The role of melatonin in targeting cell signaling pathways in neurodegeneration

The endoplasmic-reticulum (ER) stress response constitutes a cellular process that is triggered by a variety of conditions that disturb folding of proteins in the ER. Eukaryotic cells have developed an evolutionarily conserved adaptive mechanism, the unfolded protein response (UPR), which aims to clear unfolded proteins and restore ER homeostasis. In cases where ER stress cannot be reversed, cellular functions deteriorate, often leading to cell death. Accumulating evidence implicates ER stress-induced cellular dysfunction and cell death as major contributors to many diseases, making modulators of ER stress pathways potentially attractive targets for therapeutics discovery. Here, we summarize recent advances in understanding the diversity of molecular mechanisms that govern ER stress signaling in health and disease. This article is part of a Special Section entitled: Cell Death Pathways. © 2013.

Autophagy and apoptosis are basic physiologic processes contributing to the maintenance of cellular homeostasis. Autophagy encompasses pathways that target long-lived cytosolic proteins and damaged organelles. It involves a sequential set of events including double membrane formation, elongation, vesicle maturation and finally delivery of the targeted materials to the lysosome. Apoptotic cell death is best described through its morphology. It is characterized by cell rounding, membrane blebbing, cytoskeletal collapse, cytoplasmic condensation, and fragmentation, nuclear pyknosis, chromatin condensation/fragmentation, and formation of membrane-enveloped apoptotic bodies, that are rapidly phagocytosed by macrophages or neighboring cells. Neurodegenerative disorders are becoming increasingly prevalent, especially in the Western societies, with larger percentage of members living to an older age. They have to be seen not only as a health problem, but since they are care-intensive, they also carry a significant economic burden. Deregulation of autophagy plays a pivotal role in the etiology and/or progress of many of these diseases. Herein, we briefly review the latest findings that indicate the involvement of autophagy in neurodegenerative diseases. We provide a brief introduction to autophagy and apoptosis pathways focusing on the role of mitochondria and lysosomes. We then briefly highlight pathophysiology of common neurodegenerative disorders like Alzheimer's diseases, Parkinson's disease, Huntington's disease and Amyotrophic lateral sclerosis. Then, we describe functions of autophagy and apoptosis in brain homeostasis, especially in the context of the aforementioned disorders. Finally, we discuss different ways that autophagy and apoptosis modulation may be employed for therapeutic intervention during the maintenance of neurodegenerative disorders. Copyright © 2013 Elsevier Ltd. All rights reserved.

Sirtuins are nicotinamide adenine dinucleotide (NAD+)-dependent deacylases that have traditionally been linked with calorie restriction and aging in mammals. These proteins also play an important role in maintaining neuronal health during aging. During neuronal development, the SIR2 ortholog SIRT1 is structurally important, promoting axonal elongation, neurite outgrowth, and dendritic branching. This sirtuin also plays a role in memory formation by modulating synaptic plasticity. Hypothalamic functions that affect feeding behavior, endocrine function, and circadian rhythmicity are all regulated by SIRT1. Finally, SIRT1 plays protective roles in several neurodegenerative diseases including Alzheimer's, Parkinson's, and motor neuron diseases, which may relate to its functions in metabolism, stress resistance, and genomic stability. Drugs that activate SIRT1 may offer a promising approach to treat these disorders. Copyright © 2014 Elsevier Inc. All rights reserved.