Interventricular Differences of Signaling Pathways-Mediated Regulation of Cardiomyocyte Function in Response to High Oxidative Stress in the Post-Ischemic Failing Rat Heart

Right ventricular dysfunction following surgical repair of tetralogy of Fallot: Molecular pathways and therapeutic prospects

Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart disease (CHD). Although surgical correction of TOF is possible, patients often face challenges related to right ventricle dysfunction (RVD) post-surgery, which can significantly impact their long-term survival. The causes of RVD in TOF patients are complex, involving both the unique structural characteristics of the TOF heart and damage resulting from surgical interventions. Residual anatomical issues following TOF repair are often unavoidable, placing the RV under stress and leading to the activation of multiple molecular pathways. This review comprehensively outlines the causes of RVD in patients after TOF surgery, particularly focusing the molecular pathways that contribute to RVD, including established signaling pathways as well as emerging pathways identified through transcriptomic analysis of RV myocardium in TOF patients. We also highlight the features of these molecular pathways concerning RVD, as well as the influence of gender disparities on these molecular pathways. By interpreting the causes and molecular mechanisms underlying RVD after TOF surgery, this review provides new insights for managing RVD in repaired TOF, potentially paving the way for targeted therapies aimed at improving long-term outcomes for those affected by RVD.

Sex-specific cardiovascular remodeling leads to a divergent sex-dependent development of heart failure in aged hypertensive rats

INTRODUCTION

The prevalence of heart failure with preserved ejection fraction (HFpEF) is continuously rising and predominantly affects older women often hypertensive and/or obese or diabetic. Indeed, there is evidence on sex differences in the development of HF. Hence, we studied cardiovascular performance dependent on sex and age as well as pathomechanisms on a cellular and molecular level.

METHODS

We studied 15-week- and 1-year-old female and male hypertensive transgenic rats carrying the mouse Ren-2 renin gene (TG) and compared them to wild-type (WT) controls at the same age. We tracked blood pressure and cardiac function via echocardiography. After sacrificing the 1-year survivors we studied vascular smooth muscle and endothelial function. Isolated single skinned cardiomyocytes were used to determine passive stiffness and Ca2+-dependent force. In addition, Western blots were applied to analyse the phosphorylation status of sarcomeric regulatory proteins, titin and of protein kinases AMPK, PKG, CaMKII as well as their expression. Protein kinase activity assays were used to measure activities of CaMKII, PKG and angiotensin-converting enzyme (ACE).

RESULTS

TG male rats showed significantly higher mortality at 1 year than females or WT male rats. Left ventricular (LV) ejection fraction was specifically reduced in male, but not in female TG rats, while LV diastolic dysfunction was evident in both TG sexes, but LV hypertrophy, increased LV ACE activity, and reduced AMPK activity as evident from AMPK hypophosphorylation were specific to male rats. Sex differences were also observed in vascular and cardiomyocyte function showing different response to acetylcholine and Ca2+-sensitivity of force production, respectively cardiomyocyte functional changes were associated with altered phosphorylation states of cardiac myosin binding protein C and cardiac troponin I phosphorylation in TG males only. Cardiomyocyte passive stiffness was increased in TG animals. On a molecular level titin phosphorylation pattern was altered, though alterations were sex-specific. Thus, also the reduction of PKG expression and activity was more pronounced in TG females. However, cardiomyocyte passive stiffness was restored by PKG and CaMKII treatments in both TG sexes.

CONCLUSION

Here we demonstrated divergent sex-specific cardiovascular adaptation to the over-activation of the renin-angiotensin system in the rat. Higher mortality of male TG rats in contrast to female TG rats was observed as well as reduced LV systolic function, whereas females mainly developed HFpEF. Though both sexes developed increased myocardial stiffness to which an impaired titin function contributes to a sex-specific molecular mechanism. The functional derangements of titin are due to a sex-specific divergent regulation of PKG and CaMKII systems.

Abnormal phosphorylation / dephosphorylation and Ca2+ dysfunction in heart failure

Heart failure (HF) can be caused by a variety of causes characterized by abnormal myocardial systole and diastole. Ca2+ current through the L-type calcium channel (LTCC) on the membrane is the initial trigger signal for a cardiac cycle. Declined systole and diastole in HF are associated with dysfunction of myocardial Ca2+ function. This disorder can be correlated with unbalanced levels of phosphorylation / dephosphorylation of LTCC, endoplasmic reticulum (ER), and myofilament. Kinase and phosphatase activity changes along with HF progress, resulting in phased changes in the degree of phosphorylation / dephosphorylation. It is important to realize the phosphorylation / dephosphorylation differences between a normal and a failing heart. This review focuses on phosphorylation / dephosphorylation changes in the progression of HF and summarizes the effects of phosphorylation / dephosphorylation of LTCC, ER function, and myofilament function in normal conditions and HF based on previous experiments and clinical research. Also, we summarize current therapeutic methods based on abnormal phosphorylation / dephosphorylation and clarify potential therapeutic directions.

Implications of S-glutathionylation of sarcomere proteins in cardiac disorders, therapies, and diagnosis

The discovery that cardiac sarcomere proteins are substrates for S-glutathionylation and that this post-translational modification correlates strongly with diastolic dysfunction led to new concepts regarding how levels of oxidative stress affect the heartbeat. Major sarcomere proteins for which there is evidence of S-glutathionylation include cardiac myosin binding protein C (cMyBP-C), actin, cardiac troponin I (cTnI) and titin. Our hypothesis is that these S-glutathionylated proteins are significant factors in acquired and familial disorders of the heart; and, when released into the serum, provide novel biomarkers. We consider the molecular mechanisms for these effects in the context of recent revelations of how these proteins control cardiac dynamics in close collaboration with Ca2+ fluxes. These revelations were made using powerful approaches and technologies that were focused on thin filaments, thick filaments, and titin filaments. Here we integrate their regulatory processes in the sarcomere as modulated mainly by neuro-humoral control of phosphorylation inasmuch evidence indicates that S-glutathionylation and protein phosphorylation, promoting increased dynamics and modifying the Frank-Starling relation, may be mutually exclusive. Earlier studies demonstrated that in addition to cTnI as a well-established biomarker for cardiac disorders, serum levels of cMyBP-C are also a biomarker for cardiac disorders. We describe recent studies approaching the question of whether serum levels of S-glutathionylated-cMyBP-C could be employed as an important clinical tool in patient stratification, early diagnosis in at risk patients before HFpEF, determination of progression, effectiveness of therapeutic approaches, and as a guide in developing future therapies.

Pathology-related changes in cardiac energy metabolites, inflammatory response and reperfusion injury following cardioplegic arrest in patients undergoing open-heart surgery

Introduction

Changes in cardiac metabolites in adult patients undergoing open-heart surgery using ischemic cardioplegic arrest have largely been reported for non-ventricular tissue or diseased left ventricular tissue, with few studies attempting to assess such changes in both ventricular chambers. It is also unknown whether such changes are altered in different pathologies or linked to the degree of reperfusion injury and inflammatory response. The aim of the present work was to address these issues by monitoring myocardial metabolites in both ventricles and to establish whether these changes are linked to reperfusion injury and inflammatory/stress response in patients undergoing surgery using cold blood cardioplegia for either coronary artery bypass graft (CABG, n = 25) or aortic valve replacement (AVR, n = 16).

Methods

Ventricular biopsies from both left (LV) and right (RV) ventricles were collected before ischemic cardioplegic arrest and 20 min after reperfusion. The biopsies were processed for measuring selected metabolites (adenine nucleotides, purines, and amino acids) using HPLC. Blood markers of cardiac injury (Troponin I, cTnI), inflammation (IL- 6, IL-8, Il-10, and TNFα, measured using Multiplex) and oxidative stress (Myeloperoxidase, MPO) were measured pre- and up to 72 hours post-operatively.

Results

The CABG group had a significantly shorter ischemic cardioplegic arrest time (38.6 ± 2.3 min) compared to AVR group (63.0 ± 4.9 min, p = 2 x 10-6). Cardiac injury (cTnI release) was similar for both CABG and AVR groups. The inflammatory markers IL-6 and Il-8 were significantly higher in CABG patients compared to AVR patients. Metabolic markers of cardiac ischemic stress were relatively and significantly more altered in the LV of CABG patients. Comparing diabetic and non-diabetic CABG patients shows that only the RV of diabetic patients sustained major ischemic stress during reperfusion and that diabetic patients had a significantly higher inflammatory response.

Discussion

CABG patients sustain relatively more ischemic stress, systemic inflammatory response and similar injury and oxidative stress compared to AVR patients despite having significantly shorter cross-clamp time. The higher inflammatory response in CABG patients appears to be at least partly driven by a higher incidence of diabetes amongst CABG patients. In addition to pathology, the use of cold blood cardioplegic arrest may underlie these differences.

Long-Term PDE-5A Inhibition Improves Myofilament Function in Left and Right Ventricular Cardiomyocytes through Partially Different Mechanisms in Diabetic Rat Hearts

Heart failure with preserved ejection fraction (HFpEF) and right ventricular (RV) dysfunction are frequent complications of diabetic cardiomyopathy. Here we aimed to characterize RV and left ventricular (LV) remodeling and its prevention by vardenafil (a long-acting phosphodiesterase-5A (PDE-5A) inhibitor) administration in a diabetic HFpEF model. Zucker Diabetic Fatty (ZDF) and control, ZDF Lean (Lean) male rats received 10 mg/kg vardenafil (ZDF + Vard; Lean + Vard) per os, on a daily basis for a period of 25 weeks. In vitro force measurements, biochemical and histochemical assays were employed to assess cardiomyocyte function and signaling. Vardenafil treatment increased cyclic guanosine monophosphate (cGMP) levels and decreased 3-nitrotyrosine (3-NT) levels in the left and right ventricles of ZDF animals, but not in Lean animals. Cardiomyocyte passive tension (F_passive) was higher in LV and RV cardiomyocytes of ZDF rats than in those receiving preventive vardenafil treatment. Levels of overall titin phosphorylation did not differ in the four experimental groups. Maximal Ca²⁺-activated force (F_max) of LV and RV cardiomyocytes were preserved in ZDF animals. Ca²⁺-sensitivity of isometric force production (pCa₅₀) was significantly higher in LV (but not in RV) cardiomyocytes of ZDF rats than in their counterparts in the Lean or Lean + Vard groups. In accordance, the phosphorylation levels of cardiac troponin I (cTnI) and myosin binding protein-C (cMyBP-C) were lower in LV (but not in RV) cardiomyocytes of ZDF animals than in their counterparts of the Lean or Lean + Vard groups. Vardenafil treatment normalized pCa₅₀ values in LV cardiomyocytes, and it decreased pCa₅₀ below control levels in RV cardiomyocytes in the ZDF + Vard group. Our data illustrate partially overlapping myofilament protein alterations for LV and RV cardiomyocytes in diabetic rat hearts upon long-term PDE-5A inhibition. While uniform patterns in cGMP, 3-NT and F_passive levels predict identical effects of vardenafil therapy for the diastolic function in both ventricles, the uneven cTnI, cMyBP-C phosphorylation levels and pCa₅₀ values implicate different responses for the systolic function.