Astrocyte-Targeted connexin43 Hemichannel Inhibition Prevents Radiation-Induced Energy Transporter Decrease in Neurons and Astrocytic proBDNF Transport to Synapses

Abstract

Radiation therapy is widely used for treating brain tumors but also comes with off-target effects, including vascular blood–brain barrier (BBB) leakage occurring as an early event 24 h postirradiation. Here we investigated brain X-irradiation (20 Gy) effects on the astrocyte-neuronal axis starting from BBB endothelium and ending at synapses. Making use of immune-characterization of brain slices isolated 24 h after irradiation of rodents, we found significantly decreased neuronal expression of GLUT3 glucose transporters and MCT2 monocarboxylate transporters in M1/S1 cortical areas, with no changes in astrocytic GLUT1 transporters. Pre-irradiation animal treatment with the Cx43 hemichannel blocker TATGap19 targeting astrocytes completely prevented these neuronal alterations. Brain uptake of ¹⁸F-deoxy-glucose was decreased in the pre- and infra-limbic cortex 24 h postirradiation, not in other cortical areas, and was prevented by TATGap19 treatment. Electro-encephalographic recordings showed decreased power in delta, theta, beta, and gamma bands, most clearly in S1 cortex 24 h postirradiation. ProBDNF, a precursor of brain-derived neurotrophic factor associated with negative neural effects, was significantly elevated 24 h postirradiation and accompanied by strong activation of its vesicular transport in astrocytes. In particular, proBDNF uptake in astrocytic endfeet at capillary endothelial cells and its VAMP3-associated release at astrocytic extensions to tripartite synapses were both strongly increased and prevented by animal pretreatment with TATGap19. The present data show that astrocytes are a major target for radiotherapeutic intervention whereby Gap19 inhibition of the Cx43 hemichannel membrane leakage pathway prevents radiation-induced alterations in brain glucose handling and activation of vesicular proBDNF transport to tripartite synapses that disturb neural functioning.