ERN1 and Alzheimer disease: Tanshinone IIA prevents AD by preventing the abnormal expression of glucose regulated protein 78 (GRP78), eukaryotic initiation factor 2-alpha (eIF2α), inositol-requiring enzyme 1α (IRE1α) and activating transcription factor 6 (ATF6) to prevent endoplasmic reticulum (ER) stress, which would induce apoptosis and eventually AD through the CCAAT/enhancer-binding protein homologous protein (CHOP) and c-Jun N-terminal kinase (JNK) pathways, which are also hindered by tanshinone IIA (He et al., 2020).