The role of circadian rhythm in the regulation of cellular protein profiles in the brain.

Background: Circadian rhythm plays a significant role in the regulation of almost all kinds of physiological processes. In addition, it may also have a direct or indirect effect on the neurodegenerative processes, including Alzheimer's disease, Parkinson's disease, and ischemic stroke. Therefore, the identification of circadian rhythm-related proteins is crucial to be able to understand the molecular mechanism of the circadian rhythm and to define new therapeutic target for the treatment of degenerative disorders.

Methods: To identify the light and dark regulated proteins, 8-12 weeks, male Balb/C mice were used at two different time points (morning (Zeitgeber time-0 (ZT0)) and midnight (ZT18)) under physiological conditions. Therefore, brain tissues were analyzed via liquid chromatography tandem mass spectrometry.

Results: A total of 1621 different proteins were identified between ZT0 and ZT18 mice. Among these proteins, 23 proteins were differentially expressed (p < 0.05 and fold change 1.4) in ZT18 mice, 11 upregulated (AKAP10, ALDOC, BLK, NCALD, NFL, PDE10A, PICAL, PSMB6, RL10, SH3L3, and SYNJ1), and 12 downregulated (AT2A2, AT2B1, CPNE5, KAP3, MAON, NPM, PI51C, PPR1B, SAM50, TOM70, TY3H, and VAPA) as compared with ZT0 mice.

Discussion: Taken together, here we identified circadian rhythm-related proteins, and our further analysis revealed that these proteins play significant roles in molecular function, membrane trafficking, biogenesis, cellular process, metabolic process, and neurodegenerative disorders such as Parkinson's disease.