Localization of PPARδ in murine central nervous system: expression in oligodendrocytes and neurons

The peroxisome proliferator-activated receptors (PPARs), PPARδ, PPARγ and PPARα, comprise a subclass of the supergene family of nuclear receptors. As such they are ligand-regulated transcription factors whose major effects are mediated by altering expression of target genes. PPARδ has been shown to be ubiquitously expressed in mammals. However, its primary biological role(s) has yet to be defined. Several recent studies have demonstrated that PPARδ is the most highly expressed PPAR isoform in the central nervous system, but ambiguity still exists as to the specific brain sub-regions and cells in which it is expressed. Here, utilizing novel, isoform-selective PPARδ riboprobes and an anti-peptide antibody, we performed a series of in situ hybridization and immunolocalization studies to determine the distribution of PPARδ in the central nervous system (CNS) of mice. We found that PPARδ mRNA and protein is expressed throughout the brain, with particularly high levels in the entorhinal cortex, hypothalamus and hippocampus, and lower levels in the corpus callosum and caudate putamen. At the cellular level, PPARδ mRNA and protein were found to be expressed in oligodendrocytes and neurons but not astrocytes. Such results suggest a role for PPARδ in both myelination and neuronal functioning within the CNS.