The Role Of SIRT1 Protein In Anti-aging Effects Of Estrogen

The role of SIRT1 protein in anti-aging effects of estrogenAging is defined by the loss of functional reserve over time, leading to a decreased capacity to maintain homeostasis under stress and increased risk of morbidity and mortality. Aging is extremely heterogenerous between individuals and even between tissues within an organism, making it challenging to identify the molecular basis of ageing. Many studies revealed not only causes of aging, but also signaling mechanisms that both promote and protect against ageing. In all cases, the signaling pathways that influence life span are familiar mechanisms that regulate cellular metabolism, growth, proliferation, differentiation and survival. Aging is associated with a progressive imbalance between antioxidant defenses and intracellular concentrations of reactive oxygen species (ROS) as exemplified by increases in products of lipid peroxidation, protein oxidation, and DNA oxidation. Evidence shows that lifespan extension in laboratory yeast, flies and rats maintained on a caloric restriction (CR) diet. CR reduces metabolic rate and oxidative damage. In yeast, reduction in glucose levels in the media, mimicking CR, results in a substantial extension in lifespan, which is Sir2p- and NAD⁺-dependent, since mutants for Sir2p and nicotinate phosphoribosyl transferase , an enzyme required for NAD⁺ formation, failed to reproduce this effect. Sir2 belongs to the third class of histone deacetylases. Most interesting was the fact that overexpression of the gene encoding the Sir2 protein leads to a decrease in histone acetylation and an increase in life span in yeast, in the menatode Caenorhabditis elegans and in metazoans. Likewise, Sir2-activating compounds such as resveratrol promote longevity in yeast and other organisms ranging from the worm and drosophila to the mouse. On the other hand, both mutations of the Sir2 gene and pharmacological inhibition of Sir2 protein by nicotinamide induce an acceleration of aging in yeast. Since the Sir2 family of proteins are also able to exert their enzymatic activity not only on histones but also on numerous other proteins, such as the transcriptional regulators, they are involved in many cellular processes, ranging from gene silencing, DNA repair, progression of the cell cycle, to the control of aging. SIRT1, the mammalian Sir2 ortholog, controls lifespan extension under CR conditions. Females live longer than males in many mammalian species. Female Wistar rat median life span is 29 months, 14% more than in male Wistar rats. In Europe, the average life span is 73.7 years for males and 83.8 years for females. The fact that this differences occurs in animals as well as in humans, indicated that the difference cannot be attributed to sociological differences but rather to specific biological characteristics of both genders. Mitochondria from females produce approximately half the amount of hydrogen peroxide than males. Females behave as double transgenics overexpressing both superoxide dismutase and glutathione peroxidase. This is due to estrogen that acts by binding to the estrogen receptors and subsequently activating the mitogen activated protein kinase and nuclear factor kappa B signaling pathways. In addition, estrogen increases antiapoptotic proteins, which prevents activation of the permeability transition pore protection against estrogen-induced increase in mitochondrial Ca²⁺ sequestration. However, little is known about the relationship belong estrogen, SIRT1 and CR. To further understand the role of SIRT1 in anti-aging effects mediated by estrogen in cardiovascular system. In this project, we used primary vascular smooth muscle cells, ovary ectomized rats, CR rats and rat genome microarrays to investigate this mechanism.The main results of this project are as follows:1. Primary vascular smooth muscle cells were isolated from aortic arteries in female SD rats. Exposure cells to different concentration of 178-estradiol (10^-9-10^-5M), we found that 178-estradiol increased the SIRT1 protein expression, which was dosage-dependent. Antagonists of ERa and ERβblocked the increasing effects induced by 176-estradiol. We further used agonists of ERa and ERβto stimulated cultured cells. Results shown that agonist of ERa enhanced SIRT1 protein expression but agonist of ERβhad no this effect.2. We used ovary ectomized rats to study effects of 17B-estradiol on SIRT1. Three groups rats in this experiment including Sham group, ovary ectomized rats and ovary ectomized rats with exogenous 17β-estradiol treatment. All rats were kept for 4 months. Then we isolated brains, hearts, aortic arteries, livers, kidney and skeletal muscles, which were quickly put in liquid nitrogen. We detected SIRT1 in these tissues and found that protein expression of SIRT1 decreased in ovary ectomized rats in comparison with Sham group. Exogenous 17B-estradiol treatment reversed the decreased SIRT1 protein expression. 3. We further used 4 groups in this branch experiments. (1) Sham group; (2) Sham group+CR; (3) ovary ectomized rats; (4) ovary ectomized rats+CR. Totally insulin levels in serum decreased and SIRT1 protein in tissues increased in CR groups. No differences of serum estradiol were found between Sham group and Sham group+CR group. The serum estradiol and progesterone levels significantly increased in ovary ectomized rats+CR compared with ovary ectomized rats. The protein expression of SIRT1 and ERa significantly increased in CR groups.4. Exposure cultured VSMC to serum from Sham rats and ovary ectomized rats for 48h. We found that SIRT1 protein decreased in cells stimulated by serum from ovary ectomized rats in comparison with Sham rats. We further used rat genome microarrays to identify different gene expression in cells stimulated different serum from Sham rats and ovary ectomized rats for 48h. Our data indicated that 400 genes changed between two groups including metabolic enzymes, stress-related proteins, signal transduction proteins, calcium and potassium ion channels and apoptotic related genes. The cardioprotective effects of sodium tanshinoneâ…¡A sulfonate against ischemia-induced injury in rat heartsSodium tanshinoneâ…¡A sulfonate (STS) is a water soluble derivative of tanshinoneâ…¡A, a well-known Chinese medicine for treating cardiovascular disorders. Cardiomyocyte apoptosis plays a major role in the development of cardiovascular diseases. The present study was designed to investigate the effects of STS on cardiomyocyte apoptosis induced both by in vivo acute myocardial infarction (MI) in adult rats and by in vitro H₂O₂-treated neonatal rat ventricular myocytes. In MI rats, STS significantly reduced the infarct sizes, the blood lactate dehydrogenase (LDH) level and the number of apoptotic cardiomyocytes in the infarcted hearts. In the in vitro study, STS reversed the decreased effect of cell viability induced by H₂O₂. In addition, STS also markedly inhibited H₂O₂-induced cardiomyocyte apoptosis. C-Jun N-terminal kinases/stress-activated protein kinases (JNKs/SAPKs) and p38 MAPK are classic oxidative stress-activated protein kinases. Our further mechanistic study revealed that increased JNK phosphorylation stimulated by H₂O₂ was abolished by STS treatment. In conclusion, inhibition of JNK activation plays a significant role in cardioprotective effects of STS.