Intersections between Regulated Cell Death and Autophagy

Targeting Autophagy in Breast Cancer

Breast cancer is a heterogeneous disease consisting of different biological subtypes, with differences in terms of incidence, response to diverse treatments, risk of disease progression, and sites of metastases. In the last years, several molecular targets have emerged and new drugs, targeting PI3K/Akt/mTOR and cyclinD/CDK/pRb pathways and tumor microenvironment have been integrated into clinical practice. However, it is clear now that breast cancer is able to develop resistance to these drugs and the identification of the underlying molecular mechanisms is paramount to drive further drug development. Autophagy is a highly conserved homeostatic process that can be activated in response to antineoplastic agents as a cytoprotective mechanism. Inhibition of autophagy could enhance tumor cell death by diverse anti-cancer therapies, representing an attractive approach to control mechanisms of drug resistance. In this manuscript, we present a review of autophagy focusing on its interplay with targeted drugs used for breast cancer treatment.

Ferroptosis mediated by the interaction between Mfn2 and IREα promotes arsenic-induced nonalcoholic steatohepatitis

Exposure to arsenic is a risk factor for nonalcoholic steatohepatitis (NASH). Ferroptosis is a form of regulated cell death defined by the accumulation of lipid peroxidation. In the current study, we observed the occurrence of ferroptosis in arsenic-induced NASH by assessing ferroptosis related hallmarks. In vitro, we found that ferrostatin-1 effectively attenuated the executing of ferroptosis and NASH. Simultaneously, the expression of ACSL4 (acyl-CoA synthetase long-chain family member 4) was upregulated in rat's liver and L-02 cells exposed to arsenic. While, suppression of ACSL4 with rosiglitazone or ACSL4 siRNA remarkably alleviated arsenic-induced NASH and ferroptosis through diminishing 5-hydroxyeicosatetraenoic acid (5-HETE) content. Additionally, Mitofusin 2 (Mfn2), a physical tether between endoplasmic reticulum and mitochondria, has rarely been explored in the ferroptosis. Using Mfn2 siRNA or inositol-requiring enzyme 1 alpha (IRE1α) inhibitor, we found NASH and ferroptosis were obviously mitigated through reducing 5-HETE content. Importantly, Co-IP assay indicated that Mfn2 could interact with IRE1α and promoted the production of 5-HETE, ultimately led to ferroptosis and NASH. Collectively, our data showed that ferroptosis is involved in arsenic-induced NASH. These data provide insightful viewpoints into the mechanism of arsenic-induced NASH.

Ferroptosis contributes to developmental cell death in rice blast

Ferroptosis, an iron-dependent cell death process, was found to occur in Magnaporthe oryzae, and plays a key role in infection-related development therein. Ferroptosis in the rice-blast fungus was confirmed based on five basic criteria. We confirmed the dependence of ferroptosis on ferric ions, and optimized ratio-fluorescence imaging of C11-BODIPY^581/591 as a precise sensor for lipid peroxides that mediate ferroptosis in M. oryzae. We uncovered an important regulatory function for reduced glutathione and NADPH oxidases in modulating the superoxide moieties required for ferroptotic cell death. We found ferroptosis to be necessary for the developmental cell death of conidia during appressorium maturation in rice blast. Such ferroptotic cell death initiated first in the terminal cell and progressed sequentially to the entire conidium. Iron chelation or chemical inhibition of ferroptosis caused conidial cells to remain viable, and led to strong defects in host invasion by M. oryzae. Ferroptosis induction exclusively in the host severely constrained the invasive growth of M. oryzae. We found inter-reliant and independent roles for ferroptosis and autophagy in controlling such precise cell death in M. oryzae during pathogenic differentiation. Our study provides significant molecular insights into the role of developmental cell death and iron homeostasis in fungal pathogenesis.

Toxicological appraisal of the chemical fractions of ambient fine (PM2.5-0.3) and quasi-ultrafine (PM0.3) particles in human bronchial epithelial BEAS-2B cells

New toxicological research is still urgently needed to improve the current knowledge about the induction of some underlying mechanisms of toxicity by the different chemical fractions of ambient particulate matter (PM). This in vitro study sought also to better evaluate and compare the respective toxicities of fine particles (PM_2.5-0.3) and their inorganic and organic chemical fractions, and the respective toxicities of the organic chemical fractions of PM_2.5-0.3 and quasi-ultrafine particles (PM_0.3). Human bronchial epithelial BEAS-2B cells were also exposed for 6-48 h to relatively low doses of PM_2.5-0.3 and their organic extractable (OEM_2.5-0.3) and non-extractable (NEM_2.5-0.3) fractions, and the organic extractable fraction (OEM_0.3) of PM_0.3. We reported that not only PM_2.5-0.3, but also, to a lesser extent, its inorganic chemical fraction, NEM_2.5-0.3, and organic chemical fraction, OEM_2.5-0.3, were able to significantly induce ROS overproduction and oxidative damage notwithstanding the early activation of NRF2 signaling pathway. Moreover, for any exposure, inflammatory and apoptotic events were noticed. Similar results were observed in BEAS-2B cells exposed to OEM_0.3, rich of polycyclic aromatic hydrocarbons and their nitrated and oxygenated derivatives. In BEAS-2B cells exposed for 24 and 48 h to OEM_2.5-0.3 and OEM_0.3, to a higher extent, there was an alteration of the levels of some critical proteins even though crucial for the autophagy rather than a real reduction of autophagy. It is noteworthy that the toxicological effects were equal or mostly higher in BEAS-2B cells exposed for 6 and/or 24 h to PM_2.5-0.3 from those exposed to NEM_2.5-0.3 or OEM_2.5-0.3, and in BEAS-2B cells exposed for 6 and/or mostly 24 h to OEM_0.3 from those exposed to OEM_2.5-0.3. Taken together, these results revealed the higher potentials for toxicity, closely linked to their respective physical and chemical characteristics, of PM_2.5-0.3 vs NEM_2.5-0.3 and/or OEM_2.5-0.3, and OEM_0.3 vs OEM_2.5-0.3.

Regulated Necrosis in Pulmonary Disease. A Focus on Necroptosis and Ferroptosis

To date, increasing evidence suggests the possible involvement of various types of cell death in lung diseases. The recognized regulated cell death includes necrotic cell death that is immunogenic, releasing damage-associated molecular patterns and driving tissue inflammation. Necroptosis is a well-understood form of regulated necrosis that is executed by RIPK3 (receptor-interacting protein kinase 3) and the pseudokinase MLKL (mixed lineage kinase domain-like protein). Ferroptosis is a newly described caspase-independent form of regulated necrosis that is characterized by the increase of detrimental lipid reactive oxygen species produced via iron-dependent lipid peroxidation. The role of these two cell death pathways differs depending on the disease, cell type, and microenvironment. Moreover, some experimental cell death models have demonstrated shared ferroptotic and necroptotic cell death and the synergistic effect of simultaneous inhibition. This review examines the role of regulated necrotic cell death, particularly necroptosis and ferroptosis, in lung disease pathogenesis in the context of recent insights into the roles of the key effector molecules of these two cell death pathways.

The HERC1 ubiquitin ligase regulates presynaptic membrane dynamics of central synapses

HERC1 is a ubiquitin ligase protein, which, when mutated, induces several malformations and intellectual disability in humans. The animal model of HERC1 mutation is the mouse tambaleante characterized by: (1) overproduction of the protein; (2) cerebellar Purkinje cells death by autophagy; (3) dysregulation of autophagy in spinal cord motor neurons, and CA3 and neocortical pyramidal neurons; (4) impairment of associative learning, linked to altered spinogenesis and absence of LTP in the lateral amygdala; and, (5) motor impairment due to delayed action potential transmission, decrease synaptic transmission efficiency and altered myelination in the peripheral nervous system. To investigate the putative role of HERC1 in the presynaptic dynamics we have performed a series of experiments in cultured tambaleante hippocampal neurons by using transmission electron microscopy, FM1-43 destaining and immunocytochemistry. Our results show: (1) a decrease in the number of synaptic vesicles; (2) reduced active zones; (3) less clathrin immunoreactivity and less presynaptic endings over the hippocampal main dendritic trees; which contrast with (4) a greater number of endosomes and autophagosomes in the presynaptic endings of the tambaleante neurons relative to control ones. Altogether these results show an important role of HERC1 in the regulation of presynaptic membrane dynamics.

Regulation and repurposing of nutrient sensing and autophagy in innate immunity

Nutrients not only act as building blocks but also as signaling molecules. Nutrient-availability promotes cell growth and proliferation and suppresses catabolic processes, such as macroautophagy/autophagy. These effects are mediated by checkpoint kinases such as MTOR (mechanistic target of rapamycin kinase), which is activated by amino acids and growth factors, and AMP-activated protein kinase (AMPK), which is activated by low levels of glucose or ATP. These kinases have wide-ranging activities that can be co-opted by immune cells upon exposure to danger signals, cytokines or pathogens. Here, we discuss recent insight into the regulation and repurposing of nutrient-sensing responses by the innate immune system during infection. Moreover, we examine how natural mutations and pathogen-mediated interventions can alter the balance between anabolic and autophagic pathways leading to a breakdown in tissue homeostasis and/or host defense.Abbreviations: AKT1/PKB: AKT serine/threonine kinase 1; ATG: autophagy related; BECN1: beclin 1; CGAS: cyclic GMP-AMP synthase; EIF2AK4/GCN2: eukaryotic translation initiation factor 2 alpha kinase 4; ER: endoplasmic reticulum; FFAR: free fatty acid receptor; GABARAP: GABA type A receptor-associated protein; IFN: interferon; IL: interleukin; LAP: LC3-associated phagocytosis; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MAP3K7/TAK1: mitogen-activated protein kinase kinase kinase 7; MAPK: mitogen-activated protein kinase; MTOR: mechanistic target of rapamycin kinase; NLR: NOD (nucleotide-binding oligomerization domain) and leucine-rich repeat containing proteins; PI3K, phosphoinositide 3-kinase; PRR: pattern-recognition receptor; PtdIns3K: phosphatidylinositol 3-kinase; RALB: RAS like proto-oncogene B; RHEB: Ras homolog, MTORC1 binding; RIPK1: receptor interacting serine/threonine kinase 1; RRAG: Ras related GTP binding; SQSTM1/p62: sequestosome 1; STING1/TMEM173: stimulator of interferon response cGAMP interactor 1; STK11/LKB1: serine/threonine kinase 11; TBK1: TANK binding kinase 1; TLR: toll like receptor; TNF: tumor necrosis factor; TRAF6: TNF receptor associated factor 6; TRIM: tripartite motif protein; ULK1: unc-51 like autophagy activating kinase 1; V-ATPase: vacuolar-type H⁺-proton-translocating ATPase.

Autophagy as a decisive process for cell death

Autophagy is an intracellular catabolic pathway in which cellular constituents are engulfed by autophagosomes and degraded upon autophagosome fusion with lysosomes. Autophagy serves as a major cytoprotective process by maintaining cellular homeostasis and recycling cytoplasmic contents. However, emerging evidence suggests that autophagy is a primary mechanism of cell death (autophagic cell death, ACD) and implicates ACD in several aspects of mammalian physiology, including tumor suppression and psychological disorders. However, little is known about the physiological roles and molecular mechanisms of ACD. In this review, we document examples of ACD and discuss recent progress in our understanding of its molecular mechanisms.

Cyclin-Dependent Kinase 9 Inhibition Suppresses Necroptosis and Pyroptosis in the Progress of Endotoxemia

The host innate immune response stands at the first line of defense against the outburst of pathogen invasion and their byproduct release. The balanced and coordinated expression of genes in normal immune responses is compromised in the progress of endotoxemia with exacerbated inflammation and massive cell death. In the present study, we identified cyclin-dependent kinase 9 (CDK9), the functional subunit of the positive transcription elongation factor b, as a master regulator of inflammatory gene transcription in the process of promoter-proximal pausing to productive elongation. Therapeutic pharmacological inhibition of CDK9 by flavopiridol (FVD) rescued mice from death in experimental models of fatal endotoxemia. In addition to alleviation of the cytokine storm in the circulation system following lethal endotoxin injection, FVD treatment significantly dampened the onset of inflammation in the livers and lungs and reduced the necroptosis and pyroptosis in livers. Moreover, CDK9 inhibition reduced inflammatory cytokine release and decreased cell death in the pro-inflammatory pyroptotic and necroptotic cell death pathway in monocytes in responses to lipopolysaccharide. In conclusion, CDK9 inhibition may affect the progress of endotoxemia by dampening inflammation and cell death including necroptosis and pyroptosis.

Systems biology of ferroptosis: A modeling approach

Ferroptosis is a recently discovered form of iron-dependent regulated cell death (RCD) that occurs via peroxidation of phospholipids containing polyunsaturated fatty acid (PUFA) moieties. Activating this form of cell death is an emerging strategy in cancer treatment. Because multiple pathways and molecular species contribute to the ferroptotic process, predicting which tumors will be sensitive to ferroptosis is a challenge. We thus develop a mathematical model of several critical pathways to ferroptosis in order to perform a systems-level analysis of the process. We show that sensitivity to ferroptosis depends on the activity of multiple upstream cascades, including PUFA incorporation into the phospholipid membrane, and the balance between levels of pro-oxidant factors (reactive oxygen species, lipoxogynases) and antioxidant factors (GPX4). We perform a systems-level analysis of ferroptosis sensitivity as an outcome of five input variables (ACSL4, SCD1, ferroportin, transferrin receptor, and p53) and organize the resulting simulations into 'high' and 'low' ferroptosis sensitivity groups. We make a novel prediction corresponding to the combinatorial requirements of ferroptosis sensitivity to SCD1 and ACSL4 activity. To validate our prediction, we model the ferroptotic response of an ovarian cancer stem cell line following single- and double-knockdown of SCD1 and ACSL4. We find that the experimental outcomes are consistent with our simulated predictions. This work suggests that a systems-level approach is beneficial for understanding the complex combined effects of ferroptotic input, and in predicting cancer susceptibility to ferroptosis.

High cholesterol induces apoptosis and autophagy through the ROS-activated AKT/FOXO1 pathway in tendon-derived stem cells

BACKGROUND

Hypercholesterolemia increases the risk of tendon pain and tendon rupture. Tendon-derived stem cells (TDSCs) play a vital role in the development of tendinopathy. Our previous research found that high cholesterol inhibits tendon-related gene expression in TDSCs. Whether high cholesterol has other biological effects on TDSCs remains unknown.

METHODS

TDSCs isolated from female SD rats were exposed to 10 mg/dL cholesterol for 24 h. Then, cell apoptosis was assessed using flow cytometry and fluorescence microscope. RFP-GFP-LC3 adenovirus transfection was used for measuring autophagy. Signaling transduction was measured by immunofluorescence and immunoblotting. In addition, Achilles tendons from ApoE -/- mice fed with a high-fat diet were histologically assessed using HE staining and immunohistochemistry.

RESULTS

In this work, we verified that 10 mg/dL cholesterol suppressed cell proliferation and migration and induced G0/G1 phase arrest. Additionally, cholesterol induced apoptosis and autophagy simultaneously in TDSCs. Apoptosis induction was related to increased expression of cleaved caspase-3 and BAX and decreased expression of Bcl-xL. The occurrence of autophagic flux and accumulation of LC3-II demonstrated the induction of autophagy by cholesterol. Compared with the effects of cholesterol treatment alone, the autophagy inhibitor 3-methyladenine (3-MA) enhanced apoptosis, while the apoptosis inhibitor Z-VAD-FMK diminished cholesterol-induced autophagy. Moreover, cholesterol triggered reactive oxygen species (ROS) generation and activated the AKT/FOXO1 pathway, while the ROS scavenger NAC blocked cholesterol-induced activation of the AKT/FOXO1 pathway. NAC and the FOXO1 inhibitor AS1842856 rescued the apoptosis and autophagy induced by cholesterol. Finally, high cholesterol elevated the expression of cleaved caspase-3, Bax, LC3-II, and FOXO1 in vivo.

CONCLUSION

The present study indicated that high cholesterol induced apoptosis and autophagy through ROS-activated AKT/FOXO1 signaling in TDSCs, providing new insights into the mechanism of hypercholesterolemia-induced tendinopathy. High cholesterol induces apoptosis and autophagy through the ROS-activated AKT/FOXO1 pathway in tendon-derived stem cells.

Pathomechanism Heterogeneity in the Amyotrophic Lateral Sclerosis and Frontotemporal Dementia Disease Spectrum: Providing Focus Through the Lens of Autophagy

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) constitute aggressive neurodegenerative pathologies that lead to the progressive degeneration of upper and lower motor neurons and of neocortical areas, respectively. In the past decade, the identification of several genes that cause these disorders indicated that the two diseases overlap in a multifaceted spectrum of conditions. The autophagy-lysosome system has been identified as a main intersection for the onset and progression of neurodegeneration in ALS/FTD. Genetic evidence has revealed that several genes with a mechanistic role at different stages of the autophagy process are mutated in patients with ALS/FTD. Moreover, the three main proteins aggregating in ALS/FTD, including in sporadic cases, are also targeted by autophagy and affect this process. Here, we examine the varied dysfunctions and degrees of involvement of the autophagy-lysosome system that have been discovered in ALS/FTD. We argue that these findings shed light on the pathological mechanisms in the ALS/FTD spectrum and conclude that they have important consequences both for treatment options and for the basic biomolecular understanding of how this process intersects with RNA metabolism, the other major cellular process reported to be dysfunctional in part of the ALS/FTD spectrum.

Cell death induced by the ER stressor thapsigargin involves death receptor 5, a non-autophagic function of MAP1LC3B, and distinct contributions from unfolded protein response components

BACKGROUND

Cell death triggered by unmitigated endoplasmic reticulum (ER) stress plays an important role in physiology and disease, but the death-inducing signaling mechanisms are incompletely understood. To gain more insight into these mechanisms, the ER stressor thapsigargin (Tg) is an instrumental experimental tool. Additionally, Tg forms the basis for analog prodrugs designed for cell killing in targeted cancer therapy. Tg induces apoptosis via the unfolded protein response (UPR), but how apoptosis is initiated, and how individual effects of the various UPR components are integrated, is unclear. Furthermore, the role of autophagy and autophagy-related (ATG) proteins remains elusive.

METHODS

To systematically address these key questions, we analyzed the effects of Tg and therapeutically relevant Tg analogs in two human cancer cell lines of different origin (LNCaP prostate- and HCT116 colon cancer cells), using RNAi and inhibitory drugs to target death receptors, UPR components and ATG proteins, in combination with measurements of cell death by fluorescence imaging and propidium iodide staining, as well as real-time RT-PCR and western blotting to monitor caspase activity, expression of ATG proteins, UPR components, and downstream ER stress signaling.

RESULTS

In both cell lines, Tg-induced cell death depended on death receptor 5 and caspase-8. Optimal cytotoxicity involved a non-autophagic function of MAP1LC3B upstream of procaspase-8 cleavage. PERK, ATF4 and CHOP were required for Tg-induced cell death, but surprisingly acted in parallel rather than as a linear pathway; ATF4 and CHOP were independently required for Tg-mediated upregulation of death receptor 5 and MAP1LC3B proteins, whereas PERK acted via other pathways. Interestingly, IRE1 contributed to Tg-induced cell death in a cell type-specific manner. This was linked to an XBP1-dependent activation of c-Jun N-terminal kinase, which was pro-apoptotic in LNCaP but not HCT116 cells. Molecular requirements for cell death induction by therapy-relevant Tg analogs were identical to those observed with Tg.

CONCLUSIONS

Together, our results provide a new, integrated understanding of UPR signaling mechanisms and downstream mediators that induce cell death upon Tg-triggered, unmitigated ER stress. Video Abstract.

Ubenimex induces autophagy inhibition and EMT suppression to overcome cisplatin resistance in GC cells by perturbing the CD13/EMP3/PI3K/AKT/NF-κB axis

Cisplatin (CDDP)-based chemotherapy is a standard treatment for gastric cancer (GC). However, chemoresistance is a major obstacle for CDDP application. Exploring underlying mechanisms of CDDP resistance development in GC and selecting an effective strategy to overcome CDDP resistance remain a challenge. Here, we demonstrate that a transmembrane ectoenzyme, CD13, endows GC patients with insensitivity to CDDP and predicts an undesirable prognosis in GC patients with CDDP treatment. Similarly, CD13 expression is positively related with CDDP resistance in GC cells. A CD13 inhibitor, Ubenimex, reverses CDDP resistance and renders GC cells sensitivity to CDDP, for which CD13 reduction is essential, and epithelial membrane protein 3 (EMP3) is a putative target downstream of CD13. Furthermore, Ubenimex decreases EMP3 expression by boosting its CpG island hypermethylation for which CD13 down-regulation is required. In addition, EMP3 is a presumptive modifier by which CD13 exerts functions in the phosphoinositol 3-kinase/protein kinase B (PI3K/AKT) pathway. Ubenimex inhibits the activation of the CD13/EMP3/PI3K/AKT/NF-κB pathway to overcome CDDP resistance in GC cells by suppressing autophagy and epithelial-mesenchymal transition (EMT). Therefore, CD13 is a potential indicator of CDDP resistance formation, and Ubenimex may serve as a potent candidate for reversing CDDP resistance in GC.

Phenylephrine induces necroptosis and apoptosis in corneal epithelial cells dose- and time-dependently

In the present study, the toxicity of phenylephrine, a selective α1-adrenergic receptor agonist, in corneal epithelial cells and its underlying mechanisms were investigated using an in vitro model of human corneal epithelial cells (HCEPCs) and an in vivo model of New Zealand white rabbit corneas. The HCEPCs treated with phenylephrine at concentrations from 10% to 0.078125% displayed abnormal morphology, decline of cell viability and elevation of plasma membrane permeability time- and dose-dependently. Moreover, 10%-1.25% phenylephrine induce necrosis characteristics of marginalization and uneven distribution of chromatin through up-regulation of RIPK1, RIPK3 and MLKL along with inactivation of caspase-8 and caspase-2, whereas 0.625% phenylephrine induced condensed chromatin, S phase arrest, phosphatidylserine externalization, DNA fragmentation and apoptotic body formation in the HCECs through activation of caspase-2, -8, -9 and -3 as well as down-regulation of Bcl-2, up-regulation of Bad, ΔΨm disruption and release of cytochrome c and AIF into cytosol. At last, 10% phenylephrine induced destruction of the corneal epithelia and apoptosis of corneal epithelial cells in rabbit corneas. In conclusion, 10% to 1.25% phenylephrine cause necroptosis via RIPK1-RIPK3-MLKL axis and 0.625% phenylephrine induce apoptosis via a mitochondrion-dependent and death receptor-mediated signal pathway in HCEPCs.

Parkin Regulates Programmed Necrosis and Myocardial Ischemia/Reperfusion Injury by Targeting Cyclophilin-D

Aims: Cardiomyocyte death critically contributes to the pathogenesis of cardiac disorders, such as myocardial infarction, heart failure, and cardiac ischemia/reperfusion (I/R) injury. As one of the main forms of cardiac cell death, necrosis plays a critical role in heart diseases. Multiple signaling pathways of necrosis have been demonstrated, in which death receptors, receptor-interacting serine/threonine-protein 1 and 3 kinases, and cyclophilin-D (CypD) have been deeply implicated. However, the fundamental mechanism underlying myocardial necroptosis, especially the mitochondrial permeability transition pore (mPTP)-CypD-dependent death pathway, is poorly understood. Parkin functions as an E3 ubiquitin protein ligase that mainly mediates mitophagy cascades. As yet, it is not clear whether Parkin participates in regulating necrosis and myocardial I/R injury. Results: Here, our results showed that Parkin mediated mitophagy and inhibited necrosis under oxidative stress. In further exploring the underlying mechanisms, we found that Parkin suppressed mPTP opening by catalyzing the ubiquitination of CypD in necrotic cascades, which were not involved in Parkin-regulated mitophagy. Parkin inhibited necrosis, reduced myocardial I/R injury, and improved cardiac function. Innovation: Our present work reveals a highlighted connection between the mitochondrial matrix-localized Parkin and the mPTP-CypD-dependent necrotic signaling pathway in cardiac injury. Conclusion: Our results revealed a novel myocardial necrotic regulating model composed of Parkin, CypD, and mPTP, which may provide potential therapeutic targets and strategies to modulate the levels of these molecules.

Microtubule destabilization caused by silicate via HDAC6 activation contributes to autophagic dysfunction in bone mesenchymal stem cells

BACKGROUND

Silicon-modified biomaterials have been extensively studied in bone tissue engineering. In recent years, the toxicity of silicon-doped biomaterials has gradually attracted attention but requires further elucidation. This study was designed to explore whether high-dose silicate can induce a cytotoxicity effect in bone mesenchymal stem cells (BMSCs) and the role of autophagy in its cytotoxicity and mechanism.

METHODS

Morphologic changes and cell viability of BMSCs were detected after different doses of silicate exposure. Autophagic proteins (LC3, p62), LC3 turnover assay, and RFP-GFP-LC3 assay were applied to detect the changes of autophagic flux following silicate treatment. Furthermore, to identify the potential mechanism of autophagic dysfunction, we tested the acetyl-α-tubulin protein level and histone deacetylase 6 (HDAC6) activity after high-dose silicate exposure as well as the changes in microtubule and autophagic activity after HDAC6 siRNA was applied.

RESULTS

It was found that a high dose of silicate could induce a decrease in cell viability; LC3-II and p62 simultaneously increased after high-dose silicate exposure. A high concentration of silicate could induce autophagic dysfunction and cause autophagosomes to accumulate via microtubule destabilization. Results showed that acetyl-α-tubulin decreased significantly with high-dose silicate treatment, and inhibition of HDAC6 activity can restore microtubule structure and autophagic flux.

CONCLUSIONS

Microtubule destabilization caused by a high concentration of silicate via HDAC6 activation contributed to autophagic dysfunction in BMSCs, and inhibition of HDAC6 exerted a cytoprotection effect through restoration of the microtubule structure and autophagic flux.

Snail modulates JNK-mediated cell death in Drosophila

Cell death plays a pivotal role in animal development and tissue homeostasis. Dysregulation of this process is associated with a wide variety of human diseases, including developmental and immunological disorders, neurodegenerative diseases and tumors. While the fundamental role of JNK pathway in cell death has been extensively studied, its down-stream regulators and the underlying mechanisms remain largely elusive. From a Drosophila genetic screen, we identified Snail (Sna), a Zinc-finger transcription factor, as a novel modulator of ectopic Egr-induced JNK-mediated cell death. In addition, sna is essential for the physiological function of JNK signaling in development. Our genetic epistasis data suggest that Sna acts downstream of JNK to promote cell death. Mechanistically, JNK signaling triggers dFoxO-dependent transcriptional activation of sna. Thus, our findings not only reveal a novel function and the underlying mechanism of Sna in modulating JNK-mediated cell death, but also provide a potential drug target and therapeutic strategies for JNK signaling-related diseases.

Pro-Death or Pro-Survival: Contrasting Paradigms on Nanomaterial-Induced Autophagy and Exploitations for Cancer Therapy

Autophagy is a critical lysosome-mediated cellular degradation process for the clearance of damaged organelles, obsolete proteins, and invading pathogens and plays important roles in the pathogenesis and treatment of human diseases including cancer. While not a cell death process per se, autophagy is nevertheless intimately linked to a cell's live/die decision. Basal autophagy, operating constitutively at low levels in essentially every mammalian cell, is vital for maintaining cellular homeostasis and promotes cell survival. On the other hand, elevated level of autophagy is frequently observed in cells responding to a physical, chemical, or biological stress. This "induced" autophagy, a hallmark under a variety of pathological and pathophysiological conditions, may be either pro-death or pro-survival, two contrasting paradigms for cell fate determination. Research in our laboratory and other groups around the world over the last 15 years has revealed nanomaterials as a unique class of autophagy inducers, with the capability of elevating the cellular autophagy to extremely high levels. In this Account we focus on the contrasting cell fate decision impacted by nanomaterial-induced autophagy. First, we give a brief introduction to nanomaterial-induced autophagy and summarize our current understanding on how it affects a cell's live/die decision. Autophagy induced by nanomaterials, in most cases, promotes cell death, but a significant number of nanomaterials are also able to elicit pro-survival autophagy. Although not a common feature, some nanomaterials may induce pro-death autophagy in one cell type while eliciting pro-survival autophagy in a different cell type. The ability to control the level of the induced autophagy, and furthermore its pro-death/pro-survival nature, is critically important for nanomedicine. Second, we discuss several possible mechanistic insights on the pro-death/pro-survival decision for nanomaterial-induced autophagy. "Disrupted" autophagic processes, with a "block" or perhaps "diversion" at the various stages, may be a characteristic hallmark for nanomaterial-induced autophagy, rendering it intrinsically pro-death in nature. On the other hand, autophagy-mediated upregulation and activation of pro-survival factors or signaling pathways, overriding the intrinsic pro-death nature, may be a common mechanism for nanomaterial-induced pro-survival autophagy. In addition, cargo degradation and reactive oxygen species may also play important roles in the pro-death/pro-survival decision impacted by nanomaterial-induced autophagy. Finally, we focus on the situation where nanomaterials induce autophagy in cancer cells and summarize the different strategies in exploiting the pro-death or pro-survival nature of nanomaterial-induced autophagy to enhance the various modalities of cancer therapy, including direct cancer cell killing, chemotherapy and radiotherapy, photothermal therapy, and integrated diagnosis and therapy. While the details vary, the basic principle is simple and straightforward. If the induced autophagy is pro-death, maximize it. Otherwise, inhibit it. Effective exploitation of nanomaterial-induced autophagy has the potential to become a new weapon in our ever-increasing arsenal to fight cancer, particularly difficult-to-treat and drug-resistant cancer.

Nanocarriers in photodynamic therapy-in vitro and in vivo studies

Photodynamic therapy (PDT) is a minimally invasive technique which has proven to be successful in the treatment of several types of tumors. This relatively simple method exploits three inseparable elements: phototoxic compound (photosensitizer [PS]), light source, and oxygen. Upon irradiation by light with specified wavelength, PS generates reactive oxygen species, which starts the cascade of reactions leading to cell death. The positive therapeutic outcome of PDT may be limited due to several aspects, including low water solubility of PSs, hampering their effective administration and blood circulation, as well as low tumor specificity, inefficient cellular uptake and activation energies requiring prolonged illumination times. One of the promising approaches to overcome these obstacles involves the use of carrier systems modulating pharmacokinetics and pharmacodynamics of the PSs. In the present review, we summarized current in vitro and in vivo studies regarding the use of nanoparticles as potential delivery devices for PSs to enhance their cellular uptake and cytotoxic properties, and thus-the therapeutic outcome of PDT. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Fat cadherins in mouse models of degenerative ataxias

Autophagy is a lysosomal degradation pathway that plays an essential role in neuronal homeostasis and is perturbed in many neurological diseases. Transcriptional downregulation of fat was previously observed in a Drosophila model of the polyglutamine disease Dentatorubral-pallidoluysian atrophy (DRPLA) and this was shown to be partially responsible for autophagy defects and neurodegeneration. However, it is still unclear whether a downregulation of mammalian Fat orthologues is associated with neurodegeneration in mice. We hereby show that all four Fat orthologues are transcriptionally downregulated in the cerebellum in a mouse model of DRPLA. To elucidate the possible roles of single Fat genes, this study concentrates on Fat3. This fat homologue is shown to be the most widely expressed in the brain. Conditional knockout (KO) of Fat3 in brains of adult mice was attempted using the inducible Thy1Cre(ER^T2) SLICK H line. Behavioral and biochemical analysis revealed that mice with conditional KO of Fat3 in the brain display no abnormalities. This may be ascribed either to the limited efficiency of the KO strategy pursued or to the lack of effect of Fat3 KO on autophagy.

Molecular Response of Rabbit Menisci to Surgically Induced Hemarthrosis and a Single Intra-Articular Dexamethasone Treatment

Anterior cruciate ligament reconstructive surgery can restore biomechanical stability, however, such surgery cannot reliably prevent the onset of post-traumatic osteoarthritis. The aim of this study was to elucidate the molecular response that occurs within the menisci following a surgical injury that allows bleeding into the joint space, and then to investigate the effect of dexamethasone (DEX) on this molecular response. Cell viability studies following acute controlled exposure to blood and blood plus DEX were also conducted. Forty-eight New Zealand white rabbits were randomly allocated into control, sham, surgical, and surgical  + DEX groups (each group n  =  6). Animals were sacrificed at 48 h and 9 weeks, and menisci were harvested. The messenger RNA (mRNA) expression levels for key inflammatory, and degradative proteins, as well as mRNA levels for autophagy pathway molecules were quantified, and statistically significant changes were described. Meniscal cell viability was calculated by incubating groups of medial and lateral menisci in autologous blood, or autologous blood plus DEX for 48 h (each group n  =  4; total of eight medial and eight lateral menisci), and then conducting a histological live/dead assay. Results indicated a significant reduction in only medial meniscal cell viability when the tissue was exposed to blood in combination with DEX. A single administration of DEX following surgery significantly suppresses the elevated molecular expression for key inflammatory and degradative markers within menisci at 48 h and 9 weeks post-surgery. In vitro, autologous blood did not affect cell viability, but addition of DEX uniquely impacted the medial menisci. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2043-2052, 2019.

Apoptotic effects of norfloxacin on corneal endothelial cells

Norfloxacin, a frequently used ocular antibiotic, might have cytotoxic effect on human corneal endothelial cells (HCECs), subsequently damage the cornea and finally impair human vision. However, the possible mechanisms of cytotoxicity of norfloxacin to HCEC line are unclear. Herein, we investigated the cytotoxicity of norfloxacin and its underlying cellular and molecular mechanisms using in vitro cultured non-transfected HCECs and verified the cytotoxicity with cat corneal endothelium in vivo. In the present study, the cytotoxicity of norfloxacin in the in vitro cultured HCECs was recognized by causing abnormal morphology such as cell shrinkage and detachment from plate bottom, and decline of viability of in vitro cultured HCECs. Then, its cytotoxicity was verified by inducing reduction of cell density and morphological abnormality of in vivo cat corneal endothelial cells. Furthermore, the cytotoxicity of norfloxacin in HCECs was corroborated as apoptosis by elevation of plasma membrane permeability, S phase arrest, phosphatidylserine externalization, DNA fragmentation, and apoptotic body formation in in vitro cultured HCECs and apoptosis-like swollen cells in the in vivo model. Moreover, norfloxacin induced extrinsic death receptor-mediated apoptosis pathway by activating caspase-2/-8/-3 and intrinsic mitochondrion-dependent apoptosis pathway by downregulating anti-apoptotic Bcl-2 and upregulating of pro-apoptotic Bad, which disrupted mitochondrial transmembrane potential, subsequently upregulated cytoplasmic cytochrome c and apoptosis-inducing factor and finally activated caspase-9/-3. Generally, norfloxacin induces HCE cell apoptosis via a death receptor-mediated and mitochondrion-dependent signaling pathway.