Autophagy complexes cell death by necroptosis

Pharmacologic targeting of the p62 ZZ domain enhances both anti-tumor and bone-anabolic effects of bortezomib in multiple myeloma

Multiple myeloma (MM) is a malignancy of plasma cells whose antibody secretion creates proteotoxic stress relieved by the N-end rule pathway, a proteolytic system that degrades N-arginylated proteins in the proteasome. When the proteasome is inhibited, protein cargo is alternatively targeted for autophagic degradation by binding to the ZZ-domain of p62/ sequestosome-1. Here, we demonstrate that XRK3F2, a selective ligand for the ZZ-domain, dramatically improved two major responses to the proteasome inhibitor bortezomib (Btz) by increasing: i) killing of human MM cells by stimulating both Btz-mediated apoptosis and necroptosis, a process regulated by p62; and ii) preservation of bone mass by stimulating osteoblast differentiation and inhibiting osteoclastic bone destruction. Co-administration of Btz and XRK3F2 inhibited both branches of the bimodal N-end rule pathway exhibited synergistic anti-MM effects on MM cell lines and CD138+ cells from MM patients, and prevented stromal-mediated MM cell survival. In mice with established human MM, co-administration of Btz and XRK3F2 decreased tumor burden and prevented the progression of MM-induced osteolytic disease by inducing new bone formation more effectively than either single agent alone. The results suggest that p62-ZZ ligands enhance the anti- MM efficacy of proteasome inhibitors and can reduce MM morbidity and mortality by improving bone health.

Regulated cell death and its role in Alzheimer's disease and amyotrophic lateral sclerosis

Despite considerable research efforts, it is still not clear which mechanisms underlie neuronal cell death in neurodegenerative diseases. During the last 20 years, multiple pathways have been identified that can execute regulated cell death (RCD). Among these RCD pathways, apoptosis, necroptosis, pyroptosis, ferroptosis, autophagy-related cell death, and lysosome-dependent cell death have been intensively investigated. Although RCD consists of numerous individual pathways, multiple common proteins have been identified that allow shifting from one cell death pathway to another. Another layer of complexity is added by mechanisms such as the endosomal machinery, able to regulate the activation of some RCD pathways, preventing cell death. In addition, restricted axonal degeneration and synaptic pruning can occur as a result of RCD activation without loss of the cell body. RCD plays a complex role in neurodegenerative processes, varying across different disorders. It has been shown that RCD is differentially involved in Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), among the most common neurodegenerative diseases. In AD, neuronal loss is associated with the activation of not only necroptosis, but also pyroptosis. In ALS, on the other hand, motor neuron death is not linked to canonical necroptosis, whereas pyroptosis pathway activation is seen in white matter microglia. Despite these differences in the activation of RCD pathways in AD and ALS, the accumulation of protein aggregates immunoreactive for p62/SQSTM1 (sequestosome 1) is a common event in both diseases and many other neurodegenerative disorders. In this review, we describe the major RCD pathways with clear activation in AD and ALS, the main interactions between these pathways, as well as their differential and similar involvement in these disorders. Finally, we will discuss targeting RCD as an innovative therapeutic concept for neurodegenerative diseases, such as AD and ALS. Considering that the execution of RCD or "cellular suicide" represents the final stage in neurodegeneration, it seems crucial to prevent neuronal death in patients by targeting RCD. This would offer valuable time to address upstream events in the pathological cascade by keeping the neurons alive.

Photodynamic therapy reduces cell viability, migration and triggers necroptosis in prostate tumor cells

Prostate cancer is the most common cancer in American men, aside from skin cancer. As an alternative cancer treatment, photodynamic laser therapy (PDT) can be used to induce cell death. We evaluated the PDT effect, using methylene blue as a photosensitizer, in human prostate tumor cells (PC3). PC3 were subjected to four different conditions: DMEM (control); laser treatment (L-660 nm, 100 mW, 100 J.cm^-2); methylene blue treatment (MB-25 μM, 30 min), and MB treatment followed by low-level red laser irradiation (MB-PDT). Groups were evaluated after 24 h. MB-PDT treatment reduced cell viability and migration. However, because MB-PDT did not significantly increase the levels of active caspase-3 and BCL-2, apoptosis was not the primary mode of cell death. MB-PDT, on the other hand, increased the acid compartment by 100% and the LC3 immunofluorescence (an autophagy marker) by 254%. Active MLKL level, a necroptosis marker, was higher in PC3 cells after MB-PDT treatment. Furthermore, MB-PDT resulted in oxidative stress due to a decrease in total antioxidant potential, catalase levels, and increased lipid peroxidation. According to these findings, MB-PDT therapy is effective at inducing oxidative stress and reducing PC3 cell viability. In such therapy, necroptosis is also an important mechanism of cell death triggered by autophagy.

Cardiac Glycosides as Autophagy Modulators

Drug repositioning is one of the leading strategies in modern therapeutic research. Instead of searching for completely novel substances and demanding studies of their biological effects, much attention has been paid to the evaluation of commonly used drugs, which could be utilized for more distinct indications than they have been approved for. Since treatment approaches for cancer, one of the most extensively studied diseases, have still been very limited, great effort has been made to find or repurpose novel anticancer therapeutics. One of these are cardiac glycosides, substances commonly used to treat congestive heart failure or various arrhythmias. Recently, the antitumor properties of cardiac glycosides have been discovered and, therefore, these compounds are being considered for anticancer therapy. Their mechanism of antitumor action seems to be rather complex and not fully uncovered yet, however, autophagy has been confirmed to play a key role in this process. In this review article, we report on the up-to-date knowledge of the anticancer activity of cardiac glycosides with special attention paid to autophagy induction, the molecular mechanisms of this process, and the potential employment of this phenomenon in clinical practice.

Induction of Autophagy to Achieve a Human Immunodeficiency Virus Type 1 Cure

Effective antiretroviral therapy has led to significant human immunodeficiency virus type 1 (HIV-1) suppression and improvement in immune function. However, the persistence of integrated proviral DNA in latently infected reservoir cells, which drive viral rebound post-interruption of antiretroviral therapy, remains the major roadblock to a cure. Therefore, the targeted elimination or permanent silencing of this latently infected reservoir is a major focus of HIV-1 research. The most studied approach in the development of a cure is the activation of HIV-1 expression to expose latently infected cells for immune clearance while inducing HIV-1 cytotoxicity—the “kick and kill” approach. However, the complex and highly heterogeneous nature of the latent reservoir, combined with the failure of clinical trials to reduce the reservoir size casts doubt on the feasibility of this approach. This concern that total elimination of HIV-1 from the body may not be possible has led to increased emphasis on a “functional cure” where the virus remains but is unable to reactivate which presents the challenge of permanently silencing transcription of HIV-1 for prolonged drug-free remission—a “block and lock” approach. In this review, we discuss the interaction of HIV-1 and autophagy, and the exploitation of autophagy to kill selectively HIV-1 latently infected cells as part of a cure strategy. The cure strategy proposed has the advantage of significantly decreasing the size of the HIV-1 reservoir that can contribute to a functional cure and when optimised has the potential to eradicate completely HIV-1.

Targeting necroptosis as therapeutic potential in chronic myocardial infarction

Cardiovascular diseases (CVDs) are considered the predominant cause of morbidity and mortality globally. Of these, myocardial infarction (MI) is the most common cause of CVD mortality. MI is a life-threatening condition which occurs when coronary perfusion is interrupted leading to cardiomyocyte death. Subsequent to MI, consequences include adverse cardiac remodeling and cardiac dysfunction mainly contribute to the development of heart failure (HF). It has been shown that loss of functional cardiomyocytes in MI-induced HF are associated with several cell death pathways, in particular necroptosis. Although the entire mechanism underlying necroptosis in MI progression is still not widely recognized, some recent studies have reported beneficial effects of necroptosis inhibitors on cell viability and cardiac function in chronic MI models. Therefore, extensive investigation into the necroptosis signaling pathway is indicated for further study. This article comprehensively reviews the context of the underlying mechanisms of necroptosis in chronic MI-induced HF in in vitro, in vivo and clinical studies. These findings could inform ways of developing novel therapeutic strategies to improve the clinical outcomes in MI patients from this point forward.

Jia-Ji Electro-Acupuncture Improves Locomotor Function With Spinal Cord Injury by Regulation of Autophagy Flux and Inhibition of Necroptosis

Jia-Ji electro-acupuncture (EA) has been widely applied in clinic to exhibit curative effects on spinal cord injury (SCI). However, its underlying mechanisms leading to improvement of motor function after SCI remain unclear. Allen’s method was made by NYU Impactor M-III equipment to create the SCI rats model. Rats were randomly divided into four groups: Sham (only laminectomy), Model (SCI group), EA (SCI + Jia-Ji EA treatment), EA + CQ (SCI + Jia-Ji EA treatment + inhibitor chloroquine). Basso-Beattie-Bresnahan assessment showed improvement of hind limb motor function after Jia-Ji electro-acupuncture treatment. Histological change of injured spinal cord tissue was alleviated after treatment, observed by hematoxylin-eosin and Nissl staining. The mRNA and protein expression levels of RIPK1, RIPK3 and MLKL were decreased in EA group. Besides, the increased expression of LC3 and reduced expression of P62 after treatment compared with Model group, confirmed that Jia-Ji electro-acupuncture could enhance the autophagy flux. Electron microscopy imaging showed increasing the number of lysosomes, autophagosomes, and autolysosomes after Jia-Ji electro-acupuncture treatment. Furthermore, inhibition of lysosome function with CQ led to partly eliminate the effect of EA on reducing necroptosis. These data make the case that Jia-Ji electro-acupuncture treatment may improve locomotor function by promoting autophagy flux and inhibiting necroptosis.

Acid Sphingomyelinase Inhibition Attenuates Cell Death in Mechanically Ventilated Newborn Rat Lung

RATIONALE

Premature infants subjected to mechanical ventilation (MV) are prone to lung injury that may result in bronchopulmonary dysplasia. MV causes epithelial cell death and halts alveolar development. The exact mechanism of MV-induced epithelial cell death is unknown.

OBJECTIVES

To determine the contribution of autophagy to MV-induced epithelial cell death in newborn rat lungs.

METHODS

Newborn rat lungs and fetal rat lung epithelial (FRLE) cells were exposed to MV and cyclic stretch, respectively, and were then analyzed by immunoblotting and mass spectrometry for autophagy, apoptosis, and bioactive sphingolipids.

MEASUREMENTS AND MAIN RESULTS

Both MV and stretch first induce autophagy (ATG 5-12 [autophagy related 5-12] and LC3B-II [microtubule-associated proteins 1A/1B light chain 3B-II] formation) followed by extrinsic apoptosis (cleaved CASP8/3 [caspase-8/3] and PARP [poly(ADP-ribose) polymerase] formation). Stretch-induced apoptosis was attenuated by inhibiting autophagy. Coimmunoprecipitation revealed that stretch promoted an interaction between LC3B and the FAS (first apoptosis signal) cell death receptor in FRLE cells. Ceramide levels, in particular C16 ceramide, were rapidly elevated in response to ventilation and stretch, and C16 ceramide treatment of FRLE cells induced autophagy and apoptosis in a temporal pattern similar to that seen with MV and stretch. SMPD1 (sphingomyelin phosphodiesterase 1) was activated by ventilation and stretch, and its inhibition prevented ceramide production, LC3B-II formation, LC3B/first apoptosis signal interaction, caspase-3 activation, and, ultimately, FLRE cell death. SMPD1 inhibition also attenuated ventilation-induced autophagy and apoptosis in newborn rats.

CONCLUSIONS

Ventilation-induced ceramides promote autophagy-mediated cell death, and identifies SMPD1 as a potential therapeutic target for the treatment of ventilation-induced lung injury in newborns.

S‑allyl‑cysteine sulfoxide (alliin) alleviates myocardial infarction by modulating cardiomyocyte necroptosis and autophagy

S-allyl-cysteine sulfoxide (alliin) is the main organosulfur component of garlic and its preparations. The present study aimed to examine the protective effect of alliin on cardiac function and the underlying mechanism in a mouse model of myocardial infarction (MI). Notably, alliin treatment preserved heart function, attenuated the area of infarction in the myocardium of mice and reduced lesions in the myocardium, including cardiomyocyte fibrosis and death. Further mechanistic experiments revealed that alliin inhibited necroptosis but promoted autophagy in vitro and in vivo. Cell viability assays showed that alliin dose-dependently reduced the necroptotic index and inhibited the expression of necroptosis-related receptor-interacting protein 1, receptor-interacting protein 3 and tumor necrosis factor receptor-associated factor 2, whereas the levels of Beclin 1 and microtubule-associated protein 1 light chain 3, which are associated with autophagy, exhibited an opposite trend upon treatment with alliin. In addition, the level of peroxisome proliferator-activated receptor γ was increased by alliin. Collectively, these findings demonstrate that alliin has the potential to protect cardiomyocytes from necroptosis following MI and that this protective effect occurs via the enhancement of autophagy.

Valproate augments Niraparib killing of tumor cells

PARP1 inhibitors are approved therapeutic agents in ovarian carcinomas, and have clinical activity in some breast cancers. As a single agent, niraparib killed ovarian and mammary tumor cells via an ATM-AMPK-ULK1 pathway which resulted in mTOR inactivation and the formation of autophagosomes, temporally followed by autolysosome formation. In parallel, niraparib activated a CD95-FADD-caspase 8 pathway, and collectively these signals caused tumor cell death that was suppressed by knock down of Beclin1, ATG5, CD95, FADD or AIF; or by expression of c-FLIP-s, BCL-XL or dominant negative caspase 9. The HDAC inhibitors AR42 and sodium valproate enhanced niraparib lethality in a greater than additive fashion. HDAC inhibitors enhanced niraparib lethality by increasing activation of the ATM-AMPK-ULK1-autophagy and CD95-FADD-caspase 8 pathways. Knock down of eIF2α, ATM, AMPKα, ULK1, Beclin1 or ATG5 reduced tumor cell killing by the niraparib plus HDAC inhibitor combination. Blockade of either caspase 9 function or that of cathepsin B partially prevented cell death. As a single agent niraparib delayed tumor growth, but did not significantly alter the tumor control rate. Tumors previously exposed to niraparib had activated the ERK1/2 and AKT-mTOR pathways that correlated with increased plasma levels of IL-8, MIF, EGF, uPA and IL-12. Collectively our findings argue that the addition of HDAC inhibitors to niraparib enhances the anti-cancer activity of the PARP1 inhibitor niraparib.