Molecular insights on cytochrome c and nucleotide regulation of apoptosome function and its implication in cancer

Diverse functions of cytochrome c in cell death and disease

The redox-active protein cytochrome c is a highly positively charged hemoglobin that regulates cell fate decisions of life and death. Under normal physiological conditions, cytochrome c is localized in the mitochondrial intermembrane space, and its distribution can extend to the cytosol, nucleus, and extracellular space under specific pathological or stress-induced conditions. In the mitochondria, cytochrome c acts as an electron carrier in the electron transport chain, facilitating adenosine triphosphate synthesis, regulating cardiolipin peroxidation, and influencing reactive oxygen species dynamics. Upon cellular stress, it can be released into the cytosol, where it interacts with apoptotic peptidase activator 1 (APAF1) to form the apoptosome, initiating caspase-dependent apoptotic cell death. Additionally, following exposure to pro-apoptotic compounds, cytochrome c contributes to the survival of drug-tolerant persister cells. When translocated to the nucleus, it can induce chromatin condensation and disrupt nucleosome assembly. Upon its release into the extracellular space, cytochrome c may act as an immune mediator during cell death processes, highlighting its multifaceted role in cellular biology. In this review, we explore the diverse structural and functional aspects of cytochrome c in physiological and pathological responses. We summarize how posttranslational modifications of cytochrome c (e.g., phosphorylation, acetylation, tyrosine nitration, and oxidation), binding proteins (e.g., HIGD1A, CHCHD2, ITPR1, and nucleophosmin), and mutations (e.g., G41S, Y48H, and A51V) affect its function. Furthermore, we provide an overview of the latest advanced technologies utilized for detecting cytochrome c, along with potential therapeutic approaches related to this protein. These strategies hold tremendous promise in personalized health care, presenting opportunities for targeted interventions in a wide range of conditions, including neurodegenerative disorders, cardiovascular diseases, and cancer.

Cardiolipin Membranes Promote Cytochrome c Transformation of Polycyclic Aromatic Hydrocarbons and Their In Vivo Metabolites

The catalytic properties of cytochrome c (Cc) have captured great interest in respect to mitochondrial physiology and apoptosis, and hold potential for novel enzymatic bioremediation systems. Nevertheless, its contribution to the metabolism of environmental toxicants remains unstudied. Human exposure to polycyclic aromatic hydrocarbons (PAHs) has been associated with impactful diseases, and animal models have unveiled concerning signs of PAHs' toxicity to mitochondria. In this work, a series of eight PAHs with ionization potentials between 7.2 and 8.1 eV were used to challenge the catalytic ability of Cc and to evaluate the effect of vesicles containing cardiolipin mimicking mitochondrial membranes activating the peroxidase activity of Cc. With moderate levels of H2O2 and at pH 7.0, Cc catalyzed the oxidation of toxic PAHs, such as benzo[a]pyrene, anthracene, and benzo[a]anthracene, and the cardiolipin-containing membranes clearly increased the PAH conversions. Our results also demonstrate for the first time that Cc and Cc-cardiolipin complexes efficiently transformed the PAH metabolites 2-hydroxynaphthalene and 1-hydroxypyrene. In comparison to horseradish peroxidase, Cc was shown to reach more potent oxidizing states and react with PAHs with ionization potentials up to 7.70 eV, including pyrene and acenaphthene. Spectral assays indicated that anthracene binds to Cc, and docking simulations proposed possible binding sites positioning anthracene for oxidation. The results give support to the participation of Cc in the metabolism of PAHs, especially in mitochondria, and encourage further investigation of the molecular interaction between PAHs and Cc.

Advances in exercise to alleviate sarcopenia in older adults by improving mitochondrial dysfunction

Sarcopenia is a chronic degenerative disease affecting primarily older adults. A growing aging population is gradually increasing the number of patients suffering from sarcopenia, placing increasing financial pressure on patients' families and society in general. There is a strong link between mitochondrial dysfunction and sarcopenia pathogenesis. As a result, treating sarcopenia by improving mitochondrial dysfunction is an effective strategy. Numerous studies have demonstrated that exercise has a positive effect on mitochondrial dysfunction when treating sarcopenia. Exercise promotes mitochondrial biogenesis and mitochondrial fusion/division to add new mitochondria or improve dysfunctional mitochondria while maintaining mitochondrial calcium homeostasis, mitochondrial antioxidant defense system, and mitochondrial autophagy to promote normal mitochondrial function. Furthermore, exercise can reduce mitochondrial damage caused by aging by inhibiting mitochondrial oxidative stress, mitochondrial DNA damage, and mitochondrial apoptosis. Exercise effectiveness depends on several factors, including exercise duration, exercise intensity, and exercise form. Therefore, Moderate-intensity exercise over 4 weeks potentially mitigates sarcopenia in older adults by ameliorating mitochondrial dysfunction. HIIT has demonstrated potential as a viable approach to addressing sarcopenia in aged rats. However, further investigation is required to validate its efficacy in treating sarcopenia in older adults.

Cytochrome c in cancer therapy and prognosis

Cytochrome c (cyt c) is an electron transporter of the mitochondrial respiratory chain. Upon permeabilization of the mitochondrial outer membrane, cyt c is released into the cytoplasm, where it triggers the intrinsic pathway of apoptosis. Cytoplasmic cyt c can further reach the bloodstream. Apoptosis inhibition is one of the hallmarks of cancer and its induction in tumors is a widely used therapeutic approach. Apoptosis inhibition and induction correlate with decreased and increased serum levels of cyt c, respectively. The quantification of cyt c in the serum is useful in the monitoring of patient response to chemotherapy, with potential prognosis value. Several highly sensitive biosensors have been developed for the quantification of cyt c levels in human serum. Moreover, the delivery of exogenous cyt c to the cytoplasm of cancer cells is an effective approach for inducing their apoptosis. Similarly, several protein-based and nanoparticle-based systems have been developed for the therapeutic delivery of cyt c to cancer cells. As such, cyt c is a human protein with promising value in cancer prognosis and therapy. In addition, its thermal stability can be extended through PEGylation and ionic liquid storage. These processes could contribute to enhancing its therapeutic exploitation in clinical facilities with limited refrigeration conditions. Here, I discuss these research lines and how their timely conjunction can advance cancer therapy and prognosis.

Application of Cytochrome C-Related Genes in Prognosis and Treatment Prediction of Lung Adenocarcinoma

Lung adenocarcinoma (LUAD) is the most common subtype of nonsmall cell lung cancer. Cytochrome c (Cyt c), which is produced from mitochondria, interacts with a protein called Apaf-1 to form the heptameric apoptosome. This heptameric apoptosome then activates the caspase cascade, which ultimately results in the execution of apoptosis. The purpose of our research was to discover a new prognostic model that is based on cytochrome c-related genes (CCRGs) for LUAD patients. Through LASSO regression analysis conducted on the LUAD datasets included in the TCGA datasets, a CCRGs signature was created. The diagnostic accuracy of the multigene signature was verified by an independent source using the GSE31210 and GSE72094 datasets. The GO and KEGG enrichment analysis were performed. In this study, there were 159 differentially expressed CCRGs in the TCGA dataset, while there were 68 differentially expressed CCRGs in the GSE31210 dataset. Additionally, there were 57 genes that overlapped across the two datasets. Using LASSO and Cox regression analysis, a signature consisting of 12 differentially expressed CCRGs was developed from the total of 57 such genes. On the basis of their risk ratings, patients were categorized into high-risk and low-risk categories, with low-risk patients having lower risk scores and a greater likelihood of surviving the disease. Univariate and multivariate analyses both concluded that this signature is an independent risk factor for LUAD. ROC curves demonstrated that this risk signature is capable of accurately predicting the 1-year, 2-year, 3-year, and 5-year survival rates of patients who have LUAD. The infiltration of antigen-presenting cells was higher in the low-risk group, such as aDCs, DCs, pDCs, and iDCs. The expression of multiple immune checkpoints was significantly higher in the low-risk group, such as BTLA, CD28, and CD86. Finally, we showed that the signature can be used to predict the drug sensitivity of already available or under investigational drugs. Overall, patient classification and individualized therapy options may benefit from this study’s development of a powerful gene signature with high value for prognostic prediction in LUAD.

Regulatory mechanisms of tetramethylpyrazine on central nervous system diseases: A review

Central nervous system (CNS) diseases can lead to motor, sensory, speech, cognitive dysfunction, and sometimes even death. These diseases are recognized to cause a substantial socio-economic impact on a global scale. Tetramethylpyrazine (TMP) is one of the main active ingredients extracted from the Chinese herbal medicine Ligusticum striatum DC. (Chuan Xiong). Many in vivo and in vitro studies have demonstrated that TMP has a certain role in the treatment of CNS diseases through inhibiting calcium ion overload and glutamate excitotoxicity, anti-oxidative/nitrification stress, mitigating inflammatory response, anti-apoptosis, protecting the integrity of the blood-brain barrier (BBB) and facilitating synaptic plasticity. In this review, we summarize the roles and mechanisms of action of TMP on ischemic cerebrovascular disease, spinal cord injury, Parkinson’s disease, Alzheimer’s disease, cognitive impairments, migraine, and depression. Our review will provide new insights into the clinical applications of TMP and the development of novel therapeutics.

Drug and apoptosis resistance in cancer stem cells: a puzzle with many pieces

Resistance to anticancer agents and apoptosis results in cancer relapse and is associated with cancer mortality. Substantial data have provided convincing evidence establishing that human cancers emerge from cancer stem cells (CSCs), which display self-renewal and are resistant to anticancer drugs, radiation, and apoptosis, and express enhanced epithelial to mesenchymal progression. CSCs represent a heterogeneous tumor cell population and lack specific cellular targets, which makes it a great challenge to target and eradicate them. Similarly, their close relationship with the tumor microenvironment creates greater complexity in developing novel treatment strategies targeting CSCs. Several mechanisms participate in the drug and apoptosis resistance phenotype in CSCs in various cancers. These include enhanced expression of ATP-binding cassette membrane transporters, activation of various cytoprotective and survival signaling pathways, dysregulation of stemness signaling pathways, aberrant DNA repair mechanisms, increased quiescence, autophagy, increased immune evasion, deficiency of mitochondrial-mediated apoptosis, upregulation of anti-apoptotic proteins including c-FLIP [cellular FLICE (FADD-like IL-1β-converting enzyme)-inhibitory protein], Bcl-2 family members, inhibitors of apoptosis proteins, and PI3K/AKT signaling. Studying such mechanisms not only provides mechanistic insights into these cells that are unresponsive to drugs, but may lead to the development of targeted and effective therapeutics to eradicate CSCs. Several studies have identified promising strategies to target CSCs. These emerging strategies may help target CSC-associated drug resistance and metastasis in clinical settings. This article will review the CSCs drug and apoptosis resistance mechanisms and how to target CSCs.

Intravitreal injection of mitochondrial DNA induces cell damage and retinal dysfunction in rats

Background

Retinal neurodegeneration is induced by a variety of environmental insults and stresses, but the exact mechanisms are unclear. In the present study, we explored the involvement of cytosolic mitochondrial DNA (mtDNA), resulting in the cGAS-STING dependent inflammatory response and apoptosis in retinal damage in vivo.

Methods

Retinal injury was induced with white light or intravitreal injection of lipopolysaccharide (LPS). After light- or LPS-induced injury, the amount of cytosolic mtDNA in the retina was detected by PCR. The mtDNA was isolated and used to transfect retinas in vivo. WB and real-time PCR were used to evaluate the activation of cGAS-STING pathway and the levels of apoptosis-associated protein at different times after mtDNA injection. Retinal cell apoptosis rate was detected by TUNEL staining. Full-field electroretinography (ERG) was used to assess the retinal function.

Results

Light injury and the intravitreal injection of LPS both caused the leakage of mtDNA into the cytoplasm in retinal tissue. After the transfection of mtDNA in vivo, the levels of cGAS, STING, and IFN-β mRNAs and the protein levels of STING, phosph-TBK1, phospho-IRF3, and IFN-β were upregulated. mtDNA injection also induced the activation of caspase 3 and caspase 9. BAX and BAK were increased at both the mRNA and protein levels. The release of cytochrome c from the mitochondria to the cytosol was increased after mtDNA injection. The wave amplitudes on ERG decreased and retinal cell apoptosis was detected after mtDNA injection.

Conclusions

Cytosolic mtDNA triggers an inflammatory response. It also promotes apoptosis and the dysfunction of the retina.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40659-022-00390-6.

The MreA Metal-Binding Sites C40, H65, and C69 Play a Critical Role in the Metal Tolerance of Pseudomonas putida KT2440

Metal-binding proteins occur in the cytosol of most eubacteria. The hypothetical metal responsive protein MreA (PP-2969 gene; NreA) seems responsible for zinc, chromium, cadmium accumulation, and metal ion homeostasis. However, there is a lack of definitive evidence regarding the specific metal-binding sites of MreA protein. The present study aimed to identify putative metal-binding regions for MreA. In silico analysis revealed that amino acids C40, H65, and C69 (CHC region) seem critical for metal-protein interactions. We created site-directed mutants (SDM's) of MreA for interacted amino acids to validate in silico results. The differential scanning fluorimetry (DSF) and atomic absorption spectroscopy (AAS) showed that SDM strains of MreA protein curtailed metal accumulation compared to the wild types indicating C40, H65, and C69 amino acids are critical for metal binding. Thus, we report potential implications for MreA-bioengineered strains of Pseudomonas putida KT2440 for metal ion homeostasis by alleviating metal toxicity in the biological environment.

Folate-Decorated Cross-Linked Cytochrome c Nanoparticles for Active Targeting of Non-Small Cell Lung Carcinoma (NSCLC)

The folate receptor alpha (FR), which is overexpressed in solid tumors including NSCLC, can be utilized for active tumor targeting to afford more effective cancer therapies. In this context, cytochrome c (Cyt c) has drawn attention to cancer research because it is non-toxic, yet, when delivered to the cytoplasm of cancer cells, can kill them by inducing apoptosis. Cyt c nanoparticles (NPs, 169 ± 9 nm) were obtained by solvent precipitation with acetonitrile, and stabilized by reversible homo-bifunctional crosslinking to accomplish a Cyt-c-based drug delivery system that combines stimulus-responsive release and active targeting. Cyt c was released under intracellular redox conditions, due to an S–S bond in the NPs linker, while NPs remained intact without any release under extracellular conditions. The NP surface was decorated with a hydrophilic folic acid–polyethylene glycol (FA–PEG) polymer for active targeting. The FA-decorated NPs specifically recognized and killed cancer cells (IC50 = 47.46 µg/mL) that overexpressed FR, but showed no toxicity against FR-negative cells. Confocal microscopy confirmed the preferential uptake and apoptosis induction of our NPs by FR-positive cancer cells. In vivo experiments using a Lewis lung carcinoma (LLC) mouse model showed visible NP accumulation within the tumor and inhibited the growth of LLC tumors.

Folate-Decorated Cross-Linked Cytochrome c Nanoparticles for Active Targeting of Non-Small Cell Lung Carcinoma (NSCLC)

The folate receptor alpha (FR), which is overexpressed in solid tumors including NSCLC, can be utilized for active tumor targeting to afford more effective cancer therapies. In this context, cytochrome c (Cyt c) has drawn attention to cancer research because it is non-toxic, yet, when delivered to the cytoplasm of cancer cells, can kill them by inducing apoptosis. Cyt c nanoparticles (NPs, 169 ± 9 nm) were obtained by solvent precipitation with acetonitrile, and stabilized by reversible homo-bifunctional crosslinking to accomplish a Cyt-c-based drug delivery system that combines stimulus-responsive release and active targeting. Cyt c was released under intracellular redox conditions, due to an S–S bond in the NPs linker, while NPs remained intact without any release under extracellular conditions. The NP surface was decorated with a hydrophilic folic acid–polyethylene glycol (FA–PEG) polymer for active targeting. The FA-decorated NPs specifically recognized and killed cancer cells (IC50 = 47.46 µg/mL) that overexpressed FR, but showed no toxicity against FR-negative cells. Confocal microscopy confirmed the preferential uptake and apoptosis induction of our NPs by FR-positive cancer cells. In vivo experiments using a Lewis lung carcinoma (LLC) mouse model showed visible NP accumulation within the tumor and inhibited the growth of LLC tumors.

Folate-Decorated Cross-Linked Cytochrome c Nanoparticles for Active Targeting of Non-Small Cell Lung Carcinoma (NSCLC)

The folate receptor alpha (FR), which is overexpressed in solid tumors including NSCLC, can be utilized for active tumor targeting to afford more effective cancer therapies. In this context, cytochrome c (Cyt c) has drawn attention to cancer research because it is non-toxic, yet, when delivered to the cytoplasm of cancer cells, can kill them by inducing apoptosis. Cyt c nanoparticles (NPs, 169 ± 9 nm) were obtained by solvent precipitation with acetonitrile, and stabilized by reversible homo-bifunctional crosslinking to accomplish a Cyt-c-based drug delivery system that combines stimulus-responsive release and active targeting. Cyt c was released under intracellular redox conditions, due to an S–S bond in the NPs linker, while NPs remained intact without any release under extracellular conditions. The NP surface was decorated with a hydrophilic folic acid–polyethylene glycol (FA–PEG) polymer for active targeting. The FA-decorated NPs specifically recognized and killed cancer cells (IC50 = 47.46 µg/mL) that overexpressed FR, but showed no toxicity against FR-negative cells. Confocal microscopy confirmed the preferential uptake and apoptosis induction of our NPs by FR-positive cancer cells. In vivo experiments using a Lewis lung carcinoma (LLC) mouse model showed visible NP accumulation within the tumor and inhibited the growth of LLC tumors.

Role of cyclin‑dependent kinase 5 in early brain injury following experimental subarachnoid hemorrhage

Increasing evidence indicates that early brain injury (EBI) can contribute to poor outcomes following subarachnoid hemorrhage (SAH), and is associated with apoptosis. Cyclin-dependent kinase 5 (Cdk5) is a key mediator of neuronal viability. The role of Cdk5 in several neurological disorders has been elucidated; however, its role in EBI after SAH remains unclear. The present study aimed to explore the involvement of Cdk5 in EBI after SAH. The expression levels of Cdk5, Cdk5 phosphorylated at Tyr15 (Cdk5-pTyr15) and p25 (a Cdk5 activator) were assessed by western blotting, and the cell distribution of Cdk5 was demonstrated by double immunofluorescence. The expression levels of caspase-3 and cytochrome c were evaluated by western blotting to assess the severity of neuronal apoptosis. Nissl and TUNEL staining experiments were performed to observe the effects of roscovitine, a Cdk5 inhibitor, on EBI following SAH. The results indicated that the expression levels of Cdk5, p25 and Cdk5-pTyr15 significantly increased in the rat temporal cortex following SAH. Immunofluorescence staining indicated that Cdk5 was expressed in the neurons and astrocytes of the rat cortex after SAH and that Cdk5 underwent nuclear translocation in neurons. Roscovitine administration effectively inhibited Cdk5 activation. In conclusion, roscovitine treatment significantly mitigated EBI and alleviated cerebral edema following SAH. These findings suggest that Cdk5 is an important target in SAH therapy.

The anticarcinogenic and anticancer effects of the dietary flavonoid, morin: Current status, challenges, and future perspectives

Flavonoids constitute one of the most important classes of polyphenols, which have been found to have a wide range of biological activities such as anticancer effects. A large body of evidence demonstrates that morin as a pleiotropic dietary flavonoid possesses potent anticarcinogenic and anticancer activities with minimal toxicity against normal cells. The present review comprehensively elaborates the molecular mechanisms underlying antitumorigenic and anticancer effects of morin. Morin exerts its anticarcinogenic effects through multiple cancer preventive mechanisms, including reduction of oxidative stress, activation of phase II enzymes, induction of apoptosis, attenuation of inflammatory mediators, and downregulation of p-Akt and NF-κB expression. A variety of molecular targets and signaling pathways such as apoptosis, cell cycle, reactive oxygen species (ROS), matrix metalloproteinases (MMPs), epithelial-mesenchymal transition (EMT), and microRNAs (miRNAs) as well as signal transducer and activator of transcription 3 (STAT3), NF-κB, phosphatidylinositol 3-kinase (PI3K)/Akt, mitogen-activated protein kinase (MAPK), and Hippo pathways have been found to be involved in the anticancer effects of morin. In the adjuvant therapy, morin has been shown to have synergistic anticancer effects with several chemotherapeutic drugs. The findings of this review indicate that morin can act as a promising chemopreventive and chemotherapeutic agent.

Phenolics-Enriched Fraction of Pterospermum Lanceifolium Roxb. efficiently Reverses the Hepatocellular Carcinoma in NDEA-Induced HCC Rats

Hepatocellular Carcinoma is one of the most frequently diagnosed cancer and highly refractory for chemotherapeutics agents. Therefore, the study aims to explore the new therapeutic agents for HCC. Phenolics rich fraction of leaves of P. lanceifolium was studied against hepatic cancer cell lines (HepG2) and NDEA-induced HCC rat model system. The obtained results showed that PLE induces reactive oxygen species (ROS) generation and chromatin condensation in nucleus and, alters the mitochondrial membrane potential (MMP) in HepG2 cell lines. The acridine orange/propidium iodide analysis and annexin-V FITC/PI analysis confirms that PLE induces apoptosis-mediated cell death in HepG2-cell lines. In In Vivo analysis, the administration of PLE in NDEA-induced rats declined the elevated biochemicals markers (ALT, AST, ALP, and GGT), interleukins, TNF-α, α-fetoprotein, carcinoembryonic antigen, and total bilirubin. PLE reinstated the level of antioxidant enzyme (GSH, GST, catalase, SOD, and GPX) and the expression of pro-apoptotic (p53, caspase-3, caspase-9, and Bax) and anti-apoptotic (Bcl-2) genes in a dose-dependent manner. The GC-MS analysis of Pterospermum lanceifolium fraction (PLE) represents the presence of palmitic acid, myristic acid, β-sitosterol, and catechin as major bioactive phytocompounds. The study discloses the new lead for HCC that can be further useful for development of new chemopreventive agent.

Lysine 72 substitutions differently affect lipid membrane permeabilizing and proapoptotic activities of horse heart cytochrome c

Peroxidase activity of cytochrome c (cyt c)/cardiolipin (CL) complex is supposed to be involved in the initiation of apoptosis via peroxidative induction of mitochondrial membrane permeabilization. As cyt c binding to CL-containing membranes is at least partially associated with electrostatic protein/lipid interaction, we screened single-point mutants of horse heart cyt c with various substitutions of lysine at position 72, considered to play a significant role in both the binding and peroxidase activity of the protein. Contrary to expectations, K72A, K72R and K72L substitutions exerted slight effects on both the cyt c binding to CL-containing liposomal membranes and the cyt c/H₂O₂-induced calcein leakage from liposomes, used here as a membrane permeabilization assay. Both the binding and permeabilization were decreased to various extents, but not significantly, in the case of K72E and K72N mutants. A drastic difference was found between the sequence of the permeabilizing activities of the cyt c variants and the previously described order of their proapoptotic activities (Chertkova et al., 2008).

VDAC1 Conversely Correlates with Cytc Expression and Predicts Poor Prognosis in Human Breast Cancer Patients

Aim

The main objective of this article was to evaluate the association of voltage-dependent anion channel 1 (VDAC1) with Cytochrome C (Cytc) expression, various clinicopathological features, and prognosis in breast cancer (BC) patients. Meanwhile, the correlation of Cytc expression with various clinical features and 5-year disease-free survival (5-DFS) of BC was also investigated.

Methods

In vivo, expression of VDAC1 and Cytc was examined in 219 BC tissues and 100 benign breast lesions by immunohistochemical (IHC) analysis. In vitro, MTT and wound healing migration assay were performed to detect the effect of VDAC1 on BC cells.

Results

Expression of VDAC1 is conversely associated with Cytc in BC (P = 0.011), especially in triple-negative breast cancer (TNBC) (P = 0.004). Knockdown of VDAC1 inhibited proliferation (P < 0.001) and migration (P < 0.05) of MCF-7 cells. High expression of VDAC1 and low expression of Cytc had a significant association with multiple clinicopathological parameters (P < 0.05) and poor 5-DFS (P < 0.001) in BC.

Conclusion

VDAC1 was elevated in BC tissues and conversely associated with Cytc. Detection of VDAC1 may provide guidance for the poor prognosis of BC, especially TNBC.

Identification and Functional Analysis of Apoptotic Protease Activating Factor-1 (Apaf-1) from Spodoptera litura

Apoptotic protease activating factor-1 (Apaf-1) is an adaptor molecule, essential for activating initiator caspase and downstream effector caspases, which directly cause apoptosis. In fruit flies, nematodes, and mammals, Apaf-1 has been extensively studied. However, the structure and function of Apaf-1 in Lepidoptera remain unclear. This study identified a novel Apaf-1 from Spodoptera litura, named Sl-Apaf-1. Sl-Apaf-1 contains three domains: a CARD domain, as well as NOD and WD motifs, and is very similar to mammalian Apaf-1. Interference of Sl-apaf-1 expression in SL-1 cells blocked apoptosis induced by actinomycin D. Overexpression of Sl-apaf-1 significantly enhances apoptosis induced by actinomycin D in Sf9/SL-1/U2OS cells, suggesting that the function of Sl-Apaf-1 is evolutionarily conserved. Furthermore, Sl-Apaf-1 could interact with Sl-caspase-5 (a homologue of mammalian caspase-9) and yielded a binding affinity of 1.37 × 10⁶ M^-1 according isothermal titration calorimetry assay. Initiator caspase (procaspase-5) of S. litura could be activated by Sl-Apaf-1 (without WD motif) in vitro, and the activated Sl-caspase-5 could cleave Sl-procaspase-1 (a homologue of caspase-3 in mammals), which directly caused apoptosis. This study demonstrates the key role of Sl-Apaf-1 in the apoptosis pathway, suggesting that the apoptosis pathway in Lepidopteran insects and mammals is conserved.

Domesticated and optimized mitochondria: Mitochondrial modifications based on energetic status and cellular stress

Mitochondria are the main source of energy and play an important role in coupling intracellular and intercellular metabolic cooperation. Cellular stress and energetic status can affect various mitochondrial behaviors, including mitochondrial biogenesis, mitophagy, assembly of respiratory chain supercomplexes and mitochondrial distribution. These modifications usually result in adaptive adjustment of mitochondrial output and resistance to cellular stress. However, when the pro-death signals triggered by excessive damage converge to mitochondria, mitochondrial reserve and functional status can profoundly determine the direction of cell death, and even affect the survival and death of surrounding or distant tissues. In this review, we discuss multiple mitochondrial modifications in eukaryotes based on metabolic status and cellular stress, and review the emerging knowledge about the effects of mitochondrial dysfunction on the fate of cells and surrounding tissues.

Output Regulation and Function Optimization of Mitochondria in Eukaryotes

The emergence of endosymbiosis between aerobic alpha-proteobacterium and anaerobic eukaryotic cell precursors opened the chapter of eukaryotic evolution. Multiple functions of mitochondria originated from the ancient precursors of mitochondria and underwent remodeling in eukaryotic cells. Due to the dependence on mitochondrial functions, eukaryotic cells need to constantly adjust mitochondrial output based on energy demand and cellular stress. Meanwhile, eukaryotes conduct the metabolic cooperation between different cells through the involvement of mitochondria. Under some conditions, mitochondria might also be transferred to nearby cells to provide a protective mechanism. However, the endosymbiont relationship determines the existence of various types of mitochondrial injury, such as proteotoxic stress, mutational meltdown, oxidative injure, and immune activation caused by released mitochondrial contents. Eukaryotes have a repertoire of mitochondrial optimization processes, including various mitochondrial quality-control proteins, regulation of mitochondrial dynamics and activation of mitochondrial autophagy. When these quality-control processes fail, eukaryotic cells can activate apoptosis to intercept uncontrolled cell death, thereby minimizing the damage to extracellular tissue. In this review, we describe the intracellular and extracellular context-based regulation of mitochondrial output in eukaryotic cells, and introduce new findings on multifaceted quality-control processes to deal with mitochondrial defects.

Photodynamic Nanophotosensitizers: Promising Materials for Tumor Theranostics

Photodynamic theranostics/therapy (PDT) is a potential strategy for selectively imaging malignant sites and treating cancer via a non-invasive therapeutic method. Photosensitizers, the crucial components of PDT, enable colocalization of photons and light, and photon/light therapy in the therapeutic window of 400-900 nm exhibits photocytotoxicity to tumor cells. Due to their high biostability and photocytotoxicity, nanophotosensitizers (NPSs) are of much interest for malignant tumor theranostics at present. NPS-activated photons transfer energy through the absorption of a photon and convert molecular oxygen to the singlet reactive oxygen species, which leads to apoptosis and necrosis. Moreover, NPSs modified by polymers, including PLGA, PEG-PLA, PDLLA, PVCL-g-PLA, and P(VCL-co-VIM)-g-PLA, exhibit excellent biocompatibility, and a tumor-targeting molecule linked on the nanoparticle surface can precisely deliver NPSs into the tumor region. The development of NPSs will accelerate the progress in tumor theranostics through the photon/light pathway.