Methods for monitoring Ca 2+ and ion channels in the lysosome

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.

Functional characterization of endo-lysosomal compartments by correlative live-cell and volume electron microscopy

Fluorescent biosensors are valuable tools to monitor protein activities and the functional state of organelles in live cells. However, the information provided by fluorescent microscopy (FM) is mostly limited in resolution and lacks ultrastructural context information. Protein activities are confined to organelle zones with a distinct membrane morphology, which can only be seen by electron microscopy (EM). EM, however, intrinsically lacks information on protein activities. The lack of methods to integrate these two imaging modalities has hampered understanding the functional organization of cellular organelles. Here we introduce "functional correlative microscopy" (functional CLEM) to directly infer functional information from live cells to EM with nanometer resolution. We label and visualize live cells with fluorescent biosensors after which they are processed for EM and imaged using a volume electron microscopy technique. Within a single dataset we correlate hundreds of fluorescent spots enabling quantitative analysis of the functional-ultrastructural data. We employ our method to monitor essential functional parameters of late endo-lysosomal compartments, i.e., pH, calcium, enzyme activities and cholesterol content. Our data reveal a steep functional difference in enzyme activity between late endosomes and lysosomes and unexpectedly high calcium levels in late endosomes. The presented CLEM workflow is compatible with a large repertoire of probes and paves the way for large scale functional studies of all types of cellular structures.

TRPML1-Induced Lysosomal Ca2+ Signals Activate AQP2 Translocation and Water Flux in Renal Collecting Duct Cells

Lysosomes are acidic Ca²⁺ storage organelles that actively generate local Ca²⁺ signaling events to regulate a plethora of cell functions. Here, we characterized lysosomal Ca²⁺ signals in mouse renal collecting duct (CD) cells and we assessed their putative role in aquaporin 2 (AQP2)-dependent water reabsorption. Bafilomycin A1 and ML-SA1 triggered similar Ca²⁺ oscillations, in the absence of extracellular Ca²⁺, by alkalizing the acidic lysosomal pH or activating the lysosomal cation channel mucolipin 1 (TRPML1), respectively. TRPML1-dependent Ca²⁺ signals were blocked either pharmacologically or by lysosomes' osmotic permeabilization, thus indicating these organelles as primary sources of Ca²⁺ release. Lysosome-induced Ca²⁺ oscillations were sustained by endoplasmic reticulum (ER) Ca²⁺ content, while bafilomycin A1 and ML-SA1 did not directly interfere with ER Ca²⁺ homeostasis per se. TRPML1 activation strongly increased AQP2 apical expression and depolymerized the actin cytoskeleton, thereby boosting water flux in response to an hypoosmotic stimulus. These effects were strictly dependent on the activation of the Ca²⁺/calcineurin pathway. Conversely, bafilomycin A1 led to perinuclear accumulation of AQP2 vesicles without affecting water permeability. Overall, lysosomal Ca²⁺ signaling events can be differently decoded to modulate Ca²⁺-dependent cellular functions related to the dock/fusion of AQP2-transporting vesicles in principal cells of the CD.

L-type voltage-dependent Ca2+ channels expression involved in pre-neoplastic transformation of breast cancer

Background

Intracellular Ca2+ levels can modulate several cellular functions, including proliferation and other processes found altered in neoplastic cells. Helping to maintain Ca2+ homeostasis, L-type voltage-dependent Ca2+ channels had its expression identified in neoplasias, including breast cancer. Invasive breast carcinoma of no special type, the most common classification of breast cancer, has ductal hyperplasia and ductal carcinoma in situ as its possible non-obligate precursors. This channel’s role in breast cancer development from these precursors has not been investigated. Evaluate protein expression and subcellular localization of CaV1.1, CaV1.2, and CaV1.3 in mammary epithelium without alteration and neoplastic and non-neoplastic ductal proliferative lesions through immunohistochemistry was the aim of this investigation.

Methods

In the present study, CaV1.1, CaV1.2, and CaV1.3 protein expression was evaluated by immunohistochemistry in breast without alteration and in proliferative non-neoplastic and neoplastic ductal epithelial lesions of the human breast.

Results

It was observed that CaV1.3 presented a reduction in nuclear expression at neoplastic lesions, in addition to an increase in cytoplasmic CaV1.1 expression. The analyses of membrane immunostaining showed that CaV1.2 and CaV1.3 had an increase of expression as the lesions progressed in the stages leading to invasive carcinomas.

Conclusions

Changes in protein expression and subcellular localization of these channels during the progression stages indicate that they may be involved in neoplastic transformation.

NLRP3 Inflammasome Activation: A Therapeutic Target for Cerebral Ischemia–Reperfusion Injury

Millions of patients are suffering from ischemic stroke, it is urgent to figure out the pathogenesis of cerebral ischemia–reperfusion (I/R) injury in order to find an effective cure. After I/R injury, pro-inflammatory cytokines especially interleukin-1β (IL-1β) upregulates in ischemic brain cells, such as microglia and neuron. To ameliorate the inflammation after cerebral I/R injury, nucleotide-binding oligomerization domain (NOD), leucine-rich repeat (LRR), and pyrin domain-containing protein 3 (NLRP3) inflammasome is well-investigated. NLRP3 inflammasomes are complicated protein complexes that are activated by endogenous and exogenous danger signals to participate in the inflammatory response. The assembly and activation of the NLRP3 inflammasome lead to the caspase-1-dependent release of pro-inflammatory cytokines, such as interleukin (IL)-1β and IL-18. Furthermore, pyroptosis is a pro-inflammatory cell death that occurs in a dependent manner on NLRP3 inflammasomes after cerebral I/R injury. In this review, we summarized the assembly and activation of NLRP3 inflammasome; moreover, we also concluded the pivotal role of NLRP3 inflammasome and inhibitors, targeting the NLRP3 inflammasome in cerebral I/R injury.

Current Methods to Unravel the Functional Properties of Lysosomal Ion Channels and Transporters

A distinct set of channels and transporters regulates the ion fluxes across the lysosomal membrane. Malfunctioning of these transport proteins and the resulting ionic imbalance is involved in various human diseases, such as lysosomal storage disorders, cancer, as well as metabolic and neurodegenerative diseases. As a consequence, these proteins have stimulated strong interest for their suitability as possible drug targets. A detailed functional characterization of many lysosomal channels and transporters is lacking, mainly due to technical difficulties in applying the standard patch-clamp technique to these small intracellular compartments. In this review, we focus on current methods used to unravel the functional properties of lysosomal ion channels and transporters, stressing their advantages and disadvantages and evaluating their fields of applicability.

Cryo-EM structure of mouse TRPML2 in lipid nanodiscs

In mammalians, transient receptor potential mucolipin ion channels (TRPMLs) exhibit variable permeability to cations such as Ca²⁺, Fe²⁺, Zn²⁺, and Na⁺, and can be activated by the phosphoinositide PI(3,5)P2 in the endolysosomal system. Loss or dysfunction of TRPMLs has been implicated in lysosomal storage disorders, infectious diseases, and metabolic diseases. TRPML2 has recently been identified as a mechanosensitive and hypotonicity-sensitive channel in endolysosomal organelles, which distinguishes it from TRPML1 and TRPML3. However, the molecular and gating mechanism of TRPML2 remains elusive. Here, we present the cryo-EM structure of the full-length mouse TRPML2 in lipid nanodiscs at 3.14 Å resolution. The TRPML2 homo-tetramer structure at pH 7.4 in the apo state reveals an inactive conformation and some unique features of the extracytosolic/luminal domain and voltage sensor-like domain that have implications for the ion-conducting pathway. This structure enables new comparisons between the different subgroups of TRPML channels with available structures and provides structural insights into the conservation and diversity of TRPML channels. These comparisons have broad implications for understanding a variety of molecular mechanisms of TRPMLs in different pH conditions, including with and without bound agonists and antagonists.

Piperine promotes autophagy flux by P2RX4 activation in SNCA/α-synuclein-induced Parkinson disease model

Olfactory dysfunction, one of the earliest non-motor symptoms of Parkinson disease (PD), is accompanied by abnormal deposition of SNCA/α-synuclein in the olfactory bulb (OB). The macroautophagy/autophagy-lysosome pathway (ALP) plays an important role in degrading pathological SNCA and modulating this pathway may be a promising treatment strategy. P2RX4 (purinergic receptor P2X, ligand-gated ion channel 4), a member of the purinergic receptor X family, is a key molecule regulating ALP. Piperine (PIP) is a Chinese medicine with anti-inflammatory and anti-oxidant effects. The present study investigated the neuroprotective effects of PIP on SNCA overexpression-induced PD cell and mouse models. We found that PIP oral administration (25, 50 and 100 mg/kg) for 6 weeks attenuated olfactory deficits and delayed motor deficits in Thy 1-SNCA transgenic mice overexpressing human SNCA. This was accompanied by a degradation of pathological SNCA in OB. In addition, PIP improved cell viability and promoted degradation of human SNCA in SK-N-SH cells. These protective effects were exerted via autophagy flux promotion by enhancing autophagosome-lysosome membrane fusion. Furthermore, tandem mass tag proteomics analyses showed that P2RX4 plays an important role in PIP treatment-induced activation of autophagy flux. These findings demonstrate that PIP exerts neuroprotective effects in PD models via promotion of autophagy flux and may be an effective agent for PD treatment.

Abbreviations: 6-OHDA, 6-hydroxydopamine; ALP, autophagy-lysosome pathway; BafA₁, bafilomycin A₁; CoQ10, coenzyme Q10; DMSO: dimethyl sulfoxide; HPLC, high-performance liquid chromatography; IVE, ivermectin; LDH, lactate dehydrogenase; MAP1LC3/LC3-II, lipid-conjugated microtubule-associated protein 1 light chain 3; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; mRFP-GFP, tandem monomeric red fluorescent protein-green fluorescent protein; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; OB, olfactory bulb; P2RX4, purinergic receptor P2X, ligand-gated ion channel 4; PD, Parkinson disease; PBS: phosphate-buffered saline; PI: propidium iodide; PIP, piperine; PLG, piperlongumine; p-SNCA, SNCA phosphorylated at Ser129; Rap, rapamycin; RT-PCR: quantitative real-time PCR; SNARE, soluble N-ethylmaleimide-sensitive factor-attachment protein receptor; SNCA/α-synuclein, synuclein, alpha; STX17, syntaxin17; TG, transgenic; TH, tyrosine hydroxylase; UPS, ubiquitin-proteasome system; WT, wild-type

Endolysosomal Ca2+ signaling in cardiovascular health and disease

An increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i) regulates a plethora of functions in the cardiovascular (CV) system, including contraction in cardiomyocytes and vascular smooth muscle cells (VSMCs), and angiogenesis in vascular endothelial cells and endothelial colony forming cells. The sarco/endoplasmic reticulum (SR/ER) represents the largest endogenous Ca²⁺ store, which releases Ca²⁺ through ryanodine receptors (RyRs) and/or inositol-1,4,5-trisphosphate receptors (InsP₃Rs) upon extracellular stimulation. The acidic vesicles of the endolysosomal (EL) compartment represent an additional endogenous Ca²⁺ store, which is targeted by several second messengers, including nicotinic acid adenine dinucleotide phosphate (NAADP) and phosphatidylinositol 3,5-bisphosphate [PI(3,5)P₂], and may release intraluminal Ca²⁺ through multiple Ca²⁺ permeable channels, including two-pore channels 1 and 2 (TPC1-2) and Transient Receptor Potential Mucolipin 1 (TRPML1). Herein, we discuss the emerging, pathophysiological role of EL Ca²⁺ signaling in the CV system. We describe the role of cardiac TPCs in β-adrenoceptor stimulation, arrhythmia, hypertrophy, and ischemia-reperfusion injury. We then illustrate the role of EL Ca²⁺ signaling in VSMCs, where TPCs promote vasoconstriction and contribute to pulmonary artery hypertension and atherosclerosis, whereas TRPML1 sustains vasodilation and is also involved in atherosclerosis. Subsequently, we describe the mechanisms whereby endothelial TPCs promote vasodilation, contribute to neurovascular coupling in the brain and stimulate angiogenesis and vasculogenesis. Finally, we discuss about the possibility to target TPCs, which are likely to mediate CV cell infection by the Severe Acute Respiratory Disease-Coronavirus-2, with Food and Drug Administration-approved drugs to alleviate the detrimental effects of Coronavirus Disease-19 on the CV system.

Life in the lumen: The multivesicular endosome

The late endosomes/endo‐lysosomes of vertebrates contain an atypical phospholipid, lysobisphosphatidic acid (LBPA) (also termed bis[monoacylglycero]phosphate [BMP]), which is not detected elsewhere in the cell. LBPA is abundant in the membrane system present in the lumen of this compartment, including intralumenal vesicles (ILVs). In this review, the current knowledge on LBPA and LBPA‐containing membranes will be summarized, and their role in the control of endosomal cholesterol will be outlined. Some speculations will also be made on how this system may be overwhelmed in the cholesterol storage disorder Niemann‐Pick C. Then, the roles of intralumenal membranes in endo‐lysosomal dynamics and functions will be discussed in broader terms. Likewise, the mechanisms that drive the biogenesis of intralumenal membranes, including ESCRTs, will also be discussed, as well as their diverse composition and fate, including degradation in lysosomes and secretion as exosomes. This review will also discuss how intralumenal membranes are hijacked by pathogenic agents during intoxication and infection, and what is the biochemical composition and function of the intra‐endosomal lumenal milieu. Finally, this review will allude to the size limitations imposed on intralumenal vesicle functions and speculate on the possible role of LBPA as calcium chelator in the acidic calcium stores of endo‐lysosomes.

Multiple-Coated PLGA Nanoparticles Loading Triptolide Attenuate Injury of a Cellular Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease, which is associated with extracellular deposition of amyloid-β proteins (Aβ). It has been reported that triptolide (TP), an immunosuppressive and anti-inflammatory agent extracted from a Chinese herb Tripterygium wilfordii, shows potential neuroprotective effects pertinent to AD. However, the clinical use of TP for AD could be hampered due to its high toxicity, instability, poor water solubility, and nonspecific biodistribution after administration. In this paper, we reported a kind of multiple-coated PLGA nanoparticle with the entrapment of TP and surface coated by chitosan hydrochloride, Tween-80, PEG20000, and borneol/mentholum eutectic mixture (MC-PLGA-TP-NP) as a novel nasal brain targeting preparation for the first time. The obtained MC-PLGA-TP-NP was 147.5 ± 20.7 nm with PDI of 0.263 ± 0.075, zeta potential of 14.62 ± 2.47 mV, and the entrapment efficiency and loading efficiency of 93.14% ± 4.75% and 1.17 ± 0.08%, respectively. In comparison of TP, MC-PLGA-TP-NP showed sustained-release profile and better transcellular permeability to Caco-2 cells in vitro. In addition, our data showed that MC-PLGA-TP-NP remarkably reduced the cytotoxicity, attenuated the oxidative stress, and inhibited the increase of the intracellular Ca²⁺ influx in differentiated PC12 cells induced by Aβ_1-42. Therefore, it can be concluded that MC-PLGA-TP-NP is a promising preparation of TP, which exerts a better neuroprotective activity in the AD cellular model.

Two-pore channels regulate Tat endolysosome escape and Tat-mediated HIV-1 LTR transactivation

HIV-1 Tat is essential for HIV-1 replication and appears to play an important role in the pathogenesis of HIV-associated neurological complications. Secreted from infected or transfected cells, Tat has the extraordinary ability to cross the plasma membrane. In the brain, Tat can be taken up by CNS cells via receptor-mediated endocytosis. Following endocytosis and its internalization into endolysosomes, Tat must be released in order for it to activate the HIV-1 LTR promoter and facilitate HIV-1 viral replication in the nucleus. However, the underlying mechanisms whereby Tat escapes endolysosomes remain unclear. Because Tat disrupts intracellular calcium homeostasis, we investigated the involvement of calcium in Tat endolysosome escape and subsequent LTR transactivation. We demonstrated that chelating endolysosome calcium with high-affinity rhodamine-dextran or chelating cytosolic calcium with BAPTA-AM attenuated Tat endolysosome escape and LTR transactivation. Significantly, we demonstrated that pharmacologically blocking and knocking down the endolysosome-resident two-pore channels (TPCs) attenuated Tat endolysosome escape and LTR transactivation. This calcium-mediated effect appears to be selective for TPCs because knocking down TRPML1 calcium channels was without effect. Our findings suggest that calcium released from TPCs is involved in Tat endolysosome escape and subsequent LTR transactivation. TPCs might represent a novel therapeutic target against HIV-1 infection and HIV-associated neurological complications.

Molecular Mechanisms of Calcium Signaling During Phagocytosis

Calcium (Ca²⁺) is a ubiquitous second messenger involved in the regulation of numerous cellular functions including vesicular trafficking, cytoskeletal rearrangements and gene transcription. Both global as well as localized Ca²⁺ signals occur during phagocytosis, although their functional impact on the phagocytic process has been debated. After nearly 40 years of research, a consensus may now be reached that although not strictly required, Ca²⁺ signals render phagocytic ingestion and phagosome maturation more efficient, and their manipulation make an attractive avenue for therapeutic interventions. In the last decade many efforts have been made to identify the channels and regulators involved in generating and shaping phagocytic Ca²⁺ signals. While molecules involved in store-operated calcium entry (SOCE) of the STIM and ORAI family have taken center stage, members of the canonical, melastatin, mucolipin and vanilloid transient receptor potential (TRP), as well as purinergic P2X receptor families are now recognized to play significant roles. In this chapter, we review the recent literature on research that has linked specific Ca²⁺-permeable channels and regulators to phagocytic function. We highlight the fact that lipid mediators are emerging as important regulators of channel gating and that phagosomal ionic homeostasis and Ca²⁺ release also play essential parts. We predict that improved methodologies for measuring these factors will be critical for future advances in dissecting the intricate biology of this fascinating immune process.

Size Matters in the Cytotoxicity of Polydopamine Nanoparticles in Different Types of Tumors

Polydopamine has acquired great relevance in the field of nanomedicine due to its physicochemical properties. Previously, it has been reported that nanoparticles synthetized from this polymer are able to decrease the viability of breast and colon tumor cells. In addition, it is well known that the size of therapeutic particles plays an essential role in their effect. As a consequence, the influence of this parameter on the cytotoxicity of polydopamine nanoparticles was studied in this work. For this purpose, polydopamine nanoparticles with three different diameters (115, 200 and 420 nm) were synthetized and characterized. Their effect on the viability of distinct sorts of human carcinomas (breast, colon, liver and lung) and stromal cells was investigated, as well as the possible mechanisms that could be responsible for such cytotoxicity. Moreover, polydopamine nanoparticles were also loaded with doxorubicin and the therapeutic action of the resulting nanosystem was analyzed. As a result, it was demonstrated that a smaller nanoparticle size is related to a more enhanced antiproliferative activity, which may be a consequence of polydopamine's affinity for iron ions. Smaller nanoparticles would be able to adsorb more lysosomal Fe3+ and, when they are loaded with doxorubicin, a synergistic effect can be achieved.

BK channels regulate extracellular Tat-mediated HIV-1 LTR transactivation

HIV-1 Tat is essential for HIV-1 replication and plays an important role in latent HIV-1 infection, HIV-1 associated neurological complication, and other HIV-1 comorbidities. Secreted from HIV-1 infected or transfected cells, Tat can be up-taken into cells by receptor-mediated endocytosis and internalized into endolysosomes. To reach nucleus where it can facilitate HIV-1 viral replication, exogenous Tat has to escape the degradation by endolysosomes. Because of findings that endolysosome de-acidification with, for example, the weak-base anti-malarial drug chloroquine prevents exogenous Tat degradation and enhances the amount of Tat available to activate HIV-1 LTR, we hypothesize that acidifying endolysosomes may enhance Tat degradation in endolysosomes and restrict LTR transactivation. Here, we determined the involvement of endolysosome-resident transient receptor potential mucolipin 1 channel (TRPML1) and the big conductance Ca²⁺-activated potassium (BK) channel in regulating endolysosome pH, as well as Tat-mediated HIV-1 LTR transactivation in U87MG cells stably integrated with HIV-1 LTR luciferase reporter. Activating TRPML1 channels with ML-SA1 acidified endolysosomes and restricted Tat-mediated HIV-1 LTR transactivation. These effects of ML-SA1 appeared to be mediated through activation of BK channels, because the effects of ML-SA1 on Tat-mediated HIV-1 LTR transactivation were blocked using pharmacological inhibitors or shRNA knock-down of BK channels. On the other hand, activating TRPML1 and BK channels enhanced cellular degradation of exogenous Tat. These results suggest that acidifying endolysosomes by activating TRPML1 or BK channels may provide therapeutic benefit against latent HIV-1 infection, HIV-1 associated neurocognitive disorders, and other HIV-1 comorbidities.

VacA generates a protective intracellular reservoir for Helicobacter pylori that is eliminated by activation of the lysosomal calcium channel TRPML1

Helicobacter pylori infection is a proven carcinogen for gastric cancer. Its virulence factor vacuolating cytotoxin A (VacA) promotes more severe disease and gastric colonization. VacA, by an unknown mechanism, usurps lysosomal and autophagy pathways to generate a protected reservoir for H. pylori that confers bacterial survival in vitro. Here, we show the existence of a VacA-generated intracellular niche in vivo that protects the bacteria from antibiotic treatment and leads to infection recrudescence after therapy. Furthermore, we report that VacA targets the lysosomal calcium channel TRPML1 to disrupt endolysosomal trafficking and mediate these effects. Remarkably, H. pylori that lack toxigenic VacA colonize enlarged dysfunctional lysosomes in the gastric epithelium of trpml1-null mice, where they are protected from eradication therapy. Furthermore, a small molecule agonist directed against TRPML1 reversed the toxic effects of VacA on endolysosomal trafficking, culminating in the clearance of intracellular bacteria. These results suggest that TRPML1 may represent a therapeutic target for chronic H. pylori infection.

P2X4 and lysosome fusion

Similar to other members of the P2X receptor family, the P2X4 receptor at the plasma membrane forms a highly Ca²⁺ permeable, non-selective cation channel that is activated by extracellular ATP. Yet, P2X4 differs from the other subtypes, as it is predominantly localized on late endosomal, lysosomal and/or lysosome-related organelles. It is targeted there by virtue of tyrosine-based and di-leucine like trafficking motifs contained within its C-terminal and N-terminal regions respectively. The physiological role of the stable intracellular expression of P2X4 in acidic compartments has been a long-standing puzzle. Recent evidence, however, points to a dual role in the regulation of ion fluxes across lysosomal membranes to control lysosome membrane fusion and in the re-sensitization of receptors exposed to extracellular ATP.

Endolysosomal Ca2+ Signalling and Cancer Hallmarks: Two-Pore Channels on the Move, TRPML1 Lags Behind!

The acidic vesicles of the endolysosomal (EL) system are emerging as an intracellular Ca²⁺ store implicated in the regulation of multiple cellular functions. The EL Ca²⁺ store releases Ca²⁺ through a variety of Ca²⁺-permeable channels, including Transient Receptor Potential (TRP) Mucolipin 1-3 (TRPML1-3) and two-pore channels 1-2 (TPC1-2), whereas EL Ca²⁺ refilling is sustained by the proton gradient across the EL membrane and/or by the endoplasmic reticulum (ER). EL Ca²⁺ signals may be either spatially restricted to control vesicle trafficking, autophagy and membrane repair or may be amplified into a global Ca²⁺ signal through the Ca²⁺-dependent recruitment of ER-embedded channels. Emerging evidence suggested that nicotinic acid adenine dinucleotide phosphate (NAADP)-gated TPCs sustain multiple cancer hallmarks, such as migration, invasiveness and angiogenesis. Herein, we first survey the EL Ca²⁺ refilling and release mechanisms and then focus on the oncogenic role of EL Ca²⁺ signaling. While the evidence in favor of TRPML1 involvement in neoplastic transformation is yet to be clearly provided, TPCs are emerging as an alternative target for anticancer therapies.

The emerging interrelation between ROCO and related kinases, intracellular Ca2+ signaling, and autophagy

ROCO kinases form a family of proteins characterized by kinase activity in addition to the presence of the so-called ROC (Ras of complex proteins)/COR (C-terminal of ROC) domains having a role in their GTPase activity. These are the death-associated protein kinase (DAPK) 1 and the leucine-rich repeat kinases (LRRK) 1 and 2. These kinases all play roles in cellular life and death decisions and in autophagy in particular. Related to the ROCO kinases is DAPK 2 that however cannot be classified as a ROCO protein due to the absence of the ROC/COR domains. This review aims to bring together what is known about the relation between these proteins and intracellular Ca²⁺ signals in the induction and regulation of autophagy. Interestingly, DAPK 1 and 2 and LRRK2 are all linked to Ca²⁺ signaling in their effects on autophagy, though in various ways. Present evidence supports an upstream role for LRRK2 that via lysosomal and endoplasmic reticulum Ca²⁺ release can trigger autophagy induction. In contrast herewith, DAPK1 and 2 react on existing Ca²⁺ signals to stimulate the autophagic pathway. Further research will be needed for obtaining a full understanding of the role of these various kinases in autophagy and to assess their exact relation with intracellular Ca²⁺ signaling as this would be helpful in the development of novel therapeutic strategies against neurodegenerative disorders, cancer and auto-immune diseases. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

The Cellular Environment Affects Monomeric α-Synuclein Structure

The presynaptic protein α-synuclein (aSyn) is an 'intrinsically disordered protein' that is highly dynamic in conformation. Transient intramolecular interactions between its charged N and C termini, and between its hydrophobic region and the C terminus, prevent self-association. These interactions inhibit the formation of insoluble inclusions, which are the pathological hallmark of Parkinson's disease and many other synucleinopathies. This review discusses how these intramolecular interactions are influenced by the specific environment aSyn is in. We discuss how charge, pH, calcium, and salt affect the physiological structure of monomeric aSyn, and how they may favour the formation of toxic structures. The more we understand the dynamic conformations of aSyn, the better we can design desperately needed therapeutics to prevent disease progression.

Molecular chaperones and hypoxic-ischemic encephalopathy

Hypoxic-ischemic encephalopathy (HIE) is a disease that occurs when the brain is subjected to hypoxia, resulting in neuronal death and neurological deficits, with a poor prognosis. The mechanisms underlying hypoxic-ischemic brain injury include excitatory amino acid release, cellular proteolysis, reactive oxygen species generation, nitric oxide synthesis, and inflammation. The molecular and cellular changes in HIE include protein misfolding, aggregation, and destruction of organelles. The apoptotic pathways activated by ischemia and hypoxia include the mitochondrial pathway, the extrinsic Fas receptor pathway, and the endoplasmic reticulum stress-induced pathway. Numerous treatments for hypoxic-ischemic brain injury caused by HIE have been developed over the last half century. Hypothermia, xenon gas treatment, the use of melatonin and erythropoietin, and hypoxic-ischemic preconditioning have proven effective in HIE patients. Molecular chaperones are proteins ubiquitously present in both prokaryotes and eukaryotes. A large number of molecular chaperones are induced after brain ischemia and hypoxia, among which the heat shock proteins are the most important. Heat shock proteins not only maintain protein homeostasis; they also exert anti-apoptotic effects. Heat shock proteins maintain protein homeostasis by helping to transport proteins to their target destinations, assisting in the proper folding of newly synthesized polypeptides, regulating the degradation of misfolded proteins, inhibiting the aggregation of proteins, and by controlling the refolding of misfolded proteins. In addition, heat shock proteins exert anti-apoptotic effects by interacting with various signaling pathways to block the activation of downstream effectors in numerous apoptotic pathways, including the intrinsic pathway, the endoplasmic reticulum-stress mediated pathway and the extrinsic Fas receptor pathway. Molecular chaperones play a key role in neuroprotection in HIE. In this review, we provide an overview of the mechanisms of HIE and discuss the various treatment strategies. Given their critical role in the disease, molecular chaperones are promising therapeutic targets for HIE.

Deviant lysosomal Ca2+ signalling in neurodegeneration. An introduction

Lysosomes are key acidic Ca²⁺ stores. The principle Ca²⁺-permeable channels of the lysosome are TRP mucolipins (TRPMLs) and NAADP-regulated two-pore channels (TPCs). Recent studies, reviewed in this collection, have linked numerous neurodegenerative diseases to both gain and loss of function of TRPMLs/TPCs, as well as to defects in acidic Ca²⁺ store content. These diseases span rare lysosomal storage disorders such as Mucolipidosis Type IV and Niemann-Pick disease, type C, through to more common ones such as Alzheimer and Parkinson disease. Cellular phenotypes, underpinned by endo-lysosomal trafficking defects, are reversed by chemical or molecular targeting of TRPMLs and TPCs. Lysosomal Ca²⁺ channels therefore emerge as potential druggable targets in combatting neurodegeneration.