Apoptosis and autophagy in rat cerebellar granule neuron death: Role of reactive oxygen species

β-Aminoisobutyric acid, L-BAIBA, protects PC12 cells from hydrogen peroxide-induced oxidative stress and apoptosis via activation of the AMPK and PI3K/Akt pathway

β-Aminoisobutyric acid (BAIBA) is a myokine that is secreted from skeletal muscles by the exercise. Recently, increasing evidence has suggested the multifocal physiological activities of BAIBA. In this study, we investigated whether L-BAIBA has protective effects on rat pheochromocytoma (PC12) cells. Cultured PC12 cells were stimulated with L-BAIBA. Western blot analyses revealed that L-BAIBA stimulation significantly increased the phosphorylation of AMPK and Akt. In contrast, no effect was observed on neurite outgrowth by L-BAIBA. To investigate the effects of L-BAIBA on oxidative stress, PC 12 cells were exposed to hydrogen peroxide (H₂O₂) with and without L-BAIBA. Hydrogen peroxide significantly increased reactive oxygen species (ROS) production and apoptosis in PC12 cells. Pretreatment with L-BAIBA suppressed H₂O₂-induced ROS production and apoptosis, which was abolished by the inhibition of AMPK by compound C. On the other hand, the inhibitory effects of L-BAIBA on oxidative stress-induced apoptosis were abolished by the inhibition of both AMPK and PI3K/Akt. In conclusion, we demonstrated that L-BAIBA confers protection against oxidative stress in PC12 cells by activating the AMPK and PI3K/Akt pathways. These results suggest that L-BAIBA may play a crucial role on protection of neuron-like cells and become a pharmacological agent to treat neuronal diseases.

Lipin1 Alleviates Autophagy Disorder in Sciatic Nerve and Improves Diabetic Peripheral Neuropathy

Diabetic peripheral neuropathy (DPN) is a chronic complication of diabetes, and its neural mechanisms underlying the pathogenesis remain unclear. Autophagy plays an important role in neurodegenerative diseases and nerve tissue injury. Lipin1 is a phosphatidic acid phosphatase enzyme that converts phosphatidic acid (PA) into diacylglycerol (DAG), a precursor of triacylglycerol and phospholipids which plays an important role in maintaining normal peripheral nerve conduction function. However, whether Lipin1 involved in the pathogenesis of DPN via regulation of autophagy is not elucidated. Here, we show that the Lipin1 expression was downregulated in streptozotocin (STZ)-induced DPN rat model. Interestingly, STZ prevented DAG synthesis, and resulted in autophagic hyperactivity, effects which may increase the apoptosis of Schwann cells and lead to demyelination in sciatic nerve in DPN rats. More importantly, upregulation of lipin1 in the DPN rats ameliorated autophagy disorders and pathological changes of the sciatic nerve, which associated with the increase of the motor nerve conductive velocity (MNCV) in DPN rats. In contrast, knockdown of lipin1 exacerbates neuronal abnormalities and facilitates the genesis of DPN phenotypes in rats. In addition, overexpression of lipin1 in RSC96 cells also significantly decreased the autophagic hyperactivity and apoptosis induced by hyperglycemia. These results suggest that lipin1 may exert neuroprotection within the sciatic nerve anomalies and may serve as a potential therapeutic target for the treatment of DPN.

Differential ROS-Mediated Phosphorylation of Drp1 in Mitochondrial Fragmentation Induced by Distinct Cell Death Conditions in Cerebellar Granule Neurons

Reactive oxygen species (ROS) production has been associated with neuronal death. ROS are also involved in mitochondrial fission, which is mediated by Dynamin-related protein 1 (Drp1). The regulation of mitochondrial fragmentation mediated by Drp1 and its relationship to mitochondrial ROS (mtROS) in neuronal death have not been completely clarified. The aim of this study is to evaluate the role of mtROS in cell death and their involvement in the activation of Drp1 and mitochondrial fission in a model of cell death of cultured cerebellar granule neurons (CGN). Neuronal death of CGN induced by potassium deprivation (K5) and staurosporine (ST) triggers mitochondrial ROS production and mitochondrial fragmentation. K5 condition evoked an increase of Drp1 phosphorylation at Ser616, but ST treatment led to a decrease of Drp1 phosphorylation. Moreover, the death of CGN induced by both K5 and ST was markedly reduced in the presence of MitoTEMPO; however, mitochondrial morphology was not recovered. Here, we show that the mitochondria are the initial source of ROS involved in the neuronal death of CGN and that mitochondrial fragmentation is a common event in cell death; however, this process is not mediated by Drp1 phosphorylation at Ser616.

Role of NADPH oxidase-2 in the progression of the inflammatory response secondary to striatum excitotoxic damage

Background

During excitotoxic damage, neuronal death results from the increase in intracellular calcium, the induction of oxidative stress, and a subsequent inflammatory response. NADPH oxidases (NOX) are relevant sources of reactive oxygen species (ROS) during excitotoxic damage. NADPH oxidase-2 (NOX-2) has been particularly related to neuronal damage and death, as well as to the resolution of the subsequent inflammatory response. As ROS are crucial components of the regulation of inflammatory response, in this work, we evaluated the role of NOX-2 in the progression of inflammation resulting from glutamate-induced excitotoxic damage of the striatum in an in vivo model.

Methods

The striata of wild-type C57BL/6 J and NOX-2 KO mice (gp91^Cybbtm1Din/J) were stereotactically injected with monosodium glutamate either alone or in combination with IL-4 or IL-10. The damage was evaluated in histological sections stained with cresyl violet and Fluoro-Jade B. The enzymatic activity of caspase-3 and NOX were also measured. Additionally, the cytokine profile was identified by ELISA and motor activity was verified by the tests of the cylinder, the adhesive tape removal, and the inverted grid.

Results

Our results show a neuroprotective effect in mice with a genetic inhibition of NOX-2, which is partially due to a differential response to excitotoxic damage, characterized by the production of anti-inflammatory cytokines. In NOX-2 KO animals, the excitotoxic condition increased the production of interleukin-4, which could contribute to the production of interleukin-10 that decreased neuronal apoptotic death and the magnitude of striatal injury. Treatment with interleukin-4 and interleukin-10 protected from excitotoxic damage in wild-type animals.

Conclusions

The release of proinflammatory cytokines during the excitotoxic event promotes an additional apoptotic death of neurons that survived the initial damage. During the subsequent inflammatory response to excitotoxic damage, ROS generated by NOX-2 play a decisive role in the extension of the lesion and consequently in the severity of the functional compromise, probably by regulating the anti-inflammatory cytokines production.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1478-4) contains supplementary material, which is available to authorized users.

Lanthanum chloride induces autophagy in rat hippocampus through ROS-mediated JNK and AKT/mTOR signaling pathways

Lanthanum (La) can cause central nervous system damage in rats and lead to learning and memory impairment, but the relevant mechanisms have not been fully elucidated.

Neuroprotection Comparison of Rosmarinic Acid and Carnosic Acid in Primary Cultures of Cerebellar Granule Neurons

Neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease, and Parkinson's disease, are characterized by the progressive loss of neurons in specific regions of the brain and/or spinal cord. Neuronal cell loss typically occurs by either apoptotic or necrotic mechanisms. Oxidative stress and nitrosative stress, along with excitotoxicity and caspase activation, have all been implicated as major underlying causes of neuronal cell death. Diverse nutraceuticals (bioactive compounds found in common foods) have been shown to have neuroprotective effects in a variety of in vitro and in vivo disease models. In the current study, we compared the neuroprotective effects of two polyphenolic compounds, rosmarinic acid and carnosic acid, which are both found at substantial concentrations in the herb rosemary. The capacity of these compounds to rescue primary cultures of rat cerebellar granule neurons (CGNs) from a variety of stressors was investigated. Both polyphenols significantly reduced CGN death induced by the nitric oxide donor, sodium nitroprusside (nitrosative stress). Rosmarinic acid uniquely protected CGNs from glutamate-induced excitotoxicity, while only carnosic acid rescued CGNs from caspase-dependent apoptosis induced by removal of depolarizing extracellular potassium (5K apoptotic condition). Finally, we found that carnosic acid protects CGNs from 5K-induced apoptosis by activating a phosphatidylinositol 3-kinase (PI3K) pro-survival pathway. The shared and unique neuroprotective effects of these two compounds against diverse modes of neuronal cell death suggest that future preclinical studies should explore the potential complementary effects of these rosemary polyphenols on neurodegenerative disease progression.

The Mediating Role of A2A Adenosine Receptors in the Mitochondrial Pathway of Apoptotic Hippocampal Cell Death, Following the Administration of MDMA in Rat

Introduction:

The 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) is a popular recreational drug and a major source of substance abuse, which ultimately leads to sensations of well-being, elation and euphoria, moderate derealization/depersonalization, and cognitive disruptions, as well as intense sensory awareness. The mechanisms involved in memory impairment induced by MDMA are not completely understood.

Methods:

The current study used 40 Sprague-Dawley rats, weighted 200 to 250 g. Experiments were performed in four groups, each containing 10 rats. The first group of rats was used as the control, treated with dimethyl sulfoxide (DMSO). The second group was treated with MDMA. The third group was treated with MDMA and CGS (the adenosine A_2A receptor agonist, 2-[p-(2-carboxyethyl) phenethylamino]-5′-N-ethylcarboxamidoadenosine) (CGS 21680) and the fourth group was treated with MDMA and SCH (the A_2A receptor antagonist [7-(2-phenylethyl)-5-amino-2-(2-furyl-) pyrazolo-[4, 3-e]-1, 2, 4 triazolo [1,5-] pyrimidine]) (SCH 58261). The drugs in all groups were administrated intraperitoneally (i.p.) once a day for 7 days. In 5 rats of each group, following perfusion, samples were taken from hippocampi to investigate apoptosis. Accordingly, the samples were stained using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay kit, and studied by light microscopy. In other rats, fresh tissue was also removed to study the expression of bax and bcl-2 by Western blotting technique.

Results:

It was observed that the coadministration of MDMA with CGS reduced bax expression and prevented apoptosis of hippocampal cells. The coadministration of MDMA and SCH increased bax expression, and also increased the frequency of hippocampal cell apoptosis.

Conclusion:

The results of the current study showed that administration of CGS with MDMA decreased the common side effects associated with MDMA.

Neuroprotection comparison of chlorogenic acid and its metabolites against mechanistically distinct cell death-inducing agents in cultured cerebellar granule neurons

While the number of patients diagnosed with neurodegenerative disorders like Alzheimer's disease, amyotrophic lateral sclerosis, and Parkinson's disease is increasing, there are currently no effective treatments that significantly limit the neuronal cell death underlying these diseases. Chlorogenic acid (CGA), a polyphenolic compound found in high concentration in coffee, is known to possess antioxidant and free radical scavenging activity. In this study, we investigated the neuroprotective effects of CGA and its major metabolites in primary cultures of rat cerebellar granule neurons. We show that CGA and caffeic acid displayed a dramatic protective effect against the nitric oxide donor, sodium nitroprusside. In marked contrast, ferulic acid and quinic acid had no protective effect against this nitrosative stress. While CGA and quinic acid had no protective effect against glutamate-induced cell death, caffeic acid and ferulic acid significantly protected neurons from excitotoxicity. Finally, caffeic acid was the only compound to display significant protective activity against hydrogen peroxide, proteasome inhibition, caspase-dependent intrinsic apoptosis, and endoplasmic reticulum stress. These results indicate that caffeic acid displays a much broader profile of neuroprotection against a diverse range of stressors than its parent polyphenol, CGA, or the other major metabolites, ferulic acid and quinic acid. We conclude that caffeic acid is a promising candidate for testing in pre-clinical models of neurodegeneration.

Methyllycaconitine alleviates amyloid-β peptides-induced cytotoxicity in SH-SY5Y cells

Alzheimer's disease (AD) is a chronic progressive neurodegenerative disorder. As the most common form of dementia, it affects more than 35 million people worldwide and is increasing. Excessive extracellular deposition of amyloid-β peptide (Aβ) is a pathologic feature of AD. Accumulating evidence indicates that macroautophagy is involved in the pathogenesis of AD, but its exact role is still unclear. Although major findings on the molecular mechanisms have been reported, there are still no effective treatments to prevent, halt, or reverse Alzheimer's disease. In this study, we investigated whether Aβ_25–35 could trigger an autophagy process and inhibit the growth of SH-SY5Y cells. Furthermore, we examined the effect of methyllycaconitine (MLA) on the cytotoxity of Aβ_25–35. MLA had a protective effect against cytotoxity of Aβ, which may be related to its inhibition of Aβ-induced autophagy and the involvement of the mammalian target of rapamycin pathway. Moreover, MLA had a good safety profile. MLA treatment may be a promising therapeutic tool for AD.

Apoptotic and necrotic changes in the midgut glands of the wolf spider Xerolycosa nemoralis (Lycosidae) in response to starvation and dimethoate exposure

In the present study, the intensity of degenerative changes (apoptosis, necrosis) in the cells of the midgut glands of male and female wolf spiders, Xerolycosa nemoralis (Lycosidae), exposed to natural (starvation) and anthropogenic (the organophosphorous pesticide dimethoate) stressors under laboratory conditions were compared. The spiders were collected from two differentially polluted sites, both located in southern Poland: Katowice-Welnowiec, which is heavily polluted with metals, and Pilica, the reference site. Starvation and dimethoate treatment resulted in enhancement of apoptotic and necrotic changes in the midgut glands of the spiders. The frequency of degenerative changes in starving individuals was twice as high as in the specimens intoxicated with dimethoate. The percentage of apoptotic and necrotic cells was higher in starving males than in starving females. A high intensity of necrotic changes, together with increased Cas-3 like activity and a greater percentage of cells with depolarized mitochondria, were typical of starving males from the polluted site. The cell death indices observed in females depended more strongly on the type of stressor than on previous preexposure to pollutants.

Transitory phases of autophagic death and programmed necrosis during superoxide-induced neuronal cell death

Neurons can undergo a diverse range of death responses under oxidative stress, encompassing apoptosis (caspase-dependent, programmed cell death) to various forms of caspase-independent death, including necrosis. We recently showed that primary murine cortical neurons exposed acutely to hydrogen peroxide undergo caspase-independent death, both autophagic cell death and programmed necrosis. To determine how oxidative stress induced by superoxide affects the route to cellular demise, we exposed primary cortical neurons to extended superoxide insult (provided by exogenous xanthine and xanthine oxidase in the presence of catalase). Under these conditions, over 24h, the nitroblue tetrazolium-reducing activity (indicative of superoxide) rose significantly during the first 4 to 8h and then declined to background levels. As with hydrogen peroxide, this superoxide insult failed to activate downstream caspases (-3, -7, and -9). Substantial depolarization of mitochondria occurred after 1h, and nuclear morphology changes characteristic of oxidative stress became maximal after 2h. However, death indicated by plasma membrane permeabilization (cellular uptake of propidium iodide) approached maximal levels only after 4h, at which time substantial redistribution to the cytosol of death-associated mitochondrial intermembrane space proteins, notably endonuclease G, had occurred. Applying established criteria for autophagic death (knockdown of Atg7) or programmed necrosis (knockdown of endonuclease G), cells treated with the relevant siRNA showed significant blockade of each type of cell death, 4h after onset of the superoxide flux. Yet at later times, siRNA-mediated knockdown failed to prevent death, monitored by cellular uptake of propidium iodide. We conclude that superoxide initially invokes a diverse programmed caspase-independent death response, involving transient manifestation in parallel of autophagic death and programmed necrosis. Ultimately most neurons become overwhelmed by the consequences of severe oxidative stress and die. This study reveals the multiple phases of neuronal cell death modalities under extended oxidative stress.

Shedding new light on neurodegenerative diseases through the mammalian target of rapamycin

Neurodegenerative disorders affect a significant portion of the world's population leading to either disability or death for almost 30 million individuals worldwide. One novel therapeutic target that may offer promise for multiple disease entities that involve Alzheimer's disease, Parkinson's disease, epilepsy, trauma, stroke, and tumors of the nervous system is the mammalian target of rapamycin (mTOR). mTOR signaling is dependent upon the mTORC1 and mTORC2 complexes that are composed of mTOR and several regulatory proteins including the tuberous sclerosis complex (TSC1, hamartin/TSC2, tuberin). Through a number of integrated cell signaling pathways that involve those of mTORC1 and mTORC2 as well as more novel signaling tied to cytokines, Wnt, and forkhead, mTOR can foster stem cellular proliferation, tissue repair and longevity, and synaptic growth by modulating mechanisms that foster both apoptosis and autophagy. Yet, mTOR through its proliferative capacity may sometimes be detrimental to central nervous system recovery and even promote tumorigenesis. Further knowledge of mTOR and the critical pathways governed by this serine/threonine protein kinase can bring new light for neurodegeneration and other related diseases that currently require new and robust treatments.

Temporal relationship of autophagy and apoptosis in neurons challenged by low molecular weight β-amyloid peptide

Alzheimer's disease (AD) is an aging-related progressive neurodegenerative disorder. Previous studies suggested that various soluble Aβ species are neurotoxic and able to activate apoptosis and autophagy, the type I and type II programmed cell death, respectively. However, the sequential and functional relationships between these two cellular events remain elusive. Here we report that low molecular weight Aβ triggered cleavage of caspase 3 and poly (ADP-ribose) polymerase to cause neuronal apoptosis in rat cortical neurons. On the other hand, Aβ activated autophagy by inducing autophagic vesicle formation and autophagy related gene 12 (ATG12), and up-regulated the lysoso-mal machinery for the degradation of autophagosomes. Moreover, we demonstrated that activation of autophagy by Aβ preceded that of apoptosis, with death associated protein kinase phosphorylation as the potential molecular link. More importantly, under Aβ toxicity, neurons exhibiting high level of autophagosome formation were absent of apoptotic features, and inhibition of autophagy by 3-methylade-nine advanced neuronal apoptosis, suggesting that autophagy can protect neurons from Aβ-induced apoptosis.

Autophagic activity in cortical neurons under acute oxidative stress directly contributes to cell death

Primary neurons undergo insult-dependent programmed cell death. We examined autophagy as a process contributing to cell death in cortical neurons after treatment with either hydrogen peroxide (H(2)O(2)) or staurosporine. Although caspase-9 activation and cleavage of procaspase-3 were significant following staurosporine treatment, neither was observed following H(2)O(2) treatment, indicating a non-apoptotic death. Autophagic activity increased rapidly with H(2)O(2), but slowly with staurosporine, as quantified by processing of endogenous LC3. Autophagic induction by both stressors increased the abundance of fluorescent puncta formed by GFP-LC3, which could be blocked by 3-methyladenine. Significantly, such inhibition of autophagy blocked cell death induced by H(2)O(2) but not staurosporine. Suppression of Atg7 inhibited cell death by H(2)O(2), but not staurosporine, whereas suppression of Beclin 1 prevented cell death by both treatments, suggesting it has a complex role regulating both apoptosis and autophagy. We conclude that autophagic mechanisms are activated in an insult-dependent manner and that H(2)O(2) induces autophagic cell death.

The requirement of uncoordinated 51-like kinase 1 (ULK1) and ULK2 in the regulation of autophagy

Autophagy is an evolutionarily conserved physiological process of self-digestion by a cell to adapt to various stresses, including starvation. Its molecular basis involves the concerted activation of proteins encoded by the family of autophagy-related (Atg) genes. The best characterized is the serine/threonine protein kinase Atg1 in yeast which appears to be essential at the early stage of autophagy. In mammals, five Atg1 homologues have been identified as uncoordinated (UNC) 51-like kinase 1 to 4 and STK36. ULK1 and ULK2 are the most closely related members of the family, sharing 78% homology within their protein kinase domains. However, the specific function of ULK1 and ULK2 in mammalian autophagy is not fully understood. Here, we demonstrate that ULK1 and ULK2 are functionally redundant protein kinases required to mediate autophagy under nutrient-deprived conditions in fibroblasts. In contrast, ULK1, but not ULK2, is critical to induce the autophagic response of cerebellar granule neurons (CGN) to low potassium concentration in serum-free conditions. Furthermore, we found that ULK1 has a cytoprotective function in neurons. Together, these results provide strong genetic evidence that ULK1 is an essential component of the autophagic signaling pathway. The ability of ULK2 to compensate for the loss of ULK1 function is cell-type specific.

Hypersensitivity of mtDNA-depleted cells to staurosporine-induced apoptosis: roles of Bcl-2 downregulation and cathepsin B

We show that mitochondrial DNA (mtDNA)-depleted 143B cells are hypersensitive to staurosporine-induced cell death as evidenced by a more pronounced DNA fragmentation, a stronger activation of caspase-3, an enhanced poly(ADP-ribose) polymerase-1 (PARP-1) cleavage, and a more dramatic cytosolic release of cytochrome c. We also show that B-cell CLL/lymphoma-2 (Bcl-2), B-cell lymphoma extra large (Bcl-X(L)), and myeloid cell leukemia-1 (Mcl-1) are constitutively less abundant in mtDNA-depleted cells, that the inhibition of Bcl-2 and Bcl-X(L) can sensitize the parental cell line to staurosporine-induced apoptosis, and that overexpression of Bcl-2 or Bcl-X(L) can prevent the activation of caspase-3 in ρ(0)143B cells treated with staurosporine. Moreover, the inactivation of cathepsin B with CA074-Me significantly reduced cytochrome c release, caspase-3 activation, PARP-1 cleavage, and DNA fragmentation in mtDNA-depleted cells, whereas the pan-caspase inhibitor failed to completely prevent PARP-1 cleavage and DNA fragmentation in these cells, suggesting that caspase-independent mechanisms are responsible for cell death even if caspases are activated. Finally, we show that cathepsin B is released in the cytosol of ρ(0) cells in response to staurosporine, suggesting that the absence of mitochondrial activity leads to a facilitated permeabilization of lysosomal membranes in response to staurosporine.

Regulation of autophagy by ROS: physiology and pathology

Reactive oxygen species (ROS) are small and highly reactive molecules that can oxidize proteins, lipids and DNA. When tightly controlled, ROS serve as signaling molecules by modulating the activity of the oxidized targets. Accumulating data point to an essential role for ROS in the activation of autophagy. Be the outcome of autophagy survival or death and the initiation conditions starvation, pathogens or death receptors, ROS are invariably involved. The nature of this involvement, however, remains unclear. Moreover, although connections between ROS and autophagy are observed in diverse pathological conditions, the mode of activation of autophagy and its potential protective role remain incompletely understood. Notably, recent advances in the field of redox regulation of autophagy focus on the role of mitochondria as a source of ROS and on mitophagy as a means for clearance of ROS.

Analysis of different cell death processes of prepubertal rat oocytes in vitro

The processes of cell death were studied in vitro in populations of oocytes isolated from prepubertal rats. In order to identify apoptosis, the externalized phosphatidylserine was recognized with Annexin-V coupled to FITC and the fragmentation of DNA was demonstrated by means of electrophoresis. Oocytes were tested for autophagy by means of the incorporation of monodansylcadaverine and monitoring Lc3-I/Lc3-II by western blot. The expression of mRNA marker genes of autophagy and of apoptosis was studied by means of RT-PCR in pure populations of oocytes. Some oocytes expressed at least one of the following markers: caspase-3, lamp1 and Lc3. Some oocytes were positive to Annexin-V or to monodansylcadaverine. However, most of them were simultaneously positive to both markers. The relative frequency of oocytes simultaneously positive to markers of apoptosis and autophagy did not change in the different ages studied. The transformation of Lc3-I in Lc3-II was present in all populations of oocytes studied. The mRNAs for caspase-3, lamp1 and Lc3 were present in all populations of oocytes analyzed. Our results demonstrate that oocytes of rats from new born to prepubertal age are eliminated by means of three different cell death processes: apoptosis, autophagy and a mixed event in which both routes to cell death participate in the same cell.

ADF/cofilin: a functional node in cell biology

Recent findings have significantly expanded our understanding of the regulation of actin-depolymerizing factor (ADF)/cofilin proteins and the profound multifaceted impact that these well-established regulators of actin dynamics have on cell biology. In this review we discuss new aspects of previously documented regulation, such as phosphorylation, but also cover novel recently established modes of regulation and functions of ADF (also known as destrin)/cofilin. We now understand that their activity responds to a vast array of inputs far greater than previously appreciated and that these proteins not only feed back to the crucially important dynamics of actin, but also to apoptosis cascades, phospholipid metabolism, and gene expression. We argue that this ability to respond to physiological changes by modulating those same changes makes the ADF/cofilin protein family a homeostatic regulator or 'functional node' in cell biology.