Crosstalk between the Innate immune system and Angiotensin II promotes hypothalamic inflammation in neurogenic hypertension Mowry FE1, Biancardi VC1* 1Auburn University
A consistent association between dysregulation of Angiotensin II (AngII) and increase in pro-inflammatory cytokines have emerged as mechanisms by which AngII mediates its deleterious effects during hypertension. However, the precise cellular and molecular targets underlying AngII signaling within the brain remain poorly understood. We aimed to determine whether crosstalk between AngII, TLR4, and microglia contributed to the maintenance of neurogenic hypertension. We used in our studies a model of hypertension characterized by elevated circulating levels of AngII (Spontaneously hypertensive rats - SHR). PVN protein expression of TLR4 and microglia-marker IBA1 were determined by immunofluorescence (IF), with skeletal analysis used to index microglia morphology. PVN IF showed a 104% increase in TLR4 protein density in SHR compared with Wistar control (WKY). Microglia skeletal analysis showed a decrease in end-points/frame by 21%, and a 34% decrease in total branch length/frame, in SHR PVN compared to WKY. Moreover, we found a higher degree of co-localization between both markers in SHR compared to control (SHR 6.6±0.9 vs. WKY 1.32±0.2 AU, P<0.05). Blocking AT1r in SHRs (Losartan; 20mg/kg/day; gavage; 4 weeks; SHRLos) ameliorated TLR4 upregulation seen in SHR, and normalized microglial activation. These data suggest that elevated AngII upregulates TLR4 and promotes microglia activation within central cardiovascular nucleus involved in sympathetic output, likely contributing to the characteristic sympathoexcitation of neurogenic hypertension. To study whether the presence of TLR4 in vivo was necessary for AngII actions, we treated SHRs with either anti-TLR4 antibody (SHRtlr4) or non-specific IgG (SHRIgG) (1μg/ml/kg, IP for two weeks). Anti-TLR4 treatment decreased blood pressure (SHRtlr4: 129±4 vs. SHRIgG: 168±6mmHg) and ameliorated microglia density in SHRtlr4 (16.42±1.8) compared to SHR control (23.05±3.0 AU). Together, these results support functional interactions between AT1 and TLR4 in mediating AngII-dependent microglial activation within the PVN and maintenance of neurogenic hypertension. More broadly, our results support a functional interaction between the central renin-angiotensin system and innate immunity in the regulation of neurohumoral outflows from the PVN.
Funding: AHA14SDG20400015 to VCB
Credits: None available.
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