TLR4 and multiple system atrophy: Furthermore, several signaling molecules associated with activated microglia including toll-like receptor 4 (TLR4) upregulation, NFκB nuclear translocation (Stefanova et al. 2007), and myeloperoxidase (MPO) upregulation (Stefanova et al. 2012) have been suggested to contribute to the pathogenesis of MSA and have been further addressed in experimental models.