Parkin inhibits BAK and BAX apoptotic function by distinct mechanisms during mitophagy

Siah3 acts as a physiological mitophagy suppressor that facilitates axonal degeneration

Mitophagy eliminates dysfunctional mitochondria, and defects in this cellular housekeeping mechanism are implicated in various age-related diseases. Here, we found that mitophagy suppression by the protein Siah3 promoted developmental axonal remodeling in mice. Siah3-deficient mice displayed increased peripheral sensory innervation. Cultured Siah3-deficient sensory neurons exhibited delays in both axonal degeneration and caspase-3 activation in response to withdrawal of nerve growth factor. Mechanistically, Siah3 was transcriptionally induced by the loss of trophic support and formed a complex with the cytosolic E3 ubiquitin ligase parkin, a core component of mitophagy, in transfected cells. Axons of Siah3-deficient neurons mounted profound mitophagy upon initiation of degeneration but not under basal conditions. Neurons lacking both Siah3 and parkin did not exhibit the delay in trophic deprivation-induced axonal degeneration or the induction of axonal mitophagy that was seen in Siah3-deficient neurons. Our findings reveal that mitophagy regulation acts as a gatekeeper of a physiological axon elimination program.

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.

Molecular and immunohistochemical alterations in fluoride-induced neurological impediment in adult rats

This study highlights the potential neurotoxic and impaired behavioral effects associated with high fluoride concentrations in drinking water.

PURPOSE

Fluoride is known to cause neurotoxicity, evinced by lower I.Q. levels in children from high-fluoride regions as compared to those in low-fluoride regions. Thus, the present study was designed to investigate the molecular mechanism behind the neurological and behavioural changes induced by sodium fluoride in Wistar rats.

MATERIAL AND METHODS

A total of 24 female Wistar rats, aged six weeks and weighing approximately 150-220 g, were randomly divided into three groups: Group I (control) received reverse osmosis (R.O.) water, Group II received Sodium Fluoride (NaF) at 10 ppm, and Group III received NaF at 50 ppm in their drinking water for 60 days. The animals underwent behavioural tests including the Forced Swim Test (F.S.T.), Open Field Test (OFT), and Novel Object Recognition Test (N.O.R.T.), to assess any alterations in behaviour. After 60 days, the animals were euthanized, and their blood and brain samples were analysed to evaluate biochemical changes by Western Blot/I.H.C. analysis of B.A.X., Bcl2, LC3B, TLR4, PARP1, p53, Caspase, α-Synuclein, PARKIN, NeuN, KI67, DNM-1, and M.F.N. for assessing molecular pathways for toxicity.

RESULTS

Impaired locomotion, memory impairment, and behaviour resembling depression in the animals were evinced by reduced mobility index in the F.S.T., discrimination index in the N.O.R.T., and reduced locomotor activity in the open field test results. Additionally, alterations in antioxidant levels and oxidative stress parameters were observed in the brain. The expression levels of various apoptotic and inflammatory biomarkers (B.A.X., Bcl2, TLR4, PARP1, p53, and Caspase) showed apoptosis in neurons. The confocal studies showed increased expression of inflammatory (α-Synuclein, PARKIN), apoptotic (LC3B, B.A.X., p53, KI67), and mitochondrial dysfunction (NeuN, DNM-1, M.F.N.) markers in fluoride-treated animals. Toxicity was more prominent in 50 ppm of fluoride-treated animals.

CONCLUSION

Fluoride showed potent neuronal toxicity as evidenced by alterations of various molecular markers.

Oxygen vacancy-engineered cerium oxide mediated by copper-platinum exhibit enhanced SOD/CAT-mimicking activities to regulate the microenvironment for osteoarthritis therapy

Cerium oxide (CeO2) nanospheres have limited enzymatic activity that hinders further application in catalytic therapy, but they have an "oxidation switch" to enhance their catalytic activity by increasing oxygen vacancies. In this study, according to the defect-engineering strategy, we developed PtCuOX/CeO2-X nanozymes as highly efficient SOD/CAT mimics by introducing bimetallic copper (Cu) and platinum (Pt) into CeO2 nanospheres to enhance the oxygen vacancies, in an attempt to combine near-infrared (NIR) irradiation to regulate microenvironment for osteoarthritis (OA) therapy. As expected, the Cu and Pt increased the Ce3+/Ce4+ ratio of CeO2 to significantly enhance the oxygen vacancies, and simultaneously CeO2 (111) facilitated the uniform dispersion of Cu and Pt. The strong metal-carrier interaction synergy endowed the PtCuOX/CeO2-X nanozymes with highly efficient SOD/CAT-like activity by the decreased formation energy of oxygen vacancy, promoted electron transfer, the increased adsorption energy of intermediates, and the decreased reaction activation energy. Besides, the nanozymes have excellent photothermal conversion efficiency (55.41%). Further, the PtCuOX/CeO2-X antioxidant system effectively scavenged intracellular ROS and RNS, protected mitochondrial function, and inhibited the inflammatory factors, thus reducing chondrocyte apoptosis. In vivo, experiments demonstrated the biosafety of PtCuOX/CeO2-X and its potent effect on OA suppression. In particular, NIR radiation further enhanced the effects. Mechanistically, PtCuOX/CeO2-X nanozymes reduced ras-related C3 botulinum toxin substrate 1 (Rac-1) and p-p65 protein expression, as well as ROS levels to remodel the inflammatory microenvironment by inhibiting the ROS/Rac-1/nuclear factor kappa-B (NF-κB) signaling pathway. This study introduces new clinical concepts and perspectives that can be applied to inflammatory diseases.

Mitophagy-related regulated cell death: molecular mechanisms and disease implications

During oxidative phosphorylation, mitochondria continuously produce reactive oxygen species (ROS), and untimely ROS clearance can subject mitochondria to oxidative stress, ultimately resulting in mitochondrial damage. Mitophagy is essential for maintaining cellular mitochondrial quality control and homeostasis, with activation involving both ubiquitin-dependent and ubiquitin-independent pathways. Over the past decade, numerous studies have indicated that different forms of regulated cell death (RCD) are connected with mitophagy. These diverse forms of RCD have been shown to be regulated by mitophagy and are implicated in the pathogenesis of a variety of diseases, such as tumors, degenerative diseases, and ischemia‒reperfusion injury (IRI). Importantly, targeting mitophagy to regulate RCD has shown excellent therapeutic potential in preclinical trials, and is expected to be an effective strategy for the treatment of related diseases. Here, we present a summary of the role of mitophagy in different forms of RCD, with a focus on potential molecular mechanisms by which mitophagy regulates RCD. We also discuss the implications of mitophagy-related RCD in the context of various diseases.

Compartmentalized mitochondrial ferroptosis converges with optineurin-mediated mitophagy to impact airway epithelial cell phenotypes and asthma outcomes

A stable mitochondrial pool is crucial for healthy cell function and survival. Altered redox biology can adversely affect mitochondria through induction of a variety of cell death and survival pathways, yet the understanding of mitochondria and their dysfunction in primary human cells and in specific disease states, including asthma, is modest. Ferroptosis is traditionally considered an iron dependent, hydroperoxy-phospholipid executed process, which induces cytosolic and mitochondrial damage to drive programmed cell death. However, in this report we identify a lipoxygenase orchestrated, compartmentally-targeted ferroptosis-associated peroxidation process which occurs in a subpopulation of dysfunctional mitochondria, without promoting cell death. Rather, this mitochondrial peroxidation process tightly couples with PTEN-induced kinase (PINK)-1(PINK1)-Parkin-Optineurin mediated mitophagy in an effort to preserve the pool of functional mitochondria and prevent cell death. These combined peroxidation processes lead to altered epithelial cell phenotypes and loss of ciliated cells which associate with worsened asthma severity. Ferroptosis-targeted interventions of this process could preserve healthy mitochondria, reverse cell phenotypic changes and improve disease outcomes.

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

BACKGROUND

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

AIM OF REVIEW

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

KEY SCIENTIFIC CONCEPTS OF REVIEW

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

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.

Icaritin with autophagy/mitophagy inhibitors synergistically enhances anticancer efficacy and apoptotic effects through PINK1/Parkin-mediated mitophagy in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is among the deadliest malignancies worldwide and still a pressing clinical problem. Icaritin, a natural compound obtained from the Epimedium genus plant, has garnered significant attention as a potential therapeutic drug for HCC therapies. Mitophagy plays a crucial role in mitochondrial quality control through efficiently eliminating damaged mitochondria. However, the specific mechanisms of the interplay between mitophagy and apoptosis in HCC is still unclear. We aimed to explore the cross-talk between icaritin-induced mitophagy and apoptosis in HCC cells and investigate its potential mechanisms. Firstly, we confirmed that icaritin inhibits proliferation and migration while inducing mitochondrial damage and reactive oxygen species (ROS) production in HCC cells. Secondly, based on proteomics analysis, we discovered that icaritin inhibits the growth of tumor cells and disrupts their mitochondrial homeostasis through the regulation of both mitophagy and apoptosis. Thirdly, icaritin causes mitophagy mediated by PINK1-Parkin signaling via regulating feedforward loop. Furthermore, knockdown of PINK1/Parkin leads to inhibition of mitophagy, which promotes cell death induced by icaritin in HCC cells. Finally, autophagy/mitophagy inhibitors remarkably enhance icaritin-induced cell death and anticancer efficacy. Collectively, our findings reveal that icaritin suppresses growth, proliferation and migration of HCC cell through induction of mitophagy and apoptosis, while inhibition of mitophagy significantly increased the anti-cancer and pro-apoptotic effects of icaritin, indicating that targeting autophagy or mitophagy is a novel approach to overcome drug resistance and enhance anticancer therapies.

Advances in the study of mitophagy in osteoarthritis

Osteoarthritis (OA), characterized by cartilage degeneration, synovial inflammation, and subchondral bone remodeling, is among the most common musculoskeletal disorders globally in people over 60 years of age. The initiation and progression of OA involves the abnormal metabolism of chondrocytes as an important pathogenic process. Cartilage degeneration features mitochondrial dysfunction as one of the important causative factors of abnormal chondrocyte metabolism. Therefore, maintaining mitochondrial homeostasis is an important strategy to mitigate OA. Mitophagy is a vital process for autophagosomes to target, engulf, and remove damaged and dysfunctional mitochondria, thereby maintaining mitochondrial homeostasis. Cumulative studies have revealed a strong association between mitophagy and OA, suggesting that the regulation of mitophagy may be a novel therapeutic direction for OA. By reviewing the literature on mitophagy and OA published in recent years, this paper elaborates the potential mechanism of mitophagy regulating OA, thus providing a theoretical basis for studies related to mitophagy to develop new treatment options for OA.

Mitochondrial damage and clearance in retinal pigment epithelial cells

Age-related macular degeneration (AMD) is a devastating eye disease that causes permanent vision loss in the central part of the retina, known as the macula. Patients with such severe visual loss face a reduced quality of life and are at a 1.5 times greater risk of death compared to the general population. Currently, there is no cure for or effective treatment for dry AMD. There are several mechanisms thought to underlie the disease, for example, ageing-associated chronic oxidative stress, mitochondrial damage, harmful protein aggregation and inflammation. As a way of gaining a better understanding of the molecular mechanisms behind AMD and thus developing new therapies, we have created a peroxisome proliferator-activated receptor gamma coactivator 1-alpha and nuclear factor erythroid 2-related factor 2 (PGC1α/NFE2L2) double-knockout (dKO) mouse model that mimics many of the clinical features of dry AMD, including elevated levels of oxidative stress markers, damaged mitochondria, accumulating lysosomal lipofuscin and extracellular drusen-like structures in retinal pigment epithelial cells (RPE). In addition, a human RPE cell-based model was established to examine the impact of non-functional intracellular clearance systems on inflammasome activation. In this study, we found that there was a disturbance in the autolysosomal machinery responsible for clearing mitochondria in the RPE cells of one-year-old PGC1α/NFE2L2-deficient mice. The confocal immunohistochemical analysis revealed an increase in autophagosome marker microtubule-associated proteins 1A/1B light chain 3B (LC3B) as well as multiple mitophagy markers such as PTE-induced putative kinase 1 (PINK1) and E3 ubiquitin ligase (PARKIN), along with signs of damaged mitochondria. However, no increase in autolysosome formation was detected, nor was there a colocalization of the lysosomal marker LAMP2 or the mitochondrial marker, ATP synthase β. There was an upregulation of late autolysosomal fusion Ras-related protein (Rab7) in the perinuclear space of RPE cells, together with autofluorescent aggregates. Additionally, we observed an increase in the numbers of Toll-like receptors 3 and 9, while those of NOD-like receptor 3 were decreased in PGC1α/NFE2L2 dKO retinal specimens compared to wild-type animals. There was a trend towards increased complement component C5a and increased involvement of the serine protease enzyme, thrombin, in enhancing the terminal pathway producing C5a, independent of C3. The levels of primary acute phase C-reactive protein and receptor for advanced glycation end products were also increased in the PGC1α/NFE2L2 dKO retina. Furthermore, selective proteasome inhibition with epoxomicin promoted both nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and mitochondrial-mediated oxidative stress, leading to the release of mitochondrial DNA to the cytosol, resulting in potassium efflux-dependent activation of the absent in melanoma 2 (AIM2) inflammasome and the subsequent secretion of interleukin-1β in ARPE-19 cells. In conclusion, the data suggest that there is at least a relative decrease in mitophagy, increases in the amounts of C5 and thrombin and decreased C3 levels in this dry AMD-like model. Moreover, selective proteasome inhibition evoked mitochondrial damage and AIM2 inflammasome activation in ARPE-19 cells.

The interplay of mitophagy, autophagy, and apoptosis in cisplatin-induced kidney injury: involvement of ERK signaling pathway

AKI induced by CP chemotherapy remains an obstacle during patient treatments. Extracellular signal-regulated protein kinases 1/2 (ERK), key participants in CP-induced nephrotoxicity, are suggested to be involved in the regulation of mitophagy, autophagy, and apoptosis. Human renal proximal tubular cells (HK-2) and BALB/cN mice were used to determine the role of ERK in CP-induced AKI. We found that active ERK is involved in cell viability reduction during apoptotic events but exerts a protective role in the early stages of treatment. Activation of ERK acts as a maintainer of the mitochondrial population and is implicated in mitophagy initiation but has no significant role in its conduction. In the late stages of CP treatment when ATP is deprived, general autophagy that requires ERK activation is initiated as a response, in addition to apoptosis activation. Furthermore, activation of ERK is responsible for the decrease in reserve respiratory capacity and controls glycolysis regulation during CP treatment. Additionally, we found that ERK activation is also required for the induction of NOXA gene and protein expression as well as FoxO3a nuclear translocation, but not for the regular ERK-induced phosphorylation of FoxO3a on Ser294. In summary, this study gives detailed insight into the involvement of ERK activation and its impact on key cellular processes at different time points during CP-induced kidney injury. Inhibitors of ERK activation, including Mirdametinib, are important in the development of new therapeutic strategies for the treatment of AKI in patients receiving CP chemotherapy.

Sheng Mai Yin shows anti-fatigue, anti-hypoxia and cardioprotective potential in an experimental joint model of fatigue and acute myocardial infarction

ETHNOPHARMACOLOGICAL RELEVANCE

Cardiovascular disease (CVD) and fatigue are two common diseases endangering human life and health that may interact and reinforce one another. Myocardial infarction survivors frequently experience fatigue, and acute myocardial infarction (AMI) is one of the most common cardiovascular diseases that cause fatigue-induced sudden death. Sheng Mai Yin (SMY), a Chinese medicine prescription, is traditionally used for the treatment of diabetes and cardiovascular disease, and has been demonstrated to reduce fatigue and safeguard cardiac function.

AIM OF THE STUDY

This study aims to investigate the effects and underlying mechanisms of SMY in treating fatigue and AMI.

MATERIALS AND METHODS

The pharmacological mechanisms of SMY in treating fatigue and AMI were predicted by bioinformatics and network pharmacology methods. After administering SMY at high, medium and low doses, the swimming time to exhaustion, hemoglobin level, serological parameters and hypoxia tolerance time were detected in C57BL/6N mice, and the left ventricular ejection fractions (LVEF), left ventricular fractional shortening (LVFS), grasp strength, cardiac histopathology, serological parameters and the expression of PINK1 and Parkin proteins were examined in Wistar rats.

RESULTS

371 core targets for SMY and 282 disease targets for fatigue and AMI were obtained using bioinformatics and network pharmacology methods. Enrichment analysis of target genes revealed that SMY might interfere with fatigue and AMI through biological processes such as mitochondrial autophagy, apoptosis, and oxidative stress. For in vivo experiments, SMY showed significant anti-fatigue and hypoxia tolerance effects in mice; It also improved the cardiac function and grasp strength, decreased their cardiac index, myocardial injury and fibrosis degree, and induced serological parameters levels and the expression of PTEN-induced putative kinase 1 (PINK1) and Parkin proteins in myocardium, suggesting that SMY may exert cardioprotective effects in a joint rat model of fatigue and AMI by inhibiting excessive mitochondrial autophagy.

CONCLUSION

This study revealed the anti-fatigue, anti-hypoxia and cardioprotective effects of SMY in a joint model of fatigue-AMI, and the pharmacological mechanism may be related to the inhibition of mitochondrial autophagy in cardiomyocytes through the PINK1/Parkin pathway. The discoveries may provide new ideas for the mechanism study of traditional Chinese medicine, especially complex prescriptions, in treating fatigue and AMI.

Ubiquitin-proteasome pathway-mediated regulation of the Bcl-2 family: effects and therapeutic approaches

Proteasomal degradation of proteins represents an important regulatory mechanism in maintaining healthy homeostasis in cells. Deregulation of the ubiquitin-proteasome system is associated with various diseases as it controls protein abundance and turnover in cells. Furthermore, proteasomal regulation of protein turnover rate can determine a cell's response to external stimuli. The Bcl-2 family of proteins is an important group of proteins involved in mediating cell survival or cell death in response to external stimuli. Aberrant overexpression of anti-apoptotic proteins or deletion of pro-apoptotic proteins can lead to the development of cancer. Unsurprisingly, proteasomal degradation of Bcl-2 proteins also serves as an important factor regulating the level of Bcl-2 proteins and thereby affecting the functional outcome of cell death. This review aims to highlight the regulation of the Bcl-2 family of proteins with particular emphasis on proteasomal-mediated degradation pathways and the current literature on the therapeutic approaches targeting the proteasome system.

Trafficking and effect of released DNA on cGAS-STING signaling pathway and cardiovascular disease

Evidence from clinical research and animal studies indicates that inflammation is an important factor in the occurrence and development of cardiovascular disease (CVD). Emerging evidence shows that nucleic acids serve as crucial pathogen-associated molecular patterns (PAMPs) or non-infectious damage-associated molecular patterns (DAMPs), are released and then recognized by pattern recognition receptors (PRRs), which activates immunological signaling pathways for host defense. Mechanistically, the released nucleic acids activate cyclic GMP-AMP synthase (cGAS) and its downstream receptor stimulator of interferon genes (STING) to promote type I interferons (IFNs) production, which play an important regulatory function during the initiation of an innate immune response to various diseases, including CVD. This pathway represents an essential defense regulatory mechanism in an organism's innate immune system. In this review, we outline the overall profile of cGAS-STING signaling, summarize the latest findings on nucleic acid release and trafficking, and discuss their potential role in CVD. This review also sheds light on potential directions for future investigations on CVD.

Parkin-mediated ubiquitination inhibits BAK apoptotic activity by blocking its canonical hydrophobic groove

BAK permeabilizes the mitochondrial outer membrane, causing apoptosis. This apoptotic activity of BAK is stimulated by binding prodeath activators within its canonical hydrophobic groove. Parkin, an E3 ubiquitin (Ub) ligase, can ubiquitinate BAK, which inhibits BAK apoptotic activity. However, the molecular mechanism underlying the inhibition of ubiquitination remains structurally uncharacterized. Here, we utilize truncated and soluble BAK to construct a mimetic of K113-ubiquitinated BAK (disulfide-linked UbG76C ~ BAKK113C) and further present its NMR-derived structure model. The classical L8-I44-H68-V70 hydrophobic patch of the conjugated Ub subunit binds within the canonical hydrophobic groove of BAK. This Ub occludes the binding of prodeath BID activators in the groove and impairs BID-triggered BAK activation and membrane permeabilization. Reduced interaction between Ub and BAK subunits allows BID to activate K113-ubiquitinated BAK. These mechanistic insights suggest a nonsignaling function of Ub in that it directly antagonizes stimuli targeting Ub-modified proteins rather than by recruiting downstream partners for cellular messaging.

Deubiquitinases in cancer

Ubiquitination is an essential regulator of most, if not all, signalling pathways, and defects in cellular signalling are central to cancer initiation, progression and, eventually, metastasis. The attachment of ubiquitin signals by E3 ubiquitin ligases is directly opposed by the action of approximately 100 deubiquitinating enzymes (DUBs) in humans. Together, DUBs and E3 ligases coordinate ubiquitin signalling by providing selectivity for different substrates and/or ubiquitin signals. The balance between ubiquitination and deubiquitination is exquisitely controlled to ensure properly coordinated proteostasis and response to cellular stimuli and stressors. Not surprisingly, then, DUBs have been associated with all hallmarks of cancer. These relationships are often complex and multifaceted, highlighted by the implication of multiple DUBs in certain hallmarks and by the impact of individual DUBs on multiple cancer-associated pathways, sometimes with contrasting cancer-promoting and cancer-inhibiting activities, depending on context and tumour type. Although it is still understudied, the ever-growing knowledge of DUB function in cancer physiology will eventually identify DUBs that warrant specific inhibition or activation, both of which are now feasible. An integrated appreciation of the physiological consequences of DUB modulation in relevant cancer models will eventually lead to the identification of patient populations that will most likely benefit from DUB-targeted therapies.

Mechanisms of BCL-2 family proteins in mitochondrial apoptosis

The proteins of the BCL-2 family are key regulators of mitochondrial apoptosis, acting as either promoters or inhibitors of cell death. The functional interplay and balance between the opposing BCL-2 family members control permeabilization of the outer mitochondrial membrane, leading to the release of activators of the caspase cascade into the cytosol and ultimately resulting in cell death. Despite considerable research, our knowledge about the mechanisms of the BCL-2 family of proteins remains insufficient, which complicates cell fate predictions and does not allow us to fully exploit these proteins as targets for drug discovery. Detailed understanding of the formation and molecular architecture of the apoptotic pore in the outer mitochondrial membrane remains a holy grail in the field, but new studies allow us to begin constructing a structural model of its arrangement. Recent literature has also revealed unexpected activities for several BCL-2 family members that challenge established concepts of how they regulate mitochondrial permeabilization. In this Review, we revisit the most important advances in the field and integrate them into a new structure-function-based classification of the BCL-2 family members that intends to provide a comprehensive model for BCL-2 action in apoptosis. We close this Review by discussing the potential of drugging the BCL-2 family in diseases characterized by aberrant apoptosis.

Chiisanoside Mediates the Parkin/ZNF746/PGC-1α Axis by Downregulating MiR-181a to Improve Mitochondrial Biogenesis in 6-OHDA-Caused Neurotoxicity Models In Vitro and In Vivo: Suggestions for Prevention of Parkinson's Disease

The degeneration of dopamine (DA) neurons is known to be associated with defects in mitochondrial biogenesis caused by aging, environmental factors, or mutations in genes, leading to Parkinson's disease (PD). As PD has not yet been successfully cured, the strategy of using small molecule drugs to protect and restore mitochondrial biogenesis is a promising direction. This study evaluated the efficacy of synthetic chiisanoside (CSS) identified in the leaves of Acanthopanax sessiliflorus to prevent PD symptoms. The results show that in the 6-hydroxydopamine (6-OHDA) model, CSS pretreatment can effectively alleviate the reactive oxygen species generation and apoptosis of SH-SY5Y cells, thereby lessening the defects in the C. elegans model including DA neuron degeneration, dopamine-mediated food sensitivity behavioral disorders, and shortened lifespan. Mechanistically, we found that CSS could restore the expression of proliferator-activated receptor gamma coactivator-1-alpha (PGC-1α), a key molecule in mitochondrial biogenesis, and its downstream related genes inhibited by 6-OHDA. We further confirmed that this is due to the enhanced activity of parkin leading to the ubiquitination and degradation of PGC-1α inhibitor protein Zinc finger protein 746 (ZNF746). Parkin siRNA treatment abolished this effect of CSS. Furthermore, we found that CSS inhibited 6-OHDA-induced expression of miR-181a, which targets parkin. The CSS's ability to reverse the 6-OHDA-induced reduction in mitochondrial biogenesis and activation of apoptosis was abolished after the transfection of anti-miR-181a and miR-181a mimics. Therefore, the neuroprotective effect of CSS mainly promotes mitochondrial biogenesis by regulating the miR-181a/Parkin/ZNF746/PGC-1α axis. CSS potentially has the opportunity to be developed into PD prevention agents.

Premature senescence and cardiovascular disease following cancer treatments: mechanistic insights

Cardiovascular disease (CVD) is a leading cause of morbidity and mortality, especially among the aging population. The "response-to-injury" model proposed by Dr. Russell Ross in 1999 emphasizes inflammation as a critical factor in atherosclerosis development, with atherosclerotic plaques forming due to endothelial cell (EC) injury, followed by myeloid cell adhesion and invasion into the blood vessel walls. Recent evidence indicates that cancer and its treatments can lead to long-term complications, including CVD. Cellular senescence, a hallmark of aging, is implicated in CVD pathogenesis, particularly in cancer survivors. However, the precise mechanisms linking premature senescence to CVD in cancer survivors remain poorly understood. This article aims to provide mechanistic insights into this association and propose future directions to better comprehend this complex interplay.

Sporadic pituitary adenoma with somatic double-hit loss of MEN1

PURPOSE

Pituitary adenomas commonly arise in patients with MEN1 syndrome, an autosomal dominant condition predisposing to neuroendocrine tumor formation, and typically diagnosed in patients with a relevant family cancer history. In these patients with existing germline loss of MEN1 on one allele, somatic loss of the second MEN1 allele leads to complete loss of the MEN1 protein, menin, and subsequent tumor formation.

METHODS

Whole exome sequencing was performed on the tumor and matching blood under an institutional board approved protocol. DNA extraction and analysis was conducted according to previously described methods.

RESULTS

We describe a 23 year-old patient with no significant past medical history or relevant family history who underwent surgical resection of a symptomatic and medically resistant prolactinoma. Whole exome sequencing of tumor and blood samples revealed somatic loss of MEN1 at both alleles, suggesting a double hit mechanism, with no underlying germline MEN1 mutation.

CONCLUSION

To our knowledge, this is the first case of pituitary adenoma to arise from somatic loss of MEN1 and in the absence of an underlying germline MEN1 mutation.

Structural basis for proapoptotic activation of Bak by the noncanonical BH3-only protein Pxt1

Bak is a critical executor of apoptosis belonging to the Bcl-2 protein family. Bak contains a hydrophobic groove where the BH3 domain of proapoptotic Bcl-2 family members can be accommodated, which initiates its activation. Once activated, Bak undergoes a conformational change to oligomerize, which leads to mitochondrial destabilization and the release of cytochrome c into the cytosol and eventual apoptotic cell death. In this study, we investigated the molecular aspects and functional consequences of the interaction between Bak and peroxisomal testis-specific 1 (Pxt1), a noncanonical BH3-only protein exclusively expressed in the testis. Together with various biochemical approaches, this interaction was verified and analyzed at the atomic level by determining the crystal structure of the Bak-Pxt1 BH3 complex. In-depth biochemical and cellular analyses demonstrated that Pxt1 functions as a Bak-activating proapoptotic factor, and its BH3 domain, which mediates direct intermolecular interaction with Bak, plays a critical role in triggering apoptosis. Therefore, this study provides a molecular basis for the Pxt1-mediated novel pathway for the activation of apoptosis and expands our understanding of the cell death signaling coordinated by diverse BH3 domain-containing proteins.

Novel insights into Parkin-mediated mitochondrial dysfunction and neuroinflammation in Parkinson's disease

Mutations in PRKN cause the second most common genetic form of Parkinson's disease (PD)-a debilitating movement disorder that is on the rise due to population aging in the industrial world. PRKN codes for an E3 ubiquitin ligase that has been well established as a key regulator of mitophagy. Together with PTEN-induced kinase 1 (PINK1), Parkin controls the lysosomal degradation of depolarized mitochondria. But Parkin's functions go well beyond mitochondrial clearance: the versatile protein is involved in mitochondria-derived vesicle formation, cellular metabolism, calcium homeostasis, mitochondrial DNA maintenance, mitochondrial biogenesis, and apoptosis induction. Moreover, Parkin can act as a modulator of different inflammatory pathways. In the current review, we summarize the latest literature concerning the diverse roles of Parkin in maintaining a healthy mitochondrial pool. Moreover, we discuss how these recent discoveries may translate into personalized therapeutic approaches not only for PRKN-PD patients but also for a subset of idiopathic cases.

Parkin exerts the tumor-suppressive effect through targeting mitochondria

The role of PARKIN in Parkinson's disease is well established but its role in cancer has recently emerged. PARKIN serves as a tumor suppressor in many cancers and loses the tumor-suppressive function due to loss of heterozygosity and DNA copy number. But how PARKIN protects against cancer is poorly understood. Through the analysis of PARKIN substrates and their association with mitochondria, this viewpoint discussed that PARKIN exerts its anti-cancer activity through targeting mitochondria. Mitochondria function as a convergence point for many signaling pathways and biological processes, including apoptosis, cell cycle, mitophagy, energy metabolism, oxidative stress, calcium homeostasis, inflammation, and so forth. PARKIN participates in these processes through regulating its mitochondrial targets. Conversely, these mitochondrial substrates also influence the function of PARKIN under different cellular circumstances. We believe that future studies in this area may lead to novel therapeutic targets and strategies for cancer therapy.

The mechanisms and roles of selective autophagy in mammals

Autophagy is a process that targets various intracellular elements for degradation. Autophagy can be non-selective - associated with the indiscriminate engulfment of cytosolic components - occurring in response to nutrient starvation and is commonly referred to as bulk autophagy. By contrast, selective autophagy degrades specific targets, such as damaged organelles (mitophagy, lysophagy, ER-phagy, ribophagy), aggregated proteins (aggrephagy) or invading bacteria (xenophagy), thereby being importantly involved in cellular quality control. Hence, not surprisingly, aberrant selective autophagy has been associated with various human pathologies, prominently including neurodegeneration and infection. In recent years, considerable progress has been made in understanding mechanisms governing selective cargo engulfment in mammals, including the identification of ubiquitin-dependent selective autophagy receptors such as p62, NBR1, OPTN and NDP52, which can bind cargo and ubiquitin simultaneously to initiate pathways leading to autophagy initiation and membrane recruitment. This progress opens the prospects for enhancing selective autophagy pathways to boost cellular quality control capabilities and alleviate pathology.

Mitochondrial E3 ubiquitin ligase MARCHF5 controls BAK apoptotic activity independently of BH3-only proteins

Intrinsic apoptosis is principally governed by the BCL-2 family of proteins, but some non-BCL-2 proteins are also critical to control this process. To identify novel apoptosis regulators, we performed a genome-wide CRISPR-Cas9 library screen, and it identified the mitochondrial E3 ubiquitin ligase MARCHF5/MITOL/RNF153 as an important regulator of BAK apoptotic function. Deleting MARCHF5 in diverse cell lines dependent on BAK conferred profound resistance to BH3-mimetic drugs. The loss of MARCHF5 or its E3 ubiquitin ligase activity surprisingly drove BAK to adopt an activated conformation, with resistance to BH3-mimetics afforded by the formation of inhibitory complexes with pro-survival proteins MCL-1 and BCL-XL. Importantly, these changes to BAK conformation and pro-survival association occurred independently of BH3-only proteins and influence on pro-survival proteins. This study identifies a new mechanism by which MARCHF5 regulates apoptotic cell death by restraining BAK activating conformation change and provides new insight into how cancer cells respond to BH3-mimetic drugs. These data also highlight the emerging role of ubiquitin signalling in apoptosis that may be exploited therapeutically.

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.

PINK1/Parkin-mediated mitophagy inhibits osteoblast apoptosis induced by advanced oxidation protein products

Osteoblast apoptosis plays an important role in age-related bone loss and osteoporosis. Our previous study revealed that advanced oxidation protein products (AOPPs) could induce nicotinamide adenine dinucleotide phosphate oxidase (NOX)-derived reactive oxygen species (ROS) production, cause mitochondrial membrane potential (ΔΨm) depolarization, trigger the mitochondria-dependent intrinsic apoptosis pathway, and lead to osteoblast apoptosis and ultimately osteopenia and bone microstructural destruction. In this study, we found that AOPPs also induced mitochondrial ROS (mtROS) generation in osteoblastic MC3T3-E1 cells, which was closely related to NOX-derived ROS, and aggravated the oxidative stress condition, thereby further promoting apoptosis. Removing excessive ROS and damaged mitochondria is the key factor in reversing AOPP-induced apoptosis. Here, by in vitro studies, we showed that rapamycin further activated PINK1/Parkin-mediated mitophagy in AOPP-stimulated MC3T3-E1 cells and significantly alleviated AOPP-induced cell apoptosis by eliminating ROS and damaged mitochondria. Our in vivo studies revealed that PINK1/Parkin-mediated mitophagy could decrease the plasma AOPP concentration and inhibit AOPP-induced osteoblast apoptosis, thus ameliorating AOPP accumulation-related bone loss, bone microstructural destruction and bone mineral density (BMD) loss. Together, our study indicated that therapeutic strategies aimed at upregulating osteoblast mitophagy and preserving mitochondrial function might have potential for treating age-related osteoporosis.

PINK1/Parkin-mediated mitophagy inhibits osteoblast apoptosis induced by advanced oxidation protein products

Osteoblast apoptosis plays an important role in age-related bone loss and osteoporosis. Our previous study revealed that advanced oxidation protein products (AOPPs) could induce nicotinamide adenine dinucleotide phosphate oxidase (NOX)-derived reactive oxygen species (ROS) production, cause mitochondrial membrane potential (ΔΨm) depolarization, trigger the mitochondria-dependent intrinsic apoptosis pathway, and lead to osteoblast apoptosis and ultimately osteopenia and bone microstructural destruction. In this study, we found that AOPPs also induced mitochondrial ROS (mtROS) generation in osteoblastic MC3T3-E1 cells, which was closely related to NOX-derived ROS, and aggravated the oxidative stress condition, thereby further promoting apoptosis. Removing excessive ROS and damaged mitochondria is the key factor in reversing AOPP-induced apoptosis. Here, by in vitro studies, we showed that rapamycin further activated PINK1/Parkin-mediated mitophagy in AOPP-stimulated MC3T3-E1 cells and significantly alleviated AOPP-induced cell apoptosis by eliminating ROS and damaged mitochondria. Our in vivo studies revealed that PINK1/Parkin-mediated mitophagy could decrease the plasma AOPP concentration and inhibit AOPP-induced osteoblast apoptosis, thus ameliorating AOPP accumulation-related bone loss, bone microstructural destruction and bone mineral density (BMD) loss. Together, our study indicated that therapeutic strategies aimed at upregulating osteoblast mitophagy and preserving mitochondrial function might have potential for treating age-related osteoporosis.

PINK1/Parkin-mediated mitophagy inhibits osteoblast apoptosis induced by advanced oxidation protein products

Osteoblast apoptosis plays an important role in age-related bone loss and osteoporosis. Our previous study revealed that advanced oxidation protein products (AOPPs) could induce nicotinamide adenine dinucleotide phosphate oxidase (NOX)-derived reactive oxygen species (ROS) production, cause mitochondrial membrane potential (ΔΨm) depolarization, trigger the mitochondria-dependent intrinsic apoptosis pathway, and lead to osteoblast apoptosis and ultimately osteopenia and bone microstructural destruction. In this study, we found that AOPPs also induced mitochondrial ROS (mtROS) generation in osteoblastic MC3T3-E1 cells, which was closely related to NOX-derived ROS, and aggravated the oxidative stress condition, thereby further promoting apoptosis. Removing excessive ROS and damaged mitochondria is the key factor in reversing AOPP-induced apoptosis. Here, by in vitro studies, we showed that rapamycin further activated PINK1/Parkin-mediated mitophagy in AOPP-stimulated MC3T3-E1 cells and significantly alleviated AOPP-induced cell apoptosis by eliminating ROS and damaged mitochondria. Our in vivo studies revealed that PINK1/Parkin-mediated mitophagy could decrease the plasma AOPP concentration and inhibit AOPP-induced osteoblast apoptosis, thus ameliorating AOPP accumulation-related bone loss, bone microstructural destruction and bone mineral density (BMD) loss. Together, our study indicated that therapeutic strategies aimed at upregulating osteoblast mitophagy and preserving mitochondrial function might have potential for treating age-related osteoporosis.

Site-specific ubiquitination of VDAC1 restricts its oligomerization and mitochondrial DNA release in liver fibrosis

Mitochondrial DNA (mtDNA) released through protein oligomers, such as voltage-dependent anion channel 1 (VDAC1), triggers innate immune activation and thus contributes to liver fibrosis. Here, we investigated the role of Parkin, an important regulator of mitochondria, and its regulation of VDAC1-mediated mtDNA release in liver fibrosis. The circulating mitochondrial DNA (mtDNA) and protein levels of liver Parkin and VDAC1 were upregulated in patients with liver fibrosis. A 4-week CCl₄ challenge induced release of mtDNA, activation of STING signaling, a decline in autophagy, and apoptosis in mouse livers, and the knockout of Parkin aggravated these effects. In addition, Parkin reduced mtDNA release and prevented VDAC1 oligomerization in a manner dependent on its E3 activity in hepatocytes. We found that site-specific ubiquitination of VDAC1 at lysine 53 by Parkin interrupted VDAC1 oligomerization and prevented mtDNA release into the cytoplasm under stress. The ubiquitination-defective VDAC1 K53R mutant predominantly formed oligomers that resisted suppression by Parkin. Hepatocytes expressing VDAC1 K53R exhibited mtDNA release and thus activated the STING signaling pathway in hepatic stellate cells, and this effect could not be abolished by Parkin. We propose that the ubiquitination of VDAC1 at a specific site by Parkin confers protection against liver fibrosis by interrupting VDAC1 oligomerization and mtDNA release.

FGF13-Sensitive Alteration of Parkin Safeguards Mitochondrial Homeostasis in Endothelium of Diabetic Nephropathy

Studies of diabetic glomerular injury have raised the possibility of developing useful early biomarkers and therapeutic approaches for the treatment of type 2 diabetic nephropathy (T2DN). In this study, we found that FGF13 expression is induced in glomerular endothelial cells (GECs) during T2DN progression. Endothelial-specific deletion of Fgf13 potentially alleviates T2DN damage, while Fgf13 overexpression has the opposite effect. Mechanistically, Fgf13 deficiency results in improved mitochondrial homeostasis and endothelial barrier integrity in T2DN. Moreover, FGF13-sensitive alteration of Parkin safeguards mitochondrial homeostasis in endothelium of T2DN through promotion of mitophagy and inhibition of apoptosis. Additionally, it is confirmed that the beneficial effects of Fgf13 deficiency on T2DN are abolished by endothelial-specific double deletion of Fgf13 and Prkn. The effects of Fgf13 deficiency on mitophagy and apoptosis through Parkin-dependent regulation may be distinct and separable events under diabetic conditions. These data show that the bifunctional role of Fgf13 deficiency in promoting mitophagy and inhibiting apoptosis through Parkin can shape mitochondrial homeostasis regulation in GECs and T2DN progression. As a potential therapeutic target for prevention and control of T2DN, a mechanistic understanding of the biofunction of FGF13 may also be relevant to the pathogenesis of other FGF13- and Parkin-associated diseases.

R-loop-derived cytoplasmic RNA-DNA hybrids activate an immune response

R-loops are RNA-DNA-hybrid-containing nucleic acids with important cellular roles. Deregulation of R-loop dynamics can lead to DNA damage and genome instability1, which has been linked to the action of endonucleases such as XPG2-4. However, the mechanisms and cellular consequences of such processing have remained unclear. Here we identify a new population of RNA-DNA hybrids in the cytoplasm that are R-loop-processing products. When nuclear R-loops were perturbed by depleting the RNA-DNA helicase senataxin (SETX) or the breast cancer gene BRCA1 (refs. 5-7), we observed XPG- and XPF-dependent cytoplasmic hybrid formation. We identify their source as a subset of stable, overlapping nuclear hybrids with a specific nucleotide signature. Cytoplasmic hybrids bind to the pattern recognition receptors cGAS and TLR3 (ref. 8), activating IRF3 and inducing apoptosis. Excised hybrids and an R-loop-induced innate immune response were also observed in SETX-mutated cells from patients with ataxia oculomotor apraxia type 2 (ref. 9) and in BRCA1-mutated cancer cells10. These findings establish RNA-DNA hybrids as immunogenic species that aberrantly accumulate in the cytoplasm after R-loop processing, linking R-loop accumulation to cell death through the innate immune response. Aberrant R-loop processing and subsequent innate immune activation may contribute to many diseases, such as neurodegeneration and cancer.

Cell Biology of Parkin: Clues to the Development of New Therapeutics for Parkinson's Disease

Parkinson's disease is the second most prevalent neurodegenerative disease and contributes significantly to morbidity globally. Currently, no disease-modifying therapies exist to combat this disorder. Insights from the molecular and cellular pathobiology of the disease seems to indicate promising therapeutic targets. The parkin protein has been extensively studied for its role in autosomal recessive Parkinson's disease and, more recently, its role in sporadic Parkinson's disease. Parkin is an E3 ubiquitin ligase that plays a prominent role in mitochondrial quality control, mitochondrial-dependent cell death pathways, and other diverse functions. Understanding the numerous roles of parkin has introduced many new possibilities for therapeutic modalities in treating both autosomal recessive Parkinson's disease and sporadic Parkinson's disease. In this article, we review parkin biology with an emphasis on mitochondrial-related functions and propose novel, potentially disease-modifying therapeutic approaches for treating this debilitating condition.

Diverse maturity-dependent and complementary anti-apoptotic brakes safeguard human iPSC-derived neurons from cell death

In humans, most neurons are born during embryonic development and have to persist throughout the entire lifespan of an individual. Thus, human neurons have to develop elaborate survival strategies to protect against accidental cell death. We set out to decipher the developmental adaptations resulting in neuronal resilience. We demonstrate that, during the time course of maturation, human neurons install a complex and complementary anti-apoptotic signaling network. This includes i.) a downregulation of central proteins of the intrinsic apoptosis pathway including several caspases, ii.) a shift in the ratio of pro- and anti-apoptotic BCL-2 family proteins, and iii.) an elaborate regulatory network resulting in upregulation of the inhibitor of apoptosis protein (IAP) XIAP. Together, these adaptations strongly increase the threshold for apoptosis initiation when confronted with a wide range of cellular stressors. Our results highlight how human neurons are endowed with complex and redundant preemptive strategies to protect against stress and cell death.

Folic Acid Improves Parkin-Null Drosophila Phenotypes and Transiently Reduces Vulnerable Dopaminergic Neuron Mitochondrial Hydrogen Peroxide Levels and Glutathione Redox Equilibrium

Loss-of-function parkin mutations cause oxidative stress and degeneration of dopaminergic neurons in the substantia nigra. Several consequences of parkin mutations have been described; to what degree they contribute to selective neurodegeneration remains unclear. Specific factors initiating excessive reactive oxygen species production, inefficient antioxidant capacity, or a combination are elusive. Identifying key oxidative stress contributors could inform targeted therapy. The absence of Drosophila parkin causes selective degeneration of a dopaminergic neuron cluster that is functionally homologous to the substantia nigra. By comparing observations in these to similar non-degenerating neurons, we may begin to understand mechanisms by which parkin loss of function causes selective degeneration. Using mitochondrially targeted redox-sensitive GFP2 fused with redox enzymes, we observed a sustained increased mitochondrial hydrogen peroxide levels in vulnerable dopaminergic neurons of parkin-null flies. Only transient increases in hydrogen peroxide were observed in similar but non-degenerating neurons. Glutathione redox equilibrium is preferentially dysregulated in vulnerable neuron mitochondria. To shed light on whether dysregulated glutathione redox equilibrium primarily contributes to oxidative stress, we supplemented food with folic acid, which can increase cysteine and glutathione levels. Folic acid improved survival, climbing, and transiently decreased hydrogen peroxide and glutathione redox equilibrium but did not mitigate whole-brain oxidative stress.

Alleviation of doxorubicin-induced cardiomyocyte death through miR-147-y-mediated mitophagy

Doxorubicin (DOX) is a commonly used antitumor drug. However, it may cause severe cardiotoxicity, apoptosis being a major change. A recent report indicates that miR-147 expression is decreased in the myocardium of a myocardial infarction model, suggesting a potential role of this miRNA in DOX-induced cardiomyocyte toxicity. In this study, freshly isolated neonatal pig cardiomyocytes were used; following transfection of a miR-147-y mimic, the cell death induced by DOX was alleviated, represented by augmented mitophagy [indicated by a decrease in P62, and increases in LC3, PINK1, parkin mRNA, LC3Ⅱ/Ⅰ, beclin-1, PINK1, and parkin including p-parkin (Ser65) protein expression], prohibited cell apoptosis as determined by TUNEL staining, and the suppression of caspase-3 transcription and cleaved caspase-3 translation. In cells transfected with an miR-147-y inhibitor, DOX-induced mitophagy was decreased, while apoptosis was increased. Additionally, RAPTOR gene silencing in cardiomyocytes exposed to DOX increased the rate of mitophagy and decreased that of apoptosis as compared with the treatment with DOX alone. Moreover, RAPTOR overexpression downregulated the rate of mitophagy and increased that of apoptosis in cells exposed to DOX. RAPTOR was confirmed as the target gene of miR-147-y based on the results of luciferase reporter gene assays and the opposite effects of the miR-147-y mimic and miR-147-y inhibitor on RAPTOR expression. In summary, our study suggests that miR-147-y mediates DOX-induced cardiomyocyte mitophagy while suppresses apoptosis by targeting RAPTOR, thus playing a protective role in DOX-induced cardiomyocyte damage.

Therapeutic targeting of mitophagy in Parkinson's disease

Parkinson's disease is a neurodegenerative disorder characterised by cardinal motor symptoms and a diverse range of non-motor disorders in patients. Parkinson's disease is the fastest growing neurodegenerative condition and was described for the first time over 200 years ago, yet there are still no reliable diagnostic markers and there are only treatments that temporarily alleviate symptoms in patients. Early-onset Parkinson's disease is often linked to defects in specific genes, including PINK1 and Parkin, that encode proteins involved in mitophagy, the process of selective autophagic elimination of damaged mitochondria. Impaired mitophagy has been associated with sporadic Parkinson's and agents that damage mitochondria are known to induce Parkinson's-like motor symptoms in humans and animal models. Thus, modulating mitophagy pathways may be an avenue to treat a subset of early-onset Parkinson's disease that may additionally provide therapeutic opportunities in sporadic disease. The PINK1/Parkin mitophagy pathway, as well as alternative mitophagy pathways controlled by BNIP3L/Nix and FUNDC1, are emerging targets to enhance mitophagy to treat Parkinson's disease. In this review, we report the current state of the art of mitophagy-targeted therapeutics and discuss the approaches being used to overcome existing limitations to develop innovative new therapies for Parkinson's disease. Key approaches include the use of engineered mouse models that harbour pathogenic mutations, which will aid in the preclinical development of agents that can modulate mitophagy. Furthermore, the recent development of chimeric molecules (AUTACs) that can bypass mitophagy pathways to eliminate damaged mitochondria thorough selective autophagy offer new opportunities.

Organellar homeostasis and innate immune sensing

A cell is delimited by numerous borders that define specific organelles. The walls of some organelles are particularly robust, such as in mitochondria or endoplasmic reticulum, but some are more fluid such as in phase-separated stress granules. Either way, all organelles can be damaged at times, leading their contents to leak out into the surrounding environment. Therefore, an elegant way to construct an innate immune defence system is to recognize host molecules that do not normally reside within a particular compartment. Here, we provide several examples where organellar homeostasis is lost, leading to the activation of a specific innate immune sensor; these include NLRP3 activation owing to a disrupted trans-Golgi network, Pyrin activation due to cytoskeletal damage, and cGAS-STING activation following the leakage of nuclear or mitochondrial DNA. Frequently, organelle damage is observed downstream of pathogenic infection but it can also occur in sterile settings as associated with auto-inflammatory disease. Therefore, understanding organellar homeostasis is central to efforts that will identify new innate immune pathways, and therapeutics that balance organellar homeostasis, or target the breakdown pathways that trigger innate immune sensors, could be useful treatments for infection and chronic inflammatory diseases.

Bim- and Bax-mediated mitochondrial pathway dominates abivertinib-induced apoptosis and ferroptosis

Abivertinib (AC) is a novel epidermal growth factor receptor tyrosine kinase inhibitor with highly efficient antitumor activity. Here, we report the capacity of AC to induce both reactive oxygen species (ROS)-dependent apoptosis and ferroptosis in tumor cells. Our data showed that AC induced iron- and ROS-dependent cytotoxicity in MCF7, HeLa, and A549 cell lines. Flow cytometry analyses showed that AC increased ferrous ions and ROS and induced ferroptosis in MCF-7 cells. This was confirmed by the findings that AC not only decreased solute carrier family 7 member 11 (SLC7A11) and glutathione peroxidase 4 (GPX4) expression but also induced iron- and ROS-dependent aggrandized lipid ROS accumulation and plasma membrane damage. Meanwhile, AC induced nuclear condensation and increased ROS-dependent phosphatidylserine (PS) eversion, caspase-3 activation, and cleaved-PARP expression, suggesting that AC also induced ROS-dependent apoptosis. In addition, mitochondrial depletion significantly inhibited AC-induced cytotoxicity, including ferroptosis and apoptosis, indicating the key role of mitochondria in AC-induced ferroptosis and apoptosis. Moreover, knockout of Bim or Bax not only remarkably inhibited AC-induced apoptosis, but also markedly inhibited AC-triggered downregulation of SLC711 and GPX4, accumulation of lipid ROS, and damage to the plasma membrane. This suggests that Bim and Bax act upstream of SLC7A11 and GPX4 to mediate AC-induced ferroptosis. Collectively, AC induces ferroptosis and apoptosis, in which the Bim- and Bax-mediated mitochondrial pathways play a dominant role.

PINK1 signalling in neurodegenerative disease

PTEN-induced kinase 1 (PINK1) impacts cell health and human pathology through diverse pathways. The strict processing of full-length PINK1 on the outer mitochondrial membrane populates a cytoplasmic pool of cleaved PINK1 (cPINK1) that is constitutively degraded. However, despite rapid proteasomal clearance, cPINK1 still appears to exert quality control influence over the neuronal protein homeostasis network, including protein synthesis and degradation machineries. The cytoplasmic concentration and activity of this molecule is therefore a powerful sensor that coordinates aspects of mitochondrial and cellular health. In addition, full-length PINK1 is retained on the mitochondrial membrane following depolarisation, where it is a powerful inducer of multiple mitophagic pathways. This function is executed primarily through the phosphorylation of several ubiquitin ligases, including its most widely studied substrate Parkin. Furthermore, the phosphorylation of both pro- and anti-apoptotic proteins by mitochondrial PINK1 acts as a pro-cellular survival signal when faced with apoptotic stimuli. Through these varied roles PINK1 directly influences functions central to cell dysfunction in neurodegenerative disease.

Disease Duration Influences Gene Expression in Neuromelanin-Positive Cells From Parkinson's Disease Patients

Analyses of gene expression in cells affected by neurodegenerative disease can provide important insights into disease mechanisms and relevant stress response pathways. Major symptoms in Parkinson’s disease (PD) are caused by the degeneration of midbrain dopamine (mDA) neurons within the substantia nigra. Here we isolated neuromelanin-positive dopamine neurons by laser capture microdissection from post-mortem human substantia nigra samples recovered at both early and advanced stages of PD. Neuromelanin-positive cells were also isolated from individuals with incidental Lewy body disease (ILBD) and from aged-matched controls. Isolated mDA neurons were subjected to genome-wide gene expression analysis by mRNA sequencing. The analysis identified hundreds of dysregulated genes in PD. Results showed that mostly non-overlapping genes were differentially expressed in ILBD, subjects who were early after diagnosis (less than five years) and those autopsied at more advanced stages of disease (over five years since diagnosis). The identity of differentially expressed genes suggested that more resilient, stably surviving DA neurons were enriched in samples from advanced stages of disease, either as a consequence of positive selection of a less vulnerable long-term surviving mDA neuron subtype or due to up-regulation of neuroprotective gene products.

Synergistic effects of autophagy/mitophagy inhibitors and magnolol promote apoptosis and antitumor efficacy

Mitochondria as a signaling platform play crucial roles in deciding cell fate. Many classic anticancer agents are known to trigger cell death through induction of mitochondrial damage. Mitophagy, one selective autophagy, is the key mitochondrial quality control that effectively removes damaged mitochondria. However, the precise roles of mitophagy in tumorigenesis and anticancer agent treatment remain largely unclear. Here, we examined the functional implication of mitophagy in the anticancer properties of magnolol, a natural product isolated from herbal Magnolia officinalis. First, we found that magnolol induces mitochondrial depolarization, causes excessive mitochondrial fragmentation, and increases mitochondrial reactive oxygen species (mtROS). Second, magnolol induces PTEN-induced putative kinase protein 1 (PINK1)‒Parkin-mediated mitophagy through regulating two positive feedforward amplification loops. Third, magnolol triggers cancer cell death and inhibits neuroblastoma tumor growth via the intrinsic apoptosis pathway. Moreover, magnolol prolongs the survival time of tumor-bearing mice. Finally, inhibition of mitophagy by PINK1/Parkin knockdown or using inhibitors targeting different autophagy/mitophagy stages significantly promotes magnolol-induced cell death and enhances magnolol's anticancer efficacy, both in vitro and in vivo. Altogether, our study demonstrates that magnolol can induce autophagy/mitophagy and apoptosis, whereas blockage of autophagy/mitophagy remarkably enhances the anticancer efficacy of magnolol, suggesting that targeting mitophagy may be a promising strategy to overcome chemoresistance and improve anticancer therapy.

Molecular Signaling to Preserve Mitochondrial Integrity against Ischemic Stress in the Heart: Rescue or Remove Mitochondria in Danger

Cardiovascular diseases are one of the leading causes of death and global health problems worldwide, and ischemic heart disease is the most common cause of heart failure (HF). The heart is a high-energy demanding organ, and myocardial energy reserves are limited. Mitochondria are the powerhouses of the cell, but under stress conditions, they become damaged, release necrotic and apoptotic factors, and contribute to cell death. Loss of cardiomyocytes plays a significant role in ischemic heart disease. In response to stress, protective signaling pathways are activated to limit mitochondrial deterioration and protect the heart. To prevent mitochondrial death pathways, damaged mitochondria are removed by mitochondrial autophagy (mitophagy). Mitochondrial quality control mediated by mitophagy is functionally linked to mitochondrial dynamics. This review provides a current understanding of the signaling mechanisms by which the integrity of mitochondria is preserved in the heart against ischemic stress.

Contribution of Mitochondrial Dysfunction Combined with NLRP3 Inflammasome Activation in Selected Neurodegenerative Diseases

Alzheimer's disease and Parkinson's disease are the most common forms of neurodegenerative illnesses. It has been widely accepted that neuroinflammation is the key pathogenic mechanism in neurodegeneration. Both mitochondrial dysfunction and enhanced NLRP3 (nucleotide-binding oligomerization domain (NOD)-like receptor protein 3) inflammasome complex activity have a crucial role in inducing and sustaining neuroinflammation. In addition, mitochondrial-related inflammatory factors could drive the formation of inflammasome complexes, which are responsible for the activation, maturation, and release of pro-inflammatory cytokines, including interleukin-1β (IL-1β) and interleukin-18 (IL-18). The present review includes a broadened approach to the role of mitochondrial dysfunction resulting in abnormal NLRP3 activation in selected neurodegenerative diseases. Moreover, we also discuss the potential mitochondria-focused treatments that could influence the NLRP3 complex.

Regulation of mitochondrial cargo-selective autophagy by posttranslational modifications

Mitochondria are important organelles in eukaryotes. Turnover and quality control of mitochondria are regulated at the transcriptional and posttranslational level by several cellular mechanisms. Removal of defective mitochondrial proteins is mediated by mitochondria resident proteases or by proteasomal degradation of individual proteins. Clearance of bulk mitochondria occurs via a selective form of autophagy termed mitophagy. In yeast and some developing metazoan cells (e.g., oocytes and reticulocytes), mitochondria are largely removed by ubiquitin-independent mechanisms. In such cases, the regulation of mitophagy is mediated via phosphorylation of mitochondria-anchored autophagy receptors. On the other hand, ubiquitin-dependent recruitment of cytosolic autophagy receptors occurs in situations of cellular stress or disease, where dysfunctional mitochondria would cause oxidative damage. In mammalian cells, a well-studied ubiquitin-dependent mitophagy pathway induced by mitochondrial depolarization is regulated by the mitochondrial protein kinase PINK1, which upon activation recruits the ubiquitin ligase parkin. Here, we review mechanisms of mitophagy with an emphasis on posttranslational modifications that regulate various mitophagy pathways. We describe the autophagy components involved with particular emphasis on posttranslational modifications. We detail the phosphorylations mediated by PINK1 and parkin-mediated ubiquitylations of mitochondrial proteins that can be modulated by deubiquitylating enzymes. We also discuss the role of accessory factors regulating mitochondrial fission/fusion and the interplay with pro- and antiapoptotic Bcl-2 family members. Comprehensive knowledge of the processes of mitophagy is essential for the understanding of vital mitochondrial turnover in health and disease.

Dynamic reconfiguration of pro-apoptotic BAK on membranes

BAK and BAX, the effectors of intrinsic apoptosis, each undergo major reconfiguration to an activated conformer that self-associates to damage mitochondria and cause cell death. However, the dynamic structural mechanisms of this reconfiguration in the presence of a membrane have yet to be fully elucidated. To explore the metamorphosis of membrane-bound BAK, we employed hydrogen-deuterium exchange mass spectrometry (HDX-MS). The HDX-MS profile of BAK on liposomes comprising mitochondrial lipids was consistent with known solution structures of inactive BAK. Following activation, HDX-MS resolved major reconfigurations in BAK. Mutagenesis guided by our HDX-MS profiling revealed that the BCL-2 homology (BH) 4 domain maintains the inactive conformation of BAK, and disrupting this domain is sufficient for constitutive BAK activation. Moreover, the entire N-terminal region preceding the BAK oligomerisation domains became disordered post-activation and remained disordered in the activated oligomer. Removal of the disordered N-terminus did not impair, but rather slightly potentiated, BAK-mediated membrane permeabilisation of liposomes and mitochondria. Together, our HDX-MS analyses reveal new insights into the dynamic nature of BAK activation on a membrane, which may provide new opportunities for therapeutic targeting.

Peiminine Reduces ARTS-Mediated Degradation of XIAP by Modulating the PINK1/Parkin Pathway to Ameliorate 6-Hydroxydopamine Toxicity and α-Synuclein Accumulation in Parkinson's Disease Models In Vivo and In Vitro

Parkinson’s disease (PD) is a degenerative disease that can cause motor, cognitive, and behavioral disorders. The treatment strategies being developed are based on the typical pathologic features of PD, including the death of dopaminergic (DA) neurons in the substantia nigra of the midbrain and the accumulation of α-synuclein in neurons. Peiminine (PMN) is an extract of Fritillaria thunbergii Miq that has antioxidant and anti-neuroinflammatory effects. We used Caenorhabditis elegans and SH-SY5Y cell models of PD to evaluate the neuroprotective potential of PMN and address its corresponding mechanism of action. We found that pretreatment with PMN reduced reactive oxygen species production and DA neuron degeneration caused by exposure to 6-hydroxydopamine (6-OHDA), and therefore significantly improved the DA-mediated food-sensing behavior of 6-OHDA-exposed worms and prolonged their lifespan. PMN also diminished the accumulation of α-synuclein in transgenic worms and transfected cells. In our study of the mechanism of action, we found that PMN lessened ARTS-mediated degradation of X-linked inhibitor of apoptosis (XIAP) by enhancing the expression of PINK1/parkin. This led to reduced 6-OHDA-induced apoptosis, enhanced activity of the ubiquitin–proteasome system, and increased autophagy, which diminished the accumulation of α-synuclein. The use of small interfering RNA to down-regulate parkin reversed the benefits of PMN in the PD models. Our findings suggest PMN as a candidate compound worthy of further evaluation for the treatment of PD.

UQCRC1 engages cytochrome c for neuronal apoptotic cell death

Human ubiquinol-cytochrome c reductase core protein 1 (UQCRC1) is an evolutionarily conserved core subunit of mitochondrial respiratory chain complex III. We recently identified the disease-associated variants of UQCRC1 from patients with familial parkinsonism, but its function remains unclear. Here we investigate the endogenous function of UQCRC1 in the human neuronal cell line and the Drosophila nervous system. Flies with neuronal knockdown of uqcrc1 exhibit age-dependent parkinsonism-resembling defects, including dopaminergic neuron reduction and locomotor decline, and are ameliorated by UQCRC1 expression. Lethality of uqcrc1-KO is also rescued by neuronally expressing UQCRC1, but not the disease-causing variant, providing a platform to discern the pathogenicity of this mutation. Furthermore, UQCRC1 associates with the apoptosis trigger cytochrome c (cyt-c), and uqcrc1 deficiency increases cyt-c in the cytoplasmic fraction and activates the caspase cascade. Depleting cyt-c or expression of the anti-apoptotic p35 ameliorates uqcrc1-mediated neurodegeneration. Our findings identify a role for UQCRC1 in regulating cyt-c-induced apoptosis.

Apoptosis regulation at the mitochondria membrane level

Mitochondrial outer membrane permeabilization (MOMP) is a key checkpoint in apoptosis that activates the caspase cascade and irreversibly causes the majority of cells to die. The proteins of the Bcl-2 family are master regulators of apoptosis that form a complex interaction network within the mitochondrial membrane that determines the induction of MOMP. This culminates in the activation of the effector members Bax and Bak, which permeabilize the mitochondrial outer membrane to mediate MOMP. Although the key role of Bax and Bak has been established, many questions remain unresolved regarding molecular mechanisms that control the apoptotic pore. In this review, we discuss the recent progress in our understanding of the regulation of Bax/Bak activity within the mitochondrial membrane.