Calcium Waves Research Articles

Using Forward and Reverse Genetics to Understand Calcium Dysregulation in Enteric Viral Virulence

Acute gastroenteritis (AGE) remains the second leading cause of death among children under the age of 5 worldwide. AGE becomes fatal when pathogen‐associated upregulation of secretory activity across the intestinal epithelium causes severe volume depletion, hypovolemic shock, and multi‐system failure. While enteric viruses remain the most common cause of fatal AGE in kids, the drivers of their virulence (i.e. how they increase secretory activity) remain poorly understood. We recently found that cells infected with rotavirus, the most prevalent enteric virus in kids, release adenosine diphosphate (ADP) to induce coordinated signals known as “intercellular calcium waves,” which spread through uninfected neighboring cells. This dysregulates calcium signaling pathways, which enhances fluid secretion from uninfected cells and thereby contributes to volume depletion. Pharmacological blockade of calcium waves in infected mouse pups decreases disease severity, suggesting they are integral to rotavirus virulence. Understanding how rotavirus triggers intercellular calcium waves may allow us to design safer, more effective vaccines and therapeutics, but we still lack a mechanistic understanding of this process. Here, we report data showing that recombinant expression of a single rotavirus protein, non‐structural protein 4 (NSP4), is sufficient to activate intercellular calcium waves. Using the rotavirus reverse genetics system, we show that the diminished calcium wave phenotype associated with an attenuated strain of porcine rotavirus segregates with the NSP4 gene upon reassortment. Furthermore, we show that this attenuation is attributable to a single amino acid polymorphism at the c‐terminal end of NSP4. This implicates the c‐terminal end and a putative PDZ‐binding motif therein as key upstream mediators of intercellular calcium waves. These findings deepen our understanding of enteric virus pathogenesis, characterize a new role for rotavirus non‐structural protein 4, offer novel targets for anti‐secretory therapeutics, and expand foundational knowledge to support the development of improved live‐attenuated vaccines.

A Novel Non‐Linear Approach to Characterizing Astrocytic Neurovascular Coupling with Optogenetics and Computational Modeling

The role of astrocytes in neurovascular coupling remains hotly contested with various proposed mechanisms of hemodynamic response. Past findings have proven calcium activity to be the essential component in all astrocytic pathways of vascular control. However, these findings have proven contradictory over the last two decades, suggesting that an additive approach may not be appropriate for the quantification and characterization of astrocytic neurovascular coupling. We hypothesize that these astrocyte‐governed biochemical pathways have an unequal contribution and that they enact hemodynamic change in a dynamic, non‐linear fashion. Using a tetracycline‐based transgenic mice model, expressing ChR2‐EYFP solely in astrocytes, we optogenetically stimulated the production of a calcium wave in mice cortical astrocytes and evaluated hemodynamic change with a Laser Doppler Flowmetry (LDF) modality. Under these conditions, a sustained increase in localized perfusion of around 20% was found within stimulated areas. Subsequent pharmacological inhibition of phospholipase (PLA2) governed pathways facilitated the characterization of PLA2isoforms within cortical astrocytes. Furthermore, we created a computational biophysical model of hemodynamic response aiming to reproduce the experimental data generated from this study and previous ones. This data better elucidates the role of astrocytes in regional resource delivery, suggesting a new perspective in the diagnosis, treatment, and prevention of neurodegenerative diseases with vascular presentations such as Alzheimer’s Disease. We believe our findings provide a new approach by which future studies may revisit the use of pharmacology to characterize the neurovascular coupling phenomenon.

The Dictyostelium Model for Mucolipidosis Type IV.

Mucolipidosis type IV, a devastating neurological lysosomal disease linked to mutations in the transient receptor potential channel mucolipin 1, TRPML1, a calcium permeable channel in the membranes of vesicles in endolysosomal system. TRPML1 function is still being elucidated and a better understanding of the molecular pathogenesis of Mucolipidosis type IV, may facilitate development of potential treatments. We have created a model to study mucolipin function in the eukaryotic slime mould Dictyostelium discoideum by altering expression of its single mucolipin homologue, mcln. We show that in Dictyostelium mucolipin overexpression contributes significantly to global chemotactic calcium responses in vegetative and differentiated cells. Knockdown of mucolipin also enhances calcium responses in vegetative cells but does not affect responses in 6–7 h developed cells, suggesting that in developed cells mucolipin may help regulate local calcium signals rather than global calcium waves. We found that both knocking down and overexpressing mucolipin often, but not always, presented the same phenotypes. Altering mucolipin expression levels caused an accumulation or increased acidification of Lysosensor Blue stained vesicles in vegetative cells. Nutrient uptake by phagocytosis and macropinocytosis were increased but growth rates were not, suggesting defects in catabolism. Both increasing and decreasing mucolipin expression caused the formation of smaller slugs and larger numbers of fruiting bodies during multicellular development, suggesting that mucolipin is involved in initiation of aggregation centers. The fruiting bodies that formed from these smaller aggregates had proportionately larger basal discs and thickened stalks, consistent with a regulatory role for mucolipin-dependent Ca2+ signalling in the autophagic cell death pathways involved in stalk and basal disk differentiation in Dictyostelium. Thus, we have provided evidence that mucolipin contributes to chemotactic calcium signalling and that Dictyostelium is a useful model to study the molecular mechanisms involved in the cytopathogenesis of Mucolipidosis type IV.

Characterization of the mechanism by which a nonsense variant in RYR2 leads to disordered calcium handling.

Heterozygous missense variants of the cardiac ryanodine receptor gene (RYR2) cause catecholaminergic polymorphic ventricular tachycardia (CPVT). These missense variants of RYR2 result in a gain of function of the ryanodine receptors, characterized by increased sensitivity to activation by calcium that results in an increased propensity to develop calcium waves and delayed afterdepolarizations. We have recently detected a nonsense variant in RYR2 in a young patient who suffered an unexplained cardiac arrest. To understand the mechanism by which this variant in RYR2, p.(Arg4790Ter), leads to ventricular arrhythmias, human induced pluripotent stem cells (hiPSCs) harboring the novel nonsense variant in RYR2 were generated and differentiated into cardiomyocytes (RYR2‐hiPSC‐CMs) and molecular and calcium handling properties were studied. RYR2‐hiPSC‐CMs displayed significant calcium handling abnormalities at baseline and following treatment with isoproterenol. Treatment with carvedilol and nebivolol resulted in a significant reduction in calcium handling abnormalities in the RYR2‐hiPSC‐CMs. Expression of the mutant RYR2 allele was confirmed at the mRNA level and partial silencing of the mutant allele resulted in a reduction in calcium handling abnormalities at baseline. The nonsense variant behaves similarly to other gain of function variants in RYR2. Carvedilol and nebivolol may be suitable treatments for patients with gain of function RYR2 variants.

Plasmalogens Regulate Retinal Connexin 43 Expression and Müller Glial Cells Gap Junction Intercellular Communication and Migration.

Plasmalogens are a specific glycerophospholipid subtype characterized by a vinyl-ether bound at their sn-1 moiety. Their biosynthesis is initiated in the peroxisome by dihydroxyacetone phosphate-acyltransferase (DHAPAT), which is encoded by the DAPAT gene. Previous studies have shown that plasmalogen-deficient mice exhibit major physiological dysfunctions including several eye defects, among which abnormal vascular development of the retina and a reactive activation of macroglial Müller cells. Interestingly, plasmalogen deficiency in mice is also associated with a reduced expression of brain connexin 43 (Cx43). Cx43 is the main connexin subtype of retinal glial cells and is involved in several cellular mechanisms such as calcium-based gap junction intercellular communication (GJIC) or cell migration. Thus, the aim of our work was 1) to confirm the alteration of Cx43 expression in the retina of plasmalogen-deficient DAPAT−/- mice and 2) to investigate whether plasmalogens are involved in crucial functions of Müller cells such as GJIC and cell migration. First, we found that plasmalogen deficiency was associated with a significant reduction of Cx43 expression in the retina of DAPAT−/- mice in vivo. Secondly, using a siRNA targeting DHAPAT in vitro, we found that a 50%-reduction of Müller cells content in plasmalogens was sufficient to significantly downregulate Cx43 expression, while increasing its phosphorylation. Furthermore, plasmalogen-depleted Müller cells exhibited several alterations in ATP-induced GJIC, such as calcium waves of higher amplitude that propagated slower to neighboring cells, including astrocytes. Finally, in vitro plasmalogen depletion was also associated with a significant downregulation of Müller cells migration. Taken together, these data confirm that plasmalogens are critical for the regulation of Cx43 expression and for characteristics of retinal Müller glial cells such as GJIC and cell migration.

Extracellular ATP plays an important role in systemic wound response activation.

Mechanical wounding occurs in plants during biotic or abiotic stresses and is associated with the activation of long-distance signaling pathways that trigger wound responses in systemic tissues. Among the different systemic signals activated by wounding are electric signals, calcium, hydraulic, and reactive oxygen species (ROS) waves. The release of glutamate (Glu) from cells at the wounded tissues was recently proposed to trigger systemic signal transduction pathways via GLU-LIKE RECEPTORs (GLRs). However, the role of another important compound released from cells during wounding (extracellular ATP [eATP]) in triggering systemic responses is not clear. Here, we show in Arabidopsis (Arabidopsis thaliana) that wounding results in the accumulation of nanomolar levels of eATP and that these levels are sufficient to trigger the systemic ROS wave. We further show that the triggering of the ROS wave by eATP during wounding requires the PURINORECEPTOR 2 KINASE (P2K) receptor. Application of eATP to unwounded leaves triggered the ROS wave, and the activation of the ROS wave by wounding or eATP application was suppressed in mutants deficient in P2Ks (e.g. p2k1-3, p2k2, and p2k1-3p2k2). In addition, expression of systemic wound response (SWR) transcripts was suppressed in mutants deficient in P2Ks during wounding. Interestingly, the effect of Glu and eATP application on ROS wave activation was not additive, suggesting that these two compounds function in the same pathway to trigger the ROS wave. Our findings reveal that in addition to sensing Glu via GLRs, eATP sensed by P2Ks plays a key role in the triggering of SWRs in plants.

Calcium signaling in individual APP/PS1 mouse dentate gyrus astrocytes increases ex vivo with Aβ pathology and age without affecting astrocyte network activity.

Astrocytes are critical for healthy brain function. In Alzheimer’s disease, astrocytes become reactive, which affects their signaling properties. Here, we measured spontaneous calcium transients ex vivo in hippocampal astrocytes in brain slices containing the dentate gyrus of 6‐ (6M) and 9‐month‐old (9M) APPswe/PSEN1dE9 (APP/PS1) mice. We investigated the frequency and duration of calcium transients in relation to aging, amyloid‐β (Aβ) pathology, and the proximity of the astrocyte to Aβ plaques. The 6M APP/PS1 astrocytes showed no change in spontaneous calcium‐transient properties compared to wild‐type (WT) astrocytes. 9M APP/PS1 astrocytes, however, showed more hyperactivity compared to WT, characterized by increased spontaneous calcium transients that were longer in duration. Our data also revealed an effect of aging, as 9M astrocytes overall showed an increase in calcium activity compared to 6M astrocytes. Subsequent calcium‐wave analysis showed an increase in sequential calcium transients (i.e., calcium waves) in 9M astrocytes, suggesting increased network activity ex vivo. Further analysis using null models revealed that this network effect is caused by chance, due to the increased number of spontaneous transients. Our findings show that alterations in calcium signaling in individual hippocampal astrocytes of APP/PS1 mice are subject to both aging and Aβ pathology but these do not lead to a change in astrocyte network activity. These alterations in calcium dynamics of astrocytes may help to understand changes in neuronal physiology leading to cognitive decline and ultimately dementia.

FRESH 3D bioprinting a contractile heart tube using human stem cell-derived cardiomyocytes

Here we report the 3D bioprinting of a simplified model of the heart, similar to that observed in embryonic development, where the heart is a linear tube that pumps blood and nutrients to the growing embryo. To this end, we engineered a bioinspired model of the human heart tube using freeform reversible of embedding of suspended hydrogels 3D bioprinting. The 3D bioprinted heart tubes were cellularized using human stem cell-derived cardiomyocytes and cardiac fibroblasts and formed patent, perfusable constructs. Synchronous contractions were achieved ∼3–4 days after fabrication and were maintained for up to a month. Immunofluorescent staining confirmed large, interconnected networks of sarcomeric alpha actinin-positive cardiomyocytes. Electrophysiology was assessed using calcium imaging and demonstrated anisotropic calcium wave propagation along the heart tube with a conduction velocity of ∼5 cm s−1. Contractility and function was demonstrated by tracking the movement of fluorescent beads within the lumen to estimate fluid displacement and bead velocity. These results establish the feasibility of creating a 3D bioprinted human heart tube and serve as an initial step towards engineering more complex heart muscle structures.

Mechanosensory trichome cells evoke a mechanical stimuli–induced immune response in Arabidopsis thaliana

Perception of pathogen-derived ligands by corresponding host receptors is a pivotal strategy in eukaryotic innate immunity. In plants, this is complemented by circadian anticipation of infection timing, promoting basal resistance even in the absence of pathogen threat. Here, we report that trichomes, hair-like structures on the epidermis, directly sense external mechanical forces, including raindrops, to anticipate pathogen infections in Arabidopsis thaliana. Exposure of leaf surfaces to mechanical stimuli initiates the concentric propagation of intercellular calcium waves away from trichomes to induce defence-related genes. Propagating calcium waves enable effective immunity against pathogenic microbes through the CALMODULIN-BINDING TRANSCRIPTION ACTIVATOR 3 (CAMTA3) and mitogen-activated protein kinases. We propose an early layer of plant immunity in which trichomes function as mechanosensory cells that detect potential risks.

Calcium Wave Propagation Underlying Intercellular Signaling and Coordination of Tissue Responses.

Calcium Wave Propagation Underlying Intercellular Signaling and Coordination of Tissue Responses.

Initiation of calcium waves in failing cardiac myocytes is sensitive to posttranslational modifications

Calcium (Ca2+) waves in cardiac myocytes are arrhythmogenic since they can lead to triggered activities in the heart. In the healthy cell, Ca2+ waves, if they occur, are infrequent. However, under pathological conditions such as heart failure, Ca2+ waves occur more frequently. In this study, using a mathematical model of subcellular Ca2+ cycling, we investigated the initiation process of Ca2+ waves and show how transition from no waves to multiple waves may occur due to ryanodine receptor (RyR) posttranslational modifications (PTMs).

Quantifying Propagation Velocity from Engineered Cardiac Tissues with High-Speed Fluorescence Microscopy and Automated Analysis Software.

Many acquired or inherited forms of heart disease as well as drugs are known to increase the susceptibility of patients to arrhythmias. To predict arrhythmogenic events and discover new therapeutic strategies to mitigate them, approaches to efficiently quantify the velocity of propagation in engineered cardiac tissues are important research tools. In this chapter, we describe how to collect videos of propagating calcium waves in engineered cardiac tissues with a high-speed camera mounted on an inverted fluorescence microscope. We also provide instructions for downloading and using our software package to analyze these videos and calculate propagation velocity. These techniques should be compatible with a variety of voltage- or calcium-sensitive fluorescent dyes or genetically encoded sensors. Although these approaches were originally developed for engineered neonatal rat cardiac tissues, the same procedures can likely be used with human-induced pluripotent stem cell-derived cardiac myocytes, paving the way for patient-specific analysis of propagation due to features such as tissue architecture, substrate rigidity, genetic mutations, or drug treatments.

Embryonic Development of Motility: Lessons from the Chicken.

I outline here the development of intestinal motility in the chicken embryo. The first contractile events are circular smooth muscle driven calcium waves (E6), that gain a clock-like regularity when interstitial cells of Cajal become electrically active (E14). Soon after longitudinal smooth muscle contractions become prominent (E14), the enteric nervous system starts controlling motility (E16) by coupling the longitudinal and circular contractions via inhibitory neurotransmission. It gives rise to circular-longitudinal antagonism, to the migrating motor complex, and to the polarized ascending contraction-descending relaxation pressure response known as the "law of the intestine". The kinetics of gut development in the chicken appears to follow faithfully that of humans by simply converting embryonic days of chicken development into embryonic weeks of human development.

Voltage-mediated mechanism for calcium wave synchronization and arrhythmogenesis in atrial tissue

A wide range of atrial arrythmias are caused by molecular defects in proteins that regulate calcium (Ca) cycling. In many cases, these defects promote the propagation of subcellular Ca waves in the cell, which can perturb the voltage time course and induce dangerous perturbations of the action potential (AP). However, subcellular Ca waves occur randomly in cells and, therefore, electrical coupling between cells substantially decreases their effect on the AP. In this study, we present evidence that Ca waves in atrial tissue can synchronize in-phase owing to an order-disorder phase transition. In particular, we show that, below a critical pacing rate, Ca waves are desynchronized and therefore do not induce substantial AP fluctuations in tissue. However, above this critical pacing rate, Ca waves gradually synchronize over millions of cells, which leads to a dramatic amplification of AP fluctuations. We exploit an underlying Ising symmetry of paced cardiac tissue to show that this transition exhibits universal properties common to a wide range of physical systems in nature. Finally, we show that in the heart, phase synchronization induces spatially out-of-phase AP duration alternans which drives wave break and reentry. These results suggest that cardiac tissue exhibits a phase transition that is required for subcellular Ca cycling defects to induce a life-threatening arrhythmia.

Calcium Signaling in the Cerebellar Radial Glia and Its Association with Morphological Changes during Zebrafish Development.

Radial glial cells are a distinct non-neuronal cell type that, during development, span the entire width of the brain walls of the ventricular system. They play a central role in the origin and placement of neurons, since their processes form structural scaffolds that guide and facilitate neuronal migration. Furthermore, glutamatergic signaling in the radial glia of the adult cerebellum (i.e., Bergmann glia), is crucial for precise motor coordination. Radial glial cells exhibit spontaneous calcium activity and functional coupling spread calcium waves. However, the origin of calcium activity in relation to the ontogeny of cerebellar radial glia has not been widely explored, and many questions remain unanswered regarding the role of radial glia in brain development in health and disease. In this study we used a combination of whole mount immunofluorescence and calcium imaging in transgenic (gfap-GCaMP6s) zebrafish to determine how development of calcium activity is related to morphological changes of the cerebellum. We found that the morphological changes in cerebellar radial glia are quite dynamic; the cells are remarkably larger and more elaborate in their soma size, process length and numbers after 7 days post fertilization. Spontaneous calcium events were scarce during the first 3 days of development and calcium waves appeared on day 5, which is associated with the onset of more complex morphologies of radial glia. Blockage of gap junction coupling inhibited the propagation of calcium waves, but not basal local calcium activity. This work establishes crucial clues in radial glia organization, morphology and calcium signaling during development and provides insight into its role in complex behavioral paradigms.

Sponging of glutamate at the outer plasma membrane surface reveals roles for glutamate in development.

Plants use electrical and chemical signals for systemic communication. Herbivory, for instance, appears to trigger local apoplasmic glutamate accumulation, systemic electrical signals, and calcium waves that travel to report insect damage to neighboring leaves and initiate defense. To monitor extra- and intracellular glutamate concentrations in plants, we generated Arabidopsis lines expressing genetically encoded fluorescent glutamate sensors. In contrast to cytosolically localized sensors, extracellularly displayed variants inhibited plant growth and proper development. Phenotypic analyses of high-affinity display sensor lines revealed that root meristem development, particularly the quiescent center, number of lateral roots, vegetative growth, and floral architecture were impacted. Notably, the severity of the phenotypes was positively correlated with the affinity of the display sensors, intimating that their ability to sequester glutamate at the surface of the plasma membrane was responsible for the defects. Root growth defects were suppressed by supplementing culture media with low levels of glutamate. Together, the data indicate that sequestration of glutamate at the cell surface either disrupts the supply of glutamate to meristematic cells and/or impairs localized glutamatergic signaling important for developmental processes.

Direction of epithelial folding defines impact of mechanical forces on epithelial state.

Cell shape dynamics during development is tightly regulated and coordinated with cell fate determination. Triggered by an interplay between biochemical and mechanical signals, epithelia form complex tissues by undergoing coordinated cell shape changes, but how such spatiotemporal coordination is controlled remains an open question. To dissect biochemical signaling from purely mechanical cues, we developed a microfluidic system that experimentally triggers epithelial folding to recapitulate stereotypic deformations observed invivo. Using this system, we observe that the apical or basal direction of folding results in strikingly different mechanical states at the fold boundary, where the balance between tissue tension and torque (arising from the imposed curvature) controls the spread of folding-induced calcium waves at a short timescale and induces spatial patterns of gene expression at longer timescales. Our work uncovers that folding-associated gradients of cell shape and their resulting mechanical stresses direct spatially distinct biochemical responses within the monolayer.

A Spatial Model of Hepatic Calcium Signaling and Glucose Metabolism Under Autonomic Control Reveals Functional Consequences of Varying Liver Innervation Patterns Across Species.

Rapid breakdown of hepatic glycogen stores into glucose plays an important role during intense physical exercise to maintain systemic euglycemia. Hepatic glycogenolysis is governed by several different liver-intrinsic and systemic factors such as hepatic zonation, circulating catecholamines, hepatocellular calcium signaling, hepatic neuroanatomy, and the central nervous system (CNS). Of the factors regulating hepatic glycogenolysis, the extent of lobular innervation varies significantly between humans and rodents. While rodents display very few autonomic nerve terminals in the liver, nearly every hepatic layer in the human liver receives neural input. In the present study, we developed a multi-scale, multi-organ model of hepatic metabolism incorporating liver zonation, lobular scale calcium signaling, hepatic innervation, and direct and peripheral organ-mediated communication between the liver and the CNS. We evaluated the effect of each of these governing factors on the total hepatic glucose output and zonal glycogenolytic patterns within liver lobules during simulated physical exercise. Our simulations revealed that direct neuronal stimulation of the liver and an increase in circulating catecholamines increases hepatic glucose output mediated by mobilization of intracellular calcium stores and lobular scale calcium waves. Comparing simulated glycogenolysis between human-like and rodent-like hepatic innervation patterns (extensive vs. minimal) suggested that propagation of calcium transients across liver lobules acts as a compensatory mechanism to improve hepatic glucose output in sparsely innervated livers. Interestingly, our simulations suggested that catecholamine-driven glycogenolysis is reduced under portal hypertension. However, increased innervation coupled with strong intercellular communication can improve the total hepatic glucose output under portal hypertension. In summary, our modeling and simulation study reveals a complex interplay of intercellular and multi-organ interactions that can lead to differing calcium dynamics and spatial distributions of glycogenolysis at the lobular scale in the liver.

Calcium waves facilitate and coordinate the contraction of endfeet actin stress fibers in Drosophila interommatidial cells

Actomyosin contraction shapes the Drosophila eye's panoramic view. The convex curvature of the retinal epithelium, organized in ∼800 close-packed ommatidia, depends upon a fourfold condensation of the retinal floor mediated by contraction of actin stress fibers in the endfeet of interommatidial cells (IOCs). How these tensile forces are coordinated is not known. Here, we discover a previously unobserved phenomenon: Ca2+ waves regularly propagate across the IOC network in pupal and adult eyes. Genetic evidence demonstrates that IOC waves are independent of phototransduction, but require the inositol 1,4,5-triphosphate receptor (IP3R), suggesting that these waves are mediated by Ca2+ releases from endoplasmic reticulum stores. Removal of IP3R disrupts stress fibers in IOC endfeet and increases the basal retinal surface by ∼40%, linking IOC waves to facilitation of stress fiber contraction and floor morphogenesis. Furthermore, IP3R loss disrupts the organization of a collagen IV network underneath the IOC endfeet, implicating the extracellular matrix and its interaction with stress fibers in eye morphogenesis. We propose that coordinated cytosolic Ca2+ increases in IOC waves promote stress fiber contractions, ensuring an organized application of the planar tensile forces that condense the retinal floor. This article has an associated 'The people behind the papers' interview.

The people behind the papers – Donald Ready and Henry Chang

ABSTRACT Coordinating contractility across tissues is key for maintaining the fidelity of morphogenetic processes. A new paper in Development explains how cytosolic calcium waves in the interommatidial cells, the pigment-secreting cells in the Drosophila eye, lead to remodelling of the retinal floor, by activating contraction of the basal actomyosin stress fibres. We caught up with the authors, Professor Donald Ready and Associate Professor Henry Chang, both from Purdue University, to find out more about this story.