Nucleolin protects the heart from ischaemia-reperfusion injury by up-regulating heat shock protein 32

Nucleolin myocardial-specific knockout exacerbates glucose metabolism disorder in endotoxemia-induced myocardial injury

Background

Sepsis-induced myocardial injury, as one of the important complications of sepsis, can significantly increase the mortality of septic patients. Our previous study found that nucleolin affected mitochondrial function in energy synthesis and had a protective effect on septic cardiomyopathy in mice. During sepsis, glucose metabolism disorders aggravated myocardial injury and had a negative effect on septic patients.

Objectives

We investigated whether nucleolin could regulate glucose metabolism during endotoxemia-induced myocardial injury.

Methods

The study tested whether the nucleolin cardiac-specific knockout in the mice could affect glucose metabolism through untargeted metabolomics, and the results of metabolomics were verified experimentally in H9C2 cells. The ATP content, lactate production, and oxygen consumption rate (OCR) were evaluated.

Results

The metabolomics results suggested that glycolytic products were increased in endotoxemia-induced myocardial injury, and that nucleolin myocardial-specific knockout altered oxidative phosphorylation-related pathways. The experiment data showed that TNF-α combined with LPS stimulation could increase the lactate content and the OCR values by about 25%, and decrease the ATP content by about 25%. However, interference with nucleolin expression could further decrease ATP content and OCR values by about 10-20% and partially increase the lactate level in the presence of TNF-α and LPS. However, nucleolin overexpression had the opposite protective effect, which partially reversed the decrease in ATP content and the increase in lactate level.

Conclusion

Down-regulation of nucleolin can exacerbate glucose metabolism disorders in endotoxemia-induced myocardial injury. Improving glucose metabolism by regulating nucleolin was expected to provide new therapeutic ideas for patients with septic cardiomyopathy.

RGS6 drives cardiomyocyte death following nucleolar stress by suppressing Nucleolin/miRNA-21

BACKGROUND

Prior evidence demonstrated that Regulator of G protein Signaling 6 (RGS6) translocates to the nucleolus in response to cytotoxic stress though the functional significance of this phenomenon remains unknown.

METHODS

Utilizing in vivo gene manipulations in mice, primary murine cardiac cells, human cell lines and human patient samples we dissect the participation of a RGS6-nucleolin complex in chemotherapy-dependent cardiotoxicity.

RESULTS

Here we demonstrate that RGS6 binds to a key nucleolar protein, Nucleolin, and controls its expression and activity in cardiomyocytes. In the human myocyte AC-16 cell line, induced pluripotent stem cell derived cardiomyocytes, primary murine cardiomyocytes, and the intact murine myocardium tuning RGS6 levels via overexpression or knockdown resulted in diametrically opposed impacts on Nucleolin mRNA, protein, and phosphorylation.RGS6 depletion provided marked protection against nucleolar stress-mediated cell death in vitro, and, conversely, RGS6 overexpression suppressed ribosomal RNA production, a key output of the nucleolus, and triggered death of myocytes. Importantly, overexpression of either Nucleolin or Nucleolin effector miRNA-21 counteracted the pro-apoptotic effects of RGS6. In both human and murine heart tissue, exposure to the genotoxic stressor doxorubicin was associated with an increase in the ratio of RGS6/Nucleolin. Preventing RGS6 induction via introduction of RGS6-directed shRNA via intracardiac injection proved cardioprotective in mice and was accompanied by restored Nucleolin/miRNA-21 expression, decreased nucleolar stress, and decreased expression of pro-apoptotic, hypertrophy, and oxidative stress markers in heart.

CONCLUSION

Together, these data implicate RGS6 as a driver of nucleolar stress-dependent cell death in cardiomyocytes via its ability to modulate Nucleolin. This work represents the first demonstration of a functional role for an RGS protein in the nucleolus and identifies the RGS6/Nucleolin interaction as a possible new therapeutic target in the prevention of cardiotoxicity.

LncRNA Fendrr: involvement in the protective role of nucleolin against H2O2-induced injury in cardiomyocytes

Background: Nucleolin is a multifunctional nucleolar protein with RNA-binding properties. Increased nucleolin expression protects cells from H2O2-induced damage, but the mechanism remains unknown. Long noncoding RNAs (lncRNAs) play crucial roles in cardiovascular diseases. However, the biological functions and underlying mechanisms of lncRNAs in myocardial injury remain unclear.Methods: In a nucleolin-overexpressing cardiac cell line, high-throughput technology was used to identify lncRNAs controlled by nucleolin. Cell counting kit-8 assay was used to determine cell viability, lactate dehydrogenase (LDH) assay to detect cell death, caspase activity assay and propidium iodide staining to confirm cell apoptosis, and RNA immunoprecipitation to examine the interaction between Fendrr and nucleolin.Results: We found that Fendrr expression was significantly downregulated in mouse hearts subjected to myocardial ischemia-reperfusion (MI/R) injury. High Fendrr expression abrogated H2O2-mediated injury in cardiomyocytes as evidenced by increased cell viability and decreased cell apoptosis. Conversely, Fendrr knockdown exacerbated the cardiomyocytes injury. Also, nucleolin overexpression inhibits Fendrr downregulation in H2O2-induced cardiomyocyte injury. Fendrr overexpression significantly reversed the role of the suppression of nucleolin expression in H2O2-induced cardiomyocytes.Conclusion: LncRNA Fendrr is involved in the cardioprotective effect of nucleolin against H2O2-induced injury and may be a potential therapeutic target for oxidative stress-induced myocardial injury.

NUCLEOLIN PROMOTES AUTOPHAGY THROUGH PGC-1Α IN LPS-INDUCED MYOCARDIAL INJURY

ABSTRACT

As a multifunctional protein, nucleolin can participate in a variety of cellular processes. Nucleolin also has multiple protective effects on heart disease. Previous studies have shown that nucleolin could not only resist oxidative stress damage and inflammatory damage, but also regulate autophagy to play a protective role in cardiac ischemia. However, the specific mechanism has not been fully elucidated in LPS-induced myocardial injury. Therefore, the aim of this study is to explore the underlying mechanism by which nucleolin regulates autophagy to protect against LPS-induced myocardial injury in vivo and in vitro . In our study, we found that nucleolin could bind to PGC-1α, and we predicted that this interaction could promote autophagy and played a role in inhibiting cardiomyocyte apoptosis. Downregulation of nucleolin in H9C2 cells resulted in decreased autophagy and increased cell apoptosis during LPS-induced myocardial injury, while upregulation of PGC-1α had the opposite protective effect. Upregulation of nucleolin expression in cardiomyocytes could increase the level of autophagy during LPS-induced myocardial injury. In contrast, interference with PGC-1α expression resulted in a decrease in the protective effect of nucleolin, leading to reduced autophagy and thus increasing apoptosis. By using tandem fluorescent-tagged LC3 autophagic flux detection system, we observed autophagic flux and determined that PGC-1α interference could block autophagic lysosomal progression. We further tested our hypothesis in the nucleolin cardiac-specific knockout mice. Finally, we also found that inhibition of autophagy can reduce mitochondrial biogenesis as well as increase apoptosis, which demonstrated the importance of autophagy. Therefore, we can speculate that nucleolin can protect LPS-induced myocardial injury by regulating autophagy, and this protective effect may be mediated by the interaction with PGC-1α, which can positively regulate the ULK1, an autophagy-related protein. Our study provides a new clue for the cardioprotective effect of nucleolin, and may provide new evidence for the treatment of LPS-induced myocardial injury through the regulation of autophagy.

NUCLEOLIN PROTECTS CARDIOMYOCYTES BY UPREGULATING PGC-1α AND PROMOTING MITOCHONDRIAL BIOGENESIS IN LPS-INDUCED MYOCARDIAL INJURY

ABSTRACT

Background: Lipopolysaccride-induced myocardial injury was characterized by frequent mitochondrial dysfunction. Our previous studies found that nucleolin (NCL) played important protective roles in myocardial ischemia-reperfusion injury. Recently, it has been found that NCL has a protective effect on LPS-induced myocardial injury in vivo . However, the exact underlying mechanisms that how NCL protects myocardium against the LPS-induced myocardial injury remains unclear. Objective: The aim of the study is to investigate the protective role of NCL in LPS-induced myocardial injury from the aspect of mitochondrial biogenesis. Methods: The cardiac-specific NCL-knockout (NCL -/- ) or NCL f/f mice were injected with LPS (10 mg/kg) to induce LPS-induced myocardial injury. The supernatant generated after LPS stimulation of macrophages was used as the conditioned medium to stimulate H9C2 and established the injured cell model. Analysis of mRNA stability, RNA-binding protein immunoprecipitation assay, and luciferase reporter assay were performed to detect the mechanism by which NCL regulated the expression of PGC-1α. Results: The expression of NCL and PGC-1α was elevated in cardiac tissue and cardiomyocytes during LPS-induced myocardial injury. The cardiac-specific NCL-knockout decreased PGC-1α expression, inhibited mitochondrial biogenesis, and increased cardiomyocytes death during LPS-induced myocardial injury in vitro and in vivo . In contrast, the overexpression of NCL could improve mitochondrial biogenesis in H9C2 cells. Moreover, the analysis of mRNA stability and luciferase reporter assay revealed that the interaction between NCL and PGC-1α significantly promoted the stability of PGC-1α mRNA, thereby upregulating the expression of PGC-1α and exerting a cardioprotective effect. In addition, the activation of PGC-1α diminished the detrimental effects of NCL knockdown on mitochondrial biogenesis in vitro and in vivo . Conclusions: Nucleolin upregulated the gene expression of PGC-1α by directly binding to the 5'-UTR of PGC-1α mRNA and increasing its mRNA stabilities, then promoted mitochondrial biogenesis, and played protective effect on cardiomyocytes during LPS-induced myocardial injury. Taken together, all these data showed that NCL activated PGC-1α to rescue cardiomyocytes from LPS-induced myocardial injury insult, suggesting that the cardioprotective role of NCL might be a promising prospect for clinical treatment of patients with endotoxemia.

Ribosome biogenesis in disease: new players and therapeutic targets

The ribosome is a multi-unit complex that translates mRNA into protein. Ribosome biogenesis is the process that generates ribosomes and plays an essential role in cell proliferation, differentiation, apoptosis, development, and transformation. The mTORC1, Myc, and noncoding RNA signaling pathways are the primary mediators that work jointly with RNA polymerases and ribosome proteins to control ribosome biogenesis and protein synthesis. Activation of mTORC1 is required for normal fetal growth and development and tissue regeneration after birth. Myc is implicated in cancer development by enhancing RNA Pol II activity, leading to uncontrolled cancer cell growth. The deregulation of noncoding RNAs such as microRNAs, long noncoding RNAs, and circular RNAs is involved in developing blood, neurodegenerative diseases, and atherosclerosis. We review the similarities and differences between eukaryotic and bacterial ribosomes and the molecular mechanism of ribosome-targeting antibiotics and bacterial resistance. We also review the most recent findings of ribosome dysfunction in COVID-19 and other conditions and discuss the consequences of ribosome frameshifting, ribosome-stalling, and ribosome-collision. We summarize the role of ribosome biogenesis in the development of various diseases. Furthermore, we review the current clinical trials, prospective vaccines for COVID-19, and therapies targeting ribosome biogenesis in cancer, cardiovascular disease, aging, and neurodegenerative disease.

Nucleolar stress: Friend or foe in cardiac function?

Studies in the past decades have uncovered an emerging role of the nucleolus in stress response and human disease progression. The disruption of ribosome biogenesis in the nucleolus causes aberrant nucleolar architecture and function, termed nucleolar stress, to initiate stress-responsive pathways via nucleolar release sequestration of various proteins. While data obtained from both clinical and basic investigations have faithfully demonstrated an involvement of nucleolar stress in the pathogenesis of cardiomyopathy, much remains unclear regarding its precise role in the progression of cardiac diseases. On the one hand, the initiation of nucleolar stress following acute myocardial damage leads to the upregulation of various cardioprotective nucleolar proteins, including nucleostemin (NS), nucleophosmin (NPM) and nucleolin (NCL). As a result, nucleolar stress plays an important role in facilitating the survival and repair of cardiomyocytes. On the other hand, abnormalities in nucleolar architecture and function are correlated with the deterioration of cardiac diseases. Notably, the cardiomyocytes of advanced ischemic and dilated cardiomyopathy display impaired silver-stained nucleolar organiser regions (AgNORs) and enlarged nucleoli, resembling the characteristics of tissue aging. Collectively, nucleolar abnormalities are critically involved in the development of cardiac diseases.

Nicorandil alleviates cardiac remodeling and dysfunction post -infarction by up-regulating the nucleolin/autophagy axis

OBJECTIVE

The present study aimed to investigate whether the drug nicorandil can improve cardiac remodeling after myocardial infarction (MI) and the underlying mechanisms.

METHODS

Mouse MI was established by the ligation of the left anterior descending coronary artery and H9C2 cells were cultured to investigate the underlying molecular mechanisms. The degree of myocardial collagen (Col) deposition was evaluated by Masson's staining. The expressions of nucleolin, autophagy and myocardial remodeling-associated genes were measured by Western blotting, qPCR, and immunofluorescence. The apoptosis of myocardial tissue cells and H9C2 cells were detected by TUNEL staining and flow cytometry, respectively. Autophagosomes were observed by transmission electron microscopy.

RESULTS

Treatment with nicorandil mitigated left ventricular enlargement, improved the capacity of myocardial diastolic-contractility, decreased cardiomyocyte apoptosis, and inhibited myocardial fibrosis development post-MI. Nicorandil up-regulated the expression of nucleolin, promoted autophagic flux, and decreased the expressions of TGF-β1 and phosphorylated Smad2/3, while enhanced the expression of BMP-7 and phosphorylated Smad1 in myocardium. Nicorandil decreased apoptosis and promoted autophagic flux in H2O2-treated H9C2 cells. Autophagy inhibitors 3-methyladenine (3MA) and chloroquine diphosphate salt (CDS) alleviated the effects of nicorandil on apoptosis. Knockdown of nucleolin decreased the effects of nicorandil on apoptosis and nicorandil-promoted autophagic flux of cardiomyocytes treated with H2O2.

CONCLUSIONS

Treatment with nicorandil alleviated myocardial remodeling post-MI through up-regulating the expression of nucleolin, and subsequently promoting autophagy, followed by regulating TGF-β/Smad signaling pathway.

Tripartite motif-containing protein 16 protects against myocardial ischemia/reperfusion injury by affecting the Keap1/Nrf2 axis

Tripartite motif-containing protein (TRIM16) is a newly identified oxidative-stress-responsive protein. Oxidative stress is a hallmark of myocardial ischemia/reperfusion (I/R) injury and contributes to the cardiac injury. To date, whether TRIM16 plays a role in mediating oxidative stress during myocardial I/R injury is undetermined. The work is devoted to evaluate the possible relevance of TRIM16 in myocardial I/R injury. TRIM16 induction by myocardial hypoxia/reoxygenation (H/R) injury in vitro or myocardial I/R injury in vivo was observed. TRIM16 overexpression alleviated H/R-induced injury of rat cardiomyocytes. TRIM16 overexpression markedly attenuated cardiac injury, infarct size, and myocardial apoptosis induced by myocardial I/R injury. Further research revealed that TRIM16 was capable of enhancing Nrf2 activation via the regulation of Keap1. The inhibition of Nrf2 diminished TRIM16-overexpression-mediated cardioprotective effects. Overall, this work demonstrates that TRIM16 protects against myocardial I/R injury via affecting the Keap1/Nrf2 axis. This work offers new insights into the molecular mechanism underlying myocardial I/R injury and proposes TRIM16 as an attractive candidate target for cardioprotection.

LncRNA CRNDE inhibits cardiomyocytes apoptosis by YAP1 in myocardial ischaemia/reperfusion injury

BACKGROUND

Cardiomyocytes apoptosis is the basic pathological process of myocardial ischaemia/reperfusion (MI/R) injury, so inhibiting apoptosis of cardiomyocytes can effectively improve MI/R injury. Long non-coding RNA colorectal neoplasia differentially expressed (lncRNA CRNDE) can inhibit cell apoptosis, but its specific role in MI/R injury has not been studied. The aim of this study is to explore the specific effect of lncRNA CRNDE on cardiomyocytes apoptosis.

METHODS

MI/R model in vivo and hypoxia/re-oxygenation (H/R) model in vitro were constructed. Apoptotic levels were assessed by TUNEL staining assay. QRT-PCR was used to validate lncRNA CRNDE level in myocardial tissues and HL-1 cells. The protein expressions of YAP1, Bcl-2 and cleaved caspase-3 were detected by western blot analysis. Flow cytometry was used to determine the apoptosis rate of cardiomyocytes. RIP assay was used to detect the interaction between lncRNA CRNDE and YAP1.

RESULTS

The extent of cardiomyocytes apoptosis was significantly increased, and the levels of lncRNA CRNDE, YAP1 and Bcl-2 were down-regulated, while cleaved caspase-3 expression was up-regulated in MI/R mice and H/R-treated HL-1 cells. The expressions of YAP1 and Bcl-2 were decreased, while the expression of cleaved caspase-3 was increased after the knockdown of lncRNA CRNDE. Furthermore, lncRNA CRNDE could bind to YAP1 and regulated the protein level of YAP1 by ubiquitination and proteasomal degradation pathway. After transfection of Si-YAP1 in the H/R-treated HL-1 cells transfected with pc-DNA CRNDE, the protein level of Bcl-2 was decreased, while cleaved caspase-3 expression and the apoptosis rate were increased.

CONCLUSION

Our study suggested that lncRNA CRNDE could regulate YAP1 level by ubiquitination and proteasomal degradation pathway, thus inhibiting cardiomyocytes apoptosis in MI/R injury.

LncRNA H19 is involved in myocardial ischemic preconditioning via increasing the stability of nucleolin protein

Myocardial ischemic preconditioning (IP) is defined as a brief period of myocardial ischemia/reperfusion (I/R) that significantly reduces injury during the subsequent exposure to long-term I/R. However, the underlying mechanisms of myocardial IP are yet to be elucidated. This study investigated the expression and roles of long noncoding RNA (lncRNA) H19 in myocardial IP in vitro and in vivo. LncRNA H19 expression levels were analyzed by quantitative reverse-transcription polymerase chain reaction, cell viability was determined by the Cell Counting Kit-8 assay, apoptosis was evaluated based on the caspase 3 activity, and RNA immunoprecipitation was performed to examine the interaction between lncRNA H19 and nucleolin. The results of this study showed that lncRNA H19 expression was significantly upregulated in mouse hearts subjected to myocardial IP, in rat H9C2 cells exposed to H2 O2 preconditioning (H2 O2 -PC), and in neonatal rat cardiomyocytes subjected to hypoxia preconditioning. H19 knockdown abrogated the H2 O2 -PC-mediated protection in cardiomyocytes evidenced by the decreased cell viability and increased caspase-3 activity. Conversely, H19 overexpression enhanced the protective role of H2 O2 -PC in cardiomyocytes. In addition, H19 overexpression increased the expression of nucleolin, whereas H19 ablation abrogated H2 O2 -PC-induced upregulation of nucleolin in cardiomyocytes. Furthermore, H19 overexpression increased the stabilization of nucleolin; an interaction between H19 and nucleolin was identified using the RNA-protein interaction studies. Furthermore, nucleolin small interfering RNA relieved the protective role of lncRNA H19. These findings demonstrated that the lncRNA H19 is involved in myocardial IP via increasing the stability of nucleolin protein and lncRNA H19 may represent a potential therapeutic target for the treatment of the myocardial injury.

Y RNAs: Biogenesis, Function and Implications for the Cardiovascular System

In recent years, progress in the field of high-throughput sequencing technology and its application to a wide variety of biological specimens has greatly advanced the discovery and cataloging of a diverse set of non-coding RNAs (ncRNAs) that have been found to have unexpected biological functions. Y RNAs are an emerging class of highly conserved, small ncRNAs. There is a growing number of reports in the literature demonstrating that Y RNAs and their fragments are not just random degradation products but are themselves bioactive molecules. This review will outline what is currently known about Y RNA including biogenesis, structure and functional roles. In addition, we will provide an overview of studies reporting the presence and functions attributed to Y RNAs in the cardiovascular system.

CARD9 promotes autophagy in cardiomyocytes in myocardial ischemia/reperfusion injury via interacting with Rubicon directly

Autophagy in cardiomyocyte is involved in myocardial ischemia/reperfusion (M-I/R) injury. Caspase recruitment domain-containing protein 9 (CARD9) plays a critical role in cardiovascular diseases (CVDs) such as hypertension and cardiac fibrosis. However, its role in autophagy following M-I/R injury is yet to be fully elucidated. Here, we found that CARD9 expression increased in M-I/R mouse hearts, and in H9c2 or neonatal rat ventricular myocytes (NRVMs) in response to hypoxia/reoxygenation (H/R) or H₂O₂. CARD9^-/- mice exhibited a significant cardiac dysfunction following M-I/R injury (30 min of left ascending coronary (LAD) ischemia and 12 h of reperfusion) compared to wild-type (WT) mice. CARD9 deletion impaired autophagy during M-I/R in vivo and in vitro, evidenced by decrease of microtubule-associated protein 1 light chain 3 (LC3) lipidation and p62 accumulation. Conversely, CARD9 overexpression increased autophagic flux as indicated by enhanced expression of LC3 II/LC3 I and a reduction in p62. The protective effect of CARD9 on cardiomyocytes against H/R-induced oxidative stress was abolished by treatment with autophagy inhibitors, 3-methyladenine (3-MA) or Bafilomycin A1(BafA1). CARD9 interacted with RUN domain Beclin-1-interacting cysteine-rich-containing (Rubicon), a negative regulator of autophagy, and enhanced UV-irradiation-resistance-associated gene (UVRAG)-Beclin1-phosphatidylinositol 3-kinase catalytic subunit type 3 (PI3KC3) interaction and UVRAG-Vps16-mediated Rab7 activation to promote autophagosome formation, maturation, and endocytosis. Ablation of Rubicon by siRNA effectively prevented the detrimental effect of CARD9 knockdown on cardiomyocytes. These results suggest that CARD9 has protective effects on the myocardium against M-I/R injury by activating autophagy and restoring autophagic flux in vivo and in vitro.

Inhibiting nucleolin reduces inflammation induced by mitochondrial DNA in cardiomyocytes exposed to hypoxia and reoxygenation

BACKGROUND AND PURPOSE

Cellular debris causes sterile inflammation after myocardial infarction. Mitochondria constitute about 30 percent of the human heart. Mitochondrial DNA (mtDNA) is a damage-associated-molecular-pattern that induce injurious sterile inflammation. Little is known about mtDNA's inflammatory signalling pathways in cardiomyocytes and how mtDNA is internalized to associate with its putative receptor, toll-like receptor 9 (TLR9).

EXPERIMENTAL APPROACH

We hypothesized that mtDNA can be internalized in cardiomyocytes and induce an inflammatory response. Adult mouse cardiomyocytes were exposed to hypoxia-reoxygenation and extracellular DNA. Microscale thermophoresis was used to demonstrate binding between nucleolin and DNA.

KEY RESULTS

Expression of the pro-inflammatory cytokines IL-1β and TNFα were upregulated by mtDNA, but not by nuclear DNA (nDNA), in cardiomyocytes exposed to hypoxia-reoxygenation. Blocking the RNA/DNA binding protein nucleolin with midkine reduced expression of IL-1β/TNFα and the nucleolin inhibitor AS1411 reduced interleukin-6 release in adult mouse cardiomyocytes. mtDNA bound 10-fold stronger than nDNA to nucleolin. In HEK293-NF-κB reporter cells, mtDNA induced NF-κB activity in normoxia, while CpG-DNA and hypoxia-reoxygenation, synergistically induced TLR9-dependent NF-κB activity. Protein expression of nucleolin was found in the plasma membrane of cardiomyocytes and inhibition of nucleolin with midkine inhibited cellular uptake of CpG-DNA. Inhibition of endocytosis did not reduce CpG-DNA uptake in cardiomyocytes.

CONCLUSION AND IMPLICATIONS

mtDNA, but not nDNA, induce an inflammatory response in mouse cardiomyocytes during hypoxia-reoxygenation. In cardiomyocytes, nucleolin is expressed on the membrane and blocking nucleolin reduce inflammation. Nucleolin might be a therapeutic target to prevent uptake of immunogenic DNA and reduce inflammation.

LINKED ARTICLES

This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

CARD9 inhibits mitochondria-dependent apoptosis of cardiomyocytes under oxidative stress via interacting with Apaf-1

Cardiomyocyte apoptosis is known to contribute to myocardial ischemia/reperfusion (I/R) injury. Caspase recruitment domain-containing protein 9 (CARD9) play a role in cardiac fibrosis and dysfunction. However, the role of CARD9 in apoptosis of cardiomyocytes in myocardial I/R injury and its underlying mechanisms are still unclear. In this study, CARD9 expression was found to increase in H9c2 cells in response to hydrogen peroxide. Loss of CARD9 significantly increased caspase-3 activation and cardiomyocyte death following oxidative stress in vitro. Conversely, CARD9 overexpression decreased apoptosis as evidenced by a reduction in caspase-3 activation and the apoptotic rate. The caspase recruitment domain (CARD) of CARD9 was necessary for the protective effect of CARD9 against oxidative stress in cardiomyocytes. CARD9 suppressed the activation of caspase-9 by interacting with Apaf-1 via its CARD domain in H9c2 cells exposed to H₂O₂. Ablation of caspase-9 activity by z-lehd-fmk effectively prevented the detrimental effect of CARD9 deficiency on cardiomyocytes. Wild-type (WT) and CARD9^-/- mice were subjected to 30 min of left ascending coronary (LAD) ischemia and 12 h of reperfusion. TdT-mediated dUTP nick end labeling (TUNEL) staining analysis showed that CARD9^-/- mice exhibited a significantly higher number of apoptotic-positive cells after myocardial I/R injury than the WT mice. These results suggest that CARD9 protects cardiomyocytes from apoptosis by interacting with Apaf-1 and interfering with apoptosome formation following myocardial I/R injury in vivo and in vitro.

Phosphorylation of nucleolin is indispensable to upregulate miR-21 and inhibit apoptosis in cardiomyocytes

Nucleolin is a multifunctional phosphoprotein and is involved in protecting from myocardial ischemia/reperfusion (I/R) injury. The function of nucleolin is regulated by posttranslational modifications, including phosphorylation and glycosylation. To study whether phosphorylation of nucleolin (P-nucleolin) was involved in the protection from myocardial I/R injury. We investigated the expression pattern of P-nucleolin (Thr-76 and 84) in hearts subjected to I/R injury, or rat cardiac myoblast cells (H9C2) subjected to hydrogen peroxide (H 2 O 2 ). The results showed that the expression of P-nucleolin and the ratio of P-nucleolin/nucleolin were significantly increased both in vivo and in vitro. Mutant nucleolin was obtained by site directed mutagenesis in vitro: threonine at 76 and 84 was replaced by alanine, and we found that the protective effect of nucleolin on apoptosis induced by oxidative stress was dependent on its phosphorylation at 76 and 84 in H9C2 cells. Furthermore, the cardio-protective roles of P-nucleolin (Thr-76 and 84) in H9C2 cardiomyocytes, were attributable to the upregulation of microRNA (miR)-21. Further analysis found that P-nucleolin (Thr-76 and 84) could bind to miR-21, and P-nucleolin colocalized with argonaute 2 (Ago2) in cytoplasm and could interact with Ago2 in a RNA-independent manner under cell oxidative stress. The current study revealed that P-nucleolin (Thr-76 and 84) increased in I/R injury myocardium, P-nucleolin was indispensable to upregulate miR-21 and inhibited apoptosis induced by H 2 O 2 in H9C2 cardiomyocytes. These findings provided new insight into the molecular mechanisms of nucleolin in myocardial I/R injury and oxidative stress cells.

Heat Shock Proteins: Protection and Potential Biomarkers for Ischemic Injury of Cardiomyocytes After Surgery

The heat shock proteins are endogenous proteins with the ability to act as molecular chaperones. Methods that provide cell protection by way of some damage can positively influence the results of surgery. The present review summarizes current knowledge concerning the cardioprotective role of the heat shock proteins as occurs in heart damage, including relevant information about the stresses that regulate the expression of these proteins and their potential role as biomarkers of heart disease.

Nucleolin protects against doxorubicin-induced cardiotoxicity via upregulating microRNA-21

Nucleolin is a multifunctional protein and participates in many important biological processes. Our previous study found that nucleolin protects the heart against myocardial ischemia-reperfusion injury. In this study, we aimed to investigate the role of nucleolin in doxorubicin (DOX)-induced cardiotoxicity. The expression pattern of nucleolin in hearts subjected to DOX injury was investigated, and we found that administration of DOX induced nucleolin expression significantly in vivo and in vitro. Gene transfection and RNA interference approaches were used in cardiomyocytes to investigate the function of nucleolin. Nucleolin overexpression protects cardiomyocytes against DOX-induced injury. Nucleolin-ablated cardiomyocytes become susceptible to the injury induced by DOX. The hearts of cardiac-myocyte-specific nucleolin transgenic mice are more resistant to DOX injury. Furthermore, nucleolin upregulates microRNA(miRNA)-21 expression in vivo and in vitro, and the miRNA-21 inhibitor negates the protective effect of nucleolin against injury induced by DOX. These results have demonstrated that nucleolin is involved in the regulation of DOX-induced cardiac injury and dysfunction via the regulation of miRNA-21 expression, and may be a novel therapeutic target for DOX-induced cardiotoxicity.

Nucleolin mediated pro-angiogenic role of Hydroxysafflor Yellow A in ischaemic cardiac dysfunction: Post-transcriptional regulation of VEGF-A and MMP-9

Hydroxysafflor Yellow A (HSYA), a most representative ingredient of Carthamus tinctorius L., had long been used in treating ischaemic cardiovascular diseases in China and exhibited prominently anticoagulant and pro-angiogenic activities, but the underlying mechanisms remained largely unknown. This study aimed to further elucidate the pro-angiogenic effect and mechanism of HSYA on ischaemic cardiac dysfunction. A C57 mouse model of acute myocardial infarction (AMI) was firstly established, and 25 mg/kg HSYA was intraperitoneally injected immediately after operation and given once, respectively, each morning and evening for 2 weeks. It was found that HSYA significantly improved ischaemia-induced cardiac haemodynamics, enhanced the survival rate, alleviated the myocardial injury and increased the expressions of CD31, vascular endothelial growth factor-A (VEGF-A) and nucleolin in the ischaemic myocardium. In addition, HSYA promoted the migration and tube formation of human umbilical vein endothelial cells (HUVECs), enhanced the expressions of nucleolin, VEGF-A and matrix metalloproteinase-9 (MMP-9) in a dose- and time-dependent manner. However, down-regulation of nucleolin expression sharply abrogated the effect mentioned above of HSYA. Further protein-RNA coimmunoprecipitation and immunoprecipitation-RT-PCR assay showed that nucleolin binded to VEGF-A and MMP-9 mRNA and overexpression of nucleolin up-regulated the mRNA expressions of VEGF-A and MMP-9 in the HUVECs through enhancing the stability of VEGF-A and MMP-9 mRNA. Furthermore, HSYA increased the mRNA expressions of VEGF-A and MMP-9 in the extract of antinucleolin antibody-precipitated protein from the heart of AMI mice. Our data revealed that nucleolin mediated the pro-angiogenic effect of HSYA through post-transcriptional regulation of VEGF-A and MMP-9 expression, which contributed to the protective effect of HSYA on ischaemic cardiac dysfunction.

MicroRNA Profiling of Transgenic Mice with Myocardial Overexpression of Nucleolin

BACKGROUND

Nucleolin (NCL) is the most abundant RNA-binding protein in the cell nucleolus and plays an important role in chromatin stability, ribosome assembly, ribosomal RNA maturation, ribosomal DNA transcription, nucleocytoplasmic transport, and regulation of RNA stability and translation efficiency. In addition to its anti-apoptotic properties, the underlying mechanisms associated with NCL-related roles in different cellular processes remain unclear. In this study, the effect of NCL on microRNA (miRNA) expression was evaluated by generating transgenic mice with myocardial overexpression of NCL and by analyzing microarrays of mature and precursor miRNAs from mice.

METHODS

Using microinjection of alpha-MyHc clone 26-NCL plasmids, we generated transgenic mice with myocardial overexpression of NCL firstly, and then mature and precursor miRNAs expression profiles were analyzed in NCL transgenic mice (n = 3) and wild-type (WT) mice (n = 3) by miRNA microarrays. Statistical Package for the Social Sciences version 16.0 software (SPSS, Inc., Chicago, IL, USA) was used to perform Student's t-test, and statistical significance was determined at P < 0.05.

RESULTS

Several miRNAs were found to be differentially expressed, of which 11 were upregulated and 4 were downregulated in transgenic mice with myocardial overexpression of NCL compared to those in WT mice. Several differentially expressed miRNAs were subsequently confirmed and quantified by real-time quantitative reverse transcription-polymerase chain reaction. Bioinformatics analysis was used for the prediction of miRNA targets. Furthermore, in vitro experiments showed that NCL regulated miR-21 expression following hydrogen peroxide preconditioning.

CONCLUSIONS

Myocardial-protection mechanisms exerted by NCL might be mediated by the miRNAs identified in this study.

MicroRNA-126a-5p enhances myocardial ischemia-reperfusion injury through suppressing Hspb8 expression

Previously, we found several genes are involved in myocardial ischemia-reperfusion (M-I/R) injury. In this report, we first developed a mouse model of M-I/R injury and demonstrated microRNA-126a-5p was associated with the M-I/R injury by using high-throughput microRNA expression analysis. We further investigated the expression and function of microRNA-126a-5p during mouse M-I/R injury. We observed high expression of microRNA-126a-5p in the M-I/R mice and increased levels of LDH and CK-MB (damage markers) in the serum. H₂O₂ and hypoxia/reoxygenation (H/R) treatment significantly increased the expression of microRNA-126a-5p in H9C2 cells in concentration- and time-dependent manners. Moreover, microRNA-126a-5p overexpression in H9C2 cells inhibited cell viability but increased LDH release and caspase 3 activity. Cardiac function analysis based on the measurements of hemodynamic parameters showed that microRNA-126a-5p expression ablation in M-I/R injured mice led to the reversal of the symptoms caused by M-I/R injury. Transesophageal echocardiography also revealed that the values of LVIDd and LVIDs were decreased while the values of LVFS% and LVEF% were increased in M-I/R injured mice after treatment with microRNA-126a-5p inhibitor, compared with the M-I/R injured mice treated with the control. Bioinformatic analysis demonstrated that Hspb8, a protective protein in myocardium, was the target of microRNA-126a-5p. Thus, these findings indicated that microRNA-126a-5p was up-regulated in mouse M-I/R model and promoted M-I/R injury in vivo through suppressing the expression of Hspb8, which may shed light on the development of potential therapeutic target for M-I/R injury.

Nucleolin protects macrophages from oxLDL-induced foam cell formation through up-regulating ABCA1 expression

Our recent studies have indicated that nucleolin, as a multifunctional RNA-binding protein, exerts protective effects in the myocardial cells and endothelial cells under the condition of oxidative stress. However, the function of nucleolin and its potential mechanism in macrophage-derived foam cell formation remain largely unexplored. ApoE-/- mice were fed with a high-fat diet (HFD) for 10-24 weeks. Protein expression was measured by western blotting or immunofluorescence, and gene expression at the mRNA level was detected by qRT-PCR. The level of lipid in macrophages was examined by Oil Red O staining, high-performance liquid chromatography (HPLC) and NBD-cholesterol. Actinomycin D (Act D) was used to determine the stability of ABCA1 mRNA in macrophages. The interaction of nucleolin with ABCA1 mRNA was assessed using co-immunoprecipitation (co-IP). The aortas advanced plaques demonstrated significantly lower levels of nucleolin protein compared with early plaques in ApoE-/- mice, in which the macrophage foam cells occupied main body. Nucleolin expression at the mRNA and protein levels in RAW264.7 macrophages was significantly reduced by oxidized low-density lipoprotein (oxLDL) in a dose- and time-dependent manner. Furthermore, nucleolin overexpression markedly attenuated lipid accumulation in oxLDL-challenged macrophages through increasing cholesterol efflux. In addition, nucleolin overexpression significantly increased the expression of ATP-binding cassette transporter A1 (ABCA1) at the mRNA and protein levels without affecting expressions of scavenger receptors (SR)-A, SR-B1, CD36 and ATP-binding cassette transporter G1 (ABCG1) at the mRNA level. Moreover, nucleolin overexpression increased the stability of ABCA1 mRNA in macrophages, whereas nucleolin ablation abrogated the oxLDL-induced up-regulation of ABCA1. The up-regulation of ABCA1 by nucleolin resulted from its protein-RNA interaction. Our data suggested that nucleolin inhibited foam cell formation through enhancing stability of ABCA1 mRNA and subsequently increasing cholesterol efflux.

Neuroprotective Efficacy of an Aminopropyl Carbazole Derivative P7C3-A20 in Ischemic Stroke

AIM

NAMPT is a novel therapeutic target of ischemic stroke. The aim of this study was to investigate the effect of a potential NAMPT activator, P7C3-A20, an aminopropyl carbazole derivative, on ischemic stroke.

METHODS

In vitro study, neuron protection effect of P7C3-A20 was investigated by co-incubation with primary neurons subjected to oxygen-glucose deprivation (OGD) or oxygen-glucose deprivation/reperfusion (OGD/R) injury. In vivo experiment, P7C3-A20 was administrated in middle cerebral artery occlusion (MCAO) rats and infarct volume was examined. Lastly, the brain tissue nicotinamide adenine dinucleotide (NAD) levels were detected in P7C3-A20 treated normal or MCAO mice.

RESULTS

Cell viability, morphology, and Tuj-1 staining confirmed the neuroprotective effect of P7C3-A20 in OGD or OGD/R model. P7C3-A20 administration significantly reduced cerebral infarction in MCAO rats. Moreover, brain NAD levels were elevated both in normal and MCAO mice after P7C3-A20 treatment.

CONCLUSIONS

P7C3-A20 has neuroprotective effect in cerebral ischemia. The study contributes to the development of NAMPT activators against ischemic stroke and expands the horizon of the neuroprotective effect of aminopropyl carbazole chemicals.

Protective effect of soluble eggshell membrane protein hydrolysate on cardiac ischemia/reperfusion injury

BACKGROUND

Soluble eggshell membrane protein (SEP) has been proved to hold the antioxidant activity. The functional role of SEP on cardioprotection was investigated in vivo and in vitro.

METHODS

Rats and cardiomyocytes were pretreated with SP2, a hydrolysate attained from SEP, and then subjected to ischemia/reperfusion (I/R) or hypoxia/reoxygenation (H/R) and hydrogen peroxide, respectively. The measurement of myocardial infarct size, cell apoptosis assay, cell viability assay, and caspase activity assay were performed on rats and cardiomyocytes.

RESULTS

The results showed that the treatment of SP2 induced the resistance to I/R or H/R injury on rats and cardiomyocytes as indicated by decreased infarct size and decreased cellular apoptosis. The cardioprotective roles of SP2 were partly resulted from the downregulated expression and activity of caspase-3 in which the effect was similar to the caspase inhibitor, z-VAD-fmk, and could be rescued by caspase activator, PAC-1.

CONCLUSIONS

This investigation has demonstrated that SP2 attenuated the damage of I/R and H/R on rats and cardiomyocytes by the caspase-dependent pathway. This cardioprotective effect of SP2 suggested a novel therapeutic agent of SEP for ischemic-related heart diseases.

Nucleolin enhances the proliferation and migration of heat-denatured human dermal fibroblasts

Denatured dermis, a part of dermis in burned skin, has the ability to restore its normal morphology and functions after their surrounding microenvironment is improved. However, the cellular and molecular mechanisms by which the denatured dermis could improve wound healing are still unclear. This study aimed to investigate the role of nucleolin during the recovery of heat-denatured human dermal fibroblasts. Nucleolin mRNA and protein expression were significantly increased time-dependently during the recovery of heat-denatured human dermal fibroblasts (52 °C, 30 seconds). Heat-denaturation promoted a time-dependent cell proliferation, migration, chemotaxis, and scratched wound healing during the recovery of human dermal fibroblasts. These effects were prevented by knockdown of nucleolin expression with small interference RNA (siRNA), whereas overexpression of nucleolin enhanced cell proliferation, migration, and chemotaxis of human dermal fibroblasts with heat-denaturation. In addition, the expression of transforming growth factor-beta 1(TGF-β1) was significantly increased during the recovery of heat-denatured dermis and human dermal fibroblasts. TGF-β1 expression was up-regulated by nucleolin in human dermal fibroblasts. The results suggest that nucleolin expression is up-regulated, and play an important role in promoting cell proliferation, migration, and chemotaxis of human dermal fibroblasts during the recovery of heat-denatured dermis with a mechanism probably related to TGF-β1.

MiR-21 Protected Cardiomyocytes against Doxorubicin-Induced Apoptosis by Targeting BTG2

Doxorubicin (DOX) is an anthracycline drug with a wide spectrum of antineoplastic activities. However, it causes cardiac cytotoxicity, and this limits its clinical applications. MicroRNA-21 (miR-21) plays a vital role in regulating cell proliferation and apoptosis. While miR-21 is preferentially expressed in adult cardiomyocytes and involved in cardiac development and heart disease, little is known regarding its biological functions in responding to DOX-induced cardiac cytotoxicity. In this study, the effects of DOX on mouse cardiac function and the expression of miR-21 were examined in both mouse heart tissues and rat H9C2 cardiomyocytes. The results showed that the cardiac functions were more aggravated in chronic DOX injury mice compared with acute DOX-injury mice; DOX treatment significantly increased miR-21 expression in both mouse heart tissue and H9C2 cells. Over-expression of miR-21 attenuated DOX-induced apoptosis in cardiamyocytes whereas knocking down its expression increased DOX-induced apoptosis. These gain- and loss- of function experiments showed that B cell translocation gene 2 (BTG2) was a target of miR-21. The expression of BTG2 was significantly decreased both in myocardium and H9C2 cells treated with DOX. The present study has revealed that miR-21 protects mouse myocardium and H9C2 cells against DOX-induced cardiotoxicity probably by targeting BTG2.

Stressing on the nucleolus in cardiovascular disease

The nucleolus is a multifunctional organelle with multiple roles involving cell proliferation, growth, survival, ribosome biogenesis and stress response signaling. Alteration of nucleolar morphology and architecture signifies an early response to increased cellular stress. This review briefly summarizes nucleolar response to cardiac stress signals and details the role played by nucleolar proteins in cardiovascular pathophysiology. This article is part of a Special Issue entitled: Role of the Nucleolus in Human Disease.

Extracellular visfatin has nicotinamide phosphoribosyltransferase enzymatic activity and is neuroprotective against ischemic injury

AIM

Visfatin, a novel adipokine, is predominantly produced by visceral adipose tissue and exists in intracellular and extracellular compartments. The intracellular form of visfatin is proved to be nicotinamide phosphoribosyltransferase (NAMPT) and exhibits neuroprotection through maintaining intracellular NAD(+) pool. However, whether extracellular form of visfatin has NAMPT activity and the effect of extracellular visfatin in cerebral ischemia are unknown.

METHODS AND RESULTS

Plasma concentrations of visfatin, NAD(+) , and ATP were increased in mice upon cerebral ischemia. Cultured glia, but not neuron, was able to secrete visfatin. Oxygen-glucose deprivation (OGD) stress increased the secretion of visfatin from glia. Extracellular recombinant mouse wild-type visfatin, but not mouse H247A-mutant enzymatic-dead visfatin, had NAMPT enzymatic function in vitro. Treatment of wild-type visfatin, but not H247A-mutant enzymatic-dead visfatin, significantly attenuated detrimental effect of OGD on the cell viability and apoptosis in both cultured mouse neuron and glia. Treatment of neutralizing antibody, abolished the protective effect of extracellular visfatin on cell viability, but failed to block the antiapoptotic effect of extracellular visfatin. At last, we observed that plasma visfatin concentrations decreased in 6-month-old but not 3-month-old SHR-SP compared with that in age-matched Wistar-Kyoto rats. Inhibition of NAMPT enzymatic function of visfatin (by FK866) accelerated the occurrence of stroke in SHR-SP.

CONCLUSIONS

Extracellular visfatin has NAMPT enzymatic activity and maybe be neuroprotective just as intracellular visfatin in cerebral ischemic injury.

Nucleolin involved in myocardial ischaemic preconditioning via post-transcriptional control of HSPA1A expression

AIMS

Recent studies have identified the critical roles of nucleolin in a variety of cellular processes, including regulation of viral replication and tumour formation. However, the possible roles of nucleolin in myocardial preconditioning remain undefined.

METHODS AND RESULTS

We used an in vivo rat myocardial ischaemic preconditioning (IP) model (four cycles of 5 min ischaemia and 10 min reperfusion) and cellular hydrogen peroxide preconditioning (H2O2-PC) models. We found that nucleolin mRNA and protein expression showed a time-dependent increase during the recovery of myocardial ischaemic preconditioning in rats and H2O2-PC in neonatal rat cardiomyocytes. Nucleolin overexpression enhanced the protective effects of H2O2-PC, whereas nucleolin ablation abrogated the H2O2-PC-mediated protection in cardiomyocytes. On the other hand, nucleolin overexpression increased the stabilization of the HSPA1A mRNA and the expression of HSPA1A protein in cardiomyocytes, whereas nucleolin ablation abrogated the up-regulation of HSPA1A induced by H2O2-PC in cardiomyocytes. An interaction between nucleolin and HSPA1A mRNA was further identified using the RNA-protein interaction studies. Reporter gene assays, which depended on the untranslated regions (UTR) of HSPA1A mRNA, revealed that the post-transcriptional regulation was mainly attributed to the 3' UTR. Finally, HSPA1A anti-sense oligonucleotides (asODNs) attenuated the protective effect of nucleolin in cardiomyocytes.

CONCLUSION

These results indicate that nucleolin is up-regulated and involved in myocardial protection of ischaemic preconditioning via a post-transcriptional control of HSPA1A expression.

RNA-binding proteins in heart development

RNA-binding proteins (RBPs) are key players of posttranscriptional regulation occurring during normal tissue development. All tissues examined thus far have revealed the importance of RBPs in the regulation of complex networks involved in organ morphogenesis, maturation, and function. They are responsible for controlling tissue-specific gene expression by regulating alternative splicing, mRNA stability, translation, and poly-adenylation. The heart is the first organ form during embryonic development and is also the first to acquire functionality. Numerous remodeling processes take place during late cardiac development since fetal heart first adapts to birth and then undergoes a transition to adult functionality. This physiological remodeling involves transcriptional and posttranscriptional networks that are regulated by RBPs. Disruption of the normal regulatory networks has been shown to cause cardiomyopathy in humans and animal models. Here we review the complexity of late heart development and the current information regarding how RBPs control aspects of postnatal heart development. We also review how activities of RBPs are modulated adding complexity to the regulation of developmental networks.