Sim1‐PVN neurons in ADAM17 mediated neurogenic hypertension
Authors: Mukerjee Snigdha , Basting Tyler , Zsombok Andrea , Lazartigues Eric 
Published: June 2021

Within the brain, activating the classical arm of renin angiotensin system (RAS) (ACE/AngII/AT1aR) upregulates, ADAM17, a disintegrin & metalloprotease. ADAM17 sheds ACE2 from the cell membrane compromising compensatory RAS (ACE2/Ang(1–7)/MasR). We have previously published that deleting ADAM17 from the hypothalamus improves autonomic function and attenuates development of DOCA‐salt induced neurogenic hypertension. We hypothesize, ADAM17 containing neurons in the paraventricular nucleus (PVN) contribute to its excitability leading to autonomic dysfunction.

Single minded 1 (Sim1) is a transcription factor essential for neurodevelopment of the PVN. This promoter enabled specific labelling of PVN neurons with reporter tdTomato, using cre‐lox mechanism. In another group of mice (named SAT), we conditionally knocked out ADAM17 from Sim1 neurons, keeping tdTomato reporter expression. We identified pre‐sympathetic neurons within the PVN, by injecting a GFP tagged pseudorabies virus in the kidney. These neurons overlapped with Sim1 positive tdTomato reporter neurons in the PVN. The relevance of Sim1‐PVN neurons in blood pressure (BP) was evaluated through an optogenetic approach. Activating Sim1‐PVN neurons with cre driven channelrhodopsin and 20 Hz photo stimulation at 473 nm, led to increased BP, measured with radiotelemetry (+8.2 mmHg, n=1). Ganglionic blockade following chlorisondamine administration prevented this rise in BP, confirming that it is a neuronal response (+ 0.3 mmHg, n=1). Neuron sorting was employed to distinguish the ADAM17 knockout (SAT), Sim1‐tomato PVN neurons from its controls. qRT‐PCR from these neurons confirmed a 4‐fold drop in ADAM17 in knockout mice (p<0.1). Interestingly, at baseline SAT tdTomato neurons in PVN had a 4‐fold decreased FosB expression, a marker of chronic neuronal excitation (p<0.1), indicating that ADAM17 plays a critical role in maintaining neuronal excitability in the PVN.

DOCA pellets were implanted in both SAT and control mice. Followed by 15 days of 1% NaCl treatment to induce neurogenic hypertension. DOCA‐salt induced change in RAS within the hypothalamus led to greater drop in ACE (1.7‐fold, p<0.0001) and AT1aR (3.12‐fold, p<0.001) gene expression in SAT mice. Moreover, compensatory ACE2 expression was 6‐fold higher in SAT vs. controls (p<0.05) and MasR expression increased 4.6‐fold in SAT mice (p<0.0001), indicating that deleting ADAM17 preserved the compensatory RAS within SAT during a DOCA‐salt challenge. Though, DOCA‐salt induced change in systolic BP was unchanged between SAT knockouts & controls, optogenetic stimulation and FosB expression presents evidence that the Sim1‐ADAM17 neurons in the PVN contribute to autonomic function through neuronal activation. Future direction includes, studying the interaction of circumventricular injection of AngII with ADAM17 & suppression of AT1R‐induced inflammation with losartan, to understand the mechanism of ADAM17‐induced neuronal activation in the PVN. Clinical relevance is highlighted by the report that enhanced ADAM17‐induced shed ACE2 activity in the cerebrospinal fluid is correlated with systolic BP in hypertensive patients, making ADAM17 a potential new target for the treatment of hypertension.

Support or Funding Information

NIH/NHLBI HL093178

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.