Daliang Yan

Heat shock protein 70 inhibits cardiomyocyte necroptosis through repressing autophagy in myocardial ischemia/reperfusion injury.

Irreversible damage of cardiac function arisen from myocardial ischemia/reperfusion injury (MIRI) leads to an emerging challenge in the treatments of cardiac ischemic diseases. Molecular chaperone heat shock protein 70 (HSP70) attenuates heat-stimulated cell autophagy, apoptosis, and damage in the heart. Under specific conditions, autophagy may, directly or indirectly, induce cell death including necroptosis. Whether HSP70 inhibits cardiomyocyte necroptosis via suppressing autophagy during MIRI is unknown. In our study, HSP70 expression was opposite to necroptosis marker RIP1 and autophagy marker LC3A/B expression after myocardial ischemia/reperfusion (MIR) in vivo. Furthermore, in vitro primary rat cardiomyocytes mimicked MIRI by hypoxia/reoxygenation (H/R) treatment. Knockdown of HSP70 expression promoted cardiomyocyte autophagy and necroptosis following H/R treatment, while the increase tendency was downregulated by autophagy inhibitor 3-MA, showing that autophagy-induced necroptosis could be suppressed by HSP70. In summary, HSP70 downregulates cardiomyocyte necroptosis through suppressing autophagy during myocardial IR, revealing the novel protective mechanism of HSP70 and supplying a novel molecular target for the treatment of heart ischemic diseases.

Mitochondrial phosphatase PGAM5 regulates Keap1-mediated Bcl-xL degradation and controls cardiomyocyte apoptosis driven by myocardial ischemia/reperfusion injury

AbstractPhosphoglycerate mutase 5 (PGAM5) is a mitochondrial membrane protein that plays crucial roles in necroptosis and apoptosis. Though PGAM5 is known to be required for inducing intrinsic apoptosis through interacting with BCL2 associated X protein (Bax) and dynamin-related protein 1 (Drp1), the expression and role of PGAM5 in cardiomyocyte apoptosis driven by myocardial ischemia/reperfusion injury(MIRI) has not been studied. The present study shows that PGAM5 expression decreased after MIRI in vivo, positively correlated with Bcl-xL expression, negatively correlated with Kelch-ECH associating protein 1 (Keap1) expression. Furthermore, PGAM5 expression also decreased in cardiomyocytes after hypoxia/reoxygenation (H/R) treatment in vitro. PGAM5 silence promoted cardiomyocyte apoptosis and inhibited Bcl-xL expression, but with no effect on Keap1 expression. Accordingly, Keap1 overexpression further inhibited Bcl-xL and PGAM5 expression. Additionally, PGAM5-Bcl-xL-Keap1 interaction was identified, suggesting that PGAM5 might participate in the degradation of Bcl-xL mediated by Keap1. In summary, PGAM5 controls cardiomyocyte apoptosis induced by MIRI through regulating Keap1-mediated Bcl-xL degradation, which may supply a novel molecular target for acute myocardial infarction (AMI) therapy. Graphical abstractᅟ

NF45 inhibits cardiomyocyte apoptosis following myocardial ischemia-reperfusion injury

Cardiomyocyte apoptosis, which occurs during ischemia and reperfusion injury, can cause irreversible damage to cardiac function. There is accumulating evidence that nuclear factor 45 (NF45) and regulatory pathways are important in understanding reparative processes in the myocardium. NF45 is a multifunctional regulator of gene expression that participates in the regulation of DNA break repair. Recently, NF45 has been proved to be associated with tumor cell apoptosis in various human malignancies. However, the underlying mechanism of NF45 regulating myocardial ischemia-reperfusion (I/R) injury remains unclear. In this study, western blot showed that NF45 expression decreased after myocardial I/R in vivo. Double immunofluorescent staining revealed that NF45, located in the nucleus of cardiomyocyes, was correlated with cardiomyocyte apoptosis. Furthermore, NF45 expression decreased in H9c2 cells after hypoxia-reoxygenation (H/R) treatment in vitro, which was in line with the results in vivo. Overexpression of NF45 in H9c2 cells reduced cell apoptosis, as evidenced by increased Bcl-2 level, as well as decreased cleaved caspase-3, p53 and p21 expression. The expression of NF45 was reduced by LY294002 (a PI3K/Akt inhibitor), but not SB203580 (a p38 inhibitor), suggesting that NF45 prevented H/R-induced H9c2 cell apoptosis via PI3K/Akt pathway. Our data may supply a novel molecular target for acute myocardial infarction (AMI) therapy.

Heat shock protein 70 protects cardiomyocytes through suppressing SUMOylation and nucleus translocation of phosphorylated eukaryotic elongation factor 2 during myocardial ischemia and reperfusion

Myocardial ischemia and reperfusion (MIR) results in cardiomyocyte apoptosis with severe outcomes, which blocks cardiac tissue recovering from myocardial ischemia diseases. Heat shock protein 70 (HSP70) is one of protective molecule chaperones which could regulate the nucleus translocation of other proteins. In addition, eukaryotic elongation factor 2 (eEF2), which modulates protein translation process, is vital to the recovery of heart during MIR. However, the relationship between HSP70 and eEF2 and its effects on MIR are unclear. The expression and relationship between HSP70 and eEF2 is confirmed by western blot, immunoprecipitation in vitro using cardiomyocyte cell line H9c2 and in vivo rat MIR model. The further investigation was conducted in H9c2 cells with detection for cell-cycle and apoptosis. It is revealed that eEF2 interacted and be regulated by HSP70, which kept eEF2 as dephosphorylated status and preserved the function of eEF2 during MIR. In addition, HSP70 suppressed the nucleus translocation of phosphorylated eEF2, which inhibited cardiomyocyte apoptosis during myocardial reperfusion stage. Furthermore, HSP70 also interacted with C-terminal fragment of eEF2, which could reverse the nucleus translocation and cardiomyocyte apoptosis caused by N-terminal fragment of eEF2. HSP70 draw on advantage and avoid defect of MIR through regulating phosphorylation and nucleus translocation of eEF2.

Phosphorylated eEF2 is SUMOylated and induces cardiomyocyte apoptosis during myocardial ischemia reperfusion

BACKGROUND Cardiomyocyte apoptosis after myocardial ischemia reperfusion (MIR) blocks the recovery of cardiac function during revascularization treatment. Protein synthesis mediated by eukaryotic elongation factor 2 (eEF2) is vital for the recovery of MIR. eEF2 promotes peptide elongation without phosphorylation of itself. However, the exact function of eEF2 during MIR is unknown. METHODS We used suture tie-down of left coronary artery (LCA) to induce MIR in vivo, which was confirmed by electrocardiography and Evans blue/triphenyltetrazolium chloride double staining. Hypoxia/reoxygenation (H/R) treatment was utilized to stimulate H9c2 cells, which was detected by CCK8 assay to evaluate cell viability. eEF2, phosphorylated eEF2, SUMO, Bax, and Bcl-2 protein expressions and location of eEF2 and phosphorylated eEF2 were determined by western blot, immunocytochemistry and immunofluorescent staining. H9c2 cell apoptosis was assessed by flow cytometry. The effects of eEF2 full-length plasmid and its fragments on H9c2 cells were also detected. RESULTS In vivo, phosphorylated eEF2 to eEF2 ratio decreased gently in rat MIR model. Immunocytochemistry showed that phosphorylated eEF2 translocated to the nucleus of cardiomyocytes during myocardial reperfusion. Furthermore, double immunofluorescent staining in H9c2 cells after H/R treatment also showed phosphorylated eEF2 translocated to the nucleus. Meanwhile, SUMOylation of eEF2 was detected. The overexpression of eEF2 upregulated Bcl-2 expression after H/R treatment, suggesting that eEF2 might reduce cardiomyocyte apoptosis during MIR. In addition, the N-terminal fragment of eEF2 transfection could promote apoptosis. CONCLUSIONS eEF2 plays a bidirectional role in regulating cardiomyocyte apoptosis during MIR, in which eEF2 can be SUMOylated and translocate into nucleus of cardiomyocytes to promote cardiomyocyte apoptosis when eEF2 is phosphorylated.

MMP-14 promotes VSMC migration via up-regulating CD44 expression in cardiac allograft vasculopathy

Cardiac allograft vasculopathy (CAV) was the leading cause of late death in heart transplantation recipients. Matrix metalloproteinase-14 (MMP-14), as a member of the MMPs family, has been reported to play a vital role in coronary vascular lesions of allotransplanted hearts. However, concrete mechanism is still unclear. Herein, we showed that the expression of MMP-14 was different between isografts and allografts. Interestingly, we found MMP-14 could interact with CD44 in allografts. Cluster of differentiation 44 (CD44), as a cell adhesion receptor and is involved in cell migration, caused our interest in MMP-14/CD44 complex in allografts. Then we analyzed the effect of MMP-14/CD44 complex on pro-MMP-9 activation and vascular smooth muscle cell (VSMC) migration in rat VSMC TNF-α treated model. Then, we further found intervention of MMP-14/CD44 complex could inhibit VSMC migration. Our results elucidate the molecular mechanism of VSMC migration after cardiac transplantation and provide theoretical basis for seeking new specific drug targets for CAV prevention and treatment.

Nucleostemin exerts anti-apoptotic function via p53 signaling pathway in cardiomyocytes

Cardiomyocytes apoptosis following reperfusion injury causes irreversible damage to cardiac function. Understanding the mechanisms underlying cardiomyocytes death under these conditions can be helpful to identify strategies to abrogate such detrimental effects. Stem cell-specific proteins and regulatory pathways become important in understanding reparative processes in the myocardium. One such regulatory protein named nucleostemin (NS) has vital roles in cardiac ischemia. Although the relationship between NS and cell apoptosis has been studied, it is unknown how NS is controlled and how it participates in cardiomyocytes apoptosis induced by ischemia reperfusion (I/R). In the present study, we aimed to investigate the direct role of NS in myocardial I/R. In vivo, NS was highly expressed in cardiac tissues after I/R. Double immunofluorescent staining showed that NS located in the nucleolar of cardiomyocytes and correlated with cardiomyocytes apoptosis. Furthermore, in vitro primary rat cardiomyocytes increased NS expression induced by hypoxia-reoxygenation (H/R) treatment, in line with results in vivo. Suppression of NS expression by siNS promoted the expression of terminal deoxynucleotide transferase-mediated dUTP nick end labeling (TUNEL)-positive cells p53 and cleaved caspase-3, which demonstrates I/R may require increased expression of NS to suppress p53 activation and maintain cardiomyocytes survival.

Upregulated expression of Nucleostemin/GNL3 is associated with poor prognosis and Sorafenib Resistance in Hepatocellular Carcinoma

Nucleostemin (NS)/GNL3 protein has been recently documented to be a nucleolar protein that was abundantly expressed in stem cells and cancer cells. Herein, we showed that NS was upregulated in HCC tissues and the expression of NS was inversely correlated with that of p53. Overexpression of NS predicted significantly worsened prognosis in HCC patients, suggesting that NS might serve as a prognostic marker of HCC. In addition, we found that depletion of NS sensitized HCC cells to sorafenib-induced apoptosis. Moreover, we found that the mechanism underlying NS-mediated sorafenib resistance involved dysregulated expression of p53, and downstream Bax and Bcl-2 proteins. NS interacted with p53 in HCC cells. Depletion of NS increased the expression of p53 and Bax, whereas impaired the level of cellular Bcl-2. Interference of NS enhanced the cytotoxic effects of sorafenib in HCC cells. Furthermore, ectopic expression of NS impaired the apoptosis of HCC cells following sorafenib exposure. Therefore, NS may contribute to sorafenib resistance in HCC cells through the modulation of p53 pathway and Bcl-2 proteins. These findings indicated that the combination of silencing NS expression and sorafenib treatment is a promising therapeutic strategy in treatment of HCC.

Nur77 is involved in graft infiltrating T lymphocyte apoptosis in rat cardiac transplantation model

Acute allograft rejection is initiated by a large number of recipient T cells that recognize donor alloantigens. Apoptotic signals trigger Nur77 production. Nur77 translocates from the nucleus to the mitochondria to induce a loss of mitochondrial membrane potential and the release of mitochondrial cell-death mediators, including HtrA2/Omi. In this study, we investigated the relationship between Nur77, HtrA2/Omi, and T lymphocyte apoptosis during acute allograft rejection in a rat cardiac transplantation model. The median survival time of the isograft group was longer than that of the allograft group. The cardiac grafts in isogenic (Lewis to Lewis) and allogenic (Wistar to Lewis) models were subjected to HE stain, showing that no rejection occurred in the isografts and that the rejection level was increased in allografts. Compared with the rare expression in syngeneic Lewis rat hearts by western blot analysis, Nur77 protein level in allograft increased from day 1, peaked at day 5 after transplantation, and maintained the highest level until day 7. Double immunofluorescence staining on allograft tissues at day 5 showed Nur77 immunocompetence in most CD3(+) cells, and Nur77 positive T cells also showed HtrA2/Omi-positive signal. Meanwhile, active caspase-3 was apparent in these HtrA2/Omi-positive T cells. Immunohistochemical results suggested that both Nur77 and active caspase-3 were expressed in increasing infiltrating lymphocytes. Our results demonstrated that upregulated Nur77 may promote graft-infiltrating T lymphocyte apoptosis by translocating and inducing HtrA2/Omi release from mitochondria in acute rejection after cardiac transplantation.

Erythroblast transformation-specific 2 correlates with vascular smooth muscle cell apoptosis in rat heterotopic heart transplantation model

BACKGROUND Cardiac allograft vasculopathy (CAV) decreases the long-term survival of heart transplantation recipients. Vascular smooth muscle cell (VSMC) apoptosis is an important pathological feature of CAV. Erythroblast transformation-specific 2 (Ets-2), as a transcription factor, participates in cell apoptosis and plays an important role in organ transplantation. METHODS Hearts from Wistar-Furth (WF:RT1u) rats were heterotopically transplanted into Lewis (Lew:RT1(l)) rats without immunosuppression. Additional syngeneic heterotopic cardiac transplantations were performed in Lewis rats. HE staining was used to identify CAV. Ets-2 expression was examined by western blot. Ets-2 tissue location was examined by immunohistochemical assay and double immunostaining. Cleaved caspase 3 expression was detected by western blot. Co-localization of Ets-2 and cleaved caspase 3 was detected by double immunostaining. Ets-2, p53, cleaved caspase 3 and Bcl-xl expression in rat VSMC line A7R5 was examined after Ets-2 siRNA transfection. TUNEL assay was applied to detect A7R5 apoptosis with or without ETS-2 siRNA transfection. Immunoprecipitation was performed to explore the interaction between Ets-2 and p53. RESULTS Ets-2 expression decreased in the allograft group but had no obvious change in the isograft group. Meanwhile, the phenomenon of CAV was observed in the allograft group and there is neointima formation in the isograft group which is not obvious compared with allograft group. Additionally, Ets-2 expression was opposite to VSMC apoptosis in the allograft group. In vitro, Ets-2 siRNA transfection in A7R5cells resulted in enhanced cell apoptosis. Finally, Ets-2 interacted with p53. CONCLUSIONS Ets-2 might inhibit VSMC apoptosis via p53 pathway. The results further elucidate the molecular mechanism of VSMC apoptosis after heart transplantation during CAV and provide theoretical basis for seeking new specific drug targets for CAV prevention and treatment.