Mitochondrial permeabilization engages NF-κB-dependent anti-tumour activity under caspase deficiency

Pan-cell death-related signature reveals tumor immune microenvironment and optimizes personalized therapy alternations in lung adenocarcinoma

This study constructed a comprehensive analysis of cell death modules in eliminating aberrant cells and remodeling tumor microenvironment (TME). Consensus analysis was performed in 490 lung adenocarcinoma (LUAD) patients based on 4 types of cell death prognostic genes. Intersection method divided these LUAD samples into 5 cell death risk (CDR) clusters, and COX regression analysis were used to construct the CDR signature (CDRSig) with risk scores. Significant differences of TME phenotypes, clinical factors, genome variations, radiosensitivity and immunotherapy sensitivity were observed in different CDR clusters. Patients with higher risk scores in the CDRSig tended to be immune-excluded or immune-desert, and those with lower risk scores were more sensitive to radiotherapy and immunotherapy. The results from mouse model showed that intense expression of the high-risk gene PFKP was associated with low CD8+ T cell infiltration upon radiotherapy and anti-PD-L1 treatment. Deficient assays in vitro confirmed that PFKP downregulation enhanced cGAS/STING pathway activation and radiosensitivity in LUAD cells. In conclusion, our studies originally performed a comprehensive cell death analysis, suggesting the importance of CDR patterns in reprogramming TME and providing novel clues for LUAD personalized therapies.

A mitochondrial checkpoint to NF-κB signaling

Mitochondrial dysfunction can elicit multiple inflammatory pathways, especially when apoptotic caspases are inhibited. Such an inflammatory program is negatively regulated by the autophagic disposal of permeabilized mitochondria. Recent data demonstrate that the ubiquitination of mitochondrial proteins is essential for NEMO-driven NF-kB activation downstream of mitochondrial permeabilization.

The Caspase-Activated DNase drives inflammation and contributes to defense against viral infection

Mitochondria react to infection with sub-lethal signals in the apoptosis pathway. Mitochondrial signals can be inflammatory but mechanisms are only partially understood. We show that activation of the caspase-activated DNase (CAD) mediates mitochondrial pro-inflammatory functions and substantially contributes to host defense against viral infection. In cells lacking CAD, the pro-inflammatory activity of sub-lethal signals was reduced. Experimental activation of CAD caused transient DNA-damage and a pronounced DNA damage response, involving major kinase signaling pathways, NF-κB and cGAS/STING, driving the production of interferon, cytokines/chemokines and attracting neutrophils. The transcriptional response to CAD-activation was reminiscent of the reaction to microbial infection. CAD-deficient cells had a diminished response to viral infection. Influenza virus infected CAD-deficient mice displayed reduced inflammation in lung tissue, higher viral titers and increased weight loss. Thus, CAD links the mitochondrial apoptosis system and cell death caspases to host defense. CAD-driven DNA damage is a physiological element of the inflammatory response to infection.

Mitochondria and cell death

Mitochondria are cellular factories for energy production, calcium homeostasis and iron metabolism, but they also have an unequivocal and central role in intrinsic apoptosis through the release of cytochrome c. While the subsequent activation of proteolytic caspases ensures that cell death proceeds in the absence of collateral inflammation, other phlogistic cell death pathways have been implicated in using, or engaging, mitochondria. Here we discuss the emerging complexities of intrinsic apoptosis controlled by the BCL-2 family of proteins. We highlight the emerging theory that non-lethal mitochondrial apoptotic signalling has diverse biological roles that impact cancer, innate immunity and ageing. Finally, we delineate the role of mitochondria in other forms of cell death, such as pyroptosis, ferroptosis and necroptosis, and discuss mitochondria as central hubs for the intersection and coordination of cell death signalling pathways, underscoring their potential for therapeutic manipulation.

Lethal and sublethal effects of programmed cell death pathways on hematopoietic stem cells

Programmed cell death is an evolutionally conserved cellular process in multicellular organisms that eliminates unnecessary or rogue cells during development, infection, and carcinogenesis. Hematopoietic stem cells (HSCs) are a rare, self-renewing, and multipotent cell population necessary for the establishment and regeneration of the hematopoietic system. Counterintuitively, key components necessary for programmed cell death induction are abundantly expressed in long-lived HSCs, which often survive myeloablative stress by engaging a prosurvival response that counteracts cell death-inducing stimuli. Although HSCs are well known for their apoptosis resistance, recent studies have revealed their unique vulnerability to certain types of programmed necrosis, such as necroptosis and ferroptosis. Moreover, emerging evidence has shown that programmed cell death pathways can be sublethally activated to cause nonlethal consequences such as innate immune response, organelle dysfunction, and mutagenesis. In this review, we summarized recent findings on how divergent cell death programs are molecularly regulated in HSCs. We then discussed potential side effects caused by sublethal activation of programmed cell death pathways on the functionality of surviving HSCs.

Targeting immunogenic cell stress and death for cancer therapy

Immunogenic cell death (ICD), which results from insufficient cellular adaptation to specific stressors, occupies a central position in the development of novel anticancer treatments. Several therapeutic strategies to elicit ICD - either as standalone approaches or as means to convert immunologically cold tumours that are insensitive to immunotherapy into hot and immunotherapy-sensitive lesions - are being actively pursued. However, the development of ICD-inducing treatments is hindered by various obstacles. Some of these relate to the intrinsic complexity of cancer cell biology, whereas others arise from the use of conventional therapeutic strategies that were developed according to immune-agnostic principles. Moreover, current discovery platforms for the development of novel ICD inducers suffer from limitations that must be addressed to improve bench-to-bedside translational efforts. An improved appreciation of the conceptual difference between key factors that discriminate distinct forms of cell death will assist the design of clinically viable ICD inducers.

Apoptotic cells promote circulating tumor cell survival and metastasis

During tumor progression and especially following cytotoxic therapy, cell death of both tumor and stromal cells is widespread. Despite clinical observations that high levels of apoptotic cells correlate with poorer patient outcomes, the physiological effects of dying cells on tumor progression remain incompletely understood. Here, we report that circulating apoptotic cells robustly enhance tumor cell metastasis to the lungs. Using intravenous metastasis models, we observed that the presence of apoptotic cells, but not cells dying by other mechanisms, supports circulating tumor cell (CTC) survival following arrest in the lung vasculature. Apoptotic cells promote CTC survival by recruiting platelets to the forming metastatic niche. Apoptotic cells externalize the phospholipid phosphatidylserine to the outer leaflet of the plasma membrane, which we found increased the activity of the coagulation initiator Tissue Factor, thereby triggering the formation of platelet clots that protect proximal CTCs. Inhibiting the ability of apoptotic cells to induce coagulation by knocking out Tissue Factor, blocking phosphatidylserine, or administering the anticoagulant heparin abrogated the pro-metastatic effect of apoptotic cells. This work demonstrates a previously unappreciated role for apoptotic cells in facilitating metastasis by establishing CTC-supportive emboli, and suggests points of intervention that may reduce the pro-metastatic effect of apoptotic cells.

GRAPHICAL ABSTRACT

A novel signature based on twelve programmed cell death patterns to predict the prognosis of lung adenocarcinoma

Programmed cell death (PCD) plays a pivotal role in tumor initiation and progression. However, the prognostic value and clinical characteristics of PCD-related genes (PRGs) remain unclear. We collected and analyzed genes associated with twelve PCD patterns, including apoptosis, necroptosis, pyroptosis, ferroptosis, cuproptosis, entotic cell death, netotic cell death, parthanatos, lysosome-dependent cell death, autophagy-dependent cell death, alkaliptosis, and oxeiptosis to construct a gene signature. Our analysis identified 215 differentially expressed PRGs out of 1254 in lung adenocarcinoma (LUAD) and normal lung tissues. Subsequently, we performed univariate Cox regression analysis and identified 58 prognostic PRGs. Based on LASSO Cox regression analysis, we constructed a risk score using the expression levels of seven genes: DAPK2, DDIT4, E2F2, GAPDH, MET, PIM2, and FOXF1. Patients with lower risk scores showed earlier stages of cancer, longer survival times, and better immune infiltrations and functions. Notably, we found that knockdown of DDIT4 significantly increased apoptosis and impaired the proliferation of human LUAD cell lines. Our study proposes a PRG-based prognostic signature that sheds light on the potential role of PCD-related genes in LUAD and provides valuable insights into future therapeutic strategies.

The regulation of the apoptotic pore-An immunological tightrope walk

Apoptotic pore formation in mitochondria is the pivotal point for cell death during mitochondrial apoptosis. It is regulated by BCL-2 family proteins in response to various cellular stress triggers and mediates mitochondrial outer membrane permeabilization (MOMP). This allows the release of mitochondrial contents into the cytosol, which triggers rapid cell death and clearance through the activation of caspases. However, under conditions of low caspase activity, the mitochondrial contents released into the cytosol through apoptotic pores serve as inflammatory signals and activate various inflammatory responses. In this chapter, we discuss how the formation of the apoptotic pore is regulated by BCL-2 proteins as well as other cellular or mitochondrial proteins and membrane lipids. Moreover, we highlight the importance of sublethal MOMP in the regulation of mitochondrial-activated inflammation and discuss its physiological consequences in the context of pathogen infection and disease and how it can potentially be exploited therapeutically, for example to improve cancer treatment.

Immunogenic cell death in cancer: targeting necroptosis to induce antitumour immunity

Most metastatic cancers remain incurable due to the emergence of apoptosis-resistant clones, fuelled by intratumour heterogeneity and tumour evolution. To improve treatment, therapies should not only kill cancer cells but also activate the immune system against the tumour to eliminate any residual cancer cells that survive treatment. While current cancer therapies rely heavily on apoptosis - a largely immunologically silent form of cell death - there is growing interest in harnessing immunogenic forms of cell death such as necroptosis. Unlike apoptosis, necroptosis generates second messengers that act on immune cells in the tumour microenvironment, alerting them of danger. This lytic form of cell death optimizes the provision of antigens and adjuvanticity for immune cells, potentially boosting anticancer treatment approaches by combining cellular suicide and immune response approaches. In this Review, we discuss the mechanisms of necroptosis and how it activates antigen-presenting cells, drives cross-priming of CD8+ T cells and induces antitumour immune responses. We also examine the opportunities and potential drawbacks of such strategies for exposing cancer cells to immunological attacks.

Nanomedicine-induced cell pyroptosis to enhance antitumor immunotherapy

Immunotherapy is a therapeutic modality designed to elicit or augment an immune response against malignancies. Despite the immune system's ability to detect and eradicate neoplastic cells, certain neoplastic cells can elude immune surveillance and elimination through diverse mechanisms. Therefore, antitumor immunotherapy has emerged as a propitious strategy. Pyroptosis, a type of programmed cell death (PCD) regulated by Gasdermin (GSDM), is associated with cytomembrane rupture due to continuous cell expansion, which results in the release of cellular contents that can trigger robust inflammatory and immune responses. The field of nanomedicine has made promising progress, enabling the application of nanotechnology to enhance the effectiveness and specificity of cancer therapy by potentiating, enabling, or augmenting pyroptosis. In this review, we comprehensively examine the paradigms underlying antitumor immunity, particularly paradigms related to nanotherapeutics combined with pyroptosis; these treatments include chemotherapy (CT), hyperthermia therapy, photodynamic therapy (PDT), chemodynamic therapy (CDT), ion-interference therapy (IIT), biomimetic therapy, and combination therapy. Furthermore, we thoroughly discuss the coordinated mechanisms that regulate these paradigms. This review is expected to enhance the understanding of the interplay between pyroptosis and antitumor immunotherapy, broaden the utilization of diverse nanomaterials in pyroptosis-based antitumor immunotherapy, and facilitate advancements in clinical tumor therapy.

Inflammation and mitophagy are mitochondrial checkpoints to aging

Cellular and organismal aging have been consistently associated with mitochondrial dysfunction and inflammation. Accumulating evidence indicates that aging-related inflammatory responses are mechanistically linked to compromised mitochondrial integrity coupled with mtDNA-driven CGAS activation, a process that is tonically inhibited by mitophagy.

Identification of a novel form of caspase-independent cell death triggered by BH3-mimetics in diffuse large B-cell lymphoma cell lines

BH3-mimetics represent promising anti-cancer agents in tumors that rely on the anti-apoptotic function of B-Cell Lymphoma 2 (BCL2) proteins, particularly in leukemia and lymphoma cells primed for apoptosis. Mechanistically, BH3-mimetics may displace pro-apoptotic binding partners thus inducing BAX/BAK-mediated mitochondrial permeabilization followed by cytochrome c release, activation of the caspase cascade and apoptosis. Here, we describe a novel mode of caspase-independent cell death (CICD) induced by BH3-mimetics in a subset of diffuse large B-cell lymphoma (DLBCL) cells. Of note, rather than occurring via necroptosis, CICD induced immediately after mitochondrial permeabilization was associated with transcriptional reprogramming mediated by activation of c-Jun N-terminal Kinase (JNK) signaling and Activator Protein 1 (AP1). Thereby, CICD resulted in the JNK/AP1-mediated upregulation of inflammatory chemokines and increased migration of cytotoxic Natural Killer (NK) cells. Taken together, our study describes a novel mode of CICD triggered by BH3-mimetics that may alter the immune response towards dying cells.

Shedding light on mitochondrial outer-membrane permeabilization and membrane potential: State of the art methods and biosensors

Membrane structural integrity is essential for optimal mitochondrial function. These organelles produce the energy needed for all vital processes, provided their outer and inner membranes are intact. This prevents the release of mitochondrial apoptogenic factors into the cytosol and ensures intact mitochondrial membrane potential (ΔΨm) to sustain ATP production. Cell death by apoptosis is generally triggered by outer mitochondrial membrane permeabilization (MOMP), tightly coupled with loss of ΔΨ m. As these two processes are essential for both mitochondrial function and cell death, researchers have devised various techniques to assess them. Here, we discuss current methods and biosensors available for detecting MOMP and measuring ΔΨ m, focusing on their advantages and limitations and discuss what new imaging tools are needed to improve our knowledge of mitochondrial function.

Death and survival from executioner caspase activation

Executioner caspases are evolutionarily conserved regulators of cell death under apoptotic stress. Activated executioner caspases drive apoptotic cell death through cleavage of diverse protein substrates or pyroptotic cell death in the presence of gasdermin E. On the other hand, activation of executioner caspases can also trigger pro-survival and pro-proliferation signals. In recent years, a growing body of studies have demonstrated that cells can survive from executioner caspase activation in response to stress and that the survivors undergo molecular and phenotypic alterations. This review focuses on death and survival from executioner caspase activation, summarizing the role of executioner caspases in apoptotic and pyroptotic cell death and discussing the potential mechanism and consequences of survival from stress-induced executioner caspase activation.

Stress in the metastatic journey - the role of cell communication and clustering in breast cancer progression and treatment resistance

Breast cancer stands as the most prevalent malignancy afflicting women. Despite significant advancements in its diagnosis and treatment, breast cancer metastasis continues to be a leading cause of mortality among women. To metastasize, cancer cells face numerous challenges: breaking away from the primary tumor, surviving in the circulation, establishing in a distant location, evading immune detection and, finally, thriving to initiate a new tumor. Each of these sequential steps requires cancer cells to adapt to a myriad of stressors and develop survival mechanisms. In addition, most patients with breast cancer undergo surgical removal of their primary tumor and have various therapeutic interventions designed to eradicate cancer cells. Despite this plethora of attacks and stresses, certain cancer cells not only manage to persist but also proliferate robustly, giving rise to substantial tumors that frequently culminate in the patient's demise. To enhance patient outcomes, there is an imperative need for a deeper understanding of the molecular and cellular mechanisms that empower cancer cells to not only survive but also expand. Herein, we delve into the intrinsic stresses that cancer cells encounter throughout the metastatic journey and the additional stresses induced by therapeutic interventions. We focus on elucidating the remarkable strategies adopted by cancer cells, such as cell-cell clustering and intricate cell-cell communication mechanisms, to ensure their survival.

Sublethal engagement of apoptotic pathways in residual cancer

Cytotoxic chemo-, radio-, and targeted therapies frequently elicit apoptotic cancer cell death. Mitochondrial outer membrane permeabilization (MOMP) is a critical, regulated step in this apoptotic pathway. The residual cancer cells that survive treatment serve as the seeds of eventual relapse and are often functionally characterized by their transient tolerance of multiple therapeutic treatments. New studies suggest that, in these cells, a sublethal degree of MOMP, reflective of incomplete apoptotic commitment, is widely observed. Here, we review recent evidence that this sublethal MOMP drives the aggressive features of residual cancer cells while templating a host of unique vulnerabilities, highlighting how failed apoptosis may counterintuitively enable new therapeutic strategies to target residual disease (RD).

Mitochondrial outer membrane integrity regulates a ubiquitin-dependent and NF-κB-mediated inflammatory response

Mitochondrial outer membrane permeabilisation (MOMP) is often essential for apoptosis, by enabling cytochrome c release that leads to caspase activation and rapid cell death. Recently, MOMP has been shown to be inherently pro-inflammatory with emerging cellular roles, including its ability to elicit anti-tumour immunity. Nonetheless, how MOMP triggers inflammation and how the cell regulates this remains poorly defined. We find that upon MOMP, many proteins localised either to inner or outer mitochondrial membranes are ubiquitylated in a promiscuous manner. This extensive ubiquitylation serves to recruit the essential adaptor molecule NEMO, leading to the activation of pro-inflammatory NF-κB signalling. We show that disruption of mitochondrial outer membrane integrity through different means leads to the engagement of a similar pro-inflammatory signalling platform. Therefore, mitochondrial integrity directly controls inflammation, such that permeabilised mitochondria initiate NF-κB signalling.

Pan-cancer analysis of NUDT21 and its effect on the proliferation of human head and neck squamous cell carcinoma

BACKGROUND

Based on bioinformatics research of NUDT21 in pan-cancer, we aimed to clarify the mechanism of NUDT21 in HHNC by experiment.

METHODS

The correlation between differential expression of NUDT21 in pan-cancer and survival prognosis, genomic instability, tumor stemness, DNA repair, RNA methylation and with immune microenvironment were analyzed by the application of different pan-cancer analysis web databases. In addition, immunohistochemistry staining and genetic detection of NUDT21 in HHNCC tumor tissues by immunohistochemistry and qRT-PCR. Then, through in vitro cell experiments, NUDT21 was knocked down by lentivirus to detect the proliferation, cycle, apoptosis of FaDu and CNE-2Z cells, and finally by PathScan intracellular signaling array reagent to detect the apoptotic protein content.

RESULTS

Based on the pan-cancer analysis, we found that elevated expression of NUDT21 in most cancers was significantly correlated with TMB, MSI, neoantigens and chromosomal ploidy, and in epigenetics, elevated NUDT21 expression was strongly associated with genomic stability, mismatch repair genes, tumor stemness, and RNA methylation. Based on immunosuppressive score, we found that NUDT21 plays an essential role in the immunosuppressive environment by suppressing immune checkpointing effect in most cancers. In addition, using HHNSCC as a study target, PCR and pathological detection of NUDT21 in tumor tissues was significantly increased than that in paracancerous normal tissues. In vitro cellular assays, silencing NUDT21 inhibited proliferation and promoted apoptosis in FaDu and CNE-2Z cells, and blocked the cell cycle in the G2/M phase. Therefore, the experiments confirmed that NUDT21 promotes the proliferation of FaDu by suppressing the expression of apoptotic.

CD1d protects against hepatocyte apoptosis in non-alcoholic steatohepatitis

BACKGROUND & AIMS

Hepatocyte apoptosis, a well-defined form of cell death in non-alcoholic steatohepatitis (NASH), is considered the primary cause of liver inflammation and fibrosis. However, the mechanisms underlying the regulation of hepatocyte apoptosis in NASH remain largely unclear. We explored the anti-apoptotic effect of hepatocyte CD1d in NASH.

METHODS

Hepatocyte CD1d expression was analyzed in patients with NASH and mouse models. Hepatocyte-specific gene overexpression or knockdown and anti-CD1d crosslinking were used to investigate the anti-apoptotic effect of hepatocyte CD1d on lipotoxicity-, Fas-, and concanavalin (ConA)-mediated liver injuries. A high-fat diet, a methionine-choline-deficient diet, a Fas agonist, and ConA were used to induce lipotoxic and/or apoptotic liver injuries. Palmitic acid was used to mimic lipotoxicity-induced apoptosis in vitro.

RESULTS

We identified a dramatic decrease in CD1d expression in hepatocytes of patients with NASH and mouse models. Hepatocyte-specific CD1d overexpression and knockdown experiments collectively demonstrated that hepatocyte CD1d protected against hepatocyte apoptosis and alleviated hepatic inflammation and injuries in NASH mice. Furthermore, decreased JAK2-STAT3 signaling was observed in NASH patient livers. Mechanistically, anti-CD1d crosslinking on hepatocytes induced tyrosine phosphorylation of the CD1d cytoplasmic tail, leading to the recruitment and phosphorylation of JAK2. Phosphorylated JAK2 activated STAT3 and subsequently reduced apoptosis in hepatocytes, which was associated with an increase in anti-apoptotic effectors (Bcl-xL and Mcl-1) and a decrease in pro-apoptotic effectors (cleaved-caspase 3/7). Moreover, anti-CD1d crosslinking effectively protected against Fas- or ConA-mediated hepatocyte apoptosis and liver injury in mice.

CONCLUSIONS

Our study uncovered a previously unrecognized anti-apoptotic CD1d-JAK2-STAT3 axis in hepatocytes that conferred hepatoprotection and highlighted the potential of hepatocyte CD1d-directed therapy for liver injury and fibrosis in NASH, as well as in other liver diseases associated with hepatocyte apoptosis.

IMPACT AND IMPLICATIONS

Excessive and/or sustained hepatocyte apoptosis is critical in driving liver inflammation and injury. The mechanisms underlying the regulation of hepatocyte apoptosis in non-alcoholic steatohepatitis (NASH) remain largely unclear. Here, we found that CD1d expression in hepatocytes substantially decreases and negatively correlates with the severity of liver injury in patients with NASH. We further revealed a previously unrecognized anti-apoptotic CD1d-JAK2-STAT3 signaling axis in hepatocytes, which confers significant protection against liver injury in NASH and acute liver diseases. Thus, hepatocyte CD1d-targeted therapy could be a promising strategy to manipulate liver injury in both NASH and other hepatocyte apoptosis-related liver diseases.

Novel Sulforaphane Analog Disrupts Phosphatidylinositol-3-Kinase-Protein Kinase B Pathway and Inhibits Cancer Cell Progression via Reactive Oxygen Species-Mediated Caspase-Independent Apoptosis

Sulforaphane, a naturally occurring isothiocyanate, has gained attention due to its tremendous anticancer potential. Thus, an array of sulforaphane analogs were synthesized and evaluated for their cytotoxic potentials on a wide range of malignant cell lines. Among these derivatives, compound 4a displayed exceptional potency in inhibiting the proliferation of cancer cell lines and a negligible effect on normal cell lines through G2/M phase arrest. The lead compound induced reactive oxygen species (ROS)-mediated mitochondrial dysfunction, leading to apoptosis. Further mechanistic studies established the interaction of the compound 4a with the insulin-like growth factor-1 receptor (IGF-R1) and blocking of the phosphatidylinositol-3-kinase (PI3K)-protein kinase B (PKB/Akt) pathway. This led to suppression of nuclear factor erythroid 2-related factor 2 (NRF-2) protein expression, thus increasing the free radicals in the tumor cells. Moreover, compound 4a induced ROS-mediated caspase-independent apoptosis. Finally, compound 4a reduced tumor progression in a 4T1 injected BALB/c syngeneic mice tumor model. In conclusion, this study summarizes the mechanism of compound 4a-mediated ROS-mediated caspase-independent apoptosis. According to the study's findings, compound 4a can be used as a powerful new anticancer agent to enhance cancer treatment.

Research progress on mitochondria regulating tumor immunity

Tumor cells adapt their metabolism to meet the demands for energy and biosynthesis. Mitochondria, pivotal organelles in the metabolic reprogramming of tumor cells, contribute to tumorigenesis and cancer progression significantly through various dysfunctions in both tumor and immune cells. Alterations in mitochondrial dynamics and metabolic signaling pathways exert crucial regulatory influence on the activation, proliferation, and differentiation of immune cells. The tumor microenvironment orchestrates the activation and functionality of tumor-infiltrating immune cells by reprogramming mitochondrial metabolism and inducing shifts in mitochondrial dynamics, thereby facilitating the establishment of a tumor immunosuppressive microenvironment. Stress-induced leakage of mitochondrial DNA contributes multifaceted regulatory effects on anti-tumor immune responses and the immunosuppressive microenvironment by activating multiple natural immune signals, including cGAS-STING, TLR9, and NLRP3. Moreover, mitochondrial DNA-mediated immunogenic cell death emerges as a promising avenue for anti-tumor immunotherapy. Additionally, mitochondrial reactive oxygen species, a crucial factor in tumorigenesis, drives the formation of tumor immunosuppressive microenvironment by changing the composition of immune cells within the tumor microenvironment. This review focuses on the intrinsic relationship between mitochondrial biology and anti-tumor immune responses from multiple angles. We explore the core role of mitochondria in the dynamic interplay between the tumor and the host to facilitate the development of targeted mitochondrial strategies for anti-tumor immunotherapy.

Determinants for Antitumor and Protumor Effects of Programmed Cell Death

Cytotoxic anticancer therapies activate programmed cell death in the context of underlying stress and inflammatory signaling to elicit the emission of danger signals, cytokines, and chemokines. In a concerted manner, these immunomodulatory secretomes stimulate antigen presentation and T cell-mediated anticancer immune responses. In some instances, cell death-associated secretomes attract immunosuppressive cells to promote tumor progression. As it stands, cancer cell death-induced changes in the tumor microenvironment that contribute to antitumor or protumor effects remain largely unknown. This is complicated to examine because cell death is often subverted by tumors to circumvent natural, and therapy-induced, immunosurveillance. Here, we provide insights into important but understudied aspects of assessing the contribution of cell death to tumor elimination or cancer progression, including the role of tumor-associated genetics, epigenetics, and oncogenic factors in subverting immunogenic cell death. This perspective will also provide insights on how future studies may address the complex antitumor and protumor immunologic effects of cell death, while accounting for variations in tumor genetics and underlying microenvironment.

Immunogenicity of cancer cells: An overview

The immune system assumes a pivotal role in the organism's capacity to discern and obliterate malignant cells. The immunogenicity of a cancer cell pertains to its proficiency in inciting an immunological response. The prowess of immunogenicity stands as a pivotal determinant in the triumph of formulating immunotherapeutic methodologies. Immunotherapeutic strategies include immune checkpoint inhibitors, chimeric antigen receptor (CAR) T-cell therapy, and on vaccines. Immunogenic cell death (ICD) epitomizes a form of cellular demise that incites an immune response against dying cells. ICD is characterized by the liberation of distinct specific molecules that activate the immune system, thereby leading to the identification and elimination of dying cells by immunocytes. One of the salient characteristics inherent to the ICD phenomenon resides in the vigorous liberation of adenosine triphosphate (ATP) by cellular entities dedicated to embarking upon the process of programmed cell death, yet refraining from complete apoptotic demise. ICD is initiated by a sequence of molecular events that occur during cell death. These occurrences encompass the unveiling or discharge of molecules such as calreticulin, high-mobility group box 1 (HMGB1), and adenosine triphosphate (ATP) from dying cells. These molecules act as "eat me" signals, which are recognized by immune cells, thereby prompting the engulfment and deterioration of expiring cells by phagocytes including various pathways such as Necroptosis, Apoptosis, and pyroptosis. Here, we review our current understanding of the pathophysiological importance of the immune responses against dying cells and the mechanisms underlying their activation. Overall, the ICD represents an important mechanism by which the immune system recognizes and eliminates dying cells, including cancer cells. Understanding the molecular events that underlie ICD bears the potential to engender innovative cancer therapeutics that harness the power of the immune system to combat cancer.

Investigating cell death responses associated with histotripsy ablation of canine osteosarcoma

BACKGROUND

Osteosarcoma (OS) is the most frequently occurring primary bone tumor in dogs and people and innovative treatment options are profoundly needed. Histotripsy is an emerging tumor ablation modality, and it is essential for the clinical translation of histotripsy to gain knowledge about the outcome of nonablated tumor cells that could remain postablation. The objective of this study was to characterize the cell death genetic signature and proliferation response of canine OS cells post a near complete histotripsy ablation (96% ± 1.5) and to evaluate genetic cell death signatures associated with histotripsy ablation and OS in vivo.

METHODS

In the current study, we ablated three canine OS cell lines with a histotripsy dose that resulted in near complete ablation to allow for a viable tumor cell population for downstream analyses. To assess the in vivo cell death genetic signature, we characterized cell death genetic signature in histotripsy-ablated canine OS tumors collected 24-h postablation.

RESULTS

Differential gene expression changes observed in the 4% viable D17 and D418 cells, and histotripsy-ablated OS tumor samples, but not in Abrams cells, were associated with immunogenic cell death (ICD). The 4% viable OS cells demonstrated significantly reduced proliferation, compared to control OS cells, in vitro.

CONCLUSION

Histotripsy ablation of OS cell lines leads to direct and potentially indirect cell death as evident by, reduced proliferation in remaining viable OS cells and cell death genetic signatures suggestive of ICD both in vitro and in vivo.

Apoptotic dysregulation mediates stem cell competition and tissue regeneration

Since adult stem cells are responsible for replenishing tissues throughout life, it is vital to understand how failure to undergo apoptosis can dictate stem cell behavior both intrinsically and non-autonomously. Here, we report that depletion of pro-apoptotic Bax protein bestows hair follicle stem cells with the capacity to eliminate viable neighboring cells by sequestration of TNFα in their membrane. This in turn induces apoptosis in "loser" cells in a contact-dependent manner. Examining the underlying mechanism, we find that Bax loss-of-function competitive phenotype is mediated by the intrinsic activation of NFκB. Notably, winner stem cells differentially respond to TNFα, owing to their elevated expression of TNFR2. Finally, we report that in vivo depletion of Bax results in an increased stem cell pool, accelerating wound-repair and de novo hair follicle regeneration. Collectively, we establish a mechanism of mammalian cell competition, which can have broad therapeutic implications for tissue regeneration and tumorigenesis.

A1 is induced by pathogen ligands to limit myeloid cell death and NLRP3 inflammasome activation

Programmed cell death pathways play an important role in innate immune responses to infection. Activation of intrinsic apoptosis promotes infected cell clearance; however, comparatively little is known about how this mode of cell death is regulated during infections and whether it can induce inflammation. Here, we identify that the pro-survival BCL-2 family member, A1, controls activation of the essential intrinsic apoptotic effectors BAX/BAK in macrophages and monocytes following bacterial lipopolysaccharide (LPS) sensing. We show that, due to its tight transcriptional and post-translational regulation, A1 acts as a molecular rheostat to regulate BAX/BAK-dependent apoptosis and the subsequent NLRP3 inflammasome-dependent and inflammasome-independent maturation of the inflammatory cytokine IL-1β. Furthermore, induction of A1 expression in inflammatory monocytes limits cell death modalities and IL-1β activation triggered by Neisseria gonorrhoeae-derived outer membrane vesicles (NOMVs). Consequently, A1-deficient mice exhibit heightened IL-1β production in response to NOMV injection. These findings reveal that bacteria can induce A1 expression to delay myeloid cell death and inflammatory responses, which has implications for the development of host-directed antimicrobial therapeutics.

Roles of RIPK1 as a stress sentinel coordinating cell survival and immunogenic cell death

Cell death and inflammation are closely linked arms of the innate immune response to combat infection and tissue malfunction. Recent advancements in our understanding of the intricate signals originating from dying cells have revealed that cell death serves as more than just an end point. It facilitates the exchange of information between the dying cell and cells of the tissue microenvironment, particularly immune cells, alerting and recruiting them to the site of disturbance. Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is emerging as a critical stress sentinel that functions as a molecular switch, governing cellular survival, inflammatory responses and immunogenic cell death signalling. Its tight regulation involves multiple layers of post-translational modifications. In this Review, we discuss the molecular mechanisms that regulate RIPK1 to maintain homeostasis and cellular survival in healthy cells, yet drive cell death in a context-dependent manner. We address how RIPK1 mutations or aberrant regulation is associated with inflammatory and autoimmune disorders and cancer. Moreover, we tease apart what is known about catalytic and non-catalytic roles of RIPK1 and discuss the successes and pitfalls of current strategies that aim to target RIPK1 in the clinic.

Increased mitochondria are responsible for the acquisition of gemcitabine resistance in pancreatic cancer cell lines

Pancreatic ductal adenocarcinoma has a particularly poor prognosis as it is often detected at an advanced stage and acquires resistance to chemotherapy early during its course. Stress adaptations by mitochondria, such as metabolic plasticity and regulation of apoptosis, promote cancer cell survival; however, the relationship between mitochondrial dynamics and chemoresistance in pancreatic ductal adenocarcinoma remains unclear. We here established human pancreatic cancer cell lines resistant to gemcitabine from MIA PaCa-2 and Panc1 cells. We compared the cells before and after the acquisition of gemcitabine resistance to investigate the mitochondrial dynamics and protein expression that contribute to this resistance. The mitochondrial number increased in gemcitabine-resistant cells after resistance acquisition, accompanied by a decrease in mitochondrial fission 1 protein, which induces peripheral mitosis, leading to mitophagy. An increase in the number of mitochondria promoted oxidative phosphorylation and increased anti-apoptotic protein expression. Additionally, enhanced oxidative phosphorylation decreased the AMP/ATP ratio and suppressed AMPK activity, resulting in the activation of the HSF1-heat shock protein pathway, which is required for environmental stress tolerance. Synergistic effects observed with BCL2 family or HSF1 inhibition in combination with gemcitabine suggested that the upregulated expression of apoptosis-related proteins caused by the mitochondrial increase may contribute to gemcitabine resistance. The combination of gemcitabine with BCL2 or HSF1 inhibitors may represent a new therapeutic strategy for the treatment of acquired gemcitabine resistance in pancreatic ductal adenocarcinoma.

Apoptotic stress causes mtDNA release during senescence and drives the SASP

Senescent cells drive age-related tissue dysfunction partially through the induction of a chronic senescence-associated secretory phenotype (SASP)1. Mitochondria are major regulators of the SASP; however, the underlying mechanisms have not been elucidated2. Mitochondria are often essential for apoptosis, a cell fate distinct from cellular senescence. During apoptosis, widespread mitochondrial outer membrane permeabilization (MOMP) commits a cell to die3. Here we find that MOMP occurring in a subset of mitochondria is a feature of cellular senescence. This process, called minority MOMP (miMOMP), requires BAX and BAK macropores enabling the release of mitochondrial DNA (mtDNA) into the cytosol. Cytosolic mtDNA in turn activates the cGAS-STING pathway, a major regulator of the SASP. We find that inhibition of MOMP in vivo decreases inflammatory markers and improves healthspan in aged mice. Our results reveal that apoptosis and senescence are regulated by similar mitochondria-dependent mechanisms and that sublethal mitochondrial apoptotic stress is a major driver of the SASP. We provide proof-of-concept that inhibition of miMOMP-induced inflammation may be a therapeutic route to improve healthspan.

Cell-free fat extract-loaded microneedles attenuate inflammation-induced apoptosis and mitochondrial damage in tendinopathy

Existing clinical treatments for tendinopathy mainly focus on reducing pain, whereas inhibiting or reversing disease progression remains challenging. Local therapeutic drugs, such as glucocorticoids, cause adverse effects on the metabolism of tendon tissues and injection-related complications. Therefore, new administration modalities for tendinopathy need to be developed. In this study, we designed a hydrogel-based microneedle (MN) system for the long-term transdermal delivery of our novel biological cell-free fat extract (CEFFE) to treat tendinopathies. We found that CEFFE-loaded MNs (CEFFE-MNs) had good biosafety and inhibited lipopolysaccharide (LPS)-induced apoptosis and matrix degradation in Achilles tendon cells of rats. The Achilles tendons of rats returned to their maximum mechanical strength after applying CEFFE-MNs. The administration of CEFFE-MNs had better anti-apoptosis and tendon repair-promoting effects than CEFEF injections in vivo. Transcriptome sequencing indicated that the anti-apoptosis effect of CEFFE-MNs was highly related to tumor necrosis factor (TNF) signaling. CEFFE-MNs inhibited the expression of TNF, TNF receptor 1, and downstream nuclear factor-kappa B signaling. Additionally, CEFFE-MNs rescued LPS-induced mitochondrial dynamics in tendon cells via the TNF-Drp1 axis. Our study reports a novel CEFFE-MN system that exhibits long-term anti-inflammatory and anti-apoptotic effects, suggesting it as a new treatment route for tendinopathy with broad clinical translation prospects.

Construction of PANoptosis signature: Novel target discovery for prostate cancer immunotherapy

PANoptosis pathway gene sets encompassing pyroptosis, apoptosis, and necroptosis were identified from the MSigDB database. We analyzed the perturbations and crosstalk in the PANoptosis pathway in prostate adenocarcinoma (PRAD), including gene mutation, transcription, methylation, and clinical features. By constructing a PANoptosis signature, we accurately predicted the prognosis and immunotherapeutic response of PRAD patients. We further explored the molecular features and immunological roles of the signature, dividing patients into high- and low-score groups. Notably, the high-score group correlated with better survival outcomes and immunotherapeutic responses, as well as a higher mutation frequency and enrichment score in the PANoptosis and HALLMARK pathways. The PANoptosis signature also enhanced overall antitumor immunity, promoted immune cell infiltration, upregulated immune checkpoint regulators, and revealed the cold tumor characteristics of PRAD. We also identified potential drug targets based on the PANoptosis signature. These findings lead the way in identifying novel prognostic markers and therapeutic targets for patients with PRAD.

Non-lethal outcomes of engaging regulated cell death pathways in cancer

Regulated cell death (RCD) is essential for successful systemic cancer therapy. Yet, the engagement of RCD pathways does not inevitably result in cell death. Instead, RCD pathways can take part in diverse biological processes if the cells survive. Consequently, these surviving cells, for which we propose the term 'flatliners', harbor important functions. These evolutionarily conserved responses can be exploited by cancer cells to promote their own survival and growth, with challenges and opportunities for cancer therapy.

Targeting Mitochondrial DNA Transcription by POLRMT Inhibition or Depletion as a Potential Strategy for Cancer Treatment

Transcription of the mitochondrial genome is essential for the maintenance of oxidative phosphorylation (OXPHOS) and other functions directly related to this unique genome. Considerable evidence suggests that mitochondrial transcription is dysregulated in cancer and cancer metastasis and contributes significantly to cancer cell metabolism. Recently, inhibitors of the mitochondrial DNA-dependent RNA polymerase (POLRMT) were identified as potentially attractive new anti-cancer compounds. These molecules (IMT1, IMT1B) inactivate cancer cell metabolism through reduced transcription of mitochondrially-encoded OXPHOS subunits such as ND1-5 (Complex I) and COI-IV (Complex IV). Studies from our lab have discovered small molecule regulators of the mitochondrial matrix caseinolytic protease (ClpP) as probable inhibitors of mitochondrial transcription. These compounds activate ClpP proteolysis and lead to the rapid depletion of POLRMT and other matrix proteins, resulting in inhibition of mitochondrial transcription and growth arrest. Herein we present a comparison of POLRMT inhibition and ClpP activation, both conceptually and experimentally, and evaluate the results of these treatments on mitochondrial transcription, inhibition of OXPHOS, and ultimately cancer cell growth. We discuss the potential for targeting mitochondrial transcription as a cancer cell vulnerability.

Mitochondrial control of innate immune responses

Mitochondria are versatile organelles and essential components of numerous biological processes such as energy metabolism, signal transduction, and cell fate determination. In recent years, their critical roles in innate immunity have come to the forefront, highlighting impacts on pathogenic defense, tissue homeostasis, and degenerative diseases. This review offers an in-depth and comprehensive examination of the multifaceted mechanisms underlying the interactions between mitochondria and innate immune responses. We will delve into the roles of healthy mitochondria as platforms for signalosome assembly, the release of mitochondrial components as signaling messengers, and the regulation of signaling via mitophagy, particularly to cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) signaling and inflammasomes. Furthermore, the review will explore the impacts of mitochondrial proteins and metabolites on modulating innate immune responses, the polarization of innate immune cells, and their implications on infectious and inflammatory diseases.

Cell death, therapeutics, and the immune response in cancer

Induction of cell death is inexorably linked with cancer therapy, but this can also initiate wound-healing processes that have been linked to cancer progression and therapeutic resistance. Here we describe the contribution of apoptosis and the lytic cell death pathways in the response to therapy (including chemotherapy and immunotherapy). We also discuss how necroptosis, pyroptosis, and ferroptosis function to promote tumor immunogenicity, along with emerging findings that these same forms of death can paradoxically contribute to immune suppression and tumor progression. Understanding the duality of cell death in cancer may allow for the development of therapeutics that shift the balance towards regression.

Nano Delivery of Chemotherapeutic ICD Inducers for Tumor Immunotherapy

Immunogenic cell death (ICD, also known as immunogenic apoptosis) of malignant cells is confirmed to activate the host immune system to prevent, control, and eliminate tumors. Recently, a range of chemotherapeutic drugs have been repurposed as ICD inducers and applied for tumor immunotherapy. However, several hurdles to the widespread application of chemotherapeutic ICD inducers remain, namely poor water solubility, short blood circulation, non-specific tissue distribution, and severe toxicity. Recent advances in nanotechnology and pharmaceutical formulation foster the development of nano drug delivery systems to tackle the aforementioned hurdles and expedite safe, effective, and specific delivery. This review will describe delivery barriers to chemical ICD inducers and highlight recent nanoformulations for these drugs in tumor immunotherapy.

Multifunctional Nano-Biomaterials for Cancer Therapy via Inducing Enhanced Immunogenic Cell Death

Immunotherapy is considered to be one of the most promising methods to overcome cancer. Immunogenic cell death (ICD), as a special form of cell death that can trigger an antitumor immune response, has attracted increasing attention for cancer immunotherapy. Presently, ICD-mediating immunotherapy needs to overcome many hurdles including a lack of targeted delivery systems for ICD inducers, insufficient antitumor immunity, and the immunosuppressive tumor microenvironment. Recent research has demonstrated that nano-biomaterials exhibit unique biochemphysical properties at the nanoscale, providing a prospective approach to overcoming these obstacles. In this review, the authors first survey the occurrence, processes, and detection methods of ICD. Subsequently, the recent advances of nano-biomaterials applied to enhance ICD according to the key steps in the process of ICD, particularly with a focus on the mechanisms and lifting schemes are investigated. Finally, based on the achievement in the representative studies, the prospects and challenges of nanotechnology in ICD for cancer therapy are discussed to enable clinical translation.

The critical role of apoptosis in mesenchymal stromal cell therapeutics and implications in homeostasis and normal tissue repair

Mesenchymal stromal cells (MSCs) have been extensively tested for the treatment of numerous clinical conditions and have demonstrated good safety but mixed efficacy. Although this outcome can be attributed in part to the heterogeneity of cell preparations, the lack of mechanistic understanding and tools to establish cell pharmacokinetics and pharmacodynamics, as well as the poorly defined criteria for patient stratification, have hampered the design of informative clinical trials. We and others have demonstrated that MSCs can rapidly undergo apoptosis after their infusion. Apoptotic MSCs are phagocytosed by monocytes/macrophages that are then reprogrammed to become anti-inflammatory cells. MSC apoptosis occurs when the cells are injected into patients who harbor activated cytotoxic T or NK cells. Therefore, the activation state of cytotoxic T or NK cells can be used as a biomarker to predict clinical responses to MSC treatment. Building on a large body of preexisting data, an alternative view on the mechanism of MSCs is that an inflammation-dependent MSC secretome is largely responsible for their immunomodulatory activity. We will discuss how these different mechanisms can coexist and are instructed by two different types of MSC "licensing": one that is cell-contact dependent and the second that is mediated by inflammatory cytokines. The varied and complex mechanisms by which MSCs can orchestrate inflammatory responses and how this function is specifically driven by inflammation support a physiological role for tissue stroma in tissue homeostasis, and it acts as a sensor of damage and initiator of tissue repair by reprogramming the inflammatory environment.

Septin11 promotes hepatocellular carcinoma cell motility by activating RhoA to regulate cytoskeleton and cell adhesion

Septins as GTPases in the cytoskeleton, are linked to a broad spectrum of cellular functions, including cell migration and the progression of hepatocellular carcinoma (HCC). However, roles of SEPT11, the new member of septin, have been hardly understood in HCC. In the study, the clinical significance and biological function of SEPT11 in HCC was explored. SEPT11 was screened out by combining ATAC-seq with mRNA-seq. Role of SEPT11 in HCC was further investigated by using overexpression, shRNA and CRISPR/Cas9-mediated SEPT11-knockout cells or in vivo models. We found RNA-seq and ATAC-seq highlights LncRNA AY927503 (AY) induced SEPT11 transcription, resulting in Rho GTPase activation and cytoskeleton actin aggregation. The GTP-binding protein SEPT11 is thus considered, as a downstream factor of AY, highly expressed in various tumors, including HCC, and associated with poor prognosis of the patients. In vitro, SEPT11 overexpression promotes the migration and invasion of HCC cells, while SEPT11-knockout inhibits migration and invasion. In vivo, SEPT11-overexpressed HCC cells show high metastasis incidents but don't significantly affect proliferation. Meanwhile, we found SEPT11 targets RhoA, thereby regulating cytoskeleton rearrangement and abnormal cell adhesion through ROCK1/cofilin and FAK/paxillin signaling pathways, promoting invasion and migration of HCC. Further, we found SEPT11 facilitates the binding of GEF-H1 to RhoA, which enhances the activity of RhoA. Overall, our study confirmed function of SEPT11 in promoting metastasis in HCC, and preliminarily explored its related molecular mechanism. SEPT11 acts as an oncogene in HCC, also draws further interest regarding its clinical application as a potential therapeutic target.

A novel tumour enhancer function of Insulin-like growth factor II mRNA-binding protein 3 in colorectal cancer

CRC cells evolve a variety of strategies to limit or circumvent apoptosis cell death. RNA binding proteins (RBPs) regulate many of the molecular mechanisms that underlie the development of cancer. The insulin-like growth factor II mRNA-binding proteins (IMP) family are oncofoetal RBPs, consisting of IMP1, IMP2 and IMP3, which have an important role in RNA metabolism. IMP3 is highly expressed in colorectal cancer (CRC) tissue, where its expression often correlates with poor prognosis. However, the role of IMP3 in CRC is not fully understood. IMP3 expression was analysed using a public database and by Western blotting and immunohistochemistry in human colon samples derived from patients with sporadic CRC and healthy subjects. To address whether IMP3 controls cancer cell survival, we analysed cell death pathways in in vitro and in vivo experiments after IMP3 downregulation by siRNA or an antisense oligonucleotide. IMP3 was highly expressed in CRC samples compared to normal control tissues. The knockdown of IMP3 enhanced a caspase-independent cell death in CRC cell lines. Furthermore, the treatment of CRC cells with IMP3 siRNA did not alter the expression of GSDMD, GPX-4 and the activated form of RIP3, three key molecules that govern pyroptosis, ferroptosis and necroptosis, respectively. Abrogation of IMP3 in CRC significantly reduced Bcl-2 and Bcl-xL mRNA and was associated with an altered mitochondrial membrane potential that allowed the nuclear migration of the apoptosis-inducing factor (AIF). Moreover, specific immunoprecipitation experiments on CRC human cell lines indicated that IMP3 binds Bcl-2 and Bcl-xL mRNA, suggesting that IMP3 acts as a regulator of the intrinsic apoptotic pathway through the surveillance of anti-apoptotic Bcl mRNA metabolism. Finally, we showed that IMP3 block inhibited the growth of CRC cell lines in vivo after transplantation into immunodeficient mice. Altogether, these data support a novel role for IMP3 in controlling the intrinsic caspase-independent apoptotic pathway in CRC.

Mitochondrial pores at the crossroad between cell death and inflammatory signaling

Mitochondria are cellular organelles with a major role in many cellular processes, including not only energy production, metabolism, and calcium homeostasis but also regulated cell death and innate immunity. Their proteobacterial origin makes them a rich source of potent immune agonists, normally hidden within the mitochondrial membrane barriers. Alteration of mitochondrial permeability through mitochondrial pores thus provides efficient mechanisms not only to communicate mitochondrial stress to the cell but also as a key event in the integration of cellular responses. In this regard, eukaryotic cells have developed diverse signaling networks that sense and respond to the release of mitochondrial components into the cytosol and play a key role in controlling cell death and inflammatory pathways. Modulating pore formation at mitochondria through direct or indirect mechanisms may thus open new opportunities for therapy. In this review, we discuss the current understanding of the structure and molecular mechanisms of mitochondrial pores and how they function at the interface between cell death and inflammatory signaling to regulate cellular outcomes.

Executioner caspases restrict mitochondrial RNA-driven Type I IFN induction during chemotherapy-induced apoptosis

During apoptosis, mitochondrial outer membrane permeabilization (MOMP) enables certain mitochondrial matrix macromolecules to escape into the cytosol. However, the fate of mitochondrial RNA (mtRNA) during apoptosis is unknown. Here, we demonstrate that MOMP results in the cytoplasmic release of mtRNA and that executioner caspases-3 and -7 (casp3/7) prevent cytoplasmic mtRNA from triggering inflammatory signaling. In the setting of genetic or pharmacological casp3/7 inhibition, apoptotic insults result in mtRNA activation of the MDA5/MAVS/IRF3 pathway to drive Type I interferon (IFN) signaling. This pathway is sufficient to activate tumor-intrinsic Type I IFN signaling in immunologically cold cancer models that lack an intact cGAS/STING signaling pathway, promote CD8+ T-cell-dependent anti-tumor immunity, and overcome anti-PD1 refractoriness in vivo. Thus, a key function of casp3/7 is to inhibit inflammation caused by the cytoplasmic release of mtRNA, and pharmacological modulation of this pathway increases the immunogenicity of chemotherapy-induced apoptosis.

Mitochondrial control of inflammation

Numerous mitochondrial constituents and metabolic products can function as damage-associated molecular patterns (DAMPs) and promote inflammation when released into the cytosol or extracellular milieu. Several safeguards are normally in place to prevent mitochondria from eliciting detrimental inflammatory reactions, including the autophagic disposal of permeabilized mitochondria. However, when the homeostatic capacity of such systems is exceeded or when such systems are defective, inflammatory reactions elicited by mitochondria can become pathogenic and contribute to the aetiology of human disorders linked to autoreactivity. In addition, inefficient inflammatory pathways induced by mitochondrial DAMPs can be pathogenic as they enable the establishment or progression of infectious and neoplastic disorders. Here we discuss the molecular mechanisms through which mitochondria control inflammatory responses, the cellular pathways that are in place to control mitochondria-driven inflammation and the pathological consequences of dysregulated inflammatory reactions elicited by mitochondrial DAMPs.

Mitochondrial DNA in cell death and inflammation

Cytosolic DNA is recognized by the innate immune system as a potential threat. During apoptotic cell death, mitochondrial DNA (mtDNA) release activates the DNA sensor cyclic GMP-AMP synthase (cGAS) to promote a pro-inflammatory type I interferon response. Inflammation following mtDNA release during apoptotic cell death can be exploited to engage anti-tumor immunity and represents a potential avenue for cancer therapy. Additionally, various studies have described leakage of mtDNA, independent of cell death, with different underlying cues such as pathogenic infections, changes in mtDNA packaging, mtDNA stress or reduced mitochondrial clearance. The interferon response in these scenarios can be beneficial but also potentially disadvantageous, as suggested by a variety of disease phenotypes. In this review, we discuss mechanisms underlying mtDNA release governed by cell death pathways and summarize release mechanisms independent of cell death. We further highlight the similarities and differences in mtDNA release pathways, outlining gaps in our knowledge and questions for further research. Together, a deeper understanding of how and when mtDNA is released may enable the development of drugs to specifically target or inhibit mtDNA release in different disease settings.

A Cyclodiaryliodonium NOX Inhibitor for the Treatment of Pancreatic Cancer via Enzyme-Activatable Targeted Delivery by Sulfated Glycosaminoglycan Derivatives

Pancreatic cancer renders a principal cause of cancer mortalities with a dismal prognosis, lacking sufficiently safe and effective therapeutics. Here, diversified cyclodiaryliodonium (CDAI) NADPH oxidase (NOX) inhibitors are rationally designed with tens of nanomolar optimal growth inhibition, and CD44-targeted delivery is implemented using synthesized sulfated glycosaminoglycan derivatives. The self-assembled nanoparticle-drug conjugate (NDC) enables hyaluronidase-activatable controlled release and facilitates cellular trafficking. NOX inhibition reprograms the metabolic phenotype by simultaneously impairing mitochondrial respiration and glycolysis. Moreover, the NDC selectively diminishes non-mitochondrial reactive oxygen species (ROS) but significantly elevates cytotoxic ROS through mitochondrial membrane depolarization. Transcriptomic profiling reveals perturbed p53, NF-κB, and GnRH signaling pathways interconnected with NOX inhibition. After being validated in patient-derived pancreatic cancer cells, the anticancer efficacy is further verified in xenograft mice bearing heterotopic and orthotopic pancreatic tumors, with extended survival and ameliorated systemic toxicity. It is envisaged that the translation of cyclodiaryliodonium inhibitors with an optimized molecular design can be expedited by enzyme-activatable targeted delivery with improved pharmacokinetic profiles and preserved efficacy.

Piceatannol-3'-O-β-D-glucopyranoside attenuates colistin-induced neurotoxicity by suppressing oxidative stress via the NRF2/HO-1 pathway

BACKGROUND

Multidrug-resistant Gram-negative bacteria are the most pressing problem in treating infectious diseases. As one of the primary drugs for multidrug-resistant Gram-negative bacteria, the neurotoxicity of colistin has become a significant challenge in clinical practice.

PURPOSE

This study aimed to investigate the potential effect of piceatannol-3'-O-β-D glucopyranoside (PG) on colistin-induced neurotoxicity and the underlying mechanism.

METHODS

In vitro, nerve cell damage models were established by exposing N2a cells to 400 μM colistin for 24 h. The effects of PG on cell viability, apoptosis level, and oxidative stress level were analyzed. A western blot experiment was performed to determine the NRF2 pathway, apoptosis, and autophagy-related proteins. Mitochondrial morphology and mitochondrial membrane potential were detected after staining using laser confocal microscopy. In vivo, nerve injury mouse model was established by intracerebroventricular colistin administration. Morphological changes in brain tissues were observed using HE and Nissl staining.

RESULTS

PG significantly reduced colistin-induced neuronal apoptosis levels. The apoptosis-related protein expressions were suppressed after PG intervention. Mechanistically, PG increased the levels of antioxidant factors and decreased the levels of oxidative factors, which might be related to the activation of the NRF2 pathway. In addition, PG treatment reversed the deviations in mitochondrial morphology and membrane potential. PG suppressed autophagy levels in N2a cells, possibly because PG inhibited colistin-induced apoptosis, thus reducing the level of spontaneous protective autophagy in cells. Nrf2 knockdown N2a cell models were applied to confirm that the activation of the NRF2 pathway played a vital role in PG alleviating the nerve damage caused by colistin.

CONCLUSION

PG is a potential treatment option for colistin-induced neurotoxicity. It mitigated colistin-induced oxidative stress-associated injury and mitochondrial damage by activating the NRF2/HO-1 pathway, thus reducing nerve cell apoptosis.

Conjugation of the Fn14 Ligand to a SMAC Mimetic Selectively Suppresses Experimental Squamous Cell Carcinoma in Mice

The mimetic of SMAC induced cell death in cancers by depleting the inhibitor of apoptosis proteins. Recent studies showed that Fn14 is overexpressed in the cells of squamous cell carcinoma (SCC), providing a promising candidate target for selective antitumor therapy. In this study, we conjugated a small-molecule SMAC mimetic MV1 to the ligand of Fn14, TWEAK. Our results showed that TWEAK‒MV1 conjugate retained adequate binding specificity to Fn14-positive SCC cells in vitro and accumulated selectively in tumor tissue of cutaneous SCC xenografts mice after intraperitoneal administration. This conjugation compound exhibited remarkable effectiveness in suppressing tumor growth and extending overall survival without causing significant side effects in SCC xenograft mice. Moreover, TWEAK‒MV1 conjugate greatly enhanced both apoptotic and necroptotic cell death both in vitro and in vivo, accompanied by a cellular inhibitor of apoptosis proteins degradation as well as activation of receptor-interacting protein kinase. Taken together, our preclinical data suggested that the designed conjugation compound of TWEAK and MV1 might provide a potential therapeutic strategy for cutaneous SCC with improved antitumor efficacy and negligible toxicity.

Sub-lethal signals in the mitochondrial apoptosis apparatus: pernicious by-product or physiological event?

One of the tasks of mitochondria is the rule over life and death: when the outer membrane is permeabilized, the release of intermembrane space proteins causes cell death by apoptosis. For a long time, this mitochondrial outer membrane permeabilization (MOMP) has been accepted as the famous step from which no cell returns. Recent results have however shown that this quite plainly does not have to be the case. A cell can also undergo only a little MOMP, and it can efficiently repair damage it has incurred in the process. There is no doubt now that such low-scale permeabilization occurs. A major unclarified issue is the biological relevance. Is small-scale mitochondrial permeabilization an accident, a leakiness of the apoptosis apparatus, perhaps during restructuring of the mitochondrial network? Is it attempted suicide, where cell death by apoptosis is the real goal but the stimulus failed to reach the threshold? Or, more boldly, is there a true biological meaning behind the event of the release of low amounts of mitochondrial components? We will here explore this last possibility, which we believe is on one hand appealing, on the other hand plausible and supported by some evidence. Recent data are consistent with the view that sub-lethal signals in the mitochondrial apoptosis pathway can drive inflammation, the first step of an immune reaction. The apoptosis apparatus is almost notoriously easy to trigger. Sub-lethal signals may be even easier to set off. We suggest that the apoptosis apparatus is used in this way to sound the call when the first human cell is infected by a pathogen.

Endogenous and imposed determinants of apoptotic vulnerabilities in cancer

The intrinsic apoptosis pathway is controlled by the BCL-2 family of proteins. Although the pro-survival members of this family can help cancer cells evade apoptosis, they may also produce apoptotic vulnerabilities that can potentially be exploited therapeutically. Apoptotic vulnerabilities can be driven by endogenous factors including altered genetics, signaling, metabolism, structure and lineage or differentiation state as well as imposed factors, the most prominent being exposure to anti-cancer agents. The recent development of BH3 mimetics that inhibit pro-survival BCL-2 family proteins has allowed these apoptotic vulnerabilities to be targeted with demonstrable clinical success. Here, we review the key concepts that are vital for understanding, uncovering, and exploiting apoptotic vulnerabilities in cancer for the potential improvement of patient outcomes.