The long-term goal of this project is to ameliorate neurotransmission defects due to mitochondrial dysfunction,
as a way to stop disease progression to later degenerative stages, increasing healthspan in populations
increasingly subject to age-related neurological diseases. Dynamin-related protein 1 (DRP1) acts to promote
mitochondrial fission and has been identified as a therapeutic target for limiting aberrant mitochondrial
fragmentation in Alzheimer’s and Huntington’s disease. The goal of this project is to determine how DRP1
interaction with mitochondrial fission adapters impacts presynaptic terminal function. We propose that the need
for high levels of mitochondrial respiration to support synaptic transmission makes the presynaptic terminal a
high cellular stress environment. Regulated mitochondrial fission is important for cell survival in response to
cellular stressors, acting through DRP1, but the adapters utilized at the neuronal presynaptic terminal are
unknown. In Specific Aim 1, we will examine how loss of the mitochondrial fission adapter proteins MFF and
FIS1 affect mitochondria homeostasis and synaptic transmission. In Specific Aim 2, we will examine distinct
parameters of mitochondrial function and ultrastructure when DRP1 is eliminated, and attempt to rescue function
by targeting DRP1 re-expression to mitochondrial outer membrane. Phenotypic differences will be corelated with
those in Aim 1, to generate a complete picture of the effect of regulated mitochondrial fission on synaptic function.
DRP1 may also facilitate scission of plasma membrane at the synapse, but the impact of this additional function
on synaptic transmission is unresolved. In Specific Aim 3, we will test the hypothesis that DRP1 facilitates
synaptic vesicle retrieval and recycling, and determine whether membrane-associated DRP1 is sufficient to
facilitate SV retrieval, and restore synaptic transmission. In collaboration, the PI and two other world-class
investigators have developed novel approaches to allow dissection of the isoform-specific role(s) of DRP1, using
the mouse calyx of Held as a model system. Using a combination of viral-mediated transgenesis, advanced
electrophysiology, and high-resolution light and electron microscopy, the ability of specific DRP1 isoforms to
support mitochondrial fission versus synaptic transmission and presynaptic SV retrieval will be systematically
tested. In contrast to small conventional synapses, experimental accessibility of giant ‘calyx-like’ excitatory
synapses allow recordings from the presynaptic terminal, permitting manipulation of presynaptic [ATP] and
tracking membrane exo/endocytosis in real time. This approach is necessary to dissect the energy-supporting
roles of synaptic mitochondria from mechanisms underlying synaptic vesicle recycling. Results from this project
can be used to inform, predict, and test function and dysfunction at conventional glutamatergic synapses where
disease-relevant neurodegeneration first appears. Knowledge generated from this project will identify viable
routes of intervention for restoring function to synapses where DRP1 function is altered, which can be leveraged
therapeutically to alleviate disease-related synaptic dysfunction and neurodegeneration.
