Myocyte Hypertrophy Research Articles

Abstract 4138491: Association of histologic findings with long-term outcomes in symptomatic obstructive hypertrophic cardiomyopathy patients undergoing surgical myectomy

Background: In hypertrophic cardiomyopathy (HCM), histologic findings like myocyte hypertrophy&disarray, interstitial fibrosis (IF)&small intramural coronary arteriole dysplasia (SICAD) account for the left ventricular hypertrophy, diastolic dysfunction, arrhythmogenicity&microvascular ischemia. Objectives: To evaluate the association between histology&outcomes in obstructive HCM (oHCM) patients undergoing surgical myectomy (SM). Methods: This was an observational study of 1722 symptomatic oHCM patients (mean age 56±14 years, 948 [55%] men) who underwent SM at a tertiary care center between 2005-18. Baseline clinical data was collected. The SM specimen was analyzed for presence&severity of a) myocyte hypertrophy b) myocyte disarray c) IF&d) SICAD. Histologic findings were graded as 0-3 (none, mild, moderate,&severe)&a score from 0-12 was calculated. Primary endpoint was a composite of death, appropriate defibrillator discharge or cardiac transplantation during follow-up. Results: 896 (52%) were in New York Heart Association (NYHA) class III/IV, 457 (21%) had exertional syncope, 727 (42%) had ≥1 sudden death risk factor&409 (24%) had atrial fibrillation (AF). Moderate&severe histologic findings were distributed as follows: myocyte hypertrophy (1341 [78%]), disarray (237 [14%]), IF (448 [26%])&SICAD (258 [15%]). The mean total histologic score was 5.1±1.4. At 5.1±5.2 years, there were 352 (20%) primary events (317 [18%] deaths). On spline analysis (Figure 1A), a total histology score of ≥ 6 was associated with primary events. On Kaplan-Meier analysis (Figure 1B), patients with a histology score ≥ 6 had greater events vs. those with a score <6 (147/598 [25%] vs. 205/1124 [18%], log-rank p-value 0.002). On multivariable Cox analysis, age (for 10-year increase, Hazard ratio or HR 1.49 [95% confidence interval or CI 1.35-1.65], p<0.001), NYHA Class III/IV (HR 1.58 [95% CI -1.25-2.01], p<0.001), AF (HR 1.65 [95% CI 1.30-2.10], p<0.001)&histology score ≥6 (HR 1.24 [95% CI 1.03-1.54], p=0.03) were independently associated with higher primary events. Conclusions: In symptomatic oHCM patients undergoing SM, a higher histologic score was independently associated with long-term outcomes.

Association of Histologic Findings With Long-Term Outcomes in Symptomatic Obstructive Hypertrophic Cardiomyopathy Patients Undergoing Surgical Myectomy.

In hypertrophic cardiomyopathy, histologic findings like myocyte hypertrophy and disarray, interstitial fibrosis (IF), and small intramural coronary artery dysplasia (SICAD) result in left ventricular hypertrophy, diastolic dysfunction, arrhythmogenicity, and microvascular ischemia. The authors sought to evaluate the association between histology and outcomes in obstructive hypertrophic cardiomyopathy (oHCM) patients undergoing surgical myectomy (SM). The study included 1,722 symptomatic oHCM patients (mean age: 56 ± 14 years; 948 [55%] men) who underwent SM at a tertiary center between 2005 and 2018. The SM specimen was analyzed for presence and severity of: 1) myocyte hypertrophy; 2) myocyte disarray; 3) IF; and 4) SICAD. Histologic findings were graded as 0-3 (none, mild, moderate, and severe) and a score from 0-12 was calculated. Primary endpoint was a composite of death, appropriate defibrillator discharge, or cardiac transplantation during follow-up. Moderate and severe histologic findings were distributed as follows: myocyte hypertrophy (1,341 [78%]); disarray (237 [14%]); IF (448 [26%]); and SICAD (258 [15%]). The mean total histologic score was 5.1 ± 1.4. At 5.1 ± 5.2 years, there were 352 (20%) primary events (317 [18%] deaths). On spline analysis, a total histology score of >5 was associated with primary events. On Kaplan-Meier analysis, patients with a histology score >5 had greater events vs those with a score≤5 (147/598 [25%] vs 205/1124 [18%]; log-rank P value=0.002). On multivariable Cox analysis, total histology score >5 (HR: 1.24 [95%CI: 1.03-1.54]; P = 0.03) was independently associated with higher primary events. In symptomatic oHCM patients undergoing SM, a higher histologic score was independently associated with long-term outcomes.

Left ventricular hypertrophy, wall thickness, and histological myocyte alteration in end-stage heart failure: a call for a standard definition

Abstract Objective This study aimed to examine the relationship between different left ventricular hypertrophy (LVH) classification criteria according to the American Society of Echocardiography (ASE), and anatomical measurement of LV wall thickness (LVWT) and histological evidence of myocyte hypertrophy. Methods Data from 146 consecutive patients (47 years; 75% were male) who have undergone heart transplantation were analysed. Fixed ventricles were dissected and measured in weight after both atria, great vessels, and epicardial fat were removed. The fixed biventricular weight was calculated as 87% of total weight (the effect of fixed formalin reduced the total weight by 3%). Anatomical LVWT was measured with a ruler at LV free wall where maximal thickness is located. A comprehensive echocardiogram was performed in all patients before heart transplantation. LVM and relative wall thickness (RWT) (2 PWT/LVEDD) were measured by M-mode echocardiography in parasternal long-axis view. Patients were considered to have LVH when the LVM index exceeds 95 g/m2 in women and exceeds 115 g/m2 in men. Patients were considered to have concentric LVH when RWT > 0.42. LVWT was measured using 2D echocardiography perpendicular to the LV long axis. Results Of 146 explanted hearts, dilated cardiomyopathy (CM), cardiac amyloid, and hypertrophic CM were diagnosed in 53 (47%), 1 (1%), and 8 (5%) patients, respectively. Anatomic ventricular mass correlated with echocardiographic LVM (r=0.5, p < 0.01). Anatomic LVWT modestly correlated with echocardiographic LVWT (r=0.2, p=0.01). Of 146 patients, echocardiographic normal LV geometry, concentric LV remodelling, concentric LVH, and eccentric LVH were present in 22 (15%), 6 (4%), 14 (10%), and 104 (71%), respectively. Increased LVWT (≥ 13 mm) assessed by 2-D echocardiography was present in normal LV geometry (5%), concentric LV remodelling (5%), concentric LVH (57%), and eccentric LVH (33%) (p <0.001) in those classified by ASE guidelines. Anatomic LVWT (≥ 13 mm) was present in normal LV geometry (14%), concentric LV remodelling 5%), concentric LVH (14%), and eccentric LVH (80%) (p <0.001) in those classified by ASE guidelines. Histological myocyte hypertrophy was present in normal LV geometry (12%), concentric LV remodelling (2%), concentric LVH (11%), and eccentric LVH (70%) (p <0.001) in those classified by ASE guidelines. Conclusions 2D-derived echocardiographic increased LVWT in patients with LVH defined by increased LVM index was present in approximately 30-50%. Furthermore, anatomical increased LVWT in those with LVH classified by ASE guidelines was present in a varying range of 10-70%. Patients with concentric LVH had a low prevalence of histological myocyte hypertrophy (approximately 10%). Inconsistencies in classification methods reveal the need for more robust LVH terminologies and definition that is consistent across cardiac imaging and anatomico-pathological examination, particularly in patients with CM.

Unraveling Marfan hearts: ultrastructural evidence for myocardial remodeling and cardiomyopathy

Abstract Background Despite improved life expectancy for patients with Marfan syndrome (MFS), significant morbidity and mortality persist. Although primarily attributed to aortic dissection and rupture, recent studies highlight the emerging role of arrhythmias and heart failure as additional contributors to morbidity and mortality in MFS. While severe valvular heart disease is an established cause of heart failure, there is a growing recognition of primary cardiomyopathy in patients with MFS. The mechanisms underlying cardiomyopathy in MFS remain poorly understood. Purpose This study aimed to reveal insights into the ultrastructural myocardial architecture in patients with MFS, thereby elucidating the role of cardiomyopathy in MFS. Methods This study enrolled 44 patients who underwent cardiac surgery at 2 centers (Marfan syndrome patients n=27 (MFS), ascending thoracic aortic aneurysm repair patients n=5 (non-MFS), patients post-orthotopic heart transplant n=12 (controls)). Myocardial biopsy samples were subjected to histopathological analysis using transmission electron microscopy and conventional histology. Results Conventional histological analysis revealed subtle abnormalities in the cardiomyocyte morphology of MFS patients, compared to non-MFS and controls. Overall, a slight increase in interstitial fibrosis and mild myocyte hypertrophy were observed in MFS patients. Ultrastructural examination of both MFS and non-MFS patients revealed significant structural remodeling and degenerative changes in the myocardium. These changes included: extensive myofibril lysis, compromised cell membrane integrity and nuclear chromatin condensation. Degenerative lesions were often accompanied by cytoplasmic debris, lysosomal residual bodies, autophagic vacuoles, and severe mitochondrial pathology. Dense accumulation of glycogen granules and lipofuscin was evident in areas of focal myofibril lysis. Notably, only MFS patients exhibited recruitment of granulocytes, including mast cells, eosinophils and neutrophils. A subset of MFS patients displayed advanced stages of myocardial degeneration. However, these changes did not correlate with clinical myocardial failure. Conclusions To the best of our knowledge, this study represents the first evidence of ultrastructural changes in the myocardium of patients with MFS. Our data indicate various degenerative changes in the myocardial architecture, including structural and metabolic myocardial remodeling, along with inflammatory cell infiltration. We believe that our findings of ultrastructural lesions reflect the complexity of myocardial disease in MFS and emphasize the importance of careful surveillance for cardiomyopathy in MFS patients. Further studies are warranted to confirm whether the observed granulocyte influx is specific to MFS and to clarify its role in MFS myocardial disease pathophysiology.Graphical abstract

Rapid onset fibrotic remodeling and ventricular dysfunction induced by phenylephrine involve targeted reprogramming of myocyte and fibroblast transcriptomes.

Catecholamine dysregulation is a common feature of multiple acute and chronic cardiac conditions, including heart failure. To investigate the role of altered α-adrenergic stimulation on cardiac function, we developed a short-term exposure model, administering phenylephrine subcutaneously to mice for one week. Compared to vehicle-injected controls, phenylephrine-treated animals exhibited increased ejection fraction, decreased chamber size, diastolic dysfunction and ventricular hypertrophy in the absence of hypertension. Remarkably, these animals developed extensive fibrotic remodeling of the tissue that plateaued at 24 hours and myocyte hypertrophy localized to regions of fibrotic deposition after 3 days of treatment. Transcriptome analyses of purified myocyte and fibroblast populations from these hearts revealed an unexpected role for myocytes in the production of extracellular matrix. Comparison with other models of cardiac stress, including pressure overload hypertrophy and cytokine activation of fibroblasts, identified stimulus-specific transcriptional circuits associated with cardiac pathology. Given the rapid, robust fibrotic response that preceded myocyte hypertrophy, intercellular communication analyses were conducted to investigate fibroblast to myocyte signaling, identifying potential crosstalk between these cells. These studies thoroughly describe and phenotypically characterize a new model of short-term catecholamine stress and provide an atlas of transcriptional remodeling in myocytes and fibroblasts.

Case of Bone Morphogenetic Protein Receptor Type 2 (BMPR2) Mutation Complicated by Pulmonary Hypertension Encountered at Autopsy

Abstract Introduction/Objective Bone morphogenetic protein receptor type 2 is a protein encoded by the BMPR2 gene which regulates cell division and apoptosis. BMPR2 mutations result in monoclonal plexiform lesions of proliferating endothelial cells in pulmonary arterioles, which leads to elevated pulmonary artery pressures, right ventricular failure, and death. Here, we present the case of a 12-year-old male with a known history of pulmonary hypertension secondary to BMPR2 mutation referred for medical autopsy after suffering cardiac arrest and passing away. Methods/Case Report This 12-year-old male was diagnosed with pulmonary hypertension in December 2022 after suffering a syncopal episode while running at recess. Genetic testing was obtained, and he was found to have a BMPR2 mutation. His father was tested and also harbored this mutation, but did not clinically have pulmonary hypertension. The decedent was initiated on ambrisentan, tadalafil, and spironolactone, but continued to present to the Emergency Department periodically for syncopal episodes. In April 2024, he presented to the Medical University of South Carolina in cardiac arrest which began while playing outside. A complete autopsy was performed, including gross and microscopic examination of tissues and postmortem vitreous electrolyte analysis. Gross examination revealed the decedent’s heart was enlarged to 350 grams (normal mean for age = 181 grams). Both cardiac ventricles were dilated and the right ventricle was markedly hypertrophic with a thickness of 1.2 cm. Microscopic sections are pending but will presumptively show significant cardiac myocyte hypertrophy and pulmonary arteriole thickening. Cause of death is pending certification but is presumed to be sudden cardiac death resulting from BMPR2 mutation- related pulmonary hypertension. Results (if a Case Study enter NA) NA Conclusion This case highlights a common genetic presentation of pulmonary arterial hypertension, with approximately 80% of familial cases of pulmonary arterial hypertension harboring BMPR2 mutations. Further research should be done to investigate treatment options and management of this genetic presentation.

Genetic insights and clinical implication of inherited hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is one of the most common inherited genetic diseases of myocardium. It is the leading cause of unexpected mortality among young people and athletes. H.C.M. has been regarded as a sarcomere illness for the past few decades, usually with incomplete penetrance and varied expressivity arising from autosomal dominance. For the purpose of risk and treatment stratification, all diagnostic techniques—such as tissue biopsy, genetic counselling, magnetic resonance imaging, transthoracic and transoesophageal echocardiography, heart catheterization, and genetic counselling—must be used. Additionally, each patient's results should be customized based on their genotype and phenotype. About one-third of people have left ventricular outflow tract blockage at rest, and another third may be prompted to develop it. Interstitial fibrosis and myocyte hypertrophy and disarray are among the histological characteristics of H.C.M. Another common complication of the hypertrophy is left ventricular diastolic dysfunction. The pathogenesis of H.C.M is complex, and its clinical profile is variable. Functional disability resulting from heart failure and stroke (induced by atrial fibrillation) is also attributed to H.C.M. The goal of the current treatments for H.C.M., which include medication, myectomy, alcohol septal ablation, and implanted cardiac defibrillators (I.C.Ds) to avoid SCD, is to slow down the disease's progression and relieve symptoms. Multidisciplinary approaches are best suited for the diagnosis and treatment of patients with H.C.M. More individualized care and better results for this patient population have been made possible by this, as well as the enhanced safety and effectiveness of medicinal, percutaneous, and surgical therapy for H.C.M. In this review the molecular pathophysiology of H.C.M will be reviewed in light of current knowledge. In addition, describing how genetic testing is used for diagnosis and outlining the range of clinical manifestations.

Clinical Update in Heart Failure with Preserved Ejection Fraction.

To review the most recent clinical trials and data regarding epidemiology, pathophysiology, diagnosis, and treatment of heart failure with preserved ejection fraction with an emphasis on the recent trends in cardiometabolic interventions. Heart failure with preserved ejection fraction makes up approximately half of overall heart failure and is associated with significant morbidity, mortality, and overall burden on the healthcare system. It is a complex, heterogenous syndrome and clinical trials, to this point, have not revealed quite as many effective treatment options when compared to heart failure with reduced ejection fraction. Nevertheless, there is an expanding amount of data insight into the pathogenesis of this disease and the potential for newer therapies and management strategies. Heart failure with preserved ejection fraction pathology has been found to be linked to abnormal energetics, myocyte hypertrophy, cell signaling, inflammation, ischemia, and fibrosis. These mechanisms also intricately overlap with the significant comorbidities often associated with heart failure with preserved ejection fraction including, but not limited to, atrial fibrillation, chronic kidney disease, hypertension, obesity and coronary artery disease. Treatment of this disease, therefore, should focus on the management and strict regulation of these comorbidities by pharmacologic and nonpharmacologic means. In this review, a clinical update is provided reviewing the most recent clinical trials and data regarding epidemiology, pathophysiology, diagnosis, and treatment of heart failure with preserved ejection fraction with an emphasis on the recent trend in cardiometabolic interventions.

The effect of Norethisterone acetate on the uterus of albino rats: histological, histochemical and ultrastructure study

BackgroundNorethisterone acetate (NETA), also known as norethindrone acetate is a progestogens medication that is widely used in birth control pills, menopausal hormone therapy, and for the treatment of gynecological disorders as abnormal uterine bleeding and endometriosis. There is a lack of detailed histological information regarding the effects of NETA on the uterine structure. So, the present study focuses on the uterine histological, histochemical and ultrastructure changes following the exposure to NETA in the albino rats. To do this aim, fourteen adult female albino rats were used. They were randomly divided into two equally groups: Control group and NETA treated group. Albino rats of control group were administered daily food, water and orally distilled water only, while rats of NETA treated group were administered daily orally 20 µg of NETA dissolved in 2 ml distilled water, food, and water. The experiment was continued for three weeks.ResultsThe findings of the present work indicated that the use of NETA has negative effects on the endometrial epithelium (proliferation, autophagy and apoptosis), glands (necrotic, apoptotic or pseudosecretory glands) and stromal and myometrial reactions (granulocytes, connective tissue remodeling, apoptosis, myocytes hypertrophy).ConclusionThis work revealed that NETA has desynchronized progestogenic effect on the uterine tissues of the albino rat and thereby prevent implantation and pregnancy.

Novel Immunohistochemical and Morphological Approaches in a Retrospective Study of Post-Mortem Myocarditis.

Background and Objectives: This study presents a retrospective analysis of 26 autopsy cases from a single centre, primarily focusing on forensic cases, with a majority of male individuals. Materials and Methods: We systematically analysed autopsy reports and cardiac tissue slides using haematoxylin-eosin stain and immunohistochemistry for CD3, CD163, and IL-6. The histological assessment evaluated key variables such as inflammation severity, necrosis, and background changes using a standardised grading system. Quantitative analysis of immunohistochemical markers was performed, calculating the percentage of positively stained cells within the inflammatory infiltrate. Results: The average age was 51.6 years, slightly skewed towards older males. The fatalities varied widely, with sudden death and drug abuse being the most common conditions linked to myocarditis findings on histological examination. A strong correlation was found between the severity of inflammation (measured by size within a myocardium section) and the scoring system based on the number of inflammatory foci per section (p ≤ 0.001). Most cases showed mild to minimal fibrosis, with some exhibiting moderate to severe fibrosis, arteriosclerosis, and myocyte hypertrophy. The presence of protein CD3 in the inflammatory infiltrate revealed a moderate inverse correlation between the CD3 values and the severity of inflammation and necrosis, and a strong inverse correlation with neutrophil levels. CD3 levels were higher in sudden death cases and lower in cases with numerous inflammatory foci, highlighting the discreet nature of lymphocytic myocarditis. Macrophage presence, assessed using CD163, showed a moderate inverse correlation with neutrophil levels and significant differences between sudden death and non-sudden death cases. Macrophage-rich inflammation was observed in cases with pneumonia/bronchopneumonia-associated lesions. IL-6 expression showed a moderate direct correlation with inflammation severity (p = 0.028), severity of necrosis (p = 0.005), and the number of inflammatory foci per section (p = 0.047). A moderate inverse correlation was found between CD3 and IL-6 expression (p = 0.005). Conclusions: These findings highlight the need for a unique immunohistochemical approach in forensic cases of myocarditis, differing from guidelines for endomyocardial biopsies due to diverse inflammatory cells. The study suggests exploring inflammatory chemokines within myocarditis foci for their significance in clinical scenarios. Specifically, IL-6, a crucial pro-inflammatory interleukin, correlated significantly with the severity of inflammation and necrosis (p < 0.05). This study provides novel and valuable insights into the histopathological and immunological markers of myocarditis in autopsy cases.

Histological evaluation of cardiac remodelling in equine athletes

Approximately 1–2 per 100,000 young athletes die from sudden cardiac death (SCD) and extreme exercise may be associated with myocardial scar and arrhythmias. Racehorses have a high prevalence of atrial fibrillation (AF) and SCD but the presence of myocardial scar and inflammation has not been evaluated. Cardiac tissues from the left (LAA) and right (RAA) atrial appendages, left ventricular anterior (LVAPM) and posterior (LVPPM) papillary muscles, and right side of the interventricular septum (IVS-R) were harvested from racehorses with sudden cardiac death (SCD, n = 16) or other fatal injuries (OFI, n = 17), constituting the athletic group (ATH, n = 33), and compared to sedentary horses (SED, n = 10). Horses in the ATH group had myocyte hypertrophy at all sites; increased fibrosis at all sites other than the LAA; increased fibroblast infiltration but a reduction in the overall extracellular matrix (ECM) volume in the RAA, LVAPM, and IVS-R compared to SED horses. In this horse model, athletic conditioning was associated with myocyte hypertrophy and a reduction in ECM. There was an excess of fibrocyte infiltration and focal fibrosis that was not present in non-athletic horses, raising the possibility of an exercise-induced pro-fibrotic substrate.

Morphology of human sinoatrial node and its surrounding right atrial muscle in the global obesity pandemic-does fat matter?

The sinus node (SN) is the main pacemaker site of the heart, located in the upper right atrium at the junction of the superior vena cava and right atrium. The precise morphology of the SN in the human heart remains relatively unclear especially the SN microscopical anatomy in the hearts of aged and obese individuals. In this study, the histology of the SN with surrounding right atrial (RA) muscle was analyzed from young non-obese, aged non-obese, aged obese and young obese individuals. The impacts of aging and obesity on fibrosis, apoptosis and cellular hypertrophy were investigated in the SN and RA. Moreover, the impact of obesity on P wave morphology in ECG was also analyzed to determine the speed and conduction of the impulse generated by the SN. Human SN/RA specimens were dissected from 23 post-mortem hearts (preserved in 4% formaldehyde solution), under Polish local ethical rules. The SN/RA tissue blocks were embedded in paraffin and histologically stained with Masson's Trichrome. High and low-magnification images were taken, and analysis was done for appropriate statistical tests on Prism (GraphPad, USA). 12-lead ECGs from 14 patients under Polish local ethical rules were obtained. The P wave morphologies from lead II, lead III and lead aVF were analyzed. Compared to the surrounding RA, the SN in all four groups has significantly more connective tissue (P ≤ 0.05) (young non-obese individuals, aged non-obese individuals, aged obese individuals and young obese individuals) and significantly smaller nodal cells (P ≤ 0.05) (young non-obese individuals, aged non-obese individuals, aged obese individuals, young obese individuals). In aging, overall, there was a significant increase in fibrosis, apoptosis, and cellular hypertrophy in the SN (P ≤ 0.05) and RA (P ≤ 0.05). Obesity did not further exacerbate fibrosis but caused a further increase in cellular hypertrophy (SN P ≤ 0.05, RA P ≤ 0.05), especially in young obese individuals. However, there was more infiltrating fat within the SN and RA bundles in obesity. Compared to the young non-obese individuals, the young obese individuals showed decreased P wave amplitude and P wave slope in aVF lead. Aging and obesity are two risk factors for extensive fibrosis and cellular hypertrophy in SN and RA. Obesity exacerbates the morphological alterations, especially hypertrophy of nodal and atrial myocytes. These morphological alterations might lead to functional alterations and eventually cause cardiovascular diseases, such as SN dysfunction, atrial fibrillation, bradycardia, and heart failure.

Regional variations in left ventricular myocyte diameter and nuclear length in post mortem population: implications in assessing myocyte hypertrophy

ABSTRACT Cardiac hypertrophy can be appreciated microscopically by assessing for myocyte hypertrophy. Features of myocyte hypertrophy include increased myocyte diameter, together with increase in nuclear hyperchromicity, size and irregularity, and an increase in binucleated myocytes. There is limited literature to demonstrate whether these features are uniform within the myocardium in the post mortem setting. This study compared the myocyte diameter, myocyte nuclear length, and proportion binucleated myocytes between the free wall of the left ventricle and interventricular septum in 21 post mortem cases. It showed regional variation in myocyte hypertrophy parameters between the free walls of the left ventricle and intraventricular septum. Over 75% of cases showed significant differences in myocyte nuclear length and myocyte diameter (ANOVA one-way, p < 0.05), whereas binucleated myocyte nuclei did not show any significant difference. The result of this study has implication in sampling and assessing myocyte hypertrophy. Further studies are recommended to explore the reasons why this variation occurred and whether it is clinically significant.

State of the art on angiotensin-neprilysin inhibitors.

Angiotensin receptor neprilysin inhibitor (ARNI) decreases renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous systems (SNS) activity promoting vasodilation, decreasing myocardial hypertrophy and fibrosis. Beyond the SNS, RAAS and natriuretic peptide systems, ARNI results in increased circulatory and myocardial nitric oxide levels activating cGMP and protein kinase G, which reduces oxidative stress, myocyte hypertrophy, cell death and has anti-thrombotic effects. ARNIs have a class I indication by heart failure (HF) guidelines in HFrEF patients with NYHA class II to III symptoms. Beyond HFrEF, the use of ARNIs has also been expanded to other clinical settings including HF with preserved ejection fraction (EF, HFpEF), acute HF, advanced HF, hypertension, arrhythmias and chronic kidney disease. This paper reviews the clinical benefits of ARNIs in both HF and the aforementioned cardiovascular conditions. We also discuss the combined use of ARNI with SGLT2i and their potential synergistic benefits on cardiovascular outcomes.

Circadian control of histone turnover during cardiac development and growth

During postnatal cardiac hypertrophy, cardiomyocytes undergo mitotic exit, relying on DNA replication-independent mechanisms of histone turnover to maintain chromatin organization and gene transcription. In other tissues, circadian oscillations in nucleosome occupancy influence clock-controlled gene expression, suggesting a role for the circadian clock in temporal control of histone turnover and coordinated cardiomyocyte gene expression. To elucidate roles for the master circadian transcription factor, Bmal1, in histone turnover, chromatin organization, and myocyte-specific gene expression and cell growth in the neonatal period. Bmal1 knockdown in neonatal rat ventricular myocytes (NRVM) decreased myocyte size, total cellular protein synthesis, and transcription of the fetal hypertrophic gene Nppb following treatment with serum or the α-adrenergic agonist phenylephrine (PE). Depletion of Bmal1 decreased expression of clock-controlled genes Per2 and Tcap, as well as Sik1, a Bmal1 target upregulated in adult versus embryonic hearts. Bmal1 knockdown impaired Per2 and Sik1 promoter accessibility as measured by MNase-qPCR and impaired histone turnover as measured by metabolic labeling of acid-soluble chromatin fractions. Sik1 knockdown in turn decreased myocyte size, while simultaneously inhibiting Nppb transcription and activating Per2 transcription. Linking these changes to chromatin remodeling, depletion of the replication-independent histone variant H3.3a inhibited myocyte hypertrophy and prevented PE-induced changes in clock-controlled gene transcription. Bmal1 is required for neonatal myocyte growth, replication-independent histone turnover, and chromatin organization at the Sik1 promoter. Sik1 represents a novel clock-controlled gene that coordinates myocyte growth with hypertrophic and clock-controlled gene transcription. Replication-independent histone turnover is required for transcriptional remodeling of clock-controlled genes in cardiac myocytes in response to growth stimuli.

#1515 Myocardial remodeling is associated with redistribution of phosphate, PIT1/ERK1/2 up-regulation and signaling pathways alterations in mild CKD model

Abstract Background and Aims Patients with CKD have significantly increased cardiovascular risk, and heart failure is a leading cause of morbidity and mortality in these patients. Myocardial hypertrophy is a hallmark of cardiac remodeling and dysfunction in CKD and is known to be mediated by angiotensin II, catecholamines, hyperphosphatemia, hyperparathyroidism, increase in FGF23, decrease in Klotho and alterations in various signaling pathways including calcineurin, mitogen-activated protein kinase ERK1/2, calmodulin-dependent protein kinase II etc. Less well understood are the mechanisms of fibrosis and intramyocardial arterial remodeling in CKD, which may be related to hyperphosphatemia and decreased renal and systemic Klotho. The aim of this study was to evaluate the molecular and cellular features of myocardial remodeling in experimental mild CKD. Method We induced CKD by 3/4 nephrectomy (Nx) in adult male spontaneously hypertensive rats (SHR) with a follow-up period of 4 months. Animals were fed standard chow containing 0.6% phosphate. Sham-operated Wistar rats and SHR served as controls. We measured serum creatinine, renal interstitial fibrosis area, systolic blood pressure (BP), myocardial mass index (MMI), histological indices of myocardial hypertrophy, interstitial fibrosis and intramyocardial artery (IA) remodeling (H&amp;E, Masson's trichrome, von Kossa stain), myocardial phosphorus content, serum levels of inorganic phosphate (Pi), PTH and FGF23. Myocardial expression of phosphate transporters PiT1, ERK1/2, WNT, BMP, Notch, Hedgehog signaling pathways and LRG4 molecules was evaluated by PCR-RT, IHC and IF (Zeiss LSM 710; study performed at the Centre for Collective Use “Confocal Microscopy” of the Pavlov Institute of Physiology, Russian Academy of Sciences). Results Chronic kidney injury and phosphate regulatory factors did not differ, whereas BP and MMI were higher in sham SHR vs. Wistar rats (Fig. 1). Nx rats showed features of mild chronic kidney injury before the elevation of serum PTH, FGF23 levels (Fig. 1). Myocardial P content and serum Pi were higher in Nx and in the combined SHR group and directly correlated with indices of IA remodeling. Cardiomyocyte diameter, myocardial interstitial and perivascular fibrosis were higher in Nx (Figs 1, 2a) and accompanied with upregulation in Ppp3ca mRNA (calcineurin A, Fig. 2b), Mapk1 mRNA (ERK2, Fig. 2b), phospho-ERK1/2 (Figs 1, 3), PiT1 (Figs 1, 2c), Lgr4 (Fig. 2c) and downregulation of Hes1 mRNA (Fig. 2b). PiT1 and pospho-ERK1/2 were co-expressed in IA media from SHR (Fig. 2c). In Nx, nestin and LGR4 were expressed by IA adventitia and media cells, myocardial interstitial cells, and occasionally co-localized (Fig. 2c). Hes1 expression was detected in IA and capillary endothelial cells and co-localised with Gli1 in IA media; Gli1 was also detected in cardiomyocyte nuclei (Fig. 2c). In SHR, beta-catenin expression in cardiomyocytes was more pronounced in Nx (Fig. 2c). Conclusion Mild CKD is associated with histological and molecular features of cardiomyocyte hypertrophy, myocardial fibrosis and intramyocardial arterial remodeling, which are probably modulated by phosphate redistribution and its tissue retention involving upregulation of PiT1 and ERK1/2, as well as alterations in signals related to progenitor regulation and myocyte hypertrophy.

LncRNA ZNF593-AS inhibits cardiac hypertrophy and myocardial remodeling by upregulating Mfn2 expression.

lncRNA ZNF593 antisense (ZNF593-AS) transcripts have been implicated in heart failure through the regulation of myocardial contractility. The decreased transcriptional activity of ZNF593-AS has also been detected in cardiac hypertrophy. However, the function of ZNF593-AS in cardiac hypertrophy remains unclear. Herein, we report that the expression of ZNF593-AS reduced in a mouse model of left ventricular hypertrophy and cardiomyocytes in response to treatment with the hypertrophic agonist phenylephrine (PE). In vivo, ZNF593-AS aggravated pressure overload-induced cardiac hypertrophy in knockout mice. By contrast, cardiomyocyte-specific transgenic mice (ZNF593-AS MHC-Tg) exhibited attenuated TAC-induced cardiac hypertrophy. In vitro, vector-based overexpression using murine or human ZNF593-AS alleviated PE-induced myocyte hypertrophy, whereas GapmeR-induced inhibition aggravated hypertrophic phenotypes. By using RNA-seq and gene set enrichment analyses, we identified a link between ZNF593-AS and oxidative phosphorylation and found that mitofusin 2 (Mfn2) is a direct target of ZNF593-AS. ZNF593-AS exerts an antihypertrophic effect by upregulating Mfn2 expression and improving mitochondrial function. Therefore, it represents a promising therapeutic target for combating pathological cardiac remodeling.

A novel histone deacetylase inhibitor Se-SAHA attenuates isoproterenol-induced heart failure via antioxidative stress and autophagy inhibition

Heart failure is associated with histone deacetylase (HDAC) regulation of gene expression, the inhibition of which is thought to be beneficial for heart failure therapy. Here, we explored the cardioprotective effects and underlying mechanism of a novel selenium-containing HDAC inhibitor, Se-SAHA, on isoproterenol (ISO)-induced heart failure. We found that pretreatment with Se-SAHA attenuated ISO-induced cardiac hypertrophy and fibrosis in neonatal rat ventricular myocytes (NRVMs). Se-SAHA significantly attenuated the generation of ISO-induced reactive oxygen species (ROS) and restored the expression levels of superoxide dismutase 2 (SOD2) and heme oxygenase-1 (HO-1) in vitro. Furthermore, Se-SAHA pretreatment prevented the accumulation of autophagosomes. Se-SAHA reversed the high expression of HDAC1 and HDAC6 induced by ISO incubation. However, after the addition of the HDAC agonist, the effect of Se-SAHA on blocking autophagy was inhibited. Using ISO-induced mouse models, cardiac ventricular contractile dysfunction, hypertrophy, and fibrosis was reduced treated by Se-SAHA. In addition, Se-SAHA inhibited HDAC1 and HDAC6 overexpression in ISO-treated mice. Se-SAHA treatment significantly increased the activity of SOD2 and improved the ability to eliminate free radicals. Se-SAHA hindered the excessive levels of the microtubule-associated protein 1 light chain 3 (LC3)-II and Beclin-1 in heart failure mice. Collectively, our results indicate that Se-SAHA exerts cardio-protection against ISO-induced heart failure via antioxidative stress and autophagy inhibition.

Association of attenuated leptin signaling pathways with impaired cardiac function under prolonged high-altitude hypoxia

Cardiovascular function and adipose metabolism were markedly influenced under high altitudes. However, the interplay between adipokines and heart under hypoxia remains to be elucidated. We aim to explore alterations of adipokines and underlying mechanisms in regulating cardiac function under high altitudes. We investigated the cardiopulmonary function and five adipokines in Antarctic expeditioners at Kunlun Station (4,087 m) for 20 days and established rats exposed to hypobaric hypoxia (5,000 m), simulating Kunlun Station. Antarctic expeditioners exhibited elevated heart rate, blood pressure, systemic vascular resistance, and decreased cardiac pumping function. Plasma creatine phosphokinase-MB (CK-MB) and platelet-endothelial cell adhesion molecule-1 (sPecam-1) increased, and leptin, resistin, and lipocalin-2 decreased. Plasma leptin significantly correlated with altered cardiac function indicators. Additionally, hypoxic rats manifested impaired left ventricular systolic and diastolic function, elevated plasma CK-MB and sPecam-1, and decreased plasma leptin. Chronic hypoxia for 14 days led to increased myocyte hypertrophy, fibrosis, apoptosis, and mitochondrial dysfunction, coupled with reduced protein levels of leptin signaling pathways in myocardial tissues. Cardiac transcriptome analysis revealed leptin was associated with downregulated genes involved in rhythm, Na+/K+ transport, and cell skeleton. In conclusion, chronic hypoxia significantly reduced leptin signaling pathways in cardiac tissues along with significant pathological changes, thus highlighting the pivotal role of leptin in regulation of cardiac function under high altitudes.

Ataxia Telangiectasia-Mutated Kinase Deficiency Induces Cardiac Dysfunction with Increased Myocyte Apoptosis and Hypertrophy with Age

Background: Heart failure is the leading cause of death globally. The risk for heart disease increases exponentially with age. The incidence of heart disease is approximately 40% in humans that are 40-59 years old. Ataxia telangiectasia-mutated kinase (ATM), a cell cycle protein, controls growth and repair in response to double-stranded DNA damage. Mutations in the ATM gene lead to a multisystemic disease known as Ataxia Telangiectasia (A-T). These individuals exhibit signs of premature aging. A-T heterozygotes make up about 2% of the population and are more susceptible to ischemic heart disease and die 11 years earlier compared to non-carriers. Previous work has shown that ATM deficiency increases myocyte hypertrophy in 4-month-old (young) ATM heterozygous knockout (hKO) mice vs. age-matched wild-type (WT) mice. However, there was no difference in myocyte apoptosis or heart function between the two groups. Hypothesis: It is hypothesized that with age, ATM deficiency induces myocytes apoptosis and hypertrophy, and cardiac dysfunction. Methods: Heart function was measured in young and 14-month-old WT and hKO mice using echocardiography. Cross sections (5 μm) of heart were used to measure myocyte apoptosis and hypertrophy using terminal deoxynucleotidyl transferase nick end labeling (TUNEL) and rhodamine wheat germ agglutinin (WGA) staining, respectively. Results: Heart function, measured by fractional shortening (%FS) and ejection fraction (%EF), remained unchanged in young and 14-month-old WT mice. However, %FS and %EF were significantly lower in 14-month-old hKO mice vs. young hKO and age-matched WT mice. Myocyte apoptosis and cross-sectional area (hypertrophy) were significantly higher in 14-month-old hKO vs. age-matched WT mice. Conclusion: The data indicates that ATM deficiency induces cardiac dysfunction with increased myocyte apoptosis and hypertrophy with age. This research was supported by Department of Biological Sciences, Undergraduate Research Honors Program, Offce of Research and Sponsored Programs, Department of Biomedical Sciences, and Department of Health Sciences. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.