LRRK2 regulates synaptic function through modulation of actin cytoskeletal dynamics

Parkinson's disease (PD) is a multisystemic disorder that manifests through motor and non-motor symptoms. Motor dysfunction results from the degeneration of dopamine-producing neurons in the substantia nigra pars compacta. Increasing evidence suggests that synapse dysfunction precedes neuronal loss by years. Still, early synaptic alterations in PD remain poorly understood. Here, we integrate literature meta-analysis and multi-omics with biochemical, imaging, and electrophysiological measurements in Lrrk2 mouse models and human iPSC-derived neurons lacking LRRK2. We demonstrate that brain-derived neurotrophic factor (BDNF) activates LRRK2 in differentiated SH-SY5Y cells and primary mouse neurons, reshaping the LRRK2 interactome toward a network of actin cytoskeleton-related proteins. Gene-ontology analyses of both literature-curated LRRK2 interactors and phospho-proteome from striatal tissues with elevated LRRK2 activity highlight synapse-actin remodeling as major affected pathways. We further observed that loss of LRRK2 impairs BDNF signaling and alters postsynaptic density architecture. Young Lrrk2 knockout mice display structural alterations in dendritic protrusions, a phenotype that normalizes with age. In human iPSC-derived neurons, LRRK2 knockout affects maturation and BDNF-dependent regulation of spontaneous synaptic activity. Taken together, our study discloses a critical role of LRRK2 in BDNF-dependent synaptic modulation and identifies the synaptic actin cytoskeleton as a convergent site of LRRK2-associated pathophysiological processes in PD.