Hypertrophy induced KIF5B controls mitochondrial localization and function in neonatal rat cardiomyocytes

AbstractCardiac hypertrophy is associated with growth and functional changes of cardiomyocytes, including mitochondrial alterations, but the latter are still poorly understood. Here we investigated mitochondrial function and dynamic localization in neonatal rat ventricular cardiomyocytes (NRVCs) stimulated with insulin like growth factor 1 (IGF1) or phenylephrine (PE), mimicking physiological and pathological hypertrophic responses, respectively.A decreased activity of the mitochondrial electron transport chain (ETC) (state 3) was observed in permeabilized NRVCs stimulated with PE, whereas this was improved in IGF1 stimulated NRVCs. In contrast, in intact NRVCs, mitochondrial oxygen consumption rate (OCR) was increased in PE stimulated NRVCs, but remained constant in IGF1 stimulated NRVCs. After stimulation with PE, mitochondria were localized to the periphery of the cell. To study the differences in more detail, we performed gene array studies. IGF1 and PE stimulated NRVCs did not reveal major differences in gene expression of mitochondrial encoding proteins, but we identified a gene encoding a motor protein implicated in mitochondrial localization, kinesin family member 5b (Kif5b), which was clearly elevated in PE stimulated NRVCs but not in IGF1 stimulated NRVCs. We confirmed that Kif5b gene and protein expression were elevated in animal models with pathological cardiac hypertrophy. Silencing of Kif5b reverted the peripheral mitochondrial localization in PE stimulated NRVCs and diminished PE induced increases in mitochondrial OCR, indicating that KIF5B dependent localization affects cellular responses to PE stimulated NRVCs.These results indicate that KIF5B contributes to mitochondrial localization and function in cardiomyocytes and may play a role in pathological hypertrophic responses in vivo

In EXOG-depleted cardiomyocytes cell death is marked by a decreased mitochondrial reserve capacity of the electron transport chain

Depletion ofmitochondrial endo/exonuclease G-like (EXOG) in cultured neonatal cardiomyocytes stimulates mitochondrial oxygen consumption rate (OCR) and induces hypertrophy via reactive oxygen species (ROS). Here, we show that neurohormonal stress triggers cell death in endo/exonuclease G-like-depleted cells, and this is marked by a decrease in mitochondrial reserve capacity. Neurohormonal stimulation with phenylephrine (PE) did not have an additive effect on the hypertrophic response induced by endo/exonuclease G-like depletion. Interestingly, PE-induced atrial natriuretic peptide (ANP) gene expression was completely abolished in endo/exonuclease G-like-depleted cells, suggesting a reverse signaling function of endo/exonuclease G-like. Endo/exonuclease G-like depletion initially resulted in increased mitochondrial OCR, but this declined upon PE stimulation. In particular, the reserve capacity of the mitochondrial respiratory chain and maximal respiration were the first indicators of perturbations in mitochondrial respiration, and these marked the subsequent decline in mitochondrial function. Although pathological stimulation accelerated these processes, prolonged EXOG depletion also resulted in a decline in mitochondrial function. At early stages of endo/exonuclease G-like depletion, mitochondrial ROS production was increased, but this did not affect mitochondrial DNA (mtDNA) integrity. After prolonged depletion, ROS levels returned to control values, despite hyperpolarization of the mitochondrial membrane. The mitochondrial dysfunction finally resulted in cell death, which appears to be mainly a form of necrosis. In conclusion, endo/exonuclease G-like plays an essential role in cardiomyocyte physiology. Loss of endo/exonuclease G-like results in diminished adaptation to pathological stress. The decline in maximal respiration and reserve capacity is the first sign of mitochondrial dysfunction that determines subsequent cell death

Therapeutic Antibody Against Phosphorylcholine Preserves Coronary Function and Attenuates Vascular 18F-FDG Uptake in Atherosclerotic Mice

This study showed that treatment with a therapeutic monoclonal immunoglobulin-G1 antibody against phosphorylcholine on oxidized phospholipids preserves coronary flow reserve and attenuates atherosclerotic inflammation as determined by the uptake of 18F-fluorodeoxyglucose in atherosclerotic mice. The noninvasive imaging techniques represent translational tools to assess the efficacy of phosphorylcholine-targeted therapy on coronary artery function and atherosclerosis in clinical studies.</p

New genetic loci link adipose and insulin biology to body fat distribution.

Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

New insights in atrial remodeling

Boezemfibrilleren is de meest voorkomende hartritmestoornis. Risicofactoren voor boezemfibrilleren zijn leeftijd, hoge bloeddruk, diabetes, kleplijden en hartfalen. Tijdens boezemfibrilleren ontstaan er veranderingen in de boezems, de boezems kunnen bijvoorbeeld groter worden. Deze veranderingen ontstaan door boezemfibrilleren, maar kunnen ook ontstaan voordat boezemfibrilleren optreedt, bijvoorbeeld door onderliggende ziekten zoals een hoge bloeddruk of hartfalen. Het doel van dit proefschrift was om deze veranderingen te onderzoeken. Hierbij ligt er een focus op stretch (zoals wordt veroorzaakt door onderliggende hartziekten) en op geactiveerde stollingsfactoren. Als eerste hebben we verschillende aspecten van structurele veranderingen besproken, hierbij lag een focus op stretch. Daarna hebben we de effecten van stretch onderzocht in een celmodel. In dit celmodel hebben we neonatale rat boezem spiercellen gestretcht. Om onze bevindingen ook in een diermodel te onderzoeken hebben we een model gebruikt waarbij we een vernauwing van de aorta gemaakt hebben. Dit is een bekend model dat leidt tot vergroting van de kamers en uiteindelijk tot hartfalen. In dit model hebben we de veranderingen in de boezems onderzocht. Naast bekende factoren die een rol spelen bij veranderingen in de boezems, zoals stretch, zouden ook andere – tot nu toe onbekende – mechanismen een belangrijke rol kunnen spelen in bij de veranderingen die optreden in de boezems. Geactiveerde stolling zou een dergelijke factor kunnen zijn. In dit proefschrift worden de effecten van de geactiveerde stollingsfactoren factor Xa en trombine op cellulaire processen bij atherosclerose en boezemfibrilleren besproken. Daarnaast werden de effecten van geactiveerde stolling op boezemcellen bestudeerd. Atrial fibrillation is the most common cardiac arrhythmia. Risk factors for atrial fibrillation include older age, hypertension, diabetes, valve disease and heart failure. During atrial fibrillation atrial remodeling takes place. Atrial remodeling refers to changes in the atria, including structural changes such as an increase in atrial size. These structural changes are also caused by underlying diseases such as hypertension and heart failure. The aim of this thesis was to investigate this atrial remodeling. The focus is on remodeling caused by stretch (mimicking these underlying diseases) and by activated coagulation factors. First, different aspects of structural atrial remodeling are reviewed with a special focus on stretch and its contribution to structural remodeling. Next we investigated the effects of stretch in a cell model; therefore neonatal rat atrial myocytes were subjected to cyclical stretch. To translate the findings to an animal model we used a model in which the aorta is constricted. This aortic constriction leads to increased stress on the heart and results in so called ventricular hypertrophy, i.e. in a large ventricle. In this model the structural changes in the atria were studied. In addition to known factors involved in remodeling also previously unknown factors might be involved in the remodeling process. One such factor might be activated coagulation. In this thesis the effects of the activated coagulation factors thrombin and factor Xa on cellular processes in both atherosclerosis and atrial fibrillation are reviewed. In addition, the effects of thrombin on atrial fibroblasts and remodeling are studied.

Pleiotropic effects of factor Xa and thrombin:what to expect from novel anticoagulants

Factor Xa and thrombin are well-known components of the coagulation cascade and have been proven to be viable targets for effective anticoagulation treatment. However, accumulating evidence suggests that these serine proteases are also crucial modulators of other cellular mechanisms through the activation of protease-activated receptor (PAR)-mediated signalling. The involvement of factor Xa, thrombin, and PARs in normal biological and pathophysiological processes has been recognized, and their potential implications have been explored in recent years. Both factor Xa and thrombin play significant roles in mediating cellular signalling effects associated with the initial development of atherosclerosis: a chronic inflammatory vascular disease. In addition, increased expression and activation of PARs may be associated with atrial fibrillation (AF) and AF-associated thromboembolism hypercoagulability. Both pathologies are associated with hypercoagulability, suggesting that the role of cellular effects of factor Xa and thrombin and of their specific inhibitors should be studied in relation to the prevention of thrombotic and pro-arrhythmic changes. This review examines the role of factor Xa-mediated and thrombin-mediated PAR activation in modulating cellular processes involved in atherosclerosis and AF and discusses the potential implication of direct factor Xa and thrombin inhibition on effects outside coagulation

Cyclical stretch induces structural changes in atrial myocytes

<p>Atrial fibrillation (AF) often occurs in the presence of an underlying disease. These underlying diseases cause atrial remodelling, which make the atria more susceptible to AF. Stretch is an important mediator in the remodelling process. The aim of this study was to develop an atrial cell culture model mimicking remodelling due to atrial pressure overload. Neonatal rat atrial cardiomyocytes (NRAM) were cultured and subjected to cyclical stretch on elastic membranes. Stretching with 1Hz and 15% elongation for 30min. resulted in increased expression of immediate early genes and phosphorylation of Erk and p38. A 24-hr stretch period resulted in hypertrophy-related changes including increased cell diameter, reinduction of the foetal gene program and cell death. No evidence of apoptosis was observed. Expression of atrial natriuretic peptide, brain natriuretic peptide and growth differentiation factor-15 was increased, and calcineurin signalling was activated. Expression of several potassium channels was decreased, suggesting electrical remodelling. Atrial stretch-induced change in skeletal -actin expression was inhibited by pravastatin, but not by eplerenone or losartan. Stretch of NRAM results in elevation of stress markers, changes related to hypertrophy and dedifferentiation, electrical remodelling and cell death. This model can contribute to investigating the mechanisms involved in the remodelling process caused by stretch and to the testing of pharmaceutical agents.</p>

Mechanisms of atrial structural changes caused by stretch occurring before and during early atrial fibrillation

Structural remodelling occurring before, due to the underlying heart disease, and during atrial fibrillation (AF) sets the stage for permanent AF. Current therapy in AF aims to maintain sinus rhythm in symptomatic patients, but outcome is unfortunately poor. Stretch of the atria is a main contributor to atrial remodelling. In this review, we describe different aspects of structural remodelling as seen in animal models and in patients with AF, including atrial enlargement, cellular hypertrophy, dedifferentiation, fibrosis, apoptosis, and loss of contractile elements. In the second part, we describe downstream signals of mechanical stretch and their contribution to AF and structural remodelling. Ultimately, knowledge of mechanisms underlying structural remodelling may help to identify new pharmacological targets for AF prevention

Loss of mitochondrial exo/endonuclease EXOG affects mitochondrial respiration and induces ROS mediated cardiomyocyte hypertrophy

Recently, a genetic variant in the mitochondrial exo/endo nuclease EXOG, which has been implicated in mitochondrial DNA repair, was associated with cardiac function. The function of EXOG in cardiomyocytes is still elusive. Here we investigated the role of EXOG in mitochondrial function and hypertrophy in cardiomyocytes. Depletion of EXOG in primary neonatal rat ventricular cardiomyocytes (NRVCs) induced a marked increase in cardiomyocyte hypertrophy. Depletion of EXOG however, did not result in loss of mitochondrial DNA integrity. Although EXOG depletion did not induce fetal gene expression and common hypertrophy pathways were not activated, a clear increase in ribosomal S6 phosphorylation was observed, which readily explains increased protein synthesis. Using a Seahorse flux analyzer, it was shown that mitochondrial oxidative consumption rate (OCR) was increased 2.4 fold in EXOG depleted NRVCs. Moreover, ATP-linked OCR was 5.2 fold higher. This increase was not explained by mitochondrial biogenesis or alterations in mitochondrial membrane potential. Western blotting confirmed normal levels of the oxidative phosphorylation (OXPHOS) complexes. The increased OCR was accompanied by an 5.4 fold increase in mitochondrial ROS levels. These increased ROS levels could be normalized with specific mitochondrial ROS scavengers (MitoTEMPO, mnSOD). Remarkably scavenging of excess ROS strongly attenuated the hypertrophic response. In conclusion, loss of EXOG affects normal mitochondrial function resulting in increased mitochondrial respiration, excess ROS production and cardiomyocyte hypertrophy