Lysosomal cell death at a glance

Proteomic Analysis of Rat Cerebral Cortex in the Subacute to Long-Term Phases of Focal Cerebral Ischemia-Reperfusion Injury

Stroke is a leading cause of mortality and disability, and ischemic stroke accounts for more than 80% of the disease occurrence. Timely reperfusion is essential in the treatment of ischemic stroke, but it is known to cause ischemia-reperfusion (I/R) injury and the relevant studies have mostly focused on the acute phase. Here we reported on a global proteomic analysis to investigate the development of cerebral I/R injury in the subacute and long-term phases. A rat model was used, with 2 h-middle cerebral artery occlusion (MCAO) followed with 1, 7, and 14 days of reperfusion. The proteins of cerebral cortex were analyzed by SDS-PAGE, whole-gel slicing, and quantitative LC-MS/MS. Totally 5621 proteins were identified, among which 568, 755, and 492 proteins were detected to have significant dys-regulation in the model groups with 1, 7, and 14 days of reperfusion, respectively, when compared with the corresponding sham groups (n = 4, fold change ≥1.5 or ≤0.67 and p ≤ 0.05). Bioinformatic analysis on the functions and reperfusion time-dependent dys-regulation profiles of the proteins exhibited changes of structures and biological processes in cytoskeleton, synaptic plasticity, energy metabolism, inflammation, and lysosome from subacute to long-term phases of cerebral I/R injury. Disruption of cytoskeleton and synaptic structures, impairment of energy metabolism processes, and acute inflammation responses were the most significant features in the subacute phase. With the elongation of reperfusion time to the long-term phase, a tendency of recovery was detected on cytoskeleton, while inflammation pathways different from the subacute phase were activated. Also, lysosomal structures and functions might be restored. This is the first work reporting the proteome changes that occurred at different time points from the subacute to long-term phases of cerebral I/R injury and we expect it would provide useful information to improve the understanding of the mechanisms involved in the development of cerebral I/R injury and suggest candidates for treatment.

'Patchiness' and basic cancer research: unravelling the proteases

The recent developments in Cathepsin protease research have unveiled a number of key observations which are fundamental to further our understanding of normal cellular homeostasis and disease. By far, the most interesting and promising area of Cathepsin biology stems from how these proteins are linked to the fate of living cells through the phenomenon of Lysosomal Leakage and Lysosomal Membrane Permeabilisation. While extracellular Cathepsins are generally believed to be of central importance in tumour progression, through their ability to modulate the architecture of the Extracellular Matrix, intracellular Cathepsins have been established as being of extreme significance in mediating cell death through Apoptosis. With these two juxtaposed key research areas in mind, the focus of this review highlights recent advancements in how this fast-paced area of Cathepsin research has recently evolved in the context of their mechanistic regulation in cancer research. Abbreviations : ECM, Extracellular Matrix; MMP, Matrix Metalloproteases; LL, Lysosomal Leakage; LMP, Lysosomal Membrane Permeabilisation; LMA, Lysosomorphic Agents; BC, Breast Cancer; ASM, Acid Sphingomyelinase; TNF-α, Tumor Necrosis Factor-alpha; LAMP, Lysosomal Associated membrane Protein; PCD, Programmed Cell Death; PDAC, Pancreatic Ductal Adenocarcinoma; ROS, Reactive Oxygen Species; aa, amino acids.

CID1067700, a late endosome GTPase Rab7 receptor antagonist, attenuates brain atrophy, improves neurologic deficits and inhibits reactive astrogliosis in rat ischemic stroke

Increasing evidence suggests that Ras-related in brain 7 (Rab7), an endosome-localized small GTPase contributes to cerebral ischemic brain injury. In the present study, we investigated the role of Rab7 in ischemic stroke-induced formation of astrogliosis and glial scar. Rats were subjected to transient middle cerebral artery occlusion (tMCAO); the rats were injected with the Rab7 receptor antagonist CID1067700 (CID). Primary astrocytes were subjected to an oxygen and glucose deprivation and reoxygenation (OGD/Re) procedure; CID was added to the cell culture media. We found that Rab7 was significantly elevated over time in both the in vivo and in vitro astrocytic injury models, and administration of CID significantly down-regulated the glial scar markers such as glial fibillary acidic protein (GFAP), neurocan and phosphacan. Moreover, administration of CID significantly attenuated the brain atrophy and improved neurologic deficits in tMCAO rats, and protected astrocytes against OGD/Re-induced injury. Further, CID downregulated the protein levels of Lamp1 and active cathepsin B in astrocytes after OGD/Re or tMCAO injury; CID inhibited the co-localization of cathepsin B and Rab7, Lamp1 and Rab7; CID decreased OGD/Re-induced increase in lysosomal membrane permeability and blocked OGD/Re-induced release of cathepsin B from the lysosome into the cytoplasm in astrocytes. Taken together, these results suggest that Rab7 is involved in ischemic stroke-induced formation of astrogliosis and glial scar. CID administration attenuates brain atrophy and improves neurologic deficits and inhibits astrogliosis and glial scar formation after ischemic stroke via reducing the activation and release of cathepsin B from the lysosome into the cytoplasm.

Quantitative Microproteomics Based Characterization of the Central and Peripheral Nervous System of a Mouse Model of Krabbe Disease

Krabbe disease is a rare, childhood lysosomal storage disorder caused by a deficiency of galactosylceramide beta-galactosidase (GALC). The major effect of GALC deficiency is the accumulation of psychosine in the nervous system and widespread degeneration of oligodendrocytes and Schwann cells, causing rapid demyelination. The molecular mechanisms of Krabbe disease are not yet fully elucidated and a definite cure is still missing. Here we report the first in-depth characterization of the proteome of the Twitcher mouse, a spontaneous mouse model of Krabbe disease, to investigate the proteome changes in the Central and Peripheral Nervous System. We applied a TMT-based workflow to compare the proteomes of the corpus callosum, motor cortex and sciatic nerves of littermate homozygous Twitcher and wild-type mice. More than 400 protein groups exhibited differences in expression and included proteins involved in pathways that can be linked to Krabbe disease, such as inflammatory and defense response, lysosomal proteins accumulation, demyelination, reduced nervous system development and cell adhesion. These findings provide new insights on the molecular mechanisms of Krabbe disease, representing a starting point for future functional experiments to study the molecular pathogenesis of Krabbe disease. Data are available via ProteomeXchange with identifier PXD010594.

Trafficking of a Single Photosensitizing Molecule to Different Intracellular Organelles Demonstrates Effective Hydroxyl Radical-Mediated Photodynamic Therapy in the Endoplasmic Reticulum

Photodynamic therapy (PDT) is often used in preclinical and clinical treatment regimens. Reactive oxygen species (ROS) generated by photosensitizers (PSs) upon exposure to light induce cell death via diverse mechanisms. PSs can exert therapeutic effects in different cellular organelles, although the efficacy of organelle-specific PDT has yet to be determined as most previous studies use different PSs in different organelles. Here, we explored how a single PS, chlorin e6 (Ce6), targeted to different organelles altered the effectiveness of PDT. Ce6 intrinsically localizes to the ER after 4 h of incubation. Modification of Ce6 via conjugation with an octapeptide (LS765), a monosubstituted triphenylphosphonium (TPP) derivative (LS897), or a disubstituted TPP derivative (LS909) altered the intrinsic localization. We determined that LS765 and LS9897 predominantly accumulated in the lysosomes, but LS909 trafficked equally to both the mitochondria and the lysosomes. Moreover, the conjugation altered the type of ROS produced by Ce6, increasing the ratio of hydrogen peroxide to hydroxyl radicals. Irradiation of identical concentrations of the PSs in solution with 650 nm, 0.84 mW/cm² light for 10 min showed that the TPP conjugates nearly doubled the hydrogen peroxide production from ∼0.2 μM for Ce6 and LS765 to ∼0.37 μM for LS897 and LS909. In contrast, Ce6 produced ∼1.5-fold higher hydroxyl radicals than its conjugates. To compare the effect of each PS on cell death, we normalized the intracellular concentration of each PS. Hydrogen peroxide-producing PSs are effective PDT agents in the lysosomes while the hydroxyl-generating PSs are very effective in the ER. Compared to the PSs that accumulated in the lysosomes, only the ER-targeted Ce6 exerted >50% cell death at either low light power or low intracellular concentration. By delineating the contributions of cellular organelles and types of ROS produced, our work suggests that targeting hydroxyl radical-producing PSs to the ER is an exciting strategy to improve the therapeutic outcome of PDT.

Enzyme-mediated dual-targeted-assembly realizes a synergistic anticancer effect

We designed and synthesized homochiral-peptide-based boron diketonate complexes. Co-administration of the two stereoisomers in cancer cells led to molecular assembly targeting both the plasma membrane and the lysosomes mediated via membrane-bonded enzymes. The dual-targeted-assembly generates a synergistic anticancer effect with amplified cancer spheroid toxicity and enhanced inhibition efficacy on cancer cell migration.

The molecular machinery of regulated cell death

Cells may die from accidental cell death (ACD) or regulated cell death (RCD). ACD is a biologically uncontrolled process, whereas RCD involves tightly structured signaling cascades and molecularly defined effector mechanisms. A growing number of novel non-apoptotic forms of RCD have been identified and are increasingly being implicated in various human pathologies. Here, we critically review the current state of the art regarding non-apoptotic types of RCD, including necroptosis, pyroptosis, ferroptosis, entotic cell death, netotic cell death, parthanatos, lysosome-dependent cell death, autophagy-dependent cell death, alkaliptosis and oxeiptosis. The in-depth comprehension of each of these lethal subroutines and their intercellular consequences may uncover novel therapeutic targets for the avoidance of pathogenic cell loss.

Cathepsin B: A sellsword of cancer progression

Clinical, biochemical and molecular biology studies have identified lysosome-encapsulated cellular proteases as critical risk factors for cancer progression. Cathepsins represent a group of such proteases aimed at maintenance of cellular homeostasis. Nevertheless, recent reports suggest that Cathepsin B executes other cellular programs such as controlling tumor growth, migration, invasion, angiogenesis, and metastases development. In fact, elevated levels of Cathepsins are found under different pathological conditions including inflammation, infection, neurodegenerative disease, and cancer. Furthermore, the discovery of Cathepsin B secretion and function as an extracellular matrix protein has broadened our appreciation for the impact of Cathepsin B on cancer progression. Underneath a façade of an intracellular protease with limited therapeutic potential hides a central role of cathepsins in extracellular functions. Moreover, this role is incredibly diverse from one condition to the next - from driving caspase-dependent apoptosis to facilitating tumor neovascularization and metastasis. Here we discuss the role of Cathepsin B in the oncogenic process and perspective the use of Cathepsin B for diagnostic and therapeutic applications.

Emerging Therapeutic Targets in Oncologic Photodynamic Therapy

Background:

Reactive oxygen species sustain tumorigenesis and cancer progression through deregulated redox signalling which also sensitizes cancer cells to therapy. Photodynamic therapy (PDT) is a promising anti-cancer therapy based on a provoked singlet oxygen burst, exhibiting a better toxicological profile than chemo- and radiotherapy. Important gaps in the knowledge on underlining molecular mechanisms impede on its translation towards clinical applications.

Aims and Methods:

The main objective of this review is to critically analyse the knowledge lately gained on therapeutic targets related to redox and inflammatory networks underlining PDT and its outcome in terms of cell death and resistance to therapy. Emerging therapeutic targets and pharmaceutical tools will be documented based on the identified molecular background of PDT.

Results:

Cellular responses and molecular networks in cancer cells exposed to the PDT-triggered singlet oxygen burst and the associated stresses are analysed using a systems medicine approach, addressing both cell death and repair mechanisms. In the context of immunogenic cell death, therapeutic tools for boosting anti-tumor immunity will be outlined. Finally, the transcription factor NRF2, which is a major coordinator of cytoprotective responses, is presented as a promising pharmacologic target for developing co-therapies designed to increase PDT efficacy.

Conclusion:

There is an urgent need to perform in-depth molecular investigations in the field of PDT and to correlate them with clinical data through a systems medicine approach for highlighting the complex biological signature of PDT. This will definitely guide translation of PDT to clinic and the development of new therapeutic strategies aimed at improving PDT.

Regulation and Function of Mitochondria-Lysosome Membrane Contact Sites in Cellular Homeostasis

Mitochondrial and lysosomal function are intricately related and critical for maintaining cellular homeostasis, as highlighted by multiple diseases linked to dysfunction of both organelles. Recent work using high-resolution microscopy demonstrates the dynamic formation of inter-organelle membrane contact sites between mitochondria and lysosomes, allowing for their direct interaction in a pathway distinct from mitophagy or lysosomal degradation of mitochondrial-derived vesicles. Mitochondria-lysosome contact site tethering is mechanistically regulated by mitochondrial proteins promoting Rab7 GTP hydrolysis, and allows for the bidirectional crosstalk between mitochondria and lysosomes and the regulation of their organelle network dynamics, including mitochondrial fission. In this review, we summarize recent advances in mitochondria-lysosome contact site regulation and function, and discuss their potential roles in cellular homeostasis and various human diseases.

HLA class II antibodies induce necrotic cell death in human endothelial cells via a lysosomal membrane permeabilization-mediated pathway

Antibody-mediated rejection (AMR) is the major cause of allograft loss after solid organ transplantation. Circulating donor-specific antibodies against human leukocyte antigen (HLA), in particular HLA class II antibodies are critical for the pathogenesis of AMR via interactions with endothelial cells (ECs). To investigate the effects of HLA class II antibody ligation to the graft endothelium, a model of HLA-DR antibody-dependent stimulation was utilized in primary human ECs. Antibody ligation of HLA class II molecules in interferon-γ-treated ECs caused necrotic cell death without complement via a pathway that was independent of apoptosis and necroptosis. HLA-DR-mediated cell death was blocked by specific neutralization of antibody ligation with recombinant HLA class II protein and by lentiviral knockdown of HLA-DR in ECs. Importantly, HLA class II-mediated cytotoxicity was also induced by relevant native allele-specific antibodies from human allosera. Necrosis of ECs in response to HLA-DR ligation was mediated via hyperactivation of lysosomes, lysosomal membrane permeabilization (LMP), and release of cathepsins. Notably, LMP was caused by reorganization of the actin cytoskeleton. This was indicated by the finding that LMP and actin stress fiber formation by HLA-DR antibodies were both downregulated by the actin polymerization inhibitor cytochalasin D and inhibition of Rho GTPases, respectively. Finally, HLA-DR-dependent actin stress fiber formation and LMP led to mitochondrial stress, which was revealed by decreased mitochondrial membrane potential and generation of reactive oxygen species in ECs. Taken together, ligation of HLA class II antibodies to ECs induces necrotic cell death independent of apoptosis and necroptosis via a LMP-mediated pathway. These findings may enable novel therapeutic approaches for the treatment of AMR in solid organ transplantation.

DNA-stimulated cell death: implications for host defence, inflammatory diseases and cancer

The immune system detects disturbances in homeostasis that occur during infection, sterile tissue damage and cancer. This initiates immune responses that seek to eliminate the trigger of immune activation and to re-establish homeostasis. At the same time, these mechanisms can also play a crucial role in the progression of disease. The occurrence of DNA in the cytosol constitutes a potent trigger for the innate immune system, governing the production of key inflammatory cytokines such as type I interferons and IL-1β. More recently, it has become clear that cytosolic DNA also triggers other biological responses, including various forms of programmed cell death. In this article, we review the emerging literature on the pathways governing DNA-stimulated cell death and the current knowledge on how these processes shape immune responses to exogenous and endogenous challenges.

Hsp70 interactions with membrane lipids regulate cellular functions in health and disease

Beyond guarding the cellular proteome the major stress inducible heat shock protein Hsp70 has been shown to interact with lipids. Non-cytosolic Hsp70 stabilizes membranes during stress challenges and, in pathophysiological states, facilitates endocytosis, counteracts apoptotic mechanisms, sustains survival pathways or represents a signal that can be recognized by the immune system. Disease-coupled lipid-associated functions of Hsp70 may be targeted via distinct subcellular localizations of Hsp70 itself or its specific interacting lipids. With a special focus on interacting lipids, here we discuss localization-dependent roles of the membrane-bound Hsp70 in the context of its therapeutic potential, particularly in cancer and neurodegenerative diseases.

Finding Sugar in the Pantry: How Galectins Detect and Signal Lysosomal Damage

In this issue of Molecular Cell, Jia et al. (2018) identify a lysosomal damage-response pathway centered on galectin 8 and 9 that feeds back on mTORC1 signaling. In response to lysosome-damaging agents, galectins inhibits mTORC1, triggering a stress response that may help restore cellular homeostasis.

Methods to Detect Loss of Lysosomal Membrane Integrity

Loss of lysosomal membrane integrity, often referred to as lysosomal membrane permeabilization (LMP), occurs in many instances of cell death either as an initiating or as an amplifying event. Currently, the best method for detecting LMP is the galectin puncta formation assay which can be used for a broad range of sample types, both fixed and live, is easy to perform, and highly sensitive. This method, which is similar to the widely used LC3 puncta formation assay for autophagy, is based on the translocation of galectins to damaged lysosomes resulting in a change from uniform to punctate staining pattern. Here, we provide protocols for the galectin puncta formation assay in fixed and live cells and for an alternative assay based on fluorescent dextran release from damaged lysosomes, which can be performed in parallel.

Monitoring the death of single BaF3 cells under plasmonic photothermal heating induced by ultrasmall gold nanorods

Morphological changes and trypan-blue staining are temporally tracked in single cells via optical microscopy after plasmonic photothermal heating.

Zidovudine-Mediated Autophagy Inhibition Enhances Mitochondrial Toxicity in Muscle Cells

Nucleoside reverse transcriptase inhibitors (NRTI), such as zidovudine (AZT), are constituents of HIV-1 therapy and are used for the prevention of mother-to-child transmission. Prolonged thymidine analogue exposure has been associated with mitochondrial toxicities to heart, liver, and skeletal muscle. We hypothesized that the thymidine analogue AZT might interfere with autophagy in myocytes, a lysosomal degradation pathway implicated in the regulation of mitochondrial recycling, cell survival, and the pathogenesis of myodegenerative diseases. The impact of AZT and lamivudine (3TC) on C2C12 myocyte autophagy was studied using various methods based on LC3-green fluorescent protein overexpression or LC3 staining in combination with Western blotting, flow cytometry, and confocal and electron microscopy. Lysosomal and mitochondrial functions were studied using appropriate staining for lysosomal mass, acidity, cathepsin activity, as well as mitochondrial mass and membrane potential in combination with flow cytometry and confocal microscopy. AZT, but not 3TC, exerted a significant dose- and time-dependent inhibitory effect on late stages of autophagosome maturation, which was reversible upon mTOR inhibition. Inhibition of late autophagy at therapeutic drug concentrations led to dysfunctional mitochondrial accumulation with membrane hyperpolarization and increased reactive oxygen species (ROS) generation and, ultimately, compromised cell viability. These AZT effects could be readily replicated by pharmacological and genetic inhibition of myocyte autophagy and, most importantly, could be rescued by pharmacological stimulation of autophagolysosomal biogenesis. Our data suggest that the thymidine analogue AZT inhibits autophagy in myocytes, which in turn leads to the accumulation of dysfunctional mitochondria with increased ROS generation and compromised cell viability. This novel mechanism could contribute to our understanding of the long-term side effects of antiviral agents.

Lysosomal protease deficiency or substrate overload induces an oxidative-stress mediated STAT3-dependent pathway of lysosomal homeostasis

Diverse cellular processes depend on the lysosomal protease system but how cells regulate lysosomal proteolytic capacity is only partly understood. We show here that cells can respond to protease/substrate imbalance in this compartment by de novo expression of multiple lysosomal hydrolases. This response, exemplified here either by loss of asparagine endopeptidase (AEP) or other lysosomal cysteine proteases, or by increased endocytic substrate load, is not dependent on the transcription factor EB (TFEB) but rather is triggered by STAT3 activation downstream of lysosomal oxidative stress. Similar lysosomal adaptations are seen in mice and cells expressing a constitutively active form of STAT3. Our results reveal how cells can increase lysosomal protease capacity under ‘fed’ rather than ‘starved’ conditions that activate the TFEB system. In addition, STAT3 activation due to lysosomal stress likely explains the hyperproliferative kidney disease and splenomegaly observed in AEP-deficient mice.

How cells regulate their lysosomal proteolytic capacity is only partly understood. Here, the authors show that lysosomal protease deficiency or substrate overload induces lysosomal stress leading to activation of a STAT3-dependent, TFEB-independent pathway of lysosomal hydrolase expression.

Bcl-2 Inhibition to Overcome Resistance to Chemo- and Immunotherapy

Abstract: According to the World Health Organization (WHO), cancer is a leading cause of death worldwide. The identification of novel targets for cancer treatment is an area of intense work that has led Bcl-2 over-expression to be proposed as one of the hallmarks of cancer and Bcl-2 inhibition as a promising strategy for cancer treatment. In this review, we describe the different pathways related to programmed cell death, the role of Bcl-2 family members in apoptosis resistance to anti-cancer treatments, and the potential utility of Bcl-2 inhibitors to overcome resistance to chemo- and immunotherapy.

Alpha-synuclein fibrils recruit TBK1 and OPTN to lysosomal damage sites and induce autophagy in microglial cells

Autophagic dysfunction and protein aggregation have been linked to several neurodegenerative disorders, but the exact mechanisms and causal connections are not clear and most previous work was done in neurons and not in microglial cells. Here, we report that exogenous fibrillary, but not monomeric, alpha-synuclein (AS, also known as SNCA) induces autophagy in microglial cells. We extensively studied the dynamics of this response using both live-cell imaging and correlative light-electron microscopy (CLEM), and found that it correlates with lysosomal damage and is characterised by the recruitment of the selective autophagy-associated proteins TANK-binding kinase 1 (TBK1) and optineurin (OPTN) to ubiquitylated lysosomes. In addition, we observed that LC3 (MAP1LC3B) recruitment to damaged lysosomes was dependent on TBK1 activity. In these fibrillar AS-treated cells, autophagy inhibition impairs mitochondrial function and leads to microglial cell death. Our results suggest that microglial autophagy is induced in response to lysosomal damage caused by persistent accumulation of AS fibrils. Importantly, triggering of the autophagic response appears to be an attempt at lysosomal quality control and not for engulfment of fibrillar AS.This article has an associated First Person interview with the first author of the paper.

STING Signaling Promotes Apoptosis, Necrosis, and Cell Death: An Overview and Update

STING is a newly identified intracellular sensor of foreign and endogenous DNA. STING has been recognized as an activator of immune responses by TBK1/IRF3 and NF-κB pathways, and it is suggested to play critical roles in host defense, autoimmune diseases, and tumor immunity. Recent studies have revealed that the outcome of STING activation could vary between distinct cell types and scenarios. STING activation in certain cell types triggered cell death including apoptosis and necrosis. This effect could be critical for preventing unnecessary or excessive inflammatory events and maintaining host immune homeostasis. This review is dedicated to summarize recent evidences in the field of STING-mediated cell death and to demonstrate dual outcomes of STING signaling. Besides canonical immune responses represented by IFN and TNF productions, STING signaling can also induce cell death events in a variety of cell types. The double-faced characteristics of STING signaling requires further exploration and precious regulation before tailoring clinical strategies for associated diseases.

Evaluating the Remote Control of Programmed Cell Death, with or without a Compensatory Cell Proliferation

Organisms and their different component levels, whether organelle, cellular or other, come by birth and go by death, and the deaths are often balanced by new births. Evolution on the one hand has built demise program(s) in cells of organisms but on the other hand has established external controls on the program(s). For instance, evolution has established death program(s) in animal cells so that the cells can, when it is needed, commit apoptosis or senescent death (SD) in physiological situations and stress-induced cell death (SICD) in pathological situations. However, these programmed cell deaths are not predominantly regulated by the cells that do the dying but, instead, are controlled externally and remotely by the cells' superior(s), i.e. their host tissue or organ or even the animal's body. Currently, it is still unclear whether a cell has only one death program or has several programs respectively controlling SD, apoptosis and SICD. In animals, apoptosis exterminates, in a physiological manner, healthy but no-longer needed cells to avoid cell redundancy, whereas suicidal SD and SICD, like homicidal necrosis, terminate ill but useful cells, which may be followed by regeneration of the live cells and by scar formation to heal the damaged organ or tissue. Therefore, “who dies” clearly differentiates apoptosis from SD, SICD and necrosis. In animals, apoptosis can occur only in those cell types that retain a lifelong ability of proliferation and never occurs in those cell types that can no longer replicate in adulthood. In cancer cells, SICD is strengthened, apoptosis is dramatically weakened while SD has been lost. Most published studies professed to be about apoptosis are actually about SICD, which has four basic and well-articulated pathways involving caspases or involving pathological alterations in the mitochondria, endoplasmic reticula, or lysosomes.

Cellular responses to in vitro exposures to β-blocking pharmaceuticals in hard clams and Eastern oysters

Increased consumption and improper disposal of prescription medication, such as beta (β)-blockers, contribute to their introduction into waterways and may pose threats to non-target aquatic organisms. There has been rising concern about the impacts of these prescription drugs on coastal ecosystems, especially because wastewater treatment plants are not designed to eliminate them from the discharge. Few studies have characterized the sublethal effects of β-blocker exposures in marine invertebrates. The overall aim of our research is to identify cellular responses of two commercially important filter-feeding marine bivalves, hard clams (Mercenaria mercenaria) and Eastern oysters (Crassostrea virginica), upon exposures to two β-blocker drugs, propranolol and metoprolol. In vitro exposures with bivalve digestive gland and gill tissues were conducted where tissues were separately exposed to each drug for 24 h. Tissue samples were analyzed for cellular damage (lysosomal membrane destabilization and lipid peroxidation), total antioxidant capacity, and glutathione-s-transferase activity. Elevated damage and changes in enzyme activities were noted in the exposed tissues at environmentally relevant concentrations. Differences in species and tissue sensitivities and responses to exposures were also observed. These studies enhance our understanding of the potential impacts of prescription medication on coastal organisms. Additionally, this work demonstrates that filter-feeders may serve as good model organisms to examine the effects of unintended environmental exposures to β-blockers. These studies are part of our ongoing work aimed at evaluation of sublethal biomarkers of pharmaceutical exposures and identification of key events that can contribute to the development of adverse outcome pathways (AOPs).

Oncolysis with DTT-205 and DTT-304 generates immunological memory in cured animals

Oncolytic peptides and peptidomimetics are being optimized for the treatment of cancer by selecting agents with high cytotoxic potential to kill a maximum of tumor cells as well as the capacity to trigger anticancer immune responses and hence to achieve long-term effects beyond therapeutic discontinuation. Here, we report on the characterization of two novel oncolytic peptides, DTT-205 and DTT-304 that both selectively enrich in the lysosomal compartment of cancer cells yet differ to some extent in their cytotoxic mode of action. While DTT-304 can trigger the aggregation of RIP3 in ripoptosomes, coupled to the phosphorylation of MLKL by RIP3, DTT-205 fails to activate RIP3. Accordingly, knockout of either RIP3 or MLKL caused partial resistance against cell killing by DTT-304 but not DTT-205. In contrast, both agents shared common features in other aspects of pro-death signaling in the sense that their cytotoxic effects were strongly inhibited by both serum and antioxidants, partially reduced by lysosomal inhibition with bafilomycin A1 or double knockout of Bax and Bak, yet totally refractory to caspase inhibition. Both DTT-304 and DTT-205 caused the exposure of calreticulin at the cell surface, as well as the release of HMGB1 from the cells. Mice bearing established subcutaneous cancers could be cured by local injection of DTT-205 or DTT-304, and this effect depended on T lymphocytes, as it led to the establishment of a long-term memory response against tumor-associated antigens. Thus, mice that had been cured from cancer by the administration of DTT compounds were refractory against rechallenge with the same cancer type several months after the disappearance of the primary lesion. In summary, DTT-205 and DTT-304 both have the capacity to induce immunotherapeutic oncolysis.

Regulated Necrosis Orchestrates Microglial Cell Death in Manganese-Induced Toxicity

Microglia, the brain resident immune cells, play prominent roles in immune surveillance, tissue repair and neural regeneration. Despite these pro-survival actions, the relevance of these cells in the progression of several neuropathologies has been established. In the context of manganese (Mn) overexposure, it has been proposed that microglial activation contributes to enhance the neurotoxicity. However, the occurrence of a direct cytotoxic effect of Mn on microglial cells remains controversial. In the present work, we investigated the potential vulnerability of immortalized mouse microglial cells (BV-2) toward Mn²⁺, focusing on the signaling pathways involved in cell death. Evidence obtained showed that Mn²⁺ induces a decrease in cell viability which is associated with reactive oxygen species (ROS) generation. In this report we demonstrated, for the first time, that Mn²⁺ triggers regulated necrosis (RN) in BV-2 cells involving two central mechanisms: parthanatos and lysosomal disruption. The occurrence of parthanatos is supported by several cellular and molecular events: (i) DNA damage; (ii) AIF translocation from mitochondria to the nucleus; (iii) mitochondrial membrane permeabilization; and (iv) PARP1-dependent cell death. On the other hand, Mn²⁺ induces lysosomal membrane permeabilization (LMP) and cathepsin D (CatD) release into the cytosol supporting the lysosomal disruption. Pre-incubation with CatB and D inhibitors partially prevented the Mn²⁺-induced cell viability decrease. Altogether these events point to lysosomes as players in the execution of RN. In summary, our results suggest that microglial cells could be direct targets of Mn²⁺ damage. In this scenario, Mn²⁺ triggers cell death involving RN pathways.

A near-infrared fluorescent probe based on photostable Si-rhodamine for imaging hypochlorous acid during lysosome-involved inflammatory response

Hypochloric acid (HClO) is mainly distributed in acidic lysosomes of phagocytes and closely associated with numerous physiological and pathological processes, especially inflammatory response. Fluorescent probe has become an important tool for imaging HClO in lysosomes, but suffered from interference from autofluorescence in vivo, phototoxicity to biosamples and photobleaching phenomenon due to their short-wavelength excitation and emission. Unfortunately, up to now, no near-infrared (NIR) lysosome-targetable fluorescent probe has been reported for imaging HClO. In this paper, a near-infrared fluorescent probe Lyso-NIR-HClO for imaging lysosomal HClO was reported for the first time. Lyso-NIR-HClO based on Si-rhodamine is consisted of a morpholine unit as a lysosome-targetable group and a HClO-mediated cyclization reaction site as a response group, which was applied for highly selective and sensitive detection and imaging for endogenous and exogenous HClO in lysosomes, with a linear range from 5.0 × 10^-8 to 1.0 × 10^-5 M and a detection limit of 2.0 × 10^-8 M in vitro. Attributed to NIR emission and excellent photostability of Si-rhodamine, Lyso-NIR-HClO exhibits excellent performances in vivo, such as low interference from intracellular autofluorescence, stable and persistent fluorescence signal and good tissue penetration, which are in favor of accurate, time-lapse and long-term imaging for HClO. Finally, we applied the probe Lyso-NIR-HClO to visualize endogenous HClO during lysosome-involved inflammatory response including bacteria-infected cells and inflamed mouse model with satisfactory results. The above results proved that Lyso-NIR-HClO would be a potentially useful tool for the study of biological functions and pathological roles of HClO in lysosomes, especially role of lysosome in the inflammatory response.

Helicobacter pylori induces intracellular galectin-8 aggregation around damaged lysosomes within gastric epithelial cells in a host O-glycan-dependent manner

Galectin-8, a beta-galactoside-binding lectin, is upregulated in the gastric tissues of rhesus macaques infected with Helicobacter pylori. In this study, we found that H. pylori infection triggers intracellular galectin-8 aggregation in human-derived AGS gastric epithelial cells, and that these aggregates colocalize with lysosomes. Notably, this aggregation is markedly reduced following the attenuation of host O-glycan processing. This indicates that H. pylori infection induces lysosomal damage, which in turn results in the accumulation of cytosolic galectin-8 around damaged lysosomes through the recognition of exposed vacuolar host O-glycans. H. pylori-induced galectin-8 aggregates also colocalize with autophagosomes, and galectin-8 ablation reduces the activation of autophagy by H. pylori. This suggests that galectin-8 aggregates may enhance autophagy activity in infected cells. We also observed that both autophagy and NDP52, an autophagy adapter, contribute to the augmentation of galectin-8 aggregation by H. pylori. Additionally, vacuolating cytotoxin A, a secreted H. pylori cytotoxin, may contribute to the increased galectin-8 aggregation and elevated autophagy response in infected cells. Collectively, these results suggest that H. pylori promotes intracellular galectin-8 aggregation, and that galectin-8 aggregation and autophagy may reciprocally regulate each other during infection.

Rab-Effector-Kinase Interplay Modulates Intralumenal Fragment Formation during Vacuole Fusion

Upon vacuolar lysosome (or vacuole) fusion in S. cerevisiae, a portion of membrane is internalized and catabolized. Formation of this intralumenal fragment (ILF) is important for organelle protein and lipid homeostasis and remodeling. But how ILF formation is optimized for membrane turnover is not understood. Here, we show that fewer ILFs form when the interaction between the Rab-GTPase Ypt7 and its effector Vps41 (a subunit of the tethering complex HOPS) is interrupted by a point mutation (Ypt7-D44N). Subsequent phosphorylation of Vps41 by the casein kinase Yck3 prevents stabilization of trans-SNARE complexes needed for lipid bilayer pore formation. Impairing ILF formation prevents clearance of misfolded proteins from vacuole membranes and promotes organelle permeability and cell death. We propose that HOPS coordinates Rab, kinase, and SNARE cycles to modulate ILF size during vacuole fusion, regulating lipid and protein turnover important for quality control and membrane integrity.

A Calpain-Like Protein Is Involved in the Execution Phase of Programmed Cell Death of Entamoeba histolytica

Oxygen or nitrogen oxidative species and chemical stress induce the programmed cell death (PCD) of Entamoeba histolytica trophozoites. PCD caused by the aminoglycoside G418 is reduced by incubation with the cysteine protease inhibitor E-64; however, no typical caspases or metacaspases have been detected in this parasite. Calpain, a cysteine protease activated by calcium, has been suggested to be part of a specific PCD pathway in this parasite because the specific calpain inhibitor Z-Leu-Leu-Leu-al diminishes the PCD of trophozoites. Here, we predicted the hypothetical 3D structure of a calpain-like protein of E. histolytica and produced specific antibodies against it. We detected the protein in the cytoplasm and near the nucleus. Its expression gradually increased during incubation with G418, with the highest level after 9 h of treatment. In addition, a specific calpain-like siRNA sequence reduced the cell death rate by 65%. All these results support the hypothesis that the calpain-like protein is one of the proteases involved in the execution phase of PCD in E. histolytica. The hypothetical interactome of the calpain-like protein suggests that it may activate or regulate other proteins that probably participate in PCD, including those with EF-hand domains or other calcium-binding sites.

Two-Photon Excited FRET Dyads for Lysosome-Targeted Imaging and Photodynamic Therapy

Two-photon excitable fluorescent dyes with integrated functions of targeted imaging and photodynamic therapy (PDT) are highly desired for the development of cancer theranostic agents. Herein, fluorescence resonance energy transfer (FRET) dyads, AceDAN-H₂Por-Lyso (1a) and AceDAN-ZnPor-Lyso (1b), were developed for two-photon excited (TPE) lysosome-targeted fluorescence imaging and PDT of cancer cells. Under one-photon or two-photon excitation, the AceDAN donor can effectively transfer the excited state energy to the porphyrin acceptor via high efficient FRET, leading to the generation of deep-red fluorescence and singlet oxygen for cell imaging and PDT, respectively. 1a and 1b exhibit high photocytotoxicity and low dark cytotoxicity, in addition to strong lysosomal targeting capability in living cells. By taking the advantages of the two-photon absorption properties of the AceDAN donor and the properly distributed S₁ and T₁ states of the porphyrin acceptor, the AceDAN-porphyrin dyads 1a and 1b have been successfully applied to TPE-fluorescence imaging for tracking the significant morphology changes of cancer cells under two-photon laser irradiation.

Association of tamoxifen resistance and lipid reprogramming in breast cancer

Background

Tamoxifen treatment of estrogen receptor (ER)-positive breast cancer reduces mortality by 31%. However, over half of advanced ER-positive breast cancers are intrinsically resistant to tamoxifen and about 40% will acquire the resistance during the treatment.

Methods

In order to explore mechanisms underlying endocrine therapy resistance in breast cancer and to identify new therapeutic opportunities, we created tamoxifen-resistant breast cancer cell lines that represent the luminal A or the luminal B. Gene expression patterns revealed by RNA-sequencing in seven tamoxifen-resistant variants were compared with their isogenic parental cells. We further examined those transcriptomic alterations in a publicly available patient cohort.

Results

We show that tamoxifen resistance cannot simply be explained by altered expression of individual genes, common mechanism across all resistant variants, or the appearance of new fusion genes. Instead, the resistant cell lines shared altered gene expression patterns associated with cell cycle, protein modification and metabolism, especially with the cholesterol pathway. In the tamoxifen-resistant T-47D cell variants we observed a striking increase of neutral lipids in lipid droplets as well as an accumulation of free cholesterol in the lysosomes. Tamoxifen-resistant cells were also less prone to lysosomal membrane permeabilization (LMP) and not vulnerable to compounds targeting the lipid metabolism. However, the cells were sensitive to disulfiram, LCS-1, and dasatinib.

Conclusion

Altogether, our findings highlight a major role of LMP prevention in tamoxifen resistance, and suggest novel drug vulnerabilities associated with this phenotype.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4757-z) contains supplementary material, which is available to authorized users.

Lysosomal membrane permeabilization causes secretion of IL-1β in human vascular smooth muscle cells

Objective

IL-1β secretion by the inflammasome is strictly controlled and requires two sequential signals: a priming signal and an activating signal. Lysosomal membrane permeabilization (LMP) plays a critical role in the regulation of NLRP3 inflammasome, and generally acts as an activating signal. However, the role of LMP controlling NLRP3 inflammasome activation in human vascular smooth muscle cells (hVSMCs) is not well defined.

Methods

LMP was induced in hVSMCs by Leu-Leu-O-methyl ester. Cathepsin B was inhibited by CA-074 Me. Cytokine release, mRNA, and protein were quantified by enzyme-linked immunosorbent assay, quantitative PCR, and Western blot, respectively. NF-κB activity was analyzed by immunostaining of the NF-κB p65 nuclear translocation and using the dual-luciferase reporter assay system.

Results

LMP had both priming and activating roles, causing an upregulation of proIL-1β and NLRP3 and the secretion of mature IL-1β from unprimed hVSMCs. LMP activated the canonical NF-κB pathway. The priming effect of LMP was inhibited by CA-074 Me, indicating an upstream role of cathepsin B.

Conclusions

These data support a novel role of LMP as a single stimulus for the secretion of IL-1β from hVSMCs, implying the possibility that hVSMCs are an important initiator of the sterile inflammatory response caused by lysosomal disintegration.

A Cinderella story: how the vacuolar proteases Pep4 and Prb1 do more than cleaning up the cell's mass degradation processes

Recently, several research groups have assigned non-vacuolar functions to the well-known Saccharomyces cerevisiae vacuolar proteases Pep4 and Prb1, which are also known as proteinases A and B. These non-vacuolar activities seem to be autophagy-independent and stress-induced and suggest an unexplored but possibly prominent role for the proteases outside the vacuole. The functions range from the involvement in programmed cell death, to protection from hazardous protein forms and regulation of gene expression. We propose that a deeper understanding of these molecular processes will provide new insights that will be important for both fungal biology as well as studies in mammalian cells, as they might open up perspectives in the search for novel drug targets. To illustrate this, we summarize the recent literature on non-vacuolar Pep4 and Prb1 functions in S. cerevisiae and review the current data on the protein homologs in pathogenic fungi.

Interaction of Positively Charged Gold Nanoparticles with Cancer Cells Monitored by an in Situ Label-Free Optical Biosensor and Transmission Electron Microscopy

Functionalized nanoparticles (NPs) can penetrate into living cells and vesicles, opening up an extensive range of novel directions. For example, NPs are intensively employed in targeted drug delivery and biomedical imaging. However, the real-time kinetics and dynamics of NP-living cell interactions remained uncovered. In this study, we in situ monitored the cellular uptake of gold NPs-functionalized with positively charged alkaline thiol-into surface-adhered cancer cells, by using a high-throughput label-free optical biosensor employing resonant waveguide gratings. The characteristic kinetic curves upon NP exposure of cell-coated biosensor surfaces were recorded and compared to the kinetics of NP adsorption onto bare sensor surfaces. We demonstrated that from the above kinetic information, one can conclude about the interactions between the living cells and the NPs. Real-time biosensor data suggested the cellular uptake of the functionalized NPs by an active process. It was found that positively charged particles penetrate into the cells more effectively than negatively charged control particles, and the optimal size for the cellular uptake of the positively charged particles is around 5 nm. These conclusions were obtained in a cost-effective, fast, and high-throughput manner. The fate of the NPs was further revealed by electron microscopy on NP-exposed and subsequently fixed cells, well confirming the results obtained by the biosensor. Moreover, an ultrastructural study demonstrated the involvement of the endosomal-lysosomal system in the uptake of functionalized NPs and suggested the type of the internalization pathway.

Detection and Clearance of Damaged Lysosomes by the Endo-Lysosomal Damage Response and Lysophagy

Lysosomal membrane permeabilization or lysosomal rupture is recognized as a common and severe stress condition relevant for infection, cellular degeneration and cancer. However, the cellular response mechanisms that protect cells from the consequences of lysosomal damage and ensure lysosomal quality control and homeostasis have only recently been explored. Key elements of this response involve the specific sensing of the damage followed by extensive modification of the organelles with ubiquitin to mark them for clearance by selective macroautophagy, termed lysophagy. Efficient lysophagy is ensured by additional layers of regulation, including modulation by the ubiquitin-directed AAA-ATPase VCP/p97. Lysophagy shares many features with mitophagy, the macroautophagic removal of damaged mitochondria. This review aims to gather available data from different fields and to define the key steps necessary for sensing and subsequent clearance of damaged lysosomes. We conclude with a discussion of disease implications with a focus on neurodegeneration.

mTOR Inhibition via Displacement of Phosphatidic Acid Induces Enhanced Cytotoxicity Specifically in Cancer Cells

The mTOR is a central regulator of cell growth and is highly activated in cancer cells to allow rapid tumor growth. The use of mTOR inhibitors as anticancer therapy has been approved for some types of tumors, albeit with modest results. We recently reported the synthesis of ICSN3250, a halitulin analogue with enhanced cytotoxicity. We report here that ICSN3250 is a specific mTOR inhibitor that operates through a mechanism distinct from those described for previous mTOR inhibitors. ICSN3250 competed with and displaced phosphatidic acid from the FRB domain in mTOR, thus preventing mTOR activation and leading to cytotoxicity. Docking and molecular dynamics simulations evidenced not only the high conformational plasticity of the FRB domain, but also the specific interactions of both ICSN3250 and phosphatidic acid with the FRB domain in mTOR. Furthermore, ICSN3250 toxicity was shown to act specifically in cancer cells, as noncancer cells showed up to 100-fold less sensitivity to ICSN3250, in contrast to other mTOR inhibitors that did not show selectivity. Thus, our results define ICSN3250 as a new class of mTOR inhibitors that specifically targets cancer cells.Significance: ICSN3250 defines a new class of mTORC1 inhibitors that displaces phosphatidic acid at the FRB domain of mTOR, inducing cell death specifically in cancer cells but not in noncancer cells. Cancer Res; 78(18); 5384-97. ©2018 AACR.

Induction of peroxisomal changes in oligodendrocytes treated with 7-ketocholesterol: Attenuation by α-tocopherol

The involvement of organelles in cell death is well established especially for endoplasmic reticulum, lysosomes and mitochondria. However, the role of the peroxisome is not well known, though peroxisomal dysfunction favors a rupture of redox equilibrium. To study the role of peroxisomes in cell death, 158 N murine oligodendrocytes were treated with 7-ketocholesterol (7 KC: 25-50 μM, 24 h). The highest concentration is known to induce oxiapoptophagy (OXIdative stress + APOPTOsis + autoPHAGY), whereas the lowest concentration does not induce cell death. In those conditions (with 7 KC: 50 μM) morphological, topographical and functional peroxisome alterations associated with modifications of the cytoplasmic distribution of mitochondria, with mitochondrial dysfunction (loss of transmembrane mitochondrial potential, decreased level of cardiolipins) and oxidative stress were observed: presence of peroxisomes with abnormal sizes and shapes similar to those observed in Zellweger fibroblasts, lower cellular level of ABCD3, used as a marker of peroxisomal mass, measured by flow cytometry, lower mRNA and protein levels (measured by RT-qPCR and western blotting) of ABCD1 and ABCD3 (two ATP-dependent peroxisomal transporters), and of ACOX1 and MFP2 enzymes, and lower mRNA level of DHAPAT, involved in peroxisomal β-oxidation and plasmalogen synthesis, respectively, and increased levels of very long chain fatty acids (VLCFA: C24:0, C24:1, C26:0 and C26:1, quantified by gas chromatography coupled with mass spectrometry) metabolized by peroxisomal β-oxidation. In the presence of 7 KC (25 μM), slight mitochondrial dysfunction and oxidative stress were found, and no induction of apoptosis was detected; however, modifications of the cytoplasmic distribution of mitochondria and clusters of mitochondria were detected. The peroxisomal alterations observed with 7 KC (25 μM) were similar to those with 7 KC (50 μM). In addition, data obtained by transmission electron microcopy and immunofluorescence microscopy by dual staining with antibodies raised against p62, involved in autophagy, and ABCD3, support that 7 KC (25-50 μM) induces pexophagy. 7 KC (25-50 μM)-induced side effects were attenuated by α-tocopherol but not by α-tocotrienol, whereas the anti-oxidant properties of these molecules determined with the FRAP assay were in the same range. These data provide evidences that 7 KC, at concentrations inducing or not cell death, triggers morphological, topographical and functional peroxisomal alterations associated with minor or major mitochondrial changes.

Nitidine chloride represses Mcl-1 protein via lysosomal degradation in oral squamous cell carcinoma

BACKGROUND

We have shown previously that nitidine chloride (NC) induces apoptosis via inhibition of signal transducer and activator of transcription 3 (STAT3). However, its downstream molecules are not fully understood yet. Here, we report that NC as STAT3 inhibitor downregulates myeloid cell leukemia-1 (Mcl-1) protein in HSC-3 and HSC-4 human oral squamous cell carcinoma (OSCC) cells and a nude mouse tumor xenograft model.

METHODS

This study investigated the effects of NC on Mcl-1 expression in HSC-3 and HSC-4 cells using Western blotting, RT-PCR, and dual-luciferase assay. Immunohistochemistry was employed to evaluate Mcl-1 expression levels in mouse tumor tissues. Construction of Mcl-1 overexpression vector and transient transfection was done to test the apoptosis of HSC-3 cells.

RESULTS

Nitidine chloride did not affect either mRNA level or promoter activity of Mcl-1, and the decrease in Mcl-1 protein by NC was caused by lysosome-dependent degradation, but not proteasome-dependent degradation. The overexpression of Mcl-1 protein in OSCC cell lines was sufficient to block the induction of apoptosis. In addition, NC strongly reduced the expression level of Mcl-1 protein compared with other STAT3 inhibitors such as cryptotanshione and S3I-201 in OSCCs.

CONCLUSIONS

Our findings suggest that NC triggers apoptosis via lysosome-dependent Mcl-1 protein degradation and could be chosen as a promising chemotherapeutic candidate against human OSCCs.

Cell Death Pathways: a Novel Therapeutic Approach for Neuroscientists

In the first part, the following mechanisms involved in different forms of cell death are considered, with a view to identifying potential therapeutic targets: tumour necrosis factor receptors (TNFRs) and their engagement by tumour necrosis factor-alpha (TNF-α); poly [ADP-ribose] polymerase (PARP)-1 cleavage; the apoptosis signalling kinase (ASK)-c-Jun N-terminal kinase (JNK) axis; lysosomal permeability; activation of programmed necrotic cell death; oxidative stress, caspase-3 inhibition and parthanatos; activation of inflammasomes by reactive oxygen species and the development of pyroptosis; oxidative stress, calcium dyshomeostasis and iron in the development of lysosomal-mediated necrosis and lysosomal membrane permeability; and oxidative stress, lipid peroxidation, iron dyshomeostasis and ferroptosis. In the second part, there is a consideration of the role of lethal and sub-lethal activation of these pathways in the pathogenesis and pathophysiology of neurodegenerative and neuroprogressive disorders, with particular reference to the TNF-α-TNFR signalling axis; dysregulation of ASK-1-JNK signalling; prolonged or chronic PARP-1 activation; the role of pyroptosis and chronic inflammasome activation; and the roles of lysosomal permeabilisation, necroptosis and ferroptosis. Finally, it is suggested that, in addition to targeting oxidative stress and inflammatory processes generally, neuropsychiatric disorders may respond to therapeutic targeting of TNF-α, PARP-1, the Nod-like receptor NLRP3 inflammasome and the necrosomal molecular switch receptor-interacting protein kinase-3, since their widespread activation can drive and/or exacerbate peripheral inflammation and neuroinflammation even in the absence of cell death. To this end, the use is proposed of a combination of the tetracycline derivative minocycline and N-acetylcysteine as adjunctive treatment for a range of neuropsychiatric disorders.

ROS-mediated lysosomal membrane permeabilization is involved in bupivacaine-induced death of rabbit intervertebral disc cells

Bupivacaine is frequently administered for diagnosing and controlling spine-related pain in interventional spine procedures. However, the potential cytotoxic effects of bupivacaine on intervertebral disc (IVD) cells and the underlying molecular mechanisms have not yet been fully established. Here, we showed that bupivacaine decreased the viability of rabbit IVD cells in a dose- and time-dependent manner. Moreover, the short-term cytotoxicity of bupivacaine in IVD cells was primarily due to cell necrosis, as assessed by Annexin V-propidium iodide staining and live/dead cell staining. Necrosis was verified by observations of swollen organelles, plasma membrane rupture, and cellular lysis under transmission electronic microscopy. Interestingly, our data indicated that bupivacaine-induced primary necrosis might involve the necroptosis pathway. The key finding of this study was that bupivacaine was able to induce lysosomal membrane permeabilization (LMP) with the release of cathepsins into the cytosol, as evidenced by LysoTracker Red staining, acridine orange staining, and cathepsin D immunofluorescence staining. Consistently, inhibitors of lysosomal cathepsins, CA074-Me and pepstatin A, significantly reduced bupivacaine-induced cell death. Finally, we found that bupivacaine resulted in an increase in intracellular reactive oxygen species (ROS) and that inhibition of ROS by N-acetyl-L-cysteine effectively blocked bupivacaine-induced LMP and cell death. In summary, the results of this in vitro study reveal a novel mechanism underlying bupivacaine-induced cell death involving ROS-mediated LMP. Our findings establish a basis for the further investigation of bupivacaine cytotoxicity in an in vivo system.

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Bupivacaine decreases IVD cell viability in a dose- and time-dependent manner.

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The short-term cytotoxicity of bupivacaine is primarily due to cell necrosis.

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LMP is involved in bupivacaine-induced death of IVD cells.

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ROS is an important mediator in bupivacaine-induced LMP and cell death.

Organelle dynamics and viral infections: at cross roads

Viruses are obligate intracellular parasites of the host cells. A commonly accepted view is the requirement of internal membranous structures for various aspects of viral life cycle. Organelles enable favourable intracellular environment for several viruses. However, studies reporting organelle dynamics upon viral infections are scant. In this review, we aim to summarize and highlight modulations caused to various organelles upon viral infection or expression of its proteins.

Human Cytomegalovirus Protein pUL38 Prevents Premature Cell Death by Binding to Ubiquitin-Specific Protease 24 and Regulating Iron Metabolism

Human cytomegalovirus (HCMV) protein pUL38 has been shown to prevent premature cell death by antagonizing cellular stress responses; however, the underlying mechanism remains unknown. In this study, we identified the host protein ubiquitin-specific protease 24 (USP24) as an interaction partner of pUL38. Mutagenesis analysis of pUL38 revealed that amino acids TFV at positions 227 to 230 were critical for its interaction with USP24. Mutant pUL38 TFV/AAA protein did not bind to USP24 and failed to prevent cell death induced by pUL38-deficient HCMV infection. Knockdown of USP24 suppressed the cell death during pUL38-deficient HCMV infection, suggesting that pUL38 achieved its function by antagonizing the function of USP24. We investigated the cellular pathways regulated by USP24 that might be involved in the cell death phenotype by testing several small-molecule compounds known to have a protective effect during stress-induced cell death. The iron chelators ciclopirox olamine and Tiron specifically protected cells from pUL38-deficient HCMV infection-induced cell death, thus identifying deregulated iron homeostasis as a potential mechanism. Protein levels of nuclear receptor coactivator 4 (NCOA4) and lysosomal ferritin degradation, a process called ferritinophagy, were also regulated by pUL38 and USP24 during HCMV infection. Knockdown of USP24 decreased NCOA4 protein stability and ferritin heavy chain degradation in lysosomes. Blockage of ferritinophagy by genetic inhibition of NCOA4 or Atg5/Atg7 prevented pUL38-deficient HCMV infection-induced cell death. Overall, these results support the hypothesis that pUL38 binds to USP24 to reduce ferritinophagy, which may then protect cells from lysosome dysfunction-induced cell death.IMPORTANCE Premature cell death is considered a first line of defense against various pathogens. Human cytomegalovirus (HCMV) is a slow-replicating virus that encodes several cell death inhibitors, such as pUL36 and pUL37x1, which allow it to overcome both extrinsic and intrinsic mitochondrion-mediated apoptosis. We previously identified HCMV protein pUL38 as another virus-encoded cell death inhibitor. In this study, we demonstrated that pUL38 achieved its activity by interacting with and antagonizing the function of the host protein ubiquitin-specific protease 24 (USP24). pUL38 blocked USP24-mediated ferritin degradation in lysosomes, which could otherwise be detrimental to the lysosome and initiate cell death. These novel findings suggest that iron metabolism is finely tuned during HCMV infection to avoid cellular toxicity. The results also provide a solid basis for further investigations of the role of USP24 in regulating iron metabolism during infection and other diseases.