The Role of Rab Proteins in Parkinson's Disease Synaptopathy

A review on evolution, structural characteristics, interactions, and regulation of the membrane transport protein: The family of Rab proteins

Rab proteins are a key family of small GTPases that play crucial roles in vesicular trafficking, membrane dynamics, and maintaining cellular homeostasis. Studying this family of proteins is interesting as having many structural isoforms with variable evolutionary trends and wide distribution in cells. The proteins are renowned for their unique structural characteristics, which support their functional adaptability and specificity. Based on these features these proteins show different regulatory pathways and show involvement in dynamic protein-protein interactions, which is essential for intracellular signaling processes and in maintaining cellular functionality and balance. Notably, it is the first review to compile such extensive information about Rabs. Such information related to these proteins explores the molecular mechanisms in medicine based on their phylogenetic development, structural conformation changes, interaction networks, distribution, and regulation-dysregulations discussed in this review. Moreover, this review offers a consolidated resource for researchers and clinicians to understand the Rabs in different magnitudes.

Impaired unfolded protein response, BDNF and synuclein markers in postmortem dorsolateral prefrontal cortex and caudate nucleus of patients with depression and Parkinson's disease

Major depressive disorder (MDD) is characterized by significant impairment in social, emotional, and cognitive functioning. Its precise pathophysiology remains poorly understood. Alterations in protein homeostasis and some misfolded proteins have been identified within the brains of patients diagnosed with neuropsychiatric disorders. In contrast to neurodegenerative processes such as Parkinson's disease (PD), where the accumulation of aggregated α-synuclein (α-Syn) protein is a primary cause of significant neuronal loss, altered proteostasis in MDD may result in loss-of-function effects by modifying synaptic neuroplasticity. Moreover, aberrant activation of endoplasmic reticulum (ER) pathways may intensify the pathological alterations due to altered proteostasis. In this study, dorsolateral prefrontal cortex (dlPFC) and caudate nucleus from MDD patients and non-psychiatric controls were used. Postmortem samples of same brain areas from PD patients (Braak 2-3 and 5-6) and controls were also included. Protein levels of ER and unfolded protein response (UPR), synucleins (α-, β- and γ-Syn), and brain-derived neurotrophic factor (BDNF) were measured by Western-Blot. Phospho-eIF2α/eIF2α ratio was increased in the dlPFC and caudate nucleus of MDD and PD patients compared to their respective controls. Brain area-dependent changes in BiP and GRP94 levels were also found. We further detected accumulation of immature BDNF precursors and opposite changes in α- and β-Syn levels in the dlPFC of MDD and PD patients compared to controls. Our findings suggest that alterations in proteostasis contribute to the pathophysiology of MDD, as previously described in PD. A deeper understanding of the pathways involved will identify other candidate proteins and new targets with therapeutic potential.

[Parkinson's disease: from genetics to targeted therapies]

Parkinson’s disease (PD) is a multifactorial disorder involving various biological pathways. However, it is more accurate not to define PD as a unique entity, but rather as a mixture of several diseases with similar phenotypes. Attempts to classify subtypes of PD based on the clinical phenotype or biomarkers were tried. Nonetheless, for a subset of individuals, the classification based on the implied gene appears to be the most practical. Although the SNCA gene was the first identified in rare patients, pathogenic variants in GBA1 and LRRK2 are the most common genetic causes or risk factors of PD, and PRKN is the most frequent gene of autosomal recessive PD. Patients with pathogenic variants in SNCA, GBA1, LRRK2 or PRKN show various clinical, anatomopathological and biochemical aspects. Therefore, these four genes associated to PD are of particular interest for the development of targeted therapies. This fact is reinforced by the reality that current approaches are only symptomatic, and no curative treatment is available today. A number of clinical trials aiming to slow or stop disease progression are running, based on the gene involved. In this review, we will discuss the therapeutic approaches targeting SNCA, GBA1, LRRK2 and PRKN.

Role of Rab proteins in PFOA-induced changes in boar sperm motility and capacitation

Perfluorooctanoic acid (PFOA), a pervasive environmental contaminant, elicits adverse effects on sperm functions, including sperm motility and capacitation status. However, the specific mechanisms by which PFOA disrupts sperm functions during capacitation remain poorly elucidated. Therefore, this study aimed to investigate the molecular mechanisms underlying the PFOA-induced inhibition of sperm motility and capacitation in boar spermatozoa by focusing on Ras-related (Rab) proteins, which regulate membrane trafficking and play key roles in male sperm development, acrosome formation, and the acrosome reaction. Results showed significant reductions in sperm motility and various kinematic parameters following PFOA exposure. Correlation analysis revealed that Rab14 was positively correlated with dance mean (DNM) and negatively correlated with wobble (WOB), indicating that PFOA might affect sperm motility through Rab14 and potentially lead to reduced pregnancy rates. Differences in Rab25 were positively correlated with differences in total motility (MOT), progressive motility (PRG), linearity (LIN), and mean angular displacement (MAD), suggesting that PFOA might influence sperm motility by altering Rab25. Differences in Rab34 were positively correlated with differences in acrosome-reacted spermatozoa, implicating its role in the acrosome reaction. These findings provided insights into the molecular mechanism of PFOA-induced reproductive toxicity and highlighted the function of Rab proteins as biomarkers for the assessment of the effects of similar environmental toxins on male fertility.

Increased neuronal expression of the early endosomal adaptor APPL1 leads to endosomal and synaptic dysfunction with cholinergic neurodegeneration

Dysfunction of the endolysosomal system within neurons is a prominent feature of Alzheimer's disease (AD) pathology. Multiple AD-risk factors are known to cause hyper-activity of the early-endosome small GTPase rab5, resulting in neuronal endosomal pathway disruption. APPL1, an important rab5 effector protein, is an interface between endosomal and neuronal function through a rab5-activating interaction with the BACE1-generated C-terminal fragment (βCTF or C99) of the amyloid precursor protein (APP), a pathogenic APP fragment generated within endolysosomal compartments. To better understand the role of APPL1 in the AD endosomal phenotype, we generated a transgenic mouse model over-expressing human APPL1 within neurons (Thy1-APPL1 mice). Consistent with the important endosomal regulatory role of APPL1, Thy1-APPL1 mice have enlarged neuronal early endosomes and increased synaptic endocytosis due to increased rab5 activation. We additionally demonstrate pathological consequences of APPL1 overexpression, including functional changes in hippocampal long-term potentiation (LTP) and long-term depression (LTD), as well as degeneration of the large projection cholinergic neurons of the basal forebrain and impairment of hippocampal-dependent memory. Our findings show that increased neuronal APPL1 levels lead to a cascade of pathological effects within neurons, including early endosomal alterations, synaptic dysfunction, and neurodegeneration. Multiple risk factors and molecular regulators, including APPL1 activity, are known to contribute to the endosomal dysregulation seen in the early stages of AD, and these findings further highlight the shared pathobiology and consequences to a neuron of early endosomal pathway disruption.

Significance Statement

Dysfunction in the endolysosomal system within neurons is a key feature of Alzheimer's disease (AD). Multiple AD risk factors lead to hyperactivity of the early-endosome GTPase rab5, disrupting neuronal pathways including the cholinergic circuits involved early in memory decline. APPL1, a crucial rab5 effector, connects endosomal and neuronal functions through its interaction with a specific amyloid precursor protein (APP) fragment generated within endosomes. To understand APPL1's role, a transgenic mouse model over-expressing human APPL1 in neurons (Thy1-APPL1 mice) was developed. These mice show enlarged early endosomes and increased synaptic endocytosis due to rab5 activation, resulting in impaired hippocampal long-term potentiation and depression, the degeneration of basal forebrain cholinergic neurons, and memory deficits, highlighting a pathological cascade mediated through APPL1 at the early endosome.

Disruption of Dopamine Homeostasis Associated with Alteration of Proteins in Synaptic Vesicles: A Putative Central Mechanism of Parkinson's Disease Pathogenesis

Vestigial dopaminergic cells in PD have selectivity for a sub-class of hypersensitive neurons with the nigrostriatal dopamine (DA) tract. DA is modulated in pre-synaptic nerve terminals to remain stable. To be specific, proteins at DA release sites that have a function of synthesizing and packing DA in cytoplasm, modulating release and reingestion, and changing excitability of neurons, display regional discrepancies that uncover relevancy of the observed sensitivity to neurodegenerative changes. Although the reasons of a majority of PD cases are still indistinct, heredity and environment are known to us to make significant influences. For decades, genetic analysis of PD patients with heredity in family have promoted our comprehension of pathogenesis to a great extent, which reveals correlative mechanisms including oxidative stress, abnormal protein homeostasis and mitochondrial dysfunction. In this review, we review the constitution of presynaptic vesicle related to DA homeostasis and describe the genetic and environmental evidence of presynaptic dysfunction that increase risky possibility of PD concerning intracellular vesicle transmission and their functional outcomes. We summarize alterations in synaptic vesicular proteins with great involvement in the reasons of some DA neurons highly vulnerable to neurodegenerative changes. We generalize different potential targets and therapeutic strategies for different pathogenic mechanisms, providing a reference for further studies of PD treatment in the future. But it remains to be further researched on this recently discovered and converging mechanism of vesicular dynamics and PD, which will provide a more profound comprehension and put up with new therapeutic tactics for PD patients.

Endo-lysosomal dysfunction in neurodegenerative diseases: opinion on current progress and future direction in the use of exosomes as biomarkers

Over the past two decades, increased research has highlighted the connection between endosomal trafficking defects and neurodegeneration. The endo-lysosomal network is an important, complex cellular system specialized in the transport of proteins, lipids, and other metabolites, essential for cell homeostasis. Disruption of this pathway is linked to a wide range of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease and frontotemporal dementia. Furthermore, there is strong evidence that defects in this pathway create opportunities for diagnostic and therapeutic intervention. In this Opinion piece, we concisely address the role of endo-lysosomal dysfunction in five neurodegenerative diseases and discuss how future research can investigate this intracellular pathway, including extracellular vesicles with a specific focus on exosomes for the identification of novel disease biomarkers. This article is part of a discussion meeting issue 'Understanding the endo-lysosomal network in neurodegeneration'.

From Synaptic Physiology to Synaptic Pathology: The Enigma of α-Synuclein

Alpha-synuclein (α-syn) has gained significant attention due to its involvement in neurodegenerative diseases, particularly Parkinson's disease. However, its normal function in the human brain is equally fascinating. The α-syn protein is highly dynamic and can adapt to various conformational stages, which differ in their interaction with synaptic elements, their propensity to drive pathological aggregation, and their toxicity. This review will delve into the multifaceted role of α-syn in different types of synapses, shedding light on contributions to neurotransmission and overall brain function. We describe the physiological role of α-syn at central synapses, including the bidirectional interaction between α-syn and neurotransmitter systems.

Targeted protein degradation for the treatment of Parkinson's disease: Advances and future perspective

Parkinson's disease (PD) is a progressive disorder that belongs to a class of neurodegenerative disorders (NDs) called Synucleinopathies. It has characterized by the misfolding and aggregation of a-synuclein. Our understanding of PD continues to evolve, and so does our approach to treatment. including therapies aimed at delaying pathology, quitting neuronal loss, and shortening the course of the disease by selectively targeting essential proteins suspected to play a role in PD pathogenesis. One emerging approach that is generating significant interest is Targeted Protein Degradation (TPD). TPD is an innovative method that allows us to specifically break down certain proteins using specially designed molecules or peptides, like PROteolysis-TArgeting-Chimera (PROTACs). This approach holds great promise, particularly in the context of NDs. In this review, we will briefly explain PD and its pathogenesis, followed by discussing protein degradation systems and TPD strategy in PD by reviewing synthesized small molecules and peptides. Finally, future perspectives and challenges in the field are discussed.

X-Chromosome Association Study in Latin American Cohorts Identifies New Loci in Parkinson's Disease

BACKGROUND

Sex differences in Parkinson's disease (PD) risk are well-known. However, the role of sex chromosomes in the development and progression of PD is still unclear.

OBJECTIVE

The objective of this study was to perform the first X-chromosome-wide association study for PD risk in a Latin American cohort.

METHODS

We used data from three admixed cohorts: (1) Latin American Research consortium on the Genetics of Parkinson's Disease (n = 1504) as discover cohort, and (2) Latino cohort from International Parkinson Disease Genomics Consortium (n = 155) and (3) Bambui Aging cohort (n = 1442) as replication cohorts. We also developed an X-chromosome framework specifically designed for admixed populations.

RESULTS

We identified eight linkage disequilibrium regions associated with PD. We replicated one of these regions (top variant rs525496; discovery odds ratio [95% confidence interval]: 0.60 [0.478-0.77], P = 3.13 × 10-5 replication odds ratio: 0.60 [0.37-0.98], P = 0.04). rs5525496 is associated with multiple expression quantitative trait loci in brain and non-brain tissues, including RAB9B, H2BFM, TSMB15B, and GLRA4, but colocalization analysis suggests that rs5525496 may not mediate risk by expression of these genes. We also replicated a previous X-chromosome-wide association study finding (rs28602900), showing that this variant is associated with PD in non-European populations.

CONCLUSIONS

Our results reinforce the importance of including X-chromosome and diverse populations in genetic studies. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The role of microglial LRRK2 kinase in manganese-induced inflammatory neurotoxicity via NLRP3 inflammasome and RAB10-mediated autophagy dysfunction

Chronic manganese (Mn) exposure can lead to manganism, a neurological disorder sharing common symptoms with Parkinson's disease (PD). Studies have shown that Mn can increase the expression and activity of leucine-rich repeat kinase 2 (LRRK2), leading to inflammation and toxicity in microglia. LRRK2 G2019S mutation also elevates LRRK2 kinase activity. Thus, we tested if Mn-increased microglial LRRK2 kinase is responsible for Mn-induced toxicity, and exacerbated by G2019S mutation, using WT and LRRK2 G2019S knock-in mice and BV2 microglia. Mn (30 mg/kg, nostril instillation, daily for 3 weeks) caused motor deficits, cognitive impairments, and dopaminergic dysfunction in WT mice, which were exacerbated in G2019S mice. Mn induced proapoptotic Bax, NLRP3 inflammasome, IL-1β, and TNF-α in the striatum and midbrain of WT mice, and these effects were more pronounced in G2019S mice. BV2 microglia were transfected with human LRRK2 WT or G2019S, followed by Mn (250 μM) exposure to better characterize its mechanistic action. Mn increased TNF-α, IL-1β, and NLRP3 inflammasome activation in BV2 cells expressing WT LRRK2, which was elevated further in G2019S-expressing cells, while pharmacological inhibition of LRRK2 mitigated these effects in both genotypes. Moreover, the media from Mn-treated G2019S-expressing BV2 microglia caused greater toxicity to the cath.a-differentiated (CAD) neuronal cells compared to media from microglia expressing WT. Mn-LRRK2 activated RAB10 which was exacerbated in G2019S. RAB10 played a critical role in LRRK2-mediated Mn toxicity by dysregulating the autophagy-lysosome pathway and NLRP3 inflammasome in microglia. Our novel findings suggest that microglial LRRK2 via RAB10 plays a critical role in Mn-induced neuroinflammation.

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.

Synucleinopathies Take Their Toll: Are TLRs a Way to Go?

The misfolding and subsequent abnormal accumulation and aggregation of α-Synuclein (αSyn) as insoluble fibrils in Lewy bodies and Lewy neurites is the pathological hallmark of Parkinson's disease (PD) and several neurodegenerative disorders. A combination of environmental and genetic factors is linked to αSyn misfolding, among which neuroinflammation is recognized to play an important role. Indeed, a number of studies indicate that a Toll-like receptor (TLR)-mediated neuroinflammation might lead to a dopaminergic neural loss, suggesting that TLRs could participate in the pathogenesis of PD as promoters of immune/neuroinflammatory responses. Here we will summarize our current understanding on the mechanisms of αSyn aggregation and misfolding, focusing on the contribution of TLRs to the progression of α-synucleinopathies and speculating on their link with the non-motor disturbances associated with aging and neurodegenerative disorders.

The role of microglial LRRK2 in manganese-induced inflammatory neurotoxicity via NLRP3 inflammasome and RAB10-mediated autophagy dysfunction

Chronic exposure to manganese (Mn) can lead to manganism, a neurological disorder sharing common symptoms with Parkinson's disease (PD). Studies have shown that Mn can increase the expression and activity of leucine-rich repeat kinase 2 (LRRK2), leading to inflammation and toxicity in microglia. LRRK2 G2019S mutation also elevates LRRK2 kinase activity. Thus, we tested if Mn-increased microglial LRRK2 kinase is responsible for Mn-induced toxicity, and exacerbated by G2019S mutation, using WT and LRRK2 G2019S knock-in mice, and BV2 microglia. Mn (30 mg/kg, nostril instillation, daily for 3 weeks) caused motor deficits, cognitive impairments, and dopaminergic dysfunction in WT mice, which were exacerbated in G2019S mice. Mn induced proapoptotic Bax, NLRP3 inflammasome, IL-1β and TNF-α in the striatum and midbrain of WT mice, and these effects were exacerbated in G2019S mice. BV2 microglia were transfected with human LRRK2 WT or G2019S, followed by Mn (250 μM) exposure to better characterize its mechanistic action. Mn increased TNF-α, IL-1β, and NLRP3 inflammasome activation in BV2 cells expressing WT LRRK2, which was exacerbated in G2019S-expressing cells, while pharmacological inhibition of LRRK2 mitigated these effects in both genotypes. Moreover, the media from Mn-treated BV2 microglia expressing G2019S caused greater toxicity to cath.a-differentiated (CAD) neuronal cells compared to media from microglia expressing WT. Mn-LRRK2 activated RAB10, which was exacerbated in G2019S. RAB10 played a critical role in LRRK2-mediated Mn toxicity by dysregulating the autophagy-lysosome pathway, and NLRP3 inflammasome in microglia. Our novel findings suggest that microglial LRRK2 via RAB10 plays a critical role in Mn-induced neuroinflammation.

The Role of Rab Proteins in Mitophagy: Insights into Neurodegenerative Diseases

Mitochondrial dysfunction and vesicular trafficking alterations have been implicated in the pathogenesis of several neurodegenerative diseases. It has become clear that pathogenetic pathways leading to neurodegeneration are often interconnected. Indeed, growing evidence suggests a concerted contribution of impaired mitophagy and vesicles formation in the dysregulation of neuronal homeostasis, contributing to neuronal cell death. Among the molecular factors involved in the trafficking of vesicles, Ras analog in brain (Rab) proteins seem to play a central role in mitochondrial quality checking and disposal through both canonical PINK1/Parkin-mediated mitophagy and novel alternative pathways. In turn, the lack of proper elimination of dysfunctional mitochondria has emerged as a possible causative/early event in some neurodegenerative diseases. Here, we provide an overview of major findings in recent years highlighting the role of Rab proteins in dysfunctional mitochondrial dynamics and mitophagy, which are characteristic of neurodegenerative diseases. A further effort should be made in the coming years to clarify the sequential order of events and the molecular factors involved in the different processes. A clear cause-effect view of the pathogenetic pathways may help in understanding the molecular basis of neurodegeneration.

Bringing synapses into focus: Recent advances in synaptic imaging and mass-spectrometry for studying synaptopathy

Synapses are integral for healthy brain function and are becoming increasingly recognized as key structures in the early stages of brain disease. Understanding the pathological processes driving synaptic dysfunction will unlock new therapeutic opportunities for some of the most devastating diseases of our time. To achieve this we need a solid repertoire of imaging and molecular tools to interrogate synaptic biology at greater resolution. Synapses have historically been examined in small numbers, using highly technical imaging modalities, or in bulk, using crude molecular approaches. However, recent advances in imaging techniques are allowing us to analyze large numbers of synapses, at single-synapse resolution. Furthermore, multiplexing is now achievable with some of these approaches, meaning we can examine multiple proteins at individual synapses in intact tissue. New molecular techniques now allow accurate quantification of proteins from isolated synapses. The development of increasingly sensitive mass-spectrometry equipment means we can now scan the synaptic molecular landscape almost in totality and see how this changes in disease. As we embrace these new technical developments, synapses will be viewed with clearer focus, and the field of synaptopathy will become richer with insightful and high-quality data. Here, we will discuss some of the ways in which synaptic interrogation is being facilitated by methodological advances, focusing on imaging, and mass spectrometry.

The Role of α-Synuclein in the Regulation of Serotonin System: Physiological and Pathological Features

In patients affected by Parkinson's disease (PD), up to 50% of them experience cognitive changes, and psychiatric disturbances, such as anxiety and depression, often precede the onset of motor symptoms and have a negative impact on their quality of life. Pathologically, PD is characterized by the loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNc) and the presence of intracellular inclusions, called Lewy bodies and Lewy neurites, composed mostly of α-synuclein (α-Syn). Much of PD research has focused on the role of α-Syn aggregates in the degeneration of SNc DA neurons due to the impact of striatal DA deficits on classical motor phenotypes. However, abundant Lewy pathology is also found in other brain regions including the midbrain raphe nuclei, which may contribute to non-motor symptoms. Indeed, dysfunction of the serotonergic (5-HT) system, which regulates mood and emotional pathways, occurs during the premotor phase of PD. However, little is known about the functional consequences of α-Syn inclusions in this neuronal population other than DA neurons. Here, we provide an overview of the current knowledge of α-Syn and its role in regulating the 5-HT function in health and disease. Understanding the relative contributions to α-Syn-linked alterations in the 5-HT system may provide a basis for identifying PD patients at risk for developing depression and could lead to a more targeted therapeutic approach.

X-Chromosome Association Study in Latin American Cohorts Identifies New Loci in Parkinson Disease

Sex differences in Parkinson Disease (PD) risk are well-known. However, it is still unclear the role of sex chromosomes in the development and progression of PD. We performed the first X-chromosome Wide Association Study (XWAS) for PD risk in Latin American individuals. We used data from three admixed cohorts: (i) Latin American Research consortium on the GEnetics of Parkinson's Disease (n=1,504) as discover cohort and (ii) Latino cohort from International Parkinson Disease Genomics Consortium (n = 155) and (iii) Bambui Aging cohort (n= 1,442) as replication cohorts. After developing a X-chromosome framework specifically designed for admixed populations, we identified eight linkage disequilibrium regions associated with PD. We fully replicated one of these regions (top variant rs525496; discovery OR [95%CI]: 0.60 [0.478 - 0.77], p = 3.13 × 10 ^-5 ; replication OR: 0.60 [0.37-0.98], p = 0.04). rs525496 is an expression quantitative trait loci for several genes expressed in brain tissues, including RAB9B, H2BFM, TSMB15B and GLRA4 . We also replicated a previous XWAS finding (rs28602900), showing that this variant is associated with PD in non-European populations. Our results reinforce the importance of including X-chromosome and diverse populations in genetic studies.

News about Structure and Function of Synapses: Health and Diseases

During the last century, synapses have been intensely investigated as the most interesting sites of neuroscience development [...].