Pathogenic LRRK2 control of primary cilia and Hedgehog signaling in neurons and astrocytes of mouse brain.

Shahzad S Khan,Suzanne R Pfeffer,Dario R Alessi,Yuriko Sobu,Kerryn Berndsen,Herschel S Dhekne,Francesca Tonelli

doi:10.7554/elife.67900

Abstract

Activating LRRK2 mutations cause Parkinson's disease, and pathogenic LRRK2 kinase interferes with ciliogenesis. Previously, we showed that cholinergic interneurons of the dorsal striatum lose their cilia in R1441C LRRK2 mutant mice (Dhekne et al., 2018). Here, we show that cilia loss is seen as early as 10 weeks of age in these mice and also in two other mouse strains carrying the most common human G2019S LRRK2 mutation. Loss of the PPM1H phosphatase that is specific for LRRK2-phosphorylated Rab GTPases yields the same cilia loss phenotype seen in mice expressing pathogenic LRRK2 kinase, strongly supporting a connection between Rab GTPase phosphorylation and cilia loss. Moreover, astrocytes throughout the striatum show a ciliation defect in all LRRK2 and PPM1H mutant models examined. Hedgehog signaling requires cilia, and loss of cilia in LRRK2 mutant rodents correlates with dysregulation of Hedgehog signaling as monitored by in situ hybridization of Gli1 and Gdnf transcripts. Dopaminergic neurons of the substantia nigra secrete a Hedgehog signal that is sensed in the striatum to trigger neuroprotection; our data support a model in which LRRK2 and PPM1H mutant mice show altered responses to critical Hedgehog signals in the nigrostriatal pathway.

Highlights

Mutations in the kinase encoded by the LRRK2 gene represent the predominant cause of familial Parkinson’s disease (PD), a neurodegenerative disorder that results in the loss of dopaminergic neurons in the substantia nigra pars compacta (Poewe et al 2017; Alessi and Sammler, 2018)
Loss of PPM1H in wild type mouse embryonic fibroblast (MEF) cells phenocopies the loss of cilia seen upon expression of pathogenic LRRK2 (Berndsen et al, 2019)
We showed previously that cholinergic interneurons that represent about 5% of the neurons in the dorsal striatum of 7-month, R1441C LRRK2 knock-in (KI) mice have fewer primary cilia than their wild type littermates (Dhekne et al, 2018)

Summary

Introduction

Mutations in the kinase encoded by the LRRK2 gene represent the predominant cause of familial Parkinson’s disease (PD), a neurodegenerative disorder that results in the loss of dopaminergic neurons in the substantia nigra pars compacta (Poewe et al 2017; Alessi and Sammler, 2018). Increase its kinase activity in cells (West et al, 2005; Greggio et al, 2006; Jaleel et al, 2007; Ito et al, 2016; Steger et al, 2016), and interactions with other proteins including Rab. Phosphorylation of Rab proteins interferes with their abilities to be loaded with GTP by cognate guanine nucleotide exchange factors, a prerequisite for their binding to partner effector proteins (Steger et al, 2016, 2017). This alone would interfere with normal Rab GTPase function. We found previously that the rare, striatal, cholinergic interneurons that would normally sense Hh via their primary cilia are less ciliated in mice carrying the R1441C LRRK2 mutation (Dhekne et al, 2018). We show that striatal astrocytes share a broad ciliary deficit that likely impacts synaptic function

Results

Discussion

Materials and Methods