Sphingosine 1-phosphate as a therapeutic target in heart failure: more questions than answers

mRNA - A game changer in regenerative medicine, cell-based therapy and reprogramming strategies

After thirty years of intensive research shaping and optimizing the technology, the approval of the first mRNA-based formulation by the EMA and FDA in order to stop the COVID-19 pandemic was a breakthrough in mRNA research. The astonishing success of these vaccines have brought the mRNA platform into the spotlight of the scientific community. The remarkable persistence of the groundwork is mainly attributed to the exceptional benefits of mRNA application, including the biological origin, immediate but transitory mechanism of action, non-integrative properties, safe and relatively simple manufacturing as well as the flexibility to produce any desired protein. Based on these advantages, a practical implementation of in vitro transcribed mRNA has been considered in most areas of medicine. In this review, we discuss the key preconditions for the rise of the mRNA in the medical field, including the unique structural and functional features of the mRNA molecule and its vehicles, which are crucial aspects for a production of potent mRNA-based therapeutics. Further, we focus on the utility of mRNA tools particularly in the scope of regenerative medicine, i.e. cell reprogramming approaches or manipulation strategies for targeted tissue restoration. Finally, we highlight the strong clinical potential but also the remaining hurdles to overcome for the mRNA-based regenerative therapy, which is only a few steps away from becoming a reality.

Sphingosine-1-phosphate interactions in the spleen and heart reflect extent of cardiac repair in mice and failing human hearts

Sphingosine-1-phosphate (S1P) is a bioactive mediator in inflammation. Dysregulated S1P is demonstrated as a cause of heart failure (HF). However, the time-dependent and integrative role of S1P interaction with receptors in HF is unclear after myocardial infarction (MI). In this study, the sphingolipid mediators were quantified in ischemic human hearts. We also measured the time kinetics of these mediators post-MI in murine spleen and heart as an integrative approach to understand the interaction of S1P and respective S1P receptors in the transition of acute (AHF) to chronic HF (CHF). Risk-free 8-12 wk male C57BL/6 mice were subjected to MI surgery, and MI was confirmed by echocardiography and histology. Mass spectrometry was used to quantify sphingolipids in plasma, infarcted heart, spleen of mice, and ischemic and healthy human heart. The physiological cardiac repair was observed in mice with a notable increase of S1P quantity (pmol/g) in the heart and spleen significantly reduced in patients with ischemic HF. The circulating murine S1P levels were increased during AHF and CHF despite lowered substrate in CHF. The S1PR1 receptor expression was observed to coincide with the respective S1P quantity in mice and human hearts. Furthermore, selective S1P1 agonist limited inflammatory markers CCL2 and TNF-α and accelerated reparative markers ARG-1 and YM-1 in macrophages in the presence of Kdo2-Lipid A (KLA; potent inflammatory stimulant). This report demonstrated the importance of S1P/S1PR1 signaling in physiological inflammation during cardiac repair in mice. Alteration in these axes may serve as the signs of pathological remodeling in patients with ischemia.NEW & NOTEWORTHY Previous studies indicate that sphingosine-1-phosphate (S1P) has some role in cardiovascular disease. This study adds quantitative and integrative systems-based approaches that are necessary for discovery and bedside translation. Here, we quantitated sphinganine, sphingosine, sphingosine-1-phosphate (S1P) in mice and human cardiac pathobiology. Interorgan S1P quantity and respective systems-based receptor activation suggest cardiac repair after myocardial infarction. Thus, S1P serves as a therapeutic target for cardiac protection in clinical translation.

U-shaped association between plasma sphingosine-1-phosphate levels and mortality in patients with chronic systolic heart failure: a prospective cohort study

Background

The endogenous lipid molecule sphingosine-1-phosphate (S1P) has received attention in the cardiovascular field due to its significant cardioprotective effects, as revealed in animal studies. The purpose of our study was to identify the distribution characteristics of S1P in systolic heart failure patients and the prognostic value of S1P for long-term prognosis.

Methods

We recruited 210 chronic systolic heart failure patients from June 2014 to December 2015. Meanwhile 54 healthy people in the same area were selected as controls. Plasma S1P was measured by liquid chromatography-tandem mass spectrometry. Patients were grouped according to the baseline S1P level quartiles, and restricted cubic spline plots described the association between S1P and all-cause death. Cox proportional hazard analysis was used to determine the relationship between category of S1P and all-cause death.

Results

Compared with the control group, the plasma S1P in chronic heart failure patients demonstrated a higher mean level (1.269 μmol/L vs 1.122 μmol/L, P = 0.006) and a larger standard deviation (0.441 vs 0.316, P = 0.022). Based on multivariable Cox regression with restricted cubic spline analysis, a non-linear and U-shaped association between S1P levels and the risk of all-cause death was observed. After a follow-up period of 31.7 ± 10.3 months, the second quartile (0.967–1.192 μml/L) with largely normal S1P levels had the lowest all-cause mortality and either an increase (adjusted HR = 2.368, 95%CI 1.006–5.572, P = 0.048) or a decrease (adjusted HR = 0.041, 95%CI 0.002–0.808, P = 0.036) predicted a worse prognosis. The survival curves showed that patients in the lowest quartile and highest quartile were at a higher risk of death.

Conclusions

Plasma S1P levels in systolic heart failure patients are related to the long-term all-cause mortality with a U-shaped correlation.

Trial registration

CHiCTR, ChiCTR-ONC-14004463. Registered 20 March 2014.

Altering Sphingolipid Metabolism Attenuates Cell Death and Inflammatory Response After Myocardial Infarction

BACKGROUND

Sphingolipids have recently emerged as a biomarker of recurrence and mortality after myocardial infarction (MI). The increased ceramide levels in mammalian heart tissues during acute MI, as demonstrated by several groups, is associated with higher cell death rates in the left ventricle and deteriorated cardiac function. Ceramidase, the only enzyme known to hydrolyze proapoptotic ceramide, generates sphingosine, which is then phosphorylated by sphingosine kinase to produce the prosurvival molecule sphingosine-1-phosphate. We hypothesized that Acid Ceramidase (AC) overexpression would counteract the negative effects of elevated ceramide and promote cell survival, thereby providing cardioprotection after MI.

METHODS

We performed transcriptomic, sphingolipid, and protein analyses to evaluate sphingolipid metabolism and signaling post-MI. We investigated the effect of altering ceramide metabolism through a loss (chemical inhibitors) or gain (modified mRNA [modRNA]) of AC function post hypoxia or MI.

RESULTS

We found that several genes involved in de novo ceramide synthesis were upregulated and that ceramide (C16, C20, C20:1, and C24) levels had significantly increased 24 hours after MI. AC inhibition after hypoxia or MI resulted in reduced AC activity and increased cell death. By contrast, enhancing AC activity via AC modRNA treatment increased cell survival after hypoxia or MI. AC modRNA-treated mice had significantly better heart function, longer survival, and smaller scar size than control mice 28 days post-MI. We attributed the improvement in heart function post-MI after AC modRNA delivery to decreased ceramide levels, lower cell death rates, and changes in the composition of the immune cell population in the left ventricle manifested by lowered abundance of proinflammatory detrimental neutrophils.

CONCLUSIONS

Our findings suggest that transiently altering sphingolipid metabolism through AC overexpression is sufficient and necessary to induce cardioprotection post-MI, thereby highlighting the therapeutic potential of AC modRNA in ischemic heart disease.

Levels of Blood Organophosphorus Flame Retardants and Association with Changes in Human Sphingolipid Homeostasis

While a recent toxicological study has shown that organophosphorus flame retardants (OPFRs) may disrupt sphingolipid homeostasis, epidemiologic evidence is currently lacking. In this study, a total of 257 participants were recruited from Shenzhen, China. Eleven OPFRs were for the first time simultaneously determined in the human blood samples by ultraperformance liquid chromatography and tandem mass spectrometry. Six OPFRs, tributyl phosphate (TNBP), 2-ethylhexyl diphenyl phosphate (EHDPP), tris(2-chloroisopropyl) phosphate (TCIPP), tris(2-butoxyethyl) phosphate (TBOEP), triethyl phosphate (TEP), and TPHP, were detectable in at least 90% of participants, with median concentrations of 37.8, 1.22, 0.71, 0.54, 0.49, and 0.43 ng/mL, respectively. Sphingomyelin (SM) levels in the highest quartile of EHDPP, TPHP, TNBP, TBOEP, TEP, and TCIPP were 45.3% [95% confidence interval; 38.1%, 53.0%], 51.9% (45.5%, 58.6%), 153.6% (145.1%, 162.3%), 20.6% (14.5%, 27.0%), 59.0% (52.1%, 66.2%), and 62.8% (55.2%, 70.6%) higher than those in the lowest quartile, respectively, after adjusting for covariates. Sphingosine 1-phosphate (S1P) levels in the highest quartile of EHDPP, TPHP, and TNBP were 36% (-39%, -33%), 16% (-19%, -14%), and 36% (-38%, -33%) lower than those in the lowest quartile, respectively. A similar pattern emerged when exposures were modeled continuously. We for the first time found the associations between OPFRs and changes in human sphingolipid homeostasis.

Sphingosine-1-Phosphate Signaling Regulates Myogenic Responsiveness in Human Resistance Arteries

We recently identified sphingosine-1-phosphate (S1P) signaling and the cystic fibrosis transmembrane conductance regulator (CFTR) as prominent regulators of myogenic responsiveness in rodent resistance arteries. However, since rodent models frequently exhibit limitations with respect to human applicability, translation is necessary to validate the relevance of this signaling network for clinical application. We therefore investigated the significance of these regulatory elements in human mesenteric and skeletal muscle resistance arteries. Mesenteric and skeletal muscle resistance arteries were isolated from patient tissue specimens collected during colonic or cardiac bypass surgery. Pressure myography assessments confirmed endothelial integrity, as well as stable phenylephrine and myogenic responses. Both human mesenteric and skeletal muscle resistance arteries (i) express critical S1P signaling elements, (ii) constrict in response to S1P and (iii) lose myogenic responsiveness following S1P receptor antagonism (JTE013). However, while human mesenteric arteries express CFTR, human skeletal muscle resistance arteries do not express detectable levels of CFTR protein. Consequently, modulating CFTR activity enhances myogenic responsiveness only in human mesenteric resistance arteries. We conclude that human mesenteric and skeletal muscle resistance arteries are a reliable and consistent model for translational studies. We demonstrate that the core elements of an S1P-dependent signaling network translate to human mesenteric resistance arteries. Clear species and vascular bed variations are evident, reinforcing the critical need for further translational study.

The structure and function of the S1P1 receptor

Sphingosine 1-phosphate (S1P) receptors (S1PRs) belong to the class A family of G protein-coupled receptors (GPCRs). S1PRs are widely expressed on many cell types, including those of the immune, cardiovascular, and central nervous systems. The S1PR family is rapidly gaining attention as an important mediator of many cellular processes, including cell differentiation, migration, survival, angiogenesis, calcium homeostasis, inflammation and immunity. Importantly, S1PRs are known drug targets for multiple sclerosis (MS), for which the newly developed oral therapy fingolimod, an S1PR modulator, has recently been approved for clinical use. Much progress has also recently been made in the field of structural biology and in the modeling of heterotrimeric GPCRs allowing the crystal structure of the S1PR1 subtype to be elucidated and key interactions defined. Here, we outline the structure and function of S1PR1, highlighting the key residues involved in receptor activation, signaling, transmembrane interactions, ligand binding, post-translational modification, and protein-protein interactions.

Cardiovascular effects of sphingosine-1-phosphate (S1P)

Sphingosine-1-phosphate (S1P) regulates important functions in cardiac and vascular homeostasis. It has been implied to play causal roles in the pathogenesis of many cardiovascular disorders such as coronary artery disease, atherosclerosis, myocardial infarction, and heart failure. The majority of S1P in plasma is associated with high-density lipoproteins (HDL), and their S1P content has been shown to be responsible, at least in part, for several of the beneficial effects of HDL on cardiovascular risk. The attractiveness of S1P-based drugs for potential cardiovascular applications is increasing in the wake of the clinical approval of FTY720, but answers to important questions on the effects of S1P in cardiovascular biology and medicine must still be found. This chapter focuses on the current understanding of the role of S1P and its receptors in cardiovascular physiology, pathology, and disease.

Capitalizing on diversity: an integrative approach towards the multiplicity of cellular mechanisms underlying myogenic responsiveness

The intrinsic ability of resistance arteries to respond to transmural pressure is the single most important determinant of their function. Despite an ever-growing catalogue of signalling pathways that underlie the myogenic response, it remains an enigmatic mechanism. The myogenic response's mechanistic diversity has largely been attributed to 'hard-wired' differences across species and vascular beds; however, emerging evidence suggests that the mechanistic basis for the myogenic mechanism is, in fact, 'plastic'. This means that the myogenic response can change quantitatively (i.e. change in magnitude) and qualitatively (i.e. change in mechanistic basis) in response to environmental challenges (e.g. disease conditions). Consequently, understanding the dynamics of how the myogenic response capitalizes on its mechanistic diversity is key to unlocking clinically viable interventions. Using myogenic sphingosine-1-phosphate (S1P) signalling as an example, this review illustrates the remarkable plasticity of the myogenic response. We propose that currently unidentified 'organizational programmes' dictate the contribution of individual signalling pathways to the myogenic response and introduce the concept that certain signalling elements act as 'divergence points' (i.e. as the potential higher level regulatory sites). In the context of pressure-induced S1P signalling, the S1P-generating enzyme sphingosine kinase 1 serves as a divergence point, by orchestrating the calcium-dependent and -independent signalling pathways underlying microvascular myogenic responsiveness. By acting on divergence points, the proposed 'organizational programmes' could form the basis for the flexible recruitment and fine-tuning of separate signalling streams that underlie adaptive changes to the myogenic response and its distinctiveness across species and vascular beds.