Abstract P054: Inhibition of Endosomal MyD88-dependent Signaling with Chloroquine Improves Endothelial Function and Lowers Blood Pressure in Spontaneously Hypertensive Rats

Abstract

Uncontrolled inflammation and chronic immune system activation are common in hypertension. However, the exact mechanisms by which they occur are not well understood. Innate immune system recognition and response to damage-associated molecular patterns (DAMPs) is becoming an increasingly accepted mechanism. Mitochondrial DNA (mtDNA) is a DAMP that is recognized by Toll-like receptor (TLR)9 and is elevated in the circulation of spontaneously hypertensive rats (SHR). Therefore, we sought to determine the contribution of TLR9 in hypertension. We hypothesized that TLR9 inhibition with lysosomotropic agent chloroquine would improve endothelial function and lower blood pressure in SHR. We treated adult SHR and control Wistar-Kyoto rats (12 weeks old), as well as a group of young SHR (5 weeks old) with chloroquine (40 mg/kg/day, i.p.) for 21 days. Chloroquine lowered adult SHR blood pressure (Veh: 201±2 vs. CQ: 182±5 mmHg, p<0.05) and inhibited cyclooxygenase-dependent contraction to acetylcholine (ACh) in isolated mesenteric resistance arteries (MRA) from adult SHR [%NE (ACh 1 μmol/L), Veh: -31±8 vs. CQ: 70±10, p<0.05]. Chloroquine also inhibited co-localization of not only TLR9, but also TLR7 and TLR8 (MyD88-dependent endolysosomotropic TLRs) with MyD88 in adult SHR MRA, as well as expression of MyD88 in young SHR MRA. Finally, we observed that prophylactic treatment with chloroquine, during the critical pre-hypertensive stage, ameliorated the development of high blood pressure (Veh: 190±4 vs. CQ: 174±5 mmHg, p<0.05) and components of the adaptive immune system (decreased aortic-derived CD45+ leukocytes, circulating CD3+ T lymphocytes, and expression of CD44 on circulating and aortic-derived CD3+ T lymphocytes) upon maturation to adulthood in SHR. In conclusion, endosomal MyD88-dependent signaling from TLR7, 8, and 9 contribute to high blood pressure, endothelial dysfunction, and recruitment of the adaptive immune system in SHR. These findings support the involvement of the innate immune system in the pathogenesis and maintenance of hypertension.