Athymic balb c nu nu mice

All animal experiments were approved by the Institutional Animal Care and Use Committee of the Korea Institute of Radiological and Medical Sciences (Approval no. KIRAMS2018-0079). Athymic BALB/c nu/nu mice were purchased from Orient Bio Inc. (Seoul, Korea). The mice were provided standard food and tap water under specific pathogen-free conditions. Prior to injecting the U373 cells into the mouse brain, the cells were treated with GDF15 by adding rhGDF15 to the culture medium for 14 days. The culture medium was changed every three days with fresh rhGDF15-containing medium. For injecting U373 cells (1 × 10⁵/3 µL), the head of each mouse was fixed on a stereotactic device. The cells were injected into the left frontal cortex using a microinjector. On day 10 post-injection, mouse brain samples were harvested, fixed in 4% paraformaldehyde solution, embedded in paraffin, and cut into 5 µm-thick sections using a microtome (Leica, Nussloch, Germany).

All animal experiments were conducted in accordance with protocols approved by the Institutional Animal Care and Use Committee (IACUC) of the Korea Institute of Radiological and Medical Sciences (KIRAMS2018-0079). Athymic BALB/c nu/nu mice were purchased from Orient Bio Inc. (Seoul, Korea), housed under specific pathogen-free conditions, and supplied with standard rodent feed and tap water ad libitum. The animals' heads were fixed in a stereotactic frame using non-perforating bars, a midline incision was made on the scalp, and a burr hole was drilled 0.1 mm posterior and 2 mm left of the bregma. An 83NS cell suspension (1 × 10⁴ cells) was injected into the left frontal cortex at the coordinate bregma using a stereotactic frame and microinjector. The average tumor size was determined to be 5 mm³ by MRI. Mice were randomly divided into two subgroups: a control group and an irradiated group. Radiation (a single dose of 10 Gy) was administered to the entire head under anesthesia (30 mg/kg Zoletil and 10 mg/kg Rompun) using an X-Rad320 (Precision X-Ray, East Haven, CT, USA; filter: 2 mm AI; distance: 42 cm; 260 kVp, 10 mA, 10Gy/5 min).