Moreover, both in AD and PD, oligodendrocytes exhibit a reactive immunocompetent phenotype characterized by the upregulation of complement component C4b in response to amyloid beta and alpha-synuclein exposure, and accompanied by the expression of serine peptidase inhibitor, clade A, member 3N (Serpina3n), and proteasome 20S subunit beta 9 (PSMB9), respectively [494,564]. Here, PSMB9 is linked to Parkinson disease.