Frizzled-5 Receptor Is Involved in Neuronal Polarity and Morphogenesis of Hippocampal Neurons

Abstract

The Wnt signaling pathway plays important roles during different stages of neuronal development, including neuronal polarization and dendritic and axonal outgrowth. However, little is known about the identity of the Frizzled receptors mediating these processes. In the present study, we investigated the role of Frizzled-5 (Fzd5) on neuronal development in cultured Sprague-Dawley rat hippocampal neurons. We found that Fzd5 is expressed early in cultured neurons on actin-rich structures localized at minor neurites and axonal growth cones. At 4 DIV, Fzd5 polarizes towards the axon, where its expression is detected mainly at the peripheral zone of axonal growth cones, with no obvious staining at dendrites; suggesting a role of Fzd5 in neuronal polarization. Overexpression of Fzd5 during the acquisition of neuronal polarity induces mislocalization of the receptor and a loss of polarized axonal markers. Fzd5 knock-down leads to loss of axonal proteins, suggesting an impaired neuronal polarity. In contrast, overexpression of Fzd5 in neurons that are already polarized did not alter polarity, but decreased the total length of axons and increased total dendrite length and arborization. Fzd5 activated JNK in HEK293 cells and the effects triggered by Fzd5 overexpression in neurons were partially prevented by inhibition of JNK, suggesting that a non-canonical Wnt signaling mechanism might be involved. Our results suggest that, Fzd5 has a role in the establishment of neuronal polarity, and in the morphogenesis of neuronal processes, in part through the activation of the non-canonical Wnt mechanism involving JNK.

Identification of Noncanonical Wnt Receptors Required for Wnt-3a-Induced Early Differentiation of Human Neural Stem Cells

“…7a and b). FZD5 also activated this reporter, consistent with a previous report showing that FZD5 plays a role in neuronal maturation via JNK [46]. However, ATF2-dependent transcriptional activity was not further increased by ectopic expression of FZD4/5, LRP6 or ROR1 in L-Wnt-3a cells ( Supplementary Fig.…”

Wnt5a promotes differentiation and development of adult-born neurons in the hippocampus by noncanonical Wnt signaling

“…Differentiation was induced by growth factors withdrawal in the presence or absence of 50 ng/mL Wnt5a plus specific inhibitors (Figure S4): TAT‐TI‐JIP (1 μM), a 11‐mer peptide of JIP conjugated to Tat peptide that perturbs the interaction of JNK‐JIP was used to inhibit JNK activity; KN‐93 (5 μM) that binds directly to CaMKII, thus preventing kinase activation by competing with Ca 2+ /CaM; Go6976 (6.2 nM) an indolocarbazole that specifically inhibit PKC by non‐competitive inhibition with the substrate site . These inhibitors have been widely used to prevent noncanonical Wnt signaling in cultured neurons . At 4 days of differentiation, cotreatment with TAT‐TI‐JIP did not prevent the increase in the percentage of Dcx+ cells induced by Wnt5a (Figure B), suggesting that the Wnt/JNK signaling cascade is not involved.…”

Frizzled-1 receptor regulates adult hippocampal neurogenesis

“…On the other hand, no significant effect was observed in dendrite morphogenesis by knockdown of FZD1. Wnt signaling regulates dendrite development in early cultures of hippocampal neurons, which involves non-canonical Wnt signaling components [ 23 , 49 ]. β-catenin has also been involved in dendrite development, but this effect depends on the membrane cadherin/catenin adhesion complex and does not require Wnt/β-catenin-dependent transcription [ 50 ].…”