Lysosomal physiology

Recent Development of Lysosome-Targeted Organic Fluorescent Probes for Reactive Oxygen Species

Reactive oxygen species (ROS) are extremely important for various biological functions. Lysosome plays key roles in cellular metabolism and has been known as the stomach of cells. The abnormalities and malfunctioning of lysosomal function are associated with many diseases. Accordingly, the quantitative monitoring and real-time imaging of ROS in lysosomes are of great interest. In recent years, with the advancement of fluorescence imaging, fluorescent ROS probes have received considerable interest in the biomedical field. Thus far, considerable efforts have been undertaken to create synthetic fluorescent probes for sensing ROS in lysosomes; however, specific review articles on this topic are still lacking. This review provides a general introduction to fluorescence imaging technology, the sensing mechanisms of fluorescent probes, lysosomes, and design strategies for lysosome-targetable fluorescent ROS probes. In addition, the latest advancements in organic small-molecule fluorescent probes for ROS detection within lysosomes are discussed. Finally, the main challenges and future perspectives for developing effective lysosome-targetable fluorescent ROS probes for biomedical applications are presented.

Increased expression or activation of TRPML1 reduces hepatic storage of toxic Z alpha-1 antitrypsin

Mutant Z alpha-1 antitrypsin (ATZ) accumulates in globules in the liver and is the prototype of proteotoxic hepatic disease. Therapeutic strategies aiming at clearance of polymeric ATZ are needed. Transient receptor potential mucolipin-1 (TRPML1) is a lysosomal Ca2+ channel that maintains lysosomal homeostasis. In this study, we show that by increasing lysosomal exocytosis, TRPML1 gene transfer or small-molecule-mediated activation of TRPML1 reduces hepatic ATZ globules and fibrosis in PiZ transgenic mice that express the human ATZ. ATZ globule clearance induced by TRPML1 occurred without increase in autophagy or nuclear translocation of TFEB. Our results show that targeting TRPML1 and lysosomal exocytosis is a novel approach for treatment of the liver disease due to ATZ and potentially other diseases due to proteotoxic liver storage.

The role of redox-mediated lysosomal dysfunction and therapeutic strategies

Redox homeostasis refers to the dynamic equilibrium between oxidant and reducing agent in the body which plays a crucial role in maintaining normal physiological activities of the body. The imbalance of redox homeostasis can lead to the development of various human diseases. Lysosomes regulate the degradation of cellular proteins and play an important role in influencing cell function and fate, and lysosomal dysfunction is closely associated with the development of various diseases. In addition, several studies have shown that redox homeostasis plays a direct or indirect role in regulating lysosomes. Therefore, this paper systematically reviews the role and mechanisms of redox homeostasis in the regulation of lysosomal function. Therapeutic strategies based on the regulation of redox exerted to disrupt or restore lysosomal function are further discussed. Uncovering the role of redox in the regulation of lysosomes helps to point new directions for the treatment of many human diseases.

TMEM175: A lysosomal ion channel associated with neurological diseases

Lysosomes are acidic intracellular organelles with autophagic functions that are critical for protein degradation and mitochondrial homeostasis, while abnormalities in lysosomal physiological functions are closely associated with neurological disorders. Transmembrane protein 175 (TMEM175), an ion channel in the lysosomal membrane that is essential for maintaining lysosomal acidity, has been proven to coordinate with V-ATPase to modulate the luminal pH of the lysosome to assist the digestion of abnormal proteins and organelles. However, there is considerable controversy about the characteristics of TMEM175. In this review, we introduce the research progress on the structural, modulatory, and functional properties of TMEM175, followed by evidence of its relevance for neurological disorders. Finally, we discuss the potential value of TMEM175 as a therapeutic target in the hope of providing new directions for the treatment of neurodegenerative diseases.

Effect of pharmacological heart failure drugs and gene therapy on Danon's cardiomyopathy

Danon disease is a rare X-linked genetic disease resulting from LAMP2 mutations leading to defective lysosomal function. Heart failure is the main causes of morbidity and mortality. Mice with an LAMP2-exon-6-deletion (L2Δ6), develop cardiac hypertrophy followed by dilated cardiomyopathy, in association with accumulation of autophagosomes, fibrosis and oxidative stress. We investigated the effect of drugs used to treat heart failure and of LAMP2 gene therapy on the phenotype, molecular markers and ROS in LAMP2 cardiomyopathy. L2Δ6 mice were treated with Angiotensin II, Ramipril, Metoprolol or Spironolactone. Gene therapy was delivered by IP injection of Adeno-associated-virus (AAV9) -LAMP2 vector to neonates ("AAVLAMP2-Prevention"), or at 15 weeks of age ("AAVLAMP2-Treatment"). Angiotensin II markedly aggravated the cardiac phenotype. Ramipril and Spironolactone were effective in attenuating left ventricular hypertrophy and preserving the systolic function. Cardiac protection was associated with decreased autophagosome accumulation, reduced fibrosis and oxidative stress. Gene therapy effectively attenuated autophagosome accumulation and ROS in L2Δ6 hearts, lowering troponin release to nearly normal levels. AAVLAMP2-Prevention protected against systolic dysfunction and decreased hypertrophy. AAVLAMP2-Treatment prevented ventricular dilatation and dysfunction but had no effect on wall thickness. We conclude that RAAS inhibitors are highly effective against cardiomyopathy progression in an experimental mouse model of Danon's and shall be considered in human patients for this purpose until novel therapies become clinically available.

Lysosomal quality control: molecular mechanisms and therapeutic implications

Lysosomes are essential catabolic organelles with an acidic lumen and dozens of hydrolytic enzymes. The detrimental consequences of lysosomal leakage have been well known since lysosomes were discovered during the 1950s. However, detailed knowledge of lysosomal quality control mechanisms has only emerged relatively recently. It is now clear that lysosomal leakage triggers multiple lysosomal quality control pathways that replace, remove, or directly repair damaged lysosomes. Here, we review how lysosomal damage is sensed and resolved in mammalian cells, with a focus on the molecular mechanisms underlying different lysosomal quality control pathways. We also discuss the clinical implications and therapeutic potential of these pathways.

Role of the Lactide:Glycolide Ratio in PLGA Nanoparticle Stability and Release under Lysosomal Conditions for Enzyme Replacement Therapy of Lysosomal Storage Disorders

Prior studies demonstrated that encapsulation in poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) enhanced the delivery of enzymes used for replacement therapy (ERT) of lysosomal storage disorders (LSDs). This study examined how the copolymer lactide:glycolide ratio impacts encapsulation, physicochemical characteristics, stability, and release under lysosomal conditions. Hyaluronidase, deficient in mucopolysaccharidosis IX, was encapsulated in NPs synthesized using 50:50, 60:40, or 75:25 lactide:glycolide copolymers. All NPs had diameters compatible with cellular transport (≤168 nm) and polydispersity indexes (≤0.16) and ζ-potentials (≤-35 mV) compatible with colloidal stability. Yet, their encapsulation efficiency varied, with 75:25 NPs and 60:40 NPs having the lowest and highest EE, respectively (15% vs. 28%). Under lysosomal conditions, the 50:50 copolymer degraded fastest (41% in 1 week), as expected, and the presence of a targeting antibody coat did not alter this result. Additionally, 60:40 NPs destabilized fastest (<1 week) because of their smaller diameter, and 75:25 NPs did not destabilize in 4 weeks. All formulations presented burst release under lysosomal conditions (56-78% of the original load within 30 min), with 50:50 and 60:40 NPs releasing an additional small fraction after week 1. This provided 4 weeks of sustained catalytic activity, sufficient to fully degrade a substrate. Altogether, the 60:40 NP formulation is preferred given its higher EE, and 50:50 NPs represent a valid alternative, while the highest stability of 75:25 NPs may impair lysosomes. These results can guide future studies aiming to translate PLGA NP-based ERT for this and other LSDs.

A Comparative Study on the Lysosomal Cation Channel TMEM175 Using Automated Whole-Cell Patch-Clamp, Lysosomal Patch-Clamp, and Solid Supported Membrane-Based Electrophysiology: Functional Characterization and High-Throughput Screening Assay Development

The lysosomal cation channel TMEM175 is a Parkinson's disease-related protein and a promising drug target. Unlike whole-cell automated patch-clamp (APC), lysosomal patch-clamp (LPC) facilitates physiological conditions, but is not yet suitable for high-throughput screening (HTS) applications. Here, we apply solid supported membrane-based electrophysiology (SSME), which enables both direct access to lysosomes and high-throughput electrophysiological recordings. In SSME, ion translocation mediated by TMEM175 is stimulated using a concentration gradient at a resting potential of 0 mV. The concentration-dependent K+ response exhibited an I/c curve with two distinct slopes, indicating the existence of two conducting states. We measured H+ fluxes with a permeability ratio of PH/PK = 48,500, which matches literature findings from patch-clamp studies, validating the SSME approach. Additionally, TMEM175 displayed a high pH dependence. Decreasing cytosolic pH inhibited both K+ and H+ conductivity of TMEM175. Conversely, lysosomal pH and pH gradients did not have major effects on TMEM175. Finally, we developed HTS assays for drug screening and evaluated tool compounds (4-AP, Zn as inhibitors; DCPIB, arachidonic acid, SC-79 as enhancers) using SSME and APC. Additionally, we recorded EC50 data for eight blinded TMEM175 enhancers and compared the results across all three assay technologies, including LPC, discussing their advantages and disadvantages.

Bi-functional particles for real-time phagosome acidification and proteolysis multiplex assay in macrophages

Phagosome acidification and proteolysis are essential processes in the immune response to contain and eliminate pathogens. In recent years, there has been an increased desire for a rapid and accurate method of assessing these processes in real-time. Here, we outline the development of a multiplexed assay that allows simultaneous monitoring of phagosome acidification and proteolysis in the same sample using silica beads conjugated to pHrodo and DQ BSA. We describe in detail how to prepare the bi-functional particles and show proof of concept using differentially activated macrophages. This multiplexed spectrophotometric assay allows rapid and accurate assessment of phagosome acidification and proteolysis in real-time and could provide valuable information for understanding the immune response to pathogen invasion.

Glutathione displacement assay based on a fluorescent Au(I) complex

Glutathione (GSH) is an essential molecule that plays a pivotal role in maintaining intracellular redox homeostasis, as well as other physiological processes. However, the chemical mechanisms underlying the GSH-induced processes remain insufficiently understood due to the lack of appropriate detection tools. Fluorescence GSH imaging can serve as a useful principle for the rapid, convenient, and non-destructive detection of GSH in living organisms. In this study, we developed a fluorescent GSH probe based on a linear, homoleptic Au(I) complex with two 1,3-diphenylbenzimidazolium carbene ligands. The Au(I) complex produced a fluorescence turn-on response to GSH. Fluorescence GSH signaling was characterized with a short response time of a few seconds. The rapid response was attributed to the displacement of the carbene ligand with GSH, which involved a labile inner-sphere coordination interaction. Finally, we demonstrated the biological utility of our GSH probe by unambiguously discriminating between different GSH levels in normal and senescent preadipocytes.

Distinct Cleavage Properties of Cathepsin B Compared to Cysteine Cathepsins Enable the Design and Validation of a Specific Substrate for Cathepsin B over a Broad pH Range

The biological and pathological functions of cathepsin B occur in acidic lysosomes and at the neutral pH of cytosol, nuclei, and extracellular locations. Importantly, cathepsin B displays different substrate cleavage properties at acidic pH compared to neutral pH conditions. It is, therefore, desirable to develop specific substrates for cathepsin B that measure its activity over broad pH ranges. Current substrates used to monitor cathepsin B activity consist of Z-Phe-Arg-AMC and Z-Arg-Arg-AMC, but they lack specificity since they are cleaved by other cysteine cathepsins. Furthermore, Z-Arg-Arg-AMC monitors cathepsin B activity at neutral pH and displays minimal activity at acidic pH. Therefore, the purpose of this study was to design and validate specific fluorogenic peptide substrates that can monitor cathepsin B activity over a broad pH range from acidic to neutral pH conditions. In-depth cleavage properties of cathepsin B were compared to those of the cysteine cathepsins K, L, S, V, and X via multiplex substrate profiling by mass spectrometry at pH 4.6 and pH 7.2. Analysis of the cleavage preferences predicted the tripeptide Z-Nle-Lys-Arg-AMC as a preferred substrate for cathepsin B. Significantly, Z-Nle-Lys-Arg-AMC displayed the advantageous properties of measuring high cathepsin B specific activity over acidic to neutral pHs and was specifically cleaved by cathepsin B over the other cysteine cathepsins. Z-Nle-Lys-Arg-AMC specifically monitored cathepsin B activity in neuronal and glial cells which were consistent with relative abundances of cathepsin B protein. These findings validate Z-Nle-Lys-Arg-AMC as a novel substrate that specifically monitors cathepsin B activity over a broad pH range.

Intracellular Ca2+ signalling: unexpected new roles for the usual suspect

Cytosolic Ca2+ signals are organized in complex spatial and temporal patterns that underlie their unique ability to regulate multiple cellular functions. Changes in intracellular Ca2+ concentration ([Ca2+]i) are finely tuned by the concerted interaction of membrane receptors and ion channels that introduce Ca2+ into the cytosol, Ca2+-dependent sensors and effectors that translate the elevation in [Ca2+]i into a biological output, and Ca2+-clearing mechanisms that return the [Ca2+]i to pre-stimulation levels and prevent cytotoxic Ca2+ overload. The assortment of the Ca2+ handling machinery varies among different cell types to generate intracellular Ca2+ signals that are selectively tailored to subserve specific functions. The advent of novel high-speed, 2D and 3D time-lapse imaging techniques, single-wavelength and genetic Ca2+ indicators, as well as the development of novel genetic engineering tools to manipulate single cells and whole animals, has shed novel light on the regulation of cellular activity by the Ca2+ handling machinery. A symposium organized within the framework of the 72nd Annual Meeting of the Italian Society of Physiology, held in Bari on 14-16th September 2022, has recently addressed many of the unexpected mechanisms whereby intracellular Ca2+ signalling regulates cellular fate in healthy and disease states. Herein, we present a report of this symposium, in which the following emerging topics were discussed: 1) Regulation of water reabsorption in the kidney by lysosomal Ca2+ release through Transient Receptor Potential Mucolipin 1 (TRPML1); 2) Endoplasmic reticulum-to-mitochondria Ca2+ transfer in Alzheimer's disease-related astroglial dysfunction; 3) The non-canonical role of TRP Melastatin 8 (TRPM8) as a Rap1A inhibitor in the definition of some cancer hallmarks; and 4) Non-genetic optical stimulation of Ca2+ signals in the cardiovascular system.

Lysosomal LAMP proteins regulate lysosomal pH by direct inhibition of the TMEM175 channel

Maintaining a highly acidic lysosomal pH is central to cellular physiology. Here, we use functional proteomics, single-particle cryo-EM, electrophysiology, and in vivo imaging to unravel a key biological function of human lysosome-associated membrane proteins (LAMP-1 and LAMP-2) in regulating lysosomal pH homeostasis. Despite being widely used as a lysosomal marker, the physiological functions of the LAMP proteins have long been overlooked. We show that LAMP-1 and LAMP-2 directly interact with and inhibit the activity of the lysosomal cation channel TMEM175, a key player in lysosomal pH homeostasis implicated in Parkinson's disease. This LAMP inhibition mitigates the proton conduction of TMEM175 and facilitates lysosomal acidification to a lower pH environment crucial for optimal hydrolase activity. Disrupting the LAMP-TMEM175 interaction alkalinizes the lysosomal pH and compromises the lysosomal hydrolytic function. In light of the ever-increasing importance of lysosomes to cellular physiology and diseases, our data have widespread implications for lysosomal biology.

Induction of lysosomal exocytosis and biogenesis via TRPML1 activation for the treatment of uranium-induced nephrotoxicity

Uranium (U) is a well-known nephrotoxicant which forms precipitates in the lysosomes of renal proximal tubular epithelial cells (PTECs) after U-exposure at a cytotoxic dose. However, the roles of lysosomes in U decorporation and detoxification remain to be elucidated. Mucolipin transient receptor potential channel 1 (TRPML1) is a major lysosomal Ca2+ channel regulating lysosomal exocytosis. We herein demonstrate that the delayed administration of the specific TRPML1 agonist ML-SA1 significantly decreases U accumulation in the kidney, mitigates renal proximal tubular injury, increases apical exocytosis of lysosomes and reduces lysosomal membrane permeabilization (LMP) in renal PTECs of male mice with single-dose U poisoning or multiple-dose U exposure. Mechanistic studies reveal that ML-SA1 stimulates intracellular U removal and reduces U-induced LMP and cell death through activating the positive TRPML1-TFEB feedback loop and consequent lysosomal exocytosis and biogenesis in U-loaded PTECs in vitro. Together, our studies demonstrate that TRPML1 activation is an attractive therapeutic strategy for the treatment of U-induced nephrotoxicity.

Pathophysiology of Lysosomes in a Nutshell

Lysosomes are acidic organelles present in all nucleated mammalian cells [...].

Lysosomal Ca2+ flux modulates automaticity in ventricular cardiomyocytes and correlates with arrhythmic risk

Automaticity involves Ca2+ handling at the cell membrane and sarcoplasmic reticulum (SR). Abnormal or acquired automaticity is thought to initiate ventricular arrhythmias associated with myocardial ischemia. Ca2+ flux from mitochondria can influence automaticity, and lysosomes also release Ca2+. Therefore, we tested whether lysosomal Ca2+ flux could influence automaticity. We studied ventricular human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), hiPSC 3D engineered heart tissues (EHTs), and ventricular cardiomyocytes isolated from infarcted mice. Preventing lysosomal Ca2+ cycling reduced automaticity in hiPSC-CMs. Consistent with a lysosomal role in automaticity, activating the transient receptor potential mucolipin channel (TRPML1) enhanced automaticity, and two channel antagonists reduced spontaneous activity. Activation or inhibition of lysosomal transcription factor EB (TFEB) increased or decreased total lysosomes and automaticity, respectively. In adult ischemic cardiomyocytes and hiPSC 3D EHTs, reducing lysosomal Ca2+ release also inhibited automaticity. Finally, TRPML1 was up-regulated in cardiomyopathic patients with ventricular tachycardia (VT) compared with those without VT. In summary, lysosomal Ca2+ handling modulates abnormal automaticity, and reducing lysosomal Ca2+ release may be a clinical strategy for preventing ventricular arrhythmias.

2D MoS2 Nanosheets Induce Ferroptosis by Promoting NCOA4-Dependent Ferritinophagy and Inhibiting Ferroportin

The exposure of MoS₂ nanosheets can cause cytotoxicity, which causes health risks and affects its medical applications. However, knowledge of the underlying molecular mechanisms remains limited. This study reports that MoS₂ nanosheets induces ferroptosis in vivo and in vitro, which is caused by the nanosheet themselves rather than by the dissolved ions. MoS₂ nanosheets induce ferroptosis in epithelial (BEAS-2B) and macrophage (RAW264.7) cells due to nuclear receptor coactivator 4 (NCOA4)-dependent excusive ferritinophagy and the inhibition of ferroportin-1 (FPN). In this process, most of the MoS₂ nanosheets enter the cells via macropinocytosis and are localized to the lysosome, contributing to an increase in the lysosomal membrane permeability. At the same time, NCOA4-dependent ferritinophagy is activated, and ferritin is degraded in the lysosome, which generates Fe²⁺ .Fe²⁺ leaks into the cytoplasm, leading to ferroptosis. Furthermore, the inhibition of FPN further aggravates the overload of Fe²⁺ in the cell. It has also been observed that ferroptosis is increased in lung tissue in mouse models exposed to MoS₂ nanosheets. This work highlights a novel mechanism by which MoS₂ nanosheets induce ferroptosis by promoting NCOA4-dependent ferritinophagy and inhibiting FPN, which could be of importance to elucidate the toxicity and identify the medical applications of 2D nanoparticles.

Transmembrane Protein 175, a Lysosomal Ion Channel Related to Parkinson's Disease

Lysosomes are membrane-bound organelles with an acidic lumen and are traditionally characterized as a recycling center in cells. Lysosomal ion channels are integral membrane proteins that form pores in lysosomal membranes and allow the influx and efflux of essential ions. Transmembrane protein 175 (TMEM175) is a unique lysosomal potassium channel that shares little sequence similarity with other potassium channels. It is found in bacteria, archaea, and animals. The prokaryotic TMEM175 consists of one six-transmembrane domain that adopts a tetrameric architecture, while the mammalian TMEM175 is comprised of two six-transmembrane domains that function as a dimer in lysosomal membranes. Previous studies have demonstrated that the lysosomal K⁺ conductance mediated by TMEM175 is critical for setting membrane potential, maintaining pH stability, and regulating lysosome-autophagosome fusion. AKT and B-cell lymphoma 2 regulate TMEM175's channel activity through direct binding. Two recent studies reported that the human TMEM175 is also a proton-selective channel under normal lysosomal pH (4.5-5.5) as the K⁺ permeation dramatically decreased at low pH while the H⁺ current through TMEM175 greatly increased. Genome-wide association studies and functional studies in mouse models have established that TMEM175 is implicated in the pathogenesis of Parkinson's disease, which sparks more research interests in this lysosomal channel.

Nicotine exacerbates atherosclerosis and plaque instability via NLRP3 inflammasome activation in vascular smooth muscle cells

Rationale: Nicotine has been reported to be a strong risk factor for atherosclerosis. However, the underlying mechanism by which nicotine controls atherosclerotic plaque stability remain largely unknown. Objective: The aim of this study was to evaluate the impact of lysosomal dysfunction mediated NLRP3 inflammasome activation in vascular smooth muscle cell (VSMC) on atherosclerotic plaque formation and stability in advanced atherosclerosis at the brachiocephalic arteries (BA). Methods and Results: Features of atherosclerotic plaque stability and the markers for NLR Family Pyrin Domain Containing 3 (NLRP3) inflammasome were monitored in the BA from nicotine or vehicle-treated apolipoprotein E deficient (Apoe-/-) mice fed with Western-type diet (WD). Nicotine treatment for 6 weeks accelerated atherosclerotic plaque formation and enhanced the hallmarks of plaque instability in BA of Apoe-/- mice. Moreover, nicotine elevated interleukin 1 beta (IL-1β) in serum and aorta and was preferred to activate NLRP3 inflammasome in aortic vascular smooth muscle cells (VSMC). Importantly, pharmacological inhibition of Caspase1, a key downstream target of NLRP3 inflammasome complex, and genetic inactivation of NLRP3 significantly restrained nicotine-elevated IL-1β in serum and aorta, as well as nicotine-stimulated atherosclerotic plaque formation and plaque destabilization in BA. We further confirmed the role of VSMC-derived NLRP3 inflammasome in nicotine-induced plaque instability by using VSMC specific TXNIP (upstream regulator of NLRP3 inflammasome) deletion mice. Mechanistic study further showed that nicotine induced lysosomal dysfunction resulted in cathepsin B cytoplasmic release. Inhibition or knockdown of cathepsin B blocked nicotine-dependent inflammasome activation. Conclusions: Nicotine promotes atherosclerotic plaque instability by lysosomal dysfunction-mediated NLRP3 inflammasome activation in vascular smooth muscle cells.

Constant Conversion Rate of Endolysosomes Revealed by a pH-Sensitive Fluorescent Probe

Endolysosome dynamics plays an important role in autophagosome biogenesis. Hence, imaging the subcellular dynamics of endolysosomes using high-resolution fluorescent imaging techniques would deepen our understanding of autophagy and benefit the development of pharmaceuticals against endosome-related diseases. Taking advantage of the intramolecular charge-transfer mechanism, herein we report a cationic quinolinium-based fluorescent probe (PyQPMe) that exhibits excellent pH-sensitive fluorescence in endolysosomes at different stages of interest. A systematic photophysical and computational study on PyQPMe was carried out to rationalize its highly pH-dependent absorption and emission spectra. The large Stokes shift and strong fluorescence intensity of PyQPMe can effectively reduce the background noise caused by excitation light and microenvironments and provide a high signal-to-noise ratio for high-resolution imaging of endolysosomes. By applying PyQPMe as a small molecular probe in live cells, we were able to reveal a constant conversion rate from early endosomes to late endosomes/lysosomes during autophagy at the submicron level.

Silver nanoparticle toxicity on Artemia parthenogenetica nauplii hatched on axenic tryptic soy agar solid medium

The use of gnobiotic brine shrimp (Artemia spp.) for ecotoxicology and bacteria-host interaction studies is common. However, requirements for axenic culture and matrix effects of seawater media can be an obstacle. Thus, we investigated the hatching ability of Artemia cysts on a novel sterile Tryptic Soy Agar (TSA) medium. Herein, we demonstrate for the first time that Artemia cysts can hatch on a solid medium without liquid, which offers practical advantages. We further optimized the culture conditions for temperature and salinity and assessed this culture system for toxicity screening of silver nanoparticles (AgNPs) across multiple biological endpoints. Results revealed that maxima hatching (90%) of embryos occurred at 28 °C and without addition of sodium chloride. When capsulated cysts were cultured on TSA solid medium Artemia were negatively impacted by AgNPs at 30-50 mgL^-1 in terms of the embryo hatching ratio (47-51%), umbrella- to nauplii-stage transformation ratio (54-57%), and a reduction in nauplii-stage growth (60-85% of normal body length). At 50-100 mgL^-1 AgNPs and higher, evidence of damage to lysosomal storage was recorded. At 500 mgL^-1 AgNPs, development of the eye was inhibited and locomotory behavior impeded. Our study reveals that this new hatching method has applications in ecotoxicology studies and provides an efficient means to control axenic requirements to produce gnotobiotic brine shrimp.

Lysosome transporter purification and reconstitution identifies Ypq1 pH-gated lysine transport and regulation

Lysosomes achieve their function through numerous transporters that import or export nutrients across their membrane. However, technical challenges in membrane protein overexpression, purification, and reconstitution hinder our understanding of lysosome transporter function. Here, we developed a platform to overexpress and purify the putative lysine transporter Ypq1 using a constitutive overexpression system in protease- and ubiquitination-deficient yeast vacuoles. Using this method, we purified and reconstituted Ypq1 into proteoliposomes and showed lysine transport function, supporting its role as a basic amino acid transporter on the vacuole membrane. We also found that the absence of lysine destabilizes purified Ypq1 and causes it to aggregate, consistent with its propensity to be downregulated in vivo upon lysine starvation. Our approach may be useful for the biochemical characterization of many transporters and membrane proteins to understand organellar transport and regulation.

Mu opioid receptor-mediated release of endolysosome iron increases levels of mitochondrial iron, reactive oxygen species, and cell death

Objectives

Opioids including morphine and DAMGO activate mu-opioid receptors (MOR), increase intracellular reactive oxygen species (ROS) levels, and induce cell death. Ferrous iron (Fe2+) through Fenton-like chemistry increases ROS levels and endolysosomes are "master regulators of iron metabolism" and contain readily-releasable Fe2+ stores. However, mechanisms underlying opioid-induced changes in endolysosome iron homeostasis and downstream-signaling events remain unclear.

Methods

We used SH-SY5Y neuroblastoma cells, flow cytometry, and confocal microscopy to measure Fe2+ and ROS levels and cell death.

Results

Morphine and DAMGO de-acidified endolysosomes, decreased endolysosome Fe2+ levels, increased cytosol and mitochondria Fe2+ and ROS levels, depolarized mitochondrial membrane potential, and induced cell death; effects blocked by the nonselective MOR antagonist naloxone and the selective MOR antagonist β-funaltrexamine (β-FNA). Deferoxamine, an endolysosome-iron chelator, inhibited opioid agonist-induced increases in cytosolic and mitochondrial Fe2+ and ROS. Opioid-induced efflux of endolysosome Fe2+ and subsequent Fe2+ accumulation in mitochondria were blocked by the endolysosome-resident two-pore channel inhibitor NED-19 and the mitochondrial permeability transition pore inhibitor TRO.

Conclusions

Opioid agonist-induced increases in cytosolic and mitochondrial Fe2+ and ROS as well as cell death appear downstream of endolysosome de-acidification and Fe2+ efflux from the endolysosome iron pool that is sufficient to affect other organelles.

A terpene nucleoside from M. tuberculosis induces lysosomal lipid storage in foamy macrophages

Induction of lipid-laden foamy macrophages is a cellular hallmark of tuberculosis (TB) disease, which involves the transformation of infected phagolysosomes from a site of killing into a nutrient-rich replicative niche. Here, we show that a terpenyl nucleoside shed from Mycobacterium tuberculosis, 1-tuberculosinyladenosine (1-TbAd), caused lysosomal maturation arrest and autophagy blockade, leading to lipid storage in M1 macrophages. Pure 1-TbAd, or infection with terpenyl nucleoside-producing M. tuberculosis, caused intralysosomal and peribacillary lipid storage patterns that matched both the molecules and subcellular locations known in foamy macrophages. Lipidomics showed that 1-TbAd induced storage of triacylglycerides and cholesterylesters and that 1-TbAd increased M. tuberculosis growth under conditions of restricted lipid access in macrophages. Furthermore, lipidomics identified 1-TbAd-induced lipid substrates that define Gaucher's disease, Wolman's disease, and other inborn lysosomal storage diseases. These data identify genetic and molecular causes of M. tuberculosis-induced lysosomal failure, leading to successful testing of an agonist of TRPML1 calcium channels that reverses lipid storage in cells. These data establish the host-directed cellular functions of an orphan effector molecule that promotes survival in macrophages, providing both an upstream cause and detailed picture of lysosome failure in foamy macrophages.

Characterization of Endo-Lysosomal Cation Channels Using Calcium Imaging

Endo-lysosomes are membrane-bound acidic organelles that are involved in endocytosis, recycling, and degradation of extracellular and intracellular material. The membranes of endo-lysosomes express several Ca²⁺-permeable cation ion channels, including two-pore channels (TPC1-3) and transient receptor potential mucolipin channels (TRPML1-3). In this chapter, we will describe four different state-of-the-art Ca²⁺ imaging approaches, which are well-suited to investigate the function of endo-lysosomal cation channels. These techniques include (1) global cytosolic Ca²⁺ measurements, (2) peri-endo-lysosomal Ca²⁺ imaging using genetically encoded Ca²⁺ sensors that are directed to the cytosolic endo-lysosomal membrane surface, (3) Ca²⁺ imaging of endo-lysosomal cation channels, which are engineered in order to redirect them to the plasma membrane in combination with approaches 1 and 2, and (4) Ca²⁺ imaging by directing Ca²⁺ indicators to the endo-lysosomal lumen. Moreover, we will review useful small molecules, which can be used as valuable tools for endo-lysosomal Ca²⁺ imaging. Rather than providing complete protocols, we will discuss specific methodological issues related to endo-lysosomal Ca²⁺ imaging.

Lysosomal Ion Channels and Lysosome-Organelle Interactions

Intracellular organelles exchange their luminal contents with each other via both vesicular and non-vesicular mechanisms. By forming membrane contact sites (MCSs) with ER and mitochondria, lysosomes mediate bidirectional transport of metabolites and ions between lysosomes and organelles that regulate lysosomal physiology, movement, membrane remodeling, and membrane repair. In this chapter, we will first summarize the current knowledge of lysosomal ion channels and then discuss the molecular and physiological mechanisms that regulate lysosome-organelle MCS formation and dynamics. We will also discuss the roles of lysosome-ER and lysosome-mitochondria MCSs in signal transduction, lipid transport, Ca ²⁺ transfer, membrane trafficking, and membrane repair, as well as their roles in lysosome-related pathologies.

Resistance to antibody-drug conjugates in breast cancer: mechanisms and solutions

Antibody-drug conjugates (ADCs) are a rapidly developing therapeutic approach in cancer treatment that has shown remarkable activity in breast cancer. Currently, there are two ADCs approved for the treatment of human epidermal growth factor receptor 2-positive breast cancer, one for triple-negative breast cancer, and multiple investigational ADCs in clinical trials. However, drug resistance has been noticed in clinical use, especially in trastuzumab emtansine. Here, the mechanisms of ADC resistance are summarized into four categories: antibody-mediated resistance, impaired drug trafficking, disrupted lysosomal function, and payload-related resistance. To overcome or prevent resistance to ADCs, innovative development strategies and combination therapy options are being investigated. Analyzing predictive biomarkers for optimal therapy selection may also help to prevent drug resistance.

Aggregation-Induced emission photosensitizer with lysosomal response for photodynamic therapy against cancer

Photosensitizers play a key role in bioimaging and photodynamic therapy (PDT) of cancer. However, conventional photosensitizers usually do not achieve the desired efficacy in PDT due to their poor photostability, targeting ability, and responsiveness. Herein, we designed a series of photosensitizers with aggregation-induced emission (AIE) effect using benzothiazole- triphenylamine (BZT-triphenylamine) as the parent nucleus. The synthesized compound SIN ((E)-2-(4-(diphenylamino)styryl)-3-(4-iodobutyl)benzo[d]thiazol-3-ium) exhibits good biocompatibility, photostability, and bright emission in the near-infrared range (600-800 nm). The fluorescence emission intensity is responsive to viscosity, with significant fluorescence enhancement (48 times) and high fluorescence quantum yield (4.45 %) at high viscosity. Moreover, SIN has particular lysosome targeting properties with a Pearson correlation coefficient (PCC) of 0.97 and has good ¹O₂ generation ability under white light irradiation, especially in a weak acidic environment. Thus, SIN can realize good bioimaging ability and photodynamic therapeutic efficacy under the highly viscous and weakly acidic environment of lysosomes in the tumor cells. This study indicates that SIN has potential as a multifunctional organic photosensitizer for bioimaging and PDT of tumor.

Cationic amphiphilic antihistamines inhibit STAT3 via Ca2+-dependent lysosomal H+ efflux

Commonly used antihistamines and other cationic amphiphilic drugs (CADs) are emerging as putative cancer drugs. Their unique chemical structure enables CADs to accumulate rapidly inside lysosomes, where they increase lysosomal pH, alter lysosomal lipid metabolism, and eventually cause lysosomal membrane permeabilization. Here, we show that CAD-induced rapid elevation in lysosomal pH is caused by a lysosomal H+ efflux that requires P2RX4-mediated lysosomal Ca2+ release and precedes the lysosomal membrane permeabilization. The subsequent cytosolic acidification triggers the dephosphorylation, lysosomal translocation, and inactivation of the oncogenic signal transducer and activator of transcription 3 (STAT3) transcription factor. Moreover, CAD-induced lysosomal H+ efflux sensitizes cancer cells to apoptosis induced by STAT3 inhibition and acts synergistically with STAT3 inhibition in restricting the tumor growth of A549 non-small cell lung carcinoma xenografts. These findings identify lysosomal H+ efflux and STAT3 inhibition as anticancer mechanisms of CADs and reinforce the repurposing of safe and inexpensive CADs as cancer drugs with a drug combination strategy.

Study on Sgc8 Aptamer-mediated Nucleic Acid Nanomaterial-doxorubicin Complex for Tumor Targeted Therapy

Chemotherapy is one of the most important treatments for malignant cancers, but most chemotherapeutic drugs are poorly targeted, highly toxic and expensive, resulting in unsatisfactory treatment results for cancer patients. Therefore, intelligent drug delivery platforms are needed to be explored urgently to enhance drug treatment and reduce toxicity on normal cells. Nucleic acid nanomaterials are a class of nanomaterials developed on the basis of the "base complementary pairing principle", which have the advantages of good programmability, high stability, good biocompatibility, and strong targeting. Herein, we present a simple Sgc8 aptamer-modified nucleic acid nanomaterial (Sgc8NM) for the targeted delivery of Doxorubicin (Dox), a widely used chemotherapy drug in clinic. Studies have shown the Sgc8NM-Dox performed a precise treatment effect on target cells and low toxicity on non-target cells, providing a new strategy for the potential application of nanocomposite drugs in targeted cancer delivery.

Multi-Cell Line Analysis of Lysosomal Proteomes Reveals Unique Features and Novel Lysosomal Proteins

Lysosomes, the main degradative organelles of mammalian cells, play a key role in the regulation of metabolism. It is becoming more and more apparent that they are highly active, diverse, and involved in a large variety of processes. The essential role of lysosomes is exemplified by the detrimental consequences of their malfunction, which can result in lysosomal storage disorders, neurodegenerative diseases, and cancer. Using lysosome enrichment and mass spectrometry, we investigated the lysosomal proteomes of HEK293, HeLa, HuH-7, SH-SY5Y, MEF, and NIH3T3 cells. We provide evidence on a large scale for cell type-specific differences of lysosomes, showing that levels of distinct lysosomal proteins are highly variable within one cell type, while expression of others is highly conserved across several cell lines. Using differentially stable isotope-labeled cells and bimodal distribution analysis, we furthermore identify a high confidence population of lysosomal proteins for each cell line. Multi-cell line correlation of these data reveals potential novel lysosomal proteins, and we confirm lysosomal localization for six candidates. All data are available via ProteomeXchange with identifier PXD020600.

Conformational rearrangements in the second voltage sensor domain switch PIP2- and voltage-gating modes in two-pore channels

Two-pore channels (TPCs) are activated by phosphatidylinositol bisphosphate (PIP₂) binding to domain I and/or by voltage sensing in domain II (DII). Little is known about how these two stimuli are integrated, and how each TPC subtype achieves its unique preference. Here, we show that distinct conformations of DII-S4 in the voltage-sensor domain determine the two gating modes. DII-S4 adopts an intermediate conformation, and forced stabilization in this conformation was found to result in a high PIP₂-dependence in primarily voltage-dependent TPC3. In TPC2, which is PIP₂-gated and nonvoltage-dependent, a stabilized intermediate conformation does not affect the PIP₂-gated currents. These results indicate that the intermediate state represents the PIP₂-gating mode, which is distinct from the voltage-gating mode in TPCs. We also found in TPC2 that the tricyclic antidepressant desipramine induces DII-S4-based voltage dependence and that naringenin, a flavonoid, biases the mode preference from PIP₂-gating to desipramine-induced voltage gating. Taken together, our study on TPCs revealed an unprecedented mode-switching mechanism involving conformational changes in DII-S4, and its active role in integrating voltage and PIP₂ stimuli.

Proteasomal inhibition preferentially stimulates lysosome activity relative to autophagic flux in primary astrocytes

Neurons and astrocytes face unique demands on their proteome to enable proper function and survival of the nervous system. Consequently, both cell types are critically dependent on robust quality control pathways such as macroautophagy (hereafter referred to as autophagy) and the ubiquitin-proteasome system (UPS). We previously reported that autophagy is differentially regulated in astrocytes and neurons in the context of metabolic stress, but less is understood in the context of proteotoxic stress induced by inhibition of the UPS. Dysfunction of the proteasome or autophagy has been linked to the progression of various neurodegenerative diseases. Therefore, in this study, we explored the connection between autophagy and the proteasome in primary astrocytes and neurons. Prior studies largely in non-neural models report a compensatory relationship whereby inhibition of the UPS stimulates autophagy. To our surprise, inhibition of the proteasome did not robustly upregulate autophagy in astrocytes or neurons. In fact, the effects on autophagy are modest particularly in comparison to paradigms of metabolic stress. Rather, we find that UPS inhibition in astrocytes induces formation of Ub-positive aggregates that harbor the selective autophagy receptor, SQSTM1/p62, but these structures were not productive substrates for autophagy. By contrast, we observed a significant increase in lysosomal degradation in astrocytes in response to UPS inhibition, but this stimulation was not sufficient to reduce total SQSTM1 levels. Last, UPS inhibition was more toxic in neurons compared to astrocytes, suggesting a cell type-specific vulnerability to proteotoxic stress.Abbreviations: Baf A1: bafilomycin A1; CQ: chloroquine; Epox: epoxomicin; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; p-ULK1: phospho-ULK1; SQSTM1/p62: sequestosome 1; Ub: ubiquitin; ULK1: unc-51 like kinase 1; UPS: ubiquitin-proteasome system.

Polydopamine-Decorated PLCL Conduit to Induce Synergetic Effect of Electrical Stimulation and Topological Morphology for Peripheral Nerve Regeneration

Due to the limited self-repairing capacity after peripheral nerve injuries (PNI), artificial nerve conduits are widely applied to facilitate neural regeneration. Exogenous electrical stimulation (ES) that is carried out by the conductive conduit regulates the biological behavior of Schwann cells (SCs). Meanwhile, a longitudinal surface structure counts to guide axonal growth to accelerate the end-to-end connection. Currently, there are no conduits equipped with both electrical conduction and axon-guiding surface structure. Herein, a biodegradable, conductive poly(l-lactide-co-caprolactone)/graphene (PLCL/GN) composite conduit is designed. The conduit with 20.96 ± 1.26 MPa tensile strength has a micropatterned surface of 20 µm groove fabricated by microimprint technology and self-assembled polydopamine (PDA). In vitro evaluation shows that the conduits with ES effectively stimulate the directional cell migration, adhesion, and elongation, and enhance neuronal expression of SCs. The rat sciatic nerve crush model demonstrates that the conductive micropatterned conduit with ES promotes the growth of myelin sheath, faster nerve regeneration, and 20-fold functional recovery in vivo. These discoveries prove that the PLCL(G)/PDA/GN composite conduit is a promising tool for PNI treatment by providing the functional integration of physical guidance, biomimetic biological regulation, and bioelectrical stimulation, which inspires a novel therapeutic approach for nerve regeneration in the future.

Expression and functions of transient receptor potential channels in liver diseases

Liver diseases constitute a major healthcare burden globally, including acute hepatic injury resulted from acetaminophen overdose, ischemia-reperfusion or hepatotropic viral infection and chronic hepatitis, alcoholic liver disease (ALD), non-alcoholic fatty liver disease (NAFLD) and hepatocellular carcinoma (HCC). Attainable treatment strategies for most liver diseases remain inadequate, highlighting the importance of substantial pathogenesis. The transient receptor potential (TRP) channels represent a versatile signalling mechanism regulating fundamental physiological processes in the liver. It is not surprising that liver diseases become a newly explored field to enrich our knowledge of TRP channels. Here, we discuss recent findings revealing TRP functions across the fundamental pathological course from early hepatocellular injury caused by various insults, to inflammation, subsequent fibrosis and hepatoma. We also explore expression levels of TRPs in liver tissues of ALD, NAFLD and HCC patients from Gene Expression Omnibus (GEO) or The Cancer Genome Atlas (TCGA) database and survival analysis estimated by Kaplan-Meier Plotter. At last, we address the therapeutical potential and challenges by pharmacologically targeting TRPs to treat liver diseases. The aim is to provide a better understanding of the implications of TRP channels in liver diseases, contributing to the discovery of novel therapeutic targets and efficient drugs.

Lysosomal dysfunction in diabetic cardiomyopathy

Diabetes is a major risk factor for a variety of cardiovascular complications, while diabetic cardiomyopathy, a disease specific to the myocardium independent of vascular lesions, is an important causative factor for increased risk of heart failure and mortality in diabetic populations. Lysosomes have long been recognized as intracellular trash bags and recycling facilities. However, recent studies have revealed that lysosomes are sophisticated signaling hubs that play remarkably diverse roles in adapting cell metabolism to an ever-changing environment. Despite advances in our understanding of the physiological roles of lysosomes, the events leading to lysosomal dysfunction and how they relate to the overall pathophysiology of the diabetic heart remain unclear and are under intense investigation. In this review, we summarize recent advances regarding lysosomal injury and its roles in diabetic cardiomyopathy.

Lysosomal Ion Channels: What Are They Good For and Are They Druggable Targets?

Lysosomes play fundamental roles in material digestion, cellular clearance, recycling, exocytosis, wound repair, Ca²⁺ signaling, nutrient signaling, and gene expression regulation. The organelle also serves as a hub for important signaling networks involving the mTOR and AKT kinases. Electrophysiological recording and molecular and structural studies in the past decade have uncovered several unique lysosomal ion channels and transporters, including TPCs, TMEM175, TRPMLs, CLN7, and CLC-7. They underlie the organelle's permeability to major ions, including K⁺, Na⁺, H⁺, Ca²⁺, and Cl^-. The channels are regulated by numerous cellular factors, ranging from H⁺ in the lumen and voltage across the lysosomal membrane to ATP in the cytosol to growth factors outside the cell. Genetic variations in the channel/transporter genes are associated with diseases that include lysosomal storage diseases and neurodegenerative diseases. Recent studies with human genetics and channel activators suggest that lysosomal channels may be attractive targets for the development of therapeutics for the prevention of and intervention in human diseases.

Seeing Neurodegeneration in a New Light Using Genetically Encoded Fluorescent Biosensors and iPSCs

Neurodegenerative diseases present a progressive loss of neuronal structure and function, leading to cell death and irrecoverable brain atrophy. Most have disease-modifying therapies, in part because the mechanisms of neurodegeneration are yet to be defined, preventing the development of targeted therapies. To overcome this, there is a need for tools that enable a quantitative assessment of how cellular mechanisms and diverse environmental conditions contribute to disease. One such tool is genetically encodable fluorescent biosensors (GEFBs), engineered constructs encoding proteins with novel functions capable of sensing spatiotemporal changes in specific pathways, enzyme functions, or metabolite levels. GEFB technology therefore presents a plethora of unique sensing capabilities that, when coupled with induced pluripotent stem cells (iPSCs), present a powerful tool for exploring disease mechanisms and identifying novel therapeutics. In this review, we discuss different GEFBs relevant to neurodegenerative disease and how they can be used with iPSCs to illuminate unresolved questions about causes and risks for neurodegenerative disease.

The Biology of Lysosomes: From Order to Disorder

Since its discovery in 1955, the understanding of the lysosome has continuously increased. Once considered a mere waste removal system, the lysosome is now recognised as a highly crucial cellular component for signalling and energy metabolism. This notable evolution raises the need for a summarized review of the lysosome's biology. As such, throughout this article, we will be compiling the current knowledge regarding the lysosome's biogenesis and functions. The comprehension of this organelle's inner mechanisms is crucial to perceive how its impairment can give rise to lysosomal disease (LD). In this review, we highlight some examples of LD fine-tuned mechanisms that are already established, as well as others, which are still under investigation. Even though the understanding of the lysosome and its pathologies has expanded through the years, some of its intrinsic molecular aspects remain unknown. In order to illustrate the complexity of the lysosomal diseases we provide a few examples that have challenged the established single gene-single genetic disorder model. As such, we believe there is a strong need for further investigation of the exact abnormalities in the pathological pathways in lysosomal disease.

Cigarette smoke extract-induced inflammatory response via inhibition of the TFEB-mediated autophagy in NR8383 cells

Objective: Chronic pulmonary inflammation caused by long-term smoking is the core pathology of COPD. Alveolar macrophages (AMs) are involved in the pulmonary inflammation of COPD. The accumulation of damaged materials caused by impaired autophagy triggers inflammatory response in macrophages. As a key transcription regulator, transcription factor EB (TFEB) activates the transcription of target genes related autophagy and lysosome by binding to promoters, whereas it is unclarified for the relationship between inflammatory response induced by cigarette smoke extract (CSE) and TFEB-mediated autophagy. Thus, we investigated the role of TFEB-mediated autophagy in inflammatory response induced by CSE in NR8383 cells, and to explore its potential mechanism. Methods: Based on cell viability and autophagy, cells treated with 20% concentration of CSE for 24 h were selected for further studies. Cells were divided into control group, chloroquine (CQ, the autophagy inhibitor) group, CSE group, CSE + rapamycin (the autophagy inducer) group and CSE + fisetin (the TFEB inducer) group. The levels of tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and IL-6 in supernatant were detected by ELISA kits. The protein expressions were tested by western blot. The intensity of fluorescence of Lysosome-associated membrane protein 1 (LAMP1) and TFEB was detected by immunofluorescence. Lyso-Tracker Red staining was applied to detect the lysosome environment. Results: CSE inhibited the cell viability, increased the contents of TNF-α, IL-1β, IL-6, the ratio of LC3II/I, and the level of P62 protein. Besides, CSE decreased the fluorescence intensity of LAMP1 protein and Lyso-Tracker Red staining, as well as the ratio of nucleus/cytosol of TFEB protein. Activating autophagy with rapamycin alleviated CSE-induced inflammatory response. The activation of TFEB via fisetin alleviated CSE-induced autophagy impairment and lysosomal dysfunction, thus alleviated inflammatory response in NR8383 cells. Conclusion: CSE-induced inflammatory response in NR8383 cells, which may be related to the inhibition of TFEB-mediated autophagy.

Electrophysiological Techniques on the Study of Endolysosomal Ion Channels

Endolysosomal ion channels are a group of ion channel proteins that are functionally expressed on the membrane of endolysosomal vesicles. The electrophysiological properties of these ion channels in the intracellular organelle membrane cannot be observed using conventional electrophysiological techniques. This section compiles the different electrophysiological techniques utilized in recent years to study endolysosomal ion channels and describes their methodological characteristics, emphasizing the most widely used technique for whole endolysosome recordings to date. This includes the use of different pharmacological tools and genetic tools for the application of patch-clamping techniques for specific stages of endolysosomes, allowing the recording of ion channel activity in different organelles, such as recycling endosomes, early endosomes, late endosomes, and lysosomes. These electrophysiological techniques are not only cutting-edge technologies that help to investigate the biophysical properties of known and unknown intracellular ion channels but also help us to investigate the physiopathological role of these ion channels in the distribution of dynamic vesicles and to identify new therapeutic targets for precision medicine and drug screening.

Transcription factor EB as a key molecular factor in human health and its implication in diseases

Transcription factor EB, as a component of the microphthalmia family of transcription factors, has been demonstrated to be a key controller of autophagy-lysosomal biogenesis. Transcription factor EB is activated by stressors such as nutrition and deprivation of growth factors, hypoxia, lysosomal stress, and mitochondrial injury. To achieve the ultimate functional state, it is controlled in a variety of modes, such as in its rate of transcription, post-transcriptional control, and post-translational alterations. Due to its versatile role in numerous signaling pathways, including the Wnt, calcium, AKT, and mammalian target of rapamycin complex 1 signaling pathways, transcription factor EB-originally identified to be an oncogene-is now well acknowledged as a regulator of a wide range of physiological systems, including autophagy-lysosomal biogenesis, response to stress, metabolism, and energy homeostasis. The well-known and recently identified roles of transcription factor EB suggest that this protein might play a central role in signaling networks in a number of non-communicable illnesses, such as cancer, cardiovascular disorders, drug resistance mechanisms, immunological disease, and tissue growth. The important developments in transcription factor EB research since its first description are described in this review. This review helps to advance transcription factor EB from fundamental research into therapeutic and regenerative applications by shedding light on how important a role it plays in human health and disease at the molecular level.

Structure and Function of Plant and Mammalian TPC Channels

Two-pore channels (TPCs) belong to the family of voltage-gated tetrameric cation channels and are ubiquitously expressed in organelles of animals and plants. These channels are believed to be evolutionary intermediates between homotetrameric voltage-gated potassium/sodium channels and the four-domain, single subunit, voltage-gated sodium/calcium channels. Each TPC subunit contains 12 transmembrane segments that can be divided into two homologous copies of an S1-S6 Shaker-like 6-TM domain. A functional TPC channel assembles as a dimer - the equivalent of a voltage-gated tetrameric cation channel. The plant TPC channel is localized in the vacuolar membrane and is also called the SV channel for generating the slow vacuolar (SV) current observed long before its molecular identification. Three subfamilies of mammalian TPC channels have been defined - TPC1, 2, and 3 - with the first two being ubiquitously expressed in animals and TPC3 being expressed in some animals but not in humans. Mammalian TPC1 and TPC2 are localized to the endolysosomal membrane and their functions are associated with various physiological processes. TPC3 is localized in the plasma membrane and its physiological function is not well defined.

Genome Editing Tools for Lysosomal Storage Disorders

Genome editing has multiple applications in the biomedical field. They can be used to modify genomes at specific locations, being able to either delete, reduce, or even enhance gene transcription and protein expression. Here, we summarize applications of genome editing used in the field of lysosomal disorders. We focus on the development of cell lines for study of disease pathogenesis, drug discovery, and pathogenicity of specific variants. Furthermore, we highlight the main studies that use gene editing as a gene therapy platform for these disorders, both in preclinical and clinical studies. We conclude that gene editing has been able to change quickly the scenario of these disorders, allowing the development of new therapies and improving the knowledge on disease pathogenesis. Should they confirm their hype, the first gene editing-based products for lysosomal disorders could be available in the next years.

Zinc oxide nanoparticles trigger autophagy-mediated cell death through activating lysosomal TRPML1 in normal kidney cells

Zinc oxide nanoparticles (ZnO NPs) have been widely used in various materials including sunscreens, cosmetics, over-the-counter topical skin products, and pigments. As traces of the used ZnO NPs have been found in the kidney, it is crucial to uncover their potential risks. The aim of this study is to elucidate detrimental effects of ZnO NPs and the molecular mechanism behind their renal toxicity. Cytotoxic effects were measured by MTT assay after HK2 cells were exposed to ZnO NPs for 24 h and IC₅₀ value was determined. ROS and intracellular Zn²⁺ levels were detected by flow cytometry, and localization of Zn²⁺ and lysosome was determined by confocal microscopy. Occurrence of autophagy and detection of autophagic flux were determined by Western blot and confocal microscopy, respectively. We performed unpaired student t test for two groups, and one-way ANOVA with Tukey's post hoc for over three groups. ZnO NPs induced cell death in human renal proximal tubule epithelial cells, HK2. Cytosolic Zn²⁺ caused autophagy-mediated cell death rather than apoptosis. Cytosolic Zn²⁺ processed in lysosome was released by TRPML1, and inhibition of TRPML1 significantly decreased autophagic flux and cell death. The findings of this study suggest that ZnO NPs strongly induce autophagy-mediated cell death in human kidney cells. Controlling TRPML1 can be potentially used to prevent the kidney from ZnO NPs-induced toxicity.

Lysosomal Potassium Channels

Lysosomes are acidic membrane-bound organelles that use hydrolytic enzymes to break down material through pathways such as endocytosis, phagocytosis, mitophagy, and autophagy. To function properly, intralysosomal environments are strictly controlled by a set of integral membrane proteins such as ion channels and transporters. Potassium ion (K⁺) channels are a large and diverse family of membrane proteins that control K⁺ flux across both the plasma membrane and intracellular membranes. In the plasma membrane, they are essential in both excitable and non-excitable cells for the control of membrane potential and cell signaling. However, our understanding of intracellular K⁺ channels is very limited. In this review, we summarize the recent development in studies of K⁺ channels in the lysosome. We focus on their characterization, potential roles in maintaining lysosomal membrane potential and lysosomal function, and pathological implications.

The Plant Vacuole as Heterologous System to Characterize the Functional Properties of TPC Channels

Human TPC channels are an emerging family of intracellular proteins fundamental for cell physiology and involved in various severe pathologies. Their localization in the membranes of endo-lysosomes, intracellular compartments of submicrometric dimensions, makes their study difficult with usual electrophysiological techniques. In this work, we show how the plant vacuole, a versatile organelle that can occupy up to 90% of the volume in mature plant cells, can be used as a heterologous system of expression for functional characterization. For this purpose, the use of vacuoles isolated from mesophyll cells of the Arabidopsis thaliana mutant lacking the endogenous TPC avoids unwanted interferences. The patch-clamp technique can be successfully applied to plant vacuoles in all different configuration modes; of note, the whole-vacuole configuration allows to study channel modulation by cytosolic factors. The combination of patch-clamp with fluorescence techniques, for example, by using fluorescent probes sensitive to specific ions of interest, represents a useful extension to investigate the selectivity properties of the channels. Therefore, the plant vacuole, similar to Xenopus oocytes for ion channels and transporters localized in the plasma membrane, has the capability to become a model system for functional studies on intracellular ion channels and transporters.

NAADP-Mediated Ca2+ Signalling

The discovery of NAADP-evoked Ca²⁺ release in sea urchin eggs and then as a ubiquitous Ca²⁺ mobilizing messenger has introduced several novel paradigms to our understanding of Ca²⁺ signalling, not least in providing a link between cell stimulation and Ca²⁺ release from lysosomes and other acidic Ca²⁺ storage organelles. In addition, the hallmark concentration-response relationship of NAADP-mediated Ca²⁺ release, shaped by striking activation/desensitization mechanisms, influences its actions as an intracellular messenger. There has been recent progress in our understanding of the molecular mechanisms underlying NAADP-evoked Ca²⁺ release, such as the identification of the endo-lysosomal two-pore channel family of cation channels (TPCs) as their principal target and the identity of NAADP-binding proteins that complex with them. The NAADP/TPC signalling axis has gained recent prominence in pathophysiology for their roles in such disease processes as neurodegeneration, tumorigenesis and cellular viral entry.

TRPML1 and TFEB, an Intimate Affair

Ca²⁺ is a universal second messenger that plays a wide variety of fundamental roles in cellular physiology. Thus, to warrant selective responses and to allow rapid mobilization upon specific stimuli, Ca²⁺ is accumulated in organelles to keep it at very low levels in the cytoplasm during resting conditions. Major Ca²⁺ storage organelles include the endoplasmic reticulum (ER), the mitochondria, and as recently demonstrated, the lysosome (Xu and Ren, Annu Rev Physiol 77:57-80, 2015). The importance of Ca²⁺ signaling deregulation in human physiology is underscored by its involvement in several human diseases, including lysosomal storage disorders, neurodegenerative disease and cancer (Shen et al., Nat Commun 3:731, 2012; Bae et al., J Neurosci 34:11485-11503, 2014). Recent evidence strongly suggests that lysosomal Ca²⁺ plays a major role in the regulation of lysosomal adaptation to nutrient availability through a lysosomal signaling pathway involving the lysosomal Ca²⁺ channel TRPML1 and the transcription factor TFEB, a master regulator for lysosomal function and autophagy (Sardiello et al., Science 325:473-477, 2009; Settembre et al., Science 332:1429-1433, 2011; Medina et al., Nat Cell Biol 17:288-299, 2015; Di Paola et al., Cell Calcium 69:112-121, 2018). Due to the tight relationship of this lysosomal Ca²⁺ channel and TFEB, in this chapter, we will focus on the role of the TRPML1/TFEB pathway in the regulation of lysosomal function and autophagy.

Physiological roles of organelles at the pre-synapse in neurons

Mitochondria, endoplasmic reticulum and lysosomes are involved in different pathways that can regulate pre-synaptic function. In particular, they could modulate ATP availability in response to rapid changes, could control synaptic protein levels and adjust Ca²⁺ signalling, which could all impact on neuronal activity. Organelles functions in these processes need to be considered alone when describing the impact of pre-synaptic organelles on neurotransmission. However, the interplay among organelles, which occurs either via signalling pathways or through physical membranous contacts, has to be considered. In this brief review, the physiological role of organelles localized at the pre-synapse in neuronal function is discussed.