Neuritin Mediates Activity-Dependent Axonal Branch Formation in Part via FGF Signaling.

by Selleckchem | May 07 2017

Aberrant branch formation of granule cell axons (mossy fiber sprouting) is observed in the dentate gyrus of many patients with temporal lobe epilepsy and in animal models of epilepsy. However, the mechanisms underlying mossy fiber sprouting remain elusive. Based on the hypothesis that seizure-mediated gene expression induces abnormal mossy fiber growth, we screened activity-regulated genes in the hippocampus and found that neuritin, an extracellular protein anchored to the cell surface, was rapidly upregulated after electroconvulsive seizures. Overexpression of neuritin in the cultured rat granule cells promoted their axonal branching. Also, kainic acid-dependent axonal branching was abolished in the cultured granule cells fromneuritinknock-out mice, suggesting that neuritin may be involved in activity-dependent axonal branching. Moreover,neuritinknock-out mice showed less-severe seizures in chemical kindling probably by reduced mossy fiber sprouting and/or increased seizure resistance. We found that inhibition of the fibroblast growth factor (FGF) receptor attenuated the neuritin-dependent axonal branching. FGF administration also increased branching in granule neurons, whereasneuritinknock-out mice did not show FGF-dependent axonal branching. In addition, FGF and neuritin treatment enhanced the recruitment of FGF receptors to the cell surface. These findings suggest that neuritin and FGF cooperate in inducing mossy fiber sprouting through FGF signaling. Together, these results suggest that FGF and neuritin-mediated axonal branch induction are involved in the aggravation of epilepsy.

SIGNIFICANCE STATEMENT:

This study reveals the molecular mechanism underlying mossy fiber sprouting. Mossy fiber sprouting is the aberrant axonal branching of granule neurons in the hippocampus, which is observed in patients with epilepsy. Excess amounts of neuritin, a protein upregulated by neural activity, promoted axonal branching in granule neurons. A deficiency of neuritin suppressed mossy fiber sprouting and resulted in mitigation of seizure severity. Neuritin and fibroblast growth factor (FGF) cooperated in stimulating FGF signaling and enhancing axonal branching. Neuritin is necessary for FGF-mediated recruitment of FGF receptors to the cell surface. The recruitment of FGF receptors would promote axonal branching. The discovery of this new mechanism should contribute to the development of novel antiepileptic drugs to inhibit axonal branching via neuritin-FGF signaling.

Cat.No.	Product Name	Information
S1264	PD173074	PD173074 is a potent FGFR1 inhibitor with IC50 of ~25 nM and also inhibits VEGFR2 with IC50 of 100-200 nM in cell-free assays, ~1000-fold selective for FGFR1 than PDGFR and c-Src. PD173074 reduces proliferation and promotes apoptosis in gastric cancer cells.
S2801	Fexagratinib (AZD4547)	Fexagratinib (AZD4547,ABSK 091) is a novel selective FGFR inhibitor targeting FGFR1/2/3 with IC50 of 0.2 nM/2.5 nM/1.8 nM in cell-free assays, weaker activity against FGFR4, VEGFR2(KDR), and little activity observed against IGFR, CDK2, and p38. Phase 2/3.
S1102	U0126-EtOH	U0126-EtOH is a highly selective inhibitor of MEK1/2 with IC50 of 0.07 μM/0.06 μM in cell-free assays, 100-fold higher affinity for ΔN3-S218E/S222D MEK than PD98059. U0126 inhibits autophagy and mitophagy with antiviral activity.
S1105	LY294002	LY294002 (SF 1101, NSC 697286) is the first synthetic molecule known to inhibit PI3Kα/δ/β with IC50 of 0.5 μM/0.57 μM/0.97 μM, respectively; more stable in solution than Wortmannin, and also blocks autophagosome formation. It not only binds to class I PI3Ks and other PI3K-related kinases, but also to novel targets seemingly unrelated to the PI3K family. LY294002 also inhibits CK2 with IC50 of 98 nM. LY294002 is a non-specific DNA-PKcs inhibitor and activates autophagy and apoptosis.
S8011	U73122	U73122 is a potent phospholipase C (PLC) inhibitor, which reduces agonist-induced Ca²⁺ increases in platelets and PMN. U73122 potently inhibits human 5-lipoxygenase (5-LO).