Neuritin promotes neurite and spine growth in rat cerebellar granule cells via L‐type calcium channel‐mediated calcium influx.

Neuritin is a neurotrophic factor that is activated by neural activity and neurotrophins. Its major function is to promote neurite growth and branching; however, the underlying mechanisms are not fully understood. To address this issue, this study investigated the effects of neuritin on neurite and spine growth and intracellular Ca2+ concentration in rat cerebellar granule neurons (CGNs). Incubation of CGNs for 24 h with neuritin increased neurite length and spine density; this effect was mimicked by insulin and abolished by inhibiting insulin receptor (IR) or mitogen‐activated protein kinase kinase/extracellular signal‐regulated kinase (ERK) activity. Calcium imaging and western blot analysis revealed that neuritin enhanced the increase in intracellular Ca2+ level induced by high K+, and stimulated the cell surface expression of CaV1.2 and CaV1.3 α subunits of the L‐type calcium channel, which was suppressed by inhibition of IR or mitogen‐activated protein kinase kinase/ERK. Treatment with inhibitors of L‐type calcium channels, calmodulin, and calcineurin (CaN) abrogated the effects of neuritin on neurite length and spine density. A similar result was obtained by silencing nuclear factor of activated T cells c4, which is known to be activated by neuritin in CGNs. These results indicate that IR and ERK signaling as well as the Ca2+/CaN/nuclear factor of activated T cells c4 axis mediate the effects of neuritin on neurite and spine growth in CGNs. Open Practices: Open Science: This manuscript was awarded with the Open Materials Badge. For more information see: https://cos.io/our-services/open-science-badges/ Cover Image for this issue: doi: 10.1111/jnc.14195. Background: Neuritin could promote neurite growth and branching. In this study, we used cerebellar granule neurons (CGNs) to reveal the possible mechanism. Main findings and implication: Neuritin promoted neurite and spine growth by increasing Ca2+ influx through L‐type voltage‐gated calcium channel (L‐VGCC), which involves activation of the insulin receptor (IR)‐induced ERK signaling and Ca2+/ calcineurin/NFATc4 axis. Image content: Schematic illustration depicting the mechanisms of neuritin in the up‐regulation of the CaV1.2 and CaV1.3 subunits of L‐type VGCCs on the cell membrane, and the subsequent increase in neurite length, spine density, and KV4.2 expression. IRS: insulin receptor substrate. Cover Image for this issue: doi: 10.1111/jnc.14195. [ABSTRACT FROM AUTHOR]