Inhibition of phospholipase A2 in rat brain modifies different membrane fluidity parameters in opposite ways.

Fluidity is an important neuronal membrane property and it is influenced by the concentration of polyunsaturated fatty acids (PUFAs) in membrane phospholipids. Phospholipase A(2) (PLA(2)) is a key enzyme in membrane phospholipid metabolism, generating free PUFAs. In Alzheimer disease (AD), reduced PLA(2) activity, specifically of calcium-dependent cytosolic PLA(2) (cPLA(2)) and calcium-independent intracellular PLA(2) (iPLA(2)), and phospholipid metabolism was reported in the frontal cortex and hippocampus. This study investigated the effects of in vivo infusion of the dual cPLA(2) and iPLA(2) inhibitor MAFP into rat brain on PLA(2) activity and membrane fluidity parameters in the postmortem frontal cortex and dorsal hippocampus. PLA(2) activity was measured by radioenzymatic assay and membrane fluidity was determined by fluorescence anisotropy technique using three different probes: DPH, TMA-DPH, and pyrene. MAFP significantly inhibited PLA(2) activity, reduced the flexibility of fatty acyl chains (indicated by increased DPH anisotropy), increased the fluidity in the lipid-water interface (indicated by decreased TMA-DPH anisotropy), and increased the lipid lateral diffusion in the hydrocarbon core (represented by pyrene excimer formation) of membranes in both brain areas. The findings suggest that reduced cPLA(2) and iPLA(2) activities in AD brain might contribute to the cognitive impairment, in part, through alterations in membrane fluidity parameters.

Inhibition of phospholipase A2 in rat brain decreases the levels of total Tau protein.

The microtubule-associated protein Tau promotes the assembly and stability of microtubules in neuronal cells. Six Tau isoforms are expressed in adult human brain. All six isoforms become abnormally hyperphosphorylated and form neurofibrillary tangles in Alzheimer disease (AD) brains. In AD, reduced activity of phospholipase A(2) (PLA(2)), specifically of calcium-dependent cytosolic PLA(2) (cPLA(2)) and calcium-independent intracellular PLA(2) (iPLA(2)), was reported in the cerebral cortex and hippocampus, which positively correlated with the density of neurofibrillary tangles. We previously demonstrated that treatment of cultured neurons with a dual cPLA(2) and iPLA(2) inhibitor, methyl arachidonyl fluorophosphonate (MAFP), decreased total Tau levels and increased Tau phosphorylation at Ser(214) site. The aim of this study was to conduct a preliminary investigation into the effects of in vivo infusion of MAFP into rat brain on PLA(2) activity and total Tau levels in the postmortem frontal cortex and dorsal hippocampus. PLA(2) activity was measured by radioenzymatic assay and Tau levels were determined by Western blotting using the anti-Tau 6 isoforms antibody. MAFP significantly inhibited PLA(2) activity in the frontal cortex and hippocampus. The reactivity to the antibody revealed three Tau protein bands with apparent molecular weight of close to 40, 43 and 46 kDa in both brain areas. MAFP decreased the 46 kDa band intensity in the frontal cortex, and the 43 and 46 kDa band intensities in the hippocampus. The results indicate that in vivo PLA(2) inhibition in rat brain decreases the levels of total (nonphosphorylated plus phosphorylated) Tau protein and corroborate our previous in vitro findings.