XBP1 and optic nerve disorder: In animal model of optic neuropathy (traumatic injury and chronic glaucomatous neurodegeneration) it has been shown that inhibition of the protein kinase RNA-like endoplasmic reticulum kinase (PERK)-eukaryotic initiation factor 2 alpha (eIF2α)-CCAAT/enhancer-binding protein homologous protein (CHOP) pathway and activation of the X-box binding protein 1 (XBP-1) pathway play neuroprotective role in RGCs by preventing ER stress-induced protein misfolding, increasing expression of anti-apoptotic Bcl-2 gene and regulating homeostasis of Ca2+ ions in ER (Hu, 2016; Yang et al., 2016).