Transcellular degradation of axonal mitochondria

Hyperbaric oxygen therapy as an adjunt treatment for glioma and brain metastasis: a literature review

The incidence and mortality rates of malignant tumors are increasing annually, with gliomas and brain metastases linked to a poor prognosis. Hyperbaric oxygen therapy is a promising treatment modality for both gliomas and brain metastases. It can alleviate tumor hypoxia and enhance radiosensitivity. When combined with other treatments for gliomas, this therapy has the potential to enhance survival rates. This review addresses the progress in research on the use of hyperbaric oxygen therapy combined with radiotherapy. For brain metastases, the combination of hyperbaric oxygen therapy and stereotactic radiosurgery is both feasible and advantagenous. This combination not only offers protection against radiation-induced brain injury but also supports the recovery of neurological and motor functions. The incidence of adverse reactions to hyperbaric oxygen therapy is relatively low, and it is safe and manageable. Future efforts should be made to investigate the mechanisms by which hyperbaric oxygen therapy combined with radiotherapy treats gliomas and brain metastases, optimize protection of the combined treatment against brain injury, minimizing adverse reactions, conducting multidisciplinary research and clinical trials, and training healthcare providers to facilitate broader clinical application.

The context-dependent effect of cellular senescence: From embryogenesis and wound healing to aging

Aging is characterized by a steady loss of physiological integrity, leading to impaired function and increased vulnerability to death. Cell senescence is a biological process that progresses with aging and is believed to be a key driver of age-related diseases. Senescence, a hallmark of aging, also demonstrates its beneficial physiological aspects as an anti-cancer, pro-regenerative, homeostatic, and developmental mechanism. A transitory response in which the senescent cells are quickly formed and cleared may promote tissue regeneration and organismal fitness. At the same time, senescence-related secretory phenotypes associated with extended senescence can have devastating effects. The fact that the interaction between senescent cells and their surroundings is very context-dependent may also help to explain this seemingly opposing pleiotropic function. Further, mitochondrial dysfunction is an often-unappreciated hallmark of cellular senescence and figures prominently in multiple feedback loops that induce and maintain the senescent phenotype. This review summarizes the mechanism of cellular senescence and the significance of acute senescence. We concisely introduced the context-dependent role of senescent cells and SASP, aspects of mitochondrial biology altered in the senescent cells, and their impact on the senescent phenotype. Finally, we conclude with recent therapeutic advancements targeting cellular senescence, focusing on acute injuries and age-associated diseases. Collectively, these insights provide a future roadmap for the role of senescence in organismal fitness and life span extension.

Mitochondrial Treatment Improves Cognitive Impairment Induced by Lipopolysaccharide in Mice

Neuroinflammation has been proven to drive cognitive impairment associated with neurodegenerative diseases. It has been demonstrated that mitochondrial dysfunction is associated with cognitive impairment caused by neuroinflammation. We hypothesized that the transfer of exogenous mitochondria may be beneficial to the therapy of cognitive impairment induced by neuroinflammation. In the study, the effect of exogenous mitochondria on cognitive impairment induced by neuroinflammation was investigated. The results showed that mitochondrial treatment ameliorated the cognitive performance of lipopolysaccharide (LPS)-treated mice. Additionally, mitochondrial therapy attenuated neuronal injury and down-regulated the expression of proinflammatory cytokines, including TNF-α and pro- and cleaved IL-1β, and the expression of Iba-1 and GFAP in the hippocampus and cortex of LPS-treated mice. Additionally, mitochondrial treatment increased mitochondrial ΔΨm, ATP level, and SOD activity and attenuated MDA level and ROS production in the brains of LPS-treated mice. The study reports the beneficial effect of mitochondrial treatment against cognitive impairment of LPS-treated mice, thereby providing a potential strategy for the treatment of cognitive impairment caused by neuroinflammation.

Regulation of synaptic mitochondria by extracellular vesicles and its implications for neuronal metabolism and synaptic plasticity

Mitochondrial metabolism in neurons is necessary for energetically costly processes like synaptic transmission and plasticity. As post-mitotic cells, neurons are therefore faced with the challenge of maintaining healthy functioning mitochondria throughout lifetime. The precise mechanisms of mitochondrial maintenance in neurons, and particularly in morphologically complex dendrites and axons, are not fully understood. Evidence from several biological systems suggests the regulation of cellular metabolism by extracellular vesicles (EVs), secretory lipid-enclosed vesicles that have emerged as important mediators of cell communication. In the nervous system, neuronal and glial EVs were shown to regulate neuronal circuit development and function, at least in part via the transfer of protein and RNA cargo. Interestingly, EVs have been implicated in diseases characterized by altered metabolism, such as cancer and neurodegenerative diseases. Furthermore, nervous system EVs were shown to contain proteins related to metabolic processes, mitochondrial proteins and even intact mitochondria. Here, we present the current knowledge of the mechanisms underlying neuronal mitochondrial maintenance, and highlight recent evidence suggesting the regulation of synaptic mitochondria by neuronal and glial cell EVs. We further discuss the potential implications of EV-mediated regulation of mitochondrial maintenance and function in neuronal circuit development and synaptic plasticity.

Therapeutic and diagnostic potential of extracellular vesicle (EV)-mediated intercellular transfer of mitochondria and mitochondrial components

Extracellular vesicles (EVs) facilitate the transfer of biological materials between cells throughout the body. Mitochondria, membrane-bound organelles present in the cytoplasm of nearly all eukaryotic cells, are vital for energy production and cellular homeostasis. Recent studies highlight the critical role of the transport of diverse mitochondrial content, such as mitochondrial DNA (mt-DNA), mitochondrial RNA (mt-RNA), mitochondrial proteins (mt-Prots), and intact mitochondria by small EVs (<200 nm) and large EVs (>200 nm) to recipient cells, where these cargos contribute to cellular and mitochondrial homeostasis. The interplay between EVs and mitochondrial components has significant implications for health, metabolic regulation, and potential as biomarkers. Despite advancements, the mechanisms governing EV-mitochondria crosstalk and the regulatory effect of mitochondrial EVs remain poorly understood. This review explores the roles of EVs and their mitochondrial cargos in health and disease, examines potential mechanisms underlying their interactions, and emphasizes the therapeutic potential of EVs for neurological and systemic conditions associated with mitochondrial dysfunction.

Iron Metabolism and Muscle Aging: Where Ferritinophagy Meets Mitochondrial Quality Control

In older adults with reduced physical performance, an increase in the labile iron pool within skeletal muscle is observed. This accumulation is associated with an altered expression of mitochondrial quality control (MQC) markers and increased mitochondrial DNA damage, supporting the hypothesis that impaired MQC contributes to muscle dysfunction during aging. The autophagy-lysosome system plays a critical role in MQC by tagging and engulfing proteins and organelles for degradation in lysosomes. The endolysosomal system is also instrumental in transferrin recycling, which, in turn, regulates cellular iron uptake. In the neuromuscular system, the autophagy-lysosome system supports the structural integrity of neuromuscular junctions, and its dysfunction contributes to muscle atrophy. While MQC was thought to protect against iron-induced cell death, the discovery of ferroptosis, a form of iron-dependent cell death, has highlighted a complex interplay between MQC and iron-inflicted damage. Ferritinophagy, the autophagic degradation of ferritin, if overactivated, can induce ferroptosis. Alternatively, aging may impair ferritinophagy, leading to ferritin accumulation and the release of toxic labile iron under stress, exacerbating oxidative damage and cellular senescence. Physical activity supports muscle health also by preserving mitochondrial quantity and quality and enhancing bioenergetics. However, therapeutic strategies for preventing or reversing physical function decline in aging are still lacking due to the insufficient understanding of the underlying mechanisms. Unveiling how disruptions in iron homeostasis impact muscle quality in older adults may allow for the development of therapeutic strategies targeting iron handling to alleviate age-associated muscle decline.

Metabolic crosstalk between platelets and cancer: Mechanisms, functions, and therapeutic potential

Platelets, traditionally regarded as passive mediators of hemostasis, are now recognized as pivotal regulators in the tumor microenvironment, establishing metabolic feedback loops with tumor and immune cells. Tumor-derived signals trigger platelet activation, which induces rapid metabolic reprogramming, particularly glycolysis, to support activation-dependent functions such as granule secretion, morphological changes, and aggregation. Beyond self-regulation, platelets influence the metabolic processes of adjacent cells. Through direct mitochondrial transfer, platelets reprogram tumor and immune cells, promoting oxidative phosphorylation. Additionally, platelet-derived cytokines, granules, and extracellular vesicles drive metabolic alterations in immune cells, fostering suppressive phenotypes that facilitate tumor progression. This review examines three critical aspects: (1) the distinctive metabolic features of platelets, particularly under tumor-induced activation; (2) the metabolic crosstalk between activated platelets and other cellular components; and (3) the therapeutic potential of targeting platelet metabolism to disrupt tumor-promoting networks. By elucidating platelet metabolism, this review highlights its essential role in tumor biology and its therapeutic implications.

Aerobic exercise improves astrocyte mitochondrial quality and transfer to neurons in a mouse model of Alzheimer's disease

Mitochondrial dysfunction is a well-established hallmark of Alzheimer's disease (AD). Despite recent documentation of transcellular mitochondrial transfer, its role in the pathogenesis of AD remains unclear. In this study, we report an impairment of mitochondrial quality within the astrocytes and neurons of adult 5 × FAD mice. Following treatment with mitochondria isolated from aged astrocytes induced by exposure to amyloid protein or extended cultivation, cultured neurons exhibited an excessive generation of reactive oxygen species and underwent neurite atrophy. Notably, aerobic exercise enhanced mitochondrial quality by upregulating CD38 within hippocampal astrocytes of 5 × FAD mice. Conversely, the knockdown of CD38 diminished astrocytic-neuronal mitochondrial transfer, thereby abolishing the ameliorative effects of aerobic exercise on neuronal oxidative stress, β-amyloid plaque deposition, and cognitive dysfunction in 5 × FAD mice. These findings unveil an unexpected mechanism through which aerobic exercise facilitates the transference of healthy mitochondria from astrocytes to neurons, thus countering the AD-like progression.

Mitophagy in Neurons: Mechanisms Regulating Mitochondrial Turnover and Neuronal Homeostasis

Mitochondrial quality control is instrumental in regulating neuronal health and survival. The receptor-mediated clearance of damaged mitochondria by autophagy, known as mitophagy, plays a key role in controlling mitochondrial homeostasis. Mutations in genes that regulate mitophagy are causative for familial forms of neurological disorders including Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS). PINK1/Parkin-dependent mitophagy is the best studied mitophagy pathway, while more recent work has brought to light additional mitochondrial quality control mechanisms that operate either in parallel to or independent of PINK1/Parkin mitophagy. Here, we discuss our current understanding of mitophagy mechanisms operating in neurons to govern mitochondrial homeostasis. We also summarize progress in our understanding of the links between mitophagic dysfunction and neurodegeneration, and highlight the potential for therapeutic interventions to maintain mitochondrial health and neuronal function.

Cell-specific mitochondrial response in progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a main form of idiopathic tauopathy characterized neuropathologically by subcortical neurofibrillary tangles in neurons, oligodendroglial coiled bodies, and tufted astrocytes, which follow sequential distribution in the human brain. Mitochondrial dysfunction is thought to be a contributor to many neurodegenerative diseases, but its role in PSP at the cellular level remains incompletely understood. To address this, we performed cell-specific morphometric analysis of mitochondrial markers in post-mortem tissues from motor cortex of PSP patients and non-diseased controls (n = 5 each) followed by single-nuclear transcriptomics (n = 3 each) to identify changes in genes that regulate mitochondrial function. We treated iCell astrocytes with PSP brain homogenates and isolated viable astrocytes from multiple regions of PSP-affected brains. We found that PSP is characterized by significant mitochondrial changes in neurons and astrocytes at the immunohistochemical level, particularly in complex I, with distinct transcriptomic responses across cell types. Glial cells exhibited upregulation of pathways associated with mitochondrial function. In contrast, excitatory and inhibitory neurons showed downregulation in these pathways, indicating impaired mitochondrial function. Astrocytes derived from different human brain regions express varied levels of GFAP and EAAT1 immunoreactivity. Astrocytic tau pathology in cell culture derived from postmortem PSP brains mirrors that seen in corresponding brain tissue histology. Tau pathology in human astrocyte cell culture is associated with clumps of mitochondria potentially associated with impairment in their neuron supportive function. Our results underscore selective complex I damage and cell-type specific patterns that differentiate PSP from other neurodegenerative diseases.

Progranulin deficiency in the brain: the interplay between neuronal and non-neuronal cells

Heterozygous mutations in GRN gene lead to insufficient levels of the progranulin (PGRN) protein, resulting in frontotemporal dementia (FTD) with TAR DNA-binding protein 43 (TDP-43) inclusions, classified pathologically as frontotemporal lobar degeneration (FTLD-TDP). Homozygous GRN mutations are exceedingly rare and cause neuronal ceroid lipofuscinosis 11, a lysosomal storage disease with onset in young adulthood, or an FTD syndrome with late-onset manifestations. In this review, we highlight the broad spectrum of clinical phenotypes associated with PGRN deficiency, including primary progressive aphasia and behavioral variant of frontotemporal dementia. We explore these phenotypes alongside relevant rodent and in vitro human models, ranging from the induced pluripotent stem cell-derived neural progenitors, neurons, microglia, and astrocytes to genetically engineered heterotypic organoids containing both neurons and astrocytes. We summarize advantages and limitations of these models in recapitulating the main FTLD-GRN hallmarks, highlighting the role of non-cell-autonomous mechanisms in the formation of TDP-43 pathology, neuroinflammation, and neurodegeneration. Data obtained from patients' brain tissues and biofluids, in parallel with single-cell transcriptomics, demonstrate the complexity of interactions among the highly heterogeneous cellular clusters present in the brain, including neurons, astrocytes, microglia, oligodendroglia, endothelial cells, and pericytes. Emerging evidence has revealed that PGRN deficiency is associated with cell cluster-specific, often conserved, genetic and molecular phenotypes in the central nervous system. In this review, we focus on how these distinct cellular populations and their dysfunctional crosstalk contribute to neurodegeneration and neuroinflammation in FTD-GRN. Specifically, we characterize the phenotypes of lipid droplet-accumulating microglia and alterations of myelin lipid content resulting from lysosomal dysfunction caused by PGRN deficiency. Additionally, we consider how the deregulation of glia-neuron communication affects the exchange of organelles such as mitochondria, and the removal of excess toxic products such as protein aggregates, in PGRN-related neurodegeneration.

Mitochondrial quality control in hematopoietic stem cells: mechanisms, implications, and therapeutic opportunities

Mitochondrial quality control (MQC) is a critical mechanism for maintaining mitochondrial function and cellular metabolic homeostasis, playing an essential role in the self-renewal, differentiation, and long-term stability of hematopoietic stem cells (HSCs). Recent research highlights the central importance of MQC in HSC biology, particularly the roles of mitophagy, mitochondrial biogenesis, fission, fusion and mitochondrial transfer in regulating HSC function. Mitophagy ensures the removal of damaged mitochondria, maintaining low levels of reactive oxygen species (ROS) in HSCs, thereby preventing premature aging and functional decline. Concurrently, mitochondrial biogenesis adjusts key metabolic regulators such as mitochondrial transcription factor A (TFAM) and peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) to meet environmental demands, ensuring the metabolic needs of HSCs are met. Additionally, mitochondrial transfer, as an essential form of intercellular material exchange, facilitates the transfer of functional mitochondria from bone marrow stromal cells to HSCs, contributing to damage repair and metabolic support. Although existing studies have revealed the significance of MQC in maintaining HSC function, the precise molecular mechanisms and interactions among different regulatory pathways remain to be fully elucidated. Furthermore, the potential role of MQC dysfunction in hematopoietic disorders, including its involvement in disease progression and therapeutic resistance, is not yet fully understood. This review discusses the molecular mechanisms of MQC in HSCs, its functions under physiological and pathological conditions, and its potential therapeutic applications. By summarizing the current progress in this field, we aim to provide insights for further research and the development of innovative treatment strategies.

Corneal epithelial cells upregulate macropinocytosis to engulf metabolically active axonal mitochondria released by injured axons

PURPOSE

To determine the mechanisms used to internalize mitochondria by corneal epithelial cells after in vivo corneal trephine injury and in vitro in corneal epithelial cells.

METHODS

Male and female mice were subjected to trephine injury and euthanized immediately, 6, and 24 h after injury. Macropinocytosis was quantified in vivo using 70 kD fluorescent dextran. Mitochondrial content was assessed by immunofluorescence and metabolic activity quantified by Seahorse assay immediately and 6 h after injury. In vitro experiments using human corneal and limbal epithelial (HCLE) cells and isolated mitochondria were performed to assess mitochondrial transfer in the presence of the gap junction inhibitor 18α-glycyrrhetinc acid and the macropincytosis inhibitor ethylisopropylamiloride.

RESULTS

Mitochondria accumulate within apical epithelial cell layers within minutes of trephine injury. Macropinocytosis also increases within minutes of trephine injury. Oxygen Consumption Rates increase in the corneal epithelium 6 h after trephine injury in males and females. Inhibiting gap junctions increases mitochondrial engulfment while inhibiting macropinocytosis prevents engulfment of mitochondria by corneal epithelial cells in vitro.

CONCLUSIONS

Molecules released by injured cells and severed axons induce macropinocytosis in corneal epithelial cells within minutes of trephine injury. An increase in oxygen consumption rate in the corneal epithelium after trephine injury indicates that axonal mitochondria can evade lysosomal degradation for at least 6 h. In vitro studies using isolated labeled and unlabeled mitochondria and control and mechanically stressed human corneal epithelial cells confirm the involvement of macropinocytosis in the engulfment of free and vesicle bound mitochondria by corneal epithelial cells.

Resveratrol reduces RVLM neuron activity via activating the AMPK/Sirt3 pathway in stress-induced hypertension

Neuronal hyperexcitability in the rostral ventrolateral medulla (RVLM), driven by oxidative stress, plays a crucial role in stress-induced hypertension (SIH). While resveratrol (RSV) is known for its antioxidant properties, its effects on RVLM neurons in SIH remain unclear. We investigated this using an SIH rat model exposed to electric foot shocks and noise stimulation for 15 days. Analysis of RVLM tissue revealed increased mitochondrial damage, oxidative stress, apoptosis, and dysregulated ferroptosis in SIH rats. RSV microinjection into the RVLM reduced blood pressure, sympathetic vascular tone, and neuronal excitability. Both in vivo and in vitro studies showed that RSV treatment alleviated mitochondrial oxidative stress, apoptosis, and ferroptosis through AMPK activation and subsequent Sirt3 upregulation. These therapeutic effects were blocked by either AMPK inhibition or Sirt3 knockdown. Our findings demonstrate that RSV attenuates SIH by activating the AMPK/Sirt3 pathway, thereby reducing RVLM oxidative stress and cell death.

Metabolic reprogramming: a new option for the treatment of spinal cord injury

Spinal cord injuries impose a notably economic burden on society, mainly because of the severe after-effects they cause. Despite the ongoing development of various therapies for spinal cord injuries, their effectiveness remains unsatisfactory. However, a deeper understanding of metabolism has opened up a new therapeutic opportunity in the form of metabolic reprogramming. In this review, we explore the metabolic changes that occur during spinal cord injuries, their consequences, and the therapeutic tools available for metabolic reprogramming. Normal spinal cord metabolism is characterized by independent cellular metabolism and intercellular metabolic coupling. However, spinal cord injury results in metabolic disorders that include disturbances in glucose metabolism, lipid metabolism, and mitochondrial dysfunction. These metabolic disturbances lead to corresponding pathological changes, including the failure of axonal regeneration, the accumulation of scarring, and the activation of microglia. To rescue spinal cord injury at the metabolic level, potential metabolic reprogramming approaches have emerged, including replenishing metabolic substrates, reconstituting metabolic couplings, and targeting mitochondrial therapies to alter cell fate. The available evidence suggests that metabolic reprogramming holds great promise as a next-generation approach for the treatment of spinal cord injury. To further advance the metabolic treatment of the spinal cord injury, future efforts should focus on a deeper understanding of neurometabolism, the development of more advanced metabolomics technologies, and the design of highly effective metabolic interventions.

Extracellular vesicles lay the ground for neuronal plasticity by restoring mitochondrial function, cell metabolism and immune balance

Extracellular vesicles (EVs) convey complex signals between cells that can be used to promote neuronal plasticity and neurological recovery in brain disease models. These EV signals are multimodal and context-dependent, making them unique therapeutic principles. This review analyzes how EVs released from various cell sources control neuronal metabolic function, neuronal survival and plasticity. Preferential sites of EV communication in the brain are interfaces between pre- and postsynaptic neurons at synapses, between astrocytes and neurons at plasma membranes or tripartite synapses, between oligodendrocytes and neurons at axons, between microglial cells/macrophages and neurons, and between cerebral microvascular cells and neurons. At each of these interfaces, EVs support mitochondrial function and cell metabolism under physiological conditions and orchestrate neuronal survival and plasticity in response to brain injury. In the injured brain, the promotion of neuronal survival and plasticity by EVs is tightly linked with EV actions on mitochondrial function, cell metabolism, oxidative stress and immune responses. Via the stabilization of cell metabolism and immune balance, neuronal plasticity responses are activated and functional neurological recovery is induced. As such, EV lay the ground for neuronal plasticity.

Molecular Motors in Blood-Brain Barrier Maintenance by Astrocytes

The blood-brain barrier (BBB) comprises distinct cell types, including endothelial cells, pericytes, and astrocytes, and is essential for central nervous system (CNS) homeostasis by selectively regulating molecular transport and maintaining integrity. In particular, astrocytes are essential for BBB function, as they maintain BBB integrity through their end-feet, which form a physical and biochemical interface that enhances endothelial cell function and barrier selectivity. Moreover, they secrete growth factors like vascular endothelial growth factor (VEGF) and transforming growth factor-beta (TGF-β), which regulate tight junction (TJ) proteins (e.g., claudins and occludins) crucial for limiting paracellular permeability. Molecular motors like kinesins, dynein, and myosins are essential for these astrocyte functions. By facilitating vesicular trafficking and protein transport, they are essential for various functions, including trafficking of junctional proteins to support BBB integrity, the proper mitochondria localization within astrocyte processes for efficient energy supply, the polarized distribution of aquaporin (AQP)-4 at astrocyte end-feet for regulating water homeostasis across the BBB, and the modulation of neuroinflammatory responses. Moreover, myosin motors modulate actomyosin dynamics to regulate astrocyte process outgrowth, adhesion, migration, and morphology, facilitating their functional roles. Thus, motor protein dysregulation in astrocytes can compromise BBB function and integrity, increasing the risk of neurodegeneration. This review explores the complex interplay between astrocytes and molecular motors in regulating BBB homeostasis, which represents an attractive but poorly explored area of research.

Engineered mitochondria in diseases: mechanisms, strategies, and applications

Mitochondrial diseases represent one of the most prevalent and debilitating categories of hereditary disorders, characterized by significant genetic, biological, and clinical heterogeneity, which has driven the development of the field of engineered mitochondria. With the growing recognition of the pathogenic role of damaged mitochondria in aging, oxidative disorders, inflammatory diseases, and cancer, the application of engineered mitochondria has expanded to those non-hereditary contexts (sometimes referred to as mitochondria-related diseases). Due to their unique non-eukaryotic origins and endosymbiotic relationship, mitochondria are considered highly suitable for gene editing and intercellular transplantation, and remarkable progress has been achieved in two promising therapeutic strategies-mitochondrial gene editing and artificial mitochondrial transfer (collectively referred to as engineered mitochondria in this review) over the past two decades. Here, we provide a comprehensive review of the mechanisms and recent advancements in the development of engineered mitochondria for therapeutic applications, alongside a concise summary of potential clinical implications and supporting evidence from preclinical and clinical studies. Additionally, an emerging and potentially feasible approach involves ex vivo mitochondrial editing, followed by selection and transplantation, which holds the potential to overcome limitations such as reduced in vivo operability and the introduction of allogeneic mitochondrial heterogeneity, thereby broadening the applicability of engineered mitochondria.

Optical sorting: past, present and future

Optical sorting combines optical tweezers with diverse techniques, including optical spectrum, artificial intelligence (AI) and immunoassay, to endow unprecedented capabilities in particle sorting. In comparison to other methods such as microfluidics, acoustics and electrophoresis, optical sorting offers appreciable advantages in nanoscale precision, high resolution, non-invasiveness, and is becoming increasingly indispensable in fields of biophysics, chemistry, and materials science. This review aims to offer a comprehensive overview of the history, development, and perspectives of various optical sorting techniques, categorised as passive and active sorting methods. To begin, we elucidate the fundamental physics and attributes of both conventional and exotic optical forces. We then explore sorting capabilities of active optical sorting, which fuses optical tweezers with a diversity of techniques, including Raman spectroscopy and machine learning. Afterwards, we reveal the essential roles played by deterministic light fields, configured with lens systems or metasurfaces, in the passive sorting of particles based on their varying sizes and shapes, sorting resolutions and speeds. We conclude with our vision of the most promising and futuristic directions, including AI-facilitated ultrafast and bio-morphology-selective sorting. It can be envisioned that optical sorting will inevitably become a revolutionary tool in scientific research and practical biomedical applications.

Mechanisms of astrocyte aging in reactivity and disease

Normal aging alters brain functions and phenotypes. However, it is not well understood how astrocytes are impacted by aging, nor how they contribute to neuronal dysfunction and disease risk as organisms age. Here, we examine the transcriptional, cell biology, and functional differences in astrocytes across normal aging. Astrocytes at baseline are heterogenous, responsive to their environments, and critical regulators of brain microenvironments and neuronal function. With increasing age, astrocytes adopt different immune-related and senescence-associated states, which relate to organelle dysfunction and loss of homeostasis maintenance, both cell autonomously and non-cell autonomously. These perturbed states are increasingly associated with age-related dysfunction and the onset of neurodegeneration, suggesting that astrocyte aging is a compelling target for future manipulation in the prevention of disease.

Genetic and pharmacological correction of impaired mitophagy in retinal ganglion cells rescues glaucomatous neurodegeneration

Progressive loss of retinal ganglion cells (RGCs) and degeneration of optic nerve axons are the pathological hallmarks of glaucoma. Ocular hypertension (OHT) and mitochondrial dysfunction are linked to neurodegeneration and vision loss in glaucoma. However, the exact mechanism of mitochondrial dysfunction leading to glaucomatous neurodegeneration is poorly understood. Using multiple mouse models of OHT and human eyes from normal and glaucoma donors, we show that OHT induces impaired mitophagy in RGCs, resulting in the accumulation of dysfunctional mitochondria and contributing to glaucomatous neurodegeneration. Using mitophagy reporter mice, we show that impaired mitophagy precedes glaucomatous neurodegeneration. Notably, the pharmacological rescue of impaired mitophagy via Torin-2 or genetic upregulation of RGC-specific Parkin expression restores the structural and functional integrity of RGCs and their axons in mouse models of glaucoma and ex-vivo human retinal-explant cultures. Our study indicates that impaired mitophagy contributes to mitochondrial dysfunction and oxidative stress, leading to glaucomatous neurodegeneration. Enhancing mitophagy in RGCs represents a promising therapeutic strategy to prevent glaucomatous neurodegeneration.

DNA repair pathways in the mitochondria

Mitochondria contain their own small, circular genome that is present in high copy number. The mitochondrial genome (mtDNA) encodes essential subunits of the electron transport chain. Mutations in the mitochondrial genome are associated with a wide range of mitochondrial diseases and the maintenance and replication of mtDNA is crucial to cellular health. Despite the importance of maintaining mtDNA genomic integrity, fewer DNA repair pathways exist in the mitochondria than in the nucleus. However, mitochondria have numerous pathways that allow for the removal and degradation of DNA damage that may prevent accumulation of mutations. Here, we briefly review the DNA repair pathways present in the mitochondria, sources of mtDNA mutations, and discuss the passive role that mtDNA mutagenesis may play in cancer progression.

Transcript and Lipid Profile Alterations in Astrocyte-Neuron Mitochondrial Transfer Under Lipopolysaccharide Exposure: An In Vitro Study

Sepsis-associated encephalopathy (SAE) is a brain dysfunction for which no effective therapy currently exists. Recent studies suggest that transferring mitochondria from astrocytes to neurons may benefit SAE patients, though the underlying mechanism remains unclear. We cultured astrocytes and neurons from mice in vitro. Astrocytes were stimulated with lipopolysaccharide (LPS) for 24 h, and the astrocyte-conditioned medium (ACM) was collected. Neuronal cultures were then treated with ACM or mitochondria-depleted ACM (mdACM) for further analysis. Mitochondrial transfer was examined under a fluorescence microscope. Western blotting analyzed the protein expression of genes related to apoptosis and mitochondrial metabolism. RNA sequencing and mass spectrometry were employed to investigate the mechanisms underlying mitochondrial transfer. Astrocyte-derived mitochondria migrated toward and connected with LPS-exposed neurons. The addition of ACM significantly attenuated LPS-induced alterations in the proteins linked to apoptosis and mitochondrial dynamics. RNA sequencing revealed notable alterations in the transcript profile of neurons upon ACM treatment, highlighting the involvement of mitochondria metabolism, inflammation, and apoptosis-related factors. Additionally, mitochondrial transfer modified the lipid composition of neurons, increasing phosphatidylserine levels, which correlated with neuroinflammation and enriched pathways related to cytokine and MAPK signaling. Our findings suggest that astrocyte-neuron mitochondrial transfer holds therapeutic potential for alleviating SAE, possibly through the anti-inflammatory effects of lipids, particularly phosphatidylserine.

Extracellular ATP regulates phagocytic activity, mitochondrial respiration, and cytokine secretion of human astrocytic cells

The two main glial cell types of the central nervous system (CNS), astrocytes and microglia, are responsible for neuroimmune homeostasis. Recent evidence indicates astrocytes can participate in removal of pathological structures by becoming phagocytic under conditions of neurodegenerative disease when microglia, the professional phagocytes, are impaired. We hypothesized that adenosine triphosphate (ATP), which acts as damage-associated molecular pattern (DAMP), when released at high concentrations into extracellular space, upregulates phagocytic activity of human astrocytes. This study is the first to measure changes in phagocytic activity and mitochondrial respiration of human astrocytic cells in response to extracellular ATP. We demonstrate that ATP-induced phagocytic activity of U118 MG astrocytic cells is accompanied by upregulated mitochondrial oxidative phosphorylation, which likely supports this energy-dependent process. Application of a selective antagonist A438079 provides evidence identifying astrocytic purinergic P2X7 receptor (P2X7R) as the potential regulator of their phagocytic function. We also report a rapid ATP-induced increase in intracellular calcium ([Ca2+]i), which could serve as regulator of both the phagocytic activity and mitochondrial metabolism, but this hypothesis will need to be tested in future studies. Since ATP upregulates interleukin (IL)-8 secretion by astrocytes but has no effect on their cytotoxicity towards neuronal cells, we conclude that extracellular ATP affects only specific functions of astrocytes. The selectivity of P2X7R-dependent regulation of astrocyte functions by extracellular ATP could allow targeting this receptor-ligand interaction to upregulate their phagocytic function. This could have beneficial outcomes in neurodegenerative disorders, such as Alzheimer's disease, that are characterized by reactive astrocytes and defective phagocytic processes.

Mitochondrial diseases: from molecular mechanisms to therapeutic advances

Mitochondria are essential for cellular function and viability, serving as central hubs of metabolism and signaling. They possess various metabolic and quality control mechanisms crucial for maintaining normal cellular activities. Mitochondrial genetic disorders can arise from a wide range of mutations in either mitochondrial or nuclear DNA, which encode mitochondrial proteins or other contents. These genetic defects can lead to a breakdown of mitochondrial function and metabolism, such as the collapse of oxidative phosphorylation, one of the mitochondria's most critical functions. Mitochondrial diseases, a common group of genetic disorders, are characterized by significant phenotypic and genetic heterogeneity. Clinical symptoms can manifest in various systems and organs throughout the body, with differing degrees and forms of severity. The complexity of the relationship between mitochondria and mitochondrial diseases results in an inadequate understanding of the genotype-phenotype correlation of these diseases, historically making diagnosis and treatment challenging and often leading to unsatisfactory clinical outcomes. However, recent advancements in research and technology have significantly improved our understanding and management of these conditions. Clinical translations of mitochondria-related therapies are actively progressing. This review focuses on the physiological mechanisms of mitochondria, the pathogenesis of mitochondrial diseases, and potential diagnostic and therapeutic applications. Additionally, this review discusses future perspectives on mitochondrial genetic diseases.

Recommendations for mitochondria transfer and transplantation nomenclature and characterization

Intercellular mitochondria transfer is an evolutionarily conserved process in which one cell delivers some of their mitochondria to another cell in the absence of cell division. This process has diverse functions depending on the cell types involved and physiological or disease context. Although mitochondria transfer was first shown to provide metabolic support to acceptor cells, recent studies have revealed diverse functions of mitochondria transfer, including, but not limited to, the maintenance of mitochondria quality of the donor cell and the regulation of tissue homeostasis and remodelling. Many mitochondria-transfer mechanisms have been described using a variety of names, generating confusion about mitochondria transfer biology. Furthermore, several therapeutic approaches involving mitochondria-transfer biology have emerged, including mitochondria transplantation and cellular engineering using isolated mitochondria. In this Consensus Statement, we define relevant terminology and propose a nomenclature framework to describe mitochondria transfer and transplantation as a foundation for further development by the community as this dynamic field of research continues to evolve.

IGF-1 impacts neocortical interneuron connectivity in epileptic spasm generation and resolution

Little is known about the mechanisms that generate epileptic spasms following perinatal brain injury. Recent studies have implicated reduced levels of Insulin-like Growth Factor 1 (IGF-1) in these patients' brains. Other studies have reported low levels of the inhibitory neurotransmitter, GABA. In the TTX brain injury model of epileptic spasms, we undertook experiments to evaluate the impact of IGF-1 deficiencies on neocortical interneurons and their role in spasms. Quantitative immunohistochemical analyses revealed that neocortical interneurons that express glutamic acid decarboxylase, parvalbumin, or synaptotagmin 2 co-express IGF-1. In epileptic rats, expression of these three interneuron markers were reduced in the neocortex. IGF-1 expression was also reduced, but surprisingly this loss was confined to interneurons. Interneuron connectivity was reduced in tandem with IGF-1 deficiencies. Similar changes were observed in surgically resected neocortex from infantile epileptic spasms syndrome (IESS) patients. To evaluate the impact of IGF-1 deficiencies on interneuron development, IGF-1R levels were reduced in the neocortex of neonatal conditional IGF-1R knock out mice by viral injections. Four weeks later, this experimental maneuver resulted in similar reductions in interneuron connectivity. Treatment with the IGF-1 derived tripeptide, (1-3)IGF-1, abolished epileptic spasms in most animals, rescued interneuron connectivity, and restored neocortical levels of IGF-1. Our results implicate interneuron IGF-1 deficiencies, possibly impaired autocrine IGF-1 signaling and a resultant interneuron dysmaturation in epileptic spasm generation. By restoring IGF-1 levels, (1-3)IGF-1 likely suppresses spasms by rescuing interneuron connectivity. Results point to (1-3)IGF-1 and its analogues as potential novel disease-modifying therapies for this neurodevelopmental disorder.

Neuroglia in aging

Aging is associated with morphologic and functional decline of the brain active milieu and, in particular, of the neuroglia, which compromises homeostatic support and neuroprotection. Astrocytes in aging undergo complex and region specific changes, manifested by morphologic atrophy and widespread functional asthenia. Aging leads to mitochondrial malfunction and reduced protein/lipid ratio in human astrocytes. Oligodendrocyte lineage cells are the most affected cells by the aging process, which limits myelinating capacity, thus leading to a substantial reduction in the white matter and deficient brain connectome. Finally, microglia undergo a morphologic functional dystrophy in the aged human brain which curtails brain defenses and increases brain vulnerability to neuropathology and especially to age-dependent neurodegenerative disorders. Lifestyle modifications, such as enriched environment, physical exercise, and healthy dieting, boost neuroglial support, thus improving cognitive longevity.

Mitochondrial dysfunction and Alzheimer's disease: pathogenesis of mitochondrial transfer

In recent years, mitochondrial transfer has emerged as a universal phenomenon intertwined with various systemic physiological and pathological processes. Alzheimer's disease (AD) is a multifactorial disease, with mitochondrial dysfunction at its core. Although numerous studies have found evidence of mitochondrial transfer in AD models, the precise mechanisms remain unclear. Recent studies have revealed the dynamic transfer of mitochondria in Alzheimer's disease, not only between nerve cells and glial cells, but also between nerve cells and glial cells. In this review, we explore the pathways and mechanisms of mitochondrial transfer in Alzheimer's disease and how these transfer activities contribute to disease progression.

Mitochondria break free: Mitochondria-derived vesicles in aging and associated conditions

Mitophagy is the intracellular recycling system that disposes damaged/inefficient mitochondria and allows biogenesis of new organelles to ensure mitochondrial quality is optimized. Dysfunctional mitophagy has been implicated in human aging and diseases. Multiple evolutionarily selected, redundant mechanisms of mitophagy have been identified, but their specific roles in human health and their potential exploitation as therapeutic targets are unclear. Recently, the characterization of the endosomal-lysosomal system has revealed additional mechanisms of mitophagy and mitochondrial quality control that operate via the production of mitochondria-derived vesicles (MDVs). Circulating MDVs can be isolated and characterized to provide an unprecedented opportunity to study this type of mitochondrial recycling in vivo and to relate it to human physiology and pathology. Defining the role of MDVs in human physiology, pathology, and aging is hampered by the lack of standardized methods to isolate, validate, and characterize these vesicles. Hence, some basic questions about MDVs remain unanswered. While MDVs are generated directly through the extrusion of mitochondrial membranes within the cell, a set of circulating extracellular vesicles leaking from the endosomal-lysosomal system and containing mitochondrial portions have also been identified and warrant investigation. Preliminary research indicates that MDV generation serves multiple biological roles and contributes to restoring cell homeostasis. However, studies have shown that MDVs may also be involved in pathological conditions. Therefore, further research is warranted to establish when/whether MDVs are supporting disease progression and/or are extracting damaged mitochondrial components to alleviate cellular oxidative burden and restore redox homeoastasis. This information will be relevant for exploiting these vesicles for therapeutic purpose. Herein, we provide an overview of preclinical and clinical studies on MDVs in aging and associated conditions and discuss the interplay between MDVs and some of the hallmarks of aging (mitophagy, inflammation, and proteostasis). We also outline open questions on MDV research that should be prioritized by future investigations.

Transfer and fates of damaged mitochondria: role in health and disease

Intercellular communication is pivotal in mediating the transfer of mitochondria from donor to recipient cells. This process orchestrates various biological functions, including tissue repair, cell proliferation, differentiation and cancer invasion. Typically, dysfunctional and depolarized mitochondria are eliminated through intracellular or extracellular pathways. Nevertheless, increasing evidence suggests that intercellular transfer of damaged mitochondria is associated with the pathogenesis of diverse diseases. This review investigates the prevalent triggers of mitochondrial damage and the underlying mechanisms of mitochondrial transfer, and elucidates the role of directional mitochondrial transfer in both physiological and pathological contexts. Additionally, we propose potential previously unknown mechanisms mediating mitochondrial transfer and explore their prospective roles in disease prevention and therapy.

Autophagic stress activates distinct compensatory secretory pathways in neurons

Autophagic dysfunction is a hallmark of neurodegenerative disease, leaving neurons vulnerable to the accumulation of damaged organelles and proteins. However, the late onset of diseases suggests that compensatory quality control mechanisms may be engaged to delay the deleterious effects induced by compromised autophagy. Neurons expressing common familial Parkinson's disease (PD)-associated mutations in LRRK2 kinase exhibit defective autophagy. Here, we demonstrate that both primary murine neurons and human iPSC-derived neurons harboring pathogenic LRRK2 upregulate the secretion of extracellular vesicles. We used unbiased proteomics to characterize the secretome of LRRK2G2019S neurons and found that autophagic cargos including mitochondrial proteins were enriched. Based on these observations, we hypothesized that autophagosomes are rerouted toward secretion when cell-autonomous degradation is compromised, likely to mediate clearance of undegraded cellular waste. Immunoblotting confirmed the release of autophagic cargos and immunocytochemistry demonstrated that secretory autophagy was upregulated in LRRK2G2019S neurons. We also found that LRRK2G2019S neurons upregulate the release of exosomes containing miRNAs. Live-cell imaging confirmed that this upregulation of exosomal release was dependent on hyperactive LRRK2 activity, while pharmacological experiments indicate that this release staves off apoptosis. Finally, we show that markers of both vesicle populations are upregulated in plasma from mice expressing pathogenic LRRK2. In sum, we find that neurons expressing pathogenic LRRK2 upregulate the compensatory release of secreted autophagosomes and exosomes, to mediate waste disposal and transcellular communication, respectively. We propose that this increased secretion contributes to the maintenance of cellular homeostasis, delaying neurodegenerative disease progression over the short term while potentially contributing to increased neuroinflammation over the longer term.

Mechanisms Regulating Mitochondrial Transfer in Human Corneal Epithelial Cells

Purpose

The intraepithelial corneal nerves (ICNs) innervating the cornea are essential to corneal epithelial cell homeostasis. Rho-associated kinase (ROCK) inhibitors (RIs) have been reported to play roles in neuron survival after injury and in mitochondrial transfer between corneal epithelial cells. In this study, the mechanisms human corneal limbal epithelial (HCLE) cells use to control intercellular mitochondrial transfer are assessed.

Methods

Mitotracker and AAV1 mitotag eGFPmCherry were used to allow us to study mitochondrial transfer between HCLE cells and neurons in co-cultures and in HCLE cultures. A mitochondrial transfer assay was developed using HCLE cells to quantify the impact of cell stress and inhibition of phagocytosis, gap junctions, and ROCK on mitochondrial transfer, cell adhesion, migration, matrix deposition, and mitochondrial content.

Results

Bidirectional mitochondrial transfer occurs between HCLE cells and neurons. Mitochondrial transfer among HCLE cells is inhibited when gap junction function is reduced and enhanced by acid stress and by inhibition of either phagocytosis or ROCK. Media conditioned by RI-treated cells stimulates cell adhesion and mitochondrial transfer.

Conclusions

Maximal mitochondrial transfer takes place when gap junctions are functional, when ROCK and phagocytosis are inhibited, and when cells are stressed by low pH media. Treatments that reduce mitochondrial content increase HCLE cell mitochondrial transfer. ROCK inhibition in co-cultures causes the release and adhesion of mitochondria to substrates where they can be engulfed by migrating HCLE cells and growing axons and their growth cones.

The roles of migrasomes in immunity, barriers, and diseases

Migrasomes are recently identified extracellular vesicles and organelles formed in conjunction with cell migration. They are situated at the rear of migrating cells, exhibit a circular or elliptical membrane-enclosed structure, and function as a new organelle. Migrasomes selectively sort intercellular components, mediating a cell migration-dependent release mechanism known as migracytosis and modulating cell-cell communication. Accumulated evidence clarifies migrasome formation processes and indicates their diverse functional roles. Migrasomes may also be potentially correlated with the occurrence, progression, and prognosis of certain diseases. Migrasomes' involvement in physiological and pathological processes highlights their potential for expanding our understanding of biological procedures and as a target in clinical therapy. However, the precise mechanisms and full extent of their involvement in immunity, barriers, and diseases remain unclear. This review aimed to provide a comprehensive overview of the roles of migrasomes in human immunity and barriers, in addition to providing insights into their impact on human diseases. STATEMENT OF SIGNIFICANCE: Migrasomes, newly identified extracellular vesicles and organelles, form during cell migration and are located at the rear of migrating cells. These circular or elliptical structures mediate migracytosis, selectively sorting intercellular components and modulating cell-cell communication. Evidence suggests diverse functional roles for migrasomes, including potential links to disease occurrence, progression, and prognosis. Their involvement in physiological and pathological processes highlights their significance in understanding biological procedures and potential clinical therapies. However, their exact mechanisms in immunity, barriers, and diseases remain unclear. This review provides an overview of migrasomes' roles in human immunity and barriers, and their impact on diseases.

Enhancing CNS mitophagy: drug development and disease-relevant models

Mitophagy, the selective degradation of mitochondria, is impaired in many neurodegenerative diseases (NDs), resulting in an accumulation of dysfunctional mitochondria and neuronal damage. Although enhancing mitophagy shows promise as a therapeutic strategy, the clinical significance of mitophagy activators remains uncertain due to limited understanding and poor representation of mitophagy in the central nervous system (CNS). This review explores recent insights into which mitophagy pathways to target and the extent of modulation necessary to be therapeutic towards NDs. We also highlight the complexities of mitophagy in the CNS, highlighting the need for disease-relevant models. Last, we outline crucial aspects of in vitro models to consider during drug discovery, aiming to bridge the gap between preclinical research and clinical applications in treating NDs through mitophagy modulation.

Adult-onset deactivation of autophagy leads to loss of synapse homeostasis and cognitive impairment, with implications for alzheimer disease

A growing number of studies link dysfunction of macroautophagy/autophagy to the pathogenesis of diseases such as Alzheimer disease (AD). Given the global importance of autophagy for homeostasis, how its dysfunction can lead to specific neurological changes is puzzling. To examine this further, we compared the global deactivation of autophagy in the adult mouse using the atg7iKO with the impact of AD-associated pathogenic changes in autophagic processing of synaptic proteins. Isolated forebrain synaptosomes, rather than total homogenates, from atg7iKO mice demonstrated accumulation of synaptic proteins, suggesting that the synapse might be a vulnerable site for protein homeostasis disruption. Moreover, the deactivation of autophagy resulted in impaired cognitive performance over time, whereas gross locomotor skills remained intact. Despite deactivation of autophagy for 6.5 weeks, changes in cognition were in the absence of cell death or synapse loss. In the symptomatic APP PSEN1 double-transgenic mouse model of AD, we found that the impairment in autophagosome maturation coupled with diminished presence of discrete synaptic proteins in autophagosomes isolated from these mice, leading to the accumulation of one of these proteins in the detergent insoluble protein fraction. This protein, SLC17A7/Vglut, also accumulated in atg7iKO mouse synaptosomes. Taken together, we conclude that synaptic autophagy plays a role in maintaining protein homeostasis, and that while decreasing autophagy interrupts normal cognitive function, the preservation of locomotion suggests that not all circuits are affected similarly. Our data suggest that the disruption of autophagic activity in AD may have relevance for the cognitive impairment in this adult-onset neurodegenerative disease. Abbreviations: 2dRAWM: 2-day radial arm water maze; AD: Alzheimer disease; Aβ: amyloid-beta; AIF1/Iba1: allograft inflammatory factor 1; APP: amyloid beta precursor protein; ATG7: autophagy related 7; AV: autophagic vacuole; CCV: cargo capture value; Ctrl: control; DLG4/PSD-95: discs large MAGUK scaffold protein 4; GFAP: glial fibrillary acidic protein; GRIN2B/NMDAR2b: glutamate ionotropic receptor NMDA type subunit 2B; LTD: long-term depression; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; m/o: months-old; PNS: post-nuclear supernatant; PSEN1/PS1: presenilin 1; SHB: sucrose homogenization buffer; SLC32A1/Vgat: solute carrier family 32 member 1; SLC17A7/Vglut1: solute carrier family 17 member 7; SNAP25: synaptosome associated protein 25; SQSTM1/p62: sequestosome 1; SYN1: synapsin I; SYP: synaptophysin ; SYT1: synaptotagmin 1; Tam: tamoxifen; VAMP2: vesicle associated membrane protein 2; VCL: vinculin; wks: weeks.

Mitochondrial Extracellular Vesicles (mitoEVs): Emerging mediators of cell-to-cell communication in health, aging and age-related diseases

Mitochondria are metabolic and signalling hubs that integrate a plethora of interconnected processes to maintain cell homeostasis. They are also dormant mediators of inflammation and cell death, and with aging damages affecting mitochondria gradually accumulate, resulting in the manifestation of age-associated disorders. In addition to coordinate multiple intracellular functions, mitochondria mediate intercellular and inter-organ cross talk in different physiological and stress conditions. To fulfil this task, mitochondrial signalling has evolved distinct and complex conventional and unconventional routes of horizontal/vertical mitochondrial transfer. In this regard, great interest has been focused on the ability of extracellular vesicles (EVs), such as exosomes and microvesicles, to carry selected mitochondrial cargoes to target cells, in response to internal and external cues. Over the past years, the field of mitochondrial EVs (mitoEVs) has grown exponentially, revealing unexpected heterogeneity of these structures associated with an ever-expanding mitochondrial function, though the full extent of the underlying mechanisms is far from being elucidated. Therefore, emerging subsets of EVs encompass exophers, migrasomes, mitophers, mitovesicles, and mitolysosomes that can act locally or over long-distances to restore mitochondrial homeostasis and cell functionality, or to amplify disease. This review provides a comprehensive overview of our current understanding of the biology and trafficking of MitoEVs in different physiological and pathological conditions. Additionally, a specific focus on the role of mitoEVs in aging and the onset and progression of different age-related diseases is discussed.

Mitochondrial transfer from mesenchymal stem cells: Mechanisms and functions

Mesenchymal stem cells based therapy has been used in clinic for almost 20 years and has shown encouraging effects in treating a wide range of diseases. However, the underlying mechanism is far more complicated than it was previously assumed. Mitochondria transfer is one way that recently found to be employed by mesenchymal stem cells to exert its biological effects. As one way of exchanging mitochondrial components, mitochondria transfer determines both mesenchymal stem cells and recipient cell fates. In this review, we describe the factors that contribute to MSCs-MT. Then, the routes and mechanisms of MSCs-MT are summarized to provide a theoretical basis for MSCs therapy. Besides, the advantages and disadvantages of MSCs-MT in clinical application are analyzed.

Retinal damage promotes mitochondrial transfer in the visual system of a mouse model of Leber hereditary optic neuropathy

Lenadogene nolparvovec is a gene therapy which has been developed to treat Leber hereditary optic neuropathy (LHON) caused by a point mutation in the mitochondrial NADH dehydrogenase 4 (ND4) gene. Clinical trials have demonstrated a significant improvement of visual acuity up to 5 years after treatment by lenadogene nolparvovec but, surprisingly, unilateral treatment resulted in bilateral improvement of vision. This contralateral effect - similarly observed with other gene therapy products in development for MT-ND4-LHON - is supported by the migration of viral vector genomes and their transcripts to the contralateral eye, as reported in animals, and post-mortem samples from two patients. In this study, we used an AAV2 encoding fluorescent proteins targeting mitochondria to investigate whether these organelles themselves could transfer from the treated eye to the fellow one. We found that mitochondria travel along the visual system (optic chiasm and primary visual cortex) and reach the contralateral eye (optic nerve and retina) in physiological conditions. We also observed that, in a rotenone-induced model of retinal damage mimicking LHON, mitochondrial transfer from the healthy to the damaged eye was accelerated and enhanced. Our results thus provide a further explanation for the contralateral beneficial effect observed during clinical studies with lenadogene nolparvovec.

Mitochondrion-based organellar therapies for central nervous system diseases

As most traditional drugs used to treat central nervous system (CNS) diseases have a single therapeutic target, many of them cannot treat complex diseases or diseases whose mechanism is unknown and cannot effectively reverse the root changes underlying CNS diseases. This raises the question of whether multiple functional components are involved in the complex pathological processes of CNS diseases. Organelles are the core functional units of cells, and the replacement of damaged organelles with healthy organelles allows the multitargeted and integrated modulation of cellular functions. The development of therapies that target independent functional units in the cell, specifically, organelle-based therapies, is rapidly progressing. This article comprehensively discusses the pathogenesis of mitochondrial homeostasis disorders, which involve mitochondria, one of the most important organelles in CNS diseases, and the machanisms of mitochondrion-based therapies, as well as current preclinical and clinical studies on the efficacy of therapies targeting mitochondrial to treat CNS diseases, to provide evidence for use of organelle-based treatment strategies in the future.

Mitophagy-associated programmed neuronal death and neuroinflammation

Mitochondria are crucial organelles that play a central role in cellular metabolism and programmed cell death in eukaryotic cells. Mitochondrial autophagy (mitophagy) is a selective process where damaged mitochondria are encapsulated and degraded through autophagic mechanisms, ensuring the maintenance of both mitochondrial and cellular homeostasis. Excessive programmed cell death in neurons can result in functional impairments following cerebral ischemia and trauma, as well as in chronic neurodegenerative diseases, leading to irreversible declines in motor and cognitive functions. Neuroinflammation, an inflammatory response of the central nervous system to factors disrupting homeostasis, is a common feature across various neurological events, including ischemic, infectious, traumatic, and neurodegenerative conditions. Emerging research suggests that regulating autophagy may offer a promising therapeutic avenue for treating certain neurological diseases. Furthermore, existing literature indicates that various small molecule autophagy regulators have been tested in animal models and are linked to neurological disease outcomes. This review explores the role of mitophagy in programmed neuronal death and its connection to neuroinflammation.

Differential mitochondrial bioenergetics and cellular resilience in astrocytes, hepatocytes, and fibroblasts from aging baboons

Biological resilience, broadly defined as the ability to recover from an acute challenge and return to homeostasis, is of growing importance to the biology of aging. At the cellular level, there is variability across tissue types in resilience and these differences are likely to contribute to tissue aging rate disparities. However, there are challenges in addressing these cell-type differences at regional, tissue, and subject level. To address this question, we established primary cells from aged male and female baboons between 13.3 and 17.8 years spanning across different tissues, tissue regions, and cell types including (1) fibroblasts from skin and from the heart separated into the left ventricle (LV), right ventricle (RV), left atrium (LA), and right atrium (RA); (2) astrocytes from the prefrontal cortex and hippocampus; and (3) hepatocytes. Primary cells were characterized by their cell surface markers and their cellular respiration was assessed with Seahorse XFe96. Cellular resilience was assessed by modifying a live-cell imaging approach; we previously reported that monitors proliferation of dividing cells following response and recovery to oxidative (50 µM-H2O2), metabolic (1 mM-glucose), and proteostasis (0.1 µM-thapsigargin) stress. We noted significant differences even among similar cell types that are dependent on tissue source and the diversity in cellular response is stressor-specific. For example, astrocytes had a higher oxygen consumption rate and exhibited greater resilience to oxidative stress (OS) than both fibroblasts and hepatocytes. RV and RA fibroblasts were less resilient to OS compared with LV and LA, respectively. Skin fibroblasts were less impacted by proteostasis stress compared to astrocytes and cardiac fibroblasts. Future studies will test the functional relationship of these outcomes to the age and developmental status of donors as potential predictive markers.

Acute ocular hypertension in the living human eye: Model description and initial cellular responses to elevated intraocular pressure

This initial methods study presents the initial immunohistochemical and transcriptomic changes in the optic nerve head and retina from three research-consented brain-dead organ donors following prolonged and transient intraocular pressure (IOP) elevation. In this initial study, research-consented brain-dead organ donors were exposed to unilateral elevation of IOP for 7.5 h (Donor 1), 30 h (Donor 2), and 1 h (Donor 3) prior to organ procurement. Optic nerve tissue and retinal tissue was obtained following organ procurement for immunohistological and transcriptomic analysis. Optic nerve sections in Donor 1 exposed to 7.5-hours of unilateral sub-ischemic IOP elevation demonstrated higher levels of protein expression of the astrocytic marker, glial fibrillary acidic protein (GFAP), within the lamina cribrosa with greatest expression inferior temporally in the treated eye compared to control. Spatial transcriptomic analysis performed on optic nerve head tissues from Donor 2 exposed to 30 h of unilateral IOP elevation demonstrated differential transcription of mRNA across laminar and scleral regions. Immunohistochemistry of retinal sections from Donor 2 exhibited higher GFAP and IBA1 expression in the treated eye compared with control, but this was not observed in Donor 3, which was exposed to only 1-hour of IOP elevation. While there were no differences in GFAP protein expression in the retina following the 1-hour IOP elevation in Donor 3, there were higher levels of transcription of GFAP in the inner nuclear layer, and CD44 in the retinal ganglion cell layer, indicative of astrocytic and Müller glial reactivity as well as an early inflammatory response, respectively. We found that transcriptomic differences can be observed across treated and control eyes following unilateral elevation of IOP in brain dead organ donors. The continued development of this model affords the unique opportunity to define the acute mechanotranscriptomic response of the optic nerve head, evaluate the injury and repair mechanisms in the retina in response to IOP elevation, and enable correlation of in vivo imaging and functional testing with ex vivo cellular responses for the first time in the living human eye.

Exploring the role of mitochondrial uncoupling protein 4 in brain metabolism: implications for Alzheimer's disease

The brain's high demand for energy necessitates tightly regulated metabolic pathways to sustain physiological activity. Glucose, the primary energy substrate, undergoes complex metabolic transformations, with mitochondria playing a central role in ATP production via oxidative phosphorylation. Dysregulation of this metabolic interplay is implicated in Alzheimer's disease (AD), where compromised glucose metabolism, oxidative stress, and mitochondrial dysfunction contribute to disease progression. This review explores the intricate bioenergetic crosstalk between astrocytes and neurons, highlighting the function of mitochondrial uncoupling proteins (UCPs), particularly UCP4, as important regulators of brain metabolism and neuronal function. Predominantly expressed in the brain, UCP4 reduces the membrane potential in the inner mitochondrial membrane, thereby potentially decreasing the generation of reactive oxygen species. Furthermore, UCP4 mitigates mitochondrial calcium overload and sustains cellular ATP levels through a metabolic shift from mitochondrial respiration to glycolysis. Interestingly, the levels of the neuronal UCPs, UCP2, 4 and 5 are significantly reduced in AD brain tissue and a specific UCP4 variant has been associated to an increased risk of developing AD. Few studies modulating the expression of UCP4 in astrocytes or neurons have highlighted protective effects against neurodegeneration and aging, suggesting that pharmacological strategies aimed at activating UCPs, such as protonophoric uncouplers, hold promise for therapeutic interventions in AD and other neurodegenerative diseases. Despite significant advances, our understanding of UCPs in brain metabolism remains in its early stages, emphasizing the need for further research to unravel their biological functions in the brain and their therapeutic potential.

Mechanical force of uterine occupation enables large vesicle extrusion from proteostressed maternal neurons

Large vesicle extrusion from neurons may contribute to spreading pathogenic protein aggregates and promoting inflammatory responses, two mechanisms leading to neurodegenerative disease. Factors that regulate the extrusion of large vesicles, such as exophers produced by proteostressed C. elegans touch neurons, are poorly understood. Here, we document that mechanical force can significantly potentiate exopher extrusion from proteostressed neurons. Exopher production from the C. elegans ALMR neuron peaks at adult day 2 or 3, coinciding with the C. elegans reproductive peak. Genetic disruption of C. elegans germline, sperm, oocytes, or egg/early embryo production can strongly suppress exopher extrusion from the ALMR neurons during the peak period. Conversely, restoring egg production at the late reproductive phase through mating with males or inducing egg retention via genetic interventions that block egg-laying can strongly increase ALMR exopher production. Overall, genetic interventions that promote ALMR exopher production are associated with expanded uterus lengths and genetic interventions that suppress ALMR exopher production are associated with shorter uterus lengths. In addition to the impact of fertilized eggs, ALMR exopher production can be enhanced by filling the uterus with oocytes, dead eggs, or even fluid, supporting that distention consequences, rather than the presence of fertilized eggs, constitute the exopher-inducing stimulus. We conclude that the mechanical force of uterine occupation potentiates exopher extrusion from proximal proteostressed maternal neurons. Our observations draw attention to the potential importance of mechanical signaling in extracellular vesicle production and in aggregate spreading mechanisms, making a case for enhanced attention to mechanobiology in neurodegenerative disease.

Mitochondrial dysfunction and increased reactive oxygen species production in MECP2 mutant astrocytes and their impact on neurons

Studies on MECP2 function and its implications in Rett Syndrome (RTT) have traditionally centered on neurons. Here, using human embryonic stem cell (hESC) lines, we modeled MECP2 loss-of-function to explore its effects on astrocyte (AST) development and dysfunction in the brain. Ultrastructural analysis of RTT hESC-derived cerebral organoids revealed significantly smaller mitochondria compared to controls (CTRs), particularly pronounced in glia versus neurons. Employing a multiomics approach, we observed increased gene expression and accessibility of a subset of nuclear-encoded mitochondrial genes upon mutation of MECP2 in ASTs compared to neurons. Analysis of hESC-derived ASTs showed reduced mitochondrial respiration and altered key proteins in the tricarboxylic acid cycle and electron transport chain in RTT versus CTRs. Additionally, RTT ASTs exhibited increased cytosolic amino acids under basal conditions, which were depleted upon increased energy demands. Notably, mitochondria isolated from RTT ASTs exhibited increased reactive oxygen species and influenced neuronal activity when transferred to cortical neurons. These findings underscore MECP2 mutation's differential impact on mitochondrial and metabolic pathways in ASTs versus neurons, suggesting that dysfunctional AST mitochondria may contribute to RTT pathophysiology by affecting neuronal health.

Extracellular vesicles as carriers for mitochondria: Biological functions and clinical applications

In recent years, research has increasingly focused on the biogenesis of extracellular vesicles (EVs) and the sorting mechanisms for their contents. Mitochondria can be selectively loaded into EVs, serving as a way to maintain cellular mitochondrial homeostasis. EV-mediated mitochondrial transfer has also been shown to greatly impact the function of target cells. Based on the mechanism of EV-mediated mitochondrial transfer, therapies can be developed to treat human diseases. This review summarizes the recent advances in the biogenesis and molecular composition of EVs. It also highlights the sorting and trafficking mechanisms of mitochondrial components into EVs. Furthermore, it explores the current role of EV-mediated mitochondrial transfer in the development of human diseases, as well as its diagnostic and therapeutic applications.

Transcriptional profiling of retinal astrocytes identifies a specific marker and points to functional specialization

Astrocyte heterogeneity is an increasingly prominent research topic, and studies in the brain have demonstrated substantial variation in astrocyte form and function, both between and within regions. In contrast, retinal astrocytes are not well understood and remain incompletely characterized. Along with optic nerve astrocytes, they are responsible for supporting retinal ganglion cell axons and an improved understanding of their role is required. We have used a combination of microdissection and Ribotag immunoprecipitation to isolate ribosome-associated mRNA from retinal astrocytes and investigate their transcriptome, which we also compared to astrocyte populations in the optic nerve. Astrocytes from these regions are transcriptionally distinct, and we identified retina-specific astrocyte genes and pathways. Moreover, although they share much of the "classical" gene expression patterns of astrocytes, we uncovered unexpected variation, including in genes related to core astrocyte functions. We additionally identified the transcription factor Pax8 as a highly specific marker of retinal astrocytes and demonstrated that these astrocytes populate not only the retinal surface, but also the prelaminar region at the optic nerve head. These findings are likely to contribute to a revised understanding of the role of astrocytes in the retina.

Mitochondrial Transportation, Transplantation, and Subsequent Immune Response in Alzheimer's Disease: An Update

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by memory impairment and a progressive decline in cognitive function. Mitochondrial dysfunction has been identified as an important contributor to the development of AD, leading to oxidative stress and energy deficits within the brain. While current treatments for AD aim to alleviate symptoms, there is an urgent need to target the underlying mechanisms. The emerging field of mitotherapy, which involves the transplantation of healthy mitochondria into damaged cells, has gained substantial attention and has shown promising results. However, research in the context of AD remains limited, necessitating further investigations. In this review, we summarize the mitochondrial pathways that contribute to the progression of AD. Additionally, we discuss mitochondrial transfer among brain cells and mitotherapy, with a focus on different administration routes, various sources of mitochondria, and potential modifications to enhance transplantation efficacy. Finally, we review the limited available evidence regarding the immune system's response to mitochondrial transplantation in damaged brain regions.