In Vivo Assessment of Astrocyte Reactivity in Patients with Progressive Supranuclear Palsy

Objective Although astrocytic pathology is a pathological hallmark of progressive supranuclear palsy (PSP), its pathophysiological role remains unclear. This study aimed to assess astrocyte reactivity in vivo in patients with PSP. Furthermore, we investigated alterations in brain lactate levels and their relationship with astrocyte reactivity. Methods We included 30 patients with PSP‐Richardson syndrome and 30 healthy controls; in patients, tau deposition was confirmed through 18 F‐florzolotau positron emission tomography. Myo‐inositol, an astroglial marker, and lactate were quantified in the anterior cingulate cortex through magnetic resonance spectroscopy. We measured plasma biomarkers, including glial fibrillary acidic protein as another astrocytic marker. The anterior cingulate cortex was histologically assessed in postmortem samples of another 3 patients with PSP with comparable disease durations. Results The levels of myo‐inositol and plasma glial fibrillary acidic protein were significantly higher in patients than those in healthy controls ( p < 0.05); these increases were significantly associated with PSP rating scale and cognitive function scores ( p < 0.05). The lactate level was high in patients, and correlated significantly with high myo‐inositol levels. Histological analysis of the anterior cingulate cortex in patients revealed reactive astrocytes, despite mild tau deposition, and no marked synaptic loss. Interpretation We discovered high levels of astrocyte biomarkers in patients with PSP, suggesting astrocyte reactivity. The association between myo‐inositol and lactate levels suggests a link between reactive astrocytes and brain energy metabolism changes. Our results indicate that astrocyte reactivity in the anterior cingulate cortex precedes pronounced tau pathology and neurodegenerative processes in that region, and affects brain function in PSP. ANN NEUROL 2024;96:247–261