The molecular phenotype of microglia or macrophages affects the ability of these cells to phagocytose debris. For instance, activation of PPARδ in macrophages promotes clearance of apoptotic cells (Mukundan et al., 2009). This occurs through increased expression of opsonins (e.g. complement C1q) by macrophages, which increases phagocytosis of apoptotic cells (Mukundan et al., 2009). Similarly, PPARγ activation in microglia promotes phagocytosis by up-regulating the scavenger receptor CD36 (Yamanaka et al., 2012). Considering traumatic CNS injuries produce large amounts of myelin and cell debris, PPAR-induced M2 polarization of macrophages and microglia may be beneficial by promoting removal of debris in addition to the other mechanisms mentioned above.
