The major goal of my lab is to identify mechanisms to explain how biological systems function, define how dysfunction leads to the genesis of human disease, and develop novel approaches for treatment. The lab attempts to achieve these goals taking advantage of multi-disciplinary and collaborative approaches, using cutting edge cores and equipment available at LSU-HSC, along with hard work.
The spectrum of Cardiovascular and Metabolic disease represents the largest human health burden worldwide. The lab aims to define Genetic and environmental factors that affect the development of Cardiovascular and Metabolic disease including hyperglycemia, dyslipidemia, atheroslcerosis, and clinical outcomes of heart attack and stroke.
Project title: Determining roles of the pro-apoptotic UPR gene CHAC1 in atherosclerosis.
The unfolded protein response (UPR) pathway, a fundamental eukaryotic response mechanism to endoplasmic reticulum (ER) stress, has been implicated in the progression of atherosclerosis, in endothelial cells and macrophages (Mφ), and may be of importance in vascular smooth muscle cells (SMC). Using a systems biology approach examining global mRNA expression from 12 donors, we identified CHAC1 as regulated by oxidized phospholipids (ox-PAPC) in human aortic endothelial cells (HAEC). CHAC1 was contained in a co-regulated group of genes enriched for components of the ATF4 arm of the ER-stress pathway. CHAC1 mRNA is induced by ER-stress, and is specifically activated by the ATF4-ATF3- CHOP pathway. We showed an inhibitory effect of CHAC1 on TNFRSF6B (an inhibitory FASL decoy receptor), and demonstrated that CHAC1 was a pro-apoptotic factor (Mungrue et al. J Immunol). Determining the function of CHAC1 will provide insights into understanding the response of endothelial cells to oxidized phospholipids in the setting of UPR mediated apoptosis, and may also have impacts on SMC and Mφ with relevance for vascular disease. Additionally, characterizing the function of CHAC1 will define the role of the ChaC homology domain, which is conserved from bacteria to humans but whose molecular function has yet to be determined.
Aim 1: Using systems biology to determine mRNAs co-regulated with and eQTLs related to CHAC1
To characterize the roles of CHAC1, we will perform experiments to determine genes whose mRNAs are co-regulated with, and DNA loci that underlie eQTLs for CHAC1.
Hypothesis: Identifying co-regulated mRNAs will uncover novel functions of CHAC1, and determining eQTLs regulating CHAC1 mRNA will define genes that regulate the CHAC1 promoter.
Aim 2: Determining the role of CHAC1 in CHOP and UPR-induced apoptosis
To characterize the role of CHAC1 in cellular signaling, we will perform experiments to determine apoptosis signaling pathways that mediate CHOP induction of CHAC1, and CHAC1 inhibition of TNFRSF6B.
Hypothesis: CHAC1 mediates apoptosis of endothelial or smooth muscle cells downstream of CHOP and via FASL, or the ER-associated caspase 12.
Aim 3: Determining binding partners and molecular functions of CHAC1
To characterize the role of CHAC1, we will determine in vivo binding partners using the TAP method (7), and co-immuno-precipitation to validate putative binding partners in HAECs treated with UPR inducers.
Hypothesis: Determining proteins that interact with CHAC1 will highlight molecular functions of this protein, and define the role of the ChaC domain.
Aim 4: Examining atherosclerosis in CHAC1 knockout mice To characterize the role of CHAC1 in atherosclerosis we will examine the induction of CHAC1 in atherosclerotic lesions. Also, we aim to generate CHAC1 knockout mice on the LDLR-/- background and examine diet induced aortic lesion formation.
Hypothesis: CHAC1 is activated in the setting of atherosclerosis, and genetic ablation will exacerbate the development of aortic lesions through inhibiting early apoptotic cell clearing in the vessel wall.