mRNA levels of Ca(2+)-independent forms of protein kinase C in postischemic gerbil brain by northern blot analysis

Preconditioning in neuroprotection: From hypoxia to ischemia

Sublethal hypoxic or ischemic events can improve the tolerance of tissues, organs, and even organisms from subsequent lethal injury caused by hypoxia or ischemia. This phenomenon has been termed hypoxic or ischemic preconditioning (HPC or IPC) and is well established in the heart and the brain. This review aims to discuss HPC and IPC with respect to their historical development and advancements in our understanding of the neurochemical basis for their neuroprotective role. Through decades of collaborative research and studies of HPC and IPC in other organ systems, our understanding of HPC and IPC-induced neuroprotection has expanded to include: early- (phosphorylation targets, transporter regulation, interfering RNA) and late- (regulation of genes like EPO, VEGF, and iNOS) phase changes, regulators of programmed cell death, members of metabolic pathways, receptor modulators, and many other novel targets. The rapid acceleration in our understanding of HPC and IPC will help facilitate transition into the clinical setting.

Insulin, PKC signaling pathways and synaptic remodeling during memory storage and neuronal repair

Protein kinase C (PKC) is involved in synaptic remodeling, induction of protein synthesis, and many other processes important in learning and memory. Activation of neuronal protein kinase C correlates with, and may be essential for, all phases of learning, including acquisition, consolidation, and reconsolidation. Protein kinase C activation is closely tied to hydrolysis of membrane lipids. Phospholipases C and A2 produce 1,2-diacylglycerol and arachidonic acid, which are direct activators of protein kinase C. Phospholipase C also produces inositol triphosphate, which releases calcium from internal stores. Protein kinase C interacts with many of the same pathways as insulin; therefore, it should not be surprising that insulin signaling and protein kinase C activation can both have powerful effects on memory storage and synaptic remodeling. However, investigating the possible roles of insulin in memory storage can be challenging, due to the powerful peripheral effects of insulin on glucose and the low concentration of insulin in the brain. Although peripheral for insulin, synthesized in the beta-cells of the pancreas, is primarily involved in regulating glucose, small amounts of insulin are also present in the brain. The functions of this brain insulin are inadequately understood. Protein kinase C may also contribute to insulin resistance by phosphorylating the insulin receptor substrates required for insulin signaling. Insulin is also responsible insulin-long term depression, a type of synaptic plasticity that is also dependent on protein kinase C. However, insulin can also activate PKC signaling pathways via PLC gamma, Erk 1/2 MAP kinase, and src stimulation. Taken together, the available evidence suggests that the major impact of protein kinase C and its interaction with insulin in the mature, fully differentiated nervous system appears to be to induce synaptogenesis, enhance memory, reduce Alzheimer's pathophysiology, and stimulate neurorepair.

Effects of scutellarin on PKCgamma in PC12 cell injury induced by oxygen and glucose deprivation

AIM

To evaluate the neuroprotective effect and mechanisms of scutellarin (Scu) against PC12 cell injury after oxygen and glucose deprivation followed by reperfusion (OGD-Rep).

METHODS

Undifferentiated rat pheochromocytoma PC12 cells, exposed to oxygen and glucose deprivation followed by reperfusion (OGD-Rep), used as an in vitro model of ischemia/reperfusion. Cell survival was evaluated by diphenyltetrazolium bromide (MTT) assay and the amount of LDH release was determined using assay kits. [Ca2+](i) was monitored using a fluorescent Ca2+-sensitive dye Fura-2 acetoxymethyl ester. Cell apoptosis was detected by a DNA ladder and by flow cytometric detection. The expression of protein kinase C (PKC)gamma was determined using both RT-PCR and Western blotting. The translocation of PKCgamma was assayed by subcellular fractionation and Western blotting.

RESULTS

OGD-Rep injury significantly elevated the level of LDH release, [Ca2+](i), mRNA expression and the translocation of PKCgamma compared in the PC12 cells with those of the normal group. Scu (10-100 micromol/L) exerted a protective effect against OGD-Rep injury by reducing LDH release, [Ca2+](i), the percent of apoptosis, and the translocation of PKCgamma.

CONCLUSION

Scu inhibits the increase of [Ca2+](i) and the activation of PKCgamma, exerting protective effects against PC12 cell injury induced by OGD-Rep.

Suppression of deltaPKC activation after focal cerebral ischemia contributes to the protective effect of hypothermia

Mild hypothermia is a robust neuroprotective treatment for stroke. Understanding the mechanisms underlying hypothermia's benefits will lead to more effective treatments to prevent stroke damage. Delta protein kinase C (deltaPKC) is a kinase that has been strongly implicated in executing ischemic damage. We investigated the effects of hypothermia on deltaPKC activation, as determined by its subcellular translocation, proteolytic cleavage, and phosphorylation in a focal cerebral ischemia model. The amount of constitutively activated C-terminal catalytic fragment of deltaPKC (CF-deltaPKC) increased after stroke. Both hypothermia (30 degrees C) and the caspase-3-specific inhibitor, Z-DQMD-FMK, blocked the accumulation of activated deltaPKC in the penumbra. Other hallmarks of deltaPKC activation, its translocation to the mitochondria, and nucleus were observed in the penumbra as early as 10 mins after reperfusion. These events were blocked by hypothermia. Hypothermia also blocked CF-deltaPKC increases in the mitochondria and nuclei. Conversely, a specific deltaPKC activator, psideltaRACK, decreased the neuroprotective effect of hypothermia. Finally, deltaPKC activity may lead to mitochondrial injury and cytochrome c release, as the timing of cytochrome c release corresponded to the time course of deltaPKC translocation. Both cytochrome c release and deltaPKC translocation were blocked by hypothermia. In conclusion, hypothermia protects against ischemic damage in part by suppressing deltaPKC activation after stroke.

Protein kinase C inhibition attenuates vascular ETB receptor upregulation and decreases brain damage after cerebral ischemia in rat

Background

Protein kinase C (PKC) is known to be involved in the pathophysiology of experimental cerebral ischemia. We have previously shown that after transient middle cerebral artery occlusion, there is an upregulation of endothelin receptors in the ipsilateral middle cerebral artery. The present study aimed to examine the effect of the PKC inhibitor Ro-32-0432 on endothelin receptor upregulation, infarct volume and neurology outcome after middle cerebral artery occlusion in rat.

Results

At 24 hours after transient middle cerebral artery occlusion (MCAO), the contractile endothelin B receptor mediated response and the endothelin B receptor protein expression were upregulated in the ipsilateral but not the contralateral middle cerebral artery. In Ro-32-0432 treated rats, the upregulated endothelin receptor response was attenuated. Furthermore, Ro-32-0432 treatment decreased the ischemic brain damage significantly and improved neurological scores. Immunohistochemistry showed fainter staining of endothelin B receptor protein in the smooth muscle cells of the ipsilateral middle cerebral artery of Ro-32-0432 treated rats compared to control.

Conclusion

The results suggest that treatment with Ro-32-0432 in ischemic stroke decreases the ischemic infarction area, neurological symptoms and associated endothelin B receptor upregulation. This provides a new perspective on possible mechanisms of actions of PKC inhibition in cerebral ischemia.

Inhibition of PKC activity blocks the increase of ETB receptor expression in cerebral arteries

Background

Previous studies have shown that there is a time-dependent upregulation of contractile endothelin B (ET_B) receptors in middle cerebral arteries (MCA) after organ culture. This upregulation is dependent on mitogen-activated protein kinases and possibly protein kinase C (PKC). The aim of this study was to examine the effect of PKC inhibitors with different profiles on the upregulation of contractile ET_B receptors in rat MCA. Artery segments were incubated for 24 hours at 37°C. To investigate involvement of PKC, inhibitors were added to the medium before incubation. The contractile endothelin-mediated responses were measured and real-time PCR was used to detect endothelin receptor mRNA levels. Furthermore, immunohistochemistry was used to demonstrate the ET_B receptor protein distribution in the MCA and Western blot to measure which of the PKC subtypes that were affected by the inhibitors.

Results

The PKC inhibitors bisindolylmaleimide I, Ro-32-0432 and PKC inhibitor 20–28 attenuated the ET_B receptor mediated contractions. Furthermore, Ro-32-0432 and bisindolylmaleimide I decreased ET_B receptor mRNA levels while PKC inhibitor 20–28 reduced the amount of receptor protein on smooth muscle cells. PKC inhibitor 20–28 also decreased the protein levels of the five PKC subtypes studied (α, βI, γ, δ and ε).

Conclusion

The results show that PKC inhibitors are able to decrease the ET_B receptor contraction and expression in MCA smooth muscle cells following organ culture. The PKC inhibitor 20–28 affects the protein levels, while Ro-32-0432 and bisindolylmaleimide I affect the mRNA levels, suggesting differences in activity profile. Since ET_B receptor upregulation is seen in cerebral ischemia, the results of the present study provide a way to interfere with the vascular involvement in cerebral ischemia.

Increased isoform-specific membrane translocation of conventional and novel protein kinase C in human neuroblastoma SH-SY5Y cells following prolonged hypoxia

Several studies have suggested that protein kinase C (PKC) plays a key role in the mechanism of cerebral ischemic/hypoxic preconditioning (I/HPC). However, detailed information regarding PKC isoforms in response to brain ischemia/hypoxia and their potential role in neuroprotection is unclear. Previous studies in our laboratory have demonstrated that the levels in membrane translocation of conventional PKC (cPKC) betaII, gamma, and novel PKCepsilon (nPKC), but not cPKCalpha, betaI, nPKCdelta, eta, mu, theta, and atypical PKC (aPKC) zeta and iota/lambda, were increased significantly in the hippocampus and cortex of intact mice with hypoxic preconditioning. To further detect cPKC and nPKC isoforms activation following prolonged hypoxia in vitro, we tested the membrane translocation (an indicator of PKC activation) of cPKCalpha, betaI, betaII, and gamma, and nPKCdelta, epsilon, eta, mu, and theta in a human neuroblastoma SH-SY5Y cell line following sustained hypoxic exposure (1% O(2)/5% CO(2)/94% N(2)). Using Western blot and immunocytochemistry methods, we found that the levels of cPKCalpha, betaI, betaII, and nPKCepsilon, but not nPKCdelta, eta, mu, and theta, membrane translocation were increased significantly (P < 0.05, n = 8) in a time-dependent manner (from 0.5 to 24 h) following sustained hypoxic exposure. Similarly, the immunostaining experiment also showed a noticeable translocation of cPKCalpha, betaI, betaII, and nPKCepsilon from the cytosol to the perinuclear or membrane-related areas after 6 h posthypoxic exposure. In addition, no cPKCgamma was detected in this cell line under either a normoxic or hypoxic condition. These results suggested that prolonged hypoxia may induce the activation of cPKCalpha, betaI, betaII, and nPKCepsilon by triggering their membrane translocation in SH-SY5Y cells.

The Role of Protein Kinase C in Cerebral Ischemic and Reperfusion Injury

Background and Purpose— Stroke is a leading cause of disability and death in the United States, yet limited therapeutic options exist. The need for novel neuroprotective agents has spurred efforts to understand the intracellular signaling pathways that mediate cellular response to stroke. Protein kinase C (PKC) plays a central role in mediating ischemic and reperfusion damage in multiple tissues, including the brain. However, because of conflicting reports, it remains unclear whether PKC is involved in cell survival signaling, or mediates detrimental processes.

Summary of Review— This review will examine the role of PKC activity in stroke. In particular, we will focus on more recent insights into the PKC isozyme-specific responses in neuronal preconditioning and in ischemia and reperfusion-induced stress.

Conclusion— Examination of PKC isozyme activities during stroke demonstrates the clinical promise of PKC isozyme-specific modulators for the treatment of cerebral ischemia.

Identification of protein kinase C isoforms involved in cerebral hypoxic preconditioning of mice

Recently, accumulated studies have suggested that protein kinases C (PKC) play a central role in the development of ischemic-hypoxic preconditioning (I/HPC) in the brain. However, which types of PKC isoforms might be responsible for neuroprotection is still not clear, especially when the systematic investigation of PKC isoform-specific changes in brain regions was rare in animals with ischemic-hypoxic preconditioning. By using Western blot, we have demonstrated that the levels of cPKC betaII and gamma membrane translocation were increased in the early phase of cerebral hypoxic preconditioning. In this study, we combined the Western blot and immunostaining methods to investigate the effects of repetitive hypoxic exposure (H1-H4, n = 6 for each group) on membrane translocation and protein expression of several types of PKC isoforms, both in the cortex and hippocampus of mice. We found that the increased membrane translocation of nPKCepsilon (P < 0.05, versus normoxic H0) but not its protein expression levels in both the cortex and hippocampus during development of cerebral HPC in mice. However, there were no significant changes in both membrane translocation and protein expression levels of nPKCdelta, theta, eta, mu, and aPKC iota/lambda, zeta in these brain areas after hypoxic preconditioning. Similarly, an extensive subcellular redistribution of cPKCbetaII, gamma, and nPKCepsilon was observed by immunostaining in the cortex after three series of hypoxic exposures (H3). These results indicate that activation of cPKCbetaII, gamma, and nPKCepsilon might be involved in the development of cerebral hypoxic preconditioning of mice.

The effect of protein kinase C activation on colonic epithelial cellular integrity

We have investigated whether activation of protein kinase C has a direct cytotoxic effect on colonic mucosal epithelial cells and whether oxidant-induced damage to colonocytes is mediated by activation of cellular protein kinase C. Incubation of freshly harvested cells from rat colon with the protein kinase C activator, phorbol 12-myristate, resulted in a concentration-dependent increase in the extent of cell injury. Phorbol 12-myristate acetate (0.1-10 microM) also increased cellular protein kinase C activity and this was reduced significantly by treating cells with the antagonists staurosporine or 2-[1-(3-dimethylaminopropyl)-indol-3-yl]3-(-indol-3-yl)maleimide (GF 109203X; 10 microM). Phorbol 12-myristate acetate treatment also resulted in increased translocation of proteins for protein kinase C isoforms alpha, delta and epsilon from cytosol to membrane particulate fractions. The antagonists reduced the extent of cell damage in response to phorbol 12-myristate acetate. Furthermore, cell injury in response to the phorbol acetate was also inhibited by the addition of the oxidant scavengers, superoxide dismutase or catalase to the cell suspension. Addition of H(2)O(2) to the incubation medium (0.1-100 microM) resulted in an increase in cellular protein kinase C activity, an increase in the expression of the alpha, beta and zeta isoforms and a reduction in cell integrity. The cellular damaging actions of H(2)O(2) were significantly reduced by the protein kinase C antagonists, staurosporine or 2-[1-(3-dimethylaminopropyl)-indol-3-yl]-3-(-indol-3-yl)maleimide (GF 109203X). These findings suggest that protein kinase C activation results in colonic cellular injury and this damage is mediated, at least in part, by release of reactive oxidants. Furthermore, oxidant-mediated damage to these cells also involves protein kinase C activation.

Induction of protein kinase Cdelta subspecies in neurons and microglia after transient global brain ischemia

The delayed death of CA1 neurons after global brain ischemia is associated with induction of apoptosis genes and is inhibited by protein synthesis inhibitors, suggesting that the degeneration of CA1 pyramidal neurons is an active process that requires new gene expression. The transient global ischemia model has been extensively used to identify enzymes and other proteins underlying delayed neuronal cell death. The expression of protein kinase C (PKC) subspecies after 20 minutes of global brain ischemia produced by a four-vessel occlusion model in the rat was studied. From the multiple PKC subspecies studied, only PKCdelta mRNA was significantly up-regulated in CA1 pyramidal neurons at 24 hours and in activated microglia at 3 to at least 7 days after ischemia. The induction of PKCdelta mRNA was also found in the cortex at 8 hours and 3 days after ischemia. This cortical but not hippocampal induction was regulated by an alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid/kainate receptor antagonist, 6-nitro-7-sulfamobenzo[f]quinoxaline-2,3-dione, and glucocorticoids. An N-methyl-D-aspartate receptor antagonist, MK-801, was without effect on the induction of PKCdelta subspecies. The selective and prolonged induction of the PKCdelta mRNA and protein first in CA1 pyramidal neurons and at a later stage in activated microglia suggests that the PKCdelta isozyme may take part in regulation of the delayed death of CA1 neurons after transient global brain ischemia.

Selective subcellular redistributions of protein kinase C isoforms by chemical hypoxia

The mechanisms of neuronal degeneration following hypoxia/ischemia remain undefined, but the processes include increases in neurotransmitter release, elevation of cytosolic-free calcium concentration, and changes in signal transduction pathways. Activation of the multigene family of protein kinase C (PKC) has been associated with the release of neurotransmitter and the survival of neurons. Therefore, to understand which PKC isozymes are involved in hypoxia/ischemia-induced neuronal degeneration, we examined PKC isozymes after chemical hypoxia (i.e., KCN exposure) in PC12 cells. Cell toxicity, as measured by lactate dehydrogenase (LDH) release, was increased significantly by KCN in glucose-free DMEM and was exaggerated by acute 12-O-tetradecanoyl phorbol-13-acetate (TPA) pretreatment. Under parallel conditions, KCN elevated cytosolic-free calcium ([Ca2+]i) in glucose-free but not in glucose containing DMEM, and TPA pretreatment did not exaggerate KCN's effect on [Ca2+]i. Thus, increases in [Ca2+]i are not sufficient for the synergistic toxic effect of KCN and TPA. In the glucose-free DMEM, selective PKC isozyme inhibitor Go 6976 at 10 nM completely inhibited KCN-induced LDH release and at higher concentrations (1 microM) inhibited the basal levels of LDH release. The protein levels of PKCs in the nuclear, membrane, and cytosolic fractions were measured by Western blot analysis using antibodies against specific isoforms. Two Ca2+-dependent (-alpha, -gamma) and four Ca2+-independent (-delta, -epsilon, -zeta, and -lambda) isozymes were identified and two isozymes (-beta and -theta) were not detected in the subcellular fractions of PC12 cells. Treatment of the cells with TPA significantly activated translocation of conventional PKC-gamma from the cytosol to the membrane and nuclear fractions and other PKC isozymes (-alpha, -delta, and -epsilon) from the cytosol to the membrane, but not atypical PKC-zeta and -lambda. Although only the levels in the nuclear PKC-gamma but not other PKC isozymes were increased significantly following KCN, the levels of cPKC-alpha and -gamma in the membrane mainly- and those and PKC-epsilon in the nucleus-were increased when KCN was combined with TPA. In addition, this condition (TPA + KCN) did not affect the TPA insensitive atypical isozymes, PKC-zeta or -lambda. Taking the results together, differential activation/translocation of PKC isozymes by KCN and TPA is important in the regulation of chemical hypoxia-induced cell injury in PC12 cells.

Expression of Ca2+-dependent (classical) PKC mRNA isoforms after transient cerebral ischemia in gerbil hippocampus

Cerebral ischemia is known to modify the expression of genetic information in the brain. To complement this knowledge, in the present study we have estimated the expression of calcium- and phospholipid-dependent (classical) protein kinase C (c PKC) isoform mRNAs (alpha, beta1 and gamma) at different time following ischemia. Forebrain cerebral ischemia was performed on Mongolian gerbils by 5 minutes bilateral occlusion of common carotid arteries. At the pointed time the cytoplasmic RNA was extracted from hippocampus and the expression of PKC mRNA quantified by RT PCR technique using GAPDH expression as an internal standard. Results indicate that only one gamma isoform of cPKC mRNA expression becomes significantly modified in postischemic hippocampus. A transient increase up to 145% of control within the first 3 h was followed by its decline to 60-65% at a longer recirculation period. This lowered levels returned back to control at 72 h postischemic recovery. This result indicates that gamma PKC could be particularly sensitive to ischemic insult and would react in accordance with the other early signals determining ischemic outcome.

Post-ischemic changes in protein kinase C RNA in the gerbil brain following prolonged periods of recirculation: a phosphorimaging study

Northern blot analysis was performed to investigate the long-term changes in mRNA expression of protein kinase C (PKC) in the gerbil brain following transient cerebral ischemia. We have previously demonstrated an increase in mRNA levels of certain Ca(2+)-independent forms of PKC in early recirculation periods i.e., 6 h and 24 h postischemia (PI). But, since neuronal death in susceptible regions usually occurs 2-3 days following ischemia, this study examined the mRNA levels of PKC after prolonged periods of reperfusion following ischemia. The mRNA expression was also examined at an early recirculation period, i.e., 1 h, to determine how early the alterations begin to occur. Global forebrain ischemia was produced in gerbils by 10 min of bilateral carotid artery occlusion. RNA was prepared from forebrains of nonischemic controls and PI animals following 1 h, 3 d, and 7 d of recirculation (n = 3 to 4 in each group) and hybridized with synthetic oligonucleotide probes for PKC, delta, epsilon, and zeta based on cDNA sequences in rat and labelled with 32P. The autoradiographs were recorded and quantified by a sensitive system, Phosphor Imager, followed by conventional x-ray film exposure. The mRNA levels of all 3 PKC isozymes examined were found to be elevated as early as 1 h recirculation following ischemia. The increases in mRNA levels of both delta PKC following 6 h and 24 h of recirculation as well as that of zeta PKC following 24 h of recirculation, as reported earlier, return to control levels by 3 d PI and remain at that level 7 d PI.(ABSTRACT TRUNCATED AT 250 WORDS)