Missense mutations in leucine-rich repeat kinase 2 (LRRK2) cause late-onset Parkinson disease, and common genetic variation in LRRK2 modifies susceptibility to Crohn disease and leprosy. High levels of LRRK2 expression in peripheral monocytes and macrophages suggest a role for LRRK2 in these cells, yet little is known about LRRK2 expression and function in immune cells of the brain. Here, we demonstrate a role for LRRK2 in mediating microglial pro-inflammatory responses and morphology. In a murine model of neuroinflammation, we observe robust induction of LRRK2 in microglia. Experiments with TLR4-stimulated rat primary microglia show that inflammation increases LRRK2 activity and expression while inhibition of LRRK2 kinase activity or knockdown of protein attenuates TNFα secretion and iNOS induction. LRRK2 inhibition blocks TLR4 stimulated microglial process outgrowth and impairs ADP stimulated microglial chemotaxis. However, actin inhibitors that phenocopy inhibition of process outgrowth and chemotaxis fail to modify TLR4 stimulation of TNFα secretion and iNOS induction, suggesting LRRK2 acts upstream of cytoskeleton control as a stress-responsive kinase. These data demonstrate LRRK2 in regulating responses in immune cells of the brain and further implicate microglial involvement in late-onset PD.

Missense mutations in the leucine-rich repeat kinase 2 (LRRK2) gene can cause late-onset Parkinson disease. Past studies have provided conflicting evidence for the protective effects of LRRK2 knockdown in models of Parkinson disease as well as other disorders. These discrepancies may be caused by uncertainty in the pathobiological mechanisms of LRRK2 action. Previously, we found that LRRK2 knockdown inhibited proinflammatory responses from cultured microglia cells. Here, we report LRRK2 knockout rats as resistant to dopaminergic neurodegeneration elicited by intracranial administration of LPS. Such resistance to dopaminergic neurodegeneration correlated with reduced proinflammatory myeloid cells recruited in the brain. Additionally, adeno-associated virus-mediated transduction of human α-synuclein also resulted in dopaminergic neurodegeneration in wild-type rats. In contrast, LRRK2 knockout animals had no significant loss of neurons and had reduced numbers of activated myeloid cells in the substantia nigra. Although LRRK2 expression in the wild-type rat midbrain remained undetected under nonpathological conditions, LRRK2 became highly expressed in inducible nitric oxide synthase (iNOS)-positive myeloid cells in the substantia nigra in response to α-synuclein overexpression or LPS exposures. Our data suggest that knocking down LRRK2 may protect from overt cell loss by inhibiting the recruitment of chronically activated proinflammatory myeloid cells. These results may provide value in the translation of LRRK2-targeting therapeutics to conditions where neuroinflammation may underlie aspects of neuronal dysfunction and degeneration.M issense mutations in the leucine-rich repeat kinase 2 (LRRK2) gene can be found in many families that transmit classical late-onset Parkinson disease (PD) from one generation to the next. Notably, these mutations are prevalent in the Ashkenazi Jewish and North African Arab Berber populations in more than 20% of PD cases (1, 2). Genome-wide association studies further provide evidence that links LRRK2 to PD susceptibility, with several risk alleles being identified in LRRK2 (3, 4). Association studies have also linked LRRK2 to Crohn disease and Hansen disease (5, 6). Although LRRK2 is widely considered an exciting target for therapeutic approaches in PD, the pathobiological role of LRRK2 as a critical modifier of disease susceptibility is not well understood. Additional insights into LRRK2-linked molecular pathways relevant to PD and neurodegeneration may enable more predictive preclinical studies.PD is pathologically characterized by both α-synuclein inclusions called Lewy bodies and Lewy neurites and the profound loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The absence of LRRK2 has been shown to impair α-synuclein inclusion formation, neuron loss, and microglia activation in mice overexpressing mutant α-synuclein (7). However, other studies that have crossed LRRK2 knockout mice with different α-synuclein transgenic mice did not observe robust protection fr...

Background: LRRK2 kinase activity has been implicated in Parkinson disease (PD). Results: LRRK2 kinase inhibition attenuated neurodegeneration in LRRK2 transgenic and wild-type rats. Conclusion: Chronic inhibition of LRRK2 kinase activity is well tolerated in rats and provides neuroprotection from ␣-synuclein overexpression. Significance: These results warrant further studies that test the therapeutic potential of LRRK2 kinase inhibitors in additional PD models.

Proteinaceous inclusions in neurons, composed primarily of α-synuclein, define the pathology in several neurodegenerative disorders. Neurons can internalize α-synuclein fibrils that can seed new inclusions from endogenously expressed α-synuclein. The factors contributing to the spread of pathology and subsequent neurodegeneration are not fully understood, and different compositions and concentrations of fibrils have been used in different hosts. Here, we systematically vary the concentration and length of well-characterized α-synuclein fibrils and determine their relative ability to induce inclusions and neurodegeneration in different hosts (primary neurons, C57BL/6J and C3H/HeJ mice, and Sprague Dawley rats). Using dynamic-light scattering profiles and other measurements to determine fibril length and concentration, we find that femptomolar concentrations of fibrils are sufficient to induce robust inclusions in primary neurons. However, a narrow and non-linear dynamic range characterizes fibril-mediated inclusion induction in axons and the soma. In mice, the C3H/HeJ strain is more sensitive to fibril exposures than C57BL/6J counterparts, with more inclusions and dopaminergic neurodegeneration. In rats, injection of fibrils into the substantia nigra pars compacta (SNpc) results in similar inclusion spread and dopaminergic neurodegeneration as injection of the fibrils into the dorsal striatum, with prominent inclusion spread to the amygdala and several other brain areas. Inclusion spread, particularly from the SNpc to the striatum, positively correlates with dopaminergic neurodegeneration. These results define biophysical characteristics of α-synuclein fibrils that induce inclusions and neurodegeneration both in vitro and in vivo, and suggest that inclusion spread in the brain may be promoted by a loss of neurons.

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene cause late-onset Parkinson's disease (PD). Emerging evidence suggests a role for LRRK2 in the endocytic pathway. Here, we show that LRRK2 is released in extracellular microvesicles (i.e. exosomes) from cells that natively express LRRK2. LRRK2 localizes to collecting duct epithelial cells in the kidney that actively secrete exosomes into urine. Purified urinary exosomes contain LRRK2 protein that is both dimerized and phosphorylated. We provide a quantitative proteomic profile of 1673 proteins in urinary exosomes and find that known LRRK2 interactors including 14-3-3 are some of the most abundant exosome proteins. Disruption of the 14-3-3 LRRK2 interaction with a 14-3-3 inhibitor or through acute LRRK2 kinase inhibition potently blocks LRRK2 release in exosomes, but familial mutations in LRRK2 had no effect on secretion. LRRK2 levels were overall comparable but highly variable in urinary exosomes derived from PD cases and age-matched controls, although very high LRRK2 levels were detected in some PD affected cases. We further characterized LRRK2 exosome release in neurons and macrophages in culture, and found that LRRK2-positive exosomes circulate in cerebral spinal fluid (CSF). Together, these results define a pathway for LRRK2 extracellular release, clarify one function of the LRRK2 14-3-3 interaction and provide a foundation for utilization of LRRK2 as a biomarker in clinical trials.

Objective: To test whether phosphorylated Ser-1292 LRRK2 levels in urine exosomes predicts LRRK2 mutation carriers (LRRK21) and noncarriers (LRRK22) with Parkinson disease (PD1) and without Parkinson disease (PD2).Methods: LRRK2 protein was purified from urinary exosomes collected from participants in 2 independent cohorts. The first cohort included 14 men (LRRK21/PD1, n 5 7; LRRK22/PD1, n 5 4; LRRK22/PD2, n 5 3). The second cohort included 62 men (LRRK22/PD2, n 5 16; LRRK21/PD2, n 5 16; LRRK21/PD1, n 5 14; LRRK22/PD1, n 5 16). The ratio of Ser(P)-1292 LRRK2 to total LRRK2 was compared between LRRK21/PD1 and LRRK22 in the first cohort and between LRRK2 G2019S carriers with and without PD in the second cohort.Results: LRRK21/PD1 had higher ratios of Ser(P)-1292 LRRK2 to total LRRK2 than LRRK22/PD2 (4.8-fold, p , 0.001) and LRRK22/PD1 (4.6-fold, p , 0.001). Among mutation carriers, those with PD had higher Ser(P)-1292 LRRK2 to total LRRK2 than those without PD (2.2-fold, p , 0.001). Ser(P)-1292 LRRK2 levels predicted symptomatic from asymptomatic carriers with an area under the receiver operating characteristic curve of 0.844. Conclusion:Elevated ratio of phosphorylated Ser-1292 LRRK2 to total LRRK2 in urine exosomes predicted LRRK2 mutation status and PD risk among LRRK2 mutation carriers. Future studies may explore whether interventions that reduce this ratio may also reduce PD risk.

Parkinson Disease (PD) is a chronic and progressive neurodegenerative disorder of unknown etiology. Autopsy findings, genetics, retrospective studies, and molecular imaging all suggest a role for inflammation in the neurodegenerative process. However, relatively little is understood about the causes and implications of neuroinflammation in PD. Understanding how inflammation arises in PD, in particular the activation state of cells of the innate immune system, may provide an exciting opportunity for novel neuroprotective therapeutics. We analyze the evidence of immune system involvement in PD susceptibility, specifically in the context of M1 and M2 activation states. Tracking and modulating these activation states may provide new insights into both PD etiology and therapeutic strategies.

Cholinergic regulation of dopaminergic inputs into the striatum is critical for normal basal ganglia (BG) function. This regulation of BG function is thought to be primarily mediated by acetylcholine released from cholinergic interneurons (ChIs) acting locally in the striatum. We now report a combination of pharmacological, electrophysiological, optogenetic, chemogenetic, and functional magnetic resonance imaging studies suggesting extra-striatal cholinergic projections from the pedunculopontine nucleus to the substantia nigra pars reticulata (SNr) act on muscarinic acetylcholine receptor subtype 4 (M) to oppose cAMP-dependent dopamine receptor subtype 1 (D) signaling in presynaptic terminals of direct pathway striatal spiny projections neurons. This induces a tonic inhibition of transmission at direct pathway synapses and D-mediated activation of motor activity. These studies provide important new insights into the unique role of M in regulating BG function and challenge the prevailing hypothesis of the centrality of striatal ChIs in opposing dopamine regulation of BG output.