NGF induces the expression of group IIA secretory phospholipase A2 in PC12 cells: the newly synthesized enzyme is addressed to growing neurites.

We proposed that group IIA secretory phospholipase A(2) (GIIA) participates in neuritogenesis based on our observations that the enzyme migrates to growth cones and neurite tips when PC12 cells are induced to differentiate by nerve growth factor (NGF) (Ferrini et al., Neurochem Res 35:2168-2174, 2010). The involvement of other secretory PLA(2) isoforms in neuronal development has been suggested by others but through different mechanisms. In the present study, we compared the subcellular distribution of GIIA and group X sPLA(2) (GX) after stimulation of PC12 cells with NGF. We found that GIIA, but not GX, localized at the neuritic tips after treatment with NGF, as demonstrated by immunofluorescence analysis. We also found that NGF stimulated the expression and the activity of GIIA. In addition, NGF induced the expressed myc-tagged GIIA protein to migrate to neurite tips in its active form. We propose that GIIA expression, activity, and subcellular localization is regulated by NGF and that the enzyme may participate in neuritogenesis through intracellular mechanisms, most likely by facilitating the remodelling of glycerophospholipid molecular species by deacylation-reacylation reactions necessary for the incorporation of polyunsaturated fatty acids.

Reversible inhibition of hydrogen peroxide elimination by calcium in brain mitochondria.

In the present work, the Ca(2+) dependence of mitochondrial H(2) O(2) elimination was investigated. Mitochondria isolated from guinea pig brain were energized by glutamate and malate and incubated with micromolar concentrations of Ca(2+) in the presence of ADP, preventing permeability transition pore formation. After the completion of Ca(2+) uptake, mitochondria were challenged with H(2) O(2) (5 µM), then at various time points residual H(2) O(2) was determined using the Amplex red method and compared with that in mitochondria incubated with H(2) O(2) without Ca(2+) addition. Dose-dependent inhibition of H(2) O(2) elimination by Ca(2+) was detected, which was prevented by the Ca(2+) -uptake inhibitor Ru 360. Stimulation of Ca(2+) release from Ca(2+) -loaded mitochondria by a combined addition of Ru 360 and Na(+) decreased the Ca(2+) -evoked inhibition of H(2) O(2) removal. After Ca(2+) uptake (50 µM), mitochondrial aconitase activity was found to be decreased, which was partially attributable to the impaired elimination of endogenously produced reactive oxygen species. We found that the effects of Ca(2+) and H(2) O(2) on the activity of aconitase were additive. These results confirm that Ca(2+) inhibits elimination of H(2) O(2) in mitochondria and demonstrate that this effect is concentration dependent and reversible. The phenomenon described here can play a role in the modulation of ROS handling under conditions involving excessive cellular Ca(2+) load.

Low molecular weight phospholipases A2 in mammalian brain and neural cells: roles in functions and dysfunctions.

Several "low molecular weight" or "secretory" phospholipases A(2) isoforms may be expressed in mammalian neural cells. Indeed, mRNAs for GIB, GIIA, GIIE, GIII, GV, GX, and GXII were detected in brain tissues despite different levels. However, only the presence of GIB, GIIA, and GV proteins has been clearly demonstrated in neural cells or in the nervous tissue. Although the roles of GIB and GV in the nervous tissue are still elusive, there is evidence to support the involvement of GIIA in physiological and pathological events, including neurotransmission, long-term potentiation, and neuritogenesis. The neurotoxic effects of an increase in GIIA may be envisaged under pathological conditions associated with the activation of astrocytes during inflammation or through activation of neurons and enzymes due to the stimulation of the NMDA glutamate receptor. In the past, elevation of GIIA expression in many acute and chronic neurological diseases is well known. Although each neurodegenerative disease has a separate etiology, many share similar neurochemical common processes, such as excitotoxicity, oxidative stress, and mitochondrial dysfunction, phenomena where GIIA play an important role.

Group IIA secretory phospholipase A2 (GIIA) mediates apoptotic death during NMDA receptor activation in rat primary cortical neurons.

Phospholipases A(2) (PLA(2)) participate in neuronal death signalling pathways because of their ability to release lipid mediators, although the contribution of each isoform and mechanism of neurotoxicity are still elusive. Using a novel fluorogenic method to assess changes in a PLA(2) activity by flow cytometry, here we show that the group IIA secretory phospholipase A(2) isoform (GIIA) was specifically activated in cortical neurons following stimulation of N-methyl-d-aspartate glutamate receptor subtype (NMDAR). For activation, GIIA required Ca(2+) and reactive oxygen/nitrogen species, and inhibition of its activity fully prevented NMDAR-mediated neuronal apoptotic death. Superoxide, nitric oxide or peroxynitrite donors stimulated GIIA activity, which mediated neuronal death. Intriguingly, we also found that GIIA activity induced mitochondrial superoxide production after NMDAR stimulation. These results reveal a novel role for GIIA in excitotoxicity both as target and producer of superoxide in a positive-loop of activation that may contribute to the propagation of neurodegeneration.

The presence of a secretory phospholipase A2 in the nuclei of neuronal and glial cells of rat brain cortex.

Confocal immunofluorescence analysis indicated a relatively high localization of group V secretory phospholipase A(2) (GV) in the nuclei of cultured PC12 and U251 astrocytoma cells. Here, we report the biochemical evidence for the presence of a secretory PLA(2) in the nuclei of neuronal and glial cells from rat brain cortex. Enzymic activity was determined using [(3)H]oleate labelled Escherichia coli membranes in intact nuclei and in their soluble fractions in which the specific activity was significantly more elevated. The treatment of soluble nuclear fractions with inhibitors of cytosolic Ca(2+)-dependent or Ca(2+)-independent phospholipases A(2) was ineffective whereas DTT or Indoxam, a specific inhibitor of all isoforms of sPLA(2), abolished enzyme activity. The enzyme was identified as group V secretory phospholipase A(2) (GV) by Western blot analysis and its nucleoplasmic localization was demonstrated by CLSM.

Botulinum-A toxin injections into the detrusor muscle decrease nerve growth factor bladder tissue levels in patients with neurogenic detrusor overactivity.

PURPOSE: We investigated the effects of BTX-A on visceral afferent nerve transmission by measuring bladder tissue NGF levels in patients with neurogenic detrusor overactivity before and after intravesical treatment with BTX-A. We also compared the bladder tissue NGF content with clinical and urodynamic data. MATERIALS AND METHODS: A total of 23 patients underwent clinical evaluation and urodynamics with detection of the UDC threshold, maximum pressure and maximum cystometric capacity before, and at the 1 and 3-month followups. Endoscopic bladder wall biopsies were also obtained at the same time points. NGF levels were measured in tissue homogenate by enzyme-linked immunosorbent assay (Promega, Madison, Wisconsin). RESULTS: At 1 and 3 months mean catheterization and incontinent episodes were significantly decreased (p <0.05 and <0.001, respectively). On urodynamics we detected a significant increase in the UDC threshold and maximum cystometric capacity, and a significant decrease in UDC maximum pressure at the 1 and 3-month follow-ups compared to baseline (each p <0.001). At the same time points we detected a significant decrease in NGF bladder tissue content (each p <0.02). CONCLUSIONS: BTX-A intravesical treatment induces a state of NGF deprivation in bladder tissue that persists at least up to 3 months. As caused by BTX-A, the decrease in acetylcholine release at the presynaptic level may induce a decrease in detrusor contractility and in NGF production by the detrusor muscle. Alternatively BTX-A can decrease the bladder level of neurotransmitters that normally modulate NGF production and release.

Rat brain cortex mitochondria release group II secretory phospholipase A(2) under reduced membrane potential.

Activation of brain mitochondrial phospholipase(s) A(2) (PLA(2)) might contribute to cell damage and be involved in neurodegeneration. Despite the potential importance of the phenomenon, the number, identities, and properties of these enzymes are still unknown. Here, we demonstrate that isolated mitochondria from rat brain cortex, incubated in the absence of respiratory substrates, release a Ca(2+)-dependent PLA(2) having biochemical properties characteristic to secreted PLA(2) (sPLA(2)) and immunoreacting with the antibody raised against recombinant type IIA sPLA(2) (sPLA(2)-IIA). Under identical conditions, no release of fumarase in the extramitochondrial medium was observed. The release of sPLA(2) from mitochondria decreases when mitochondria are incubated in the presence of respiratory substrates such as ADP, malate, and pyruvate, which causes an increase of transmembrane potential determined by cytofluorimetric analysis using DiOC(6)(3) as a probe. The treatment of mitochondria with the uncoupler carbonyl cyanide 3-chlorophenylhydrazone slightly enhances sPLA(2) release. The increase of sPLA(2) specific activity after removal of mitochondrial outer membrane indicates that the enzyme is associated with mitoplasts. The mitochondrial localization of the enzyme has been confirmed by electron microscopy in U-251 astrocytoma cells and by confocal laser microscopy in the same cells and in PC-12 cells, where the structurally similar isoform type V-sPLA(2) has mainly nuclear localization. In addition to sPLA(2), mitochondria contain another phospholipase A(2) that is Ca(2+)-independent and sensitive to bromoenol lactone, associated with the outer mitochondrial membrane. We hypothesize that, under reduced respiratory rate, brain mitochondria release sPLA(2)-IIA that might contribute to cell damage.

Metabolism and functions of phosphatidylserine in mammalian brain.

Phosphatidylserine (PtdSer) is involved in cell signaling and apoptosis. The mechanisms regulating its synthesis and degradation are still not defined. Thus, its role in these processes cannot be clearly established at molecular level. In higher eukaryotes, PtdSer is synthesized from phosphatidylethanolamine or phosphatidylcholine through the exchange of the nitrogen base with free serine. PtdSer concentration in the nervous tissue membranes varies with age, brain areas, cells, and subcellular components. At least two serine base exchange enzymes isoforms are present in brain, and their biochemical properties and regulation are still largely unknown because their activities vary with cell type and/or subcellular fraction, developmental stage, and differentiation. These peculiarities may explain the apparent contrasting reports. PtdSer cellular levels also depend on its decarboxylation to phosphatidylethanolamine and conversion to lysoPtdSer by phospholipases. Several aspects of brain PtdSer metabolism and functions seem related to the high polyunsaturated fatty acids content, particularly docosahexaenoic acid (DHA).

Activation of PAF-synthesizing enzymes in rat brain stem slices after LTP induction in the medial vestibular nuclei.

LysoPAF acetyltransferase (lysoPAF-AT) and PAF-synthesizing phosphocholinetransferase (PAF-PCT) are the two enzymes which catalyze the final reactions for the synthesis of PAF. Their activities, assayed in the homogenate of rat brain stem slices and under their optimal conditions, increased 5 min after high frequency stimulation of vestibular afferents, inducing LTP in the medial vestibular nuclei. The activity of phosphatidylcholine-synthesizing phosphocholinetransferase, was not affected. Sixty minutes from the induction of LTP, PAF-PCT activity, but not that of lysoPAF-AT, was still significantly higher with respect to 5 min test stimulated control. We used AP-5 to verify whether this increase was strictly dependent upon LTP induction, which requires NMDA receptor activation. In AP-5 treated slices, lysoPAF-acetyltransferase and PAF-synthesizing phosphocholinetransferase activities increased, but they were reduced after high frequency stimulation under AP-5. In conclusion, we have demonstrated that the activities of PAF-synthesizing enzymes are activated soon after the induction of LTP and that this effect is linked to the activation of NMDA-receptors. We suggest that the enzyme activation by AP-5, preventing LTP, might be due to glutamate enhancement but, in neurons showing LTP and under normal conditions, the activation of potentiation mechanisms is critical for the enhancement of enzyme activities.