Endoplasmic Reticulum Stress in Neurodegenerative Diseases

Endoplasmic reticulum (ER) stress is a detrimental cellular phenomenon in the cells and is activated by the accumulation of unfolded or misfolded proteins in the ER. The unfolded protein accumulation activates the unfolded protein response (UPR), an adaptive mechanism designed to mitigate cellular stress by enhancing the ER's protein-folding capacity and protecting cells from apoptotic stimuli in neuroinflammation and neurodegenerative diseases. However, chronic ER stress and prolonged activation of the UPR can have adverse effects, including the activation of pro-apoptotic and inflammatory signaling pathways, which contribute to the development and progression of neurodegenerative disorders. Neurodegenerative diseases are complex and devastating conditions with underlying pathogenesis that are not fully understood. Genetic mutations leading to the accumulation of misfolded or phosphorylated tau proteins and amyloid-beta in the ER can induce ER stress, resulting in neuroinflammation and neuronal death. Several studies have reported the involvement of increased ER stress and UPR signaling proteins in the pathogenesis and progression of neurodegenerative diseases. Thus, inhibiting ER stress and neuroinflammation and targeting their associated signaling pathways represent a significant area of research interest. This review discusses the critical signaling molecules involved in ER stress, their mechanisms in the progression of neurodegenerative diseases, and the latest developments in the available ER stress inhibitors. Despite the extensive development of ER stress inhibitors over the years, only a limited number have been approved as pharmaceutical drugs. There remains a critical need for effective ER stress inhibitors to provide efficient treatments for neurodegenerative diseases, including Alzheimer's disease.