Implantable Patch of Oxidized Nanofibrillated Cellulose and Lysozyme Amyloid Nanofibrils for the Regeneration of Infarcted Myocardium Tissue and Local Delivery of RNA-Loaded Nanoparticles

Biopolymeric implantable patches are popular scaffolds for myocardial regeneration applications. Besides being biocompatible, they can be tailored to have required properties and functionalities for this application. Recently, fibrillar biobased nanostructures prove to be valuable in the development of functional biomaterials for tissue regeneration applications. Here, periodate-oxidized nanofibrillated cellulose (OxNFC) is blended with lysozyme amyloid nanofibrils (LNFs) to prepare a self-crosslinkable patch for myocardial implantation. The OxNFC:LNFs patch shows superior wet mechanical properties (60 MPa for Young's modulus and 1.5 MPa for tensile stress at tensile strength), antioxidant activity (70% scavenging activity under 24 h), and bioresorbability ratio (80% under 91 days), when compared to the patches composed solely of NFC or OxNFC. These improvements are achieved while preserving the morphology, required thermal stability for sterilization, and biocompatibility toward rat cardiomyoblast cells. Additionally, both OxNFC and OxNFC:LNFs patches reveal the ability to act as efficient vehicles to deliver spermine modified acetalated dextran nanoparticles, loaded with small interfering RNA, with 80% of delivery after 5 days. This study highlights the value of simply blending OxNFC and LNFs, synergistically combining their key properties and functionalities, resulting in a biopolymeric patch that comprises valuable characteristics for myocardial regeneration applications.

Myoglobin modulates the Hippo pathway to promote cardiomyocyte differentiation

The endogenous mechanisms that propagate cardiomyocyte differentiation and prevent de-differentiation remain unclear. While the expression of the heme protein myoglobin increases by over 50% during cardiomyocyte differentiation, a role for myoglobin in regulating cardiomyocyte differentiation has not been tested. Here, we show that deletion of myoglobin in cardiomyocyte models decreases the gene expression of differentiation markers and stimulates cellular proliferation, consistent with cardiomyocyte de-differentiation. Mechanistically, the heme prosthetic group of myoglobin catalyzes the oxidation of the Hippo pathway kinase LATS1, resulting in phosphorylation and inactivation of yes-associated protein (YAP). In vivo, myoglobin-deficient zebrafish hearts show YAP dephosphorylation and accelerated cardiac regeneration after apical injury. Similarly, myoglobin knockdown in neonatal murine hearts shows increased YAP dephosphorylation and cardiomyocyte cycling. These data demonstrate a novel role for myoglobin as an endogenous driver of cardiomyocyte differentiation and highlight myoglobin as a potential target to enhance cardiac development and improve cardiac repair and regeneration.

Injectable Nanocomposite Hydrogels of Gelatin-Hyaluronic Acid Reinforced with Hybrid Lysozyme Nanofibrils-Gold Nanoparticles for the Regeneration of Damaged Myocardium

Biopolymeric injectable hydrogels are promising biomaterials for myocardial regeneration applications. Besides being biocompatible, they adjust themselves, perfectly fitting the surrounding tissue. However, due to their nature, biopolymeric hydrogels usually lack desirable functionalities, such as antioxidant activity and electrical conductivity, and in some cases, mechanical performance. Protein nanofibrils (NFs), such as lysozyme nanofibrils (LNFs), are proteic nanostructures with excellent mechanical performance and antioxidant activity, which can work as nanotemplates to produce metallic nanoparticles. Here, gold nanoparticles (AuNPs) were synthesized in situ in the presence of LNFs, and the obtained hybrid AuNPs@LNFs were incorporated into gelatin-hyaluronic acid (HA) hydrogels for myocardial regeneration applications. The resulting nanocomposite hydrogels showed improved rheological properties, mechanical resilience, antioxidant activity, and electrical conductivity, especially for the hydrogels containing AuNPs@LNFs. The swelling and bioresorbability ratios of these hydrogels are favorably adjusted at lower pH levels, which correspond to the ones in inflamed tissues. These improvements were observed while maintaining important properties, namely, injectability, biocompatibility, and the ability to release a model drug. Additionally, the presence of AuNPs allowed the hydrogels to be monitorable through computer tomography. This work demonstrates that LNFs and AuNPs@LNFs are excellent functional nanostructures to formulate injectable biopolymeric nanocomposite hydrogels for myocardial regeneration applications.

The preventive effect of Mori Ramulus on oxidative stress-induced cellular damage in skeletal L6 myoblasts through Nrf2-mediated activation of HO-1

The aim of the present study is to investigate the preventive effect of water extract of Mori Ramulus (MRWE) on oxidative stress-mediated cellular damages in rat skeletal L6 myoblasts. Our results demonstrated that MRWE pretreatment markedly improved cell survival and suppressed cell cycle arrest at the G2/M phase and apoptosis in hydrogen peroxide (H2O2)-treated L6 cells. H2O2-triggered DNA damage was also notably reduced by MRWE, which since it was correlated with protection of reactive oxygen species (ROS) production. Additionally, H2O2 stimulated cytosolic release of cytochrome c and up-regulation of Bax/Bcl-2 ratio, whereas MRWE suppressed these changes following by H2O2. Moreover, MRWE inhibited the cleavage of poly(ADP-ribose) polymerase as well as the activity of caspase-3 by H2O2. Furthermore, MRWE enhanced H2O2-mediated expression of nuclear factor erythroid 2-associated factor 2 (Nrf2) and its representative downstream enzyme, heme oxygenase-1 (HO-1). However, the protective effects of MRWE on H2O2-induced ROS production, cell cycle arrest and apoptosis were significantly attenuated by HO-1 inhibitor. In conclusion, our present results suggests that MRWE could protect L6 myoblasts from H2O2-induced cellular injury by inhibiting ROS generation along with Nrf2-mediated activation of HO-1, indicating this finding may expand the scope of application of Mori Ramulus in medicine.

H2S protects from oxidative stress-driven ACE2 expression and cardiac aging

Cystathionine gamma-lyase (CSE)-derived hydrogen sulfide (H₂S) plays an essential role in preserving cardiac functions. Angiotensin-converting enzyme 2 (ACE2) acts as the negative regulator of the renin-angiotensin system, exerting anti-oxidative stress and anti-inflammatory properties within the body. The interplays of CSE/H₂S signaling and ACE2 in cardiac aging are unclear. In this study, the regulatory roles of H₂S on ACE2 expression in mouse heart tissue and rat cardiomyocytes under different stress conditions were investigated. It was found that ACE2 protein level was lower in heart tissues from old mice (56-week-old) than young mice (8-week-old), and the knockout of CSE (CSE KO) induced moderate oxidative stress and further inhibited ACE2 protein level in mouse hearts at both young and old age. Incubation of rat cardiac cells (H9C2) with a low dose of H₂O₂ (50 µM) suppressed ACE2 protein level and induced cellular senescence, which was completely reversed by co-incubation with 30 µM NaHS (a H₂S donor). Prolonged nutrient excess is an increased risk of heart disorders by causing metabolic dysfunction and cardiac remodeling. We further found high-fat diet feeding stimulated ACE2 expression and induced severe oxidative stress in CSE KO heart in comparison with wild-type heart. Lipid overload in H9C2 cells to mimic a status of nutrient excess also enhanced the expression of ACE2 protein and induced severe oxidative stress and cell senescence, which were significantly attenuated by the supplementation of exogenous H₂S. Furthermore, the manipulation of ACE2 expression partially abolished the protective role of H₂S against cellular senescence. These results demonstrate the dynamic roles of H₂S in the maintenance of ACE2 levels under different levels of oxidative stress, pointing to the potential implications in targeting the CSE/H₂S system for the interruption of aging and diabetes-related heart disorders.

Perturbation of calcium homeostasis and multixenobiotic resistance by nanoplastics in the ciliate Tetrahymena thermophila

Microplastics (MPs) are an environmental hazard of growing concern, including their potential toxic effects on the biota of different trophic levels. Nevertheless, the molecular mechanisms underlying MP-induced toxicity remain largely unknown. In the present study, Tetrahymena thermophila was exposed to polystyrene nanoplastics (PS-NPs) and the responses of this relatively sensitive ciliate were then followed using transcriptome analysis together with several other verification methods. The results showed that PS-NPs perturbed calcium (Ca) homeostasis, by inducing the inositol-1,4,5-trisphosphate-dependent liberation of Ca from the endoplasmic reticulum into the cytosol. The high cytosolic concentration of Ca induced Ca accumulation in mitochondria, which increased mitochondrial permeability and the generation of reactive oxygen species, finally leading to growth inhibition. Such toxicity is the so-called direct effects of PS-NPs. By contrast, PS-NPs also inhibited the activity of multixenobiotic resistance transporter, by down-regulating the ATP-binding cassette transporter genes Abcb15 and Abcc52. This additional effect may alter cellular responses to other pollutants and implicates PS-NPs in the risks to the organism posed by subsequent toxic exposures, which was named as the indirect effects of PS-NPs. Our study highlights the importance of considering both direct and indirect biological effects of MPs in evaluations of their environmental and health risks.

Therapeutic Potential of Reactive Oxygen Species: State of the Art and Recent Advances

In the last decade, several studies have proven that when at low concentration reactive oxygen species (ROS) show an adaptive beneficial effect and posited the idea that they can be utilized as inexpensive and convenient inducers of tissue regeneration. On the other hand, the recent discovery that cancer cells are more sensitive to oxidative damage paved the way for their use in the selective killing of tumor cells, and sensors to monitor ROS production during cancer treatment are under extensive investigation. Nevertheless, although ROS-activated signaling pathways are well established, less is known about the mechanisms underlying the switch from an anabolic to a cytotoxic response. Furthermore, a high variability in biological response is observed between different modalities of administration, cell types, donor ages, eventual concomitant diseases, and external microenvironment. On the other hand, available preclinical studies are scarce, whereas the quest for the most suitable systems for in vivo delivery is still elusive. Furthermore, new strategies to control the temporal pattern of ROS release need to be developed, if considering their tumorigenic potential. This review initially discusses ROS mechanisms of action and their potential application in stem cell biology, tissue engineering, and cancer therapy. It then outlines the state of art of ROS-based drugs and identifies challenges faced in translating ROS research into clinical practice.

Loss of Mitochondrial DNA by Gemcitabine Triggers Mitophagy and Cell Death

Gemcitabine (2,2-difluorodeoxycytidine nucleic acid), an anticancer drug exhibiting a potent ability to kill cancer cells, is a frontline chemotherapy drug. Although some chemotherapeutic medicines are known to induce nuclear DNA damage, no investigation into mitochondrial DNA (mtDNA) damage currently exists. When we treated insulinoma pancreatic β-cells (line INS-1) with high mitochondrial activity with gemcitabine for 24 h, the mtDNA contents were decreased. Gemcitabine induced a decrease in the number of mitochondria and the average potential of mitochondrial membrane in the cell but increased the superoxide anion radical levels. We observed that treatment with gemcitabine to induce cell death accompanied by autophagy-related protein markers, Atg5 and Atg7; these were significantly prevented by the autophagy inhibitors. The localization of Atg5 co-occurred with the location of mitochondria with membranes having high potential and mitophagy in cells treated with gemcitabine. The occurrence of mitophagy was inhibited by the inhibitors of the phosphatidylinositol 3-kinase/Akt pathway. Our results led us to the conclusion that gemcitabine induced cell death through mitophagy with the loss of mtDNA. These findings may provide a rationale for the combination of mtDNA damage with mitophagy in future clinical applications for cancer cells.

Selenium supplementation protects against oxidative stress-induced cardiomyocyte cell cycle arrest through activation of PI3K/AKT

Oxidative stress significantly contributes to heart disease, and thus might be a promising target for ameliorating heart failure. Mounting evidence suggests that selenium has chemotherapeutic potential for treating heart disease due to its regulation of selenoproteins, which play antioxidant regulatory roles. Oxidative stress-induced cardiomyocyte cell cycle arrest contributes to the loss of cardiomyocytes during heart failure. The protective effects and mechanism of selenium against oxidative stress-induced cell cycle arrest in cardiomyocytes warrant further study. H9c2 rat cardiomyoblast cells were treated with hydrogen peroxide in the presence or absence of selenium supplementation. Na2SeO3 pretreatment alleviated H2O2-induced oxidative stress, increased thioredoxin reductase (TXNRD) activity and glutathione peroxidase (GPx) activity and counteracted the H2O2-induced cell cycle arrest at the S phase. These effects were accompanied by attenuation of the H2O2-induced strengthening of the G2/M-phase inhibitory system, including increased mRNA and protein levels of cyclin-dependent kinase 1 (CDK1) and decreased p21 mRNA levels. Notably, Na2SeO3 pretreatment activated the PI3K/AKT signaling pathway, and inhibition of PI3K counteracted the protective effects of selenium on H2O2-induced cell cycle arrest. We corroborated our findings in vivo by inducing oxidative stress in pig heart by feeding a selenium deficient diet, which decreased the TXNRD activity, inactivated PI3K/AKT signaling and strengthened the G2/M-phase inhibitory system. We concluded that the cardioprotective effects of selenium supplementation against oxidative stress-induced cell cycle arrest in cardiomyocytes might be mediated by the selenoprotein-associated (GPx and TXNRD) antioxidant capacity, thereby activating redox status-associated PI3K/AKT pathways, which promote cell cycle progression by targeting the G2/M phase inhibitory system. This study provides new insight into the underlying mechanisms of cardioprotection effects of selenium at the cellular level.

Single nanomolar doxorubicin exposure triggers compensatory mitochondrial responses in H9c2 cardiomyoblasts

Dose-dependent and cumulative cardiotoxicity associated with doxorubicin (DOX) is the main limitation of anticancer therapy. Pediatric cancer survivors are particularly vulnerable, and no effective prevention measures are available. The aim of the present study was to investigate the persistent effects of nanomolar DOX concentrations and determine whether a pretreatment would induce mitochondrial adaptations in H9c2 cardiomyoblasts. H9c2 cells were incubated with DOX (10 and 25 nM) for 24 h, followed by 9 days of recovery in drug-free medium. We found that the sub-therapeutic DOX treatment induced persistent hypertrophy and dose-dependent cell cycle arrest in G2/M. Glycolytic activity, indirectly based on extracellular acidification rate, and basal respiration were significantly decreased in DOX-treated cells compared to controls, although both groups showed similar maximal respiration. Additionally, nanomolar DOX pretreatment resulted in upregulation of mitochondrial DNA transcripts accompanied by a decrease in DNA methyltransferase 1 (DNMT1) and global methylation levels. Finally, the pretreatment with DOX ameliorated H9c2 cells resistance against a subsequent exposure to DOX. These results suggest that nanomolar DOX pretreatment induced a beneficial and possibly epigenetic-based mitochondrial adaptation, raising the possibility that an early sub-therapeutic DOX treatment can be used as a preconditioning and protective approach during anticancer therapies.

Chemically induced strong cellular hypertrophy often reduces the accuracy of cytotoxicity measurements obtained using the ATP assay

The ATP assay is a highly sensitive and versatile method for measuring cytotoxicity. However, the correlation between the cell viability results obtained using the ATP assay and those obtained using direct cell counting has not been widely reported. Therefore, to evaluate the reliability and limitations of the ATP assay, we compared the results of ATP assay with those of automatic cell counter, which can measure the number and diameter of cells directly, by using 24 compounds and repeating individual experiments thrice. The correlation between the data was low for 7 of the 24 compounds (r² < 0.8, at least 2 out of 3 experiments). These were the top 7 of the 11 compounds that induced cell hypertrophy. These 7 compounds were also observed to increase the area of mitochondria. However, the last 4 of the 11 compounds increased the cell size but did not increase the mitochondrial area. For the remaining 13 compounds, which had no effect on cell size, a good correlation was observed between the results of the two methods (r² > 0.8, at least 2 out of 3 experiments), and the cell size was effectively the same as that of the controls. We concluded that the poor correlation between the two methods was attributable to an increase in the content of intracellular ATP because of the chemically induced cell and mitochondrial hypertrophy. We showed that the ATP assay is unsuitable for assessing the cytotoxicity of compounds that induce cell hypertrophy with increase in the mitochondrial area and ATP content.

The Citrus Flavanone Naringenin Protects Myocardial Cells against Age-Associated Damage

In recent years, the health-promoting effects of the citrus flavanone naringenin have been examined. The results have provided evidence for the modulation of some key mechanisms involved in cellular damage by this compound. In particular, naringenin has been revealed to have protective properties such as an antioxidant effect in cardiometabolic disorders. Very recently, beneficial effects of naringenin have been demonstrated in old rats. Because aging has been demonstrated to be directly related to the occurrence of cardiac disorders, in the present study, the ability of naringenin to prevent cardiac cell senescence was investigated. For this purpose, a cellular model of senescent myocardial cells was set up and evaluated using colorimetric, fluorimetric, and immunometric techniques. Relevant cellular senescence markers, such as X-gal staining, cell cycle regulator levels, and the percentage of cell cycle-arrested cells, were found to be reduced in the presence of naringenin. In addition, cardiac markers of aging-induced damage, including radical oxidative species levels, mitochondrial metabolic activity, mitochondrial calcium buffer capacity, and estrogenic signaling functions, were also modulated by the compound. These results suggested that naringenin has antiaging effects on myocardial cells.

The Citrus Flavanone Naringenin Produces Cardioprotective Effects in Hearts from 1 Year Old Rat, through Activation of mitoBK Channels

Background and Purpose: Incidence of cardiovascular disorders increases with age, because of a dramatic fall of endogenous self-defense mechanisms and increased vulnerability of myocardium. Conversely, the effectiveness of many cardioprotective drugs is blunted in hearts of 1 year old rat. The Citrus flavanone naringenin (NAR) was reported to promote cardioprotective effects against ischemia/reperfusion (I/R) injury, through the activation of mitochondrial large conductance calcium-activated potassium channel (mitoBK). These effects were observed in young adult rats, but no data are available about the possible cardioprotective effects of NAR in aged animals.

Experimental Approach: This study aimed at evaluating the potential cardioprotective effects of NAR against I/R damage in 1 year old rats, and the possible involvement of mitoBK.

Key Results: Naringenin protected the hearts of 1 year old rats in both ex vivo and in vivo I/R protocols. Noteworthy, these effects were antagonized by paxilline, a selective BK-blocker. The cardioprotective effects of NAR were also observed in senescent H9c2 cardiomyoblasts. In isolated mitochondria from hearts of 1 year old, NAR exhibited the typical profile of a mitoBK opener. Finally, Western Blot analysis confirmed a significant (albeit reduced) presence of BK-forming alpha and beta subunits, both in cardiac tissue of 1 year old rats and in senescent H9c2 cells.

Conclusion and Implications: This is the first work reporting cardioprotective effects of NAR in 1 year old rats. Although further studies are needed to better understand the whole pathway involved in the NAR-mediated cardioprotection, these preliminary data represent a promising perspective for a rational nutraceutical use of NAR in aging.

Changes in the Transcriptome of Human Astrocytes Accompanying Oxidative Stress-Induced Senescence

Aging is a major risk factor for many neurodegenerative disorders. A key feature of aging biology that may underlie these diseases is cellular senescence. Senescent cells accumulate in tissues with age, undergo widespread changes in gene expression, and typically demonstrate altered, pro-inflammatory profiles. Astrocyte senescence has been implicated in neurodegenerative disease, and to better understand senescence-associated changes in astrocytes, we investigated changes in their transcriptome using RNA sequencing. Senescence was induced in human fetal astrocytes by transient oxidative stress. Brain-expressed genes, including those involved in neuronal development and differentiation, were downregulated in senescent astrocytes. Remarkably, several genes indicative of astrocytic responses to injury were also downregulated, including glial fibrillary acidic protein and genes involved in the processing and presentation of antigens by major histocompatibility complex class II proteins, while pro-inflammatory genes were upregulated. Overall, our findings suggest that senescence-related changes in the function of astrocytes may impact the pathogenesis of age-related brain disorders.

Pharmacological Ascorbate Radiosensitizes Pancreatic Cancer

The toxicity of pharmacologic ascorbate is mediated by the generation of H2O2 via the oxidation of ascorbate. Because pancreatic cancer cells are sensitive to H2O2 generated by ascorbate, they would also be expected to become sensitized to agents that increase oxidative damage such as ionizing radiation. The current study demonstrates that pharmacologic ascorbate enhances the cytotoxic effects of ionizing radiation as seen by decreased cell viability and clonogenic survival in all pancreatic cancer cell lines examined, but not in nontumorigenic pancreatic ductal epithelial cells. Ascorbate radiosensitization was associated with an increase in oxidative stress-induced DNA damage, which was reversed by catalase. In mice with established heterotopic and orthotopic pancreatic tumor xenografts, pharmacologic ascorbate combined with ionizing radiation decreased tumor growth and increased survival, without damaging the gastrointestinal tract or increasing systemic changes in parameters indicative of oxidative stress. Our results demonstrate the potential clinical utility of pharmacologic ascorbate as a radiosensitizer in the treatment of pancreatic cancer.

Cardiac phase-targeted dynamic load on left ventricle differentially regulates phase-sensitive gene expressions and pathway activation

The heart has remarkable capacity to adapt to mechanical load and to dramatically change its phenotype. The mechanism underlying such diverse phenotypic adaptations remains unknown. Since systolic overload induces wall thickening, while diastolic overload induces chamber enlargement, we hypothesized that cardiac phase-sensitive mechanisms govern the adaptation. We inserted a balloon into the left ventricle (LV) of a Langendorff perfused rat heart, and controlled LV volume (LVV) using a high performance servo-pump. We created isolated phasic systolic overload (SO) by isovolumic contraction (peak LV pressure >170mmHg) at unstressed diastolic LVV [end-diastolic pressure (EDP)=0mmHg]. We also created pure phasic diastolic overload (DO) by increasing diastolic LVV until EDP >40mmHg and unloading completely in systole. After 3hours under each condition, the myocardium was analyzed using DNA microarray. Gene expressions under SO and DO conditions were compared against unloaded control condition using gene ontology and pathway analysis (n=4 each). SO upregulated proliferation-related genes, whereas DO upregulated fibrosis-related genes (P<10(-5)). Both SO and DO upregulated genes related functionally to cardiac hypertrophy, although the gene profiles were totally different. Upstream regulators confirmed by Western blot indicated that SO activated extracellular signal-regulated kinase 1/2, c-Jun NH2-terminal kinase, and Ca(2+)/calmodulin-dependent protein kinase II (3.2-, 2.0-, and 4.7-fold versus control, P<0.05, n=5), whereas DO activated p38 (2.9-fold, P<0.01), which was consistent with the downstream gene expressions. In conclusion, pure isolated systolic and diastolic overload permits elucidation of cardiac phase-sensitive gene regulation. The genomic responses indicate that mechanisms governing the cardiac phase-sensitive adaptations are different.

Type II diabetes increases mitochondrial DNA mutations in the left ventricle of the Goto-Kakizaki diabetic rat

Mitochondrial dysfunction has a significant role in the development of diabetic cardiomyopathy. Mitochondrial oxidant stress has been accepted as the singular cause of mitochondrial DNA (mtDNA) damage as an underlying cause of mitochondrial dysfunction. However, separate from a direct effect on mtDNA integrity, diabetic-induced increases in oxidant stress alter mitochondrial topoisomerase function to propagate mtDNA mutations as a contributor to mitochondrial dysfunction. Both glucose-challenged neonatal cardiomyocytes and the diabetic Goto-Kakizaki (GK) rat were studied. In both the GK left ventricle (LV) and in cardiomyocytes, chronically elevated glucose presentation induced a significant increase in mtDNA damage that was accompanied by decreased mitochondrial function. TTGE analysis revealed a number of base pair substitutions in the 3' end of COX3 from GK LV mtDNA that significantly altered the protein sequence. Mitochondrial topoisomerase DNA cleavage activity in isolated mitochondria was significantly increased in the GK LV compared with Wistar controls. Both hydroxycamptothecin, a topoisomerase type 1 inhibitor, and doxorubicin, a topoisomerase type 2 inhibitor, significantly exacerbated the DNA cleavage activity of isolated mitochondrial extracts indicating the presence of multiple functional topoisomerases in the mitochondria. Mitochondrial topoisomerase function was significantly altered in the presence of H2O2 suggesting that separate from a direct effect on mtDNA, oxidant stress mediated type II diabetes-induced alterations of mitochondrial topoisomerase function. These findings are significant in that the activation/inhibition state of the mitochondrial topoisomerases will have important consequences for mtDNA integrity and the well being of the diabetic myocardium.

Isoproterenol induced hypertrophy and associated signaling pathways are modulated by somatostatin in H9c2 cells

BACKGROUND

Somatostatin (SST), a growth hormone inhibitory peptide plays key role in regulation of cell proliferation via modulation of mitogen activated protein kinases (MAPKs) and cell survival pathway. In cardiac physiology, β-Adrenergic receptors (β-ARs) play crucial role in regulation of downstream signaling pathways in receptor specific manner. The aim of the current study was to delineate the mechanistic insight for the role of SST on β-AR mediated signaling which promotes hypertrophy and apoptosis in rat fetal cardiomyocytes (H9c2 cells). Accordingly, SST dependent changes in signaling molecules including second messenger cAMP, PKA/CREB as well as MAPKs including ERK and p38 which are key mediators of hypertrophy and apoptosis were analyzed.

METHODS AND RESULTS

In the present study, we determined receptor specific effects on intracellular cAMP levels, signaling by western blot analysis and apoptosis by using JC-1 and Hoechst-33258 staining. Here, we present the data which indicates that SST inhibits isoproterenol induced hypertrophy and apoptosis in H9c2 cells. Importantly, SST inhibits β-ARs agonist induced cAMP activation and SST mediated inhibition of cAMP was enhanced in presence of β-ARs antagonist. SST enhances β2AR agonist formoterol mediated effects on PKA, CREB and ERK1/2 phosphorylations whereas it inhibits isoproterenol mediated ERK1/2 and p38 signaling in concentration dependent manner.

CONCLUSIONS

Taken together, these results presented here provide a novel insight for the potential role of SST in regulation of β-AR mediated effects on hypertrophy and modulation of hypertrophy promoting signaling in H9c2 cells.

Curcumin affects cell survival and cell volume regulation in human renal and intestinal cells

Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1E,6E-heptadiene-3,5-dione or diferuloyl methane) is a polyphenol derived from the Curcuma longa plant, commonly known as turmeric. This substance has been used extensively in Ayurvedic medicine for centuries for its anti-oxidant, analgesic, anti-inflammatory and antiseptic activity. More recently curcumin has been found to possess anti-cancer properties linked to its pro-apoptotic and anti-proliferative actions. The underlying mechanisms of these diverse effects are complex, not fully elucidated and subject of intense scientific debate. Despite increasing evidence indicating that different cation channels can be a molecular target for curcumin, very little is known about the effect of curcumin on chloride channels. Since, (i) the molecular structure of curcumin indicates that the substance could potentially interact with chloride channels, (ii) chloride channels play a role during the apoptotic process and regulation of the cell volume, and (iii) apoptosis is a well known effect of curcumin, we set out to investigate whether or not curcumin could (i) exert a modulatory effect (direct or indirect) on the swelling activated chloride current ICl(swell) in a human cell system, therefore (ii) affect cell volume regulation and (iii) ultimately modulate cell survival. The ICl(swell) channels, which are essential for regulating the cell volume after swelling, are also known to be activated under isotonic conditions as an early event in the apoptotic process. Here we show that long-term exposure of a human kidney cell line to extracellular 0.1-10 μM curcumin modulates ICl(swell) in a dose-dependent manner (0.1 μM curcumin is ineffective, 0.5-5.0 μM curcumin increase, while 10 μM curcumin decrease the current), and short-term exposure to micromolar concentrations of curcumin does not affect ICl(swell) neither if applied from the extracellular nor from the intracellular side - therefore, a direct effect of curcumin on ICl(swell) can be ruled out. Furthermore, we show that curcumin exposure induces apoptosis in human kidney cells, and at a concentration of 5.0-10 μM induces the appearance of a sub-population of cells with a dramatically increased volume. In these cells the regulation of the cell volume seems to be impaired, most likely as a consequence of the ICl(swell) blockade. Similarly, 50 μM curcumin induced apoptosis, caused cell cycle arrest in G1-phase and increased the volume of human colorectal adenocarcinoma HT-29 cells. The cell cycle arrest in G1 phase may be the mechanism underlying the volume increase observed in this cell line after exposure to curcumin.

C-reactive protein induces p53-mediated cell cycle arrest in H9c2 cardiac myocytes

C-reactive protein (CRP) is one of the most important biomarker for cardiovascular diseases. Recent studies have shown that CRP affects cell survival, differentiation and apoptosis. However, the effect of CRP on the cell cycle has not been studied yet. We investigated the cell cycle alterations and cellular mechanisms induced by CRP in H9c2 cardiac myocytes. Flow cytometry analysis showed that CRP-treated H9c2 cells displayed cell cycle arrest in G0/G1 phase. CRP treatment resulted in a significant reduction in the levels of CDK4, CDK6 and cyclin D1 in a concentration-dependent manner. Interestingly, CRP caused an increase in the p53 accumulation and its phosphorylation on Ser15, leading to induce p21 upregulation. Treatment with a specific p53 inhibitor, PFT-α restored the levels of CDK4 and CDK6. A significant increase of ERK1/2 phosphorylation level was detected in CRP-treated cells. Furthermore, pretreatment of a specific ERK inhibitor resulted in decreased p53 phosphorylation and p21 induction. ERK inhibitor pretreatment induced significant restoration of protein levels of CDK4 and CDK6, leading to re-entry into the cell cycle. In addition, increased phosphorylation of p53 and ERK induced by CRP was considerably reversed by Fc gamma receptor IIIa (FcγRIIIa) knock-down using siRNA. FcγRIIIa siRNA transfection also restored the levels of cell cycle proteins. Our study has provided the first proposal on the novel insights into how CRP directly affects cell cycle in cells.