Positive allosteric modulation of alpha‐7 nicotinic receptors promotes cell death by inducing Ca 2+ release from the endoplasmic reticulum

Positive allosteric modulation of α7 isoform of nicotinic acetylcholine receptors (α7‐nAChRs) is emerging as a promising therapeutic approach for central nervous system disorders such as schizophrenia or Alzheimer's disease. However, its effect on Ca 2+ signaling and cell viability remains controversial. This study focuses on how the type II positive allosteric modulator (PAM II) PNU 120596 affects intracellular Ca 2+ signaling and cell viability. We used human SH ‐ SY 5Y neuroblastoma cells overexpressing α7‐nAChRs (α7‐SH) and their control (C‐ SH ). We monitored cytoplasmic and endoplasmic reticulum ( ER ) Ca 2+ with Fura‐2 and the genetically encoded cameleon targeting the ER , respectively. Nicotinic inward currents were measured using patch‐clamp techniques. Viability was assessed using methylthiazolyl blue tetrazolium bromide or propidium iodide staining. We observed that in the presence of a nicotinic agonist, PNU 120596 (i) reduced viability of α7‐ SH but not of C‐ SH cells; (ii) significantly increased inward nicotinic currents and cytosolic Ca 2+ concentration; (iii) released Ca 2+ from the ER by a Ca 2+ ‐induced Ca 2+ release mechanism only in α7‐ SH cells; (iv) was cytotoxic in rat organotypic hippocampal slice cultures; and, lastly, all these effects were prevented by selective blockade of α7‐ nAChR s, ryanodine receptors, or IP 3 receptors. In conclusion, positive allosteric modulation of α7‐ nAChR s with the PAM II PNU 120596 can lead to dysregulation of ER Ca 2+ , overloading of intracellular Ca 2+ , and neuronal cell death.This study focuses on how the type II positive allosteric modulator PNU120596 (PAM II PNU12) affects intracellular Ca 2+ signaling and cell viability. Using SH‐SY5Y neuroblastoma cells overexpressing α7‐nAChRs (α7‐SH) and their control (C‐SH), we find that PAM of α7‐nAChRs with PNU120596: (i) increases inward calcium current (I Ca ) and cytosolic Ca 2+ concentration ([Ca 2+ ] cyt ); (ii) releases Ca 2+ from the ER ([Ca 2+ ] ER ) by a Ca 2+ ‐induced Ca 2+ release mechanism; and (iv) reduces cell viability. These findings were corroborated in rat hippocampal organotypic cultures. [Ca 2+ ] cyt , cytosolic Ca 2+ concentration; [Ca 2+ ] ER , endoplasmic reticulum Ca 2+ concentration; α7 nAChR, α7 isoform of nicotinic acetylcholine receptors; α7‐SH, SH‐SY5Y stably overexpressing α7 nAChRs cells; C‐SH, control SH‐SY5Y cells; Nic, nicotine; PNU12, PNU120596.