Dantrolene suppresses spontaneous Ca2+ release without altering excitation-contraction coupling in cardiomyocytes of aged mice

Altering Calcium Sensitivity in Heart Failure: A Crossroads of Disease Etiology and Therapeutic Innovation

Heart failure (HF) presents a significant clinical challenge, with current treatments mainly easing symptoms without stopping disease progression. The targeting of calcium (Ca2+) regulation is emerging as a key area for innovative HF treatments that could significantly alter disease outcomes and enhance cardiac function. In this review, we aim to explore the implications of altered Ca2+ sensitivity, a key determinant of cardiac muscle force, in HF, including its roles during systole and diastole and its association with different HF types-HF with preserved and reduced ejection fraction (HFpEF and HFrEF, respectively). We further highlight the role of the two rate constants kon (Ca2+ binding to Troponin C) and koff (its dissociation) to fully comprehend how changes in Ca2+ sensitivity impact heart function. Additionally, we examine how increased Ca2+ sensitivity, while boosting systolic function, also presents diastolic risks, potentially leading to arrhythmias and sudden cardiac death. This suggests that strategies aimed at moderating myofilament Ca2+ sensitivity could revolutionize anti-arrhythmic approaches, reshaping the HF treatment landscape. In conclusion, we emphasize the need for precision in therapeutic approaches targeting Ca2+ sensitivity and call for comprehensive research into the complex interactions between Ca2+ regulation, myofilament sensitivity, and their clinical manifestations in HF.

L-Carnitine improves mechanical responses of cardiomyocytes and restores Ca2+ homeostasis during aging

L-Carnitine (β-hydroxy-γ-trimethylaminobutyric acid, LC) is a crucial molecule for the mitochondrial oxidation of fatty acids. It facilitates the transport of long-chain fatty acids into the mitochondrial matrix. The reduction in LC levels during the aging process has been linked to numerous cardiovascular disorders, including contractility dysfunction, and disrupted intracellular Ca2+ homeostasis. The aim of this study was to examine the effects of long-term (7 months) LC administration on cardiomyocyte contraction and intracellular Ca2+ transients ([Ca2+]i) in aging rats. Male albino Wistar rats were randomly assigned to either the control or LC-treated groups. LC (50 mg/kg body weight/day) was dissolved in distilled water and orally administered for a period of 7 months. The control group received distilled water alone. Subsequently, ventricular single cardiomyocytes were isolated, and the contractility and Ca2+ transients were recorded in aging (18 months) rats. This study demonstrates, for the first time, a novel inotropic effect of long-term LC treatment on rat ventricular cardiomyocyte contraction. LC increased cardiomyocyte cell shortening and resting sarcomere length. Furthermore, LC supplementation led to a reduction in resting [Ca2+]i level and an increase in the amplitude of [Ca2+]i transients, indicative of enhanced contraction. Consistent with these results, decay time of Ca2+ transients also decreased significantly in the LC-treated group. The long-term administration of LC may help restore the Ca2+ homeostasis altered during aging and could be used as a cardioprotective medication in cases where myocyte contractility is diminished.

Arrhythmogenesis in the aged heart following ischaemia-reperfusion: role of transient receptor potential vanilloid 4

AIMS

Cardiomyocyte Ca2+ homoeostasis is altered with ageing and predisposes the heart to Ca2+ intolerance and arrhythmia. Transient receptor potential vanilloid 4 (TRPV4) is an osmotically activated cation channel with expression in cardiomyocytes of the aged heart. The objective of this study was to examine the role of TRPV4 in Ca2+ handling and arrhythmogenesis following ischaemia-reperfusion (I/R), a pathological scenario associated with osmotic stress.

METHODS AND RESULTS

Cardiomyocyte membrane potential was monitored prior to and following I/R in Langendorff-perfused hearts of Aged (19-28 months) male and female C57BL/6 mice ± TRPV4 inhibition (1 μM HC067047, HC). Diastolic resting membrane potential was similar between Aged and Aged HC at baseline, but following I/R Aged exhibited depolarized diastolic membrane potential vs. Aged HC. The effects of TRPV4 on cardiomyocyte Ca2+ signalling following I/R were examined in isolated hearts of Aged cardiac-specific GCaMP6f mice (±HC) using high-speed confocal fluorescence microscopy, with cardiomyocytes of Aged exhibiting an increased incidence of pro-arrhythmic Ca2+ signalling vs. Aged HC. In the isolated cell environment, cardiomyocytes of Aged responded to sustained hypoosmotic stress (250mOsm) with an increase in Ca2+ transient amplitude (fluo-4) and higher incidence of pro-arrhythmic diastolic Ca2+ signals vs. Aged HC. Intracardiac electrocardiogram measurements in isolated hearts following I/R revealed an increased arrhythmia incidence, an accelerated time to ventricular arrhythmia, and increased arrhythmia score in Aged vs. Aged HC. Aged exhibited depolarized resting membrane potential, increased pro-arrhythmic diastolic Ca2+ signalling, and greater incidence of arrhythmia when compared with Young (3-5 months).

CONCLUSION

TRPV4 contributes to pro-arrhythmic cardiomyocyte Ca2+ signalling, electrophysiological abnormalities, and ventricular arrhythmia in the aged mouse heart.

6-Gingerol exerts a protective effect against hypoxic injury through the p38/Nrf2/HO-1 and p38/NF-κB pathway in H9c2 cells

Ginger, one of the most widely consumed condiment for various foods and beverages, has many pharmacological effects. 6-gingerol, a naturally occurring phenol, is one of the major pungent constituents of ginger. The purpose of this study was to characterize the effect of 6-gingerol on the p38/Nrf2/HO-1 and p38/NF-κB signaling pathway, as a possible means of combating hypoxia-related oxidative stress. H9c2 cells were chemically induced with CoCl₂ to mimic hypoxia-associated cellular damage. Cardiomyocyte injury was assessed by lactate dehydrogenase and creatine kinase. Reactive oxygen species production was assessed by 2',7'-dichlorodihydrofluorescein diacetate. The antioxidative property of 6-gingerol was measured by estimating the activities of superoxide dismutase, catalase, glutathione and glutathione disulfide. Apoptosis was detected by flow cytometry after Annexin V-FITC-propidium iodide double staining. Western blotting was used to evaluate levels of p-p38, p38, cytoplasm p65, nuclear p65, total p65, nuclear Nrf2, total Nrf2, Keap1, HIF-1α, and HO-1. 6-gingerol was able to counter hypoxia-induced cardiomyocyte injury as evidenced by inhibiting the levels of oxidative stress indexes and increasing the percentage of apoptosis. Furthermore, 6-gingerol was able to down-regulate p-p38/p38, nuclear p65, total p65 and Keap1 expression induced by CoCl₂ stimulation and increased cytoplasm p65, nuclear Nrf2, total Nrf2, HO-1, and HIF-1α expression. However, treatment with specific Nrf2 inhibitor blunted the activation of Nrf2 signaling and removed the protective effects of 6-gingerol. These experiments provide evidence that 6-gingerol exerts cytoprotective effects, which may be associated with the regulation of oxidative stress and apoptosis, potentially through activating the Nrf2 pathway and inhibiting the p38/NF-κB pathways.

Cardioprotective effects of dantrolene in doxorubicin-induced cardiomyopathy in mice

BACKGROUND

Doxorubicin (Dox) is a potent chemotherapeutic agent, but its usage is limited by dose-dependent cardiotoxicity. Intracellular calcium dysregulation has been reported to be involved in doxorubicin-induced cardiomyopathy (DICM). The cardioprotective role of RyR stabilizer dantrolene (Dan) on the calcium dynamics of DICM has not yet been explored.

OBJECTIVE

To evaluate the effects of dantrolene on intracellular calcium dysregulation and cardiac contractile function in a DICM model.

METHODS

Adult male C57BL/6 mice were randomized into 4 groups: (1) Control, (2) Dox Only, (3) Dan Only, and (4) Dan + Dox. Fractional shortening (FS) and left ventricular ejection fraction (LVEF) were assessed by echocardiography. In addition, mice were sacrificed 2 weeks after doxorubicin injection for optical mapping of the heart in a Langendorff setup.

RESULTS

Treatment with Dox was associated with a reduction in both FS and LVEF at 2 weeks (P < .0001) and 4 weeks (P < .006). Dox treatment was also associated with prolongation of calcium transient durations CaTD50 (P = .0005) and CaTD80 (P < .0001) and reduction of calcium amplitude alternans ratio (P < .0001). Concomitant treatment with Dan prevented the Dox-induced decline in FS and LVEF (P < .002 at both 2 and 4 weeks). Dan also prevented Dox-induced prolongation of CaTD50 and CaTD80 and improved the CaT alternans ratio (P < .0001). Finally, calcium transient rise time was increased in the doxorubicin-treated group, indicating RyR2 dyssynchrony, and dantrolene prevented this prolongation (P = .02).

CONCLUSION

Dantrolene prevents cardiac contractile dysfunction following doxorubicin treatment by mitigating dysregulation of calcium dynamics.

Stretch-induced sarcoplasmic reticulum calcium leak is causatively associated with atrial fibrillation in pressure-overloaded hearts

AIMS

Despite numerous reports documenting an important role of hypertension in the development of atrial fibrillation (AF), the detailed mechanism underlying the pathological process remains incompletely understood. Here, we aim to test the hypothesis that diastolic sarcoplasmic reticulum (SR) Ca2+ leak in atrial myocytes, induced by mechanical stretch due to elevated pressure in the left atrium (LA), plays an essential role in the AF development in pressure-overloaded hearts.

METHODS AND RESULTS

Isolated mouse atrial myocytes subjected to acute axial stretch displayed an immediate elevation of SR Ca2+ leak. Using a mouse model of transverse aortic constriction (TAC), the relation between stretch, SR Ca2+ leak, and AF susceptibility was further tested. At 36 h post-TAC, SR Ca2+ leak in cardiomyocytes from the LA (with haemodynamic stress), but not right atrium (without haemodynamic stress), significantly increased, which was further elevated at 4 weeks post-TAC. Accordingly, AF susceptibility to atrial burst pacing in the 4-week TAC mice were also significantly increased, which was unaffected by inhibition of atrial fibrosis or inflammation via deletion of galectin-3. Western blotting revealed that type 2 ryanodine receptor (RyR2) in left atrial myocytes of TAC mice was oxidized due to activation and up-regulation of Nox2 and Nox4. Direct rescue of dysfunctional RyR2 with dantrolene or rycal S107 reduced diastolic SR Ca2+ leak in left atrial myocytes and prevented atrial burst pacing stimulated AF.

CONCLUSION

Our study demonstrated for the first time the increased SR Ca2+ leak mediated by enhanced oxidative stress in left atrial myocytes that is causatively associated with higher AF susceptibility in pressure-overloaded hearts.

Ageing-associated increase in SGLT2 disrupts mitochondrial/sarcoplasmic reticulum Ca2+ homeostasis and promotes cardiac dysfunction

The prevalence of death from cardiovascular disease is significantly higher in elderly populations; the underlying factors that contribute to the age‐associated decline in cardiac performance are poorly understood. Herein, we identify the involvement of sodium/glucose co‐transporter gene (SGLT2) in disrupted cellular Ca²⁺‐homeostasis, and mitochondrial dysfunction in age‐associated cardiac dysfunction. In contrast to younger rats (6‐month of age), older rats (24‐month of age) exhibited severe cardiac ultrastructural defects, including deformed, fragmented mitochondria with high electron densities. Cardiomyocytes isolated from aged rats demonstrated increased reactive oxygen species (ROS), loss of mitochondrial membrane potential and altered mitochondrial dynamics, compared with younger controls. Moreover, mitochondrial defects were accompanied by mitochondrial and cytosolic Ca²⁺ ([Ca²⁺]_i) overload, indicative of disrupted cellular Ca²⁺‐homeostasis. Interestingly, increased [Ca²⁺]_i coincided with decreased phosphorylation of phospholamban (PLB) and contractility. Aged‐cardiomyocytes also displayed high Na⁺/Ca²⁺‐exchanger (NCX) activity and blood glucose levels compared with young‐controls. Interestingly, the protein level of SGLT2 was dramatically increased in the aged cardiomyocytes. Moreover, SGLT2 inhibition was sufficient to restore age‐associated defects in [Ca²⁺]_i‐homeostasis, PLB phosphorylation, NCX activity and mitochondrial Ca²⁺‐loading. Hence, the present data suggest that deregulated SGLT2 during ageing disrupts mitochondrial function and cardiac contractility through a mechanism that impinges upon [Ca²⁺]_i‐homeostasis. Our studies support the notion that interventions that modulate SGLT2‐activity can provide benefits in maintaining [Ca²⁺]_i and cardiac function with advanced age.

TRPV4 increases cardiomyocyte calcium cycling and contractility yet contributes to damage in the aged heart following hypoosmotic stress

Aims

Cardiomyocyte Ca2+ homeostasis is altered with aging via poorly-understood mechanisms. The Transient Receptor Potential Vanilloid 4 (TRPV4) ion channel is an osmotically-activated Ca2+ channel, and there is limited information on the role of TRPV4 in cardiomyocytes. Our data show that TRPV4 protein expression increases in cardiomyocytes of the aged heart. The objective of this study was to examine the role of TRPV4 in cardiomyocyte Ca2+ homeostasis following hypoosmotic stress and to assess the contribution of TRPV4 to cardiac contractility and tissue damage following ischaemia-reperfusion (I/R), a pathological condition associated with cardiomyocyte osmotic stress.

Methods and results

TRPV4 protein expression increased in cardiomyocytes of Aged (24-27 months) mice compared with Young (3-6 months) mice. Immunohistochemistry revealed TRPV4 localization to microtubules and the t-tubule network of cardiomyocytes of Aged mice, as well as in left ventricular myocardium of elderly patients undergoing surgical aortic valve replacement for aortic stenosis. Following hypoosmotic stress, cardiomyocytes of Aged, but not Young exhibited an increase in action-potential induced Ca2+ transients. This effect was mediated via increased sarcoplasmic reticulum Ca2+ content and facilitation of Ryanodine Receptor Ca2+ release and was prevented by TRPV4 antagonism (1 μmol/L HC067047). A similar hypoosmotic stress-induced facilitation of Ca2+ transients was observed in Young transgenic mice with inducible TRPV4 expression in cardiomyocytes. Following I/R, isolated hearts of Young mice with transgenic TRPV4 expression exhibited enhanced contractility vs. hearts of Young control mice. Similarly, hearts of Aged mice exhibited enhanced contractility vs. hearts of Aged TRPV4 knock-out (TRPV4-/-) mice. In Aged, pharmacological inhibition of TRPV4 (1 μmol/L, HC067047) prevented hypoosmotic stress-induced cardiomyocyte death and I/R-induced cardiac damage.

Conclusions

Our findings provide a new mechanism for hypoosmotic stress-induced cardiomyocyte Ca2+ entry and cell damage in the aged heart. These finding have potential implications in treatment of elderly populations at increased risk of myocardial infarction and I/R injury.

Altered Intracellular Calcium Homeostasis and Arrhythmogenesis in the Aged Heart

Aging of the heart is associated with a blunted response to sympathetic stimulation, reduced contractility, and increased propensity for arrhythmias, with the risk of sudden cardiac death significantly increased in the elderly population. The altered cardiac structural and functional phenotype, as well as age-associated prevalent comorbidities including hypertension and atherosclerosis, predispose the heart to atrial fibrillation, heart failure, and ventricular tachyarrhythmias. At the cellular level, perturbations in mitochondrial function, excitation-contraction coupling, and calcium homeostasis contribute to this electrical and contractile dysfunction. Major determinants of cardiac contractility are the intracellular release of Ca²⁺ from the sarcoplasmic reticulum by the ryanodine receptors (RyR2), and the following sequestration of Ca²⁺ by the sarco/endoplasmic Ca²⁺-ATPase (SERCa2a). Activity of RyR2 and SERCa2a in myocytes is not only dependent on expression levels and interacting accessory proteins, but on fine-tuned regulation via post-translational modifications. In this paper, we review how aberrant changes in intracellular Ca²⁺ cycling via these proteins contributes to arrhythmogenesis in the aged heart.

Functional recovery after dantrolene-supplementation of cold stored hearts using an ex vivo isolated working rat heart model

The ryanodine receptor antagonist dantrolene inhibits calcium release from the sarcoplasmic reticulum and reduces cardiac ischaemia-reperfusion injury (IRI) in global warm ischaemia models however the cardioprotective potential of dantrolene under hypothermic conditions is unknown. This study addresses whether the addition of dantrolene during cardioplegia and hypothermic storage of the donor heart can improve functional recovery and reduce IRI. Using an ex vivo isolated working heart model, Wistar rat (3 month and 12 month) hearts were perfused to acquire baseline haemodynamic measurements of aortic flow, coronary flow, cardiac output, pulse pressure and heart rate. Hearts were arrested and stored in Celsior preservation solution supplemented with 0.2–40 μM dantrolene for 6 hours at 4°C, then reperfused (15 min Langendorff, 30 min working mode). In 3-month hearts, supplementation with 1 μM dantrolene significantly improved aortic flow and cardiac output compared to unsupplemented controls however lactate dehydrogenase (LDH) release and contraction bands were comparable. In contrast, 40 μM dantrolene-supplementation yielded poor cardiac recovery, increased post-reperfusion LDH but reduced contraction bands. All 3-month hearts stored in dantrolene displayed significantly reduced cleaved-caspase 3 intensities compared to controls. Analysis of cardioprotective signalling pathways showed no changes in AMPKα however dantrolene increased STAT3 and ERK1/2 signaling in a manner unrelated to functional recovery and AKT activity was reduced in 1 μM dantrolene-stored hearts. In contrast to 3-month hearts, no significant improvements were observed in the functional recovery of 12-month hearts following prolonged storage in 1 μM dantrolene. Conclusions: Dantrolene supplementation at 1 μM during hypothermic heart preservation improved functional recovery of young, but not older (12 month) hearts. Although the molecular mechanisms responsible for dantrolene-mediated cardioprotection are unclear, our studies show no correlation between improved functional recovery and SAFE and RISK pathway activation.

Reduced threshold for store overload-induced Ca2+ release is a common defect of RyR1 mutations associated with malignant hyperthermia and central core disease

Mutations in the skeletal muscle ryanodine receptor (RyR1) cause malignant hyperthermia (MH) and central core disease (CCD), whereas mutations in the cardiac ryanodine receptor (RyR2) lead to catecholaminergic polymorphic ventricular tachycardia (CPVT). Most disease-associated RyR1 and RyR2 mutations are located in the N-terminal, central, and C-terminal regions of the corresponding ryanodine receptor (RyR) isoform. An increasing body of evidence demonstrates that CPVT-associated RyR2 mutations enhance the propensity for spontaneous Ca²⁺ release during store Ca²⁺ overload, a process known as store overload-induced Ca²⁺ release (SOICR). Considering the similar locations of disease-associated RyR1 and RyR2 mutations in the RyR structure, we hypothesize that like CPVT-associated RyR2 mutations, MH/CCD-associated RyR1 mutations also enhance SOICR. To test this hypothesis, we determined the impact on SOICR of 12 MH/CCD-associated RyR1 mutations E2347-del, R2163H, G2434R, R2435L, R2435H, and R2454H located in the central region, and Y4796C, T4826I, L4838V, A4940T, G4943V, and P4973L located in the C-terminal region of the channel. We found that all these RyR1 mutations reduced the threshold for SOICR. Dantrolene, an acute treatment for MH, suppressed SOICR in HEK293 cells expressing the RyR1 mutants R164C, Y523S, R2136H, R2435H, and Y4796C. Interestingly, carvedilol, a commonly used β-blocker that suppresses RyR2-mediated SOICR, also inhibits SOICR in these RyR1 mutant HEK293 cells. Therefore, these results indicate that a reduced SOICR threshold is a common defect of MH/CCD-associated RyR1 mutations, and that carvedilol, like dantrolene, can suppress RyR1-mediated SOICR. Clinical studies of the effectiveness of carvedilol as a long-term treatment for MH/CCD or other RyR1-associated disorders may be warranted.

Cardiomyocyte Ca2+ homeostasis as a therapeutic target in heart failure with reduced and preserved ejection fraction

Heart failure is a highly prevalent syndrome of multiple etiologies and associated comorbidities, and aberrant intracellular Ca²⁺ homeostasis is a hallmark finding in heart failure patients. The cyclical changes in Ca²⁺ concentration within cardiomyocytes control cycles of cardiac contraction and relaxation, and dysregulation of Ca²⁺ handling processes leads to systolic dysfunction, diastolic dysfunction, and adverse remodeling. For this reason, greater understanding of Ca²⁺ handling mechanisms in heart failure is critical for selection of appropriate treatment strategies. In this review, we summarize the mechanisms of altered Ca²⁺ handling in two subsets of heart failure, heart failure with reduced ejection fraction and heart failure with preserved ejection fraction, and outline current and experimental treatments that target cardiomyocyte Ca²⁺ handling processes.

Antiarrhythmic effects of dantrolene in human diseased cardiomyocytes

BACKGROUND

Cardiac type 2 ryanodine receptors (RyR₂s) play a pivotal role in cellular electrophysiology and contractility. Increased RyR₂-mediated diastolic sarcoplasmic reticulum (SR) Ca²⁺ release is linked to heart failure (HF) and arrhythmias. Dantrolene, a drug used for the treatment of malignant hyperthermia, is known to stabilize RyRs in skeletal muscle.

OBJECTIVE

The purpose of this study was to investigate the effects of dantrolene on arrhythmogenic triggers and contractile function in human atrial fibrillation (AF) and HF cardiomyocytes (CM).

METHODS

Human CM were isolated from either patients with HF (ventricular) or patients with AF (atrial), and Ca²⁺ imaging, patch-clamp, or muscle strip experiments were performed.

RESULTS

After exposure to dantrolene, human atrial AF and left ventricular HF CM showed significant reductions in proarrhythmic SR Ca²⁺ spark frequency and diastolic SR Ca²⁺ leak. Moreover, dantrolene decreased the frequency of Ca²⁺ waves and spontaneous Ca²⁺ transients in HF CM. Patch-clamp experiments revealed that dantrolene significantly suppressed delayed afterdepolarizations in HF and AF CM. Importantly, dantrolene had no effect on action potential duration in AF or in HF CM. In addition, dantrolene had neutral effects on contractile force of human isometrically twitching ventricular HF trabeculae.

CONCLUSION

Our study showed that dantrolene beneficially influenced disrupted SR Ca²⁺ homeostasis in human HF and AF CM. Cellular arrhythmogenic triggers were potently suppressed by dantrolene, whereas action potential duration and contractility were not affected. As a clinically approved drug for the treatment of malignant hyperthermia, dantrolene may be a potential antiarrhythmic drug for patients with rhythm disorders and merits further clinical investigation.

Inositol 1,4,5-trisphosphate-mediated sarcoplasmic reticulum-mitochondrial crosstalk influences adenosine triphosphate production via mitochondrial Ca2+ uptake through the mitochondrial ryanodine receptor in cardiac myocytes

AIMS

Elevated levels of inositol 1,4,5-trisphosphate (IP3) in adult cardiac myocytes are typically associated with the development of cardiac hypertrophy, arrhythmias, and heart failure. IP3 enhances intracellular Ca(2+ )release via IP3 receptors (IP3Rs) located at the sarcoplasmic reticulum (SR). We aimed to determine whether IP3-induced Ca(2+ )release affects mitochondrial function and determine the underlying mechanisms.

METHODS AND RESULTS

We compared the effects of IP3Rs- and ryanodine receptors (RyRs)-mediated cytosolic Ca(2+ )elevation achieved by endothelin-1 (ET-1) and isoproterenol (ISO) stimulation, respectively, on mitochondrial Ca(2+ )uptake and adenosine triphosphate (ATP) generation. Both ET-1 and isoproterenol induced an increase in mitochondrial Ca(2+ )(Ca(2 +) m) but only ET-1 led to an increase in ATP concentration. ET-1-induced effects were prevented by cell treatment with the IP3 antagonist 2-aminoethoxydiphenyl borate and absent in myocytes from transgenic mice expressing an IP3 chelating protein (IP3 sponge). Furthermore, ET-1-induced mitochondrial Ca(2+) uptake was insensitive to the mitochondrial Ca(2+ )uniporter inhibitor Ru360, however was attenuated by RyRs type 1 inhibitor dantrolene. Using real-time polymerase chain reaction, we detected the presence of all three isoforms of IP3Rs and RyRs in murine ventricular myocytes with a dominant presence of type 2 isoform for both receptors.

CONCLUSIONS

Stimulation of IP3Rs with ET-1 induces Ca(2+ )release from the SR which is tunnelled to mitochondria via mitochondrial RyR leading to stimulation of mitochondrial ATP production.

How cardiomyocyte excitation, calcium release and contraction become altered with age

Cardiovascular disease is the main cause of death globally, accounting for over 17 million deaths each year. As the incidence of cardiovascular disease rises markedly with age, the overall risk of cardiovascular disease is expected to increase dramatically with the aging of the population such that by 2030 it could account for over 23 million deaths per year. It is therefore vitally important to understand how the heart remodels in response to normal aging for at least two reasons: i) to understand why the aged heart is increasingly susceptible to disease; and ii) since it may be possible to modify treatment of disease in older adults if the underlying substrate upon which the disease first develops is fully understood. It is well known that age modulates cardiac function at the level of the individual cardiomyocyte. Generally, in males, aging reduces cell shortening, which is associated with a decrease in the amplitude of the systolic Ca(2+) transient. This may arise due to a decrease in peak L-type Ca(2+) current. Sarcoplasmic reticulum (SR) Ca(2+) load appears to be maintained during normal aging but evidence suggests that SR function is disrupted, such that the rate of sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA)-mediated Ca(2+) removal is reduced and the properties of SR Ca(2+) release in terms of Ca(2+) sparks are altered. Interestingly, Ca(2+) handling is modulated by age to a lesser degree in females. Here we review how cellular contraction is altered as a result of the aging process by considering expression levels and functional properties of key proteins involved in controlling intracellular Ca(2+). We consider how changes in both electrical properties and intracellular Ca(2+) handling may interact to modulate cardiomyocyte contraction. We also reflect on why cardiovascular risk may differ between the sexes by highlighting sex-specific variation in the age-associated remodeling process. This article is part of a Special Issue entitled CV Aging.

Role of S100A1 in hypoxia-induced inflammatory response in cardiomyocytes via TLR4/ROS/NF-κB pathway

Objectives

S100A1 plays a crucial role in hypoxia-induced inflammatory response in cardiomyocytes. However, the role of S100A1 in hypoxia-induced inflammatory response in cardiomyocytes is still unknown.

Methods

enzyme-linked immunosorbent assay (ELISA) was performed for the determination of inflammatory cytokines. Immunocytochemistry and immunofluorescence, Western blot analysis and Real-time polymerase chain reaction (RT-PCR) were conducted to assess protein or mRNA expressions. Fluorogenic probe dihydroethidium (DHE) was used to evaluate the generation of reactive oxygen species (ROS) while Hoechst 33342 staining for apoptosis. Small interfering RNA (siRNA) for S100A1 was used to evaluate the role of S100A1.

Key findings

The levels of ROS and inflammatory cytokine including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 and IL-8 in H9c2 cells were increased remarkably by hypoxia. However, IL-37 protein or mRNA levels were decreased significantly. Both Toll-like receptor 4 (TLR4) inhibitor Ethyl (6R)-6-[N-(2-Chloro-4fluorophenyl)sulfamoyl]cyclohex-1-ene-1-carboxylate (TAK-242) treatment or siRNA S100A1 downregulated TLR4 expression and inflammatory cytokine level and mRNA in H9c2 cells, as well as weakening ROS and phospho-p65 Nuclear factor (NF)-κB levels. Further, S100A1 treatment significantly reduced TNF-α protein or mRNA level whereas enhanced IL-37 protein or mRNA level, and could attenuate ROS and phospho-p65 NF-κB levels.

Conclusions

Our results demonstrate that S100A1 can regulate the inflammatory response and oxidative stress in H9C2 cells via TLR4/ROS/NF-κB pathway. These findings provide an interesting strategy for protecting cardiomyocytes from hypoxia-induced inflammatory response.