My laboratory is engaged in system biology approaches to investigate cardiovascular diseases. We leverage modern techniques of functional genomics, epigenetics, transcriptomics, proteomics, gene editing and model-driven experimentation to understand the underlying causes of atherosclerosis and metabolic syndrome and discover therapeutic targets. Our work involves population and family-based genetic studies, high throughput sequencing to identify disease genes, with a focus on coronary artery disease (CAD) and metabolic syndrome (MetS). We then proceed to characterize the identified genes in vivo and in vitro. By recruiting more than thousand kindreds with early onset CAD and multiple metabolic risk factors for genetics and metabolic studies we have been able to map, identify and characterize a dozen of human disease genes for CAD and MetS, which have been reported in leading journals such as Nat Genet, Science, NEJM, Cell Metab, JCI, PNAS, AJHG, etc. We were the first group to show the role of Wnt signaling in atherosclerosis and the first to establish a genetic link between exocrine and endocrine pancreas in pathogenesis of diabetes. Most recently, we have established techniques of high throughput gene editing and multiple parallel reporter assays in my laboratory and have successfully mapped the regulatory landscape of a number of GWAS disease genes. Subsequent molecular and physiological studies in human mutation carriers and animal models have allowed us to unravel novel functions of the identified genes, to delineate their cognate pathways and to discover new targets for pharmaceutical intervention. These groundbreaking achievements have made us one of the leading laboratories in investigation of metabolic syndrome. We have developed expertise in in vivo investigation of lipid and glucose metabolism, insulin secretion and sensitivity, and vascular biology and in human physiological studies, leading to discovery of attractive drug targets that have been either patented or being investigated for their utility in treatment of fatty liver disease and diabetes in 2 clinical trials in the outlier populations of Fars/Iran. One of our groundbreaking discoveries was the identification of founder mutations in the DYRK1B gene, underlying atherosclerosis, metabolic syndrome, and fatty liver disease. The encoded protein is upregulated in human steatosis (NASH). Our studies in mice have shown that this upregulation results in mTOR activation, lipogenesis and development of NASH and dyslipidemia. Strikingly, knockdown of Dyrk1b is protective against these traits, motivating further investigations to characterize the protein as an attractive therapeutic target. One of our recent groundbreaking discoveries was the identification of novel loss of function mutations in a gene encoding the pancreatic exocrine elastase Cela2a in patients with diabetes, CAD and MetS traits, including obesity, hypertension, hypertriglyceridemia, NAFLD (OMIM: AOMS4). The characterization of this protein in vivo has shown that it widely expressed in different tissues and circulates in the blood, its levels rise after food intake in humans and stimulates insulin secretion and sensitivity and inhibits platelet aggregation. We are now fully characterizing this protein and evaluating its utility as a drug target for diabetes, dyslipidemia, and fatty liver disease. These discoveries are the results of lengthy and high risk studies, which would have not been accomplished without the R35 grant mechanism and the hard work and devotion of students, residents , fellows and visiting scholars in my laboratory, many of whom have gone to establish their own labs, or join the industry. Alone 7 former lab members have joined academia over the past 5 years and 11 a pursuing a career in research as trainees.
1. (AHA Young Investigator award Finalist) Fatemehsadat Esteghamat, James Samuel Broughton, Emily Smith, Rebecca Cardone, Tarun Tyagi, Mateus Guerra, András Szabó, , Nelson Ugwu, Mitra Mani, Bani Azari, Gerald Kayingo, Sunny Chung, Mohsen Fathzadeh, Ephraim Weiss, Jeffrey Bender, Shrikant Mane5, Richard Lifton, Adebowale Adeniran, Michael Nathanson, Fred Gorelick, John Hwa, Miklós Sahin-Tóth, Renata Belfort-DeAguiar, Richard Kibbey, Arya Mani,. CELA2A mutations predispose to early-onset atherosclerosis and metabolic syndrome and affect plasma insulin and platelet activation. Nat Genet, 2019, 1233-1243. PMID:31358993
2. (Recommended by F1000Prime/AHA Young Investigator Award Finalist) Keramati AR, Fathzadeh M, Singh R, Lin A, Faramarzi S, Choi M, Mane S, Kasae M, Babaee Bigi, Malekzadeh R, Hosseinian Babaie M, Lifton RP, and Mani A. A form of the metabolic syndrome associated with mutations in DYRK1B. NEJM, 2014 ;370(20):1909-19, PMID: 24827035
3. (Editors’ choice) Mani A (co-corresponding author), Radhakrishnan J, Wang H, Mani A, Mani MA, Nelson-Williams C, Carew KS, Mane S, Najmabadi H, Wu D, Lifton RP. LRP6 Mutation in a Family with Early Coronary Disease and Metabolic Risk Factors. Science 2007;315:1278-82. PMC2945222
1. Hyperlipidemia and fatty liver disease
Wnt coreceptor LDL receptor-related protein 6 (LRP6) gene was the very first monogenic cause of coronary artery disease (OMIM: ADCAD2) and MetS (Science 2007), which we discovered in our lab. Genotype phenotype correlation showed that the mutations impact a number of metabolic phenotypes, including hypercholesterolemia and nonalcoholic fatty liver disease (NAFLD). This discovery caused a paradigm shift by establishing a causal link between impaired LRP6 /Wnt signaling and CAD and its associated metabolic traits. Having unique access to the study populations, we investigated the role of LRP6 in regulation of cholesterol uptake in primary human cells and tissues and demonstrated its role in clathrin-mediated LDLR endocytosis. Mice generated in our lab with the human LRP6 mutation (LRP6R611C) exhibited elevated plasma LDL and TG levels and developed steatohepatitis and steatofibrosis. The molecular dissection of the disease pathways showed that the LRP6 mutation triggers hepatic de-novo lipogenesis (DNL) via TCF7L2-dependent activation of mTOR nutrient sensing pathway. These traits were rescued by in vivo administration of rmWnt3a, identifying Wnt pathways as an attractive therapeutic target against NASH. The investigation of a large, inbred population with extremely high prevalence obesity, MetS and NAFLD led to the discovery of founder mutations in DYRK1B gene as the second monogenic cause of MetS and NAFLD. Further studies revealed that DYRK1B protein levels are increased in the liver of most patients with NASH and in mice fed with a high calorie diet. Strikingly, the induction of hepatic Dyrk1b in mice on chow diet enhanced de novo lipogenesis (DNL), fatty-acid uptake, and TAG secretion and caused NASH and hyperlipidemia by activating mTORC2 pathway. Conversely, knockdown of Dyrk1b was protective against these traits. These findings identify DYRK1B as an attractive target for NAFLD, motivating further investigations into the utility of Dyrk1a/b proteins as attractive drug targets for NAFLD.
2. Atherosclerosis Our lab was the first to discover the role of altered Wnt signaling in atherosclerosis. In collaboration with a team of cardiothoracic surgeons at Yale we showed the dramatic increase in expression of Wnt coreceptor LRP6 in human atherosclerotic coronary arteries as a response to injury. By dissecting the molecular pathways in human VSMCs, we were able to show that LRP6 forms a complex with PDGFR-β, enhances its lysosomal degradation, increases VSMC differentiation and prevents excessive proliferation. These functions were severely impaired by LRP6 mutations resulting in the activation of noncanonical Wnt signaling. Our findings implicated LRP6 as a critical modulator of PDGF-dependent regulation of cell cycle in VSMC and showed that loss of this function contributes to development of early onset atherosclerosis. One of the most exciting developments in our lab was the generation of a novel coronary artery disease mouse model. Mice carrying the human LRP6R611C mutation displayed dramatic obstructive CAD on high fat diet and exhibited an accelerated atherosclerotic burden on LDLR knockout background. The dissection of disease pathways revealed that impaired LRP6 activity triggers non-canonical Wnt signaling, culminating in diminished TCF7L2 and increased activation of PDGF signaling. Strikingly, Wnt3a administration to LRP6R611C mice improved the activity of LRP6 and its downstream signaling pathway, led to TCF7L2-dependent VSMC differentiation, and rescued post carotid injury neointima formation. Accordingly, we showed in a separate study that mice deficient for TCF7L2 develop wire injury-induced carotid intimal hyperplasia, while the overexpression of TCF7L2 is protective against it and can rescue post-injury intimal hyperplasia of LRP6R611C mice. These findings underscored the critical role of intact Wnt signaling in maintaining the normal structure of the vessel wall, established a causal link between impaired LRP6/TCF7L2 activities and arterial disease and identified Wnt/TCF7L2 as an attractive target for the treatment of CAD. Motivated by these remarkable findings, we are currently working with the industry to study the effect of Wnt-inhibitors antagonists to treat intimal hyperplasia.
c. Srivastava R, Rolyan H, Xie Y, Li N, Bhat N, Hong L, Esteghamat F, Adeniran A, Geirsson A, Zhang J, Ge G, Nobrega M, Martin KA, Mani A. TCF7L (Transcription Factor 7-Like ) Regulation of GATA6 (GATA-Binding Protein 6)-Dependent and -Independent Vascular Smooth Muscle Cell Plasticity and Intimal Hyperplasia Arterioscler Thromb Vasc Biol. 2019 Feb;39(2):250-262 PMID:30567484
3. Molecular Genetics of Diabetes and Insulin Resistance The molecular mechanisms underlying insulin resistance are poorly understood. Our studies using different genetic mouse models have revealed that altered function of skeletal muscle, endothelial cells, and hepatocytes can all impair glucose tolerance. Our human genetic studies had established a causal link between missense mutations in LRP6 and DYRK1B genes and type 2 diabetes. LRP6 mutation carriers exhibited hyperinsulinemia and reduced insulin sensitivity compared to noncarrier relatives in response to oral glucose ingestion, which correlated with a significant decline in the skeletal muscle expression of the insulin receptor and canonical insulin signaling activity. Further investigations showed that the LRP6(R611C) mutation diminishes TCF7L2-dependent transcription of the IR while it triggers mTORC1-dependent IRS1/2-phosphorylation and inactivation. We have recently shown Dyrk1b gain of function causes insulin resistance by increasing plasma membrane sn-1,2-diacylglyerol levels and PKCε-mediated IRKT1150 phosphorylation in the liver, which results in impaired activation of hepatic insulin signaling and reduced hepatic glycogen storage. In a separate study we showed that the loss of Apelin in the endothelial cell increases fatty acid uptake and causes insulin resistance.
4. The molecular genetics of patent ductus arteriosus My laboratory has been interested in the pathogenesis of patent ductus arteriosus as a gateway to the discovery of pathways that maintain patency of arterial lumens. We have mapped and identified disease genes for syndromic and nonsyndromic, autosomal dominant and recessive patent ductus arteriosus. The in vivo and in vitro characterization of disease genes has led to discovery of genetic networks that alter neural crest cell migration and differentiation. Specifically, we discovered that increased Wnt activation causes the patency of the ductus by impairing smooth muscle cell proliferation, a process that is sharply opposite to the pathogenesis of CAD in mice with defective Wnt coreceptor LRP6. This finding supports our earlier discoveries, implicating Wnt signaling in vascular remodeling.
5. Genetics of Atrial fibrillation (AF) and arrhythmias
As the director of the Cardiovascular Genetics program, I have access to a large number of outlier kindreds with rare familial cardiovascular disorders. This has provided us with a unique opportunity to discover novel genes for diseases of the heart rhythm. The strong relationship between cardiac arrhythmias and atherosclerosis and metabolic syndrome in particular drives our interest. Our investigations resulted recently in identification of the first disease gene for slow atrial fibrillation and the establishment of its link to stroke.
Cardiology; Genetics; Heart; Heart Defects, Congenital; Metabolic Syndrome; Lipid Metabolism Disorders; Hyperlactatemia