Early metabolic changes in the brain of Alzheimer's disease rats are driven by GLAST+ cells

Glucose metabolic dysfunction is a hallmark of Alzheimer's disease (AD) pathology and is used to diagnose the disease or predict imminent cognitive decline. The main method to measure brain metabolism in vivo is positron emission tomography with 2-Deoxy-2-[¹⁸F]fluoroglucose ([¹⁸F]FDG-PET). The cellular origin of changes in the [¹⁸F]FDG-PET signal in AD is controversial. We addressed this by combining [¹⁸F]FDG-PET with subsequent cell-sorting and γ-counting of [¹⁸F]FDG-accumulation in sorted cell populations. 7-month-old male TgF344-AD rats and wild-type controls (n = 24/group) received sham or ceftriaxone (200 mg/kg) injection prior to [¹⁸F]FDG-PET imaging to increase glutamate uptake and glucose utilisation. The same animals were injected again one week later, and radiolabelled brains were dissected, with hippocampi taken for magnetically-activated cell sorting of radioligand-treated tissues (MACS-RTT). Radioactivity in sorted cell populations was measured to quantify cell-specific [¹⁸F]FDG uptake. Transcriptional analyses of metabolic enzymes/transporters were also performed. Hypometabolism in the frontal association cortex of TgF344-AD rats was identified using [¹⁸F]FDG-PET, whereas hypermetabolism was identified in the hippocampus using MACS-RTT. Hypermetabolism was primarily driven by GLAST+ cells. This was supported by transcriptional analyses which showed alteration to metabolic apparatus, including upregulation of hexokinase 2 and altered expression of glucose/lactate transporters. See Figure 1 for summary.