Identification of postsynaptic phosphatidylinositol-4,5-bisphosphate (PIP2) roles for synaptic plasticity using chemically induced dimerization

Su-Jeong Kim,Yun-Beom Choi,Joung-Hun Kim,Hee-Jung Jo,Min-Jae Jeong,Bong-Kiun Kaang,Jung Hoon Jung

doi:10.1038/s41598-017-03520-3

Abstract

Phosphatidylinositol-4,5-bisphosphate (PIP2), one of the key phospholipids, directly interacts with several membrane and cytosolic proteins at neuronal plasma membranes, leading to changes in neuronal properties including the feature and surface expression of ionotropic receptors. Although PIP2 is also concentrated at the dendritic spines, little is known about the direct physiological functions of PIP2 at postsynaptic as opposed to presynaptic sites. Most previous studies used genetic and pharmacological methods to modulate enzymes that alter PIP2 levels, making it difficult to delineate time- or region-specific roles of PIP2. We used chemically-induced dimerization to translocate inositol polyphosphate 5-phosphatase (Inp54p) to plasma membranes in the presence of rapamycin. Upon redistribution of Inp54p, long-term depression (LTD) induced by low-frequency stimulation was blocked in the mouse hippocampal CA3-CA1 pathway, but the catalytically-dead mutant did not affect LTD induction. Collectively, PIP2 is critically required for induction of LTD whereas translocation of Inp54p to plasma membranes has no effect on the intrinsic properties of the neurons, basal synaptic transmission, long-term potentiation or expression of LTD.

Highlights

Phosphatidylinositol-4,5-bisphosphate (PIP2) is a substrate for the generation of the second messengers inositol triphosphate (IP3) and diacylglycerol (DAG), PIP2 itself interacts with membrane and cytosolic proteins to regulate a number of cellular processes in neurons
To resolve the discrepancy and to obtain better insight into the direct effects of PIP2 on long-term depression (LTD), we developed a means to acutely deplete PIP2 in hippocampal neurons using chemically-induced dimerization (CID), which utilized the heterodimerization of the domain from the FK506-binding protein (FKBP) and the FKBP rapamycin-binding (FRB) domain from the mechanistic target of rapamycin
We examined whether the application of rapamycin could lead to recruitment of Inp54p to the plasma membrane and subsequently reduce of the membrane PIP2 level

Summary

Introduction

Phosphatidylinositol-4,5-bisphosphate (PIP2) is a substrate for the generation of the second messengers inositol triphosphate (IP3) and diacylglycerol (DAG), PIP2 itself interacts with membrane and cytosolic proteins to regulate a number of cellular processes in neurons. Such previous studies reported conflicting results and do not provide unequivocal evidence supporting whether and how PIP2 controls synaptic plasticity[14,15,16] This ambiguity is likely due to methodological differences among different studies, as modulation of PIP2 levels was achieved by genetic and pharmacological modifications of PIP2-metabolic enzymes, such as synaptojanin 1, phosphatase and tensin homolog (PTEN), phospholipase C (PLC), and phosphatidylinositol 4-phosphate 5-kinases (PIP5Ks). A PIP2-specific phosphatase, inositol polyphosphate 5-phosphatase (Inp54p), was translocated to the plasma membrane of neurons in the presence of rapamycin and promptly depleted PIP2, as previously shown in other cell types[20,21,22,23] Using this CID system, we determined whether PIP2 controls synaptic transmission and plasticity in the Schaffer collateral-CA1 pathway in mouse hippocampus. Our results indicated that PIP2 is necessary for the induction of LTD but not for LTD expression or synaptic transmission

Methods

Results

Conclusion