The Caveolin Scaffolding Domain Modifies 2-Amino-3-hydroxy-5-methyl-4-isoxazole Propionate Receptor Binding Properties by Inhibiting Phospholipase A2 Activity

Abstract

Activation of the enzyme phospholipase (PLA 2 ) has been proposed to be part of the molecular mechanism involved in the alteration of 2-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) glutamate receptor responsiveness during long term changes in synaptic plasticity (long term potentiation). This study assesses the effect of the caveolin-1 scaffolding domain (CSD) on the activity of the regulatory enzyme PLA 2 . Caveolin-1 is a 22-kDa cholesterol-binding membrane protein known to inhibit the activity of most of its interacting partners. Our results show that the calcium-dependent cytosolic form of PLA 2 (cPLA 2 ) and caveolin-1 co-localized in mouse primary hippocampal neuron cultures and that they were co-immunoprecipitated from mouse hippocampal homogenates. A peptide corresponding to the scaffolding domain of caveolin-1 (Cav-(82-101)) dramatically inhibited cPLA 2 activity in purified hippocampal synaptoneurosomes. Activation of endogenous PLA 2 activity with KCl or melittin increased the binding of [ 3 H]AMPA to its receptor. This effect was almost completely abolished by the addition of the CSD peptide to these preparations. Moreover, we demonstrated that the inhibitory action of the CSD peptide on AMPA receptor binding properties is specific (because a scrambled version of this peptide failed to have any effect) and that it is mediated by an inhibition of PLA 2 enzymatic activity (because the CSD peptide failed to have an effect in membrane preparations lacking endogenous PLA 2 activity). These results raised the possibility that caveolin-1, via the inhibition of cPLA 2 enzymatic activity, may interfere with synaptic facilitation and long term potentiation formation in the hippocampus.Phospholipase (PLA 2 ) 1 belongs to a superfamily of enzymes that play a central role in the regulation of arachidonic acid (AA) release from membrane phospholipids and catalyze the production of various metabolites. PLA 2 activity has been postulated to play an important role in key metabolic pathways. In addition to its involvement in signal transduction, membrane repair, neurodegeneration, and apoptosis (1), there is a growing body of evidence suggesting a role in the modulation of neurotransmitter release and long term potentiation (LTP) (2-4). Changes in synaptic function observed with LTP are thought to be the result of modifications of postsynaptic currents mediated by the 2-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) subtype of glutamate receptors (5, 6). PLA 2 activity was shown to be part of the molecular mechanisms regulating AMPA receptor function during long term changes in synaptic operation (7-9). It has been proposed that during high frequency stimulation a large entry of calcium mediated by N-methyl-D-aspartate (NMDA) glutamate receptor activation might cause an increase in PLA 2 activity. The enzyme would augment AMPA receptor affinity by changing the lipid environment of AMPA receptors, thereby producing LTP (10). Recently, it has been reported that detergent-insoluble caveolin-rich membran...

Phospholipase A2 activation as a therapeutic approach for cognitive enhancement in early-stage Alzheimer disease

“…For example, activation of cPLA 2 is regulated by p38MAPK (Zhou et al 2003), p42MAPK (Lin et al 1993;Nemenoff et al 1993;Gordon et al 1996), CaMK II (Muthalif et al 2001), and PKC phosphorylation (Wijkander and Sundler 1991;Nemenoff et al 1993), and iPLA 2 activation is regulated by PKC phosphorylation (Underwood et al 1998;Akiba et al 1999). In turn, stimulation of PLA 2 activity (with the PLA 2 activator melittin) in the presence of Ca 2+ in rodent cortical and hippocampal slices as well as membrane preparations increased [ 3 H]AMPA and [ 3 H]glutamate binding to the AMPA receptor (Massicotte and Baudry 1990;Baudry et al 1991;Massicotte et al 1991;Tocco et al 1992;Catania et al 1993;Bernard et al 1995;Chabot et al 1998;Gaudreault et al 2004), whereas PLA 2 inhibition and the Ca 2+ chelator EGTA reduced agonist binding to AMPA (Bernard et al 1993(Bernard et al , 1995Catania et al 1993). Additionally, PLA 2 inhibition in rat hippocampal slices prevented Ca 2+ -dependent formation of LTP in the CA1 field as well as the increase of [ 3 H]AMPA binding to the AMPA receptor that characterizes LTP (Bernard et al 1994).…”

The Cytosolic Phospholipase A2 Pathway, a Safeguard of β2-Adrenergic Cardiac Effects in Rat

“…Our study provides evidence for ␤ 2 -AR-induced translocation of the cPLA 2 to platforms constituted of caveolae tightly connected to SR membranes. PLA 2 activity has been implicated in constitutive membrane trafficking (45); however, only one recent study reported the presence of the cPLA 2 in caveolin 1-enriched membrane fractions isolated from hippocampal preparations (46). Most caveolin-interacting proteins identified so far contain a caveolin-binding motif located within their enzymatically active catalytic site (41).…”

The role of phospholipases A2 in schizophrenia

“…[32][33][34][35] PLA2 inhibitors block AMPAR-associated LTP, while increasing PLA2 activity enhances LTP. 34 PLA2 enhancement of LTP is halted by sequestering free AA, but not by removing calcium or blocking eicosanoid production.…”