LRRK2: Genetic mechanisms vs genetic subtypes

Unraveling Molecular Targets for Neurodegenerative Diseases Through Caenorhabditis elegans Models

Neurodegenerative diseases (NDDs), including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and prion disease, represent a group of age-related disorders that pose a growing and formidable challenge to global health. Despite decades of extensive research that has uncovered key genetic factors and biochemical pathways, the precise molecular mechanisms underlying these diseases and effective therapeutic strategies remain elusive. Caenorhabditis elegans (C. elegans) has emerged as a powerful model organism for studying NDDs due to its unique biological features such as genetic tractability, conserved molecular pathways, and ease of high-throughput screening. This model provides an exceptional platform for identifying molecular targets associated with NDDs and developing novel therapeutic interventions. This review highlights the critical role of C. elegans in elucidating the complex molecular mechanisms of human NDDs, with a particular focus on recent advancements and its indispensable contributions to the discovery of molecular targets and therapeutic strategies for these NDDs.

Clinical and functional evidence for the pathogenicity of the LRRK2 p.Arg1067Gln variant

LRRK2-related Parkinson's disease (LRRK2-PD) is the most frequent form of monogenic PD worldwide, with important therapeutic opportunities, exemplified by the advancement in LRRK2 kinase inhibition studies/trials. However, many LRRK2 variants, especially those found in underrepresented populations, remain classified as variants of uncertain significance (VUS). Leveraging on Malaysian, Singaporean, and mainland Chinese PD datasets (n = 4901), we describe 12 Chinese-ancestry patients harboring the LRRK2 p.Arg1067Gln variant, more than doubling the number of previously reported cases (total n = 23, 87% East Asian, mean age of onset: 53.9 years). We determine that this variant is enriched in East Asian PD patients compared to population controls (OR = 8.0, 95% CI: 3.0-20.9), and provide supportive data for its co-segregation with PD, albeit with incomplete penetrance. Utilizing established experimental workflows, this variant showed increased LRRK2 kinase activity, by ~2-fold compared to wildtype and higher than the p.Gly2019Ser variant. Taken together, p.Arg1067Gln should be reclassified from a VUS to pathogenic for causing LRRK2-PD.

Updated MDSGene review on the clinical and genetic spectrum of LRRK2 variants in Parkinson´s disease

Pathogenic variants in the LRRK2 gene are one of the most commonly identifiable monogenic causes of Parkinson´s disease (PD, PARK-LRRK2). This systematic MDSGene literature review comprehensively summarizes published demographic, clinical, and genetic findings related to LRRK2 variants ( https://www.mdsgene.org/ ). Data on 4660 individuals with 283 different variants were curated. The median age at onset in the PD patients with available information was 56 years, notably, with approximately one-third having PD onset <50 years. Tremor was the most frequently reported initial symptom and more common than reported in other dominantly inherited forms of PD. Of the 211 potentially PD-causing variants, 25 were classified as pathogenic or likely pathogenic, and the remaining 186 (88.2%) were variants of uncertain significance. p.G2019S was the most frequently reported pathogenic variant, followed by p.R1441G and p.R1441C. This systematic review represents the most extensive database on PARK-LRRK2 to date and provides a vital resource to improve precision medicine.

Uncovering the genetic basis of Parkinson's disease globally: from discoveries to the clinic

Knowledge on the genetic basis of Parkinson's disease has grown tremendously since the discovery of the first monogenic form, caused by a mutation in α-synuclein, and with the subsequent identification of multiple other causative genes and associated loci. Genetic studies provide insights into the phenotypic heterogeneity and global distribution of Parkinson's disease. By shedding light on the underlying biological mechanisms, genetics facilitates the identification of new biomarkers and therapeutic targets. Several clinical trials of genetics-informed therapies are ongoing or imminent. International programmes in populations who have been under-represented in Parkinson's disease genetics research are fostering collaboration and capacity-building, and have already generated novel findings. Many challenges remain for genetics research in these populations, but addressing them provides opportunities to obtain a more complete and equitable understanding of Parkinson's disease globally. These advances facilitate the integration of genetics into the clinic, to improve patient management and personalised medicine.

Low-dose radiation decreases Lrrk2 levels in the striatum of large mammalian brains: New venues to treat Parkinson's disease?

INTRODUCTION

Among gene mutations and variants linked to an increased risk of PD, mutations of leucine-rich repeat kinase 2 gene (LRRK2) are among the most frequently associated with early- and late-onset PD. Clinical and neuropathological characteristics of idiopathic-PD (iPD) and LRRK2-PD are similar, and these similarities suggest that the pathomechanisms between these two conditions are shared. LRRK2 mutations determine a gain-of-function and yield higher levels of lrrk2 across body tissues, including brain. On another side, recent animal studies supported the potential use of low dose radiation (LDR) to modify the pathomechanisms of diseases such as Alzheimer's disease (AD).

METHODS

We assessed if a single total-body LDR (sLDR) exposure in normal swine could alter expression levels of the following PD-associated molecules: alpha-synuclein (α-syn), phosphorylated-α-synuclein (pα-syn), parkin, tyrosine hydroxylase (th), lrrk2, phosphorylated-lrrk2 (pS935-lrrk2), and some LRRK2 substrates (Rab8a, Rab12) across different brain regions. These proteins were measured in frontal cortex, hippocampus, striatum, thalamus/hypothalamus, and cerebellum of 9 radiated (RAD) vs. 6 sham (SH) swine after 28 days from a sLDR of 1.79Gy exposure.

RESULTS

Western Blot analyses showed lowered lrrk2 levels in the striatum of RAD vs. SH swine (p < 0.05), with no differences across the remaining brain regions. None of the other protein levels differed between RAD and SH swine in any examined brain regions. No lrrk2 and p-lrrk2 (S935) levels differed in the lungs of RAD vs. SH swine.

CONCLUSIONS

These findings show a specific striatal lrrk2 lowering effect due to LDR and support the potential use of LDR to interfere with the pathomechanisms of PD.

Recombinant Antibody Fragments for Immunotherapy of Parkinson's Disease

Parkinson's disease (PD) is the second most common age-related neurodegenerative disorder. Multiple genetic and environmental factors leading to progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SN) and consequent depletion of dopamine were described. Current clinical approaches, such as dopamine replacement or deep brain stimulation using surgically implanted probes, provide symptomatic relief but cannot modify disease progression. Therefore, disease-modifying therapeutic tools are urgently needed. Immunotherapy approaches, including passive transfer of protective antibodies and their fragments, have shown therapeutic efficacy in several animal models of neurodegenerative diseases, including PD. Recombinant antibody fragments are promising alternatives to conventional full-length antibodies. Modern computational approaches and molecular biology tools, directed evolution methodology, and the design of tissue-penetrating fusion peptides allowed for the development of recombinant antibody fragments with superior specificity and affinity, reduced immunogenicity, the capacity to target hidden epitopes and cross the blood-brain barrier (BBB), higher solubility and stability, the ability to refold after heat denaturation, and inexpensive large-scale production. In addition, antibody fragments do not induce microglia Fcγ receptor (FcγR)-mediated proinflammatory response and tissue damage in the central nervous system (CNS), because they lack the Fc portion of the immunoglobulin molecule. In the present review, we summarized data on recombinant antibody fragments evaluated as immunotherapeutics in preclinical models of PD and discussed their potential for developing therapeutic and preventive protocols for patients with PD.

Recalibrating the Why and Whom of Animal Models in Parkinson Disease: A Clinician's Perspective

Animal models have been used to gain pathophysiologic insights into Parkinson's disease (PD) and aid in the translational efforts of interventions with therapeutic potential in human clinical trials. However, no disease-modifying therapy for PD has successfully emerged from model predictions. These translational disappointments warrant a reappraisal of the types of preclinical questions asked of animal models. Besides the limitations of experimental designs, the one-size convergence and oversimplification yielded by a model cannot recapitulate the molecular diversity within and between PD patients. Here, we compare the strengths and pitfalls of different models, review the discrepancies between animal and human data on similar pathologic and molecular mechanisms, assess the potential of organoids as novel modeling tools, and evaluate the types of questions for which models can guide and misguide. We propose that animal models may be of greatest utility in the evaluation of molecular mechanisms, neural pathways, drug toxicity, and safety but can be unreliable or misleading when used to generate pathophysiologic hypotheses or predict therapeutic efficacy for compounds with potential neuroprotective effects in humans. To enhance the translational disease-modification potential, the modeling must reflect the biology not of a diseased population but of subtypes of diseased humans to distinguish What data are relevant and to Whom.