Fibrillar Abeta triggers insulin degrading enzyme (IDE) over-expression by glial cells in old Tg2576 mice

LEAL M.C.,; DORFMAN V.B; FERNÁNDEZ GAMBA AC; FRANGIONE B; WISNIEWSKI T; CASTAÑO EM; SIGURDSSON AM; MORELLI L.

Madrid, España

Conferencia; Alzheimer´s Association 10th International Conference on Alzheimer´s Disease and Related Disorders; 2006

Alzheimer´s Association

It was proposed that IDE participates in the clearance of amyloid b (Ab) in the brain and its low expression or activity may be relevant for the progression of Alzheimer’s disease (AD). Our aim was to study the profile of IDE during the neurodegenerative process in transgenic mice (Tg2576) brains, which carry the amyloid precursor protein with the Swedish mutation. Tg2576 mice and non-Tg (NTg) littermates of 4.5, 11 and 16 months of age (m) (n=4/group) were used to determine IDE protein and activity levels by ELISA, western-blot (WB) and immunoprecipitation assays. IDE transcripts were quantified by competitive RT-PCR. Brain sections were subjected to immunohistochemistry with anti-IDE, anti-Ab, anti-GFAP and L. esculentum lectin. Results: At 16 m Tg2576 mice showed a significant 2-fold increment in IDE protein levels as compared to 11 m (612 ± 54.3 vs. 291.96 ± 23.7 ng/mg, respectively) that was fully active using 125I-insulin as a substrate. No significant differences were found in the amount of IDE transcripts in whole brain homogenates, suggesting that IDE increment was not due to a widespread increase in its mRNA levels. The peak of soluble IDE was in synchrony with a sharp accumulation of SDS-soluble Ab40 (355.046 ng/mg ± 2.096), and massive Ab deposition into plaques. Moreover, at this stage, IDE appeared surrounding amyloid deposits within GFAP-positive astrocytes and activated microglia. This suggested that IDE was locally over-expressed by glial cells in the context of an inflammatory response triggered by fibrillar Ab. To explore this possibility, primary rat astrocytes were used to test IDE levels after exposure to soluble or fibrillar Ab. After treatment with 5 mM fibrillar Ab, IDE protein and transcripts increased 2-fold as detected by WB, immunofluorescence and RT-PCR compared to soluble Ab or control cultures. Our results suggest that the defective clearance of Ab due to IDE lower expression or activity is not an accelerating factor in Tg2576 mice amyloid deposition. Moreover, IDE over-expression associated to late-stages of the neuropathologic process in this animal model may be part of an inflammatory response, suggesting a new role for IDE in the brain that deserves future investigation.