Phosphatidylinositol (4,5)-Bisphosphate Regulation ofN-Methyl-d-aspartate Receptor Channels in Cortical Neurons

Abstract

The membrane phospholipid phosphatidylinositol (4,5)-bisphosphate (PIP 2 ) has been implicated in the regulation of several ion channels and transporters. In this study, we examined the impact of PIP 2 on N-methyl-D-aspartate receptors (NMDARs) in cortical neurons. Blocking PIP 2 synthesis by inhibiting phosphoinositide-4 kinase, or stimulating PIP 2 hydrolysis via activation of phospholipase C (PLC), or blocking PIP 2 function with an antibody caused a significant reduction of NMDAR-mediated currents. On the other hand, inhibition of PLC or application of PIP 2 caused an enhancement of NMDAR currents. These electrophysiological effects were accompanied by changes in NMDAR surface clusters induced by agents that manipulate PIP 2 levels. The PIP 2 regulation of NMDAR currents was abolished by the dynamin inhibitory peptide, which blocks receptor internalization. Agents perturbing actin stability prevented PIP 2 regulation of NMDAR currents, suggesting the actin-dependence of this effect of PIP 2 . Cofilin, a major actin depolymerizing factor, which has a common binding sequence for actin and PIP 2 , was required for PIP 2 regulation of NMDAR currents. It is noteworthy that the PIP 2 regulation of NMDAR channels was impaired in a transgenic mouse model of Alzheimer's disease, probably because of the amyloid-␤ disruption of PIP 2 metabolism. Taken together, our data suggest that continuous synthesis of PIP 2 at the membrane might be important for the maintenance of NMDARs at the cell surface. When PIP 2 is lost, cofilin is released from the PIP 2 complex and is rendered free to depolymerize actin. With the actin cytoskeleton no longer intact, NMDARs are internalized via a dynamin/clathrindependent mechanism, leading to reduced NMDAR currents.The N-methyl-D-aspartate receptor (NMDAR), one of the major glutamate receptor channels in central neurons, plays a key role in multiple neuronal functions, including synapse formation, synaptic plasticity, learning, and memory. Dysregulation of NMDARs has been implicated in ischemia, epilepsy, and neuropsychiatric disorders (Dingledine et al., 1999;Lau and Zukin, 2007). Synaptic targeting and incorporation of NMDA receptors are dynamically regulated (Wenthold et al., 2003). After being released from the endoplasmic reticulum, NMDARs are rapidly transported along microtubule tracks in dendritic shafts (Washbourne et al., 2002;Yuen et al., 2005), followed by being delivered to actinrich dendritic spines. NMDARs are tethered to actin cytoskeleton via scaffolding and adaptor proteins, such as ␣-actinin and postsynaptic density-95 (Wyszynski et al., 1997;Pak et al., 2001). Several mechanisms have been proposed to be important for stabilizing and/or promoting surface NMDA receptor expression, including the PDZ domain-mediated interactions between NR2 subunits and postsynaptic density-95 (Kornau et al., 1995;Roche et al., 2001;Lin et al., 2004) and tyrosine dephosphorylation of NR2 subunits that triggers clathrin-dependent endocytosis (Vissel et al., 2001;Prybylowski et al., ...

Dual Effect of Phosphatidyl (4,5)-Bisphosphate PIP2 on Shaker K+ Channels

“…Examples of PIP 2 -dependent ion channels and receptors include inwardly rectifying K ϩ channels (Kir) (3,4), voltagegated K ϩ channels (Kv) (5)(6)(7)(8), voltage-gated Ca 2ϩ channels (9), TRP channels (10), and NMDA receptors (11,12).…”

Shank3 Deficiency Induces NMDA Receptor Hypofunction via an Actin-Dependent Mechanism

“…The dephosphorylated cofilin binds to F-actin, leading to actin severing and depolymerization (Morgan et al, 1993). Our previous studies have shown that cofilin-regulated actin dynamics is critically involved in the regulation of NMDAR trafficking and function (Mandal and Yan, 2009;Gu et al, 2012). Since the Ser3 residue of cofilin acts as a switch for actin assembly (F-actin stabilization) and disassembly (F-actin severing), we used a Ser3-phosphorylated cofilin peptide (Aizawa et al, 2001;Zhou et al, 2004) to inhibit the activation of endogenous cofilin.…”

Dysfunctional synapse in Alzheimer's disease – A focus on NMDA receptors

“…Blocking PIP 2 reduces NMDAR-mediated currents, whereas application of PIP 2 enhances these currents (Mandal and Yan, 2009). Moreover, cofilin, an actin depolymerizing factor which links actin and PIP 2 is required for NMDARs regulation, suggesting that a decrease in PIP 2 leads to cofilin release and actin depolymerization, which in turn promotes NMDARs internalization (Mandal and Yan, 2009).…”

“…Moreover, cofilin, an actin depolymerizing factor which links actin and PIP 2 is required for NMDARs regulation, suggesting that a decrease in PIP 2 leads to cofilin release and actin depolymerization, which in turn promotes NMDARs internalization (Mandal and Yan, 2009). Active myosin light chain kinase enhances NMDARs-mediated whole-cell and synaptic currents, increasing actin-myosin contractility, which leads to increased membrane tension on NMDARs or to altered physical relationships between NMDAR anchored proteins, such as PSD-95 (Kornau et al, 1995) and cytoskeleton (Lei et al, 2001).…”

“…Evidences for cytoskeletal and plasma membrane involvement in NMDARs regulation are numerous and affect NMDAR presence at the synapse. The membrane phospholipid phosphatidylinositol bisphosphate (PIP 2 ) is important for the maintenance of NMDARs at the cell surface (Mandal and Yan, 2009). …”