Prohibitin confers cytoprotection against ISO-induced hypertrophy in H9c2 cells via attenuation of oxidative stress and modulation of Akt/Gsk-3β signaling

The prohibitin complex regulates macrophage fatty acid composition, plasma membrane packing, and lipid raft-mediated inflammatory signaling

Prohibitins (PHB1 and PHB2) are ubiquitously expressed proteins which play critical roles in multiple biological processes, and together form the ring-like PHB complex found in phospholipid-rich cellular compartments including lipid rafts. Recent studies have implicated PHB1 as a mediator of fatty acid transport as well as a membrane scaffold mediating B lymphocyte and mast cell signal transduction. However, the specific role of PHBs in the macrophage have not been characterized, including their role in fatty acid uptake and lipid raft-mediated inflammatory signaling. We hypothesized that the PHB complex regulates macrophage inflammatory signaling through the formation of lipid rafts. To evaluate our hypothesis, RAW 264.7 macrophages were transduced with shRNA against PHB1, PHB2, or scrambled control (Scr), and then stimulated with lipopolysaccharide (LPS) or tumor necrosis factor-alpha (TNF-α), which activate lipid raft-dependent receptor signaling (CD14/TLR4 and TNFR1, respectively). PHB1 knockdown was lethal, whereas PHB2 knockdown (PHB2kd), which also resulted in decreased PHB1 expression, led to attenuated nuclear factor-kappa-B (NF-κB) activation and subsequent cytokine and chemokine production. PHB2kd macrophages also had decreased cell surface TNFR1, CD14, TLR4, and lipid raft marker ganglioside GM1 at baseline and post-stimuli. Post-LPS, PHB2kd macrophages did not increase the concentration of cellular saturated, monounsaturated, and polyunsaturated fatty acids. This was accompanied by decreased lipid raft formation and modified plasma membrane molecular packing, further supporting the PHB complex's importance in lipid raft formation. Taken together, these data suggest a critical role for PHBs in regulating macrophage inflammatory signaling via maintenance of fatty acid composition and lipid raft structure. SUMMARY: Prohibitins are proteins found in phospholipid-rich cellular compartments, including lipid rafts, that play important roles in signaling, transcription, and multiple other cell functions. Macrophages are key cells in the innate immune response and the presence of membrane lipid rafts is integral to signal transduction, but the role of prohibitins in macrophage lipid rafts and associated signaling is unknown. To address this question, prohibitin knockdown macrophages were generated and responses to lipopolysaccharide and tumor necrosis factor-alpha, which act through lipid raft-dependent receptors, were analyzed. Prohibitin knockdown macrophages had significantly decreased cytokine and chemokine production, transcription factor activation, receptor expression, lipid raft assembly and membrane packing, and altered fatty acid remodeling. These data indicate a novel role for prohibitins in macrophage inflammatory signaling through regulation of fatty acid composition and lipid raft formation.

Prohibitin1 maintains mitochondrial quality in isoproterenol-induced cardiac hypertrophy in H9C2 cells

BACKGROUND INFORMATION

Various types of stress initially induce a state of cardiac hypertrophy (CH) in the heart. But, persistent escalation of cardiac stress leads to progression from an adaptive physiological to a maladaptive pathological state. So, elucidating molecular mechanisms that can attenuate CH is imperative in developing cardiac therapies. Previously, we showed that Prohibitin1 (PHB1) has a protective role in CH-induced oxidative stress. Nevertheless, it is unclear how PHB1, a mitochondrial protein, has a protective role in CH. Therefore, we hypothesized that PHB1 maintains mitochondrial quality in CH. To test this hypothesis, we used Isoproterenol (ISO) to induce CH in H9C2 cells overexpressing PHB1 and elucidated mitochondrial quality control pathways.

RESULTS

We found that overexpressing PHB1 attenuates ISO-induced CH and restores mitochondrial morphology in H9C2 cells. In addition, PHB1 blocks the pro-hypertrophic IGF1R/AKT pathway and restores the mitochondrial membrane polarization in ISO-treated cells. We observed that overexpressing PHB1 promotes mitochondrial biogenesis, improves mitochondrial respiratory capacity, and triggers mitophagy.

CONCLUSION

We conclude that PHB1 maintains mitochondrial quality in ISO-induced CH in H9C2 cells.

SIGNIFICANCE

Based on our results, we suggest that small molecules that induce PHB1 in cardiac cells may prove beneficial in developing cardiac therapies.

Lotus Bee Pollen Extract Inhibits Isoproterenol-Induced Hypertrophy via JAK2/STAT3 Signaling Pathway in Rat H9c2 Cells

Bee pollen possesses an anti-cardiomyocyte injury effect by reducing oxidative stress levels and inhibiting inflammatory response and apoptosis, but the possible effect mechanism has rarely been reported. This paper explores the effect of the extract of lotus bee pollen (LBPE) on cardiomyocyte hypertrophy (CH) and its mechanism. The main components of LBPE were identified via UPLC-QTOF MS. An isoproterenol-induced rat H9c2 CH model was subsequently used to evaluate the protection of LBPE on cells. LBPE (100, 250 and 500 μg∙mL^-1) reduced the surface area, total protein content and MDA content, and increased SOD activity and GSH content in CH model in a dose-dependent manner. Meanwhile, quantitative real-time PCR trials confirmed that LBPE reduced the gene expression levels of CH markers, pro-inflammatory cytokines and pro-apoptosis factors, and increased the Bcl-2 mRNA expression and Bcl-2/Bax ratio in a dose-dependent manner. Furthermore, target fishing, bioinformatics analysis and molecular docking suggested JAK2 could be a pivotal target protein for the main active ingredients in the LBPE against CH. Ultimately, Western blot (WB) trials confirmed that LBPE can dose-dependently inhibit the phosphorylation of JAK2 and STAT3. The results show that LBPE can protect against ISO-induced CH, possibly via targeting the JAK2/STAT3 pathway, also suggesting that LBPE may be a promising candidate against CH.

Alleviation of Inflammation and Oxidative Stress in Pressure Overload-Induced Cardiac Remodeling and Heart Failure via IL-6/STAT3 Inhibition by Raloxifene

BACKGROUND

Inflammation and oxidative stress are involved in the initiation and progress of heart failure (HF). However, the role of the IL6/STAT3 pathway in the pressure overload-induced HF remains controversial.

METHODS AND RESULTS

Transverse aortic constriction (TAC) was used to induce pressure overload-HF in C57BL/6J mice. 18 mice were randomized into three groups (Sham, TAC, and TAC+raloxifene, n = 6, respectively). Echocardiographic and histological results showed that cardiac hypertrophy, fibrosis, and left ventricular dysfunction were manifested in mice after TAC treatment of eight weeks, with aggravation of macrophage infiltration and interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) expression in the myocardium. TAC (four and eight weeks) elevated the phosphorylation of signal transducer and activator of transcription 3 (p-STAT3) and prohibitin2 (PHB2) protein expression. Importantly, IL-6/gp130/STAT3 inhibition by raloxifene alleviated TAC-induced myocardial inflammation, cardiac remodeling, and dysfunction. In vitro, we demonstrated cellular hypertrophy with STAT3 activation and oxidative stress exacerbation could be elicited by IL-6 (25 ng/mL, 48 h) in H9c2 myoblasts. Sustained IL-6 stimulation increased intracellular reactive oxygen species, repressed mitochondrial membrane potential (MMP), decreased intracellular content of ATP, and led to decreased SOD activity, an increase in iNOS protein expression, and increased protein expression of Pink1, Parkin, and Bnip3 involving in mitophagy, all of which were reversed by raloxifene.

CONCLUSION

Inflammation and IL-6/STAT3 signaling were activated in TAC-induced HF in mice, while sustained IL-6 incubation elicited oxidative stress and mitophagy-related protein increase in H9c2 myoblasts, all of which were inhibited by raloxifene. These indicated IL-6/STAT3 signaling might be involved in the pathogenesis of myocardial hypertrophy and HF.

Lamprey PHB2 maintains mitochondrial stability by tanslocation to the mitochondria under oxidative stress

Before we have reported lamprey PHB2 could enhance the cellular oxidative-stressed tolerance, here the aim was to explore its mechanisms. We used flow cytometry analysis to identify a Lampetra morii homologue of PHB2 (Lm-PHB2) that could significantly decrease the levels of ROS generation in HEK293T cells. According to confocal microscopy observations, Lm-PHB2 contributed to maintain the mitochondrial morphology of HEK293T cells, and then both cellular nuclear location and translocation from the nucleus to mitochondria of Lm-PHB2 were also examined in HEK293T cells under oxidative stress. We also examined the expressions and locations of various Lm-PHB2 deletion mutants and the amino acid mutant by confocal microscopy and the results showed that the translocation of Lm-PHB2 into mitochondria was dependent on the Lm-PHB2_1-50aa region and the 17th, 48th and 57th three arginines (R) of N-terminal were very critical. In addition, the analyses of QRT-PCR and Western blot demonstrated that Lm-PHB2 increased the expression levels of OPA1 and HAX1 in HEK293T cells treated with H₂O₂. The analyses of immunofluorescence and immunoprecipitation showed that Lm-PHB2 could interact with OPA1 and HAX1, respectively. The above mentioned results indicate that Lm-PHB2 could assist OPA1 and HAX1 to maintain mitochondrial morphology and decrease ROS levels by the translocation from the nucleus to mitochondria under oxidative stress.

Silencing of soluble epoxide hydrolase 2 gene reduces H2O2-induced oxidative damage in rat intestinal epithelial IEC-6 cells via activating PI3K/Akt/GSK3β signaling pathway

Oxidative stress plays a vital role in the occurrence and development of intestinal injury. Soluble epoxide hydrolase 2 gene (EPHX2) is a class of hydrolytic enzymes. We aim to explore the effects and molecular mechanism of siEPHX2 on H2O2-induced oxidative damage in rat intestinal epithelial IEC-6 cells. IEC-6 cells were transfected with EPHX2-siRNA and control si RNA plasmids by lipofectamine™ 2000 transfection reagent. The transfected samples were treated with H2O2 (50, 100, 200, 300, 400, and 500 µmol/L) for 12, 24, and 48 h, respectively. Cell viability was determined by cell counting kit-8 (CCK-8). Lactate dehydrogenase (LDH), malondialdehyde (MDA), and superoxide dismutase (SOD) were assessed by respective detection kits. Mitochondrial membrane potential (MMP), cell apoptosis and reactive oxygen species (ROS) and the levels of factors were determined by flow cytometer, quantitative real-time PCR (qRT-PCR) and western blot assays, respectively. We found that the IC50 of H2O2 was 200 µmol/L at 24 h, and the transfection of siEHPX2 in H2O2-induced IEC-6 cells significantly promoted the cell viability, SOD activity and MMP rate, and reduced the rates of ROS and apoptosis as well as LDH and MDA contents. siEHPX2 up-regulated the B-cell lymphoma-2 (Bcl-2) level and down-regulated the levels of fibroblast-associated (Fas), Fas ligand (Fasl), Bcl-2 associated X protein (Bax), and Caspase-3. Moreover, the phosphorylation levels of phosphoinositide 3 kinase (PI3K), protein kinase B (Akt), and glycogen synthase kinase3β (GSK3β) were up-regulated. We proved that siEPHX2 had a protective effect on H2O2-induced oxidative damage in IEC-6 cells through activating PI3K/Akt/GSK3β signaling pathway.

Loss of nuclear ARC contributes to the development of cardiac hypertrophy in rats

AIM

Cardiac hypertrophy and myocardial apoptosis are two major factors in heart failure. As a classical regulator of apoptosis, apoptosis repressor with caspase recruitment domain (ARC) has recently also been found to have a protective effect against hypertrophy. However, the mechanism underlying this effect is still not fully understood.

METHODS

In the present study, we established animal and cellular models to monitor the changes in total and nuclear ARC during cardiac hypertrophic processes. The preventive effects of nuclear ARC in cellular hypertrophy were verified by ARC regulation and nuclear export inhibition. To further explore the mechanism for nuclear ARC superficially, we analysed proteins that interact with ARC in the nucleus via Co-IP and mass spectrometry.

RESULTS

The expression of total ARC in hypertrophic myocardial tissue and H9C2 cells remained invariant, while the level of nuclear ARC decreased dramatically. By altering the content of ARC in H9C2 cells, we found that both nuclear ARC transfection and nuclear ARC export blockade attenuated norepinephrine or angiotensin II-induced hypertrophy, while ARC knockdown had an inverse effect. Co-IP data showed that ARC interacted with prohibitin (PHB) in the nucleus and might participate in maintaining the level of PHB in cells.

CONCLUSIONS

These findings suggest a novel mechanism for ARC in cardiac hypertrophy prevention and also indicate that the anti-hypertrophic roles of ARC are probably associated with its localization in nucleus, which imply the nuclear ARC as a potential therapeutic target for cardiac hypertrophy.

CTCF inhibits endoplasmic reticulum stress and apoptosis in cardiomyocytes by upregulating RYR2 via inhibiting S100A1

AIMS

Pediatric heart failure is a common cardiovascular disease in clinical pediatrics. CCCTC-binding factor (CTCF), a novel transcriptional repressor, was reported to participate in the occurrence of various cardiovascular diseases. The present study focuses on exploring the effects of CTCF on tunicamycin (TM)-induced endoplasmic reticulum (ER) stress, and investigating the underlying mechanisms.

MATERIALS AND METHOD

Expression of CTCF in blood samples of heart failure children and TM-induced cardiomyocytes were evaluated by real-time quantitative PCR (RT-qPCR). Apoptotic rate of cardiomyocytes was detected by Annexin v assay. Western blotting and enzyme-linked immunosorbent assay (ELISA) were applied to examine the effect of CTCF on ER stress. Co-immunoprecipitation and western blotting were devoted to explore the mechanism by which CTCF contributes to ER stress.

KEY FINDINGS

We proved that CTCF was lowly expressed in blood samples of heart failure children and TM-induced cardiomyocytes, and overexpression of CTCF weaken the TM-induced ER stress. Using co-immunoprecipitation and protein blots, we demonstrated that CTCF upregulates RYR2 by inhibiting S100A1, thus mediating the PERK signaling pathway and regulating ER stress.

SIGNIFICANCE

Our data revealed that CTCF protects cardiomyocytes from ER stress through S100A1-RYR2 axis, and can be applied as a therapeutic target for the treatment of pediatric heart failure in future.

Characterization and functionality of two members of the SPFH protein superfamily, prohibitin 1 and 2 in Leishmania major

Background

Leishmaniasis, a disease caused by parasites of the genus Leishmania, infects roughly 12 million people worldwide, with about two million new cases per year. Prohibitins (PHBs) are highly conserved proteins belonging to the stomatin-prohibitin flotillin-HflC/K (SPFH) protein superfamily. In this study, we examine the potential functions of two proteins of Leishmania major, PHB1 and PHB2, as well as how they might help protect the protozoan against oxidative stress.

Results

By immunolocalization in the parasite cells, PHB1 appeared in the mitochondria and plasma membrane, whereas PHB2 was grouped in the nucleus. When Leishmania cells were under oxidative stress, PHB1 migrates towards the plasma membrane and the paraxial rod, while PHB2 remained in the nucleus and near the kinetoplast. PHB1 presented higher mRNA levels than PHB2 in the amastigotes and the infective metacyclic forms. The mRNA expression of both prohibitins was affected by the presence of the Fe³⁺ ion. PHBs inhibited the Fenton reaction, where reactive oxygen species could nick DNA, implying that they play a crucial role in controlling oxidative stress.

Conclusions

Here, we propose that PHBs may help to protect membranes and DNA against superoxide ions, thus enhancing the survival capacity of the protozoan by controlling the ROS within the phagosome of the macrophages where the parasite multiplies.

Mitochondrial Quality Control Mechanisms and the PHB (Prohibitin) Complex

Mitochondrial functions are essential for life, critical for development, maintenance of stem cells, adaptation to physiological changes, responses to stress, and aging. The complexity of mitochondrial biogenesis requires coordinated nuclear and mitochondrial gene expression, owing to the need of stoichiometrically assemble the oxidative phosphorylation (OXPHOS) system for ATP production. It requires, in addition, the import of a large number of proteins from the cytosol to keep optimal mitochondrial function and metabolism. Moreover, mitochondria require lipid supply for membrane biogenesis, while it is itself essential for the synthesis of membrane lipids. To achieve mitochondrial homeostasis, multiple mechanisms of quality control have evolved to ensure that mitochondrial function meets cell, tissue, and organismal demands. Herein, we give an overview of mitochondrial mechanisms that are activated in response to stress, including mitochondrial dynamics, mitophagy and the mitochondrial unfolded protein response (UPR^mt). We then discuss the role of these stress responses in aging, with particular focus on Caenorhabditis elegans. Finally, we review observations that point to the mitochondrial prohibitin (PHB) complex as a key player in mitochondrial homeostasis, being essential for mitochondrial biogenesis and degradation, and responding to mitochondrial stress. Understanding how mitochondria responds to stress and how such responses are regulated is pivotal to combat aging and disease.

Salvianic acid A sodium protects HUVEC cells against tert-butyl hydroperoxide induced oxidative injury via mitochondria-dependent pathway

Salvianic acid A (Danshensu) is a major water-soluble component extracted from Salvia miltiorrhiza (Danshen), which has been widely used in clinic in China for treatment of cardiovascular diseases (CVDs). This study aimed to investigate the protective effects of salvianic acid A sodium (SAAS) against tert-butyl hydroperoxide (t-BHP) induced human umbilical vein endothelial cell (HUVEC) oxidative injury and the underlying molecular mechanisms. In the antioxidant activity-assessing model, SAAS pretreatment significantly ameliorated the cell growth inhibition and apoptosis induced by t-BHP. An ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) based-metabolic profiling was developed to investigate the metabolic changes of HUVEC cells in response to t-BHP and SAAS. The results revealed that t-BHP injury upregulated 13 metabolites mainly involved in tryptophan metabolism and phenylalanine metabolism which were highly correlated with mitochondrial function and oxidative stress, and 50 μM SAAS pretreatment effectively reversed these metabolic changes. Further biomedical research indicated that SAAS pretreatment reduced the t-BHP induced increase of lactate dehydrogenase (LDH), intracellular reactive oxygen species (ROS), malondialdehyde (MDA) and mitochondrial membrane potential (MMP), and the decrease of key antioxidant enzymes through mitochondria antioxidative pathways via JAK2/STAT3 and PI3K/Akt/GSK-3β signalings. Taken together, our results suggested that SAAS may protect HUVEC cells against t-BHP induced oxidative injury via mitochondrial antioxidative defense system.

Insulin and β Adrenergic Receptor Signaling: Crosstalk in Heart

Recent advances show that insulin may affect β adrenergic receptor (βAR) signaling in the heart to modulate cardiac function in clinically relevant states, such as diabetes mellitus (DM) and heart failure (HF). Conversely, activation of βAR regulates cardiac glucose uptake and promotes insulin resistance (IR) in HF. Here, we discuss the recent characterization of the interaction between the cardiac insulin receptor (InsR) and βAR in the myocardium, in which insulin stimulation crosstalks with cardiac βAR via InsR substrate (IRS)-dependent and G-protein receptor kinase 2 (GRK2)-mediated phosphorylation of β₂AR. The insulin-induced phosphorylation promotes β₂AR coupling to G_i and expression of phosphodiesterase 4D, which both inhibit cardiac adrenergic signaling and compromise cardiac contractile function. These recent developments could support new approaches for the effective prevention or treatment of obesity- or DM-related HF.