The results showed that the expression of p-IRE1α, p-JNK, GRP78, p-eIF2α, CHOP as well as cleaved caspase-3 increased significantly in both SNpc (Fig. 10E–L) and striatum (Fig. 11E–L) of PD model mice, implying that the level of ER stress was enhanced and apoptosis was induced in the brains of MPTP-challenged mice. The gene discussed is DDIT3; the disease is Parkinson disease.