Also, gene silencing studies revealed that genetic ablation of ATF4 has contradictory effects in different models of PD: in PC12 cells exposed to 6-OHDA or MPP+ [35], it enhanced cell death, whereas a separate study has demonstrated that ATF4-deficient dopaminergic neurons are resistant to cell death induced by 6-OHDA, MPP+, and α-synuclein preformed fibrils [31]. Here, SNCA is linked to Parkinson disease.