Protein Kinase C Epsilon Overexpression Is Associated With Poor Patient Outcomes in AML and Promotes Daunorubicin Resistance Through p-Glycoprotein-Mediated Drug Efflux

The protein kinase C (PKC) family of serine/threonine kinases are pleiotropic signaling regulators and are implicated in hematopoietic signaling and development. Only one isoform however, PKCϵ, has oncogenic properties in solid cancers where it is associated with poor outcomes. Here we show that PKCϵ protein is significantly overexpressed in acute myeloid leukemia (AML; 37% of patients). In addition, PKCϵ expression in AML was associated with a significant reduction in complete remission induction and disease-free survival. Examination of the functional consequences of PKCϵ overexpression in normal human hematopoiesis, showed that PKCϵ promotes myeloid differentiation, particularly of the monocytic lineage, and decreased colony formation, suggesting that PKCϵ does not act as an oncogene in hematopoietic cells. Rather, in AML cell lines, PKCϵ overexpression selectively conferred resistance to the chemotherapeutic agent, daunorubicin, by reducing intracellular concentrations of this agent. Mechanistic analysis showed that PKCϵ promoted the expression of the efflux pump, P-GP (ABCB1), and that drug efflux mediated by this transporter fully accounted for the daunorubicin resistance associated with PKCϵ overexpression. Analysis of AML patient samples also showed a link between PKCϵ and P-GP protein expression suggesting that PKCϵ expression drives treatment resistance in AML by upregulating P-GP expression.

Endoplasmic Reticulum Stress Induces CAP2 Expression Promoting Epithelial-Mesenchymal Transition in Liver Cancer Cells

Cyclase-associated protein 2 (CAP2) has been addressed as a candidate biomarker in various cancer types. Previously, we have shown that CAP2 is expressed during multi-step hepatocarcinogenesis; however, its underlying mechanisms in liver cancer cells are not fully elucidated yet. Here, we demonstrated that endoplasmic reticulum (ER) stress induced CAP2 expression, and which promoted migration and invasion of liver cancer cells. We also found that the ER stress-induced CAP2 expression is mediated through activation of protein kinase C epsilon (PKCε) and the promotor binding of activating transcription factor 2 (ATF2). In addition, we further demonstrated that CAP2 expression promoted epithelial-mesenchymal transition (EMT) through activation of Rac1 and ERK. In conclusion, we suggest that ER stress induces CAP2 expression promoting EMT in liver cancers cells. Our results shed light on the novel functions of CAP2 in the metastatic process of liver cancer cells.

TRIM47 activates NF-κB signaling via PKC-ε/PKD3 stabilization and contributes to endocrine therapy resistance in breast cancer

Increasing attention has been paid to roles of tripartite motif-containing (TRIM) family proteins in cancer biology, often functioning as E3 ubiquitin ligases. In the present study, we focus on a contribution of TRIM47 to breast cancer biology, particularly to endocrine therapy resistance, which is a major clinical problem in breast cancer treatment. We performed immunohistochemical analysis of TRIM47 protein expression in 116 clinical samples of breast cancer patients with postoperative endocrine therapy using tamoxifen. Our clinicopathological study showed that higher immunoreactivity scores of TRIM47 were significantly associated with higher relapse rate of breast cancer patients (P = 0.012). As functional analyses, we manipulated TRIM47 expression in estrogen receptor-positive breast cancer cells MCF-7 and its 4-hydroxytamoxifen (OHT)-resistant derivative OHTR, which was established in a long-term culture with OHT. TRIM47 promoted both MCF-7 and OHTR cell proliferation. MCF-7 cells acquired tamoxifen resistance by overexpressing exogenous TRIM47. We found that TRIM47 enhances nuclear factor kappa-B (NF-κB) signaling, which further up-regulates TRIM47. We showed that protein kinase C epsilon (PKC-ε) and protein kinase D3 (PKD3), known as NF-κB-activating protein kinases, are directly associated with TRIM47 and stabilized in the presence of TRIM47. As an underlying mechanism, we showed TRIM47-dependent lysine 27-linked polyubiquitination of PKC-ε. These results indicate that TRIM47 facilitates breast cancer proliferation and endocrine therapy resistance by forming a ternary complex with PKC-ε and PKD3. TRIM47 and its associated kinases can be a potential diagnostic and therapeutic target for breast cancer refractory to endocrine therapy.

Electroacupuncture Regulates Pain Transition Through Inhibiting PKCε and TRPV1 Expression in Dorsal Root Ganglion

Many cases of acute pain can be resolved with few side effects. However, some cases of acute pain may persist beyond the time required for tissue injury recovery and transit to chronic pain, which is hard to treat. The mechanisms underlying pain transition are not entirely understood, and treatment strategies are lacking. In this study, the hyperalgesic priming model was established on rats to study pain transition by injection of carrageenan (Car) and prostaglandin E2 (PGE2). The expression levels of protein kinase C epsilon (PKCε) and transient receptor potential vanilloid 1 (TRPV1) in the L4–L6 dorsal root ganglion (DRG) were investigated. Electroacupuncture (EA) is a form of acupuncture in which a small electric current is passed between a pair of acupuncture needles. EA was administrated, and its effect on hyperalgesia and PKCε and TRPV1 expression was investigated. The PKCε–TRPV1 signaling pathway in DRG was implicated in the pain transition. EA increased the pain threshold of model animals and regulated the high expression of PKCε and TRPV1. Moreover, EA also regulated hyperalgesia and high TRPV1 expression induced by selective PKCε activation. We also found that EA partly increased chronic pain threshold, even though it was only administered between the Car and PGE2 injections. These findings suggested that EA could prevent the transition from acute to chronic pain by inhibiting the PKCε and TRPV1 expression in the peripheral nervous system.

Role of GABAAR in the Transition From Acute to Chronic Pain and the Analgesic Effect of Electroacupuncture on Hyperalgesic Priming Model Rats

Chronic pain is a costly health problem that impairs health-related quality of life when not effectively treated. Regulating the transition from acute to chronic pain is a new therapeutic strategy for chronic pain that presents a major clinical challenge. The underlying mechanisms of pain transition are not entirely understood, and strategies for preventing this transition are lacking. Here, a hyperalgesic priming model was used to study the potential mechanism by which γ-aminobutyric acid receptor type A (GABAAR) in the dorsal root ganglion (DRG) contributes to pain transition. Furthermore, electroacupuncture (EA), a modern method of acupuncture, was administered to regulate pain transition, and the mechanism underlying EA’s regulatory effect was investigated. Hyperalgesic priming was induced by intraplanar injection of carrageenan (Car)/prostaglandin E₂ (PGE₂). The decrease in mechanical withdrawal threshold (MWT) induced by PGE₂ returned to baseline 4 h after injection in NS + PGE₂ group, and still persisted 24 h after injection in Car + PGE₂ group. Lower expression of GABAAR in the lumbar DRG was observed in the model rats. Furthermore, activating or blocking GABAAR could reversed the long-lasting hyperalgesia induced by Car/PGE₂ injection or produced a persistent hyperalgesia. In addition, GABAAR may be involved in Protein Kinase C epsilon (PKCε) activation in the DRG, a mark molecular of pain transition. EA considerably increased the mechanical pain thresholds of hyperalgesic priming model mammals in both the acute and chronic phases. Furthermore, EA upregulated the expression of GABAAR and inhibited the activation of PKCε in the DRG. In addition, peripheral administration of picrotoxin blocked the analgesic effect of EA on the model rats and abolished the regulatory effect of EA on PKCε activation. These findings suggested that GABAAR plays a key role in both the transition from acute to chronic pain and the analgesic effect of EA on hyperalgesic priming.

Bidirectional sex-dependent regulation of α6 and β3 nicotinic acetylcholine receptors by protein kinase Cε

Nicotine and alcohol are the most commonly abused substances worldwide and are frequently coabused. Nicotinic acetylcholine receptors (nAChRs) containing the α6 and β3 subunits are expressed in neural reward circuits and are critical for nicotine and alcohol reward. nAChRs are dynamically regulated by signaling molecules such as protein kinase C epsilon (PKCε), which impact transcription of α6 and β3 subunit mRNA (Chrna6 and Chrnb3, respectively). Previous work found decreased expression of Chrna6 and Chrnb3 transcripts in the ventral midbrain of male PKCε^-/- mice, who also consume less nicotine and alcohol compared with wild-type (WT) littermates. Using RT-qPCR, we show that female PKCε^-/- mice have higher expression of Chrna6 and Chrnb3 transcripts in the ventral midbrain, which functionally impacts nAChR-dependent behavior as female but not male PKCε^-/- mice exhibit locomotor hypersensitivity to low-dose (0.25 mg/kg i.p.) nicotine. Female PKCε^-/- mice show no differences in alcohol-induced sedation in the loss-of-righting reflex assay (4.0 g/kg i.p.) compared with WT littermates, whereas male PKCε^-/- mice have enhanced sedation compared with WT mice. Female PKCε^-/- mice also show reduced immobility time in response to varenicline (1.0 mg/kg i.p.) compared with WT littermates in the tail suspension test, and this effect was absent in male mice. Additionally, we found that female PKCε^-/- mice show altered alcohol and nicotine consumption patterns in chronic voluntary two-bottle choice assays. Our data reveal a bidirectional effect of sex in the transcriptional regulation of nicotinic receptors by PKCε, highlighting the importance of studying both sexes in preclinical animal models.

Deconstructing the Role of PKC Epsilon in Glucose Homeostasis

The failure of insulin to suppress glucose production by the liver is a key aspect of the insulin resistance seen in type 2 diabetes. Lipid-activated protein kinase C epsilon has long been identified as an important mediator of diet-induced glucose intolerance and hepatic insulin resistance and the current view emphasizes a mechanism involving phosphorylation of the insulin receptor by the kinase to inhibit downstream insulin action. However, the significance of this direct effect in the liver has now been challenged by tissue-specific deletion of PKCε, which demonstrated a more prominent role for the kinase in adipose tissue to promote glucose intolerance. New insights regarding the role of PKCε therefore contribute to the understanding of indirect effects on hepatic glucose metabolism.

The central role of protein kinase C epsilon in cyanide cardiotoxicity and its treatment

In adult mouse myocytes, brief exposure to sodium cyanide (CN) in the presence of glucose does not decrease ATP levels, yet produces profound reduction in contractility, intracellular Ca2+ concentration ([Ca2+]i) transient and L-type Ca2+ current (ICa) amplitudes. We analyzed proteomes from myocytes exposed to CN, focusing on ionic currents associated with excitation-contraction coupling. CN induced phosphorylation of α1c subunit of L-type Ca2+ channel and α2 subunit of Na+-K+-ATPase. Methylene blue (MB), a CN antidote that we previously reported to ameliorate CN-induced reduction in contraction, [Ca2+]i transient and ICa amplitudes, was able to reverse this phosphorylation. CN decreased Na+-K+-ATPase current contributed by α2 but not α1 subunit, an effect that was also counteracted by MB. Peptide consensus sequences suggested CN-induced phosphorylation was mediated by protein kinase C epsilon (PKCε). Indeed, CN stimulated PKC kinase activity and induced PKCε membrane translocation, effects that were prevented by MB. Pre-treatment with myristoylated PKCε translocation activator or inhibitor peptides mimicked and inhibited the effects of CN on ICa and myocyte contraction, respectively. We conclude that CN activates PKCε, which phosphorylates L-type Ca2+ channel and Na+-K+-ATPase, resulting in depressed cardiac contractility. We hypothesize that this inhibition of ion fluxes represents a novel mechanism by which the cardiomyocyte reduces its ATP demand (decreased ion fluxes and contractility), diminishes ATP turnover and preserves cell viability. However, this cellular protective effect translates into life-threatening cardiogenic shock in vivo, thereby creating a profound disconnect between survival mechanisms at the cardiomyocyte level from those at the level of the whole organism.

Activating transcription factor 3 modulates protein kinase C epsilon activation in diabetic peripheral neuropathy

Background

Skin denervation that develops in patients with diabetes mellitus as a neuropathic manifestation is known as diabetic peripheral neuropathy (DPN). Skin denervation is parallel to neuronal injuries that alter intracellular signaling. To date, the correlation between nerve injury and the activation of intracellular responses to neuropathic manifestations has not been elucidated; specifically, whether activating transcription factor 3 (ATF3) is responsible for neuronal injury and a critical molecule that modulates the activation of intracellular protein kinase C epsilon (p-PKCε) and pain development in DPN is a crucial question.

Methods

To address, ATF3 knockout (atf3^−/− group, C57/B6 genetic background) and wild-type mice (atf3^+/+ group) received a single dose of streptozotocin (200 mg/kg) to generate a mouse model of DPN.

Results

Both atf3^+/+ and atf3^−/− mice exhibited hyperglycemia and the same pathology of skin denervation at posttreatment month 2, but only atf3^+/+ mice developed thermal hyperalgesia (P<0.001) and mechanical allodynia (P=0.002). The atf3^+/+ group, but not the atf3^−/− group, had preferential ATF3 upregulation on p-PKCε(+) neurons with a ratio of 37.7%±6.1% in p-PKCε(+):ATF3(+) neurons (P<0.001). In addition, B-cell lymphoma-extra large (Bcl-_XL), an antiapoptotic Bcl2 family protein, exhibited parallel patterns to p-PKCε (ie, Bcl-_XL upregulation was reversed in atf3^−/− mice). These two molecules were colocalized and increased by approximately two-fold in the atf3^+/+ group compared with the atf3^−/− group (30.0%±3.4% vs 13.7% ± 6.2%, P=0.003). Furthermore, linear analysis results showed that the densities of p-PKCε and Bcl-_XL had a reverse linear relationship with the degrees of thermal hyperalgesia and mechanical allodynia.

Conclusion

Collectively, this report suggested that ATF3 is a critical upstream molecule that modulates p-PKCε and Bcl-_XL expression, which consequently mediated the development of neuropathic manifestation in DPN.

Atorvastatin Attenuates Myocardial Hypertrophy Induced by Chronic Intermittent Hypoxia In Vitro Partly through miR-31/PKCε Pathway

Atorvastatin is proven to ameliorate cardiac hypertrophy induced by chronic intermittent hypoxia (CIH). However, little is known about the mechanism by which atorvastatin modulates CIH-induced cardiac hypertrophy, and whether specific hypertrophyrelated microRNAs are involved in the modulation. MiR-31 plays key roles in the development of cardiac hypertrophy induced by ischemia/hypoxia. This study examined whether miR-31 was involved in the protective role of atorvastatin against CIH-induced myocardial hypertrophy. H9c2 cells were subjected to 8-h intermittent hypoxia per day in the presence or absence of atorvastatin for 5 days. The size of cardiomyocytes, and the expression of caspase 3 and miR-31 were determined by Western blotting and RT-PCR, respectively. MiR-31 mimic or Ro 31-8220, a specific inhibitor of protein kinase C epsilon (PKCε), was used to determine the role of miR-31 in the anti-hypertrophic effect of atorvastatin on cardiomyocytes. PKCε in the cardiomyocytes with miR-31 upregulation or downregulation was detected using RT-PCR and Western blotting. The results showed that CIH induced obvious enlargement of cardiomyocytes, which was paralleled with increased atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and slow/beta cardiac myosin heavy-chain (MYH7) mRNA levels. All these changes were reversed by the treatment with atorvastatin. Meanwhile, miR-31 was increased by CIH in vitro. Of note, the atorvastatin pretreatment significantly increased the mRNA and protein expression of PKCe and decreased that of miR-31. Moreover, overexpression of miR-31 abolished the anti-hypertrophic effect of atorvastatin on cardiomyocytes. Upregulation and downregulation of miR-31 respectively decreased and increased the mRNA and protein expression of PKCε. These results suggest that atorvastatin provides the cardioprotective effects against CIH probably via up-regulating PKCε and down-regulating miR-31.

Metabolomics Based Identification of SIRT5 and Protein Kinase C Epsilon Regulated Pathways in Brain

The role of Sirtuins in brain function is emerging, yet little is known about SIRT5 in this domain. Our previous work demonstrates that protein kinase C epsilon (PKCε)-induced protection from focal ischemia is lost in SIRT5-/- mice. Thus, metabolic regulation by SIRT5 contributes significantly to ischemic tolerance. The aim of this study was to identify the SIRT5-regulated metabolic pathways in the brain and determine which of those pathways are linked to PKCε. Our results show SIRT5 is primarily expressed in neurons and endothelial cells in the brain, with mitochondrial and extra-mitochondrial localization. Pathway and enrichment analysis of non-targeted primary metabolite profiles from Sirt5-/- cortex revealed alterations in several pathways including purine metabolism (urea, adenosine, adenine, xanthine), nitrogen metabolism (glutamic acid, glycine), and malate-aspartate shuttle (malic acid, glutamic acid). Additionally, perturbations in β-oxidation and carnitine transferase (pentadecanoic acid, heptadecanoic acid) and glutamate transport and glutamine synthetase (urea, xylitol, adenine, adenosine, glycine, glutamic acid) were predicted. Metabolite changes in SIRT5-/- coincided with alterations in expression of amino acid (SLC7A5, SLC7A7) and glutamate (EAAT2) transport proteins as well as key enzymes in purine (PRPS1, PPAT), fatty acid (ACADS, HADHB), glutamine-glutamate (GAD1, GLUD1), and malate-aspartate shuttle (MDH1) metabolic pathways. Moreover, PKCε activation induced alternations in purine metabolites (urea, glutamine) that overlapped with putative SIRT5 pathways in WT but not in SIRT5-/- mice. Finally, we found that purine metabolism is a common metabolic pathway regulated by SIRT5, PKCε and ischemic preconditioning. These results implicate Sirt5 in the regulation of pathways central to brain metabolism, with links to ischemic tolerance.

Roles of Diacylglycerols and Ceramides in Hepatic Insulin Resistance

Although ample evidence links hepatic lipid accumulation with hepatic insulin resistance, the mechanistic basis of this association is incompletely understood and controversial. Diacylglycerols (DAGs) and ceramides have emerged as the two best-studied putative mediators of lipid-induced hepatic insulin resistance. Both lipids were first associated with insulin resistance in skeletal muscle and were subsequently hypothesized to mediate insulin resistance in the liver. However, the putative roles for DAGs and ceramides in hepatic insulin resistance have proved more complex than originally imagined, with various genetic and pharmacologic manipulations yielding a vast and occasionally contradictory trove of data to sort. In this review we examine the state of this field, turning a critical eye toward both DAGs and ceramides as putative mediators of lipid-induced hepatic insulin resistance.

Deletion of the aquaporin-4 gene alters expression and phosphorylation of protective kinases in the mouse heart

AIM

Aquaporins are channel-forming proteins highly permeable to water and some small molecular solutes. We have previously shown that aquaporin-4 knockout mice have increased tolerance to ischemia. However, the mechanism of cardioprotection was unclear. The aim of the current study was to investigate the effects of aquaporin-4 deletion on baseline expression and phosphorylation of some cardioprotective protein kinases.

METHODS

Proteins were extracted from hearts of aquaporin-4 knockout mice and littermate wild-type controls and analyzed with Western blot. Samples were taken from young (≤ 6 months of age), and old (≥ 1 year) mice.

RESULTS

Western blots showed three different isoforms of aquaporin-4 in wild types, likely representing M1, M23, and Mz. Total AMP-dependent kinase expression was decreased in aquaporin-4 knockout hearts by 18 ± 13% (p = 0.02), while the expression of Akt kinase, extracellular signal regulated kinase 1/2, protein kinase C-epsilon, mitogen-associated kinase P38 and C-Jun N-terminal kinase was unchanged. The phosphorylation of Akt kinase was reduced in hearts from knockout mice by 41 ± 16% (p = 0.01). No other alterations in phosphorylation were found. These effects were only detected in young mice.

CONCLUSION

Deletion of the aquaporin-4 gene decreased AMP-dependent kinase expression and Akt kinase phosphorylation in the heart. These changes may influence energy metabolism and endogenous cardioprotection.

Peripheral systems: neuropathy

Long-term, excessive consumption of alcoholic beverages produces a peripheral neuropathy with symptoms of decreased superficial sensation, hyperalgesia, and weakness. Alcoholic neuropathy is characterized by axonal degeneration with reduced density of both small and large fibers and axonal sprouting. Electrophysiologic studies reveal a marked reduction in the amplitude of sensory potentials and moderate slowing of nerve conduction, mainly in the lower extremities. Dietary deficiency of vitamins, which are often associated with chronic alcoholism, can contribute to the pathogenesis. Recent studies using animal models have identified several mechanisms by which ethanol impacts peripheral nerve function. Ethanol can exert direct neurotoxic effects on peripheral nerves via its metabolite acetaldehyde and by enhancing oxidative stress. Ethanol activation of protein kinase Cε signaling in primary afferent nociceptors plays an important role in lowering nociceptive threshold. Further, ethanol causes cytoskeletal dysfunction and inhibits both anterograde and retrograde axonal transport. Alcoholic neuropathy is potentially reversible and treatments include abstinence from alcoholic beverages and consumption of a nutritionally balanced diet supplemented with B vitamins. However, response to these treatment strategies can be variable, which underscores the need for novel therapeutic strategies. In this review, we provide an overview of the clinical findings and insights on molecular mechanisms from animal models.

High-dose erythropoietin during cardiac resuscitation lessens postresuscitation myocardial stunning in swine

We investigated the metabolic and functional myocardial effects of erythropoietin (EPO) administered during resuscitation from cardiac arrest using an open-chest pig model of ventricular fibrillation and resuscitation by extracorporeal circulation, after having reported in rats a reversal of postresuscitation myocardial dysfunction associated with activation of mitochondrial protective pathways. Ventricular fibrillation was induced in 16 male domestic pigs and left untreated for 8 minutes, after which extracorporeal circulation was started and maintained for 10 additional minutes, adjusting the extracorporeal flow to provide a coronary perfusion pressure of 10 mmHg. Defibrillation was accomplished and the extracorporeal flow was adjusted to secure a mean aortic pressure of 40 mmHg or greater during spontaneous circulation for up to 120 minutes. Pigs were randomized 1:1 to receive EPO (1200 U/kg) or 0.9% NaCl before starting extracorporeal circulation. Severe postresuscitation myocardial dysfunction developed in both groups. However, recovery of myocardial function-comparing baseline with 120 minutes postresuscitation-was better in pigs treated with EPO than NaCl, as shown for left ventricular ejection fraction (from 45 ± 8% to 36 ± 9% in EPO, not significant; and from 46 ± 8% to 26 ± 8% in NaCl, P < 0.001) and for peak systolic pressure/end-systolic volume (from 2.7 ± 0.8 mmHg/mL to 2.4 ± 0.7 mmHg/mL in EPO, not significant; and from 3.0 ± 1.1 mmHg/mL to 1.8 ± 0.6 mmHg/mL, P < 0.001 in NaCl). The EPO effect was associated with significantly higher myocardial O2 consumption (12 ± 6 mL/min/unit of tissue vs 6 ± 2 mL/min/unit of tissue, P < 0.017) without effects on myocardial lactate consumption. Thus, EPO administered during resuscitation from ventricular fibrillation lessened postresuscitation myocardial stunning-an effect that could be useful clinically to help promote postresuscitation hemodynamic stability.

Ectopic lipid accumulation: A potential cause for metabolic disturbances and a contributor to the alteration of kidney function

Ectopic lipid accumulation is now known to be a mechanism that contributes to organ injury in the context of metabolic diseases. In muscle and liver, accumulation of lipids impairs insulin signaling. This hypothesis accounts for the mechanism of insulin resistance in obesity, type 2 diabetes, aging and lipodystrophy. Increasing data suggest that lipid accumulation in the kidneys could also contribute to the alteration of kidney function in the context of metabolic syndrome and obesity. Furthermore and more unexpectedly, animal models of kidney disease exhibit a decreased adiposity and ectopic lipid redistribution suggesting that kidney disease may be a state of lipodystrophy. However, whether this abnormal lipid partitioning during chronic kidney disease (CKD) may have any functional impact in these tissues needs to be investigated. Here, we provide a perspective by defining the problem and analyzing the possible causes and consequences. Further human studies are required to strengthen these observations, and provide novel therapeutic approaches.

Activation of STAT3 is involved in neuroprotection by electroacupuncture pretreatment via cannabinoid CB1 receptors in rats

Pretreatment with electroacupuncture (EA) attenuates cerebral ischemic injury through the endocannabinoid system, although the molecular mechanisms mediate this neuroprotection are unknown. It is well-known that signal transducer and activator of transcription 3 (STAT3) plays an essential role in cell survival and proliferation. Therefore, we investigated whether STAT3 is involved in EA pretreatment-induced neuroprotection via cannabinoid CB1 receptors (CB1R) after transient focal cerebral ischemia in rats. Two hours after EA pretreatment, focal cerebral ischemia was induced by middle cerebral artery occlusion (MACO) for 120 min. The expression of pSTAT3(Ser727), which is necessary for STAT3 activation, was examined in the ipsilateral ischemic penumbra. Infarct volumes and neurological scores were evaluated at 72 h after MACO in the presence or absence of the STAT3 inhibitor peptide (PpYLKTK). Neuronal apoptosis and the Bax/Bcl-2 ratio were also evaluated 24h after reperfusion. Our results showed that EA pretreatment significantly enhanced neuronal expression of pSTAT3(Ser727) in the ischemic penumbra 6h after reperfusion. Moreover, EA pretreatment reduced infarct volume, improved neurological outcome, inhibited neuronal apoptosis and decreased the Bax/Bcl-2 ratio following reperfusion. The beneficial effects of EA were attenuated by PpYLKTK administered 30 min before MACO, and PpYLKTK effectively reversed the increase in pSTAT3(Ser727) expression. Furthermore, CB1R antagonist or CB1R knockdown with siRNA blocked the elevation of pSTAT3(Ser727) expression by EA pretreatment, whereas the two CB1R agonists increased STAT3 activation. In conclusion, EA pretreatment enhances STAT3 activation via CB1R to protect against cerebral ischemia, suggesting that STAT3 activation may be a novel target for stroke intervention.