Korea Basic Science Institute

Alzheimer's disease (AD) is characterized by aggregation and deposition of the amyloid-beta (Aβ) protein in patients' brains, with aging contributing through oxidative stress and neuroinflammation. Sleep disturbances are common in patients with AD and exacerbate cognitive impairment. However, it remains unclear how aggregation of specific Aβ species in distinct brain regions contributes to sleep dysfunction. To address this, we characterized amyloid fibrils formed by Aβ1-40 (Aβ40) and Aβ1-42 (Aβ42) by assessing their structural and surface properties using fluorescence, CD, and NMR spectroscopy. Their morphology was also visualized using TEM and AFM. These analyses revealed that Aβ42 aggregates faster than Aβ40 and forms amyloid fibrils with distinct structural, surface, and morphological properties. To investigate their effects in vivo, we bilaterally injected Aβ40 and Aβ42 fibrils into the hippocampus of wild-type mice and recorded the electroencephalogram and electromyogram under freely moving conditions. Aβ42 amyloid fibrils significantly disrupted sleep architecture, particularly REM sleep, and altered oscillations, accompanied by neuronal loss. In contrast, Aβ40 amyloid fibrils mainly affected cortical activity with minimal neuronal loss and caused comparatively modest changes in sleep. These findings demonstrate that a single administration of Aβ amyloid fibril is sufficient to alter sleep/wakefulness state and cortical oscillations. The observed effects differ depending on the type of Aβ administered, suggesting that the physicochemical properties of the fibrils are closely linked to their capacity to induce sleep impairment. These findings shed light on AD-associated sleep disorders, which are differentially affected by the distinct properties of Aβ40 and Aβ42 aggregates.

Jeju Island, South Korea, is a volcanic island where the population depends entirely on groundwater for freshwater supply, and the island exhibits unique hydrogeological characteristics. This study examines groundwater recharge processes by analyzing the stable isotopes of oxygen (δ¹⁸O) and hydrogen (δ²H) in monthly precipitation and groundwater. Precipitation isotopes showed clear seasonal variability, characterized by a strong summer monsoon effect. Northern-slope precipitation was slightly more depleted in ¹ ⁸O and has lower d -excess values compared to other slopes. Groundwater in this area exhibited similarly depleted isotopic signatures, suggesting that high-elevation recharge moves downgradient along preferential flow pathways toward coastal areas. Mixing analysis indicates that high-elevation summer rainfall is the dominant source of groundwater recharge. These findings significantly enhance the understanding of the linkages between precipitation patterns and groundwater recharge dynamics on the island. • Summer rainfall is the primary source of recharge. • Isotope mixing analysis indicates high-altitude summer rainfall as the main source. • Low δ¹ ⁸O in northern-slope indicates rapid flow of high-altitude recharge. • Long-term isotope monitoring is vital for sustainable water management.