Like PPARγ, PPARδ also appears to be important in oligodendrocyte lineage cell regulation. It is expressed by OPCs in the adult CNS (Figure 2) and, after SCI, the number of PPARδ-expressing OPCs increases along the lesion border where robust oligodendrocyte genesis occurs (Tripathi and McTigue, 2007; Almad and McTigue, 2010). In EAE, PPARδ promotes oligodendrocyte differentiation by limiting the effects of BMPs (bone morphogenetic proteins). Oligodendrocytes express BMPs and their receptors, and during CNS development, BMPs restrict OPC maturation (Gross et al., 1996; Hardy and Friedrich, 1996). PPARδ activation counteracts BMP signaling by increasing the expression of noggin, a BMP antagonist produced by astrocytes. In the presence of noggin, BMPs are inhibited and the number of myelin-producing oligodendrocytes is increased (Simonini et al., 2010). Thus, these findings further indicate a direct role for PPARδ in the regulation of oligodendrocytes.
