Cardiomyocyte-specific RXFP1 overexpression protects against pressure overload-induced cardiac dysfunction independently of Relaxin

Heart failure (HF) prevalence is rising due to reduced early mortality and demographic change. Relaxin (RLN) mediates protective effects in the cardiovascular system through Relaxin-receptor 1 (RXFP1). Cardiac overexpression of RXFP1 with additional RLN supplementation attenuated HF in the pressure-overload transverse aortic constriction (TAC) model. Here, we hypothesized that robust transgenic RXFP1 overexpression in cardiomyocytes (CM) protects from TAC-induced HF even in the absence of RLN. Hence, transgenic mice with a CM-specific overexpression of human RXFP1 (hRXFP1tg) were generated. Receptor functionality was demonstrated by in vivo hemodynamics, where the administration of RLN induced positive inotropy strictly in hRXFP1tg. An increase in phospholamban-phosphorylation at serine 16 was identified as a molecular correlate. hRXFP1tg were protected from TAC without additional RLN administration, presenting not only less decline in systolic left ventricular (LV) function but also abrogated LV dilation and pulmonary congestion compared to WT mice. Molecularly, transgenic hearts exhibited not only a significantly attenuated fetal and fibrotic gene activation but also demonstrated less fibrotic tissue and CM hypertrophy in histological sections. These protective effects were evident in both sexes. Similar cardioprotective effects of hRXFP1tg were detectable in a RLN-knockout model, suggesting an alternative mechanism of receptor activation through intrinsic activity, alternative endogenous ligands or crosstalk with other receptors. In summary, CM-specific RXFP1 overexpression provides protection against TAC even in the absence of endogenous RLN. This suggests RXFP1 overexpression as a potential therapeutic approach for HF, offering baseline protection with optional RLN supplementation for specific activation.

Chronic heart failure as a sequel of severe burn injury: first insight into a novel pathological heart-skin axis

Research question

Our clinical research unveiled chronic heart failure with preserved ejection fraction (HFpEF) as a long-term sequel in survivors of severe pediatric burn injury due to a yet unknown molecular pathomechanism (1). Applying a standardized scald injury rat model, which is widely used in burn research, we systematically determined the pathophysiological impact of burn injury on cardiac performance to uncover systemic and molecular pathomechanisms that may cause post-burn injury HFpEF development.

Methods

Male adolescent SD-rats were subjected to a 60% total body surface area (TBSA) full-thickness burn- or sham-trauma and subsequently characterized by serial transthoracic echocardiography, bulk myocardial next-generation sequencing and proteomics as well as RT-PCR, immuno-blotting (IB), histology and plasma proteomics for cardiac performance and molecular alterations, for up to 90 days (3, 7, 30 and 90d).

Results

In comparison to the sham-group (SG, n=10), animals from the burn-group (BG, n=10; survival rate 100%) recapitulated typical post-burn clinical traits, such as significant loss in body weight (BG 27% less than SG at 30d, p<0.05) or skeletal muscle wasting (i.e., 27% less at 30d, p<0.05) in accord with elevated molecular atrophy markers throughout the observation period. Our focus on the heart revealed for the first-time post-burn cardiac muscle wasting (BG 22% less at 30d, p<0.05) and persistent markers of cardiac dysfunction in accord with significant histological cardiomyocyte hypotrophy (BG −8% at 30d, p<0.05) and significantly diminished left ventricular (LV) global longitudinal strain and isovolumic relaxation time in BGs, while LV-EF remained unchanged. Subsequent IB analysis uncovered diminished protein synthesis activity and diminished mTOR pathway activity in BG hearts. Weighted gene network correlation analysis i.e., from bulk myocardial NGS and clinical traits related activation of immunological and pro-fibrotic pathways in post-burn injury hearts to cardiac dysfunction in BGs. Subsequent RT-PCR and histology confirmed significant myocardial accumulation of cardio-depressive damage associated molecular patterns (i.e., S100A8 and A9) and infiltration by granulocytes (myeloperoxidase+) and monocytes (CD 68+) as well as significant LV fibrosis. Serial plasma proteomic analysis indicated elevated plasma levels i.e., of S100A8 and A9 and other heart failure markers that mirrored similar changes in human post-burn injury plasma samples.

Conclusion

Here we report for the first time the development of HFpEF as a novel systemic consequence of severe burn injury in a rodent model, which prepares the ground for further mechanistic and translational studies. The initial observation of cardiac inflammation and fibrosis, which are known to negatively impact cardiac performance, may be mechanistic key findings that will guide further therapeutic studies and subsequent validation of post-burn heart failure biomarkers.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Rolf-Schwiete Stiftung

P5377A SUMO1-SIM motif within the C-terminal alpha-helical domain of S100A1 prevents its proteasomal degradation in cardiomyocytes

Acknowledgement/Funding

DZHK

Enhanced Cardiac S100A1 Expression Improves Recovery from Global Ischemia-Reperfusion Injury

Gene-targeted therapy with the inotropic Ca2 + -sensor protein S100A1 rescues contractile function in post-ischemic heart failure and is being developed towards clinical trials. Its proven beneficial effect on cardiac metabolism and mitochondrial function suggests a cardioprotective effect of S100A1 in myocardial ischemia-reperfusion injury (IRI). Fivefold cardiomyocyte-specific S100A1 overexpressing, isolated rat hearts perfused in working mode were subjected to 28 min ischemia (37 °C) followed by 60 min reperfusion. S100A1 overexpressing hearts showed superior hemodynamic recover: Left ventricular pressure recovered to 57 ± 7.3% of baseline compared to 51 ± 4.6% in control (p = 0.025), this effect mirrored in LV work and dP/dt(max). Troponin T and lactate dehydrogenase was decreased in the S100A1 group, as well as FoxO pro-apoptotic transcription factor, indicating less tissue necrosis, whereas phosphocreatine content was higher after reperfusion. This is the first report of a cardioprotective effect of S100A1 overexpression in a global IRI model.

Therapeutic safety of high myocardial expression levels of the molecular inotrope S100A1 in a preclinical heart failure model

Low levels of the molecular inotrope S100A1 are sufficient to rescue post-ischemic heart failure (HF). As a prerequisite to clinical application and to determine the safety of myocardial S100A1 DNA-based therapy, we investigated the effects of high myocardial S100A1 expression levels on the cardiac contractile function and occurrence of arrhythmia in a preclinical large animal HF model. At 2 weeks after myocardial infarction domestic pigs presented significant left ventricular (LV) contractile dysfunction. Retrograde application of AAV6-S100A1 (1.5 × 10(13) tvp) via the anterior cardiac vein (ACV) resulted in high-level myocardial S100A1 protein peak expression of up to 95-fold above control. At 14 weeks, pigs with high-level myocardial S100A1 protein overexpression did not show abnormalities in the electrocardiogram. Electrophysiological right ventricular stimulation ruled out an increased susceptibility to monomorphic ventricular arrhythmia. High-level S100A1 protein overexpression in the LV myocardium resulted in a significant increase in LV ejection fraction (LVEF), albeit to a lesser extent than previously reported with low S100A1 protein overexpression. Cardiac remodeling was, however, equally reversed. High myocardial S100A1 protein overexpression neither increases the occurrence of cardiac arrhythmia nor causes detrimental effects on myocardial contractile function in vivo. In contrast, this study demonstrates a broad therapeutic range of S100A1 gene therapy in post-ischemic HF using a preclinical large animal model.

Targeting GRK2 by gene therapy for heart failure: benefits above β-blockade

Heart failure (HF) is a common pathological end point for several cardiac diseases. Despite reasonable achievements in pharmacological, electrophysiological and surgical treatments, prognosis for chronic HF remains poor. Modern therapies are generally symptom oriented and do not currently address specific intracellular molecular signaling abnormalities. Therefore, new and innovative therapeutic approaches are warranted and, ideally, these could at least complement established therapeutic options if not replace them. Gene therapy has potential to serve in this regard in HF as vectors can be directed toward diseased myocytes and directly target intracellular signaling abnormalities. Within this review, we will dissect the adrenergic system contributing to HF development and progression with special emphasis on G-protein-coupled receptor kinase 2 (GRK2). The levels and activity of GRK2 are increased in HF and we and others have demonstrated that this kinase is a major molecular culprit in HF. We will cover the evidence supporting gene therapy directed against myocardial as well as adrenal GRK2 to improve the function and structure of the failing heart and how these strategies may offer complementary and synergistic effects with the existing HF mainstay therapy of β-adrenergic receptor antagonism.

Gene therapy targets in heart failure: the path to translation

Heart failure (HF) is the common end point of cardiac diseases. Despite the optimization of therapeutic strategies and the consequent overall reduction in HF-related mortality, the key underlying intracellular signal transduction abnormalities have not been addressed directly. In this regard, the gaps in modern HF therapy include derangement of β-adrenergic receptor (β-AR) signaling, Ca(2+) disbalances, cardiac myocyte death, diastolic dysfunction, and monogenetic cardiomyopathies. In this review we discuss the potential of gene therapy to fill these gaps and rectify abnormalities in intracellular signaling. We also examine current vector technology and currently available vector-delivery strategies, and we delineate promising gene therapy structures. Finally, we analyze potential limitations related to the transfer of successful preclinical gene therapy approaches to HF treatment in the clinic, as well as impending strategies aimed at overcoming these limitations.

S100A1 gene transfer in myocardium

S100A1, a Ca superset2+-binding protein of the EF-hand type, is preferentially expressed in myocardial tissue and has been shown to enhance cardiac contractile performance by regulating both sarcoplasmic reticulum (SR) Ca superset2+-handling and myofibrillar Ca superset2+-responsiveness. In cardiac disease, the expression of S100A1 is dynamically altered as it is significantly down-regulated in end stage human heart failure (HF), and it is up-regulated in compensated hypertrophy. Therefore, the delivery of a transgene encoding for S100A1 to the myocardium might be an attractive strategy for improving cardiac function in HF by replacing lost endogenous S100A1. In this study we sought to test whether exogenous S100A1 gene delivery to alter global cardiac function is feasible in the normal rabbit heart. An adenoviral S100A1 transgene (AdvS100A1) also containing the green fluorescent protein (GFP) was delivered using an intracoronary injection method with a dose of 5 x 10 superset11 total virus particles (tvp) (n = 8). Rabbits treated with either a GFP-only adenovirus (AdvGFP) or saline were used as control groups (n = 11 each). Seven days after global myocardial in vivo gene delivery hemodynamic parameters were assessed. S100A1 overexpression as a result of the intracoronary delivery of AdvS100A1 significantly increased left ventricular (LV) +dP/dt subsetmax, -dP/dt subsetmin and systolic ejection pressure (SEP) compared to both control groups after administration of isoproterenol (0.1, 0.5 and 1.0 microg/kgBW/min), while contractile parameters remained unchanged under basal conditions. These results demonstrate that global myocardial in vivo gene delivery is possible and that myocardial S100A1 overexpression can increase cardiac performance. Therefore, substitution of down-regulated S100A1 protein expression levels may represent a potential therapeutic strategy for improving the cardiac performance of the failing heart.

S100A1 increases the gain of excitation–contraction coupling in isolated rabbit ventricular cardiomyocytes

The effect of S100A1 protein on cardiac excitation-contraction (E-C) coupling was studied using recombinant human S100A1 protein (0.01-10 microM) introduced into single rabbit ventricular cardiomyocytes via a patch pipette. Voltage clamp experiments (20 degrees C) indicated that 0.1 microM S100A1 increased Ca(2+) transient amplitude by approximately 41% but higher or lower S100A1 concentrations had no significant effect. L-type Ca(2+) current amplitude or Ca(2+) efflux rates via the Na(+)/Ca(2+) exchanger (NCX) were unaffected. The rate of Ca(2+) uptake associated with the SR Ca(2+)-ATPase (SERCA2a) was increased by approximately 22% with 0.1 microM S100A1, but not at other S100A1 concentrations. Based on the intracellular Ca(2+) and I(NCX) signals in response to 10 mM caffeine, no significant change in SR Ca(2+) content was observed with S100A1 (0.01-10 microM). Therefore, 0.1 microM S100A1 appeared to increase the fractional Ca(2+) release from the SR. This result was confirmed by measurements of Ca(2+) transient amplitude at a range of SR Ca(2+) contents. The hyperbolic relationship between these two parameters was shifted to the left by 0.1 microM S100A1. [(3)H]-ryanodine binding studies indicated that S100A1 increased ryanodine receptor (RyR) activity at 0.1 and 0.3 microM Ca(2). As with the effects on E-C coupling, 0.1 microM S100A1 produced the largest effect. Co-immunoprecipitation studies on a range of Ca(2+)-handling proteins support the selective interaction of S100A1 on SERCA2a and RyR. In summary, S100A1 had a stimulatory action on RyR2 and SERCA2a in rabbit cardiomyocytes. Under the conditions of this study, the net effect of this dual action is to enhance the Ca(2+) transient amplitude without significantly affecting the SR Ca(2+) content.

S100A1: a regulator of myocardial contractility

S100A1, a Ca(2+) binding protein of the EF-hand type, is preferentially expressed in myocardial tissue and has been found to colocalize with the sarcoplasmic reticulum (SR) and the contractile filaments in cardiac tissue. Because S100A1 is known to modulate SR Ca(2+) handling in skeletal muscle, we sought to investigate the specific role of S100A1 in the regulation of myocardial contractility. To address this issue, we investigated contractile properties of adult cardiomyocytes as well as of engineered heart tissue after S100A1 adenoviral gene transfer. S100A1 gene transfer resulted in a significant increase of unloaded shortening and isometric contraction in isolated cardiomyocytes and engineered heart tissues, respectively. Analysis of intracellular Ca(2+) cycling in S100A1-overexpressing cardiomyocytes revealed a significant increase in cytosolic Ca(2+) transients, whereas in functional studies on saponin-permeabilized adult cardiomyocytes, the addition of S100A1 protein significantly enhanced SR Ca(2+) uptake. Moreover, in Triton-skinned ventricular trabeculae, S100A1 protein significantly decreased myofibrillar Ca(2+) sensitivity ([EC(50%)]) and Ca(2+) cooperativity, whereas maximal isometric force remained unchanged. Our data suggest that S100A1 effects are cAMP independent because cellular cAMP levels and protein kinase A-dependent phosphorylation of phospholamban were not altered, and carbachol failed to suppress S100A1 actions. These results show that S100A1 overexpression enhances cardiac contractile performance and establish the concept of S100A1 as a regulator of myocardial contractility. S100A1 thus improves cardiac contractile performance both by regulating SR Ca(2+) handling and myofibrillar Ca(2+) responsiveness.

Cardiac troponin T levels at 96 hours reflect myocardial infarct size: a pathoanatomical study

We determined the utility of single-point measurements of circulating cardiac troponin T (cTnT) for the noninvasive estimation of infarct size in 16 beagle dogs after left anterior descending artery (LAD) ligation. Pathoanatomical infarct sizes were determined by the triphenyltetrazolium chloride method and correlated with serum concentration changes of cTnT. Peak cTnT levels (14.10 +/- 4.71 microg/l) were reached after 110 +/- 21 h. A significant correlation was found between peak cTnT levels (p = 0.0001, r = 0. 83) or cumulative cTnT levels and relative infarct size (p = 0.0010, r = 0.72). A single cTnT measurement 96 h after LAD ligation was equally predictive of infarct size (p = 0.0010, r = 0.74) as peak or cumulative cTnT levels derived from serial sampling. cTnT levels at 96 h may thus be useful for practical and cost-effective estimation of infarct size.

Purification of the Ca2+-binding protein S100A1 from myocardium and recombinant Escherichia coli

S100A1 is a new regulatory protein of myocardial contractility that is differentially expressed in early and late stages of myocardial hypertrophy. In order to further investigate the multiple functions of S100A1 in various assay systems we developed a new strategy for isolating biologically active S100A1 protein. After EDTA extraction of myocardium or recombinant bacteria, S100A1 was purified by Octyl-Sepharose hydrophobic interaction chromatography and HiTrapQ anion-exchange chromatography yielding 1.4-2.0 mg/100 g wet tissue and 0.7-1.0 mg/100 ml bacterial culture. Native porcine as well as human recombinant S100A1 revealed biological activity in physiological and biochemical assays.