Science

Molecular link found between sleep and mood

By Natasha Fiera

Have you ever heard the phrase ‘someone’s got out of the wrong side of the bed’? For years it has been believed that there is a link between the duration of sleep and mood. Studies have indicated that even partial sleep deprivation has a significant effect on mood – showing individuals to be more stressed, angry, sad and mentally exhausted when lacking sleep. On a molecular level, recent research has identified several rare genetic mutations on the gene associated with both sleep and mood.

In general, people who often have disruptive sleep patterns are those suffering from mania, depression or seasonal affective disorder (SAD). It is unclear exactly why sleep is altered in these individuals; however, it is clear that the two are correlated.

Sleep can affect mood but mental states also have the ability to affect sleep – such as stress or anxiety. In addition changes in light exposure have been found to influence sufferers of SAD, so it is uncertain whether mood causes poor sleep, poor sleep affects mood or whether there is a third influential factor. According to Michael McCarthy a neurobiologist at the San Diego Veterans’ Affair Medical Centre and the University of California (UC), San Diego states there is “no definitive factor that proves causality or indicates the direction of the relationship.” This is despite the enticing factors associated with sleeping patterns and mood.

A study looked at the genetics of a family suffering from mood disorders (including SAD and advanced sleep phase) and abnormal sleep patterns. This aimed to identify whether a link could be discovered between mood, sleep and the circadian clock. After screening for mutations in the key genes in the family, two rare variants of the PERIOD3 (PER3) gene were identified in the family members who suffered from SAD and abnormal sleep phase. Lead Researcher, Ying-Hui Fu at UC San Francisco stated, “we found a genetic change in people who have both season affective disorder and the morning lark trait.” These mutations were then tested for in the general population by the research team and were identified in less than one per cent of samples – indicating them as extremely rare.

The research team at UC San Francisco genetically modified mice so that they carried the specific PER3 gene mutation. The transgenic mice portrayed abnormal sleeping patterns with regarding their sleep-wake cycles and were less resistant when being handled by the researchers – displaying signs of depression. The circadian clock exists in most living things which makes it possible for organisms to coordinate their biology and behaviour with daily environmental changes in the day-night cycle. Lower levels of a circadian rhythm protein, PER2 were also found in the transgenic mice when compared with the normal, unchanged mice – possibly giving an explanation for the unusual sleeping patterns in the family. This research supports the link between the PER3 mutations, sleep and mood. The research team explored further and looked at mice lacking the PER3 gene. These mice had symptoms of SAD and when the amount of daylight was reduced in the laboratory, the mice portrayed more severe depression.

Both these investigations indicate that the PERIOD3 has a likely role in regulation of the sleep-wake cycle. In particular, this gene has an influence on mood and the relationship between depression and seasonal changes in light availability – reported in the Proceedings of the National Academy of Sciences by the research team.

In order to apply this to the general population, further research will need to be carried out to see how well these results coincide with individuals suffering from mood and sleep disorders. If the results obtained are consistent this could potentially lead to new strategies in the production of new drugs for treating sleep and mood disorders.

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