Spatiotemporal roles of AMPK in PARP-1- and autophagy-dependent retinal pigment epithelial cell death caused by UVA.

BACKGROUND: Although stimulating autophagy caused by UV has been widely demonstrated in skin cells to exert cell protection, it remains unknown the cellular events in UVA-treated retinal pigment epithelial (RPE) cells. METHODS: Human ARPE-19 cells were used to measure cell viability, mitochondrial reactive oxygen species (ROS), mitochondrial membrane potential (MMP), mitochondrial mass and lysosomal mass by flow cytometry. Mitochondrial oxygen consumption rate (OCR) was recorded using Seahorse XF flux analyzer. Confocal microscopic images were performed to indicate the mitochondrial dynamics, LC3 level, and AMPK translocation after UVA irradiation. RESULTS: We confirmed mitochondrial ROS production and DNA damage are two major features caused by UVA. We found the cell death is prevented by autophagy inhibitor 3-methyladenine and gene silencing of ATG5, and UVA induces ROS-dependent LC3II expression, LC3 punctate and TFEB expression, suggesting the autophagic death in the UVA-stressed RPE cells. Although PARP-1 inhibitor olaparib increases DNA damage, ROS production, and cell death, it also blocks AMPK activation caused by UVA. Interestingly we found a dramatic nuclear export of AMPK upon UVA irradiation which is blocked by N-acetylcysteine and olaparib. In addition, UVA exposure gradually decreases lysosomal mass and inhibits cathepsin B activity at late phase due to lysosomal dysfunction. Nevertheless, cathepsin B inhibitor, CA-074Me, reverses the death extent, suggesting the contribution of cathepsin B in the death pathway. When examining the role of EGFR in cellular events caused by UVA, we found that UVA can rapidly transactivate EGFR, and treatment with EGFR TKIs (gefitinib and afatinib) enhances the cell death accompanied by the increased LC3II formation, ROS production, loss of MMP and mass of mitochondria and lysosomes. Although AMPK activation by ROS-PARP-1 mediates autophagic cell death, we surprisingly found that pretreatment of cells with AMPK activators (A769662 and metformin) reverses cell death. Concomitantly, both agents block UVA-induced mitochondrial ROS production, autophagic flux, and mitochondrial fission without changing the inhibition of cathepsin B. CONCLUSION: UVA exposure rapidly induces ROS-PARP-1-AMPK-autophagic flux and late lysosomal dysfunction. Pre-inducing AMPK activation can prevent cellular events caused by UVA and provide a new protective strategy in photo-oxidative stress and photo-retinopathy.

Enhanced cancer therapy with pH-dependent and aptamer functionalized doxorubicin loaded polymeric (poly D, L-lactic-co-glycolic acid) nanoparticles.

Aptamer based drug delivery systems are gaining the importance in anticancer therapy due to their targeted drug delivery efficiency without harming the normal cells. The present work formulated the pH-dependent aptamer functionalized polymer-based drug delivery system against human lung cancer. The prepared aptamer functionalized doxorubicin (DOX) loaded poly (D, L-lactic-co-glycolic acid) (PLGA), poly (N-vinylpyrrolidone) (PVP) nanoparticles (APT-DOX-PLGA-PVP NPs) were spherical in shape with an average size of 87.168 nm. The crystallography and presence of the PLGA (poly (D, L-lactic-co-glycolic acid)) and DOX (doxorubicin) in APT-DOX-PLGA-PVP NPs were indicated by the X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), and 1H and 13C nuclear magnetic resonance spectrometer (NMR). The pH-dependent aptamer AS1411 based drug release triggered the cancer cell death was evidenced by cytotoxicity assay, flow cytometry, and fluorescent microscopic imaging. In addition, the cellular uptake of the DOX was determined and the apoptosis-related signaling pathway in the A549 cells was studied by Western blot analysis. Further, the in vivo study revealed that mice treated with APT-DOX-PLGA-PVP NPs were significantly recovered from cancer as evident by mice weight and tumor size followed by the histopathological study. It was reported that the APT-DOX-PLGA-PVP NPs induced the apoptosis through the activation of the apoptosis-related proteins. Hence, the present study revealed that the APT-DOX-PLGA-PVP NPs improved the therapeutic efficiency through the nucleolin receptor endocytosis targeted drug release.

Reactive oxygen species-dependent mitochondrial dynamics and autophagy confer protective effects in retinal pigment epithelial cells against sodium iodate-induced cell death.

BACKGROUND: Oxidative stress is a major factor in retinal pigment epithelium (RPE) cells injury that contributes to age-related macular degeneration (AMD). NaIO3 is an oxidative toxic agent and its selective RPE cell damage makes it as a reproducible model of AMD. Although NaIO3 is an oxidative stress inducer, the roles of ROS in NaIO3-elicited signaling pathways and cell viability have not been elucidated, and the effect of NaIO3 on autophagy in RPE cells remains elusive. METHODS: In human ARPE-19 cells, we used Annexin V/PI staining to determine cell viability, immunoblotting to determine protein expression and signaling cascades, confocal microscopy to determine mitochondrial dynamics and mitophagy, and Seahorse analysis to determine mitochondrial oxidative phosphorylation. RESULTS: We found that NaIO3 can dramatically induce cytosolic but not mitochondrial ROS production. NaIO3 can also activate ERK, p38, JNK and Akt, increase LC3II expression, induce Drp-1 phosphorylation and mitochondrial fission, but inhibit mitochondrial respiration. Confocal microscopic data indicated a synergism of NaIO3 and bafilomycin A1 on LC3 punctate formation, indicating the induction of autophagy. Using cytosolic ROS antioxidant NAC, we found that p38 and JNK are downstream signals of ROS and involve in NaIO3-induced cytotoxicity but not in mitochondrial dynamics, while ROS is also involved in LC3II expression. Unexpectedly NAC treatment upon NaIO3 stimulation leads to an enhancement of mitochondrial fragmentation and cell death. Moreover, inhibition of autophagy and Akt further enhances cell susceptibility to NaIO3. CONCLUSIONS: We conclude that NaIO3-induced oxidative stress and cytosolic ROS production exert multiple signaling pathways that coordinate to control cell death in RPE cells. ROS-dependent p38 and JNK activation lead to cytotoxicity, while ROS-mediated autophagy and mitochondrial dynamic balance counteract the cell death mechanisms induced by NaIO3 in RPE cells.

Correction to: Reactive oxygen species-dependent mitochondrial dynamics and autophagy confer protective effects in retinal pigment epithelial cells against sodium iodate-induced cell death.

After the publication of this article [1], the authors would like to clarify that some immunoblotting data in Figs. 2f, 3a and 4b were obtained from the same samples but individual SDS-PAGE gels.

AMPK-dependent and independent actions of P2X7 in regulation of mitochondrial and lysosomal functions in microglia.

BACKGROUND: P2X7 is ubiquitously expressed in myeloid cells and regulates the pathophysiology of inflammatory diseases. Since mitochondrial function in microglia is highly associated with microglial functions in controlling neuronal plasticity and brain homeostasis, we interested to explore the roles of P2X7 in mitochondrial and lysosomal functions as well as mitophagy in microglia. METHODS: P2X7-/- bone marrow-derived macrophages (BMDM), primary microglia and BV-2 immortalized microglial cells were used to detect the particular protein expression by immunoblotting. Mitochondrial reactive oxygen species (mitoROS), intracellular calcium, mitochondrial mass and lysosomal integrity were examined by flow cytometry. Mitochondrial oxygen consumption rate (OCR) was recorded using Seahorse XF flux analyzer. Confocal microscopic images were performed to indicate the mitochondrial dynamics and mitophagy after P2X7 activation. RESULTS: In primary microglia, BV-2 microglial cells and BMDM, P2X7 agonist BzATP triggered AMPK activation and LC3II accumulation through reactive oxygen species (ROS) and CaMKKII pathways, and these effects were abolished by P2X7 antagonist A438079 and P2X7 deficiency. Moreover, we detected the dramatic decreases of mitochondrial OCR and mass following P2X7 activation. AMPK inhibition by compound C or AMPK silencing reversed the P2X7 actions in reduction of mitochondrial mass, induction of mitochondrial fission and mitophagy, but not in uncoupling of mitochondrial respiration. Interestingly, we found that P2X7 activation induced nuclear translocation of TFEB via an AMPK-dependent pathway and led to lysosomal biogenesis. Mimicking the actions of BzATP, nigericin also induced ROS-dependent AMPK activation, mitophagy, mitochondrial fission and respiratory inhibition. Longer exposure of BzATP induced cell death, and this effect was accompanied by the lysosomal instability and was inhibited by autophagy and cathepsin B inhibitors. CONCLUSION: Altogether ROS- and CaMKK-dependent AMPK activation is involved in P2X7-mediated mitophagy, mitochondrial dynamics and lysosomal biogenesis in microglial cells, which is followed by cytotoxicity partially resulting from mitophagy and cathepsin B activation.

CASK Mediates Oxidative Stress-Induced Microglial Apoptosis-Inducing Factor-Independent Parthanatos Cell Death via Promoting PARP-1 Hyperactivation and Mitochondrial Dysfunction.

Calcium/calmodulin-dependent serine protein kinase (CASK) is a scaffold protein and plays critical roles in neuronal synaptic formation and brain development. Previously, CASK was shown to associate with EGFR to maintain the vulval cell differentiation in C. elegans. In this study, we explored the role of CASK in CHME3 microglial cells. We found that CASK silencing protects cells from H2O2-induced cell death by attenuating PARP-1 activation, mitochondrial membrane potential loss, reactive oxygen species production, and mitochondrial fission, but it increases oxidative phosphorylation. The PARP-1 inhibitor olaparib blocks H2O2-induced cell death, suggesting the death mode of parthanatos. CASK silencing also increases AKT activation but decreases AMPK activation under H2O2 treatment. Pharmacological data further indicate that both signaling changes contribute to cell protection. Different from the canonical parthanatos pathway, we did not observe the AIF translocation from mitochondria into the nucleus, suggesting a non-canonical AIF-independent parthanatos in H2O2-treated CHME3 cells. Moreover, we found that CASK silencing upregulates the EGFR gene and protein expression and increases H2O2-induced EGFR phosphorylation in CHME3 microglia. However, EGFR activation does not contribute to cell protection caused by CASK silencing. In conclusion, CASK plays a crucial role in microglial parthanatos upon H2O2 treatment via stimulation of PARP-1 and AMPK but the inhibition of AKT. These findings suggest that CASK might be an ideal therapeutic target for CNS disorders.

Metformin inhibits methylglyoxal-induced retinal pigment epithelial cell death and retinopathy via AMPK-dependent mechanisms: Reversing mitochondrial dysfunction and upregulating glyoxalase 1.

Diabetic retinopathy (DR) is a major cause of blindness in adult, and the accumulation of advanced glycation end products (AGEs) is a major pathologic event in DR. Methylglyoxal (MGO), a highly reactive dicarbonyl compound, is a precursor of AGEs. Although the therapeutic potential of metformin for retinopathy disorders has recently been elucidated, possibly through AMPK activation, it remains unknown how metformin directly affects the MGO-induced stress response in retinal pigment epithelial cells. Therefore, in this study, we compared the effects of metformin and the AMPK activator A769662 on MGO-induced DR in mice, as well as evaluated cytotoxicity, mitochondrial dynamic changes and dysfunction in ARPE-19 cells. We found MGO can induce mitochondrial ROS production and mitochondrial membrane potential loss, but reduce cytosolic ROS level in ARPE-19 cells. Although these effects of MGO can be reversed by both metformin and A769662, we demonstrated that reduction of mitochondrial ROS production rather than restoration of cytosolic ROS level contributes to cell protective effects of metformin and A769662. Moreover, MGO inhibits AMPK activity, reduces LC3II accumulation, and suppresses protein and gene expressions of MFN1, PGC-1α and TFAM, leading to mitochondrial fission, inhibition of mitochondrial biogenesis and autophagy. In contrast, these events of MGO were reversed by metformin in an AMPK-dependent manner as evidenced by the effects of compound C and AMPK silencing. In addition, we observed an AMPK-dependent upregulation of glyoxalase 1, a ubiquitous cellular enzyme that participates in the detoxification of MGO. In intravitreal drug-treated mice, we found that AMPK activators can reverse the MGO-induced cotton wool spots, macular edema and retinal damage. Functional, histological and optical coherence tomography analysis support the protective actions of both agents against MGO-elicited retinal damage. Metformin and A769662 via AMPK activation exert a strong protection against MGO-induced retinal pigment epithelial cell death and retinopathy. Therefore, metformin and AMPK activator can be therapeutic agents for DR.

P2X7 Is Involved in the Mouse Retinal Degeneration via the Coordinated Actions in Different Retinal Cell Types.

Adenosine triphosphate (ATP) released from dying cells with high concentrations is sensed as a danger signal by the P2X7 receptor. Sodium iodate (NaIO3) is an oxidative toxic agent, and its retinal toxicity has been used as the model of dry age-related macular degeneration (AMD). In this study, we used NaIO3-treated mice and cultured retinal cells, including BV-2 microglia, 661W photoreceptors, rMC1 Müller cells and ARPE-19 retinal epithelial cells, to understand the pathological action of P2X7 in retinal degeneration. We found that NaIO3 can significantly decrease the photoreceptor function by reducing a-wave and b-wave amplitudes in electroretinogram (ERG) analysis. Optical coherence tomography (OCT) analysis revealed the degeneration of retinal epithelium and ganglion cell layers. Interestingly, P2X7-/- mice were protected from the NaIO3-induced retinopathy and inflammatory NLRP3, IL-1ß and IL-6 gene expression in the retina. Hematoxylin and eosin staining indicated that the retinal epithelium was less deteriorated in P2X7-/- mice compared to the WT group. Although P2X7 was barely detected in 661W, rMC1 and ARPE-19 cells, its gene and protein levels can be increased after NaIO3 treatment, leading to a synergistic cytotoxicity of BzATP [2'(3')-O-(4-benzoylbenzoyl)adenosine-5'-triphosphate tri(triethyleneammonium)salt] and NaIO3 administration in ARPE-19 cells. In conclusion, the paracrine action of the ATP/P2X7 axis via cell-cell communication is involved in NaIO3-induced retinal injury. Our results show that P2X7 antagonist might be a potential therapy in inflammation-related retinal degeneration.

Pan-Caspase Inhibitor zVAD Induces Necroptotic and Autophagic Cell Death in TLR3/4-Stimulated Macrophages.

In addition to inducing apoptosis, caspase inhibition contributes to necroptosis and/or autophagy depending on the cell type and cellular context. In macrophages, necroptosis can be induced by co-treatment with Toll-like receptor (TLR) ligands (lipopolysaccharide [LPS] for TLR4 and polyinosinic-polycytidylic acid [poly I:C] for TLR3) and a cell-permeable pan-caspase inhibitor zVAD. Here, we elucidated the signaling pathways and molecular mechanisms of cell death. We showed that LPS/zVAD- and poly I:C/zVAD-induced cell death in bone marrow-derived macrophages (BMDMs) was inhibited by receptor-interacting protein kinase 1 (RIP1) inhibitor necrostatin-1 and autophagy inhibitor 3-methyladenine. Electron microscopic images displayed autophagosome/autolysosomes, and immunoblotting data revealed increased LC3II expression. Although zVAD did not affect LPS- or poly I:C-induced activation of IKK, JNK, and p38, it enhanced IRF3 and STAT1 activation as well as type I interferon (IFN) expression. In addition, zVAD inhibited ERK and Akt phosphorylation induced by LPS and poly I:C. Of note, zVAD-induced enhancement of the IRF3/IFN/STAT1 axis was abolished by necrostatin-1, while zVAD-induced inhibition of ERK and Akt was not. Our data further support the involvement of autocrine IFNs action in reactive oxygen species (ROS)-dependent necroptosis, LPS/zVAD-elicited ROS production was inhibited by necrostatin-1, neutralizing antibody of IFN receptor (IFNR) and JAK inhibitor AZD1480. Accordingly, both cell death and ROS production induced by TLR ligands plus zVAD were abrogated in STAT1 knockout macrophages. We conclude that enhanced TRIF-RIP1-dependent autocrine action of IFNß, rather than inhibition of ERK or Akt, is involved in TLRs/zVAD-induced autophagic and necroptotic cell death via the JAK/STAT1/ROS pathway.

Decoy Receptor 3 Inhibits Monosodium Urate-Induced NLRP3 Inflammasome Activation via Reduction of Reactive Oxygen Species Production and Lysosomal Rupture.

Gout is a common inflammatory arthritis caused by the deposition of monosodium urate (MSU) crystals in the joints. This activates the macrophages into a proinflammatory state by inducing NLRP3-dependent interleukin-1ß (IL-1ß) secretion, resulting in neutrophil recruitment. Soluble decoy receptor 3 (DcR3) is an immune modulator and can exert biological functions via decoy and non-decoy actions. Previously, we showed that DcR3 suppresses lipopolysaccharides (LPS)- and virus-induced inflammatory responses in the macrophages and promotes the macrophages into the M2 phenotype. In this study, we clarified the actions of DcR3 and its non-decoy action motif heparin sulfate proteoglycan (HSPG) binding domain (HBD) in the MSU crystal-induced NLRP3 inflammasome activation in the macrophages and in mice. In bone marrow-derived macrophages, THP-1 and U937 cells, we found that the MSU crystal-induced secretion of IL-1ß and activation of NLRP3 were suppressed by both DcR3.Fc and HBD.Fc. The suppression of the MSU-induced NLRP3 inflammasome activation is accompanied by the inhibition of lysosomal rupture, mitochondrial production of the reactive oxygen species (ROS), expression of cathepsins, and activity of cathepsin B, without affecting the crystal uptake and the expression of NLRP3 or pro-IL-1ß. In the air pouch mice model of gout, MSU induced less amounts of IL-1ß and chemokines secretion, an increased M2/M1 macrophage ratio, and a reduction of neutrophil recruitment in DcR3-transgenic mice, which expresses DcR3 in myeloid cells. Similarly, the mice intravenously treated with DcR3.Fc or HBD.Fc displayed less inflammation response. These findings indicate that HBD of DcR3 can reduce MSU crystal-induced NLRP3 inflammasome activation via modulation of mitochondrial and lysosomal functions. Therefore, we, for the first time, demonstrate a new therapeutic potential of DcR3 for the treatment of gout.

Different Effects of Metformin and A769662 on Sodium Iodate-Induced Cytotoxicity in Retinal Pigment Epithelial Cells: Distinct Actions on Mitochondrial Fission and Respiration.

Oxidative stress-associated retinal pigment epithelium (RPE) cell death is critically implicated in the pathogenesis of visual dysfunction and blindness of retinal degenerative diseases. Sodium iodate (NaIO3) is an oxidative retinotoxin and causes RPE damage. Previously, we found that NaIO3 can induce human ARPE-19 cell death via inducing mitochondrial fission and mitochondrial dysfunction. Although metformin has been demonstrated to benefit several diseases possibly via AMP-activated protein kinase (AMPK) activation, it remains unknown how AMPK affects retinopathy in NaIO3 model. Therefore, in this study, we compared the effects of metformin and AMPK activator A769662 on NaIO3-induced cellular stress and toxicity. We found that A769662 can protect cells against NaIO3-induced cytotoxicity, while metformin exerts an enhancement in cell death. The mitochondrial reactive oxygen species (ROS) production as well as mitochondrial membrane potential loss induced by NaIO3 were not altered by both agents. In addition, NaIO3-induced cytosolic ROS production, possibly from nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation and counteracting cell death, was not altered by A769662 and metformin. Notably, NaIO3-induced mitochondrial fission and inhibition of mitochondrial respiration for ATP turnover were reversed by A769662 but not by metformin. In agreement with the changes on mitochondrial morphology, the ERK-Akt signal axis dependent Drp-1 phosphorylation at S616 (an index of mitochondrial fission) under NaIO3 treatment was blocked by A769662, but not by metformin. In summary, NaIO3-induced cell death in ARPE cells primarily comes from mitochondrial dysfunction due to dramatic fission and inhibition of mitochondrial respiration. AMPK activation can exert a protection by restoring mitochondrial respiration and inhibition of ERK/Akt/Drp-1 phosphorylation, leading to a reduction in mitochondrial fission. However, inhibition of respiratory complex I by metformin might deteriorate mitochondrial dysfunction and cell death under NaIO3 stress.

The Mycobacterial Adjuvant Analogue TDB Attenuates Neuroinflammation via Mincle-Independent PLC-γ1/PKC/ERK Signaling and Microglial Polarization.

Microglial activation has long been recognized as a hallmark of neuroinflammation. Recently, the bacillus Calmette-Guerin (BCG) vaccine has been reported to exert neuroprotective effects against several neurodegenerative disorders. Trehalose-6,6'-dibehenate (TDB) is a synthetic analogue of trehalose-6,6'-dimycolate (TDM, also known as the mycobacterial cord factor) and is a new adjuvant of tuberculosis subunit vaccine currently in clinical trials. Both TDM and TDB can activate macrophages and dendritic cells through binding to C-type lectin receptor Mincle; however, its action mechanism in microglia and their relationship with neuroinflammation are still unknown. In this article, we found that TDB inhibited LPS-induced M1 microglial polarization in primary microglia and BV-2 cells. However, TDB itself had no effects on IKK, p38, and JNK activities or cytokine expression. In contrast, TDB activated ERK1/2 through PLC-γ1/PKC signaling and in turn decreased LPS-induced NF-κB nuclear translocation. Furthermore, TDB-induced AMPK activation via PLC-γ1/calcium/CaMKKß-dependent pathway and thereby enhanced M2 gene expressions. Interestingly, knocking out Mincle did not alter the anti-inflammatory and M2 polarization effects of TDB in microglia. Conditional media from LPS-stimulated microglial cells can induce in vitro neurotoxicity, and this action was attenuated by TDB. Using a mouse neuroinflammation model, we found that TDB suppressed LPS-induced M1 microglial activation and sickness behavior, but promoted M2 microglial polarization in both WT and Mincle-/- mice. Taken together, our results suggest that TDB can act independently of Mincle to inhibit LPS-induced inflammatory response through PLC-γ1/PKC/ERK signaling and promote microglial polarization towards M2 phenotype via PLC-γ1/calcium/CaMKKß/AMPK pathway. Thus, TDB may be a promising therapeutic agent for the treatment of neuroinflammatory diseases.

Coordinate effects of P2X7 and extracellular acidification in microglial cells.

Extracellular adenosine 5'-triphosphate (ATP) is a damage-associated molecular pattern and contributes to inflammation associated diseases including cancer. Extracellular acidosis is a novel danger signal in the inflammatory sites, where it can modulate inflammation, immunity and tumor growth. Extracellular acidification was shown to inhibit P2X7-mediated channel currents, while it remains unknown how acidification and P2X7 together affect cellular responses. Here, we treated BV-2 microglial cells with ATP in a short period (<15 min) or a sustained acidified condition. For short acidification we compared the actions of neutralized ATP and acidic ATP in a condition with pH buffering. For sustained acidification, we treated cells with neutralized ATP in acidic medium or acidic ATP in medium without pH buffering. In the short acidified condition, neutralized ATP induced higher responses than acidic ATP to increase intracellular calcium and reactive oxygen species, decrease intracellular potassium and induce cell death. In contrast, these cellular responses and mitochondrial fission caused by neutralized ATP were enhanced by pH 6.0 and pH 4.5 media. P2X7 activation can also rapidly block mitochondrial ATP turnover and respiration capacity, both of which were mimicked by nigericin and enhanced by acidity. Taken together P2X7-mediated ionic fluxes and reactive oxygen species production are attenuated under short acidification, while sustained acidification itself can induce mitochondrial toxicity which deteriorates the mitochondrial function under P2X7 activation.