Wednesday, May 8, 2024
5/8/2024
With prevalence as high as 55% for individuals aged 55 and older in United States, hypertension (HTN) is a major risk factor contributing to cardiovascular diseases (CVD) and global mortality, hence remaining an increasingly important medical and public health issue. The role of the brain renin-angiotensin system (RAS) in the maintenance of normal blood pressure (BP) and in the neuro-cardiovascular dysregulation leading to HTN has been firmly established. Angiotensin (Ang)-II, by means of its type 1 receptor (AT1R), promotes increased sympathetic nerve activity, salt and water reabsorption, vasoconstriction, aldosterone and vasopressin release and inflammation, all contributing to HTN. While numerous overexpression studies, from our group and others, have established the benefits of ACE2 (Angiotensin Converting Enzyme type 2) in preventing the progression and improving the treatment of HTN in experimental models, our group was the first to demonstrate that ADAM17 (A Disintegrin And Metalloprotease) mediates ACE2 shedding in neurogenic HTN, thus reducing ACE2 compensatory activity in mice and humans. ADAM17-mediated ACE2 shedding, a process by which the protein ectodomain is cleaved from the plasma membrane and secreted into the surrounding milieu, has since been confirmed in many tissues including heart and kidney. ADAM17 is thought to mediate neuroinflammation through soluble TNFa, IL-6 trans-signaling, CX3CL1 and other cytokines, yet this mechanism has not been studied in neurogenic HTN. DOCA-salt HTN is associated with increased levels of TNFa, IL-6 and reduced ACE2 activity in the brain, while deletion of ADAM17 from neurons reduces BP, restores ACE2 activity and decreases pro- inflammatory cytokines. Although ADAM17 is thought to be a major drug target for inflammation, the development of selective inhibitors has failed. Recent work, deemed revolutionary, shows that ADAM17 maturation is tightly regulated by rhomboid proteins in the brain (iRhom1 in neurons and iRhom2 in microglia), opening the door for novel targeting strategies. Accordingly, we hypothesize that targeting ADAM17 maturation will reverse sympatho-excitation and neuro-inflammation in neurogenic HTN. We will test this new targeting strategy in the following two specific aims. Using a combination of human stem cells-derived neurons and microglia, unique transgenic and conditional knockout mice, with selective deletion of ADAM17 in microglia (Cx3Cr1ERT2-ADAM17tom) and targeted knockdown of ADAM17 maturation in neurons (Rhom1) or microglia (iRhom2), the immediate objectives of this application are to: 1) Understand how ADAM17 upregulation takes place throughout pre-sympathetic networks; 2) Assess the feed-forward role of ADAM17 in neuro-inflammation and microglia activation; and 3) Test new clinically-relevant targeting strategies to prevent ADAM17 activation and the development of resistant HTN.
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