title: Cross talk between AT1 receptors and Toll-like receptor 4 in microglia contributes to angiotensin II-derived ROS production in the hypothalamic paraventricular nucleus.
abstract: ANG II is thought to increase sympathetic outflow by increasing oxidative stress and promoting local inflammation in the paraventricular nucleus (PVN) of the hypothalamus. However, the relative contributions of inflammation and oxidative stress to sympathetic drive remain poorly understood, and the underlying cellular and molecular targets have yet to be examined. ANG II has been shown to enhance Toll-like receptor (TLR)4-mediated signaling on microglia. Thus, in the present study, we aimed to determine whether ANG II-mediated activation of microglial TLR4 signaling is a key molecular target initiating local oxidative stress in the PVN. We found TLR4 and ANG II type 1 (AT1) receptor mRNA expression in hypothalamic microglia, providing molecular evidence for the potential interaction between these two receptors. In hypothalamic slices, ANG II induced microglial activation within the PVN (∼65% increase, P < 0.001), an effect that was blunted in the absence of functional TLR4. ANG II increased ROS production, as indicated by dihydroethidium fluorescence, within the PVN of rats and mice (P < 0.0001 in both cases), effects that were also dependent on the presence of functional TLR4. The microglial inhibitor minocycline attenuated ANG II-mediated ROS production, yet ANG II effects persisted in PVN single-minded 1-AT1a knockout mice, supporting the contribution of a non-neuronal source (likely microglia) to ANG II-driven ROS production in the PVN. Taken together, these results support functional interactions between AT1 receptors and TLR4 in mediating ANG II-dependent microglial activation and oxidative stress within the PVN. 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.
authors.affiliation: Department of Physiology, Medical College of Georgia, Georgia Regents University, Augusta, Georgia; vbiancardi@gru.edu.
authors.forename: Vinicia Campana
authors.initials: VC
authors.lastname: Biancardi
authors.affiliation: Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Georgia Regents University, Augusta, Georgia;
authors.forename: Alexis M
authors.initials: AM
authors.lastname: Stranahan
authors.affiliation: Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, Florida.
authors.forename: Eric G
authors.initials: EG
authors.lastname: Krause
authors.affiliation: Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, Florida.
authors.forename: Annette D
authors.initials: AD
authors.lastname: de Kloet
authors.affiliation: Department of Physiology, Medical College of Georgia, Georgia Regents University, Augusta, Georgia;
authors.forename: Javier E
authors.initials: JE
authors.lastname: Stern
mesh_terms: D000804:Angiotensin II / Q000276:immunology / Q000378:metabolism*; D047228:Angiotensin II Type 1 Receptor Blockers / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D007113:Immunity, Innate / Q000276:immunology; D007249:Inflammation; D019808:Losartan / Q000494:pharmacology; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D018345:Mice, Knockout; D017628:Microglia / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D008911:Minocycline / Q000494:pharmacology; D018384:Oxidative Stress / Q000235:genetics / Q000276:immunology; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000276:immunology / Q000378:metabolism*; D044140:Receptor, Angiotensin, Type 1 / Q000235:genetics* / Q000378:metabolism; D012084:Renin-Angiotensin System / Q000235:genetics / Q000276:immunology; D051197:Toll-Like Receptor 4 / Q000276:immunology / Q000378:metabolism*
chemical_list: D047228:Angiotensin II Type 1 Receptor Blockers; D000900:Anti-Bacterial Agents; D017382:Reactive Oxygen Species; D044140:Receptor, Angiotensin, Type 1; C493487:Tlr4 protein, mouse; C495347:Tlr4 protein, rat; D051197:Toll-Like Receptor 4; D000804:Angiotensin II; D008911:Minocycline; D019808:Losartan
keywords: Toll-like receptor; angiotensin II; angiotensin II type 1 receptor; microglia; paraventricular nucleus