Ionotropic and Metabotropic Mechanisms of Allosteric Modulation of α7 Nicotinic Receptor Intracellular Calcium

Abstract

The pharmacological targeting of the 7 nicotinic acetylcholine receptor (7) is a promising strategy in the development of new drugs for neurologic diseases. Because 7 receptors regulate cellular calcium, we investigated how the prototypical type II-positive allosteric modulator PNU120596 affects7-mediated calcium signaling. Live imaging experiments show that PNU120596 augments ryanodine receptor-driven calcium-induced calcium release (CICR), inositol-induced calcium release (IICR), and phospholipase C activation by the 7 receptor. Both influx of calcium through the7 nicotinic acetylcholine receptor (nAChR) channel as well as the binding of intracellular G proteins were involved in the effect of PNU120596 on intracellular calcium. This is evidenced by the findings that chelation of extracellular calcium, expression of 7 or 7 mutant subunits, or blockade of calcium store release compromised the ability of PNU120596 to increase intracellular calcium transients generated by 7 ligand activation. Spatiotemporal stochastic modeling of calcium transient responses corroborates these results and indicates that7 receptor activation enables calcium microdomains locally and to lesser extent in the distant cytosol. From the model, allosteric modulation of the receptor activates CICR locally via ryanodine receptors and augments IICR through enhanced calcium influx due to prolonged 7 nAChR opening. These findings provide a new mechanistic framework for understanding the effect of7 receptor allosteric modulation on both local and global calcium dynamics.

Alpha 7 nicotinic receptors attenuate neurite development through calcium activation of calpain at the growth cone

“…In future studies it will be interesting to determine if α7 nAChR activation leads to the activity of calpain 1, 2, or both and if this is cell type and compartment specific. For example, high calcium levels within α7 nAChR and ER containing cellular microdmains that have been suggested in the growth cone [ 56 ] may drive the activation of the low calcium affinity type 2 calpain while broad calcium transients may drive calpain 1 in other parts of the cells. In future studies it will be interesting to discern specificity between α7 nAChR calcium signals and calpain isoform function.…”

“…Co-localization of the α7 nAChR and the ER within the central zone appears important for calcium signaling as evidenced by previous findings that demonstrate that blockade of the IP 3 R receptor, or uncoupling from Gαq signaling, decreases the ability of α7 nAChRs to mediate calcium transients in the growth cone [ 20 , 22 ]. Based on experimental and computational findings, calcium levels produced by α7 interactions with the ER at the growth cone are sufficient for calcium activation of calpain and thus can directly drive spectrin breakdown locally [ 56 ]. Our findings support this model and show that pharmacological blockade of calcium release from the ER through the ryanodine receptor or the IP 3 R is sufficient to inhibit calpain function in the EB3 comet assay.…”

Activation of α7 Nicotinic Acetylcholine Receptor Upregulates HLA-DR and Macrophage Receptors: Potential Role in Adaptive Immunity and in Preventing Immunosuppression

“…There is much evidence for the presence of α7 nAChRs in the human MDMs [3,[27][28][29], while here we analyzed functional expression of these receptors in macrophages obtained after differentiation of the THP-1 cells. Calcium imaging is preferable to measure α7 nAChRs activity in macrophages, since most of previous studies failed to find evidence of their ion channel activity in such cells [30][31][32], referring to their metabotropic rather than ionotropic intracellular signaling [33,34]. Application of non-selective nAChRs agonists nicotine (100 µM) led to calcium rise in some cells ( Figure 3A,K).…”

“…Biomolecules 2020, 10, x 8 of 18 [33,34]. Application of non-selective nAChRs agonists nicotine (100 µ M) led to calcium rise in some cells ( Figure 3A,K).…”

Nicotinic Receptor Subunits Atlas in the Adult Human Lung

“…Nicotine, one of the components of cigarette smoke, acts as an agonist implicated in the inhibition of apoptosis and oxidative stress responses, ultimately leading to lung impairments due to long-term exposure [ 4 , 21 , 22 ]. Although nicotinic receptors are ionotropic complexes, they may display metabotropic signalling properties via their association with trimeric GTP-binding proteins to regulate downstream pathways and cytokine expression [ 23 , 24 ].…”