Biology subjects

Yule, D. I.

Publications and source records attributed to Yule, D. I..

15 recordsLinked to original sources

bioRxiv2025

Ascl3+ ionocytes in murine salivary gland ducts are innervated sensory cells that display unique calcium signaling characteristics and contribute to the composition of saliva

Ionocytes are distinct epithelial sensory cells scattered throughout the ductal system of the salivary glands. These cells are distinguished by their unusual morphology, as well as by a specific transcriptomic signature that includes expression of the Foxi1 and Ascl3 transcription factors. Currently, little is known about the biology or function of ionocytes in the salivary glands. To facilitate characterization of these cells, we generated an inducible Cre mouse allele driven by the Ascl3 promoter. This strain was crossed with a reporter to fluorescently label Ascl3+ ionocytes, highlighting that they are the site of enriched CFTR expression in the salivary glands, and demonstrating the proximity of these cells to neurons. Conditional Cre-mediated cell ablation, using diphtheria toxin (DTA), removed Ascl3+ ionocytes from the salivary glands and resulted in an altered pH of total saliva, supporting a function for ionocytes in transepithelial ion flow. Finally, Cre-mediated expression of the calcium indicator GCaMP6f revealed that Ascl3+ ionocytes exhibit unique properties not observed in acinar or surrounding duct cells, including elevated basal [Ca2+]I, spontaneous blinking in the absence of stimulation, and a rapid loss of [Ca2+]I following nerve stimulation. These unique properties distinguish ionocytes as a specialized subset of salivary gland duct cells.

physiology↗

bioRxiv2024

Functional investigation of a putative calcium-binding site involved in the inhibition of inositol 1,4,5-trisphosphate receptor activity

A wide variety of factors influence inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) activity resulting in modulation of intracellular Ca2+ release. This regulation is thought to define the spatio-temporal patterns of Ca2+ signals necessary for the appropriate activation of downstream effectors. The binding of both IP3 and Ca2+ are obligatory for IP3R channel opening, however, Ca2+ regulates IP3R activity in a biphasic manner. Mutational studies have revealed that Ca2+ binding to a high-affinity pocket formed by the ARM3 domain and linker domain promotes IP3R channel opening without altering the Ca2+ dependency for channel inactivation. These data suggest a distinct low-affinity Ca2+ binding site is responsible for the reduction in IP3R activity at higher [Ca2+]. We determined the consequences of mutating a cluster of acidic residues in the ARM2 and central linker domain reported to coordinate Ca2+ in cryo-EM structures of the IP3R type 3. This site is termed the "CD Ca2+ binding site" and is well-conserved in all IP3R sub-types. We show that the CD site Ca2+ binding mutants where the negatively charged glutamic acid residues are mutated to alanine exhibited enhanced sensitivity to IP3-generating agonists. Ca2+ binding mutants displayed spontaneous elemental Ca2+ events (Ca2+ puffs) and the number of IP3-induced Ca2+ puffs was significantly augmented in cells stably expressing Ca2+ binding site mutants. When measured with "on-nucleus" patch clamp, the inhibitory effect of high [Ca2+] on single channel-open probability (Po) was reduced in mutant channels and this effect was dependent on [ATP]. These results indicate that Ca2+ binding to the putative CD Ca2+ inhibitory site facilitates the reduction in IP3R channel activation when cytosolic [ATP] is reduced and suggest that at higher [ATP], additional Ca2+ binding motifs may contribute to the biphasic regulation of IP3-induced Ca2+ release.

biochemistry↗

bioRxiv2024

Dysregulated Ca2+ signaling, fluid secretion, and mitochondrial function in a mouse model of early Sjögren's syndrome

Saliva is essential for oral health. The molecular mechanisms leading to physiological fluid secretion are largely established, but factors that underlie secretory hypofunction, specifically related to the autoimmune disease Sjogrens syndrome (SS) are not fully understood. A major conundrum is the lack of association between the severity of inflammatory immune cell infiltration within the salivary glands and glandular hypofunction. In this study, we investigated in a mouse model system, mechanisms of glandular hypofunction caused by the activation of the stimulator of interferon genes (STING) pathway. Glandular hypofunction and SS-like disease were induced by treatment with 5,6-Dimethyl-9-oxo-9H-xanthene-4-acetic acid (DMXAA), a small molecule agonist of murine STING. Contrary to our expectations, despite a significant reduction in fluid secretion in DMXAA-treated mice, in vivo imaging demonstrated that neural stimulation resulted in greatly enhanced spatially averaged cytosolic Ca2+ levels. Notably, however, the spatiotemporal characteristics of the Ca2+ signals were altered to signals that propagated throughout the entire cytoplasm as opposed to largely apically confined Ca2+ rises observed without treatment. Despite the augmented Ca2+ signals, muscarinic stimulation resulted in reduced activation of TMEM16a, although there were no changes in channel abundance or absolute sensitivity to Ca2+. However, super-resolution microscopy revealed a disruption in the intimate colocalization of Inositol 1,4,5-trisphosphate receptor Ca2+ release channels in relation to TMEM16a. TMEM16a channel activation was also reduced when intracellular Ca2+ buffering was increased. These data are consistent with altered local coupling between the channels contributing to the reduced activation of TMEM16a. Appropriate Ca2+ signaling is also pivotal for mitochondrial morphology and bioenergetics and secretion is an energetically expensive process. Disrupted mitochondrial morphology, a depolarized mitochondrial membrane potential, and reduced oxygen consumption rate were observed in DMXAA-treated animals compared to control animals. We report that early in SS disease, dysregulated Ca2+ signals lead to decreased fluid secretion and disrupted mitochondrial function contributing to salivary gland hypofunction and likely the progression of SS disease.

physiology↗

bioRxiv2024

Loss of STIM1 and STIM2 in salivary glands disrupts ANO1 function but does not induce Sjogren's disease

Sjogrens disease (SjD) is an autoimmune disease characterized by xerostomia (dry mouth), lymphocytic infiltration into salivary glands and the presence of SSA and SSB autoantibodies. Xerostomia is caused by hypofunction of the salivary glands and has been involved in the development of SjD. Saliva production is regulated by parasympathetic input into the glands initiating intracellular Ca2+ signals that activate the store operated Ca2+ entry (SOCE) pathway eliciting sustained Ca2+ influx. SOCE is mediated by the STIM1 and STIM2 proteins and the ORAI1 Ca2+ channel. However, there are no studies on the effects of lack of STIM1/2 function in salivary acini in animal models and its impact on SjD. Here we report that male and female mice lacking Stim1 and Stim2 (Stim1/2K14Cre) in salivary glands showed reduced intracellular Ca2+ levels via SOCE in parotid acini and hyposalivate upon pilocarpine stimulation. Bulk RNASeq of the parotid glands of Stim1/2K14Cre mice showed a decrease in the expression of Stim1/2 but no other Ca2+ associated genes mediating saliva fluid secretion. SOCE was however functionally required for the activation of the Ca2+ activated chloride channel ANO1. Despite hyposalivation, ageing Stim1/2K14Cre mice showed no evidence of lymphocytic infiltration in the glands or elevated levels of SSA or SSB autoantibodies in the serum, which may be linked to the downregulation of the toll-like receptor 8 (Tlr8). By contrast, salivary gland biopsies of SjD patients showed increased STIM1 and TLR8 expression, and induction of SOCE in a salivary gland cell line increased the expression of TLR8. Our data demonstrate that SOCE is an important activator of ANO1 function and saliva fluid secretion in salivary glands. They also provide a novel link between SOCE and TLR8 signaling which may explain why loss of SOCE does not result in SjD.

physiology↗

bioRxiv2024

A PACAP-activated network for secretion requires coordination of calcium influx and calcium mobilization

Chromaffin cells of the adrenal medulla transduce sympathetic nerve activity into stress hormone secretion. The two neurotransmitters principally responsible for coupling cell stimulation to secretion are acetylcholine and pituitary adenylate activating polypeptide (PACAP). In contrast to acetylcholine, PACAP evokes a persistent secretory response from chromaffin cells. However, the mechanisms by which PACAP acts are poorly understood. Here, it is shown that PACAP induces sustained increases in cytosolic Ca2+ which are disrupted when Ca2+ influx through L-type channels is blocked or internal Ca2+ stores are depleted. PACAP liberates stored Ca2+ via inositol trisphosphate receptors (IP3Rs) on the endoplasmic reticulum (ER), thereby functionally coupling Ca2+ mobilization to Ca2+ influx and supporting Ca2+-induced Ca2+-release. These Ca2+ influx and mobilization pathways are unified by an absolute dependence on phospholipase C epsilon (PLC{varepsilon}) activity. Thus, the persistent secretory response that is a defining feature of PACAP activity, in situ, is regulated by a signaling network that promotes sustained elevations in intracellular Ca2+ through multiple pathways.

cell biology↗

bioRxiv2023

Architecture of Ca2+ tunneling, a basic Ca2+ signaling modality important for secretion

Ca2+ tunneling is a signaling modality that requires both Store-operated Ca2+ entry (SOCE) and Ca2+ release from the endoplasmic reticulum (ER). Tunneling expands the SOCE microdomain at ER-plasma membrane (PM) contact sites (ERPMCS) through Ca2+ uptake by the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) into the ER lumen where it diffuses and is released via open inositol trisphosphate (IP3) receptors (IP3Rs). In this study using high resolution imaging, we outline the spatial remodeling of the Ca2+ tunneling machinery (IP3R1; SERCA; PMCA; and Ano1 as an effector) relative to STIM1 in response to store depletion. We show that store depletion leads to redistribution of these Ca2+ signaling modulators to distinct subdomains laterally at the PM and axially within the cortical ER. To functionally define the role of Ca2+ tunneling, we engineered a Ca2+ tunneling attenuator (CaTAr) that blocks tunneling without affecting Ca2+ release or SOCE. CaTAr inhibits Cl- secretion in sweat gland cells. Viral mediated expression of CaTAr in the mouse reduces sweating, showing that Ca2+ tunneling is important physiologically. Collectively our findings outline the architecture of the Ca2+ tunneling machinery and show that it is a fundamental physiological pertinent Ca2+ signaling modality.

cell biology↗

bioRxiv2023

Tools for Quantitative Analysis of Calcium Signaling Data Using Jupyter-Lab Notebooks

Calcium signaling data analysis has become increasing complex as the size of acquired datasets increases. In this paper we present a Ca2+ signaling data analysis method that employs custom written software scripts deployed in a collection of Jupyter-Lab "notebooks" which were designed to cope with this complexity. The notebook contents are organized to optimize data analysis workflow and efficiency. The method is demonstrated through application to several different Ca2+ signaling experiment types.

cell biology↗

bioRxiv2022

Structural dynamics underlying gating and regulation in IP3R channel

Inositol-1,4,5-trisphosphate receptors (IP3Rs) are activated by IP3 and Ca2+ and their gating is regulated by various intracellular messengers that finely tune the channel activity. Here, using single particle cryo-EM analysis we determined 3D structures of the nanodisc-reconstituted IP3R1 channel in two ligand-bound states. These structures provide unprecedented details governing binding of IP3, Ca2+ and ATP in IP3R1, revealing conformational changes that couple ligand-binding to channel opening. Using a GMM based deep learning approach and 3D variability analysis, we extracted dynamic properties of the key protein domains. From this, we find that IP3 binding relies upon intrinsic flexibility of the cytoplasmic ARM2 domain. Our results highlight a key role of dynamic side chains surrounding the ion conduction path in regulating gating behavior of IP3R channels. Altogether, this work defines a structural platform for mechanistic understanding of the molecular dynamics underlying ligand-binding, activation and regulation of the IP3R activity.

biophysics↗

bioRxiv2022

Functional Determination of Calcium Binding Sites Required for the Activation of Inositol 1,4,5-trisphosphate receptors.

Inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) initiate a diverse array of physiological responses by carefully orchestrating intracellular calcium (Ca2+) signals in response to various external cues. Notably, IP3R channel activity is determined by several obligatory factors including IP3, Ca2+ and ATP. The critical basic amino acid residues in the N-terminal IP3-binding core (IBC) region that facilitate IP3 binding are well characterized. In contrast, the residues conferring the biphasic regulation by Ca2+ are yet to be ascertained. Using comparative structural analysis of Ca2+ binding sites identified in two main families of intracellular Ca2+-release channels, ryanodine receptors (RyRs) and IP3Rs, we identified putative acidic residues coordinating Ca2+ in the cytosolic calcium sensor region in IP3Rs. We determined the consequences of substituting putative Ca2+ binding, acidic residues in IP3R family members. We show that the agonist-induced Ca2+ release, single channel open probability (P0) and Ca2+ sensitivities are markedly altered when the negative charge on the conserved acidic side chain residues are neutralized. Remarkably, neutralizing the negatively charged side chain on two of the residues individually in the putative Ca2+ binding pocket shifted the Ca2+ required to activate IP3R to higher concentrations, indicating that these residues likely are a component of the Ca2+ activation site in IP3R. Taken together, our findings indicate that Ca2+ binding to a well conserved activation site is a common underlying mechanism resulted in increased channel activity shared by IP3Rs and RyRs.

physiology↗

bioRxiv2021

Functional Communication between IP3R and STIM2 at sub-threshold stimuli is a critical checkpoint for initiation of SOCE

Stromal interaction molecules, STIM1 and STIM2, sense decreases in the endoplasmic reticulum (ER) [Ca2+] ([Ca2+]ER) and cluster in ER-plasma membrane (ER-PM) junctions where they recruit and activate Orai1. While STIM1 responds when [Ca2+]ER is relatively low, STIM2 displays constitutive clustering in the junctions and is suggested to regulate basal Ca2+ entry. The cellular cues that determine STIM2 clustering under basal conditions is not known. By using gene editing to fluorescently tag endogenous STIM2, we report that endogenous STIM2 is constitutively localized in mobile and immobile clusters. The latter associate with ER-PM junctions and recruit Orai1 under basal conditions. Agonist stimulation increases immobile STIM2 clusters which co- ordinate recruitment of Orai1 and STIM1 to the junctions. Extended synaptotagmin (E-Syt)2/3 are required for forming the ER-PM junctions, but are not sufficient for STIM2 clustering. Importantly, inositol 1,4,5-triphosphate receptor (IP3R) function and local [Ca2+]ER are the main drivers of immobile STIM2 clusters. Enhancing, or decreasing, IP3R function at ambient [IP3] causes corresponding increase, or attenuation, of immobile STIM2 clusters. We show that immobile STIM2 clusters denote decreases in local [Ca2+]ER mediated by IP3R that is sensed by the STIM2-N terminus. Finally, under basal conditions, ambient PIP2-PLC activity of the cell determines IP3R function, immobilization of STIM2, and basal Ca2+ entry while agonist stimulation augments these processes. Together, our findings reveal that immobilization of STIM2 clusters within ER-PM junctions, a first response to ER-Ca2+ store depletion, is facilitated by the juxtaposition of IP3R and marks a checkpoint for initiation of Ca2+ entry. SignificanceSTIM proteins sense decreases in [Ca2+]ER and cluster in endoplasmic reticulum (ER)-plasma membrane (PM) junctions where they recruit and activate Orai1. While STIM1 clustering requires substantial [Ca2+]ER decrease, STIM2 displays pre-clustering under resting conditions and regulates basal Ca2+ entry. The mechanism(s) underlying constitutive clustering of STIM2 is not known. We show herein that endogenous STIM2 assembles as mobile and immobile clusters and that Orai1 is recruited to the latter. Anchoring of STIM2 clusters is triggered by decreases in local [Ca2+]ER that is mediated by ambient activity of IP3R and sensed by the STIM2 N-terminus. This functional link between IP3R and STIM2 governs constitutive STIM2 clustering and ensures coupling of [Ca2+]ER decrease at sub-threshold stimuli with activation of Ca2+ entry.

physiology↗

bioRxiv2021

CREB regulates the expression of Type 1 Inositol 1,4,5-trisphosphate receptors

Inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) play a central role in regulating intracellular calcium signals in response to a variety of internal/external cues. Dysregulation of IP3R signaling is the underlying cause for numerous pathological conditions. It is also well established that the activity of IP3Rs is governed by several post-translational modifications including phosphorylation by protein kinase A (PKA). However, the long-term effects of PKA activation on expression of IP3R sub-types, remains largely unexplored. In this report, we investigate the effect of chronic activation of PKA on expression of IP3R sub-types. We demonstrate that expression of IP3R1 is augmented upon prolonged activation of PKA or upon ectopic over-expression of CREB but does not alter IP3R2 and IP3R3 sub-type abundance. Conversely, inhibition of PKA or blocking endogenous CREB diminished IP3R1 expression. We also demonstrate that agonist-induced Ca2+-release mediated by IP3R1 is significantly attenuated upon blocking endogenous CREB. Moreover, CREB by regulating the expression of KRAS-induced actin-interacting protein (KRAP) ensures proper localization and licensing of IP3R1. Overall, we report a crucial role for CREB in governing both the expression and proper localization of IP3R1. Summary statementWe report a critical role of CREB in regulating the expression and proper localization of IP3R1. Agonist-induced Ca2+ release and Ca2+ puffs generated by IP3R1 are diminished upon blocking the function of endogenous CREB.

physiology↗

bioRxiv2021

Regulation of Interorganellar Ca2+ Transfer and NFAT Activation by the Mitochondrial Ca2+ Uniporter

Mitochondrial Ca2+ uptake is crucial for coupling receptor stimulation to cellular bioenergetics. Further, Ca2+ uptake by respiring mitochondria prevents Ca2+-dependent inactivation (CDI) of store-operated Ca2+ release-activated Ca2+ (CRAC) channels and inhibits Ca2+ extrusion to sustain cytosolic Ca2+ signaling. However, how Ca2+ uptake by the mitochondrial Ca2+ uniporter (MCU) shapes receptor-evoked interorganellar Ca2+ signaling is unknown. Here, we generated several cell lines with MCU-knockout (MCU-KO) as well as tissue-specific MCU-knockdown mice. We show that mitochondrial depolarization, but not MCU-KO, inhibits store-operated Ca2+ entry (SOCE). Paradoxically, despite enhancing Ca2+ extrusion and promoting CRAC channel CDI, MCU-KO increased cytosolic Ca2+ in response to store depletion. Further, physiological agonist stimulation in MCU-KO cells led to enhanced frequency of cytosolic Ca2+ oscillations, endoplasmic reticulum Ca2+ refilling, NFAT nuclear translocation and proliferation. However, MCU-KO did not affect inositol-1,4,5-trisphosphate receptor activity. Mathematical modeling supports that MCU-KO enhances cytosolic Ca2+, despite limiting CRAC channel activity.

cell biology↗

bioRxiv2021

The characteristics of intracellular Ca2+ signals in vivo necessitate a new model for salivary fluid secretion

Salivary fluid secretion involves an intricate choreography to result in the trans-epithelial movement of NaCl and water into the acinus lumen. Current models are based on experimental observations in enzymatically isolated cells where the Ca2+ signal invariably propagates globally and thus appears ideally suited to activate spatially separated Cl and K channels. We monitored Ca2+ signals and salivary secretion in live mice expressing GCamp6F, following stimulation of the nerves innervating the submandibular gland. Consistent with in vitro studies, Ca2+ signals were initiated in the apical endoplasmic reticulum. In marked contrast to in vitro data, highly localized trains of Ca2+ transients that failed to propagate from the apical region were observed. Following stimuli optimum for secretion, large apical-basal gradients were elicited. Given this incompatibility to the previous model, a new mathematical model was constructed to explain how salivary secretion can be efficiently stimulated by apically localized Ca2+ signals.

physiology↗

bioRxiv2020

Omnitemporal choreographies of IP3R and all five STIM/Orai underlie the complexity of mammalian Ca2+ signaling

Invertebrates express one endoplasmic reticulum (ER)-resident Ca2+-sensing stromal-interaction molecule (Stim) and one Orai plasma membrane channel protein. Stim conveys store depletion to Orai, mediating the evolutionarily conserved Ca2+ release-activated Ca2+ (CRAC) current. The crucial role of their vertebrate homologues, STIM1 and Orai1 in mediating CRAC activity in mammals is well-established. However, mammals possess two STIM and three Orai isoforms and the choreography of their interactions under physiological receptor activation is unknown. We show that the five mammalian STIM1/2 and Orai1/2/3 isoforms have non-redundant functions. Yet, all five isoforms are always required together to ensure the graded diversity of mammalian Ca2+ signaling events in response to the full spectrum of agonist strengths. Receptor-activated Ca2+ signaling across the range of stimulus intensities requires functional interactions between not only STIM1/2 and Orai1/2/3, but also IP3R, ensuring that receptor-mediated Ca2+ release is precisely tailored to Ca2+ entry and activation of nuclear factor of activated T-cells (NFAT). This is orchestrated by two interdependent and counterbalancing paradigms: the N-termini Ca2+-binding ER-luminal domains of unactivated STIM1/2 inhibit IP3R-evoked Ca2+ release. Gradual increase in agonist intensity leads to gradual STIM1/2 activation and relief of IP3R inhibition. Concomitantly, the cytosolic C-termini of activated STIM1/2 differentially interact with Orai1/2/3 proteins as agonist intensity increases. Thus, coordinated and omnitemporal functions of all five STIM/Orai proteins and IP3Rs at the ER-lumen and cytosol translate the strength of agonist stimulation to precise levels of Ca2+ release, Ca2+ entry and NFAT induction, ensuring the diversity and fidelity of complex mammalian Ca2+ signaling. HighlightsO_LIAll five STIM/Orai and IP3R are always required together in mammalian Ca2+ signalling C_LIO_LIUnactivated STIM1/2 inhibit IP3R and activated STIM1/2 cooperatively activate Orai1/2/3 C_LIO_LISTIM1 contribution increases and that of STIM2 decreases as agonist intensifies C_LIO_LIGraded IP3R disinhibition and Orai activation tailor receptor activity to NFAT induction C_LI O_FIG O_LINKSMALLFIG WIDTH=192 HEIGHT=200 SRC="FIGDIR/small/325480v1_ufig1.gif" ALT="Figure 1"> View larger version (65K): org.highwire.dtl.DTLVardef@f6172dorg.highwire.dtl.DTLVardef@6bbb09org.highwire.dtl.DTLVardef@c45c80org.highwire.dtl.DTLVardef@194d7e4_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2018

Acetylcholine inhibits platelet activation and regulates hemostasis

Platelets are key mediators of thrombosis. Many agonists of platelet activation are known, but there are fewer identified endogenous inhibitors of platelets, such as prostacyclin and nitric oxide (NO). Acetylcholinesterase inhibitors such as donepezil can cause bleeding in patients, but the underlying mechanisms are not well understood. We hypothesized that acetylcholine is an endogenous inhibitor of platelets.\n\nWe measured the effect of acetylcholine or analogues of acetylcholine upon human platelet activation ex vivo. We characterized expression of components of the acetylcholine signaling pathway in human platelets. We tested the effect of a subunit of the acetylcholine receptor, CHRNA7, on acetylcholine signaling in platelets. Acetylcholine and analogues of acetylcholine inhibited platelet activation, as measured by P-selectin translocation and GPIIbIIIA conformational changes. Conversely, we found that antagonists of the acetylcholine receptor such as pancuronium enhance platelet activation. Furthermore, drugs inhibiting acetylcholinesterase such as donepezil also inhibit platelet activation, suggesting that platelets release acetylcholine. We found that NO mediates acetylcholine inhibition of platelets. Human platelets express members of the acetylcholine signaling pathway including CHRNA2, CHRNA7, CHRNB1, and ACHE. Platelets from mice lacking Chrna7 are hyperactive when stimulated by thrombin and resistant to inhibition by acetylcholine. Furthermore, acetylcholinesterase inhibitors prolonged bleeding in wild-type mice. Knockout mice lacking Chrna7 subunits of the acetylcholine receptor display prolonged bleeding as well.\n\nOur data suggest that acetylcholine is an endogenous inhibitor of platelet activation. The cholinergic system may be a novel target for anti-thrombotic therapies.

pharmacology and toxicology↗