Generation and Release of Mitochondrial-Derived Vesicles in Health, Aging and Disease

Elimination of damaged mitochondria during UVB-induced senescence is orchestrated by NIX-dependent mitophagy

Skin aging is the result of two types of aging, "intrinsic aging" an inevitable consequence of physiologic and genetically determined changes and "extrinsic aging," which is dependent on external factors such as exposure to sunlight, smoking, and dietary habits. UVB causes skin injury through the generation of free radicals and other oxidative byproducts, also contributing to DNA damage. Appearance and accumulation of senescent cells in the skin are considered one of the hallmarks of aging in this tissue. Mitochondria play an important role for the development of cellular senescence, in particular stress-induced senescence of human cells. However, many aspects of mitochondrial physiology relevant to cellular senescence and extrinsic skin aging remain to be unraveled. Here, we demonstrate that mitochondria damaged by UVB irradiation of human dermal fibroblasts (HDF) are eliminated by NIX-dependent mitophagy and that this process is important for cell survival under these conditions. Additionally, UVB-irradiation of human dermal fibroblasts (HDF) induces the shedding of extracellular vesicles (EVs), and this process is significantly enhanced in UVB-irradiated NIX-depleted cells. Our findings establish NIX as the main mitophagy receptor in the process of UVB-induced senescence and suggest the release of EVs as an alternative mechanism of mitochondrial quality control in HDF.

The phospholipids cardiolipin and phosphatidylethanolamine differentially regulate MDC biogenesis

Cells utilize multiple mechanisms to maintain mitochondrial homeostasis. We recently characterized a pathway that remodels mitochondria in response to metabolic alterations and protein overload stress. This remodeling occurs via the formation of large membranous structures from the mitochondrial outer membrane called mitochondrial-derived compartments (MDCs), which are eventually released from mitochondria and degraded. Here, we conducted a microscopy-based screen in budding yeast to identify factors that regulate MDC formation. We found that two phospholipids, cardiolipin (CL) and phosphatidylethanolamine (PE), differentially regulate MDC biogenesis. CL depletion impairs MDC biogenesis, whereas blocking mitochondrial PE production leads to constitutive MDC formation. Additionally, in response to metabolic MDC activators, cellular and mitochondrial PE declines, and overexpressing mitochondrial PE synthesis enzymes suppress MDC biogenesis. Altogether, our data indicate a requirement for CL in MDC biogenesis and suggest that PE depletion may stimulate MDC formation downstream of MDC-inducing metabolic stress.

Mitochondria-Derived Vesicles, Sterile Inflammation, and Pyroptosis in Liver Cancer: Partners in Crime or Innocent Bystanders?

Alterations in cellular signaling, chronic inflammation, and tissue remodeling contribute to hepatocellular carcinoma (HCC) development. The release of damage-associated molecular patterns (DAMPs) upon tissue injury and the ensuing sterile inflammation have also been attributed a role in HCC pathogenesis. Cargoes of extracellular vesicles (EVs) and/or EVs themselves have been listed among circulating DAMPs but only partially investigated in HCC. Mitochondria-derived vesicles (MDVs), a subpopulation of EVs, are another missing link in the comprehension of the molecular mechanisms underlying the onset and progression of HCC biology. EVs have been involved in HCC growth, dissemination, angiogenesis, and immunosurveillance escape. The contribution of MDVs to these processes is presently unclear. Pyroptosis triggers systemic inflammation through caspase-dependent apoptotic cell death and is implicated in tumor immunity. The analysis of this process, together with MDV characterization, may help capture the relationship among HCC development, mitochondrial quality control, and inflammation. The combination of immune checkpoint inhibitors (i.e., atezolizumab and bevacizumab) has been approved as a synergistic first-line systemic treatment for unresectable or advanced HCC. The lack of biomarkers that may allow prediction of treatment response and, therefore, patient selection, is a major unmet need. Herein, we overview the molecular mechanisms linking mitochondrial dysfunction, inflammation, and pyroptosis, and discuss how immunotherapy targets, at least partly, these routes.

Defects of mitochondria-lysosomes communication induce secretion of mitochondria-derived vesicles and drive chemoresistance in ovarian cancer cells

BACKGROUND

Among the mechanisms of mitochondrial quality control (MQC), generation of mitochondria-derived vesicles (MDVs) is a process to avoid complete failure of mitochondria determining lysosomal degradation of mitochondrial damaged proteins. In this context, RAB7, a late endocytic small GTPase, controls delivery of MDVs to late endosomes for subsequent lysosomal degradation. We previously demonstrated that RAB7 has a pivotal role in response to cisplatin (CDDP) regulating resistance to the drug by extracellular vesicle (EVs) secretion.

METHODS

Western blot and immunofluorescence analysis were used to analyze structure and function of endosomes and lysosomes in CDDP chemosensitive and chemoresistant ovarian cancer cell lines. EVs were purified from chemosensitive and chemoresistant cells by ultracentrifugation or immunoisolation to analyze their mitochondrial DNA and protein content. Treatment with cyanide m-chlorophenylhydrazone (CCCP) and RAB7 modulation were used, respectively, to understand the role of mitochondrial and late endosomal/lysosomal alterations on MDV secretion. Using conditioned media from chemoresistant cells the effect of MDVs on the viability after CDDP treatment was determined. Seahorse assays and immunofluorescence analysis were used to study the biochemical role of MDVs and the uptake and intracellular localization of MDVs, respectively.

RESULTS

We observed that CDDP-chemoresistant cells are characterized by increased MDV secretion, impairment of late endocytic traffic, RAB7 downregulation, an increase of RAB7 in EVs, compared to chemosensitive cells, and downregulation of the TFEB-mTOR pathway overseeing lysosomal and mitochondrial biogenesis and turnover. We established that MDVs can be secreted rather than delivered to lysosomes and are able to deliver CDDP outside the cells. We showed increased secretion of MDVs by chemoresistant cells ultimately caused by the extrusion of RAB7 in EVs, resulting in a dramatic drop in its intracellular content, as a novel mechanism to regulate RAB7 levels. We demonstrated that MDVs purified from chemoresistant cells induce chemoresistance in RAB7-modulated process, and, after uptake from recipient cells, MDVs localize to mitochondria and slow down mitochondrial activity.

CONCLUSIONS

Dysfunctional MQC in chemoresistant cells determines a block in lysosomal degradation of MDVs and their consequent secretion, suggesting that MQC is not able to eliminate damaged mitochondria whose components are secreted becoming effectors and potential markers of chemoresistance.

Age-related bone diseases: Role of inflammaging

Bone aging is characterized by an imbalance in the physiological and pathological processes of osteogenesis, osteoclastogenesis, adipogenesis, and chondrogenesis, resulting in exacerbated bone loss and the development of age-related bone diseases, including osteoporosis, osteoarthritis, rheumatoid arthritis, and periodontitis. Inflammaging, a novel concept in the field of aging research, pertains to the persistent and gradual escalation of pro-inflammatory reactions during the aging process. This phenomenon is distinguished by its low intensity, systemic nature, absence of symptoms, and potential for management. The mechanisms by which inflammaging contribute to age-related chronic diseases, particularly in the context of age-related bone diseases, remain unclear. The precise manner in which systemic inflammation induces bone aging and consequently contributes to the development of age-related bone diseases has yet to be fully elucidated. This article primarily examines the mechanisms underlying inflammaging and its association with age-related bone diseases, to elucidate the potential mechanisms of inflammaging in age-related bone diseases and offer insights for developing preventive and therapeutic strategies for such conditions.

Mitochondria-derived Vesicle Packaging as a Novel Therapeutic Mechanism in Pulmonary Hypertension

Increasing evidence suggests that mitochondrial dysfunction in pulmonary endothelial cells (ECs) plays a causative role in the initiation and progression of pulmonary hypertension (PH); how mitochondria become dysfunctional in PH remains elusive. Mitochondria-derived vesicles (MDVs) are small subcellular vesicles that excise from mitochondria. Whether MDV deregulation causes mitochondrial dysfunction in PH is unknown. The aim of this study was to determine MDV regulation in ECs and to elucidate how MDV deregulation in ECs leads to PH. MDV formation and mitochondrial morphology/dynamics were examined in ECs of EC-specific liver kinase B1 (LKB1) knockout mice (LKB1ec-/-), in monocrotaline-induced PH rats, and in lungs of patients with PH. Pulmonary ECs of patients with PH and hypoxia-treated pulmonary ECs exhibited increased mitochondrial fragmentation and disorganized mitochondrial ultrastructure characterized by electron lucent-swelling matrix compartments and concentric layering of the cristae network, together with defective MDV shedding. MDVs actively regulated mitochondrial membrane dynamics and mitochondrial ultrastructure via removing mitofission-related cargoes. The shedding of MDVs from parental mitochondria required LKB1-mediated mitochondrial recruitment of Rab9 GTPase. LKB1ec-/- mice spontaneously developed PH with decreased mitochondrial pools of Rab9 GTPase, defective MDV shedding, and disequilibrium of the mitochondrial fusion-fission cycle in pulmonary ECs. Aerosol intratracheal delivery of adeno-associated virus LKB1 reversed PH, together with improved MDV shedding and mitochondrial function in rats in vivo. We conclude that LKB1 regulates MDV shedding and mitochondrial dynamics in pulmonary ECs by enhancing mitochondrial recruitment of Rab9 GTPase. Defects of LKB1-mediated MDV shedding from parental mitochondria instigate EC dysfunction and PH.

Mitochondrial Proteomes in Neural Cells: A Systematic Review

Mitochondria are ancient endosymbiotic double membrane organelles that support a wide range of eukaryotic cell functions through energy, metabolism, and cellular control. There are over 1000 known proteins that either reside within the mitochondria or are transiently associated with it. These mitochondrial proteins represent a functional subcellular protein network (mtProteome) that is encoded by mitochondrial and nuclear genomes and significantly varies between cell types and conditions. In neurons, the high metabolic demand and differential energy requirements at the synapses are met by specific modifications to the mtProteome, resulting in alterations in the expression and functional properties of the proteins involved in energy production and quality control, including fission and fusion. The composition of mtProteomes also impacts the localization of mitochondria in axons and dendrites with a growing number of neurodegenerative diseases associated with changes in mitochondrial proteins. This review summarizes the findings on the composition and properties of mtProteomes important for mitochondrial energy production, calcium and lipid signaling, and quality control in neural cells. We highlight strategies in mass spectrometry (MS) proteomic analysis of mtProteomes from cultured cells and tissue. The research into mtProteome composition and function provides opportunities in biomarker discovery and drug development for the treatment of metabolic and neurodegenerative disease.

Mitochondrial-Derived Vesicles: The Good, the Bad, and the Ugly

Mitophagy is crucial for maintaining mitochondrial quality. However, its assessment in vivo is challenging. The endosomal-lysosomal system is a more accessible pathway through which subtypes of extracellular vesicles (EVs), which also contain mitochondrial constituents, are released for disposal. The inclusion of mitochondrial components into EVs occurs in the setting of mild mitochondrial damage and during impairment of lysosomal function. By releasing mitochondrial-derived vesicles (MDVs), cells limit the unload of mitochondrial damage-associated molecular patterns with proinflammatory activity. Both positive and negative effects of EVs on recipient cells have been described. Whether this is due to the production of EVs other than those containing mitochondria, such as MDVs, holding specific biological functions is currently unknown. Evidence on the existence of different MDV subtypes has been produced. However, their characterization is not always pursued, which would be relevant to exploring the dynamics of mitochondrial quality control in health and disease. Furthermore, MDV classification may be instrumental in understanding their biological roles and promoting their implementation as biomarkers in clinical studies.

To eat or not to eat mitochondria? How do host cells cope with mitophagy upon bacterial infection?

Mitochondria fulfil a plethora of cellular functions ranging from energy production to regulation of inflammation and cell death control. The fundamental role of mitochondria makes them a target of choice for invading pathogens, with either an intracellular or extracellular lifestyle. Indeed, the modulation of mitochondrial functions by several bacterial pathogens has been shown to be beneficial for bacterial survival inside their host. However, so far, relatively little is known about the importance of mitochondrial recycling and degradation pathways through mitophagy in the outcome (success or failure) of bacterial infection. On the one hand, mitophagy could be considered as a defensive response triggered by the host upon infection to maintain mitochondrial homeostasis. However, on the other hand, the pathogen itself may initiate the host mitophagy to escape from mitochondrial-mediated inflammation or antibacterial oxidative stress. In this review, we will discuss the diversity of various mechanisms of mitophagy in a general context, as well as what is currently known about the different bacterial pathogens that have developed strategies to manipulate the host mitophagy.

Methods to Evaluate Changes in Mitochondrial Structure and Function in Cancer

Mitochondria are regulators of key cellular processes, including energy production and redox homeostasis. Mitochondrial dysfunction is associated with various human diseases, including cancer. Importantly, both structural and functional changes can alter mitochondrial function. Morphologic and quantifiable changes in mitochondria can affect their function and contribute to disease. Structural mitochondrial changes include alterations in cristae morphology, mitochondrial DNA integrity and quantity, and dynamics, such as fission and fusion. Functional parameters related to mitochondrial biology include the production of reactive oxygen species, bioenergetic capacity, calcium retention, and membrane potential. Although these parameters can occur independently of one another, changes in mitochondrial structure and function are often interrelated. Thus, evaluating changes in both mitochondrial structure and function is crucial to understanding the molecular events involved in disease onset and progression. This review focuses on the relationship between alterations in mitochondrial structure and function and cancer, with a particular emphasis on gynecologic malignancies. Selecting methods with tractable parameters may be critical to identifying and targeting mitochondria-related therapeutic options. Methods to measure changes in mitochondrial structure and function, with the associated benefits and limitations, are summarized.

The Potential Use of Mitochondrial Extracellular Vesicles as Biomarkers or Therapeutical Tools

The mitochondria play a crucial role in cellular metabolism, reactive oxygen species (ROS) production, and apoptosis. Aberrant mitochondria can cause severe damage to the cells, which have established a tight quality control for the mitochondria. This process avoids the accumulation of damaged mitochondria and can lead to the release of mitochondrial constituents to the extracellular milieu through mitochondrial extracellular vesicles (MitoEVs). These MitoEVs carry mtDNA, rRNA, tRNA, and protein complexes of the respiratory chain, and the largest MitoEVs can even transport whole mitochondria. Macrophages ultimately engulf these MitoEVs to undergo outsourced mitophagy. Recently, it has been reported that MitoEVs can also contain healthy mitochondria, whose function seems to be the rescue of stressed cells by restoring the loss of mitochondrial function. This mitochondrial transfer has opened the field of their use as potential disease biomarkers and therapeutic tools. This review describes this new EVs-mediated transfer of the mitochondria and the current application of MitoEVs in the clinical environment.

The Role of Rab Proteins in Mitophagy: Insights into Neurodegenerative Diseases

Mitochondrial dysfunction and vesicular trafficking alterations have been implicated in the pathogenesis of several neurodegenerative diseases. It has become clear that pathogenetic pathways leading to neurodegeneration are often interconnected. Indeed, growing evidence suggests a concerted contribution of impaired mitophagy and vesicles formation in the dysregulation of neuronal homeostasis, contributing to neuronal cell death. Among the molecular factors involved in the trafficking of vesicles, Ras analog in brain (Rab) proteins seem to play a central role in mitochondrial quality checking and disposal through both canonical PINK1/Parkin-mediated mitophagy and novel alternative pathways. In turn, the lack of proper elimination of dysfunctional mitochondria has emerged as a possible causative/early event in some neurodegenerative diseases. Here, we provide an overview of major findings in recent years highlighting the role of Rab proteins in dysfunctional mitochondrial dynamics and mitophagy, which are characteristic of neurodegenerative diseases. A further effort should be made in the coming years to clarify the sequential order of events and the molecular factors involved in the different processes. A clear cause–effect view of the pathogenetic pathways may help in understanding the molecular basis of neurodegeneration.

Human Brain Microvascular Endothelial Cells Exposure to SARS-CoV-2 Leads to Inflammatory Activation through NF-κB Non-Canonical Pathway and Mitochondrial Remodeling

Neurological effects of COVID-19 and long-COVID-19, as well as neuroinvasion by SARS-CoV-2, still pose several questions and are of both clinical and scientific relevance. We described the cellular and molecular effects of the human brain microvascular endothelial cells (HBMECs) in vitro exposure by SARS-CoV-2 to understand the underlying mechanisms of viral transmigration through the blood-brain barrier. Despite the low to non-productive viral replication, SARS-CoV-2-exposed cultures displayed increased immunoreactivity for cleaved caspase-3, an indicator of apoptotic cell death, tight junction protein expression, and immunolocalization. Transcriptomic profiling of SARS-CoV-2-challenged cultures revealed endothelial activation via NF-κB non-canonical pathway, including RELB overexpression and mitochondrial dysfunction. Additionally, SARS-CoV-2 led to altered secretion of key angiogenic factors and to significant changes in mitochondrial dynamics, with increased mitofusin-2 expression and increased mitochondrial networks. Endothelial activation and remodeling can further contribute to neuroinflammatory processes and lead to further BBB permeability in COVID-19.

The emerging mechanisms and functions of microautophagy

'Autophagy' refers to an evolutionarily conserved process through which cellular contents, such as damaged organelles and protein aggregates, are delivered to lysosomes for degradation. Different forms of autophagy have been described on the basis of the nature of the cargoes and the means used to deliver them to lysosomes. At present, the prevailing categories of autophagy in mammalian cells are macroautophagy, microautophagy and chaperone-mediated autophagy. The molecular mechanisms and biological functions of macroautophagy and chaperone-mediated autophagy have been extensively studied, but microautophagy has received much less attention. In recent years, there has been a growth in research on microautophagy, first in yeast and then in mammalian cells. Here we review this form of autophagy, focusing on selective forms of microautophagy. We also discuss the upstream regulatory mechanisms, the crosstalk between macroautophagy and microautophagy, and the functional implications of microautophagy in diseases such as cancer and neurodegenerative disorders in humans. Future research into microautophagy will provide opportunities to develop novel interventional strategies for autophagy- and lysosome-related diseases.

Mitochondrial Transplantation in Mitochondrial Medicine: Current Challenges and Future Perspectives

Mitochondrial diseases (MDs) are inherited genetic conditions characterized by pathogenic mutations in nuclear DNA (nDNA) or mitochondrial DNA (mtDNA). Current therapies are still far from being fully effective and from covering the broad spectrum of mutations in mtDNA. For example, unlike heteroplasmic conditions, MDs caused by homoplasmic mtDNA mutations do not yet benefit from advances in molecular approaches. An attractive method of providing dysfunctional cells and/or tissues with healthy mitochondria is mitochondrial transplantation. In this review, we discuss what is known about intercellular transfer of mitochondria and the methods used to transfer mitochondria both in vitro and in vivo, and we provide an outlook on future therapeutic applications. Overall, the transfer of healthy mitochondria containing wild-type mtDNA copies could induce a heteroplasmic shift even when homoplasmic mtDNA variants are present, with the aim of attenuating or preventing the progression of pathological clinical phenotypes. In summary, mitochondrial transplantation is a challenging but potentially ground-breaking option for the treatment of various mitochondrial pathologies, although several questions remain to be addressed before its application in mitochondrial medicine.

The Double-Edged Role of Extracellular Vesicles in the Hallmarks of Aging

The exponential growth in the elderly population and their associated socioeconomic burden have recently brought aging research into the spotlight. To integrate current knowledge and guide potential interventions, nine biochemical pathways are summarized under the term hallmarks of aging. These hallmarks are deeply inter-related and act together to drive the aging process. Altered intercellular communication is particularly relevant since it explains how damage at the cellular level translates into age-related loss of function at the organismal level. As the main effectors of intercellular communication, extracellular vesicles (EVs) might play a key role in the aggravation or mitigation of the hallmarks of aging. This review aims to summarize this role and to provide context for the multiple emerging EV-based gerotherapeutic strategies that are currently under study.

Bambusa vulgaris leaves reverse mitochondria dysfunction in diabetic rats through modulation of mitochondria biogenic genes

OBJECTIVES

There is evidence that mitochondrial dysfunction mediated by hyperglycemia increases the incidence of diabetes and age-related insulin resistance. Thus, maintaining mitochondrial integrity may provide alternative therapeutic approach in diabetes treatment. This study aimed to evaluate the effect of Bambusa vulgaris leaf extract on mitochondrial biogenesis in the pancreas of diabetic rats.

METHODS

11 weeks old male rats (n=30) were purchased, and sorted into the following groups: control, diabetic control, diabetes + metformin (100 mg/kg), diabetes + Aq. B. vulgaris (100 mg/kg), diabetes + Aq. B. vulgaris (200 mg/kg), and diabetes + Aq. B. vulgaris (300 mg/kg). Diabetes was induced in the rats by a single dose of 65 mg/kg streptozotocin (STZ). The mRNA expression of genes related to mitochondria biogenesis (pgc-1α, Nrf2, GSK3β, AMPK and SIRT2) and genes of Nrf2-Keap1-ARE signaling pathway were determined by reverse transcriptase polymerase chain reaction. Molecular docking studies including lock and key docking and prime MM-GBSA were incorporated to identify the lead chemical compounds in Bambusa vulgari.

RESULTS

The results showed that B. vulgaris leaf extract promotes mitochondrial biogenesis via altering the mRNA expression of mitochondrial master regulator pgc-1α, other upstream genes, and the Nrf2-Keap1-ARE antioxidant pathway. Through molecular docking results, cryptochlorogenic acid, hesperidin, orientin, vitexin, scopolin, and neochlorogenic were found as the crucial chemicals in B. vulgaris with the most modulating effect on PGC-1α, AMPK, and GSK3.

CONCLUSIONS

This study thus suggests that B. vulgaris leaf extract restores the integrity of mitochondria in diabetic rats.

Relationship between Mitochondrial Quality Control Markers, Lower Extremity Tissue Composition, and Physical Performance in Physically Inactive Older Adults

Altered mitochondrial quality and function in muscle may be involved in age-related physical function decline. The role played by the autophagy-lysosome system, a major component of mitochondrial quality control (MQC), is incompletely understood. This study was undertaken to obtain initial indications on the relationship between autophagy, mitophagy, and lysosomal markers in muscle and measures of physical performance and lower extremity tissue composition in young and older adults. Twenty-three participants were enrolled, nine young (mean age: 24.3 ± 4.3 years) and 14 older adults (mean age: 77.9 ± 6.3 years). Lower extremity tissue composition was quantified volumetrically by magnetic resonance imaging and a tissue composition index was calculated as the ratio between muscle and intermuscular adipose tissue volume. Physical performance in older participants was assessed via the Short Physical Performance Battery (SPPB). Protein levels of the autophagy marker p62, the mitophagy mediator BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3), the lysosomal markers transcription factor EB, vacuolar-type ATPase, and lysosomal-associated membrane protein 1 were measured by Western immunoblotting in vastus lateralis muscle biopsies. Older adults had smaller muscle volume and lower tissue composition index than young participants. The protein content of p62 and BNIP3 was higher in older adults. A negative correlation was detected between p62 and BNIP3 and the tissue composition index. p62 and BNIP3 were also related to the performance on the 5-time sit-to-stand test of the SPPB. Our results suggest that an altered expression of markers of the autophagy/mitophagy-lysosomal system is related to deterioration of lower extremity tissue composition and muscle dysfunction. Additional studies are needed to clarify the role of defective MQC in human muscle aging and identify novel biological targets for drug development.

Cocaine perturbs mitovesicle biology in the brain

Cocaine, an addictive psychostimulant, has a broad mechanism of action, including the induction of a wide range of alterations in brain metabolism and mitochondrial homeostasis. Our group recently identified a subpopulation of non-microvesicular, non-exosomal extracellular vesicles of mitochondrial origin (mitovesicles) and developed a method to isolate mitovesicles from brain parenchyma. We hypothesised that the generation and secretion of mitovesicles is affected by mitochondrial abnormalities induced by chronic cocaine exposure. Mitovesicles from the brain extracellular space of cocaine-administered mice were enlarged and more numerous when compared to controls, supporting a model in which mitovesicle biogenesis is enhanced in the presence of mitochondrial alterations. This interrelationship was confirmed in vitro. Moreover, cocaine affected mitovesicle protein composition, causing a functional alteration in mitovesicle ATP production capacity. These data suggest that mitovesicles are previously unidentified players in the biology of cocaine addiction and that target therapies to fine-tune brain mitovesicle functionality may be beneficial to mitigate the effects of chronic cocaine exposure.

The compartmentalised nature of neuronal mitophagy: molecular insights and implications

The maintenance of a healthy mitochondrial network and the ability to adjust organelle population in response to internal or external stimuli are essential for the function and the survival of eukaryotic cells. Over the last two decades several studies have demonstrated the paramount importance of mitophagy, a selective form of autophagy that removes damaged and/or superfluous organelles, in organismal physiology. Post-mitotic neuronal cells are particularly vulnerable to mitochondrial damage, and mitophagy impairment has emerged as a causative factor in multiple neurodegenerative pathologies, including Alzheimer's disease and Parkinson's disease among others. Although mitochondrial turnover is a multifaceted process, neurons have to tackle additional complications, arising from their pronounced bioenergetic demands and their unique architecture and cellular polarisation that render the degradation of distal organelles challenging. Mounting evidence indicates that despite the functional conservation of mitophagy pathways, the unique features of neuronal physiology have led to the adaptation of compartmentalised solutions, which serve to ensure seamless mitochondrial removal in every part of the cell. In this review, we summarise the current knowledge concerning the molecular mechanisms that mediate mitophagy compartmentalisation and discuss their implications in various human pathologies.

Mitochondrial Dysfunction in Parkinson’s Disease: From Mechanistic Insights to Therapy

Parkinson’s disease (PD) is one of the most common neurodegenerative movement disorders worldwide. There are currently no cures or preventative treatments for PD. Emerging evidence indicates that mitochondrial dysfunction is closely associated with pathogenesis of sporadic and familial PD. Because dopaminergic neurons have high energy demand, cells affected by PD exhibit mitochondrial dysfunction that promotes the disease-defining the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The mitochondrion has a particularly important role as the cellular “powerhouse” of dopaminergic neurons. Therefore, mitochondria have become a promising therapeutic target for PD treatments. This review aims to describe mitochondrial dysfunction in the pathology of PD, outline the genes associated with familial PD and the factors related to sporadic PD, summarize current knowledge on mitochondrial quality control in PD, and give an overview of therapeutic strategies for targeting mitochondria in neuroprotective interventions in PD.

Insulin and Its Key Role for Mitochondrial Function/Dysfunction and Quality Control: A Shared Link between Dysmetabolism and Neurodegeneration

Insulin was discovered and isolated from the beta cells of pancreatic islets of dogs and is associated with the regulation of peripheral glucose homeostasis. Insulin produced in the brain is related to synaptic plasticity and memory. Defective insulin signaling plays a role in brain dysfunction, such as neurodegenerative disease. Growing evidence suggests a link between metabolic disorders, such as diabetes and obesity, and neurodegenerative diseases, especially Alzheimer's disease (AD). This association is due to a common state of insulin resistance (IR) and mitochondrial dysfunction. This review takes a journey into the past to summarize what was known about the physiological and pathological role of insulin in peripheral tissues and the brain. Then, it will land in the present to analyze the insulin role on mitochondrial health and the effects on insulin resistance and neurodegenerative diseases that are IR-dependent. Specifically, we will focus our attention on the quality control of mitochondria (MQC), such as mitochondrial dynamics, mitochondrial biogenesis, and selective autophagy (mitophagy), in healthy and altered cases. Finally, this review will be projected toward the future by examining the most promising treatments that target the mitochondria to cure neurodegenerative diseases associated with metabolic disorders.

SARS-CoV-2 infection of human brain microvascular endothelial cells leads to inflammatory activation through NF-κB non-canonical pathway and mitochondrial remodeling

Neurological effects of COVID-19 and long-COVID-19 as well as neuroinvasion by SARS-CoV-2 still pose several questions and are of both clinical and scientific relevance. We described the cellular and molecular effects of the human brain microvascular endothelial cells (HBMECs) in vitro infection by SARS-CoV-2 to understand the underlying mechanisms of viral transmigration through the Blood-Brain Barrier. Despite the low to non-productive viral replication, SARS-CoV-2-infected cultures displayed increased apoptotic cell death and tight junction protein expression and immunolocalization. Transcriptomic profiling of infected cultures revealed endothelial activation via NF-κB non-canonical pathway, including RELB overexpression, and mitochondrial dysfunction. Additionally, SARS-CoV-2 led to altered secretion of key angiogenic factors and to significant changes in mitochondrial dynamics, with increased mitofusin-2 expression and increased mitochondrial networks. Endothelial activation and remodeling can further contribute to neuroinflammatory processes and lead to further BBB permeability in COVID-19.

SARS-CoV-2 infection of human brain microvascular endothelial cells leads to inflammatory activation through NF-κB non-canonical pathway and mitochondrial remodeling

Neurological effects of COVID-19 and long-COVID-19 as well as neuroinvasion by SARS-CoV-2 still pose several questions and are of both clinical and scientific relevance. We described the cellular and molecular effects of the human brain microvascular endothelial cells (HBMECs) in vitro infection by SARS-CoV-2 to understand the underlying mechanisms of viral transmigration through the Blood-Brain Barrier. Despite the low to non- productive viral replication, SARS-CoV-2-infected cultures displayed increased apoptotic cell death and tight junction protein expression and immunolocalization. Transcriptomic profiling of infected cultures revealed endothelial activation via NF-κB non-canonical pathway, including RELB overexpression, and mitochondrial dysfunction. Additionally, SARS-CoV-2 led to altered secretion of key angiogenic factors and to significant changes in mitochondrial dynamics, with increased mitofusin-2 expression and increased mitochondrial networks. Endothelial activation and remodeling can further contribute to neuroinflammatory processes and lead to further BBB permeability in COVID-19.

Age-Associated Glia Remodeling and Mitochondrial Dysfunction in Neurodegeneration: Antioxidant Supplementation as a Possible Intervention

Aging induces substantial remodeling of glia, including density, morphology, cytokine expression, and phagocytic capacity. Alterations of glial cells, such as hypertrophy of lysosomes, endosomes and peroxisomes, and the progressive accumulation of lipofuscin, lipid droplets, and other debris have also been reported. These abnormalities have been associated with significant declines of microglial processes and reduced ability to survey the surrounding tissue, maintain synapses, and recover from injury. Similarly, aged astrocytes show reduced capacity to support metabolite transportation to neurons. In the setting of reduced glial activity, stressors and/or injury signals can trigger a coordinated action of microglia and astrocytes that may amplify neuroinflammation and contribute to the release of neurotoxic factors. Oxidative stress and proteotoxic aggregates may burst astrocyte-mediated secretion of pro-inflammatory cytokines, thus activating microglia, favoring microgliosis, and ultimately making the brain more susceptible to injury and/or neurodegeneration. Here, we discuss the contribution of microglia and astrocyte oxidative stress to neuroinflammation and neurodegeneration, highlight the pathways that may help gain insights into their molecular mechanisms, and describe the benefits of antioxidant supplementation-based strategies.

Mitochondrial Dysfunction in Oxidative Stress-Mediated Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) is the most common contributor to low back pain (LBP). Recent studies have found that oxidative stress and reactive oxygen species (ROS) play an important role in IVDD. As a by‐product of aerobic respiration, ROS is mainly produced in the mitochondria by the electron transport chain and other mitochondrial located proteins. With the excessive accumulation of ROS, mitochondria are also the primary target of ROS attack in disc cells. A disrupted balance between intracellular ROS production and antioxidant capacity will lead to oxidative stress, which is the key contributor to cell apoptosis, cell senescence, excessive autophagy, and mitochondrial dysfunction. As the pivotal ingredient of oxidative stress, mitochondrial dysfunction manifests as imbalanced mitochondrial dynamics and dysregulated mitophagy. Mitochondria can alter their own dynamics through the process of fusion and fission, so that disabled mitochondria can be separated from the mitochondrial pool. Moreover, mitophagy participates by clearing these dysfunctional mitochondria. Abnormality in any of these processes either increases the production or decreases the clearance of ROS, leading to a vicious cycle that results in the death of intervertebral disc cells in large quantities, combined with degradation of the extracellular matrix and overproduction of matrix metalloproteinase. In this review, we explain the changes in mitochondrial morphology and function during oxidative stress‐mediated IVDD and highlight the important role of mitochondria in this process. Eventually, we summarize the IVDD therapeutic strategies targeting mitochondrial dysfunction based on current understanding of the role of oxidative stress in IVDD.

Nanomaterials alleviating redox stress in neurological diseases: mechanisms and applications

Overproduced reactive oxygen and reactive nitrogen species (RONS) in the brain are involved in the pathogenesis of several neurological diseases, such as Alzheimer's disease, Parkinson's disease, traumatic brain injury, and stroke, as they attack neurons and glial cells, triggering cellular redox stress. Neutralizing RONS, and, thus, alleviating redox stress, can slow down or stop the progression of neurological diseases. Currently, an increasing number of studies are applying nanomaterials (NMs) with anti-redox activity and exploring the potential mechanisms involved in redox stress-related neurological diseases. In this review, we summarize the anti-redox mechanisms of NMs, including mimicking natural oxidoreductase activity and inhibiting RONS generation at the source. In addition, we propose several strategies to enhance the anti-redox ability of NMs and highlight the challenges that need to be resolved in their application. In-depth knowledge of the mechanisms and potential application of NMs in alleviating redox stress will help in the exploration of the therapeutic potential of anti-redox stress NMs in neurological diseases.

Mitochondrial-derived vesicles: Recent insights

The generation of vesicles is a constitutive attribute of mitochondria inherited from bacterial ancestors. The physiological conditions and mild oxidative stress promote oxidation and dysfunction of certain proteins and lipids within the mitochondrial membranes; these constituents are subsequently packed as small mitochondrial‐derived vesicles (MDVs) (70–150 nm in diameter) and are transported intracellularly to lysosomes and peroxisomes to be degraded. In this way, MDVs remove the damaged mitochondrial components, preserve mitochondrial structural and functional integrity and restore homeostasis. An outline of the current knowledge on MDVs seems to be necessary for understanding the potential impact of this research area in cellular (patho)physiology. The present synopsis is an attempt towards the accomplishment of this demand, highlighting also the still unclear issues related to MDVs. Here, we discuss (i) MDVs budding and generation (molecules and mechanisms), (ii) the distinct cargoes packed and transported by MDVs, (iii) the MDVs trafficking pathways and (iv) the biological role of MDVs, from quality controllers to the involvement in organellar crosstalk, mitochondrial antigen presentation and peroxisome de novo biogenesis. These complex roles uncover also mitochondria integration into the cellular environment. As the therapeutic exploitation of MDVs is currently limited, future insights into MDVs cell biology are expected to direct to novel diagnostic tools and treatments.

Mitochondrial autophagy: molecular mechanisms and implications for cardiovascular disease

Mitochondria are highly dynamic organelles that participate in ATP generation and involve calcium homeostasis, oxidative stress response, and apoptosis. Dysfunctional or damaged mitochondria could cause serious consequences even lead to cell death. Therefore, maintaining the homeostasis of mitochondria is critical for cellular functions. Mitophagy is a process of selectively degrading damaged mitochondria under mitochondrial toxicity conditions, which plays an essential role in mitochondrial quality control. The abnormal mitophagy that aggravates mitochondrial dysfunction is closely related to the pathogenesis of many diseases. As the myocardium is a highly oxidative metabolic tissue, mitochondria play a central role in maintaining optimal performance of the heart. Dysfunctional mitochondria accumulation is involved in the pathophysiology of cardiovascular diseases, such as myocardial infarction, cardiomyopathy and heart failure. This review discusses the most recent progress on mitophagy and its role in cardiovascular disease.

Fluorescent Silica Nanoparticles Targeting Mitochondria: Trafficking in Myeloid Cells and Application as Doxorubicin Delivery System in Breast Cancer Cells

Fluorescent silica nanoparticles (SiNPs) appear to be a promising imaging platform, showing a specific subcellular localization. In the present study, we first investigated their preferential mitochondrial targeting in myeloid cells, by flow cytometry, confocal microscopy and TEM on both cells and isolated mitochondria, to acquire knowledge in imaging combined with therapeutic applications. Then, we conjugated SiNPs to one of the most used anticancer drugs, doxorubicin (DOX). As an anticancer agent, DOX has high efficacy but also an elevated systemic toxicity, causing multiple side effects. Nanostructures are usually employed to increase the drug circulation time and accumulation in target tissues, reducing undesired cytotoxicity. We tested these functionalized SiNPs (DOX-NPs) on breast cancer cell line MCF-7. We evaluated DOX-NP cytotoxicity, the effect on the cell cycle and on the expression of CD44 antigen, a molecule involved in adhesion and in tumor invasion, comparing DOX-NP to free DOX and stand-alone SiNPs. We found a specific ability to release a minor amount of CD44+ extracellular vesicles (EVs), from both CD81 negative and CD81 positive pools. Modulating the levels of CD44 at the cell surface in cancer cells is thus of great importance for disrupting the signaling pathways that favor tumor progression.

Obesity Exacerbates Coxsackievirus Infection via Lipid-Induced Mitochondrial Reactive Oxygen Species Generation

Coxsackievirus B3 (CVB3) infection causes acute pancreatitis and myocarditis. However, its pathophysiological mechanism is unclear. Here, we investigated how lipid metabolism is associated with exacerbation of CVB3 pathology using high-fat diet (HFD)-induced obese mice. Mice were intraperitoneally inoculated with 1×10⁶ pfu/mouse of CVB3 after being fed a control or HFD to induce obesity. Mice were treated with mitoquinone (MitoQ) to reduce the level of mitochondrial ROS (mtROS). In obese mice, lipotoxicity of white adipose tissue-induced inflammation caused increased replication of CVB3 and mortality. The coxsackievirus adenovirus receptor increased under obese conditions, facilitating CVB3 replication in vitro. However, lipid-treated cells with receptor-specific inhibitors did not reduce CVB3 replication. In addition, lipid treatment increased mitochondria-derived vesicle formation and the number of multivesicular bodies. Alternatively, we found that inhibition of lipid-induced mtROS decreased viral replication. Notably, HFD-fed mice were more susceptible to CVB3-induced mortality in association with increased levels of CVB3 replication in adipose tissue, which was ameliorated by administration of the mtROS inhibitor, MitoQ. These results suggest that mtROS inhibitors can be used as potential treatments for CVB3 infection.

Identification of long-lived proteins in the mitochondria reveals increased stability of the electron transport chain

In order to combat molecular damage, most cellular proteins undergo rapid turnover. We have previously identified large nuclear protein assemblies that can persist for years in post-mitotic tissues and are subject to age-related decline. Here, we report that mitochondria can be long lived in the mouse brain and reveal that specific mitochondrial proteins have half-lives longer than the average proteome. These mitochondrial long-lived proteins (mitoLLPs) are core components of the electron transport chain (ETC) and display increased longevity in respiratory supercomplexes. We find that COX7C, a mitoLLP that forms a stable contact site between complexes I and IV, is required for complex IV and supercomplex assembly. Remarkably, even upon depletion of COX7C transcripts, ETC function is maintained for days, effectively uncoupling mitochondrial function from ongoing transcription of its mitoLLPs. Our results suggest that modulating protein longevity within the ETC is critical for mitochondrial proteome maintenance and the robustness of mitochondrial function.

Exosomes in Ageing and Motor Neurone Disease: Biogenesis, Uptake Mechanisms, Modifications in Disease and Uses in the Development of Biomarkers and Therapeutics

Intercellular communication between neurons and their surrounding cells occurs through the secretion of soluble molecules or release of vesicles such as exosomes into the extracellular space, participating in brain homeostasis. Under neuro-degenerative conditions associated with ageing, such as amyotrophic lateral sclerosis (ALS), Alzheimer's or Parkinson's disease, exosomes are suspected to propagate toxic proteins. The topic of this review is the role of exosomes in ageing conditions and more specifically in ALS. Our current understanding of exosomes and exosome-related mechanisms is first summarized in a general sense, including their biogenesis and secretion, heterogeneity, cellular interaction and intracellular fate. Their role in the Central Nervous System (CNS) and ageing of the neuromotor system is then considered in the context of exosome-induced signaling. The review then focuses on exosomes in age-associated neurodegenerative disease. The role of exosomes in ALS is highlighted, and their use as potential biomarkers to diagnose and prognose ALS is presented. The therapeutic implications of exosomes for ALS are considered, whether as delivery vehicles, neurotoxic targets or as corrective drugs in and of themselves. A diverse set of mechanisms underpin the functional roles, both confirmed and potential, of exosomes, generally in ageing and specifically in motor neurone disease. Aspects of their contents, biogenesis, uptake and modifications offer many plausible routes towards the development of novel biomarkers and therapeutics.

Mitochondrial Dysfunction, Protein Misfolding and Neuroinflammation in Parkinson's Disease: Roads to Biomarker Discovery

Parkinson’s Disease (PD) is a highly prevalent neurodegenerative disease among older adults. PD neuropathology is marked by the progressive loss of the dopaminergic neurons of the substantia nigra pars compacta and the widespread accumulation of misfolded intracellular α-synuclein (α-syn). Genetic mutations and post-translational modifications, such as α-syn phosphorylation, have been identified among the multiple factors supporting α-syn accrual during PD. A decline in the clearance capacity of the ubiquitin-proteasome and the autophagy-lysosomal systems, together with mitochondrial dysfunction, have been indicated as major pathophysiological mechanisms of PD neurodegeneration. The accrual of misfolded α-syn aggregates into soluble oligomers, and the generation of insoluble fibrils composing the core of intraneuronal Lewy bodies and Lewy neurites observed during PD neurodegeneration, are ignited by the overproduction of reactive oxygen species (ROS). The ROS activate the α-syn aggregation cascade and, together with the Lewy bodies, promote neurodegeneration. However, the molecular pathways underlying the dynamic evolution of PD remain undeciphered. These gaps in knowledge, together with the clinical heterogeneity of PD, have hampered the identification of the biomarkers that may be used to assist in diagnosis, treatment monitoring, and prognostication. Herein, we illustrate the main pathways involved in PD pathogenesis and discuss their possible exploitation for biomarker discovery.

Intercellular transfer of mitochondrial DNA carrying metastasis-enhancing pathogenic mutations from high- to low-metastatic tumor cells and stromal cells via extracellular vesicles

Background

Mitochondrial DNA (mtDNA) carrying certain pathogenic mutations or single nucleotide variants (SNVs) enhances the invasion and metastasis of tumor cells, and some of these mutations are homoplasmic in tumor cells and even in tumor tissues. On the other hand, intercellular transfer of mitochondria and cellular components via extracellular vesicles (EVs) and tunneling nanotubes (TNTs) has recently attracted intense attention in terms of cell-to-cell communication in the tumor microenvironment. It remains unclear whether metastasis-enhancing pathogenic mutant mtDNA in tumor cells is intercellularly transferred between tumor cells and stromal cells. In this study, we investigated whether mtDNA with the NADH dehydrogenase subunit 6 (ND6) G13997A pathogenic mutation in highly metastatic cells can be horizontally transferred to low-metastatic cells and stromal cells in the tumor microenvironment.

Results

When MitoTracker Deep Red-labeled high-metastatic Lewis lung carcinoma A11 cells carrying the ND6 G13997A mtDNA mutation were cocultured with CellLight mitochondria-GFP-labeled low-metastatic P29 cells harboring wild-type mtDNA, bidirectional transfer of red- and green-colored vesicles, probably mitochondria-related EVs, was observed in a time-dependent manner. Similarly, intercellular transfer of mitochondria-related EVs occurred between A11 cells and α-smooth muscle actin (α-SMA)-positive cancer-associated fibroblasts (CAFs, WA-mFib), macrophages (RAW264.7) and cytotoxic T cells (CTLL-2). Intercellular transfer was suppressed by inhibitors of EV release. The large and small EV fractions (L-EV and S-EV, respectively) prepared from the conditioned medium by differential ultracentrifugation both were found to contain mtDNA, although only S-EVs were efficiently incorporated into the cells. Several subpopulations had evidence of LC3-II and contained degenerated mitochondrial components in the S-EV fraction, signaling to the existence of autophagy-related S-EVs. Interestingly, the S-EV fraction contained a MitoTracker-positive subpopulation, which was inhibited by the respiration inhibitor antimycin A, indicating the presence of mitochondria with membrane potential. It was also demonstrated that mtDNA was transferred into mtDNA-less ρ⁰ cells after coculture with the S-EV fraction. In syngeneic mouse subcutaneous tumors formed by a mixture of A11 and P29 cells, the mitochondria-related EVs released from A11 cells reached distantly positioned P29 cells and CAFs.

Conclusions

These results suggest that metastasis-enhancing pathogenic mtDNA derived from metastatic tumor cells is transferred to low-metastatic tumor cells and stromal cells via S-EVs in vitro and in the tumor microenvironment, inferring a novel mechanism of enhancement of metastatic potential during tumor progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12860-021-00391-5.

Extracellular Mitochondrial Components and Effects on Cardiovascular Disease

Besides being powerhouses of the cell, mitochondria released into extracellular space act as intercellular signaling. Mitochondria and their components mediate cell-to-cell communication in free form or embedded in a carrier. The pathogenesis of cardiovascular disease is complex, which shows close relationship with inflammation and metabolic abnormalities. Since mitochondria sustain optimal function of the heart, extracellular mitochondria are emerging as a key regulator in the development of cardiovascular disease. In this review, we provide recent findings in the presence and forms of mitochondria transfer between cells, as well as the effects of these mitochondria on vascular inflammation and ischemic myocardium. Mitochondrial transplantation is a novel treatment paradigm for patients suffering from acute cardiovascular accident and challenges the traditional methods of mitochondria isolation.

Understanding the interactions between inorganic-based nanomaterials and biological membranes

The interactions between inorganic-based nanomaterials (NMs) and biological membranes are among the most important phenomena for developing NM-based therapeutics and resolving nanotoxicology. Herein, we introduce the structural and functional effects of inorganic-based NMs on biological membranes, mainly the plasma membrane and the endomembrane system, with an emphasis on the interface, which involves highly complex networks between NMs and biomolecules (such as membrane proteins and lipids). Significant efforts have been devoted to categorizing and analyzing the interaction mechanisms in terms of the physicochemical characteristics and biological effects of NMs, which can directly or indirectly influence the effects of NMs on membranes. Importantly, we summarize that the biological membranes act as platforms and thereby mediate NMs-immune system contacts. In this overview, the existing challenges and potential applications in the areas are addressed. A strong understanding of the discussed concepts will promote therapeutic NM designs for drug delivery systems by leveraging the NMs-membrane interactions and their functions.

Extracellular Vesicles and Hematopoietic Stem Cell Aging

[Figure: see text].

Exosomes in Liquid Biopsy: The Nanometric World in the Pursuit of Precision Oncology

Among the different components that can be analyzed in liquid biopsy, the utility of exosomes is particularly promising because of their presence in all biological fluids and their potential for multicomponent analyses. Exosomes are extracellular vesicles with an average size of ~100 nm in diameter with an endosomal origin. All eukaryotic cells release exosomes as part of their active physiology. In an oncologic patient, up to 10% of all the circulating exosomes are estimated to be tumor-derived exosomes. Exosome content mirrors the features of its cell of origin in terms of DNA, RNA, lipids, metabolites, and cytosolic/cell-surface proteins. Due to their multifactorial content, exosomes constitute a unique tool to capture the complexity and enormous heterogeneity of cancer in a longitudinal manner. Due to molecular features such as high nucleic acid concentrations and elevated coverage of genomic driver gene sequences, exosomes will probably become the "gold standard" liquid biopsy analyte in the near future.

The effect of extracellular vesicles on the regulation of mitochondria under hypoxia

Mitochondria are indispensable organelles for maintaining cell energy metabolism, and also are necessary to retain cell biological function by transmitting information as signal organelles. Hypoxia, one of the important cellular stresses, can directly regulates mitochondrial metabolites and mitochondrial reactive oxygen species (mROS), which affects the nuclear gene expression through mitochondrial retrograde signal pathways, and also promotes the delivery of signal components into cytoplasm, causing cellular injury. In addition, mitochondria can also trigger adaptive mechanisms to maintain mitochondrial function in response to hypoxia. Extracellular vesicles (EVs), as a medium of information transmission between cells, can change the biological effects of receptor cells by the release of cargo, including nucleic acids, proteins, lipids, mitochondria, and their compositions. The secretion of EVs increases in cells under hypoxia, which indirectly changes the mitochondrial function through the uptake of contents by the receptor cells. In this review, we focus on the mitochondrial regulation indirectly through EVs under hypoxia, and the possible mechanisms that EVs cause the changes in mitochondrial function. Finally, we discuss the significance of this EV-mitochondria axis in hypoxic diseases.

Improving Age-Related Cognitive Decline through Dietary Interventions Targeting Mitochondrial Dysfunction

Aging is inevitable and it is one of the major contributors to cognitive decline. However, the mechanisms underlying age-related cognitive decline are still the object of extensive research. At the biological level, it is unknown how the aging brain is subjected to progressive oxidative stress and neuroinflammation which determine, among others, mitochondrial dysfunction. The link between mitochondrial dysfunction and cognitive impairment is becoming ever more clear by the presence of significant neurological disturbances in human mitochondrial diseases. Possibly, the most important lifestyle factor determining mitochondrial functioning is nutrition. Therefore, with the present work, we review the latest findings disclosing a link between nutrition, mitochondrial functioning and cognition, and pave new ways to counteract cognitive decline in late adulthood through diet.

Next-Generation Cancer Biomarkers: Extracellular Vesicle DNA as a Circulating Surrogate of Tumor DNA

Extracellular vesicles (EVs) are produced by healthy tissues and tumor cells and are released in various bodily fluids, including blood. They are limited by bilayer phospholipidic membranes, and they carry a rich content in biomolecules. Their release cleanses the cells of their waste or serves as functional local and distant cell-cell communication and molecular exchange particles. This rich and heterogeneous content has been given intense attention in cancer physiopathology because EVs support cancer control and progression. Because of their specific active cargo, they are being evaluated as carriers of liquid biopsy biomarkers. Compared to soluble circulating biomarkers, their complexity might provide rich information on tumor and metastases status. Thanks to the acquired genomic changes commonly observed in oncogenic processes, double-stranded DNA (dsDNA) in EVs might be the latest most promising biomarker of tumor presence and complexity. This review will focus on the recent knowledge on the DNA inclusion in vesicles, the technical aspects of EV-DNA detection and quantification, and the use of EV-DNA as a clinical biomarker.

Depletion of Mitochondrial Components from Extracellular Vesicles Secreted from Astrocytes in a Mouse Model of Fragile X Syndrome

Mitochondrial dysfunction contributes to neurodegenerative diseases and developmental disorders such as Fragile X syndrome (FXS). The cross-talk between mitochondria and extracellular vesicles (EVs) suggests that EVs may transfer mitochondrial components as intermediators for intracellular communication under physiological and pathological conditions. In the present study, the ability of EVs to transfer mitochondrial components and their role in mitochondrial dysfunction in astrocytes were examined in the brains of Fmr1 knockout (KO) mice, a model of FXS. The amounts of mitochondrial transcription factor NRF-1, ATP synthases ATP5A and ATPB, and the mitochondrial membrane protein VDAC1 in EVs were reduced in cerebral cortex samples and astrocytes from Fmr1 KO mice. These reductions correspond to decreased mitochondrial biogenesis and transcriptional activities in Fmr1 KO brain, along with decreased mitochondrial membrane potential (MMP) with abnormal localization of vimentin intermediate filament (VIF) in Fmr1 KO astrocytes. Our results suggest that mitochondrial dysfunction in astrocytes is associated with the pathogenesis of FXS and can be monitored by depletion of components in EVs. These findings may improve the ability to diagnose developmental diseases associated with mitochondrial dysfunction, such as FXS and autism spectrum disorders (ASD).

Mitochondrial Fission Protein 1: Emerging Roles in Organellar Form and Function in Health and Disease

Mitochondrial fission protein 1 (Fis1) was identified in yeast as being essential for mitochondrial division or fission and subsequently determined to mediate human mitochondrial and peroxisomal fission. Yet, its exact functions in humans, especially in regard to mitochondrial fission, remains an enigma as genetic deletion of Fis1 elongates mitochondria in some cell types, but not others. Fis1 has also been identified as an important component of apoptotic and mitophagic pathways suggesting the protein may have multiple, essential roles. This review presents current perspectives on the emerging functions of Fis1 and their implications in human health and diseases, with an emphasis on Fis1's role in both endocrine and neurological disorders.

Targeting cellular senescence based on interorganelle communication, multilevel proteostasis, and metabolic control

Cellular senescence, a stable cell division arrest caused by severe damage and stress, is a hallmark of aging in vertebrates including humans. With progressing age, senescent cells accumulate in a variety of mammalian tissues, where they contribute to tissue aging, identifying cellular senescence as a major target to delay or prevent aging. There is an increasing demand for the discovery of new classes of small molecules that would either avoid or postpone cellular senescence by selectively eliminating senescent cells from the body (i.e., ‘senolytics’) or inactivating/switching damage‐inducing properties of senescent cells (i.e., ‘senostatics/senomorphics’), such as the senescence‐associated secretory phenotype. Whereas compounds with senolytic or senostatic activity have already been described, their efficacy and specificity has not been fully established for clinical use yet. Here, we review mechanisms of senescence that are related to mitochondria and their interorganelle communication, and the involvement of proteostasis networks and metabolic control in the senescent phenotype. These cellular functions are associated with cellular senescence in in vitro and in vivo models but have not been fully exploited for the search of new compounds to counteract senescence yet. Therefore, we explore possibilities to target these mechanisms as new opportunities to selectively eliminate and/or disable senescent cells with the aim of tissue rejuvenation. We assume that this research will provide new compounds from the chemical space which act as mimetics of caloric restriction, modulators of calcium signaling and mitochondrial physiology, or as proteostasis optimizers, bearing the potential to counteract cellular senescence, thereby allowing healthy aging.

Altered Expression of Mitoferrin and Frataxin, Larger Labile Iron Pool and Greater Mitochondrial DNA Damage in the Skeletal Muscle of Older Adults

Mitochondrial dysfunction and iron (Fe) dyshomeostasis are invoked among the mechanisms contributing to muscle aging, possibly via a detrimental mitochondrial-iron feed-forward loop. We quantified the labile Fe pool, Fe isotopes, and the expression of mitochondrial Fe handling proteins in muscle biopsies obtained from young and older adults. The expression of key proteins of mitochondrial quality control (MQC) and the abundance of the mitochondrial DNA common deletion (mtDNA4977) were also assessed. An inverse association was found between total Fe and the heavier Fe isotope (56Fe), indicating an increase in labile Fe abundance in cells with greater Fe content. The highest levels of labile Fe were detected in old participants with a Short Physical Performance Battery (SPPB) score ≤ 7 (low-functioning, LF). Protein levels of mitoferrin and frataxin were, respectively, higher and lower in the LF group relative to young participants and older adults with SPPB scores ≥ 11 (high-functioning, HF). The mtDNA4977 relative abundance was greater in old than in young participants, regardless of SPPB category. Higher protein levels of Pink1 were detected in LF participants compared with young and HF groups. Finally, the ratio between lipidated and non-lipidated microtubule-associated protein 1A/1B-light chain 3 (i.e., LC3B II/I), as well as p62 protein expression was lower in old participants regardless of SPPB scores. Our findings indicate that cellular and mitochondrial Fe homeostasis is perturbed in the aged muscle (especially in LF older adults), as reflected by altered levels of mitoferrin and frataxin, which, together with MQC derangements, might contribute to loss of mtDNA stability.

Mitochondrial transformations in the aging human placenta

Mitochondria play a key role in homeostasis and are central to one of the leading hypotheses of aging, the free radical theory. Mitochondria function as a reticulated network, constantly adapting to the cellular environment through fusion (joining), biogenesis (formation of new mitochondria), and fission (separation). This adaptive response is particularly important in response to oxidative stress, cellular damage, and aging, when mitochondria are selectively removed through mitophagy, a mitochondrial equivalent of autophagy. During this complex process, mitochondria influence surrounding cell biology and organelles through the release of signaling molecules. Given that the human placenta is a unique organ having a transient and somewhat defined life span of ∼280 days, any adaption or dysfunction associated with mitochondrial physiology as a result of aging will have a dramatic impact on the health and function of both the placenta and the fetus. Additionally, a defective placenta during gestation, resulting in reduced fetal growth, has been shown to influence the development of chronic disease in later life. In this review we focus on the mitochondrial adaptions and transformations that accompany gestational length and share similarities with age-related diseases. In addition, we discuss the role of such changes in regulating placental function throughout gestation, the etiology of gestational complications, and the development of chronic diseases later in life.

Extracellular Vesicles and Damage-Associated Molecular Patterns: A Pandora's Box in Health and Disease

Sterile inflammation develops as part of an innate immunity response to molecules released upon tissue injury and collectively indicated as damage-associated molecular patterns (DAMPs). While coordinating the clearance of potential harmful stimuli, promotion of tissue repair, and restoration of tissue homeostasis, a hyper-activation of such an inflammatory response may be detrimental. The complex regulatory pathways modulating DAMPs generation and trafficking are actively investigated for their potential to provide relevant insights into physiological and pathological conditions. Abnormal circulating extracellular vesicles (EVs) stemming from altered endosomal-lysosomal system have also been reported in several age-related conditions, including cancer and neurodegeneration, and indicated as a promising route for therapeutic purposes. Along this pathway, mitochondria may dispose altered components to preserve organelle homeostasis. However, whether a common thread exists between DAMPs and EVs generation is yet to be clarified. A deeper understanding of the highly complex, dynamic, and variable intracellular and extracellular trafficking of DAMPs and EVs, including those of mitochondrial origin, is needed to unveil relevant pathogenic pathways and novel targets for drug development. Herein, we describe the mechanisms of generation of EVs and mitochondrial-derived vesicles along the endocytic pathway and discuss the involvement of the endosomal-lysosomal in cancer and neurodegeneration (i.e., Alzheimer's and Parkinson's disease).

Biomarkers of Physical Frailty and Sarcopenia: Coming up to the Place?

Physical frailty and sarcopenia (PF&S) recapitulates all the hallmarks of aging and has become a focus in geroscience. Factors spanning muscle-specific processes (e.g., mitochondrial dysfunction in skeletal myocytes) to systemic changes (e.g., inflammation and amino acid dysmetabolism) have been pinpointed as possible contributors to PF&S pathophysiology. However, the search for PF&S biomarkers allowing the early identification and tracking of the condition over time is ongoing. This is mainly due to the phenotypic heterogeneity of PF&S, its unclear pathophysiology, and the frequent superimposition of other age-related conditions. Hence, presently, the identification of PF&S relies upon clinical, functional, and imaging parameters. The adoption of multi-marker approaches (combined with multivariate modeling) has shown great potential for addressing the complexity of PF&S pathophysiology and identifying candidate biological markers. Well-designed longitudinal studies are necessary for the incorporation of reliable biomarkers into clinical practice and for unveiling novel targets that are amenable to interventions.