Altered PPARc expression and activation after transient focal ischemia in rats N. A. Victor, 1 * E. W. Wanderi, 1 * J. Gamboa, 1 X. Zhao, 2 J. Aronowski, 2 K. Deininger 1 , W.D. Lust, 3 G. E. Landreth 1,4 and S. Sundararajan 1,4 1 Department of Neurology, Case Western Reserve University, 11100 Euclid Ave., Cleveland, Ohio 44106, USA 2 Department of Neurology, University of Texas-Houston, Houston, TX, USA 3 Department of Neurosurgery, Case Western Reserve University, Cleveland, Ohio, USA 4 Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio, USA Keywords: inflammation, neuroprotection, nuclear receptors, stroke Abstract Stroke is a devastating disease with limited treatment options. Recently, we found that the peroxisome proliferator-activated receptor- c (PPARc) agonists troglitazone and pioglitazone reduce injury and inflammation in a rat model of transient cerebral ischemia. The mechanism of this protection is unclear, as these agents can act through PPAR-c activation or through PPAR-c-independent mechanisms. Therefore, we examined PPAR-c expression, DNA binding and transcriptional activity following stroke. In addition, we used a PPAR-c antagonist, T0070907, to determine the role of PPAR-c during ischemia. Using immunohistochemical techniques and real-time PCR, we found low levels of PPAR-c mRNA and PPAR-c immunoreactivity in nonischemic brain; however, PPAR-c expression dramatically increased in ischemic neurons, peaking 24 h following middle cerebral artery occlusion. Interestingly, we found that in both vehicle- and agonist-treated brains, DNA binding was reduced in the ischemic hemisphere relative to the contralateral hemisphere. Expression of a PPAR-c target gene, lipoprotein lipase, was also reduced in ischemic relative to nonischemic brain. Both DNA binding and lipoprotein lipase expression were increased by the addition of the PPAR-c agonist rosiglitazone. Finally, we found that rosiglitazone-mediated protection after stroke was reversed by the PPAR-c antagonist T0070907. Interestingly, infarction size was also increased by T0070907 in the absence of PPAR-c agonist, suggesting that endogenous PPAR-c ligands may mitigate the effects of cerebral ischemia. Introduction Stroke is the third leading cause of death and the leading cause of disability in the United States. Unfortunately, development of effective therapies is limited by the rapid development of irreversible injury following ischemia. Recently we, along with others, found that thiazolidinediones (TZDs), a class of drugs prescribed to treat a major risk factor for stroke, type 2 diabetes, reduce infarction size and improve functional recovery from stroke in rats (Shimazu et al., 2005; Sundararajan et al., 2005; Zhao et al., 2005; Luo et al., 2006). Improvement is associated with reduced inflammation and this is a probable mechanism of protection (Sundararajan et al., 2005; Zhao et al., 2005; Luo et al., 2006). Improvement is seen both with pretreatment and when TZDs are given after middle cerebral artery occlusion (MCAO) onset (Sundararajan et al., 2005; Luo et al., 2006). Similar benefits of TZD treatment have been found in models of other central nervous system diseases including Alzheimer’s disease (Combs et al., 2000; Heneka et al., 2005; Inestrosa et al., 2005), experimental autoimmune encephalitis (Niino et al., 2001; Diab et al., 2002; Feinstein et al., 2002; Natarajan & Bright, 2002), Parkinson’s disease (Breidert et al., 2002) and amyotrophic lateral sclerosis (Nishijima et al., 2001; Kiaei et al., 2005). TZDs are under investigation for use in a variety of diseases, including as a secondary preventative agent in stroke for nondiabetic insulin-resistant patients. These drugs are particularly promising as patients who take them daily would benefit from their neuroprotective actions at the onset of ischemia. TZDs, including troglitazone, pioglitazone and rosiglitazone, are agonists for peroxisome proliferator-activated receptor (PPAR)c,a ligand-activated transcription factor best characterized in adipocytes, where it regulates lipid metabolism and reduces insulin resistance. Several endogenous PPARc ligands have been described, including fatty acids and eicosanoid derivatives (Berger & Moller, 2002). PPARs form heterodimers with retinoid X receptors which, in the inactive state, bind corepressor molecules. When agonist binding occurs, the corepressor is released and coactivator proteins are bound. This complex then binds PPAR response elements (PPREs) in the promotor region of its target genes and acts to regulate gene expression (Berger & Moller, 2002). In addition, PPARc agonists inhibit gene expression independently of PPRE binding through receptor-dependent trans- repression (Daynes & Jones, 2002). Effects on inflammation are due, in part, to PPARc’s ability to antagonize three important regulators of inflammatory gene expression, the transcription factors activator protein-1, Stat 1 and nuclear factor-jB (NFjB; Ricote et al., 1998b). It has also been proposed that PPARc agonists may modulate inflammatory gene expression through PPARc-independent mecha- nisms and studies of embryonic stem cells possessing a PPARc-null mutation support this concept (Chawla et al., 2001; Moore et al., 2001). Correspondence: Dr Sophia Sundararajan, 1 Department of Neurology, as above. E-mail: sophia.sundararajan@case.edu *N.A.V. and E.W.W. contributed equally to this study. Received 7 February 2006, revised 22 May 2006, accepted 15 June 2006 European Journal of Neuroscience, Vol. 24, pp. 1653–1663, 2006 doi:10.1111/j.1460-9568.2006.05037.x ª The Authors (2006). Journal Compilation ª Federation of European Neuroscience Societies and Blackwell Publishing Ltd