Local redox environment beneath biological membranes probed by palmitoylated-roGFP

Resilience to diabetic retinopathy

Chronic elevation of blood glucose at first causes relatively minor changes to the neural and vascular components of the retina. As the duration of hyperglycemia persists, the nature and extent of damage increases and becomes readily detectable. While this second, overt manifestation of diabetic retinopathy (DR) has been studied extensively, what prevents maximal damage from the very start of hyperglycemia remains largely unexplored. Recent studies indicate that diabetes (DM) engages mitochondria-based defense during the retinopathy-resistant phase, and thereby enables the retina to remain healthy in the face of hyperglycemia. Such resilience is transient, and its deterioration results in progressive accumulation of retinal damage. The concepts that co-emerge with these discoveries set the stage for novel intellectual and therapeutic opportunities within the DR field. Identification of biomarkers and mediators of protection from DM-mediated damage will enable development of resilience-based therapies that will indefinitely delay the onset of DR.

Small Extracellular Vesicles Maintain Homeostasis of Senescent Mesenchymal Stem Cells at Least Through Excreting Harmful Lipids

Mesenchymal stem cells (MSCs) play an essential role in multiple physiological processes in vivo and a promising cell-based therapy for various diseases. Nonetheless, MSCs suffer from senescence with expansion culture, leading to a limitation for their clinical application. Recently, it was reported that small extracellular vesicles (sEVs) are involved in regulation of senescence in tumor cells and fibroblasts. However, the biological roles of sEVs in senescent MSCs (Sen MSCs) are poorly understood. In this study, we established a replicative senescence model of MSCs by successive passages and compared the phenotypic changes between presenescent MSCs (Pre-Sen MSCs) and Sen MSCs and found that Sen MSCs exhibited a diminished adipogenic and osteogenic differentiation potential and elevated senescence-associated secretory phenotype levels. In addition, we found that sEV secretion was increased in Sen MSCs, and inhibition of sEV secretion led to apoptosis, DNA damage, and decreased cell viability, suggesting that increased sEV secretion plays an important role in maintaining Sen MSC homeostasis. To further investigate the molecular mechanisms, metabolomic profiling of Pre-Sen MSC-derived sEVs (Pre-Sen-sEVs) and Sen MSC-derived sEVs (Sen-sEVs) was performed. The results showed that lipid metabolites were significantly increased in Sen-sEVs and these significantly upregulated lipid metabolites were shown to be toxic for inducing cellular senescence and apoptosis in previous studies. Kyoto Encyclopedia of Genes and Genomes analysis revealed enrichment of differential metabolites between Pre-Sen-sEVs and Sen-sEVs mainly in 25 signaling pathways, of which 21 metabolic pathways have been shown to be closely associated with senescence. Taken together, our findings suggested that increased sEV secretion maintains Sen MSC homeostasis, at least in part, by excreting harmful lipids, thus providing new insights into the regulation of senescence by sEVs.

ATP13A2 modifies mitochondrial localization of overexpressed TOM20 to autolysosomal pathway

Mutations in ATP13A2 cause Kufor-Rakeb Syndrome (KRS), a juvenile form of Parkinson's Disease (PD). The gene product belongs to a diverse family of ion pumps and mediates polyamine influx from lysosomal lumen. While the biochemical and structural studies highlight its unique mechanics, how PD pathology is linked to ATP13A2 function remains unclear. Here we report that localization of overexpressed TOM20, a mitochondrial outer-membrane protein, is significantly altered upon ATP13A2 expression to partially merge with lysosome. Using Halo-fused version of ATP13A2, ATP13A2 was identified in lysosome and autophagosome. Upon ATP13A2 co-expression, overexpressed TOM20 was found not only in mitochondria but also within ATP13A2-containing autolysosome. This modification of TOM20 localization was inhibited by adding 1-methyl-4-phenylpyridinium (MPP+) and not accompanied with mitophagy induction. We suggest that ATP13A2 may participate in the control of overexpressed proteins targeted to mitochondrial outer-membrane.

Irisin activates Opa1-induced mitophagy to protect cardiomyocytes against apoptosis following myocardial infarction

Myocardial infarction is characterized by sudden ischemia and cardiomyocyte death. Mitochondria have critical roles in regulating cardiomyocyte viability and can sustain damage under ischemic conditions. Mitophagy is a mechanism by which damaged mitochondria are removed by autophagy to maintain mitochondrial structure and function. We investigated the role of the dynamin-like GTPase optic atrophy 1 (Opa1) in mitophagy following myocardial infarction. Opa1 expression was downregulated in infarcted hearts in vivo and in hypoxia-treated cardiomyocytes in vitro. We found that Opa1 overexpression protected cardiomyocytes against hypoxia-induced damage and enhanced cell viability by inducing mitophagy. Opa1-induced mitophagy was activated by treatment with irisin, which protected cardiomyocytes from further damage following myocardial infarction. Opa1 knockdown abolished the cardioprotective effects of irisin resulting in an enhanced inflammatory response, increased oxidative stress, and mitochondrial dysfunction in cardiomyocytes. Our data indicate that Opa1 plays an important role in maintaining cardiomyocyte viability and mitochondrial function following myocardial infarction by inducing mitophagy. Irisin can activate Opa1-induced mitophagy and protect against cardiomyocyte injury following myocardial infarction.

Visualization of the Redox Status of Cytosolic Glutathione Using the Organelle- and Cytoskeleton-Targeted Redox Sensors

Glutathione is a small thiol-containing peptide that plays a central role in maintaining cellular redox homeostasis. Glutathione serves as a physiologic redox buffer by providing thiol electrons for catabolizing harmful oxidants and reversing oxidative effects on biomolecules. Recent evidence suggests that the balance of reduced and oxidized glutathione (GSH/GSSG) defines the redox states of Cys residues in proteins and fine-tunes their stabilities and functions. To elucidate the redox balance of cellular glutathione at subcellular resolution, a number of redox-sensitive green fluorescent protein (roGFP) variants have been developed. In this study, we constructed and functionally validated organelle- and cytoskeleton-targeted roGFP and elucidated the redox status of the cytosolic glutathione at a subcellular resolution. These new redox sensors firmly established a highly reduced redox equilibrium of cytosolic glutathione, wherein significant deviation was observed among cells. By targeting the sensor to the cytosolic and lumen sides of the Golgi membrane, we identified a prominent redox gradient across the biological membrane at the Golgi body. The results demonstrated that organelle- and cytoskeleton-targeted sensors enable the assessment of glutathione oxidation near the cytosolic surfaces of different organelle membranes.

Sphingosine kinase 1 promotes cerebral ischemia-reperfusion injury through inducing ER stress and activating the NF-κB signaling pathway

Endoplasm reticulum stress and inflammation response have been found to be linked to cerebral ischemia-reperfusion (IR) injury. Sphingosine kinase 1 (SPHK1) has been reported to be a novel endoplasm reticulum regulator. The aim of our study is to figure out the role of SPHK1 in cerebral IR injury and verify whether it has an ability to regulate inflammation and endoplasm reticulum stress. Hydrogen peroxide was used to induce cerebral IR injury. Enzyme-linked immunosorbent assay, quantitative polymerase chain reaction, western blots, and immunofluorescence were used to measure the alterations of cell viability, inflammation response, and endoplasm reticulum stress. The results demonstrated that after exposure to hydrogen peroxide, cell viability was reduced whereas SPHK1 expression was significantly elevated. Knockdown of SPHK1 attenuated hydrogen peroxide-mediated cell death and reversed cell viability. Our data also demonstrated that SPHK1 deletion reduced endoplasm reticulum stress and alleviated inflammation response in hydrogen peroxide-treated cells. In addition, we also found that SHPK1 modulated endoplasm reticulum stress and inflammation response to through the NF-κB signaling pathway. Inhibition of NF-κB signaling pathway has similar results when compared with the cells with SPHK1 deletion. Altogether, our results demonstrated that SPHK1 upregulation, induced by hydrogen peroxide, is responsible for cerebral IR injury through inducing endoplasm reticulum stress and inflammation response in a manner working through the NF-κB signaling pathway. This finding provides new insight into the molecular mechanism to explain the neuron death induced by cerebral IR injury.

Yes-associated protein reduces neuroinflammation through upregulation of Sirt3 and inhibition of JNK signaling pathway

Objective: Neuroinflammation is linked to a series of neurodegenerative diseases through the unknown mechanisms.Aim: The aim of this study was to investigate the role of Yes-associated protein (Yap) in the regulation of neuroinflammation.Methods: BV-2 neuroglia cells were treated with TNFα in vitro. Then, western blots, qPCR, immunofluorescence, and ELISA were used to verify the influence of Yap in BV-2 cells neuroinflammation response.Results: After exposure to TNFα, viability of BV-2 cells decreased whereas apoptosis index was increased. Of note, Yap expression in BV-2 cells was significantly reduced, when compared to the normal cells. Interestingly, adenovirus-induced Yap overexpression was capable to reverse cell viability and thus reduce apoptotic index in TNFα-treated BV-2 cells. Molecular investigation demonstrated that Yap overexpression was linked to Sirt3 upregulation. Increased Sirt3 reduced endoplasmic reticulum (ER) stress, attenuated mitochondrial damage, and blocked JNK pro-apoptotic pathway. Interestingly, loss of Sirt3 abolished the protective effects induced by Yap overexpression in TNFα-treated BV-2 cells.Conclusions: Altogether, our results demonstrated that neuroinflammation could be caused by Yap downregulation, possible driven through Sirt3 inhibition and JNK activation. However, overexpression of Yap could protect BV-2 cells against TNFα-mediated apoptosis through modulating Sirt3-JNK signaling pathways.

[Analyzing the Redox Status of Intracellular Glutathione and Its Application to an Intestinal Bowel Disease Model]

Oxidative stress, including reactive oxygen species (ROS) generation and resulting glutathione oxidation, have been implicated in numerous aspects of cell physiology and human pathology such as cell senescence, cell differentiation, and inflammation. Significant effort has been made to establish methods of analyzing ROS levels and glutathione oxidation within a living cell. The recent development of redox-sensitive green fluorescent protein (GFP) variants enables a robust and accurate estimation of ROS level and glutathione oxidation at subcellular resolution. We created membrane-targeted versions of glutathione and hydrogen peroxide sensors by attaching palmitoylation signals to existing sensors (Grx1-roGFP2 and roGFP2-Orp1, respectively), and demonstrated the nonuniform distribution of these oxidative elements within cytosol. In living cells, cytosolic glutathione is highly reduced, and hydrogen peroxide is barely detected. Nevertheless, near the cytoplasmic side of intracellular vesicular membranes, significant glutathione oxidation and hydrogen peroxide were successfully probed by our sensors, clearly showing the difference between various areas within cytosol. Currently, these sensors are being applied to an intestinal inflammation model which is constituted by co-culturing intestinal epithelial cells and macrophage-like inflammatory cells derived from THP-1. This review covers the current status of studies regarding the association of oxidative stress and intestinal inflammation, with a focus on the redox regulation of intracellular glutathione.

Self-fluorescent antibiotic MoOx-hydroxyapatite: a nano-theranostic platform for bone infection therapies

Nowadays, the repair of large-size bone defects represents a huge medical challenge. A line of attack is the construction of advanced biomaterials having multifunctional properties. In this work, we show the creation of biocompatible MoOx-hydroxyapatite nanoparticles (nano-HA/MoOx) that simultaneously exhibit self-activated fluorescence and antibiotic skills. Along this text, we demonstrate that the insertion of molybdenum, an essential trace element, into the non-stoichiometric calcium deficient hydroxyapatite lattice generates intrinsic electronic point defects that exacerbate its epifluorescence blue emission and provokes new red emissions, preserving, always, its bioactivity. Furthermore, these point defects, acting as electron acceptors, stimulate the materials' biological redox status and promote the death of pathogen microorganisms after their direct contact. A putative mechanism, by which bacteria lose electrons from their metabolic circuit that alter the function of their cytoplasmic membrane and potentially die, agrees with our results. Our findings highlight the importance of tuning the electronic communications between biomaterial interfaces and biological units, and support the use of self-fluorescent MoOx-hydroxyapatite nanoparticles as fundamental building blocks for new real-time imaging platforms against bone infection.

Mitofusin-2 regulates inflammation-mediated mouse neuroblastoma N2a cells dysfunction and endoplasmic reticulum stress via the Yap-Hippo pathway

Endoplasmic reticulum (ER) stress is involved in inflammation-induced neurotoxicity. Mitofusin 2 (Mfn2), a member of the GTPase family of proteins, resides in the ER membrane and is known to regulate ER stress. However, the potential role and underlying mechanism of Mfn2 in inflammation-induced neuronal dysfunction is unknown. In our study, we explored the potential of Mfn2 to attenuate inflammation-mediated neuronal dysfunction by inhibiting ER stress. Our data show that Mfn2 overexpression significantly ameliorated tumor necrosis factor alpha (TNFα)-induced ER stress, as indicated by the downregulation of the ER stress proteins PERK, GRP78 and CHOP. Mfn2 overexpression also prevented the TNFα-mediated activation of caspase-3, caspase-12 and cleaved poly (ADP-ribose) polymerase (PARP). Cellular antioxidant dysfunction and reactive oxygen species overproduction were also improved by Mfn2 in the setting of TNFα in mouse neuroblastoma N2a cells in vitro. Similarly, disordered calcium homeostasis, indicated by disturbed levels of calcium-related proteins and calcium overloading, was corrected by Mfn2, as evidenced by the increased expression of store-operated calcium entry (SERCA), decreased levels of inositol trisphosphate receptor (IP3R), and normalized calcium content in TNFα-treated N2a cells. Mfn2 overexpression was found to elevate Yes-associated protein (Yap) expression; knockdown of Yap abolished the regulatory effects of Mfn2 on ER stress, oxidative stress, calcium balance, neural death and inflammatory injury. These results lead us to conclude that re-activation of the Mfn2-Yap signaling pathway alleviates TNFα-induced ER stress and dysfunction of mouse neuroblastoma N2a cells. Our findings provide a better understanding of the regulatory role of Mfn2-Yap-ER stress in neuroinflammation and indicate that the Mfn2-Yap axis may be a focus of research in terms of having therapeutic value for the treatment of neurodegenerative diseases.

Ripk3 mediates cardiomyocyte necrosis through targeting mitochondria and the JNK-Bnip3 pathway under hypoxia-reoxygenation injury

Context: Cardiomyocyte necrosis following myocardial infarction drastically the progression of heart failure.Objective: In the current study, we explored the upstream mediator for cardiomyocytes necrosis induced by hypoxia-reoxygenation (HR) injury with a focus on mitochondrial function and JNK-Bnip3 pathway.Materials and methods: Cell necrosis was determined via MTT assay, TUNEL staining and PI staining. siRNA transfection was performed to inhibit Ripk3 activation in response to HR injury. Pathway blocker was applied to prevent JNK activation.Results: Ripk3 was rapidly increased in HR-treated cardiomyocytes and correlated with the necrosis of cardiomyocytes. Interestingly, silencing of Ripk3 attenuated HR-mediated cardiomyocytes necrosis. At the molecular levels, Ripk3 deletion sustained mitochondrial bioenergetics and stabilized mitochondrial glucose metabolism. Besides, Ripk3 deletion also reduced mitochondrial oxidative stress and inhibited mPTP opening. To the end, we found Ripk3 activation was along with JNK pathway activation and Bnip3 upregulation. Interestingly, blockade of JNK pathway abolished the harmful effects of HR injury on mitochondrial function, energy metabolism and redox balance. Moreover, overexpression of Bnip3 abrogated the protection action played by Ripk3 deletion on cardiomyocytes survival.Conclusions: Taken together, these data may identify Ripk3 upregulation, mitochondrial dysfunction and JNK-Bnip3 axis activation as the novel mechanisms underlying cardiomyocytes necrosis achieved by HR injury. Thereby, approaches targeted to the Ripk3-JNK-Bnip3-mitochondria cascade have the potential to ameliorate the progression of HR-related cardiomyocytes necrosis in the clinical practice.

Hippo/Mst1 overexpression induces mitochondrial death in head and neck squamous cell carcinoma via activating β-catenin/Drp1 pathway

Mammalian Ste20-like kinase 1 (Mst1) is associated with cell apoptosis. In the current study, we explored the regulatory effects of Mst1 on squamous cell carcinoma of the head and neck (SCCHN) in vitro. SCCHN Cal27 cells and Tu686 cells were transfected with adenovirus-loaded Mst1 to detect the role of Mst1 in cell viability. Then, siRNA against Drp1 was transfected into cells to evaluate the influence of mitochondrial fission in cancer survival. Our data illustrated that Mst1 overexpression promoted SCCHN Cal27 cell and Tu686 cell death via activating mitochondria-related apoptosis. Cells transfected with adenovirus-loaded Mst1 have increased expression of DRP1 and higher DRP1 promoted mitochondrial fission. Active mitochondrial fission mediated mitochondrial damage, as evidenced by increased mitochondrial oxidative stress, decreased mitochondrial energy production, and reduced mitochondrial respiratory complex function. Moreover, Mst1 overexpression triggered mitochondria-dependent cell apoptosis via DRP1-related mitochondrial fission. Further, we found that Mst1 overexpression controlled mitochondrial fission via the β-catenin/DRP1 pathways; inhibition of β-catenin and/or knockdown of DRP1 abolished the pro-apoptotic effects of Mst1 overexpression on SCCHN Cal27 cells and Tu686 cells, leading to the survival of cancer cells in vitro. In sum, our results illustrate that Mst1/β-catenin/DRP1 axis affects SCCHN Cal27 cell and Tu686 cell viability via controlling mitochondrial dynamics balance. This finding identifies Mst1 activation might be an effective therapeutic target for the treatment of SCCHN.

Mammalian STE20-like Kinase 1 Knockdown Attenuates TNFα-Mediated Neurodegenerative Disease by Repressing the JNK Pathway and Mitochondrial Stress

Neuroinflammation has been acknowledged as a primary factor contributing to the pathogenesis of neurodegenerative disease. However, the molecular mechanism underlying inflammation stress-mediated neuronal dysfunction is not fully understood. The aim of our study was to explore the influence of mammalian STE20-like kinase 1 (Mst1) in neuroinflammation using TNFα and CATH.a cells in vitro. The results of our study demonstrated that the expression of Mst1 was dose-dependently increased after TNFα treatment. Interestingly, knockdown of Mst1 using siRNA transfection significantly repressed TNFα-induced neuronal death. We also found that TNFα treatment was associated with mitochondrial stress, including mitochondrial ROS overloading, mitochondrial permeability transition pore (mPTP) opening, mitochondrial membrane potential reduction, and mitochondrial pro-apoptotic factor release. Interestingly, loss of Mst1 attenuated TNFα-triggered mitochondrial stress and sustained mitochondrial function in CATH.a cells. We found that Mst1 modulated mitochondrial homeostasis and cell viability via the JNK pathway in a TNFα-induced inflammatory environment. Inhibition of the JNK pathway abolished TNFα-mediated CATH.a cell death and mitochondrial malfunction, similar to the results obtained via silencing of Mst1. Taken together, our results indicate that inflammation-mediated neuronal dysfunction is implicated in Mst1 upregulation, which promotes mitochondrial stress and neuronal death by activating the JNK pathway. Accordingly, our study identifies the Mst1-JNK-mitochondria axis as a novel signaling pathway involved in neuroinflammation.

Melatonin enhances TNF-α-mediated cervical cancer HeLa cells death via suppressing CaMKII/Parkin/mitophagy axis

Background

Tumor necrosis factor-α (TNF-α) immunotherapy controls the progression of human cervical cancer. Here, we explored the detailed molecular mechanisms played by melatonin in human cervical cancer (HeLa cells) death in the presence of TNF-α injury, with a particular attention to the mitochondrial homeostasis.

Methods

HeLa cells were incubated with TNFα and then cell death was determined via MTT assay, TUNEL staining, caspase ELISA assay and western blotting. Mitochondrial function was detected via analyzing mitochondrial membrane potential using JC-1 staining, mitochondrial oxidative stress using flow cytometry and mitochondrial apoptosis using western blotting.

Results

Our data exhibited that treatment with HeLa cells using melatonin in the presence of TNF-α further triggered cancer cell cellular death. Molecular investigation demonstrated that melatonin enhanced the caspase-9 mitochondrion death, repressed mitochondrial potential, increased ROS production, augmented mPTP opening rate and elevated cyt-c expression in the nucleus. Moreover, melatonin application further suppressed mitochondrial ATP generation via reducing the expression of mitochondrial respiratory complex. Mechanistically, melatonin augmented the response of HeLa cells to TNF-α-mediated cancer death via repressing mitophagy. TNF-α treatment activated mitophagy via elevating Parkin expression and excessive mitophagy blocked mitochondrial apoptosis, ultimately alleviating the lethal action of TNF-α on HeLa cell. However, melatonin supplementation could prevent TNF-α-mediated mitophagy activation via inhibiting Parkin in a CaMKII-dependent manner. Interestingly, reactivation of CaMKII abolished the melatonin-mediated mitophagy arrest and HeLa cell death.

Conclusions

Overall, our data highlight that melatonin enhances TNF-α-induced human cervical cancer HeLa cells mitochondrial apoptosis via inactivating the CaMKII/Parkin/mitophagy axis.

Mechanotransduction in talin through the interaction of the R8 domain with DLC1

The mechanical unfolding of proteins is a cellular mechanism for force transduction with potentially broad implications in cell fate. Despite this, the mechanism by which protein unfolding elicits differential downstream signalling pathways remains poorly understood. Here, we used protein engineering, atomic force microscopy, and biophysical tools to delineate how protein unfolding controls cell mechanics. Deleted in liver cancer 1 (DLC1) is a negative regulator of Ras homolog family member A (RhoA) and cell contractility that regulates cell behaviour when localised to focal adhesions bound to folded talin. Using a talin mutant resistant to force-induced unfolding of R8 domain, we show that talin unfolding determines DLC1 downstream signalling and, consequently, cell mechanics. We propose that this new mechanism of mechanotransduction may have implications for a wide variety of associated cellular processes.