Ca²⁺ store depletion and endoplasmic reticulum stress are involved in P2X7 receptor‐mediated neurotoxicity in differentiated NG108‐15 cells

Abstract

P2X7 receptor (P2X7R) activation by extracellular ATP triggers influx of Na(+) and Ca(2+), cytosolic Ca(2+) overload and consequently cytotoxicity. Whether disturbances in endoplasmic reticulum (ER) Ca(2+) homeostasis and ER stress are involved in P2X7R-mediated cell death is unknown. In this study, a P2X7R agonist (BzATP) was used to activate P2X7R in differentiated NG108-15 neuronal cells. In a concentration-dependent manner, application of BzATP (10-100 µM) immediately raised cytosolic Ca(2+) concentration ([Ca(2+)]i) and caused cell death after a 24-h incubation. P2X7R activation for 2 h did not cause cell death but resulted in a sustained reduction in ER Ca2+ pool size, as evidenced by a diminished cyclopiazonic acid-induced Ca(2+) discharge (fura 2 assay) and a lower fluorescent signal in cells loaded with Mag-fura 2 (ER-specific Ca(2+)-fluorescent dye). Furthermore, P2X7R activation (2 h) led to the appearance of markers of ER stress [phosphorylated α subunit of eukaryotic initiation factor 2 (p-eIF2α) and C/EBP homologous protein (CHOP)] and apoptosis (cleaved caspase 3). Xestospongin C (XeC), an antagonist of inositol-1,4,5-trisphosphate (IP3) receptor (IP3R), strongly inhibited BzATP-triggered [Ca(2+)]i elevation, suggesting that the latter involved Ca(2+) release via IP3R. XeC pretreatment not only attenuated the reduction in Ca(2+) pool size in BzATP-treated cells, but also rescued cell death and prevented BzATP-induced appearance of ER stress and apoptotic markers. These novel observations suggest that P2X7R activation caused not only Ca(2+) overload, but also Ca(2+) release via IP3R, sustained Ca(2+) store depletion, ER stress and eventually apoptotic cell death.

Impaired calcium homeostasis via advanced glycation end products promotes apoptosis through endoplasmic reticulum stress in human nucleus pulposus cells and exacerbates intervertebral disc degeneration in rats

“…As the principal organelle involved in Ca 2+ homeostasis, the ER tightly regulates Ca 2+ homeostasis in the ER lumen in order to maintain well protein folding and chaperone function [22,30]. Previous studies indicate that disturbance of intracellular Ca 2+ homeostasis induces ER stress and subsequent apoptosis associated with a variety of pathological conditions [21,[41][42][43]. We hypothesized that sustained dysregulation of intracellular Ca 2+ homeostasis plays a potential role in AGEs-induced ER stress and apoptosis in NP cells.…”

P2X7 Receptor is Involved in Mitochondrial Dysfunction Induced by Extracellular Alpha Synuclein in Neuroblastoma SH-SY5Y Cells

“…Recently, the involvement of ER that form structural and functional networks with mitochondria, in the mitochondrial membrane permeabilization and apoptosis under various pathophysiological conditions, was suggested [97]. Moreover, it was previously demonstrated that ER stress is involved in P2X7R-mediated neurotoxicity in neuronal cells in the manner that is largely dependent from sustained Ca 2+ depletion from ER stores [98]. Since Ca 2+ released from ER is taken up by mitochondria that results in calcium overload and induces depolarization of mitochondrial membrane and opening of permeability transition pore (PTP) to release apoptotic proteins able to stimulate caspase cascade [99], it is though possible that P2X7R-mediated Ca 2+ release from ER might be responsible for mitochondria dysfunction.…”

Morphine Protects Spinal Cord Astrocytes from Glutamate-Induced Apoptosis via Reducing Endoplasmic Reticulum Stress

“…It was known that sustained elevation of [Ca 2+ ] i could induce some deleterious effect, for example, ER stress [17,32]. Ca 2+ overload causes dysfunction in ER Ca 2+ depletion, subsequently inducing accumulation of misfolded proteins in ER, this is termed unfolded protein response (UPR) [33].…”