Synaptic Vesicular Alterations after Traumatic Brain Injury

Abstract
Enduring cognitive, somatic, and emotional impairments, including difficulties with memory, attention, and
learning, are reported as major contributors to reduced quality of life from patients living with a traumatic brain
injury (TBI). Previous preclinical studies highlight the contribution of altered neurotransmission and synaptic
dysfunction in the development of cognitive impairments after a TBI. We recently identified a novel synaptic
pathology in which the density and distribution of the intrasynaptic vesicular pool is drastically reduced after an
experimental TBI, with direct implications for impaired neurotransmission and cognition. A similar finding of
altered vesicle docking was observed after low intensity blast injury, suggesting these alterations may occur
across a broad spectrum of injury severity. Under normal conditions, neurotransmitter-containing vesicles are
replenished and the vesicular pool is maintained through the primary recycling mechanism of clathrin-mediated
endocytosis (CME). In the synapse, clathrin light chain (CLC) plays a central role in vesicular recycling through
interaction with clathrin heavy chain and CME associated proteins for vesicle formation and replenishment of the
vesicular pool. The effect of TBI on CLC and the contribution of CME deficits in synaptic dysfunction have not
been examined. We provide preliminary data highlighting reductions in CLC and CME proteins for weeks post-
injury in a rat model of controlled cortical impact (CCI). We also provide novel evidence of impaired hippocampal
evoked neurotransmitter release, a functional readout of vesicular pool integrity and CME function. We
hypothesize TBI-induced reductions in CME impairs the vesicular pool and neurotransmitter release, and that a
targeted strategy to promote endocytosis improves neurotransmission and cognitive function after TBI. We
propose utilizing innovative approaches to mechanistically interrogate the role of CLC and CME in post-traumatic
synaptic dysfunction and investigate the functional effects of targeted therapeutic intervention on CLC
abundance and CME function. In Aim 1, the effect of TBI on regional and sex-dependent changes in CLC and
CME will be assessed in the early to subchronic recovery period following CCI. In Aim 2, we will examine the
effect of a targeted strategy to increase CLC expression using neuron-specific adeno-associated viral modulation
on CME function on protein readouts, evoked neurotransmission and cognitive function following CCI. Aim 3 will
utilize an innovative and integrative Quantitative Systems Pharmacology approach to computationally model
gene changes in network map pathways altered after TBI and to identify perturbed pathways responsive to AAV-
CLC modulation after TBI. Successful completion of this work will bridge an important knowledge gap in
understanding the detrimental effects of TBI on the synapse and identify CLC and CME function as a novel
therapeutic target to promote functional recovery after a TBI.

Grant Number: 5R01NS124730-04
NIH Institute/Center: NIH
Principal Investigator: SHAUN CARLSON