PS-B05-8: AGTR1A RECEPTORS IN NEURONS OF THE SUBFORNICAL ORGAN AND THE PARAVENTRICULAR NUCLEUS OF HYPOTHALAMUS ACTIVATE SPLENIC IMMUNITY TO HYPERTENSIVE STIMULI

Abstract

Angiotensin II (AngII) is an important modulator of the sympathetic nervous system (SNS), activating type 1a AT receptors (AT1aRs), densely expressed in brain regions controlling cardiovascular function. Circumventricular organs (CVOs) locating in proximity of the ventricles are characterized by a leaky blood brain barrier, with the subfornical organ (SFO) particularly, exposed to circulating substances like AngII. Interestingly, the SFO is structurally and functionally connected to the paraventricular nucleus of the hypothalamus (PVN), a key regulator of the SNS. In our previous works, we demonstrated that AngII is capable to increase blood pressure by recruiting the splenic sympathetic nervous system (SSNA) and adaptive immune response in mice. Whether the splenic SNS and immune response are under brain control in hypertension is still unknown. To investigate the role of SFO, we exploited the stereotaxic injection of a recombinant adenovirus, encoding a Cre-recombinase and a GFP-reporter (AT1aR-KO-SFO), or GFP alone as control (AT1aR-WT-SFO), in the SFO of AT1aRflox mice. To selectively target AT1aRs in the PVN, we crossed AT1aRflox with mice expressing a Cre recombinase under Sim1 promoter, which typically characterize PVN neurons (AT1aR KO-PVN and AT1aR WT-PVN mice). Efficacy of gene deletion was evaluated by RT-PCR in brain samples obtained by laser microdissection (Figure 1) and AngII or vehicle were infused for 28 days through osmotic minipumps. First, we evaluated SSNA by microneurography, finding a significant reduction in firing frequency of mice with AT1aR KO in SFO. Then we analyzed whether the SSNA inhibition also hampered immune activation in the spleen and by immunofluorescence analysis of splenic white pulp area containing CD3 T cell, we observed that AT1aR KO-SFO mice displayed a reduced egression of T cells after chronic AngII infusion from the spleen towards target organs of hypertension. Further supporting the observation that AT1aR signaling in the brain SFO are necessary to prime T cell egression from the spleen, we found a significantly reduced infiltration of CD8 and CD4 T cells, and less renal damage, typical hallmarks of hypertension. More important, we also observed that AT1aR KO-PVN mice were significantly protected from AngII-induced hypertension, when compared to their respective controls showing a protection from T cells egression and infiltration in kidneys. Our data demonstrate the existence of a SFO-PVN-splenic axis as the main neural regulator of AngII-induced immune response and blood pressure increase. JOURNAL/jhype/04.03/00004872-202301001-00918/figure1/v/2023-10-24T163949Z/r/image-jpeg