title: Saturated fatty acids induce insulin resistance in human podocytes: implications for diabetic nephropathy.
abstract: BACKGROUND
  Cellular insulin resistance is the hallmark of type 2 diabetes and predominantly affects adipose and muscle cells. The saturated free fatty acid palmitate is elevated in insulin-resistant states and may directly contribute to cellular insulin resistance. A spectrum of renal disease is associated with increased markers of insulin resistance, although direct causal mechanisms are not known. In the kidney, glomerular podocytes are novel insulin-sensitive cells that have the ability to rapidly transport glucose. In this study, we tested the hypothesis that palmitate would induce insulin resistance in podocytes.
  
  
  METHODS
  Conditionally immortalized human podocytes were cultured for up to 24 h with 375-750 muM palmitate. Functional effects on glucose uptake and ceramide production were measured. Gene expression was investigated using a focused gene array, and protein signalling and trafficking were studied with Western blotting and immunofluorescence.
  
  
  RESULTS
  We found that palmitate blocked insulin-stimulated glucose uptake in human podocytes. This was associated with increased ceramide production, and use of the ceramide inhibitors myriocin and fumonisin B1 partially recovered the insulin sensitivity. At the level of transcription, palmitate downregulated genes associated with several pathways involved in insulin signalling. At the protein level, phosphorylation of the insulin receptor, IRS1 and PKB was reduced and there was impaired translocation of GLUT4 to the cell surface.
  
  
  CONCLUSIONS
  This is the first study to demonstrate a direct effect of saturated fatty acids on podocyte function. These findings may represent a novel link between systemic insulin resistance and the development of nephropathy.
authors: Academic and Children's, Renal Unit, Paul O'Gorman Lifeline Centre, University of Bristol, Southmead Hospital, Bristol BS10, UK.
authors: Rachel
authors: R
authors: Lennon
authors: Deborah
authors: D
authors: Pons
authors: Matthew A
authors: MA
authors: Sabin
authors: Christina
authors: C
authors: Wei
authors: Julian P
authors: JP
authors: Shield
authors: Richard J
authors: RJ
authors: Coward
authors: Jeremy M
authors: JM
authors: Tavaré
authors: Peter W
authors: PW
authors: Mathieson
authors: Moin A
authors: MA
authors: Saleem
authors: Gavin I
authors: GI
authors: Welsh
mesh_terms: D000255:Adenosine Triphosphate / Q000032:analysis; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002518:Ceramides / Q000096:biosynthesis; D003928:Diabetic Nephropathies / Q000209:etiology*; D005227:Fatty Acids / Q000494:pharmacology*; D020869:Gene Expression Profiling; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D006801:Humans; D007333:Insulin Resistance; D019308:Palmitic Acid / Q000494:pharmacology; D050199:Podocytes / Q000187:drug effects* / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D002518:Ceramides; D005227:Fatty Acids; D051275:Glucose Transporter Type 4; C495692:SLC2A4 protein, human; D019308:Palmitic Acid; D000255:Adenosine Triphosphate; D005947:Glucose