Cellular mechanisms of activity dependent regulation of CPEB3 expression in mouse cerebellar stellate cells

BARH K; BENDER C; LIU SQ

NEW ORLEANS

Jornada; Summer student meeting; 2012

LSUHSC

Information processing in the central nervous system is based on the balance of the actions of excitatory and inhibitory neurons. Most excitatory neurons use glutamate as their neurotransmitter. AMPA type glutamate receptors are essential for moderating this excitatory synaptic transmission.The GluR2 subunit of AMPA receptors (AMPARs) in cerebellar stellate cellsplay a key role in associative learning and memory. A single fear-inducing stimulus causes an increase in GluR2-containing AMPARs.? Cytoplasmic Polyadenylation Element Binding protein 3 (CPEB3) regulates GluR2 synthesis and is associated with learning and human episodic memory. Preliminary study in our lab show that action potential (AP) firing increasesCPEB3 expression and reduces synaptic GluR2 receptors. Therefore, we examined the mechanism that regulates CPEB3 expression. We investigated 1) the role of calcium entry via Voltage Gated Calcium Channels (VGCC) during spontaneous acation potential firing; 2) its effect on protein synthesis and protein degradation of CPEB3. Understanding the mechanism that regulates CPEB3 expression helps in identifying mechanisms that regulates GluR2 and hence, the neuroplasticity associated to this receptor. Inhibition of action potentials by TTX causes a significant decrease of ~25% in CPEB3 expression in mouse cerebellar stellate cells. Membrane depolarization can activate voltage gated calcium channels (VGCC). Here we found that blocking N-, T- and L-type VGCCs,each causes a reduction in CPEB3 expression, and inhibition of all three channels reduces the CPEB3 levels to that of TTX treatment. Thus voltage-gated calcium channels play a key role in regulating CPEB3 expression. The TTX-induced decrease in CPEB3 expression could result from an enhanced protein degradation or suppression of synthesis of CPEB3 protein. Our preliminary results show that MG132 completely prevents the TTX-induced reduction in CPEB3 levels, indicating that inhibition of action potential activity increases protein degradation of CPEB3 protein.