Hydrogen peroxide induces lysosomal protease alterations in PC12 cells

The Intricate Balance between Life and Death: ROS, Cathepsins, and Their Interplay in Cell Death and Autophagy

Cellular survival hinges on a delicate balance between accumulating damages and repair mechanisms. In this intricate equilibrium, oxidants, currently considered physiological molecules, can compromise vital cellular components, ultimately triggering cell death. On the other hand, cells possess countermeasures, such as autophagy, which degrades and recycles damaged molecules and organelles, restoring homeostasis. Lysosomes and their enzymatic arsenal, including cathepsins, play critical roles in this balance, influencing the cell's fate toward either apoptosis and other mechanisms of regulated cell death or autophagy. However, the interplay between reactive oxygen species (ROS) and cathepsins in these life-or-death pathways transcends a simple cause-and-effect relationship. These elements directly and indirectly influence each other's activities, creating a complex web of interactions. This review delves into the inner workings of regulated cell death and autophagy, highlighting the pivotal role of ROS and cathepsins in these pathways and their intricate interplay.

A new lysosome-targeted fluorescent probe for hydrogen peroxide based on a benzothiazole derivative

As an important member of reactive oxygen species, hydrogen peroxide (H2O2) plays a key role in oxidative stress and cell signaling. Abnormal levels of H2O2 in lysosomes can induce damage or even loss of lysosomal function, leading to certain diseases. Therefore, real-time monitoring of H2O2 in lysosomes is very important. In this work, we designed and synthesized a novel lysosome-targeted fluorescent probe for H2O2-specific detection based on a benzothiazole derivative. A morpholine group was used as a lysosome-targeted unit and a boric acid ester was chosen as the reaction site. In the absence of H2O2, the probe exhibited very weak fluorescence. In the presence of H2O2, the probe showed an increased fluorescence emission. The fluorescence intensity of the probe for H2O2 displayed a good linear relationship in the concentration range of H2O2 from 8.0 × 10-7 to 2.0 × 10-4 mol·L-1. The detection limit was estimated to be 4.6 × 10-7 mol·L-1 for H2O2. The probe possessed high selectivity, good sensitivity and short response time for the detection of H2O2. Moreover, the probe had almost no cytotoxicity and had been successfully applied to confocal imaging of H2O2 in lysosomes of A549 cells. These results illustrated that the developed fluorescent probe in this study could provide a good tool for the determination of H2O2 in lysosomes.

Associations of serum cystatin C with depressive symptoms and suicidal ideation in major depressive disorder

BACKGROUND

Individuals with major depressive disorder (MDD) have high suicidal ideation. There is evidence that serum cystatin C (Cys C) may be involved in the pathophysiology of MDD. The present study aimed to investigate Cys C concentration in patients with MDD and clarify its possible association with depressive symptoms and suicidal ideation.

METHODS

An online cross-sectional survey of 159 patients diagnosed with MDD was conducted. Serum Cys C levels were measured using ADVIA 2400 biochemical analyzer. The 24-item Hamilton Depression Scale (HAMD-24) was administered to evaluate the depressive symptoms. Generalized linear regression, logistic regression and restricted cubic spline models were used to examine the association of serum Cys C levels with depressive symptoms and suicidal ideation.

RESULTS

Serum Cys C levels were higher in MDD patients than in controls (p = 0.001) and were positively associated with scores on HAMD-24 in unadjusted (gender distribution, age, smoking, alcohol consumption, family history of depression and traumatic life events; (p = 0.003) and fully adjusted linear regression model (p = 0.005). The fully adjusted regression coefficient with 95% confidence intervals for serum Cys C levels and HAMD-24 score was 30.339 (9.602 to 51.077). The level of Cys C in the suicidal ideation (SI) group was significantly higher than that in the non-suicide ideation (non-SI) group (p = 0.001). Serum Cys C levels were positively associated with suicidal ideation in each logistic regression model (all p <  0.05).

CONCLUSION

Serum Cys C levels were elevated in MDD patients and appeared to be positively correlated with depressive symptoms and suicidal ideation. These findings suggest that the dysfunction of Cys C may be involved in the severity of depression and in the pathophysiological process of MDD. Thus, regulation of serum Cys C could potentially be an effective predictor of the severity of depression and potentially, play a role in reducing the risk of suicide in MDD patients.

The response of yeast vacuolar proteins: A novel rapid tool for Salmonella sp. screening

Human health is recently affected by several factors in which food contamination is one of the most dangerous elements that damage directly on our bodies. In this study, we provided a novel approach for the rapid detection of Salmonella sp. at the molecular level using the response of Saccharomyces cerevisiae's vacuoles. First, an augmentation of vacuoles intensity was observed by confocal microscopy after treating Salmonella strains with yeast cells. Second, the vacuolar enzymes were isolated and then analyzed by two-dimensional electrophoresis for the screening of specific biomarkers. After that, various recombinant yeasts containing exclusive biomarkers were constructed by fusing these biomarkers with several fluorescent proteins. Finally, the recombinant strains showed the ability to detect Salmonella strains specifically by appropriate fluorescent signals from 20 CFU/mL after 15 Min of exposure.

Redox-Mediated Post-Translational Modifications of Proteolytic Enzymes and Their Role in Protease Functioning

Proteolytic enzymes play a crucial role in metabolic processes, providing the cell with amino acids through the hydrolysis of multiple endogenous and exogenous proteins. In addition to this function, proteases are involved in numerous protein cascades to maintain cellular and extracellular homeostasis. The redox regulation of proteolysis provides a flexible dose-dependent mechanism for proteolytic activity control. The excessive reactive oxygen species (ROS) and reactive nitrogen species (RNS) in living organisms indicate pathological conditions, so redox-sensitive proteases can swiftly induce pro-survival responses or regulated cell death (RCD). At the same time, severe protein oxidation can lead to the dysregulation of proteolysis, which induces either protein aggregation or superfluous protein hydrolysis. Therefore, oxidative stress contributes to the onset of age-related dysfunction. In the present review, we consider the post-translational modifications (PTMs) of proteolytic enzymes and their impact on homeostasis.

Regulation of the Proteolytic Activity of Cysteine Cathepsins by Oxidants

Besides their primary involvement in the recycling and degradation of proteins in endo-lysosomal compartments and also in specialized biological functions, cysteine cathepsins are pivotal proteolytic contributors of various deleterious diseases. While the molecular mechanisms of regulation via their natural inhibitors have been exhaustively studied, less is currently known about how their enzymatic activity is modulated during the redox imbalance associated with oxidative stress and their exposure resistance to oxidants. More specifically, there is only patchy information on the regulation of lung cysteine cathepsins, while the respiratory system is directly exposed to countless exogenous oxidants contained in dust, tobacco, combustion fumes, and industrial or domestic particles. Papain-like enzymes (clan CA, family C1, subfamily C1A) encompass a conserved catalytic thiolate-imidazolium pair (Cys25-His159) in their active site. Although the sulfhydryl group (with a low acidic pKa) is a potent nucleophile highly susceptible to chemical modifications, some cysteine cathepsins reveal an unanticipated resistance to oxidative stress. Besides an introductory chapter and peculiar attention to lung cysteine cathepsins, the purpose of this review is to afford a concise update of the current knowledge on molecular mechanisms associated with the regulation of cysteine cathepsins by redox balance and by oxidants (e.g., Michael acceptors, reactive oxygen, and nitrogen species).

Neuroprotective Effects of Necrostatin-1 Against Oxidative Stress-Induced Cell Damage: an Involvement of Cathepsin D Inhibition

Necroptosis, a recently discovered form of non-apoptotic programmed cell death, can be implicated in many pathological conditions including neuronal cell death. Moreover, an inhibition of this process by necrostatin-1 (Nec-1) has been shown to be neuroprotective in in vitro and in vivo models of cerebral ischemia. However, the involvement of this type of cell death in oxidative stress–induced neuronal cell damage is less recognized. Therefore, we tested the effects of Nec-1, an inhibitor of necroptosis, in the model of hydrogen peroxide (H₂O₂)-induced cell damage in human neuroblastoma SH-SY5Y and murine hippocampal HT-22 cell lines. The data showed that Nec-1 (10–40 μM) attenuated the cell death induced by H₂O₂ in undifferentiated (UN-) and neuronal differentiated (RA-) SH-SY5Y cells with a higher efficacy in the former cell type. Moreover, Nec-1 partially reduced cell damage induced by 6-hydroxydopamine in UN- and RA-SH-SY5Y cells. The protective effect of Nec-1 was of similar magnitude as the effect of a caspase-3 inhibitor in both cell phenotypes and this effect were not potentiated after combined treatment. Furthermore, the non-specific apoptosis and necroptosis inhibitor curcumin augmented the beneficial effect of Nec-1 against H₂O₂-evoked cell damage albeit only in RA-SH-SY5Y cells. Next, it was found that the mechanisms of neuroprotective effect of Nec-1 against H₂O₂-induced cell damage in SH-SY5Y cells involved the inhibition of lysosomal protease, cathepsin D, but not caspase-3 or calpain activities. In HT-22 cells, Nec-1 was protective in two models of oxidative stress (H₂O₂ and glutamate) and that effect was blocked by a caspase inhibitor. Our data showed neuroprotective effects of the necroptosis inhibitor, Nec-1, against oxidative stress–induced cell damage and pointed to involvement of cathepsin D inhibition in the mechanism of its action. Moreover, a cell type–specific interplay between necroptosis and apoptosis has been demonstrated.

The antifungal activity of the peptide, periplanetasin-2, derived from American cockroach Periplaneta americana

The cockroach, which is a household insect, is an established model organism in research. Periplanetasin-2, derived from the American cockroach Periplaneta americana, exerted potent antifungal effect against pathogenic fungi without causing hemolysis. Periplanetasin-2 induced oxidative stress by generation of reactive oxygen species (ROS) and lipid peroxidation. Periplanetasin-2 also caused apoptosis by exposure of phosphatidylserine and fragmentation of DNA, exerted in a concentration-dependent manner. Hence, we investigated the mitochondrial apoptotic mechanism of periplanetasin-2 in Candida albicans. After treatment with periplanetasin-2, we observed mitochondrial depolarization and calcium accumulation. Moreover, we observed a decrease in cytosolic glutathione, and an increase in mitochondrial glutathione, indicating that periplanetasin-2 induced oxidative stress and high ROS production in the mitochondria. Because of this mitochondrial dysfunction, cytochrome c was released from the mitochondria into the cytosol, and caspase was activated in a time-dependent manner. In summary, the antifungal peptide periplanetasin-2 activates apoptotic signals in the mitochondria by induction of oxidative stress.

The ATM kinase inhibitor KU-55933 provides neuroprotection against hydrogen peroxide-induced cell damage via a γH2AX/p-p53/caspase-3-independent mechanism: Inhibition of calpain and cathepsin D

The role of the kinase ataxia-telangiectasia mutated (ATM), a well-known protein engaged in DNA damage repair, in the regulation of neuronal responses to oxidative stress remains unexplored. Thus, the neuroprotective efficacy of KU-55933, a potent inhibitor of ATM, against cell damage evoked by oxidative stress (hydrogen peroxide, H₂O₂) has been studied in human neuroblastoma SH-SY5Y cells and compared with the efficacy of this agent in models of doxorubicin (Dox)- and staurosporine (St)-evoked cell death. KU-55933 inhibited the cell death induced by H₂O₂ or Dox but not by St in undifferentiated (UN-) and retinoic acid-differentiated (RA)-SH-SY5Y cells, with a more pronounced effect in the latter cell phenotype. Furthermore, this ATM inhibitor attenuated the Dox- but not H₂O₂-induced caspase-3 activity in both UN- and RA-SH-SY5Y cells. Although KU-55933 inhibited the H₂O₂- and Dox-induced activation of ATM, it attenuated the toxin-induced phosphorylation of the proteins H2AX and p53 only in the latter model of cell damage. Moreover, the ATM inhibitor prevented the H₂O₂-evoked increases in calpain and cathepsin D activity and attenuated cell damage to a similar degree as inhibitors of calpain (MDL28170) and cathepsin D (pepstatin A). Finally, we confirmed the neuroprotective potential of KU-55933 against the H₂O₂- and Dox-evoked cell damage in primary mouse cerebellar granule cells and in the mouse hippocampal HT-22 cell line. Altogether, our results extend the neuroprotective portfolio of KU-55933 to a model of oxidative stress, with this effect not involving inhibition of the γH2AX/p-p53/caspase-3 pathway and instead associated with the attenuation of calpain and cathepsin D activity.

Toxicity detection using lysosomal enzymes, glycoamylase and thioredoxin fused with fluorescent protein in Saccharomyces cerevisiae

Saccharomyces cerevisiae is the simplest and a favorite eukaryotic system that contains lysosome and thus, is a suitable organism for monitoring some toxic effects in environmental pollution. In this study, S. cerevisiae was transformed with two recombinant plasmids. Sporulation-specific glycoamylase (SGA1), which was upregulated in response to arsenic, was fused with the blue fluorescent protein (BFP) for the construction of an oxidative stress-causing chemicals sensor. Additionally, thioredoxin (TRX2), a protein overexpressed exclusively under tetracycline's influence, fused with the cyan fluorescent protein (CFP) to create a detector for this kind of chemical. In summary, we developed two recombinant S. cerevisiae that facilitate the detection of both kinds of toxic chemicals, specifically visualized by different color indicators.

Oxidative stress leads to increased mutation frequency in a murine model of myelodysplastic syndrome

The myelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis, dysplasia, and transformation to acute myeloid leukemia (AML). Although it has been suggested that additional mutations lead to progression of MDS to AML, the causative agent(s) for such mutations remains unclear. Oxidative stress is a potential cause, therefore, we evaluated levels of reactive oxygen species (ROS) in NUP98-HOXD13 (NHD13) transgenic mice, a murine model for MDS. Increased levels of ROS were detected in bone marrow nucleated cells (BMNC) that express CD71, a marker for cell proliferation, as well as immature, lineage negative bone marrow nucleated cells from NHD13 mice. In addition to the increase in ROS, increased DNA double strand breaks and activation of a G2/M phase cell cycle checkpoint were noted in NHD13 BMNC. Finally, using an in vivo assay for mutation frequency, we detected an increased mutation frequency in NHD13 BMNC. These results suggest that oxidative stress may contribute to disease progression of MDS to AML through ineffective repair of DNA damage and acquisition of oncogenic mutations.

Endosomes and lysosomes are involved in early steps of Tl(III)-mediated apoptosis in rat pheochromocytoma (PC12) cells

The mechanisms that mediate thallium (Tl) toxicity are still not completely understood. The exposure of rat pheochromocytoma (PC12) cells to Tl(I) or Tl(III) activates both mitochondrial (Tl(I) and Tl(III)) and extrinsic (Tl(III)) pathways of apoptosis. In this work we evaluated the hypothesis that the effects of Tl(III) may be mediated by the damage to lysosomes, where it might be incorporated following the route of iron uptake. PC12 cells exposed for 3 h to 100 μM Tl(III) presented marked endosomal acidification, effect that was absent when cells were incubated in a serum-free medium and that was fully recovered when the latter was supplemented with transferrin. After 6 h of incubation the colocalization of cathepsins D and B with the lysosomal marker Lamp-1 was decreased together with an increase in the total activity of the enzymes. A permanent damage to lysosomes after 18 h of exposure was evidenced from the impairment of acridine orange uptake. Cathepsin D caused the cleavage of pro-apoptotic protein BID that is involved in the activation of the intrinsic pathway of apoptosis. Supporting that, BID cleavage and the activation of caspase 3 by Tl(III) were fully prevented when cells were preincubated with cathepsin D inhibitor (pepstatin A) and only partially prevented when cathepsin B inhibitor (E64d) was used. None of these inhibitors affected BID cleavage or caspase 3 activation in Tl(I)-treated cells. Together, experimental results support the role of Tl(III) uptake by the acidic cell compartments and their involvement in the early steps of Tl(III)-mediated PC12 cells apoptosis.

Protective effect of trifluoperazine on hydrogen peroxide-induced apoptosis in PC12 cells

This study investigated effects of trifluoperazine (TFP) against the cytotoxicity induced by H₂O₂ in PC12 cells and the mechanisms thereof. Different concentrations of H₂O₂ (100-500 μM) induced a significant decrease in cell viability accompanied by increased oxidative stress and cell apoptosis. Pretreatment with TFP inhibited H₂O₂-induced cell viability loss. The flow cytometric assay showed that TFP can inhibit intracellular reactive oxygen species (ROS) generation and reduce the cell apoptosis. The electrophysiological recordings indicated that when treated with H₂O₂, the calcium current was significantly increased. Pretreatment with TFP increased mitochondrial membrane potential (MMP) in cells of oxidative injury. These results suggested that TFP can reduce apoptosis by inhibiting ROS generation and preventing loss of MMP in cells. Meanwhile, the protective effect of TFP on the cell apoptosis may be related to the calcium overload. TFP may inhibit the calcium overload process to achieve the protection against apoptosis.