Tumor necrosis factor-α-mediated downregulation of the cystic fibrosis transmembrane conductance regulator drives pathological sphingosine-1-phosphate signaling in a mouse model of heart failure.

BACKGROUND: Sphingosine-1-phosphate (S1P) signaling is a central regulator of resistance artery tone. Therefore, S1P levels need to be tightly controlled through the delicate interplay of its generating enzyme sphingosine kinase 1 and its functional antagonist S1P phosphohydrolase-1. The intracellular localization of S1P phosphohydrolase-1 necessitates the import of extracellular S1P into the intracellular compartment before its degradation. The present investigation proposes that the cystic fibrosis transmembrane conductance regulator transports extracellular S1P and hence modulates microvascular S1P signaling in health and disease. METHODS AND RESULTS: In cultured murine vascular smooth muscle cells in vitro and isolated murine mesenteric and posterior cerebral resistance arteries ex vivo, the cystic fibrosis transmembrane conductance regulator (1) is critical for S1P uptake; (2) modulates S1P-dependent responses; and (3) is downregulated in vitro and in vivo by tumor necrosis factor-α, with significant functional consequences for S1P signaling and vascular tone. In heart failure, tumor necrosis factor-α downregulates the cystic fibrosis transmembrane conductance regulator across several organs, including the heart, lung, and brain, suggesting that it is a fundamental mechanism with implications for systemic S1P effects. CONCLUSIONS: We identify the cystic fibrosis transmembrane conductance regulator as a critical regulatory site for S1P signaling; its tumor necrosis factor-α-dependent downregulation in heart failure underlies an enhancement in microvascular tone. This molecular mechanism potentially represents a novel and highly strategic therapeutic target for cardiovascular conditions involving inflammation.

Proximal cerebral arteries develop myogenic responsiveness in heart failure via tumor necrosis factor-α-dependent activation of sphingosine-1-phosphate signaling.

BACKGROUND: Heart failure is associated with neurological deficits, including cognitive dysfunction. However, the molecular mechanisms underlying reduced cerebral blood flow in the early stages of heart failure, particularly when blood pressure is minimally affected, are not known. METHODS AND RESULTS: Using a myocardial infarction model in mice, we demonstrate a tumor necrosis factor-α (TNFα)-dependent enhancement of posterior cerebral artery tone that reduces cerebral blood flow before any overt changes in brain structure and function. TNFα expression is increased in mouse posterior cerebral artery smooth muscle cells at 6 weeks after myocardial infarction. Coordinately, isolated posterior cerebral arteries display augmented myogenic tone, which can be fully reversed in vitro by the competitive TNFα antagonist etanercept. TNFα mediates its effect via a sphingosine-1-phosphate (S1P)-dependent mechanism, requiring sphingosine kinase 1 and the S1P(2) receptor. In vivo, sphingosine kinase 1 deletion prevents and etanercept (2-week treatment initiated 6 weeks after myocardial infarction) reverses the reduction of cerebral blood flow, without improving cardiac function. CONCLUSIONS: Cerebral artery vasoconstriction and decreased cerebral blood flow occur early in an animal model of heart failure; these perturbations are reversed by interrupting TNFα/S1P signaling. This signaling pathway may represent a potential therapeutic target to improve cognitive function in heart failure.

Cardioprotective and vasodilatory actions of glucagon-like peptide 1 receptor are mediated through both glucagon-like peptide 1 receptor-dependent and -independent pathways.

BACKGROUND: The glucagon-like peptide 1 receptor (GLP-1R) is believed to mediate glucoregulatory and cardiovascular effects of the incretin hormone GLP-1(7-36) (GLP-1), which is rapidly degraded by dipeptidyl peptidase-4 (DPP-4) to GLP-1(9-36), a truncated metabolite generally thought to be inactive. Novel drugs for the treatment of diabetes include analogues of GLP-1 and inhibitors of DPP-4; however, the cardiovascular effects of distinct GLP-1 peptides have received limited attention. METHODS AND RESULTS: Here, we show that endothelium and cardiac and vascular myocytes express a functional GLP-1R as GLP-1 administration increased glucose uptake, cAMP and cGMP release, left ventricular developed pressure, and coronary flow in isolated mouse hearts. GLP-1 also increased functional recovery and cardiomyocyte viability after ischemia-reperfusion injury of isolated hearts and dilated preconstricted arteries from wild-type mice. Unexpectedly, many of these actions of GLP-1 were preserved in Glp1r(-/-) mice. Furthermore, GLP-1(9-36) administration during reperfusion reduced ischemic damage after ischemia-reperfusion and increased cGMP release, vasodilatation, and coronary flow in wild-type and Glp1r(-/-) mice, with modest effects on glucose uptake. Studies using a DPP-4-resistant GLP-1R agonist and inhibitors of DPP-4 and nitric oxide synthase showed that the effects of GLP-1(7-36) were partly mediated by GLP-1(9-36) through a nitric oxide synthase-requiring mechanism that is independent of the known GLP-1R. CONCLUSIONS: These data describe cardioprotective actions of GLP-1(7-36) mediated through the known GLP-1R and novel cardiac and vascular actions of GLP-1(7-36) and its metabolite GLP-1(9-36) independent of the known GLP-1R. Our data suggest that the extent to which GLP-1 is metabolized to GLP-1(9-36) may have functional implications in the cardiovascular system.

Protein-energy malnutrition impairs functional outcome in global ischemia.

We investigated whether protein-energy malnutrition (PEM) exacerbates brain injury in global ischemia. It was hypothesized that PEM would increase secondary brain damage by worsening ischemia-induced depletion of glutathione (GSH) and increasing oxidative stress. Adult male gerbils were fed an adequate protein (12.5%; C) or low protein (2%; PEM) diet for 4 weeks and subjected to 5 min of bilateral carotid artery occlusion (Ischemia) or sham surgery (Sham). At 12 h post-ischemia, GSH and markers of oxidative stress were measured in hippocampus and neocortex. The remaining gerbils were tested in the open field on days 3, 7, and 10, with viable hippocampal CA1 neurons assessed on day 10. Although the habituation of C-Ischemia gerbils in the open field was normal by day 7, PEM-Ischemia gerbils failed to habituate even by day 10 and spent greater time in the outer zone (P < 0.05). Mean (+/-SEM) total number of viable CA1 neurons at 10 days post-ischemia were C-Sham = 713 (13), C-Ischemia = 264 (48), PEM-Sham = 716 (12), and PEM-Ischemia = 286 (66). Although PEM did not increase CA1 neuron loss caused by ischemia, a subset (4/12) of PEM-Ischemia gerbils showed dramatic reactive gliosis accompanied by extensive neuronal loss. Hippocampal protein thiols were decreased by PEM and ischemia. Although the mechanism is yet to be established, the finding that PEM worsens functional outcome following global ischemia is clinically relevant since 16% of elderly are nutritionally compromised at the time of admission for stroke.

Dietary approach to attenuate oxidative stress, hypertension, and inflammation in the cardiovascular system.

Imbalance between production and scavenging of superoxide anion results in hypertension by the inactivation of nitric oxide, and the increased oxidative stress from the resultant peroxynitrite that is produced promotes inflammatory processes such as atherosclerosis. Induction of phase 2 proteins promotes oxidant scavenging. We hypothesized that intake of dietary phase 2 protein inducers would ameliorate both hypertension and atherosclerotic changes in the spontaneously hypertensive stroke-prone rat. For 5 days/week for 14 weeks, we fed rats 200 mg/day of dried broccoli sprouts that contained glucoraphanin, which is metabolized into the phase 2 protein-inducer sulforaphane (Group A), sprouts in which most of the glucoraphanin was destroyed (Group B), or no sprouts (Group C). After 14 weeks of treatment, no significant differences were seen between rats in Groups B and C. Rats in Group A had significantly decreased oxidative stress in cardiovascular and kidney tissues, as shown by increased glutathione (GSH) content and decreased oxidized GSH, decreased protein nitrosylation, as well as increased GSH reductase and GSH peroxidase activities. Decreased oxidative stress correlated with better endothelial-dependent relaxation of the aorta and significantly lower (20 mm Hg) blood pressure. Tissues from Groups B and C had considerable numbers of infiltrating activated macrophages, indicative of inflammation, whereas animals in Group A had few detectable infiltrating macrophages. There is interest in dietary phase 2 protein inducers as means of reducing cancer incidence. We conclude that a diet containing phase 2 protein inducers also reduces the risk of developing cardiovascular problems of hypertension and atherosclerosis.