Glial cell line-derived neurotrophic factor (GDNF) induces neuritogenesis in the cochlear spiral ganglion via neural cell adhesion molecule (NCAM)

Abstract

Glial cell line-derived neurotrophic factor (GDNF) increases survival and neurite extension of spiral ganglion neurons (SGNs), the primary neurons of the auditory system, via yet unknown signaling mechanisms. In other cell types, signaling is achieved by the GPI-linked GDNF family receptor α1 (GFRα1) via recruitment of transmembrane receptors: Ret (re-arranged during transformation) and/or NCAM (neural cell adhesion molecule). Here we show that GDNF enhances neuritogenesis in organotypic cultures of spiral ganglia from 5-day-old rats and mice. Addition of GFRα1-Fc increases this effect. GDNF/GFRα1-Fc stimulation activates intracellular PI3K/Akt and MEK/Erk signaling cascades as detected by Western blot analysis of cultures prepared from rats at postnatal days 5 (P5, before the onset of hearing) and 20 (P20, after the onset of hearing). Both cascades mediate GDNF stimulation of neuritogenesis, since application of the Akt inhibitor Wortmannin or the Erk inhibitor U0126 abolished GDNF/GFRα1-Fc stimulated neuritogenesis in P5 rats. Since cultures of P5 NCAM-deficient mice failed to respond by neuritogenesis to GDNF/GFRα1-Fc, we conclude that NCAM serves as a receptor for GDNF signaling responsible for neuritogenesis in early postnatal spiral ganglion.

Neurotrophic factor GDNF promotes survival of salivary stem cells

“…RET activates the PI3K/AKT, MEK/ERK, and SRC pathways, and NCAM activates the FYN/FAK pathway. Through these downstream targets, GDNF prevents apoptosis and promotes proliferation and differentiation in neurons (33,34,(38)(39)(40), ureteric bud (35,36), and spermatogonial SCs (37). Our results show that GDNF and its receptor, GFRα1, are found primarily in SSCs, suggesting that GDNF mainly acts as an autocrine factor.…”

“…GDNF preferentially binds to the GDNF family receptor α 1 (GFRα1), which mediates the activation of the RET receptor tyrosine kinase and functions through the PI3K/AKT, MEK/ERK and SRC pathways in neurons (33,34), ureteric buds (35,36), and spermatogonial SCs (37). Recent studies indicated that the neural cell adhesion molecule (NCAM) and the downstream targets FYN/FAK may function as alternative pathways for GDNF in regulating axonal guidance and corneal regeneration (38)(39)(40)(41).…”

GFRα1 Regulates Purkinje Cell Migration by Counteracting NCAM Function

“…On the other hand, we found NCAM to be co-expressed with GFRα1 in embryonic PCs, and in situ PLA experiments indicated that they are associated in vivo. Earlier work has shown that the GFRα1/NCAM complex provides a high-affinity binding site for GDNF (Paratcha et al., 2003) and mediates effects of this ligand on cell migration, neurite outgrowth, and axon guidance (Charoy et al., 2012, Duveau and Fritschy, 2010, Euteneuer et al., 2013, Paratcha et al., 2006). Having ruled out an effect of GDNF on embryonic PC migration, we considered possible direct effects of GFRα1 on NCAM function independently of GDNF.…”

Neural Cell Adhesion Molecule NrCAM Is Expressed in the Mammalian Inner Ear and Modulates Spiral Ganglion Neurite Outgrowth in an In Vitro Alternate Choice Assay

“…Similarly, the cellular mechanism by which NrCAM influences type I SG neurite growth could be probed using cell signaling inhibitors, as we have used for other guidance factors (e.g., Aletsee et al 2001; Mullen et al 2012; Euteneuer et al 2013). …”