Parkinson’s disease (PD) is a common neurodegenerative disease clinically characterized by bradykinesia,
rigidity and resting tremor. Recent studies have enlightened that synaptic dysfunction, implicated in
numerous studies of animal models of PD, is both a key factor in PD and an early stage marker in
presymptomatic patients. Although the majority of cases are sporadic, mutations in the Leucine-rich
repeat kinase 2 (LRRK2) gene (PARK8; OMIM 609007) are linked to late-onset autosomal dominant
Parkinson’s disease. Mutations in LRRK2 account for up to 13% of familial PD cases compatible with
dominant inheritance and 1 to 2% of sporadic PD patients, thus suggesting this protein as the most
significant player in PD pathogenesis identified to date. The LRRK2 protein has a molecular weight of
approximately 280 kDa and contains several domains including a kinase domain. Robust literature suggests
that the pathological mutations bring to an increase of LRRK2 kinase activity. Despite its predominance in
PD, the physiological function of LRRK2 is not known and also its precise role in the aetiology of PD is far
from being understood. Strikingly, neurotransmission defects have been repeatedly observed in different
LRRK2 models. Accordingly, we have recently shown that electrophysiological properties as well as
vesicular trafficking in the presynaptic pool depend on the presence of LRRK2 as an integral part of
presynaptic protein complex. Given the presynaptic alteration seen in LRRK2 disease model, an attractive
hypothesis is that LRRK2 influences synaptic structure and function through effects on presynaptic
proteins. One possibility is that mutated LRRK2 alters synaptic vesicles (SV) trafficking via impaired
phosphorylation of presynaptic proteins. Our major aim is to identify and understand the molecular basis
behind PD onset and progression. Thus we aim to uncover if presynaptic proteins critical for SV trafficking
are target of the pathological kinase activity of LRRK2 and how this mechanism influences proper synaptic
function. Finally, given that inhibitors of LRRK2 kinase activity have been recently characterized, we
propose to evaluate their effect on subtle neuron functions in different LRRK2 PD in vitro models. The
pharmacological inhibition of LRRK2 kinase activity is in fact a promising therapeutic modality for the
treatment of neurodegeneration in PD, but its real potential and eventual side effect have to be deeply
evaluated. In order to move the first step towards the targeting of LRRK2 kinase activity as a therapeutic
strategy, we will evaluate the effect of LRRK2 kinase inhibitor in terms of capability to rescue functional
phenotype. In order to gain more physiological information, we will test selected candidates on a high
complexity model specifically developed for this project: dopaminergic neurons derived from LRRK2
patients. In fact, patient derived iPS cells constitute the best tool to gain information about a multi-factor
disease as PD where genomic background has a deep effect on age of onset and clinical phenotype. We
expect that these studies will provide a framework to identify what the direct biochemical and
physiological consequences of LRRK2 mutations are, providing a better understanding of LRRK2 function
and, potentially, new molecular handle to design the diagnosis and the treatment of the disease.