing a loss of protein function are incompatible with life, some mutations result in various diseases and syndromes, including epilepsy, hearing loss and DOORS syndrome (deafness, onychodystrophy, osteodystrophy, mental retardation and seizures). These diseases are remarkably similar to those caused by mutations in the TBC1D24 gene. We discovered recently that V-ATPase physically binds to Tbc1d24, as well as four other proteins that are structurally similar. They all contain a so-called TLDc conserved domain. We found that some mutations in the TLDc domain of one of these other proteins, called Ncoa7, disrupted its ability to bind to V-ATPase, which inhibited its acid-pumping capacity. Importantly, some of these “inhibitory” mutations correspond to the known pathogenic mutations within the Tbc1d24 protein in affected patients. Therefore, we hypothesize and aim to prove that some TBC1D24 pathogenic mutations destabilize the interaction of Tbc1d24 with V-ATPase, resulting in impaired acidification of vesicles within cells, including neuronal cells. We also plan to study where precisely the Tbc1d24/V-ATPase interaction takes place to better understand which intracellular vesicles are more severely affected by the mutations. This will facilitate the development of new treatment strategies and drugs specifically designed to target (stabilize) Tbc1d24-V-ATPase interactions. The hope is that if we can repair this interaction, it will restore the process (e. g., acidification) or pathways disrupted by at least some of pathogenic mutations in the TBC1D24 gene.