Our biological rhythms are tuned to the day-night cycles, light-dark cycles in which we live because the cells of our body have an in-built timekeeping capacity. Each cell has an internal clock, driven by the cyclic expression of certain genes, which in turn is kept in time by a master clock in the brain. A group led by Jun Li in the University of Michigan Medical School has recently found that this internal clock has fallen out of sync with the solar day in patients with depression.
The team, who published their results in the Proceedings of the National Academy of Sciences, analysed the patterns of gene expression in six regions of the brain from 55 individuals who did not suffer depression and 34 patients who did.
The team analysed the genes that were active at the time of death of the non-depressed individuals and looked at those whose activity varied throughout the day. They found that people who died at a similar time of day had very similar patterns of gene expression, whereas people who died at opposite times of the day had very different ones. Their statistical analysis was so powerful that the pattern of gene expression could predict the time of death of those individuals for which it was not known.
This was not the case for people who did suffer depression: the cyclic patterns in gene expression seen in the controls were disrupted, and more importantly, they found a shift in timing in comparison to the controls. Importantly, this disruption could not be attributed to patients’s medication.
These findings now raise the challenge of identifying why the internal clock is disrupted in patients with depression.
Written by Ana I. Leal Cervantes.