Perspectives of Targeting mTORC1–S6K1 in Cardiovascular Aging

The global population aging is accelerating and age-associated diseases including cardiovascular diseases become more challenging. The underlying mechanisms of aging and age-associated cardiovascular dysfunction remain elusive. There are substantial evidences demonstrating a pivotal role of the mammalian target of rapamycin complex 1 (mTORC1) and its down-stream effector S6K1 signaling in mammalian lifespan regulation and age-related diseases such as type II diabetes mellitus and cancer. The role of mTORC1–S6K1 in age-related cardiovascular diseases is, however, largely unknown and the available experimental results are controversial. This review article primarily summarizes the most recent advances toward understanding the role of mTORC1–S6K1 in cardiovascular aging and discusses the future perspectives of targeting mTORC1–S6K1 signaling as a healthy lifespan extension modality in anti-aging and anti-cardiovascular aging

Sirolimus increases tissue factor expression but not activity in cultured human vascular smooth muscle cells

BACKGROUND: Sirolimus-eluting stents (CYPHER stents) demonstrated remarkable efficacy in reducing restenosis rates in patients with coronary artery disease. There is a concern of sub-acute and late stent thrombosis. Tissue factor (TF) is critical in thrombosis. This study investigated the effect of sirolimus on TF expression and activity in cultured human vascular smooth muscle cells (SMCs). METHODS: SMCs were cultured from human saphenous veins and aortas. Quiescent cells were stimulated with sirolimus (0.1 – 20 ng/ml) over 24 hours. Cellular TF expression and activity released into culture medium were measured. The effect of sirolimus on activation of mammalian target of rapamycin (mTOR) was measured by phosphorylation of the substrate p70s6k at T389, and activation of RhoA was measured by pull-down assay. RESULTS: Sirolimus increased TF protein level in cultured human SMCs in a concentration and time-dependent manner (about 2-fold, p < 0.01) reaching maximal effect at 5 ng/ml. The stimulation of TF expression by sirolimus was associated with inhibition of basal activity of mTOR. No effects of sirolimus on RhoA or p38mapk activation that are positive regulators of TF in vascular wall cells were observed. The stimulation of TF expression by sirolimus (20 ng/ml) was prevented by the HMG-CoA reductase inhibitor fluvastatin (1 μmol/L). However, no increase in TF activity released from SMC into culture medium was observed after sirolimus treatment. CONCLUSION: Although sirolimus stimulates TF protein expression in human SMC associated with inhibition of mTOR, it does not enhance TF activity released from the cells, suggesting a relatively safe profile of CYPHER stents. The inhibition of TF expression by fluvastatin favors clinical use of statins in patients undergoing coronary stenting

O-linked β-N-acetylglucosamine during hyperglycemia exerts both anti-inflammatory and pro-oxidative properties in the endothelial system

Elevated cellular levels of protein O-linked β-N-acetylglucosamine (O-GlcNAc) through hexosamine biosynthesis pathway (HBP) are suggested to contribute to cardiovascular adverse effects under chronic hyperglycemic condition associated with oxidative stress and inflammation. Conversely, enhancing O-GlcNAc levels have also been demonstrated being protective against myocardial ischemia/reperfusion injury. We recently demonstrated that hyperglycemia increases oxidative stress and HBP flux in endothelial cells and enhances endothelial expression of vascular adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) in response to tumor necrosis factor-α (TNFα) through oxidative stress rather than HBP pathway. Here we present further complementary data showing that enhancing O-GlcNAc levels by glucosamine does not mimic hyperglycemia's effect on TNFα-induced endothelial VCAM-1 and ICAM-1 expression. Glucosamine however inhibits ICAM-1 (not VCAM-1) expression and induces superoxide generation in the cells. The results further suggest that increased O-GlcNAc levels do not mediate the enhancing effect of hyperglycemia on the endothelial inflammatory responses to TNFα. In contrast, it exerts certain anti-inflammatory effects accompanied by pro-oxidative properties. Further work should delineate the exact role of HPB pathway in different aspects of cardiovascular functions, especially those of diabetic cardiovascular complications

Arginase-ii deficiency extends lifespan in mice

The mitochondrial arginase type II (Arg-II) has been shown to interact with ribosomal protein S6 kinase 1 (S6K1) and mitochondrial p66Shc and to promote cell senescence, apoptosis and inflammation under pathological conditions. However, the impact of Arg-II on organismal lifespan is not known. In this study, we demonstrate a significant lifespan extension in mice with Arg-II gene deficiency (Arg-II-/-) as compared to wild type (WT) control animals. This effect is more pronounced in the females than in the males. The gender difference is associated with higher Arg-II expression levels in the females than in the males in skin and heart at both young and old age. Ablation of Arg-II gene significantly reduces the aging marker p16INK4a levels in these tissues of old female mice, whereas in the male mice this effect of Arg- II deficiency is weaker. In line with this observation, age-associated increases in S6K1 signaling and p66Shc levels in heart are significantly attenuated in the female Arg-II-/- mice. In the male mice, only p66Shc but not S6K1 signaling is reduced. In summary, our study demonstrates that Arg-II may play an important role in the acceleration of aging in mice. Genetic disruption of Arg-II in mouse extends lifespan predominantly in females, which relates to inhibition of S6K1, p66Shc, and p16INK4a. Thus, Arg-II may represent a promising target to decelerate aging process and extend lifespan as well as to treat age-related diseases

The sequence flanking the N-terminus of the CLV3 peptide is critical for its cleavage and activity in stem cell regulation in Arabidopsis

The "Shakespeare Authorship Question"—regarding the identity of the poet-playwright—has been debated for over 150 years. Now, with the growing list of signatories to the "Declaration of Reasonable Doubt," the creation of a Master's Degree program in Authorship Studies at Brunel University in London, the opening of the Shakespeare Authorship Research Studies Center at the Library of Concordia University in Portland, and the release of two competing high-profile books both entitled Shakespeare Beyond Doubt, academic libraries are being presented with a unique and timely opportunity to participate in and encourage this debate, which has long been considered a taboo subject in the academy.https://journal.lib.uoguelph.ca/index.php/perj/article/view/280

"En Face" detection of nitric oxide and superoxide in endothelial layer of intact arteries

Endothelium-derived nitric oxide (NO) produced from endothelial NO-synthase (eNOS) is one of the most important vasoprotective molecules in cardiovascular physiology. Dysfunctional eNOS such as uncoupling of eNOS leads to decrease in NO bioavailability and increase in superoxide anion (O₂.−) production, and in turn promotes cardiovascular diseases. Therefore, appropriate measurement of NO and O₂.− levels in the endothelial cells are pivotal for research on cardiovascular diseases and complications. Because of the extremely labile nature of NO and O₂.−, it is difficult to measure NO and O₂.− directly in a blood vessel. Numerous methods have been developed to measure NO and O₂.− production. It is, however, either insensitive, or non-specific, or technically demanding and requires special equipment. Here we describe an adaption of the fluorescence dye method for en face simultaneous detection and visualization of intracellular NO and O₂.− using the cell permeable diaminofluorescein-2 diacetate (DAF-2DA) and dihydroethidium (DHE), respectively, in intact aortas of an obesity mouse model induced by high-fat-diet feeding. We could demonstrate decreased intracellular NO and enhanced O₂.− levels in the freshly isolated intact aortas of obesity mouse as compared to the control lean mouse. We demonstrate that this method is an easy technique for direct detection and visualization of NO and O₂.− in the intact blood vessels and can be widely applied for investigation of endothelial (dys)function under (physio)pathological conditions

Arginase-II activates mTORC1 through myosin-1b in vascular cell senescence and apoptosis

Type-II L-arginine:ureahydrolase, arginase-II (Arg-II), is shown to activate mechanistic target of rapamycin complex 1 (mTORC1) pathway and contributes to cell senescence and apoptosis. In an attempt to elucidate the underlying mechanism, we identified myosin-1b (Myo1b) as a mediator. Overexpression of Arg-II induces re-distribution of lysosome and mTOR but not of tuberous sclerosis complex (TSC) from perinuclear area to cell periphery, dissociation of TSC from lysosome and activation of mTORC1- ribosomal protein S6 kinase 1 (S6K1) pathway. Silencing Myo1b prevents all these alterations induced by Arg-II. By overexpressing Myo1b or its mutant with point mutation in its pleckstrin homology (PH) domain we further demonstrate that this effect of Myo1b is dependent on its PH domain that is required for Myo1b-lysosome association. Notably, Arg-II promotes association of Myo1b with lysosomes. In addition, we show that in senescent vascular smooth muscle cells with elevated endogenous Arg-II, silencing Myo1b prevents Arg-II-mediated lysosomal positioning, dissociation of TSC from lysosome, mTORC1 activation and cell apoptosis. Taken together, our study demonstrates that Myo1b mediates the effect of Arg-II in activating mTORC1-S6K1 through promoting peripheral lysosomal positioning, that results in spatial separation and thus dissociation of TSC from lysosome, leading to hyperactive mTORC1-S6K1 signaling linking to cellular senescence/apoptosis

Arginase-II Deficiency Extends Lifespan in Mice

The mitochondrial arginase type II (Arg-II) has been shown to interact with ribosomal protein S6 kinase 1 (S6K1) and mitochondrial p66Shc and to promote cell senescence, apoptosis and inflammation under pathological conditions. However, the impact of Arg-II on organismal lifespan is not known. In this study, we demonstrate a significant lifespan extension in mice with Arg-II gene deficiency (Arg-II−/−) as compared to wild type (WT) control animals. This effect is more pronounced in the females than in the males. The gender difference is associated with higher Arg-II expression levels in the females than in the males in skin and heart at both young and old age. Ablation of Arg-II gene significantly reduces the aging marker p16INK4a levels in these tissues of old female mice, whereas in the male mice this effect of Arg-II deficiency is weaker. In line with this observation, age-associated increases in S6K1 signaling and p66Shc levels in heart are significantly attenuated in the female Arg-II−/− mice. In the male mice, only p66Shc but not S6K1 signaling is reduced. In summary, our study demonstrates that Arg-II may play an important role in the acceleration of aging in mice. Genetic disruption of Arg-II in mouse extends lifespan predominantly in females, which relates to inhibition of S6K1, p66Shc, and p16INK4a. Thus, Arg-II may represent a promising target to decelerate aging process and extend lifespan as well as to treat age-related diseases

P38 mitogen-activated protein kinase is involved in arginase-II-mediated eNOS-Uncoupling in Obesity

Background Endothelial nitric oxide synthase (eNOS)-uncoupling links obesity-associated insulin resistance and type-II diabetes to the increased incidence of cardiovascular disease. Studies have indicated that increased arginase is involved in eNOS-uncoupling through competing with the substrate L-arginine. Given that arginase-II (Arg-II) exerts some of its biological functions through crosstalk with signal transduction pathways, and that p38 mitogen-activated protein kinase (p38mapk) is involved in eNOS-uncoupling, we investigated here whether p38mapk is involved in Arg-II-mediated eNOS-uncoupling in a high fat diet (HFD)-induced obesity mouse model. Methods Obesity was induced in wild type (WT) and Arg-II-deficient (Arg-II-/-) mice on C57BL/6 J background by high-fat diet (HFD, 55% fat) for 14 weeks starting from age of 7 weeks. The entire aortas were isolated and subjected to 1) immunoblotting analysis of the protein level of eNOS, Arg-II and p38mapk activation; 2) arginase activity assay; 3) endothelium-dependent and independent vasomotor responses; 4) en face staining of superoxide anion and NO production with Dihydroethidium and 4,5-Diaminofluorescein Diacetate, respectively, to assess eNOS-uncoupling. To evaluate the role of p38mapk, isolated aortas were treated with p38mapk inhibitor SB203580 (10 μmol/L, 1 h) prior to the analysis. In addition, the role of p38mapk in Arg-II-induced eNOS-uncoupling was investigated in cultured human endothelial cells overexpressing Arg-II in the absence or presence of shRNA against p38mapk. Results HFD enhanced Arg-II expression/activity and p38mapk activity, which was associated with eNOS-uncoupling as revealed by decreased NO and enhanced L-NAME-inhibitable superoxide in aortas of WT obese mice. In accordance, WT obese mice revealed decreased endothelium-dependent relaxations to acetylcholine despite of higher eNOS protein level, whereas Arg-II-/- obese mice were protected from HFD-induced eNOS-uncoupling and endothelial dysfunction, which was associated with reduced p38mapk activation in aortas of the Arg-II-/- obese mice. Moreover, overexpression of Arg-II in human endothelial cells caused eNOS-uncoupling and augmented p38mapk activation. The Arg-II-induced eNOS-uncoupling was prevented by silencing p38mapk. Furthermore, pharmacological inhibition of p38mapk recouples eNOS in isolated aortas from WT obese mice. Conclusions Taking together, we demonstrate here for the first time that Arg-II causes eNOS-uncoupling through activation of p38 mapk in HFD-induced obesity