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Insulin receptor signaling mediates APP processing and ?-amyloid accumulation without altering survival in a transgenic mouse model of Alzheimer's disease.

ABSTRACT: In brains from patients with Alzheimer's disease (AD), expression of insulin receptor (IR), insulin-like growth factor-1 receptor (IGF-1R), and insulin receptor substrate proteins is downregulated. A key step in the pathogenesis of AD is the accumulation of amyloid precursor protein (APP) cleavage products, ?-amyloid (A?)(1-42) and A?(1-40). Recently, we and others have shown that central IGF-1 resistance reduces A? accumulation as well as A? toxicity and promotes survival. To define the role of IR in this context, we crossed neuron-specific IR knockout mice (nIR(-/-)) with Tg2576 mice, a well-established mouse model of an AD-like pathology. Here, we show that neuronal IR deficiency in Tg2576 (nIR(-/-)Tg2576) mice leads to markedly decreased A? burden but does not rescue premature mortality of Tg2576 mice. Analyzing APP C-terminal fragments (CTF) revealed decreased ?-/?-CTFs in the brains of nIR(-/-)Tg2576 mice suggesting decreased APP processing. Cell based experiments showed that inhibition of the PI3-kinase pathway suppresses endosomal APP cleavage and decreases ?- as well as ?-secretase activity. Deletion of only one copy of the neuronal IGF-1R partially rescues the premature mortality of Tg2576 mice without altering total amyloid load. Analysis of Tg2576 mice expressing either a dominant negative or constitutively active form of forkhead box-O (FoxO)1 did not reveal any alteration of amyloid burden, APP processing and did not rescue premature mortality in these mice. Thus, our findings identified IR signaling as a potent regulator of A? accumulation in vivo. But exclusively decreased IGF-1R expression reduces AD-associated mortality independent of ?-amyloid accumulation and FoxO1-mediated transcription.

SUBMITTER: Stohr O

PROVIDER: S-EPMC3543743 | biostudies-literature | 2013 Feb

REPOSITORIES: biostudies-literature

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Insulin receptor signaling mediates APP processing and β-amyloid accumulation without altering survival in a transgenic mouse model of Alzheimer's disease.

Stöhr Oliver O Schilbach Katharina K Moll Lorna L Hettich Moritz M MM Freude Susanna S Wunderlich F Thomas FT Ernst Marianne M Zemva Johanna J Brüning Jens C JC Krone Wilhelm W Udelhoven Michael M Schubert Markus M

Age (Dordrecht, Netherlands) 20111106 1

In brains from patients with Alzheimer's disease (AD), expression of insulin receptor (IR), insulin-like growth factor-1 receptor (IGF-1R), and insulin receptor substrate proteins is downregulated. A key step in the pathogenesis of AD is the accumulation of amyloid precursor protein (APP) cleavage products, β-amyloid (Aβ)(1-42) and Aβ(1-40). Recently, we and others have shown that central IGF-1 resistance reduces Aβ accumulation as well as Aβ toxicity and promotes survival. To define the role of ...[more]

PMID: 22057897

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Project description:BackgroundThe role of mitochondrial dysfunction has long been implicated in age-related brain pathology, including Alzheimer's disease (AD). However, the mechanism by which mitochondrial dysfunction may cause neurodegeneration in AD is unclear. To model mitochondrial dysfunction in vivo, we utilized mice that harbor a knockin mutation that inactivates the proofreading function of mitochondrial DNA polymerase ? (PolgA D257A), so that these mice accumulate mitochondrial DNA mutations with age. PolgA D257A mice develop a myriad of mitochondrial bioenergetic defects and physical phenotypes that mimic premature ageing, with subsequent death around one year of age.ResultsWe crossed the D257A mice with a well-established transgenic AD mouse model (APP/Ld) that develops amyloid plaques. We hypothesized that mitochondrial dysfunction would affect A? synthesis and/or clearance, thus contributing to amyloidogenesis and triggering neurodegeneration. Initially, we discovered that A?42 levels along with A?42 plaque density were increased in D257A; APP/Ld bigenic mice compared to APP/Ld monogenic mice. Elevated A? production was not responsible for increased amyloid pathology, as levels of BACE1, PS1, C99, and C83 were unchanged in D257A; APP/Ld compared to APP/Ld mice. However, the levels of a major A? clearance enzyme, insulin degrading enzyme (IDE), were reduced in mice with the D257A mutation, suggesting this as mechanism for increased amyloid load. In the presence of the APP transgene, D257A mice also exhibited significant brain atrophy with apparent cortical thinning but no frank neuron loss. D257A; APP/Ld mice had increased levels of 17 kDa cleaved caspase-3 and p25, both indicative of neurodegeneration. Moreover, D257A; APP/Ld neurons appeared morphologically disrupted, with swollen and vacuolated nuclei.ConclusionsOverall, our results implicate synergism between the effects of the PolgA D257A mutation and A? in causing neurodegeneration. These findings provide insight into mechanisms of mitochondrial dysfunction that may contribute to the pathogenesis of AD via decreased clearance of A?.

Dataset Information

Insulin receptor signaling mediates APP processing and ?-amyloid accumulation without altering survival in a transgenic mouse model of Alzheimer's disease.

Publications

Insulin receptor signaling mediates APP processing and β-amyloid accumulation without altering survival in a transgenic mouse model of Alzheimer's disease.

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