Edinburgh Napier University

  Stroke is one of the major causes of death and disability worldwide. The harm caused by the interruption of blood flow to the brain unfolds in the subsequent hours and days, so it is critical to identify new therapeutic targets that could reduce neuronal death associated with the spread of the damage. The area that surrounds the infarcted core is the location of the continuing damage that takes place hours and days following an insult, an is referred to as the penumbra. The expression of the chloride co-transporters, NKCC1 and KCC2, mediators of the GABAergic response, was assessed following hypoxia in differentiated PC12 and NT2 neuronal like cells and in a photothrombotic model of stroke in mice. Differentiated PC12 and NT2 cells were exposed to hypoxia (1% oxygen) for 8 hours in a hypoxic modular chamber before gene and protein expression was analysed by qPCR and immunoblotting. Following hypoxia, the expression of KCC2 was significantly decreased at both the transcript and protein level whereas NKCC1 expression remained unmodified. In the in vivo model, the development of the penumbra in the days following injury was assessed with the specific markers HSP70 and GFAP. Two distinct areas were identified, the penumbra up to 200 m from the ischaemic core and a glial migration zone up to 400 m. In the penumbra, a significant neuronal loss was observed up to 5 days following the insult.
Our results show an increase in the number of neurons expressing NKCC1 in the penumbra up to 5 days following the insult when compared to the contralateral hemisphere. On the contrary, KCC2 positive cells were dramatically decreased in this area. Mice were treated with bumetanide and CLP257, an NKCC1 antagonist and a KCC2 agonist respectively. Neuronal loss was significantly reduced 3 and 5 days following the insult in the penumbra following bumetanide treatment. The reversal on NKCC1 and KCC2 might contribute to the excitotoxic damage that promotes the development of the penumbra in the days following an ischaemic event by interrupting or even reversing GABAergic mediated inhibition. Our results show how treatments targeting chloride co-transporters might represent a novel strategy to reduce the damage associated with stroke.