ADAM17 in glutamatergic neurons promote pre-sympathetic neuronal activation through microglia-mediated blockade of GABAergic inputs

Abstract

The brain renin-angiotensin system (RAS) plays an important role in regulating autonomic function. We have demonstrated that A Disintegrin and Metalloproteinase 17 (ADAM17) in glutamatergic neurons facilitate activation of presympathetic neurons (PSN) upon angiotensin II (Ang-II) stimulation and promote development of salt-sensitive hypertension. However, in PVN, glutamatergic neurons express limited angiotensin-converting enzyme 2, a substrate of ADAM17 and crucial member of regulatory RAS, thus bringing question regarding how ADAM17 supports PSN activation in the PVN. Using whole-cell patch clamp, the PVN-RVLM-projecting PSN in wildtype (WT) mice exhibited a dramatical reduction in the frequency of miniature inhibitory postsynaptic currents (mIPSC), when Ang-II was bath-supplied (2 μM). By contrast, Ang-II-associated suppression of mIPSC frequency in RVLM-projecting PSN, from mice lacking ADAM17 in glutamatergic neurons (A17GKO), was significantly smaller (suppression ratio: WT vs. A17GKO = 46.39±10.59 vs. 19.27±15.03, P<0.0001). Meanwhile, no difference was detected in the amplitude of mIPSC in either case of baseline or Ang-II bath-incubation, indicating that only presynaptic GABAergic inputs, rather than postsynaptic receptors of GABA, was affected by Ang-II. Considering the sheddase role of ADAM17, we then hypothesized that ADAM17 in glutamatergic neurons mediated blockade of GABAergic inputs via extracellular mechanism. Via immunoelectron microscopy, we observed co-localization of PSN, microglia and GABA. Using DOCA-salt hypertension model (1mg/g body weight, 1%NaCl, 21 days), we observed that DOCA-salt-induced reduction of GABA (LC-MS), together with increase of TNFα, IL-6, and TGFβ (ELISA), which were closely related to microglial activation, were abolished in the PVN of A17GKO mice. These findings all suggested an involvement of microglial activation in blockade of GABAergic inputs during hypertension development. Accordingly, TRAM34, a small molecule that freezes microglia, was introduced in whole-cell patch clamp recording of mIPSC. With pre-incubation of TRAM34, Ang-II-associated suppression of mIPSC frequency in the PVN-RVLM projecting PSN was blunted, in a similar manner as A17GKO (suppression ratio: WT vs. WT+ TRAM34 = 46.39±10.59 vs. 15.38±6.28, P<0.0001). In addition, contacts between microglia and PSN were increased in WT mice during the early stage of hypertension development (1st week of DOCA-salt treatment), and they were significantly less in A17GKO (percentage of neurons being touched: WT+DOCA vs. A17GKO+DOCA = 28.59±1.9% vs. 11.83±2.27%, P<0.0001). Together, our data provided preliminary evidence that ADAM17 in glutamatergic neurons mediates the blockade of tonic GABAergic inputs via facilitating chemotaxis of PSN, therefore supporting PSN activation and development of hypertension. National Natural Science Foundation of China, 82100454 to JX. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.