Remo D. Spescha

Sirt1 inhibition promotes in vivo arterial thrombosis and tissue factor expression in stimulated cells

AIMS The mammalian silent information regulator-two 1 (Sirt1) blunts the noxious effects of cardiovascular risk factors such as type 2 diabetes mellitus and obesity. Nevertheless, the role of Sirt1 in regulating the expression of tissue factor (TF), the key trigger of coagulation, and arterial thrombus formation remains unknown. METHODS AND RESULTS Human as well as mouse cell lines were used for in vitro experiments, and C57Bl/6 mice for in vivo procedures. Sirt1 inhibition by splitomicin or sirtinol enhanced cytokine-induced endothelial TF protein expression as well as surface activity, while TF pathway inhibitor protein expression did not change. Sirt1 inhibition further enhanced TF mRNA expression, TF promoter activity, and nuclear translocation as well as DNA binding of the p65 subunit of nuclear factor-kappa B (NFκB/p65). Sirt1 siRNA enhanced TF protein and mRNA expression, and this effect was reduced in NFκB/p65(-/-) mouse embryonic fibroblasts reconstituted with non-acetylatable Lys(310)-mutant NFκB/p65. Activation of the mitogen-activated protein kinases p38, c-Jun NH(2)-terminal kinase, and p44/42 (ERK) remained unaffected. In vivo, mice treated with the Sirt1 inhibitor splitomicin exhibited enhanced TF activity in the arterial vessel wall and accelerated carotid artery thrombus formation in a photochemical injury model. CONCLUSION We provide pharmacological and genetic evidence that Sirt1 inhibition enhances TF expression and activity by increasing NFκB/p65 activation in human endothelial cells. Furthermore, Sirt1 inhibition induces arterial thrombus formation in vivo. Hence, modulation of Sirt1 may offer novel therapeutic options for targeting thrombosis.

Deletion of the ageing gene p66Shc reduces early stroke size following ischaemia/reperfusion brain injury

AIMS Stroke is a leading cause of morbidity and mortality, and its incidence increases with age. Both in animals and in humans, oxidative stress appears to play an important role in ischaemic stroke, with or without reperfusion. The adaptor protein p66(Shc) is a key regulator of reactive oxygen species (ROS) production and a mediator of ischaemia/reperfusion damage in ex vivo hearts. Hence, we hypothesized that p66(Shc) may be involved in ischaemia/reperfusion brain damage. To this end, we investigated whether genetic deletion of p66(Shc) protects from ischaemia/reperfusion brain injury. METHODS AND RESULTS Transient middle cerebral artery occlusion (MCAO) was performed to induce ischaemia/reperfusion brain injury in wild-type (Wt) and p66(Shc) knockout mice (p66(Shc-/-)), followed by 24 h of reperfusion. Cerebral blood flow and blood pressure measurements revealed comparable haemodynamics in both experimental groups. Neuronal nuclear antigen immunohistochemical staining showed a significantly reduced stroke size in p66(Shc-/-) when compared with Wt mice (P < 0.05, n = 7-8). In line with this, p66(Shc-/-) mice exhibited a less impaired neurological function and a decreased production of free radicals locally and systemically (P < 0.05, n = 4-5). Following MCAO, protein levels of gp91phox nicotinamide adenine dinucleotide phosphate oxidase subunit were increased in brain homogenates of Wt (P < 0.05, n = 4), but not of p66(Shc-/-) mice. Further, reperfusion injury in Wt mice induced p66(Shc) protein in the basilar and middle cerebral artery, but not in brain tissue, suggesting a predominant involvement of vascular p66(Shc). CONCLUSION In the present study, we show that the deletion of the ageing gene p66(Shc) protects mice from ischaemia/reperfusion brain injury through a blunted production of free radicals. The ROS mediator p66(Shc) may represent a novel therapeutical target for the treatment of ischaemic stroke.

Expression of the aging gene p66Shc is increased in peripheral blood monocytes of patients with acute coronary syndrome but not with stable coronary artery disease.

OBJECTIVE The interplay between oxidative stress and inflammation is crucial in the pathogenesis of atherosclerosis. The adaptor protein p66Shc is implicated in atherogenesis and oxidative stress related responses in animal models of diseases. However, its role in humans remains to be defined. In this study, we hypothesized that expression of p66Shc increases in peripheral blood monocytes of patients affected by acute coronary syndromes (ACS). METHODS Male subjects aged 59±4 (mean±SD) years admitted for cardiac catheterization were subdivided in three groups: (a) no local stenosis for the control group, (b) at least one stenosis ≥75% in either left, circumflex or right coronary artery for the coronary artery disease (CAD) group or (c) ST-elevation/non-ST-elevation myocardial infarction for the ACS group. Monocytes were isolated from whole blood and p66Shc RNA levels were determined by quantitative real time PCR. RESULTS p66Shc RNA levels were increased in ACS patients as compared to CAD (p=0.007) and controls (p=0.0249). Furthermore, malondialdehyde (MDA) and C-reactive protein (CRP) were increased in plasma of ACS patients. Levels of MDA correlated positively to p66Shc (r=0.376, p=0.01). Our data demonstrate increased p66Shc levels in monocytes of ACS but not CAD patients. CONCLUSION This study suggests an involvement of p66Shc in the transition of a stable CAD to an ACS patient. p66Shc was associated with states of increased oxidative stress. Further work is needed to understand whether p66Shc may represent a possible pharmacological target or whether it represents an interesting novel biomarker.

Peripheral blood monocyte Sirt1 expression is reduced in patients with coronary artery disease.

Background Inflammation plays a key role in atherosclerosis. Sirt1 regulates transcription factors involved in inflammatory processes and blunts atherosclerosis in mice. However, its role in humans remains to be defined. This study was therefore designed to investigate the role of Sirt1 in the development of atherosclerosis. Methods and Results 48 male subjects admitted for cardiac catheterization were subdivided into healthy subjects, patients with stable coronary artery disease (CAD), and with acute coronary syndromes (ACS). Monocytes were isolated and Sirt1 mRNA levels were determined. Sirt1 gene expression was higher in healthy subjects as compared to patients with CAD or ACS (P<0.05), respectively. Interestingly, HDL levels correlated positively with Sirt1 expression. Thus, HDL from the three groups was isolated and incubated with THP-1 monocytes to determine the effects of HDL on Sirt1 protein in controlled experimental conditions. HDL from healthy subjects stimulated Sirt1 expression in THP-1 monocytes to a higher degree than HDL from CAD and ACS patients (P<0.05). Paraoxonase-1 (PON-1), a HDL-associated enzyme, showed a reduced activity in HDL isolated from CAD and ACS patients as compared to the controls (P<0.001). Conclusions Monocytic Sirt1 expression is reduced in patients with stable CAD and ACS. Experiments on THP-1 monocytes suggest that this effect is HDL-dependent and is mediated by a reduced activity of HDL-associated enzyme PON1.

Post-ischaemic silencing of p66Shc reduces ischaemia/reperfusion brain injury and its expression correlates to clinical outcome in stroke

AIM Constitutive genetic deletion of the adaptor protein p66(Shc) was shown to protect from ischaemia/reperfusion injury. Here, we aimed at understanding the molecular mechanisms underlying this effect in stroke and studied p66(Shc) gene regulation in human ischaemic stroke. METHODS AND RESULTS Ischaemia/reperfusion brain injury was induced by performing a transient middle cerebral artery occlusion surgery on wild-type mice. After the ischaemic episode and upon reperfusion, small interfering RNA targeting p66(Shc) was injected intravenously. We observed that post-ischaemic p66(Shc) knockdown preserved blood-brain barrier integrity that resulted in improved stroke outcome, as identified by smaller lesion volumes, decreased neurological deficits, and increased survival. Experiments on primary human brain microvascular endothelial cells demonstrated that silencing of the adaptor protein p66(Shc) preserves claudin-5 protein levels during hypoxia/reoxygenation by reducing nicotinamide adenine dinucleotide phosphate oxidase activity and reactive oxygen species production. Further, we found that in peripheral blood monocytes of acute ischaemic stroke patients p66(Shc) gene expression is transiently increased and that this increase correlates with short-term neurological outcome. CONCLUSION Post-ischaemic silencing of p66(Shc) upon reperfusion improves stroke outcome in mice while the expression of p66(Shc) gene correlates with short-term outcome in patients with ischaemic stroke.

Adaptor protein p66(Shc) mediates hypertension-associated, cyclic stretch-dependent, endothelial damage.

Increased cyclic stretch to the vessel wall, as observed in hypertension, leads to endothelial dysfunction through increased free radical production and reduced nitric oxide bioavailability. Genetic deletion of the adaptor protein p66Shc protects mice against age-related and hyperglycemia-induced endothelial dysfunction, as well as atherosclerosis and stroke. Furthermore, p66Shc mediates vascular dysfunction in hypertensive mice. However, the direct role of p66Shc in mediating mechanical force–induced free radical production is unknown; thus, we studied the effect of cyclic stretch on p66Shc activation in primary human aortic endothelial cells and aortic endothelial cells isolated from normotensive and hypertensive rats. Exposure of human aortic endothelial cells to cyclic stretch led to a stretch- and time-dependent p66Shc phosphorylation at Ser36 downstream of integrin &agr;5&bgr;1 and c-Jun N-terminal kinase. In parallel, nicotinamide adenine dinucleotide phosphate oxidase activation, as well as production of reactive oxygen species, increased, whereas nitric oxide bioavailability decreased. Silencing of p66Shc blunted stretch-increased superoxide anion production and nicotinamide adenine dinucleotide phosphate oxidase activation and restored nitric oxide bioavailability. In line with the above, activation of p66Shc increased in isolated aortic endothelial cells of spontaneously hypertensive rats compared with normotensive ones. Pathological stretch by activating integrin &agr;5&bgr;1 and c-Jun N-terminal kinase phosphorylates p66Shc at Ser36, augments reactive oxygen species production via nicotinamide adenine dinucleotide phosphate oxidase, and in turn reduces nitric oxide bioavailability. This novel molecular pathway may be relevant for endothelial dysfunction and vascular disease in hypertension.

Aging Induces Endothelial Dysfunction While Sparing Arterial Thrombosis

Objective—To assess the effects of aging on arterial thrombus formation by comparing 2-year-old with 11-week-old C57Bl6 mice. Methods and Results—Aging is a major risk factor for cardiovascular disease. In humans, assessing the direct effects of aging on vascular homeostasis is difficult because it occurs in the presence of other risk factors. Arterial thrombosis is the critical event in cardiovascular diseases; however, it is not known whether aging per se promotes its occurrence. Mice represent an interesting system to address this issue because they age without spontaneously developing other risk factors. Organ chamber experiments confirmed the advanced level of aging of old mice. As previously shown, old mice exhibited endothelial dysfunction; however, arterial thrombosis induced by photochemical injury was unchanged. Arterial tissue factor expression and activity; expressions of tissue factor pathway inhibitor, thrombomodulin, and plasminogen activator inhibitor 1; prothrombin time; partial thromboplastin time; thrombin-antithrombin complex; and platelet activation were comparable in both groups. Conclusion—Although these results cannot be directly extrapolated to humans, this study contributes novel important information on the direct effect of aging on arterial thrombosis and underscores the importance of controlling modifiable risk factors in aged individuals.

Reduced nitric oxide bioavailability mediates cerebroarterial dysfunction independent of cerebral amyloid angiopathy in a mouse model of Alzheimer’s disease

In Alzheimers disease (AD), cerebral arteries, in contrast to cerebral microvessels, show both cerebral amyloid angiopathy (CAA) -dependent and -independent vessel wall pathology. However, it remains unclear whether CAA-independent vessel wall pathology affects arterial function, thereby chronically reducing cerebral perfusion, and, if so, which mechanisms mediate this effect. To this end, we assessed the ex vivo vascular function of the basilar artery and a similar-sized peripheral artery (femoral artery) in the Swedish-Arctic (SweArc) transgenic AD mouse model at different disease stages. Furthermore, we used quantitative immunohistochemistry to analyze CAA, endothelial morphology, and molecular pathways pertinent to vascular relaxation. We found that endothelium-dependent, but not smooth muscle-dependent, vasorelaxation was significantly impaired in basilar and femoral arteries of 15-mo-old SweArc mice compared with that of age-matched wild-type and 6-mo-old SweArc mice. This impairment was accompanied by significantly reduced levels of cyclic GMP, indicating a reduced nitric oxide (NO) bioavailability. However, no age- and genotype-related differences in oxidative stress as measured by lipid peroxidation were observed. Although parenchymal capillaries, arterioles, and arteries showed abundant CAA in the 15-mo-old SweArc mice, no CAA or changes in endothelial morphology were detected histologically in the basilar and femoral artery. Thus our results suggest that, in this AD mouse model, dysfunction of large intracranial, extracerebral arteries important for brain perfusion is mediated by reduced NO bioavailability rather than by CAA. This finding supports the growing body of evidence highlighting the therapeutic importance of targeting the cerebrovasculature in AD. NEW & NOTEWORTHY We show that vasorelaxation of the basilar artery, a large intracranial, extracerebral artery important for cerebral perfusion, is impaired independent of cerebral amyloid angiopathy in a transgenic mouse model of Alzheimers disease. Interestingly, this dysfunction is specifically endothelium related and is mediated by impaired nitric oxide-cyclic GMP bioavailability.

Endothelial LOX-1 activation differentially regulates arterial thrombus formation depending on oxLDL levels: role of the Oct-1/SIRT1 and ERK1/2 pathways

Aims The lectin-like oxLDL receptor-1 (LOX-1) promotes endothelial uptake of oxidized low-density lipoprotein (oxLDL) and plays an important role in atherosclerosis and acute coronary syndromes (ACS). However, its role in arterial thrombus formation remains unknown. We investigated whether LOX-1 plays a role in arterial thrombus formation in vivo at different levels of oxLDL using endothelial-specific LOX-1 transgenic mice (LOX-1TG) and a photochemical injury thrombosis model of the carotid artery. Methods and results In mice fed a normal chow diet, time to arterial occlusion was unexpectedly prolonged in LOX-1TG as compared to WT. In line with this, tissue factor (TF) expression and activity in carotid arteries of LOX-1TG mice were reduced by half. This effect was mediated by activation of octamer transcription factor 1 (Oct-1) leading to upregulation of the mammalian deacetylase silent information regulator-two 1 (SIRT1) via binding to its promoter and subsequent inhibition of NF-&kgr;B signaling. In contrast, intravenous injection of oxLDL as well as high cholesterol diet for 6 weeks led to a switch from the Oct-1/SIRT1 signal transduction pathway to the ERK1/2 pathway and in turn to an enhanced thrombotic response with shortened occlusion time. Conclusions Thus, LOX-1 differentially regulates thrombus formation in vivo depending on the degree of activation by oxLDL. At low oxLDL levels LOX-1 activates the protective Oct-1/SIRT1 pathway, while at higher levels of the lipoprotein switches to the thrombogenic ERK1/2 pathway. These findings may be important for arterial thrombus formation in ACS and suggest that SIRT1 may represent a novel therapeutic target in this context.

Angiopoietin-like 4 and ischaemic stroke: a promising start

This editorial refers to ‘Protective effects of angiopoietin-like 4 on cerebrovascular and functional damages in ischaemic stroke,[†][1]’ by C. Bouleti et al. , on page 3657 Stroke is a global cause of morbidity and mortality, ranking fourth among all causes of death.1 Although considerable progress has been made in developing effective tools for acute stroke treatment, at present the only drug approved is recombinant tissue plasminogen activator (rt-PA); thus, new strategies for its effective prevention and treatment are essential. Following ischaemia/reperfusion, the blood–brain barrier (BBB) becomes more permeable and, in doing so, it promotes an increased infiltration of pro-inflammatory cells, resulting in the so-called ‘reperfusion injury’.2 Given its key role in mediating ischaemia/reperfusion-related neuronal damage, the BBB is a central target for the development of novel therapeutical strategies. Bouleti and colleagues have provided an elegant study reporting a new target improving stroke outcome in mice.3 Their study shows that angiopoietin-like 4 (ANGPTL4) modulates endothelial permeability following ischaemia/reperfusion and thus represents a potential new therapeutical target for the treatment of stroke. ANGPTL4, first discovered in 2000, was originally classified as an adipokine playing roles in lipid metabolism.4 Over the last decade, ANGPTL4 has been recognized to play additional roles in tumorigenesis, angiogenesis, and redox regulation.4 Bouleti and colleagues investigated the role of ANGPTL4 in stroke by using a transient focal cerebral ischaemia murine model, where the middle cerebral artery was occluded for 1 h, followed by 24 h of reperfusion. Indeed, they could show that recombinant human ANGPTL4 (rhANGPTL4) treatment prior to the ischaemic episode greatly reduced the stroke size and consequent neurological deficit. To provide additional supporting evidence for the protective effects of ANGPTL4, Bouleti et al . analysed stroke outcome in ANGPTL4 knockout mice undergoing ischaemic stroke. Moreover, to translate their findings into a more … [1]: #fn-2