*2.1. Animal Experiments and Ethical Approval*

Forty male Fischer 344 rats were randomly divided into four groups according to age: very young (VYG, 1 month old; n = 10), young (YG, 4 months old; n = 10), middle-aged (MG, 10 months old; n = 10), and old (OG, 20 months old; n = 10). All rats were housed (two per cage) under standardized conditions (20 ± 2 ◦C; 12 h light:dark cycle). Standard laboratory chow (LabDiet 5L79, Orient Bio, Gyeonggi-Do, Korea) and water were provided ad libitum. The experimental protocol was approved by the Institutional Animal Care and Use Committee of the Kyung Hee University (approval number: KHUASP [SE]-17-089), and was performed in accordance with the animal care guidelines of the ethics committee.
