Circadian clock –dependent regulation of physiological processes is required for homeostasis maintenance. Dysregulated circadian rhythms contribute to many neurodegenerative diseases. Abnormal protein aggregates and compromised antioxidant function are hallmarks of neurodegenerative diseases which are influenced by clock genes and proteins. Alterations in sleep patterns as typical characteristics of neurodegeneration and age-related diseases are related to disrupted gene expression in suprachiasmatic nucleus (SCN) of hypothalamus and peripheral clocks. Hippocampus-related learning and memory are under control of circadian rhythm which is adjusted by the time of day through modulatory effects of clock genes on rhythmic expression of proteins and neurotransmitters. Disturbances in circadian processes such as sleep/awake cycle, hormone secretion, body temperature, metabolic status manifested as symptoms of neurodegenerative diseases. In Alzheimer’s disease phase oscillation of circadian genes is dysregulated, also vasopressin and VIP secretory neurons are degenerated. In Parkinson’s disease circadian oscillation of melatonin release and Bmal1 expression in peripheral blood monocytes exhibit out of phase rhythmicity. In animal models of Huntington’s disease impaired neural network rather than intrinsic clock genes and reduced expression of VIP neurotransmitter within in SCN cells contribute to behavioral dysfunction. In addition, in temporal lobe epilepsy reprogrammed hippocampal genes and imbalanced inhibition and exhibition lead to seizure onset . It has been observed that clock protein of PER2 decreased in SCN of tauopathy animal model accompanied with different level of phosphorylated tau in hippocampus cause impaired learning and memory. Likewise, cell cycle events during neurogenesis are under control of circadian proteins PERIOD and BMAL1. Age-related loss of rhytmic expression of clock genes influences on proliferation of neural progenitor cells. Here we review bidirectional interactions of neurodegenerative diseases and dysregulation of circadian clock.

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