Arya Mani MD, FACC
Associate Professor of Medicine (Cardiology) and of Genetics; Director, Cardiovascular Genetics Program
Identification of cardiovascular disorders that have strong familial pattern
Despite our recent advances in Cardiovascular Medicine, the cardiovascular disease remains the leading cause of death in the world. With the break through brought about by The Human Genome project, we are now in a unique position to dissect the genetic causes of cardiovascular diseases to better understand the pathways that lead to disease in human and subsequently try to find therapies tailored to the specific genetic abnormality.
My interest is to identify cardiovascular disorders that have strong familial pattern. We identify kindreds with these disorders and collect DNA samples from the extended family members to proceed with the technique of positional cloning to identify the disease-causing genes.
Thus far, I, and my colleagues have mapped and identified several gene mutation for congenital heart diseases including patent ductus arteriosus and bicuspid aortic valve. Recently my group identified a gene mutation in LRP6, a co-receptor for Wnt, in a kindred with coronary artery disease and several metabolic phenotypes. We have shown that the mutation impairs a signaling pathway known as Wnt. We have created knockin and knockout mouse models of this gene and are conducting in vivo and in vitro functional studies using human cells, in vitro transfection models, human clinical studies as well as studies on lipid and glucose metabolism in mice in collaboration with Dr. Gerald Shulman, The GCRC, and The Mouse Metabolic Phenotyping Center. We are also investigating the genetic causes of premature coronary artery disease in South Asians. South Asians suffer largely from coronary artery disease in young ages and have high risk for developing diabetes, a constellation of phenotypes commonly referred to as metabolic syndrome. Our preliminary data suggests, that we have identified at least one gene locus for this disorder. We are currently collaborating with several medical centers across the world and in India to recruit new families and individuals with premature coronary artery disease with or without metabolic syndrome to refine the mapped region and identify the gene mutation.
We use several different techniques in our laboratory, which includes positional cloning using DNA microarrays, techniques used for protein chemistry, subcloning, tissue culture, confocal microscopy, FACS, real time PCR and animal model.
Extensive Research Description
My main mission in the Section of Cardiovascular Medicine has been Development of a Cardiovascular Research Program for identification of genetic causes of cardiovascular diseases and understanding of the disease mechanisms that lead to a variety of cardiovascular disorders. During first years of the faculty position my effort has been to establish an infrastructure that utilizes all resources at national and international level to identify extreme disease populations with major cardiovascular disorder and to recruit them for basic human Genetic studies. Through collaborative studies with physicians and scientist across the world we have been successful in identifying number of genetic mutations that are responsible for common congenital and familial cardiovascular diseases. Among disease genes that I and people working with me have identified are genetic mutations causing syndromic autosomal dominant patent ductus arteriosus and recessive causes of nonsyndromic patent ductus arteriosus. Since identification of a genetic cause of metabolic syndrome and CAD the major focus of my lab has been on study of the disease pathogenesis caused by this mutation. Detail of this follows. Coronary artery disease (CAD) is the most common cause of morbidity and mortality worldwide. A cluster of metabolic phenotypes known as metabolic syndrome has been established as a major risk factor for CAD. The mechanisms that link these phenotypes to one another and to CAD are not well understood. My research group has identified the disease causing gene in a large family with autosomal dominant early onset coronary artery disease (CAD), diabetes, hyperlipidemia, and hypertension. The mutation, substitutes cysteine for arginine (R611C) at a highly conserved residue of the second epidermal growth factor precursor domain in the LDL receptor like protein (LRP6), which encodes a co-receptor in the Wnt signaling pathway. To our knowledge this is the first gene that links CAD to hypertension, hyperlipidemia and diabetes. My goal is to dissect pathways that link this mutation to the individual phenotypes. A second mutation (R473Q) was identified in a large American kindred with early onset CAD and phenotypes that are consistent with the overall picture of the metabolic syndrome. In vitro studies have indicated that these mutations impair Wnt signaling. Genotype phenotype correlation showed that the mutations impact number of the metabolic phenotypes that are present in these kindreds. These findings have established a causal link between Wnt signaling impairment caused by LRP6 mutation and coronary artery/metabolic syndrome and raise the possibility of complex downstream effects of the mutation which warrants further investigation. Having unique access to the study kindred, we have had the opportunity to carry out clinical studies to investigate the mechanisms of disease. Oral glucose tolerance tests in nondiabetic R611C mutation carriers have shown that they are hyperinsulinemic, indicating that insulin resistance is likely the major cause of impaired glucose tolerance in the mutation carriers. The mechanisms of insulin resistance caused by LRP6 mutation are not known. A focus of my lab is to understand the pathophysiology of the metabolic syndrome caused by LRP6 mutation. We have created knockout, knockin, and LRP6flox/flox mice. Goal is to carry out metabolic studies to understand the mechanism of insulin resistance and hyperlipidemia. Defect in glycogen synthesis of the skeletal muscle is thought to be one of the major causes of insulin resistance. The rate limiting enzyme for glycogen synthesis, glycogen synthase (GS), is phosphorylated and inactivated by glycogen synthase kinase 3ß (GSK3ß). GSK3ß is negatively regulated by Wnt signaling activation. The expression and activity of GSK3ß is increased in lymphoblastoid cells of the mutation carriers. We hypothesize that LRP6 mutation directly affect glycogen synthesis by impairment of glycogen synthase activity. To examine this hypothesis and to identify the major site of insulin resistance, insulin-stimulated glucose disposal rate and sensitivity to insulin suppression of hepatic glucose output will be measured with infusion of [6, 6- 2H]-glucose isotope in both nondiabetic mutation carriers and non-carrier family members in the two kindreds. Glycogen synthesis and GS activity in the skeletal muscle biopsies of the mutation carriers and non-carriers will be compared. In addition, to explore the prevalence and spectrum of LRP6 mutations in patients with metabolic syndrome and CAD, a large cohort of patients with early onset CAD, diabetes and metabolic syndrome will be screened for non conservative mutation(s) in the coding region of LRP6. These studies hold great promise in providing important insight into the pathophysiology of metabolic syndrome and CAD and identifying novel biomarkers and therapeutic targets for these disorders. We have localized LRP6 to apical brush borders of the proximal renal tubules and are studying its interaction with NHE3, dopamine and adrenalin in vitro and vivo to study the effect of LRP6 on blood pressure. We intend to create an atherosclerosis model by crossing smooth muscle-specific LRP6 inactivated mice (sm22LRP6-) with LDLR-/- mice. We have also mapped two genes for early onset CAD in two independent large Iranian populations and plan to densely cover the linked interval with tag SNPs to identify linkage disequilibrium(s). Moreover, we have identified a disease causing gene for bicuspid aortic valve by positional cloning and have established association between aortic valve disease and number of non-synonymous SNPs within this gene. My goal is to combine genetic approaches with clinical and cell biological investigations in order to understand pathophysiology of these diseases with the goal of identification of novel risk factors and developing novel therapeutics.