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Numerous studies in Alzheimer’s Disease (AD) animal models show that overproduction of Aβ peptides and their
oligomerization can distort dendrites, damage synapses, and decrease the number of dendritic spines and synapses. Aβ
may trigger synapse loss by modulating activity of actin-regulating proteins, such as Rac1 and cofilin. Indeed, Aβ1-42
oligomers can activate actin severing protein cofilin through calcineurin-mediated activation of phosphatase slingshot
and inhibit an opposing pathway that suppresses cofilin phosphorylation through Rac-mediated activation of LIMK1.
Excessive activation of actin-severing protein cofilin triggers the formation of a non-dynamic actin bundles, called rods
that are found in AD brains and cause loss of synapses. Hence, regulation of these actin-regulating proteins in dendritic
spines could potentially provide useful tools for preventing the synapse/spine loss associated with earlier stages of AD
neuropathology. However, lack of spatiotemporal control over their activity is a key limitation. Recently, optogenetic
advancements have provided researchers with convenient light-activating proteins such as photoactivatable Rac (PARac).
Here, we transfected cultured primary hippocampal neurons and human embryonic kidney (HEK) cells with a PARac/
mCherry-containing plasmid and the mCherry-positive cells were identified and imaged using an inverted
fluorescence microscope. Rac1 activation was achieved by irradiation with blue light (480nm) and live changes in
dendritic spine morphology were observed using mCherry (587nm). Rac activation was confirmed by immunostaining
for phosphorylated form of effector proteinP21 protein-activated kinase 1 (PAK1) and reorganization of actin. Thus, our
studies confirm the feasibility of using the PA-Rac construct to trigger actin re-organization in the dendritic spines.
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