by
Elliot J. Mufson;
Bin He;
Muhammad Nadeem;
Sylvia E. Perez;
Scott E. Counts;
Sue Leurgans;
Jason Fritz;
James Lah;
Stephen D. Ginsberg;
Joanne Wuu;
Stephen W. Scheff
Hippocampal precursor of nerve growth factor (proNGF)/NGF signaling occurs in conjunction with A-amyloid (Aβ) accumulations in Alzheimer disease (AD). To assess the involvement of this pathway in AD progression, we quantified these proteins and their downstream pathway activators in postmortem tissues from the brains of subjects with no cognitive impairment (NCI), mild cognitive impairment (MCI), and AD using immunoblotting and ELISA. Hippocampal proNGF was significantly greater in AD cases compared with those in NCI and MCI cases. TrkA was significantly reduced in MCI compared with those in NCI and AD, whereas p75 neurotrophin receptor, sortilin, and neurotrophin receptor homolog 2 remained stable. Akt decreased from NCI to MCI to AD, whereas phospho- Akt and phospho-AktYtoYAkt ratio were elevated in AD compared with those in MCI and NCI. No differences were found in phospho- Erk, Erk, or their ratio across groups. Although c-jun kinase (JNK) remained stable across groups, phospho-JNK and the phospho- JNKYtoYJNK ratio increased significantly in AD compared with those in NCI and MCI. Expression levels of Aβ1-40, Aβ 1-42, and Aβ40/42 ratio were stable. Statistical analysis revealed a strong positive correlation between proNGF and phospho-JNK, although only proNGF was negatively correlated with cognitive function and only TrkA was negatively associated with pathologic criteria. These findings suggest that alterations in the hippocampal NGF signaling pathway in MCI and AD favor proNGF-mediated proapoptotic pathways, and that this is independent of Aβ accumulation during AD progression.
Casein kinase 2 (CK2) is highly activated in Alzheimer disease (AD) and is associated with neurofibrillary tangles formation. Phosphorylated SET, a potent PP2A inhibitor, mediates tau hyperphosphorylation in AD. However, whether CK2 phosphorylates SET and regulates tau pathological phosphorylation in AD remains unclear. Here, we show that CK2 phosphorylating SET at Ser9 induced tau hyperphosphorylation in AD. We found that either Aβ treatment or tau overexpression stimulated CK2 activation leading to SET Ser9 hyperphosphorylation in neurons and animal models, while inhibition of CK2 by TBB abolished this event. Overexpression of CK2 in mouse hippocampus via virus injection induced cognitive deficit associated with SET Ser9 hyperphosphorylation. Injection of SET Ser9 phosphorylation mimetic mutant induced tau pathology and behavior impairments. Conversely co-injection of non-phosphorylated SET S9A with CK2 abolished the CK2 overexpression-induced AD pathology and cognitive deficit. Together, our data demonstrate that CK2 phosphorylates SET at Ser9 leading to SET cytoplasmic translocation and inhibition of PP2A resulting in tau pathology and cognitive impairments.