Cardiac-specific overexpression of E3 ligase Nrdp1 increases ischemia and reperfusion-induced cardiac injury

Nrdp1-mediated Macrophage Phenotypic Regulation Promotes Functional Recovery in Mice with Mild Neurological Impairment after Intracerebral Hemorrhage

Neuregulin receptor degradation protein 1 (Nrdp1) is a ring finger E3 ubiquitin ligase involved in some inflammation through ubiquitination, including macrophage polarization following cerebral hemorrhage. However, there is limited understanding regarding the mechanisms through which Nrdp1 modulates macrophage polarization and the potential impact of this modulation on neurological function. Using stereotactic injection and adenoviral transfection techniques, the corresponding animal models were constructed through injecting adenovirus, saline, or blood into the mouse striatum at different periods of time in this research. The alteration in the ratio of various M1/M2 phenotype-associated markers (e.g., CD86, CD206, IL-6, IL-10, etc.) was evaluated through immunohistochemistry, immunofluorescence, western blotting, and elisa assays. Additionally, neurological function scores and behavioral tests were utilized to evaluate changes in neurological function in mice after cerebral hemorrhage. Our results show that overexpression of Nrdp1 promotes the expression of a variety of M2 macrophage-associated markers and enhance transcriptional activity of arginase-1 (Arg1) protein through ubiquitination for early regulation M2 macrophage polarization. Additionally, Nrdp1 promotes hematoma absorption, increases IL-10 expression, inhibits inducible nitric oxide synthase (iNOS), IL-6, and TNF-α production, alleviates neurological impairment and brain edema, and accelerates functional recovery. These findings suggest that modulating macrophage polarization through Nrdp1 could be a therapeutic strategy for neurofunctional impairment in cerebral hemorrhage.

The E3 ubiquitin ligases regulate inflammation in cardiovascular diseases

Accumulating evidence has illustrated that the E3 ubiquitin ligases critically participate in the development and progression of cardiovascular diseases. Dysregulation of E3 ubiquitin ligases exacerbates cardiovascular diseases. Blockade or activation of E3 ubiquitin ligases mitigates cardiovascular performance. Therefore, in this review, we mainly introduced the critical role and underlying molecular mechanisms of E3 ubiquitin ligase NEDD4 family in governing the initiation and progression of cardiovascular diseases, including ITCH, WWP1, WWP2, Smurf1, Smurf2, Nedd4-1 and Nedd4-2. Moreover, the functions and molecular insights of other E3 ubiquitin ligases, such as F-box proteins, in cardiovascular disease development and malignant progression are described. Furthermore, we illustrate several compounds that alter the expression of E3 ubiquitin ligases to alleviate cardiovascular diseases. Therefore, modulation of E3 ubiquitin ligases could be a novel and promising strategy for improvement of therapeutic efficacy of deteriorative cardiovascular diseases.

ACE2 activation alleviates sepsis-induced cardiomyopathy by promoting MasR-Sirt1-mediated mitochondrial biogenesis

Sepsis-induced cardiomyopathy (SIC), caused by a dysregulated host response to infection, is a major contributor to high mortality. Angiotensin-converting enzyme 2 (ACE2), a crucial component of the renin-angiotensin system (RAS), has protective effects against several cardiovascular diseases, such as myocardial infarction and heart failure. However, the role of ACE2 in the pathogenesis of SIC and underlying mechanisms remain unknown. The present study was designed to examine the effects of ACE2 activation or inhibition on SIC in C57BL/6 mice. The ACE2 activator diminazene aceturate (DIZE) and ACE2 inhibitor MLN-4760 were applied for treatment. Myocardial function, inflammatory response, oxidative stress, apoptosis and mitochondrial biogenesis were investigated. Major assays were echocardiography, H&E staining, immunofluorescence staining, DHE staining, TUNEL staining, Western blot, qPCR analysis, ELISA and corresponding kits. We confirmed that ACE2 was markedly downregulated in septic heart tissues. Pharmacological activation of ACE2 by DIZE ameliorated cecal ligation puncture (CLP)-induced mortality, cardiac dysfunction, inflammatory response, oxidative stress and the cardiomyocyte apoptosis by promoting MasR-Sirt1-mediated mitochondrial biogenesis. In contrast, SIC was aggravated via inhibiting MasR-Sirt1-mediated mitochondrial biogenesis by the use of ACE2 inhibitor MLN-4760. Consequently, activation of ACE2 may protect against SIC by promoting MasR-Sirt1-mediated mitochondrial biogenesis.

Substrate-dependent interaction of SPOP and RACK1 aggravates cardiac fibrosis following myocardial infarction

Speckle-type pox virus and zinc finger (POZ) protein (SPOP), a substrate recognition adaptor of cullin-3 (CUL3)/RING-type E3 ligase complex, is investigated for its role in cardiac fibrosis in our study. Cardiac fibroblasts (CFs) activation was achieved with TGF-β1 (20 ng/mL) and MI mouse model was established by ligation of the left anterior descending coronary, and lentivirus was employed to mediate interference of SPOP expression. SPOP was increased both in fibrotic post-MI mouse hearts and TGF-β1-treated CFs. The gain-of-function of SPOP promoted myofibroblast transformation in CFs, and exacerbated cardiac fibrosis and cardiac dysfunction in MI mice, while the loss-of-function of SPOP exhibited the opposite effects. Mechanistically, SPOP bound to the receptor of activated protein C kinase 1 (RACK1) and induced its ubiquitination and degradation by recognizing Ser/Thr-rich motifs on RACK1, leading to Smad3-mediated activation of CFs. Forced RACK1 expression canceled the effects of SPOP on cardiac fibrosis. The study reveals therapeutic targets for fibrosis-related cardiac diseases.

Resveratrol inhibits autophagy against myocardial ischemia-reperfusion injury through the DJ-1/MEKK1/JNK pathway

Resveratrol (RES), a natural polyphenolic compound found in red wine and grape skins, has attracted significant attention due to its cardioprotective properties. DJ-1, a multifunctional protein that participated in transcription regulation and antioxidant defense, was shown to provide a significant protective impact in cardiac cells treated with ischemia-reperfusion. We created a myocardial ischemia-reperfusion (I/R) model in vivo and in vitro by ligating the left anterior descending branch of rats and subjecting H9c2 cells to anoxia/reoxygenation (A/R) to investigate whether RES reduces myocardial ischemia-reperfusion injury by upregulating DJ-1. We discovered that RES dramatically enhanced cardiac function in rats with I/R. Subsequently, we found that RES prevented the rise in autophagy (P62 degradation and LC3-II/LC3-I increase) induced by cardiac ischemia-reperfusion in vitro and in vivo. Notably, the autophagic agonist rapamycin (RAPA) eliminated RES-induced cardioprotective effects. In addition, Further data showed that RES significantly increased the expression of DJ-1 in the myocardium with the treatment of I/R. At the same time, pretreatment with RES reduced phosphorylation of MAPK/ERK kinase kinase 1 (MEKK1) and Jun N-terminal Kinase (JNK) stimulated by cardiac ischemia-reperfusion, and Beclin-1 mRNA and protein levels while decreasing lactate dehydrogenase (LDH) and improving cell viability. However, the lentiviral shDJ-1 and JNK agonist anisomycin disrupted the effects of RES. In summary, RES could inhibit autophagy against myocardial ischemia-reperfusion injury through DJ-1 modulation of the MEKK1/JNK pathway, providing a novel therapeutic strategy for cardiac homeostasis.

Deficiency of a novel lncRNA-HRAT protects against myocardial ischemia reperfusion injury by targeting miR-370-3p/RNF41 pathway

Accumulating evidence indicates that long non-coding RNAs (lncRNAs) contribute to myocardial ischemia/reperfusion (I/R) injury. However, the underlying mechanisms by which lncRNAs modulate myocardial I/R injury have not been thoroughly examined and require further investigation. A novel lncRNA named lncRNA-hypoxia/reoxygenation (H/R)-associated transcript (lncRNA-HRAT) was identified by RNA sequencing analysis. The expression of lncRNA-HRAT exhibited a significant increase in the I/R mice hearts and cardiomyocytes treated with H/R. LncRNA-HRAT overexpression facilitates H/R-induced cardiomyocyte apoptosis. Furthermore, cardiomyocyte-specific deficiency of lncRNA-HRAT in vivo after I/R decreased creatine kinase (CK) release in the serum, reduced myocardial infarct area, and improved cardiac dysfunction. Molecular mechanistic investigations revealed that lncRNA-HRAT serves as a competing endogenous RNA (ceRNA) of miR-370-3p, thus upregulating the expression of ring finger protein 41 (RNF41), thereby aggravating apoptosis in cardiomyocytes induced by H/R. This study revealed that the lncRNA-HRAT/miR-370-3p/RNF41 pathway regulates cardiomyocyte apoptosis and myocardial injury. These findings suggest that targeted inhibition of lncRNA-HRAT may offer a novel therapeutic method to prevent myocardial I/R injury.

Blockage of Fibronectin 1 Ameliorates Myocardial Ischemia/Reperfusion Injury in Association with Activation of AMP-LKB1-AMPK Signaling Pathway

Myocardial ischemia/reperfusion injury (I/RI) is closely associated with energy substrate metabolism. Fibronectin 1 (Fn1) was markedly elevated in the heart of I/R pigs and ischemic patients, but its role in myocardial I/RI is controversial and the precise mechanism involved remains elusive. Herein, we tested whether blockage of Fn1 with its inhibitor (fibronectin tetrapeptide, RGDS) would alleviate myocardial I/RI. Wild-type (WT) mice were administered with RGDS once 3 h before I/R operation and once at 24 or 48 h postreperfusion, and sacrificed at 24 or 72 h post-I/R, respectively. Cardiac function was evaluated by echocardiography. Myocardial infarction size, apoptosis, fibrosis, and inflammation were examined via histological staining. Uptake of glucose and fatty acids were detected by positron emission tomography (PET) and computer tomography (CT) with [¹⁸F]-2-fluoro-2-deoxy-D-glucose (FDG) and [¹⁸F]-fluoro-6-thia-heptadecanoic acid (FTHA), respectively. Our results showed that administration of RGDS to mice remarkably limited the I/R-induced myocardial infarct size, myocyte apoptosis, inflammation, oxidative stress, and fibrosis and improved cardiac contractile dysfunction. These protective effects were associated with upregulation of the AMP/ATP ratio and the activation of LKB1-AMPK signaling, which subsequently increased AS160-GLUT4-mediated glucose and fatty acid uptake, improved mitochondrial dynamic imbalance, and inactivated TGF-β and NF-κB signals in the I/R heart. In conclusion, the current study identified that blocking Fn1 protects against myocardial I/RI likely through activating the LKB1-AMPK-dependent signals and highlights that inhibition of Fn1 may be a novel therapeutic option for treating ischemic heart diseases.

Long non-coding RNA MIR4435-2HG/microRNA-125a-5p axis is involved in myocardial ischemic injuries

This study aimed to investigate whether and how long non-coding RNA (lncRNA) MIR4435-2 host gene (MIR4435-2HG) involved in acute myocardial ischemia/reperfusion (I/R). Blood samples were collected from acute myocardial infarction (AMI) patients to detect MIR4435-2HG expression. In vivo myocardial I/R mice model and in vitro H₂O₂-induced oxidative stress model were established. Echocardiography, TUNEL assay and lactate dehydrogenase (LDH) detection were performed to assess heart infarction and myocardium apoptosis. Relationship among microRNA-125a-5p (miR-125a-5p), MIR4435-2HG and Mitochondrial fission protein 1 (MTFP1) was predicted by Targetscan and verified by luciferase reporter assay. MIR4435-2HG was notably upregulated in AMI patients, myocardial I/R mice and H₂O₂-treated cells. Knockdown of MIR4435-2HG notably alleviated infraction volume, ejection fraction (EF) and fractional shortening (FS) levels, cell apoptosis portion and pro-apoptotic cleaved-caspase-3 and Cyt c expression caused by myocardial I/R and oxidative stress, as well as improved cardiomyocytes viability. Transfection with miR-125a-5p alleviated MIR4435-2HG-caused cardiomyocytes apoptosis during oxidative stress. MiR-125a-5p overexpression decreased luciferase activity of the wild-type MIR4435-2HG compared with the mutated MIR4435-2HG. The expression levels of MTFP1 were elevated in myocardium from MI mice model and H₂O₂-treated AC16 cardiomyocytes. In addition, miR-125a-5p overexpression inhibited MTFP1 expression, and could stimulate the wild-type MTFP1 promoter luciferase activity but not the mutated one. Our findings revealed the role of MIR4435-2HG in MI-induced myocardium injury and cardiomyocytes apoptosis, disclosed a novel MIR4435-2HG/miR-125a-5p regulatory axis during myocardial I/R, and thus identified a potential target for the therapy of myocardial IR injury.

The Role of Epidermal Growth Factor Receptor Family of Receptor Tyrosine Kinases in Mediating Diabetes-Induced Cardiovascular Complications

Diabetes mellitus is a major debilitating disease whose global incidence is progressively increasing with currently over 463 million adult sufferers and this figure will likely reach over 700 million by the year 2045. It is the complications of diabetes such as cardiovascular, renal, neuronal and ocular dysfunction that lead to increased patient morbidity and mortality. Of these, cardiovascular complications that can result in stroke and cardiomyopathies are 2- to 5-fold more likely in diabetes but the underlying mechanisms involved in their development are not fully understood. Emerging research suggests that members of the Epidermal Growth Factor Receptor (EGFR/ErbB/HER) family of tyrosine kinases can have a dual role in that they are beneficially required for normal development and physiological functioning of the cardiovascular system (CVS) as well as in salvage pathways following acute cardiac ischemia/reperfusion injury but their chronic dysregulation may also be intricately involved in mediating diabetes-induced cardiovascular pathologies. Here we review the evidence for EGFR/ErbB/HER receptors in mediating these dual roles in the CVS and also discuss their potential interplay with the Renin-Angiotensin-Aldosterone System heptapeptide, Angiotensin-(1-7), as well the arachidonic acid metabolite, 20-HETE (20-hydroxy-5, 8, 11, 14-eicosatetraenoic acid). A greater understanding of the multi-faceted roles of EGFR/ErbB/HER family of tyrosine kinases and their interplay with other key modulators of cardiovascular function could facilitate the development of novel therapeutic strategies for treating diabetes-induced cardiovascular complications.

GPCR-ErbB transactivation pathways and clinical implications

Cell surface receptors including the epidermal growth factor receptor (EGFR) family and G-protein coupled receptors (GPCRs) play quintessential roles in physiology, and in diseases, including cardiovascular diseases. While downstream signaling from these individual receptor families has been well studied, the cross-talk between EGF and GPCR receptor families is still incompletely understood. Including members of both receptor families, the number of receptor and ligand combinations for unique interactions is vast, offering a frontier of pharmacologic targets to explore for preventing and treating disease. This molecular cross-talk, called receptor transactivation, is reviewed here with a focus on the cardiovascular system featuring the well-studied GPCR receptors, but also discussing less-studied receptors from both families for a broad understanding of context of expansile interactions, repertoire of cellular signaling, and disease consequences. Attention is given to cell type, level of chronicity, and disease context given that transactivation and comorbidities, including diabetes, hypertension, coronavirus infection, impact cardiovascular disease and health outcomes.

LncRNA AK020546 protects against cardiac ischemia-reperfusion injury by sponging miR-350-3p

Long non-coding RNAs (lncRNAs) have been implicated in the development of cardiovascular diseases. We observed that lncRNA AK020546 was downregulated following ischemia/reperfusion injury to the myocardium and following H2O2 treatment in H9c2 cardiomyocytes. In vivo and in vitro studies showed that AK020546 overexpression attenuated the size of the ischemic area, reduced apoptosis among H9c2 cardiomyocytes, and suppressed the release of reactive oxygen species, lactic acid dehydrogenase, and malondialdehyde. AK020546 served as a competing endogenous RNA for miR-350-3p and activated the miR-350-3p target gene ErbB3. MiR-350-3p overexpression reversed the effects of AK020546 on oxidative stress injury and apoptosis in H9c2 cardiomyocytes. Moreover, ErbB3 knockdown alleviated the effects of AK020546 on the expression of ErbB3, Bcl-2, phosphorylated AKT, cleaved Caspase 3, and phosphorylated Bad. These findings suggest lncRNA AK020546 protects against ischemia/reperfusion and oxidative stress injury by sequestering miR-350-3p and activating ErbB3, which highlights its potential as a therapeutic target for ischemic heart diseases.

Baicalin regulates macrophages polarization and alleviates myocardial ischaemia/reperfusion injury via inhibiting JAK/STAT pathway

CONTEXT

Baicalin is an active compound which demonstrates cardioprotection effects against myocardial ischaemia/reperfusion injury (MI/RI).

OBJECTIVE

To investigate how baicalin protects against myocardial injury and to explore its potential mechanism. We hypothesized that baicalin-modulated macrophages change from M1 (pro-inflammatory subset) to M2 (anti-inflammatory subset) under I/R stress.

MATERIALS AND METHODS

We established an ischaemia/reperfusion (I/R) model using Sprague Dawley (SD) rat, then baicalin was intragastric administration (20, 60 or 120 mg/kg) for 24 h. The rats were randomly divided into five groups (n = 10): control, I/R, I/R + baicalin (20 mg/kg), I/R + baicalin (60 mg/kg) and I/R + baicalin (120 mg/kg). Cardiac function was detected by echocardiography, HE staining and ELISA, respectively. Macrophage phenotype was examined by flow cytometry. Furthermore, IHC, qRT-PCR and WB were employed to analyse the related mechanisms.

RESULTS

The study showed that baicalin (20, 60 or 120 mg/kg) significantly improved cardiac function and impeded cardiac apoptosis in rats. In addition, the repair of myocardial morphology (reduced neutrophil infiltration) further confirmed its cardiacprotective effect. Moreover, baicalin effectively decreased iNOS, IL-1β and IL-6, and up-regulated Arg-1, IL-10 and TGF-β via changing the macrophage phenotype (from M1 towards M2). Notably, treatment with baicalin also inhibited the phosphorylation levels of JAK2 and STAT3. Discussion and conclusions: It was confirmed that baicalin alleviated post-I/R myocardial injury and reduced inflammation via JAK/STAT pathway, and baicalin treatment might be recommended as a new approach for myocardial ischaemic complications.

Quantitative proteomics and phosphoproteomic analyses of mouse livers after tick-borne Babesia microti infection

Babesia microti is a tick-borne protozoan parasite that infects the red blood cells of mice, humans, and other mammals. The liver tissues of BALB/c mice infected with B. microti exhibit severe injury. To further investigate the molecular mechanisms underlying liver injury and liver self-repair after B. microti infection, data-independent acquisition (DIA) quantitative proteomics was used to analyse changes in the expression and phosphorylation of proteins in liver tissues of BALB/c mice during a B. microti infection period and a recovery period. The expression of FABP1 and ACBP, which are related to fatty acid transport in the liver, was downregulated after infection with B. microti, as was the expression of Acox1, Ehhadh and Acaa1a, which are crucial rate-limiting enzymes in the process of fatty acid β oxidation. The phosphorylation levels of AMP-activated protein kinase (AMPK) and Hormone-sensitive lipase (HSL) were also downregulated. In addition, the expression of PSMB9, CTSC, and other immune-related proteins was increased, reflecting an active immune regulation mechanism in the mice. The weights of mice infected with B. microti were significantly reduced, and the phosphorylation levels of IRS-1, c-Raf, mTOR, and other proteins related to growth and development were downregulated.

E3-ubiquitin ligase TRIM6 aggravates myocardial ischemia/reperfusion injury via promoting STAT1-dependent cardiomyocyte apoptosis

Cardiomyocyte apoptosis is a major cause of myocardial ischemia/reperfusion (MI/R) injury, in which the activation of the signal transducer and activator of transcription 1 (STAT1) plays an important role. The E3-ubiquitin ligase TRIM6 has been implicated in regulating STAT1 activity, however, whether it is associated with MI/R injury and the underlying mechanism are not determined. In this study, by investigating a mouse MI/R injury model, we show that TRIM6 expression is induced in mouse heart following MI/R injury. Additionally, TRIM6 depletion reduces and its overexpression increases myocardial infarct size, serum creatine phosphokinase (CPK) level and cardiomyocyte apoptosis in mice subjected to MI/R injury, indicating that TRIM6 functions to aggravate MI/R injury. Mechanistically, TRIM6 promotes IKKε-dependent STAT1 activation, and the inhibition of IKKε or STAT1 with the specific inhibitor, CAY10576 or fludarabine, abolishes TRIM6 effects on cardiomyocyte apoptosis and MI/R injury. Similarly, TRIM6 mutant lacking the ability to ubiquitinate IKKε and induce IKKε/STAT1 activation also fails to promote cardiomyocyte apoptosis and MI/R injury. Thus, these results suggest that TRIM6 aggravates MI/R injury through promoting IKKε/STAT1 activation-dependent cardiomyocyte apoptosis, and that TRIM6 might represent a novel therapeutic target for alleviating MI/R injury.

Role of the Nrdp1 in Brain Injury Induced by Chronic Intermittent Hypoxia in Rats via Regulating the Protein Levels of ErbB3

Obstructive sleep apnea syndrome (OSAS) is known as a repeated obstruction of the upper airway during sleep, leading to generalized hypoxia episodes and associated with cardiovascular and cerebrovascular diseases. We mainly explored the role of neuregulin receptor degradation protein-1 (Nrdp1, also known as FLRF) in brain injury induced by chronic intermittent hypoxia (CIH) in rats. Wistar rats were randomly divided into 4 groups (n = 12 per group), including the sham + adeno-associated virus-NC (AAV-NC) group, the sham + AAV-siNrdp1 group, the IH-4w (intermittent hypoxia for 4 weeks) + AAV-NC group, and the IH-4w + AAV-siNrdp1 group. Morphologic changes in brain tissue were observed by hematoxylin and eosin (HE) staining. Apoptosis in the hippocampus was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining. Spatial learning and memory were assessed by the Morris water maze test. The expression of Nrdp1 mRNA and protein in the hippocampus was detected by qualitative real-time polymerase chain reaction (qRT-PCR) and Western blotting. The concentration of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in serum was detected via enzyme-linked immunosorbent assay (ELISA) kits. Nrdp1 expression was increased after intermittent hypoxia exposure over time. Western blotting and H&E results showed that pathological changes of hippocampus neurons in chronic intermittent hypoxia rat were diminished by shNrdp1. Western blotting and TUNEL staining showed that apoptotic cells in the hippocampus of CIH rats were decreased by shNrdp1. The Morris water maze results proved that shNrdp1 improved spatial learning performance of chronic intermittent hypoxia rats. ELISA kits results showed that CIH-induced inflammatory response was decreased by shNrdp1. Western blotting and qRT-PCR results showed protein expression of ErbB3 in the hippocampus of CIH rats. Nrdp1 could regulate ErbB3 protein levels in brain-injured rats with CIH, which demonstrates that Nrdp1 is a potential therapeutic target in the cognition deficits associated with OSAS.

Downregulation of miR-3568 Protects Against Ischemia/Reperfusion-Induced Cardiac Dysfunction in Rats and Apoptosis in H9C2 Cardiomyocytes Through Targeting TRIM62

microRNA-3568 (miR-3568) has been reported to be associated with atherosclerosis. Only few data describe the expression and underlying mechanism of miR-3568 in regulating cardiac ischemia-reperfusion (I/R) injury such as apoptosis. In this study, we therefore sought to investigate the potential function of miR-3568 in simulated I/R-induced apoptosis in H9C2 cardiomyocytes and related signaling pathways involved. Flow cytometry was performed to examine the cell apoptosis. The expression of miR-3568, Survivin, Bcl-2, ERK, JNK, p38, AKT, and STAT3 was measured by western blot and quantitative real-time PCR. The correlation between TRIM62 and p-STAT3 was measured by co-immunoprecipitation and ubiquitination. We found that miR-3568 expression in simulated I/R-induced H9C2 cardiomyocytes was increased in a time-dependent manner. miR-3568 mimic transfection in H9C2 cardiomyocytes significantly enhanced cell apoptosis, decreased the expression of Bcl-2 and Survivin, and activated STAT3 signaling, which were reversed by miR-3568 inhibitor. The direct interaction between miR-3568 and the 3'-untranslated region (UTR) of TRIM62 mRNA was confirmed by dual-luciferase reporter assay. TRIM62 overexpression or AG490, a selective inhibitor of JAK2/STAT3 significantly, significantly inhibited I/R and miR-3568 mimic induced cell apoptosis and STAT3 activation. TRIM62 was found to interact with and induce ubiquitination of p-STAT3. The facilitating role of miR-3568 in I/R injury was also observed in our in vivo rat models. In conclusion, our study suggests that miR-3568 promotes simulated I/R-induced apoptosis in H9C2 cardiomyocytes through targeting TRIM62.

Nrdp1 is involved in hippocampus apoptosis in cardiopulmonary bypass-induced cognitive dysfunction via the regulation of ErbB3 protein levels

The cardiopulmonary bypass (CPB) is an important risk factor for the development of postoperative cognitive dysfunction (POCD). The pathological mechanism of the neuro-modulation receptor degradation protein ring finger protein 41 (Nrdp1) in CPB-induced cognitive dysfunction remains unclear. In the present study, aged Sprague-Dawley male rats and CPB treatment were selected to duplicate the POCD model. A hypoxia/reoxygeneration (H/R) model was established to evaluate the effect of Nrdp1 in vitro. Apoptosis in the hippocampus regions were measured using a terminal deoxynucleotidyl-transferase-mediated dUTP nick end labelling assay, the viability and apoptosis level of the cells were measured via an MTT assay and flow cytometry, respectively, and the expression levels of Nrdp1, erb-b2 receptor tyrosine kinase 3 (ErbB3), phosphorylated-protein kinase B (p-AKT) and cleaved (c-) caspase-3 were detected using western blot analysis. Then, Nrdp1 was upregulated and downregulated in vitro and in vivo through lentivirus infection to further investigate the effect of Nrdp1 in the rats following CPB. The results revealed that Nrdp1 is associated with hippocampus neuronal apoptosis and POCD following CPB in rats. The overexpression of Nrdp1 altered the cognitive function of the rats which was inhibited by CPB, and additionally inhibited the viability and increased the apoptosis of primary hippocampus neuron cells under H/R treatment. Furthermore, knockdown of Nrdp1 promoted the viability of primary hippocampus neuron cells and decreased the apoptosis of cells under H/R treatment. Further study indicated that Nrdp1 regulates the protein expression of ErbB3, p-AKT, cytochrome c, BCL2-associated X, apoptosis regulator, BCL2, apoptosis regulator and c-caspase-3. The results of the present study suggested that CPB may induce apoptosis in the hippocampus of aged rats. Nrdp1 serves an important role in regulating the apoptosis induced by CPB in vivo and in vitro through regulating ErbB3 and p-AKT protein levels.

USP49 inhibits ischemia-reperfusion-induced cell viability suppression and apoptosis in human AC16 cardiomyocytes through DUSP1-JNK1/2 signaling

Dual-specificity protein phosphatases (DUSP) also known as mitogen-activated protein kinase (MAPK) phosphatases (MKPs) can dephosphorylate MAPKs, including extracellular signal-regulated kinase, c-Jun N-terminal kinase (JNK), and p38. DUSP1-mediated JNK dephosphorylation has been found to play an antiapoptotic role against cardiac ischemia-reperfusion (I/R) injury. However, the regulation of DUSP1-JNK pathway remains unclear. In the current study, ubiquitin-specific peptidase 49 (USP49) expression in human AC16 cardiomyocytes following I/R injury was measured by real-time polymerase chain reaction and western blot analysis. Cell viability, apoptosis, the Bax, Bcl-2, and DUSP1 expression, and the activity of MAPKs in AC16 cardiomyocytes following indicated treatment was measured by CCK-8, flow cytometry, and western blot analysis. The direct interaction between USP49 and DUSP1 was measured by coimmunoprecipitation and ubiquitination analysis. The effect of USP49 on apoptosis and JNK activity in rat cardiomyocytes following I/R injury was also measured by TUNEL and western blot analysis. Here, we found that USP49 expression was time-dependently increased in AC16 cardiomyocytes following I/R. I/R-induced cell apoptosis and JNK1/2 activation both in in vivo and in vitro reversed by USP49 overexpression in AC16 cardiomyocytes. Inhibiting JNK1/2 activation significantly inhibited USP49 knockdown-induced the cell viability inhibition, apoptosis and the JNK1/2 activation in AC16 cardiomyocytes. Moreover, USP49 positively regulated DUSP1 expression through deubiquitinating DUSP1. Overall, our findings establish USP49 as a novel regulator of DUSP1-JNK1/2 signaling pathway with a protective role in cardiac I/R injury.

The role of K63-linked polyubiquitination in cardiac hypertrophy

Ubiquitination, also known as ubiquitylation, is a vital post‐translational modification of proteins that play a crucial role in the multiple biological processes including cell growth, proliferation and apoptosis. K63‐linked ubiquitination is one of the vital post‐translational modifications of proteins that are involved in the activation of protein kinases and protein trafficking during cell survival and proliferation. It also contributes to the development of various disorders including cancer, neurodegeneration and cardiac hypertrophy. In this review, we summarize the role of K63‐linked ubiquitination signalling in protein kinase activation and its implications in cardiac hypertrophy. We have also provided our perspectives on therapeutically targeting K63‐linked ubiquitination in downstream effector molecules of growth factor receptors for the treatment of cardiac hypertrophy.

Vitamin D attenuates pressure overload-induced cardiac remodeling and dysfunction in mice

Vitamin D (VD) and its analogues play critical roles in metabolic and cardiovascular diseases. Recent studies have demonstrated that VD exerts a protective role in cardiovascular diseases. However, the beneficial effect of VD on pressure overload-induced cardiac remodeling and dysfunction and its underlying mechanisms are not fully elucidated. In this study, cardiac dysfunction and hypertrophic remodeling in mice were induced by pressure overload. Cardiac function was evaluated by echocardiography, and myocardial histology was detected by H&E and Masson's trichrome staining. Cardiomyocyte size was detected by wheat germ agglutinin staining. The protein levels of signaling mediators were examined by western blotting while mRNA expression of hypertrophic and fibrotic markers was examined by qPCR analysis. Oxidative stress was detected by dihydroethidine staining. Our results showed that administration of VD3 significantly ameliorates pressure overload-induced contractile dysfunction, cardiac hypertrophy, fibrosis and inflammation in mice. In addition, VD3 treatment also markedly inhibited cardiac oxidative stress and apoptosis. Moreover, protein levels of calcineurin A, ERK1/2, AKT, TGF-β, GRP78, cATF6, and CHOP were significantly reduced whereas SERCA2 level was upregulated in the VD3-treated hearts compared with control. These results suggest that VD3 attenuates cardiac remodeling and dysfunction induced by pressure overload, and this protective effect is associated with inhibition of multiple signaling pathways.

High-Confidence Interactome for RNF41 Built on Multiple Orthogonal Assays

Ring finger protein 41 (RNF41) is an E3 ubiquitin ligase involved in the ubiquitination and degradation of many proteins including ErbB3 receptors, BIRC6, and parkin. Next to this, RNF41 regulates the intracellular trafficking of certain JAK2-associated cytokine receptors by ubiquitinating and suppressing USP8, which, in turn, destabilizes the ESCRT-0 complex. To further elucidate the function of RNF41 we used different orthogonal approaches to reveal the RNF41 protein complex: affinity purification-mass spectrometry, BioID, and Virotrap. We combined these results with known data sets for RNF41 obtained with microarray MAPPIT and Y2H screens. This way, we establish a comprehensive high-resolution interactome network comprising 175 candidate protein partners. To remove potential methodological artifacts from this network, we distilled the data into a high-confidence interactome map by retaining a total of 19 protein hits identified in two or more of the orthogonal methods. AP2S1, a novel RNF41 interaction partner, was selected from this high-confidence interactome for further functional validation. We reveal a role for AP2S1 in leptin and LIF receptor signaling and show that RNF41 stabilizes and relocates AP2S1.

The Regulatory Effects of Lateral Hypothalamus Area GABAB Receptor on Gastric Ischemia-Reperfusion Injury in Rats

HIGHLIGHTS

The aim of the research was to determine the functional effects and molecular mechanisms of GABA_B receptor on ischemia reperfusion-induced gastric injury in rats.

The lateral hypothalamus area GABA_B receptor attenuated the ischemia reperfusion-induced gastric injury by up-regulating the production of GABA, GABA_BR, and down-regulating P-GABA_BR in the brain.

This work would provide a new therapeutic strategy for acute gastric injury.

Gastric ischemia-reperfusion (GI-R) injury progression is largely associated with excessive activation of the greater splanchnic nerve (GSN). This study aims to investigate the protective effects of GABA_B receptor (GABA_BR) in the lateral hypothalamic area (LHA) on GI-R injury. A model of GI-R injury was established by clamping the celiac artery for 30 min and then reperfusion for 1 h. The coordinate of FN and LHA was identified in Stereotaxic Coordinates and then the L-Glu was microinjected into FN, GABA_B receptor agonist baclofen, or GABA_B receptor antagonist CGP35348 was microinjected into the LHA, finally the GI-R model was prepared. The expression of GABA_BR, P-GABA_BR, NOX2, NOX4, and SOD in the LHA was detected by western blot, PCR, and RT-PCR. The expression of IL-1β, NOX2, and NXO4 in gastric mucosa was detected by western blot. We found that microinjection of L-Glu into the FN or GABA_B receptor agonist (baclofen) into the LHA attenuated GI-R injury. Pretreatment with GABA_B receptor antagonist CGP35348 reversed the protective effects of FN stimulation or baclofen into the LHA. Microinjection of baclofen into the LHA obviously reduced the expression of inflammatory factor IL-1β, NOX2, and NOX4 in the gastric mucosa.

Conclusion: The protective effects of microinjection of GABA_BR agonist into LHA on GI-R injury in rats could be mediated by up-regulating the production of GABA, GABA_BR, and down-regulating P-GABA_BR in the LHA.

Nrdp1 Increases Ischemia Induced Primary Rat Cerebral Cortical Neurons and Pheochromocytoma Cells Apoptosis Via Downregulation of HIF-1α Protein

Neuregulin receptor degradation protein-1 (Nrdp1) is an E3 ubiquitin ligase that targets proteins for degradation and regulates cell growth, apoptosis and oxidative stress in various cell types. We have previously shown that Nrdp1 is implicated in ischemic cardiomyocyte death. In this study, we investigated the change of Nrdp1 expression in ischemic neurons and its role in ischemic neuronal injury. Primary rat cerebral cortical neurons and pheochromocytoma (PC12) cells were infected with adenoviral constructs expressing Nrdp1 gene or its siRNA before exposing to oxygen-glucose deprivation (OGD) treatment. Our data showed that Nrdp1 was upregulated in ischemic brain tissue 3 h after middle cerebral artery occlusion (MCAO) and in OGD-treated neurons. Of note, Nrdp1 overexpression by Ad-Nrdp1 enhanced OGD-induced neuron apoptosis, while knockdown of Nrdp1 with siRNA attenuated this effect, implicating a role of Nrdp1 in ischemic neuron injury. Moreover, Nrdp1 upregulation is accompanied by increased protein ubiquitylation and decreased protein levels of ubiquitin-specific protease 8 (USP8) in OGD-treated neurons, which led to a suppressed interaction between USP8 and HIF-1α and subsequently a reduction in HIF-1α protein accumulation in neurons under OGD conditions. In conclusion, our data support an important role of Nrdp1 upregulation in ischemic neuronal death, and suppressing the interaction between USP8 and HIF-1α and consequently the hypoxic adaptive response of neurons may account for this detrimental effect.

Myocardial ischemia/reperfusion upregulates the transcription of the Neuregulin1 receptor ErbB3, but only postconditioning preserves protein translation: Role in oxidative stress

BACKGROUND

Neuregulin1 (Nrg1) and its receptors ErbB are crucial for heart development and for adult heart structural maintenance and function and Nrg1 has been proposed for heart failure treatment. Infarct size is the major determinant of heart failure and the mechanism of action and the role of each ErbB receptor remain obscure, especially in the post-ischemic myocardium. We hypothesized that Nrg1 and ErbB are affected at transcriptional level early after ischemia/reperfusion (I/R) injury, and that the protective postconditioning procedure (PostC, brief cycles of ischemia/reperfusion carried out after a sustained ischemia) can influence this pathway.

METHODS AND RESULTS

The Langendorff's heart was used as an ex-vivo model to mimic an I/R injury in the whole rat heart; after 30min of ischemia and 2h of reperfusion, with or without PostC, Nrg1 and ErbB expression were analysed by quantitative real-time PCR and Western blot. While no changes occur for ErbB2, ErbB4 and Nrg1, an increase of ErbB3 expression occurs after I/R injury, with and without PostC. However, I/R reduces ErbB3 protein, whereas PostC preserves it. An in vitro analysis with H9c2 cells exposed to redox-stress indicated that the transient over-expression of ErbB3 alone is able to increase cell survival (MTT assay), limiting mitochondrial dysfunction (JC-1 probe) and apoptotic signals (Bax/Bcl-2 ratio).

CONCLUSIONS

This study suggests ErbB3 as a protective factor against death pathways activated by redox stress and supports an involvement of this receptor in the pro-survival responses.

Transcriptional Effects of E3 Ligase Nrdp1 on Hypertrophy in Neonatal Rat Cardiomyocytes by Microarray and Integrated Gene Network Analysis

Objective: Neuregulin receptor degradation protein-1 (Nrdp1) is a novel E3 ubiquitin ligase, and we have previously shown that overexpression of Nrdp1 increased cardiomyocyte injury. However, the role of Nrdp1 in myocardial hypertrophy is unclear. In the present study, we clarified the molecular mechanisms of angiotensin II (Ang II)-induced cardiomyocyte hypertrophy regulated by Nrdp1 based on genome-wide transcriptional analysis. Methods: Neonatal rat cardiomyocytes were infected with adenoviruses containing green fluorescent protein (Ad-GFP) or wild-type Nrdp1 (Ad-Nrdp1), and then treated with Ang II for 36 h. Detection of differentially expressed genes was achieved with an Affymetrix Rat Gene 2.0 Array and Cluster and Java TreeView software. Results and Conclusion: Microarray data analysis demonstrated that Nrdp1 overexpression affected the expression of 12,140 mRNA genes in Ang II-induced cardiomyocyte hypertrophy, including the upregulation of 12,044 and the downregulation of 96. Gene ontology and globe signal transduction network analysis showed that Nrdp1 affected the expression of many genes related to stimulus response, the cell receptor pathway, and cell growth. Pathway network analysis identified myocardial metabolism, DNA replication, and the cell cycle as the most important pathways targeted by Nrdp1. lncRNA-mRNA coexpression network analysis showed that two core lncRNAs, NONRATT057160 and NONRATT054243, were involved in cardiomyotrophy regulated by Nrdp1 in cardiomyocytes. Taken together, these data provide compelling clues for further exploration of the function of Nrdp1 in heart disease.

The ER structural protein Rtn4A stabilizes and enhances signaling through the receptor tyrosine kinase ErbB3

ErbB3 and ErbB4 are receptor tyrosine kinases that are activated by the neuregulin (NRG) family of growth factors. These receptors govern various developmental processes, and their dysregulation contributes to several human disease states. The abundance of ErbB3 and ErbB4, and thus signaling through these receptors, is limited by the E3 ubiquitin ligase Nrdp1, which targets ErbB3 and ErbB4 for degradation. Reticulons are proteins that influence the morphology of the endoplasmic reticulum (ER) by promoting the formation of tubules, a response of cells to some stressors. We found that the ER structural protein reticulon 4A (Rtn4A, also known as Nogo-A) increased ErbB3 abundance and proliferative signaling by suppressing Nrdp1 function. Rtn4A interacted with Nrdp1 and stabilized ErbB3 in an Nrdp1-dependent manner. Rtn4A overexpression induced the redistribution of Nrdp1 from a cytosolic or perinuclear localization to ER tubules. Rtn4A knockdown in human breast tumor cells decreased ErbB3 abundance, NRG-stimulated signaling, and cellular proliferation and migration. Because proteins destined for the plasma membrane are primarily synthesized in the sheet portions of the ER, our observations suggest that Rtn4A counteracts the Nrdp1-mediated degradation of ErbB3 by sequestering the ubiquitin ligase into ER tubules. The involvement of a reticulon suggests a molecular link between ER structure and the sensitivity of cells to receptor tyrosine kinase-mediated survival signals at the cell surface.

Cardiac-Specific Deletion of the Pdha1 Gene Sensitizes Heart to Toxicological Actions of Ischemic Stress

Pyruvate dehydrogenase (PDH) plays a key role in aerobic energy metabolism and occupies a central crossroad between glycolysis and the tricarboxylic acid cycle. We generated inducible cardiac-specific PDH E1α knockout (CreER(T2)-PDH(flox/flox)) mice that demonstrated a high mortality rate. It was hypothesized that PDH modulating cardiac glucose metabolism is crucial for heart functions under normal physiological and/or stress conditions. The myocardial infarction was conducted by a ligation of the left anterior descending coronary arteries. Cardiac PDH E1α deficiency caused large myocardial infarcts size and macrophage infiltration in the hearts (P < .01 vs wild-type [WT]). Wheat germ agglutinin and Masson trichrome staining revealed significantly increased hypertrophy and fibrosis in PDH E1α-deficient hearts (P < .05 vs WT). Measurements of heart substrate metabolism in an ex vivo working heart perfusion system demonstrated a significant impairment of glucose oxidation in PDH E1α-deficient hearts during ischemia/reperfusion (P < .05 vs WT). Dichloroacetate, a PDH activator, increased glucose oxidation in WT hearts during ischemia/reperfusion and reduced myocardial infarct size in WT, but not in PDH E1α-deficient hearts. Immunoblotting results demonstrated that cardiac PDH E1α deficiency leads to an impaired ischemic AMP-activated protein kinase activation through Sestrin2-liver kinase B1 interaction which is responsible for an increased susceptibility of PDH E1α-deficient heart to ischemic insults. Thus, cardiac PDH E1α deficiency impairs ischemic AMP-activated protein kinase signaling and sensitizes hearts to the toxicological actions of ischemic stress.

CHIP Is an Essential Determinant of Neuronal Mitochondrial Stress Signaling

AIMS

Determine the mechanism by which C-terminus of HSC70-interacting protein (CHIP) induction alters neuronal survival under conditions of mitochondrial stress induced by oxygen glucose deprivation.

RESULTS

We report that animals deficient in the E3 ubiquitin ligase, CHIP, have high baseline levels of central nervous system protein oxidation and lipid peroxidation, reduced antioxidant defenses, and decreased energetic status. Stress-associated molecules typically linked to Parkinson's disease such as the mitochondrial kinase, PTEN-inducible putative kinase 1 (PINK1), and another E3 ligase, Parkin, are upregulated in brains from CHIP knockout (KO) animals. Utilizing a novel biotin-avidin capture technique, we found that the oxidation status of Parkin and the mitochondrial fission protein, dynamin-related protein 1 (Drp1), are altered in a CHIP-dependent manner. We also found that following oxygen-glucose deprivation (OGD), the expression of CHIP, PINK1, and the autophagic marker, LC3, increase and there is activation of the redox-sensitive kinase p66(shc). Under conditions of OGD, CHIP relocalizes from the cytosol to mitochondria. Mitochondria from CHIP KO mice have profound impairments in stress response induced by calcium overload, resulting in accelerated permeability transition activity. While CHIP-deficient neurons are morphologically intact, they are more susceptible to OGD consistent with a previously unknown neuroprotective role for CHIP in maintaining mitochondrial homeostasis.

INNOVATION

CHIP relocalization to the mitochondria is essential for the regulation of mitochondrial integrity and neuronal survival following OGD.

CONCLUSIONS

CHIP is an essential regulator of neuronal bioenergetics and redox tone. Altering the expression of this protein has profound effects on neuronal survival when cells are exposed to OGD.

Nrdp1 is Associated with Neuronal Apoptosis in Lipopolysaccharide-Induced Neuroinflammation

Neuregulin receptor degradation protein-1 (Nrdp1), a kind of ring finger E3 ubiquitin ligase, is expressed in several adult tissues, including the heart, testis, prostate and brain. Studies of this molecule have demonstrated its great importance in regulating cell growth, apoptosis and oxidative stress in various cell types. However, information regarding its expression and possible function in the central nervous system is still limited. In this study, we performed a neuroinflammation model by lipopolysaccharide (LPS) lateral ventral injection in adult rats. It was found that the expression of Nrdp1 was significantly increased in cerebral cortex after LPS injection. Immunofluorescence indicated that Nrdp1 was located in the neurons, but not astrocytes or microglia. Furthermore, there was a concomitant up-regulation of active caspase-3 and decreased expression of BRUCE (an inhibitor of apoptosis protein). In addition, decreasing Nrdp1 levels by RNA interference in cortical primary neurons reduced active caspase-3 expression but induced up-regulation of BRUCE. Collectively, all these results suggested that Nrdp1 might play a role in neuronal apoptosis by reducing the expression of BRUCE in neuroinflammation after LPS injection.

Inhibition of 12/15 lipoxygenase by baicalein reduces myocardial ischemia/reperfusion injury via modulation of multiple signaling pathways

12/15-Lipoxygenase (LOX) is a member of the LOX family that catalyzes the step from arachidonic acid to hydroxy-eicosatetraenoic acids (HETEs). Previous studies demonstrated that 12/15-LOX plays a critical role in the development of atherosclerosis, hypertension, heart failure, and other diseases; however, its role in myocardial ischemic injury was contraversal. Here, we investigated the inhibition of 12/15-LOX by baicalein on acute cardiac injury and dissected its molecular mechanism. In a mouse model of acute ischemia/reperfusion (I/R) injury, 12/15-LOX was significantly upregulated in the peri-infarct area surrounding the primary infarction. In cultured cardiac myocytes, baicalein suppressed apoptosis and caspase 3 activity in response to simulated ischemia/reperfusion (I/R). Moreover, administration of 12/15-LOX inhibitor, baicalein, significantly attenuated myocardial infarct size induced by I/R injury. Moreover, baicalein treatment significantly inhibited cardiomyocyte apoptosis, inflammatory responses and oxidative stress in the heart after I/R injury. The mechanisms underlying these effects were associated with the activation of ERK1/2 and AKT pathways and inhibition of activation of p38 MAPK, JNK1/2, and NF-kB/p65 pathways in the I/R-treated hearts and neonatal cardiomyoctes. Our data indicated that 12/15-LOX inhibitor baicalein can prevent myocardial I/R injury by modulation of multiple mechanisms, and suggest that baicalein could represent a novel therapeutic drug for acute myocardial infarction.

Characterization of E3 ubiquitin ligase neuregulin receptor degradation protein-1 (Nrdp1) in the large yellow croaker (Larimichthys crocea) and its immune responses to Cryptocaryon irritans

Neuregulin receptor degradation protein-1 (Nrdp1) was recently identified in humans as an important immune factor responding to the challenge of virus, LPS or cytokine. Its role in fish immune defense and whether it is involved in anti-parasite immunity have not been proven yet. In this report, the full-length cDNA sequence and genomic structure of Nrdp1 in the large yellow croaker Larimichthys crocea (LcNrdp1) were identified and characterized. The full-length cDNA of LcNrdp1 was 1248bp, including a 5' untranslated region (UTR) of 32bp, a 3' UTR of 259bp and an open reading frame (ORF) of 937bp, encoding a polypeptide of 318 amino acid residues. The full-length genomic DNA sequence of LcNrdp1 was composed of 2635 nucleotides, including four exons and three introns. The putative LcNrdp1 protein had no signal peptide sequence and contained a characteristic Nrdp1 consensus motif C3HC3D ring finger and a Coiled-coil domain. Phylogenetic analysis showed that Nrdp1 in fish was closer with that in other vertebrates (79%-90% amino acid identity) than in invertebrates and bacteria (27%-65%). In fishes, Nrdp1 in large yellow croaker was closer with that in Takifugu rubripes. The expression profile showed that LcNrdp1 was constitutively expressed in all tested tissues, especially highly expressed in brain, muscle and kidney. Post-infection (PI) with Cryptocaryon irritans, an increased expression of LcNrdp1 was induced in infection sites (skin and gill), whereas in immune organs, the expression of LcNrdp1 was up-regulated in spleen (except the 1st d and 10th d PI) but suppressed in head kidney. These results suggested that LcNrdp1 might play an important immune role in the finfish L. crocea in the defense against the parasite C. irritans.

Lower expression of Nrdp1 in human glioma contributes tumor progression by reducing apoptosis

Ubiquitin ligase Nrdp1 (neuregulin receptor degradation protein 1) plays important roles in multiple physiological process because it can ubiquitinate various substrates such as ErbB3, BRUCE, MyD88, C/EBPβ, and Parkin, and so forth. In addition to the physiological function, it was also found to be involved in tumor progression. It has been shown that loss of Nrdp1 enhances breast cancer cell growth. Up to now, the role of Nrdp1 in glioma has not been elucidated. Here, we reported that Nrdp1 as well as cleaved caspase 3 was lower expressed in human glioma tissues comparing with the nontumorous. And then we found that the expression of Nrdp1 and cleaved caspase 3 was increased in the treatment of Temozolomide (TMZ), a drug for glioma chemotherapy. Further investigation indicated that transient transfection of Nrdp1 significantly promoted cell apoptosis by aggravating the degradation of BRUCE and activation of caspase 3. In addition, overexpression of Nrdp1 augmented TMZ induced apoptosis by evaluating the degradation of BRUCE and the activation of caspase 3, while silencing of Nrdp1 reduced the sensitivity to the TMZ by inhibiting the degradation of BRUCE and the activation of caspase 3 in human glioma cells. These observations show that Nrdp1 is a pro-apoptotic protein in human glioma and lower expression of Nrdp1 in human glioma may promote tumor progression by reducing apoptosis, suggesting that Nrdp1 may be an important regulator in the development of human glioma.

Protein quality control in the endoplasmic reticulum

THE TOPOLOGICAL BARRIERS DEFINED BY BIOLOGICAL MEMBRANES ARE NOT IMPERMEABLE: from small solutes to intact proteins, specialized transport and translocation mechanisms adjust to the cell's needs. Here, we review the removal of unwanted proteins from the endoplasmic reticulum (ER) and emphasize the need to extend observations from tissue culture models and simple eukaryotes to studies in whole animals. The variation in protein production and composition that characterizes different cell types and tissues requires tailor-made solutions to exert proper control over both protein synthesis and breakdown. The ER is an organelle essential to achieve and maintain such homeostasis.

Diggin' on u(biquitin): a novel method for the identification of physiological E3 ubiquitin ligase substrates

The ubiquitin-proteasome system (UPS) plays a central role in maintaining protein homeostasis, emphasized by a myriad of diseases that are associated with altered UPS function such as cancer, muscle-wasting, and neurodegeneration. Protein ubiquitination plays a central role in both the promotion of proteasomal degradation as well as cellular signaling through regulation of the stability of transcription factors and other signaling molecules. Substrate-specificity is a critical regulatory step of ubiquitination and is mediated by ubiquitin ligases. Recent studies implicate ubiquitin ligases in multiple models of cardiac diseases such as cardiac hypertrophy, atrophy, and ischemia/reperfusion injury, both in a cardioprotective and maladaptive role. Therefore, identifying physiological substrates of cardiac ubiquitin ligases provides both mechanistic insights into heart disease as well as possible therapeutic targets. Current methods identifying substrates for ubiquitin ligases rely heavily upon non-physiologic in vitro methods, impeding the unbiased discovery of physiological substrates in relevant model systems. Here we describe a novel method for identifying ubiquitin ligase substrates utilizing tandem ubiquitin binding entities technology, two-dimensional differential in gel electrophoresis, and mass spectrometry, validated by the identification of both known and novel physiological substrates of the ubiquitin ligase MuRF1 in primary cardiomyocytes. This method can be applied to any ubiquitin ligase, both in normal and disease model systems, in order to identify relevant physiological substrates under various biological conditions, opening the door to a clearer mechanistic understanding of ubiquitin ligase function and broadening their potential as therapeutic targets.

Oligomerization of the Nrdp1 E3 ubiquitin ligase is necessary for efficient autoubiquitination but not ErbB3 ubiquitination

Overexpression of the ErbB3 receptor tyrosine kinase protein in breast and other cancers contributes to tumor malignancy and therapeutic resistance. The RBCC/TRIM family RING finger E3 ubiquitin ligase Nrdp1 mediates the ubiquitination of ErbB3 in normal mammary epithelial cells to facilitate receptor degradation and suppress steady-state receptor levels. Post-transcriptional loss of Nrdp1 in patient breast tumors allows ErbB3 overexpression and receptor contribution to tumor progression, and elevated lability through autoubiquitination contributes to the observed loss of Nrdp1 in tumors relative to normal tissue. To begin to understand the mechanisms underlying Nrdp1 protein self-regulation through lability, we investigated the structural determinants required for efficient autoubiquitination and ErbB3 ubiquitination. Using mutagenesis, chemical cross-linking, size exclusion chromatography, and native polyacrylamide gel electrophoresis, we demonstrate that Nrdp1 self-associates into a stable oligomeric complex in cells. Deletion of its coiled-coil domain abrogates oligomerization but does not affect Nrdp1-mediated ErbB3 ubiquitination or degradation. On the other hand, the presence of the coiled-coil domain is necessary for efficient Nrdp1 autoubiquitination via a trans mechanism, indicating that Nrdp1 ubiquitination of its various targets is functionally separable. Finally, a GFP fusion of the coiled-coil domain stabilizes Nrdp1 and potentiates ErbB3 ubiquitination and degradation. These observations point to a model whereby the coiled-coil domain plays a key role in regulating Nrdp1 lability by promoting its assembly into an oligomeric complex, and raise the possibility that inhibition of ligase oligomerization via its coiled-coil domain could be of therapeutic benefit to breast cancer patients by restoring Nrdp1 protein.

NADPH oxidases mediate a cellular "memory" of angiotensin II stress in hypertensive cardiac hypertrophy

A long-term "memory" of hyperglycemic stress, even when glycemia is normalized, has been previously reported in diabetes. In this report we propose a similar hypothesis that exposure to continuous high angiotensin II (Ang II) results in a cellular "memory" in isolated cardiomyocytes and in the heart tissues, and we investigate the role of NADPH oxidases in this phenomenon. Continuous high Ang II for 3 days markedly increased cardiomyocyte size, TUNEL-positive apoptotic cardiomyocytes, expression of inflammatory cytokines, and oxidative stress. These deleterious effects were also observed in the memory condition (high Ang II for 2 days followed by normal medium for 1 day). Furthermore, in a mouse model, Ang II infusion for 3 weeks significantly increased cardiac hypertrophy, apoptosis, inflammation, and ROS generation but decreased cardiac function compared with control mice, and similar effects were also observed in mice in the memory condition. Importantly, blockade of NADPH oxidase using apocynin diminished the induction of high Ang II stress markers in isolated cardiomyocytes and in the mouse heart. These effects were associated with inhibition of NADPH oxidase-mediated AKT/mTOR/S6K and ERK signaling pathways. The present results demonstrate the hypothesis that exposure to continuous high Ang II results in a hypertensive cellular memory that remains, even when cells or mice are switched back to normal Ang II. This phenomenon was associated with NADPH oxidase-mediated oxidative stress.

Role for granulocyte colony stimulating factor in angiotensin II-induced neutrophil recruitment and cardiac fibrosis in mice

BACKGROUND

Granulocyte colony stimulating factor (G-CSF) is a key mediator of neutrophil infiltration and is profibrotic in the liver, lung, and infarcted heart, but its roles in angiotensin II (Ang II)-induced hypertension and cardiac remodeling have not been fully determined. Thus, we sought to investigate the causal relation of G-CSF to neutrophil recruitment and cardiac fibrosis in C57BL/6J mice.

METHODS

Hypertension and cardiac fibrosis were induced in wild-type (WT) mice receiving continuous infusion of Ang II (1,500ng/kg/min). After 7 days, heart sections were stained with hematoxylin and eosin, Masson's trichrome, and immunohistochemistry. The mRNA expression of cytokines was detected by real-time polymerase chain reaction analysis. The protein levels were measured by Western blot analysis.

RESULTS

After Ang II infusion, myocardial G-CSF expression was significantly elevated in the hearts. Moreover, WT mice exhibited increased blood pressure, marked neutrophil accumulation, proinflammatory cytokine expression, reactive oxygen species production, and cardiac fibrosis after 7 days of Ang II infusion. However, administration of anti-G-CSF neutralizing antibody, but not with control immunoglobulin G, significantly attenuated these effects. In addition, neutralizing G-CSF antibody reversed Ang II-induced activation of ERK1/2, STAT3, and AKT signaling pathways in the hearts.

CONCLUSIONS

This study demonstrates that G-CSF plays a critical role in hypertension and cardiac fibrosis and targeting this cytokine may be a novel therapeutic strategy to ameliorate hypertensive heart disease.

Regulation of the proteasome by ATP: implications for ischemic myocardial injury and donor heart preservation

Several lines of evidence suggest that proteasomes are involved in multiple aspects of myocardial physiology and pathology, including myocardial ischemia-reperfusion injury. It is well established that the 26S proteasome is an ATP-dependent enzyme and that ischemic heart disease is associated with changes in the ATP content of the cardiomyocyte. A functional link between the 26S proteasome, myocardial ATP concentrations, and ischemic cardiac injury, however, has been suggested only recently. This review discusses the currently available data on the pathophysiological role of the cardiac proteasome during ischemia and reperfusion in the context of the cellular ATP content. Depletion of the myocardial ATP content during ischemia appears to activate the 26S proteasome via direct regulatory effects of ATP on 26S proteasome stability and activity. This implies pathological degradation of target proteins by the proteasome and could provide a pathophysiological basis for beneficial effects of proteasome inhibitors in various models of myocardial ischemia. In contrast to that in the ischemic heart, reduced and impaired proteasome activity is detectable in the postischemic heart. The paradoxical findings that proteasome inhibitors showed beneficial effects when administered during reperfusion in some studies could be explained by their anti-inflammatory and immune suppressive actions, leading to reduction of leukocyte-mediated myocardial reperfusion injury. The direct regulatory effects of ATP on the 26S proteasome have implications for the understanding of the contribution of the 26S proteasome to the pathophysiology of the ischemic heart and its possible role as a therapeutic target.

Cellular FLICE-inhibitory protein protects against cardiac remodelling after myocardial infarction

Cellular FLICE-inhibitory protein (cFLIP) is a member of the tumour necrosis factor signalling pathway and a regulator of apoptosis, and it has a role in cardiac remodelling following myocardial infarction (MI) that remains largely uncharacterised. This study aimed to determine the function of cFLIP as a potential mediator of post-infarction cardiac remodelling. Our results show diminished cFLIP expression in failing human and murine post-infarction hearts. Genetically engineered cFLIP heterozygous (cFLIP+/-, HET) mice, cardiac-specific cFLIP-overexpressing transgenic (TG) mice and their respective wild-type (WT) and non-transgenic controls were subjected to MI by permanent ligation of their left anterior descending artery. Cardiac structure and function were assessed by echocardiography and pressure-volume loop analysis. Apoptosis, inflammation, angiogenesis, and fibrosis were evaluated in the myocardium. The HET mice showed exacerbated left ventricular (LV) contractile dysfunction, dilatation, and remodelling compared with WT mice 28 days after MI. Impaired LV function in the HET mice was associated with increases in infarct size, hypertrophy, apoptosis, inflammation, and interstitial fibrosis, and reduced capillary density. The TG mice displayed the opposite phenotype after MI. Moreover, adenovirus-mediated overexpression of cFLIP decreased LV dilatation and improved LV function and remodelling in both HET and WT mice. Further analysis of signalling events suggests that cFLIP promotes cardioprotection by interrupting JNK1/2 signalling and augmenting Akt signalling. In conclusion, our results indicate that cFLIP protects against the development of post-infarction cardiac remodelling. Thus, cFLIP gene delivery shows promise as a clinically powerful and novel therapeutic strategy for the treatment of heart failure after MI.

Chronic Akt activation accentuates aging-induced cardiac hypertrophy and myocardial contractile dysfunction: role of autophagy

Aging is often accompanied with geometric and functional changes in the heart, although the underlying mechanisms remain unclear. Recent evidence has described a potential role of Akt and autophagy in aging-associated organ deterioration. This study was to examine the impact of cardiac-specific Akt activation on aging-induced cardiac geometric and functional changes and underlying mechanisms involved. Cardiac geometry, contractile and intracellular Ca(2+) properties were evaluated using echocardiography, edge-detection and fura-2 techniques. Level of insulin signaling and autophagy was evaluated by western blot. Our results revealed cardiac hypertrophy (enlarged chamber size, wall thickness, myocyte cross-sectional area), fibrosis, decreased cardiac contractility, prolonged relengthening along with compromised intracellular Ca(2+) release and clearance in aged (24-26 month-old) mice compared with young (3-4 month-old) mice, the effects of which were accentuated by chronic Akt activation. Aging enhanced Akt and mTOR phosphorylation while reducing that of PTEN, AMPK and ACC with a more pronounced response in Akt transgenic mice. GSK3β phosphorylation and eNOS levels were unaffected by aging or Akt overexpression. Levels of beclin-1, Atg5 and LC3-II-to-LC3-I ratio were decreased in aged hearts, the effect of which with the exception of Atg 5 was exacerbated by Akt overactivation. Levels of p62 were significantly enhanced in aged mice with a more pronounced increase in Akt mice. Neither aging nor Akt altered β-glucuronidase activity and cathepsin B although aging reduced LAMP1 level. In addition, rapamycin reduced aging-induced cardiomyocyte contractile and intracellular Ca(2+) dysfunction while Akt activation suppressed autophagy in young but not aged cardiomyocytes. In conclusion, our data suggest that Akt may accentuate aging-induced cardiac geometric and contractile defects through a loss of autophagic regulation.

Overexpression of Nrdp1 in the heart exacerbates doxorubicin-induced cardiac dysfunction in mice

Background

Cardiac cell death and generation of oxidative stress contribute to doxorubicin (DOX)-induced cardiac dysfunction. E3 ligase Nrdp1 plays a critical role in the regulation of cell apoptosis, inflammation and production of reactive oxygen species (ROS), which may contribute to heart failure. However, the role of Nrdp1 in DOX-induced cardiac injury remains to be determined.

Methods and Results

We examined the effect of Nrdp1 overexpression with DOX treatment in rat neonatal cardiomyocytes and mouse heart tissue. Cardiomyocytes were infected with adenovirus containing GFP (Ad-GFP), Nrdp1 wild-type (Ad-Nrdp1) or the dominant-negative form of Nrdp1 (Ad-Dn-Nrdp1), then treated with DOX for 24 hr. DOX treatment increased cell death and apoptosis, with Ad-Nrdp1 infection enhancing these actions but Ad-Dn-Nrdp1 infection attenuating these effects. Furthermore, 5 days after a single injection of DOX (20 mg/kg, intraperitoneally), Nrdp1 transgenic mice (TG) showed decreased cardiac function and increased apoptosis, autophagy and oxidative stress as compared with wild-type (WT) mice (P<0.01). Survival rate was significantly lower in Nrdp1 TG mice than in WT mice 10 days after DOX injection (P<0.01).

Conclusions/Significance

These results were associated with decreased activation of Akt, extracellular signal-regulated kinase 1/2 (ERK1/2) and signal transducer and activator of transcription 3 (STAT3) signaling pathways. Nrdp1 may be a key mediator in the development of cardiac dysfunction after DOX treatment and associated with inhibition of Akt, ERK1/2 and STAT3. Nrdp1 may be a new therapeutic target in protecting against the cardiotoxic effects of DOX.