Prosaposin-derived 18-mer peptide (PS18) reduced neurodegeneration in cellular and animal models of PD by decreasing the expression of the two UPR pathways, PERK/CHOP and ATF6 [54], whereas other proteins and peptides like SH3BP5, carnosine, albumin, or erythropoietin were shown to specifically inhibit JNK activity and thus exert protection against 6-OHDA [55,56,57,58]. Here, MAPK8 is linked to Parkinson disease.