title: Impaired phosphorylation of JAK2-STAT5b signaling in fibroblasts from uremic children.
abstract: BACKGROUND
  Chronic kidney disease (CKD) in children is characterized by severe growth failure. The growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis in uremic animals shows a post-receptor impaired phosphorylation of Janus kinase 2/signal transducer and activator of transcription (JAK-STAT) proteins. The objective of our study was to characterize the intracellular phosphorylation of JAK-STAT signaling in fibroblasts from children with CKD on chronic peritoneal dialysis (PD).
  
  
  METHODS
  Serum GH-binding protein (GHBP), IGF-1 and IGFBP3 were measured in 15 prepubertal CKD stage-5 children on PD. Cytoplasmic JAK2, cytoplasmic/nuclear STAT5b and nuclear IGFBP3, acid-labile subunit (ALS) and IGF-1 mRNA expression were quantified in fibroblasts obtained from skin biopsies before and after stimulation with 200 ng/ml recombinant human growth hormone (rhGH). Phosphorylation activity at both the cytoplasmic and nuclear level was expressed as the ratio phosphorylated (p)/total (t) abundance of the product (p/t) at 30 and 60 min. Fifteen healthy children were recruited as the control group. Values were expressed in arbitrary units (AU) and normalized for comparison. Significance was defined as p < 0.05.
  
  
  RESULTS
  Thirty minutes after rhGH stimulus, the cytoplasmic (p/t) JAK2 ratio was significantly lower in patients than in controls [median and interquartile range (IQR): 7.4 (4.56) vs. 20.5 (50.06) AU]. At 60 min after rhGH stimulation, median JAK2 phosphorylation activity was still significantly lower in the patients [7.14 (IQR 3.8) vs. 10.2 (IQR 29.8) AU; p < 0.05]. The increase in the cytoplasmic (p/t) STAT5b/β-actin ratio was lower at both measurement points in the patients compared to the controls, without reaching statistical significance between groups. Median IGFBP3 mRNA abundance was significantly decreased in fibroblasts from uremic patients 24 h after rhGH stimulation compared to the healthy controls [1.27 (IQR 0.83) vs. 2.37 (IQR 0.80) AU]. Median ALS and IGF-1 mRNA expression changed in response to rhGH stimuli at 24 and 48 h.
  
  
  CONCLUSIONS
  In this study, children with CKD undergoing PD therapy showed an impaired phosphorylation of JAK2/STAT5b signaling in fibroblasts after GH stimulation, as well as impaired IGFBP3 mRNA abundance. Both impairments may be partially responsible for the observed resistance to the growth-promoting actions of GH in chronic kidney failure.
authors.affiliation: Department of Pediatric Endocrinology, Molecular Physiology Laboratory and Public Health Department, Faculty of Medicine, Universidad de los Andes, Santiago, Chile.
authors.forename: Francisca
authors.initials: F
authors.lastname: Ugarte
authors.affiliation: Department of Pediatric Endocrinology, Molecular Physiology Laboratory and Public Health Department, Faculty of Medicine, Universidad de los Andes, Santiago, Chile.
authors.forename: Carlos
authors.initials: C
authors.lastname: Irarrazabal
authors.affiliation: Department of Pediatric Nephrology, University Medical Center Hamburg/Eppendorf, Hamburg, Germany.
authors.forename: Jun
authors.initials: J
authors.lastname: Oh
authors.affiliation: Department of Pediatric Nephrology, University Medical Center Hamburg/Eppendorf, Hamburg, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Dettmar
authors.affiliation: Division of Pediatric Nephrology, Luis Calvo Mackenna Children's Hospital, Faculty of Medicine, Universidad de Chile, Santiago, Chile.
authors.forename: María L
authors.initials: ML
authors.lastname: Ceballos
authors.affiliation: Division of Pediatric Nephrology, Luis Calvo Mackenna Children's Hospital, Faculty of Medicine, Universidad de Chile, Santiago, Chile.
authors.forename: Angélica
authors.initials: A
authors.lastname: Rojo
authors.affiliation: Division of Pediatric Nephrology, Luis Calvo Mackenna Children's Hospital, Faculty of Medicine, Universidad de Chile, Santiago, Chile.
authors.forename: M José
authors.initials: MJ
authors.lastname: Ibacache
authors.affiliation: Department of Pediatric Endocrinology, Molecular Physiology Laboratory and Public Health Department, Faculty of Medicine, Universidad de los Andes, Santiago, Chile.
authors.forename: Cristián
authors.initials: C
authors.lastname: Suazo
authors.affiliation: Department of Pediatric Endocrinology, Molecular Physiology Laboratory and Public Health Department, Faculty of Medicine, Universidad de los Andes, Santiago, Chile.
authors.forename: Mauricio
authors.initials: M
authors.lastname: Lozano
authors.affiliation: Department of Biostatistics, Universidad del Desarrollo, Santiago, Chile.
authors.forename: Iris
authors.initials: I
authors.lastname: Delgado
authors.affiliation: Department of Pediatric Endocrinology, Molecular Physiology Laboratory and Public Health Department, Faculty of Medicine, Universidad de los Andes, Santiago, Chile.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Cavada
authors.affiliation: Division of Pediatric Nephrology, Luis Calvo Mackenna Children's Hospital, Faculty of Medicine, Universidad de Chile, Santiago, Chile.
authors.forename: Marta
authors.initials: M
authors.lastname: Azocar
authors.affiliation: Division of Pediatric Nephrology, Luis Calvo Mackenna Children's Hospital, Faculty of Medicine, Universidad de Chile, Santiago, Chile.
authors.forename: Angela
authors.initials: A
authors.lastname: Delucchi
authors.affiliation: Division of Pediatric Nephrology, Luis Calvo Mackenna Children's Hospital, Faculty of Medicine, Universidad de Chile, Santiago, Chile. fcanosch@gmail.com.
authors.forename: Francisco
authors.initials: F
authors.lastname: Cano
mesh_terms: D000199:Actins / Q000378:metabolism; D001706:Biopsy; D002352:Carrier Proteins / Q000097:blood; D002648:Child; D002675:Child, Preschool; D004268:DNA-Binding Proteins / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000378:metabolism*; D019382:Human Growth Hormone / Q000494:pharmacology; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000378:metabolism; D053614:Janus Kinase 2 / Q000378:metabolism*; D008297:Male; D010530:Peritoneal Dialysis; D010766:Phosphorylation; D061251:Primary Cell Culture; D011994:Recombinant Proteins / Q000494:pharmacology; D051436:Renal Insufficiency, Chronic / Q000378:metabolism* / Q000628:therapy; D050799:STAT5 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction; D012867:Skin / Q000166:cytology / Q000473:pathology; D014511:Uremia / Q000378:metabolism*
chemical_list: D000199:Actins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C515497:IGFBP3 protein, human; D018972:Insulin-Like Growth Factor Binding Protein 3; D011994:Recombinant Proteins; D050799:STAT5 Transcription Factor; C494095:STAT5B protein, human; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; C507924:JAK2 protein, human; D053614:Janus Kinase 2; C051815:somatotropin-binding protein
keywords: Chronic kidney disease; Growth hormone; IGF-1; IGFBP3; JAK2; Peritoneal dialysis; STAT5b