Regulation of spinogenesis in mature Purkinje cells via mGluR/PKC-mediated phosphorylation of CaMKIIβ

Abstract

Dendritic spines of Purkinje cells form excitatory synapses with parallel fiber terminals, which are the primary sites for cerebellar synaptic plasticity. Nevertheless, how density and morphology of these spines are properly maintained in mature Purkinje cells is not well understood. Here we show an activity-dependent mechanism that represses excessive spine development in mature Purkinje cells. We found that CaMKIIβ promotes spine formation and elongation in Purkinje cells through its F-actin bundling activity. Importantly, activation of group I mGluR, but not AMPAR, triggers PKC-mediated phosphorylation of CaMKIIβ, which results in dissociation of the CaMKIIβ/ F-actin complex. Defective function of the PKC-mediated CaMKIIβ phosphorylation promotes excess F-actin bundling and leads to abnormally numerous and elongated spines in mature IP 3 R1-deficient Purkinje cells. Thus, our data suggest that phosphorylation of CaMKIIβ through the mGluR/IP 3 R1/PKC signaling pathway represses excessive spine formation and elongation in mature Purkinje cells.n the cerebellum, Purkinje cells are the sole output from the neural circuit of the cerebellar cortex, and integrate numerous synaptic inputs (1). Spines along the distal dendrites of Purkinje cells form excitatory synapses with parallel fiber terminals, which are the primary sites of cerebellar synaptic plasticity (1, 2). Spine density and morphology of Purkinje cells change significantly during development (3, 4), and morphological abnormalities of spines are closely associated with many neurological disorders (5-7). Recent studies also demonstrated that some forms of training for cerebellar motor learning results in altered spine density in Purkinje cells (8,9). Thus, maintenance of proper spine density and morphology of Purkinje cells is a critical aspect of cerebellar functions. However, the precise molecular mechanisms that maintain Purkinje cell spine density and morphology remain unclear.The actin filaments are a major structural element of the regulation of dendritic spine formation and morphology of neurons (10, 11). The actin dynamics in spines are regulated by many actinrelated molecules including Ca 2+ /calmodulin-dependent protein kinase II (CaMKII) (12), which is one of the most abundant proteins in the brain (13). Among CaMKII isoforms (α, β, γ, and δ), CaMKIIβ possesses a specific F-actin binding domain (14) and plays an important role for regulating dendritic spine structure in hippocampal neurons. It is reported that suppression of CaMKIIβ expression leads to reduced spine formation, and conversely, overexpression of CaMKIIβ increases synapse number and motility of filopodia in hippocampal neurons (15,16). The effect of CaMKIIβ on maintaining mature spine structure requires its F-actin binding and bundling activity, but not its kinase activity (17). In addition, a recent study reported that in hippocampal neurons, activation of CaMKIIβ by postsynaptic Ca 2+ influx through the NMDA receptor and resultant autophosphorylation within the F-actin binding dom...

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“…Ca 2+ may bind to synaptotagmin to trigger synaptic vesicle release (Emptage et al, 2001). Ca 2+ also binds to calmodulin (CaM) to form CaM-Ca 2+ complex, activating Ca 2+ /CaM-dependent protein kinases (CAMKs) or the Ca 2+ /CaM-dependent serine/threonine phosphatase calcineurin, which plays an important role in the regulation of synaptic plasticity (Yakel, 1997;Wayman et al, 2008;Kim et al, 2016;Sugawara et al, 2017). Ca 2+ activates the FIGURE 5 | E2 and G-1 stimulate phosphorylation of MOR in a PKC-dependent manner.…”

DGKγ Knock-Out Mice Show Impairments in Cerebellar Motor Coordination, LTD, and the Dendritic Development of Purkinje Cells through the Activation of PKCγ

“…PKCg regulates spinogenesis and the morphology of the spines of distal dendrites through the phosphorylation of CaMKIIb (Sugawara et al, 2017). Purkinje cells in DGKg KO mice showed retracted distal dendrites, but the basic electrophysiological properties of PFs were normal, indicating that DGKg KO mice retained basic excitatory circuitry.…”

CaMKIIβ in Neuronal Development and Plasticity: An Emerging Candidate in Brain Diseases

“…Similarly, in Purkinje cells, CaMKIIβ promotes spine formation and elongation via its F-actin bundling activity [ 45 ]. In addition, protein kinase C (PKC)-mediated phosphorylation of CaMKIIβ is responsible for the maintenance of the appropriate spine density and morphology in these cells.…”

“…In addition, protein kinase C (PKC)-mediated phosphorylation of CaMKIIβ is responsible for the maintenance of the appropriate spine density and morphology in these cells. More precisely, PKC phosphorylates CaMKIIβ at S315 under the control of group I metabotropic glutamate receptor (mGluR1) signaling, and this event results in dissociation of the CaMKIIβ/F-actin complex, which then represses excessive spine formation and elongation in mature Purkinje cells [ 45 ].…”