Signalling Characterization Of ER Stress Induced-apoptosis In Cerebellar Granule Neurons

The study of neuron ability to tolerate environmental and genetic challenges currently represents an important field of investigation. Indeed, neuron death and survival is a common feature encountered in various neurodegenerative diseases such as Parkinson, Alzheimer or Huntington's diseases, in genetic diseases such as ALS but also during brain ischemia which is a landmark of stroke or oxidative stress. This enhanced neuronal death may have deleterious functional consequences and it is of interest to better understand the mechanisms underlying neuronal adaptation and resistance to these particular situations. Recently Endoplasmic Reticulum (ER) stress signalling pathways have been shown to participate in neuronal cell death. The ER is an essential eukaryotic cell organelle, mainly responsible for ensuring secretory protein folding. ER functions can be altered in many physiological and physiopathological situations which result in the accumulation of misfolded proteins in the ER lumen. This leads to the disruption of ER homeostasis and functions. A major stress response is therefore triggered to restore this homeostasis by reducing the ER client protein load (attenuation of protein translation), and increasing the clearance of misfolded proteins (increased folding capacity and increased ER-associated degradation). This stress response is mediated by three major ER resident stress sensors named PERK,ATF6, and IRE1. Endoplasmic reticulum (ER) stress signalling pathways are involved in various alterations of the central nervous system such as neurodegenerative diseases or ischemia. The current mechanisms linking ER stress activation to neuronal cell fate upon chronic or acute stresses remain however to be fully understood. Recent studies have associated ER stress severity and the relative activation levels of certain output pathways to influence cell-fate decisions.In this study, these results confirm that NCK-1 protein and PI3K/AKTsignalling pathway play an important protective role on FGF2 anti-apoptosis effect, we show that FGF2 treatment activated PI3K/AKT signalling pathway to attenuate ER stress-induced CGNs apoptosis through PERK-eIF2αsignalling pathway with altering intracellular CHOP level. In addition, we have shown that NCK-1 play an important protective role on FGF2 anti-apoptosis effect. FGF2 significantly abrogated the expression level of NCK-1 in CGNs. Interestingly, overexpression of NCK-1 not only resulted in a more significant abrogated in duration of AKT phosphorylation induced by FGF2, but also resulted in a more significant abrogated in the phosphorylation levels of eIF2αand a more significant increased in the CHOP expression.To further test the impact of ER stress severity on neuronal survival, we designed an experimental system recapitulating acute and chronic stress in cerebellar granule neurons (CGNs) and c17.2 mouse neural stem cells (NSCs). Two well characterized ER stress inducers, tunicamycin (TM) and dithiothreitol (DTT), were used to induce"slow motion"and"fast motion"stresses, respectively. We show that the duration of JNK activation is critical for cell survival upon ER stress. TM-induced transient JNK activation is a protective event in CGNs and c17.2 NSCs via the phosphorylation of BAD, while DTT-induced prolonged JNK activation mediates pro-apoptotic signalling. we demonstrate that ER stress mediated MKP-1/DUSP1 expression regulates JNK activation kinetics. MKP-1 phosphorylation and protein expression level are differentially altered upon TM and DTT treatment. Increased MKP-1 protein stability via its phosphorylation on ser359 induced by TM accounts for transient JNK activation and the resulting cell survival in CGNs and c17.2 NSCs subjected to ER stress. These results suggest that MKP-1 plays a pivotal role in ER stress-induced cell apoptosis through regulating JNK-BAD signalling. In addition, TM-induced prolonged GSK3βphosphorylation on Ser9, while DTT-induced inhibited significantly GSK3βphosphorylation on Ser9. TM effected ER stress-induced cell apoptosis through regulating JNK-GSK3βsignalling.