title: Indoxyl sulfate downregulates expression of Mas receptor via OAT3/AhR/Stat3 pathway in proximal tubular cells.
abstract: Renin-angiotensin system (RAS) plays a pivotal role in chronic kidney disease (CKD). Angiotensin converting enzyme-related carboxypeptidase 2 (ACE2)/angiotensin (Ang)-(1-7)/Mas receptor axis counteracts the deleterious actions of Ang II. ACE2 exerts its actions by cleaving Ang II into Ang-(1-7) which activates Mas receptor. This study aimed to determine if the expression of Mas receptor is altered in the kidneys of CKD rats, and if indoxyl sulfate (IS), a uremic toxin, affects the expression of Mas receptor in rat kidneys and cultured human proximal tubular cells (HK-2 cells). The expression of Mas receptor was examined in the kidneys of CKD and AST-120-treated CKD rats using immunohistochemistry. Further, the effects of IS on Mas receptor expression in the kidneys of normotensive and hypertensive rats were examined. The effects of IS on the expression of Mas receptor and phosphorylation of endothelial nitric oxide synthase (eNOS) in HK-2 cells were examined using immunoblotting. CKD rats showed reduced renal expression of Mas receptor, while AST-120 restored its expression. Administration of IS downregulated Mas receptor expression in the kidneys of normotensive and hypertensive rats. IS downregulated Mas receptor expression in HK-2 cells in a time- and dose-dependent manner. Knockdown of organic anion transporter 3 (OAT3), aryl hydrocarbon receptor (AhR), and signal transducer and activator of transcription 3 (Stat3) inhibited IS-induced downregulation of Mas receptor and phosphorylated eNOS. N-acetylcysteine, an antioxidant, also inhibited IS-induced downregulation of Mas receptor and phosphorylated eNOS. Ang-(1-7) attenuated IS-induced transforming growth factor-β1 (TGF-β1) expression.
  
  
  CONCLUSIONS
  Mas receptor expression is reduced in the kidneys of CKD rats. IS downregulates renal expression of Mas receptor via OAT3/AhR/Stat3 pathway in proximal tubular cells. IS-induced downregulation of Mas receptor might be involved in upregulation of TGF-β1 in proximal tubular cells.
authors.affiliation: Department of Advanced Medicine for Uremia, Nagoya University Graduate School of Medicine, Nagoya, Japan; Division of Nephrology, Department of Internal Medicine, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung, Taiwan.
authors.forename: Hwee-Yeong
authors.initials: HY
authors.lastname: Ng
authors.affiliation: Department of Advanced Medicine for Uremia, Nagoya University Graduate School of Medicine, Nagoya, Japan.
authors.forename: Maimaiti
authors.initials: M
authors.lastname: Yisireyili
authors.affiliation: Department of Advanced Medicine for Uremia, Nagoya University Graduate School of Medicine, Nagoya, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Saito
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung, Taiwan.
authors.forename: Chien-Te
authors.initials: CT
authors.lastname: Lee
authors.affiliation: Department of Advanced Medicine for Uremia, Nagoya University Graduate School of Medicine, Nagoya, Japan.
authors.forename: Yelixiati
authors.initials: Y
authors.lastname: Adelibieke
authors.affiliation: Biomedical Research Laboratories, Kureha Co., Tokyo, Japan.
authors.forename: Fuyuhiko
authors.initials: F
authors.lastname: Nishijima
authors.affiliation: Department of Advanced Medicine for Uremia, Nagoya University Graduate School of Medicine, Nagoya, Japan.
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Niwa
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D000809:Angiotensins / Q000494:pharmacology; D000818:Animals; D015536:Down-Regulation / Q000187:drug effects*; D006801:Humans; D007150:Immunohistochemistry; D007200:Indican / Q000008:administration & dosage / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008954:Models, Biological; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D029362:Organic Anion Transporters, Sodium-Independent / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D020303:Rats, Inbred Dahl; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D051436:Renal Insufficiency, Chronic / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D053773:Transforming Growth Factor beta1 / Q000378:metabolism
chemical_list: D000809:Angiotensins; D029362:Organic Anion Transporters, Sodium-Independent; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; D018336:Receptors, Aryl Hydrocarbon; D043562:Receptors, G-Protein-Coupled; D050796:STAT3 Transcription Factor; D053773:Transforming Growth Factor beta1; C114338:organic anion transport protein 3; D052250:Nitric Oxide Synthase Type III; D007200:Indican; D000111:Acetylcysteine