ATM mediates spermidine-induced mitophagy via PINK1 and Parkin regulation in human fibroblasts

Research progress on the role of mitochondria in the process of hepatic ischemia-reperfusion injury

During liver ischemia-reperfusion injury, existing mechanisms involved oxidative stress, calcium overload, and the activation of inflammatory responses involve mitochondrial injury. Mitochondrial autophagy, a process that maintains the normal physiological activity of mitochondria, promotes cellular metabolism, improves cellular function, and facilitates organelle renewal. Mitochondrial autophagy is involved in oxidative stress and apoptosis, of which the PINK1-Parkin pathway is a major regulatory pathway, and the deletion of PINK1 and Parkin increases mitochondrial damage, reactive oxygen species production, and inflammatory response, playing an important role in mitochondrial quality regulation. In addition, proper mitochondrial permeability translational cycle regulation can help maintain mitochondrial stability and mitigate hepatocyte death during ischemia-reperfusion injury. This mechanism is also closely related to oxidative stress, calcium overload, and the aforementioned autophagy pathway, all of which leads to the augmentation of the mitochondrial membrane permeability transition pore opening and cause apoptosis. Moreover, the release of mitochondrial DNA (mtDNA) due to oxidative stress further aggravates mitochondrial function impairment. Mitochondrial fission and fusion are non-negligible processes required to maintain the dynamic renewal of mitochondria and are essential to the dynamic stability of these organelles. The Bcl-2 protein family also plays an important regulatory role in the mitochondrial apoptosis signaling pathway. A series of complex mechanisms work together to cause hepatic ischemia-reperfusion injury (HIRI). This article reviews the role of mitochondria in HIRI, hoping to provide new therapeutic clues for alleviating HIRI in clinical practice.

Non-linear associations of serum spermidine with type 2 diabetes mellitus and fasting plasma glucose: a cross-sectional study

Background

Previous animal experiments have demonstrated the potential of spermidine to mitigate glucose intolerance, insulin resistance, and hyperinsulinemia. However, there remains a scarcity of epidemiological evidence supporting these findings. Therefore, we aimed to elucidate the associations of serum spermidine with T2DM and FPG.

Materials and methods

The cross-sectional study was conducted from June to August 2019 in the rural areas of Fuxin County, Liaoning Province, China. A total of 4,437 participants were included in the study. The serum spermidine was detected using high-performance liquid chromatography with a fluorescence detector. FPG was measured using the hexokinase method. T2DM was defined as participants with a FPG level of 7.0 mmol/L or greater, or self-reported diagnosis of diabetes by a doctor. Restricted cubic spline model and piecewise linear regression model were used to explore the associations of serum spermidine with T2DM and FPG, respectively.

Results

The mean (SD) age of the participants was 59.3 (10.0) years, with 622 out of 4,437 participants being defined as T2DM. The serum spermidine in participants stratified by age and BMI categories was significantly different, with p values of 0.006 and 0.001, respectively. Among all the participants, the association of serum spermidine with T2DM was J-shaped. The log (spermidine) was negatively associated with T2DM (OR = 0.68, 95% CI: 0.52 to 0.92, p = 0.01) below the inflection point, while log (spermidine) was not significantly associated with T2DM (OR = 1.97, 95% CI: 0.93 to 4.15, p = 0.07) above the inflection point. Among the participants without T2DM, the association of serum spermidine with FPG was inverted J-shaped. The log (spermidine) was positively associated with FPG (β = 0.13, 95% CI: 0.05 to 0.21, p = 0.001) below the inflection point, while log (spermidine) was negatively associated with FPG (β = -0.29, 95% CI: -0.42 to -0.16, p < 0.001) above the inflection point.

Conclusion

In conclusion, non-linear associations of serum spermidine with T2DM and FPG were found in the cross-sectional study in Chinese rural adults. This provided insights into the use of spermidine for the prevention of T2DM, highlighting the potential role in public health prevention strategies of spermidine.

Metabolic control of mitophagy

Mitochondrial dysfunction is a major hallmark of ageing and related chronic disorders. Controlled removal of damaged mitochondria by the autophagic machinery, a process known as mitophagy, is vital for mitochondrial homeostasis and cell survival. The central role of mitochondria in cellular metabolism places mitochondrial removal at the interface of key metabolic pathways affecting the biosynthesis or catabolism of acetyl-coenzyme A, nicotinamide adenine dinucleotide, polyamines, as well as fatty acids and amino acids. Molecular switches that integrate the metabolic status of the cell, like AMP-dependent protein kinase, protein kinase A, mechanistic target of rapamycin and sirtuins, have also emerged as important regulators of mitophagy. In this review, we discuss how metabolic regulation intersects with mitophagy. We place special emphasis on the metabolic regulatory circuits that may be therapeutically targeted to delay ageing and mitochondria-associated chronic diseases. Moreover, we identify outstanding knowledge gaps, such as the ill-defined distinction between basal and damage-induced mitophagy, which must be resolved to boost progress in this area.

Antiaging Strategies and Remedies: A Landscape of Research Progress and Promise

Aging is typified by a gradual loss of physiological fitness and accumulation of cellular damage, leading to deteriorated functions and enhanced vulnerability to diseases. Antiaging research has a long history throughout civilization, with many efforts put forth to understand and prevent the effects of aging. Multiple strategies aiming to promote healthy aging and extend the lifespan have been developed including lifestyle adjustments, medical treatments, and social programs. A multitude of antiaging medicines and remedies have also been explored. Here, we use data from the CAS Content Collection to analyze the publication landscape of recent research related to antiaging strategies and treatments. We review the recent advances and delineate trends in research headway of antiaging knowledge and practice across time, geography, and development pipelines. We further assess the state-of-the-art antiaging approaches and explore their correlations with age-related diseases. The landscape of antiaging drugs has been outlined and explored. Well-recognized and novel, currently evaluated antiaging agents have also been summarized. Finally, we review clinical applications of antiaging products with their development pipelines. The objective of this review is to summarize current knowledge on preventive strategies and treatment remedies in the field of aging, to outline challenges and evaluate growth opportunities, in order to further efforts to solve the problems that remain.

Polyamine Signal through HCC Microenvironment: A Key Regulator of Mitochondrial Preservation and Turnover in TAMs

Hepatocellular carcinoma (HCC) is the most common primary liver cancer, and, with increasing research on the tumor immune microenvironment (TIME), the immunosuppressive micro-environment of HCC hampers further application of immunotherapy, even though immunotherapy can provide survival benefits to patients with advanced liver cancer. Current studies suggest that polyamine metabolism is not only a key metabolic pathway for the formation of immunosuppressive phenotypes in tumor-associated macrophages (TAMs), but it is also profoundly involved in mitochondrial quality control signaling and the energy metabolism regulation process, so it is particularly important to further investigate the role of polyamine metabolism in the tumor microenvironment (TME). In this review, by summarizing the current research progress of key enzymes and substrates of the polyamine metabolic pathway in regulating TAMs and T cells, we propose that polyamine biosynthesis can intervene in the process of mitochondrial energy metabolism by affecting mitochondrial autophagy, which, in turn, regulates macrophage polarization and T cell differentiation. Polyamine metabolism may be a key target for the interactive dialog between HCC cells and immune cells such as TAMs, so interfering with polyamine metabolism may become an important entry point to break intercellular communication, providing new research space for developing polyamine metabolism-based therapy for HCC.

Effects of Methionine Restriction from Different Sources on Sperm Quality in Aging Mice

Decreased sperm quality causing poor pregnancy outcomes in aging males is a common problem. The aim of this study was to investigate the ameliorative effect of methionine restriction on sperm quality in aging mice, using methionine or 2-hydroxy-4-(methylthio)butanoate (HMTBA) as the methionine source, with a view to providing nutritional strategies to mitigate the decline in sperm quality in aging livestock. Fifty-one 6-week-old male mice were randomly divided into four groups: the non-aging group (NA, 0.86% methionine), the control diet group (CD, 0.86% methionine), the methionine-restricted group (MR, 0.17% methionine) and the HMTBA-restricted group (HR, 0.17% methionine). The mice in the CD, MR and HR groups were injected with a daily dose of 0.25 mL/20 g body weight of 10% D-galactose to establish an aging model. The test period was 42 days. The results showed that aging mice in the CD group had impaired testicular morphology and significantly decreased sperm quality compared to those in the NA group. Aging mice in the MR and HR groups showed attenuated impaired testicular morphology and improved sperm quality, especially sperm acrosomal integrity and membrane integrity, compared to mice in the CD group. In addition, mice in the MR and HR groups had reduced testicular inflammation and oxidative stress, increased spermidine levels, and reduced sperm RNA N6-methyladenosine (m6A) and DNA 5-methylcytosine (5mC) levels. Spermidine levels were positively correlated, whereas sperm RNA m6A and DNA 5mC levels were negatively correlated with sperm quality parameters. Our study suggests that methionine restriction alleviates the decline in sperm quality in aging mice, which may be related to changes in methionine metabolism and inhibition of sperm DNA and RNA methylation.

A Crosstalk Between Castration-Resistant Prostate Cancer Cells, M2 Macrophages, and NK Cells: Role of the ATM-PI3K/AKT-PD-L1 Pathway

Castration-resistant prostate cancer (CRPC) in males is associated with a poor prognosis and a higher risk of treatment-related adverse effects, with high mortality among cancers globally. It is thus imperative to explore novel potential molecules with dual therapeutic and biomarker functions. Based on the recent research findings, the expression levels of ataxia telangiectasia mutant kinase (ATM) in prostate cancer (PC) tissues collected from CRPC patients were higher than hormone-dependent PC patients. Using CRPC cell lines (C4-2 and CWR22Rv1), the transwell chamber experiments revealed ATM promoted macrophage recruitment in CRPC cells in vitro via C-X-C motif chemokine ligand 12 (CXCL12). Further in vitro investigations demonstrated that polarized macrophages prevented NK cell recruitment and reduced the immunocidal activity of NK cells against CRPC cell lines. Moreover, ATM boosted programmed death receptor ligand 1 (PD-L1) expression while inhibiting NK group 2D (NKG2D) ligand expression in selected cell lines via PI3K/AKT signaling pathway. The in vivo investigations revealed ATM induced proliferation of CRPC and macrophage recruitment, while the NK cell recruitment was found to suppress ATM expression and CRPC proliferation. In conclusion, it could be demonstrated that inhibiting ATM increased the susceptibility of CRPC to NK cell inhibitors by dampening the CXCL12 and PI3K/AKT-PD-L1 pathways, thereby offering a novel and individualized treatment protocol for treating CRPC.

Current Advances in Mitochondrial Targeted Interventions in Alzheimer's Disease

Alzheimer's disease is the most prevalent neurodegenerative disorder and affects the lives not only of those who are diagnosed but also of their caregivers. Despite the enormous social, economic and political burden, AD remains a disease without an effective treatment and with several failed attempts to modify the disease course. The fact that AD clinical diagnosis is most often performed at a stage at which the underlying pathological events are in an advanced and conceivably irremediable state strongly hampers treatment attempts. This raises the awareness of the need to identify and characterize the early brain changes in AD, in order to identify possible novel therapeutic targets to circumvent AD's cascade of events. One of the most auspicious targets is mitochondria, powerful organelles found in nearly all cells of the body. A vast body of literature has shown that mitochondria from AD patients and model organisms of the disease differ from their non-AD counterparts. In view of this evidence, preserving and/or restoring mitochondria's health and function can represent the primary means to achieve advances to tackle AD. In this review, we will briefly assess and summarize the previous and latest evidence of mitochondria dysfunction in AD. A particular focus will be given to the recent updates and advances in the strategy options aimed to target faulty mitochondria in AD.

Ionizing radiation triggers mitophagy to enhance DNA damage in cancer cells

Radiotherapy is an important cancer treatment strategy that causes DNA damage in tumor cells either directly or indirectly. Autophagy is a physiological process linked to DNA damage. Mitophagy is a form of autophagy, which specifically targets and eliminates impaired mitochondria, thereby upholding cellular homeostasis. However, the connection between DNA damage and mitophagy has yet to be fully elucidated. We found that mitophagy, as an upstream signal, increases ionizing radiation-induced DNA damage by downregulating or overexpressing key mitophagy proteins Parkin and BNIP3. Enhancing the basal level of mitophagy in conjunction with X-ray irradiation can potentially diminish cell cycle arrest at the G2/M phase, substantially elevate the accumulation of γ-H2AX, 53BP1, and PARP1 foci within the nucleus, augment DNA damage, and facilitate the demise of tumor cells. Consequently, this approach prolongs the survival of melanoma-bearing mice. The findings of this study are anticipated to offer a therapeutic approach for enhancing the therapeutic effectiveness of radiotherapy.

CLEC16A-An Emerging Master Regulator of Autoimmunity and Neurodegeneration

CLEC16A is emerging as an important genetic risk factor for several autoimmune disorders and for Parkinson disease (PD), opening new avenues for translational research and therapeutic development. While the exact role of CLEC16A in health and disease is still being elucidated, the gene plays a critical role in the regulation of autophagy, mitophagy, endocytosis, intracellular trafficking, immune function, and in biological processes such as insulin secretion and others that are important to cellular homeostasis. As shown in both human and animal modeling studies, CLEC16A hypofunction predisposes to both autoinflammatory phenotype and neurodegeneration. While the two are clearly related, further functional studies are needed to fully understand the mechanisms involved for optimized therapeutic interventions. Based on recent data, mitophagy-inducing drugs may be warranted, and such therapy should be tested in clinical trials as these drugs would tackle the underlying pathogenic mechanism (s) and could treat or prevent symptoms of autoimmunity and neurodegeneration in individuals with CLEC16A risk variants. Accordingly, interventions directed at reversing the dysregulated mitophagy and the consequences of loss of function of CLEC16A without activating other detrimental cellular pathways could present an effective therapy. This review presents the emerging role of CLEC16A in health and disease and provides an update on the disease processes that are attributed to variants located in the CLEC16A gene, which are responsible for autoimmune disorders and neurodegeneration with emphasis on how this information is being translated into practical and effective applications in the clinic.

SIM2s directed Parkin-mediated mitophagy promotes mammary epithelial cell differentiation

The functionally differentiated mammary gland adapts to extreme levels of stress from increased demand for energy by activating specific protective mechanisms to support neonatal health. Here, we identify the breast tumor suppressor gene, single-minded 2 s (SIM2s) as a novel regulator of mitophagy, a key component of this stress response. Using tissue-specific mouse models, we found that loss of Sim2 reduced lactation performance, whereas gain (overexpression) of Sim2s enhanced and extended lactation performance and survival of mammary epithelial cells (MECs). Using an in vitro model of MEC differentiation, we observed SIM2s is required for Parkin-mediated mitophagy, which we have previously shown as necessary for functional differentiation. Mechanistically, SIM2s localizes to mitochondria to directly mediate Parkin mitochondrial loading. Together, our data suggest that SIM2s regulates the rapid recycling of mitochondria via mitophagy, enhancing the function and survival of differentiated MECs.

Mitochondrial Signaling Pathways Associated with DNA Damage Responses

Under physiological and stress conditions, mitochondria act as a signaling platform to initiate biological events, establishing communication from the mitochondria to the rest of the cell. Mitochondrial adenosine triphosphate (ATP), reactive oxygen species, cytochrome C, and damage-associated molecular patterns act as messengers in metabolism, oxidative stress response, bystander response, apoptosis, cellular senescence, and inflammation response. In this review paper, the mitochondrial signaling in response to DNA damage was summarized. Mitochondrial clearance via fusion, fission, and mitophagy regulates mitochondrial quality control under oxidative stress conditions. On the other hand, damaged mitochondria release their contents into the cytoplasm and then mediate various signaling pathways. The role of mitochondrial dysfunction in radiation carcinogenesis was discussed, and the recent findings on radiation-induced mitochondrial signaling and radioprotective agents that targeted mitochondria were presented. The analysis of the mitochondrial radiation effect, as hypothesized, is critical in assessing radiation risks to human health.

Exploration of the Antioxidant Effect of Spermidine on the Ovary and Screening and Identification of Differentially Expressed Proteins

Spermidine is a naturally occurring polyamine compound that has many biological functions, such as inducing autophagy and anti-inflammatory and anti-aging effects. Spermidine can affect follicular development and thus protect ovarian function. In this study, ICR mice were fed exogenous spermidine drinking water for three months to explore the regulation of ovarian function by spermidine. The results showed that the number of atretic follicles in the ovaries of spermidine-treated mice was significantly lower than that in the control group. Antioxidant enzyme activities (SOD, CAT, T-AOC) significantly increased, and MDA levels significantly decreased. The expression of autophagy protein (Beclin 1 and microtubule-associated protein 1 light chain 3 LC3 II/I) significantly increased, and the expression of the polyubiquitin-binding protein p62/SQSTM 1 significantly decreased. Moreover, we found 424 differentially expressed proteins (DEPs) were upregulated, and 257 were downregulated using proteomic sequencing. Gene Ontology and KEGG analyses showed that these DEPs were mainly involved in lipid metabolism, oxidative metabolism and hormone production pathways. In conclusion, spermidine protects ovarian function by reducing the number of atresia follicles and regulating the level of autophagy protein, antioxidant enzyme activity, and polyamine metabolism in mice.

Differential Role of Active Compounds in Mitophagy and Related Neurodegenerative Diseases

Neurodegenerative diseases, such as Alzheimer’s disease or Parkinson’s disease, significantly reduce the quality of life of patients and eventually result in complete maladjustment. Disruption of the synapses leads to a deterioration in the communication of nerve cells and decreased plasticity, which is associated with a loss of cognitive functions and neurodegeneration. Maintaining proper synaptic activity depends on the qualitative composition of mitochondria, because synaptic processes require sufficient energy supply and fine calcium regulation. The maintenance of the qualitative composition of mitochondria occurs due to mitophagy. The regulation of mitophagy is usually based on several internal mechanisms, as well as on signals and substances coming from outside the cell. These substances may directly or indirectly enhance or weaken mitophagy. In this review, we have considered the role of some compounds in process of mitophagy and neurodegeneration. Some of them have a beneficial effect on the functions of mitochondria and enhance mitophagy, showing promise as novel drugs for the treatment of neurodegenerative pathologies, while others contribute to a decrease in mitophagy.

Mitophagy: A promising therapeutic target for neuroprotection during ageing and age-related diseases

Mitochondria and mitochondria-mediated signalling pathways are known to control synaptic signalling, as well as long-lasting changes in neuronal structure and function. Mitochondrial impairment is linked to synaptic dysfunction in normal ageing and age-associated neurodegenerative ailments, including Parkinson's disease (PD) and Alzheimer's disease (AD). Both proteolysis and mitophagy perform a major role in neuroprotection, by maintaining a healthy mitochondrial population during ageing. Mitophagy, a highly evolutionarily conserved cellular process, helps in the clearance of damaged mitochondria and thereby maintains the mitochondrial and metabolic balance, energy supply, neuronal survival and neuronal health. Besides the maintenance of brain homeostasis, hippocampal mitophagy also helps in synapse formation, axonal development, dopamine release and long-term depression. In contrast, defective mitophagy contributes to ageing and age-related neurodegeneration by promoting the accumulation of damaged mitochondria leading to cellular dysfunction. Exercise, stress management, maintaining healthy mitochondrial dynamics and administering natural or synthetic pharmacological compounds are some of the strategies used for neuroprotection during ageing and age-related neurological diseases. The current review discusses the impact of defective mitophagy in ageing and age-associated neurodegenerative conditions, the underlying molecular pathways and potential therapies based on recently elucidated mitophagy-inducing strategies.

PINK1/Parkin-mediated mitophagy in neurodegenerative diseases

Mitochondria play key roles in bioenergetics, metabolism, and signaling; therefore, stable mitochondrial function is essential for cell survival, particularly in energy-intensive neuronal cells. In neurodegenerative diseases, damaged mitochondria accumulate in neurons causing associated bioenergetics deficiency, impaired cell signaling, defective cytoplasmic calcium buffering, and other pathological changes. Mitochondrial quality control is an important mechanism to ensure the maintenance of mitochondrial health, homeostasis, and mitophagy, the latter of which is a pathway that delivers defective mitochondria to the lysosome for degradation. Defective mitophagy is thought to be responsible for the accumulation of damaged mitochondria, which leads to cellular dysfunction and/or death in neurodegenerative diseases. PINK1/Parkin mainly regulates ubiquitin-dependent mitophagy, which is crucial for many aspects of mitochondrial physiology, particularly the initiation of autophagic mechanisms. Therefore, in the present review, we summarize the current knowledge of the conventional mitophagy pathway, focusing on the molecular mechanisms underlying mitophagy dysregulation in prion disease and other age-related neurodegenerative diseases, especially in relation to the PINK1/Parkin pathway. Moreover, we list the inducers of mitophagy that possess neuroprotective effects, in addition to their mechanisms related to the PINK1/Parkin pathway. These mechanisms may provide potential interventions centered on the regulation of mitophagy and offer therapeutic strategies for the treatment of neurodegenerative diseases.

Distinct designer diamines promote mitophagy, and thereby enhance healthspan in C. elegans and protect human cells against oxidative damage

Impaired mitophagy is a primary pathogenic event underlying diverse aging-associated diseases such as Alzheimer and Parkinson diseases and sarcopenia. Therefore, augmentation of mitophagy, the process by which defective mitochondria are removed, then replaced by new ones, is an emerging strategy for preventing the evolvement of multiple morbidities in the elderly population. Based on the scaffold of spermidine (Spd), a known mitophagy-promoting agent, we designed and tested a family of structurally related compounds. A prototypic member, 1,8-diaminooctane (VL-004), exceeds Spd in its ability to induce mitophagy and protect against oxidative stress. VL-004 activity is mediated by canonical aging genes and promotes lifespan and healthspan in C. elegans. Moreover, it enhances mitophagy and protects against oxidative injury in rodent and human cells. Initial structural characterization suggests simple rules for the design of compounds with improved bioactivity, opening the way for a new generation of agents with a potential to promote healthy aging.

Mitophagy in Alzheimer's disease: Molecular defects and therapeutic approaches

Mitochondrial dysfunctions are central players in Alzheimer's disease (AD). In addition, impairments in mitophagy, the process of selective mitochondrial degradation by autophagy leading to a gradual accumulation of defective mitochondria, have also been reported to occur in AD. We provide an updated overview of the recent discoveries and advancements on mitophagic molecular dysfunctions in AD-derived fluids and cells as well as in AD brains. We discuss studies using AD cellular and animal models that have unraveled the contribution of relevant AD-related proteins (Tau, Aβ, APP-derived fragments and APOE) in mitophagy failure. In accordance with the important role of impaired mitophagy in AD, we report on various therapeutic strategies aiming at stimulating mitophagy in AD and we summarize the benefits of these potential therapeutic strategies in human clinical trials.

Mechanisms of spermidine-induced autophagy and geroprotection

Aging involves the systemic deterioration of all known cell types in most eukaryotes. Several recently discovered compounds that extend the healthspan and lifespan of model organisms decelerate pathways that govern the aging process. Among these geroprotectors, spermidine, a natural polyamine ubiquitously found in organisms from all kingdoms, prolongs the lifespan of fungi, nematodes, insects and rodents. In mice, it also postpones the manifestation of various age-associated disorders such as cardiovascular disease and neurodegeneration. The specific features of spermidine, including its presence in common food items, make it an interesting candidate for translational aging research. Here, we review novel insights into the geroprotective mode of action of spermidine at the molecular level, as we discuss strategies for elucidating its clinical potential.

Exploring therapeutic potential of mitophagy modulators using Drosophila models of Parkinson’s disease

Parkinson’s disease (PD) is the second most popular age-associated neurodegenerative disorder after Alzheimer’s disease. The degeneration of dopaminergic neurons, aggregation of α-synuclein (α-syn), and locomotor defects are the main characteristic features of PD. The main cause of a familial form of PD is associated with a mutation in genes such as SNCA, PINK1, Parkin, DJ-1, LRKK2, and others. Recent advances have uncovered the different underlying mechanisms of PD but the treatment of PD is still unknown due to the unavailability of effective therapies and preventive medicines in the current scenario. The pathophysiology and genetics of PD have been strongly associated with mitochondria in disease etiology. Several studies have investigated a complex molecular mechanism governing the identification and clearance of dysfunctional mitochondria from the cell, a mitochondrial quality control mechanism called mitophagy. Reduced mitophagy and mitochondrial impairment are found in both sporadic and familial PD. Pharmacologically modulating mitophagy and accelerating the removal of defective mitochondria are of common interest in developing a therapy for PD. However, despite the extensive understanding of the mitochondrial quality control pathway and its underlying mechanism, the therapeutic potential of targeting mitophagy modulation and its role in PD remains to be explored. Thus, targeting mitophagy using chemical agents and naturally occurring phytochemicals could be an emerging therapeutic strategy in PD prevention and treatment. We discuss the current research on understanding the role of mitophagy modulators in PD using Drosophila melanogaster as a model. We further explore the contribution of Drosophila in the pathophysiology of PD, and discuss comprehensive genetic analysis in flies and pharmacological drug screening to develop potential therapeutic molecules for PD.

Mitophagy and reactive oxygen species interplay in Parkinson's disease

Mitophagy impairment and oxidative stress are cardinal pathological hallmarks in Parkinson's disease (PD), a common age-related neurodegenerative condition. The specific interactions between mitophagy and reactive oxygen species (ROS) have attracted considerable attention even though their exact interplay in PD has not been fully elucidated. We highlight the interactions between ROS and mitophagy, with a focus on the signalling pathways downstream to ROS that triggers mitophagy and draw attention to potential therapeutic compounds that target these pathways in both experimental and clinical models. Identifying a combination of ROS inhibitors and mitophagy activators to provide a physiologic balance in this complex signalling pathways may lead to a more optimal outcome. Deciphering the exact temporal relationship between mitophagy and oxidative stress and their triggers early in the course of neurodegeneration can unravel mechanistic clues that potentially lead to the development of compounds for clinical drug trials focusing on prodromic PD or at-risk individuals.

The emerging role of autophagy and mitophagy in tauopathies: From pathogenesis to translational implications in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease, affecting more than 55 million individuals worldwide in 2021. In addition to the "amyloid hypothesis," an increasing number of studies have demonstrated that phosphorylated tau plays an important role in AD pathogenesis. Both soluble tau oligomers and insoluble tau aggregates in the brain can induce structural and functional neuronal damage through multiple pathways, eventually leading to memory deficits and neurodegeneration. Autophagy is an important cellular response to various stress stimuli and can generally be categorized into non-selective and selective autophagy. Recent studies have indicated that both types of autophagy are involved in AD pathology. Among the several subtypes of selective autophagy, mitophagy, which mediates the selective removal of mitochondria, has attracted increasing attention because dysfunctional mitochondria have been suggested to contribute to tauopathies. In this review, we summarize the latest findings on the bidirectional association between abnormal tau proteins and defective autophagy, as well as mitophagy, which might constitute a vicious cycle in the induction of neurodegeneration. Neuroinflammation, another important feature in the pathogenesis and progression of AD, has been shown to crosstalk with autophagy and mitophagy. Additionally, we comprehensively discuss the relationship between neuroinflammation, autophagy, and mitophagy. By elucidating the underlying molecular mechanisms governing these pathologies, we highlight novel therapeutic strategies targeting autophagy, mitophagy and neuroinflammation, such as those using rapamycin, urolithin, spermidine, curcumin, nicotinamide, and actinonin, for the prevention and treatment of AD.

The hallmarks of aging in Ataxia-Telangiectasia

Ataxia-telangiectasia (A-T) is caused by absence of the catalytic activity of ATM, a protein kinase that plays a central role in the DNA damage response, many branches of cellular metabolism, redox and mitochondrial homeostasis, and cell cycle regulation. A-T is a complex disorder characterized mainly by progressive cerebellar degeneration, immunodeficiency, radiation sensitivity, genome instability, and predisposition to cancer. It is increasingly recognized that the premature aging component of A-T is an important driver of this disease, and A-T is therefore an attractive model to study the aging process. This review outlines the current state of knowledge pertaining to the molecular and cellular signatures of aging in A-T and proposes how these new insights can guide novel therapeutic approaches for A-T.

Investigating the Role of Spermidine in a Model System of Alzheimer’s Disease Using Correlative Microscopy and Super-resolution Techniques

Background: Spermidine has recently received major attention for its potential therapeutic benefits in the context of neurodegeneration, cancer, and aging. However, it is unclear whether concentration dependencies of spermidine exist, to differentially enhance autophagic flux. Moreover, the relationship between low or high autophagy activity relative to basal neuronal autophagy flux and subsequent protein clearance as well as cellular toxicity has remained largely unclear.

Methods: Here, we used high-resolution imaging and biochemical techniques to investigate the effects of a low and of a high concentration of spermidine on autophagic flux, neuronal toxicity, and protein clearance in in vitro models of paraquat (PQ) induced neuronal toxicity and amyloid precursor protein (APP) overexpression, as well as in an in vivo model of PQ-induced rodent brain injury.

Results: Our results reveal that spermidine induces autophagic flux in a concentration-dependent manner, however the detectable change in the autophagy response critically depends on the specificity and sensitivity of the method employed. By using correlative imaging techniques through Super-Resolution Structured Illumination Microscopy (SR-SIM) and Focused Ion Beam Scanning Electron Microscopy (FIB-SEM), we demonstrate that spermidine at a low concentration induces autophagosome formation capable of large volume clearance. In addition, we provide evidence of distinct, context-dependent protective roles of spermidine in models of Alzheimer’s disease. In an in vitro environment, a low concentration of spermidine protected against PQ-induced toxicity, while both low and high concentrations provided protection against cytotoxicity induced by APP overexpression. In the in vivo scenario, we demonstrate brain region-specific susceptibility to PQ-induced neuronal toxicity, with the hippocampus being highly susceptible compared to the cortex. Regardless of this, spermidine administered at both low and high dosages protected against paraquat-induced toxicity.

Conclusions: Taken together, our results demonstrate that firstly, administration of spermidine may present a favourable therapeutic strategy for the treatment of Alzheimer’s disease and secondly, that concentration and dosage-dependent precision autophagy flux screening may be more critical for optimal autophagy and cell death control than previously thought.

PINK1/Parkin-mediated mitophagy in cardiovascular disease: From pathogenesis to novel therapy

Cardiovascular disease(CVD)is one of the predominant causes of death and morbidity. Mitochondria play a key role in maintaining cardiac energy metabolism. However, mitochondrial dysfunction leads to excessive production of ROS, resulting in oxidative damage to cardiomyocytes and contributing to a variety of cardiovascular diseases. In such a case, the clearance of impaired mitochondria is necessary. Currently, most studies have indicated an essential role for mitophagy in maintaining cardiac homeostasis and regulating CVD-related metabolic transition. Recent studies have implicated that PTEN-induced putative kinase 1 (PINK1)/Parkin-mediated mitophagy has been implicated in maintaining cardiomyocyte homeostasis. Here, we discuss the physiological and pathological roles of PINK1/Parkin-mediated mitophagy in the cardiovascular system, as well as potential therapeutic strategies based on PINK1/Parkin-mediated mitophagy modulation, which are of great significance for the prevention and treatment of cardiovascular diseases.

Acetaldehyde Induces Cytotoxicity via Triggering Mitochondrial Dysfunction and Overactive Mitophagy

Overconsumption of alcohol damages brain tissue and causes cognitive dysfunction. It has been suggested that the neurotoxicity caused by excessive alcohol consumption is largely mediated by acetaldehyde, the most toxic metabolite of ethanol. Evidence shows that acetaldehyde impairs mitochondrial function and induces cytotoxicity of neuronal cells; however, the exact mechanisms are not fully understood. The aim of this study was to investigate the role of mitophagy in acetaldehyde-induced cytotoxicity. It was found that acetaldehyde treatment induced mitophagic responses and caused cytotoxicity in SH-SY5Y cells. The levels of light chain 3 (LC3)-II, Beclin1, autophagy-related protein (Atg) 5 and Atg16L1, PTEN-induced putative kinase (PINK)1, and Parkin were significantly elevated, while the level of p62 was reduced in acetaldehyde-treated cells. Acetaldehyde also promoted the accumulation of PINK1 and Parkin on mitochondria and caused a remarkable decrease of mitochondrial mass. Treatment with autophagy inhibitors prevented the decline of mitochondrial mass and alleviated the cytotoxicity induced by acetaldehyde, suggesting that overactive mitophagy might be an important mechanism contributing to acetaldehyde-induced cytotoxicity. Antioxidant N-acetyl-L-cysteine significantly attenuated the mitophagic responses and alleviated the cytotoxicity induced by acetaldehyde, indicating that oxidative stress was a major mediator of the excessive mitophagy induced by acetaldehyde. Taken together, these findings provided new insights into the role of mitophagy and oxidative stress in acetaldehyde-induced cytotoxicity.

Metabolic Stress and Mitochondrial Dysfunction in Ataxia-Telangiectasia

The ataxia-telangiectasia mutated (ATM) protein kinase is, as the name implies, mutated in the human genetic disorder ataxia-telangiectasia (A-T). This protein has its “finger in many pies”, being responsible for the phosphorylation of many thousands of proteins in different signaling pathways in its role in protecting the cell against a variety of different forms of stress that threaten to perturb cellular homeostasis. The classical role of ATM is the protection against DNA damage, but it is evident that it also plays a key role in maintaining cell homeostasis in the face of oxidative and other forms of non-DNA damaging stress. The presence of ATM is not only in the nucleus to cope with damage to DNA, but also in association with other organelles in the cytoplasm, which suggests a greater protective role. This review attempts to address this greater role of ATM in protecting the cell against both external and endogenous damage.

Ultrafine black carbon caused mitochondrial oxidative stress, mitochondrial dysfunction and mitophagy in SH-SY5Y cells

Exposure to ambient ultrafine black carbon (uBC, with aerodynamic diameter less than 100 nm) is associated with many neurodegenerative diseases. Oxidative stress is the predominantly reported neurotoxic effects caused by uBC exposure. Mitochondrion is responsible for production of majority of ROS in cells and mitochondrial dysfunction is closely related to adverse nervous outcomes. Mitophagy is an important cellular process to eliminate dysfunctional or damaged mitochondria. However, the mechanisms that modulate mitophagy and mitochondrial dysfunction initiated by uBC remain to be elucidated. The purpose of this study was to investigate how mitochondrial oxidative stress regulated mitochondrial dysfunction and mitophagy in human neuroblastoma cell line (SH-SY5Y) after uBC treatment. RNA interference was further applied to explore the roles of mitophagy in mitochondrial dysfunction. We found uBC triggered cell apoptosis via ROS-mitochondrial apoptotic pathway. The uBC also caused serious mitochondrial damage and respiratory dysfunction, indicated by the abnormalities in mitochondrial division and fusion related proteins, decreased mitochondria number and ATP level. Increased PTEN induced putative kinase 1 (PINK1) and Parkin protein levels and the autolysosome numbers suggested uBC could promote Pink1/Parkin-dependent mitophagy process in SH-SY5Y cells. Mitophagy inhibition could reserve mitochondria number and ATP activity, but not fusion and division related protein levels in SH-SY5Y cells exposed to uBC. Administration of a mitochondria-targeted antioxidant (mitoquinone) significantly eliminated uBC caused apoptosis, mitochondrial dysfunction and mitophagy. Our data suggested mitochondrial oxidative stress regulated uBC induced mitochondrial dysfunction and PINK1/Parkin-dependent mitophagy. PINK1/Parkin-dependent mitophagy probably participated in regulating uBC caused mitochondrial dysfunction but not by controlling mitochondrial fusion and division related proteins. Our results may provide some new insights and evidences to understand the mechanisms of neurotoxicity induced by uBC.

Circulating primitive murine erythroblasts undergo complex proteomic and metabolomic changes during terminal maturation

Terminal maturation of primary murine primitive erythroid precursors is characterized by loss of organelles and anabolic components.

Metabolic reprogramming includes depression of mitochondrial metabolism and upregulation of the pentose phosphate pathway and redox metabolism.

Primitive erythropoiesis is a critical component of the fetal cardiovascular network and is essential for the growth and survival of the mammalian embryo. The need to rapidly establish a functional cardiovascular system is met, in part, by the intravascular circulation of primitive erythroid precursors that mature as a single semisynchronous cohort. To better understand the processes that regulate erythroid precursor maturation, we analyzed the proteome, metabolome, and lipidome of primitive erythroblasts isolated from embryonic day (E) 10.5 and E12.5 of mouse gestation, representing their transition from basophilic erythroblast to orthochromatic erythroblast (OrthoE) stages of maturation. Previous transcriptional and biomechanical characterizations of these precursors have highlighted a transition toward the expression of protein elements characteristic of mature red blood cell structure and function. Our analysis confirmed a loss of organelle-specific protein components involved in messenger RNA processing, proteostasis, and metabolism. In parallel, we observed metabolic rewiring toward the pentose phosphate pathway, glycolysis, and the Rapoport-Luebering shunt. Activation of the pentose phosphate pathway in particular may have stemmed from increased expression of hemoglobin chains and band 3, which together control oxygen-dependent metabolic modulation. Increased expression of several antioxidant enzymes also indicated modification to redox homeostasis. In addition, accumulation of oxylipins and cholesteryl esters in primitive OrthoE cells was paralleled by increased transcript levels of the p53-regulated cholesterol transporter (ABCA1) and decreased transcript levels of cholesterol synthetic enzymes. The present study characterizes the extensive metabolic rewiring that occurs in primary embryonic erythroid precursors as they prepare to enucleate and continue circulating without internal organelles.

Compromised autophagy and mitophagy in brain ageing and Alzheimer's diseases

Alzheimer's disease (AD) is one of the most persistent and devastating neurodegenerative disorders of old age, and is characterized clinically by an insidious onset and a gradual, progressive deterioration of cognitive abilities, ranging from loss of memory to impairment of judgement and reasoning. Despite years of research, an effective cure is still not available. Autophagy is the cellular 'garbage' clearance system which plays fundamental roles in neurogenesis, neuronal development and activity, and brain health, including memory and learning. A selective sub-type of autophagy is mitophagy which recognizes and degrades damaged or superfluous mitochondria to maintain a healthy and necessary cellular mitochondrial pool. However, emerging evidence from animal models and human samples suggests an age-dependent reduction of autophagy and mitophagy, which are also compromised in AD. Upregulation of autophagy/mitophagy slows down memory loss and ameliorates clinical features in animal models of AD. In this review, we give an overview of autophagy and mitophagy and their link to the progression of AD. We also summarize approaches to upregulate autophagy/mitophagy. We hypothesize that age-dependent compromised autophagy/mitophagy is a cause of brain ageing and a risk factor for AD, while restoration of autophagy/mitophagy to more youthful levels could return the brain to health.

Calorie Restriction for Cancer Prevention and Therapy: Mechanisms, Expectations, and Efficacy

Cancer is one of the most frequently diagnosed diseases, and despite the continuous efforts in searching for new and more effective treatments, its morbidity and mortality remain a significant health problem worldwide. Calorie restriction, a dietary manipulation that consists in a reduction of the calorie intake, is gaining attention as a potential adjuvant intervention for preventing and/or fighting cancer. Several forms of energy reduction intake, which includes caloric restriction tout-court, dietary restrictions, and intermittent fasting, are being explored for their ability to prevent or slow down cancer progression. Additionally, another anti-cancer approach being under investigation relies on the use of nutraceuticals known as “Caloric Restriction Mimetics” that can provide caloric restriction-mediated benefits without subjecting the patients to a strict diet. Preclinical in vitro and in vivo studies consistently show that diet modifiers reducing the calorie have impact on tumor microenvironment and cancer metabolism, resulting in reduced growth and progression of cancer. Preliminary clinical studies show that patients subjected to a reduced nutrient/energy intake experience improved outcomes from chemo- and radiotherapy while better tolerating the side effects. Here, we review the state of the art on the therapeutic potential of calorie restriction and of caloric restriction mimetics in preventing or retarding tumor development by modulating a subset of cellular processes. The most recent clinical progresses with caloric restriction mimetics in the clinical practice are also discussed.

An anaplerotic approach to correct the mitochondrial dysfunction in ataxia-telangiectasia (A-T)

BACKGROUND

ATM, the protein defective in the human genetic disorder, ataxia-telangiectasia (A-T) plays a central role in response to DNA double-strand breaks (DSBs) and in protecting the cell against oxidative stress. We showed that A-T cells are hypersensitive to metabolic stress which can be accounted for by a failure to exhibit efficient endoplasmic reticulum (ER)-mitochondrial signalling and Ca2+ transfer in response to nutrient deprivation resulting in mitochondrial dysfunction. The objective of the current study is to use an anaplerotic approach using the fatty acid, heptanoate (C7), a metabolic product of the triglyceride, triheptanoin to correct the defect in ER-mitochondrial signalling and enhance cell survival of A-T cells in response to metabolic stress.

METHODS

We treated control cells and A-T cells with the anaplerotic agent, heptanoate to determine their sensitivity to metabolic stress induced by inhibition of glycolysis with 2- deoxyglucose (2DG) using live-cell imaging to monitor cell survival for 72 h using the Incucyte system. We examined ER-mitochondrial signalling in A-T cells exposed to metabolic stress using a suite of techniques including immunofluorescence staining of Grp75, ER-mitochondrial Ca2+ channel, the VAPB-PTPIP51 ER-mitochondrial tether complexes as well as proximity ligation assays between Grp75-IP3R1 and VAPB1-PTPIP51 to establish a functional interaction between ER and mitochondria. Finally, we also performed metabolomic analysis using LC-MS/MS assay to determine altered levels of TCA intermediates A-T cells compared to healthy control cells.

RESULTS

We demonstrate that heptanoate corrects all aspects of the defective ER-mitochondrial signalling observed in A-T cells. Heptanoate enhances ER-mitochondrial contacts; increases the flow of calcium from the ER to the mitochondrion; restores normal mitochondrial function and mitophagy and increases the resistance of ATM-deficient cells and cells from A-T patients to metabolic stress-induced killing. The defect in mitochondrial function in ATM-deficient cells was accompanied by more reliance on aerobic glycolysis as shown by increased lactate dehydrogenase A (LDHA), accumulation of lactate, and reduced levels of both acetyl CoA and ATP which are all restored by heptanoate.

CONCLUSIONS

We conclude that heptanoate corrects metabolic stress in A-T cells by restoring ER-mitochondria signalling and mitochondrial function and suggest that the parent compound, triheptanoin, has immense potential as a novel therapeutic agent for patients with A-T.

Autophagy and the hallmarks of aging

Autophagy, an essential cellular process that mediates degradation of proteins and organelles in lysosomes, has been tightly linked to cellular quality control for its role as part of the proteostasis network. The current interest in identifying the cellular and molecular determinants of aging, has highlighted the important contribution of malfunctioning of autophagy with age to the loss of proteostasis that characterizes all old organisms. However, the diversity of cellular functions of the different types of autophagy and the often reciprocal interactions of autophagy with other determinants of aging, is placing autophagy at the center of the aging process. In this work, we summarize evidence for the contribution of autophagy to health- and lifespan and provide examples of the bidirectional interplay between autophagic pathways and several of the so-called hallmarks of aging. This central role of autophagy in aging, and the dependence on autophagy of many geroprotective interventions, has motivated a search for direct modulators of autophagy that could be used to slow aging and extend healthspan. Here, we review some of those ongoing therapeutic efforts and comment on the potential of targeting autophagy in aging.

Possible relationship between mitochondrial changes and oxidative stress under low dose-rate irradiation

Objectives: High dose-rate ionizing radiation (IR) causes severe DSB damage, as well as reactive oxygen species (ROS) accumulation and oxidative stress. However, it is unknown what biological processes are affected by low dose-rate IR; therefore, the molecular relationships between mitochondria changes and oxidative stress in human normal cells was investigated after low dose-rate IR.Methods: We compared several cellular response between high and low dose-rate irradiation using cell survival assay, ROS/RNS assay, immunofluorescence and western blot analysis.Results: Reduced DSB damage and increased levels of ROS, with subsequent oxidative stress responses, were observed in normal cells after low dose-rate IR. Low dose-rate IR caused several mitochondrial changes, including morphology mass, and mitochondrial membrane potential, suggesting that mitochondrial damage was caused. Although damaged mitochondria were removed by mitophagy to stop ROS leakage, the mitophagy-regulatory factor, PINK1, was reduced following low dose-rate IR. Although mitochondrial dynamics (fission/fusion events) are important for the proper mitophagy process, some mitochondrial fusion factors decreased following low dose-rate IR.Discussion: The dysfunction of mitophagy pathway under low dose-rate IR increased ROS and the subsequent activation of the oxidative stress response.

Cell Death and Survival Pathways Involving ATM Protein Kinase

Cell death is the ultimate form of cellular dysfunction, and is induced by a wide range of stresses including genotoxic stresses. During genotoxic stress, two opposite cellular reactions, cellular protection through DNA repair and elimination of damaged cells by the induction of cell death, can occur in both separate and simultaneous manners. ATM (ataxia telangiectasia mutated) kinase (hereafter referred to as ATM) is a protein kinase that plays central roles in the induction of cell death during genotoxic stresses. It has long been considered that ATM mediates DNA damage-induced cell death through inducing apoptosis. However, recent research progress in cell death modality is now revealing ATM-dependent cell death pathways that consist of not only apoptosis but also necroptosis, ferroptosis, and dysfunction of autophagy, a cellular survival mechanism. In this short review, we intend to provide a brief outline of cell death mechanisms in which ATM is involved, with emphasis on pathways other than apoptosis.

Targeting Cardiovascular Risk Factors Through Dietary Adaptations and Caloric Restriction Mimetics

The average human life expectancy continues to rise globally and so does the prevalence and absolute burden of cardiovascular disease. Dietary restriction promotes longevity and improves various cardiovascular risk factors, including hypertension, obesity, diabetes mellitus, and metabolic syndrome. However, low adherence to caloric restriction renders this stringent dietary intervention challenging to adopt as a standard practice for cardiovascular disease prevention. Hence, alternative eating patterns and strategies that recapitulate the salutary benefits of caloric restriction are under intense investigation. Here, we first provide an overview of alternative interventions, including intermittent fasting, alternate-day fasting and the Mediterranean diet, along with their cardiometabolic effects in animal models and humans. We then present emerging pharmacological alternatives, including spermidine, NAD+ precursors, resveratrol, and metformin, as promising caloric restriction mimetics, and briefly touch on the mechanisms underpinning their cardiometabolic and health-promoting effects. We conclude that implementation of feasible dietary approaches holds the promise to attenuate the burden of cardiovascular disease and facilitate healthy aging in humans.

The multifaceted regulation of mitophagy by endogenous metabolites

Owing to the dominant functions of mitochondria in multiple cellular metabolisms and distinct types of regulated cell death, maintaining a functional mitochondrial network is fundamental for the cellular homeostasis and body fitness in response to physiological adaptations and stressed conditions. The process of mitophagy, in which the dysfunctional or superfluous mitochondria are selectively engulfed by autophagosome and subsequently degraded in lysosome, has been well formulated as one of the major mechanisms for mitochondrial quality control. To date, the PINK1-PRKN-dependent and receptors (including proteins and lipids)-dependent pathways have been characterized to determine the mitophagy in mammalian cells. The mitophagy is highly responsive to the dynamics of endogenous metabolites, including iron-, calcium-, glycolysis-TCA-, NAD⁺-, amino acids-, fatty acids-, and cAMP-associated metabolites. Herein, we summarize the recent advances toward the molecular details of mitophagy regulation in mammalian cells. We also highlight the key regulations of mammalian mitophagy by endogenous metabolites, shed new light on the bidirectional interplay between mitophagy and cellular metabolisms, with attempting to provide a perspective insight into the nutritional intervention of metabolic disorders with mitophagy deficit.Abbreviations: acetyl-CoA: acetyl-coenzyme A; ACO1: aconitase 1; ADCYs: adenylate cyclases; AMPK: AMP-activated protein kinase; ATM: ATM serine/threonine kinase; BCL2L1: BCL2 like 1; BCL2L13: BCL2 like 13; BNIP3: BCL2 interacting protein 3; BNIP3L: BCL2 interacting protein 3 like; Ca²⁺: calcium ion; CALCOCO2: calcium binding and coiled-coil domain 2; CANX: calnexin; CO: carbon monoxide; CYCS: cytochrome c, somatic; DFP: deferiprone; DNM1L: dynamin 1 like; ER: endoplasmic reticulum; FKBP8: FKBP prolyl isomerase 8; FOXO3: forkhead box O3; FTMT: ferritin mitochondrial; FUNDC1: FUN14 domain containing 1; GABA: γ-aminobutyric acid; GSH: glutathione; HIF1A: hypoxia inducible factor 1 subunit alpha; IMMT: inner membrane mitochondrial protein; IRP1: iron regulatory protein 1; ISC: iron-sulfur cluster; ITPR2: inositol 1,4,5-trisphosphate type 2 receptor; KMO: kynurenine 3-monooxygenase; LIR: LC3 interacting region; MAM: mitochondria-associated membrane; MAP1LC3: microtubule associated protein 1 light chain 3; MFNs: mitofusins; mitophagy: mitochondrial autophagy; mPTP: mitochondrial permeability transition pore; MTOR: mechanistic target of rapamycin kinase; NAD⁺: nicotinamide adenine dinucleotide; NAM: nicotinamide; NMN: nicotinamide mononucleotide; NO: nitric oxide; NPA: Niemann-Pick type A; NR: nicotinamide riboside; NR4A1: nuclear receptor subfamily 4 group A member 1; NRF1: nuclear respiratory factor 1; OPA1: OPA1 mitochondrial dynamin like GTPase; OPTN: optineurin; PARL: presenilin associated rhomboid like; PARPs: poly(ADP-ribose) polymerases; PC: phosphatidylcholine; PHB2: prohibitin 2; PINK1: PTEN induced kinase 1; PPARG: peroxisome proliferator activated receptor gamma; PPARGC1A: PPARG coactivator 1 alpha; PRKA: protein kinase AMP-activated; PRKDC: protein kinase, DNA-activated, catalytic subunit; PRKN: parkin RBR E3 ubiquitin protein ligase; RHOT: ras homolog family member T; ROS: reactive oxygen species; SIRTs: sirtuins; STK11: serine/threonine kinase 11; TCA: tricarboxylic acid; TP53: tumor protein p53; ULK1: unc-51 like autophagy activating kinase 1; VDAC1: voltage dependent anion channel 1.

High-Dose Irradiation Inhibits Motility and Induces Autophagy in Caenorhabditis elegans

Radiation damages many cellular components and disrupts cellular functions, and was previously reported to impair locomotion in the model organism Caenorhabditis elegans. However, the response to even higher doses is not clear. First, to investigate the effects of high-dose radiation on the locomotion of C. elegans, we investigated the dose range that reduces whole-body locomotion or leads to death. Irradiation was performed in the range of 0-6 kGy. In the crawling analysis, motility decreased after irradiation in a dose-dependent manner. Exposure to 6 kGy of radiation affected crawling on agar immediately and caused the complete loss of motility. Both γ-rays and carbon-ion beams significantly reduced crawling motility at 3 kGy. Next, swimming in buffer was measured as a motility index to assess the response over time after irradiation and motility similarly decreased. However, swimming partially recovered 6 h after irradiation with 3 kGy of γ-rays. To examine the possibility of a recovery mechanism, in situ GFP reporter assay of the autophagy-related gene lgg-1 was performed. The fluorescence intensity was stronger in the anterior half of the body 7 h after irradiation with 3 kGy of γ-rays. GFP::LGG-1 induction was observed in the pharynx, neurons along the body, and the intestine. Furthermore, worms were exposed to region-specific radiation with carbon-ion microbeams and the trajectory of crawling was measured by image processing. Motility was lower after anterior-half body irradiation than after posterior-half body irradiation. This further supported that the anterior half of the body is important in the locomotory response to radiation.

Pb induced mitochondrial fission of fibroblast cells via ATM activation

Previous study showed that lead (Pb) could induce ATM-dependent mitophagy. However, whether Pb has any impact on mitochondrial fusion and fission, the upstream events of mitophagy, and how ATM connects to these processes remain unclear. In this study, we found that Pb can disrupt mitochondrial network morphology as indicated by increased percentage of shortened mitochondria and by decreased mitochondrial footprints. Correspondingly, the expression of fission protein Drp1 and its association with mitochondrial marker Hsp60 were significantly increased, while those of fusion proteins Mfn2 and Opa1 and their co-localization with Hsp60 were drastically attenuated. Notably, the expression of p-Drp1 (Ser616) and its translocation to mitochondria were dramatically elevated. Moreover, a small amount of ATM could be detected in the cytoplasm around mitochondria in response to Pb, and the co-localization of p-ATM (Ser1981) with Drp1 and p-Drp1 (Ser616) was obviously increased while its co-localization with Mfn2 and Opa1 was dramatically decreased. Furthermore, siRNA silencing of ATM evidently promoted greater fission in response to Pb stress, indicating that ATM is involved in mitochondrial fragmentation. Our results suggest that cytoplasmic ATM is an important regulator of Pb-induced mitochondrial fission.

ATM at the crossroads of reactive oxygen species and autophagy

Reactive oxygen species (ROS) are generally small, short-lived and highly reactive molecules, initially thought to be a pathological role in the cell. A growing amount of evidence in recent years argues for ROS functioning as a signaling intermediate to facilitate cellular adaptation in response to pathophysiological stress through the regulation of autophagy. Autophagy is an essential cellular process that plays a crucial role in recycling cellular components and damaged organelles to eliminate sources of ROS in response to various stress conditions. A large number of studies have shown that DNA damage response (DDR) transducer ataxia-telangiectasia mutated (ATM) protein can also be activated by ROS, and its downstream signaling pathway is involved in autophagy regulation. This review aims at providing novel insight into the regulatory mechanism of ATM activated by ROS and its molecular basis for inducing autophagy, and revealing a new function that ATM can not only maintain genome homeostasis in the nucleus, but also as a ROS sensor trigger autophagy to maintain cellular homeostasis in the cytoplasm.

The interplay between mitochondrial functionality and genome integrity in the prevention of human neurologic diseases

As mitochondria are vulnerable to oxidative damage and represent the main source of reactive oxygen species (ROS), they are considered key tuners of ROS metabolism and buffering, whose dysfunction can progressively impact neuronal networks and disease. Defects in DNA repair and DNA damage response (DDR) may also affect neuronal health and lead to neuropathology. A number of congenital DNA repair and DDR defective syndromes, indeed, show neurological phenotypes, and a growing body of evidence indicate that defects in the mechanisms that control genome stability in neurons acts as aging-related modifiers of common neurodegenerative diseases such as Alzheimer, Parkinson's, Huntington diseases and Amyotrophic Lateral Sclerosis. In this review we elaborate on the established principles and recent concepts supporting the hypothesis that deficiencies in either DNA repair or DDR might contribute to neurodegeneration via mechanisms involving mitochondrial dysfunction/deranged metabolism.

Atg32-dependent mitophagy sustains spermidine and nitric oxide required for heat-stress tolerance in Saccharomycescerevisiae

In Saccharomyces cerevisiae, the selective autophagic degradation of mitochondria, termed mitophagy, is critically regulated by the adapter protein Atg32. Despite our knowledge about the molecular mechanisms by which Atg32 controls mitophagy, its physiological roles in yeast survival and fitness remains less clear. Here, we demonstrate a requirement for Atg32 in promoting spermidine production during respiratory growth and heat-induced mitochondrial stress. During respiratory growth, mitophagy-deficient yeast exhibit profound heat-stress induced defects in growth and viability due to impaired biosynthesis of spermidine and its biosynthetic precursor S-adenosyl methionine. Moreover, spermidine production is crucial for the induction of cytoprotective nitric oxide (NO) during heat stress. Hence, the re-addition of spermidine to Atg32 mutant yeast is sufficient to both enhance NO production and restore respiratory growth during heat stress. Our findings uncover a previously unrecognized physiological role for yeast mitophagy in spermidine metabolism and illuminate new interconnections between mitophagy, polyamine biosynthesis and NO signaling.

ATM: Main Features, Signaling Pathways, and Its Diverse Roles in DNA Damage Response, Tumor Suppression, and Cancer Development

ATM is among of the most critical initiators and coordinators of the DNA-damage response. ATM canonical and non-canonical signaling pathways involve hundreds of downstream targets that control many important cellular processes such as DNA damage repair, apoptosis, cell cycle arrest, metabolism, proliferation, oxidative sensing, among others. Of note, ATM is often considered a major tumor suppressor because of its ability to induce apoptosis and cell cycle arrest. However, in some advanced stage tumor cells, ATM signaling is increased and confers remarkable advantages for cancer cell survival, resistance to radiation and chemotherapy, biosynthesis, proliferation, and metastasis. This review focuses on addressing major characteristics, signaling pathways and especially the diverse roles of ATM in cellular homeostasis and cancer development.

Dietary spermidine improves cognitive function

Decreased cognitive performance is a hallmark of brain aging, but the underlying mechanisms and potential therapeutic avenues remain poorly understood. Recent studies have revealed health-protective and lifespan-extending effects of dietary spermidine, a natural autophagy-promoting polyamine. Here, we show that dietary spermidine passes the blood-brain barrier in mice and increases hippocampal eIF5A hypusination and mitochondrial function. Spermidine feeding in aged mice affects behavior in homecage environment tasks, improves spatial learning, and increases hippocampal respiratory competence. In a Drosophila aging model, spermidine boosts mitochondrial respiratory capacity, an effect that requires the autophagy regulator Atg7 and the mitophagy mediators Parkin and Pink1. Neuron-specific Pink1 knockdown abolishes spermidine-induced improvement of olfactory associative learning. This suggests that the maintenance of mitochondrial and autophagic function is essential for enhanced cognition by spermidine feeding. Finally, we show large-scale prospective data linking higher dietary spermidine intake with a reduced risk for cognitive impairment in humans.

Autophagic Organelles in DNA Damage Response

Autophagy is an important subcellular event engaged in the maintenance of cellular homeostasis via the degradation of cargo proteins and malfunctioning organelles. In response to cellular stresses, like nutrient deprivation, infection, and DNA damaging agents, autophagy is activated to reduce the damage and restore cellular homeostasis. One of the responses to cellular stresses is the DNA damage response (DDR), the intracellular pathway that senses and repairs damaged DNA. Proper regulation of these pathways is crucial for preventing diseases. The involvement of autophagy in the repair and elimination of DNA aberrations is essential for cell survival and recovery to normal conditions, highlighting the importance of autophagy in the resolution of cell fate. In this review, we summarized the latest information about autophagic recycling of mitochondria, endoplasmic reticulum (ER), and ribosomes (called mitophagy, ER-phagy, and ribophagy, respectively) in response to DNA damage. In addition, we have described the key events necessary for a comprehensive understanding of autophagy signaling networks. Finally, we have highlighted the importance of the autophagy activated by DDR and appropriate regulation of autophagic organelles, suggesting insights for future studies. Especially, DDR from DNA damaging agents including ionizing radiation (IR) or anti-cancer drugs, induces damage to subcellular organelles and autophagy is the key mechanism for removing impaired organelles.

Ataxia Telangiectasia Mutated Protein Kinase: A Potential Master Puppeteer of Oxidative Stress-Induced Metabolic Recycling

Ataxia Telangiectasia Mutated protein kinase (ATM) has recently come to the fore as a regulatory protein fulfilling many roles in the fine balancing act of metabolic homeostasis. Best known for its role as a transducer of DNA damage repair, the activity of ATM in the cytosol is enjoying increasing attention, where it plays a central role in general cellular recycling (macroautophagy) as well as the targeted clearance (selective autophagy) of damaged mitochondria and peroxisomes in response to oxidative stress, independently of the DNA damage response. The importance of ATM activation by oxidative stress has also recently been highlighted in the clearance of protein aggregates, where the expression of a functional ATM construct that cannot be activated by oxidative stress resulted in widespread accumulation of protein aggregates. This review will discuss the role of ATM in general autophagy, mitophagy, and pexophagy as well as aggrephagy and crosstalk between oxidative stress as an activator of ATM and its potential role as a master regulator of these processes.

Perspective: Low Risk of Parkinson's Disease in Quasi-Vegan Cultures May Reflect GCN2-Mediated Upregulation of Parkin

Mitochondrial dysfunction in dopaminergic neurons of the substantia nigra (SN) appears to be a key mediating feature of Parkinson's disease (PD), a complex neurodegenerative disorder of still unknown etiology. Parkin is an E3 ubiquitin ligase that promotes mitophagy of damaged depolarized mitochondria while also boosting mitochondrial biogenesis-thereby helping to maintain efficient mitochondrial function. Boosting Parkin expression in the SN with viral vectors is protective in multiple rodent models of PD. Conversely, homozygosity for inactivating mutations of Parkin results in early-onset PD. Moderate protein plant-based diets relatively low in certain essential amino acids have the potential to boost Parkin expression by activating the kinase GCN2, which in turn boosts the expression of ATF4, a factor that drives transcription of the Parkin gene. Protein-restricted diets also upregulate the expression of PINK1, a protein that binds to the outer membrane of depolarized mitochondria and then recruits and activates Parkin. This effect of protein restriction is mediated by the downregulation of the kinase activity of mammalian target of rapamycin complex 1; the latter suppresses PINK1 expression at the transcriptional level. During the 20th century, cultures in East Asia and sub-Sahara Africa consuming quasi-vegan diets were found to be at notably decreased risk of PD compared with the USA or Europe. It is proposed that such diets may provide protection from PD by boosting Parkin and PINK1 expression in the SN. Other measures that might be expected to upregulate protective mitophagy include supplemental N-acetylcysteine (precursor for hydrogen sulfide) and a diet rich in spermidine-a polyamine notably high in corn.

Ataxia-telangiectasia mutated interacts with Parkin and induces mitophagy independent of kinase activity. Evidence from mantle cell lymphoma

Ataxia telangiectasia mutated (ATM), a critical DNA damage sensor with protein kinase activity, is frequently altered in human cancers including mantle cell lymphoma. Loss of ATM protein is linked to accumulation of nonfunctional mitochondria and defective mitophagy in both murine thymocytes and in ataxia-telangiectasia cells. However, the mechanistic role of ATM kinase in cancer cell mitophagy is unknown. Here, we provide evidence that FCCP-induced mitophagy in mantle cell lymphoma and other cancer cell lines is dependent on ATM but independent of its kinase function. While Granta-519 mantle cell lymphoma cells possess single copy kinase-dead ATM and are resistant to FCCP-induced mitophagy, both Jeko-1 and Mino cells are ATMproficient and induce mitophagy. Stable knockdown of ATM in Jeko-1 and Mino cells conferred resistance to mitophagy and was associated with reduced ATP production, oxygen consumption, and increased mitochondrial reactive oxygen species. ATM interacts with the E3 ubiquitin ligase Parkin in a kinase-independent manner. Knockdown of ATM in HeLa cells resulted in proteasomal degradation of GFP-Parkin which was rescued by the proteasome inhibitor, MG132, suggesting that the ATMParkin interaction is important for Parkin stability. Neither loss of ATM kinase activity in primary B-cell lymphomas nor inhibition of ATM kinase in mantle cell lymphoma, ataxia-telangiectasia and HeLa cell lines mitigated FCCP- or CCCP-induced mitophagy suggesting that ATM kinase activity is dispensable for mitophagy. Malignant B-cell lymphomas without detectable ATM, Parkin, Pink1, and Parkin-Ub^Ser65 phosphorylation were resistant to mitophagy, providing the first molecular evidence of the role of ATM in mitophagy in mantle cell lymphoma and other B-cell lymphomas.

Impaired endoplasmic reticulum-mitochondrial signaling in ataxia-telangiectasia

There is evidence that ATM mutated in ataxia-telangiectasia (A-T) plays a key role in protecting against mitochondrial dysfunction, the mechanism for which remains unresolved. We demonstrate here that ATM-deficient cells are exquisitely sensitive to nutrient deprivation, which can be explained by defective cross talk between the endoplasmic reticulum (ER) and the mitochondrion. Tethering between these two organelles in response to stress was reduced in cells lacking ATM, and consistent with this, Ca2+ release and transfer between ER and mitochondria was reduced dramatically when compared with control cells. The impact of this on mitochondrial function was evident from an increase in oxygen consumption rates and a defect in mitophagy in ATM-deficient cells. Our findings reveal that ER-mitochondrial connectivity through IP3R1-GRP75-VDAC1, to maintain Ca2+ homeostasis, as well as an abnormality in mitochondrial fusion defective in response to nutrient stress, can account for at least part of the mitochondrial dysfunction observed in A-T cells.