Ji Zuo

Effect of GRP75/mthsp70/PBP74/mortalin overexpression on intracellular ATP level, mitochondrial membrane potential and ROS accumulation following glucose deprivation in PC12 cells.

Glucose regulated protein 75 (GRP75) is an important molecular chaperon belonged to the heat shock protein (HSP) family. To evaluate the effect of GRP75 overexpression on PC12 cells under glucose deprivation, cell viability and mitochondrial function of GRP75-overexpressing PC12 cells and the vector transfected control PC12 cells were monitored during glucose deprivation. Upon exposure to glucose deprivation, GRP75-overexpressing PC12 cells exhibited more moderate cell damage than control PC12 cells. Both of the two groups of cells showed a decreased ATP level following an early increase in the condition of glucose deprivation, and the mitochondrial potential were also reduced in the similar manner in the two groups of cells. Control PC12 cells showed an immediate and rapid increase in ROS accumulation after the onset of GD treatment, and this accumulation was slowed and reduced in GRP75-overexpressing PC12 cells. These findings suggested that GRP75 could inhibit the ROS accumulation, and it may be associated with the cytoprotective effect of GRP75 overexpression upon glucose deprivation. (Mol Cell Biochem 268: 45–51, 2005)

Glucose deprivation induces mitochondrial dysfunction and oxidative stress in PC12 cell line

Glucose metabolism plays a pivotal role in many physiological and pathological conditions. To investigate the effect of hypoglycemia (obtained by glucose deprivation) on PC12 cell line, we analyzed the cell viability, mitochondrial function (assessed by MTT reduction, cellular ATP level, mitochondrial transmembrane potential), and the level of reactive oxygen species (ROS) after glucose deprivation (GD). Upon exposure to GD, ROS level increased and MTT reduction decreased immediately, intracellular ATP level increased in the first 3 hours, followed by progressive decrease till the end of GD treatment, and the mitochondrial transmembrane potential (ΔΨm) dropped after 6 hours. Both necrosis and apoptosis occurred apparently after 24 hours which was determined by nuclei staining with propidium iodide(PI) and Hoechst 33342. These data suggested that cytotoxity of GD is mainly due to ROS accumulation and ATP depletion in PC12 cells.

Mitochondrial dysfunction induced by knockdown of mortalin is rescued by Parkin

Mutations in the parkin gene are the most common cause of autosomal recessive Parkinsons disease (PD). As an E3-ubiquitin ligase, Parkin is associated with mitochondrial dynamics and mitophagy. Mortalin, a molecular chaperone, is located primarily in mitochondria, where it functions to maintain mitochondrial homeostasis and antagonize oxidative stress injury. A reduced expression level of mortalin has been observed in the affected brain regions of PD patients. Mortalin also interacts with a variety of PD-related proteins and plays an indispensible role in helping native protein refolding and importing proteins into the mitochondrial matrix. Thus, the main aims of the present study were to investigate mitochondrial dysfunction induced by knockdown of mortalin and to test whether Parkin overexpression could rescue this effect. We found that lentivirus-mediated knockdown of mortalin in HeLa cells resulted in a collapse of mitochondrial membrane potential, an abnormal accumulation of reactive oxygen species and apparent alterations in mitochondrial morphology under H(2)O(2)-induced stress conditions. Remarkably, Parkin overexpression rescued these mitochondrial abnormalities. In HeLa cells expressing Parkin, co-immunoprecipitation of endogenous mortalin and wild-type Parkin was detected when they were treated with carbonyl cyanide 3-chlorophenylhydrazone (CCCP). In conclusion, we indicate that the relatively decreased mortalin expression level and its impaired interaction with Parkin could affect its roles in mitochondrial function.

Expression of Dishevelled-1 in wound healing after acute myocardial infarction: possible involvement in myofibroblast proliferation and migration.

One of our previous studies indicated that the expression of β‐catenin, which is the key factor of wnt‐frizzled pathway, increased significantly in the ischemic area of the rat heart 7 days after myocardial infarction (MI). Together with the results of other recent studies, we made an assumption that wnt‐frizzled pathway may be involved in the controlled cell proliferation and migration during repair processes after MI. To verify this assumption we tried to investigate the expression of another signal transduction molecule called Dishevelled in wnt‐frizzled pathway during the wound healing process after MI. The left descending coronary arteries of rats were ligated to induce MI. Immunohistochemistry SABC method and in situ hybridization were performed to detect the expression of Dishevelled‐1. The results showed, that one day after MI, Dishevelled‐1 mRNA but not protein expression was detected in the cells at the border zone of the infarction area; 4 days after MI the expression of Dishevelled‐1 increased exclusively and cytoplasmic Dishevelled‐1 was observed not only at the border zone but also in the infarct area; 7 days after MI, it seems that the expression reached its peak, the positive staining even spread into the endothelial and smooth muscle cells of the newly formed and pre‐existing blood vessels in the infarction area; after that the Dishevelled‐1 expression decreased abruptly and could hardly be detected 28 days after MI. Thus cytoplasmic Dishevelled‐1 may be involved in the controlled proliferation and migration of myofibroblasts and vascular endothelial cells, hence play a role during the wound healing process after MI.

Astaxanthin inhibits apoptosis in alveolar epithelial cells type II in vivo and in vitro through the ROS-dependent mitochondrial signalling pathway

Oxidative stress is an important molecular mechanism underlying lung fibrosis. The mitochondrion is a major organelle for oxidative stress in cells. Therefore, blocking the mitochondrial signalling pathway may be the best therapeutic manoeuver to ameliorate lung fibrosis. Astaxanthin (AST) is an excellent antioxidant, but no study has addressed the pathway of AST against pulmonary oxidative stress and free radicals by the mitochondrion‐mediated signalling pathway. In this study, we investigated the antioxidative effects of AST against H2O2‐ or bleomycin (BLM)‐induced mitochondrial dysfunction and reactive oxygen species (ROS) production in alveolar epithelial cells type II (AECs‐II) in vivo and in vitro. Our data show that AST blocks H2O2‐ or BLM‐induced ROS generation and dose‐dependent apoptosis in AECs‐II, as characterized by changes in cell and mitochondria morphology, translocation of apoptotic proteins, inhibition of cytochrome c (Cyt c) release, and the activation of caspase‐9, caspase‐3, Nrf‐2 and other cytoprotective genes. These data suggest that AST inhibits apoptosis in AECs‐II cells through the ROS‐dependent mitochondrial signalling pathway and may be of potential therapeutic value in lung fibrosis treatment.

Targeting GRP75 improves HSP90 inhibitor efficacy by enhancing p53-mediated apoptosis in hepatocellular carcinoma.

Heat shock protein 90 (HSP90) inhibitors are potential drugs for cancer therapy. The inhibition of HSP90 on cancer cell growth largely through degrading client proteins, like Akt and p53, therefore, triggering cancer cell apoptosis. Here, we show that the HSP90 inhibitor 17-AAG can induce the expression of GRP75, a member of heat shock protein 70 (HSP70) family, which, in turn, attenuates the anti-growth effect of HSP90 inhibition on cancer cells. Additionally, 17-AAG enhanced binding of GRP75 and p53, resulting in the retention of p53 in the cytoplasm. Blocking GRP75 with its inhibitor MKT-077 potentiated the anti-tumor effects of 17-AAG by disrupting the formation of GRP75-p53 complexes, thereby facilitating translocation of p53 into the nuclei and leading to the induction of apoptosis-related genes. Finally, dual inhibition of HSP90 and GRP75 was found to significantly inhibit tumor growth in a liver cancer xenograft model. In conclusion, the GRP75 inhibitor MKT-077 enhances 17-AAG-induced apoptosis in HCCs and increases p53-mediated inhibition of tumor growth in vivo. Dual targeting of GRP75 and HSP90 may be a useful strategy for the treatment of HCCs.

Protective effect of Cordyceps polysaccharide on hydrogen peroxide-induced mitochondrial dysfunction in HL-7702 cells

Multiple reports have suggested that reactive oxygen species (ROS) are implicated in hepatic fibrosis and that they are capable of causing hepatocyte apoptosis in hepatic fibrosis by causing oxidative damage to the liver. Thus, the study of antioxidant compounds may shed light on the treatment of hepatic fibrosis. The aim of the current study was to investigate the protective effects of Cordyceps polysaccharide (CPS), a major antioxidative component of Cordyceps militaris, on hydrogen peroxide (H2O2)-induced cell apoptosis. The data showed that CPS markedly inhibited H2O2-induced mitochondrial dysfunction, lowered cell viability, increased the apoptotic rate, boosted ROS production, decreased mitochondrial membrane potential (MMP), reduced the intracellular adenosine triphosphate (ATP) level, increased the Bax/Bcl-2 ratio and promoted cytochrome C (Cyt C) release. These results indicated that CPS protected HL-7702 cells, which are used as the main model of hepatic fibrosis, against H2O2-induced mitochondrial dysfunction by decreasing ROS production and regulating mitochondrial apoptotic signaling through the Cyt C, Bax and Bcl-2 apoptosis-related proteins.

Inhibition of mortalin expression reverses cisplatin resistance and attenuates growth of ovarian cancer cells

The heat shock protein mortalin is frequently overexpressed in human malignancies. In this study, an assessment of mortalin expression using ovarian cancer tissue microarrays suggested that mortalin overexpression might be related to drug resistance. Using a short hairpin (sh) RNA approach, we evaluated the effect of reducing mortalin expression in vitro and in vivo. The results of our study show that elevated levels of mortalin expression increase cancer cell resistance to cisplatin-induced cytotoxicity and identify mortalin as a potential therapeutic target for improved treatment of drug-resistant ovarian cancer.

Upregulated Parkin expression protects mitochondrial homeostasis in DJ-1 konckdown cells and cells overexpressing the DJ-1 L166P mutation.

Rare genetic mutations in the DJ-1 and Parkin genes cause recessive Parkinsonism, however, the relationship between these two genes is not fully elucidated. Current emerging evidence suggests that these genes are involved in mitochondrial homeostasis, and that a deficiency in either of these two genes is associated with damages in mitochondrial function and morphology. In this study, we demonstrated that knockdown of DJ-1 expression or the overexpression of the DJ-1 L166P mutation results in a damaged phenotype in mitochondria and a hypersensitivity to H2O2-induced cell apoptosis. These phenotypes result from increased levels of endogenous oxidative stress. However, overexpression of wild-type Parkin rescued the phenotypes observed in the mitochondria of DJ-1 knockdown and DJ-1 L166P mutant cells. We also determined that there were differences between the two cell models. Furthermore, both H2O2 treatment and the DJ-1 L166P mutation weakened the interaction between DJ-1 and Parkin. Taken together, these findings suggested that DJ-1 and Parkin were linked through oxidative stress, and that overexpression of Parkin protects DJ-1 protein-deficient and DJ-1 L166P mutant-expressing cells via inhibition of oxidative stress.

Expression of Mortalin Detected in Human Liver Cancer by Tissue Microarrays

Mortalin is a highly conserved molecular chaperone in the heat shock protein (HSP) 70 family, which plays a role in carcinogenesis. The relationship between tumors and the expression of Mortalin is not fully elucidated. In this study, human tumor specimens from various organs of liver cancer at different stages and cultured liver cancer cells were used to study the expression pattern of Mortalin. Through immunohistochemistry we showed that Mortalin was significantly higher in tumors than in adjacent benign tissues. Using liver tissue microarrays tested on hepatocellular carcinomas, Mortalin expression was consecutively higher with advanced tumor stages. Mortalin expression on the cultured liver cancer cells were characterized with immunocytochemistry, Real‐time PCR, and western blot. The results showed that the expression level is markedly higher in the SMMC 7721 (a liver‐derived tumor cell line) than in the HL 7702 (a normal liver cell line) in the protein level only. Understanding the role of Mortalin in tumors may lead to development of a new therapeutic target in cancer treatment. Anat Rec, 2011.