Parkin regulates amino acid homeostasis at mitochondria-lysosome (M/L) contact sites in Parkinson's disease

Deletion of ZNRF2 Exacerbates MPTP-Induced Parkinson's Disease by Activating mTOR-Mediated Neuroinflammatory Pathways

Parkinson's disease (PD) imposes a significant health burden among older adults and may be related to zinc and ring finger 2 (ZNRF2)-a member of the ubiquitination family. To investigate the role and mechanism of action of ZNRF2 in the regulation of mammalian target of rapamycin (mTOR)-mediated neuroinflammation in a mouse model of PD. Healthy mice were injected intraperitoneally with either saline (control) or MPTP 30 mg/kg. Mouse behavior was tested using rotarod and open field tests. The distribution and expression of tyrosine hydroxylase (TH) were determined by immunoblotting and immunohistochemistry. Inflammatory factors were evaluated using immunoblotting, enzyme-linked immunosorbent assay, and immunofluorescence assay. Compared with mice injected with saline, MPTP-treated mice showed significantly impaired locomotor activity, a significant decrease in the number of TH neurons, and a markedly altered morphology. ZNRF2 expression was significantly increased in the mesencephalon of MPTP-treated mice compared to that in control mice. ZNRF2 knockdown exacerbated motor dysfunction, accelerated dopamine neuron degeneration and death, increased the levels of pro-inflammatory factors (e.g., interleukin (IL)-1β, IL-6), and suppressed the expression of anti-inflammatory factors (e.g., IL-4, IL-10) in the central nervous system of MPTP-treated mice, with more pronounced activation of microglia and astrocytes. ZNRF2 knockdown significantly elevated phosphorylated mTOR protein levels after MPTP treatment; subsequently, phosphorylated mTOR protein levels were inhibited; dyskinesia and dopamine neuronal damage were significantly ameliorated, and neuroinflammation was suppressed in PD mice. ZNRF2 regulates the pathogenesis of MPTP-induced PD in mice via mechanisms related to mTOR-mediated neuroinflammation.

The key role of the ferroptosis mechanism in neurological diseases and prospects for targeted therapy

Neurological disorders represent a major global health concern owing to their intricate pathological processes. Ferroptosis, defined as a form of cell death that is reliant on iron, has been closely linked to various neurological conditions. The fundamental process underlying ferroptosis is defined by the excessive buildup of iron ions, which initiates lipid peroxidation processes leading to cellular demise. Neurons, as highly metabolically active cells, are susceptible to oxidative stress, and imbalances in iron metabolism can directly initiate the ferroptosis process. In neurodegenerative disorders like Alzheimer's disease and Parkinson's disease, ferroptosis driven by iron accumulation represents a fundamental pathological connection. Although the connection between ferroptosis and neurological diseases is clear, clinical application still faces challenges, such as precise regulation of iron metabolism, development of specific drugs, and assessment of efficacy. The limited comprehension of the ferroptosis mechanism hinders the development of personalized treatment approaches. Consequently, subsequent investigations must tackle these obstacles to facilitate the clinical application of ferroptosis-associated therapies in neurological disorders. This article provides a comprehensive overview of the most recent advancements regarding the underlying mechanisms of ferroptosis. Subsequently, the study investigates the mechanistic contributions of ferroptosis within the nervous system. In conclusion, we evaluate and deliberate on targeted therapeutic strategies associated with ferroptosis and neurological disorders.

Mitochondria-membranous organelle contacts at a glance

Mitochondrial contact sites are specialized interfaces where mitochondria physically interact with other organelles. Stabilized by molecular tethers and defined by unique proteomic and lipidomic profiles, these sites enable direct interorganellar communication and functional coordination, playing crucial roles in cellular physiology and homeostasis. Recent advances have expanded our knowledge of contact site-resident proteins, illuminated the dynamic and adaptive nature of these interfaces, and clarified their contribution to pathophysiology. In this Cell Science at a Glance article and the accompanying poster, we summarize the mitochondrial contacts that have been characterized in mammals, the molecular mechanisms underlying their formation, and their principal functions.

Pathogenesis of Parkinson's Disease

Both genetic and environmental factors modulate the risk of Parkinson's disease. In this article, all these pathophysiologic processes that contribute to damages at the tissue, cellular, organelle, and molecular levels, and their effects are talked about.

Inborn errors of canonical autophagy in neurodegenerative diseases

Neurodegenerative disorders (NDDs), characterized by a progressive loss of neurons and cognitive function, are a severe burden to human health and mental fitness worldwide. A hallmark of NDDs such as Alzheimer's disease, Huntington's disease, Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and prion diseases is disturbed cellular proteostasis, resulting in pathogenic deposition of aggregated protein species. Autophagy is a major cellular process maintaining proteostasis and integral to innate immune defenses that mediates lysosomal protein turnover. Defects in autophagy are thus frequently associated with NDDs. In this review, we discuss the interplay between NDDs associated proteins and autophagy and provide an overview over recent discoveries in inborn errors in canonical autophagy proteins that are associated with NDDs. While mutations in autophagy receptors seems to be associated mainly with the development of ALS, errors in mitophagy are mainly found to promote PD. Finally, we argue whether autophagy may impact progress and onset of the disease, as well as the potential of targeting autophagy as a therapeutic approach. Concludingly, understanding disorders due to inborn errors in autophagy-"autophagopathies"-will help to unravel underlying NDD pathomechanisms and provide unique insights into the neuroprotective role of autophagy, thus potentially paving the way for novel therapeutic interventions.

Disturbances in mitochondrial quality control and mitochondria-lysosome contact underlie the cerebral cortex and heart damage of mucopolysaccharidosis type II mice

Mucopolysaccharidosis type II (or Hunter syndrome) is a lysosomal disease caused by mutations in the IDS gene, which encodes the enzyme iduronate 2-sulfatase. MPS II patients present with systemic clinical manifestations and, in the most severe cases, with severe central nervous system abnormalities. Cardiac alterations are also commonly observed. In this study, we evaluated the communication between mitochondria and lysosomes, as well as mitochondrial dynamics and bioenergetics, mitophagy/autophagy, and redox homeostasis in the cerebral cortex and heart of 6-month-old MPS II mice. Our findings showed a reduction in the content of protein TBC1D15 in the cerebral cortex and heart of MPS II mice and an increase in Rab7 in the heart of these animals, suggesting disturbances in the communication between mitochondria and lysosomes. Furthermore, decreased Drp1 levels, indicative of reduced fission, and increased VDAC1 and COX IV, suggesting an increase in mitochondrial mass, were seen in both tissues. Tom20 was also augmented in the cortex. Changes in parkin levels were also verified, indicating disrupted mitophagy. In the field of bioenergetics, we observed reduced activities of citrate synthase and malate dehydrogenase in the cortex, as well as decreased activities of isocitrate dehydrogenase, creatine kinase, and pyruvate kinase, along with diminished mitochondrial respiration in the cardiac tissue of deficient mice. However, a mild increase in lipid peroxidation was seen only in the heart. Our findings suggest that mitochondria-lysosome crosstalk disruption and bioenergetic failure contribute to the pathophysiology of brain and heart alterations in MPS II.

Commander complex regulates lysosomal function and is implicated in Parkinson's disease risk

Variants in GBA1 resulting in decreased lysosomal glucocerebrosidase (GCase) activity are a common risk factor for Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Incomplete penetrance of GBA1 variants suggests that additional genes contribute to PD and DLB manifestation. By using a pooled genome-wide CRISPR interference screen, we identified copper metabolism MURR1 domain-containing 3 (COMMD3) protein, a component of the COMMD/coiled-coil domain-containing protein 22 (CCDC22)/CCDC93 (CCC) and Commander complexes, as a modifier of GCase and lysosomal activity. Loss of COMMD3 increased the release of lysosomal proteins through extracellular vesicles, leading to their impaired delivery to endolysosomes and consequent lysosomal dysfunction. Rare variants in the Commander gene family were associated with increased PD risk. Thus, COMMD genes and related complexes regulate lysosomal homeostasis and may represent modifiers in PD and other neurodegenerative diseases associated with lysosomal dysfunction.

N-acetyl-l-leucine lowers pS129-synuclein and improves synaptic function in models of Parkinson's disease

N-acetyl-L-leucine (NALL), a derivative of the branched-chain amino acid leucine, has shown therapeutic potential in neurodegenerative diseases, including in prodromal stages of Parkinson's disease (PD). However, the mechanism of its protective effects has been largely unknown. Using discovery-based proteomics, we found that treatment with NALL led to upregulation of lysosomal, mitochondrial, and synaptic proteins in PD patient-derived dopaminergic neurons. NALL reduced levels of pathological pS129-alpha-synuclein in dopaminergic neurons from patients harboring GBA1 or LRRK2 mutations. This decrease in pS129-syn was dependent on serine protease HTRA1 that was induced by NALL treatment of dopaminergic neurons. NALL also upregulated expression of wild-type parkin in both GBA1 and LRRK2 mutant neurons, leading to an increase in functional dopamine transporter and synaptic membrane-associated synaptojanin-1, suggesting improved synaptic function. Furthermore, NALL treatment of mutant LRRK2R1441C knock-in mice led to decreased pS129-alpha-synuclein, increased parkin and improved dopamine-dependent motor learning deficits. These findings highlight the therapeutic potential of NALL in PD by its protective effects on α-synuclein pathology and synaptic function in vulnerable dopaminergic neurons.

Heavy metal-induced disruption of the autophagy-lysosomal pathway: implications for aging and neurodegenerative disorders

Heavy metals such as lead, mercury, cadmium, magnesium, manganese, arsenic, copper pose considerable threats to neuronal health and are increasingly recognized as factors contributing to aging-related neurodegeneration. Exposure to these environmental toxins disrupts cellular homeostasis, resulting in oxidative stress and compromising critical cellular processes, particularly the autophagy-lysosomal pathway. This pathway is vital for preserving cellular integrity by breaking down damaged proteins and organelles; however, toxicity from heavy metals can hinder this function, leading to the buildup of harmful substances, inflammation, and increased neuronal injury. As individuals age, the consequences of neurodegeneration become more significant, raising the likelihood of developing disorders like Alzheimer's and Parkinson's disease. This review explores the intricate relationship between heavy metal exposure, dysfunction of the autophagy-lysosomal pathway, and aging-related neurodegeneration, emphasizing the urgent need for a comprehensive understanding of these mechanisms. The insights gained from this analysis are crucial for creating targeted therapeutic approaches aimed at alleviating the harmful effects of heavy metals on neuronal health and improving cellular resilience in aging populations.

TNF-α disrupts the malate-aspartate shuttle, driving metabolic rewiring in iPSC-derived enteric neural lineages from Parkinson's Disease patients

Gastrointestinal (GI) dysfunction emerges years before motor symptoms in Parkinson's disease (PD), implicating the enteric nervous system (ENS) in early disease progression. However, the mechanisms linking the PD hallmark protein, α-synuclein (α-syn), to ENS dysfunction - and whether these mechanisms are influenced by inflammation - remains elusive. Using iPSC-derived enteric neural lineages from patients with α-syn triplications, we reveal that TNF-α increases mitochondrial-α-syn interactions, disrupts the malate-aspartate shuttle, and forces a metabolic shift toward glutamine oxidation. These alterations drive mitochondrial dysfunction, characterizing metabolic impairment under cytokine stress. Interestingly, targeting glutamate metabolism with Chicago Sky Blue 6B restores mitochondrial function, reversing TNF-α-driven metabolic disruption. Our findings position the ENS as a central player in PD pathogenesis, establishing a direct link between cytokines, α-syn accumulation, metabolic stress and mitochondrial dysfunction. By uncovering a previously unrecognized metabolic vulnerability in the ENS, we highlight its potential as a therapeutic target for early PD intervention.

Mitochondrial quality control in cardiomyocytes: safeguarding the heart against disease and ageing

Mitochondria are multifunctional organelles that are important for many different cellular processes, including energy production and biosynthesis of fatty acids, haem and iron-sulfur clusters. Mitochondrial dysfunction leads to a disruption in these processes, the generation of excessive reactive oxygen species, and the activation of inflammatory and cell death pathways. The consequences of mitochondrial dysfunction are particularly harmful in energy-demanding organs such as the heart. Loss of terminally differentiated cardiomyocytes leads to cardiac remodelling and a reduced ability to sustain contraction. Therefore, cardiomyocytes rely on multilayered mitochondrial quality control mechanisms to maintain a healthy population of mitochondria. Mitochondrial chaperones protect against protein misfolding and aggregation, and resident proteases eliminate damaged proteins through proteolysis. Irreparably damaged mitochondria can also be degraded through mitochondrial autophagy (mitophagy) or ejected from cells inside vesicles. The accumulation of dysfunctional mitochondria in cardiomyocytes is a hallmark of ageing and cardiovascular disease. This accumulation is driven by impaired mitochondrial quality control mechanisms and contributes to the development of heart failure. Therefore, there is a strong interest in developing therapies that directly target mitochondrial quality control in cardiomyocytes. In this Review, we discuss the current knowledge of the mechanisms involved in regulating mitochondrial quality in cardiomyocytes, how these pathways are altered with age and in disease, and the therapeutic potential of targeting mitochondrial quality control pathways in cardiovascular disease.

Analysis of dopaminergic neuron-specific mitochondrial morphology and function using tyrosine hydroxylase reporter iPSC lines

Changes in mitochondrial function and morphology contribute to the development of many neurological diseases. Parkinson's disease is one of the neurodegenerative diseases suspected to be associated with defects in mitochondrial function and quality control. The loss of dopaminergic neurons in the substantia nigra pars compacta is a well-known pathological feature of Parkinson's disease. It is important for elucidating the pathogenesis of Parkinson's disease to analyze mitochondrial function and morphology specific to dopaminergic neurons using live-cell imaging or electron microscopy. However, the cells differentiated into dopaminergic neurons from induced pluripotent stem cells generally comprise heterogeneous populations. We generated tyrosine hydroxylase (TH) reporter iPSC lines to distinguish dopaminergic neurons from other cells for live-cell imaging and electron microscopy. This review summarizes previous studies utilizing the TH reporter iPSC lines and discusses the importance of studying mitochondria specific to dopaminergic neurons. Additionally, it provides overviews of recent studies reporting changes in endoplasmic reticulum-mitochondrial contact sites in Parkinson's disease models.

Arginine: at the crossroads of nitrogen metabolism

L-arginine is the most nitrogen-rich amino acid, acting as a key precursor for the synthesis of nitrogen-containing metabolites and an essential intermediate in the clearance of excess nitrogen. Arginine's side chain possesses a guanidino group which has unique biochemical properties, and plays a primary role in nitrogen excretion (urea), cellular signaling (nitric oxide) and energy buffering (phosphocreatine). The post-translational modification of protein-incorporated arginine by guanidino-group methylation also contributes to epigenetic gene control. Most human cells do not synthesize sufficient arginine to meet demand and are dependent on exogenous arginine. Thus, dietary arginine plays an important role in maintaining health, particularly upon physiologic stress. How cells adapt to changes in extracellular arginine availability is unclear, mostly because nearly all tissue culture media are supplemented with supraphysiologic levels of arginine. Evidence is emerging that arginine-deficiency can influence disease progression. Here, we review new insights into the importance of arginine as a metabolite, emphasizing the central role of mitochondria in arginine synthesis/catabolism and the recent discovery that arginine can act as a signaling molecule regulating gene expression and organelle dynamics.

Dysregulation of mitochondrial α-ketoglutarate dehydrogenase leads to elevated lipid peroxidation in CHCHD2-linked Parkinson's disease models

Dysregulation of mitochondrial function has been implicated in Parkinson's disease (PD), but the role of mitochondrial metabolism in disease pathogenesis remains to be elucidated. Using an unbiased metabolomic analysis of purified mitochondria, we identified alterations in α-ketoglutarate dehydrogenase (KGDH) pathway upon loss of PD-linked CHCHD2 protein. KGDH, a rate-limiting enzyme complex in the tricarboxylic acid cycle, was decreased in CHCHD2-deficient male mouse brains and human dopaminergic neurons. This deficiency of KGDH led to elevated α-ketoglutarate and increased lipid peroxidation. Treatment of CHCHD2-deficient dopaminergic neurons with lipoic acid, a KGDH cofactor and antioxidant agent, resulted in decreased levels of lipid peroxidation and phosphorylated α-synuclein. CHCHD10, a close homolog of CHCHD2 that is primarily linked to amyotrophic lateral sclerosis/frontotemporal dementia, did not affect the KGDH pathway or lipid peroxidation. Together, these results identify KGDH metabolic pathway as a targetable mitochondrial mechanism for correction of increased lipid peroxidation and α-synuclein in Parkinson's disease.

BOK-engaged mitophagy alleviates neuropathology in Alzheimer's disease

Mitochondrial malfunction associated with impaired mitochondrial quality control and self-renewal machinery, known as mitophagy, is an under-appreciated mechanism precipitating synaptic loss and cognitive impairments in Alzheimer's disease. Promoting mitophagy has been shown to improve cognitive function in Alzheimer's disease animals. However, the regulatory mechanism was unclear, which formed the aim of this study. Here, we found that a neuron-specific loss of Bcl-2 family member BOK in patients with Alzheimer's disease and APPswe/PS1dE9 (APP/PS1) mice is closely associated with mitochondrial damage and mitophagy defects. We further revealed that BOK is the key to the Parkin-mediated mitophagy through competitive binding to the MCL1/Parkin complex, resulting in Parkin release and translocation to damaged mitochondria to initiate mitophagy. Furthermore, overexpressing bok in hippocampal neurons of APP/PS1 mice alleviated mitophagy and mitochondrial malfunction, resulting in improved cognitive function. Conversely, the knockdown of bok worsened the aforementioned Alzheimer's disease-related changes. Our findings uncover a novel mechanism of BOK signalling through regulating Parkin-mediated mitophagy to mitigate amyloid pathology, mitochondrial and synaptic malfunctions, and cognitive decline in Alzheimer's disease, thus representing a promising therapeutic target.

Matrix stiffness regulates mitochondria-lysosome contacts to modulate the mitochondrial network, alleviate the senescence of MSCs

The extracellular microenvironment encompasses the extracellular matrix, neighbouring cells, cytokines, and fluid components. Anomalies in the microenvironment can trigger aging and a decreased differentiation capacity in mesenchymal stem cells (MSCs). MSCs can perceive variations in the firmness of the extracellular matrix and respond by regulating mitochondrial function. Diminished mitochondrial function is intricately linked to cellular aging, and studies have shown that mitochondria-lysosome contacts (M-L contacts) can regulate mitochondrial function to sustain cellular equilibrium. Nonetheless, the influence of M-L contacts on MSC aging under varying matrix stiffness remains unclear. In this study, utilizing single-cell RNA sequencing and atomic force microscopy, we further demonstrate that reduced matrix stiffness in older individuals leads to MSC aging and subsequent decline in osteogenic ability. Mechanistically, augmented M-L contacts under low matrix stiffness exacerbate MSC aging by escalating mitochondrial oxidative stress and peripheral division. Moreover, under soft matrix stiffness, cytoskeleton reorganization facilitates rapid movement of lysosomes. The M-L contacts inhibitor ML282 ameliorates MSC aging by reinstating mitochondrial network and function. Overall, our findings confirm that MSC aging is instigated by disruption of the mitochondrial network and function induced by matrix stiffness, while also elucidating the potential mechanism by which M-L Contact regulates mitochondrial homeostasis. Crucially, this presents promise for cellular anti-aging strategies centred on mitochondria, particularly in the realm of stem cell therapy.

Microenvironment Remodeling Microgel Repairs Degenerated Intervertebral Disc via Programmed Delivery of MicroRNA-155

The progression of intervertebral disc degeneration (IVDD) is associated with increased cell apoptosis and reduced extracellular matrix (ECM) production, both of which are driven by ongoing inflammation. Thus, alleviating the acidic inflammatory microenvironment and mitigating the apoptosis of nucleus pulposus cells (NPCs) are essential for intervertebral disc (IVD) regeneration. Regulating pH levels in the local environment can reduce inflammation and promote tissue recovery. In this study, a lactic acid-capturing microgel carrying a functionalized miRNA-155 nanocarrier was designed for IVD regeneration. microRNA-155 was loaded into the NPC-targeted nanogel via host-guest binding. The miR-155 nanocarrier (NGM) achieved lactic acid-sensitive release of miRNA-155, resulting in rapid regulation of apoptosis. Moreover, SS31, which dissociated from the nanogel network, had the ability to regulate mitochondrial metabolism. Moreover, the microgel was constructed using a matrix metalloproteinase-responsive peptide. The chitosan coating on the microgel system was ingeniously employed to capture lactic acid and enable pH-responsive dissociation, thereby alleviating the acidic microenvironment to protect cell viability and facilitate the delivery of the NGM. The microgel system effectively promoted IVD regeneration by alleviating the acidic microenvironment and preventing NPC apoptosis.

Novel strategies targeting mitochondria-lysosome contact sites for the treatment of neurological diseases

Mitochondria and lysosomes are critical for neuronal homeostasis, as highlighted by their dysfunction in various neurological diseases. Recent studies have identified dynamic membrane contact sites between mitochondria and lysosomes, independent of mitophagy and the lysosomal degradation of mitochondrial-derived vesicles (MDVs), allowing bidirectional crosstalk between these cell compartments, the dynamic regulation of organelle networks, and substance exchanges. Emerging evidence suggests that abnormalities in mitochondria-lysosome contact sites (MLCSs) contribute to neurological diseases, including Parkinson's disease, Charcot-Marie-Tooth (CMT) disease, lysosomal storage diseases, and epilepsy. This article reviews recent research advances regarding the tethering processes, regulation, and function of MLCSs and their role in neurological diseases.

Deficiency in NPC2 results in disruption of mitochondria-late endosome/lysosomes contact sites and endo-lysosomal lipid dyshomeostasis

Dysfunction of the endo-lysosomal intracellular Cholesterol transporter 2 protein (NPC2) leads to the onset of Niemann-Pick Disease Type C (NPC), a lysosomal storage disorder. Metabolic and homeostatic mechanisms are disrupted in lysosomal storage disorders (LSDs) hence we characterized a cellular model of NPC2 knock out, to assess alterations in organellar function and inter-organellar crosstalk between mitochondria and lysosomes. We performed characterization of lipid alterations and confirmed altered lysosomal morphology, but no overt changes in oxidative stress markers. Using several techniques, we demonstrated that contacts between mitochondria and late endosomes/lysosomes are reduced in NPC2-/- HEK cells, we observed that the acidic compartments are swollen and lipid dense. Quantification of endogenous lipids in HEKNPC2-/- cells by mass spectrometry reveals accumulation of lipid species indicative of sphingolipid metabolic dysregulation within the lysosome. Specifically, HEK NPC2-/- cells exhibit marked elevation of glucosylsphingosine and glucosylceramides, substrates of beta glucocerebroside (GBA), as well as accumulation of sphingosine and sphingomyelins. Our studies suggest an involvement of NPC2 in the formation of contact sites between mitochondria and lysosomes and support the hypothesis of a role for NPC2 in the endo-lysosomal trafficking pathway and dynamic organellar crosstalk.

Mitochondria-Lysosome Contact Sites: Emerging Players in Cellular Homeostasis and Disease

Mitochondria and lysosomes regulate a multitude of biological processes that are essential for the maintenance of nutrient and metabolic homeostasis and overall cell viability. Recent evidence reveals that these pivotal organelles, similarly to others previously studied, communicate through specialized membrane contact sites (MCSs), hereafter referred to as mitochondria-lysosome contacts (or MLCs), which promote their dynamic interaction without involving membrane fusion. Signal integration through MLCs is implicated in key processes, including mitochondrial fission and dynamics, and the exchange of calcium, cholesterol, and amino acids. Impairments in the formation and function of MLCs are increasingly associated with age-related diseases, specifically neurodegenerative disorders and lysosomal storage diseases. However, MLCs may play roles in other pathological contexts where lysosomes and mitochondria are crucial. In this review, we introduce the methodologies used to study MLCs and discuss known molecular players and key factors involved in their regulation in mammalian cells. We also argue other potential regulatory mechanisms depending on the acidic lysosomal pH and their impact on MLC's function. Finally, we explore the emerging implications of dysfunctional mitochondria-lysosome interactions in disease, highlighting their potential as therapeutic targets in cancer.

A promising therapeutic: Exosome-mediated mitochondrial transplantation

Mitochondrial dysfunction has been identified as a trigger for cellular autophagy dysfunction and programmed cell death. Emerging studies have revealed that, in pathological contexts, intercellular transfer of mitochondria takes place, facilitating the restoration of mitochondrial function, energy metabolism, and immune homeostasis. Extracellular vesicles, membranous structures released by cells, exhibit reduced immunogenicity and enhanced stability during the transfer of mitochondria. Thus, this review provides a concise overview of mitochondrial dysfunction related diseases and the mechanism of mitochondrial dysfunction in diseases progression, and the composition and functions of the extracellular vesicles, along with elucidating the principal mechanisms underlying intercellular mitochondrial transfer. In this article, we will focus on the advancements in both animal models and clinical trials concerning the therapeutic efficacy of extracellular vesicle-mediated mitochondrial transplantation across various systemic diseases in neurodegenerative diseases and cardiovascular diseases. Additionally, the review delves into the multifaceted roles of extracellular vesicle-transplanted mitochondria, encompassing anti-inflammatory actions, promotion of tissue repair, enhancement of cellular function, and modulation of metabolic and immune homeostasis within diverse pathological contexts, aiming to provide novel perspectives for extracellular vesicle transplantation of mitochondria in the treatment of various diseases.

Revolutionizing our understanding of Parkinson's disease: Dr. Heinz Reichmann's pioneering research and future research direction

Millions of individuals around the world are afflicted with Parkinson's disease (PD), a prevalent and incapacitating neurodegenerative disorder. Dr. Reichmann, a distinguished professor and neurologist, has made substantial advancements in the domain of PD research, encompassing both fundamental scientific investigations and practical applications. His research has illuminated the etiology and treatment of PD, as well as the function of energy metabolism and premotor symptoms. As a precursor to a number of neurotransmitters and neuromodulators that are implicated in the pathophysiology of PD, he has also investigated the application of tryptophan (Trp) derivatives in the disease. His principal findings and insights are summarized and synthesized in this narrative review article, which also emphasizes the challenges and implications for future PD research. This narrative review aims to identify and analyze the key contributions of Reichmann to the field of PD research, with the ultimate goal of informing future research directions in the domain. By examining Reichmann's work, the study seeks to provide a comprehensive understanding of his major contributions and how they can be applied to advance the diagnosis and treatment of PD. This paper also explores the potential intersection of Reichmann's findings with emerging avenues, such as the investigation of Trp and its metabolites, particularly kynurenines, which could lead to new insights and potential therapeutic strategies for managing neurodegenerative disorders like PD.

α-synuclein overexpression and the microbiome shape the gut and brain metabolome in mice

Pathological forms of α-synuclein contribute to synucleinopathies, including Parkinson's disease (PD). Most cases of PD arise from gene-environment interactions. Microbiome composition is altered in PD, and gut bacteria are causal to symptoms in animal models. We quantitatively profiled nearly 630 metabolites in the gut, plasma, and brain of α-synuclein-overexpressing (ASO) mice, compared to wild-type (WT) animals, and comparing germ-free (GF) to specific pathogen-free (SPF) animals (n = 5 WT-SPF; n = 6 ASO-SPF; n = 6 WT-GF; n = 6 ASO-GF). Many differentially expressed metabolites in ASO mice are also dysregulated in human PD patients, including amine oxides, bile acids and indoles. The microbial metabolite trimethylamine N-oxide (TMAO) strongly correlates from the gut to the plasma to the brain in mice, notable since TMAO is elevated in the blood and cerebrospinal fluid of PD patients. These findings uncover broad metabolomic changes that are influenced by the intersection of host genetics and microbiome in a mouse model of PD.

Dopaminergic neuron metabolism: relevance for understanding Parkinson's disease

BACKGROUND

Dopaminergic neurons from the substantia nigra pars compacta (SNc) have a higher susceptibility to aging-related degeneration, compared to midbrain dopaminergic cells present in the ventral tegmental area (VTA); the death of dopamine neurons in the SNc results in Parkinson´s disease (PD). In addition to increased loss by aging, dopaminergic neurons from the SNc are more prone to cell death when exposed to genetic or environmental factors, that either interfere with mitochondrial function, or cause an increase of oxidative stress. The oxidation of dopamine is a contributing source of reactive oxygen species (ROS), but this production is not enough to explain the differences in susceptibility to degeneration between SNc and VTA neurons.

AIM OF REVIEW

In this review we aim to highlight the intrinsic differences between SNc and VTA dopamine neurons, in terms of gene expression, calcium oscillations, bioenergetics, and ROS responses. Also, to describe the changes in the pentose phosphate pathway and the induction of apoptosis in SNc neurons during aging, as related to the development of PD.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Recent work showed that neurons from the SNc possess intrinsic characteristics that result in metabolic differences, related to their intricate morphology, that render them more susceptible to degeneration. In particular, these neurons have an elevated basal energy metabolism, that is required to fulfill the demands of the constant firing of action potentials, but at the same time, is associated to higher ROS production, compared to VTA cells. Finally, we discuss how mutations related to PD affect metabolic pathways, and the related mechanisms, as revealed by metabolomics.

Ubiquitin system mutations in neurological diseases

Neuronal ubiquitin balance impacts the fate of countless cellular proteins, and its disruption is associated with various neurological disorders. The ubiquitin system is critical for proper neuronal cell state transitions and the clearance of misfolded or aggregated proteins that threaten cellular integrity. This article reviews the state of and recent advancements in our understanding of the disruptions to components of the ubiquitin system, in particular E3 ligases and deubiquitylases, in neurodevelopmental and neurodegenerative diseases. Specific focus is on enzymes with recent progress in their characterization, including identifying enzyme-substrate pairs, the use of stem cell and animal models, and the development of therapeutics for ubiquitin-related diseases.

The p53 target DRAM1 modulates calcium homeostasis and ER stress by promoting contact between lysosomes and the ER through STIM1

It is well established that DNA Damage Regulated Autophagy Modulator 1 (DRAM1), a lysosomal protein and a target of p53, participates in autophagy. The cellular functions of DRAM1 beyond autophagy remain elusive. Here, we show p53-dependent upregulation of DRAM1 in mitochondrial damage-induced Parkinson's disease (PD) models and exacerbation of disease phenotypes by DRAM1. We find that the lysosomal location of DRAM1 relies on its intact structure including the cytosol-facing C-terminal domain. Excess DRAM1 disrupts endoplasmic reticulum (ER) structure, triggers ER stress, and induces protective ER-phagy. Mechanistically, DRAM1 interacts with stromal interacting molecule 1 (STIM1) to tether lysosomes to the ER and perturb STIM1 function in maintaining intracellular calcium homeostasis. STIM1 overexpression promotes cellular health by restoring calcium homeostasis, ER stress response, ER-phagy, and AMP-activated protein kinase (AMPK)-Unc-51 like autophagy activating kinase 1 (ULK1) signaling in cells with excess DRAM1. Thus, by promoting organelle contact between lysosomes and the ER, DRAM1 modulates ER structure and function and cell survival under stress. Our results suggest that DRAM1 as a lysosomal protein performs diverse roles in cellular homeostasis and stress response. These findings may have significant implications for our understanding of the role of the p53/DRAM1 axis in human diseases, from cancer to neurodegenerative diseases.

TBC1 domain-containing proteins are frequently involved in triple-negative breast cancers in connection with the induction of a glycolytic phenotype

Metabolic plasticity is a hallmark of cancer, and metabolic alterations represent a promising therapeutic target. Since cellular metabolism is controlled by membrane traffic at multiple levels, we investigated the involvement of TBC1 domain-containing proteins (TBC1Ds) in the regulation of cancer metabolism. These proteins are characterized by the presence of a RAB-GAP domain, the TBC1 domain, and typically function as attenuators of RABs, the master switches of membrane traffic. However, a number of TBC1Ds harbor mutations in their catalytic residues, predicting biological functions different from direct regulation of RAB activities. Herein, we report that several genes encoding for TBC1Ds are expressed at higher levels in triple-negative breast cancers (TNBC) vs. other subtypes of breast cancers (BC), and predict prognosis. Orthogonal transcriptomics/metabolomics analysis revealed that the expression of prognostic TBC1Ds correlates with elevated glycolytic metabolism in BC cell lines. In-depth investigations of the three top hits from the previous analyses (TBC1D31, TBC1D22B and TBC1D7) revealed that their elevated expression is causal in determining a glycolytic phenotype in TNBC cell lines. We further showed that the impact of TBC1D7 on glycolytic metabolism of BC cells is independent of its known participation in the TSC1/TSC2 complex and consequent downregulation of mTORC1 activity. Since TBC1D7 behaves as an independent prognostic biomarker in TNBC, it could be used to distinguish good prognosis patients who could be spared aggressive therapy from those with a poor prognosis who might benefit from anti-glycolytic targeted therapies. Together, our results highlight how TBC1Ds connect disease aggressiveness with metabolic alterations in TNBC. Given the high level of heterogeneity among this BC subtype, TBC1Ds could represent important tools in predicting prognosis and guiding therapy decision-making.

Extracellular vesicles: opening up a new perspective for the diagnosis and treatment of mitochondrial dysfunction

Mitochondria are crucial organelles responsible for energy generation in eukaryotic cells. Oxidative stress, calcium disorders, and mitochondrial DNA abnormalities can all cause mitochondrial dysfunction. It is now well documented that mitochondrial dysfunction significantly contributes to the pathogenesis of numerous illnesses. Hence, it is vital to investigate innovative treatment methods targeting mitochondrial dysfunction. Extracellular vesicles (EVs) are cell-derived nanovesicles that serve as intercellular messengers and are classified into small EVs (sEVs, < 200 nm) and large EVs (lEVs, > 200 nm) based on their sizes. It is worth noting that certain subtypes of EVs are rich in mitochondrial components (even structurally intact mitochondria) and possess the ability to transfer them or other contents including proteins and nucleic acids to recipient cells to modulate their mitochondrial function. Specifically, EVs can modulate target cell mitochondrial homeostasis as well as mitochondria-controlled apoptosis and ROS generation by delivering relevant substances. In addition, the artificial modification of EVs as delivery carriers for therapeutic goods targeting mitochondria is also a current research hotspot. In this article, we will focus on the ability of EVs to modulate the mitochondrial function of target cells, aiming to offer novel perspectives on therapeutic approaches for diverse conditions linked to mitochondrial dysfunction.

Diverse Functions of Parkin in Midbrain Dopaminergic Neurons

Parkinson's disease (PD) is characterized by preferential degeneration of midbrain dopaminergic neurons that contributes to its typical clinical manifestation. Mutations in the parkin gene (PARK2) represent a relatively common genetic cause of early onset PD. Parkin has been implicated in PINK1-dependent mitochondrial quantity control by targeting dysfunctional mitochondria to lysosomes via mitophagy. Recent evidence suggests that parkin can be activated in PINK1-independent manner to regulate synaptic function in human dopaminergic neurons. Neuronal activity triggers CaMKII-mediated activation of parkin and its recruitment to synaptic vesicles where parkin promotes binding of synaptojanin-1 to endophilin A1 and facilitates vesicle endocytosis. In PD patient neurons, disruption of this pathway on loss of parkin leads to defective recycling of synaptic vesicles and accumulation of toxic oxidized dopamine that at least in part explains preferential vulnerability of midbrain dopaminergic neurons. These findings suggest a convergent mechanism for PD-linked mutations in parkin, synaptojanin-1, and endophilin A1 and highlight synaptic dysfunction as an early pathogenic event in PD. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Lysosomal membrane contact sites: Integrative hubs for cellular communication and homeostasis

Lysosomes are more than just cellular recycling bins; they play a crucial role in regulating key cellular functions. Proper lysosomal function is essential for growth pathway regulation, cell proliferation, and metabolic homeostasis. Impaired lysosomal function is associated with lipid storage disorders and neurodegenerative diseases. Lysosomes form extensive and dynamic close contacts with the membranes of other organelles, including the endoplasmic reticulum, mitochondria, peroxisomes, and lipid droplets. These membrane contacts sites (MCSs) are vital for many lysosomal functions. In this chapter, we will explore lysosomal MCSs focusing on the machinery that mediates these contacts, how they are regulated, and their functional implications on physiology and pathology.

α-Synuclein Overexpression and the Microbiome Shape the Gut and Brain Metabolome in Mice

Pathological forms of the protein α-synuclein contribute to a family of disorders termed synucleinopathies, which includes Parkinson's disease (PD). Most cases of PD are believed to arise from gene-environment interactions. Microbiome composition is altered in PD, and gut bacteria are causal to symptoms and pathology in animal models. To explore how the microbiome may impact PD-associated genetic risks, we quantitatively profiled nearly 630 metabolites from 26 biochemical classes in the gut, plasma, and brain of α-synuclein-overexpressing (ASO) mice with or without microbiota. We observe tissue-specific changes driven by genotype, microbiome, and their interaction. Many differentially expressed metabolites in ASO mice are also dysregulated in human PD patients, including amine oxides, bile acids and indoles. Notably, levels of the microbial metabolite trimethylamine N-oxide (TMAO) strongly correlate from the gut to the plasma to the brain, identifying a product of gene-environment interactions that may influence PD-like outcomes in mice. TMAO is elevated in the blood and cerebral spinal fluid of PD patients. These findings uncover broad metabolomic changes that are influenced by the intersection of host genetics and the microbiome in a mouse model of PD.

Key genes and convergent pathogenic mechanisms in Parkinson disease

Parkinson disease (PD) is a neurodegenerative disorder marked by the preferential dysfunction and death of dopaminergic neurons in the substantia nigra. The onset and progression of PD is influenced by a diversity of genetic variants, many of which lack functional characterization. To identify the most high-yield targets for therapeutic intervention, it is important to consider the core cellular compartments and functional pathways upon which the varied forms of pathogenic dysfunction may converge. Here, we review several key PD-linked proteins and pathways, focusing on the mechanisms of their potential convergence in disease pathogenesis. These dysfunctions primarily localize to a subset of subcellular compartments, including mitochondria, lysosomes and synapses. We discuss how these pathogenic mechanisms that originate in different cellular compartments may coordinately lead to cellular dysfunction and neurodegeneration in PD.

Mitochondria-lysosome-extracellular vesicles axis and nanotheranostics in neurodegenerative diseases

The intricate functional interactions between mitochondria and lysosomes play a pivotal role in maintaining cellular homeostasis and proper cellular functions. This dynamic interplay involves the exchange of molecules and signaling, impacting cellular metabolism, mitophagy, organellar dynamics, and cellular responses to stress. Dysregulation of these processes has been implicated in various neurodegenerative diseases. Additionally, mitochondrial-lysosomal crosstalk regulates the exosome release in neurons and glial cells. Under stress conditions, neurons and glial cells exhibit mitochondrial dysfunction and a fragmented network, which further leads to lysosomal dysfunction, thereby inhibiting autophagic flux and enhancing exosome release. This comprehensive review synthesizes current knowledge on mitochondrial regulation of cell death, organelle dynamics, and vesicle trafficking, emphasizing their significant contributions to neurodegenerative diseases. Furthermore, we explore the emerging field of nanomedicine in the management of neurodegenerative diseases. The review provides readers with an insightful overview of nano strategies that are currently advancing the mitochondrial-lysosome-extracellular vesicle axis as a therapeutic approach for mitigating neurodegenerative diseases.

Alterations in Blood Methylome as Potential Epigenetic Biomarker in Sporadic Parkinson's Disease

OBJECTIVE

To characterize DNA methylation (DNAm) differences between sporadic Parkinson's disease (PD) and healthy control (HC) individuals enrolled in the Parkinson's Progression Markers Initiative (PPMI).

METHODS

Using whole blood, we characterized longitudinal differences in DNAm between sporadic PD patients (n = 196) and HCs (n = 86) enrolled in PPMI. RNA sequencing (RNAseq) was used to conduct gene expression analyses for genes mapped to differentially methylated cytosine-guanine sites (CpGs).

RESULTS

At the time of patient enrollment, 5,178 CpGs were differentially methylated (2,683 hypermethylated and 2,495 hypomethylated) in PD compared to HC. Of these, 579 CpGs underwent significant methylation changes over 3 years. Several differentially methylated CpGs were found near the cytochrome P450 family 2 subfamily E member 1 (CYP2E1) gene. Additionally, multiple hypermethylated CpGs were associated with the N-myc downregulated gene family member 4 (NDRG4) gene. RNA-Seq analyses showed 75 differentially expressed genes in PD patients compared to controls. An integrative analysis of both differentially methylated sites and differentially expressed genes revealed 20 genes that exhibited hypomethylation concomitant with overexpression. Additionally, 1 gene, cathepsin H (CTSH), displayed hypermethylation that was associated with its decreased expression.

INTERPRETATION

We provide initial evidence of alterations in DNAm in blood of PD patients that may serve as potential epigenetic biomarker of disease. To evaluate the significance of these changes throughout the progression of PD, additional profiling at longer intervals and during the prodromal stages of disease will be necessary. ANN NEUROL 2024;95:1162-1172.

VPS13C regulates phospho-Rab10-mediated lysosomal function in human dopaminergic neurons

Loss-of-function mutations in VPS13C are linked to early-onset Parkinson's disease (PD). While VPS13C has been previously studied in non-neuronal cells, the neuronal role of VPS13C in disease-relevant human dopaminergic neurons has not been elucidated. Using live-cell microscopy, we investigated the role of VPS13C in regulating lysosomal dynamics and function in human iPSC-derived dopaminergic neurons. Loss of VPS13C in dopaminergic neurons disrupts lysosomal morphology and dynamics with increased inter-lysosomal contacts, leading to impaired lysosomal motility and cellular distribution, as well as defective lysosomal hydrolytic activity and acidification. We identified Rab10 as a phospho-dependent interactor of VPS13C on lysosomes and observed a decreased phospho-Rab10-mediated lysosomal stress response upon loss of VPS13C. These findings highlight an important role of VPS13C in regulating lysosomal homeostasis in human dopaminergic neurons and suggest that disruptions in Rab10-mediated lysosomal stress response contribute to disease pathogenesis in VPS13C-linked PD.

PARKIN is not required to sustain OXPHOS function in adult mammalian tissues

Loss-of-function variants in the PRKN gene encoding the ubiquitin E3 ligase PARKIN cause autosomal recessive early-onset Parkinson's disease (PD). Extensive in vitro and in vivo studies have reported that PARKIN is involved in multiple pathways of mitochondrial quality control, including mitochondrial degradation and biogenesis. However, these findings are surrounded by substantial controversy due to conflicting experimental data. In addition, the existing PARKIN-deficient mouse models have failed to faithfully recapitulate PD phenotypes. Therefore, we have investigated the mitochondrial role of PARKIN during ageing and in response to stress by employing a series of conditional Parkin knockout mice. We report that PARKIN loss does not affect oxidative phosphorylation (OXPHOS) capacity and mitochondrial DNA (mtDNA) levels in the brain, heart, and skeletal muscle of aged mice. We also demonstrate that PARKIN deficiency does not exacerbate the brain defects and the pro-inflammatory phenotype observed in mice carrying high levels of mtDNA mutations. To rule out compensatory mechanisms activated during embryonic development of Parkin-deficient mice, we generated a mouse model where loss of PARKIN was induced in adult dopaminergic (DA) neurons. Surprisingly, also these mice did not show motor impairment or neurodegeneration, and no major transcriptional changes were found in isolated midbrain DA neurons. Finally, we report a patient with compound heterozygous PRKN pathogenic variants that lacks PARKIN and has developed PD. The PARKIN deficiency did not impair OXPHOS activities or induce mitochondrial pathology in skeletal muscle from the patient. Altogether, our results argue that PARKIN is dispensable for OXPHOS function in adult mammalian tissues.

Cell biology of Parkinson's disease: Mechanisms of synaptic, lysosomal, and mitochondrial dysfunction

Parkinson's disease (PD) is a growing cause of disability worldwide and there is a critical need for the development of disease-modifying therapies to slow or stop disease progression. Recent advances in characterizing the genetics of PD have expanded our understanding of the cell biology of this disorder. Mitochondrial oxidative stress, defects in synaptic function, and impaired lysosomal activity have been shown to be linked in PD, resulting in a pathogenic feedback cycle involving the accumulation of toxic oxidized dopamine and alpha-synuclein. In this review, we will highlight recent data on a subset of PD-linked genes which have key roles in these pathways and the pathogenic cycle. We will furthermore discuss findings highlighting the importance of dynamic mitochondria-lysosome contact sites that mediate direct inter-organelle cross-talk in the pathogenesis of PD and related disorders.

Super-resolution microscopy: Insights into mitochondria-lysosome crosstalk in health and disease

Live super-resolution microscopy has allowed for new insights into recently identified mitochondria-lysosome contact sites, which mediate crosstalk between mitochondria and lysosomes, including co-regulation of Rab7 GTP hydrolysis and Drp1 GTP hydrolysis. Here, we highlight recent findings and future perspectives on this dynamic pathway and its roles in health and disease.

Lysosomes in senescence and aging

Dysfunction of lysosomes, the primary hydrolytic organelles in animal cells, is frequently associated with aging and age-related diseases. At the cellular level, lysosomal dysfunction is strongly linked to cellular senescence or the induction of cell death pathways. However, the precise mechanisms by which lysosomal dysfunction participates in these various cellular or organismal phenotypes have remained elusive. The ability of lysosomes to degrade diverse macromolecules including damaged proteins and organelles puts lysosomes at the center of multiple cellular stress responses. Lysosomal activity is tightly regulated by many coordinated cellular processes including pathways that function inside and outside of the organelle. Here, we collectively classify these coordinated pathways as the lysosomal processing and adaptation system (LYPAS). We review evidence that the LYPAS is upregulated by diverse cellular stresses, its adaptability regulates senescence and cell death decisions, and it can form the basis for therapeutic manipulation for a wide range of age-related diseases and potentially for aging itself.

Ca2+ signalling: A common language for organelles crosstalk in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease caused by multifactorial pathogenic mechanisms. Familial PD is linked with genetic mutations in genes whose products are either associated with mitochondrial function or endo-lysosomal pathways. Of note, mitochondria are essential to sustain high energy demanding synaptic activity of neurons and alterations in mitochondrial Ca2+ signaling have been proposed as causal events for neurodegenerative process, although the mechanisms responsible for the selective loss of specific neuronal populations in the different neurodegenerative diseases is still not clear. Here, we specifically discuss the importance of a correct mitochondrial communication with the other organelles occurring at regions where their membranes become in close contact. We discuss the nature and the role of contact sites that mitochondria establish with ER, lysosomes, and peroxisomes, and how PD related proteins participate in the regulation/dysregulation of the tethering complexes. Unravelling molecular details of mitochondria tethering could contribute to identify specific therapeutic targets and develop new strategies to counteract the progression of the disease.

Misregulation of mitochondria-lysosome contact dynamics in Charcot-Marie-Tooth Type 2B disease Rab7 mutant sensory peripheral neurons

Inter-organelle contact sites between mitochondria and lysosomes mediate the crosstalk and bidirectional regulation of their dynamics in health and disease. However, mitochondria-lysosome contact sites and their misregulation have not been investigated in peripheral sensory neurons. Charcot-Marie-Tooth type 2B disease is an autosomal dominant axonal neuropathy affecting peripheral sensory neurons caused by mutations in the GTPase Rab7. Using live super-resolution and confocal time-lapse microscopy, we showed that mitochondria-lysosome contact sites dynamically form in the soma and axons of peripheral sensory neurons. Interestingly, Charcot-Marie-Tooth type 2B mutant Rab7 led to prolonged mitochondria-lysosome contact site tethering preferentially in the axons of peripheral sensory neurons, due to impaired Rab7 GTP hydrolysis-mediated contact site untethering. We further generated a Charcot-Marie-Tooth type 2B mutant Rab7 knock-in mouse model which exhibited prolonged axonal mitochondria-lysosome contact site tethering and defective downstream axonal mitochondrial dynamics due to impaired Rab7 GTP hydrolysis as well as fragmented mitochondria in the axon of the sciatic nerve. Importantly, mutant Rab7 mice further demonstrated preferential sensory behavioral abnormalities and neuropathy, highlighting an important role for mutant Rab7 in driving degeneration of peripheral sensory neurons. Together, this study identifies an important role for mitochondria-lysosome contact sites in the pathogenesis of peripheral neuropathy.

Regulation of Endosomal Trafficking by Rab7 and Its Effectors in Neurons: Clues from Charcot-Marie-Tooth 2B Disease

Intracellular endosomal trafficking controls the balance between protein degradation and synthesis, i.e., proteostasis, but also many of the cellular signaling pathways that emanate from activated growth factor receptors after endocytosis. Endosomal trafficking, sorting, and motility are coordinated by the activity of small GTPases, including Rab proteins, whose function as molecular switches direct activity at endosomal membranes through effector proteins. Rab7 is particularly important in the coordination of the degradative functions of the pathway. Rab7 effectors control endosomal maturation and the properties of late endosomal and lysosomal compartments, such as coordination of recycling, motility, and fusion with downstream compartments. The spatiotemporal regulation of endosomal receptor trafficking is particularly challenging in neurons because of their enormous size, their distinct intracellular domains with unique requirements (dendrites vs. axons), and their long lifespans as postmitotic, differentiated cells. In Charcot-Marie-Tooth 2B disease (CMT2B), familial missense mutations in Rab7 cause alterations in GTPase cycling and trafficking, leading to an ulcero-mutilating peripheral neuropathy. The prevailing hypothesis to account for CMT2B pathologies is that CMT2B-associated Rab7 alleles alter endocytic trafficking of the neurotrophin NGF and its receptor TrkA and, thereby, disrupt normal trophic signaling in the peripheral nervous system, but other Rab7-dependent pathways are also impacted. Here, using TrkA as a prototypical endocytic cargo, we review physiologic Rab7 effector interactions and control in neurons. Since neurons are among the largest cells in the body, we place particular emphasis on the temporal and spatial regulation of endosomal sorting and trafficking in neuronal processes. We further discuss the current findings in CMT2B mutant Rab7 models, the impact of mutations on effector interactions or balance, and how this dysregulation may confer disease.