Association of the sirtuin and mitochondrial uncoupling protein genes with carotid intima-media thickness

The role of sirtuins and uncoupling proteins on vascular aging: The Northern Manhattan Study experience

Aging affects all organs. Arteries, in particular, are among the most affected. Vascular aging (VA) is defined as age-associated changes in function and structure of vessels. Classical VA phenotypes are carotid intima-media thickness (IMT), carotid plaque (CP), and arterial stiffness (STIFF). Individuals have different predisposition to these VA phenotypes and their associated risk of cardiovascular events. Some develop an early vascular aging (EVA), and others are protected and identified as having supernormal vascular aging (SUPERNOVA). The mechanisms leading to these phenotypes are not well understood. In the Northern Manhattan Study (NOMAS), we found genetic variants in the 7 Sirtuins (SIRT) and 5 Uncoupling Proteins (UCP) to be differently associated with risk to developing VA phenotypes. In this article, we review the results of genetic-epidemiology studies to better understand which of the single nucleotide polymorphisms (SNPs) in SIRT and UCP are responsible for both EVA and SUPERNOVA.

Sirtuins and their Biological Relevance in Aging and Age-Related Diseases

Sirtuins, initially described as histone deacetylases and gene silencers in yeast, are now known to have many more functions and to be much more abundant in living organisms. The increasing evidence of sirtuins in the field of ageing and age-related diseases indicates that they may provide novel targets for treating diseases associated with aging and perhaps extend human lifespan. Here, we summarize some of the recent discoveries in sirtuin biology that clearly implicate the functions of sirtuins in the regulation of aging and age-related diseases. Furthermore, human sirtuins are considered promising therapeutic targets for anti-aging and ageing-related diseases and have attracted interest in scientific communities to develop small molecule activators or drugs to ameliorate a wide range of ageing disorders. In this review, we also summarize the discovery and development status of sirtuin-targeted drug and further discuss the potential medical strategies of sirtuins in delaying aging and treating age-related diseases.

Carotid plaque-thickness and common carotid IMT show additive value in cardiovascular risk prediction and reclassification

Background and aims

Carotid plaque size and the mean common carotid intima-media thickness measured in plaque-free areas (PF CC-IMT_mean) have been identified as predictors of vascular events (VEs), but their complementarity in risk prediction and stratification is still unresolved. The aim of this study was to evaluate the independence of carotid plaque thickness and PF CC-IMT_mean in cardiovascular risk prediction and risk stratification.

Methods

The IMPROVE-study is a European cohort (n = 3703), where the thickness of the largest plaque detected in the whole carotid tree was indexed as cIMT_max. PF CC-IMT_mean was also assessed. Hazard Ratios (HR) comparing the top quartiles of cIMT_max and PF CC-IMT_meanversus their respective 1–3 quartiles were calculated using Cox regression.

Results

After a 36.2-month follow-up, there were 215 VEs (125 coronary, 73 cerebral and 17 peripheral). Both cIMT_max and PF CC-IMT_mean were mutually independent predictors of combined-VEs, after adjustment for center, age, sex, risk factors and pharmacological treatment [HR (95% CI) = 1.98 (1.47, 2.67) and 1.68 (1.23, 2.29), respectively]. Both variables were independent predictors of cerebrovascular events (ischemic stroke, transient ischemic attack), while only cIMT_max was an independent predictor of coronary events (myocardial infarction, sudden cardiac death, angina pectoris, angioplasty, coronary bypass grafting). In reclassification analyses, PF CC-IMT_mean significantly adds to a model including both Framingham Risk Factors and cIMT_max (Integrated Discrimination Improvement; IDI = 0.009; p = 0.0001) and vice-versa (IDI = 0.02; p < 0.0001).

Conclusions

cIMT_max and PF CC-IMT_mean are independent predictors of VEs, and as such, they should be used as additive rather than alternative variables in models for cardiovascular risk prediction and reclassification.

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Taken by themselves, both cIMT_max and PF CC-IMT_mean are associated with the incidence of cardiovascular disease.

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Complementarity of cIMT_max and PF CC-IMT_mean in cardiovascular risk prediction/reclassification is still under debate.

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In our study, both cIMT_max and PF CC-IMT_mean were mutually independent predictors of cerebral and coronary vascular events.

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In reclassification analyses, PF CC-IMT_mean adds to a model including Framingham Risk Factors and cIMT_max and vice-versa.

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cIMT_max and PF CC-IMT_mean should be used as additive rather than alternative variables in risk prediction/reclassification.

Sirtuins and Cancer: Role in the Epithelial-Mesenchymal Transition

The human sirtuins (SIRT1–SIRT7) enzymes are a highly conserved family of NAD⁺-dependent histone deacetylases, which play a critical role in the regulation of a large number of metabolic pathways involved in stress response and aging. Cancer is an age-associated disease, and sirtuins may have a considerable impact on a plethora of processes that regulate tumorigenesis. In particular, growing evidence suggests that sirtuins may modulate epithelial plasticity by inducing transcriptional reprogramming leading to epithelial-mesenchymal transition (EMT), invasion, and metastases. Though commonly regarded as EMT inducers, sirtuins may also suppress this process, and their functional properties seem to largely depend on the cellular context, stage of cancer development, tissue of origin, and microenvironment architecture. Here, we review the role of sirtuins in cancer biology with particular emphasis on their role in EMT.

In Search of New Therapeutic Targets in Obesity Treatment: Sirtuins

Most of the available non-invasive medical therapies for obesity are non-efficient in a long-term evaluation; therefore there is a constant need for new methods of treatment. Research on calorie restriction has led to the discovery of sirtuins (silent information regulators, SIRTs), enzymes regulating different cellular pathways that may constitute potential targets in the treatment of obesity. This review paper presents the role of SIRTs in the regulation of glucose and lipid metabolism as well as in the differentiation of adipocytes. How disturbances of SIRTs’ expression and activity may lead to the development of obesity and related complications is discussed. A special emphasis is placed on polymorphisms in genes encoding SIRTs and their possible association with susceptibility to obesity and metabolic complications, as well as on data regarding altered expression of SIRTs in human obesity. Finally, the therapeutic potential of SIRTs-targeted strategies in the treatment of obesity and related disorders is discussed.

Sirtuin/uncoupling protein gene variants and carotid plaque area and morphology

BACKGROUND

Sirtuins and uncoupling proteins have been implicated in cardiovascular diseases by controlling oxidative stress.

AIMS

We sought to investigate the association of sirtuins and uncoupling proteins single nucleotide polymorphisms with total carotid plaque area and morphology measured by ultrasonographic gray scale median.

METHODS

We analyzed 1356 stroke-free subjects (60% women, mean age = 68 ± 9 years) from the Northern Manhattan Study. Multiple linear regression models were used to evaluate the association of 85 single nucleotide polymorphisms in 11 sirtuins/uncoupling protein genes with total plaque area and gray scale median after controlling for demographics, vascular risk factors (RFs), and population stratification. We investigated effect modifications of these relationship by gender and RFs and performed stratified analysis if the interaction effect had P < 0·005.

RESULTS

Among individuals with present plaque (55%), the mean total plaque area was 20·3 ± 20·8 mm(2) and gray scale median 90 ± 29. After adjustment, SIRT6 rs107251 was significantly associated with total plaque area (β = 0·30 per copy of T allele increase, Bonferroni-corrected P = 0·005). T allele carriers of rs1430583 in UCP1 showed a decreased gray scale median in women but not in men. The minor allele carriers of rs4980329 and rs12363280 in SIRT3 had higher gray scale median in men but not in women. Variants in UCP3 gene were significantly associated with higher mean gray scale median in individuals with dyslipidemia.

CONCLUSION

Our findings suggest that polymorphisms in SIRT6/UCP1 genes may be important for increased carotid plaque burden and echodensity, but translation of these findings to an individual risk of cerebrovascular events needs further investigation. Significant associations of rs1430583 in women, rs12363280 in men, and rs1685354 in those with dyslipidemia also deserve further investigations.

The relationship between carotid intima-media thickness and carotid plaque in the Northern Manhattan Study

OBJECTIVE

Carotid intima-media thickness (cIMT) and carotid plaque (CP) are proposed biomarkers of subclinical atherosclerosis associated with stroke risk. Whether cIMT and CP are distinct phenotypes or single traits at different stages of atherosclerotic development is unclear. We explored the relationship between these markers in the population-based Northern Manhattan Study.

METHODS

We used high-resolution ultrasound and validated imaging protocols to study the cross-sectional (N = 1788 stroke-free participants) and prospective relationship (N = 768 with follow-up scan; mean years between examinations = 3.5) between CP and cIMT measured in plaque-free areas.

RESULTS

The mean age was 66 ± 9 (40% male, 19% black, 17% white, 61% Hispanic). The mean baseline cIMT was 0.92 ± 0.09 mm, 0.94 ± 0.09 mm among the 58% with prevalent plaque, 0.90 ± 0.08 mm among the 42% without prevalent plaque (p < 0.0001). Each 0.1 mm increase in baseline cIMT was associated with a 1.72-fold increased odds of plaque presence (95%CI = 1.50-1.97), increased plaque thickness (effect on the median = 0.46 mm, p < 0.0001), and increased plaque area (effect on the median = 3.45 mm(2), p < 0.0001), adjusting for demographics and vascular risk factors. Elevated baseline cIMT was associated with an increased risk of new plaque in any location at follow-up, but after adjusting for demographics and vascular risk factors this association was no longer present. No association was observed in carotid segment-specific analyses.

CONCLUSION

Increased cIMT was associated with baseline prevalent plaque but did not predict incident plaque independent of other vascular risk factors. This finding suggests that increased cIMT is not an independent predictor of plaque development although these atherosclerotic phenotypes often coexist and share some common vascular determinants.

Genetics and genomics of ischemic tolerance: focus on cardiac and cerebral ischemic preconditioning

A subthreshold ischemic insult applied to an organ such as the heart and/or brain may help to reduce damage caused by subsequent ischemic episodes. This phenomenon is known as ischemic tolerance mediated by ischemic preconditioning (IPC) and represents the most powerful endogenous mechanism against ischemic injury. Various molecular pathways have been implicated in IPC, and several compounds have been proposed as activators or mediators of IPC. Recently, it has been established that the protective phenotype in response to ischemia depends on a coordinated response at the genomic, molecular, cellular and tissue levels by introducing the concept of 'genomic reprogramming' following IPC. In this article, we sought to review the genetic expression profiles found in cardiac and cerebral IPC studies, describe the differences between young and aged organs in IPC-mediated protection, and discuss the potential therapeutic application of IPC and pharmacological preconditioning based on the genomic response.

Seven sirtuins for seven deadly diseases of aging

Sirtuins are a class of NAD(+)-dependent deacetylases having beneficial health effects. This extensive review describes the numerous intracellular actions of the seven mammalian sirtuins, their protein targets, intracellular localization, the pathways they modulate, and their role in common diseases of aging. Selective pharmacological targeting of sirtuins is of current interest in helping to alleviate global disease burden. Since all sirtuins are activated by NAD(+), strategies that boost NAD(+) in cells are of interest. While most is known about SIRT1, the functions of the six other sirtuins are now emerging. Best known is the involvement of sirtuins in helping cells adapt energy output to match energy requirements. SIRT1 and some of the other sirtuins enhance fat metabolism and modulate mitochondrial respiration to optimize energy harvesting. The AMP kinase/SIRT1-PGC-1α-PPAR axis and mitochondrial sirtuins appear pivotal to maintaining mitochondrial function. Downregulation with aging explains much of the pathophysiology that accumulates with aging. Posttranslational modifications of sirtuins and their substrates affect specificity. Although SIRT1 activation seems not to affect life span, activation of some of the other sirtuins might. Since sirtuins are crucial to pathways that counter the decline in health that accompanies aging, pharmacological agents that boost sirtuin activity have clinical potential in treatment of diabetes, cardiovascular disease, dementia, osteoporosis, arthritis, and other conditions. In cancer, however, SIRT1 inhibitors could have therapeutic value. Nutraceuticals such as resveratrol have a multiplicity of actions besides sirtuin activation. Their net health benefit and relative safety may have originated from the ability of animals to survive environmental changes by utilizing these stress resistance chemicals in the diet during evolution. Each sirtuin forms a key hub to the intracellular pathways affected.