Release of secretory phospholipase A2 from rat neuronal cells and its possible function in the regulation of catecholamine secretion

Abstract

Here we show that secretory phospholipase A2 (sPLA2) that is immunochemically indistinguishable from type II sPLA2 is (i) stored in neuroendocrine cells, (ii) released in response to neurotransmitters or depolarization, and (iii) involved in the regulation of catecholamine secretion by these cells. Rat brain synaptic vesicle fractions contained PLA2 activity, which was neutralized completely by an antibody raised against rat type II sPLA2. sPLA2 immunoreactive with anti-(type II sPLA2) antibody was released from synaptosomes in response to depolarization evoked by a high concentration of potassium in the presence of Ca2+. Rat pheochromocytoma PC12 cells, which differentiated into adherent cells similar to sympathetic neurons in response to nerve growth factor, were used for the detailed analysis of the dynamics and function of sPLA2 in neuronal cells. Antibody against rat type II sPLA2 precipitated approximately 80% of the PLA2 activity in PC12 cell lysates. Transcript for type II sPLA2 was detected in PC12 cells by reverse transcriptase-PCR. When neuronally differentiated PC12 cells were stimulated with carbamylcholine or potassium, sPLA2 was released into the medium and reached a maximal approximately 40% release by 15 min. Inhibitors specific to type II sPLA2 suppressed catecholamine secretion by PC12 cells which had been activated by carbamylcholine. Furthermore, treatment of PC12 cells with exogenous type II sPLA2 alone elicited catecholamine secretion. These observations indicate that sPLA2 released from neuronal cells may regulate the degranulation process leading to release of neurotransmitters and are compatible with our earlier finding that this enzyme is involved in the degranulation of rat mast cells.

Chronic Lithium Chloride Administration Attenuates Brain NMDA Receptor-Initiated Signaling via Arachidonic Acid in Unanesthetized Rats

“…Although both cPLA 2 and sPLA 2 were activated in some of those studies (Kim et al, 1995), it is likely that mainly cPLA 2 was activated in ours, as cPLA 2 is sensitive to the low Ca 2 + concentrations, 300 nM to 1 mM (Clark et al, 1995;Ismailov et al, 2004) that occur during normal neuronal activation. sPLA 2 activation requires a much higher Ca 2 + concentration, 16-18 mM, and is involved mainly in the presynaptic release of synaptic vesicles (Dennis, 1994;Matsuzawa et al, 1996;Wei et al, 2003). iPLA 2 is Ca 2 + -independent and selective for DHA acid rather than AA (Dennis, 1994;Strokin et al, 2004).…”

“…cPLA 2 has been localized at postsynaptic neuronal membranes in the brain (Basavarajappa et al, 1998;Ong et al, 1999;Pardue et al, 2003) and is activated by 300 nM to 1 mM Ca 2 + (Clark et al, 1995), in the physiological range of intracellular Ca 2 + during neuronal activation (Ismailov et al, 2004). sPLA 2 is activated at much higher Ca 2 + concentrations, 16-18 mM (Dennis, 1994), and is localized in presynaptic vesicles that are released by exocytosis during membrane depolarization (Matsuzawa et al, 1996;Wei et al, 2003).…”

Neuronal Expression and Neuritogenic Action of Group X Secreted Phospholipase A2

“…For neural differentiation, the cells (10 4 cells/ml) were cultured with appropriate concentrations of rat nerve growth factor (NGF; Sigma) in type I collagen-coated 6-or 12-well plates (Iwaki Glass) for up to 3 days (14). Normal human pulmonary fibroblasts (NHPF) and culture media with supplements for these cells were purchased from BioWhittaker.…”

“…2D), indicating that sPLA 2 -X accumulates in the Golgi prior to secretion. sPLA 2 -X Induces Neurite Outgrowth in PC12 Cells-In an attempt to identify some functional aspects of sPLA 2 -X in peripheral neuronal cells, we took advantage of PC12 cells, which differentiate into sympathetic neuron-like cells following culture with 100 ng/ml NGF (14), as shown in Fig. 3A.…”

Lysophosphatidic Acid Induces Necrosis and Apoptosis in Hippocampal Neurons

“…Several phospholipases A2 have been identified that preferentially hydrolyze phosphatidic acid. These include a phospholipase A2 activity enriched in the brain and a secretory phospholipase A2, which is synthesized in astrocytes in response to inflammatory mediators, elevated in activity on cerebral ischemia/reperfusion, and released in conjunction with neurotransmitter release from synaptic vesicles (Oka and Arita, 1991;Lauritzen et a!., 1994;Fourcade et a!., 1995;Thomson and Clark, 1995;Matsuzawa et al, 1996;Snitko eta!., 1997). It is interesting that a related secretory phospho!ipase A2, was found to synergize with glutamate in the stimulation of neuronal death (Kolko et a!., 1996).…”