Ryanodine receptor-mediated Ca2+release and atlastin-2 GTPase activity contribute to IP3-induced dendritic Ca2+signals in primary hippocampal neurons

Neuronal Ca2+ signals are fundamental for synaptic transmission and activity-dependent changes in gene expression. Voltage-gated Ca2+ channels and N-methyl-D-aspartate receptors play major roles in mediating external Ca2+ entry during action potential firing and glutamatergic activity. Additionally, the inositol-1,4,5trisphosphate receptor (IP3R) and the ryanodine receptor (RyR) channels expressed in the endoplasmic reticulum (ER) also contribute to the generation of Ca2+ signals in response to neuronal activity. The ER forms a network that pervades the entire neuronal volume, allowing intracellular Ca2+ release in dendrites, soma and presynaptic boutons. Despite its unique morphological features, the contributions of ER structure and of ERshaping proteins such as atlastin - an ER enriched GTPase that mediates homotypic ER tubule fusion - to the generation of Ca2+ signals in dendrites remains unreported. Here, we investigated the contribution of RyRmediated Ca2+ release to IP3-generated Ca2+ signals in dendrites of cultured hippocampal neurons. We also employed GTPase activity-deficient atlastin-2 (ATL2) mutants to evaluate the potential role of atlastin on Ca2+ signaling and ER-resident Ca2+ channel distribution. We found that pharmacological suppression of RyR channel activity increased the rising time and reduced the magnitude and propagation of IP3-induced Ca2+ signals. Additionally, ATL2 mutants induced specific ER morphological alterations, delayed the onset and increased the rising time of IP3-evoked Ca2+ signals, and caused RyR2 and IP3R1 aggregation and RyR2 redistribution. These results indicate that both RyR and ATL2 activity regulate IP3-induced Ca2+ signal dynamics through RyRmediated Ca2+-induced Ca2+ release, ER shaping and RyR2 distribution.

Automated summary

Neuronal Ca2+ signals are essential for synaptic transmission and gene expression changes. Voltage-gated Ca2+ channels and N-methyl-D-aspartate receptors are important for Ca2+ entry during action potential firing. The endoplasmic reticulum (ER), including RyR and IP3R channels, contributes to Ca2+ signal generation in response to neuronal activity. The study investigates the role of RyR-mediated Ca2+ release in IP3-generated Ca2+ signals in dendrites and the potential impact of atlastin on Ca2+ signaling and ER-resident Ca2+ channel distribution.