The role of leucine-rich repeat kinase 2 (LRRK2) in Parkinson's disease

Irisin's emerging role in Parkinson's disease research: A review from molecular mechanisms to therapeutic prospects

Parkinson's disease (PD), a neurodegenerative disorder characterized by impaired motor function, is typically treated with medications and surgery. However, recent studies have validated physical exercise as an effective adjunct therapy, significantly improving both motor and non-motor symptoms in PD patients. Irisin, a myokine, has garnered increasing attention for its beneficial effects on the nervous system. Research has shown that irisin plays a crucial role in regulating metabolic balance, optimizing autophagy, maintaining mitochondrial quality, alleviating oxidative stress and neuroinflammation, and regulating cell death-all processes intricately linked to the pathogenesis of PD. This review examines the mechanisms through which irisin may counteract PD, provides insights into its biological effects, and considers its potential as a target for therapeutic strategies.

New opportunities for antioxidants in amelioration of neurodegenerative diseases

This comprehensive review elucidates the critical role of antioxidants to mitigate oxidative stress, a common denominator in an array of neurodegenerative disorders. Oxidative stress-induced damage has been linked to the development of diseases such as Alzheimer's, Parkinson's, Huntington's disease and amyotrophic lateral sclerosis. This article examines a wide range of scientific literature and methodically delineates the several methods by which antioxidants exercise their neuroprotective benefits. It also explores into the complex relationship between oxidative stress and neuroinflammation, focusing on how antioxidants can alter signaling pathways and transcription factors to slow neurodegenerative processes. Key antioxidants, such as vitamins C and E, glutathione, and polyphenolic compounds, are tested for their ability to combat reactive oxygen and nitrogen species. The dual character of antioxidants, which operate as both direct free radical scavengers and regulators of cellular redox homeostasis, is investigated in terms of therapeutic potential. Furthermore, the study focuses on new antioxidant-based therapy techniques and their mechanisms including Nrf-2, PCG1α, Thioredoxin etc., which range from dietary interventions to targeted antioxidant molecules. Insights into ongoing clinical studies evaluating antioxidant therapies in neurodegenerative illnesses offer an insight into the translational potential of antioxidant research. Finally, this review summarizes our present understanding of antioxidant processes in neurodegenerative illnesses, providing important possibilities for future study and treatment development.

LRRK2 kinase activity is necessary for development and regeneration in Nematostella vectensis

BACKGROUND

The starlet sea anemone, Nematostella vectensis, is an emerging model organism with a high regenerative capacity, which was recently found to possess an orthologue to the human Leucine Rich Repeat Kinase 2 (LRRK2) gene. Mutations in this gene are the most common cause of inherited Parkinson's Disease (PD), highlighting the importance of understanding its function. Despite two decades of research, however, the function of LRRK2 is not well established.

METHODS

To investigate the function of LRRKs in Nematostella vectensis, we applied small molecule inhibitors targeting the kinase activity of LRRK2 to examine its function in development, homeostasis and regeneration in Nematostella vectensis.

RESULTS

In vivo analyses inhibiting the kinase function of this enzyme demonstrated a role of nvLRRK2 in development and regeneration of N. vectensis. These findings implicate a developmental role of LRRK2 in Nematostella, adding to the expanding knowledge of its physiological function.

CONCLUSIONS

Our work introduces a new model organism with which to study LRRK biology. We report that LRRK kinase activity is necessary for the development and regeneration of Nematostella. Given the short generation time, genetic trackability and in vivo imaging capabilities, this work introduces Nematostella vectensis as a new model in which to study genes linked to neurodegenerative diseases such as Parkinson's.

Pressure sensing of lysosomes enables control of TFEB responses in macrophages

Polymers are endocytosed and hydrolysed by lysosomal enzymes to generate transportable solutes. While the transport of diverse organic solutes across the plasma membrane is well studied, their necessary ongoing efflux from the endocytic fluid into the cytosol is poorly appreciated by comparison. Myeloid cells that employ specialized types of endocytosis, that is, phagocytosis and macropinocytosis, are highly dependent on such transport pathways to prevent the build-up of hydrostatic pressure that otherwise offsets lysosomal dynamics including vesiculation, tubulation and fission. Without undergoing rupture, we found that lysosomes incurring this pressure owing to defects in solute efflux, are unable to retain luminal Na+, which collapses its gradient with the cytosol. This cation 'leak' is mediated by pressure-sensitive channels resident to lysosomes and leads to the inhibition of mTORC1, which is normally activated by Na+-coupled amino acid transporters driven by the Na+ gradient. As a consequence, the transcription factors TFEB/TFE3 are made active in macrophages with distended lysosomes. In addition to their role in lysosomal biogenesis, TFEB/TFE3 activation causes the release of MCP-1/CCL2. In catabolically stressed tissues, defects in efflux of solutes from the endocytic pathway leads to increased monocyte recruitment. Here we propose that macrophages respond to a pressure-sensing pathway on lysosomes to orchestrate lysosomal biogenesis as well as myeloid cell recruitment.

Rab10-CAV1 mediated intraluminal vesicle transport to migrasomes

Migrasomes, vesicular organelles generated on the retraction fibers of migrating cells, play a crucial role in migracytosis, mediating intercellular communication. The cargoes determine the functional specificity of migrasomes. Migrasomes harbor numerous intraluminal vesicles, a pivotal component of their cargoes. The mechanism underlying the transportation of these intraluminal vesicles to the migrasomes remains enigmatic. In this study, we identified that Rab10 and Caveolin-1 (CAV1) mark the intraluminal vesicles in migrasomes. Transport of Rab10-CAV1 vesicles to migrasomes required the motor protein Myosin Va and adaptor proteins RILPL2. Notably, the phosphorylation of Rab10 by the kinase LRRK2 regulated this process. Moreover, CSF-1 can be transported to migrasomes through this mechanism, subsequently fostering monocyte-macrophage differentiation in skin wound healing, which served as a proof of the physiological importance of this transporting mechanism.

Exploring potential developmental origins of common neurodegenerative disorders

In the United States, it is now estimated that 6.7 million people over the age of 65 are afflicted by Alzheimer's disease (AD), over 1 million people are living with Parkinson's disease (PD), and over 200 000 have or are at risk for developing Huntington's disease (HD). All three of these neurodegenerative diseases result in the ultimate death of distinct neuronal subtypes, and it is widely thought that age-related damage is the single biggest contributing factor to this neuronal death. However, recent studies are now suggesting that developmental defects during early neurogenesis could also play a role in the pathology of neurodegenerative diseases. Loss or overexpression of proteins associated with HD, PD, and AD also result in embryonic phenotypes but whether these developmental defects slowly unmask over time and contribute to age-related neurodegeneration remains highly debated. Here, we discuss known links between embryonic neurogenesis and neurodegenerative disorders (including common signaling pathways), potential compensatory mechanisms that could delay presentation of neurodegenerative disorders, and the types of model systems that could be used to study these links in vivo.

p.L1795F LRRK2 variant is a common cause of Parkinson's disease in Central Europe

Pathogenic variants in LRRK2 are one of the most common genetic risk factors for Parkinson's disease (PD). Recently, the lesser-known p.L1795F variant was proposed as a strong genetic risk factor for PD, however, further families are currently lacking in literature. A multicentre young onset and familial PD cohort (n = 220) from 9 movement disorder centres across Central Europe within the CEGEMOD consortium was screened for rare LRRK2 variants using whole exome sequencing data. We identified 4 PD cases with heterozygous p.L1795F variant. All 4 cases were characterised by akinetic-rigid PD phenotype with early onset of severe motor fluctuations, 2 receiving LCIG therapy and 2 implanted with STN DBS; all 4 cases showed unsatisfactory effect of advanced therapies on motor fluctuations. Our data also suggest that p.L1795F may represent the most common currently known pathogenic LRRK2 variant in Central Europe compared to the more studied p.G2019S, being present in 1.81% of PD cases within the Central European cohort and 3.23% of familial PD cases. Together with the ongoing clinical trials for LRRK2 inhibitors, this finding emphasises the urgent need for more ethnic diversity in PD genetic research.

Leucine-rich repeat kinase 2 limits dopamine D1 receptor signaling in striatum and biases against heavy persistent alcohol drinking

The transition from hedonic alcohol drinking to problematic drinking is a hallmark of alcohol use disorder that occurs only in a subset of drinkers. This transition requires long-lasting changes in the synaptic drive and the activity of striatal neurons expressing dopamine D1 receptor (D1R). The molecular mechanisms that generate vulnerability in some individuals to undergo the transition are less understood. Here, we report that the Parkinson's-related protein leucine-rich repeat kinase 2 (LRRK2) modulates striatal D1R function to affect the behavioral response to alcohol and the likelihood that mice transition to heavy, persistent alcohol drinking. Constitutive deletion of the Lrrk2 gene specifically from D1R-expressing neurons potentiated D1R signaling at the cellular and synaptic level and enhanced alcohol-related behaviors and drinking. Mice with cell-specific deletion of Lrrk2 were more prone to heavy alcohol drinking, and consumption was insensitive to punishment. These findings identify a potential novel role for LRRK2 function in the striatum in promoting resilience against heavy and persistent alcohol drinking.

Regulation of mitophagy and mitochondrial function: Natural compounds as potential therapeutic strategies for Parkinson's disease

Mitochondrial damage is associated with the development of Parkinson's disease (PD), indicating that mitochondrial-targeted treatments could hold promise as disease-modifying approaches for PD. Notably, natural compounds have demonstrated the ability to modulate mitochondrial-related processes. In this review article, we discussed the possible neuroprotective mechanisms of natural compounds against PD in modulating mitophagy and mitochondrial function. A comprehensive literature search on natural compounds related to the treatment of PD by regulating mitophagy and mitochondrial function was conducted from PubMed, Web of Science and Chinese National Knowledge Infrastructure databases from their inception until April 2023. We summarize recent advancements in mitophagy's molecular mechanisms, including upstream and downstream processes, and its relationship with PD-related genes or proteins. Importantly, we highlight how natural compounds can therapeutically regulate various mitochondrial processes through multiple targets and pathways to alleviate oxidative stress, neuroinflammation, Lewy's body aggregation and apoptosis, which are key contributors to PD pathogenesis. Unlike the single-target strategy of modern medicine, natural compounds provide neuroprotection against PD by modulating various mitochondrial-related processes, including ameliorating mitophagy by targeting the PINK1/parkin pathway, the NIX/BNIP3 pathway, and autophagosome formation (i.e., LC3 and p62). Given the prevalence of mitochondrial damage in various neurodegenerative diseases, exploring the exact mechanism of natural compounds on mitophagy and mitochondrial dysfunction could shed light on the development of highly effective disease-modifying or adjuvant therapies targeting PD and other neurodegenerative disorders.

Causal role of immune cells on risk of Parkinson's disease: a Mendelian randomization study

Background

Previous observational studies have suggested a correlation between immune cells and Parkinson's disease (PD), yet specific investigations into the causal relationship between the two remain limited. This study aims to explore this potential causal relationship.

Methods

We utilized genome-wide association study (GWAS) data on immune cells and Parkinson's Disease, conducting a two-sample Mendelian randomization (MR) analysis using single nucleotide polymorphisms (SNPs). To estimate causality, we employed inverse variance weighting (IVW), MR-Egger, and weighted median (WM) methods. For sensitivity analysis, we used Cochran's Q-test, MR-Egger intercept, leave-one-out analysis, and funnel plots.

Results

After false discovery rate (FDR) correction, the effects of PD on immune cells, and vice versa, were not statistically significant. These include CX3CR1 on CD14+ CD16-monocyte (OR = 0.91, 95% CI = 0.86-0.96, p = 0.0003 PFDR = 0.152), CD62L-CD86+ myeloid DC AC (OR = 0.93, 95% CI = 0.89-0.97, p = 0.0005, PFDR = 0.152),CD11b on Mo (OR = 1.08, 95% CI = 1.03-1.13, p = 0.001, PFDR = 0.152), CD38 on igd+ cd24- (OR = 1.14, 95% CI = 1.06-1.23, p = 0.001, PFDR = 0.152), D14+ cd16+ monocyte %monocyte (OR = 1.10, 95% CI = 1.04-1.17, p = 0.001, PFDR = 0.159). Additionally, PD may be causally related to the immune phenotype of CM CD8br %T cell (beta = 0.10, 95% CI = 1.14-1.16, p = 0.0004, PFDR = 0.151), SSC-A on monocyte (beta = 0.11, 95% CI = 1.15-1.18, p = 0.0004, PFDR = 0.1 SSC-A on monocyte). No pleiotropy was determined.

Conclusion

This study suggested a potential causal link between immune cells and Parkinson's Disease through the MR method, which could provide a new direction for the mechanistic research and clinical treatment of PD.

Protein Translation in the Pathogenesis of Parkinson's Disease

In recent years, research into Parkinson's disease and similar neurodegenerative disorders has increasingly suggested that these conditions are synonymous with failures in proteostasis. However, the spotlight of this research has remained firmly focused on the tail end of proteostasis, primarily aggregation, misfolding, and degradation, with protein translation being comparatively overlooked. Now, there is an increasing body of evidence supporting a potential role for translation in the pathogenesis of PD, and its dysregulation is already established in other similar neurodegenerative conditions. In this paper, we consider how altered protein translation fits into the broader picture of PD pathogenesis, working hand in hand to compound the stress placed on neurons, until this becomes irrecoverable. We will also consider molecular players of interest, recent evidence that suggests that aggregates may directly influence translation in PD progression, and the implications for the role of protein translation in our development of clinically useful diagnostics and therapeutics.

Advancements in Genetic and Biochemical Insights: Unraveling the Etiopathogenesis of Neurodegeneration in Parkinson's Disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative movement disorder worldwide, which is primarily characterized by motor impairments. Even though multiple hypotheses have been proposed over the decades that explain the pathogenesis of PD, presently, there are no cures or promising preventive therapies for PD. This could be attributed to the intricate pathophysiology of PD and the poorly understood molecular mechanism. To address these challenges comprehensively, a thorough disease model is imperative for a nuanced understanding of PD's underlying pathogenic mechanisms. This review offers a detailed analysis of the current state of knowledge regarding the molecular mechanisms underlying the pathogenesis of PD, with a particular emphasis on the roles played by gene-based factors in the disease's development and progression. This study includes an extensive discussion of the proteins and mutations of primary genes that are linked to PD, including α-synuclein, GBA1, LRRK2, VPS35, PINK1, DJ-1, and Parkin. Further, this review explores plausible mechanisms for DAergic neural loss, non-motor and non-dopaminergic pathologies, and the risk factors associated with PD. The present study will encourage the related research fields to understand better and analyze the current status of the biochemical mechanisms of PD, which might contribute to the design and development of efficacious and safe treatment strategies for PD in future endeavors.

Infections in the Etiology of Parkinson's Disease and Synucleinopathies: A Renewed Perspective, Mechanistic Insights, and Therapeutic Implications

Increasing evidence suggests a potential role for infectious pathogens in the etiology of synucleinopathies, a group of age-related neurodegenerative disorders including Parkinson's disease (PD), multiple system atrophy and dementia with Lewy bodies. In this review, we discuss the link between infections and synucleinopathies from a historical perspective, present emerging evidence that supports this link, and address current research challenges with a focus on neuroinflammation. Infectious pathogens can elicit a neuroinflammatory response and modulate genetic risk in PD and related synucleinopathies. The mechanisms of how infections might be linked with synucleinopathies as well as the overlap between the immune cellular pathways affected by virulent pathogens and disease-related genetic risk factors are discussed. Here, an important role for α-synuclein in the immune response against infections is emerging. Critical methodological and knowledge gaps are addressed, and we provide new future perspectives on how to address these gaps. Understanding how infections and neuroinflammation influence synucleinopathies will be essential for the development of early diagnostic tools and novel therapies.

A Systematic Review of Various In-vivo Screening Models as well as the Mechanisms Involved in Parkinson's Disease Screening Procedures

BACKGROUND

Parkinson's disease is the second most common neurological ailment. It is also known that it affects practically all other brain components, although only gradually. Animal models are mostly used to test the efficacy of treatment against a specific enzyme and aid in creating a new drug dose.

OBJECTIVE

The purpose of this review is to highlight in vivo Parkinson's disease screening approaches, as well as the mechanism of action of each drug involved in Parkinson's disease development, and discuss the limitations of each model. In addition, it also sheds light on Parkinson's disease genetic models.

METHODS

The data for the publication was gathered from databases, such as PubMed, Bentham Science, Elsevier, Springer Nature, Wiley, and Research Gate, after a thorough examination of diverse research findings linked to Parkinson's disease and its screening models.

RESULTS

Each chemical or drug has a unique mechanism for causing disease, whether through the production of reactive oxygen species or the blockage of the dopamine receptor. Almost every disease symptom, whether physical or behavioral, is covered by each of the constructed models' unique set of indicators and symptoms.

CONCLUSION

Animal models are typically used to assess a medicine's activity against a specific enzyme and aid in the creation of a new drug dose. The process, restrictions, and mechanisms interfering with the screening, as well as the level of animal suffering, must all be thoroughly reviewed before any model for screening for Parkinson's disease can be implemented.

Inhibition of LRRK2 kinase activity rescues deficits in striatal dopamine physiology in VPS35 p.D620N knock-in mice

Dysregulation of dopamine neurotransmission profoundly affects motor, motivation and learning behaviors, and can be observed during the prodromal phase of Parkinson's disease (PD). However, the mechanism underlying these pathophysiological changes remains to be elucidated. Mutations in vacuolar protein sorting 35 (VPS35) and leucine-rich repeat kinase 2 (LRRK2) both lead to autosomal dominant PD, and VPS35 and LRRK2 may physically interact to govern the trafficking of synaptic cargos within the endo-lysosomal network in a kinase-dependent manner. To better understand the functional role of VPS35 and LRRK2 on dopamine physiology, we examined Vps35 haploinsufficient (Haplo) and Vps35 p.D620N knock-in (VKI) mice and how their behavior, dopamine kinetics and biochemistry are influenced by LRRK2 kinase inhibitors. We found Vps35 p.D620N significantly elevates LRRK2-mediated phosphorylation of Rab10, Rab12 and Rab29. In contrast, Vps35 haploinsufficiency reduces phosphorylation of Rab12. While striatal dopamine transporter (DAT) expression and function is similarly impaired in both VKI and Haplo mice, that physiology is normalized in VKI by treatment with the LRRK2 kinase inhibitor, MLi-2. As a corollary, VKI animals show a significant increase in amphetamine induced hyperlocomotion, compared to Haplo mice, that is also abolished by MLi-2. Taken together, these data show Vps35 p.D620N confers a gain-of-function with respect to LRRK2 kinase activity, and that VPS35 and LRRK2 functionally interact to regulate DAT function and striatal dopamine transmission.

Exploring Parkinson-associated kinases for CRISPR/Cas9-based gene editing: beyond alpha-synuclein

Parkinson's disease (PD) is a debilitating neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substania nigra (SN) and is associated with progressive motor impairment. PD is classified into familial and sporadic forms. The first genetic association studies in PD reported the involvement of Synuclein alpha (SNCA) mutations in the pathobiology of familial PD. Subsequent studies suggested mutations in PTEN-induced putative kinase 1 (PINK1), PARKIN, leucine repeat kinase-2 (LRRK2), and DJ-1 causing familial PD. In addition, kinase dysregulation has been embroiled in the pathogenesis of PD. The genome-editing mechanism CRISPR (clustered regularly interspaced short palindromic repeats) has recently influenced industry and scientific discoveries and is expected to expedite neurodegenerative disease research. This review will discuss the structure, function, and history of the CRISPR/Cas9 genome editing system. Moreover, it summarizes genes-encoding kinases involved in PD pathogenesis and targeted by CRISPR/Cas9 technology, including LRRK2, PINK1, Protein kinase C-delta (PKC-γ), and adenosine monophosphate-activated protein kinase (AMPK). We provide an overview of novel kinases to be targeted by the CRISPR/Cas9 system such as G-protein coupled receptor kinases (GRKs), cyclin-G-associated kinases (GAKs), cyclin-dependent kinase 5 (CDK5), Ataxia telangiectasia mutated (ATM), c-ABL, and rearranged during transfection (RET) receptors. Additionally, we will explain the off-target effects of CRISPR/Cas9 system and how to address them. Also, we will shed light on the associated challenges and future directions that are enabling the efficient use of CRISPR/Cas9 technology in kinases research in PD. In conclusion, gene editing, in addition to gene therapy, might be a possible promising strategy for PD therapy.

LRRK2 kinase activity is necessary for development and regeneration in Nematostella vectensis

Background

The starlet sea anemone, Nematostella vectensis, is an emerging model organism with a high regenerative capacity, which was recently found to possess an orthologue to the human LRRK2 gene (nvLRRK2). The leucine rich repeat kinase 2 (LRRK2) gene, when mutated, is the most common cause of inherited Parkinson's Disease (PD). Its protein product (LRRK2) has implications in a variety of cellular processes, however, the full function of LRRK2 is not well established. Current research is focusing on understanding the function of LRRK2, including both its physiological role as well as its pathobiological underpinnings.

Methods

We used bioinformatics to determine the cross-species conservation of LRRK2, then applied drugs targeting the kinase activity of LRRK2 to examine its function in development, homeostasis and regeneration in Nematostella vectensis.

Results

An in-silico characterization and phylogenetic analysis of nvLRRK2 comparing it to human LRRK2 highlighted key conserved motifs and residues. In vivo analyses inhibiting the kinase function of this enzyme demonstrated a role of nvLRRK2 in development and regeneration of N. vectensis. These findings implicate a developmental role of LRRK2 in Nematostella, adding to the expanding knowledge of its physiological function.

Conclusions

Our work introduces a new model organism with which to study LRRK biology. We show a necessity for LRRK2 in development and regeneration. Given the short generation time, genetic trackability and in vivo imaging capabilities, this work introduces Nematostella vectensis as a new model in which to study genes linked to neurodegenerative diseases such as Parkinson's.

Elevated serum anti-Saccharomyces cerevisiae antibody accompanied by gut mycobiota dysbiosis as a biomarker of diagnosis in patients with de novo Parkinson disease

BACKGROUND AND PURPOSE

Intestinal inflammation and gut microbiota dysbiosis contribute to Parkinson disease (PD) pathogenesis, and growing evidence suggests associations between inflammatory bowel diseases (IBD) and PD. Considered as markers of chronic gastrointestinal inflammation, elevated serum anti-Saccharomyces cerevisiae antibody (ASCA) levels, against certain gut fungal components, are related to IBD, but their effect on PD is yet to be investigated.

METHODS

Serum ASCA IgG and IgA levels were measured using an enzyme-linked immunosorbent assay, and the gut mycobiota communities were investigated using ITS2 sequencing and analyzed using the Qiime pipeline.

RESULTS

The study included 393 subjects (148 healthy controls [HCs], 140 with PD, and 105 with essential tremor [ET]). Both serum ASCA IgG and IgA levels were significantly higher in the PD group than in the ET and HC groups. Combining serum ASCA levels and the occurrence of constipation could discriminate patients with PD from controls (area under the curve [AUC] = 0.81, 95% confidence interval [CI] = 0.76-0.86) and from patients with ET (AUC = 0.85, 95% CI = 0.79-0.89). Furthermore, the composition of the gut fungal community differed between the PD and HC groups. The relative abundances of Saccharomyces cerevisiae, Aspergillus, Candida solani, Aspergillus flavus, ASV601_Fungi, ASV866_Fungi, and ASV755_Fungi were significantly higher in the PD group, and enriched Malassezia restricta was found in the HC group.

CONCLUSIONS

Our study identified elevated serum ASCA levels and enriched gut Saccharomyces cerevisiae in de novo PD.

LRRK2 Attenuates Antioxidant Response in Familial Parkinson's Disease Derived Neural Stem Cells

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease, characterized by the loss of midbrain dopaminergic neurons which leads to impaired motor and cognitive functions. PD is predominantly an idiopathic disease; however, about 5% of cases are linked to hereditary mutations. The most common mutation in both familial and sporadic PD is the G2019S mutation of leucine-rich repeat kinase 2 (LRRK2). Currently, it is not fully understood how this mutation leads to PD pathology. In this study, we isolated self-renewable, multipotent neural stem cells (NSCs) from induced pluripotent stem cells (iPSCs) harboring the G2019S LRRK2 mutation and compared them with their isogenic gene corrected counterparts using single-cell RNA-sequencing. Unbiased single-cell transcriptomic analysis revealed perturbations in many canonical pathways, specifically NRF2-mediated oxidative stress response, and glutathione redox reactions. Through various functional assays, we observed that G2019S iPSCs and NSCs exhibit increased basal levels of reactive oxygen species (ROS). We demonstrated that mutant cells show significant increase in the expression for KEAP1 and decrease in NRF2 associated with a reduced antioxidant response. The decreased viability of mutant NSCs in the H2O2-induced oxidative stress assay was rescued by two potent antioxidant drugs, PrC-210 at concentrations of 500 µM and 1 mM and Edaravone at concentrations 50 µM and 100 µM. Our data suggest that the hyperactive LRRK2 G2019S kinase activity leads to increase in KEAP1, which binds NRF2 and leads to its degradation, reduction in the antioxidant response, increased ROS, mitochondria dysfunction and cell death observed in the PD phenotype.

LRRK2 is involved in the chemotaxis of neutrophils and differentiated HL-60 cells, and the inhibition of LRRK2 kinase activity increases fMLP-induced chemotactic activity

BACKGROUND

Neutrophils depend heavily on glycolysis for energy production under normal conditions. In contrast, neutrophils require energy supplied by mitochondrial oxidative phosphorylation (OXPHOS) during chemotaxis. However, the mechanism by which the energy supply changes from glycolysis to OXPHOS remains unknown. Leucine-rich repeat kinase 2 (LRRK2) is partially present in the outer mitochondrial membrane fraction. Lrrk2-deficient cells show mitochondrial fragmentation and reduced OXPHOS activity. We have previously reported that mitofusin (MFN) 2 is involved in chemotaxis and OXPHOS activation upon chemoattractant N-formyl-Met-Leu-Phe (fMLP) stimulation in differentiated HL-60 (dHL-60) cells. It has been previously reported that LRRK2 binds to MFN2 and partially colocalizes with MFN2 at the mitochondrial membranes. This study investigated the involvement of LRRK2 in chemotaxis and MFN2 activation in neutrophils and dHL-60 cells.

METHODS

Lrrk2 knockout neutrophils and Lrrk2 knockdown dHL-60 cells were used to examine the possible involvement of LRRK2 in chemotaxis. Lrrk2 knockdown dHL-60 cells were used a tetracycline-inducible small hairpin RNA (shRNA) system to minimize the effects of LRRK2 knockdown during cell culture. The relationship between LRRK2 and MFN2 was investigated by measuring the GTP-binding activity of MFN2 in Lrrk2 knockdown dHL-60 cells. The effects of LRRK2 kinase activity on chemotaxis were examined using the LRRK2 kinase inhibitor MLi-2.

RESULTS

fMLP-induced chemotactic activity was reduced in Lrrk2 knockout neutrophils in vitro and in vivo. Lrrk2 knockdown in dHL-60 cells expressing Lrrk2 shRNA also reduced fMLP-induced chemotactic activity. Lrrk2 knockdown dHL-60 cells showed reduced OXPHOS activity and suppressed mitochondrial morphological change, similar to Mfn2 knockdown dHL-60 cells. The amount of LRRK2 in the mitochondrial fraction and the GTP-binding activity of MFN2 increased upon fMLP stimulation, and the MFN2 GTP-binding activity was suppressed in Lrrk2 knockdown dHL-60 cells. Furthermore, the kinase activity of LRRK2 and Ser935 phosphorylation of LRRK2 were reduced upon fMLP stimulation, and LRRK2 kinase inhibition by MLi-2 increased the migration to fMLP.

CONCLUSIONS

LRRK2 is involved in neutrophil chemotaxis and the GTP-binding activity of MFN2 upon fMLP stimulation. On the other hand, the kinase activity of LRRK2 shows a negative regulatory effect on fMLP-induced chemotactic activity in dHL-60 cells. Video Abstract.

LRRK2 aggravates kidney injury through promoting MFN2 degradation and abnormal mitochondrial integrity

Mitochondrial dysfunction is one of the key features of acute kidney injury (AKI) and associated fibrosis. Leucine-rich repeat kinase 2 (LRRK2) is highly expressed in kidneys and regulates mitochondrial homeostasis. How it functions in AKI is unclear. Herein we reported that LRRK2 was dramatically downregulated in AKI kidneys. Lrrk2-/- mice exhibited less severity of AKI when compared to wild-type counterparts with less mitochondrial fragmentation and decreased reactive oxygen species (ROS) production in proximal renal tubular cells (PTCs) due to mitofusin 2 (MFN2) accumulation. Overexpression of LRRK2 in human PTC cell lines promoted LRRK2-MKK4/JNK-dependent phosphorylation of MFN2Ser27 and subsequently ubiquitination-mediated MFN2 degradation, which in turn exaggerated mitochondrial damage upon ischemia/reperfusion (I/R) mimicry treatment. Lrrk2 deficiency also alleviated AKI-to-chronic kidney disease (CKD) transition with less fibrosis. In vivo pretreatment of LRRK2 inhibitors attenuated the severity of AKI as well as CKD, potentiating LRRK2 as a novel target to alleviate AKI and fibrosis.

LRRK2 Gly2019Ser Mutation Promotes ER Stress via Interacting with THBS1/TGF-β1 in Parkinson's Disease

The gene mutations of LRRK2, which encodes leucine-rich repeat kinase 2 (LRRK2), are associated with one of the most prevalent monogenic forms of Parkinson's disease (PD). However, the potential effectors of the Gly2019Ser (G2019S) mutation remain unknown. In this study, the authors investigate the effects of LRRK2 G2019S on endoplasmic reticulum (ER) stress in induced pluripotent stem cell (iPSC)-induced dopamine neurons and explore potential therapeutic targets in mice model. These findings demonstrate that LRRK2 G2019S significantly promotes ER stress in neurons and mice. Interestingly, inhibiting LRRK2 activity can ameliorate ER stress induced by the mutation. Moreover, LRRK2 mutation can induce ER stress by directly interacting with thrombospondin-1/transforming growth factor beta1 (THBS1/TGF-β1). Inhibition of LRRK2 kinase activity can effectively suppress ER stress and the expression of THBS1/TGF-β1. Knocking down THBS1 can rescue ER stress by interacting with TGF-β1 and behavior burden caused by the LRRK2 mutation, while suppression of TGF-β1 has a similar effect. Overall, it is demonstrated that the LRRK2 mutation promotes ER stress by directly interacting with THBS1/TGF-β1, leading to neural death in PD. These findings provide valuable insights into the pathogenesis of PD, highlighting potential diagnostic markers and therapeutic targets.

Unveiling the Selectivity Mechanism of Type-I LRRK2 Inhibitors by Computational Methods: Insights from Binding Thermodynamics and Kinetics Simulation

Understanding the selectivity mechanisms of inhibitors toward highly similar proteins is very important in new drug discovery. Developing highly selective targeting of leucine-rich repeat kinase 2 (LRRK2) kinases for the treatment of Parkinson's disease (PD) is challenging because of the similarity of the kinase ATP binding pocket. During the development of LRRK2 inhibitors, off-target effects on other kinases, especially TTK and JAK2 kinases, have been observed. As a result, significant time and resources have been devoted to improving the selectivity for the LRRK2 target. DNL201 is an LRRK2 kinase inhibitor entering phase I clinical studies. The experiments have shown that DNL201 significantly inhibits LRRK2 kinase activity, with >167-fold selectivity over JAK2 and TTK kinases. However, the potential mechanisms of inhibitor preferential binding to LRRK2 kinase are still not well elucidated. In this work, to reveal the underlying general selectivity mechanism, we carried out several computational methods and comprehensive analyses from both the binding thermodynamics and kinetics on two representative LRRK2 inhibitors (DNL201 and GNE7915) to LRRK2. Our results suggest that the structural and kinetic differences between the proteins may play a key role in determining the activity of the selective small-molecule inhibitor. The selectivity mechanisms proposed in this work could be helpful for the rational design of novel selective LRRK2 kinase inhibitors against PD.

Role of dopamine in the pathophysiology of Parkinson's disease

A pathological feature of Parkinson's disease (PD) is the progressive loss of dopaminergic neurons and decreased dopamine (DA) content in the substantia nigra pars compacta in PD brains. DA is the neurotransmitter of dopaminergic neurons. Accumulating evidence suggests that DA interacts with environmental and genetic factors to contribute to PD pathophysiology. Disturbances of DA synthesis, storage, transportation and metabolism have been shown to promote neurodegeneration of dopaminergic neurons in various PD models. DA is unstable and can undergo oxidation and metabolism to produce multiple reactive and toxic by-products, including reactive oxygen species, DA quinones, and 3,4-dihydroxyphenylacetaldehyde. Here we summarize and highlight recent discoveries on DA-linked pathophysiologic pathways, and discuss the potential protective and therapeutic strategies to mitigate the complications associated with DA.

Leucine-rich repeat kinase 2 at a glance

Leucine-rich repeat kinase 2 (LRRK2) is a multidomain scaffolding protein with dual guanosine triphosphatase (GTPase) and kinase enzymatic activities, providing this protein with the capacity to regulate a multitude of signalling pathways and act as a key mediator of diverse cellular processes. Much of the interest in LRRK2 derives from mutations in the LRRK2 gene being the most common genetic cause of Parkinson's disease, and from the association of the LRRK2 locus with a number of other human diseases, including inflammatory bowel disease. Therefore, the LRRK2 research field has focused on the link between LRRK2 and pathology, with the aim of uncovering the underlying mechanisms and, ultimately, finding novel therapies and treatments to combat them. From the biochemical and cellular functions of LRRK2, to its relevance to distinct disease mechanisms, this Cell Science at a Glance article and the accompanying poster deliver a snapshot of our current understanding of LRRK2 function, dysfunction and links to disease.

Prediction of Parkinson's disease pathogenic variants using hybrid Machine learning systems and radiomic features

PURPOSE

In Parkinson's disease (PD), 5-10% of cases are of genetic origin with mutations identified in several genes such as leucine-rich repeat kinase 2 (LRRK2) and glucocerebrosidase (GBA). We aim to predict these two gene mutations using hybrid machine learning systems (HMLS), via imaging and non-imaging data, with the long-term goal to predict conversion to active disease.

METHODS

We studied 264 and 129 patients with known LRRK2 and GBA mutations status from PPMI database. Each dataset includes 513 features such as clinical features (CFs), conventional imaging features (CIFs) and radiomic features (RFs) extracted from DAT-SPECT images. Features, normalized by Z-score, were univariately analyzed for statistical significance by the t-test and chi-square test, adjusted by Benjamini-Hochberg correction. Multiple HMLSs, including 11 features extraction (FEA) or 10 features selection algorithms (FSA) linked with 21 classifiers were utilized. We also employed Ensemble Voting (EV) to classify the genes.

RESULTS

For prediction of LRRK2 mutation status, a number of HMLSs resulted in accuracies of 0.98 ± 0.02 and 1.00 in 5-fold cross-validation (80% out of total data points) and external testing (remaining 20%), respectively. For predicting GBA mutation status, multiple HMLSs resulted in high accuracies of 0.90 ± 0.08 and 0.96 in 5-fold cross-validation and external testing, respectively. We additionally showed that SPECT-based RFs added value to the specific prediction of of GBA mutation status.

CONCLUSION

We demonstrated that combining medical information with SPECT-based imaging features, and optimal utilization of HMLS can produce excellent prediction of the mutations status in PD patients.

Regulation of LRRK2 mRNA stability by ATIC and its substrate AICAR through ARE-mediated mRNA decay in Parkinson's disease

Mutations in LRRK2 are the most common genetic causes of Parkinson's disease (PD). While the enzymatic activity of LRRK2 has been linked to PD, previous work has also provided support for an important role of elevated LRRK2 protein levels, independent of enzymatic activity, in PD pathogenesis. However, the mechanisms underlying the regulation of LRRK2 protein levels remain unclear. Here, we identify a role for the purine biosynthesis pathway enzyme ATIC in the regulation of LRRK2 levels and toxicity. AICAr, the precursor of ATIC substrate, regulates LRRK2 levels in a cell-type-specific manner in vitro and in mouse tissue. AICAr regulates LRRK2 levels through AUF1-mediated mRNA decay. Upon AICAr treatment, the RNA binding protein AUF1 is recruited to the AU-rich elements (ARE) of LRRK2 mRNA leading to the recruitment of the decapping enzyme complex DCP1/2 and decay of LRRK2 mRNA. AICAr suppresses LRRK2 expression and rescues LRRK2-induced dopaminergic neurodegeneration and neuroinflammation in PD Drosophila and mouse models. Together, this study provides insight into a novel regulatory mechanism of LRRK2 protein levels and function via LRRK2 mRNA decay that is distinct from LRRK2 enzymatic functions.

LRRK2 and Parkinson's disease: from genetics to targeted therapy

LRRK2 variants are implicated in both familial and sporadic PD. LRRK2-PD has a generally benign clinical presentation and variable pathology, with inconsistent presence of Lewy bodies and marked Alzheimer's disease pathology. The mechanisms underlying LRRK2-PD are still unclear, but inflammation, vesicle trafficking, lysosomal homeostasis, and ciliogenesis have been suggested, among others. As novel therapies targeting LRRK2 are under development, understanding the role and function of LRRK2 in PD is becoming increasingly important. Here, we outline the epidemiological, pathophysiological, and clinical features of LRRK2-PD, and discuss the arising therapeutic approaches targeting LRRK2 and possible future directions for research.

Drosophila melanogaster as a model to study autophagy in neurodegenerative diseases induced by proteinopathies

Proteinopathies are a large group of neurodegenerative diseases caused by both genetic and sporadic mutations in particular genes which can lead to alterations of the protein structure and to the formation of aggregates, especially toxic for neurons. Autophagy is a key mechanism for clearing those aggregates and its function has been strongly associated with the ubiquitin-proteasome system (UPS), hence mutations in both pathways have been associated with the onset of neurodegenerative diseases, particularly those induced by protein misfolding and accumulation of aggregates. Many crucial discoveries regarding the molecular and cellular events underlying the role of autophagy in these diseases have come from studies using Drosophila models. Indeed, despite the physiological and morphological differences between the fly and the human brain, most of the biochemical and molecular aspects regulating protein homeostasis, including autophagy, are conserved between the two species.In this review, we will provide an overview of the most common neurodegenerative proteinopathies, which include PolyQ diseases (Huntington's disease, Spinocerebellar ataxia 1, 2, and 3), Amyotrophic Lateral Sclerosis (C9orf72, SOD1, TDP-43, FUS), Alzheimer's disease (APP, Tau) Parkinson's disease (a-syn, parkin and PINK1, LRRK2) and prion diseases, highlighting the studies using Drosophila that have contributed to understanding the conserved mechanisms and elucidating the role of autophagy in these diseases.

Gastrointestinal disorders in Parkinson's disease and other Lewy body diseases

Parkinson's disease (PD) is pathologically characterized by the abnormal accumulation of α-synuclein fibrils (Lewy bodies) in the substantia nigra and other brain regions, although the role of Lewy bodies remains elusive. Constipation usually precedes the motor symptoms in PD, which is in accordance with the notion that α-synuclein fibrils start from the intestinal neural plexus and ascend to the brain in at least half of PD patients. The gut microbiota is likely to be involved in intestinal and brain pathologies. Analyses of the gut microbiota in PD, rapid-eye-movement sleep behavior disorder, and dementia with Lewy bodies suggest three pathological pathways. First, Akkermansia, which is increased in PD, degrades the intestinal mucus layer and increases intestinal permeability, which triggers inflammation and oxidative stress in the intestinal neural plexus. Second, decreased short-chain fatty acids (SCFAs)-producing bacteria in PD reduce the number of regulatory T cells. Third, SCFAs also aggravate microglial activation with an unelucidated pathway. In addition, in dementia with Lewy bodies (DLB), which is another form of α-synucleinopathies, increased genera, Ruminococcus torques and Collinsella, may mitigate neuroinflammation in the substantia nigra by increasing secondary bile acids. Interventions for the gut microbiota and their metabolites may potentially delay or mitigate the development and progression of PD and other Lewy body diseases.

Neuroprotective Effects of the Neural-Induced Adipose-Derived Stem Cell Secretome against Rotenone-Induced Mitochondrial and Endoplasmic Reticulum Dysfunction

Mesenchymal stem cells (MSCs) have therapeutic effects on neurodegenerative diseases (NDDs) known by their secreted molecules, referred to as the “secretome”. The mitochondrial complex I inhibitor, rotenone (ROT), reproduces α-synuclein (α-syn) aggregation seen in Parkinson’s disease (PD). In this present study, we examined the neuroprotective effects of the secretome from neural-induced human adipose tissue-derived stem cells (NI-ADSC-SM) during ROT toxicity in SH-SY5Y cells. Exposure to ROT significantly impaired the mitophagy by increased LRRK2, mitochondrial fission, and endoplasmic reticulum (ER) stress (ERS). ROT also increased the levels of calcium (Ca2+), VDAC, and GRP75, and decreased phosphorylated (p)-IP3R Ser1756/total (t)-IP3R1. However, NI-ADSC-SM treatment decreased Ca2+ levels along with LRRK2, insoluble ubiquitin, mitochondrial fission by halting p-DRP1 Ser616, ERS by reducing p-PERK Thr981, p-/t-IRE1α, p-SAPK, ATF4, and CHOP. In addition, NI-ADSC-SM restored the mitophagy, mitochondrial fusion, and tethering to the ER. These data suggest that NI-ADSC-SM decreases ROT-induced dysfunction in mitochondria and the ER, which subsequently stabilized tethering in mitochondria-associated membranes in SH-SY5Y cells.

Artificial intelligence-based clustering and characterization of Parkinson's disease trajectories

Parkinson's disease (PD) is a highly heterogeneous disease both with respect to arising symptoms and its progression over time. This hampers the design of disease modifying trials for PD as treatments which would potentially show efficacy in specific patient subgroups could be considered ineffective in a heterogeneous trial cohort. Establishing clusters of PD patients based on their progression patterns could help to disentangle the exhibited heterogeneity, highlight clinical differences among patient subgroups, and identify the biological pathways and molecular players which underlie the evident differences. Further, stratification of patients into clusters with distinct progression patterns could help to recruit more homogeneous trial cohorts. In the present work, we applied an artificial intelligence-based algorithm to model and cluster longitudinal PD progression trajectories from the Parkinson's Progression Markers Initiative. Using a combination of six clinical outcome scores covering both motor and non-motor symptoms, we were able to identify specific clusters of PD that showed significantly different patterns of PD progression. The inclusion of genetic variants and biomarker data allowed us to associate the established progression clusters with distinct biological mechanisms, such as perturbations in vesicle transport or neuroprotection. Furthermore, we found that patients of identified progression clusters showed significant differences in their responsiveness to symptomatic treatment. Taken together, our work contributes to a better understanding of the heterogeneity encountered when examining and treating patients with PD, and points towards potential biological pathways and genes that could underlie those differences.

LRRK2 Quantification in Cerebrospinal Fluid of Patients with Parkinson's Disease and Atypical Parkinsonian Syndromes

BACKGROUND

The alteration of leucine-rich repeat kinase 2 (LRRK2) kinase activity is thought to be involved in Parkinson's disease (PD) pathogenesis beyond familiar cases, and LRRK2 inhibitors are currently under investigation. Preliminary data suggest a relationship between LRRK2 alteration and cognitive impairment in PD.

OBJECTIVE

To investigate cerebrospinal fluid (CSF) LRRK2 levels in PD and other parkinsonian disorders, also correlating them with cognitive impairment.

METHODS

In this study, we retrospectively investigated by means of a novel highly sensitive immunoassay the levels of total and phosphorylated (pS1292) LRRK2 in CSF of cognitively unimpaired PD (n = 55), PD with mild cognitive impairment (n = 49), PD with dementia (n = 18), dementia with Lewy bodies (n = 12), atypical parkinsonian syndromes (n = 35), and neurological controls (n = 30).

RESULTS

Total and pS1292 LRRK2 levels were significantly higher in PD with dementia with respect to PD with mild cognitive impairment and PD, and also showed a correlation with cognitive performances.

CONCLUSIONS

The tested immunoassay may represent a reliable method for assessing CSF LRRK2 levels. The results appear to confirm an association of LRRK2 alteration with cognitive impairment in PD. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The Relationship between Iron and LRRK2 in a 6-OHDA-Induced Parkinson's Disease Model

The pathogenesis of Parkinson's disease (PD) is very complex and still needs further exploration. Leucine-rich repeat kinase 2 (LRRK2) is associated with familial PD in mutant forms and sporadic PD in the wild-type form. Abnormal iron accumulation is found in the substantia nigra of PD patients, but its exact effects are not very clear. Here, we show that iron dextran exacerbates the neurological deficit and loss of dopaminergic neurons in 6-OHDA lesioned rats. 6-OHDA and ferric ammonium citrate (FAC) significantly increase the activity of LRRK2 as reflected by the phosphorylation of LRRK2, at S935 and S1292 sites. 6-OHDA-induced LRRK2 phosphorylation is attenuated by the iron chelator deferoxamine, especially at the S1292 site. 6-OHDA and FAC markedly induce the expression of pro-apoptotic molecules and the production of ROS by activating LRRK2. Furthermore, G2019S-LRRK2 with high kinase activity showed the strongest absorptive capacity for ferrous iron and the highest intracellular iron content among WT-LRRK2, G2019S-LRRK2, and kinase-inactive D2017A-LRRK2 groups. Taken together, our results demonstrate that iron promotes the activation of LRRK2, and active LRRK2 accelerates ferrous iron uptake, suggesting that there exists an interplay between iron and LRRK2 in dopaminergic neurons, providing a new perspective to uncover the underlying mechanisms of PD occurrence.

Translational molecular imaging and drug development in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder that primarily affects elderly people and constitutes a major source of disability worldwide. Notably, the neuropathological hallmarks of PD include nigrostriatal loss and the formation of intracellular inclusion bodies containing misfolded α-synuclein protein aggregates. Cardinal motor symptoms, which include tremor, rigidity and bradykinesia, can effectively be managed with dopaminergic therapy for years following symptom onset. Nonetheless, patients ultimately develop symptoms that no longer fully respond to dopaminergic treatment. Attempts to discover disease-modifying agents have increasingly been supported by translational molecular imaging concepts, targeting the most prominent pathological hallmark of PD, α-synuclein accumulation, as well as other molecular pathways that contribute to the pathophysiology of PD. Indeed, molecular imaging modalities such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) can be leveraged to study parkinsonism not only in animal models but also in living patients. For instance, mitochondrial dysfunction can be assessed with probes that target the mitochondrial complex I (MC-I), while nigrostriatal degeneration is typically evaluated with probes designed to non-invasively quantify dopaminergic nerve loss. In addition to dopaminergic imaging, serotonin transporter and N-methyl-D-aspartate (NMDA) receptor probes are increasingly used as research tools to better understand the complexity of neurotransmitter dysregulation in PD. Non-invasive quantification of neuroinflammatory processes is mainly conducted by targeting the translocator protein 18 kDa (TSPO) on activated microglia using established imaging agents. Despite the overwhelming involvement of the brain and brainstem, the pathophysiology of PD is not restricted to the central nervous system (CNS). In fact, PD also affects various peripheral organs such as the heart and gastrointestinal tract - primarily via autonomic dysfunction. As such, research into peripheral biomarkers has taken advantage of cardiac autonomic denervation in PD, allowing the differential diagnosis between PD and multiple system atrophy with probes that visualize sympathetic nerve terminals in the myocardium. Further, α-synuclein has recently gained attention as a potential peripheral biomarker in PD. This review discusses breakthrough discoveries that have led to the contemporary molecular concepts of PD pathophysiology and how they can be harnessed to develop effective imaging probes and therapeutic agents. Further, we will shed light on potential future trends, thereby focusing on potential novel diagnostic tracers and disease-modifying therapeutic interventions.

On the Chemical and Biological Characteristics of Multifunctional Compounds for the Treatment of Parkinson's Disease

Protein aggregation, mitochondrial dysfunction, iron dyshomeostasis, increased oxidative damage and inflammation are pathognomonic features of Parkinson's disease (PD) and other neurodegenerative disorders characterized by abnormal iron accumulation. Moreover, the existence of positive feed-back loops between these pathological components, which accelerate, and sometimes make irreversible, the neurodegenerative process, is apparent. At present, the available treatments for PD aim to relieve the symptoms, thus improving quality of life, but no treatments to stop the progression of the disease are available. Recently, the use of multifunctional compounds with the capacity to attack several of the key components of neurodegenerative processes has been proposed as a strategy to slow down the progression of neurodegenerative processes. For the treatment of PD specifically, the necessary properties of new-generation drugs should include mitochondrial destination, the center of iron-reactive oxygen species interaction, iron chelation capacity to decrease iron-mediated oxidative damage, the capacity to quench free radicals to decrease the risk of ferroptotic neuronal death, the capacity to disrupt α-synuclein aggregates and the capacity to decrease inflammatory conditions. Desirable additional characteristics are dopaminergic neurons to lessen unwanted secondary effects during long-term treatment, and the inhibition of the MAO-B and COMPT activities to increase intraneuronal dopamine content. On the basis of the published evidence, in this work, we review the molecular basis underlying the pathological events associated with PD and the clinical trials that have used single-target drugs to stop the progress of the disease. We also review the current information on multifunctional compounds that may be used for the treatment of PD and discuss the chemical characteristics that underlie their functionality. As a projection, some of these compounds or modifications could be used to treat diseases that share common pathology features with PD, such as Friedreich's ataxia, Multiple sclerosis, Huntington disease and Alzheimer's disease.

Lysosomal Pathogenesis of Parkinson's Disease: Insights From LRRK2 and GBA1 Rodent Models

The discovery of mutations in LRRK2 and GBA1 that are linked to Parkinson's disease provided further evidence that autophagy and lysosome pathways are likely implicated in the pathogenic process. Their protein products are important regulators of lysosome function. LRRK2 has kinase-dependent effects on lysosome activity, autophagic efficacy and lysosomal Ca2+ signaling. Glucocerebrosidase (encoded by GBA1) is a hydrolytic enzyme contained in the lysosomes and contributes to the degradation of alpha-synuclein. PD-related mutations in LRRK2 and GBA1 slow the degradation of alpha-synuclein, thus directly implicating the dysfunction of the process in the neuropathology of Parkinson's disease. The development of genetic rodent models of LRRK2 and GBA1 provided hopes of obtaining reliable preclinical models in which to study pathogenic processes and perform drug validation studies. Here, I will review the extensive characterization of these models, their impact on understanding lysosome alterations in the course of Parkinson's disease and what novel insights have been obtained. In addition, I will discuss how these models fare with respect to the features of a "gold standard" animal models and what could be attempted in future studies to exploit LRRK2 and GBA1 rodent models in the fight against Parkinson's disease.

Endo-Lysosomal Two-Pore Channels and Their Protein Partners

Two-pore channels are ion channels expressed on acidic organelles such as the various vesicles that constitute the endo-lysosomal system. They are permeable to Ca2+ and Na+ and activated by the second messenger NAADP as well as the phosphoinositide, PI(3,5)P2 and/or voltage. Here, we review the proteins that interact with these channels including recently identified NAADP receptors.

Discovery and Optimization of Potent, Selective, and Brain-Penetrant 1-Heteroaryl-1H-Indazole LRRK2 Kinase Inhibitors for the Treatment of Parkinson's Disease

Inhibition of leucine-rich repeat kinase 2 (LRRK2) kinase activity represents a genetically supported, chemically tractable, and potentially disease-modifying mechanism to treat Parkinson's disease. Herein, we describe the optimization of a novel series of potent, selective, central nervous system (CNS)-penetrant 1-heteroaryl-1H-indazole type I (ATP competitive) LRRK2 inhibitors. Type I ATP-competitive kinase physicochemical properties were integrated with CNS drug-like properties through a combination of structure-based drug design and parallel medicinal chemistry enabled by sp³-sp² cross-coupling technologies. This resulted in the discovery of a unique sp³-rich spirocarbonitrile motif that imparted extraordinary potency, pharmacokinetics, and favorable CNS drug-like properties. The lead compound, 25, demonstrated exceptional on-target potency in human peripheral blood mononuclear cells, excellent off-target kinase selectivity, and good brain exposure in rat, culminating in a low projected human dose and a pre-clinical safety profile that warranted advancement toward pre-clinical candidate enabling studies.

Pathogenesis of α-Synuclein in Parkinson's Disease: From a Neuron-Glia Crosstalk Perspective

Parkinson's disease (PD) is a progressive neurodegenerative disorder. The classical behavioral defects of PD patients involve motor symptoms such as bradykinesia, tremor, and rigidity, as well as non-motor symptoms such as anosmia, depression, and cognitive impairment. Pathologically, the progressive loss of dopaminergic (DA) neurons in the substantia nigra (SN) and the accumulation of α-synuclein (α-syn)-composed Lewy bodies (LBs) and Lewy neurites (LNs) are key hallmarks. Glia are more than mere bystanders that simply support neurons, they actively contribute to almost every aspect of neuronal development and function; glial dysregulation has been implicated in a series of neurodegenerative diseases including PD. Importantly, amounting evidence has added glial activation and neuroinflammation as new features of PD onset and progression. Thus, gaining a better understanding of glia, especially neuron-glia crosstalk, will not only provide insight into brain physiology events but also advance our knowledge of PD pathologies. This review addresses the current understanding of α-syn pathogenesis in PD, with a focus on neuron-glia crosstalk. Particularly, the transmission of α-syn between neurons and glia, α-syn-induced glial activation, and feedbacks of glial activation on DA neuron degeneration are thoroughly discussed. In addition, α-syn aggregation, iron deposition, and glial activation in regulating DA neuron ferroptosis in PD are covered. Lastly, we summarize the preclinical and clinical therapies, especially targeting glia, in PD treatments.

R1441C and G2019S LRRK2 knockin mice have distinct striatal molecular, physiological, and behavioral alterations

LRRK2 mutations are closely associated with Parkinson's disease (PD). Convergent evidence suggests that LRRK2 regulates striatal function. Here, by using knock-in mouse lines expressing the two most common LRRK2 pathogenic mutations-G2019S and R1441C-we investigated how LRRK2 mutations altered striatal physiology. While we found that both R1441C and G2019S mice displayed reduced nigrostriatal dopamine release, hypoexcitability in indirect-pathway striatal projection neurons, and alterations associated with an impaired striatal-dependent motor learning were observed only in the R1441C mice. We also showed that increased synaptic PKA activities in the R1441C and not G2019S mice underlie the specific alterations in motor learning deficits in the R1441C mice. In summary, our data argue that LRRK2 mutations' impact on the striatum cannot be simply generalized. Instead, alterations in electrochemical, electrophysiological, molecular, and behavioral levels were distinct between LRRK2 mutations. Our findings offer mechanistic insights for devising and optimizing treatment strategies for PD patients.

The endoplasmic reticulum contributes to lysosomal tubulation/sorting driven by LRRK2

Lysosomes are dynamic organelles that can remodel their membrane as an adaptive response to various cell signaling events including membrane damage. Recently, we have discovered that damaged lysosomes form and sort tubules into moving vesicles. We named this process LYTL for LYsosomal Tubulation/sorting driven by LRRK2, as the Parkinson's disease protein LRRK2 promotes tubulation by recruiting the motor adaptor protein JIP4 to lysosomes via phosphorylated RAB proteins. Here we use spinning-disk microscopy combined with superresolution to further characterize LYTL after membrane damage with LLOMe (l-leucyl-l-leucine methyl ester). We identified the endoplasmic reticulum (ER) colocalizing with sites of fission of lysosome-derived tubules. In addition, modifying the morphology of the ER by reducing ER tubules leads to a decrease in LYTL sorting, suggesting that contact with tubular ER is necessary for lysosomal membrane sorting. Given the central roles of LRRK2 and lysosomal biology in Parkinson's disease, these discoveries are likely relevant to disease pathology and highlight interactions between organelles in this model.

LRRK2 recruitment, activity, and function in organelles

Protein coding mutations in leucine-rich repeat kinase 2 (LRRK2) cause familial Parkinson's disease (PD), and noncoding variations around the gene increase the risk of developing sporadic PD. It is generally accepted that pathogenic LRRK2 mutations increase LRRK2 kinase activity, resulting in a toxic hyperactive protein that is inferred to lead to the PD phenotype. LRRK2 has long been linked to different membrane trafficking events, but the specific role of LRRK2 in these events has been difficult to resolve. Recently, several papers have reported the activation and translocation of LRRK2 to cellular organelles under specific conditions, which suggests that LRRK2 may influence intracellular membrane trafficking. Here, we review what is known about the role of LRRK2 at various organelle compartments.

Human Induced Pluripotent Stem Cell Phenotyping and Preclinical Modeling of Familial Parkinson's Disease

Parkinson's disease (PD) is primarily idiopathic and a highly heterogenous neurodegenerative disease with patients experiencing a wide array of motor and non-motor symptoms. A major challenge for understanding susceptibility to PD is to determine the genetic and environmental factors that influence the mechanisms underlying the variations in disease-associated traits. The pathological hallmark of PD is the degeneration of dopaminergic neurons in the substantia nigra pars compacta region of the brain and post-mortem Lewy pathology, which leads to the loss of projecting axons innervating the striatum and to impaired motor and cognitive functions. While the cause of PD is still largely unknown, genome-wide association studies provide evidence that numerous polymorphic variants in various genes contribute to sporadic PD, and 10 to 15% of all cases are linked to some form of hereditary mutations, either autosomal dominant or recessive. Among the most common mutations observed in PD patients are in the genes LRRK2, SNCA, GBA1, PINK1, PRKN, and PARK7/DJ-1. In this review, we cover these PD-related mutations, the use of induced pluripotent stem cells as a disease in a dish model, and genetic animal models to better understand the diversity in the pathogenesis and long-term outcomes seen in PD patients.

Structure-Based Virtual Screening and De Novo Design to Identify Submicromolar Inhibitors of G2019S Mutant of Leucine-Rich Repeat Kinase 2

Missense mutations of leucine-rich repeat kinase 2 (LRRK2), including the G2019S mutant, are responsible for the pathogenesis of Parkinson's disease. In this work, structure-based virtual screening of a large chemical library was carried out to identify a number of novel inhibitors of the G2019S mutant of LRRK2, the biochemical potencies of which ranged from the low micromolar to the submicromolar level. The discovery of these potent inhibitors was made possible due to the modification of the original protein-ligand binding energy function in order to include an accurate ligand dehydration energy term. The results of extensive molecular docking simulations indicated that the newly identified inhibitors were bound to the ATP-binding site of the G2019S mutant of LRRK2 through the multiple hydrogen bonds with backbone amide groups in the hinge region as well as the hydrophobic interactions with the nonpolar residues in the P-loop, hinge region, and interdomain region. Among 18 inhibitors derived from virtual screening, 4-(2-amino-5-phenylpyrimidin-4-yl)benzene-1,3-diol (Inhibitor 2) is most likely to serve as a new molecular scaffold to optimize the biochemical potency, because it revealed submicromolar inhibitory activity in spite of its low molecular weight (279.3 amu). Indeed, a highly potent inhibitor (Inhibitor 2n) of the G2019S mutant was derived via the structure-based de novo design using the structure of Inhibitor 2 as the molecular core. The biochemical potency of Inhibitor 2n surged to the nanomolar level due to the strengthening of hydrophobic interactions in the ATP-binding site, which were presumably caused by the substitutions of small nonpolar moieties. Due to the high biochemical potency against the G2019S mutant of LRRK2 and the putatively good physicochemical properties, Inhibitor 2n is anticipated to serve as a new lead compound for the discovery of antiparkinsonian medicines.

Druggable transcriptomic pathways revealed in Parkinson's patient-derived midbrain neurons

Complex genetic predispositions accelerate the chronic degeneration of midbrain substantia nigra neurons in Parkinson’s disease (PD). Deciphering the human molecular makeup of PD pathophysiology can guide the discovery of therapeutics to slow the disease progression. However, insights from human postmortem brain studies only portray the latter stages of PD, and there is a lack of data surrounding molecular events preceding the neuronal loss in patients. We address this gap by identifying the gene dysregulation of live midbrain neurons reprogrammed in vitro from the skin cells of 42 individuals, including sporadic and familial PD patients and matched healthy controls. To minimize bias resulting from neuronal reprogramming and RNA-seq methods, we developed an analysis pipeline integrating PD transcriptomes from different RNA-seq datasets (unsorted and sorted bulk vs. single-cell and Patch-seq) and reprogramming strategies (induced pluripotency vs. direct conversion). This PD cohort’s transcriptome is enriched for human genes associated with known clinical phenotypes of PD, regulation of locomotion, bradykinesia and rigidity. Dysregulated gene expression emerges strongest in pathways underlying synaptic transmission, metabolism, intracellular trafficking, neural morphogenesis and cellular stress/immune responses. We confirmed a synaptic impairment with patch-clamping and identified pesticides and endoplasmic reticulum stressors as the most significant gene-chemical interactions in PD. Subsequently, we associated the PD transcriptomic profile with candidate pharmaceuticals in a large database and a registry of current clinical trials. This study highlights human transcriptomic pathways that can be targeted therapeutically before the irreversible neuronal loss. Furthermore, it demonstrates the preclinical relevance of unbiased large transcriptomic assays of reprogrammed patient neurons.

Parkinson-causing mutations in LRRK2 impair the physiological tetramerization of endogenous α-synuclein in human neurons

α-Synuclein (αSyn) aggregation in Lewy bodies and neurites defines both familial and 'sporadic' Parkinson's disease. We previously identified α-helically folded αSyn tetramers, in addition to the long-known unfolded monomers, in normal cells. PD-causing αSyn mutations decrease the tetramer:monomer (T:M) ratio, associated with αSyn hyperphosphorylation and cytotoxicity in neurons and a motor syndrome of tremor and gait deficits in transgenic mice that responds in part to L-DOPA. Here, we asked whether LRRK2 mutations, the most common genetic cause of cases previously considered sporadic PD, also alter tetramer homeostasis. Patient neurons carrying G2019S, the most prevalent LRRK2 mutation, or R1441C each had decreased T:M ratios and pSer129 hyperphosphorylation of their endogenous αSyn along with increased phosphorylation of Rab10, a widely reported substrate of LRRK2 kinase activity. Two LRRK2 kinase inhibitors normalized the T:M ratio and the hyperphosphorylation in the G2019S and R1441C patient neurons. An inhibitor of stearoyl-CoA desaturase, the rate-limiting enzyme for monounsaturated fatty acid synthesis, also restored the αSyn T:M ratio and reversed pSer129 hyperphosphorylation in both mutants. Coupled with the recent discovery that PD-causing mutations of glucocerebrosidase in Gaucher's neurons also decrease T:M ratios, our findings indicate that three dominant genetic forms of PD involve life-long destabilization of αSyn physiological tetramers as a common pathogenic mechanism that can occur upstream of progressive neuronal synucleinopathy. Based on αSyn's finely-tuned interaction with certain vesicles, we hypothesize that the fatty acid composition and fluidity of membranes regulate αSyn's correct binding to highly curved membranes and subsequent assembly into metastable tetramers.

The Role of Rab Proteins in Parkinson's Disease Synaptopathy

In patients affected by Parkinson's disease (PD), the most common neurodegenerative movement disorder, the brain is characterized by the loss of dopaminergic neurons in the nigrostriatal system, leading to dyshomeostasis of the basal ganglia network activity that is linked to motility dysfunction. PD mostly arises as an age-associated sporadic disease, but several genetic forms also exist. Compelling evidence supports that synaptic damage and dysfunction characterize the very early phases of either sporadic or genetic forms of PD and that this early PD synaptopathy drives retrograde terminal-to-cell body degeneration, culminating in neuronal loss. The Ras-associated binding protein (Rab) family of small GTPases, which is involved in the maintenance of neuronal vesicular trafficking, synaptic architecture and function in the central nervous system, has recently emerged among the major players in PD synaptopathy. In this manuscript, we provide an overview of the main findings supporting the involvement of Rabs in either sporadic or genetic PD pathophysiology, and we highlight how Rab alterations participate in the onset of early synaptic damage and dysfunction.

Association of a common genetic variant with Parkinson's disease is mediated by microglia

Studies of multiple neurodegenerative disorders have identified many genetic variants that are associated with risk of disease throughout a lifetime. For example, Parkinson's disease (PD) risk is attributed in part to both coding mutations in the leucine-rich repeat kinase 2 (LRRK2) gene and to a common noncoding variation in the 5' region of the LRRK2 locus, as identified by genome-wide association studies (GWAS). However, the mechanisms linking GWAS variants to pathogenicity are largely unknown. Here, we found that the influence of PD-associated noncoding variation on LRRK2 expression is specifically propagated through microglia and not by other cell types that express LRRK2 in the human brain. We find microglia-specific regulatory chromatin regions that modulate the LRRK2 expression in human frontal cortex and substantia nigra and confirm these results in a human-induced pluripotent stem cell-derived microglia model. We showed, using a large-scale clustered regularly interspaced short palindromic repeats interference (CRISPRi) screen, that a regulatory DNA element containing the single-nucleotide variant rs6581593 influences the LRRK2 expression in microglia. Our study demonstrates that cell type should be considered when evaluating the role of noncoding variation in disease pathogenesis and sheds light on the mechanism underlying the association of the 5' region of LRRK2 with PD risk.

G2019S LRRK2 Mutation Enhances MPP+-Induced Inflammation of Human Induced Pluripotent Stem Cells-Differentiated Dopaminergic Neurons

Induced pluripotent stem cells (iPSCs) offer an unprecedented opportunity to mimic human diseases of related cell types, but it is unclear whether they can successfully mimic age-related diseases such as Parkinson’s disease (PD). We generated iPSCs lines from three patients with familial PD associated with the G2019S mutation in the LRRK2 gene and one age-matched healthy individual (control). During long-term culture, dopaminergic (DA) neurons differentiated from iPSCs of G2019S LRRK2 PD patients exhibited morphological changes, including a reduced number of neurites and neurite arborization, which were not evident in DA neurons differentiated from control iPSCs. To mimic PD pathology in vitro, we used 1-methyl-4-phenylpyridium (MPP⁺) to damage DA neurons and found that DA neurons differentiated from patients with G2019S LRRK2 mutation significantly reduced the survival rate and increased apoptosis compared with the controls. We also found that the mRNA level of inflammatory factors [interleukin (IL)-1β, tumor necrosis factor-α, cyclooxygenase-2, IL-6, and inducible NO synthase] with G2019S LRRK2 mutation were higher than control group after exposure to MPP⁺. Our study provides an in vitro model based on iPSCs that captures the patients’ genetic complexity and investigates the pathogenesis of familial PD cases in a disease-associated cell type.