Ciro Isidoro

Autophagic‐lysosomal perturbation enhances tau aggregation in transfectants with induced wild‐type tau expression

The intracellular assembly of tau aggregates is a pathological hallmark shared by Alzheimers disease and other neurodegenerative disorders known collectively as tauopathies. To model how tau fibrillogenesis evolves in tauopathies, we previously established transfectant M1C cultures from human neuroblastoma BE(2)‐M17D cells that inducibly express human tau. In the present study, these cells were used to determine the role of the autophagic‐lysosomal system in the degradation and aggregation of wild‐type tau. Tau induction for 5 days led to the accumulation of tau with nominal assembly of tau aggregates within cells. When the lysosomotropic agent, chloroquine (CQ), was added following the termination of tau induction, tau clearance was delayed. Decreased tau truncation and increased levels of intact tau were observed. When present during tau induction, CQ led to tau accumulation and promoted the formation of sarkosyl‐insoluble aggregates containing both truncated and full‐length tau. CQ treatment significantly decreased the activities of cathepsins D, B and L, and the inhibition of cathepsins B and L mimicked the effect of CQ and increased tau levels in cells. Additionally, exposure of cells to the autophagy inhibitor, 3‐methyladenine, led to tau accumulation and aggregation. These results suggest that the autophagic‐lysosomal system plays a role in the clearance of tau, and that dysfunction of this system results in the formation of tau oligomers and insoluble aggregates.

Suppression of autophagy precipitates neuronal cell death following low doses of methamphetamine

Methamphetamine abuse is toxic to dopaminergic neurons, causing nigrostriatal denervation and striatal dopamine loss. Following methamphetamine exposure, the number of nigral cell bodies is generally preserved, but their cytoplasm features autophagic‐like vacuolization and cytoplasmic accumulation of α‐synuclein‐, ubiquitin‐ and parkin‐positive inclusion‐like bodies. Whether autophagy is epiphenomenal or it plays a role in the mechanism of methamphetamine toxicity and, in the latter case, whether its role consists of counteracting or promoting the neurotoxic effect remains obscure. We investigated the signaling pathway and the significance (protective vs. toxic) of autophagy activation and the convergence of the autophagic and the ubiquitin‐proteasome pathways at the level of the same intracellular bodies in a simple cell model of methamphetamine toxicity. We show that autophagy is rapidly up‐regulated in response to methamphetamine. Confocal fluorescence microscopy and immuno‐electron microscopy studies demonstrated the presence of α‐synuclein aggregates in autophagy‐lysosomal structures in cells exposed to methamphetamine, a condition compatible with cell survival. Inhibition of autophagy either by pharmacologic or genetic manipulation of the class III Phosphatidylinositol‐3 kinase‐mediated signaling prevented the removal of α‐synuclein aggregates and precipitated a bax‐mediated mitochondrial apoptosis pathway.

Autophagy and amyotrophic lateral sclerosis: The multiple roles of lithium.

In a pilot clinical study that we recently published we found that lithium administration slows the progression of Amyotrophic Lateral Sclerosis (ALS) in human patients. This clinical study was published in addition with basic (in vitro) and pre-clinical (in vivo) data demonstrating a defect of autophagy as a final common pathway in the genesis of ALS. In fact, lithium was used as an autophagy inducer. In detailing the protective effects of lithium we found for the first time that this drug stimulates the biogenesis of mitochondria in the central nervous system and, uniquely in the spinal cord, it induces neuronogenesis and neuronal differentiation. In particular, the effects induced by lithium can be summarized as follows: (i) the removal of altered mitochondria and protein aggregates; (ii) the biogenesis of well-structured mitochondria; (iii) the suppression of glial proliferation; (iv) the differentiation of newly formed neurons in the spinal cord towards a specific phenotype. In this addendum we focus on defective autophagy as a “leit motif” in ALS and the old and novel features of lithium which bridge autophagy activation to concomitant effects that may be useful for the treatment of a variety of neurodegenerative disorders. In particular, the biogenesis of mitochondria and the increase of calbindin D 28K-positive neurons, which are likely to support powerful neuroprotection towards autophagy failure, mitochondriopathy, and neuronal loss in the spinal cord. Addendum to: Fornai F, Longone P, Cafaro L, Kastsiuchenka O, Ferrucci M, Manca ML, Lazzeri G, Spalloni A, Bellio N, Lenzi P, Modugno N, Siciliano G, Isidoro C, Murri L, Ruggieri S, Paparelli A. Lithium delays progression of amyotrophic lateral sclerosis. Proc Natl Acad Sci U S A 2008; 105:2052-2057.

Cathepsin D released by lactating rat mammary epithelial cells is involved in prolactin cleavage under physiological conditions.

The 16 kDa prolactin fragment arises from partial proteolysis of the native 23 kDa prolactin pituitary hormone. The mammary gland has been involved in this processing, although it has not been clarified whether it occurs in stroma or epithelial cells or extracellularly. Also, the processing enzyme has not been defined yet. Here we show that the incubation medium of stroma-deprived mammary acini from lactating rat contains an enzymatic activity able to cleave, in a temperature- and time-dependent fashion, the 23 kDa prolactin to generate a 16 kDa prolactin detectable under reducing conditions. This cleavage was not impaired in the presence of hirudin, a thrombin inhibitor, but strongly weakened in the presence of pepstatin A, a cathepsin D inhibitor. Cathepsin D immuno-depletion abolished the capability of acini-conditioned medium to cleave the 23 kDa prolactin. Brefeldin A treatment of acini, a condition that largely abolished the apical secretion of milk proteins, did not impair the secretion of the enzymatically active single chain of cathepsin D. These results show that mature cathepsin D from endosomes or lysosomes is released, likely at the baso-lateral site of mammary epithelial cells, and that a cathepsin D-dependent activity is required to effect, under physiological conditions, the cleavage of 23 kDa prolactin in the extracellular medium. This is the first report demonstrating that cathepsin D can perform a limited proteolysis of a substrate at physiological pH outside the cell.

Defective autophagy in Parkinson's disease: Role of oxidative stress

Parkinson’s disease (PD) is a paradigmatic example of neurodegenerative disorder with a critical role of oxidative stress in its etiopathogenesis. Genetic susceptibility factors of PD, such as mutations in Parkin, PTEN-induced kinase 1, and DJ-1 as well as the exposure to pesticides and heavy metals, both contribute to altered redox balance and degeneration of dopaminergic neurons in the substantia nigra. Dysregulation of autophagy, a lysosomal-driven process of self degradation of cellular organelles and protein aggregates, is also implicated in PD and PD-related mutations, and environmental toxins deregulate autophagy. However, experimental evidence suggests a complex and ambiguous role of autophagy in PD since either impaired or abnormally upregulated autophagic flux has been shown to cause neuronal loss. Finally, it is generally believed that oxidative stress is a strong proautophagic stimulus. However, some evidence coming from neurobiology as well as from other fields indicate an inhibitory role of reactive oxygen species and reactive nitrogen species on the autophagic machinery. This review examines the scientific evidence supporting different concepts on how autophagy is dysregulated in PD and attempts to reconcile apparently contradictory views on the role of oxidative stress in autophagy regulation. The complex relationship between autophagy and oxidative stress is also considered in the context of the ongoing search for a novel PD therapy.

Biocompatibility, endocytosis, and intracellular trafficking of mesoporous silica and polystyrene nanoparticles in ovarian cancer cells: effects of size and surface charge groups.

Background and methods Nanoparticles engineered to carry both a chemotherapeutic drug and a sensitive imaging probe are valid tools for early detection of cancer cells and to monitor the cytotoxic effects of anticancer treatment simultaneously. Here we report on the effect of size (10–30 nm versus 50 nm), type of material (mesoporous silica versus polystyrene), and surface charge functionalization (none, amine groups, or carboxyl groups) on biocompatibility, uptake, compartmentalization, and intracellular retention of fluorescently labeled nanoparticles in cultured human ovarian cancer cells. We also investigated the involvement of caveolae in the mechanism of uptake of nanoparticles. Results We found that mesoporous silica nanoparticles entered via caveolae-mediated endocytosis and reached the lysosomes; however, while the 50 nm nanoparticles permanently resided within these organelles, the 10 nm nanoparticles soon relocated in the cytoplasm. Naked 10 nm mesoporous silica nanoparticles showed the highest and 50 nm carboxyl-modified mesoporous silica nanoparticles the lowest uptake rates, respectively. Polystyrene nanoparticle uptake also occurred via a caveolae-independent pathway, and was negatively affected by serum. The 30 nm carboxyl-modified polystyrene nanoparticles did not localize in lysosomes and were not toxic, while the 50 nm amine-modified polystyrene nanoparticles accumulated within lysosomes and eventually caused cell death. Ovarian cancer cells expressing caveolin-1 were more likely to endocytose these nanoparticles. Conclusion These data highlight the importance of considering both the physicochemical characteristics (ie, material, size and surface charge on chemical groups) of nanoparticles and the biochemical composition of the cell membrane when choosing the most suitable nanotheranostics for targeting cancer cells.

AUTOPHAGY, LITHIUM, AND AMYOTROPHIC LATERAL SCLEROSIS

In this article we provide an overview of the intersection between amyotrophic lateral sclerosis (ALS) and the autophagy pathway and discuss the potential protective effects of lithium through mechanisms that recruit autophagy and other effects. The autophagy pathway is recruited during motor neuron (MN) death both in vitro and in vivo. Despite a few controversial issues concerning the significance (detrimental/protective) of autophagy in ALS, recent findings indicate a protective role. Lithium in low doses is a well‐known autophagy inducer that clears misfolded proteins and altered mitochondria from MNs. Moreover, lithium preserves mitochondria and sustains their genesis. This effect is replicated by rapamycin, which is an autophagy inducer but with a different mechanism from lithium. Lithium also increases the number of Renshaw cells that are affected early during the progression of experimental ALS. Again, lithium has been reported to decrease glial proliferation in the ALS spinal cord and induces sprouting in corticospinal fibers. Muscle Nerve 40: 173–194, 2009

Inhibition of PI3k class III-dependent autophagy prevents apoptosis and necrosis by oxidative stress in dopaminergic neuroblastoma cells.

Hydrogen peroxide (H(2)O(2)) is an extremely reactive oxidoradical that is normally produced as a by-product of the mitochondrial activity and also under several metabolic stress conditions. Autophagy, a lysosomal degradation pathway, is triggered by oxidative stress as a defensive response. How autophagy and death pathways are coordinated in cells subjected to oxidative stress is still poorly understood. In human neuroblastoma SH-SY5Y cells, 200microM H(2)O(2) rapidly induced the formation of LC3-positive autophagic vacuoles and of beclin1-Vps34 double-positive macroaggregates. Vacuolar LC3 and beclin1 aggregates did not form when oxidative stress was performed in cells pretreated with 3-methyladenine (3MA), an inhibitor of Vps34, or infected with a recombinant adenovirus expressing a dominant-negative mutant of Vps34. H(2)O(2) provoked the permeabilization of lysosomes (at 30 min) and of mitochondria, the concomitant oligomerization of bax, and eventually (at 2 h), cell death in about 50% of the cell culture. Inactivation of Vps34-dependent autophagy in oxidative-stressed cells abrogated lysosome leakage, bax activation, and caspase-dependent apoptosis and conferred protection for as long as 16 h. Inhibition of caspase activity (by ZVAD-fmk) did not trigger an alternative cell death pathway but rather afforded complete protection from oxidative toxicity, despite the ongoing generation of oxidoradicals and the cellular accumulation of autophagic vacuoles and of leaking lysosomes. On long-term (16 h) exposure to H(2)O(2), signs of necrotic cell death became apparent in LC3-positive cells, which could be prevented by ZVAD-fmk. The present data highlight the pivotal role of autophagy in H(2)O(2)-induced cell death in dopaminergic neuroblastoma cells.

Chelation of Lysosomal Iron Protects Dopaminergic SH-SY5Y Neuroblastoma Cells from Hydrogen Peroxide Toxicity by Precluding Autophagy and Akt Dephosphorylation

In human neuroblastoma SH-SY5Y cells, hydrogen peroxide (H(2)O(2), 200μM) rapidly (< 5 min) induced autophagy, as shown by processing and vacuolar relocation of light chain 3(LC3). Accumulation of autophagosome peaked at 30 min of H(2)O(2) exposure. The continuous presence of H(2)O(2) eventually (at > 60 min) caused autophagy-dependent annexin V-positive cell death. However, the cells exposed to H(2)O(2) for 30 min and then cultivated in fresh medium could recover and grow, despite ongoing autophagy. H(2)O(2) rapidly (5 min) triggered the formation of dichlorofluorescein-sensitive HO(·)-free radicals within mitochondria, whereas the mitochondria-associated oxidoradicals revealed by MitoSox (O(2)(·-)) became apparent after 30 min of exposure to H(2)O(2). 3-Methyladenine inhibited autophagy and cell death, but not the generation of HO(·). Genetic silencing of beclin-1 prevented bax- and annexin V-positive cell death induced by H(2)O(2), confirming the involvement of canonical autophagy in peroxide toxicity. The lysosomotropic iron chelator deferoxamine (DFO) prevented the mitochondrial generation of both HO(.) and O(2)(·-) and suppressed the induction of autophagy and of cell death by H(2)O(2). Upon exposure to H(2)O(2), Akt was intensely phosphorylated in the first 30 min, concurrently with mammalian target of rapamycin inactivation and autophagy, and it was dephosphorylated at 2 h, when > 50% of the cells were dead. DFO did not impede Akt phosphorylation, which therefore was independent of reactive oxygen species (ROS) generation but inhibited Akt dephosphorylation. In conclusion, exogenous H(2)O(2) triggers two parallel independent pathways, one leading to autophagy and autophagy-dependent apoptosis, the other to transient Akt phosphorylation, and both are inhibited by DFO. The present work establishes HO(·) as the autophagy-inducing ROS and highlights the need for free lysosomal iron for its production within mitochondria in response to hydrogen peroxide.

Autophagy-active beclin-1 correlates with favourable clinical outcome in non-Hodgkin lymphomas

The expression of beclin-1, an oncosuppressor monoallelically deleted in >60% epithelial cancers, has been shown to be developmentally regulated in T and B lymphocytes. By interacting with either bcl-2 or class III phosphatidyl-inositol-3-phosphate kinase, beclin-1 regulates apoptosis and autophagy, two processes crucial for lymphatic tissue homeostasis. We analyzed the potential link between beclin-1-mediated autophagy and the malignant behaviour of lymphomas. The tissue expression of beclin-1 was analyzed in a large series of non-Hodgkin lymphomas and correlated with patients clinical outcome. By immunofluorescence, beclin-1 staining showed faintly detectable and diffusely distributed in the cytoplasm (regarded as negative) or confined to the perinuclear region as large and brilliant puncta suggestive of macro-aggregate reactivity (regarded as positive). The positive expression of beclin-1 well correlated with the presence of LC3-positive autophagic vacuoles and was inversely correlated with the expression of bcl-2. Non-Hodgkin lymphomas in which ⩾20% of tumour cells expressed high level of beclin-1 aggregates were associated with a complete (57%) or partial (35%) remission. The 5-year overall survival probability, calculated by the Kaplan–Meier method, was 92% and 42% in beclin-1-expressing non-Hodgkin lymphomas with ⩾20% and <20% positive cells, respectively (log-rank test, P<0.000.1). In Cox multivariate analysis, the level of beclin-1 expression, adjusted for patients age and pathologic stage, revealed to be significantly correlated with patients survival (P<0.0001). This is the first demonstration of the involvement of beclin-1 and autophagy in the clinical behaviour of non-Hodgkin lymphomas. The present data are compatible with the hypothesis that non-Hodgkin lymphomas with upregulated autophagy are more responsive to chemotherapy and indicate that beclin-1 could be a valuable independent prognostic factor in this heterogeneous group of tumours.