Effect Of Estrogen Replacement On The Expression Of Spinophilin And δ-catenin In The Cerebellum Of Ovariectomized Rat

Dendritic spines are small protrusions from neuronal dendrites. They contain 90% of the excitatory synapses in mature brain with a total volume ranging from less than 0.01 to 0.8μm3 and their highly heterogeneous morphology is thought to be the morphological basis for synaptic plasticity. Spinophilin andδ-catenin are important proteins in the dendritic spines, they are colocalized with F-actin at post synaptic density.Spinophilin often binds to protein phosphatase 1 and anchors at post synaptic density, it also binds to F-actin and they colocalized at post synaptic membrane. Spinophilin may bind to the catalytic subunit of PP1 and control PP1 enzyme activity. Its N-terminal has an actin binding domain containing some phosphorylation sites which can be phosphorylated by protein kinase A, protein kinase C and Ca/calmodulin(CaM) dependent protein kinase. After phosphorylated, spinophilin seperates from actin and causes the dendritic spines to loss their morphology stability, and leads to structural lost of dendritic spines. Spinophilin also contains a PSD95/DLGy/zo-1(PDZ) consistent sequence that is PDZ binding domain. It has characteristics of cystoskeleton scaffolding protein which may orientate signaling molecule and affect the function of neuron including synapse plasticity. Therefore, spinophlin has significant effect on regulation of the excitatory synaptic transmission and morphology of dendritic spines.δ-catenin belongs to the p120-catenin (p120ctn) protein family specially in nervous system, which is characterized by ten, characteristically spaced Armadillo repeats that bind to the juxtamembrane segment of the classical cadherins. It limits at postsynaptic element and forms asymmetry adheren junction at synaptic area.δ-catenin binds to many PDZ binding domain proteins via its C-terminal binding site and play a role in cell junction. It forms protein complex and directly combines to F-actin.δ-catenin can induce the branching of dendrite-like processes in 3T3 cells and enhance dendritic morphogenesis in primary hippocampal neurons. Targeted mutation of mouseδ-catenin gene shows that it plays an important role in normal synaptic function. As a component of both adherens and synaptic junctions,δ-catenin can link the adherens junction to the synapse and, thereby, coordinate synaptic input with changes in the adherens junction. In addition,δ-catenin is able to bind to F-actin and co-modulate the morphology and density of dendritic spines with spinophlin; then they further contribute to affect the dendritic spines synaptic plasticity.Estrogen including estrodiol, estrone and estriol is secreted by follicular granular cells and lutein cells. Estrodiol is the most active and its secretory volume is the maximum among estrogen. Estrogen may contribute to anti-aging in female animal. Through its receptor, estrogen influences female's function in many aspects, such as behavior, mood, cognitive and memory. Estrogen may regulate the expression of spinophilin andδ-catenin then further affect the morphology and density of dendritic spines.The aim of this experiment is to study the effect of estrogen replacement therapy on the expression of spinophilin andδ-catenin in the rat cerebellum. In this experiment, we select SD rats and establish a model of ovariectomized rats, followed by estrogen replacement therapy. The methods, such as western blot, immunohistochemistry and RT-PCR were used to examine the expression change of spinophilin andδ-catenin. The immunohistochemical method showed that in the cerebellum of rat, puncta of spinophilin andδ-catenin was localized in molecular layer and granule cell layer. There were several positive puncta in the purkinje cell. The expression of spinophilin andδ-catenin in the cerebellum of placebo group was significantly lower than those of other two groups, the expression of spinophilin andδ-catenin in rat cerebellum of sham group was stronger than that of estrogen replacement group, but this difference was not significant in statistics. Western blot results demonstrated that the expression of spinophilin andδ-catenin in the cerebellum of placebo group was the lowest in the three groups, but the expression of spinophilin andδ-catenin between the rats of sham group and estrogen replacement therapy group showed no significant difference. RT-PCR indicated that the mRNA level of spinophilin was identical in rat cerebellums of three groups. The mRNA level ofδ-catenin of the placebo group was the lowest in three groups, but no significant difference in mRNA level ofδ-catenin was found between sham group and estrogen replacement group. Therefore, we conclude that estrogen can play an important role in maintaining the normal level of spinophilin andδ-catenin, as well as structural stability of synapse of rat cerebellum.