Abstract
The peroxisome proliferator-activated receptors (PPARs) represent pharmacological target molecules to improve insulin resistance in type 2 diabetes mellitus. Here we assessed a functional connection between pharmacological activation of PPAR and vascular endothelial growth factor (VEGF) expression in keratinocytes and during diabetes-impaired acute skin repair in obese/obese (ob/ob) mice. PPARβ/δ agonist 4-[3-[4-acetyl-3-hydroxy-2-propylphenoxy)propoxy]phenoxy]acetic acid (L165,041) and PPARγ agonists ciglitazone and troglitazone, but not rosiglitazone, potently induced VEGF mRNA and protein expression from cultured keratinocytes. Inhibitor studies revealed a strong functional dependence of troglitazone- and L165,041-induced VEGF expression on p38 and p42/44 mitogen-activated protein kinase (MAPK) activation in keratinocytes. Rosiglitazone also induced activation of p38 MAPK but failed to mediate the activation of p42/44 MAPK in the cells. Functional ablation of PPARβ/δ and PPARγ from keratinocytes by small interfering RNA did not abrogate L165,041- and troglitazone-induced VEGF biosynthesis and suggested VEGF induction as a pleiotropic, PPAR-independent effect of both drugs in the cells. In accordance with the in vitro situation, we found activated p38 MAPK in wound keratinocytes from acute wounds of rosiglitazone- and troglitazone-treated diabetic obese/obese mice, whereas keratinocyte-specific VEGF protein signals were only prominent upon troglitazone treatment. In summary, our data from cell culture and wound healing experiments suggested p38 MAPK activation as a side effect of thiazolidinediones; however, only troglitazone, but not rosiglitazone, seemed to translate p38 MAPK activation into a PPARγ-independent induction of VEGF from keratinocytes.
Footnotes
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This work was supported by the Deutsche Forschungsgemeinschaft (SFB 553, grant FR 1540/1-2, GRK 1172).
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D.S. and O.S. contributed equally to this work.
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ABBREVIATIONS: TZD, thiazolidinedione; PPAR, peroxisome proliferator-activated receptor; VEGF, vascular endothelial growth factor; L165,041, 4-[3-[4-acetyl-3-hydroxy-2-propylphenoxy)propoxy]phenoxy]acetic acid; MAPK, mitogen-activated protein kinase; siRNA, small interfering RNA; TNF, tumor necrosis factor; IL, interleukin; nt, nucleotide; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; EGF, epidermal growth factor; WTM, wortmannin; Act D, actinomycin D; LPS, lipopolysaccharide; IFN-γ, interferon-γ; ELISA, enzyme-linked immunosorbent assay; ANOVA, analysis of variance; PI3K, phosphoinositide 3-kinase; wm, wound margin; iw, inner wound; WY14643, 4-chloro-6-(2,3-xylidino)-2-pyrimidinyl-)thioacetic acid; U0126, 1,4-diamino-2,3-dicyano-1,4-bis(methylthio)butadiene; SB203580, 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole; GW9662, 2-chloro-5-nitrobenzanilide.
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↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
- Received June 2, 2008.
- Accepted July 1, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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