@article {123124, title = {ER-Ca2+ stores and the regulation of Store-operated Ca2+ Entry in neurons.}, journal = {J Physiol}, year = {2023}, month = {2023 Jan 24}, abstract = {

Key components of endoplasmic reticular (ER) Ca release and store-operated Ca entry (SOCE) are likely expressed in all metazoan cells. Due to the complexity of canonical Ca entry mechanisms in neurons, the functional significance of ER-Ca release and SOCE has been difficult to identify and establish. In this review we present evidence of how these two related mechanisms of Ca signaling impact multiple aspects of neuronal physiology and discuss their interaction with the better understood classes of ion channels that are gated by either voltage changes or extracellular ligands in neurons. Given how a small imbalance in Ca homeostasis can have strongly detrimental effects on neurons, leading to cell death, it is essential that neuronal SOCE is carefully regulated. We go onto discuss mechanisms of SOCE regulation identified in Drosophila and mammalian neurons. These include specific splice variants of STIM, different classes of membrane interacting proteins and an ER-Ca channel. So far these appear distinct from the mechanisms of SOCE regulation identified in non-excitable cells. Finally we touch upon the significance of these studies in the context of certain human neurodegenerative diseases. Abstract figure legend Store-operated Ca entry in neuronal cells is regulated by both positive (left) and negative regulators (right). This article is protected by copyright. All rights reserved.

}, issn = {1469-7793}, doi = {10.1113/JP283827}, author = {Chakraborty, Pragnya and Hasan, Gaiti} } @article {79802, title = {SEPT7 regulates Ca entry through Orai channels in human neural progenitor cells and neurons.}, journal = {Cell Calcium}, volume = {90}, year = {2020}, month = {2020 Jul 09}, pages = {102252}, abstract = {

Human neural progenitor cells (hNPCs) are self-renewing cells of neural lineage that can be differentiated into neurons of different subtypes. Here we show that SEPT7, a member of the family of filament-forming GTPases called septins, prevents constitutive Ca entry through the store-operated Ca entry channel, Orai in hNPCs and in differentiated neurons and is thus required for neuronal calcium homeostasis. Previous work in Drosophila neurons has shown that loss of one copy of the evolutionarily-conserved dSEPT7 gene leads to elevated Ca entry via Orai, in the absence of ER-Ca store depletion. We have identified an N-terminal polybasic region of SEPT7, known to interact with membrane-localized phospholipids, as essential for spontaneous calcium entry through Orai in hNPCs, whereas the GTPase domain of dSEPT7 is dispensable for this purpose. Re-organisation of Orai1 and the ER-Ca sensor STIM1 observed near the plasma membrane in SEPT7 KD hNPCs, supports the idea that Septin7 containing heteromers prevent Ca entry through a fraction of STIM-Orai complexes. Possible mechanisms by which SEPT7 reduction leads to opening of Orai channels in the absence of store-depletion are discussed.

}, issn = {1532-1991}, doi = {10.1016/j.ceca.2020.102252}, author = {Deb, Bipan K and Chakraborty, Pragnya and Gopurappilly, Renjitha and Hasan, Gaiti} } @article {47058, title = {IP3 receptors and Ca2+ entry}, journal = {Biochim Biophys Acta Mol Cell Res}, volume = {1866}, year = {2019}, month = {2018 Nov 15}, pages = {1092-1100}, abstract = {

Inositol 1,4,5-trisphosphate receptors (IPR) are the most widely expressed intracellular Ca release channels. Their activation by IP and Ca allows Ca to pass rapidly from the ER lumen to the cytosol. The resulting increase in cytosolic [Ca] may directly regulate cytosolic effectors or fuel Ca uptake by other organelles, while the decrease in ER luminal [Ca] stimulates store-operated Ca entry (SOCE). We are close to understanding the structural basis of both IPR activation, and the interactions between the ER Ca-sensor, STIM, and the plasma membrane Ca channel, Orai, that lead to SOCE. IPRs are the usual means through which extracellular stimuli, through ER Ca release, stimulate SOCE. Here, we review evidence that the IPRs most likely to respond to IP are optimally placed to allow regulation of SOCE. We also consider evidence that IPRs may regulate SOCE downstream of their ability to deplete ER Ca stores. Finally, we review evidence that IPRs in the plasma membrane can also directly mediate Ca entry in some cells.

}, issn = {1879-2596}, doi = {10.1016/j.bbamcr.2018.11.007}, author = {Thillaiappan, Nagendra Babu and Chakraborty, Pragnya and Hasan, Gaiti and Taylor, Colin W} } @article {62768, title = {Measurement of Store-Operated Calcium Entry in Human Neural Cells: From Precursors to Differentiated Neurons.}, journal = {Methods Mol Biol}, volume = {2029}, year = {2019}, month = {2019}, pages = {257-271}, abstract = {

Calcium imaging in an ex-vivo\ setup is used to understand the calcium status of isolated cells or tissue. In this chapter we explain the use of the ratiometric chemical indicator Fura-2 which can be loaded into isolated cells in the form of lipophilic acetomethyl (AM) esters. Fura-2 is a combination of calcium chelator and fluorophore, and can be used with dual wavelength excitation (340/380\ nm) for quantitative calcium concentrations. The cells can then be viewed using a fluorescence microscope and captured by a CCD camera. We specifically discuss the technique involved in understanding the endoplasmic reticulum (ER)-driven store-operated calcium entry (SOCE) in human neural precursors (NPCs)\ and spontaneously differentiated neurons derived from a pluripotent human\ embryonic stem cell\ (hESC) line. The derivation of neural precursors from stem cells and their subsequent spontaneous neural differentiation is also explained. The method can be used for various non-excitable and excitable cell types including neurons, be it freshly isolated, from frozen vials, or derived from different stem cell lines.

}, issn = {1940-6029}, doi = {10.1007/978-1-4939-9631-5_20}, author = {Gopurappilly, Renjitha and Deb, Bipan Kumar and Chakraborty, Pragnya and Hasan, Gaiti} } @article {36788, title = {Stable Knockdown in Self-Renewing Human Neural Precursors Promotes Premature Neural Differentiation.}, journal = {Front Mol Neurosci}, volume = {11}, year = {2018}, month = {2018}, pages = {178}, abstract = {

Ca signaling plays a significant role in the development of the vertebrate nervous system where it regulates neurite growth as well as synapse and neurotransmitter specification. Elucidating the role of Ca signaling in mammalian neuronal development has been largely restricted to either small animal models or primary cultures. Here we derived human neural precursor cells (NPCs) from human embryonic stem cells to understand the functional significance of a less understood arm of calcium signaling, Store-operated Ca entry or SOCE, in neuronal development. Human NPCs exhibited robust SOCE, which was significantly attenuated by expression of a stable shRNA-miR targeted toward the SOCE molecule, STIM1. Along with the plasma membrane channel Orai, STIM is an essential component of SOCE in many cell types, where it regulates gene expression. Therefore, we measured global gene expression in human NPCs with and without knockdown. Interestingly, pathways down-regulated through knockdown were related to cell proliferation and DNA replication processes, whereas post-synaptic signaling was identified as an up-regulated process. To understand the functional significance of these gene expression changes we measured the self-renewal capacity of NPCs with knockdown. The knockdown NPCs demonstrated significantly reduced neurosphere size and number as well as precocious spontaneous differentiation toward the neuronal lineage, as compared to control cells. These findings demonstrate that mediated SOCE in human NPCs regulates gene expression changes, that are likely to physiologically modulate the self-renewal and differentiation of NPCs.

}, issn = {1662-5099}, doi = {10.3389/fnmol.2018.00178}, author = {Gopurappilly, Renjitha and Deb, Bipan Kumar and Chakraborty, Pragnya and Hasan, Gaiti} }