Phospholipase C activity in cerebrospinal fluid following subarachnoid hemorrhage related to brain damage

Evidence that a lipolytic enzyme--hematopoietic-specific phospholipase C-β2--promotes mobilization of hematopoietic stem cells by decreasing their lipid raft-mediated bone marrow retention and increasing the promobilizing effects of granulocytes

Hematopoietic stem/progenitor cells (HSPCs) reside in the bone marrow (BM) microenvironment and are retained there by the interaction of membrane lipid raft-associated receptors, such as the α-chemokine receptor CXCR4 and the α4β1-integrin (VLA-4, very late antigen 4 receptor) receptor, with their respective specific ligands, stromal-derived factor 1 and vascular cell adhesion molecule 1, expressed in BM stem cell niches. The integrity of the lipid rafts containing these receptors is maintained by the glycolipid glycosylphosphatidylinositol anchor (GPI-A). It has been reported that a cleavage fragment of the fifth component of the activated complement cascade, C5a, has an important role in mobilizing HSPCs into the peripheral blood (PB) by (i) inducing degranulation of BM-residing granulocytes and (ii) promoting their egress from the BM into the PB so that they permeabilize the endothelial barrier for subsequent egress of HSPCs. We report here that hematopoietic cell-specific phospholipase C-β2 (PLC-β2) has a crucial role in pharmacological mobilization of HSPCs. On the one hand, when released during degranulation of granulocytes, it digests GPI-A, thereby disrupting membrane lipid rafts and impairing retention of HSPCs in BM niches. On the other hand, it is an intracellular enzyme required for degranulation of granulocytes and their egress from BM. In support of this dual role, we demonstrate that PLC-β2-knockout mice are poor mobilizers and provide, for the first time, evidence for the involvement of this lipolytic enzyme in the mobilization of HSPCs.

Influence of experimental subarachnoid hemorrhage on nicotine-induced contraction of the rat basilar artery in relation to arachidonic acid metabolites signaling pathway

BACKGROUND

Smoking is one of the most important risk factors for cerebral circulatory disorders. The purpose of this study was to investigate the influence of experimental subarachnoid hemorrhage (SAH) on nicotine-induced contraction (arachidonic acid metabolites) in the basilar arteries of rats.

METHODS

Rats were killed at 1 hour and 1 week after blood injection, and the basilar artery was isolated and cut into a spiral strip.

RESULTS

Testing of cyclooxygenase-1 (COX-1) and 5-lipoxygenase (5-LOX) inhibitors revealed no significant differences in their effects on normal and SAH (1 hour and 1 week). Phospholipase C (PLC) inhibitor (1-(6-((17beta-3-methoxyestra-1,3,5(10)-trien-17yl)amino)hexyl)-1H-pyrrole-2,5,-dione [U-73122]) slightly inhibited contraction of SAH (1 hour and 1 week) when compared to controls. Phospholipase A2 (PLA2) inhibitor (manoalide) and cytosolic PLA2 (cPLA2) inhibitor (arachidonyltrifluoromenthylketone [AACOCF3]) more strongly attenuated contraction in SAH (1 hour and 1 week) than in controls. Secreted PLA2 (sPLA2) inhibitor (indoxam), PLC inhibitor (2-nitro-4-carboxyphenyl N, N-diphenylcarbamate [NCDC]), and COX-2 inhibitors (nimesulide, (5-methanesulfonamido-6-(2,4-difluorothiophenyl)-1-indanone) [L-745337], and celecoxib) only slightly inhibited contraction of SAH (1 week) when compared to normal and SAH (1 hour). The calcium-independent PLA2 (iPLA2) inhibitor bromoenol lactone (BEL) showed greater inhibition of contraction in SAH (1 hour) when compared to normal and SAH (1 week).

CONCLUSIONS

One week after exposure to SAH, PLC, sPLA2, and COX-2 activity were enhanced and cPLA2 activity was inhibited. One hour after exposure to SAH, PLC activity was enhanced and cPLA2 and iPLA2 activity was inhibited. Such changes of inflammatory arachidonic acid metabolites by smoking after SAH may play important roles in fatal cerebral circulatory disorders, suggesting important implications for the etiology and pathogenesis of SAH.

Differential protein kinase C isoform abundance in ascending aortic aneurysms from patients with bicuspid versus tricuspid aortic valves

BACKGROUND

It is recognized that different events contribute to the initiation of ascending thoracic aortic aneurysms (ATAAs) in patients with bicuspid aortic valves (BAV) versus patients with tricuspid aortic valves (TAV), but the molecular signaling pathways driving aneurysm formation remain unclear. Protein kinase C (PKC) is a superfamily of kinases which differentially mediate signaling events that lead to altered gene expression and cellular function, and may regulate downstream mediators of vascular remodeling. The present study tested the hypothesis that ATAA development in patients with BAV versus TAV proceeds by independent signaling pathways involving differential PKC signaling.

METHODS AND RESULTS

ATAA samples were collected from BAV (n=57) and TAV (n=55) patients and assessed for 10 different PKC isoforms by immunoblotting. Results were expressed as a percent change in abundance (mean+/-SEM) from a nonaneurysmal control group (100%, n=21). Correlation analysis was performed, and relationships between PKC and matrix metalloproteinase abundance were reported. In the BAV group, classic and novel PKC isoforms (PKC-alpha, betaI, gamma, epsilon, theta) were increased, whereas PKC-eta and atypical PKC-zeta were decreased. In the TAV group, classic and novel isoforms were decreased and atypical PKC-zeta was elevated. Positive correlations between PKC and matrix metalloproteinase abundance were identified.

CONCLUSIONS

Differential PKC isoform abundance was observed in ATAA samples from patients with BAV versus TAV, suggesting independent molecular signaling pathways may be operative. Induction of independent transcriptional programs may result and may provide a mechanistic foundation for developing selective diagnostic/therapeutic strategies for patients with ATAAs secondary to BAV or TAV.

Protein kinase C and cerebral vasospasm

Twenty-five years after the discovery of protein kinase C (PKC), the physiologic function of PKC, and especially its role in pathologic conditions, remains a subject of great interest with 30,000 studies published on these aspects. In the cerebral circulation, PKC plays a role in the regulation of myogenic tone by sensitization of myofilaments to calcium. Protein kinase C phosphorylates various ion channels including augmenting voltage-dependent Ca2+ channels and inhibiting K+ channels, which both lead to vessel contraction. These actions of PKC amplify vascular reactivity to different agonists and may be critical in the regulation of cerebral artery tone during vasospasm. Evidence accumulated during at least the last decade suggest that activation of PKC in cerebral vasospasm results in a delayed but prolonged contraction of major arteries after subarachnoid hemorrhage. Most of the experimental results in vitro or in animal models support the view that PKC is involved in cerebral vasospasm. Implication of PKC in cerebral vasospasm helps explain increased arterial narrowing at the signal transduction level and alters current perceptions that the pathophysiology is caused by a combination of multiple receptor activation, hemoglobin toxicity, and damaged neurogenic control. Activation of protein kinase C also interacts with other signaling pathways such as myosin light chain kinase, nitric oxide, intracellular Ca2+, protein tyrosine kinase, and its substrates such as mitogen-activated protein kinase. Even though identifying PKC revolutionized the understanding of cerebral vasospasm, clinical advances are hampered by the lack of clinical trials using selective PKC inhibitors.

Effects of tirilazad mesylate on vasospasm and phospholipid hydroperoxides in a primate model of subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Tirilazad mesylate has been used in the attempt to prevent cerebral vasospasm after subarachnoid hemorrhage (SAH), although the actual targets of this agent in vivo have thus far been controversial. Chemiluminescence/high-performance liquid chromatography provided a new method for direct measurements of phosphatidylcholine hydroperoxide (PCOOH) and phosphatidylethanolamine hydroperoxide (PEOOH) in vivo and showed that phosphatidylcholine is the lipid class most susceptible to lipid peroxidation. In the present study we measured those levels in a primate model of SAH for determination of the effects of tirilazad on vasospasm.

METHODS

Fourteen Macaca monkeys of both sexes were randomly assigned into 2 groups: a tirilazad group receiving a dosage of 0.3 mg/kg and a placebo group receiving only the vehicle in which tirilazad was delivered. After the induction of experimental SAH around the right middle cerebral artery on day 0, tirilazad or vehicle was administered intravenously every 8 hours for 6 days. On day 7, the animals were killed after angiography and regional cerebral blood flow measurements were performed. The levels of PCOOH and PEOOH were measured in the clots, bilateral parietal cortices, right frontal cortex contact with clots, cerebellar hemispheres, bilateral middle cerebral arteries, and basilar arteries.

RESULTS

In the placebo group, a significant vasospasm occurred in the cerebral arteries on both sides, but most prominently on the right side. The degree of vasospasm in the cerebral arteries was significantly attenuated in the tirilazad group (P<0.005). There were no significant differences in regional cerebral blood flow, PCOOH, and PEOOH levels in the clots, cerebral cortices, and cerebellar hemispheres between the 2 groups. In contrast, the levels of PCOOH in the cerebral arteries were significantly higher in the placebo group than in the tirilazad group (P<0.025). It was remarkable that the tirilazad treatments eliminated PCOOH in any vascular territory after SAH.

CONCLUSIONS

PCOOH in the artery wall may be an important indicator for vasospasm, and the inhibition of PCOOH may explain the efficacy of tirilazad on vasospasm.

Biosynthesis of prostaglandin D2 by motoneurons and dorsal horn microneurons: a biochemical and high resolution immunocytochemical study in chick spinal cord

Prostaglandin D2 is one of the major prostanoids formed from [14C]arachidonic acid by the central nervous system. The aim of the present study is to specify the prostaglandin D2 biosynthetic capacity in the chick spinal cord and to identify the cell type involved in this synthesis. A highly specific and sensitive enzyme immunoassay allowed us to demonstrate that the amount of newly formed prostaglandin D2 increases proportionally with the concentration of free arachidonic acid of either exogenous or endogenous origin and reaches concentration values ranging from 10(-9) to 10(-6) M. The sites of prostaglandin D2 synthesis were localized in Vibratome sections of spinal cord after incubation with antibodies raised against glutathione-independent prostaglandin D synthase; controls were performed with anti-glutathione-dependent prostaglandin D synthase antibodies and non-immune rabbit or goat serum. After immunoprocessing, electron microscope examination revealed that the specific immunoreactivity was confined to small neurons of laminae II and III in the dorsal horn and to motoneurons in the ventral horn of the spinal cord. The immunodeposits were associated with rough endoplasmic reticulum profiles distributed throughout the dorsal horn neurons or restricted to limited subsurface areas of perikarya and dendrites in motoneurons. Since the immunoreactive neurons in the dorsal horn were closely related to blood capillaries, prostaglandin D2 may be suspected to play a role in the regulation of the microcirculation. The accumulation of prostaglandin D synthase in motoneuron areas facing astrocytic membrane stacks suggests that prostaglandin D2 could interact with astrocytic functions.