The fundamental function of the Endoplasmic Reticulum (ER) is to process nascent membrane and secretory proteins in a calcium-dependent manner. Disruption of ER function by the depletion of ER calcium results in ER stress, which triggers apoptosis if prolonged. ER stress has been shown to play a role in the pathogenesis of Motor Neuron Diseases (MNDs) and CAG-repeat disorders. Kennedy’s Disease (KD) is an X-linked neurodegenerative disease that is classified as both a MND and CAG-repeat disorder. In this Thesis I investigate whether ER Stress also plays a role in the pathogenesis of KD.
Using a mouse model of KD, primary motoneuron cultures from both KD and wild-type (WT) embryos were established. Confocal microscopy was used to infer ER calcium levels, and markers of ER stress and ER stress-induced apoptosis were examined using western blot analysis and immunocytochemistry.
KD motoneurons were found to have reduced levels of ER calcium and elevated levels of markers of ER stress and ER stress-induced apoptosis relative to WT controls. ER stress-induced apoptosis appears to contribute to the motoneuron death observed in KD mice, since inhibition of ER stress with Salubrinal increases ER Ca2+, decreases ER stress-induced apoptosis and consequentially improves KD motoneuron survival.
Examination of markers of ER stress in the spinal cord of KD mice revealed higher expression levels compared to WT controls, with the most significant increase detected between E13 and 3 months of age i.e. pre-symptomatically. Mitochondrial dysfunction and impaired mitochondrial biogenesis was also observed in KD motoneurons. However, increasing mitochondrial biogenesis was not as effective as inhibition of ER stress in improving KD motoneuron viability.
These results show that ER stress may play an early, causal role in the pathogenesis of KD and suggest that inhibition of ER stress may be a potential therapeutic strategy for the treatment of KD
