Gαq regulates mitochondrial motility and interacts with ALEX3, MIRO1 and TRAK proteins

Abstract

G proteins transduce a myriad of signals from receptors at the plasma membrane. Recent reports point to a novel localization of G proteins at the mitochondria and other endomembranes where they regulate the physiology of these organelles. In particular, the Gαq subfamily is required to keep the proper balance between mitochondria fusion and fission acting at both outer and inner membrane, 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. Subsequent immunoprecipitation and pull-down studies demonstrated a specific interaction of Gαq with the mitochondrial Rho GTPase 1 (Miro1) and both milton adaptor proteins TRAK1 and 2, that couple mitochondria to kinesin and dynein motor proteins and constitute the main regulators of mitochondrial transport in neurons. To analyze the physiological role of those interactions, we have 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.