SUMMARY Studies of Parkinson’s disease (PD) have been greatly hindered by lack of access to affected human dopaminergic (DA) neurons. Here, we report generation of induced pluripotent stem cells that carry the p.G2019S mutation (G2019S-iPSCs) in the Leucine-Rich Repeat Kinase-2 (LRRK2) gene, the most common PD-related mutation. We demonstrate that these G2019S-iPSCs were able to differentiate into DA neurons and showed increased expression of key oxidative stress response genes and α-synuclein protein. Moreover, G2019S-mutant DA neurons were more sensitive to caspase-3 activation, caused by exposure to hydrogen peroxide, MG-132, and 6-hydroxydopamine, compared to unaffected DA neurons. These findings suggest that G2019S-iPSC-derived DA neurons exhibit early phenotypes linked to PD. Due to high penetrance of the LRRK2 mutation and its clinical resemblance to sporadic PD, these neurons may provide a valuable platform for identification of novel pharmacological agents and diagnostics for modeling and alleviation of a subset of disease phenotypes.

SUMMARY Mitochondrial movements are tightly controlled to maintain energy homeostasis and prevent oxidative stress. Miro is an outer mitochondrial membrane protein that anchors mitochondria to microtubule motors, and is removed to stop mitochondrial motility as an early step in clearance of dysfunctional mitochondria. Here, using human iPSC-derived neurons and other complementary models, we build on a previous connection of Parkinson’s disease (PD)-linked PINK1 and Parkin to Miro, by showing that a third PD-related protein, LRRK2, promotes Miro removal via forming a complex with Miro. Pathogenic LRRK2G2019S disrupts this function, delaying the arrest of damaged mitochondria and consequently slowing the initiation of mitophagy. Remarkably, partial reduction of Miro levels in LRRK2G2019S human neuron and Drosophila PD models rescues neurodegeneration. Miro degradation and mitochondrial motility are also impaired in sporadic PD patients. We reveal that prolonged retention of Miro, and the downstream consequences that ensue, may constitute a central component of PD pathogenesis.

The induced pluripotent stem (iPS) cell field promises a new era for in vitro disease modeling. However, identifying innate cellular pathologies, particularly for age-related neurodegenerative diseases, has been challenging. Here, we exploited mutation correction of iPS cells and conserved proteotoxic mechanisms from yeast to human to discover and reverse phenotypic responses to α-Synuclein (αSyn), a key protein involved in Parkinson’s disease (PD). We generated cortical neurons from iPS cells of patients harboring αSyn mutations, who are at high risk of developing PD dementia. Genetic modifiers from unbiased screens in a yeast model of αSyn toxicity led to identification of early pathogenic phenotypes in patient neurons. These included nitrosative stress, accumulation of ER-associated degradation (ERAD) substrates and ER stress. A small molecule identified in a yeast screen, and the ubiquitin ligase Nedd4 it activates, reversed pathologic phenotypes in these neurons.

Copy number mutations implicate excess production of α-synuclein as a possibly causative factor in Parkinson’s disease (PD). Using an unbiased screen targeting endogenous gene expression, we discovered that the β2-adrenoreceptor (β2AR) is a regulator of the α-synuclein gene (SNCA). β2AR ligands modulate SNCA transcription through histone 3 lysine 27 acetylation of its promoter and enhancers. Over 11 years of follow-up in 4 million Norwegians, the β2AR agonist salbutamol, a brain-penetrant asthma medication, was associated with reduced risk of developing PD (rate ratio, 0.66; 95% confidence interval, 0.58 to 0.76). Conversely, a β2AR antagonist correlated with increased risk. β2AR activation protected model mice and patient-derived cells. Thus, β2AR is linked to transcription of α-synuclein and risk of PD in a ligand-specific fashion and constitutes a potential target for therapies.

Parkinson’s disease-associated LRRK2 kinase phosphorylates multiple Rab GTPases, including Rab8A and Rab10. We show here that LRRK2 kinase interferes with primary cilia formation in cultured cells, human LRRK2 G2019S iPS cells and in the cortex of LRRK2 R1441C mice. Rab10 phosphorylation strengthens its intrinsic ability to block ciliogenesis by enhancing binding to RILPL1. Importantly, the ability of LRRK2 to interfere with ciliogenesis requires both Rab10 and RILPL1 proteins. Pathogenic LRRK2 influences the ability of cells to respond to cilia-dependent, Hedgehog signaling as monitored by Gli1 transcriptional activation. Moreover, cholinergic neurons in the striatum of LRRK2 R1441C mice show decreased ciliation, which will decrease their ability to sense Sonic hedgehog in a neuro-protective circuit that supports dopaminergic neurons. These data reveal a molecular pathway for regulating cilia function that likely contributes to Parkinson’s disease-specific pathology.Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).