Sustained AMPAR expression in CA3 neurons may mediate neuroprotection following FLASH-RT

To elucidate the early mechanisms underlying the long-term neuroprotective effect of FLASH-RT in the normal brain, spatial transcriptomics (Nanostring) were performed after whole-brain irradiation of C57BL/6J mice with either 1 or 3 fractions of 10 Gy at 5.6 × 106 Gy/s (1 pulse-FLASH) or at conventional dose-rate 0.1 Gy/s. FLASH-RT induced a distinct transcriptomic signature in the cornu ammonis region 3 (CA3) and dentate gyrus (DG) neurons, with upregulation of genes encoding glutamate receptors involved in calcium signaling, long-term potentiation, and mitochondrial OXPHOS.

Early transcriptional upregulation of Gria genes translated into increased AMPAR protein levels at 48 h in the DG and CA3 region and sustained higher AMPAR expression at 2 and 4 weeks post-FLASH. These findings support a durable activation of AMPAR. We propose a mechanism to explain FLASH-induced neuroprotection initiated by early calcium influx and subsequent sustained expression of glutamate AMPARs in neurons and/or neural progenitors of the CA3, potentially contributing to long-term cognitive sparing.