ABSTRACT
Mitochondrial trafficking is influenced by neuronal activity, but it remains unclear how mitochondrial positioning influences neuronal transmission and plasticity. Here, we use live cell imaging with the genetically encoded presynaptically targeted Ca2+ indicator, SyGCaMP5, to address whether presynaptic Ca2+ responses are altered by mitochondria in synaptic terminals. We find that presynaptic Ca2+ signals, as well as neurotransmitter release, are significantly decreased in terminals containing mitochondria. Moreover, the localisation of mitochondria at presynaptic sites can be altered during long-term activity changes, dependent on the Ca2+-sensing function of the mitochondrial trafficking protein, Miro1. In addition, we find that Miro1-mediated activity-dependent synaptic repositioning of mitochondria allows neurons to homeostatically alter the strength of presynaptic Ca2+ signals in response to prolonged changes in neuronal activity. Our results support a model in which mitochondria are recruited to presynaptic terminals during periods of raised neuronal activity and are involved in rescaling synaptic signals during homeostatic plasticity.
Subject(s)
Calcium Signaling , Homeostasis , Mitochondria/metabolism , Neuronal Plasticity , Presynaptic Terminals/metabolism , rho GTP-Binding Proteins/metabolism , Animals , Calcium/metabolism , Cells, Cultured , Gene Expression , Mice , Mitochondrial Proteins/genetics , Mitochondrial Proteins/metabolism , Neurons/metabolism , Rats , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolismABSTRACT
Correct mitochondrial distribution is critical for satisfying local energy demands and calcium buffering requirements and supporting key cellular processes. The mitochondrially targeted proteins Miro1 and Miro2 are important components of the mitochondrial transport machinery, but their specific roles in neuronal development, maintenance, and survival remain poorly understood. Using mouse knockout strategies, we demonstrate that Miro1, as opposed to Miro2, is the primary regulator of mitochondrial transport in both axons and dendrites. Miro1 deletion leads to depletion of mitochondria from distal dendrites but not axons, accompanied by a marked reduction in dendritic complexity. Disrupting postnatal mitochondrial distribution in vivo by deleting Miro1 in mature neurons causes a progressive loss of distal dendrites and compromises neuronal survival. Thus, the local availability of mitochondrial mass is critical for generating and sustaining dendritic arbors, and disruption of mitochondrial distribution in mature neurons is associated with neurodegeneration.
Subject(s)
Dendrites/genetics , Mitochondrial Proteins/genetics , Nerve Degeneration/genetics , Neurogenesis/genetics , rho GTP-Binding Proteins/genetics , Animals , Axons/metabolism , Axons/pathology , Dendrites/metabolism , Disease Models, Animal , Humans , Mice , Mice, Knockout , Mitochondria/genetics , Mitochondria/metabolism , Nerve Degeneration/metabolism , Nerve Degeneration/pathology , Neurons/metabolism , Neurons/pathologyABSTRACT
Effective inhibitory synaptic transmission requires efficient stabilization of GABA(A) receptors (GABA(A)Rs) at synapses, which is essential for maintaining the correct excitatory-inhibitory balance in the brain. However, the signaling mechanisms that locally regulate synaptic GABA(A)R membrane dynamics remain poorly understood. Using a combination of molecular, imaging, and electrophysiological approaches, we delineate a GIT1/ßPIX/Rac1/PAK signaling pathway that modulates F-actin and is important for maintaining surface GABA(A)R levels, inhibitory synapse integrity, and synapse strength. We show that GIT1 and ßPIX are required for synaptic GABA(A)R surface stability through the activity of the GTPase Rac1 and downstream effector PAK. Manipulating this pathway using RNAi, dominant-negative and pharmacological approaches leads to a disruption of GABA(A)R clustering and decrease in the strength of synaptic inhibition. Thus, the GIT1/ßPIX/Rac1/PAK pathway plays a crucial role in regulating GABA(A)R synaptic stability and hence inhibitory synaptic transmission with important implications for inhibitory plasticity and information processing in the brain.
