Caspase-8 Regulates Endoplasmic Reticulum Stress-Induced Necroptosis Independent of the Apoptosis Pathway in Auditory Cells

Organellophagy regulates cell death:A potential therapeutic target for inflammatory diseases

BACKGROUND

Dysregulated alterations in organelle structure and function have a significant connection with cell death, as well as the occurrence and development of inflammatory diseases. Maintaining cell viability and inhibiting the release of inflammatory cytokines are essential measures to treat inflammatory diseases. Recently, many studies have showed that autophagy selectively targets dysfunctional organelles, thereby sustaining the functional stability of organelles, alleviating the release of multiple cytokines, and maintaining organismal homeostasis. Organellophagy dysfunction is critically engaged in different kinds of cell death and inflammatory diseases.

AIM OF REVIEW

We summarized the current knowledge of organellophagy (e.g., mitophagy, reticulophagy, golgiphagy, lysophagy, pexophagy, nucleophagy, and ribophagy) and the underlying mechanisms by which organellophagy regulates cell death.

KEY SCIENTIFIC CONCEPTS OF REVIEW

We outlined the potential role of organellophagy in the modulation of cell fate during the inflammatory response to develop an intervention strategy for the organelle quality control in inflammatory diseases.

Endoplasmic reticulum stress-induced necroptosis promotes cochlear inflammation: Implications for age-related hearing loss

Age-related hearing loss (ARHL) is the most common sensory disorder associated with human aging. Chronic inflammation is supposed to be an important contributor to ARHL. Yet, the underlying mechanisms of developing cochlear inflammation are still not well understood. In this study, we found that the inflammation, endoplasmic reticulum (ER) stress and necroptosis signalings are activated in the cochlea of aged C57BL/6 mice. ER stress activator tunicamycin (TM) induced necroptosis in cochlear HEI-OC1 cells and cochlear explants, while necroptosis inhibitors protected cochlear cells from ER stress-induced cell death. The antioxidants inhibited necroptosis and protected HEI-OC1 cells from TM insults. Necroptotic HEI-OC1 cells promoted the activation of the co-cultured macrophages via Myd88 signaling. Moreover, necroptosis inhibitor protected from TM-induced hearing loss, and inhibited inflammation in C57BL/6 mice. These findings suggest that ER stress-induced necroptosis promotes cochlear inflammation and hearing loss. Targeting necroptosis serves as a potential approach for the treatment of cochlear inflammation and ARHL.

Exosomal microRNAs in regulation of tumor cells resistance to apoptosis

Exosomes are a type of extracellular vesicle that contains bioactive molecules that can be secreted by most cells. Nevertheless, the content of these cells differs depending on the cell from which they originate. The exosome plays a crucial role in modulating intercellular communication by conveying molecular messages to neighboring or distant cells. Cancer-derived exosomes can transfer several types of molecules into the tumor microenvironment, including high levels of microRNA (miRNA). These miRNAs significantly affect cell proliferation, angiogenesis, apoptosis resistance, metastasis, and immune evasion. Increasing evidence indicates that exosomal miRNAs (exomiRs) are crucial to regulating cancer resistance to apoptosis. In cancer cells, exomiRs orchestrate communication channels between them and their surrounding microenvironment, modulating gene expression and controlling apoptosis signaling pathways. This review presents an outline of present-day knowledge of the mechanisms that affect target cells and drive cancer resistance to apoptosis. Also, our study looks at the regulatory role of exomiRs in mediating intercellular communication between tumor cells and surrounding microenvironmental cells, specifically stromal and immune cells, to evade therapy-induced apoptosis.

Endoplasmic Reticulum Stress Disrupts Mitochondrial Bioenergetics, Dynamics and Causes Corneal Endothelial Cell Apoptosis

Purpose

Endoplasmic reticulum (ER) and mitochondrial stress are independently associated with corneal endothelial cell (CEnC) loss in many corneal diseases, including Fuchs' endothelial corneal dystrophy (FECD). However, the role of ER stress in mitochondrial dysfunction contributing to CEnC apoptosis is unknown. The purpose of this study is to explore the crosstalk between ER and mitochondrial stress in CEnC.

Methods

Human corneal endothelial cell line (HCEnC-21T) and human corneal endothelial tissues were treated with ER stressor tunicamycin. ER stress-reducing chemical 4-phenyl butyric acid (4-PBA) was used in HCEnC-21T after tunicamycin. Fuchs' corneal endothelial cell line (F35T) was used to determine differential activation of ER stress with respect to HCEnC-21T at the baseline. ER stress, mitochondrial-mediated intrinsic apoptotic, mitochondrial fission, and fusion proteins were determined using immunoblotting and immunohistochemistry. Mitochondrial bioenergetics were assessed by mitochondrial membrane potential (MMP) loss and ATP production at 48 hours after tunicamycin. Mitochondria dynamics (shape, area, perimeter) were also analyzed at 24 hours using transmission electron microscopy.

Results

Treatment of HCEnC-21T cell line with tunicamycin activated three ER stress pathways (PERK-eIF2α-CHOP, IRE1α-XBP1, and ATF6), reduced cell viability, upregulated mitochondrial-mediated intrinsic apoptotic molecules (cleaved caspase 9, caspase 3, PARP, Bax, cytochrome C), downregulated anti-apoptotic Bcl-2 protein, initiated mitochondrial dysfunction by loss of MMP and lowering of ATP production, and caused mitochondrial swelling and fragmentation with increased expression of mitochondrial fission proteins (Fis1 and p-Drp1). Fuchs' CEnC (F35T) cell line also showed activation of the ER stress-related proteins (p-eIF2α, GRP78, CHOP, XBP1) compared to HCEnC-21T at the baseline. The 4-PBA ameliorated cell loss and reduced cleaved caspase 3 and 9, thereby rescuing tunicamycin-induced cell death but not mitochondrial bioenergetics in HCEnC-21T cell line.

Conclusions

Tunicamycin-induced ER stress disrupts mitochondrial bioenegetics, dynamics and contributes to the loss of CEnC viability. This novel study highlights the importance of ER-mitochondria crosstalk and its contribution to CEnCs apoptosis, seen in many corneal diseases, including FECD.

Antagonistic effect of selenium on programmed necrosis of testicular Leydig cells caused by cadmium through endoplasmic reticulum stress in chicken

Cadmium (Cd) is a widely distributed environmental contaminant that is highly toxic to animals and humans. However, detailed reports on Cd-induced programmed necrosis have not been seen in chicken testicular Leydig cells. Selenium (Se) is a trace element in the human body that has cytoprotective effects in a variety of pathological damages caused by heavy metals. This study investigated the potential mechanisms of Cd-induced programmed cell necrosis and the antagonistic effect of Se on Cd toxicity. Chicken testis Leydig cells were divided into six groups, namely, control, Se (5 µmol/L Na2SeO3), Cd (20 µmol/L CdCl2), Se + Cd (5 µmol/L Na2SeO3 and 20 µmol/L CdCl2), 4-phenylbutyric acid (4-PBA) + Cd (10 mmol/L 4-phenylbutyric acid and 20 µmol/L CdCl2), and Necrostatin-1 (Nec-1) + Cd (60 µmol/L Necrostatin-1 and 20 µmol/L CdCl2). The results showed that Cd exposure decreased the activity of CAT, GSH-Px, and SOD and the concentration of GSH, and increased the concentration of MDA and the content of ROS. Relative mRNA and protein expression of GRP78, PERK, ATF6, IRE1, CHOP, and JNK increased in the Cd group, and mRNA and protein expression of TNF-α, TNFR1, RIP1, RIP3, MLKL, and PARP1 significantly increased in the Cd group, while Caspase-8 mRNA and protein expression significantly decreased. The abnormal expression of endoplasmic reticulum stress-related proteins was significantly reduced by 4-PBA pretreatment; the increased expression of TNF-α, TNFR1, RIP1, RIP3, MLKL, and PARP1 caused by Cd toxicity was alleviated; and the expression of caspase-8 was upregulated. Conversely, the increased mRNA and protein expression of endoplasmic reticulum stress marker genes (GRP78, ATF6, PERK, IRE1, CHOP, JNK) caused by Cd was not affected after pretreatment with Nec-1. We also found that these Cd-induced changes were significantly attenuated in the Se + Cd group. We clarified that Cd can cause programmed necrosis of chicken testicular Leydig cells through endoplasmic reticulum stress, and Se can antagonize Cd-induced programmed necrosis of chicken testicular Leydig cells.

The Unfolded Protein Response: A Double-Edged Sword for Brain Health

Efficient brain function requires as much as 20% of the total oxygen intake to support normal neuronal cell function. This level of oxygen usage, however, leads to the generation of free radicals, and thus can lead to oxidative stress and potentially to age-related cognitive decay and even neurodegenerative diseases. The regulation of this system requires a complex monitoring network to maintain proper oxygen homeostasis. Furthermore, the high content of mitochondria in the brain has elevated glucose demands, and thus requires a normal redox balance. Maintaining this is mediated by adaptive stress response pathways that permit cells to survive oxidative stress and to minimize cellular damage. These stress pathways rely on the proper function of the endoplasmic reticulum (ER) and the activation of the unfolded protein response (UPR), a cellular pathway responsible for normal ER function and cell survival. Interestingly, the UPR has two opposing signaling pathways, one that promotes cell survival and one that induces apoptosis. In this narrative review, we discuss the opposing roles of the UPR signaling pathways and how a better understanding of these stress pathways could potentially allow for the development of effective strategies to prevent age-related cognitive decay as well as treat neurodegenerative diseases.

Self-assembly nanoplatform of platinum (Ⅳ) prodrug for enhanced ovarian cancer therapy

Cisplatin is a metal platinum complex commonly used in the field of anti-tumor and one of the most commonly used drugs in combination chemotherapy. However, chemotherapy with Cisplatin induced overexpression of cyclooxygenase-2 (COX-2) protein in tumor cells, which could impair the therapeutic effect of chemotherapy on tumor progression. Here, we presented a novel method for the treatment of ovarian cancer with a self-assembly based nano-system. Cisplatin and tolfenamic acid were each linked to linoleic acid to give them the ability to self-assemble into nanoparticles in water. TPNPs had flexible drug ratio adjustability, homogeneous stability, and high drug loading capacity. Compared with Cisplatin, TPNPs could promote cellular uptake and tumor aggregation, co-induce enhanced apoptosis and tumor growth inhibition by inhibiting COX-2 in the mice xenograft model of human ovarian cancer, and reduce systemic toxicity. Therefore, TPNPs is a promising antitumor drug as a kind of self-assembly nano-prodrug with high drug load.

Cryptotanshinone induces apoptosis of activated hepatic stellate cells via modulating endoplasmic reticulum stress

BACKGROUND

Cryptotanshinone (CPT) has wide biological functions, including anti-oxidative, antifibrosis, and anti-inflammatory properties. However, the effect of CPT on hepatic fibrosis is unknown.

AIM

To investigate the effects of CPT treatment on hepatic fibrosis and its underlying mechanism of action.

METHODS

Hepatic stellate cells (HSCs) and normal hepatocytes were treated with different concentrations of CPT and salubrinal. The CCK-8 assay was used to determine cell viability. Flow cytometry was used to measure apoptosis and cell cycle arrest. Reverse transcription polymerase chain reaction (RT-PCR) and Western blot analyses were used to measure mRNA levels and protein expression of endoplasmic reticulum stress (ERS) signaling pathway related molecules, respectively. Carbon tetrachloride (CCL₄) was used to induce in vivo hepatic fibrosis in mice. Mice were treated with CPT and salubrinal, and blood and liver samples were collected for histopathological examination.

RESULTS

We found that CPT treatment significantly reduced fibrogenesis by modulating the synthesis and degradation of the extracellular matrix in vitro. CPT inhibited cell proliferation and induced cell cycle arrest at the G2/M phase in cultured HSCs. Furthermore, we found that CPT promoted apoptosis of activated HSCs by upregulating expression of ERS markers (CHOP and GRP78) and activating ERS pathway molecules (PERK, IRE1α, and ATF4), which were inhibited by salubrinal. Inhibition of ERS by salubrinal partially eliminated the therapeutic effect of CPT in our CCL₄-induced hepatic fibrosis mouse model.

CONCLUSION

CPT can promote apoptosis of HSCs and alleviate hepatic fibrosis through modulating the ERS pathway, which represents a promising strategy for treating hepatic fibrosis.

Interrelation between Programmed Cell Death and Immunogenic Cell Death: Take Antitumor Nanodrug as an Example

Programmed cell death (PCD, mainly including apoptosis, necrosis, ferroptosis, pyroptosis, and autophagy) and immunogenic cell death (ICD), as important cell death mechanisms, are widely reported in cancer therapy, and understanding the relationship between the two is significant for clinical tumor treatments. Considering that vast nanodrugs are developed to induce tumor PCD and ICD simultaneously, in this review, the interrelationship between PCD and ICD is described using nanomedicines as examples. First, an overview of PCD patterns and focus on the morphological differences and interconnections among them are provided. Then the interrelationship between apoptosis and ICD in terms of endoplasmic reticulum stress is described by introducing various cancer treatments and the recent developments of nanomedicines with inducible immunogenicity. Next, the crosstalk between non-apoptotic (including necrosis, ferroptosis, pyroptosis, and autophagy) signaling pathways and ICD is introduced and their relationship through various nanomedicines as examples is further illustrated. Finally, the relationship between PCD and ICD and its application prospects in the development of new ICD nanomaterials are summarized. This review is believed to deepen the understanding of the relationship between PCD and ICD, extend the biomedical applications of various nanodrugs, and promote the progress of clinical tumor therapy.

KW2449 ameliorates collagen-induced arthritis by inhibiting RIPK1-dependent necroptosis

Objective

Necroptosis has recently been found to be associated with the pathogenesis of many autoimmune diseases, including rheumatoid arthritis (RA). This study was undertaken to explore the role of RIPK1-dependent necroptosis in the pathogenesis of RA and the potential new treatment options.

Methods

The plasma levels of receptor-interacting protein kinase 1 (RIPK1) and mixed lineage kinase domain-like pseudokinase (MLKL) in 23 controls and 42 RA patients were detected by ELISA. Collagen-induced arthritis (CIA) rats were treated with KW2449 by gavage for 28 days. Arthritis index score, H&E staining, and Micro-CT analysis were used to evaluate joint inflammation. The levels of RIPK1-dependent necroptosis related proteins and inflammatory cytokines were detected by qRT-PCR, ELISA and Western blot, and the cell death morphology was detected by flow cytometry analysis and high-content imaging analysis.

Results

The plasma levels of RIPK1 and MLKL in RA patients were higher than those in healthy people, and were positively correlated with the severity of RA. KW2449 could reduce joint swelling, joint bone destruction, tissue damage, and the plasma levels of inflammatory cytokines in CIA rats. Lipopolysaccharide combined with zVAD (LZ) could induce necroptosis in RAW 264.7 cells, which could be reduced by KW2449. RIPK1-dependent necroptosis related proteins and inflammatory factors increased after LZ induction and decreased after KW2449 treatment or knockdown of RIPK1.

Conclusion

These findings suggest that the overexpression of RIPK1 is positively correlated with the severity of RA. KW2449, as a small molecule inhibitor targeting RIPK1, has the potential to be a therapeutic strategy for RA treatment by inhibiting RIPK1-dependent necroptosis.

Cannabidiol regulates apoptosis and autophagy in inflammation and cancer: A review

Cannabidiol (CBD) is a terpenoid naturally found in plants. The purified compound is used in the treatment of mental disorders because of its antidepressive, anxiolytic, and antiepileptic effects. CBD can affect the regulation of several pathophysiologic processes, including autophagy, cytokine secretion, apoptosis, and innate and adaptive immune responses. However, several authors have reported contradictory findings concerning the magnitude and direction of CBD-mediated effects. For example, CBD treatment can increase, decrease, or have no significant effect on autophagy and apoptosis. These variable results can be attributed to the differences in the biological models, cell types, and CBD concentration used in these studies. This review focuses on the mechanism of regulation of autophagy and apoptosis in inflammatory response and cancer by CBD. Further, we broadly elaborated on the prospects of using CBD as an anti-inflammatory agent and in cancer therapy in the future.

The Role of the Hypoxia-Related Unfolded Protein Response (UPR) in the Tumor Microenvironment

Despite our understanding of the unfolded protein response (UPR) pathways, the crosstalk between the UPR and the complex signaling networks that different cancers utilize for cell survival remains to be, in most cases, a difficult research barrier. A major problem is the constant variability of different cancer types and the different stages of cancer as well as the complexity of the tumor microenvironments (TME). This complexity often leads to apparently contradictory results. Furthermore, the majority of the studies that have been conducted have utilized two-dimensional in vitro cultures of cancer cells that were exposed to continuous hypoxia, and this approach may not mimic the dynamic and cyclic conditions that are found in solid tumors. Here, we discuss the role of intermittent hypoxia, one of inducers of the UPR in the cellular component of TME, and the way in which intermittent hypoxia induces high levels of reactive oxygen species, the activation of the UPR, and the way in which cancer cells modulate the UPR to aid in their survival. Although the past decade has resulted in defining the complex, novel non-coding RNA-based regulatory networks that modulate the means by which hypoxia influences the UPR, we are now just to beginning to understand some of the connections between hypoxia, the UPR, and the TME.

Comparing the Anticancer Activities of Green-Synthesized Ginsenoside and Transformed Ginsenoside Nanoconjugates (Ag, Au, and Pt)

Aim: To assess the anticancer activity of nanoparticles synthesized via a green method using American ginseng (AG). Methods: Stem-leaf saponins from AG (SAG) and heat-transformed stem-leaf saponins from AG (TSAG) were used to synthesize different SAG nanoparticles (SAG-NPs) and TSAG nanoparticles (TSAG-NPs). The NPs were characterized, and their anticancer activity was assessed in vitro. Results: The NPs, which differed in size (16.69 nm∼253.8 nm), were spherical or polyhedral with a low PDI and good stability. The TSAG-NPs inhibited cancer cells by inhibiting proliferation, promoting cancer cell apoptosis and directly leading cancer cells to necrosis. The small cell lung cancer cell line (SCLC) NCI-H446 was the most sensitive to the TSAG-AgNPs, with an IC50 value of 20.71±2.38 μg/mL, and the TSAG-AgNPs inhibited invasiveness and reduced the risk of metastasis. Conclusion: TSAG-AgNPs, selected from many SAG-NPs and TSAG-NPs, are sensitive to SCLC and provide a new approach to the currently limited treatment.

Curcumol alleviates liver fibrosis by inducing endoplasmic reticulum stress-mediated necroptosis of hepatic stellate cells through Sirt1/NICD pathway

Liver fibrosis is a repair response process after chronic liver injury. During this process, activated hepatic stellate cells (HSCs) will migrate to the injury site and secrete extracellular matrix (ECM) to produce fibrous scars. Clearing activated HSCs may be a major strategy for the treatment of liver fibrosis. Curcumol isolated from plants of the genus Curcuma can effectively induce apoptosis of many cancer cells, but whether it can clear activated HSCs remains to be clarified. In the present study, we found that the effect of curcumol in treating liver fibrosis was to clear activated HSCs by inducing necroptosis of HSCs. Receptor-interacting protein kinase 3 (RIP3) silencing could impair necroptosis induced by curcumol. Interestingly, endoplasmic reticulum (ER) stress-induced cellular dysfunction was associated with curcumol-induced cell death. The ER stress inhibitor 4-PBA prevented curcumol-induced ER stress and necroptosis. We proved that ER stress regulated curcumol-induced necroptosis in HSCs via Sirtuin-1(Sirt1)/Notch signaling pathway. Sirt1-mediated deacetylation of the intracellular domain of Notch (NICD) led to degradation of NICD, thereby inhibiting Notch signalling pathway to alleviate liver fibrosis. Specific knockdown of Sirt1 by HSCs in male ICR mice further exacerbated CCl₄-induced liver fibrosis. Overall, our study elucidates the anti-fibrotic effect of curcumol and reveals the underlying mechanism between ER stress and necroptosis.

Diverse Cell Death Mechanisms Are Simultaneously Activated in Macrophages Infected by Virulent Mycobacterium tuberculosis

Macrophages are necessary to eliminate pathogens. However, some pathogens have developed mechanisms to avoid the immune response. One of them is modulating the cell death mechanism to favor pathogen survival. In this study, we evaluated if virulent Mycobacterium tuberculosis (M. tb) can simultaneously activate more than one cell death mechanism. We infected human monocyte-derived macrophages (MDM) in vitro with avirulent (H37Ra) and virulent (H37Rv) strains, and then we measured molecules involved in apoptosis, necroptosis, and pyroptosis. Our data showed that H37Rv infection increased the BCL-2 transcript and protein, decreased the BAX transcript, and increased phosphorylated BCL-2 at the protein level. Moreover, H37Rv infection increased the expression of the molecules involved in the necroptotic pathway, such as ASK1, p-38, RIPK1, RIPK3, and caspase-8, while H37Ra increased caspase-8 and decreased RIPK3 at the transcriptional level. In addition, NLRP3 and CASP1 expression was increased at low MOI in both strains, while IL-1β was independent of virulence but dependent on infection MOI, suggesting the activation of pyroptosis. These findings suggest that virulent M. tb inhibits the apoptosis mediated by BCL-2 family molecules but, at the same time, increases the expression of molecules involved in apoptosis, necroptosis, and pyroptosis at the transcriptional and protein levels, probably as a mechanism to avoid the immune response and guarantee its survival.

Activation of endoplasmic reticulum-mitochondria coupling drives copper-induced autophagy in duck renal tubular epithelial cells

Copper (Cu) as a transition metal can be toxic to public and ecosystem health at high level, but the specific mechanism of Cu-evoked nephrotoxicity remains elusive. Here, we first revealed the crosstalk between mitofusin2 (Mfn2)-dependent mitochondria-associated endoplasmic reticulum membrane (MAM) dynamics and autophagy in duck renal tubular epithelial cells under Cu exposure. Primary duck renal tubular epithelial cells were treated with 100 and 200 μM Cu sulfate for 12 h and exposed to lentivirus to deliver mitofusin2 (Mfn2). We found that excessive Cu disrupted MAM integrity, decreased the mitochondrial calcium level, co-localization of IP3R and VDAC1, the mRNA levels of PACS2, Mfn2, IP3R and MCU, and Mfn2 and VDAC1 protein levels, causing MAM dysfunction. Furthermore, Mfn2 overexpression ameliorated Cu-induced MAM dysfunction, and increased Cu-evoked autophagy in duck renal tubular epithelial cells accompanied with the elevation of autophagosomes number, ROS level, LC3 puncta, Atg5 and LC3B mRNA levels, and Beclin1, Atg14, LC3BII/LC3BI protein levels. Accordingly, our data proved that excessive Cu could trigger MAM dysfunction and autophagy in duck renal tubular epithelial cells, and Cu-induced autophagy could be activated through Mfn2-dependent MAM, providing evidence on the toxicological exploration mechanisms of Cu.

Downregulation of RIP3 Improves the Protective Effect of ATF6 in an Acute Liver Injury Model

Background

Activating transcription factor 6 (ATF6) and receptor-interacting protein 3 (RIP3) are important signaling proteins in endoplasmic reticulum (ER) stress and necroptosis, respectively. However, their regulatory relationship and clinical significance are unknown. We investigate the impact of ATF6 on RIP3 expression, and its role in hepatocyte necroptosis in an acute liver injury model.

Methods

In vivo and in vitro experiments were carried out. LO2 cells were treated with thapsigargin (TG). In vivo, male BALB/c mice were treated with carbon tetrachloride (CCl₄, 1 mL/kg) or tunicamycin (TM, 2 mg/kg). Then, the impact of ATF6 or RIP3 silencing on liver injury, hepatocyte necroptosis, and ER stress-related protein expression was examined.

Results

TG induced ER stress and necroptosis and ATF6 and RIP3 expression in LO2 cells. The knockdown of ATF6 significantly decreased RIP3 expression (p < 0.05) and increased ER stress and necroptosis. The downregulation of RIP3 significantly reduced necroptosis and ER stress (p < 0.05). Similar results were observed in CCl₄ or the TM-induced mouse model. The knockdown of ATF6 significantly decreased CCl₄-induced RIP3 expression and increased liver injury, necroptosis, and ER stress in mice livers (p < 0.05). In contrast, the downregulation of RIP3 significantly reduced liver injury, hepatocyte necroptosis, and ER stress.

Conclusions

Hepatocyte ATF6 has multiple roles in acute liver injury. It reduces hepatocyte necroptosis via negative feedback regulation of ER stress. In addition, ATF6 can upregulate the expression of RIP3, which is not helpful to the recovery process. However, downregulating RIP3 reduces hepatocyte necroptosis by promoting the alleviation of ER stress. The findings suggest that RIP3 could be a plausible target for the treatment of liver injury.

Necroptosis in Pulmonary Diseases: A New Therapeutic Target

In the past decades, apoptosis has been the most well-studied regulated cell death (RCD) that has essential functions in tissue homeostasis throughout life. However, a novel form of RCD called necroptosis, which requires receptor-interacting protein kinase-3 (RIPK3) and mixed-lineage kinase domain-like pseudokinase (MLKL), has recently been receiving increasing scientific attention. The phosphorylation of RIPK3 enables the recruitment and phosphorylation of MLKL, which oligomerizes and translocates to the plasma membranes, ultimately leading to plasma membrane rupture and cell death. Although apoptosis elicits no inflammatory responses, necroptosis triggers inflammation or causes an innate immune response to protect the body through the release of damage-associated molecular patterns (DAMPs). Increasing evidence now suggests that necroptosis is implicated in the pathogenesis of several human diseases such as systemic inflammation, respiratory diseases, cardiovascular diseases, neurodegenerative diseases, neurological diseases, and cancer. This review summarizes the emerging insights of necroptosis and its contribution toward the pathogenesis of lung diseases.

The latest information on the RIPK1 post-translational modifications and functions

RIPK1 is a protein kinase that simultaneously regulates inflammation, apoptosis, and necroptosis. It is thought that RIPK1 has separate functions through its scaffold structure and kinase domains. Moreover, different post-translational modifications in RIPK1 play distinct or even opposing roles. Under different conditions, in different cells and species, and/or upon exposure to different stimuli, infections, and substrates, RIPK1 activation can lead to diverse results. Despite continuous research, many of the conclusions that have been drawn regarding the complex interactions of RIPK1 are controversial. This review is based on an examination and analysis of recent studies on the RIPK1 structure, post-translational modifications, and activation conditions, which can affect its functions. Finally, because of the diverse functions of RIPK1 and their relevance to the pathogenesis of many diseases, we briefly introduce the roles of RIPK1 in inflammatory and autoimmune diseases and the prospects of its use in future diagnostics and treatments.

Pyroptosis: A New Regulating Mechanism in Cardiovascular Disease

Pyroptosis is a kind of pro-inflammatory cell death. Compared with autophagy and apoptosis, pyroptosis has unique characteristics in morphology and mechanism. Specifically, pyroptosis is a kind of cell lysis mediated by the Gasdermin family, releases inflammatory cytokines IL-1β and IL-18. There are three different forms of mechanism, which are caspase-1-mediated, caspase-4/5/11-mediated and caspase-3-mediated. A large number of studies have proved that pyroptosis is closely related to cardiovascular disease. This paper reviewed the recent progress in the related research on pyroptosis and myocardial infarction, ischemia-reperfusion, atherosclerosis, diabetic cardiomyopathy, arrhythmia, heart failure hypertension and Kawasaki disease. Therefore, we believe that pyroptosis may be a new therapeutic target in the cardiovascular field.

Modulation of vigabatrin induced cerebellar injury: the role of caspase-3 and RIPK1/RIPK3-regulated cell death pathways

Vigabatrin is the drug of choice in resistant epilepsy and infantile spasms. Ataxia, tremors, and abnormal gait have been frequently reported following its use indicating cerebellar involvement. This study aimed, for the first time, to investigate the involvement of necroptosis and apoptosis in the VG-induced cerebellar cell loss and the possible protective role of combined omega-3 and vitamin B12 supplementation. Fifty Sprague-Dawley adult male rats (160-200 g) were divided into equal five groups: the control group received normal saline, VG200 and VG400 groups received VG (200 mg or 400 mg/kg, respectively), VG200 + OB and VG400 + OB groups received combined VG (200 mg or 400 mg/kg, respectively), vitamin B12 (1 mg/kg), and omega-3 (1 g/kg). All medications were given daily by gavage for four weeks. Histopathological changes were examined in H&E and luxol fast blue (LFB) stained sections. Immunohistochemical staining for caspase-3 and receptor-interacting serine/threonine-protein kinase-1 (RIPK1) as well as quantitative real-time polymerase chain reaction (qRT-PCR) for myelin basic protein (MBP), caspase-3, and receptor-interacting serine/threonine-protein kinase-3 (RIPK3) genes were performed. VG caused a decrease in the granular layer thickness and Purkinje cell number, vacuolations, demyelination, suppression of MBP gene expression, and induction of caspases-3, RIPK1, and RIPK3 in a dose-related manner. Combined supplementation with B12 and omega-3 improved the cerebellar histology, increased MBP, and decreased apoptotic and necroptotic markers. In conclusion, VG-induced neuronal cell loss is dose-dependent and related to both apoptosis and necroptosis. This could either be ameliorated (in low-dose VG) or reduced (in high-dose VG) by combined supplementation with B12 and omega-3.

Obinutuzumab in Combination with Chemotherapy Enhances Direct Cell Death in CD20-Positive Obinutuzumab-resistant Non-Hodgkin Lymphoma Cells

Follicular lymphoma commonly recurs and is difficult to cure. Obinutuzumab is a humanized glycoengineered type II anti-CD20 antibody with a mode of action that includes induction of antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis, and direct cell death. There is no evidence on the effectiveness of retreatment with obinutuzumab in patients with prior obinutuzumab treatment. Using obinutuzumab-induced direct-cell-death-resistant cells, we investigated the efficacy of obinutuzumab retreatment in combination with chemotherapeutic agents used in follicular lymphoma treatment. Human non-Hodgkin lymphoma SU-DHL-4 cells were sustainably exposed to obinutuzumab in vitro, and 17 resistant clones expressing CD20 and showing 100-fold higher IC₅₀ of obinutuzumab than parental cells were established. The growth inhibition effect of obinutuzumab in combination with bendamustine, 4-hydroperoxy-cyclophosphamide, doxorubicin, vincristine, or prednisolone was estimated using an interaction index based on the Bliss independence model. For each clone, there were various combinations of obinutuzumab and chemotherapeutic agents that showed supra-additive effects. Obinutuzumab combined with doxorubicin enhanced caspase-dependent apoptosis and growth inhibition effect. Obinutuzumab combined with prednisolone enhanced DNA fragmentation and G₀-G₁ arrest. These combinations also had an antitumor effect in mouse xenograft models. Our results indicate that retreatment with obinutuzumab, when it is combined with chemotherapeutic agents, is effective in the CD20-positive obinutuzumab-induced direct-cell-death-resistant cells.

Endoplasmic reticulum stress aggravates copper-induced apoptosis via the PERK/ATF4/CHOP signaling pathway in duck renal tubular epithelial cells

Copper (Cu) is a vital micronutrient required for numerous fundamental biological processes, but excessive Cu poses potential detrimental effects on public and ecosystem health. However, the molecular details linking endoplasmic reticulum (ER) stress and apoptosis in duck renal tubular epithelial cells have not been fully elucidated. In this study, duck renal tubular epithelial cells exposed to Cu sulfate (CuSO₄) (0, 100 and 200 μM) and a PERK inhibitor (GSK2606414, GSK, 1 μM) for 12 h were used to investigate the crosstalk between ER stress and apoptosis under Cu exposure. Cell and ER morphological and functional characteristics, intracellular calcium (Ca²⁺) levels, apoptotic rates, ER stress and apoptosis-related mRNA and protein levels were examined. The results showed that excessive Cu could cause ER expansion and swelling, increase the expression levels of ER stress-associated genes (PERK, eIF2α, ATF4 and CHOP) and proteins (p-PERK and CHOP), induce intracellular Ca²⁺ overload, upregulate the expression levels of apoptosis-associated genes (Bax, Bak1, Caspase9 and Caspase3) and the cleaved-Caspase3 protein, downregulate Bcl-xl and Bcl2 mRNA levels and trigger apoptosis. PERK inhibitor treatment could ameliorate the above changed factors caused by Cu. In conclusion, these findings indicate that excessive Cu could trigger ER stress via activation of the PERK/ATF4/CHOP signaling pathway and that ER stress might aggravate Cu-induced apoptosis in duck renal tubular epithelial cells.

MicroRNA and ER stress in cancer

The development of biological technologies in genomics, proteomics, and bioinformatics has led to the identification and characterization of the complete set of coding genes and their roles in various cellular pathways in cancer. Nevertheless, the cellular pathways have not been fully figured out like a jigsaw puzzle with missing pieces. The discovery of noncoding RNAs including microRNAs (miRNAs) has provided the missing pieces of the cellular pathways. Likewise, miRNAs have settled many questions of inexplicable patches in the endoplasmic reticulum (ER) stress pathways. The ER stress-caused pathways typified by the unfolded protein response (UPR) are pivotal processes for cellular homeostasis and survival, rectifying uncontrolled proteostasis and determining the cell fate. Although various factors and pathways have been studied and characterized, the understanding of the ER stress requires more wedges to fill the cracks of knowledge about the ER stress pathways. Moreover, the roles of the ER stress and UPR are still controversial in cancer despite their strong potential to promote cancer. The noncoding RNAs, in particular, miRNAs aid in a better understanding of the ER stress and its role in cancer. In this review, miRNAs that are the more-investigated subtype of noncoding RNAs are focused on the interpretation of the ER stress in cancer, following the introduction of miRNA and ER stress.

Impact of Endoplasmic Reticulum Stress in Otorhinolaryngologic Diseases

The endoplasmic reticulum (ER) is an important organelle for normal cellular function and homeostasis in most living things. ER stress, which impairs ER function, occurs when the ER is overwhelmed by newly introduced immature proteins or when calcium in the ER is depleted. A number of diseases are associated with ER stress, including otorhinolaryngological diseases. The relationship between ER stress and otorhinolaryngologic conditions has been the subject of investigation over the last decade. Among otologic diseases associated with ER stress are otitis media and hearing loss. In rhinologic diseases, chronic rhinosinusitis, allergic rhinitis, and obstructive sleep apnea are also significantly associated with ER stress. In this review, we provide a comprehensive overview of the relationship between ER stress and otorhinolaryngological diseases, focusing on the current state of knowledge and mechanisms that link ER stress and otorhinolaryngologic diseases.

Unfolded protein response (UPR) integrated signaling networks determine cell fate during hypoxia

During hypoxic conditions, cells undergo critical adaptive responses that include the up-regulation of hypoxia-inducible proteins (HIFs) and the induction of the unfolded protein response (UPR). While their induced signaling pathways have many distinct targets, there are some important connections as well. Despite the extensive studies on both of these signaling pathways, the exact mechanisms involved that determine survival versus apoptosis remain largely unexplained and therefore beyond therapeutic control. Here we discuss the complex relationship between the HIF and UPR signaling pathways and the importance of understanding how these pathways differ between normal and cancer cell models.

TRAIL receptor signaling: From the basics of canonical signal transduction toward its entanglement with ER stress and the unfolded protein response

The cytokine tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the large TNF superfamily that can trigger apoptosis in transformed or infected cells by binding and activating two receptors, TRAIL receptor 1 (TRAILR1) and TRAIL receptor 2 (TRAILR2). Compared to other death ligands of the same family, TRAIL induces apoptosis preferentially in malignant cells while sparing normal tissue and has therefore been extensively investigated for its suitability as an anti-cancer agent. Recently, it was noticed that TRAIL receptor signaling is also linked to endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). The role of TRAIL receptors in regulating cellular apoptosis susceptibility therefore is broader than previously thought. Here, we provide an overview of TRAIL-induced signaling, covering the core signal transduction during extrinsic apoptosis as well as its link to alternative outcomes, such as necroptosis or NF-κB activation. We discuss how environmental factors, transcriptional regulators, and genetic or epigenetic alterations regulate TRAIL receptors and thus alter cellular TRAIL susceptibility. Finally, we provide insight into the role of TRAIL receptors in signaling scenarios that engage the unfolded protein response and discuss how these findings might be translated into new combination therapies for cancer treatment.