Neuronal necrosis inhibition by insulin through protein kinase C activation

Insulin neuroprotection and the mechanisms

Objective:

To analyze the mechanism of neuroprotection of insulin and which blood glucose range was benefit for insulin exerting neuroprotective action.

Data Sources:

The study is based on the data from PubMed.

Study Selection:

Articles were selected with the search terms “insulin”, “blood glucose”, “neuroprotection”, “brain”, “glycogen”, “cerebral ischemia”, “neuronal necrosis”, “glutamate”, “γ-aminobutyric acid”.

Results:

Insulin has neuroprotection. The mechanisms include the regulation of neurotransmitter, promoting glycogen synthesis, and inhibition of neuronal necrosis and apoptosis. Insulin could play its role in neuroprotection by avoiding hypoglycemia and hyperglycemia.

Conclusions:

Intermittent and long-term infusion insulin may be a benefit for patients with ischemic brain damage at blood glucose 6–9 mmol/L.

Insulin and the Brain: A Sweet Relationship With Intensive Care

BACKGROUND

Insulin receptors (IRs) in the brain have unique molecular features and a characteristic pattern of distribution. Their possible functions extend beyond glucose utilization. In this systematic review, we explore the interactions between insulin and the brain and its implications for anesthesiologists, critical care physicians, and other medical disciplines.

METHODS

A literature search of published preclinical and clinical studies between 1978 and 2014 was conducted, yielding 5996 articles. After applying inclusion and exclusion criteria, 92 studies were selected for this systematic review.

RESULTS

The IRs have unique molecular features, pattern of distribution, and mechanism of action. It has effects on neuronal function, metabolism, and neurotransmission. The IRs are involved in neuronal apoptosis and neurodegenerative processes.

CONCLUSION

In this systematic review, we present a close relationship between insulin and the brain, with discernible effects on memory, learning abilities, and motor functions. The potential therapeutic effects extend from acute brain insults such as traumatic brain injury, brain ischemia, and hemorrhage, to chronic neurodegenerative diseases such as Alzheimer and Parkinson disease. An understanding of the wider effects of insulin conveyed in this review will prompt anaesthesiologists and critical care physicians to consider its therapeutic potential and guide future studies.

Insulin in central nervous system: more than just a peripheral hormone

Insulin signaling in central nervous system (CNS) has emerged as a novel field of research since decreased brain insulin levels and/or signaling were associated to impaired learning, memory, and age-related neurodegenerative diseases. Thus, besides its well-known role in longevity, insulin may constitute a promising therapy against diabetes- and age-related neurodegenerative disorders. More interestingly, insulin has been also faced as the potential missing link between diabetes and aging in CNS, with Alzheimer's disease (AD) considered as the "brain-type diabetes." In fact, brain insulin has been shown to regulate both peripheral and central glucose metabolism, neurotransmission, learning, and memory and to be neuroprotective. And a future challenge will be to unravel the complex interactions between aging and diabetes, which, we believe, will allow the development of efficient preventive and therapeutic strategies to overcome age-related diseases and to prolong human "healthy" longevity. Herewith, we aim to integrate the metabolic, neuromodulatory, and neuroprotective roles of insulin in two age-related pathologies: diabetes and AD, both in terms of intracellular signaling and potential therapeutic approach.

RACK1 affects morphine reward via BDNF

Chronic morphine addiction may trigger functional changes in the mesolimbic dopamine system, which is believed to be the neurobiological substrate of opiate addiction. Brain derived neurotrophic factor (BDNF) has been implicated in addiction-related pathology in animal studies. Our previous studies have shown that RACK1 is involved in morphine reward in mice. The recent research indicates nuclear RACK1 by localizing at the promoter IV region of the BDNF gene and the subsequent chromatin modifications leads to the activation of the promoter and transcription of BDNF. The present study was designed to investigate if shRACK1 (a short hairpin RNA of RACK1) could reverse the mice's behavioral responses to morphine and BDNF expression in hippocampus and prefrontal cortex. No significant changes were observed in vehicle-infused mice which received no morphine treatment (CONC) and shRACK1-infused mice which received no morphine treatment (CONR), whereas vehicle-infused mice preceded the morphine injection (MIC) showed increased BDNF expression in hippocampus and prefrontal cortex, as compared to vehicle-infused mice which received no morphine treatment (CONC). Intracerebroventricular shRACK1 treatment reversed these, and in fact, ShRACK1-infused mice preceded the morphine injection (MIR) showed reduced BDNF expression in hippocampus and prefrontal cortex, as compared to MIC. In the conditioned place preference (CPP) test, inactivating RACK1 markedly reduces morphine-induced conditioned place preference. Non-specific changes in CPP could not account for these effects since general CPP of shRACK1- and vehicle-infused animals was not different. Combined behavioral and molecular approaches have support the possibility that the RACK1-BDNF system plays an important role in the response to morphine-induced reward.

Endocrine disrupting chemicals bind to a novel receptor, microtubule-associated protein 2, and positively and negatively regulate dendritic outgrowth in hippocampal neurons

The present study demonstrates a novel high-affinity neuronal target for endocrine disrupting chemicals (EDCs), which potentially cause psychological disorders. EDCs competitively inhibited the binding of bovine serum albumin-conjugated progesterone to recombinant human microtubule-associated protein 2C (rhMAP2C) with an inhibition constant at picomolar levels. In the rhMAP2C-stimulated tubulin assembly assay, agonistic enhancement was observed with dibutyl phthalate and pentachlorphenol and pregnenolone, while an inverse agonistic effect was observed with 4-nonylphenol. In contrast, progesterone and many of the EDCs, including bisphenol A, antagonized the pregnenolone-induced enhancement of rhMAP2C-stimulated tubulin assembly. These agonistic and inverse agonistic actions were not observed in tubulin assembly stimulated with Delta1-71 rhMAP2C, which lacks the steroid-binding site. Using a dark-field microscopy, pregnenolone and pentachlorphenol were observed to generate characteristic filamentous microtubules in a progesterone- or bisphenol A-reversible manner. In cultured hippocampal neurons, similar agonist-antagonist relationships were reproduced in terms of dendritic outgrowth. Fluorescent recovery after photobleaching of hippocampal neurons showed that pregnenolone and agonistic EDCs enhanced, but that 4-nonylphenol inhibited the MAP2-mediated neurite outgrowth in a progesterone- or antagonistic EDC-reversible manner. Furthermore, none of the examined effects were affected by mifepristone or ICI-182,786 i.e. the classical progesterone and estrogen receptor antagonists. Taken together, these results suggest that EDCs cause a wide variety of significant disturbances to dendritic outgrowth in hippocampal neurons, which may lead to psychological disorders following chronic exposure during early neuronal development.

Lysophosphatidic acid-induced membrane ruffling and brain-derived neurotrophic factor gene expression are mediated by ATP release in primary microglia

We examined the effects of lysophosphatidic acid (LPA) on microglia, which may play an important role in the development and maintenance of neuropathic pain. LPA caused membrane ruffling as detected by scanning electron microscopy, and increased the expression of brain-derived neurotrophic factor (BDNF) in a primary culture of rat microglia, which express LPA(3), but not LPA(1) or LPA(2) receptors. These actions were inhibited by a Galpha(q/11)-antisense oligodeoxynucleotide (AS-ODN), U73122, an inhibitor of phospholipase C (PLC), and apyrase, which specifically degrades ATP and ADP. When ATP release was measured using a luciferin-luciferase bioluminescence assay, LPA was shown to increase it in an LPA(3) and PLC inhibitor-reversible manner. However, LPA-induced ATP release was also blocked by the Galpha(q/11) AS-ODN, but not by pertussis toxin. These results suggest that LPA induces the release of ATP from rat primary cultured microglia via the LPA(3) receptor, Galpha(q/11) and PLC, and that the released ATP or ectopically converted ADP may in turn cause membrane ruffling via P2Y(12) receptors and Galpha(i/o) activation, and BDNF expression via activation of P2X(4) receptors.

Glutamate preconditioning prevents neuronal death induced by combined oxygen-glucose deprivation in cultured cortical neurons

The study of ischemic tolerance is critical in the development of strategies for the treatment of ischemic stroke. We used the oxygen and glucose deprivation (OGD) paradigm in cultured cortical neurons as an in vitro approach to elucidate the mechanism of protection conferred by glutamate preconditioning. Pretreatment of neurons with N-methyl-d-aspartate (NMDA) receptor antagonists prevented OGD-induced cell death whereas alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor and voltage-dependent Ca(++) channel (VDCC) blockers were without effect. Neurons preconditioned with glutamate exhibited resistant to damage induced by OGD. The ischemic tolerance depended on the duration of preconditioning exposure and the interval between preconditioning exposure and test challenge. Protective efficacy was blocked by the NMDA or AMPA receptor antagonists but not by the VDCC blocker. Furthermore, neuroprotective effect was not seen if extracellular Ca(++) was omitted or removed with EGTA. Pretreatment with staurosporin and 2-[N-(2-hydroxyethyl)]-N-(4-methoxybenzenesulfonyl)] amino-N-(4-chlorocinnamyl)-N-methylbenzylamine (KN93) but not 2-(4-Morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one (LY294002) or 1,4-diamino-2,3-dicyano-1, 4-bis[2-aminophenylthio] butadiene (U0126) significantly reduced ischemic tolerance. Preconditioning increased phosphorylated levels of cAMP responsive element binding protein (CREB) and pretreatment with CRE-decoy oligonucleotide completely blocked preconditioning-induced increase in cell viability. Importantly, glutamate preconditioning increased Bcl-2 expression that was blocked by KN93, staurosporin and CRE-decoy oligonucleotide. These results suggest that preconditioning with glutamate conferred neuroprotection against subsequent OGD by inducing p-CREB-mediated Bcl-2 expression.

Acute plasmalemma permeability and protracted clearance of injured cells after controlled cortical impact in mice

Cell death after traumatic brain injury (TBI) evolves over days to weeks. Despite advances in understanding biochemical mechanisms that contribute to posttraumatic brain cell death, the time course of cell injury, death, and removal remains incompletely characterized in experimental TBI models. In a mouse controlled cortical impact (CCI) model, plasmalemma permeability to propidium iodide (PI) was an early and persistent feature of posttraumatic cellular injury in cortex and hippocampus. In cortical and hippocampal brain regions known to be vulnerable to traumatic cell death, the number of PI+ cells peaked early after CCI, and increased with increasing injury severity in hippocampus but not cortex (P<0.05). Propidium iodide labeling correlated strongly with hematoxylin and eosin staining in injured cells (r=0.99, P<0.001), suggesting that plasmalemma damage portends fatal cellular injury. Using PI pulse labeling to identify and follow the fate of a cohort of injured cells, we found that many PI+ cells recovered plasmalemma integrity by 24 h and were terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling negative, but nonetheless disappeared from injured brain by 7 days. Propidium iodide-positive cells in dentate gyrus showed significant ultrastructural damage, including plasmalemma and nuclear membrane damage or overt membrane loss, in all cells when examined by laser capture microdissection and transmission electron microscopy 1 to 24 h after CCI. The data suggest that plasmalemma damage is a fundamental marker of cellular injury after CCI; some injured cells might have an extended window for potential rescue by neuroprotective strategies.

Insulin restores metabolic function in cultured cortical neurons subjected to oxidative stress

We previously demonstrated that insulin has a neuroprotective role against oxidative stress, a deleterious condition associated with diabetes, ischemia, and age-related neurodegenerative diseases. In this study, we investigated the effect of insulin on neuronal glucose uptake and metabolism after oxidative stress in rat primary cortical neurons. On oxidative stress, insulin stimulates neuronal glucose uptake and subsequent metabolism into pyruvate, restoring intracellular ATP and phosphocreatine. Insulin also increases intracellular and decreases extracellular adenosine, counteracting the effect of oxidative stress. Insulin effects are apparently mediated by phosphatidylinositol 3-K and extracellular signal-regulated kinase signaling pathways. Extracellular adenosine under oxidative stress is largely inhibited after blockade of ecto-5'-nucleotidase, suggesting that extracellular adenosine results preferentially from ATP release and catabolism. Moreover, insulin appears to interfere with the ATP release induced by oxidative stress, regulating extracellular adenosine levels. In conclusion, insulin neuroprotection against oxidative stress-mediated damage involves 1) stimulation of glucose uptake and metabolism, increasing energy levels and intracellular adenosine and, ultimately, uric acid formation and 2) a decrease in extracellular adenosine, which may reduce the facilitatory activity of adenosine receptors.

Neuroprotective effect of N-acetylcysteine on neuronal apoptosis induced by a synthetic gingerdione compound: Involvement of ERK and p38 phosphorylation

Besides being used as a spice, ginger has been applied in oriental medicine to ameliorate symptoms such as inflammatory, rheumatic disorders, and gastrointestinal discomforts. The effects of ginger on neuronal cells, however, have not been explored. We investigate the effect of 1-(3,4-dimethoxyphenyl)-3,5-dodecenedione (I(6)), a derivative of gingerdione, on cultured cortical neurons. After a 5-day maturation period in vitro, cortical neurons were treated with I(6) for 24 hr and cell viability was assessed using MTT assay. I(6) induced neuronal death in a concentration-dependent manner. Hoechst 33342, propidium iodide (PI), and TUNEL staining confirmed that the reduced cell viability by I(6) was due to apoptosis. Pre-treatment of cell with N-acetylcysteine (NAC) prevented cell death in a concentration-dependent manner. N-acetylcysteine increased phosphorylated levels of p42 and p44 extracellular signal-regulated kinases (ERKs). In parallel, farnesyltransferase and MEK inhibitors blocked ERK phosphorylation and neuroprotective effect of NAC. Unexpectedly, NAC also increased phosphorylated level of p38 mitogen-activated protein kinase (MAPK) and p38 specific inhibitors dose-dependently attenuated the effect of NAC. Farnesyltransferase and MEK inhibitors completely abolished NAC-induced p38 phosphorylation whereas p38 inhibitor did not influence NAC-induced ERK phosphorylation. These results show that NAC serially activates ERKs and p38 MAPK, and ERKs and p38 work together to mediate the neuroprotective effect of NAC.

Morphine-induced overexpression of prepro-nociceptin/orphanin FQ in cultured astrocytes

The effects of morphine on the gene expression of prepro-nociceptin/orphanin FQ (ppN/OFQ) in various primary cultured brain cells from embryonic day 17, rats were studied by use of real-time RT-PCR method. The basal level of ppN/OFQ mRNA in terms of ratio to the beta-actin in astrocytes was equivalent to that in neurons, but 10-times higher than that in microglia. The addition of 1 microM morphine significantly enhanced the ppN/OFQ mRNA levels in cultured astrocytes, but not neurons or microglia. The enhancement was observed as early as 1h after the addition of morphine, reached maximum at 6h. There was a concentration-dependency between 30 nM to 1 microM. The morphine-induced enhancement was abolished by naloxone, an antagonist of mu opioid peptide receptor (MOP), wortmannin, a phosphoinositide 3-kinase (PI3K) inhibitor, and PD98059, a MEK inhibitor, but not by 1,10-phenanthroline, a metalloprotease inhibitor and U73122, a phospholipase C inhibitor. These profiles contrast to the data with morphine-induced enhancement of brain-derived growth factor (BDNF) gene expression in microglia, where 1,10-phenanthroline abolished the expression. Furthermore, the ELISA analysis revealed that the immunoreactive ppN/OFQ or N/OFQ level was also increased by morphine. The present findings suggest that astrocytes could play roles in the neuronal plasticity during morphine chronic treatments by enhancing gene expression of anti-opioid peptide, N/OFQ.

Insulin neuroprotection against oxidative stress in cortical neurons--involvement of uric acid and glutathione antioxidant defenses

In this study we investigated the effect of insulin on neuronal viability and antioxidant defense mechanisms upon ascorbate/Fe2+-induced oxidative stress, using cultured cortical neurons. Insulin (0.1 and 10 microM) prevented the decrease in neuronal viability mediated by oxidative stress, decreasing both necrotic and apoptotic cell death. Moreover, insulin inhibited ascorbate/Fe2+-mediated lipid and protein oxidation, thus decreasing neuronal oxidative stress. Increased 4-hydroxynonenal (4-HNE) adducts on GLUT3 glucose transporters upon exposure to ascorbate/Fe2+ were also prevented by insulin, suggesting that this peptide can interfere with glucose metabolism. We further analyzed the influence of insulin on antioxidant defense mechanisms in the cortical neurons. Oxidative stress-induced decreases in intracellular uric acid and GSH/GSSG levels were largely prevented upon treatment with insulin. Inhibition of phosphatidylinositol-3-kinase (PI-3K) or mitogen-induced extracellular kinase (MEK) reversed the effect of insulin on uric acid and GSH/GSSG, suggesting the activation of insulin-mediated signaling pathways. Moreover, insulin stimulated glutathione reductase (GRed) and inhibited glutathione peroxidase (GPx) activities under oxidative stress conditions, further supporting that insulin neuroprotection was related to the modulation of the glutathione redox cycle. Thus, insulin may be useful in preventing oxidative stress-mediated injury that occurs in several neurodegenerative disorders.

Morphine-induced chemotaxis and brain-derived neurotrophic factor expression in microglia

The addition of morphine at 1 mum induced morphological changes of cultured microglia such that they changed from having globular or bipolar rod-like shapes to being flat and lamellipodial, with membrane ruffling at the edge, which was stained with phalloidin. The membrane ruffling was clearly colocalized with Rac. Morphine also induced chemotaxis in Boyden chamber analysis at concentrations of 1 mum or more in microglia and the microglial cell line EOC 2. All of these changes were abolishable by naloxone, antisense oligodeoxynucleotide for mu-opioid receptor (MOR), pertussis toxin (PTx), and wortmannin, but not genistein or 1,10-phenanthroline. The addition of morphine to microglia stimulated the gene expression of brain-derived neurotrophic factor (BDNF) as early as the 1 hr point, and this lasted for >12 hr. Morphine induced BDNF gene expression and ERK1/2 (extracellular signal-regulated kinase 1/2) phosphorylation, and these were abolishable by naloxone, wortmannin, PD98059, genistein, and 1,10-phenanthroline. The addition of conditioned medium derived from the culture of morphine-treated microglia also increased the phosphorylation of ERK1/2. All of these findings suggest that morphine induces significant changes in both morphology and gene expression at relatively high concentrations, but the underlying signaling pathways downstream of MOR and G(i/o) appear to be different from each other. Phosphoinositide 3-kinase gamma activation and Rac activation are involved in chemotaxis, whereas indirect pathways through ERK1/2 phosphorylation induced by unknown growth factors generated through an MOR-mediated metalloprotease activation are linked to the enhanced BDNF gene expression.

Cell death mode switch from necrosis to apoptosis in brain

In brain ischemia, cell destructive necrosis occurs in the core, which in turn links to cell death expansion in the vicinity. Apoptosis, on the other hand, occurs in the surroundings of the core, called the penumbra, several days later. As cells showing apoptosis disappear by microglial phagocytosis in the brain, cell death induced by ischemic stress should eventually be terminated. Thus, the authors propose the hypothesis that the cell death mode switch in the event of brain ischemia is an in vivo self-protective mechanism. The authors attempt to overview the current understanding of the molecular mechanisms of necrosis and apoptosis in relation to the ATP hypothesis, and also introduce novel mechanisms for an in vitro cell death mode switch.

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.

Peripheral nerve endoneurial microangiopathy and necrosis in rats with insulinoma

Peripheral nerve pathology related to chronic hyperinsulinemia and hypoglycemia has yet to be fully explored. Here we conducted a systematic quantitative analysis of morphological alterations in peripheral sensory and motor nerve fibers and endoneurial microvasculature in longstanding insulinoma-carrying rats (I-rats; n=12). Age-matched normal rats (n=6) served as controls. Over the 15-month observation period, two of I-rats developed paresis of the hind limbs when their blood glucose level fell below 1.7 mmol/l. These animals showed a massive myelinated fiber loss associated with active degeneration of residual myelinated fibers and multiple endoneurial microvascular occlusions at the sciatic nerve level. The rest of the non-paretic I-rats showed a decreased density of large myelinated fibers with axonal degeneration in the peroneal nerve and an increased density of small myelinated fibers with preserved morphology in the sural nerve. This was associated with endoneurial microangiopathic changes indicative of endoneurial ischemia/hypoxia in the sciatic and peroneal nerves, and an increase in endoneurial microvascular density in the sciatic and sural nerves. In conjunction with previous data, these findings suggest that the observed increase in endoneurial microvascular density may be a compensatory response to endoneurial ischemia/hypoxia induced by chronic hyperinsulinemia in I-rats without paresis. In conclusion, the present study showed characteristic morphological alterations in peripheral sensory and motor nerve fibers associated with microangiopathy indicative of endoneurial ischemia/hypoxia in the sciatic and peroneal nerves, and provides the first evidence for the occurrence of endoneurial necrosis in the sciatic nerve, to which the hind limb paresis can be ascribed in I-rats.

Trophic support delays but does not prevent cell-intrinsic degeneration of neurons deficient for munc18-1

The stability of neuronal networks is thought to depend on synaptic transmission which provides activity-dependent maintenance signals for both synapses and neurons. Here, we tested the relationship between presynaptic secretion and neuronal maintenance using munc18-1-null mutant mice as a model. These mutants have a specific defect in secretion from synaptic and large dense-cored vesicles [Verhage et al. (2000), Science, 287, 864-869; Voets et al. (2001), Neuron, 31, 581-591]. Neuronal networks in these mutants develop normally up to synapse formation but eventually degenerate. The proposed relationship between secretion and neuronal maintenance was tested in low-density and organotypic cultures and, in vivo, by conditional cell-specific inactivation of the munc18-1 gene. Dissociated munc18-1-deficient neurons died within 4 days in vitro (DIV). Application of trophic factors, insulin or BDNF delayed degeneration up to 7 DIV. In organotypic cultures, munc18-1-deficient neurons survived until 9 DIV. On glial feeders, these neurons survived up to 10 DIV and 14 DIV when insulin was applied. Co-culturing dissociated mutant neurons with wild-type neurons did not prolong survival beyond 4 DIV, but coculturing mutant slices with wild-type slices prolonged survival up to 19 DIV. Cell-specific deletion of munc18-1 expression in cerebellar Purkinje cells in vivo resulted in the specific loss of these neurons without affecting connected or surrounding neurons. Together, these data allow three conclusions. First, the lack of synaptic activity cannot explain the degeneration in munc18-1-null mutants. Second, trophic support delays but cannot prevent degeneration. Third, a cell-intrinsic yet unknown function of munc18-1 is essential for prolonged survival.

Inhibition of protein kinase C promotes neuronal survival in low potassium through an Akt-dependent pathway

Cerebellar granule cell neurons undergo apoptotic cell death when subjected to serum-free conditions at physiological concentrations of potassium (5 mM). Protein kinase C (PKC) is known to play a role in preventing neuronal apoptosis under trophic factor deprivation, but its role in protecting cerebellar neurons from cell death under conditions of low potassium is unknown. This study sought to determine the involvement of PKC in neuronal survival and to determine if PKC regulated the phosphatidylinositol 3-kinase (PI 3-K)/Akt pathway in low physiologic concentrations of potassium. Incubation with a pan-PKC inhibitor, Ro-31-8220 (2 microm), or a specific PKCAlpha inhibitor, Gö6976, protected cerebellar granule cell neurons from low potassium-mediated cell death. In contrast, phorbol ester (TPA, 100 nm), a PKC activator, increased cell death. Incubation with, Ro-31-8220 rescued neurons from cell death induced by the PI 3-K inhibitor, LY294002, suggesting that Ro-31-8220 may affect Akt phosphorylation. Western blot analysis showed that serum-free, low potassium conditions decreased Akt phosphorylation, which was exacerbated by treatment with LY294002. In contrast, PKC inhibitors, Gö6976 or Ro-31-8220, increased Akt phosphorylation approximately two and four-fold, respectively in low potassium conditions. Because Akt activation appears to be critical in promoting neuronal survival under these culture conditions, increased Akt phosphorylation brought about by inhibiting PKC promotes neuronal survival.