Sleep fragmentation impairs cognitive function and exacerbates Alzheimer's disease-related pathology in a mouse model by disrupting mitochondrial biogenesis

A large proportion of Alzheimer's disease (AD) patients suffer from various types of chronic sleep disturbances, including sleep fragmentation (SF). In addition, impaired mitochondrial biogenesis is an important feature of AD, but whether it is altered in sleep disorders has not been fully elucidated. Hence, we aimed to investigate the relationship between SF and mitochondrial biogenesis and the possible impact of SF on AD-related pathology. In this study, thirty-six 9-month-old 3xTgAD model mice and thirty-six 9-month-old wild-type (WT) C57BL/6 J mice were divided into a control group (6 weeks of normal sleep), a SF group (6 weeks of SF) and a SF + recovery sleep group (6 weeks of SF followed by 2 weeks of recovery sleep). Cognitive functions were assessed by behavioural experiments. Mitochondrial structure and function and the activity of a classic mitochondrial biogenesis signalling pathway were investigated using transmission electron microscopy (TEM), reverse transcription quantitative polymerase chain reaction (RT–qPCR), immunofluorescence and Western blotting. Markers of AD-related pathology, including the levels of amyloid β (Aβ) and tau proteins, were assessed by immunofluorescence and Western blotting. The expression of insulin-degrading enzyme (IDE) was assessed by Western blotting. We found that long-term SF impaired the cognitive functions of the mice. In addition, chronic SF reduced the expression of mitochondrial respiratory chain components, the number of mitochondria, the fluorescence intensity of COX-IV, the level of mitochondrial DNA (mtDNA) and the expression of crucial regulators of the AMPK/SIRT-1/PGC-1α signalling pathway in the mouse prefrontal cortex and hippocampus, while recovery sleep could partly abrogate these effects. Moreover, SF reduced the protein level of IDE and increased the Aβ burden and tau hyperphosphorylation. This study demonstrates that chronic SF can negatively regulate the AMPK/SIRT-1/PGC-1α signalling pathway to disrupt mitochondrial biogenesis in the brains of mice, which may subsequently exacerbate AD-related pathology by decreasing the expression of IDE.