Target Identification and Characterization in Transgenic Cardiovascular Disease Models of Atherosclerosis and Heart Failure

Autor: Abd Alla, Joshua
Přispěvatelé: Quitterer, Ursula, Hall, Jonathan
Jazyk: angličtina
Rok vydání: 2017
Předmět:
DOI: 10.3929/ethz-b-000235286
Popis: Myocardial infarction and ensuing heart failure are leading causes of death worldwide with limited treatment options. The major aim of my thesis was to identify new pathways involved in the pathogenesis of these diseases, which could be exploited as possible drug targets in the future. Atherosclerosis is the major cause for coronary artery disease and myocardial infarction. Current therapeutic strategies target the atherosclerosis-promoting lipid profile, mostly low- density lipoprotein (LDL) cholesterol. In search for possible new therapeutic approaches, I focused on inhibition of the angiotensin-converting enzyme. In addition to the established beneficial profile of angiotensin-converting enzyme (ACE) inhibitors in hypertensive patients, recent data indicate that this class of drugs could also interfere with pathomechanisms of atherosclerosis without targeting lipids, but underlying mechanisms are less clear. The first project of my thesis focused on the identification of atheroprotective mechanisms induced by treatment with the prototypic ACE inhibitor, captopril, in ApoE-deficient mice as an experimental model of atherosclerosis. Beneficial effects of ACE inhibition are mostly attributed to inhibition of angiotensin II-mediated AT1 receptor activation, which promotes the generation of reactive oxygen species (ROS) and thereby could aggravate atherosclerotic plaque formation. To differentiate between ROS-dependent and ROS-independent therapeutic effects of ACE inhibition, I performed a comparative study between the ACE inhibitor captopril and the antioxidant vitamin E. Treatment effects were monitored on a whole genome basis by microarray gene expression profiling and by quantitation of atherosclerotic lesion size in the aorta. My study showed that captopril treatment led to a stronger reduction of atherosclerotic plaque area in the aorta by 88.1 ± 7.5 % compared to vitamin E, which reduced the lesion area by 45.8 ± 11.5 %. While more than 30 % of vitamin E-regulated probes were concordantly regulated with captopril, only 14 % of captopril-regulated genes showed concordant regulation with vitamin E. Among concordantly regulated genes, gene ontology analysis indicated that the antioxidant capacity of captopril and vitamin E counteracted the proliferative and synthetic phenotype of vascular smooth muscle cells. In contrast, captopril, but not vitamin E, reduced the migration of pro-inflammatory and pro-atherogenic monocytes and T-lymphocytes into the aorta. In addition, only captopril was able to prevent the atherosclerosis-induced down-regulation of 30 perivascular nerve-specific genes, a treatment effect that was not recognized before with any other atherosclerotic treatment. Conclusions based on microarray gene expression profiling were confirmed by immunohistological analyses. Taken together my study identified several previously unrecognized mechanisms, which underlie the atheroprotective activity of captopril. The second part of my thesis focused on pathomechanisms of heart failure, which is another cardiovascular disease with a high mortality. In frame of our previous studies on pathomechanisms by whole genome microarray gene expression profiling we found a strong up-regulation of the major lipid-synthesizing enzyme, fatty acid synthase (FASN) in experimental models of heart failure induced by major cardiovascular risk factors, i.e. chronic pressure overload and atherosclerosis. This up-regulation of FASN was also a characteristic feature of cardiac biopsies of heart failure patients. Since the role of FASN in heart failure was not known, the aim of my thesis was to investigate the (patho-) physiological function of FASN up-regulation in the heart. To this end I generated transgenic mice with myocardium-specific expression of FASN under control of the alpha-MHC promoter. Phenotype analysis of the transgenic mice showed that the sole expression of FASN was sufficient to induce major symptoms of heart failure such as reduced cardiac function, cardiac hypertrophy, and cardiotoxic lipid deposition in cardiomyocytes causing cell death. As the underlying pathomechanism I identified that FASN induced heart failure-specific metabolic changes in vivo and in isolated cardiomyocytes, which could be attributed to activation of the adipogenic transcription factor Pparg (peroxisome proliferator-activated receptor-gamma). In search for a treatment approach, I analyzed the impact of inhibition of G-protein-coupled receptor kinase-2 (GRK2) because direct inhibition of FASN is not possible due to severe side effects. My data show that inhibition of GRK2 by transgenic expression of a peptide inhibitor of GRK2 (GRKInh) retards the heart failure phenotype induced by FASN. GRK2 inhibition counteracted the activation of Pparg by promoting MAPK-pathway-dependent phosphorylation of Pparg on serine 273. This mechanism was supported by the generation of transgenic mice with expression of the PPARG mutant PPARG-S273A, which does not undergo inactivation by the MAPK pathway. PPARG-S273A mice developed severe signs of heart failure, which were resistant to the beneficial effects of GRK2 inhibition. Thus, the second part of my thesis identified FASN as a previously unrecognized factor in heart failure pathogenesis, which can be targeted by inhibition of GRK2. Taken together my thesis investigated pathomechanisms of disease in transgenic disease models of atherosclerosis and heart failure. The first part of my study elucidated pathomechanisms of atherosclerosis, which can be targeted by the ACE inhibitor captopril. The second part of my thesis identified FASN as a new player in the lipotoxicity of end-stage heart failure, which can be counteracted by GRK2 inhibition.
Databáze: OpenAIRE
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