Transient Opening of the Mitochondrial Permeability Transition Pore Induces Microdomain Calcium Transients in Astrocyte Processes

Sg-snn: a self-organizing spiking neural network based on temporal information

Neurodynamic observations indicate that the cerebral cortex evolved by self-organizing into functional networks, These networks, or distributed clusters of regions, display various degrees of attention maps based on input. Traditionally, the study of network self-organization relies predominantly on static data, overlooking temporal information in dynamic neuromorphic data. This paper proposes Temporal Self-Organizing (TSO) method for neuromorphic data processing using a spiking neural network. The TSO method incorporates information from multiple time steps into the selection strategy of the Best Matching Unit (BMU) neurons. It enables the coupled BMUs to radiate the weight across the same layer of neurons, ultimately forming a hierarchical self-organizing topographic map of concern. Additionally, we simulate real neuronal dynamics, introduce a glial cell-mediated Glial-LIF (Leaky Integrate-and-fire) model, and adjust multiple levels of BMUs to optimize the attention topological map.Experiments demonstrate that the proposed Self-organizing Glial Spiking Neural Network (SG-SNN) can generate attention topographies for dynamic event data from coarse to fine. A heuristic method based on cognitive science effectively guides the network's distribution of excitatory regions. Furthermore, the SG-SNN shows improved accuracy on three standard neuromorphic datasets: DVS128-Gesture, CIFAR10-DVS, and N-Caltech 101, with accuracy improvements of 0.3%, 2.4%, and 0.54% respectively. Notably, the recognition accuracy on the DVS128-Gesture dataset reaches 99.3%, achieving state-of-the-art (SOTA) performance.

The roles of mitochondria in global and local intracellular calcium signalling

Activation of Ca2+ channels in Ca2+ stores in organelles and the plasma membrane generates cytoplasmic calcium ([Ca2+]c) signals that control almost every aspect of cell function, including metabolism, vesicle fusion and contraction. Mitochondria have a high capacity for Ca2+ uptake and chelation, alongside efficient Ca2+ release mechanisms. Still, mitochondria do not store Ca2+ in a prolonged manner under physiological conditions and lack the capacity to generate global [Ca2+]c signals. However, mitochondria take up Ca2+ at high local [Ca2+]c signals that originate from neighbouring organelles, and also during sustained global elevations of [Ca2+]c. Accumulated Ca2+ in the mitochondria stimulates oxidative metabolism and upon return to the cytoplasm, can produce spatially confined rises in [Ca2+]c to exert control over processes that are sensitive to Ca2+. Thus, the mitochondrial handling of [Ca2+]c is of physiological relevance. Furthermore, dysregulation of mitochondrial Ca2+ handling can contribute to debilitating diseases. We discuss the mechanisms and relevance of mitochondria in local and global calcium signals.

Calcium Signaling in Astrocytes and Its Role in the Central Nervous System Injury

Astrocytes are the most abundant glial cells in the central nervous system (CNS). Due to their extensive processes, they can interconnect with many neighboring cells and play critical roles in regulating synaptic plasticity, integrating neuronal signals, and maintaining the stability of the extracellular environment. These functions are largely dependent on calcium (Ca2+) signaling. In light of these considerations, the powerful functions of Ca2+ signaling in astrocytes have been actively studied in recent years. This review summarizes the mechanisms related to Ca2+ waves in astrocytes as well as their physiological and pathological functions mediated by various calcium signaling, the characteristics of calcium waves, and the role of Ca2+ in astrocytes in the CNS injuries of spinal cord injury (SCI) and traumatic brain injury (TBI) recently. However, inhibited L-type voltage-gated Ca2+ channels (LTCCs) activity and reduced Ca2+ concentration result in an opposite phenomenon that promoting or reducing astrogliosis. This highlights the importance of focusing not only on Ca2⁺ concentration but also on the downstream signaling pathways initiated by Ca2⁺. Therefore, we summarize diverse signaling pathways in various physiological and pathological contexts.

Three-photon in vivo imaging of neurons and glia in the medial prefrontal cortex with sub-cellular resolution

The medial prefrontal cortex (mPFC) is important for higher cognitive functions, including working memory, decision making, and emotional control. In vivo recordings of neuronal activity in the mPFC have been achieved via invasive electrical and optical approaches. Here we apply low invasive three-photon in vivo imaging in the mPFC of the mouse at unprecedented depth. Specifically, we measure neuronal and astrocytic Ca2+-transient parameters in awake head-fixed mice up to a depth of 1700 µm. Furthermore, we longitudinally record dendritic spine density (0.41 ± 0.07 µm-1) deeper than 1 mm for a week. Using 1650 nm wavelength to excite red fluorescent microglia, we quantify their processes' motility (58.9 ± 2% turnover rate) at previously unreachable depths (1100 µm). We establish three-photon imaging of the mPFC enabling neuronal and glial recordings with subcellular resolution that will pave the way for novel discoveries in this brain region.

Fast, accurate, and versatile data analysis platform for the quantification of molecular spatiotemporal signals

Optical recording of intricate molecular dynamics is becoming an indispensable technique for biological studies, accelerated by the development of new or improved biosensors and microscopy technology. This creates major computational challenges to extract and quantify biologically meaningful spatiotemporal patterns embedded within complex and rich data sources, many of which cannot be captured with existing methods. Here, we introduce activity quantification and analysis (AQuA2), a fast, accurate, and versatile data analysis platform built upon advanced machine-learning techniques. It decomposes complex live-imaging-based datasets into elementary signaling events, allowing accurate and unbiased quantification of molecular activities and identification of consensus functional units. We demonstrate applications across a wide range of biosensors, cell types, organs, animal models, microscopy techniques, and imaging approaches. As exemplar findings, we show how AQuA2 identified drug-dependent interactions between neurons and astroglia, as well as distinct sensorimotor signal propagation patterns in the mouse spinal cord.

Astrocyte regulation of behavioral outputs: the versatile roles of calcium

Behavior arises from coordinated brain-wide neural and glial networks, enabling organisms to perceive, interpret, and respond to stimuli. Astrocytes play an important role in shaping behavioral output, yet the underlying molecular mechanisms are not fully understood. Astrocytes respond to intrinsic and extrinsic cues with calcium (Ca2+) fluctuations, which are highly heterogeneous across spatio-temporal scales, contexts, and brain regions. This heterogeneity allows astrocytes to exert dynamic regulatory effects on neuronal function but has made it challenging to understand the precise mechanisms and pathways linking astrocytic Ca2+ to specific behavioral outcomes, and the functional relevance of these signals remains unclear. Here, we review recent literature uncovering roles for astrocytic Ca2+ signaling in a wide array of behaviors, including cognitive, homeostatic, and affective focusing on its physiological roles, and potential pathological implications. We specifically highlight how different types of astrocytic Ca2+ signals are linked to distinct behavioral outcomes and discuss limitations and unanswered questions that remain to be addressed.

Spatiotemporal calcium dynamics orchestrate oligodendrocyte development and myelination

Oligodendrocyte lineage cells (OLCs), comprising oligodendrocyte precursor cells (OPCs) and oligodendrocytes, are pivotal in sculpting central nervous system (CNS) architecture and function. OPCs mature into oligodendrocytes, which enwrap axons with myelin sheaths that are critical for enhancing neural transmission. Notably, OLCs actively respond to neuronal activity, modulating neural circuit functions. Understanding neuron-OLC interactions is key to unraveling how OLCs contribute to CNS health and pathology. This review highlights insights from zebrafish and mouse models, revealing how synaptic and extrasynaptic pathways converge to shape spatiotemporal calcium (Ca2+) dynamics within OLCs. We explore how Ca2+ signal integration across spatial and temporal scales acts as a master regulator of OLC fate determination and myelin plasticity.

Natural products alleviate atrial fibrillation by modulating mitochondrial quality control

BACKGROUND

Atrial fibrillation (AF), one of the most common cardiac arrhythmias, is associated with high mortality rates and significant healthcare burdens. Mitochondrial homeostasis has recently emerged as a critical factor in AF pathogenesis but remains at the experimental stage. Current drug and surgical treatments for AF often involve side effects and require ongoing treatment plan evaluation and adjustment. In contrast, natural products (NPs), which have been utilized in China for over 2,000 years, show remarkable efficacy in treating AF and are receiving growing attention.

PURPOSE

We aimed to investigate the regulatory effects of NPs on mitochondrial quality control (MQC) and their impact on AF occurrence and progression. By constructing a novel NP-mitochondria-AF axis, we propose a framework to translate experimental findings into clinical practice and identify potential therapeutic strategies for AF.

METHODS

Databases such as PubMed, Web of Science, and China National Knowledge Infrastructure were searched (up to October 2024) using the following keywords: "atrial fibrillation," "traditional Chinese medicine," "mitochondrial biogenesis," "mitochondrial dynamics," "mitophagy," "apoptosis," "oxidative stress," "inflammation," and "Ca2+ concentration." NP targets were identified using the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform, while disease targets were retrieved from Online Mendelian Inheritance in Man, GeneCards, and Therapeutic Target Database. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis was performed using the Metascape database. Protein-protein interactions were analyzed using the STRING database, and core monomers and hub genes were identified using Cytoscape 3.7.2.

RESULTS

We found a strong relationship between mitochondrial homeostasis and AF development. KEGG pathway analysis indicated that commonly used NPs regulate mitochondrial homeostasis, affecting AF progression through various hub genes, including protein kinase B-alpha (AKT1), jun proto-oncogene (JUN), and tumor necrosis factor (TNF). Molecular docking analysis revealed that NP core monomers exhibited binding affinities to hub genes below -5 kcal/mol and to transforming growth factor-β (TGF-β) below -7 kcal/mol.

CONCLUSION

NPs, including traditional Chinese medicine (TCM) compounds, TCM monomers, and traditional Chinese patent medicines, alleviate AF by modulating MQC with minimal side effects and high efficacy. These findings highlight the therapeutic potential of NPs as promising candidates for AF treatment and further underscore the importance of MQC in AF pathogenesis.

Müller cells trophism and pathology as the next therapeutic targets for retinal diseases

Müller cells are a crucial retinal cell type involved in multiple regulatory processes and functions that are essential for retinal health and functionality. Acting as structural and functional support for retinal neurons and photoreceptors, Müller cells produce growth factors, regulate ion and fluid homeostasis, and facilitate neuronal signaling. They play a pivotal role in retinal morphogenesis and cell differentiation, significantly contributing to macular development. Due to their radial morphology and unique cytoskeletal organization, Müller cells act as optical fibers, efficiently channeling photons directly to the photoreceptors. In response to retinal damage, Müller cells undergo specific gene expression and functional changes that serve as a first line of defense for neurons, but can also lead to unwarranted cell dysfunction, contributing to cell death and neurodegeneration. In some species, Müller cells can reactivate their developmental program, promoting retinal regeneration and plasticity-a remarkable ability that holds promising therapeutic potential if harnessed in mammals. The crucial and multifaceted roles of Müller cells-that we propose to collectively call "Müller cells trophism"-highlight the necessity of maintaining their functionality. Dysfunction of Müller cells, termed "Müller cells pathology," has been associated with a plethora of retinal diseases, including age-related macular degeneration, diabetic retinopathy, vitreomacular disorders, macular telangiectasia, and inherited retinal dystrophies. In this review, we outline how even subtle disruptions in Müller cells trophism can drive the pathological cascade of Müller cells pathology, emphasizing the need for targeted therapies to preserve retinal health and prevent disease progression.

The IP3R2 Knockout Mice in Behavior: A Blessing or a Curse?

The inositol 1,4,5-triphosphate receptor type 2 (IP3R2) plays a critical role in intracellular calcium (Ca2+) signaling, particularly in astrocytes, where it mediates Ca2+ release from the endoplasmic reticulum. This mechanism is vital for astrocytic modulation of neuronal networks, impacting synaptic transmission and broader neural circuit functions. The IP3R2 knockout (IP3R2KO) mouse model has been instrumental in unraveling the nuances of astrocytic somatic Ca2+ dynamics and their implications for brain function. Despite early findings suggesting no significant behavioral or synaptic transmission changes in IP3R2KO mice, further research highlights the model's benefit in exploring cognitive, emotional, and neurodevelopmental processes. IP3R2KO mice revealed key insights into astrocytic Ca2+ signaling diversity, encompassing bulk somatic events and localized microdomain responses, which exhibit temporal and spatial variability. These animals retain alternative Ca2+ mechanisms, likely explaining the absence of severe phenotypes in some contexts. Nevertheless, IP3R2KO mice exhibit impairments in long-term memory retention, working memory, and fear memory, alongside age-related preservation of spatial memory, linking astrocytic IP3R2 signaling to higher-order cognitive functions. Additionally, studies suggest a connection between IP3R2 pathways and depression-like behaviors, with alterations in Brain-Derived Neurotrophic Factor (BDNF) levels and GABAergic signaling, highlighting its relevance to psychiatric conditions. Despite its limitations, such as residual astrocytic Ca2+ activity and inconsistent findings, the IP3R2KO model remains a valuable tool for studying astrocytic contributions to synaptic plasticity and brain function. This underscores the importance of integrating, rather than dismissing, the IP3R2KO model in the development of new methodologies for studying astrocytic Ca2+ dynamics. The use of this model will continue to elucidate the complex interplay between astrocytes and neuronal circuits, fostering advances in understanding astrocytic Ca2+ signaling's role in health and disease.

Microsecond pulsed electric fields induce myocardial ablation by secondary mitochondrial damage and cell death mechanisms

Microsecond pulsed electric field (µsPEF) is a newer treatment modality to replace catheter ablation treatment of Atrial fibrillation (AF) due to its fewer side effects. This study aims to find out experimental parameters that effectively induce cardiomyocyte death and the precise mechanisms for microsecond pulsed electric fields (µsPEFs) ablation of cardiomyocytes. CCK8 and flow apoptosis analysis were employed to examine the effects of different µsPEFs on cardiomyocytes in vitro. The mechanisms by which the µsPEFs ablation works were explored through a combination of transcriptome study, transmission electron microscope (TEM) observation of mitochondria, pathway enrichment analysis, and interaction network analysis. In vivo experiments on mice involving HE, Masson, TUNEL and Immunofluorescence staining examinations were conducted to confirm the in vitro experimental results. When more than 30 pulses were applied, a continuous decline in post-ablation relative cell activity was observed, decreasing from 0.36 at 3 h to 0.13 (p < 0.01) at 48 h. Notably, at a voltage of 1500 V/cm and a pulse count of 50, the apoptosis rate exceeded 95%, coupled with a more stable and consistent cell ablation. Following ablation, a notable upregulation in mitochondria-related transcription levels was observed, accompanied by mitochondrial membrane disruption and an increase in Cytochrome C levels. Within a certain range, an increase in voltage and number of electric pulses corresponded to a greater quantity of cell mortality in the ablation zone. The µsPEFs induced cell injury by impairing mitochondrial function and potentially triggering the mitochondrial apoptosis pathway.

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.

The Glutamate/GABA-Glutamine Cycle: Insights, Updates, and Advances

Synaptic homeostasis of the principal neurotransmitters glutamate and GABA is tightly regulated by an intricate metabolic coupling between neurons and astrocytes known as the glutamate/GABA-glutamine cycle. In this cycle, astrocytes take up glutamate and GABA from the synapse and convert these neurotransmitters into glutamine. Astrocytic glutamine is subsequently transferred to neurons, serving as the principal precursor for neuronal glutamate and GABA synthesis. The glutamate/GABA-glutamine cycle integrates multiple cellular processes, including neurotransmitter release, uptake, synthesis, and metabolism. All of these processes are deeply interdependent and closely coupled to cellular energy metabolism. Astrocytes display highly active mitochondrial oxidative metabolism and several unique metabolic features, including glycogen storage and pyruvate carboxylation, which are essential to sustain continuous glutamine release. However, new roles of oligodendrocytes and microglia in neurotransmitter recycling are emerging. Malfunction of the glutamate/GABA-glutamine cycle can lead to severe synaptic disruptions and may be implicated in several brain diseases. Here, I review central aspects and recent advances of the glutamate/GABA-glutamine cycle to highlight how the cycle is functionally connected to critical brain functions and metabolism. First, an overview of glutamate, GABA, and glutamine transport is provided in relation to neurotransmitter recycling. Then, central metabolic aspects of the glutamate/GABA-glutamine cycle are reviewed, with a special emphasis on the critical metabolic roles of glial cells. Finally, I discuss how aberrant neurotransmitter recycling is linked to neurodegeneration and disease, focusing on astrocyte metabolic dysfunction and brain lipid homeostasis as emerging pathological mechanisms. Instead of viewing the glutamate/GABA-glutamine cycle as individual biochemical processes, a more holistic and integrative approach is needed to advance our understanding of how neurotransmitter recycling modulates brain function in both health and disease.

FAST: Fast, Free, Consistent, and Unsupervised Oligodendrocyte Segmentation and Tracking System

To develop reparative therapies for neurological disorders like multiple sclerosis (MS), we need to better understand the physiology of loss and replacement of oligodendrocytes, the cells that make myelin and are the target of damage in MS. In vivo two-photon fluorescence microscopy allows direct visualization of oligodendrocytes in the intact brain of transgenic mouse models, promising a deeper understanding of the longitudinal dynamics of replacing oligodendrocytes after damage. However, the task of tracking the fate of individual oligodendrocytes requires extensive effort for manual annotation and is especially challenging in three-dimensional images. While several models exist for annotating cells in two-dimensional images, few models exist to annotate cells in three-dimensional images and even fewer are designed for tracking cells in longitudinal imaging. Notably, existing options often come with a substantial financial investment, being predominantly commercial or confined to proprietary software. Furthermore, the complexity of processes and myelin formed by individual oligodendrocytes can result in the failure of algorithms that are specifically designed for tracking cell bodies alone. Here, we propose a fast, free, consistent, and unsupervised beta-mixture oligodendrocyte segmentation system (FAST) that is written in open-source software, and can segment and track oligodendrocytes in three-dimensional images over time with minimal human input. We showed that the FAST model can segment and track oligodendrocytes similarly to a blinded human observer. Although FAST was developed to apply to our studies on oligodendrocytes, we anticipate that it can be modified to study four-dimensional in vivo data of any brain cell with associated complex processes.

Calcium-Dependent Signaling in Astrocytes: Downstream Mechanisms and Implications for Cognition

Astrocytes are glial cells recognized for their diverse roles in regulating brain circuit structure and function. They can sense and adapt to changes in the microenvironment due to their unique structural and biochemical properties. A key aspect of astrocytic function involves calcium (Ca2+)-dependent signaling, which serves as a fundamental mechanism for their interactions with neurons and other cells in the brain. However, while significant progress has been made in understanding the spatio-temporal properties of astrocytic Ca2+ signals, the downstream molecular pathways and exact mechanisms through which astrocytes decode these signals to regulate homeostatic and physiological processes remain poorly understood. To address this topic, we review here the available literature on the sources of intracellular Ca2+, as well as its downstream mechanisms and signaling pathways. We review the well-studied Ca2+-dependent exocytosis but draw attention to additional intracellular Ca2+-dependent mechanisms that are less understood and are, most likely, highly influential for many other cellular functions. Finally, we review how intracellular Ca2+ is thought to underlie neuron-astrocyte signaling in brain regions involved in cognitive processing.

Unveiling the functional connectivity of astrocytic networks with AstroNet, a graph reconstruction algorithm coupled to image processing

Astrocytes form extensive networks with diverse calcium activity, yet the organization and connectivity of these networks across brain regions remain largely unknown. To address this, we developed AstroNet, a data-driven algorithm that uses two-photon calcium imaging to map temporal correlations in astrocyte activation. By organizing individual astrocyte activation events chronologically, our method reconstructs functional networks and extracts local astrocyte correlations. We create a graph of the astrocyte network by tallying direct co-activations between pairs of cells along these activation pathways. Applied to the CA1 hippocampus and motor cortex, AstroNet reveals notable differences: astrocytes in the hippocampus display stronger connectivity, while cortical astrocytes form sparser networks. In both regions, smaller, tightly connected sub-networks are embedded within a larger, loosely connected structure. This method not only identifies astrocyte activation paths and connectivity but also reveals distinct, region-specific network patterns, providing new insights into the functional organization of astrocytic networks in the brain.

Cognitive disorders: Potential astrocyte-based mechanism

Cognitive disorders are a common clinical manifestation, including a deterioration in the patient's memory ability, attention, executive power, language, and other functions. The contributing factors of cognitive disorders are numerous and diverse in nature, including organic diseases and other mental disorders. Neurodegenerative diseases are a common type of organic disease related to the pathology of neuronal death and disruption of glial cell balance, ultimately accompanied with cognitive impairment. Thus, cognitive disorder frequently serves as an extremely critical indicator of neurodegenerative disorders. Cognitive impairments negatively affect patients' daily lives. However, our understanding of the precise pathogenic pathways of cognitive defects remains incomplete. The most prevalent kind of glial cells in the central nervous system are called astrocytes. They have a unique significance in cerebral function because of their wide range of functions in maintaining homeostasis in the central nervous system, regulating synaptic plasticity, and so on. Dysfunction of astrocytes is intimately linked to cognitive disorders, and we are attempting to understand this phenomenon predominantly from those perspectives: neuroinflammation, astrocytic senescence, connexin, Ca2 + signaling, mitochondrial dysfunction, and the glymphatic system.

Cellular component transfer between photoreceptor cells of the retina

Photoreceptor transplantation is a potential therapeutic strategy for degenerative retinal diseases. Studies on mechanisms contributing to retinal regeneration and vision repair identified cellular components transfer (CCT) as playing a role, in addition to somatic augmentation (referred to as "cell replacement" in this paper). In CCT, donor photoreceptors shuttle proteins, RNA, and mitochondria to host photoreceptors through intercellular connections. The discovery of CCT in the transplantation context triggered a re-interpretation of prior transplantation studies that generally did not include specific CCT assays and thereby broadly emphasized the cell replacement model, reflecting the prevailing understanding of retinal transplantation biology at that time. In addition to clarifying our understanding of photoreceptor biology, CCT has raised the possibility of developing treatments to replenish molecular deficiencies in diseased photoreceptor cells. As the CCT field evolves, investigators have used diverse terminology, and implemented different CCT assays following transplantation in animal models. The non-standardized terminology of CCT and absent minimal assay standards for detection can hinder communication between investigators and comparison between studies. In this review, we discuss the current understanding of CCT, provide an overview of transplantation and regeneration studies in small and large animals, and propose terminology and a minimal assay standard for CCT. Further research on CCT may eventually provide new avenues to treat a range of hereditary and acquired retinopathies while illuminating mechanisms of cell-cell interaction in the retina.

Animal-based approaches to understanding neuroglia physiology in vitro and in vivo

This chapter describes the pivotal role of animal models for unraveling the physiology of neuroglial cells in the central nervous system (CNS). The two rodent species Mus musculus (mice) and Rattus norvegicus (rats) have been indispensable in scientific research due to their remarkable resemblance to humans anatomically, physiologically, and genetically. Their ease of maintenance, short gestation times, and rapid development make them ideal candidates for studying the physiology of astrocytes, oligodendrocyte-lineage cells, and microglia. Moreover, their genetic similarity to humans facilitates the investigation of molecular mechanisms governing neural physiology. Mice are largely the predominant model of neuroglial research, owing to advanced genetic manipulation techniques, whereas rats remain invaluable for applications requiring larger CNS structures for surgical manipulations. Next to rodents, other animal models, namely, Danio rerio (zebrafish) and Drosophila melanogaster (fruit fly), will be discussed to emphasize their critical role in advancing our understanding of glial physiology. Each animal model provides distinct advantages and disadvantages. By combining the strengths of each of them, researchers can gain comprehensive insights into glial function across species, ultimately promoting the understanding of glial physiology in the human CNS and driving the development of novel therapeutic interventions for CNS disorders.

Characterization of the Astrocyte Calcium Response to Norepinephrine in the Ventral Tegmental Area

Astrocytes from different brain regions respond with Ca2+ elevations to the catecholamine norepinephrine (NE). However, whether this noradrenergic-mediated signaling is present in astrocytes from the ventral tegmental area (VTA), a dopaminergic circuit receiving noradrenergic inputs, has not yet been investigated. To fill in this gap, we applied a pharmacological approach along with two-photon microscopy and an AAV strategy to express a genetically encoded calcium indicator in VTA astrocytes. We found that VTA astrocytes from both female and male young adult mice showed a strong Ca2+ response to NE at both soma and processes. Our results revealed that Gq-coupled α1 adrenergic receptors, which elicit the production of IP3, are the main mediators of the astrocyte response. In mice lacking the IP3 receptor type-2 (IP3R2-/- mice), we found that the astrocyte response to NE, even if reduced, is still present. We also found that in IP3R2-/- astrocytes, the residual Ca2+ elevations elicited by NE depend on the release of Ca2+ from the endoplasmic reticulum, through IP3Rs different from IP3R2. In conclusion, our results reveal VTA astrocytes as novel targets of the noradrenergic signaling, opening to new interpretations of the cellular and molecular mechanisms that mediate the NE effects in the VTA.

A spatial threshold for astrocyte calcium surge

Astrocytes are active cells involved in brain function through the bidirectional communication with neurons, in which astrocyte calcium plays a crucial role. Synaptically evoked calcium increases can be localized to independent subcellular domains or expand to the entire cell, i.e., calcium surge. Because a single astrocyte may contact ~100,000 synapses, the control of the intracellular calcium signal propagation may have relevant consequences on brain function. Yet, the properties governing the spatial dynamics of astrocyte calcium remains poorly defined. Imaging subcellular responses of cortical astrocytes to sensory stimulation in mice, we show that sensory-evoked astrocyte calcium responses originated and remained localized in domains of the astrocytic arborization, but eventually propagated to the entire cell if a spatial threshold of >23% of the arborization being activated was surpassed. Using Itpr2-/- mice, we found that type-2 IP3 receptors were necessary for the generation of astrocyte calcium surge. We finally show using in situ electrophysiological recordings that the spatial threshold of the astrocyte calcium signal consequently determined the gliotransmitter release. Present results reveal a fundamental property of astrocyte physiology, i.e., a spatial threshold for astrocyte calcium propagation, which depends on astrocyte intrinsic properties and governs astrocyte integration of local synaptic activity and subsequent neuromodulation.

Membrane Associated RNA-Containing Vesicles Regulate Cortical Astrocytic Microdomain Calcium Transients in Awake Ischemic Stroke Mice

Astrocytic processes minutely regulate neuronal activity via tripartite synaptic structures. The precision-tuning of the function of astrocytic processes is garnering increasing attention because of its significance in promoting brain repair following ischemic stroke. Microdomain calcium (Ca2+) transients in astrocytic processes are pivotal for the functional regulation of these processes. However, the understanding of the alterations and regulatory mechanism of microdomain Ca2+ transients during stroke remains limited. In the present study, a fast high-resolution, miniaturized two-photon microscopy is used to show that the levels of astrocytic microdomain Ca2+ transients are significantly reduced in the peri-infarct area of awake ischemic stroke mice. This finding correlated with the behavioral deficits shown by these mice under freely-moving conditions. Mitochondrial Ca2+ activity is an important factor driving the microdomain Ca2+ transients. DEAD Box 1 (DDX1) bound to circSCMH1 (a circular RNA involved in vascular post-stroke repair) facilitates the formation of membrane-associated RNA-containing vesicles (MARVs) and enhances the activity of astrocytic microdomain Ca2+ transients, thereby promoting behavioral recovery. These results show that targeting astrocytic microdomain Ca2+ transients is a potential therapeutic approach in stroke intervention.

Revisiting astrocytic calcium signaling in the brain

Astrocytes, characterized by complex spongiform morphology, participate in various physiological processes, and abnormal changes in their calcium (Ca2+) signaling are implicated in central nervous system disorders. However, medications targeting the control of Ca2+ have fallen short of the anticipated therapeutic outcomes in clinical applications. This underscores the fact that our comprehension of this intricate regulation of calcium ions remains considerably incomplete. In recent years, with the advancement of Ca2+ labeling, imaging, and analysis techniques, Ca2+ signals have been found to exhibit high specificity at different spatial locations within the intricate structure of astrocytes. This has ushered the study of Ca2+ signaling in astrocytes into a new phase, leading to several groundbreaking research achievements. Despite this, the comprehensive understanding of astrocytic Ca2+ signaling and their implications remains challenging area for future research.

Structural and molecular characterization of astrocyte and vasculature connectivity in the mouse hippocampus and cortex

The relation of astrocytic endfeet to the vasculature plays a key functional role in the neuro-glia-vasculature unit. We characterize the spatial organization of astrocytes and the structural aspects that facilitate their involvement in molecular exchanges. Using double transgenic mice, we performed co-immunostaining, confocal microscopy, and three-dimensional digital segmentation to investigate the biophysical and molecular organization of astrocytes and their intricate endfoot network at the micrometer level in the isocortex and hippocampus. The results showed that hippocampal astrocytes had smaller territories, reduced endfoot dimensions, and fewer contacts with blood vessels compared with those in the isocortex. Additionally, we found that both connexins 43 and 30 have a higher density in the endfoot and the former is overexpressed relative to the latter. However, due to the limitations of the method, further studies are needed to determine the exact localization on the endfoot. The quantitative information obtained in this study will be useful for modeling the interactions of astrocytes with the vasculature.

Deep-Learning-Based Segmentation of Cells and Analysis (DL-SCAN)

With the recent surge in the development of highly selective probes, fluorescence microscopy has become one of the most widely used approaches to studying cellular properties and signaling in living cells and tissues. Traditionally, microscopy image analysis heavily relies on manufacturer-supplied software, which often demands extensive training and lacks automation capabilities for handling diverse datasets. A critical challenge arises if the fluorophores employed exhibit low brightness and a low signal-to-noise ratio (SNR). Consequently, manual intervention may become a necessity, introducing variability in the analysis outcomes even for identical samples when analyzed by different users. This leads to the incorporation of blinded analysis, which ensures that the outcome is free from user bias to a certain extent but is extremely time-consuming. To overcome these issues, we developed a tool called DL-SCAN that automatically segments and analyzes fluorophore-stained regions of interest such as cell bodies in fluorescence microscopy images using deep learning. We demonstrate the program's ability to automate cell identification and study cellular ion dynamics using synthetic image stacks with varying SNR. This is followed by its application to experimental Na+ and Ca2+ imaging data from neurons and astrocytes in mouse brain tissue slices exposed to transient chemical ischemia. The results from DL-SCAN are consistent, reproducible, and free from user bias, allowing efficient and rapid analysis of experimental data in an objective manner. The open-source nature of the tool also provides room for modification and extension to analyze other forms of microscopy images specific to the dynamics of different ions in other cell types.

Mitochondrial fission controls astrocyte morphogenesis and organization in the cortex

Dysfunctional mitochondrial dynamics are a hallmark of devastating neurodevelopmental disorders such as childhood refractory epilepsy. However, the role of glial mitochondria in proper brain development is not well understood. We show that astrocyte mitochondria undergo extensive fission while populating astrocyte distal branches during postnatal cortical development. Loss of mitochondrial fission regulator, Dynamin-related protein 1 (Drp1), decreases mitochondrial localization to distal astrocyte processes, and this mitochondrial mislocalization reduces astrocyte morphological complexity. Functionally, astrocyte-specific conditional deletion of Drp1 induces astrocyte reactivity and disrupts astrocyte organization in the cortex. These morphological and organizational deficits are accompanied by loss of astrocytic gap junction protein Connexin 43. These findings uncover a crucial role for mitochondrial fission in coordinating astrocytic morphogenesis and organization, revealing the regulation of astrocytic mitochondria dynamics as a critical step in neurodevelopment.

Multifunctional mesoporous nanoselenium delivery of metformin breaks the vicious cycle of neuroinflammation and ROS, promotes microglia regulation and alleviates Alzheimer's disease

Clinical trials based on a single molecular target continue to fail, and the adverse effects of Aβ protein aggregation and neuroinflammation need to be solved and treatment of Alzheimer's disease. Herein, by designed a nano-sized flower mesoporous selenium transport carrier (Met@MSe@Tf) with high enzyme-like activity, metformin (Met) was loaded, and transferrin (Tf) was modified to bind to transferrin receptor to promote receptor-mediated transport across the BBB. In the AD lesion environment, with the acidic environment response dissociation, promote the release of metformin by nanoflower to achieve therapeutic effect in the brain lesion site. Metformin, a major anti-diabetic drug in diabetic metabolism, has been found to be a promising new therapeutic target in neurodegenerative diseases. Further studies showed that the metformin drug release from the designed and synthesized transport nanoparticles showed high intrinsic activity and the ability to degrade the substrate involved, especially the degradation of Aβ deposition in the cortex and hippocampus, increased the phagocytosis of microglia, thus relieving neuroinflammation simultaneously. Collectively, in vivo experiments demonstrated that Met@MSe@Tf significantly increased the number of NeuN-positive neurons in the hippocampus of AD mice, promoted neurovascular normalization in the brain, and improved cognitive dysfunction in AD transgenic AD mice. Thus, it provides a preclinical proof of concept for the construction of a highly modular accurate drug delivery platform for Alzheimer's disease.

The Role of Mitochondrial Permeability Transition in Bone Metabolism, Bone Healing, and Bone Diseases

Bone is a dynamic organ with an active metabolism and high sensitivity to mitochondrial dysfunction. The mitochondrial permeability transition pore (mPTP) is a low-selectivity channel situated in the inner mitochondrial membrane (IMM), permitting the exchange of molecules of up to 1.5 kDa in and out of the IMM. Recent studies have highlighted the critical role of the mPTP in bone tissue, but there is currently a lack of reviews concerning this topic. This review discusses the structure and function of the mPTP and its impact on bone-related cells and bone-related pathological states. The mPTP activity is reduced during the osteogenic differentiation of mesenchymal stem cells (MSCs), while its desensitisation may underlie the mechanism of enhanced resistance to apoptosis in neoplastic osteoblastic cells. mPTP over-opening triggers mitochondrial swelling, regulated cell death, and inflammatory response. In particular, mPTP over-opening is involved in dexamethasone-induced osteoblast dysfunction and bisphosphonate-induced osteoclast apoptosis. In vivo, the mPTP plays a significant role in maintaining bone homeostasis, with many bone disorders linked to its excessive opening. Genetic deletion or pharmacological inhibition of the over-opening of mPTP has shown potential in enhancing bone injury recovery and alleviating bone diseases. Here, we review the findings on the relationship of the mPTP and bone at both the cellular and disease levels, highlighting novel avenues for pharmacological approaches targeting mitochondrial function to promote bone healing and manage bone-related disorders.

A pathogenic mutation in the ALS/FTD gene VCP induces mitochondrial hypermetabolism by modulating the permeability transition pore

Valosin-containing protein (VCP) is a ubiquitously expressed type II AAA+ ATPase protein, implicated in both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). This study aimed to explore the impact of the disease-causing VCPR191Q/wt mutation on mitochondrial function using a CRISPR/Cas9-engineered neuroblastoma cell line. Mitochondria in these cells are enlarged, with a depolarized mitochondrial membrane potential associated with increased respiration and electron transport chain activity. Our results indicate that mitochondrial hypermetabolism could be caused, at least partially, by increased calcium-induced opening of the permeability transition pore (mPTP), leading to mild mitochondrial uncoupling. In conclusion, our findings reveal a central role of the ALS/FTD gene VCP in maintaining mitochondrial homeostasis and suggest a model of pathogenesis based on progressive alterations in mPTP physiology and mitochondrial energetics.

Astrocyte Calcium Signaling

Astrocytes are predominant glial cells that tile the central nervous system and participate in well-established functional and morphological interactions with neurons, blood vessels, and other glia. These ubiquitous cells display rich intracellular Ca2+ signaling, which has now been studied for over 30 years. In this review, we provide a summary and perspective of recent progress concerning the study of astrocyte intracellular Ca2+ signaling as well as discussion of its potential functions. Progress has occurred in the areas of imaging, silencing, activating, and analyzing astrocyte Ca2+ signals. These insights have collectively permitted exploration of the relationships of astrocyte Ca2+ signals to neural circuit function and behavior in a variety of species. We summarize these aspects along with a framework for mechanistically interpreting behavioral studies to identify directly causal effects. We finish by providing a perspective on new avenues of research concerning astrocyte Ca2+ signaling.

Nuclear GAPDH in cortical microglia mediates cellular stress-induced cognitive inflexibility

We report a mechanism that underlies stress-induced cognitive inflexibility at the molecular level. In a mouse model under subacute cellular stress in which deficits in rule shifting tasks were elicited, the nuclear glyceraldehyde dehydrogenase (N-GAPDH) cascade was activated specifically in microglia in the prelimbic cortex. The cognitive deficits were normalized with a pharmacological intervention with a compound (the RR compound) that selectively blocked the initiation of N-GAPDH cascade without affecting glycolytic activity. The normalization was also observed with a microglia-specific genetic intervention targeting the N-GAPDH cascade. At the mechanistic levels, the microglial secretion of High-Mobility Group Box (HMGB), which is known to bind with and regulate the NMDA-type glutamate receptors, was elevated. Consequently, the hyperactivation of the prelimbic layer 5 excitatory neurons, a neural substrate for cognitive inflexibility, was also observed. The upregulation of the microglial HMGB signaling and neuronal hyperactivation were normalized by the pharmacological and microglia-specific genetic interventions. Taken together, we show a pivotal role of cortical microglia and microglia-neuron interaction in stress-induced cognitive inflexibility. We underscore the N-GAPDH cascade in microglia, which causally mediates stress-induced cognitive alteration.

STARDUST: A pipeline for the unbiased analysis of astrocyte regional calcium dynamics

Calcium imaging has become a popular way to probe astrocyte activity, but few techniques holistically capture discrete calcium signals occurring across the astrocyte domain. Here, we introduce STARDUST, a pipeline for the spatio-temporal analysis of regional dynamics and unbiased sorting of transients from fluorescence recordings of astrocytes. We describe steps for installing software, detecting active pixel patches, obtaining region of activity (ROA) maps, and extracting time series from ROAs. We then detail procedures for extracting signal features using custom-made code.

Metabolic Reprogramming of Astrocytes in Pathological Conditions: Implications for Neurodegenerative Diseases

Astrocytes play a pivotal role in maintaining brain energy homeostasis, supporting neuronal function through glycolysis and lipid metabolism. This review explores the metabolic intricacies of astrocytes in both physiological and pathological conditions, highlighting their adaptive plasticity and diverse functions. Under normal conditions, astrocytes modulate synaptic activity, recycle neurotransmitters, and maintain the blood-brain barrier, ensuring a balanced energy supply and protection against oxidative stress. However, in response to central nervous system pathologies such as neurotrauma, stroke, infections, and neurodegenerative diseases like Alzheimer's and Huntington's disease, astrocytes undergo significant morphological, molecular, and metabolic changes. Reactive astrocytes upregulate glycolysis and fatty acid oxidation to meet increased energy demands, which can be protective in acute settings but may exacerbate chronic inflammation and disease progression. This review emphasizes the need for advanced molecular, genetic, and physiological tools to further understand astrocyte heterogeneity and their metabolic reprogramming in disease states.

Mitochondrial network reorganization and transient expansion during oligodendrocyte generation

Oligodendrocyte precursor cells (OPCs) give rise to myelinating oligodendrocytes of the brain. This process persists throughout life and is essential for recovery from neurodegeneration. To better understand the cellular checkpoints that occur during oligodendrogenesis, we determined the mitochondrial distribution and morphometrics across the oligodendrocyte lineage in mouse and human cerebral cortex. During oligodendrocyte generation, mitochondrial content expands concurrently with a change in subcellular partitioning towards the distal processes. These changes are followed by an abrupt loss of mitochondria in the oligodendrocyte processes and myelin, coinciding with sheath compaction. This reorganization and extensive expansion and depletion take 3 days. Oligodendrocyte mitochondria are stationary over days while OPC mitochondrial motility is modulated by animal arousal state within minutes. Aged OPCs also display decreased mitochondrial size, volume fraction, and motility. Thus, mitochondrial dynamics are linked to oligodendrocyte generation, dynamically modified by their local microenvironment, and altered in the aging brain.

Spontaneous calcium transients in hair cell stereocilia

The hair bundle of auditory and vestibular hair cells converts mechanical stimuli into electrical signals through mechanoelectrical transduction (MET). The MET apparatus is built around a tip link that connects neighboring stereocilia that are aligned in the direction of mechanosensitivity of the hair bundle. Upon stimulation, the MET channel complex responds to changes in tip-link tension and allows a cation influx into the cell. Ca2+ influx in stereocilia has been used as a signature of MET activity. Using genetically encoded Ca2+ sensors (GCaMP3, GCaMP6s) and high-performance fluorescence confocal microscopy, we detect spontaneous Ca2+ transients in individual stereocilia in developing and fully formed hair bundles. We demonstrate that this activity is abolished by MET channel blockers and thus likely originates from putative MET channels. We observe Ca2+ transients in the stereocilia of mice in tissue explants as well as in vivo in zebrafish hair cells, indicating this activity is functionally conserved. Within stereocilia, the origin of Ca2+ transients is not limited to the canonical MET site at the stereocilia tip but is also present along the stereocilia length. Remarkably, we also observe these Ca2+ transients in the microvilli-like structures on the hair cell surface in the early stages of bundle development, prior to the onset of MET. Ca2+ transients are also present in the tallest rows of stereocilia in auditory hair cells, structures not traditionally thought to contain MET channels. We hypothesize that this newly described activity may reflect stochastic and spontaneous MET channel opening. Localization of these transients to other regions of the stereocilia indicates the presence of a pool of channels or channel precursors. Our work provides insights into MET channel assembly, maturation, function, and turnover.

A spatial threshold for astrocyte calcium surge

Astrocytes are active cells involved in brain function through the bidirectional communication with neurons, in which the astrocyte calcium signal plays a crucial role. Synaptically-evoked calcium increases can be localized to independent subcellular domains or expand to the entire cell, i.e., calcium surge. In turn, astrocytes may regulate individual synapses by calcium-dependent release of gliotransmitters. Because a single astrocyte may contact ∼100,000 synapses, the control of the intracellular calcium signal propagation may have relevant consequences on brain function by regulating the spatial range of astrocyte neuromodulation of synapses. Yet, the properties governing the spatial dynamics of the astrocyte calcium signal remains poorly defined. Imaging subcellular responses of cortical astrocytes to sensory stimulation in mice, we show that sensory-evoked astrocyte calcium responses originated and remained localized in domains of the astrocytic arborization, but eventually propagated to the entire cell if a spatial threshold of >23% of the arborization being activated was surpassed. Using transgenic IP 3 R2 -/- mice, we found that type-2 IP 3 receptors were necessary for the generation of the astrocyte calcium surge. We finally show using in situ electrophysiological recordings that the spatial threshold of the astrocyte calcium signal consequently determined the gliotransmitter release. Present results reveal a fundamental property of astrocyte calcium physiology, i.e., a spatial threshold for the astrocyte intracellular calcium signal propagation, which depends on astrocyte intrinsic properties and governs the astrocyte integration of local synaptic activity and the subsequent neuromodulation.

One-Sentence Summary

There is a spatial threshold for the astrocyte intracellular calcium signal propagation that is determined by astrocyte intrinsic properties and controls gliotransmission.

Astrocyte switch to the hyperactive mode

Increasing pieces of evidence have suggested that astrocyte function has a strong influence on neuronal activity and plasticity, both in physiological and pathophysiological situations. In epilepsy, astrocytes have been shown to respond to epileptic neuronal seizures; however, whether they can act as a trigger for seizures has not been determined. Here, using the copper implantation method, spontaneous neuronal hyperactivity episodes were reliably induced during the week following implantation. With near 24-h continuous recording for over 1 week of the local field potential with in vivo electrophysiology and astrocyte cytosolic Ca2+ with the fiber photometry method, spontaneous occurrences of seizure episodes were captured. Approximately 1 day after the implantation, isolated aberrant astrocyte Ca2+ events were often observed before they were accompanied by neuronal hyperactivity, suggesting the role of astrocytes in epileptogenesis. Within a single developed episode, astrocyte Ca2+ increase preceded the neuronal hyperactivity by ~20 s, suggesting that actions originating from astrocytes could be the trigger for the occurrence of epileptic seizures. Astrocyte-specific stimulation by channelrhodopsin-2 or deep-brain direct current stimulation was capable of inducing neuronal hyperactivity. Injection of an astrocyte-specific metabolic inhibitor, fluorocitrate, was able to significantly reduce the magnitude of spontaneously occurring neuronal hyperactivity. These results suggest that astrocytes have a role in triggering individual seizures and the reciprocal astrocyte-neuron interactions likely amplify and exacerbate seizures. Therefore, future epilepsy treatment could be targeted at astrocytes to achieve epilepsy control.

Drp1 and neuroinflammation: Deciphering the interplay between mitochondrial dynamics imbalance and inflammation in neurodegenerative diseases

Neuroinflammation and mitochondrial dysfunction are closely intertwined with the pathophysiology of neurological disorders. Recent studies have elucidated profound alterations in mitochondrial dynamics across a spectrum of neurological disorders. Dynamin-related protein 1 (DRP1) emerges as a pivotal regulator of mitochondrial fission, with its dysregulation disrupting mitochondrial homeostasis and fueling neuroinflammation, thereby exacerbating disease severity. In addition to its role in mitochondrial dynamics, DRP1 plays a crucial role in modulating inflammation-related pathways. This review synthesizes important functions of DRP1 in the central nervous system (CNS) and the impact of epigenetic modification on the progression of neurodegenerative diseases. The intricate interplay between neuroinflammation and DRP1 in microglia and astrocytes, central contributors to neuroinflammation, is expounded upon. Furthermore, the use of DRP1 inhibitors to influence the activation of microglia and astrocytes, as well as their involvement in processes such as mitophagy, mitochondrial oxidative stress, and calcium ion transport in CNS-mediated neuroinflammation, is scrutinized. The modulation of microglia to astrocyte crosstalk by DRP1 and its role in inflammatory neurodegeneration is also highlighted. Overall, targeting DRP1 presents a promising avenue for ameliorating neuroinflammation and enhancing the therapeutic management of neurological disorders.

Astrocyte morphology

Astrocytes are predominant glial cells that tile the central nervous system (CNS). A cardinal feature of astrocytes is their complex and visually enchanting morphology, referred to as bushy, spongy, and star-like. A central precept of this review is that such complex morphological shapes evolved to allow astrocytes to contact and signal with diverse cells at a range of distances in order to sample, regulate, and contribute to the extracellular milieu, and thus participate widely in cell-cell signaling during physiology and disease. The recent use of improved imaging methods and cell-specific molecular evaluations has revealed new information on the structural organization and molecular underpinnings of astrocyte morphology, the mechanisms of astrocyte morphogenesis, and the contributions to disease states of reduced morphology. These insights have reignited interest in astrocyte morphological complexity as a cornerstone of fundamental glial biology and as a critical substrate for multicellular spatial and physiological interactions in the CNS.

Pharmacological mechanism of natural antidepressants: The role of mitochondrial quality control

BACKGROUND

Depression is a mental illness characterized by persistent sadness and a reduced capacity for pleasure. In clinical practice, SSRIs and other medications are commonly used for therapy, despite their various side effects. Natural products present distinct advantages, including synergistic interactions among multiple components and targeting multiple pathways, suggesting their tremendous potential in depression treatment. Imbalance in mitochondrial quality control (MQC) plays a significant role in the pathology of depression, emphasizing the importance of regulating MQC as a potential intervention strategy in addressing the onset and progression of depression. However, the role and mechanism through which natural products regulate MQC in depression treatments still need to be comprehensively elucidated, particularly in clinical and preclinical settings.

PURPOSE

This review was aimed to summarize the findings of recent studies and outline the pharmacological mechanisms by which natural products modulate MQC to exert antidepressant effects. Additionally, it evaluated current research limitations and proposed new strategies for future preclinical and clinical applications in the depression domain.

METHODS

To study the main pharmacological mechanisms underlying the regulation of MQC by natural products in the treatment of depression, we conducted a thorough search across databases such as PubMed, Web of Science, and ScienceDirect databases to classify and summarize the relationship between MQC and depression, as well as the regulatory mechanisms of natural products.

RESULTS

Numerous studies have shown that irregularities in the MQC system play an important role in the pathology of depression, and the regulation of the MQC system is involved in antidepressant treatments. Natural products mainly regulate the MQC system to induce antidepressant effects by alleviating oxidative stress, balancing ATP levels, promoting mitophagy, maintaining calcium homeostasis, optimizing mitochondrial dynamics, regulating mitochondrial membrane potential, and enhancing mitochondrial biogenesis.

CONCLUSIONS

We comprehensively summarized the regulation of natural products on the MQC system in antidepressants, providing a unique perspective for the application of natural products within antidepressant therapy. However, extensive efforts are imperative in clinical and preclinical investigations to delve deeper into the mechanisms underlying how antidepressant medications impact MQC, which is crucial for the development of effective antidepressant treatments.

STARDUST: a pipeline for the unbiased analysis of astrocyte regional calcium dynamics

Calcium imaging has become a popular way to probe astrocyte activity, but few analysis methods holistically capture discrete calcium signals that occur across the astrocyte domain. Here, we introduce STARDUST, a pipeline for the Spatio-Temporal Analysis of Regional Dynamics & Unbiased Sorting of Transients from fluorescence recordings of astrocytes, and provide step-by-step guidelines. STARDUST yields fluorescence time-series from data-defined regions of activity and performs systematic signal detection and feature extraction, enabling the in-depth and unbiased study of astrocyte calcium signals.

Fast, Accurate, and Versatile Data Analysis Platform for the Quantification of Molecular Spatiotemporal Signals

Optical recording of intricate molecular dynamics is becoming an indispensable technique for biological studies, accelerated by the development of new or improved biosensors and microscopy technology. This creates major computational challenges to extract and quantify biologically meaningful spatiotemporal patterns embedded within complex and rich data sources, many of which cannot be captured with existing methods. Here, we introduce Activity Quantification and Analysis (AQuA2), a fast, accurate, and versatile data analysis platform built upon advanced machine learning techniques. It decomposes complex live imaging-based datasets into elementary signaling events, allowing accurate and unbiased quantification of molecular activities and identification of consensus functional units. We demonstrate applications across a wide range of biosensors, cell types, organs, animal models, and imaging modalities. As exemplar findings, we show how AQuA2 identified drug-dependent interactions between neurons and astroglia, and distinct sensorimotor signal propagation patterns in the mouse spinal cord.

Targeting Reactive Astrocytes in Vascular Dementia: Investigation of Neuronal-Astrocyte-Vascular Interactions

Historically known as neuronal support cells, astrocytes are now widely studied for their close structural and functional interactions with multiple neural cell types and cerebral vessels where they maintain an ideal environment for optimized brain function. Under pathological conditions, astrocytes become reactive and lose key protective functions. In this commentary, we discuss our recent work in The Journal of Neuroscience (Sompol et al., 2023) that showed Ca2+ dysregulation in reactive astrocytes, as well as hyperactivation of the Ca2+-dependent protein phosphatase calcineurin (CN) and the Nuclear Factor of Activated T Cells (NFATs), in a diet-induced hyperhomocystienemia (HHcy) mouse model of Vascular Contributions to Cognitive Impairment and Dementia (VCID). Intravital multiphoton imaging coupled with whisker stimulation was used to explore astrocyte Ca2+ signaling and neurovascular function under active phase, fully awake conditions. Interestingly, evoked Ca2+ transients in individual astrocytes were greater, even though intercorrelated Ca2+ signaling across networks of astrocytes was impaired in HHcy mice. Blockade of astrocytic CN/NFAT reduced signs of astrocyte reactivity, normalized cerebrovascular function, and improved hippocampal synaptic strength and hippocampal dependent cognition in HHcy mice, revealing a previously unrecognized deficit regarding neuron-astrocyte-vascular interactions. These findings strongly support the use of astrocyte targeting strategies to mitigate pathophysiological changes associated with VCID and other Alzheimer's-related dementias.

Astrocyte mitochondria: Potential therapeutic targets for epilepsy

Epilepsy is a chronic, relapsing neurological disorder, and current treatments focus primarily on neurons, yet one-third of patients still develop drug-resistant epilepsy. Therefore, there is an urgent need to explore new therapeutic targets. Interestingly, astrocytes can transfer their healthy mitochondria into neighboring neurons, thus preventing neuronal damage. Astrocyte mitochondria have been shown to have a therapeutic role in stroke and neurodegenerative diseases. However, their therapeutic effect in epilepsy and its related mechanisms have been less studied. In this review, we mainly summarize the regulatory role of astrocyte mitochondria in glutamate, calcium ion, and adenosine triphosphate (ATP) homeostasis and outline the protective role of astrocyte mitochondria in nervous system diseases, revealing a new target for epilepsy treatment.

Astrocyte ryanodine receptors facilitate gliotransmission and astroglial modulation of synaptic plasticity

Intracellular Ca2+-signaling in astrocytes is instrumental for their brain "housekeeping" role and astroglial control of synaptic plasticity. An important source for elevating the cytosolic Ca2+ level in astrocytes is a release from endoplasmic reticulum which can be triggered via two fundamental pathways: IP3 receptors and calcium-induced calcium release (CICR) mediated by Ca2+-sensitive ryanodine receptors (RyRs). While the physiological role for glial IP3 became a focus of intensive research and debate, ryanodine receptors received much less attention. We explored the role for ryanodine receptors in the modulation of cytosolic Ca2+-signaling in the cortical and hippocampal astrocytes, astrocyte-neuron communication and astroglia modulation of synaptic plasticity. Our data show that RyR-mediated Ca2+-induced Ca2+-release from ER brings substantial contribution into signaling in the functional microdomains hippocampal and neocortical astrocytes. Furthermore, RyR-mediated CICR activated the release of ATP and glutamate from hippocampal and neocortical astrocytes which, in turn, elicited transient purinergic and tonic glutamatergic currents in the neighboring pyramidal neurons. The CICR-facilitated release of ATP and glutamate was inhibited after intracellular perfusion of astrocytes with ryanodine and BAPTA and in the transgenic dnSNARE mice with impaired astroglial exocytosis. We also found out that RyR-mediated amplification of astrocytic Ca2+-signaling enhanced the long-term synaptic potentiation in the hippocampus and neocortex of aged mice. Combined, our data demonstrate that ryanodine receptors are essential for astrocytic Ca2+-signaling and efficient astrocyte-neuron communications. The RyR-mediated CICR contributes to astrocytic control of synaptic plasticity and can underlie, at least partially, neuroprotective and cognitive effects of caffein.

Brain energy metabolism: A roadmap for future research

Although we have learned much about how the brain fuels its functions over the last decades, there remains much still to discover in an organ that is so complex. This article lays out major gaps in our knowledge of interrelationships between brain metabolism and brain function, including biochemical, cellular, and subcellular aspects of functional metabolism and its imaging in adult brain, as well as during development, aging, and disease. The focus is on unknowns in metabolism of major brain substrates and associated transporters, the roles of insulin and of lipid droplets, the emerging role of metabolism in microglia, mysteries about the major brain cofactor and signaling molecule NAD+, as well as unsolved problems underlying brain metabolism in pathologies such as traumatic brain injury, epilepsy, and metabolic downregulation during hibernation. It describes our current level of understanding of these facets of brain energy metabolism as well as a roadmap for future research.

Centripetal integration of past events in hippocampal astrocytes regulated by locus coeruleus

An essential feature of neurons is their ability to centrally integrate information from their dendrites. The activity of astrocytes, in contrast, has been described as mostly uncoordinated across cellular compartments without clear central integration. Here we report conditional integration of calcium signals in astrocytic distal processes at their soma. In the hippocampus of adult mice of both sexes, we found that global astrocytic activity, as recorded with population calcium imaging, reflected past neuronal and behavioral events on a timescale of seconds. Salient past events, indicated by pupil dilations, facilitated the propagation of calcium signals from distal processes to the soma. Centripetal propagation to the soma was reproduced by optogenetic activation of the locus coeruleus, a key regulator of arousal, and reduced by pharmacological inhibition of α1-adrenergic receptors. Together, our results suggest that astrocytes are computational units of the brain that slowly and conditionally integrate calcium signals upon behaviorally relevant events.

Mitochondrial calcium uniporter channel gatekeeping in cardiovascular disease

The mitochondrial calcium (mCa2+) uniporter channel (mtCU) resides at the inner mitochondrial membrane and is required for Ca2+ to enter the mitochondrial matrix. The mtCU is essential for cellular function, as mCa2+ regulates metabolism, bioenergetics, signaling pathways and cell death. mCa2+ uptake is primarily regulated by the MICU family (MICU1, MICU2, MICU3), EF-hand-containing Ca2+-sensing proteins, which respond to cytosolic Ca2+ concentrations to modulate mtCU activity. Considering that mitochondrial function and Ca2+ signaling are ubiquitously disrupted in cardiovascular disease, mtCU function has been a hot area of investigation for the last decade. Here we provide an in-depth review of MICU-mediated regulation of mtCU structure and function, as well as potential mtCU-independent functions of these proteins. We detail their role in cardiac physiology and cardiovascular disease by highlighting the phenotypes of different mutant animal models, with an emphasis on therapeutic potential and targets of interest in this pathway.

Lactate as a supplemental fuel for synaptic transmission and neuronal network oscillations: Potentials and limitations

Lactate shuttled from the blood circulation, astrocytes, oligodendrocytes or even activated microglia (resident macrophages) to neurons has been hypothesized to represent a major source of pyruvate compared to what is normally produced endogenously by neuronal glucose metabolism. However, the role of lactate oxidation in fueling neuronal signaling associated with complex cortex function, such as perception, motor activity, and memory formation, is widely unclear. This issue has been experimentally addressed using electrophysiology in hippocampal slice preparations (ex vivo) that permit the induction of different neural network activation states by electrical stimulation, optogenetic tools or receptor ligand application. Collectively, these studies suggest that lactate in the absence of glucose (lactate only) impairs gamma (30-70 Hz) and theta-gamma oscillations, which feature high energy demand revealed by the cerebral metabolic rate of oxygen (CMRO2, set to 100%). The impairment comprises oscillation attenuation or moderate neural bursts (excitation-inhibition imbalance). The bursting is suppressed by elevating the glucose fraction in energy substrate supply. By contrast, lactate can retain certain electric stimulus-induced neural population responses and intermittent sharp wave-ripple activity that features lower energy expenditure (CMRO2 of about 65%). Lactate utilization increases the oxygen consumption by about 9% during sharp wave-ripples reflecting enhanced adenosine-5'-triphosphate (ATP) synthesis by oxidative phosphorylation in mitochondria. Moreover, lactate attenuates neurotransmission in glutamatergic pyramidal cells and fast-spiking, γ-aminobutyric acid (GABA)ergic interneurons by reducing neurotransmitter release from presynaptic terminals. By contrast, the generation and propagation of action potentials in the axon is regular. In conclusion, lactate is less effective than glucose and potentially detrimental during neural network rhythms featuring high energetic costs, likely through the lack of some obligatory ATP synthesis by aerobic glycolysis at excitatory and inhibitory synapses. High lactate/glucose ratios might contribute to central fatigue, cognitive impairment, and epileptic seizures partially seen, for instance, during exhaustive physical exercise, hypoglycemia and neuroinflammation.

Tissue-specific differences in Ca2+ sensitivity of the mitochondrial permeability transition pore (PTP). Experiments in male rat liver and heart

Permeability transition pore (PTP) opening dissipates ion and electron gradients across the internal mitochondrial membrane (IMM), including excess Ca2+ in the mitochondrial matrix. After opening, immediate PTP closure must follow to prevent outer membrane disruption, loss of cytochrome c, and eventual apoptosis. Flickering, defined as the rapid alternative opening/closing of PTP, has been reported in heart, which undergoes frequent, large variations in Ca2+. In contrast, in tissues that undergo depolarization events less often, such as the liver, PTP would not need to be as dynamic and thus these tissues would not be as resistant to stress. To evaluate this idea, it was decided to follow the reversibility of the permeability transition (PT) in isolated murine mitochondria from two different tissues: the very dynamic heart, and the liver, which suffers depolarizations less frequently. It was observed that in heart mitochondria PT remained reversible for longer periods and at higher Ca2+ loads than in liver mitochondria. In all cases, Ca2+ uptake was inhibited by ruthenium red and PT was delayed by Cyclosporine A. Characterization of this phenomenon included measuring the rate of oxygen consumption, organelle swelling and Ca2+ uptake and retention. Results strongly suggest that there are tissue-specific differences in PTP physiology, as it resists many more Ca2+ additions before opening in a highly active organ such as the heart than in an organ that seldom suffers Ca2+ loading, such as the liver.