The Ryanodine receptor stabilizer S107 fails to support motor neuronal neuritogenesis in vitro

Calcium homeostasis is essential for neuronal cell survival/differentiation. Imbalance of the Ca²⁺ homeostasis due to excessive Ca²⁺ overload is essential for spinal cord injury (SCI). The overload resulted from Ca²⁺ flux across the plasma membrane and from internal Ca²⁺ store release (mitochondria, endoplasmic reticulum, ER). Inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) are involved in releasing Ca²⁺ from ER contributing to axonal degeneration following SCI. In turn, block of both receptors is axoprotective. The calstabin RyR subunit, stabilizing the channel in a state of reduced activity, prevents pathological Ca²⁺ release too. We investigated whether S107, a RyR-stabilizing compound (Rycal), is beneficial for survival and neuritogenesis of spinal cord motor neurons in vitro. We used a spinal cord slice model and the motor neuron-like NSC-34 cell line. Effects of S107 were tested by propidium iodide/fluorescein diacetate vital staining, mitotic index determination via BrdU-incorporation, and neurite sprouting parameters. Results showed that S107 (i) had no effect on gliosis resulting from slices preparation; (ii) had no effect on motor neuronal survival and proliferation; and (iii) impaired neurite sprouting, no matter whether it was a differentiation (NSC-34 cells) or regeneration (spinal cord slices) process. The results underline the need for a flexible Ca²⁺homeostasis provided by the ER for re-initiation of neuritogenesis.