Multiscale Modeling Indicates That Temperature Dependent [Ca2+]i Spiking in Astrocytes Is Quantitatively Consistent with Modulated SERCA Activity

Investigations of Astrocyte Calcium Signaling and Imaging with Classical and Nonclassical Light

The application of light in studying and influencing cellular behavior with improved temporal and spatial resolution remains a key objective in fields such as chemistry, physics, medicine, and engineering. In the brain, nonexcitable cells called astrocytes play essential roles in regulating homeostasis and cognitive function through complex calcium signaling pathways. Understanding these pathways is vital for deciphering brain physiology and neurological disorders like Parkinson's and Alzheimer's. Despite challenges in selectively targeting astrocyte signaling pathways due to shared molecular equipment with neurons, recent advancements in laser technology offer promising avenues. However, the effort to use laser light properties to study astroglial cell function is still limited. This work aims to exploit an in-depth pharmacological analysis of astrocyte calcium channels to determine the physiological mechanism induced by exposure to classical nanosecond-pulsed light. We herein report molecular clues supporting the use of visible-nanosecond laser pulses as a promising approach to excite primary rat neocortical astrocytes and unprecedentedly report on the implementation of entangled two-photon microscopy to image them.

Temporal multiscale modeling of biochemical regulatory networks: Calcium-regulated hepatocyte lipid and glucose metabolism

Hepatocyte lipid and glucose metabolism is regulated not only by major hormones like insulin and glucagon but also by many other factors, including calcium ions. Recently, mitochondria-associated membrane (MAM) dysfunction combined with incorrect IP3-receptor regulation has been shown to result in abnormal calcium signaling in hepatocytes. This dysfunction could further lead to hepatic metabolism pathology. However, the exact contribution of MAM dysfunction, incorrect IP3-receptor regulation and insulin resistance to the calcium-insulin-glucagon interplay is not understood yet. In this work, we analyze the role of abnormal calcium signaling and insulin dysfunction in hepatocytes by proposing a model of hepatocyte metabolic regulatory network with a detailed focus on the model construction details besides the biological aspect. In this work, we analyze the role of abnormal calcium signaling and insulin dysfunction in hepatocytes by proposing a model of hepatocyte metabolic regulatory network. We focus on the model construction details, model validation, and predictions. We describe the dynamic regulation of signaling processes by sigmoid Hill function. In particular, we study the effect of both the Hill function slope and the distance between Hill function extremes on metabolic processes in hepatocytes as a model of nonspecific insulin dysfunction. We also address the significant time difference between characteristic time of glucose hepatic processing and a typical calcium oscillation period in hepatocytes. Our modeling results show that calcium signaling dysfunction results in an abnormal increase in postprandial glucose levels, an abnormal glucose decrease in fasting, and a decreased amount of stored glycogen. An insulin dysfunction of glucose phosphorylation, glucose dephosphorylation, and glycogen breakdown also cause a noticeable effect. We also get some insight into the so-called hepatic insulin resistance paradox, confirming the hypothesis regarding indirect insulin action on hepatocytes via dysfunctional adipocyte lipolysis.

Calcium oscillations optimize the energetic efficiency of mitochondrial metabolism

Energy transduction is central to living organisms, but the impact of enzyme regulation and signaling on its thermodynamic efficiency is generally overlooked. Here, we analyze the efficiency of ATP production by the tricarboxylic acid cycle and oxidative phosphorylation, which generate most of the chemical energy in eukaryotes. Calcium signaling regulates this pathway and can affect its energetic output, but the concrete energetic impact of this cross-talk remains elusive. Calcium enhances ATP production by activating key enzymes of the tricarboxylic acid cycle while calcium homeostasis is ATP-dependent. We propose a detailed kinetic model describing the calcium-mitochondria cross-talk and analyze it using nonequilibrium thermodynamics: after identifying the effective reactions driving mitochondrial metabolism out of equilibrium, we quantify the mitochondrial thermodynamic efficiency for different conditions. Calcium oscillations, triggered by extracellular stimulation or energy deficiency, boost the thermodynamic efficiency of mitochondrial metabolism, suggesting a compensatory role of calcium signaling in mitochondrial bioenergetics.

Analysis of Network Models with Neuron-Astrocyte Interactions

Neural networks, composed of many neurons and governed by complex interactions between them, are a widely accepted formalism for modeling and exploring global dynamics and emergent properties in brain systems. In the past decades, experimental evidence of computationally relevant neuron-astrocyte interactions, as well as the astrocytic modulation of global neural dynamics, have accumulated. These findings motivated advances in computational glioscience and inspired several models integrating mechanisms of neuron-astrocyte interactions into the standard neural network formalism. These models were developed to study, for example, synchronization, information transfer, synaptic plasticity, and hyperexcitability, as well as classification tasks and hardware implementations. We here focus on network models of at least two neurons interacting bidirectionally with at least two astrocytes that include explicitly modeled astrocytic calcium dynamics. In this study, we analyze the evolution of these models and the biophysical, biochemical, cellular, and network mechanisms used to construct them. Based on our analysis, we propose how to systematically describe and categorize interaction schemes between cells in neuron-astrocyte networks. We additionally study the models in view of the existing experimental data and present future perspectives. Our analysis is an important first step towards understanding astrocytic contribution to brain functions. However, more advances are needed to collect comprehensive data about astrocyte morphology and physiology in vivo and to better integrate them in data-driven computational models. Broadening the discussion about theoretical approaches and expanding the computational tools is necessary to better understand astrocytes' roles in brain functions.

Elucidating regulators of astrocytic Ca2+ signaling via multi-threshold event detection (MTED)

Recent achievements in indicator optimization and imaging techniques promote the advancement of functional imaging to decipher complex signaling processes in living cells, such as Ca²⁺ activity patterns. Astrocytes are important regulators of the brain network and well known for their highly complex morphology and spontaneous Ca²⁺ activity. However, the astrocyte community is lacking standardized methods to analyze and interpret Ca²⁺ activity recordings, hindering global comparisons. Here, we present a biophysically-based analytical concept for deciphering the complex spatio-temporal changes of Ca²⁺ biosensor fluorescence for understanding the underlying signaling mechanisms. We developed a pixel-based multi-threshold event detection (MTED) analysis of multidimensional data, which accounts for signal strength as an additional signaling dimension and provides the experimenter with a comprehensive toolbox for a differentiated and in-depth characterization of fluorescence signals. MTED was validated by analyzing astrocytic Ca²⁺ activity across Ca²⁺ indicators, imaging setups, and model systems from primary cell culture to awake, head-fixed mice. We identified extended Ca²⁺ activity at 25°C compared to 37°C physiological body temperature and dissected how neuronal activity shapes long-lasting astrocytic Ca²⁺ activity. Our MTED strategy, as a parameter-free approach, is easily transferrable to other fluorescent indicators and biosensors and embraces the additional dimensionality of signaling activity strength. It will also advance the definition of standardized procedures and parameters to improve comparability of research data and reports.

Advances in Astrocyte Computational Models: From Metabolic Reconstructions to Multi-omic Approaches

The growing importance of astrocytes in the field of neuroscience has led to a greater number of computational models devoted to the study of astrocytic functions and their metabolic interactions with neurons. The modeling of these interactions demands a combined understanding of brain physiology and the development of computational frameworks based on genomic-scale reconstructions, system biology, and dynamic models. These computational approaches have helped to highlight the neuroprotective mechanisms triggered by astrocytes and other glial cells, both under normal conditions and during neurodegenerative processes. In the present review, we evaluate some of the most relevant models of astrocyte metabolism, including genome-scale reconstructions and astrocyte-neuron interactions developed in the last few years. Additionally, we discuss novel strategies from the multi-omics perspective and computational models of other glial cell types that will increase our knowledge in brain metabolism and its association with neurodegenerative diseases.

Protective effect of gastrodin on myocardial ischemia-reperfusion injury and the expression of Bax and Bcl-2

The protective effects of gastrodin on myocardial ischemia-reperfusion injury in rats and the underlying mechanism were investigated. Sprague Dawley (SD) rats were randomly divided into three groups, of which the gastrodin group was treated with gastrodin, and the other two groups were treated with normal saline. In the myocardial ischemia-reperfusion model group, myocardial ischemia was induced by ligation of the left anterior descending coronary artery, and myocardial reperfusion was performed by ligature removal. Only thread without ligation for the sham operation group was conducted. The rats were euthanized 8 days after surgery. Heart tissues were harvested and used for measurement of apoptotic rate and expression levels of apoptosis-related proteins. Serum levels of cytokines were measured also using blood samples. Compared with the myocardial ischemia-reperfusion model group, significant reduction of cardiomyocyte apoptosis was observed in the gastrodin group (P<0.05). In the gastrodin group, the protein and mRNA expression levels for Bax and activated caspase-3 decreased, while for Bcl-2 increased (P<0.05). Gastrodin can downregulate inflammatory cytokines (P<0.05) and upregulate anti-inflammatory cytokines such as IL-10 (P<0.05) in serum of SD rats. Therefore, gastrodin played a protective role in myocardial ischemia-reperfusion injury by regulating the expression levels of apoptosis-related signaling proteins and inflammatory cytokines.

Computational Models for Calcium-Mediated Astrocyte Functions

The computational neuroscience field has heavily concentrated on the modeling of neuronal functions, largely ignoring other brain cells, including one type of glial cell, the astrocytes. Despite the short history of modeling astrocytic functions, we were delighted about the hundreds of models developed so far to study the role of astrocytes, most often in calcium dynamics, synchronization, information transfer, and plasticity in vitro, but also in vascular events, hyperexcitability, and homeostasis. Our goal here is to present the state-of-the-art in computational modeling of astrocytes in order to facilitate better understanding of the functions and dynamics of astrocytes in the brain. Due to the large number of models, we concentrated on a hundred models that include biophysical descriptions for calcium signaling and dynamics in astrocytes. We categorized the models into four groups: single astrocyte models, astrocyte network models, neuron-astrocyte synapse models, and neuron-astrocyte network models to ease their use in future modeling projects. We characterized the models based on which earlier models were used for building the models and which type of biological entities were described in the astrocyte models. Features of the models were compared and contrasted so that similarities and differences were more readily apparent. We discovered that most of the models were basically generated from a small set of previously published models with small variations. However, neither citations to all the previous models with similar core structure nor explanations of what was built on top of the previous models were provided, which made it possible, in some cases, to have the same models published several times without an explicit intention to make new predictions about the roles of astrocytes in brain functions. Furthermore, only a few of the models are available online which makes it difficult to reproduce the simulation results and further develop the models. Thus, we would like to emphasize that only via reproducible research are we able to build better computational models for astrocytes, which truly advance science. Our study is the first to characterize in detail the biophysical and biochemical mechanisms that have been modeled for astrocytes.

Aberrant astrocyte Ca2+ signals "AxCa signals" exacerbate pathological alterations in an Alexander disease model

Alexander disease (AxD) is a rare neurodegenerative disorder caused by gain of function mutations in the glial fibrillary acidic protein (GFAP) gene. Accumulation of GFAP proteins and formation of Rosenthal fibers (RFs) in astrocytes are hallmarks of AxD. However, malfunction of astrocytes in the AxD brain is poorly understood. Here, we show aberrant Ca²⁺ responses in astrocytes as playing a causative role in AxD. Transcriptome analysis of astrocytes from a model of AxD showed age-dependent upregulation of GFAP, several markers for neurotoxic reactive astrocytes, and downregulation of Ca²⁺ homeostasis molecules. In situ AxD model astrocytes produced aberrant extra-large Ca²⁺ signals "AxCa signals", which increased with age, correlated with GFAP upregulation, and were dependent on stored Ca²⁺ . Inhibition of AxCa signals by deletion of inositol 1,4,5-trisphosphate type 2 receptors (IP3R2) ameliorated AxD pathogenesis. Taken together, AxCa signals in the model astrocytes would contribute to AxD pathogenesis.

Sexual Dimorphism in a Reciprocal Interaction of Ryanodine and IP3 Receptors in the Induction of Hyperalgesic Priming

Hyperalgesic priming, a model of pain chronification in the rat, is mediated by ryanodine receptor-dependent calcium release. Although ryanodine induces priming in both sexes, females are 5 orders of magnitude more sensitive, by an estrogen receptor α (EsRα)-dependent mechanism. An inositol 1,4,5-triphosphate (IP₃) receptor inhibitor prevented the induction of priming by ryanodine. For IP₃ induced priming, females were also more sensitive. IP₃-induced priming was prevented by pretreatment with inhibitors of the sarcoendoplasmic reticulum calcium ATPase and ryanodine receptor. Antisense to EsRα prevented the induction of priming by low-dose IP₃ in females. The induction of priming by an EsRα agonist was ryanodine receptor-dependent and prevented by the IP₃ antagonist. Thus, an EsRα-dependent bidirectional interaction between endoplasmic reticulum IP₃ and ryanodine receptor-mediated calcium signaling is present in the induction of hyperalgesic priming, in females. In cultured male DRG neurons, IP₃ (100 μm) potentiated depolarization-induced transients produced by extracellular application of high-potassium solution (20 mm, K20), in nociceptors incubated with β-estradiol. This potentiation of depolarization-induced calcium transients was blocked by the IP₃ antagonist, and not observed in the absence of IP₃ IP₃ potentiation was also blocked by ryanodine receptor antagonist. The application of ryanodine (2 nm), instead of IP₃, also potentiated K20-induced calcium transients in the presence of β-estradiol, in an IP₃ receptor-dependent manner. Our results point to an EsRα-dependent, reciprocal interaction between IP₃ and ryanodine receptors that contributes to sex differences in hyperalgesic priming.SIGNIFICANCE STATEMENT The present study demonstrates a mechanism that plays a role in the marked sexual dimorphism observed in a model of the transition to chronic pain, hyperalgesic priming. This mechanism involves a reciprocal interaction between the endoplasmic reticulum receptors, IP₃ and ryanodine, in the induction of priming, regulated by estrogen receptor α in the nociceptor of female rats. The presence of this signaling pathway modulating the susceptibility of nociceptors to develop plasticity may contribute to our understanding of sex differences observed clinically in chronic pain syndromes.

Inhibition of the mitochondrial calcium uniporter rescues dopaminergic neurons in pink1-/- zebrafish

Mutations in PTEN-induced putative kinase 1 (PINK1) are a cause of early onset Parkinson's disease (PD). Loss of PINK1 function causes dysregulation of mitochondrial calcium homeostasis, resulting in mitochondrial dysfunction and neuronal cell death. We report that both genetic and pharmacological inactivation of the mitochondrial calcium uniporter (MCU), located in the inner mitochondrial membrane, prevents dopaminergic neuronal cell loss in pink1^Y431 * mutant zebrafish (Danio rerio) via rescue of mitochondrial respiratory chain function. In contrast, genetic inactivation of the voltage dependent anion channel 1 (VDAC1), located in the outer mitochondrial membrane, did not rescue dopaminergic neurons in PINK1 deficient D. rerio. Subsequent gene expression studies revealed specific upregulation of the mcu regulator micu1 in pink1^Y431 * mutant zebrafish larvae and inactivation of micu1 also results in rescue of dopaminergic neurons. The functional consequences of PINK1 deficiency and modified MCU activity were confirmed using a dynamic in silico model of Ca²⁺ triggered mitochondrial activity. Our data suggest modulation of MCU-mediated mitochondrial calcium homeostasis as a possible neuroprotective strategy in PINK1 mutant PD.

Gastrodin Pretreatment Impact on Sarcoplasmic Reticulum Calcium Transport ATPase (SERCA) and Calcium Phosphate (PLB) Expression in Rats with Myocardial Ischemia Reperfusion

Background

Calcium overload, inflammation, and apoptosis play important roles in myocardial ischemia-reperfusion injury (MIRI). Gastrodin pretreatment can alleviate MIRI. This study observed sarcoplasmic reticulum calcium transport ATPase (Ca²⁺-ATPase, SERCA) and calcium phosphate (PLB) protein expression in the ventricular remodeling process after myocardial infarction to explore the effect of gastrodin pretreatment on MIRI.

Material/Methods

Healthy 7-week-old male SD rats were randomly divided into a sham group (A), a model group (B), and gastrodin pretreatment groups C, D, and E (100, 200, and 400 mg/kg, respectively) with 20 in each group. Anterior descending coronary artery ligation method was used to establish a rat MIRI model with 30-min ischemia and 120-min reperfusion. Cardiac electrophysiological activity was recorded. Serum IL-6 and IL10 levels were determined by ELISA. SERCA activity was tested by colorimetric phosphorus method. SERCA, PLB, and pSer-PLB protein expression were detected by Western blot.

Results

Compared with the sham group, IL-6 and IL-10 levels were elevated, SERCA2a expression was downregulated, and PLB protein was elevated in the model group (P<0.05). pSer16-PLB showed no significant difference among groups, and the ratio of pSer16-PLB/PLB obviously decreased (P<0.05). IL-6 level gradually declined and IL-10 increased in the gastrodin group following concentration elevation. SERCA 2a expression rose in the gastrodin group in a dose-dependent manner (P<0.05). Elevated PLB protein expression showed no significant difference, while pSer16-PLB protein increased (P<0.05), leading to elevated pSer16 PLB/PLB ratio (P<0.05).

Conclusions

Gastrodin pretreatment alleviates MIRI and inflammation injury by regulating SERCA and PLB expression to decrease calcium overload.