Cellular aging in cardiovascular diseases

As we progress to a society with an increasing average age, the problems that are associated with advanced age becoming more prominent. This is particularly visible by the increase onset of aging associated diseases, such as atherosclerosis, heart failure and diabetes mellitus type II. On a cellular level, the process of cellular aging is termed cellular senescence and the number of senescent cells in an organism increases in an age dependent manner. In our research we focused on the presence and development of cellular senescence in cardiovascular diseases. The role of the telomeres and the enzyme telomerase during aging, and in cardiovascular diseases is discussed. In a model for telomere shortening we describe that telomere length is associated with a striking decrease in voluntary exercise, but this was not directly associated with a cardiovascular phenotype. In the second part of this thesis we focus more on endothelial senescence and the pathways that are involved in the prevention of senescence. In endothelial cell culture models and in a model for diabetes type II we show that cellular senescence can be prevented by activating specific receptors that are present on the endothelial cells. Although these results have to be extended with studies in a human population, these results give new fundamental insights into the development of cellular senescence and open up new targets that eventually might help to fight the deleterious effects of cellular aging in cardiovascular diseases.

Telomere biology in healthy aging and disease

Aging is a biological process that affects most cells, organisms and species. Telomeres have been postulated as a universal biological clock that shortens in parallel with aging in cells. Telomeres are located at the end of the chromosomes and consist of an evolutionary conserved repetitive nucleotide sequence ranging in length from a few hundred base pairs in yeast till several kilo base pairs in vertebrates. Telomeres associate with shelterin proteins and form a complex protecting the chromosomal deoxyribonucleic acid (DNA) from recognition by the DNA damage-repair system. Due to the “end-replication problem” telomeres shorten with each mitotic cycle resulting in cumulative telomere attrition during aging. When telomeres reach a critical length the cell will not further undergo cell divisions and become senescent or otherwise dysfunctional. Telomere shortening has not only been linked to aging but also to several age associated diseases, including tumorigenesis, coronary artery disease, and heart failure. In the current review, we will discuss the role of telomere biology in relation to aging and aging associated diseases

Bradykinin Protects Against Oxidative Stress-Induced Endothelial Cell Senescence

Premature aging (senescence) of endothelial cells might play an important role in the development and progression of hypertension and atherosclerosis. We hypothesized that bradykinin, a hormone that mediates vasoprotective effects of angiotensin-converting enzyme inhibitors, protects endothelial cells from oxidative stress-induced senescence. Bradykinin treatment (0.001 to 1 nmol/L) dose-dependently decreased senescence induced by 25 mu mol/L of H2O2 in cultured bovine aortic endothelial cells, as witnessed by a complete inhibition of increased senescent cell numbers and a 34% reduction of the levels of the senescence-associated cell cycle protein p21. Because H2O2 induces senescence through superoxide-induced DNA damage, single-cell DNA damage was measured by comet assay. Bradykinin reduced DNA damage to control levels. The protective effect of bradykinin also resulted in a significant increase in the migration of H2O2-treated bovine aorta endothelial cells in an in vitro endothelial injury model, or "scratch" assay. The protective effect of bradykinin was abolished by the bradykinin B2 receptor antagonist HOE-140 and the NO production inhibitor N-omega-methyl-L-arginine acetate salt. Therefore, we conclude that bradykinin protects endothelial cells from superoxide-induced senescence through bradykinin B2 receptor-and NO-mediated inhibition of DNA damage. (Hypertension. 2009; 53[part 2]: 417-422.

Glucagon-Like Peptide 1 Prevents Reactive Oxygen Species-Induced Endothelial Cell Senescence Through the Activation of Protein Kinase A

Objective-Endothelial cell senescence is an important contributor to vascular aging and is increased under diabetic conditions. Here we investigated whether the antidiabetic hormone glucagon-like peptide 1 (GLP-1) could prevent oxidative stress-induced cellular senescence in endothelial cells. Methods and Results-In Zucker diabetic fatty rats, a significant 2-fold higher level of vascular senescence was observed compared with control lean rats. Dipeptidyl-peptidase 4 (DPP-4) inhibition significantly increased GLP-1 levels in these animals and reduced senescence almost to lean animal levels. In vitro studies with human umbilical vein endothelial cells showed that GLP-1 had a direct protective effect on oxidative stress (H(2)O(2))-induced senescence and was able to attenuate oxidative stress-induced DNA damage and cellular senescence. The GLP-1 analogue exendin-4 provided similar results, whereas exendin fragment 9-39, a GLP-1 receptor antagonist, abolished this effect. Intracellular signaling by the phosphoinositide 3-kinase (PI3K)/Akt survival pathway did not appear to be involved. Further analysis revealed that GLP-1 activates the cAMP response element-binding (CREB) transcription factor in a cAMP/protein kinase A (PKA)-dependent manner, and inhibition of the cAMP/PKA pathway abolished the GLP-1 protective effect. Expression analysis revealed that GLP-1 can induce the oxidative defense genes HO-1 and NQO1. Conclusion-Dipeptidyl-peptidase 4 inhibition protects against vascular senescence in a diabetic rat model. In vitro studies with human umbilical vein endothelial cells showed that reactive oxygen species-induced senescence was attenuated by GLP-1 in a receptor-dependent manner involving downstream PKA signaling and induction of antioxidant genes. (Arterioscler Thromb Vasc Biol. 2010; 30: 1407-1414.

Genetic variation and gender determine bradykinin type 1 receptor responses in human tissue: implications for the ACE-inhibitor-induced effects in patients with coronary artery disease

The efficacy of the ACE (angiotensin-converting enzyme) inhibitor perindopril in coronary artery disease [EUROPA (European trial on reduction of cardiac events with perindopril in stable coronary artery disease) study] is associated with the rs12050217 A/G single nucleotide polymorphism in the B-1 receptor (bradykinin type 1 receptor) gene. To investigate the underlying mechanism, we examined the effect of this polymorphism on B-1-receptor-mediated coronary artery dilation and peripheral blood mononuclear cell activation. Vasorelaxant responses of human coronary microarteries from subjects without coronary disease to des-Arg(9)-bradykinin and to bradykinin were studied in organ bath experiments. Des-Arg(9)-bradykinin responses were endothelium-dependent and exclusively mediated by B-1 receptors, whereas responses to bradykinin were induced through B-2 receptors (bradykinin type 2 receptors). The presence of the G allele reduced the response to 3x10(-8) mol/l des-Arg(9)-bradykinin by 29% [AA (n = 13) compared with AG/GG (n = 8); P < 0.03], and tended to lower concentration-related responses (P = 0.065) to this agonist, whereas the responses to bradykinin were unaffected by the rs12050217 genotype. In freshly obtained human mononuclear cells 1 mu mol/l des-Arg(9)-bradykinin increased expression of the pro-inflammatory factors CXCL5 (CXC chemokine ligand 5) and IL6 (interleukin-6). These responses were not affected by genotype and exclusively occurred in blood cells from women, correlating (in the case of CXCL5) with their plasma 17 beta-oestradiol levels (r(2) = 0.32, P = 0.02; n=17). IL-1 beta (interleukin-1 beta) increased CXCL5 and IL6 expression in both genders, and this response was not associated with 17 beta-oestradiol levels. The gender difference in responses to B-1 receptor stimulation in blood mononuclear cells implies possible gender differences in the response to ACE inhibitor therapy, which needs to be studied more comprehensively. The observed decrease in coronary vasodilator response might contribute to the impaired treatment response to perindopril of G allele carriers found in the EUROPA study

Telomere biology in cardiovascular disease:the TERC-/- mouse as a model for heart failure and ageing

Atherosclerosis and heart failure are major causes of morbidity and mortality in Western countries. Recent studies are suggesting involvement of telomere biology in the development and progression of age-associated conditions, including hypertension, atherosclerosis, and heart failure. Whether any of these reported associations are based on causal relationships remains to be elucidated. The construction of telomerase-deficient (telomerase RNA component, TERC-/-) mice might provide a potential instrumental model to study the involvement of telomere biology in cardiovascular disease. Here, we review the current available information from all studies performed in TERC-/- mice providing information on the cardiovascular phenotypic characteristics. Although this mouse model has proven its value in the understanding of the role of telomere biology in cancer, stem cell, and basic telomere research, only few studies were specifically designed to answer cardiovascular-related questions. The TERC-/- mice provide exciting opportunities to expand our knowledge of telomere biology in cardiovascular disease and the potential identification of novel targets of treatment