HSPA5 and Parkinson disease: Elevated levels of ROS and calcium homeostasis imbalance during episodes of PD lead to changes in proteins containing α-synuclein, which stimulate the activation of UPR-regulated proteins, such as PERK kinase, inositol 1α-dependent enzyme (Ire1α), transcription factor 6α (ATF6α), and GRP78/Bip (Wang et al., 2009; Gorbatyuk et al., 2012; Sen, 2015).