Regulation of the sphingolipid signaling pathways in the growing and hypoxic rat heart

Metabolomic Signatures Associated With Pulmonary Arterial Hypertension Outcomes

BACKGROUND

Pulmonary arterial hypertension (PAH) is a complex disease characterized by progressive right ventricular (RV) failure leading to significant morbidity and mortality. Investigating metabolic features and pathways associated with RV dilation, mortality, and measures of disease severity can provide insight into molecular mechanisms, identify subphenotypes, and suggest potential therapeutic targets.

METHODS

We collected data from a prospective cohort of PAH participants and performed untargeted metabolomic profiling on 1045 metabolites from circulating blood. Analyses were intended to identify metabolomic differences across a range of common metrics in PAH (eg, dilated versus nondilated RV). Partial least squares discriminant analysis was first applied to assess the distinguishability of relevant outcomes. Significantly altered metabolites were then identified using linear regression, and Cox regression models (as appropriate for the specific outcome) with adjustments for age, sex, body mass index, and PAH cause. Models exploring RV maladaptation were further adjusted for pulmonary vascular resistance. Pathway enrichment analysis was performed to identify significantly dysregulated processes.

RESULTS

A total of 117 participants with PAH were included. Partial least squares discriminant analysis showed cluster differentiation between participants with dilated versus nondilated RVs, survivors versus nonsurvivors, and across a range of NT-proBNP (N-terminal pro-B-type natriuretic peptide) levels, REVEAL 2.0 composite scores, and 6-minute-walk distances. Polyamine and histidine pathways were associated with differences in RV dilation, mortality, NT-proBNP, REVEAL score, and 6-minute walk distance. Acylcarnitine pathways were associated with NT-proBNP, REVEAL score, and 6-minute walk distance. Sphingomyelin pathways were associated with RV dilation and NT-proBNP after adjustment for pulmonary vascular resistance.

CONCLUSIONS

Distinct plasma metabolomic profiles are associated with RV dilation, mortality, and measures of disease severity in PAH. Polyamine, histidine, and sphingomyelin metabolic pathways represent promising candidates for identifying patients at high risk for poor outcomes and investigation into their roles as markers or mediators of disease progression and RV adaptation.

The effect of adaptation to hypoxia on cardiac tolerance to ischemia/reperfusion

The acute myocardial infarction (AMI) and sudden cardiac death (SCD), both associated with acute cardiac ischemia, are one of the leading causes of adult death in economically developed countries. The development of new approaches for the treatment and prevention of AMI and SCD remains the highest priority for medicine. A study on the cardiovascular effects of chronic hypoxia (CH) may contribute to the development of these methods. Chronic hypoxia exerts both positive and adverse effects. The positive effects are the infarct-reducing, vasoprotective, and antiarrhythmic effects, which can lead to the improvement of cardiac contractility in reperfusion. The adverse effects are pulmonary hypertension and right ventricular hypertrophy. This review presents a comprehensive overview of how CH enhances cardiac tolerance to ischemia/reperfusion. It is an in-depth analysis of the published data on the underlying mechanisms, which can lead to future development of the cardioprotective effect of CH. A better understanding of the CH-activated protective signaling pathways may contribute to new therapeutic approaches in an increase of cardiac tolerance to ischemia/reperfusion.

p53 and Ceramide as Collaborators in the Stress Response

The sphingolipid ceramide mediates various cellular processes in response to several extracellular stimuli. Some genotoxic stresses are able to induce p53-dependent ceramide accumulation leading to cell death. However, in other cases, in the absence of the tumor suppressor protein p53, apoptosis proceeds partly due to the activity of this "tumor suppressor lipid", ceramide. In the current review, we describe ceramide and its roles in signaling pathways such as cell cycle arrest, hypoxia, hyperoxia, cell death, and cancer. In a specific manner, we are elaborating on the role of ceramide in mitochondrial apoptotic cell death signaling. Furthermore, after highlighting the role and mechanism of action of p53 in apoptosis, we review the association of ceramide and p53 with respect to apoptosis. Strikingly, the hypothesis for a direct interaction between ceramide and p53 is less favored. Recent data suggest that ceramide can act either upstream or downstream of p53 protein through posttranscriptional regulation or through many potential mediators, respectively.

Control of metabolism and signaling of simple bioactive sphingolipids: Implications in disease

Simple bioactive sphingolipids include ceramide, sphingosine and their phosphorylated forms sphingosine 1-phosphate and ceramide 1-phosphate. These molecules are crucial regulators of cell functions. In particular, they play important roles in the regulation of angiogenesis, apoptosis, cell proliferation, differentiation, migration, and inflammation. Decoding the mechanisms by which these cellular functions are regulated requires detailed understanding of the signaling pathways that are implicated in these processes. Most importantly, the development of inhibitors of the enzymes involved in their metabolism may be crucial for establishing new therapeutic strategies for treatment of disease.

Modulation of total ceramide and constituent ceramide species in the acutely and chronically hypoxic mouse heart at different ages

Ceramide has been implicated in regulatory processes vital for cell survival under different stressors, most notably hypoxia. Little has been done to investigate the contributions of the different ceramide species to the regulation of cell survival. This study aims to highlight the patterns of variation in total ceramide and its species in the growing and hypoxic mouse heart. Mus musculus mice were placed in a hypoxic environment at birth. Control animals remained in room air. The hearts were extracted at different time points: 1 day, 1 week, 4 weeks, and 8 weeks. The total ceramide content and the amounts of component species were assayed by a modified diacylglycerol kinase assay and high-performance liquid chromatography-tandem mass spectroscopy, respectively. Data was collected from both ventricles in hypoxic and control conditions. There was significant polycythemia in the hypoxic versus control animals with a nearly twofold increase in hematocrit levels. Hypoxic right ventricle (RV) mass significantly increased over that of controls at different age groups. When ceramide content was compared in the hypoxic versus control animals, there was a significant increase at day 1 and a significant decrease at week 4 in the left ventricle, whereas a significant decrease was found in the RV at 1 week, 4 weeks, and 8 weeks. There was also a differential involvement of the RV with regard to levels of N-palmitoyl-D-erythro-sphingosine (C16-Cer) and its synthetic precursor dihydro-N-palmitoyl-D-erythro-sphinganine (DHC-16-Cer). The decrease in C16-Cer observed in both hypoxic and control RV's over time was paralleled by a significant increase in DHC-16-Cer in hypoxic (142.1+/-15.0 pmol; p<0.05) but not control (52.8+/-4.0 pmol) RV's suggesting a role for DHC-16-Cer in the RV adaptive response to hypoxia. Another species, N-arachidoyl-D-erythro-sphingosine (C20-Cer), was specifically and significantly decreased in the hypoxic RV. These studies support the presence of distinct roles for different ceramide species and their precursors. A better assessment of cyanotic congenital heart disease in light of the mechanism and timing of cardiomyocyte death, will lead to punctual interventions and even novel cardioprotective strategies.

Expression of sphingomyelin synthase 1 gene in rat brain focal ischemia

Metabolites of the sphingomyelin cycle are reported to play an important role in neuronal death after ischemia. To elucidate the involvement of the key enzyme of this cycle, sphingomyelin synthase (SMS), in the mechanism underlying cerebral ischemia, we, for the first time, investigated changes in the mRNA expression of the SMS1 gene in rats after focal cerebral ischemia. According to our histological analysis, the damaged area is localized only in the ipsilateral cortex. In the ischemic cortex, the level of SMS1 transcripts was decreased at 3 and 24 h after occlusion, and at 72 h it had returned to the control level. A reduced level of SMS1 mRNA expression in the subcortex of rats with occlusion and sham-operated animals also was appeared during the first 24 h after surgery. This could be attributed to the effect of surgical stress. Seventy-two hours after occlusion, SMS1 mRNA expression in subcortex of ischemic rats was still at a decreased level; this may be considered to be a somewhat distant extended effect. Our results show the early response of the SMS1 gene that can be induced by both ischemia and stress. The results also suggest that inhibition of SMS1 mRNA expression may contribute to ceramide accumulation in a damaged cortex.

Pioglitazone induces de novo ceramide synthesis in the rat heart

Ceramide (CER) is an important mediator of lipotoxicity in the heart. It was found that Zucker diabetic fatty rats develop an age-dependent accumulation of myocardial CER leading to cardiomyocyte apoptosis. However, administration of peroxisome proliferator-activated receptor (PPAR) gamma agonist decreased the content of CER and prevented cardiomyocyte apoptosis [Zhou et al. Proc Natl Acad Sci USA 2000;97:1784-9]. These data suggest that PPARgamma activators affect myocardial CER metabolism. Therefore, the aim of our study was to examine the effects of pioglitazone, a selective PPARgamma agonist, on the content of CER and its metabolites and on the activity of key enzymes of CER metabolism in the heart. The experiments were conducted on rats fed either a standard chow (STD) or a high-fat diet (HFD) for 21 days. Each group was divided into two subgroups: control and treated with pioglitazone for 14 days. Surprisingly, administration of PPARgamma agonist significantly increased myocardial CER content in both STD and HFD rats. In the latter group an elevation in the amount of sphingomyelin was also observed. In STD rats pioglitazone treatment increased the activity of neutral sphingomyelinase and acid ceramidase. However, in HFD group the compound did not affect the activity of the aforementioned enzymes. Interestingly, the activity of serine palmitoyltransferase in both STD and HFD rats increased two-fold after pioglitazone treatment. We conclude that pioglitazone induced accumulation of CER in rat myocardium as a result of augmented CER synthesis de novo. However, in the STD group increased activity of neutral sphingomyelinase could also contributed to this effect.

Hypoxia and lipid signaling

Sufficient oxygen supply is crucial for the development and physiology of mammalian cells and tissues. When simple diffusion of oxygen becomes inadequate to provide the necessary flow of substrate, evolution has provided cells with tools to detect and respond to hypoxia by upregulating the expression of specific genes, which allows an adaptation to hypoxia-induced stress conditions. The modulation of cell signaling by hypoxia is an emerging area of research that provides insight into the orchestration of cell adaptation to a changing environment. Cell signaling and adaptation processes are often accompanied by rapid and/or chronic remodeling of membrane lipids by activated lipases. This review highlights the bi-directional relation between hypoxia and lipid signaling mechanisms.