title: Toll-like receptor 4 promotes autonomic dysfunction, inflammation and microglia activation in the hypothalamic paraventricular nucleus: role of endoplasmic reticulum stress.
abstract: OBJECTIVE
  Toll-like receptor 4 (TLR4) signaling induces tissue pro-inflammatory cytokine release and endoplasmic reticulum (ER) stress. We examined the role of TLR4 in autonomic dysfunction and the contribution of ER stress.
  
  
  METHODS
  Our study included animals divided in 6 experimental groups: rats treated with saline (i.v., 0.9%), LPS (i.v., 10mg/kg), VIPER (i.v., 0.1 mg/kg), or 4-PBA (i.p., 10 mg/kg). Two other groups were pretreated either with VIPER (TLR4 viral inhibitory peptide) LPS + VIPER (i.v., 0.1 mg/kg) or 4-Phenyl butyric acid (4-PBA) LPS + PBA (i.p., 10 mg/kg). Arterial pressure (AP) and heart rate (HR) were measured in conscious Sprague-Dawley rats. AP, HR variability, as well as baroreflex sensitivity (BrS), was determined after LPS or saline treatment for 2 hours. Immunofluorescence staining for NeuN, Ib1a, TLR4 and GRP78 in the hypothalamic paraventricular nucleus (PVN) was performed. TNF-α, TLR4 and GRP78 protein expression in the PVN were evaluated by western blot. Plasma norepinephrine levels were determined by ELISA.
  
  
  RESULTS
  Acute LPS treatment increased HR and plasma norepinephrine concentration. It also decreased HR variability and high frequency (HF) components of HR variability, as well BrS. Acute LPS treatment increased TLR4 and TNF-α protein expression in the PVN. These hemodynamic and molecular effects were partially abrogated with TLR4 blocker or ER stress inhibitor pretreatment. In addition, immunofluorescence study showed that TLR4 is co-localized with GRP78in the neurons. Further inhibition of TLR4 or ER stress was able to attenuate the LPS-induced microglia activation.
  
  
  CONCLUSIONS
  TLR4 signaling promotes autonomic dysfunction, inflammation and microglia activation, through neuronal ER stress, in the PVN.
authors: Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, United States of America; Department of Physiology and Biophysics, Biomedical Sciences Institute, University of Sao Paulo, Sao Paulo, Brazil.
authors: Gustavo S
authors: GS
authors: Masson
authors: Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, United States of America.
authors: Anand R
authors: AR
authors: Nair
authors: Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, United States of America.
authors: Rahul B
authors: RB
authors: Dange
authors: Department of Pharmacology, Fluminense Federal University, Rio De Janeiro, Brazil.
authors: Pedro Paulo
authors: PP
authors: Silva-Soares
authors: Department of Physiology and Biophysics, Biomedical Sciences Institute, University of Sao Paulo, Sao Paulo, Brazil.
authors: Lisete C
authors: LC
authors: Michelini
authors: Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, United States of America.
authors: Joseph
authors: J
authors: Francis
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D015870:Gene Expression; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D007249:Inflammation / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D017628:Microglia / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism; D009638:Norepinephrine / Q000096:biosynthesis; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D000091342:Endoplasmic Reticulum Chaperone BiP
chemical_list: D006360:Heat-Shock Proteins; D008070:Lipopolysaccharides; D009638:Norepinephrine; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; C051684:GRP78 protein, rat; D000091342:Endoplasmic Reticulum Chaperone BiP