H2S Prodrug, SG-1002, Protects Against Myocardial Oxidative Damage and Hypertrophy via Induction of Cystathionine β-Synthase and Antioxidant Proteins

Endogenously produced hydrogen sulfide (H2S) is critical for cardiovascular homeostasis. Therapeutic strategies aimed at increasing H2S levels have proven cardioprotective in models of acute myocardial infarction (MI) and heart failure (HF). The present study was undertaken to investigate the effects of a novel H2S prodrug, SG-1002, on stress induced hypertrophic signaling in murine HL-1 cardiac muscle cells. Treatment of HL-1 cells with SG-1002 under serum starvation without or with H2O2 increased the levels of H2S, H2S producing enzyme, cystathionine β-synthase (CBS) as well as antioxidant protein levels, such as super oxide dismutase1 (SOD1) and catalase and decreased oxidative stress. SG-1002 also decreased the expression of hypertrophic/HF protein markers such as atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in stressed HL-1 cells. Treatment with SG-1002 caused a significant induction of cell viability and a marked reduction of cellular cytotoxicity in HL-1 cells under serum starvation incubated or with H2O2. Experimental results of this study suggest that SG-1002 attenuates myocardial cellular oxidative damage and/or hypertrophic signaling via increasing H2S levels or H2S producing enzyme, CBS and antioxidant proteins.

Enhancing calmodulin binding to cardiac ryanodine receptor completely inhibits pressure-overload induced hypertrophic signaling

Cardiac hypertrophy is a well-known major risk factor for poor prognosis in patients with cardiovascular diseases. Dysregulation of intracellular Ca2+ is involved in the pathogenesis of cardiac hypertrophy. However, the precise mechanism underlying cardiac hypertrophy remains elusive. Here, we investigate whether pressure-overload induced hypertrophy can be induced by destabilization of cardiac ryanodine receptor (RyR2) through calmodulin (CaM) dissociation and subsequent Ca2+ leakage, and whether it can be genetically rescued by enhancing the binding affinity of CaM to RyR2. In the very initial phase of pressure-overload induced cardiac hypertrophy, when cardiac contractile function is preserved, reactive oxygen species (ROS)-mediated RyR2 destabilization already occurs in association with relaxation dysfunction. Further, stabilizing RyR2 by enhancing the binding affinity of CaM to RyR2 completely inhibits hypertrophic signaling and improves survival. Our study uncovers a critical missing link between RyR2 destabilization and cardiac hypertrophy.

N2A Titin: Signaling Hub and Mechanical Switch in Skeletal Muscle

Since its belated discovery, our understanding of the giant protein titin has grown exponentially from its humble beginning as a sarcomeric scaffold to recent recognition of its critical mechanical and signaling functions in active muscle. One uniquely useful model to unravel titin’s functions, muscular dystrophy with myositis (mdm), arose spontaneously in mice as a transposon-like LINE repeat insertion that results in a small deletion in the N2A region of titin. This small deletion profoundly affects hypertrophic signaling and muscle mechanics, thereby providing insights into the function of this specific region and the consequences of its dysfunction. The impact of this mutation is profound, affecting diverse aspects of the phenotype including muscle mechanics, developmental hypertrophy, and thermoregulation. In this review, we explore accumulating evidence that points to the N2A region of titin as a dynamic “switch” that is critical for both mechanical and signaling functions in skeletal muscle. Calcium-dependent binding of N2A titin to actin filaments triggers a cascade of changes in titin that affect mechanical properties such as elastic energy storage and return, as well as hypertrophic signaling. The mdm phenotype also points to the existence of as yet unidentified signaling pathways for muscle hypertrophy and thermoregulation, likely involving titin’s PEVK region as well as the N2A signalosome.

P0094KLOTHO DECLINE IS ASSOCIATED WITH PRO-HYPERTROPHIC SIGNALING IN MYOCARDIUM OF NEPHRECTOMIZED SPONTANEOUSELY HYPERTENSIVE RATS (PILOT SYUDY)

Background and Aims Klotho deficiency is suggested to be involved in cardiac complications in chronic kidney disease (CKD) through modulation of intracellular pro-hypertrophic signaling pathways. The aim of this study was to investigate the molecular mechanisms of myocardial remodeling in the settings of Klotho decline in experimental CKD. Method Systolic blood pressure (BP), myocardial mass index (MMI), serum and urinary creatinine (Cr), serum urea (Ur), inorganic phosphate (Pi), 25-hydroxyvitamin D (25OHD), parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), Klotho, myocardial Klotho, calcineurin/ NFAT and beta-catenin expression (IHC), quantitative morphometry of cardiomyocite (CM) thickness and nuclei area (hematoxylin and eosin), myocardial perivascular (PF) and interstitial fibrosis (IF), renal fibrosis (RF) (Masson’s trichrome) and Klotho expression (rKl, IHC) were analyzed in spontaneously hypertensive rats with 3/4 or 5/6 nephrectomy (Nx) and duration of experimental exposure 1 and 2 mo (Nx1, n = 9; Nx2, n = 8). Controls were sham operated (SO) animals (SO1, n = 9; SO2, n = 9). Results The experimental model was corresponded to the initial stages of CKD (Ur level was between 6.64 and 13.36 mmol/L, serum Cr increased less than 50% vs SO, RF did not exceed 22 % FOV). Serum concentration of Klotho and rKl expression decreased, while MMI, CM thickness increased in both Nx1 and Nx2 (Table). There were no differences in serum Pi, FGF23 and PTH levels in Nx1 vs SO (Table). In Nx2 Klotho decline was accompanied by the development of IF and PF, serum 25OHD decrease, Pi and FGF23 increase vs SO2 (Table). In multiple regression analyzes including SO and Nx animals rKl was independently associated with MMI (β = -0.38 ± 0.16, p = 0.026), and CM thickness (β = -0.64 ± 0.14, p <0.001). Myocardial fibrosis was associated with rKl level (IF: β = -0.87 ± 0.19, p = 0.001) and serum 25OHD (PF: β =-0.34 ± 0.15, p=0.032). According to pilot data of IHC, in Nx rat myocardium Klotho protein expression decreased, cytoplasmic calcineurin and nuclear NFAT in CM were observed (Figure), suggesting an increase in the activity of the calcineurin / NFAT signaling pathway. An intracellular redistribution of β-catenin from the cytoskeleton to the cytoplasm and nuclei were observed in CM of Nx rats (Figure), likely corresponding to increase in the activity of Wnt signaling. Conclusion Associations of CM hypertrophy, myocardial fibrosis and Klotho decline in CKD may be mediated by calcineurin / NFAT and Wnt signaling in myocardium.

Analysis of cardiac differentiation at single cell resolution reveals a requirement of hypertrophic signaling for HOPX transcription

Differentiation into diverse cell lineages requires the orchestration of gene regulatory networks guiding diverse cell fate choices. Utilizing human pluripotent stem cells, we measured expression dynamics of 17,718 genes from 43,168 cells across five time points over a thirty day time-course of in vitro cardiac-directed differentiation. Unsupervised clustering and lineage prediction algorithms were used to map fate choices and transcriptional networks underlying cardiac differentiation. We leveraged this resource to identify strategies for controlling in vitro differentiation as it occurs in vivo. HOPX, a non-DNA binding homeodomain protein essential for heart development in vivo was identified as dys-regulated in in vitro derived cardiomyocytes. Utilizing genetic gain and loss of function approaches, we dissect the transcriptional complexity of the HOPX locus and identify the requirement of hypertrophic signaling for HOPX transcription in hPSC-derived cardiomyocytes. This work provides a single cell dissection of the transcriptional landscape of cardiac differentiation for broad applications of stem cells in cardiovascular biology.