Atherosclerosis Mechanisms: Angiotensin II production and action

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Abstract The renin angiotensin system (RAS) plays a critical role in the development of atherosclerosis. Mechanisms by which the RAS contributes to atherosclerosis have been focusing on effects of angiotensin II (AngII) production and its action through AT1a receptors within atherosclerotic lesions. On the basis of our preliminary data, we challenge this concept and propose a new hypothesis: Renal AngII production through a megalin-mediated pathway in proximal convoluted tubules (PCTs) promotes atherosclerosis via its local stimulation of AT1a receptors. Angiotensinogen (AGT), the substrate of the RAS, derived from hepatocytes is filtered through glomeruli and retained by megalin, a member of LDL receptor superfamily, in PCTs. Our protein sequence and structure analyses identified two conserved sequences that may associate with its binding to megalin. Aim 1 will define how hepatocyte-derived AGT regulates renal AngII production and contributes to atherosclerosis. We will use site-mutagenesis, surface plasmon resonance, and cell culture system to determine how AGT and megalin interact in vitro. Subsequently, we will use an adeno-associated viral (AAV) system to manipulate conserved sequences of AGT in hepatocyte-specific AGT deficient mice to determine whether conserved sequences of AGT influence renal AngII production and atherosclerosis. Effects of megalin on renal AngII production and atherosclerosis will be determined using PCT-specific megalin deficient mice. Since AGT is cleaved by two critical enzymes, renin and angiotensin-converting enzyme (ACE), to produce AngII, Aim 2 will first determine whether renin or ACE derived from PCTs contributes to renal AngII production and atherosclerosis using PCT-specific renin and ACE deficient mice, respectively. Studies proposed in Aim 1 for AGT and megalin interaction and Aim 2 for the two enzymes (renin and ACE) do not provide direct evidence whether AngII produced in PCTs contributes to atherosclerosis. To answer this question, we will use a transgenic mouse model that has restricted production of AngII in PCTs. AngII promotes atherosclerosis through AT1a receptor- mediated mechanism. Therefore, subsequent experiments will determine whether PCTs are the location for AT1a receptors to promote atherosclerosis. Completion of proposed studies will provide evidence whether renal PCTs are the major source for each classic RAS component to promote atherosclerosis. Demonstration of this new concept may change our understanding of the AngII/AT1a receptor-mediated mechanisms of atherosclerosis, which may also provide insights into developing new therapeutic strategies.