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Background: Leucine-rich repeat kinase 2 is a potential therapeutic target for the treatment of Parkinson's disease, and clinical trials of leucine-rich repeat kinase 2 inhibitors are in development. The objective of this study was to evaluate phosphorylation of a new leucine-rich repeat kinase 2 substrate, Rab10, for potential use as a target engagement biomarker and/or patient enrichment biomarker for leucine-rich repeat kinase 2 inhibitor clinical trials.Methods: Peripheral blood mononuclear cells and neutrophils were isolated from Parkinson's disease patients and matched controls, and treated ex vivo with a leucine-rich repeat kinase 2 inhibitor. Immunoblotting was used to measure levels of leucine-rich repeat kinase 2 and Rab10 and their phosphorylation. Plasma inflammatory cytokines were measured by multiplex enzyme-linked immunosorbent assay.Results: Mononuclear cells and neutrophils of both controls and Parkinson's disease patients responded the same to leucine-rich repeat kinase 2 inhibitor treatment. Leucine-rich repeat kinase 2 levels in mononuclear cells were the same in controls and Parkinson's disease patients, whereas leucine-rich repeat kinase 2 was significantly increased in Parkinson's disease neutrophils. Rab10 T73 phosphorylation levels were similar in controls and Parkinson's disease patients and did not correlate with leucine-rich repeat kinase 2 levels. Immune-cell levels of leucine-rich repeat kinase 2 and Rab10 T73 phosphorylation were associated with plasma inflammatory cytokine levels.Conclusions: Rab10 T73 phosphorylation appears to be a valid target engagement biomarker for potential use in leucine-rich repeat kinase 2 inhibitor clinical trials. However, a lack of association between leucine-rich repeat kinase 2 and Rab10 phosphorylation complicates the potential use of Rab10 phosphorylation as a patient enrichment biomarker. Although replication is required, increased leucine-rich repeat kinase 2 levels in neutrophils from Parkinson's disease patients may have the potential for patient stratification. leucine-rich repeat kinase 2 activity in peripheral immune cells may contribute to an inflammatory phenotype. © 2018 International Parkinson and Movement Disorder Society. [ABSTRACT FROM AUTHOR]

Missense mutations in leucine-rich repeat kinase 2 (LRRK2) are pathogenic for familial Parkinson's disease. However, it is unknown whether levels of LRRK2 protein in the brain are altered in patients with LRRK2-associated Parkinson's disease. Because LRRK2 mutations are relatively rare, accounting for approximately 1% of all Parkinson's disease, we accessioned cases from five international brain banks to investigate levels of the LRRK2 protein, and other genetically associated Parkinson's disease proteins. Brain tissue was obtained from 17 LRRK2 mutation carriers (12 with the G2019S mutation and five with the I2020T mutation) and assayed by immunoblot. Compared to matched controls and idiopathic Parkinson's disease cases, we found levels of LRRK2 protein were reduced in the LRRK2 mutation cases. We also measured a decrease in two other proteins genetically implicated in Parkinson's disease, the core retromer component, vacuolar protein sorting associated protein 35 (VPS35), and the lysosomal hydrolase, glucocerebrosidase (GBA). Moreover, the classical retromer cargo protein, cation-independent mannose-6-phosphate receptor (MPR300, encoded by IGF2R), was also reduced in the LRRK2 mutation cohort and protein levels of the receptor were correlated to levels of LRRK2. These results provide new data on LRRK2 protein expression in brain tissue from LRRK2 mutation carriers and support a relationship between LRRK2 and retromer dysfunction in LRRK2-associated Parkinson's disease brain. [ABSTRACT FROM AUTHOR]

Mutations in leucine-rich repeat kinase 2 (LRRK2) are strongly associated with late-onset autosomal dominant Parkinson's disease. We employed a new, parallel, compound-centric approach to identify a potent and selective LRRK2 inhibitor, LRRK2-IN-1, and demonstrated that inhibition of LRRK2 induces dephosphorylation of Ser910 and Ser935 and accumulation of LRRK2 within aggregate structures. LRRK2-IN-1 will serve as a versatile tool to pharmacologically interrogate LRRK2 biology and study its role in Parkinson's disease. [ABSTRACT FROM AUTHOR]

Background: Parkinson's disease (PD) is the most common neurodegenerative movement disease. Human endogenous retroviruses (HERVs) are proviral remnants of ancient retroviral infection of germ cells that now constitute about 8% of the human genome. Under certain disease conditions, HERV genes are activated and partake in the disease process. However, virtually nothing is known about the pathological relationship, if any, between HERV and PD., Objective: The objectives of this study were to unravel the pathological relationship between human endogenous retrovirus K (HERV-K) and PD, determine the localization of HERV-K in the brain, determine whether HERV-K levels are altered in PD brain and blood, and examine whether HERV-K could serve as a biomarker for PD., Methods: In situ HERV-K and glial fibrillary acidic protein (GFAP) expression in the superior frontal and fusiform cortices of PD and control brain were analyzed using immunofluorescence and confocal microscopy. HERV-K load and copy number in PD and control blood were measured by digital droplet polymerase chain reaction and GFAP by single-molecule array. HERV-K load was analyzed in relation to the Hoehn and Yahr Scale and Movement Disorder Society Unified Parkinson's Disease Rating Scale Part III., Results: HERV-K is predominantly expressed in astrocytes and colocalized with astrocytic GFAP, with decreased expression of both HERV-K and GFAP in PD brain compared with controls. Consistent with this, HERV-K levels were decreased in PD blood compared with controls and were correlated to blood GFAP levels. HERV-K levels were inversely correlated to PD severity and duration., Conclusions: These findings suggest that HERV-K is related to astrocyte function and to PD progression, and that HERV-K could be neuroprotective. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society., (© 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.)

Major advances in understanding how genetics underlies Parkinson's disease (PD) have provided new opportunities for understanding disease pathogenesis and potential new targets for therapeutic intervention. One such target is leucine-rich repeat kinase 2 (LRRK2), an enigmatic enzyme implicated in both familial and idiopathic PD risk. Both academia and industry have promoted the development of potent and selective inhibitors of LRRK2, and these are currently being employed to assess the safety and efficacy of such compounds in preclinical models of PD. This review examines the evidence that LRRK2 kinase activity contributes to the pathogenesis of PD and outlines recent progress on inhibitor development and early results from preclinical safety and efficacy testing. This review also looks at some of the challenges remaining for translation of LRRK2 inhibitors to the clinic, if indeed this is ultimately warranted. As a disease with no current cure that is increasing in prevalence in line with an aging population, there is much need for developing new treatments for PD, and targeting LRRK2 is currently a promising option., Competing Interests: The authors report no conflicts of interest in this work.