title: The molecular mechanism of leptin secretion and expression induced by aristolochic acid in kidney fibroblast.
abstract: BACKGROUND
  Leptin is a peptide hormone playing pivotal role in regulating food intake and energy expenditure. Growing evidence has suggested the pro-inflammatory and fibrogenic properties of leptin. In addition, patients with renal fibrosis have higher level of plasma leptin, which was due to the increased leptin production. Aristolochic acid (AA) is a botanical toxin characterized to associate with the development of renal fibrosis including tubulointerstitial fibrosis. However, whether leptin is upregulated to participate in AA-induced kidney fibrosis remain completely unknown.
  
  
  RESULTS
  In this study, leptin expression was increased by sublethal dose of AA in kidney fibroblast NRK49f determined by enzyme-linked immunosorbent assay and Western blot. Data from real-time reverse transcriptase-polymerase chain reaction revealed that leptin was upregulated by AA at transcriptional level. DNA binding activity of CCAAT enhancer binding protein α (C/EBP α), one of the transcription factors for leptin gene, was enhanced in DNA affinity precipitation assay and chromatin immunoprecipitation experiments. Knockdown of C/EBP α expression by small interfering RNA markedly reduced AA-induced leptin expression. Moreover, AA promoted Akt interaction with p-PDK1, and increased phosphorylated activation of Akt. Akt knockdown, and inhibition of Akt signaling by LY294002 and mTOR inhibitor rapamycin reduced leptin expression. Furthermore, treatment of LY294002 or rapamycin significantly suppressed AA-induced C/EBP α DNA-binding activity. These results suggest that Akt and C/EBP α activation were involved in AA-regulated leptin expression.
  
  
  CONCLUSIONS
  Our findings demonstrate the first that AA could induce secretion and expression of fibrogenic leptin in kidney fibroblasts, which reveal potential involvement of leptin in the progression of kidney fibrosis in aristolochic acid nephropathy.
authors.affiliation: Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan, Republic of China.
authors.forename: Tsung-Chieh
authors.initials: TC
authors.lastname: Lin
authors.forename: Tien-Chiang
authors.initials: TC
authors.lastname: Lee
authors.forename: Shih-Lan
authors.initials: SL
authors.lastname: Hsu
authors.forename: Chung-Shi
authors.initials: CS
authors.lastname: Yang
mesh_terms: D000818:Animals; D034341:Aristolochic Acids / Q000494:pharmacology* / Q000633:toxicity; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism / Q000502:physiology; D002273:Carcinogens / Q000494:pharmacology / Q000633:toxicity; D002478:Cells, Cultured; D018450:Disease Progression; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism; D005355:Fibrosis / Q000139:chemically induced; D005786:Gene Expression Regulation / Q000187:drug effects; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D020738:Leptin / Q000235:genetics* / Q000378:metabolism*; D051058:Oncogene Protein v-akt / Q000378:metabolism / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D034341:Aristolochic Acids; D022762:CCAAT-Enhancer-Binding Proteins; D002273:Carcinogens; D020738:Leptin; D014157:Transcription Factors; C000228:aristolochic acid I; D019869:Phosphatidylinositol 3-Kinases; D051058:Oncogene Protein v-akt