Ischemic Postconditioning Mediates Cardioprotection Via PI3K/GSK-3β/β-Catenin Signaling Pathway in Ischemic Rat Myocardium

Soluble Epoxide Hydrolase Inhibitors Regulate Ischemic Arrhythmia by Targeting MicroRNA-1

Background: Soluble epoxide hydrolase inhibitors (sEHis) inhibit the degradation of epoxyeicosatrienoic acids (EETs) in cells, and EETs have antiarrhythmic effects. Our previous experiments confirmed that t-AUCB, a preparation of sEHis, inhibited ischemic arrhythmia by negatively regulating microRNA-1 (miR-1), but its specific mechanism remained unclear. Aim: This study aimed to examine the role of serum response factor (SRF) and the PI3K/Akt/GSK3β pathway in t-AUCB-mediated regulation of miR-1 and the interaction between them. Methods/Results: We used SRF small interfering RNA (siSRF), SRF small hairpin (shSRF) RNA sequence adenovirus, PI3K/Akt/GSK3β pathway inhibitors, t-AUCB, and 14,15-EEZE (a preparation of EETs antagonists) to treat mouse cardiomyocytes overexpressing miR-1 and mice with myocardial infarction (MI). We found that silencing SRF attenuated the effects on miR-1 and its target genes KCNJ2 and GJA1 in the presence of t-AUCB, and inhibition of the PI3K/Akt/GSK3β pathway antagonized the effects of t-AUCB on miR-1, KCNJ2, and GJA1, which were associated with PI3Kα, Akt, and Gsk3β but not PI3Kβ or PI3Kγ. Moreover, the PI3K/Akt/GSK3β pathway was involved in the regulation of SRF by t-AUCB, and silencing SRF inhibited the t-AUCB-induced increases in Akt and Gsk3β phosphorylation. Conclusions: Both the SRF and the PI3K/Akt/GSK3β pathway are involved in the t-AUCB-mediated regulation of miR-1, and these factors interact with each other.

Differential expression of miR-142-3p protects cardiomyocytes from myocardial ischemia-reperfusion via TLR4/NFkB axis

Our research aims to explore the impact of miR-142 on myocardial apoptosis in the mouse ischemia and reperfusion (IR) model and investigate the underlying mechanisms at the molecular level. A considerable downregulation of miR-142 was observed in the cardiac area of mice post IR modeling. To understand the regulatory function of IR-induced miR-142 downregulation, the animals were categorized into four groups: IR model group; IR + agomir-142 group (IR mice treated with agomir-142); IR + antagomir-142 group (IR mice treated with antagomir-142); IR + agomir-142 + negative control (NC) group (IR mice processed with agomir-NC). The results indicated that agomir-142 upregulation was capable of shrinking IR damage-triggered infarction of the ventriculus sinister, strengthening myocardial function, and guarding against cardiomyocyte apoptosis, whereas further decreased miR-142 with antagomir-142 infection displayed negative influence of miR-142 against mice IR damage. In the cellular assay, miR-142 overexpression significantly improved proliferation and inhibited the apoptosis of neonatal rat cardiomyocytes (NRCs). Moreover, we found that miR-142 reduced the Bcl-2/Bax ratio and upregulated hydrogen peroxide (H₂ O₂ )-induced caspase-3 expression. Furthermore, transfection with an miR-142 mimic prevented the upregulation of TLR4/NFkB expression and activation in H₂ O₂ -treated NRCs. Our findings also revealed that miR-142 is linked to the 3'-untranslated area of the TLR4 gene. In addition, TLR4 overexpression considerably ablated the protective effects of miR-142 in terms of the cell viability of H₂ O₂ -treated NRCs. Taken together, miR-142 agomir injection in mice and miR-142 mimic transfection in NRCs plays a role in protecting the heart from IR damage and malfunction via the TLR4/NFkB axis both in vivo and in vitro.

Resveratrol protects against apoptosis induced by interleukin-1β in nucleus pulposus cells via activating mTOR/caspase-3 and GSK-3β/caspase-3 pathways

Objective: The purpose of the present study was to investigate the specific downstream signaling pathway mediated by PI3K/Akt in resveratrol (RES) anti-apoptosis of nucleus pulposus cells (NPCs).

Materials and methods: Human NPCs were cultured and divided into six groups. Interleukin (IL)-1β was used to induce apoptosis and RES to inhibit apoptosis. Fluorescence-activated cell sorting (FACS) analysis was used to test apoptotic incidence of NPCs, cell counting kit-8 (CCK-8) assay was performed to detect cell viability, The expression level of caspase-3 mRNA was detected by RT-qPCR, and protein levels were determined by Western blot.

Results: Flow cytometry analysis showed that IL-1β increased the apoptosis rate of NPCs in each group, and RES significantly decreased the apoptosis rate, while rapamycin (RAPA) and SB216763 inhibited the effect of RES and increased the apoptosis rate again. Similarly, CCK-8 showed that IL-1β decreased activity of NPCs in each group, while RES increased cell activity, RAPA and SB216763 inhibited the effect of RES and decreased cell activity. RT-qPCR results showed IL-1β significantly increased the level of caspase-3 expression, but it was significantly decreased by using RES, RAPA and SB216763 respectively attenuated effects of RES. Western blot results showed that activated caspase-3 was inhibited by RES effect, and was up-regulated again after the addition of RAPA and SB216763. In addition, p-mTOR and p-GSK-3β were up-regulated by RES and down-regulated by RAPA and SB216763.

Conclusion: RES can inhibit apoptosis induced by IL-1β in human NPCs. PI3K/Akt/mTOR/caspase-3 and PI3K/Akt/GSK-3β/caspase-3 pathways are potential mechanisms underlying this process.

Regulation of the cerebrovascular smooth muscle cell phenotype by mitochondrial oxidative injury and endoplasmic reticulum stress in simulated microgravity rats via the PERK-eIF2α-ATF4-CHOP pathway

Microgravity exposure results in vascular remodeling and cardiovascular dysfunction. Here, the effects of mitochondrial oxidative stress on vascular smooth muscle cells (VSMCs) in rat cerebral arteries under microgravity simulated by hindlimb unweighting (HU) was studied. Endoplasmic reticulum (ER)-resident transmembrane sensor proteins and phenotypic markers of rat cerebral VSMCs were examined. In HU rats, CHOP expression was increased gradually, and the upregulation of the PERK-eIF2α-ATF4 pathway was the most pronounced in cerebral arteries. Furthermore, PERK/p-PERK signaling, CHOP, GRP78 and reactive oxygen species were augmented by PERK overexpression but attenuated by the mitochondria-targeting antioxidant MitoTEMPO. Meanwhile, p-PI3K, p-Akt and p-mTOR protein levels in VSMCs were increased in HU rat cerebral arteries. Compared with the control, HU rats exhibited lower α-SMA, calponin, SM-MHC and caldesmon protein levels but higher OPN and elastin levels in cerebral VSMCs. The cerebral VSMC phenotype transition from a contractile to synthetic phenotype in HU rats was augmented by PERK overexpression and 740Y-P but reversed by MitoTEMPO and the ER stress inhibitors tauroursodeoxycholic acid (TUDCA) and 4-phenylbutyric acid (4-PBA). In summary, mitochondrial oxidative stress and ER stress induced by simulated microgravity contribute to phenotype transition of cerebral VSMCs through the PERK-eIF2a-ATF4-CHOP pathway in a rat model.

Tumour suppressor candidate 3 inhibits biological function and increases endoplasmic reticulum stress of melanoma cells WM451 by regulating AKT/GSK3-β/β-catenin pathway

Melanoma is a highly malignant and is a life-threatening disease with no effective treatment currently. This study aims to evaluate the significance of TUSC3, an endoplasmic reticulum stress (ERS)-inducible gene and explore its relationship with AKT/GSK3-β/β-catenin signalling pathway in melanoma cell WM451. We investigated TUSC3 expression in melanoma cell by qRT-PCR, CCK-8 and clonal formation assays were utilized to evaluate cell proliferation. Wound healing and transwell experiments detected cell migration and invasion. Flow cytometry detected the level of apoptosis. Western blot analysed MMP2, MMP9, p-AKT, p-GSK3-β, β-catenin and AKT, GSK3-β, ERS-related proteins and apoptosis-related proteins in WM451 cells. The results revealed that TUSC3 was remarkably decreased in melanoma cell lines. Overexpression of TUSC3 significantly inhibits melanoma cell WM451 biological functions and promotes expression of ERS-related proteins in WM451 cells, increases ERS in WM451 cells by inhibiting AKT/GSK3-β/β-catenin pathway. These finding suggest that TUSC3 regulates biological functions of melanoma cells WM451 and increases ERS in melanoma cells WM451 via the inhibition of the AKT/GSK3-β/β-catenin signalling pathway. SIGNIFICANCE OF THE STUDY: Melanoma is a highly malignant and is a life-threatening disease with no effective treatment currently. Therefore, studying the molecular mechanism of melanoma occurrence and metastasis is essential for the treatment of melanoma. Meanwhile, mounting studies suggest that TUSC3 is considered to be closely associated with the development of various malignancies. TUSC3 regulates proliferation, migration and epithelial-to-mesenchymal transition, but the molecular mechanism of the tumour suppressor effects of TUSC3 on melanoma cells is not well understood. Our study demonstrates that TUSC3 inhibits biological function of melanoma cells and increases ERS in melanoma cells by inhibiting AKT/GSK3-β/β-catenin pathway. And this is expected to be a new target and method for the treatment of melanoma.

Application quantitative proteomics approach to identify differentially expressed proteins associated with cardiac protection mediated by cycloastragenol in acute myocardial infarction rats

Acute myocardial infarction (AMI) is an acute heart disease. Cycloastragenol, as a natural product, inhibits inflammation and protects cardiomyocytes. Cycloastragenol (Y006) modulates inflammation in AMI is not known. To explore the function of Cycloastragenol in AMI, this study investigated the effect of Y006 and its mechanisms both in vitro and in vivo. Y006 influences the concentration of 11 proteins, as shown by a proteomics analysis, immunohistochemistry and western blotting. Among these 11 proteins, Erk1/2, PLCG1, IKBKG, and ZEB1 are related to inflammatory regulation. BAX, COX2, and GSK3β are involved in modulating cardiomyocyte apoptosis, and RhoA and DSC2 are directly associated with myocardial function. However, the functions of ARHGAP17 and Rit2 in heart are less well established. Additionally, Y006 suppressed TNF-α, IFN-γ and IL-17 production in PBMCs (peripheral blood monocytes) from patients with acute myocardial infarction and enhanced IL-10 and IL-4 expression. Similar results were obtained in a rat model of AMI by flow cytometry detection and ELISA. Our findings indicate that Y006 protects rats from AMI through direct or indirect inhibition of inflammation and cardiomyocyte apoptosis. However, the specific mechanism of Y006's protective function requires further study. Nonetheless, this research revealed a novel aspect for the treatment of myocardial infarction. SIGNIFICANCE: In the present study, we undertook the first proteomic evaluation of Cycloastragenol (Y006) function in acute myocardial infarction (AMI). Y006 significantly improved myocardial function in vivo by regulating multiple molecular expressions. Hypoxia is a direct reason for AMI. And our data support a role of Y006 in gene expression, cell apoptosis under hypoxia. The conclusions of this research assist to explain the potential molecular mechanism in Cycloastragenol treating AMI and supply a new method for ameliorating AMI.

GSK-3β inhibition confers cardioprotection associated with the restoration of mitochondrial function and suppression of endoplasmic reticulum stress in sevoflurane preconditioned rats following ischemia/reperfusion injury

Background:

Sevoflurane has been shown to protect against myocardial ischemia/reperfusion (I/R) injury in animals, while its cardioprotection is lost if the ischemic insult is too long. In this study, we proposed a prevailing hypothesis that GSK-3β inhibitor-mediated activation of GSK-3β/β-catenin signaling pathway provides additional cardioprotection in sevoflurane preconditioned rats following I/R injury.

Methods:

Rats were subjected to treatment with TDZD-8, a GSK-3β inhibitor, 5 minutes prior to sevoflurane preconditioning and 30-minute ischemia and 120-minute reperfusion. Furthermore, in order to find out whether this cardioprotection is linked with mitochondrial function and endoplasmic reticulum stress (ERS), we isolated mitochondria from rat hearts perfused with TDZD-8 and determined the alternations of ERS markers.

Results:

Sevoflurane preconditioning or GSK-3β inhibitor treatment prevented cardiomyocyte apoptosis, phosphorylated GSK-3β and accelerated total β-catenin expression levels, reduced mitochondrial permeability transition pore (MPTP) activity, promoted the recovery of mitochondrial membrane potential and decreased the expression levels of GRP78, caspase-12 and C/EBP homology protein (CHOP) in rats under I/R condition, suggesting sevoflurane preconditioning or TDZD-8 activate the GSK-3β/β-catenin signaling pathway, improve mitochondria function and suppress ERS occurrence.

Conclusions:

Taken together, the findings obtained from the study support the concept that sevoflurane preconditioning confers cardioprotection against myocardial I/R injury and GSK-3β/β-catenin signaling activation mediated by TDZD-8 as a novel target to prolong cardioprotection by sevoflurane anaesthesia.

Effects of Dexmedetomidine Postconditioning on Myocardial Ischemia/Reperfusion Injury in Diabetic Rats: Role of the PI3K/Akt-Dependent Signaling Pathway

OBJECTIVE

The present study was designed to determine whether dexmedetomidine (DEX) exerts cardioprotection against myocardial I/R injury in diabetic hearts and the mechanisms involved.

METHODS

A total of 30 diabetic rats induced by high-glucose-fat diet and streptozotocin (STZ) were randomly assigned to five groups: diabetic sham-operated group (DM-S), diabetic I/R group (DM-I/R), diabetic DEX group (DM-D), diabetic DEX + Wort group (DM-DW), and diabetic Wort group (DM-W). Another 12 age-matched male normal SD rats were randomly divided into two groups: sham-operated group (S) and I/R group (I/R). All rats were subjected to 30 min myocardial ischemia followed by 120 min reperfusion except sham groups. Plasmas were collected to measure the malondialdehyde (MDA), creatine kinase isoenzymes (CK-MB), and lactate dehydrogenase (LDH) levels and superoxide dismutase (SOD) activity at the end of reperfusion. Pathologic changes in myocardial tissues were observed by H-E staining. The total and phosphorylated form of Akt and GSK-3β protein expressions were measured by western blot. The ratio of Bcl-2/Bax at mRNA level was detected by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

DEX significantly reduced plasma CK-MB, MDA concentration, and LDH level and increased SOD activity caused by I/R. The phosphorylation of Akt and GSK-3β was increased, Bcl-2 mRNA and the Bcl-2/Bax ratio was increased, and Bax mRNA was decreased in the DEX group as compared to the I/R group, while posttreatment with Wort attenuated the effects induced by DEX.

CONCLUSION

The results of this study suggest that DEX postconditioning may increase the phosphorylation of GSK-3β by activating the PI3K/Akt signaling pathway and may inhibit apoptosis and oxidative stress of the myocardium, thus exerting protective effects in diabetic rat hearts suffering from I/R injury.

Myocardial ischemic post-conditioning protects the lung against myocardial ischemia/reperfusion-induced damage by activating GSK-3β

Purpose:

To investigate whether modulating GSK-3β could attenuate myocardial ischemia reperfusion injury (MIRI) induced acute lung injury (ALI) and analyze the underlying mechanism.

Methods:

Male SD rats were subjected to MIRI with or without myocardial ischemic post-conditioning in the presence or absence of GSK-3β inhibitor. GSK-3β inhibitor was injected peritoneally 10min before MIRI. Lung W/D weight ratio, MPO, PMNs, histopathological changes, TUNEL, Bax, Bcl-2, IL-6, IL-8, IL-10, GSK-3β, and caspase-3 were evaluated in the lung tissues of all rats.

Results:

After MIRI, lung injury was significantly increased manifested as significant morphological changes and increased leukocytes in the interstitial capillaries, Lung W/D ratio, MPO, and PMN in BALF, which was associated with enhanced inflammation evidenced by increased expressions of IL-6, IL-8 and reduced expression of IL-10. MIRI significantly increased cell apoptosis in the lung as increased levels of apoptotosis, Bax, cleaved caspase-3, and reduced expression of Bcl-2 was observed, which was concomitant with reduced p-GSK-3β. All these changes were reversed/prevented by ischemic post-conditioning, while these beneficial effects of ischemic post-conditioning were abolished by GSK-3β inhibition.

Conclusion:

Myocardial ischemia reperfusion injury induces acute lung injury by induction of inflammation and cell apoptosis. Ischemic post-conditioning protects the lung from ALI following MIRI by increasing p-GSK-3β.

Glucose variability aggravates cardiac fibrosis by altering AKT signalling path

OBJECTIVE

To study the effect of blood glucose variability on cardiac fibrosis and its mechanism in a model of diabetic cardiomyopathy.

METHODS

A total of 45 Sprague Dawley rats were randomly divided into three groups: control, control diabetes mellitus and fluctuated blood glucose groups. Fluctuated blood glucose was induced by daily subcutaneous insulin and intraperitoneal glucose injections at different time points. Blood lipids and glycosylated haemoglobin A1c were assessed. Super oxide dismutase activity and malondialdehyde level in rat heart homogenates were determined by assay kit. Structural cardiac tissue changes were observed by haematoxylin and eosin staining and Masson's trichrome staining. Collagen type 3, fibronectin, phosphorylated Ser/Thr protein kinase, phosphorylated glycogen synthase kinase-3 beta, glycogen synthase kinase-3 beta, nuclear factor kappa-light-chain-enhancer of activated B cells, cleaved-cysteinyl aspartate-specific proteinase-3 (caspase-3) and tumour necrosis factor-α levels were determined by western blot.

RESULTS

Compared with the control group, cardiac fibrosis and oxidative stress in heart tissue were aggravated in diabetic rats, which were more pronounced in glucose variability rats. However, the expression levels of AKT and glycogen synthase kinase-3 beta were not significantly different in three groups, but the expression levels of phosphorylated Ser/Thr protein kinase and phosphorylated glycogen synthase kinase-3 beta were significantly decreased in the control diabetes mellitus and fluctuated blood glucose groups compared to control group, and levels in the fluctuated blood glucose group were significantly less than in the control diabetes mellitus group. In addition, the expression levels of nuclear factor kappa B and caspase-3 in both the control diabetes mellitus and fluctuated blood glucose groups were higher than in the control group, with the highest levels measured in the fluctuated blood glucose group.

CONCLUSION

Blood glucose variability can aggravate heart tissue fibrosis, possibly involving oxidative stress by inhibiting AKT signalling path.

Inhibition of Endoplasmic Reticulum Stress Apoptosis by Estrogen Protects Human Umbilical Vein Endothelial Cells Through the PI3 Kinase-Akt Signaling Pathway

We aimed to investigate whether the cardioprotective effect of estrogen is mediated by inhibiting the apoptosis induced by endoplasmic reticulum stress (ERS) and to explore the underlying signaling pathway responsible for this effect. The effect of estrogen on ERS apoptosis, the mechanism responsible for that effect, and the ERS signaling pathways were examined in human umbilical vein endothelial cells (HUVECs) and measured using Western blot, Hoechst stains and caspase-3 activity assay. In vitro, 10^-8 mol/l estrogen directly inhibited the up-regulation of the ERS marker glucose-regulated protein 78 (GRP78) and ERS apoptosis marker C/EBP homologous protein (CHOP). ERS was induced using the ERS inducer tunicamycin (TM, 10 µmol/l) or dithiothreitol (DTT, 2 mmol/l) in HUVECs. Estrogen can also decrease the apoptosis cells mediated by ERS, based on the results of Hoechst stains. Protein expression in the three main ERS signaling pathways was upregulated in TM- or DTT-induced HUVEC ERS. Increases in p-PERK/PERK were the most obvious, and estrogen significantly inhibited the upregulation of p-PERK/PERK, p-IRE1/IRE1, and ATF6. These inhibitory effects were abolished by specific estrogen receptor antagonists (ICI182, 780, and G15) and inhibitors of the E₂ post-receptor signaling pathway, including phosphoinositide 3-kinase (PI3K) inhibitor LY294002, p38-mitogen activated protein kinase (p38-MAPK) inhibitor SB203580, c-Jun N-terminal kinase (JNK) inhibitor SP600125 and extracellular signal-regulated kinases1/2 (ERK1/2) inhibitor U0126; of these inhibitors, LY294002 was the most effective. Further experiments showed that when the PI3K pathway was blocked, the inhibitory effect of estrogen on ERS apoptosis was reduced. Estrogen can prevent HUVEC apoptosis by inhibiting the ERS apoptosis triggered by the PERK pathway, which may protect vascular endothelial cells and the cardiovascular system. The main mechanism responsible for ERS inhibition is the activation of the PI3K-Akt pathway for the activated estrogen receptor. J. Cell. Biochem. 118: 4568-4574, 2017. © 2017 Wiley Periodicals, Inc.

The role of glycogen synthase kinase 3 beta in brain injury induced by myocardial ischemia/reperfusion injury in a rat model of diabetes mellitus

Myocardial ischemia/reperfusion injury can lead to severe brain injury. Glycogen synthase kinase 3 beta is known to be involved in myo-cardial ischemia/reperfusion injury and diabetes mellitus. However, the precise role of glycogen synthase kinase 3 beta in myocardial ischemia/reperfusion injury-induced brain injury is unclear. In this study, we observed the effects of glycogen synthase kinase 3 beta on brain injury induced by myocardial ischemia/reperfusion injury in diabetic rats. Rat models of diabetes mellitus were generated via intraperitoneal injection of streptozotocin. Models of myocardial ischemia/reperfusion injury were generated by occluding the anterior descending branch of the left coronary artery. Post-conditioning comprised three cycles of ischemia/reperfusion. Immunohistochemical staining and western blot assays demonstrated that after 48 hours of reperfusion, the structure of the brain was seriously damaged in the experimental rats compared with normal controls. Expression of Bax, interleukin-6, interleukin-8, terminal deoxynucleotidyl transferase dUTP nick end labeling, and cleaved caspase-3 in the brain was significantly increased, while expression of Bcl-2, interleukin-10, and phospho-glycogen synthase kinase 3 beta was decreased. Diabetes mellitus can aggravate inflammatory reactions and apoptosis. Ischemic post-conditioning with glycogen synthase kinase 3 beta inhibitor lithium chloride can effectively reverse these changes. Our results showed that myocardial ischemic post-conditioning attenuated myocardial ischemia/reperfusion injury-induced brain injury by activating glyco-gen synthase kinase 3 beta. According to these results, glycogen synthase kinase 3 beta appears to be an important factor in brain injury induced by myocardial ischemia/reperfusion injury.

Pressure Combined with Ischemia/Reperfusion Injury Induces Deep Tissue Injury via Endoplasmic Reticulum Stress in a Rat Pressure Ulcer Model

Pressure ulcer is a complex and significant health problem in long-term bedridden patients, and there is currently no effective treatment or efficient prevention method. Furthermore, the molecular mechanisms and pathogenesis contributing to the deep injury of pressure ulcers are unclear. The aim of the study was to explore the role of endoplasmic reticulum (ER) stress and Akt/GSK3β signaling in pressure ulcers. A model of pressure-induced deep tissue injury in adult Sprague-Dawley rats was established. Rats were treated with 2-h compression and subsequent 0.5-h release for various cycles. After recovery, the tissue in the compressed regions was collected for further analysis. The compressed muscle tissues showed clear cellular degenerative features. First, the expression levels of ER stress proteins GRP78, CHOP, and caspase-12 were generally increased compared to those in the control. Phosphorylated Akt and phosphorylated GSK3β were upregulated in the beginning of muscle compression, and immediately significantly decreased at the initiation of ischemia-reperfusion injury in compressed muscles tissue. These data show that ER stress may be involved in the underlying mechanisms of cell degeneration after pressure ulcers and that the Akt/GSK3β signal pathway may play an important role in deep tissue injury induced by pressure and ischemia/reperfusion.

Long-term insulin treatment restores cardioprotection induced by sufentanil postconditioning in diabetic rat heart

Sufentanil, a commonly used opioid analgesic, could mimic ischemia postconditioning to attenuate ischemia reperfusion injury, but this effect might be hindered in diabetic animals by inhibition of glycogen synthase kinase-3β phosphorylation. Also, diabetes can abrogate the cardioprotection of sevoflurane (an inhaled anesthetic) against ischemia reperfusion injury, and short-term insulin treatment does not restore protection by sevoflurane postconditioning. We hypothesized that long-term insulin treatment might restore the cardioprotective effect of sufentanil postconditioning in diabetic rats via phosphorylation of glycogen synthase kinase-3β. Streptozotocin (55 mg/kg)-induced diabetic rats received insulin (Novolin N, 6-8 u/d) for two days or two weeks, then were exposed to 30-min ischemia and 120-min reperfusion. Sufentanil postconditioning was performed 5 min before the onset of reperfusion. Controls included non-diabetic rats, sham surgery for ischemia/reperfusion, and sufentanil vehicle. Infarct size, cardiac troponin I, and phosphorylated glycogen synthase kinase-3β were examined. Sufentanil postconditioning reduced infarct size by 46% in non-diabetic rats (P < 0.001), but diabetes prevented this protective effect. Two-day insulin treatment was not effective, but two-week treatment reduced infarct size by 45% (P < 0.001), reduced cardiac troponin I by 33% (P < 0.001), and increased phosphorylated glycogen synthase kinase-3β levels (P < 0.001) in the diabetic sufentanil postconditioning group. In conclusion, sufentanil-induced cardioprotection was restored by long-term insulin treatment. The underlying mechanism may be increased phosphorylation of glycogen synthase kinase-3β.

GLP1 protects cardiomyocytes from palmitate-induced apoptosis via Akt/GSK3b/b-catenin pathway

Activation of apoptosis in cardiomyocytes by saturated palmitic acids contributes to cardiac dysfunction in diabetic cardiomyopathy. Beta-catenin (b-catenin) is a transcriptional regulator of several genes involved in survival/anti-apoptosis. However, its role in palmitate-induced cardiomyocyte apoptosis remains unclear. Glucagon-like peptide 1 (GLP1) has been shown to exhibit potential cardioprotective properties. This study was designed to evaluate the role of b-catenin signalling in palmitate-induced cardiomyocyte apoptosis and the molecular mechanism underlying the protective effects of GLP1 on palmitate-stressed cardiomyocytes. Exposure of neonatal rat cardiomyocytes to palmitate increased the fatty acid transporter CD36-mediated intracellular lipid accumulation and cardiomyocyte apoptosis, decreased accumulation and nuclear translocation of active b-catenin, and reduced expression of b-catenin target protein survivin and BCL2. These detrimental effects of palmitate were significantly attenuated by GLP1 co-treatment. However, the anti-apoptotic effects of GLP1 were markedly abolished when b-catenin was silenced with a specific short hairpin RNA. Furthermore, analysis of the upstream molecules and mechanisms responsible for GLP1-associated cardiac protection revealed that GLP1 restored the decreased phosphorylation of protein kinase B (Akt) and glycogen synthase kinase-3b (GSK3b) in palmitate-stimulated cardiomyocytes. In contrast, inhibition of Akt with an Akt-specific inhibitor MK2206 or blockade of GLP1 receptor (GLP1R) with a competitive antagonist exendin-(9-39) significantly abrogated the GLP1-mediated activation of GSK3b/b-catenin signalling, leading to increased apoptosis in palmitate-stressed cardiomyocytes. Collectively, our results demonstrated for the first time that the attenuated b-catenin signalling may contribute to palmitate-induced cardiomyocyte apoptosis, while GLP1 can protect cardiomyocytes from palmitate-induced apoptosis through activation of GLP1R/Akt/GSK3b-mediated b-catenin signalling.

Cardioprotective Signature of Short-Term Caloric Restriction

Objective

To understand the molecular pathways underlying the cardiac preconditioning effect of short-term caloric restriction (CR).

Background

Lifelong CR has been suggested to reduce the incidence of cardiovascular disease through a variety of mechanisms. However, prolonged adherence to a CR life-style is difficult. Here we reveal the pathways that are modulated by short-term CR, which are associated with protection of the mouse heart from ischemia.

Methods

Male 10-12 wk old C57bl/6 mice were randomly assigned to an ad libitum (AL) diet with free access to regular chow, or CR, receiving 30% less food for 7 days (d), prior to myocardial infarction (MI) via permanent coronary ligation. At d8, the left ventricles (LV) of AL and CR mice were collected for Western blot, mRNA and microRNA (miR) analyses to identify cardioprotective gene expression signatures. In separate groups, infarct size, cardiac hemodynamics and protein abundance of caspase 3 was measured at d2 post-MI.

Results

This short-term model of CR was associated with cardio-protection, as evidenced by decreased infarct size (18.5±2.4% vs. 26.6±1.7%, N=10/group; P=0.01). mRNA and miR profiles pre-MI (N=5/group) identified genes modulated by short-term CR to be associated with circadian clock, oxidative stress, immune function, apoptosis, metabolism, angiogenesis, cytoskeleton and extracellular matrix (ECM). Western blots pre-MI revealed CR-associated increases in phosphorylated Akt and GSK3ß, reduced levels of phosphorylated AMPK and mitochondrial related proteins PGC-1α, cytochrome C and cyclooxygenase (COX) IV, with no differences in the levels of phosphorylated eNOS or MAPK (ERK1/2; p38). CR regimen was also associated with reduced protein abundance of cleaved caspase 3 in the infarcted heart and improved cardiac function.

Ventricular hypertrophy abrogates intralipid-induced cardioprotection by alteration of reperfusion injury salvage kinase/glycogen synthase kinase 3β signal

Recent studies have demonstrated that intralipid (ILP) conferred myocardial protection against ischemia-reperfusion (IR) injury through activation of reperfusion injury salvage kinase (RISK) pathway. As RISK signal has been shown to be impaired in hypertrophied myocardium, we investigated whether ILP-induced cardiac protection was maintained in hypertrophied rat hearts. Transverse aortic constriction was performed on male Sprague-Dawley rats to induce left ventricular hypertrophy, then sham-operated or hypertrophied rat hearts were isolated and perfused retrogradely by the Langendorff for 30 min (equilibration) followed by 40 min of ischemia and then 120 min of reperfusion. The isolated hearts received 15-min episode of 1% ILP separated by 15 min of washout or three episodes of 5-min ischemia followed by 5-min reperfusion before ischemia. The hemodynamics, infarct size, apoptosis, phosphorylated protein kinase B (p-Akt), phosphorylated extracellular regulated protein kinase 1/2 (ERK1/2), phosphorylated glycogen synthase kinase 3β (GSK3β), Bcl-2, phosphorylated Bad, and Bax were determined. We found that ILP significantly improved left ventricular hemodynamics and reduced infarct size and the number of TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling)-positive cells in the sham-operated rat hearts exposed to IR. However, such myocardial infarct-sparing effect of ILP was completely blocked by phosphatidylinositol-3-kinase inhibitor wortmannin, but only partially by mitogen-activated protein kinase kinase inhibitor PD98059 in sham-operated hearts. Intralipd upregulated the phosphorylation of Akt, extracellular regulated protein kinase 1/2 (ERK1/2), and their downstream target of GSK3β and antiapoptotic Bcl-2 expression in healthy rat hearts. Nonetheless, ILP failed to improve left ventricular hemodynamics and reduced infarct size and apoptosis and increase the phosphorylated Akt, ERK1/2, GSK3β, and antiapoptotic Bcl-2 in hypertrophied myocardium. In contrast, ischemic preconditioning increased the phosphorylation of Akt, ERK1/2 and GSK3β, improved heart pump function, and reduced myocardial necrosis in sham-operated hearts, a phenomenon partially attenuated by ventricular hypertrophy. Interestingly, GSK inhibitor SB216763 conferred cardioprotection against IR injury in sham-operated hearts, but failed to exert cardioprotection in hypertrophied myocardium. Our results indicated that ventricular hypertrophy abrogated ILP-induced cardioprotection against IR injury by alteration of RISK/GSK3β signal.

A small molecule activator of AKT does not reduce ischemic injury of the rat heart

Background

Activation of protein kinase AKT is required for cardioprotection by ischemic preconditioning, and transgenic overexpression of AKT protects the heart against ischemia. However, it is unknown whether acute pharmacological activation of AKT alone, using a therapeutically relevant strategy, induces cardioprotection. In this study we provide the first evidence to clarify this question.

Methods

We used a recently described specific activator of AKT, the small molecule SC79, to treat rat hearts submitted to ischemia and reperfusion. Initially, isolated rat hearts were perfused with increasing doses of SC79 to verify the magnitude of AKT activation. Low and high doses were determined and used to treat hearts submitted to ischemia (35 minutes) and reperfusion (60 minutes), in a randomized and blinded design. AKT activation was verified by western immunobloting. Metabolic profile was determined by cardiac ATP content and mitochondrial enzyme activity, while cytosolic levels of cytochrome C and caspase-3 activity were used as markers of apoptosis. Ischemic injury was assessed by quantification of infarct size and cardiac release of creatine kinase and lactate dehydrogenase.

Results

SC79 activated cardiac AKT within 30 minutes in a dose-dependent fashion. ATP content was largely reduced by ischemia, but was not rescued by SC79. Similarly, mitochondrial enzyme activity was not affected by SC79. SC79 administered before ischemia or at reperfusion did not prevent cytosolic accumulation of cytochrome C and overactivation of caspase-3. Finally, SC79 failed to reduce infarct size or release of cardiac injury biomarkers at reperfusion.

Conclusion

We conclude that selective AKT activation by the synthetic molecule SC79 does not protect the rat heart against ischemic injury, indicating that acute pharmacological activation of AKT is not sufficient for cardioprotection.

Anaesthetic Postconditioning at the Initiation of CPR Improves Myocardial and Mitochondrial Function in a Pig Model of Prolonged Untreated Ventricular Fibrillation

BACKGROUND

Anaesthetic postconditioning (APoC) attenuates myocardial injury following coronary ischaemia/reperfusion. We hypothesised that APoC at the initiation of cardiopulmonary resuscitation (CPR) will improve post resuscitation myocardial function along with improved mitochondrial function in a pig model of prolonged untreated ventricular fibrillation.

METHODS

In 32 pigs isoflurane anaesthesia was discontinued prior to induction of ventricular fibrillation that was left untreated for 15 min. At the initiation of CPR, 15 animals were randomised to controls (CON), and 17 to APoC with 2 vol% sevoflurane during the first 3 min CPR. Pigs were defibrillated after 4 min of CPR. After return of spontaneous circulation (ROSC), isoflurane was restarted at 0.8-1.5 vol% in both groups. Systolic and diastolic blood pressures were measured continuously. Of the animals that achieved ROSC, eight CON and eight APoC animals were randomised to have their left ventricular ejection fraction (LVEF%) assessed by echocardiography at 4h. Seven CON and nine APoC were randomised to euthanasia 15 min after ROSC to isolate mitochondria from the left ventricle for bioenergetic studies.

RESULTS

ROSC was achieved in 10/15 CON and 15/17 APoC animals. APoC improved haemodynamics during CPR and post-CPR LVEF%. Mitochondrial ATP synthesis, coupling of oxidative phosphorylation and calcium retention capacity were improved in cardiac mitochondria isolated after APoC.

CONCLUSIONS

In a porcine model of prolonged untreated cardiac arrest, APoC with inhaled sevoflurane at the initiation of CPR, is associated with preserved mitochondrial function and improved post resuscitation myocardial dysfunction. Approved by the Institutional Animal Care Committee of the Minneapolis Medical Research Foundation of Hennepin County Medical Center (protocol number 11-05).

Blood pressure-targeted stepwise resuscitation for hemorrhagic shock in rats

BACKGROUND

Generation of reactive oxygen species (ROS) is an important mechanism of ischemia-reperfusion injury. Abrupt reoxygenation compared with slow reoxygenation has been known to increase ROS generation. Thus, slow and stepwise reperfusion can reduce ROS generation and subsequent ischemia-reperfusion injury. This study investigated the effect of slow reperfusion by blood pressure-targeted stepwise resuscitation (PSR) in hemorrhagic shock.

METHODS

Pressure-controlled hemorrhagic shock was induced in male Sprague-Dawley rats for 1 hour. Rats were then allocated to one of three groups (no-resuscitation group, n = 14; PSR group, n = 15; rapid normalization of blood pressure (RR) group, n = 15). Survival time and hemodynamic changes were recorded and compared. Blood samples and liver tissue were harvested after 6 hours of resuscitation in surviving rats.

RESULTS

All of the rats in the no-resuscitation group were expired before the end of the 6-hour observation period. Survival times were significantly longer in the PSR group than in the RR group (survival rates, 11 of 15 vs. 5 of 15, log rank p = 0.032). Plasma amino alanine transferase, histologic liver injury, and ROS generation in the liver tissue were significantly lower in the PSR group than in the RR group (all findings significant, p < 0.05). In addition, PSR significantly decreased plasma nitric oxide, liver interleukin 1β, and liver interleukin 6 compared with rapid resuscitation in addition to augmenting Akt survival pathways (all p < 0.05).

CONCLUSION

Slow reperfusion by PSR decreased mortality, ROS generation, and liver injury in rats undergoing hemorrhagic shock. Stepwise resuscitation also decreased inflammatory cytokine production and augmented Akt survival pathways.

Up-regulation of hypoxia-inducible factor-1α enhanced the cardioprotective effects of ischemic postconditioning in hyperlipidemic rats

Hyperlipidemia is an independent risk factor in the development of ischemic heart disease, which can increase myocardial susceptibility to ischemia/reperfusion (I/R) injury. Ischemic postconditioning (PostC) has now been demonstrated as a novel strategy to harness nature's protection against myocardial I/R injury in normal conditions. However, the effect of PostC on hyperlipidemic animals remains elusive. It has been shown in our previous study that PostC reduces the myocardial I/R injury, and hypoxia-inducible factor-1α (HIF-1α) may play an important role in the cardioprotective mechanisms of PostC on normal rats. Here, we tested the hypothesis that the cardioprotection of PostC on hyperlipidemic rats is associated with the up-regulated HIF-1α expression. Male Wistar rats were fed with a high-fat diet for 8 weeks, and then randomly divided into five groups: sham, I/R, dimethyloxalylglycine (DMOG) + I/R, PostC, and DMOG + PostC group. The detrimental indices induced by I/R injury included infarct size, plasma creatine kinase (CK) activity and caspase-3 activity. The results showed that PostC could reduce the infarct size, when compared with the I/R group, which was consistent with the significant lower levels of plasma CK activity and caspase-3 activity, and that it increased the expression of HIF-1α in hyperlipidemic rats. When DMOG was given before PostC to up-regulate HIF-1α protein level, the degree of I/R injury was attenuated. In conclusion, these data suggested that the up-regulation of HIF-1α may be one of the cardioprotective mechanisms of PostC against I/R injury in hyperlipidemic rats.

Ischemic postconditioning-mediated miRNA-21 protects against cardiac ischemia/reperfusion injury via PTEN/Akt pathway

Background

Ischemic postconditioning (IPost) protects the reperfused heart from infarction which has drawn much attention recently. However, studies to date have rarely investigated the role of microRNAs (miRNAs) in IPost. The aims of this study were to investigate whether miR-21 is involved in the protective effect of IPost against myocardial ischemia-reperfusion (I/R) injury and disclose the potential molecular mechanisms involved.

Methods and Results

We found that miR-21 was remarkably up-regulated in mouse hearts after IPost. To determine the protective role of IPost-induced miR-21 up-regulation, the mice were divided into the following four groups: I/R group; I/R+IPost group (I/R mice treated with IPost); Antagomir-21+IPost+I/R group (I/R mice treated with anagomir-21 and IPost); Scramble+IPost+I/R group (I/R mice treated with scramble and IPost). The results showed IPost could reduce I/R injury-induced infarct size of the left ventricle, improve cardiac function, and prevent myocardial apoptosis, while knockdown of miR-21 with antagomir-21 could reverse these protective effects of IPost against mouse I/R injury. Furthermore, we confirmed that miR-21 plays a protective role in myocardial apoptosis through PTEN/Akt signaling pathway, which was abrogated by the PI3K inhibitor LY294002. The protective effect of miR-21 on myocardial apoptosis was further revealed in mouse hearts after IPost treatment in vivo.

Conclusions

Our data clearly demonstrate that miR-21 is involved in IPost-mediated cardiac protection against I/R injury and dysfunction through the PTEN/Akt signaling pathway in vivo. Identifying the beneficial roles of IPost-regulated miRNAs in cardiac protection, which may be a rational target selection for ischemic cardioprotection.

miR-145 inhibits isoproterenol-induced cardiomyocyte hypertrophy by targeting the expression and localization of GATA6

Excessive βAR stimulation is an independent factor in inducing pathological cardiac hypertrophy. Here, we report miR-145 regulates both expression and localization of GATA6, thereby protecting the heart against cardiomyocyte hypertrophy induced by isoproterenol (ISO). The protective activity of miR-145 was associated with down-regulation of ANF, BNP and β-MHC expression, a decreased rate of protein synthesis, inhibited cardiomyocyte growth and the modulation of several signaling pathways including ERK1/2, JNK and Akt-GSK3β. The anti-hypertrophic effect was abrogated by exogenous over-expression of transcription factor GATA6 which was further identified as a direct target of miR-145. In addition, GSK3β antagonists, LiCl and TDZD8, restored the nuclear accumulation of GATA6, which was attenuated by miR-145 Finally, we observed a dynamic pattern of miR-145 expression in ISO-treated NRCMs and in the hearts of TAC mice. Together, our results identify miR-145 as an important regulator in cardiac hypertrophy.