Striatal leucine-rich repeat kinase 2 mRNA is increased in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned common marmosets (Callithrix jacchus) with L-3, 4-dihydroxyphenylalanine methyl ester-induced dyskinesia

LRRK2, a puzzling protein: insights into Parkinson's disease pathogenesis

Leucine-rich repeat kinase 2 (LRRK2) is a large, ubiquitous protein of unknown function. Mutations in the gene encoding LRRK2 have been linked to familial and sporadic Parkinson's disease (PD) cases. The LRRK2 protein is a single polypeptide that displays GTPase and kinase activity. Kinase and GTPase domains are involved in different cellular signaling pathways. Despite several experimental studies associating LRRK2 protein with various intracellular membranes and vesicular structures such as endosomal/lysosomal compartments, the mitochondrial outer membrane, lipid rafts, microtubule-associated vesicles, the golgi complex, and the endoplasmic reticulum its broader physiologic function(s) remain unidentified. Additionally, the cellular distribution of LRRK2 may indicate its role in several different pathways, such as the ubiquitin-proteasome system, the autophagic-lysosomal pathway, intracellular trafficking, and mitochondrial dysfunction. This review discusses potential mechanisms through which LRRK2 may mediate neurodegeneration and cause PD.

Ghrelin is neuroprotective in Parkinson's disease: molecular mechanisms of metabolic neuroprotection

Ghrelin is a circulating orexigenic signal that rises with prolonged fasting and falls postprandially. Ghrelin regulates energy homeostasis by stimulating appetite and body weight; however, it also has many nonmetabolic functions including enhanced learning and memory, anxiolytic effects as well as being neuroprotective. In Parkinson's disease, ghrelin enhances dopaminergic survival via reduced microglial and caspase activation and improved mitochondrial function. As mitochondrial dysfunction contributes to Parkinson's disease, any agent that enhances mitochondrial function could be a potential therapeutic target. We propose that ghrelin provides neuroprotective effects via AMPK (5' adenosine monophosphate-activated protein kinase) activation and enhanced mitophagy (removal of damaged mitochondria) to ultimately enhance mitochondrial bioenergetics. AMPK activation shifts energy balance from a negative to a neutral state and has a role in regulating mitochondrial biogenesis and reducing reactive oxygen species production. Mitophagy is important in Parkinson's disease because damaged mitochondria produce reactive oxygen species resulting in damage to intracellular proteins, lipids and DNA predisposing them to neurodegeneration. Many genetic mutations linked to Parkinson's disease are due to abnormal mitochondrial function and mitophagy, for example LRRK2, PINK1 and Parkin. An interaction between ghrelin and these classic Parkinson's disease markers has not been observed, however by enhancing mitochondrial function, ghrelin or AMPK is a potential therapeutic target for slowing the progression of Parkinson's disease symptoms, both motor and nonmotor.

Parkinson's disease: leucine-rich repeat kinase 2 and autophagy, intimate enemies

Parkinson's disease is the second common neurodegenerative disorder, after Alzheimer's disease. It is a clinical syndrome characterized by loss of dopamine-generating cells in the substancia nigra, a region of the midbrain. The etiology of Parkinson's disease has long been through to involve both genetic and environmental factors. Mutations in the leucine-rich repeat kinase 2 gene cause late-onset Parkinson's disease with a clinical appearance indistinguishable from Parkinson's disease idiopathic. Autophagy is an intracellular catabolic mechanism whereby a cell recycles or degrades damage proteins and cytoplasmic organelles. This degradative process has been associated with cellular dysfunction in neurodegenerative processes including Parkinson's disease. We discuss the role of leucine-rich repeat kinase 2 in autophagy, and how the deregulations of this degradative mechanism in cells can be implicated in the Parkinson's disease etiology.

LRRK2 expression in idiopathic and G2019S positive Parkinson's disease subjects: a morphological and quantitative study

AIMS

Mutations in the gene encoding leucine-rich repeat kinase-2 (LRRK2) have been established as a common genetic cause of Parkinson's disease (PD). The distribution of LRRK2 mRNA and protein in the human brain has previously been described, although it has not been reported in PD cases with the common LRRK2 G2019S mutation.

METHODS

To further elucidate the role of LRRK2 in PD, we determined the localization of LRRK2 mRNA and protein in post-mortem brain tissue from control, idiopathic PD (IPD) and G2019S positive PD cases.

RESULTS

Widespread neuronal expression of LRRK2 mRNA and protein was recorded and no difference was observed in the morphological localization of LRRK2 mRNA or protein between control, IPD and G2019S positive PD cases. Using quantitative real-time polymerase chain reaction, we demonstrated that there is no regional variation in LRRK2 mRNA in normal human brain, but we have identified differential expression of LRRK2 mRNA with significant reductions recorded in limbic and neocortical regions of IPD cases compared with controls. Semi-quantitative analysis of LRRK2 immunohistochemical staining demonstrated regional variation in staining intensity, with weak LRRK2 immunoreactivity consistently recorded in the striatum and substantia nigra. No clear differences were identified in LRRK2 immunoreactivity between control, IPD and G2019S positive PD cases. LRRK2 protein was identified in a small proportion of Lewy bodies.

CONCLUSIONS

Our data suggest that widespread dysregulation of LRRK2 mRNA expression may contribute to the pathogenesis of IPD.

Update on the functional biology of Lrrk2

The etiology of Parkinson's disease (PD) was long thought to be due to environmental factors. Following the discovery of autosomal-dominant mutations in the α-synuclein gene, and later recessive mutations in the DJ-1, Parkin and PINK-1 genes, the field of PD genetics exploded. In 2004, it was discovered that mutations in the PARK8 locus - leucine-rich repeat kinase 2 (LRRK2, Lrrk2) - are the most important genetic cause of autosomal-dominant PD. Lrrk2 substitutions also account for sporadic PD in certain ethnic populations and have been shown to increase the risk of PD in Asian populations. Drug therapies targeting Lrrk2 activity may therefore be beneficial to both familial and sporadic PD patients, hence understanding the role of Lrrk2 in health and disease is critical. This review aims to highlight the research effort concentrated on elucidating the functional biological role of Lrrk2, and to provide some future therapeutic perspectives.