Edinburgh Napier University

  Stroke is one of the major causes of death and disability worldwide. The area that surrounds the infarcted core is the location of the continuing damage that takes place hours and days following an insult, and is referred to as the penumbra. By creating an oxygen deprived environment in the neuronal-like PC12 and NT2 cells and an in vivo photothrombotic model of stroke (PTS) in mice, two different strategies were created to replicate the conditions of an ischaemic brain.
In differentiated PC12 and NT2 cells, following hypoxia, preferential activation of HIF-2α transcription and protein expression was detected. Increased expression of the neural progenitor stem cell-like markers, thought to be transcriptionally regulated by HIF-2α, were also observed. Furthermore, hypoxia caused loss of neuronal characteristics in differentiated cells. This is highly significant as it shows neuronal cells possess molecular mechanisms which could trigger recovery following ischaemic insult.
The expression of the chloride co-transporters, NKCC1 and KCC2, mediators of the GABAergic response, was assessed following hypoxia in differentiated PC12 and NT2 cells and PTS. In PC12 and NT2 cells exposed to 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 specific markers allowing the identification of the penumbra up to 200 ❍m from the ischaemic core and a progressive neuronal loss was observed within. 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. In mice treated with bumetanide, an NKCC1 antagonist, a significant reduction in neuronal loss was observed. Our results show a reversal on the chloride co-transporters expression in vitro and in vivo and how treatments targeting these channels might represent a novel strategy to reduce the damage associated with stroke.