Functional genomics of inborn errors and therapeutic interventions in high density lipoprotein (HDL) metabolism 

Project Sumary 

Despite considerable progress in prevention and therapy, coronary artery disease remains the most frequent cause of death. High density lipoproteins (HDL) are promising targets to further reduce morbidity and mortality because low HDL cholesterol plasma concentrations increase cardiovascular risk and because HDL exert many cardio- and vasoprotective functions. There is also great need in improving the diagnostic and prognostic value of the biomarker HDL cholesterol as HDL function is determined by the quality rather than by the quantity of HDL. Therefore, this HDLomics project will apply functional genomics approaches including genomics, proteomics and lipidomics as well as new clinical diagnostic tools to study the effects of differential regulation of HDL metabolism on pathophysiological events relevant for atherosclerosis:

1) Using genome wide linkage analysis in families with Mendelian inheritance of low HDL cholesterol we will search new major genes regulating HDL cholesterol.

2) Using high throughput sequencing and allele specific genotyping technology we will elucidate the impact of mutations in candidate genes for the variation of HDL cholesterol as well as other lipid traits and the occurrence of cardiovascular events.

3) Using knock-out and transgenic mouse models we will study the metabolic and vascular impact of mutated candidate genes on HDL metabolism.

4) We will employ proteomic and lipidomic tools for the characterisation of HDL and finding specific effects of mutations or interventions on the structure and function of HDL as well as on lipid metabolism and atherosclerosis.

5.) We will develop and evaluate new therapies including gene therapy protocols for the correction of inborn errors of HDL metabolism in humans.

The ultimate goals of HDLomics are hence the identification and validation of new targets, which can be used in differential diagnosis, prognosis, therapy, prevention, and therapy monitoring of low HDL cholesterol and atherosclerosis.

Problem

Fifty per cent of the population of Europe dies of coronary heart disease (CHD). Of these, current preventive and therapeutic measures, notably lowering of low density lipoprotein (LDL)  cholesterol and blood pressure can probably save 30%. For the remaining seventy percent there will be only hope if new targets for therapeutic intervention are identified. One of the most interesting targets is high density lipoprotein (HDL) cholesterol. The great clinical interest in HDL has been generated by numerous epidemiological studies that have found an increased risk of fatal and non-fatal CHD events, such as myocardial infarction, being associated with low HDL cholesterol. In addition, HDL particles as well as HDL-associated proteins and lipids exert a broad scope of anti-atherogenic effects. In agreement with these protective effects, the development of atherosclerotic lesions could be inhibited or even reverted in animal models by elevation of HDL cholesterol levels. With the exception of nicotinic acid, which increases HDL cholesterol by about 20% (but with significant side effects), the currently available lipid modifying drugs have little effect on HDL cholesterol levels. Hence, there exists a great interest in finding treatment modalities that increase HDL cholesterol concentration in plasma. Moreover, there is strong evidence that the atheroprotective effect of HDL is determined by the quality rather than by the quantity indicating that there is also great need in improving the diagnostic and prognostic value of the biomarker HDL cholesterol. Therefore and in agreement with the call LSH-2005-2.1.1.4, this HDLomics project will apply functional genomics approaches including genomics, proteomic and lipidomics as well as new clinical diagnostic tools to improve insight in HDL metabolism in disease states and pathophysiological events relevant to atherosclerosis. The ultimate goal of HDLomics is the identification of new targets to reduce the burden of CHD.

Aims

Þ Using genome wide linkage analysis approaches in families with Mendelian inheritance of low HDL cholesterol, we will try to identify new major genes regulating HDL cholesterol.

Þ    Using high throughput sequencing and allele specific genotyping technology, we will elucidate the impact of rare and frequent polymorphisms in candidate genes for the regulation of HDL cholesterol as well as other lipid and lipoprotein traits and the occurrence of cardiovascular events in families and the population.

Þ    Using a large well-characterized prospective cohort study with incident CHD events and non-invasive diagnostic imaging tools, we will investigate the impact of mutations in pivotal genes of HDL metabolism on atherogenesis as well as the effect of experimental HDL modulating therapies on the course of subclinical atherosclerosis

Þ    Using gene therapy in mouse models of HDL metabolism, we will study the impact of mutated candidate genes on HDL metabolism, lipid homeostasis and atherosclerosis

Þ    We will develop and evaluate new therapies including gene therapy protocols for the correction of inborn errors of HDL metabolism in humans

Þ    We will develop and use new proteomics and lipidomics tools for the characterization of HDL and finding associations between mutations, HDL function, and atherosclerosis in both humans and mouse models.

Þ    The ultimate goal of HDLomicsis  the identification and validation of new targets, which can be used in differential diagnosis, prognosis, therapy, prevention, and therapy monitoring of low HDL cholesterol and atherosclerosis.  

Expected results

High-throughput methods and tools for a better characterization of HDL metabolism and function are establishedNew proteomic, lipidomic and functional markers of HDL function and metabolism are identified Novel genes and mutations affecting HDL metbolism are discovered Novel clinical and animal models for a better characterization of HDL metabolism and function are establishedThe effects of HDL-related genes and mutations on atherosclerosis and coronary artery disease are determined Low HDL cholesterol and atherosclerosis in mice can be corrected by therapeutic interventions which are useful for further clinical  developmentThe results of the consortium are disseminated and exploited with regard to development of diagnostic tests or therapies  which ultimately help to reduce morbidity and mortality associated with cardiovascular diseases

Potential applications

We hope that the results of the consortium applied with regard to the development of both diagnostics and therapies which ultimately help to reduce morbidity and mortality associated with cardiovascular diseases. In more detail we expect the development of laboratory tests which can be used for the identification of patients with increased cardiovascular risk and for the monitoring of treatment effects in these patients. In addition newly identified genes important in HDL metabolism may turn out as important targets for the development of drugs which help to prevent, stop or even revert atherosclerosis. Finally, we expect to develop gene therapy protocols to treat inborn errors of HDL metabolism.

key words

animal models, atherosclerosis, cardiovascular disease, genetics, inborn errors of metabolism, high density lipoproteins, lipids, lipidomics, prevention, proteomics, functional genomics, systems biology

Coordinator

University of Zurich, Switzerland (Arnold von Eckardstein) 

Partners

Universiteit van Amsterdam - Academisch Ziekenhuis, Amsterdam, The Netherlands (John J.P. Kastelein, Jan-Albert Kuivenhoven)

Rigshospitalet, University of Copenhagen, Denmark (Anne Tybjaerg-Hansen, Ruth Frikke-Schmidt)

Linköping University, Sweden (Mats Lindahl)

National Centre of Scientific Research “Demokritos”, Athens, Greece (Angelika Chroni)

Foundation for Research and Technology – Hellas, Iraklion, Greece (Vassilis I. Zannis, Dmitri Kardasis)

Amsterdam Molecular Therapeutics Inc., Amsterdam, The Netherlands (Jaap Twisk)