Sleep loss changes microRNA levels in the brain: a possible mechanism for state-dependent translational regulation.

MicroRNAs (miRNAs) are small ( approximately 22 nucleotides) non-coding RNA strands that base pair with mRNA to degrade it or inhibit its translation. Because sleep and sleep loss induce changes in many mRNA species, we hypothesized that sleep loss would also affect miRNA levels in the brain. Rats were sleep-deprived for 8h then decapitated; hippocampus, prefrontal and somatosensory cortices and hypothalamus tissues were harvested and frozen in liquid nitrogen. miRNA was extracted and then characterized using microarrays. Several let-7 miRNA microarray results using hippocampus and prefrontal cortex samples were verified by PCR. From the array data it was determined that about 50 miRNA species were affected by sleep loss. For example, in the hippocampus of sleep-deprived rats, miRNA expression increased compared to cage control samples. In contrast, the majority of miRNA species in the somatosensory and prefrontal cortices decreased, while in the hypothalamus miRNA species were both up- and down-regulated after sleep deprivation. The number of miRNA species affected by sleep loss, their differential expression in separate brain structures and their predicted targets suggest that they have a role in site-specific sleep mechanisms. Current results are, to our knowledge, the first demonstration of the homeostatic process, sleep, altering brain miRNA levels.