Chronic Knockdown of the Nucleus of the Solitary Tract AT1 Receptors Increases Blood Inflammatory-Endothelial Progenitor Cell Ratio and Exacerbates Hypertension in the Spontaneously Hypertensive Rat

AT(1) receptor subtype a (AT(1)Ra) expression is increased in the nucleus of the solitary tract (NTS) in spontaneously hypertensive rat (SHR) compared with Wistar Kyoto controls. However, the chronic role of AT(1)Ra in the NTS for cardiovascular control is not well understood. In this study, we investigated the hypothesis that the NTS AT(1)Ra is involved in the neural regulation of the peripheral inflammatory status and linked with hypertension. Transduction of brain neuronal cultures with recombinant adeno-associated virus type 2 (AAV2)-AT(1)R-small hairpin RNA (shRNA) resulted in a 72% decrease in AT(1)Ra mRNA and attenuated angiotensin II-induced increase in extracellular signal-regulated kinase 1/2 phosphorylation and neuronal firing. Specific NTS microinjection of AAV2-AT(1)R-shRNA vector in the SHR resulted in a approximate to 30 mm Hg increase in the mean arterial pressure compared with control vector-injected animals (Sc-shRNA: 154 +/- 4 mm Hg; AT(1)R-shRNA: 183 +/- 10 mm Hg) and induced a resetting of the baroreflex control of heart rate to higher mean arterial pressure. In addition, AAV2-AT(1)R-shRNA-treated SHRs exhibited a 74% decrease in circulating endothelial progenitor cells (CD90(+), CD4(-)/CD5(-)/CD8(-)) and a 300% increase in the circulating inflammatory cells, including CD4(+)+CD8(+), CD45(+)/3(+) T lymphocytes, and macrophages (CD68(+)). As a result, the endothelial progenitor cell/inflammatory cells ratio was decreased by 8- to 15-fold in the AT(1)R-shRNA-treated SHR. However, identical injection of AAV2-AT(1)R-shRNA into the NTS of Wistar Kyoto rats had no effect on mean arterial pressure and inflammatory cells. These observations suggest that increased expression of the AT(1)Ra in SHR NTS may present a counterhypertensive mechanism involving inflammatory/angiogenic cells.