I019 Dissecting the effects of cholesterol at the cortico-striatal synapse in Huntington’s disease

<h3>Background</h3> Over the past 25 years, our laboratory has gathered compelling evidence indicating a reduction in brain cholesterol levels and biosynthesis in Huntington’s disease (HD) mice. This finding has significant implications for understanding HD pathophysiology and for developing potential therapeutic strategies. Consistent with this, all strategies developed so far to increase cholesterol levels in the HD mouse brain have resulted in motor and cognitive improvements, as well as in significant reduction in aggregates and improvement in synaptic parameters. <h3>Aim</h3> Given the variety of functional and structural roles of cholesterol in many aspects of synaptic physiology, our current focus is to identify the synaptic mechanisms restored upon cholesterol administration in HD. <h3>Methods</h3> Wild-type and HD primary neuronal monocultures obtained from the striatum and cortex, along with a two-compartment microfluidic device, were employed to reconstruct functional neuronal networks in vitro. Cholesterol was administered in acute and chronic paradigms. Excitatory and inhibitory synapses were identified by immunolabeling pre-synaptic and post-synaptic markers, and synapse connectivity was evaluated following cholesterol administration. <h3>Results</h3> A time-course characterization of synapse dysfunction in vitro revealed an early loss of synaptic contacts in HD neuronal cultures, as evidenced by the decreased colocalization of pre-synaptic and post-synaptic marker puncta. Notably, cholesterol administration to symptomatic primary HD neurons rescued the synaptic phenotype. <h3>Conclusion</h3> These results indicate that direct cholesterol administration acts at the synapse to increase connectivity in an HD neuronal network reconstructed in vitro. Funded by the HDF (Leslie Gehry Prize for Innovation in Science) and partially by NSC-Reconstruct (European Union, # 874758).