Lysosomal calcium and autophagy

The ion channels of endomembranes

The endomembrane system consists of organellar membranes in the biosynthetic pathway [endoplasmic reticulum (ER), Golgi apparatus, and secretory vesicles] as well as those in the degradative pathway (early endosomes, macropinosomes, phagosomes, autophagosomes, late endosomes, and lysosomes). These endomembrane organelles/vesicles work together to synthesize, modify, package, transport, and degrade proteins, carbohydrates, and lipids, regulating the balance between cellular anabolism and catabolism. Large ion concentration gradients exist across endomembranes: Ca2+ gradients for most endomembrane organelles and H+ gradients for the acidic compartments. Ion (Na+, K+, H+, Ca2+, and Cl-) channels on the organellar membranes control ion flux in response to cellular cues, allowing rapid informational exchange between the cytosol and organelle lumen. Recent advances in organelle proteomics, organellar electrophysiology, and luminal and juxtaorganellar ion imaging have led to molecular identification and functional characterization of about two dozen endomembrane ion channels. For example, whereas IP3R1-3 channels mediate Ca2+ release from the ER in response to neurotransmitter and hormone stimulation, TRPML1-3 and TMEM175 channels mediate lysosomal Ca2+ and H+ release, respectively, in response to nutritional and trafficking cues. This review aims to summarize the current understanding of these endomembrane channels, with a focus on their subcellular localizations, ion permeation properties, gating mechanisms, cell biological functions, and disease relevance.

Interplay between myotubularins and Ca2+ homeostasis

The myotubularin family, encompassing myotubularin 1 (MTM1) and 14 myotubularin-related proteins (MTMRs), represents a conserved group of phosphatases featuring a protein tyrosine phosphatase domain. Nine members are characterized by an active phosphatase domain C(X)5R, dephosphorylating the D3 position of PtdIns(3)P and PtdIns(3,5)P2. Mutations in myotubularin genes result in human myopathies, and several neuropathies including X-linked myotubular myopathy and Charcot-Marie-Tooth type 4B. MTM1, MTMR6 and MTMR14 also contribute to Ca2+ signaling and Ca2+ homeostasis that play a key role in many MTM-dependent myopathies and neuropathies. Here we explore the evolving roles of MTM1/MTMRs, unveiling their influence on critical aspects of Ca2+ signaling pathways.

Channels of Evolution: Unveiling Evolutionary Patterns in Diatom Ca2+ Signalling

Diatoms are important primary producers in marine and freshwater environments, but little is known about the signalling mechanisms they use to detect changes in their environment. All eukaryotic organisms use Ca2+ signalling to perceive and respond to environmental stimuli, employing a range of Ca2+-permeable ion channels to facilitate the movement of Ca2+ across cellular membranes. We investigated the distribution of different families of Ca2+ channels in diatom genomes, with comparison to other members of the stramenopile lineage. The four-domain voltage-gated Ca2+ channels (Cav) are present in some centric diatoms but almost completely absent in pennate diatoms, whereas single-domain voltage-gated EukCatA channels were found in all diatoms. Glutamate receptors (GLRs) and pentameric ligand-gated ion channels (pLGICs) also appear to have been lost in several pennate species. Transient receptor potential (TRP) channels are present in all diatoms, but have not undergone the significant expansion seen in brown algae. All diatom species analysed lacked the mitochondrial uniporter (MCU), a highly conserved channel type found in many eukaryotes, including several stramenopile lineages. These results highlight the unique Ca2+-signalling toolkit of diatoms and indicate that evolutionary gains or losses of different Ca2+ channels may contribute to differences in cellular-signalling mechanisms between species.

Alterations in Proteostasis Mechanisms in Niemann-Pick Type C Disease

Niemann-Pick Type C (NPC) represents an autosomal recessive disorder with an incidence rate of 1 in 150,000 live births, classified within lysosomal storage diseases (LSDs). The abnormal accumulation of unesterified cholesterol characterizes the pathophysiology of NPC. This phenomenon is not unique to NPC, as analogous accumulations have also been observed in Alzheimer's disease, Parkinson's disease, and other neurodegenerative disorders. Interestingly, disturbances in the folding of the mutant protein NPC1 I1061T are accompanied by the aggregation of proteins such as hyperphosphorylated tau, α-synuclein, TDP-43, and β-amyloid peptide. These accumulations suggest potential disruptions in proteostasis, a regulatory process encompassing four principal mechanisms: synthesis, folding, maintenance of folding, and protein degradation. The dysregulation of these processes leads to excessive accumulation of abnormal proteins that impair cell function and trigger cytotoxicity. This comprehensive review delineates reported alterations across proteostasis mechanisms in NPC, encompassing changes in processes from synthesis to degradation. Additionally, it discusses therapeutic interventions targeting pharmacological facets of proteostasis in NPC. Noteworthy among these interventions is valproic acid, a histone deacetylase inhibitor (HDACi) that modulates acetylation during NPC1 synthesis. In addition, various therapeutic options addressing protein folding modulation, such as abiraterone acetate, DHBP, calnexin, and arimoclomol, are examined. Additionally, treatments impeding NPC1 degradation, exemplified by bortezomib and MG132, are explored as potential strategies. This review consolidates current knowledge on proteostasis dysregulation in NPC and underscores the therapeutic landscape targeting diverse facets of this intricate process.

Driving autophagy - the role of molecular motors

Most of the vesicular transport pathways inside the cell are facilitated by molecular motors that move along cytoskeletal networks. Autophagy is a well-explored catabolic pathway that is initiated by the formation of an isolation membrane known as the phagophore, which expands to form a double-membraned structure that captures its cargo and eventually moves towards the lysosomes for fusion. Molecular motors and cytoskeletal elements have been suggested to participate at different stages of the process as the autophagic vesicles move along cytoskeletal tracks. Dynein and kinesins govern autophagosome trafficking on microtubules through the sequential recruitment of their effector proteins, post-translational modifications and interactions with LC3-interacting regions (LIRs). In contrast, myosins are actin-based motors that participate in various stages of the autophagic flux, as well as in selective autophagy pathways. However, several outstanding questions remain with regard to how the dominance of a particular motor protein over another is controlled, and to the molecular mechanisms that underlie specific disease variants in motor proteins. In this Review, we aim to provide an overview of the role of molecular motors in autophagic flux, as well as highlight their dysregulation in diseases, such as neurodegenerative disorders and pathogenic infections, and ageing.

Neurodegenerative Disease: From Molecular Basis to Therapy

Neurodegenerative diseases are a heterogeneous group of age-related disorders characterised by the progressive degeneration or death of neurons in the central or peripheral nervous system [...].

Effects of curcumin on non-alcoholic fatty liver disease: A scientific metrogy study

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases encountered in clinical practice. Curcumin can alleviate insulin resistance, inhibit oxidative stress response, reduce inflammation, reduce liver fat deposition, and effectively improve NAFLD through various modalities, inhibiting the progression into cirrhosis and fibrosis.

PURPOSE

To explore the current status, hot spots, and developing trends of curcumin in NAFLD treatment through quantitative scientific analysis to serve as a reference for subsequent studies.

STUDY DESIGN

A comprehensive analysis of the mechanism of action of curcumin in the treatment of NAFLD and methods to increase curcumin bioavailability using bibliometric analysis and literature review.

METHODS

This study used VOSviewer software to analyze the literature related to curcumin treatment of NAFLD in the Web of Science (WOS) core set database. A comprehensive and in-depth review was conducted based on the results of scientific econometric research and literature review.

RESULTS

The review observed that curcumin can activate various signaling pathways such as AMPK and NF-κB to inhibit oxidative stress and apoptosis, thereby reflecting its pharmacological effects: lowering lipid, anti-inflammatory, reducing insulin resistance, and anti-fibrosis. These mechanisms improve or even reverse the complex pathological features of lipid metabolism disorders associated with NAFLD. Curcumin also can potentially serve as a primary regulatory target for treating hepatic steatosis using gut microbiota. However, these pharmacological effects of curcumin were limited owing to its low bioavailability.

CONCLUSION

This review discusses NAFLD treatment with curcumin, analyzes the reasons for its low bioavailability, and introduces models for studying and methods for improving curcumin bioavailability. As research on NAFLD grows, future research should capture the trend of basic research, pay attention to clinical research, and continuously explore the therapeutic potential of curcumin.

Impaired Autophagic Clearance with a Gain-of-Function Variant of the Lysosomal Cl-/H+ Exchanger ClC-7

ClC-7 is a ubiquitously expressed voltage-gated Cl-/H+ exchanger that critically contributes to lysosomal ion homeostasis. Together with its β-subunit Ostm1, ClC-7 localizes to lysosomes and to the ruffled border of osteoclasts, where it supports the acidification of the resorption lacuna. Loss of ClC-7 or Ostm1 leads to osteopetrosis accompanied by accumulation of storage material in lysosomes and neurodegeneration. Interestingly, not all osteopetrosis-causing CLCN7 mutations from patients are associated with a loss of ion transport. Some rather result in an acceleration of voltage-dependent ClC-7 activation. Recently, a gain-of-function variant, ClC-7Y715C, that yields larger ion currents upon heterologous expression, was identified in two patients with neurodegeneration, organomegaly and albinism. However, neither the patients nor a mouse model that carried the equivalent mutation developed osteopetrosis, although expression of ClC-7Y715C induced the formation of enlarged intracellular vacuoles. Here, we investigated how, in transfected cells with mutant ClC-7, the substitution of this tyrosine impinged on the morphology and function of lysosomes. Combinations of the tyrosine mutation with mutations that either uncouple Cl- from H+ counter-transport or strongly diminish overall ion currents were used to show that increased ClC-7 Cl-/H+ exchange activity is required for the formation of enlarged vacuoles by membrane fusion. Degradation of endocytosed material was reduced in these compartments and resulted in an accumulation of lysosomal storage material. In cells expressing the ClC-7 gain-of-function mutant, autophagic clearance was largely impaired, resulting in a build-up of autophagic material.

Identification of a small chemical as a lysosomal calcium mobilizer and characterization of its ability to inhibit autophagy and viral infection

We previously identified glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as one of the cyclic adenosine diphosphoribose (cADPR)'s binding proteins and found that GAPDH participates in cADPR-mediated Ca2+ release from endoplasmic reticulum via ryanodine receptors (RyRs). Here, we aimed to chemically synthesise and pharmacologically characterise novel cADPR analogues. Based on the simulated cADPR-GAPDH complex structure, we performed the structure-based drug screening, identified several small chemicals with high docking scores to cADPR's binding pocket in GAPDH and showed that two of these compounds, C244 and C346, are potential cADPR antagonists. We further synthesised several analogues of C346 and found that its analogue, G42, also mobilised Ca2+ release from lysosomes. G42 alkalised lysosomal pH and inhibited autophagosome-lysosome fusion. Moreover, G42 markedly inhibited Zika virus (ZIKV, a flavivirus) or murine hepatitis virus (MHV, a β-coronavirus) infections of host cells. These results suggest that G42 inhibits virus infection, likely by triggering lysosomal Ca2+ mobilisation and inhibiting autophagy.

The role of sphingosine-1-phosphate in autophagy and related disorders

S1P, also referred to as sphingosine-1-phosphate, is a lipid molecule with bioactive properties involved in numerous cellular processes such as cell growth, movement, programmed cell death, self-degradation, cell specialization, aging, and immune system reactions. Autophagy is a meticulously controlled mechanism in which cells repurpose their elements to maintain cellular balance. There are five stages in autophagy: initiation, nucleation, elongation and maturation, fusion, and degradation. New research has provided insight into the complex connection between S1P and autophagy, uncovering their interaction in both normal and abnormal circumstances. Gaining knowledge about the regulatory mechanism of S1P signaling on autophagy can offer a valuable understanding of its function in well-being and illness, potentially leading to innovative therapeutic concepts for diverse ailments. Hence, this review analyzes the essential stages in mammalian autophagy, with a specific emphasis on recent research exploring the control of each stage by S1P. Additionally, it sheds light on the roles of S1P-induced autophagy in various disorders.

A fixed 20:1 combination of cafedrine/theodrenaline increases cytosolic Ca2+ concentration in human tracheal epithelial cells via ryanodine receptor-mediated Ca2+ release

Mucociliary clearance is a pivotal physiological mechanism that protects the lung by cleaning the airways from pollution and colonization, thereby preventing infection. Ciliary function is influenced by various signal transduction cascades, and Ca2+ represents a key second messenger. A fixed 20:1 combination of cafedrine and theodrenaline has been widely used to treat perioperative hypotension and emergency hypotensive states since the 1960s; however, its effect on the intracellular Ca2+ concentration ([Ca2+]i) of respiratory epithelium remains unknown. Therefore, human tracheal epithelial cells were exposed to the clinically applied 20:1 mixture of cafedrine/theodrenaline and the individual substances separately. [Ca2+]i was assessed by FURA-2 340/380 fluorescence ratio. Pharmacological inhibitors were applied to elucidate relevant signal transduction cascades, and reverse transcription polymerase chain reaction (RT-PCR) was performed on murine tracheal epithelium to analyze ryanodine receptor (RyR) subtype expression. All three pharmacological preparations instantaneously induced a steep increase in [Ca2+]i that quickly returned to its baseline value despite the persistence of each substance. Peak [Ca2+]i following the administration of 20:1 cafedrine/theodrenaline, cafedrine alone, and theodrenaline alone increased in a dose-dependent manner, with median effective concentrations of 0.35 mM (7.32 mM cafedrine and 0.35 mM theodrenaline), 3.14 mM, and 3.45 mM, respectively. When extracellular Ca2+ influx was inhibited using a Ca2+-free buffer solution, the peak [Ca2+]i following the administration of cafedrine alone and theodrenaline alone were reduced but not abolished. No alteration in [Ca2+]i compared with baseline [Ca2+]i was observed during β-adrenergic receptor inhibition. Depletion of caffeine-sensitive stores and inhibition of RyR, but not IP3 receptors, completely abolished any increase in [Ca2+]i. However, [Ca2+]i still increased following the depletion of mitochondrial Ca2+ stores using 2,4-dinitrophenol. RT-PCR revealed RyR-2 and RyR-3 expression on murine tracheal epithelium. Although our experiments showed that cafedrine/theodrenaline, cafedrine alone, or theodrenaline alone release Ca2+ from intracellular stores through mechanisms that are exclusively triggered by β-adrenergic receptor stimulation, which most probably lead to RyR activation, clinical plasma concentrations are considerably lower than those used in our experiments to elicit an increase in [Ca2+]i; therefore, further studies are needed to evaluate the ability of cafedrine/theodrenaline to alter mucociliary clearance in clinical practice.

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.

Lysosomes, curcumin, and anti-tumor effects: how are they linked?

Curcumin is a natural active ingredient from traditional Chinese medicine (TCM) that has multi-target characteristics to exert extensive pharmacological activities and thus has been applied in the treatment of various diseases such as cancer, cardiovascular diseases, nervous system, and autoimmune disorders. As an important class of membranous organelles in the intracellular membrane system, lysosomes are involved in biological processes such as programmed cell death, cell metabolism, and immune regulation, thus affecting tumor initiation and progression. It has been shown that curcumin can modulate lysosomal function through the aforementioned pathways, thereby affecting tumor proliferation, invasion, metastasis, drug resistance, and immune function. This review briefly elaborated the regulatory mechanisms of lysosome biogenesis and summarized curcumin-related studies with its anti-tumor effect, providing a reference for the clinical application of curcumin and anti-tumor research targeting lysosomes.

Coronavirus Porcine Epidemic Diarrhea Virus Utilizes Chemokine Interleukin-8 to Facilitate Viral Replication by Regulating Ca2+ Flux

Chemokine production by epithelial cells is crucial for neutrophil recruitment to sites of inflammation during viral infection. However, the effect of chemokine on epithelia and how chemokine is involved in coronavirus infection remains to be fully understood. Here, we identified an inducible chemokine interleukin-8 (CXCL8/IL-8), which could promote coronavirus porcine epidemic diarrhea virus (PEDV) infection in African green monkey kidney epithelial cells (Vero) and Lilly Laboratories cell-porcine kidney 1 epithelial cells (LLC-PK1). IL-8 deletion restrained cytosolic calcium (Ca2+), whereas IL-8 stimulation improved cytosolic Ca2+. The consumption of Ca2+ restricted PEDV infection. PEDV internalization and budding were obvious reductions when cytosolic Ca2+ was abolished in the presence of Ca2+ chelators. Further study revealed that the upregulated cytosolic Ca2+ redistributes intracellular Ca2+. Finally, we identified that G protein-coupled receptor (GPCR)-phospholipase C (PLC)-inositol trisphosphate receptor (IP3R)-store-operated Ca2+ (SOC) signaling was crucial for enhancive cytosolic Ca2+ and PEDV infection. To our knowledge, this study is the first to uncover the function of chemokine IL-8 during coronavirus PEDV infection in epithelia. PEDV induces IL-8 expression to elevate cytosolic Ca2+, promoting its infection. Our findings reveal a novel role of IL-8 in PEDV infection and suggest that targeting IL-8 could be a new approach to controlling PEDV infection. IMPORTANCE Coronavirus porcine epidemic diarrhea virus (PEDV) is a highly contagious enteric coronavirus that caused severe economic losses worldwide, and more effort is needed to develop economical and efficient vaccines to control or eliminate this disease. The chemokine interleukin-8 (CXCL8/IL-8) is indispensable for the activation and trafficking of inflammatory mediators and tumor progression and metastasis. This study evaluated the effect of IL-8 on PEDV infection in epithelia. We found that IL-8 expression improved cytosolic Ca2+ in epithelia, facilitating PEDV rapid internalization and egress. G protein-coupled receptor (GPCR)-phospholipase C (PLC)-inositol trisphosphate receptor (IP3R)-SOC signaling was activated by IL-8, releasing the intracellular Ca2+ stores from endoplasmic reticulum (ER). These findings provide a better understanding of the role of IL-8 in PEDV-induced immune responses, which will help develop small-molecule drugs for coronavirus cure.

Ca2+ signaling and cell death

Multiple forms of regulated cell death (RCD) have been characterized, each of which originates from the activation of a dedicated molecular machinery. RCD can occur in purely physiological settings or upon failing cellular adaptation to stress. Ca²⁺ions have been shown to physically interact with - and hence regulate - various components of the RCD machinery. Moreover, intracellular Ca²⁺ accumulation can promote organellar dysfunction to degree that can be overtly cytotoxic or sensitize cells to RCD elicited by other stressors. Here, we provide an overview of the main links between Ca²⁺and different forms of RCD, including apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, lysosome-dependent cell death, and parthanatos.

"Dirty Dancing" of Calcium and Autophagy in Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia. There is a growing body of evidence that dysregulation in neuronal calcium (Ca²⁺) signaling plays a major role in the initiation of AD pathogenesis. In particular, it is well established that Ryanodine receptor (RyanR) expression levels are increased in AD neurons and Ca²⁺ release via RyanRs is augmented in AD neurons. Autophagy is important for removing unnecessary or dysfunctional components and long-lived protein aggregates, and autophagy impairment in AD neurons has been extensively reported. In this review we discuss recent results that suggest a causal link between intracellular Ca²⁺ signaling and lysosomal/autophagic dysregulation. These new results offer novel mechanistic insight into AD pathogenesis and may potentially lead to identification of novel therapeutic targets for treating AD and possibly other neurodegenerative disorders.

NAADP-Evoked Ca2+ Signaling Leads to Mutant Huntingtin Aggregation and Autophagy Impairment in Murine Astrocytes

Huntington’s disease (HD) is a progressive neurodegenerative disease characterized by mutations in the huntingtin gene (mHtt), causing an unstable repeat of the CAG trinucleotide, leading to abnormal long repeats of polyglutamine (poly-Q) in the N-terminal region of the huntingtin, which form abnormal conformations and aggregates. Alterations in Ca2+ signaling are involved in HD models and the accumulation of mutated huntingtin interferes with Ca2+ homeostasis. Lysosomes are intracellular Ca2+ storages that participate in endocytic and lysosomal degradation processes, including autophagy. Nicotinic acid adenine dinucleotide phosphate (NAADP) is an intracellular second messenger that promotes Ca2+ release from the endo-lysosomal system via Two-Pore Channels (TPCs) activation. Herein, we show the impact of lysosomal Ca2+ signals on mHtt aggregation and autophagy blockade in murine astrocytes overexpressing mHtt-Q74. We observed that mHtt-Q74 overexpression causes an increase in NAADP-evoked Ca2+ signals and mHtt aggregation, which was inhibited in the presence of Ned-19, a TPC antagonist, or BAPTA-AM, a Ca2+ chelator. Additionally, TPC2 silencing revert the mHtt aggregation. Furthermore, mHtt has been shown co-localized with TPC2 which may contribute to its effects on lysosomal homeostasis. Moreover, NAADP-mediated autophagy was also blocked since its function is dependent on lysosomal functionality. Taken together, our data show that increased levels of cytosolic Ca2+ mediated by NAADP causes mHtt aggregation. Additionally, mHtt co-localizes with the lysosomes, where it possibly affects organelle functions and impairs autophagy.

Pharmacological inhibition of lysosomal two-pore channel 2 (TPC2) confers neuroprotection in stroke via autophagy regulation

Lysosomal function and organellar Ca²⁺ homeostasis become dysfunctional in Stroke causing disturbances in autophagy, the major process for the degradation of abnormal protein aggregates and dysfunctional organelles. However, the role of autophagy in Stroke is controversial since excessive or prolonged autophagy activation exacerbates ischemic brain injury. Of note, glutamate evokes NAADP-dependent Ca²⁺ release via lysosomal TPC2 channels thus controlling basal autophagy. Considering the massive release of excitotoxins in Stroke, autophagic flux becomes uncontrolled with abnormal formation of autophagosomes causing, in turn, disruption of excitotoxins clearance and neurodegeneration. Here, a fine regulation of autophagy via a proper pharmacological modulation of lysosomal TPC2 channel has been tested in preclinical Stroke models. Primary cortical neurons were subjected to oxygen and glucose deprivation+reoxygenation to reproduce in vitro brain ischemia. Focal brain ischemia was induced in rats by transient middle cerebral artery occlusion (tMCAO). Under these conditions, TPC2 protein expression as well as autophagy and endoplasmic reticulum (ER) stress markers were studied by Western blotting, while TPC2 localization and activity were measured by immunocytochemistry and single-cell video-imaging, respectively. TPC2 protein expression and immunosignal were highly modulated in primary cortical neurons exposed to extreme hypoxic conditions causing dysfunction in organellar Ca²⁺ homeostasis, ER stress and autophagy-induced cell death. TPC2 knocking down and pharmacological inhibition by Ned-19 during hypoxia induced neuroprotection. The effect of Ned-19 was reversed by the permeable form of TPC2 endogenous agonist, NAADP-AM. Of note, Ned-19 prevented ER stress, as measured by GRP78 (78 kDa glucose-regulated protein) protein reduction and caspase 9 downregulation. In this way Ned-19 restored organellar Ca²⁺ level. Interestingly, Ned-19 reduced the infarct volume and neurological deficits in rats subjected to tMCAO and prevented hypoxia-induced cell death by blocking autophagic flux. Collectively, the pharmacological inhibition of TPC2 lysosomal channel by Ned-19 protects from focal ischemia by hampering a hyperfunctional autophagy.

Quantitative assessment of mitophagy in irradiated cancer cells

Mitophagy is a finely regulated mechanism through which eukaryotic cells selectively dispose of supernumerary, permeabilized or otherwise damaged mitochondria through lysosomal degradation. Dysfunctional mitochondria are prone to release potentially cytotoxic factors including reactive oxygen species (ROS) and caspase activators, such as cytochrome c, somatic (CYCS). Thus, proficient mitophagic responses mediate prominent cytoprotective functions. Moreover, the rapid degradation of permeabilized mitochondria limits the release of mitochondrial components that may drive inflammatory reactions, such as mitochondrial DNA (mtDNA) and transcription factor A, mitochondrial (TFAM), implying that mitophagy also mediates potent anti-inflammatory effects. Here, we detail a simple, flow cytometry-assisted protocol for the specific measurement of mitophagic responses as driven by radiation therapy (RT) in mouse hormone receptor (HR)⁺ mammary carcinoma TS/A cells. With some variations, this method - which relies on the mitochondria-restricted expression of a fluorescent reporter that is sensitive to pH and hence changes excitation wavelength within lysosomes (mt-mKeima) - can be adapted to a variety of human and mouse cancer cell lines and/or straightforwardly implemented on fluorescence microscopy platforms.

The inhibition of TRPML1/TFEB leads to lysosomal biogenesis disorder, contributes to developmental fluoride neurotoxicity

Fluoride is capable of inducing developmental neurotoxicity; regrettably, the mechanism is obscure. We aimed to probe the role of lysosomal biogenesis disorder in developmental fluoride neurotoxicity-specifically, the regulating effect of the transient receptor potential mucolipin 1 (TRPML1)/transcription factor EB (TFEB) signaling pathway on lysosomal biogenesis. Sprague-Dawley rats were given fluoridated water freely, during pregnancy to the parental rats to 2 months after delivery to the offspring. In addition, neuroblastoma SH-SY5Y cells were treated with sodium fluoride (NaF), with or without mucolipin synthetic agonist 1 (ML-SA1) or adenovirus TFEB (Ad-TFEB) intervention. Our findings revealed that NaF impaired learning and memory as well as memory retention capacities in rat offspring, induced lysosomal biogenesis disorder, and decreased lysosomal degradation capacity, autophagosome accumulation, autophagic flux blockade, apoptosis, and pyroptosis. These changes were evidenced by the decreased expression of TRPML1, nuclear TFEB, LAMP2, CTSB, and CTSD, as well as increased expression of LC3-II, p62, cleaved PARP, NLRP3, Caspase1, and IL-1β. Furthermore, TRPML1 activation and TFEB overexpression both restored TFEB nuclear protein expression and promoted lysosomal biogenesis while enhancing lysosomal degradation capacity, recovering autophagic flux, and attenuating NaF-induced apoptosis and pyroptosis. Taken together, these results show that NaF promotes the progression of developmental fluoride neurotoxicity by inhibiting TRPML1/TFEB expression and impeding lysosomal biogenesis. Notably, the activation of TRPML1/TFEB alleviated NaF-induced developmental neurotoxicity. Therefore, TRPML1/TFEB may be promising markers of developmental fluoride neurotoxicity.

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.

Myo1b Promotes Premature Endothelial Senescence and Dysfunction via Suppressing Autophagy: Implications for Vascular Aging

Endothelial cell (EC) senescence characterized by an irreversible growth arrest leading to endothelial dysfunction has been implicated in vascular aging and aging-associated cardiovascular diseases. Autophagy plays a crucial role in the modulation of cellular senescence. Our previous showed that myosin 1b (Myo1b), one family of nonfilamentous class-1 myosin, was reported to be involved in the modulation of human smooth muscle cell senescence. However, the role of Myo1b in the modulation of EC senescence with links to autophagy has yet to be elucidated. In this study, we sought to explore the role of Myo1b in endothelial senescence and further elucidate the underlying mechanisms. Here, we show prominent upregulation of Myo1b in senescent ECs in comparison with nonsenescence ECs in both mRNA and protein expression levels. Silencing Myo1b in senescent cells ameliorates endothelial dysfunctions and reverses endothelial senescence phenotypic changes such as senescence-associated-β-galactosidase activity, cyclin-dependent kinase inhibitor p21^WAF1, expression of vascular adhesion molecule-1 (VCAM1) and intercellular adhesion molecule-1 (ICAM1), and the senescence-associated cytokines. In contrast, in nonsenescent cells, overexpressing Myo1b promotes endothelial senescence and suppresses autophagy through the impairment of autophagosome and lysosome fusion. The interaction between Myo1b and LRRK2 through Myo1b tail domain promotes intracellular calcium elevation, which results in the inhibition of autophagic flux. In vitro and in vivo aging models, Myo1b knockdown in senescent ECs and wild type-aged mice is able to enhance autophagy and ameliorate aging-associated endothelial dysfunction. Taken together, our studies reveal a new function for Myo1b, that is, to couple LRRK2 assembly to promote an increase in intracellular calcium level, which impairs the autophagosome-lysosome fusion, and ultimately the promotion of EC senescence and vascular aging.

PI(3,5)P2 and NAADP: Team players or lone warriors? - New insights into TPC activation modes

NAADP (nicotinic acid adenine dinucleotide phosphate) is a second messenger, releasing Ca²⁺ from acidic calcium stores such as endosomes and lysosomes. PI(3,5)P₂ (phosphatidylinositol 3,5-bisphosphate) is a phospho-inositide, residing on endolysosomal membranes and likewise releasing Ca²⁺ from endosomes and lysosomes. Both compounds have been shown to activate endolysosomal two-pore channels (TPCs) in mammalian cells. However, their effects on ion permeability as demonstrated specifically for TPC2 differ. While PI(3,5)P₂ elicits predominantly Na⁺-selective currents, NAADP increases the Ca²⁺ permeability of the channel. What happens when both compounds are applied simultaneously was unclear until recently.