N-acetyl L-cysteine and Growth Factors Impede Endoplasmic Reticulum Stress and Inflammatory Responses in Astrocytes to Amyloid-β in Serum-free Culture.

Background: Astrocytes play an integral role in Alzheimer's disease (AD) pathology, where they may act as a double-edged sword. The existing serum-supplemented in vitro astrocyte culture models are not suitable to study certain stress response mechanisms that occur in AD.

Purpose: Here, we tried to develop a serum-free murine primary cortical astrocyte culture model to study endoplasmic reticulum (ER) stress and inflammation to investigate the effect of amyloid-beta (Aβ_1-42).

Methods: Astrocytes were cultured in a controlled serum-free environment to minimise interference from serum components. Serum-free astrocytes were exposed to oligomeric Aβ and subjected to imaging, immunocytochemistry, real-time PCR and western blot analysis.

Results: Using an established protocol, no significant activation of eIF2α, a key marker of ER stress, was observed under serum-free conditions, but with the removal of N-acetyl cysteine (NAC), ER stress response was enhanced after 24 hours of Aβ exposure. Subsequently, the Aβ-induced inflammatory response, assessed through TNF-α expression, which was minimal in the presence of growth factors, became pronounced when these factors were withdrawn. Concomitantly, a significant increase in astrocytes reactivity, assessed by GFAP expression upon 24 hours of Aβ exposure, was observed. Transcript analysis revealed a time-dependent shift in the expression of inflammatory molecules, with early time points showing an increase in anti-inflammatory markers, while late exposure promoting pro-inflammatory responses.

Conclusion: This study identifies that NAC and growth factors impede ER stress and inflammatory responses in astrocytes upon Aβ exposure in serum-free culture. These findings also highlight the potential of a serum-free culture system for studying ER stress and inflammation in astrocytes to understand the complex role of these cells in AD pathophysiology.