TRAIL Receptors Serve as Stress-Associated Molecular Patterns to Promote ER-Stress-Induced Inflammation

Endoplasmic reticulum stress: A key player in immune cell regulation and autoimmune disorders

The endoplasmic reticulum (ER) is a large organelle, found in all eukaryotes, that is essential for normal cellular function. This function encompasses protein folding and quality control, post-translational modifications, lipid regulation, and the storage of intracellular calcium, among others. These diverse processes are essential for maintaining proteome stability. Therefore, a robust surveillance system is established under stress to ensure cell homeostasis. Sources of stress can originate from the cellular environment, including nutrient deprivation, hypoxia, and low pH, as well as from endogenous signals within the cell, such as metabolic challenges and increased demands for protein production. When cellular homeostasis is altered by one of these triggers, ER primary functions are altered which leads to the accumulation of misfolded proteins. These impaired proteins trigger the activation of the Unfolded Protein Response (UPR) pathway. This response aims at reducing ER stress by implementing the induction of complex programs to restore cell homeostasis. However, extended ER stress can modify the UPR response, shifting its signals from promoting survival to triggering pathways that reprogram or eliminate affected cells.

Regulation of ER stress-induced apoptotic and inflammatory responses via YAP/TAZ-mediated control of the TRAIL-R2/DR5 signaling pathway

In tumors, cancer cells are frequently exposed to adverse environmental conditions that result in endoplasmic reticulum (ER) stress. Mechanical signals emerging from extracellular matrix (ECM) rigidity and cell shape regulate the activity of transcriptional co-activators Yes-associated protein (YAP) and its paralog Transcriptional Coactivator with PDZ-binding motif (TAZ). However, the role of ECM rigidity and YAP/TAZ in tumor cell fate decisions under ER stress remains relatively unexplored. Our results suggest that the YAP/TAZ system plays an important role in the control of ER stress-induced cell death by mechanical signaling arising from ECM stiffness in tumor cells. Mechanistically, YAP/TAZ regulates apoptosis induced by ER stress in tumor cells by controlling the activation of the TRAIL-R2/DR5-mediated extrinsic apoptotic pathway through a dual mechanism. On the one hand, the YAP/TAZ system prevents intracellular TRAIL-R2/DR5 clustering in tumor cells. On the other hand, it inhibits cFLIP down-regulation in tumor cells experiencing ER stress. In addition, YAP/TAZ controls the expression of pro-inflammatory interleukin-8 (IL-8/CXCL8) in tumor cells undergoing ER stress by a TRAIL-R2/DR5/caspase-8-dependent mechanism. Although other mechanisms may also be involved in controlling cell death and inflammation in tumor cells facing environmental stress, our results support a model in which regulation of the subcellular localization and activity of the YAP/TAZ transcriptional co-activators could contribute to the microenvironmental control of cell fate decisions in tumor cells undergoing ER stress.

Disturbing microtubule-endoplasmic reticulum dynamics by gold nanoclusters for improved triple-negative breast cancer treatment

Microtubules are highly dynamic structures, and their dynamic instability is indispensable for not only cell growth and movement, but also stress responses, such as endoplasmic reticulum (ER) stress. Docetaxel, a microtubule targeting agent (MTA), is the first-line drug for cancer treatment by simultaneously promoting microtubule dysregulation- and ER stress-induced cell death. However, it also causes adverse effects and drug resistance, especially in triple-negative breast cancer (TNBC) with a poor prognosis and high mortality rate. In this study, we developed a peptide-templated gold nanocluster, namely GA. GA significantly sensitizes TNBC cells to docetaxel, causing severe cell death. This effect is further validated by a 3D tumor spheroid model. Mechanistically, GA disrupted microtubule dynamic instability, meanwhile promoting PERK-mediated ER stress. Interestingly, ER stress inhibitors profoundly suppressed microtubule dysregulation, suggesting a retrograde regulation of ER stress on microtubules. In vivo, the combined administration of docetaxel and GA significantly suppresses tumor growth while docetaxel alone cannot. GA similarly elevated the level of caspases and PERK within tumors as in vitro. Importantly, GA treatment also profoundly promoted the production of anti-tumor inflammatory cytokines. Collectively, we developed an ER-microtubule regulatory nanomaterial that enhanced the therapeutic effect of docetaxel by elevating tumor cell death and anti-tumor cytokine production, providing a potential supplemental strategy for TNBC treatment.

Xeroderma pigmentosum protein XPD controls caspase-mediated stress responses

Caspases regulate and execute a spectrum of functions including cell deaths, non-apoptotic developmental functions, and stress responses. Despite these disparate roles, the same core cell-death machinery is required to enzymatically activate caspase proteolytic activities. Thus, it remains enigmatic how distinct caspase functions are differentially regulated. In this study, we show that Xeroderma pigmentosum protein XPD has a conserved function in activating the expression of stress-responsive caspases in C. elegans and human cells without triggering cell death. Using C. elegans, we show XPD-1-dependent activation of CED-3 caspase promotes survival upon genotoxic UV irradiation and inversely suppresses responses to non-genotoxic insults such as ER and osmotic stressors. Unlike the TFDP ortholog DPL-1 which is required for developmental apoptosis in C. elegans, XPD-1 only activates stress-responsive functions of caspase. This tradeoff balancing responses to genotoxic and non-genotoxic stress may explain the seemingly contradictory nature of caspase-mediated stress resilience versus sensitivity under different stressors.

Peripheral biomarkers of Parkinson's disease and its correlation with clinical symptoms: a case-control study

BACKGROUND

Inflammation significantly impacts Parkinson's disease (PD), yet the intricate relationship between inflammatory markers and PD remains elusive.

OBJECTIVE

To identify the peripheral biomarkers of PD and its correlation with the motor and non-motor symptoms of PD.

METHODS

79 PD patients and 65 controls were included in this study. Clinical information and the serum levels of IL-8, IL-27, IL-33, β-NGF, AgRP, and TRAILR2 in the participants were collected. Appropriate scales were used to assess the symptoms of PD. For the factors with significant differences in the two groups, multivariable logistic regression was used to determine its relationship with PD. Moreover, spearman correlation was conducted to explore the correlation between the factors and PD related symptoms. The IL-27 level was compared between the cognitively healthy PD group and the mild cognitive impairment in PD (PD-MCI). The serum level of TRAILR2 was positively correlated with age and was not associated with other clinical characteristics related to PD.

RESULTS

Compared to controls, the serum levels of IL-27(P = 0.013) were increased whereas the levels of TRAILR2(P = 0.008) were decreased in PD patients. IL-8, IL-33, β-NGF, and AgRP showed no significant differences between the two groups. After controlling for the other variables, IL-27 was considered as an independent risk factor for PD in the multivariable logistic regression model. The receiver operating characteristic (ROC) curve for diagnosing PD with IL-27 yielded an area under the curve (AUC) of 0.621. Additionally, IL-27 level in PD patients was positively correlated with age, the disease duration, LEDD and negatively correlated with the MoCA scores. However, no significant difference was found in IL-27 levels between cognitively healthy PD and PD-MCI groups.

CONCLUSION

Elevated serum IL-27 was a risk factor for PD and positively correlated with the cognitive decline in PD.

Activating Transcription Factor 6 Mediates Inflammation in Experimental Varicocele-Induced Epididymal Epithelial Cells

Introduction

Varicocele is a dilatation of the internal spermatic vein and it is generally recognized as one cause of male infertility. This study aimed to analyze the roles of activating transcription factor 6 (ATF-6) in experimental varicocele-induced epididymal epithelial cells.

Methods

Experimental left varicocele was established in rats through partial left renal vein ligation. At 8 weeks after surgery, the left epididymal damage was observed using H&E and TUNEL staining. The expressions of neutral α-glucosidase (NAG), ATF-6, tumor necrosis factor (TNF)-α, and phospho-nuclear factor (p-NF)-κB p65 (S536) in the left epididymis were measured by immunohistochemistry. ATF-6 silence in rat epididymal epithelial cells was established by ATF-6 siRNA transfection. The cells were treated with hypoxia for 24 h, and cell viability was measured by CCK-8, levels of NAG, TNF-α, and interleukin (IL)-8 in cells were measured by ELISA, levels of p-NF-κB p65 (S536)/NF-κB p65 protein in cells were measured by Western blotting.

Results

The results showed that the experimental left varicocele induced hypertrophy and apoptosis of epididymal epithelial cells (p<0.05), and decreased the expressions of NAG in the epididymal epithelial cells compared with the sham-operated control rats (p<0.01). Meanwhile, the expressions of ATF-6, TNF-α, and p-NF-κB p65 (S536) were increased in the epididymal epithelial cells after the experimental left varicocele compared with the sham-operated control rats (p<0.05). In the hypoxia-treated cells, ATF-6 silence increased the cell viability and decreased the levels of TNF-α, IL-8, and p-NF-κB p65 (S536) compared with the control cells (p<0.05).

Discussion

The ATF-6 pathway was activated in a rat's left varicocele-induced epididymal damage. Inhibition of the ATF-6 pathway might be a possible novel therapeutic approach for left varicocele-induced epididymal damage.

Friendly fire: recognition of self by the innate immune system

The innate immune system employs two different strategies to detect pathogens: first, it recognizes microbial components as ligands of pattern recognition receptors (pattern-triggered immunity [PTI]), and second, it detects the activities of pathogen-encoded effectors (effector-triggered immunity [ETI]). Recently, these pathogen-centric concepts were expanded to include sensing of self-derived signals during cellular distress or damage (damage-triggered immunity [DTI]). This extension relied on broadening the PTI model to include damage-associated molecular patterns (DAMPs). However, applying the pattern recognition framework of PTI to DTI overlooks the critical role of sterile activation of ETI pathways. We argue that both PTI and ETI pathways are prone to erroneous detection of self, which is largely attributable to 'friendly fire' rather than protective immune activation. This erroneous activation is inherent to the trade-off between sensitivity and specificity of immune sensing and might be tolerated because its detrimental effects emerge late in life, a phenomenon known as antagonistic pleiotropy.

Porcine γδ T cells express cytotoxic cell-associated markers and display killing activity but are not selectively cytotoxic against PRRSV- or swIAV-infected macrophages

Background

Gamma-delta (γδ) T cells are a major immune cell subset in pigs. Approximately 50% of circulating T cells are γδ T cells in young pigs and up to 30% in adult sows. Despite this abundance, the functions of porcine γδ T cells are mostly unidentified. In humans and mice, activated γδ T cells exhibit broad innate cytotoxic activity against a wide variety of stressed, infected, and cancerous cells through death receptor/ligand-dependent and perforin/granzyme-dependent pathways. However, so far, it is unknown whether porcine γδ T cells have the ability to perform cytotoxic functions.

Methods

In this study, we conducted a comprehensive phenotypic characterization of porcine γδ T cells isolated from blood, lung, and nasal mucosa. To further analyze the cytolytic potential of γδ T cells, in vitro cytotoxicity assays were performed using purified γδ T cells as effector cells and virus-exposed or mock-treated primary porcine alveolar macrophages as target cells.

Results

Our results show that only CD2+ γδ T cells express cytotoxic markers (CD16, NKp46, perforin) with higher perforin and NKp46 expression in γδ T cells isolated from lung and nasal mucosa. Moreover, we found that γδ T cells can exhibit cytotoxic functions in a cell-cell contact and degranulation-dependent manner. However, porcine γδ T cells did not seem to specifically target Porcine Reproductive and Respiratory Syndrome Virus or swine Influenza A Virus-infected macrophages, which may be due to viral escape mechanisms.

Conclusion

Porcine γδ T cells express cytotoxic markers and can exhibit cytotoxic activity in vitro. The specific mechanisms by which porcine γδ T cells recognize target cells are not fully understood but may involve the detection of cellular stress signals.

Identification of unique cell type responses in pancreatic islets to stress

Diabetes involves the death or dysfunction of pancreatic β-cells. Analysis of bulk sequencing from human samples and studies using in vitro and in vivo models suggest that endoplasmic reticulum and inflammatory signaling play an important role in diabetes progression. To better characterize cell type-specific stress response, we perform multiplexed single-cell RNA sequencing to define the transcriptional signature of primary human islet cells exposed to endoplasmic reticulum and inflammatory stress. Through comprehensive pair-wise analysis of stress responses across pancreatic endocrine and exocrine cell types, we define changes in gene expression for each cell type under different diabetes-associated stressors. We find that β-, α-, and ductal cells have the greatest transcriptional response. We utilize stem cell-derived islets to study islet health through the candidate gene CIB1, which was upregulated under stress in primary human islets. Our findings provide insights into cell type-specific responses to diabetes-associated stress and establish a resource to identify targets for diabetes therapeutics.

Death receptors 4/5 mediate tumour sensitivity to natural killer cell-mediated cytotoxicity in mismatch repair deficient colorectal cancer

BACKGROUND

Identifying the target of natural killer (NK) cells in colorectal cancer (CRC) is critical for optimising the clinical use of NK cell-mediated immunotherapy. Mismatch repair deficiency (dMMR) is associated with high immune cell infiltration and MHC Class I defects. Whether dMMR CRC responses to NK cell therapy remains unclear.

METHODS

MLH1, DR4, and DR5 knockout cell lines were established using CRISPR-Cas9 system. NK92-MI or NK cell isolated from BABL/C mice were used as effector cells against tumour cells. Inflammatory cytokines secretion by CRC cells was assessed via cytokine analysis. NK-cell-deficient/proficient animal models were used to validate the NK cell sensitivity.

RESULTS

We observed that dMMR CRC cells were more sensitive to NK cell-mediated cytotoxicity than were mismatch-repair-proficient (pMMR) CRC cells. In dMMR CRC, Death receptor (DR)4/5 was upregulated and mediated sensitivity to NK cell-mediated cytotoxicity. DR4/5-mediated secretion of interleukin -12 sustained NK cell viability in dMMR CRC. NK cell depletion induced dMMR CRC tumour growth, and NK cell transfer inhibited lung metastasis of dMMR CRC with DR4/5 expression in vivo. TP53 upregulated DR4/DR5 expression in dMMR CRC.

CONCLUSIONS

dMMR associated with increased sensitivity to NK cell-mediated cytotoxicity in CRC. DR4/DR5 sensitise dMMR CRC to NK cell-mediated cytotoxicity.

Blocking the TRAIL-DR5 Pathway Reduces Cardiac Ischemia-Reperfusion Injury by Decreasing Neutrophil Infiltration and Neutrophil Extracellular Traps Formation

PURPOSE

Acute myocardial infarction (AMI) is a leading cause of mortality. Neutrophils penetrate injured heart tissue during AMI or ischemia-reperfusion (I/R) injury and produce inflammatory factors, chemokines, and extracellular traps that exacerbate heart injury. Inhibition of the TRAIL-DR5 pathway has been demonstrated to alleviate cardiac ischemia-reperfusion injury in a leukocyte-dependent manner. However, it remains unknown whether TRAIL-DR5 signaling is involved in regulating neutrophil extracellular traps (NETs) release.

METHODS

This study used various models to examine the effects of activating the TRAIL-DR5 pathway with soluble mouse TRAIL protein and inhibiting the TRAIL-DR5 signaling pathway using DR5 knockout mice or mDR5-Fc fusion protein on NETs formation and cardiac injury. The models used included a co-culture model involving bone marrow-derived neutrophils and primary cardiomyocytes and a model of myocardial I/R in mice.

RESULTS

NETs formation is suppressed by TRAIL-DR5 signaling pathway inhibition, which can lessen cardiac I/R injury. This intervention reduces the release of adhesion molecules and chemokines, resulting in decreased neutrophil infiltration and inhibiting NETs production by downregulating PAD4 in neutrophils.

CONCLUSION

This work clarifies how the TRAIL-DR5 signaling pathway regulates the neutrophil response during myocardial I/R damage, thereby providing a scientific basis for therapeutic intervention targeting the TRAIL-DR5 signaling pathway in myocardial infarction.

IRE1 RNase controls CD95-mediated cell death

Signalling by the Unfolded Protein Response (UPR) or by the Death Receptors (DR) are frequently activated towards pro-tumoral outputs in cancer. Herein, we demonstrate that the UPR sensor IRE1 controls the expression of the DR CD95/Fas, and its cell death-inducing ability. Both genetic and pharmacologic blunting of IRE1 activity increased CD95 expression and exacerbated CD95L-induced cell death in glioblastoma (GB) and Triple-Negative Breast Cancer (TNBC) cell lines. In accordance, CD95 mRNA was identified as a target of Regulated IRE1-Dependent Decay of RNA (RIDD). Whilst CD95 expression is elevated in TNBC and GB human tumours exhibiting low RIDD activity, it is surprisingly lower in XBP1s-low human tumour samples. We show that IRE1 RNase inhibition limited CD95 expression and reduced CD95-mediated hepatic toxicity in mice. In addition, overexpression of XBP1s increased CD95 expression and sensitized GB and TNBC cells to CD95L-induced cell death. Overall, these results demonstrate the tight IRE1-mediated control of CD95-dependent cell death in a dual manner through both RIDD and XBP1s, and they identify a novel link between IRE1 and CD95 signalling.

TNF-Related Apoptosis-Inducing Ligand: Non-Apoptotic Signalling

TNF-related apoptosis-inducing ligand (TRAIL or Apo2 or TNFSF10) belongs to the TNF superfamily. When bound to its agonistic receptors, TRAIL can induce apoptosis in tumour cells, while sparing healthy cells. Over the last three decades, this tumour selectivity has prompted many studies aiming at evaluating the anti-tumoral potential of TRAIL or its derivatives. Although most of these attempts have failed, so far, novel formulations are still being evaluated. However, emerging evidence indicates that TRAIL can also trigger a non-canonical signal transduction pathway that is likely to be detrimental for its use in oncology. Likewise, an increasing number of studies suggest that in some circumstances TRAIL can induce, via Death receptor 5 (DR5), tumour cell motility, potentially leading to and contributing to tumour metastasis. While the pro-apoptotic signal transduction machinery of TRAIL is well known from a mechanistic point of view, that of the non-canonical pathway is less understood. In this study, we the current state of knowledge of TRAIL non-canonical signalling.

CD169+ classical monocyte as an important participant in Graves' ophthalmopathy through CXCL12-CXCR4 axis

Patients with Graves' disease (GD) can develop Graves' ophthalmopathy (GO), but the underlying pathological mechanisms driving this development remain unclear. In our study, which included patients with GD and GO, we utilized single-cell RNA sequencing (scRNA-seq) and multiplatform analyses to investigate CD169+ classical monocytes, which secrete proinflammatory cytokines and are expanded through activated interferon signaling. We found that CD169+ clas_mono was clinically significant in predicting GO progression and prognosis, and differentiated into CD169+ macrophages that promote inflammation, adipogenesis, and fibrosis. Our murine model of early-stage GO showed that CD169+ classical monocytes accumulated in orbital tissue via the Cxcl12-Cxcr4 axis. Further studies are needed to investigate whether targeting circulating monocytes and the Cxcl12-Cxcr4 axis could alleviate GO progression.

Protein-rich foods, sea foods, and gut microbiota amplify immune responses in chronic diseases and cancers - Targeting PERK as a novel therapeutic strategy for chronic inflammatory diseases, neurodegenerative disorders, and cancer

The endoplasmic reticulum (ER) is a cellular organelle that is physiologically responsible for protein folding, calcium homeostasis, and lipid biosynthesis. Pathological stimuli such as oxidative stress, ischemia, disruptions in calcium homeostasis, and increased production of normal and/or folding-defective proteins all contribute to the accumulation of misfolded proteins in the ER, causing ER stress. The adaptive response to ER stress is the activation of unfolded protein response (UPR), which affect a wide variety of cellular functions to maintain ER homeostasis or lead to apoptosis. Three different ER transmembrane sensors, including PKR-like ER kinase (PERK), activating transcription factor 6 (ATF6), and inositol-requiring enzyme-1 (IRE1), are responsible for initiating UPR. The UPR involves a variety of signal transduction pathways that reduce unfolded protein accumulation by boosting ER-resident chaperones, limiting protein translation, and accelerating unfolded protein degradation. ER is now acknowledged as a critical organelle in sensing dangers and determining cell life and death. On the other hand, UPR plays a critical role in the development and progression of several diseases such as cardiovascular diseases (CVD), metabolic disorders, chronic kidney diseases, neurological disorders, and cancer. Here, we critically analyze the most current knowledge of the master regulatory roles of ER stress particularly the PERK pathway as a conditional danger receptor, an organelle crosstalk regulator, and a regulator of protein translation. We highlighted that PERK is not only ER stress regulator by sensing UPR and ER stress but also a frontier sensor and direct senses for gut microbiota-generated metabolites. Our work also further highlighted the function of PERK as a central hub that leads to metabolic reprogramming and epigenetic modification which further enhanced inflammatory response and promoted trained immunity. Moreover, we highlighted the contribution of ER stress and PERK in the pathogenesis of several diseases such as cancer, CVD, kidney diseases, and neurodegenerative disorders. Finally, we discuss the therapeutic target of ER stress and PERK for cancer treatment and the potential novel therapeutic targets for CVD, metabolic disorders, and neurodegenerative disorders. Inhibition of ER stress, by the development of small molecules that target the PERK and UPR, represents a promising therapeutic strategy.

The role of endoplasmic reticulum stress, mitochondrial dysfunction and their crosstalk in intervertebral disc degeneration

Low back pain (LBP) is a pervasive global health issue. Roughly 40% of LBP cases are attributed to intervertebral disc degeneration (IVDD). While the underlying mechanisms of IVDD remain incompletely understood, it has been confirmed that apoptosis and extracellular matrix (ECM) degradation caused by many factors such as inflammation, oxidative stress, calcium (Ca2+) homeostasis imbalance leads to IVDD. Endoplasmic reticulum (ER) stress and mitochondrial dysfunction are involved in these processes. The initiation of ER stress precipitates cell apoptosis, and is also related to inflammation, levels of oxidative stress, and Ca2+ homeostasis. Additionally, mitochondrial dynamics, antioxidative systems, disruption of Ca2+ homeostasis are closely associated with Reactive Oxygen Species (ROS) and inflammation, promoting cell apoptosis. However, numerous crosstalk exists between the ER and mitochondria, where they interact through inflammatory cytokines, signaling pathways, ROS, or key molecules such as CHOP, forming positive and negative feedback loops. Furthermore, the contact sites between the ER and mitochondria, known as mitochondria-associated membranes (MAM), facilitate direct signal transduction such as Ca2+ transfer. However, the current attention towards this issue is insufficient. Therefore, this review summarizes the impacts of ER stress and mitochondrial dysfunction on IVDD, along with the possibly potential crosstalk between them, aiming to unveil novel avenues for IVDD intervention.

cFLIPL acts as a suppressor of TRAIL- and Fas-initiated inflammation by inhibiting assembly of caspase-8/FADD/RIPK1 NF-κB-activating complexes

TRAIL and FasL are potent inducers of apoptosis but can also promote inflammation through assembly of cytoplasmic caspase-8/FADD/RIPK1 (FADDosome) complexes, wherein caspase-8 acts as a scaffold to drive FADD/RIPK1-mediated nuclear factor κB (NF-κB) activation. cFLIP is also recruited to FADDosomes and restricts caspase-8 activity and apoptosis, but whether cFLIP also regulates death receptor-initiated inflammation is unclear. Here, we show that silencing or deletion of cFLIP leads to robustly enhanced Fas-, TRAIL-, or TLR3-induced inflammatory cytokine production, which can be uncoupled from the effects of cFLIP on caspase-8 activation and apoptosis. Mechanistically, cFLIPL suppresses Fas- or TRAIL-initiated NF-κB activation through inhibiting the assembly of caspase-8/FADD/RIPK1 FADDosome complexes, due to the low affinity of cFLIPL for FADD. Consequently, increased cFLIPL occupancy of FADDosomes diminishes recruitment of FADD/RIPK1 to caspase-8, thereby suppressing NF-κB activation and inflammatory cytokine production downstream. Thus, cFLIP acts as a dual suppressor of apoptosis and inflammation via distinct modes of action.

Stressed target cancer cells drive nongenetic reprogramming of CAR T cells and solid tumor microenvironment

The poor efficacy of chimeric antigen receptor T-cell therapy (CAR T) for solid tumors is due to insufficient CAR T cell tumor infiltration, in vivo expansion, persistence, and effector function, as well as exhaustion, intrinsic target antigen heterogeneity or antigen loss of target cancer cells, and immunosuppressive tumor microenvironment (TME). Here we describe a broadly applicable nongenetic approach that simultaneously addresses the multiple challenges of CAR T as a therapy for solid tumors. The approach reprograms CAR T cells by exposing them to stressed target cancer cells which have been exposed to the cell stress inducer disulfiram (DSF) and copper (Cu)(DSF/Cu) plus ionizing irradiation (IR). The reprogrammed CAR T cells acquire early memory-like characteristics, potent cytotoxicity, enhanced in vivo expansion, persistence, and decreased exhaustion. Tumors stressed by DSF/Cu and IR also reprogram and reverse the immunosuppressive TME in humanized mice. The reprogrammed CAR T cells, derived from peripheral blood mononuclear cells of healthy donors or metastatic female breast cancer patients, induce robust, sustained memory and curative anti-solid tumor responses in multiple xenograft mouse models, establishing proof of concept for empowering CAR T by stressing tumor as a promising therapy for solid tumors.

Endoplasmic Reticulum Stress: A Key Regulator of Cardiovascular Disease

The problems associated with economic development and social progress have led to an increase in the occurrence of cardiovascular diseases (CVDs), which affect the health of an increasing number of people and are a leading cause of disease and population mortality worldwide. Endoplasmic reticulum stress (ERS), a hot topic of interest for scholars in recent years, has been confirmed in numerous studies to be an important pathogenetic basis for many metabolic diseases and play an important role in maintaining physiological processes. The endoplasmic reticulum (ER) is a major organelle that is involved in protein folding and modification synthesis, and ERS occurs when several physiological and pathological factors allow excessive amounts of unfolded/misfolded proteins to accumulate. ERS often leads to initiation of the unfolded protein response (UPR) in a bid to re-establish tissue homeostasis; however, UPR has been documented to induce vascular remodeling and cardiomyocyte damage under various pathological conditions, leading to or accelerating the development of CVDs such as hypertension, atherosclerosis, and heart failure. In this review, we summarize the latest knowledge gained concerning ERS in terms of cardiovascular system pathophysiology, and discuss the feasibility of targeting ERS as a novel therapeutic target for the treatment of CVDs. Investigation of ERS has immense potential as a new direction for future research involving lifestyle intervention, the use of existing drugs, and the development of novel drugs that target and inhibit ERS.

CRISPR screens identify novel regulators of cFLIP dependency and ligand-independent, TRAIL-R1-mediated cell death

Kaposi's sarcoma-associated herpesvirus (KSHV) causes primary effusion lymphoma (PEL). PEL cell lines require expression of the cellular FLICE inhibitory protein (cFLIP) for survival, although KSHV encodes a viral homolog of this protein (vFLIP). Cellular and viral FLIP proteins have several functions, including, most importantly, the inhibition of pro-apoptotic caspase 8 and modulation of NF-κB signaling. To investigate the essential role of cFLIP and its potential redundancy with vFLIP in PEL cells, we first performed rescue experiments with human or viral FLIP proteins known to affect FLIP target pathways differently. The long and short isoforms of cFLIP and molluscum contagiosum virus MC159L, which are all strong caspase 8 inhibitors, efficiently rescued the loss of endogenous cFLIP activity in PEL cells. KSHV vFLIP was unable to fully rescue the loss of endogenous cFLIP and is therefore functionally distinct. Next, we employed genome-wide CRISPR/Cas9 synthetic rescue screens to identify loss of function perturbations that can compensate for cFLIP knockout. Results from these screens and our validation experiments implicate the canonical cFLIP target caspase 8 and TRAIL receptor 1 (TRAIL-R1 or TNFRSF10A) in promoting constitutive death signaling in PEL cells. However, this process was independent of TRAIL receptor 2 or TRAIL, the latter of which is not detectable in PEL cell cultures. The requirement for cFLIP is also overcome by inactivation of the ER/Golgi resident chondroitin sulfate proteoglycan synthesis and UFMylation pathways, Jagunal homolog 1 (JAGN1) or CXCR4. UFMylation and JAGN1, but not chondroitin sulfate proteoglycan synthesis or CXCR4, contribute to TRAIL-R1 expression. In sum, our work shows that cFLIP is required in PEL cells to inhibit ligand-independent TRAIL-R1 cell death signaling downstream of a complex set of ER/Golgi-associated processes that have not previously been implicated in cFLIP or TRAIL-R1 function.

Magnetic Control of Protein Expression via Magneto-mechanical Actuation of ND-PEGylated Iron Oxide Nanocubes for Cell Therapy

Engineered cells used as smart vehicles for delivery of secreted therapeutic proteins enable effective treatment of cancer and certain degenerative, autoimmune, and genetic disorders. However, current cell-based therapies use mostly invasive tools for tracking proteins and do not allow for controlled secretion of therapeutic proteins, which could result in unconstrained killing of surrounding healthy tissues or ineffective killing of host cancer cells. Regulating the expression of therapeutic proteins after success of therapy remains elusive. In this study, a noninvasive therapeutic approach mediated by magneto-mechanical actuation (MMA) was developed to remotely regulate the expression of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) protein, which is secreted by transduced cells. Stem cells, macrophages, and breast cancer cells were transduced with a lentiviral vector encoding the SGpL2TR protein. SGpL2TR comprises TRAIL and GpLuc domains optimized for cell-based applications. Our approach relies on the remote actuation of cubic-shape highly magnetic field responsive superparamagnetic iron oxide nanoparticles (SPIONs) coated with nitrodopamine PEG (ND-PEG), which are internalized within the cells. Cubic ND-PEG-SPIONs actuated by superlow frequency alternating current magnetic fields can translate magnetic forces into mechanical motion and in turn spur mechanosensitive cellular responses. Cubic ND-PEG-SPIONs were artificially designed to effectively operate at low magnetic field strengths (<100 mT) retaining approximately 60% of their saturation magnetization. Compared to other cells, stems cells were more sensitive to the interaction with actuated cubic ND-PEG-SPIONs, which clustered near the endoplasmic reticulum (ER). Luciferase, ELISA, and RT-qPCR analyses revealed a marked TRAIL downregulation (secretion levels were depleted down to 30%) when intracellular particles at 0.100 mg/mL Fe were actuated by magnetic fields (65 mT and 50 Hz for 30 min). Western blot studies indicated actuated, intracellular cubic ND-PEG-SPIONs can cause mild ER stress at short periods (up to 3 h) of postmagnetic field treatment thus leading to the unfolded protein response. We observed that the interaction of TRAIL polypeptides with ND-PEG can also contribute to this response. To prove the applicability of our approach, we used glioblastoma cells, which were exposed to TRAIL secreted from stem cells. We demonstrated that in the absence of MMA treatment, TRAIL essentially killed glioblastoma cells indiscriminately, but when treated with MMA, we were able to control the cell killing rate by adjusting the magnetic doses. This approach can expand the capabilities of stem cells to serve as smart vehicles for delivery of therapeutic proteins in a controlled manner without using interfering and expensive drugs, while retaining their potential to regenerate damaged tissue after treatment. This approach brings forth new alternatives to regulate protein expression noninvasively for cell therapy and other cancer therapies.

Cellular battle against endoplasmic reticulum stress and its adverse effect on health

The endoplasmic reticulum (ER) is a dynamic organelle and a reliable performer for precisely folded proteins. To maintain its function and integrity, arrays of sensory and quality control systems enhance protein folding fidelity and resolve the highest error-prone areas. Yet numerous internal and external factors disrupt its homeostasis and trigger ER stress responses. Cells try to reduce the number of misfolded proteins via the UPR mechanism, and ER-related garbage disposals systems like ER-associated degradation (ERAD), ER-lysosome-associated degradation (ERLAD), ER-Associated RNA Silencing (ERAS), extracellular chaperoning, and autophagy systems, which activates and increase the cell survival rate by degrading misfolded proteins, prevent the aggregated proteins and remove the dysfunctional organelles. Throughout life, organisms must confront environmental stress to survive and develop. Communication between the ER & other organelles, signaling events mediated by calcium, reactive oxygen species, and inflammation are linked to diverse stress signaling pathways and regulate cell survival or cell death mechanisms. Unresolved cellular damages can cross the threshold limit of their survival, resulting in cell death or driving for various diseases. The multifaceted ability of unfolded protein response facilitates the therapeutic target and a biomarker for various diseases, helping with early diagnosis and detecting the severity of diseases.

Molecular superglue-mediated higher-order assembly of TRAIL variants with superior apoptosis induction and antitumor activity

Prompting higher-order death receptor (DR) clustering by increasing the valency of DR agonist is efficient to induce apoptosis of tumor cells. As an attractive DR agonist with superior biosafety, the trimeric tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) exerts limited antitumor effect in patients, which is predominantly attributed to its low DR clustering ability and short serum half-life. Previous antibody scaffolds-based engineering strategies to increase the valency and/or prolong the serum half-life of TRAIL improve apoptosis induction, however, often produce large proteins with poor tumor penetration. Covalent protein ligation mediated by small molecular superglues such as SpyTag/SpyCatcher might be a novel strategy to assemble higher-order TRAIL variants. Upon fusion to TRAIL promotor, SpyTag/SpyCatcher molecular superglue preferentially ligated two trimeric TRAIL to produce a hexameric TRAIL variant, HexaTR, exhibiting a significantly increased apoptosis induction. In addition, an albumin-binding HexaTR, ABD-HexaTR, with a prolonged serum half-life by binding to endogenous albumin was also produced using the same strategy. Compared to the trimeric TRAIL, the hexameric HexaTR and ABD-HexaTR showed 20-50 times greater in vivo antitumor effect, resulting in eradication of several types of large (150-300 mm³) tumor xenografts. Combination with bortezomib carried by liposome further improved the antitumor effects of the hexavalent HexaTR and ABD-HexaTR in refractory cancer. Our results indicate that the superglue-mediated higher-order assembly is promising to improve the DR clustering and proapoptotic signaling of TRAIL, showing great advantages in constructing the next generation of DR agonists for cancer therapy.

Targeting alarmin release reverses Sjogren's syndrome phenotype by revitalizing Ca2+ signalling

BACKGROUND

Primary Sjogren's syndrome (pSS) is a systemic autoimmune disease that is embodied by the loss of salivary gland function and immune cell infiltration, but the mechanism(s) are still unknown. The aim of this study was to understand the mechanisms and identify key factors that leads to the development and progression of pSS.

METHODS

Immunohistochemistry staining, FACS analysis and cytokine levels were used to detect immune cells infiltration and activation in salivary glands. RNA sequencing was performed to identify the molecular mechanisms involved in the development of pSS. The function assays include in vivo saliva collection along with calcium imaging and electrophysiology on isolated salivary gland cells in mice models of pSS. Western blotting, real-time PCR, alarmin release, and immunohistochemistry was performed to identify the channels involved in salivary function in pSS.

RESULTS

We provide evidence that loss of Ca2+ signaling precedes a decrease in saliva secretion and/or immune cell infiltration in IL14α, a mouse model for pSS. We also showed that Ca2+ homeostasis was mediated by transient receptor potential canonical-1 (TRPC1) channels and inhibition of TRPC1, resulting in the loss of salivary acinar cells, which promoted alarmin release essential for immune cell infiltration/release of pro-inflammatory cytokines. In addition, both IL14α and samples from human pSS patients showed a decrease in TRPC1 expression and increased acinar cell death. Finally, paquinimod treatment in IL14α restored Ca2+ homeostasis that inhibited alarmin release thereby reverting the pSS phenotype.

CONCLUSIONS

These results indicate that loss of Ca2+ signaling is one of the initial factors, which induces loss of salivary gland function along with immune infiltration that exaggerates pSS. Importantly, restoration of Ca2+ signaling upon paquinimod treatment reversed the pSS phenotype thereby inhibiting the progressive development of pSS.

Breast tumors interfere with endothelial TRAIL at the premetastatic niche to promote cancer cell seeding

Endothelial cells (ECs) grant access of disseminated cancer cells to distant organs. However, the molecular players regulating the activation of quiescent ECs at the premetastatic niche (PMN) remain elusive. Here, we find that ECs at the PMN coexpress tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its cognate death receptor 5 (DR5). Unexpectedly, endothelial TRAIL interacts intracellularly with DR5 to prevent its signaling and preserve a quiescent vascular phenotype. In absence of endothelial TRAIL, DR5 activation induces EC death and nuclear factor κB/p38-dependent EC stickiness, compromising vascular integrity and promoting myeloid cell infiltration, breast cancer cell adhesion, and metastasis. Consistently, both down-regulation of endothelial TRAIL at the PMN by proangiogenic tumor-secreted factors and the presence of the endogenous TRAIL inhibitors decoy receptor 1 (DcR1) and DcR2 favor metastasis. This study discloses an intracrine mechanism whereby TRAIL blocks DR5 signaling in quiescent endothelia, acting as gatekeeper of the vascular barrier that is corrupted by the tumor during cancer cell dissemination.

When cell death goes wrong: inflammatory outcomes of failed apoptosis and mitotic cell death

Apoptosis is a regulated cellular pathway that ensures that a cell dies in a structured fashion to prevent negative consequences for the tissue or the organism. Dysfunctional apoptosis is a hallmark of numerous pathologies, and treatments for various diseases are successful based on the induction of apoptosis. Under homeostatic conditions, apoptosis is a non-inflammatory event, as the activation of caspases ensures that inflammatory pathways are disabled. However, there is an increasing understanding that under specific conditions, such as caspase inhibition, apoptosis and the apoptotic machinery can be re-wired into a process which is inflammatory. In this review we discuss how the death receptor and mitochondrial pathways of apoptosis can activate inflammation. Furthermore, we will highlight how cell death due to mitotic stress might be a special case when it comes to cell death and the induction of inflammation.

TRAIL receptors promote constitutive and inducible IL-8 secretion in non-small cell lung carcinoma

Interleukin-8 (IL-8/CXCL8) is a pro-angiogenic and pro-inflammatory chemokine that plays a role in cancer development. Non-small cell lung carcinoma (NSCLC) produces high amounts of IL-8, which is associated with poor prognosis and resistance to chemo-radio and immunotherapy. However, the signaling pathways that lead to IL-8 production in NSCLC are unresolved. Here, we show that expression and release of IL-8 are regulated autonomously by TRAIL death receptors in several squamous and adenocarcinoma NSCLC cell lines. NSCLC constitutively secrete IL-8, which could be further enhanced by glucose withdrawal or by treatment with TRAIL or TNFα. In A549 cells, constitutive and inducible IL-8 production was dependent on NF-κB and MEK/ERK MAP Kinases. DR4 and DR5, known regulators of these signaling pathways, participated in constitutive and glucose deprivation-induced IL-8 secretion. These receptors were mainly located intracellularly. While DR4 signaled through the NF-κB pathway, DR4 and DR5 both regulated the ERK-MAPK and Akt pathways. FADD, caspase-8, RIPK1, and TRADD also regulated IL-8. Analysis of mRNA expression data from patients indicated that IL-8 transcripts correlated with TRAIL, DR4, and DR5 expression levels. Furthermore, TRAIL receptor expression levels also correlated with markers of angiogenesis and neutrophil infiltration in lung squamous carcinoma and adenocarcinoma. Collectively, these data suggest that TRAIL receptor signaling contributes to a pro-tumorigenic inflammatory signature associated with NSCLC.

Targeting endoplasmic reticulum stress-the responder to lipotoxicity and modulator of non-alcoholic fatty liver diseases

INTRODUCTION

Endoplasmic reticulum (ER) stress occurs with aberrant lipid accumulation and resultant adverse effects and widely exists in nonalcoholic fatty liver disease (NAFLD). It triggers the unfolded protein response (UPR) to restore ER homeostasis and actively participates in NAFLD pathological processes, including hepatic steatosis, inflammation, hepatocyte death, and fibrosis. Such acknowledges drive the discovery of novel NAFLD biomarker and therapeutic targets and the development of ER-stress targeted NAFLD drugs.

AREAS COVERED

This article discusses and updates the role of ER stress and UPR in NAFLD, the underlying action mechanism, and especially their full participation in NAFLD pathophysiology. It characterizes key molecular targets useful for the prevention and treatment of NAFLD and highlights the recent ER stress-targeted therapeutic strategies for NAFLD.

EXPERT OPINION

Targeting ER Stress is a valuable and promising strategy for NAFLD treatment, but its smooth translation into clinical application still requires better clarification of the different UPR patterns in diverse NAFLD physiological states. Further understanding of the distinct effects of these various patterns on NAFLD, the thresholds deciding their final impacts, and their actions via non-liver tissues and cells would be of great help to develop a precise and effective therapy for NAFLD. [Figure: see text].

A soluble DR5-Fc chimeric protein attenuates inflammatory responses induced by coronavirus MHV-A59 and SARS-CoV-2

Mortality in coronavirus disease 2019 (COVID-19) patients has been linked to the presence of a "cytokine storm" induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, which involves elevated levels of circulating cytokines and immune-cell hyperactivation. Targeting cytokines during the management of COVID-19 patients has the potential to improve survival rates and reduce mortality. Although cytokine blockers and immune-host modulators are currently being tested in severely ill COVID-19 patients to cope with the overwhelming systemic inflammation, there is not too many successful cases, thus finding new cytokine blockers to attenuate the cytokine storm syndrome is meaningful. In this paper, we significantly attenuated the inflammatory responses induced by mouse hepatitis viruses A59 and SARS-CoV-2 through a soluble DR5-Fc (sDR5-Fc) chimeric protein that blocked the TNF-related apoptosis-inducing ligand-death receptor 5 (TRAIL-DR5) interaction. Our findings indicates that blocking the TRAIL-DR5 pathway through the sDR5-Fc chimeric protein is a promising strategy to treat COVID-19 severe patients requiring intensive care unit  admission or with chronic metabolic diseases.

NF-κB and its crosstalk with endoplasmic reticulum stress in atherosclerosis

Atherosclerosis (AS) is a common cardiovascular disease with complex pathogenesis, in which multiple pathways and their interweaving regulatory mechanism remain unclear. The primary transcription factor NF-κB plays a critical role in AS via modulating the expression of a series of inflammatory mediators under various stimuli such as cytokines, microbial antigens, and intracellular stresses. Endoplasmic reticulum (ER) stress, caused by the disrupted synthesis and secretion of protein, links inflammation, metabolic signals, and other cellular processes via the unfolded protein response (UPR). Both NF-κB and ER stress share the intersection regarding their molecular regulation and function and are regarded as critical individual contributors to AS. In this review, we summarize the multiple interactions between NF-κB and ER stress activation, including the UPR, NLRP3 inflammasome, and reactive oxygen species (ROS) generation, which have been ignored in the pathogenesis of AS. Given the multiple links between NF-κB and ER stress, we speculate that the integrated network contributes to the understanding of molecular mechanisms of AS. This review aims to provide an insight into these interactions and their underlying roles in the progression of AS, highlighting potential pharmacological targets against the atherosclerotic inflammatory process.

The "Yin and Yang" of Unfolded Protein Response in Cancer and Immunogenic Cell Death

Physiological and pathological burdens that perturb endoplasmic reticulum homeostasis activate the unfolded protein response (UPR), a conserved cytosol-to-nucleus signaling pathway that aims to reinstate the vital biosynthetic and secretory capacity of the ER. Disrupted ER homeostasis, causing maladaptive UPR signaling, is an emerging trait of cancer cells. Maladaptive UPR sustains oncogene-driven reprogramming of proteostasis and metabolism and fosters proinflammatory pathways promoting tissue repair and protumorigenic immune responses. However, when cancer cells are exposed to conditions causing irreparable ER homeostasis, such as those elicited by anticancer therapies, the UPR switches from a survival to a cell death program. This lethal ER stress response can elicit immunogenic cell death (ICD), a form of cell death with proinflammatory traits favoring antitumor immune responses. How UPR-driven pathways transit from a protective to a killing modality with favorable immunogenic and proinflammatory output remains unresolved. Here, we discuss key aspects of the functional dichotomy of UPR in cancer cells and how this signal can be harnessed for therapeutic benefit in the context of ICD, especially from the aspect of inflammation aroused by the UPR.

TNF Receptor Associated Factor 2 (TRAF2) Signaling in Cancer

Simple Summary

Tumor necrosis factor (TNF) receptor associated factor-2 (TRAF2) is an intracellular adapter protein with E3 ligase activity, which interacts with a plethora of other signaling proteins, including plasma membrane receptors, kinases, phosphatases, other E3 ligases, and deubiquitinases. TRAF2 is involved in various cancer-relevant cellular processes, such as the activation of transcription factors of the NFκB family, stimulation of mitogen-activated protein (MAP) kinase cascades, endoplasmic reticulum (ER) stress signaling, autophagy, and the control of cell death programs. In a context-dependent manner, TRAF2 promotes tumor development but it can also act as a tumor suppressor. Based on a general description, how TRAF2 in concert with TRAF2-interacting proteins and other TRAF proteins act at the molecular level is discussed for its importance for tumor development and its potential usefulness as a therapeutic target in cancer therapy.

Abstract

Tumor necrosis factor (TNF) receptor associated factor-2 (TRAF2) has been originally identified as a protein interacting with TNF receptor 2 (TNFR2) but also binds to several other receptors of the TNF receptor superfamily (TNFRSF). TRAF2, often in concert with other members of the TRAF protein family, is involved in the activation of the classical NFκB pathway and the stimulation of various mitogen-activated protein (MAP) kinase cascades by TNFRSF receptors (TNFRs), but is also required to inhibit the alternative NFκB pathway. TRAF2 has also been implicated in endoplasmic reticulum (ER) stress signaling, the regulation of autophagy, and the control of cell death programs. TRAF2 fulfills its functions by acting as a scaffold, bringing together the E3 ligase cellular inhibitor of apoptosis-1 (cIAP1) and cIAP2 with their substrates and various regulatory proteins, e.g., deubiquitinases. Furthermore, TRAF2 can act as an E3 ligase by help of its N-terminal really interesting new gene (RING) domain. The finding that TRAF2 (but also several other members of the TRAF family) interacts with the latent membrane protein 1 (LMP1) oncogene of the Epstein–Barr virus (EBV) indicated early on that TRAF2 could play a role in the oncogenesis of B-cell malignancies and EBV-associated non-keratinizing nasopharyngeal carcinoma (NPC). TRAF2 can also act as an oncogene in solid tumors, e.g., in colon cancer by promoting Wnt/β-catenin signaling. Moreover, tumor cell-expressed TRAF2 has been identified as a major factor-limiting cancer cell killing by cytotoxic T-cells after immune checkpoint blockade. However, TRAF2 can also be context-dependent as a tumor suppressor, presumably by virtue of its inhibitory effect on the alternative NFκB pathway. For example, inactivating mutations of TRAF2 have been associated with tumor development, e.g., in multiple myeloma and mantle cell lymphoma. In this review, we summarize the various TRAF2-related signaling pathways and their relevance for the oncogenic and tumor suppressive activities of TRAF2. Particularly, we discuss currently emerging concepts to target TRAF2 for therapeutic purposes.

Single-cell analyses highlight the proinflammatory contribution of C1q-high monocytes to Behçet's disease

Behçet's disease (BD) is a chronic vasculitis characterized by systemic immune aberrations. However, a comprehensive understanding of immune disturbances in BD and how they contribute to BD pathogenesis is lacking. Here, we performed single-cell and bulk RNA sequencing to profile peripheral blood mononuclear cells (PBMCs) and isolated monocytes from BD patients and healthy donors. We observed prominent expansion and transcriptional changes in monocytes in PBMCs from BD patients. Deciphering the monocyte heterogeneity revealed the accumulation of C1q-high (C1q^hi) monocytes in BD. Pseudotime inference indicated that BD monocytes markedly shifted their differentiation toward inflammation-accompanied and C1q^hi monocyte-ended trajectory. Further experiments showed that C1q^hi monocytes enhanced phagocytosis and proinflammatory cytokine secretion, and multiplatform analyses revealed the significant clinical relevance of this subtype. Mechanistically, C1q^hi monocytes were induced by activated interferon-γ (IFN-γ) signaling in BD patients and were decreased by tofacitinib treatment. Our study illustrates the BD immune landscape and the unrecognized contribution of C1q^hi monocytes to BD hyperinflammation, showing their potential as therapeutic targets and clinical assessment indexes.

Endoplasmic Reticulum Stress: An Emerging Therapeutic Target for Intervertebral Disc Degeneration

Low back pain (LBP) is a global health issue. Intervertebral disc degeneration (IDD) is a major cause of LBP. Although the explicit mechanisms underpinning IDD are unclear, endoplasmic reticulum (ER) stress caused by aberrant unfolded or misfolded proteins may be involved. The accumulation of unfolded/misfolded proteins may result in reduced protein synthesis and promote aberrant protein degradation to recover ER function, a response termed the unfolded protein response. A growing body of literature has demonstrated the potential relationships between ER stress and the pathogenesis of IDD, indicating some promising therapeutic targets. In this review, we summarize the current knowledge regarding the impact of ER stress on the process of IDD, as well as some potential therapeutic strategies for alleviating disc degeneration by targeting different pathways to inhibit ER stress. This review will facilitate understanding the pathogenesis and progress of IDD and highlights potential therapeutic targets for treating this condition.

The Critical Roles of Proteostasis and Endoplasmic Reticulum Stress in Atrial Fibrillation

Atrial fibrillation (AF) remains the most common arrhythmia seen clinically. The incidence of AF is increasing due to the aging population. AF is associated with a significant increase in morbidity and mortality, yet current treatment paradigms have proven largely inadequate. Therefore, there is an urgent need to develop new effective therapeutic strategies for AF. The endoplasmic reticulum (ER) in the heart plays critical roles in the regulation of excitation-contraction coupling and cardiac function. Perturbation in the ER homeostasis due to intrinsic and extrinsic factors, such as inflammation, oxidative stress, and ischemia, leads to ER stress that has been linked to multiple conditions including diabetes mellitus, neurodegeneration, cancer, heart disease, and cardiac arrhythmias. Recent studies have documented the critical roles of ER stress in the pathophysiological basis of AF. Using an animal model of chronic pressure overload, we demonstrate a significant increase in ER stress in atrial tissues. Moreover, we demonstrate that treatment with a small molecule inhibitor to inhibit the soluble epoxide hydrolase enzyme in the arachidonic acid metabolism significantly reduces ER stress as well as atrial electrical and structural remodeling. The current review article will attempt to provide a perspective on our recent understandings and current knowledge gaps on the critical roles of proteostasis and ER stress in AF progression.

The evolution of regulated cell death pathways in animals and their evasion by pathogens

The coevolution of host-pathogen interactions underlies many human physiological traits associated with protection from or susceptibility to infections. Among the mechanisms that animals utilize to control infections are the regulated cell death pathways of pyroptosis, apoptosis, and necroptosis. Over the course of evolution these pathways have become intricate and complex, coevolving with microbes that infect animal hosts. Microbes, in turn, have evolved strategies to interfere with the pathways of regulated cell death to avoid eradication by the host. Here, we present an overview of the mechanisms of regulated cell death in Animalia and the strategies devised by pathogens to interfere with these processes. We review the molecular pathways of regulated cell death, their roles in infection, and how they are perturbed by viruses and bacteria, providing insights into the coevolution of host-pathogen interactions and cell death pathways.

Stress-induced inflammation evoked by immunogenic cell death is blunted by the IRE1α kinase inhibitor KIRA6 through HSP60 targeting

Mounting evidence indicates that immunogenic therapies engaging the unfolded protein response (UPR) following endoplasmic reticulum (ER) stress favor proficient cancer cell-immune interactions, by stimulating the release of immunomodulatory/proinflammatory factors by stressed or dying cancer cells. UPR-driven transcription of proinflammatory cytokines/chemokines exert beneficial or detrimental effects on tumor growth and antitumor immunity, but the cell-autonomous machinery governing the cancer cell inflammatory output in response to immunogenic therapies remains poorly defined. Here, we profiled the transcriptome of cancer cells responding to immunogenic or weakly immunogenic treatments. Bioinformatics-driven pathway analysis indicated that immunogenic treatments instigated a NF-κB/AP-1-inflammatory stress response, which dissociated from both cell death and UPR. This stress-induced inflammation was specifically abolished by the IRE1α-kinase inhibitor KIRA6. Supernatants from immunogenic chemotherapy and KIRA6 co-treated cancer cells were deprived of proinflammatory/chemoattractant factors and failed to mobilize neutrophils and induce dendritic cell maturation. Furthermore, KIRA6 significantly reduced the in vivo vaccination potential of dying cancer cells responding to immunogenic chemotherapy. Mechanistically, we found that the anti-inflammatory effect of KIRA6 was still effective in IRE1α-deficient cells, indicating a hitherto unknown off-target effector of this IRE1α-kinase inhibitor. Generation of a KIRA6-clickable photoaffinity probe, mass spectrometry, and co-immunoprecipitation analysis identified cytosolic HSP60 as a KIRA6 off-target in the IKK-driven NF-κB pathway. In sum, our study unravels that HSP60 is a KIRA6-inhibitable upstream regulator of the NF-κB/AP-1-inflammatory stress responses evoked by immunogenic treatments. It also urges caution when interpreting the anti-inflammatory action of IRE1α chemical inhibitors.

ER Stress in Cardiometabolic Diseases: From Molecular Mechanisms to Therapeutics

The endoplasmic reticulum (ER) hosts linear polypeptides and fosters natural folding of proteins through ER-residing chaperones and enzymes. Failure of the ER to align and compose proper protein architecture leads to accumulation of misfolded/unfolded proteins in the ER lumen, which disturbs ER homeostasis to provoke ER stress. Presence of ER stress initiates the cytoprotective unfolded protein response (UPR) to restore ER homeostasis or instigates a rather maladaptive UPR to promote cell death. Although a wide array of cellular processes such as persistent autophagy, dysregulated mitophagy, and secretion of proinflammatory cytokines may contribute to the onset and progression of cardiometabolic diseases, it is well perceived that ER stress also evokes the onset and development of cardiometabolic diseases, particularly cardiovascular diseases (CVDs), diabetes mellitus, obesity, and chronic kidney disease (CKD). Meanwhile, these pathological conditions further aggravate ER stress, creating a rather vicious cycle. Here in this review, we aimed at summarizing and updating the available information on ER stress in CVDs, diabetes mellitus, obesity, and CKD, hoping to offer novel insights for the management of these cardiometabolic comorbidities through regulation of ER stress.

From Immunogenic Cell Death to Immunogenic Modulation: Select Chemotherapy Regimens Induce a Spectrum of Immune-Enhancing Activities in the Tumor Microenvironment

Cancer treatment has rapidly entered the age of immunotherapy, and it is becoming clear that the effective therapy of established tumors necessitates rational multi-combination immunotherapy strategies. But even in the advent of immunotherapy, the clinical role of standard-of-care chemotherapy regimens still remains significant and may be complementary to emerging immunotherapeutic approaches. Depending on dose, schedule, and agent, chemotherapy can induce immunogenic cell death, resulting in the release of tumor antigens to stimulate an immune response, or immunogenic modulation, sensitizing surviving tumor cells to immune cell killing. While these have been previously defined as distinct processes, in this review we examine the published mechanisms supporting both immunogenic cell death and immunogenic modulation and propose they be reclassified as similar effects termed "immunogenic cell stress." Treatment-induced immunogenic cell stress is an important result of cytotoxic chemotherapy and future research should consider immunogenic cell stress as a whole rather than just immunogenic cell death or immunogenic modulation. Cancer treatment strategies should be designed specifically to take advantage of these effects in combination immunotherapy, and novel chemotherapy regimens should be designed and investigated to potentially induce all aspects of immunogenic cell stress.

Insight into the Web of Stress Responses Triggered at Gene Expression Level by Porphyrin-PDT in HT29 Human Colon Carcinoma Cells

Photodynamic therapy (PDT), a highly targeted therapy with acceptable side effects, has emerged as a promising therapeutic option in oncologic pathology. One of the issues that needs to be addressed is related to the complex network of cellular responses developed by tumor cells in response to PDT. In this context, this study aims to characterize in vitro the stressors and the corresponding cellular responses triggered by PDT in the human colon carcinoma HT29 cell line, using a new asymmetric porphyrin derivative (P2.2) as a photosensitizer. Besides investigating the ability of P2.2-PDT to reduce the number of viable tumor cells at various P2.2 concentrations and fluences of the activating light, we assessed, using qRT-PCR, the expression levels of 84 genes critically involved in the stress response of PDT-treated cells. Results showed a fluence-dependent decrease of viable tumor cells at 24 h post-PDT, with few cells that seem to escape from PDT. We highlighted following P2.2-PDT the concomitant activation of particular cellular responses to oxidative stress, hypoxia, DNA damage and unfolded protein responses and inflammation. A web of inter-connected stressors was induced by P2.2-PDT, which underlies cell death but also elicits protective mechanisms that may delay tumor cell death or even defend these cells against the deleterious effects of PDT.

Possible protective effect of resolvin D1 on inflammation in atrial fibrillation: involvement of ER stress mediated the NLRP3 inflammasome pathway

Atrial fibrillation (AF) is the most common type of cardiac rhythm disturbance. At the cellular level, excessive ROS generation during AF is associated with ER stress, which induces an inflammatory response by activating the unfolded protein response (UPR) pathway and the nuclear factor-kappa B (NF-kB) signaling pathway. Activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome has been linked to the pathogenesis of AF through NF-kB activation and inflammatory cytokine secretion. It has been shown that NLRP3 inflammasome activation by endoplasmic reticulum (ER) stress is dependent on NF-kB activation. The anti-inflammatory role of resolvin D1 (RvD1), a pro-resolving mediator derived from omega-3 fatty acids, has demonstrated that the NF-κB/NLRP3 inflammasome pathway in different tissues is attenuated after treatment with RvD1. However, the mechanism of the anti-inflammatory activity of RvD1 in AF has not been clarified. This review suggests that RvD1 may inhibit ER stress-induced NLRP3 inflammasome through suppressing NF-κB in cardiac tissue and, thus ameliorate AF.

Tissue Homeostasis and Inflammation

There is a growing interest in understanding tissue organization, homeostasis, and inflammation. However, despite an abundance of data, the organizing principles of tissue biology remain poorly defined. Here, we present a perspective on tissue organization based on the relationships between cell types and the functions that they perform. We provide a formal definition of tissue homeostasis as a collection of circuits that regulate specific variables within the tissue environment, and we describe how the functional organization of tissues allows for the maintenance of both tissue and systemic homeostasis. This leads to a natural definition of inflammation as a response to deviations from homeostasis that cannot be reversed by homeostatic mechanisms alone. We describe how inflammatory signals act on the same cellular functions involved in normal tissue organization and homeostasis in order to coordinate emergency responses to perturbations and ultimately return the system to a homeostatic state. Finally, we consider the hierarchy of homeostatic and inflammatory circuits and the implications for the development of inflammatory diseases.

Endoplasmic reticulum stress and unfolded protein response in cardiovascular diseases

Cardiovascular diseases (CVDs), such as ischaemic heart disease, cardiomyopathy, atherosclerosis, hypertension, stroke and heart failure, are among the leading causes of morbidity and mortality worldwide. Although specific CVDs and the associated cardiometabolic abnormalities have distinct pathophysiological and clinical manifestations, they often share common traits, including disruption of proteostasis resulting in accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER). ER proteostasis is governed by the unfolded protein response (UPR), a signalling pathway that adjusts the protein-folding capacity of the cell to sustain the cell's secretory function. When the adaptive UPR fails to preserve ER homeostasis, a maladaptive or terminal UPR is engaged, leading to the disruption of ER integrity and to apoptosis. ER stress functions as a double-edged sword, with long-term ER stress resulting in cellular defects causing disturbed cardiovascular function. In this Review, we discuss the distinct roles of the UPR and ER stress response as both causes and consequences of CVD. We also summarize the latest advances in our understanding of the importance of the UPR and ER stress in the pathogenesis of CVD and discuss potential therapeutic strategies aimed at restoring ER proteostasis in CVDs.

Health and Fitness at the Single-Cell Level

Genetically identical cells in a tissue can respond differently to perturbations in their environment or "stress." Such stresses can be physicochemical, mechanical, or infectious or may come from competition with other cells in the tissue. Here, I discuss how the varying responses to stress influence the decision of a cell to repair or die, and how one cell's response can have effects on surrounding cells. Such responses control the health and fitness of single cells and how they compete with other genetically identical cells.See related article on p. 129.

Endoplasmic reticulum stress signals in the tumour and its microenvironment

Protein handling, modification and folding in the endoplasmic reticulum (ER) are tightly regulated processes that determine cell function, fate and survival. In several tumour types, diverse oncogenic, transcriptional and metabolic abnormalities cooperate to generate hostile microenvironments that disrupt ER homeostasis in malignant and stromal cells, as well as infiltrating leukocytes. These changes provoke a state of persistent ER stress that has been demonstrated to govern multiple pro-tumoural attributes in the cancer cell while dynamically reprogramming the function of innate and adaptive immune cells. Aberrant activation of ER stress sensors and their downstream signalling pathways have therefore emerged as key regulators of tumour growth and metastasis as well as response to chemotherapy, targeted therapies and immunotherapy. In this Review, we discuss the physiological inducers of ER stress in the tumour milieu, the interplay between oncogenic signalling and ER stress response pathways in the cancer cell and the profound immunomodulatory effects of sustained ER stress responses in tumours.

ER Stress Leaves an Inflammatory TRAIL

Cell stress often triggers inflammation as a protective response to tissue damage or infection. In this issue of Developmental Cell, Sullivan et al. (2020) reveal an unexpected role for TRAIL receptors in ER-stress-induced inflammation.

Proteotoxic Stress and Cell Death in Cancer Cells

To maintain proteostasis, cells must integrate information and activities that supervise protein synthesis, protein folding, conformational stability, and also protein degradation. Extrinsic and intrinsic conditions can both impact normal proteostasis, causing the appearance of proteotoxic stress. Initially, proteotoxic stress elicits adaptive responses aimed at restoring proteostasis, allowing cells to survive the stress condition. However, if the proteostasis restoration fails, a permanent and sustained proteotoxic stress can be deleterious, and cell death ensues. Many cancer cells convive with high levels of proteotoxic stress, and this condition could be exploited from a therapeutic perspective. Understanding the cell death pathways engaged by proteotoxic stress is instrumental to better hijack the proliferative fate of cancer cells.

The pseudo-caspase FLIP(L) regulates cell fate following p53 activation

p53 is the most frequently mutated, well-studied tumor-suppressor gene, yet the molecular basis of the switch from p53-induced cell-cycle arrest to apoptosis remains poorly understood. Using a combination of transcriptomics and functional genomics, we unexpectedly identified a nodal role for the caspase-8 paralog and only human pseudo-caspase, FLIP(L), in regulating this switch. Moreover, we identify FLIP(L) as a direct p53 transcriptional target gene that is rapidly up-regulated in response to Nutlin-3A, an MDM2 inhibitor that potently activates p53. Genetically or pharmacologically inhibiting expression of FLIP(L) using siRNA or entinostat (a clinically relevant class-I HDAC inhibitor) efficiently promoted apoptosis in colorectal cancer cells in response to Nutlin-3A, which otherwise predominantly induced cell-cycle arrest. Enhanced apoptosis was also observed when entinostat was combined with clinically relevant, p53-activating chemotherapy in vitro, and this translated into enhanced in vivo efficacy. Mechanistically, FLIP(L) inhibited p53-induced apoptosis by blocking activation of caspase-8 by the TRAIL-R2/DR5 death receptor; notably, this activation was not dependent on receptor engagement by its ligand, TRAIL. In the absence of caspase-8, another of its paralogs, caspase-10 (also transcriptionally up-regulated by p53), induced apoptosis in Nutlin-3A-treated, FLIP(L)-depleted cells, albeit to a lesser extent than in caspase-8-proficient cells. FLIP(L) depletion also modulated transcription of canonical p53 target genes, suppressing p53-induced expression of the cell-cycle regulator p21 and enhancing p53-induced up-regulation of proapoptotic PUMA. Thus, even in the absence of caspase-8/10, FLIP(L) silencing promoted p53-induced apoptosis by enhancing PUMA expression. Thus, we report unexpected, therapeutically relevant roles for FLIP(L) in determining cell fate following p53 activation.

Targeting of BCL-2 Family Members during Anticancer Treatment: A Necessary Compromise between Individual Cell and Ecosystemic Responses?

The imbalance between BCL-2 homologues and pro-death counterparts frequently noted in cancer cells endows them with a cell autonomous survival advantage. To eradicate ectopic cells, inhibitors of these homologues (BH3 mimetics) were developed to trigger, during anticancer treatment, full activation of the canonical mitochondrial apoptotic pathway and related caspases. Despite efficiency in some clinical settings, these compounds do not completely fulfill their initial promise. We herein put forth that a growing body of evidence indicates that mitochondrial integrity, controlled by BCL-2 family proteins, and downstream caspases regulate other cell death modes and influence extracellular signaling by committed cells. Moreover, intercellular communications play a key role in spreading therapeutic response across cancer cell populations and in engaging an immune response. We thus advocate that BH3 mimetics administration would be more efficient in the long term if it did not induce apoptosis in all sensitive cells at the same time, but if it could instead allow (or trigger) death signal production by non-terminally committed dying cell populations. The development of such a trade-off strategy requires to unravel the effects of BH3 mimetics not only on each individual cancer cell but also on homotypic and heterotypic cell interactions in dynamic tumor ecosystems.

Stress Management: Death Receptor Signalling and Cross-Talks with the Unfolded Protein Response in Cancer

Throughout tumour progression, tumour cells are exposed to various intense cellular stress conditions owing to intrinsic and extrinsic cues, to which some cells are remarkably able to adapt. Death Receptor (DR) signalling and the Unfolded Protein Response (UPR) are two stress responses that both regulate a plethora of outcomes, ranging from proliferation, differentiation, migration, cytokine production to the induction of cell death. Both signallings are major modulators of physiological tissue homeostasis and their dysregulation is involved in tumorigenesis and the metastastic process. The molecular determinants of the control between the different cellular outcomes induced by DR signalling and the UPR in tumour cells and their stroma and their consequences on tumorigenesis are starting to be unravelled. Herein, I summarize the main steps of DR signalling in relation to its cellular and pathophysiological roles in cancer. I then highlight how the UPR and DR signalling control common cellular outcomes and also cross-talk, providing potential opportunities to further understand the development of malignancies.