Hyperhomocysteinemia and Cardiovascular Disease: Is the Adenosinergic System the Missing Link?

The influence of hyperhomocysteinemia (HHCy) on cardiovascular disease (CVD) remains unclear. HHCy is associated with inflammation and atherosclerosis, and it is an independent risk factor for CVD, stroke and myocardial infarction. However, homocysteine (HCy)-lowering therapy does not affect the inflammatory state of CVD patients, and it has little influence on cardiovascular risk. The HCy degradation product hydrogen sulfide (H2S) is a cardioprotector. Previous research proposed a positive role of H2S in the cardiovascular system, and we discuss some recent data suggesting that HHCy worsens CVD by increasing the production of H2S, which decreases the expression of adenosine A2A receptors on the surface of immune and cardiovascular cells to cause inflammation and ischemia, respectively.

Adenosine Receptor Reserve and Long-Term Potentiation: Unconventional Adaptive Mechanisms in Cardiovascular Diseases?

While the concept of a receptor reserve (spare receptors) is old, their presence on human cells as an adaptive mechanism in cardiovascular disease is a new suggestion. The presence of spare receptors is suspected when the activation of a weak fraction of receptors leads to maximal biological effects, in other words, when the half-maximal effective concentration (EC50) for a biological effect (cAMP production, for example) is lower than the affinity (KD) of the ligand for a receptor. Adenosine is an ATP derivative that strongly impacts the cardiovascular system via its four membrane receptors, named A1R, A2AR, A2BR, and A3R, with the A1R being more particularly involved in heart rhythm, while the A2AR controls vasodilation. After a general description of the tools necessary to explore the presence of spare receptors, this review focuses on the consequences of the presence of spare adenosine receptors in cardiovascular physiopathology. Finally, the role of the adenosinergic system in the long-term potentiation and its possible consequences on the physiopathology are also mentioned.

Homocysteine concentration and adenosine A2A receptor production by peripheral blood mononuclear cells in coronary artery disease patients.

Hyperhomocysteinemia is associated with coronary artery disease (CAD). The mechanistic aspects of this relationship are unclear. In CAD patients, homocysteine (HCy) concentration correlates with plasma level of adenosine that controls the coronary circulation via the activation of adenosine A2A receptors (A2A R). We addressed in CAD patients the relationship between HCy and A2A R production, and in cellulo the effect of HCy on A2A R function. 46 patients with CAD and 20 control healthy subjects were included. We evaluated A2A R production by peripheral blood mononuclear cells using Western blotting. We studied in cellulo (CEM human T cells) the effect of HCy on A2A R production as well as on basal and stimulated cAMP production following A2A R activation by an agonist-like monoclonal antibody. HCy concentration was higher in CAD patients vs controls (median, range: 16.6 [7-45] vs 8 [5-12] µM, P < 0.001). A2A R production was lower in patients vs controls (1.1[0.62-1.6] vs 1.53[0.7-1.9] arbitrary units, P < 0.001). We observed a negative correlation between HCy concentration and A2A R production (r = -0.43; P < 0.0001), with decreased A2A R production above 25 µM HCy. In cellulo, HCy inhibited A2A R production, as well as basal and stimulated cAMP production. In conclusion, HCy is negatively associated with A2A R production in CAD patients, as well as with A2A R and cAMP production in cellulo. The decrease in A2A R production and function, which is known to hamper coronary blood flow and promote inflammation, may support CAD pathogenesis.

Hsp70s transcription-translation relationship depends on the heat shock temperature in zebrafish.

Virtually all organisms respond to heat shock by transcription of genes encoding for heat shock proteins (HSPs), but the mechanisms behind post-transcriptional regulation are not known in detail. When we exposed zebrafish to 5 and 7 °C above normal rearing temperature for 30 min, hsp70 mRNA expression was 28 and 150 -fold higher than in control, respectively. Protein expression, on the other hand, showed no significant change at the +5 °C and a 2-fold increase at the +7 °C exposure. This suggests that the transcription of hsp70 gene does not immediately correspond to translation to related proteins under certain stress temperatures, but, when the temperature is higher, and potentially detrimental, transcription and translation are intimately coupled. Those results confirm that temperature is an important abiotic factor involved in heat shock post-transcriptional regulation mechanisms in fish. However, further studies are needed to determine the relationship between this environmental factor and post-transcriptional regulation mechanisms. Earlier, the coupling/uncoupling of hsp transcription and translation has only been studied using cold-water fish, or zebrafish embryos. With current findings, we suggest this mechanism might be present even in adult warm water fish like the zebrafish.

Adenosine and Its Receptors: An Expected Tool for the Diagnosis and Treatment of Coronary Artery and Ischemic Heart Diseases.

Adenosine is an endogenous nucleoside which strongly impacts the cardiovascular system. Adenosine is released mostly by endothelial cells and myocytes during ischemia or hypoxia and greatly regulates the cardiovascular system via four specific G-protein-coupled receptors named A1R, A2AR, A2BR, and A3R. Among them, A2 subtypes are strongly expressed in coronary tissues, and their activation increases coronary blood flow via the production of cAMP in smooth muscle cells. A2A receptor modulators are an opportunity for intense research by the pharmaceutical industry to develop new cardiovascular therapies. Most innovative therapies are mediated by the modulation of adenosine release and/or the activation of the A2A receptor subtypes. This review aims to focus on the specific exploration of the adenosine plasma level and its relationship with the A2A receptor, which seems a promising biomarker for a diagnostic and/or a therapeutic tool for the screening and management of coronary artery disease. Finally, a recent class of selective adenosine receptor ligands has emerged, and A2A receptor agonists/antagonists are useful tools to improve the management of patients suffering from coronary artery disease.

Adenosine plasma level in patients with paroxysmal or persistent atrial fibrillation and normal heart during ablation procedure and/or cardioversion.

The mechanism of atrial fibrillation (AF) in patients with normal heart remains unclear. While exogenous adenosine can trigger AF, nothing is known about the behavior of endogenous adenosine plasma level (APL) at the onset of AF and during ablation procedure. Ninety-one patients (68 with paroxysmal AF: 40 males, 66 ± 16 years; 23 with persistent AF: 14 males, 69 ± 11 years) and 18 controls were included. Among paroxysmal patients: i) medical therapy alone was performed in 45 cases and ablation procedure in 23. AF was spontaneously resolutive in 6 cases; ii) 23 underwent ablation procedure and blood was collected simultaneously in a brachial vein and in the left atrium; 17 were spontaneously in sinus rhythm while 6 were in sinus rhythm after direct current cardioversion. Among persistent patients: i) in 17 patients, blood samples were collected in a brachial vein before and after direct current cardioversion; ii) in 6 patients, blood samples were collected simultaneously in a brachial vein and in left atrium before and after cardioversion during ablation procedure. CV-APL was higher in patients with persistent AF vs patients with paroxysmal AF (median [range]: 0.9[0.6-1.1] vs 0.7[0.4-1.1] µM; p < 0.001). In patients with paroxysmal AF, LA-APL increased during the AF episode (0.95[0.85-1.4] vs 2.7[1.5-7] µM; p = 0.03) and normalized in sinus rhythm after DCCV. In patients with persistent AF, LA-APL was higher than CV-APL (1.2[0.7-1.8] vs 0.9[0.6-1.1] µM; p < 0.001), and both normalized in sinus rhythm (CV-APL: 0.8[0.6-1.1] vs 0.75[0.4-1] µM; p = 0.03), (LA-APL: 1.95[1.3-3] vs 1[0.5-1.15] µM; p = 0.03). The occurrence of AF is associated with a strong increase of APL in the atrium. The cause of this increase needs further investigations.

Adenosine Receptor Profiling Reveals an Association between the Presence of Spare Receptors and Cardiovascular Disorders.

Adenosine and its receptors exert a potent control on the cardiovascular system. This review aims to present emerging experimental evidence supporting the existence and implication in cardiovascular disorders of specific adenosinergic pharmacological profiles, conforming to the concept of "receptor reserve", also known as "spare receptors". This kind of receptors allow agonists to achieve their maximal effect without occupying all of the relevant cell receptors. In the cardiovascular system, spare adenosine receptors appear to compensate for a low extracellular adenosine level and/or a low adenosine receptor number, such as in coronary artery disease or some kinds of neurocardiogenic syncopes. In both cases, the presence of spare receptors appears to be an attempt to overcome a weak interaction between adenosine and its receptors. The identification of adenosine spare receptors in cardiovascular disorders may be helpful for diagnostic purposes.

Adenosine Plasma Level and A2A Receptor Expression in Patients With Cardiogenic Shock.

OBJECTIVES: To investigate whether adenosine A2A receptors lead to vasodilation and positive inotropic function under stimulation and whether they play a role in the control of blood pressure in patients with cardiogenic shock. DESIGN: Prospective observational study. SETTING: Monocentric, Hopital Nord, Marseille, France. SUBJECTS: Patients with cardiogenic shock (n = 16), acute heart failure (n = 16), and acute myocardial infarction (n = 16). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Arterial adenosine plasma level and A2A receptor expression on peripheral blood mononuclear cells were evaluated by mass spectrometry and Western blot, respectively, at admission and after 24 hours. Hemodynamic parameters, including systemic vascular resistance, were also assessed. Mean adenosine plasma level at admission was significantly higher in patients with cardiogenic shock (2.74 ± 1.03 µM) versus acute heart failure (1.33 ± 0.27) or acute myocardial infarction (1.19 ± 0.27) (normal range, 0.4-0.8 µM) (p < 0.0001). No significant correlation was found between adenosine plasma level and systemic vascular resistance. Mean adenosine plasma level decreased significantly by 24 hours after admission in patients with cardiogenic shock (2.74 ± 1.03 to 1.53 ± 0.68; p < 0.001). Mean A2A receptor expression was significantly lower in patients with cardiogenic shock (1.18 ± 0.11) versus acute heart failure (1.18 ± 0.11 vs 1.39 ± 0.08) (p = 0.005). CONCLUSIONS: We observed high adenosine plasma level and low A2A receptor expression at admission in patients with cardiogenic shock versus acute heart failure or acute myocardial infarction. This may contribute to the physiopathology of cardiogenic shock.

Uric acid levels are associated with endothelial dysfunction and severity of coronary atherosclerosis during a first episode of acute coronary syndrome.

The role of serum uric acid in coronary artery disease has been extensively investigated. It was suggested that serum uric acid level (SUA) is an independent predictor of endothelial dysfunction and related to coronary artery lesions. However, the relationship between SUA and severity of coronary atherosclerosis evaluated via endothelial dysfunction using peripheral arterial tone (PAT) and the reactive hyperhemia index (RHI) has not been investigated during a first episode of acute coronary syndrome (ACS). The aim of our study was to address this point. We prospectively enrolled 80 patients with a first episode of ACS in a single-center observational study. All patients underwent coronary angiography, evaluation of endothelial function via the RHI, and SUA measurement. The severity of the coronary artery lesion was assessed angiographically, and patients were classified in three groups based on the extent of disease and Gensini and SYNTAX scores. Endothelial function was considered abnormal if RHI < 1.67. We identified a linear correlation between SUA and RHI (R2 = 0.66 P < 0.001). In multivariable analyses, SUA remained associated with RHI, even after adjustment for traditional cardiovascular risk factors and renal function. SUA was associated with severity of coronary artery disease. SUA is associated with severity of coronary atherosclerosis in patients with asymptomatic hyperuricemia. This inexpensive, readily measured biological parameter may be useful to monitor ACS patients.

High homocysteine levels prevent via H2 S the CoCl2 -induced alteration of lymphocyte viability.

High homocysteine (HCy) levels are associated with lymphocyte-mediated inflammatory responses that are sometimes in turn related to hypoxia. Because adenosine is a potent lymphocyte suppressor produced in hypoxic conditions and shares metabolic pathways with HCy, we addressed the influence of high HCy levels on the hypoxia-induced, adenosine-mediated, alteration of lymphocyte viability. We treated mitogen-stimulated human lymphocytes isolated from healthy individuals and the human lymphoma T-cell line CEM with cobalt chloride (CoCl2 )to reproduce hypoxia. We found that CoCl2 -altered cell viability was dose-dependently reversed using HCy. In turn, the HCy effect was inhibited using DL-propargylglycine, a specific inhibitor of the hydrogen sulphide (H2 S)-synthesizing enzyme cystathionine-γ-lyase involved in HCy catabolism. We then addressed the intracellular metabolic pathway of adenosine and HCy, and the role of the adenosine A2A receptor (A2 A R). We observed that: (i) hypoxic conditions lowered the intracellular concentration of HCy by increasing adenosine production, which resulted in high A2 A R expression and 3', 5'-cyclic adenosine monophosphate production; (ii) increasing intracellular HCy concentration reversed the hypoxia-induced adenosinergic signalling despite high adenosine concentration by promoting both S-adenosylhomocysteine and H2 S production; (iii) DL-propargylglycine that inhibits H2 S production abolished the HCy effect. Together, these data suggest that high HCy levels prevent, via H2 S production and the resulting down-regulation of A2 A R expression, the hypoxia-induced adenosinergic alteration of lymphocyte viability. We point out the relevance of these mechanisms in the pathophysiology of cardiovascular diseases.

Spare Adenosine A2a Receptors Are Associated With Positive Exercise Stress Test In Coronary Artery Disease.

During exercise, cardiac oxygen-consumption increases and the resulting low oxygen level in myocardium triggers coronary vasodilation. This response to hypoxia is controlled notably by the vasodilator adenosine and its A2A receptor (A2AR). According to the "spare receptor" pharmacological model, a strong A2AR-mediated response can occur in the context of a large number of receptors remaining unoccupied, activation of only a weak fraction of A2AR (evaluated using KD) resulting in maximal cAMP production (evaluated using EC50), and hence in maximal coronary vasodilation. In coronary artery disease (CAD), myocardial ischemia limits adaptation to exercise, which is commonly detected using the exercise stress test (EST). We hypothesized that spare A2AR are present in CAD patients to correct ischemia. Seventeen patients with angiographically-documented CAD and 17 control subjects were studied. We addressed adenosine-plasma concentration and A2AR-expression at the mononuclear cell-surface, which reflects cardiovascular expression. The presence of spare A2AR was tested using an innovative pharmacological approach based on a homemade monoclonal antibody with agonist properties. EST was positive in 82% of patients, and in none of the controls. Adenosine plasma-concentration increased by 60% at peak exercise in patients only (p<0.01). Most patients (65%), and none of the controls, had spare A2AR (identified when EC50/KD≤0.1) and a low A2AR-expression (mean: -37% vs controls; p<0.01). All patients with spare A2AR had a positive EST whereas the subjects without spare A2AR had a negative EST (p<0.05). Spare A2AR are therefore associated with positive EST in CAD patients and their detection may be used as a diagnostic marker.

Low Density Lipoprotein Cholesterol Decreases the Expression of Adenosine A2A Receptor and Lipid Rafts-Protein Flotillin-1: Insights on Cardiovascular Risk of Hypercholesterolemia.

High blood levels of low-density lipoprotein (LDL)-cholesterol (LDL-C) are associated with atherosclerosis, mainly by promoting foam cell accumulation in vessels. As cholesterol is an essential component of cell plasma membranes and a regulator of several signaling pathways, LDL-C excess may have wider cardiovascular toxicity. We examined, in untreated hypercholesterolemia (HC) patients, selected regardless of the cause of LDL-C accumulation, and in healthy participants (HP), the expression of the adenosine A2A receptor (A2AR), an anti-inflammatory and vasodilatory protein with cholesterol-dependent modulation, and Flotillin-1, protein marker of cholesterol-enriched plasma membrane domains. Blood cardiovascular risk and inflammatory biomarkers were measured. A2AR and Flotillin-1 expression in peripheral blood mononuclear cells (PBMC) was lower in patients compared to HP and negatively correlated to LDL-C blood levels. No other differences were observed between the two groups apart from transferrin and ferritin concentrations. A2AR and Flotillin-1 proteins levels were positively correlated in the whole study population. Incubation of HP PBMCs with LDL-C caused a similar reduction in A2AR and Flotillin-1 expression. We suggest that LDL-C affects A2AR expression by impacting cholesterol-enriched membrane microdomains. Our results provide new insights into the molecular mechanisms underlying cholesterol toxicity, and may have important clinical implication for assessment and treatment of cardiovascular risk in HC.

Ligand of Numb proteins LNX1p80 and LNX2 interact with the human glycoprotein CD8α and promote its ubiquitylation and endocytosis.

E3 ubiquitin ligases give specificity to the ubiquitylation process by selectively binding substrates. Recently, their function has emerged as a crucial modulator of T-cell tolerance and immunity. However, substrates, partners and mechanism of action for most E3 ligases remain largely unknown. In this study, we identified the human T-cell co-receptor CD8 α-chain as binding partner of the ligand of Numb proteins X1 (LNX1p80 isoform) and X2 (LNX2). Both LNX mRNAs were found expressed in T cells purified from human blood, and both proteins interacted with CD8α in human HPB-ALL T cells. By using an in vitro assay and a heterologous expression system we showed that the interaction is mediated by the PDZ (PSD95-DlgA-ZO-1) domains of LNX proteins and the cytosolic C-terminal valine motif of CD8α. Moreover, CD8α redistributed LNX1 or LNX2 from the cytosol to the plasma membrane, whereas, remarkably, LNX1 or LNX2 promoted CD8α ubiquitylation, downregulation from the plasma membrane, transport to the lysosomes, and degradation. Our findings highlight the function of LNX proteins as E3 ligases and suggest a mechanism of regulation for CD8α localization at the plasma membrane by ubiquitylation and endocytosis.

A novel function for the Rab5 effector Rabenosyn-5 in planar cell polarity.

In addition to apicobasal polarization, some epithelia also display polarity within the plane of the epithelium. To what extent polarized endocytosis plays a role in the establishment and maintenance of planar cell polarity (PCP) is at present unclear. Here, we investigated the role of Rabenosyn-5 (Rbsn-5), an evolutionarily conserved effector of the small GTPase Rab5, in the development of Drosophila wing epithelium. We found that Rbsn-5 regulates endocytosis at the apical side of the wing epithelium and, surprisingly, further uncovered a novel function of this protein in PCP. At early stages of pupal wing development, the PCP protein Fmi redistributes between the cortex and Rab5- and Rbsn-5-positive early endosomes. During planar polarization, Rbsn-5 is recruited at the apical cell boundaries and redistributes along the proximodistal axis in an Fmi-dependent manner. At pre-hair formation, Rbsn-5 accumulates at the bottom of emerging hairs. Loss of Rbsn-5 causes intracellular accumulation of Fmi and typical PCP alterations such as defects in cell packing, in the polarized distribution of PCP proteins, and in hair orientation and formation. Our results suggest that establishment of planar polarity requires the activity of Rbsn-5 in regulating both the endocytic trafficking of Fmi at the apical cell boundaries and hair morphology.

Myogenesis in C2C12 Cells Requires Phosphorylation of ATF6α by p38 MAPK.

Activating transcription factor 6α (ATF6α) is an endoplasmic reticulum protein known to participate in unfolded protein response (UPR) during ER stress in mammals. Herein, we show that in mouse C2C12 myoblasts induced to differentiate, ATF6α is the only pathway of the UPR activated. ATF6α stimulation is p38 MAPK-dependent, as revealed by the use of the inhibitor SB203580, which halts myotube formation and, at the same time, impairs trafficking of ATF6α, which accumulates at the cis-Golgi without being processed in the p50 transcriptional active form. To further evaluate the role of ATF6α, we knocked out the ATF6α gene, thus inhibiting the C2C12 myoblast from undergoing myogenesis, and this occurred independently from p38 MAPK activity. The expression of exogenous ATF6α in knocked-out ATF6α cells recover myogenesis, whereas the expression of an ATF6α mutant in the p38 MAPK phosphorylation site (T166) was not able to regain myogenesis. Genetic ablation of ATF6α also prevents the exit from the cell cycle, which is essential for muscle differentiation. Furthermore, when we inhibited differentiation by the use of dexamethasone in C2C12 cells, we found inactivation of p38 MAPK and, consequently, loss of ATF6α activity. All these findings suggest that the p-p38 MAPK/ATF6α axis, in pathophysiological conditions, regulates myogenesis by promoting the exit from the cell cycle, an essential step to start myoblasts differentiation.

Increased fecal ethanol and enriched ethanol-producing gut bacteria Limosilactobacillus fermentum, Enterocloster bolteae, Mediterraneibacter gnavus and Streptococcus mutans in nonalcoholic steatohepatitis.

Background: Non-alcoholic steatohepatitis (NASH) has become a major public health issue as one of the leading causes of liver disease and transplantation worldwide. The instrumental role of the gut microbiota is emerging but still under investigation. Endogenous ethanol (EtOH) production by gut bacteria and yeasts is an emerging putative mechanism. Microbial metagenomics and culture studies targeting enterobacteria or yeasts have been reported, but no culturomics studies have been conducted so far. Aim: To assess fecal EtOH and other biochemical parameters, characterize NASH-associated dysbiosis and identify EtOH-producing gut microbes associated with the disease, fecal samples from 41 NASH patients and 24 controls were analyzed. High-performance liquid chromatography (HPLC) was used for EtOH, glucose, total proteins, triglyceride and total cholesterol. Viable bacteria were assessed with microbial culturomics. Microbial genetic material was assessed using 16S metagenomics targeting the hypervariable V3V4 region. Results: Fecal EtOH and glucose was elevated in the stools of NASH patients (p < 0.05) but not triglyceride, total cholesterol or proteins. In culturomics, EtOH-producing Enterocloster bolteae and Limosilactobacillus fermentum were enriched in NASH. V3V4 16S rRNA amplicon sequencing confirmed the enrichment in EtOH-producing bacteria including L. fermentum, Mediterraneibacter gnavus and Streptococcus mutans, species previously associated with NASH and other dysbiosis-associated diseases. Strikingly, E. bolteae was identified only by culturomics. The well-known Lacticaseibacillus casei was identified in controls but never isolated in patients with NASH (p < 0.05). Conclusion: Elevated fecal EtOH and glucose is a feature of NASH. Several different EtOH-producing gut bacteria may play an instrumental role in the disease. Culturomics and metagenomics, two complementary methods, will be critical to identify EtOH-producing bacteria for future diagnostic markers and therapeutic targets for NASH. Suppression of EtOH-producing gut microbes and L. casei administration are options to be tested in NASH treatment.

Adenosinergic System and Neuroendocrine Syncope: What Is the Link?

Although very common, the precise mechanisms that explain the symptomatology of neuroendocrine syncope (NES) remain poorly understood. This disease, which can be very incapacitating, manifests itself as a drop in blood pressure secondary to vasodilation and/or extreme slowing of heart rate. As studies continue, the involvement of the adenosinergic system is becoming increasingly evident. Adenosine, which is an ATP derivative, may be involved in a large number of cases. Adenosine acts on G protein-coupled receptors with seven transmembrane domains. A1 and A2A adenosine receptor dysfunction seem to be particularly implicated since the activation leads to severe bradycardia or vasodilation, respectively, two cardinal symptoms of NES. This mini-review aims to shed light on the links between dysfunction of the adenosinergic system and NHS. In particular, signal transduction pathways through the modulation of cAMP production and ion channels in relation to effects on the cardiovascular system are addressed. A better understanding of these mechanisms could guide the pharmacological development of new therapeutic approaches.

Hyperhomocysteinemia and cardiovascular diseases.

Homocysteine (Hcy) is a sulfhydryl-containing amino acid, which is not acquired through the diet, but rather synthesized as an intermediate metabolite in the methionine cycle. Hcy is present in plasma, with normal levels between 5 and 15 µmol/L, a slightly elevated level between 15 to 30 µmol/L, moderate from 30 to 100 µmol/L and a value > 100 µmol/L classified as severe hyperhomocysteinemia (HHcy). HHcy has been associated with inflammation and atherosclerosis and is considered an independent risk factor for cardiovascular diseases (CVD). Here, we review the main evidence showing the association and the possible involvement of HHcy in the most common CVD.

Copper exposure improves the upper thermal tolerance in a sex-specific manner, irrespective of fish thermal history.

Ectotherms can respond to climate change via evolutionary adaptation, usually resulting in an increase of their upper thermal tolerance. But whether such adaptation influences the phenotypic plasticity of thermal tolerance when encountering further environmental stressors is not clear yet. This is crucial to understand because organisms experience multiple stressors, besides warming climate, in their natural environment and pollution is one of those. Here, we studied the phenotypic plasticity of thermal tolerance in three-spined stickleback populations inhabiting spatially replicated thermally polluted and pristine areas before and after exposing them to a sublethal concentration of copper for one week. We found that the upper thermal tolerance and its phenotypic plasticity after copper exposure did not depend on the thermal history of fish, suggesting that five decades of thermal pollution did not result in evolutionary adaptation to thermal tolerance. The upper thermal tolerance of fish was, on the other hand, increased by ∼ 1.5 °C after 1-week copper exposure in a sex-specific manner, with males having higher plasticity. To our knowledge this is the first study that shows an improvement of the upper thermal tolerance as a result of metal exposure. The results suggest that three-spined sticklebacks are having high plasticity and they are capable of surviving in a multiple-stressor scenario in the wild and that male sticklebacks seem more resilient to fluctuating environmental conditions than female.

FGF10 promotes cardiac repair through a dual cellular mechanism increasing cardiomyocyte renewal and inhibiting fibrosis.

AIMS: Promoting cardiomyocyte renewal represents a major therapeutic approach for heart regeneration and repair. Our study aims to investigate the relevance of FGF10 as a potential target for heart regeneration. METHODS AND RESULTS: Our results first reveal that Fgf10 levels are up-regulated in the injured ventricle after MI. Adult mice with reduced Fgf10 expression subjected to MI display impaired cardiomyocyte proliferation and enhanced cardiac fibrosis, leading to a worsened cardiac function and remodelling post-MI. In contrast, conditional Fgf10 overexpression post-MI revealed that, by enhancing cardiomyocyte proliferation and preventing scar-promoting myofibroblast activation, FGF10 preserves cardiac remodelling and function. Moreover, FGF10 activates major regenerative pathways including the regulation of Meis1 expression levels, the Hippo signalling pathway and a pro-glycolytic metabolic switch. Finally, we demonstrate that elevated FGF10 levels in failing human hearts correlate with reduced fibrosis and enhanced cardiomyocyte proliferation. CONCLUSIONS: Altogether, our study shows that FGF10 promotes cardiac regeneration and repair through two cellular mechanisms: elevating cardiomyocyte renewal and limiting fibrosis. This study thus identifies FGF10 as a clinically relevant target for heart regeneration and repair in man.