Profiling cytokines in temporal lobe epilepsy

Abstract

Temporal lobe epilepsy (TLE) is one of the most common types of partial epilepsy. Because about 30% of the TLE patients poorly respond to medication, identification of new drug targets to treat TLE is imperative. This requires detailed knowledge of the pathophysiology of TLE . The aim of this thesis was to provide such new information through profiling of surgically removed brain tissue and cerebrospinal fluid (CSF) of TLE patients. The complex changes in the TLE brain indicate simultaneous dis-regulation of multiple pathways, possibly by microRNAs (miRNAs). These are newly discovered molecular switches which can control expression of multiple proteins by regulating translation of transcribed mRNA into protein. Expression profiling all human miRNAs in the human TLE brain (Chapter 2) revealed distinct miRNA expression profiles TLE patients with and without hippocampal sclerosis. In TLE patients we found an over representation of miRNAs regulation proteins in the immune system. Two of these miRNAs (221 and 222) regulated glial expression of ICAM1, a protein important in the blood-brain barrier, which is impaired in TLE tissue. Thus, microRNAs may act as molecular switches in TLE, particularly in regulation of the inflammatory response (activated immune system). In Chapter 3 we therefore profiled the activated immune system in TLE. Using a high-throughput ELISA system we simultaneously measured 40 inflammatory proteins in brain tissue of TLE patients. This study replicated the up-regulation of a number of inflammatory mediators previously implicated in TLE studies, and also identified new inflammatory proteins up-regulated in the TLE brain. Principle component analysis showed that individual patients segregate into groups based on their unique expression profile. Moreover, up-regulation of the immune system in TLE occurs in clusters or networks. Interestingly, these up-regulated networks of immunological mediators contained both potentially pro- and anti-epileptogenic proteins. These results provide an explanation for the limited success of general anti-inflammatory treatment in TLE and suggest that treatment strategies should be directed to immune therapy interfering with specific pro-epileptogenic pathways. In chapter 4 we showed that part of the immune profiles identified in brain tissue of TLE patients could also be detected in CSF of these patients. These data indicate that immune profiling of CSF may have diagnostic potential for TLE. In chapter 5 we studied whether expression changes of a subset of up-regulated inflammatory mediators (chemokines), maybe causally involved in TLE. We analysed expression of chemokines at different times after the induction of epileptogenesis in an animal model for TLE. Our results showed that some chemokines are up-regulated early in epileptogenesis, way before the clinical symptoms of TLE occur (spontaneous recurrent seizures). Thus our data suggest a causal role of these chemokines in epileptogenesis. In all, this thesis constructs a detailed picture of the posttranscriptional TLE brain and indicate that profiles of miRNA and inflammatory mediators may contribute to the diagnosis of TLE and provide leads to devise new treatment strategies