Wnt-5a/JNK Signaling Promotes the Clustering of PSD-95 in Hippocampal Neurons

Abstract

During the formation of synapses, specific regions of pre-and postsynaptic cells associate to form a single functional transmission unit. In this process, synaptogenic factors are necessary to modulate pre-and postsynaptic differentiation. In mammals, different Wnt ligands operate through canonical and noncanonical Wnt pathways, and their precise functions to coordinate synapse structure and function in the mature central nervous system are still largely unknown. Here, we studied the effect of different Wnt ligands on postsynaptic organization. We found that Wnt-5a induces short term changes in the clustering of PSD-95, without affecting its total levels. Wnt-5a promotes the recruitment of PSD-95 from a diffuse dendritic cytoplasmic pool to form new PSD-95 clusters in dendritic spines. Moreover, Wnt-5a acting as a non-canonical ligand regulates PSD-95 distribution through a JNK-dependent signaling pathway, as demonstrated by using the TAT-TI-JIP peptide in mature hippocampal neurons. Finally, using adult rat hippocampal slices, we found that Wnt-5a modulates glutamatergic synaptic transmission through a postsynaptic mechanism. Our studies indicate that the Wnt-5a/JNK pathway modulates the postsynaptic region of mammalian synapse directing the clustering and distribution of the physiologically relevant scaffold protein, PSD-95.During the formation of synapses, pre-and postsynaptic sides contain specific molecules that are involved in the regulation and plasticity of synaptic transmission (1-3). Although much is known about the molecular mechanisms of synaptic differentiation, major gaps remain in our understanding of the process, particularly with regard to the signals mediating the structuring of the postsynaptic apparatus of central mammalian synapses (2, 4). At excitatory synapses, the postsynaptic side is characterized by an electrodense thick matrix, called postsynaptic density (PSD).3 The PSD contains key molecules involved in the regulation of glutamate receptor targeting and trafficking (1, 5). There is considerable interest in elucidating the molecular mechanism that controls synaptic targeting and trafficking of these proteins in the postsynaptic region because of their essential role in synaptic plasticity (6). Moreover, in neurodegenerative pathologies, such as Alzheimer disease, it has been evidenced that the postsynaptic region, including several proteins of the PSD, is the primary target of the synaptotoxic effect of the amyloid ␤-peptide (7-9).Wnt signaling is essential for neuronal development and the maintenance of the nervous system (10 -12). Wnt regulates synapse formation; in fact, the pioneering work of Salinas and co-workers (12-15) established that Wnt-7a induces the clustering of presynaptic proteins in young primary cerebellar cultures. Also, Wnt ligands regulate neurogenesis of hippocampal stem cells in the adult rat (16), and Wnt-3a modulates long term potentiation in mouse hippocampal slices (17, 18).The expression of Wnt ligands and proteins of the Wnt signaling machinery in the matu...

Activation of Wnt signaling by lithium and rosiglitazone reduced spatial memory impairment and neurodegeneration in brains of an APPswe/PSEN1ΔE9 mouse model of Alzheimer's disease

“…In fact, we found that Wnt/b-catenin modulates the synaptic vesicle cycle and synaptic transmission in rat hippocampal neurons, 76 and non-canonical Wnt signaling also modulates PSD-95 clustering. 33 Therefore, these possible mechanisms needed to be explored in APP-PS1 animals treated with lithium and rosiglitazone. Recently, He and Shen 77 reported that the renewal capacity of glial progenitor cells isolated from AD patients is reduced compared with that of cells from healthy controls, and this reduced neurogenesis capacity was correlated with GSK-3b activity and an increased phosphorylation of bcatenin.…”

“…Western blot assays were carried out as previously described. [31][32][33] Slot-blots assays were performed as previously described. 34 Briefly, the total protein extract was centrifuged to eliminate fibrillar aggregates at 20 000 g for 1 h. The protein concentration of the soluble fraction was determined and 6 mg of protein was spotted in 0.45 mm 2 nitrocellulose (Millipore, Bedford, MA, USA), blocked with PBS-T gelatin 0.4% and incubated using an anti-oligomeric antibody A11 (Chemicon) 1/5000 for 4 h at 4 1C.…”

Canonical and noncanonical Wnt signaling in neural stem/progenitor cells

“…Induced proliferation of hESCs/mNSCs [65,66] Recombinant Wnt-3a Induced proliferation and differentiation of hESCs [67] Wnt-4 silencing Impaired early differentiation in hECCs [68] Wnt-5a KO Impaired neurite development in the olfactory bulb (OB) [44] Wnt-1 and Wnt-5a DKO Impaired neurogenesis of midbrain dopaminergic neurons [52] Wnt-5a KO Impaired axon growth and guidance of dopaminergic neurons [45] Wnt-5a CM Increased synaptogenesis and maturation of hippocampal progenitors [69,70] Wnt-5a overexpression Induced axonal differentiation in hippocampal cultures [71] Wnt-7a KO Delayed morphological maturation of glomerular rosettes and synapsin I accumulation [46] Wnt-7a KO Impaired ventral midbrain neurogenesis [47] Wnt-7a and Dvl DKO Defective spine morphogenesis and mossy fiber-CA3 synaptic transmission [48] Wnt-7a Proposed as a key element in the regulation of NSC self-renewal/differentiation; altered spindle- Canonical Wnt receptors are also important for correct neural development (Table 2): FZD3 KO mice show impaired axonal guidance [73] while LRP6 KO mice present cortical defects [74]. Also, FZD1 has been shown to be the receptor for canonical Wnt-1 in mouse tyrosine hydroxylase positive neurons, which activates β-catenin-dependent signaling promoting neuroprotection in dopaminergic neurons [75].…”

“…In cultured hippocampal neurons, Wnt-5a activates a signaling cascade leading to activation of AP-1 [69] and increases dendritic spine morphogenesis [70]. Wnt-7a 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 similarly increases dendritic spine density and maturity, albeit through a CAMKIIdependent mechanism [48].…”

Erratum: Disruption of the non-canonical Wnt gene PRICKLE2 leads to autism-like behaviors with evidence for hippocampal synaptic dysfunction

“…The Wnt signaling pathway regulates a myriad of neurodevelopmental processes, e.g., cell fate determination, axon migration, dendritic arborization, and synapse formation (10)(11)(12)(13)(14)(15)(16)(17)(18). There are two major pathways that define the Wnt signaling pathway; the canonical and non-canonical pathways.…”