| Mutations in leucine-rich repeat kinase 2 (LRRK2) underlie a form of Parkinson's disease (PD) that is clinically indistinguishable from sporadic PD. The function of LRRK2 is not well understood, but it has become widely accepted that LRRK2 kinase activity, which is increased by the commonly observed mutation (G2019S), regulates neurite length. However, it is not known differences in length correspond to altered growth or retraction, whether axons or dendrites are impacted differentially or whether effects observed are transient or sustained. To address this, we compared several developmental milestones in primary hippocampus neurons cultured from mice overexpressing a bacterial artificial chromosome transgene overexpressing mouse wildtype-LRRK2 (LRRK2-WTOE) or mutant LRRK2-G2019S (LRRK2-G2019SOE ), as well as Lrrk2 knockout mice (KO) and non-transgenic mice (NT).;Over the course of three weeks of development on laminin, there is sustained, negative effect of LRRK2-G2019SOE on dendritic growth and arborization, but counter to expectation, dendrites from KO do not elaborate more rapidly than NT dendrites. In contrast, young neurons cultured on a slower growth substrate, poly-L-lysine, show significantly reduced axonal and dendritic motility in Lrrk2 transgenic neurons and greater motility in KO neurons with no significant changes in length. Our findings support that LRRK2 can regulate patterns of axonal and dendritic growth, but they also show that effects vary depending on growth substrate and stage of development.;Previous work indicated that LRRK2 has mixed effects on synapse development, but any effect on the balance of excitatory and inhibitory connections is unknown. LRRK2 has mixed effects on synapse development. KO neurons formed more inhibitory appositions (GAD/gephyrin) compared to other genotypes, while LRRK2-G2019SOE neurons formed significantly more excitatory appositions (VGLUT/Shank) compared to other genotypes. KO neurons form larger presynaptic SV2 clusters at 7 and 21 DIV compared to other genotypes, indicating that KO synapses mature faster than other genotypes and that accelerated development is sustained. Endocytosis of FM dye was equal between genotypes, but the rate of exocytosis was greater in KO and LRRK2-WTOE neurons. LRRK2 kinase activity negatively affects presynaptic function while another LRRK2 function could be having a positive effect at the same time that counteracts this. |
