Abrogation of α-synuclein–mediated dopaminergic neurodegeneration in LRRK2-deficient rats

Abstract

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...

Unique Functional and Structural Properties of the LRRK2 Protein ATP-binding Pocket

“…Also, in contrast to our previous observations with LRRK2-IN-1, we could not detect a change in TNF levels with acute exposures to 11. Rather, a 3-day compound 11 exposure protocol attenuated TNF levels in response to LPS, potentially consistent with RNAi experiments in primary macrophages (35) and the reduced proinflammatory macrophage responses observed in vivo in the LRRK2 knockout rat (44). Furthermore, these results are consistent with a role for LRRK2 in the maturation of myeloid cells (e.g.…”

Leucine-rich Repeat Kinase 2 (LRRK2) Pharmacological Inhibition Abates α-Synuclein Gene-induced Neurodegeneration

“…We found previously that LRRK2 knockout rats are protected from neurodegeneration (16). In that study, we hypothesized that LRRK2 kinase inhibition might phenocopy neuroprotection associated with LRRK2 deficiency.…”

“…Virus Production and Surgeries-Recombinant adeno-associated virus 2/1 (rAAV2/1)-␣-synuclein was obtained from the Virus Core of the University of North Carolina and has been described previously (16). Intracranial viral or vehicle control injections were conducted under isoflurane anesthesia using a digital stereotaxic frame (David Kopf) with a thermal adjustable height stage (Physiotemp).…”

LRRK2 mutations and neurotoxicant susceptibility

“…These discrepancies are difficult to interpret, as mammalian studies have shown that LRRK2 expression occurs in specific neuronal and glial populations and also systemically in immune cells. [48][49][50] In Drosophila, the majority of studies show that expression of human LRRK2 may be sufficient to induce DA neurodegeneration. Expression of disease-causing mutations typically results in heightened DA cell loss.…”

“…55 In contrast, LRRK2 knock-out in rats abrogated DA degeneration induced by intracranial LPS administration or adenovirus-mediated human a-synuclein overexpression. 48 Similarly, inhibition of LRRK2 kinase activity (inhibitors) or LRRK2 knockdown (RNAi) attenuated microglial inflammatory responses that were induced by intracranial LPS infusion. 27 In experiments examining gene-gene interactions, WT LRRK2 or G2019S LRRK2 equally exacerbated accumulation of a-synuclein, neuronal loss, and microglial activation that were induced in transgenic mice overexpressing A53T a-synuclein.…”