title: High Glucose Impairs Insulin Signaling in the Glomerulus: An In Vitro and Ex Vivo Approach.
abstract: OBJECTIVE
  Chronic hyperglycaemia, as seen in type II diabetes, results in both morphological and functional impairments of podocytes in the kidney. We investigated the effects of high glucose (HG) on the insulin signaling pathway, focusing on cell survival and apoptotic markers, in immortalized human glomerular cells (HGEC; podocytes) and isolated glomeruli from healthy rats.
  
  
  RESULTS
  HGEC and isolated glomeruli were cultured for various time intervals under HG concentrations in the presence or absence of insulin. Our findings indicated that exposure of HGEC to HG led to downregulation of all insulin signaling markers tested (IR, p-IR, IRS-1, p-Akt, p-Fox01,03), as well as to increased sensitivity to apoptosis (as seen by increased PARP cleavage, Casp3 activation and DNA fragmentation). Short insulin pulse caused upregulation of insulin signaling markers (IR, p-IR, p-Akt, p-Fox01,03) in a greater extent in normoglycaemic cells compared to hyperglycaemic cells and for the case of p-Akt, in a PI3K-dependent manner. IRS-1 phosphorylation of HG-treated podocytes was negatively regulated, favoring serine versus tyrosine residues. Prolonged insulin treatment caused a significant decrease of IR levels, while alterations in glucose concentrations for various time intervals demonstrated changes of IR, p-IR and p-Akt levels, suggesting that the IR signaling pathway is regulated by glucose levels. Finally, HG exerted similar effects in isolated glomeruli.
  
  
  CONCLUSIONS
  These results suggest that HG compromises the insulin signaling pathway in the glomerulus, promoting a proapoptotic environment, with a possible critical step for this malfunction lying at the level of IRS-1 phosphorylation; thus we herein demonstrate glomerular insulin signaling as another target for investigation for the prevention and/ or treatment of diabetic nephropathy.
authors.affiliation: Institute of Biosciences and Applications, National Center for Scientific Research 'Demokritos', Athens, Greece.
authors.forename: Elias N
authors.initials: EN
authors.lastname: Katsoulieris
authors.affiliation: Institute of Biosciences and Applications, National Center for Scientific Research 'Demokritos', Athens, Greece.
authors.forename: Garyfalia I
authors.initials: GI
authors.lastname: Drossopoulou
authors.affiliation: Institute of Biosciences and Applications, National Center for Scientific Research 'Demokritos', Athens, Greece.
authors.forename: Eleni S
authors.initials: ES
authors.lastname: Kotsopoulou
authors.affiliation: 2nd Department of Propaedeutic Medicine, Attikon University Hospital, Athens, Greece.
authors.forename: Dimitrios V
authors.initials: DV
authors.lastname: Vlahakos
authors.affiliation: Department of Pathology, National and Kapodistrian University of Athens, Medical School, Athens, Greece.
authors.forename: Elias A
authors.initials: EA
authors.lastname: Lianos
authors.affiliation: Institute of Biosciences and Applications, National Center for Scientific Research 'Demokritos', Athens, Greece.
authors.forename: Effie C
authors.initials: EC
authors.lastname: Tsilibary
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002461:Cell Line, Transformed; D000071161:Forkhead Box Protein O1 / Q000235:genetics / Q000378:metabolism; D000071316:Forkhead Box Protein O3 / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D006943:Hyperglycemia / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins / Q000235:genetics* / Q000378:metabolism; D008297:Male; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D050199:Podocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D046509:Tissue Culture Techniques; D014443:Tyrosine / Q000378:metabolism
chemical_list: C085126:FOXO1 protein, human; C499517:FOXO3 protein, human; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D014443:Tyrosine; D012694:Serine; D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; D051057:Proto-Oncogene Proteins c-akt; D005947:Glucose