Reduction of orexin-expressing neurons and a unique sleep phenotype in the Tg-SwDI mouse model of Alzheimer’s disease

Sleep disturbances are common in Alzheimer's disease (AD) and AD-related dementia (ADRD). We performed a sleep study on Tg-SwDI mice, a cerebral amyloid angiopathy (CAA) model, and age-matched wild-type (WT) control mice. The results showed that at 12 months of age, the hemizygous Tg-SwDI mice spent significantly more time in non-rapid eye movement (NREM) sleep (44.6 ± 2.4% in Tg-SwDI versus 35.9 ± 2.5% in WT) and had a much shorter average length of wake bout during the dark (active) phase (148.5 ± 8.7 s in the Tg-SwDI versus 203.6 ± 13.0 s in WT). Histological analysis revealed stark decreases of orexin immunoreactive (orexin-IR) neuron number and soma size in these Tg-SwDI mice (cell number: 2187 ± 97.1 in Tg-SwDI versus 3318 ± 137.9 in WT. soma size: 109.1 ± 8.1 μm² in Tg-SwDI versus 160.4 ± 6.6 μm² in WT), while the number and size of melanin-concentrating hormone (MCH) immunoreactive (MCH-IR) neurons remained unchanged (cell number: 4256 ± 273.3 in Tg-SwDI versus 4494 ± 326.8 in WT. soma size: 220.1 ± 13.6 μm² in Tg-SwDI versus 202.0 ± 7.8 μm² in WT). The apoptotic cell death marker cleaved caspase-3 immunoreactive (Caspase-3-IR) percentage in orexin-IR neurons was significantly higher in Tg-SwDI mice than in WT controls. This selective loss of orexin-IR neurons could be associated with the abnormal sleep phenotype in these Tg-SwDI mice. Further studies are needed to determine the cause of the selective death of orexin-IR cells and relevant effects on cognition impairments in this mouse model of microvascular amyloidosis.