Hypertension is a leading cause of morbidity and mortality worldwide. Historically, an increase of the sympathetic nerve activity represents one of the principal features of hypertension. Mounting evidence suggests that novel players also contribute to the development of the disease as the immune system. In fact, how the immunity is activated after a hypertensive stimulus is to date an intriguing question. In this dissertation, we show how hypertensive challenges activate the sympathetic nerve drive to prime immune responses in the spleen causing the onset of the disease. First, we observe that the splenic sympathetic nerve activity is significantly increased in mice upon 3 days of chronic AngiotensinII (AngII) or Deoxycorticosterone acetate (DOCA)-salt as compared to mice treated with vehicle or placebo, respectively. Then, we show that the splenic nerve discharge is absent in both coeliac vagotomized mice and in mice lacking nicotinic cholinergic receptors (7nAChR) upon AngII. Indeed, we find that a vagus-splenic nerve pathway, mediated by 7nAChR expressed in the coeliac ganglion, is modulated by chronic infusion of AngII. The integrity of this cholinergic-sympathetic pathway is necessary for the activation of T cell and their egression towards target organs of hypertension, as kidneys and vasculature. In order to evaluate whether the sympathetic neuro-immune drive is relevant for hypertension, we perform the denervation of the splenic artery by thermoablation in mice infused with chronic AngII, finding a protection from the increase of blood pressure levels induced by this hypertensive stimulus. We also confirm the efficacy of the splenic denervation by injecting a retrograde neurotracer in the spleen, which label neurons of coeliac ganglion only in sham mice but not in denervated mice. This novel experimental procedure suggests new clinical strategies for resistant hypertension. To evaluate how the activation of the immune system is mediated in the spleen, we explore the role of the neuro-splenic sympathetic drive in the murine model of DOCA-salt hypertension. This model of hypertension completely resembles the excessive salt consumption in humans and it is optimal to obtain a peripheral low-circulation of renin-angiotensin system (RAS) activity, contemporary to en elevation of RAS activity in the brain. First, we challenge splenectomized mice with DOCA-salt for 21 days finding that they are protected from blood pressure elevation induced by this hypertensive stimulus. We observe the same results in mice with left coeliac ganglionectomy (CGX) equally treated with DOCA-salt. Then, by ELISA and immunofluorescence quantitative analysis, we measure the levels of the placental growth factor (PlGF) upon DOCA-salt showing an increased expression in mice with an intact neuro-splenic axis but not in CGX mice. Therefore, PlGF KO mice are significantly protected from blood pressure increase induced by DOCA-salt, as compared to WT mice. Additionally, the absence of PlGF hinders the costimulation pathway of T cells with a consequent reduction of their migration toward kidneys. Kidneys of WT mice show an increased deposition of fibrotic tissue upon DOCA-salt, in both glomeruli and tubules, suggesting that infiltrating T cells determinate structural alterations that deteriorate renal function. We assesse key parameters of renal function in PlGF KO and WT mice placed in metabolic cages after DOCA-salt or placebo administration. PlGF KO mice show a reduced urine output as compared to WT mice after DOCA-salt. The creatinine clearance is significantly reduced in WT mice but not in PlGF KO mice and similarly, PlGF KO mice are protected from DOCA-salt induced renal damage observed in WT mice in terms of protein excretion. These data demonstrate that the coupling of nervous and immune system activation in the marginal zone of the spleen is established through a sympathetic-mediated PlGF release, suggesting that this pathway could be a valid therapeutic target for hypertension.
|Titolo:||A cholinergic-sympathetic pathway mediates the activation of immune system in hypertension|
|Data di pubblicazione:||20-mar-2018|
|Appare nelle tipologie:||8.1 Tesi di dottorato|