Mechanisms of synapse-to-nucleus calcium signalling in striatal neurons and impairments in Huntington's disease

Huntington's disease (HD) is a monogenic disorder with autosomal dominant inheritance. In HD patients, neurons in the striatum and cortex degenerate, leading to motor, psychiatric and cognitive disorders. Dysregulated synaptic function and calcium handling are common in many neurodegenerative diseases, including HD. N-methyl-D-aspartate (NMDA) receptor function is enhanced in HD at extrasynaptic sites, altering the balance of calcium-dependent neuronal survival versus death signalling pathways. Endoplasmic reticulum (ER) calcium handling is also abnormal in HD. The ER, which is continuous with the nuclear envelope, is purportedly involved in nuclear calcium signalling; based on this, we hypothesised that nuclear calcium signalling is altered in HD. We explored this hypothesis with calcium imaging techniques, including simultaneous epifluorescent imaging of cytosolic and nuclear calcium using jRCaMP1b and GCaMP3 sensors, respectively, in striatal spiny projection neurons in cortical-striatal co-cultures from the YAC128 mouse model of HD. Our data show contributions from a variety of calcium channels to nuclear calcium signalling. NMDA receptors (NMDARs) play an essential role in initiating action potential-dependent calcium signalling to the nucleus, and ryanodine receptors (RyR) contribute to both cytosolic and nuclear calcium signals. Unlike previous reports in glutamatergic hippocampal and cortical neurons, we found that in GABAergic striatal neurons, L-type voltage-gated calcium channels (CaV) contribute to cytosolic, but not nuclear calcium signalling. Calcium imaging also suggests impairments in nuclear calcium signalling in HD striatal neurons, where spontaneous action potential-dependent calcium transients in the nucleus were smaller in YAC128 striatal neurons compared to those of wild-type (WT). Our results elucidate mechanisms involved in action potential-dependent nuclear calcium signalling in GABAergic striatal neurons, and have revealed a clear deficit in this signalling in HD.

Loose-patch clamp analysis applied to voltage-gated ionic currents following pharmacological ryanodine receptor modulation in murine hippocampal cornu ammonis-1 pyramidal neurons

Introduction

The loose-patch clamp technique was first developed and used in native amphibian skeletal muscle (SkM), offering useful features complementing conventional sharp micro-electrode, gap, or conventional patch voltage clamping. It demonstrated the feedback effects of pharmacological modification of ryanodine receptor (RyR)-mediated Ca2+ release on the Na+ channel (Nav1.4) currents, initiating excitation-contraction coupling in native murine SkM. The effects of the further RyR and Ca2+-ATPase (SERCA) antagonists, dantrolene and cyclopiazonic acid (CPA), additionally implicated background tubular-sarcoplasmic Ca2+ domains in these actions.

Materials and methods

We extend the loose-patch clamp approach to ion current measurements in murine hippocampal brain slice cornu ammonis-1 (CA1) pyramidal neurons. We explored the effects on Na+ currents of pharmacologically manipulating RyR and SERCA-mediated intracellular store Ca2+ release and reuptake. We adopted protocols previously applied to native skeletal muscle. These demonstrated Ca2+-mediated feedback effects on the Na+ channel function.

Results

Experiments applying depolarizing 15 ms duration loose-patch clamp steps to test voltages ranging from -40 to 120 mV positive to the resting membrane potential demonstrated that 0.5 mM caffeine decreased inward current amplitudes, agreeing with the previous SkM findings. It also decreased transient but not prolonged outward current amplitudes. However, 2 mM caffeine affected neither inward nor transient outward but increased prolonged outward currents, in contrast to its increasing inward currents in SkM. Furthermore, similarly and in contrast to previous SkM findings, both dantrolene (10 μM) and CPA (1 μM) pre-administration left both inward and outward currents unchanged. Nevertheless, dantrolene pretreatment still abrogated the effects of subsequent 0.5- and 2-mM caffeine challenges on both inward and outward currents. Finally, CPA abrogated the effects of 0.5 mM caffeine on both inward and outward currents, but with 2 mM caffeine, inward and transient outward currents were unchanged, but sustained outward currents increased.

Conclusion

We, thus, extend loose-patch clamping to establish pharmacological properties of murine CA1 pyramidal neurons and their similarities and contrasts with SkM. Here, evoked though not background Ca2+-store release influenced Nav and Kv excitation, consistent with smaller contributions of background store Ca2+ release to resting [Ca2+]. This potential non-canonical mechanism could modulate neuronal membrane excitability or cellular firing rates.

An updated view of the structural basis for dihydropyridine receptors-ryanodine receptors direct molecular interaction in skeletal muscle

This presentation reviews images of electron micrographs from various skeletal muscles identifying a consistent association of diydropyridine receptors (DHPR) tetrads with  alternate ryanodine receptors. Imaging of the junctional gap in triads from various sources  provide direct evidence for the  association of four diydropyridine receptors (DHPRs), clustered into tetrads, with alternate ryanodine receptors (RyRs). It is not clear whether firing of all four components of a tetrad is necessary to fully activate the opening of the RyR channel.

Construction of a risk scoring system using clinical factors and RYR2 polymorphisms for bleeding complications in patients on direct oral anticoagulants

Introduction: Bleeding is one of the most undesirable complications of direct oral anticoagulants (DOACs). While the ryanodine receptor (RYR2) has been related to cardiac diseases, research on bleeding complications is lacking. This study aimed to elucidate the association between RYR2 and bleeding risk to develop the risk scoring system in patients treated with DOACs. Methods: This study was a retrospective analysis of prospectively collected samples. We selected ten SNPs within the RYR2 gene, and two models were constructed (Model I: demographic factors only, Model II: demographic and genetic factors) in multivariable analysis. Independent risk factors for bleeding were used to develop a risk scoring system. Results: A total of 447 patients were included, and 49 experienced either major bleeding or clinically relevant non-major bleeding. In Model I, patients using rivaroxaban and experiencing anemia exhibited an increased bleeding risk after adjusting for covariates. Upon incorporating genetic factors into Model I, a significant association with bleeding was also observed in cases of overdosing on DOACs and in patients with a creatinine clearance (CrCl) < 30 mL/min, in addition to rivaroxaban and anemia (Model II). Among genetic factors, RYR2 rs12594 GG, rs17682073 AA, rs3766871 GG, and rs6678625 T alleles were associated with bleeding complications. The area under the receiver operating characteristic curve (AUROC) of Model I was 0.670, whereas that of Model II increased to 0.803, demonstrating better performance with the inclusion of genetic factors. Using the significant variables in Model II, a risk scoring system was constructed. The predicted bleeding risks for scores of 0, 1-2, 3-4, 5-6, 7-8, and 9-10 points were 0%, 1.2%, 4.6%, 15.7%, 41.7%, and 73.3%, respectively. Conclusion: This study revealed an association between RYR2 and bleeding complications among patients taking DOACs and established a risk scoring system to support individualized DOAC treatment for these patients.

Dysregulated Calcium Handling in Cirrhotic Cardiomyopathy

Cirrhotic cardiomyopathy is a syndrome of blunted cardiac systolic and diastolic function in patients with cirrhosis. However, the mechanisms remain incompletely known. Since contractility and relaxation depend on cardiomyocyte calcium transients, any factors that impact cardiac contractile and relaxation functions act eventually through calcium transients. In addition, calcium transients play an important role in cardiac arrhythmias. The present review summarizes the calcium handling system and its role in cardiac function in cirrhotic cardiomyopathy and its mechanisms. The calcium handling system includes calcium channels on the sarcolemmal plasma membrane of cardiomyocytes, the intracellular calcium-regulatory apparatus, and pertinent proteins in the cytosol. L-type calcium channels, the main calcium channel in the plasma membrane of cardiomyocytes, are decreased in the cirrhotic heart, and the calcium current is decreased during the action potential both at baseline and under stimulation of beta-adrenergic receptors, which reduces the signal to calcium-induced calcium release. The study of sarcomere length fluctuations and calcium transients demonstrated that calcium leakage exists in cirrhotic cardiomyocytes, which decreases the amount of calcium storage in the sarcoplasmic reticulum (SR). The decreased storage of calcium in the SR underlies the reduced calcium released from the SR, which results in decreased cardiac contractility. Based on studies of heart failure with non-cirrhotic cardiomyopathy, it is believed that the calcium leakage is due to the destabilization of interdomain interactions (dispersion) of ryanodine receptors (RyRs). A similar dispersion of RyRs may also play an important role in reduced contractility. Multiple defects in calcium handling thus contribute to the pathogenesis of cirrhotic cardiomyopathy.

To the Mechanism of the Antiarrhythmic Action of Compound ALM-802: the Role of Ryanodine Receptors

The effect of the compound N¹-(2,3,4-trimethoxy)-N²-{2-[(2,3,4-trimethoxybenzyl)amino]ethyl}-1,2-ethane-diamine (code ALM-802) on the amplitude of the Ca²⁺ response in the cell was studied in in vitro experiments. The concentration of intracellular calcium was assessed using a Fura-2 two-wave probe. The experiments were performed on a culture of isolated rat hippocampal neurons. The effect of compound ALM-802 on the activity of ryanodine receptors (RyR2) was studied on an isolated strip of rat myocardium. The compound ALM-802 (69.8 μM) in hippocampal neurons causes a significant decrease in the amplitude of the Ca²⁺ response induced by addition of KCl to the medium. Experiments performed on an isolated myocardial strip showed that compound ALM-802 (10^-5 M) almost completely blocked the positive inotropic reaction of the strip to the RyR2 agonist caffeine (5×10^-5 M). The data obtained indicate that the decrease in the concentration of Ca²⁺ ions in the cell caused by ALM-802 is due to its ability to block RyR2 located on the membrane of the sarcoplasmic reticulum, which can be associated with the antiarrhythmic activity of the compound.

Augmenting workload drives T-tubule assembly in developing cardiomyocytes

Contraction of cardiomyocytes is initiated at subcellular elements called dyads, where L-type Ca2+ channels in t-tubules are located within close proximity to ryanodine receptors in the sarcoplasmic reticulum. While evidence from small rodents indicates that dyads are assembled gradually in the developing heart, it is unclear how this process occurs in large mammals. We presently examined dyadic formation in fetal and newborn sheep (Ovis aries), and the regulation of this process by fetal cardiac workload. By employing advanced imaging methods, we demonstrated that t-tubule growth and dyadic assembly proceed gradually during fetal sheep development, from 93 days of gestational age until birth (147 days). This process parallels progressive increases in fetal systolic blood pressure, and includes step-wise colocalization of L-type Ca2+ channels and the Na+ /Ca2+ exchanger with ryanodine receptors. These proteins are upregulated together with the dyadic anchor junctophilin-2 during development, alongside changes in the expression of amphiphysin-2 (BIN1) and its partner proteins myotubularin and dynamin-2. Increasing fetal systolic load by infusing plasma or occluding the post-ductal aorta accelerated t-tubule growth. Conversely, reducing fetal systolic load with infusion of enalaprilat, an angiotensin converting enzyme inhibitor, blunted t-tubule formation. Interestingly, altered t-tubule densities did not relate to changes in dyadic junctions, or marked changes in the expression of dyadic regulatory proteins, indicating that distinct signals are responsible for maturation of the sarcoplasmic reticulum. In conclusion, augmenting blood pressure and workload during normal fetal development critically promotes t-tubule growth, while additional signals contribute to dyadic assembly. KEY POINTS: T-tubule growth and dyadic assembly proceed gradually in cardiomyocytes during fetal sheep development, from 93 days of gestational age until the post-natal stage. Increasing fetal systolic load by infusing plasma or occluding the post-ductal aorta accelerated t-tubule growth and hypertrophy. In contrast, reducing fetal systolic load by enalaprilat infusion slowed t-tubule development and decreased cardiomyocyte size. Load-dependent modulation of t-tubule maturation was linked to altered expression patterns of the t-tubule regulatory proteins junctophilin-2 and amphiphysin-2 (BIN1) and its protein partners. Altered t-tubule densities did not influence dyadic formation, indicating that distinct signals are responsible for maturation of the sarcoplasmic reticulum.

The Role of Ryanodine Receptors in Regulating Neuronal Activity and Its Connection to the Development of Alzheimer's Disease

Research into the early impacts of Alzheimer's disease (AD) on synapse function is one of the most promising approaches to finding a treatment. In this context, we have recently demonstrated that the Abeta42 peptide, which builds up in the brain during the processing of the amyloid precursor protein (APP), targets the ryanodine receptors (RyRs) of mouse hippocampal neurons and potentiates calcium (Ca²⁺) release from the endoplasmic reticulum (ER). The uncontrolled increase in intracellular calcium concentration ([Ca²⁺]_i), leading to the development of Ca²⁺ dysregulation events and related excitable and synaptic dysfunctions, is a consolidated hallmark of AD onset and possibly other neurodegenerative diseases. Since RyRs contribute to increasing [Ca²⁺]_i and are thought to be a promising target for AD treatment, the goal of this review is to summarize the current level of knowledge regarding the involvement of RyRs in governing neuronal function both in physiological conditions and during the onset of AD.

Ca2+ Release or Ca2+ Entry, that is the Question: What Governs Ca2+ Oscillations in Pancreatic Beta Cells?

The standard model for Ca²⁺ oscillations in insulin-secreting pancreatic beta cells centers on Ca²⁺ entry through voltage-activated Ca²⁺ channels. These work in combination with ATP-dependent K⁺ channels, which are the bridge between the metabolic state of the cells and plasma membrane potential. This partnership underlies the ability of the beta cells to secrete insulin appropriately on a minute-to-minute time scale to control whole-body plasma glucose. Though this model, developed over more than 40 years through many cycles of experimentation and mathematical modeling, has been very successful, it has been challenged by a hypothesis that calcium-induced calcium release from the endoplasmic reticulum through ryanodine or IP3 receptors is instead the key driver of islet oscillations. We show here that the alternative model is in fact incompatible with a large body of established experimental data and that the new observations offered in support of it can be better explained by the standard model.

Design, Synthesis, and Insecticidal Activities of Novel N-pyridylpyrazole Amide Derivatives Containing a Maleimide

To discover "me-better" insecticidal active molecules targeting ryanodine receptors (RyRs), a series of novel N-pyridylpyrazole amide derivatives containing a maleimide were designed and synthesized in accordance with the prior investigations of our group. Preliminary bioassay findings indicated some compounds containing a maleimide exhibited good larvicidal activities against lepidopteran pests at a concentration of 500 mg L-1. Compound 9j showed 60% larvicidal activities against M. Separata at 50 mg L-1. Compound 9b exhibited 40% larvicidal activities against P. xylostella at 50 mg L-1. Molecular docking study indicated that H-bonds, π-π interaction and cation-π interaction made for the binding of compounds 9b, 9j with P. Xylostella RyR. These results indicated that compounds 9b and 9j could be developed as novel and promising insecticidal leads.

Knockdown of Amyloid Precursor Protein Increases Ion Channel Expression and Alters Ca2+ Signaling Pathways

Although the physiological role of the full-length Amyloid Precursor Protein (APP) and its proteolytic fragments remains unclear, they are definitively crucial for normal synaptic function. Herein, we report that the downregulation of APP in SH-SY5Y cells, using short hairpin RNA (shRNA), alters the expression pattern of several ion channels and signaling proteins that are involved in synaptic and Ca²⁺ signaling. Specifically, the levels of GluR2 and GluR4 subunits of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptors (AMPAR) were significantly increased with APP knockdown. Similarly, the expression of the majority of endoplasmic reticulum (ER) residing proteins, such as the ER Ca²⁺ channels IP₃R (Inositol 1,4,5-triphosphate Receptor) and RyR (Ryanodine Receptor), the Ca²⁺ pump SERCA2 (Sarco/endoplasmic reticulum Ca²⁺ ATPase 2) and the ER Ca²⁺ sensor STIM1 (Stromal Interaction Molecule 1) was upregulated. A shift towards the upregulation of p-AKT, p-PP2A, and p-CaMKIV and the downregulation of p-GSK, p-ERK1/2, p-CaMKII, and p-CREB was observed, interconnecting Ca²⁺ signal transduction from the plasma membrane and ER to the nucleus. Interestingly, we detected reduced responses to several physiological stimuli, with the most prominent being the ineffectiveness of SH-SY5Y/APP- cells to mobilize Ca²⁺ from the ER upon carbachol-induced Ca²⁺ release through IP₃Rs and RyRs. Our data further support an emerging yet perplexing role of APP within a functional molecular network of membrane and cytoplasmic proteins implicated in Ca²⁺ signaling.

Insights into the role of intracellular calcium signaling in the neurobiology of neurodevelopmental disorders

Calcium (Ca²⁺) comprises a critical ionic second messenger in the central nervous system that is under the control of a wide array of regulatory mechanisms, including organellar Ca²⁺ stores, membrane channels and pumps, and intracellular Ca²⁺-binding proteins. Not surprisingly, disturbances in Ca²⁺ homeostasis have been linked to neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. However, aberrations in Ca²⁺ homeostasis have also been implicated in neuropsychiatric disorders with a strong neurodevelopmental component including autism spectrum disorder (ASD) attention-deficit hyperactivity disorder (ADHD) and schizophrenia (SCZ). While plasma membrane Ca²⁺ channels and synaptic Ca²⁺-binding proteins have been extensively studied, increasing evidence suggests a prominent role for intracellular Ca²⁺ stores, such as the endoplasmic reticulum (ER), in aberrant neurodevelopment. In the context of the current mini-review, we discuss recent findings implicating critical intracellular Ca²⁺-handling regulators such as the sarco-ER Ca²⁺ ATPase 2 (SERCA2), ryanodine receptors (RyRs), inositol triphosphate receptors (IP₃Rs), and parvalbumin (PVALB), in the emergence of ASD, SCZ, and ADHD.

The spatio-temporal properties of calcium transients in hippocampal pyramidal neurons in vitro

The spatio-temporal properties of calcium signals were studied in cultured pyramidal neurons of the hippocampus using two-dimensional fluorescence microscopy and ratiometric dye Fura-2. Depolarization-induced Ca²⁺ transients revealed an asynchronous delayed increase in free Ca²⁺ concentration. We found that the level of free resting calcium in the cell nucleus is significantly lower compared to the soma, sub-membrane, and dendritic tree regions. Calcium release from the endoplasmic reticulum under the action of several stimuli (field stimulation, high K⁺ levels, and caffeine) occurs in all areas studied. Under depolarization, calcium signals developed faster in the dendrites than in other areas, while their amplitude was significantly lower since larger and slower responses inside the soma. The peak value of the calcium response to the application of 10 mM caffeine, ryanodine receptors (RyRs) agonist, does not differ in the sub-membrane zone, central region, and nucleus but significantly decreases in the dendrites. In the presence of caffeine, the delay of Ca²⁺ signals between various areas under depolarization significantly declined. Thirty percentage of the peak amplitude of Ca²⁺ transients at prolonged electric field stimulation corresponded to calcium release from the ER store by RyRs, while short-term stimulation did not depend on them. 20 μM dantrolene, RyRs inhibitor, significantly reduces Ca²⁺ transient under high K⁺ levels depolarization of the neuron. RyRs-mediated enhancement of the Ca²⁺ signal is more pronounced in the central part and nucleus compared to the sub-membrane or dendrites regions of the neuron. In summary, using the ratiometric imaging allowed us to obtain additional information about the involvement of RyRs in the intracellular dynamics of Ca²⁺ signals induced by depolarization or electrical stimulation train, with an underlying change in Ca²⁺ concentration in various regions of interest in hippocampal pyramidal neurons.

The ryanodine receptor-calstabin interaction stabilizer S107 protects hippocampal neurons from GABAergic synaptic alterations induced by Abeta42 oligomers

The oligomeric form of the peptide amyloid beta 42 (Abeta42) contributes to the development of synaptic abnormalities and cognitive impairments associated with Alzheimer's disease (AD). To date, there is a gap in knowledge regarding how Abeta42 alters the elementary parameters of GABAergic synaptic function. Here we found that Abeta42 increased the frequency and amplitude of miniature GABAergic currents as well as the amplitude of evoked inhibitory postsynaptic currents. When we focused on paired pulse depression (PPD) to establish whether GABA release probability was affected by Abeta42, we did not observe any significant change. On the other hand, a more detailed investigation of the presynaptic effects induced by Abeta42 by means of multiple probability fluctuation analysis and cumulative amplitude analysis showed an increase in both the size of the readily releasable pool responsible for synchronous release and the number of release sites. We further explored whether ryanodine receptors (RyRs) contributed to exacerbating these changes by stabilizing the interaction between RyRs and the accessory protein calstabin. We observed that the RyR-calstabin interaction stabilizer S107 restored the synaptic parameters to values comparable to those measured in control conditions. In conclusion, our results clarify the mechanisms of potentiation of GABAergic synapses induced by Abeta42. We further suggest that RyRs are involved in the control of synaptic activity during the early stage of AD onset and that their stabilization could represent a new therapeutical approach for AD treatment. KEY POINTS: Accumulation of the peptide amyloid beta 42 (Abeta42) is a key characteristic of Alzheimer's disease (AD) and causes synaptic dysfunctions. To date, the effects of Abeta42 accumulation on GABAergic synapses are poorly understood. The findings reported here suggest that, similarly to what is observed on glutamatergic synapses, Abeta42 modifies GABAergic synapses by targeting ryanodine receptors and causing calcium dysregulation. The GABAergic impairments can be restored by the ryanodine receptor-calstabin interaction stabilizer S107. Based on this research, RyRs stabilization may represent a novel pharmaceutical strategy for preventing or delaying AD.

Functional Characterization of the Ryanodine Receptor Gene in Diaphorina citri

The Asian citrus psyllid Diaphorina citri (Hemiptera: Liviidae) is a major citrus pest spread around the world. It is also a vector of the bacterium 'Candidatus Liberibacter asiaticus', considered the cause of the fatal citrus disease huanglongbing (HLB). Insect ryanodine receptors (RyRs) are the primary target sites of diamide insecticides. In this study, full-length RyR cDNA from D. citri (named DcRyR) was isolated and identified. The 15,393 bp long open reading frame of DcRyR encoded a 5130 amino acid protein with a calculated molecular weight of 580,830 kDa. This protein had a high sequence identity (76-79%) with other insect homologs and a low sequence identity (43-46%) with mammals. An MIR domain, two RIH domains, three SPRY domains, four RyR repeat domains, an RIH-associated domain at the N-terminus, two consensus calcium-binding EF-hands, and six transmembrane domains were among the characteristics that DcRyR shared with insect and vertebrate RyRs. In expression analysis, the DcRyR gene displayed transcript abundance in all tissues and developmental stages as well as gene-differential and stage-specific patterns. In addition, diagnostic PCR experiments revealed that DcRyR had three potential alternative splice variants and that splicing events might have contributed to the various functions of DcRyR. However, diamide resistance-related amino acid residue mutations I4790M/K and G4946E were not found in DcRyR. These results can serve as the basis for further investigation into the target-based diamide pesticide resistance of D. citri.

Doxorubicin-Induced TrkAIII Activation: A Selection Mechanism for Resistant Dormant Neuroblastoma Cells

Patients with advanced neuroblastoma (NB) receive multimodal clinical therapy, including the potent anthracycline chemotherapy drug doxorubicin (Dox). The acquisition of Dox resistance, however, is a major barrier to a sustained response and leads to a poor prognosis in advanced disease states, reinforcing the need to identify and inhibit Dox resistance mechanisms. In this context, we report on the identification and inhibition of a novel Dox resistance mechanism. This mechanism is characterized by the Dox-induced activation of the oncogenic TrkAIII alternative splice variant, resulting in increased Dox resistance, and is blocked by lestaurtinib, entrectinib, and crizotinib tyrosine kinase and LY294002 IP3-K inhibitors. Using time lapse live cell imaging, conventional and co-immunoprecipitation Western blots, RT-PCR, and inhibitor studies, we report that the Dox-induced TrkAIII activation correlates with proliferation inhibition and is CDK1- and Ca²⁺-uniporter-independent. It is mediated by ryanodine receptors; involves Ca²⁺-dependent interactions between TrkAIII, calmodulin and Hsp90; requires oxygen and oxidation; occurs within assembled ERGICs; and does not occur with fully spliced TrkA. The inhibitory effects of lestaurtinib, entrectinib, crizotinib, and LY294002 on the Dox-induced TrkAIII and Akt phosphorylation and resistance confirm roles for TrkAIII and IP3-K consistent with Dox-induced, TrkAIII-mediated pro-survival IP3K/Akt signaling. This mechanism has the potential to select resistant dormant TrkAIII-expressing NB cells, supporting the use of Trk inhibitors during Dox therapy in TrkAIII-expressing NBs.

Design, synthesis and biological activity of diamide compounds based on 3-substituent of the pyrazole ring†

BACKGROUND

Diamide insecticides have attracted significant attention due to their high efficacy and low toxicity to non-target organisms since they were introduced to the market. In order to tackle the problems of insecticide resistance and ecological safety, 16 novel nitrobenzene substituted anthranilic diamides with ester, hydroxyl or sulfonyl at the 3-position of the pyrazole ring were designed and synthesized.

RESULTS

All of these compounds possessed good activity against the ryanodine receptor (RyR) from Spodoptera frugiperda and relatively lower activity against mammalian RyR1, showing a better insect-selectivity compared to chlorantraniliprole in a cell-based assay. The molecular docking analysis predicted the binding conformations of these compounds, which showed a good correlation between the insecticidal activity and the binding scores. In vitro studies using a calcium imaging method demonstrated that the novel compounds could not only activate the RyR but may also target the dihydropyridine receptor on the plasma membrane of insect neurons, implicating a similar but not same mode of action.

CONCLUSION

Substituted anthranilic diamides with an ester at the 3-position of the pyrazole ring exhibited a promising insecticidal activity and better insect-selectivity, which provided insight into the rational design of a new generation of effective diamide insecticides.

Modulation of Ryanodine Receptors Activity Alters the Course of Experimental Autoimmune Encephalomyelitis in Mice

Ryanodine receptors (RyRs), the intracellular Ca²⁺ release channels, are expressed in T lymphocytes and other types of immune cells. Modulation of RyRs has been shown to affect T cell functions in vitro and immune responses in vivo. The effects of modulation of RyRs on the development of autoimmune diseases have not been investigated. Here we studied how modulation of RyRs through administration of RyR inhibitor dantrolene or introducing a gain-of-function RYR1-p.R163C mutation affects clinical progression of experimental autoimmune encephalomyelitis (EAE) in mice, a T cell-mediated autoimmune neuroinflammatory disease. We found that daily intraperitoneal administration of 5 or 10 mg/kg dantrolene beginning at the time of EAE induction significantly reduced the severity of EAE clinical symptoms and dampened inflammation in the spinal cord. The protective effect of dantrolene on EAE was reversible. Dantrolene administration elicited dose-dependent skeletal muscle weakness: mice that received 10 mg/kg dose developed a waddling gait, while 5 mg/kg dantrolene dose administration produced a reduction in four-limb holding impulse values. Mice bearing the gain-of-function RYR1-p.R163C mutation developed the EAE clinical symptoms faster and more severely than wild-type mice. This study demonstrates that RyRs play a significant role in EAE pathogenesis and suggests that inhibition of RyRs with low doses of dantrolene may have a protective effect against autoimmunity and inflammation in humans.

Marine and Anthropogenic Bromopyrroles Alter Cellular Ca2+ Dynamics of Murine Cortical Neuronal Networks by Targeting the Ryanodine Receptor and Sarco/Endoplasmic Reticulum Ca2+-ATPase

Bromopyrroles (BrPyr) are synthesized naturally by marine sponge symbionts and produced anthropogenically as byproducts of wastewater treatment. BrPyr interact with ryanodine receptors (RYRs) and sarco/endoplasmic reticulum (SR/ER) Ca²⁺-ATPase (SERCA). Influences of BrPyr on the neuronal network activity remain uncharted. BrPyr analogues with differing spectra of RYR/SERCA activities were tested using RYR-null or RYR1-expressing HEK293 and murine cortical neuronal/glial cocultures (NGCs) loaded with Fluo-4 to elucidate their mechanisms altering Ca²⁺ dynamics. The NGC electrical spike activity (ESA) was measured from NGCs plated on multielectrode arrays. Nanomolar tetrabromopyrrole (TBP, 1) potentiated caffeine-triggered Ca²⁺ release independent of extracellular [Ca²⁺] in RYR1-HEK293, whereas higher concentrations produce slow and sustained rise in cytoplasmic [Ca²⁺] independent of RYR1 expression. TBP, 2,3,5-tribromopyrrole (2), pyrrole (3), 2,3,4-tribromopyrrole (4), and ethyl 4-bromopyrrole-2-carboxylate (5) added acutely to NGC showed differential potency; rank order TBP (IC₅₀ ≈ 220 nM) > 2 ≫ 5, whereas 3 and 4 were inactive at 10 μM. TBP >2 μM elicited sustained elevation of cytoplasmic [Ca²⁺] and loss of neuronal viability. TBP did not alter network ESA. BrPyr from marine and anthropogenic sources are ecological signaling molecules and emerging anthropogenic pollutants of concern to environmental and human health that potently alter ER Ca²⁺ dynamics and warrant further investigation in vivo.

Phosphoprotein Phosphatase 1 but Not 2A Activity Modulates Coupled-Clock Mechanisms to Impact on Intrinsic Automaticity of Sinoatrial Nodal Pacemaker Cells

Spontaneous AP (action potential) firing of sinoatrial nodal cells (SANC) is critically dependent on protein kinase A (PKA) and Ca²⁺/calmodulin-dependent protein kinase II (CaMKII)-dependent protein phosphorylation, which are required for the generation of spontaneous, diastolic local Ca²⁺ releases (LCRs). Although phosphoprotein phosphatases (PP) regulate protein phosphorylation, the expression level of PPs and phosphatase inhibitors in SANC and the impact of phosphatase inhibition on the spontaneous LCRs and other players of the oscillatory coupled-clock system is unknown. Here, we show that rabbit SANC express both PP1, PP2A, and endogenous PP inhibitors I-1 (PPI-1), dopamine and cyclic adenosine 3′,5′-monophosphate (cAMP)-regulated phosphoprotein (DARPP-32), kinase C-enhanced PP1 inhibitor (KEPI). Application of Calyculin A, (CyA), a PPs inhibitor, to intact, freshly isolated single SANC: (1) significantly increased phospholamban (PLB) phosphorylation (by 2–3-fold) at both CaMKII-dependent Thr¹⁷ and PKA-dependent Ser¹⁶ sites, in a time and concentration dependent manner; (2) increased ryanodine receptor (RyR) phosphorylation at the Ser²⁸⁰⁹ site; (3) substantially increased sarcoplasmic reticulum (SR) Ca²⁺ load; (4) augmented L-type Ca²⁺ current amplitude; (5) augmented LCR’s characteristics and decreased LCR period in intact and permeabilized SANC, and (6) increased the spontaneous basal AP firing rate. In contrast, the selective PP2A inhibitor okadaic acid (100 nmol/L) had no significant effect on spontaneous AP firing, LCR parameters, or PLB phosphorylation. Application of purified PP1 to permeabilized SANC suppressed LCR, whereas purified PP2A had no effect on LCR characteristics. Our numerical model simulations demonstrated that PP inhibition increases AP firing rate via a coupled-clock mechanism, including respective increases in the SR Ca²⁺ pumping rate, L-type Ca²⁺ current, and Na⁺/Ca²⁺-exchanger current. Thus, PP1 and its endogenous inhibitors modulate the basal spontaneous firing rate of cardiac pacemaker cells by suppressing SR Ca²⁺ cycling protein phosphorylation, the SR Ca²⁺ load and LCRs, and L-type Ca²⁺ current.

Pachymic Acid Attenuated Doxorubicin-Induced Heart Failure by Suppressing miR-24 and Preserving Cardiac Junctophilin-2 in Rats

Defects in cardiac contractility and heart failure (HF) are common following doxorubicin (DOX) administration. Different miRs play a role in HF, and their targeting was suggested as a promising therapy. We aimed to target miR-24, a suppressor upstream of junctophilin-2 (JP-2), which is required to affix the sarcoplasmic reticulum to T-tubules, and hence the release of Ca²⁺ in excitation–contraction coupling using pachymic acid (PA) and/or losartan (LN). HF was induced with DOX (3.5 mg/kg, i.p., six doses, twice weekly) in 24 rats. PA and LN (10 mg/kg, daily) were administered orally for four weeks starting the next day of the last DOX dose. Echocardiography, left ventricle (LV) biochemical and histological assessment and electron microscopy were conducted. DOX increased serum BNP, HW/TL, HW/BW, mitochondrial number/size and LV expression of miR-24 but decreased EF, cardiomyocyte fiber diameter, LV content of JP-2 and ryanodine receptors-2 (RyR2). Treatment with either PA or LN reversed these changes. Combined PA + LN attained better results than monotherapies. In conclusion, HF progression following DOX administration can be prevented or even delayed by targeting miR-24 and its downstream JP-2. Our results, therefore, suggest the possibility of using PA alone or as an adjuvant therapy with LN to attain better management of HF patients, especially those who developed tolerance toward LN.

Population structure and insecticide resistance status of Tuta absoluta populations from Turkey

BACKGROUND

Tuta absoluta is a devastating pest in tomato production areas worldwide. After its first introduction to Turkey in 2009, it quickly became the major pest of tomato-growing areas. Although some biocontrol agents have been used, especially in greenhouses, the main control of T. absoluta relies heavily on chemical insecticides. However, failure in chemical control has often been reported due to resistance development. In this study, we investigated (i) the population structure of 22 T. absoluta populations across Turkey by analysing haplotypes, based on the cytochrome oxidase subunit I gene; (ii) the efficacy of three registered insecticides from different classes (metaflumizone, chlorantraniliprole and spinosad) in real field-greenhouse conditions; and (iii) the geographic distribution of target-site mutations associated with insecticide resistance.

RESULTS

The efficacy of spinosad was higher than that of chlorantraniliprole and metaflumizone in the greenhouse trials, as documented by the mortality rates obtained, up to 14 days post application. Known resistance mutations in ryanodine receptors (RyR) (i.e. the I4790M/K and G4946E), nicotinic acetylcholine receptors (G275E), acetylcholinesterases (A201S) and voltage-gated sodium channels (F1845Y and V1848I) were found at various frequencies across the populations genotyped. The I4790K diamide resistance mutation in the RyR has been reported for the first time in T. absoluta populations. Although a total of eight haplotypes were found, the overall mean genetic distance was lower than 0.001, indicating the high genetic homogeneity among Turkish T. absoluta populations.

CONCLUSION

The results will contribute to design area-wide resistance management programs in T. absoluta control in Turkey. However, more monitoring studies are needed to implement evidence-based insecticide resistance management strategies in the frame of integrated pest management. © 2021 Society of Chemical Industry.

Efficacy of RyR2 inhibitor EL20 in induced pluripotent stem cell-derived cardiomyocytes from a patient with catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited cardiac arrhythmia syndrome that often leads to sudden cardiac death. The most common form of CPVT is caused by autosomal-dominant variants in the cardiac ryanodine receptor type-2 (RYR2) gene. Mutations in RYR2 promote calcium (Ca2+ ) leak from the sarcoplasmic reticulum (SR), triggering lethal arrhythmias. Recently, it was demonstrated that tetracaine derivative EL20 specifically inhibits mutant RyR2, normalizes Ca2+ handling and suppresses arrhythmias in a CPVT mouse model. The objective of this study was to determine whether EL20 normalizes SR Ca2+ handling and arrhythmic events in induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from a CPVT patient. Blood samples from a child carrying RyR2 variant RyR2 variant Arg-176-Glu (R176Q) and a mutation-negative relative were reprogrammed into iPSCs using a Sendai virus system. iPSC-CMs were derived using the StemdiffTM kit. Confocal Ca2+ imaging was used to quantify RyR2 activity in the absence and presence of EL20. iPSC-CMs harbouring the R176Q variant demonstrated spontaneous SR Ca2+ release events, whereas administration of EL20 diminished these abnormal events at low nanomolar concentrations (IC50  = 82 nM). Importantly, treatment with EL20 did not have any adverse effects on systolic Ca2+ handling in control iPSC-CMs. Our results show for the first time that tetracaine derivative EL20 normalized SR Ca2+ handling and suppresses arrhythmogenic activity in iPSC-CMs derived from a CPVT patient. Hence, this study confirms that this RyR2-inhibitor represents a promising therapeutic candidate for treatment of CPVT.

Fitness Costs of Chlorantraniliprole Resistance Related to the SeNPF Overexpression in the Spodoptera exigua (Lepidoptera: Noctuidae)

Spodopteraexigua, a multifeeding insect pest, has developed a high level of resistance to chlorantraniliprole, which is a benzoylurea insecticide that targets the ryanodine receptors (RyRs). Herein, the resistant strain (SE-Sel) and sensitive strain (SE-Sus) were obtained by bidirectional screening for six generations. The potential oviposited eggs and oviposition rate of the SE-Sel strain were dramatically lower than those of the SE-Sus strain; on the contrary, the weights of prepupae and preadult were significantly increased. As a post-mating response, the higher number of non-oviposited eggs in the SE-Sel strain was caused by a lower mating rate. In addition, the expression levels of vitellogenin (SeVg) and its receptor (SeVgR) in the SE-Sel strain were consistently lower than those in the SE-Sus strain. An RyR^I4743M mutation, contributing to the resistance to chlorantraniliprole, was located in the S3 transmembrane segments and might have affected the release of calcium ions; it led to the upregulated expression of the neuropeptide SeNPF and its receptor SeNPFR, and the mating and oviposition rate were significantly recovered when the SeNPF was knocked down though RNA interference (RNAi) in the male adult of the SE-Sel strain. Moreover, the expression of the juvenile hormone-binding proteins SeJHBWDS3 and SeJHBAN in the male adult of the SE-Sel strain was significantly decreased, which proved the existence of a fitness cost from another angle. Therefore, these results indicate that the fitness cost accompanied by chlorantraniliprole resistance in S. exigua may be related to the decrease in mating desire due to SeNPF overexpression.

Role of protons in calcium signaling

Thirty-six years after the publication of the important article by Busa and Nuccitelli on the variability of intracellular pH (pHi) and the interdependence of pHi and intracellular Ca2+ concentration ([Ca2+]i), little research has been carried out on pHi and calcium signaling. Moreover, the results appear to be contradictory. Some authors claim that the increase in [Ca2+]i is due to a reduction in pHi, others that it is caused by an increase in pHi. The reasons for these conflicting results have not yet been discussed and clarified in an exhaustive manner. The idea that variations in pHi are insignificant, because cellular buffers quickly stabilize the pHi, may be a limiting and fundamentally wrong concept. In fact, it has been shown that protons can move and react in the cell before they are neutralized. Variations in pHi have a remarkable impact on [Ca2+]i and hence on some of the basic biochemical mechanisms of calcium signaling. This paper focuses on the possible triggering role of protons during their short cellular cycle and it suggests a new hypothesis for an IP3 proton dependent mechanism of action.

CaMKII-dependent ryanodine receptor phosphorylation mediates sepsis-induced cardiomyocyte apoptosis

Sepsis is associated with cardiac dysfunction, which is at least in part due to cardiomyocyte apoptosis. However, the underlying mechanisms are far from being understood. Using the colon ascendens stent peritonitis mouse model of sepsis (CASP), we examined the subcellular mechanisms that mediate sepsis‐induced apoptosis. Wild‐type (WT) CASP mice hearts showed an increase in apoptosis respect to WT‐Sham. CASP transgenic mice expressing a CaMKII inhibitory peptide (AC3‐I) were protected against sepsis‐induced apoptosis. Dantrolene, used to reduce ryanodine receptor (RyR) diastolic sarcoplasmic reticulum (SR) Ca²⁺ release, prevented apoptosis in WT‐CASP. To examine whether CaMKII‐dependent RyR2 phosphorylation mediates diastolic Ca²⁺ release and apoptosis in sepsis, we evaluated apoptosis in mutant mice hearts that have the CaMKII phosphorylation site of RyR2 (Serine 2814) mutated to Alanine (S2814A). S2814A CASP mice did not show increased apoptosis. Consistent with RyR2 phosphorylation‐dependent enhancement in diastolic SR Ca²⁺ release leading to mitochondrial Ca²⁺ overload, mitochondrial Ca²⁺ retention capacity was reduced in mitochondria isolated from WT‐CASP compared to Sham and this reduction was absent in mitochondria from CASP S2814A or dantrolene‐treated mice. We conclude that in sepsis, CaMKII‐dependent RyR2 phosphorylation results in diastolic Ca²⁺ release from SR which leads to mitochondrial Ca²⁺ overload and apoptosis.

Disturbances in Calcium Homeostasis Promotes Skeletal Muscle Atrophy: Lessons From Ventilator-Induced Diaphragm Wasting

Mechanical ventilation (MV) is often a life-saving intervention for patients in respiratory failure. Unfortunately, a common and undesired consequence of prolonged MV is the development of diaphragmatic atrophy and contractile dysfunction. This MV-induced diaphragmatic weakness is commonly labeled “ventilator-induced diaphragm dysfunction” (VIDD). VIDD is an important clinical problem because diaphragmatic weakness is a major risk factor for the failure to wean patients from MV; this inability to remove patients from ventilator support results in prolonged hospitalization and increased morbidity and mortality. Although several processes contribute to the development of VIDD, it is clear that oxidative stress leading to the rapid activation of proteases is a primary contributor. While all major proteolytic systems likely contribute to VIDD, emerging evidence reveals that activation of the calcium-activated protease calpain plays a required role. This review highlights the signaling pathways leading to VIDD with a focus on the cellular events that promote increased cytosolic calcium levels and the subsequent activation of calpain within diaphragm muscle fibers. In particular, we discuss the emerging evidence that increased mitochondrial production of reactive oxygen species promotes oxidation of the ryanodine receptor/calcium release channel, resulting in calcium release from the sarcoplasmic reticulum, accelerated proteolysis, and VIDD. We conclude with a discussion of important and unanswered questions associated with disturbances in calcium homeostasis in diaphragm muscle fibers during prolonged MV.

Maurocalcin and its analog MCaE12A facilitate Ca2+ mobilization in cardiomyocytes

Ryanodine receptors are responsible for the massive release of calcium from the sarcoplasmic reticulum that triggers heart muscle contraction. Maurocalcin (MCa) is a 33 amino acid peptide toxin known to target skeletal ryanodine receptor. We investigated the effect of MCa and its analog MCaE12A on isolated cardiac ryanodine receptor (RyR2), and showed that they increase RyR2 sensitivity to cytoplasmic calcium concentrations promoting channel opening and decreases its sensitivity to inhibiting calcium concentrations. By measuring intracellular Ca2+ transients, calcium sparks and contraction on cardiomyocytes isolated from adult rats or differentiated from human-induced pluripotent stem cells, we demonstrated that MCaE12A passively penetrates cardiomyocytes and promotes the abnormal opening of RyR2. We also investigated the effect of MCaE12A on the pacemaker activity of sinus node cells from different mice lines and showed that, MCaE12A improves pacemaker activity of sinus node cells obtained from mice lacking L-type Cav1.3 channel, or following selective pharmacologic inhibition of calcium influx via Cav1.3. Our results identify MCaE12A as a high-affinity modulator of RyR2 and make it an important tool for RyR2 structure-to-function studies as well as for manipulating Ca2+ homeostasis and dynamic of cardiac cells.

Enhanced Klotho availability protects against cardiac dysfunction induced by uraemic cardiomyopathy by regulating Ca2+ handling

BACKGROUND AND PURPOSE

Klotho is a membrane-bound or soluble protein, originally identified as an age-suppressing factor and regulator of mineral metabolism. Klotho deficiency is associated with the development of renal disease, but its role in cardiac function in the context of uraemic cardiomyopathy is unknown.

EXPERIMENTAL APPROACH

We explored the effects of Klotho on cardiac Ca2+ cycling. We analysed Ca2+ handling in adult cardiomyocytes from Klotho-deficient (kl/kl) mice and from a murine model of 5/6 nephrectomy (Nfx). We also studied the effect of exogenous Klotho supplementation, by chronic recombinant Klotho treatment, or endogenous Klotho overexpression, using transgenic mice overexpressing Klotho (Tg-Kl), on uraemic cardiomyopathy. Hearts from Nfx mice were used to study Ca2+ sensitivity of ryanodine receptors and their phosphorylation state.

KEY RESULTS

Cardiomyocytes from kl/kl mice showed decreased amplitude of intracellular Ca2+ transients and cellular shortening together with an increase in pro-arrhythmic Ca2+ events compared with cells from wild-type mice. Cardiomyocytes from Nfx mice exhibited the same impairment in Ca2+ cycling as kl/kl mice. Changes in Nfx cardiomyocytes were explained by higher sensitivity of ryanodine receptors to Ca2+ and their increased phosphorylation at the calmodulin kinase type II and protein kinase A sites. Ca2+ mishandling in Nfx-treated mice was fully prevented by chronic recombinant Klotho administration or transgenic Klotho overexpression.

CONCLUSIONS AND IMPLICATIONS

Klotho emerges as an attractive therapeutic tool to improve cardiac Ca2+ mishandling observed in uraemic cardiomyopathy. Strategies that improve Klotho availability are good candidates to protect the heart from functional cardiac alterations in renal disease.

Synthesis, Insecticidal Evaluation, and 3D-QASR of Novel Anthranilic Diamide Derivatives Containing N-Arylpyrrole as Potential Ryanodine Receptor Activators

To cope with the global food shortage and insect pest, there is an urgent need to discover new pesticides with novel modes of actions. Ryanodine receptor (RyR) insecticides showed great promise in integrated pest management. Herein, we report the synthesis of novel anthranilic diamide derivatives incorporating pyrrole moieties targeting at insect RyRs. The structures were confirmed by ¹H NMR, ¹³C NMR, ¹⁹F NMR, and high-resolution mass spectrometry. The preliminary bioassay results indicated that most of the title compounds showed good to excellent insecticidal activities against the oriental armyworm (Mythimna separata) and diamondback moth (Plutella xylostella). For the oriental armyworm, Ij displayed the same level of larvicidal activity as the positive control chlorantraniliprole, with an LC₅₀ value of 0.21 mg/L. For the diamondback moth, In, Io, Ip, and Iq exhibited higher insecticidal activities than chlorantraniliprole. In particular, In had 50% larvicidal activity at 0.00001 mg/L. The calcium imaging technique was applied to study the effect of Ij, In, and Ip on the intracellular calcium ion concentration ([Ca²⁺]_i) in central neurons isolated from the oriental armyworm. The results indicated that the tested compounds, such as chlorantraniliprole, could activate the insect RyRs. Furthermore, comparative molecular field analysis and density functional theory calculations were carried out to study the structure-activity relationship.

Interactions of Dichlorodiphenyltrichloroethane (DDT) and Dichlorodiphenyldichloroethylene (DDE) With Skeletal Muscle Ryanodine Receptor Type 1

Dichlorodiphenyltrichloroethane (DDT) and its metabolite dichlorodiphenyldichloroethylene (DDE) are ubiquitous in the environment and detected in tissues of living organisms. Although DDT owes its insecticidal activity to impeding closure of voltage-gated sodium channels, it mediates toxicity in mammals by acting as an endocrine disruptor (ED). Numerous studies demonstrate DDT/DDE to be EDs, but studies examining muscle-specific effects mediated by nonhormonal receptors in mammals are lacking. Therefore, we investigated whether o,p'-DDT, p,p'-DDT, o,p'-DDE, and p,p'-DDE (DDx, collectively) alter the function of ryanodine receptor type 1 (RyR1), a protein critical for skeletal muscle excitation-contraction coupling and muscle health. DDx (0.01-10 µM) elicited concentration-dependent increases in [3H]ryanodine ([3H]Ry) binding to RyR1 with o,p'-DDE showing highest potency and efficacy. DDx also showed sex differences in [3H]Ry-binding efficacy toward RyR1, where [3H]Ry-binding in female muscle preparations was greater than male counterparts. Measurements of Ca2+ transport across sarcoplasmic reticulum (SR) membrane vesicles further confirmed DDx can selectively engage with RyR1 to cause Ca2+ efflux from SR stores. DDx also disrupts RyR1-signaling in HEK293T cells stably expressing RyR1 (HEK-RyR1). Pretreatment with DDx (0.1-10 µM) for 100 s, 12 h, or 24 h significantly sensitized Ca2+-efflux triggered by RyR agonist caffeine in a concentration-dependent manner. o,p'-DDE (24 h; 1 µM) significantly increased Ca2+-transient amplitude from electrically stimulated mouse myotubes compared with control and displayed abnormal fatigability. In conclusion, our study demonstrates DDx can directly interact and modulate RyR1 conformation, thereby altering SR Ca2+-dynamics and sensitize RyR1-expressing cells to RyR1 activators, which may ultimately contribute to long-term impairments in muscle health.

Elementary calcium signaling in arterial smooth muscle

Vascular smooth muscle cells (VSMCs) of small peripheral arteries contribute to blood pressure control by adapting their contractile state. These adaptations depend on the VSMC cytosolic Ca²⁺ concentration, regulated by complex local elementary Ca²⁺ signaling pathways. Ca²⁺ sparks represent local, transient, rapid calcium release events from a cluster of ryanodine receptors (RyRs) in the sarcoplasmic reticulum. In arterial SMCs, Ca²⁺ sparks activate nearby calcium-dependent potassium channels, cause membrane hyperpolarization and thus decrease the global intracellular [Ca²⁺] to oppose vasoconstriction. Arterial SMC Ca_v1.2 L-type channels regulate intracellular calcium stores content, which in turn modulates calcium efflux through RyRs. Ca_v3.2 T-type channels contribute to a minor extend to Ca²⁺ spark generation in certain types of arteries. Their localization within cell membrane caveolae is essential. We summarize present data on local elementary calcium signaling (Ca²⁺ sparks) in arterial SMCs with focus on RyR isoforms, large-conductance calcium-dependent potassium (BK_Ca) channels, and cell membrane-bound calcium channels (Ca_v1.2 and Ca_v3.2), particularly in caveolar microdomains.

A highly selective and sensitive fluorescence probe for a specific binding site on insect ryanodine receptors

There is a significant need to study the binding of active compounds to the specific sites on insect ryanodine receptors (RyRs) that are the targets of two novel classes of diamide insecticides to which insects are becoming increasingly resistant. Here, we describe a rapid assay to study the action of potential compounds on the flubendiamide (Flu) binding site of insect RyRs that uses a fluorescence polarization assay with the fluorescence probe Flu-R-L that we synthesized. The IC₅₀ of Flu for inhibiting probe binding on insect RyR was 18.82 ng/mL. The binding of 86 novel phthalic diamide derivatives on insect RyRs was studied using this newly established assay, and the compounds that exhibited high-affinity binding in the assay also possessed in vivo insecticidal activity against Plutella xylostella. Thus, Flu-R-L is a highly selective and sensitive fluorescence probe for studying the binding affinity of novel compounds to the Flu binding site of insect RyRs. The assay based on Flu-R-L is a rapid, accurate, and sensitive method for the screening of potentially bioactive molecules that bind specifically to insect RyRs.

Australian Scorpion Hormurus waigiensis Venom Fractions Show Broad Bioactivity Through Modulation of Bio-Impedance and Cytosolic Calcium

Scorpion venoms are a rich source of bioactive molecules, but characterisation of toxin peptides affecting cytosolic Ca2+, central to cell signalling and cell death, is limited. We undertook a functional screening of the venom of the Australian scorpion Hormurus waigiensis to determine the breadth of Ca2+ mobilisation. A human embryonic kidney (HEK293) cell line stably expressing the genetically encoded Ca2+ reporter GCaMP5G and the rabbit type 1 ryanodine receptor (RyR1) was developed as a biosensor. Size-exclusion Fast Protein Liquid Chromatography separated the venom into 53 fractions, constituting 12 chromatographic peaks. Liquid chromatography mass spectroscopy identified 182 distinct molecules with 3 to 63 components per peak. The molecular weights varied from 258 Da-13.6 kDa, with 53% under 1 kDa. The majority of the venom chromatographic peaks (tested as six venom pools) were found to reversibly modulate cell monolayer bioimpedance, detected using the xCELLigence platform (ACEA Biosciences). Confocal Ca2+ imaging showed 9/14 peak samples, with molecules spanning the molecular size range, increased cytosolic Ca2+ mobilization. H. waigiensis venom Ca2+ activity was correlated with changes in bio-impedance, reflecting multi-modal toxin actions on cell physiology across the venom proteome.

Age attenuates the T-type CaV 3.2-RyR axis in vascular smooth muscle

Caveolae position Ca_V3.2 (T‐type Ca²⁺ channel encoded by the α‐3.2 subunit) sufficiently close to RyR (ryanodine receptors) for extracellular Ca²⁺ influx to trigger Ca²⁺ sparks and large‐conductance Ca²⁺‐activated K⁺ channel feedback in vascular smooth muscle. We hypothesize that this mechanism of Ca²⁺ spark generation is affected by age. Using smooth muscle cells (VSMCs) from mouse mesenteric arteries, we found that both Ca_v3.2 channel inhibition by Ni²⁺ (50 µM) and caveolae disruption by methyl‐ß‐cyclodextrin or genetic abolition of Eps15 homology domain‐containing protein (EHD2) inhibited Ca²⁺ sparks in cells from young (4 months) but not old (12 months) mice. In accordance, expression of Ca_v3.2 channel was higher in mesenteric arteries from young than old mice. Similar effects were observed for caveolae density. Using SMAKO Ca_v1.2^−/− mice, caffeine (RyR activator) and thapsigargin (Ca²⁺ transport ATPase inhibitor), we found that sufficient SR Ca²⁺ load is a prerequisite for the Ca_V3.2‐RyR axis to generate Ca²⁺ sparks. We identified a fraction of Ca²⁺ sparks in aged VSMCs, which is sensitive to the TRP channel blocker Gd³⁺ (100 µM), but insensitive to Ca_V1.2 and Ca_V3.2 channel blockade. Our data demonstrate that the VSMC Ca_V3.2‐RyR axis is down‐regulated by aging. This defective Ca_V3.2‐RyR coupling is counterbalanced by a Gd³⁺ sensitive Ca²⁺ pathway providing compensatory Ca²⁺ influx for triggering Ca²⁺ sparks in aged VSMCs.

Propofol affects mouse embryonic fibroblast survival and proliferation in vitro via ATG5- and calcium-dependent regulation of autophagy

Propofol is a commonly used intravenous anesthetic agent, which has been found to affect cell survival and proliferation especially in early life. Our previous studies show that propofol-induced neurodegeneration and neurogenesis are closely associated with cell autophagy. In the present study we explored the roles of autophagy-related gene 5 (ATG5) in propofol-induced autophagy in mouse embryonic fibroblasts (MEF) in vitro. We showed that ATG5 was functionally related to propofol-induced cell survival and damage: propofol significantly enhanced cell survival and proliferation at a clinically relevant dose (10 µM), but caused cell death at an extremely high concentration (200 µM) in ATG5^−/− MEF, but not in WT cells. The dual effects found in ATG5^−/− MEF could be blocked by intracellular Ca²⁺ channel antagonists. We also found that propofol evoked a moderate (promote cell growth) and extremely high (cause apoptosis) cytosolic Ca²⁺ elevation at the concentrations of 10 µM and 200 µM, respectively, only in ATG5^−/− MEF. In addition, ATG5^−/− MEF themselves released more Ca²⁺ in cytosolic space and endoplasmic reticulum compared with WT cells, suggesting that autophagy deficiency made intracellular calcium signaling more vulnerable to external stimuli (propofol). Altogether, our results reveal that ATG5 plays a crucial role in propofol regulation of cell survival and proliferation by affecting intracellular Ca²⁺ homeostasis.

Alternative splicing and insect ryanodine receptor

Phylogenetic tree of the ryanodine receptor (RyR) family based on maximum likelihood estimation.

One or Two Ca2+ Stores in the Neuronal Endoplasmic Reticulum?

It is generally accepted that the endoplasmic reticulum (ER) has one continuous lumen and operates as one unified Ca²⁺ store, but new data from Chen-Engerer et al. in hippocampal neurons now challenge this idea and indicate that receptors for inositol trisphosphate (IP₃) and ryanodine may be located in two functionally distinct Ca²⁺ stores. Are both these stores in the ER?

TNF Induces Pathogenic Programmed Macrophage Necrosis in Tuberculosis through a Mitochondrial-Lysosomal-Endoplasmic Reticulum Circuit

Necrosis of infected macrophages constitutes a critical pathogenetic event in tuberculosis by releasing mycobacteria into the growth-permissive extracellular environment. In zebrafish infected with Mycobacterium marinum or Mycobacterium tuberculosis, excess tumor necrosis factor triggers programmed necrosis of infected macrophages through the production of mitochondrial reactive oxygen species (ROS) and the participation of cyclophilin D, a component of the mitochondrial permeability transition pore. Here, we show that this necrosis pathway is not mitochondrion-intrinsic but results from an inter-organellar circuit initiating and culminating in the mitochondrion. Mitochondrial ROS induce production of lysosomal ceramide that ultimately activates the cytosolic protein BAX. BAX promotes calcium flow from the endoplasmic reticulum into the mitochondrion through ryanodine receptors, and the resultant mitochondrial calcium overload triggers cyclophilin-D-mediated necrosis. We identify ryanodine receptors and plasma membrane L-type calcium channels as druggable targets to intercept mitochondrial calcium overload and necrosis of mycobacterium-infected zebrafish and human macrophages.

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TNF induces mitochondrial ROS to cause necrosis of mycobacterium-infected macrophages

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Mitochondrial ROS activate lysosomal enzymes that lead to BAX activation

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BAX activates ER ryanodine receptors to cause Ca²⁺ flow into the mitochondrion

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Drugs preventing mitochondrial Ca²⁺ overload prevent pathogenic macrophage necrosis in TB

New Linear Precursors of cIDPR Derivatives as Stable Analogs of cADPR: A Potent Second Messenger with Ca2+-Modulating Activity Isolated from Sea Urchin Eggs

Herein, we report on the synthesis of a small set of linear precursors of an inosine analogue of cyclic ADP-ribose (cADPR), a second messenger involved in Ca2+ mobilization from ryanodine receptor stores firstly isolated from sea urchin eggs extracts. The synthesized compounds were obtained starting from inosine and are characterized by an N1-alkyl chain replacing the "northern" ribose and a phosphate group attached at the end of the N1-alkyl chain and/or 5'-sugar positions. Preliminary Ca2+ mobilization assays, performed on differentiated C2C12 cells, are reported as well.

Early Alterations of Hippocampal Neuronal Firing Induced by Abeta42

We studied the effect of Amyloid β 1-42 oligomers (Abeta42) on Ca2+ dependent excitability profile of hippocampal neurons. Abeta42 is one of the Amyloid beta peptides produced by the proteolytic processing of the amyloid precursor protein and participates in the initiating event triggering the progressive dismantling of synapses and neuronal circuits. Our experiments on cultured hippocampal network reveal that Abeta42 increases intracellular Ca2+ concentration by 46% and inhibits firing discharge by 19%. More precisely, Abeta42 differently regulates ryanodine (RyRs), NMDA receptors (NMDARs), and voltage gated calcium channels (VGCCs) by increasing Ca2+ release through RyRs and inhibiting Ca2+ influx through NMDARs and VGCCs. The overall increased intracellular Ca2+ concentration causes stimulation of K+ current carried by big conductance Ca2+ activated potassium (BK) channels and hippocampal network firing inhibition. We conclude that Abeta42 alters neuronal function by means of at least 4 main targets: RyRs, NMDARs, VGCCs, and BK channels. The development of selective modulators of these channels may in turn be useful for developing effective therapies that could enhance the quality of life of AD patients during the early onset of the pathology.

Role of Ryanodine Type 2 Receptors in Elementary Ca2+ Signaling in Arteries and Vascular Adaptive Responses

Background Hypertension is the major risk factor for cardiovascular disease, the most common cause of death worldwide. Resistance arteries are capable of adapting their diameter independently in response to pressure and flow-associated shear stress. Ryanodine receptors (RyRs) are major Ca2+-release channels in the sarcoplasmic reticulum membrane of myocytes that contribute to the regulation of contractility. Vascular smooth muscle cells exhibit 3 different RyR isoforms (RyR1, RyR2, and RyR3), but the impact of individual RyR isoforms on adaptive vascular responses is largely unknown. Herein, we generated tamoxifen-inducible smooth muscle cell-specific RyR2-deficient mice and tested the hypothesis that vascular smooth muscle cell RyR2s play a specific role in elementary Ca2+ signaling and adaptive vascular responses to vascular pressure and/or flow. Methods and Results Targeted deletion of the Ryr2 gene resulted in a complete loss of sarcoplasmic reticulum-mediated Ca2+-release events and associated Ca2+-activated, large-conductance K+ channel currents in peripheral arteries, leading to increased myogenic tone and systemic blood pressure. In the absence of RyR2, the pulmonary artery pressure response to sustained hypoxia was enhanced, but flow-dependent effects, including blood flow recovery in ischemic hind limbs, were unaffected. Conclusions Our results establish that RyR2-mediated Ca2+-release events in VSCM s specifically regulate myogenic tone (systemic circulation) and arterial adaptation in response to changes in pressure (hypoxic lung model), but not flow. They further suggest that vascular smooth muscle cell-expressed RyR2 deserves scrutiny as a therapeutic target for the treatment of vascular responses in hypertension and chronic vascular diseases.

IP3R and RyR channels are involved in traffic-related PM2.5-induced disorders of calcium homeostasis

Traffic-related PM_2.5 can result in immune system damage and diseases; however, the possible mechanism of its effect remains unclear. Calcium (Ca²⁺) is a critical signaling molecule in a variety of cells. Indeed, Ca²⁺ is involved in numerous basic functions, including cell growth and death. In this study, Jurkat T cells were used to explore the possible mechanisms of PM_2.5-elicited intracellular Ca²⁺signal responses. The results indicate that PM_2.5 could raise the level of intracellular Ca²⁺ concentration ([Ca²⁺]i). The [Ca²⁺]i in Jurkat T cells significantly decreased after treatment with heparin as an inhibitor of inositol trisphosphate receptors (IP3 R), or procaine as an inhibitor of ryanodine receptors (RyR). The expression of calmodulin (CAM) protein decreased in a time-dependent manner after exposure to PM_2.5, whereas the activity of Ca²⁺-Mg²⁺-ATPase seemed to show a slight drop trend after exposure to PM_2.5. Our findings demonstrate that PM_2.5 stimulation to Jurkat T cells would result in an increase in [Ca²⁺]i, which is modulated by IP3 R and RyR, as well as CAM.

Estradiol-Mediated Axogenesis of Hypothalamic Neurons Requires ERK1/2 and Ryanodine Receptors-Dependent Intracellular Ca2+ Rise in Male Rats

17β-estradiol (E2) induces axonal growth through extracellular signal-regulated kinase 1 and 2 (ERK1/2)-MAPK cascade in hypothalamic neurons of male rat embryos in vitro, but the mechanism that initiates these events is poorly understood. This study reports the intracellular Ca²⁺ increase that participates in the activation of ERK1/2 and axogenesis induced by E2. Hypothalamic neuron cultures were established from 16-day-old male rat embryos and fed with astroglia-conditioned media for 48 h. E2-induced ERK phosphorylation was completely abolished by a ryanodine receptor (RyR) inhibitor (ryanodine) and partially attenuated by an L-type voltage-gated Ca²⁺ channel (L-VGCC) blocker (nifedipine), an inositol-1,4,5-trisphosphate receptor (IP₃R) inhibitor (2-APB), and a phospholipase C (PLC) inhibitor (U-73122). We also conducted Ca²⁺ imaging recording using primary cultured neurons. The results show that E2 rapidly induces an increase in cytosolic Ca²⁺, which often occurs in repetitive Ca²⁺ oscillations. This response was not observed in the absence of extracellular Ca²⁺ or with inhibitory ryanodine and was markedly reduced by nifedipine. E2-induced axonal growth was completely inhibited by ryanodine. In summary, the results suggest that Ca²⁺ mobilization from extracellular space as well as from the endoplasmic reticulum is necessary for E2-induced ERK1/2 activation and axogenesis. Understanding the mechanisms of brain estrogenic actions might contribute to develop novel estrogen-based therapies for neurodegenerative diseases.

Ca2+-dependent calmodulin binding to cardiac ryanodine receptor (RyR2) calmodulin-binding domains

The Ca²⁺ sensor calmodulin (CaM) regulates cardiac ryanodine receptor (RyR2)-mediated Ca²⁺ release from the sarcoplasmic reticulum. CaM inhibits RyR2 in a Ca²⁺-dependent manner and aberrant CaM-dependent inhibition results in life-threatening cardiac arrhythmias. However, the molecular details of the CaM–RyR2 interaction remain unclear. Four CaM-binding domains (CaMBD1a, -1b, -2, and -3) in RyR2 have been proposed. Here, we investigated the Ca²⁺-dependent interactions between CaM and these CaMBDs by monitoring changes in the fluorescence anisotropy of carboxytetramethylrhodamine (TAMRA)-labeled CaMBD peptides during titration with CaM at a wide range of Ca²⁺ concentrations. We showed that CaM bound to all four CaMBDs with affinities that increased with Ca²⁺ concentration. CaM bound to CaMBD2 and -3 with high affinities across all Ca²⁺ concentrations tested, but bound to CaMBD1a and -1b only at Ca²⁺ concentrations above 0.2 µM. Binding experiments using individual CaM domains revealed that the CaM C-domain preferentially bound to CaMBD2, and the N-domain to CaMBD3. Moreover, the Ca²⁺ affinity of the CaM C-domain in complex with CaMBD2 or -3 was so high that these complexes are essentially Ca²⁺ saturated under resting Ca²⁺ conditions. Conversely, the N-domain senses Ca²⁺ exactly in the transition from resting to activating Ca²⁺ when complexed to either CaMBD2 or -3. Altogether, our results support a binding model where the CaM C-domain is anchored to RyR2 CaMBD2 and saturated with Ca²⁺ during Ca²⁺ oscillations, while the CaM N-domain functions as a dynamic Ca²⁺ sensor that can bridge noncontiguous regions of RyR2 or clamp down onto CaMBD2.

Caffeine chelates calcium in the lumen of the endoplasmic reticulum

Cytosolic Ca²⁺ signals are often amplified by massive calcium release from the endoplasmic reticulum (ER). This calcium-induced calcium release (CICR) occurs by activation of an ER Ca²⁺ channel, the ryanodine receptor (RyR), which is facilitated by both cytosolic- and ER Ca²⁺ levels. Caffeine sensitizes RyR to Ca²⁺ and promotes ER Ca²⁺ release at basal cytosolic Ca²⁺ levels. This outcome is frequently used as a readout for the presence of CICR. By monitoring ER luminal Ca²⁺ with the low-affinity genetic Ca²⁺ probe erGAP3, we find here that application of 50 mM caffeine rapidly reduces the Ca²⁺ content of the ER in HeLa cells by ∼50%. Interestingly, this apparent ER Ca²⁺ release does not go along with the expected cytosolic Ca²⁺ increase. These results can be explained by Ca²⁺ chelation by caffeine inside the ER. Ca²⁺-overloaded mitochondria also display a drop of the matrix Ca²⁺ concentration upon caffeine addition. In contrast, in the cytosol, with a low free Ca²⁺ concentration (10^-7 M), no chelation is observed. Expression of RyR3 sensitizes the responses to caffeine with effects both in the ER (increase in Ca²⁺ release) and in the cytosol (increase in Ca²⁺ peak) at low caffeine concentrations (0.3-1 mM) that have no effects in control cells. Our results illustrate the fact that simultaneous monitoring of both cytosolic- and ER Ca²⁺ are necessary to understand the action of caffeine and raise concerns against the use of high concentrations of caffeine as a readout of the presence of CICR.

Shining New Light on the Structural Determinants of Cardiac Couplon Function: Insights From Ten Years of Nanoscale Microscopy

Remodelling of the membranes and protein clustering patterns during the pathogenesis of cardiomyopathies has renewed the interest in spatial visualisation of these structures in cardiomyocytes. Coincidental emergence of single molecule (super-resolution) imaging and tomographic electron microscopy tools in the last decade have led to a number of new observations on the structural features of the couplons, the primary sites of excitation-contraction coupling in the heart. In particular, super-resolution and tomographic electron micrographs have revised and refined the classical views of the nanoscale geometries of couplons, t-tubules and the organisation of the principal calcium handling proteins in both healthy and failing hearts. These methods have also allowed the visualisation of some features which were too small to be detected with conventional microscopy tools. With new analytical capabilities such as single-protein mapping, in situ protein quantification, correlative and live cell imaging we are now observing an unprecedented interest in adapting these research tools across the cardiac biophysical research discipline. In this article, we review the depth of the new insights that have been enabled by these tools toward understanding the structure and function of the cardiac couplon. We outline the major challenges that remain in these experiments and emerging avenues of research which will be enabled by these technologies.

Activation of CaMKIIδA promotes Ca2+ leak from the sarcoplasmic reticulum in cardiomyocytes of chronic heart failure rats

Activation of the Ca²⁺/calmodulin-dependent protein kinase II isoform δA (CaMKIIδA) disturbs intracellular Ca²⁺ homeostasis in cardiomyocytes during chronic heart failure (CHF). We hypothesized that upregulation of CaMKIIδA in cardiomyocytes might enhance Ca²⁺ leak from the sarcoplasmic reticulum (SR) via activation of phosphorylated ryanodine receptor type 2 (P-RyR2) and decrease Ca²⁺ uptake by inhibition of SR calcium ATPase 2a (SERCA2a). In this study, CHF was induced in rats by ligation of the left anterior descending coronary artery. We found that CHF caused an increase in the expression of CaMKIIδA and P-RyR2 in the left ventricle (LV). The role of CaMKIIδA in regulation of P-RyR2 was elucidated in cardiomyocytes isolated from neonatal rats in vitro. Hypoxia induced upregulation of CaMKIIδA and activation of P-RyR2 in the cardiomyocytes, which both were attenuated by knockdown of CaMKIIδA. Furthermore, we showed that knockdown of CaMKIIδA significantly decreased the Ca²⁺ leak from the SR elicited by hypoxia in the cardiomyocytes. In addition, CHF also induced a downregulation of SERCA2a in the LV of CHF rats. Knockdown of CaMKIIδA normalized hypoxia-induced downregulation of SERCA2a in cardiomyocytes in vitro. The results demonstrate that the inhibition of CaMKIIδA may improve cardiac function by preventing SR Ca²⁺ leak through downregulation of P-RyR2 and upregulation of SERCA2a expression in cardiomyocytes in CHF.