Protein kinase C-gamma and calcium/calmodulin-dependent protein kinase II-alpha are persistently translocated to cell membranes of the rat brain during and after middle cerebral artery occlusion

Remote Ischemia Postconditioning Mitigates Hippocampal Neuron Impairment by Modulating Cav1.2-CaMKIIα-Aromatase Signaling After Global Cerebral Ischemia in Ovariectomized Rats

Brain-derived estrogen (BDE2) is gaining attention as an endogenous neurotransmitter. Recent research has revealed that selectively removing the aromatase gene, the pivotal enzyme responsible for BDE2 synthesis, in forebrain neurons or astrocytes can lead to synaptic loss and cognitive impairment. It is worth noting that remote ischemia post-conditioning (RIP), a non-invasive technique, has been shown to activate natural protective mechanisms against severe ischemic events. The aim of our study was to investigate whether RIP triggers aromatase-BDE2 signaling, shedding light on its neuroprotective mechanisms after global cerebral ischemia (GCI) in ovariectomized rats. Our findings are as follows: (1) RIP was effective in mitigating ischemic damage in hippocampal CA1 neurons and improved cognitive function after GCI. This was partially due to increased Aro-BDE2 signaling in CA1 neurons. (2) RIP intervention efficiently enhanced pro-survival kinase pathways, such as AKT, ERK1/2, CREB, and suppressed CaMKIIα signaling in CA1 astrocytes induced by GCI. Remarkably, inhibiting CaMKIIα activity led to elevated Aro-BDE2 levels and replicated the benefits of RIP. (3) We also identified the positive mediation of Cav1.2, an LVGCC calcium channel, on CaMKIIα-Aro/BDE2 pathway response to RIP intervention. (4) Significantly, either RIP or CaMKIIα inhibition was found to alleviate reactive astrogliosis, which was accompanied by increased pro-survival A2-astrocyte protein S100A10 and decreased pro-death A1-astrocyte marker C3 levels. In summary, our study provides compelling evidence that Aro-BDE2 signaling is a critical target for the reparative effects of RIP following ischemic insult. This effect may be mediated through the CaV1.2-CaMKIIα signaling pathway, in collaboration with astrocyte-neuron interactions, thereby maintaining calcium homeostasis in the neuronal microenvironment and reducing neuronal damage after ischemia.

Pyramidal and parvalbumin neurons modulate the process of electroacupuncture stimulation for stroke rehabilitation

Electroacupuncture (EA) stimulation has been shown to be beneficial in stroke rehabilitation; however, little is known about the neurological mechanism by which this peripheral stimulation approach treats for stroke. This study showed that both pyramidal and parvalbumin (PV) neuronal activity increased in the contralesional primary motor cortex forelimb motor area (M1FL) after ischemic stroke induced by focal unilateral occlusion in the M1FL. EA stimulation reduced pyramidal neuronal activity and increased PV neuronal activity. These results were obtained by a combination of fiber photometry recordings, in vivo and in vitro electrophysiological recordings, and immunofluorescence. Moreover, EA was found to regulate the expression/function of N-methyl-D-aspartate receptors (NMDARs) altered by stroke pathology. In summary, our findings suggest that EA could restore disturbed neuronal activity through the regulation of the activity of pyramidal and PV neurons. Furthermore, NMDARs we shown to play an important role in EA-mediated improvements in sensorimotor ability during stroke rehabilitation.

Protein kinase C mediates hypoxia-induced long-term potentiation of NMDA neurotransmission in the visual retinocollicular pathway

The identification of processes and mechanisms underlying the early stage of hypoxic injury of the retinocollicular pathway may be beneficial for the future prevention and treatment of navigation, orientation, and visual attention impairments. Previously, we have demonstrated that short-term hypoxia led to long-term potentiation (LTP) of NMDA neurotransmission in the background of long-term depression of GABA_A retinocollicular transmission. Here, we sought to obtain insight into the mechanisms of hypoxia-induced LTP of NMDA retinocollicular neurotransmission and the role of the protein kinase C (PKC) signaling pathway in it. To investigate these, we recorded pharmacologically isolated NMDA transmission in cocultivated pairs of rat retinal ganglion cells and superficial superior colliculus neurons under normoxic and hypoxic conditions, using the paired patch-clamp technique and method of fast local superfusion. We tested the involvement of the PKC by adding the potent and selective inhibitor chelerythrine chloride (ChC, 5 μM). We observed that hypoxia-induced LTP of NMDA neurotransmission is associated with the shortening of current kinetics. We also found that the PKC signaling pathway mediates hypoxia-induced LTP and associated shortening of NMDA currents. The ChC completely blocked the induction of LTP by hypoxia and associated kinetic changes. Contrary effects of ChC were observed with already induced LTP. ChC led to the reversal of LTP to the initial synaptic strength but the current kinetics remain irreversibly shortened. Our results show that ChC is a promising agent for the prevention and treatment of hypoxic injuries of NMDA retinocollicular neurotransmission and provide necessary electrophysiological basics for further research.

CaMKIIα as a Promising Drug Target for Ischemic Grey Matter

Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a major mediator of Ca2+-dependent signaling pathways in various cell types throughout the body. Its neuronal isoform CaMKIIα (alpha) centrally integrates physiological but also pathological glutamate signals directly downstream of glutamate receptors and has thus emerged as a target for ischemic stroke. Previous studies provided evidence for the involvement of CaMKII activity in ischemic cell death by showing that CaMKII inhibition affords substantial neuroprotection. However, broad inhibition of this central kinase is challenging because various essential physiological processes like synaptic plasticity rely on intact CaMKII regulation. Thus, specific strategies for targeting CaMKII after ischemia are warranted which would ideally only interfere with pathological activity of CaMKII. This review highlights recent advances in the understanding of how ischemia affects CaMKII and how pathospecific pharmacological targeting of CaMKII signaling could be achieved. Specifically, we discuss direct targeting of CaMKII kinase activity with peptide inhibitors versus indirect targeting of the association (hub) domain of CaMKIIα with analogues of γ-hydroxybutyrate (GHB) as a potential way to achieve more specific pharmacological modulation of CaMKII activity after ischemia.

Role of Ca2+/Calmodulin-Dependent Protein Kinase Type II in Mediating Function and Dysfunction at Glutamatergic Synapses

Glutamatergic synapses harbor abundant amounts of the multifunctional Ca²⁺/calmodulin-dependent protein kinase type II (CaMKII). Both in the postsynaptic density as well as in the cytosolic compartment of postsynaptic terminals, CaMKII plays major roles. In addition to its Ca²⁺-stimulated kinase activity, it can also bind to a variety of membrane proteins at the synapse and thus exert spatially restricted activity. The abundance of CaMKII in glutamatergic synapse is akin to scaffolding proteins although its prominent function still appears to be that of a kinase. The multimeric structure of CaMKII also confers several functional capabilities on the enzyme. The versatility of the enzyme has prompted hypotheses proposing several roles for the enzyme such as Ca²⁺ signal transduction, memory molecule function and scaffolding. The article will review the multiple roles played by CaMKII in glutamatergic synapses and how they are affected in disease conditions.

Calcium/Calmodulin-Dependent Protein Kinase II in Cerebrovascular Diseases

Cerebrovascular disease is the most common life-threatening and debilitating condition that often leads to stroke. The multifunctional calcium/calmodulin-dependent protein kinase II (CaMKII) is a key Ca2+ sensor and an important signaling protein in a variety of biological systems within the brain, heart, and vasculature. In the brain, past stroke-related studies have been mainly focused on the role of CaMKII in ischemic stroke in neurons and established CaMKII as a major mediator of neuronal cell death induced by glutamate excitotoxicity and oxidative stress following ischemic stroke. However, with growing understanding of the importance of neurovascular interactions in cerebrovascular diseases, there are clearly gaps in our understanding of how CaMKII functions in the complex neurovascular biological processes and its contributions to cerebrovascular diseases. Additionally, emerging evidence demonstrates novel regulatory mechanisms of CaMKII and potential roles of the less-studied CaMKII isoforms in the ischemic brain, which has sparked renewed interests in this dynamic kinase family. This review discusses past findings and emerging evidence on CaMKII in several major cerebrovascular dysfunctions including ischemic stroke, hemorrhagic stroke, and vascular dementia, focusing on the unique roles played by CaMKII in the underlying biological processes of neuronal cell death, neuroinflammation, and endothelial barrier dysfunction triggered by stroke. We also highlight exciting new findings, promising therapeutic agents, and future perspectives for CaMKII in cerebrovascular systems.

Interleukin-15 modulates the response of cortical neurons to ischemia

OBJECTIVE

Stroke is a major cause of death and disability in the United States. Current acute stroke therapy consists of clot-dissolving drugs, catheter-based interventions and physical rehabilitation. To date, there are no therapies that directly enhance neuronal survival after a stroke. Previous work from our lab demonstrated that Interleukin-15 (IL-15) peptide could rescue cardiomyocytes subjected to hypoxia. We sought to extend these findings to cortical neurons since IL-15 has been implicated to have an important role in neuronal homeostasis.

METHODS

We have evaluated the effect of IL-15 peptide on primary cortical neurons derived from embryonic rats in vitro under conditions of anoxia and glucose deprivation, and in vivo following middle cerebral artery occlusion.

RESULTS

IL-15 administration rescued neuronal cells subjected to anoxia coupled with glucose deprivation (AGD), as well as with reoxygenation. A hallmark of stroke is the ischemic microenvironment and associated oxidative stress, which results in DNA damage and ER stress, both of which contribute to neuronal cell damage and death. The expression of anoxia, ER stress, and DNA damage factors/markers was evaluated via western blot and correlated with the cellular survival effects of IL-15 in vitro. In addition, IL-15 effect of alleviating ER stress and increasing cell survival was also observed in vivo.

INTERPRETATION

Our data indicate, for the first time, that administration of the pleiotropic factor IL-15 reduces neuronal cell death during AGD, which correlates with modulation of multiple cellular stress pathways.

PKCγ and PKCε are Differentially Activated and Modulate Neurotoxic Signaling Pathways During Oxygen Glucose Deprivation in Rat Cortical Slices

Cerebral ischemia is known to trigger a series of intracellular events such as changes in metabolism, membrane function and intracellular transduction, which eventually leads to cell death. Many of these processes are mediated by intracellular signaling cascades that involve protein kinase activation. Among all the kinases activated, the serine/threonine kinase family, protein kinase C (PKC), particularly, has been implicated in mediating cellular response to cerebral ischemic and reperfusion injury. In this study, using oxygen-glucose deprivation (OGD) in acute cortical slices as an in vitro model of cerebral ischemia, I show that PKC family of isozymes, specifically PKCγ and PKCε are differentially activated during OGD. Detecting the expression and activation levels of these isozymes in response to different durations of OGD insult revealed an early activation of PKCε and delayed activation of PKCγ, signifying their roles in response to different durations and stages of ischemic stress. Specific inhibition of PKCγ and PKCε significantly attenuated OGD induced cytotoxicity, rise in intracellular calcium, membrane depolarization and reactive oxygen species formation, thereby enhancing neuronal viability. This study clearly suggests that PKC family of isozymes; specifically PKCγ and PKCε are involved in OGD induced intracellular responses which lead to neuronal death. Thus isozyme specific modulation of PKC activity may serve as a promising therapeutic route for the treatment of acute cerebral ischemic injury.

cPKCγ alleviates ischemic injury through modulating synapsin Ia/b phosphorylation in neurons of mice

Conventional protein kinase C (cPKC)γ and synapsin Ia/b have been implicated in the development of ischemic stroke, but their relationships and functions are unclear. In the present study, the oxygen-glucose deprivation (OGD)-induced ischemic insult in primary cultured cortical neurons in vitro and middle cerebral artery occlusion (MCAO)-induced ischemic stroke model in vivo were used to elucidate the function of cPKCγ and its modulation on synapsin Ia/b phosphorylation in ischemic stroke. We found that cPKCγ knockout significantly increased the infarct volume of mice after 1 h MCAO/72 h reperfusion by using triphenyltetrazolium chloride (TTC) staining. In the primarily cultured cortical neurons, cPKCγ knockout also aggravated the OGD-induced cell death and morphological damage of neurites, while cPKCγ restoration could alleviate the ischemic injury. Among the five phosphorylation sites of synapsin Ia/b, only the phosphorylation levels of Ser549 and 553 could be modulated by cPKCγ in neurons following 0.5 h OGD/24 h reoxygenation. In addition, we found that cPKCγ and synapsin Ia/b could be reciprocally co-immunoprecipitated in the cerebral cortex of MCAO mice. Taken together, we proposed that cPKCγ alleviates ischemic injury through modulating Ser549/553- synapsin Ia/b phosphorylation in neurons of mice.

cPKCγ-mediated down-regulation of UCHL1 alleviates ischaemic neuronal injuries by decreasing autophagy via ERK-mTOR pathway

Stroke is one of the leading causes of death in the world, but its underlying mechanisms remain unclear. Both conventional protein kinase C (cPKC)γ and ubiquitin C-terminal hydrolase L1 (UCHL1) are neuron-specific proteins. In the models of 1-hr middle cerebral artery occlusion (MCAO)/24-hr reperfusion in mice and 1-hr oxygen-glucose deprivation (OGD)/24-hr reoxygenation in cortical neurons, we found that cPKCγ gene knockout remarkably aggravated ischaemic injuries and simultaneously increased the levels of cleaved (Cl)-caspase-3 and LC3-I proteolysis product LC3-II, and the ratio of TUNEL-positive cells to total neurons. Moreover, cPKCγ gene knockout could increase UCHL1 protein expression via elevating its mRNA level regulated by the nuclear factor κB inhibitor alpha (IκB-α)/nuclear factor κB (NF-κB) pathway in cortical neurons. Both inhibitor and shRNA of UCHL1 significantly reduced the ratio of LC3-II/total LC3, which contributed to neuronal survival after ischaemic stroke, but did not alter the level of Cl-caspase-3. In addition, UCHL1 shRNA reversed the effect of cPKCγ on the phosphorylation levels of mTOR and ERK rather than that of AMPK and GSK-3β. In conclusion, our results suggest that cPKCγ activation alleviates ischaemic injuries of mice and cortical neurons through inhibiting UCHL1 expression, which may negatively regulate autophagy through ERK-mTOR pathway.

Galanin Protects from Caspase-8/12-initiated Neuronal Apoptosis in the Ischemic Mouse Brain via GalR1

Galanin (GAL) plays key role in many pathophysiological processes, but its role in ischemic stroke remains unclear. Here, the models of 1 h middle cerebral artery occlusion (MCAO)/1-7 d reperfusion (R)-induced ischemic stroke and in vitro cell ischemia of 1 h oxygen-glucose deprivation (OGD)/24 h reoxygenation in primary cultured cortical neurons were used to explore GAL’s effects and its underlying mechanisms. The results showed significant increases of GAL protein levels in the peri-infarct region (P) and infarct core (I) within 48 h R of MCAO mice (p<0.001). The RT-qPCR results also demonstrated significant increases of GAL mRNA during 24-48 h R (p<0.001), and GAL receptors GalR1-2 (but not 3) mRNA levels in the P region at 24 h R of MCAO mice (p<0.001). Furthermore, the significant decrease of infarct volume (p<0.05) and improved neurological outcome (p<0.001-0.05) were observed in MCAO mice following 1 h pre- or 6 h post-treatment of GAL during 1-7 d reperfusion. GalR1 was confirmed as the receptor responsible for GAL-induced neuroprotection by using GalR2/3 agonist AR-M1896 and Lentivirus-based RNAi knockdown of GalR1. GAL treatment inhibited Caspase-3 activation through the upstream initiators Capsases-8/-12 (not Caspase-9) in both P region and OGD-treated cortical neurons. Meanwhile, GAL’s neuroprotective effect was not observed in cortical neurons from conventional protein kinase C (cPKC) γ knockout mice. These results suggested that exogenous GAL protects the brain from ischemic injury by inhibiting Capsase-8/12-initiated apoptosis, possibly mediated by GalR1 via the cPKCγ signaling pathway.

Beneficial Effects of a CaMKIIα Inhibitor TatCN21 Peptide in Global Cerebral Ischemia

Aberrant calcium influx is a common feature following ischemic reperfusion (I/R) in transient global cerebral ischemia (GCI) and causes delayed neuronal cell death in the CA1 region of the hippocampus. Activation of calcium-calmodulin (CaM)-dependent protein kinase IIα (CaMKIIα) is a key event in calcium signaling in ischemic injury. The present study examined the effects of intracerebroventricular (icv) injection of tatCN21 in ischemic rats 3 h after GCI reperfusion. Cresyl violet and NeuN staining revealed that tatCN21 exerted neuroprotective effects against delayed neuronal cell death of hippocampal CA1 pyramidal neurons 10 days post-GCI. In addition, TatCN21 administration ameliorated GCI-induced spatial memory deficits in the Barnes maze task as well as anxiety-like behaviors and spontaneous motor activity in the elevated plus maze and open field test, respectively. Mechanistic studies showed that the administration of tatCN21 decreased GCI-induced phosphorylation, translocation, and membrane targeting of CaMKIIα. Treatment with tatCN21 also inhibited the level of CaMKIIα-NR2B interaction and NR2B phosphorylation. Our results revealed an important role of tatCN21 in inhibiting CaMKIIα activation and its beneficial effects in neuroprotection and memory preservation in an ischemic brain injury model.

Neuroprotective hypothermia - Why keep your head cool during ischemia and reperfusion

BACKGROUND

Targeted temperature management (TTM) is the induced cooling of the entire body or specific organs to help prevent ischemia and reperfusion (I/R) injury, as may occur during major surgery, cardiac resuscitation, traumatic brain injury and stroke. Ischemia and reperfusion induce neuronal damage by mitochondrial dysfunction and oxidative injury, ER stress, neuronal excitotoxicity, and a neuroinflammatory response, which may lead to activation of apoptosis pathways.

SCOPE OF REVIEW

The aim of the current review is to discuss TTM targets that convey neuroprotection and to identify potential novel pharmacological intervention strategies for the prevention of cerebral ischemia and reperfusion injury.

MAJOR CONCLUSIONS

TTM precludes I/R injury by reducing glutamate release and oxidative stress and inhibiting release of pro-inflammatory factors and thereby counteracts mitochondrial induced apoptosis, neuronal excitotoxicity, and neuroinflammation. Moreover, TTM promotes regulation of the unfolded protein response and induces SUMOylation and the production of cold shock proteins. These advantageous effects of TTM seem to depend on the clinical setting, as well as type and extent of the injury. Therefore, future aims should be to refine hypothermia management in order to optimize TTM utilization and to search for pharmacological agents mimicking the cellular effects of TTM.

GENERAL SIGNIFICANCE

Bundling knowledge about TTM in the experimental, translational and clinical setting may result in better approaches for diminishing I/R damage. While application of TTM in the clinical setting has some disadvantages, targeting its putative protective pathways may be useful to prevent I/R injury and reduce neurological complications.

The role of Akt (protein kinase B) and protein kinase C in ischemia-reperfusion injury

Stroke is a leading cause of long-term disability and death in the United States. Currently, tissue plasminogen activator (tPA), is the only Food and Drug Administration-approved treatment for acute ischemic stroke. However, the use of tPA is restricted to a small subset of acute stroke patients due to its limited 3-h therapeutic time window. Given the limited therapeutic options at present and the multi-factorial progression of ischemic stroke, emphasis has been placed on the discovery and use of combination therapies aimed at various molecular targets contributing to ischemic cell death. Protein kinase C (PKC) and Akt (protein kinase B) are serine/threonine kinases that play a critical role in mediating ischemic-reperfusion injury and cellular growth and survival, respectively. The present review will examine the role of PKC and Akt in the cellular response to ischemic-reperfusion injury.

Ischemic preconditioning protects the brain against injury via inhibiting CaMKII-nNOS signaling pathway

Although studies have shown that cerebral ischemic preconditioning (IPC) can ameliorate ischemia/reperfusion (I/R) induced brain damage, but its precise mechanisms remain unknown. Therefore, the aim of this study was to investigate the neuroprotective mechanisms of IPC against ischemic brain damage induced by cerebral I/R and to explore whether the Calcium/calmodulin-dependent protein kinase II (CaMKII)-mediated up-regulation of nNOS ser847-phosphorylation signaling pathway contributed to the protection provided by IPC. Transient global brain ischemia was induced by 4-vessel occlusion in adult male Sprague-Dawley rats. The rats were pretreated with 3 min of IPC alone or KN62 (selective antagonist of CaMKII) treatment before IPC, after reperfusion for 3 days, 6 min ischemia was induced. Cresyl violet staining was used to examine the survival of hippocampal CA1 pyramidal neurons. Immunoblotting was performed to measure the phosphorylation of CaMKII, nNOS, c-Jun and the expression of FasL. Immunoprecipitation was used to examine the binding between PSD95 and nNOS. The results showed that IPC could significantly protect neurons against cerebral I/R injury, furthermore, the combination of PSD95 and nNOS was increased, coinstantaneously the phosphorylation of CaMKII and nNOS (ser847) were up-regulated, however the activation of c-Jun and FasL were reduced. Conversely, KN62 treatment before IPC reversed all these effects of IPC. Taken together, the results suggest that IPC could diminish ischemic brain injury through CaMKII-mediated up-regulation of nNOS ser847-phosphorylation signaling pathway.

Brief low [Mg(2+)]o-induced Ca(2+) spikes inhibit subsequent prolonged exposure-induced excitotoxicity in cultured rat hippocampal neurons

Reducing [Mg²⁺]_o to 0.1 mM can evoke repetitive [Ca²⁺]_i spikes and seizure activity, which induces neuronal cell death in a process called excitotoxicity. We examined the issue of whether cultured rat hippocampal neurons preconditioned by a brief exposure to 0.1 mM [Mg²⁺]_o are rendered resistant to excitotoxicity induced by a subsequent prolonged exposure and whether Ca²⁺ spikes are involved in this process. Preconditioning by an exposure to 0.1 mM [Mg²⁺]_o for 5 min inhibited significantly subsequent 24 h exposure-induced cell death 24 h later (tolerance). Such tolerance was prevented by both the NMDA receptor antagonist D-AP5 and the L-type Ca²⁺ channel antagonist nimodipine, which blocked 0.1 mM [Mg²⁺]_o-induced [Ca²⁺]_i spikes. The AMPA receptor antagonist NBQX significantly inhibited both the tolerance and the [Ca²⁺]_i spikes. The intracellular Ca²⁺ chelator BAPTA-AM significantly prevented the tolerance. The nonspecific PKC inhibitor staurosporin inhibited the tolerance without affecting the [Ca²⁺]_i spikes. While Gö6976, a specific inhibitor of PKCα had no effect on the tolerance, both the PKCε translocation inhibitor and the PKCζ pseudosubstrate inhibitor significantly inhibited the tolerance without affecting the [Ca²⁺]_i spikes. Furthermore, JAK-2 inhibitor AG490, MAPK kinase inhibitor PD98059, and CaMKII inhibitor KN-62 inhibited the tolerance, but PI-3 kinase inhibitor LY294,002 did not. The protein synthesis inhibitor cycloheximide significantly inhibited the tolerance. Collectively, these results suggest that low [Mg²⁺]_o preconditioning induced excitotoxic tolerance was directly or indirectly mediated through the [Ca²⁺]_i spike-induced activation of PKCε and PKCξ, JAK-2, MAPK kinase, CaMKII and the de novo synthesis of proteins.

Bryostatin improves survival and reduces ischemic brain injury in aged rats after acute ischemic stroke

BACKGROUND AND PURPOSE

Bryostatin, a potent protein kinase C (PKC) activator, has demonstrated therapeutic efficacy in preclinical models of associative memory, Alzheimer disease, global ischemia, and traumatic brain injury. In this study, we tested the hypothesis that administration of bryostatin provides a therapeutic benefit in reducing brain injury and improving stroke outcome using a clinically relevant model of cerebral ischemia with tissue plasminogen activator reperfusion in aged rats.

METHODS

Acute cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery (MCAO) in 18- to 20-month-old female Sprague-Dawley rats using an autologous blood clot with tissue plasminogen activator-mediated reperfusion. Bryostatin was administered at 6 hours post-MCAO, then at 3, 6, 9, 12, 15, and 18 days after MCAO. Functional assessment was conducted at 2, 7, 14, and 21 days after MCAO. Lesion volume and hemispheric swelling/atrophy were performed at 2, 7, and 21 days post-MCAO. Histological assessment of PKC isozymes was performed at 24 hours post-MCAO.

RESULTS

Bryostatin-treated rats showed improved survival post-MCAO, especially during the first 4 days. Repeated administration of bryostatin post-MCAO resulted in reduced infarct volume, hemispheric swelling/atrophy, and improved neurological function at 21 days post-MCAO. Changes in αPKC expression and εPKC expression in neurons were noted in bryostatin-treated rats at 24 hours post-MCAO.

CONCLUSIONS

Repeated bryostatin administration post-MCAO protected the brain from severe neurological injury post-MCAO. Bryostatin treatment improved survival rate, reduced lesion volume, salvaged tissue in infarcted hemisphere by reducing necrosis and peri-infarct astrogliosis, and improved functional outcome after MCAO.

Hypnotic effect of volatile anesthetics is mediated by PKC-γ dynamics

BACKGROUND

Although protein kinase C-γ (PKC-γ) is a target for the effects of volatile anesthetics, the molecular mechanisms of the kinase function remain unclear. We examined the effects of different types of anesthetics on PKC-γ knockout mice, and investigated the dynamics of the kinase in mouse brain.

METHODS

We measured the required number of times for loss of righting reflex (rtfLORR) after administration of isoflurane, sevoflurane, and propofol on PKC-γ knockout mice and compared with those of wild-type mice. We also used immunoblotting to investigate the intracellular distribution of PKC-γ and phosphorylated PKC-γ (p-PKC-γ) in brain of wild-type mice anesthetized by these anesthetics.

RESULTS

Isoflurane and sevoflurane significantly prolonged the rtfLORRs in PKC-γ knockout mice compared with those in wild-type mice, while no significant difference was observed between knockout and wild-type mice treated with propofol. Examination of the cellular fractions showed that PKC-γ was significantly decreased, whereas p-PKC-γ was significantly increased in the synaptic membrane fraction (P2). There was no significant change in the supernatant fraction (S). In propofol-treated mice, PKC-γ and p-PKC-γ showed no significant changes in P2 or S.

CONCLUSION

Our results provide new evidence to support the possibility of the involvement of PKC-γ in the actions of volatile anesthetics.

Effects of different types of anesthetic agents on cellular protein kinase C-γ dynamics in mouse brain

BACKGROUND/AIMS

Although protein kinase C-γ (PKC-γ) is a target for the effects of volatile anesthetics, the molecular mechanisms of the kinase function during their action remain unclear. We examined the effects of different types of anesthetics on PKC-γ knockout mice. Furthermore, we investigated the dynamics of the kinase in brain cells obtained from mice anesthetized with these anesthetics.

METHODS

We measured the required times for loss of righting reflex (rtfLORR) after administration of isoflurane, sevoflurane, or propofol on PKC-γ knockout mice and compared the times with those of wild-type mice. We also used immunoblotting to investigate the intracellular distribution of PKC-γ and phosphorylated PKC-γ (p-PKC-γ) in brain cell fractions obtained from wild-type mice during the loss of righting reflex induced by these anesthetics.

RESULTS

Isoflurane (2.6%) and sevoflurane (3.4%) used at twice the minimum alveolar concentration significantly prolonged the rtfLORRs in PKC-γ knockout mice compared to those in wild-type mice. On the other hand, no significant difference was observed between knockout and wild-type mice treated with propofol (200 mg/kg). Examination of the cellular fractions isolated from volatile anesthetic-treated mouse brains showed that PKC-γ was significantly decreased in the synaptic membrane fraction (P2), whereas p-PKC-γ was significantly increased in P2. There was no significant change in the supernatant fraction (S). In propofol-treated mice, PKC-γ and p-PKC-γ showed no significant changes in P2 or S.

CONCLUSION

Our results provide new evidence to support the possibility of the involvement of PKC-γ in the actions of volatile anesthetics.

The role of the ubiquitin proteasome system in ischemia and ischemic tolerance

Ubiquitin modification targets a protein for rapid degradation by the proteasome. However, polyubiquitination of proteins can result in multiple functions depending on the topology of the ubiquitin chain. Therefore, ubiquitin signaling offers a more complex and versatile biology compared with many other posttranslational modifications. One area of potential for the application of this knowledge is the field of ischemia-induced brain damage, as occurs following a stroke. The ubiquitin proteasome system may exert a dual role on neuronal outcome following ischemia. Harmful ischemia results in an overload of the ubiquitin proteasome system, and blocking the proteasome reduces brain infarction following ischemia. However, the rapid and selective degradation of proteins following brief ischemia results in endogenous protection against ischemia. Therefore, further understanding of the molecular signaling mechanisms that regulate the ubiquitin proteasome system may reveal novel therapeutic targets to reduce brain damage when ischemia is predicted or reduce the activation of the cell death mechanisms and the inflammatory response following stroke. The aim of this review is to discuss some of the recent advances in the understanding of protein ubiquitination and its implications for novel stroke therapies.

Nonclassical mechanisms of progesterone action in the brain: I. Protein kinase C activation in the hypothalamus of female rats

The modulation of gene regulation by progesterone (P) and its classical intracellular regulation by progestin receptors in the brain, resulting in alterations in physiology and behavior has been well studied. The mechanisms mediating the short latency effects of P are less well understood. Recent studies have revealed rapid nonclassical signaling action of P involving the activation of intracellular signaling pathways. We explored the involvement of protein kinase C (PKC) in P-induced rapid signaling in the ventromedial nucleus of the hypothalamus (VMN) and preoptic area (POA) of the rat brain. Both the Ca2+-independent (basal) PKC activity representing the activation of PKC by the in vivo treatments and the Ca+2-dependent (total) PKC activity assayed in the presence of exogenous cofactors in vitro were determined. A comparison of the two activities demonstrated the strength and temporal status of PKC regulation by steroid hormones in vivo. P treatment resulted in a rapid increase in basal PKC activity in the VMN but not the POA. Estradiol benzoate priming augmented P-initiated increase in PKC basal activity in both the VMN and POA. These increases were inhibited by intracerebroventricular administration of a PKC inhibitor administered 30 min prior to P. The total PKC activity remained unchanged demonstrating maximal PKC activation within 30 min in the VMN. In contrast, P regulation in the POA significantly attenuated total PKC activity +/- estradiol benzoate priming. These rapid changes in P-initiated PKC activity were not due to changes in PKC protein levels or phosphorylation status.

Isoflurane inhibits protein kinase Cgamma and calcium/calmodulin dependent protein kinase ii-alpha translocation to synaptic membranes in ischemic mice brains

Volatile anesthetics isoflurane possibly improves the ischemic brain injury. However, its molecular actions are still unclear. In ischemia, protein kinase C (PKC)gamma and calcium/calmodulin dependent protein kinase II (CaMKII)-alpha are persistently translocated from cytosol to cell membranes, and diminish these translocation suggested to be neuroprotective. We thus tested a hypothesis that isoflurane inhibits PKCgamma and CaMKII-alpha translocation after ischemic brain insults. C57Bl/6J male mice were made to inhale 1 or 2 MAC isoflurane, after which 3 or 5 min cerebral ischemia was induced by decapitation. The sampled cerebrum cortex was then homogenized and centrifuged into crude synaptosomal fractions (P2), cytosolic fractions (S3), and particulate fractions (P3). CaMKII-alpha and PKCgamma levels of these fractions were analyzed by immunoblotting. PKCgamma and CaMKII-alpha are translocated to synaptic membrane from cytosol by cerebral ischemia, although isoflurane significantly inhibited such translocation. These results may explain in part the cellular and molecular mechanisms of neuroprotective effects of isoflurane.

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.

Protein kinase C as a stress sensor

While there are many reviews which examine the group of proteins known as protein kinase C (PKC), the focus of this article is to examine the cellular roles of two PKCs that are important for stress responses in neurological tissues (PKC gamma and epsilon) and in cardiac tissues (PKC epsilon). These two kinases, in particular, seem to have overlapping functions and interact with an identical target, connexin 43 (Cx43), a gap junction protein which is central to proper control of signals in both tissues. While PKC gamma and PKC epsilon both help protect neural tissue from ischemia, PKC epsilon is the primary PKC isoform responsible for responding to decreased oxygen, or ischemia, in the heart. Both do this through Cx43. It is clear that both PKC gamma and PKC epsilon are necessary for protection from ischemia. However, the importance of these kinases has been inferred from preconditioning experiments which demonstrate that brief periods of hypoxia protect neurological and cardiac tissues from future insults, and that this depends on the activation, translocation, or ability for PKC gamma and/or PKC epsilon to interact with distinct cellular targets, especially Cx43. This review summarizes the recent findings which define the roles of PKC gamma and PKC epsilon in cardiac and neurological functions and their relationships to ischemia/reperfusion injury. In addition, a biochemical comparison of PKC gamma and PKC epsilon and a proposed argument for why both forms are present in neurological tissue while only PKC epsilon is present in heart, are discussed. Finally, the biochemistry of PKCs and future directions for the field are discussed, in light of this new information.

Gö 6983: A Fast Acting Protein Kinase C Inhibitor that Attenuates Myocardial Ischemia/Reperfusion Injury

Reperfusion injury is characterized by a decrease in endothelial release of nitric oxide within 5 min after reperfusion, increased leukocyte-endothelium interaction, and transmigration of leukocytes into the myocardium, producing cardiac contractile dysfunction. Gö 6983 is a fast acting, lipid soluble, broad spectrum protein kinase C inhibitor. When administered at the beginning of reperfusion, it can restore cardiac function within 5 min and attenuate the deleterious effects associated with acute ischemia/reperfusion. Gö 6983 may offer greater cardioprotection than other broad-spectrum PKC inhibitors in postischemic reperfusion injury because it inhibits PKC(zeta) as well as four other isoforms. The cardioprotection is associated with decreased leukocyte superoxide release and increased endothelial derived nitric oxide from vascular tissue. In vitro studies of human tissue showed that Gö 6983 significantly inhibited antigen-induced superoxide release from leukocytes of patients previously sensitized to tree pollen. In human vascular tissue, Gö 6983 inhibited intracellular Ca(2+) accumulation, suggesting a mechanism for its vasodilator properties. These studies suggest that Gö 6983 would be an effective compound to use in a clinical ischemia/reperfusion setting of organ transplantation and/or cerebral ischemia where inhibiting superoxide release and vasoconstriction in postischemic tissues would allow for better restoration of organ function during reperfusion. However, given the broad-spectrum action of Gö 6983, careful titration of the dose regimen would be recommended to ensure a successful outcome in the setting of organ transplantation and/or cerebral ischemia.

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.

Insulin receptor-protein kinase C-gamma signaling mediates inhibition of hypoxia-induced necrosis of cortical neurons

Ischemic stress causes neuronal death and functional impairment. Evidence has suggested that cells in the ischemic core first lose viability due to the decline in blood flow and cellular energy metabolism and then die by necrosis. Although inhibition of necrosis could be a potent therapeutic target for brain ischemia, known neurotrophic factors are ineffective for neuronal necrosis. We previously reported that insulin, but not brain-derived neurotrophic factor or insulin like-growth factor-1, inhibited neuronal necrosis under serum-free starvation stress. Although insulin receptors are abundant in the central nervous system as well as in peripheral tissues, neurons are not dependent upon insulin for their glucose supply, indicating that insulin receptors have other roles in the central nervous system. In the present study, by using hypoxia-reperfusion stress, we showed that cortical neurons rapidly died by necrosis as evaluated by propidium iodide staining and transmission electron microscopic analysis. As expected, insulin treatment significantly inhibited neuronal necrosis, although this effect was blocked by pretreatment with an antisense oligonucleotide for the insulin receptor. Furthermore, an inhibitor of protein kinase C (PKC) eliminated the insulin-induced antinecrotic effect. The addition of insulin induced significant translocation of only the PKC-gamma isoform, whereas antisense oligonucleotide treatment for this isoform abolished the insulin-induced inhibition of necrosis. Together, these results suggest that insulin mediates inhibition of neuronal necrosis through a novel mechanism involving PKC-gamma activation.

Magnesium blocks the loss of protein kinase C, leads to a transient translocation of PKCα and PKCε, and improves recovery after anoxia in rat hippocampal slices

Magnesium is a potent neuroprotective agent against damage to synaptic transmission during cerebral anoxia and reoxygenation. We investigated the mechanisms of anoxic transmission damage and magnesium neuroprotection by examining the response of PKC isoforms to an anoxic insult in the rat hippocampal slice model. A 2-min anoxic period, which resulted in almost complete recovery of synaptic function, did not result in PKC downregulation. In contrast, inducing long-term damage with 10-min anoxia resulted in the downregulation of the conventional PKCs betaI, betaII and gamma immediately after the insult and after 1-h reoxygenation. There was additional loss of PKC(alpha) and PKC(epsilon) after 1-h reoxygenation. Magnesium treatment improved the recovery of synaptic transmission, blocked the loss of PKC and resulted in a transient translocation of PKC(alpha) and PKC(epsilon) to the membrane fraction. Selective downregulation of cPKCs and PKC(epsilon) correlated with permanent damage to synaptic transmission while translocation of PKC(alpha) and PKC(epsilon) correlated with preservation of synaptic function. The mechanisms of magnesium neuroprotection may include altering the PKC response to an anoxic insult.

Differential subcellular targeting of PKC-epsilon in response to pharmacological or ischemic stimuli in intestinal epithelia

Ischemia is the central pathogenic factor underlying a spectrum of intestinal disorders. The study of the cellular signaling responses to ischemic stress in nonepithelial cells has progressed substantially in the previous several years, but little is known about the response in epithelial cells. Unique features of the epithelial response to ischemic stress suggest differential regulation with regards to signaling. The PKC family of proteins has been implicated in ischemic stress in nonepithelial systems. The role of PKC isoforms in chemical ischemia in intestinal epithelial cells is evaluated in this study. Additionally, the phosphorylation of the F-actin cross-linking protein myristoylated alanine-rich C kinase substrate (MARCKS) is also studied. Chemical ischemia resulted in the transient activation of only the isoform PKC-epsilon as detected by translocation employing the subcellular fractionation technique. The pharmacological agonists phorbol 12-myristate 13-acetate and carbachol also led to the translocation of PKC-epsilon. By immunofluoresence, MARCKS is noted to be located at the lateral membrane under control conditions. In response to carbachol, MARCKS translocates to the cytosol, indicating its phosphorylation, which is additionally confirmed biochemically. Consistent with this observation, carbachol induces the translocation of PKC-epsilon to proximity with MARCKS at the lateral membrane. In response to chemical ischemia, MARCKS fails to translocate and phosphorylation does not increase. Additionally, the translocation of PKC-epsilon is not to the lateral membrane but rather basally. The data suggest that the differential translocation of PKC-epsilon in response to pharmacological agonists versus ischemic stress may lead to different effects on downstream targets.

Hydrogen peroxide potentiates volume-sensitive excitatory amino acid release via a mechanism involving Ca2+/calmodulin-dependent protein kinase II

Excessive excitatory amino acid (EAA) release in cerebral ischemia is a major mechanism responsible for neuronal damage and death. A substantial fraction of ischemic EAA release occurs via volume-regulated anion channels (VRACs). Hydrogen peroxide (H2O2), which is abundantly produced during ischemia and reperfusion, activates a number of protein kinases critical for VRAC functioning and has recently been reported to activate VRACs. In the present study, we explored the effects of H2O2 on volume-dependent EAA release in cultured astrocytes, measured as the release of preloaded D-[3H]aspartate. 100-1,000 microm H2O2 enhanced swelling-induced EAA release by approximately 2.5-3-fold (EC50 approximately 10 microM). The VRAC blockers ATP, phloretin, and 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) potently inhibited both control swelling-induced and the H2O2-potentiated release, suggesting a role for VRACs. The H2O2-induced component of EAA release was attenuated by the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA-AM) and completely eliminated by the calmodulin antagonists trifluoperazine and W-7 and the Ca2+/calmodulin-dependent protein kinase II (CaMKII) inhibitor KN-93. Inhibitors of tyrosine kinases, protein kinase C, and the myosin light chain kinase were ineffective in blocking the H2O2 response. H2O2 treatment of swollen astrocytes, but not swelling alone, resulted in CaMKII activation that was inhibited by KN-93, as determined by a phospho-Thr286 CaMKII antibody. These data demonstrate that H2O2 strongly up-regulates astrocytic volume-sensitive EAA release via a CaMKII-dependent mechanism and in this way may potently promote pathological EAA release and brain damage in ischemia.