JNK Activation in Alzheimer?s Disease Is Driven by Amyloid ? and Is Associated with Tau Pathology

c-Jun N-terminal kinase 3 (JNK3) is suggested to play a key role in neurodegenerative disorders, especially in Alzheimer's disease (AD). However, it remains unclear whether JNK or amyloid beta (A beta) appears first in the disease onset. Postmortem brain tissues from four dementia subtypes of patients dementia, and AD) were used to measure activated JNK (pJNK) and A beta levels. pJNK expression is significantly increased in AD; however, similar pJNK expression was found in other dementias. Furthermore, there was a significant correlation, co-localization, and direct interaction between pJNK expression and A beta levels in AD. Significant increased levels of pJNK were also found in Tg2576 mice, a model of AD. In this line, A beta 42 intracerebroventricular injection in wild-type mice was able to induce a significant elevation of pJNK levels. JNK3 overexpression, achieved by intrahippocampal injection of an adeno-associated viral vector expressing this protein, was enough to induce cognitive deficiencies and precipitate Tau aberrant misfolding in Tg2576 mice without accelerating amyloid pathology. JNK3 overexpression may therefore be triggered by increased A beta. The latter, together with subsequent involvement of Tau pathology, may be underlying cognitive alterations in early stages of AD.