Gαq regulates mitochondrial motility and interacts with alex3, miro1 and trak proteins
- Autores: Ismael Izquierdo Villalba
- Directores de la Tesis: Anna Aragay Combas (dir. tes.)
- Lectura: En la Universitat de Barcelona ( España ) en 2020
- Idioma: español
- Tribunal Calificador de la Tesis: José Antonio Enríquez Domínguez (presid.), Guillermo López Doménech (secret.), Cristiane Beninca (voc.)
- Programa de doctorado: Programa de Doctorado en Biotecnología por la Universidad de Barcelona
- Materias:
- Texto completo no disponible (Saber más ...)
- Resumen
SUMMARY Neurons are differentiated cells with a unique structure highly specialized in signal transmission through a processes called synapsis. Because synapsis are energy demanding and in neurons most of their energy is obtained from oxidation of sugars at the mitochondrion, mitochondria need to be hauled to the places with high neuronal activity, frequently located at the tips of the axons and dendrites.
Mitochondria are usually transported along microtubule cytoskeleton thanks to the kinesin (which mediates anterograde movement, towards the axonal tips) and dynein (which mediates the retrograde movement, towards the soma). Both kinesin and dynein are GTPases that couple to mitochondria through a series of adaptors. The best documented are the atypical GTPases Miro1 and 2. Miro proteins usually couple microtubule motors through the coiled-coiled-containing milton adaptors TRAK1 and 2. Whereas TRAK1 couples preferentially to kinesin to mediate the anterograde transport, TRAK2 can couple both motors, but shows a tendency to bind dynein. Together, they constitute a trafficking complex. Many signaling and adaptor proteins regulate the activity and function of the transport complex. Dysfunctions in mitochondrial transport compromises neuronal physiology and is an important cause of neurodegenerative disorders.
In this regard, G proteins constitute some of the best-characterized signal transducers from metabotropic receptors at the plasma membrane, including the muscarinic, glutamate and opioid like receptors. More interestingly, recent reports point to a novel localization of G proteins at the mitochondria, where they regulate the physiology of these organelles. In particular, the Gαq subfamily is essential to maintain the balance between fusion and fission acting at the inner and outer mitochondrial membranes, among other functions. In order to unveil the putative effectors of Gαq that mediate those effects at the mitochondria, our group has undertaken a mass-spectrometry analysis based on Gαq immunoprecipitates from cellular endomembranes. The “mito-interactome” study provided evidence of Gαq interaction with the armadillo domain-containing proteins Alex3 and Armc10. Both arm-containing proteins have been recently characterized as essential regulators of mitochondrial transport by associating with Miro1 and TRAK2. Subsequent immunoprecipitations and pull-down studies unveiled a specific interaction between Gαq and Miro1 GTPase, as well as TRAK adaptors.
Such finding prompted us to study the implications of Gαq in mitochondrial motility in axons from hippocampal neurons. For that purpose, we performed tracking analysis of mitochondria along the axons of hippocampal neurons overexpressing Gαq or its constitutive-active mutant, GαqR183C, as well as activating a Gαq -specific GPCR (DREADD) with its specific agonist. The results of these studies reveal a significant increase in anterograde movement upon Gαq expression, whereas Gαq activation by either expressing the active-mutant or activating the Gαq -specific GPCR induces mitochondrial arrest. In contrast, depletion of Gαq using short-hairpin RNAs increases the number of motile mitochondria and their speed and promotes retrograde transport. Both activation of Gαq or its depletion alter mitochondrial dynamics including fusion/fission events, whereas expression of active-Gαq also alters neuronal physiology by reducing their complexity and dendritic branching. In summary, our group postulates a new non-canonical mitochondrial function of Gαq acting as a molecular switch through its association with Alex3, Miro1 and TRAK2. Gαq would associate to Alex3 and Miro1 to allow mitochondrial movement, whereas its GTP-bound conformation would associate to TRAK2 to halt motility. This process would be regulated by Alex3, which could play crucial roles as an adaptor for the protein complex and Gαq transactivation.
