Abstract 1792: Radiation-induced downregulation of GLT-1 glutamate transporter mRNA expression is reversed by renin-angiotensin system inhibitors

Abstract

Abstract Fractionated partial or whole brain irradiation (fWBI) is often required to treat metastatic brain cancer. Unfortunately, fWBI can lead to the development of a progressive, irreversible cognitive impairment in patients who survive longer than six months following treatment. Prior studies suggest that neuroinflammation and alterations in neuronal plasticity may play a role in this treatment-related side effect. In the current study we determined that radiation-induced inflammatory activation of primary rat cortical astrocytes results in downregulation of mRNA and protein for the GLT-1 glutamate transporter, which functions to regulate glutamate signaling at excitatory synapses. Furthermore, we show that delivery of clinically-relevant fWBI (40Gy, 5Gy/fraction, 2x/week) to young adult male rats results in 51% decrease in Glt-1 mRNA in the cortex at 48 hours. Two months after completion of fWBI, cortical GLT-1 mRNA is further decreased to 25% the levels observed in sham controls, while at six months following fWBI GLT-1 levels remain 43% decreased compared to controls. We have previously identified two classes of compounds, the renin-angiotensin system inhibitors and PPAR agonists, which ameliorate the fWBI-induced cognitive impairment in this rodent model, although the full mechanisms by which these compounds protect cognition remain unknown. We found that dietary administration of the angiotensin receptor blocker L-158-809, but not the ACE inhibitor Ramipril, prevents fWBI-induced loss of cortical GLT-1 mRNA at 48 hours, while both cognition-sparing compounds restored GLT-1 expression at 2 months post-fWBI. Similarly, administration of the PPARδ agonist GW0742 prevented the fWBI-induced decrease of GLT-1 mRNA observed 6 months post-fWBI. Together these data suggest that radiation-induced downregulation of GLT-1 is a potential mechanism contributing to the development of radiation-induced brain injury, including cognitive impairment, and that GLT-1 may represent a druggable target to prevent this treatment-related cognitive decline. (Supported by NIH CA112593) Citation Format: Mitra Kooshki, Christine Naczki, Michael E. Robbins, Linda J. Metheny-Barlow. Radiation-induced downregulation of GLT-1 glutamate transporter mRNA expression is reversed by renin-angiotensin system inhibitors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1792. doi:10.1158/1538-7445.AM2015-1792