Endothelial SIRT6 deficiency promotes arterial thrombosis in mice

OBJECTIVE Arterial thrombosis may be initiated by endothelial inflammation or denudation, activation of blood-borne elements or the coagulation system. Tissue factor (TF), a central trigger of the coagulation cascade, is regulated by the pro-inflammatory NF-κB-dependent pathways. Sirtuin 6 (SIRT6) is a nuclear member of the sirtuin family of NAD$^{+}$-dependent deacetylases and is known to inhibit NF-κB signaling. Its constitutive deletion in mice shows early lethality with hypoglycemia and accelerated aging. Of note, the role of SIRT6 in arterial thrombosis remains unknown. Thus, we hypothesized that endothelial SIRT6 protects from arterial thrombosis by modulating inhibition of NF-κB-associated pathways. APPROACH AND RESULTS Using a laser-induced carotid thrombosis model, in vivo arterial occlusion occurred 45% faster in 12-week-old male endothelial-specific Sirt6$^{-/-}$ mice as compared to Sirt6$^{fl/fl}$ controls (n ≥ 9 per group; p = 0.0012). Levels of procoagulant TF were increased in animals lacking endothelial SIRT6 as compared to control littermates. Similarly, in cultured human aortic endothelial cells, SIRT6 knockdown increased TF mRNA, protein and activity. Moreover, SIRT6 knockdown increased mRNA levels of NF-κB-associated genes tumor necrosis factor alpha (TNF-α), poly [ADP-ribose] polymerase 1 (PARP-1), vascular cell adhesion molecule 1 (VCAM-1), and cyclooxygenase-2 (COX-2); at the protein level, COX-2, VCAM-1, TNF-α, and cleaved PARP-1 remained increased after Sirt6 knockdown. CONCLUSIONS Endothelium-specific Sirt6 deletion promotes arterial thrombosis in mice. In cultured human aortic endothelial cells, SIRT6 silencing enhances TF expression and activates pro-inflammatory pathways including TNF-α, cleaved PARP-1, VCAM-1 and COX-2. Hence, endogenous endothelial SIRT6 exerts a protective role in experimental arterial thrombosis

Energy densification of animal waste lignocellulose biomass and raw biomass

The need to reduce carbon emissions has encouraged more research into use of biomass energy in place of coal. Biomass is carbon neutral; its use can therefore lower net emissions. Biomass can be upgraded to a fuel similar to coal by torrefaction. Different biomass have been torrefied but there is limited research in possible use of lignocellulose biomass from animal waste. This study aims to compare extent of energy densification of torrefied cow dung, corn cob and pine wood. They were dried, ground and sieved. Proximate and ultimate analysis was conducted. The samples were then torrefied at 200, 250 and 300 °C at 10 °C/min for 40 min. The resulting biochar were characterized using mass yield, higher heating value, energy yield and density. Biochar obtained at 250 °C were analyzed for elemental composition. Results were compared to Anglo bituminous coal and other torrefied biomass in literature. Corn cob and pine wood reached a maximum of 25.98 MJ/kg and 20.90 MJ/kg in heating value respectively whilst cow dung only increased to a maximum of 18.60 MJ/kg. Increase in heating value for corn cob was attributed to reduction in oxygen due to release of volatiles as well as water. This lowered the O/C ratio thereby densifying the fuel. The O/C and H/C ratio for corncob and wood moved towards that of bituminous coal unlike that of cow dung. Cow dung had a high inorganic composition so its heating value could not be upgraded as much as the other 2 biomass. Its use as a torrefaction raw material was therefore discouraged. Keywords: Torrefaction, Biomass, Temperature, Cow dung, Corn cobs, Pine woo

Loss of Sirt3 accelerates arterial thrombosis by increasing formation of neutrophil extracellular traps and plasma tissue factor activity

BACKGROUND: Sirtuin 3 (Sirt3) is a mitochondrial, nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase that reduces oxidative stress by activation of superoxide dismutase 2 (SOD2). Oxidative stress enhances arterial thrombosis. This study investigated the effects of genetic Sirt3 deletion on arterial thrombosis in mice in an inflammatory setting and assessed the clinical relevance of these findings in patients with ST-elevation myocardial infarction (STEMI). Methods and Results: Using a laser-induced carotid thrombosis model with lipopolysaccharide (LPS) challenge, in vivo time to thrombotic occlusion in Sirt3-/- mice (n = 6) was reduced by half compared to Sirt3+/+ wildtype (WT, n = 8, p<0.01) controls. Ex vivo analyses of whole blood using rotational thromboelastometry (ROTEM) revealed accelerated clot formation and increased clot stability in Sirt3-/- compared to WT blood. ROTEM of cell-depleted plasma showed accelerated clotting initiation in Sirt3-/- mice, whereas overall clot formation and firmness remained unaffected. Ex vivo LPS-induced neutrophil extracellular trap (NET) formation was increased in Sirt3-/- bone marrow (BM)-derived neutrophils. Plasma tissue factor (TF) levels and activity were elevated in Sirt3-/- mice, whereas plasma levels of other coagulation factors and TF expression in arterial walls remained unchanged. SOD2 expression in BM-derived Sirt3-/- neutrophils was reduced. In STEMI patients, transcriptional levels of Sirt3 and its target SOD2 were lower in CD14+ leukocytes compared with healthy donors (n = 10 each, p<0.01). CONCLUSIONS: Sirt3 loss-of-function enhances experimental thrombosis in vivo via an increase of NETs and elevation of TF suggesting thrombo-protective effects of endogenous Sirt3. Acute coronary thrombosis in STEMI patients is associated with lower expression levels of SIRT3 and SOD2 in CD14+ leukocytes. Therefore, enhancing SIRT3 activity by pan-sirtuin activating NAD+-boosters may provide a novel therapeutic target to prevent or treat thrombotic arterial occlusion in myocardial infarction or stroke

Endothelial SIRT6 blunts stroke size and neurological deficit by preserving blood-brain barrier integrity: a translational study

AIMS: Aging is an established risk factor for stroke; genes regulating longevity are implicated in the pathogenesis of ischaemic stroke where to date, therapeutic options remain limited. The blood-brain barrier (BBB) is crucially involved in ischaemia/reperfusion (I/R) brain injury thus representing an attractive target for developing novel therapeutic agents. Given the role of endothelial cells in the BBB, we hypothesized that the endothelial-specific expression of the recently described longevity gene SIRT6 may exhibit protective properties in stroke. METHODS AND RESULTS: SIRT6 endothelial expression was reduced following stroke. Endothelial-specific Sirt6 knockout (eSirt6-/-) mice, as well as animals in which Sirt6 overexpression was post-ischaemically induced, underwent transient middle cerebral artery occlusion (tMCAO). eSirt6-/- animals displayed increased infarct volumes, mortality, and neurological deficit after tMCAO, as compared to control littermates. Conversely, post-ischaemic Sirt6 overexpression decreased infarct size and neurological deficit. Analysis of ischaemic brain sections revealed increased BBB damage and endothelial expression of cleaved caspase-3 in eSIRT6-/- mice as compared to controls. In primary human brain microvascular endothelial cells (HBMVECs), hypoxia/reoxygenation (H/R) reduced SIRT6 expression and SIRT6 silencing impaired the barrier function (transendothelial resistance) similar to what was observed in mice exposed to I/R. Further, SIRT6-silenced HBMVECs exposed to H/R showed reduced viability, increased cleaved caspase-3 expression and reduced activation of the survival pathway Akt. In ischaemic stroke patients, SIRT6 expression was higher in those with short-term neurological improvement as assessed by NIHSS scale and correlated with stroke outcome. CONCLUSION: Endothelial SIRT6 exerts a protective role in ischaemic stroke by blunting I/R-mediated BBB damage and thus, it may represent an interesting novel therapeutic target to be explored in future clinical investigation