Nanoparticles restore lysosomal acidification defects: Implications for Parkinson and other lysosomal-related diseases

Role of Lysosomal Acidification Dysfunction in Mesenchymal Stem Cell Senescence

Mesenchymal stem cell (MSC) transplantation has been widely used as a potential treatment for a variety of diseases. However, the contradiction between the low survival rate of transplanted cells and the beneficial therapeutic effects has affected its clinical use. Lysosomes as organelles at the center of cellular recycling and metabolic signaling, play essential roles in MSC homeostasis. In the first part of this review, we summarize the role of lysosomal acidification dysfunction in MSC senescence. In the second part, we summarize some of the potential strategies targeting lysosomal proteins to enhance the therapeutic effect of MSCs.

Are Lysosomes Potential Therapeutic Targets for Parkinson's Disease?

Parkinson´s Disease (PD) is the second most common neurodegenerative disorder, affecting ~2-3% of the population over 65 years old. In addition to progressive degeneration of nigrostriatal neurons, the histopathological feature of PD is the accumulation of misfolded α-synuclein protein in abnormal cytoplasmatic inclusions, known as Lewy Bodies (LBs). Recently, Genome-Wide Association Studies (GWAS) have indicated a clear association of variants within several lysosomal genes with risk for PD. Newly evolving data have been shedding light on the relationship between lysosomal dysfunction and alpha-synuclein aggregation. Defects in lysosomal enzymes could lead to the insufficient clearance of neurotoxic protein materials, possibly leading to selective degeneration of dopaminergic neurons. Specific modulation of lysosomal pathways and their components could be considered a novel opportunity for therapeutic intervention for PD. The purpose of this review is to illustrate lysosomal biology and describe the role of lysosomal dysfunction in PD pathogenesis. Finally, the most promising novel therapeutic approaches designed to modulate lysosomal activity, as a potential disease-modifying treatment for PD will be highlighted.

The mTOR-lysosome axis at the centre of ageing

Age‐related diseases represent some of the largest unmet clinical needs of our time. While treatment of specific disease‐related signs has had some success (for example, the effect of statin drugs on slowing progression of atherosclerosis), slowing biological ageing itself represents a target that could significantly increase health span and reduce the prevalence of multiple age‐related diseases. Mechanistic target of rapamycin complex 1 (mTORC1) is known to control fundamental processes in ageing: inhibiting this signalling complex slows biological ageing, reduces age‐related disease pathology and increases lifespan in model organisms. How mTORC1 inhibition achieves this is still subject to ongoing research. However, one mechanism by which mTORC1 inhibition is thought to slow ageing is by activating the autophagy–lysosome pathway. In this review, we examine the special bidirectional relationship between mTORC1 and the lysosome. In cells, mTORC1 is located on lysosomes. From this advantageous position, it directly controls the autophagy–lysosome pathway. However, the lysosome also controls mTORC1 activity in numerous ways, creating a special two‐way relationship. We then explore specific examples of how inhibition of mTORC1 and activation of the autophagy–lysosome pathway slow the molecular hallmarks of ageing. This body of literature demonstrates that the autophagy–lysosome pathway represents an excellent target for treatments that seek to slow biological ageing and increase health span in humans.

Targeting lysosomes in human disease: from basic research to clinical applications

In recent years, accumulating evidence has elucidated the role of lysosomes in dynamically regulating cellular and organismal homeostasis. Lysosomal changes and dysfunction have been correlated with the development of numerous diseases. In this review, we interpreted the key biological functions of lysosomes in four areas: cellular metabolism, cell proliferation and differentiation, immunity, and cell death. More importantly, we actively sought to determine the characteristic changes and dysfunction of lysosomes in cells affected by these diseases, the causes of these changes and dysfunction, and their significance to the development and treatment of human disease. Furthermore, we outlined currently available targeting strategies: (1) targeting lysosomal acidification; (2) targeting lysosomal cathepsins; (3) targeting lysosomal membrane permeability and integrity; (4) targeting lysosomal calcium signaling; (5) targeting mTOR signaling; and (6) emerging potential targeting strategies. Moreover, we systematically summarized the corresponding drugs and their application in clinical trials. By integrating basic research with clinical findings, we discussed the current opportunities and challenges of targeting lysosomes in human disease.

Genetically Encoded Fluorescent Biosensors for Biomedical Applications

One of the challenges of modern biology and medicine is to visualize biomolecules in their natural environment, in real-time and in a non-invasive fashion, so as to gain insight into their physiological behavior and highlight alterations in pathological settings, which will enable to devise appropriate therapeutic strategies. Genetically encoded fluorescent biosensors constitute a class of imaging agents that enable visualization of biological processes and events directly in situ, preserving the native biological context and providing detailed insight into their localization and dynamics in cells. Real-time monitoring of drug action in a specific cellular compartment, organ, or tissue type; the ability to screen at the single-cell resolution; and the elimination of false-positive results caused by low drug bioavailability that is not detected by in vitro testing methods are a few of the obvious benefits of using genetically encoded fluorescent biosensors in drug screening. This review summarizes results of the studies that have been conducted in the last years toward the fabrication of genetically encoded fluorescent biosensors for biomedical applications with a comprehensive discussion on the challenges, future trends, and potential inputs needed for improving them.

Protein clearance strategies for disease intervention

Protein homeostasis, or proteostasis, is essential for cell function and viability. Unwanted, damaged, misfolded and aggregated proteins are degraded by the ubiquitin–proteasome system (UPS) and the autophagy-lysosome pathway. Growing evidence indicates that alterations in these major proteolytic mechanisms lead to a demise in proteostasis, contributing to the onset and development of distinct diseases. Indeed, dysregulation of the UPS or autophagy is linked to several neurodegenerative, infectious and inflammatory disorders as well as cancer. Thus, modulation of protein clearance pathways is a promising approach for therapeutics. In this review, we discuss recent findings and open questions on how targeting proteolytic mechanisms could be applied for disease intervention.

Critical Evaluation of Different Lysosomal Labeling Methods Used to Analyze RNA Nanocarrier Trafficking in Cells

The use of nucleic acids to regulate gene expression is a rapidly developing field with immense clinical potential. Nanomaterials are frequently used to deliver nucleic acids into cells as they can overcome the poor cellular uptake and endo/lysosomal degradation of bare nucleic acids. For these nanocarriers to be effective, they must escape endo/lysosomal compartments to deliver their nucleic acid cargo into the cytosol (for ribonucleic acid (RNA)) or nucleus (for deoxyribonucleic acid (DNA)). This process is poorly understood and remains an area of active research toward the goal of developing effective delivery strategies. Fluorescent endo/lysosomal markers are among the most widely employed tools used to evaluate the endosomal escape of nucleic acid nanocarriers. However, the endo/lysosomal labeling method may alter the extent of and route of nanocarrier uptake by cells. The impact of these markers on cellular function and cell-nanocarrier interactions has not been probed in a systematic manner. To investigate this, we compared the effects of several common lysosomal labeling methods, namely, LysoTracker Red (LT Red), transient lysosomal-associated membrane protein 1-mutant green fluorescent protein (LAMP1-mGFP) transfection (Transient GFP), and stable lentiviral LAMP1-mGFP transfection (Stable GFP), on cellular metabolic activity, nanocarrier uptake, nanocarrier/lysosomal label colocalization, and gene silencing potency in U87 glioblastoma and MDA-MB-231 breast cancer cells using polyethyleneimine (PEI)/ribonucleic acid (RNA) polyplexes as a model nanocarrier. In both U87s and MDA-MB-231s, Transient GFP and LT Red labeling reduced metabolic activity relative to untransfected (Parental) cells, while Stable GFP labeling increased metabolic activity. Congruently, flow cytometry indicates Stable GFP cells have greater polyplex uptake than LT Red-labeled cells in both cell lines. Despite these similar trends in uptake, polyplex intracellular trafficking differs in the two cell lines, as confocal imaging revealed greater polyplex/lysosome colocalization in Stable GFP U87 cells than LT Red-labeled U87 cells, while the trend was reversed in MBA-MB-231s. The level of RNA-mediated gene silencing achieved in Parental versus Stable GFP U87 and MDA-MB-231 cells agreed with the observed levels of polyplex/lysosome colocalization, supporting the established concept that endosomal escape is the rate-limiting step for RNA interference. These findings indicate that lysosomal labels can profoundly alter cellular function and cell-nanocarrier interactions, presenting critical new considerations for researchers investigating nanoparticle trafficking.

Encapsulation of Large-Size Plasmids in PLGA Nanoparticles for Gene Editing: Comparison of Three Different Synthesis Methods

The development of new gene-editing technologies has fostered the need for efficient and safe vectors capable of encapsulating large nucleic acids. In this work we evaluate the synthesis of large-size plasmid-loaded PLGA nanoparticles by double emulsion (considering batch ultrasound and microfluidics-assisted methodologies) and magnetic stirring-based nanoprecipitation synthesis methods. For this purpose, we characterized the nanoparticles and compared the results between the different synthesis processes in terms of encapsulation efficiency, morphology, particle size, polydispersity, zeta potential and structural integrity of loaded pDNA. Our results demonstrate particular sensibility of large pDNA for shear and mechanical stress degradation during double emulsion, the nanoprecipitation method being the only one that preserved plasmid integrity. However, plasmid-loaded PLGA nanoparticles synthesized by nanoprecipitation did not show cell expression in vitro, possibly due to the slow release profile observed in our experimental conditions. Strong electrostatic interactions between the large plasmid and the cationic PLGA used for this synthesis may underlie this release kinetics. Overall, none of the methods evaluated satisfied all the requirements for an efficient non-viral vector when applied to large-size plasmid encapsulation. Further optimization or alternative synthesis methods are thus in current need to adapt PLGA nanoparticles as delivery vectors for gene editing therapeutic technologies.

Molecular targets and approaches to restore autophagy and lysosomal capacity in neurodegenerative disorders

Autophagy is a catabolic process that promotes cellular fitness by clearing aggregated protein species, pathogens and damaged organelles through lysosomal degradation. The autophagic process is particularly important in the nervous system where post-mitotic neurons rely heavily on protein and organelle quality control in order to maintain cellular health throughout the lifetime of the organism. Alterations of autophagy and lysosomal function are hallmarks of various neurodegenerative disorders. In this review, we conceptualize some of the mechanistic and genetic evidence pointing towards autophagy and lysosomal dysfunction as a causal driver of neurodegeneration. Furthermore, we discuss rate-limiting pathway nodes and potential approaches to restore pathway activity, from autophagy initiation, cargo sequestration to lysosomal capacity.

Nucleolipid Acid-Based Nanocarriers Restore Neuronal Lysosomal Acidification Defects

Increasing evidence suggests that lysosomal dysfunction has a pathogenic role in neurodegenerative diseases. In particular, an increase in lysosomal pH has been reported in different cellular models of Parkinson's disease. Thus, targeting lysosomes has emerged as a promising approach. More specifically, regulating its pH could play a central role against the neurodegeneration process. To date, only a few agents specifically targeting lysosomal pH are reported in the literature, partly due to the challenge of crossing the Blood-Brain-Barrier (BBB), preventing drug penetration into the central nervous system (CNS). To develop chronic treatments for neurodegenerative diseases, crossing the BBB is crucial. We report herein the conception and synthesis of an innovative DNA derivative-based nanocarrier. Nucleolipids, carrying a biocompatible organic acid as an active ingredient, were designed and synthesized as prodrugs. They were successfully incorporated into an oil-in-water nanoemulsion vehicle to cross biological membranes and then release effectively biocompatible acidic components to restore the functional lysosomal pH of neuronal cells. Biological assays on a genetic cell model of Parkinson's disease highlighted the non-toxicity of such nucleolipids after cellular uptake and their ability (at c = 40 µM) to fully restore lysosomal acidity.

Understanding the interactions between inorganic-based nanomaterials and biological membranes

The interactions between inorganic-based nanomaterials (NMs) and biological membranes are among the most important phenomena for developing NM-based therapeutics and resolving nanotoxicology. Herein, we introduce the structural and functional effects of inorganic-based NMs on biological membranes, mainly the plasma membrane and the endomembrane system, with an emphasis on the interface, which involves highly complex networks between NMs and biomolecules (such as membrane proteins and lipids). Significant efforts have been devoted to categorizing and analyzing the interaction mechanisms in terms of the physicochemical characteristics and biological effects of NMs, which can directly or indirectly influence the effects of NMs on membranes. Importantly, we summarize that the biological membranes act as platforms and thereby mediate NMs-immune system contacts. In this overview, the existing challenges and potential applications in the areas are addressed. A strong understanding of the discussed concepts will promote therapeutic NM designs for drug delivery systems by leveraging the NMs-membrane interactions and their functions.

PLGA-Based Nanoparticles for Neuroprotective Drug Delivery in Neurodegenerative Diseases

Treatment of neurodegenerative diseases has become one of the most challenging topics of the last decades due to their prevalence and increasing societal cost. The crucial point of the non-invasive therapeutic strategy for neurological disorder treatment relies on the drugs' passage through the blood-brain barrier (BBB). Indeed, this biological barrier is involved in cerebral vascular homeostasis by its tight junctions, for example. One way to overcome this limit and deliver neuroprotective substances in the brain relies on nanotechnology-based approaches. Poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) are biocompatible, non-toxic, and provide many benefits, including improved drug solubility, protection against enzymatic digestion, increased targeting efficiency, and enhanced cellular internalization. This review will present an overview of the latest findings and advances in the PLGA NP-based approach for neuroprotective drug delivery in the case of neurodegenerative disease treatment (i.e., Alzheimer's, Parkinson's, Huntington's diseases, Amyotrophic Lateral, and Multiple Sclerosis).

Genetically Encoded, pH-Sensitive mTFP1 Biosensor for Probing Lysosomal pH

Lysosomes are important sites for macromolecular degradation, defined by an acidic lumenal pH of ∼4.5. To better understand lysosomal pH, we designed a novel, genetically encoded, fluorescent protein (FP)-based pH biosensor called Fluorescence Indicator REporting pH in Lysosomes (FIRE-pHLy). This biosensor was targeted to lysosomes with lysosomal-associated membrane protein 1 (LAMP1) and reported lumenal pH between 3.5 and 6.0 with monomeric teal fluorescent protein 1 (mTFP1), a bright cyan pH-sensitive FP variant with a pKa of 4.3. Ratiometric quantification was enabled with cytosolically oriented mCherry using high-content quantitative imaging. We expressed FIRE-pHLy in several cellular models and quantified the alkalinizing response to bafilomycin A1, a specific V-ATPase inhibitor. In summary, we have engineered FIRE-pHLy, a specific, robust, and versatile lysosomal pH biosensor, that has broad applications for investigating pH dynamics in aging- and lysosome-related diseases, as well as in lysosome-based drug discovery.

Live imaging of intra-lysosome pH in cell lines and primary neuronal culture using a novel genetically encoded biosensor

Disorders of lysosomal physiology have increasingly been found to underlie the pathology of a rapidly growing cast of neurodevelopmental disorders and sporadic diseases of aging. One cardinal aspect of lysosomal (dys)function is lysosomal acidification in which defects trigger lysosomal stress signaling and defects in proteolytic capacity. We have developed a genetically encoded ratiometric probe to measure lysosomal pH coupled with a purification tag to efficiently purify lysosomes for both proteomic and in vitro evaluation of their function. Using our probe, we showed that lysosomal pH is remarkably stable over a period of days in a variety of cell types. Additionally, this probe can be used to determine that lysosomal stress signaling via TFEB is uncoupled from gross changes in lysosomal pH. Finally, we demonstrated that while overexpression of ARL8B GTPase causes striking alkalinization of peripheral lysosomes in HEK293 T cells, peripheral lysosomes per se are no less acidic than juxtanuclear lysosomes in our cell lines.Abbreviations: ARL8B: ADP ribosylation factor like GTPase 8B; ATP: adenosine triphosphate; ATP5F1B/ATPB: ATP synthase F1 subunit beta; ATP6V1A: ATPase H+ transporting V1 subunit A; Baf: bafilomycin A1; BLOC-1: biogenesis of lysosome-related organelles complex 1; BSA: bovine serum albumin; Cos7: African green monkey kidney fibroblast-like cell line; CQ: chloroquine; CTSB: cathepsin B; CYCS: cytochrome c, somatic; DAPI: 4',6-diamidino -2- phenylindole; DIC: differential interference contrast; DIV: days in vitro; DMEM: Dulbecco's modified Eagle's medium;‎ E8: embryonic day 8; EEA1: early endosome antigen 1; EGTA: ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid; ER: endoplasmic reticulum; FBS: fetal bovine serum; FITC: fluorescein isothiocyanate; GABARAPL2: GABA type A receptor associated protein like 2; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GOLGA2/GM130: golgin A2; GTP: guanosine triphosphate; HEK293T: human embryonic kidney 293 cells, that expresses a mutant version of the SV40 large T antigen; HeLa: Henrietta Lacks-derived cell; HEPES: 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; HRP: horseradish peroxidase; IGF2R/ciM6PR: insulin like growth factor 2 receptor; LAMP1/2: lysosomal associated membrane protein 1/2; LMAN2/VIP36: lectin, mannose binding 2; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MTORC1: mechanistic target of rapamycin kinase complex 1; PCR: polymerase chain reaction; PDL: poly-d-lysine; PGK1p: promotor from human phosphoglycerate kinase 1; PIKFYVE: phosphoinositide kinase, FYVE-type zinc finger containing; PPT1/CLN1: palmitoyl-protein thioesterase 1; RPS6KB1/p70: ribosomal protein S6 kinase B1; STAT3: signal transducer and activator of transcription 3; TAX1BP1: Tax1 binding protein 1; TFEB: transcription factor EB; TGN: trans-Golgi network; TGOLN2/TGN46: trans-Golgi network protein 2; TIRF: total internal reflection fluorescence; TMEM106B: transmembrane protein 106B; TOR: target of rapamycin; TRPM2: transient receptor potential cation channel subfamily M member 2; V-ATPase: vacuolar-type proton-translocating ATPase; VPS35: VPS35 retromer complex component.

Physiological and Pathological Factors Affecting Drug Delivery to the Brain by Nanoparticles

The prevalence of neurological/neurodegenerative diseases, such as Alzheimer's disease is known to be increasing due to an aging population and is anticipated to further grow in the decades ahead. The treatment of brain diseases is challenging partly due to the inaccessibility of therapeutic agents to the brain. An increasingly important observation is that the physiology of the brain alters during many brain diseases, and aging adds even more to the complexity of the disease. There is a notion that the permeability of the blood-brain barrier (BBB) increases with aging or disease, however, the body has a defense mechanism that still retains the separation of the brain from harmful chemicals in the blood. This makes drug delivery to the diseased brain, even more challenging and complex task. Here, the physiological changes to the diseased brain and aged brain are covered in the context of drug delivery to the brain using nanoparticles. Also, recent and novel approaches are discussed for the delivery of therapeutic agents to the diseased brain using nanoparticle based or magnetic resonance imaging guided systems. Furthermore, the complement activation, toxicity, and immunogenicity of brain targeting nanoparticles as well as novel in vitro BBB models are discussed.

Lysosomal Stress Response (LSR): Physiological Importance and Pathological Relevance

Extensive work has characterized endoplasmic reticulum (ER) and mitochondrial stress responses. In contrast, very little has been published about stress responses in lysosomes; subcellular acidic organelles that are physiologically important and are of pathological relevance. The greater lysosomal system is dynamic and is comprised of endosomes, lysosomes, multivesicular bodies, autophagosomes, and autophagolysosomes. They are important regulators of cellular physiology, they represent about 5% of the total cellular volume, they are heterogeneous in their sizes and distribution patterns, they are electron dense, and their subcellular positioning within cells varies in response to stimuli, insults and pH. These organelles are also integral to the pathogenesis of lysosomal storage diseases and it is increasingly recognized that lysosomes play important roles in the pathogenesis of such diverse conditions as neurodegenerative disorders and cancer. The purpose of this review is to focus attention on lysosomal stress responses (LSR), compare LSR with better characterized stress responses in ER and mitochondria, and form a framework for future characterizations of LSR. We synthesized data into the concept of LSR and present it here such that the definition of LSR can be modified as new knowledge is added and specific therapeutics are developed.

Conquering the Nuclear Envelope Barriers by EBV Lytic Replication

The nuclear envelope (NE) of eukaryotic cells has a highly structural architecture, comprising double lipid-bilayer membranes, nuclear pore complexes, and an underlying nuclear lamina network. The NE structure is held in place through the membrane-bound LINC (linker of nucleoskeleton and cytoskeleton) complex, spanning the inner and outer nuclear membranes. The NE functions as a barrier between the nucleus and cytoplasm and as a transverse scaffold for various cellular processes. Epstein-Barr virus (EBV) is a human pathogen that infects most of the world's population and is associated with several well-known malignancies. Within the nucleus, the replicated viral DNA is packaged into capsids, which subsequently egress from the nucleus into the cytoplasm for tegumentation and final envelopment. There is increasing evidence that viral lytic gene expression or replication contributes to the pathogenesis of EBV. Various EBV lytic proteins regulate and modulate the nuclear envelope structure in different ways, especially the viral BGLF4 kinase and the nuclear egress complex BFRF1/BFRF2. From the aspects of nuclear membrane structure, viral components, and fundamental nucleocytoplasmic transport controls, this review summarizes our findings and recently updated information on NE structure modification and NE-related cellular processes mediated by EBV.

Is γ-secretase a beneficial inactivating enzyme of the toxic APP C-terminal fragment C99?

Genetic, biochemical, and anatomical grounds led to the proposal of the amyloid cascade hypothesis centered on the accumulation of amyloid beta peptides (Aβ) to explain Alzheimer's disease (AD) etiology. In this context, a bulk of efforts have aimed at developing therapeutic strategies seeking to reduce Aβ levels, either by blocking its production (γ- and β-secretase inhibitors) or by neutralizing it once formed (Aβ-directed immunotherapies). However, so far the vast majority of, if not all, clinical trials based on these strategies have failed, since they have not been able to restore cognitive function in AD patients, and even in many cases, they have worsened the clinical picture. We here propose that AD could be more complex than a simple Aβ-linked pathology and discuss the possibility that a way to reconcile undoubted genetic evidences linking processing of APP to AD and a consistent failure of Aβ-based clinical trials could be to envision the pathological contribution of the direct precursor of Aβ, the β-secretase-derived C-terminal fragment of APP, βCTF, also referred to as C99. In this review, we summarize scientific evidences pointing to C99 as an early contributor to AD and postulate that γ-secretase should be considered as not only an Aβ-generating protease, but also a beneficial C99-inactivating enzyme. In that sense, we discuss the limitations of molecules targeting γ-secretase and propose alternative strategies seeking to reduce C99 levels by other means and notably by enhancing its lysosomal degradation.

NANOTECHNOLOGY-MEDIATED THERAPEUTIC STRATEGIES AGAINST SYNUCLEINOPATHIES IN NEURODEGENERATIVE DISEASE

Synucleinopathies are a subset of debilitating neurodegenerative disorders for which clinically approved therapeutic options to either halt or retard disease progression are currently unavailable. Multiple synergistic pathological mechanisms in combination with the characteristic misfolding of proteins are attributable to disease pathogenesis and progression. This complex interplay, as well as the difficult and multiscale nature of therapeutic delivery into the central nervous system, make finding effective treatments difficult. Nanocarriers (NCs) are a class of materials that can significantly improve therapeutic brain delivery and enable multifunctional therapies. In this review, an update on the known pathology of synucleinopathies is presented. Then, NC-enabled therapeutics designed to target the multiple mechanisms by combination therapies and multiscale targeting methods is reviewed. The implications of these strategies are synthesized and evaluated to suggest opportunities for the rational design of anti-neurodegenerative NC therapeutics.

Mitochondrial and Organellar Crosstalk in Parkinson's Disease

Mitochondrial dysfunction is a well-established pathological event in Parkinson's disease (PD). Proteins misfolding and its impaired cellular clearance due to altered autophagy/mitophagy/pexophagy contribute to PD progression. It has been shown that mitochondria have contact sites with endoplasmic reticulum (ER), peroxisomes and lysosomes that are involved in regulating various physiological processes. In pathological conditions, the crosstalk at the contact sites initiates alterations in intracellular vesicular transport, calcium homeostasis and causes activation of proteases, protein misfolding and impairment of autophagy. Apart from the well-reported molecular changes like mitochondrial dysfunction, impaired autophagy/mitophagy and oxidative stress in PD, here we have summarized the recent scientific reports to provide the mechanistic insights on the altered communications between ER, peroxisomes, and lysosomes at mitochondrial contact sites. Furthermore, the manuscript elaborates on the contributions of mitochondrial contact sites and organelles dysfunction to the pathogenesis of PD and suggests potential therapeutic targets.

Unraveling GLUT-mediated transcytosis pathway of glycosylated nanodisks

Glucose transporter (GLUT)-mediated transcytosis has been validated as an efficient method to cross the blood-brain barrier and enhance brain transport of nanomedicines. However, the transcytosis process remains elusive. Glycopeptide-modified nanodisks (Gly-A7R-NDs), which demonstrated high capacity of brain targeting via GLUT-mediated transcytosis in our previous reports, were utilized to better understand the whole transcytosis process. Gly-A7R-NDs internalized brain capillary endothelial cells mainly via GLUT-mediated/clathrin dependent endocytosis and macropinocytosis. The intracellular Gly-A7R-NDs remained intact, and the main excretion route of Gly-A7R-NDs was lysosomal exocytosis. Glycosylation of nanomedicine was crucial in GLUT-mediated transcytosis, while morphology did not affect the efficiency. This study highlights the pivotal roles of lysosomal exocytosis in the process of GLUT-mediated transcytosis, providing a new impetus to development of brain targeting drug delivery by accelerating lysosomal exocytosis.

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.

Modulating lysosomal pH: a molecular and nanoscale materials design perspective

Lysosomes, membrane-bound organelles, play important roles in cellular processes including endocytosis, phagocytosis, and autophagy. Lysosomes maintain cellular homeostasis by generating a highly acidic environment of pH 4.5 - 5.0 and by housing hydrolytic enzymes that degrade engulfed biomolecules. Impairment of lysosomal function, especially in its acidification, is a driving force in the pathogenesis of diseases including neurodegeneration, cancer, metabolic disorders, and infectious diseases. Therefore, lysosomal pH is an attractive and targetable site for therapeutic intervention. Currently, there is a dearth of strategies or materials available to specifically modulate lysosomal acidification. This review focuses on the key aspects of how lysosomal pH is implicated in various diseases and discusses design strategies and molecular or nanoscale agents for lysosomal pH modulation, with the ultimate goal of developing novel therapeutic solutions.

ATP13A2-mediated endo-lysosomal polyamine export counters mitochondrial oxidative stress

Mutations in ATP13A2 cause a spectrum of related neurodegenerative disorders. ATP13A2 is a lysosomal exporter of polyamines that contributes to lysosomal health and controls cellular polyamine content. Conversely, loss of ATP13A2 leads to lysosomal dysfunction, a hallmark of neurodegeneration. Here, we show that polyamines transported by ATP13A2 provide cellular protection by lowering reactive oxygen species (ROS), which may relate to the antioxidant properties of polyamines. Consequently, dysfunctional ATP13A2 sensitizes cells to oxidative stress, which impairs mitochondria, and induces toxicity and cell death. ATP13A2-mediated polyamine transport represents a conserved pathway that protects against mitochondrial oxidative stress. The combined protective impact of ATP13A2 on lysosomal health and mitochondrial oxidative stress may explain why ATP13A2 exerts potent neuroprotective effects.

Recessive loss-of-function mutations in ATP13A2 (PARK9) are associated with a spectrum of neurodegenerative disorders, including Parkinson’s disease (PD). We recently revealed that the late endo-lysosomal transporter ATP13A2 pumps polyamines like spermine into the cytosol, whereas ATP13A2 dysfunction causes lysosomal polyamine accumulation and rupture. Here, we investigate how ATP13A2 provides protection against mitochondrial toxins such as rotenone, an environmental PD risk factor. Rotenone promoted mitochondrial-generated superoxide (MitoROS), which was exacerbated by ATP13A2 deficiency in SH-SY5Y cells and patient-derived fibroblasts, disturbing mitochondrial functionality and inducing toxicity and cell death. Moreover, ATP13A2 knockdown induced an ATF4-CHOP-dependent stress response following rotenone exposure. MitoROS and ATF4-CHOP were blocked by MitoTEMPO, a mitochondrial antioxidant, suggesting that the impact of ATP13A2 on MitoROS may relate to the antioxidant properties of spermine. Pharmacological inhibition of intracellular polyamine synthesis with α-difluoromethylornithine (DFMO) also increased MitoROS and ATF4 when ATP13A2 was deficient. The polyamine transport activity of ATP13A2 was required for lowering rotenone/DFMO-induced MitoROS, whereas exogenous spermine quenched rotenone-induced MitoROS via ATP13A2. Interestingly, fluorescently labeled spermine uptake in the mitochondria dropped as a consequence of ATP13A2 transport deficiency. Our cellular observations were recapitulated in vivo, in a Caenorhabditis elegans strain deficient in the ATP13A2 ortholog catp-6. These animals exhibited a basal elevated MitoROS level, mitochondrial dysfunction, and enhanced stress response regulated by atfs-1, the C. elegans ortholog of ATF4, causing hypersensitivity to rotenone, which was reversible with MitoTEMPO. Together, our study reveals a conserved cell protective pathway that counters mitochondrial oxidative stress via ATP13A2-mediated lysosomal spermine export.

Current Evidence for a Bidirectional Loop Between the Lysosome and Alpha-Synuclein Proteoforms

Cumulative evidence collected in recent decades suggests that lysosomal dysfunction contributes to neurodegenerative diseases, especially if amyloid proteins are involved. Among these, alpha-synuclein (aSyn) that progressively accumulates and aggregates in Lewy bodies is undisputedly a main culprit in Parkinson disease (PD) pathogenesis. Lysosomal dysfunction is evident in brains of PD patients, and mutations in lysosomal enzymes are a major risk factor of PD. At first glance, the role of protein-degrading lysosomes in a disease with pathological protein accumulation seems obvious and should guide the development of straightforward and rational therapeutic targets. However, our review demonstrates that the story is more complicated for aSyn. The protein can possess diverse posttranslational modifications, aggregate formations, and truncations, all of which contribute to a growing known set of proteoforms. These interfere directly or indirectly with lysosome function, reducing their own degradation, and thereby accelerating the protein aggregation and disease process. Conversely, unbalanced lysosomal enzymatic processes can produce truncated aSyn proteoforms that may be more toxic and prone to aggregation. This highlights the possibility of enhancing lysosomal function as a treatment for PD, if it can be confirmed that this approach effectively reduces harmful aSyn proteoforms and does not produce novel, toxic proteoforms.

CNS-Targeting Therapies for Lysosomal Storage Diseases: Current Advances and Challenges

During the past decades, several therapeutic approaches have been developed and made rapidly available for many patients afflicted with lysosomal storage disorders (LSDs), inborn organelle disorders with broad clinical manifestations secondary to the progressive accumulation of undegraded macromolecules within lysosomes. These conditions are individually rare, but, collectively, their incidence ranges from 1 in 2,315 to 7,700 live-births. Most LSDs are manifested by neurological symptoms or signs, including developmental delay, seizures, acroparesthesia, motor weakness, and extrapyramidal signs. The chronic and later-onset clinical forms are at one end of the continuum spectrum and are characterized by a subtle and slow progression of neurological symptoms. Due to its inherent physiological properties, unfortunately, the blood-brain barrier (BBB) constitutes a significant obstacle for current and upcoming therapies to achieve the central nervous system (CNS) and treat neurological problems so prevalent in these conditions. To circumvent this limitation, several strategies have been developed to make the therapeutic agent achieve the CNS. This narrative will provide an overview of current therapeutic strategies under development to permeate the BBB, and address and unmet need for treatment of the progressive neurological manifestations, which are so prevalent in these inherited lysosomal disorders.

Autophagy and Redox Homeostasis in Parkinson's: A Crucial Balancing Act

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated primarily from endogenous biochemical reactions in mitochondria, endoplasmic reticulum (ER), and peroxisomes. Typically, ROS/RNS correlate with oxidative damage and cell death; however, free radicals are also crucial for normal cellular functions, including supporting neuronal homeostasis. ROS/RNS levels influence and are influenced by antioxidant systems, including the catabolic autophagy pathways. Autophagy is an intracellular lysosomal degradation process by which invasive, damaged, or redundant cytoplasmic components, including microorganisms and defunct organelles, are removed to maintain cellular homeostasis. This process is particularly important in neurons that are required to cope with prolonged and sustained operational stress. Consequently, autophagy is a primary line of protection against neurodegenerative diseases. Parkinson's is caused by the loss of midbrain dopaminergic neurons (mDANs), resulting in progressive disruption of the nigrostriatal pathway, leading to motor, behavioural, and cognitive impairments. Mitochondrial dysfunction, with associated increases in oxidative stress, and declining proteostasis control, are key contributors during mDAN demise in Parkinson's. In this review, we analyse the crosstalk between autophagy and redoxtasis, including the molecular mechanisms involved and the detrimental effect of an imbalance in the pathogenesis of Parkinson's.

Nanomaterial-mediated autophagy: coexisting hazard and health benefits in biomedicine

BACKGROUND

Widespread biomedical applications of nanomaterials (NMs) bring about increased human exposure risk due to their unique physicochemical properties. Autophagy, which is of great importance for regulating the physiological or pathological activities of the body, has been reported to play a key role in NM-driven biological effects both in vivo and in vitro. The coexisting hazard and health benefits of NM-mediated autophagy in biomedicine are nonnegligible and require our particular concerns.

MAIN BODY

We collected research on the toxic effects related to NM-mediated autophagy both in vivo and in vitro. Generally, NMs can be delivered into animal models through different administration routes, or internalized by cells through different uptake pathways, exerting varying degrees of damage in tissues, organs, cells, and organelles, eventually being deposited in or excreted from the body. In addition, other biological effects of NMs, such as oxidative stress, inflammation, necroptosis, pyroptosis, and ferroptosis, have been associated with autophagy and cooperate to regulate body activities. We therefore highlight that NM-mediated autophagy serves as a double-edged sword, which could be utilized in the treatment of certain diseases related to autophagy dysfunction, such as cancer, neurodegenerative disease, and cardiovascular disease. Challenges and suggestions for further investigations of NM-mediated autophagy are proposed with the purpose to improve their biosafety evaluation and facilitate their wide application. Databases such as PubMed and Web of Science were utilized to search for relevant literature, which included all published, Epub ahead of print, in-process, and non-indexed citations.

CONCLUSION

In this review, we focus on the dual effect of NM-mediated autophagy in the biomedical field. It has become a trend to use the benefits of NM-mediated autophagy to treat clinical diseases such as cancer and neurodegenerative diseases. Understanding the regulatory mechanism of NM-mediated autophagy in biomedicine is also helpful for reducing the toxic effects of NMs as much as possible.

Significance of cytosolic cathepsin D in Alzheimer's disease pathology: Protective cellular effects of PLGA nanoparticles against β-amyloid-toxicity

BACKGROUND

Evidence suggests that amyloid β (Aβ) peptides play an important role in the degeneration of neurons during the development of Alzheimer's disease (AD), the prevalent cause of dementia affecting the elderly. The endosomal-lysosomal system, which acts as a major site for Aβ metabolism, has been shown to exhibit abnormalities in vulnerable neurons of the AD brain, reflected by enhanced levels/expression of lysosomal enzymes including cathepsin D (CatD). At present, the implication of CatD in selective neuronal vulnerability in AD pathology remains unclear.

METHODS

We evaluated the role of CatD in the degeneration of neurons in Aβ-treated cultures, transgenic AD mouse model (that is 5xFAD) and post mortem AD brain samples.

RESULTS

Our results showed that Aβ_1-42 -induced toxicity in cortical cultured neurons is associated with impaired lysosomal integrity, enhanced levels of carbonylated proteins and tau phosphorylation. The cellular and cytosolic levels/activity of CatD are also elevated in cultured neurons following exposure to Aβ peptide. Additionally, we observed that CatD cellular and subcellular levels/activity are increased in the affected cortex, but not in the unaffected cerebellum, of 5xFAD mice and post mortem AD brains. Interestingly, treatment of cultured neurons with nanoparticles PLGA, which targets lysosomal system, attenuated Aβ toxicity by reducing the levels of carbonylated proteins, tau phosphorylation and the level/distribution/activity of CatD.

CONCLUSION

Our study reveals that increased cytosolic level/activity of CatD play an important role in determining neuronal vulnerability in AD. Additionally, native PLGA can protect neurons against Aβ toxicity by restoring lysosomal membrane integrity, thus signifying its implication in attenuating AD.

Carbon dots for lysosome targeting and imaging of lysosomal pH and Cys/Hcy in living cells

The abnormal concentrations of both biothiols and pH in lysosomes are seriously related to many major diseases, such as Parkinson's and Alzheimer's diseases. Up to now, there are few reports that clearly illustrate the relationship between lysosomal pH and biothiols via fluorescence assay. Herein, novel carbon dots (Scy-CDs) are prepared with good water dispersibility and excellent photostability, and a large Stokes shift of 106 nm is exhibited under an excitation wavelength of 450 nm. The remarkable pH-dependent behavior of Scy-CDs is presented with the fluorescence quenching based on the donor-excited photoinduced electron transfer (d-PET) process. The pKa value is 5.30, which is in good agreement with the range of the normal and abnormal lysosomal pH. Upon the addition of cysteine (Cys) or homocysteine (Hcy), the d-PET process is effectively inhibited with fluorescence recovery totally. The significant co-localization of Scy-CDs with Lyso-Tracker Deep Red in HEp-2 cells and the Pearson correlation coefficient 0.88 strongly suggest that the Scy-CDs can target lysosomal pH and Cys/Hcy in living cells.

The emerging roles of vacuolar-type ATPase-dependent Lysosomal acidification in neurodegenerative diseases

Background

Lysosomes digest extracellular material from the endocytic pathway and intracellular material from the autophagic pathway. This process is performed by the resident hydrolytic enzymes activated by the highly acidic pH within the lysosomal lumen. Lysosome pH gradients are mainly maintained by the vacuolar (H⁺) ATPase (or V-ATPase), which pumps protons into lysosomal lumen by consuming ATP. Dysfunction of V-ATPase affects lysosomal acidification, which disrupts the clearance of substrates and leads to many disorders, including neurodegenerative diseases.

Main body

As a large multi-subunit complex, the V-ATPase is composed of an integral membrane V0 domain involved in proton translocation and a peripheral V1 domain catalyzing ATP hydrolysis. The canonical functions of V-ATPase rely on its H⁺-pumping ability in multiple vesicle organelles to regulate endocytic traffic, protein processing and degradation, synaptic vesicle loading, and coupled transport. The other non-canonical effects of the V-ATPase that are not readily attributable to its proton-pumping activity include membrane fusion, pH sensing, amino-acid-induced activation of mTORC1, and scaffolding for protein-protein interaction. In response to various stimuli, V-ATPase complex can reversibly dissociate into V1 and V0 domains and thus close ATP-dependent proton transport. Dysregulation of pH and lysosomal dysfunction have been linked to many human diseases, including neurodegenerative disorders such as Alzheimer disease, Parkinson’s disease, amyotrophic lateral sclerosis as well as neurodegenerative lysosomal storage disorders.

Conclusion

V-ATPase complex is a universal proton pump and plays an important role in lysosome acidification in all types of cells. Since V-ATPase dysfunction contributes to the pathogenesis of multiple neurodegenerative diseases, further understanding the mechanisms that regulate the canonical and non-canonical functions of V-ATPase will reveal molecular details of disease process and help assess V-ATPase or molecules related to its regulation as therapeutic targets.

The Application of Nanomaterials in Cell Autophagy

Autophagy is defined as separation and degradation of cytoplasmic components through autophagosomes, which plays an essential part in physiological and pathological events. Hence it is also essential for cellular homeostasis. Autophagy disorder may bring about the failure of stem cells to maintain the fundamental transformation and metabolism of cell components. However, for cancer cells, the disorder of autophagy is a feasible antitumor idea. Nanoparticles, referring to particles of the size range 1-100 nanometers, are appearing as a category of autophagy regulators. These nanoparticles may revolutionize and broaden the therapeutic strategies of many diseases, including neurodegenerative diseases, tumors, muscle disease, and so on. Researches of autophagy-induced nanomaterials mainly focus on silver particles, gold particles, silicon particles, and rare earth oxides. But in recent years, more and more materials have been found to regulate autophagy, such as nano-nucleic acid materials, nanofiber scaffolds, quantum dots, and so on. The review highlights that various kinds of nanoparticles have the power to regulate autophagy intensity in stem cells of interest and further control biological behaviors, which may become a reliable treatment choice for disease therapy.

Synthesis and Intracellular Uptake of Rhodamine-Nucleolipid Conjugates into a Nanoemulsion Vehicle

Neurodegenerative diseases represent some of the greatest challenges for both basic science and clinical medicine. Due to their prevalence and the lack of known biochemical-based treatments, these complex pathologies result in an increasing societal cost. Increasing genetic and neuropathological evidence indicates that lysosomal impairment may be a common factor linking these diseases, demanding the development of therapeutic strategies aimed at restoring the lysosomal function. Here, we propose the design and synthesis of a nucleolipid conjugate as a nonviral chemical nanovector to specifically target neuronal cells and intracellular organelles. Herein, thymidine, appropriately substituted to increase its lipophilicity, was used as a model nucleoside and a fluorophore moiety, covalently bound to the nucleoside, allowed the monitoring of nucleolipid internalization in vitro. To improve nucleolipid protection and cellular uptake, these conjugates were formulated in nanoemulsions. In vitro biological assays demonstrated cell uptake- and internalization-associated colocalization with lysosomal markers. Overall, this nucleolipid-nanoemulsion-based formulation represents a promising drug-delivery tool to target the central nervous system, able to deliver drugs to restore the impaired lysosomal function.

Targeting with nanoparticles for the therapeutic treatment of brain diseases

Brain diseases including neurodegenerative disorders and tumours are among the most serious health problems, degrading the quality of life and causing massive economic cost. Nanoparticles that load and deliver drugs and genes have been intensively studied for the treatment of brain diseases, and have demonstrated some biological effects in various animal models. Among other efforts taken in the nanoparticle development, targeting of blood brain barrier, specific cell type or local intra-/extra-cellular space is an important strategy to enhance the therapeutic efficacy of the nanoparticle delivery systems. This review underlies the targeting issue in the nanoparticle development for the treatment of brain diseases, taking key exemplar studies carried out in various in vivo models.

Acidifying Endolysosomes Prevented Low-Density Lipoprotein-Induced Amyloidogenesis

Cholesterol dyshomeostasis has been linked to the pathogenesis of sporadic Alzheimer's disease (AD). In furthering the understanding of mechanisms by which increased levels of circulating cholesterol augments the risk of developing sporadic AD, others and we have reported that low-density lipoprotein (LDL) enters brain parenchyma by disrupting the blood-brain barrier and that endolysosome de-acidification plays a role in LDL-induced amyloidogenesis in neurons. Here, we tested the hypothesis that endolysosome de-acidification was central to amyloid-β (Aβ) generation and that acidifying endolysosomes protects against LDL-induced increases in Aβ levels in neurons. We demonstrated that LDL, but not HDL, de-acidified endolysosomes and increased intraneuronal and secreted levels of Aβ. ML-SA1, an agonist of endolysosome-resident TRPML1 channels, acidified endolysosomes, and TRPML1 knockdown attenuated ML-SA1-induced endolysosome acidification. ML-SA1 blocked LDL-induced increases in intraneuronal and secreted levels of Aβ as well as Aβ accumulation in endolysosomes, prevented BACE1 accumulation in endolysosomes, and decreased BACE1 activity levels. LDL downregulated TRPML1 protein levels, and TRPML1 knockdown worsens LDL-induced increases in Aβ. Our findings suggest that endolysosome acidification by activating TRPML1 may represent a protective strategy against sporadic AD.

β2-adrenergic Agonists Rescue Lysosome Acidification and Function in PSEN1 Deficiency by Reversing Defective ER-to-lysosome Delivery of ClC-7

Lysosomal dysfunction is considered pathogenic in Alzheimer disease (AD). Loss of presenilin-1 (PSEN1) function causing AD impedes acidification via defective vacuolar ATPase (vATPase) V0a1 subunit delivery to lysosomes. We report that isoproterenol (ISO) and related β2-adrenergic agonists reacidify lysosomes in PSEN1 Knock out (KO) cells and fibroblasts from PSEN1 familial AD patients, which restores lysosomal proteolysis, calcium homeostasis, and normal autophagy flux. We identify a novel rescue mechanism involving Portein Kinase A (PKA)-mediated facilitation of chloride channel-7 (ClC-7) delivery to lysosomes which reverses markedly lowered chloride (Cl^-) content in PSEN1 KO lysosomes. Notably, PSEN1 loss of function impedes Endoplasmic Reticulum (ER)-to-lysosome delivery of ClC-7. Transcriptomics of PSEN1-deficient cells reveals strongly downregulated ER-to-lysosome transport pathways and reversibility by ISO, thus accounting for lysosomal Cl^- deficits that compound pH elevation due to deficient vATPase and its rescue by β2-adrenergic agonists. Our findings uncover a broadened PSEN1 role in lysosomal ion homeostasis and novel pH modulation of lysosomes through β2-adrenergic regulation of ClC-7, which can potentially be modulated therapeutically.

Mucopolysaccharidosis IVA: Diagnosis, Treatment, and Management

Mucopolysaccharidosis type IVA (MPS IVA, or Morquio syndrome type A) is an inherited metabolic lysosomal disease caused by the deficiency of the N-acetylglucosamine-6-sulfate sulfatase enzyme. The deficiency of this enzyme accumulates the specific glycosaminoglycans (GAG), keratan sulfate, and chondroitin-6-sulfate mainly in bone, cartilage, and its extracellular matrix. GAG accumulation in these lesions leads to unique skeletal dysplasia in MPS IVA patients. Clinical, radiographic, and biochemical tests are needed to complete the diagnosis of MPS IVA since some clinical characteristics in MPS IVA are overlapped with other disorders. Early and accurate diagnosis is vital to optimizing patient management, which provides a better quality of life and prolonged life-time in MPS IVA patients. Currently, enzyme replacement therapy (ERT) and hematopoietic stem cell transplantation (HSCT) are available for patients with MPS IVA. However, ERT and HSCT do not have enough impact on bone and cartilage lesions in patients with MPS IVA. Penetrating the deficient enzyme into an avascular lesion remains an unmet challenge, and several innovative therapies are under development in a preclinical study. In this review article, we comprehensively describe the current diagnosis, treatment, and management for MPS IVA. We also illustrate developing future therapies focused on the improvement of skeletal dysplasia in MPS IVA.

ATP13A2 deficiency disrupts lysosomal polyamine export

ATP13A2 (PARK9) is a late endolysosomal transporter that is genetically implicated in a spectrum of neurodegenerative disorders, including Kufor-Rakeb syndrome-a parkinsonism with dementia¹-and early-onset Parkinson's disease². ATP13A2 offers protection against genetic and environmental risk factors of Parkinson's disease, whereas loss of ATP13A2 compromises lysosomes³. However, the transport function of ATP13A2 in lysosomes remains unclear. Here we establish ATP13A2 as a lysosomal polyamine exporter that shows the highest affinity for spermine among the polyamines examined. Polyamines stimulate the activity of purified ATP13A2, whereas ATP13A2 mutants that are implicated in disease are functionally impaired to a degree that correlates with the disease phenotype. ATP13A2 promotes the cellular uptake of polyamines by endocytosis and transports them into the cytosol, highlighting a role for endolysosomes in the uptake of polyamines into cells. At high concentrations polyamines induce cell toxicity, which is exacerbated by ATP13A2 loss due to lysosomal dysfunction, lysosomal rupture and cathepsin B activation. This phenotype is recapitulated in neurons and nematodes with impaired expression of ATP13A2 or its orthologues. We present defective lysosomal polyamine export as a mechanism for lysosome-dependent cell death that may be implicated in neurodegeneration, and shed light on the molecular identity of the mammalian polyamine transport system.

Differential effects of N-TiO2 nanoparticle and its photo-activated form on autophagy and necroptosis in human melanoma A375 cells

The manipulation of autophagy provides a new opportunity for highly effective anticancer therapies. Recently, we showed that photodynamic therapy (PDT) with nitrogen-doped titanium dioxide (N-TiO₂ ) nanoparticles (NPs) could promote the reactive oxygen species (ROS)-dependent autophagy in leukemia cells. However, the differential autophagic effects of N-TiO₂ NPs in the dark and light conditions and the potential of N-TiO_2- based PDT for the treatment of melanoma cells remain unknown. Here we show that depending on the visible-light condition, the autophagic response of human melanoma A375 cells to N-TiO₂ NPs switches between two different statuses (ie., flux or blockade) with the opposite outcomes (ie., survival or death). Mechanistically, low doses of N-TiO₂ NPs (1-100 µg/ml) stimulate a nontoxic autophagy flux response in A375 cells, whereas their photo-activation leads to the impairment of the autophagosome-lysosome fusion, the blockade of autophagy flux and consequently the induction of RIPK1-mediated necroptosis via ROS production. These results confirm that photo-controllable autophagic effects of N-TiO₂ NPs can be utilized for the treatment of cancer, particularly melanoma.

Autophagy and Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease characterized by motor system dysfunction. The etiology of PD has been linked with aging, environmental toxins and genetic mutation, while molecular pathogenesis of PD includes various factors, such as impaired protein homeostasis, oxidative stress, mitochondria dysfunction, synaptic transmission impairment, calcium homeostasis imbalance, prion-like α-synuclein transmission and neuron inflammation. Autophagy is a conserved bulk degradation process to maintain cellular homeostasis. Impairment of autophagy has been reported to be involved in the pathogenesis of PD. Coding proteins of several PD-related genes, such as SNCA, LRRK2, GBA, ATP13A2, VPS35 and FBXO7, are implicated in or affected by autophagy process. Furthermore, various pathogenic events during PD directly or indirectly interfere with the autophagy pathway, and dysregulation of autophagy has been observed in different neurotoxic PD models. Autophagy has been regarded as a potential therapeutic target for PD treatment. Indeed, modulations of autophagy-regulated genes (BECN1 and TFEB) expression exerted neuroprotection against PD models, and various autophagy regulators, such as rapamycin, trehalose, lysosome modulators and other small molecule autophagy inducers, have displayed neuroprotective effects in experimental PD models. Taken together, autophagy dysfunction has been implicated in the pathogenesis of PD, and pharmacological modulation of autophagy may be a new therapeutic strategy for the PD treatment.

A novel role of UBQLNs (ubiquilins) in regulating autophagy, MTOR signaling and v-ATPase function

UBQLNs (ubiquilins) are highly conserved proteins across species, characterized by interactions with proteasomes and ubiquitinated proteins via UBA and UBL domains, respectively. The role of UBQLNs as chaperone proteins of the ubiquitin-proteasome system (UPS) is well-defined; however, the connections between UBQLNs and autophagy remain unclear. A recent study published in Nature Cell Biology from Dr. Hugo J. Bellen's lab showed a novel role of UBQLNs in macroautophagy/autophagy regulation through v-ATPase-MTOR signaling using Drosophila and mammalian neuronal cells. Notably, the highlighted article also investigated the autophagy phenotype of a common amyotrophic lateral sclerosis (ALS)-associated mutation in the gene encoding UBQLN2, demonstrating the contribution of abnormal v-ATPase-MTOR-mediated autophagy in ALS pathogenesis.

IFNα Impairs Autophagic Degradation of mtDNA Promoting Autoreactivity of SLE Monocytes in a STING-Dependent Fashion

Interferon α (IFNα) is a prompt and efficient orchestrator of host defense against nucleic acids but upon chronicity becomes a potent mediator of autoimmunity. Sustained IFNα signaling is linked to pathogenesis of systemic lupus erythematosus (SLE), an incurable autoimmune disease characterized by aberrant self-DNA sensing that culminates in anti-DNA autoantibody-mediated pathology. IFNα instructs monocytes differentiation into autoinflammatory dendritic cells (DCs) than potentiates the survival and expansion of autoreactive lymphocytes, but the molecular mechanism bridging sterile IFNα-danger alarm with adaptive response against self-DNA remains elusive. Herein, we demonstrate IFNα-mediated deregulation of mitochondrial metabolism and impairment of autophagic degradation, leading to cytosolic accumulation of mtDNA that is sensed via stimulator of interferon genes (STING) to promote induction of autoinflammatory DCs. Identification of mtDNA as a cell-autonomous enhancer of IFNα signaling underlines the significance of efficient mitochondrial recycling in the maintenance of peripheral tolerance. Antioxidant treatment and metabolic rescue of autolysosomal degradation emerge as drug targets in SLE and other IFNα-related pathologies.

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IFNα obstructs autophagic flux in SLE monocytes through lysosomal alkalinization

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IFNα signaling induces oxidative stress that affects lysosomal pH through mTOR

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Impaired clearance of damaged mitochondria leads to cytosolic mtDNA accumulation

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Autophagic escape of mtDNA is sensed by STING and primes monocytes autoimmunity

Lysosomal Dysfunction at the Centre of Parkinson's Disease and Frontotemporal Dementia/Amyotrophic Lateral Sclerosis

Parkinson's disease (PD) and frontotemporal dementia/amyotrophic lateral sclerosis (FTD/ALS) are insidious and incurable neurodegenerative diseases that represent a significant burden to affected individuals, caregivers, and an ageing population. Both PD and FTD/ALS are defined at post mortem by the presence of protein aggregates and the loss of specific subsets of neurons. We examine here the crucial role of lysosome dysfunction in these diseases and discuss recent evidence for converging mechanisms. This review draws upon multiple lines of evidence from genetic studies, human tissue, induced pluripotent stem cells (iPSCs), and animal models to argue that lysosomal failure is a primary mechanism of disease, rather than merely reflecting association with protein aggregate end-points. This review provides compelling rationale for targeting lysosomes in future therapeutics for both PD and FTD/ALS.

Rifampicin attenuates rotenone-treated microglia inflammation via improving lysosomal function

Mounting evidence suggests that lysosome dysfunction promotes the progression of several neurodegenerative diseases via hampering autophagy flux. While regulation of autophagy in microglia may affect chronic inflammation involved in Parkinson's disease (PD). Our previous studies have reported rifampicin inhibits rotenone-induced microglia inflammation by enhancing autophagy, however the precise mechanism remains unclear. Human microglia (HM) cells were pretreated with 100 μM rifampicin for 2 h followed by exposure to 0.1 μM rotenone. We found that rifampicin pretreatment suppressed the gene expression of IL-1β and IL-6 via inhibiting activation of JNK after rotenone induction, but the anti-inflammatory effect of rifampicin was reversed by chloroquine. Moreover, rifampicin pretreatment not only improved the ratio of LC3-II/LC3-I in rotenone-treated cells, but also increased autolysosomes and decreased autophagosomes in RFP-GFP-LC3B transfected HM cells exposed to rotenone, thus indicating rifampicin improves autophagy flux in rotenone-treated HM cells. Finally, we verified rifampicin pretreatment enhanced ATP6V0A1 expression when compared to that exposed to rotenone alone. ATP6V0A1 knockdown inhibited the effect of rifampicin on maintaining lysosome acidification and autophagosome-lysosome fusion in rotenone-treated microglia. Taken together, our results indicated that rifampicin attenuates rotenone-induced microglia inflammation partially via elevating ATP6V0A1. Modulation of lysosomal function by rifampicin may be a novel therapeutic strategy for PD.

UVA-induced photoaging inhibits autophagic degradation by impairing lysosomal function in dermal fibroblasts

Autophagy has been associated with a variety of diseases especially aging. Human dermal fibroblasts (HDFs) can internalize and then degrade elastin, collagen and advanced glycation end products (AGEs) in lysosomes, which plays prominent roles in extracellular matrix homeostasis and AGEs removal in the dermis. Although autophagy has been reported to be decreased in photoaged fibroblasts, the underlying mechanism and its relevance to photoaging remain elusive. Here, we showed that GFP-LC3 puncta per cell, LC3Ⅰ/Ⅱ conversion and p62 expression were significantly increased, whereas beclin1 expression was not altered in UVA-induced photoaged fibroblasts compared with non-photoaged control. Moreover, autophagic flux was not significantly affected by chloroquine treatment, but was remarkably induced by rapamycin treatment in photoaged fibroblasts, suggesting that UVA-induced photoaging might inhibit autophagy at the degradation stage. Further lysosomal function studies demonstrated that degradation of formed autophagosomes, LC3Ⅱprotein and DQ-Green BSA was all dramatically decreased in photoaged fibroblasts. LysoSensor yellow/blue DND 160 staining and flow cytometry assays demonstrated that photoaging obviously attenuated lysosomal acidification. Also, decreased expression of cathepsin B, L and D was found in photoaged fibroblasts. These data suggest that lowered lysosomal acidity and decreased cathepsins expression might contribute to the inhibition of autophagic degradation, which might be crucial in the development of photoaging through impairing intracellular degradation.

Biodegradable PLGA nanoparticles restore lysosomal acidity and protect neural PC-12 cells against mitochondrial toxicity

Exposure of mitochondrial parkinsonian neurotoxin 1-methyl-4-phenylpyridinium ion (MPP+) to PC-12 cells results in significant cell death, decreases lysosomal acidity, and inhibits autophagic flux. Biodegradable poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) of ≈100 nm diameter localize to the lysosome, degrade, and subsequently release their acidic components to acidify the local lysosomal environment. The performance of PLGA NPs with different lysosomal pH modulating capabilities is investigated in PC-12 cells under MPP+ induced mitochondrial toxicity. PLGA NPs perform in a compositional dependent manner, where NPs with a higher glycolic acid to lactic acid ratio content degrade faster, and yield greater degrees of lysosomal pH modulation as well as autophagic flux modulation in PC-12 cells under MPP+ insult. These results show that slight compositional changes of the polymeric NP give rise to differing degrees of lysosomal acidification in PC-12 cells and afford improved cellular degradative activity.