Does Hsp27 protect cortical neurons against amyloid?

King, Michael T. C. (Michael Thomas Cecil) (2009) Does Hsp27 protect cortical neurons against amyloid? Masters thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (5MB)

Abstract

Neurofibrillary tangles (NFTs) and plaques are considered to be hallmarks of Alzheimer's disease (AD), although it is still not clear whether these aggregates contribute to disease progress or whether they might even play an initial protective role. A number of studies have shown that the small heat shock protein Hsp27 can afford protection against oxidative stress, growth factor withdrawal or excitotoxicity in neuronal cell types. A moderate preconditioning heat shock (HS) is sufficient to upregulate levels of Hsp27 in cells, and the degree of protection correlates with the level of expression of Hsp27. There are reports of increased Hsp27 in AD brains and accumulation of Hsps in plaques, NFTs and Lewy bodies. Whether this represents a potentially protective response to the stress or is part of the disease process is not known. My hypothesis is that increased expression of Hsp27 can promote survival and stabilize the axonal cy to skeleton resulting in maintenance of neurite growth and axonal transport in the face of stressors such as amyloid. My specific aim was to determine whether Hsp27 is important for neuronal survival and neurite growth in primary cortical neurons in the presence or absence of β-amyloid peptides. -- Cultures of primary rat cortical neurons were subjected to HS in an effort to upregulate endogenous Hsp27, while in other experiments Hsp27 was overexpressed in cortical neurons by nucleofection. Efforts to upregulate endogenous Hsp27 in cortical neurons were unsuccessful, despite the fact that the neurons do express heat shock factor-1 (Hsf1) and increase activation of Hsf1 in response to heat stress. In fact, it was seen that HS resulted in a reduction in neuronal survival, although previous data from our lab and the literature suggest that a thermal stress can provide protection against a more lethal subsequent stress. Consequently, I introduced a GFP-Hsp27 fusion protein at the time of plating and examined the potential effects of exogenous Hsp27 on neurite survival and growth using morphological and biochemical analyses. -- My results suggest that the presence of Hsp27 in cortical neurons provides them with a level of protection against β-amyloid. After treatment with Aβ₁₋₄₂, cells with Hsp27 appeared healthier and had greater survival than those without. Interestingly, Aβ₂₅₋₃₅ was not shown to be toxic to these neurons, whereas it has been previously shown to be toxic in a variety of experimental paradigms. Further, my data indicate that cells expressing Hsp27 have greater total neurite growth compared to the empty vector alone. Knowing that phosphorylation affects Hsp27 activity, I also investigated the effects of Hsp27∆ on survival and growth. Hsp27∆ is a mutated form of Hsp27 lacking the S15 phosphorylation site. My data show that Hsp∆ has similar effects on neurite outgrowth and survival as Hsp27WT, providing important preliminary data for future studies investigating the importance of phosphorylation in Hsp27 activity.

Actions (login required)

View Item