The effect of amyloid associated proteins on the expression of genes involved in amyloid-β clearance by adult human astrocytes.

Astrocytes appear to be important mediators in the clearance of amyloid beta1-42 (Aβ), the key component of senile plaques characteristic of Alzheimer's disease (AD). Recently, we found the amyloid associated proteins (AAPs) α1-antichymotrypsin (ACT), apolipoprotein J and E (ApoJ and ApoE) and a mixture of serum amyloid P (SAP) and C1q (SAP-C1q) to modify Aβ-uptake by human astrocytes. Here we investigated the effect of oligomeric (Aβoligo) and fibrillar Aβ (Aβfib), alone and in combination with a panel of AAPs on the astrocytic expression of genes proposed to be involved in Aβ-uptake and degradation. Primary human astrocytes (isolated from non-demented control (n=4) and AD patient (n=4) brain specimens) were exposed to either Aβoligo or Aβfib preparations with or without the above mentioned AAPs. Quantitative gene expression analysis of Aβ-receptors Scavenger receptor B1 (SCARB1), macrophage receptor with collagenous structure (MARCO) and low density lipoprotein receptor related protein-2 (LRP2 or megalin) as well as of Aβ-degrading enzymes neprilysin (NEP), insulin-degrading enzyme (IDE) and metalloproteinase-9 (MMP-9) was performed by real-time PCR. Basal expression of NEP, IDE and SCARB1 was easily detected whereas expression of MARCO, LRP2 and MMP-9 could only be detected upon pre-amplification. Basal expression of NEP, IDE and SCARB1 did not change upon exposure to Aβoligo or Aβfib alone in any of the investigated astrocyte cultures. Interestingly NEP expression was increased upon exposure to ApoE in combination with both Aβ-preparations, and also SCARB1 expression was induced upon treatment with ApoE in combination with Aβfib in astrocytes from non-demented controls. Further, SAP-C1q increased SCARB1 expression in control astrocytes when combined with Aβoligo. These alterations were not found in astrocytes from AD patients. Thus, we conclude that Aβ alone apparently does not affect the astrocytic expression of IDE, NEP or SCARB1. However, NEP and SCARB1 expression is increased in astrocytes from non-demented subjects when exposed to Aβ combined with AAPs like ApoE. These astrocytic gene expression-regulatory mechanisms appear to be defective in AD and thus might contribute to the development and progression of AD pathology.