Antisense oligonucleotide against GSK-3β in brain of SAMP8 mice improves learning and memory and decreases oxidative stress: Involvement of transcription factor Nrf2 and implications for Alzheimer disease

Abstract

Glycogen synthase kinase (GSK) -3β is a multifunctional protein that has been implicated in the pathological characteristics of Alzheimer’s disease (AD), including the heightened levels of neurofibrillary tangles, amyloid-beta (Aβ) and neurodegeneration. In this study we used 12 month old SAMP8 mice, an AD model, to examine the effects GSK-3β may cause regarding the cognitive impairment and oxidative stress associated with AD. To suppress the level of GSK-3β, SAMP8 mice were treated with an antisense oligonucleotide (GAO) directed at this kinase. We measured a decreased level of GSK-3β in the cortex of the mice, indicating the success of the antisense treatment. Learning and memory assessments of the SAMP8 mice were tested post-antisense treatment using an aversive T-maze and object recognition test, both of which observably improved. In cortex samples of the SAMP8 mice, decreased levels of protein carbonyl and protein-bound HNE were measured indicating decreased oxidative stress. Nuclear factor erythroid -2-related factor 2 (Nrf2) is a transcription factor known to increase the level of many antioxidants, including glutathione-S transferase (GST), and is negatively regulated by the activity of GSK-3β. Our results indicated the increased nuclear localization of Nrf2 and level of GST, suggesting the increased activity of the transcription factor as a result of GSK-3β suppression, consistent with the decreased oxidative stress observed. Consistent with the improved learning and memory, and consistent with GSK-3b being a tau kinase, we observed decreased tau phosphorylation in brain of GAO-treated SAMP8 mice compared to that of RAO-treated SAMP8 mice. Lastly, we examined the ability of GAO to cross the blood-brain barrier and determined it to be possible. The results presented in this study demonstrate that reducing GSK-3 with a phosphorothionated antisense against GSK-3 improves learning and memory, reduces oxidative stress, possibly coincident with increased levels of the antioxidant transcriptional activity of Nrf2, and decreases tau phosphorylation. Our study supports the notion of GAO as a possible treatment for AD.

Limb ischemic preconditioning protects against contrast-induced acute kidney injury in rats via phosphorylation of GSK-3β

“…Together, these data show that LIPC inhibits oxidative stress and inflammation in CI-AKI rats through the suppression of GSK-3β activity. These observations are consistent with other studies also showing that GSK-3β regulates Nrf2 activity [57][58][59][60][61], that Nrf2 has antioxidant effects [54,55,[60][61][62], and that Nrf2-mediated heme oxygenase-1 expression attenuates inflammatory responses by inhibiting NF-κB activation [63,64].…”

Nrf2 activation in the treatment of neurodegenerative diseases: a focus on its role in mitochondrial bioenergetics and function

“…The authors show that GSK-3 suppression was responsible for an increase in the nuclear localization of Nrf2 and the levels of its target enzyme glutathione S-transferase, which led to decreased oxidative stress. Together with this, tau phosphorylation was reduced and there was an improvement in learning and memory, suggesting that antisense nucleotide directed at GSK-3β may be considered as possible treatment for AD (Farr et al, 2014).…”

Molecular mechanisms linking amyloid β toxicity and Tau hyperphosphorylation in Alzheimer׳s disease

“…Furthermore, GSK3β phosphorylates Tau in most of its serine and threonine residues and contributes both to Aβ production and to Aβ-mediated neuronal death [48]. Downregulation of GSK3β in brain of SAMP8 mice, which deposits Aβ as a function of accelerating aging, leads to increased Nrf-2-mediated upregulation of antioxidant enzymes, decreased oxidative stress, and decreased Tau phosphorylation [49]. Hyperphosphorylation of Tau is not only due to the increased Tau kinase activity, but also to the lower rate 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 3...…”