Neuroprotective Effect Of Heat Shock Protein22in Epileptic Mice Hipocampus

BackgroundTemporal lobe epilepsy (TLE) is not only the most common form of epilepsy but also the most resistant to pharmacological treatment. Heat shock protein22(Hsp22) is one of the recently discovered small heat shock proteins with chaperone properties that contains a typical a-crystallin region and has the ability to interact with other heat shock proteins (Hsps). Following environmental insults, the central nervous system, like other systems throughout the body, uses some Survival strategies to repair and protect itself. Epileptogenesis definitely put the brain at risk, therefore cascade of events is triggered by the brain intended to avoid further neuronal damage. Under such conditions, HSPs expression temporarily increase to play a crucial protective role against irreversible cell damage and promote the recovery of the cells exposed to stress by enhancing the ability of the cell to cope with increased concentrations of unfolded or denatured proteins in order to keep proteins on the productive folding pathway that assist cellular recovery and inhibit the apoptosis cascade.ObjectiveTo identify the effect of seizure activity on the expression of Hsp22in the Mouse hippocampus during the first week subsequent to PISE in order to define the neuroprotective effect of Hsp22by correlating these changes with caspase-3.MethodsThe experimental study was conducted at central south university, Xiangya medical collage, first Xiangya hospital, Hunan, China from2011-2012. Eighty mice were weighting22-27g were used throughout. The animals were assigned to control and epileptic groups. The control group consisted of30animals received intraperitonial injection of normal saline, all of which survived. The remaining50animals received pilocarpine. Pilocarpine was initially injected in a dose of330mg/kg, followed by165.mg/kg at30min intervals until SE ensued. Thirty minutes prior to pilocarpine application animals were subcutaneously injected with scopolamine lmg/kg. Each epileptic mouse was scored by Racine’s scale. SE was terminated after1h with injections of diazepam4mg/kg, i.p.. Mice were sacrificed at1,3and7days following the onset of SE. To determine whether hippocampal neuronal population are affected by hippocampal seizures, immuonohistochemical assay were performed in brain sections obtained from both age-matched control and epileptic mice. The pathological changes of hippocampus were observed by Nissl stain.The neuroprotective effect of Hsp22were assessed using western blot to correlate the expression of Hsp22and caspase-3in the hippocampus.ResultIn the experimental group60%(n=30) of mice developed a status epilepticus (SE),28%(n=14) mice were died and12%(n=6) did not enter into status epilepticus. The hippocampus of epileptic mice showed a neuronal cell loss pattern with comparable subregions to hippocampus of the control group.Our result revealed that dramatic cell loss was in CA1and CA3areas in the epileptic mice at1day,3days and7days subsequent to SE. There were significant differences between control and experimental groups (p<0.05). Quantitative analysis revealed significant difference between control and experimental mice in the number of Hsp22positive cells at1day,3days and7days (p<0.05). These cells were distributed in CAland CA3areas of both control and experimental mice but were more in the hippocampus of experimental mice. However transient more increasing of Hsp22positive neurons was observed in CA1and CA3between1day and7days post-SE (p<0.05). Hsp22interneurons were mostly located in CA1for epileptic mice and in CA3for control. Western blotting analysis of Hsp22expression demonstrated that in untreated mice, Hsp22was not obviously detectable in protein extracts from hippocampus, whereas Hsp22expression was apparent and prominent at1,3and7days post-SE in which the strongest expression was detected at3days post-PISE. There were significant differences between control and experimental mice (p<0.05). On the other hand, the expression of activated caspase-3was observed and peaked at1day after PISE onset. Caspase-3declined at3days and7days post-PISE. There were significant differences between control and experimental mice (p<0.05).ConclusionOur findings demonstrate that the expression of Hsp22in the hippocampus may exert neuroprotective effects on seizure severity and overall survival subsequent to PISE. Also we provided evidence that Hsp22expression was sustained, which may reflect an additional pivotal role of Hsp22in remodeling events in the days following seizures. These essential roles of Hsp22may open a new field in epilepsy therapy.