Mi Liu

Panax Quinquefolium Saponin Attenuates Cardiomyocyte Apoptosis and Opening of the Mitochondrial Permeability Transition Pore in a Rat Model of Ischemia/ Reperfusion

Aims: Opening of the mitochondrial permeability transition pore (mPTP) is a critical event during ischemia/reperfusion (I/R) injury. Recently, we showed that Panax quinquefolium saponin (PQS) alleviates apoptosis of cardiomyocytes by suppressing excessive endoplasmic reticulum stress (ERS) during I/R injury. Here, we hypothesized that this anti-apoptotic effect might be mediated through inhibition of mPTP and the mitochondrial apoptotic pathway. Methods: Ninety-six healthy male Sprague-Dawley rats were randomly divided into sham, I/R, I/R+PQS (200 mg/kg/d), Cyclosporine A (CsA, 10 mg/kg), I/R+CsA (10 mg/kg), and I/R+PQS+CsA. I/R was modeled in rats by ligating the left anterior descending artery (LAD) for 30 min followed by 120 min of reperfusion. To evaluate the cardioprotective function of PQS, we measured hemodynamics, serum content of creatine kinase-MB (CK-MB), myocardial infarct size, and myocardial apoptotic index (AI). We investigated the underlying mechanism by examining changes in the mitochondrial ultrastructure and membrane potential (ΔΨm), dynamics of mPTP opening, expression of cleaved caspase-3, cleaved caspase-9 in the myocardium, Bcl-2 and Bax in the mitochondria versus cytosol, and translocation of cytochrome c. Results: Administration of PQS to I/R rats significantly reduced serum CK-MB level, infarct size and AI. In addition, PQS protected the mitochondrial structure, markedly inhibited mPTP opening and ΔΨm depolarization, led to upregulation of Bcl-2 and downregulation of Bax in the mitochondria compared to the cytosol, and suppressed the expression of cleaved caspase-9 and cleaved caspase-3, as well as I/R induced translocation of cytochrome c to the cytoplasm. Conclusion: Our results show that PQS can alleviate apoptosis of cardiomyocytes during I/R injury, possibly due to repressed mitochondrial apoptotic pathway associated with the opening of mPTP induced by myocardial I/R injury.

Panax quinquefolium saponin attenuates ventricular remodeling after acute myocardial infarction by inhibiting chop-mediated apoptosis.

ABSTRACT Panax quinquefolium saponin (PQS) alleviates hypoxia-reoxygenation injury of cardiomyocytes in vitro by inhibiting excessive endoplasmic reticulum stress (ERS)–related apoptosis. We hypothesized that inhibition of excessive ERS-related apoptosis contributes to cardioprotection in ventricular remodeling after acute myocardial infarction (AMI). Sprague-Dawley rats subjected to AMI were randomly treated with water, PQS (50 mg/kg per day, 100 mg/kg per day, or 200 mg/kg per day), or taurine (300 mg/kg per day), an ERS inhibitor, for 4 weeks. Left ventricular (LV) fractional shortening, ejection fraction, and structure were then evaluated using echocardiography. Myocardial infarct size was measured by Evans blue and 2,3,5-triphenyhetrazolium chloride staining. The hydroxyproline level was assayed using the colorimetric method. Cardiomyocyte apoptosis was detected using terminal deoxynucleotidyl transferase–mediated dUTP biotin nick end labeling. In addition, expression of ERS molecules in the noninfarcted myocardium was detected using Western blotting. We found that PQS treatment significantly reduced infarct size and LV dilation and improved LV ejection fraction and fractional shortening in rat hearts. Panax quinquefolium saponin treatment also decreased hydroxyproline level in noninfarcted myocardium. Panax quinquefolium saponin treatment significantly decreased expression of glucose regulating protein 78, calreticulin, C/EBP homologous protein (CHOP), and Bax protein, as well as increased Bcl-2 protein expression in noninfarcted myocardium. Panax quinquefolium saponin treatment (200 mg/kg per day) mimicked the results achieved from the taurine-treated rats. Expression of CHOP positively correlated with the apoptosis index of cardiomyocytes in the noninfarcted myocardium (r = 0.797, P < 0.01). Taken together, PQS treatment significantly improves AMI-induced LV remodeling, and this may be attributed to inhibiting CHOP-mediated ERS-related apoptosis.

Panax quinquefolium saponin attenuates cardiomyocyte apoptosis induced by thapsigargin through inhibition of endoplasmic reticulum stress

Background Endoplasmic reticulum (ER) stress-related apoptosis is involved in the pathophysiology of many cardiovascular diseases, and Panax quinquefolium saponin (PQS) is able to inhibit excessive ER stress-related apoptosis of cardiomyocytes following hypoxia/reoxygenation and myocardial infarction. However, the pathway by which PQS inhibits the ER stress-related apoptosis is not well understood. To further investigate the protective effect of PQS against ER stress-related apoptosis, primary cultured cardiomyocytes were stimulated with thapsigargin (TG), which is widely used to model cellular ER stress, and it could induce apoptotic cell death in sufficient concentration. Methods Primary cultured cardiomyocytes from neonatal rats were exposed to TG (1 µmol/L) treatment for 24 h, following PQS pre-treatment (160 µg/mL) for 24 h or pre-treatment with small interfering RNA directed against protein kinase-like endoplasmic reticulum kinase (Si-PERK) for 6 h. The viability and apoptosis rate of cardiomyocytes were detected by cell counting kit-8 and flow cytometry respectively. ER stress-related protein expression, such as glucose-regulated protein 78 (GRP78), calreticulin, PERK, eukaryotic translation initiation factor 2α (eIF2α), activating transcription factor 4 (ATF4), and C/EBP homologous protein (CHOP) were assayed by western blotting. Results Both PQS pre-treatment and PERK knockdown remarkably inhibited the cardiomyocyte apoptosis induced by TG, increased cell viability, decreased phosphorylation of both PERK and eIF2α, and decreased protein levels of both ATF4 and CHOP. There was no statistically significant difference between PQS pre-treatment and PERK knockdown in the cardioprotective effect. Conclusions Our data indicate that the PERK-eIF2α-ATF4-CHOP pathway of ER stress is involved in the apoptosis induced by TG, and PQS might prevent TG-induced cardiomyocyte apoptosis through a mechanism involving the suppression of this pathway. These findings provide novel data regarding the molecular mechanisms by which PQS inhibits cardiomyocyte apoptosis.

Kidney protection against ischemia/reperfusion injury by myofibrillogenesis regulator-1.

Background/Aims: Ischemia/reperfusion (I/R) injury is characterized by cytoskeletal reorganization and loss of polarity in proximal tubule epithelial cells. Previously, we showed that myofibrillogenesis regulator (MR)-1 promoted actin organization in cardiomyocytes. MR-1 is also expressed in the kidney. Methods: In this study, we investigated MR-1 expression in acute renal failure induced by I/R in Sprague-Dawley rats. We determined the MR-1 expression and the ratio of fibrous actin (F-actin) to globular actin (G-actin). HK-2 cells were treated with or without hypoxia/reoxygenation (H/R), and MR-1 levels were increased by adenoviral overexpression or silenced by RNA interference. Results: I/R and H/R resulted in cellular injury and decreases of MR-1, the F-/G-actin ratio, and myosin light chain (MLC)-2. MR-1 overexpression attenuated H/R-induced cell injury and loss of surface membrane polarity of actin. MR-1 overexpression also increased the expression and phosphorylation of MLC-2 and MLC kinase, which were decreased in MR-1-silenced and H/R-treated cells. Conclusion: Together, these data show that MR-1 promoted actin polarity on the membrane surface and protected HK-2 cells from H/R injury. The mechanism might involve the rapid organization of F-actin through the upregulation and phosphorylation of MLC-2.

Myofibrillogenesis regulator-1 attenuates hypoxia/reoxygenation-induced injury by repairing microfilaments in neonatal rat cardiomyocytes.

Hypoxia/reoxygenation (H/R) injury is characterized by microfilament reorganization in cardiomyocytes. Previous studies have shown that myofibrillogenesis regulator-1 (MR-1) is expressed in the myocardium and promotes actin organization in cardiomyocytes. The purpose of this study was to investigate the role of MR-1 in attenuating hypoxia/reoxygenation injury in cardiomyocytes through promoting restoration of the microfilament. To address this aim, an H/R model of cultured neonatal cardiomyocytes was used to assess filamentous actin (F-actin) and α-actinin organization through immunofluorescence microscopy analysis. RT-PCR was used to detect mRNA levels of MR-1 and myosin regulatory light chain-2 (MLC-2). Western blot analysis was used to detect protein levels of MR-1 and filamentous actin/globular actin (F-/G-actin) as well as MLC-2 and myosin light chain kinase (MLCK) phosphorylation and protein expression. We also explored the effects of overexpressing or knocking down MR-1 on H/R injury and the MLCK/MLC-2/F-actin pathway. We found that H/R induced cardiomyocyte injury and disruption of F-actin and α-actinin with a decrease in the F-/G-actin ratio compared with controls. Compared with the H/R group, MR-1 overexpression attenuated H/R-induced injury and disruption of F-actin and α-actinin in cardiomyocytes with an increase in the F-/G-actin ratio. MR-1 overexpression also up-regulated H/R-induced MLCK and MLC-2 phosphorylation. However, MR-1 knockdown aggravated H/R injury by further disrupting F-actin and α-actinin, as well as decreasing the F-/G-actin ratio. MR-1 knockdown also down-regulated MLCK and MLC-2 phosphorylation induced by H/R injury. These findings suggest that MR-1 attenuates H/R-induced cardiomyocyte injury by promoting microfilament reorganization through the activation of the MLCK/MLC-2 pathway.

Calreticulin Protects Rat Microvascular Endothelial Cells against Microwave Radiation-induced Injury by Attenuating Endoplasmic Reticulum Stress

This study was designed to evaluate whether exogenous CRT was beneficial for alleviating MR‐induced injury by suppressing ER stress in rat MMECs.

Zedoarondiol Inhibits Platelet-Derived Growth Factor-Induced Vascular Smooth Muscle Cells Proliferation via Regulating AMP-Activated Protein Kinase Signaling Pathway

Background/Aims: Vascular smooth muscle cells (VSMCs) proliferation contributes significantly to atherosclerosis and in-stent restenosis. Platelet-derived growth factor-BB (PDGF-BB) plays a vital role in VSMCs proliferation. Zedoarondiol, a sesquiterpene lactone compound, has an anti-inflammatory activity. However, the role of zedoarondiol in PDGF-BB-mediated VSMCs proliferation remains unclear. In this study, we investigated the effects of zedoarondiol on PDGF-BB-induced VSMCs proliferation and explored the possible mechanisms. Methods: The inhibitory effects of zedoarondiol on PDGF-BB-induced VSMCs proliferation were evaluated by direct cell counting and the Cell Counting Kit-8 (CCK-8) assay. DNA synthesis was examined by bromodeoxyuridine (BrdU) incorporation assay. Cell cycle was assessed by propidium iodide staining. Western blotting was performed to determine the expression of cyclin-dependent kinase 2 (CDK2), cyclin E, p53, p21, total and phosphorylated adenosine monophosphate-activated protein kinase (AMPK), acetyl CoA carboxylase (ACC), mammalian target of rapamycin (mTOR), and p70 ribosomal protein S6 kinase (p70S6K). Results: Zedoarondiol suppressed PDGF-BB-induced VSMCs proliferation and DNA synthesis, and induced cell cycle arrest in G0/G1 phase. In addition, zedoarondiol activated AMPK and ACC, inhibited the phosphorylation of mTOR and p70S6K, increased the expression of p53 and p21, and decreased the expression of CDK2 and cyclin E. Compound C (an AMPK inhibitor) abrogated, whereas 5-aminoimidazole-4-carboxamide 1-β-ribofuranoside (AICAR, an AMPK activator) enhanced zedoarondiol-mediated inhibition of VSMCs proliferation and DNA synthesis. Conclusion: Zedoarondiol inhibits PDGF-BB-induced VSMCs proliferation via AMPK-mediated down-regulation of the mTOR/p70S6K pathway and up-regulation of the p53/p21 pathway. These findings suggest that zedoarondiol might be a promising compound against atherosclerosis and in-stent restenosis.

Cytosolic calreticulin inhibits microwave radiation-induced microvascular endothelial cell injury through the integrin-focal adhesion kinase pathway.

To determine the effects of cytosolic CRT on MR‐induced MMEC injury, and the underlying mechanism.

Myofibrillogenesis Regulator 1 Rescues Renal Ischemia/Reperfusion Injury by Recruitment of PI3K-Dependent P-AKT to Mitochondria.

ABSTRACT To investigate whether myofibrillogenesis regulator 1 (MR-1) attenuates renal ischemia/reperfusion (I/R) injury via inhibiting phosphorylated Akt (p-Akt) mitochondrial translocation-mediated opening of the mitochondrial permeability transition pore (mPTP), we injected adenovirus containing MR-1 gene or its siRNAs to the left kidney subcapsular areas of Sprague-Dawley rats, which subsequently underwent experimental renal I/R injury. Renal functions and the severity of the tubular injury were evaluated by the serum creatinine and blood urea nitrogen levels and the pathological scores. We also examined the mitochondrial morphology and functions. Total/p-Akt were assessed by western blot using the mitochondrial and the cytosolic fractions of cortex of renal tissue, respectively. We found that mitochondrial and cytosolic MR-1 levels and mitochondrial p-Akt decreased, and cytosolic p-Akt increased after reperfusion. Subcapsular injection of adenovirus led to higher MR-1 expression in the mitochondria/cytosol, inhibited mPTP opening, and alleviated renal I/R injury; adenovirus injection also upregulated mitochondrial total and p-Akt levels more prominently compared with the normal saline (NS) group. Subcapsular injection of MR-1 siRNAs significantly lowered MR-1 expression and induced renal injury, with increased mPTP opening and mitochondrial damage, similar to I/R injury. MR-1 interacted with Akt in renal cortex homogenate. Wortmannin, a phosphatidylinositol 3 kinase (PI3K) inhibitor, abolished both mitochondrial p-Akt recruitment and the protective effect of MR-1 overexpression on I/R injury. To conclude, MR-1 protects kidney against I/R injury through inhibiting mPTP opening and maintaining mitochondrial integrity, through the recruitment of PI3K-dependent p-Akt to the mitochondria. MR-1 could be a new therapeutic strategy for renal I/R injury.

Microwave Radiation Injures Microvasculature Through Inducing Endoplasmic Reticulum Stress

The study aimed to investigate the effect of microwave radiation on microvasculature as well as the underlying mechanisms.