In addition to neuritic plaques and neurofibrillary tangles, Alzheimer's disease is characterized by neuroinflammation and neuronal loss. The association of proteins such as apolipoprotein E, alpha 1-antichymotrypsin (ACT), complement factors, and cytokines with the plaques led to the hypothesis that these inflammatory proteins play a role in the development of AD pathology. Studies from our lab and others have shown that ACT induces accelerated plaque formation and cognitive deficit in APP transgenic mice. Recently we showed that ACT also induces tau hyperphorylation and these tau epitopes are similar to the ones that are associated with neurofibrillary tangles. In vitro studies with ACT were done in cultured cortical neurons. Tau phosphorylation in cells and sections were determined by immunohistochemistry. In vivo studies were done in mice expressing APP, human tau or ACT transgenes. ACT infusion was done using alzet pump. To determine whether the effect of ACT on tau hyperphosphorylation was A-beta dependent, we performed experiments in cultured neurons from APP knockout mice. We found that ACT induces tau hyperphosphorylation in these neurons suggesting that the effect of ACT is not A-beta dependent. To study the in vivo effect of ACT, it was infused into the hippocampus on one hemisphere of the mouse brain while the other hemisphere received artificial CSF for the same period of time. After two weeks of infusion the mice were sacrificed and tau phosphorylation determined using specific P-tau antibodies. We found that the hemisphere that received ACT showed an induction of tau hyperphosphorylation compared to the hemisphere that received artificial CSF. This further confirms that inflammatory proteins, namely ACT induces tangle pathology. To further understand the mechanisms involved in ACT's effect on tau, transgenic mice overexpressing human tau in a mouse tau null background (htau) were crossed with human ACT expressing mice. Preliminary studies suggest that mice expressing htau/ACT show increased tau hyperphosphorylation compared to age-matched htau only mice. ACT induces tau hyperphosphorylation in vitro and in vivo independent of A-beta. htau/ACT mice are excellent models for studying age-dependent changes in inflammation-induced neurodegeneration as well as assessing the efficacy of anti-inflammatory drugs.

Amyloid plaques and neurofibrillary tangles are key pathological features of Alzheimer's disease. Alzheimer's disease pathology is also characterized by neuroinflammation and neuronal degeneration, with the proteins associated with inflammatory responses being found in tight association with the plaques. One such protein is the serine protease inhibitor alpha-1-antichymotrypsin (ACT). ACT has been shown to promote Abeta polymerization in vitro and in vivo, and levels of ACT protein in plasma and cerebrospinal fluid from Alzheimer's patients have been found to correlate with progression of dementia. Here we investigated the possible involvement of ACT in tau phosphorylation and tangle formation. As was previously found for Alzheimer's disease, brains from patients with non-Alzheimer's tauopathies exhibited an enhanced expression of ACT, which correlated with the level of tau hyperphosphorylation. Transgenic mice expressing human ACT alone or ACT along with mutant human amyloid precursor protein (APP) showed a significant increase in tau phosphorylation, suggesting that this inflammatory protein can induce tau hyperphosphorylation. The increase in phosphorylation was observed at PHF-1 (P-Ser396/P-Thr404), P-Ser202 and P-Thr231 sites on tau, the P-tau epitopes that are associated with tangles in the patients. This result was further confirmed by the finding that addition of purified ACT induced the same Alzheimer's disease-related tau hyperphosphorylation in cortical neurons cultured in vitro. This correlated with an increase in extracellular signal regulated kinase (ERK) and glycogen synthase kinase-3 activation, indicating their involvement in ACT-induced tau phosphorylation. The ACT-treated neurons showed neurite loss and subsequently underwent apoptosis. Approximately 40-50% of neurons were TUNEL positive by 6 and at 24 h >70% of the neurons showed staining suggesting that ACT was inducing apoptosis in these neurons. These findings indicate that inappropriate inflammatory responses are a potential threat to the brain and that intervention directed at inhibiting the expression or function of ACT could be of therapeutic value in neurodegenerative diseases such as Alzheimer's and other tauopathies.