title: In vitro responsiveness of human muscle cell peroxisome proliferator-activated receptor δ reflects donors' insulin sensitivity in vivo.
abstract: BACKGROUND
  Peroxisome proliferator-activated receptor δ (PPARδ) activation enhances muscular fatty acid oxidation and oxidative phosphorylation, and muscle's oxidative capacity positively associates with whole-body insulin sensitivity. Therefore, we asked here whether human muscle cell PPARD expression is a determinant of donors' insulin sensitivity.
  
  
  METHODS
  Skeletal muscle cells derived from 38 nondiabetic donors were differentiated in vitro to myotubes, and gene (mRNA) expression was quantified by real-time RT-PCR. Donors' insulin sensitivity was calculated from plasma insulin and glucose levels during oral glucose tolerance test (OGTT) and hyperinsulinemic-euglycemic clamp.
  
  
  RESULTS
  Basal myotube PPARD expression was closely related to the expression of its target genes PDK4 and ANGPTL4 (P = 0·0312 and P = 0·0003, respectively). Basal PPARD, PDK4 and ANGPTL4 expression levels were not associated with donors' insulin sensitivity (P > 0·2, all). Treatment of myotubes with a selective high-affinity PPARδ agonist (GW501516) did not change mean PPARD, but enhanced mean PDK4 and ANGPTL4 expression 13- and 16-fold, respectively (P < 0·0001, both). The individual PDK4 and ANGPTL4 expression levels reached upon GW501516 treatment were associated with donors' insulin sensitivity neither (P > 0·2, both). However, GW501516-mediated fold increments in PDK4 and ANGPTL4 expression, reflecting PPARδ responsiveness, were positively associated with donors' insulin sensitivity derived from OGTT (P = 0·0182 and P = 0·0231, respectively) and hyperinsulinemic-euglycemic clamp (P = 0·0046 and P = 0·0258, respectively).
  
  
  CONCLUSIONS
  Using a highly selective pharmacological tool, we show here that the individual responsiveness of human muscle cell PPARδ, rather than the absolute PPARD expression level, represents a major determinant of insulin sensitivity.
authors: Division of Endocrinology, Diabetology, Angiology, Nephrology, and Clinical Chemistry, Department of Internal Medicine, Member of the German Center for Diabetes Research (DZD e.V.), Eberhard Karls University Tübingen, Tübingen, Germany.
authors: Anna-Maria
authors: AM
authors: Ordelheide
authors: Martin
authors: M
authors: Heni
authors: Claus
authors: C
authors: Thamer
authors: Fausto
authors: F
authors: Machicao
authors: Andreas
authors: A
authors: Fritsche
authors: Norbert
authors: N
authors: Stefan
authors: Hans-Ulrich
authors: HU
authors: Häring
authors: Harald
authors: H
authors: Staiger